Multi-wind-field virtual direct-axis transient reactance design method for expanding wind power transmission limit

Abstract

The invention belongs to the technical field of new energy high-permeability novel power system voltage support, and provides a multi-wind-field virtual direct-axis transient reactance design method for expanding the wind power transmission limit. Comprising the steps of calculation of an original wind power transmission limit value, calculation of an original wind power expansion range, calculation of an original equivalent transient reactance value, introduction of virtual direct current transient reactance, calculation of an improved wind power transmission limit, calculation of an initial optimal transient impedance value, calculation of a dynamic voltage critical value and calculation of a dynamic wind power transmission limit. And calculating a real-time power difference value and calculating an optimal real-time transient impedance value. According to the method, the virtual direct-current transient reactance is introduced, the optimal transient impedance value is calculated by utilizing the improved wind power transmission limit, the voltage supporting potential of the wind turbine generator is fully exerted, and the power transmission stability of the wind power transmission system is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the field of voltage support technology for a new type of power system with high penetration of new energy, and in particular to a multi-wind farm virtual direct-axis transient reactance design method for expanding the wind power transmission limit. Background Art

[0002] As the penetration rate of renewable energy power generation continues to increase, the short-circuit capacity of systems with a high proportion of new energy has decreased, resulting in insufficient system short-circuit ratio, which has seriously threatened voltage stability.

[0003] However, the calculation of the transmission capacity limit of traditional wind turbines only considers the impact of synchronous generators, and does not take into account the voltage support capacity of new energy units. In a multi-feed system, the mutual impact between sites is calculated into the transient reactance of wind turbines. Quantifying the voltage active support capacity of wind turbines and ensuring the transient reactance requirements of wind turbines under the real-time transmission capacity safety constraints of wind turbines are necessary requirements for achieving high penetration of new energy. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, the purpose of the present invention is to provide a multi-wind farm virtual direct-axis transient reactance design method that expands the wind power transmission limit. By introducing virtual DC transient reactance and utilizing the improved wind power transmission limit to calculate the optimal transient impedance value, the voltage support potential of wind turbines can be brought into play and the power transmission stability of the wind power transmission system can be improved.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A multi-wind farm virtual direct-axis transient reactance design method for expanding the wind power transmission limit, comprising:

[0007] Calculate the original wind power transmission limit value of the original multi-feed system;

[0008] Calculate the original wind power expansion range according to the wind power transmission limit value and the real-time transmission capacity;

[0009] Calculating the original equivalent transient reactance value of the original multi-feed system according to the original wind power expansion range;

[0010] Introducing a virtual DC transient reactance into the original multi-infeed system to obtain an improved multi-infeed system;

[0011] calculating an improved wind power transmission limit of the improved multi-feed system;

[0012] When the real-time transmission capacity is less than or equal to the improved wind power transmission limit, the optimal impedance of the improved multi-feed system is calculated according to the original wind power expansion range to obtain an initial optimal transient impedance value;

[0013] Perform voltage critical calculation according to the initial optimal transient impedance value to obtain a dynamic voltage critical value;

[0014] dynamic wind power transmission limit of the improved multi-feed system according to the dynamic voltage threshold;

[0015] When the real-time transmission capacity is less than or equal to the dynamic wind power transmission limit, calculating the difference between the real-time transmission capacity and the dynamic wind power transmission limit to obtain a real-time power difference;

[0016] The optimal real-time impedance of the improved multi-feed system is calculated according to the real-time power difference to obtain the optimal real-time transient impedance value.

[0017] Preferably, the calculation formula of the original wind power transmission limit value is:

[0018]

[0019] Among them, P WFmax is the original wind power transmission limit value; P WFi is the real-time power transmitted by the i-th wind farm; P WFj The real-time power transmitted by the jth wind farm; E′ is the virtual electromotive force; U Wcri is the critical voltage value of the grid connection point of the i-th wind farm; X T is the per unit value of the equivalent reactance of the line transformer; X n is the per unit value of the equivalent reactance on the AC system side; S ac is the short-circuit capacity of the grid-connected point; K ji ; n is the number of wind farms in the system.

[0020] Preferably, the calculation formula for the original wind power expansion range is:

[0021] ΔP T =P WT0 -P WFmax ;

[0022] Among them, ΔP T The original wind power expansion range is P WT0 is the real-time transmission capacity.

