Virtual Resistor Active Damping with Selective Harmonics Control of LCL-Filtered VSCs

Abstract

LCL filter is widely adopted for strict standard compliance of grid-tied voltage source converters (VSCs). The third order low-pass filtering provides great attenuation for the high frequency harmonics generated by the power electronics guaranteeing low output currents noise injection into the grid. A major concern of the implementation of the LCL-filter is to safeguard the system stability by providing effective damping of the filter resonances. Active damping methods are preferred because it does not result in substantial power losses as it would result by the utilization of passive damping circuits. Capacitor-current active damping (CCAD) technique can be effective while realizing only a proportional feedback. However, the suitable feedback gain for maintaining stability remains to be identified. Another control issue related to the grid-tied VSC is the harmonics compensation of the currents due to the grid voltage distortion. Therefore, this paper proposes an improved resonator with phase compensation to suppress the harmonics distortion while maintaining stability with properly design capacitor current feedback. The capacitor feedback gain for stability is analytically derived in this paper. The proposed control scheme is verified by both simulation and experimental results.