Flexible Grid-connection Method and Device for Flexible DC System of Offshore Wind Farm

Abstract

The present disclosure provides a flexible grid connection method and device for a flexible DC system of an offshore wind farm. The method includes obtaining the rated frequency and rated voltage of the grid-side grid connection point, the measured reactive power value and reactive power reference value of the grid-side converter, the measured DC voltage value and DC voltage rated value on the DC side of the grid-side converter, and the measured AC voltage value on the AC side of the grid-side converter; calculating a phase reference value based on the rated frequency, the measured DC voltage value and the DC voltage rated value, and calculating a voltage reference value based on the rated voltage, the measured reactive power value and the reactive power reference value; calculating a three-phase voltage reference value based on the measured AC voltage value, the phase reference value and the voltage reference value, and controlling the grid-side converter based on the three-phase voltage reference value, thereby completing flexible grid connection. According to the method of the present disclosure, the flexible DC transmission system of the offshore wind farm can have a strong voltage support ability for connecting to the power grid.

Description

Technical Field

[0001] The present disclosure relates to the field of flexible DC power transmission for offshore wind farms, and particularly to a flexible grid connection method and device for a flexible DC system of an offshore wind farm. Background Art

[0002] With the rapid development of new energy power generation, wind power generation gradually accounts for a large proportion in the power system. Wind power generation includes onshore wind power generation and offshore wind power generation. For offshore wind power generation, the flexible DC power transmission technology is currently the mainstream method for transmitting large-scale wind power in the deep sea and far sea. There are two grid connection points in the offshore wind power flexible DC transmission system. One is the grid connection point where the onshore converter station is connected to the large power grid (i.e., the onshore main grid), and the other is the grid connection point where the offshore converter station is connected to the wind farm. Generally, for the onshore power grid, it usually does not require the wind power flexible DC system to participate in system voltage and frequency regulation. However, with the continuous increase in the scale of offshore wind power grid connection, the impact of wind power on the connected power grid is becoming greater and greater. The onshore large power grid hopes that the wind farm connected to the flexible DC system can play a certain supporting role in the voltage of the grid connection point to which it is connected to a certain extent. Therefore, there is an urgent need for a flexible grid connection technology for an offshore wind farm flexible DC system with strong supporting ability for the voltage of the grid connection point to which it is connected to the power grid. Summary of the Invention

[0003] The present disclosure aims to solve at least one of the technical problems in the related art to some extent.

[0004] To this end, the first object of the present disclosure is to propose a flexible grid connection method for an offshore wind farm flexible DC system, and the main object is to enable the offshore wind farm flexible DC power transmission system to have strong voltage support ability for connecting to the power grid.

[0005] The second object of the present disclosure is to propose a flexible grid connection device for an offshore wind farm flexible DC system.

[0006] The third object of the present disclosure is to propose a flexible grid connection device for an offshore wind farm flexible DC system.

[0007] To achieve the above object, an embodiment of the first aspect of the present disclosure proposes a flexible grid connection method for an offshore wind farm flexible DC system. The offshore wind farm flexible DC system includes a grid-side converter and a grid-side grid connection point. The grid-side converter is connected to the onshore main grid via the grid-side grid connection point. The method includes:

[0008] Obtain the rated frequency and rated voltage of the grid-side grid connection point, the measured value and reference value of the reactive power of the grid-side converter, the measured value and rated value of the DC voltage on the DC side of the grid-side converter, and the measured value of the AC voltage on the AC side of the grid-side converter;

[0009] A phase reference value is calculated based on the rated frequency, the measured DC voltage value, and the rated DC voltage value, and a voltage reference value is calculated based on the rated voltage, the measured reactive power value, and the reactive power reference value;

[0010] A three-phase voltage reference value is calculated based on the measured AC voltage value, the phase reference value, and the voltage reference value, and the grid-side converter is controlled based on the three-phase voltage reference value, thereby completing flexible grid connection.

[0011] In an embodiment of the present disclosure, the calculating the phase reference value based on the rated frequency, the measured DC voltage value, and the rated DC voltage value includes: calculating a reference frequency based on the regulating voltage, the measured DC voltage value, and the rated DC voltage value, and obtaining the phase reference value based on the reference frequency, where the regulating voltage is obtained based on a first damping coefficient, the reference frequency, and the rated frequency.

[0012] In an embodiment of the present disclosure, the calculating the voltage reference value based on the rated voltage, the measured reactive power value, and the reactive power reference value includes: calculating the voltage reference value based on the regulating power, the measured reactive power value, and the reactive power reference value, where the regulating power is obtained based on a second damping coefficient, the voltage reference value, and the rated voltage.

[0013] In an embodiment of the present disclosure, the calculating the three-phase voltage reference value based on the measured AC voltage value, the phase reference value, and the voltage reference value includes: obtaining a d-axis voltage component and a q-axis voltage component based on the measured AC voltage value and the phase reference value by using Park transformation; obtaining the three-phase voltage reference value based on the d-axis voltage component, the q-axis voltage component, and the voltage reference value by using inverse Park transformation.

