Active energy calling method and device of offshore wind power direct current sending-out system and medium

Abstract

The invention relates to the technical field of electric power systems, and discloses an active energy calling method and device for an offshore wind power direct current sending-out system and a medium, and the method comprises the steps: predicting a frequency change track of the offshore wind power direct current sending-out system after power disturbance based on a land alternating current power grid frequency response model; calculating a support power reference value of the land MMC participating in the primary frequency modulation of the system; predicting operation variables of the offshore wind power direct current sending-out system after power disturbance based on the direct current system operation variable prediction model, and judging whether the system has an operation safety problem or not; if yes, controlling the supporting power of the land MMC according to the supporting power reference value, so that the land MMC participates in primary frequency modulation; and if not, optimizing the power reference values of the land MMC and the OWF by using the control variable optimization model, and controlling the output power of the MMC and the OWF. According to the technical scheme, the frequency modulation potential of the offshore wind plant can be fully utilized, the working efficiency of the system is improved, and the reliability of wind power output is improved.

Description

Technical Field

[0001] Embodiments of the present invention relate to the technical field of power systems, and specifically to an active energy calling method, device, equipment and computer-readable storage medium for an offshore wind power direct current transmission system. Background Art

[0002] The effective consumption of offshore wind power is of great significance for the construction of a new power system. As offshore wind power development gradually advances to deep sea, high-voltage direct current transmission technology based on modular multilevel converters (MMC) has become one of the main solutions for offshore wind power transmission. Due to the disadvantages of MMC such as high investment cost and difficult maintenance, some scholars have proposed an offshore platform solution based on diode rectifiers (DR). DR has the advantages of low cost and high power density. The use of lightweight direct current transmission based on offshore DR and onshore MMC is a promising offshore wind power transmission solution.

[0003] When the proportion of offshore wind power in the onshore AC power grid reaches a certain level, offshore wind power needs to participate in the system frequency regulation. Considering the safe operation of the DC system, its frequency regulation is essentially the coordinated control of DC voltage and AC frequency by the onshore MMC. As the scale of offshore wind power transmission continues to grow, a single point-to-point DC transmission system is difficult to meet the needs of transmission capacity and wind farm distribution. The use of multi-terminal DR-MMC DC grid transmission can improve the reliability of wind power transmission. Compared with the two-terminal DR-MMC DC transmission system, the operating variables of the multi-terminal DR-MMC grid are greatly increased, which brings great difficulties to the coordinated control of DC voltage and AC grid frequency. The existing frequency regulation method of the lightweight offshore wind power DC transmission system of the multi-terminal DR-MMC grid cannot fully utilize the frequency regulation potential of offshore wind farms, which leads to low system efficiency. Summary of the invention

[0004] In view of the above problems, the embodiments of the present invention provide an active energy calling method, device, equipment and computer-readable storage medium for an offshore wind power DC transmission system, which are used to solve the problem that the frequency regulation method of the existing multi-terminal DR-MMC power grid's lightweight offshore wind power DC transmission system cannot fully utilize the frequency regulation potential of offshore wind farms.

[0005] According to one aspect of an embodiment of the present invention, a method for actively calling energy of an offshore wind power DC transmission system is provided, which is applied to the offshore wind power DC transmission system, wherein the offshore wind power DC transmission system includes a plurality of OWFs (offshore wind farms), a plurality of DRs and a plurality of MMCs. The method includes: predicting the frequency change trajectory of the offshore wind power DC transmission system after a power disturbance occurs based on an onshore AC power grid frequency response model to obtain a frequency prediction result;

[0006] Calculating a reference value of supporting power for the onshore MMC to participate in the primary frequency regulation of the system according to the frequency prediction result;

[0007] Based on the DC system operation variable prediction model, the operation variables of the offshore wind power DC transmission system after the power disturbance occurs are predicted; according to the operation variables, whether the system has an operation safety problem;

[0008] If the system has no operational safety problems, the onshore MMC support power is controlled according to the support power reference value, so that the onshore MMC participates in a frequency modulation;

[0009] If the system has operational safety problems, the control variable optimization model is used to optimize the power reference values ​​of the onshore MMC and OWF; and the output power of the MMC and OWF is controlled according to the optimized power reference values ​​of the onshore MMC and OWF.

[0010] In an optional manner, the onshore AC power grid frequency response model is expressed as:

[0011]

[0012] Among them, Δδ represents the power angle change of the synchronous generator of the AC power grid, Δω represents the speed change of the synchronous generator, and Δθ s Indicates the phase change of the bus voltage connected to the MMC, Δf s Indicates the change in MMC output frequency, Δθ d Indicates the phase change of the bus voltage connected to the load, ΔP m Represents the change in mechanical power of the synchronous generator. The dot above each change represents the derivative of the change with respect to time t, ΔP d Indicates the change in load active power, A pfr represents the system matrix, E pfr Represents the input matrix.

[0013] In an optional manner, the frequency change trajectory of the offshore wind power DC transmission system after the power disturbance is predicted based on the onshore AC power grid frequency response model to obtain a frequency prediction result, including:

[0014] Inputting the power flow data of the offshore wind power DC transmission system into the onshore AC power grid frequency response model to obtain the onshore AC power grid frequency response data based on the state space;

[0015] Based on the frequency response data, the frequency change trajectory of the offshore wind power DC transmission system after the power disturbance occurs is predicted to obtain a frequency prediction result.

