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A Neutral Point Clamped (NPC) type three-level inverter has the advantages of a low switch voltage and a high-quality output waveform. However, there are inherent problems, such as neutral point potential asymmetry and common mode interferences, which easily affect the symmetry of the three-phase output voltage and the safe operation of the inverter. Firstly, according to the different modulation degrees, the fluctuation of midpoint potential can be suppressed by adding an action time correction factor to the traditional space vector pulse-width (SVPWM) modulation strategy and virtual space vector pulse-width (VSVPWM) modulation strategy, respectively. Secondly, considering the suppression of common mode voltage, a new virtual space vector pulse-width (NVSVPWM) modulation strategy is proposed, which uses a set of new vector synthesis methods. Finally, the simulation and experiment prove that the NVSVPWM strategy with an action time correction factor can suppress the fluctuation of the neutral point potential and common mode voltage at the same time, and the effect is significant. [ABSTRACT FROM AUTHOR]

The carrier-based pulse width modulation (CBPWM) with zero-sequence component injection is equivalent to the space-vector PWM (SVPWM), and hence it can be taken as a simplified alternative to the SVPWM. However, it is quite complex to calculate the zero-sequence component in CBPWM for three-level (3L) converters such as the T-type converter, making the 3L SVPWM still have a large computation burden. In this letter, unified expressions for the zero-sequence component are analytically derived, and the modulation waves of 3L SVPWM can be directly calculated by only 7 simple equations with 3 steps. The computation burden for implementing 3L SVPWM is therefore significantly reduced without sector determination, calculation and assignment of dwell times. [ABSTRACT FROM AUTHOR]

Given the high complexity of the conventional three-level space-vector pulsewidth modulation (3L SVPWM), simplified SVPWM algorithms are usually adopted instead. However, existing simplifications for 3L SVPWM still have a large computation burden, which limits its applications, e.g., in high-switching-frequency silicon-carbide converters with a short computation period. In this letter, based on a typical simplified algorithm known as the center-aligned 3L SVPWM, a simplified analytical algorithm in abc coordinate is proposed. The reference-voltage-vector adjustment and the calculation of modulation waves are unified based on the center-aligned SVPWM. The modulation waves can be analytically derived by only eight simple equations, without sector determination, calculation, and assignment of dwell times. Consequently, the complexity of implementing the 3L SVPWM is significantly reduced. [ABSTRACT FROM AUTHOR]