Wind turbine virtual inertia evaluation method based on wind turbine rotating speed variation

Abstract

The invention discloses a fan virtual inertia evaluation method based on fan rotating speed variation. The method comprises the following steps: step 1, establishing a fan grid-connected power generation system frequency response model and obtaining a system frequency response expression; 2, according to the inertia time constant definition of the synchronous machine and in combination with the system rotating speed response extreme value time, a relational expression between the system rotating speed response extreme value time and the system virtual inertia is obtained; and step 3, providing a fan virtual inertia evaluation method based on the fan rotating speed variation in combination with the wind turbine rotating speed and output power variation constraints.

Description

Technical Field

[0001] This invention relates to the field of frequency regulation demand assessment in new power systems with high penetration of new energy sources, and in particular to a method for assessing the virtual inertia of wind turbines based on changes in wind turbine speed. Background Technology

[0002] With the continuous development of new energy power generation technologies, wind power, as a clean and renewable energy source, is seeing its installed capacity and grid connection ratio increase daily. However, the large-scale grid connection of wind farms brings new challenges to the stable operation of the power system. The equivalent virtual inertia of wind farms, as an important indicator for assessing their contribution to grid inertia, is crucial for ensuring the stability of the power system. Currently, existing methods for evaluating the virtual inertia of wind turbines are mainly based on estimates constrained by system frequency changes and the rate of change of system frequency. While these methods can meet the system's safety requirements, they cannot provide an accurate value for the virtual inertia of the wind turbines. To overcome the limitations of existing evaluation methods, this invention proposes a method for evaluating the virtual inertia of wind turbines based on changes in turbine rotational speed. This method utilizes an anemometer to monitor wind speed and direction in real time, providing reliable data support for accurately evaluating the virtual inertia of wind turbines. Summary of the Invention

[0003] This invention provides a method for evaluating the virtual inertia of a wind turbine based on changes in wind turbine speed. First, a frequency response model of the wind turbine grid-connected power generation system is established and the system frequency response expression is obtained. Second, based on the definition of the inertial time constant of the synchronous machine and combined with the extreme time of the system speed response, the relationship between the inertial time constant and the virtual inertia of the system is obtained. Finally, combined with the constraints of changes in wind turbine speed and output power, an evaluation method for the virtual inertia of a wind turbine based on changes in wind turbine speed is proposed.

[0004] To achieve the above objectives, the present invention provides the following solution:

[0005] A method for evaluating the virtual inertia of a wind turbine based on changes in turbine rotational speed includes the following steps:

[0006] Step 1: Establish the frequency response model of the wind turbine grid-connected power generation system and obtain the system frequency response expression;

[0007] Step 2: Based on the definition of the inertial time constant of the synchronizer and combined with the extreme time of the system speed response, obtain the relationship between it and the system virtual inertia;

[0008] Step 3: Combining the constraints of wind turbine speed and output power variation, a method for evaluating the virtual inertia of the wind turbine based on the variation of wind turbine speed is proposed.

[0009] Optionally, step 1: establishing a frequency response model of the wind turbine grid-connected power generation system and obtaining the system frequency response expression specifically includes: the frequency response of the wind power combined system after receiving a power disturbance can be regarded as being composed of the frequency responses of modules such as the synchronous machine, wind turbine, and load. After the wind power combined system encounters an external active power disturbance, the new energy units in the system should work together to complete the power support task as required to ensure the stable and safe operation of the wind power grid-connected power generation system.

[0010] To analyze the dynamic frequency response characteristics of a wind power grid-connected system, this paper establishes a frequency response model including a synchronous machine, wind turbine, and energy storage module, which can be expressed as:

[0011] (2H s p+D sys Δf(t)=ΔP m +ΔP L +ΔP w -ΔP d

[0012] In the formula, ΔP m For synchronous generator power output; ΔP L For load adjustment signal,

[0013] ΔP L =K L Δf, K L ΔP is the load adjustment coefficient. W For the power output of the wind turbine, ΔP d This represents the system disturbance power.

