Two-Stage Transient Control for VSG Considering Fault Current Limitation and Transient Angle Stability

Transient angle instability and fault overcurrent are two serious problems affecting the safe operation of the virtual synchronous generator during grid faults. However, the two aspects are mostly treated as two independent problems in existing studies. In this article, taking both transient angle instability and fault overcurrent into consideration, a two-stage transient control collaboratively utilizing virtual impedance (VI) and switching PI is put forward. In stage one, the VI is switched to the boundary value determined by the iteration algorithm to avoid fault overcurrent. In stage two, the proportional loop or integral loop in switching PI, which can embed virtual damping or virtual torque into the traditional swing equation, respectively, is activated to prohibit two types of transient angle instability induced by VI. By adaptively tuning VI and activating different loops, fault current limitation and transient angle stability are guaranteed simultaneously under different fault degrees. Furthermore, inertia support is maintained, and transient performance is improved. The proposed control is also capable for a multi-inverter system. Simulation and experimental tests validate the effectiveness of the proposed control.