Method for compensating three-phase unbalanced currents on basis of SVG (static var generator)

Abstract

The invention relates to a method for compensating three-phase unbalanced currents on the basis of an SVG (static var generator). The method includes determining whether load currents needs to be compensated or not via three-phase unbalanced judging links by the aid of load current signals which are used as control input; acquiring frequencies and phases of power grid voltages via adaptive frequency locking and phase locking links when the load currents need to be compensated; filtering harmonic current components in the load currents by the aid of discrete second-order generalized integrators; computing negative-sequence current values required to be converted for various phases if the three-phase unbalanced currents are in balanced states; transmitting the negative-sequence current values to control instruction computation modules in SVB devices; driving IGBT (insulated gate bipolar transistors) to act; generating currents equal to fundamental negative-sequence components in the load currents so that the three-phase unbalanced currents can be in the balanced states. The negative-sequence current values are used as reference current signals. The directions of the currents are opposite to the directions of the fundamental negative-sequence components in the load currents. The method has the advantages that the three-phase unbalanced currents can be dynamically compensated, and accordingly the stability and the reliability of power grids can be improved; low-pass filters can be omitted when negative-sequence currents are extracted, and accordingly the method is low in computational burden and high in response speed and tracking precision.

Description

technical field [0001] The invention relates to a three-phase unbalanced current compensation method, in particular to a method for compensating three-phase unbalanced current by using a SVG of a fully-controlled converter device. Background technique [0002] The three-phase current unbalance phenomenon means that the magnitude of the three-phase current is asymmetrical, and its causes can be summarized as accidents and normality. The former refers to the failure of one or two phases in the three-phase power system, resulting in three-phase imbalance; the latter refers to the fact that a large number of user loads are single-phase loads, and the power consumption is not simultaneous, and the distribution system is prone to three-phase Phase imbalance, especially for loads such as electrified railways, whose traction load is a high-power load with single-phase movement and frequent amplitude changes. balance. [0003] In recent years, with the increasing number of unbalanc...

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Problems solved by technology

The synchronous rotating coordinate method needs to use a low-pass filter to filter the rotated current, which will increase the calculation burden and convergence time; while the Fourier transform method needs a power frequency cycle to calculate the reference current to be compensated, which is not conducive t

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