Vehicle-to-Grid (V2G) Research: A Decade of Progress, Achievements, and Future Directions

Abstract

Vehicle-to-Grid (V2G) technology enables bidirectional power exchange between electric vehicles (EVs) and the power grid, allowing EVs to serve as distributed energy resources that enhance grid flexibility and stability. Its core concept leverages the aggregated capacity of EV batteries to buffer fluctuations from variable renewable energy sources. This study systematically reviews 200 high-impact publications from 2015 to early 2024 to trace shifts in research priorities. Unlike previous reviews that focused on specific technical or social aspects of V2G, this work adopts a quantitative bibliometric approach to provide a broader and more integrated perspective of the field. By mapping representative high-impact studies, it identifies the structural relationships among subfields, reveals the distribution of research hotspots, and tracks their temporal evolution, thereby offering a systematic roadmap for future V2G research. The analysis divides the decade into two periods (2015–2019 and 2020–2024) to capture temporal trends. Findings show a dominant focus on bidirectional charging technologies and V2G network management strategies. Earlier studies emphasized infrastructure integration and regulatory frameworks, while recent research increasingly targets optimization algorithms, communication protocols, and hardware standardization. Three key trends emerge: first, growing regional divergence in interface standards and product design—for example, China prioritizes high-power asymmetric DC interfaces, whereas Europe focuses on lower-power AC systems and interoperability; second, a shift from microgrid-based implementations toward centralized V2G management to support coordinated, grid-level operations; and third, rising emphasis on economic viability models to enable large-scale system deployment.

1. Introduction

Countries around the world are increasingly committed to achieving carbon emission reduction targets established by international agreements, such as the 2015 Paris Agreement [1]. To meet these objectives, the proportion of renewable energy generation is rapidly expanding. However, the rapid increase in renewable energy generation—characterized by high intermittency—has intensified the mismatch between production peaks and residential demand cycles. This temporal misalignment places stress not only on national transmission systems, which must handle greater peak loads and reverse flows, but also on regional distribution grids, which are more directly affected by fluctuations in local supply and demand [2].

For instance, in the UK, local governments are under unprecedented pressure to upgrade distribution infrastructure and enhance capacity planning in order to accommodate bidirectional flows and mitigate voltage instability. In parallel, the national grid has also faced significant challenges. In 2020, the National Grid allocated £826 million for upgrading transmission infrastructure and balancing the transmission and distribution networks to accommodate the growing demand for renewable energy integration [3]. These investments highlight the growing imbalance between the pace of renewable energy deployment and the availability of grid-flexibility resources—emphasizing the urgent need for new forms of distributed energy storage capable of mitigating the volatility of bidirectional power flows.

Positioning energy storage devices equipped with bidirectional charging capabilities within the grid is recognized as one of the most effective methods for addressing the periodic imbalances in load distribution over time [4]. In addition to fixed energy storage stations within regional grids, EVs are increasingly viewed as potential energy storage mediums and distributed generation resources due to their substantial numbers and flexible availability [5]. Statistical analyses of EV operating patterns indicate that for approximately 22 h each day, most EVs remain dormant, effectively serving as underutilized assets [6]. Research forecasts suggest that if family EVs can connect to the grid at both home and work locations, they could contribute to power grid optimization for up to 81% of their service life expectancy [7]. Furthermore, if EV charging stations are equipped with bidirectional charging technology to automatically connect with the grid during idle periods, these vehicles can be reactivated as distributed buffering mediums within the grid. This bidirectional energy transmission mode, known as vehicle-to-grid (V2G), encompasses specialized connection technologies and optimized transmission strategies aimed at enhancing regional grid performance [8]. When the interconnected grid approaches peak load conditions, the stored electrical energy in EVs can be utilized to support the grid; conversely, during off-peak times, EVs can charge their batteries from the grid, thereby mitigating unnecessary energy waste caused by excess power generation [9]. Consequently, the proposed V2G system facilitates a spontaneous response to peak load demands, enables bidirectional energy management, provides spinning reserves, and assists in regulating system power parameters, particularly in optimizing load distributions from unpredictable and intermittent renewable energy sources [10].

Early research on V2G systems primarily focused on the evolution of hardware architectures [11]. Initial bidirectional charging models were designed to simplify electric power transmission and minimize potential conflicts among electronic components [12,13]. These early models employed a single control circuit to facilitate period-decoupled bidirectional electricity flow between electric vehicles (EVs) and a single power exchange unit, enabling configurations such as vehicle-to-load (V2L), vehicle-to-building (V2B), and vehicle-to-home (V2H) [7]. The microgrid-based V2G system, as defined by the Consortium for Electric Reliability Technology Solutions (CERTS), exemplifies this approach [14]. It operates as an auxiliary interconnection method by establishing a centralized microgrid management framework in family-oriented or standalone buildings, which acts as a buffer between the target EV and the regional grid [15]. To respond to power fluctuations from higher-level grids, independent microgrid control schemes were replicated and stacked into modular structures, allowing scalable management of larger regional power networks [16].

Alongside these hardware developments, operational and usage patterns evolved to meet emerging user needs and grid requirements. While household charging provided independent services, EVs increasingly relied on centralized or distributed charging stations directly connected to the regional grid [15]. Public bidirectional charging scenarios were proposed to overcome the limitations of basic control circuits used in standalone services, which often rely on simplistic feedback mechanisms insufficient for supporting direct EV-to-grid interconnection under non-periodic load fluctuations and complex power conditions [17]. In addition, security and privacy concerns related to the transmission of sensitive data during public charging continue to pose significant barriers to large-scale adoption [18,19].

Figure 1 illustrates the topological structure of power and information transmission chains among components within a V2G system. The figure shows that a fully functional V2G system involves intensive information exchange and processing across all layers of interaction. To address these challenges, researchers [20,21] have focused on improving real-time control systems and instantaneous response circuit structures. The goal is to enable bidirectional power transfer with negative feedback between the power grid and electric vehicles under various energy configurations. This includes updating charging circuit connectors [13] and establishing information transformation protocols [22] to effectively respond to demand fluctuations in the grid while ensuring a secure data transmission environment. Drawing on current technological advancements in hardware devices within V2G networks, particularly the significant progress made in external bidirectional transmission facilities and the built-in battery management systems (BMSs) of EVs [9], researchers have proposed diversified management strategies and optimization algorithms that focus on V2G network management and optimizations in complex bidirectional charging scenarios. These management schemes are designed to address varying demands by coordinating the periodic differences between EV charging behaviors and grid load distributions from social, economic, and environmental perspectives.

Accordingly, the interplay between technological innovation and market demand has driven V2G research to evolve into increasingly specialized subfields. Over the past decade, the generalized V2G research framework has developed into a multidisciplinary and integrative domain encompassing hardware development [23], management algorithm design [24], and the evaluation of ethical considerations [25], etc. A comparison of research outcomes across different periods reveals that conflicts between new technological paradigms and established conclusions highlight the highly iterative nature of V2G research. By “iterative,” we refer to a continuous feedback process in which emerging innovations prompt the reassessment of prior findings, leading to updated models, refined algorithms, and revised theoretical insights [26]. Understanding these developmental patterns and recent achievements is therefore critical for forecasting future trends, accelerating technological advancements, and guiding the ongoing evolution of the V2G field.

