Offshore wind power flexible direct current power transmission system network construction control method

Abstract

The invention discloses a network construction control method for an offshore wind power flexible direct-current power transmission system. The method comprises the following steps: acquiring a direct-current side voltage of a receiving-end converter of the offshore wind power flexible direct-current power transmission system, a power grid voltage and current of a grid-connected point of the receiving-end converter, and a reference value of a power grid voltage amplitude; calculating a phase reference value of a receiving-end converter and a reference value of modulation voltage in a dq rotating coordinate system; and according to the phase reference value of the receiving-end converter and the reference value of the modulation voltage under the dq rotating coordinate system, calculating the reference value of the modulation voltage of the receiving-end converter under the abc static coordinate system. According to the invention, the receiving end converter controls the DC voltage of the point-to-point flexible DC power transmission system and the voltage and frequency of the receiving end AC power grid at the same time, and dual-network control of the DC voltage and the receiving end AC voltage is realized. And the transmitting-end converter adopts island control. The offshore wind power flexible direct current system controlled by the method can adapt to different receiving end power grid strengths, and can reliably operate under the conditions of power fluctuation, alternating current faults and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of offshore wind power flexible direct current grid-connected system control, and in particular to an offshore wind power flexible direct current transmission system network control method, a network control device, a computer device and a storable medium. Background Art

[0002] Modular multilevel converters (MMCs) are widely used in large-scale offshore wind power integration scenarios. Mainstream MMC control methods can be categorized into two types: grid-following and grid-forming. Grid-following control requires a stable voltage source from synchronous generators or synchronous condensers. However, with the increasing penetration of renewable energy, grid-following control can become unstable when voltage disturbances occur. In contrast, MMC grid-forming control, which can maintain a stable voltage, is more suitable for large-scale renewable energy integration scenarios. Existing grid-forming control methods can also be broadly categorized into AC grid-forming and DC grid-forming. In AC grid-forming control, the MMC AC side generates a stable AC voltage amplitude and phase angle, but requires a stable DC voltage source to establish the DC side voltage. DC grid-forming control, in contrast, generates a stable DC voltage amplitude, tracking the strong AC grid. With the integration of large-scale offshore wind power into the grid and the large number of DC transmission lines located at load centers, grid voltage and frequency stability issues are becoming increasingly prominent. Flexible DC transmission systems, with their large capacity and flexible control, require certain active support system capabilities.

[0003] However, both AC and DC grid control are unilateral grid control of MMC, which makes it difficult to provide active support for new power systems with a high proportion of energy and a high proportion of power electronic equipment. In the point-to-point offshore wind power transmission scenario, after large-capacity offshore wind power is collected, it is converted into DC power by the AC grid-type MMC at the sending end and transmitted to the shore, and then converted into AC power by the DC grid-type MMC at the receiving end to be connected to the remote power grid, such as Figure 2 As shown in the figure. For flexible HVDC transmission systems using traditional control, the receiving-end DC grid-forming MMC relies heavily on phase-locked loop communication. A failure in the onshore AC system can lead to instability in the DC voltage grid-forming control of the receiving-end MMC. Without a strong DC voltage source, the AC voltage grid-forming control of the sending-end MMC will also become unstable, leading to instability of the entire offshore wind power transmission system. Therefore, it is urgent to develop a flexible HVDC transmission system control strategy that can actively support the receiving-end large grid. Summary of the Invention

[0004] The main purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a method, device, computer equipment, and storage medium for controlling the network construction of an offshore wind power flexible direct current transmission system. The sending-end converter uses island control to establish the voltage and frequency of the offshore wind farm, and the receiving-end converter uses constant DC voltage and constant AC voltage control to simultaneously establish a stable system DC voltage and receiving-end AC voltage. A flexible direct current system using this control method can adapt to different receiving-end grid strengths and maintain stable operation after power disturbances and AC faults, possessing a certain degree of proactive support for establishing a grid at the receiving end.

