A DC TO DC PWM SERIES RESONANT CONVERTER OPERATED AT RESONANT-FREQUENCY

Resonant DC-DC converters that are usually operated in frequency modulation to achieve regulation have the disadvantage of wideband frequency modulation. An alternate regulation scheme that uses fixed-frequency pulse-width modulation (PWM) is proposed. This control scheme is applied to the series-loaded series-resonant converter. Analysis shows that such a converter has two modes of operation, depending on the load. The modes are characterized by continuous or discontinuous resonant inductor currents. The converter can therefore be operated as a resonant or quasiresonant converter. Quasiresonance is emphasized as it presents low switching stresses. When operated in a full-bridge configuration and with a variation of PWM that can be described as a phase shift modulation between the two sets of switches, the converter presents even lower switching stresses. Analytical results include V A rating and stresses on critical active and passive components as a function of input voltage variation. A 200-kHz 700-W 48-Vdc output offline converter was realized using this concept, and some experimental results are presented to corroborate the analysis.