CN104901569A - Fuzzy control-based modular multilevel converter voltage equalizing method - Google Patents
Fuzzy control-based modular multilevel converter voltage equalizing method Download PDFInfo
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- CN104901569A CN104901569A CN201510259378.8A CN201510259378A CN104901569A CN 104901569 A CN104901569 A CN 104901569A CN 201510259378 A CN201510259378 A CN 201510259378A CN 104901569 A CN104901569 A CN 104901569A
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Abstract
Provided is a fuzzy control-based modular multilevel converter voltage equalizing method. According to the invention, numbers of modules put into the period are calculated according to a converter control and protection system; a valve control system calculates the cut modules put in the former period, calculates numbers which should be put into/cut and alternated in this period according to the bridge arm current direction and bridge current size of this period, and calculates numbers of modules which should be alternated according to the bridge arm current value and the subordinating degree function in the bridge arm current intra-area, thereby adjusting numbers of modules which should be alternated in real time and performing voltage equalizing control for a modular multilevel converter.
Description
Technical field
The present invention relates to a kind of flexible high pressure DC transmission system modularization multi-level converter module voltage balance control method based on fuzzy control.
Background technology
In recent years, little and increasing concern can be received to the passive network plurality of advantages such as to power in direct current transportation field with its better flexibility, controllability, filter based on the flexible high pressure DC transmission system of voltage source converter (Voltage Source Converter, VSC).Particularly modularization multi-level converter (Modular Multilevel Converter in recent years, MMC) proposition, its modular design makes the raising of voltage become very easy, for flexible high pressure direct current transportation is filled with new vitality, Multi-end flexible direct current transmission is also made to be easy to realize.Up to now, the flexible DC power transmission engineering that the whole world puts into operation has exceeded 20, comprise the soft straight engineering of Nan ' ao Island, Guangdong ± 160kV/200MW/100MW/50MW tri-end, the soft straight engineering of Zhoushan Of Zhejiang Province archipelago ± 200kV five terminal, the soft straight engineering of Xiamen of Fujian Province ± 320kV/1000MW and Yunnan western Shandong ± soft straight engineering of 350kV/1000MW etc.
A large amount of power models is contained in modular multi-level converter inside for flexible high pressure DC transmission system, in actual moving process, must control the capacitance voltage of all power models, in the scope that the fluctuation range of its voltage be can bear at modular multi-level converter internal switch device (IGBT, IGCT etc.) and electric capacity.
Switching device for the modular multi-level converter inside of flexible high pressure DC transmission system is numerous, generally has thousands of switching tubes.When being applied to the larger occasion of transmitted power, the switching frequency of every switching device can not be too high, and too high switching frequency can not only cause the reduction of system operation reliability and efficiency, and bring lot of challenges for the design of Cooling System of whole current transformer.
In order to address this problem, Patents it is also proposed algorithm.Chinese patent CN 103427692 A is by dividing into groups to the module dropping in the cycle and excise, the number of modules that this cycle that converter control and protection system issues should drop into, valve control system calculated according to the statistics of the input in a upper cycle and excision number of modules the number of modules Δ N that should drop into or excise that this cycle increases newly.According to bridge arm current direction, from the module group of having excised, select the N number of module of Δ to drop into, or from the module group dropped into, select the N number of module excision of Δ.The method significantly can reduce switching frequency.But this method can cause module capacitance voltage fluctuation obvious, especially in the flexible DC power transmission engineering being applied to high-voltage large-capacity, larger bridge arm current causes the module capacitance voltage being in input for a long time to become very high, adds the risk of system safety reliability service.
Summary of the invention
Main purpose of the present invention is the shortcoming overcoming prior art, proposes a kind of modularization multi-level converter method for equalizing voltage based on fuzzy control.The present invention both can realize the Pressure and Control of modularization multi-level converter under compared with low switching frequency condition, the module of corresponding number can be selected to carry out rotation according to the size of bridge arm current again, eliminate unnecessary switch motion.
The present invention based on the control system of modularization multi-level converter comprise Control protection system and the valve control system of converter.Control protection system is top level control system, and the entirety being responsible for converter valve controls and protection.Valve control system is that lower floor controls, and is responsible for converter valve internal control, comprises the triggering etc. of switching device.
The present invention utilizes the Control protection system of modularization multi-level converter and valve control system to carry out Pressure and Control to module.The Control protection system each cycle of modularization multi-level converter issues this cycle should the number of modules of conducting; valve control system calculates this cycle according to the input of a upper cycle module and excision situation and should increase newly and drop into or newly-increased excision module number; according to direction and the inner ranking results to module voltage of valve control system of bridge arm current, the module of respective numbers is selected to drop into or excision.
