Search Results (76)

With the increasing penetration of distributed generation and the diversification of electrical equipment, distribution networks face issues like three-phase unbalance and harmonic currents, while the voltage stability and inertia of the grid-connected system also decrease. A certain amount of energy storage is needed in a Distribution Static Synchronous Compensator (DSTATCOM) to manage power quality and actively support voltage and inertia in the network. This paper first addresses the limitations of traditional $dq0$ compensation algorithms in effectively filtering out negative-sequence twice-frequency components. An improved $dq0$ compensation algorithm is proposed to reduce errors in detecting positive-sequence fundamental current under unbalanced three-phase conditions. Second, considering the impedance ratio characteristics of the distribution network, while reactive power voltage regulation is common, active power regulation is more effective in high-resistance distribution networks. A grid-forming model-based active and reactive power coordinated voltage regulation method is proposed. This method uses synchronous control to establish a virtual three-phase voltage internal electromotive force, forming a comprehensive compensation strategy that combines power quality improvement and active voltage support, exploring the potential of energy storage DSTATCOM applications in distribution networks. Finally, simulation and experimental results demonstrate the effectiveness of the proposed control method. Full article

For power electronic interfaces, Direct Power Control (DPC) has emerged as a leading control technique, especially in applications such as synchronous motors, induction motors, and other electric drives; renewable energy sources (such as photovoltaic inverters and wind turbines); and converters that are grid-connected, such as Virtual Synchronous Generator (VSG) and Static Compensator (STATCOM) configurations. DPC accomplishes several significant goals by avoiding the inner current control loops and doing away with coordinating transformations. The application of STATCOM based on three- and five-level diode-clamped inverters is covered in this work. The study checks the abilities of DPC during power control adjustments during diverse grid operation scenarios while detailing how multilevel inverters affect system stability and power reliability. Proportional Integral (PI) controllers are used to control active and reactive power levels as part of the control approach. This study shows that combining DPC with Sinusoidal Pulse Width Modulation (SPWM) increases the system’s overall electromagnetic performance and control accuracy. The performance of STATCOM systems in power distribution and transient response under realistic operating conditions is assessed using simulation tools applied to three-level and five-level inverter topologies. In addition to providing improved voltage quality and accurate reactive power control, the five-level inverter structure surpasses other topologies by maintaining a total harmonic distortion (THD) below 5%, according to the main findings. The three-level inverter operates efficiently under typical grid conditions because of its straightforward design, which uses less processing power and computational complexity. Full article

This paper addresses the challenge of poor dynamic performance in Modular Multilevel Converter-based High-Voltage Direct Current (MMC-HVDC) systems within weak power grids when conventional control strategies are applied. To enhance system performance, a novel grid-connected power control method integrating Virtual Synchronous Generators (VSGs) and Passivity-Based Control (PBC) is proposed. The passivity characteristics of the MMC and the roles of virtual inertia and damping in VSG control are thoroughly examined. Based on the passivity property of the MMC, PBC is implemented in the current inner loop, while VSG control, leveraging its unique working characteristics, is incorporated into the power outer loop. To further optimize performance, adaptive virtual inertia and damping compensation mechanisms, utilizing sigmoid functions, are introduced within the VSG framework. The synergistic operation of PBC and adaptive VSGs significantly improves the dynamic response and robustness of the MMC-HVDC system. The effectiveness and feasibility of the proposed method are validated through simulation experiments in MATLAB/Simulink, conducted under power variations, grid voltage variations, and load changes. Full article

With the increasing popularity of low-cost, clean, and environmentally friendly new energy sources, the proportion of grid-connected new energy units has increased significantly. However, since these units are frequency decoupled from the grid through a power electronic interface, they are unable to provide inertia support during active power perturbations, which leads to a decrease in system inertia and reduced frequency stability. In this study, the urgent need to accurately assess inertia is addressed by developing an energy-function-based inertia identification technique that eliminates the effect of damping terms. By integrating vibration mechanics, the proposed method calculates the inertia value after a perturbation using port measurements (active power, voltage phase, and frequency). Simulation results of the Western System Coordinating Council (WSCC) 9-bus system show that the inertia estimation error of the method is less than 1%, which is superior to conventional methods such as rate-of-change-of-frequency (RoCoF) and least squares methods. Notably, the technique accurately evaluates the inertia of synchronous generators and doubly fed induction generators (DFIGs) under virtual inertia control, providing a robust inertia evaluation framework for low-inertia power systems with high renewable energy penetration. This research deepens the understanding of inertial dynamics and contributes to practical applications in grid stability analysis and control strategy optimalization. Full article