[0014] In an embodiment of the present disclosure, the voltage reference value includes a d-axis voltage reference component and a q-axis voltage reference component, and the obtaining the three-phase voltage reference value based on the d-axis voltage component, the q-axis voltage component, and the voltage reference value by using inverse Park transformation includes: obtaining a d-axis voltage target value based on the d-axis voltage component and the d-axis voltage reference component; obtaining a q-axis voltage target value based on the q-axis voltage component and the q-axis voltage reference component; obtaining the three-phase voltage reference value based on the d-axis voltage target value and the q-axis voltage target value by using inverse Park transformation.

[0015] To achieve the above object, an embodiment of the second aspect of the present disclosure provides a flexible grid connection device for a flexible DC system of an offshore wind farm. The flexible DC system of the offshore wind farm includes a grid-side converter and a grid-side connection point. The grid-side converter is connected to the onshore main grid via the grid-side connection point. The device includes:

[0016] An acquisition module, configured to acquire the rated frequency and rated voltage of the grid-side connection point, the measured reactive power value and the reactive power reference value of the grid-side converter, the measured DC voltage value and the rated DC voltage value on the DC side of the grid-side converter, and the measured AC voltage value on the AC side of the grid-side converter;

[0017] A calculation module, configured to calculate a phase reference value based on the rated frequency, the measured DC voltage value and the rated DC voltage value, and calculate a voltage reference value based on the rated voltage, the measured reactive power value and the reactive power reference value;

[0018] A control module, configured to calculate a three-phase voltage reference value based on the measured AC voltage value, the phase reference value and the voltage reference value, and control the grid-side converter based on the three-phase voltage reference value, so as to complete flexible grid connection.

[0019] In an embodiment of the present disclosure, the calculation module is specifically configured to: calculate a reference frequency based on an adjustment voltage, the measured DC voltage value and the rated DC voltage value, and obtain the phase reference value based on the reference frequency, where the adjustment voltage is obtained based on a first damping coefficient, the reference frequency and the rated frequency.

[0020] In an embodiment of the present disclosure, the calculation module is specifically configured to: calculate a voltage reference value based on an adjustment power, the measured reactive power value and the reactive power reference value, where the adjustment power is obtained based on a second damping coefficient, the voltage reference value and the rated voltage.

[0021] In an embodiment of the present disclosure, the control module is specifically configured to: obtain a d-axis voltage component and a q-axis voltage component based on the measured AC voltage value and the phase reference value by using Park transformation; obtain the three-phase voltage reference value based on the d-axis voltage component, the q-axis voltage component and the voltage reference value by using inverse Park transformation.

[0022] To achieve the above object, an embodiment of the third aspect of the present disclosure provides a flexible grid connection device for a flexible DC system of an offshore wind farm, including: at least one processor; and a memory communicatively connected to the at least one processor; wherein, the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the flexible grid connection method of the flexible DC system of the offshore wind farm according to the embodiment of the first aspect of the present disclosure.

[0023] In one or more embodiments of the present disclosure, the flexible DC system of an offshore wind farm includes a grid-side converter and a grid-side connection point. The grid-side converter is connected to the onshore main grid via the grid-side connection point. The flexible grid connection method includes: obtaining the rated frequency and rated voltage of the grid-side connection point, the measured reactive power value and the reference reactive power value of the grid-side converter, the measured DC voltage value and the rated DC voltage value on the DC side of the grid-side converter, and the measured AC voltage value on the AC side of the grid-side converter; calculating a phase reference value based on the rated frequency, the measured DC voltage value and the rated DC voltage value, and calculating a voltage reference value based on the rated voltage, the measured reactive power value and the reference reactive power value; calculating a three-phase voltage reference value based on the measured AC voltage value, the phase reference value and the voltage reference value, and controlling the grid-side converter based on the three-phase voltage reference value, thereby completing the flexible grid connection. In this case, the three-phase voltage reference value is obtained by comprehensively considering the rated frequency and rated voltage of the grid-side connection point, the measured reactive power value and the reference reactive power value of the grid-side converter, the measured DC voltage value and the rated DC voltage value on the DC side of the grid-side converter, and the measured AC voltage value on the AC side of the grid-side converter, and the grid-side converter is controlled using the three-phase voltage reference value. At this time, the flexible DC system can still maintain the stability of the DC voltage when there are small disturbances in the connected onshore main grid. Therefore, the method according to the present disclosure can enable the flexible DC transmission system of the offshore wind farm to have a strong voltage support ability for connecting to the power grid.