[0014] Among them, the power output ΔP of the synchronous generator m Wind power penetration rate λ W Steam turbine parameters F G T G The influence of the adjustment coefficient R can be expressed as:

[0015]

[0016] ΔP m ΔP L Substituting the expression into the system frequency response expression, we obtain the frequency response model of the wind-solar-storage system in the complex domain as follows:

[0017]

[0018] Furthermore, from the frequency response model of the wind turbine system in the complex domain, the time-domain expression of the system frequency response can be obtained:

[0019]

[0020] In the formula, m is the primary frequency regulation coefficient of the synchronous generator unit taking into account wind power penetration; K GLD The equivalent primary frequency regulation coefficient of the wind power system without additional control can be expressed as follows:

[0021] m=(1-λ w ) / R

[0022] K GLD =m+K L +D sys

[0023] Assuming a load disturbance occurs in the system at time t=0, the general initial conditions at the time of the load disturbance are as follows:

[0024]

[0025] Substituting the initial conditions, we can obtain the analytical solution to the differential equation of Δf versus time t:

[0026]

[0027] In the formula,

[0028]

[0029] The extreme value time of the system speed response is an important basis for dividing the virtual multi-segment speed regulation range of wind power into the extreme value arrival stage, the wind power conversion stage, and the static error recovery stage. Taking the derivative of the above equation, the moment when the derivative is 0 is the extreme value point of the speed response, and the extreme value time t of the system speed response can be calculated. ex for:

[0030]

[0031] Furthermore, both system inertia support and primary frequency modulation support can share the burden of system frequency modulation and assist in system frequency recovery, but their control laws differ. Specifically, inertia support uses differential feedback control of the system frequency, which has a leading characteristic and can quickly respond to the rate of change of the system frequency. However, inertia support is only a short-term impulse power support, and the accumulated energy generated is limited. When the system frequency no longer changes, the power of inertia support immediately becomes 0, but the system frequency deviation may still exist at this time.

[0032] Primary frequency modulation (PMDM) is a proportional feedback control of the system frequency. Unlike inertia support, PMDM responds to the system frequency deviation. In the initial stages of a frequency change, the frequency deviation is small, so the power output of PMDM is also small and relatively slow. However, PMDM provides continuous power support; as long as the system frequency deviation exists, the PMDM power remains, preventing the system frequency from falling or rising and stabilizing it at a new steady-state level. Therefore, while inertia support primarily affects the system's rate of frequency change and has almost no impact on the steady-state frequency deviation, PMDM directly affects the system's maximum frequency deviation and steady-state deviation.

[0033] Optionally, step 2: Based on the definition of the inertial time constant of the synchronizer and combined with the extreme time of the system rotational speed response, obtain its relationship with the system's virtual inertia, specifically including:

[0034] The inherent inertial time constant H of the synchronous generator set g1 Depends on rotational kinetic energy, which is an inherent mechanical characteristic of conventional power sources and can be considered a constant, expressed as:

[0035]

[0036] In the formula, J g ω is the moment of inertia of the synchronous machine. e For synchronous angular velocity; S NG This refers to the rated capacity of the synchronizing machine.

[0037] Under virtual inertia control, wind turbines can adjust their rotational kinetic energy to provide inertial support to the system after it is disturbed. During the inertial response process, the rotational kinetic energy of the wind turbine can be expressed as:

[0038]

[0039] In the formula, J w ω represents the inherent inertia of the wind turbine. r This represents the real-time angular velocity of the fan rotor.

[0040] Combining the above two equations, we define J vw The virtual inertia of the wind turbine is represented as:

[0041]

[0042] Referring to the definition of the inertial time constant of a synchronous machine, the virtual inertial time constant of the wind turbine can be expressed as:

[0043]

[0044] In the formula, S NW H is the rated capacity of the fan. wThis is the inherent inertial time constant of the wind turbine.

[0045] After obtaining virtual inertia under the additional differential, the wind turbine theoretically possesses an inertial response capability similar to that of a synchronous machine. This virtual inertia can be superimposed on the inherent inertia of the synchronous machine, thus allowing the system inertia H to be calculated. s Represented as:

[0046]

[0047] Among them, H g H vw These are the synchronous machine inertia and the fan virtual inertia, respectively; λ g , λ w These represent the proportions of synchronous machines and fans in the system, respectively.

[0048] By combining the extreme time of the system's rotational speed response, t can be obtained. ex With system inertia H s The expression between them can be represented as:

[0049]

[0050] Among them, H g H vw These are the synchronous machine inertia and the fan virtual inertia, respectively; λ g , λ w These represent the proportions of synchronous machines and fans in the system, respectively.

