Mitigation of Low Harmonic Ripples Based on the Three-Phase Dual Active Bridge Converter in Charging Station Applications

To minimize the recharge time of EVs, Level 3 charging stations utilizing DC fast charging systems have become increasingly prevalent. Additionally, these systems offer bidirectional functionality, aiding in stabilizing the DC grid during peak hour. As a result, the DC-DC converters utilized in such systems must be capable of bidirectional energy transfer. Among existing typologies, DAB converters are preferred due to their simplicity and sustainability. The three-phase DAB (DAB3) is favored because the output ripple is lower compared to the single-phase structure. This characteristic assists in mitigating the negative effects on the battery caused by high-frequency current ripple. However, the input to DAB3 converters typically originates from AC-DC stages, leading to the inclusion of low harmonic frequency ripples (e.g., multiples of 360 Hz). These ripples are then transferred to the battery, increasing its temperature. To address this issue, this paper proposes a technique to mitigate negative effects by attenuating these low frequencies in the charging current. Simulations were conducted to demonstrate the effectiveness of the proposed technique. Scaled-down experiments utilizing a DAB3 prototype were conducted to corroborate the simulations. The findings demonstrated a reduction in ripple from 8.66% to below 2.67% when compared to the original controller. This reduction enabled the solution to meet the limiting current ripple criteria outlined in the CHAdeMO standard.