Abnormal Voltage Compensation for Phase-Shifted PWM-Based Multisampled Cascaded H-Bridge Converters in EV Fast Charging Stations

초록

This article proposes an abnormal voltage compensation method for phase-shifted PWM-based multisampled cascaded H-bridge (CHB) converters in electric vehicle (EV) fast charging (FC) station applications. Given that CHBs can interface directly with medium-voltage (MV) grids, they are regarded as suitable candidates for next-generation EV FC stations. In practice, CHBs adopt multisampling techniques, which enhance the performance of the control loop but also introduce adverse effects, such as counter-phase vertical crossing. This vertical crossing occurs when the carrier magnitude lies between the present and the subsequent samples of the modulating wave. In systems employing digital signal processors (DSPs), this phenomenon can cause missed switching-pulse updates, thereby generating abnormal voltages. As EV FC stations are grid-connected systems, the occurrence of such abnormal voltages ultimately induces severe surges in the CHB input current, which can compromise overall system stability. To address this issue, the occurrence of vertical crossing in each CHB cell is identified at every sampling instance. When a vertical crossing occurs, the switching pulse of the cell with vertical crossing is held at its previous value, whereas those of the remaining cells is adjusted. Through this proposed method, abnormal voltages can be effectively mitigated. The proposed method ensures accurate output voltage generation under multisampling conditions. Its validity is verified through experimental results performed with a single-phase three-cell CHB setup.