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Pulse width modulation in voltage source inverters with an arbitrary number of phases is analyzed in this paper. The problem is treated as purely algebraic, without any use of space vectors. Regardless of avoiding space vectors, the same results are achieved. It is shown that the problem of determining duty ratio values does not have a unique solution, and that there is one degree of freedom to choose one duty ratio, but within a limited range. Limits of the range are derived. Feasibility constraints for the required set of line voltages are derived, reducing to the requirement that the highest of the line voltages should be lower than the DC bus voltage. The analysis is illustrated in cases varying from two to five phases, and experimentally verified in the case of three phases. The method is simple and could be applied to any number of phases, even for the voltages that are not sinusoidal.

Integration of the impacts of time and space harmonics simultaneously during the design stages of inverter-fed induction machines (IMs) is crucial for the accurate calculation of electromagnetic (EM) torque and ripples. Traditional magnetic field-based models offer an analytical approach for determining the EM torque in IMs by calculating inductances. However, by assuming infinite core permeabilities, these models neglect the impact of the core magnetomotive force (MMF) drops due to the difficulties in accurately calculating these drops and the impracticality of isolating the contribution from each phase, which is essential for inductances calculations. These factors contribute to deficiencies in this modeling approach, which become more noticeable when the combined impacts of time and space harmonics on MMF drop calculations are also disregarded. Therefore, this paper introduces a novel magnetic-field-based model to predict the torque and torque ripples of inverter-fed induction motors by addressing the above limitations. This involves modifying the turns and winding function, and calculating the core MMF drops based on the timely variation of non-sinusoidal core flux densities, considering their major and minor flux-density loop effects. Consequently, the associated energy is used to calculate the net available energy, thereby enhancing torque calculations. Compared to the experimental results obtained from an 11kW prototyped induction motor, the proposed model exhibits notable enhancements, achieving average accuracies of 96.4% for average torque and 94.51% for torque ripples, in contrast to the respective traditional model accuracies, 81.1% and 45.1%.

This paper proposes a novel virtual vector space vector pulse width modulation (SVPWM) method called Average Zero common mode voltage (AZCMV) PWM to mitigate low-frequency CMV in four-level neutral point clamped (4L-NPC) inverters. Due to the absence of zero CMV vectors in the space vector diagram (SVD) of 4L inverter, the proposed SVPWM method introduces virtual average zero CMV vectors, which are the combination of active vectors, and have an average CMV of zero. The SVPWM scheme is simply implemented in the transformed two-level (2L) SVD by the aid of base vectors. Then, three types of 2L SVD are presented. Effective and hybrid 2L-SVPWM control strategy based on four nearest vectors SVPWM, symmetrical and asymmetrical SVPWM is proposed to optimize output harmonic and switching losses. With the proposed SVPWM method, the peak-to-peak value of CMV can be reduced to one ninth of the total DC link voltage, which is lower up to five times as compared to the sinusoidal PWM (SPWM). Furthermore, the average value of CMV is zero in a switching sequence. The effectiveness of the proposed method has been verified by simulation and experimental results.