An Upfc Three-Phase Unbalance Optimization Method Based on Nonlinear Control

Abstract

The invention relates to a UPFC (unified power flow controller) three-phase imbalance optimization method based on nonlinear control. The method comprises steps as follows: 1), a modularized multi-level UPFC is constructed; 2), an inner current loop in a parallel side current converter adopts a passive sliding mode variable structure control mode, reactive regulation is performed through q-axis component, and active regulation is performed through d-axis component; 3), an inner current loop in a series side current converter adopts the passive sliding mode variable structure control mode, voltage with controllable amplitude and phase angle is injected by a series side transformer, positive sequence component is used for realizing phase shift adjustment and series compensation of alternating voltage, negative sequence component is used for offsetting negative sequence voltage component of an imbalanced part of an electric transmission line, and three-phase imbalance optimization is realized. Compared with the prior art, the method has the advantages of being high in dynamic response speed, high in robustness, safe, economic and stable and inhibiting zero-sequence current, and parameters are easy to adjust.

Description

technical field [0001] The invention relates to the field of smart grids, in particular to a nonlinear control-based UPFC three-phase unbalance optimization method. Background technique [0002] With the rapid advancement of smart grid construction and future energy Internet construction, Unified Power Flow Controller (UPFC), as a typical FACTS (flexible AC transmission systems, FACTS) component, can fully tap the potential of the existing power grid, save power transmission corridors, and promote power grid construction to Environmentally friendly development will surely be applied in important load centers in the future, such as power transmission and distribution systems in super modern cities. At present, domestic and foreign research on the unified power flow controller based on modular multilevel converter (MMC-UPFC) mainly focuses on the topology improvement, power flow control strategy, engineering application and many other aspects of MMC and UPFC, and all It is ba...

AI Technical Summary

Problems solved by technology

However, with the access of high-power single-phase loads, the unbalanced distribution of single-phase loads in the three-phase system, and the asymmetry of the AC voltage at the receiving end caused by asymmetrical faults, the three-phase voltage of the power grid is unbalanced.

When the three-phase power grid is unbalanced, the existence of negative sequence components in the power grid will lead to problems such as unbalanced three-phase current of the converter, voltage fluctuations on the DC side, power fluctuations, and increased circulating currents, shortening the life of the converter, and affecting the MMC-UPFC. performance is adversely affected

[0003] At present, the control strategy proposed for three-phase unbalance control is mainly the traditional PI double closed-loop control strategy of MMC-UPFC under the positive and negative sequence synchronous rotating coordinate system. Although this method can obtain good control effect, the traditional PI double closed-loop control strategy The control has disadvantages such as difficult parameter debugging, slow dynamic response, and limited stable operation range.

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