[0016] In an optional manner, according to the frequency prediction result, calculating the support power reference value of the onshore MMC participating in the primary frequency regulation of the system includes:

[0017] According to the frequency prediction result, a maximum frequency deviation predicted after a power disturbance occurs in the system is obtained;

[0018] Based on the predicted maximum frequency deviation, a change in the onshore MMC power reference value after a power disturbance occurs in the system is calculated;

[0019] According to the change in the onshore MMC power reference value after the power disturbance occurs in the system, a supporting power reference value for the onshore MMC to participate in the primary frequency modulation of the system is obtained.

[0020] In an optional manner, the expression for calculating the change in the onshore MMC power reference value after the system has a power disturbance is:

[0021]

[0022] in, represents the change in the onshore MMC power reference value after the kth disturbance, and They represent the inertia constant and damping coefficient after the kth disturbance, Δf represents the frequency deviation, and v c Indicates the frequency change rate when the control strategy switches, ΔP max Indicates the maximum allowable power change of the onshore MMC, represents the maximum frequency change rate after k disturbances, represents the maximum frequency deviation predicted after the kth disturbance.

[0023] In an optional manner, the DC system operation variable prediction model is expressed as:

[0024]

[0025] in, represents the DC voltage of MMC at time t, represents the AC voltage of DR at time t, represents the power reference value of MMC at time t, represents the active power reference value of OWF at time t, and C is the parameter matrix.

[0026] In an optional manner, judging whether the system has an operation safety problem according to the operation variable includes:

[0027] If any operating variable exceeds the corresponding variable limit range, it is determined that the system has an operating safety problem;

[0028] If all operating variables do not exceed the corresponding variable limit ranges, it is determined that the system has no operating safety issues.

[0029] In an optional manner, if the system has an operational safety problem, the control variable optimization model is used to optimize the power reference values ​​of the onshore MMC and OWF, and correct the output power of the MMC and OWF, including:

[0030] The control variable optimization model includes: objective function and constraints;

[0031] The expression of the objective function is:

[0032]

[0033] The constraint condition is expressed as:

[0034]

[0035] in, It represents the MMC support power required when the frequency is controlled at time t. represents the power reference value of MMC at time t, represents the active power reference value of OWF at time t, Indicates the initial power reference value of MMC. represents the active power reference value of OWF at the previous moment, w represents the number of OWFs, m represents the number of onshore MMCs, and U ed Indicates the DC voltage of DR, U ac Indicates the AC voltage of DR, U mmc Indicates the DC voltage of MMC, represents the OWF output power, η is the penalty factor, which indicates the impact of not meeting the expected frequency support; and U ed They represent the upper and lower limits of the DC voltage of DR, and U ac Respectively represent the upper and lower limits of the AC voltage of DR, and U mmc Respectively represent the upper and lower limits of the DC voltage of the MMC, and and represent the upper and lower limits of OWF output power respectively;

[0036] The objective function is solved according to the constraint conditions to optimize the power reference values ​​of the onshore MMC and the OWF.

[0037] According to another aspect of an embodiment of the present invention, there is provided an energy active calling device for an offshore wind power DC transmission system, which is applied to the offshore wind power DC transmission system, wherein the offshore wind power DC transmission system comprises a plurality of OWFs, a plurality of DRs and a plurality of MMCs, and the device comprises: a calculation module, a judgment module and a control module;

[0038] A calculation module is used to predict the frequency change trajectory of the offshore wind power DC transmission system after the power disturbance occurs based on the onshore AC power grid frequency response model to obtain a frequency prediction result; according to the frequency prediction result, calculate the support power reference value of the onshore MMC participating in the primary frequency regulation of the system;

[0039] A judgment module is used to predict the operating variables of the offshore wind power DC transmission system after the power disturbance occurs based on the DC system operating variable prediction model; and judge whether the system has an operating safety problem according to the operating variables;

[0040] The control module is used for controlling the onshore MMC support power according to the support power reference value to enable the onshore MMC to participate in primary frequency modulation if the system has no operational safety problems; optimizing the power reference values ​​of the onshore MMC and OWF by using a control variable optimization model if the system has operational safety problems; and controlling the output power of the MMC and OWF according to the optimized power reference values ​​of the onshore MMC and OWF.

[0041] According to another aspect of an embodiment of the present invention, there is provided an active energy calling device for an offshore wind power DC transmission system, comprising: a processor, a memory, a communication interface and a communication bus, wherein the processor, the memory and the communication interface communicate with each other via the communication bus; the memory is used to store at least one executable instruction, wherein the executable instruction enables the processor to perform the operation of the active energy calling method for an offshore wind power DC transmission system as described in any one of the above items.

[0042] According to another aspect of an embodiment of the present invention, a computer-readable storage medium is provided, wherein the storage medium stores at least one executable instruction, wherein the executable instruction enables an energy active invocation device / apparatus of an offshore wind power DC transmission system to perform an operation of an energy active invocation method of an offshore wind power DC transmission system as described in any one of the above.

