Segmented frequency control method for wind power system with cooperation of power reserve and short-term over-generation

Abstract

The invention relates to a segmented frequency control method for a wind power system cooperating with power reserve and short-term over-generation. The method comprises the following steps: S1, obtaining operation data when the wind power system is disturbed; s2, considering the real-time rotating speed of a rotor of the wind power system in an inertia response stage based on the operation data during disturbance, and introducing a short-term power overrunning control method to increase the output power of a fan in a short term, so as to realize frequency control of the fan system in the inertia response stage; and S3, the wind power system enters a primary frequency modulation stage, and frequency control of the fan system in the primary frequency modulation stage is realized by adopting a continuous power output method based on power reserve. Compared with the prior art, the method has the advantages that the frequency recovery process under a longer time scale is considered, and the economic performance and the energy utilization efficiency are better while the frequency safety is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of wind power systems, and in particular to a segmented frequency control method for a wind power system that coordinates power reserve and short-term overgeneration. Background Art

[0002] As the penetration rate of wind power systems increases, the system's rotational inertia gradually decreases, and the frequency stability of the power grid faces severe challenges. New energy systems including wind power are urgently needed to provide frequency support for the power grid. However, the frequency support capacity of the wind power system is limited. Different frequency control measures need to be taken at different stages for the dynamic process after the frequency is disturbed, so as to maximize the frequency safety of the power grid while improving resource utilization efficiency. For example, the frequency of the power grid suddenly drops after the disturbance, and the excessive frequency change rate may cause the generator protection to trip. Subsequently, in the middle and late stages of the disturbance, the system frequency will gradually recover. At this time, the power grid needs continuous power support to prevent the frequency from falling further. Therefore, in order to achieve the optimal frequency support effect, the wind power system needs to provide both fast power support in a short period of time and continuous stable power. Wind power systems usually use virtual inertia control and frequency droop control with fixed coefficients. However, the former will cause a secondary drop in frequency in the speed recovery stage, and the latter has the problem of low energy utilization. In addition, conventional control usually focuses on the frequency control effect and ignores the actual position of the wind turbine speed or pitch angle, which may cause the wind turbine speed to be too high or too low, resulting in increased losses or even failures.

[0003] Since wind turbines in wind power systems are not directly connected to the grid but are connected to the grid through power electronic converters, the output power of wind power systems cannot directly respond to frequency fluctuations and cannot provide frequency support. With the increase in the penetration rate of wind power systems and the continuous investment in power electronic equipment, the rotational inertia of the grid is gradually decreasing, and the system is gradually evolving into a low-inertia system, which will increase the unbalanced power impact of the system, weaken the system frequency control capability, and threaten the system frequency security. In order to ensure the safe and stable operation of the system and improve the frequency stability and security of the grid, the wind power system should participate in the grid frequency control.

[0004] In order to realize the frequency response function of the wind power system, a frequency response link is usually added to the power control loop of the wind power system, such as virtual inertia control and frequency damping control, so that the output power changes with the frequency change rate and frequency deviation respectively. However, the virtual inertia control with a fixed coefficient has the problem of secondary frequency drop, and the frequency damping control with a fixed coefficient cannot optimize the use of the adjustable capacity of the wind turbine under different rotor speeds, and may have the problem of low energy utilization. The existing technology has also been improved through various measures. For example, measure 1: The document "Coordinated Power Reserve Control of Wind Farm for Frequency Regulation" linearizes the mathematical relationship between the rotor speed change and the power change, and uses the maximization of the linear part of the rotor kinetic energy that can be released as the objective function for linear programming solution. However, when the design differences of the wind turbines are large, the calculation amount is too large, the process is too complicated, and the system response speed is slow. Measure 2: The document "Coordinated Frequency Control Method of Variable Speed ​​Wind Turbines Based on Inertia / Droop Control" provides frequency support by introducing virtual inertia control and frequency damping control of the wind power system. The control parameters are usually designed as fixed values. Whether the actual operation of the wind turbine can meet the power demand under safe and economic conditions is not considered, and the support requirements at different stages after the frequency is disturbed are not considered. There may be a situation where the wind turbine generates excessive power for a long time and has a high degree of wear. Measure 3: The document "Coordinated Rotor Speed ​​and Pitch Angle Control of Wind Turbines for Accurate and Efficient Frequency Response" and the document "Primary Frequency Regulation Strategy of Variable Speed ​​Wind Turbines Based on Improved Coordinated Control of Rotor Speed ​​and Pitch Angle" use the mechanical power curve to reduce the load by changing the rotor speed, and combine the variable pitch control to coordinate and change the operating point to output additional power. Although most of these methods have tried to avoid frequent changes in pitch angles, they do not consider the risk of secondary frequency drop caused by sudden changes in wind power system output during the speed recovery phase. Summary of the invention

