VSG low-voltage ride-through control method and system based on power grid imbalance fault

A low-voltage ride-through and unbalanced power grid technology, applied in the field of distribution network, can solve problems such as current asymmetry on the AC side of three-phase inverters, affecting inverter operation, and increasing transformer losses, so as to avoid serious distortion and reduce Loss, the effect of improving operating efficiency

Inactive Publication Date: 2020-10-13
CHINA ELECTRIC POWER RES INST +3
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

The existence of negative sequence current will make the current asymmetry on the AC side of the three-phase inverter, which will seriously affect the operation of the inverter.
And a large number of low-order harmonics will cause the distortion of the grid voltage, which will cause a series of problems such as the increase of the loss of the filter inductor and transformer on the AC side.

Method used

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  • VSG low-voltage ride-through control method and system based on power grid imbalance fault
  • VSG low-voltage ride-through control method and system based on power grid imbalance fault
  • VSG low-voltage ride-through control method and system based on power grid imbalance fault

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Embodiment 1

[0057] The embodiment of the present invention provides a VSG low voltage ride-through control method based on an unbalanced power grid fault. The specific implementation process is as follows: figure 1 shown, including:

[0058] S101: When an unbalanced sag fault occurs in the power grid, based on a preset unbalanced fault control strategy, the positive and negative sequence dual current control of the inverter is performed to obtain the positive sequence current and negative sequence current that the inverter VSG system needs to output for normal grid-connected operation. sequence current;

[0059] S102: Superimpose the positive sequence current and the negative sequence current signal to obtain a modulation signal, and modulate the modulation signal to obtain a switching signal of each bridge arm of the inverter.

[0060] Specifically, in step S101, when an unbalanced sag fault occurs in the power grid, the positive and negative sequence dual current control of the inverte...

Embodiment 2

[0099] When the grid voltage is unbalanced, its fundamental voltage can be decomposed into positive sequence fundamental voltage E P , negative sequence fundamental voltage E N and zero-sequence fundamental voltage E 0 . Generally, the distributed grid-connected system adopts a three-phase three-wire system, so the component of the unbalanced grid voltage does not contain the zero-sequence component E. 0 , that is, the unbalanced grid voltage can be expressed as:

[0100] E=E P +E N (1)

[0101] If the voltage of each phase is expressed as an instantaneous value, it is as follows

[0102]

[0103] where:

[0104] e a , e b , e c ——Instantaneous value of each phase of grid voltage;

[0105] E Pm - the fundamental amplitude of the positive sequence component of the grid voltage;

[0106] E Nm - the fundamental amplitude of the negative sequence component of the grid voltage;

[0107] ——the initial phase angle of the positive sequence fundamental wave compone...

Embodiment 3

[0124] Based on the same inventive concept, the present invention also provides a VSG low-voltage ride-through control system under grid unbalanced faults, such as Image 6 As shown, the system includes:

[0125] The judgment module is used to obtain the current grid-connected point voltage and judge whether the power grid has an unbalanced drop fault;

[0126] The fault control module is used to control the positive and negative sequence dual currents of the inverter based on the preset unbalanced fault control strategy when an unbalanced sag fault occurs in the power grid, so as to obtain the positive output required for the normal grid-connected operation of the inverter VSG system. sequence current and negative sequence current;

[0127] The modulation output module is used to superimpose the positive sequence current and negative sequence current signals to obtain a modulation signal, and modulate the modulation signal to obtain switching signals of each bridge arm of th...

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Abstract

The invention provides a VSG low-voltage ride-through control method based on a power grid imbalance fault. The method comprises the following steps: when an unbalanced drop fault occurs in a power grid, performing inverter positive and negative sequence double-current control based on a preset unbalanced fault control strategy to obtain a positive sequence current and a negative sequence currentwhich need to be output for normal grid-connected operation of an inverter VSG system, and superposing the positive sequence current and negative sequence current signals to obtain a modulation signal. According to the technical scheme provided by the invention, a positive-sequence current controller and a negative-sequence current controller are adopted for the unbalanced drop fault of the powergrid, positive-sequence current reactive compensation control is added while the negative-sequence current is suppressed, and the low-voltage ride-through fault is realized while the normal operationof the inverter is ensured.

Description

technical field [0001] The present invention is in the field of distribution network, in particular to a VSG low voltage ride-through control method and system under unbalanced power grid faults. Background technique [0002] In the actual operation of the power grid, the unbalanced three-phase load, single-phase or multi-phase grounding short-circuit, inter-phase short-circuit and other faults will cause the unbalance of the power grid. The probability (95%) is much greater than the probability (5%) of the grid voltage sag fault. [0003] In the conventional inverter control design, it is generally assumed that the three-phase grid is balanced. When the grid voltage is unbalanced, if the inverter still uses the control strategy in the balanced state, the following effects will occur. : When the grid voltage is unbalanced, there will be a negative sequence component of the grid electromotive force, which will lead to the generation of AC negative sequence current. Through t...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H02J3/38
CPCH02J3/38
Inventor 吴鸣宋振浩吕志鹏孙丽敬郑楠徐斌王刘芳
Owner CHINA ELECTRIC POWER RES INST
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