Self-adaptive virtual inertia control method for doubly-fed fan based on superconducting magnetic energy storage system

Abstract

The invention discloses a double-fed fan adaptive virtual inertia control method based on a superconducting magnetic energy storage system, and belongs to the technical field of power generation, power transformation or power distribution. The method comprises the following steps: constructing a superconducting magnetic energy storage-doubly-fed fan hybrid system; adaptively adjusting an inertia support coefficient according to the running state of the superconducting magnetic energy storage system, generating a virtual synchronous adaptive inertia response instruction of the superconducting magnetic energy storage system, and performing direct current virtual synchronous control on the superconducting magnetic energy storage system; and obtaining operation data of the superconducting magnetic energy storage-doubly-fed fan hybrid system, adjusting the virtual rotational inertia coefficient in real time according to the adaptively adjusted inertia support coefficient to perform virtual synchronous inertia control on the doubly-fed fan, and generating a doubly-fed fan virtual inertia control instruction and a doubly-fed fan network side virtual synchronous control instruction. According to the method, the energy of the superconducting magnetic energy storage system is reasonably distributed in the disturbance process, the response speed of the doubly-fed wind turbine to wind speed and power demand changes is increased, and then the stability of the doubly-fed wind power generation system is effectively improved.

Description

Technical Field

[0001] The present invention relates to superconducting magnetic energy storage technology and wind power generation technology, and specifically discloses an adaptive virtual inertia control method for a doubly-fed wind turbine based on a superconducting magnetic energy storage system, belonging to the technical field of power generation, transformation or distribution. Background Art

[0002] Doubly-fed wind power generation, as an important part of wind power generation technology, has the advantages of high efficiency and high reliability, but its control strategy is relatively complex. Under sudden fluctuations in grid frequency such as power outages and load mutations, the traditional control strategy of doubly-fed wind turbines is faced with the risk of partial wind power disconnection because the wind turbine units controlled by power electronic devices cannot support the change of grid frequency itself. Under the traditional control strategy, the doubly-fed wind turbine lacks inertia and is very sensitive to external disturbances, and is prone to system oscillation and instability under large external disturbances. Therefore, it is very important to study a new control strategy to improve the anti-interference ability and stability of doubly-fed wind turbines.

[0003] In order to effectively cope with grid frequency fluctuations and improve the stability of wind power grid connection, a variety of frequency modulation control strategies including virtual inertia control, load shedding control, droop control, virtual synchronous generator (VSG) technology and energy storage control have been widely applied.

[0004] Virtual inertia control, as a new inertia control method based on control theory, quickly adjusts the frequency based on the rotor kinetic energy of the doubly-fed wind turbine. Without adding physical devices, it is realized through software control algorithms, which can effectively improve the response speed and stability of the doubly-fed wind turbine, especially providing inertial support for the power grid under disturbance conditions. When the grid frequency fluctuates, the active power output is changed by adjusting the rotor speed of the doubly-fed wind turbine, that is: when the grid frequency drops, the rotor speed of the doubly-fed wind turbine is reduced to release the rotor kinetic energy, thereby increasing the active power output; conversely, when the grid frequency rises, the rotor speed of the doubly-fed wind turbine is increased to absorb the excess energy and reduce the active power output. This process is called inertial response, which belongs to an energy transient regulation process and can quickly respond to the change of grid frequency in a short time. However, the implementation of virtual inertia control needs to solve key problems such as how to control the installation angle of the doubly-fed wind turbine blades according to wind speed and power demand, and how to achieve the virtual inertia control effect. If the rotor speed adjustment amplitude is too large, the grid frequency may have a secondary fluctuation when the rotor speed returns to the initial speed; at the same time, when the unit releases the reserved active power, its output torque also changes accordingly, and this process will cause obvious fatigue of the transmission system. And because of the need to reserve active capacity, the fan needs to overspeed and unload, and cannot operate on the MPPT curve, which affects its power generation efficiency and reduces the wind energy utilization rate.

[0005] Energy storage control is a frequency modulation method that has gradually emerged in recent years with the development of energy storage technology. By configuring an energy storage system in a wind farm, the insufficient inertia of wind turbines can be effectively compensated. The energy storage system can quickly respond when the power grid frequency changes and participate in primary frequency modulation by increasing or absorbing power through charge and discharge operations.

[0006] As a new energy storage technology, the superconducting magnetic energy storage system has advantages such as millisecond-level response speed, long service life, low energy loss, and high power density. Compared with conventional copper conductors, superconductors have advantages such as nearly zero loss and high current density, and have been applied to new energy power systems in recent years. Compared with the current conventional battery energy storage method, the superconducting magnetic energy storage (Superconducting Magnetic Energy Storage, SMES) has a faster dynamic response speed and can be used to solve millisecond-level power problems, providing a new solution idea for the virtual inertia control strategy of doubly-fed wind turbines.

[0007] Therefore, the present invention aims to propose an adaptive virtual inertia control method for doubly-fed wind turbines based on a superconducting magnetic energy storage system, combining the superconducting magnetic energy storage system with the doubly-fed wind turbine, and reasonably utilizing the energy stored in the superconducting magnetic energy storage device to overcome the defects of the existing virtual inertia control of doubly-fed wind turbines. Summary of the Invention

[0008] The object of the present invention is to address the deficiencies of the above background technology and provide an adaptive virtual inertia control method for doubly-fed wind turbines based on a superconducting magnetic energy storage system. By reasonably distributing the energy of the superconducting magnetic energy storage system during the disturbance process, the object of the invention is achieved, which is to improve the response speed of the doubly-fed wind turbine to changes in wind speed and power demand, and thus effectively improve the stability of the doubly-fed wind power generation system, and solve the technical problem that the existing virtual inertia control of doubly-fed wind turbines cannot provide effective inertia support under the conditions of rapid fluctuations in grid load, large fluctuations in new energy output, or changes in the grid topology structure.

