| Abstract |
PWM rectifier harmonic analysis is usually performed with an assumption of constant DC current (idealized analysis). But in practical DC drive such assumption is not realistic. In this paper a method of voltage and current harmonic analysis which takes into account influence of DC current ripple is presented. The method, based on linear approximation of DC current wave shape, is classified as quasi-real analysis. lts advantage over more accurate real analysis is that it enables explicit expressions for voltage and current harmonics and saves computer time. The presented method is performed on different types of PWM techniques, different values of modulation index, number of pulses, lead time constant and is verified by comparison with method of real analysis. The results show that the method is specially useful in cases of low number of pulses and small load time constant when DC current ripple is the most expressed. The method is applied for analysis of PWM rectifier voltage and current harmonics and calculation of AC filter component values. Results of simulation show significant negative effects of DC current ripple: increase of harmonics values and necessary AC filter size. |
