A variable inertia response time calculation method based on virtual inertia control

Abstract

This invention discloses a method for calculating variable inertia response time based on virtual inertia control. The technical solution adopted in this invention is as follows: Analyzing the frequency response characteristics of wind turbines, and mimicking the inertial response capability of synchronous turbines by adding virtual inertia control to the wind turbines; analyzing the frequency response characteristics of the wind power grid-connected system under load abrupt changes, and establishing a frequency response model including virtual inertia control parameters; then, based on the frequency response model of the wind power grid-connected system, obtaining the inertia response time required for the frequency to drop (rise) to the lowest (highest) point. This invention can quantitatively calculate the inertia response time of the wind power grid-connected system after adding virtual inertia control. This invention can evaluate the inertia response time under different virtual inertia control coefficients, providing reliable supporting data for the system frequency response.

Description

Technical Field

[0001] This invention relates to the field of wind power grid connection system technology, and in particular to a method for calculating variable inertia response time based on virtual inertia control. Background Technology

[0002] Large-scale wind power integration has reduced the proportion of traditional generating units in the power grid, lowering the inertia level and posing a serious challenge to the frequency stability of the power grid. By adding virtual inertia control to the wind turbines, the inertial response capability of synchronous generators can be simulated, thereby improving system frequency stability. Without virtual inertia control, the system's inertial response time hardly changes with wind power penetration. After adding virtual inertia control, the system frequency response process differs under different virtual inertia control coefficients, and the corresponding inertial response time also varies.

[0003] Therefore, how to calculate the inertial response time in the frequency response process after the addition of inertial response has become an urgent problem to be solved. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a variable inertia response time calculation method based on virtual inertia control, which can quantify the inertia response time of wind power grid-connected system after virtual inertia control is added, and provide reliable supporting data for system frequency response.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for calculating variable inertia response time based on virtual inertia control, comprising:

[0006] Step 1: Analyze the frequency response characteristics of the wind turbine and simulate the inertial response capability of a synchronous unit by adding virtual inertia control to the wind turbine.

[0007] Step 2: Analyze the frequency response characteristics of the wind power grid-connected system under load abrupt changes and establish a frequency response model including virtual inertia control parameters;

[0008] Step 3: Based on the frequency response model of the wind power grid-connected system, obtain the inertial response time required when the frequency drops (rises) to the lowest (highest) point.

[0009] Optionally, step 1, analyzing the frequency response characteristics of the wind turbine, simulates the inertial response capability of a synchronous generator by adding virtual inertia control to the wind turbine. Specifically, this includes: introducing a system frequency change signal into the active power control section of the wind turbine, and releasing or absorbing energy through rapid active power adjustment to simulate rotational inertia. Referring to the definition of rotational kinetic energy of a synchronous generator, when the rotor speed of the wind turbine changes, the rotational kinetic energy released or absorbed by the unit can be expressed as:

[0010]

[0011] In the formula, J w ω represents the inherent moment of inertia of the wind turbine generator. s ω represents the angular velocity of the synchronous generator. r J represents the rotor angular velocity of the wind turbine; vir The virtual moment of inertia of the wind turbine is expressed as:

[0012]

[0013] In the formula, Δω r Δω is the change in fan speed. s ω represents the change in synchronous generator speed, λ is the speed regulation coefficient, and ω is the speed variation. r0 Let ω be the initial electric angular velocity of the wind turbine. e ω represents the angular velocity of the synchronous generator.

[0014] It can be seen that in the virtual inertia control process, the variable speed wind turbine can set the speed adjustment coefficient λ according to the grid demand. When the effective inertia of the system is less than 4s, λ>>1 is set to virtually generate a larger rotational inertia than that of a synchronous generator, thus avoiding frequency abrupt changes.

[0015] Optionally, step 2, analyzing the frequency response characteristics of the wind power grid-connected system under load abrupt changes and establishing a frequency response model with virtual inertia control parameters, specifically includes: taking short-time frequency drops as an example, analyzing the frequency dynamic response characteristics of the wind power grid-connected system:

[0016] At the start of the disturbance at time t0, if a power disturbance occurs, such as a sudden increase in load, the system frequency will drop significantly. The synchronous generator sets and wind turbine sets in the system should respond quickly to the frequency change and compensate for the system's power demand through multi-source fast active power support.

