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

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

Example Embodiment

[0034] Example 1:

[0035] 2 bridge arm simultaneously fault, such as bridge arm Au, BU

[0036] Since the bridge arm Au and the bridge arm BU are connected to the U phase of the power frequency AC system, the system cannot be converted into the HEXVERTER mode, and the system is directly locked.

Example Embodiment

[0037] Example 2:

[0038] Single bridge arm fault, such as bridge arm AU failure

[0039] The first step: assume that the initial state, the MMMC is running normally run, and then a single bridge arm Au fault (such as the bridge arm Au control system failure) is generated;

[0040] Step 2: MMMC Transient Control Suppressing Fault Bridge Arm Current to zero value, then jumps the circuit breaker on both sides of the bridge arm to cut the branch Au;

[0041] Step 3: Remove the B-phase and C-phase of the connecting wind power low frequency grid, and there are two different cutings at this time. Therefore, there is a total of 2 * 3 = 6 different transitions to HEXVERTER;

[0042] Method 1: At the same time, the bridge arm BV and bridge arms CW, figure 2 Reasonable image 3 (a) Symmetric circuit structure of the Hexverter shown. It is also an AC / AC direct frequency conversion device based on modular multi-level techniques. Hexverter only contains 6 bridge arms, the structure is simple...

Example Embodiment

[0046] Example 3:

[0047] 3 bridge arm simultaneously fault, such as bridge arm Au, BV and CW failure

[0048] Since the bridge arms Au, BV, and CW are in three different sub-transformers, the different phases in the three-phase system, the system can be converted into the HEXVERTER mode, and the result of the method of the case 2 after the case The same, the final result is like image 3 (a) shown.

[0049] The present invention writes programs, commissioning and verification by electromagnetic transit professional simulation tools of power systems. This method is suitable for application scenarios for low-frequency transmission, which can be simple and easy to use, and can choose different processing response methods in the transient process of different bridge arms and location failures in MMMC, and the maximum probability When the bridge arm is faulty, ensure smooth switching to the HEXVERTER symmetrical operation, with great engineering practical value.

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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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