[0043] The embodiment of the present invention establishes an onshore AC power grid frequency response model for the offshore wind power grid-connected system to predict the frequency change trajectory after the power disturbance occurs in the system; proposes a power control strategy for MMC to participate in primary frequency regulation based on frequency prediction, and calculates the support power reference value of onshore MMC to participate in primary frequency regulation; establishes a DR-MMC DC power grid operation variable prediction model to predict the DC system operation variables; predicts whether there are operational safety issues based on the DC system operation variable prediction model; establishes a control variable optimization model that considers the DC system operation safety constraints, optimizes the power reference values ​​of onshore MMC and OWF, and corrects the output power of MMC and OWF. The embodiment of the present invention performs primary frequency regulation control through an energy active call method of a lightweight offshore wind power DC transmission system based on a multi-terminal DR-MMC power grid, fully utilizes the frequency regulation potential of offshore wind farms, improves system work efficiency, and improves the reliability of wind power transmission.

[0044] The above description is only an overview of the technical solution of the embodiment of the present invention. In order to more clearly understand the technical means of the embodiment of the present invention, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the embodiment of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The accompanying drawings are only used to illustrate the embodiments and are not to be considered as limiting the present invention. In addition, the same reference symbols are used to represent the same components throughout the accompanying drawings. In the accompanying drawings:

[0046] Figure 1 A flow chart showing an embodiment of a method for actively calling energy of an offshore wind power DC transmission system provided by the present invention;

[0047] Figure 2 A schematic diagram of the power grid structure of a modified IEEE 39-node system in a preferred embodiment of the energy active call method for an offshore wind power DC transmission system provided by the present invention is shown;

[0048] Figure 3 A schematic diagram showing frequency response curves of the bus 4 in four control modes in a preferred embodiment of the method for actively calling energy of an offshore wind power DC transmission system provided by the present invention is shown;

[0049] Figure 4 The DC voltage variation curves of each converter station in the preferred embodiment of the energy active call method of the offshore wind power DC transmission system provided by the present invention are shown;

[0050] Figure 5 A structural schematic diagram showing an embodiment of an energy active calling device for an offshore wind power DC transmission system provided by the present invention;

[0051] Figure 6 A structural schematic diagram of an embodiment of an energy active call device for an offshore wind power DC transmission system provided by the present invention is shown. DETAILED DESCRIPTION

[0052] Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0053] Figure 1 The flowchart of an embodiment of the method for actively calling energy of an offshore wind power DC transmission system of the present invention is shown, which is applied to an offshore wind power DC transmission system, wherein the offshore wind power DC transmission system includes several OWFs (offshore wind farms), several DRs and several MMCs, and the method is executed by a control device. Figure 1 As shown, the method comprises the following steps:

[0054] Step 110: Based on the onshore AC power grid frequency response model, the frequency change trajectory of the offshore wind power DC transmission system after the power disturbance occurs is predicted to obtain a frequency prediction result; based on the frequency prediction result, a support power reference value of the onshore MMC participating in the primary frequency regulation of the system is calculated.

[0055] In some embodiments of the present invention, the frequency deviation of the onshore power grid is caused by active power imbalance, and the active power change has little effect on the AC voltage. Therefore, the influence of reactive power flow and AC voltage can be ignored in the primary frequency modulation. The DC power flow model shown in formula (1) is used to calculate the active power flow.

[0056]

[0057] In the formula, ΔP e Indicates the change in electromagnetic power of the synchronous machine, ΔP s Represents the output power change vector of the onshore MMC, ΔP d represents the change in active load, B represents the admittance matrix, Δδ represents the change in power angle, Δθ s Indicates the phase change of the bus voltage connected to the MMC, Δθ d Indicates the phase change of the bus voltage connected to the load.

[0058] Eliminate Δθ in (1) d , we can get:

[0059] ΔP e =E gg Δδ+E gs Δθ s +W gd ΔP d(2)

[0060] Where:

[0061]

[0062] Similarly, there are:

[0063] ΔP s =E sg Δδ+E ss Δθ s +W sd ΔP d (4)

[0064] Where:

[0065]

[0066] The rotor motion equation of the synchronous machine can be expressed as:

[0067]

[0068] Where: Δδ i represents the power angle change of the i-th synchronous machine, Δω i represents the speed change of the i-th synchronous machine, represents the mechanical power change of the i-th synchronous machine, represents the change in electromagnetic power of the i-th synchronous machine, and represent the rotor inertia constant and the damping coefficient of the i-th synchronous machine respectively.

[0069] Mechanical power change Determined by the speed regulator, the simplified model of the speed regulator can be written as formula (7).

[0070]

[0071] Where: is the reheating time constant, R i represents the adjustment coefficient of the ith synchronous machine, Indicates the proportion of the total power produced by the high pressure turbine.

[0072] Considering that MMC uses virtual synchronous control to participate in a frequency modulation, the phase change of MMC is and output power change Formula (8) should be satisfied.

[0073]

[0074] In the formula, Indicates the frequency deviation of MMC, represents the virtual inertia of MMC, Represents the virtual damping coefficient of MMC.

[0075] Combining equations (2) to (8), the frequency response of the onshore power grid based on the state space can be obtained, that is, the expression of the onshore AC power grid frequency response model is:

[0076]

[0077] Among them, Δδ represents the power angle change of the synchronous generator of the AC power grid, Δω represents the speed change of the synchronous generator, and Δθ s Indicates the phase change of the bus voltage connected to the MMC, Δf s Indicates the change in MMC output frequency, Δθ d Indicates the phase change of the bus voltage connected to the load, ΔP m Represents the change in mechanical power of the synchronous generator. The dot above each change represents the derivative of the change with respect to time t, ΔP d Indicates the change in load active power, A pfr represents the system matrix, E pfr Represents the input matrix, and the detailed expression is:

[0078]

[0079]

[0080] In an optional manner, the frequency change trajectory of the offshore wind power DC transmission system after the power disturbance is predicted based on the onshore AC power grid frequency response model to obtain a frequency prediction result, including:

[0081] Inputting the power flow data of the offshore wind power DC transmission system into the onshore AC power grid frequency response model to obtain the onshore AC power grid frequency response data based on the state space;

[0082] Based on the frequency response data, the frequency change trajectory of the offshore wind power DC transmission system after the power disturbance occurs is predicted to obtain a frequency prediction result.

