CN110212800A - Modularization multi-level converter universal control method based on Model Predictive Control - Google Patents

Modularization multi-level converter universal control method based on Model Predictive Control Download PDF

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CN110212800A
CN110212800A CN201910603319.6A CN201910603319A CN110212800A CN 110212800 A CN110212800 A CN 110212800A CN 201910603319 A CN201910603319 A CN 201910603319A CN 110212800 A CN110212800 A CN 110212800A
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bridge arm
phase
output voltage
submodule
period
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CN110212800B (en
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杨珺
孙泽军
张化光
刘鑫蕊
孙秋野
黄博南
马大中
王智良
王占山
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Northeastern University China
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Northeastern University China
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • 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
    • 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
    • H02M7/53—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 using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/5387—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
    • H02M7/53871—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Inverter Devices (AREA)

Abstract

The present invention provides a kind of modularization multi-level converter universal control method based on Model Predictive Control, is related to flexible DC transmission technology field.The method include the steps that step 1: obtaining the Model Predictive Control collection W of the three-phase lower bridge arm output voltage in next period according to the three-phase lower bridge arm output voltage and constraint condition of current period；Step 2: calculating the electric current cost function of each output voltage in domination set W, obtain electric current cost set G；Step 3: selecting three kinds of voltage output modes of electric current cost minimization in set G；Step 4: calculating the capacitance voltage cost function and switch cost function of different switching schemes；Step 5: calculating every seed module switching scheme totle drilling cost function, retain the corresponding submodule switching scheme of minimum total cost, generate each submodule switching of switching signal control module multilevel converter.This method reduces optimizing amount by reducing the size of domination set, and reduces voltage fluctuation of capacitor, reduces switching frequency.

Description

Modularization multi-level converter universal control method based on Model Predictive Control
Technical field
The present invention relates to flexible DC transmission technology field more particularly to a kind of modularization based on Model Predictive Control are more Level converter universal control method.
Background technique
Due to having, there is no change modularization multi-level converter (Modular Multilevel Converter, MMC) Mutually failure, can with it is separately adjustable it is active with reactive power, convenient for modular arrangements, harmonics level is low and can supply to passive system The features such as electric, is widely applied in high-voltage dc transmission electrical domain.But it is how defeated in control with simpler and more direct quick method Difficult point of the balanced capacitor voltage as all kinds of control methods while electric current out.
The characteristics of Model Predictive Control is that dynamic response is fast, strong robustness and linearized can not realize multiple target Control, is a kind of nonlinear optimal control method.With the development and application of microprocessor, Model Predictive Control gradually by It is applied in power electronic system, is mainly based upon the Model Predictive Control of limited domination set, by constructing multiple-objection optimization letter Number, predicts the limited Switch State Combination in Power Systems of converter, and assesses the system mode of each prediction, selects more Control program of the smallest Switch State Combination in Power Systems of objective optimization function result as next period.But Model Predictive Control is each It needs to assess all possible future state of system in the control period, so the optimizing amount of control process is very big, And switching frequency is higher.And in the case where system switching combination is more, constraint condition is more, calculation amount is even more can be at double Rise.So how reducing Model Predictive Control calculation amount, accelerating optimal speed is the hot spot studied at present.
Summary of the invention
It is a kind of based on model prediction control the technical problem to be solved by the present invention is in view of the above shortcomings of the prior art, provide The modularization multi-level converter universal control method of system, this method reduce optimizing by reducing the size of domination set Amount, and voltage fluctuation of capacitor is reduced, reduce switching frequency.
