Neutral-point voltage balance control method of three-level converter

Abstract

The invention discloses a neutral-point voltage balance control method of a three-level converter. The neutral-point voltage balance control comprises the following steps: converting three-phase voltage vector to a two-phase static coordinate system, and carrying out per-unit transformation on two-phase voltage vector according to a direct-current voltage value; step two, judging the serial number of a section where the voltage vector is according to the value of the two-phase voltage vector; step three, when the voltage vector is not in a first section, using coordination conversion to perform unified naturalization on the voltage vector to the first section; step four, obtaining four effective duty ratios according to a duty ratio calculation formula; and step five, distributing the numerical value of the four effective duty ratios to fix pairs of bridge arm switches of a three-phase bridge arm of the three-level converter, and converting the three-phase bridge arm duty ratio to a modulating wave comparison value to generate corresponding PWM driving pulse signals. According to the method disclosed by the invention, the average value of current flowing into a capacitance neutral-point in each switching period is guaranteed to be zero, so that the voltage increment on the capacitor in one switching period is zero, and the balance of neutral-point voltage is maintained.

Description

technical field [0001] The invention relates to an elevator control method, in particular to a midpoint voltage balance control method of a three-level converter. Background technique [0002] The traditional three-level converter space vector algorithm requires a series of complex steps such as large sector judgment, small sector judgment and duty cycle calculation of the vector position. In the process of calculating the duty cycle, the calculation formulas of the duty cycle in different small sectors are different, so complex table look-up and other operations are required, resulting in a cumbersome implementation process. In addition, the traditional three-level converter space vector algorithm theoretically has an inherent midpoint voltage offset problem, so additional measures need to be taken to suppress the offset of the midpoint voltage and realize the voltage equalization control of the capacitor on the DC bus and the lower capacitor . The traditional method most...

AI Technical Summary

Problems solved by technology

In the process of calculating the duty cycle, the formulas for calculating the duty cycle in different small sectors are different, so complex operations such as table lookup are required, resulting in a cumbersome implementation process

In addition, the traditional three-level converter space vector algorithm theoretically has an inherent midpoint voltage offset problem, so additional measures need to be taken to suppress the offset of the midpoint voltage and realize the voltage equalization control of the capacitor on the DC bus and the lower capacitor

The traditional method mostly uses the method of adjusting the action time of a pair of redundant small vectors to control the offset of the neutral point voltage. It often takes multiple switching cycles to control the midpoint potential to zero, resulting in large fluctuations in the midpoint voltage

[0003] Existing published patent documents, such as the Chinese invention patent document CN1481067, disclose a method for balancing the midpoint voltage of a three-level inverter based on charge balance, which generates a charging and discharging time for a DC capacitor by applying a small vector of voltage within a switching cycle. The principle of equality is used to determine the length of the voltage application time, so that the charge increment on the capacitor in one cycle is zero, but this method needs to calculate the action time of the vector in each small sector, so the algorithm implementation is more complicated, and the method It can only realize the theoretical midpoint voltage control to be zero, without considering the midpoint voltage offset problem caused by calculation errors and cumulative deviation effects in practical applications

[0004] Chinese invention patent document CN102843055 "A Three-Level Inverter Midpoint Potential Balance Control Device and Method", proposes a midpoint voltage balance control device, which is controlled by proportional integral control by real-time detection of the upper and lower capacitor voltages on the bus to generate a control amount , and then control the pulse width duty ratio of the voltage regulation unit according to the control amount, so as to control the midpoint voltage within a small range. This method is simple to implement and will not affect the modulation algorithm of the original inverter. , but need to increase the hardware cost of the system

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