[0083] In an optional manner, according to the frequency prediction result, calculating the support power reference value of the onshore MMC participating in the primary frequency regulation of the system includes:

[0084] According to the frequency prediction result, a maximum frequency deviation predicted after a power disturbance occurs in the system is obtained;

[0085] Based on the predicted maximum frequency deviation, a change in the onshore MMC power reference value after a power disturbance occurs in the system is calculated;

[0086] According to the change in the onshore MMC power reference value after the power disturbance occurs in the system, a supporting power reference value for the onshore MMC to participate in the primary frequency modulation of the system is obtained.

[0087] In some embodiments of the present invention, when the frequency of the AC system changes rapidly, the MMC should provide inertial support for the system; when the frequency changes gradually stabilize, if the MMC continues to provide inertial support for the onshore AC system, it will hinder the speed of frequency recovery. At this time, the MMC should provide damping support for the onshore AC system. Based on this, the change in the onshore MMC power reference value after the system has a power disturbance is calculated as shown in formula (12):

[0088]

[0089] In the formula, represents the change in the power reference value after the kth disturbance, and They represent the inertia constant and damping coefficient after the kth disturbance, Δf represents the frequency deviation, and v c represents the RoCoF when the strategy is switched, which is a negative value and satisfies equation (13).

[0090]

[0091] By adjusting and The switching point of the strategy can be controlled. When it approaches 0, the MMC enters the damping control mode at the initial working point. When it is close to 0, MMC enters the damping control mode at the lowest frequency. and It can be reasonably set according to the frequency change prediction result, which is expressed as formula (14).

[0092]

[0093] In the formula, ΔP max Indicates the maximum allowable power change of the MMC, represents the maximum RoCoF after k perturbations, It represents the maximum frequency deviation predicted by the onshore AC power grid frequency response model after the kth disturbance.

[0094] Step 120: predicting the operating variables of the offshore wind power DC transmission system after the power disturbance occurs based on the DC system operating variable prediction model; and judging whether the system has an operating safety problem according to the operating variables.

[0095] In some embodiments of the present invention, the DR-MMC DC network resistance model is shown in formula (15):

[0096]

[0097] Where: U dc Represents the DC voltage vector; R L Represents the resistance matrix of the DC network; I dc represents the DC current vector; P dc represents the injected active power vector.

[0098] The DC side model of DR can be regarded as a voltage source with impedance, and its electromotive force is proportional to the voltage on the AC side of DR, which can be expressed as formula (16).

[0099] U ed =K dr U ac (16)

[0100] Where U ed represents the electromotive force vector of the internal node, U ac K represents the AC voltage vector of DR. dr Represents the scaling factor matrix.

[0101] Linearizing equation (15), we can obtain:

[0102]

[0103] Where: ΔP mmc and ΔP w They represent the active power changes of MMC and offshore wind farm, ΔU mmc Indicates the DC voltage change of MMC, ΔU ed Indicates the change in the AC electromotive force of DR, J mm , J mw , J wm and J ww Submatrix representing the Jacobian matrix of the DC network.

[0104] Without considering the change of DC voltage reference value, the operating variables of DR-MMC DC system can be obtained by equation (18).

[0105]

[0106] Where: ΔP mmc and ΔP w Represent the active power changes of MMC and OWF, ΔU mmc Indicates the DC voltage change of MMC, ΔU ac Indicates the AC voltage change of DR, ΔP mref and ΔP wrefRespectively represent the changes in the active power reference values ​​of MMC and OWF. A and C are parameter matrices, and the detailed expressions are:

[0107]

[0108]

[0109] In the dynamic process, the active power change of MMC also needs to consider the lumped capacitance. Therefore, the active power change of MMC should be corrected as:

[0110]

[0111] Where ΔP ma It represents the power change vector of MMC after considering the MMC capacitor, C eq represents the diagonal matrix consisting of the lumped capacitances of the MMC.

[0112] The derivation of formula (18) adopts the idea of ​​linearization. In order to reduce the error caused by linearization, formula (22) is used instead of (18), that is, the expression of the DC system operation variable prediction model is:

[0113]

[0114] Where: represents the DC voltage of MMC at time t, represents the AC voltage of DR at time t, It represents the power reference value of MMC at time t, represents the active power reference value of OWF at time t, and C is the parameter matrix.

[0115] In an optional manner, judging whether the system has an operation safety problem according to the operation variable includes:

[0116] If any operating variable exceeds the corresponding variable limit range, it is determined that the system has an operating safety problem;

[0117] If all operating variables do not exceed the corresponding variable limit ranges, it is determined that the system has no operating safety issues.

[0118] Step 130: If the system has no operational safety problem, the onshore MMC support power is controlled according to the support power reference value, so that the onshore MMC participates in a frequency modulation;

[0119] If the system has operational safety problems, the control variable optimization model is used to optimize the power reference values ​​of the onshore MMC and OWF; and the output power of the MMC and OWF is controlled according to the optimized power reference values ​​of the onshore MMC and OWF.

