A novel active damping method for LCL-filter-based shunt Active Power Filter

Three-phase shunt Active Power Filters (APFs) are connected to the grid through inductance or LCL filter. Comparing to single L filter, LCL filter is more effective, e.g. better switching harmonics suppression and lower output impedance, but such solution causes stability problems. In order to assure stable operation either a damping resistor or active damping algorithm has to be used. However, extra resistor causes additional losses and active damping algorithm usually needs extra sensors. This paper proposed a novel active method to stabilize the system by inserting a damp function into the control loop to suppress the resonance. Moreover, to achieve high quality grid current waveform both at low and high frequency, repetitive control algorithm with differential compensator is adopted to compensate control loop phase lag caused by control plant and digital implementation. The stability of the scheme with respect to the grid impedance variation and sampling frequency selecting are also analyzed. Finally, experimental results of a 16.5 kVA prototype confirm the validity of the theoretical expectation.