Shifting of Load Harmonic in the Single Phase AC-to-AC Phase Control Converters

Many AC-to-AC single-phase controllers generate low sub-frequency harmonic that causes flickers and requires large filters. Shifting the harmonic frequency to a higher location from the fundamental will result in smaller and cheaper filtering element. Harmonic frequency can be shifted to high frequency location by using pulse width modulation. The PWM control the switching of the power device incorporated in the AC-to-AC conversion circuit. Using specified PWM pattern, the fundamental component can be controlled with the switching harmonics generated at higher than the fundamental frequency. The first harmonic is located at a frequency that depends on the switching frequency of the controlling devices. The paper presents simple pulse modulated controllers that control the switching instants of AC-to-AC single-phase controller to produce continuous variable AC voltage with easy to filter harmonic. The PWM controller replaces the phase control technique that normally employed in many ac electronic regulators used in heaters, light dimmers and the control of many single-phase fractional horsepower motors.