[0005] In order to achieve the above-mentioned objectives, the first aspect of the present invention discloses a method for controlling the network construction of an offshore wind power flexible DC transmission system. The offshore wind farm is connected to the onshore AC power grid through the offshore wind power flexible DC transmission system. The end of the offshore wind power flexible DC transmission system connected to the onshore AC power grid through a modular multi-level converter is called the receiving end, and the corresponding converter is referred to as the receiving end converter. The system topology is as follows: Figure 2 As shown in the figure, HVDC stands for High Voltage Direct Current. The receiving end converter control block diagram is as follows Figure 3 As shown in the figure, i v Indicates the current at the inverter grid connection point, u s Represents the voltage at the grid connection point of the converter. The end of the offshore wind power flexible DC transmission system connected to the offshore wind farm through the modular multilevel converter is called the sending end, and the corresponding converter is referred to as the sending end converter. The control method includes the following steps:

[0006] S1. Obtain the grid voltage and current at the receiving-end converter grid connection point, where the receiving-end converter grid connection point refers to the connection point between the receiving-end converter and the onshore AC grid, and perform dq decomposition on the grid voltage and current at the receiving-end converter grid connection point to obtain the d-axis and q-axis components of the grid voltage and current at the receiving-end converter grid connection point in a dq rotating coordinate system, respectively. Obtain the actual values ​​of the DC voltage output by the receiving-end converter, the AC voltage and frequency at the receiving-end converter grid connection point, and obtain reference values ​​of the DC voltage of the receiving-end converter, the voltage amplitude and frequency at the receiving-end converter grid connection point;

[0007] S2. Calculate the phase reference value of the receiving-end converter;

[0008] S3. Calculate the d-axis voltage reference value of the receiving-end converter grid connection point;

[0009] S4. Calculate the d-axis current reference value and the q-axis current reference value of the receiving-end converter grid connection point;

[0010] S5. Calculate the d-axis voltage reference value and the q-axis voltage reference value of the modulation voltage of the receiving-end converter;

[0011] S6. Calculate the a-axis voltage reference value, the b-axis voltage reference value, and the c-axis voltage reference value of the modulation voltage of the receiving-end converter in the abc stationary coordinate system;

[0012] S7. Based on the reference value of the modulation voltage and using the pulse width modulation theory, a corresponding control pulse is generated to realize the control of the receiving-end converter of the offshore wind power flexible direct current transmission system.

[0013] Furthermore, in order to improve the stability of the receiving-end converter grid connection, the q-axis component U of the receiving-end converter grid connection point voltage is added on the basis of proportional control. sq The coupling amount is adjusted by an adaptive coefficient in the synchronous control loop, and the phase reference value of the receiving converter is The calculation formula is as follows:

[0014]

[0015] Where s is the Laplace operator, k is the reference value of the receiving end AC system frequency, a is the adaptive coefficient of the synchronous control loop, and are the reference value and actual value of DC voltage respectively, U sq is the q-axis component of the grid-connected voltage of the receiving converter, k pll is the proportionality coefficient, k T is the DC voltage droop coefficient.

[0016] Furthermore, in order to control the reactive power of the receiving converter, the reactive power droop and proportional parameter k are introduced. pq , d-axis voltage reference value of the receiving converter grid connection point and q-axis voltage reference value The calculation formula is as follows:

[0017]

[0018] in, is the q-axis voltage reference value of the receiving converter grid connection point, U sm is the reference value of the voltage amplitude at the grid connection point of the wind turbine in the offshore wind farm, Q * and Q s are the reference value and actual value of active power of wind turbines in offshore wind farms; k pq is a proportional parameter. The above equation controls the q-axis component of the receiving converter's grid-connection point voltage to zero. This is done to ensure that the voltage vector at the receiving converter's grid-connection point coincides with the d-axis of the synchronously rotating coordinate system, effectively aligning the d-axis component. In this case, the amplitude of the d-axis component is the same as the amplitude of the receiving converter's grid-connection point voltage, facilitating controller design.

[0019] Furthermore, the d-axis current reference value i of the receiving-end converter grid connection point is * vd and q-axis current reference value i * vq The calculation formula is as follows:

[0020]

[0021] Among them, u sd and u sq are the d-axis component and q-axis component of the grid-connected point voltage of the receiving converter respectively; C is the capacitance value of the LC filter on the AC side of the receiving converter; k pu and k iu are the proportional parameter and integral parameter of the voltage inner loop controller respectively, and ω is the actual value of the receiving end AC grid frequency.

[0022] Furthermore, the d-axis voltage reference value u of the modulation voltage of the receiving-end converter is * vd and q-axis voltage reference value u * vq The calculation formula is as follows:

[0023]

[0024] Among them, i vd and i vq are the d-axis and q-axis components of the output current of the receiving-end converter respectively; L is the connection reactance value of the receiving-end converter; k pi and k ii These are the proportional and integral parameters of the voltage inner loop controller, respectively. The dual inner loop control is primarily used to quickly regulate and limit the current to prevent overcurrent in the converter and potentially damage the equipment.

