Search Results (139)

This study investigates the coordinated impact of a synchronous condenser (SC), battery energy storage system (BESS), and static synchronous compensator (STATCOM) on enhancing voltage and frequency stability in a modified IEEE 9-bus power system under severe disturbances. The aim is to quantify the individual and combined contributions of these technologies during both fault ride-through (FRT) and load-increment events. The methodology includes dynamic modelling of all three devices in DIgSILENT PowerFactory. The SC is represented as a synchronous machine with inertia and AVR-based voltage control; the BESS employs converter-based active power and frequency-droop control; and the STATCOM provides fast reactive power injection through a dual-loop voltage regulator. Key indicators include nadir (minimum frequency), Rate of Change of Frequency (RoCoF), steady-state deviation, voltage sag depth, and recovery characteristics. Results indicate distinct roles for each device. The SC increases inertia and improves damping, but it also introduces small, well-damped oscillations. The BESS significantly enhances frequency stability by mitigating nadir, reducing RoCoF, and accelerating recovery, with negligible effect on voltage regulation. The STATCOM substantially reduces voltage sag and speeds up voltage recovery, but it does not influence frequency behaviour. When combined, the hybrid SC–BESS–STATCOM system demonstrates strong complementarity: the SC supports inertia, the BESS stabilizes active-power imbalance, and the STATCOM ensures fast reactive-power compensation. Full article

The output voltage harmonics of electric vehicle (EV) charging converters directly affect grid power quality. This paper proposes a harmonic analysis method based on geometric algebra (GA), which employs a multivector representation of signals and least squares estimation to accurately extract fundamental, integer-order, and inter-harmonics. A coupling coefficient is defined to quantify the phase correlation between frequency components. Based on measured data, harmonic characteristics under four typical operating conditions are analyzed, and an adaptive PID controller is designed to dynamically adjust the virtual resistance for harmonic suppression. The results show that the GA method significantly reduces spectral leakage under non-integer-period sampling conditions, with amplitude estimation errors below ±2%. The total harmonic distortion (THD) decreases with increasing active power and increases with reactive power injection. The droop coefficient exhibits a non-monotonic effect, while reducing the proportional gain raises the THD. Adaptive control reduces the average THD by 14.0–28.5% with a total response time of less than 0.05 s. The coupling coefficient $C_{13}$ is strongly positively correlated with THD and negatively correlated with the maximum Lyapunov exponent computed using the Rosenstein small-data method (correlation coefficient −0.85), confirming the intrinsic relationship between coupling and stability. Compared with fast Fourier transform (FFT) and other methods, GA achieves higher accuracy under short data records and non-integer-period sampling. This paper provides a complete theoretical framework and engineering solution for harmonic suppression in charging converters. Full article

The increasing penetration of renewable energy has led to the large-scale integration of power electronic devices into the power grid. In weakly connected grids, such devices are connected to the grid via voltage source converters (VSCs) using grid-forming (GFM) control strategies. Ideally, the point of common coupling (PCC) with the grid is treated as a purely inductive circuit. However, in weak grids, the resistance-to-inductance ratio (R/X) cannot be ignored, which leads to the power coupling problem between active power (P) and reactive power (Q). This phenomenon impedes the precise control of P and Q, potentially resulting in steady-state power deviations and even system instability. Traditional power-decoupling methods based on virtual inductance (VI) have inherent limitations and fail to achieve complete decoupling between P and Q. To address this issue, this paper first analyzes the influencing factors of power coupling through an established power coupling model. Comparisons between the output voltage and the degree of power coupling demonstrate that power decoupling can be achieved by compensating the output voltage. Consequently, an improved power-decoupling strategy based on apparent power feedforward (APPFF) is proposed. The proposed APPFF method realizes complete P-Q decoupling, with a steady-state reactive power error of less than 1% of the rated value. Compared with the PI-decoupling method, the reactive power overshoot is reduced by about 24%, and no additional active power overshoot is introduced. Compared with the conventional virtual inductance method that only reduces coupling by up to 35%, APPFF eliminates the power coupling fundamentally while retaining the reactive power–voltage droop characteristics and fast dynamic response. By directly compensating the reference voltage to the ideal value using apparent power as the feedforward variable, the proposed method is essentially different from the existing voltage/angle compensation schemes. The feasibility and effectiveness of the proposed decoupling method are verified under various working conditions, such as different R/X ratios, line resistances and power references, through both Simulink simulations and experimental results. Full article

