A fan virtual inertia evaluation method and system based on variable frequency extreme time

Abstract

The application discloses a fan virtual inertia evaluation method and system based on variable frequency extreme time, first, a fan virtual inertia evaluation method is proposed according to the frequency response characteristics of a wind power grid-connected system; second, a frequency response simplified model of a high-permeability wind power system is established and variable frequency extreme time is calculated; third, the running state constraint of the fan is determined according to the initial rotating speed of the fan; then, the rotating speed change range and the virtual inertia range of the fan within the variable frequency extreme time are evaluated according to the variable frequency extreme time constraint and the running state constraint. The method can quantitatively evaluate the virtual inertia of the fan within the variable frequency extreme time. The fan virtual inertia evaluation method based on the variable frequency extreme time can evaluate the virtual inertia range of the fan within the variable frequency extreme time under different initial rotating speeds, and provide reliable inertia support data for the frequency response of the fan.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of inertia evaluation of new energy high penetration power system, and particularly relates to a wind turbine virtual inertia evaluation method and system based on variable frequency extreme time. BACKGROUND

[0002] The wind turbine can have similar inertia response ability as the synchronous machine through additional control, but the virtual rotational inertia through additional control is different from the constant inherent inertia of the synchronous machine, and is not only dependent on the inherent inertia, initial speed and control parameters of the wind turbine, but also closely related to the system frequency change, resulting in complex and variable characteristics, but also more flexible and controllable. At present, it is difficult to evaluate the virtual inertia of the wind turbine, and further research is needed. Since the initial wind speed determines the kinetic energy reserve of the wind turbine, and the speed of the wind turbine is simultaneously affected by the power tracking control, additional inertia control and system frequency characteristics, the virtual inertia is always in dynamic change, which is not only complex to quantify, but also has operation risks. Therefore, there is an urgent need for a wind turbine virtual inertia evaluation method and system based on variable frequency extreme time, which can constrain multiple variables through reasonable time scale to complete the virtual inertia evaluation of the wind turbine. SUMMARY

[0003] In order to solve the above technical problems, the purpose of the present application is to provide a wind turbine virtual inertia evaluation method and system based on variable frequency extreme time, which can evaluate the speed change range and virtual inertia range of the wind turbine under different initial speeds according to the variable frequency extreme time and the running state of the wind turbine.

[0004] In order to achieve the above technical purpose, the present application provides a wind turbine virtual inertia evaluation method based on variable frequency extreme time, comprising the following steps:

[0005] Obtain the variable frequency extreme time of the wind power grid-connected system, wherein the variable frequency extreme time is used to represent the time experienced by the frequency from the initial value falling or rising to the maximum frequency deviation after the system is disturbed;

[0006] According to the initial speed of the wind turbine, the first maximum speed change of the wind turbine under the kinetic energy reserve constraint and the second maximum speed change of the wind turbine under the wind turbine power constraint are obtained to generate the maximum speed change of the wind turbine;

[0007] Based on the maximum speed change, the virtual inertia of the wind turbine is evaluated through the variable frequency extreme time to generate the maximum inertia time constant of the wind turbine.

[0008] Preferably, in the process of obtaining the variable frequency extreme time of the wind power grid-connected system, the first frequency response of the synchronous machine, the wind turbine and the load is obtained to generate the second frequency response of the wind power high penetration system after the wind turbine is disturbed by power;

[0009] The system power disturbance is equivalent to a step disturbance without considering the inertia response of the fan, and the variable frequency extreme time is obtained.

[0010] Preferably, in the process of generating the second frequency response, the expression of the second frequency response is:

[0011]

[0012] wherein ΔP d is the load surge, ΔP w is the fan power response signal, G(t) is a transfer function between the power response signal and the frequency response signal, b, c, w, ζ, are calculation parameters, k is the wind power penetration, K L is the load adjustment coefficient, σ is the difference coefficient, D is the system damping coefficient, and t is the frequency response time.

