A simple analog controller for single-phase half-bridge rectifier

A simple analog controller is proposed for the single-phase half-bridge pulsewidth modulation rectifier to maintain near unity power factor at the input and balance the voltages across each half of the dc bus. The controller works in the principle of constant-frequency current programmed control. The required gating pulses are generated by comparing the input current with a linear and bipolar carrier without sensing the input voltage. Two voltage controllers and a single reset-integrator are used to generate the carrier. All the necessary control operations are performed without using any phase locked loop, multiplier, and/or divider circuits. Resistor based sensors are used to measure the voltages across two halves of the dc bus and the input current. The controller can be fabricated as a single integrated circuit. The averaged small signal models and all the necessary design equations are provided. The condition of stability against subharmonic oscillation is analyzed. Calculation of switching and conduction losses is presented. The control concept is validated through simulation and also experimentally on an 800-W half-bridge rectifier. Experimental results are presented for ac-dc application, and also for ac-dc-ac application with both linear and nonlinear loads at two different output fundamental frequencies (50 and 60 Hz).