Previous reviews [27,28] on V2G have typically concentrated on specific technical or social dimensions of the field—such as communication technologies, control algorithms, or the social acceptability of V2G adoption. While these topic-focused studies offer valuable depth and insight for researchers working on mature subtopics, they often lack horizontal breadth across the broader V2G landscape. In contrast, several systematic reviews [8,29] have provided more comprehensive overviews that summarize research outcomes across multiple V2G subfields. However, these works generally fall short in revealing the quantitative distribution of research hotspots within the domain and thus offer limited guidance for early-stage researchers or practitioners seeking to identify promising research pathways and thematic directions. This review establishes a foundational framework for examining the scope of V2G research and its associated segmented fields, along with subordinate research directions. Utilizing this analytical framework, a systematic evaluation of selected V2G literature is conducted to identify the distribution and evolution of research focuses across both thematic domains and chronological phases. Methodologically, the review adopts a combined approach of quantitative and qualitative analysis. It scientifically categorizes and evaluates key publications from the past decade based on their publication years and respective research areas. Furthermore, the review conducts a detailed analysis of the differences and interconnections among major research outcomes at various stages within each subfield. Finally, the review identifies overlooked research elements and proposes technological needs and research priorities for the V2G field in the near term.

2. Methodology

Using the unified search query “V2G” OR “Vehicle to Grid”, a dual-dimensional dataset was compiled, incorporating Cumulative Citation Counts (CCCs) and Relative Citation Ratios (RCRs) for each relevant publication from the past decade (2015 to April 2024). A Python-based data retrieval pipeline (Python 3.10) extracted these citation metrics from bibliographic records. To identify high-impact literature, a composite evaluation metric was applied: publications were first ranked by RCR (as a field-normalized measure of impact) and then sub-sorted by CCC within similar RCR ranges to differentiate between works of comparable influence. This two-step hierarchical sorting ensured that both field-adjusted impact and absolute citation volume were considered in selection. To ensure consistency and minimize bias introduced by platform differences or author visibility, all data was sourced from NUsearch [30], the University of Nottingham’s integrated bibliographic search engine. The ten-year review window was divided into two equal sub-periods: 2015–2019 and 2020–2024. From each period, the top 100 publications were selected based on the composite citation metric described above, yielding a reference dataset of 200 articles. Incomplete records, such as conference abstracts or inaccessible full texts, were excluded. This curated dataset then underwent both qualitative and quantitative analyses to explore subdomain distribution and research evolution. Specifically, thematic classification was conducted through manual coding of abstracts and keywords, while bibliometric mapping (e.g., keyword co-occurrence) and dynamic topic modeling (DTM) were employed to identify long-term patterns and emerging research trends. These methods are detailed in the subsequent analysis sections.

It is important to note that the citation-based selection framework employed in this study follows established practices in bibliometric and systematic review methodologies [31,32]. The decision to focus on the top 100 publications within each sub-period was made to balance representativeness and analytical clarity—capturing high-impact literature that has substantially shaped the discourse of V2G research while maintaining a manageable sample size for in-depth qualitative coding. This “high-impact subset” approach is widely adopted in scientometric analyses to uncover disciplinary evolution and intellectual structure without the confounding effects of citation noise from less influential works.

However, this approach also entails certain limitations. First, emphasizing highly cited publications inevitably introduces selection bias, as citation accumulation tends to favor earlier works and English-language journals, even though a dual-layer evaluation based on both RCR and CCC was employed to minimize such bias. Second, comparisons of absolute publication counts or topic prevalence between the two periods should be interpreted as relative trends within the top-tier literature rather than as precise reflections of the total publication output. Third, the unified search query (“V2G” OR “Vehicle to Grid”) may underrepresent studies from adjacent fields—such as energy economics or foundational electrical engineering research on bidirectional power transmission—where different technical terminologies (e.g., “bidirectional” or “bi-directional”) are commonly used. These limitations were considered throughout the analysis, and the results are therefore presented as indicative of major research directions rather than exhaustive quantitative measures.

This systematic review is structured into three stages to organize and evaluate the achievements of selected papers across the selected decade research period. The first stage employs a multi-level qualitative analysis method to categorize the literature into subdivided research fields:

• Determine Secondary Research Fields: To identify the primary subdomains within the V2G literature, a thematic analysis was conducted. Articles were screened using a composite citation-based criterion, selecting the top 100 most influential publications in each period based on a combination of RCR and CCC, as described earlier. Following selection, abstracts and author-provided keywords from each article were manually reviewed and coded using an inductive thematic analysis approach. This process involved open coding of recurring topics, clustering of similar codes into broader categories, and iterative refinement to ensure consistency. Through an iterative process, recurrent research themes were identified and grouped, ensuring that the categorization was grounded in empirically observed patterns within the literature. This analytical procedure resulted in the following distinct categories (as illustrated in Figure 2):
  • Power Supply Side: This includes studies on load distribution in regional power grids and the generation characteristics of specific sustainable energy resources.
  • Bidirectional Charging Interaction: This area focuses on innovations in circuit connectors for V2G charging and protocols for V2G data transmission.
  • Electric Vehicles (EVs): This field encompasses the performance assessment of EV batteries and in-vehicle sensing systems.
  • V2G Network Management and Optimization: This segment explores management strategies for V2G networks and optimization algorithms for bidirectional charging systems.
  • Other: This category includes literature reviews, interviews, and observational records.
• Classify Subordinate Research Directions and Experimental Depth: This phase involves a systematic analysis of research outcomes within each subdomain through a comprehensive literature review. The primary objective is to identify variations in research findings across different temporal and regional contexts within the same subdomain. The classification is established based on key scholarly contributions documented in the literature, with evaluation criteria including:
  • The degree of coincidence and uniqueness of research purposes and corresponding results.
  • The regional context and the temporal relevance of research targets and related achievements.
  • The research methodology and generalizability of the established experiments.
  • Influencing factors and relevant technical parameters in the research processes.

During the aforementioned coding process, the thematic classification was conducted manually by a single researcher. To enhance the reliability and transparency of the coding results, a detailed coding protocol was established prior to analysis, specifying explicit inclusion criteria and definitions for each subdomain. This procedure minimized subjective bias during the classification stage. After the initial coding, the dataset was re-examined in two independent rounds conducted several weeks apart to ensure internal consistency. Any discrepancies identified during this self-audit were reviewed and corrected according to the predefined rules, ensuring that the final classification framework remained stable and reproducible.

For papers that spanned multiple thematic categories, classification was based on the primary research contribution of each work. In such cases, the subdomain assignment reflected the field most directly associated with the study’s main output rather than its secondary or supporting findings. For example, certain studies on V2G optimization not only proposed optimization strategies but also assessed the economic feasibility of these strategies through parameterized experiments. However, since these papers did not develop generally applicable economic models, they were classified under the V2G management and optimization subdomain rather than economic analysis. This approach ensured that each publication was uniquely categorized according to its dominant research focus, thereby minimizing bias and avoiding duplication in the quantitative distribution of literature across subfields.

The second phase of the analysis employs quantitative methodologies to assess publications along both horizontal and vertical dimensions. The horizontal comparison quantitatively examines the relationship between research themes and prevailing trends within specific time periods. This analysis reveals three key aspects: (1) the distribution of research focus across subdomains, as evidenced by publication volumes, which indicates current research hotspots and trends; (2) the stratification of research directions within each subdomain, ranked by their respective research output; and (3) the geographical distribution of research objects and outcomes within each subdomain, elucidating region-specific characteristics through the correlation between research achievements and geographic locations. Furthermore, this comparative approach uncovers subtle regional variations in research emphasis, particularly those influenced by governmental policy frameworks and local market dynamics. In conducting the horizontal analysis, articles from the same research period are evaluated based on the following criteria:

• The distribution of article quantities and their corresponding weight across the different secondary research fields.
• A further subdivision of research directions within each secondary field, with a ranking of these subfields based on the volume of research output.
• The absolute publication counts per secondary research field, along with the geographic distribution of research subjects and outcomes within each field, demonstrating the relationship between research achievements and regional characteristics.