[0013] The calculation parameters are expressed as:

[0014]

[0015] Preferably, in the process of obtaining the first frequency response of the synchronous machine, the fan and the load, the expression of the first frequency response is:

[0016]

[0017] wherein ΔP m is the synchronous machine power response signal; ΔP L is the load power response signal; H is the system inertia time constant, and Δf represents the frequency deviation.

[0018] Preferably, in the process of obtaining the synchronous machine power response signal, the synchronous machine power response signal is expressed as:

[0019]

[0020] wherein a is a turbine characteristic coefficient, T is an equivalent inertia time constant of the turbine, and Δf is the frequency deviation.

[0021] Preferably, in the process of obtaining the system inertia time constant, the system inertia time constant depends on the system capacity and the wind power penetration, and is expressed as:

[0022]

[0023] wherein H g is the inertia time constant of the synchronous machine; S g is the installed capacity of the synchronous machine; and S B is the total capacity of the system.

[0024] Preferably, in the process of acquiring the variable frequency extreme value time of the wind power grid-connected system, the variable frequency extreme value time tf m is expressed as:

[0025]

[0026] Preferably, in the process of acquiring the maximum speed variation amount, the kinetic energy reserve constraint is expressed as:

[0027]

[0028] In the formula, ΔE kwmax is the kinetic energy reserve of the wind turbine; ω r0 is the initial speed before the inertia response of the wind turbine; ω min , ω max are the minimum speed and the maximum speed allowed for stable operation of the wind turbine, and are usually 0.7pu and 1.2pu;

[0029] Under the kinetic energy reserve constraint, the first maximum speed variation amount Δω rmax1 is expressed as:

[0030]

[0031] In the formula, Δω r is the speed variation amount of the wind turbine;

[0032] The wind turbine power constraint is expressed as:

[0033]

[0034] In the formula, P n is the rated power of the wind turbine; P min is the power corresponding to the minimum speed for stable operation of the wind turbine; P opt is the active output power of the wind turbine under MPPT control; k opt is the maximum power tracking coefficient; ω r0 is the initial speed of the wind turbine; ω min is the minimum speed allowed for stable operation of the wind turbine; ΔP d is the power disturbance;

[0035] Under the wind turbine power constraint, the second maximum speed variation amount Δω rmax2 is expressed as:

[0036]

[0037] In the formula, k opt is the maximum power tracking coefficient; ω r0 is the initial speed of the wind turbine; P n is the rated power of the wind turbine; H w is the inherent inertia time constant of the wind turbine.

[0038] Preferably, in the process of acquiring the maximum inertia time constant of the fan, the maximum inertia time constant H vir is expressed as:

[0039]

[0040] In the formula, λ opt is the optimal tip speed ratio; v is the real-time wind speed; R is the radius of the wind wheel, ω max is the maximum rotational speed allowed for stable operation of the fan; v min is the cut-in wind speed; v max is the maximum wind speed before the start of the pitch control.

[0041] The application discloses a fan virtual inertia evaluation system based on a variable-frequency extreme time, which is used for quantitatively evaluating the virtual inertia of a fan within a variable-frequency extreme time and comprises the following steps:

[0042] A variable-frequency extreme time generation module is configured to acquire a variable-frequency extreme time of a wind power grid-connected system, wherein the variable-frequency extreme time is used to represent a time during which the frequency of the system falls or rises from an initial value to a maximum frequency deviation after the system is disturbed;

[0043] A maximum rotational speed variation generation module is configured to acquire a first maximum rotational speed variation of a fan under kinetic energy reserve constraint and a second maximum rotational speed variation of the fan under fan power constraint according to an initial rotational speed of the fan, and generate a maximum rotational speed variation of the fan.

[0044] An evaluation module is configured to evaluate the virtual inertia of the fan based on the maximum rotational speed variation and the variable-frequency extreme time, and acquire a maximum inertia time constant of the fan.

