Active support control method and system suitable for offshore wind power dc transmission system

Abstract

The application belongs to the technical field of power system DC transmission, and provides an active support control method and system suitable for offshore wind power DC transmission system, which overcomes the defects that the active power will be borne by the hybrid MMC when the traditional active support control strategy of the flexible DC system is transplanted to the DR-hybrid MMC topology, especially when the hybrid MMC operates at zero DC voltage, the hybrid MMC can avoid increasing the active power it transmits, reduce the rated capacity of the hybrid MMC, and improve the economic benefit of the system. The frequency and voltage support capability of the DR-hybrid MMC series topology DC transmission system to the receiving end power grid is effectively improved, which helps to enhance the stability of the power grid in the scene of high proportion of new energy access to the power grid.

Description

Technical Field

[0001] This invention belongs to the technical field of DC power transmission in power systems, and particularly relates to an active support control method and system applicable to offshore wind power DC transmission systems. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Offshore wind power, with its advantages of stable wind speed, high utilization hours, small footprint, and environmental friendliness, is gradually becoming a renewable energy source with broad development prospects. In offshore wind power transmission systems, high-voltage direct current (HVDC) transmission technology is commonly used. However, traditional HVDC technology requires the construction of expensive offshore converter platforms to boost the DC voltage, resulting in high costs and construction difficulties. In contrast, the DC transmission scheme based on the DR-hybrid MMC series topology uses converters with lower costs, smaller offshore converter platforms, easier construction, and significant economic benefits, demonstrating good application potential. Furthermore, the hybrid MMC has overmodulation capability, achieving constant zero DC voltage operation in steady state, meaning it does not handle active power but only provides reactive power compensation to the system, further reducing the rated capacity of the hybrid MMC and lowering costs.

[0004] In offshore wind power transmission systems via a DR-hybrid MMC series topology DC transmission system, the control system plays a crucial role. Because the receiving-end converter station uses an MMC, it has the ability to independently control active and reactive power. When the grid is disturbed, it can provide frequency and voltage support to the system through an effective active support control strategy. In the current grid environment where the penetration rate of new energy sources is constantly increasing, this control method is of great significance for enhancing grid stability. In traditional flexible DC transmission systems, the communication-free active support control strategy is achieved by the receiving-end converter station converting information about changes in the receiving-end grid frequency into changes in the system DC voltage and transmitting this information to the sending-end MMC. Therefore, in a DR-hybrid MMC series topology DC transmission system, it is also possible to not control the DC voltage at the hybrid MMC's ports to be constant, allowing the hybrid MMC to handle changes in the system DC voltage. In this case, most of the increased active power will be transmitted by the hybrid MMC. However, considering the relatively low capacity design of hybrid MMCs, especially when the hybrid MMC operates at zero DC voltage, it is necessary to avoid increasing the active power it transmits. Furthermore, due to the presence of the DR (Diverter), the change in the DC port voltage of the hybrid MMC is not entirely equivalent to the change in the system DC voltage; it is also related to the system DC current, meaning the transmitted receiving-end grid frequency information is inaccurate. In summary, the traditional approach of using hybrid MMCs to transmit receiving-end system frequency information based on DC voltage changes is not suitable for the DR-hybrid MMC series topology. Therefore, researching an active support control strategy suitable for offshore wind power DC transmission systems via the DR-hybrid MMC series topology has significant theoretical value and engineering application prospects.

[0005] Existing technologies have proposed a black-start and coordinated control strategy for a parallel topology of DR and MMC. This coordinated control strategy can control the power output of MMC under wind power variations, effectively avoiding the phenomenon of MMC active power backfeeding. However, it does not mention an active support control strategy. There is also a review of active support technologies for offshore wind power flexible DC transmission systems, summarizing currently proposed active support control strategies for flexible DC transmission systems and classifying them into two categories. One category is a grid-following active support control strategy, where the receiving-end converter station adopts grid-following control, detecting the receiving-end grid frequency information through a phase-locked loop and transmitting this information to the wind farm through DC voltage changes to achieve active support. The other category is a grid-based active support control strategy, where the receiving-end converter station adopts grid-based control. However, this scheme requires an additional DC voltage outer loop, making control complex and parameter tuning difficult. Neither of these strategies can be directly applied to the DR-hybrid MMC series topology.

