Harmonic State Space Modeling for the MLCL-Type Grid-Connected Inverter with Nonlinear Inductors

The impact of nonlinear inductor is conventionally studied based on the linear time invariant (LTI) small signal model, and its frequency coupling effect (FCE) is usually described in time domain. In this paper, a small signal harmonic state space (HSS) model is proposed for the MLCL (Modified LCL) type grid-connected inverter considering the FCE of the nonlinear inductor. Based on the HSS model, sideband harmonics and resonance stability affected by the FCE of nonlinear inductor can be precisely described. Finally, simulations and experiments are conducted to verify the theoretical analysis result based on a 228 kW PV string inverter.