In this topic, you study Multiple Pulse Width Modulation Technique of Inverter – Definition, Diagram & Theory.
In this method, the switching devices are turned ON and OFF many times in a half-cycle to obtain several pulses in the half-cycle. The signals used for triggering the switching devices (transistors / MOSFET/ IGBT) are generated by comparing a reference signal with a triangular carrier wave as shown in Thus, the output voltage can be expressed as,
(a) Block diagram
(b) Gating signal generation, and output voltage waveform
Fig. 3.9 : Multiple-pulse-width modulation
The triggering pulses are obtained at the point of intersection of the carrier and a reference signal (square wave). The switching devices (transistors) are ON until the magnitude of triangular wave is greater than reference square wave else they are turned OFF. It is clear that the frequency (fo) of the output voltage signal depends on the frequency of reference signal (fr) and also the carrier frequency (fc). It also gives the number of pulses (P) present in the output voltage in the given half cycle.
Pulse width of carrier signal = 1/fc
Pulse width of reference signal (half of the square wave) = 1/2fc
Hence, the number of pulses in each half cycle, (P), = Width of half-cycle/ Pulse width of carrier signal
Thus the width of ö can be known if Vr, Vc and number of pulses in each half cycle are predefined.
The value of RMS output voltage is given by,