Generalized symmetrical angle PWM technique for ac voltage controller

Conventional methods of ac voltage controllers, such as on-off control and phase-angle control, are known to produce harmonic voltages in the ac supply lines. The paper introduces the use of forced commutated techniques in ac voltage controllers, namely a symmetrical angle pulse width modulation technique. Symmetrically displaced pulses within the sinusoidal voltage waveform are adopted. The advantages of a unity displacement factor and high frequency harmonic currents, which are easy to filter, can be gained in the suggested control technique. The resulting harmonic currents from the proposed technique are analyzed and compared on the basis of the phase-angle control technique. Simple LC filters can be introduced in the supply input side of the voltage controllers to improve the quality of the supply voltage waveform. The analysis of the harmonic currents shows that noticeable reduction is gained by increasing the number of pulses per half cycle.