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Symmetry
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Symmetry/Asymmetry Studies in Modern Power Systems
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Symmetry/Asymmetry Studies in Modern Power Systems

A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Engineering and Materials".

Deadline for manuscript submissions: 30 June 2025 | Viewed by 12145

Special Issue Editors

Dr. Cheng Wang

E-Mail Website
Guest Editor
Associate Professor, School of Automation, Nanjing University of Science and Technology, Nanjing 210094, China
Interests: high-power power electronic conversion systems; new energy generation and grid integration; distributed control of AC/DC microgrids; the application of artificial intelligence in power electronic conversion
Dr. Zhong Chen

E-Mail Website
Guest Editor
Researcher, School of Electrical Engineering, Southeast University, Nanjing 210096, China
Interests: power system planning, operation and control; application of artificial intelligence in power system; intelligent dispatching and intelligent operation and maintenance of power grid; electric vehicles and energy Internet intelligent interaction
Dr. Lei Chen

E-Mail Website
Guest Editor
Associate Professor, Department of Electrical Engineering, Tsinghua University, Beijing 100084, China
Interests: power system stability; dynamic analysis; control of power systems
Dr. Tao Zhou

E-Mail Website
Guest Editor
Assistant Professor, School of Automation, Nanjing University of Science and Technology, Nanjing 210094, China
Interests: power system operation and control; the application of artificial intelligence in power systems; small disturbance stability; frequency stability of new power systems; new energy grid-connected control; flexible DC transmission

Special Issue Information

Dear Colleagues,

Symmetry and asymmetry concepts play a fundamental role in the design, operation, and stability of modern power systems. This Special Issue provides a platform for in-depth exploration of the relationship between symmetry and power systems, aiming to enhance our understanding of the impact of symmetry on system performance, reliability, and efficiency. This Special Issue will delve into various aspects of symmetry in power systems, including its application in fault diagnosis, system planning, and design. It will also highlight the role of symmetry in improving operational efficiency, enhancing system stability, and ensuring the reliable delivery of electricity. By exploring the intricate connections between symmetry and power systems, this Special Issue aims to foster a deeper understanding of the complexities involved and to provide valuable insights to improve power system design and operations.

This Special Issue invites researchers to contribute original research articles and reviews that explore various aspects related to symmetry and asymmetry in modern power systems. Applied case studies are especially welcome. Topics of interest for this Special Issue include, but are not limited to, the following:

  • Basic theory and practice of symmetry and asymmetry in power systems;
  • Fault diagnosis and prevention of symmetry and asymmetry in power systems;
  • Optimization, design, and planning of symmetry and asymmetry in power systems;
  • Energy efficiency management of symmetry and asymmetry in power systems;
  • Symmetry/asymmetry of power flow and transmission;
  • Symmetry/asymmetry of power system topology;
  • Symmetry/asymmetry in multiphase power systems;
  • Active symmetry and balance of power systems;
  • Reactive symmetry and balance of power systems;
  • Symmetry/asymmetry in power electronics devices and renewable energy components;
  • Algorithms for studying symmetry in power systems;
  • Influence of symmetry on power system operation, renewable energy integration, and smart grid technologies;
  • Symmetry/asymmetry of power system transients and influence on system stability;
  • Symmetry/asymmetry of power electronic-based power systems;
  • Grid-forming/grid-following control of multiple converters with asymmetries.

Dr. Cheng Wang
Dr. Zhong Chen
Dr. Lei Chen
Dr. Tao Zhou
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Symmetry is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • power systems
  • power electronics
  • symmetrical faults
  • asymmetrical faults
  • power system stability
  • balanced conditions
  • grid-forming converters

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Further information on MDPI's Special Issue policies can be found here.

