CN108736700A - MMC submodule capacitor voltage static equilibrium control methods during off-network inverter circuit starts - Google Patents
MMC submodule capacitor voltage static equilibrium control methods during off-network inverter circuit starts Download PDFInfo
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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
- H02M1/00—Details of apparatus for conversion
- H02M1/36—Means for starting or stopping converters
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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
- H02M7/53—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
- H02M7/5375—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 with special starting equipment
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Abstract
MMC submodule capacitor voltage static equilibrium control methods in starting the invention discloses a kind of off-network inverter circuit.When the exchange side of inverter circuit is the capacitance precharge of off-network type load, i.e. MMC submodules, it is only capable of completing charging by the busbar voltage of DC side.Method includes：First, precharge is not controlled to all MMC submodules the first preset duration of progress；Then, all MMC submodules are ranked up according to capacitance voltage, according to certain rule, all submodules is carried out with the controllable precharge of the second preset duration；Finally, system is switched into normal inversion operating mode, system overall startup is completed.Pass through the above method, it is main solve due to the capacitance rated nominal parameter of MMC submodules is inconsistent and the voltage of capacitance is inconsistent when precharge being caused to be completed, so that DC side will appear larger surge current when inverter circuit normal operation input, the problems such as to influence MMC systems safety and be unfavorable for the voltage balance control of the capacitance of MMC submodules in normal course of operation.
Description
Technical field
The present invention relates to power electronics field, MMC submodules in starting in particular to a kind of off-network inverter circuit
Block capacitance voltage static equilibrium control method.
Background technology
Modularization multi-level converter (Modular Multilevel Converter, MMC) is because it is with modularization journey
The advantages that degree is high, autgmentability is strong, output power quality is high, voltage harmonic content is few, voltage distortion rate is small, in recent years by the country
The extensive concern of outer scholar and engineer, especially in the field D.C. high voltage transmission (HVDC), the achievement in research about MMC is rich,
It has at home and abroad been applied in some demonstration projects simultaneously.In addition, as the research of the inverter circuit to MMC structures is constantly deep
Entering, there is reference to may be applied to power quality controlling, power frequency speed control system of high, energy-storage system etc. in the future.
Inverter circuit based on modularization multi-level converter (MMC) structure is before normal operation, urgent need to resolve first
MMC submodule capacitor voltages static equilibrium problem in pre-boot process.The off-network type inverter circuit of MMC structures is opened in advance at present
It is dynamic not consider following situation：Since the capacitance parameter of submodule causes there are error (general error amount is no more than ± 20%)
The capacitance voltage of MMC submodules inconsistent problem when precharge is completed, so working as inverter circuit normal operation input moment, directly
Stream side still will appear larger surge current, to influence the safety of MMC systems and be unfavorable for MMC in normal course of operation
The voltage balance control of capacitance in submodule.
Invention content
In view of this, MMC submodule capacitor voltages in starting the purpose of the present invention is to provide a kind of off-network inverter circuit
Static equilibrium control method, MMC submodules when solving that precharge is caused to be completed due to the capacitance parameter error of MMC submodules
The inconsistent problem of capacitance voltage, will appear larger surge current to avoid DC side when inverter circuit normal operation input
The problem of, to avoid the safety for influencing MMC systems and the voltage for being unfavorable for the capacitance of MMC submodules in normal course of operation
The problems such as Balance route.