[0005] The purpose of the present invention is to provide a wind power system segmented frequency control method for coordinated power reserve and short-term overgeneration to ensure frequency safety of the wind power system after being disturbed.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A wind power system segmented frequency control method for coordinated power reserve and short-term overgeneration comprises the following steps:

[0008] Step S1, obtaining operation data of a wind power system when a disturbance occurs;

[0009] Step S2: based on the operation data during the disturbance, the real-time speed of the wind power system rotor is considered in the inertial response stage, and a short-term power over-generation control method is introduced to increase the output power of the wind turbine in the short term, so as to realize the frequency control of the wind turbine system in the inertial response stage;

[0010] Step S3: the wind power system enters a primary frequency modulation stage, and a continuous power output method based on power reserve is used to implement frequency control of the wind turbine system in the primary frequency modulation stage.

[0011] Furthermore, the execution steps of step S2 include:

[0012] The wind power system enters the inertial response phase, and determines whether the frequency deviation exceeds the set frequency control dead zone based on the operating data.

[0013] If not, the frequency control is performed according to the MPPT power in the MPPT mode as the power reference value;

[0014] If so, switch from MPPT mode to power overshoot mode, adopt short-term power overgeneration control method to increase short-term power overgeneration reference value based on MPPT power, obtain control activation power reference value, and perform frequency control until the increased short-term power overgeneration reference value drops to zero.

[0015] Furthermore, the calculation process of the power reference value in the MPPT mode includes:

[0016] According to the principles of aerodynamics, the power of the fan is calculated as follows:

[0017]

[0018] Where P wind is power, ρ is air density, R is fan blade radius, v w is the wind speed, C p is the wind energy utilization coefficient of the wind turbine, ω r is the fan rotor speed;

[0019] Substitute equation 2) into equation 1) and replace C p Take the maximum value to get the power reference value in MPPT mode. The expression is:

[0020]

[0021] Where P opt Indicates the MPPT maximum power value, that is, the power reference value in MPPT mode. C p The maximum value of λ optrepresents the optimal tip speed ratio for the current wind speed, k opt Represents the optimal power curve coefficient.

[0022] Furthermore, the calculation expression of the control activation power reference value is:

[0023]

[0024] Where P FFC is the power reference value of the machine-side converter after activating the frequency control, that is, the control activation power reference value, k opt represents the optimal power curve coefficient, ω r is the wind turbine rotor speed, t0 is the disturbance moment, Δt is the time required for the additional power to decrease to zero, and ΔP0 is the initial additional power after the disturbance.

[0025] Furthermore, the expression of the initial additional power after the disturbance is:

[0026] ΔP0=k add ·P opt0

[0027] Where P opt0 is the maximum power of the fan before the disturbance, k add is the proportionality coefficient.

[0028] Furthermore, the expression of the proportionality coefficient is:

[0029]

[0030] Where k0 is the initial proportional coefficient, ω0 is the rotor speed before the disturbance, and ω max and ω min are the maximum and minimum limits for the rotor speed.

[0031] Furthermore, the execution steps of step S3 include:

[0032] In the primary frequency regulation stage, the short-term power over-generation control is switched to the MPPT mode, and the backup power is used for continuous power output control. At the same time, the power-frequency droop coefficient is set as the control coefficient based on the real-time speed of the wind turbine rotor until the frequency returns to the set frequency control dead zone.

