Single-Phase LLCL-Filter-based Grid-Tied Inverter with Low-Pass Filter Based Capacitor Current Feedback Active damper

The capacitor-current-feedback active damping method is attractive for high-order-filter-based high power grid-tied inverter when the grid impedance varies within a wide range. In order to improve the system control bandwidth and attenuate the high order grid background harmonics by using the quasi-PR control method, the digital delay is preferred to be reduced as much as possible. However, when the time between the sampling point and the updating point is reduced, the disturbance caused by the switching noises will be easily introduced into the sampling signals, resulting in possible disability. In this paper, a low pass filter is proposed to be inserted in the capacitor current feedback loop of LLCL-filter based grid-tied inverter together with a digital proportional and differential compensator. The detailed theoretical analysis is given. For verification, simulations on a 2kW/220V/10kHz LLCL-filter-based grid-tied inverter have been presented.