A Programmed Pulse Width Modulation Strategy for AC Voltage Controllers

摘要

Pulse Width Modulation (PWM) control schemes are receiving increased attention on account of their ability to control the harmonic content of the output voltage and/or input current. The main advantage of the PWM technique is the flexibility with which it can be built to generate the firing pulses. Though a number of schemes are in existence, each one is characterized by its own claims. This paper attempts to develop a digital PWM strategy based on equal area criterion with a view to improve the performance of the ac-ac conversion system by making the input current vector to closely follow the source voltage. The basic idea of the proposed area equalization method (AEM) is that the area under any sample of the required sinusoidal-fundamental output and the area of the pulse occur during the same sampling time in the actual output are made equal. The AEM amends the width of each pulse and conjures to extract a distortion less waveform for both output voltage and input current. The twin objectives of the proposed low frequency PWM method, lowering the total harmonic distortion (THD) in the output voltage and improving the input power factor, are elucidated using derived mathematical relations. The values of performance indices derived are authenticated using MATLAB7.1 based simulation study and validated with those obtained from the fabricated prototype module.