In order to solve the problem of frequency and voltage stability degradation caused by high proportion of renewable energy grid connection, this paper proposes a multi-energy dynamic coordinated control framework, which integrates the inertia damping characteristics of virtual synchronous generator (VSG) and the flexible load regulation capability of virtual synchronous motor (VSM) to build a two-way interactive mechanism. For the first time, a virtual inertia dynamic compensation algorithm based on VSG is proposed. By introducing the frequency change rate adaptive inertia coefficient adjustment mechanism, the system’s active support capability for wind and solar power fluctuations is improved by 32% compared with the traditional fixed inertia strategy; a breakthrough design of the VSM-driven hydrogen production system dynamic matching control strategy is made, and an electrolyzer efficiency-power dual variable coupling model is established to achieve optimal control of hydrogen production efficiency fluctuation rate ≤ ±2.1% within a wide power range of 10–95%; an innovative mixed integer quadratic programming real-time optimization model considering battery SOC safety constraints is constructed, and the wind and solar consumption efficiency is improved by 28.6% compared with the single energy storage mode through energy storage-hydrogen production complementary scheduling. A simulation platform was built based on Simulink to verify the system performance under three conditions: load mutation, source-grid fluctuation, and simultaneous source-load change. The simulation results show that under different working conditions, the fluctuation range of the system frequency can be stabilized within ±0.15Hz, and the voltage deviation is less than 2%; through the coordinated scheduling of the battery and the hydrogen production system, the battery charge state is always maintained in a safe range of 15–85%, and the hydrogen production power regulation rate reaches 1.5 kW/s. The study shows that the proposed control strategy can significantly enhance the inertia response capability of the system, achieve dynamic power balance and power quality optimization under multiple working conditions, and provide a feasible technical path for the high proportion of renewable energy grid connection and efficient preparation of green hydrogen. Full article

As an innovative solution, the virtual synchronous generator (VSG) facilitates the seamless incorporation of renewable energy into power grids. It also exhibits the ability to reconfigure system inertia and deliver damping effects, thereby assuming a progressively vital role in contemporary power systems. Three-phase voltage imbalance, a common phenomenon in power grids, causes current distortion. Imbalance, a common phenomenon in power grids, causes current distortion in VSG outputs, thereby affecting power quality. Therefore, ensuring symmetrical current injection into the grid has become a critical challenge in grid-connected technology. To resolve this challenge, a dual-module VSG control scheme is introduced, enabling precise regulation of the VSG’s power delivery. This approach effectively distinguishes and separately manages the positive-sequence and negative-sequence power outputs of the VSG. Furthermore, virtual impedance and quasi-PR control are incorporated into the current control loop to achieve zero negative-sequence power output from VSG, ensuring a stable power supply. Simulation results validate the reliability of this approach, providing both a theoretical foundation and practical evidence for its future application. Full article

The inertia control ability of photovoltaic power stations is weak. This leads to the problem that photovoltaic power stations cannot provide effective physical inertia support in the grid-connected system. In this paper, a photovoltaic power station controlled by a synchronous generator and virtual synchronous power generation is taken as the research object. A station-level dynamic inertia control model with synchronous machine and inverter control parameters coordinated is established. Firstly, the weakening of system inertia after a high-proportion photovoltaic grid connection is analyzed. Inertia compensation analysis based on an MW-level synchronous unit is carried out. According to the principle of virtual synchronous control of inverter, the virtual inertia control method and physical mechanism of a grid-connected inverter in a photovoltaic station are studied. Secondly, the inertia characteristics of the DC side of the grid-connected inverter are analyzed. The cooperative inertia control method of the photovoltaic grid-connected inverter and synchronous machine is established. Then, the influence of inertia on the system frequency is studied. The frequency optimization of the grid-connected parameter optimization of a photovoltaic station based on inertia control is carried out. Finally, aiming at the grid-connected control parameters, the inertia control parameter setting method of the photovoltaic station is carried out. The neural network predictive control model is established. At the same time, the grid-connected control model of the MW-level synchronous machine is embedded. The control system has the inertia characteristics of the synchronous generator and the fast-response dynamic characteristics of the power inverter. Full article