In order to solve the above technical problems, the technical solution used in the present invention is:
The present invention provides a kind of modularization multi-level converter universal control method based on Model Predictive Control, including with Lower step:
Step 1: according to modularization multi-level converter under the three-phase lower bridge arm output voltage and three-phase of current period k The constraint condition of bridge arm output voltage obtains the Model Predictive Control collection W=of the three-phase lower bridge arm output voltage of next period k+1 {w1、w2、…、wρ, wherein wρFor the ρ kind combined situation of the three-phase lower bridge arm output voltage of k+1 period MMC,The specific method is as follows:
Step 1.1: the first of k+1 period three-phase lower bridge arm output voltage is obtained according to k period three-phase lower bridge arm output voltage Beginning Model Predictive Control collectionWhereinFor k+1 period MMC three-phase lower bridge arm Output voltage Ula(k+1)、Ulb(k+1)、Ulc(k+1)Kind combined situation,The level maximum number of transitions between the period；
Step 1.2: according to the characteristic of modularization multi-level converter and the constraint condition of three-phase lower bridge arm output voltage Removal Model Predictive Control concentrates the lower bridge arm output voltage values for not meeting constraint, obtains the three-phase lower bridge arm output in next period The Model Predictive Control collection W={ w of voltage1、w2、…、wρ}；
The constraint condition of three-phase lower bridge arm output voltage are as follows:
Wherein, N is MMC bridge arm submodule sum,For submodule capacitor voltage rating；；
And three-phase output voltage Ua,Ub,UcMeet:
Wherein, UaFor the output voltage of k+1 period a phase, UbFor the output voltage of k+1 period b phase, UcFor k+1 period c phase Output voltage；Ula、Ulb、UlcRespectively represent k+1 period a, b, c phase lower bridge arm output voltage values；UdcFor the specified electricity of DC side Pressure；
Step 2: calculate electric current obtained in step 1 in Model Predictive Control collection W in the case of each output voltage at This function gi, obtain control colleeting comb cost setWhereinFeelings are combined for ρ kind output voltage Electric current cost under condition；
Step 3: according to control colleeting comb cost setSelect wherein electric current cost minimization Three kinds of voltage output mode wα、wδ、wζ, wherein wα∈ W, wδ∈ W, wζ∈W；
Parameter g is seti1、gi2、gi3, and it is initially gi1=gi2=gi3=+∞, the control current collection for then obtaining step 2 Flow cost setSuccessively with gi1, gi2, gi3It makes comparisons, manner of comparison is as follows:
IfThen enable gi3=gi2、gi2=gi1、And save the corresponding three-phase output electricity of each cost function Press combination；
IfThen enable gi3=gi2、gi1=gi1, and save the corresponding three-phase of each cost function Output voltage combination；
IfThengi2=gi2、gi1=gi1, and it is defeated to save the corresponding three-phase of each cost function Combinations of voltages mode out；
IfThen give up
After successively comparing, output cost function is the smallestObtain its corresponding three Phase lower bridge arm output voltage combination wα、wδ、wζ；Wherein wα∈ W, wδ∈ W, wζ∈W；
Step 4: three kinds of three-phase lower bridge arm output voltage combination w according to obtained in step 3α、wδ、wζ, calculate different The capacitance voltage cost function and switch cost function of switching scheme；
Specific step is as follows:
Step 4.1: the three kinds of three-phase lower bridge arm output voltage combination w obtained according to step Cα、wδ、wζ, calculate every kind Each bridge arm needs the submodule number put into combination:
Y phase lower bridge arm:
Bridge arm in y phase: Npyz=N-Nlyz
Wherein, NlyzY phase lower bridge arm needs the submodule number put into when representing combination as z, wherein z=wαOr wδOr wζ, y=a, b, c；NpyzBridge arm needs the submodule number put into y phase when representing combination as z；UlyzCombination is represented as z When y phase lower bridge arm output voltage,For submodule rated capacity voltage value, N is MMC bridge arm submodule sum；[] is to take Integral symbol；
The quantity of the corresponding submodule switching scheme of each output voltage combination are as follows:
Wherein, whereinIt represents from N number of different elements, appoints and take NxycA element and at one group, the number of combinations possessed It measures, wherein x=l, p；MzSubmodule switching amount of projects when for combination being z；Submodule switching scheme total amount is M, In
Step 4.2: calculating separately three kinds of output voltage combination wα、wδ、wζIn every seed module switching scheme capacitor Voltage cost function；