[0120] In an optional manner, the control variable optimization model includes: an objective function and constraints.

[0121] In some embodiments of the present invention, by optimizing the output power of MMC and OWF, it is possible to achieve offshore wind power participating in the primary frequency regulation of the onshore AC system and ensure that the DC voltage is within the normal range. If the DC voltage cannot be limited to the normal range by OWF alone, part of the support power of MMC must be abandoned. Optimization objective function (23):

[0122]

[0123] Where: It represents the MMC support power vector required for frequency control at time t, and η is the penalty factor, which represents the impact of not meeting the expected frequency support.

[0124] The constraints that each operating variable in the system needs to meet are:

[0125]

[0126] Where: Constraint (a) ensures that the DC voltage of the DR does not exceed the limit. Constraint (b) ensures that the AC voltage of the DR does not exceed the limit. Constraint (d) ensures that the active power of the OWF does not exceed the limit. and U ed They represent the upper and lower limits of the DC voltage of DR, and U ac Respectively represent the upper and lower limits of the AC voltage of DR, and U mmc Respectively represent the upper and lower limits of the DC voltage of the MMC, and And they represent the upper and lower limits of OWF power respectively.

[0127] In an optional manner, the objective function is solved according to the constraint conditions to optimize the power reference values ​​of the onshore MMC and the OWF.

[0128] The embodiment of the present invention establishes an onshore AC power grid frequency response model for the offshore wind power grid-connected system to predict the frequency change trajectory after the power disturbance occurs in the system; proposes a power control strategy for MMC to participate in primary frequency regulation based on frequency prediction, and calculates the support power reference value of onshore MMC to participate in primary frequency regulation; establishes a DR-MMC DC power grid operation variable prediction model to predict the DC system operation variables; predicts whether there are operational safety issues based on the DC system operation variable prediction model; establishes a control variable optimization model that considers the DC system operation safety constraints, optimizes the power reference values ​​of onshore MMC and OWF, and corrects the output power of MMC and OWF. The embodiment of the present invention performs primary frequency regulation control through an energy active call method of a lightweight offshore wind power DC transmission system based on a multi-terminal DR-MMC power grid, fully utilizes the frequency regulation potential of offshore wind farms, improves system work efficiency, and improves the reliability of wind power transmission.

[0129] As one of the preferred embodiments, a case study was conducted in a modified IEEE39 node system to verify the effectiveness of the proposed method for active energy call of lightweight offshore wind power DC transmission system based on model predictive control. The grid structure of the modified IEEE39 node system is as follows: Figure 2 The three OWFs are connected to a seven-terminal DR-MMC grid, and the four onshore MMCs are connected to a modified IEEE39 node system. The main parameters of the DR-MMC grid are shown in Tables 1 and 2. To ensure the balance between supply and demand, the load of each node is increased in the same proportion.

[0130] Table 1 Main parameters of converter station

[0131] property value Rated DC voltage(kV) 400 MMC rated capacity (MVA) 400 DR rated capacity (MVA) 500 MMC control mode <![CDATA[P-U dc Droop Control]]> MMC1 reference power (MW) 300 MMC2 reference power (MW) 250 MMC3 reference power (MW) 250 MMC4 reference power (MW) 300 DR1 output power (MW) 410 DR2 output power (MW) 410 DR3 output power (MW) 300

[0132] Table 2 Line impedance

[0133] line Impedance(Ω) 1 1.1 2 4.5 3 1.3 4 5.6 5 1.1 6 1.1 7 3.2

[0134] The frequency modulation method proposed in the present invention is applied to the onshore MMC2. A 500MW load step is applied to bus 16, and the inertia constant of MMC2 is set according to the frequency change rate of bus 4. The reserve capacity of MMC2 is 150MVA, and the RoCoF of bus 4 is -0.18Hz / s when the disturbance occurs. According to formula (14), the inertia constant of MMC2 under the system benchmark is 4.89s. Assuming that MMC2 participates in a frequency modulation in the constant inertia control mode, the predicted minimum frequency point of bus 4 is -0.17Hz. When the frequency deviation of bus 4 reaches -0.17Hz, MMC2 outputs maximum power in the damping control mode. According to formula (14), the damping coefficient of MMC2 under the system benchmark is 27.58. During the primary frequency modulation, the control mode of MMC2 switches between inertia control and damping control, and the switching logic is formula (12). To verify the effectiveness of the proposed frequency modulation method, simulations were performed under four control modes: the control method proposed in this invention, constant power control, constant inertia control, and VSG control. In the constant inertia and VSG control modes, the inertia constant of MMC2 was set to 4.89s, and the damping coefficient in the VSG control mode was taken as the typical value of 2 for synchronous machines.

[0135] Figure 3 The frequency response curves of bus 4 under four control modes are shown in Figure 2. Compared with the other three control modes, the frequency response is significantly improved in terms of the lowest frequency point and the recovery speed after the frequency modulation method proposed in this article is adopted. Constant inertia control or VSG control will increase the lowest frequency point, but the time for the frequency to reach the lowest point will be delayed, and the subsequent recovery speed will also be reduced. Constant inertia control or VSG control will reduce the response speed of the system due to the increase in equivalent inertia, making the frequency recovery slower. The simulation results show that the frequency modulation method proposed in this invention can automatically switch the MMC to the damping control mode in the suppression stage, thereby accelerating the frequency recovery speed and achieving better primary frequency modulation performance.

