CN109921665A - A kind of MMC capacitance voltage balance policy based on average voltage - Google Patents
A kind of MMC capacitance voltage balance policy based on average voltage Download PDFInfo
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- CN109921665A CN109921665A CN201910276434.7A CN201910276434A CN109921665A CN 109921665 A CN109921665 A CN 109921665A CN 201910276434 A CN201910276434 A CN 201910276434A CN 109921665 A CN109921665 A CN 109921665A
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Abstract
The invention discloses a kind of MMC capacitance voltage balance policy based on average voltage, when putting into submodule, the difference between the current switching state of submodule and capacitance voltage and average value is considered simultaneously, and submodule is divided into set A and set B, submodule in switching in preferential switching set A, to reduce the switching frequency of submodule under the premise of guaranteeing that voltage fluctuation of capacitor is lesser, submodule capacitor voltage Balance route is completed.
Description
Technical field
The invention belongs to power electronic system technical fields, and in particular to a kind of MMC capacitor electricity based on average voltage
Press balance policy.
Background technique
With flourishing for power electronic technique, it is based on modularization multi-level converter (Modular Multilevel
Converter, MMC) D.C. high voltage transmission (HighVoltage Direct Current, HVDC) technology be considered most suitable
Close one of the technology for carrying out mesohigh transmission of electricity.It is compared with other voltage source converter topologys, modularization multi-level converter tool
There is significant advantage；Due to the form using basic operation sub-module cascade, which avoids a large amount of switching devices and directly connects,
The problems such as there is no consistent triggerings, reduces the manufacture difficulty of equipment；The topology also possesses lower switching frequency simultaneously and changes
Device loss is flowed, there is very strong economy, therefore the topology is applied to rapidly new-energy grid-connected in recent years, offshore wind farm is sent out
Etc. occasions.
In recent years, flexible DC transmission technology large capacity overhead line occasion be faced with huge opportunity and it is wide before
Scape.From the perspective of Energy distribution and electric power flow direction, there is the primary demand of extensive high efficiency transmission of electricity, country in China always
" 13 " ENERGY PLANNING explicitly points out extra-high voltage large capacity remote conveying power technology development to be actively pushed forward；From electric network composition
It sees, following as the increase of transregional flow of power scale and a large amount of DC engineerings put into operation, " alternating current-direct current Power System Interconnection, load center are straight
Fall point is intensive " will become China's power grid architecture grown form, and flexible direct current technology be not present commutation failure the defects of, can
The effectively resolution more feed-in problems of Traditional DC；In terms of economic benefit, using overhead line replacement cables system of laying, transportable appearance
It measures big and cheap；Develop from technology, with the proposition and application of modular concept, converter bridge arm is with power cell grade
The structure type of connection forms, and System Expansion pressurization is very convenient.MMC inverter in the soft straight engineering of high voltage is usually using more
Bridge arm submodule, therefore also to the Pressure and Control of inverter submodule capacitor voltage, more stringent requirements are proposed simultaneously.
The submodule capacitor voltage Balance route of inverter is always the emphasis paid close attention in Practical Project, typical three-phase
The system structure of MMC inverter as shown in Figure 1, inverter includes 6 bridge arms altogether, wherein every bridge arm include N number of submodule with
An and bridge arm reactance.Enable bridge arm current positive direction as shown in fig. 1, i.e., bridge arm current is positive, and puts into the submodule electricity of state
Appearance is electrically charged, and when bridge arm current is negative, the submodule for putting into state is discharged.Each submodule capacitor is independent mutually, and submodule
The charge and discharge time and capacitor difference will make its capacitance voltage occur it is unbalanced, influence the normal operation of inverter entirety.