The capacitance voltage cost function of h kind switching scheme when combination is z is calculated, wherein h ∈ Mz:
According to capacitance characteristic, there are following relationships for submodule capacitor voltage:
Wherein, USMIt (k+1) is k+1 period submodule capacitor voltage；USMIt (k) is k period submodule capacitor voltage value；The current value of submodule capacitor is flowed through for the k period；C is submodule capacitance；
According to submodule switching group S1Condition discrimination submodule investment and excision:
Flow through the electric current of capacitorAre as follows:
Wherein, ixy(k) be k period y phase x bridge arm current value, wherein x=l, p；
Define submodule capacitor voltage predicted value:
Wherein,For the capacitance voltage predicted value of y phase x n-th of submodule of bridge arm；For y phase x The capacitance voltage measured value of n-th of submodule of bridge arm；For the current measurement value of k period y phase x bridge arm；C is submodule electricity Capacitance；TsFor the sampling period of Model Predictive Control；Wherein, x=l, p, n ∈ N；
Submodule capacitor voltage reference value are as follows:
Wherein, N is MMC bridge arm submodule sum；
The capacitance voltage cost function of h kind switching scheme when combination is z
Step 4.3: calculating separately three kinds of output voltage combination wα、wδ、wζIn every seed module switching scheme open Close cost function；
Compare k+1 period and k period each submodule switching group S1State, state switching needed for on-off times B:
The switch cost function of h kind switching scheme when combination is z
Wherein, S1_xynIt (k+1) is n-th of submodule switching group S of+1 period of kth y phase x bridge arm1State；S1_xyn(k) it is N-th of submodule switching group S of kth period y phase x bridge arm1State；
Step 5: according to every seed module switching scheme by electric current cost function, capacitance voltage cost function and switch at This function calculates every seed module switching scheme totle drilling cost function, retains the corresponding submodule switching side of minimum total cost function Case generates switching signal, each submodule switching of control module multilevel converter.
Every phase lower bridge arm output voltage includes in the step 1.1Kind is possible:
Wherein, Ula(k+1)、Ulb(k+1)、Ulc(k+1) k+1 period a, b, c phase lower bridge arm output voltage values are respectively represented； Ula(k)、Ulb(k)、Ulc(k) k period a, b, c phase lower bridge arm output voltage values are respectively represented；Obtaining value method it is as follows:
Wherein, UsFor the amplitude for exchanging side voltage rating；TsFor the sampling period of Model Predictive Control；It willValue takes upwards It is whole,For the symbol that rounds up.
Specific step is as follows for the step 2:
Following formula is obtained according to the topological structure of MMC and Kirchoff s voltage theorem:
Following formula is obtained according to the topological structure of MMC and kirchhoff electric current theorem:
iy=ipy-ily
Wherein, UpyFor the bridge arm output voltage in y phase under current period, wherein y=a, b, c；UlyFor under current period Y phase lower bridge arm output voltage；ipyFor the electric current for flowing through bridge arm in y phase；ilyFor the electric current for flowing through y phase lower bridge arm；iyIt is exported for y phase Electric current；lm、rm、l0、r0Respectively bridge arm inductance, arm resistance, Inductor and exchange measuring resistance；V0For common-mode voltage Value, common-mode voltage are as follows:
The characteristic equation of ac circuit is obtained according to voltage theorem formula and electric current theorem formula are as follows:
The predicted value of electric current is exported using y phase when the preceding prediction k+1 period to Euler method
Y phase exports current reference value when obtaining the k+1 period using Lagrangian second order extrapolation above-mentioned formula
According to the predicted value of output electric currentAnd reference valueCalculating current cost function giAre as follows:
The electric current cost of all combined situations in Model Predictive Control collection W is found out according to electric current cost function.
The specific method is as follows for the step 5:
It calculatesThe totle drilling cost function of corresponding M submodule switching scheme:
Wherein, GminFor the minimum value in M totle drilling cost function；For for the electric current under θ kind output voltage combined situation Cost function, wherein θ=α, δ, ζ；λi、λv、λBFor the weight system of electric current cost function, capacitance voltage cost function, switching frequency Number, is determined by actual requirement of engineering.