[0017] t0~t nadir The first stage is the inertia response stage. The wind turbine shares the unbalanced power borne by the synchronous machine by adding virtual inertia control, thereby slowing down the rate of system frequency drop and avoiding excessive frequency change rate that could lead to excessive system frequency drop and increase the probability of new energy units being disconnected from the grid.

[0018] t nadir ~t p Stage: t nadir At that moment, the frequency dropped to its lowest point, t nadirAfter a certain time, the system frequency begins to recover, and the rate of frequency change changes from negative (df / dt<0) to positive (df / dt>0). Before the frequency stabilizes, the output direction of the wind turbine must remain unchanged. However, if the wind turbine uses a differential element for virtual inertia control, during the frequency recovery phase, the turbine's inertial response output will be opposite to the system demand. Under virtual inertia control, it will absorb power, increasing the frequency regulation burden on the synchronous generator, which can cause slow frequency recovery or even a secondary frequency drop. p This indicates the end time of a single frequency modulation.

[0019] When a load disturbance occurs in the system, the generators in the system respond to the load change. Considering the load response, the generator's inertial response, and primary frequency regulation, a frequency response model with virtual inertia control parameters is established:

[0020]

[0021] In the formula, H is the inertia constant of the synchronous machine, Δf(t) is the frequency value at time t, and ΔP M ΔP1 is the power response signal of the synchronous machine, and ΔP is the power response signal of the wind turbine. L Let D be the load disturbance of the system, and D be the unit regulation power coefficient.

[0022] Optionally, step 3, obtaining the inertial response time required for the frequency to drop (rise) to the lowest (highest) point based on the frequency response model of the wind power grid-connected system, specifically includes: defining the time required for the frequency to drop or rise from the initial value to the maximum value after the system is disturbed as the inertial response time; and obtaining the dynamic equation of the system's frequency response based on the frequency dynamic response calculation model of the wind power grid-connected system as shown in the following formula.

[0023]

[0024] In the formula, D is the system load frequency regulation effect coefficient, ρ represents the wind power penetration rate, and R G F is the droop coefficient of the speed governor. H F is the characteristic coefficient of the turbine, 0 < F H <1,T R Let ΔP be the reheater time constant of the steam turbine. d This represents the initial overload of the system.

[0025] By rearranging the above equation, performing Laplace calculations, and simplifying, we can obtain the relationship between the frequency deviation Δf(s) and time t as shown in the following equation.

[0026]

[0027] in:

[0028]

[0029] The time-domain expression of the frequency response can be obtained by performing the inverse Laplace transform:

[0030]

[0031] in:

[0032]

[0033] Taking the derivative, we can obtain the inertial response time t of the wind power grid-connected system participating in frequency regulation. nadir for:

[0034]

[0035] It can be seen that the inertial response time and parameter w of the wind power grid-connected system n Related to ε, when other parameters in the wind power grid-connected system are constant, the inertial response time of the wind power grid-connected system varies with the parameters of the additional controller of the wind turbine. In order to study the influence of virtual inertia control on the inertial response time of the wind-storage combined system, the values ​​of k1 and wind power penetration rate ρ are changed and plotted. When ρ is constant, the relationship between the inertial response time and k1 is approximately a linear function. By fitting this function, the expression for the inertial response time can be obtained as follows:

[0036] t nadir =a·k1+b

[0037] In the formula, the values ​​of a and b are related to the additional droop control coefficient k1 of the wind turbine and the wind power penetration rate ρ. When ρ is constant, a and b are constant values.

[0038] When the parameters of the additional virtual inertia controller are given, the specific value of the inertial response time for wind power grid connection and frequency regulation can be obtained.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] This invention addresses the issue of frequency changes caused by load disturbances in a system. It simulates the inertial response of synchronous turbines by adding virtual inertia control to the wind turbines, establishing a frequency response model with virtual inertia control parameters. Then, based on the frequency response model of the wind power grid-connected system, it calculates the inertial response time required for the frequency to drop (rise) to its lowest (highest) point. This invention allows for the quantitative calculation of the inertial response time of a wind power grid-connected system with added virtual inertia control. Attached Figure Description

[0041] 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.

[0042] Figure 1 This is a flowchart of the variable inertia response time calculation method based on virtual inertia control in an embodiment of the present invention;

[0043] Figure 2 This is a frequency response characteristic diagram of the wind power grid-connected system in an embodiment of the present invention;

[0044] Figure 3 This is a simplified frequency model diagram of a power system that takes wind power into account in an embodiment of the present invention;

[0045] Figure 4 This is a graph showing the relationship between inertial response time and fan controller parameters in an embodiment of the present invention;

[0046] Figure 5 This is a system simulation topology diagram in an embodiment of the present invention;

[0047] Figure 6 This is a frequency response curve diagram under different additional virtual inertial control coefficients in the embodiments of the present invention. Detailed Implementation

[0048] 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.

