A method for constructing a network of a marine wind power flexible direct current power transmission system

Abstract

The application discloses a kind of offshore wind power flexible DC transmission system network construction control methods, steps are as follows: obtaining offshore wind power flexible DC transmission system receiving end converter DC side voltage, receiving end converter grid-connected point's grid voltage and current and grid voltage amplitude reference value;The phase reference value of receiving end converter and the reference value of modulation voltage under dq rotating coordinate system are calculated;According to the phase reference value of receiving end converter and the reference value of modulation voltage under dq rotating coordinate system, the reference value of modulation voltage under abc stationary coordinate system of receiving end converter is calculated.The receiving end converter in the application simultaneously controls the DC voltage of point-to-point flexible DC transmission system and the voltage and frequency of receiving end AC grid, realizes double-network construction control of DC voltage and receiving end AC voltage.Island control is adopted for sending end converter.Offshore wind power flexible DC system controlled by the application can adapt to different receiving end grid intensity, and can reliably operate under power fluctuation, AC fault and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of offshore wind power flexible DC grid-connected system control, in particular to an offshore wind power flexible DC transmission system grid-connection control method, a grid-connection control device, computer equipment and a storage medium. BACKGROUND

[0002] Modular Multilevel Converter (MMC) is widely used in large-scale offshore wind power access to large power grid scenarios. The mainstream MMC control can be divided into two categories: grid-following control and grid-forming control. Among them, the grid-following control needs a synchronous generator or a synchronous compensator to provide a stable voltage source. However, as the penetration rate of new energy continues to increase, when the voltage is disturbed, the grid-following control is easy to be unstable. On the contrary, the MMC grid-forming control is more suitable for large-scale new energy access scenarios because it can establish a stable voltage. The existing grid-forming control can also be roughly divided into two categories: AC grid-forming and DC grid-forming. In AC grid-forming control, the MMC AC side forms a stable AC voltage amplitude and phase angle, but a stable DC voltage source is needed to establish the MMC DC side voltage. On the contrary, in DC grid-forming control, the MMC forms a stable DC voltage amplitude, following the strong AC grid. With the large-scale integration of offshore wind power into the grid and the large number of DC transmission load centers, the voltage stability and frequency stability of the power grid have become increasingly prominent. Flexible DC transmission has large capacity and flexible control, and needs to provide certain active support system capabilities.

[0003] However, whether it is AC grid-forming control or DC grid-forming control, it is a single-sided grid-forming control of MMC, which is difficult to provide active support for new power systems with high proportion of new energy and high proportion of power electronic devices. In the point-to-point offshore wind power sending scenario, after large-capacity offshore wind power is collected, it is converted into DC power by the sending-end AC grid-forming MMC and transmitted to the shore, and then converted into AC power by the receiving-end DC grid-forming MMC and accessed to the far-end grid, as shown in Figure 2 For the flexible DC transmission system using traditional control, the receiving-end DC grid-forming MMC is very dependent on the communication of the phase-locked loop. Once the onshore AC system fails, the DC voltage grid-forming control of the receiving-end MMC will be unstable, and when the strong DC voltage source is lost, the AC voltage grid-forming control of the sending-end MMC will also be unstable, thereby causing the instability of the entire offshore wind power sending system. Therefore, it is urgent to propose a flexible DC transmission system control strategy that can actively support the receiving-end large power grid. SUMMARY

[0004] The main purpose of the present application is to overcome the shortcomings and deficiencies of the prior art, and provide a kind of offshore wind power flexible DC transmission system network control method, device, computer equipment and storage medium. Wherein, the sending end converter adopts island control to establish the voltage and frequency of offshore wind farm, and the receiving end converter adopts fixed DC voltage and fixed AC voltage control to establish stable system DC voltage and receiving end AC voltage. The flexible DC system using the control method can adapt to different receiving end grid intensity, and can maintain stable operation after power disturbance and AC fault, and has certain active support for the receiving end to establish the ability of power grid.