[0006] In summary, current research on DR-MMC topologies primarily focuses on black-start and steady-state control strategies, while studies on active support control are relatively scarce. Research findings in this area are mainly found in traditional flexible DC transmission systems, constituting a current research gap. Therefore, to improve the applicability and reliability of this topology in practical engineering, it is urgent to design an active support control strategy suitable for DR-hybrid MMC series topology DC transmission systems. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, this invention provides an active support control method and system suitable for offshore wind power DC transmission systems, which effectively improves the frequency and voltage support capability of the DR-hybrid MMC series topology DC transmission system for the receiving-end grid, and helps to enhance the stability of the grid in scenarios where a high proportion of new energy sources are connected to the grid.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides an active support control method for offshore wind power DC transmission systems, applied to a DR-hybrid MMC series topology DC transmission system, the method comprising:

[0010] When the receiving-end power grid is subjected to frequency disturbance, the DC voltage change value is calculated based on the detected frequency deviation of the receiving-end MMC, and the receiving-end MMC dynamically adjusts the DC voltage of the DC transmission system based on the DC voltage change value.

[0011] The voltage amplitude control quantity is obtained by the sending end hybrid MMC controller, and the voltage amplitude control quantity is decoupled from the DC current to obtain the DC voltage of the DC transmission system. The frequency regulation quantity of the wind farm is determined based on the DC voltage of the DC transmission system.

[0012] The frequency change information of the receiving-end AC grid is reconstructed based on the frequency regulation of the wind farm, and the output active power of the wind turbine is adjusted according to the frequency change information of the receiving-end AC grid to achieve frequency support for the receiving-end AC grid.

[0013] Secondly, the present invention provides an active support control system suitable for offshore wind power DC transmission systems, applied to DR-hybrid MMC series topology DC transmission systems, including:

[0014] The receiving-end MMC response module is configured to: when the receiving-end power grid is subjected to frequency disturbance, calculate the DC voltage change value based on the detected frequency deviation of the receiving-end MMC, and dynamically adjust the DC voltage of the DC transmission system based on the DC voltage change value;

[0015] The sending-end MMC response module is configured to: obtain the voltage amplitude control quantity through the sending-end hybrid MMC controller, decouple the voltage amplitude control quantity from the DC current to obtain the DC voltage of the DC transmission system, and determine the wind farm frequency regulation quantity based on the DC voltage of the DC transmission system;

[0016] The wind turbine response module is configured to: reconstruct the frequency change information of the receiving-end AC grid based on the frequency adjustment of the wind farm, and adjust the output active power of the wind turbine according to the frequency change information of the receiving-end AC grid, so as to achieve frequency support for the receiving-end AC grid.

[0017] Thirdly, the present invention provides an electronic device including a memory and a processor, and computer instructions stored in the memory and running on the processor, wherein the computer instructions, when executed by the processor, perform the method described in the first aspect.

[0018] Fourthly, the present invention provides a computer-readable storage medium for storing computer instructions, which, when executed by a processor, perform the method described in the first aspect.

[0019] The above one or more technical solutions have the following beneficial effects:

[0020] The active support control method proposed in this invention, applicable to offshore wind power DC transmission systems, overcomes the defect that the active power is borne by the hybrid MMC when the active support control strategy of the traditional flexible DC system is transplanted to the DR-hybrid MMC topology through three stages: receiving-end MMC response, sending-end MMC response, and wind turbine response. In particular, when the hybrid MMC is operating at zero DC voltage, it can avoid the hybrid MMC from increasing its transmitted active power, reducing the rated capacity of the hybrid MMC, and improving the economic efficiency of the system.

[0021] The active support control method proposed in this invention, applicable to offshore wind power DC transmission systems, fills the gap in the current research on active support control strategies for DR-hybrid MMC series topologies. It effectively improves the frequency and voltage support capability of the system for the receiving-end grid, and helps to enhance grid stability in scenarios where a high proportion of new energy sources are connected to the grid.

[0022] The active support control method proposed in this invention, applicable to offshore wind power DC transmission systems, requires only the active support controller to collect the voltage amplitude control quantity of the wind farm AC system output by the sending-end MMC controller and the DC current flowing through the sending-end MMC to calculate the system DC voltage. No additional measuring device is required, resulting in low cost.

