Wind-storage coordinated frequency control method based on virtual synchronous machine variable parameter algorithm

Abstract

The present invention discloses a wind-storage coordinated frequency control method based on a virtual synchronous machine variable parameter algorithm. First, the frequency response curve of the system after the load disturbance is determined in stages for different processes; then, a virtual synchronous machine variable parameter algorithm is proposed for the frequency modulation demand of the wind power system, and a wind turbine frequency response control model based on the VSG variable parameter algorithm is established; then, an energy storage module is added to establish a wind-storage system model based on the VSG variable parameter algorithm; finally, a wind-storage coordinated control method is proposed, and the active output of the wind turbine and the energy storage module is allocated according to the system frequency modulation demand, and the frequency is adjusted together. The frequency control method of the present invention enables the system to have a strong frequency response capability, improves its transient and steady-state frequency deviations when the system is subject to frequency disturbance, solves the problem of secondary frequency drop caused by the virtual inertia frequency modulation of the wind power system, and requires less energy storage capacity to be configured, so that wind power can be used to the greatest extent for frequency modulation.

Description

Technical Field

[0001] The present invention relates to a wind-storage coordinated frequency control method based on a variable parameter algorithm of a virtual synchronous machine, and belongs to the technical field of wind-storage coordinated control. Background Art

[0002] With the depletion of fossil energy and increasingly strict carbon emission requirements, the energy system dominated by traditional synchronous energy is gradually being replaced by asynchronous energy such as wind and light. As of the end of February 2023, the total installed capacity of wind power in China reached 350 million kilowatts. Since wind power is connected to the power grid through power electronic components, the transmission power is decoupled from the power grid frequency and cannot actively provide inertial support. Therefore, the system frequency stability of a power system with a high proportion of new energy is extremely vulnerable to threats and damage under load disturbances. To reduce the impact of new energy units connected to the power grid, it has become an inevitable requirement to make new energy units or energy storage participate in frequency modulation through control means.

[0003] Common frequency modulation means for wind turbines include rotor overspeed control, pitch angle control, virtual inertia synthesis control, virtual synchronous generator (VSG), etc. Rotor overspeed control, also known as overspeed load shedding, affects the tip speed ratio by changing the speed, leaving a part of active power reserve for the unit to improve the frequency modulation ability, but it can only operate at medium and low wind speeds (considering a 20% load shedding, the wind speed critical value is 8.2 m / s). Pitch angle control realizes load shedding reserve by changing the pitch angle, but it will cause frequent pitch changes, exacerbate the mechanical wear of the unit, and shorten the service life. Virtual inertia synthesis control includes inertia control and droop control. This method has more control parameters and is more complex to control. VSG control is to simulate the mathematical model of a synchronous generator, enabling the wind turbine to have similar inertia response, damping characteristics, and primary frequency modulation characteristics as a synchronous generator. It is not restricted by physical characteristics and is relatively flexible and simple.

[0004] When VSG control is adopted, the withdrawal of wind power from frequency modulation will bring a large power deficit to the system, thus causing a secondary frequency drop. As a high-quality frequency regulation source with fast response speed and adjustable parameters, energy storage can inject a large amount of active power into a low-inertia power system in a short time to support the power grid frequency and compensate for the secondary drop.

[0005] Existing wind-storage coordinated control mostly targets doubly-fed wind power systems, and most of the existing wind-storage frequency modulation methods only start from the perspective of the control methods of wind and storage themselves. The control process is relatively complex, ignoring the coordination and cooperation between the characteristics of wind and storage and their control methods. Therefore, it is of great significance to propose a wind-storage coordinated frequency control method based on the VSG variable parameter algorithm for permanent magnet synchronous generators. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a wind-storage coordinated frequency control method based on a variable parameter algorithm of a virtual synchronous generator, which improves the system frequency response ability through the variable parameter algorithm, and at the same time solves the problem of frequency secondary dip through the wind-storage coordination strategy, reducing the demand for the energy storage configuration capacity of the system.

