A method for identifying a frequency oscillation mode of a power system

Abstract

The application discloses a power system frequency oscillation mode distinguishing method, when frequency oscillation occurs, mode distinguishing indexes of PFR and AGC links are respectively calculated, if the mode distinguishing index of the PFR link is greater than the mode distinguishing index of the AGC link, it is judged as the PFR mode, otherwise, it is the AGC mode; the application can quickly and accurately distinguish the oscillation mode by establishing the DTA model containing the PFR and the AGC, reconstructing the signal, establishing the transfer function of the control signal to the oscillation link, and then calculating the damping torques provided by the PFR and the AGC link, and comparing the damping torque size, which is helpful to take timely and effective suppression measures for the frequency oscillation of the power system.

Description

Technical Field

[0001] This invention relates to the field of power system frequency stability analysis, and in particular to a method for identifying power system frequency oscillation modes. Background Technology

[0002] With my country's advancement in building a power system primarily based on new energy sources, the increased proportion of new energy has led to a decrease in system inertia, making frequency stability a significant concern. In recent years, frequency oscillations have been observed in actual power grids, typically within the range of 0.01-0.1 Hz. These oscillations are mainly caused by AGC (Automatic Generation Control) and PFR (Primary Frequency Regulation) mechanisms. Oscillations caused by the system's AGC are called AGC modes, while those strongly correlated with the generator speed governor and prime mover are called PFR modes. Current research on these two modes primarily focuses on analyzing the damping torque coefficient under specific modes. The damping torque coefficient is determined by decomposing the mechanical power of the prime mover system to study the damping characteristics during frequency regulation. However, the positive and negative signs of the damping torque coefficient can appear in both modes, lacking a clear boundary between the two modes. Furthermore, the coefficient calculation process is complex and often used for analyzing single-unit, single-load systems. Analysis in complex multi-zone systems is difficult, and a universal identification formula cannot be established. Therefore, it is currently difficult to quickly and accurately identify the system's frequency oscillation mode when it occurs, thus hindering rapid control of the frequency oscillations. Summary of the Invention

[0003] Purpose of the invention: The purpose of this invention is to provide a method for quickly and accurately identifying the frequency oscillation pattern when frequency oscillations occur in a power system.

[0004] Technical solution: The power system frequency oscillation mode identification method of the present invention includes the following steps: when frequency oscillation occurs, the mode identification index of the PFR link and the AGC link are calculated respectively. If the mode identification index of the PFR link is greater than the mode identification index of the AGC link, it is determined to be the PFR mode; otherwise, it is the AGC mode.

[0005] The calculation method of the mode discrimination index is as follows: establish a damping torque analysis model including PFR control signal and AGC control signal, reconstruct the signal according to linear control theory, and calculate the damping torque provided by the PFR link and AGC link to each generator at complex frequency. The mode discrimination index represents the magnitude of the damping torque.

[0006] Furthermore, the pattern discrimination index D dampj =|Re[F j (λi )G j (λ i )γ j (λ i )]|, where j is PFR or AGC, representing the PFR stage or the AGC stage respectively, λ i For the i-th oscillation mode, F j (λ i ) is the transfer function from the PFR control signal or AGC control signal to the generator; G j (λ i ) is the transfer function of the PFR or AGC stage; γ j (λ i ) represents the reconstruction coefficient of the PFR control signal or AGC control signal.

[0007] Furthermore, the establishment of the damping torque analysis model including PFR control signal and AGC control signal includes: establishing a state-space equation model based on the dynamic characteristics of the frequency oscillation analysis system, and calculating the transfer functions of the PFR link and the AGC link respectively; wherein the PFR link adopts the structure of prime mover and speed governor as the forward channel, and the feedback channel incorporates the droop coefficient of the PFR link; the AGC link includes a PI link and a delay link.

