Power grid and unit integration model construction method based on electromechanical transient theory

Abstract

The invention provides a power grid and unit integration model construction method based on an electromechanical transient theory, relates to the technical field of power systems, and finally obtains a dynamic simulation system by constructing a power grid model based on the electromechanical transient theory and a unit model based on the electromechanical transient theory. The power grid-unit accident fault prediction based on the electromechanical transient theory is realized; according to the construction of the power grid model based on the electromechanical transient theory, a topological structure of a power grid is firstly obtained, and then a load flow calculation model, a short circuit calculation model and an electromechanical transient process calculation model are obtained; the unit model based on the electromechanical transient theory comprises a water turbine model and a generator model; the accuracy of the mathematical model is enhanced, and the dynamic state of the power system is accurately described; the power grid model simulation function is optimized, and the relationship between the system and the plant station and the fault condition are comprehensively reflected.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a method for constructing an integrated model of a power grid and a generator set based on electromechanical transient theory. Background Art

[0002] Power grid and generator simulation technology plays a vital role in the operation and research of power systems. As power systems continue to expand in scale and become more complex, the performance requirements for power grid and generator simulation systems are also increasing. Currently, power grid and generator simulation systems face several challenges in practical applications. For example, some simulation systems exhibit poor stability when faced with complex operating conditions or fault conditions, prone to system crashes or model freezes, making them unable to meet the requirements of long-term simulation and training. Furthermore, the mathematical models of some simulation systems are not precise enough to accurately describe the dynamic processes of power systems, resulting in significant deviations between simulation results and actual operation.

[0003] In terms of power grid model simulation, some existing technologies are unable to accurately reflect the dynamic relationship between the power system and the power station. There are differences between the simulation operations under the centralized control mode and the actual operating conditions, and it is impossible to accurately simulate the various phenomena, actions and processing processes when faults or accidents occur.

[0004] The turbine and generator models also have limitations when it comes to unit model simulation. The turbine model may not fully account for the nonlinear changes in the turbine under various operating conditions, resulting in discrepancies between the turbine's key operating parameters and actual conditions. The generator model is not precise enough in describing the generator's various operating characteristics, making it difficult to simulate its dynamic behavior in real time under various operating conditions. Furthermore, under abnormal and accidental conditions, the consistency of meter and parameter changes with actual physical laws needs to be improved.

[0005] Furthermore, existing accident and failure simulation models lack accuracy and real-time performance when dealing with naturally occurring failures, equipment defects, and human error, and cannot truly reflect actual production failure scenarios and their handling processes. Furthermore, the simulation system's performance indicators, such as static performance, dynamic performance, real-time performance, and reliability, also struggle to fully meet actual needs.

[0006] In the field of power systems, current grid and unit simulation technologies have many defects.

[0007] In terms of stability, some simulation systems are prone to crashing during operating state switching and accident conditions. Misoperation often renders the system inoperable, limiting simulation and training. In terms of mathematical model accuracy, the power grid model does not accurately describe the dynamic process, and the turbine model does not consider nonlinear changes in all operating conditions, causing the simulation results to deviate from reality and affecting analysis and decision-making. The simulation function of the power grid model is limited, making it difficult to simulate the dynamic relationship between the system and the plant. The centralized control operation and fault simulation do not match reality and cannot reflect the logical relationship between equipment. In the unit model, the dynamic connection between the turbine model parameters is inaccurate, key factors are not considered, and there is a lack of correction. The generator model cannot accurately reflect the characteristics of different operating conditions, and the changes in meters and parameters do not conform to the laws of physics.

