CN104734189A - Wind power dispersion and integration droop control method based on VSC-HVDC - Google Patents

Abstract

The invention discloses a wind power dispersion and integration droop control method based on the VSC-HVDC. The method includes the steps that first, a VSC-HVDC system structure model for single wind power plant integration is established; second, a constant DC voltage controller for a power distribution network side inverter of the VSC-HVDC system structure model is established; third, an AC voltage droop controller for a wind power plant side rectifier of the VSC-HVDC system structure model is established; fourth, the VSC-HVDC system structure model for multiple-wind-power-plant integration in an AC dispersion mode at the sending end is established according to power distribution network distribution, the power distribution network side inverter is controlled by the constant DC voltage controller, and the wind power plant side rectifier is controlled by the AC voltage droop controller. According to the wind power dispersion and integration droop control method based on the VSC-HVDC, an effective solution can be provided for dispersion wind power plant joint coordination operation in an AC converging mode at the receiving end, and the method is suitable for remote wind power plant integration control.

Description

Wind-powered electricity generation based on VSC-HVDC disperses grid-connected droop control method

Technical field

The invention belongs to wind-electricity integration control technology field, be specifically related to a kind of wind-powered electricity generation based on VSC-HVDC and disperse grid-connected droop control method.

Background technology

Because the resource exception of wind power generation is abundant, technology relative maturity, global installed capacity of wind-driven power constantly increases in recent years, and has engendered the trend from land to coastal waters development.Along with the scale of offshore wind farm is develop and useedd, ac transmission more and more can not satisfy the demands completely because of system synchronicity, the transmission of electricity technical bottleneck such as stability, power transmission efficiency problem.For solving the remote grid-connected problem of Large marine wind-powered electricity generation, flexible DC power transmission (VSC-HVDC) technology based on voltage source converter is widely used, its transmission capacity is not by distance limit, good dynamic reactive can be provided to support for wind energy turbine set, the isolation of wind energy turbine set and AC network can also be realized.Because flexible DC power transmission has special advantage for the application of offshore wind farm, thus study its control technology and have great importance for wind-electricity integration field.

Most of flexible DC power transmission engineering is all two ends power transmission engineering in the world at present, its control strategy is generally side converter and adopts constant DC voltage control to ensure that system power balances, opposite side converter adopts power limitation control to transmit desirable performance number, and introduce coupling frequency control strategy or prediction direct Power Control strategy etc. on this basis, to improve control performance.But above control mode often can only be used for the single-ended grid-connected situation of wind energy turbine set, and do not relate to the cooperation control that wind energy turbine set multiterminal power.

For solving multiple feed or the powered transmission of electricity problem of many drop points, Multi-end flexible direct current transmission technology (MTDC) is now risen gradually.Xu L etc. ^[1]the multiterminal coordination control strategy based on direct voltage deviation is proposed for the four end MTDC systems containing two power distribution networks; Wang Wei etc. ^[2]traditional control policy grounds is introduced additional direct voltage droop control link.But MTDC Controlling model is after wind energy turbine set carries out power delivery by cable often, then direct current points of common connection punishment is at sea loose transfers to each land load center and power.

And in actual conditions, if wind energy turbine set comparatively will to be disperseed and the more weak land load center of electrical link is powered for multiple physical distance, then carry out the selection that direct current dispersion might not be most convenient and economy, and should consider to adopt sending end to exchange decentralized model by wind energy turbine set, and directly powered respectively to each land load center by the cable of many shortest paths.Under this connection mode, the strategies such as above-mentioned direct voltage droop control just no longer prove effective.

Following list of references is related in literary composition:

[1] the .DC grid management of a multi-terminal HVDC transmission system for largeoffshore wind farms. meeting " Sustainable Power Generation and Supply 2009; InternationalConference on.IEEE " such as Xu L, 2009:1-7.

[2] Wang Wei etc. marine multi-terminal direct current transmission system cooperation control grinds [J]. electric power network technique, 2014,38 (1): 8-15.

Summary of the invention

For prior art Problems existing, the invention provides a kind of wind-powered electricity generation based on VSC-HVDC and disperse grid-connected droop control method, the method is applicable to the wind-powered electricity generation multiterminal cutting-in control under sending end interchange decentralized model.

The Baseline Control Strategy of alternating voltage droop control strategy and VSC-HVDC organically combines by the present invention, introduce in flexible direct current power transmission system droop control without the need to writing to each other, the advantage such as the high and reasonable dynamic assignment of reliability, thus to adopt sending end to exchange decentralized model to wind energy turbine set be that the coordinated operation that multiterminal power distribution network is powered provides effective solution route.