Traditional capacitance voltage Balance route strategy are as follows: (1) detect the capacitor electricity of bridge arm current direction and each submodule
It presses and is ranked up；(2) it if bridge arm current charges to sub- module capacitance, is put into according to the sequence of capacitance voltage from low to high
The submodule of corresponding number；If bridge arm current discharges to sub- module capacitance, thrown according to the sequence of capacitance voltage from high to low
Enter corresponding submodule.But since it does not account for the state of submodule, sort algorithm is unconditionally applied to each control
Period results in the unnecessary switching repeatedly of submodule, increases the switching frequency of device and the running wastage of converter station, thus
Reduce the operational efficiency of modularization multi-level converter.Therefore need to propose a kind of suitable capacitance voltage balance policy, to the greatest extent
Amount reduces the switching frequency of MMC operational process Neutron module, reduces overall switching frequency, while can guarantee submodule capacitor again
Certain equilibrium is kept between voltage.
Summary of the invention
In view of above-mentioned, the present invention provides a kind of MMC capacitance voltage balance policy based on average voltage can protected
Under the premise of card voltage fluctuation of capacitor is lesser, the switching frequency of submodule is reduced, completes submodule capacitor voltage Balance route.
A kind of MMC capacitance voltage balance policy based on average voltage, includes the following steps:
(1) for any bridge arm in MMC, the submodule capacitor voltage average value u of the bridge arm is calculatedcave；
(2) according to ucaveCalculate the submodule capacitor voltage upper limit value u of the bridge armmaxWith lower limit value umin；
(3) initially the submodule for being in investment state in the current time bridge arm is put into set A, is in excision state
Submodule be put into set B；
(4) submodule in set A and B is adjusted according to bridge arm current and submodule capacitor voltage size and is moved
It moves；
(5) the submodule quantity N in statistics set AA, calculated by top level control algorithm (such as nearest level approximatioss)
Obtain the submodule quantity N that the subsequent time bridge arm need to be put intoon, and calculate the difference N of the twodiff=Non-NA；
(6) according to bridge arm current and NdiffSwitching control is carried out to the submodule in set A and B.
Further, submodule capacitor voltage average value u is calculated by the following formula in the step (1)cave；
Wherein: uc,iFor the capacitance voltage of i-th of submodule in the bridge arm, N is the submodule quantity that bridge arm includes.
Further, submodule capacitor voltage upper limit value u is calculated by the following formula in the step (2)maxAnd lower limit value
umin；
Wherein: k is given capacitance voltage equalizing coefficient (the generally value between 0.01~0.05), UcnFor submodule electricity
Hold voltage rating.
Further, the capacitance voltage equalizing coefficient k is by being artificially adjusted, when needing reduces switching frequency,
Then enhancement coefficient k；Conversely, when need to reduce capacitance voltage is unbalanced spend when, then reduction ratio k.
Further, the unbalanced degree of the capacitance voltage is positively correlated with voltage fluctuation of capacitor rate Z, the voltage fluctuation of capacitor
The expression formula of rate Z is as follows:
Wherein: Δ UiFor i-th of submodule in bridge arm in steady state operation capacitance voltage maxima and minima it
Between difference, UcnFor submodule capacitor voltage rated value, i is natural number and 1≤i≤N, N are the submodule quantity that bridge arm includes.
Further, the capacitance voltage rated value UcnExpression formula it is as follows:
Wherein: UdcnFor the DC voltage rated value of MMC, N is the submodule quantity that bridge arm includes.
Further, the concrete methods of realizing of the step (4) are as follows: enable bridge arm current iarmPositive direction is high-voltage end stream
To low-pressure end, if iarmCapacitance voltage in set A is greater than u by > 0maxSubmodule be moved in set B, by capacitor in set B
Voltage is less than uminSubmodule be moved in set A；If iarm≤ 0, capacitance voltage in set B is greater than umaxSubmodule move
It moves in set A, capacitance voltage in set A is less than uminSubmodule be moved in set B.
Further, the concrete methods of realizing of the step (6) are as follows: in NdiffIn the case of > 0, if iarm> 0, by set A
In all submodules investment, while the preceding N that capacitance voltage in set B is minimumdiffA submodule investment, remaining submodule are complete
Portion's excision；If iarm≤ 0, all submodules in set A are put into, while by the highest preceding N of capacitance voltage in set BdiffIt is a
Submodule investment, remaining submodule complete resection；
In NdiffIn the case of≤0, if iarm> 0 cuts off all submodules in set B, while by capacitor in set A
The minimum preceding N of voltageonA submodule investment, remaining submodule complete resection；If iarm≤ 0, by all submodules in set B
Excision, while by the highest preceding N of capacitance voltage in set AonA submodule investment, remaining submodule complete resection.