In contrast, the vertical comparison focuses on the temporal evolution of research interests, with particular emphasis on the influence of critical factors, such as advancements in innovative technologies and market fluctuations. The vertical analysis evaluates the selected articles for each year using the following criteria:

• Comparison of Proportional Distributions: Analyzing changes in the proportion of articles across each secondary research field.
• Shifts in Interests and Corresponding Quantities: Examining changes in the interests and the number of articles in further-subdivided research directions within each secondary research field.
• Quantification of High-Impact Articles: Assessing the number of high-impact articles published in each studied year.

Building on the statistical results from the comprehensive analysis, the third phase of comparative predictive evaluation focuses on exploring the transformation of research emphases and identifying potential technical demands within V2G research segmentation fields. Additionally, the fluctuations in the distribution of research hotspots identified in the second phase are analyzed to forecast mainstream research directions and broader market expectations in the short term.

3. V2G Research: Technical Achievements and Hotspot Distribution

As summarized in Figure 3, V2G research primarily focuses on products related to bidirectional charging interaction and V2G network management and optimization fields. Except for a temporary decline in publication volume during 2020–2021 due to specific external factors, academic interest in V2G has demonstrated steady annual growth within each five-year period. Figure 4 shows a keyword co-occurrence network analysis of 200 key V2G publications, created using VOSviewer (VOSviewer 1.6.20), a software tool developed for constructing and visualizing bibliometric maps based on scientific literature data [33]. Common generic terms like “energy” and “engineering” were excluded, and only keywords appearing at least five times were included in the analysis. In the network, larger nodes represent more frequent keywords, and the density (or proximity) of connecting lines reflects stronger co-occurrence relationships between terms. Different color clusters reflect the thematic structure emerging from co-occurrence patterns. For example, red nodes primarily relate to V2G and grid environment analysis, yellow nodes emphasize economic evaluation, green clusters suggest hardware-oriented research, blue nodes focus on management optimization, and purple clusters relate to communication or data transmission. While these VOSviewer-derived clusters are not identical to the thematic classification introduced in the methodology section (i.e., power supply side, bidirectional charging, EVs, V2G network management, and other), there is notable thematic overlap. For instance, keywords from the blue and purple clusters align broadly with topics under V2G network management and optimization, while the green cluster reflects the power-supply hardware dimension. This correspondence supports the relevance of the proposed subdomain framework, though the clustering reflects the network-based statistical relationships rather than predefined thematic boundaries.

The labels shown in Figure 4 were automatically generated by VOSviewer using a TF–IDF-based algorithm, which identifies the most representative and distinctive terms within each cluster. These labels objectively reveal the latent relationships among research keywords and highlight implicit linkages between thematic hotspots. However, from the perspective of constructing a structured domain taxonomy, keyword frequency alone does not constitute a rigorous basis for defining technological subfields. Moreover, because the VOSviewer clustering is built upon co-occurrence of research terms, it may underrepresent certain publication types—such as review or interview-based studies—that contribute conceptually but do not introduce new technical results. This can lead to blurred categorical boundaries.

In contrast, the manually constructed classification framework developed in the methodology section is grounded in domain-specific knowledge and evaluates papers according to their substantive technical contributions, thereby offering stronger logical coherence and interpretability at the research field level. Nevertheless, manual classification inevitably involves some degree of subjectivity. By combining both approaches—algorithmic, data-driven clustering and knowledge-based manual categorization—this study achieves a form of mutual validation. The convergence between the two systems enhances classification robustness, mitigates individual bias, and allows for a more comprehensive and systematic understanding of the structural composition of the V2G research landscape.

Figure 4. Co-occurrence Analysis of Keywords from 200 V2G Studies Based on VOSviewer Network Mapping.

Figure 4. Co-occurrence Analysis of Keywords from 200 V2G Studies Based on VOSviewer Network Mapping.

Note: Node size indicates keyword frequency. The proximity and density of connecting lines reflect the strength of co-occurrence relationships—terms that co-occur more frequently tend to be positioned closer and connected more densely. Colors represent clustered research themes identified by VOSviewer’s clustering algorithm:

• Red—Grid environment and V2G integration (this corresponds to Section 3.1 Power Supply Side, which reviews studies on grid operation, stability, and integration with V2G systems).
• Green—Hardware-oriented studies (these are reflected in Section 3.2 Bidirectional Charging Interaction, particularly in the discussion of V2G hardware design, such as connectors and technical interfaces).
• Purple—Communication and data transmission (this relates to Section 3.2 Bidirectional Charging Interaction, focusing on data transmission and communication design within V2G systems).
• Blue—Management and optimization strategies (these align with Section 3.4.1 Management Strategy, which addresses energy scheduling, load balancing, and system-level optimization approaches).
• Yellow—Economic evaluation (this is consistent with Section 3.4.2 Economic Strategy, where cost–benefit analyses, pricing mechanisms, and economic optimization are examined).

3.1. Power Supply Side

One of the design intentions of V2G is to respond to fluctuations in electricity generation from the power supply side as a downstream link in the grid. In terms of research intensity in the field of power supply, the level of focus on this area has decreased over time. From a macro perspective, natural renewable energy sources, such as photovoltaic (PV) and wind energy, exhibit similar generation characteristics and cyclical trends. Examining research outputs in this area over the past decade reveals that studies (e.g., [5,34]) increasingly focus on the variability and distribution characteristics of renewable energy generation within integrated regional power grids incorporating V2G services. These studies also explore the coupling effects between renewable energy generation characteristics and regional grid dynamics, rather than treating renewable energy sources as independent power units at the grid level. In this context, most analyses (e.g., [35,36]) of generation characteristics also propose corresponding management strategies or optimization models for the V2G system. In earlier studies, particularly those published between 2018 and 2019, 50% of the prominent articles in this research direction consider wind power as a form of distributed energy within the grid [5] and propose V2G management strategies for specific public scenarios [37]. For micro-transmission networks, such as microgrids incorporating V2G services, this represents the most prevalent V2G framework in earlier studies. These studies mostly focus on constructing multi-source integrated generation sides to provide continuous power support within the studied network [34]. This model, to some extent, alleviates the high-frequency reverse power flow pressure in the V2G system [10].

In terms of annual publication volume, research articles focusing on the power supply side consistently rank the lowest among various categories of V2G studies. Notably, after 2020, the number of V2G papers related to power supply-side management dropped to half of the previous publication volume. While this does not necessarily reflect the total publication volume across the entire V2G literature, it indicates a potential shift in research focus among highly cited works. Furthermore, compared to the energy-efficient schemes that dominated earlier research phases, load distribution is no longer the sole constraint. To adapt to the rapid changes in international energy markets, the recent literature [34] has developed economically preferential management strategies that consider both the characteristics of power generation and fluctuations in real-time electricity tariffs. These innovative strategies shift the focus to evaluating energy generation behaviors and V2G management from the perspective of energy consumers. Consequently, the impact models established based on this framework exhibit distinct timeliness and regional characteristics [38].

Beyond the coupling of multi-source power grid structures and V2G systems discussed in the selected high-impact literature, several studies in the electrical engineering domain have highlighted energy management challenges in active distribution networks with high V2G penetration. Specifically, research indicates that the integration of large numbers of bidirectional EVs can induce significant fluctuations in load profiles, affecting both real-time balancing and peak demand management [39]. High-density V2G deployment also impacts voltage regulation, as reverse power flows from EV discharging can lead to localized over-voltages in low-voltage feeders [40]. Moreover, the dynamic and stochastic behavior of aggregated V2G resources presents challenges for distribution network stability, including frequency deviations and transient voltage oscillations, particularly when coupled with intermittent renewable generation [41]. To address these issues, a range of coordinated control strategies have been proposed at the microgrid and feeder levels, including hierarchical dispatch algorithms, voltage-aware V2G scheduling, and real-time optimization frameworks that jointly account for load balancing, voltage constraints, and grid stability [42]. A practical example of these approaches is provided by Lee et al. [39], who demonstrated that V2G-based EV scheduling can significantly improve distribution network reliability by optimizing fault recovery and minimizing supply interruption costs, confirming the potential benefits of coordinated V2G integration in real-world scenarios.

