Improved transient stability of virtual synchronous generators for grid voltage cascading faults

Abstract

• The basis of the investigation is a cascading fault of a grid-connected inverter in both low and high voltage power grids. • Pay attention to the fault with equilibrium point and the fault without equilibrium point while dealing with low-voltage faults, and utilize the phase portrait to assess stability. Finally, a control technique is given to ensure that the two defects are well controlled. • The equal area method is utilized to assess the fault in high voltage faults, and it is inferred that there must be an equilibrium point in high voltage faults. Finally, a control technique for active power transient overshoot mitigation and PCC voltage support during faults is provided. The topic of VSG grid voltage fault ride through has drawn increasing attention as virtual synchronous generator (VSG) technology has been widely applied in the field of renewable energy power generation. Due to the delay of the reactive power compensation device after the low-voltage fault recovery, the high-voltage fault will happen immediately after the grid's low-voltage fault is resolved. This phenomenon is known as low and high voltage cascading faults. There is not enough research on this specific voltage fault right now. For specific investigation, the low and high voltage cascading faults in this paper are separated into low-voltage fault stages and high-voltage fault stages. The equal area criterion (EAC) is used to analyze the specific process at the low-voltage fault stage. In addition, the dynamic damping control (DDC) is utilized to resolve the problem of low-voltage fault stability. Under low voltage fault, the phase portrait studies the single-period stability with an equilibrium point in a single-period and the multi-period stability without an equilibrium point in a single-period, respectively. Using a phase portrait to analyze system performance during a high voltage fault, and a virtual capacitor feedback control (VCFC) is offered to effectively reduce active power overshoot due to high voltage fault. The EAC is used to analyze the specific process of the high voltage stage, it is concluded that there is always an equilibrium point in the high-voltage fault where IGBT limitations are ignored. Finally, the correctness and feasibility of the theory are verified by simulation, and the specific analysis results are given.