An Average Model for Three-Phase Five-level Flying Capacitor Converters with Phase-Shifted PWM

This paper presents a new full-order ABC frame average model for three-phase five-level voltage source converters (VSCs) with flying capacitors (FCs) under the phase-shifted pulse width modulation (PS-PWM) scheme. By applying the average operator on the multi-level converter switch control functions over every quarter of the switching cycle, a switch duty cycle which is time-varying and discontinuous within one switching cycle can be derived for each converter power cell. The equivalence to the switching network was established by excluding actual FC components in the state-space average circuit, while the averaged dynamic behaviors on FCs can be still preserved without the switching functions for two consecutive cells cancelling each other out. A medium voltage (MV) back-to-back five-level FC power conditioning system was built in the MATLAB-Simulink platform based on the proposed mathematical model. Simulation results are provided for validation purposes. An FC parameter design methodology based on the proposed FC converter model was also developed.