An analytical method for the influence of hydropower unit excitation system on ultra-low frequency oscillation.

Abstract

This invention provides an analytical method for the influence of the excitation system of a hydropower unit on ultra-low frequency oscillations. Based on a multi-unit system, an equivalent single-unit, single-load model for analyzing ultra-low frequency oscillation modes is constructed. An improved four-unit, two-zone system model of the excitation control system based on a power system stabilizer is constructed and trained. The transfer function in the equivalent single-unit, single-load model is solved using the trained improved four-unit, two-zone system model to obtain the poles of the transfer function, and the mechanism by which the excitation system influences ultra-low frequency oscillations is analyzed. This invention analyzes the mechanism by obtaining the eigenvalues ​​corresponding to the oscillation modes of the improved four-unit, two-zone system, providing a basis for studying the mechanism by which the excitation system influences ultra-low frequency oscillations. Furthermore, transfer function and damping torque analyses are performed for cases where network losses are ignored and the voltage regulation effect of the load is considered, providing a more detailed analysis of the mechanism by which the excitation system of a hydropower unit influences ultra-low frequency oscillations, thus filling the gap in the study of how the excitation system suppresses ultra-low frequency oscillations.

Description

Technical Field

[0001] This invention relates to the field of carrier-based aircraft scheduling, specifically to an analytical method for the influence of hydroelectric generator excitation systems on ultra-low frequency oscillations. Background Technology

[0002] Existing research on ultra-low frequency (ULF) oscillations has largely focused on the prime mover system, consisting of the governor and the prime mover. Currently, the main method for preventing ULF oscillations in China is to optimize governor parameters and increase the damping of the prime mover system. However, as a mechanical component, the governor's sensitivity is limited in practical applications, and frequent operation can lead to wear and other problems. Furthermore, adjusting governor parameters to improve ULF oscillation damping may worsen the unit's primary frequency response. In fact, the power system stabilizer (PSS) and excitation system also affect ULF oscillations, and the excitation system is easier to control than the governor, offering a new ULF oscillation suppression scheme.

[0003] Existing technologies indicate that for ultra-low frequency oscillations below 0.1Hz, some simple and practical power system stabilizer (PSS) devices are no longer adequate to meet the new and higher requirements. After studying and analyzing the PSS4B model, it was found that the PSS4B device, which provides damping in the ultra-low frequency band, can meet the requirements well and ultimately improve the stability of the system. In addition, the possibility of reactive power modulation to solve frequency stability has been studied, and simulations have shown that reactive power modulation will affect primary frequency regulation.

[0004] However, there is currently a lack of research on the impact of excitation systems and power system stabilizers (PSS) on ultra-low frequency oscillations. Further clarification is needed on the mechanism by which PSS suppresses ultra-low frequency oscillations in the excitation system, so as to provide direction and theoretical basis for using PSS and excitation control to suppress ultra-low frequency oscillations. Summary of the Invention

[0005] To address the aforementioned shortcomings in existing technologies, this invention provides an analytical method for the impact of the excitation system of a hydropower unit on ultra-low frequency oscillations. By analyzing the mechanism by which the excitation system affects ultra-low frequency oscillations, this invention innovatively analyzes the impact from the perspective of coupled active power frequency control and reactive power voltage control. Furthermore, it analyzes the principle and process of how the additional PSS of the excitation system affects the damping of ultra-low frequency oscillations from the perspective of network losses and load voltage regulation effects that couple these two processes.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0007] An analytical method for analyzing the impact of the excitation system of a hydropower unit on ultra-low frequency oscillations includes the following steps:

[0008] S1. Construct and analyze an equivalent single-machine single-load model of the ultra-low frequency oscillation mode based on a multi-machine system;

[0009] S2. Construct and train an improved four-machine two-zone system model based on the excitation control system of the power system stabilizer;

[0010] S3. Using the improved four-machine two-zone system model after training, the mechanism of the excitation system affecting overfrequency oscillation is analyzed based on the equivalent single-machine single-load model.

[0011] Preferably, step S1 specifically includes the following sub-steps:

[0012] S11. Construct the rotor motion equations for each generator in the multi-machine system;

[0013] S12. Calculate the transfer function between the deviation of the generator output electromagnetic power and the deviation of the generator speed based on the rotor motion equation of each generator.

[0014] S13. Construct the transfer function of the speed control system consisting of the governor and the prime mover based on the transfer function, and obtain the equivalent single-machine single-load model.

