CN105634259A - Reliability analysis and redundancy configuration calculation method for hybrid modular multilevel converter - Google Patents
Reliability analysis and redundancy configuration calculation method for hybrid modular multilevel converter Download PDFInfo
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Abstract
The invention relates to a reliability analysis and redundancy configuration calculation method for a hybrid modular multilevel converter. The reliability analysis and redundancy configuration calculation method has the beneficial effects as follows: under the premise of ensuring reliable direct current fault current cut-off of the hybrid modular multilevel converter, an initial critical proportion of the number of different types of sub modules of the hybrid modular multilevel converter is analyzed, and an optimized redundancy sub module configuration method for the hybrid modular multilevel converter is further proposed. The method considers the reliability of the converter as well as the effective utilization ratio of an insulated gate bipolar transistor in the redundancy sub modules, so that reliability and economical efficiency are both taken into consideration. The reliability analysis and redundancy configuration calculation method proposed by the invention can provide references to engineering design.
Description
Technical Field
The invention belongs to the technical field of power transmission and distribution, and particularly relates to a reliability analysis and redundancy configuration calculation method for a hybrid modular multilevel converter.
Background
Modular multilevel converter based dhighvoltagedirect current transmission systems (MMC-HVDC) are gaining increasing attention. Compared with a traditional two-level and three-level Voltage Source Converter (VSC), the MMC has the advantages that a large number of IGBTs are not needed to be connected in series, the device bearing Voltage change rate is low, the harmonic content of an output waveform is low, and the like. It is anticipated that MMC-HVDC will find wider application in the future.
At present, direct current short circuit fault is an important problem of MMC-HVDC. In practical engineering, Half-bridge sub-modules (HBSM) are mostly adopted, but the Half-bridge sub-modules do not have direct-current fault ride-through capability, and the application of the Half-bridge sub-modules in the field of overhead lines is greatly limited. Although a dc breaker (DCCB) can rapidly isolate a dc short-circuit fault, the dc breaker is still rarely applied to high-voltage and high-capacity occasions due to immature technology. In such a technical background, a practical and feasible solution is to adopt a sub-module topology with a clampable dc fault current to form an MMC with dc fault ride-through capability, a main Full-bridge sub-module (FBSM), a double-clamped sub-module (CDSM), and a single-clamped sub-module (CSSM). However, compared with the HBSM, the sub-module topology with dc fault current clamping capability requires more power electronic devices and is more expensive to manufacture. One feasible technical solution is to use a hybrid MMC consisting of two types of sub-module topologies, one of which is HBSM, and the other sub-module topology has a dc fault current clamping capability. Under the condition of a steady state, the two sub-module topologies support direct current together, the current converter is locked under the condition of a direct current short-circuit fault, and the sub-module topology with the direct current fault current clamping capability cuts off the direct current fault.
In actual engineering, each bridge arm of the MMC has hundreds of sub-modules, and sub-module faults may occur at any time in engineering, so that a certain number of redundant sub-modules are often configured. The number of redundant sub-modules has a significant impact on the reliability and engineering cost of the MMC. Since the hybrid MMC generally consists of two types of sub-module topologies, and the redundancy configurations of the two types of sub-modules affect each other, the redundancy configuration of the hybrid MMC is a very complex decision process, and has an important influence on the reliability and the economy of engineering.
Disclosure of Invention
The invention aims to solve the technical problem of a reliability analysis and submodule redundancy configuration method of a hybrid MMC. To facilitate the explanation of the method, the present invention is described by taking as an example a hybrid MMC consisting of an HBSM and a CSSM, wherein the CSSM has a dc fault current clamping capability.
The method specifically comprises the following steps:
step 1: on the premise that the hybrid MMC reliably crosses the direct-current bipolar short-circuit fault, under the condition of not considering redundancy, the minimum proportion of the number of CSSMs in each bridge arm under the condition of steady-state operation is calculated.
