Optimization of PWM for overmodulation region of two-level inverters

Two optimized PWM techniques for the overmodulation region of two-level inverter-fed ac drives are investigated from harmonic loss minimization point of view. The optimization is elaborated for the lowest loss-factor, which is proportional to the square of rms 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, respect to the motor heating and torque ripples, the acceptable drive condition can be guaranteed by relatively low value of inverter switching frequency up to 96–97% of maximal possible motor voltage. Furthermore, it is shown that, the so-called Three vector method, introduced in the paper, has considerably better performance in the lower part of the overmodulation region than the so-called Two vector method or the standard PWM techniques for the same number of switching. The theoretical results are verified by experimental tests.