[0007] The present invention adopts the following technical solutions to solve the above technical problems:

[0008] A wind-storage coordinated frequency control method based on a variable parameter algorithm of a virtual synchronous generator includes the following steps:

[0009] Step 1: Divide the frequency response change of the wind power system after suffering a load disturbance into different stages, and determine the frequency modulation demand of the wind power system in each stage;

[0010] Step 2: Establish a frequency response control model of the wind power system based on the variable parameter algorithm of the virtual synchronous generator according to the frequency modulation demand of the wind power system;

[0011] Step 3: Add an energy storage system on the basis of Step 2, establish a wind-storage system model based on the variable parameter algorithm of the virtual synchronous generator, and allocate the active power output of the wind power system and the energy storage system respectively according to the wind-storage coordinated control method to achieve common frequency regulation.

[0012] Compared with the prior art, the present invention adopting the above technical solutions has the following technical effects:

[0013] 1. Compared with the fixed parameter algorithm, the present invention enhances the system frequency response ability through the advantages of the variable parameter algorithm.

[0014] 2. The present invention can effectively reduce the extreme value of the frequency deviation, compensate for the problem of secondary dip caused by wind power frequency modulation, and requires a smaller energy storage capacity for the method of directly compensating the secondary dip by energy storage under similar results. Description of the Drawings

[0015] Figure 1 is a schematic diagram of the wind-storage coordinated frequency control method based on the variable parameter algorithm of the virtual synchronous generator of the present invention;

[0016] Figure 2 is the rotor angular frequency oscillation curve, where (a) is the sudden increase of the load and (b) is the sudden decrease of the load;

[0017] Figure 3 is the design diagram of the feasible region of the VSG moment of inertia and damping coefficient;

[0018] Figure 4 is the wind-storage coordinated control flow chart;

[0019] Figure 5 is the system frequency response curve when the load change rate is 5%;

[0020] Figure 6 It is the system frequency response curve when the load change rate is 15%;

[0021] Figure 7 It is the output curve of the wind turbine when the load change rate is 15%;

[0022] Figure 8 It is the output curve of the energy storage when the load change rate is 15%. Specific implementation manners

[0023] The following details the implementation manners of the present invention. The examples of the implementation manners are shown in the accompanying drawings. The implementation manners described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention and should not be construed as a limitation to the present invention.

[0024] As Figure 1 shown, it is a schematic diagram of the wind-storage coordinated frequency control method based on the virtual synchronous generator variable parameter algorithm of the present invention, including the following steps:

[0025] (1) Divide the frequency response stages after the wind power system suffers from load disturbances, and determine the frequency regulation requirements of the system in different stages;

[0026] (2) In response to the frequency regulation requirements of the wind power system, propose a virtual synchronous generator variable parameter algorithm, and establish a frequency response control model of the wind turbine based on VSG;

[0027] (3) Establish a wind-storage system model based on the virtual synchronous generator variable parameter algorithm, and allocate the active power outputs of the wind turbine and the energy storage module respectively according to the wind-storage coordinated control method to jointly perform frequency regulation.

[0028] Embodiment 1

[0029] In this embodiment, a wind-storage system is built in MATLAB / Simulink to verify the improvement effect of the wind-storage coordinated strategy based on VSG variable parameters on the dynamic performance of the system frequency response.

[0030] The analysis of this embodiment includes the following steps:

[0031] (1) Divide the frequency response stages after the system suffers from load disturbances, and determine the frequency regulation requirements of the system in different stages.

[0032] Among them, taking the sudden increase in load as an example, the rotor angular frequency oscillation curve can be divided into four stages, as Figure 2 (a) shown. t 1 ~t 2 In the stage, the angular frequency decreases and the angular frequency change rate is negative. At this time, it is necessary to increase the moment of inertia to slow down the decrease of the angular frequency and prevent the rotational speed from overshooting too much. At this time, the damping coefficient should be adjusted smaller to optimize the active power-frequency droop characteristic of the system; t 2~t 3 The stage frequency rises from the lowest point to the initial value. The angular frequency deviation is still negative, but the change rate is positive. At this time, the moment of inertia should be adjusted downwards to stabilize the angular frequency to the rated value as soon as possible, and at the same time, the damping coefficient should be adjusted upwards to increase the frequency recovery rate; t 3 ~t 4 During the stage when the frequency rises from the initial value to the highest point, the values of J and D are the same as those at t 1 ~t 2 stage; t 4 ~t 5 During the stage of frequency recovery, the values of J and D are the same as those at t 2 ~t 3 stage.