[0045] The application discloses the following technical effects:

[0046] The application realizes quantitative evaluation of the virtual inertia of the fan within the variable-frequency extreme time, and fills the technical gap in the field. DETAILED DESCRIPTION

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0048] Figure 1 is a flow chart of the fan virtual inertia evaluation method based on the variable-frequency extreme time according to the embodiments of the present application;

[0049] Figure 2 is a power support and system frequency dynamic response curve of a generator set of an embodiment of the present application;

[0050] Figure 3 is a simplified model of a system frequency response of a high-wind-power-proportion system of an embodiment of the present application;

[0051] Figure 4 is a frequency response curve of a high-wind-power-proportion system of an embodiment of the present application under different wind power penetrations;

[0052] Figure 5 is an evaluation result of a maximum speed variation of a wind turbine of an embodiment of the present application;

[0053] Figure 6 is an evaluation result of a maximum virtual inertia of a wind turbine of an embodiment of the present application;

[0054] Figure 7 is a topology diagram of a simulation system of a high-wind-power-proportion system of an embodiment of the present application;

[0055] Figure 8 is a frequency response curve of a simulation system of an embodiment of the present application after a load surge occurs;

[0056] Figure 9 is a wind turbine power and speed response curve of a simulation system of an embodiment of the present application after a load surge occurs. DETAILED DESCRIPTION

[0057] To make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application. The components of the embodiments of the present application described and shown in the accompanying drawings can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0058] As shown in Figures 1-9 , the present application provides a wind turbine virtual inertia evaluation method and system based on variable-frequency extreme value time, to make the above-mentioned purposes, features and advantages of the present application more obvious and understandable, the present application will be described in further detail below with reference to the accompanying drawings and specific embodiments.

[0059] Figure 1 is a flowchart of a wind turbine virtual inertia evaluation method based on variable-frequency extreme value time of an embodiment of the present application, as shown in Figure 1 , the method comprises the following steps:

[0060] Step 1: A wind turbine virtual inertia evaluation method is proposed according to the frequency response characteristics of the wind power grid-connected system;

[0061] Step 2: A simplified frequency response model of the high-penetration wind power system is established, and the variable frequency extreme time is calculated;

[0062] Step 3: The operating state constraint of the wind turbine is determined according to the initial speed of the wind turbine;

[0063] Step 4: The speed variation range and virtual inertia range of the wind turbine within the variable frequency extreme time are evaluated according to the variable frequency extreme time constraint and the operating state constraint.

[0064] After the active disturbance of the high-penetration wind power system, the system frequency support should be completed by the synchronous generator set and the wind turbine. In order to improve the utilization rate of wind energy, the current wind farm usually does not use the load shedding operation mode to reserve standby for primary frequency regulation. In this mode, the virtual inertia response will be the active frequency support function that the wind power urgently needs to have. In the wind power grid-connected system, the synchronous generator and the wind turbine should jointly complete the inertia support.

[0065] Taking a short-term frequency drop as an example, Figure 2 is the power support curve of the generator set and the dynamic response curve of the system frequency. Let t0 be the frequency drop time, t b be the primary frequency action time, t fm be the time when the frequency drops to the lowest value, and t p be the end time of the primary frequency regulation. If the load suddenly increases ΔP d at t0, the system frequency will drop sharply, and the synchronous generator set and the wind turbine need to quickly respond to the frequency change and compensate the system power demand through fast active power support, i.e. ΔP e = ΔP d .

[0066] t0~t fm stage: After the wind turbine starts the inertia support control, it will share the unbalanced power borne by the synchronous generator, thereby slowing down the system frequency drop speed. The common virtual inertia control of the wind turbine uses a differential element, and the power response is as follows:

[0067] ΔP w = -K I ×df / dt (1)

[0068] In the formula, ΔP w is the inertia support power of the wind turbine; K I is the differential control coefficient; and df / dt is the frequency change rate. During the frequency drop (df / dt < 0), the power response ΔP w>0. In this phase, the synchronous generator and the wind turbine jointly maintain the inertia support power and meet the load demand ΔP d , the wind turbine reduces the kinetic energy demand of the synchronous generator by releasing kinetic energy.