[0009] The present invention adopts the following technical solutions to achieve the above object:

[0010] An adaptive virtual inertia control method for doubly-fed wind turbines based on a superconducting magnetic energy storage system, comprising:

[0011] Step 1: Connect the superconducting magnetic energy storage system to the DC bus on the machine side of the doubly-fed wind turbine to construct a superconducting magnetic energy storage-doubly-fed wind turbine hybrid system;

[0012] Step 2: Adaptively adjust the inertia support coefficient according to the operating state of the superconducting magnetic energy storage system, generate a virtual synchronous adaptive inertia response command for the superconducting magnetic energy storage system, and perform DC virtual synchronous control on the superconducting magnetic energy storage system;

[0013] Step 3: Obtain the operation data of the superconducting magnetic energy storage - doubly fed induction generator (DFIG) hybrid system, and adjust the virtual inertia coefficient in real time according to the inertia support coefficient adaptively adjusted in Step 2, perform virtual synchronous inertia control on the DFIG, and generate the virtual inertia control instruction of the DFIG and the virtual synchronous control instruction on the grid side of the DFIG.

[0014] As a further optimization scheme of the adaptive virtual inertia control method for DFIG based on the superconducting magnetic energy storage system, in Step 1, the superconducting magnetic energy storage system includes: a power conditioning system, a boost DC / DC converter, a superconducting magnetic energy storage coil, a refrigeration system, and a control system; the power conditioning system is used to achieve bidirectional exchange of active power and reactive power between the superconducting magnetic energy storage coil and the power grid; the boost DC / DC converter has its high-voltage DC port side connected to the DC bus of the unit; the superconducting magnetic energy storage coil is connected in parallel on the low-voltage DC port side of the boost DC / DC converter, used to store electromagnetic energy, and adjust the active power output in response to the virtual synchronous adaptive inertia response instruction of the superconducting magnetic energy storage system; the refrigeration system is used to provide and maintain a low-temperature environment for the superconducting magnetic energy storage coil; the control system is used to monitor and control the operation state of the superconducting magnetic energy storage system, and issue instructions to the power conditioning system according to the preset control strategy, and issue instructions to the refrigeration system when the current, magnetic field strength or temperature of the superconducting magnetic energy storage coil exceeds the safety threshold.

[0015] As a further optimization scheme of the adaptive virtual inertia control method for DFIG based on the superconducting magnetic energy storage system, in Step 2, the inertia support coefficient is adaptively adjusted according to the operation state of the superconducting magnetic energy storage system, specifically: , where is the virtual inertia coefficient of the i-th superconducting magnetic energy storage system after adaptive adjustment, is the virtual inertia coefficient of the i-th superconducting magnetic energy storage system, is the actual value of the DC bus voltage on the machine side of the DFIG, is the reference value of the DC bus voltage on the machine side of the DFIG, is the deviation threshold of the DC bus voltage on the machine side of the DFIG, is the dynamic evaluation coefficient of the i-th superconducting magnetic energy storage system, , is the maximum active power of the superconducting magnetic energy storage system, is the current active power of the i-th superconducting magnetic energy storage system, is the reference value of the active power of the i-th superconducting magnetic energy storage system, and a is a fixed value related to the capacity of the DFIG unit, the scale of the superconducting magnetic energy storage, and the operation state of the hybrid system.

[0016] As a further optimization scheme of the adaptive virtual inertia control method for DFIG based on the superconducting magnetic energy storage system, in Step 2, generate the virtual synchronous adaptive inertia response instruction of the superconducting magnetic energy storage system, specifically:

[0017] When the DC bus voltage drop of the doubly-fed wind turbine unit is greater than , the i-th superconducting magnetic energy storage system increases the active power output with as the maximum power margin to adjust the inertia support coefficient.

[0018] When the DC bus voltage rise of the doubly-fed wind turbine unit is greater than , the i-th superconducting magnetic energy storage system reduces the active power output with as the maximum power margin to adjust the inertia support coefficient.

[0019] When the DC bus voltage of the doubly-fed wind turbine unit is equal to the reference value, the i-th superconducting magnetic energy storage system maintains the virtual inertia coefficient and keeps the active power output unchanged.

[0020] As a further optimization scheme of the adaptive virtual inertia control method for the doubly-fed wind turbine based on the superconducting magnetic energy storage system, in step 2, DC virtual synchronous control is performed on the superconducting magnetic energy storage system, specifically: , where and are constants related to the droop coefficient and the damping coefficient, is the rated voltage, is the DC bus current on the machine side of the doubly-fed wind turbine.

[0021] As a further optimization scheme of the adaptive virtual inertia control method for the doubly-fed wind turbine based on the superconducting magnetic energy storage system, in step 3, the operation data of the superconducting magnetic energy storage-doubly-fed wind turbine hybrid system is obtained, including but not limited to: the operating frequency of the public power grid, the DC bus voltage on the machine side, the rotational speed of the doubly-fed wind turbine, and the active power of the machine-side inverter.

[0022] As a further optimization scheme of the adaptive virtual inertia control method for the doubly-fed wind turbine based on the superconducting magnetic energy storage system, in step 3, the virtual synchronous inertia control is performed on the doubly-fed wind turbine by adaptively adjusting the virtual inertia coefficient according to the inertia support coefficient adaptively adjusted in step 2, specifically:

[0023] Predict the virtual inertia coefficient according to the inertia support coefficient adaptively adjusted in step 2, , , is the virtual synchronous generator at time, the virtual inertia coefficient at time;

[0024] Establish the active power equation for the joint control of the virtual synchronous machine and the superconducting magnetic energy storage system: , where is the electrical angular frequency of the output voltage of the virtual rotor shaft in the virtual synchronous machine, is the active power command value of the doubly-fed wind turbine unit, is the virtual primary frequency regulation coefficient, is the rated electrical angular frequency of the power system, is the actual output electromagnetic power on the stator side of the doubly-fed wind turbine, is the damping coefficient, is the electrical angular frequency of the common power grid.

