Virtual Impedance Current Limiting for Inverters in Microgrids With Synchronous Generators

This paper focuses on current limiting for voltage-controlled inverters during overloads caused by poor transient load sharing between inverters and synchronous generators in islanded microgrids. The use of simple current reference saturation limiters can cause instability when the voltage regulator loses control after the current reference saturates. The use of virtual impedance for current limiting is shown to improve transient stability during current limiting when operating in parallel with synchronous generators. Small-signal analysis is used to set the virtual impedance magnitude and X/R ratio, and validation is provided by simulation and experimental results.