A method for avoiding frequency secondary drop in cooperative operation control of multiple wind turbines

Abstract

The application provides a kind of multi-wind turbine cooperative operation control method for avoiding frequency secondary drop, comprising the following steps: first, the required DFIG for frequency support is dynamically selected by the real-time disturbance power of power grid and the speed level of each DFIG.Second, the virtual inertia control parameter is adaptively adjusted according to the system frequency and the speed change of DFIG participating in frequency support, to meet the demand of frequency support.Finally, the rotor kinetic energy of the remaining DFIG is released to support the recovery of the selected DFIG speed, to reduce the energy absorbed from the power grid in this process.The application adaptively adjusts the virtual inertia control parameter according to the system frequency and the speed change of DFIG participating in frequency support, to meet the demand of frequency support.And the rotor kinetic energy of the remaining DFIG is released to support the recovery of the selected DFIG speed, to reduce the energy absorbed from the power grid in this process, reduce the probability of frequency secondary drop and excessive speed drop of DFIG, so that DFIG can actively support the system frequency more stably.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of new energy access and control technology, in particular to a multi-wind turbine cooperative operation control method for avoiding frequency secondary drop. BACKGROUND

[0002] As an important part of new energy power generation, wind power has the characteristics of clean and environmental protection, strong regional adaptability, low operation cost, etc., and has developed very rapidly in recent years. Doubly fed induction generator (DFIG) is the mainstream model of wind power generation. Since the DFIG rotor is connected to the grid through a converter, the rotor speed frequency is completely decoupled and cannot effectively respond to system frequency changes. With the continuous increase of wind power penetration, the system frequency stability is continuously declining.

[0003] In order to improve the frequency active support capability of DFIG after grid connection, additional power control can be used to release the rotor kinetic energy of DFIG at the moment of frequency drop to support the frequency, and the DFIG needs to absorb energy to restore the speed after exiting the frequency response. If too much energy is absorbed from the grid, it is easy to cause the secondary drop of system frequency. Moreover, the rotor kinetic energy levels of each DFIG in the wind farm are different, so excessive use of rotor kinetic energy will exacerbate the problem of secondary frequency drop and cause the DFIG with lower speed to exit operation. SUMMARY

[0004] In view of the deficiencies in the prior art, the present application aims to provide a multi-wind turbine cooperative operation control method for avoiding frequency secondary drop, in order to solve the problems raised in the background art. The present application effectively avoids the excessive release of DFIG rotor kinetic energy while ensuring the frequency support effect, thereby reducing the possibility of frequency secondary drop and greatly reducing the energy absorbed from the grid to avoid the occurrence of frequency secondary drop phenomenon.

[0005] In order to achieve the above-mentioned purpose, the present application is realized by the following technical scheme: a multi-wind turbine cooperative operation control method for avoiding frequency secondary drop, comprising the following steps:

[0006] S1: obtaining system frequency response model equivalent parameters through offline mass data, and dynamically selecting DFIGs required to participate in frequency support after online detection that the system frequency deviation exceeds the threshold value;

[0007] S2: comparing the number of selected DFIGs with the total number of DFIGs, and performing adaptive virtual inertia control based on the frequency change and the rotor kinetic energy of each DFIG participating in frequency support to ensure the frequency support effect;

[0008] S3: If the number of selected DFIGs is less than the total number of DFIGs, the unselected DFIGs are controlled to release the stored rotor kinetic energy to support the recovery of the rotational speed of each DFIG for a certain period of time, and then all DFIGs enter the rotational speed recovery stage until the initial value is restored. Otherwise, all DFIGs enter the rotational speed recovery stage after the end of frequency support.

[0009] Further, the off-line mass data in step S1 includes historical frequency drop, load disturbance data, DFIG number n and system wind power penetration rate p, and the equivalent parameters of the system frequency response model include the droop coefficient R of the equivalent synchronous machine, the reheating time constant T of the turbine, the power proportion coefficient F of the high-pressure cylinder RH , the equivalent damping coefficient D. HP , the equivalent damping coefficient D. S , the equivalent damping coefficient D.