[0025] As a further optimization scheme of the adaptive virtual inertia control method for doubly-fed wind turbines based on a superconducting magnetic energy storage system, the step 3 generates a virtual inertia control command for the doubly-fed wind turbine and a virtual synchronous control command for the grid side of the doubly-fed wind turbine, specifically as follows:

[0026] Generate a virtual inertia control command for the doubly-fed wind turbine: when the active power released by the superconducting magnetic energy storage system is sufficient, reduce the inertia response of the doubly-fed wind turbine; when the active power released by the superconducting magnetic energy storage system is insufficient, enhance the inertia response of the doubly-fed wind turbine;

[0027] Generate a virtual synchronous control command for the grid side of the doubly-fed wind turbine: use a double closed-loop control strategy of voltage outer loop - current inner loop to calculate the grid side current command value.

[0028] An electronic device includes a memory and a processor. The memory stores a computer program that runs on the processor. When the processor runs the computer program, it executes the steps of the above-mentioned adaptive virtual inertia control method for doubly-fed wind turbines.

[0029] A computer-readable storage medium stores a computer program. When the computer program runs, it executes the steps of the above-mentioned adaptive virtual inertia control method for doubly-fed wind turbines.

[0030] The present invention adopts the above technical solutions and has the following beneficial effects:

[0031] (1) The adaptive virtual inertia control method proposed by the present invention constructs a superconducting magnetic energy storage - doubly-fed wind turbine hybrid system architecture. The superconducting magnetic energy storage system is connected to the DC side of the unit and is connected in parallel with the DC capacitor. Through the DC virtual synchronous technology of the superconducting magnetic energy storage system, the inertia support coefficient is adaptively adjusted. When the power grid fluctuates, the rotor motion equation is introduced, and an active power control equation for the joint control of VSG and superconducting magnetic energy storage is constructed. The virtual moment of inertia coefficient is adjusted through the adaptive inertia support coefficient to simulate the inertia and damping characteristics of a synchronous generator. When the power grid frequency and voltage change, it shows dynamic characteristics similar to those of a traditional generator, enabling the doubly-fed wind turbine to respond to adaptive inertia control and improving the stability of wind power grid connection.

[0032] (2) The present invention generates a virtual synchronous adaptive inertia response command for a superconducting magnetic energy storage system with a flexible adjustable inertia support coefficient through the DC virtual synchronous technology of the superconducting magnetic energy storage system. By using the virtual synchronous adaptive inertia response command of the superconducting magnetic energy storage system to assist the doubly-fed wind turbine in participating in the primary frequency regulation of the power grid, the inertial support of the doubly-fed wind turbine system is realized. It can not only increase the overall equivalent inertia of the unit, but also reduce the reserved active power capacity of the unit, ensure the power generation of the unit as much as possible, weaken the fatigue of the unit's drive chain, and enhance the anti-interference ability of the power grid while ensuring economy.

[0033] (3) On the basis of realizing the virtual synchronous control on the machine side of the doubly-fed wind turbine system, the present invention acquires the system operation data, generates the grid-side control command of the doubly-fed wind turbine based on the double closed-loop control strategy, controls the action of the doubly-fed wind turbine system, and provides effective inertia support for the doubly-fed wind turbine while stably outputting active power. Description of the Drawings

[0034] Figure 1 It is a flowchart of the adaptive virtual inertia control method for a doubly-fed wind turbine based on a superconducting magnetic energy storage system proposed by the present invention.

[0035] Figure 2 It is a diagram of the superconducting magnetic energy storage-doubly-fed wind turbine hybrid system architecture and control strategy provided by an embodiment of the present invention.

[0036] Figure 3 It is a diagram of the superconducting magnetic energy storage system architecture provided by an embodiment of the present invention.

[0037] Figure 4 It is an effect diagram of inertia support provided by an embodiment of the present invention.

[0038] Figure 5 It is a power curve diagram of the superconducting magnetic energy storage system under disturbance conditions provided by an embodiment of the present invention. Detailed Embodiment

[0039] The technical solution of the invention will be described in detail below with reference to the drawings.

[0040] Please refer to Figure 1 , Figure 1 It is a flowchart of the adaptive virtual inertia control method for a doubly-fed wind turbine based on a superconducting magnetic energy storage system proposed by the present invention, and this method includes Step 1 to Step 3.

[0041] Step 1, construct a superconducting magnetic energy storage-doubly-fed wind turbine hybrid system architecture

[0042] The doubly-fed induction generator is one of the most widely used models in current practical engineering applications. The core components of the superconducting magnetic energy storage doubly-fed wind turbine include: the wind turbine blade system, the doubly-fed induction generator (DFIG), the machine-side converter, the grid-side converter, and the gearbox. Among them, the gearbox is not shown in the attached drawings, but those skilled in the art can know the mechanical / electrical connection relationship between the gearbox and other core components. Due to its special winding design, the doubly-fed motor is also called a wound-rotor asynchronous generator. Its stator side can directly transmit energy to the power grid, while the rotor side realizes energy transmission through a back-to-back converter. This design enables both the stator side and the rotor side to have the ability to transmit energy to the power grid. Usually, the converter closer to the rotor side is named the rotor-side converter or the machine-side inverter, while the converter on the other side is called the stator-side converter or the grid-side rectifier. The DC side of the machine-side inverter is connected to the DC side of the grid-side rectifier to construct the DC bus of the unit. The rotor-side converter can accurately control parameters such as the amplitude, phase, and frequency of the excitation, while the stator-side converter can transmit electric energy with a constant frequency to the power grid, thus ensuring the stable operation of the entire wind turbine and its compatibility with the power grid.

