实验技术与管理

在高比例新能源接入背景下，虚拟同步发电机（VSG）在电网大扰动期间易发生暂态失稳以及短路过电流等问题，严重威胁系统安全运行。为提升VSG的暂态稳定性和故障穿越能力，提出一种基于动态电压偏差耦合的暂态有功修正控制策略，并设计了适用于电压跌落工况的电压-电流双约束无功参考电压调节方法。该策略依据暂态功角特性以及等面积定则，建立状态方程分析修正系数与稳定性边界的关系，明确不同参数配置下的稳定条件。同时，通过调节无功环电压参考值，有效抑制了故障初期的短路电流。实验结果验证了所提控制策略的有效性。

[Objective] To facilitate the high-penetration and integration of renewable energy into existing systems, grid-connected inverters must possess robust grid support capabilities. Virtual Synchronous Generator(VSG) technology provides inertia and damping support to the grid by emulating the characteristics of synchronous generators. However, when confronted with severe grid disturbances such as deep voltage sags, conventional VSG control is prone to transient instability and excessive fault currents, posing a serious threat to the security and stable operation of the system. Consequently, enhancing the transient stability and fault ride-through capability of VSGs in the presence of extreme grid faults is a critical issue requiring urgent resolution. This study focuses on the power angle instability and uncontrollable fault current issues facing VSGs during grid voltage faults. [Methods] A comprehensive, enhanced control strategy is proposed and designed for VSGs, aiming to collaboratively address the transient instability and overcurrent issues. To tackle the transient instability, a dynamic active power correction strategy based on grid voltage deviation coupling is introduced. The core of this strategy lies in real-time sensing of the grid voltage sag depth and dynamically adjusting the active power reference command of VSG. Specifically, a correction term proportional to the real-time grid voltage deviation is incorporated as feedback into the active power control loop. This correction term automatically reduces the active power reference value. Based on the classical transient power angle characteristic model of synchronous generators and the Equal Area Criterion stability principle, the state-space representation of the VSG system incorporating the proposed correction strategy is derived. Thorough analysis of the quantitative relationship between the key control parameters and the transient stability boundary provides a clear theoretical foundation for parameter selection and optimization. To address the fault current suppression challenge, a dual-constraint reactive power reference voltage dynamic regulation method is proposed. This method dynamically calculates the reference voltage for the reactive power control loop while simultaneously considering the voltage support requirements and preset current safety limits. It explicitly accounts for the grid voltage sag depth, current limits, and the operating power angle. [Results] The proposed integrated control strategy effectively resolves the instability and overcurrent issues affecting conventional VSGs in the event of deep voltage sags. Compared to the severe power angle oscillations and excessively high output current peaks caused by conventional control, the proposed strategy significantly suppresses power-angle oscillations and substantially reduces the short-circuit current peak. By optimizing the key parameters, the system maintains complete stability during faults, with negligible active-power and power-angle oscillations. Concurrently, the dual-constrained reactive power control successfully restricts the fault current peak strictly within the preset safety thresholds. The proposed active power correction strategy effectively expands the deceleration area, thus inhibiting divergence of the power angle by adaptively reducing the active power reference, whereas the dual-constrained voltage regulation precisely controls the magnitude of the output voltage, thereby limiting the current. [Conclusions] This study proposes and validates an integrated control strategy for enhancing the performance of VSG under severe grid voltage disturbances. It prevents instability in the power angle through voltage-deviation-coupled active power dynamic regulation and suppresses fault current peaks via dual-constrained reactive power control. The collaborative operation of these strategies ensures stable VSG operation and restricts fault currents within safe limits, significantly enhancing the transient stability and security in grids with high-penetration renewable energy.