[0069] t fm ~t p Phase: during frequency recovery (df / dt>0), at this time the power response of virtual inertia ΔP w <0. In this phase, the wind turbine absorbs power from the system under virtual inertia control, and the wind turbine changes from releasing kinetic energy to absorbing kinetic energy, increasing the primary frequency regulation burden of the synchronous generator, causing the frequency recovery speed to slow down.

[0070] Considering the grid connection safety problem of virtual inertia, at present, GB / T19963.1-2021 “Technical Regulation for Wind Farm Integration into Power System” has stipulated that the wind turbine needs to have inertia support function after accessing the system, but the starting additional controller needs to meet the condition: Δf×df / dt>0. Obviously, the wind turbine should set the time t fm as the end time of virtual inertia control to meet the grid connection requirement.

[0071] It is worth noting that determining the inertia support end time t fm , the frequency signal at the grid connection point of the wind turbine needs to be detected, and the differential signal has high-frequency noise in the field test. Combined with the actual test situation, it is difficult to realize the condition that Δf×df / dt is greater than zero. In addition, at the inertia support end time, the wind turbine has released kinetic energy, causing the speed to decrease. After recovering to the maximum power tracking control, since the wind turbine speed has decreased, the output power of the wind turbine will still be lower than the initial level before the frequency drop. Therefore, even if the inertia control can end in time, the wind turbine will still absorb power, accelerate the rotor, store kinetic energy, and complete the maximum power tracking goal, but this will be not conducive to the frequency recovery in the primary frequency regulation process.

[0072] According to the above analysis, during the frequency active support period, the virtual inertia control of the wind turbine cannot continuously provide effective active power support for the system, and combined with the inertia starting condition stipulated in the grid connection standard, the effective time of inertia response is defined as the frequency extreme value time t fm , that is, the time experienced by the system after suffering disturbance, the frequency drops or rises from the initial value to the maximum frequency deviation.

[0073] Obviously, before adopting virtual inertia control, if the fan can estimate the frequency conversion extreme value time, it will not only ensure the safety of additional control, effectively avoid erroneous operation caused by large frequency differential signal monitoring errors, but also help solve the current problems that plague the quantitative evaluation of virtual inertia, and thus provide a more reliable calculation method for the inertia demand under system frequency safety.

[0074] To solve this problem, a time scale must be introduced to constrain the virtual inertia. The present invention uses the frequency conversion extreme value time as the effective time of the inertial response of the fan, and fm Internal, Δω e With Δf max If the per-unit values ​​are equal, the fan virtual inertia time constant H vir It can be expressed as:

[0075]

[0076] Where Δω r is the change in fan speed; H w is the inherent inertia time constant of the fan; Δf max is the frequency deviation extreme value; ω r0 is the initial speed of the fan before inertial response; opt is the optimal tip speed ratio; v is the real-time wind speed; R is the rotor radius; ω max The maximum speed allowed for stable operation of the fan; v min is the cut-in wind speed; v max The maximum wind speed before pitch control is activated.

[0077] According to the above formula, when other parameters are known, Δω r Decided H vir The size of the fan's virtual inertia can be quantitatively assessed based on the speed change during the frequency conversion extreme time. Therefore, calculating the system frequency conversion extreme time and obtaining the speed change after the fan inertia response is the key to evaluating the fan's virtual inertia.