[0008] Furthermore, the state-space equation model is as follows:

[0009]

[0010] Where x(t)=[Δf ΔP m ΔP PFR ΔP AGC ΔP tie ] T , Δf is the differential of x(t); Δp is the frequency deviation; m For mechanical power deviation; ΔP PFR For PFR control signal; ΔP AGC For AGC control signal; ΔP tie The tie-line power deviation is y(t) = [ACE ∫ACE] T ACE represents the regional control deviation; u(t) = ΔP c ΔP c A represents the load interference signal; B represents the state matrix; C represents the input matrix; and the values ​​of A, B, and C are set according to the power system model.

[0011] Furthermore, the signal reconstruction based on linear control theory, and the calculation of the damping torque provided to each generator by the PFR and AGC links at complex frequencies, include:

[0012] Calculate the transfer function from the PFR control signal to the generator. Based on linear control theory, reconstruct the feedback signal of the PFR control to obtain the PFR signal reconstruction coefficient. Calculate the damping torque provided by the PFR link to the generator based on the transfer function of the PFR link, the PFR signal reconstruction coefficient, and the transfer function from the PFR control signal to the generator.

[0013] Calculate the transfer function from the AGC control signal to the generator. Based on linear control theory, reconstruct the AGC control feedback signal to obtain the AGC signal reconstruction coefficients. Calculate the damping torque provided by the AGC link to the generator based on the transfer function of the AGC link, the AGC signal reconstruction coefficients, and the transfer function from the AGC control signal to the generator.

[0014] Furthermore, the transfer function G of the PFR stage PFR (s) is:

[0015]

[0016] Among them, T g R is the governor response time constant; G is the droop coefficient; gov (s) is the governor transfer function;

[0017] The transfer function G of the AGC stage AGC (s) is:

[0018]

[0019] Where τ is the delay parameter; K P K is the proportional coefficient of the controller. I This represents the integral coefficient of the controller.

[0020] Furthermore, the transfer function from the PFR control signal to the generator Where ΔP m For mechanical power deviation, ΔP PFR For PFR control signal, G P (s) is the transfer function of the prime mover system;

[0021] Feedback signals in the PFR stage G PFR (s) is the transfer function of the PFR stage;

[0022] Based on linear control theory, the feedback signal of the PFR element is reconstructed to obtain:

[0023]

[0024] Δy1=γ PFR (s)·Δf

[0025] Where γ PFR (s) represents the PFR signal reconstruction coefficients; C 11 C 21 C 31 d1 and d1 are the coefficients after the PFR output variables are reconstructed. The damping torque provided by the PFR link to each generator is:

[0026] ΔT PFR =D dampPFR Δf=Re[F PFR (λ i )G PFR (λ i )γ PFR (λ i )]Δf

[0027] Where Δf is the frequency deviation.

[0028] Furthermore, the transfer function from the AGC control signal to the generator is:

[0029]

[0030] Where ΔP m For mechanical power deviation, ΔP AGC For AGC control signals, G gov (s) is the governor transfer function, G P (s) is the transfer function of the prime mover system;

[0031] Feedback signals in the AGC process Based on linear control theory, the feedback signal of the AGC (Automatic Generation Control) stage can be reconstructed to obtain:

[0032]

[0033] Δy2=γ AGC (s)·Δf

[0034] Where, γ AGC (s) represents the AGC signal reconstruction coefficients; C 12 C 22 C 32 d2 and d2 are the coefficients after the AGC output variables are reconstructed; the damping torque provided by the AGC circuit to each generator is:

[0035] ΔT AGC =D dampAGC Δf=Re[F AGC (λ i )G AGC (λ i )γ AGC (λ i )]Δf.

[0036] The electronic device of the present invention includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the computer program is loaded onto the processor, it implements the power system frequency oscillation mode identification method.

[0037] The computer-readable storage medium of the present invention stores a computer program, which, when executed by a processor, implements the power system frequency oscillation mode identification method.

[0038] Beneficial effects: Compared with the prior art, the advantages of this invention are: (1) The mode identification index proposed in this invention reveals the process by which the PFR and AGC control processes provide damping torque to the generator in the system, and then the contribution of the generator's damping torque is transformed into the influence on the damping of the oscillation mode, thereby explaining the initiation and influence mechanism of frequency oscillation and providing a new idea for frequency oscillation analysis. (2) The mode identification index proposed in this invention can effectively reflect the damping magnitude provided by different frequency modulation links to the oscillation mode, and the physical meaning is clear. Through the solution and analysis of this index, the mode identification of frequency oscillation can be performed quickly and accurately, which helps to take timely and effective suppression measures for the frequency oscillation that occurs in the system. Attached Figure Description

[0039] Figure 1 This is a flowchart of the frequency oscillation mode identification method of the present invention.

