ZVS Resonant Switched Capacitor Converter with 1.5x or 2.0x Step-Up Conversion Ratio for High-Voltage EV Batteries and Powertrains

The voltages in the powertrains and lithium-ion batteries (LIBs) of electric vehicles are increasing to 600-800V, whereas ordinary fast chargers are designed for 400-V systems. An additional on-board or internal voltage conversion stage is needed to adapt traditional chargers to high-voltage powertrains. This paper presents a resonant switched capacitor converter (RSCC) with a conversion ratio of either 1.5 or 2.0 to bridge the voltage gap between 400-V chargers and 600- or 800-V systems. The proposed RSCC contains a 3-level flying capacitor circuit that realizes the changeable conversion ratio between 1.5 and 2.0. Furthermore, a zero-voltage switching (ZVS) cell, which comprises a tiny inductor and capacitor, is added to eliminate losses due to the parasitic capacitances of MOSFETs and diodes. Experimental tests using a 1-kW prototype demonstrated power conversion efficiencies in both the 1.5x and 2.0x conversion modes that exceeded 98% in the medium- and heavy-load regions.