[0078] Figure 3 It is a simplified model of the system response with high wind power penetration. The frequency response of the high wind power penetration system after power disturbance can be regarded as composed of the frequency responses of the synchronous machine, wind turbine and load, which can be expressed as:

[0079]

[0080] Where ΔP m is the synchronous machine power response signal; ΔP w is the wind turbine power response signal; ΔP L is the load power response signal; H is the system inertia time constant. mDepending on the damping coefficient of the synchronous machine and the turbine parameters, is expressed as:

[0081]

[0082] wherein k is the wind power penetration rate; σ is the damping coefficient; a is the turbine characteristic coefficient, T is the equivalent inertia time constant of the turbine, Δf is the frequency deviation; ΔP L Depending on the load regulation coefficient, is expressed as:

[0083] ΔP L = K L × Δf (5)

[0084] wherein K L is the load regulation coefficient. H is then dependent on the system capacity and the wind power penetration rate, and is expressed as:

[0085]

[0086] wherein H g is the inertia time constant of the synchronous machine; S g is the installed capacity of the synchronous machine; S B is the total system capacity, and the system frequency response Δf(t) can be calculated according to the above analysis and is expressed as:

[0087]

[0088] wherein G(t) is the transfer function between the power response signal and the frequency response signal, b, c, w, ζ, are the calculation parameters and are expressed as follows:

[0089]

[0090] Without considering the inertia response of the wind turbine, the system power disturbance is equivalent to a step disturbance, and the above equation is solved to obtain the frequency variation extreme time t fm of the system, which can be expressed as:

[0091]

[0092] Figure 4 is the frequency response curve of the embodiment of the present application under different wind power penetration rates; by substituting the typical parameters of the synchronous machine into the above equation, it can be calculated that when the wind power penetration rate is 0%, 20% and 40%, the frequency variation extreme time t fm of the system is respectively 2.305s, 2.298s and 2.295s. Therefore, when the inertia of the wind turbine is evaluated within the frequency variation extreme time, the frequency variation extreme time t fm may be equal to 2.3s. Within this time, the change in the speed of the wind turbine can be calculated through the operating state constraint of the wind turbine, and the virtual inertia of the wind turbine can be estimated.

[0093] The operating state constraints of the wind turbine include kinetic energy reserve constraint and wind turbine power constraint. Firstly, the wind turbine virtual inertia depends on its kinetic energy reserve, which is closely related to the initial rotational speed ω r0 ; in addition, the wind turbine initial active power P we0 determines the adjustment range of the power support ΔP w , and further affects the wind turbine kinetic energy release or absorption capacity.

[0094] 1) Kinetic energy reserve constraint

[0095] The wind turbine kinetic energy reserve depends on the rotational speed change allowance value within the variable frequency extreme time period. When the disturbance power ΔP d > 0, the system appears power shortage, and the wind turbine needs to release the rotor kinetic energy; when ΔP d < 0, the system has power surplus, and the wind turbine needs to absorb energy and store it as rotor kinetic energy. Therefore, the kinetic energy reserve constraint of the wind turbine can be expressed as:

[0096]

[0097] In the formula, ΔE kwmax is the wind turbine kinetic energy reserve; ω r0 is the wind turbine rotational speed at the beginning of the inertia response; ω min and ω max are the allowable minimum rotational speed and the maximum rotational speed of the wind turbine stable operation, and are usually 0.7pu and 1.2pu. Under the kinetic energy reserve constraint, the change range of Δω r within the variable frequency extreme time is expressed as:

[0098]

[0099] In the formula, Δω rmax1 is the maximum rotational speed change under the kinetic energy reserve constraint.

[0100] 2) Wind turbine power constraint

[0101] In order to ensure the safety of the wind turbine operation, the support power provided by the virtual inertia control is not allowed to exceed the limit. According to the rated power and the minimum power of the wind turbine during grid-connected operation, the wind turbine power constraint can be expressed as:

[0102]

[0103] In the formula, P n is the rated power of the wind turbine; P min is the power corresponding to the minimum rotational speed of the wind turbine stable operation; P opt is the active output power of the wind turbine under MPPT control; k opt is the maximum power tracking coefficient; ω r0 is the initial rotational speed of the wind turbine; ωmin The minimum allowable speed of the fan for stable operation; ΔP d The power disturbance.