[0049] This invention provides a method for calculating variable inertia response time based on virtual inertia control. 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.

[0050] Figure 1 This is a flowchart of the variable inertia response time calculation method based on virtual inertia control according to an embodiment of the present invention, as shown below. Figure 1 As shown, it includes the following steps:

[0051] Step 1: Analyze the frequency response characteristics of the wind turbine and simulate the inertial response capability of a synchronous unit by adding virtual inertia control to the wind turbine.

[0052] Step 2: Analyze the frequency response characteristics of the wind power grid-connected system under load abrupt changes and establish a frequency response model including virtual inertia control parameters;

[0053] Step 3: Based on the frequency response model of the wind power grid-connected system, obtain the inertial response time required when the frequency drops (rises) to the lowest (highest) point.

[0054] By introducing a system frequency change signal into the active power control section of the wind turbine, energy is released or absorbed through rapid active power regulation, thus simulating a rotational inertia. Referring to the definition of rotational kinetic energy of a synchronous generator, the rotational kinetic energy released or absorbed by the unit when the rotor speed of the wind turbine changes can be expressed as:

[0055]

[0056] In the formula, J w ω represents the inherent moment of inertia of the wind turbine generator. s ω represents the angular velocity of the synchronous generator. r J represents the rotor angular velocity of the wind turbine; vir The virtual moment of inertia of the wind turbine is expressed as:

[0057]

[0058] In the formula, Δω r Δω is the change in fan speed. s ω represents the change in synchronous generator speed, λ is the speed regulation coefficient, and ω is the speed variation. r0 Let ω be the initial electric angular velocity of the wind turbine. e ω represents the angular velocity of the synchronous generator.

[0059] As can be seen from equation (2), in the virtual inertia control process, the variable speed wind turbine can set the speed adjustment coefficient λ according to the grid demand. When the effective inertia of the system is less than 4s, λ>>1 can be set to virtually generate a larger rotational inertia than the synchronous generator, thus avoiding frequency abrupt changes.

[0060] Figure 2 This is a frequency response characteristic diagram of a wind power grid-connected system. Taking short-time frequency sag as an example, the dynamic frequency response characteristics of the wind power grid-connected system are analyzed:

[0061] At the start of the disturbance at time t0, if a power disturbance occurs, such as a sudden increase in load, the system frequency will drop significantly. The synchronous generator sets and wind turbine sets in the system should respond quickly to the frequency change and compensate for the system's power demand by providing multi-source fast active power support.

[0062] t0~t nadirThe first stage is the inertia response stage. During this stage, the wind turbine uses additional virtual inertia control to share the unbalanced power load from the synchronous machine, thereby slowing down the system frequency drop rate and preventing excessive frequency fluctuations that could lead to large system frequency drops and increase the probability of grid disconnection for renewable energy units. nadir This represents the inertial response time.

[0063] t nadir ~t p Stage: t nadir At that moment, the frequency dropped to its lowest point, t nadir After a certain time, the system frequency begins to recover, and the rate of frequency change changes from negative (df / dt<0) to positive (df / dt>0). Before the frequency stabilizes, the output direction of the wind turbine must remain unchanged. However, if the wind turbine uses a differential element for virtual inertia control, during the frequency recovery phase, the turbine's inertial response output will be opposite to the system demand. Under virtual inertia control, it will absorb power, increasing the frequency regulation burden on the synchronous generator, which can cause slow frequency recovery or even a secondary frequency drop. p This indicates the end time of a single frequency modulation.

[0064] Figure 3 This is a simplified frequency model diagram of a power system that takes wind power into account. When load disturbances occur in the system, the generators in the system respond to load changes. Considering the load response, the generator inertial response, and primary frequency regulation, a frequency response model with virtual inertia control parameters is established:

[0065]

[0066] In the formula, H is the inertia constant of the synchronous machine, Δf(t) is the frequency value at time t, and ΔP M ΔP1 is the power response signal of the synchronous machine, and ΔP is the power response signal of the wind turbine. L Let D be the load disturbance of the system, and D be the unit regulation power coefficient.