[0025] Furthermore, the modulation voltage of the receiving converter is the reference value of the a-axis voltage in the abc stationary coordinate system. , b-axis voltage reference value and c-axis voltage reference value The calculation formula is as follows:

[0026]

[0027] in, The phase reference value of the receiving-end converter is used to control the trigger signals of the various switching devices in the MMC based on the reference value of the modulation voltage of the receiving-end converter in the abc stationary three-phase coordinate system, thus realizing the network control of the receiving-end converter.

[0028] A second aspect of the present invention discloses a network construction control device for an offshore wind power flexible direct current transmission system, which is used to execute the above-mentioned network construction control method for an offshore wind power flexible direct current transmission system. The network construction control device includes:

[0029] A flexible DC transmission system parameter acquisition module is used to obtain the grid voltage and current at the receiving-end converter grid connection point, where the receiving-end converter grid connection point refers to the access point between the receiving-end converter and the onshore AC grid, and perform dq decomposition on the grid voltage and current at the receiving-end converter grid connection point to obtain the d-axis and q-axis components of the grid voltage and current at the receiving-end converter grid connection point in the dq rotating coordinate system, respectively. The module also obtains the actual values ​​of the DC voltage output by the receiving-end converter, the AC voltage and frequency at the receiving-end converter grid connection point, and reference values ​​of the DC voltage of the receiving-end converter, the voltage amplitude at the receiving-end converter grid connection point, and the frequency.

[0030] A first calculation module is used to calculate a phase reference value of a receiving-end converter;

[0031] The second calculation module is used to calculate the d-axis voltage reference value of the receiving-end converter grid connection point;

[0032] The third calculation module is used to calculate the d-axis current reference value and the q-axis current reference value of the receiving-end converter grid connection point;

[0033] a fourth calculation module, configured to calculate a d-axis voltage reference value and a q-axis voltage reference value of a modulation voltage of a receiving-end converter;

[0034] A fifth calculation module is used to calculate an a-axis voltage reference value, a b-axis voltage reference value, and a c-axis voltage reference value of the modulation voltage of the receiving-end converter in the abc stationary coordinate system;

[0035] The control pulse generation module is used to generate corresponding control pulses according to the reference value of the modulation voltage and use the pulse width modulation theory to realize the control of the receiving-end converter of the offshore wind power flexible direct current transmission system.

[0036] The third aspect of the present invention discloses a computer device, including a processor and a memory for storing a program executable by the processor. When the processor executes the program stored in the memory, it implements the above-mentioned offshore wind power flexible direct current transmission system network control method.

[0037] A fourth aspect of the present invention discloses a storage medium storing a program. When the program is executed by a processor, the above-mentioned offshore wind power flexible direct current transmission system network control method is implemented.

[0038] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0039] (1) The present invention first establishes the relationship between the DC side voltage and the AC side frequency of the receiving converter. On the one hand, it can open up the information transmission chain of "offshore wind turbine-flexible DC transmission system-receiving power grid", that is, by reflecting the frequency deviation information of the receiving power grid into the DC system, the sending power grid can obtain the frequency deviation information of the receiving power grid by detecting the DC voltage. On the other hand, by changing the adaptive coefficient k of the synchronous control loop a The value of u can be changed sq The proportion of the receiving-end converter in the synchronous control loop is then changed, thereby changing the equivalent damping and equivalent active power output of the receiving-end converter, so that during an AC fault in the receiving-end grid, the output power angle of the receiving-end converter does not diverge, thereby achieving fault ride-through. According to the disclosed offshore wind power flexible DC transmission system network control method, the receiving-end converter can establish the amplitude and frequency of the DC side voltage and the grid connection point voltage, so that the receiving-end converter exhibits voltage source characteristics on both its DC and AC sides, providing frequency / voltage support for the receiving-end grid.

[0040] (2) The control method of the present invention is applicable to the steady-state operation and fault operation of the point-to-point offshore wind power flexible DC transmission system. Through theoretical analysis and simulation examples, it is verified that the offshore wind power flexible DC transmission system adopting the control method of the present invention can maintain reliable synchronous operation under conditions such as a wide range of short-circuit ratio changes, power fluctuations, and AC faults. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0042] Figure 1 This is a flow chart of the network construction control method of the offshore wind power flexible direct current transmission system disclosed in the present invention;

[0043] Figure 2 This is the topology diagram of the 1000MW offshore wind power flexible DC transmission system;

[0044] Figure 3 This is the control block diagram of the receiving-end converter;

[0045] Figure 4 1 is a schematic diagram of system simulation waveforms when the short-circuit ratio of the receiving-end power grid changes from 5 to 2 when the control method of the present invention is adopted;

[0046] Figure 5 1 is a schematic diagram of system simulation waveforms when the active load at the receiving end increases by 100MW using the control method of the present invention;

[0047] Figure 6 1 is a schematic diagram of system simulation waveforms when the active load at the receiving end is reduced by 100MW using the control method of the present invention;

[0048] Figure 7 1 is a schematic diagram of system simulation waveforms before and after a three-phase short-circuit grounding fault occurs at the receiving end when the control method of the present invention is adopted;

[0049] Figure 8 This is a schematic diagram of system simulation waveforms before and after a three-phase short-circuit grounding fault occurs at the receiving end under the traditional receiving-end-following-grid MMC control.