Published Papers (9 papers)

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Research

24 pages, 7046 KiB  
Article
Stability Control Method Utilizing Grid-Forming Converters for Active Symmetry in the Elastic Balance Region of the Distribution Grid
by Zhipeng Lv, Bingjian Jia, Zhenhao Song, Hao Li, Shan Zhou and Zhizhou Li
Symmetry 2025, 17(2), 263; https://doi.org/10.3390/sym17020263 - 9 Feb 2025
Cited by 1 | Viewed by 570
Abstract
The development of the elastic balance area within the distribution network places greater demands on the interaction between sources and loads, which impacts the stability of the power system. While achieving symmetry in active power is essential for stable operation, it is challenging [...] Read more.
The development of the elastic balance area within the distribution network places greater demands on the interaction between sources and loads, which impacts the stability of the power system. While achieving symmetry in active power is essential for stable operation, it is challenging to attain perfection due to various disruptions that can exacerbate frequency and voltage instability. Additionally, due to the inherent resonance characteristics of LCL filters and the time-varying nature of weak grid line impedance, grid-connected inverters may interact with the grid, potentially leading to oscillation issues. A grid-forming inverter control method that incorporates resonance suppression is proposed to address these challenges. First, a control model for the grid-forming inverter based on the Virtual Synchronous Generator (VSG) is established, enabling the system to exhibit inertia and damping characteristics. Considering the interaction between the VSG grid-connected system and the weak grid, sequence impedance models of the VSG system, which feature voltage and current double loops within the αβ coordinate system, are developed using harmonic linearization techniques. By combining the impedance analysis method, the stability of the system under weak grid conditions is evaluated using the Nyquist criterion. The validity of the analysis is confirmed through simulations. Finally, in order to ensure the effectiveness and correctness of the simulation, an experimental prototype of an NPC three-level LCL grid-forming inverter is built, and the experimental results have verified that the system has good elastic support capability and resonance suppression capability in the elastic region. Full article
(This article belongs to the Special Issue Symmetry/Asymmetry Studies in Modern Power Systems)
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22 pages, 7192 KiB  
Article
An Adaptive Voltage Reference-Based Multi-Objective Optimal Control Method for the Power Flow Symmetry of Multi-Terminal DC Systems with the Large-Scale Integration of Offshore Wind Farms
by Yuanshi Zhang, Yiwen Feng, Tongxin Xu, Yilei Li, Xinye Du, Chaoyang Yuan and Hongrui Chen
Symmetry 2025, 17(1), 105; https://doi.org/10.3390/sym17010105 - 11 Jan 2025
Viewed by 838
Abstract
The optimization of the symmetry of MTDC systems after a contingency is crucial for the stable and economic operation of the MTDC systems. In this paper, a multi-objective optimal control method for the power flow symmetry of MTDC systems for the large-scale integration [...] Read more.
The optimization of the symmetry of MTDC systems after a contingency is crucial for the stable and economic operation of the MTDC systems. In this paper, a multi-objective optimal control method for the power flow symmetry of MTDC systems for the large-scale integration of offshore wind farms is proposed. A mirror relationship between the available headroom of DC lines and VSCs and their actual power flow distribution performance is established. A corresponding symmetry index is established for the MTDC network, and the multi-objective optimization problem is converted into a series of single-objective problems by the normal boundary intersection method, and solved by the original dyadic interior point method, so as to obtain the Pareto optimal solution with uniform distribution. The compromise optimal solution is decided according to the entropy weight double-basis point method, which provides decision-making guidance for the operators. The simulation results show that the normal boundary intersection method can solve the multi-objective dynamic optimal control problem of the VSC-HVDC system quickly and efficiently, and improve the symmetry of the power flow in an MTDC network. Full article
(This article belongs to the Special Issue Symmetry/Asymmetry Studies in Modern Power Systems)
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18 pages, 3004 KiB  
Article
Bi-Level Optimization Scheduling Strategy for PIES Considering Uncertainties of Price-Based Demand Response
by Xiaoyuan Chen, Jiazhi Lei and Xiangliang Zhang
Symmetry 2025, 17(1), 43; https://doi.org/10.3390/sym17010043 - 29 Dec 2024
Viewed by 570
Abstract