[0008] Accident and fault simulations have low accuracy and real-time performance, with inaccurate simulations of various faults. Fault phenomena and handling processes differ significantly from actual conditions, hindering personnel training and system safety. In terms of performance indicators, static performance indicators include large instrument errors and out-of-range deviations in key parameters. Dynamic performance indicators include non-compliance with procedures for dynamic processes, inconsistent parameter changes with analysis results, inconsistent alarm actions, and large deviations in the transient characteristics of key parameters. Real-time indicators include excessively long operation response and calculation steps, slow screen refresh and model calculation cycles, and long operation response times. System reliability indicators include short mean time between failures for the host, system, and interface, low availability, and insufficient continuous operation time, severely restricting the application of simulation systems. Summary of the Invention

[0009] In view of the shortcomings of the existing technology, the present invention provides a method for constructing an integrated model of power grid and generator set based on electromechanical transient theory;

[0010] A method for constructing an integrated model of a power grid and a generator set based on electromechanical transient theory includes the following steps:

[0011] Step 1: Construct a power grid model based on electromechanical transient theory;

[0012] Step 1.1: Determine the basic components and topology of the power grid system and obtain the topology of the power grid;

[0013] Step 1.2: Set component parameters;

[0014] The component parameters specifically include: generator parameters, transformer parameters, line parameters, circuit breaker, disconnector, and grounding switch parameters;

[0015] Step 1.3: Establish a power flow calculation model;

[0016] The power flow calculation model is based on Kirchhoff's law, and its goal is to solve the voltage amplitude U of each bus in the power grid. i and phase angle θ iAnd the power flow of each branch; for a power grid with n buses, its power flow equation is expressed in polar coordinate form as follows:

[0017] (1) Active power balance equation:

[0018]

[0019] Among them, P Gi is the active power injected by the generator connected to bus i, P Li is the active power consumed by the load connected to bus i, G ij and B ij are the conductance and susceptance elements in the node admittance matrix, θ j is the voltage phase angle of bus j;

[0020] (2) Reactive power balance equation:

[0021]

[0022] Among them, Q Gi is the reactive power injected by the generator connected to bus i, Q Li is the reactive power consumed by the load connected to bus i;

[0023] By iteratively solving the active power balance equation and the reactive power balance equation, the power flow distribution of the power grid under normal operating conditions is obtained, and then the static characteristics of the power grid are analyzed;

[0024] Step 1.4: Establish a short-circuit calculation model;

[0025] For a three-phase short-circuit fault, the short-circuit current at the short-circuit point is assumed to be I k , the short-circuit impedance is Z k , according to Ohm's law, the short-circuit current calculation formula is obtained, and the short-circuit calculation model is obtained:

[0026]

[0027] Among them, U c is the calculated voltage at the short-circuit point;

[0028] Step 1.5: Construct a calculation model for electromechanical transient processes;

[0029] The generator rotor motion equation is expressed as:

[0030]

[0031] Where ω is the angular velocity of the generator rotor, ω s is the synchronous angular velocity, T m is the mechanical torque input by the prime mover, T eis the electromagnetic torque output by the generator, H is the inertia time constant, and δ is the power angle of the generator rotor;

[0032] Step 1.6: Construct a power grid model based on electromechanical transient theory and perform simulation;

[0033] Step 1.6.1: Switching operation simulation;

[0034] Based on actual operating rules and the interlocking and interlocking relationships between various switchgear, program logic is written to simulate the equipment's action sequence and state changes during the switching operation, as well as the impact on power flow, voltage, current distribution, and electrical characteristics of the network structure system;

[0035] Step 1.6.2: Calculate network topology;

[0036] Real-time monitoring of changes in the connection status of each component in the power grid, updating the network topology, and regenerating the basic structured data of the node admittance matrix, branch admittance information, and network connectivity;

[0037] Step 1.6.3: Simulate the operation of relay protection and automatic devices;

[0038] Based on the operating principles and setting values ​​of different protection devices, when a fault or abnormal operation occurs in the power grid, it determines whether the protection device should operate, simulates its operating behavior and the action logic of subsequent automatic devices, and simultaneously updates the system parameters of the power grid's operating status, power flow distribution, node voltage, electrical equipment status, and network topology.

[0039] Step 1.7: Verify and calibrate the constructed power grid model based on electromechanical transient theory;

[0040] The equipment operating parameters obtained during power flow calculation and transient simulation, including bus voltage, frequency, line active power, reactive power, and the dynamic changes of current over time, are compared and analyzed with actual on-site operating data to verify the accuracy of the power grid model and complete calibration through parameter correction.

