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Asymmetric operational control method of direct current side monopolar grounding fault of MMC-HVDC system

A MMC-HVDC, single-pole ground fault technology, applied in the direction of power transmission AC network, emergency treatment AC circuit layout, etc., can solve the problems of high construction cost, increase the difficulty of manufacturing transformers and related equipment in the connection area, and achieve low construction cost , Improve active defense capabilities, low technical requirements

Active Publication Date: 2016-03-16
HUAZHONG UNIV OF SCI & TECH
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, compared with the MMC-HVDC system with unipolar symmetrical wiring, this wiring method requires the AC side of each pole to bear the DC bias of half the rated DC voltage during normal operation, thus improving the relationship between the transformer and the connection area. The equipment is difficult to manufacture and the construction cost is high. At present, the only flexible direct current transmission project in the world that adopts this connection method is the Caprivi project connecting Namibia and Zambia

Method used

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  • Asymmetric operational control method of direct current side monopolar grounding fault of MMC-HVDC system
  • Asymmetric operational control method of direct current side monopolar grounding fault of MMC-HVDC system
  • Asymmetric operational control method of direct current side monopolar grounding fault of MMC-HVDC system

Examples

Experimental program
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Effect test

Embodiment 1

[0048] For the MMC-HVDC system with parallel reactance on the AC side and an external resistance grounding method, after a single-pole ground fault occurs on the negative line, each bridge arm is equivalent to a controllable voltage source, then the ground electrode on the AC side, the sub-module capacitor and the fault connection on the DC side locations that make up the fault loop, such as Figure 10 Shown by the dotted line.

[0049] According to Kirchhoff's voltage law, the following relationship can be derived:

[0050] ( R g + R f ) I f a u l t ...

Embodiment 2

[0066] For the MMC-HVDC system with the Y winding of the AC side transformer connected to ground with an external resistance, after a single-pole ground fault occurs, the fault path is as follows: Figure 14 shown by the dotted line, with Figure 10 The grounding method of the external resistance of the shunt reactor on the AC side is similar. Also according to Kirchhoff's voltage and current law, it can be deduced that after the negative bus unipolar ground fault occurs, the positive and negative DC bus voltages in the steady state are:

[0067] U d c p = U d c 0 - 0.5 U ...

Embodiment 3

[0077] For the MMC-HVDC system with parallel clamping and large resistance grounding on the DC side, when a single-pole grounding fault occurs, the simplified equivalent circuit is as follows Figure 17 As shown, the grounding point changes from position ① to position ②. Since the resistance value of the resistors connected in parallel on the DC side is extremely large, it is approximately an open circuit. There is no discharge path between the capacitors of each module and the fault ground point, the capacitor voltage remains stable, and the capacitor current component is consistent with that before the fault. Also due to the change of the ground point, the replacement At this time, the voltage on the AC side of the converter is equivalent to the voltage of the lower bridge arm, and a DC bias of half the rated DC voltage appears. At this time, the non-faulty pole DC line bears all the DC voltage, which is doubled before the fault. It can be seen that the single-pole ground fa...

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Abstract

The invention discloses an asymmetric operational control method of the direct current side monopolar grounding fault of an MMC-HVDC system. For the MMC-HVDC system based on monopolar symmetric wiring, after a direct current side monopolar grounding fault occurs, over voltage and fault current at AC and DC sides can be rapidly eliminated by setting the DC component of the output voltage of a bridge arm of a fault pole without locking a current converter, and further the insulation threat to AC / DC systems can be eliminated. Through adjusting phase angles of alternating components of different bridge arm voltages, the system still can continue transmitting half of a rated active power and provide reactive power support for the AC system while isolating the direct current side monopolar grounding fault, which has positive significance for the stability of the connected AC / DC systems; during the fault period, the current converter does not need to exit from operating, the restore speed of the system is high, the current converter is in a controlled state in the whole process, and therefore the active defense capability of the MMC-HVDC system based on monopolar symmetric wiring against the direct current side monopolar grounding fault can be improved.

Description

technical field [0001] The invention belongs to the technical field of multilevel power electronic converters, and more specifically relates to an asymmetrical operation control method for single-pole grounding faults on the DC side of an MMC-HVDC system. Background technique [0002] The DC power grid technology based on flexible DC transmission is considered to be the most effective technical solution in terms of large-scale distributed renewable energy access, power supply in oceanic islands, transmission from offshore wind farm clusters, and construction of new urban power grids. The research hotspot in the field of international electric power. The technology and construction of DC transmission network have become an important development direction and part of the future power grid. The ModularMultilevelConverterBasedHighVoltageDirectCurrent (MMC-HVDC) system based on the modular multilevel converter has made important achievements in the flexible DC transmission techn...

Claims

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Application Information

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IPC IPC(8): H02J3/36
CPCH02J3/001H02J3/36Y02E60/60
Inventor 胡家兵徐克成万敏
Owner HUAZHONG UNIV OF SCI & TECH
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