[0136] The DC voltage variation curve of each converter station is as follows: Figure 4 As shown, it can be seen that when the power provided by MMC2 to the onshore power grid increases, the DC voltage of each converter station decreases significantly, and the output power of OWF3 begins to increase, ensuring that the DC voltage of each converter station is not less than 0.95pu. As the output power of MMC2 decreases, the DC voltage of each converter station increases, and the output power of OWF3 decreases, ensuring that the DC voltage of each converter station does not exceed 1.025pu. Therefore, the frequency modulation method proposed in the present invention can effectively ensure that the operating variables of the DR-MMC power grid do not exceed the limit.

[0137] Figure 5 The structure diagram of an embodiment of the energy active calling device of the offshore wind power DC transmission system of the present invention is shown; Figure 5As shown, the device 500 is applied to an offshore wind power DC transmission system, the offshore wind power DC transmission system includes a plurality of OWFs, a plurality of DRs and a plurality of MMCs, and the device includes: a calculation module 510, a judgment module 520 and a control module 530;

[0138] The calculation module 510 is used to predict the frequency change trajectory of the offshore wind power DC transmission system after the power disturbance occurs based on the onshore AC power grid frequency response model to obtain a frequency prediction result; according to the frequency prediction result, calculate the support power reference value of the onshore MMC participating in the primary frequency regulation of the system;

[0139] The judgment module 520 is used to predict the operating variables of the offshore wind power DC transmission system after the power disturbance occurs based on the DC system operating variable prediction model; and judge whether the system has an operating safety problem according to the operating variables;

[0140] The control module 530 is used to control the onshore MMC support power according to the support power reference value if there is no operational safety problem in the system, so that the onshore MMC participates in a frequency modulation; if there is an operational safety problem in the system, optimize the power reference values ​​of the onshore MMC and OWF by using the control variable optimization model; and control the output power of the MMC and OWF according to the optimized power reference values ​​of the onshore MMC and OWF.

[0141] In an optional manner, the onshore AC power grid frequency response model is expressed as:

[0142]

[0143] Among them, Δδ represents the power angle change of the synchronous generator of the AC power grid, Δω represents the speed change of the synchronous generator, and Δθ s Indicates the phase change of the bus voltage connected to the MMC, Δf s Indicates the change in MMC output frequency, Δθ d Indicates the phase change of the bus voltage connected to the load, ΔP m Represents the change in mechanical power of the synchronous generator. The dot above each change represents the derivative of the change with respect to time t, ΔP d Indicates the change in load active power, A pfr represents the system matrix, E pfr Represents the input matrix.

[0144] In an optional manner, the frequency change trajectory of the offshore wind power DC transmission system after the power disturbance is predicted based on the onshore AC power grid frequency response model to obtain a frequency prediction result, including:

[0145] Inputting the power flow data of the offshore wind power DC transmission system into the onshore AC power grid frequency response model to obtain the onshore AC power grid frequency response data based on the state space;

[0146] Based on the frequency response data, the frequency change trajectory of the offshore wind power DC transmission system after the power disturbance occurs is predicted to obtain a frequency prediction result.

[0147] In an optional manner, according to the frequency prediction result, calculating the support power reference value of the onshore MMC participating in the primary frequency regulation of the system includes:

[0148] According to the frequency prediction result, a maximum frequency deviation predicted after a power disturbance occurs in the system is obtained;

[0149] Based on the predicted maximum frequency deviation, a change in the onshore MMC power reference value after a power disturbance occurs in the system is calculated;

[0150] According to the change in the onshore MMC power reference value after the power disturbance occurs in the system, a supporting power reference value for the onshore MMC to participate in the primary frequency modulation of the system is obtained.

[0151] In an optional manner, the expression for calculating the change in the onshore MMC power reference value after the system has a power disturbance is:

[0152]

[0153] in, represents the change in the onshore MMC power reference value after the kth disturbance, and They represent the inertia constant and damping coefficient after the kth disturbance, Δf represents the frequency deviation, and v c Indicates the frequency change rate when the control strategy switches, ΔP max Indicates the maximum allowable power change of the onshore MMC, represents the maximum frequency change rate after k disturbances, represents the maximum frequency deviation predicted after the kth disturbance.

[0154] In an optional manner, the DC system operation variable prediction model is expressed as:

[0155]

[0156] Where: represents the DC voltage of MMC at time t, represents the AC voltage of DR at time t, It represents the power reference value of MMC at time t, represents the active power reference value of OWF at time t, and C is the parameter matrix.

[0157] In an optional manner, judging whether the system has an operation safety problem according to the operation variable includes:

[0158] If any operating variable exceeds the corresponding variable limit range, it is determined that the system has an operating safety problem;

[0159] If all operating variables do not exceed the corresponding variable limit ranges, it is determined that the system has no operating safety issues.