[0023] The active support control method proposed in this invention, applicable to offshore wind power DC transmission systems, transmits frequency change information of the receiving-end grid through the system's DC voltage. The active support controller installed on the sending-end MMC can calculate the system's DC voltage locally, without needing to measure the relevant operating parameters of the diode converter. After the sending-end MMC calculates the system's DC voltage, it converts the extracted receiving-end grid frequency change information into a change in the frequency of the wind farm's AC system. The wind turbine can respond after detecting this change. The entire process requires no communication and does not rely on additional communication devices, resulting in high control reliability.

[0024] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0025] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0026] Figure 1 This is a topology diagram of an offshore wind power transmission system via DR-hybrid MMC DC transmission.

[0027] Figure 2 Equivalent circuit diagram of the DC side of the DR-hybrid MMC converter station at the sending end;

[0028] Figure 3 This is a diagram of the active support control structure of the receiving-end hybrid MMC in Embodiment 1 of the present invention;

[0029] Figure 4 This is a diagram of the active support control structure for the feed-end hybrid MMC in Embodiment 1 of the present invention;

[0030] Figure 5 This is a diagram of the active support and collaborative control structure in Embodiment 1 of the present invention. Detailed Implementation

[0031] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0032] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations of the present invention.

[0033] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0034] Example 1

[0035] The topology of offshore wind power transmitted via a DR-hybrid MMC series DC transmission system is as follows: Figure 1 As shown in the diagram, the sending-end converter station in this topology uses a diode rectifier connected in series with a hybrid MMC (Multi-Module Connector) of full-bridge and half-bridge submodules on the DC side and in parallel on the AC side. The receiving-end converter station also uses a hybrid MMC of full-bridge and half-bridge submodules. During steady-state operation, the receiving-end converter station uses constant Udc and Q control, while the sending-end hybrid MMC uses constant Vf control to provide a voltage reference for the wind farm's AC system. Simultaneously, a constant DC voltage control is added. By adjusting the voltage amplitude of the wind farm's AC system, the DC voltage at the DR port is adjusted to maintain a constant DC voltage in the sending-end hybrid MMC. Therefore, when the hybrid MMC is subjected to the aforementioned constant DC voltage control, the changes in the system's DC voltage will be borne by the DR.

[0036] A diode rectifier on the DC side can be equivalently represented by a controlled voltage source connected in series with a virtual internal resistance. The output voltage of the controlled voltage source is affected by the AC voltage at the AC side port. The magnitude of the virtual internal resistance is related to the leakage inductance of the transformer connected to the diode converter station, and the corresponding mathematical expression is:

[0037] (1)

[0038] In the formula, V dcDR This is the equivalent controlled voltage source voltage on the DC side of the DR. k T For the DR transformer turns ratio, U l This refers to the line voltage amplitude of the AC system in the wind farm. R The virtual internal resistance of the DR on the DC side. ω s For the electric angular velocity of the AC system, L T This refers to the leakage inductance of the DR transformer.

[0039] The equivalent circuit of the DC side of the offshore wind power transmission system via DR-hybrid MMC is as follows: Figure 2 As shown.

[0040] Based on the topology, steady-state control strategy, and DC-side equivalent circuit diagram of the offshore wind power transmission system via DR-hybrid MMC, the active support control strategy of the system is explained. The active support control strategy of the system mainly includes three stages: receiving-end MMC response, sending-end MMC response, and wind turbine response.

[0041] The first stage is the receiving-end MMC response. When the receiving-end power grid is subjected to a frequency disturbance, the receiving-end MMC's phase-locked loop detects the frequency deviation Δ. f grid This generates a DC voltage change value Δ. Udc This transmits the information about frequency changes to the system's DC voltage, Δ f grid With Δ U dc The relationship is:

[0042] (2)

[0043] In the formula, k This is the proportionality coefficient.