[0033] Taking the change curve of the rotor angular frequency when the load suddenly drops as a reference, the oscillation curve of the rotor angular frequency can be divided into four stages, as shown in Figure 2 (b) of. t 1 ~t 2 stage, t 1 At the moment of t, a disturbance is encountered, and the angular frequency begins to increase with a positive change rate. At this time, the moment of inertia J needs to be adjusted upwards to slow down the increase of ω and prevent excessive overshoot of the rotational speed. At this time, D should be adjusted downwards to optimize the active power - frequency droop characteristic of the system. t 2 ~t 3 During this stage, the angular frequency deviation is still positive, but the change rate is negative. At this time, J should be adjusted downwards to stabilize ω to the rated value as soon as possible, and at the same time, D should be adjusted upwards to increase the attenuation rate. t 3 ~t 4 During this stage, both the angular frequency deviation and the change rate are negative, and the values of J and D are the same as those at t 1 ~t 2 stage. t 4 ~t 5 During this stage, the angular frequency deviation is negative and the change rate is positive, and the values of J and D are the same as those at t 2 ~t 3 stage.

[0034] (2) A virtual synchronous generator variable - parameter algorithm is proposed for the frequency regulation requirements of the wind power system, and a frequency - response control model of the wind turbine based on VSG is established:

[0035]

[0036]

[0037] Among them, J and D are the moment of inertia and damping coefficient in the virtual synchronous generator control model. J 0 、D 0 are the initial values of the moment of inertia and damping coefficient, K is the moment - of - inertia adjustment coefficient, ω is the system angular frequency, Δω is the angular - frequency offset, ω setis the set minimum offset value, and t is time. To prevent output fluctuations caused by frequent parameter changes during small disturbances, K d1 is a value less than 1, generally taken as 0.1 - 0.3, and K d2 is a value greater than 1, generally taken as 1.05 - 1.2.

[0038] Meanwhile, the moment of inertia and damping coefficient also have certain value boundaries. When the active power loop is at the cut-off frequency, the magnitude of the loop gain is 1, and the expression for the moment of inertia at this time is:

[0039]

[0040] where f cp is the cut-off frequency, ω n is the rated angular frequency, X s is the sum of the output impedance of the VSG and the system impedance, V g is the system voltage, E n is the effective value of the fundamental wave of the midpoint voltage of the inverter bridge arm.

[0041] To ensure that the value inside the square root of the above formula is greater than zero, it is necessary to ensure:

[0042]

[0043] Also, because the moment of inertia is also limited by the phase margin, and its relationship is:

[0044]

[0045] where PM is the phase margin. When the VSG reactive power loop is in droop control, the phase margin is set at 30 - 90°. Then the maximum value of J is limited by the phase margin. The smaller J is, the larger the corner frequency of the filtering link is, and the larger the phase margin is. To meet the system's phase margin requirements, the value of J should be restricted within a certain range. After determining the range of J, the range of D can be determined by exploring the relationship between D and J. Since the optimal damping ratio of the second-order system is generally and to maintain frequency stability, the system characteristic roots generally need to be appropriately far from the imaginary axis, taking the maximum value -10. The schematic diagram of the feasible region of the parameters related to D and J is as Figure 3 shown.

[0046] (3) Establish a wind storage system model based on the virtual synchronous generator variable parameter algorithm, allocate the active power outputs of the wind turbine and the energy storage module respectively according to the wind storage coordinated control method, and jointly perform frequency regulation to improve the extreme values of the transient and steady-state frequency deviations after load disturbances.