The asymmetry-induced uncertainty in both sources and loads is a crucial and continuously spotlighted issue within modern power systems. Applying optimization scheduling method to deal with this asymmetry is a feasible solution. Accordingly, this paper proposes a bi-level park-level integrated energy system (PIES) [...] Read more.
The asymmetry-induced uncertainty in both sources and loads is a crucial and continuously spotlighted issue within modern power systems. Applying optimization scheduling method to deal with this asymmetry is a feasible solution. Accordingly, this paper proposes a bi-level park-level integrated energy system (PIES) optimization strategy considering uncertainties of price-based load demand response (PLDR). Firstly, a model for characterizing the uncertainties of the PLDR is developed based on fuzzy theory. Secondly, a bi-level two-stage PIES optimization model that includes multiple device models is established. In the first stage, the dynamic pricing optimization is carried out with the aim of maximizing user satisfaction. In the second stage, the PIES scheduling strategy optimization is performed with the aim of minimizing the operation costs of PIES. Finally, multiple scenarios are set to conduct comparative validation, which demonstrates that the proposed method not only improves the renewable energy integration capacity of the system, optimizes the load profiles, and enhances the economic and low-carbon performance, but also increases user satisfaction, thus providing a reference for the dispatch and operation of the park-level integrated energy system. Full article
(This article belongs to the Special Issue Symmetry/Asymmetry Studies in Modern Power Systems)
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20 pages, 3981 KiB  
Article
Inertia Support Capability Evaluation for Wind Turbine Generators Based on Symmetrical Operation
by Zaiyu Chen, Yang Li and Qian Zhou
Symmetry 2025, 17(1), 31; https://doi.org/10.3390/sym17010031 - 27 Dec 2024
Viewed by 575
Abstract
With the increasing integration of new energy into the grid, the level of system inertia has been significantly reduced, posing a severe challenge to frequency stability. Consequently, there is an urgent need for wind turbine generators (WTGs) to actively provide inertia support through [...] Read more.
With the increasing integration of new energy into the grid, the level of system inertia has been significantly reduced, posing a severe challenge to frequency stability. Consequently, there is an urgent need for wind turbine generators (WTGs) to actively provide inertia support through virtual inertia control. Assessing the inertia support capability of WTGs reasonably and setting appropriate controller parameters based on this assessment is a topic worthy of discussion. As WTGs’ characteristics are mostly ignored in the evaluation of inertia support capability for WTGs, an evaluation method based on symmetrical operation is proposed. The proposed method considers the impact of real inertia and aerodynamic characteristics, thereby helping to determine reasonable virtual inertia coefficients and de-loading reserve capacity for WTGs. With the proposed method, it can be determined that large WTGs can provide inertia support capabilities close to those of synchronous generators to the grid without exceeding a 0.1% reduction in reserve capacity during de-loading operation. Full article
(This article belongs to the Special Issue Symmetry/Asymmetry Studies in Modern Power Systems)
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17 pages, 4709 KiB  
Article
Top-Oil Temperature Prediction of Power Transformer Based on Long Short-Term Memory Neural Network with Self-Attention Mechanism Optimized by Improved Whale Optimization Algorithm
by Dexu Zou, He Xu, Hao Quan, Jianhua Yin, Qingjun Peng, Shan Wang, Weiju Dai and Zhihu Hong
Symmetry 2024, 16(10), 1382; https://doi.org/10.3390/sym16101382 - 17 Oct 2024
Cited by 1 | Viewed by 1567
Abstract
The operational stability of the power transformer is essential for maintaining the symmetry, balance, and security of power systems. Once the power transformer fails, it will lead to heightened instability within grid operations. Accurate prediction of oil temperature is crucial for efficient transformer [...] Read more.
The operational stability of the power transformer is essential for maintaining the symmetry, balance, and security of power systems. Once the power transformer fails, it will lead to heightened instability within grid operations. Accurate prediction of oil temperature is crucial for efficient transformer operation. To address challenges such as the difficulty in selecting model hyperparameters and incomplete consideration of temporal information in transformer oil temperature prediction, a novel model is constructed based on the improved whale optimization algorithm (IWOA) and long short-term memory (LSTM) neural network with self-attention (SA) mechanism. To incorporate holistic and local information, the SA is integrated with the LSTM model. Furthermore, the IWOA is employed in the optimization of the hyper-parameters for the LSTM-SA model. The standard IWOA is improved by incorporating adaptive parameters, thresholds, and a Latin hypercube sampling initialization strategy. The proposed method was applied and tested using real operational data from two transformers within a practical power grid. The results of the single-step prediction experiments demonstrate that the proposed method significantly improves the accuracy of oil temperature prediction for power transformers, with enhancements ranging from 1.06% to 18.85% compared to benchmark models. Additionally, the proposed model performs effectively across various prediction steps, consistently outperforming benchmark models. Full article