[0160] In an optional manner, if the system has an operational safety problem, the control variable optimization model is used to optimize the power reference values ​​of the onshore MMC and OWF, and correct the output power of the MMC and OWF, including:

[0161] The control variable optimization model includes: objective function and constraints;

[0162] The expression of the objective function is:

[0163]

[0164] The constraint condition is expressed as:

[0165]

[0166] in, It represents the MMC support power required when the frequency is controlled at time t. represents the power reference value of MMC at time t, represents the active power reference value of OWF at time t, Indicates the initial power reference value of MMC. represents the active power reference value of OWF at the previous moment, w represents the number of OWFs, m represents the number of onshore MMCs, and U ed Indicates the DC voltage of DR, U ac Indicates the AC voltage of DR, U mmc Indicates the DC voltage of MMC, represents the OWF output power, η is the penalty

[0167] The penalty factor represents the impact of not meeting the frequency support expectations; and U ed They represent the upper and lower limits of the DC voltage of DR, and U ac Respectively represent the upper and lower limits of the AC voltage of DR, and U mmcRespectively represent the upper and lower limits of the DC voltage of the MMC, and and represent the upper and lower limits of OWF output power respectively;

[0168] The objective function is solved according to the constraint conditions to optimize the power reference values ​​of the onshore MMC and the OWF.

[0169] As for the device embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0170] Figure 6 A structural schematic diagram of an embodiment of an energy active call device of an offshore wind power DC transmission system of the present invention is shown. The specific embodiment of the present invention does not limit the specific implementation of the device.

[0171] like Figure 6 As shown, the energy active calling device of the offshore wind power DC transmission system may include: a processor (processor) 602, a communication interface (Communications Interface) 604, a memory (memory) 606, and a communication bus 608.

[0172] The processor 602, the communication interface 604, and the memory 606 communicate with each other via a communication bus 608. The communication interface 604 is used to communicate with other devices such as a client or other server network elements. The processor 602 is used to execute a program 610, which can specifically execute the relevant steps in the above-mentioned energy active call method embodiment for an offshore wind power DC transmission system.

[0173] Specifically, the program 610 may include program code including computer executable instructions.

[0174] The processor 602 may be a central processing unit (CPU), or an application-specific integrated circuit (ASIC), or one or more integrated circuits configured to implement the embodiment of the present invention. The one or more processors included in the energy active call device of the offshore wind power DC transmission system may be processors of the same type, such as one or more CPUs; or processors of different types, such as one or more CPUs and one or more ASICs.

[0175] The memory 606 is used to store the program 610. The memory 606 may include a high-speed RAM memory, and may also include a non-volatile memory (non-volatile memory), such as at least one disk memory.

[0176] The algorithms or displays provided herein are not inherently related to any particular computer, virtual system or other device. In addition, the embodiments of the present invention are not directed to any particular programming language.

[0177] In the description provided herein, a large number of specific details are described. However, it is understood that embodiments of the present invention can be practiced without these specific details. Similarly, in order to simplify the present invention and help understand one or more of the various inventive aspects, in the above description of exemplary embodiments of the present invention, the various features of the embodiments of the present invention are sometimes grouped together into a single embodiment, figure, or description thereof. Wherein, the claims that follow the specific embodiment are hereby expressly incorporated into the specific embodiment, wherein each claim itself is a separate embodiment of the present invention.

[0178] Those skilled in the art will appreciate that the modules in the devices in the embodiments may be adaptively changed and arranged in one or more devices different from the embodiments. The modules or units or components in the embodiments may be combined into one module or unit or component, and further may be divided into a plurality of submodules or subunits or subcomponents. Except that at least some of such features and / or processes or units are mutually exclusive.

[0179] It should be noted that the above embodiments illustrate the present invention rather than limit it, and that those skilled in the art may design alternative embodiments without departing from the scope of the appended claims. In the claims, any reference symbol between brackets shall not be construed as a limitation on the claims. The word "comprising" does not exclude the presence of elements or steps not listed in the claims. The word "one" or "an" preceding an element does not exclude the presence of a plurality of such elements. The present invention may be implemented by means of hardware comprising a number of different elements and by means of a suitably programmed computer. In a unit claim that lists a number of devices, several of these devices may be embodied by the same hardware item. The use of the words first, second, and third, etc. does not indicate any order. These words may be interpreted as names. The steps in the above embodiments, unless otherwise specified, should not be understood as limitations on the order of execution.

Claims

1. A method for actively calling energy of an offshore wind power direct current transmission system, characterized in that: Applied to an offshore wind power DC transmission system, the offshore wind power DC transmission system includes a plurality of OWFs, a plurality of DRs and a plurality of MMCs, and the method includes: Based on the onshore AC power grid frequency response model, the frequency change trajectory of the offshore wind power DC transmission system after the power disturbance is predicted to obtain the frequency prediction result; Calculating a reference value of supporting power for the onshore MMC to participate in the primary frequency regulation of the system according to the frequency prediction result; Based on the DC system operation variable prediction model, the operation variables of the offshore wind power DC transmission system after the power disturbance occurs are predicted; according to the operation variables, whether the system has an operation safety problem; If the system has no operational safety problems, the onshore MMC support power is controlled according to the support power reference value, so that the onshore MMC participates in a frequency modulation; If the system has operational safety problems, the control variable optimization model is used to optimize the power reference values ​​of the onshore MMC and OWF; and the output power of the MMC and OWF is controlled according to the optimized power reference values ​​of the onshore MMC and OWF.

2. The method for actively calling energy of an offshore wind power DC transmission system according to claim 1, characterized in that: The expression of the onshore AC power grid frequency response model is: Among them, Δδ represents the power angle change of the synchronous generator of the AC power grid, Δω represents the speed change of the synchronous generator, and Δθ s Indicates the phase change of the bus voltage connected to the MMC, Δf s Indicates the change in MMC output frequency, Δθ d Indicates the phase change of the bus voltage connected to the load, ΔP m Represents the change in mechanical power of the synchronous generator. The dot above each change represents the derivative of the change with respect to time t, ΔP d Indicates the change in load active power, A pfr represents the system matrix, E pfr Represents the input matrix.

