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Method for coping with MMMC bridge arm fault

A coping method and post-failure technology, applied in wind power generation, output power conversion devices, electrical components, etc., can solve the problems of no longer symmetrical system, complex control algorithm, difficult to achieve, etc., to achieve smooth transition, simple control algorithm, The effect of obvious economic value and social value

Pending Publication Date: 2022-03-08
西安端怡科技有限公司 +2
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0003] Since MMMC has a total of 9 bridge arms, each bridge arm is composed of hundreds or even thousands of SM sub-modules connected in series, the control system is relatively complex, and there is a certain probability of failure rate
If there are no more than three bridge arms that fail at the same time, there is a switch to the Hexverter mode (such as image 3 Shown) the possibility of operation, especially if a single bridge arm fails (due to control system failure, too few redundant modules, etc.), it can still run in 8-bridge arm mode, but the system is no longer symmetrical in this mode, and the control Algorithms are too complex to implement

Method used

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  • Method for coping with MMMC bridge arm fault
  • Method for coping with MMMC bridge arm fault
  • Method for coping with MMMC bridge arm fault

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0035] Two bridge arms fail at the same time, such as bridge arms au and bu fail at the same time

[0036] Because the bridge arm au and bridge arm bu are connected to the u phase of the power frequency AC system at the same time, the system cannot be converted to the Hexverter mode, and the system is directly blocked.

Embodiment 2

[0038] Single bridge arm failure, such as bridge arm au failure

[0039] Step 1: Assuming the initial state, MMMC operates at normal rated power, and then a single bridge arm au fault occurs at a certain moment (such as a bridge arm au control system failure);

[0040] Step 2: The MMMC transient control function suppresses the current of the faulty bridge arm to near zero, and then jumps the circuit breakers on both sides of the branch of the bridge arm to cut off the branch au;

[0041] The third step: respectively cut off a bridge arm branch connected to phase b and phase c of the low-frequency wind power grid. At this time, there are two different cutting methods. Therefore, there are a total of 2*3=6 different ways of transitioning to Hexverter in MMMC;

[0042] Method 1: Removal of bridge arm bv and bridge arm cw at the same time, for figure 2 Rearrange to get image 3 (a) The symmetrical circuit structure of the Hexverter shown. At this time, it is also an AC / AC dir...

Embodiment 3

[0047] Simultaneous failure of 3 bridge arms, such as simultaneous failure of bridge arms au, bv and cw

[0048] Since the bridge arms au, bv and cw are located in three different sub-converters and connected to different phases in the three-phase system, the system can be converted to Hexverter mode. In this case, the result after processing is the same as that of method 1 in case 2 Consistently, the final result is as image 3 (a) shown.

[0049] The invention uses the electric power system electromagnetic transient professional simulation tool PSCAD / EMTDC to program, debug and verify. This method is suitable for the application scenario where offshore wind power is sent out through low-frequency transmission. Its control method is simple and easy to use. During the transient process of MMMC with different bridge arm numbers and position faults, different processing methods can be selected. In the most probable single When the bridge arm fails, it can ensure smooth switchi...

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Abstract

The invention discloses a handling method after MMMC bridge arm faults, which is applied to an offshore wind power transmission system through low-frequency power transmission, an MMMC is located on the land, and two sides of a bridge arm of the MMMC are respectively connected with a circuit breaker in series. When the MMMC has a fault of four bridge arms and more than four bridge arms at the same time, the converter is directly locked; when 2-3 bridge arm faults happen to the MMMC at the same time, if the MMMC can be switched to the Hexverter operation mode, the MMMC is switched to the Hexverter operation mode for operation, and then if the bridge arm successive faults still happen, the converter is directly locked; and when the MMMC has a single bridge arm fault, synchronously selecting to cut off one bridge arm in each of the other two corresponding sub-converters, thereby transitioning to a Hexverter mode to ensure the symmetry of the system, and if the bridge arm cascading fault still occurs, directly locking the converter. The method for coping with MMMC bridge arm faults under different conditions of the MMMC is achieved, the temporary transition process is simple, the symmetry of a system after faults is good, and economical efficiency is good.

Description

technical field [0001] The invention belongs to the field of offshore new energy wind power transmission and AC / AC conversion technology, and specifically relates to a response method after MMMC bridge arm failure. Background technique [0002] With the increase in research enthusiasm for offshore wind power development and transmission methods, the academic and industrial circles have gradually realized that the investment in offshore converter stations required for DC transmission schemes is too expensive, the maintenance of offshore converter stations is inconvenient, and the economic performance is not good. With the use of AC low-frequency transmission, the converter station can be built on land, eliminating the need for offshore converter stations. On the one hand, it can have similar grid-connected performance as the DC transmission scheme, and on the other hand, it can significantly reduce the economic cost of the power transmission link. Increase transmission capaci...

Claims

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Application Information

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IPC IPC(8): H02J3/36H02M5/458H02M1/32H02H7/12H02M7/483
CPCH02J3/36H02M5/4585H02M1/32H02H7/1216H02M7/483Y02E10/76Y02E60/60
Inventor 苏匀李少华姚东晓刘沈全
Owner 西安端怡科技有限公司
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