Compared with prior art, the present invention has following advantageous effects:
(1) present invention can significantly reduce submodule under the premise of unobvious increase submodule capacitor voltage stability bandwidth
Switching frequency and MMC running wastage.
(2) present invention can adjust power electronic devices switching frequency and son by thinking to change capacitance voltage equalizing coefficient
Relationship between module capacitance voltage fluctuation.
Detailed description of the invention
Fig. 1 is the structural schematic diagram of modularization multi-level converter.
Fig. 2 is the flow diagram of capacitance voltage balance policy of the present invention.
Bridge arm submodule in modularization multi-level converter A phase in the case that Fig. 3 is capacitance voltage equalizing coefficient k=0.02
The simulation waveform of capacitance voltage.
Specific embodiment
In order to more specifically describe the present invention, with reference to the accompanying drawing and specific embodiment is to technical solution of the present invention
And its relative theory is described in detail.
Ensemble average value of the control strategy of the present invention based on submodule capacitor voltages all in bridge arm, only in submodule capacitor
The difference of voltage and the value changes the switching state of submodule when being more than limit value, to reduce unnecessary switching operation, reduces
The switching frequency of switching device, reduces the running wastage of MMC.
The present invention is based on the MMC capacitance voltage balance policies of average voltage, for any one in six bridge arms of MMC
The detailed process of bridge arm, the capacitance voltage Balance route strategy is as shown in Figure 2:
(1) the bridge arm submodule capacitor voltage average value is calculated using following formula.
Wherein: uc,iFor the capacitance voltage of i-th of submodule in the bridge arm, N is the submodule quantity that each bridge arm includes.
(2) upper limit u of submodule capacitor voltage at this time is calculatedmaxWith lower limit umin。
Wherein: k be capacitance voltage equalizing coefficient, generally can between 0.01~0.05 value；UcnIt is specified for capacitance voltage
Value, is given by, wherein UdcnFor MMC DC voltage rated value.
Capacitance voltage equalizing coefficient k, when needing reduces switching frequency, can increase k taking human as being adjusted；Instead
It, when need to reduce capacitance voltage is unbalanced spend when, can reduce k.It can use voltage fluctuation of capacitor rate Z and carry out constant capacitor electricity
The unbalanced degree of pressure, expression formula are as follows:
Wherein: Δ UiFor i-th of submodule in bridge arm in steady state operation capacitance voltage maxima and minima it
Between difference.
(3) submodules in investment state all at this time are put into set A, all excision state submodules are put into set
B。
(4) bridge arm current i is enabledarmDirection is identical with Fig. 1.Work as iarmWhen greater than 0, all capacitance voltages are greater than umax's
Submodule is moved to set B, and all capacitance voltages are less than uminSubmodule be moved to set A；Work as iarmIt, will when less than or equal to 0
All capacitance voltages are greater than umaxSubmodule be moved to set A, all capacitance voltages are less than uminSubmodule be moved to set
B。
(5) quantity of the submodule in set of computations A is NA, the son for needing to put at this time that upper controller is calculated
Module number is Non, the departure N of the two is calculated with following formuladiff。
Ndiff=Non-NA
(6) work as NdiffWhen greater than 0: if iarmGreater than 0, the submodule of all set A is put into, and in the submodule of set B
The minimum N of middle investment voltagediffA submodule, by remaining submodule complete resection；If iarmLess than or equal to 0, by all set
The submodule of A is put into, and the highest N of voltage is put into the submodule of set BdiffA submodule is complete by remaining submodule
Portion's excision.
