A Simplified Common-Mode Voltage Suppression and Neutral-Point Potential Control for the NPC Three-Level Inverter
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Neutral-point potential unbalancing is an inherent disadvantage of NPC three-level inverter. Traditional control methods, e.g. the space vector PWM (SVPWM) considering balance factor or the model predictive control (MPC), usually needs large amounts of calculation and the common-mode voltage usually keeps large due to the zero vectors being involved in the modulation or the roll optimization. Aiming at above problems, this paper proposes a simplified model predictive algorithm based on the characteristics analysis on the unbalancing and common-mode voltage. Firstly, an approximate two-level structure containing 12 vectors is proposed by the reduced-order processing for the three-level structure, which solves the calculation complexity problem. Meanwhile, multi-constraints including switching frequency, neutral-point potential deviation and the common-mode voltage, are constructed within the roll optimization items of the MPC scheme to make common-mode voltage being restricted less than 1/6 DC voltage while the switching frequency is almost constant. Finally, experiments were carried out to verify that this method can realize a neutral-point voltage balance and a low common-mode voltage along with less execution time.
KeywordsNPC three-level inverter Neutral-point potential Common-mode voltage Reduced-order processing
Funding was provided by Shanghai Sailing Program (CN) (Grant no. 18YF1418300) and Key Laboratory of Control Power Transmission and Conversion (SJTU CN) (Grant no. 2016AC04).
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