Resonance features of multi-paralleled grid-connected inverters and its damping method

The resonance problem in multi-paralleled grid-connected inverters in microgrid is more complex than single one. The Norton´s equivalent circuit associated with grid-connected inverter with LCL filter is figured out in this paper. And in terms of different reasons of causing resonance, resonance problems associated with multi-paralleled grid-connected inverters are categorized into three types: individual resonance, parallel resonance, series resonance. In order to attenuate resonance peak, an active damping compensation term associated with filter capacitor voltage feedback is embedded into current control forward path. The proposed active damping approach is based on the concept of virtual damping resistor which acts as an additional resistor paralleled with filter capacitor. The virtual resistance is deliberately designed to guarantee the requirement of effective resonance damping. Comparative study is conducted to verify the feasibility and effectiveness of resonance damping.