虚拟同步发电机暂态稳定性分析与控制策略

Transient stability analysis and control strategy of virtual synchronous generator

虚拟同步发电机(VSG)通过模拟同步发电机的运行特性,主动参与并网点电压支撑和电网频率调节,可有效提高电力电子化电力系统的稳定性。当电网故障时,VSG存在与同步发电机类似的功角失稳问题,此时传统的小信号稳定性分析理论已不再适用。针对这一问题,首先建立VSG的数学模型,采用相平面法解析VSG的暂态功角轨迹,研究电压跌落深度、控制参数和有功出力水平对VSG暂态稳定性的影响,考虑阻尼情况下,根据扩展等面积法分析了VSG的暂态稳定边界条件;然后,提出一种电网故障期间自适应调节有功功率参考值的暂态控制策略,降低有功功率不平衡,在电网严重故障期间确保稳态工作点的存在,提高系统的暂态稳定裕度;最后,通过基于RT-LAB的半实物仿真平台验证理论分析的正确性和控制策略的有效性。

The virtual synchronous generator(VSG) can effectively improve the stability of the power electronic power system by simulating the operating characteristics of the synchronous generator and actively participating in the voltage support of the grid connection point and the frequency regulation of the grid. When the power grid fails, the VSG has the same power angle instability problem as the synchronous generator. At this time, the traditional small-signal stability analysis theory is no longer applicable. In order to solve this problem, the mathematical model of VSG is first established. Based on this, the phase portrait method was used to analyze the transient power angle trajectory of VSG, and the effects of voltage sag depth, control parameters, and active power output level on VSG transient stability were studied.According to the extended equal area method, the transient stability boundary conditions of VSG considering damping were given. Then, a transient control strategy that adaptively adjusts the active power reference value during grid faults was proposed to reduce the active power imbalance, ensure the existence of steady-state operating points during severe grid faults, and improve the transient stability margin of the system. Finally, the correctness of the theoretical analysis and the effectiveness of the control strategy were verified by the hardware-in-the-loop simulation platform based on RT-LAB.