[0033] Furthermore, the calculation expression of the continuous output control power is:

[0034] ΔP PFC =-k d (f-f0)

[0035] Where ΔP PFC Indicates the additional power size for continuous power output control, k drepresents the power-frequency droop control coefficient, f represents the system frequency, and f0 represents the frequency at the moment before the disturbance.

[0036] Furthermore, the expression of the power-frequency droop control coefficient is:

[0037]

[0038] Where ΔE k , ΔE k,max are the rotor kinetic energy of the fan at the disturbance moment and the rotor kinetic energy corresponding to the maximum rotor speed of the fan, k n The droop factor required for the system to ensure that the frequency does not exceed the safety boundary, ω r Indicates the speed, the subscript 0 indicates the speed before the disturbance, the subscript max indicates the maximum speed of the disturbance, and the subscript min indicates the minimum speed of the disturbance.

[0039] Furthermore, the ΔE k , ΔE k,max The expression is:

[0040]

[0041] In the formula, E k represents kinetic energy, the subscript 0 represents the kinetic energy at the current moment, the subscript min represents the kinetic energy corresponding to the minimum speed, the subscript max represents the kinetic energy corresponding to the maximum speed, and H represents the inertia time constant of the wind power system.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1) In view of the frequency disturbance of the wind power system, the present invention divides the disturbance stage into an inertial response stage and a primary frequency regulation stage. In the inertial response stage, a short-term power overgeneration control method is introduced to increase the output power of the wind turbine in a short period of time, thereby reducing the instantaneous frequency change rate in a short period of time and ensuring the frequency safety in the inertial response stage. In the primary frequency regulation stage, a continuous power output method based on power reserve is adopted to provide continuous power for the wind power system, guide the frequency to slowly recover to the rated value, and ensure the frequency safety in the primary frequency regulation stage.

[0044] (2) In the inertial response stage, the present invention determines whether the frequency deviation exceeds the frequency control dead zone, and adopts a combination of MPPT mode and power overshoot mode to alleviate the secondary frequency drop caused by the sudden change in the output of the wind power system during the frequency and speed recovery stage.

[0045] (3) In the primary frequency regulation stage, the present invention considers the droop control coefficient coupling output power and frequency deviation of the wind power system rotor speed and the actual position of the pitch angle, and the continuous power output power control based on power reserve enables the wind power system to adjust the frequency difference, maximize the use of wind turbine frequency regulation resources, and support frequency recovery.

[0046] (4) The present invention takes into account the frequency recovery process on a longer time scale, and takes into account the actual operating conditions of the wind turbine rotor and pitch angle in the additional power size, thereby ensuring frequency safety while having better economic performance and energy utilization efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic diagram of the method flow of the present invention;

[0048] Figure 2 is the frequency response characteristic curve of the wind power system of the present invention;

[0049] Figure 3 The present invention is a schematic diagram of the short-term power over-generation control principle and control structure of a wind turbine, wherein (a) is a short-term power over-generation control structure diagram, and (b) is a diagram showing the change of the wind turbine operating point on the mechanical power curve during the frequency regulation process;

[0050] Figure 4 This is a structural diagram of continuous power output control in the primary frequency modulation stage of the present invention;

[0051] Figure 5 The structure diagram and principle diagram of the wind power system segmented frequency control for coordinated power reserve and short-term power overgeneration of the present invention;

[0052] Figure 6 A structural diagram of a wind power system according to an embodiment of the present invention;

[0053] Figure 7 The system frequency and frequency change rate simulation results of the embodiment of the present invention, wherein (a) is the frequency simulation result, and (b) is the frequency change rate simulation result;

[0054] Figure 8 1 and 2 are simulation results of output power, rotation speed and pitch angle of an embodiment of the present invention, wherein (a) is the simulation result of wind turbine power, (b) is the simulation result of pitch angle, and (c) is the simulation result of rotor rotation speed. DETAILED DESCRIPTION

[0055] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0056] This embodiment provides a segmented frequency control method for a wind power system that coordinates power reserve and short-term overgeneration. In the inertial response stage corresponding to the initial stage of a disturbance event, the wind power system will over-generate a certain amount of power in a short period of time according to an adaptive proportional coefficient. The over-generation power decays within a set time and decays to zero at the end of the set time to ensure frequency safety during the inertial response stage. Subsequently, it enters a primary frequency regulation stage in the middle and late stages of the disturbance event, and uses a droop control coefficient that takes into account the actual position of the wind power system rotor speed and pitch angle to couple the output power and frequency deviation, thereby maximizing the use of wind turbine frequency regulation resources and supporting frequency recovery. Figure 1 As shown, the method comprises the following steps:

[0057] Step 1. Establish the wind turbine output power model and frequency response characteristics.