Step 2: establishing a relation model between the redundancy number and the reliability of the hybrid MMC, and calculating the reliability of the hybrid MMC based on the HBSM and the CSSMR MMC；
And step 3: definition ofN 0HAndN 0CSrespectively calculating the number of redundant sub-modules of HBSM and CSSM in each bridge arm by using first-order backward differenceR MMCTo pairN 0HAndN 0CSthe rate of change of (c);
and 4, step 4: screening for a threshold value whenN 0HAndN 0CSwhen the value of (a) is greater than the critical value,R MMCis small (less than a set threshold);
and 5: calculating the effective utilization rate of the insulated gate bipolar transistor in the redundant sub-module at the critical value;
step 6: considering the influence of the number of redundant modules on the reliability and the economic performance of the hybrid MMC, establishing the consideration weightUsing the target function at the threshold value in step 3R MMCAnd selecting the optimal redundancy configuration of the sub-modules in the mixed MMC according to the calculation result in the step 4.
Through the 6 steps, the optimal redundancy configuration of the hybrid MMC can be calculated on the basis of the reliability analysis of the hybrid MMC on the premise of ensuring that the hybrid MMC reliably cuts off direct-current fault current, and reference is provided for engineering design.
Drawings
Fig. 1 is a basic topology of MMC, wherein SM denotes a Sub-module (SM),Lin order to be a bridge arm reactor,U dcis the dc side voltage. Fig. 2 is a topology of the HBSM, where T1, T2 denote Insulated Gate Bipolar Transistors (IGBTs), D1, D2 denote diodes, C denotes a capacitance,U Cthe dashed line is the current path in the submodule in different current directions when the converter is blocked, which is the capacitor voltage. Fig. 3 is a CSSM topology where T1, T2, and T3 represent IGBTs, D1, D2, D3, and D4 represent diodes, and the dashed lines are the current paths in the sub-modules in different current directions when the inverter is latched. Fig. 4 shows a current path in the hybrid MMC during latching, wherein a dotted line is a current path, and an a-phase upper arm and a C-phase lower arm are taken as examples.
Detailed Description
The reliability analysis and redundancy calculation method of the hybrid MMC to which the present invention relates will be described in detail below. It should be emphasized that the following description is merely exemplary in nature and is not intended to limit the scope of the invention or its application.
The invention aims to solve the technical problem that the optimal configuration scheme of the hybrid MMC is selected by calculating the reliability of the hybrid MMC and the effective utilization rate of the IGBT in the redundancy sub-module on the premise of ensuring the direct-current fault ride-through capability of the hybrid MMC. The invention is realized by adopting the following technical scheme:
the invention is realized by the following six steps:
step 1: on the premise that the hybrid MMC reliably crosses the direct-current bipolar short-circuit fault, under the condition of not considering redundancy, the minimum proportion of the number of CSSMs in each bridge arm under the condition of steady-state operation is calculated.
When the redundancy is not counted, the number of HBSM and CSSM modules required in each bridge arm of the mixed MMC is assumed to be respectivelyN HAndN CSsubmodule capacitor voltage ofU CThen mixed MMC DC voltageU dcAnd the alternating voltage as shown in formula (1).
（1）
In the formula (1), the first and second groups,mis a modulation ratio ofm<1），U phAndU Lthe amplitudes of the alternating-current phase voltage and the line voltage on the secondary side of the converter transformer are respectively. As shown in fig. 4, the fault current flows between the upper and lower arms of different phases, and the a-phase upper arm and the C-phase lower arm are described as an example. The fault current path has 2N CSThe capacitors are connected in series, and in order to ensure the direct current fault ride-through capability of the hybrid MMC, the number of CSSM in each bridge arm should meet the requirement of a formula (2).
