不对称电压跌落下虚拟同步机改进低电压穿越控制策略

虚拟同步机(Virtual Synchronous Generator, VSG)是提高以新能源为主体的新型电力系统稳定性的有效途径。应用于逆变型新能源(Inverter-Interfaced Renewable Generation, IIRG)并网的虚拟同步机在不对称电压跌落情况下可能丧失VSG特性，并因低压穿越能力不足或电压电流越限而导致切机，危害电力系统安全稳定运行。对此，提出了一种新型VSG控制策略。该方法在不对称电压跌落情况下，既能持续提供系统惯性和阻尼，又能提供主动电压支撑，有效提高VSG低压穿越能力，并保证扰动下的系统稳定性。首先，分析了传统VSG在不平衡电压跌落情况下的响应特性。然后，提出了一种基于平衡电流的改进VSG控制结构，将传统VSG单电流环控制改为双电流环控制，维持VSG在电压跌落条件下的惯性阻尼特性，并实现对正负序分量的精准控制。接着，基于改进的双电流环控制拓扑，在逆变器安全运行条件下，对正负序参考电流整定方法进行优化，以实现VSG主动电压支撑和电流限幅。最后，基于Matlab/Simulink仿真平台，验证了所提控制策略在多种系统运行条件下的响应特性及有效性。

Improved low voltage ride-through control strategy of a virtual synchronous generator during unbalanced voltage sags

The virtual synchronous generator (VSG) is an effective way to improve the stability of a new power system based on new energy. The VSG applied to inverter-interfaced renewable generation (IIRG) may lose VSG characteristics under unbalanced voltage drops, and may cause generator tripping because of insufficient low-voltage ride-through capability or voltage and current over-limit. This endangers the safe and stable operation of the power system. A new VSG control strategy is proposed in this paper. This method can not only provide system inertia and damping, but also provide active voltage support when there is unbalanced voltage drop, effectively improve the low voltage ride-through capability of VSG, and ensure system stability under disturbance. First, the response characteristics of a traditional VSG with an unbalanced voltage drop are analyzed. Then, an improved control structure based on balanced current is proposed, one which changes the traditional single current loop control of VSG to double current loop control, maintains the inertial damping characteristics of VSG under voltage drop conditions, and realizes the accurate control of positive and negative sequence components. Then, based on the improved control topology, in a safe operational condition of the inverter, the positive and negative sequence reference current setting is optimized to realize VSG active voltage support and current limiting. Finally, based on the Matlab/Simulink simulation platform, the response characteristics of the proposed control strategy in various system operating conditions are verified. This ensures the effectiveness of the method. This work is supported by the National Natural Science Foundation of China (No. 61873159).