Search Results (184)

Solar energy solutions have become increasingly popular worldwide due to the growing need for renewable energy. This article presents a photovoltaic (PV) system connected to a three-phase power grid, modeled under varying climatic conditions. It consists of two conversion stages, a DC-DC Boost converter and a DC-AC inverter. The former uses a variable-step P&O based on fuzzy logic control to maximize the power of the photovoltaic panels, allowing for greater tracking accuracy than traditional P&O techniques. Inverters with phase-locked loop technology improve the performance of grid-connected PV systems by using a conventional PI controller that has a faster response. Using Matlab/Simulink environments, the entire system and control techniques are evaluated and verified. The simulation results confirm the effectiveness and robustness of the proposed system. Full article

In this work, a controller hardware-in-the-loop (CHIL) simulation of a grid-connected three-phase inverter equipped with an LCL filter is implemented using a real-time digital simulator (RTDS) as the plant and a digital signal processor (DSP) as the control hardware. This work identifies and discusses the critical aspects of the CHIL implementation process, emphasizing the relevance of the control delays that arise from sampling, computation, and pulse width modulation (PWM), which also adversely affect system stability, accuracy, and performance. Time and frequency domains are used to validate the modeling of the system, either to represent large-signal or small-signal models. This work shows multiple representations of the system under study: the fundamental frequency model, the switched model, and the switched model controlled by the DSP, are used to validate the nonlinear model, whereas the impedance-based modeling is followed to validate the linear representation. The results demonstrate a strong correlation among the models, confirming that the delay effects are accurately captured in the different simulation approaches. This comparison provides valuable insights into configuration practices that improve the fidelity of CHIL-based validation and supports impedance-based stability analysis in power electronic systems. The findings are particularly relevant for wideband modeling and real-time studies in electromagnetic transient analysis. Full article

This study aims to develop an event-triggered control strategy of grid-connected inverters, based on the linear parameter-varying (LPV) modeling approach. Regarding the changes in grid voltage, filter capacitance and inductance, and random electromagnetic interference, a stochastic LPV model for three-phase two-level inverters is established. To reduce computation burden, an event trigger with a continuous-time form is adopted to derive the state feedback controller for the LPV plant. Unlike the existing common approach to dealing with event-triggered mechanisms, a predesignated event-triggering threshold is used to determine the triggering instant of the event condition. Using parameter-dependent Lyapunov functions, sufficient conditions reliant on parameters are introduced. Based on the derived conditions, the corresponding event-triggered controllers are engineered to ensure uniform ultimate bounded stability for the resulting event-triggered LPV inverter system subject to exogenous disturbance. The simulation results are presented to confirm the efficacy of the proposed methods. Full article

Partial shading condition (PSC) for photovoltaic (PV) arrays complicates the operation of PV systems at peak power due to the existence of multiple peak points on the power–voltage (P–V) characteristic curve. Identifying the global peak among multiple peaks presents challenges, as the system may become trapped at a local peak, potentially resulting in significant power loss. Power generation is reduced, and hot-spot issues might arise, which can cause shaded modules to fail, under the partly shaded case. In this paper, instead of focusing on local peaks, several effective, precise, and dependable maximum power point tracker (MPPT) systems monitor the global peak using a fuzzy logic controller. The suggested method can monitor the total of all PV array peaks using an interleaved boost converter DC/DC (IBC), not only the global peaks. A DC/DC class boost converter (CBC), the current gold standard for traditional control methods, is pitted against the suggested converter. Four PSC-PV systems employ three-phase inverters to connect their converters to the power grid. Full article

The research demonstrates, through simulation and laboratory validation, the development of a low-voltage DC-link (LVDC) back-to-back converter system that enables multi-frequency power transfer. The system operates in two distinct modes, which include a three-phase grid-connected converter transferring fundamental and 5th and 7th harmonic power to a three-phase residential inverter supplying a clean 50 Hz load and another mode that uses a DC–DC buck–boost converter to integrate a battery storage unit for single-phase load supply. The system allows independent control of each harmonic component and maintains a clean sinusoidal voltage at the load side through DC-link isolation. The LVDC link functions as a frequency-selective barrier to suppress non-standard harmonic signals on the load side, effectively isolating the multi-frequency power grid from standard-frequency household loads. The proposed solution fills the gap between the multi-frequency power systems and the single-frequency loads because it allows the transfer of total multi-frequency grid power to the traditional household loads with pure fundamental frequency. Experimental results and simulation outcomes demonstrate that the system achieves high efficiency, robust harmonic isolation, and dynamic adaptability when load conditions change. Full article