To achieve the above object, the embodiment of the present invention adopts the following technical scheme that：
MMC submodule capacitor voltage static equilibrium control methods during a kind of off-network inverter circuit starts, the control method packet
Include following steps：
Step 1：Control three-phase inverting circuit in each MMC submodules switching tube in the block (VT1) open, switching tube
(VT2) it turns off, so that all capacitances (C) are in charged state；
Step 2：Dc switch is disconnected so that DC bus-bar voltage passes through current-limiting resistance (R0) it is applied to all capacitances
(C), alternating-current switch is disconnected to cut off the connection with AC load, is carried out at the same time not with the capacitance (C) to all MMC submodules
Control precharge, wherein the time for not controlling precharge is the first preset duration；
Step 3：DC bus-bar voltage is accessed, current-limiting resistance (R is passed through0) capacitance (C) in three-phase inverting circuit is carried out
Controllable precharge, wherein the time being controllably pre-charged is the second preset duration, and includes following sub-step：
The current voltage value that the capacitance (C) of all MMC submodules is acquired by voltage sensor, by each MMC of each phase
Submodule is ranked up according to corresponding current voltage value and is divided into two groups from small to large, wherein arbitrary in three-phase inverting circuit
The quantity of all capacitances (C) of one-phase circuit is 2N, and the smaller N number of MMC submodules of current voltage value are low-voltage group, current electricity
It is high voltage group that pressure, which is worth larger N number of MMC submodules,；
The MMC submodules of control low-voltage group are in input state so that corresponding capacitance (C) is in charged state, i.e.,
The switching tube (VT1) of all MMC submodules in low-voltage group is opened, switching tube (VT2) turns off, and controls the MMC of high voltage group
Submodule is in excision state, cuts off corresponding capacitance (C) charging, i.e., the switching tube of all MMC submodules in high voltage group
(VT1) shutdown, switching tube (VT2) are open-minded；
DC bus-bar voltage is accessed, current-limiting resistance (R is passed through0) to the N of the low-voltage group of each phase in three-phase inverting circuit
The capacitance (C) of a MMC submodules charges；
Above-mentioned each sub-step is repeated according to certain period or frequency, so that by the controllable pre- of the second preset duration
The current voltage value of the capacitance (C) of all MMC submodules belongs in preset range after charging, wherein the preset range isUdcFor DC bus-bar voltage, ε is the voltage fluctuation coefficient of capacitance, and 0<ε<1；
Step 4：The switching tube (VT1) for controlling all MMC submodules opens, switching tube (VT2) shutdown, so that each capacitance
(C) it is in charged state；
Step 5：It is closed dc switch and alternating-current switch, to cut off current-limiting resistance (R0), and incoming transport loads；
Step 6：Start inversion operating mode program, system is made to enter normal operating conditions, system overall startup is completed.
In the embodiment of the present invention preferably selects, the MMC submodule capacitor voltages in the startup of above-mentioned off-network inverter circuit
In static equilibrium control method, the formula for calculating the first preset duration includes：
(primary condition is:
Wherein, it takest0For calculative first preset duration, time constant τref=R0·
Ceq_ref, equivalent capacity Ceq_ref, t is the response time, and the voltage responsive for not controlling preliminary filling electrical equivalent circuit isElectric current
Response isThe voltage responsive of the capacitance of MMC submodules isCrefFor capacitance nominal value.
In the embodiment of the present invention preferably selects, the MMC submodule capacitor voltages in the startup of above-mentioned off-network inverter circuit
In static equilibrium control method, the formula for calculating the second preset duration includes：
Wherein, it takesThe Initial Voltage Value of the capacitance of MMC submodules is taken as
t-t0For calculative second preset duration, t0For the first preset duration, CrefFor capacitance nominal value, t0Not control charging complete
When time, t is response time, equivalent capacity C "eq, timeconstantτ " and=R0·C”eq, voltage responsive isElectric current
Response isThe capacitance voltage response of MMC submodules is uc”(t)。
MMC submodule capacitor voltage static equilibrium control methods during off-network inverter circuit provided by the invention starts, pass through
Pre-charging stage and controllable pre-charging stage are not controlled by being divided into the charging of capacitance, and in controllable pre-charging stage according to capacitance
Current voltage value carries out charge control, can lead to each capacitance after the completion in precharge due to parameter is inconsistent to avoid each capacitance
The inconsistent problem of voltage, to avoid inverter control circuit when carrying out inversion work because DC side will appear larger surge
The problem of electric current, and then avoid influencing the safety of MMC systems and be unfavorable for the capacitance of MMC submodules in normal course of operation
The problems such as voltage balance control.Also, control algolithm is simple in this method, it is easy to accomplish.
To enable the above objects, features and advantages of the present invention to be clearer and more comprehensible, special embodiment below, and appended by cooperation
Attached drawing is described in detail below.