Wind power-to-hydrogen has emerged as an important pathway for the large-scale utilization of renewable energy. However, the inherent intermittency and randomness of wind power pose significant challenges to power balance and stable operation in off-grid wind–hydrogen systems. To address these issues, this paper investigates coordinated control strategies for an off-grid wind-powered hydrogen production system. On the wind turbine side, a rotor-speed droop control strategy based on wind speed input is proposed to regulate the turbine power output and mitigate power fluctuations caused by wind variations. On the electrolyzer side, a degradation-aware power allocation strategy is developed for multiple proton exchange membrane water electrolyzers (PEMWE), considering their voltage degradation characteristics under different operating conditions. The simulation results demonstrate that the proposed strategy effectively enhances system performance and operational stability under off-grid conditions. The overall system efficiency is improved by 5%, while the RMS deviation of the DC bus voltage is reduced by 17.31%, indicating improved power balance and smoother operation of the off-grid wind–hydrogen system. Full article

Grid-forming inverters (GFIs) are emerging as a key enabling technology for maintaining stability in renewable-dominated power systems, where conventional synchronous generation is progressively displaced by inverter-based resources. This paper presents a comprehensive technical review of GFI control strategies applied to photovoltaic (PV) systems, with focused attention on small-signal stability, transient dynamic performance, and overcurrent-limiting capabilities. In contrast to grid-following inverters (GFLIs), which rely on phase-locked-loop synchronization, GFIs operate as voltage sources capable of forming and regulating grid voltage and frequency. The reviewed control approaches, including droop control, virtual synchronous generator (VSG), synchronverter, matching control, virtual oscillator control (VOC), model predictive control (MPC), and intelligent techniques such as fuzzy logic control (FLC), artificial neural networks (ANNs), and adaptive neuro-fuzzy inference systems (ANFISs), are systematically compared based on dynamic response characteristics, robustness under weak-grid conditions, control complexity, and practical implementation challenges. The paper synthesizes recent findings on stability margins, inertia emulation, transient current response, and protection requirements, highlighting remaining research gaps related to large-disturbance ride-through capability, coordination of multiple GFIs, and protection integration. These insights aim to support future deployments of reliable grid-forming photovoltaic systems in resilient inverter-dominated power networks. Full article

The lack of power system inertia caused by the large-scale integration of renewable energy seriously threatens frequency stability. In this paper, a control strategy for collaborating multiple wind farms in frequency support considering the frequency distribution characteristic is presented. Firstly, the DC power flow analysis model of the power system is established, the analytical relation between the node frequency and the active power disturbance is derived, and the system frequency distribution characteristic is mathematically analyzed. Secondly, based on the frequency distribution characteristic, a control strategy for collaborating multiple wind farms using virtual inertia control and droop control to provide frequency support is presented. Finally, the four-machine two-area system integrated with two wind farms is implemented in Matlab 2020, and the effectiveness of the proposed collaborative control strategy for frequency support is validated through simulation results. Full article

Photovoltaic-storage direct current (DC) flexible (PEDF) systems are susceptible to DC bus voltage disturbances, with the constant power load (CPL) characteristics further exacerbating the risk of system instability. To address these challenges, a collaborative control scheme integrating distributed consensus and demand-side response (DSR) based on a consensus protocol is proposed in this study. A fully distributed control architecture is constructed, wherein the upper layer achieves power coordination through voltage deviation of parallel DC/DC converters and neighborhood interaction, whilst the lower layer dynamically optimizes inter-unit power allocation via the DSR mechanism. Distributed state estimation (DSE) is incorporated to enhance voltage control accuracy. Simulations conducted in the MATLAB (R2022a)/Simulink environment demonstrate that the proposed strategy enables rapid stabilization of bus voltage under load step changes and photovoltaic fluctuation scenarios, with system disturbance rejection capability being effectively enhanced. The effectiveness of the approach in maintaining stable system operation and optimizing power distribution is validated. The results indicate that the voltage deviation of the PEDF system remains below 2% under compound disturbances, with the steady-state error being controlled within 2%. The proposed control strategy, through the integration of the power DSR mechanism, effectively improves the system’s anti-disturbance capability. Compared with conventional droop control methods, which typically result in voltage deviations of 3–5%, the proposed strategy achieves a reduction in voltage deviation of over 50%, demonstrating superior voltage regulation performance. Full article