Enhancing the resilience of renewable energy systems in ultra-weak grids is crucial for promoting sustainable energy adoption and ensuring a reliable power supply during disturbances. Ultra-weak grids characterized by a very low Short-Circuit Ratio, less than 2, and high grid impedance significantly impair voltage and frequency stability, imposing challenging conditions for Inverter-Based Resources. To address these challenges, this paper considers a 110 KVA, three-phase, two-level Voltage Source Converter, interfacing a 700 V DC link to a 415 V AC ultra-weak grid. X/R = 1 is controlled using Sinusoidal Pulse Width Modulation, where the Grid-Connected Converter operates in Grid-Forming Mode to maintain voltage and frequency stability under a steady state. During symmetrical and asymmetrical faults, the converter transitions to Grid-Following mode with current control to safely limit fault currents and protect the system integrity. After fault clearance, the system seamlessly reverts to Grid-Forming Mode to resume voltage regulation. This paper proposes an improved control strategy that integrates voltage feedforward reactive power support and virtual capacitor-based virtual inertia using Active Disturbance Rejection Control, a robust, model-independent controller, which rapidly rejects disturbances by regulating d and q-axes currents. To test the practicality of the proposed system, real-time implementation is carried out using the OPAL-RT OP4610 platform, and the results are experimentally validated. The results demonstrate improved fault current limitation and enhanced DC link voltage stability compared to a conventional PI controller, validating the system’s robust Fault Ride-Through performance under ultra-weak grid conditions. Full article

The quality of a grid-injected current in LCL-type grid-connected inverters (GCI) degrades under ultra-weak grid conditions, posing serious challenges to the stability of the GCI system. For this purpose, the sliding mode control (SMC) approach has been utilized to integrate DC energy seamlessly into the grid. The control performance of a GCI equipped with an LCL filter is greatly reduced when it is operating in a power grid with varying impedance and fluctuating grid voltages, which may result in poor current quality and possible instability in the system. A non-singular double integral terminal sliding mode (DIT-SMC) control is presented in this paper for a three-phase GCI with an LCL filter. The proposed method is presented in the α, β frame of reference without adopting an active or passive damping approach, reducing the computational burden. MATLAB/Simulink Version R2023b is leveraged to simulate the mathematical model of the proposed control system. The capability of the DIT-SMC method is validated through the OPAL-RT hardware-in-loop (HIL) platform. The effectiveness of the proposed method is first compared with SMC and integral terminal SMC, and then the DIT-SMC method is rigorously analyzed under resonance frequency events, grid impedance variation, and grid voltage distortions. It is demonstrated by the experimental results that the proposed control is highly effective in delivering a high-quality current into the grid, in spite of the simultaneous occurrence of power grid impedance variations in 6 mH and large voltage distortions. Full article

The analysis and accurate identification of DC-side grounding faults in grid-connected photovoltaic (PV) inverters is a critical step in enhancing operation and maintenance capabilities and ensuring the safe operation of PV grid-connected systems. However, the characteristics of DC-side grounding faults remain unclear, and effective methods for identifying such faults are lacking. To address the need for leakage characteristic analysis and fault identification of DC-side grounding faults in grid-connected PV inverters, this paper first establishes an equivalent analysis model for DC-side grounding faults in three-phase grid-connected inverters. The formation mechanism and frequency-domain characteristics of residual current under DC-side fault conditions are analyzed, and the specific causes of different frequency components in the residual current are identified. Based on the leakage current mechanisms and statistical characteristics of grid-connected PV inverters, a multi-type DC-side grounding fault identification method is proposed using the light gradient-boosting machine (LGBM) algorithm. In the simulation case study, the proposed fault identification method, which combines mechanism characteristics and statistical characteristics, achieved an accuracy rate of 99%, which was significantly superior to traditional methods based solely on statistical characteristics and other machine learning algorithms. Real-time simulation verification shows that introducing mechanism-based features into grid-connected photovoltaic inverters can significantly improve the accuracy of identifying grounding faults on the DC side. Full article

