CN108233408B - A kind of MMC-MTDC system self-adaption droop control method - Google Patents
A kind of MMC-MTDC system self-adaption droop control method Download PDFInfo
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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
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract
The invention discloses a kind of MMC-MTDC system self-adaption droop control methods, it is characterized in that, introduce power impact factor, line impedance impact factor, using the active power of converter station exchange side PPC point input as input quantity, using sagging coefficient as output quantity, it adjusts sagging coefficient in real time under the action of impact factor, makes P-V characteristic curve under the premise of not depending on high-speed communication to optimal power allocation direction approximation.Advantageous effects of the invention: the main application of the present invention is the MMC-MTDC system applied to extensive offshore grid-connected wind farm.Power impact factor, line impedance impact factor are introduced, sagging coefficient is adjusted in real time under the action of impact factor, makes P-V characteristic curve to optimal power allocation direction approximation.The present invention, which has, does not depend on high-speed communication, and DC voltage deviation is small, the low advantage of line loss.
Description
Technical field
The present invention relates to a kind of MMC-MTDC system self-adaption droop control methods, belong to electrical engineering technical field.
Background technique
In recent years, due to extensive renewable energy is grid-connected, asynchronous Power System Interconnection, the remote electric energy transmission of large capacity need
It asks, the Multi-end flexible direct current transmission based on voltage source converter receives more and more attention.It is defeated compared to traditional both ends direct current
Electricity, Multi-end flexible direct current transmission have preferable flexibility, economy, stability, are to solve clean energy resource " on not ", " send
Do not go out ", one of the effective means of " hardly possible consumption " Three Difficult Issues.Modularization multi-level converter is a kind of novel voltage source converter
Device has many advantages, such as that DC voltage polarity is constant when low voltage class height, harmonic content, tide turns, flexible for multiterminal straight
Stream transmission of electricity develops to large capacity, remote direction to be of great significance.Therefore the present invention is directed to MMC-MTDC system.
MTDC system wiring mode is broadly divided into three classes: parallel connection type, tandem type, mixed type.Match from adjustable range, insulation
Close, extend flexibility etc. considers that parallel connection type MTDC topology has more technical advantage.Parallel connection type MTDC system coordination control
Core is DC voltage control, and the minimum requirements of safe operation is to meet N-1 rule.
The sagging control of tradition realizes multiple station shared DC voltage controls using the P-V Slope relationship of each converter station
Purpose, essence is that the adjusting of active power is participated in using DC voltage static difference as cost.The sagging control of tradition is without high speed
Voltage overshoot is small when communication and active power step.But the sagging control of tradition, using fixed sagging coefficient, there are direct currents
The disadvantages of quality of voltage is low, power distribution is not independent, flexibility, economy are poor.
Summary of the invention
To solve the deficiencies in the prior art, the purpose of the present invention is to provide a kind of sagging controls of MMC-MTDC system self-adaption
Method processed, to solve the problems, such as that the sagging control quality of voltage of tradition is low, power distribution is not independent.
In order to achieve the above objectives, the present invention adopts the following technical scheme that:
A kind of MMC-MTDC system self-adaption droop control method, characterized in that introduce power impact factor, line impedance
Impact factor, using the active power of converter station exchange side PPC point input as input quantity, using sagging coefficient as output quantity,
Sagging coefficient is adjusted under the action of impact factor in real time, makes P-V characteristic curve under the premise of not depending on high-speed communication to optimal
Power distribution direction approximation.
A kind of MMC-MTDC system self-adaption droop control method above-mentioned, characterized in that include the following steps:
Step 1) is distributed according to marine wind electric field position, land AC network tie point, submarine cable determines MTDC system
Parameter setting, complete fixed sagging coefficient kdroopi_fixedWith line impedance factor εiAdjusting work；
Step 2) measures local electrical quantities, i.e. converter station i exchanges the active-power P that PCC point in side flows intoi, which is sent
To local controller；
Step 3) local controller according toPiNIt is the rated active power of converter station i, calculates
Instantaneous sagging coefficient kdroopiValue, as new instantaneous sagging coefficient kdroopi_fixed, controller is using new instantaneous sagging system
Number participates in MTDC system coordination control, forms new sagging curve.