The beneficial effects of adopting the technical scheme are that provided by the invention a kind of based on Model Predictive Control Modularization multi-level converter universal control method, this method will not be big using the output voltage of modularization multi-level converter The characteristics of range jumps reduces the quantity of subsequent time switching scheme, to reduce the optimizing amount of Model Predictive Control.And And the constraint of capacitance voltage and switching frequency is increased on this basis, it can be further reduced voltage fluctuation of capacitor, reduce system System loss, increases stability.
Detailed description of the invention
Fig. 1 is the general graph of topology of Modular multilevel converter provided in an embodiment of the present invention；
Fig. 2 is the submodule topological diagram of Modular multilevel converter provided in an embodiment of the present invention；
Fig. 3 is the overall control scheme flow chart of Model Predictive Control strategy provided in an embodiment of the present invention；
Fig. 4 is the process of three kinds of voltage output modes provided in an embodiment of the present invention for selecting wherein electric current cost minimization Figure.
Specific embodiment
With reference to the accompanying drawings and examples, specific embodiments of the present invention will be described in further detail.Implement below Example is not intended to limit the scope of the invention for illustrating the present invention.
As Figure 1-Figure 2, modularization multi-level converter is by a, and b, six bridge arms compositions of c three-phase, each bridge arm is by bridge Arm equivalent reactance lm, bridge arm equivalent resistance rmIt is constituted with N number of half-bridge submodule, one direct current of DC side parallel of each submodule Capacitor C, switching group S1、S2It is made of large power all-controlled device.
The present invention for Model Predictive Control in modularization multi-level converter using existing computationally intensive, optimizing is multiple The deficiencies of miscellaneous, proposes a kind of modularization multi-level converter universal control method based on Model Predictive Control, passes through reduction The size of domination set reduces optimizing amount, and reduces voltage fluctuation of capacitor, reduces switching frequency.
As shown in figure 3, the method for the present embodiment is as described below.
Step 1: according to modularization multi-level converter under the three-phase lower bridge arm output voltage and three-phase of current period k The constraint condition of bridge arm output voltage obtains the Model Predictive Control collection W=of the three-phase lower bridge arm output voltage of next period k+1 {w1、w2、…、wρ, wherein wρFor the ρ kind combined situation of the three-phase lower bridge arm output voltage of k+1 period MMC,
The specific method is as follows:
Step 1.1: the first of k+1 period three-phase lower bridge arm output voltage is obtained according to k period three-phase lower bridge arm output voltage Beginning Model Predictive Control collectionWhereinFor k+1 period MMC three-phase lower bridge arm Output voltage Ula(k+1)、Ulb(k+1)、Ulc(k+1)Kind combined situation；
Every phase lower bridge arm output voltage includesKind is possible:
Wherein, Ula(k+1)、Ulb(k+1)、Ulc(k+1) k+1 period a, b, c phase lower bridge arm output voltage values are respectively represented； Ula(k)、Ulb(k)、Ulc(k) k period a, b, c phase lower bridge arm output voltage values are respectively represented；For the specified electricity of submodule capacitor Pressure；The level maximum number of transitions between the period,Obtaining value method it is as follows:
Wherein, UsFor the amplitude for exchanging side voltage rating；TsFor the sampling period of Model Predictive Control；It is accurate in order to improve Property, it willValue rounds up,For the symbol that rounds up；
Step 1.2: according to the spy of modularization multi-level converter (Modular Multilevel Converter, MMC) Property and three-phase lower bridge arm output voltage constraint condition removal Model Predictive Control concentrate do not meet constraint lower bridge arm output Voltage value obtains the Model Predictive Control collection W={ w of the three-phase lower bridge arm output voltage in next period1、w2、…、wρ}；