[0023] Preferably, the calculation formula of the original equivalent transient reactance value is:

[0024]

[0025] Among them, X′ dΣ is the original equivalent transient reactance value; X′ di is the transient reactance per unit value of the i-th wind farm; X′ djis the per unit transient reactance value of the jth wind farm.

[0026] Preferably, the calculation formula for the improved wind power transmission limit is:

[0027]

[0028] Among them, P Dmax For the improved wind power delivery limit.

[0029] Preferably, the calculation formula of the initial optimal transient impedance value is:

[0030]

[0031] Among them, X′ dN0 is the initial optimal transient impedance value; ΔP T is the expansion range of the original wind power; E is the system equivalent potential.

[0032] Preferably, the calculation formula of the dynamic voltage threshold is:

[0033]

[0034] Among them, U Tcri is the dynamic voltage critical value; Q WF is the reactive power generated by the wind turbine; X is the sum of the internal impedance of the synchronous motor and the line impedance.

[0035] Preferably, the calculation formula of the dynamic wind power transmission limit is:

[0036]

[0037] Among them, P Tmax is the dynamic wind power delivery limit.

[0038] Preferably, the calculation formula of the optimal real-time transient impedance value is:

[0039]

[0040] Among them, X′ dNT is the optimal real-time transient impedance value; ΔP is the real-time power difference value.

[0041] The present invention discloses the following technical effects:

[0042] The present invention provides a multi-wind farm virtual direct-axis transient reactance design method for expanding the wind power transmission limit. By introducing virtual DC transient reactance, improving the wind power transmission limit and the initial optimal transient impedance value, the disadvantage that the existing system does not take into account the voltage support capacity of new energy units is solved, and the optimal coordination of transient impedance parameters of wind turbines is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0044] Figure 1 A schematic diagram of a multi-wind farm virtual direct-axis transient reactance design process for expanding the wind power transmission limit provided by an embodiment of the present invention;

[0045] Figure 2 An equivalent circuit diagram of a new energy multi-feed system provided by an embodiment of the present invention;

[0046] Figure 3 A flow chart of transient reactance parameter design of a wind turbine generator system provided by an embodiment of the present invention;

[0047] Figure 4 A topological diagram of a simulation system provided by an embodiment of the present invention;

[0048] Figure 5 The wind power transmission limit P provided in the embodiment of the present invention is Tmax Lower voltage limit value simulation diagram;

[0049] Figure 6 The wind power transmission limit P after adding virtual transient control provided by the embodiment of the present invention Tmax Simulation diagram of lower voltage limit value. DETAILED DESCRIPTION

[0050] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] The purpose of the present invention is to provide a multi-wind farm virtual direct-axis transient reactance design method that expands the wind power transmission limit. By introducing virtual DC transient reactance and utilizing the improved wind power transmission limit to calculate the optimal transient impedance value, the voltage support potential of wind turbines can be brought into play and the power transmission stability of the wind power transmission system can be improved.

[0052] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0053] Figure 1 A schematic diagram of a multi-wind farm virtual direct-axis transient reactance design process for expanding the wind power transmission limit provided by an embodiment of the present invention is shown in FIG. Figure 1 As shown, the present invention provides a multi-wind farm virtual direct-axis transient reactance design method for expanding the wind power transmission limit, comprising:

[0054] Calculate the original wind power transmission limit value of the original multi-feed system;

[0055] Calculate the original wind power expansion range based on the wind power transmission limit value and real-time transmission capacity;

[0056] Calculate the original equivalent transient reactance value of the original multi-feed system according to the original wind power expansion range;

[0057] The virtual DC transient reactance is introduced into the original multi-infeed system to obtain an improved multi-infeed system.

[0058] Calculate the improved wind power delivery limit of the improved multi-feed system;

[0059] When the real-time transmission capacity is less than or equal to the improved wind power transmission limit, the optimal impedance of the improved multi-feed system is calculated according to the original wind power expansion range to obtain the initial optimal transient impedance value;

[0060] The voltage critical value is calculated according to the initial optimal transient impedance value to obtain the dynamic voltage critical value;

[0061] Improvement of dynamic wind power transmission limit of multi-feed system based on dynamic voltage threshold;

[0062] When the real-time transmission capacity is less than or equal to the dynamic wind power transmission limit, the difference between the real-time transmission capacity and the dynamic wind power transmission limit is calculated to obtain the real-time power difference;

[0063] The optimal real-time impedance of the improved multi-feed system is calculated according to the real-time power difference, and the optimal real-time transient impedance value is obtained.