[0005] In order to achieve the above purpose, the first aspect of the present application discloses a kind of offshore wind power flexible DC transmission system network control method, offshore wind farm is connected to onshore AC grid through offshore wind power flexible DC transmission system, offshore wind power flexible DC transmission system is connected to onshore AC grid through the end of modular multilevel converter, which is called receiving end, and the corresponding converter is called receiving end converter. The system topology is as shown in Figure 2 The receiving end converter control block diagram is as shown in Figure 3 In the figure, i v represents the current of converter grid-connected point, u s represents the voltage of converter grid-connected point. Offshore wind power flexible DC transmission system is connected to offshore wind farm through the end of modular multilevel converter, which is called sending end, and the corresponding converter is called sending end converter, the control method comprises the following steps:

[0006] S1, the grid voltage and current of receiving end converter grid-connected point are obtained, and the grid voltage and current of receiving end converter grid-connected point are dq decomposed, to obtain the d-axis and q-axis components of the grid voltage and current of receiving end converter grid-connected point in dq rotating coordinate system, the actual values of DC voltage output by receiving end converter, receiving end converter grid-connected point AC voltage and frequency are obtained, the reference values of DC voltage of receiving end converter, voltage amplitude and frequency of receiving end converter grid-connected point are obtained;

[0007] S2, the phase reference value of receiving end converter is calculated;

[0008] S3, the d-axis voltage reference value of receiving end converter grid-connected point is calculated;

[0009] S4, the d-axis current reference value and q-axis current reference value of receiving end converter grid-connected point are calculated;

[0010] S5, the d-axis voltage reference value and q-axis voltage reference value of receiving end converter modulation voltage are calculated;

[0011] S6, calculating 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, generating corresponding control pulses to realize the control of the receiving-end converter of the offshore wind power flexible DC power transmission system according to the reference value of the modulation voltage by using the pulse width modulation theory.

[0013] Further, in order to improve the stability of the grid connection of the receiving-end converter, a coupling quantity of the q-axis component U sq of the grid connection point voltage of the receiving-end converter is added to the proportional control, and an adaptive coefficient is used to adjust the proportion of the coupling quantity in the synchronous control loop, and the calculation formula of the phase reference value of the receiving-end converter is as follows:

[0014]

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

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

[0017]

[0018] wherein is the q-axis voltage reference value of the grid connection point of the receiving-end converter, U sm is the reference value of the voltage amplitude of the grid connection point of the offshore wind farm wind turbine, Q * and Q s are the active power reference value and the actual value of the offshore wind farm wind turbine; and k pq is the proportional parameter. The above formula controls the q-axis component of the grid connection point voltage of the receiving-end converter to be zero, and the main purpose of this is to realize the coincidence of the grid connection point voltage vector of the receiving-end converter with the d-axis of the synchronous rotating coordinate system, i.e. the d-axis component is oriented. In this case, the d-axis component amplitude is the amplitude of the grid connection point voltage of the receiving-end converter, which is convenient for the design of the controller.

[0019] Further, the d-axis current reference value i * vd and the q-axis current reference value i * vq The calculation formula is as follows:

[0020]

[0021] wherein u sd and u sq are the d-axis component and the q-axis component of the grid-connection 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 the integral parameter of the voltage inner loop controller respectively, and ω is the actual value of the frequency of the receiving AC power grid.

[0022] Further, the d-axis voltage reference value u * vd and the q-axis voltage reference value u * vq The calculation formula is as follows:

[0023]

[0024] wherein i vd and i vq are the d-axis component and the q-axis component of the output current of the receiving converter respectively; L is the joint reactance value of the receiving converter; k pi and k ii are the proportional parameter and the integral parameter of the voltage inner loop controller respectively. The function of the double inner loop control is mainly to quickly regulate and limit the current, so as to avoid overcurrent and damage the equipment of the converter.

[0025] Further, 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 converter in the abc stationary coordinate system are calculated as follows:

[0026]

[0027] wherein, is the phase reference value of the receiving converter. According to the reference value of the modulation voltage of the receiving converter in the abc stationary three-phase coordinate system, the trigger signals of each switching device in the MMC can be controlled to generate, so as to realize the grid-connection control of the receiving converter.

[0028] The second aspect of the present application discloses a network construction control device of a marine wind power flexible DC power transmission system, which is used to execute the network construction control method of the marine wind power flexible DC power transmission system.