3.2. Bidirectional Charging Interaction

Bidirectional charging interactions represent the second most prominent research field, accounting for more than 40% of publications across different years. The majority of these studies focus on developing advanced circuit connectors and corresponding communication protocols, which regulate power and data transmission between EVs and charging devices (see Figure 5). However, the models and execution standards for charging devices vary significantly across different regions, leading to regional limitations in the achievements within this research field. From a temporal perspective, research outcomes across various periods are largely shaped by existing hardware conditions and often cater to specific technical environments. For instance, Zahid [13] introduced a redesigned 3.5 kW DC-DC resonant converter for CLLC-type (Capacitor–Inductor–Inductor–Capacitor) resonant networks in 2015, with the 3.5 kW reverse transmission power being recognized as a universal output power for V2G bidirectional transmission at that time. In contrast, Zhu [43], also focusing on CLLC-type resonant networks, demonstrated in 2024 that the presence of large double line frequency (DLF) resonant currents can lead to additional transmission losses and system fluctuations when the same converter design principles are applied in different output power environments.

As a subfield of research within the power transmission chain, the investigation of circuit connectors accounts for more than 50% of the literature in the bidirectional charging interaction domain. The primary research achievements related to circuit connectors include chargers, converters, controllers, and inverters. These contributions encompass nearly all critical functions necessary to facilitate bidirectional power exchange under various transmission environments, such as power parameter adjustment [43], asymmetric bidirectional transmission control [44], and AC-DC or DC-DC resonant transformation [45]. Considering the characteristics of local grid topology and the demands of the charging market, specific research directions within this field may conflict with one another depending on the research stage and region. A review of the sample articles reveals that in early studies, aside from Zahid’s 2015 proposal of a bidirectional equal-power DC-DC model [13], most researchers concentrated on developing AC-DC-oriented bidirectional resonant converters tailored for V2G applications. However, compared to the AC-DC solutions extensively explored around 2017, recent research hotspots have gradually shifted toward the development of integrated or external DC-DC converter models. These newer studies particularly focus on addressing bidirectional, high-disparity, asymmetric power scenarios.

In the study of interactions between EVs and charging infrastructure, the reliability of V2G communication protocols has emerged as the second most prominent research focus, following hardware interface development. As the core component at the software level, research in this domain is closely coupled with advancements in hardware, such as circuit connectors. Existing literature identifies four key areas of focus in V2G communication protocol research: optimization of information transmission paths, development of security mechanisms, data persistence strategies, and adaptation to international protocol standards. As shown in Table 1—which summarizes 13 highly cited representative works in the field—and further visualized through the citation network in Figure 6, the time-series citation patterns reveal a clear trajectory of academic development. Specifically, the communication protocol subfield demonstrates a continuous chain of technical iterations, with recent studies forming distinct annual clusters based on earlier breakthroughs and the integration of emerging technologies.

An analysis of the literature reveals that early-stage communication solutions, particularly those before and around 2017–2018, primarily relied on cloud-based services for data management [46]. However, as the integration of V2G communication and data management technologies has deepened, more recent studies (e.g., [44,47]) increasingly favor layered blockchain architectures over traditional centralized cloud platforms. This shift is largely motivated by the need to mitigate risks associated with single points of failure and data breaches—issues inherent in centralized systems. The paradigm shift in communication protocol design is directly driven by the exponential growth in demand for data security and privacy in bidirectional communication scenarios. Consequently, research papers reflect a notable transformation in the proposed architecture and design of V2G communication pathways, although such transformations are primarily conceptual and have not necessarily been implemented in real-world V2G systems.

Bibliometric analysis indicates that over the past decade, more than 85% of highly cited studies on V2G communication protocols have involved innovations in privacy-preserving technologies. Major technological breakthroughs in this field include the application of homomorphic encryption for secure energy transaction data [48], polymorphic signature schemes supporting dynamic access control [22], and anonymous communication frameworks based on the Tor network [49].

Although research approaches in this domain have become increasingly diversified, efforts to establish unified international standards remain relatively limited. This is primarily due to the mutually exclusive nature of competing solutions and the rapid pace of technological iteration. For example, the International Organization for Standardization (ISO) 15118 [50] aims to enable secure plug-and-play communication via a Public Key Infrastructure (PKI) and digital certificates. However, its reliance on classical public-key cryptographic systems raises concerns, especially given the potential security threats posed by advances in quantum computing.

In the sampled literature, interest in international standardization is relatively low. Only Park [51] and Kester [52] specifically address ISO 15118 [50], proposing enhanced automatic authentication mechanisms and improved adaptability to market conditions. To compensate for the limitations of public-key cryptography, recent studies have explored several complementary approaches. Chen [53] introduced a cyber–physical co-authentication protocol tailored for Plug-and-Charge (PnC) scenarios. By leveraging smart contracts, this scheme ensures tamper-resistant energy transaction records, resists man-in-the-middle and replay attacks, and maintains user anonymity and data integrity. For resource-constrained environments, Xiao [54] proposed a lightweight authentication scheme based on Chebyshev chaotic maps and hash functions. This approach offers forward security for EV devices with limited resources, achieving a 37% reduction in communication overhead while maintaining strong robustness against impersonation attacks. Addressing risks from physical tampering, scheme [55] adopts a Physically Unclonable Function (PUF)-based authentication protocol, which effectively mitigates information leakage caused by device-level attacks. Compared to traditional methods, it improves resource efficiency by 52%. In particular, the QSKA protocol [19] introduced in 2024 utilizes superdense coding to construct a quantum-secure communication channel. Formally verified through the Coq proof assistant, this protocol achieves unconditional security and provides a theoretical foundation for post-quantum V2G communication. It shows strong potential as a future replacement for classical public-key encryption systems.

Table 1. Representative V2G Communication Protocol Papers with Highest Citation Network Density: Authors, Year, Summary, and Citation Networks.