The large-scale integration of doubly fed wind turbines reduces the inertia level of power systems and increases the risk of frequency instability. This paper analyzes the performance characteristics and application ranges of different types of energy storage technologies and addresses the limitations of conventional control methods, which cannot adjust energy storage power output in real time according to frequency variations and may hinder frequency recovery during the restoration stage. Based on a grid-forming doubly fed wind turbine model, this study adopts a hybrid ultracapacitor energy storage system as the auxiliary storage device. The hybrid configuration increases energy density and extends the effective support duration of the storage system, thereby meeting the requirements of longer-term frequency regulation. Furthermore, the paper proposes an adaptive inertia control strategy that combines an improved variable-K droop control with adaptive virtual inertia control to enhance the stability of doubly fed wind turbines under load fluctuations. Simulation studies conducted in MATLAB 2022/Simulink demonstrate that the proposed method significantly improves frequency stability in load disturbance scenarios. The strategy not only strengthens the frequency support capability of grid-connected wind turbine units but also accelerates frequency recovery, which plays an important role in maintaining power system frequency stability. Full article

With the rapid development of new energy, high-proportion new energy power systems have significantly reduced inertia and voltage support capacity, facing severe stability challenges. Virtual Synchronous Generator (VSG) control, which simulates the inertia and voltage source characteristics of traditional synchronous generators, enables friendly grid connection of new energy converters and has become a key technology for large-scale new energy applications. This paper addresses two key issues in low-voltage ride through (LVRT) of grid-forming converters under VSG control: (1) converter overcurrent suppression during LVRT; (2) reduced reactive power support due to retaining voltage-reactive power droop control during faults. It proposes an adaptive virtual impedance-based overcurrent suppression method and a frozen reactive power–voltage droop-based reactive support method. Based on the converter’s mathematical model, a DIgSILENT/PowerFactory simulation model is built. Time-domain simulations verify the converter’s operating characteristics and the improved LVRT strategy’s effect, providing theoretical and technical support for large-scale applications of grid-forming converters. Full article

Silicon carbide (SiC) three-phase converters are widely adopted in parallel power distribution systems for their high efficiency, yet their performance is challenged by high switching frequency and communication constraints. For the parallel inverter system, problems such as uneven power distribution and circulating current may occur. Therefore, the droop control method was proposed. The droop control method is limited in precise power sharing and circulating current mitigation. To address these issues in the communication-free parallel inverter system, a hybrid droop-enhanced virtual impedance method is proposed. The methodology integrates droop characteristics with frequency-selective virtual impedance compensation, enabling concurrent optimization of power sharing and circulating current suppression. Through simulation, the droop control method and the improved droop control method were compared and analyzed. Finally, the effectiveness of the improved droop control method was verified through experiments. Full article

Current microgrid research primarily focuses on radial topologies and their control strategies, while exploration of the time-domain dynamic behavior of closed-loop controlled microgrids remains relatively insufficient. This research gap makes it difficult to directly observe and deeply analyze the evolution mechanisms of critical phenomena, such as oscillations and instability, when they occur. Therefore, conducting time-domain analysis on closed-loop structures is crucial for revealing system instability mechanisms and ensuring their safe and stable operation. This paper establishes a state-space model for a closed-loop microgrid structure composed of multiple parallel inverters and conducts time-domain stability analysis under grid-connected operation. First, a mathematical model of the closed-loop microgrid system is constructed using state-space equations. Subsequently, time-domain analysis of small-signal stability is performed on the model. By varying key parameters such as the droop coefficient, the influence patterns on system stability are investigated. The results indicate that the droop control coefficient and LC filter parameters exert the most significant impact on system dynamic characteristics. Simulation experiments validate the correctness and effectiveness of the theoretical model. Finally, the time-domain characteristics of this model were further analyzed and validated through simulations. Results demonstrate that the system maintains robust stability under disturbances even in grid-connected mode. Full article

