STATCOM unbalance compensation control method based on modular multilevel converter

Abstract

The invention discloses a STATCOM unbalance compensation control method based on a modular multilevel converter (MMC). The method comprises a converter compensation current dead-beat control method and a converter interphase circular current active damping control method. A comprehensive compensation current dead-beat control part is used for compensating active loss in the MMC by controlling active current, reactive current and negative-sequence current which are output by the MMC so as to eliminate unbalance of the current of a power grid and compensate reactive power; the interphase circular current active damping control method is used for summing by detecting the bridge arm current of upper and lower bridge arms of each phase and multiplying by 0.5 to obtain the circular current of each phase, and superposing the output of three-phase current passing through an active damping controller to dead-beat control output so as to inhibit the alternating current component of the circular current, reduce the current stress of converter devices and reduce the loss of the converter. Through the adoption of the method provided by the invention, compensation of the negative-sequence current and reactive current of unbalanced load of the power grid is realized, inhibition of the interphase double frequency circular current of the MMC is simple, the response speed is high and the stability is high.

Description

technical field [0001] The invention relates to a static synchronous compensator based on a modular multilevel converter, in particular to a STATCOM unbalance compensation control method based on a modular multilevel converter. Background technique [0002] The existence of a large number of unbalanced industrial loads and single-phase large-capacity loads such as industrial AC electric arc furnaces and electrified railways, as well as the widespread use of power electronic devices, have brought a large amount of reactive power and negative sequence current to the power system, which not only increases losses, but also It will endanger the power equipment and seriously threaten the safety and economic operation of the power system. It is very necessary to develop a comprehensive compensation device for reactive power and negative sequence current. Devices that are suitable for medium and high voltage power grids and can realize comprehensive compensation of reactive power an...

AI Technical Summary

Problems solved by technology

[0005] Ideally, the capacitor voltage of the MMC half H-bridge sub-module is kept balanced, and the bridge arm current only contains the power frequency component and the DC component. In actual engineering, it is affected by parameters such as sub-module capacitance, reactance inductance, and sub-module loss. , the cyclic charging and discharging of the sub-modules makes the capacitor voltages of the sub-modules impossible to be exactly the same, or even has a large deviation, which leads to distortion of the actual bridge arm current, and the generated inter-phase circulating AC component not only increases the loss of the converter, but also affects the commutation It is of great significance to study a simple and effective control method to suppress the AC component in the circulating current.

The existing methods to suppress the circulating current mainly include increasing the bridge arm reactance, double synchronous rotating coordinate transformation and PI control of the circulating current component. Extraction methods rarely mentioned

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