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
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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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