[0043] Construct as Figure 2 the superconducting magnetic energy storage-doubly-fed wind turbine hybrid system architecture shown. Connect the energy storage system to the DC bus of the unit and parallel it with the DC capacitor. Through the DC virtual synchronous technology of the superconducting magnetic energy storage system, introduce the rotor motion equation during grid fluctuations, change the machine-side control strategy, so that it can simulate the inertia and damping characteristics of a synchronous generator, show dynamic characteristics similar to those of a traditional generator when the grid frequency and voltage change, improve the stability of wind power grid connection, and enhance the anti-interference ability of the power grid.

[0044] Figure 3 Shows the superconducting magnetic energy storage system architecture diagram proposed by the present invention, mainly including: a power conditioning system, a boost DC / DC, a superconducting magnetic energy storage coil, a refrigeration system, and a control system.

[0045] The power conditioning system is the energy conversion interface between the superconducting magnetic energy storage system and the power grid, mainly responsible for realizing the bidirectional exchange of active power and reactive power between the superconducting magnetic energy storage coil and the power grid.

[0046] The boost DC / DC usually consists of a bidirectional converter and can quickly respond to power demands. In an embodiment of the present invention, the boost DC / DC adopts a full-bridge topology, that is, the superconducting magnetic energy storage coil is connected in parallel to the low-voltage DC port side of the full bridge, and the high-voltage DC port side of the full bridge is connected to the DC bus of the unit to achieve the functions of power conversion and boosting.

[0047] The superconducting magnetic energy storage coil is the core component of the superconducting magnetic energy storage system and is used to store electromagnetic energy. The superconducting magnetic energy storage coil is wound by superconducting materials, and its structural forms mainly include toroidal coils and solenoid coils, which can store energy without loss for a long time in a zero-resistance state.

[0048] The superconducting magnetic energy storage coil needs to be in a low-temperature environment to maintain the superconducting state. Therefore, the refrigeration system is the core auxiliary part of the superconducting magnetic energy storage system. The main function of the refrigeration system is to provide and maintain a low-temperature environment for the superconducting magnetic energy storage coil. Common refrigeration methods include refrigerant cooling, cryogenic cooler cooling, and combined cooling of refrigerant and cryogenic cooler, and liquid helium or liquid nitrogen is usually used as the cooling medium. In an embodiment of the present invention, a refrigeration method of cooling by immersing in cryogenic liquid is adopted to realize the zero-volatility mode operation of the refrigeration system, thereby reducing the operating cost.

[0049] The control system is the control center of the superconducting magnetic energy storage system, responsible for monitoring and controlling the operating state of the entire system, and issuing instructions to the power regulation system according to the preset control strategy to achieve dynamic power compensation for the superconducting magnetic energy storage system. The control system also has self-checking and protection functions. When the current, magnetic field intensity or temperature of the superconducting magnetic energy storage coil exceeds the safety threshold, it can timely issue instructions to the refrigeration system to take measures to protect the system safety.

[0050] In the superconducting magnetic energy storage system proposed by the present invention, the power regulation system, boost DC / DC, superconducting magnetic energy storage coil, and refrigeration system work together and cooperate with the doubly-fed fan system to finally achieve functions such as rapid power regulation, improvement of power quality, and enhancement of power grid stability.

[0051] Step 2: Adaptively adjust the inertia support coefficient according to the operating state of the superconducting magnetic energy storage system, generate a virtual synchronous adaptive inertia response instruction for the superconducting magnetic energy storage system, and perform DC virtual synchronous control on the operation of the superconducting magnetic energy storage system

[0052] The basic principle of the superconducting magnetic energy storage (SMES) system is as follows: When the temperature drops below the critical temperature of the superconducting material, a superconducting magnet made of superconducting tapes with zero resistance generates a continuous induced current due to electromagnetic induction. The electromagnetic energy is stored in the magnetic field in the form of a direct current flowing in a superconducting coil, completing the energy storage process. When releasing energy, the magnetic field energy stored in the superconducting coil is converted into alternating current through a power conditioning system and sent reversely to the power grid. On the DC bus side of a doubly-fed wind turbine, the voltage is the only indicator to measure the power balance within the system. Therefore, different from an AC system, the inertia of a DC system should be reflected in preventing sudden changes in the DC bus voltage, and the damping is reflected in the ability to suppress voltage oscillations. Due to the isolation effect of power electronic devices in the DC system, a power source with rotational kinetic energy cannot directly respond to changes in the DC voltage. The SMES in the DC system directly stores electromagnetic energy using a superconducting coil and can release the electromagnetic energy when needed. Ideally, the SMES can be regarded as a large inductor, and the stored energy can be expressed by Equation (1):

[0053] (1)

[0054] The instantaneous active power is shown in Equation (2):

[0055] (2)

[0056] The charge quantity can be expressed as in Equation (3):

[0057] (3)

[0058] In Equations (1) to (3), represents the energy stored in the SMES system, represents the inductance of the SMES system, represents the current flowing through the SMES system during operation, represents the instantaneous active power of the SMES system, represents the charge quantity of the SMES system, represents the energy storage capacity of the SMES system, represents the initial charge quantity of the SMES system. The SMES system has the advantages of fast response speed, high conversion efficiency, long-term lossless energy storage, long service life, and simple maintenance, and has the ability to stabilize the voltage. Therefore, when the power of a doubly-fed wind turbine fluctuates, the SMES system can quickly mobilize the stored energy to alleviate the voltage fluctuation. Based on this, the relationship between frequency and power when the rotor speed changes can be analogized, and the corresponding current relationship formula can be derived. Considering the power stored in the SMES system as a substitute for the rotor kinetic energy, the expression shown in Equation (4) can be obtained:

[0059] (4)

[0060] In formula (4), 、 and are the inertia current, input current, and damping current respectively, is the DC bus voltage of the unit, is the virtual inertia coefficient. After that, the rated voltage is introduced in the inertia link, and the DC bus voltage is introduced as a feedback signal into the primary voltage regulation and damping links.

