A Novel LCL Resonant Converter With Inherent CC-CV Output for On-Board Chargers of Plug-In Electric Vehicles

The LLC Resonant converter is widely used in on-board charger applications for its high efficiency. However, conventional LLC converter with pulse-frequency-modulation suffers from a wide switching frequency range for realizing constant current (CC) and constant voltage (CV) charges. To address this problem, different from the traditional solution, a novel LCL resonant converter operating at a fixed resonant frequency with inherent CC and CV output characteristics is proposed in this letter. In the proposed concept, the CC and CV charges are accomplished by the special LCL tank. With the increasing of battery voltage during charging process, the resonant tank of the proposed converter is equal to the conventional LCL tank and LC tank for CC mode and CV mode, respectively. Thus, the sensing and control circuits are canceled while the wide zero-voltage-switching operation for primary switches and zero-current-switching for secondary diodes still be maintained. Therefore, the fixed resonant frequency operation, high efficiency, high reliability, and low cost are key features of the proposed converter. A 1-kW prototype with 400 V input and 250-400 V output is built and tested. The full load efficiency of 96.7% and higher than 96% for the CC mode were both achieved. The experimental results demonstrate the advance and validity of the proposed converter.