24-09-2013, 04:41 PM
PULSE WIDTH MODULATION TECHNIQUES FOR VOLTAGE –FED INVERTERS
TECHNIQUES FOR VOLTAGE.ppt (Size: 625 KB / Downloads: 41)
Introduction
While the 3 6-step inverter offers simple control and low switching loss, lower order harmonics are relatively high leading to high distortion of the current wave (unless significant filtering is performed).
PWM inverter offers better harmonic control of the output than 6-step inverter.
PWM Principle
The dc input to the inverter is “chopped” by switching devices in the inverter. The amplitude and harmonic content of the ac waveform is controlled by the duty cycle of the switches. The fundamental voltage v1 has max. amplitude = 4Vd/ for a square wave output but by creating notches, the amplitude of v1 is reduced (see next slide).
Sinusoidal PWM
The most common PWM approach is sinusoidal PWM. In this method a triangular wave is compared to a sinusoidal wave of the desired frequency and the relative levels of the two waves is used to control the switching of devices in each phase leg of the inverter.
CONCLUSION
THIS IS BEST FROM ALL OTHER TECHNIQUES.
DUE TO ITS LOW COST & BETTER CONTROL.
PWM TECHNIQUES CONTROL HARMONICS LOSSES.