[0067] The inertial response time is defined as the time required for the frequency to drop or rise from its initial value to reach its maximum value after the system is disturbed. According to the frequency dynamic response calculation model of the wind power grid-connected system, the dynamic equation of the system's frequency response can be obtained as shown in the following equation.

[0068]

[0069] In the formula, D is the system load frequency regulation effect coefficient, ρ represents the wind power penetration rate, and R G F is the droop coefficient of the speed governor. H F is the characteristic coefficient of the turbine, 0 < F H <1,T R Let ΔP be the reheater time constant of the steam turbine. dThis represents the initial overload of the system.

[0070] By rearranging equation (4), performing Laplace calculations, and simplifying, the relationship between frequency deviation Δf(s) and time t is obtained as follows:

[0071]

[0072] in:

[0073]

[0074] Taking the inverse Laplace transform of equation (5) yields the time-domain expression for the frequency response:

[0075]

[0076] in:

[0077]

[0078] Differentiating equation (7) yields the inertial response time t of the wind power grid-connected system participating in frequency regulation. nadir for:

[0079]

[0080] Figure 4 This is a graph showing the relationship between the inertial response time and the wind turbine controller parameters in an embodiment of the present invention; combined with equation (6), it can be seen that the inertial response time and parameter w of the wind power grid-connected system are... n Related to ε, when other parameters in the wind power grid-connected system are constant, the inertial response time of the system varies with the parameters of the additional controller of the wind turbine. To study the impact of virtual inertia control on the inertial response time of the wind-storage combined system, the values ​​of k1 and wind power penetration rate ρ are changed and plotted. When ρ is constant, the relationship between the inertial response time and k1 is approximately a linear function. Fitting this function, as shown... Figure 4 As shown, the expression for the inertial response time can be obtained:

[0081] t nadir =a·k1+b (10)

[0082] In the formula, the values ​​of a and b are related to the additional droop control coefficient k1 of the wind turbine and the wind power penetration rate ρ. When ρ is constant, a and b are constant values.

[0083] When the parameters of the additional virtual inertia controller are given, the specific value of the inertial response time for wind power grid connection and frequency regulation can be obtained.

[0084] Establish a simulation model of the wind power grid connection system. Figure 5 This is a system simulation topology diagram of an embodiment of the present invention, such as... Figure 5As shown, the system includes loads L1, L2, and L3, and the power source includes a wind farm consisting of multiple doubly fed wind turbines connected in parallel, as well as equivalent synchronous generators G1, G2, and G3.

[0085] This embodiment is based on the DIGSILENT / Power Factory simulation platform to build a three-machine simulation system for wind farm integration. The simulation system includes three synchronous generators with capacities of 600MVA, 600MVA and 900MVA respectively, and a DFIG of 300 × 2MW doubly fed wind turbine units. The initial penetration rate of wind turbine units is 30%.

[0086] When the additional virtual inertia control coefficient of the wind turbine is set to 0, 10 and 20 respectively, a system disturbance with a sudden load increase of 20% is set at 2s. Figure 6 These are the frequency response curves under different additional virtual inertia coefficients. As the additional virtual inertia coefficient of the wind turbine increases, the inertial response time of the system increases. According to equation (9), when the additional virtual inertia control coefficients of the wind turbine are 0, 10, and 20, the theoretical values ​​are 2.59s, 3.33s, and 4.00s, respectively, and the simulation results are approximately 2.61s, 3.35s, and 4.03s, respectively. The error between the simulation results and the calculation results is within 5%. The simulation results verify the correctness of the inertial response time calculation and analysis results.