[0050] Figure 9 This is a structural block diagram of the offshore wind power flexible direct current transmission system network control device disclosed in Example 5 of the present invention;

[0051] Figure 10 This is a structural block diagram of the computer device in Example 6 of the present invention. DETAILED DESCRIPTION

[0052] In order to enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0053] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described in this application may be combined with other embodiments.

[0054] Example 1

[0055] This embodiment discloses a method for controlling the network construction of an offshore wind power flexible direct current transmission system, which is applicable to Figure 2 In the system shown in the figure, HVDC stands for High Voltage Direct Current. The control method includes the following steps:

[0056] S1. Obtain the grid voltage and current at the receiving-end converter grid connection point. The receiving-end converter grid connection point refers to the access point between the receiving-end converter and the onshore AC grid. Perform dq decomposition on the grid voltage and current at the receiving-end converter grid connection point to obtain the d-axis and q-axis components of the grid voltage and current at the receiving-end converter grid connection point in the dq rotating coordinate system, respectively. Obtain the actual values ​​of the DC voltage output by the receiving-end converter, the AC voltage and frequency at the receiving-end converter grid connection point, and obtain reference values ​​of the DC voltage of the receiving-end converter, the voltage amplitude and frequency at the receiving-end converter grid connection point.

[0057] S2. Calculate the phase reference value of the receiving-end converter. The calculation formula is as follows:

[0058]

[0059] Where s is the Laplace operator, k is the reference value of the receiving end AC system frequency, a is the adaptive coefficient of the synchronous control loop, and are the reference value and actual value of DC voltage respectively, U sq is the q-axis component of the grid-connected voltage of the receiving converter, k pll is the proportionality coefficient, k T is the DC voltage droop coefficient.

[0060] S3, calculate the d-axis voltage reference value of the receiving-end converter grid-connected point, the d-axis voltage reference value of the receiving-end converter grid-connected point The calculation formula is as follows:

[0061]

[0062] in, is the q-axis voltage reference value of the receiving converter grid connection point, U sm is the reference value of the voltage amplitude at the grid connection point of the wind turbine in the offshore wind farm, Q * and Q s are the reference value and actual value of active power of wind turbines in offshore wind farms; k pq is the scale parameter.

[0063] S4, calculate the d-axis current reference value and q-axis current reference value of the receiving-end converter grid-connected point, the d-axis current reference value i of the receiving-end converter grid-connected point * vd and q-axis current reference value i * vq The calculation formula is as follows:

[0064]

[0065] Among them, i * vd and i * vq are the reference values ​​of the d-axis and q-axis components of the grid-connected current of the receiving converter; u sd and u sq are the d-axis and q-axis voltages at the receiving-end converter grid connection point respectively; C is the capacitance value of the LC filter on the AC side of the receiving-end converter; k pu and k iu are the proportional parameter and integral parameter of the voltage inner loop controller respectively, and ω is the actual value of the receiving end AC grid frequency.

[0066] S5. Calculate the d-axis voltage reference value and the q-axis voltage reference value of the modulation voltage of the receiving-end converter. The d-axis voltage reference value u of the modulation voltage of the receiving-end converter is * vd and q-axis voltage reference value u * vq The calculation formula is as follows:

[0067]

[0068] Among them, i vd and i vq are the d-axis and q-axis components of the output current of the receiving-end converter respectively; L is the connection reactance value of the receiving-end converter; k pi and k ii are the proportional parameter and integral parameter of the voltage inner loop controller respectively.

[0069] S6, calculate the a-axis voltage reference value, b-axis voltage reference value and c-axis voltage reference value of the modulation voltage of the receiving-end converter in the abc stationary coordinate system, the a-axis voltage reference value of the modulation voltage of the receiving-end converter in the abc stationary coordinate system , b-axis voltage reference value and c-axis voltage reference value The calculation formula is as follows:

[0070]

[0071] in, is the phase reference value of the receiving-end converter.

