The Influence of Nonlinear Factors on System Stability in Cascaded H-Bridge Grid-Connected Inverters

The output characteristics of the inverter are affected by nonlinear factors, which will lead to poor output performance of the inverter. This paper focuses on cascaded H-bridge (CHB) inverter, taking into account the dead-time, the non-ideal characteristics of power devices and the nonlinear factors of digital control delay. By using the description function method to linearize the nonlinear part, that an impedance model is established that includes dead-time effect, non ideal characteristics of power devices, and digital control delays. The stability analysis is carried out based on the impedance stability criterion. The results show that the dead-time effect and the non-ideal characteristics of power devices will affect the output impedance of the inverter in the grid-connected system, but the impact is small and will not cause the system instability problem, which can be ignored. Digital control delay will change the output impedance of the inverter, resulting in unstable operation of the system.