[0041] Step 2: Construct a unit model based on electromechanical transient theory;

[0042] Step 2.1: Build a turbine model;

[0043] Based on the turbine's operating and regulation characteristics, including the operating characteristic curve, runaway operating condition curve, force characteristics, and the nonlinear relationship between head, flow, and guide vane opening, a turbine model covering the water diversion system and the water discharge system is established;

[0044] The turbine output power P is expressed as a function of the head H, flow rate Q, and efficiency η, and is modeled using the following expression:

[0045] P=ρgQHη

[0046] Where ρ is the density of water and g is the acceleration due to gravity;

[0047] The relationship between the turbine torque, power and speed is:

[0048] P=Mω=M·2πn, so

[0049] M represents the mechanical torque on the turbine output shaft. The water head H, flow Q, speed n, and guide vane opening a are described by the turbine characteristic curve, which can be expressed in the form of a function:

[0050] H=f1(Q,n,a)

[0051] Q=f2(H,n,a)

[0052] n=f3(H,Q,a)

[0053] a=f4(H,Q,n)

[0054] Among them, functions f1 to f4 are corresponding relationships obtained by fitting the actual turbine characteristic test data or querying the characteristic curve;

[0055] Step 2.1.1: Collect data;

[0056] Collect data on the prototype turbine's operating characteristic curves, runaway operating curves, and related force characteristics;

[0057] Step 2.1.2: Establish a basic relationship model;

[0058] Based on the relationship between the turbine's torque, power, and speed, mathematical expressions are constructed between the operating parameters of head, flow, efficiency, speed, torque, and guide vane opening;

[0059] Step 2.1.3: Fit the characteristic curve relationship;

[0060] Using the data collected in step 2.1.1, determine the specific function expressions, i.e., functions f1 to f4, through data fitting methods;

[0061] Step 2.1.4: Consider dynamics and calibrate the model;

[0062] Taking into account dynamic torque, moment of inertia, head change, flow inertia, guide vane adjustment lag, and damping torque dynamic factors, the dynamic characteristics of the turbine model are improved to accurately reflect the parameter changes of the turbine during the dynamic process. Using the operating characteristic curve of the prototype unit, the turbine model data is corrected by three-dimensional interpolation to improve the model accuracy and ensure that the system parameter changes are consistent with the simulation prototype;

[0063] Step 2.2: Build the generator model;

[0064] Specifically, a set of electromechanical transient differential equations is used to describe the generator characteristics, including the generator rotor motion equations, voltage and current equations, and the mathematical model of the excitation system;

[0065] The generator rotor motion equation:

[0066]

[0067] Wherein, J is the moment of inertia of the generator rotor;

[0068] The voltage-current equation:

[0069]

[0070] Among them, E q 、E d are the quadrature axis and direct axis potentials of the generator respectively; U q 、U d are the quadrature-axis and direct-axis components of the generator terminal voltage respectively; I q , I d are the quadrature-axis and direct-axis components of the stator current respectively; R a is the stator winding resistance; X q 、X d are the direct-axis synchronous reactance and quadrature-axis synchronous reactance of the generator respectively.

[0071] The mathematical model of the excitation system:

[0072]

[0073] Among them, T f is the time constant of the excitation system, E f is the excitation voltage, U ref is the reference voltage of the excitation system, K e is the magnification of the excitation system;

[0074] Step 2.2.1: Establish a mathematical model of the generator;

[0075] According to the physical principles of the generator and electromechanical transient theory, the rotor motion equation, voltage and current equations and the mathematical model of the excitation system are selected, and the variables and parameters involved in the equations are determined.

[0076] Step 2.2.2: Get parameter values;

[0077] Obtain the parameters required to build the generator model, including: moment of inertia, mechanical torque, and electromagnetic torque in the rotor motion submodel; stator resistance, synchronous reactance, potential, and quadrature and direct axis components of current in the voltage and current submodel; and excitation time constant, gain, excitation voltage, and reference in the excitation system submodel.

[0078] Step 2.3: Collect data;

[0079] Substitute the obtained parameter values ​​into step 2.2 to construct a complete set of electromechanical transient differential equations. During the actual simulation or analysis process, numerical calculation methods are used to solve the electromechanical transient differential equations to obtain the changes in the generator operating parameters at different times, thereby simulating the operating characteristics of the generator under various operating conditions.

