Search

Inverter‐dependent renewable energy sources are being integrated into the grid, raising several stability‐related difficulties. This is because these renewable sources have less inertia than synchronous generators. Since the power grid's overall inertia has improved, the introduction of virtual synchronous generators (VSG) has gained much attention. A robust microgrid system requires an effortless transition from grid‐connected to autonomous mode. This can be easily achieved with the help of VSGs. The angle, frequency, and magnitude of the grid voltage needed for synchronization have traditionally been determined by phase‐locked‐loop (PLL). The virtual synchronizing torque and voltage‐based synchronization controller for simple switching between islanding and grid‐connected modes are presented in this study. The proposed method requires no additional controller to identify the unwanted islanding situations because the operating mode can be identified with the help of synchronizing torque. The proposed method does not need to shift to different control algorithms while changing between grid connection and stand‐alone modes. The effectiveness of the suggested controller is established by comparing the experimental prototype of the VSG incorporating the proposed controller to the existing synchronization methods. [ABSTRACT FROM AUTHOR]

There are many effective techniques for virtual inertia emulation in DC microgrids that can help DC bus voltage stability through power exchange with virtual inertia injection. But one of the vexingly complicated challenges in virtual inertia emulation is the connection of unbalanced loads on the AC side of a DC microgrid. Unbalanced AC loads connected to a DC microgrid may cause severe fluctuations in DC bus voltage and battery power, as well as distorting AC side voltage. The need to solve this issue is very important because it can be a threat to the microgrid DC bus voltage stability and feed sensitive loads. One effective method to mimic the real inertia feature and dampen the unfavourable unbalanced conditions is to employ a virtual synchronous generator (VSG) equipped with a decoupled double synchronous reference frame (DDSRF) approach. The DDSRF can extract positive and negative components with high precision and create pure DC signals for the control system to improve accuracy and controllability. Hence, this paper investigates a combination of a VSG structure enhanced with a DDSRF technique to attenuate the fluctuations of DC bus voltage, battery power, and AC-side voltage caused by an unbalanced AC load in an islanded DC microgrid. The simulation results confirm that the unbalanced loads connected to the AC side of the microgrid are destructive for DC bus voltage, battery power, and also create voltage imbalances for AC loads. Furthermore, the proposed DDSRF-based VSG control system that has been implemented on the AC side of the microgrid can strongly dampen the fluctuations on the DC bus, battery, and AC loads. [ABSTRACT FROM AUTHOR]

Hybrid energy storage plays a critical role in primary frequency regulation during large-scale renewable energy integration. Rational power distribution between multiple types of energy storage, as well as the use of a VSG control technique, are effective approaches to improving primary frequency regulation capability. To that end, this paper presents an adaptive Virtual Synchronous Generator (VSG) characteristics and state of charge (SOC) management technique for photovoltaic (PV) - hybrid energy storage system (HESS) primary frequency regulation. First, a power distribution mechanism for HESS on the direct current side is implemented. Second, a primary frequency control strategy is proposed based on adaptive rotational inertia and damping coefficient of VSG and SOC regulation of energy storage. Finally, a simulation analysis confirms the feasibility of the proposed primary frequency control strategy under transient conditions. The relevant results are presented as follows. Compared to traditional control strategies, the improved adaptive VSG parameter and energy storage SOC control strategy reduces the overshoot and adjustment time of VSG active power and frequency response by 68.57%, 23.94%, 19.05% and 9.80%, respectively. The decline in SOC of battery energy storage is decreased by 3.18%. The proposed control strategy also limits grid frequency fluctuation within ±0.2 Hz, with a recovery time of less than 0.5 s. The overall root mean square error of frequency f RMSE is a maximum of 0.02 Hz. The primary frequency regulation capability of the PV-HESS is enhanced, ensuring the operational safety of energy storage systems and effectively improving the stability while also improving grid stability and security. • A power distribution control strategy for hybrid energy storage system is introduced. • An adaptive VSG parameters and SOC control strategy for PV-HESS primary frequency regulation is proposed. • The PV and hybrid energy storage primary frequency regulation model is established. [ABSTRACT FROM AUTHOR]