[0015] This preferred solution has the following beneficial effects:

[0016] An equivalent single-machine single-load model was constructed for analyzing ultra-low frequency oscillation modes, and the transfer function of the speed regulation system was obtained, providing parameter basis for further solving the characteristic values ​​corresponding to the oscillation modes of the improved four-machine two-zone system.

[0017] Preferably, step S12 specifically includes the following sub-steps:

[0018] S121. Calculate the sum of the deviations in the output electromagnetic power of each generator in a multi-machine system, expressed as:

[0019]

[0020] Where Δω is the generator speed deviation, P L0j Let K be the rated active load of the j-th load, Δf be the frequency deviation of the multi-machine system, and K be the active load rating. L Here is the frequency modulation effect coefficient, ΔP ei Let ΔP be the deviation of the electromagnetic power output by the i-th generator. Lj Let be the actual active load deviation of the j-th time.

[0021] S122. Calculate the sum of the rotor motion equations of each generator in the multi-machine system based on the sum of the deviations in the output electromagnetic power of each generator, expressed as:

[0022]

[0023] Among them, D iLet T be the damping coefficient of the i-th generator. Ji Let ΔP be the inertial time constant of the i-th generator, t be time, and ΔP be the inertial time constant. mi The input mechanical power deviation of the i-th generator;

[0024] S123. Perform a Laplace transform on the sum of the rotor motion equations of each generator in the multi-machine system to obtain the transfer function between the deviation of the generator output electromagnetic power and the deviation of the generator speed.

[0025] This preferred solution has the following beneficial effects:

[0026] By equating multi-machine systems to single-machine single-load models, the analysis process is simplified.

[0027] Preferably, the transfer function in step S123 is expressed as:

[0028]

[0029] Among them, G gen (s) is the transfer function of the equivalent generator, T Ji K is the frequency modulation effect coefficient. L P is the frequency modulation effect coefficient. L0j Let D be the rated active power of the j-th load. i Let Δω(s) be the damping coefficient of the i-th generator, Δω(s) be the generator speed deviation, and ΔP be the damping coefficient of the i-th generator. m (s) represents the total input mechanical power deviation of the equivalent generator, and s is the complex frequency.

[0030] Preferably, step S2 specifically includes:

[0031] By replacing the generator in the basic four-machine two-zone system with a generator based on a fourth-order model of the excitation control system of the power system stabilizer, an improved four-machine two-zone system model is obtained. The parameters of the improved four-machine two-zone system model are then adjusted to obtain the improved four-machine two-zone system model.

[0032] This preferred solution has the following beneficial effects:

[0033] An improved four-machine two-zone system was constructed to analyze the impact of the excitation system on ultra-low frequency oscillations.

[0034] Preferably, the control strategy of the excitation control system based on the power system stabilizer in step S2 includes the following sub-steps:

[0035] A1. The transfer function of the power system stabilizer is expressed as:

[0036]

[0037] Among them, G EX(s) is the transfer function of the excitation control system, K A and T A Here, represents the gain and time constant of the excitation control, respectively, and s is a complex parameter variable.

[0038] A2. Construct the transfer function of the excitation control system, expressed as:

[0039]

[0040] Among them, G EX (s) is the transfer function of the excitation control system, K A and T A These are the gain and time constant of the excitation control, respectively.

[0041] Preferably, step S3 specifically includes the following sub-steps:

[0042] S31. Ignoring the voltage regulation effect, use the improved four-machine two-zone system model after training to solve the closed-loop system transfer function corresponding to the equivalent single-machine single-load model, and obtain the solution result.

[0043] S32. Analyze the mechanism by which the excitation system affects overfrequency oscillation based on the solution results.

[0044] This preferred solution has the following beneficial effects:

[0045] By simplifying the analysis process by equating a multi-machine system to a single-machine single-load system, and conducting ultra-low frequency oscillation mode analysis based on an improved four-machine two-zone system, the analysis method and mechanism research on the influence of the excitation system on ultra-low frequency oscillations were improved.