[0072] S7. Based on the reference value of the modulation voltage and using the pulse width modulation theory, a corresponding control pulse is generated to realize the control of the receiving-end converter of the offshore wind power flexible direct current transmission system.

[0073] Example 2

[0074] Based on the network control method of an offshore wind power flexible DC transmission system disclosed in Example 1, this embodiment uses a 1000MW offshore wind power flexible DC transmission system for simulation verification. The system topology is as follows: Figure 2 The system adopts the control method proposed in this paper. The sending-end MMC adopts island control, and the receiving-end MMC adopts fixed DC voltage and fixed AC voltage dual-grid control. The receiving-end converter control block diagram is shown in Figure 3 As shown. Assume that the system has entered a steady state at t=2s. At t=8s, the receiving-end grid short-circuit ratio suddenly changes from 5 to 2. The system DC voltage, frequency, receiving-end MMC output power angle, receiving-end MMC output active power and reactive power are as follows: Figure 4 As shown. Figure 4 It can be seen that when the receiving-end power grid changes from a strong network to a weak network, the system can recover stability in a relatively short time. Among them, the stable values ​​of the MMC output active power and reactive power, system DC voltage and frequency after the disturbance are not much different from the original values. The output power angle of the receiving-end MMC jumps from 0.19 to about 0.46, proving that the proposed control method can adapt to a wide range of short-circuit ratio changes in the receiving-end power grid.

[0075] Example 3

[0076] Based on the offshore wind power flexible DC transmission system grid control method disclosed in Example 1, this embodiment uses a 1000MW offshore wind power flexible DC transmission system for simulation verification. The system adopts the control method proposed in this article, the sending-end MMC adopts island control, and the receiving-end MMC adopts constant DC voltage and constant AC voltage dual grid control. Assume that the system has entered a steady state at t=2s. At t=8s, a power disturbance occurs, and the receiving-end grid load suddenly increases and decreases by 100MW, respectively. Figure 5 and Figure 6 The waveforms of the system DC voltage, frequency, output power angle of the receiving MMC, and active and reactive power of the receiving grid are shown in the two cases respectively. As can be seen from the simulation diagram, when the load increases or decreases suddenly, the system can adapt well to the load change and reach a stable operating state in a very short time, proving that the proposed control method can cope with a certain degree of power fluctuation. Figure 5 It can be seen from the figure that when the output power of the receiving generator suddenly increases by 100MW, the frequency decreases by about 0.3Hz due to the power imbalance of the receiving grid. Under the action of the DC voltage synchronization control loop, the DC voltage and frequency change simultaneously, but the DC voltage change range is within 5%. Figure 6 It can be seen from the figure that when the output power of the receiving-end generator suddenly decreases by 100MW, the frequency increases by about 0.3Hz due to the power imbalance of the receiving-end grid. Under the action of the DC voltage synchronization control loop, the DC voltage and frequency increase simultaneously, but the DC voltage change range is within 5%.

[0077] Example 4

[0078] Based on a grid control method for an offshore wind power flexible direct current transmission system disclosed in Example 1, this embodiment uses a 1000MW offshore wind power to conduct simulation verification through a flexible direct current transmission system. Control scheme 1 adopts the control method proposed in this article, the sending-end MMC adopts island control, and the receiving-end MMC adopts a dual-grid control of fixed DC voltage and fixed AC voltage. Control scheme 2 adopts a traditional flexible direct current control method, the sending-end MMC adopts island control, and the receiving-end MMC adopts a fixed DC voltage control. Assume that the system has entered a steady state at t=2s. At t=3s, a three-phase short-circuit grounding fault occurs in the receiving-end power grid, causing the receiving-end power grid voltage to drop to 0. The system DC voltage, the receiving-end MMC output power angle, the receiving-end power grid active power and reactive power waveforms under control schemes 1 and 2 are respectively as shown below. Figure 7 and Figure 8 As shown. Figure 7 It can be seen from the figure that, when the traditional receiving-end grid-following MMC control method is used, the MMC output power angle, the receiving-end grid active power and reactive power will oscillate, and the DC voltage will continue to rise, indicating that the MMC using the traditional grid-following control method cannot pass through the receiving-end AC three-phase short-circuit grounding fault. Figure 8 It can be seen that by using the control method proposed in this paper, by reducing k a The swing amplitude of the MMC output power angle becomes smaller. After a certain period of transient process, the MMC output power angle, MMC output power and DC voltage can return to the original stable operating point, indicating that the control method proposed in this paper can well ride through severe AC faults in the receiving power grid.