[0061] The present invention particularly considers the expression of the relationship between voltage and current, and adopts droop control as the primary voltage regulation link to provide a certain voltage support for the system, and its rated current . The present invention innovatively proposes the expression of the DC virtual synchronous control of the superconducting magnetic energy storage system as:

[0062] (5)

[0063] For formula (5), and are constants related to the droop coefficient and damping coefficient, and take values as constants related to the actual system, is the reference value of the DC bus voltage of the unit. Considering that the fixed virtual inertia coefficient can often only be designed and set based on a certain specific working condition or typical scenario, and cannot flexibly adapt to the dynamic changes of the power grid operation scenario. For example, in the case of rapid fluctuations in grid load, large fluctuations in new energy output, or changes in the grid topology structure, the fixed virtual inertia coefficient may not be able to effectively maintain the stability of the system, and may even cause the system frequency deviation to exceed the allowable range, thus affecting the safe and stable operation of the entire power grid.

[0064] In order to better cope with the diversification and uncertainty of the power grid operation scenario and improve the flexibility and adaptability of the system, the present invention innovatively proposes a DC virtual synchronous control method for the superconducting magnetic energy storage system based on an adaptive virtual inertia coefficient. The core idea of this control method is to dynamically adjust the magnitude of the inertia support coefficient by real-time monitoring of the operating state parameters of the superconducting magnetic energy storage system.

[0065] Define the dynamic evaluation coefficient as the ratio of the real-time maximum power margin to the initial power margin of the i-th superconducting magnetic energy storage system. To prevent the inertia support coefficient from fluctuating frequently, introduce the coefficient . Generally, can take 0.05, and are the maximum active power of the superconducting magnetic energy storage system and the current active power of the i-th superconducting magnetic energy storage system respectively, is the reference value of the active power of the i-th superconducting magnetic energy storage system.

[0066] (6)

[0067] In formula (6), is the dynamic evaluation coefficient of the i-th superconducting magnetic energy storage system, and a is a fixed value related to the capacity of the doubly-fed fan unit, the scale of the superconducting magnetic energy storage, and the operating state of the hybrid system.

[0068] After introducing the dynamic evaluation coefficient, the inertia support coefficient , can be expressed as:

[0069] (7)

[0070] Generate the virtual synchronous adaptive inertia response instruction of the superconducting magnetic energy storage system, specifically: when there is a power disturbance such as a sudden change in wind speed in the doubly-fed fan system, and the voltage drop amplitude of the DC bus of the unit is greater than the coefficient , the i-th superconducting magnetic energy storage system adjusts the inertia support coefficient to increase the active power with as the maximum power margin; when there is surplus power that cannot be absorbed in the doubly-fed fan system, and the voltage rise amplitude of the DC bus of the unit is greater than the coefficient , the i-th superconducting magnetic energy storage system adjusts the inertia support coefficient to reduce the active power with as the maximum power margin, so as to realize the reasonable distribution of unbalanced power and provide effective inertia support for the system; when the DC bus voltage of the unit is equal to the reference value, the i-th superconducting magnetic energy storage system maintains the virtual inertia coefficient to keep the active power output unchanged.

[0071] Replacing in formula (5) with can realize the DC virtual synchronous control of the superconducting magnetic energy storage system of the present invention.

[0072] Step 3, obtain the operation data of the superconducting magnetic energy storage-doubly-fed fan hybrid system, adjust the virtual moment of inertia coefficient in real time according to the adaptively adjusted inertia support coefficient, perform virtual synchronous inertia control on the doubly-fed fan, and generate the doubly-fed fan control instruction

[0073] As the center of the hybrid system, the central controller is responsible for comprehensively collecting real-time information from other devices, generating accurate control instructions through calculations, and adjusting the operating states of the doubly-fed wind turbine and the superconducting magnetic energy storage system in real time according to the grid operation conditions. Although the central controller is not shown in the drawings, those skilled in the art can understand that it conducts data collection and issues control instructions through the communication links with the information collection devices and the superconducting magnetic energy storage system. Each edge sensor collects the grid operation status, mainly including information such as the public grid operation frequency, the DC bus voltage on the machine side, the rotational speed of the doubly-fed wind turbine, and the active power signal of the machine-side inverter. The collection method can be in the form of analog signals or digital signals. In the analog signal implementation, each distributed node converts continuous physical quantities such as voltage and current into corresponding analog electrical signals through measuring devices such as sensors. These analog signals are transmitted to the central controller through media such as wires and cables. In the control center, corresponding analog signal processing circuits, such as filters, amplifiers, and analog-to-digital converters, need to be configured to preprocess, amplify, and digitally convert the received analog signals for subsequent digital processing and analysis. Its equipment cost is relatively low, and it has good real-time performance for the transmission of high-frequency signals, but the problems of signal attenuation and distortion are relatively prominent. In the digital signal implementation, the physical quantities collected by the measuring devices are directly converted into digital signals, and digital communication protocols, such as RS-232, CAN bus, Ethernet, etc., are used for efficient and reliable transmission. It has strong anti-interference ability, stable and reliable signal transmission, high data transmission rate, large information volume, and is also convenient for encryption processing to improve data security. Considering the need for high-real-time data collection in the application scenario of the present invention, the transmission scheme is selected as digital signals, and preferably the widely used Ethernet transmission scheme, and the efficient transmission of data is realized by constructing a local area network based on the TCP / IP protocol. Each node device is built with an Ethernet interface, encapsulates the collected data into IP data packets, and performs broadcast or point-to-point transmission on the Ethernet through media such as twisted pairs and optical fibers. The central controller, as the server side, listens for and receives data packets from each node and performs parsing and processing.