Description of the drawings
Fig. 1 is that the inverter circuit based on MMC starts control system main circuit topology figure；
Fig. 2 is MMC system sub-modules capacitance in the equivalent circuit for not controlling pre-charging stage, and (a) is that pre-charge process is equivalent
Circuit；(b) it is RC single order zero state response circuits；
Fig. 3 is equivalent circuit of the MMC system sub-modules capacitance in controllable pre-charging stage, and (a) is that pre-charge process is equivalent
Circuit；(b) it is RC single order total regression circuits；
Fig. 4 is all submodule capacitor voltage waveforms of inverter circuit A phases based on MMC；
Fig. 5 is the inverter circuit DC side current waveform based on MMC；
Fig. 6 is the inverter circuit exchange lateral load A phase voltage waveforms based on MMC；
Fig. 7 is the inverter circuit exchange lateral load A phase current waveforms based on MMC.
Specific implementation mode
In order to make the object, technical scheme and advantages of the embodiment of the invention clearer, below in conjunction with the embodiment of the present invention
In attached drawing, technical scheme in the embodiment of the invention is clearly and completely described, it is clear that described embodiment only
It is a part of the embodiment of the present invention, instead of all the embodiments.The present invention being usually described and illustrated herein in the accompanying drawings
The component of embodiment can be arranged and be designed with a variety of different configurations.
Therefore, below the detailed description of the embodiment of the present invention to providing in the accompanying drawings be not intended to limit it is claimed
The scope of the present invention, but be merely representative of the present invention selected embodiment.Based on the embodiments of the present invention, this field is common
The every other embodiment that technical staff is obtained without creative efforts belongs to the model that the present invention protects
It encloses.
It should be noted that：Similar label and letter indicate similar terms in following attached drawing, therefore, once a certain Xiang Yi
It is defined, then it further need not be defined and explained in subsequent attached drawing in a attached drawing.In description of the invention
In, term " first ", " second " etc. are only used for distinguishing description, and should not be understood as only or imply relative importance.
In the description of the present invention unless specifically defined or limited otherwise, term " setting ", " connected ", " connection " are answered
It is interpreted broadly, for example, it may be being fixedly connected, may be a detachable connection, or be integrally connected；Can be that machinery connects
It connects, can also be electrical connection；It can be directly connected, can also can be indirectly connected through an intermediary in two elements
The connection in portion.For the ordinary skill in the art, the tool of above-mentioned term in the present invention can be understood with concrete condition
Body meaning.
As shown in Figure 1, an embodiment of the present invention provides a kind of off-network type inverter circuit charge control system based on MMC structures
System main circuit topology figure.Wherein, each phase of three-phase inverting circuit is made of upper and lower two bridge arms, and each bridge arm has N number of MMC
Module SMij, a bridge arm inductance Larm。
Each MMC submodules SMijIt is by two switching tube VT1 and VT2 series connection, while respectively one two pole of electric power of inverse parallel
Pipe VD1 and VD2 are connected in parallel with a capacitor the half-bridge structure of C compositions again later.The DC side of three-phase inverting circuit passes through dc switch
Direct current contact KM1 connect with DC bus-bar voltage, also, direct current contact KM1 is normally opened contact, and is parallel with current-limiting resistance
R0.Also, the three exchange contact KM2 and AC load (equivalent resistance that the exchange side of three-phase inverting circuit passes through alternating-current switch
R, equivalent inductance L) connection, and three exchange contact KM2 are normally opened contact.
In three-phase inverting circuit, MMC submodules SMijThere are two types of working conditions, respectively：Input state, excision state.
Wherein, in the state of input, switching tube VT1 is opened, switching tube VT2 is turned off.In the state of excision, switching tube VT1 shutdowns, switch
Pipe VT2 is open-minded.