[0010] Further, the grid frequency deviation Δf satisfies the following relationship expression:

[0011] Δf = f - f N

[0012] In the formula, f is the actual measured frequency of the grid, f N is the rated frequency of the grid; and the system frequency deviation threshold in step S1 is ±0.02 Hz.

[0013] Further, the dynamic selection process of the DFIG participating in frequency support in step S1 is as follows: when |Δf|≥0.02 Hz, set the initial value K Di,0 and K Ii,0 of the virtual inertia control parameter of each DFIG, arrange each DFIG in descending order according to the rotational speed, and select k=1 to start iteration. The effect of each selected DFIG on frequency support is as follows:

[0014]

[0015] Further, after calculating the result of each iteration, it is compared with the system frequency support constraint. When the condition shown in the following formula is met, the iteration is stopped, and k DFIGs that meet the frequency support requirement of this time are obtained:

[0016]

[0017] In the formula, Δf m and |dΔf(t) / dt| m are the maximum frequency drop value and the maximum frequency change value allowed in the system frequency change process, respectively.

[0018] Further, a threshold value ε is set to fully guarantee the frequency support level, and k=k+ε is set.

[0019] Further, the comparison of the number of selected DFIGs with the total number of DFIGs in step S2 refers to comparing with the total number n of DFIGs in the wind farm, if k < n, only the part of DFIGs need to be called to participate in frequency regulation, otherwise all DFIGs in the wind farm need to be fully called to support frequency.

[0020] Further, the adaptive virtual inertia control of DFIG refers to the virtual inertia control parameters K Di and K Ii will be adaptively adjusted according to the real-time change of frequency and its speed:

[0021]

[0022] In the formula, ω r,max and ω r,min are the maximum and minimum values of the speed of DFIG when it can run stably.

[0023] Further, in the case that the number of selected DFIGs is less than the total number of DFIGs in step S3, t1 and t2 are set as the starting time and the exit time of frequency support, respectively, (t1, t2) time period, only the release of rotor kinetic energy of the dynamically selected k DFIGs, k DFIGs start to recover the speed at t2 time, the remaining n-k DFIGs which do not participate in the frequency support stage are taken as the second group of wind turbines, and the rotor kinetic energy is released in the (t2, t2+5) time period, and the additional power control parameter is set to the initial value K Di,0 and K Ii,0 Then, after t2+5, all DFIGs enter the speed recovery stage and recover the speed to the initial value.

[0024] The beneficial effects of the present application are:

[0025] 1. The present application dynamically selects the number of DFIGs required for frequency support by real-time disturbance power and the speed level of each DFIG, adaptively adjusts the virtual inertia control parameters according to the system frequency and the speed change of the DFIG participating in frequency support, and meets the frequency support demand. And the rest of the DFIG releases the rotor kinetic energy to support the speed recovery of the selected DFIG, so as to reduce the additional energy absorbed from the power grid in the process.

[0026] 2. The multi-wind turbine cooperative operation control method for avoiding frequency secondary drop can effectively avoid the excessive release of DFIG rotor kinetic energy in the process while ensuring the frequency support effect, thereby reducing the possibility of frequency secondary drop and providing technical support for the operation of high-proportion new energy power grid. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1A flow chart of a coordinated operation control method of multiple wind turbines;

[0028] Figure 2 A DFIG adaptive virtual inertia control diagram;

[0029] Figure 3 A schematic diagram of rotor kinetic energy interaction of two groups of DFIGs. DETAILED DESCRIPTION

[0030] In order to make the technical means, creative features, purposes and effects achieved by the present application easy to understand, the present application will be further described below in combination with specific embodiments.

[0031] Please refer to Figures 1 to 3 , the present application provides the following technical solutions: a coordinated operation control method of multiple wind turbines for avoiding secondary frequency drop, and the specific solutions are as follows:

[0032] First, according to the real-time monitoring of the grid frequency variation, the grid frequency deviation is calculated, and it is judged whether the grid needs to be frequency-regulated, if so, the number of DFIGs required for frequency support is dynamically selected through real-time disturbance power and the level of DFIG rotational speed, and the virtual inertia control parameters are adaptively adjusted according to the system frequency and the DFIG rotational speed variation of the DFIGs participating in the frequency support, so as to meet the frequency support requirements; finally, the remaining DFIGs release the rotor kinetic energy to support the recovery of the selected DFIG rotational speed, so as to reduce the energy absorbed from the grid in this process and reduce the possibility of secondary frequency drop and excessive drop of DFIG rotational speed.