[0029] The flexible DC power transmission system parameter acquisition module is used to acquire the grid voltage and current of the receiving end converter grid connection point, which is the access point of the receiving end converter and the onshore AC grid, and perform dq decomposition on the grid voltage and current of the receiving end converter grid connection point to obtain the d-axis and q-axis components of the grid voltage and current of the receiving end converter grid connection point in the dq rotating coordinate system, acquire the actual values of the DC voltage output by the receiving end converter, the AC voltage and frequency of the receiving end converter grid connection point, and acquire the reference values of the DC voltage of the receiving end converter, the voltage amplitude and frequency of the receiving end converter grid connection point;

[0030] The first calculation module is used to calculate the phase reference value of the 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] The fourth calculation module is used to calculate the d-axis voltage reference value and the q-axis voltage reference value of the modulation voltage of the receiving end converter.

[0034] The fifth calculation module is used to 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.

[0035] The control pulse generation module is used to generate corresponding control pulses to realize the control of the receiving end converter of the marine wind power flexible DC power transmission system according to the reference values of the modulation voltage by using the pulse width modulation theory.

[0036] The third aspect of the present application discloses a computer device, which comprises a processor and a memory for storing a program executable by the processor, and when the processor executes the program stored in the memory, the network construction control method of the marine wind power flexible DC power transmission system is realized.

[0037] The fourth aspect of the present application discloses a storage medium, which stores a program, and when the program is executed by a processor, the network construction control method of the marine wind power flexible DC power transmission system is realized.

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

[0039] (1) The application firstly establishes the relationship between the DC side voltage of the receiving end converter and the frequency of the AC side. On the one hand, the information transmission chain of "offshore wind turbine-flexible DC power transmission system-receiving end power grid" can be broken through, that is, the frequency deviation information of the receiving end power grid is reflected to the DC system, and then the sending end power grid can obtain the frequency deviation information of the receiving end power grid by detecting the DC voltage. On the other hand, by changing the value of the adaptive coefficient k a of the synchronous control loop, the proportion of u sq in the synchronous control loop can be changed, and then the equivalent damping and equivalent active power output of the receiving end converter are changed, so that the power angle output of the receiving end converter does not diverge during the AC fault of the receiving end power grid, and then the fault ride-through is realized. According to the offshore wind power flexible DC power transmission system network control method disclosed by the application, 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 shows voltage source characteristics on its DC side and AC side, and realizes the frequency / voltage support for the receiving end power grid.

[0040] (2) The control method of the application is suitable for the steady-state operation and fault operation of the point-to-point offshore wind power flexible DC power transmission system. Through theoretical analysis and simulation examples, it is verified that the offshore wind power flexible DC power transmission system using the control method of the application can maintain reliable synchronous operation under the conditions of wide range short-circuit ratio change, power fluctuation, AC fault and the like. BRIEF DESCRIPTION OF DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0042] Figure 1 is a flow chart of the offshore wind power flexible DC power transmission system network control method disclosed by the application;

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

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

[0045] Figure 4 is a system simulation waveform schematic diagram when the short-circuit ratio of the receiving end power grid jumps from 5 to 2 under the condition of using the control method of the application;

[0046] Figure 5 is a system simulation waveform schematic diagram when the active load of the receiving end power grid increases by 100MW under the condition of using the control method of the application;

[0047] Figure 6 is a system simulation waveform schematic diagram under the condition that the active load of the receiving end is reduced by 100 MW using the control method of the application;

[0048] Figure 7 is a system simulation waveform schematic diagram before and after a three-phase short-circuit grounding fault occurs at the receiving end using the control method of the application;

[0049] Figure 8 is a system simulation waveform schematic diagram before and after a three-phase short-circuit grounding fault occurs at the receiving end using the traditional receiving-end MMC control;

[0050] Figure 9 is a structural block diagram of the offshore wind power flexible HVDC power transmission system network control device disclosed in Embodiment 5 of the application;

[0051] Figure 10 is a structural block diagram of the computer device in Embodiment 6 of the application. DETAILED DESCRIPTION

[0052] In order to enable personnel in the art to better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0053] In the present application, the phrase “embodiment” means that the specific features, structures or characteristics described in conjunction with the embodiment can be included in at least one embodiment of the present application. The appearance of this phrase at various places in the specification does not necessarily mean the same embodiment, nor is it an independent or alternative embodiment to other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described in the present application can be combined with other embodiments.

