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

A new method to extend the linearity of a sinusoidal pulsewidth modulation (PWM) is presented. A square wave is added to each of the phase voltage commands in the pulse dropping region. 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 overmodulate the phase voltage commands to extend linearity, resulting in increased dynamic range for the associated control. The magnitude of the square wave is governed by a function of the modulation index. Analytical expressions are derived for the required function. A simple approximation of this function is suggested and its effectiveness demonstrated for actual implementation. All analytical results are experimentally verified on a 100 kW three-phase AC-DC converter