For solving the problems of the technologies described above, the present invention adopts following technical scheme:

Based on the dispersion wind-electricity integration droop control method of VSC-HVDC, comprise step:

Step 1, the single wind farm grid-connected VSC-HVDC system structure model of foundation, comprise wind energy turbine set, power distribution network, rectifier, inverter, hvdc transmission line, filter, load and between connected mode, wind farm side rectifier adopts alternating voltage droop control, and power distribution network side inverter adopts constant DC voltage control; Described rectifier and inverter are VSC converter;

Step 2, builds the constant DC voltage control device being used for VSC-HVDC system structure model power distribution network side inverter;

Step 3, builds the alternating voltage droop control device being used for VSC-HVDC system structure model wind farm side rectifier;

Step 4, the VSC-HVDC system structure model grid-connected according to the wind-powered electricity generation multiterminal under the distribution situation structure sending end interchange decentralized model of multiple power distribution network, based on the VSC-HVDC system structure model that wind-powered electricity generation multiterminal are grid-connected, adopt constant DC voltage control device to control power distribution network side inverter, adopt alternating voltage droop control device to control wind farm side rectifier.

Step 2 is specially:

D axle is oriented to voltage vector direction, inverter side points of common connection PCC2 place, inner ring current controller adopts voltage feed-forward control to control and current decoupled control, obtains following constant DC voltage control device:

$\left[\begin{array}{c}{v}_{d2}^{*}\\ v_{q2}^{*}\end{array}\right]=\left[\begin{array}{cc}-(k_p+\frac{k_i}{s})& 0\\ 0& -(k_p+\frac{k_i}{s})\end{array}\right]\left[\begin{array}{c}{i}_d^{*}\\ i_q^{*}\end{array}\right]+\left[\begin{array}{cc}(k_p+\frac{k_i}{s})& \mathrm{wL}\\ -\mathrm{wL}& (k_p+\frac{k_i}{s})\end{array}\right]\left[\begin{array}{c}{i}_d\\ i_q\end{array}\right]+\left[\begin{array}{c}1\\ 0\end{array}\right]v_d$

Wherein, L is the inductance of linked reactor, and w is system angle frequency; v _dfor inverter side points of common connection PCC2 place voltage actual value, be respectively the voltage reference value of inverter outlet place d axle, q axle, be respectively the line current reference value of d axle, q axle, i _d, i _qbe respectively the line current actual value of d axle, q axle, k _p, k _ifor pi controller parameter, s is Laplacian.

Step 3 comprises sub-step further:

3.1 build P-f, Q-V droop control device $\left\{\begin{array}{c}{f-f}_n=-1/a\left({P-P}_n\right)\\ {V-V}_n=-1/b\left({Q-Q}_n\right)\end{array}\right.,$ Wherein, 1/a and 1/b is respectively the sagging coefficient of frequency and voltage; f _nand V _nbe respectively the rated value of frequency and voltage amplitude; P _nand Q _nbe respectively the active power of circuit and the rated value of reactive power; P and Q is respectively active power and the reactive power of the circuit calculated by the alternating voltage of current collection and alternating current; F and V is respectively the reference value of the frequency and voltage amplitude determined according to power under current state;

3.2 to flow through the electric current of wind farm side filter capacitor for inner ring control object, regards load current and wind farm side rectifier entrance electric current as be on electric current loop forward path disturbance, builds Double closed-loop of voltage and current device $\left\{\begin{array}{c}{I}_{\mathrm{cd}}^{*}=C_{f1}{\mathrm{dV}}_d^{*}/\mathrm{dt}-\mathrm{\ω}{C}_{f1}{V}_q^{*}\\ I_{\mathrm{cq}}^{*}=C_{f1}{\mathrm{dV}}_q^{*}/\mathrm{dt}+\mathrm{\ω}{C}_{f1}{V}_d^{*}\end{array}\right.,$ Wherein, C _f1for wind farm side filter capacitor, be respectively d axle component and the q axle component of the rectification side points of common connection place voltage reference value that droop control device exports, be respectively d axle component and the q axle component of the current reference value flowing through wind farm side filter capacitor, w is system angle frequency, and t represents the time;

The 3.3 rectification side points of common connection place voltage reference values exported by P-f, Q-V droop control device, as the input of Double closed-loop of voltage and current device, build alternating voltage droop control device.

Compared with prior art, the present invention has the following advantages and beneficial effect:

1) the present invention can ensure grid-connected system operation stability by the impact of load fluctuation, and rectification side is gained merit, system in droop control of following the tracks of flexibly of exerting oneself is gained merit the change of rated value.

