Method and device for enabling MMC station to access DC power grid

A technology of DC power grid and DC line, applied in the direction of power transmission AC network, etc., can solve the problem of lack of isolated MMC stations connected to the DC power grid, and achieve the effect of easy implementation and strong engineering practice

Active Publication Date: 2017-12-22
GLOBAL ENERGY INTERCONNECTION RES INST CO LTD +3
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defect in the prior art that the isolated MMC station is connected to the DC power grid online, thereby providing a method and device for connecting the MMC station to the DC power grid

Method used

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  • Method and device for enabling MMC station to access DC power grid
  • Method and device for enabling MMC station to access DC power grid
  • Method and device for enabling MMC station to access DC power grid

Examples

Experimental program
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Effect test

Embodiment 1

[0029] Embodiment 1 provides a method for connecting an MMC station to a DC power grid, wherein the MMC station includes an MMC, an AC power supply system, and a converter transformer, the MMC includes a first bridge arm and a second bridge arm, and the first bridge arm and the second bridge arm Capacitors and switching device sub-modules are respectively arranged in the two bridge arms. The method for connecting the MMC station to the DC power grid provided by Embodiment 1, such as figure 1 As shown, it includes the following steps:

[0030] Step S1: When the MMC station is in a locked state, use an AC power supply system to charge the capacitors in the first bridge arm and the second bridge arm. The MMC station is in a locked state, which means that the MMC station is disconnected from the power grid. The AC system charges the capacitor in the isolated MMC station through an uncontrolled rectification circuit. The uncontrolled rectification circuit is a rectification circ...

Embodiment 2

[0039] Embodiment 2 provides a method for connecting an MMC station to a DC power grid, including all the steps in Embodiment 1. To avoid repetition, details are not repeated here. like figure 2 As shown, the method for connecting the MMC station to the DC power grid in embodiment 2 adds step S7 after step S6: after the MMC station is unlocked, reduce the number of connections in the first bridge arm and / or the second bridge arm of the MMC station. The number of submodules to the rated number.

[0040] The number of sub-modules connected in the first bridge arm and / or the second bridge arm cannot be reduced from a large number to the rated number immediately, but should be completed with a fixed slope and a certain period of time. decrease. This is because the control system has a certain response time, and the charging of the capacitor also takes time. That is to say, after the control command for the number of input sub-modules is given, the voltage equalization control o...

Embodiment 3

[0043] Embodiment 3 provides a method for connecting an MMC station to a DC power grid, including all the steps in Embodiment 1. To avoid repetition, details are not repeated here. Embodiment 3 provides the number N of submodules input by the first bridge arm and / or the second bridge arm of the MMC station at the initial moment of unlocking in step S6 0 For the specific method, see formula 1.

[0044] N 0 =2*U dc *N / U cm2 =2*N / (m+1) (1)

[0045] Among them, U dc is the rated unipolar DC voltage value, U cm2 is the final value of the sub-module voltage at the end of step S3, m is the modulation ratio, and N is the rated number of sub-modules of the first bridge arm and / or the second bridge arm. Since the final value of the submodule voltage should be the first preset threshold at the end of step S3, the first preset threshold can be used as U cm2 Substitute into formula 1 for calculation.

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Abstract

The invention provides a method and device for enabling an MMC station to access a DC power grid. The method comprises the following steps: when the MMC station is in a locking state, utilizing an AC power supply system to supply power for capacitors; connecting the AC system with a negative pole DC line of the DC power grid to charge the capacitor of a first bridge arm; connecting the AC system with a positive pole DC line of the DC power grid to charge the capacitor of a second bridge arm; and increasing the number of switch device submodules accessed in the first bridge arm and/ or the second bridge arm to match the DC voltage of the DC power grid, and enabling the MMC station to access the DC power grid successfully. By closing DC isolation switches connected with an isolated MMC station and controlling to increase the number of the bridge arm submodules during unlocking, surge current obtained at the moment when each switch is closed and the moment when the isolated MMC station is unlocked is allowed to be small enough so as not to cause influence on the normally-operating DC power grid; and the method is an effect method for allowing the isolated MMC station to access the DC power grid online smoothly.

Description

technical field [0001] The invention relates to the technical field of direct current transmission, in particular to a method and a device for connecting an MMC station to a direct current power grid. Background technique [0002] Flexible DC transmission based on Modular Multilevel Converter (MMC) has the advantages of high modularity, flexible control of active and reactive power, and the ability to supply power to passive loads. It is widely used in wind farm grid connection, Island and weak grid power supply and urban power supply and other fields. The DC grid technology based on flexible DC transmission can well solve the problems of "abandoning wind" and "abandoning light" caused by new energy grid integration and consumption. Considering the flexible and scalable nature of the DC power grid, the use of MMC stations including AC systems, converter transformers and MMCs to achieve new energy grid integration will play a greater role in the future power system, so isola...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H02J3/36
CPCH02J3/36Y02E60/60
Inventor 赵成勇杨杰吴亚楠许建中韩乃峥
Owner GLOBAL ENERGY INTERCONNECTION RES INST CO LTD
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