[0074] After obtaining the basic operation information of the hybrid system, the virtual synchronous control command of the grid-side of the doubly-fed wind turbine is further calculated. In a traditional power system, due to the mechanical coupling relationship between the prime mover rotor and the synchronous generator, the change in the mechanical power input of the prime mover will be directly reflected in the mechanical power input of the synchronous generator. Therefore, the frequency regulation function is mainly borne by the speed regulation system of the synchronous generator. When there are active load fluctuations or faults in the power system, the system frequency will change accordingly. If the output power of the synchronous generator remains unchanged, a decrease in the active load will cause the frequency to rise, and vice versa. The frequency change will trigger the response of the synchronous generator speed regulation system. By adjusting the mechanical power input of the prime mover and utilizing the inherent inertia and damping characteristics of the synchronous generator, the rate of frequency change can be effectively suppressed and its fluctuation amplitude can be reduced. After the speed regulation system completes the regulation, a power balance is re-established between the load and the power source, and the system frequency tends to be stable. In this process, the corresponding relationship between the active power and the frequency of the synchronous generator speed governor reflects the static frequency regulation characteristics of the synchronous generator. Assume that the synchronous generator initially operates at the stable operating point A, where the system electrical angular frequency is , and the output power is . When the grid load increases, the static frequency characteristic curve of the load moves from a to b. If the speed regulation system does not respond in time, the system frequency will deviate from the balanced state and drop to . After the speed regulation system intervenes, the synchronous generator increases its active power output, so that the system reaches a new balance state at the operating point B, and the angular frequency stabilizes at . Finally, the change in the system electrical angular frequency is . The static frequency regulation effect coefficient of the synchronous generator is , which is the absolute value of the slope of the droop characteristic curve, and its expression is:

[0075] (8)

[0076] Introducing the characteristics of the synchronous generator speed governor into the virtual synchronous control strategy can construct a virtual speed governor, and its mathematical expression is:

[0077] (9)

[0078] In the given formula (9), represents the virtual input mechanical power of the virtual synchronous generator, which is composed of the active power command value of the doubly-fed wind turbine unit and the output of the virtual speed governor. represents the static frequency regulation effect coefficient of the VSG virtual speed governor, is also called the virtual primary frequency regulation coefficient, refers to the rated electrical angular frequency of the power system, is the electrical angular frequency of the output voltage of the VSG virtual rotor shaft.

[0079] However, during the process of inertia simulation, the rotor kinetic energy needs to be quickly released, while the speed regulation process requires continuous power support. The difference in time scales between the two is likely to cause power oscillation. At the same time, when the wind speed is low, the stored energy of the rotor is insufficient, and the inertial support ability drops sharply. The parameter mismatch of multiple VSGs under high penetration may trigger subsynchronous oscillation. Based on the above parameters and variables, the present invention innovatively constructs an active power control equation for the combined control of VSG and superconducting magnetic energy storage. This equation simulates the rotor motion equation of the synchronous generator and the speed regulation effect, and adjusts the virtual moment of inertia coefficient in real time according to the adaptive inertia support coefficient determined by the operating state of the superconducting magnetic energy storage system, and finally acts on the virtual synchronous control of the machine-side inverter. The mathematical expression of the active power control equation for the combined control of VSG and superconducting magnetic energy storage can be expressed as:

[0080] (10)

[0081] In the above expression, represents the electrical angular frequency of the power grid; and are the virtual input mechanical power of the virtual synchronous machine and the actual output electromagnetic power of the DFIG stator side respectively; is the damping coefficient; represents the virtual moment of inertia of the VSG, which is a variable related to the operating information and time of the superconducting magnetic energy storage system, and its unit is :

[0082] (11)

[0083] In formula (11), 、 represent the virtual moment of inertia coefficients of the virtual synchronous generator at moment and moment, and is the adaptively adjustable inertia support coefficient mentioned in step 2. is the virtual synchronous control command of the machine side of the doubly-fed wind turbine.

[0084] The implementation method of the present invention for generating the virtual inertia control command of the doubly-fed wind turbine is: dynamically adjust the virtual synchronous control of the doubly-fed wind turbine according to the operating state of the superconducting magnetic energy storage system. When the release capacity of the superconducting magnetic energy storage system is strong, minimize the inertia response of the doubly-fed wind turbine to make the doubly-fed wind turbine output more smoothly without changing the operating state of the doubly-fed wind turbine; on the contrary, when it is detected that the release capacity of the superconducting magnetic energy storage system is weak, only then make the doubly-fed wind turbine act on the system in a stronger inertia response manner to maintain the overall stable operation of the system.

[0085] After obtaining the basic operating information of the system, the virtual synchronous control command of the grid side of the doubly-fed fan is further calculated. In the rotating coordinate system, due to the axis voltage coupling, the feedforward decoupling control is adopted, and the dq-axis output voltages of the grid side rectifier can be obtained 、 as:

[0086] (12)

[0087] In formula (12), are the command values of the d-axis and q-axis currents respectively, 、 are the proportional and integral coefficients respectively, are the actual values of the d-axis and q-axis currents respectively, L is the inductor of the grid side rectifier, 、 are the calculated electromotive forces of the d-axis and q-axis respectively.