• The three-phase short-circuit fault experiment in the actual grid-connected system is simulated. • The improvement of transient stability is expounded in combination with grid voltage drop and three-phase short circuit fault. • The experimental results show that the improved VSG has frequency regulation characteristics. • The experimental results show that the control strategy presented in this paper performs well in addressing various grid faults. The virtual impedance solution effectively addresses the power coupling issues and improves small-signal stability in grid-connected Virtual Synchronous Generator (VSG) systems but can deteriorate the system's transient synchronous stability, particularly in high-voltage lines with significant line inductance exacerbating this effect. To address these contradictions, the paper first analyzes the power coupling mechanisms of the system, highlighting how the line reactance ratio (R / X) and power angle (δ) affect system stability, and describes the transient stability of VSGs using the equal area criterion. Leveraging the advantages of quasi-Z-source inverters, they are applied to VSG grid-connected systems, proposing an improved VSG control strategy tailored for quasi-Z-source photovoltaic grid-connected systems. This strategy introduces virtual active power at the point of common coupling (PCC) and uses it as power feedback in the control loop, instead of using real active power. The control model is validated on an experimental platform, demonstrating that the VSG control strategy with transient power compensation significantly enhances system transient stability while preserving small-signal stability. This comprehensive approach bridges the gap between maintaining essential stability functions and enhancing dynamic performance under various operational conditions. [ABSTRACT FROM AUTHOR]

• A novel frequency constrained unit commitment for asynchronous interconnected system with high share of renewable energy sources. • Modeling of bidirectional transmission power in steady state and frequency support in transient state of VSC HVDC. • A method is proposed that utilizes an intelligent sampling-based SVM to convexify the nonlinear expression of the maximum frequency deviation constraints. • The uncertainty of renewable energy sources is addressed using the distributionally robust chance constrained approach. • A two-stage decomposition algorithm for solving the frequency constrained unit commitment. The increasing share of renewable energy source (RES) poses a challenge to the frequency security of the power system. Frequency constrained unit commitment (FCUC) serves as an effective measure to address this challenge at the operational level. This paper introduces a novel FCUC model applicable to the asynchronous interconnected system connected by voltage source converter based HVDC (VSC HVDC), fully taking into account the frequency support capability of VSC HVDC in order to reduce the demand for synchronous generators' inertia and reserve while ensuring frequency security, thereby lowering operating costs. Additionally, the uncertainty of RES is also considered. The constraint expressions for three frequency indicators are derived based on a system frequency response model that includes frequency support from VSC HVDC. The proposed model optimizes unit commitment, generation and reserve dispatch and VSC HVDC transmission power and frequency response parameters, while addressing RES uncertainty using the distributionally robust chance constrained approach. In response to the highly nonlinear characteristics of the maximum frequency derivation (MFD) constraints, we propose an intelligent sampling-based support vector machine to convexify the MFD constraints and introduce a two-stage decomposition algorithm for solving the model. The effectiveness of the proposed model is demonstrated based on a modified IEEE RTS-79 system. [ABSTRACT FROM AUTHOR]

Virtual synchronous generators (VSGs) are effective solutions for low-inertia issues caused by the high penetration of inverter-based resources. However, low-frequency oscillation (LFO) is introduced as a side effect owing to the simulated swing equations in the VSGs. Although LFO has been widely researched in synchronous generator-dominated power systems, the mechanisms and mitigation strategies of VSG-related LFO have been found to be quite distinct. This study presents a comprehensive review of this emerging issue. First, the different causes of VSG-related LFO are sorted, and a unified explanation from the perspective of power-angle dynamics is provided. Then, control strategies to suppress VSG-related LFO are classified, and the advantages, disadvantages, and applicable scenarios of each method are compared. Finally, several topics for future research are discussed, including the aggregation of massive VSGs, wide-area monitoring and source detection, and advanced suppression strategies. • Various mechanisms of virtual synchronous generator (VSG)-related low-frequency oscillation (LFO) are classified and compared with the traditional synchronous generator-related LFO. • Modeling, analysis methods and suppression strategies for the VSG-related LFO are reviewed and compared. • Future research trends for the VSG-related LFO are presented. [ABSTRACT FROM AUTHOR]