Resonance elimination of LLCL filters based on virtual resistor for single-phase PWM inverters

In this paper, an active damping control scheme based on virtual resistors is proposed for LLCL filters in the single-phase grid inverters. In comparison with the well-known LCL filters, a very small-size inductor is inserted in series with the filter capacitor, by which the series resonance at the switching frequency may occur. By the LC filter branch, the switching ripple in the grid-side current is suppressed, from which the inductor size in the grid side is minimized. However, the resonance phenomena in this filter may also occur, which needs to be investigated to guarantee the system stability. A resonance suppression scheme based on virtual resistors is proposed for LLCL filters in single-phase grid inverters. The simulation results for a 3-kW single-phase system have verified the effectiveness of the proposed control scheme.