Voltage modulation method for access of weak current AC power grid

An AC power grid and voltage modulation technology, applied in the direction of AC network voltage adjustment, power transmission AC network, etc., can solve the problems affecting the voltage stability of weak AC power grid, AC side voltage fluctuation, etc., to improve voltage stability and suppress AC voltage Fluctuation problem, high stability effect

Active Publication Date: 2018-03-06
CHINA ELECTRIC POWER RES INST +2
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

In this case, if the MMC adopts the traditional NLM modulation strategy, when the system operation mode changes or a fault occurs, the AC side voltage output by the MMC will fluctuate due to the weak AC power grid’s ability to support the AC voltage, which will have a weak impact Voltage Stability of AC Grid

Method used

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  • Voltage modulation method for access of weak current AC power grid
  • Voltage modulation method for access of weak current AC power grid
  • Voltage modulation method for access of weak current AC power grid

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Embodiment Construction

[0041] The present invention will be described in further detail below in conjunction with the accompanying drawings.

[0042] Such as figure 1 As shown, it is an MMC topology. Each phase unit is composed of upper and lower bridge arms. There are 6 bridge arms in total. Each bridge arm is composed of N submodules (SM) with the same structure and a bridge arm reactor L 0 Composed in series.

[0043] where U dc is the voltage between the positive and negative DC bus bars of the MMC DC side, u a , u b , u c is the AC side three-phase voltage output by MMC, U C is the capacitor voltage of the sub-module.

[0044] Each SM can be regarded as a controllable voltage source. By controlling the turn-on and turn-off of two IGBTs, the input or cut-off of the sub-module can be realized, and the output voltage of the sub-module is correspondingly U C and 0, specifically: S1 is turned on and S2 is turned off, then the sub-module is put into operation, and the output voltage is U C ; ...

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Abstract

The invention provides a voltage modulation method for the access of a weak current AC power grid, and the method comprises the steps: enabling an MMC valve controller to obtain an AC voltage reference value uref from an electrode controller; calculating and obtaining the capacitor voltage mean values UC_avg_p and UC_avg_n of the upper and lower bridge arms of the MMC valve controller; calculatingand obtaining the number of submodules, put into use, of the upper and lower bridge arms; and determining the switching states of the submodules according to a capacitor voltage balancing strategy. The method improves the obtaining method of the number of submodules, put into use, of the upper and lower bridge arms, and enables the AC voltage outputted by the MMC to be higher in stability duringDC voltage fluctuation.

Description

technical field [0001] The invention relates to a voltage modulation method for grid access, in particular to a voltage modulation method for weak AC grid access. Background technique [0002] Flexible DC transmission technology has the characteristics of no need to provide commutation current on the AC side, no reactive power compensation and commutation failure problems, and can be connected with weak or passive grids. Therefore, it is considered to be the best application in weak AC grid scenarios. solution. [0003] The flexible DC transmission system in the project adopts Modular Multilevel Converter (MMC). The control system of the flexible direct current transmission provides the AC reference voltage of each phase to the MMC, and the MMC determines the number of switching of the upper and lower bridge arm sub-modules according to the reference voltage, thereby outputting a given AC voltage. This process is called voltage modulation of the MMC. In actual engineering,...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H02J3/12H02J3/36
CPCH02J3/12H02J3/36Y02E60/60
Inventor 王铁柱万磊侯俊贤董毅峰王毅
Owner CHINA ELECTRIC POWER RES INST
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