A kind of MMC-MTDC system self-adaption droop control method above-mentioned, characterized in that sagging system in the step 1)
Number kdroopi_fixedSetting method is as follows:
Note is a using the total m of converter station of sagging control, to realize each converter station while fully loaded purpose under extreme case,
kdroopi_fixedMeet: kdroop(n+1)_fixed:kdroop(n+2)_fixed:…:kdroop(n+m)_fixed=P(n+1)N:P(n+2)N:…:P(n+m)N。
A kind of MMC-MTDC system self-adaption droop control method above-mentioned, characterized in that step 1) the middle line roadlock
Anti- impact factor εiSetting method is as follows:
For i-th of converter station, power accounting a when optimal power allocation is introducedi%, according to when m output node most
Excellent power distribution condition are as follows:Know εiPower accounting b when=0i%,
It can be obtained according to P-V curve:
Introduce the voltage deviation △ U of underload pointlow_load, ε can be obtainediSetting valve:
Advantageous effects of the invention: the main application of the present invention is to be applied to extensive offshore grid-connected wind farm
MMC-MTDC system.Power impact factor, line impedance impact factor are introduced, under adjusting in real time under the action of impact factor
Hang down coefficient, makes P-V characteristic curve to optimal power allocation direction approximation.The present invention, which has, does not depend on high-speed communication, DC voltage
Deviation is small, the low advantage of line loss.
Detailed description of the invention
Fig. 1 is the control block diagram of adaptive droop control method of the invention；
Fig. 2 is a kind of MTDC system topological of typical connection marine wind electric field of the invention；
Fig. 3 is the MTDC system of two output nodes；
Fig. 4 (a) is -1 < εiGSCi P-V characteristic curve when < 0, is (b) εiGSCi P-V characteristic curve when > 0；
Fig. 5 is using line loss schematic diagram when adaptive droop control method of the invention；
Fig. 6 is a four end MMC-MTDC system test platform schematic diagrames；
Fig. 7 is GSC3P-V characteristic curve (ε in the embodiment of the present invention3=1.88)；
Fig. 8 is GSC4P-V characteristic curve (ε in the embodiment of the present invention4=-0.53)；
Fig. 9 is to be responded in the embodiment of the present invention using GSC3 DC voltage when Different Strategies；
Figure 10 is Approximation effect schematic diagram in the embodiment of the present invention；
Active power wave simulation result when Figure 11 (a) is steady-state operation in the embodiment of the present invention；
DC voltage waveform simulation result when Figure 11 (b) is steady-state operation in the embodiment of the present invention；
GSC when Figure 11 (c) is steady-state operation in the embodiment of the present invention3Bridge arm submodule capacitor voltage emulation knot in A phase
Fruit；
GSC when Figure 11 (d) is steady-state operation in the embodiment of the present invention3AC current waveform simulation result；
Active power wave simulation result when Figure 12 (a) is power swing in the embodiment of the present invention；
Active power waveform (ε when Figure 12 (b) is power swing in the embodiment of the present invention3=ε4=0) simulation result；
Approximation effect simulation result when Figure 12 (c) is power swing in the embodiment of the present invention；
Figure 13 (a) is active power wave simulation result when N-1 is run in the embodiment of the present invention；
Figure 13 (b) is GSC when N-1 is run in the embodiment of the present invention4DC voltage Udc4Simulation result；
Figure 13 (c) is GSC when N-1 is run in the embodiment of the present invention3Alternating current simulation result；
Figure 13 (d) is GSC when N-1 is run in the embodiment of the present invention4Alternating current simulation result.
Specific embodiment
The invention will be further described below in conjunction with the accompanying drawings.Following embodiment is only used for clearly illustrating the present invention
Technical solution, and not intended to limit the protection scope of the present invention.
PI refers to pi regulator in Fig. 1, is used for DAZ gene designated value, is widely used in field of power electronics.
This method includes the following steps:
Step 1: being determined according to factors such as marine wind electric field position, land AC network tie point, submarine cable distributions
MTDC system design parameter completes fixed sagging coefficient kdroopi_fixedWith line impedance factor εiAdjusting work.
Step 2: measurement local electrical quantities, i.e. converter station i exchange the active-power P that PCC point in side flows intoi, which is sent
To local controller.
Step 3: local controller according toPiNIt is the rated active power of converter station i, calculates
Instantaneous sagging coefficient kdroopiValue, as new instantaneous sagging coefficient kdroopi_fixed, controller is using new instantaneous sagging system
Number participates in MTDC system coordination control, forms new sagging curve.
Further, using the converter station of adaptive droop control method, P-V curve representation formula such as (1).In formula, Udci、Udci *For the DC voltage actual value of converter station i and reference
Value, Udci *=1p.u., 0.95p.u. < Udci<1.05p.u.；Pi、Pi *For the active power actual value and reference value of converter station i,
Pi *=0p.u., -1p.u. < Pi<0p.u.；kdroopi_fixedFor the sagging coefficient of fixation of converter station i, kdroopi_fixed> 0, p.u.