This research proposes a novel adaptive virtual synchronous generator (VSG) control strategy for a photovoltaic-energy storage (PV-storage) hybrid system. In comparison to the traditional VSG control approach, the adaptive control strategy presented in this research markedly diminishes the fluctuations in output power. This improvement is accomplished through the dynamic adjustment of virtual inertia (J) and damping coefficient (D), which enables real-time responsiveness to variations in light intensity, converter power, and load power factors that traditional VSG controls are unable to address promptly. Initially, a small signal model of VSG’s active power closed-loop system is established and analyzed for a grid-connected converter in a PV-storage hybrid system. The influence of these parameters on the response speed and stability of the PV-storage system is discussed by analyzing the step response and root locus corresponding to varying J and D conditions. Then, this study employs the power angle and frequency oscillation characteristics of synchronous generators (SGs) to formulate criteria for selecting the J and D. Based on the established criteria, a parameter-adaptive VSG control strategy is proposed. Ultimately, the efficacy of the proposed strategy is validated in MATLAB/Simulink under three distinct conditions: abrupt changes in light intensity, converter power, and load power. The results indicate that the strategy is capable of diminishing power oscillation amplitude, effectively mitigating instantaneous impulse current, and notably alleviating frequency overshoot. Full article

This paper proposes a grid-forming (GFM) photovoltaic system transient control strategy based on the combination of dynamic virtual impedance and the radial basis function (RBF) algorithm. First, the virtual synchronous generator (VSG) model is analyzed to understand how virtual impedance affects current surges and system stability during faults. By using dynamic virtual impedance throughout the fault, the strategy suppresses current spikes and improves stability. The RBF neural network dynamically adjusts virtual inertia and damping coefficients to optimize transient power-angle characteristics and speed up recovery during fault restoration. Simulation results show that the strategy reduces transient current surges, improves angle recovery, and boosts system stability during voltage sag. This approach offers an effective solution for low-voltage ride-through (LVRT) and transient control in photovoltaic grid-connected systems, ensuring the resilience and stability of renewable energy integration into the grid. Full article

The energy crisis has accelerated the rapid development of photovoltaic resources. However, the integration of large-scale photovoltaic (PV) systems into the power grid has significantly reduced system inertia, posing significant challenges to grid frequency stability. To enhance the frequency response characteristics of grid-connected PV systems, this paper proposes a rotor inertial power source (RIPS) control strategy for coordinated adjustable self-standby PV systems. First, based on the P-V operating characteristics of a PV system, a control strategy for estimating the maximum power of the PV system and implementing variable step size voltage control is proposed, enabling self-standby control for PV systems to provide primary frequency control capability. Second, by analyzing the transient response of the virtual synchronous generator (VSG) and leveraging its rotor operating characteristics, a RIPS control strategy is introduced to extract rotor inertial power, which increases the system’s inertia. Third, by utilizing the inertial power provided by RIPS in coordination with self-standby PV systems for grid connection, the inertia of the PV grid-connected system is effectively increased, thereby equivalently enhancing the frequency stability of the PV grid connection. The simulation results validate the effectiveness of the proposed control method, providing new insights for the expansion of PV system integration into the grid. Full article

