Wireless parallel operation of 400-Hz high-power inverters in ground power units for airplanes

This paper deals with parallel operation of 400Hz inverters in ground power units (GPU) for airplanes. For high-power 400-Hz inverters, the modulation frequency ratio is fairly low, which causes difficulties to the parallel operation. To reach low THD content in output voltage, resonant controllers are used for control of each 400-Hz inverter in the paralleled GPUs. With resonant controllers, very small phase difference between the paralleled inverters may cause huge circulating current because the output impedance is rather low. As is known, the conventional droop method has to trade off between sharing effect and voltage regulation, and effective load sharing cannot be achieved if the initial phases of the paralleled inverters are unknown. This paper proposes a novel method for parallel operation of 400-Hz inverters. Compared with the conventional droop method, the proposed method can improve the load sharing significantly together with improved dynamic response. What is more, satisfactory sharing of the power can also be achieved even under low line impedance while maintaining good frequency regulation (<;1Hz). Simulation and experimental results show validity and effectiveness of the proposed method.