[0024] Additional aspects and advantages of the present disclosure will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the specific embodiments of the present disclosure or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present disclosure. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings. The above-mentioned and / or additional aspects and advantages of the present disclosure will become apparent and easy to understand from the following description of the embodiments in conjunction with the drawings, where:

[0026] Figure 1 is a schematic diagram of the topological structure of the flexible DC system of the offshore wind farm provided by the embodiment of the present disclosure;

[0027] Figure 2 is a schematic diagram of the flow of the flexible grid connection method of the flexible DC system of the offshore wind farm provided by the embodiment of the present disclosure;

[0028] Figure 3 is a partial schematic diagram of the DC voltage outer loop control of the grid-side converter provided by the embodiment of the present disclosure;

[0029] Figure 4 Another schematic diagram of the DC voltage outer loop control of the grid-side converter provided by the embodiments of the present disclosure;

[0030] Figure 5 A block diagram of a flexible grid-connection device of a flexible DC system for an offshore wind farm provided by the embodiments of the present disclosure;

[0031] Figure 6 It is a block diagram of a flexible grid-connection device of a flexible DC system for an offshore wind farm, which is used to implement the flexible grid-connection method of the flexible DC system for an offshore wind farm in the embodiments of the present disclosure. Detailed implementation manners

[0032] Here, the exemplary embodiments will be described in detail, and the examples are shown in the drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementation manners described in the following exemplary embodiments do not represent all the implementation manners consistent with the embodiments of the present disclosure. On the contrary, they are only examples of devices and methods consistent with some aspects of the embodiments of the present disclosure as detailed in the appended claims.

[0033] In the description of this specification, the description referring to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0034] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present disclosure, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. It should also be understood that the term "and / or" used in the present disclosure refers to and includes any or all possible combinations of one or more of the associated listed items.

[0035] Embodiments of the present disclosure are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present disclosure, and should not be construed as limiting the present disclosure.

[0036] The present disclosure provides a flexible grid-connected method and device for an offshore wind farm flexible DC system, the main purpose of which is to enable the offshore wind farm flexible DC transmission system to have a stronger voltage support capability for accessing the power grid.

[0037] For ease of understanding, the offshore wind farm flexible DC system disclosed herein is also referred to as an offshore wind farm flexible DC transmission system. The offshore wind farm flexible DC system includes a grid-side converter, a grid-side connection point, a generator-side converter, and a generator-side connection point. The grid-side converter is connected to the onshore main grid via the grid-side connection point, and the generator-side converter is connected to the offshore wind farm via the generator-side connection point.

[0038] Figure 1 This is a schematic diagram of the topological structure of the flexible DC system for offshore wind farms provided by the embodiment of the present disclosure. Figure 1 As shown, the offshore wind farm flexible DC system includes a generator-side connection transformer, an offshore converter station, a cable line, an onshore converter station, and a grid-side connection transformer, all connected in sequence. One end of the generator-side connection transformer is connected to the offshore converter station (i.e., the generator-side converter), while the other end is connected to the offshore wind farm. The connection point between the generator-side connection transformer and the offshore wind farm is the generator-side grid connection point. One end of the grid-side connection transformer is connected to the onshore converter station (i.e., the grid-side converter), while the other end is connected to the onshore main grid. The connection point between the grid-side connection transformer and the onshore main grid is the grid-side grid connection point. Both the onshore and offshore converter stations utilize voltage source converters (VSCs). The cable line transmits high-voltage DC power. Energy dissipation devices are installed near the onshore converter station on the cable line. These devices dissipate excess power on the DC side of the flexible DC transmission system, assist in facilitating AC fault ride-through in the flexible DC system, and provide time for wind turbine operation if a fault cannot be cleared, thereby improving the safety and reliability of the entire flexible DC system.

[0039] In a first embodiment, Figure 2 This is a flow chart of the flexible grid-connected method for the flexible DC system of an offshore wind farm provided by the embodiment of the present disclosure. Figure 2 As shown, the flexible grid-connected method of the offshore wind farm flexible DC system includes the following steps:

[0040] Step S11: Obtain the rated frequency and rated voltage of the grid-connected point on the grid side, the measured reactive power value and the reactive power reference value of the grid-side converter, the measured DC voltage value and the rated DC voltage value on the DC side of the grid-side converter, and the measured AC voltage value on the AC side of the grid-side converter.

[0041] Specifically, in Step S11, the rated frequency of the grid-connected point on the grid side obtained can be represented by the symbol ω ref The rated voltage of the grid-connected point on the grid side obtained can be represented by the symbol V mref The measured reactive power value of the grid-side converter obtained can be represented by the symbol Q, and the reactive power reference value of the grid-side converter obtained can be represented by the symbol Q ref The measured DC voltage value on the DC side of the grid-side converter obtained can be represented by the symbol U dc The rated DC voltage value of the grid-side converter obtained can be represented by the symbol U dcref The measured AC voltage value on the AC side of the grid-side converter obtained can be represented by the symbol V ABC The measured AC voltage value on the AC side of the grid-side converter obtained can be represented by the symbol V.

[0042] Step S12: Calculate the phase reference value based on the rated frequency, the measured DC voltage value and the rated DC voltage value, and calculate the voltage reference value based on the rated voltage, the measured reactive power value and the reactive power reference value.