Grid-connected photovoltaic (PV) systems require a power converter to extract maximum power and deliver high-quality electricity to the grid. Traditional control methods, such as proportional-integral (PI) control for DC-link voltage regulation, often struggle under abnormal operating conditions, resulting in voltage fluctuations and instability in the maximum power point tracker (MPPT). This paper proposes a synergistic control strategy that combines a musical chairs algorithm (MCA) MPPT with sliding mode control (SMC) together for the boost converter DC-link control. This approach enhances DC-link voltage stability by switching the MPPT to SMC of the boost converter when the DC-link voltage exceeds the predefined limit. This strategy enhances the stability of the DC-link voltage and allows for a smaller DC-link capacitor, thereby reducing system cost and improving the power quality of PV systems. A phase-locked loop (PLL) further ensures effective grid synchronization. The reduction in DC-link voltage overshoot (from 570 V to 522 V) improved stability under varying irradiance conditions. Moreover, a 48 V reduction in overshoot voltage and a 66% decrease in DC-link voltage ripple (standard deviation from 17.93 V to 5.92 V) occurred. Simulation and experimental results demonstrate the superiority of the proposed strategy compared to the case without coordination between the DC-DC converter and inverter controllers, particularly under challenging conditions. Full article

Microgrids (MGs) offer substantial environmental, economic, and technological benefits by supplying electrical energy to the grid or local consumers via power electronic inverter-interfaced Distributed Energy Resources (DERs). However, the design, control, and stability analysis of inverter-interfaced MGs present significant challenges, as numerous system parameters influence the overall stability of these MGs. While extensive research has been conducted on MG stability, predominantly through eigenvalue-based state-space models, further refinement is necessary for more accurate stability assessments. This paper provides an accurate and detailed stability analysis of MGs, focusing specifically on parallel-connected grid-forming inverters (GFIs) operating in island mode. The novelty of this paper lies in three key contributions: (1) accurately considering a time delay in regard to the dq-axis synchronous reference frame, (2) the enhanced accuracy of the small-signal model for the purpose of the voltage control loop, and (3) the enhanced accuracy of the small-signal model for the purpose of the current control loop. In the literature, digital control-induced time delays are typically incorporated directly into the dq-axis, while the effect of the phase shift is then neglected, leading to inaccurate stability assessment results. Accordingly, the motivation of this paper is to consider the time delay, which naturally exists in regard to the abc-axis, and accurately represent it in regard to the dq-axis by modeling the phase shift effect for precise stability analysis. These contributions enable a precise small-signal model to be developed and eigenvalue-based stability analysis to be carried out by not only incorporating an accurate representation of the time delay, but also considering the voltage control loop and the current control loop in regard to the dq-axis synchronous reference frame. To achieve this aim, a full-order state-space and small-signal model of GFIs is developed, considering all the subsystem dynamics. The theoretical analysis conducted within the MATLAB m-file code environment (other programming languages, such as C or Python, could also be employed) and the real-time simulation results obtained using PLECS show excellent agreement, verifying the accuracy of the proposed method and highlighting its superior precision compared to conventional stability analysis. The real-time simulation results show that the proposed small-signal model has less than 5% deviation in regard to both active and reactive power droop coefficient limits, while the conventional model deviates by 22% and 530% in regard to active and reactive power droop, respectively. Consequently, this study determines the critical boundaries of the control parameters that ensure MG stability, providing a more accurate foundation for stability analysis and control design. Full article

A split-phase three-level LCL grid-connected inverter is proposed to match the single-phase three-wire split-phase output power grids in countries such as those in North America. However, influencing factors such as grid impedance and background harmonics in non-ideal power grids may lead to distortion and even instability of the output waveform of the grid-connected inverter. To address the aforementioned issues, through a stability analysis of the dual-feedback system of inverter-side current control and capacitor current active damping, a composite active damping strategy is put forward to enhance the stability of the LCL grid-connected inverter. This composite active damping strategy encompasses a standardized method for designing the robust capacitor current feedback coefficient and a method of embedding leading-phase correction to improve system stability. The strategy proposed in this paper is more streamlined and standardized when calculating the capacitor current feedback coefficient, enabling the system to operate stably under a wide range of grid impedance variations. Moreover, an analysis of the mechanism by which grid background harmonics affect the grid-connected current waveform is conducted, and the PR controller is replaced with a multiple proportional-resonant (MPR) controller. The MPR controller can achieve infinite gain at specific harmonics, thereby suppressing specific low-order harmonics in the grid and reducing the total harmonic distortion (THD) of the grid-connected current. Finally, the effectiveness of the proposed control strategy is verified on a 12 kW experimental platform. The results indicate that, compared with the inverter-side current feedback active damping (ICFAD) method, the composite active damping strategy proposed in this paper exhibits stronger robustness, and the added MPR controller significantly enhances the anti-interference ability of the grid-connected inverter against grid harmonics. Full article