[0058] The fan captures power P from the air wind Will be used as the mechanical power input to the wind turbine generator. According to the principles of aerodynamics, P wind The expression is

[0059]

[0060] Where: ρ is the air density, R is the fan blade radius, v w is the wind speed, λ is the tip speed ratio, ω r is the fan rotor speed, C p is the wind energy utilization coefficient of the wind turbine. If we substitute formula (2) into formula (1) and replace C p Taking the maximum value, we can get the maximum power point tracking (MPPT) algorithm power reference value:

[0061]

[0062] Where P opt Indicates the maximum power value of MPPT, λ opt represents the optimal tip speed ratio for the current wind speed, k opt Represents the optimal power curve coefficient.

[0063] Under normal operation, the wind turbine outputs power according to formula (3). At this time, since it has reached the maximum output power, the power response frequency cannot be increased. Therefore, the wind turbines participating in frequency support are usually required to reserve a certain amount of spare power. When the frequency is disturbed, the spare power can be used to increase the power required by the power grid, thereby completing the frequency support. The system frequency response characteristic curve is shown in Figure 2As shown. In the figure, the system is disturbed at t=0s. The inertial response stage is within 5-10s after the disturbance. The frequency change rate has the greatest impact on the system frequency safety in this stage. After the inertial response stage, it is the primary frequency modulation stage, which is about 10-60s after the disturbance occurs. In this stage, the frequency deviation has the greatest impact on the system frequency safety. The traditional frequency support method directly uses comprehensive frequency control, that is, activating virtual inertial control and frequency damping control at the same time to suppress system frequency changes and reduce frequency deviations, respectively. It does not specifically consider the parameters that pose the greatest threat to system frequency safety at different stages, resulting in low energy utilization. In addition, there is a risk of secondary frequency drop when absorbing power from the system when the speed recovers, and noise is introduced. Therefore, the fan needs to use different power control methods based on the frequency response stage to adjust the output power and improve energy utilization.

[0064] Step 2. Short-term power overgeneration control principle and control structure during the inertial response phase.

[0065] In the inertial response stage, the wind turbine needs to provide a large power in a short time. Although coupling the frequency change rate in the power control loop is feasible, it introduces noise, which is not conducive to system operation. Therefore, a short-term power over-generation control is proposed. d (The frequency control dead zone can be safely set according to the local grid frequency guidelines. For example, for grids with a capacity of 3 million kilowatts or more, the deviation shall not exceed ±0.2Hz, i.e. Δf d =0.2Hz. ), the system can be regarded as disturbed and enter the inertial response stage, activating the short-term power over-generation control. The short-term power over-generation control principle and control structure diagram are shown in Figure 3 shown. Figure 3 Figure (a) is the short-term power over-generation control structure diagram. Before the frequency exceeds the control dead zone, the MPPT power is used as the power reference value by default, satisfying formula (3). When the frequency exceeds the control dead zone, the short-term power over-generation control is activated, and the control loop is switched. After the switch, the power reference value is:

[0066]

[0067] Where: P FFC is the power reference value of the machine-side converter after activating frequency control, and the second term is the short-term power over-generation reference value, where t0 is the disturbance time, Δt is the time required for the additional power to decrease to zero, and ΔP0 is the initial additional power after the disturbance. The expression is:

[0068] ΔP0=k add ·P opt0 (5)

[0069] Where: k add is the proportionality coefficient, P opt0is the maximum fan power before the disturbance. The proportionality coefficient is determined by the following formula:

[0070]

[0071] Where: k0 is the initial proportional coefficient, ω0 is the rotor speed before the disturbance, ω max and ω min are the maximum and minimum limits for the rotor speed.

