CN110061644A - A kind of inhibition strategy for isolated form MMC bridge arm out-of-balance current - Google Patents
A kind of inhibition strategy for isolated form MMC bridge arm out-of-balance current Download PDFInfo
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- CN110061644A CN110061644A CN201811623231.2A CN201811623231A CN110061644A CN 110061644 A CN110061644 A CN 110061644A CN 201811623231 A CN201811623231 A CN 201811623231A CN 110061644 A CN110061644 A CN 110061644A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
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Abstract
The invention discloses a kind of inhibition strategies for isolated form MMC bridge arm out-of-balance current, the following steps are included: for any bridge arm, acquire bridge arm voltage, to acquisition ac output current and direct current upper and lower bridge arm electric current, bridge arm output voltage and bridge arm current are respectively obtained according to the mathematical model of isolated form MMC circuit；Initial value is distributed to each submodule of bridge arm and driving signal；The DC component relationship for comparing upper and lower bridge arm electric current industrial frequency AC component relationship and voltage by making the difference obtains the out-of-balance current for mutually including and voltage swing；Submodule current working status is analyzed, and is modified using voltage prediction value of the bridge arm output voltage to each submodule, the driving control signal of submodule subsequent time is obtained.The invention has the advantages that the DC side for solving the problems, such as isolated form modular system includes AC compounent, power loss is reduced, under the premise of control system is stablized, realize device energy efficiently utilizes and saved manufacturing cost.
Description
Technical field
The present invention relates to a kind of inhibition strategies for isolated form MMC bridge arm out-of-balance current.
Background technique
With being substantially improved for electronic power switch device voltage grade and power grade, the height applied to large-power occasions
Pressure direct current transportation (High Voltage Direct Current, HVDC) receives the extensive concern of industry and academia,
Development is swift and violent.Compared with conventional multi-level voltage source code converter, isolated form Modular multilevel converter
(Isolated Modular Multilevel Converter, I-MMC) has high modularization, is easy extension and output wave
Shape harmonic content few advantage reduces the volume of device, saves cost, simultaneously instead of multiwinding transformer in structure
Modular system structure is also that the Redundancy Design of system brings convenience, and the series-parallel design scheme of multimode avoids switch
Device it is direct series-parallel, solve the contradiction between power device grade and high-voltage web system grade, greatly pushed soft
The development of property HVDC Transmission Technology.But a large amount of submodule series and parallel structure also brings asking for multivoltage current sensor
Topic, in high-pressure system, while meeting the voltage and accuracy class of sensor, design difficulty is very big.One kind can be by primary
Conversion simultaneously realize high voltage direct current end direct current output exchange with high-voltage alternating end export isolated form MMC topological structure meet need and
Out.This novel topological structure compared to traditional MMC there is high-pressure side not have isolation capacitance, without assisting multiloop control etc. excellent
Point, but due to containing high frequency transformer among the topology submodule, and the leakage inductance of high frequency transformer will lead to secondary side voltage
It loses, and then causes having difference to the voltage effective value in each submodule output voltage, and then lead to high voltage direct current side
Voltage be no longer simple comprising DC component, but contain a small amount of asymmetrical alternating current component simultaneously, this exchange point
Amount can cause a series of baneful influence to the load of DC terminal, also require further expansion to the selection of electric capacity of voltage regulation, that is, drop
The low quality of electric energy, also reduces economy.Therefore solve the problems, such as that this is necessary.
Summary of the invention
The purpose of the present invention is to provide a kind of inhibition strategies for isolated form MMC bridge arm out-of-balance current, solve
The DC side of isolated form modular system includes AC compounent problem, power loss is reduced, in the premise that control system is stable
Under, realize device energy efficiently utilizes and has saved manufacturing cost.
In order to solve the above-mentioned technical problem, the present invention is achieved by the following technical solutions: one kind being directed to isolated form MMC
The inhibition strategy of bridge arm out-of-balance current, comprising the following steps:
1) bridge arm any for isolated form MMC acquires bridge arm voltage, to isolated form MMC acquisition ac output current and directly
Upper and lower bridge arm electric current is flowed, bridge arm output voltage and bridge arm current are respectively obtained according to the mathematical model of isolated form MMC circuit；
2) initial value is distributed to each submodule of bridge arm and driving signal；
3) compare upper and lower bridge arm electric current industrial frequency AC component relationship by making the difference, show that the out-of-balance current for mutually including is big
It is small；The DC component relationship for comparing upper and lower bridge arm voltage by making the difference obtains the uneven DC voltage size for mutually including；
4) according to the value at each submodule current time, submodule current working status is analyzed, and defeated using bridge arm
Voltage is modified the voltage prediction value of each submodule out, obtains the driving control signal of submodule subsequent time.