MMC submodule capacitor voltage static equilibriums control during a kind of off-network inverter circuit provided in an embodiment of the present invention starts
Method, the control method may comprise steps of：
Step 1：Each MMC submodule switching tube VT1 in the block is opened in control three-phase inverting circuit, switching tube VT2 is closed
It is disconnected, so that all capacitance C are in charged state；
Step 2：Dc switch is disconnected so that DC bus-bar voltage passes through current-limiting resistance R0All capacitance C are applied to, are broken
Alternating-current switch is opened to cut off the connection with AC load, is carried out at the same time with the capacitance C to all MMC submodules and does not control preliminary filling
Electricity, wherein the time for not controlling precharge is the first preset duration；
Step 3：DC bus-bar voltage is accessed, current-limiting resistance R is passed through0Capacitance C in three-phase inverting circuit is carried out controllable
Precharge, wherein the time being controllably pre-charged is the second preset duration, and includes following sub-step：
The current voltage value that the capacitance C of all MMC submodules is acquired by voltage sensor, by each MMC of each phase
Module is ranked up according to corresponding current voltage value and is divided into two groups from small to large, wherein any one in three-phase inverting circuit
The quantity of all capacitance C of circuitry phase is 2N, and the smaller N number of MMC submodules of current voltage value are low-voltage group, current voltage value
Larger N number of MMC submodules are high voltage group；
The MMC submodules of control low-voltage group are in input state so that corresponding capacitance C is in charged state, i.e., low
The switching tube VT1 of all MMC submodules in voltage group is opened, switching tube VT2 is turned off, and controls the MMC submodules of high voltage group
In excision state, cut off corresponding capacitance C chargings, i.e., the switching tube VT1 shutdowns of all MMC submodules in high voltage group,
Switching tube VT2 is open-minded；
DC bus-bar voltage is accessed, current-limiting resistance R is passed through0To in three-phase inverting circuit the low-voltage group of each phase it is N number of
The capacitance C of MMC submodules charges；
Above-mentioned each sub-step is repeated according to certain period or frequency, so that by the controllable pre- of the second preset duration
The current voltage value of the capacitance C of all MMC submodules belongs in preset range after charging, wherein the preset range isUdcFor DC bus-bar voltage, ε is the voltage fluctuation coefficient of capacitance, and 0<ε<1；
Step 4：The switching tube VT1 for controlling all MMC submodules opens, switching tube VT2 shutdowns, so that each capacitance C is in
Charged state；
Step 5：It is closed dc switch and alternating-current switch, to cut off current-limiting resistance R0, and incoming transport loads；
Step 6：Start inversion operating mode program, system is made to enter normal operating conditions, system overall startup is completed.
In above steps, step 1 and step 2 are not control pre-charging stage.Wherein, precharge time is not controlled (i.e.
First preset duration) it can be obtained by calculation.In detail, by step 1 it is found that not controlling pre-charging stage, all MMC
Module is all in input state, that is to say, that 2N capacitance of each phase is carried out at the same time charging.It can be with according to this course of work
Shown in equivalent circuit such as Fig. 2 (a) when establishing charging, the capacitance of each MMC submodules is Cij, for simplifying the analysis, ignore
Bridge arm inductance LarmInfluence, then equivalent capacity total Fig. 2 (a) be Ceq, the equivalent capacity per phase is Cj, calculation formula is：
Ceq=∑ Cj(j=a, b, c) (1)
Cij=Cref±ΔCij(i=1,2,3 ..., 2N；J=a, b, c) (3)
Wherein, CrefFor capacitance nominal value, Δ CijFor the error amount of capacitance, i is the MMC submodules to charge, j tri-
The a certain phase of phase inverter circuit, j=a, b, c.
According to above-mentioned equivalent capacity, then the process to charge can be equivalent to RC single order zero state response circuits, such as Fig. 2 (b)
Shown, voltage responsive isCurrent-responsive isWherein, UdcFor DC bus
Voltage, timeconstantτ=R0·Ceq, it is the time constant of RC firstorder circuits, t is the response time.Because MMC systems are per phase at this time
Electric current accurately solve relatively difficult, cause the capacitance voltage of each MMC submodules to be not easy to solve, so making at following simplify
Reason.
