CN108429477B - MMC submodule optimized voltage-sharing method based on mixing of double half bridges and parallel full bridges - Google Patents
MMC submodule optimized voltage-sharing method based on mixing of double half bridges and parallel full bridges Download PDFInfo
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- CN108429477B CN108429477B CN201810104338.XA CN201810104338A CN108429477B CN 108429477 B CN108429477 B CN 108429477B CN 201810104338 A CN201810104338 A CN 201810104338A CN 108429477 B CN108429477 B CN 108429477B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
- H02M7/4835—Converters with outputs that each can have more than two voltages levels comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage
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Abstract
The invention relates to an MMC submodule optimized voltage-sharing method based on mixing of a double half-bridge submodule and a parallel full-bridge submodule. The invention has the advantages that the traditional capacitor voltage sequencing algorithm and the self-voltage-sharing algorithm are combined together to adapt to the voltage-sharing strategy of the double-half-bridge and parallel full-bridge mixed sub-modules, and the voltage-sharing strategies of the two algorithms are optimized simultaneously and organically combined. The method has the advantages that the dependence on capacitance voltage measurement and sequencing is obviously reduced, so that the requirements on the real-time performance of capacitance voltage monitoring, the operation speed of the controller and the amount of hardware resources are greatly reduced, the flexible operation characteristic is kept, the control logic is greatly simplified, the requirements on the sensor and the controller are reduced, the method has a good engineering application prospect, and the hybrid MMC is expected to be boosted to develop to a higher voltage level and a larger capacity. The method provided by the invention has important reference value for researchers in the research directions of MMC submodule voltage-sharing control, semi-full mixed submodule topology and the like.
Description
Technical Field
The invention belongs to the technical field of power transmission and distribution, and particularly relates to an optimized voltage-sharing method of an MMC submodule based on the mixing of a double half bridge and a parallel full bridge.
Background
As a topology of flexible direct current transmission, compared with conventional power grid commutation direct current transmission, Modular Multilevel Converter high voltage direct current transmission (MMC-HVDC) has the advantages of no commutation failure, good harmonic characteristics, independent and controllable power, and the like, and gradually becomes a hotspot of direct current transmission research and application.
Common MMC Sub-module topologies in dc power transmission include a Half-bridge Sub-module (HBSM), a Full-bridge Sub-module (FBSM), a Clamped Double Sub-module (CDSM), and the like. HBSM devices are small in number but lack the DC fault-ride-through capability of FBSM and CDSM; the direct current fault type submodules represented by FBSM and CDSM can be processed, and have the characteristics of more devices, poor economy and high loss. In order to seek the balance between performance and economy, a sub-module hybrid MMC (also called hybrid MMC) has come into play in combination with the modular characteristics of MMC. The hybrid MMC is formed by the two sub-modules in a certain quantity and proportion, so that the converter has the direct-current fault processing capacity and better economy, and the hybrid MMC has wide application prospect in the MMC field.
With the continuous improvement of voltage grade and transmission capacity, the hybrid MMC faces similar difficulties with the traditional single-type submodule MMC, and the contradiction between insufficient voltage resistance and insufficient current capacity of the submodule device is gradually prominent. On one hand, in order to solve the problem of voltage resistance, a large number of sub-modules are required to be cascaded, which means that in a control period of a mu s level, a system needs to complete the acquisition, monitoring and sequencing equalization of capacitor voltages of thousands of sub-modules in each station, and thus a great challenge is formed on a secondary system; on the other hand, the switching device can continuously flow through the full current of the bridge arm, and the current stress caused by the full current cannot be avoided.
Aiming at the traditional MMC voltage-sharing method, in order to reduce the calculation complexity, the existing literature is improved and designed from the aspects of sequencing theory, retention factors, grouping and layering, voltage prediction, modulation, harmonic waves and the like. However, when the existing voltage-sharing algorithm is applied to the hybrid MMC, negative effects such as increase of calculation complexity, reduction of voltage-sharing effect and the like occur.
Therefore, for the demand in the adaptation reality engineering, how to realize mixing MMC's voltage-sharing control, reduce the computational complexity, improve the voltage-sharing effect, the difficult problem that needs to solve is promptly reduced the system to sensor and control system's requirement simultaneously.