[0104] In the process of inertia response, the rotor motion equation of the wind turbine can be expressed as:

[0105]

[0106] In the formula, P we The electromagnetic power output by the fan; P wm The mechanical power captured by the fan; H w The inherent inertia time constant of the fan; ω r The speed of the fan; ΔP w The power response signal of the fan.

[0107] Simultaneous equations (12), (13), under the constraint of the fan power, the maximum speed change Δω r The range of variation is:

[0108]

[0109] In the formula, Δω rmax2 The maximum speed change under the constraint of the fan power; k opt The maximum power tracking coefficient; ω r0 The initial speed of the fan; P n The rated power of the fan; H w The inherent inertia time constant of the fan; t fm The frequency conversion extreme time; ΔP d The power disturbance.

[0110] In order to meet the kinetic energy reserve constraint and the fan power constraint at the same time, the maximum speed change Δω rmax of the fan can be expressed as:

[0111] Δω rmax = min{Δ rmax1 , Δω rmax2} (15)

[0112] In the formula, Δω rmax1 The maximum speed change under the constraint of the kinetic energy reserve; Δω rmax2 The maximum speed change under the constraint of the fan power.

[0113] Taking the typical parameters of a 2MW doubly-fed wind turbine as an example, H w = 4s, k opt = 1 / 1.2 3 , ω min = 0.7pu, ωmax ＝ 1.2pu, tfm = 2.3 s. Figure 5 is the evaluation result of the maximum speed variation of the fan in the embodiment of the application. When ΔP d > 0, the fan needs to release the kinetic energy of the rotor, and when the initial speed of the fan is small, the kinetic energy reserve is small but the inertial support power that can be provided is large, and at this time, Δω rmax is determined by the kinetic energy reserve constraint; when the initial speed of the fan is large, the kinetic energy reserve is large but the inertial support power that can be provided is small, and at this time, Δω max is determined by the power constraint of the fan. When the initial speed of the fan is 0.905 pu, Δω rmax1 = Δω rmax2 , and at this initial speed, Δω rmax reaches a maximum of 0.205 pu. When ΔP d < 0, the fan needs to absorb energy, and Δω rmax is related to the speed constraint in a manner completely opposite to that when ΔP d < 0, and when the initial speed of the fan is small, Δω rmax is determined by the power constraint of the fan, and when the initial speed of the fan is large, Δω rmax is determined by the kinetic energy reserve constraint, and when the initial speed of the fan is 1.07 pu, Δω rmax reaches a maximum of 0.13 pu.

[0114] In summary, within the frequency extreme time, when ΔP d > 0, the range of the speed variation that can be provided by the fan under the constraint of the operating state of the fan is 0-0.205 pu; and when ΔP d < 0, the range of the speed variation that can be provided by the fan under the constraint of the operating state of the fan is 0-0.13 pu.

[0115] As can be seen from equation (5), the size also depends on Δf max . Since the lower limit of the frequency safety of the power system is 48 Hz, the fan should limit the frequency deviation extreme value of the system within this range after the inertial response. Obviously, since the fan has fast power response capability, the fan can be set to complete the predetermined virtual inertia support within the frequency safety range. Therefore, the application takes Δf max = 2 Hz, which is used to conservatively estimate the virtual inertia of the fan. According to the evaluation result of Δω rmax , within the frequency extreme time, the maximum inertial time constant H virmax of the fan can be expressed as:

[0116] H virmax = min{H virmax1 , H virmax2}

[0117] In the equation, H virmax1 , H virmax2The maximum inertia time constant of the fan under the rotor kinetic energy constraint and the power constraint, respectively.