[0051] Based on the above formula, if the system parameters are known, then t can be determined. ex It is only related to the change in the speed of the variable speed wind turbine and the change in the synchronous speed.

[0052] Optionally, step 3: combining the constraints of wind turbine speed and output power variation, proposes an evaluation method for the virtual inertia of the wind turbine based on the variation of wind turbine speed, specifically including:

[0053] When the disturbance power ΔP d When the speed is greater than 0, the fan needs to release kinetic energy to compensate for the unbalanced power, and the rotor speed ω r Decrease; when the disturbance power ΔP d When the speed is less than 0, the fan needs to absorb kinetic energy, and the rotational speed ω r The fan speed constraint can be expressed as:

[0054]

[0055] In the formula, Δω max1 ω represents the maximum change in fan speed under speed safety constraints. r0 ω is the initial speed of the fan. rmax The maximum operating speed for safe operation of the fan; ω rminThe minimum operating speed for safe operation of the wind turbine.

[0056] To ensure the safe operation of the wind turbine, its output power must be limited within a specified range. The wind turbine output power can be expressed as:

[0057]

[0058] In the formula, P ew To output electromagnetic power to the fan; k opt ω0 is the maximum power point tracking proportional coefficient; P is the starting speed of the wind turbine when entering the maximum power point tracking region; n This refers to the rated power of the fan.

[0059] From the above equation, it can be seen that, under power constraints, the power support limit of a wind turbine can be expressed as:

[0060]

[0061] When the wind turbine participates in the inertial response, its rotor motion equation can be expressed as:

[0062] ΔP w =P mw -P ew =2H w ω r dω r / dt

[0063] In the formula, ΔP w P mw These represent the power change and mechanical power of the fan, respectively.

[0064] Based on the above formula, by integrating both sides of the equation under power constraints, we can obtain the maximum speed change Δω of the wind turbine during the inertial response time. max2 , represented as:

[0065]

[0066] To simultaneously satisfy both constraints, the maximum change in the fan speed should be the minimum of the two, i.e., Δω. max =min{Δω max1 ,Δω max2}

[0067] Currently, to prevent the activation of low-frequency load shedding devices in power systems under heavy load disturbances, my country's "State Grid Corporation Power Supply Service Quality Standards" stipulates that the maximum transient frequency deviation of the power grid must not exceed 1 Hz. Therefore, this invention sets the initial activation value of the low-frequency load shedding device as the system's maximum transient frequency deviation constraint. Under the 1 Hz frequency deviation constraint, the variation range of the synchronization angular frequency is 0.98–1 p.u. To conservatively evaluate the virtual inertia of the wind turbine, this paper takes Δω.e =0.02, this value can be adjusted according to the actual operation of the power grid.

[0068] Based on the above and the description in claim 3, the following system of equations can be obtained:

[0069]

[0070] After obtaining the new energy penetration rate, conventional unit type and configuration ratio through the above set of equations, we can obtain the virtual inertia of the wind turbine and the relationship between wind speed and the extreme value time of system rotational speed response by measuring the wind speed with the measuring device.

[0071] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0072] Figure 1 This is a flowchart of the method for evaluating the virtual inertia of a wind turbine based on changes in wind turbine speed, according to an embodiment of the present invention.

[0073] Figure 2 This is a simplified model diagram of a wind turbine grid-connected power generation system;

[0074] Figure 3 It is the change in fan speed under safety constraints;

[0075] Figure 4 This is the evaluation result of the virtual inertia requirement of the wind turbine under real-time wind speed in the embodiments of the present invention;

[0076] Figure 5 This is the evaluation result of the extreme value time of the system rotational speed response under real-time wind speed in the embodiments of the present invention; Detailed Implementation

[0077] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0078] This invention provides a method for evaluating the virtual inertia of a wind turbine based on changes in wind turbine speed. To make the above-mentioned objectives, features, and advantages of this invention more apparent and understandable, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0079] Figure 1 This is a flowchart of a method for evaluating the virtual inertia of a wind turbine based on changes in wind turbine speed, according to an embodiment of the present invention. Figure 1 As shown, it includes the following steps:

[0080] Step 1: Establish the frequency response model of the wind turbine grid-connected power generation system and obtain the system frequency response expression;

[0081] Step 2: Based on the definition of the inertial time constant of the synchronizer and combined with the extreme time of the system speed response, obtain the relationship between it and the system virtual inertia;

[0082] Step 3: Combining the constraints of wind turbine speed and output power variation, a method for evaluating the virtual inertia of the wind turbine based on the variation of wind turbine speed is proposed.

