To reduce the losses caused by a switching element with its stable operation, by keeping constant the ratio of a modulating wave to a carrier, controlling the power factor at 1, and performing constant-DC-voltage control.
The control portion of this converter has a dead-time adjusting circuit 21 as well as a PWM control signal generator 12 and a PLL control circuit 10 including a power factor detector 9. One arm, which is connected to a phase with the minimum and maximum absolute value of a three-phase AC voltage, controls a switching element in PWM to suppress higher-harmonic currents. Also, the other two phases are commutated continuously to give to this converter a DC voltage characteristic similar to the diode-bridge converter. Then, when the DC voltage is increased, the PLL control circuit 10 detects a power-factor angle from the power supply voltage and AC current and adjusts the value of the power factor to 1. On the other hand, the dead-time adjusting circuit 21 adjusts the value of a Y-axis component from the input AC current and the power-factor angle of the power factor sensor 9 to make the vaue zero. Thereby, stable operation is maintained and the losses of the switching element can be reduced.
TOKUNAGA KIICHI
BANDO AKIRA
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