[0088] The grid side rectifier adopts a double closed-loop control mechanism of the DC voltage outer loop and the current inner loop. The core of this mechanism is to construct two interdependent and coordinated control loops to achieve precise management of the grid side rectifier. Specifically, the DC voltage closed-loop is the dominant one, focusing on maintaining the stability of the DC bus voltage on the machine side. The central controller then compares the actual voltage value of the DC bus on the machine side with the preset reference voltage value in detail and calculates the voltage deviation. Based on this voltage deviation signal, efficient control strategies such as the proportional-integral control algorithm are used for in-depth processing, and finally a control command for adjusting the set value of the current inner loop is output. The purpose of the command is to reduce the voltage deviation of the DC bus on the machine side, especially when the load changes, to ensure that the DC bus voltage on the machine side can be stably maintained near the preset reference value. At the same time, the current closed-loop focuses on precisely regulating the grid side current of the common power grid. It uses a current detection device to sample the grid side current in real time to obtain its actual value, and compares these sampled grid side current values with the current command value A comparison is made to obtain the current deviation. Subsequently, the current controller uses methods such as PI control to process this current deviation and generate a pulse width modulation signal. The control signal of the power switch tube in the grid-side rectifier obtained after the dq-abc conversion of the pulse width modulation signal accurately controls the on-off state of the power switch device in the grid-side rectifier, thereby effectively regulating the grid-side current and enabling it to quickly and accurately track the current command. When encountering dynamic events such as load mutations and grid voltage fluctuations, the current closed-loop can quickly respond and adjust the current, effectively shortening the transient process of the current, enhancing the system's resistance to various disturbances, and improving the stability and reliability of the system. This dual closed-loop control mechanism forms a tight whole, where the output of the outer loop serves as the set value of the inner loop. Through close cooperation of the two loops, the grid-side rectifier demonstrates excellent stability, fast dynamic response, precise power control, and strong anti-interference ability when dealing with complex and changing power system operating conditions. It can not only effectively suppress the fluctuations of the DC voltage and grid-side current, ensuring the reliable operation of the power system, but also quickly adjust the current in various dynamic situations, achieve rapid power balance and distribution, and reduce the adverse effects on the system. In addition, it can accurately regulate the active power and reactive power exchange between the grid-side rectifier and the grid, improve the operating efficiency and power quality of the power system, and provide a strong guarantee for the stable, efficient, and high-quality operation of the power system. The current command calculated by the dual closed-loop control strategy adopted by the grid-side rectifier is:

[0089] (13)

[0090] In formula (13), is the current command value, is the actual value of the DC bus voltage on the machine side, is the measured value of the grid-side current of the common power grid. That is, the virtual synchronous control command on the grid side of the doubly-fed wind turbine. The virtual inertia control command of the doubly-fed wind turbine and the virtual synchronous control command on the grid side of the doubly-fed wind turbine constitute the control command of the doubly-fed wind turbine.

[0091] Figure 4 Figure shows the virtual inertia control support effect of the doubly-fed wind turbine based on the superconducting magnetic energy storage system proposed in this study. Without adopting any virtual synchronous control strategy, the grid frequency drops to a minimum of 49.65 Hz, and then there is a frequency overshoot phenomenon. The system tends to be stable after about 30 s of oscillation. When only the virtual synchronous control of the doubly-fed wind turbine is adopted, under the same power disturbance conditions, the amplitude of the system frequency drop is significantly reduced, and the oscillation duration is shortened to about 20 s. When the combined virtual synchronous control strategy of the superconducting magnetic energy storage system and the doubly-fed wind turbine is adopted, the system shows the best frequency response characteristics, with the smallest frequency fluctuation amplitude, and the system oscillation can be completely eliminated in only 15 s.

[0092] Figure 5 Further demonstrates the power support characteristics of the proposed double-fed wind turbine inertia support system based on superconducting magnetic energy storage system under disturbance conditions. The experimental results show that during the system frequency drop, the superconducting magnetic energy storage system can quickly provide effective power support and timely compensate for the system power shortage. This scheme has a small overshoot and significantly improves the operation stability of the double-fed wind power generation system. In addition, by introducing an adaptive variable virtual synchronous control mechanism, the power optimal distribution of the double-fed wind turbine system is realized, effectively suppressing the power oscillation phenomenon and providing a reliable guarantee for the safe and stable operation of the power system.

[0093] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above specific embodiments, and the above specific embodiments and the descriptions in the specification are only for further explaining the principles and preparation effects of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope claimed by the present invention. The scope claimed by the present invention is defined by the claims and their equivalents.

Claims

1. An adaptive virtual inertia control method for a doubly-fed wind turbine based on a superconducting magnetic energy storage system, characterized in that Including: Step 1: Connect the superconducting magnetic energy storage system to the machine-side DC bus of the doubly-fed fan to construct a superconducting magnetic energy storage-doubly-fed fan hybrid system; Step 2: Adaptively adjust the inertia support coefficient according to the operating state of the superconducting magnetic energy storage system, generate a virtual synchronous adaptive inertia response command for the superconducting magnetic energy storage system, and perform DC virtual synchronous control on the superconducting magnetic energy storage system; Step 3: Obtain the operation data of the superconducting magnetic energy storage-doubly-fed fan hybrid system, and adjust the virtual moment of inertia coefficient in real time according to the inertia support coefficient adaptively adjusted in Step 2 to perform virtual synchronous inertia control on the doubly-fed fan, and generate a virtual inertia control command for the doubly-fed fan and a virtual synchronous control command for the grid side of the doubly-fed fan.