[0118] Figure 6 is the maximum virtual inertia evaluation result of the fan in the embodiment of the application. When ΔP d < 0, the fan releases rotor kinetic energy and the speed decreases, and H virmax is determined by the rotor kinetic energy constraint, H virmax is determined by the fan power constraint, and H virmax ranges from 0 to 18.61 s; when ΔP d < 0, the fan absorbs energy and the speed increases, and H virmax is determined by the fan power constraint, H virmax is determined by the rotor kinetic energy constraint, and H virmax ranges from 0 to 13.85 s.

[0119] However, Δf max is related to the disturbance power, and when the disturbance power is small, Δf max is less than 2 Hz, and at this time, H virmax of the fan will be greater than the evaluation result, and the fan can be ensured to have reliable inertia support capability.

[0120] Figure 7 is a topology diagram of a high wind power penetration simulation system in the embodiment of the application, and the three-machine simulation system of the wind farm is built based on the DIGSILENT / PowerFactory simulation platform, the simulation system includes two synchronous generators with a capacity of 350 MVA and one double-fed wind turbine generator unit (DFIG) with 150 units×2 MW, the wind power penetration rate is 30%, and a 30% load surge is set to occur at t=2 s. The accuracy of the virtual inertia evaluation method of the fan based on the variable-frequency extreme time proposed in the application is verified under the initial speeds of 0.8 pu and 1.1 pu, respectively.

[0121] Figure 8 is a frequency response curve of the simulation system in the embodiment of the application after the load surge occurs; Figure 9 is a fan power and speed response curve of the simulation system in the embodiment of the application after the load surge occurs. According to Figure 8 , 9 , when the initial speed of the fan is 1.1 pu, H Figure 5 , 6 According to theoretical analysis, the maximum speed change of the fan within t fm is 0.062 pu, and the maximum inertia is 7.44 s. As shown in Figure 8 , 9 , when ΔP d>0, the rotor kinetic energy of the fan can be released, although it is larger, but due to the power constraint, the speed change of the fan in the variable frequency extreme time is only 0.06pu, which can improve the maximum frequency deviation by 0.3Hz, and the maximum inertia H vir =7.56s.

[0122] When the initial speed of the fan ω r0 =0.8pu, the maximum speed change of the fan in t fm is 0.1pu, and the maximum inertia is 8s. As shown in FIGS. Figure 8 9 Due to the constraint of the rotor kinetic energy reserve, the inertia response exits immediately after the speed of the fan drops to the minimum value of 0.7pu in the variable frequency extreme time, which will cause the frequency to drop twice, but due to the large inertia support power provided at this speed, the maximum frequency deviation can be improved by 0.4Hz, and the maximum inertia H vir =10s exhibited by the fan in the variable frequency extreme time. The simulation results are close to the calculation results, which verifies the accuracy of the virtual inertia evaluation method of the fan based on the variable frequency extreme time.

[0123] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms is not necessarily directed to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, different embodiments or examples described in the present specification and the features of different embodiments or examples can be combined and combined by those skilled in the art without contradiction.

[0124] Although the embodiments of the present application have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

[0125] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer usable program code.​

