| 摘要 |
This invention provides a power controller for an electrical load (4) of variable power factor, comprising switching means (1, 2, 3) which control alternating currents supplied to the load (4), and control means (12-19) which control the non-conduction angle of the switching means (1, 2, 3) such that the non-conduction angle is proportional to an applied control reference voltage (f) and such that the non-conduction angle is substantially independent of the load power factor. The power controller can improve the efficiency of a motor (4) when the motor is operating under reduced load conditions. The described power controller can also be used to adjust the applied voltage to the motor (4) in such a manner that the start current equals a preset current until the motor has reached full speed. In one embodiment, efficiency of the motor is improved by monitoring the angle between the voltage and current zero crossing, comparing this monitored angle with a reference angle and controlling the voltage in such a manner as to maintain this angle equal to a preset angle for applied voltages less than full voltage. |