Disclosure of Invention
The invention provides an optimized voltage-sharing method of an MMC submodule based on mixing of a double half bridge and a parallel full bridge, which comprises the following steps:
step 1: generating voltage modulation wave by system level control, further processing to obtain bridge arm voltage reference wave, obtaining bridge arm level number command value by nearest level approximation modulation, setting asn ON。
Novel hybrid MMC bridge armN DD-HBSM andN Pa P-FBSM consisting ofN=2N D+N P) A capacitor ofN+1) Level MMC system. Selecting a capacitor voltage in each D-HBSMU iD(i=1~N D) Participating in pressure equalization among valve sections; in addition, a capacitor voltage of the P-FBSM valve section is selectedU PRepresenting all the capacitance voltages of the valve section. Generating voltage modulation wave by system level control, further obtaining bridge arm voltage reference wave, obtaining bridge arm level number instruction value by nearest level approximation modulation, setting asn ON；
Step (ii) of2: firstly, carrying out pressure equalizing control between valve sections: in each sequencing cycle, allU iDAndU Pa voltage sequence is obtained by sequencing from small to large, andU Pis set toP. At each moment willn ONAndPandN Pcomparing to obtain the number n of sub-modules which are respectively required to be opened by the D-HBSM and the P-FBSMDAnd nP。
When the bridge arm current is greater than 0, a module with small voltage should be put into the bridge arm. When in usen ON<2(P1) time, let nD=n ON，nP= 0; when 2(P-1)<n ON<2(P-1)+ N PWhen, let nP= n ON-2(P-1), nD= 2(P-1); when in usen ON>2(P-1)+ N PWhen, let nP= N P, nD= n ON -N P。
When the bridge arm current is less than 0, a module with high voltage should be put into the bridge arm. When in usen ON<2(N D+1- P) When, let nD=n ON，nP= 0; when 2(N D +1-P)<n ON<2(N D+1- P)+ N PWhen, let nP= n ON-2(N D+1- P), nD=2(N D+1- P) (ii) a When in usen ON>2(N D+1- P)+ N PWhen, let nP=N P, nD= n ON- N P。
And step 3: obtaining the number n of sub-modules which are respectively required to be opened by the D-HBSM and the P-FBSMDAnd nPAnd then, carrying out pressure equalizing control in the valve sections, namely determining which sub-modules need to be opened specifically in each valve section to output the required level number.
For the D-HBSM valve section, simplified sequencing is performed, andN Dthe individual capacitor voltages are sequenced. When in usen D≤N DThen, two capacitors of each sub-module are connected in parallel to output +U CA level, in which a capacitor with a small voltage is put in during charging and a capacitor with a large voltage is put in during discharging; when in usen D>N DIn order to satisfy the level output, the following should be maden D-N D) Sub-module series output +2U CLevel, the rest is +U CLevel, sub-module output +2 which should be made lower in voltage during chargingU CLevel, sub-module output +2 which should be made higher in voltage during dischargeU CA level.
For P-FBSM valve sections, dynamic distribution pressure-sharing control is adopted, i.e. based onn PThe capacitors are connected in parallel in a segmented mode to the maximum extent, and the voltage-sharing effect is optimized.
Drawings
FIG. 1 is a diagram of a MMC topology with a mixture of double half-bridges and parallel full-bridges;
FIG. 2 is a diagram of a double half-bridge (D-HBSM) MMC topology;
FIG. 3 is a diagram of a parallel full bridge (P-FBSM) MMC topology;
FIG. 4 is a schematic diagram of parallel current paths inside a double half-bridge (D-HBSM) MMC topology sub-module;
FIG. 5 is a flow chart of hybrid MMC valve inter-segment pressure equalization control;
FIG. 6 is a flow chart of pressure equalization control within a hybrid MMC valve section.
Detailed Description
In order to further illustrate the principle of the invention, the optimized voltage-sharing algorithm of the double half-bridge and parallel full-bridge hybrid sub-modules related to the invention is described in detail below with reference to the accompanying drawings. 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.
Fig. 1 is a diagram of a MMC topology structure in which a double half bridge and a parallel full bridge are mixed. A certain number of parallel full-bridge submodules and half-bridge submodules are connected in series to form a bridge arm, and the modules can be sequentially switched in and out under the instruction of voltage-sharing control according to the requirements of a system in operation, so that the voltage-sharing effect is ensured, and meanwhile, the required level is output.
Fig. 2 is a double half-bridge (D-HBSM) MMC topology structure diagram, and it can be seen that two adjacent sub-modules in a conventional half-bridge are split into two rows and run in a row, and at the same time, the switching devices at the same position are kept at the same on-off state at any time, which can still be regarded as two original switching tubes, but the current capacity is twice as high as that before, and the durability of the system is greatly improved.
Fig. 3 is a topological structure diagram of a parallel full bridge (P-FBSM) MMC, and it can be seen that a sub-module in a conventional full bridge is split into two rows and operated in a row, and meanwhile, a switching device at the same position keeps the same on-off state at any time, which can still be regarded as an original switching tube, but the current capacity is doubled before, and the durability of the system is greatly improved.
As shown in fig. 4, the double half-bridge topology can realize parallel connection of two adjacent capacitors through two different current paths, so that two modules can realize local voltage sharing while one capacitor voltage is ensured to be output externally; from another perspective, if regard as two original submodule pieces with two half-bridge modules, can guarantee the voltage-sharing process when output voltage, this effect of voltage-sharing has been promoted notably.
The specific implementation steps of the optimized voltage-sharing algorithm referred to herein are illustrated here:
is provided withN PIs a number of 10 and is provided with,N Dis 5, and at some point in time,U Prank at bit 3 of the voltage sequence:
bridge arm current is greater than 0:
when in usen ON<4 hours later, addn ON0P-FBSM module is added into each D-HBSM module;
when 4 is present<n ON<14 hours, put 4D-HBSM modules inton ON-4P-FBSM modules;
when in usen ON>At 14 hours, put inn ON10D-HBSM modules, invested in 10P-FBSM modules.