[0054] Embodiment 1

[0055] The present embodiment discloses a network control method for an offshore wind power flexible HVDC power transmission system, which is applied to a system as shown in Figure 2 The control method comprises the following steps:

[0056] S1, acquire grid voltage and current of the receiving end converter grid-connected point, the receiving end converter grid-connected point refers to the access point of the receiving end converter and the onshore alternating current grid, and perform dq decomposition on the grid voltage and current of the receiving end converter grid-connected point to obtain d-axis and q-axis components of the grid voltage and current of the receiving end converter grid-connected point in the dq rotating coordinate system, acquire actual values of the DC voltage output by the receiving end converter, the receiving end converter grid-connected point alternating current voltage and frequency, acquire reference values of the DC voltage of the receiving end converter, the receiving end converter grid-connected point voltage amplitude and frequency.

[0057] S2, calculate the phase reference value of the receiving end converter, the phase reference value of the receiving end converter The calculation formula is as follows:

[0058]

[0059] Wherein, s is the Laplace operator, is the reference value of the receiving end alternating current system frequency, k a is the adaptive coefficient of the synchronous control loop, and are the reference value and the actual value of the DC voltage, U sq is the q-axis component of the receiving end converter grid-connected point voltage, k pll is the proportional 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] Wherein, is the q-axis voltage reference value of the receiving end converter grid-connected point, U sm is the reference value of the offshore wind farm wind turbine grid-connected point voltage amplitude, Q * and Q s are the active power reference value and the actual value of the offshore wind farm wind turbine; k pq is the proportional parameter.

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

[0064]

[0065] wherein, i * vd and i * vq are the d-axis and q-axis component reference values of the grid-connected point current of the receiving converter respectively; u sd and u sq are the d-axis and q-axis voltages of the grid-connected point 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 frequency of the AC power grid on the receiving side.

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

[0067]

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

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

[0070]

[0071] wherein, is the phase reference value of the receiving converter.

[0072] S7, according to the reference value of the modulation voltage, using the pulse width modulation theory, generating the corresponding control pulse to realize the control of the receiving converter of the offshore wind power flexible DC power transmission system.

[0073] Embodiment 2

[0074] Based on the offshore wind power flexible DC transmission system network control method disclosed in embodiment 1, in this embodiment, 1000MW offshore wind power is simulated and verified through a flexible DC transmission system, and the system topology is as shown in 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 double network control of fixed DC voltage and fixed AC voltage. The control block diagram of the receiving end converter is as shown in Figure 3 It is assumed that the system has entered a steady state at t=2s. At t=8s, the short-circuit ratio of the receiving end power grid suddenly changes from 5 to 2, and the system DC voltage, frequency, receiving end MMC output power angle, receiving end MMC output active power and reactive power are as shown in Figure 4 From Figure 4 It can be seen that when the receiving end power grid changes from a strong grid to a weak grid, the system can recover to a stable state in a short time, wherein the stable values of the MMC output active power and reactive power, the system DC voltage and frequency after disturbance are not much different from the original values, and the receiving end MMC output power angle 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 of the receiving end power grid.

[0075] Embodiment 3

[0076] Based on the offshore wind power flexible DC transmission system network control method disclosed in embodiment 1, in this embodiment, 1000MW offshore wind power is simulated and verified through a flexible DC transmission system. The system adopts the control method proposed in this paper, the sending end MMC adopts island control, and the receiving end MMC adopts double network control of fixed DC voltage and fixed AC voltage. It is assumed that the system has entered a steady state at t=2s. At t=8s, a power disturbance occurs, and the load of the receiving end power grid suddenly increases by 100MW and suddenly decreases by 100MW, Figure 5 and Figure 6 respectively show the system DC voltage, frequency, receiving end MMC output power angle, receiving end power grid active power and reactive power waveforms under two conditions. From the simulation diagram, it can be seen that when the load suddenly increases and decreases, the system can well adapt 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. From Figure 5 It can be seen that when the output power of the receiving end generator suddenly increases by 100MW, the frequency decreases by about 0.3Hz due to the power imbalance of the receiving end power grid, and under the action of the DC voltage synchronous control ring, the DC voltage and frequency decrease, but the change range of the DC voltage is within 5%. From Figure 6 It can be seen 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 power grid, and under the action of the DC voltage synchronous control ring, the DC voltage and frequency increase, but the change range of the DC voltage is within 5%.