[0046] The present invention has the following beneficial effects:

[0047] Based on the analysis of the equivalent single-machine single-load model of the ultra-low frequency oscillation mode in the multi-machine system, and the improved four-machine two-zone system model with the excitation control system based on the power system stabilizer after construction and training, the transfer function in the equivalent single-machine single-load model is solved using the improved four-machine two-zone system model. The poles of the transfer function are obtained, which are the characteristic values ​​corresponding to the oscillation mode of the improved four-machine two-zone system. This determines the main cause of the ultra-low frequency oscillation phenomenon and provides a basis for studying the mechanism of the excitation system affecting ultra-low frequency oscillation. Furthermore, the transfer function and damping torque are analyzed for cases where network losses are ignored and the voltage regulation effect of the load is considered. The detailed process of the excitation system affecting the damping of ultra-low frequency oscillation is obtained. The mechanism of the hydropower unit excitation system affecting ultra-low frequency oscillation is analyzed in detail, filling the gap in the excitation system's ability to suppress ultra-low frequency oscillation. Attached Figure Description

[0048] Figure 1A flowchart illustrating the steps of an analytical method for the influence of the excitation system of a hydropower unit on ultra-low frequency oscillations, provided by this invention.

[0049] Figure 2 This is a flowchart of the steps in step S1;

[0050] Figure 3 This is a flowchart of the steps in step S12;

[0051] Figure 4 This is a system block diagram for an equivalent single-machine, single-load model;

[0052] Figure 5 The control flowchart of the excitation control system of the power system stabilizer;

[0053] Figure 6 This is a control block diagram of an excitation control system based on a power system stabilizer (PSS).

[0054] Figure 7 This is a flowchart of the steps in step S3;

[0055] Figure 8 This is a flowchart of the steps in step S31;

[0056] Figure 9 This is a control block diagram showing the transfer function from system frequency deviation to load-side voltage deviation and then to load power deviation. Detailed Implementation

[0057] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0058] like Figure 1 As shown in the figure, this invention provides an analysis method for the influence of the excitation system of a hydropower unit on ultra-low frequency oscillations, including the following steps:

[0059] S1. Construct and analyze an equivalent single-machine single-load model of the ultra-low frequency oscillation mode based on a multi-machine system;

[0060] Optionally, in a multi-generator system (a power system with multiple generator sets (power sources)), all generators have the same speed and phase, and all generators have the same speed deviation. If grid losses and the voltage regulation effect of the load are ignored, an equivalent single-generator single-load model can be established for analyzing ultra-low frequency oscillation modes.

[0061] like Figure 2As shown, preferably, step S1 specifically includes the following sub-steps:

[0062] S11. Construct the rotor motion equations for each generator in the multi-machine system;

[0063] Optionally, when ultra-low frequency oscillations occur in a multi-machine system, all generators oscillate together with the same speed and phase. Therefore, the speed deviation of all generators is the same, denoted by Δω. The linearized rotor motion equation of the i-th generator is shown.

[0064]

[0065] Among them, T J Δω is the generator's inertial time constant; Δω is the generator speed deviation; ΔP m The deviation of the output mechanical power of the prime mover; ΔP e denoted as denoted as , where is the deviation of the generator's output electromagnetic power; D is the generator's damping coefficient.

[0066] S12. Calculate the transfer function between the deviation of the generator output electromagnetic power and the deviation of the generator speed based on the rotor motion equation of each generator.

[0067] like Figure 3 As shown, preferably, step S12 specifically includes the following sub-steps:

[0068] S121. Calculate the sum of the deviations in the output electromagnetic power of each generator in a multi-machine system, expressed as:

[0069]

[0070] Where Δω is the generator speed deviation, P L0j Let K be the rated active load of the j-th load, Δf be the frequency deviation of the multi-machine system, and K be the active load rating. L Here is the frequency modulation effect coefficient, ΔP ei Let ΔP be the deviation of the electromagnetic power output by the i-th generator. Lj Let be the actual active load deviation of the j-th time.

[0071] Optionally, if the generators have the same speed deviation, various energy losses in the power grid transmission are ignored, and the load only considers the effect of frequency regulation while ignoring the voltage regulation effect, the output electromagnetic power of each generator in the multi-machine system can be obtained.

[0072] S122. Calculate the sum of the rotor motion equations of each generator in the multi-machine system based on the sum of the deviations in the output electromagnetic power of each generator, expressed as:

[0073]

[0074] Among them, Di Let T be the damping coefficient of the i-th generator. Ji Let ΔP be the inertial time constant of the i-th generator, t be time, and ΔP be the inertial time constant. mi The input mechanical power deviation of the i-th generator;

[0075] S123. Perform a Laplace transform on the sum of the rotor motion equations of each generator in the multi-machine system to obtain the transfer function.