2. The adaptive virtual inertia control method for a doubly-fed wind turbine based on a superconducting magnetic energy storage system according to claim 1, wherein In the above Step 1, the superconducting magnetic energy storage system includes: A power conditioning system for realizing bidirectional exchange of active power and reactive power between the superconducting magnetic energy storage coil and the power grid; A boost DC / DC, whose high-voltage DC port side is connected to the unit DC side bus; A superconducting magnetic energy storage coil, which is connected in parallel to the low-voltage DC port side of the boost DC / DC, is used to store electromagnetic energy, and adjusts the active output in response to the virtual synchronous adaptive inertia response command of the superconducting magnetic energy storage system; A refrigeration system for providing and maintaining a low-temperature environment for the superconducting magnetic energy storage coil; and A control system for monitoring and controlling the operating state of the superconducting magnetic energy storage system, and sending commands to the power conditioning system according to a preset control strategy, and sending commands to the refrigeration system when the current, magnetic field intensity or temperature of the superconducting magnetic energy storage coil exceeds the safety threshold.

3. The adaptive virtual inertia control method for a doubly-fed wind turbine based on a superconducting magnetic energy storage system according to claim 1, wherein Step 2 adaptively adjusts the inertia support coefficient according to the operating state of the superconducting magnetic energy storage system, specifically as follows: , where is the virtual inertia coefficient of the i-th superconducting magnetic energy storage system after adaptive adjustment, is the virtual inertia coefficient of the i-th superconducting magnetic energy storage system, is the actual value of the DC bus voltage on the machine side of the doubly-fed wind turbine, is the reference value of the DC bus voltage on the machine side of the doubly-fed wind turbine, is the deviation threshold of the DC bus voltage on the machine side of the doubly-fed wind turbine, is the dynamic evaluation coefficient of the i-th superconducting magnetic energy storage system, , is the maximum active power of the superconducting magnetic energy storage system, is the current active power of the i-th superconducting magnetic energy storage system, is the reference value of the active power of the i-th superconducting magnetic energy storage system, and a is a fixed value related to the capacity of the doubly-fed wind turbine unit, the scale of the superconducting magnetic energy storage, and the operating state of the hybrid system.

4. The adaptive virtual inertia control method for a doubly-fed wind turbine based on a superconducting magnetic energy storage system according to claim 3, wherein The specific method for generating the virtual synchronous adaptive inertia response command of the superconducting magnetic energy storage system in Step 2 is as follows: When the DC bus voltage drop amplitude of the doubly-fed wind turbine unit is greater than , the i-th superconducting magnetic energy storage system uses as the inertia support coefficient for maximum power margin regulation and increases the active power output; The rising amplitude of the DC bus voltage of the doubly-fed fan unit is greater than , and the i-th superconducting magnetic energy storage system uses as the inertia support coefficient for regulating the maximum power margin, and reduces the active power output; When the DC bus voltage of the doubly-fed fan unit is equal to the reference value, the i-th superconducting magnetic energy storage system maintains the virtual inertia coefficient and keeps the active output unchanged.

5. The adaptive virtual inertia control method for a doubly-fed wind turbine based on a superconducting magnetic energy storage system according to claim 4, wherein Step 2 performs DC virtual synchronous control on the superconducting magnetic energy storage system, specifically: , where and are constants related to the droop coefficient and damping coefficient, is the rated voltage, is the grid-side DC bus current of the doubly-fed wind turbine.

6. The adaptive virtual inertia control method for a doubly-fed wind turbine based on a superconducting magnetic energy storage system according to claim 5, wherein The operation data of the superconducting magnetic energy storage-doubly-fed fan hybrid system obtained in Step 3 includes, but is not limited to: the operating frequency of the common power grid, the machine-side DC bus voltage, the speed of the doubly-fed fan, and the active power of the machine-side inverter.

7. The adaptive virtual inertia control method for a doubly-fed wind turbine based on a superconducting magnetic energy storage system according to claim 6, wherein The specific method for performing virtual synchronous inertia control on the doubly-fed fan by adjusting the virtual moment of inertia coefficient in real time according to the inertia support coefficient adaptively adjusted in Step 2 in Step 3 is as follows: Predict the virtual inertia coefficient according to the inertia support coefficient adaptively adjusted in step 2 , 、 are the virtual inertia coefficients of the virtual synchronous generator at time and time respectively; Establish the active power equation for the combined control of the virtual synchronous machine and the superconducting magnetic energy storage system: , where is the electrical angular frequency of the output voltage of the virtual rotor shaft in the virtual synchronous machine, is the active power command value of the doubly-fed wind turbine unit, is the virtual primary frequency modulation coefficient, is the rated electrical angular frequency of the power system, is the actual output electromagnetic power on the stator side of the doubly-fed wind turbine, is the damping coefficient, is the electrical angular frequency of the common power grid.

8. The adaptive virtual inertia control method for a doubly-fed wind turbine based on a superconducting magnetic energy storage system according to claim 7, wherein The specific method for generating the virtual inertia control command for the doubly-fed fan and the virtual synchronous control command for the grid side of the doubly-fed fan in Step 3 is as follows: Generating a virtual inertia control command for the doubly-fed fan: When the active power released by the superconducting magnetic energy storage system is sufficient, reduce the inertia response of the doubly-fed fan; when the active power released by the superconducting magnetic energy storage system is insufficient, enhance the inertia response of the doubly-fed fan; Generating a virtual synchronous control command for the grid side of the doubly-fed fan: Using a double closed-loop control strategy of voltage outer loop-current inner loop to calculate the grid side current command value.

9. An electronic device, including a memory and a processor, where a computer program is stored on the memory and runs on the processor, and when the processor runs the computer program, it executes the steps of the doubly-fed fan adaptive virtual inertia control method according to any one of claims 1 to 8.

10. A computer-readable storage medium, on which a computer program is stored, and when the computer program runs, it executes the steps of the double-fed fan adaptive virtual inertia control method according to any one of claims 1 to 8.

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