[0079] Example 5

[0080] like Figure 9 As shown, this embodiment provides a network construction control device for an offshore wind power flexible DC transmission system. The network construction control device includes: a flexible DC transmission system parameter acquisition module 901, a first calculation module 902, a second calculation module 903, a third calculation module 904, a fourth calculation module 905, a fifth calculation module 906, and a control pulse generation module 907. The specific functions of each module are as follows:

[0081] Flexible DC transmission system parameter acquisition module 901 is used to obtain the grid voltage and current at the receiving-end converter grid connection point, where the receiving-end converter grid connection point refers to the connection point between the receiving-end converter and the onshore AC grid, and perform dq decomposition on the grid voltage and current at the receiving-end converter grid connection point to obtain the d-axis and q-axis components of the grid voltage and current at the receiving-end converter grid connection point in the dq rotating coordinate system, respectively, to obtain the actual values ​​of the DC voltage output by the receiving-end converter, the AC voltage and frequency at the receiving-end converter grid connection point, and to obtain reference values ​​of the DC voltage of the receiving-end converter, the voltage amplitude at the receiving-end converter grid connection point, and the frequency;

[0082] A first calculation module 902 is configured to calculate a phase reference value of a receiving-end converter;

[0083] The second calculation module 903 is used to calculate the d-axis voltage reference value of the receiving-end converter grid connection point;

[0084] The third calculation module 904 is used to calculate the d-axis current reference value and the q-axis current reference value of the receiving-end converter grid connection point;

[0085] A fourth calculation module 905 is configured to calculate a d-axis voltage reference value and a q-axis voltage reference value of the modulation voltage of the receiving-end converter;

[0086] A fifth calculation module 906 is configured to calculate an a-axis voltage reference value, a b-axis voltage reference value, and a c-axis voltage reference value of the modulation voltage of the receiving-end converter in the abc stationary coordinate system;

[0087] The control pulse generating module 907 is used to generate corresponding control pulses according to the reference value of the modulation voltage and utilize the pulse width modulation theory to realize the control of the receiving-end converter of the offshore wind power flexible DC transmission system.

[0088] Example 6

[0089] This embodiment provides a computer device, which can be a computer, such as Figure 10 As shown, the system comprises a processor 1002, a memory, an input device 1003, a display 1004 and a network interface 1005 connected via a system bus 1001. The processor is used to provide computing and control capabilities. The memory includes a non-volatile storage medium 1006 and an internal memory 1007. The non-volatile storage medium 1006 stores an operating system, a computer program and a database. The internal memory 1007 provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The processor 1002 executes the computing stored in the memory. When the machine program is executed, a network control method for an offshore wind power flexible direct current transmission system proposed in the above embodiment 1 is implemented. The offshore wind farm is connected to the onshore AC power grid through the offshore wind power flexible direct current transmission system. The end where the offshore wind power flexible direct current transmission system is connected to the onshore AC power grid through the modular multilevel converter is called the receiving end, and the corresponding converter is referred to as the receiving end converter. The end where the offshore wind power flexible direct current transmission system is connected to the offshore wind farm through the modular multilevel converter is called the sending end, and the corresponding converter is referred to as the sending end converter. The above network control method includes the following steps:

[0090] S1. Obtain the grid voltage and current at the receiving-end converter grid connection point, where the receiving-end converter grid connection point refers to the connection point between the receiving-end converter and the onshore AC grid, and perform dq decomposition on the grid voltage and current at the receiving-end converter grid connection point to obtain the d-axis and q-axis components of the grid voltage and current at the receiving-end converter grid connection point in a dq rotating coordinate system, respectively. Obtain the actual values ​​of the DC voltage output by the receiving-end converter, the AC voltage and frequency at the receiving-end converter grid connection point, and obtain reference values ​​of the DC voltage of the receiving-end converter, the voltage amplitude and frequency at the receiving-end converter grid connection point;

[0091] S2. Calculate the phase reference value of the receiving-end converter;

[0092] S3. Calculate the d-axis voltage reference value of the receiving-end converter grid connection point;

[0093] S4. Calculate the d-axis current reference value and the q-axis current reference value of the receiving-end converter grid connection point;

[0094] S5. Calculate the d-axis voltage reference value and the q-axis voltage reference value of the modulation voltage of the receiving-end converter;

[0095] S6. Calculate the a-axis voltage reference value, the b-axis voltage reference value, and the c-axis voltage reference value of the modulation voltage of the receiving-end converter in the abc stationary coordinate system;

[0096] S7. Based on the reference value of the modulation voltage and using the pulse width modulation theory, a corresponding control pulse is generated to realize the control of the receiving-end converter of the offshore wind power flexible direct current transmission system.