Work as NdiffWhen less than or equal to 0: if iarmGreater than 0, the minimum N of voltage is put into the submodule of set AonA submodule
Block, by remaining submodule complete resection；If iarmLess than or equal to 0, the highest N of voltage is put into the submodule of set AonIt is a
Submodule, by remaining submodule complete resection.
(7) the MMC capacitance voltage Balance route based on average voltage is so far completed.
As shown in Figure 1, modularization multi-level converter uses six bridge arm structure of three-phase, each bridge arm is by several half-bridges
Submodule and a bridge arm reactor are composed in series, for the three-phase alternating current of AC network to be converted to direct current.Half-bridge submodule
Block output voltage exists just with 0 two kinds of level, and bridge arm reactor is able to suppress the bridge arm change of current, inhibition is played in DC Line Fault
Fault current rises, the effect of the devices such as protection IGBT.Half-bridge submodule is by two IGBT pipe T1~T2 and a capacitor C structure
At；Wherein, the output end of IGBT pipe T1 is connected with the input terminal of IGBT pipe T2 and constitutes one end of half-bridge submodule, IGBT pipe T1
Input terminal be connected with one end of capacitor C, the output end of IGBT pipe T2 is connected with the other end of capacitor C and constitutes half-bridge submodule
The other end.
It is as shown in table 1 using the modularization multi-level converter parameter in present embodiment in conjunction with Fig. 1.
Table 1
(1) the capacitance voltage equalizing coefficient k that sets is taken wherein to represent when k=0 and use traditional electricity as 0 to 0.05 respectively
Hold electric voltage equalization strategy.According to simulation result, the submodule of bridge arm is averaged switching frequency and capacitor in the A phase under different settings
Voltage fluctuation rate is as shown in table 2.It can be seen that using after capacitance voltage balance policy proposed by the invention, in capacitance voltage wave
In the case that dynamic rate does not significantly increase, the submodule switching frequency that is averaged has obtained significant reduction.Meanwhile by changing capacitor
Electric voltage equalization coefficient k, the relationship between adjustable switching frequency and voltage fluctuation of capacitor rate.
(2) when the capacitance voltage equalizing coefficient k set is 0.02,20 sub- module capacitances electricity of bridge arm in A phase are obtained
Simulation waveform is pressed as shown in figure 3, switching frequency is reduced to 183Hz from 1981Hz, and maximum electric compared to corresponding conventional method
Hold voltage fluctuation rate and only rises to 9.8% from 8.3%.
Table 2
The above-mentioned description to embodiment is for that can understand and apply the invention convenient for those skilled in the art.
Person skilled in the art obviously easily can make various modifications to above-described embodiment, and described herein general
Principle is applied in other embodiments without having to go through creative labor.Therefore, the present invention is not limited to the above embodiments, ability
Field technique personnel announcement according to the present invention, the improvement made for the present invention and modification all should be in protection scope of the present invention
Within.
Claims (8)
1. a kind of MMC capacitance voltage balance policy based on average voltage, includes the following steps:
(1) for any bridge arm in MMC, the submodule capacitor voltage average value u of the bridge arm is calculatedcave；
(2) according to ucaveCalculate the submodule capacitor voltage upper limit value u of the bridge armmaxWith lower limit value umin；
(3) initially the submodule that investment state is in the current time bridge arm is put into set A, the son in excision state
Module is put into set B；
(4) migration is adjusted to the submodule in set A and B according to bridge arm current and submodule capacitor voltage size；
(5) the submodule quantity N in statistics set AA, calculating acquisition subsequent time bridge arm by top level control algorithm needs to put into
Submodule quantity Non, and calculate the difference N of the twodiff=Non-NA；
(6) according to bridge arm current and NdiffSwitching control is carried out to the submodule in set A and B.
2. MMC capacitance voltage balance policy according to claim 1, it is characterised in that: by following in the step (1)
Formula computational submodule capacitance voltage average value ucave；
Wherein: uc,iFor the capacitance voltage of i-th of submodule in the bridge arm, N is the submodule quantity that bridge arm includes.