[0040] Figure 2 This is a schematic diagram of the damping torque transmission in the frequency modulation stage of the present invention.

[0041] Figure 3 This is a schematic diagram illustrating the effect of the frequency modulation stage on the damping of the frequency oscillation mode in this invention.

[0042] Figure 4 This is a single-region system diagram in an embodiment of the present invention.

[0043] Figure 5 This is a PFR mode oscillation curve diagram in an embodiment of the present invention.

[0044] Figure 6 This is an oscillation curve diagram of the AGC mode in an embodiment of the present invention.

[0045] Figure 7 This is a diagram of PFR and AGC power adjustment commands in PFR mode according to an embodiment of the present invention.

[0046] Figure 8 This is a diagram of PFR and AGC power adjustment commands in the AGC mode of this invention.

[0047] Figure 9This is a two-region system diagram in an embodiment of the present invention.

[0048] Figure 10 This is a diagram of the two-region PFR oscillation mode in an embodiment of the present invention.

[0049] Figure 11 This is a four-region system diagram in an embodiment of the present invention.

[0050] Figure 12 This is a diagram of the AGC oscillation mode of the four-region system in an embodiment of the present invention. Detailed Implementation

[0051] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0052] like Figure 1 As shown, the power system frequency oscillation mode identification method includes the following steps:

[0053] Step 1: Obtain wide-area measurement information of the power system based on the wide-area measurement system, and extract measured data such as power signal and terminal frequency.

[0054] Step 2: Build a DTA model that includes PFR and AGC.

[0055] Step 3: In the model established in Step 2, the signal is reconstructed according to linear control theory, the transfer function of the control signal to the oscillating element is established, and the transmission process of damping provided by the PFR and AGC elements is studied, such as... Figure 2 As shown.

[0056] Step 4: Analyze the transmission process constructed in Step 3, considering the different damping torques provided by different stages to the oscillation mode, such as... Figure 3 As shown, a pattern discrimination index is proposed.

[0057] Step 5: Based on the mode identification index proposed in Step 4, by comparing the magnitude of the damping torque provided to the generator by the two frequency modulations, the system frequency oscillation can be identified as either PFR mode or AGC mode.

[0058] Step 2 establishes a damping torque analysis model that includes primary frequency regulation and automatic generation control. This model is based on a multi-regional power system frequency control model. The damping characteristics of the PFR control loop and AGC control loop are derived and analyzed to establish a complete damping torque analysis model under frequency oscillation analysis.

[0059] The specific process for establishing the damping torque analysis model, which includes primary frequency regulation and automatic generation control, in step 2 is as follows:

[0060] Step 2-1: Establish a state-space equation model based on the dynamic characteristics of the frequency oscillation analysis system:

[0061]

[0062] Where x(t)=[ΔfΔP m ΔP PFR ΔP AGC ΔP tie ] T , Δf is the differential of x(t); Δp is the frequency deviation; m For mechanical power deviation; ΔP PFR For PFR control signal; ΔP AGC For AGC control signal; ΔP tie The tie-line power deviation is y(t); y(t) = [ACE∫ACE] T ACE represents the regional control deviation; u(t) = ΔP c ΔP c This represents the load interference signal; A is the state matrix, B is the input matrix, and C is the output matrix, the values ​​of which are set according to the specific system model.