[0033] In order to better understand the above technical solutions, the above technical solutions will be described in detail in combination with the drawings of the specification and specific embodiments.

[0034] Please refer to Figure 1 , Figure 2 and Figure 3 , the present application provides a double-fed wind turbine primary frequency regulation method based on a variable rotational speed coefficient, which specifically includes the following steps:

[0035] S1: acquiring equivalent parameters of a system frequency response model through offline mass data, and dynamically selecting DFIGs required to participate in frequency support after detecting that the system frequency deviation exceeds a threshold value.

[0036] Specifically, as shown in Figure 1 , the offline mass data includes historical frequency drop, load disturbance data, DFIG number n and system wind power penetration rate p. The equivalent parameters of the system frequency response model include the droop coefficient R of the equivalent synchronous machine, the reheating time constant T RH of the turbine, the high-pressure cylinder power proportion coefficient F HP , and the system equivalent inertia time constant H S, equivalent damping coefficient D, etc. The grid frequency deviation Δf satisfies the following relationship expression:

[0037] Δf = f - f N

[0038] In the formula, f is the actual measured frequency of the grid, f N is the rated frequency of the grid; the system frequency deviation threshold is ±0.02 Hz.

[0039] The dynamic selection process of the DFIG participating in frequency support is as follows: when |Δf|≥0.02 Hz, the initial values of the virtual inertia control parameters K Di,0 and K Ii,0 of each DFIG are set, each DFIG is arranged in descending order according to the speed, and iteration is started from k=1 to select the DFIG participating in frequency support each time, that is, the following formula:

[0040]

[0041] After the result of each iteration is calculated, it needs to be compared with the system frequency support constraint, and when the condition shown in the following formula is met, the iteration is stopped, and the k DFIGs meeting the frequency support requirement of this time are obtained.

[0042]

[0043] In the formula, Δf m and |dΔf(t) / dt| m are the maximum frequency drop value and the maximum frequency change value allowed in the system frequency change process. Considering the accuracy of iteration and better frequency support effect, a threshold ε is set to fully guarantee the frequency support level, and k=k+ε is set.

[0044] S2: compare the number of selected DFIGs with the total number of DFIGs, and perform adaptive virtual inertia control based on the frequency change and the rotor kinetic energy of the DFIGs participating in frequency support, to guarantee the frequency support effect.

[0045] Specifically, as shown in Figure 2 , the number k of selected DFIGs is compared with the total number n of DFIGs, if k Di and K Ii will be adaptively adjusted according to the real-time frequency change and the speed of the DFIGs:

[0046]

[0047] where ω r,max and ω r,min are respectively the maximum and minimum values of the rotational speed when the DFIG can operate stably.

[0048] S3: If the number of selected DFIGs is less than the total number of DFIGs, during the rotational speed recovery stage, control the unselected DFIGs to release the stored rotor kinetic energy to support the rotational speed recovery of each DFIG within a certain period of time, and then all DFIGs enter the rotational speed recovery stage until the initial value is restored. Otherwise, all DFIGs enter the rotational speed recovery stage after the frequency support ends.

[0049] Specifically, as Figure 3 shown, in the case of k < n, assume that t1 and t2 are respectively the start time and the exit time of the frequency support. During the period (t1, t2), only the dynamically selected k DFIGs release rotor kinetic energy. After t2, the k DFIGs start to recover the rotational speed. The remaining n - k DFIGs that did not participate in the frequency support stage are used as the second group of wind turbines and release rotor kinetic energy during the period (t2, t2 + 5). The additional power control parameters are set to the initial values K Di,0 and K Ii,0 , and then after t2 + 5, all DFIGs enter the rotational speed recovery stage and restore the rotational speed to the initial value.