[0076] Preferably, the transfer function in step S123 is expressed as:

[0077]

[0078] Among them, G gen (s) is the transfer function of the equivalent generator, T Ji K is the frequency modulation effect coefficient. L P is the frequency modulation effect coefficient. L0j Let D be the rated active power of the j-th load. i Let Δω(s) be the damping coefficient of the i-th generator, Δω(s) be the generator speed deviation, and ΔP be the damping coefficient of the i-th generator. m (s) represents the total input mechanical power deviation of the equivalent generator, where s is a complex parameter variable.

[0079] Optionally, a Laplace transform is performed on the sum of the rotor motion equations of each generator in the multi-machine system to obtain the deviation Δω between the generator speed deviation and the output mechanical power ΔP of the prime mover. m The transfer function.

[0080] S13. Based on the transfer function, construct the transfer function of the speed control system consisting of the governor and the prime mover, and obtain the equivalent single-machine single-load model, which is expressed as:

[0081]

[0082] Among them, G m (s) is the transfer function of the velocity system.

[0083] Optionally, in this case, the multi-machine system can be equivalent to a single-machine, single-load system. This equivalent single-machine, single-load system is as follows: Figure 4 As shown.

[0084] S2. Construct and train an improved four-machine two-zone system model based on the excitation control system of the power system stabilizer;

[0085] Optionally, an improved four-machine two-zone system model with an excitation control system based on a power system stabilizer is constructed to simulate and analyze the coupling mode of the active power control process and the reactive power voltage regulation process. In the original four-machine two-zone system, a generator with an excitation control system based on a power system stabilizer is adopted, and the parameters of the excitation system and the prime mover system, i.e., the speed governor and the prime mover, are set to provide data support for subsequent solution of system characteristic comparison under different conditions and analysis of the impact of the excitation system on ultra-low frequency oscillation.

[0086] Preferably, step S2 specifically includes:

[0087] By replacing the generator in the basic four-machine two-zone system with a generator based on a fourth-order model of the excitation control system of the power system stabilizer, an improved four-machine two-zone system model is obtained. The parameters of the improved four-machine two-zone system model are then adjusted to obtain the improved four-machine two-zone system model.

[0088] Optionally, all generators use parallel-type proportional-integral-derivative (PID) speed governors, whose transfer function G gov The expression for (s) is: Where: Δω(s) is the generator speed deviation; Δμ(s) is the change in the opening of the turbine guide vanes or steam turbine valves; K P K I K D These are the proportional, integral, and derivative coefficients of the speed governor; B P T is the adjustment coefficient; G Let be the time constant of the servo system; s is a complex parameter variable that satisfies s = σ + jω, and set the droop coefficient B. P =0.01, the speed controller ratio is K P =1, the integral coefficient K of the speed governor I =0.5, the differential coefficient K of the speed governor D =0.5, the time constant T of the servo system G =0.2s;

[0089] Furthermore, in the four-machine system, G1 and G2 are hydro-generator units, and G3 and G4 are steam turbine generator units. For the hydro-turbine transfer function G... ht (s) and turbine transfer function G st The expressions for (s) are as follows:

[0090]

[0091]

[0092] Among them, T W F is the water start-up time (i.e., the time constant of the water hammer effect); HPThe ratio of the steady-state output power of the high-pressure cylinder to the total output power of the turbine; T CH Main intake volume effect time constant; T RH Let T be the time constant for the volumetric effect of the intermediate reheat steam, and set the water start-up time T for turbines G1 and G2. W The steady-state output power of the G3 high-pressure cylinder in the steam turbine accounts for 0.5s and 2s; the proportion of F of the total output power of the steam turbine to the steady-state output power of the G3 high-pressure cylinder. HP Main intake volume effect time constant T CH Intermediate reheat steam volume effect time constant T RH The steady-state output power of the high-pressure cylinder G4 in the steam turbine is 0.3s, 0.1s, and 4s respectively; the proportion of F of the steady-state output power of the high-pressure cylinder in the steam turbine to the total output power of the steam turbine. HP Main intake volume effect time constant T CH Intermediate reheat steam volume effect time constant T RH The times were 0.3, 0.3s, and 10s, respectively.

