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Absiraciqn the inverter-fed ac drives the space vector modulation technique is the most popular and wide spread one since it produces a high quality inverter-fed ac drive especially for low and middle amplitudes of motor voltages. For realization of the space vector PWM usually two different PWM methods can be applied. This paper deals with the analysis and comparison of voltage spectra of these methods and the derivation of the analytical equations of motor voltage harmonics for these PWM methods. It is shown that for the infinite value of the sampling frequency all realization methods produce the same voltage spectrum which is characterized by the relatively simple equation. This expression also ensures an accurate computation of voltage, current and torque harmonics for the relatively low value of the sampling frequency.Index Term-space vector PWM, naiural and regular PWMs, harmonic amplitudes.

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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.