Current Balancing Method in Parallel Connected Inverter Circuit for Megahertz WPT System

This paper proposes a current balancing circuit of a parallel-connected inverter for a WPT system operated in megahertz. Current unbalance, which causes a thermal unbalance and deterioration of the devices, occurs at the output of each inverter when the output voltage has a difference between the inverters. Thus, the current balancing circuit, which is able to be applied for megahertz operation, is required. In this paper, the current balance circuit is investigated to achieve a parallel operation. The current balance circuit is composed of two transformers. A self-inductance ratio of the transformers, which is used in the balance circuit, is calculated by an analytical consideration to achieve the current balance condition. The proposed circuit is implemented into a prototype of the parallel-connected inverter operated around 6.78 MHz. From the experiments, it is demonstrated that the current unbalance of each inverter is 6.7% with the proposed balance circuit.