[0043] In Step S12, the phase reference value can be represented by the symbol θ, and the voltage reference value can be represented by the symbol V.

[0044] In Step S12, calculating the phase reference value based on the rated frequency, the measured DC voltage value and the rated DC voltage value includes: calculating the reference frequency based on the regulating voltage, the measured DC voltage value and the rated DC voltage value, and obtaining the phase reference value based on the reference frequency, where the regulating voltage is obtained based on the first damping coefficient, the reference frequency and the rated frequency.

[0045] In Step S12, calculating the voltage reference value based on the rated voltage, the measured reactive power value and the reactive power reference value includes: calculating the voltage reference value based on the regulating power, the measured reactive power value and the reactive power reference value, where the regulating power is obtained based on the second damping coefficient, the voltage reference value and the rated voltage.

[0046] Specifically, Figure 3 This is a partial schematic diagram of the DC voltage outer-loop control of the grid-side converter provided by the embodiments of the present disclosure.

[0047] In some embodiments, as Figure 3 shown, calculate the sum of the regulating voltage △U and the rated DC voltage U dcref and then calculate the result of the summation and the measured DC voltage U dcThe first difference is sent to a PI regulator (i.e., a proportional-integral controller) and utilized with the first inertia coefficient J p for integral calculation (1 / S represents integral operation) to obtain a reference frequency ω. The reference frequency ω is sent to the PI regulator for integral calculation to obtain a phase reference value θ. Here, during the initial calculation, the regulating voltage △U is set with an initial value, and during subsequent calculations, the regulating voltage △U is updated in real time based on the first damping coefficient D p , the reference frequency ω, and the rated frequency ω ref . Specifically, the second difference between the rated frequency ω ref and the reference frequency ω is calculated and sent to the PI regulator to be multiplied by the first damping coefficient D P to obtain the regulating voltage △U. The sum of the regulating power △Q and the reactive power reference value Q ref is calculated, and then the third difference between the result of the summation and the measured reactive power value Q is calculated and sent to the PI regulator to be used with the second inertia coefficient J q for integral calculation to obtain a voltage reference value V. Here, during the initial calculation, the regulating power △Q is set with an initial value, and during subsequent calculations, the regulating power △Q is updated in real time based on the second damping coefficient D q , the voltage reference value V, and the rated voltage V mref . Specifically, the fourth difference between the rated voltage V mref and the voltage reference value V is calculated and sent to the PI regulator to be multiplied by the second damping coefficient D q to obtain the regulating power △Q.

[0048] Step S13: Calculate three-phase voltage reference values based on the AC voltage measurement values, the phase reference value, and the voltage reference value, and control the grid-side converter based on the three-phase voltage reference values to complete flexible grid connection.

[0049] In step S13, calculating the three-phase voltage reference values based on the AC voltage measurement values, the phase reference value, and the voltage reference value includes: obtaining the d-axis voltage component and the q-axis voltage component based on the AC voltage measurement values and the phase reference value using Park transformation; obtaining the three-phase voltage reference values based on the d-axis voltage component, the q-axis voltage component, and the voltage reference value using inverse Park transformation. It is easy to understand that Park transformation projects the currents or voltages of the a, b, c three phases onto the direct axis (d-axis) and the quadrature axis (q-axis), which simplifies the operation analysis of synchronous motors, that is, transforming the abc coordinate system to the dq coordinate system. Inverse Park transformation (i.e., Park matrix inverse transformation) transforms the dq coordinate system to the abc coordinate system.

[0050] In step S13, the voltage reference value includes a d-axis voltage reference component and a q-axis voltage reference component. Based on the Park inverse transformation, three-phase voltage reference values are obtained from the d-axis voltage component, the q-axis voltage component, and the voltage reference value, including: obtaining a d-axis voltage target value based on the d-axis voltage component and the d-axis voltage reference component; obtaining a q-axis voltage target value based on the q-axis voltage component and the q-axis voltage reference component; and obtaining three-phase voltage reference values based on the d-axis voltage target value and the q-axis voltage target value using the Park inverse transformation.

[0051] In step S13, the d-axis voltage component can be denoted by the symbol V d . The q-axis voltage component can be denoted by the symbol V q . The d-axis voltage reference component can be denoted by the symbol V dref . The q-axis voltage reference component can be denoted by the symbol V qref . The d-axis voltage target value can be denoted by the symbol V cd . The q-axis voltage target value can be denoted by the symbol V cq .

[0052] Specifically, Figure 4 is another schematic diagram of the DC voltage outer loop control of the grid-side converter provided by the embodiments of the present disclosure.

