Feedback control method for midpoint potential of three-level inverter based on dual-modulating wave carrier modulation

Abstract

The invention discloses a feedback control method for a midpoint potential of a three-level inverter based on dual-modulating wave carrier modulation. The feedback control method comprises the following steps: collecting midpoint potential imbalanced information from a direct current side, injecting zero-sequence components into three-phase modulating waves, compensating the three-phase modulating waves, and carrying out modulating wave decomposition on one phase in the compensated three-phase modulating waves, so as to acquire midpoint potential balanced positive and negative modulating wave expressions; and making comparison on the compensated modulating waves, decomposed dual-modulating waves and carriers, so as to finally obtain switch sequences of all power switch tubes of a three-level NPC inverter. Compared with the prior art, the feedback control method has the advantages that the average midpoint current in a switching period under any imbalanced degree, power factor and modulation degree can be zero, and the distortion of a load current fundamental component caused by the low-frequency fluctuation and imbalanced midpoint of the midpoint potential can be completely eliminated; and the method is applicable to occasions that requirements on the balance of the midpoint potential are relatively strict or upper and lower groups of direct voltages need to be independently controlled.

Description

Technical field [0001] The invention belongs to the technical field of inverter control, and in particular relates to a three-level inverter midpoint potential feedback control strategy based on dual modulation wave carrier modulation. Background technique [0002] Multi-level technology solves the voltage equalization problem of power devices directly connected in series. It has the advantages of low du / dt, high waveform quality, low switching frequency, and high efficiency. It has been widely used in medium and high voltage large capacity converter systems. Among the three multilevel inverter topologies, compared with flying capacitor type and H-bridge cascaded multilevel inverters, the neutral-point-clamped (NPC) inverter is not It requires many flying capacitors and independent DC voltage sources, is small in size, compact in structure, easy to implement, and is widely welcomed. The diode-clamped three-level inverter, also known as the three-level NPC inverter, is a typical ...

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Problems solved by technology

Xie Luyao et al. proposed a neutral point potential feedback control based on zero sequence injection method, realizes the arbitrary adjustment of the midpoint potential, and eliminates the output voltage waveform distortion and fundamental wave deviation caused by the unbalanced midpoint; but in terms of control effect, this method cannot completely eliminate the low frequency fluctuation of the midpoint potential, and the DC The capacity of the side capacitance is large, and the midpoint current control capability of the system is weak when the modulation ratio is high and the power factor is low

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