[0077] Embodiment 4

[0078] Based on the offshore wind power flexible DC transmission system network control method disclosed in embodiment 1, this embodiment adopts 1000MW offshore wind power through flexible DC transmission system for simulation verification. Control scheme 1 adopts the control method proposed in this paper, the sending end MMC adopts island control, and the receiving end MMC adopts double network control of fixed DC voltage and fixed AC voltage. Control scheme 2 adopts the traditional flexible DC control method, the sending end MMC adopts island control, and the receiving end MMC adopts fixed DC voltage control. It is assumed that the system has entered steady state at t=2s. When t=3s, the receiving end grid voltage drops to 0 due to three-phase short-circuit ground fault of the receiving end grid. The system DC voltage, receiving end MMC output power angle, receiving end grid active power and reactive power waveforms under control scheme 1 and scheme 2 are shown in Figure 7 and Figure 8 It can be seen from Figure 7 that by using the traditional receiving end network following type MMC control method, the MMC output power angle, the receiving end grid active power and the reactive power will oscillate, and the DC voltage will continue to rise, indicating that the MMC with traditional network following control cannot pass through the receiving end AC three-phase short-circuit ground fault. It can be seen from Figure 8 that by using the control method proposed in this paper, by reducing the value of k a , the swing amplitude of the MMC output power angle becomes smaller, and after a certain time of transient process, the MMC output power angle, the MMC output power and the DC voltage can all return to the original stable operating point, indicating that the control method proposed in this paper can pass through the severe AC fault of the receiving end grid well.

[0079] Embodiment 5

[0080] As shown in Figure 9 , the embodiment provides a network control device for offshore wind power flexible DC transmission system, the network control device comprises: 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, and the specific functions of each module are as follows:

[0081] The flexible DC transmission system parameter acquisition module 901 is used for acquiring the grid voltage and current at the receiving end converter grid connection point, which is the access point of the receiving end converter to the onshore AC grid, and performing 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, acquiring the actual values of the DC voltage output by the receiving end converter, the receiving end converter grid connection point AC voltage and frequency, and acquiring the reference values of the DC voltage of the receiving end converter, the voltage amplitude and frequency of the receiving end converter grid connection point;

[0082] The first calculation module 902 is used to calculate the phase reference value of the receiving-end converter;

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

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

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

[0086] The fifth calculation module 906 is used to 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;

[0087] The control pulse generation module 907 is used to generate corresponding control pulses based on the reference value of the modulation voltage and the pulse width modulation theory to control 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 processor 1002, memory, input device 1003, display 1004, and network interface 1005 are connected via system bus 1001. The processor provides computing and control capabilities. The memory includes a non-volatile storage medium 1006 and internal memory 1007. The non-volatile storage medium 1006 stores the operating system, computer programs, and database. The internal memory 1007 provides an environment for the operation of the operating system and computer programs in the non-volatile storage medium. The processor 1002 performs calculations stored in the memory. When the program is executed, it implements the grid construction control method for the offshore wind power flexible DC transmission system proposed in Embodiment 1 above. The offshore wind farm is connected to the onshore AC grid through the offshore wind power flexible DC transmission system. The connection end of the offshore wind power flexible DC transmission system with the onshore AC grid through the modular multilevel converter is called the receiving end, and the corresponding converter is called the receiving end converter. The connection end of the offshore wind power flexible DC transmission system with the offshore wind farm through the modular multilevel converter is called the sending end, and the corresponding converter is called the sending end converter. The above grid construction control method includes the following steps:

[0090] S1, obtain grid voltage and current of the receiving-end converter grid-connected point, the receiving-end converter grid-connected point refers to the access point of the receiving-end converter and the onshore AC grid, and perform dq decomposition on the grid voltage and current of the receiving-end converter grid-connected point to obtain d-axis and q-axis components of the grid voltage and current of the receiving-end converter grid-connected point in the dq rotating coordinate system, obtain actual values of DC voltage output by the receiving-end converter, AC voltage and frequency of the receiving-end converter grid-connected point, obtain reference values of DC voltage of the receiving-end converter, voltage amplitude and frequency of the receiving-end converter grid-connected 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-connected point;

[0093] S4, calculate the d-axis current reference value and the q-axis current reference value of the receiving-end converter grid-connected 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, according to the reference value of the modulation voltage, generate corresponding control pulses to realize the control of the receiving-end converter of the offshore wind power flexible DC power transmission system by using the pulse width modulation theory.