[0053] In some embodiments, as Figure 4 shown, after the AC voltage measurement value V ABC and the phase reference value θ are processed by the Park transformation (i.e., the Park matrix transformation), the d-axis voltage component V d and the q-axis voltage component V q are obtained. The voltage reference value V includes the d-axis voltage reference component V dref and the q-axis voltage reference component V qref , where (V dref ) 2 +(V qref ) 2 =V 2 . Calculate the difference between the d-axis voltage reference component V dref and the d-axis voltage component V d , and send the difference into a PI regulator to calculate the d-axis voltage target value V cd ; calculate the difference between the q-axis voltage reference component V qref and the q-axis voltage component V q , and send the difference into a PI regulator to calculate the q-axis voltage target value V cq .

[0054] In step S13, for the d-axis voltage target value V cd and the q-axis voltage target value V cqPerform Park inverse transformation (i.e., Park matrix inverse transformation) to obtain the three-phase voltage reference values, and control the grid-side converter based on the three-phase voltage reference values, thereby completing flexible grid connection. Among them, the three-phase voltage reference values are the modulation reference waves of the grid-side converter and participate in the control and regulation of the voltage and reactive power of the grid-side converter. Controlling the grid-side converter based on the obtained three-phase voltage reference values can ensure the stability of the DC voltage.

[0055] In the flexible grid connection method of the flexible DC system of the offshore wind farm in the embodiment of the present disclosure, the flexible DC system of the offshore wind farm includes a grid-side converter and a grid-side connection point. The grid-side converter is connected to the onshore main grid via the grid-side connection point. The flexible grid connection method includes: obtaining the rated frequency and rated voltage of the grid-side connection point, the measured reactive power value and reactive power reference value of the grid-side converter, the DC voltage measurement value and DC voltage rated value on the DC side of the grid-side converter, and the AC voltage measurement value on the AC side of the grid-side converter; calculating the phase reference value based on the rated frequency, DC voltage measurement value and DC voltage rated value, and calculating the voltage reference value based on the rated voltage, measured reactive power value and reactive power reference value; calculating the three-phase voltage reference values based on the AC voltage measurement value, phase reference value and voltage reference value, and controlling the grid-side converter based on the three-phase voltage reference values, thereby completing flexible grid connection. In this case, the three-phase voltage reference values are obtained by comprehensively considering the rated frequency and rated voltage of the grid-side connection point, the measured reactive power value and reactive power reference value of the grid-side converter, the DC voltage measurement value and DC voltage rated value on the DC side of the grid-side converter, and the AC voltage measurement value on the AC side of the grid-side converter. The grid-side converter is controlled by using the three-phase voltage reference values. At this time, the flexible DC system can still maintain the stability of the DC voltage when there are small disturbances in the connected onshore main grid. Therefore, according to the method of the present disclosure, the flexible DC transmission system of the offshore wind farm can have a strong voltage support ability for connecting to the power grid. Compared with the traditional constant DC voltage control, the present disclosure changes the DC voltage outer loop based on the fact that the flexible DC system itself has a certain DC voltage fluctuation ability, so as to provide a control method that can support the grid connection point voltage of the power grid under small disturbances in the connected power grid.

[0056] The following is an embodiment of the device of the present disclosure, which can be used to execute the embodiment of the method of the present disclosure. For the details not disclosed in the embodiment of the device of the present disclosure, please refer to the embodiment of the method of the present disclosure.

[0057] The present disclosure relates to a flexible grid connection device for a flexible DC system of an offshore wind farm. Using the flexible grid connection device of the flexible DC system of the offshore wind farm can enable the flexible DC transmission system of the offshore wind farm to have a strong voltage support ability for connecting to the power grid. Among them, the flexible DC system of the offshore wind farm includes a grid-side converter and a grid-side connection point. The grid-side converter is connected to the onshore main grid via the grid-side connection point.

[0058] Please refer to Figure 5 , Figure 5 which is a block diagram of a flexible grid-connection device for a flexible DC system of an offshore wind farm provided by an embodiment of the present disclosure. The flexible grid-connection device 10 of the flexible DC system of the offshore wind farm includes an acquisition module 11, a calculation module 12, and a control module 13, where:

[0059] The acquisition module 11 is configured to acquire the rated frequency and rated voltage of the grid-side connection point, the measured reactive power value and the reactive power reference value of the grid-side converter, the measured DC voltage value and the DC voltage rated value on the DC side of the grid-side converter, and the measured AC voltage value on the AC side of the grid-side converter;

[0060] The calculation module 12 is configured to calculate a phase reference value based on the rated frequency, the measured DC voltage value, and the DC voltage rated value, and calculate a voltage reference value based on the rated voltage, the measured reactive power value, and the reactive power reference value;

[0061] The control module 13 is configured to calculate a three-phase voltage reference value based on the measured AC voltage value, the phase reference value, and the voltage reference value, and control the grid-side converter based on the three-phase voltage reference value, so as to complete flexible grid connection.

[0062] Optionally, the calculation module 12 is specifically configured to: calculate a reference frequency based on an adjustment voltage, the measured DC voltage value, and the DC voltage rated value, and obtain a phase reference value based on the reference frequency, where the adjustment voltage is obtained based on a first damping coefficient, the reference frequency, and the rated frequency.

