A new method to linearize any triangle-comparison-based PWM by reshaping the modulation command

Abstract

A new method, which linearizes any triangle-comparison-based pulsewidth modulation (PWM) in the pulse-dropping region, is presented. Based on the original modulating command, the method produces a modified command as a function of the modulation index. This modified command compensates for the volt-sec which are lost due to a portion of the original modulating command exceeding the boundaries of the triangle carrier. The method eliminates the need to overmodulate in the pulse-dropping region and prevents erosion of the dynamic range of the associated control. This method is applied to three common PWM algorithms. Analytical expressions are derived for each case and verified on a 100 kW AC/DC converter.