3. The method for actively calling energy of an offshore wind power DC transmission system according to claim 2 is characterized in that: Based on the onshore AC power grid frequency response model, the frequency change trajectory of the offshore wind power DC transmission system after the power disturbance is predicted, and the frequency prediction results are obtained, including: Inputting the power flow data of the offshore wind power DC transmission system into the onshore AC power grid frequency response model to obtain the onshore AC power grid frequency response data based on the state space; Based on the frequency response data, the frequency change trajectory of the offshore wind power DC transmission system after the power disturbance occurs is predicted to obtain a frequency prediction result.

4. The method for actively calling energy of an offshore wind power DC transmission system according to claim 1, characterized in that: According to the frequency prediction result, a reference value of supporting power for the onshore MMC to participate in the primary frequency regulation of the system is calculated, including: According to the frequency prediction result, a maximum frequency deviation predicted after a power disturbance occurs in the system is obtained; Based on the predicted maximum frequency deviation, a change in the onshore MMC power reference value after a power disturbance occurs in the system is calculated; According to the change in the onshore MMC power reference value after the power disturbance occurs in the system, a supporting power reference value for the onshore MMC to participate in the primary frequency modulation of the system is obtained.

5. The method for actively calling energy of an offshore wind power DC transmission system according to claim 4 is characterized in that: The expression for calculating the change in the onshore MMC power reference value after the system has a power disturbance is: in, represents the change in the onshore MMC power reference value after the kth disturbance, and They represent the inertia constant and damping coefficient after the kth disturbance, Δf represents the frequency deviation, and v c Indicates the frequency change rate when the control strategy switches, ΔP max Indicates the maximum allowable power variation of the onshore MMC, represents the maximum frequency change rate after k disturbances, represents the maximum frequency deviation predicted after the kth disturbance.

6. The method for actively calling energy of an offshore wind power DC transmission system according to claim 1, characterized in that: The expression of the DC system operation variable prediction model is: in, represents the DC voltage of MMC at time t, represents the AC voltage of DR at time t, represents the power reference value of MMC at time t, represents the active power reference value of OWF at time t, and C is the parameter matrix.

7. The method for actively calling energy of an offshore wind power DC transmission system according to claim 1, characterized in that: Judging whether the system has an operation safety problem according to the operation variable includes: If any operating variable exceeds the corresponding variable limit range, it is determined that the system has an operating safety problem; If all operating variables do not exceed the corresponding variable limit ranges, it is determined that the system has no operating safety issues.

8. The method for actively calling energy of an offshore wind power DC transmission system according to claim 1, characterized in that: If the system has operational safety problems, the control variable optimization model is used to optimize the power reference values ​​of the onshore MMC and OWF, and correct the output power of the MMC and OWF, including: The control variable optimization model includes: objective function and constraints; The expression of the objective function is: The constraint condition is expressed as: in, It represents the MMC support power required when the frequency is controlled at time t. represents the power reference value of MMC at time t, represents the active power reference value of OWF at time t, Indicates the initial power reference value of MMC. represents the active power reference value of OWF at the previous moment, w represents the number of OWFs, m represents the number of onshore MMCs, and U ed Indicates the DC voltage of DR, U ac Indicates the AC voltage of DR, U mmc Indicates the DC voltage of MMC, represents the OWF output power, η is the penalty factor, which indicates the impact of not meeting the expected frequency support; and U ed They represent the upper and lower limits of the DC voltage of DR, and U ac Respectively represent the upper and lower limits of the AC voltage of DR, and U mmc Respectively represent the upper and lower limits of the DC voltage of the MMC, and and represent the upper and lower limits of OWF output power respectively; The objective function is solved according to the constraint conditions to optimize the power reference values ​​of the onshore MMC and the OWF.

9. An energy active call device for an offshore wind power DC transmission system, characterized in that: Applicable to an offshore wind power DC transmission system, the offshore wind power DC transmission system includes a plurality of OWFs, a plurality of DRs and a plurality of MMCs, and the device includes: a calculation module, a judgment module and a control module; A calculation module is used to predict the frequency change trajectory of the offshore wind power DC transmission system after the power disturbance occurs based on the onshore AC power grid frequency response model to obtain a frequency prediction result; according to the frequency prediction result, calculate the support power reference value of the onshore MMC participating in the primary frequency regulation of the system; A judgment module is used to predict the operating variables of the offshore wind power DC transmission system after the power disturbance occurs based on the DC system operating variable prediction model; and judge whether the system has an operating safety problem according to the operating variables; The control module is used for controlling the onshore MMC support power according to the support power reference value to enable the onshore MMC to participate in primary frequency modulation if the system has no operational safety problems; optimizing the power reference values ​​of the onshore MMC and OWF by using a control variable optimization model if the system has operational safety problems; and controlling the output power of the MMC and OWF according to the optimized power reference values ​​of the onshore MMC and OWF.

10. A computer-readable storage medium, characterized in that: The storage medium stores at least one executable instruction. When the executable instruction is executed on the energy active invocation device / apparatus of the offshore wind power DC transmission system, the energy active invocation device / apparatus of the offshore wind power DC transmission system executes the operation of the energy active invocation method of the offshore wind power DC transmission system as described in any one of claims 1-8.

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