Each cycle selects to drop into or the module of excision can adopt the method for module rotation to realize, selects part excision, simultaneously from the module of upper cycle excision, select part input in the module namely dropped into from a upper cycle.Less in current transformer bridge arm current, select less module to carry out rotation time namely not obvious to the discharge and recharge of module capacitance, comparatively large in current transformer bridge arm current, time namely obvious to the discharge and recharge of module, select more module to carry out rotation.
Bridge arm current, based on fuzzy control, is divided into several domains by the number choosing method of described Rotation Module, arranges membership function to each domain.Valve control system does difference according to the number of modules that this cycle received should drop in the number of modules of conducting and a upper cycle and calculates this cycle and should increase newly and drop into number of modules Δ N.Calculating this cycle according to the membership function of sampling in the bridge arm current value that obtains and this bridge arm current domain should the number of modules N of rotation
change, according to result of calculation, Pressure and Control are carried out to modular multi-level converter:
If 1 now bridge arm current direction be to module charging, control method is as follows:
(1) if this cycle does not need newly-increased input or excision module, then from the module of a upper cycle input, N is selected
changethe module excision that individual voltage is higher, the N selecting voltage lower from the module of upper cycle excision
changeindividual module drops into;
(2) if this cycle needs newly-increased input module Δ N number of, then from the module of upper cycle excision, Δ N+N is selected
changethe module that individual voltage is lower drops into, and selects N from the module of a upper cycle input simultaneously
changethe module excision that individual voltage is higher;
(3) this cycle needs newly-increased excision module Δ N number of, then from the module of a upper cycle input, select Δ N+N
changethe module excision that individual voltage is higher, selects N simultaneously from the module of upper cycle excision
changethe module that individual voltage is lower drops into.
If 2 now bridge arm current direction be that control method is as follows to module discharge:
(1) if this cycle does not need newly-increased input or excision module, then from the module of a upper cycle input, N is selected
changethe module excision that individual voltage is lower, the N selecting voltage higher from the module of upper cycle excision
changeindividual module drops into;
(2) if this cycle needs newly-increased input module Δ N number of, then a cycle of going up selects Δ N+N from the module of excision
changethe module that individual voltage is higher drops into, and selects N from the module of a upper cycle input simultaneously
changethe module excision that individual voltage is lower;
(3) if this cycle needs newly-increased excision module Δ N number of, then from the module of a upper cycle input, Δ N+N is selected
changethe module excision that individual voltage is lower, selects N simultaneously from the module of upper cycle excision
changethe module that individual voltage is higher drops into.
Membership function computational methods in described bridge arm current domain are: first bridge arm current is divided into several domains between negative maximum and positive maximum, arranges corresponding membership function respectively in each domain interval; Wherein bridge arm current be respectively just maximum and negative maximum time select N
changecomparatively large, bridge arm current positive secondary maximum with bear secondary maximum time N
changegreatly secondary, by that analogy, when final bridge arm current is near zero, select N
changeminimum; Each cycle, according to the bridge arm current obtained of sampling, judges that the domain at its place is interval, calculates N according to the membership function in each domain interval
changenumerical value weight and need the number of modules of rotation under obtaining this bridge arm current size cases.N
changefor should the number of modules of rotation.
Accompanying drawing explanation
Fig. 1 is the topological structure of modular multi-level converter;
Fig. 2 is that the domain of bridge arm current divides the membership function with corresponding domain;
Fig. 3 is the flow process of the modular multi-level converter module method for equalizing voltage based on fuzzy control.
Embodiment
The present invention is further illustrated below in conjunction with the drawings and specific embodiments.
Fig. 1 is the topological structure of modular multi-level converter (MMC), and the every of modularization multi-level converter is made up of upper and lower two brachium pontis, and each brachium pontis comprises a reactor L
armwith N number of power model SM be connected in series
1-SM
n, N>=1.
Fig. 2 is that the domain of bridge arm current divides the membership function with corresponding domain.The positive and negative interval of bridge arm current is equally divided into 3 domains, in order to simplify calculating, the simplest triangle of each domain interval selection and trapezoidal membership function, the module rotation number N that its membership function is corresponding
max, N
minand N
nomdetermine according to power system capacity and bridge arm module number, general 0≤N
min≤ 2,1≤N
nom≤ 4,4≤N
max≤ 6.Each cycle valve control system calculates this cycle according to the bridge arm current that obtains of sampling should the number of modules of rotation, and circular is:
(1) when
(2) when
N
change＝N
nom
(3) when
(4) when
(5) when
N
change＝N
nom
(6) when
Wherein, N
changethis cycle Rotation Module number, N
max, N
minand N
nomthe Rotation Module number corresponding to different membership function, N
minthat bridge arm current is at I
n/ 3 ~ I
pthe Rotation Module number that/3 interval upper membership functions are corresponding, N
nomthat bridge arm current is at I
p/ 3 ~ 2I
p/ 3 and I
n/ 3 ~ 2I
nthe Rotation Module number that/3 interval upper membership functions are corresponding, N
maxthat bridge arm current is at 2I
p/ 3 ~ I
pand 2I
n/ 3 ~ I
nthe Rotation Module number that on interval, membership function is corresponding.I
armthe bridge arm current obtained of sampling, I
pthe positive maximum of bridge arm current, I
nit is the maximum that bridge arm current is born.