[0072] Figure 3 Figure (b) shows the change of the wind turbine operating point on the mechanical power curve during the frequency regulation process. When the frequency drops, the wind turbine enters the frequency support stage, and the power reference value of the machine-side converter first increases from A to B, and its additional power will decrease with time. When the power reference value of the wind turbine drops to C, the electromagnetic power is equal to the mechanical power, and the rotor speed reaches the lowest point. Subsequently, the wind turbine enters the recovery stage, the additional power drops to zero at point D, and the power reference value control mode switches to MPPT control until the wind turbine stably operates at the maximum power point, that is, point A. The proposed power control method effectively alleviates the secondary frequency drop problem caused by the wind turbine directly switching to the MPPT mode (that is, switching from point C to point C') after providing frequency support.

[0073] When the frequency deviation exceeds the dead zone, the wind turbine switches from MPPT mode to power overshoot mode. The additional power gradually decreases over time and drops to zero after Δt, and the wind turbine switches back to MPPT mode. It is worth noting that the setting of Δt will affect the frequency support effect. A smaller Δt will accelerate the power change and ensure the rapid recovery of the rotor speed. However, too small Δt may cause a secondary frequency drop. On the contrary, a larger Δt can ensure a smaller secondary frequency drop and a better frequency support effect, but due to the slow power change, the rotor speed recovery process is longer. Therefore, the setting of the attenuation time Δt needs to comprehensively consider the frequency support effect and speed recovery requirements. This method ensures frequency safety in the inertial response stage (i.e., within a few seconds after the disturbance), but the frequency is still in a fluctuating state at this time, and the system still requires continuous power input.

[0074] Step 3. Principle of continuous power output control in the primary frequency modulation stage.

[0075] If the fan is in an over-generation state for a long time, the damage to the fan will be aggravated, causing damage such as rotor cracks. Therefore, a method of continuously providing power is needed after a short-term power over-generation. When it is detected that the additional power of the short-term power over-generation control in the inertial response stage drops to zero, it indicates that the primary frequency modulation stage has been entered and the continuous power output control can be activated. At this time, the fan runs at Figure 3Point D in the figure. When the wind turbine just switches back to the MPPT algorithm to control power (point D) in the short-term power over-generation control, it is not allowed to continue to restore the rotor speed, but the power-frequency droop coefficient is set based on the wind turbine rotor speed at this time. Since the essence of wind turbine frequency control is to convert rotor kinetic energy into electrical energy, the size of the rotor kinetic energy can be used to determine the power size that can provide frequency support, as shown in formula (7).

[0076]

[0077] In the formula, E k represents kinetic energy, the subscript 0 represents the kinetic energy at the current moment, the subscript min represents the kinetic energy corresponding to the minimum speed, H represents the inertia time constant of the wind power system, ω r Represents the speed, and the subscript 0 represents the speed before the disturbance.

[0078] If the rotor speed is at the maximum value, it can use the rotor kinetic energy to the maximum, and it can set a larger droop coefficient to provide additional power. At this time, the available kinetic energy is:

[0079]

[0080] Wherein, the subscript max represents the maximum speed or the rotor kinetic energy corresponding to the maximum speed.

[0081] At this time, the kinetic energy that can be used is the largest, and a larger droop coefficient can be set. The droop coefficient k required by the frequency system that does not exceed the safety boundary can be set. n Based on this, the power-frequency droop coefficient can be set according to the ratio of the available kinetic energy of the rotor before the disturbance to the maximum available kinetic energy, that is:

[0082]

[0083] In the formula, k d represents the power-frequency droop control coefficient. The wind power system will always use this value as the control coefficient and output power according to formula (10) until the frequency recovers to the control dead zone.