No.	Authors (Partial)	Publication Year	Summary	Citation Network
A1 [46]	N. Saxena et.al.	2016	Proposes a robust authentication mechanism to support flexible bidirectional energy transfer for mobile EVs in V2G systems.	Cited by later works that build upon authentication protocols for secure communication and energy trading in V2G environments.
A2 [56]	J. Shen et.al.	2018	Proposes a lightweight, privacy-preserving key agreement protocol to secure communications in V2G networks under the Social Internet of Things (SIoT) framework.	Widely cited by subsequent studies focusing on secure key exchange and privacy protection in V2G and IoT-integrated smart grid systems.
A3 [49]	Y. Li et.al.	2018	Proposes a differential privacy-based approach to protect electric vehicle location data in V2G networks, preventing sensitive information leakage.	Cited in research addressing privacy-preserving mechanisms in V2G communication, especially those employing differential privacy or location obfuscation techniques.
A4 [57]	A. Braeken et.al.	2018	Introduces AAA, an autonomous and anonymous user authentication protocol tailored for V2G networks, focusing on balancing security, anonymity, and system efficiency.	Cited by subsequent studies developing anonymous authentication and lightweight security protocols in V2G and smart grid environments.
A5 [58]	M. Tao et.al.	2018	Proposes AccessAuth, a capacity-aware and secure authentication protocol for federated IoT-enabled V2G networks, enhancing both scalability and security access control.	Cited by research focused on scalable authentication mechanisms in V2G systems, especially within federated IoT and smart grid infrastructures.
A6 [59]	L.F.A. Roman et.al.	2019	Proposes a pairing-based protocol designed for secure and efficient mutual authentication between EVs and the smart grid in V2G networks.	Cited by later works focusing on cryptographic approaches to authentication in smart grid and V2G environments.
A7 [24]	K. Park et.al.	2019	Proposes a dynamic key management protocol with privacy-preserving features for V2G systems in SIoT environments, aimed at enhancing secure communication and user privacy.	Cited by studies focused on lightweight and dynamic cryptographic solutions for secure V2G and SIoT integration.
A8 [18]	M.H. Eiza et.al.	2019	Proposes an efficient and privacy-preserving PMIPv6 protocol designed for V2G networks, ensuring seamless mobility, secure authentication, and data protection for electric vehicles.	Cited by multiple studies that focus on secure mobility and handover protocols within V2G communications.
A9 [22]	G. Bansal et.al.	2020	Proposes a lightweight mutual authentication protocol for V2G networks using Physical Unclonable Functions (PUFs) to achieve secure and efficient identity verification between EVs and the grid.	Cited in research on hardware-based authentication and lightweight cryptographic solutions for V2G systems.
A10 [60]	Y. Su et.al.	2020	Proposes a novel authentication scheme for V2G networks that preserves user privacy and guarantees secure communication using advanced cryptographic techniques.	Referenced in studies focusing on privacy protection and secure identity verification in V2G authentication frameworks.
A11 [61]	Y. Zhang et.al.	2021	Proposes a privacy-preserving authentication protocol for V2G networks that efficiently reduces computational costs while ensuring user anonymity and security.	Cited in recent research that addresses lightweight and privacy-focused authentication mechanisms in V2G systems.
A12 [2]	J. Hu et.al.	2022	Proposes a distributed Model Predictive Control (MPC) approach utilizing reactive power from V2G systems to enable real-time voltage regulation in distribution networks.	Cited by recent works focusing on grid stability and real-time control strategies using V2G-enabled electric vehicles.
A13 [62]	W. Hou et.al.	2023	Proposes a lightweight, privacy-preserving authentication protocol for secure and efficient EV charging reservations within 5G-enabled V2G networks.	Referenced by emerging studies on integrating 5G technology with secure V2G communication, particularly in the context of lightweight cryptographic protocols.

Table 1. Representative V2G Communication Protocol Papers with Highest Citation Network Density: Authors, Year, Summary, and Citation Networks.

No.	Authors (Partial)	Publication Year	Summary	Citation Network
A1 [46]	N. Saxena et.al.	2016	Proposes a robust authentication mechanism to support flexible bidirectional energy transfer for mobile EVs in V2G systems.	Cited by later works that build upon authentication protocols for secure communication and energy trading in V2G environments.
A2 [56]	J. Shen et.al.	2018	Proposes a lightweight, privacy-preserving key agreement protocol to secure communications in V2G networks under the Social Internet of Things (SIoT) framework.	Widely cited by subsequent studies focusing on secure key exchange and privacy protection in V2G and IoT-integrated smart grid systems.
A3 [49]	Y. Li et.al.	2018	Proposes a differential privacy-based approach to protect electric vehicle location data in V2G networks, preventing sensitive information leakage.	Cited in research addressing privacy-preserving mechanisms in V2G communication, especially those employing differential privacy or location obfuscation techniques.
A4 [57]	A. Braeken et.al.	2018	Introduces AAA, an autonomous and anonymous user authentication protocol tailored for V2G networks, focusing on balancing security, anonymity, and system efficiency.	Cited by subsequent studies developing anonymous authentication and lightweight security protocols in V2G and smart grid environments.
A5 [58]	M. Tao et.al.	2018	Proposes AccessAuth, a capacity-aware and secure authentication protocol for federated IoT-enabled V2G networks, enhancing both scalability and security access control.	Cited by research focused on scalable authentication mechanisms in V2G systems, especially within federated IoT and smart grid infrastructures.
A6 [59]	L.F.A. Roman et.al.	2019	Proposes a pairing-based protocol designed for secure and efficient mutual authentication between EVs and the smart grid in V2G networks.	Cited by later works focusing on cryptographic approaches to authentication in smart grid and V2G environments.
A7 [24]	K. Park et.al.	2019	Proposes a dynamic key management protocol with privacy-preserving features for V2G systems in SIoT environments, aimed at enhancing secure communication and user privacy.	Cited by studies focused on lightweight and dynamic cryptographic solutions for secure V2G and SIoT integration.
A8 [18]	M.H. Eiza et.al.	2019	Proposes an efficient and privacy-preserving PMIPv6 protocol designed for V2G networks, ensuring seamless mobility, secure authentication, and data protection for electric vehicles.	Cited by multiple studies that focus on secure mobility and handover protocols within V2G communications.
A9 [22]	G. Bansal et.al.	2020	Proposes a lightweight mutual authentication protocol for V2G networks using Physical Unclonable Functions (PUFs) to achieve secure and efficient identity verification between EVs and the grid.	Cited in research on hardware-based authentication and lightweight cryptographic solutions for V2G systems.
A10 [60]	Y. Su et.al.	2020	Proposes a novel authentication scheme for V2G networks that preserves user privacy and guarantees secure communication using advanced cryptographic techniques.	Referenced in studies focusing on privacy protection and secure identity verification in V2G authentication frameworks.
A11 [61]	Y. Zhang et.al.	2021	Proposes a privacy-preserving authentication protocol for V2G networks that efficiently reduces computational costs while ensuring user anonymity and security.	Cited in recent research that addresses lightweight and privacy-focused authentication mechanisms in V2G systems.
A12 [2]	J. Hu et.al.	2022	Proposes a distributed Model Predictive Control (MPC) approach utilizing reactive power from V2G systems to enable real-time voltage regulation in distribution networks.	Cited by recent works focusing on grid stability and real-time control strategies using V2G-enabled electric vehicles.
A13 [62]	W. Hou et.al.	2023	Proposes a lightweight, privacy-preserving authentication protocol for secure and efficient EV charging reservations within 5G-enabled V2G networks.	Referenced by emerging studies on integrating 5G technology with secure V2G communication, particularly in the context of lightweight cryptographic protocols.

In addition to the scholarly research contributions highlighted in the literature, which have played a pivotal role in advancing V2G communication protocols, industry trends have exerted a similarly intrinsic influence [63]. The deployment of large-scale commercial electric vehicle fleets and smart charging infrastructures, spearheaded by companies such as Tesla and Siemens, has accelerated the adoption of standardized interfaces like ISO 15118. In particular, industry demand for seamless “Plug-and-Charge” user experiences and cross-network interoperability has prompted standardization bodies to implement practical enhancements in both security and scalability [64]. Furthermore, policy frameworks in leading regions for V2G development, such as the United States [65], addressing interoperability have further driven the evolution of V2G communication protocols toward improved privacy protection and post-quantum security. Conversely, the fragmentation of the EV market and associated charging infrastructure presents a countervailing challenge to the establishment of universal standards.

3.3. EV—Battery Performance

Only approximately 5% to 10% of the articles in the sample analyzed the V2G execution environment from the perspective of EV systems, particularly battery performance characteristics. However, within the sample of papers analyzed, the number of publications addressing this research area roughly doubled in the last five years (2020–2024) compared to the first five years (2015–2019) covered in this review. These studies focus on examining the synergistic mechanisms and underlying transmission control logic between external V2G charging devices and the internal EV battery management system (BMS). Among these articles, researchers have designed a series of advanced detection experiments for various EV batteries to assess their bidirectional charging performance and structural integrity in complex grid transmission environments. A notable example is Uddin [66], who developed a battery degradation model for commercial C6/LiNiCoAlO₂ batteries and demonstrated that the intelligent V2G system not only does not exacerbate battery capacity degradation but can also extend the lifespan of EV batteries.

