Study on Active Damping Methods for Voltage Source Converter with LCL Input Filter

Compared with L type filters, used in the AC side of voltage source PWM converters (VSC), the third-order LCL filters can suppress the switching frequency current ripples more effectively. However, the underdamped characteristics of LCL filters will bring control system stability problems. In order to assure stable operation of VSC control system, a novel active damping control strategy based on feedforward control of the transient components of the AC-side capacitor voltages is proposed. Compared with the conventional lead-lag element based one, the proposed active damping control method not only can eliminate the capacitor voltage sensors, but also can improve the dynamic response of VSC system. In this reporter, the LCL-VSC is modeled and the resonance is analyzed firstly, and then, based on the mathematic models, the selection of the system control parameters and the effection of the deviation of LCL-filter parameters on the system stability are analyzed by Matlab tools. At last, to validate the designed control strategy, a 15kW LCL-VSC prototype is built and some experimental results are reported.