Discrete-time current control of voltage-fed three-phase PWM inverters

The discrete-time current control of three-phase voltage-fed pulsewidth modulation (PWM) inverters is discussed, with emphasis on important practical aspects. The inverter feeds a balanced three-phase load of R-L impedances in series with back-EMFs. The inverter-load system is modeled by using space vectors. The practical difficulties of the predictive control method are pointed out. In particular, effects of the delayed application of the manipulated voltage caused by controller computing time are investigated. A modified control law that eliminates the undesirable effects of the computing delay is introduced. Also, prediction of current reference is utilized, which would enable operation with any reference function. An estimation and prediction procedure for the back EMF is also introduced. Steady-state errors in the load current due to these predictions are calculated for sinusoidal operation. Simulation results for the predictive control and the modified control laws are presented and discussed