AC voltage controllers as power converters used in many application between power ranges from few watts up to fractions of megawatts, such as light dimmers, induction motor soft starter, industrial heating and cycloconverters. Overall efficiency of power system controlled by some advanced methods in power converters is very important which covers supply and load power factor, harmonic distortion at both supply and load side. One of these advanced methods that is best used is the conventional controller, with phase angle control (PAC) of thyristors and it is a known method in contolling AC voltage applied to specific loads. However, these controllers are found to create some problems whose main problems are introduction of high level low order harmonics in current at the load and supply side, poor supply power factor and also low efficiency. This paper presents a proposed three phase AC voltage contoller scheme which allows the application of extinction angle control (EAC) to overcome these problems. Also, a comparison is given between proposed and conventional controllers on the basis of simulation under this viewpoints. The improvements are obtained in terms of high supply power factor, low harmonic content in the load current and high efficiency by proposed controller on comparing to conventional controllers.
Key words: AC voltage controller, soft starter, thyristor, power factor, harmonic.
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