2) the present invention effectively can improve the antijamming capability of wind energy turbine set to receiving end AC system voltage dip, also can effectively suppress the short trouble of wind farm side on the impact of receiving end AC system, has good alternating current-direct current Fault Isolation function.

3) the present invention when Wind turbines cuts out system, can realize trend reversion fast, by power distribution network for load provides power to support, maintains system safety stable operation.And the requirement to high-speed communication between each converter can be avoided, in each power distribution network side according to the meritorious rated value reasonable distribution dynamic power of system, realize the autonomous cooperation control of wind energy turbine set dispersion grid-connected system when trend is reversed.

Accompanying drawing explanation

Fig. 1 is particular flow sheet of the present invention;

Fig. 2 is single wind farm grid-connected VSC-HVDC system model structure chart in concrete enforcement;

Fig. 3 is constant DC voltage control device structured flowchart in concrete enforcement;

Fig. 4 is alternating voltage droop control device structured flowchart in concrete enforcement;

Fig. 5 is the grid-connected model structure figure of wind-powered electricity generation three end under sending end exchanges decentralized model;

Fig. 6 is the simulation result of example one of the present invention, wherein, figure (a) is system active power simulation result, and figure (b) is system frequency simulation result, figure (c) is system dc voltage simulation result, and figure (d) is system alternating current simulation result;

Fig. 7 is the simulation result of example two of the present invention, wherein, figure (a) is system dc voltage simulation result, figure (b) is system active power simulation result, figure (c) is system reactive power simulation result, figure (d) is system alternating voltage simulation result, and figure (e) is system frequency simulation result;

Fig. 8 is the simulation result of example three of the present invention.

Embodiment

The present invention, on the basis of flexible DC power transmission Traditional control strategy, retains the constant DC voltage control of distribution side inverter, to ensure that system power balances; And adopt alternating voltage droop control at wind field side rectifier, to replace original power limitation control, thus introduce droop control without the need to writing to each other and the advantage such as reasonable dynamic assignment.The present invention passes through simulation analysis, demonstrate the inventive method and can not only ensure meritorious flexible automatic tracking system rated value of exerting oneself, but also there is certain load fluctuation tolerance and alternating current-direct current Fault Isolation function, and when powering to multiterminal power distribution network wind energy turbine set adopts sending end to exchange decentralized model while, trend reversion can be realized fast when blower fan cuts out system, to ensure system power supply reliability, and can be automatic according to specified ratio reasonable distribution dynamic power between each power distribution network, for wind energy turbine set disperses grid-connected coordinated operation to provide effective solution route.

The specific embodiment of the present invention is further illustrated below in conjunction with accompanying drawing.

See Fig. 1, concrete steps of the present invention are as follows:

Step 1, the single wind farm grid-connected VSC-HVDC system structure model of foundation, specify the connected mode of wind energy turbine set, power distribution network, rectifier, inverter, hvdc transmission line, filter and load, and adopting alternating voltage droop control at wind farm side rectifier, power distribution network side inverter adopts constant DC voltage control.

In this concrete enforcement, single wind farm grid-connected VSC-HVDC system model structure is shown in Fig. 2.Wherein, wind farm side is connected with two ends AC system respectively by equiva lent impedance with the VSC converter of power distribution network side, and two ends AC system characterizes marine wind electric field and its distribution network system accessed at a distance respectively.The operating state of two VSC converters is determined by the flow direction of active power in system, and namely sending end wind farm side VSC converter works in rectification state, and receiving end power distribution network side VSC converter works in inverter mode.The DC side of each converter is parallel with electric capacity, to improve power adjustments characteristic and the transmittability of system.DC line adopts PI type equivalent model.The higher harmonic components brought to suppress PWM generator, two ends AC system is respectively equipped with filter, and rectification side points of common connection PCC1 place is connected to local island load Z _ld, and inverter side points of common connection PCC2 place is connected to AC load P _ld.

Each VSC converter has the control freedom degree of two dimension, and a usual dimension is used for controlling active power or direct voltage, and another dimension is used for controlling reactive power or alternating voltage.Embody the same as input power in AC system by frequency with the difference of power output, in direct current system, active power balance whether index is whether direct voltage is stablized.Therefore in the present invention, inverter side VSC converter adopts constant DC voltage control strategy, to ensure that system power balances.And rectification side VSC converter adopts alternating voltage droop control strategy, for determining the transmission value of active power, to ensure that the economical and effective of system is run, can also introduce simultaneously droop control without the need to writing to each other, the reasonable feature such as dynamic assignment, provide effective solution route for wind energy turbine set is run by multiple VSC-HVDC system dispersion grid-connected coordination.