[0097] Embodiment 7

[0098] The embodiment provides a storage medium, which is a computer readable storage medium, and stores a computer program, the computer program is executed by a processor to realize the offshore wind power flexible DC power transmission system network construction control method provided in the above embodiment 1, the offshore wind farm is connected to the onshore AC grid through the offshore wind power flexible DC power transmission system, the connection end of the offshore wind power flexible DC power transmission system and the onshore AC grid is called the receiving end, and the corresponding converter is called the receiving-end converter, the connection end of the offshore wind power flexible DC power transmission system and the offshore wind farm is called the sending end, and the corresponding converter is called the sending-end converter, and the network construction control method comprises the following steps:

[0099] S1, acquire grid voltage and current of the receiving end converter grid-connected point, the receiving end converter grid-connected point refers to the access point of the receiving end converter and the onshore alternating current grid, and perform dq decomposition on the grid voltage and current of the receiving end converter grid-connected point to obtain d-axis and q-axis components of the grid voltage and current of the receiving end converter grid-connected point in the dq rotating coordinate system, acquire actual values of the output direct current voltage of the receiving end converter, the receiving end converter grid-connected point alternating current voltage and frequency, acquire reference values of the direct current voltage of the receiving end converter, the receiving end converter grid-connected point voltage amplitude and frequency;

[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-connected point;

[0102] S4, calculate the d-axis current reference value and the q-axis current reference value of the receiving end converter grid-connected 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, according to the reference value of the modulation voltage, generate corresponding control pulses to realize the control of the receiving end converter of the offshore wind power flexible direct current power transmission system by using the pulse width modulation theory.

[0106] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program. The program can be stored in a non-volatile computer readable storage medium, and when the program is executed, the processes of the above-mentioned embodiment methods can be included. Any reference to memory, storage, database or other medium used in the embodiments provided in the present 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 but not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), 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), etc.

[0107] Any combination of the technical features of the above embodiments can be made. In order to make the description simple, all possible combinations of the technical features in the above embodiments are not described, however, as long as the combination of the technical features does not exist, it should be considered as the scope of the present application.

[0108] The above embodiments are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above embodiments, and any changes, modifications, substitutions, combinations and simplifications of the embodiments of the present application without departing from the spirit and principles of the present application shall be equivalent replacement methods, and shall be included in the protection scope of the present application.

Claims

1. A method for offshore wind farm flexible direct current transmission system grid connection control, the offshore wind farm is connected to the onshore alternating current grid through the offshore wind farm flexible direct current transmission system, the connection end of the offshore wind farm flexible direct current transmission system to the onshore alternating current grid through the modular multilevel converter is called the receiving end, and the corresponding converter is called the receiving end converter for short, the connection end of the offshore wind farm flexible direct current transmission system to the offshore wind farm through the modular multilevel converter is called the sending end, and the corresponding converter is called the sending end converter for short, characterized in that, The network construction control method comprises the following steps: S1, obtaining grid voltage and current of the receiving-end converter grid connection point, the receiving-end converter grid connection point being an access point of the receiving-end converter to the onshore AC grid, and performing dq decomposition on the grid voltage and current of the receiving-end converter grid connection point to obtain d-axis and q-axis components of the grid voltage and current of the receiving-end converter grid connection point in a dq rotating coordinate system, obtaining actual values of DC voltage output by the receiving-end converter, AC voltage and frequency of the receiving-end converter grid connection point, and obtaining reference values of DC voltage of the receiving-end converter, voltage amplitude and frequency of the receiving-end converter grid connection point; S2, calculating the phase reference value of the receiving end converter, wherein the phase reference value of the receiving end converter The calculation formula is as follows: Wherein s is the Laplace operator, is the reference value of the receiving end AC system frequency, k a is the adaptive coefficient of the synchronous control loop, And respectively, the reference value and the actual value of the DC voltage, U sq is the q-axis component of the receiving end converter grid point voltage, k pll is the proportional coefficient, k T is the DC voltage droop coefficient; S3, calculating a d-axis voltage reference value of the receiving-end converter grid connection point; S4, calculating d-axis and q-axis current reference values of the receiving-end converter grid connection point; S5, calculating d-axis and q-axis voltage reference values of the modulation voltage of the receiving-end converter; S6, calculating a-axis, b-axis and c-axis voltage reference values of the modulation voltage of the receiving-end converter in an abc stationary coordinate system; S7, generating corresponding control pulses to realize control of the receiving-end converter of the offshore wind power flexible DC power transmission system according to the reference values of the modulation voltage by using a pulse width modulation theory.