[0080] Step 2.4: Verify and calibrate the generator model;

[0081] Compare and verify the results calculated by the generator model with the operating data of the actual generator under the corresponding working conditions. If there is any deviation, analyze the cause and adjust the model parameters or optimize the model;

[0082] Step 3: Construct a dynamic simulation system based on the power grid model and unit model based on electromechanical transient theory, and perform accident and fault prediction for the power grid-unit based on electromechanical transient theory;

[0083] Based on electromechanical transient theory, the dynamic process of the power system is described by the state space equation:

[0084]

[0085] in, represents the time derivative of the state variable x, the function f() is a nonlinear function that reflects the dynamic characteristics of the system, and the parameters u and f represent the input variable and the fault disturbance term respectively;

[0086] When the fault disturbance term f≠0, that is, a fault occurs, it is necessary to superimpose the additional disturbance term caused by the fault so that the state space equation becomes:

[0087]

[0088] Where Δf is the additional impact function caused by the fault, which is related to the fault type as well as the current state variable x, input u and system parameter θ;

[0089] Step 3.1: Initialization phase;

[0090] Determine the initial values ​​of system parameters θ based on the actual power system topology and component parameter configuration; specifically, the rated power, synchronous reactance, and moment of inertia of each generator; the capacity, ratio, and short-circuit impedance of the transformer; the resistance, reactance, susceptance, and length of the line; the operating time and blocking logic parameters of switchgear such as circuit breakers; and the initialization of the active and reactive load setting parameters of the load nodes;

[0091] Set the value of the initial state variable x so that it is in a state corresponding to a certain stable operating condition;

[0092] Set the input variable u to the control input information corresponding to the initial working condition:

[0093] The fault identification variable f′ is initialized to 0, indicating that the system is in normal operation and has no faults;

[0094] Step 3.2: Fault injection phase, corresponding to the case where f′≠0;

[0095] Failures caused by natural occurrence or equipment defects: f′ = 1;

[0096] According to the specific fault type to be simulated, the corresponding fault parameters are set through the trainer station, the fault identification variable f′ is modified to 1, and the specific form of the corresponding additional influence function Δf is determined. The disturbance caused by the fault is superimposed on the state space equation through the additional influence function Δf, and the change of the system state variable x is calculated.

[0097] Fault caused by human error: f′=2;

[0098] When simulating operator misoperation in the dynamic simulation system, the dynamic simulation system detects the misoperation in real time, immediately changes the fault identification variable f′ to 2, and determines the corresponding additional impact function Δf based on the fault mechanism corresponding to the misoperation. This additional impact is superimposed on the state space equation, and the change process of the system state variable x is tracked in real time.

[0099] Step 3.3: Dynamic simulation stage;

[0100] The state space equation with fault additional term is solved by numerical calculation method. Solve the problem and gradually advance the calculation according to the set time step Δt to obtain the value of the system state variable x at different times, thereby simulating the dynamic change process of the system after the fault occurs;

[0101] Step 3.4: Result output and analysis;

[0102] According to the calculated values ​​of the system state variable x at different times, the corresponding phenomenon information is output to make it consistent with the fault phenomenon and action conditions in actual production;

[0103] Observe the operator's operation to handle the fault, modify the input variable u again according to the operation situation, continue dynamic simulation, and judge whether the operation can alleviate the impact of the fault or restore the normal operation of the system. Otherwise, continue to observe the changes in the system status to see whether it will cause the fault to expand;

[0104] The beneficial effects of adopting the above technical solution are:

[0105] The present invention provides a method for constructing an integrated model of power grids and units based on electromechanical transient theory. The present invention improves the stability of the simulation system, enabling it to continue operating under complex working conditions; enhances the accuracy of the mathematical model, accurately describing the dynamics of the power system; optimizes the simulation function of the power grid model, comprehensively reflecting the relationship between the system and the plant and station and fault conditions; improves the simulation effect of the unit model, accurately presenting the various operating characteristics of the unit; enhances the authenticity of accident and fault simulation, covering all types of fault simulation; meets performance index requirements, including static, dynamic, real-time and reliability indicators, and provides strong support for power system operation, maintenance, training and research. BRIEF DESCRIPTION OF THE DRAWINGS

