Current controller in synchronous reference frame for high performance AC drives

Current controlled high performance ac drives (for spindles application for example) require quick current response in transient state and low harmonic current content in steady state. In addition the transition between PWM and square wave operation has to be soft and not to cause undesirable currents and torque transients. Thus, the classical stationary reference frame P-I current regulator operates in speed and torque reduced range over which the current can be regulated instantaneously and, as a consequence, the inverter has to be derated. The authors propose a new current regulator in synchronous reference frame based on the space vector PWM modulation. The voltage reference is get through the regulation of the fundamental harmonic of the torque and flux current components in synchronous reference frame, up to when the machine back emf can be overcome. In square wave operation the drive outer control loops (speed and flux) are still active, but only the feedforward voltage control is applied. Complete simulation results are carried out in order to evaluate the validity of the proposed method in the whole speed range of operation.