Modelling and control of three-phase/switch/level fixed-frequency PWM rectifier: state-space averaged model

A new and simple state model of a three-phase, three-switch, three-level, fixed-frequency pulse-width-modulated rectifier is presented. The modelling approach uses the state-space averaging technique in continuous current mode. The averaging process is applied on two time intervals: the switching period for average current evaluation, and the mains period for average voltage computation. A basic mathematical model of the converter is first established. A simplified time-invariant model is then deduced using the rotating Park transformation. The steady-state regime is analysed on the basis of the model obtained, and converter design criteria consequently discussed. The proposed modelling approach is then verified numerically through a digital implementation of the converter in the Matlab/Simulink framework, using the switching function approach. The numerical results show the reliability of the proposed model that would be then easily applied to the design of suitable duty-cycle-based control schemes.