Preferably, the step 1 includes the following steps: that following equation shows the V of each submodule (SB)dcL、VuiOr
VliAnd total end voltage V of each armsuOr VslBetween relationship, as shown by the equations
dui, dli(i=1 ..., n) is the equivalent modulation ratio of modules, kuiAnd kli(i=1 ..., n) is the change of each module
Depressor ratio, generally may be assumed that du=dui,dl=dli, k=kui=kli(i=1 ..., n)
Upper and lower bridge arm output voltage are as follows:
duAnd dlIt is necessary to meet following condition
Wherein HVDC Modulation index D can be set to identical with MMC 0.5, AC modulation index daAmplitude peak be
0.5, to ensure dU, lTotal value 0 and 1 between to meet the service condition of submodule.
Based on above formula it can be concluded that
Meanwhile acquiring DC bus current IdcHWith ac output current iac, obtain the upper and lower bridge arm current difference of bridge arm
Are as follows:
Wherein IdcHInclude AC compounent Ix。
Preferably, step 3) the following steps are included:
1) pass through bridge arm current IsuAnd Isl, obtain the practical out-of-balance current I of bridge armx；
2) closed-loop control is carried out to bridge arm out-of-balance current, obtains additional out-of-balance current modulation voltage, and then obtained pair
Answer duAnd dlAdjusted value.To realize that the AC compounent out-of-balance current to DC side inhibits.
Compared with prior art, the invention has the advantages that
1, the uneven band that the present invention includes for DC side of the solution isolated form MMC under alternating voltage unbalance voltage
The AC compounent come, it is suppressed that DC terminal AC compounent fluctuation.
2, it the present invention is based on instantaneous power theory analysis, proposes and devises a kind of based on the direct out-of-balance current that inhibits
Unbalance control device.
3, the isolated form MMC controller principle and uncomplicated designed by the present invention is suitable under balance and unbalance voltage
The case where, greatly improve system stability.
Detailed description of the invention
Fig. 1 is that the single-phase isolated form modularization based on High Frequency Link in the present invention cascades transformer configuration schematic diagram；
Fig. 2 is the output waveform figure of single stage type isolated form module of the invention；
Fig. 3 is that isolated form modular stages join the complete control block diagram of converter in the present invention；
Fig. 4 is the simulation waveform without balance control in the present invention；
Fig. 5 is in the present invention using the simulation waveform of balance control.
Specific embodiment
The embodiment of the present invention is described below in detail, examples of the embodiments are shown in the accompanying drawings.Below with reference to
The embodiment of attached drawing description is exemplary, it is intended to is used to explain the present invention, and is not considered as limiting the invention.
The inhibition strategy of out-of-balance current, each by detecting between a kind of bridge arm inhibiting isolated form modularization cascade converter
Bridge arm voltage, electric current go out bridge arm output electricity according to the Derivation of Mathematical Model of the single-phase bridge arm of isolated form Modular multilevel converter
Pressure and bridge arm current, are balanced control to each bridge arm voltage, and then the unbalanced current component between bridge arm is inhibited to play
The double effects of balance module voltage and the control of bridge arm out-of-balance current.
The present invention solves above-mentioned technical problem, and the technical scheme comprises the following steps:
1) upper bridge arm voltage, lower bridge arm electricity are made to the value of upper bridge arm voltage, lower bridge arm voltage by adjusting duty ratio control
Pressure is intended to target reference；
2) AC compounent of out-of-balance current is controlled by isolated form MMC out-of-balance current controller；
3) compare upper and lower bridge arm electric current industrial frequency AC component relationship by making the difference, show that the out-of-balance current for mutually including is big
It is small；The DC component relationship for comparing upper and lower bridge arm voltage by making the difference obtains the uneven DC voltage size for mutually including.
dui, dli(i=1 ..., n) is the equivalent modulation ratio of modules, kuiAnd kli(i=1 ..., n) is the change of each module
Depressor ratio, generally may be assumed that du=dui,dl=dli, k=kui=kli(i=1 ..., n).
