Multi-wind turbine generator cooperative operation control method capable of avoiding frequency secondary drop

Abstract

The invention provides a multi-wind turbine generator cooperative operation control method capable of avoiding frequency secondary drop. The method comprises the following steps: firstly, dynamically selecting a DFIG required by frequency support according to the real-time disturbance power of a power grid and the rotating speed level of each DFIG; secondly, according to the system frequency and the rotating speed change condition of the DFIG participating in frequency supporting, the virtual inertia control parameters are adjusted in a self-adaptive mode, and the frequency supporting requirement is met. And finally, controlling other DFIGs to release the kinetic energy of the rotor to support the rotation speed recovery of the selected DFIGs so as to reduce the energy additionally absorbed from the power grid in the process. According to the method, the virtual inertia control parameters are adaptively adjusted according to the system frequency and the rotating speed change condition of the DFIG participating in frequency support, and the frequency support requirement is met. And the other DFIGs are controlled to release the kinetic energy of the rotor to support the rotation speed recovery of the selected DFIG, so that the energy additionally absorbed from the power grid in the process is reduced, the probability of frequency secondary drop and excessive drop of the rotation speed of the DFIG is reduced, and the DFIG performs frequency active support on the system more stably.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy access and control, and in particular to a method for controlling the coordinated operation of multiple wind turbines to avoid secondary frequency drops. Background Art

[0002] As an important part of renewable energy power generation, wind power has the characteristics of cleanness, environmental protection, strong regional adaptability and low operating cost. It has developed 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 power grid through a converter, its rotor speed frequency is completely decoupled and cannot effectively respond to system frequency changes. With the continuous increase in wind power penetration, the system frequency stability continues to decline.

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

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for coordinated operation control of multiple wind turbines to avoid secondary frequency drops, so as to solve the problems raised in the above background technology. The present invention can effectively avoid excessive release of DFIG rotor kinetic energy in the process while ensuring the frequency support effect, thereby reducing the possibility of secondary frequency drops, and can significantly reduce the energy absorbed from the power grid to avoid the occurrence of secondary frequency drops.

[0005] In order to achieve the above object, the present invention is implemented through the following technical solution: a method for controlling the coordinated operation of multiple wind turbines to avoid secondary frequency drop, comprising the following steps:

[0006] S1: Obtain equivalent parameters of the system frequency response model through offline massive data, and dynamically select the DFIG required to participate in frequency support after online detection that the system frequency deviation exceeds the threshold;

[0007] S2: Compare the number of selected DFIGs with the total number of DFIGs, and perform adaptive virtual inertial control based on the frequency change and the rotor kinetic energy of each DFIG supported by the frequency input to ensure the frequency support effect;

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

[0009] Furthermore, the offline massive data in step S1 includes historical frequency drops, load disturbance data, the number of DFIGs n and the system wind power penetration rate ρ, and the equivalent parameters of the system frequency response model include the synchronous machine adjustment coefficient R under the equivalent value, the reheating time constant T of the steam turbine RH , High-pressure cylinder power proportional coefficient F HP , system equivalent inertia time constant H S , equivalent damping coefficient D.

[0010] Furthermore, the grid frequency deviation Δf satisfies the following relational expression:

[0011] Δf=ff N

[0012] 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.

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

[0014]

[0015] Furthermore, after calculating the result of each iteration, it is necessary to compare it with the system frequency support constraint. When the conditions shown in the following formula are met, the iteration is stopped to obtain k DFIGs that meet the frequency support requirements of this time:

[0016]

[0017] Where Δf m and |dΔf(t) / dt| m They are respectively the maximum frequency drop value and the maximum frequency change value allowed during the system frequency change process.

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

[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 this part of DFIGs needs to be called to participate in frequency regulation. Otherwise, all DFIGs in the wind farm need to be fully called for frequency support.

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

[0021]

[0022] 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.

[0023] Further, when the number of selected DFIGs in step S3 is less than the total number of DFIGs, t1 and t2 are set as the start time and exit time of frequency support respectively. During the time period (t1, t2), only the released rotor kinetic energy of the dynamically selected k DFIGs. 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 the rotor kinetic energy during the time period (t2, t2 + 5). Its additional power control parameters are set as the initial values K Di,0 and K Ii,0 , and then after t2 + 5, all DFIGs enter the rotational speed recovery stage and recover the rotational speed to the initial value.