The Virtual Synchronous Generator (VSG) control strategy has garnered widespread application during the low-voltage ride-through (LVRT) of distributed energy resources integrated into power grids, primarily due to its inertia and damping properties. However, grid voltage dips frequently coincide with unbalanced conditions and harmonic disturbances, against which traditional VSG LVRT control strategies offer limited resilience, resulting in unbalanced and unstable grid-connected currents. Consequently, this impacts the VSG’s support for voltage at the point of common coupling (PCC) during LVRT, potentially leading to control system failure. To tackle this challenge, this paper introduces a VSG LVRT control strategy tailored for complex grid faults. Initially, a mathematical model is developed to analyze the impact on the VSG control system’s grid-connected current when the PCC voltage of the LC filter experiences harmonic-laden unbalanced dips. Subsequently, the traditional dual second-order generalized integrator phase-locked loop (DSOGI-PLL) is enhanced to bolster its filtering capabilities. Additionally, PCC voltage feedforward control is incorporated, with a meticulously derived feedforward function to counteract the disturbances caused by unbalanced grid voltage dips, thereby enhancing the VSG system’s anti-interference ability and stabilizing the grid-connected current. This enables effective VSG LVRT control in the face of complex grid faults and ensures successful LVRT of the grid-connected system. Ultimately, the efficacy of the proposed control strategy is confirmed through PSCAD simulations. Full article

Existing hybrid energy storage control methods typically allocate power between different energy storage types by controlling DC/DC converters on the DC bus. Due to its dependence on the DC bus, this method is typically limited to centralized energy storage and is challenging to apply in enhancing the operation of distributed energy storage. To address this issue, this paper proposes a distributed hybrid energy storage control strategy based on grid-forming converters. By flexibly utilizing Virtual Synchronous Generator (VSG) control and virtual impedance control, the power distribution capability of the grid-forming converter is enhanced to meet the needs of hybrid energy storage. At the same time, a strategy based on multi-agent theory is employed to enable multiple distributed energy storage sources to collaboratively achieve hybrid energy storage. This strategy can be directly applied to energy storage systems connected to the AC grid, facilitating more efficient utilization of renewable energy. It also enhances the reliability of distributed energy storage systems, contributing to sustainable development goals. Furthermore, leveraging multi-agent theory, it offers advantages such as low communication overhead and high flexibility. Hardware-in-the-loop (HIL) simulation experiments have validated the effectiveness of this strategy. Full article

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

In view of the sudden grid voltage distortions, such as voltage sags and unbalances, that may occur in photovoltaic (PV) grid-connected systems under local shading conditions, this paper proposes a control strategy integrating a linear active disturbance rejection controller (LADRC)-based virtual synchronous generator (VSG) and an active disturbance rejection controller (ADRC)-based dynamic voltage restorer (DVR). To enhance the stability and response speed of the PV inverter system, a novel LADRC-based voltage–current dual closed-loop control strategy with pre-synchronization is designed, ensuring stable operation of the inverter and load. To address the overshooting issues found in traditional PI control under local shading, the ADRC-based DVR compensates for PV system voltage fluctuations, achieving rapid voltage distortion compensation and ensuring grid-connected system safety. Simulink experiments verify the feasibility and effectiveness of the proposed control strategy in improving transient voltage quality in PV systems affected by local shading. The total harmonic distortion rates of voltage and current are both less than 0.5%, which significantly improves the performance compared to existing research. Full article

To mitigate the challenges posed by transient oscillations and steady-state deviations in the traditional virtual synchronous generator (TVSG) that is subjected to active power and grid frequency disturbances, a VSG control strategy based on Transient Damping Compensation and Virtual Inertia Adaptation is presented. Initially, a closed-loop small-signal model for the grid-connected active power loop (APL) of the TVSG is constructed, which highlights the contradiction between the dynamic and static characteristics of TVSG output power through the analysis of root locus distribution trends. Secondly, a VSG control strategy based on Transient Damping Compensation (TDC) is proposed. The influence of APL system parameters introduced by TDC on system stability is qualitatively analyzed based on pole distribution trends and frequency response, and a comprehensive parameter design scheme is presented. In addition, based on the TDC algorithm, an improved virtual inertia adaptive strategy utilizing the Inverse Square Root Unit (ISRU) approach is designed, and the tuning range of parameters is provided. Finally, simulations and experiments verify that the proposed strategy exhibits superior active response performance and transient oscillation suppression capabilities, effectively eliminating active steady-state deviations caused by frequency disturbances in the power grid. Full article