[0106] Figure 1 This is an overall flow chart of the method for constructing an integrated model of a power grid and a generator set based on electromechanical transient theory of the present invention. DETAILED DESCRIPTION

[0107] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0108] A method for constructing an integrated model of power grid and generator set based on electromechanical transient theory, such as Figure 1 As shown, the following steps are included:

[0109] Step 1: Construct a power grid model based on electromechanical transient theory;

[0110] Step 1.1: Determine the basic components and topology of the power grid system and obtain the topology of the power grid;

[0111] First, it's necessary to identify the various components in the power grid, such as busbars, generators, transformers, lines, circuit breakers, disconnectors, and earthing switches, and to map out their connections to form the grid's topology. This can be accomplished by collecting data such as actual grid wiring diagrams and plant and substation layouts.

[0112] Step 1.2: Set component parameters;

[0113] The component parameters specifically include: generator parameters, transformer parameters, line parameters, circuit breaker, disconnector, and grounding switch parameters;

[0114] The generator parameters include rated power (i.e., the rated active power that the generator can output during normal operation), rated voltage (i.e., the rated output line voltage of the generator), synchronous reactance (i.e., the electromagnetic characteristics within the generator, used to reflect the electromagnetic interaction between the generator and the power grid in the calculation of electromechanical transient processes), and inertia time constant (i.e., the rotational inertia characteristics of the generator rotor, which plays a key role in considering dynamic characteristics such as speed changes during electromechanical transient processes).

[0115] The transformer parameters include rated capacity (the apparent power rating that the transformer can transmit when operating normally), transformation ratio (the proportional relationship of voltage transformation), and short-circuit reactance (i.e., calculation of short-circuit current and analysis of the transformer's impact on voltage and power flow distribution in the power grid).

[0116] The line parameters include resistance, reactance, susceptance, and line length.

[0117] The parameters of the circuit breaker, disconnector and earthing switch mainly consider their operating time, current interrupting capacity, etc., and are used for simulation operation and locking and interlocking logic judgment.

[0118] Step 1.3: Establish a power flow calculation model;

[0119] The power flow calculation model is based on Kirchhoff's law, and its goal is to solve the voltage amplitude U of each bus in the power grid. i and phase angle θ i And the power flow of each branch; for a power grid with n buses, its power flow equation is expressed in polar coordinate form as follows:

[0120] (1) Active power balance equation:

[0121]

[0122] Among them, P Gi is the active power injected by the generator connected to bus i, P Li is the active power consumed by the load connected to bus i, G ij and B ij are the conductance and susceptance elements in the node admittance matrix, θ j is the voltage phase angle of bus j, which is used to represent its relative position to the reference angle in the AC system and is an important variable for calculating power flow and network status. i The difference determines the direction and magnitude of the active power flow;

[0123] (2) Reactive power balance equation:

[0124]

[0125] Among them, Q Gi is the reactive power injected by the generator connected to bus i, Q Li is the reactive power consumed by the load connected to bus i;

[0126] By iteratively solving the active power balance equation and the reactive power balance equation, the power flow distribution of the power grid under normal operating conditions is obtained, and then the static characteristics of the power grid are analyzed;

[0127] Step 1.4: Establish a short-circuit calculation model;

[0128] Common methods for short-circuit calculation include per-unit method. For a three-phase short-circuit fault, the short-circuit current at the short-circuit point is assumed to be I k , the short-circuit impedance is Z k , according to Ohm's law, the short-circuit current calculation formula is obtained, and the short-circuit calculation model is obtained:

[0129]

[0130] Among them, U c is the calculated voltage at the short-circuit point; the short-circuit impedance Z k The short-circuit calculation can determine the short-circuit current, short-circuit point voltage and other parameters under fault conditions, and analyze the characteristics of the power grid under fault conditions.

