A Circular Current Suppression Method for Converters Running in Parallel

Abstract

The invention discloses a circulating current inhibition method of a parallel operation converter, and aims at solving the problem of high-frequency circulating current, caused by inconsistent modulated carrier waves, of a plurality of converter units. According to the method, grid-connected current of the converter units is detected in real time to obtain variable quantity of the high-frequency circulating current within a half switching period, thereby determining relative positions of the carrier waves of the converter units. The high-frequency circulating current of a parallel system is effectively inhibited by inserting a synchronization period, adjusting a carrier wave frequency and achieving resynchronization of the modulated carrier waves. The method disclosed by the invention has the advantages of being simple and practical, convenient to control, fast in dynamic response and the like.

Description

technical field [0001] The invention relates to a method for suppressing circulating currents of converters operating in parallel, which is used for suppressing high-frequency circulating currents caused by inconsistencies in modulation carrier waves of multiple converter units. Background technique [0002] With the development of power electronics technology, the use of parallel structure converters can expand the system capacity and has been widely used. The parallel structure of converters mainly has the following advantages: (1) without increasing the current stress of power devices, the system capacity can be doubled, which is more suitable for large-capacity and high-voltage occasions; (2) through the reasonable distribution of load power to achieve Efficiency optimization control, replacing serialization with modularization, shortens the research and development cycle, reduces production costs, and effectively improves the efficiency of the system; (3) realizes redun...

AI Technical Summary

Problems solved by technology

However, due to the shared positive and negative DC bus and AC bus, the circulating current between the converter modules becomes an important indicator restricting its performance

[0003] For the circulation problem caused by the parallel operation of converters, the most basic method is to use hardware to block the circulation path, including the use of independent DC power supplies for each converter unit and the use of multi-winding transformers on the grid side to achieve electrical isolation. This method can completely eliminate Circulation, but adds cost and volume to the system

Secondly, some existing circuit design guidelines design filter circuits to suppress circulating currents based on the quantitative relationship between high-frequency circulating currents and actual circuit parameters. However, it is more complicated to implement because the actual parameters of circuit components are difficult to measure.

In addition, by establishing an equivalent model of zero-sequence circulating current, analyzing the mechanism of zero-sequence circulating current, a method of changing the ratio of zero-sequence circulating current to suppress zero-sequence circulating current is proposed, which greatly increases the switching loss of power devices

Images