When being completed due to not controlling pre-charge process, it is directly transferred to controllable pre-charging stage, it is normal not participate in system directly
The switching of inversion, the length in charging time will not impact the security performance of system, and therefore, the charging time is chosen
It can carry out simplifying calculating, select one relatively reasonable not control precharge time.It can it can be seen from the above, not controlling pre-charge process
It is equivalent to RC single order zero state response circuits.Therefore, the capacitance of all MMC submodules can be taken as nominal value, calculates one
A precharge time for being closer to actual value.At this point, time constant is denoted as τref=R0·Ceq_ref, equivalent capacity Ceq_ref,
Voltage responsive isCurrent-responsive isThe voltage responsive of capacitance isSpecific response computation formula is such as
Under：
(primary condition is:
It is calculated by above-mentioned analysis, can obtain not controlling preliminary filling in the first preset duration, that is, step 1 and step 2
The duration of electricity can make the current voltage value of each capacitance after the completion of not controlling precharge close by the duration
Or it is equal to Udc/2N。
In above steps, step 3 is controllable pre-charging stage, and the duration is controllable precharge duration (i.e. second
Preset duration).By it is multiple it is controllable be pre-charged after, the voltage value of the capacitance of each MMC submodules is close to Udc/N。
Wherein, the second preset duration can be obtained by calculation.In detail, by step 3 it is found that in three-phase inverting circuit
Per phase, shared 2N MMC submodule participates in sequence, but any time only has N number of MMC submodules (three-phase MMC submodules per phase
Charge simultaneously, share 3N submodule) it charges in input state, the capacitance in charged state is ensured that in this way
Voltage opposite have preferable consistency.Also, more to MMC submodule block sequencing numbers, the voltage consistency of each capacitance is better.Root
It can be established according to this course of work shown in equivalent circuit such as Fig. 3 (a) when precharge, the capacitance of each MMC submodules is
Cij, value is only related with 2N MMC submodule N number of capacitance of MMC submodules in the block.For simplifying the analysis, ignore bridge arm electricity
Feel LarmInfluence.Then equivalent capacity total Fig. 3 (a) is C'eq, the equivalent capacity per phase is C'j, calculation formula is：
C'eq=∑ C'j(j=a, b, c) (8)
Cij=Cref±ΔCij(i=1,2,3 ..., N；J=a, b, c) (10)
Wherein, N is the submodule quantity to charge.
According to above-mentioned equivalent capacity, then the process to charge can be equivalent to RC single order total regression circuits, as shown in Fig. 3 (b),
Its voltage responsive isCurrent-responsive isCapacitance
Voltage initial valueWherein, UdcFor DC bus-bar voltage, t0For the time for not controlling when charging complete, the time is normal
Number τ '=R0·C'eq, it is the time constant of RC firstorder circuits, t is the response time.
It can be seen from the above, charging process can be equivalent to RC single order total regression circuits, then make equivalent capacity voltageCharging
Close to DC voltage Udc, the length in charging time is by the close degree co-determination of timeconstantτ and the two.In order to more
It rapidly finds out the capacitance voltage of each MMC submodules and ensures that the time of all MMC submodules capacitor chargings is more abundant, then
It is further simplified analysis, it is C "=1.2C to take maximum limit to the capacitance of all MMC submodulesref, the electricity of MMC submodules
Hold Initial Voltage Value to be taken asAt this point, the time constant of RC single order total regressions will increase, time constant is denoted as
τ "=R0·C”eq, equivalent capacity C "eq, voltage responsive isCurrent-responsive isThe capacitance electricity of MMC submodules
Pressure response is uc”(t), specific response computation formula is as follows：
It is longer according to the above formula charging time, the voltage when capacitance voltage of MMC submodules is closer to normal work, but
It is that the charging time can not possibly be too long in practice.MMC network analyses when according to normal operation, the capacitance of MMC submodules is due to one
Straight to be in charging, electric discharge two states, then capacitance voltage is in fluctuation status, and voltage fluctuation of capacitor coefficient is ε (0<ε<1),
The value just has determined when system main circuit parameter designs.Then MMC submodule capacitor voltages fluctuation range isTherefore the voltage on the capacitance of MMC submodules should at least reachDefine m
For charging time coefficient, if t-t0=m τ ", then the capacitance voltage of MMC submodules be
Then can further it obtain：
M=-ln2 ε (15)
Thereby it is ensured that the electricity of per mutually N number of MMC submodules (three-phase MMC submodules charge simultaneously, share 3N submodule)
The capacity charge time should be more than m τ ".The size of τ " and current-limiting resistance R0It chooses and equivalent capacity C'e'qIt is related.When MMC submodules
Capacitance C " value fix when, R0Value it is bigger, then τ " is bigger, and the capacitance voltage of MMC submodules reachesIt is required
Time it is longer, have the advantage that the capacitance of MMC submodules is smaller in the current spike value of pre-charging stage DC side.When
One timing of τ " values, ε is smaller, then m values are bigger, and the capacitance voltage of MMC submodules reachesThe required time is longer,
The capacitance voltage of MMC submodules is closer to Udc/ N, then surge current when MMC systems are switched to normal inversion from pre-charging stage
Kurtosis is with regard to smaller.According to the size of DC bus-bar voltage and per the particular number of phase MMC submodules, considers selection and close
Suitable current-limiting resistance R0Make the capacitance voltages of MMC submodules close to U within the charging time as short as possible with m valuesdc/N。
Optionally, the period or frequency that the division of high voltage group and low-voltage group is carried out in step 3 can be according to reality
Application demand is configured.Also, the period or frequency determine the switching frequency of pre-charging stage switching tube, for ease of split
The radiator for closing pipe is designed, the switching tube when switching frequency of pre-charging stage switching tube should be no more than normal inversion operating mode
Switching frequency.