Claims

1. A method for calculating the variable inertia response time based on virtual inertia control, characterized in that, include: Step 1: Analyze the frequency response characteristics of the wind turbine and simulate the inertial response capability of a synchronous unit by adding virtual inertia control to the wind turbine. Step 2: Analyze the frequency response characteristics of the wind power grid-connected system under load abrupt changes, and establish a frequency response model of the wind power grid-connected system including virtual inertia control parameters; Step 3: Based on the frequency response model of the wind power grid-connected system, calculate the inertial response time required when the frequency drops to the lowest point and the inertial response time required when the frequency rises to the highest point. Step 2 includes the following: When a load disturbance occurs in the system, the generators in the system respond to the load change. Considering the load response, the generator's inertial response, and primary frequency regulation, a frequency response model with virtual inertia control parameters is established: In the formula, H is the inertia constant of the synchronous machine. In order to be in t Frequency value at time, For synchronous machine power response signal, This is the power response signal of the wind turbine. Where D is the load disturbance of the system, and D is the unit regulating power coefficient; Step 3 includes the following: The inertial response time is defined as the time required for the frequency to drop or rise from its initial value to reach its maximum value after a disturbance. Based on the frequency dynamic response calculation model of the wind power grid-connected system, the dynamic equation of the system's frequency response is as follows: In the formula, Expressed as wind power penetration rate, R G This is the droop coefficient of the speed controller. F H For turbine characteristic coefficients, 0 < F H <1, T R Let be the reheater time constant of the steam turbine. For the initial overload of the system, This indicates the additional droop control coefficient for the fan; Organize the dynamic equations of the system's frequency response, perform Laplace calculations, and simplify to obtain the frequency deviation. With time t The relationship is shown in the following formula: in: The time-domain expression of the frequency response obtained by performing the inverse Laplace transform is as follows: in: The inertial response time of the wind power grid-connected system participating in frequency regulation is obtained by differentiation. t nadir is: ； Inertial response time and parameters of wind power grid-connected systems and The two are related. When other parameters in a wind power grid-connected system are constant, the inertial response time of the system varies with the parameters of the additional controller of the wind turbine. To study the impact of virtual inertia control on the inertial response time of the wind-storage integrated system, k1 and wind power penetration rate are changed. The values ​​are plotted and graphed. At a given time, the relationship between the inertial response time and k1 is approximately a linear function. By fitting this function, the expression for the inertial response time is obtained as follows: In the formula, the values ​​of a and b are related to the additional droop control coefficient k1 of the wind turbine and the wind power penetration rate. Related, when At a given time, a and b are constant values.

2. The method for calculating variable inertia response time based on virtual inertia control according to claim 1, characterized in that, Step 1 includes the following: By introducing system frequency change signals into the active power control section of the wind turbine, energy is released or absorbed through rapid active power regulation, thus simulating a rotational inertia. Referring to the definition of rotational kinetic energy of a synchronous generator, when the rotor speed of the wind turbine changes, the rotational kinetic energy released or absorbed by the unit... Represented as: In the formula, This represents the inherent moment of inertia of the wind turbine. This represents the angular velocity of the synchronous generator; This indicates the angular velocity of the wind turbine rotor; This represents the virtual moment of inertia of the wind turbine.

3. The method for calculating variable inertia response time based on virtual inertia control according to claim 2, characterized in that, Virtual moment of inertia of wind turbine Represented as: In the formula, This represents the change in fan speed. This represents the change in the speed of the synchronous generator. This is the speed adjustment coefficient. The initial electric angular velocity of the wind turbine. ω represents the angular velocity of the synchronous generator.

4. The method for calculating variable inertia response time based on virtual inertia control according to claim 3, characterized in that, During virtual inertial control, the variable-speed wind turbine sets its speed regulation coefficient according to grid demand. When the system's effective inertia is less than 4s, set >>1, virtualizes a larger moment of inertia than a synchronous generator, avoiding frequency abrupt changes.

5. The method for calculating variable inertia response time based on virtual inertia control according to claim 1, characterized in that, In step 2, the steps for analyzing the frequency dynamic response characteristics of the wind power grid-connected system are as follows: Disturbance start time t 0. If the load suddenly increases, the system frequency will drop significantly. The synchronous generator sets and wind turbine sets in the system should respond quickly to the frequency change and compensate for the power demand of the system by supporting the rapid active power from multiple sources. t 0~ t nadir Phase 1: Inertial response phase, the wind turbine shares the unbalanced power load from the synchronous machine by adding virtual inertial control. t nadir Indicates the inertial response time; t nadir ~ t p stage: t nadir At that moment, the frequency dropped to its lowest point. t nadir After a certain time, the system frequency begins to recover, and the rate of change of frequency changes from negative to positive. Before the frequency recovers and stabilizes, the output direction of the wind turbine must remain unchanged. However, if the wind turbine uses a differential element for virtual inertia control, during the frequency recovery phase, the inertial response output of the wind turbine will be opposite to the system demand. Under virtual inertia control, it will absorb power, increasing the frequency regulation burden of the synchronous generator, which will cause slow frequency recovery or even a secondary drop. t p This indicates the end time of a single frequency modulation.

6. The method for calculating variable inertia response time based on virtual inertia control according to claim 1, characterized in that, When the parameters of the additional virtual inertia controller are given, the specific value of the inertial response time for wind power grid connection and frequency regulation is obtained.

Images