Decoupled control of inverters in parallel operation for AC motor drives

A decoupled parallel control of PWM inverters for AC motor drives is proposed in this paper. The control for sinusoidal reference synchronization, with variable frequency, and the control for load current sharing are decoupled by a local feedback. At first, the phase angle of the sinusoidal reference of each inverter is represented as a square signal and shared among the inverters. And the phase angle mentioned is pre-synchronized beyond the current sharing regulation. Then the current sharing is regulated by introducing the circulating current into the adjustment of the sinusoidal references. The system control is simplified with both easy implementation and good performance. Operational principle is analyzed and a prototype is built with two digital controlled inverters in parallel to feed an asynchronous motor. Simulation and experimental results under 20 Hz-50 Hz operation are given to verify the control proposed.