Under the condition of asymmetric system voltage, grid-connected inverters exhibit obvious sequence impedance frequency coupling characteristics, which can easily lead to resonance and the misoperation of protection and control devices. Currently, targeted quantitative analyses are insufficient. To address this limitation, this paper identifies dominant harmonic pairs and develops an analytical model of an inverter’ second-order admittance under unbalanced grid voltage conditions. Considering the influence of the phase-locked loop and current control loop, the sequence impedance characteristics of a grid-connected inverter were quantitatively analyzed. The simulation results verified the accuracy of the model. The conclusion of the paper provides a foundation for subsequent research on the instability mechanism and oscillation suppression strategy of the grid-connected inverter and grid interconnection system. Full article

Grid-connected photovoltaic (PV) systems inject nonsinusoidal currents into the grid at the point of their connection. The technology of the inverter utilized for the conversion of DC power into AC is directly associated with distortion characteristics. Even though pulse-width-modulated (PWM) converters generate considerably lower harmonic distortion than their predecessors, they are responsible for the emergence of a new power quality issue in distribution grids known as supraharmonics, which can cause problems such as overheating and malfunctions of equipment. PV systems are known sources of supraharmonics, but their impact has not yet been thoroughly researched. Due to the multitude of parameters affecting their performance, a more rigorous treatment is required compared to more common nonlinear devices. In this paper, emissions from a three-phase grid-connected PV system are examined by means of a dedicated simulation tool taking into account the specifics of inverter switching action without overly increasing computational cost. The impact of environmental parameters as well as factors affecting the switch control of the converter is investigated. The dependence of the supraharmonic emission of the PV system on the converter characteristics rather than environmental conditions is demonstrated. Furthermore, simulation studies on a network comprising the PV system and an additional supraharmonic-emitting system in simultaneous operation are conducted. Their combined effect on the distortion at the connection point of the network to the grid is assessed by means of a power flow-based approach, capable of quantifying interactions within this network. From the viewpoint of the grid, an increase of supraharmonic-related disturbance at low irradiance conditions is revealed. Full article

The limits of direct current (DC) injection and output current distortion of grid-connected photovoltaic (PV) inverters are specified in the IEEE 1547-2018 standard. The standard prescribes limits of output current harmonics, but the input voltage and power at which output current distortion is measured are not specified. This manuscript presents the results of DC injection and output current distortion measurements for three commercial single-phase PV inverters, with 3 kVA, 3.3 kVA, and 6 kVA rated power. During the measurements, the inverters are powered by a programmable DC source that emulates the power voltage characteristic of a PV array, providing different input conditions. In addition to steady-state measurements at constant input voltage and power, the change in the output current spectrum over time during the maximum power point tracking (MPPT) is also measured. The results show that the output current distortion depends on the input voltage and power. Moreover, the current distortion of some of the tested inverters exceeds the limits specified by the standard in some cases. The presented results suggest that further research on the dependence of the output current distortion from PV inverters on their input power and voltage is needed. Full article

This article introduces a frequency-adaptive control strategy for a three-phase shunt active power filter, aimed at improving energy efficiency and ensuring high power quality in consumer-oriented power systems. The proposed control system utilizes real-time frequency estimation to dynamically adjust the gain of a proportional-integral–resonant (PIR) controller, facilitating precise harmonic compensation under challenging unbalanced grid conditions, such as unbalanced three-phase loads, grid impedance variations, and diverse nonlinear loads like three-phase rectifiers and induction motors. These scenarios often increase total harmonic distortion (THD) at the point of common coupling (PCC), degrading the performance of connected loads and reducing the efficiency of induction motors. The PIR controller integrates both proportional-integral (PI) and proportional-resonant (PR) control features, achieving improved stability and reduced overshoot. A novel voltage sensorless control method is proposed, requiring only current measurements to determine reference currents for the inverter, thereby simplifying the implementation. Validation of the frequency adaptive control scheme through MATLAB/Simulink simulations and real-time experiments on a dSPACE (DS1202) platform demonstrates significant improvements in harmonic compensation, energy efficiency, and system stability across varying grid frequencies. This approach offers a robust consumer-oriented solution for managing power quality, positioning the SAPF as a key technology for advancing sustainable energy management in smart applications. Full article