[0064] Furthermore, the calculation formula of the original wind power transmission limit value is:

[0065]

[0066] Among them, P WFmax is the original wind power transmission limit value; P WFi is the real-time power transmitted by the i-th wind farm; P WFj The real-time power transmitted by the jth wind farm; E′ is the virtual electromotive force; U Wcri is the critical voltage value of the grid connection point of the i-th wind farm; X T is the per unit value of the equivalent reactance of the line transformer; X nis the per unit value of the equivalent reactance on the AC system side; S ac is the short-circuit capacity of the grid-connected point; K ji ; n is the number of wind farms in the system.

[0067] Specifically, the calculation formula for the original wind power expansion range is:

[0068] ΔP T =P WT0 -P WFmax ;

[0069] Among them, ΔP T Expand the range for original wind power; P WT0 For real-time transmission capacity.

[0070] Furthermore, the calculation formula of the original equivalent transient reactance value is:

[0071]

[0072] Among them, X′ dΣ is the original equivalent transient reactance value; X′ di is the transient reactance per unit value of the i-th wind farm; X′ dj is the per unit transient reactance value of the jth wind farm.

[0073] Specifically, the calculation formula of the improved wind power transmission limit is:

[0074]

[0075] Among them, P Dmax To improve wind power delivery limits.

[0076] Furthermore, the calculation formula of the initial optimal transient impedance value is:

[0077]

[0078] Among them, X′ dN0 is the initial optimal transient impedance value; ΔP T is the expansion range of the original wind power; E is the system equivalent potential.

[0079] Specifically, the calculation formula of the dynamic voltage threshold is:

[0080]

[0081] Among them, U Tcri is the dynamic voltage critical value; Q WF is the reactive power generated by the wind turbine; X is the sum of the internal impedance of the synchronous motor and the line impedance.

[0082] Furthermore, the calculation formula of the dynamic wind power transmission limit is:

[0083]

[0084] Among them, P Tmax is the dynamic wind power delivery limit.

[0085] Specifically, the calculation formula for the optimal real-time transient impedance value is:

[0086]

[0087] Among them, X′ dNT is the optimal real-time transient impedance value; ΔP is the real-time power difference value.

[0088] refer to Figure 2 and Figure 3 , a wind power transmission module of a multi-infeed wind power system obtains the equivalent transient reactance value of the multi-infeed wind power system taking into account the virtual direct axis transient reactance under the wind power transmission limit.

[0089] Specifically, the calculation method of wind power transmission limit in the renewable energy multi-station transmission system should first monitor the voltage change on a renewable energy station grid-connected bus. When voltage changes occur on other buses, the monitored bus will generate voltage disturbance. The quantified voltage disturbance is defined as the interaction factor K between bus i and bus j. ij =ΔU Wi / ΔU Wj , where ΔU Wi The voltage fluctuation ΔU of the grid-connected bus j Wj The voltage change caused by wind farm bus i when .

[0090] Furthermore, in a multi-input wind power system, the original wind power transmission limit value can be expressed as:

[0091]

[0092] Among them, S ac =EU N / X1; X1 is the equivalent reactance of the wind power grid-connected system.

[0093] Specifically, the wind power transmission limit expansion module designs the transient reactance value of the wind turbine in the multi-feed system according to the real-time transmission power of the wind turbine under the dynamic voltage change; in the multi-feed wind power system, the real-time transmission capacity of the wind turbine is P WT0 When it is judged that the real-time power exceeds the transmission limit, the virtual transient reactance control is started, and the wind power transmission limit P obtained without taking into account the virtual direct axis transient reactance of the wind turbine is WFmax With P WT0Take the difference to obtain the power difference, that is, the extended range of the original wind power, which is expressed as:

[0094] ΔP T = P WT0 - P WFmax

[0095] To improve the power generation efficiency of the wind turbine, the virtual direct-axis transient reactance is introduced into the control system of the wind turbine and taken into account in the wind power transmission limit of the multi-infeed wind power system, actively playing the role of the wind turbine in supporting the voltage. In the multi-infeed system, the original equivalent transient reactance value of the wind turbine is:

[0096]

[0097] After introducing the virtual DC transient reactance, the improved wind power transmission limit should be:

[0098]

[0099] At this time, P Dmax should satisfy P WT0 , that is, P Dmax = P WT0 .