（2）
Combining equation (1) and equation (2), the number ratio of CSSM in each bridge arm can be obtained, as shown in equation (3):
（3）
step 2: establishing a relation model between the redundancy number and the reliability of the hybrid MMC, and calculating the reliability of the hybrid MMC based on the HBSM and the CSSMR MMC。
As the 6 bridge arms of the MMC are completely symmetrical electrically, the reliability of the MMC can be represented to a certain degree by the reliability of one bridge arm, and the reliability of the MMC is represented by the reliability of one bridge arm. The number of HBSM and CSSM in case of failure in each bridge arm is respectivelyi HAndi CSthe number of CSSM in the bridge arm affects the dc fault ride-through capability of the MMC. In order to ensure reliability of the MMC, it is specified that the redundant CSSM can be used to replace the faulty HBSM and CSSM, while the redundant HBSM can only replace the faulty HBSM and cannot replace the faulty CSSM, otherwise the number of CSSMs in the bridge arm that can normally operate is reduced, which may cause the hybrid MMC to lose dc fault ride-through capability. Therefore, the reliability calculation should include two parts according to the number of sub-modules with faults:
1）i H≤N0H，i CS≤N 0CSthe MMC reliability isR 1As shown in equation (4):
(4)
2）i H>N 0H，i CS≤N 0H+N 0CS-i Hthe MMC reliability isR 2As shown in equation (5):
(5)
in the formula (4) and the formula (5)CIs the number of combinations. The reliability of the hybrid MMC after comprehensively considering the two conditionsR MMCCan be expressed by equation (6):
(6)
for the convenience of calculation, willR MMCPut the values of (A) into a matrixRIn (5), as shown in formula (7):
(7)
wherein,N HandN CSrespectively the number of HBSM and CSSM in each leg in steady state operation,N 0HandN 0CSfor the redundancy numbers of HBSM and CSSM in each leg respectively,N 0HmandN 0CSmare respectivelyN 0HAndN 0CSmaximum value of (i.e.N 0HFrom 1 toN 0HmThe change is that the number of the first and second,N 0CSfrom 1 toN 0CSmChange, corresponding to each groupN 0HAndN 0CScan calculate corresponding valuesR MMCI.e. to calculate the reliability of the converter under different redundancy configurations. It is to be noted thati H、i CS、N 0H、N 0CS、N 0HmAndN 0CSmare all integers.
And step 3: definition ofN 0HAndN 0CSrespectively calculating the number of redundant sub-modules of HBSM and CSSM in each bridge arm by using first-order backward differenceR MMCTo pairN 0HAndN 0CSthe rate of change of (c).
Because of the fact thatN 0HAndN 0CSare all positive numbers, and are thus obtained from step 1R MMCIs aboutN 0HAndN 0CSa binary discrete function of (a). For dispersionData, approximately represented by differencesR MMCWith followingN 0HAndN 0CSthe change rule of (2).
For the convenience of calculation, willR MMCTo pairN 0HAndN 0CSare respectively put into the matrixD HAndD CSin, matrixD HAndD CSthe calculation methods of the medium element are shown in equations (8) and (9), respectively.
(8)
(9)
And 4, step 4: screening for a threshold value whenN 0HAndN 0CSwhen the value of (a) is greater than the critical value,R MMCis small (less than a set threshold);
setting a threshold valuetThe method of selecting the critical point is as shown in equation (10) and equation (11).
(10)
(11)
Satisfying formula (10) and formula (11)N 0HAndN 0CSthe value of (d) is the threshold value.
And 5: and calculating the effective utilization rate of the insulated gate bipolar transistor in the redundant sub-module at the critical value.
Firstly, calculating the effective number of the IGBTs in the redundancy sub-module, similar to the reliability calculation, the calculation of the effective number of the IGBTs in the redundancy sub-module is also divided into two parts, which are respectively shown as a formula (12) and a formula (13):
(12)
(13)
the effective number of IGBTs in the redundant sub-moduleQCan be represented by equation (14):
(14)
effective utilization rate of IGBT in redundant sub-moduleηIs defined as shown in formula (15):
(15)
step 6: considering the influence of the number of the redundant modules on the reliability and the economic performance of the hybrid MMC, establishing an objective function considering the weight, and utilizing the critical value in the step 3R MMCAnd selecting the optimal redundancy configuration of the sub-modules in the mixed MMC according to the calculation result in the step 4.
In order to comprehensively consider the influence of the number of redundant modules on the reliability of the hybrid MMC and the effective utilization rate of IGBTs in the redundant modules, an objective function as shown in equation (16) is proposed:
(16)
whereinω 1Andω 2are weight coefficients. The calculation of the objective function uses the values obtained by the equations (10) and (11)N 0HAndN 0CSis measured. And an objective functionFCorresponds to the maximum value ofN 0HAndN 0CSnamely, the optimal redundancy configuration of the hybrid MMC.
The method has the advantages that on the premise of ensuring that the mixed MMC can reliably cut off the direct current fault current, the initial critical proportion of the number of the sub-modules of different types in the mixed MMC is analyzed, and then the optimal redundant sub-module configuration method of the mixed MMC is provided, and the reliability of the current converter and the effective utilization rate of the IGBT in the redundant sub-module are considered at the same time.
