Control strategy of multi-circuit MMC (modular multilevel converter)-HVDC (high voltage direct-current ) fed extremely-weak grid

A technology of MMC-HVDC and control strategy, applied in the field of control strategy of multi-circuit MMC-HVDC feeding into extremely weak power grid, can solve problems such as reducing the strength of regional power grid, and achieve the effect of eliminating frequency deviation and avoiding overcurrent

Active Publication Date: 2017-05-31
ZHEJIANG UNIV +3
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Problems solved by technology

With the continuous development of MMC technology and the decline of manufacturing costs, the transmission capacity of MMC-HVDC will further increase, whic

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  • Control strategy of multi-circuit MMC (modular multilevel converter)-HVDC (high voltage direct-current ) fed extremely-weak grid
  • Control strategy of multi-circuit MMC (modular multilevel converter)-HVDC (high voltage direct-current ) fed extremely-weak grid
  • Control strategy of multi-circuit MMC (modular multilevel converter)-HVDC (high voltage direct-current ) fed extremely-weak grid

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[0041] In order to describe the present invention more specifically, the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0042] figure 2 is the equivalent structure of single-phase MMC connected to the AC system, where u sk is the k-phase grid voltage (k=a, b, c, representing abc three-phase), i vk is the MMC output current, i pk , i nk Represent the upper and lower arm currents, respectively, u pk , u nk respectively represent the voltage of the upper and lower bridge arms, i cirk represents the bridge arm circulation, R 0 is the bridge arm equivalent resistance, L 0 is the bridge arm inductance, L ac is the equivalent inductance between the outlet of the converter and the equivalent potential of the AC system (including the equivalent inductance of the system and the leakage inductance of the transformer), U dc Indicates DC voltage.

[0043] The mathematical mode...

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Abstract

The invention discloses a control strategy of a multi-circuit MMC (modular multilevel converter)-HVDC (high voltage direct-current ) fed extremely-weak grid. The control strategy includes that 1), a synchronous generator simulation control method is adopted to all the MMCs, an active-frequency loop is used for simulating the swinging process of a synchronous generator, an idle-voltage loop is used for simulating an excitation system of the synchronous generator, and failure current is limited and MMC response speed is increased by adopting an inner current loop; 2), a dynamic power distribution control method is adopted to power distribution among the MMCs, a preset power reference value is not used any longer, and the power reference value is dynamically adjusted according to specific proportion according to changes of system load. By the arrangement, the MMC-HVDC fed extremely-weak grid is enabled to run stably, power distribution can be rapidly and effectively performed, frequency deviation caused by power fluctuation to the system is removed, the MMCs can have inertia effect as the synchronous generator, and high reference meaning and use value in engineering are achieved.

Description

technical field [0001] The invention belongs to the technical field of electric power system transmission, and in particular relates to a control strategy for feeding a multi-circuit MMC-HVDC into an extremely weak power grid. Background technique [0002] Modular multilevel converter (MMC) is the most competitive and promising converter topology for voltage source converter type direct current (HVDC) transmission system. Due to its low manufacturing difficulty, low loss, high waveform quality, and ability to supply power to passive networks, MMC has been widely used in various fields. [0003] With the gradual increase of MMC-HVDC projects, a regional power grid is likely to form two or more MMC-HVDC feeds into the same AC bus, or the electrical distance between them is very close. For example, in the German wind power grid-connected project, the HVDC Borwin1 project and HVDC Borwin2 project that have been put into operation are located in Diele, Germany, and the HVDC Dolw...

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Application Information

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IPC IPC(8): H02J3/36H02J3/16H02J3/24
CPCH02J3/16H02J3/24H02J3/36H02J2203/20Y02E60/60Y02E40/30
Inventor 徐政肖晃庆王世佳曹冬明
Owner ZHEJIANG UNIV
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