It is the unit of per unit value, electrical subject usually uses in theory analysis.
By line impedance factor εi=0 curve is set as with reference to sagging curve.
With reference to the power impact factor ξ of sagging curvei0It indicates, active power Pi0It indicates.Its P-V curve representation formula
Compared to reference sagging curve, as -1 < εi< 0, | Pi|>|Pi0|, i-th of converter station GSCiUndertake more power point
Match.Work as εi> 0, | Pi|<|Pi0|, GSCiUndertake less power distribution.
Different εiIt will lead to GSCiP-V characteristic curve occur in various degree, the offsets of different directions.By reasonable
Setting principle, the P-V characteristic curve after making offset are realized to optimal power allocation direction approximation and are not being depended on high-speed communication
Under the premise of optimize line loss purpose.
By the adaptive droop control method and traditional droop control method comparison in the present invention.
Using the converter station of traditional droop control method, P-V curve representation formula such as formula (3).
Adaptive sagging control voltage deviation is set as △ U1, the sagging control voltage deviation of tradition is set as △ U2, then
By Pi≤ 0, kdroopi_fixed> 0,0≤ξi≤ 1, therefore △ U1≤△U2。
Therefore the MTDC system of the method for the present invention is used to have the advantages that voltage deviation is small.
A kind of MTDC system topological of typical connection marine wind electric field involved in this embodiment is as shown in Fig. 2: n
The converter station (WFC) of a connection marine wind electric field, the electric energy that wind power plant issues is rectified to DC network；PCC1、PCC2It refers both to straight
Flow points of common connection, PCC1Locate electric energy through submarine cable l0It is delivered to PCC2；The converter station (GSC) of m connection AC network, will
From PCC2The electric energy inversion of distribution networks.MTDC system includes n input node, m output node, and design parameter is usually by sea
Windward electric field location, land AC network tie point, submarine cable distribution determine.
In general, the converter station of connection marine wind electric field is using power control or determines alternating voltage control, AC network is connected
Converter station using the adaptive sagging control strategy of the present invention.
The present invention has the advantages that the low concept for being based primarily upon optimal power allocation of line loss.Power distribution pertains only to adopt
With the output node of sagging control.
Optimal power allocation condition is proved by taking the MTDC system of two output nodes as an example.By Fig. 3, formula (5), formula can be obtained
(6)。
PPCC2=Ploss+P3+P4(6) in formula, PlossRefer to PCC2To GSC3、GSC4Line loss, R3Refer to PCC2Point arrives GSC3
Cable l3Equivalent impedance (branch impedance is reduced to resistance), R4Refer to PCC2Point arrives GSC4Cable l4Equivalent impedance (branch impedance
It is reduced to resistance).
Ignore Udc3、Udc4P in deviation and formula (6)lossInfluence, joint type (5), formula (6).
PPCC2、Udc3Under the premise of certain, formula (7) is one about P3Quadratic equation with one unknown.By quadratic equation with one unknown
Characteristic it is found that two output nodes optimal power allocation condition such as formula (8).
According to existing conclusion, optimal power allocation condition such as formula (9) when m output node.
In formula, Rn+1、Rn+2···、Rn+mRefer to PCC2Point arrives the equivalent impedance (branch impedance of corresponding receiving end converter station cable
It is reduced to resistance).
The factor for influencing the loss of MTDC system line includes two aspects: DC voltage, power distribution.DC voltage influences
The whole line loss of DC network, DC voltage is higher, and whole line loss is lower.But DC voltage is excessively high, and main equipment insulate in system
Nargin can reduce, and main equipment may damage.Compared to reduce line loss, DC voltage quality be MTDC System Priority consider because
Element.Power distribution then influences PCC2To the line loss of GSC.Power distribution is closer to optimal power allocation, PCC2To the line of GSC
Path loss consumption is lower.Therefore, the optimal power allocation condition of formula (9) is of great significance for reducing MTDC system line loss.
Present invention introduces line impedance impact factor εi, make converter station P-V characteristic curve that different degrees of, different directions occur
Offset.By reasonable setting principle, make the P-V characteristic curve after deviating to optimal power allocation direction approximation, Jin Ershi
Optimize the purpose of line loss under the premise of not depending on high-speed communication now.Using the adaptive sagging control strategy change of current of the invention
The P-V characteristic curve such as Fig. 4 to stand.
Work as Udci0=Udci, joint type (1), (2) have
As -1 < εi< 0, | Pi|>|Pi0|, GSCiMore power distributions are undertaken, as shown in Fig. 4 (a)；Work as εi> 0, | Pi|<
|Pi0|, GSCiLess power distribution is undertaken, as shown in Fig. 4 (b).In addition, need to particularly point out: determining active power curves is εi
=-1 special case；The sagging control of tradition is εiThe special case of=∞.