(This article belongs to the Special Issue Symmetry/Asymmetry Studies in Modern Power Systems)
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25 pages, 8256 KiB  
Article
Small-Signal Modeling and Frequency Support Capacity Analysis of Power Load Considering Voltage Variation Effect
by Tao Zhou, Yuxin Zheng, Cheng Wang, Lei Chen, Bo Liu and Zhong Chen
Symmetry 2024, 16(7), 918; https://doi.org/10.3390/sym16070918 - 18 Jul 2024
Viewed by 1539
Abstract
The frequency support capacity of power loads is essential for maintaining active power symmetry and balance between the generation and demand sides of power systems. As the proportion of renewable energy sources and power electronic equipment increases, the inertia on the power generation [...] Read more.
The frequency support capacity of power loads is essential for maintaining active power symmetry and balance between the generation and demand sides of power systems. As the proportion of renewable energy sources and power electronic equipment increases, the inertia on the power generation side decreases, highlighting the growing importance of frequency support on the load side. As it is generally believed that the active power balance of power systems determines the frequency stability, few studies have considered the effect of voltage variation on the frequency response dynamics. It is important to note that the node voltage keeps fluctuating throughout the frequency dynamic process, which affects the active power of loads and should not be neglected. Based on the aforementioned rationales, this paper endeavors to investigate the modeling of power load frequency response and analyze its support capability considering the voltage variation effect. This paper initially establishes the small-signal model of dynamic load under frequency dynamics, derives the transfer function relating active power to system frequency deviation, and subsequently develops its frequency response model. Subsequently, commencing with the ZIP model of static load, the power fluctuation of load nodes is derived from the influence of preceding nodes, and the frequency response model of the static load is formulated and its frequency support capacity is scrutinized. Based on this foundation, a comprehensive aggregation model of the complex load is constructed, and its frequency support capability is assessed using actual data. Finally, the proposed model and analysis results are validated through simulation, confirming their correctness and effectiveness. Full article
(This article belongs to the Special Issue Symmetry/Asymmetry Studies in Modern Power Systems)
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25 pages, 4811 KiB  
Article
Power Transformer On-Load Capacity-Regulating Control and Optimization Based on Load Forecasting and Hesitant Fuzzy Control
by Dexu Zou, Xinyu Sun, Hao Quan, Jianhua Yin, Qingjun Peng, Shan Wang, Weiju Dai and Zhihu Hong
Symmetry 2024, 16(6), 679; https://doi.org/10.3390/sym16060679 - 1 Jun 2024
Cited by 1 | Viewed by 896
Abstract
The operational stability of a power transformer exerts an extremely important impact on the power symmetry, balance, and security of power systems. When the grid load fluctuates greatly, if the load factor of the transformer cannot be maintained within a reasonable range, it [...] Read more.
The operational stability of a power transformer exerts an extremely important impact on the power symmetry, balance, and security of power systems. When the grid load fluctuates greatly, if the load factor of the transformer cannot be maintained within a reasonable range, it leads to increased instability in grid operation. Adjusting the transformer capacity based on load changes is of great significance. The existing control methods for on-load capacity-regulating (OLCR) transformers have low timeliness, and the daily switching frequency of the capacity-regulating switch is not controlled. To ensure the safe and stable operation of transformers, this paper proposes a control method for OLCR transformers based on load prediction and fuzzy control. Firstly, the operating principle of OLCR transformers is analyzed, and a multi-strategy enhanced dung beetle optimizer (MSDBO) combined with a CNN−LSTM model is proposed for load forecasting. On this basis, the daily switching frequency of the capacity-regulating transformer is introduced, and hesitant fuzzy control is used to select the optimal capacity-regulating strategy relying on three factors: loss, economy, and switching frequency. Finally, simulation models are constructed using the MATLAB/SIMULINK platform and simulation analysis is conducted to verify the effectiveness and superiority of the proposed control method. For the three scenarios in this paper, the method reduces daily power loss by 28.5% to 56.3% and daily operating costs by 25.4% to 50.8%. The method used in this paper can sacrifice 3.5% to 9.2% of the loss reduction capability in exchange for reducing the number of switch operations by 28.6% to 57.1%, significantly extending the lifespan of the switches and thereby increasing the operational lifespan of the transformer. Full article