[0047] Among them, the flowchart of the wind storage coordinated control is as Figure 4As shown below. First, build a wind power and energy storage system model with VSG and determine the frequency regulation margin of the wind power and energy storage system; then, detect whether the frequency of the wind power system is within the normal range. If the frequency deviation value Δf exceeds 0.03 Hz, calculate the required frequency regulation power of the wind power system, and then send the frequency regulation power to the energy storage system and the wind power system; according to the principle of priority compensation of energy storage, judge whether the energy storage power P s is greater than the required frequency regulation power of the system at this moment. Only when the maximum energy storage power P s_max is not less than the required frequency regulation power of the system and the change in its SOC is less than 0.1% within 1 minute when the energy storage is fully involved in frequency regulation, all of the frequency regulation power P is borne by the energy storage system; when the maximum energy storage power P s_max is greater than the required frequency regulation power of the system, the frequency regulation power is borne by both of them. The energy storage system bears the steady-state power required for the primary frequency regulation of the system, and the wind turbine bears the power demand during the transient process.

[0048] The formula for calculating the required frequency regulation power of the wind power system is:

[0049]

[0050] where, f N is the rated frequency of the system, f is the real-time frequency of the system, K f is the active frequency regulation coefficient of the virtual synchronous generator, T j is the virtual inertia constant of the wind turbine, P N is the rated capacity of the system.

[0051] In this embodiment, the system wind speed is set to 10 m / s, the wind power penetration rate is 20%, the wind turbine operates in the MPPT mode, and a 5% load increase occurs at 3 s. To verify the effectiveness of the proposed strategy of the present invention, three scenarios will be set in this example for case analysis and compare their implementation effects:

[0052] Scenario 1: Neither wind power nor energy storage participates in the system frequency regulation;

[0053] Scenario 2: Adopt the wind power and energy storage collaborative frequency regulation strategy, but the VSG parameters adopt fixed parameters;

[0054] Scenario 3: Adopt the wind power and energy storage collaborative frequency regulation strategy, but the VSG parameters adopt variable parameter algorithms.

[0055] Perform simulations using the above three scenarios respectively, and obtain the frequency response curves as shown in Figure 5 . According to the graph, the dynamic performance of the system frequency response is shown in Table 1.

[0056] Table 1 Dynamic performance of frequency response

[0057]

[0058] As can be seen from Table 1, the wind-storage coordinated frequency control method based on the variable parameter algorithm of the virtual synchronous generator can effectively improve the system frequency regulation ability. The extreme value of the transient frequency deviation is reduced by 18.5% and 2.3% respectively compared with non-frequency regulation and fixed parameter frequency regulation, and the extreme value of the steady-state frequency deviation is reduced by 12.2% compared with non-frequency regulation.

[0059] Embodiment 2

[0060] In this embodiment, a wind-storage system is built in MATLAB / Simulink to verify the improvement effect of the wind-storage coordinated strategy based on VSG variable parameters on the secondary frequency dip of the system and the optimization of the required energy storage regulation capacity. The system wind speed is set to 10 m / s, the wind power penetration rate is 20%, the wind turbine operates in the MPPT mode, and a 15% load increase occurs at 3 s.

[0061] To verify the effectiveness of the strategy proposed in the present invention, this embodiment adopts the same method as Embodiment 1 and sets three schemes for case analysis to compare their implementation effects:

[0062] Scheme 1: Only wind power participates in the system frequency regulation;

[0063] Scheme 2: Adopt a direct compensation frequency secondary dip control strategy for energy storage based on VSG variable parameters, that is, when it is detected that the output power of the wind turbine is lower than the rated power, the energy storage device starts to provide compensation power to the system;

[0064] Scheme 3: Adopt a wind-storage coordinated frequency regulation strategy based on VSG variable parameters.