[0083] First, a frequency response model of the wind turbine grid-connected power generation system is established and the system frequency response expression is obtained. To analyze the dynamic frequency response characteristics of the wind-solar-storage grid-connected system, this paper establishes, as follows: Figure 2 The frequency response model shown, which includes a synchronizing machine and a fan module, can be represented as follows:

[0084] (2H s p+D sys Δf(t)=ΔP m +ΔP L +ΔP w -ΔP d (1)

[0085] In the formula, ΔP m For synchronous generator power output; ΔP L For load regulation signal, ΔP L =K L Δf, K L ΔP is the load adjustment coefficient. W For the power output of the wind turbine, ΔP d This represents the system disturbance power.

[0086] Among them, the power output ΔPm of the synchronous generator is affected by the wind power penetration rate λ. w Steam turbine parameters F G T G The influence of the adjustment coefficient R can be expressed as:

[0087]

[0088] ΔP m ΔP L Substituting the expression into the system frequency response expression, we obtain the frequency response model of the wind turbine system in the complex domain as follows:

[0089]

[0090] Furthermore, from the frequency response model of the wind turbine system in the complex domain, the time-domain expression of the system frequency response can be obtained:

[0091]

[0092] In the formula, m is the primary frequency regulation coefficient of the synchronous generator unit taking into account wind power penetration; K GLD The equivalent primary frequency regulation coefficient of the wind power system without additional control can be expressed as follows:

[0093]

[0094] The specific values ​​for the fan system are shown in Tables 1 and 2 below:

[0095] Table 1. Specific Values ​​of Fan Parameters

[0096] Fan parameters <![CDATA[H w / s]]> <![CDATA[R t / m]]> <![CDATA[N t ]]> <![CDATA[p n ]]> <![CDATA[λ opt ]]> <![CDATA[λ w ]]> numerical values 4 49 45 2 9 0.2

[0097] Table 2. Specific values ​​of synchronous machine parameters.

[0098] Synchronizer parameters <![CDATA[H g1 ]]> <![CDATA[T G ]]> R <![CDATA[D sys ]]> <![CDATA[K L ]]> <![CDATA[F G ]]> numerical values 8 8 0.04 0 1 0.3

[0099] Assuming a load disturbance occurs in the system at time t=0, the general initial conditions at the time of the load disturbance are as follows:

[0100]

[0101] Substituting the initial conditions, we can obtain the analytical solution to the differential equation of Δf versus time t:

[0102]

[0103] In the formula,

[0104]

[0105] The extreme value time of the system speed response is an important basis for dividing the virtual multi-segment speed regulation range of wind power into the extreme value arrival stage, the wind power conversion stage, and the static error recovery stage. Taking the derivative of the above equation, the moment when the derivative is 0 is the extreme value point of the speed response, and the extreme value time t of the system speed response can be calculated. ex for:

[0106]

[0107] The inherent inertial time constant H of the synchronous generator set g1 Depends on rotational kinetic energy, which is an inherent mechanical characteristic of conventional power sources and can be considered a constant, expressed as:

[0108]

[0109] In the formula, J g ω is the moment of inertia of the synchronous machine. e For synchronous angular velocity; S NG This refers to the rated capacity of the synchronizing machine.

[0110] Under virtual inertia control, wind turbines can adjust their rotational kinetic energy to provide inertial support to the system after it is disturbed. During the inertial response process, the rotational kinetic energy of the wind turbine can be expressed as:

[0111]

[0112] In the formula, J w ω represents the inherent inertia of the wind turbine. r This represents the real-time angular velocity of the fan rotor.

[0113] Combining equations (10) and (11), J is defined. vw The virtual inertia of the wind turbine is represented as:

[0114]

[0115] Referring to the definition of the inertial time constant of a synchronous machine, the virtual inertial time constant of the wind turbine can be expressed as:

[0116]

[0117] In the formula, S NW H is the rated capacity of the fan. w This is the inherent inertial time constant of the wind turbine.