In addition to targeted research on EV batteries, which serve as the actual electricity exchange terminals in V2G systems, the literature also presents numerous auxiliary management systems for battery management systems (BMSs) aimed at optimizing the bidirectional electric transmission process within vehicles. The related studies include the development of built-in battery health assessment models [67], assisted sensing systems for ground pad configurations [68], and predictive economic evaluation models [9], among others. In practical marketing applications, these auxiliary research achievements are expected to facilitate EV manufacturers in launching a greater number of V2G-supported products.

3.4. V2G Network Management and Optimization

V2G network management and optimization represents the final link in the chain of V2G networks and is the most extensively studied field in the sampled articles. Nearly half of the papers address potential optimized management patterns and have spawned numerous subordinate research directions related to this topic, including fundamental management strategies, economically oriented optimization, user behavior analysis, estimation models, and control algorithms (see Figure 7).

3.4.1. Management Strategy

The V2G management strategy constitutes the core research focus of V2G network management and optimization studies, with research publications accounting for approximately 40% of the sample articles analyzed from the pool of 200 publications. It is important to distinguish this category from the power supply-side subdomain. While the power supply-side research primarily models the operational conditions of the electricity grid—such as network parameters, generation variability, and load profiles—to create feasible environments for V2G operation and identify potential technical challenges, the management strategy category focuses on the scheduling and control logic of V2G itself. Specifically, it addresses how V2G dispatch strategies are designed to achieve particular objectives, such as economic optimization, frequency regulation, or coordinated load balancing. In this discussion, detailed control mechanisms for specific transmission conditions are not addressed in depth so as to maintain the focus on broader strategic patterns. This approach allows for the comparison of diverse strategies and the identification of common principles across the selected studies. Based on the management scale and underlying allocation logic of the research subjects, mainstream management strategies can be classified as follows:

• Centralized interconnection (number of samples: 5 articles) is recognized as the most management-efficient mode of V2G in regional grid applications, encompassing community-level microgrids, commercial district networks, and larger-scale regional power systems. This planning mechanism relies on predefined management strategies and grid transmission schedules to facilitate the exchange of energy between plug-in EVs and the regional grid [16]. The centralized interconnection method effectively leverages the integration of EVs within a specific region. As a comprehensive, scalable solution, it facilitates the centralized management of the dynamic charging behaviors and on-board power status of all EVs within the area. By deploying a unified optimization algorithm, the system coordinates regional power grid fluctuations with the charging and discharging patterns of available EVs, thereby ensuring optimal operational cost efficiency throughout grid power distribution cycles. However, this interconnection method lacks adequate consideration of vehicle owners’ benefits and flexible usage demands. In practical applications, centralized management methods require the aggregation of a sufficient number of EVs at specific locations within a given timeframe to enhance the regulating and buffering capabilities of the regional grid.
• The distributed interconnection method (number of samples: 11 articles), also known as the autonomous interconnection method, seeks to develop scattered EVs as potential resources [69]. To address the management flexibility limitations inherent in centralized interconnected systems, the distributed interconnection approach focuses on the development of vehicle-mounted bidirectional smart chargers that enable EVs to connect with community-level grids at various access points [70]. These smart chargers are equipped with autonomous control architectures that manage bidirectional transmission in V2G systems based on real-time information from terminal interfaces, including the active and reactive power demands of the grid, real-time prices (RTPs), electrical characteristics of output interfaces, and the state of charge (SOC) of the batteries [71]. While the distributed interconnection method offers maximum flexibility and autonomy for individual vehicles, it simultaneously introduces uncontrollable stochastic factors into the overall transmission and distribution of the grid. This may result in a limited rate of integrated optimization and subsequently reduce system reliability. Additionally, the implementation of vehicle-mounted bidirectional smart chargers increases the manufacturing and design costs of EVs [17].
• The microgrid-based integrated interconnection model (number of samples: 27 articles), as defined by the Consortium for Electric Reliability Technology Solutions (CERTS), aims to mitigate the adverse impacts of distributed generation on main grids [72]. A complete microgrid comprises distributed generation sources, energy storage devices, energy conversion units, and overload protection and monitoring systems. When structured as interconnected cells, multiple microgrid systems collectively form an optimized secondary community-level grid. In this subordinate transmission approach, the energy systems of EVs serve the microgrid directly, rather than connecting to the main network. This configuration significantly reduces uncontrolled disturbances to the primary grid, particularly when the main grid incorporates heterogeneous devices (including generation units, energy storage systems, and load equipment) exhibiting mutually incompatible power exchange patterns with the grid’s inherent time-varying characteristics—a situation that can lead to operational conflicts and reciprocal interference among these devices [73]. Furthermore, this model represents one of the most extensively studied (e.g., [72,74]) V2G interconnection frameworks in earlier research.
• Battery-pack-based interconnection (number of samples: 1 article) offers a novel approach to facilitate V2G integration within community-level grids by accommodating the flexible usage schedules of EVs. This method utilizes battery packs at specialized EV battery stations as secondary buffer mediums between vehicles and the grid, allowing EV owners to replace their batteries at these stations according to their needs, rather than connecting their vehicles directly to the regional grid [75]. The design logic and transmission architecture of this approach resemble those of the centralized interconnection model. However, unlike the centralized interconnection, which primarily focuses on management mode, switching stations must ensure that a certain percentage of batteries remain fully charged to meet regular replacement demands. This method combines the advantages of optimized transmission and distribution algorithms associated with centralized interconnection and the benefits of fast-charging infrastructure. Nonetheless, the need for standardized performance parameters and interface specifications for the concerted operation of battery packs poses a significant limitation to the broader adoption of this interconnection method.

3.4.2. Economic Strategy

Cost–benefit analysis and economic strategy research in V2G systems primarily focus on the evaluation of battery degradation costs and overall market viability. Among the studies reviewed across two research phases, approximately 30% of those proposing management strategies also included corresponding economic optimization models to validate their financial feasibility and practical applicability.

Aside from a limited number of specialized studies that directly examine the impact of compensation mechanisms on V2G profitability, most research adopts a case-based approach centered on specific regional contexts. These studies typically develop user-oriented optimization strategies and integrate localized energy market mechanisms to construct economic assessment models. Common economic indicators used include average annual V2G revenue, battery degradation costs, and net present value (NPV), which are employed to quantify the financial implications of V2G deployment [76].

From a market and policy perspective, although most of the proposed economic models share similar foundational cost–benefit calculation frameworks, their specific optimization results vary significantly depending on the compensation mechanisms and local market conditions in place. Nonetheless, the literature suggests that under current market environments, V2G services demonstrate both cost competitiveness and profit potential—particularly for high-usage scenarios and large-scale, centralized vehicle groups, such as fleet operators.

Importantly, regardless of contextual differences, all case studies consistently emphasize the critical role of battery degradation costs in economic evaluation. Empirical research from typical application scenarios reveals the following:

• Fixed Dispatch Scenarios (e.g., Public Transit Systems): A U.S.-based case study [77] involving the provision of 70 kW frequency regulation services in the PJM market showed a 14-year Net Present Cost (NPC) of $24,200 per seat (with average annual V2G revenue of $4500 per unit). The results indicate limited economic feasibility due to extended payback periods under current technical constraints.
• Non-residential Variable Load Scenarios: A commercial V2G study in the UK [10] demonstrated that, over a 10-year period including infrastructure costs, vehicles participating in electricity markets three times per week could achieve an NPV of £8400 (with average annual income of £840 per vehicle). While economically viable, battery degradation costs were found to significantly impact overall profitability.
• Microgrid Integration Scenarios: Three studies [14,15,71] consistently confirmed that integrating V2G technology can significantly reduce total microgrid operating costs, with one EU case reporting average annual returns of up to €3046.81. While the absolute monetary value of battery degradation costs in certain cases—for example, a £38.62 increase over three years in the UK study—may appear small relative to total revenues, these costs exert a disproportionate influence on overall project viability. This is because battery degradation directly affects lifespan and replacement cycles, and even minor variations in degradation rates can significantly shift break-even thresholds and NPV outcomes, thereby eroding the net financial benefits of V2G deployment [78].