Step 2, determine the constant DC voltage control rule of power distribution network side inverter, and design constant DC voltage control device.

Constant DC voltage control is the very important basic control mode of one in VSC-HVDC control system, when inverter side VSC converter adopts constant DC voltage control, by regulating d shaft current to control direct voltage, its control law is such as formula shown in (1):

$i_d^{*}=(k_p+k_i/s)(v_{\mathrm{dc}}^{*}-v_{\mathrm{dc}})---\left(1\right)$

In formula (1): v _dcwith be respectively actual value and the reference value of system dc voltage, usually 1pu is set to; for the d axle reference value of line current; k _pand k _ifor the parameter of pi controller, s is Laplacian.

The q axle reference value of line current in like manner can be obtained by system alternating voltage

D axle is oriented on voltage vector direction, inverter side points of common connection PCC2 place, for eliminating the coupling between d axle active current and q axle reactive current, and suppressing the impact of grid disturbances, inner ring current controller adopts voltage feed-forward control to control and current decoupled control.Its control law is such as formula shown in (2):

$\left[\begin{array}{c}{v}_{d2}^{*}\\ v_{q2}^{*}\end{array}\right]=\left[\begin{array}{cc}-(k_p+\frac{k_i}{s})& 0\\ 0& -(k_p+\frac{k_i}{s})\end{array}\right]\left[\begin{array}{c}{i}_d^{*}\\ i_q^{*}\end{array}\right]+\left[\begin{array}{cc}(k_p+\frac{k_i}{s})& \mathrm{wL}\\ -\mathrm{wL}& (k_p+\frac{k_i}{s})\end{array}\right]\left[\begin{array}{c}{i}_d\\ i_q\end{array}\right]+\left[\begin{array}{c}1\\ 0\end{array}\right]v_d---\left(2\right)$

In formula (2): L is the inductance of linked reactor, w is system angle frequency; v _dfor inverter side points of common connection PCC2 place voltage actual value, be respectively the voltage reference value of inverter outlet place d axle, q axle, be respectively the line current reference value of d axle, q axle, i _d, i _qbe respectively the line current actual value of d axle, q axle, k _p, k _ifor pi controller parameter, s is Laplacian.

Convolution (1) and formula (2), constant DC voltage control device structured flowchart is shown in Fig. 3, and wherein, the output variable of inner ring current controller is as the first-harmonic reference value of VSC inverter output voltage, be passed to PWM trigger element, complete corresponding triggering work.

Step 3, determine the alternating voltage droop control rule of wind farm side rectifier, and design communication voltage droop control device.

This step specifically comprises following sub-step:

Step 3.1, design P-f, Q-V droop control device:

In inductive circuit, the relation of system power and voltage is as follows:

$\left\{\begin{array}{c}\mathrm{\δ}\≈{\mathrm{XP}}_A/V_A{V}_B\\ V_A-V_B\≈{\mathrm{XQ}}_A/V_A\end{array}\right.---\left(3\right)$

In formula (3), V _aand V _bcan regard rectification side points of common connection PCC1 place's voltage and rectifier porch voltage respectively as, δ is circuit merit angle, and X is line reactance, P _aand Q _afor active power and the reactive power of circuit.

Formula (3) shows, the phase difference δ (i.e. circuit merit angle) of both end voltage is main relevant with active power, and the difference in magnitude of both end voltage is then determined by reactive power.Consider the differential relationship between phase place and frequency, P-f, Q-V droop control device can be formulated by formula (3), as follows:

$\left\{\begin{array}{c}{f-f}_n=-1/a\left({P-P}_n\right)\\ {V-V}_n=-1/b\left({Q-Q}_n\right)\end{array}\right.---\left(4\right)$

In formula (4), 1/a and 1/b is respectively the sagging coefficient of frequency and voltage; f _nand V _nbe respectively the rated value of frequency and voltage amplitude; P _nand Q _nbe respectively the rated value of active power and reactive power; P and Q is respectively the active power and reactive power that are obtained as calculated by the alternating voltage of current collection, electric current; F and V is respectively the reference value of the frequency and voltage amplitude determined by power under current state.

Sagging coefficient is generally determined by commissioning experience, and follows the principle that sagging coefficient and rated power is inversely proportional to, as rated power be 4MW/0MVar time, 1/a and 1/b is set to 9 × 10 respectively ^-8with 2.7 × 10 ^-6, and when rated power is 5MW/0MVar, 1/a and 1/b is set to 7.2 × 10 respectively ^-8with 2.16 × 10 ^-6, the rest may be inferred.

