Time-Varying Modelling and Stability Analysis Method of Grid-Connected Inverter under the Long-Term Operation

Small signal analysis methods based on linear time-invariant theory have been frequently proposed to assess stability of grid-connected inverter. However, these analysis methods fail to deal with the effects of time-varying operation points caused by parameters perturbation or system degradation under a long-term operation. The concept and stability criteria of linear time-invariant system are no more effective in time-varying system. This paper presents a time-varying modelling and stability analysis method for grid-connected inverter based on Lyapunov energy function method, which is able to investigate the effects of time-varying operation points on long-term stability. Simulation and experimental results are provided to validate the proposed time-varying modelling and stability analysis method. The proposed method is able to predict potential instability issues of grid-connected inverter within lifetime of passive components, and to optimize passive components at design stage.