Optimization of PWM for the Overmodulation Region of Two-Level Inverters

Three optimized pulse-width modulated (PWM) techniques for the overmodulation region of two-level inverter-fed ac drives are introduced and investigated from the harmonic loss minimization point of view. The optimization is elaborated for the lowest loss-factor, which is proportional to the square of the root mean square value of current harmonics. The loss-factors are computed for different switching numbers as the function of the motor fundamental voltage. It is shown that, with respect to the motor heating and torque ripples, the acceptable drive condition can be guaranteed by a relatively low value of an inverter switching frequency up to 96%–97% of maximal possible motor voltage. Furthermore, it is shown that the so-called three-vector methods have considerably better performance in the lower part of the overmodulation region than the so-called two-vector method for the same number of switching. The performance of the techniques is compared with other existing PWM techniques. This paper discusses the implementation details of the proposed optimal PWM techniques. The theoretical results are verified by experimental and simulation tests.