Step 3.2, design voltage current double-closed loop controller:

As shown in Figure 2, wind farm side filter capacitor C is flow through _f1electric current I _cfor:

I _c＝I _f-(I _ld+I _inv) (5)

In formula (5), I _invfor rectifier entrance electric current, I _ldfor flowing through the electric current of rectification side points of common connection PCC1 place's load, I _ffor flowing to the electric current of rectification side points of common connection PCC1.

Therefore, using capacitance current as inner ring control object, regard load current and converter entrance electric current as be on electric current loop forward path disturbance, and it is effectively suppressed, thus floating voltage reference value better, steady load voltage.

Under dq0 coordinate system, the differential equation of filter capacitor is:

$\left\{\begin{array}{c}{I}_{\mathrm{cd}}^{*}=C_{f1}{\mathrm{dV}}_d^{*}/\mathrm{dt}-\mathrm{\ω}{C}_{f1}{V}_q^{*}\\ I_{\mathrm{cq}}^{*}=C_{f1}{\mathrm{dV}}_q^{*}/\mathrm{dt}+\mathrm{\ω}{C}_{f1}{V}_d^{*}\end{array}\right.---\left(6\right)$

In formula (6), C _f1for wind farm side filter capacitor, be respectively d axle component and the q axle component of the rectification side points of common connection place voltage reference value that droop control device exports, be respectively d axle component and the q axle component of the current reference value flowing through wind farm side filter capacitor, w is system angle frequency, and t represents the time.

The control strategy that step 3.3, zygote step 3.1 and sub-step 3.2 obtains, is designed for the alternating voltage droop control device of wind farm side rectifier.

The rectification side points of common connection PCC1 place reference voltage exported by droop control device (see formula (4)) is as the input of Double closed-loop of voltage and current device (see formula (6)), and Double closed-loop of voltage and current device outputs signal as PWM generator provides trigger impulse.Fig. 4 is the alternating voltage droop control device set up according to P-f, Q-V droop control device and Double closed-loop of voltage and current device.

Step 4, to set up according to power distribution network distributing position sending end exchange decentralized model under wind-powered electricity generation multiterminal grid connected structure model, wind farm side rectifier all adopts alternating voltage droop control, and power distribution network side inverter all adopts constant DC voltage control.

Be that three physical distances are comparatively disperseed for wind energy turbine set and the more weak power distribution network of electrical link is powered, it adopts sending end to exchange decentralized model to be connected with each power distribution network respectively by three VSC-HVDC systems, and Fig. 5 is shown in by its structure chart simultaneously.

Step 5, according to line parameter circuit value and power system capacity, determine the PI controller parameter in control system, based on the sagging coefficient of policy setting each sending end converter that sagging coefficient and rated power ratio are inversely proportional to.

If the ratio of the rated power set in the alternating voltage droop control device of three VSC-HVDC systems is a:b:c, the ratio of the sagging coefficient of each system should be d:e:f, then should ensure ad=be=cf.

The present invention is further illustrated below in conjunction with application example.

Embodiment 1

Grid-connected by VSC-HVDC transmission system with wind energy turbine set single shown in Fig. 2, its system parameters is as shown in table 1, determines each PI controller parameter, in table 2 according to power system capacity and line parameter circuit value.

The single wind farm grid-connected system parameters of table 1

In table 1, L _f1, R _f1and C _f1be respectively the filter inductance of wind farm side, filter resistance and filter capacitor; L _f2, R _f2and C _f2be respectively the filter inductance of power distribution network side, filter resistance and filter capacitor; R ₁/ L ₁, R ₂/ L ₂and R ₃/ L ₃represent line impedance Z in Fig. 2 respectively ₁, Z ₂and Z ₃resistance and inductance; R _ld/ L _ldfor load Z in island in Fig. 2 _ldresistance and inductance; P _ldfor power distribution network side load power in Fig. 2; with be respectively the rated value of wind farm side points of common connection PCC1 place and points of common connection PCC2 place, power distribution network side voltage; P _nand Q _nfor the rated value of the active power that arranges in droop control and reactive power; f _nfor system frequency rated value; for the rated value of AC line voltage; L _dcfor the length of DC line; R _dc, L _dcand C _dcbe respectively resistance parameter, inductance parameters and the capacitance parameter in DC line PI type equivalent model; T ₁and T ₂represent the voltage ratio of wind farm side and power distribution network side transformer respectively; S ₁and S ₂represent rated voltage and the rated frequency of wind farm side AC power and power distribution network side AC power respectively.