The reliability analysis and optimal redundancy configuration method provided by the invention can be popularized and applied to any mixed MMC with different types and containing more than two types of sub-module topologies, and has engineering practical value.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (2)
1. A reliability analysis and redundancy configuration calculation method of a hybrid modular multilevel converter is characterized in that on the premise of ensuring the direct current fault ride-through capability of the hybrid Modular Multilevel Converter (MMC), an optimal configuration scheme of the hybrid MMC is selected by calculating the reliability of the hybrid modular multilevel converter and the effective utilization rate of an insulated gate bipolar transistor in a redundancy submodule, and the method comprises the following steps: step 1: on the premise of reliable ride-through of the hybrid MMC through the direct-current bipolar short-circuit fault, under the condition of not considering redundancy, each MMC is calculated under the condition of steady-state operationMinimum ratio of number of single clamping sub-modules (CSSM) in bridge arm, step 2: establishing a relation model of redundancy number and reliability of the hybrid MMC, and calculating the reliability of the hybrid MMC based on a half-bridge sub-module (HBSM) and CSSMR MMC(ii) a And step 3: definition ofN 0HAndN 0CSrespectively calculating the number of redundant sub-modules of HBSM and CSSM in each bridge arm by using first-order backward differenceR MMCTo pairN 0HAndN 0CSthe rate of change of (c); and 4, step 4: screening for a threshold value whenN 0HAndN 0CSwhen the value of (a) is greater than the critical value,R MMCis small (less than a set threshold); and 5: calculating the effective utilization rate of the insulated gate bipolar transistor in the redundant sub-module at the critical value; step 6: considering the influence of the number of the redundant modules on the reliability and the economic performance of the hybrid MMC, establishing an objective function considering the weight, and utilizing the critical value in the step 3R MMCAnd selecting the optimal redundancy configuration of the sub-modules in the mixed MMC according to the calculation result in the step 4.
2. The method for reliability analysis and calculation of redundancy configuration of a hybrid modular multilevel converter according to claim 1, wherein steps 1, 2, 3, 4, 5 and 6 are taken as the whole as the invention, and 6 steps are organic and indivisible.
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| CN106452143A (en) * | 2016-10-31 | 2017-02-22 | 华北电力大学 | MMC (modular multi-level converter) hot redundancy strategy based on carrier phase-shifting |
| CN107748313A (en) * | 2017-10-16 | 2018-03-02 | 华北电力大学 | Based on or logic identification HBSM MMC internal short circuit faults method |
| CN108509674A (en) * | 2018-02-06 | 2018-09-07 | 重庆大学 | A kind of improvement mixing MMC operation reliability evaluations model and method based on Multiple Time Scales thermal damage |
| CN109510495A (en) * | 2018-12-12 | 2019-03-22 | 长沙理工大学 | The mixed type MMC inverter Cost Optimization Approach blocked based on DC Line Fault |
| CN110061483A (en) * | 2019-05-28 | 2019-07-26 | 华北电力大学 | The reciprocal current-limiting type high voltage DC breaker of single clamper modular type with flow-limiting valve section |
| CN110112944A (en) * | 2019-05-28 | 2019-08-09 | 福州大学 | Modularization multi-level converter analysis method for reliability based on Copula function |
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| CN106452143A (en) * | 2016-10-31 | 2017-02-22 | 华北电力大学 | MMC (modular multi-level converter) hot redundancy strategy based on carrier phase-shifting |
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| CN108509674A (en) * | 2018-02-06 | 2018-09-07 | 重庆大学 | A kind of improvement mixing MMC operation reliability evaluations model and method based on Multiple Time Scales thermal damage |
| CN108509674B (en) * | 2018-02-06 | 2021-10-26 | 重庆大学 | Improved hybrid MMC (modular multilevel converter) operation reliability evaluation model and method |
| CN109510495A (en) * | 2018-12-12 | 2019-03-22 | 长沙理工大学 | The mixed type MMC inverter Cost Optimization Approach blocked based on DC Line Fault |
| CN110061483A (en) * | 2019-05-28 | 2019-07-26 | 华北电力大学 | The reciprocal current-limiting type high voltage DC breaker of single clamper modular type with flow-limiting valve section |
| CN110112944A (en) * | 2019-05-28 | 2019-08-09 | 福州大学 | Modularization multi-level converter analysis method for reliability based on Copula function |
| CN110112716A (en) * | 2019-05-28 | 2019-08-09 | 华北电力大学 | The reciprocal current-limiting type high voltage DC breaker of single clamper modular type with diode bidirectional bridge |
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