[0093] For the improved four-machine two-zone system, the reactive load adopts a constant impedance model, while the active load adopts a constant impedance plus constant power static model considering the frequency regulation effect. The active load P... L express:

[0094]

[0095] Among them, P L0 K represents the rated active load. Z and 1-K Z These represent the ratios of constant impedance and constant power loads, respectively; U and U0 represent the actual and rated values ​​of the load node voltage, respectively; and K... L Δf is the frequency regulation effect coefficient, and Δf is the deviation of the system frequency.

[0096] like Figure 5 As shown, preferably, the control strategy of the excitation control system based on the power system stabilizer in step S2 includes the following sub-steps:

[0097] A1. The transfer function of the power system stabilizer is expressed as:

[0098]

[0099] Among them, G PSS (s) is the transfer function of the power system stabilizer, K STAB For the gain of the power system stabilizer PSS, T W T1 is the time constant of the DC blocking element, T2 is the time constant of the leading element, and s is a complex parameter variable.

[0100] A2. Construct the transfer function of the excitation control system, expressed as:

[0101]

[0102] Among them, G EX (s) is the transfer function of the excitation control system, K A and T A These are the gain and time constant of the excitation control, respectively.

[0103] Optionally, the transfer function of the excitation control system satisfies: Among them, U t U is the voltage reference value for the improved four-machine two-zone system. ref The actual voltage of the improved four-machine two-zone system;

[0104] The control block diagram of the excitation control system based on the power system stabilizer (PSS) is as follows: Figure 6 As shown, K STAB For the gain of the power system stabilizer PSS, T W T1 is the time constant of the DC blocking element, T2 is the time constant of the leading element, and K is the time constant of the lagging element. A and T A These are the gain and time constant for excitation control, respectively, and the parameter is set as: K STAB =9.5, T W =1.4s, T1=0.154s, T2=0.033s, K A =50,T A =0.05s.

[0105] S3. Using the improved four-machine two-zone system model after training, and based on the equivalent single-machine single-load model, analyze the mechanism by which the excitation system affects overfrequency oscillation.

[0106] like Figure 7 As shown, preferably, step S3 specifically includes the following sub-steps:

[0107] S31. Ignoring the voltage regulation effect, use the improved four-machine two-zone system model after training to solve the closed-loop system transfer function corresponding to the equivalent single-machine single-load model, and obtain the solution result.

[0108] Optionally, based on the improved four-machine two-zone system model, the voltage regulation effect of neglecting network losses and loads (line resistance is 0, K) is considered. Z =0), neglecting network losses and considering the voltage regulation effect of the load (line resistance is 0, K Z =0.4) and considering the voltage regulation effect of neglecting load due to network loss (line resistance is not 0, K Z=0) Simulation analysis was performed on three cases. The parameters of the excitation control or power system stabilizer PSS were modified to obtain the characteristic value tables corresponding to the three ultra-low frequency oscillation modes as shown in Table 1, Table 2 and Table 3 below;

[0109] Comparative analysis revealed that in scenario 1, modifying the parameters of the excitation control or PSS did not change the eigenvalues. In scenarios 2 or 3, modifying the parameters of the excitation control or the power system stabilizer PSS changed the eigenvalues. This indicates that the external factors affecting ultra-low frequency oscillations in the excitation system are network losses or the voltage regulation effect of the load. In scenario 2, removing the power system stabilizer PSS and changing only the excitation control parameters did not change the eigenvalues. This indicates that the internal factor affecting ultra-low frequency oscillations in the excitation system is the power system stabilizer PSS attached to the excitation system.

[0110] Furthermore, considering the addition of a power system stabilizer to the excitation system and taking into account the voltage regulation effect of the load while ignoring network losses, the above table and figure show that the power system stabilizer PSS and the voltage regulation effect of the load are the key factors in coupling the active power frequency control process and the reactive power voltage control process. After considering the above two factors, the relationship between the system frequency deviation and the load power deviation is further determined.

[0111] Table 1 Simulation results of the 4-machine 2-zone system under scenario 1

[0112] Simulation Examples <![CDATA[K A ]]> <![CDATA[T A ]]> <![CDATA[K STAB ]]> <![CDATA[T W ]]> <![CDATA[T1]]> <![CDATA[T2]]> Eigenvalues 1 50 0.05 9.5 1.4 0.154 0.033 -0.041+0.264i 2 50 0.05 19 1.4 0.154 0.033 -0.040+0.265i 3 50 0.05 9.5 2.8 0.154 0.033 -0.040+0.264i 4 50 0.05 9.5 1.4 0.308 0.033 -0.041+0.264i 5 50 0.05 9.5 1.4 0.154 0.066 -0.041+0.264i