[0063] Step 2-2: The PFR stage uses the structure of the prime mover and governor as the forward channel, and the feedback channel incorporates the droop coefficient of the PFR. The transfer function G of the PFR stage... PFR (s) is:

[0064]

[0065] Among them, T g R is the governor response time constant; G is the droop coefficient; gov (s) is the governor transfer function;

[0066] Steps 2-3: The AGC (Automatic Guided Vehicle) stage calculates the area control deviation (ACE) in real time, calculates the system power regulation using a PI controller, and considers the effects of signal transmission delay and control command cycle. Therefore, the AGC stage includes a PI controller and a delay stage, making it a nonlinear system. The transfer function G of the AGC control stage is... AGC (s) is:

[0067]

[0068] Where τ is the delay parameter; K P K is the proportional coefficient of the controller. I The integral coefficient of the controller;

[0069] The calculation method for the area control deviation (ACE) can be expressed as follows:

[0070] ACE = ΔP tie +βΔf (4)

[0071] Where β is the frequency deviation coefficient.

[0072] In step 3, signal reconstruction is performed based on linear control theory to establish the transfer function from the control signal to the oscillating element. The transmission process of damping provided by the PFR and AGC elements is studied. The specific steps are as follows:

[0073] Step 3-1: For the PFR frequency regulation stage, the transfer function F from the speed governor control signal to the generator is... PFR (s) is:

[0074]

[0075] Among them, G P (s) is the transfer function of the prime mover system, and the feedback signal Δy1 of the PFR element is:

[0076]

[0077] Based on linear control theory, the feedback signal of PFR control can be reconstructed to obtain:

[0078]

[0079] Δy1=γ PFR (s)·Δf (8)

[0080] Where, γ PFR (s) represents the PFR signal reconstruction coefficients; C 11 C 21 C 31 d1 represents the coefficients of the PFR output variables after reconstruction;

[0081] Combining equations (7) and (8) yields γ PFR (s), if the system frequency oscillation is associated with the i-th oscillation mode of the system, the damping torque provided by PFR to each generator at the complex frequency can be obtained as:

[0082] ΔT PFR =D dampPFR Δf=Re[F PFR (λ i )G PFR (λ i )γ PFR (λ i )]Δf (9)

[0083] Step 3-2: For the AGC frequency regulation stage, the transfer function F from the AGC control signal to the generator... AGC (s) is:

[0084]

[0085] The feedback signal Δy2 of the AGC stage is:

[0086]

[0087] Based on linear control theory, the feedback signal of AGC control can be reconstructed to obtain:

[0088]

[0089] Δy2=γ AGC (s)·Δf (13)

[0090] Where, γ AGC (s) represents the AGC signal reconstruction coefficients; C 12 C 22 C 32 d2 represents the coefficients of the reconstructed AGC output variables;

[0091] Combining equations (12) and (13) yields γ AGC (s), if the system frequency oscillation is associated with the i-th oscillation mode of the system, the damping torque provided by the AGC to each generator at the complex frequency can be obtained as:

[0092] ΔT AGC =D dampAGC Δf=Re[F AGC (λ i )G AGC (λ i )γ AGC (λ i )]Δf (14)

[0093] The mode discrimination index in step 4 is to analyze the transmission process constructed in step 3 and propose a mode discrimination index based on the different damping torques provided by different links to the oscillation mode.

[0094] By comparing the magnitudes of the damping torques supplied to the generator by the two frequency modulations, the oscillation modes of the system frequency oscillation can be identified, and a mode identification index can be defined:

[0095] D dampj =|Re[F j (λ i )G j (λ i )γ j (λ i )]| (15)

[0096] Where j represents the PFR stage and AGC stage, respectively; λ i For the i-th oscillation mode; F j (λi ) represents the forward path of frequency regulation control to the generator, i.e., the transfer function of frequency regulation control to the generator; G j (λ i ) is the transfer function for frequency modulation control; γ j (λ i ) represents the reconstruction coefficient of the control signal; D dampj Consistent with the calculation methods in formulas (9) and (14), the absolute value is taken to facilitate comparison of the magnitude of the damping torque.

[0097] The mode identification method in step 5 is based on the mode identification index proposed in step C. By comparing the magnitude of the damping torque provided to the generator by the two frequency regulators, the system frequency oscillation can be identified as either PFR mode or AGC mode.

[0098] If D dampPFR <D dampAGC This indicates that the damping torque provided by the AGC stage is relatively large, indicating an AGC oscillation mode; if D dampPFR >D dampAGC If the damping torque provided by the PFR stage is large, it indicates a PFR oscillation mode.