3.4.3. User Behaviors

Systematic analysis of the studied literature on scenario-based power consumption patterns and EV user behaviors reveals that user electricity usage across different application contexts significantly alters the cyclical load distribution patterns of regional power grids. Key impacts include variations in peak-valley load differences, seasonal fluctuation characteristics, and the periodicity of power distribution [79,80]. Consequently, the articles aimed to enhance the overall efficiency of V2G network management and optimization by optimizing the charging behaviors of private EVs and exploring new V2G application scenarios. Notably, after 2019, the intrinsic daily operational patterns of private EVs were disrupted due to unpredictable changes in work schedules [81]. Recent research, particularly from 2021 and 2022, proposed diverse user-driven charging strategies, including instantaneously planned charge–discharge rhythms and autonomous power parameter adjustments. These approaches replaced the preset charging models commonly used in V2G management studies published prior to 2019. In addition to conventional V2G application scenarios, studies also investigated unique scenarios to address power demand. For instance, Shirazi [77] and Manzolli [16] conducted cost–benefit assessments and explored potential economic strategies for eBus-oriented V2G systems in Philadelphia, USA, and Portugal, respectively. Building on distributed V2G interconnection theories, Jafari [73] introduced the concept of V2S (EV to Subway) and its control model to optimize load management within urban subway systems.

3.5. Other

In addition to directly investigating technical advancements in the V2G field, some studies aim to assess the feasibility and reliability of V2G systems from the perspectives of synthesizing existing technological achievements for cross-sectional comparison and examining social environments. In this segment of the literature, earlier research primarily employed two approaches: literature reviews and social investigations. Literature reviews focused on summarizing technical achievements within specific disciplinary domains underlying V2G systems—such as fundamental communication technologies [27]—thereby illustrating the developmental trajectory of V2G within a given subfield. However, differences in regional technical standards restrict the broader applicability of some findings. Regarding the social environment, authors engaged in discussions with industry experts [29] and the public [82] to evaluate the adaptability and feasibility of V2G systems. By gathering social attitudes toward V2G service systems, these studies highlighted potential management deficiencies, specific environmental constraints, and barriers to market promotion. With the increasing social recognition and market penetration of V2G technologies, more recent review-oriented studies [8] shifted their focus toward economic analyses and energy market assessments, adopting a cross-sectional comparison of published schemes in terms of their benefits. This line of work has increasingly adopted an econometric modeling perspective, treating V2G as an emerging commercially viable technology rather than continuing with qualitative social feasibility studies. Methodologically, compared to the basic social feedback approaches commonly used in articles published between 2017 and 2019, high-impact studies published after this period transitioned away from qualitative social investigation methods and embraced precise, quantitative econometric models grounded in real-world power transmission environments [83].

4. Where Will V2G Research Go? Future Development Directions and Research Approaches

4.1. Regional Characteristic

Based on the comparative analysis presented in Section 3, which highlighted the heterogeneous development trajectories of V2G technologies across regions, the future evolution of standardization is likely to follow distinct regional patterns rather than converging on a single global framework. The review revealed that while the iterative development of ISO 15118-20 [84] and IEC 61851-23 [85] has promoted international harmonization, persistent discrepancies in physical interfaces and communication protocols continue to shape region-specific technical and research priorities (see Table 2). This observation provides the empirical foundation for the following evidence-based expectations regarding the future direction of V2G standardization research.

In Europe, as noted in Section 3.2, most studies emphasize AC-based converter topologies (7–22 kW), aligning with the grid’s existing single/three-phase infrastructure and its relatively low power transmission requirements. This suggests that European research will likely continue refining cost-optimized AC V2G systems compatible with the IEC 61851 framework [86,87], prioritizing integration efficiency and grid adaptability rather than power scaling.

Conversely, studies from China and Japan have focused on non-symmetric bidirectional DC charging architectures, optimized for high-power transfer (200–400 kW) and ultra-fast operation. As recent developments such as China’s ChaoJi 3.0 standard demonstrate, these regions are expected to further advance next-generation DC V2G interfaces capable of supporting higher voltage and current ranges while maintaining backward compatibility with legacy GB/T and CHAdeMO systems [88].

Drawing on these observed regional trajectories, future standardization research may increasingly prioritize:

• Regulatory Harmonization: As cross-border energy exchange becomes more prevalent, the literature [89] suggests that harmonized governance frameworks will be needed to bridge discrepancies between regimes such as the EU GDPR and China’s Cybersecurity Law.
• Technological Integration: Evidence from recent cross-standard hardware proposals [65] indicates a growing movement toward modular, multi-standard-compatible charging architectures and secure quantum-encryption-based communication schemes.
• Policy Coordination: As identified in Section 3.4, disparities in compensation and market access remain major barriers to interoperability. Consequently, future policy-driven research is likely to emphasize adaptive settlement mechanisms and standardized data models for transnational electricity markets.

Collectively, these trajectories should be viewed not as speculative forecasts but as evidence-informed projections derived from the synthesis of current literature and standardization trends across major regions [90,91].

Table 2. Scope Comparison of Major EV Charging Standards Across Regions.

Standard	Region	Communication	Interface	Power Transmission	Charging Type	V2G Support
IEC 61851 [86]	Global	Basic communication (PWM)	Conductive charging interface	Specifies power transmission	AC and DC	Limited support (mainly DC)
IEC 62196 [92]	Global	Not specified	Defines connector types	Specifies power transmission	AC and DC	Not specified
ISO 15118 [50]	Global	Full protocol stack (ISO/OSI model)	High-level communication interface	Specifies power transmission	Mainly DC (some AC supported)	Supported
SAE J1772 [93]	North America	Basic communication (PWM)	Connector and interface defined	Specifies power transmission	AC and DC (with Combo variant)	Limited support
SAE J3068 [94]	North America	Communication defined for AC	AC connector and interface	Specifies power transmission	AC only	Not supported
SAE J3072 [95]	North America	Power-line communication (PLC)	Conductive charging	Specifies power transmission	AC (Level 2)	Limited support (AC)
CHAdeMO [96]	Japan, Global	CAN-based communication protocol	Proprietary DC interface	Specifies power transmission	DC only	Supported
GB/T 20234 [97]	China	Not specified	Defines connector types	Specifies power transmission	AC and DC	Not specified
GB/T 27930 [98]	China	CAN-based communication protocol	Not specified	Not specified	DC only	Supported
CCS [99]	Europe, Global	Based on ISO 15118 or DIN 70121 [100]	Combo connector interface	Specifies power transmission	AC and DC	Supported (with ISO 15118)

Table 2. Scope Comparison of Major EV Charging Standards Across Regions.