[0084] ΔP PFC =-k d ·(f-f0) (10)

[0085] Where ΔP PFC represents the additional power size of continuous power output control, f represents the system frequency, and f0 represents the frequency at the moment before the disturbance. The additional power size is limited by the maximum power that can be captured by the wind turbine. The maximum additional power amount does not exceed the reserve power size reserved during stable operation. The wind turbine provides additional power to release the remaining reserve power after short-term power over-generation control. The control block diagram of this method is as follows Figure 4When the additional power of the short-term power over-generation control is detected to be zero during the frequency inertia response phase, the continuous power output control is activated to utilize the reserve power until the frequency returns to the set dead zone, and then the wind turbine returns to MPPT control.

[0086] Step 4. Segmented frequency control method for wind power system with coordinated power reserve and short-term over-generation

[0087] Combined with the short-term power over-generation control and continuous power output control described above, the structure diagram and principle diagram of the wind power system segmented frequency control for coordinated power reserve and short-term power over-generation in the whole frequency response process can be established as shown in the following figure. Figure 5 As shown in the figure, β1 is the pitch angle of the initial wind turbine load reduction operation, β2 is the pitch angle corresponding to the wind turbine when the additional power is zero after short-term power over-generation control, and β3 is the pitch angle of the wind turbine that can meet the power demand in continuous power output control. Figure 5 As shown in Figure (a), when the frequency exceeds the dead zone Δf>Δf d When t-t0=Δt, the wind power system enters the inertial response stage, and the additional power control changes from zero to short-term power over-generation control. As time goes by, the increase in short-term power over-generation control gradually decreases, and t-t0 gradually approaches the Δt value. When t-t0=Δt, the increase in power decreases to zero, and the system will enter the primary frequency modulation stage. The additional power control changes from short-term power over-generation control to continuous power output control. When the frequency returns to the dead zone, that is, Δf<Δf d After that, the additional power control becomes zero again. Figure 5 As shown in Figure (b), the power reference value of the machine-side converter first increases from A to B, and its additional power will decrease with time. When the power reference value of the wind turbine set drops to C, the electromagnetic power is equal to the mechanical power, the rotor speed reaches the lowest point, and then the additional power drops to zero at point D. At this time, the additional power control mode switches to continuous power output control. According to the variable speed and variable pitch control logic, it will first change the speed to the maximum power point E under the current pitch angle. If the frequency regulation requirement is not met at this time, the pitch angle is reduced and the speed is fine-tuned until the power requirement is met (point F). When the system frequency returns to the dead zone, it switches back to MPPT control.

[0088] The segmented frequency control method proposed in the present invention realizes two stages of frequency control - the inertial response stage and the primary frequency modulation stage. In the former stage, short-term power overgeneration control quickly provides power to reduce the instantaneous frequency change rate in the short term; in the latter stage, continuous power output control enables the wind power system to adjust the frequency difference, provide continuous power within the primary frequency modulation time scale, and guide the frequency to slowly recover to the rated value. This method realizes the coordinated control of power reserve and short-term power overgeneration. Compared with the frequency control method that only uses short-term power overgeneration, the method proposed in the present invention takes into account the frequency recovery process under a longer time scale, and takes into account the actual operating conditions of the wind turbine rotor and pitch angle in the additional power size, while ensuring frequency safety, it has better economic performance and energy utilization efficiency.

[0089] Verification background:

[0090] The proposed wind power system segmented frequency control method for coordinated power reserve and short-term power over-generation is verified in PSCAD / EMTDC. Figure 6 As shown, it includes a permanent magnet direct drive wind turbine, a synchronous generator SG to represent the power grid equivalently, a fixed load PL1 and a switchable load PL2. The system parameters are shown in Table 1. The capacity of PL1 is P+jQ=1MW+j0.1 MVAR, and the default capacity of PL2 is P+jQ=0.05MW.

[0091] Table 1 Example system parameters

[0092]

[0093] Verification scheme:

[0094] In this case study, three simulations are set up: a. Wind turbine MPPT operation without additional control; b. Only short-term power over-generation control is used; c. Wind turbine adopts the proposed segmented frequency control method. n =15, Δt=5s, k0=0.09, ω r,max and ω r,min The operating wind speed is set to 10m / s. PL2 is added at the simulation time t=20s to simulate a 5% load step disturbance. The system frequency waveform and frequency change rate are as follows: Figure 7 As shown in Figure 2, the wind turbine output power, speed and pitch angle are as follows: Figure 8 shown.

