Improving the Regulation Range of EV Battery Chargers With L3C2 Resonant Converters

The demand for electric vehicles has expanded rapidly for both industrial and transportation applications. In parallel, new battery technologies capable of deeply discharging and powering electric vehicles over long periods of time have been introduced and made available in the market. Due to the increasing complexity of charging algorithms, battery chargers are exposed to demanding operating requirements. Chargers should not only work under different loading conditions (from absolutely zero to maximum output power) but also regulate a wide output voltage range (from near zero to 1.5 times nominal voltage). In this paper, a multiresonant L3C2 resonant converter is introduced that can cover nearly all of the regions in the battery V-I plane, from near zero output voltage, zero output current to maximum output power. By adding one capacitor, the topology is able to extend the operating frequency beyond the LLC topology and achieve significant regulation improvements. Near free-ripple charging current for batteries charging is achieved in different states of charge without using burst mode operation, effectively increasing the battery life cycle. In addition, soft transitions are obtained for all the switches (MOSFETs and diodes) resulting in high efficiency, reliability, power density, and low-noise operation of the charger. A complete set of simulation and experimental results, extracted from a 96-VDC 950-W L3C2 resonant converter, demonstrates the characteristic features of the proposed topology for battery charger applications, while providing a comparative example with the LLC topology.