A Circulating Current Suppression Method for Parallel EV Charging Modules Based on 0-Axis Current Control

The phenomenon of current circulation will inevitably occur when AC/DC modules in a supercharging station are connected in parallel. Excessive circulating current can lead to various issues that destabilize the system stability, such as waveform distortion, power quality reduction and so on. Aiming this situation, this paper proposes a circulating current suppression method by introducing the 0 -axis current control. Firstly, the equivalent circuit of circulating current is built to analyze the mechanism of circulating current generation. Secondly, instead of the traditional d-q transformation, the d-q-0 transformation is adopted to get the 0 -axis current, which contains asymmetric components caused by the circulating current. Thirdly, a 0 -axis control is designed to suppress the 0 -axis current, which can concurrently suppress the circulating current between AC/DC modules. The designed 0 -axis controller can be viewed as a virtual impedance of the equivalent circulating current circuit. The larger the virtual impedance, the more obvious the circulation inhibition effect. Furthermore, theoretical analysis and experimental results prove the feasibility of this method.