[0131] Step 1.5: Construct a calculation model for electromechanical transient processes;

[0132] The electromechanical transient process involves the coupling of the generator rotor motion equation and the electromagnetic transient equation. The generator rotor motion equation is expressed as:

[0133]

[0134] Where ω is the angular velocity of the generator rotor, ω s is the synchronous angular velocity, T m is the mechanical torque input by the prime mover, T e is the electromagnetic torque output by the generator, H is the inertia time constant, and δ is the power angle of the generator rotor;

[0135] The existing electromagnetic transient equations are related to the voltage, current and internal reactance of the generator. By combining the simultaneous equations and the characteristic equations of other components in the power grid during transient processes, it is possible to analyze the dynamic changes of the power system during electromechanical transient processes, such as power angle swings and frequency changes, thereby describing the dynamic characteristics of the power system.

[0136] Step 1.6: Construct a power grid model based on electromechanical transient theory and perform simulation;

[0137] Step 1.6.1: Switching operation simulation;

[0138] Based on actual operating rules and the interlocking and interlocking relationships between various switchgear devices, program logic is written to simulate the device action sequence and state changes during switching operations, as well as their impact on power flow, voltage, current distribution, and the electrical characteristics of the network structure system. For example, when performing a line power outage, the sequence of opening the circuit breaker first and then the disconnector is achieved by changing the state variables of the corresponding devices in the power grid model, and the power flow calculation results are updated in real time.

[0139] Step 1.6.2: Calculate network topology;

[0140] Real-time monitoring of connection status changes of various components in the power grid (such as switch opening and closing, disconnector operation, grounding switch input, bus switching), updating the network topology, and regenerating the node admittance matrix, branch admittance information and basic structured data of network connectivity relationships for subsequent numerical calculations of power flow calculations, short-circuit analysis, transient simulation and other power grid state evolution processes.

[0141] Step 1.6.3: Simulate the operation of relay protection and automatic devices;

[0142] Based on the operating principles and setting values ​​of different protection devices (such as overcurrent protection and distance protection), when a fault or abnormal operation occurs in the power grid, it is determined whether the protection device should operate, and its operating behavior (such as tripping the circuit breaker, etc.) and the subsequent operation logic of automatic devices such as automatic reclosing are simulated. At the same time, the system parameters of the power grid's operating status, power flow distribution, node voltage, electrical equipment status and network topology are updated to support the dynamic evolution of the subsequent simulation process.

[0143] Step 1.7: Verify and calibrate the constructed power grid model based on electromechanical transient theory;

[0144] The equipment operating parameters obtained during the power flow calculation and transient simulation process, including the dynamic changes of bus voltage, frequency, active power, reactive power and current of the line over time, are compared and analyzed with the actual on-site operating data to verify the accuracy of the power grid model and complete the calibration through parameter correction.

[0145] Step 2: Construct a unit model based on electromechanical transient theory;

[0146] Step 2.1: Build a turbine model;

[0147] Based on the turbine's operational and regulatory characteristics, including operating characteristic curves, runaway operating curves, force characteristics, and the nonlinear relationship between head, flow, and guide vane opening, a turbine model was established, encompassing both the diversion and discharge systems. The goal was to ensure that the relationships between the turbine's head, flow, torque, speed, and guide vane opening were as consistent as possible with the prototype.

[0148] The turbine output power P is expressed as a function of the head H, flow rate Q, and efficiency η, and is modeled using the following expression:

[0149] P=ρgQHη

[0150] Where ρ is the density of water and g is the acceleration due to gravity;

[0151] The relationship between the turbine torque, power and speed is:

[0152] P=Mω=M·2πn, so

[0153] M represents the mechanical torque on the turbine output shaft. There is a complex nonlinear relationship between the head H, flow Q, speed n, and guide vane opening a, which is described by the turbine characteristic curve (such as the operating characteristic curve), that is, expressed in function form as follows:

[0154] H=f1(Q,n,a)

[0155] Q=f2(H,n,a)

[0156] n=f3(H,Q,a)

[0157] a=f4(H,Q,n)

[0158] Among them, functions f1 to f4 are corresponding relationships obtained by fitting the actual turbine characteristic test data or querying the characteristic curve;

[0159] Step 2.1.1: Collect data;

[0160] Collect the operating characteristic curve, runaway condition curve and related force characteristic data of the prototype turbine; these data usually come from the turbine manufacturer's factory test or actual on-site test measurements.

