Three-level inverter neutral-point potential balance control system and control method

Abstract

The invention discloses a tri-sync inverter neutral-point potential balance control system and a control method, and belongs to the technical field of power electronic multi-level convertors. The system comprises a direct tri-sync power inverter unit, a voltage space vector modulation unit, a positive / negative small vector selection unit, a neutral-point potential deviation quantification factor calibration unit, a positive / negative small vector action time redistribution unit and a fuzzy-integral mixed controller. The neutral-point balance control method corrects the quantification factor ofthe calibration unit in real time according to the unbalance of the neutral-point potential, simultaneously detects the direction of the load current, judges whether the current small vector is positive or negative, and adjusts the action time of the positive / negative small vector in real time according to the designed fuzzy rules, thereby finally realizing dynamic balance of the neutral-point potential. The invention can control both static errors and dynamic errors within a small range, thereby achieving the effect of accurate balance of the neutral-point potential and enhancing the reliability of the multi-level power inverter system.

Description

technical field The invention relates to a power electronic multilevel converter and a driving control method thereof, in particular to a balance control system and a control method for self-tuning midpoint potential parameters of a direct three-level inverter. Background technique The direct three-level inverter has the advantages of compact structure, low harmonic content of output voltage and current, small dv / dt, and the voltage borne by the switching tube is only 1 / 2 of the DC bus voltage. It has become a research hotspot in the field of power electronic conversion technology. It has broad application prospects in the fields of medium and high voltage motor drive systems, reactive power compensation of power grids, etc. However, the direct three-level inverter has the problem of midpoint potential balance, which limits its use to a certain extent. If the midpoint potential imbalance cannot be effectively controlled, there will be the following hazards: (1) the output...

AI Technical Summary

Problems solved by technology

However, the direct three-level inverter has the problem of midpoint potential balance, which limits its use to a certain extent.

If the midpoint potential imbalance cannot be effectively controlled, there will be the following hazards: (1) the output voltage will be distorted, containing a large number of low-order harmonics, which will cause vibration of the motor shaft in the motor drive system, and more seriously will cause the output voltage level number to be lost

(2) When unbalanced, the voltage borne by the switch tube is no longer 1 / 2 of the DC voltage of the bus

may damage the switching tube

(3) The imbalance of capacitor voltage will also affect the service life of capacitors on the DC bus

Hardware processing needs to set up an auxiliary working bridge arm and an independent charge and discharge inductor, which increases the volume and weight of the converter, and the manufacturing cost is high and the control is difficult.

Some software processing methods add zero-sequence voltage to the command voltage to control the fluctuation of the midpoint and give an effective control range, but this method is more complicated and is not conducive to digital realization; some do not use it to affect the midpoint The medium vector, and the method of evenly distributing large vectors, this method increases the harmonic content of the output voltage and affects the modulation effect; some switch the positive and negative small vectors within a certain tolerance range to control the balance of the midpoint potential, which will The number of power tube switches increases, and the loss of the converter increases; some also add fuzzy control, which simplifies the calculation of the balance factor to a certain extent, and has a good control effect on the nonlinear system, but the upper and lower capacitance pressure difference signal Uncertainty, the selection of the input quantization factor lacks accuracy, and the balance accuracy is difficult to maintain

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