Midpoint Potential Feedback Control Method of Three-level Inverter Based on Dual Modulation Wave Carrier Modulation

Abstract

The invention discloses a midpoint potential feedback control method of a three-level inverter based on double modulation wave carrier modulation. Collect mid-point potential unbalance information from the DC side, inject zero-sequence components into the three-phase modulation wave and then compensate, and decompose one phase of the compensated three-phase modulation wave to obtain the positive and negative points that meet the mid-point potential balance. Modulation wave expression; compare the compensated modulation wave and the decomposed double modulation wave with the carrier, and finally obtain the switching sequence of all power switch tubes of the three-level NPC inverter. Compared with the existing technology, the present invention can ensure that the average midpoint current in the switching cycle is zero under any unbalance degree, power factor and modulation degree, and completely eliminate the low-frequency fluctuation of the midpoint potential and the load current caused by the midpoint unbalance Distortion of the fundamental wave component is suitable for occasions where the requirements for midpoint potential balance are relatively strict or independent control of the upper and lower DC voltages is required.

Description

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

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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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