Method for designing parameters of LC coupling type SVG (static var generators) in unbalanced power grids, and method and system for controlling LC coupling type SVG

Abstract

The invention discloses a method for designing parameters of LC coupling type SVG (static var generators) in unbalanced power grids, and a method and a system for controlling the LC coupling type SVG.The methods and the system have the advantages that reactive and negative-sequence currents in the unbalanced power grids can be compensated by the aid of the method for designing the parameters whenminimum voltages are required by direct-current sides; voltages inverted and outputted by the VSC are lower than voltages of the power grids when the LC coupling type SVG determined by the aid of themethod for designing the parameters are used for compensating capacitive reactive power, accordingly, capacitive voltages on the direct-current sides can be lowered to a great extent, power and switching loss can be reduced, and the cost can be decreased; the method for controlling the LC coupling type SVG is based on unbalance control strategies with combination of compensation reference voltagedetection of improved SOGI (second-order generalized integrators) and QPR (quasi-proportional-resonant) control, compensation reference currents are directly tracked and controlled by the aid of theQPR control in alpha beta coordinate systems, integral control links are quite simple, and delay and errors in control procedures can be eliminated.

Description

technical field [0001] The invention belongs to the field of power grid control, and in particular relates to a parameter design method of an LC coupling type SVG under an unbalanced power grid, a control method and a system thereof. Background technique [0002] At present, the distribution network mainly faces power quality problems such as low system power factor and three-phase imbalance. The low power factor of the system is caused by excessive reactive current, which will increase equipment and line losses, reduce the utilization rate of power transmission and transformation equipment, and thus increase operating costs; while three-phase imbalance will generate negative sequence current, negative sequence The current will cause additional heat loss inside the generator and transformer, and also cause relay protection and automatic device malfunction. The above problems have increasingly seriously affected the safe and stable operation of the distribution network and e...

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Problems solved by technology

[0007] 1. The traditional SVG can comprehensively solve power quality problems such as reactive power and three-phase imbalance in the grid. However, when this topology compensates capacitive reactive power, the voltage output by the VSC inverter is greater than the grid voltage, resulting in DC The side capacitor voltage is relatively large, generally about twice the grid voltage, so that the apparent power output by the VSC is relatively high, correspondingly increasing the cost of the compensation device and switching loss, affecting its popularization and application

[0008] 2. LC-coupled SVG can effectively reduce the DC side capacitor voltage, but most of them are currently used in balanced systems and only compensate reactive power. At this time, the design of series LC parameters on the grid-connected branch is generally based on the required reactive capacity The LC parameter design method is not suitable for the comprehensive compensation of reactive power and negative sequence in unbalanced systems, and cannot minimize the DC side voltage

[0009] 3. The control strategy currently proposed for the LC-coupled SVG system only includes the balance control of reactive power compensation and DC voltage stability, and cannot compensate the negative sequence current in the unbalanced system, and lacks a corresponding unbalanced control Strategy

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