[0095] Figure 7 Figures (a) and (b) show the simulation results of frequency and frequency change rate respectively. Figure 7As shown in Figure (a), since MPPT control cannot respond to frequency, its lowest frequency point is 49.52Hz, while short-term power over-generation control and the proposed method provide more additional power when suppressing the frequency change rate. Compared with MPPT control, the system imbalance is smaller at the same time, so its lowest frequency point is also improved to 49.57Hz. Around 25s of simulation, since the proposed method continues the power output control after the short-term power over-generation control, its frequency recovery speed after 25s of simulation is significantly improved compared with the short-term power over-generation control only, and its overshoot is close to that of the short-term power over-generation only. Figure 7 As shown in Figure (b), due to the absence of additional power in MPPT control, its frequency change rate reaches about -0.4Hz / s at the moment of disturbance, while the frequency change rate of only short-term power over-generation control and the proposed method is almost 0, which shows its suppression effect on the frequency change rate. At about 25s of simulation, since the proposed method activates continuous power output control to provide additional power, the frequency recovery speed is accelerated, so the frequency change rate has an obvious spike, but it recovers to normal levels in a relatively fast time.

[0096] Figure 8 Figures (a), (b), and (c) in the figure show the simulation results of wind turbine power, pitch angle, and rotor speed, respectively. Since the difference between the proposed method and short-term power overgeneration control is the presence or absence of continuous power output control, and this control is not activated until 25 seconds after the simulation, the simulation results of the two methods are consistent before this. It is worth noting that Figure 8 In Figure (c), the fan speed drops to a certain extent at 25 seconds under the proposed method. This is because after activating the continuous power output control, the fan should release a certain amount of rotor kinetic energy to provide additional power.

[0097] In summary, the proposed method, under the premise of considering the operating conditions of the wind power system, effectively suppresses the frequency change rate while accelerating the frequency recovery speed, reducing the risk of secondary frequency drop, and achieving higher energy utilization.

[0098] In summary, the method proposed in this embodiment uses different power control methods to coordinate the frequency control at different stages of frequency response. In the inertial response stage, the wind turbine short-term power over-generation method is adopted to increase the output power of the wind turbine in a short term according to the size of the wind turbine rotor speed, and slowly change the reference value to the maximum power point during the speed recovery process to alleviate the frequency secondary drop caused by the sudden change in the output of the wind power system in the frequency speed recovery stage. Subsequently, in the primary frequency modulation stage (that is, the subsequent stage after the frequency is disturbed and passes the oscillation peak), the frequency droop coefficient of the continuous power output control is set based on the speed when the wind turbine switches back to MPPT control, and based on this coefficient, continuous power output is provided to the power grid. Compared with measure 1, the present invention simplifies the calculation process and achieves a faster response speed; compared with measure 2, the calculation of the control coefficient of the present invention takes into account the actual operating conditions of the wind turbine rotor speed and the pitch angle position, and the economic performance is better and the energy utilization is more reasonable; compared with measure 3, the present invention takes into account the influence of the reference power mutation when switching between short-term power overshoot control and MPPT control in the wind turbine speed recovery stage, and uses the proportional coefficient considering the rotor speed to make the reference power smoothly transition, effectively reducing the risk of secondary frequency drop.

[0099] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0100] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A wind power system segmented frequency control method for coordinated power reserve and short-term over-generation, characterized in that: The following steps are involved: Step S1, obtaining operation data of a wind power system when a disturbance occurs; Step S2: based on the operation data during the disturbance, the real-time speed of the wind power system rotor is considered in the inertial response stage, and a short-term power over-generation control method is introduced to increase the output power of the wind turbine in the short term, so as to realize the frequency control of the wind turbine system in the inertial response stage; Step S3: the wind power system enters a primary frequency modulation stage, and a continuous power output method based on power reserve is used to implement frequency control of the wind turbine system in the primary frequency modulation stage.

