Wednesday, 21 December 2011
The applications of ac–dc rectifiers are prerequisite nowadays in the power electronics industry. Due to tougher regulations on the input current harmonics, many topologies of the switch-mode boost-type power factor corrector (PFC) circuits have been presented in recent years. In this paper, a four-switch voltage-doubler boost rectifier is analyzed. A new control scheme is proposed to eliminate the output voltage imbalance when the load is unevenly distributed across the two output dc rails. Unipolar pulse width modulation switching patterns are adopted to slow down the discharging rate of the output capacitor with the lower voltage. No dc or out-of phase component is injected in the source current. Thus, the unity input power factor can be genuinely achieved. Two hysteresis comparators are employed in the presented controller. One is used for the source current to track its command. The other comparator is to confine the output voltage imbalance within a reasonable level. Modified averaged circuit models are adopted to derive the limits of the ratio of the dual loads for output voltage balance. Experimental results on prototype circuits confirm tightly with the theoretical analysis.
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