The constraint condition of three-phase lower bridge arm output voltage are as follows:
Wherein, N is MMC bridge arm submodule sum；
And three-phase output voltage Ua,Ub,UcMeet:
Wherein, UaFor the output voltage of k+1 period a phase, UbFor the output voltage of k+1 period b phase, UcFor k+1 period c phase Output voltage；Ula、Ulb、UlcRespectively represent k+1 period a, b, c phase lower bridge arm output voltage values；UdcFor the specified electricity of DC side Pressure；
So (k+1) period MMC three-phase output voltage Ua,Ub,UcIt is up toKind combined situation；
Step 2: calculate electric current obtained in step 1 in Model Predictive Control collection W in the case of each output voltage at This function gi, obtain control colleeting comb cost setWhereinFeelings are combined for ρ kind output voltage Electric current cost under condition；
Specific step is as follows:
Following formula is obtained according to the topological structure of MMC and Kirchoff s voltage theorem:
Following formula is obtained according to the topological structure of MMC and kirchhoff electric current theorem:
iy=ipy-ily
Wherein, UpyFor the bridge arm output voltage in y phase under current period；UlyFor under current period y phase lower bridge arm export Voltage；ipyFor the electric current for flowing through bridge arm in y phase；ilyFor the electric current for flowing through y phase lower bridge arm；iyElectric current is exported for y phase；lm、rm、l0、 r0Respectively bridge arm inductance, arm resistance, Inductor and exchange measuring resistance；V0For common-mode voltage value, common-mode voltage are as follows:
The characteristic equation of ac circuit is obtained according to voltage theorem formula and electric current theorem formula are as follows:
The predicted value of electric current is exported using y phase when the preceding prediction k+1 period to Euler method
Y phase exports current reference value when obtaining the k+1 period using Lagrangian second order extrapolation above-mentioned formula
According to the predicted value of output electric currentAnd reference valueCalculating current cost function giAre as follows:
The electric current cost of all combined situations in Model Predictive Control collection W is found out according to electric current cost function；
Step 3: according to control colleeting comb cost setSelect wherein electric current cost minimization Three kinds of voltage output mode w α, wδ、wζ, wherein w α ∈ W, wδ∈ W, wζ∈ W such as schemes into next stage Model Predictive Control Shown in 4；
Specific step is as follows:
Parameter g is seti1、gi2、gi3, and it is initially gi1=gi2=gi3=+∞, the control current collection for then obtaining step 2 Flow cost setSuccessively with gi1, gi2, gi3It makes comparisons, manner of comparison is as follows:
IfThen enable gi3=gi2、gi2=gi1、And save the corresponding three-phase output electricity of each cost function Press combination；According to sequential write assignment；
IfThen enable gi3=gi2、gi1=gi1, and save the corresponding three-phase of each cost function Output voltage combination；
IfThengi2=gi2、gi1=gi1, and it is defeated to save the corresponding three-phase of each cost function Combinations of voltages mode out；
IfThen give up
After successively comparing, output cost function is the smallestObtain its corresponding three Phase lower bridge arm output voltage combination wα、wδ、wζ；Wherein wα∈ W, wδ∈ W, wζ∈W；
Step 4: three kinds of three-phase lower bridge arm output voltage combination w according to obtained in step 3α、wδ、wζ, calculate different The capacitance voltage cost function and switch cost function of switching scheme；
Specific step is as follows:
Step 4.1: the three kinds of three-phase lower bridge arm output voltage combination w obtained according to step Cα、wδ、wζ, calculate every kind Each bridge arm needs the submodule number put into combination:
Y phase lower bridge arm:
Bridge arm in y phase: Npyz=N-Nlyz
Wherein, NlyzY phase lower bridge arm needs the submodule number put into when representing combination as z, wherein z=wαOr wδOr wζ；NpyzBridge arm needs the submodule number put into y phase when representing combination as z；UlyzBridge under y phase when representing combination as z The output voltage of arm,For submodule rated capacity voltage value, N is MMC bridge arm submodule sum；[] is to be rounded symbol；