[0065] The above three schemes are respectively used for simulation, and the frequency response curves are obtained as Figure 6 shown, the output power curve of the wind turbine is as Figure 7 shown, and the output power curve of the energy storage is as Figure 8 shown. According to the image analysis, when the secondary dip occurs in the wind power system, the active power of the wind farm drops by 5.2%. Under the direct compensation of the secondary dip by the energy storage and the wind-storage coordinated control, the power of the wind farm drops by 1.5% and 0.9% respectively. And under the condition of similar frequency regulation results, the method of directly compensating the secondary dip by the energy storage needs to configure an energy storage capacity of 9.3%, while the wind-storage coordinated control only needs to configure 6.9%, saving 25.8%. Therefore, adopting wind-storage coordinated control can improve the secondary frequency dip of the system while more efficiently using wind power and energy storage for frequency regulation.

[0066] In summary, when a load disturbance occurs in the wind-storage system, the wind-storage coordinated frequency regulation strategy based on the variable parameters of the virtual synchronous generator proposed in the present invention can improve the system frequency response ability, reduce the extreme values of the transient and steady-state frequency deviations of the system, and solve the problem of the secondary frequency dip caused by the withdrawal of wind power from frequency regulation. This method has a fast response speed, requires less configured energy storage capacity, and is economical and efficient.

[0067] Based on the same inventive concept, an embodiment of the present application provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of the foregoing wind energy storage collaborative frequency control method based on the virtual synchronous machine variable parameter algorithm are implemented.

[0068] Based on the same inventive concept, an embodiment of the present application provides a computer-readable storage medium storing a computer program, and when the computer program is executed by a processor, the steps of the foregoing wind energy storage collaborative frequency control method based on the virtual synchronous machine variable parameter algorithm are implemented.

[0069] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memory, CD-ROM, optical memory, etc.) containing computer-usable program code.

[0070] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present invention. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of flows and / or blocks in the flowcharts and / or block diagrams, can be realized by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate means for realizing the specified functions in one Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0071] These computer program instructions can also be stored in a computer-readable memory capable of guiding a computer or other programmable data processing devices to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured article including instruction means, and the instruction means realizes the specified functions in one Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0072] These computer program instructions can also be loaded onto a computer or other programmable data processing devices, so that a series of operation steps are executed on the computer or other programmable devices to generate a computer-implemented process, and thus the instructions executed on the computer or other programmable devices provide for realizing the process inFigure 1 one process or multiple processes and / or boxes Figure 1 steps of functions specified in one box or multiple boxes.

[0073] The above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention cannot be limited thereby. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the present invention.

