A modified CLC‐T resonant converter with inherent constant current ‐ constant voltage battery charging

Abstract

AbstractFrequency‐modulated (FM) resonant converters are widely used in onboard battery chargers for constant current (CC) ‐ constant voltage (CV) charging of lithium‐ion batteries in electric vehicles. One of the significant challenges of FM converters is that they require precise control of current followed by voltage to avoid risks due to overcurrents and overvoltages. Also, there is an increased backflow current, peak current stress, magnetic losses, and switching losses when the frequency of operation is away from the resonant frequency. To overcome these issues, this paper proposes a modified CLC‐T resonant converter that operates only at resonant switching frequency but has an inherent smooth transition from CC to CV for battery charging. During CC charging, the resonant tank is CLC‐T, and the secondary circuit is a full‐bridge rectifier. As the battery voltage increases and reaches the rated value, the secondary diodes enter into cut‐off mode, modifying the secondary circuit into a half‐bridge rectifier. Thus, the resonant tank is automatically converted to CL, and there is a shift into CV charging. During the entire charging operation, the switches and diodes are soft‐switched. The switches attain either near‐zero phase angle or zero‐voltage switching operation, whereas the diodes attain zero‐current switchings. A hardware prototype of 400 V input and 320–420 V output battery charger was developed, tested, and validated in the laboratory. The highest efficiency of the overall charging system is 97.4%.