[0024] Advantages of the present invention:

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

[0026] 2. The multi-wind turbine collaborative operation control method for avoiding secondary frequency dips effectively avoids the excessive release of the rotor kinetic energy of DFIGs during this process while ensuring the frequency support effect, thereby reducing the possibility of secondary frequency dips and providing technical support for the operation of a high-proportion new energy power grid. Description of the Drawings

[0027] Figure 1It is a flow chart of the control method for the coordinated operation of multiple wind turbines;

[0028] Figure 2 It is the DFIG adaptive virtual inertial control diagram;

[0029] Figure 3 Schematic diagram of the interaction between the kinetic energy of two groups of DFIG rotors. DETAILED DESCRIPTION

[0030] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0031] See also Figures 1 to 3 The present invention provides the following technical solution: a method for controlling the coordinated operation of multiple wind turbines to avoid secondary frequency drops, and the specific solution is as follows:

[0032] Firstly, based on the real-time monitoring of grid frequency changes, the grid frequency deviation is calculated to determine whether the grid needs frequency modulation. If so, the number of DFIGs required for frequency support is dynamically selected through the real-time disturbance power and the speed level of each DFIG. The virtual inertia control parameters are adaptively adjusted according to the changes in the system frequency and the speed of the DFIGs participating in the frequency support to meet the frequency support requirements. Finally, the remaining DFIGs are controlled to release the rotor kinetic energy to support the speed recovery of the selected DFIG, so as to reduce the extra energy absorbed from the grid in the process and reduce the possibility of secondary frequency drop and excessive speed drop of the DFIG.

[0033] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0034] See also Figure 1 , Figure 2 and Figure 3 The embodiment of the present invention provides a primary frequency modulation method of a doubly-fed wind turbine generator system based on a variable speed coefficient, which specifically includes the following steps:

[0035] S1: Obtain the equivalent parameters of the system frequency response model through offline massive data, and dynamically select the DFIG required to participate in frequency support after online detection that the system frequency deviation exceeds the threshold.

[0036] Specifically, Figure 1 As shown in the figure, the offline massive data includes historical frequency drops, load disturbance data, the number of DFIGs n and the system wind power penetration rate ρ. The equivalent parameters of the system frequency response model include the synchronous machine adjustment coefficient R under the equivalent value, the reheating time constant T of the steam turbine RH , High-pressure cylinder power proportional coefficient F HP , system equivalent inertia time constant H S, equivalent damping coefficient D, etc. The grid frequency deviation Δf satisfies the following relational expression:

[0037] Δf = f - f N

[0038] where f is the actually measured grid frequency, and f N is the rated grid frequency; the system frequency deviation threshold is ±0.02 Hz.

[0039] The dynamic selection process of DFIGs participating in frequency support is as follows: When |Δf| ≥ 0.02 Hz, set the initial values of the virtual inertia control parameters K Di,0 and K Ii,0 for each DFIG, arrange all DFIGs in descending order according to their rotational speeds, and select k = 1 to start iterating. The effect of frequency support for each selected DFIG is given by the following formula:

[0040]

[0041] After calculating the results of each iteration, it is necessary to compare with the system frequency support constraint. When the conditions shown in the following formula are met, stop the iteration and obtain k DFIGs that meet the frequency support requirements of this time.

[0042]

[0043] where Δf m and |dΔf(t) / dt| m are respectively the maximum allowable frequency drop value and the maximum frequency change value during the system frequency change process. Considering the iteration accuracy problem and better frequency support effect, a threshold ε will be 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 situation and the rotor kinetic energy of each DFIG participating in frequency support to ensure the frequency support effect.

[0045] Specifically, as Figure 2 shown, compare the number k of selected DFIGs with the total number n of DFIGs. If k < n, only this part of DFIGs need to be called to participate in frequency regulation, otherwise all DFIGs in the wind farm need to be fully called for frequency support. DFIG adaptive virtual inertia control means that the virtual inertia control parameters K Di and K Ii of each DFIG will be adaptively adjusted according to the real-time frequency change and its rotational speed:

[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 time, and then all DFIGs enter the rotational speed recovery stage until they recover to the initial value. Otherwise, all DFIGs enter the rotational speed recovery stage after the end of frequency support.