[0044] Figure 3 This is a diagram of the active support control structure of the receiving-end hybrid MMC. u sm * and u sm These are the rated and actual values ​​of the average capacitor voltage of the receiving-end hybrid MMC submodule, respectively. Q ref and Q These are the commanded and actual reactive power values, respectively. i vd * and i vq * These are the d-axis current reference values ​​and q-axis current reference values ​​output by the outer loop controller, respectively. i vd and i vq These are the actual values ​​of the d-axis current and the q-axis current, respectively. i cird and i cirq These are the actual values ​​of the d-axis circulation and the q-axis circulation, respectively. u sd and u sq These are the actual values ​​of the d-axis voltage and the q-axis voltage, respectively. u diffd * and u diffq * These represent the d-axis and q-axis command values ​​of the differential mode voltage of the upper and lower bridge arms of the MMC output from the inner current loop, respectively. u comd * and u comq * These are the d-axis and q-axis command values ​​of the common-mode voltage of the upper and lower bridge arms of the MMC output by the circulating current suppression controller, respectively. u diffj and ucomj (j=a,b,c) represent the differential-mode fundamental frequency component command value and the common-mode second harmonic frequency component command value of phases A, B, and C in the abc coordinate system, respectively. U s The three-phase AC voltage of the receiving-end AC system. θ The electrical angle of the receiving-end AC system is obtained from the receiving-end MMC phase-locked loop. U * dc and U dc These are the rated and actual DC voltage values ​​for the DR-hybrid MMC DC transmission system, respectively. I * dc and I dc These represent the DC current command value and the actual DC current value of the DR-hybrid MMC DC transmission system output from the DC outer loop controller, respectively. u comj2 (j=a,b,c) represents the DC component command values ​​of the upper and lower bridge arm voltages output by the DC inner loop controller.

[0045] like Figure 3 As shown, the receiver-side hybrid MMC adopts a traditional fixed-position method. U dc Q control employs classic dual-closed-loop control, with the average capacitor voltage of the active outer loop control submodule being [value missing]. u sm Based on the rated value of the average capacitor voltage of the receiving end hybrid MMC submodule u sm * Compared with actual value u sm The deviation generates the d-axis current reference value. i vd * The reactive power outer loop control circuit adopts constant reactive power control to control the reactive power generated by the receiving end hybrid MMC. Q Based on the reactive power command value Q ref Compared with actual value Q The deviation generates a q-axis current reference value. i vq * The inner current loop controls the d-axis current. i vd With q-axis current i vq Tracking d-axis current reference value i vd * q-axis current reference value ivq * It outputs the differential-mode fundamental frequency voltage command value. u diffj (j=a,b,c). The circulating current suppressor uses a classic control structure to suppress the internal circulating current of the receiving-end mixed MMC. i cird and i cirq Suppression is set to zero, and the common-mode second harmonic component command value is output. u comj (j=a,b,c). The DC control loop also adopts the classic dual closed-loop control, with the outer DC loop controlling the DC voltage of the DR-hybrid MMC DC output system. U dc It also outputs the DC current command value of the DR-hybrid MMC DC output system. I * dc The DC outer loop will control the system's DC voltage. U dc Controlled to rated value U * dc And superimposed the above DC voltage change value Δ U dc The DC voltage of the system U dc Control as U * dc +Δ U dc This transmits the frequency change information to the DC voltage of the DR-hybrid MMC DC output system; the DC inner loop controls the DC current of the system. I dc Tracking reference values I * dc It also outputs the DC component command values ​​of the upper and lower bridge arm voltages. u comj2 (j=a,b,c). The differential-mode fundamental frequency voltage command value... u diffj (j=a,b,c), Common-mode second harmonic component command value u comj (j=a,b,c) and command values ​​of DC components of upper and lower bridge arm voltages u comj2 The input of (j=a,b,c) superimposed values ​​is approximated by the nearest level modulator to achieve control of the receiving end hybrid MMC.

[0046] The second stage is the sending-end MMC response. When the receiving-end grid is disturbed, the receiving-end MMC will dynamically adjust the DC voltage of the system within a small range. The change in the DC voltage of this system will be borne by the sending-end DR, and the magnitude of the DC voltage at the DR port is related to the voltage amplitude of the wind farm's AC system. U l Related. Therefore, the target value of the line voltage amplitude of the wind farm AC system output by the sending-end hybrid MMC supplemented constant DC voltage controller. U * l With the system's DC voltage U dc The relevant, specific relationship is as follows:

[0047] (3)

[0048] In the formula, U * l The target value of the line voltage amplitude of the wind farm AC system is obtained by adding a constant DC voltage controller to the hybrid MMC at the sending end. U dc The DC voltage of the DC system. ω s For the electric angular velocity of the AC system, L T For DR transformer leakage inductance, I dc The system's DC current, U dcMMCN The rated DC voltage of the MMC at the sending end. k T This refers to the turns ratio of the DR transformer. In the first stage, the receiving-end hybrid MMC transmits the DC voltage from the DR-hybrid MMC to the system. U dc Control as U * dc +Δ U dc ,in U * dc For the rated value, Δ U dc This is the DC voltage change value generated based on the frequency deviation of the receiving-end power grid.

