Neutral-point voltage balance control system and method based on power factor angle

Abstract

The invention discloses a neutral-point voltage balance control system and method based on a power factor angle. The system comprises a multi-level inverter and a digital processing control module. The digital processing control module comprises a sampling unit, a closed-loop control unit, a digital phase-locked loop unit, a neutral-point voltage control unit and an SPWM pulse width modulation unit. The sampling unit collects direct-current bus voltage signals of the multi-level inverter, direct-current bus neutral-point voltage signals of the multi-level inverter, and three-phase voltage and three-phase current signals output by the multi-level inverter, the signals are processed through the closed-loop control unit to obtain three-phase modulating waves, the three-phase modulating waves are calculated through the digital phase-locked loop unit to obtain the power factor angle, the three-phase modulating waves, the power factor angle and the direct-current bus neutral-point voltage signals are processed through the neutral-point voltage control unit to obtain new three-phase modulating waves, the new three-phase modulating waves are processed through the SPWM pulse width modulation unit to obtain the pulse width modulation control signals, and the signals control the working state of each switching tube of the multi-level inverter through a drive circuit. According to the method, the low-frequency pulse amplitude of neutral-point voltage can be lowered, and neutral-point voltage balance can be achieved.

Description

technical field [0001] The invention belongs to the field of control technology in power electronic conversion technology, in particular to a midpoint voltage balance control system and method based on power factor angle. Background technique [0002] In recent years, multilevel inverters have been widely used in high-voltage, medium-to-high-power conversion occasions; their circuit topology and control methods have become a research hotspot today. Compared with the two-level inverter, the multi-level inverter has more output levels, and the obtained ladder wave platform has more orders, so the closer to the standard sine wave, the less its harmonic components. [0003] The topology of multilevel inverters can be roughly divided into three categories: diode-clamped, cascaded, and flying-capacitor-type, of which the most widely used is the diode-clamped inverter. Taking the three-level inverter as an example, the three-level diode-clamped inverter can be divided into a neutr...

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Problems solved by technology

For example: Literature 1 (Gong Bo, Cheng Shanmei, Qin Yi. Carrier-based three-level neutral point voltage balance control strategy [J]. Journal of Electrotechnical Society, 2013,28(6):172-177.) and patent 1( Cheng Shanmei, Gong Bo, Ning Bowen, Liu Jiang. A mid-point voltage control method for NPC type three-level inverter based on carrier amplitude shift: China, CN201210140269.0.2012-09-19.) A carrier-based The variable-amplitude SPWM control scheme realizes midpoint voltage balance by sampling the midpoint voltage and changing the carrier amplitude in real time. The low-frequency pulsation has no control effect, and the adjustment period is long and the adjustment accuracy is not high

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