Table 2 controller parameter

In order to verify the inventive method validity, design following example:

Example one

During 2.0s, PCC2 place active load becomes 2MW from 3.2MW, restores during 2.6s.During 3.0s, system instruction of gaining merit becomes 3MW from 4MW.Exchange wind-powered electricity generation multiterminal grid connected structure model under decentralized model and simulation run in MATLAB/Simulink platform construction sending end, in acquisition system, each parameter in PCC1 and PCC2 place curve over time, is shown in Fig. 6.

Fig. 6 (a) shows, because distribution lateral load during 2.0s reduces to some extent, the meritorious output in PCC1 place still keeps rated value constant, and the active power therefore transferring to PCC2 place has the rising of corresponding amplitude.This also demonstrates, and wind farm side is meritorious exerts oneself after the load of supply local island, be transmitted by DC line and under the prerequisite meeting receiving end PCC2 place load feed-in power distribution network again, and the power loss in HVDC system makes the size of difference slightly larger than PCC2 place load of two place's active power.

Before 3.0s, PCC1 place all the time can according to the rated value 4MW arranged in droop control to direct current system active power of output.Subsequently, meritorious rated value declines, and PCC1 place active power also can respond immediately, is down to new rated value 3MW gradually.And now bearing power no longer changes, the active power therefore transferring to PCC2 place also reduces gradually with identical trend.Fig. 6 (b) shows, system frequency slightly fluctuates when 3.0s, but after PCC1 place active power reaches new rated value, frequency also returns to 50Hz.In addition, can find out that PCC1 alternating voltage slightly increases from Fig. 6 (d), but still be in error allowed band.

Because the active power at VSC-HVDC system two ends has consistent variation tendency under adopted constant DC voltage control method, therefore the power-balance of DC power transmission line can be met all the time, make to gain merit in the process of rated value change in distribution lateral load fluctuation and system, direct voltage shown in Fig. 6 (c) can remain constant all the time, thus completely cut off the fluctuation of wind farm side alternating voltage further, the alternating voltage at PCC2 place as Suo Shi Fig. 6 (d) also can be remained unchanged.

Example two

During 2.0s, the alternating voltage generation flickering of power distribution network side, recovers rated value when 2.2s subsequently by 0.85 times that is down to rated voltage temporarily.The single-phase grounding fault of 0.15s, subsequently failture evacuation when PCC1 occurs as when being in 2.4s, System recover normally runs.Exchange wind-powered electricity generation multiterminal grid connected structure model under decentralized model and simulation run in MATLAB/Simulink platform construction sending end, in acquisition system, each parameter in PCC1 and PCC2 place curve over time, is shown in Fig. 7.

As can be seen from Fig. 7 (a), no matter, system dc voltage effectively can remain constant under this control method if there is voltage dip or wind farm side generation unbalanced fault in power distribution network side.

2.0s time, the voltage at PCC2 place shown in Fig. 7 (d) obviously reduces by the impact of power distribution network, now its reactive power absorbed increases to some extent, to provide support for system dc voltage, thus guarantee receiving end PCC1 place alternating voltage also can remain constant further.The significant difference of both sides AC system voltage between 2.0s ~ 2.2s, shows that this control method can make wind energy turbine set from the impact of distribution side voltage dip, effectively improves the stability of wind-electricity integration, has good alternating current-direct current Fault Isolation function.

During 2.4s, there is single phase ground fault in PCC1 place, and Fig. 7 (b) shows that PCC2 place active power is negative by rotating forward along with meritorious decline the in PCC1 place, and namely power distribution network is automatically for load provides certain power to support, to maintain system power balance.As can be seen from Fig. 7 (e), now system frequency is inverse change according to droop characteristic and active power, but remains within allowed band always.As can be seen from Fig. 7 (c), PCC2 place reactive power hardly by fault effects, thus PCC2 place alternating current pressure energy shown in Fig. 7 (d) is made to remain constant while the voltage fluctuation of fault side.This control method visible effectively can improve the antijamming capability of receiving-end system to wind farm side fault, again demonstrates the alternating current-direct current Fault Isolation function of this control method.

Embodiment 2

For wind energy turbine set single shown in Fig. 5 by VSC-HVDC system respectively to the power distribution network decentralized power supply of three zoness of different, verify that control strategy of the present invention disperses multiterminal to power correctness under situation and validity in wind energy turbine set.Wherein, the load of system two ends and impedance parameter are in table 3, and all the other system parameterss and controling parameters are all identical with above example.