[0049] Given the system parameters, the controller calculates and adjusts the voltage amplitude control quantity. U * l Decoupling from the DC current, the DC voltage of the system is obtained as follows:

[0050] (4)

[0051] In the formula, U dcCAL This is the calculated value of the system's DC voltage.

[0052] The sending-end hybrid MMC calculates the real-time system DC voltage by measuring the system's DC current. The difference between this calculated DC voltage and the system's rated DC voltage is then passed through a proportional circuit and output as the wind farm frequency regulation variable Δ. f wind The input is then fed into the MMC constant Vf controller at the sending end to dynamically adjust the frequency of the wind farm's AC system. f wind The frequency change information of the receiving-end power grid is transmitted to the AC system of the wind farm. The wind farm frequency regulation amount Δ f wind The calculated DC voltage of the system satisfies the following formula:

[0053] (5)

[0054] In the formula, k ’ This is the proportionality coefficient. U dcN This is the rated DC voltage of the system.

[0055] Figure 4 This is a diagram of the active support control structure for the hybrid MMC at the sending end. U dcMMCN This is the reference value for the DC voltage of the MMC at the sending end. U dcMMC This represents the actual value of the mixed MMC DC voltage at the sending end. u * sd To provide a reference value for the d-axis voltage output from the additional DC voltage controller. u * sq This is the reference value for the q-axis voltage. u sd and u sq These are the actual values ​​of the d-axis voltage and the q-axis voltage, respectively. i vd * and i vq * These are the d-axis current reference values ​​and q-axis current reference values ​​output by the outer loop controller, respectively. i vd and i vq These are the actual values ​​of the d-axis current and the q-axis current, respectively. i cird and icirq These are the actual values ​​of the d-axis circulation and the q-axis circulation, respectively. u diffd * and u diffq * These represent the d-axis and q-axis command values ​​of the differential mode voltage of the upper and lower bridge arms of the MMC output from the inner current loop, respectively. u comd * and u comq * These are the d-axis and q-axis command values ​​of the common-mode voltage of the upper and lower bridge arms of the MMC output by the circulating current suppression controller, respectively. u diffj and u comj (j=a,b,c) represent the differential-mode fundamental frequency component command value and the common-mode second harmonic frequency component command value of phases A, B, and C in the abc coordinate system, respectively. ω The electric angular velocity of the AC system of the sending-end wind farm. θ For the electrical angle of the AC system of the sending-end wind farm, u sm * and u sm These are the rated and actual values ​​of the average capacitor voltage of the hybrid MMC submodule at the sending end, respectively. I * dc and I dc These are the command value and the actual value of the mixed MMC DC current output from the DC outer loop controller. u comj2 (j=a,b,c) represents the DC component command values ​​of the upper and lower bridge arm voltages output by the DC inner loop controller.