[0097] Example 7

[0098] This embodiment provides a storage medium, which is a computer-readable storage medium and stores a computer program. When the computer program is executed by a processor, it implements a network control method for an offshore wind power flexible direct current transmission system proposed in the above-mentioned embodiment 1. The offshore wind farm is connected to the onshore AC power grid through the offshore wind power flexible direct current transmission system. The end where the offshore wind power flexible direct current transmission system is connected to the onshore AC power grid through a modular multilevel converter is called a receiving end, and the corresponding converter is referred to as a receiving-end converter. The end where the offshore wind power flexible direct current transmission system is connected to the offshore wind farm through the modular multilevel converter is called a sending end, and the corresponding converter is referred to as a sending-end converter. The above-mentioned network control method includes the following steps:

[0099] S1. Obtain the grid voltage and current at the receiving-end converter grid connection point, where the receiving-end converter grid connection point refers to the connection point between the receiving-end converter and the onshore AC grid, and perform dq decomposition on the grid voltage and current at the receiving-end converter grid connection point to obtain the d-axis and q-axis components of the grid voltage and current at the receiving-end converter grid connection point in a dq rotating coordinate system, respectively. Obtain the actual values ​​of the DC voltage output by the receiving-end converter, the AC voltage and frequency at the receiving-end converter grid connection point, and obtain reference values ​​of the DC voltage of the receiving-end converter, the voltage amplitude and frequency at the receiving-end converter grid connection point;

[0100] S2. Calculate the phase reference value of the receiving-end converter;

[0101] S3. Calculate the d-axis voltage reference value of the receiving-end converter grid connection point;

[0102] S4. Calculate the d-axis current reference value and the q-axis current reference value of the receiving-end converter grid connection point;

[0103] S5. Calculate the d-axis voltage reference value and the q-axis voltage reference value of the modulation voltage of the receiving-end converter;

[0104] S6. Calculate the a-axis voltage reference value, the b-axis voltage reference value, and the c-axis voltage reference value of the modulation voltage of the receiving-end converter in the abc stationary coordinate system;

[0105] S7. Based on the reference value of the modulation voltage and using the pulse width modulation theory, a corresponding control pulse is generated to realize the control of the receiving-end converter of the offshore wind power flexible direct current transmission system.

[0106] Those skilled in the art will appreciate that all or part of the processes in the above-mentioned embodiment methods can be implemented by instructing the relevant hardware through a computer program. The program can be stored in a non-volatile computer-readable storage medium. When the program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. As an illustration and not limitation, RAM is available in many forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus), direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM).

[0107] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0108] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for controlling a network of an offshore wind power flexible direct current transmission system, wherein an offshore wind farm is connected to an onshore AC power grid through the offshore wind power flexible direct current transmission system. The end where the offshore wind power flexible direct current transmission system is connected to the onshore AC power grid through a modular multilevel converter is called a receiving end, and the corresponding converter is referred to as a receiving end converter. The end where the offshore wind power flexible direct current transmission system is connected to the offshore wind farm through a modular multilevel converter is called a sending end, and the corresponding converter is referred to as a sending end converter. The method is characterized in that: The network control method comprises the following steps: S1. Obtain the grid voltage and current at the receiving-end converter grid connection point, where the receiving-end converter grid connection point refers to the connection point between the receiving-end converter and the onshore AC grid, and perform dq decomposition on the grid voltage and current at the receiving-end converter grid connection point to obtain the d-axis and q-axis components of the grid voltage and current at the receiving-end converter grid connection point in a dq rotating coordinate system, respectively. Obtain the actual values ​​of the DC voltage output by the receiving-end converter, the AC voltage and frequency at the receiving-end converter grid connection point, and obtain reference values ​​of the DC voltage of the receiving-end converter, the voltage amplitude and frequency at the receiving-end converter grid connection point; S2. Calculate the phase reference value of the receiving-end converter; S3. Calculate the d-axis voltage reference value of the receiving-end converter grid connection point; S4. Calculate the d-axis current reference value and the q-axis current reference value of the receiving-end converter grid connection point; S5. Calculate the d-axis voltage reference value and the q-axis voltage reference value of the modulation voltage of the receiving-end converter; S6. Calculate the a-axis voltage reference value, the b-axis voltage reference value, and the c-axis voltage reference value of the modulation voltage of the receiving-end converter in the abc stationary coordinate system; S7. Based on the reference value of the modulation voltage and using the pulse width modulation theory, a corresponding control pulse is generated to realize the control of the receiving-end converter of the offshore wind power flexible direct current transmission system.

