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Pulse Width Modulation Control
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The most efficient method of controlling the output voltage is to incorporate pulse width modulation control (PWM control) within the inverters. In this method, a fixed d.c. input voltage is supplied to the inverter and a controlled a.c. output voltage is obtained by adjusting the on-and-off periods of the inverter devices.

The PWM control has the following advantages:

(i) The output voltage control can be obtained without any additional components.

(ii) With this type of control, lower order harmonics can be eliminated or minimized along with its output voltage control. The filtering requirements are minimized as higher order harmonics can be filtered easily.

The main drawback of this method is that the SCRs used in this method must have very low turn-on and turn-off times (inverter-grade SCRs), therefore, they are very expensive.

The commonly used PWM control techniques are:

(a) Single-pulse width modulation (SPWM)

(b) Multiple-pulse width modulation (MPWM)

(c) Sinusoidal pulse width modulation (sin PWM)

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