In this topic, you study Single Pulse Width Modulation Technique of Inverter – Definition, Diagram & Theory.
The Output voltage of a single phase bridge inverter is as shown in Fig. 3.8 (a). The Output voltage is square wave in nature. The Fourier series Of the Output square voltage is given by,
Thus, the square wave output voltage contains odd harmonics. Here, in single pulse modulation (SPM), the output pulse delay in the beginning while it is advanced at the end by equal interval of(Tt — ö)/2 shown in following Fig. 3.8 (b).
Where width of the output pulse.
Fig. 3.8 (b) : Quasi-square wave output (output with modulation)
The nature of the output waveform is called a quasi-square wave. The Fourier series of the quasi-square wave is same as that of a square wave,
And the Fourier co-efficient are given by,
It is observed that for lower values of i.e. pulse widths i.e.450, the 5th and 7th harmonic components become almost comparable to the fundamental component. Thus one can conclude that reducing ö, introduces the lower odd harmonics with amplitudes comparable to that of the fundamental output signal.
