Improved current control technique of VSI PWM inverters with constant modulation frequency and extended voltage range

A hysteresis control method for three-phase, current-controlled, VSI PWM (pulse width modulation) inverters characterized by constant switching frequency is presented. The method is based on substantial improvement of the principle of minimization of interference among modulations of the various phases, which does not require any knowledge of load parameters or EMF, provided the load is symmetric. Interference minimization allows PLL (phase-locked loop) control of switching frequency. The inherent benefits of the proposed technique are full exploitation of inverter voltage capabilities and a definite reduction ion commutation losses. The method minimizes commutation losses and current ripple while allowing maximum output AC voltage to be obtained from the inverter. The method exhibits all the favorable characteristics of hysteresis controls: fast response, good accuracy, and robustness. Experimental tests confirmed theoretical forecasts, showing excellent performance of the control