A comparison of resonant converters operating with a double-layer capacitor source

Double-layer capacitors, with their high energy storage capability, may be utilized to supply peak power requirements in systems such as electric vehicles. As energy is drawn from a bank of double-layer capacitors, the voltage at the terminals of the capacitor bank decreases. Seventy-five percent of the initial energy stored in the capacitor bank can be utilized if the voltage is allowed to decrease to one-half of its initial value. The capacitor bank can be augmented with a DC-DC power converter to present a constant voltage to an external system as the capacitor bank voltage decreases. Discussed in this paper is a comparison of three basic resonant DC-DC power converter circuits when used as the converter with such a capacitor bank. Simple equivalent circuits are developed for each converter using a single frequency approximation of the various converter waveforms. Expressions for the voltage gain and the phase angle of the input current for each converter are derived from these equivalent circuits and plotted as a function of frequency. Issues related to the selection and design of a converter for this application are discussed