Integration of Magnified Alternating Current in Battery Fast Chargers Based on DC-DC Converters Using Transformerless Resonant Filter Design

For safety and longevity reasons, in subzero temperatures, lithium-ion batteries (LIBs) can only be charged after precommissioning their temperature. Therefore, in such conditions, fast charging depends on fast heating. Recently, the injection of ac currents into LIBs has been reported as a technique with the potential to decrease heating time. This paper proposes a method based on a multi-objective algorithm for dc-dc converter design using transformerless resonant filters. The method enables the dc-dc converters to produce magnified ac current in addition to the dc current. Using the proposed design method, a topological survey of dc-dc converters with magnified ac current capability composed of either half-or full-bridge switch arrangements is carried out. In the presented experimental setup, it is demonstrated that by using an LCL circuit with specific component values and a full-bridge switch arrangement, magnifications of up to 15.7 may be reached. Furthermore, by matching the switching frequency with the frequency where the LCL and the battery resonate, for the same injected ac current, the current flowing in the semiconductors and the switching frequency could be reduced. This allowed a loss reduction in the semiconductors of up to 75%, when compared with an equivalent dc-dc converter enabled to produce a nonmagnified ac current.