Parallel-connected three-phase inverters for railway auxiliary power supply without sensing output currents

This paper presents the implementation of a wireless controlled three-phase parallel-connected inverter system which supplies auxiliary power for railway facilities. In order to implement droop method without the use of output currents sensors, a power computation scheme based on the virtual output currents establishment is proposed in this paper. The overall control scheme consists of an inner loop for three-phase output-voltage regulation and an outer loop for the automatic loads sharing. For the outer loop, the Proportional-Derivative droop controller is adopted in order to deal with trade-off between the good dynamic performance and small deviation of frequency and amplitude. For the inner loop regulation, repetitive controller is employed in the system under d-q frame supplying power to nonlinear loads. The whole system is described, and the simulations as well as experimental results of a two 15kVA-parallel-connected inverters prototype are presented to demonstrate the validity of the proposed system.