[0118] After obtaining virtual inertia under the additional differential, the wind turbine theoretically possesses an inertial response capability similar to that of a synchronous machine. This virtual inertia can be superimposed on the inherent inertia of the synchronous machine, thus allowing the system inertia H to be calculated. s Represented as:

[0119]

[0120] Among them, H g H vw These are the synchronous machine inertia and the fan virtual inertia, respectively; λ g , λ w These represent the proportions of synchronous machines and fans in the system, respectively.

[0121] By combining the extreme time of the system's rotational speed response, t can be obtained. ex With system inertia H s The expression between them can be represented as:

[0122]

[0123] Among them, H g Hvw These are the synchronous machine inertia and the fan virtual inertia, respectively; λ g , λ w These represent the proportions of synchronous machines and fans in the system, respectively.

[0124] When the disturbance power ΔP d When the speed is greater than 0, the fan needs to release kinetic energy to compensate for the unbalanced power, and the rotor speed ω r Decrease; when the disturbance power ΔP d When the speed is less than 0, the fan needs to absorb kinetic energy, and the rotational speed ω r The fan speed constraint can be expressed as:

[0125]

[0126] In the formula, Δω max1 ω represents the maximum change in fan speed under speed safety constraints. r0 ω is the initial speed of the fan. rmax The maximum operating speed for safe operation of the fan; ω rmin The minimum operating speed for safe operation of the wind turbine.

[0127] To ensure the safe operation of the wind turbine, its output power must be limited within a specified range. The wind turbine output power can be expressed as:

[0128]

[0129] In the formula, P ew To output electromagnetic power to the fan; k opt ω0 is the maximum power point tracking proportional coefficient; P is the starting speed of the wind turbine when entering the maximum power point tracking region; n This refers to the rated power of the fan.

[0130] From the above equation, it can be seen that, under power constraints, the power support limit of a wind turbine can be expressed as:

[0131]

[0132] When the wind turbine participates in the inertial response, its rotor motion equation can be expressed as:

[0133] ΔP w =P mw -P ew =2H w ω r dω r / dt (19)

[0134] In the formula, ΔP w P mw These represent the power change and mechanical power of the fan, respectively.

[0135] According to equation (20), by integrating both sides of the equation under the power constraint, the maximum speed change Δω of the wind turbine during the inertial response time can be obtained. max2 , represented as:

[0136]

[0137] To simultaneously satisfy both constraints, the maximum change in the fan speed should be the minimum of the two, i.e., Δω. max =min{Δω max1 ,Δω max2 Taking a 2MW wind turbine as an example, let Hw = 4s, k opt =1 / (1.23), ω rmax =1.2pu, ω rmin =0.8pu,t ex = 3.09s. According to equations (16) and (20), the maximum change in speed Δω under different initial speeds of the fan can be obtained. max ,like Figure 3 As shown.

[0138] Currently, to prevent the activation of low-frequency load shedding devices in power systems under heavy load disturbances, my country's "State Grid Corporation Power Supply Service Quality Standards" stipulates that the maximum transient frequency deviation of the power grid must not exceed 1 Hz. Therefore, this invention sets the initial activation value of the low-frequency load shedding device as the system's maximum transient frequency deviation constraint. Under the 1 Hz frequency deviation constraint, the variation range of the synchronization angular frequency is 0.98–1 p.u. To conservatively evaluate the virtual inertia of the wind turbine, this paper takes Δω. e =0.02, this value can be adjusted according to the actual operation of the power grid.

[0139] Combining the statements in equations (14-20), we can obtain the following system of equations:

[0140]

[0141] After obtaining the new energy penetration rate, conventional unit type and configuration ratio through the above set of equations, we can obtain the virtual inertia of the wind turbine and the relationship between the extreme value time of the system speed response and the change in wind turbine speed by measuring the change in wind turbine speed with the measuring device.

[0142] Figure 4 This is the evaluation result of the virtual inertia requirement of the fan under the fan speed change in the embodiment of the present invention;

[0143] Figure 5 This is the evaluation result of the system speed response extreme value time under the fan speed change in the embodiment of the present invention;

[0144] The wind turbine virtual inertia assessment method proposed in this invention effectively improves the accuracy of wind turbine virtual inertia, laying the foundation for ensuring system frequency security in the future.

