An analysis method for harmonic resonance and stability of multi-paralleled LCL-filtered inverters

Paralleled grid-connected inverters with LCL-filters are coupled through the non-negligible grid impedance. However, the coupling effects among inverters and grid are usually ignored during the design, which may lead to unexpected system resonance and even instability. This paper thus investigates the resonance characteristic and stability analysis in multi-paralleled grid-connected inverters with LCL-filters. An intuitive analytical method based on equivalent grid impedance has been proposed. The analysis clearly describes the open loop resonance characteristic and provides a relatively easy method to define the stable region of multi-inverters system. Experimental results are provided for verifying the theoretical analysis.