Multi-level inverter and modulation method thereof

Abstract

The invention discloses a multi-level inverter. A five-level inverter comprises four capacitors and twelve switch tubes. Each switch tube is reversely connected with a diode in parallel. Compared with a five-level inverter in the prior art, clamping diodes and flying capacitors in the five-level inverter in the prior art are not included, the number of diodes and capacitors is decreased, the cost and size of the inverter are reduced, and the efficiency of the inverter is improved. Meanwhile, the five-level inverter can be extended into the multi-level inverter conveniently, and has better universality.

Description

technical field [0001] The invention relates to the technical field of power electronics, in particular to a multilevel inverter and a modulation method thereof. Background technique [0002] At present, multi-level inverters are widely used in medium-voltage and large-capacity applications. The current five-level inverters are mainly diode-clamped and flying capacitor structures. To be introduced below. [0003] see Figure 1a , which is a topology diagram of a conventional diode-clamped five-level inverter. [0004] Figure 1a The diodes in are used for voltage clamping for each switching tube. Although the switching tube devices withstand the same voltage when they are turned off, each clamping diode needs to withstand different reverse current directions, and it is usually necessary to select diodes that withstand different reverse voltage levels. [0005] In order to select diodes with the same reverse voltage level in topological circuits, multiple diodes with the s...

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Problems solved by technology

[0005] In order to select diodes with the same reverse voltage level in topological circuits, multiple diodes with the same nominal name are usually connected in series in practical applications, such as Figure 1b As shown, due to the dispersion of the diodes and the influence of the stray parameters of the line, the reverse voltages that the diodes with the same nominal value can withstand are not exactly the same, so that the series connection may cause some diodes to be damaged due to overvoltage at both ends, so Need to take voltage equalization measures and RC snubber circuit, but this increases the volume and cost of the system

[0006] to solve Figure 1b Existing problems, put forward an improvement measure, such as Figure 1c As shown, this topology can clamp the voltage of each diode within the unit level voltage and there is no diode series connection, which has great advantages in multilevel inverters, but the number of clamping diodes is too large. Big

[0007] like figure 2 The topology shown is a flying-capacitor five-level inverter. The capacitors in the topology circuit act as voltage equalizers. However, due to the large number of capacitors used, the volume of the system is relatively large.

[0008] To sum up, in the existing technology, the two kinds of five-level inverter topology circuits require a large number of diodes or capacitors, resulting in a large cost and volume of the system, while the efficiency of the system is relatively low

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