[0050] The above shows and describes the basic principles, main features and advantages of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic features of the present invention.

[0051] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for avoiding frequency secondary drop in coordinated operation control of multiple wind turbines, characterized in that, The method comprises the following steps: S1: obtaining equivalent parameters of a frequency response model through an offline mass data acquisition system, and dynamically selecting DFIGs required to participate in frequency support after detecting that the system frequency deviation exceeds a threshold value online; S2: comparing the number of selected DFIGs with the total number of DFIGs, and performing adaptive virtual inertia control based on the frequency variation and the rotor kinetic energy of each DFIG participating in frequency support, so as to guarantee the frequency support effect; S3: if the number of selected DFIGs is less than the total number of DFIGs, controlling the DFIGs not selected to release the stored rotor kinetic energy to support the recovery of the rotational speed of each DFIG within a certain time during the rotational speed recovery stage, and then all DFIGs enter the rotational speed recovery stage until the rotational speed is restored to the initial value, otherwise all DFIGs enter the rotational speed recovery stage after the end of frequency support; The DFIG dynamic selection process participating in frequency support in step S1 is as follows: when |Δf|≥0.02 Hz, set the initial value of the virtual inertia control parameter of each DFIG K Di,0 and K Ii,0 Each DFIG is arranged in descending order according to the speed, and iteration starts from k=1. The effect of the selected DFIG on frequency support is as follows:

2. The method of claim 1, wherein the method further comprises: The off-line mass data in the step S1 includes historical frequency drop, load disturbance data, DFIG number n and system wind power penetration rate p, and the equivalent parameters of system frequency response model include the droop coefficient R of equivalent under-synchronous machine, the reheating time constant T of steam turbine RH , high-pressure cylinder power proportionality coefficient F HP , system equivalent inertia time constant H S , equivalent damping coefficient D.

3. The method of claim 2, wherein the method further comprises: The power grid frequency deviation Δf satisfies the following relationship expression: Δf = f - f N where f is the actual measured frequency of the power grid, f N is the rated frequency of the power grid; and the system frequency deviation threshold in step S1 is ±0.02 Hz.

4. The method of claim 1, wherein the method further comprises: After calculating the result of each iteration, the result needs to be compared with the system frequency support constraint, and when the condition shown in the following formula is met, the iteration is stopped, and k DFIGs meeting the frequency support requirement of this time are obtained: where Δf m and |dΔf(t) / dt| m are the maximum frequency drop value and the maximum frequency change value, respectively, allowed during the system frequency change process.

5. The method of claim 4, wherein the method further comprises: A threshold value ε is set to sufficiently guarantee the frequency support level, and k=k+ε is set.

6. The method of claim 1, wherein the method further comprises: The comparison of the number of selected DFIGs with the total number of DFIGs in the step S2 refers to comparing with the total number n of DFIGs in the wind farm, if k<n, only the DFIGs need to be called to participate in frequency regulation, otherwise all DFIGs in the wind farm need to be fully called to support the frequency.

7. The method of claim 6, wherein the method further comprises: DFIG adaptive virtual inertia control refers to the virtual inertia control parameters K of each DFIG Di With K Ii Will be adapted to the real-time changes in frequency and its rotational speed: In the formula, ω r,max and ω r,min are the maximum and minimum values of the rotational speed of the DFIG when it is able to operate stably.

8. The method of claim 1, wherein the method further comprises: In the case that the number of the selected DFIGs in the step S3 is less than the total number of the DFIGs, t1 and t2 are set as the starting time and the exiting time of the frequency support, respectively, (t1, t2) is the time period, only the rotor kinetic energy of the k DFIGs selected dynamically is released, the k DFIGs start to recover the rotating speed after the time t2, the remaining n-k DFIGs not participating in the frequency support stage are taken as the second group of wind turbines, the rotor kinetic energy of the n-k DFIGs is released in the time period (t2, t2+5), and the additional power control parameter of the n-k DFIGs is set as the initial value K Di,0 and K Ii,0 Then, after the time t2+5, all the DFIGs enter the rotating speed recovery stage and recover the rotating speed to the initial value.

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