[0145] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0146] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. This invention discloses a method for evaluating the virtual inertia of a wind turbine based on changes in wind turbine speed, characterized in that, Includes the following steps: Step 1: Establish the frequency response model of the wind turbine grid-connected power generation system and obtain the system frequency response expression; Step 2: Based on the definition of the inertial time constant of the synchronizer and combined with the extreme time of the system speed response, obtain the relationship between it and the system virtual inertia; Step 3: Combining the constraints of wind turbine speed and output power variation, a method for evaluating the virtual inertia of the wind turbine based on the variation of wind turbine speed is proposed.

2. The method for evaluating the virtual inertia of a wind turbine based on changes in wind turbine speed, as described in claim 1, is characterized in that... Step 1: Establishing a frequency response model of the wind power grid-connected power generation system and obtaining the system frequency response expression, specifically including: The frequency response of the wind power combined system after receiving a power disturbance can be regarded as being composed of the frequency responses of modules such as the synchronous machine, wind turbine, and load. After the wind power combined system encounters an external active power disturbance, the new energy units in the system should work together to complete the power support task as required to ensure the stable and safe operation of the wind power grid-connected power generation system. To analyze the dynamic frequency response characteristics of a wind power grid-connected system, this paper establishes a frequency response model including a synchronous machine, wind turbine, and energy storage module, which can be expressed as: (2H s p+D sys )Δf(t)=ΔP m +ΔP L +ΔP w -ΔP d In the formula, ΔP m For synchronous generator power output; ΔP L For load adjustment signal, ΔP L =K L Δf, K L ΔP is the load adjustment coefficient. W For the power output of the wind turbine, ΔP d This refers to the system disturbance power; Among them, the power output ΔP of the synchronous generator m Wind power penetration rate λ W Steam turbine parameters F G T G The influence of the adjustment coefficient R can be expressed as: ΔP m ΔP L Substituting the expression into the system frequency response expression, we obtain the frequency response model of the wind-solar-storage system in the complex domain as follows: Furthermore, from the frequency response model of the wind turbine system in the complex domain, the time-domain expression of the system frequency response can be obtained: In the formula, m is the primary frequency regulation coefficient of the synchronous generator unit taking into account wind power penetration; K GLD The equivalent primary frequency regulation coefficient of the wind power system without additional control can be expressed as follows: m=(1-λ w ) / R K GLD =m+K L +D sys Assuming a load disturbance occurs in the system at time t=0, the general initial conditions at the time of the load disturbance are as follows: Substituting the initial conditions, we can obtain the analytical solution to the differential equation of Δf versus time t: In the formula, The extreme value time of the system speed response is an important basis for dividing the virtual multi-segment speed regulation range of wind power into the extreme value arrival stage, the wind power conversion stage, and the static error recovery stage. Taking the derivative of the above equation, the moment when the derivative is 0 is the extreme value point of the speed response, and the extreme value time t of the system speed response can be calculated. ex for: Furthermore, both system inertia support and primary frequency modulation support can share the burden of system frequency modulation and assist in system frequency recovery, but their control laws differ. Specifically, inertia support uses differential feedback control of the system frequency, which has a leading characteristic and can quickly respond to the rate of change of the system frequency. However, inertia support is only a short-term impulse power support, and the accumulated energy generated is limited. When the system frequency no longer changes, the power of inertia support immediately becomes 0, but the system frequency deviation may still exist at this time. Primary frequency modulation (PMDM) is a proportional feedback control of the system frequency. Unlike inertia support, PMDM responds to the system frequency deviation. In the initial stages of a frequency change, the frequency deviation is small, so the power output of PMDM is also small and relatively slow. However, PMDM provides continuous power support; as long as the system frequency deviation exists, the PMDM power remains, preventing the system frequency from falling or rising and stabilizing it at a new steady-state level. Therefore, while inertia support primarily affects the system's rate of frequency change and has almost no impact on the steady-state frequency deviation, PMDM directly affects the system's maximum frequency deviation and steady-state deviation.

