A capacitive self-equalizing three-phase multilevel converter circuit with a DC bus

Abstract

The invention relates to a capacitor self-equalizing three-phase multi-level converter circuit with a DC bus, which belongs to the technical field of electric power equipment. The multilevel converter circuit is composed of a three-phase valve body with a common DC bus. Each phase valve body is divided into two parts, left and right, and each part contains N (N is an even number greater than zero) half-bridge power units connected in series. Each half-bridge power unit is composed of a diode, a capacitor and two power switches in series; the left and right sides of each phase valve body are connected in a quasi-symmetrical form, using the diode of the power unit, six connecting inductors and a middle diode A valve body topology with capacitive self-balancing function is formed, and the three-phase valve body is connected in parallel to the DC bus, so that the circuit can also realize functions such as negative sequence component processing and four-quadrant operation on the basis of capacitive self-balancing function. The invention has simple circuit topology and simple control, and can be widely used in medium and high-voltage large-capacity AC / DC conversion occasions.

Description

technical field [0001] The invention relates to a multilevel converter, in particular to a capacitor self-equalizing three-phase multilevel converter circuit with a DC bus, which belongs to the technical field of electric equipment. Background technique [0002] Large capacity, high voltage, high controllability and informatization are the development trend of power conversion technology. High voltage and large capacity multilevel converters are more and more widely used in industrial production and life, and are rapidly replacing traditional low frequency based converters. Thyristor converters, especially in power reactive power compensation, DC transmission and high voltage motor drive. Compared with traditional two-level converters, multi-level converters have greatly developed in terms of withstand voltage and increased capacity. At the same time, the output voltage dv / dt of multi-level converters is small, and the equivalent switching frequency is high, especially based...

AI Technical Summary

Problems solved by technology

[0003] However, among the above two types of multilevel converter topologies, each structure also has significant disadvantages:

Capacitor voltage equalization control of this type of multi-level topology can be realized in a steady state through special software control, but the control complexity is greatly increased

[0005] For the conventional diode-clamped multilevel converter topology, due to the complexity of the clamping diode circuit, the circuit is relatively simple when the number of levels of the converter is relatively low, but as the number of levels increases, the number of clamping diodes increases rapidly, and The modularity is very poor, and the entire circuit connection is intricate, which greatly increases the complexity of engineering implementation in actual engineering and reduces reliability

In addition, after the number of levels of conventional diode-clamped multilevel converters increases, the number of clamping capacitors will also increase, and the voltage of each capacitor needs to be specially controlled, which increases the difficulty of engineering implementation. These are conventional diode clamping Key Issues in Multilevel Converter Topologies

[0006] Literature: A DC-link Voltage Self-balance Method for Diode-Clamped Modular Multilevel Converter with Minimum Voltage Sensors (Congzhe Gao, Xinjian Jiang, Yongdong Li, et al. With Minimum Number of Voltage Sensors, IEEE Transactions on Power Electronics, vol 28, no.5pp:2125-2139, May 2013.) and a new type of self-balancing diode-clamped cascaded active filter (Gao Congzhe, Jiang Xinjian, Li Yongdong .A new self-balancing diode-clamped cascaded active filter. Automation of Power Systems, Volume 36, Issue 12, pp:94-100, 2012.) To a multilevel with a new type of diode clamp The converter has been researched, but the circuit can only equalize voltage in one direction, and cannot achieve two-way voltage equalization. It needs an energy feedback circuit or software algorithm for special control, and the voltage equalization ability is poor; at the same time, the three-phase valve body is connected in star form and does not have DC The busbar is not conducive to negative sequence component processing, nor can it be used in motor drive and other occasions, and its practicability is limited

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