[0063] Optionally, the calculation module 12 is specifically configured to: calculate a voltage reference value based on an adjustment power, the measured reactive power value, and the reactive power reference value, where the adjustment power is obtained based on a second damping coefficient, the voltage reference value, and the rated voltage.

[0064] Optionally, the control module 13 is specifically configured to: obtain a d-axis voltage component and a q-axis voltage component based on the measured AC voltage value and the phase reference value by using Park transformation; obtain a three-phase voltage reference value based on the d-axis voltage component, the q-axis voltage component, and the voltage reference value by using inverse Park transformation.

[0065] Optionally, the voltage reference value includes a d-axis voltage reference component and a q-axis voltage reference component. The control module 13 is specifically configured to: obtain a d-axis voltage target value based on the d-axis voltage component and the d-axis voltage reference component; obtain a q-axis voltage target value based on the q-axis voltage component and the q-axis voltage reference component; obtain a three-phase voltage reference value based on the d-axis voltage target value and the q-axis voltage target value by using inverse Park transformation.

[0066] It should be noted that the foregoing explanation of the flexible grid connection method embodiment of the flexible DC system of the offshore wind farm is also applicable to the flexible grid connection device of the flexible DC system of the offshore wind farm in this embodiment, and will not be elaborated here.

[0067] In the flexible grid connection device of the flexible DC system of the offshore wind farm according to the embodiment of the present disclosure, an acquisition module acquires the rated frequency and rated voltage of the grid-side connection point, the measured reactive power value and the reactive power reference value of the grid-side converter, the measured DC voltage value and the rated DC voltage value on the DC side of the grid-side converter, and the measured AC voltage value on the AC side of the grid-side converter; a calculation module calculates a phase reference value based on the rated frequency, the measured DC voltage value and the rated DC voltage value, and calculates a voltage reference value based on the rated voltage, the measured reactive power value and the reactive power reference value; a control module calculates a three-phase voltage reference value based on the measured AC voltage value, the phase reference value and the voltage reference value, and controls the grid-side converter based on the three-phase voltage reference value, thereby completing flexible grid connection. In this case, a three-phase voltage reference value is obtained by comprehensively considering the rated frequency and rated voltage of the grid-side connection point, the measured reactive power value and the reactive power reference value of the grid-side converter, the measured DC voltage value and the rated DC voltage value on the DC side of the grid-side converter, and the measured AC voltage value on the AC side of the grid-side converter, and the grid-side converter is controlled by using the three-phase voltage reference value. At this time, the flexible DC system can still maintain the stability of the DC voltage when there are small disturbances in the connected onshore main grid. Therefore, the device according to the present disclosure can enable the flexible DC transmission system of the offshore wind farm to have a strong voltage support ability for connecting to the grid. Compared with the traditional fixed DC voltage control, the present disclosure changes the DC voltage outer loop based on the fact that the flexible DC system itself has a certain DC voltage fluctuation ability, so as to provide a control device that can support the voltage of the connection point of the grid voltage under small disturbances in the connected grid.

[0068] According to the embodiments of the present disclosure, the present disclosure also provides a flexible grid connection device for a flexible DC system of an offshore wind farm, a readable storage medium, and a computer program product.

[0069] Figure 6It is a block diagram of a flexible grid - connection device for a flexible DC system of an offshore wind farm, which is used to implement the flexible grid - connection method of the flexible DC system of the offshore wind farm. The flexible grid - connection device of the flexible DC system of the offshore wind farm is intended to represent various forms of digital computers, such as laptop computers, desktop computers, workstations, personal digital assistants, servers, blade servers, mainframe computers, and other suitable computers. The flexible grid - connection device of the flexible DC system of the offshore wind farm can also represent various forms of mobile devices, such as personal digital processors, cellular phones, smart phones, wearable electronic devices, and other similar computing devices. The components, connections and relationships of the components, and the functions of the components shown in this disclosure are only examples and are not intended to limit the implementation of the disclosure described and / or claimed in this disclosure.

[0070] As Figure 6 shown, the flexible grid - connection device 20 of the flexible DC system of the offshore wind farm includes a computing unit 21, which can perform various appropriate actions and processes according to computer programs stored in a read - only memory (ROM) 22 or computer programs loaded from a storage unit 28 into a random - access memory (RAM) 23. In the RAM 23, various programs and data required for the operation of the flexible grid - connection device 20 of the flexible DC system of the offshore wind farm can also be stored. The computing unit 21, the ROM 22, and the RAM 23 are connected to each other through a bus 24. An input / output (I / O) interface 25 is also connected to the bus 24.

[0071] A plurality of components in the flexible grid - connection device 20 of the flexible DC system of the offshore wind farm are connected to the I / O interface 25, including: an input unit 26, such as a keyboard, a mouse, etc.; an output unit 27, such as various types of displays, speakers, etc.; a storage unit 28, such as a magnetic disk, an optical disc, etc., and the storage unit 28 is communicatively connected to the computing unit 21; and a communication unit 29, such as a network card, a modem, a wireless communication transceiver, etc. The communication unit 29 allows the flexible grid - connection device 20 of the flexible DC system of the offshore wind farm to exchange information / data with other flexible grid - connection devices of the flexible DC system of the offshore wind farm through a computer network such as the Internet and / or various telecommunication networks.