[0113] Table 2 Simulation results of the 4-machine 2-zone system under scenario 2

[0114] Simulation Examples <![CDATA[K A ]]> <![CDATA[T A ]]> <![CDATA[K STAB ]]> <![CDATA[T W ]]> <![CDATA[T1]]> <![CDATA[T2]]> Eigenvalues 6 50 0.05 9.5 1.4 0.154 0.033 -0.0194+0.171i 7 50 0.05 19 1.4 0.154 0.033 -0.0184+0.136i 8 50 0.05 9.5 2.8 0.154 0.033 -0.0242+0.138i 9 50 0.05 9.5 1.4 0.308 0.033 -0.0182+0.171i 10 50 0.05 9.5 1.4 0.154 0.066 -0.0198+0.171i 11 50 0.05 0 1.4 0.154 0.033 0.005+0.263i 12 100 0.05 0 1.4 0.154 0.033 0.006+0.264i 13 50 0.1 0 1.4 0.154 0.033 0.005+0.263i

[0115] Table 3 Simulation results of the 4-machine 2-zone system under scenario 3

[0116] Simulation Examples <![CDATA[K A ]]> <![CDATA[T A ]]> <![CDATA[K STAB ]]> <![CDATA[T W ]]> <![CDATA[T1]]> <![CDATA[T2]]> Eigenvalues 1 50 0.05 9.5 1.4 0.154 0.033 -0.041+0.264i 2 50 0.05 19 1.4 0.154 0.033 -0.040+0.265i 3 50 0.05 9.5 2.8 0.154 0.033 -0.040+0.264i 4 50 0.05 9.5 1.4 0.308 0.033 -0.041+0.264i 5 50 0.05 9.5 1.4 0.154 0.066 -0.041+0.264i

[0117] S32. Analyze the mechanism by which the excitation system affects overfrequency oscillation based on the solution results using the damping torque method.

[0118] like Figure 8 As shown, preferably, step S32 specifically includes the following sub-steps:

[0119] S321. Construct the transfer function of system frequency deviation and load power deviation, expressed as:

[0120]

[0121] Among them, G L (s) represents the transfer function value of the system frequency deviation and the load power deviation, Δf represents the system frequency deviation, and ΔP represents the load power deviation. e G is the deviation of the generator's output electromagnetic power, i.e., the load power deviation.PSS (s), G EX (s) are the transfer functions of the excitation control and power system stabilizer components, respectively, G F (s) represents the partial transfer function of the excitation winding, and K1 represents the generator transient electromotive force ΔE. q ′ and terminal voltage ΔU i The proportionality coefficient; K2 is the generator voltage ΔU i With load voltage ΔU j The proportionality coefficient, K3 is the generator voltage ΔU i Deviation from load power ΔP e The proportionality coefficient;

[0122] like Figure 9 As shown, optionally, the transfer function of the system frequency deviation and load power deviation determines the path of coupling active frequency control and reactive voltage control of the excitation system.

[0123] S322. By analyzing the transfer function of system frequency deviation and load power deviation using the damping torque method, the mechanism by which the excitation system affects overfrequency oscillation is obtained.

[0124] Optionally, the model can be further analyzed using the damping torque method to obtain a detailed process of how the excitation system affects the damping of ultra-low frequency oscillations. Let the ultra-low frequency oscillation of the system be ω. d , s=jω d Substituting the transfer function of system frequency deviation and load power deviation, it can be expressed as: G L (jω d ) = K D +jK S In the formula, K D =Re[G L (jω d [)] is the damping coefficient of electromagnetic power; a positive value is beneficial for the attenuation of oscillations; K S This is the electromagnetic power synchronization coefficient;

[0125] This invention provides an analytical method for the impact of the excitation system of a hydropower unit on ultra-low frequency oscillations. The method analyzes the ultra-low frequency oscillation modes to determine the causes of these oscillations. Then, through simulation analysis in a four-unit, two-zone system, it obtains the pathways for coupling active power frequency control and reactive power voltage control in the excitation system. Finally, considering the voltage regulation effect of the load while ignoring network losses, it performs transfer function and damping torque analysis to obtain a detailed process of how the excitation system affects the damping of ultra-low frequency oscillations. This invention provides a relatively detailed analysis of the mechanism by which the excitation system of a hydropower unit affects ultra-low frequency oscillations, filling the gap in the suppression of ultra-low frequency oscillations by the excitation system.