(This article belongs to the Special Issue Symmetry/Asymmetry Studies in Modern Power Systems)
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19 pages, 3140 KiB  
Article
A Coordinated Control Strategy of Multi-Type Flexible Resources and Under-Frequency Load Shedding for Active Power Balance
by Jian Zhang, Jiaying Wang, Yongji Cao, Baoliang Li and Changgang Li
Symmetry 2024, 16(4), 479; https://doi.org/10.3390/sym16040479 - 15 Apr 2024
Cited by 3 | Viewed by 1784
Abstract
With the increasing expansion of power systems, there is a growing trend towards active distribution networks for decentralized power generation and energy management. However, the instability of distributed renewable energy introduces complexity to power system operation. The active symmetry and balance of power [...] Read more.
With the increasing expansion of power systems, there is a growing trend towards active distribution networks for decentralized power generation and energy management. However, the instability of distributed renewable energy introduces complexity to power system operation. The active symmetry and balance of power systems are becoming increasingly important. This paper focuses on the characteristics of distributed resources and under-frequency load shedding, and a coordinated operation and control strategy based on the rapid adjustment of energy storage power is proposed. The characteristics of various controllable resources are analyzed to explore the rapid response capabilities of energy storage. The energy storage types are categorized based on the support time, and the final decision is achieved with power allocation and adjustment control of the energy storage system. Additionally, a comprehensive control strategy for under-frequency load shedding and hierarchical systems is provided for scenarios with insufficient active support. The feasibility of the proposed model and methods is verified via a multi-energy system case. Full article
(This article belongs to the Special Issue Symmetry/Asymmetry Studies in Modern Power Systems)
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15 pages, 1124 KiB  
Article
Deep Reinforcement Learning for Load Frequency Control in Isolated Microgrids: A Knowledge Aggregation Approach with Emphasis on Power Symmetry and Balance
by Min Wu, Dakui Ma, Kaiqing Xiong and Linkun Yuan
Symmetry 2024, 16(3), 322; https://doi.org/10.3390/sym16030322 - 7 Mar 2024
Cited by 6 | Viewed by 2347
Abstract
To address the issues of instability and inefficiency that the fluctuating and uncertain characteristics of renewable energy sources impose on low-carbon microgrids, this research introduces a novel Knowledge-Data-Driven Load Frequency Control (KDD-LFC) approach. This advanced strategy seamlessly combines pre-existing knowledge frameworks with the [...] Read more.
To address the issues of instability and inefficiency that the fluctuating and uncertain characteristics of renewable energy sources impose on low-carbon microgrids, this research introduces a novel Knowledge-Data-Driven Load Frequency Control (KDD-LFC) approach. This advanced strategy seamlessly combines pre-existing knowledge frameworks with the capabilities of deep learning neural networks, enabling the adaptive management and multi-faceted optimization of microgrid functionalities, with a keen emphasis on the symmetry and equilibrium of active power. Initially, the process involves the cultivation of foundational knowledge through established methodologies to augment the reservoir of experience. Following this, a Knowledge-Aggregation-based Proximal Policy Optimization (KA-PPO) technique is employed, which proficiently acquires an understanding of the microgrid’s state representations and operational tactics. This strategy meticulously navigates the delicate balance between the exploration of new strategies and the exploitation of known efficacies, ensuring the harmonization of frequency stability, precision in tracking, and the optimization of control expenditures through the strategic formulation of the reward function. The empirical validation of the KDD-LFC method’s effectiveness and its superiority are demonstrated via simulation tests conducted on the load frequency control (LFC) framework of the Sansha isolated island microgrid, which is under the administration of the China Southern Grid. Full article
(This article belongs to the Special Issue Symmetry/Asymmetry Studies in Modern Power Systems)
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