VSVPWM (Virtual Space Vector Pulse Width Modulation)-based three-level inverter neutral point potential compensation balance control strategy

Abstract

The invention discloses a VSVPWM (Virtual Space Vector Pulse Width Modulation)-based three-level inverter neutral point potential compensation balance control strategy. A virtual median vector is introduced on the basis of the conventional SVPWM, the current which flows by a neutral point in each sampling period can be zero through recombination of a small vector and the median vector. The invention provides the VSVPWM-based neutral point potential accurate compensation control strategy. According to the method, a voltage adjustment coefficient is introduced according to detected neutral point potential deviation, three-phase output current and direct current side neutral point current direction to set different adjustment coefficients for different small vectors so as to increase the control capacity of corresponding positive or negative small vector to the neutral point current and reduce the fluctuation of the neutral point potential.

Description

technical field [0001] The invention belongs to the field of high-voltage and high-power AC frequency conversion speed regulation, and relates to a three-level inverter midpoint potential compensation balance control strategy based on virtual space voltage vector modulation (VSVPWM). Background technique [0002] Compared with the traditional two-level inverter, the diode-clamped (NPC) three-level inverter has less common-mode interference, the output voltage is closer to a sine wave, the equivalent switching frequency is high, and the harmonic content is small. The voltage value of a switching device is equivalent to half of the original DC voltage, and has been widely used in medium-high voltage and high-power occasions. The output end of each phase bridge arm of the NPC three-level inverter is connected to the midpoint of the capacitor on the DC side through a clamp diode, so when the inverter is working, current will flow into or out of the midpoint of the capacitor, and...

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Problems solved by technology

[0003] The unbalance of the midpoint potential will bring the following serious harms: the output voltage waveform is severely distorted, causing low-order harmonics to be input into the asynchronous motor, causing the load of the motor to generate torque ripples and affecting the performance of the frequency conversion speed regulation system; The switching devices of the transformer are subjected to different voltage stresses, resulting in an increase in the withstand voltage level of the switching devices, increasing the cost of the project, and causing a waste of resources; the fluctuation of the midpoint potential reduces the use time of the capacitor. During the power transfer process, if Failure to take certain measures will lead to the degradation of the level number of the inverter

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