Empirical compensation of low order harmonics due to flat top modulation the "BATMAN" modulator

Abstract

The 60° flat-top modulation technique (also called two phase or discontinuous modulation) is a widely used method in the industry to reduce switching losses in three phase PWM inverters. This technique reduces the number of switchings via adding a zero sequence component to the output voltage. The added component is chosen such that one of the phase legs is not switched, but the phase-to-phase voltage still remains sinusoidal. In this article it is shown that 60° flat-top modulation can cause low order harmonic distortion. The cause and the magnitude of this effect is investigated, and an empirical method is given to decrease the distortion, which uses a modified version of the 60° flat-top modulator. The new method significantly decreases the current THD, at the cost of a minor increase in converter losses.