[0056] like Figure 4 As shown, the sending end hybrid MMC adopts a constant V / f The control employs a classic dual-closed-loop control system. The outer loop controls the AC voltage of the wind farm's AC system, maintaining the line voltage amplitude at a specific value. U * l The outer loop controller is based on the d-axis voltage reference value. u * sd Compared with actual value u sd The deviation generates the d-axis current reference value. i vd * Based on the q-axis current reference valueu * sq Compared with actual value u sq The deviation generates the q-axis current reference value. i vq * d-axis voltage reference value u * sd The additional DC voltage controller is based on the DC voltage reference value of the MMC at the sending end. U dcMMCN Compared with actual value U dcMMC The deviation is generated by the PI controller; the frequency controller sets the frequency of the wind farm's AC system. f wind The frequency is controlled at the rated value of 50Hz, plus the aforementioned wind farm frequency regulation amount Δ. f wind This transmits frequency variation information from the receiving-end power grid to the wind farm's AC system; the inner current loop then controls the d-axis current. i vd With q-axis current i vq Tracking d-axis current reference value i vd * q-axis current reference value i vq * It outputs the differential-mode fundamental frequency voltage command value. u diffj (j=a,b,c). The circulating current suppressor uses a classic control structure to suppress the internal circulating current of the MMC at the sending end. i cird and i cirq Suppression is set to zero, and the common-mode second harmonic component command value is output. u comj (j=a,b,c). The DC control loop also adopts the classic dual closed-loop control, with the average capacitor voltage of the DC outer loop control submodule being... u sm Rated value u sm * It also outputs the DC current command value of the DR-hybrid MMC DC output system. I * dc The DC inner loop controls the DC current of the system. I dc Tracking reference values I * dc It also outputs the DC component command values ​​of the upper and lower bridge arm voltages.u comj2 (j=a,b,c). The differential-mode fundamental frequency voltage command value... u diffj (j=a,b,c), Common-mode second harmonic component command value u comj (j=a,b,c) and command values ​​of DC components of upper and lower bridge arm voltages u comj2 (j=a,b,c) are superimposed and input to the nearest level approximation modulator to realize the control of the sending end mixed MMC.

[0057] The third stage is the wind turbine response, where the phase-locked loop of the wind turbine's generator-side converter detects the frequency of the wind farm's AC system. f’ wind With frequency rating f * The frequency deviation is obtained by subtraction, and then the active power command value adjustment Δ of the wind turbine is generated through a proportional circuit. P Adjusting the active power generated by the wind turbine to achieve frequency support for the receiving-end AC power grid, Δ P and f’ wind Satisfy the following formula:

[0058] (6)

[0059] In the formula, k p This is the proportionality coefficient.

[0060] The coordinated control structure of the entire process is as follows: Figure 5 As shown.

[0061] The active support control method proposed in this embodiment, applicable to offshore wind power DC transmission systems, overcomes the defect that when the active support control strategy of traditional flexible DC systems is transplanted to the DR-hybrid MMC topology, the active power will be borne by the hybrid MMC. In particular, when the hybrid MMC is operating at zero DC voltage, it can avoid the hybrid MMC increasing its transmitted active power, reducing the rated capacity of the hybrid MMC, and improving the economic efficiency of the system.

[0062] The active support control method for offshore wind power DC transmission systems proposed in this embodiment fills the gap in the current research on active support control strategies for DR-hybrid MMC series topologies. It effectively improves the frequency and voltage support capability of the system for the receiving-end grid and helps to enhance grid stability in scenarios where a high proportion of new energy sources are connected to the grid.

[0063] The active support control method for offshore wind power DC transmission systems proposed in this embodiment only requires the active support controller to collect the voltage amplitude control quantity of the wind farm AC system output by the sending-end MMC controller and the DC current flowing through the sending-end MMC to calculate the DC voltage of the system. No additional measuring device is required, resulting in low cost. Furthermore, the entire control process does not require additional communication devices, making it low-cost and highly reliable. It can effectively improve the frequency support capability of the system for the receiving-end grid and help enhance the stability of the grid in scenarios where a high proportion of new energy is connected to the grid.

[0064] The active support control method proposed in this embodiment, applicable to offshore wind power DC transmission systems, transmits frequency change information of the receiving-end grid through the system's DC voltage. The active support controller installed on the sending-end MMC can calculate the system's DC voltage locally without needing to measure the relevant operating parameters of the diode converter. After the sending-end MMC calculates the system's DC voltage, it converts the extracted receiving-end grid frequency change information into a change in the frequency of the wind farm's AC system. The wind turbine can respond after detecting this change. The entire process requires no communication and does not rely on additional communication devices, resulting in high control reliability.

[0065] Example 2

[0066] The purpose of this embodiment is to provide an active support control system suitable for offshore wind power DC transmission systems, applied to DR-hybrid MMC series topology DC transmission systems, including:

[0067] The receiving-end MMC response module is configured to calculate the DC voltage change value based on the detected frequency deviation of the receiving-end MMC when the receiving-end power grid is subjected to frequency disturbance.

[0068] The sending-end MMC response module is configured to: dynamically adjust the DC voltage of the DC transmission system based on the DC voltage change value, obtain the voltage amplitude control quantity through the sending-end hybrid MMC controller, decouple the voltage amplitude control quantity from the DC current to obtain the DC voltage of the DC transmission system, and determine the wind farm frequency adjustment quantity based on the DC voltage of the DC transmission system.