As shown in Figure 3, the flow process that the present invention is based on the modular multi-level converter module method for equalizing voltage of fuzzy control is as follows:
Each control cycle converter control protection system issues this cycle should the number of modules of conducting; valve control system should the number of modules of conducting according to this cycle received; and the input of a upper cycle module and excision situation; calculating this cycle should increase newly and drop into or excision number of modules Δ N; and carry out module rotation, idiographic flow is:
If 1 bridge arm current is charge to module:
(1) this cycle does not need newly-increased input to excise module, if the number of modules that a upper cycle drops into is less than N
changeor the number of modules of excision is less than N
change, then keep the control command in this cycle constant, namely do not carry out the rotation of module; If do not meet the number of modules dropped into or excise to be less than N
change, then from the module of upper cycle excision, N is selected
changethe module that individual voltage is lower drops into, from the module that a upper cycle drops into, selected N
changethe module excision that individual voltage is higher, namely to the module rotation N dropped into and excise
changeindividual;
(2) this cycle needed newly-increased input module Δ N, if the number of modules that a upper cycle drops into is less than N
changeor the number of modules of excision is less than Δ N+N
change, then from upper one the cycle drop into module in select excise module number be: excision number of modules subtract the higher module of the N number of voltage of Δ, do not carry out the rotation of module; If the number of modules dropped into does not meet input number of modules be less than N
changeor excision number of modules is less than Δ N+N
change, then from the module of excision, Δ N+N is selected
changethe module that individual voltage is lower drops into, from the module dropped into, select N
changethe module excision that individual voltage is higher, namely to the module rotation N dropped into and excise
changeindividual;
(3) this cycle needs newly-increased excision module Δ N, if the number of modules of excision is less than N
changeor the number of modules dropped into is less than Δ N+N
change, then from the module of upper cycle excision, select the module dropped into, the module that selected quantity drops into is drop into number of modules to subtract the lower module of the N number of voltage of Δ, does not carry out the rotation of module; If the number of modules of excision does not meet excision number of modules be less than N
changeor drop into number of modules and be less than Δ N+N
change, then from the module of a upper cycle input, Δ N+N is selected
changethe module excision that individual voltage is higher, selects N from the module of upper cycle excision
changethe module that individual voltage is lower drops into, namely to the module rotation N dropped into and excise
changeindividual.
If 2 bridge arm current are to module discharge:
(1) this cycle does not need newly-increased input to excise module, if the number of modules dropped into is less than N
change, or the number of modules of excision is less than N
change, then keep the control command in this cycle constant, namely do not carry out the rotation of module; If do not meet the number of modules dropped into or excise to be less than N
change, then from the module of upper cycle excision, N is selected
changethe module that individual voltage is higher drops into, from the module that a upper cycle drops into, selected N
changethe module excision that individual voltage is lower, namely to the module rotation N dropped into and excise
changeindividual;
(2) this cycle needs newly-increased input module Δ N, if the number of modules dropped into is less than N
changeor the number of modules of excision is less than Δ N+N
change, then from the module of a upper cycle input, selection excision number of modules is: excision number of modules subtracts the lower module of the N number of voltage of Δ, does not carry out the rotation of module; If the module number dropped into does not meet input number of modules be less than N
changeor excision number of modules is less than Δ N+N
change, then from the module of upper cycle excision, Δ N+N is selected
changethe module that individual voltage is higher drops into, from the module that a upper cycle drops into, selected N
changethe module excision that individual voltage is lower, namely to the module rotation N dropped into and excise
changeindividual;
(3) this cycle needs newly-increased excision module Δ N, if the number of modules of excision is less than N
change, or the number of modules dropped into is less than Δ N+N
change, then from the module of upper cycle excision, selection input module is: drop into number of modules and subtract the higher module of the N number of voltage of Δ, do not carry out module rotation; If do not meet excision number of modules to be less than N
changeor drop into number of modules and be less than Δ N+N
change, then from the module of a upper cycle input, Δ N+N is selected
changethe module excision that individual voltage is lower, selects N from the module of upper cycle excision
changethe module that individual voltage is higher drops into, namely to the module rotation N dropped into and excise
changeindividual.