The quantity of the corresponding submodule switching scheme of each output voltage combination are as follows:
Wherein, whereinIt represents from N number of different elements, appoints and take NxycA element and at one group, the number of combinations possessed It measures, wherein x=l, p, y=a, b, c；MzSubmodule switching amount of projects when for combination being z；Submodule switching scheme is total Amount is M, wherein
Step 4.2: calculating separately three kinds of output voltage combination wα、wδ、wζIn every seed module switching scheme capacitor Voltage cost function；
The capacitance voltage cost function of h kind switching scheme when combination is z is calculated, wherein h ∈ Mz:
According to capacitance characteristic, there are following relationships for submodule capacitor voltage:
Wherein, USMIt (k+1) is k+1 period submodule capacitor voltage；USMIt (k) is k period submodule capacitor voltage value；The current value of submodule capacitor is flowed through for the k period；C is submodule capacitance；
According to submodule switching group S1Condition discrimination submodule investment and excision:
Flow through the electric current of capacitorAre as follows:
Wherein, ixy(k) be k period y phase x bridge arm current value, wherein x=l, p；
Define submodule capacitor voltage predicted value:
Wherein,For the capacitance voltage predicted value of y phase x n-th of submodule of bridge arm；For y phase x The capacitance voltage measured value of n-th of submodule of bridge arm；For the current measurement value of k period y phase x bridge arm；C is submodule electricity Capacitance；TsFor the sampling period of Model Predictive Control, wherein x=l, p；
Submodule capacitor voltage reference value are as follows:
Wherein, N is MMC bridge arm submodule sum；
The capacitance voltage cost function of h kind switching scheme when combination is z
Step 4.3: calculating separately three kinds of output voltage combination wα、wδ、wζIn every seed module switching scheme open Close cost function；
Compare k+1 period and k period each submodule switching group S1State, state switching needed for on-off times B:
The switch cost function of h kind switching scheme when combination is z
Wherein, S1_xynIt (k+1) is n-th of submodule switching group S of+1 period of kth y phase x bridge arm1State；S1_xyn(k) it is N-th of submodule switching group S of kth period y phase x bridge arm1State；
Step 5: according to every seed module switching scheme by electric current cost function, capacitance voltage cost function and switch at This function calculates every seed module switching scheme totle drilling cost function, retains the corresponding submodule switching side of minimum total cost function Case generates switching signal, each submodule switching of control module multilevel converter；
The specific method is as follows:
It calculatesThe totle drilling cost function of corresponding M submodule switching scheme:
Wherein, GminFor the minimum value in M totle drilling cost function；For for the electric current under θ kind output voltage combined situation Cost function, wherein θ=α, δ, ζ；λi、λv、λBFor the weight system of electric current cost function, capacitance voltage cost function, switching frequency Number, is determined by actual requirement of engineering；Electric current and submodule capacitor voltage are constraint of equal importance, and switching frequency is secondary constraint； The value can also require to be adjusted according to Practical Project, finally choose minimum total cost function pair in the above M totle drilling cost function The submodule switching scheme answered generates the switching that switching signal controls each submodule.
Finally, it should be noted that the above embodiments are merely illustrative of the technical solutions of the present invention, rather than its limitations；Although Present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that: it still may be used To modify to technical solution documented by previous embodiment, or some or all of the technical features are equal Replacement；And these are modified or replaceed, model defined by the claims in the present invention that it does not separate the essence of the corresponding technical solution It encloses.