The present invention relates to the adjusting of two parameters, fixed sagging coefficient kdroopi_fixed, line impedance impact factor εi。
Fixed sagging coefficient kdroopi_fixedSetting method is as follows:
By Fig. 2 MTDC system topological it is found that the total m of GSC using sagging control is a.To prevent single converter station overload and shadow
The phenomenon that ringing whole system operation, need to rationally be arranged kdroopi_fixedValue, realize that each converter station is fully loaded simultaneously under extreme case
Purpose.To reach the purpose, only formula (1) need to be allowed to meet Udci=Udcimax, Pi=PiN?.
Under normal conditions, m GSC possesses identical Udc *、Udcmax, therefore kdroopi_fixedMeet formula (12).
kdroop(n+1)_fixed:kdroop(n+2)_fixed…:kdroop(n+m)_fixed=P(n+1)N:P(n+2)N…:P(n+m)N (12)
Line impedance impact factor εiSetting method is as follows:
After determining MMC-MTDC system design parameter, ε can be carried outiAdjusting work.With GSCiFor, introduce optimal function
Power accounting a when rate is distributedi% is derived by formula (9)；εiPower accounting b when=0i% is pushed away by formula (2), formula (12) simultaneous
Lead (bi% is set up for each operating point).
Enable Udci0=Udci, joint type (1), formula (14) can obtain and use PCC when with reference to sagging curve2The active power of point:
Introduce the voltage deviation △ U of underload pointlow_load.Adaptive sagging curve passes through (ai%PPCC2, Udci *+△
Ulow_load), GSC can be madeiMeet optimal power allocation condition at underload point. Udci>Udci *+△Ulow_loadWhen, it is optimal
The effect of power distribution can be gradually weak, i.e., on underload point, the method for the present invention, which is constantly in, forces optimal power allocation
Nearly state.
By (ai%PPCC2, Udci *+△Ulow_load) formula (1) is substituted into, ε can be obtainediSetting valve.
It examines
Otherwise it needs to adjust by boundary value respectively.
On underload point, the effect of optimal power allocation can be gradually weak, provides proof procedure here.
Complete εiAfter adjusting, there is only variable P on the right side of formula (10)i。PiIt is reduced to -1p.u. from 0p.u., as -1 < εi< 0,
Pi/Pi0Monotone decreasing；Work as εi> 0, Pi/Pi0Monotonic increase.Therefore, as -1 < εi< 0, Pi/Pi0From a of underload pointi%/bi%
(ai%/bi% > 1) decay to 1；Work as εi> 0, Pi/Pi0From a of underload pointi%/bi% (ai%/bi% < 1) decay to 1.
Fig. 5 provides -1 < εiLine loss schematic diagram when < 0.Whole line loss can subtract with the increase of DC voltage
It is small, therefore ordinate PlossFlexibility and changeability.Fig. 5 only provides GSCiInfluence of the power allocation case for line loss.Using this hair
Bright method, when underload point, in A point in figure；When greater than underload point, in workspace in figure；When rated power, in figure
Middle B point.Overcompensation phenomenon can only occur in the very small extreme case of power.
Embodiment 1: based on building four ends MMC-MTDC as shown in FIG. 6 in electromagnetic transient simulation software PSCAD/EMTDC
Simulation model.WFC1And WFC2Wind farm side converter station is represented, input node is belonged to, using power control；GSC3And GSC4It represents
Grid side converter station, belongs to output node, using adaptive sagging control strategy herein.l1=30km, l2=20km, l3=
40km, l4=20km, l0=80km, cable unit distance impedance value are 0.01 Ω/km.Simulating, verifying steady-state operation, power waves
When dynamic, N-1 is run, control effect of the control method proposed by the present invention to system.
The major parameter of 1 analogue system of table.
Parameter tuning principle according to the present invention completes parameter tuning.kdroop3=20, kdroop4=20.ε3=1.88, ε4=-
0.53。
GSC3、GSC4P-V characteristic curve such as Fig. 7, Fig. 8.Amplitude limit link is in order to avoid system when instantaneously sagging coefficient is excessive
The unstable phenomenon being likely to occur.Amplitude limit link k in this exampledroop=100.
To test characteristic of the invention, WFC comprehensively1And WFC2Change to the active power that MTDC is inputted from 0~400MW.
