Voltage self-balancing method for low-modulation-degree direct-current-side capacitors of five-level NPC converter

Abstract

The invention discloses a voltage self-balancing method for low-modulation-degree direct-current-side capacitors of a five-level NPC converter. According to the method, first, region division is performed on a space vector diagram of the five-level converter according to modulation degrees, and the region, where reference voltage vectors V<ref> are located, is judged according to the modulation degrees; second, action time of each reference voltage vector V<ref> is calculated; third, voltage values corresponding to the four capacitors at the direct-current side of the five-level converter aredetected, a voltage deviation value between each voltage value and 1 / 4U<dc> is calculated, and the locations of the direct-current-side capacitors corresponding to two high voltage deviation values are determined; and last, according to the obtained locations of the direct-current-side capacitors corresponding to the two high voltage deviation values, the directions of three-phase currents I, I and I<c> and the space vector diagram of the five-level converter, the capacitors are charged and discharged continuously to maintain balance. Compared with model prediction, through the method, rapidity is greatly improved, and the problems of voltage fluctuation and unbalance, caused by non-modulation factors, of the direct-current capacitors are suppressed.

Description

technical field [0001] The invention belongs to the technical field of power electronics and power systems, and in particular relates to a self-balancing method for DC side capacitor voltage of a five-level NPC converter with low modulation degree. Background technique [0002] Among the currently applied multilevel topologies, the NPC topology is the most widely used because of its simple structure and high cost performance. In particular, the three-level NPC topology has been widely used in various medium and low voltage fields below 3kV, which greatly improves the output performance of power electronic equipment. In the medium and high voltage field above 6kV, the five-level NPC topology is a very competitive topology and has broad application prospects. In the relevant research content of multilevel NPC converter, the balance control of DC capacitor voltage is of outstanding importance. If the DC capacitor voltage is unbalanced, it will not only affect the output volta...

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Problems solved by technology

[0004] In order to overcome the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a five-level NPC converter low-modulation DC side capacitor voltage self-balancing method, which solves the problem of modulation speed in the DC side capacitor voltage self-balancing control process of the existing method. slower problem

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