Parallel Bi-directional DC-DC Converter for Energy Storage System

A scalable parallel bidirectional DC-DC converter system has been developed and evaluated. Fast and efficient seamless control is achieved by using an H-bridge topology. Although the control structure is simple, four drive modes can be handled. It was extended for use in simple parallel converter management. A parallel function auto-rotation scheme is used to control which units are active on the basis of tracked power. This method achieves high efficiency over a wide load range, especially for light loads. The automatic rotation of which converter acts as the output master distributes the load more evenly, resulting in less load damage. The only hardware required are a power line and communication cable connection. All other functions are provided by software and operate autonomously. A 5-kW prototype converter was constructed and evaluated in a three-unit parallel converter system. The estimated efficiency for 15-kW rated discharge was 97.8% for 333-V battery pack power and 380-V DC-link power.