The module voltage of step control module Multilevel Inverters (MMC), can either ensure the equilibrium of module capacitance voltage according to the method described above, has and effectively can reduce switching frequency, improves system effectiveness.
Claims (2)
1., based on a modularization multi-level converter method for equalizing voltage for fuzzy control, described method for equalizing voltage utilizes the Control protection system of modularization multi-level converter and valve control system to carry out Pressure and Control to module, the Control protection system each cycle of described modularization multi-level converter issues this cycle should the number of modules of conducting, described valve control system calculates this cycle according to the input of a upper cycle module and excision situation and should increase newly and drop into or newly-increased excision module number, according to the direction of bridge arm current and valve control system to the ranking results of module voltage, part excision was selected from the module that a upper cycle drops into, from the module of upper cycle excision, select a part to drop into simultaneously, carry out module rotation, it is characterized in that, described module rotation is based on the method for fuzzy control: the number of modules that this cycle issued according to the Control protection system of converter should drop into and valve control system be the number of modules that dropped into of a cycle statistically, calculate the number of modules Δ N that this cycle increases input/excision newly, valve control system calculates this cycle according to the membership function of sampling in the bridge arm current value that obtains and this bridge arm current domain should the number of modules N of rotation
change, according to result of calculation, Pressure and Control are carried out to modular multi-level converter:
If one now bridge arm current direction be to module charging, control method is as follows:
(1) if this cycle does not need newly-increased input or excision module, then from the module of a upper cycle input, N is selected
changethe module excision that individual voltage is higher, the N selecting voltage lower from the module of upper cycle excision
changeindividual module drops into;
(2) this cycle needs newly-increased input module to be that Δ is N number of, then from the module of upper cycle excision, select Δ N+N
changethe module that individual voltage is lower drops into, and selects N from the module of a upper cycle input simultaneously
changethe module excision that individual voltage is higher;
(3) if this cycle needs newly-increased excision module to be that Δ is N number of, then from the module of a upper cycle input, Δ N+N is selected
changethe module excision that individual voltage is higher, selects N simultaneously from the module of upper cycle excision
changethe module that individual voltage is lower drops into;
If two now bridge arm current direction be that control method is as follows to module discharge:
(1) if this cycle does not need newly-increased input or excision module, then from the module of a upper cycle input, N is selected
changethe module excision that individual voltage is lower, the N selecting voltage higher from the module of upper cycle excision
changeindividual module drops into;
(2) if this cycle needs newly-increased input module Δ N number of, then from the module of upper cycle excision, Δ N+N is selected
changethe module that individual voltage is higher drops into, and selects N from the module of a upper cycle input simultaneously
changethe module excision that individual voltage is lower;
(3) if this cycle needs newly-increased excision module Δ N number of, then from the module of a upper cycle input, Δ N+N is selected
changethe module excision that individual voltage is lower, selects N simultaneously from the module of upper cycle excision
changethe module that individual voltage is higher drops into.
2. the method for equalizing voltage of modularization multi-level converter as claimed in claim 1, it is characterized in that, membership function computational methods in described bridge arm current domain are: first bridge arm current is divided into several domains between negative maximum and positive maximum, arranges corresponding membership function respectively in each domain interval; Wherein bridge arm current be respectively just maximum and negative maximum time select N
changecomparatively large, bridge arm current positive secondary maximum with bear secondary maximum time N
changegreatly secondary, by that analogy, when final bridge arm current is near zero, select N
changeminimum; Each cycle, according to the bridge arm current obtained of sampling, judges that the domain at its place is interval, calculates N according to the membership function in each domain interval
changenumerical value weight and need the number of modules of rotation under obtaining this bridge arm current size cases; N
changefor should the number of modules of rotation.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN108959756A (en) * | 2018-06-27 | 2018-12-07 | 广东电网有限责任公司 | A kind of linear pressure sequence method and device |
| CN112865568A (en) * | 2021-01-28 | 2021-05-28 | 重庆大学 | Voltage-sharing control method for optimizing average switching frequency of MMC (Modular multilevel converter) |
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| CN102969922A (en) * | 2012-11-23 | 2013-03-13 | 中国科学院电工研究所 | Modularization multilevel convertor power module capacitive voltage voltage-sharing method |
| CN103427692A (en) * | 2013-07-30 | 2013-12-04 | 浙江大学 | Modular multilevel converter modulation method based on double queues |
| CN103683995A (en) * | 2013-09-25 | 2014-03-26 | 浙江大学 | A balanced control method for full bridge MMC capacitor voltages |
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| CN102904417A (en) * | 2011-12-24 | 2013-01-30 | 许继集团有限公司 | Adaptive modulation method for submodule capacitor voltage of modular multi-level commutation device |
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