[0049] Specifically, as Figure 3 shown, when k < n, assume that t1 and t2 are respectively the start time and the exit time of frequency support. During the time 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 time 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 recover 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 without departing from the spirit or basic features of the present invention, the present invention can be implemented in other specific forms.

[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 controlling the coordinated operation of multiple wind turbines to avoid secondary frequency drops, characterized in that: It includes the following steps: S1: Obtain the equivalent parameters of the system frequency response model through the offline massive data. After the system frequency deviation is detected online and exceeds the threshold, dynamically select the DFIGs required to participate in the frequency support. S2: Compare the number of selected DFIGs with the total number of DFIGs, and perform adaptive virtual inertia control based on the frequency change situation and the rotor kinetic energy of each DFIG participating in the frequency support to ensure the frequency support effect. S3: If the number of selected DFIGs is less than the total number of DFIGs, during the speed recovery stage, control the unselected DFIGs to release the stored rotor kinetic energy to support the speed recovery of each DFIG within a certain time, and then all DFIGs enter the speed recovery stage until they recover to the initial value. Otherwise, all DFIGs enter the speed recovery stage after the frequency support ends.

2. A method for controlling the coordinated operation of multiple wind turbines to avoid secondary frequency drops according to claim 1, characterized in that: The offline massive data in step S1 includes historical frequency drops, load disturbance data, the number of DFIGs n and the system wind power penetration rate ρ, and the equivalent parameters of the system frequency response model include the synchronous machine adjustment coefficient R under the equivalent value, the reheating time constant T of the steam turbine RH , High-pressure cylinder power proportional coefficient F HP , system equivalent inertia time constant H S , equivalent damping coefficient D.

3. A method for controlling the coordinated operation of multiple wind turbines to avoid secondary frequency drops according to claim 2, characterized in that: The grid frequency deviation Δf satisfies the following relational 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 for controlling the coordinated operation of multiple wind turbines to avoid secondary frequency drop according to claim 1 is characterized in that: The dynamic selection process of the DFIG participating in the frequency support in step S1 is as follows: When |Δf|≥0.02Hz, set the initial value K of each DFIG virtual inertial control parameter Di,0 With K Ii,0 , arrange the DFIGs in descending order according to the speed, select k = 1 to start iteration, and the effect of frequency support of each selected DFIG is as follows:

5. The method for controlling the coordinated operation of multiple wind turbines to avoid secondary frequency drop according to claim 4 is characterized in that: After calculating the result of each iteration, it is necessary to compare it with the system frequency support constraint. After meeting the conditions shown in the following formula, stop the iteration and obtain k DFIGs that meet the frequency support requirements of this time: Where Δf m and |dΔf(t) / dt| m They are respectively the maximum frequency drop value and the maximum frequency change value allowed during the system frequency change process.

6. A method for controlling the coordinated operation of multiple wind turbines to avoid secondary frequency drops according to claim 5, characterized in that: Set a threshold ε to fully ensure the frequency support level, and set k = k + ε.

7. The method for controlling the coordinated operation of multiple wind turbines to avoid secondary frequency drop according to claim 1, characterized in that: 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 this part of DFIGs needs to be called to participate in the frequency regulation. Otherwise, all DFIGs in the wind farm need to be fully called for frequency support.

8. The method for controlling the coordinated operation of multiple wind turbines to avoid secondary frequency drops according to claim 7 is characterized in that: DFIG adaptive virtual inertia control refers to the virtual inertia control parameter K of each DFIG. Di With K Ii It will be adaptively adjusted according to the real-time changes in frequency and its speed: In the formula, ω r,max With ω r,min They are respectively the maximum and minimum speeds at which DFIG can operate stably.

9. The method for controlling the coordinated operation of multiple wind turbines to avoid secondary frequency drop according to claim 1, characterized in that: When the number of DFIGs selected in step S3 is less than the total number of DFIGs, t1 and t2 are set as the frequency support start time and exit time respectively. In the time period (t1, t2), only the dynamically selected k DFIGs release the rotor kinetic energy. After time t2, the k DFIGs begin to recover the speed. The remaining nk DFIGs that do not participate in the frequency support stage are used as the second group of fans. They release the rotor kinetic energy in the time period (t2, t2+5). The additional power control parameter is set to the initial value K. Di,0 With K Ii,0 , and then after time t2+5, all DFIGs enter the speed recovery phase and restore the speed to the initial value.

Images