3. The method for evaluating the virtual inertia of a wind turbine based on changes in wind turbine speed according to claim 1, characterized in that, Step 2: Based on the definition of the inertial time constant of the synchronizer and combined with the extreme time of the system rotational speed response, obtain its relationship with the system's virtual inertia, specifically including: The inherent inertial time constant H of the synchronous generator set g1 Depends on rotational kinetic energy, which is an inherent mechanical characteristic of conventional power sources and can be considered a constant, expressed as: In the formula, J g ω is the moment of inertia of the synchronous machine. e For synchronous angular velocity; S NG This refers to the rated capacity of the synchronizing machine. Under virtual inertia control, wind turbines can adjust their rotational kinetic energy to provide inertial support to the system after it is disturbed. During the inertial response process, the rotational kinetic energy of the wind turbine can be expressed as: In the formula, J w ω represents the inherent inertia of the wind turbine. r This represents the real-time angular velocity of the fan rotor. Combining the above two equations, we define J vw The virtual inertia of the wind turbine is represented as: Referring to the definition of the inertial time constant of a synchronous machine, the virtual inertial time constant of the wind turbine can be expressed as: In the formula, S NW H is the rated capacity of the fan. w This is the inherent inertial time constant of the wind turbine. After obtaining virtual inertia under the additional derivative, the wind turbine theoretically possesses an inertial response capability similar to that of a synchronous machine. This virtual inertia can be superimposed on the inherent inertia of the synchronous machine, thus allowing the system inertia H to be calculated. s Represented as: Among them, H g H vw These are the synchronous machine inertia and the fan virtual inertia, respectively; λ g , λ w These represent the proportions of synchronous machines and fans in the system, respectively. By combining the extreme time of the system's rotational speed response, t can be obtained. ex With system inertia H s The expression between them can be represented as: Among them, H g H vw These are the synchronous machine inertia and the fan virtual inertia, respectively; λ g , λ w These represent the proportions of synchronous machines and fans in the system, respectively. Based on the above formula, if the system parameters are known, then t can be determined. ex It is only related to the change in the speed of the variable speed wind turbine and the change in the synchronous speed.

4. The method for evaluating the virtual inertia of a wind turbine based on changes in wind turbine speed according to claim 1, characterized in that, Step 3: Combining the requirements of wind turbine speed constraints and output power variation constraints, a method for evaluating the virtual inertia of the system wind turbine is proposed, specifically including: When the disturbance power ΔP d When the speed is greater than 0, the fan needs to release kinetic energy to compensate for the unbalanced power, and the rotor speed ω r Decrease; when the disturbance power ΔP d When the speed is less than 0, the fan needs to absorb kinetic energy, and the rotational speed ω r The fan speed constraint can be expressed as: In the formula, Δω max1 ω represents the maximum change in fan speed under speed safety constraints. r0 ω is the initial speed of the fan. rmax The maximum operating speed for safe operation of the fan; ω rmin The minimum operating speed for safe operation of the wind turbine. To ensure the safe operation of the wind turbine, its output power must be limited within a specified range. The wind turbine output power can be expressed as: In the formula, P ew To output electromagnetic power to the fan; k opt This is the maximum power point tracking proportional coefficient; ω0 is the starting speed of the wind turbine when it enters the maximum power tracking region; P n This refers to the rated power of the fan. From the above equation, it can be seen that, under power constraints, the power support limit of a wind turbine can be expressed as: When the wind turbine participates in the inertial response, its rotor motion equation can be expressed as: ΔP w =P mw -P ew =2H w ω r dω r / dt In the formula, ΔP w P mw These represent the power change and mechanical power of the fan, respectively. Based on the above formula, by integrating both sides of the equation under power constraints, we can obtain the maximum speed change Δω of the wind turbine during the inertial response time. max2 , is represented as: To simultaneously satisfy both constraints, the maximum change in the fan speed should be the minimum of the two, i.e., Δω. max =min{Δω max1 ,Δω max2 } Currently, to prevent the activation of low-frequency load shedding devices in power systems under heavy load disturbances, my country's "State Grid Corporation Power Supply Service Quality Standards" stipulates that the maximum transient frequency deviation of the power grid must not exceed 1 Hz. Therefore, this invention sets the initial activation value of the low-frequency load shedding device as the system's maximum transient frequency deviation constraint. Under the 1 Hz frequency deviation constraint, the variation range of the synchronization angular frequency is 0.98–1 p.u. To conservatively evaluate the virtual inertia of the wind turbine, this paper takes Δω. e =0.02, this value can be adjusted according to the actual operation of the power grid. Based on the above and the description in claim 3, the following system of equations can be obtained: After obtaining the new energy penetration rate, conventional unit type and configuration ratio through the above set of equations, we can obtain the virtual inertia of the wind turbine and the relationship between the extreme value time of the system speed response and the change in wind turbine speed by measuring the change in wind turbine speed with the measuring device.

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