The fast-growing integration of renewable energy sources into the utility grids jeopardizes the system’s performance and stability at risk. Particularly, the increasing tendency of power electronics converters in the current renewables-based power generation and their integration to utility grids through long sub-sea cables compromises the grid strength and amplifies the risk of system instability during disturbances. To sustain grid stability and ensure effective regulation during transients, grid-following (GFL) and grid-forming (GFM) control approaches have been extensively proposed for power systems with inverter-based resources (IBRs). The former approach is solely based on a phase-locked loop (PLL) to track the phase angle of grid voltage, which reduces the system stability margin, particularly in weak-grid scenarios. Consequently, grid-forming control is increasingly recognized for its ability to maintain stability and ensure reliable operation under weak-grid conditions. Droop control is one of the most widely used grid-forming control strategies owing to its capability to emulate the behavior of synchronous machines, achieve autonomous power sharing, and ensure stable voltage and frequency regulation even under varying grid conditions. This paper aims to evaluate the impact of grid impedance and its characteristics (i.e., resistive or inductive grid impedance) on the dynamic performance of a droop control GFM grid-connected converter. To that end, first, a detailed MATLAB/Simulink model of a voltage source converter implementing the proposed droop-based GFM control is developed. Then, the overall system will be validated by performing on distinct case studies including weak and stiff power grids with inductive, resistive and nonlinear impedances in response to various grid disturbances. Full article

To mitigate voltage transients caused by power fluctuations in microgrid systems, this study investigates model predictive control and virtual inertia control for the voltage regulation strategy of energy storage unit converters. By drawing an analogy with the virtual synchronous machine equation in AC systems, the virtual capacitor inertia equation is derived for DC systems. Subsequently, model predictive control (MPC) is integrated with virtual inertia (VI) control, leading to the development of an MPC-VI cooperative control method. The reference value for the inner control loop is computed in real time using model prediction, enabling the injection of a counteracting signal opposite to the direction of DC bus voltage fluctuation during disturbances. This approach effectively suppresses rapid voltage variations and enhances system inertia. Furthermore, by incorporating a threshold-based mechanism, the issue of prolonged dynamic response time is mitigated. Simulation and experimental results demonstrate that, compared to conventional control strategies, the proposed MPC-VI method significantly attenuates instantaneous and severe voltage fluctuations, allowing for a more gradual voltage transition during transient events. Additionally, with the implementation of the threshold equation, the system returns to steady state without notable delay, preserving the droop characteristics of the control scheme. Full article

With a large number of traditional thermal power units being replaced by inverter-based resources, the system inertia and regulation capability have significantly decreased in certain countries, exposing a critical gap in traditional generation-side-dominated frequency regulation strategies. The decline in system inertia deteriorates frequency dynamics, creating a critical need for load-side regulation. To enhance frequency stability in low-inertia power systems, this paper proposes a frequency regulation strategy for thermostatically controlled loads (TCLs). The strategy incorporates a differential deadband that adjusts response thresholds based on frequency deviation, along with dynamic droop coefficients that self-adapt according to real-time TCL capacity. First, the operational principles of TCLs and the frequency response characteristics of thermal power units are analyzed to establish the foundation for load-side frequency regulation. Second, building upon the spatiotemporal distribution characteristics of system frequency, the nodal frequency under high renewable energy penetration is derived, and a differential dead zone setting method for TCLs is proposed. Then, a dynamic droop coefficient tuning method is developed to enable adaptive parameter adjustment according to the real-time regulation capacity of TCLs. Finally, these key elements are integrated within a hybrid control framework to formulate the complete TCL frequency regulation strategy. Simulation results demonstrate a 0.342% improvement in frequency nadir and 0.253% reduction in settling time compared to conventional methods, while ensuring reliable TCL operation. This work presents a validated solution for enhancing frequency stability in renewable-rich power systems, where the proposed framework with nodal frequency-based deadbands and adaptive droop coefficients demonstrates effective regulation capability under low-inertia conditions. Full article

This paper proposes a novel hybrid control strategy integrating a Finite Control Set Model Predictive Controller (FCS-MPC) with a universal droop controller (UDC) for effective load power sharing in inverter-fed microgrids. Traditional droop-based methods, though widely adopted for their simplicity and decentralized nature, suffer from limitations such as steady-state inaccuracies and poor transient response, particularly under mismatched impedance conditions. To overcome these drawbacks, the proposed scheme incorporates detailed modeling of inverter and source dynamics within the predictive controller to enhance accuracy, stability, and response speed. The UDC complements the predictive framework by ensuring coordination among inverters with different impedance characteristics. Simulation results under various load disturbances demonstrate that the proposed approach significantly outperforms conventional PI-based droop control in terms of voltage and frequency regulation, transient stability, and balanced power sharing. The performance is further validated through real-time simulations, affirming the scheme’s potential for practical deployment in dynamic microgrid environments. Full article