Virtual Impedance Current Sharing Control of Parallel Connected Converters for AC Motor Drives

The paper presents a new current sharing control scheme for parallel connected three phase converters. The proposed method, based on the representation of the three phase converter currents by the magnitude of the current space vector, is shown to obtain good current distribution with minimum shared information between the parallel connected converters. Converter output voltage magnitudes are modified in proportional to the current space vector magnitudes with the effect of appearing as a virtual impedance connected in series with the current sharing reactors. The converter algorithm uses only one control loop to obtain good current distribution between the converters. Each converter uses only its local information to limit the circulating current, improving the reliability and redundancy of the scheme. The performance of the new current sharing control strategy is tested and verified experimentally using a test rig comprised of two parallel connected 110V, 1.25kVA three-phase voltage fed converters feeding a 2.2 kW three-phase induction motor.