Eliminate the adverse effects of PWM operation [in AC motor drives]

The increased application of PWM ASDs for efficient speed/torque control of AC motors has resulted in a growing number of costly motor-drive-related process failures. This paper presents a novel resonant converter ASD that is designed to provide sinusoidal voltages and currents at controlled slip for speed and torque control of AC motors. The approach inherently eliminates the adverse effects of PWM ASDs including overvoltages, shaft voltage/bearing currents and EMI. This resonant power converter technology employs isolated series resonant inverters and a reverse power circuit to generate fast response variable amplitude/frequency sine wave currents and voltages. A description of the power converter configuration, control circuits and simulation results are presented.