Wherein, during be controllably pre-charged, if the capacitance voltage and three-phase inverting circuit to MMC submodules are straight
When the ripple of stream side requires relatively low, the frequency of the above-mentioned division being ranked up can be smaller, to reduce switching tube in precharge rank
The power attenuation of section, and reduce the calculation amount for the controller for carrying out control work.
Further, the present embodiment also provides a kind of using example, in this example, DC bus-bar voltage Udc=1000V,
Current-limiting resistance R0=50 Ω, bridge arm inductance Larm=5mH, capacitance nominal value Cref=2mF, the ripple factor of capacitance voltage be ε≤
5%, error amount Δ C limiting values are ± the 20% of nominal value, then the value range of capacitance is：1.6mF≤(Cref+ΔC)≤
2.4mF, the capacitances of all MMC submodules random value within this range, each bridge arm submodule number N=4, AC load resistance
R=50 Ω, AC load inductance L=15mH, startup stage MMC submodule are 100Hz according to the frequency that capacitance voltage sorts,
When MMC systems switch to normal inversion operating mode, (certainly, carrier wave stacking modulation plan is controlled using phase-shifting carrier wave modulation strategy
Slightly, nearest level approaches modulation strategy and is also suitable), load side voltage waveform is the output result of five level.
It is calculated according to above-mentioned parameter it is found that when not controlling precharge completion, the capacitance voltage of MMC submodules is in reference voltage
Uref_NNear=125V.When controllable precharge is completed, voltages approach reference voltage Uref_2N=250V.It is imitative according to above-mentioned parameter
Very available, the voltage fluctuation of capacitor of the MMC submodules in normal inverse variable working condition is ranging from：245V≤Ucref≤
255V, then voltage fluctuation of capacitor coefficient ε=2% of MMC submodules, meet the ripple factor ε of the capacitance voltage of MMC submodules≤
Charging time Coefficient m=3.219 can be then calculated in 5% requirement.In the capacitance of MMC submodules there are in the case of error,
Pre-charging stage is not controlled, MMC systems charge constant τ at this time can be calculated according to above-mentioned analysisref=0.0375s, then not
When control precharge is completed, the capacitance voltage of MMC submodules reaches 0.95Uref_N, required time t0=0.12s.Controllable precharge rank
Section, MMC systems charge constant τ "=0.09s at this time can be calculated according to above-mentioned analysis, then when controllable precharge is completed,
T-t the time required to charging is completed to N number of MMC submodules (three-phase MMC submodules charge simultaneously, share 3N submodule)0=
0.290s, then it is 2 (t-t to give the time required to all MMC submodules charging completes0)=0.58s.Since the charging time is longer, MMC
The capacitance voltage of submodule is closer to Udc/ N, MMC system are switched to DC side electricity when normal inversion operating mode by pre-charging stage
The fluctuation of the capacitance voltage of stream, bridge arm surge current and MMC modules is smaller.It opens in view of switching tube and is also required to shutdown simultaneously
Regular hour, then it is 0.68s, the then total charging of MMC systems to take the capacitor charging time of controllable pre-charging stage MMC submodules
Time is t=0.8s, and switching at 0.8s makes MMC systems enter normally inverse variable parameter operation.
In conclusion MMC submodule capacitor voltages static equilibrium control in off-network inverter circuit pretrigger provided by the invention
Method processed does not control pre-charging stage and controllable pre-charging stage by will be divided into the charging of capacitance, and in controllably precharge rank
Section according to the current voltage value of capacitance carry out charge control, can to avoid each capacitance due to parameter is inconsistent after the completion of precharge
The problem for causing the voltage of each capacitance inconsistent, to avoid inverter control circuit when carrying out inversion work because DC side can go out
The problem of showing larger surge current, and then avoid influencing the safety of MMC systems and be unfavorable for MMC in normal course of operation
The problems such as voltage balance control of the capacitance of module.Also, control algolithm is simple in this method, it is easy to accomplish.
