Performance analysis of online dual slope delta modulated PWM inverter

Delta modulation (DM) is a simple pulse width modulation (PWM) scheme especially suitable for AC machine drives where a constant flux operation is desired. However, the modulator has inferior characteristics when compared to conventional sine PWM and therefore it is not normally used. The disadvantages of delta modulators can be significantly reduced by allowing online parameter variation and synchronous operation. This paper attempts to identify the modulation parameters of a delta modulator, which can be varied during constant and variable frequency operation of the three-phase voltage source inverter (VSI) so as to improve the performance in terms of harmonic content and fundamental voltage availability. A new technique of implementing the delta modulator by a microcomputer is proposed. The method is novel in the sense that it uses an algebraic equation to generate the PWM pulses to control the inverter. Experiments, carried out by online microcomputer operation, show that dual slope and dual slope-variable window width operation result in improved performance.