Optimization of PWM for overmodulation region of two-level inverters

Abstract

Three optimized PWM techniques for the overmodulation region of two-level inverter-fed ac drives are introduced and 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 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. The paper discusses the implementation details of the proposed optimal PWM techniques. The theoretical results are verified by experimental and simulation tests.

Space Vector Based Investigation of Overmodulation Region of Inverter Fed Multiphase AC Drives

“…4) are determined by Newton-Rapson method for the smallest value of loss-factor. The method of calculation for three-phase system is introduced in [11]. Due to the symmetry of vector paths computations were performed only for the −π/14 ≤ ω 1 t ≤ π/14 region.…”

“…The overmodulation region of multi-phase inverter-fed ac drives is investigated in [9], [11] by computation of phase and line voltages of multi-phase system. This paper uses space (Park) vector method for study harmonic losses of multiphase drives in the overmodulation region.…”