MTDC system dc voltage responsive such as Fig. 9.Except zero energy and Operation at full power, the DC voltage deviation of strategy, which is respectively less than, herein is passed
It unites sagging control strategy.The excellent weak process of power distribution such as Figure 10. P4/P32 from underload point gradually decay to 1.Figure 10
Decaying is the result by amplitude limit link and coordinate interval (40MW) combined influence since 1.9.
When table 2 provides output of wind electric field variation, l3、l4Line loss comparing result.The strategy of comparison is respectively: using
ε3=ε4The MTDC system of reference sagging curve when=0；Using adaptive droop control method of the invention.Two kinds of tactful phases
There is the deviation of maximum 0.1kV with the DC voltage of node, eliminates DC voltage deviation by being averaged here for whole
The influence of body line loss.As can be seen from Table 2, the line loss of the method for the present invention reduction has preferable economical at kW grades
Benefit.
Table 2
Figure 11~13 show the simulation waveform using adaptive droop control method proposed by the present invention.
Wherein, the simulation waveform of MTDC system when Figure 11 is steady-state operation.
The simulation waveform of MTDC system when Figure 12 is changed power, simulation be wind speed variation operating condition, document [15]
Strategy, strategy when being exactly using with reference to sagging curve, bibliography [15] are as follows: Luo Yongjie, Li Yaohua, Wang Ping wait multiterminal soft
Property the sagging control strategy of DC transmission system DC voltage adaptive study [J] Proceedings of the CSEE, 2016 (10):
2588-2599. shows the Approximation effect to optimal power allocation, and then introduce route by being compared with document strategy
Low advantage is lost.
Figure 13 is the simulation waveform of MTDC system when converter station 3 is out of service.
From simulation result as can be seen that control method proposed by the invention can be stablized under various operating conditions, reliably transport
Row, has the advantages that voltage deviation is small, line loss is low.
The above is only a preferred embodiment of the present invention, it is noted that for the ordinary skill people of the art
For member, without departing from the technical principles of the invention, several improvement and deformations can also be made, these improvement and deformations
Also it should be regarded as protection scope of the present invention.
Claims (3)
1. a kind of MMC-MTDC system self-adaption droop control method, characterized in that introduce power impact factor, line impedance shadow
The factor is rung, using the active power of converter station exchange side PCC point input as input quantity, using sagging coefficient as output quantity, in shadow
Sagging coefficient is adjusted in real time under the action of the sound factor, makes P-V characteristic curve under the premise of not depending on high-speed communication to optimal function
Rate distributes direction approximation；Specifically comprise the following steps:
Step 1) is distributed the ginseng for determining MTDC system according to marine wind electric field position, land AC network tie point, submarine cable
Fixed sagging coefficient k is completed in number settingdroopi_fixedWith line impedance factor εiAdjusting work；The MTDC system includes n
A input node, m output node；
Step 2) measures local electrical quantities, i.e. converter station i exchanges the active-power P that PCC point in side flows intoi, which is sent to local
Controller；
Step 3) local controller according toPiNIt is the rated active power of converter station i, calculates instantaneous
Sagging coefficient kdroopiValue, as new instantaneous sagging coefficient kdroopi_fixed, controller is using new instantaneous sagging coefficient ginseng
It is controlled with MTDC system coordination, forms new sagging curve.
2. a kind of MMC-MTDC system self-adaption droop control method according to claim 1, characterized in that the step
1) sagging coefficient k indroopi_fixedSetting method is as follows:
To realize each converter station while fully loaded purpose, k under extreme casedroopi_fixedMeet:UdcimaxFor the DC voltage maximum value of converter station i, Udci *For the DC voltage of converter station i
Reference value.
3. a kind of MMC-MTDC system self-adaption droop control method according to claim 1, characterized in that the step
1) line impedance impact factor ε iniSetting method is as follows:
For i-th of converter station, power accounting a when optimal power allocation is introducedi%, according to optimal power when m output node
Distributive condition are as follows:Wherein, Pn+i, i=1,2 ..., m are indicated i-th
The optimal power of output node, Rn+1、Rn+2…、Rn+mRefer to direct current points of common connection PCC2Point arrives corresponding receiving end converter station cable
Equivalent impedance, it is known that εiPower accounting b when=0i% can be obtained according to P-V curve:
Introduce the voltage deviation Δ U of underload pointlow_load, ε can be obtainediSetting valve:
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| CN109274113B (en) * | 2018-09-06 | 2022-02-18 | 华北电力大学（保定） | Nonlinear droop control method for hybrid multi-terminal direct current transmission system |
| CN110289647B (en) * | 2019-06-28 | 2020-08-21 | 合肥工业大学 | Adaptive droop and hysteresis control method for interconnected converters in alternating current-direct current hybrid microgrid |
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