A Novel Decoupled Current-Sharing Scheme Based on Circulating-Impedance in Parallel multi-Inverter System

Parallel multi-inverter systems can be designed to have the advantages of expandable output power, improved reliability, and easy N+X redundancy operation. However, a current-sharing control scheme has to be employed to enable the inverters to share the load current equally. The concept of circulating impedance is proposed in the paper, and introduced into current-sharing control scheme in parallel multi-inverter systems. The mathematical model of circulating impedance is set up. By introducing circulating-impedance control regulator, the characteristic of circulating-impedance is controlled to be similar to that of the pure resistance or inductance. Then the relationship between the circulating-current phasor and the amplitude, the phase of inverter module´s output voltage reference is decoupled. Experimental 220 Vac/3 KVA inverter modules are built and parallel operated. The results of experiment verify that the current-sharing scheme based on circulating impedance is available and efficient.