2. A wind power system segmented frequency control method for coordinated power reserve and short-term over-generation according to claim 1, characterized in that: The execution steps of step S2 include: The wind power system enters the inertial response phase, and determines whether the frequency deviation exceeds the set frequency control dead zone based on the operating data. If not, the frequency control is performed according to the MPPT power in the MPPT mode as the power reference value; If so, switch from MPPT mode to power overshoot mode, adopt short-term power overgeneration control method to increase short-term power overgeneration reference value based on MPPT power, obtain control activation power reference value, and perform frequency control until the increased short-term power overgeneration reference value drops to zero.

3. A wind power system segmented frequency control method for coordinated power reserve and short-term over-generation according to claim 2, characterized in that: The calculation process of the power reference value in the MPPT mode includes: According to the principles of aerodynamics, the power of the fan is calculated as follows: Where P wind is power, ρ is air density, R is fan blade radius, v w is the wind speed, C p is the wind energy utilization coefficient of the wind turbine, ω r is the fan rotor speed; Substitute equation 2) into equation 1) and replace C p Take the maximum value to get the power reference value in MPPT mode. The expression is: Where P opt Indicates the MPPT maximum power value, that is, the power reference value in MPPT mode. C p The maximum value of λ opt represents the optimal tip speed ratio for the current wind speed, k opt Represents the optimal power curve coefficient.

4. A wind power system segmented frequency control method for coordinated power reserve and short-term overgeneration according to claim 2, characterized in that: The calculation expression of the control activation power reference value is: Where P FFC is the power reference value of the machine-side converter after activating the frequency control, that is, the control activation power reference value, k opt represents the optimal power curve coefficient, ω r is the wind turbine rotor speed, t0 is the disturbance moment, Δt is the time required for the additional power to decrease to zero, and ΔP0 is the initial additional power after the disturbance.

5. A wind power system segmented frequency control method for coordinated power reserve and short-term overgeneration according to claim 4, characterized in that: The expression of the initial additional power after the disturbance is: ΔP0=k add ·P opt0 Where P opt0 is the maximum power of the fan before the disturbance, k add is the proportionality coefficient.

6. A wind power system segmented frequency control method for coordinated power reserve and short-term overgeneration according to claim 5, characterized in that: The expression of the proportionality coefficient is: Where k0 is the initial proportional coefficient, ω0 is the rotor speed before the disturbance, and ω max and ω min are the maximum and minimum limits for the rotor speed.

7. A wind power system segmented frequency control method for coordinated power reserve and short-term overgeneration according to claim 1, characterized in that: The execution steps of step S3 include: In the primary frequency modulation stage, the short-term power over-generation control is switched to the MPPT mode, and the backup power is used for continuous power output control. At the same time, the power-frequency droop coefficient is set as the control coefficient based on the real-time speed of the wind turbine rotor until the frequency returns to the set frequency control dead zone.

8. A method for controlling the frequency of a wind power system in a coordinated manner with power reserve and short-term over-generation according to claim 7, characterized in that: The calculation expression of the continuous output control power is: ΔP PFC =-k d ·(f-f0) In the formula, ΔP PFC Indicates the additional power size for continuous power output control, k d represents the power-frequency droop control coefficient, f represents the system frequency, and f0 represents the frequency at the moment before the disturbance.

9. A wind power system segmented frequency control method for coordinated power reserve and short-term overgeneration according to claim 8, characterized in that: The expression of the power-frequency droop control coefficient is: In the formula, ΔE k , ΔE k,max are the rotor kinetic energy of the fan at the disturbance moment and the rotor kinetic energy corresponding to the maximum rotor speed of the fan, k n The droop factor required for the system to ensure that the frequency does not exceed the safety boundary, ω r Indicates the speed, the subscript 0 indicates the speed before the disturbance, the subscript max indicates the maximum speed of the disturbance, and the subscript min indicates the minimum speed of the disturbance.

10. A wind power system segmented frequency control method for coordinated power reserve and short-term overgeneration according to claim 9, characterized in that: The ΔE k , ΔE k,max The expression is: In the formula, E k represents kinetic energy, the subscript 0 represents the kinetic energy at the current moment, the subscript min represents the kinetic energy corresponding to the minimum speed, the subscript max represents the kinetic energy corresponding to the maximum speed, and H represents the inertia time constant of the wind power system.

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