Low Voltage Charging Technique for Electric Vehicles with 800 v Battery

It has been suggested that the main battery voltage of electric vehicles is increased from 400 to 800 V to improve the charging speed and driving distance. However, the secondary components in the dc/dc converter of the on-board charger have high voltage stresses due to the increased battery voltage. Therefore, this article proposes a low voltage charging technique. The previously designed and optimized dc/dc converter for 400 V battery is used to charge 800 V battery. The battery stack is divided into two modules. Dc/dc converter charges one of two modules alternatively using the battery selection circuit (BSC). Since the BSC has low voltage stresses, the proposed converter can have low voltage stresses on all the dc/dc and BSC parts. Moreover, the dc/dc converter and BSC can be decoupled by turning off the dc/dc converter while changing the charged battery. Therefore, the loss of BSC can be minimized by operating it with low frequency because the switching frequency of BSC can be independent of that of the dc/dc converter. The design process can also be simpler owing to decoupling operation. The LLC converter was adopted for dc/dc converter with 3.3 kW output to verify the proposed technique.