[0099] The method described in this invention will be verified through specific experiments below.

[0100] Taking a single-region system as an example, the pattern discrimination index proposed in this invention is verified and analyzed, such as... Figure 4 As shown;

[0101] The system was simulated, and the frequency oscillation curve was obtained as follows: Figure 5 and Figure 6 As shown. For Figure 5 Prony analysis was performed on the oscillation curves to obtain characteristic quantities such as amplitude, phase, and damping ratio of the dominant oscillation mode of the system, as shown in Table 1. Eigenvalue analysis of the system yielded eight eigenvalues, including four real eigenvalues ​​and two pairs of conjugate complex eigenvalues, representing two oscillation modes. The oscillation modes are shown in Table 2, indicating that oscillation mode 1 is the dominant frequency oscillation mode of the system under this condition. The mode discrimination index proposed in this invention is calculated as D. dampPFR =18.6810 and D dampAGC =18.0734, which shows that D dampPFR >D dampAGC Therefore, it can be determined that the oscillation mode at this time is the PFR oscillation mode.

[0102] Table 1. Prony Analysis Results for PFR Mode

[0103]

[0104] Table 2 PFR Oscillation Modes

[0105]

[0106] Similarly to Figure 6 Prony analysis was performed on the oscillation curves, and the results are shown in Table 3. Eigenvalue analysis results are shown in Table 4. Oscillation mode 1 is the dominant frequency oscillation mode of the system under this condition. The mode discrimination index proposed in this invention is calculated as D. dampPFR =7.6203 and D dampAGC =8.1112, which shows that D dampPFR <D dampAGC Therefore, it can be determined that the oscillation mode at this time is the AGC oscillation mode.

[0107] Table 3. Prony Analysis Results for AGC Mode

[0108]

[0109] Table 4 AGC Oscillation Modes

[0110]

[0111]

[0112] Figure 7 and Figure 8 The power regulation commands for the system's PFR and AGC are given for the two oscillation modes described above. Figure 5 In the oscillation mode, PFR mainly participates in the action, which is the PFR oscillation mode. Figure 6 In the oscillation mode, AGC mainly participates in the action, which is the AGC oscillation mode, consistent with the results identified by this invention, thus verifying the correctness of the method proposed in this invention.

[0113] Subsequently, time-domain simulations were performed on the multi-region AGC system, and the PFR oscillation modes of the two-region AGC system and the two-region system were shown as follows: Figure 9 and Figure 10 As shown in Table 5, the characteristic values, oscillation frequency, mode discrimination index, and damping ratio of the system oscillations reveal that when PFR oscillations occur in the two-region system, the PFR process provides more damping torque to the generator, indicating a PFR mode. The four-region AGC system and its AGC oscillation mode are shown in Table 5. Figure 11 and Figure 12 As shown in Table 6, the characteristic values, oscillation frequency, mode discrimination index, and damping ratio of the system oscillation are shown. It can be concluded that when AGC oscillation occurs in the four-region system, the AGC process provides more damping torque to the generator, which is the AGC mode.

[0114] Table 5. Characteristic quantities of the PFR model of the two-region system.

[0115]

[0116] Table 6. Characteristic quantities of the AGC mode in the four-region system.

[0117]

[0118] Based on the same inventive concept, the electronic device of the present invention includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the computer program is loaded onto the processor, it implements the power system frequency oscillation mode identification method.

[0119] The computer-readable storage medium of the present invention stores a computer program, which, when executed by a processor, implements the power system frequency oscillation mode identification method.

[0120] The computer-readable storage medium may include RAM, ROM, EEPROM, CD-ROM or other optical disc storage devices, magnetic disk storage devices or other magnetic storage devices, flash memory, or any other media that can be used to store desired program code in the form of instructions or data structures and is accessible by a computer.

[0121] The processor is used to execute a computer program stored in memory to implement the various steps in the methods described in the above embodiments.