[0069] The wind turbine response module is configured to: reconstruct the frequency change information of the receiving-end AC grid based on the frequency adjustment of the wind farm, and adjust the output active power of the wind turbine according to the frequency change information of the receiving-end AC grid, so as to achieve frequency support for the receiving-end AC grid.

[0070] In further embodiments, the following is also provided:

[0071] An electronic device includes a memory and a processor, as well as computer instructions stored in the memory and running on the processor. When executed by the processor, the computer instructions perform the method described in Embodiment 1. For brevity, further details are omitted here.

[0072] It should be understood that in this embodiment, the processor can be a central processing unit (CPU), or it can be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor, etc.

[0073] Memory may include read-only memory and random access memory, and provides instructions and data to the processor. A portion of memory may also include non-volatile random access memory. For example, memory may also store information about the device type.

[0074] A computer-readable storage medium for storing computer instructions, which, when executed by a processor, perform the method described in Embodiment 1.

[0075] The method in Embodiment 1 can be directly implemented by a hardware processor, or implemented by a combination of hardware and software modules within the processor. The software modules can reside in readily available storage media in the art, such as random access memory, flash memory, read-only memory, programmable read-only memory, electrically erasable programmable memory, or registers. This storage medium is located in memory; the processor reads information from the memory and, in conjunction with its hardware, completes the steps of the above method. To avoid repetition, a detailed description is not provided here.

[0076] A computer program product includes a computer program that, when executed by a processor, implements the method described in Embodiment 1.

[0077] The present invention also provides at least one computer program product tangibly stored on a non-transitory computer-readable storage medium. The computer program product includes computer-executable instructions, such as instructions included in program modules, which execute in a device on a target real or virtual processor to perform the processes / methods described above. Typically, program modules include routines, programs, libraries, objects, classes, components, data structures, etc., that perform specific tasks or implement specific abstract data types. In various embodiments, the functionality of program modules can be combined or divided among program modules as needed. The machine-executable instructions for the program modules can execute within a local or distributed device. In a distributed device, the program modules can reside in both local and remote storage media.

[0078] The computer program code used to implement the methods of the present invention may be written in one or more programming languages. This computer program code may be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing device, such that when executed by the computer or other programmable data processing device, the program code causes the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code may be executed entirely on a computer, partially on a computer, as a stand-alone software package, partially on a computer and partially on a remote computer, or entirely on a remote computer or server.

[0079] In the context of this invention, computer program code or related data may be carried by any suitable carrier to enable a device, apparatus, or processor to perform the various processes and operations described above. Examples of carriers include signals, computer-readable media, and the like. Examples of signals may include electrical, optical, radio, sound, or other forms of propagation signals, such as carrier waves, infrared signals, etc.

[0080] Those skilled in the art will recognize that the units and algorithm steps described in conjunction with the embodiments herein can be implemented in electronic hardware or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0081] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. An active support control method applicable to offshore wind power DC transmission systems, specifically applied to DR-hybrid MMC series topology DC transmission systems, characterized in that... The method includes: When the receiving-end power grid is subjected to frequency disturbance, the DC voltage change value is calculated based on the detected frequency deviation of the receiving-end MMC, and the receiving-end MMC dynamically adjusts the DC voltage of the DC transmission system based on the DC voltage change value. The voltage amplitude control value is obtained through the sending-end hybrid MMC controller, specifically: in, U * l This represents the target value for the line voltage amplitude of the AC system in the wind farm. U dc The DC voltage of the DC system. ω s For the electric angular velocity of the AC system, L T For DR transformer leakage inductance, I dc The system's DC current, U dcMMCN The rated DC voltage of the MMC at the sending end. k T The turns ratio of the DR transformer; The voltage amplitude control quantity is decoupled from the DC current to obtain the DC voltage of the DC transmission system, and the frequency regulation quantity of the wind farm is determined based on the DC voltage of the DC transmission system. The frequency change information of the receiving-end AC grid is reconstructed based on the frequency regulation of the wind farm, and the output active power of the wind turbine is adjusted according to the frequency change information of the receiving-end AC grid to achieve frequency support for the receiving-end AC grid.

