Development of high input-power-factor power supplies

Switching power supplies with a high-input power factor and efficiency are being used in various applications. The standard voltage available from ac mains is to be converted into either a dc voltage suitable for dc distribution or a variable-frequency ac voltage suitable for ac motor drives. The efficiency of the power conversion system is increased by employing zero voltage switching (ZVS) or zero current switching (ZCS). These techniques help to reduce the switching loss, simplify the snubber requirements, and maximize the power density. The power converter should also operate with minimum input current distortion so that the performance of other ac-operated subsystems is not affected.;A typical power conversion system will consist of a pre-regulator which converts the mains ac voltage into a fixed-voltage dc, a dc-dc converter which converts the fixed-voltage dc into a variable voltage dc, and a dc-ac inverter which inverts the fixed-voltage dc into an ac voltage whose amplitude and frequency vary. The project proposed certain modifications in each of the three stages of the conversion system allowing operation under ZVS or ZCS condition.;The project first presented a second-harmonic-injected modulation to improve the input power factor and reduce the input-current distortion in an ac-dc converter. A conductance model was developed primarily to understand the operation and to arrive at the design parameters. An experimental converter with a total harmonic distortion (THD) less than 5% was built and tested.;The project also proposed a novel full-bridge converter configuration using a saturable core reactor which replaced the auxiliary switches used in the existing converter topology. In the proposed converter, the power and control circuits were simple and the power density high.;The project developed a new dc-ac inverter in which an auxiliary network with a nonlinear core transformer provided ZVS condition for all the switches in the inverter. The saturable core transformer essentially varied the impedance of the resonant network, thereby decreasing the current stress on the switches of the inverter. The voltage and current waveforms obtained on an experimental inverter are presented.