Method and apparatus for supplying AC power while meeting the European flicker and harmonic requirements

摘要

An improved control method is provided that combines conventional ON-OFF control and conventional phase-angle control to reduce the AC inrush current to an electrical load, such as a tungsten halogen lamp used as a heating element in a laser printer, so that the power control circuit can satisfy both the European flicker and European harmonic requirements. Phase-angle control is applied to the load for a very short time period when it is initially energized, then the control circuit quickly switches from phase-angle control to standard ON-OFF control to reduce the harmonics generated by conventional phase-angle control methodologies. The electrical load exhibits three possible states: power full OFF, power ramp-up, and power full ON. During the power ramp-up state, power supplied to the load is adjusted by delaying the phase angle of the firing pulse relative to the start of each AC half cycle. Depending upon whether or not the system demand has been satisfied, the load's state can be changed from either power ramp-up to power full ON, or from power ramp-up to power full OFF. The phase-angle control methodology used during the power ramp-up state must be of sufficient time duration to reduce the amount of flicker to pass the European flicker test. However, this power ramp-up time interval must also be as short as possible to keep the harmonics as small as possible to the load, without the requirement of adding a large AC current harmonic attenuation inductor, which would otherwise be needed to pass the European harmonic test.