2. The offshore wind power flexible direct current transmission system network control method according to claim 1, characterized in that: In step S2, the phase reference value of the receiving end converter The calculation formula is as follows: Where s is the Laplace operator, k is the reference value of the receiving end AC system frequency, a is the adaptive coefficient of the synchronous control loop, and are the reference value and actual value of DC voltage respectively, U sq is the q-axis component of the grid-connected voltage of the receiving converter, k pll is the proportionality coefficient, k T is the DC voltage droop coefficient.

3. The offshore wind power flexible direct current transmission system network control method according to claim 1, characterized in that: In step S3, the d-axis voltage reference value of the receiving-end converter grid connection point is The calculation formula is as follows: in, is the q-axis voltage reference value of the receiving converter grid connection point, U sm is the reference value of the voltage amplitude at the grid connection point of the wind turbine in the offshore wind farm, Q * and Q s are the reference value and actual value of active power of wind turbines in offshore wind farms; k pq is the scale parameter.

4. The offshore wind power flexible direct current transmission system network control method according to claim 1, characterized in that: In step S4, the d-axis current reference value i of the receiving-end converter grid connection point is * vd and q-axis current reference value i * vq The calculation formula is as follows: Among them, u sd and u sq are the d-axis and q-axis voltages at the receiving-end converter grid connection point respectively; C is the capacitance value of the LC filter on the AC side of the receiving-end converter; k pu and k iu are the proportional parameter and integral parameter of the voltage inner loop proportional-integral controller respectively, and ω is the actual value of the receiving end AC grid frequency.

5. The offshore wind power flexible direct current transmission system network control method according to claim 4, characterized in that: In step S5, the d-axis voltage reference value u of the modulation voltage of the receiving-end converter is * vd and q-axis voltage reference value u * vq The calculation formula is as follows: Among them, i vd and i vq are the d-axis and q-axis components of the output current of the receiving-end converter respectively; L is the connection reactance value of the receiving-end converter; k pi and k ii They are the proportional parameter and integral parameter of the current inner loop proportional-integral controller respectively.

6. The offshore wind power flexible direct current transmission system network control method according to claim 1, characterized in that: In step S6, the modulation voltage of the receiving-end converter is the a-axis voltage reference value in the abc stationary coordinate system. , b-axis voltage reference value and c-axis voltage reference value The calculation formula is as follows: in, is the phase reference value of the receiving-end converter.

7. A network control device for an offshore wind power flexible direct current transmission system, configured to execute the network control method for an offshore wind power flexible direct current transmission system according to any one of claims 1 to 6, characterized in that: The network control device includes: A flexible DC transmission system parameter acquisition module is used to obtain the grid voltage and current at the receiving-end converter grid connection point, where the receiving-end converter grid connection point refers to the access point between the receiving-end converter and the onshore AC grid, and perform dq decomposition on the grid voltage and current at the receiving-end converter grid connection point to obtain the d-axis and q-axis components of the grid voltage and current at the receiving-end converter grid connection point in the dq rotating coordinate system, respectively. The module also obtains the actual values ​​of the DC voltage output by the receiving-end converter, the AC voltage and frequency at the receiving-end converter grid connection point, and reference values ​​of the DC voltage of the receiving-end converter, the voltage amplitude at the receiving-end converter grid connection point, and the frequency. A first calculation module is used to calculate a phase reference value of a receiving-end converter; The second calculation module is used to calculate the d-axis voltage reference value of the receiving-end converter grid connection point; The third calculation module is used to calculate the d-axis current reference value and the q-axis current reference value of the receiving-end converter grid connection point; a fourth calculation module, configured to calculate a d-axis voltage reference value and a q-axis voltage reference value of a modulation voltage of a receiving-end converter; A fifth calculation module is used to calculate an a-axis voltage reference value, a b-axis voltage reference value, and a c-axis voltage reference value of the modulation voltage of the receiving-end converter in the abc stationary coordinate system; The control pulse generation module is used to generate corresponding control pulses according to the reference value of the modulation voltage and use the pulse width modulation theory to realize the control of the receiving-end converter of the offshore wind power flexible direct current transmission system.

8. A computer device comprising a processor and a memory for storing a program executable by the processor, characterized in that: When the processor executes the program stored in the memory, it implements the offshore wind power flexible direct current transmission system network control method described in any one of claims 1 to 6.

9. A storage medium storing a program, characterized in that: When the program is executed by a processor, a network control method for an offshore wind power flexible direct current transmission system as described in any one of claims 1 to 6 is implemented.

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