Time-Domain-Based Phase-Shift Control Strategy for LLC Converters in EV Charger with Small DC-Link Capacitance

Electric vehicle (EV) chargers with small DC-link capacitance have recently garnered significant attention in both industry and academia due to their enhanced lifespan, particularly under high temperatures. However, this design, featuring low capacitance in the DC-link, leads to continuous fluctuations in the input voltage for the back-end LLC converter. Therefore, a wider voltage gain is essential to maintain a stable output voltage. While phase shift control is a prevalent method for extending the voltage gain range in LLC converters, traditional approaches often result in the converter continuously switching operation modes under fluctuating input voltages. To solve this issue, a novel phase-shift control is proposed, where the frequency is constant and the feedforward phase-shift angle is derived based on time-domain analysis to minimize the mode-switching transient. Herein, experiment results validate the effectiveness of this strategy.