Accurate s-Domain PWM Model for Stability Analysis of LCL-filtered VSC

The pulse width modulation (PWM) is widely used with power electronic converters. To study the control dynamics of power converters, the accurate modeling of PWM is necessary. Currently, the common practice of modeling PWM is to consider it as a zero-order-hold (ZOH) block or time delay. In this case, the comparator process is simplified as a unity gain, which leads to an inaccurate modeling. In this paper, an accurate s-domain PWM model is proposed by studying the comparator process in detail. To validate the proposed model, a case study of current control for an LCL-filtered voltage source converter is presented. The analytical results show that, by using the conventional ZOH model and the proposed model, the critical conditions for a stable current control are different. It is validated by the experimental results that the proposed model can precisely predict the stability condition, while the ZOH model loses its accuracy.