Bridge arm current is less than 0:
when in usen ON<At 6 hours, put inton ON0P-FBSM module is added into each D-HBSM module;
when 6 is<n ON<16 hours, 6D-HBSM modules are put inn ON-6P-FBSM modules;
when in usen ON>16 hours later, addn ON10D-HBSM modules, invested in 10P-FBSM modules.
The above part is the pressure equalizing between valve sections, and fig. 5 is a flow chart of the pressure equalizing between valve sections.
For the D-HBSM valve section, simplified sequencing is performed, andN Dthe individual capacitor voltages are sequenced. When in usen D≤N DThen, two capacitors of each sub-module are connected in parallel to output +U CA level, in which a capacitor with a small voltage is put in during charging and a capacitor with a large voltage is put in during discharging; when in usen D>N DIn order to satisfy the level output, the following should be maden D-N D) Sub-module series output +2U CLevel, the rest is +U CLevel, sub-module output +2 which should be made lower in voltage during chargingU CLevel, sub-module output +2 which should be made higher in voltage during dischargeU CA level.
For P-FBSM valve sections, dynamic distribution pressure-sharing control is adopted, i.e. based onn PThe capacitors are connected in parallel in a segmented mode to the maximum extent, and the voltage-sharing effect is optimized.
The above is the pressure equalizing in the valve section, and fig. 6 is a flow chart of the pressure equalizing between the valve sections.
Claims (1)
1. An MMC submodule optimized voltage-sharing method based on mixing of double half-bridge submodules and parallel full-bridge submodules is characterized in that sorting voltage-sharing and self-voltage-sharing are combined in the voltage-sharing method, and the voltage-sharing process is divided into inter-valve-section voltage-sharing and intra-valve-section voltage-sharing; the double half-bridge submodule structure is as follows: connecting two traditional 4 half bridges in parallel to form an upper part and a lower part of a double-half bridge submodule, connecting input terminals of a left half bridge and a right half bridge of the upper part, connecting output terminals of a left half bridge and a right half bridge of the lower part, connecting an output terminal of a left half bridge of the upper part with an input terminal of a left half bridge of the lower part, and connecting an output terminal of a right half bridge of the upper part with an input terminal of a right half bridge of the lower part; the parallel full-bridge submodule structure is as follows: connecting two traditional full bridges in parallel, wherein two terminals in the middle of a left full bridge arm are used as input terminals, and two terminals in the middle of a right full bridge arm are used as output terminals; the pressure equalizing method comprises the following steps:
step 1: generating voltage modulation wave by system level control, further processing to obtain bridge arm voltage reference wave, obtaining bridge arm level number command value by nearest level approximation modulation, setting as nON；
Step 2: firstly, carrying out pressure equalizing control between valve sections: in each sequencing cycle, all U's are addedDiAnd UPObtaining a voltage sequence from small to large, and sequencing UPIs set to P; at each moment in time according to nONP and NPThe values of the three are calculated by using a specific expression, wherein N isPRepresenting the number of parallel full-bridge submodules in one bridge arm; obtaining the conduction number n required by the double half-bridge sub-module (D-HBSM) and the parallel full-bridge sub-module (P-FBSM)DAnd nP(ii) a When the number of the sub-modules is distributed, the current direction of a bridge arm is considered, the current direction is regular, and the current direction is preferably input into a low-voltage module, and the current direction is negative, and the current direction is preferably input into a high-voltage module;
wherein U isDiRepresents the capacitance voltage of the ith double half-bridge submodule; u shapePRepresenting the capacitance voltage of a representative parallel full-bridge submodule; p represents that after the voltage sequencing is finished, UPA variable of the rank;
and step 3: obtaining the number n of submodules which need to be switched on respectively in the double half-bridge submodule and the parallel full-bridge submoduleDAnd nPAnd then, carrying out pressure equalizing control in the valve sections, namely determining which sub-modules need to be opened specifically in each valve section to output the required level number.
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| CN109256964B (en) * | 2018-10-15 | 2020-05-15 | 中国矿业大学 | MMC model prediction control method for mixing half-bridge submodule and full-bridge submodule |
| CN113794393B (en) * | 2021-09-08 | 2023-09-29 | 山东理工大学 | Hybrid MMC device loss optimization method based on module decoupling control |
| CN115864879A (en) * | 2022-12-15 | 2023-03-28 | 山东大学 | Submodule grouping and sequencing method and system for hybrid MMC (Modular multilevel converter) |
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| CN103633871B (en) * | 2013-11-20 | 2016-10-05 | 华南理工大学 | Mixed type multilevel converter based on full-bridge and half-bridge module and control method thereof |
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| CN105897019A (en) * | 2016-05-26 | 2016-08-24 | 华北电力大学 | Equality constraint based modular multilevel converter (MMC) automatic voltage sharing topology |
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