[0072] The computing unit 21 can be various general-purpose and / or special-purpose processing components with processing and computing capabilities. Some examples of the computing unit 21 include, but are not limited to, a central processing unit (CPU), a graphics processing unit (GPU), various dedicated artificial intelligence (AI) computing chips, various computing units running machine learning model algorithms, a digital signal processor (DSP), and any suitable processor, controller, microcontroller, etc. The computing unit 21 executes the various methods and processes described above, such as executing the flexible grid connection method of the flexible DC system of an offshore wind farm. For example, in some embodiments, the flexible grid connection method of the flexible DC system of an offshore wind farm can be implemented as a computer software program, which is tangibly incorporated in a machine-readable medium, such as the storage unit 28. In some embodiments, part or all of the computer program can be loaded and / or installed onto the flexible grid connection device 20 of the flexible DC system of an offshore wind farm via the ROM 22 and / or the communication unit 29. When the computer program is loaded into the RAM 23 and executed by the computing unit 21, one or more steps of the flexible grid connection method of the flexible DC system of an offshore wind farm described above can be executed. Alternatively, in other embodiments, the computing unit 21 can be configured to execute the flexible grid connection method of the flexible DC system of an offshore wind farm by any other suitable means (e.g., by means of firmware).

[0073] The various embodiments of the systems and techniques described above in this disclosure can be implemented in digital electronic circuit systems, integrated circuit systems, field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), application-specific standard products (ASSPs), systems-on-chip (SOCs), complex programmable logic devices (CPLDs), computer hardware, firmware, software, and / or combinations thereof. These various embodiments can include: being implemented in one or more computer programs, which can be executed and / or interpreted on a programmable system including at least one programmable processor, which can be a dedicated or general-purpose programmable processor, and can receive data and instructions from a storage system, at least one input device, and at least one output device, and transmit the data and instructions to the storage system, the at least one input device, and the at least one output device.

[0074] The program code for implementing the methods of this disclosure can be written in any combination of one or more programming languages. These program codes can be provided to a processor or controller of a general-purpose computer, a special-purpose computer, or other programmable data processing devices, such that when the program codes are executed by the processor or controller, the functions / operations specified in the flowcharts and / or block diagrams are implemented. The program codes can be executed entirely on the machine, partially on the machine, executed partially on the machine and partially on a remote machine as an independent software package, or executed entirely on a remote machine or server.

[0075] In this disclosure, a machine-readable medium can be a tangible medium that can contain or store a program for use by or in connection with an instruction execution system, apparatus, or device. A machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. A machine-readable medium can include, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, or any suitable combination of the foregoing. More specific examples of a machine-readable storage medium would include an electrical connection based on one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0076] To provide for interaction with a user, the systems and techniques described herein can be implemented on a computer having: a display device (e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor) for displaying information to the user; and a keyboard and a pointing device (e.g., a mouse or a trackball) by which the user can provide input to the computer. Other kinds of devices can also be used to provide for interaction with the user; for example, feedback provided to the user can be any form of sensory feedback (e.g., visual feedback, auditory feedback, or tactile feedback); and input from the user can be received in any form (including acoustic input, voice input, or tactile input).

[0077] The systems and techniques described herein can be implemented in a computing system that includes back-end components (e.g., as a data server), or a computing system that includes middleware components (e.g., an application server), or a computing system that includes front-end components (e.g., a user computer having a graphical user interface or a web browser through which the user can interact with an implementation of the systems and techniques described herein), or a computing system that includes any combination of such back-end components, middleware components, or front-end components. The components of the system can be interconnected by any form or medium of digital data communication (e.g., a communication network). Examples of communication networks include: a local area network (LAN), a wide area network (WAN), the Internet, and a blockchain network.

[0078] A computer system may include a client and a server. The client and the server are generally far from each other and usually interact via a communication network. The relationship between the client and the server is generated by computer programs running on respective computers and having a client-server relationship with each other. The server may be a cloud server, also known as a cloud computing server or a cloud host, which is a host product in the cloud computing service system, and solves the defects of difficult management and weak business scalability existing in traditional physical hosts and VPS services ("Virtual Private Server", or simply "VPS" for short). The server may also be a server of a distributed system or a server combined with a blockchain.

[0079] It should be understood that various forms of processes shown above can be used, steps can be reordered, added or deleted. For example, the steps recited in the present disclosure can be executed in parallel, sequentially or in a different order, as long as the desired results of the technical solutions disclosed in the present disclosure can be achieved, and the present disclosure does not limit this here.

[0080] The above specific embodiments do not constitute a limitation on the protection scope of the present disclosure. Those skilled in the art should understand that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present disclosure shall be included within the protection scope of the present disclosure.

