Gaining Reactive Power Capacity in EV Fast Charging Stations with Vienna Rectifier

Nowadays, numerous electric vehicle (EV) charging stations are installed in low-voltage (LV) distribution networks. Significant voltage oscillations in LV networks may occur, leading to detrimental impacts on the network operation, mainly in remote feeder. Thus, reactive power flow control for EV charging stations is necessary for voltage support. Considering the cost factor, most manufacturers tend to select the unidirectional Vienna rectifier coupled with isolated DC-DC converters. By injecting zero-sequence voltage, Vienna rectifier can operate at non-unity power factor. This paper derived the permissible maximum power factor range under different bus voltage levels. Considering the varying bus voltage, an operating point switching method is proposed to avoid over-modulation and distorted current. Finally, a systematic control structure is proposed to ensure voltage support capability. Preliminary simulation and experimental results are given to illustrate the practical value. Balanced and unbalanced grid conditions are analyzed to demonstrate the control robustness.