A small-signal harmonic model of a closed-loop power converter

Power converters are inherently nonlinear and time-varying. If power electronic devices can be accurately linearized, it can be incorporated into a harmonic power flow program to analyze a large interconnected power system or a microgrid system where several distributed converters are connected. While there have been many methods to obtain the small-signal models of DC-DC converters, most of these methods cannot be directly applied to AC-DC converters. This paper presents a new method, which can be used to obtain the small-signal models of AC-DC converters. A small-signal harmonic model of a closed-loop pulse-width modulated voltage source converter with synchronous dq frame current controllers and a dc voltage controller is derived based on the proposed method. The results are in good agreement with large-signal simulations by means of PSCAD/EMTDC.