Passivity Based Impedance Shaping Method for LCL Filtered Voltage Source Converter

LCL filter has been extensively promoted in distributed power generation system (DPGS) to eliminate the high frequency harmonics. It has been proven to get smaller system inductance and cost. Nevertheless, LCL filter may trigger serious resonance issues. The existence of weak grid impedance also deteriorates system stability. According to impedance-based stability criterion (IBSC), harmonic instability only arises in the non-passive region of converter output impedance. Previous studies have been proposed to eliminate the non-passive region by optimized design of filter parameters, which requires a complicated iteration process. What’s worse, additional hardware cost may be needed for a given converter system. This paper first analyzes the impact of control delay on converter non-passive region. Different cases are also discussed. On this basis, impedance shaping method is proposed by adjusting the digital control delay in different cases to eliminate the non-passive region. Shifting PWM updating instant is more preferred than changing sampling frequency. The Matlab/Simulink simulation results also prove the validation of proposed method.