The system parameters that table 3 wind energy turbine set dispersion multiterminal are grid-connected

R 1(Ω)	L 1(mH)	R 2(Ω)	L 2(mH)	R 3(Ω)
					0.04	0.02	0.08	0.04	0.16
L 3(mH)	R ld1(Ω)	L ld1(mH)	R ld2(Ω)	L ld2(mH)
					0.08	62.5	25	37.5	20
R ld3(Ω)	L ld3(mH)	P ld1(MW)	P ld2(MW)	P ld3(MW)
					5.625	15	3.2	4	4.8

In table 3, R ₁/ L ₁, R ₂/ L ₂and R ₃/ L ₃represent line impedance Z in Fig. 5 respectively ₁, Z ₂and Z ₃resistance and inductance; R _ld1/ L _ld1, R _ld2/ L _ld2and R _ld3/ L _ld3represent island load Z in Fig. 5 respectively _ld1, Z _ld2and Z _ld3resistance and inductance; P _ld1, P _ld2and P _ld3represent the load power of each power distribution network side in Fig. 5 respectively.

Each sending end converter sets sagging coefficient, in table 4 by the mode be inversely proportional to rated power.

The droop control coefficient of each rectifier of table 4

Example three

During 2.0s, because marine wind speed change is excessive, Wind turbines is caused to cut out from system; During 3.0s, system and PCC1 place power distribution network disconnect and running.Exchange wind-powered electricity generation multiterminal grid connected structure model under decentralized model and simulation run in MATLAB/Simulink platform construction sending end, in acquisition system, each parameter in PCC1 and PCC2 place curve over time, is shown in Fig. 8.

Figure 8 shows that each receiving end points of common connection place active power over time.During 2.0s, because Wind turbines is out of service, therefore need receiving end off-shore wind to be system two ends load supplyings, trend reversion now just can occur, namely the active power at PCC1-PCC3 place is negative by rotating forward as shown in the figure.Because now the ratio (10:12:15) of the sagging coefficient of each receiving end converter and the ratio (6:5:4) of its rated power are inversely proportional to, and system frequency variable quantity is certain, then from formula (4), the steady-state value ratio after the variation of each receiving end PCC4-PCC6 place active power also coefficient ratio sagging with it is inversely proportional to.Again because rated value of generally gaining merit is all design according to the load proportion size of distribution side, therefore comprehensive above-mentioned two meritorious ratio situations flowed to, the ratio of known now PCC1-PCC3 place active power is by identical with the gain merit ratio of rated value of system, i.e.-5.4MW:-4.5MW:-3.6MW=6:5:4, system dynamic power obtains an equitable breakdown.

During 2.2s, No. 1 power distribution network is out of service, and its active power reduces to 0 instantaneously, and Line 1 road creates serious power shortage.In order to ensure the uninterrupted power supply to Line 1 road load as far as possible, PCC2 and PCC3 place active power increases all to some extent, and dynamic power presses specified pro rate, i.e.-5MW:-4MW=5:4 again between these two systems.The two is supported for Line 1 road provides certain power jointly by cooperation, and system switches to new poised state smoothly.

Meanwhile, as can be seen from the figure, during 2.6s, the active power at PCC2 place and PCC3 place has reached new poised state all, but PCC1 place power resume speed is slightly slow compared with it.This illustrates that larger sagging coefficient can increase system response time, improves dynamic performance.

As can be seen from the above results, under the effect of this control strategy, if the method to set up of the sagging coefficient be inversely proportional to rated power, dynamic active power can be made between each system by specified pro rate, system imbalance power is born to each power distribution network by automatically reasonable distribution, thus ensure that the uniformity of whole HVDC system medium frequency and voltage, and simple and reliable without the need to writing to each other, controlling in whole process.Visible, the autonomous coordinated operation that grid-connected droop control method should be disperseed to adopt sending end interchange decentralized model to power to multiterminal power distribution network for wind energy turbine set based on the wind-powered electricity generation of VSC-HVDC has very large directive significance.

The present invention, by introducing alternating voltage droop control, proposes based on the grid-connected coordination control strategy of the wind energy turbine set multiterminal of the adaptation employing sending end interchange decentralized model of VSC-HVDC.On the basis of flexible DC power transmission Traditional control strategy, retain the constant DC voltage control of distribution side inverter, to ensure that system power balances; And make wind field side rectifier adopt alternating voltage droop control, to replace original power limitation control, thus introduce droop control without the need to writing to each other and the advantage such as reasonable dynamic assignment.Herein by simulation analysis, demonstrating the above-mentioned wind-powered electricity generation based on VSC-HVDC disperses grid-connected droop control strategy can not only ensure meritorious flexible automatic tracking system rated value of exerting oneself, but also there is certain load fluctuation tolerance and alternating current-direct current Fault Isolation function, and when powering to multiterminal power distribution network wind energy turbine set adopts sending end to exchange decentralized model while, trend reversion can be realized fast when blower fan cuts out system, to ensure system power supply reliability, and can automatically according to specified ratio reasonable distribution dynamic power between each power distribution network, for wind-powered electricity generation disperses grid-connected coordinated operation to provide effective solution route.