[0100] Based on the power difference ΔP, the initial optimal transient impedance value of the wind power transmission limit that meets the real-time transmission capacity can be obtained as:

[0101]

[0102] Furthermore, the transient reactance parameter design module of the multi-infeed wind power system, based on the transient reactance that meets the real-time transmission capacity of the wind turbine, obtains a new voltage critical value, determines whether to start the virtual transient reactance control, and calculates the transient impedance value of the wind power transmission limit that meets the real-time transmission capacity.

[0103] Specifically, the voltage critical value is related to the virtual DC transient reactance. Since R << X, usually R = 0, and the dynamic voltage critical value of the wind turbine connection point changing with the virtual DC transient reactance can be expressed as:

[0104]

[0105] After introducing the virtual DC transient reactance, with the change of the critical voltage value at the connection point, the dynamic wind power transmission limit is:

[0106]

[0107] At this time, by judging whether P Tmax satisfies P WT0 , it is determined whether to continue to start the virtual transient reactance control.

[0108] If virtual transient reactance control is required, based on the power difference ΔP = P WT0 -P Tmax , the optimal real-time transient impedance value of the wind power transmission limit that meets the real-time transmission capacity can be obtained as:

[0109]

[0110] refer to Figure 4 This embodiment is based on the DigSILENTPowerFactory 15.2 simulation environment to build the following Figure 4 The basic parameters of the 3-machine 9-node grid-connected simulation system with high wind power penetration are shown in Table 1 and Table 2, where, ... T1 , X T2 , X T3 , X T4 , X T5 is the per unit value of transformer impedance, X L1 , X L2 , X L3 is the per unit value of line impedance, X G1 , X G2 , X G3 is the transient reactance of generators G1, G2, and G3; Table 2 shows the parameters of the double-fed wind turbine, where R s is the stator resistance, R r is the rotor resistance, L s is the stator self-inductance of the fan, L m is the mutual inductance between stator and rotor, L r is the fan rotor self-inductance, I rmax is the maximum value of the rotor current.

[0111] Table 1

[0112]

[0113]

[0114] Table 2

[0115]

[0116] Furthermore, according to the impedance parameters of the simulation system in Table 1, through line X L1 , X L2 , X L3 The parallel and series calculation of the impedance after the star-delta transformation can obtain the Thevenin equivalent impedance X on the synchronous motor side of bus B9 n =1.1pu, that is, the equivalent impedance of the AC system side X pu=1.1pu, assuming the system rated capacity is 1000MW, the short-circuit capacity provided by the AC system is about 900MW, and the theoretical limit value of the grid connection point voltage and the theoretical limit value of the wind turbine output power are about 450MW and 0.714pu respectively.

[0117] refer to Figure 5 In the maximum power tracking area, the wind turbine speed and the unit output power increase with the wind speed and enter the constant speed area. The wind turbine rotor speed increases rapidly to the maximum value of 1.2pu, and the output power also increases rapidly to the maximum transmission power value of 437MW. Then the wind turbine enters the power constant area. However, as the output of the wind turbine unit increases further, the grid connection point voltage decreases significantly. At 90s, the DFIG transmission power reaches the maximum value of 437MW, and the voltage at the grid connection point reaches the minimum value of 0.717pu.

[0118] Specifically, according to the impedance parameters of the simulation system in Table 1, through line X L1 , X L2 , X L3 The parallel and series calculation of the impedance after the star-delta transformation can obtain the Thevenin equivalent impedance X on the synchronous motor side of bus B9 n =1.1pu, that is, the equivalent impedance of the AC system side X pu =1.1pu, due to the addition of virtual transient reactance control, the system equivalent impedance is X = X pu +X d ' Σ , setting the rated capacity to 1000MW, the theoretical limit value of the grid connection point voltage and the theoretical limit value of the wind turbine output power have changed.

[0119] Further, Figure 6 and Figure 5 In comparison, when the wind power transmission capacity remains unchanged, the voltage limit value of the grid connection point is raised by starting the virtual transient reactance control.

