Design of a compact, battery-powered rep-rate charger for an 88-kJ capacitor bank for EML applications

The Materials Testing Facility (MTF) at the U.S. Naval Research Laboratory (NRL) is developing a battery-powered, rep-rate charger for an 88-kJ capacitor bank. The goal is to charge a 7000-μF capacitor to 5-kV in four seconds for a fifty shot burst. A bank of LiFePO4 batteries is used with a full H-bridge converter, a transformer, and a rectifier to transform the 500V battery voltage to a 5-kV secondary voltage. A key parameter is to minimize the converter weight and volume; therefore the switching frequency needs to be as high as possible to reduce the size of filter components and transformers. However, as the frequency increases, switching losses will begin to dominate and a practical limit will be reached before the device switching maximum is reached. In addition to the design of stable battery packs, most of the work has been focused on switch design and driver optimization, utilizing techniques such as resonate switching and active feedback control systems. This paper will present simulation data and results from experiments.