Advanced charging system with bipolar DC-link and energy storage

This paper investigates an advanced electric vehicle fast-charging system with a bipolar DC-link rated at +/- 750 V. The bipolar dc grid concept is known to provide lower on-state loss and much higher flexibility compared to conventional unipolar systems. However, multilevel structure also requires a proper balancing mechanism. The system described in the article contains three types of bidirectional three-level converters based on 1200 V SiC power devices: active-neutral-point-clamped (ANPC) grid converter, non-isolated DC/DC converter for battery energy storage, and isolated dual active-bridge as interface with electric vehicles. All of the converters use the same submodule. The crucial part of the infrastructure is energy storage which enables managing power flow across the converters, thus providing more independence from the grid, such as exceeding maximal charging power from the grid or providing standalone work in case of grid failure. Moreover, bidirectional converters also enable to operate as grid backup energy storage or return energy from the vehicle batteries in vehicle-to-grid (V2G) operation. The study is focused on the various operation modes of the presented fast-charging station, grounded on the theoretical and simulation-based analysis. (Abstract)