3. MMC capacitance voltage balance policy according to claim 1, it is characterised in that: by following in the step (2)
Formula computational submodule capacitance voltage upper limit value umaxWith lower limit value umin；
Wherein: k is given capacitance voltage equalizing coefficient, UcnFor submodule capacitor voltage rated value.
4. MMC capacitance voltage balance policy according to claim 3, it is characterised in that: the capacitance voltage equalizing coefficient k
By being artificially adjusted, when needing reduces switching frequency, then enhancement coefficient k；Conversely, when needing to reduce capacitance voltage unevenness
When weighing apparatus is spent, then reduction ratio k.
5. MMC capacitance voltage balance policy according to claim 4, it is characterised in that: the unbalanced degree of capacitance voltage
It is positively correlated with voltage fluctuation of capacitor rate Z, the expression formula of the voltage fluctuation of capacitor rate Z is as follows:
Wherein: Δ UiIt is i-th of submodule in bridge arm in the difference in steady state operation between capacitance voltage maxima and minima
Value, UcnFor submodule capacitor voltage rated value, i is natural number and 1≤i≤N, N are the submodule quantity that bridge arm includes.
6. the MMC capacitance voltage balance policy according to claim 3 or 5, it is characterised in that: the capacitance voltage rated value
UcnExpression formula it is as follows:
Wherein: UdcnFor the DC voltage rated value of MMC, N is the submodule quantity that bridge arm includes.
7. MMC capacitance voltage balance policy according to claim 1, it is characterised in that: the specific implementation of the step (4)
Method are as follows: enable bridge arm current iarmPositive direction is that high-voltage end flows to low-pressure end, if iarmCapacitance voltage in set A is greater than by > 0
umaxSubmodule be moved in set B, by capacitance voltage in set B be less than uminSubmodule be moved in set A；If iarm
≤ 0, capacitance voltage in set B is greater than umaxSubmodule be moved in set A, by capacitance voltage in set A be less than umin's
Submodule is moved in set B.
8. MMC capacitance voltage balance policy according to claim 3, it is characterised in that: the specific implementation of the step (6)
Method are as follows: in NdiffIn the case of > 0, if iarm> 0 puts into all submodules in set A, while capacitor in set B is electric
Press minimum preceding NdiffA submodule investment, remaining submodule complete resection；If iarm≤ 0, by all submodules in set A
Investment, while by the highest preceding N of capacitance voltage in set BdiffA submodule investment, remaining submodule complete resection；
In NdiffIn the case of≤0, if iarm> 0 cuts off all submodules in set B, while most by capacitance voltage in set A
Low preceding NonA submodule investment, remaining submodule complete resection；If iarm≤ 0, all submodules in set B are cut off, together
When by the highest preceding N of capacitance voltage in set AonA submodule investment, remaining submodule complete resection.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109274285A (en) * | 2018-10-24 | 2019-01-25 | 南方电网科学研究院有限责任公司 | A kind of capacitor voltage balance method of mixed type module multilevel converter |
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| CN103956925A (en) * | 2014-04-28 | 2014-07-30 | 浙江大学 | Hybrid MMC capacitor voltage balance control method |
| CN103986308A (en) * | 2014-05-04 | 2014-08-13 | 清华大学 | Dynamic voltage-sharing circuit of direct-current capacitor of multilevel converter |
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2019
- 2019-04-08 CN CN201910276434.7A patent/CN109921665A/en active Pending
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103956925A (en) * | 2014-04-28 | 2014-07-30 | 浙江大学 | Hybrid MMC capacitor voltage balance control method |
| CN103986308A (en) * | 2014-05-04 | 2014-08-13 | 清华大学 | Dynamic voltage-sharing circuit of direct-current capacitor of multilevel converter |
Non-Patent Citations (1)
| Title |
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| 陆羿等: "基于电容电压波动的模块化多电平换流器电容电压均衡策略", 《基于电容电压波动的模块化多电平换流器电容电压均衡策略》 * |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109274285A (en) * | 2018-10-24 | 2019-01-25 | 南方电网科学研究院有限责任公司 | A kind of capacitor voltage balance method of mixed type module multilevel converter |
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