Claims

1. A wind-storage coordinated frequency control method based on a virtual synchronous machine variable parameter algorithm, characterized in that: The steps include: Step 1: divide the frequency response change of the wind power system after the load disturbance into different stages, and determine the frequency regulation demand of the wind power system in each stage; In step 1, the frequency response change of the wind power system after being subjected to load disturbance includes the following two situations: 1) When the load suddenly increases, the frequency response changes into four stages Phase 1: The frequency drops from the initial frequency to the lowest point, the angular frequency decreases and the rate of change of the angular frequency is negative. The moment of inertia needs to be increased and the damping coefficient needs to be reduced to optimize the system active power-frequency droop characteristics; Stage 2: The frequency rises from the lowest point to the initial frequency. The angular frequency deviation is negative and the angular frequency change rate is positive. The moment of inertia needs to be reduced to stabilize the angular frequency to the rated value, and the damping coefficient needs to be increased. Stage 3: The frequency continues to rise from the initial frequency to the highest point, the angular frequency deviation and the angular frequency change rate are both positive, and the changes in the moment of inertia and damping coefficient are the same as in stage 1; Stage 4: The frequency recovers from the highest point to the initial frequency, the angular frequency deviation is positive and the angular frequency change rate is negative, and the change requirements of the moment of inertia and damping coefficient are the same as those in stage 2; 2) Load drop, frequency response changes are divided into four stages Phase I: The frequency rises from the initial frequency to the highest point, the angular frequency increases and the rate of change of the angular frequency is positive. The moment of inertia needs to be increased, and the damping coefficient needs to be reduced to optimize the system's active power-frequency droop characteristics; Phase II: The frequency drops from the highest point to the initial frequency, the angular frequency deviation is positive and the angular frequency change rate is negative. The moment of inertia needs to be reduced to stabilize the angular frequency to the rated value, and the damping coefficient needs to be increased. Phase III: The frequency continues to drop from the initial frequency to the lowest point, the angular frequency deviation and the angular frequency change rate are both negative, and the changes in the moment of inertia and damping coefficient are the same as in Phase I; Phase IV: The frequency recovers from the lowest point to the initial frequency, the angular frequency deviation is negative and the angular frequency change rate is positive, and the change requirements of the moment of inertia and damping coefficient are the same as those of Phase II; Step 2: According to the frequency regulation requirements of the wind power system, a frequency response control model of the wind power system based on the virtual synchronous machine variable parameter algorithm is established; In step 2, the specific formula of the wind power system frequency response control model based on the virtual synchronous machine variable parameter algorithm is as follows: Where J and D are the moment of inertia and damping coefficient in the virtual synchronous machine control model, J0 and D0 are the initial values ​​of the moment of inertia and damping coefficient, K is the moment of inertia adjustment coefficient, ω is the system angular frequency, Δω is the angular frequency offset, ω set is the minimum offset value, t is the time, K d1 is a value less than 1, K d2 is a value greater than 1; At the same time, the moment of inertia J satisfies the following conditions: Among them, f cp is the cut-off frequency, V g is the system voltage, E n is the effective value of the fundamental voltage at the midpoint of the inverter bridge arm, X s is the sum of the output impedance of the virtual synchronous machine and the system impedance, ω n is the rated angular frequency, PM is the phase margin; Step 3: Add the energy storage system based on step 2, establish a wind-storage system model based on the virtual synchronous machine variable parameter algorithm, allocate the active output of the wind power system and the energy storage system according to the wind-storage collaborative control method, and realize joint frequency regulation.

2. The wind-storage coordinated frequency control method based on virtual synchronous machine variable parameter algorithm according to claim 1 is characterized in that: The specific process of step 3 is as follows: Step 31, adding an energy storage system on the basis of step 2, establishing a wind-storage system model based on a virtual synchronous machine variable parameter algorithm, and determining a frequency regulation margin of the wind-storage system; Step 32, detecting whether the frequency of the wind power system is within a normal range, that is, whether the frequency deviation value Δf is less than or equal to 0.03 Hz. When Δf exceeds 0.03 Hz, calculating the frequency modulation power P required by the wind power system; Step 33: According to the principle of energy storage priority compensation, the energy storage power P s Based on the current SOC status, the wind-storage coordinated frequency regulation principle is determined, and the frequency regulation power is sent to the energy storage system and wind power system; Step 34, when the maximum energy storage power P s_max When the frequency modulation power P is not less than the frequency modulation power P required by the system and the SOC change within 1 minute is less than 0.1% when the energy storage system fully participates in the frequency modulation, the frequency modulation power P is entirely borne by the energy storage system; Step 35, when the maximum energy storage power P s_max When the frequency modulation power P is less than the system's required frequency modulation power, the frequency modulation power is shared by the energy storage system and the wind power system. s is the steady-state power required for the primary frequency regulation of the system, and the frequency regulation power of the wind power system P w is the power required for the transient process.

3. The wind-storage coordinated frequency control method based on virtual synchronous machine variable parameter algorithm according to claim 2 is characterized in that: The calculation formula of the frequency modulation power P required by the wind power system is as follows: Among them, f N is the rated frequency of the system, f is the real-time frequency of the system, K f is the active frequency modulation coefficient of the virtual synchronous machine, T j is the virtual inertia constant of the fan, P N is the system rated capacity, and t is the time.

4. A computer device comprising a memory, a processor, and a computer program stored in the memory and capable of running on the processor, characterized in that: When the processor executes the computer program, the steps of the wind-storage coordinated frequency control method based on the virtual synchronous machine variable parameter algorithm as described in any one of claims 1 to 3 are implemented.

5. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the wind-storage coordinated frequency control method based on a virtual synchronous machine variable parameter algorithm as described in any one of claims 1 to 3 are implemented.

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