[0126] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0127] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0128] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0129] Specific embodiments have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

[0130] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. An analysis method for the influence of a hydroelectric generating unit excitation system on ultra-low frequency oscillations, characterized in that, The method comprises the following steps: S1, constructing an equivalent single-machine single-load model for analyzing the ultra-low frequency oscillation mode according to a multi-machine system construction analysis, specifically comprising the following steps: S11, constructing a rotor motion equation of each generator in the multi-machine system; S12, calculating a transfer function between a deviation of the electromagnetic power output of the generator and a deviation amount of the generator speed according to the rotor motion equation of each generator; S13, constructing a transfer function of a speed regulating system formed by the speed regulator and the prime mover according to the transfer function, to obtain the equivalent single-machine single-load model; S2, constructing and training an improved four-machine two-area system model of the excitation control system based on the power system stabilizer; specifically, replacing the generators in the basic four-machine two-area system with a four-order model of the excitation control system based on the power system stabilizer to obtain the improved four-machine two-area system model, and adjusting parameters of the improved four-machine two-area system model to obtain the improved four-machine two-area system model; S3, using the trained improved four-machine two-area system model to analyze a mechanism of the excitation system affecting the ultra-frequency oscillation according to the equivalent single-machine single-load model, comprising the following steps: S31, under the condition of ignoring the voltage regulation effect, using the trained improved four-machine two-area system model to solve a closed-loop system transfer function corresponding to the equivalent single-machine single-load model, to obtain a solution result; S32, analyzing the mechanism of the excitation system affecting the ultra-frequency oscillation according to the solution result, specifically comprising the following steps: S321, constructing a transfer function of the system frequency deviation and the load power deviation, expressed as: wherein is the transfer function value of the system frequency deviation and the load power deviation, is the system frequency deviation, is the deviation of the generator output electromagnetic power, i.e. the load power deviation, , are the excitation control and power system stabilizer loop transfer functions, respectively, is the excitation winding partial transfer function, is the generator transient electromotive force is the proportionality coefficient of the generator voltage to the terminal voltage; is the proportionality coefficient of the generator voltage to the load voltage , is the proportionality coefficient of the generator voltage to the load power deviation . S322, using the damping torque method to analyze the transfer function of the system frequency deviation and the load power deviation, to obtain the mechanism of the excitation system affecting the ultra-frequency oscillation.

2. The method of claim 1, wherein the method is characterized by: Step S12 specifically comprises the following steps: S121, calculating a sum of the deviations of the electromagnetic power output of each generator in the multi-machine system, expressed as: wherein, is a generator speed deviation, is a first j load active load rating, is a multi-machine system frequency deviation, is a frequency regulation effect coefficient, is a first i generator output electromagnetic power deviation, is a first j actual active load deviation. S122, calculating a sum of the rotor motion equations of each generator in the multi-machine system according to the sum of the deviations of the electromagnetic power output of each generator, expressed as: in, For the first i The damping coefficient of a generator, For the first i The inertial time constant of a generator, t For time, For the first i Input mechanical power deviation of each generator; S123, performing Laplace transformation on the sum of the rotor motion equations of each generator in the multi-machine system, to obtain the transfer function between the deviation of the electromagnetic power output of the generator and the deviation amount of the generator speed.

3. The method of claim 2, wherein the method is characterized by: The transfer function in step S123 is expressed as: wherein Gp is the transfer function of the equivalent generator, Tj is the inertia time constant of the jth generator, i Kj is the damping coefficient of the jth generator, Kf is the frequency regulation effect coefficient, Pj is the active load rating of the jth load, j Pj is the active load rating of the jth load, Kj is the damping coefficient of the jth generator, i Kj is the damping coefficient of the jth generator, Kj is the damping coefficient of the jth generator, Kj is the damping coefficient of the jth generator, 4. The method of claim 1, wherein the method is characterized by: The control strategy of the excitation control system with the power system stabilizer in step S2 comprises the following steps: A1, constructing a transfer function of the power system stabilizer, expressed as: wherein is a transfer function of a power system stabilizer, is a gain of the power system stabilizer PSS, is a time constant of a direct current blocking section, is a time constant of a lead section, is a time constant of a lag section, and s is a complex variable. A2, constructing a transfer function of the excitation control system, expressed as: wherein, is a transfer function of the excitation control system, and are a gain and a time constant of the excitation control, respectively.

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