2. The active support control method for offshore wind power DC transmission systems as described in claim 1, characterized in that, The DC voltage of the DC transmission system is obtained by decoupling the voltage amplitude control quantity from the DC current. Specifically: in, k T For the DR transformer turns ratio, ω s For the electric angular velocity of the AC system, L T For DR transformer leakage inductance, I dc The system's DC current; U dcCAL This is the calculated value of the system's DC voltage.

3. The active support control method for offshore wind power DC transmission systems as described in claim 1, characterized in that, The difference between the DC voltage of the DC transmission system and the real-time DC voltage of the DC transmission system is used to obtain the frequency regulation of the wind farm through a proportional circuit.

4. The active support control method for offshore wind power DC transmission systems as described in claim 1, characterized in that, Also includes: The specific control of the receiving-end hybrid MMC is as follows: The inner current loop controls the d-axis current and q-axis current to track the d-axis current reference value and q-axis current reference value, and outputs the differential mode fundamental frequency voltage command value; The internal circulating current and suppression of the receiving-end hybrid MMC are zero, and the common-mode second harmonic component command value is output. The DC inner loop controls the DC current of the system to track the DC current command value and outputs the DC component command values ​​of the upper and lower bridge arm voltages. The differential-mode fundamental frequency voltage command value, the common-mode second harmonic component command value, and the DC component command values ​​of the upper and lower bridge arm voltages are superimposed and input to the nearest level approximation modulator to realize the control of the receiving end hybrid MMC.

5. The active support control method for offshore wind power DC transmission systems as described in claim 1, characterized in that, This also includes: The control of the feed-end hybrid MMC specifically includes: The inner current loop controls the d-axis current and q-axis current to track the d-axis current reference value and the q-axis current reference value, and outputs the differential mode fundamental frequency voltage command value; The internal circulating current of the sending-end hybrid MMC is suppressed to zero, and the common-mode second harmonic component command value is output. The DC inner loop controls the DC current of the system to track the reference value and outputs the DC component command values ​​of the upper and lower bridge arm voltages. The differential-mode fundamental frequency voltage command value, the common-mode second harmonic component command value, and the DC component command of the upper and lower bridge arm voltages are superimposed and input to the nearest level approximation modulator to realize the control of the hybrid MMC at the sending end.

6. The active support control method for offshore wind power DC transmission systems as described in claim 1, characterized in that, The phase-locked loop of the wind turbine's converter detects the frequency of the wind farm's AC system, calculates the difference between the frequency and the rated frequency, and then generates the active power command value adjustment amount of the wind turbine through a proportional circuit. This adjusts the active power generated by the wind turbine to achieve frequency support for the receiving-end AC grid.

7. An active support control system suitable for offshore wind power DC transmission systems, applied to DR-hybrid MMC series topology DC transmission systems, characterized in that... include: The receiving-end MMC response module is configured to: when the receiving-end power grid is subjected to frequency disturbance, calculate the DC voltage change value based on the detected frequency deviation of the receiving-end MMC, and dynamically adjust the DC voltage of the DC transmission system based on the DC voltage change value; The sending-end MMC response module is configured to obtain the voltage amplitude control value through the sending-end hybrid MMC controller, specifically: in, U * l This represents the target value for the line voltage amplitude of the AC system in the wind farm. U dc The DC voltage of the DC system. ω s For the electric angular velocity of the AC system, L T For DR transformer leakage inductance, I dc The system's DC current, U dcMMCN The rated DC voltage of the MMC at the sending end. k T The turns ratio of the DR transformer; The voltage amplitude control quantity is decoupled from the DC current to obtain the DC voltage of the DC transmission system, and the frequency regulation quantity of the wind farm is determined based on the DC voltage of the DC transmission system. The wind turbine response module is configured to: reconstruct the frequency change information of the receiving-end AC grid based on the frequency adjustment of the wind farm, and adjust the output active power of the wind turbine according to the frequency change information of the receiving-end AC grid, so as to achieve frequency support for the receiving-end AC grid.

8. An electronic device, characterized in that, It includes a memory and a processor, as well as computer instructions stored in the memory and running on the processor, which, when executed by the processor, perform the method according to any one of claims 1-6.

9. A computer-readable storage medium, characterized in that, Used to store computer instructions, which, when executed by a processor, perform the method described in any one of claims 1-6.

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