Claims (4)

1. a kind of modularization multi-level converter universal control method based on Model Predictive Control, it is characterised in that: including with Lower step:
Step 1: according to modularization multi-level converter current period k three-phase lower bridge arm output voltage and three-phase lower bridge arm The constraint condition of output voltage obtains the Model Predictive Control collection W={ w of the three-phase lower bridge arm output voltage of next period k+11、 w2、...、wρ, wherein wρFor the ρ kind combined situation of the three-phase lower bridge arm output voltage of k+1 period MMC, The level maximum number of transitions between the period；The specific method is as follows:
Step 1.1: the introductory die of k+1 period three-phase lower bridge arm output voltage is obtained according to k period three-phase lower bridge arm output voltage Type PREDICTIVE CONTROL collectionWhereinFor the output of k+1 period MMC three-phase lower bridge arm Voltage Ula(k+1)、Ulb(k+1)、Ulc(k+1)Kind combined situation；
Step 1.2: being removed according to the characteristic of modularization multi-level converter and the constraint condition of three-phase lower bridge arm output voltage Model Predictive Control concentrates the lower bridge arm output voltage values for not meeting constraint, obtains the three-phase lower bridge arm output voltage in next period Model Predictive Control collection W={ w1、w2、...、wρ}；
The constraint condition of three-phase lower bridge arm output voltage are as follows:
Wherein, N is MMC bridge arm submodule sum,For submodule capacitor voltage rating；；
And three-phase output voltage Ua,Ub,UcMeet:
Wherein, UaFor the output voltage of k+1 period a phase, UbFor the output voltage of k+1 period b phase, UcFor the defeated of k+1 period c phase Voltage out；Ula、Ulb、UlcRespectively represent k+1 period a, b, c phase lower bridge arm output voltage values；UdcFor DC side voltage rating；
Step 2: calculating the electric current cost letter in Model Predictive Control collection W obtained in step 1 in the case of each output voltage Number gi, obtain control colleeting comb cost setWhereinFor under ρ kind output voltage combined situation Electric current cost；
Step 3: according to control colleeting comb cost setThree kinds for selecting wherein electric current cost minimization Voltage output mode wα、wδ、wζ, wherein wα∈ W, wδ∈ W, wζ∈W；
Parameter g is seti1、gi2、gi3, and it is initially gi1=gi2=gi3=+∞, the control colleeting comb for then obtaining step 2 at This setSuccessively with gi1, gi2, gi3It makes comparisons, manner of comparison is as follows:
IfThen enable gi3=gi2gi2=gi1、And save the corresponding three-phase output voltage group of each cost function Conjunction mode；
IfThen enable gi3=gi2、gi1=gi1, and save the corresponding three-phase output of each cost function Combinations of voltages mode；
IfThengi2=gi2、gi1=gi1, and save the corresponding three-phase output voltage of each cost function Combination；
IfThen give up
After successively comparing, output cost function is the smallestIt obtains under its corresponding three-phase Bridge arm output voltage combination wα、wδ、wζ；Wherein wα∈ W, wδ∈ W, wζ∈W；
Step 4: three kinds of three-phase lower bridge arm output voltage combination w according to obtained in step 3α、wδ、wζ, calculate different switchings The capacitance voltage cost function and switch cost function of scheme；
Specific step is as follows:
Step 4.1: the three kinds of three-phase lower bridge arm output voltage combination w obtained according to step Cα、wδ、wζ, calculate every kind of combination Each bridge arm needs the submodule number put into mode:
Y phase lower bridge arm:
Bridge arm in y phase: Npyz=N-Nlyz
Wherein, NlyzY phase lower bridge arm needs the submodule number put into when representing combination as z, wherein z=wαOr wδOr wζ, y= a,b,c；NpyzBridge arm needs the submodule number put into y phase when representing combination as z；UlyzY phase when representing combination as z The output voltage of lower bridge arm,For submodule rated capacity voltage value, N is MMC bridge arm submodule sum；[] is to be rounded symbol Number；
The quantity of the corresponding submodule switching scheme of each output voltage combination are as follows:
Wherein, whereinIt represents from N number of different elements, appoints and take NxycA element and at one group, the number of combinations possessed, Middle x=l, p；MzSubmodule switching amount of projects when for combination being z；Submodule switching scheme total amount is M, wherein
Step 4.2: calculating separately three kinds of output voltage combination wα、wδ、wζIn every seed module switching scheme capacitance voltage Cost function；
The capacitance voltage cost function of h kind switching scheme when combination is z is calculated, wherein h ∈ Mz:
According to capacitance characteristic, there are following relationships for submodule capacitor voltage:
Wherein, USMIt (k+1) is k+1 period submodule capacitor voltage；USMIt (k) is k period submodule capacitor voltage value；For The k period flows through the current value of submodule capacitor；C is submodule capacitance；
According to submodule switching group S1Condition discrimination submodule investment and excision:
Flow through the electric current of capacitorAre as follows:
Wherein, ixy(k) be k period y phase x bridge arm current value, wherein x=l, p；
Define submodule capacitor voltage predicted value:
Wherein,For the capacitance voltage predicted value of y phase x n-th of submodule of bridge arm；For y phase x bridge arm The capacitance voltage measured value of n submodule；For the current measurement value of k period y phase x bridge arm；C is submodule capacitance；Ts For the sampling period of Model Predictive Control；Wherein, x=l, p, n ∈ N；
Submodule capacitor voltage reference value are as follows:
Wherein, N is MMC bridge arm submodule sum；
The capacitance voltage cost function of h kind switching scheme when combination is z
Step 4.3: calculating separately three kinds of output voltage combination wα、wδ、wζIn every seed module switching scheme switch at This function；
Compare k+1 period and k period each submodule switching group S1State, state switching needed for on-off times B:
The switch cost function of h kind switching scheme when combination is z
Wherein, S1_xynIt (k+1) is n-th of submodule switching group S of+1 period of kth y phase x bridge arm1State；S1_xynIt (k) is kth week N-th of submodule switching group S of phase y phase x bridge arm1State；
Step 5: according to every seed module switching scheme by electric current cost function, capacitance voltage cost function and switch cost letter Number calculates every seed module switching scheme totle drilling cost function, retains the corresponding submodule switching scheme of minimum total cost function, raw At switching signal, each submodule switching of control module multilevel converter.
2. a kind of modularization multi-level converter general controls side based on Model Predictive Control according to claim 1 Method, it is characterised in that: every phase lower bridge arm output voltage includes in the step 1.1Kind is possible:
Wherein, Ula(k+1)、Ulb(k+1)、Ulc(k+1) k+1 period a, b, c phase lower bridge arm output voltage values are respectively represented；Ula (k)、Ulb(k)、Ulc(k) k period a, b, c phase lower bridge arm output voltage values are respectively represented；Obtaining value method it is as follows:
Wherein, UsFor the amplitude for exchanging side voltage rating；TsFor the sampling period of Model Predictive Control；It willValue rounds up,For the symbol that rounds up.
3. a kind of modularization multi-level converter general controls side based on Model Predictive Control according to claim 1 Method, it is characterised in that: specific step is as follows for the step 2:
Following formula is obtained according to the topological structure of MMC and Kirchoff s voltage theorem:
Following formula is obtained according to the topological structure of MMC and kirchhoff electric current theorem:
iy=ipy-ily
Wherein, UpyFor the bridge arm output voltage in y phase under current period, wherein y=a, b, c；UlyFor under the y phase under current period Bridge arm output voltage；ipyFor the electric current for flowing through bridge arm in y phase；ilyFor the electric current for flowing through y phase lower bridge arm；iyElectric current is exported for y phase； lm、rm、l0、r0Respectively bridge arm inductance, arm resistance, Inductor and exchange measuring resistance；V0For common-mode voltage value, common mode Voltage are as follows:
The characteristic equation of ac circuit is obtained according to voltage theorem formula and electric current theorem formula are as follows:
The predicted value of electric current is exported using y phase when the preceding prediction k+1 period to Euler method
Y phase exports current reference value when obtaining the k+1 period using Lagrangian second order extrapolation above-mentioned formula
According to the predicted value of output electric currentAnd reference valueCalculating current cost function giAre as follows:
The electric current cost of all combined situations in Model Predictive Control collection W is found out according to electric current cost function.
4. a kind of modularization multi-level converter general controls side based on Model Predictive Control according to claim 1 Method, it is characterised in that: the specific method is as follows for the step 5:
It calculatesThe totle drilling cost function of corresponding M submodule switching scheme:
Wherein, GminFor the minimum value in M totle drilling cost function；For for the electric current cost under θ kind output voltage combined situation Function, wherein θ=α, δ, ζ；λi、λv、λBFor electric current cost function, capacitance voltage cost function, switching frequency weight coefficient, It is determined by actual requirement of engineering.
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