Large signal model of variable frequency drive and motor system for transient stability analysis

Nowadays, variable frequency drive (VFD) system is more and more widely used in induction motor (IM) systems. Due to the characteristics of VFD motor are different from that of IM, if the traditional load model based on IM is adopted as usual, the credibility of power system transient stability analysis will be challenged. Therefore, the large signal model of VFD motor based on switching function is established and the switching function is treated continuously by using Fourier series. In this model, diode bridge rectifier with LC filter is replaced by a cascaded system consisting of a controlled rectifier with constant DC pulse period and constant conduction angle and Boost chopper with small duty cycle, and the switching functions of the controlled rectifier and Boost chopper are obtained. The proposed model is compared with the detailed simulation model of the VFD motor established in MATLAB/SIMULINK. The results show that the proposed large signal model can effectively describe the characteristics of the VFD motor when large disturbance occurs, which is helpful for the transient stability analysis.