Upper and lower bridge arm output voltage are as follows:
duAnd dlIt is necessary to meet following condition
Based on above formula it can be concluded that
Meanwhile acquiring DC bus current IdcHWith ac output current Iac, obtain the upper and lower bridge arm current of each bridge arm
It is respectively as follows:
Wherein IdcHInclude AC compounent Ix。
Step 3) the following steps are included:
1) pass through bridge arm current IsuAnd Isl, obtain the practical out-of-balance current I of bridge armx；
2) closed-loop control is carried out to bridge arm out-of-balance current, obtains additional out-of-balance current modulation voltage, and then obtained pair
Answer duAnd dlAdjusted value.To realize that the AC compounent out-of-balance current to DC side inhibits.
Step 4: according to the value at each submodule current time, submodule current working status being analyzed, and utilizes bridge arm
Output voltage is modified the voltage prediction value of each submodule, obtains the driving control signal of submodule subsequent time, in turn
It realizes and the out-of-balance current of DC side is inhibited.
Fig. 1, Fig. 2 are the object single stage type high-frequency isolation type modular multilevel transformation that this out-of-balance current inhibits strategy
Device, on high-tension side submodule terminal by controlled voltage source vuiOr vli(i=1 ..., n) is indicated, mixing AC and the DC tune of foundation
System ratio is shown below:
The instantaneous output power of the high pressure side of submodule consists of two parts: PHVACu(l)iAnd PHVDCu(l)i。
It is zero in traditional MMC, which means that the power of submodule DC side is equal to HV to HV exchange side and hands over
The power for flowing side exchanges side to submodule.Single-phase branch Neutron module general power fluctuation be transferred to public direct-current side,
And by common electrical vessel buffers, this is different from the MMC buffered by each capacitor of submodule.Bridge arm output voltage and bridge arm
The expression formula of electric current is as follows:
The AC compounent of out-of-balance current, i.e. bridge arm out-of-balance current, need to be suppressed to zero, to unbalanced current component
It directly controls；Designed controller is as follows:
The parameter error of high-frequency isolation transformer between different submodules can cause between stability problem, such as arm
Voltage unbalance and circulating current.However, the secondary-side voltage of all submodules is all based on phase compared with traditional MMC structure
Same VdcL, current manufacturing process can guarantee that submodule in reasonable range, is not needed in the voltage error in same arm
Submodule voltage balancing control.Although the voltage error between two arms will lead to arm Voltage unbalance, arm voltage is put down
Weighing apparatus can be controlled by additional auxiliary to realize, simpler than traditional MMC structure.
As shown in figure 3, entire control strategy includes two parts: balance control strategy and hybrid modulation stratgy.By bridge arm electricity
Flow IACAnd IAUInput quantity of the AC component as PR controller.The AC modulation ratio d of upper bridge armauEqual to AC modulation dacIt subtracts
PR controller daOutput, and the AC modulation of lower bridge arm ratio dauEqual to-dacSubtract da.When variable is more than 0, dauReduce, it is no
Then dauIncrease, dalVariation it is exactly the opposite.VdcuAnd VdclDC component between difference be PI controller input item.When
VdcuDC component be greater than VdclWhen, PI controls DdcHOutput valve be positive, otherwise DdcHIt is negative.DDUD is subtracted equal to DdcH, DDLDeng
In D plus DdcH.The hybrid modulation variable of upper and lower arms is DUAnd DL。
In order to verify the validity of boost voltage balance control, the simulation model of the structure is established.In upper arm, one
The transformer turn ratio of submodule is different from others.Fig. 4 and Fig. 5 respectively illustrates no auxiliary balance control and has auxiliary balance
The result of control.Obviously, as shown in figure 4, there are unbalanced voltage and circulating current between upper and lower arms, while VdcHIt is
Fluctuation.Fig. 5 shows the waveform when unbalanced construction under balance control.Assist control strategy can effectively counter-jib
Voltage reduces out-of-balance current.VDCHFluctuation be obviously reduced.