[0120] The beneficial effects of the present invention are as follows:

[0121] The present invention introduces virtual DC transient reactance and uses the improved wind power transmission limit to calculate the optimal transient impedance value, which fully utilizes the voltage support potential of the wind turbine and significantly improves the power transmission stability of the wind power transmission system.

[0122] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0123] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A multi-wind farm virtual direct-axis transient reactance design method for expanding the wind power transmission limit, characterized in that: include: Calculate the original wind power transmission limit value of the original multi-feed system; Calculate the original wind power expansion range according to the wind power transmission limit value and the real-time transmission capacity; Calculating the original equivalent transient reactance value of the original multi-feed system according to the original wind power expansion range; Introducing a virtual DC transient reactance into the original multi-infeed system to obtain an improved multi-infeed system; calculating an improved wind power transmission limit of the improved multi-feed system; When the real-time transmission capacity is less than or equal to the improved wind power transmission limit, the optimal impedance of the improved multi-feed system is calculated according to the original wind power expansion range to obtain an initial optimal transient impedance value; Perform voltage critical calculation according to the initial optimal transient impedance value to obtain a dynamic voltage critical value; dynamic wind power transmission limit of the improved multi-feed system according to the dynamic voltage threshold; When the real-time transmission capacity is less than or equal to the dynamic wind power transmission limit, calculating the difference between the real-time transmission capacity and the dynamic wind power transmission limit to obtain a real-time power difference; The optimal real-time impedance of the improved multi-feed system is calculated according to the real-time power difference to obtain the optimal real-time transient impedance value.

2. A multi-wind farm virtual direct-axis transient reactance design method for expanding wind power transmission limit according to claim 1, characterized in that: The calculation formula of the original wind power transmission limit value is: Among them, P WFmax is the original wind power transmission limit value; P WFi is the real-time power transmitted by the i-th wind farm; P WFj The real-time power transmitted by the jth wind farm; E′ is the virtual electromotive force; U Wcri is the critical voltage value of the grid connection point of the i-th wind farm; X T is the per unit value of the equivalent reactance of the line transformer; X n is the per unit value of the equivalent reactance on the AC system side; S ac is the short-circuit capacity of the grid-connected point; K ji ; n is the number of wind farms in the system.

3. A multi-wind farm virtual direct-axis transient reactance design method for expanding the wind power transmission limit according to claim 2, characterized in that: The calculation formula of the original wind power expansion range is: ΔP T =P WT0 -P WFmax ; Among them, ΔP T P is the original wind power expansion range; WT0 is the real-time transmission capacity.

4. A multi-wind farm virtual direct-axis transient reactance design method for expanding wind power transmission limit according to claim 3, characterized in that: The calculation formula of the original equivalent transient reactance value is: Among them, X′ dΣ is the original equivalent transient reactance value; X′ di is the transient reactance per unit value of the i-th wind farm; X′ dj is the per unit transient reactance value of the jth wind farm.

5. A multi-wind farm virtual direct-axis transient reactance design method for expanding wind power transmission limit according to claim 4, characterized in that: The calculation formula of the improved wind power transmission limit is: Among them, P Dmax For the improved wind power delivery limit.

6. A multi-wind farm virtual direct-axis transient reactance design method for expanding wind power transmission limit according to claim 5, characterized in that: The calculation formula of the initial optimal transient impedance value is: Among them, X′ dN0 is the initial optimal transient impedance value; ΔP T is the expansion range of the original wind power; E is the system equivalent potential.

7. A multi-wind farm virtual direct-axis transient reactance design method for expanding wind power transmission limit according to claim 6, characterized in that: The calculation formula of the dynamic voltage critical value is: Among them, U Tcri is the dynamic voltage critical value; Q WF is the reactive power generated by the wind turbine; X is the sum of the internal impedance of the synchronous motor and the line impedance.

8. A multi-wind farm virtual direct-axis transient reactance design method for expanding wind power transmission limit according to claim 7, characterized in that: The calculation formula of the dynamic wind power transmission limit is: Among them, P Tmax is the dynamic wind power delivery limit.

9. A multi-wind farm virtual direct-axis transient reactance design method for expanding wind power transmission limit according to claim 8, characterized in that: The calculation formula of the optimal real-time transient impedance value is: Among them, X′ dNT is the optimal real-time transient impedance value; ΔP is the real-time power difference value.

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