Latched Limit Strategy for Single-phase Synchronous Inverter for Realization of Designed Grid Forming Performance

Abstract

Single-phase synchronous inverters (SSIs) with synthetic inertia connect to single-phase circuits and stabilize the grid. They also improve grid resilience by forming and operating an islanded single-phase microgrid when disasters disconnect the single-phase circuits from the bulk power system. Generally, voltage and current feedback controllers are implemented in grid-connected converters to track the output voltage to the voltage reference and protect themselves from overcurrent when the fault occurs. However, controllers with multiple feedback control loops in SSIs impair the grid stabilization performance depending on grid frequency variations. Without optimal parameter tuning according to grid conditions, they also cause instability of the controller during the islanding operation of a single-phase microgrid. This paper proposes a controller to realize the designed grid forming performance and avoid the above problems inherent in SSIs. The SSI with the proposed controller works as a grid forming inverter in a normal condition without the multiple feedback loops, stabilizing the grid and operating a single-phase microgrid stably. When an overcurrent is detected, the SSI shifts from a grid forming mode to a current control mode using a latched limit strategy to protect semiconductor devices from the overcurrent. Since the appropriate switching between the two modes is essential for realizing the designed performance of the SSI, the proposed controller employs a modified current-trip voltage-reset limit. Numerical simulations and experiments demonstrate that the proposed controller provides the designed performance in both normal and faulted conditions.