2. The offshore wind power flexible HVDC transmission system network construction control method according to claim 1, characterized in that, The d-axis voltage reference value of the grid-connected point of the receiving converter in the step S3 The calculation formula is as follows: Wherein, is the q-axis voltage reference value of the grid-connected point of the receiving converter, U sm is the reference value of the voltage amplitude of the grid-connected point of the wind turbine of the offshore wind farm, Q * and Q s are the active power reference value and the actual value of the wind turbine of the offshore wind farm respectively; k pq is a proportional parameter. 3.The offshore wind power flexible HVDC system network control method according to claim 1, characterized in that, The d-axis current reference value i of the receiving-end converter grid-connection point in the step S4 * vd and the q-axis current reference value i * vq The calculation formula is as follows: Wherein, u sd and u sq are the d-axis and q-axis voltages of 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 power grid frequency.

4. The offshore wind power flexible HVDC transmission system network construction control method according to claim 3, characterized in that, The d-axis voltage reference value u * vd and the q-axis voltage reference value u * vq The calculation formula is as follows: Wherein, i vd and i vq are the d-axis and q-axis components of the output current of the receiving converter; L is the connection reactance value of the receiving converter; k pi and k ii are the proportional parameter and integral parameter of the current inner loop proportional-integral controller, respectively.

5. The method of claim 1, wherein, In the step S6, the modulation voltage of the receiving converter in the a-axis voltage reference value, the b-axis voltage reference value and the c-axis voltage reference value in the abc stationary coordinate system are calculated according to the following formulae: ​​​ wherein, is the phase reference value of the receiving converter.

6. A device for offshore wind power flexible DC transmission system network construction control, used for executing the offshore wind power flexible DC transmission system network construction control method in any one of claims 1 to 5, characterized in that, The network construction control device comprises: a flexible DC power transmission system parameter acquisition module configured to obtain grid voltage and current of the receiving-end converter grid connection point, the receiving-end converter grid connection point being an access point of the receiving-end converter to the onshore AC grid, and perform dq decomposition on the grid voltage and current of the receiving-end converter grid connection point to obtain d-axis and q-axis components of the grid voltage and current of the receiving-end converter grid connection point in a dq rotating coordinate system, obtain actual values of DC voltage output by the receiving-end converter, AC voltage and frequency of the receiving-end converter grid connection point, and obtain reference values of DC voltage of the receiving-end converter, voltage amplitude and frequency of the receiving-end converter grid connection point; a first calculation module configured to calculate phase reference values of the receiving-end converter; a second calculation module configured to calculate a d-axis voltage reference value of the receiving-end converter grid connection point; a third calculation module configured to calculate d-axis and q-axis current reference values of the receiving-end converter grid connection point; a fourth calculation module configured to calculate d-axis and q-axis voltage reference values of the modulation voltage of the receiving-end converter; a fifth calculation module configured to calculate a-axis, b-axis and c-axis voltage reference values of the modulation voltage of the receiving-end converter in an abc stationary coordinate system; a control pulse generation module configured to generate corresponding control pulses to realize control of the receiving-end converter of the offshore wind power flexible DC power transmission system according to the reference values of the modulation voltage by using a pulse width modulation theory.

7. A computer device comprising a processor and a memory for storing a processor executable program, characterized in that, The processor executes a program stored in the memory to implement the offshore wind power flexible DC power transmission system network construction control method of any one of claims 1 to 5.

8. A storage medium storing a program, characterized by comprising: The program is executed by the processor to implement the offshore wind power flexible DC power transmission system network construction control method of any one of claims 1 to 5.

Images