High-frequency high-efficiency DC-DC converter for distributed energy storage modularization

Battery is one of the most important energy storage devices in high power energy storage applications. It is widely used in the plug-in hybrid electric vehicles (PHEVs) and energy storage systems for renewable power generation such as wind and PV. In conventional series-connected high capacity battery string, due to the imbalance of battery cells, there are a few issues such as the cell damage due to over charge or over discharge, reliability and safety concerns. Conventional approaches to address these issues include the battery monitor system (BMS) and cell equalizer circuits. With BMS battery pack performance is still limited by the weakest cell in the string. The cell equalizer is limited by the current rating of the circuit, the equalization speed and the additional cost and weight. In this paper, a new concept of distributed energy storage device (DESD) module is proposed. Instead of using one high power DC-DC converter which connects to the whole battery string, a few distributed high voltage gain, high frequency and high efficiency bi-directional DC-DC converters are integrated with small battery packs respectively to form DESD modules. The module outputs are connected in parallel to form a battery energy storage system. The advantages and challenges of the DESD module are presented in this paper. A 200kHz, 400V to 12.8V, 256W soft switched bi-directional DC-DC converter is demonstrated for DESD modularization.