Claims

1. A method for identifying frequency oscillation modes in a power system, characterized in that, The process includes the following steps: When frequency oscillation occurs, calculate the pattern discrimination index of the PFR stage and the AGC stage respectively. If the pattern discrimination index of the PFR stage is greater than the pattern discrimination index of the AGC stage, it is judged as PFR mode; otherwise, it is AGC mode. The calculation method of the mode discrimination index is as follows: establish a damping torque analysis model including PFR control signal and AGC control signal, reconstruct the signal according to linear control theory, and calculate the damping torque provided by the PFR link and AGC link to each generator at complex frequency. The mode discrimination index represents the magnitude of the damping torque. The pattern discrimination index Where j is PFR or AGC, representing the PFR stage or the AGC stage respectively. For the i-th oscillation mode, This is the transfer function from the PFR control signal or AGC control signal to the generator; For the transfer function of the PFR or AGC stage; These are the reconstruction coefficients for the PFR control signal or AGC control signal; A state-space equation model is established based on the dynamic characteristics of the frequency oscillation analysis system, and the transfer functions of the PFR and AGC links are calculated respectively. The PFR link adopts the structure of prime mover and speed governor as the forward channel, and the feedback channel incorporates the droop coefficient of the PFR link. The AGC link includes a PI link and a delay link. The state-space equation model is as follows: ； in, , for The differential; This is for frequency deviation; This is for mechanical power deviation; This is the PFR control signal; For AGC control signals; For tie line power deviation; ACE stands for Regional Control Deviation; , For load interference signals; A is the state matrix, B is the input matrix, and C is the output matrix. The values ​​of A, B, and C are set according to the power system model. The signal reconstruction based on linear control theory, and the calculation of the damping torque provided to each generator by the PFR and AGC links at complex frequencies, include: Calculate the transfer function from the PFR control signal to the generator. Based on linear control theory, reconstruct the feedback signal of the PFR control to obtain the PFR signal reconstruction coefficient. Calculate the damping torque provided by the PFR link to the generator based on the transfer function of the PFR link, the PFR signal reconstruction coefficient, and the transfer function from the PFR control signal to the generator. Calculate the transfer function from the AGC control signal to the generator. Based on linear control theory, reconstruct the AGC control feedback signal to obtain the AGC signal reconstruction coefficients. Calculate the damping torque provided by the AGC link to the generator based on the transfer function of the AGC link, the AGC signal reconstruction coefficients, and the transfer function from the AGC control signal to the generator.

2. The method for identifying frequency oscillation modes in a power system according to claim 1, characterized in that, Transfer function of PFR stage for: ； in, R is the governor response time constant; R is the droop coefficient. For the speed controller transfer function; Transfer function of AGC stage for: ； in, For delay parameters; This refers to the proportional gain of the controller. This represents the integral coefficient of the controller.

3. The method for identifying frequency oscillation modes in a power system according to claim 1, characterized in that, The transfer function of the PFR control signal to the generator ,in For mechanical power deviation, This is the PFR control signal. Let the transfer function be the prime mover system. Feedback signals in the PFR stage , The transfer function of the PFR stage; Based on linear control theory, the feedback signal of the PFR element is reconstructed to obtain: ； ； in These are the PFR signal reconstruction coefficients; , , and The coefficients after PFR output variable reconstruction are given. The damping torque provided by the PFR stage to each generator is: ； in This represents the frequency deviation.

4. The method for identifying frequency oscillation modes in a power system according to claim 1, characterized in that, The transfer function from the AGC control signal to the generator is: ； in For mechanical power deviation, For AGC control signals, For the governor transfer function, Let the transfer function be the prime mover system. Feedback signals in the AGC process , This is the transfer function for the AGC (Automatic Generative Control) stage; Based on linear control theory, the feedback signal of the AGC (Automatic Generation Control) stage can be reconstructed to obtain: ； ； in, These are the AGC signal reconstruction coefficients; , , and The coefficients are the reconstructed output variables of the AGC; the damping torque provided by the AGC circuit to each generator is: ； in This represents the frequency deviation.

5. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the computer program is loaded into the processor, it implements the power system frequency oscillation mode identification method according to any one of claims 1-4.

6. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the power system frequency oscillation mode identification method according to any one of claims 1-4.

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