A method to improve linearity of a sinusoidal PWM in the overmodulation region

A new method to extend the linearity of a sinusoidal PWM is presented. A square wave is added to each of the phase voltage commands in the pulse dropping region. The magnitude of the square wave is governed by a function of the modulation index. Addition of the square wave maintains the fundamental component gain of the PWM in the pulse dropping region and extends the PWM linearity all the way to the six step mode of operation. The method eliminates the need to over modulate the phase voltage commands to extend linearity, resulting in increased dynamic range for the associated control. Analytical expressions are derived for the required function of the modulation index. A very simple function is suggested and its effectiveness demonstrated for actual implementation. All analytical results are experimentally verified on a 100 kW three phase AC/spl rlhar2/DC converter.