The result shows that control method proposed in this paper overcomes the disadvantage, out-of-balance current control inhibitory effect is significant, together
When restrained effectively the fluctuation of system active power.
Above is only a specific embodiment of the present invention, but technical characteristic of the invention is not limited thereto, Ren Heben
Within the field of the present invention, made changes or modifications all cover within the scope of the patent of the present invention the technical staff in field.
Claims (3)
1. a kind of inhibition strategy for isolated form MMC bridge arm out-of-balance current, it is characterised in that: the following steps are included:
1) bridge arm any for isolated form MMC acquires bridge arm voltage, acquires on ac output current and direct current to isolated form MMC
Lower bridge arm electric current respectively obtains bridge arm output voltage and bridge arm current according to the mathematical model of isolated form MMC circuit；
2) initial value is distributed to each submodule of bridge arm and driving signal；
3) compare upper and lower bridge arm electric current industrial frequency AC component relationship by making the difference, obtain the out-of-balance current size for mutually including；
The DC component relationship for comparing upper and lower bridge arm voltage by making the difference obtains the uneven DC voltage size for mutually including；
4) according to the value at each submodule current time, submodule current working status is analyzed, and exports electricity using bridge arm
Pressure is modified the voltage prediction value of each submodule, obtains the driving control signal of submodule subsequent time.
2. a kind of inhibition strategy for isolated form MMC bridge arm out-of-balance current as described in claim 1, it is characterised in that:
The step 1 includes the following steps: that following equation shows the V of each submoduledcL、VuiOr VliAnd total end of each arm
Voltage VsuOr VslBetween relationship, as shown by the equations
dui, dli(i=1 ..., n) is the equivalent modulation ratio of modules, kuiAnd kli(i=1 ..., n) is the transformer of each module
Than generally may be assumed that du=dui,dl=dli, k=kui=kli(i=1 ..., n)
Upper and lower bridge arm output voltage are as follows:
duAnd dlIt is necessary to meet following condition
Wherein HVDC Modulation index D can be set to identical with MMC 0.5, AC modulation index daAmplitude peak be 0.5, with
Ensure dU, lTotal value 0 and 1 between to meet the service condition of submodule；
Based on above formula it can be concluded that
Meanwhile acquiring DC bus current IdcHWith ac output current iac, the upper and lower bridge arm current for obtaining bridge arm is respectively as follows:
Wherein IdcHInclude AC compounent Ix。
3. a kind of inhibition strategy for isolated form MMC bridge arm out-of-balance current as claimed in claim 2, it is characterised in that:
Step 3) the following steps are included:
1) pass through bridge arm current IsuAnd Isl, obtain the practical out-of-balance current I of bridge armx；
2) closed-loop control is carried out to bridge arm out-of-balance current, obtains additional out-of-balance current modulation voltage, and then obtain corresponding duWith
dlAdjusted value, the AC compounent out-of-balance current of DC side is inhibited to realize.
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| CN201811623231.2A CN110061644B (en) | 2018-12-28 | 2018-12-28 | Suppression strategy for unbalanced current of isolated MMC bridge arm |
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| CN201811623231.2A CN110061644B (en) | 2018-12-28 | 2018-12-28 | Suppression strategy for unbalanced current of isolated MMC bridge arm |
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| CN110061644B CN110061644B (en) | 2020-09-11 |
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Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104811067A (en) * | 2015-04-30 | 2015-07-29 | 山东大学 | PR (proportional resonant) controller-based NMC-HVDC (modular multilevel converter-high voltage direct current) circulating current suppression method |
| CN107863895A (en) * | 2017-09-29 | 2018-03-30 | 广东电网有限责任公司电力调度控制中心 | The balance method of upper and lower bridge arm capacitive energy during a kind of bridge arm asymmetry |
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- 2018-12-28 CN CN201811623231.2A patent/CN110061644B/en active Active
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104811067A (en) * | 2015-04-30 | 2015-07-29 | 山东大学 | PR (proportional resonant) controller-based NMC-HVDC (modular multilevel converter-high voltage direct current) circulating current suppression method |
| CN107863895A (en) * | 2017-09-29 | 2018-03-30 | 广东电网有限责任公司电力调度控制中心 | The balance method of upper and lower bridge arm capacitive energy during a kind of bridge arm asymmetry |
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