Electrical Engineering (ABSTRACT)Two novel clamped-mode resonant converters are analyzed. These clamped-mode converters operate at a constant frequency while retaining many desired features of conventional resonant converters such as fast responses, zero-voltage turn-on or zerocurrent turn-off, and low EMI levels, etc. The converters are able to regulate the output from no load to full load and are particularly suitable for off-line, high-power applications.To provide insights to the operations and derive design guidelines for the clamped-;mode resonant converters, a complete dc characterization of both the clamped-mode series-resonant converter and the clamped-mode parallel-resonant converter, operating above and below resonant frequency, is performed. State-plane analysis techniques are employed. By portraying the converters' operation on a state-plane diagram, various circuit operating modes are identified. The boundaries between different operating modes are determined. The regions for natural and force commutation of the active switches are defined. Important dc characteristics, such as control-to-output transfer ratio, rms inductor current, peak capacitor voltage, rms switch currents, average diode currents, switch turn-on currents, and switch turn-off currents. are derived to facilitate the converter designs.To illustrate the converter designs in different operating regions, several design examples are given. Finally, three prototype circuits are built to verify the analytica! results.
AeknowledgementsAeknowledgements iii Acltnowlcelgemcnts iv Depending upon the operating frequency and the load, the controlled switches in the resonant converters can be naturally commutated or force commutated [18,19,3l]. In general, natural commutation of the switches occurs when the converter operates below the resonant frequency of the LC tank, while force commutation occurs when the converter operates above the tank's resonant frequency.When natural commutation is achieved, the switches' turn-off losses are eliminated.However, since the diodes are commutated at high currents fast antiparallel diodes are required to minimize the cross conductions in the totem-pole switch-diode pairs caused by the reverse recovery of the diodes. When force-commutation is achieved, the power switches operate with zero-voltage turn·on and the switches' tum-on losses are eliminated. Slow antiparallel diodes and simple losseless capacitor snubbers can be used for the switches since the diodes are commutated at zero current and the switches always turn on at zero voltage.Due to the line and/or load variations, the operating frequency of the conventional resonant converters usually has to vary over a wide range to regulate their outputs. This results in a penalty in the magnetics and lilter design and lowers the overall conversion efliciency.To optimize the design of magnetic components and lilters, several circuit topologies and control techniques able to operate at a constant frequency were proposed [33][34][35][36][37][38][39][40][41][42][...
