Midpoint voltage control and common mode voltage suppression method and system of three-level inverter

Abstract

The invention discloses a midpoint voltage control and common mode voltage suppression method and system of a three-level inverter. The method comprises steps that through constructing virtual small vectors and medium vectors reasonably, the amount of change in the midpoint charge of each virtual vector is zero in one control period, and the vectors making the common mode voltage increase are eliminated to guarantee that the common mode voltage of the output voltage is minimized when the virtual vectors are constructed; a midpoint voltage balance factor is added based on the above, the midpoint voltage balance factor is adjusted by detecting voltage difference of upper and lower capacitors and the three-phase current in real time, and thereby the charge is made to flow into or out of the midpoint to adjust the midpoint voltage balance. The method is advantaged in that as the virtual vectors are reasonably constructed, and the midpoint voltage balance factor is further added, the virtual small vectors and the medium vectors are both variable, and the method has the feature of adjusting the midpoint voltage balance in the full modulation ratio range while reducing the common mode voltage.

Description

technical field [0001] The invention belongs to the technical field of power electronics, and in particular relates to a method for midpoint voltage control and common mode voltage suppression of a three-level inverter based on a variable virtual vector. Background technique [0002] Compared with the traditional two-level inverter, the output voltage of the three-level inverter is closer to a sine wave, and the harmonics of the output waveform are small under the same switching frequency. Under the same conditions, the equivalent switching frequency is high and the switching loss Therefore, it is widely used in medium and high voltage high power conversion fields such as medium and high voltage frequency conversion speed regulation, active power filter and power system reactive power compensation. However, there is an inherent midpoint voltage balance problem in a three-level inverter. Inconsistent DC bus capacitor parameters, inconsistent switch parameters, unbalanced loa...

AI Technical Summary

Problems solved by technology

The small vectors have a redundant state, and each pair of redundant small vectors has the opposite effect on the midpoint voltage. Therefore, the neutral point voltage balance can generally be adjusted by adjusting the action time of the positive and negative small vectors, but the neutral point voltage balance ability of this method limited

At the same time, because the influence of the neutral vector on the neutral point voltage is related to the direction of the current, the influence of the neutral vector on the neutral point voltage is uncertain, resulting in fluctuations in the neutral point voltage

[0005] Aiming at the problem of mid-point voltage fluctuation caused by redundant small vectors with limited balance ability under high modulation ratio and uncertain influence of mid-point voltage on mid-point voltage, a variable virtual mid-vector method is proposed, but the variable virtual mid-vector method is Under low modulation ratio due to the action time T of the vector in the virtual m Small, so there is a problem of insufficient regulation of the midpoint voltage at low modulation ratios

[0006] In the inverter-driven motor system, the common-mode voltage output by the inverter will cause many hazards, such as damaging the motor stator insulation, interacting with parasitic capacitance to generate common-mode leakage current to form common-mode interference, and excessive leakage current will cause motor protection. Therefore, the effective reduction of the inverter output common-mode voltage has an important impact on the life of the motor

Images