The foregoing is only a preferred embodiment of the present invention, is not intended to restrict the invention, for the skill of this field
For art personnel, the invention may be variously modified and varied.All within the spirits and principles of the present invention, any made by repair
Change, equivalent replacement, improvement etc., should all be included in the protection scope of the present invention.
Claims (3)
- MMC submodule capacitor voltage static equilibrium control methods during 1. a kind of off-network inverter circuit starts, which is characterized in that the control Method processed includes the following steps：Step 1：Each MMC submodules switching tube in the block (VT1) is opened in control three-phase inverting circuit, switching tube (VT2) closes It is disconnected, so that all capacitances (C) are in charged state；Step 2：Dc switch is disconnected so that DC bus-bar voltage passes through current-limiting resistance (R0) all capacitances (C) are applied to, break Alternating-current switch is opened to cut off the connection with AC load, is carried out at the same time with the capacitance (C) to all MMC submodules and does not control preliminary filling Electricity, wherein the time for not controlling precharge is the first preset duration；Step 3：DC bus-bar voltage is accessed, current-limiting resistance (R is passed through0) capacitance (C) in three-phase inverting circuit is carried out controllably Precharge, wherein the time being controllably pre-charged is the second preset duration, and includes following sub-step：The current voltage value that the capacitance (C) of all MMC submodules is acquired by voltage sensor, by each MMC submodules of each phase Block is ranked up according to corresponding current voltage value and is divided into two groups from small to large, wherein any one phase in three-phase inverting circuit The quantity of all capacitances (C) of circuit is 2N, and the smaller N number of MMC submodules of current voltage value are low-voltage group, current voltage value Larger N number of MMC submodules are high voltage group；The MMC submodules of control low-voltage group are in input state so that corresponding capacitance (C) is in charged state, i.e., low electricity The switching tube (VT1) of all MMC submodules in pressure group is opened, switching tube (VT2) turns off, and controls the MMC submodules of high voltage group Block is in excision state, cuts off corresponding capacitance (C) charging, i.e., the switching tube (VT1) of all MMC submodules in high voltage group Shutdown, switching tube (VT2) are open-minded；DC bus-bar voltage is accessed, current-limiting resistance (R is passed through0) to N number of MMC of the low-voltage group of each phase in three-phase inverting circuit The capacitance (C) of submodule charges；Above-mentioned each sub-step is repeated according to certain period or frequency, so that the controllable precharge by the second preset duration The current voltage value of the capacitance (C) of all MMC submodules belongs in preset range afterwards, wherein the preset range isUdcFor DC bus-bar voltage, ε is the voltage fluctuation coefficient of capacitance, and 0<ε<1；Step 4：The switching tube (VT1) for controlling all MMC submodules opens, switching tube (VT2) shutdown, so that at each capacitance (C) In charged state；Step 5：It is closed dc switch and alternating-current switch, to cut off current-limiting resistance (R0), and incoming transport loads；Step 6：Start inversion operating mode program, system is made to enter normal operating conditions, system overall startup is completed.
- MMC submodule capacitor voltage static equilibrium control methods during 2. off-network inverter circuit according to claim 1 starts, It is characterized in that, the formula for calculating the first preset duration includes：(primary condition is:)；Wherein, it takest0For calculative first preset duration, time constant τref=R0· Ceq_ref, equivalent capacity Ceq_ref, t is the response time, and the voltage responsive for not controlling preliminary filling electrical equivalent circuit isElectric current Response isThe voltage responsive of the capacitance of MMC submodules isCrefFor capacitance nominal value.
- MMC submodule capacitor voltage static equilibrium control methods during 3. off-network inverter circuit according to claim 1 starts, It is characterized in that, the formula for calculating the second preset duration includes：Wherein, it takesThe Initial Voltage Value of the capacitance of MMC submodules is taken as t-t0For calculative second preset duration, t0For the first preset duration, CrefFor capacitance nominal value, t0Not control charging complete When time, t is response time, equivalent capacity C "eq, timeconstantτ " and=R0·C”eq, voltage responsive isElectric current Response isThe capacitance voltage response of MMC submodules is uc”(t)。
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