Claims

1. A flexible grid connection method for a flexible DC system of an offshore wind farm, characterized in that, The flexible DC system of the offshore wind farm includes a grid-side converter and a grid-side connection point. The grid-side converter is connected to the onshore main grid via the grid-side connection point. The method includes: Obtaining the rated frequency and rated voltage of the grid-side connection point, the measured reactive power value and the reactive power reference value of the grid-side converter, the measured DC voltage value and the rated DC voltage value on the DC side of the grid-side converter, and the measured AC voltage value on the AC side of the grid-side converter; Calculating a phase reference value based on the rated frequency, the measured DC voltage value and the rated DC voltage value, and calculating a voltage reference value based on the rated voltage, the measured reactive power value and the reactive power reference value; Calculating a three-phase voltage reference value based on the measured AC voltage value, the phase reference value and the voltage reference value, and controlling the grid-side converter based on the three-phase voltage reference value to complete flexible grid connection; The calculating the phase reference value based on the rated frequency, the measured DC voltage value and the rated DC voltage value includes: Calculating a reference frequency based on an adjustment voltage, the measured DC voltage value and the rated DC voltage value, and obtaining the phase reference value based on the reference frequency, where the adjustment voltage is obtained based on a first damping coefficient, the reference frequency and the rated frequency; The calculating the voltage reference value based on the rated voltage, the measured reactive power value and the reactive power reference value includes: Calculating the voltage reference value based on an adjustment power, the measured reactive power value and the reactive power reference value, where the adjustment power is obtained based on a second damping coefficient, the voltage reference value and the rated voltage.

2. The flexible grid connection method of the flexible DC system of the offshore wind farm according to claim 1, characterized in that, The calculating the three-phase voltage reference value based on the measured AC voltage value, the phase reference value and the voltage reference value includes: Obtaining a d-axis voltage component and a q-axis voltage component based on the measured AC voltage value and the phase reference value by using Park transformation; obtaining the three-phase voltage reference value based on the d-axis voltage component, the q-axis voltage component and the voltage reference value by using inverse Park transformation.

3. The flexible grid connection method of the flexible DC system of the offshore wind farm according to claim 2, characterized in that, The voltage reference value includes a d-axis voltage reference component and a q-axis voltage reference component. The obtaining the three-phase voltage reference value based on the d-axis voltage component, the q-axis voltage component and the voltage reference value by using inverse Park transformation includes: Obtaining a d-axis voltage target value based on the d-axis voltage component and the d-axis voltage reference component; Obtaining a q-axis voltage target value based on the q-axis voltage component and the q-axis voltage reference component; Obtaining the three-phase voltage reference value based on the d-axis voltage target value and the q-axis voltage target value by using inverse Park transformation.

4. A flexible grid-connection device for a flexible DC system of an offshore wind farm, characterized in that, The flexible DC system of the offshore wind farm includes a grid-side converter and a grid-side connection point. The grid-side converter is connected to the onshore main grid via the grid-side connection point. The device includes: An obtaining module, configured to obtain the rated frequency and rated voltage of the grid-side connection point, the measured reactive power value and the reactive power reference value of the grid-side converter, the measured DC voltage value and the rated DC voltage value on the DC side of the grid-side converter, and the measured AC voltage value on the AC side of the grid-side converter; A calculation module, configured to calculate a phase reference value based on the rated frequency, the measured DC voltage value, and the rated DC voltage value, and calculate a voltage reference value based on the rated voltage, the measured reactive power value, and the reactive power reference value; A control module, configured to calculate a three-phase voltage reference value based on the measured AC voltage value, the phase reference value, and the voltage reference value, and control the grid-side converter based on the three-phase voltage reference value, so as to complete flexible grid connection; The calculation module is specifically configured to: Calculate a reference frequency based on the regulated voltage, the measured DC voltage value, and the rated DC voltage value, and obtain the phase reference value based on the reference frequency, where the regulated voltage is obtained based on a first damping coefficient, the reference frequency, and the rated frequency; Calculate a voltage reference value based on the regulated power, the measured reactive power value, and the reactive power reference value, where the regulated power is obtained based on a second damping coefficient, the voltage reference value, and the rated voltage.

5. The flexible grid-connection device of the flexible DC system for an offshore wind farm according to claim 4, characterized in that, The control module is specifically configured to: Obtain a d-axis voltage component and a q-axis voltage component based on the measured AC voltage value and the phase reference value by using Park transformation; obtain the three-phase voltage reference value based on the d-axis voltage component, the q-axis voltage component, and the voltage reference value by using inverse Park transformation.

6. A flexible grid-connected device for a flexible DC system of an offshore wind farm, characterized in that, Comprising: At least one processor; And A memory communicatively connected to the at least one processor; wherein, The memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor, so that the at least one processor can execute the flexible grid connection method of the flexible DC system of an offshore wind farm according to any one of claims 1-3.

Images