Standard	Region	Communication	Interface	Power Transmission	Charging Type	V2G Support
IEC 61851 [86]	Global	Basic communication (PWM)	Conductive charging interface	Specifies power transmission	AC and DC	Limited support (mainly DC)
IEC 62196 [92]	Global	Not specified	Defines connector types	Specifies power transmission	AC and DC	Not specified
ISO 15118 [50]	Global	Full protocol stack (ISO/OSI model)	High-level communication interface	Specifies power transmission	Mainly DC (some AC supported)	Supported
SAE J1772 [93]	North America	Basic communication (PWM)	Connector and interface defined	Specifies power transmission	AC and DC (with Combo variant)	Limited support
SAE J3068 [94]	North America	Communication defined for AC	AC connector and interface	Specifies power transmission	AC only	Not supported
SAE J3072 [95]	North America	Power-line communication (PLC)	Conductive charging	Specifies power transmission	AC (Level 2)	Limited support (AC)
CHAdeMO [96]	Japan, Global	CAN-based communication protocol	Proprietary DC interface	Specifies power transmission	DC only	Supported
GB/T 20234 [97]	China	Not specified	Defines connector types	Specifies power transmission	AC and DC	Not specified
GB/T 27930 [98]	China	CAN-based communication protocol	Not specified	Not specified	DC only	Supported
CCS [99]	Europe, Global	Based on ISO 15118 or DIN 70121 [100]	Combo connector interface	Specifies power transmission	AC and DC	Supported (with ISO 15118)

4.2. Centralized Management Trend

As presented, early research on V2G management strategies primarily evaluated operational performance within isolated microgrid environments. However, as observed in multiple studies [5,34], the increasing penetration of renewable energy is substantially altering grid supply–demand dynamics. In particular, reliance on single microgrid modules is insufficient to absorb the variability induced by large-scale renewable integration, while independent operation of multiple microgrids introduces delays in system-wide response, limiting the ability to meet fast-response requirements at the transmission level. Economically, analyses indicate that the marginal benefits of small-scale systems diminish with higher penetration rates, suggesting an approaching performance ceiling for microgrid-based V2G applications [101].

These observed limitations provide an evidence-based rationale for the ongoing shift toward centralized management of V2G resources, which manifests in two interrelated dimensions. First, the physical scale of control is expanding: V2G aggregation and scheduling are evolving from isolated microgrids to regional or national-level systems. Second, the control architecture is undergoing evolution: to manage large numbers of centralized or distributed EV resources efficiently, control schemes must transition from single-logic, microgrid-specific frameworks to hierarchical or distributed optimization architectures founded on centralized V2G scheduling [102,103]. This transformation allows local microgrid controllers to operate as subtasks within a global optimization objective, thereby ensuring scalability, robustness, and real-time performance.

Although experimental studies focused solely on isolated microgrids have declined—accounting for only approximately 4% of selected publications over the past five years—this trend is encouraging, as it indicates a growing research emphasis on aggregating individual microgrids into larger, coordinated clusters to study higher-level V2G management and network optimization. Such aggregation not only enhances system-level responsiveness but also creates new economic efficiencies through shared resources and optimized cross-grid coordination. Building on this trend, the establishment of unified V2G management frameworks, which treat large-scale EV clusters as virtual energy storage systems capable of dynamic power dispatch based on real-time pricing and grid conditions, emerges as a promising approach for managing modern power fluctuations.

From an actionable research perspective, the literature suggests several directions for advancing this field:

• Infrastructure Adaptation: Particularly in regions such as Europe with existing grid limitations, rather than relying on costly upgrades to the upper-level transmission or distribution infrastructure, research should explore approaches that enable stable, predominantly unidirectional power flows from community-scale grids to the higher-level grid. By optimizing coordination and dispatch at the neighborhood level, these methods can mitigate fluctuations and reduce stress on the broader grid while still accommodating the integration of V2G resources.
• Standardization and Communication Protocols: Expanding existing protocols such as IEC 61851 [86] to develop dedicated V2G communication standards is crucial. Research should prioritize secure, scalable, and interoperable communication frameworks suitable for large-scale, centralized V2G deployments.
• Control Strategy Development: Studies indicate that hierarchical or distributed optimization methods provide superior performance in aggregated V2G systems [90,91]. Future work should develop and experimentally validate modular control architectures capable of coordinating heterogeneous EV clusters in community-level grids.

4.3. Economic Orientation

Based on the studies reviewed in Section 3, V2G technology has the potential to generate economies of scale as EV penetration increases, but this effect is non-linear. Empirical and modeling studies [4,26,76] indicate that when a sufficient number of EVs participate simultaneously in the same region, their aggregated discharging can depress wholesale electricity prices, reducing the marginal revenue for each vehicle. These dynamics are further influenced by structural transformations in energy markets and large-scale renewable integration, which introduce unpredictable real-time price fluctuations and implicit cost burdens on the grid, such as compensation for curtailed renewable energy and investments to enhance system flexibility.

Drawing on these findings, several evidence-informed future directions can be identified. First, research should focus on the development of joint optimization frameworks that integrate battery aging models with economic performance metrics. Prior studies demonstrate that carefully managed charging and discharging schedules can mitigate battery degradation and, under certain conditions, even extend battery life [76]. Second, the design of aggregated V2G dispatch strategies at multiple scales—ranging from neighborhood microgrids to regional EV clusters—can maximize system-level economic benefits while minimizing the self-cannibalization effect observed in high-density deployments. Third, the literature suggests that flexible market mechanisms and ancillary service participation (including frequency response, balancing, and reserve markets) provide additional revenue streams that can offset declining energy market prices [26,76].

At the end-user level, prior analyses indicate that net benefits depend on system scale, market maturity, and dispatch intelligence. Based on these insights, future research should explore decentralized revenue-sharing models and scenario-based economic implementation frameworks. These could include dynamic pricing in urban centers, cross-regional trading along highway corridors, and virtual power plant configurations in residential communities, ensuring that users receive equitable and context-specific returns. By grounding these recommendations in empirical observations and prior modeling results, the proposed directions provide actionable pathways for optimizing both user-level and system-level economic performance, rather than speculative forecasts.

5. Conclusions

The main academic contribution of this study lies in its integrated, data-driven perspective on the V2G research landscape. Unlike prior reviews that primarily focused on isolated technical or social aspects of V2G—such as communication architectures, control mechanisms, or user acceptance—this work quantitatively maps the field as a whole. Through bibliometric and quantitative analysis of 200 high-impact publications, it identifies the structural relationships among major V2G subdomains and reveals the spatiotemporal evolution of research priorities over the past decade. This dual horizontal–vertical analytical framework not only bridges fragmented research areas but also uncovers emerging hotspots and developmental trajectories. As a result, the study provides a systematic roadmap that guides future research directions and supports both new and experienced scholars in navigating the rapidly evolving V2G domain.

Specifically, this study systematically reviews high-impact research in the V2G domain over the past decade using bibliometric analysis. A combined horizontal (cross-sectional categorization of research themes) and vertical (longitudinal analysis of thematic evolution) approach categorizes existing research into five key subfields while analyzing their thematic evolution. The results demonstrate sustained growth in scholarly attention toward V2G, with existing literature covering diverse grid design scenarios that validate the technical feasibility of V2G systems across different applications.

A detailed analysis reveals that current research predominantly focuses on bidirectional charging interactions and human–vehicle interface design, while comprehensive evaluations of battery system performance in V2G environments remain underexplored. Notably, core research areas—such as V2G hardware interfaces, communication protocols, and system optimization strategies—exhibit distinct spatiotemporal variations. Regionally, these variations stem from differing technical standards and grid requirements, while temporally, they reflect paradigm shifts driven by technological advancements. For instance, hardware interface research has transitioned from AC-DC slow charging toward bidirectional DC-DC asymmetric designs, while management strategy studies have evolved from microgrid feasibility assessments to localized economic impact evaluations.

Based on current trends, this study identifies three major directions for future V2G development. First, hardware interface design and standardization will increasingly emphasize regional adaptability. Second, management strategy research is expected to evolve from microgrid-focused applications to scenarios involving centralized, large-scale grid operations. Third, economic evaluations will expand across multiple contexts, with integrated battery degradation–profitability optimization emerging as a key research priority.