Control of Parallel Voltage Source Inverters in AC Variable-speed Drive Systems

Abstract

The parallel structure of two voltage inverters sharing a single standard three-phase machine is analyzed in the paper. In ac variable-speed drive systems, Parallel inverters work under Variable-voltage-variable-frequency (VVVF) conditions, so the problems of synchronization and load sharing must be solved. In order to tackle the problems, the paper presents the global-local method of double close-loops. Through the global speed regulator, the reference current of each inverter is achieved. To the local current loop, a simple method of paralleling structures with carrier-based PWM current regulators to independently regulate each inverter’s current is employed. Meanwhile, the control of the zero-sequence current is also analyzed in the local current regulator. The simulation results confirm the feasibility of the control scheme and show the motor current can be shared and has good dynamic characteristics, being superior to single module.