Technique for pulse dropping in pulse-width modulated inverters

Abstract

The maximum output voltage obtainable from a pulse-width modulated inverter is less than that obtained when the inverter output waveform is a square wave of wanted frequency. Therefore, in order to realise the full potential of the inverter it is necessary to make the transition from a PWM output waveform to a square wave. Due to the practical limitations of the power circuit, it is not possible to reduce the width of unwanted pulses in the PWM waveform gradually to zero, but instead, pulses of a finite width must be dropped abruptly from the waveform. This results in step changes in the output voltage which can produce large current transients in the power circuit and the load. It is shown that the traditional method of pulse dropping is unsatisfactory and a new method is proposed which produces much smaller step changes in output voltage.