Claims

1. A method for evaluating virtual inertia of a wind turbine based on variable frequency extreme time, characterized in that: The following steps are involved: Obtaining the frequency conversion extreme value time of the wind power grid-connected system, wherein the frequency conversion extreme value time is used to represent the time it takes for the frequency to drop or rise from the initial value to reach the maximum value after the system is disturbed; generating a maximum speed variation of the fan by obtaining, according to the initial speed of the fan, a first maximum speed variation of the fan under a kinetic energy reserve constraint and a second maximum speed variation of the fan under a fan power constraint; Based on the maximum speed change, the fan is evaluated for virtual inertia by using the frequency conversion extreme time to generate a maximum inertia time constant of the fan; In the process of obtaining the frequency conversion extreme value time of the wind power grid-connected system, a second frequency response of the wind power high penetration system of the wind turbine is generated after being subjected to a power disturbance by obtaining the first frequency response of the synchronous machine, the wind turbine and the load; Without considering the inertial response of the wind turbine, the system power disturbance is equivalent to a step disturbance to obtain the frequency conversion extreme value time; In the process of obtaining the first frequency response of the synchronous machine, the fan and the load, the expression of the first frequency response is: Where ΔP m is the synchronous machine power response signal; ΔP L is the load power response signal; H is the system inertia time constant; In the process of obtaining the synchronous machine power response signal, the synchronous machine power response signal is expressed as: Where a is the turbine characteristic coefficient, T is the turbine equivalent inertia time constant, and Δf is the frequency deviation; In the process of obtaining the system inertia time constant, the system inertia time constant depends on the system capacity and wind power penetration rate, and is expressed as: Where H g is the inertia time constant of the synchronous machine; S g is the installed capacity of synchronous machine; S B is the total system capacity; In the process of generating the second frequency response, the expression of the second frequency response is: Where ΔP d is the power disturbance signal, ΔP w is the wind turbine power response signal, G(t) is the transfer function between the power response signal and the frequency response signal, b, c, w, ζ, is the calculation parameter, k is the wind power penetration rate, K L is the load adjustment coefficient, σ is the adjustment coefficient, D is the system damping coefficient, and t is the frequency response time; The calculation parameters are expressed as: In the process of obtaining the frequency conversion extreme value time of the wind power grid-connected system, the frequency conversion extreme value time t fm Expressed as:

2. The method for evaluating wind turbine virtual inertia based on frequency conversion extreme time according to claim 1, characterized in that: In the process of obtaining the maximum speed change, the kinetic energy reserve constraint is expressed as: Where, ΔE kwmax For wind power reserve; r0 is the initial speed of the fan before inertial response; ω min 、ω max The minimum and maximum speeds allowed for stable operation of the fan are 0.7 pu and 1.2 pu respectively; Under the kinetic energy reserve constraint, the first maximum speed change Δω rmax1 Expressed as: Among them, Δω r is the change in fan speed; The wind turbine power constraint is expressed as: Where, P n is the rated power of the fan; k opt is the maximum power tracking coefficient; ω r0 is the initial speed of the fan; ω min The minimum speed allowed for stable operation of the fan; ΔP d is the power disturbance; Under the fan power constraint, the second maximum speed change Δω rmax2 Expressed as: Where k opt is the maximum power tracking coefficient; ω r0 is the initial speed of the fan; P n is the rated power of the fan; H w is the inherent inertia time constant of the fan.

3. The method for evaluating wind turbine virtual inertia based on frequency conversion extreme time according to claim 2, characterized in that: In the process of obtaining the maximum inertia time constant of the wind turbine, the maximum inertia time constant H vir Expressed as: Where λ opt is the optimal tip speed ratio; v is the real-time wind speed; R is the rotor radius, ω max The maximum speed allowed for stable operation of the fan; v min is the cut-in wind speed; v max The maximum wind speed before pitch control is activated.

4. A wind turbine virtual inertia evaluation system based on variable frequency extreme time, applied to the wind turbine virtual inertia evaluation method based on variable frequency extreme time according to any one of claims 1 to 3, characterized in that: include: A frequency conversion extreme value time generation module is used to obtain the frequency conversion extreme value time of the wind power grid-connected system, wherein the frequency conversion extreme value time is used to represent the time it takes for the frequency to drop or rise from the initial value to reach the maximum value after the system is disturbed; a maximum speed variation generating module, configured to generate a maximum speed variation of the fan by obtaining, based on the initial speed of the fan, a first maximum speed variation of the fan under a kinetic energy reserve constraint and a second maximum speed variation of the fan under a fan power constraint; An evaluation module is configured to evaluate the virtual inertia of the fan based on the maximum speed change and the frequency conversion extreme time, so as to obtain a maximum inertia time constant of the fan.

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