Claims (3)

1., based on the dispersion wind-electricity integration droop control method of VSC-HVDC, it is characterized in that, comprise step:

Step 1, the single wind farm grid-connected VSC-HVDC system structure model of foundation, comprise wind energy turbine set, power distribution network, rectifier, inverter, hvdc transmission line, filter, load and between connected mode, described rectifier and inverter are VSC converter;

Step 2, builds the constant DC voltage control device being used for VSC-HVDC system structure model power distribution network side inverter;

Step 3, builds the alternating voltage droop control device being used for VSC-HVDC system structure model wind farm side rectifier;

Step 4, the VSC-HVDC system structure model grid-connected according to the wind-powered electricity generation multiterminal under the distribution situation structure sending end interchange decentralized model of multiple power distribution network, based on the VSC-HVDC system structure model that wind-powered electricity generation multiterminal are grid-connected, adopt constant DC voltage control device to control power distribution network side inverter, adopt alternating voltage droop control device to control wind farm side rectifier.

2., as claimed in claim 1 based on the dispersion wind-electricity integration droop control method of VSC-HVDC, it is characterized in that:

Step 2 is specially:

D axle is oriented to voltage vector direction, inverter side points of common connection PCC2 place, inner ring current controller adopts voltage feed-forward control to control and current decoupled control, obtains following constant DC voltage control device:

$\left[\begin{array}{c}{v}_{d2}^{*}\\ v_{q2}^{*}\end{array}\right]=\left[\begin{array}{cc}-(k_p+\frac{k_i}{s})& 0\\ 0& -(k_p+\frac{k_i}{s})\end{array}\right]\left[\begin{array}{c}{i}_d^{*}\\ i_q^{*}\end{array}\right]+\left[\begin{array}{cc}(k_p+\frac{k_i}{s})& \mathrm{wL}\\ -\mathrm{wL}& (k_p+\frac{k_i}{s})\end{array}\right]\left[\begin{array}{c}{i}_d\\ i_q\end{array}\right]+\left[\begin{array}{c}1\\ 0\end{array}\right]v_d$

Wherein, L is the inductance of linked reactor, and w is system angle frequency; v _dfor inverter side points of common connection PCC2 place voltage actual value, be respectively the voltage reference value of inverter outlet place d axle, q axle, be respectively the line current reference value of d axle, q axle, i _d, i _qbe respectively the line current actual value of d axle, q axle, k _p, k _ifor pi controller parameter, s is Laplacian.

3., as claimed in claim 1 based on the dispersion wind-electricity integration droop control method of VSC-HVDC, it is characterized in that:

Step 3 comprises sub-step further:

3.1 build P-f, Q-V droop control device $\left\{\begin{array}{c}f-f_n=-1/a(P-P_n)\\ V-V_n=-1/b(Q-Q_n)\end{array}\right.,$ Wherein, 1/a and 1/b is respectively the sagging coefficient of frequency and voltage; f _nand V _nbe respectively the rated value of frequency and voltage amplitude; P _nand Q _nbe respectively the active power of circuit and the rated value of reactive power; P and Q is respectively active power and the reactive power of the circuit calculated by the alternating voltage of current collection and alternating current; F and V is respectively the reference value of the frequency and voltage amplitude determined according to power under current state;

3.2 to flow through the electric current of wind farm side filter capacitor for inner ring control object, regards load current and wind farm side rectifier entrance electric current as be on electric current loop forward path disturbance, builds Double closed-loop of voltage and current device $\left\{\begin{array}{c}{I}_{\mathrm{cd}}^{*}=C_{f1}{\mathrm{dV}}_d^{*}/\mathrm{dt}-\mathrm{\ω}{C}_{f1}{V}_q^{*}\\ I_{\mathrm{cq}}^{*}=C_{f1}d{V}_q^{*}/\mathrm{dt}+\mathrm{\ω}{C}_{f1}{V}_d^{*}\end{array}\right.,$ Wherein, C _f1for wind farm side filter capacitor, be respectively d axle component and the q axle component of the rectification side points of common connection place voltage reference value that droop control device exports, be respectively d axle component and the q axle component of the current reference value flowing through wind farm side filter capacitor, w is system angle frequency, and t represents the time;

The 3.3 rectification side points of common connection place voltage reference values exported by P-f, Q-V droop control device, as the input of Double closed-loop of voltage and current device, build alternating voltage droop control device.