[0161] Step 2.1.2: Establish a basic relationship model;

[0162] Based on the relationship formulas between the turbine's torque, power, and speed (such as the relationship between power and head, flow, and efficiency, the relationship between torque and power and speed, and the nonlinear relationship between guide vane opening and head and flow), mathematical expressions are constructed between the operating parameters of head, flow, efficiency, speed, torque, and guide vane opening;

[0163] Step 2.1.3: Fit the characteristic curve relationship;

[0164] In view of the complex relationships between parameters such as head, flow, speed, and guide vane opening, the data collected in step 2.1.1 are used to determine specific function expressions, namely functions f1 to f4, through data fitting methods (such as polynomial fitting, spline interpolation fitting, etc.), so that the changing relationships between these parameters are consistent with the actual situation of the turbine prototype.

[0165] Step 2.1.4: Consider dynamics and calibrate the model;

[0166] Taking into account dynamic torque, moment of inertia, head change, flow inertia, guide vane adjustment lag, and damping torque dynamic factors, the dynamic characteristics of the turbine model are improved to enable it to accurately reflect the parameter changes of the turbine during the dynamic process. Using the operating characteristic curve of the prototype unit, three-dimensional interpolation (for example, for the three dimensions of head, flow, and guide vane opening) is used to correct the turbine model data to improve model accuracy and ensure that the system parameter changes are consistent with the simulation prototype;

[0167] Step 2.2: Build the generator model;

[0168] Specifically, a set of electromechanical transient differential equations is used to describe the generator characteristics, including the generator rotor motion equations, voltage and current equations, and the mathematical model of the excitation system, so as to accurately and in real time reflect the operating characteristics of the generator under different working conditions.

[0169] The generator rotor motion equation:

[0170]

[0171] Among them, J is the moment of inertia of the generator rotor; this equation describes the rotation of the generator rotor under the action of mechanical torque and electromagnetic torque, and is an important equation reflecting the electromechanical transient process of the generator.

[0172] The voltage and current equation (here taking the three-phase stable and symmetrical operation of the synchronous generator as an example) is:

[0173]

[0174] Among them, E q 、E d are the quadrature axis and direct axis potentials of the generator respectively; U q 、U d are the quadrature-axis and direct-axis components of the generator terminal voltage respectively; I q , I d are the quadrature-axis and direct-axis components of the stator current respectively; R a is the stator winding resistance; Xq 、X d are the direct-axis synchronous reactance and quadrature-axis synchronous reactance of the generator respectively.

[0175] The mathematical model of the excitation system (here taking the first-order inertia link as an example):

[0176]

[0177] Among them, T f is the time constant of the excitation system, E f is the excitation voltage, U ref is the reference voltage of the excitation system, K e is the magnification of the excitation system;

[0178] Step 2.2.1: Establish a mathematical model of the generator;

[0179] According to the physical principles of the generator and electromechanical transient theory, the rotor motion equation, voltage and current equations and the mathematical model of the excitation system are selected, and the variables and parameters involved in the equations are determined.

[0180] Step 2.2.2: Get parameter values;

[0181] Obtain the parameters required to construct the generator model from the generator's design data, manufacturer's data sheets, or field test measurements. Specifically, these parameters include: moment of inertia, mechanical torque, and electromagnetic torque in the rotor motion submodel; stator resistance, synchronous reactance, potential, and quadrature and direct axis components of current in the voltage and current submodel; and excitation time constant, gain, excitation voltage, and reference in the excitation system submodel. These parameters should be determined based on the actual generator model and excitation device characteristics.

[0182] Step 2.3: Collect data;

[0183] Substitute the obtained parameter values ​​into step 2.2 to construct a complete set of electromechanical transient differential equations; in the actual simulation or analysis process, numerical calculation methods (such as the Euler method, the Runge-Kutta method, etc.) are used to solve the electromechanical transient differential equations to obtain the changes in the generator operating parameters (such as speed, voltage, current, etc.) at different times, thereby simulating the operating characteristics of the generator under various operating conditions such as no-load operation, parallel operation, decoupling, speed increase, speed decrease, adjustment of active power, reactive power, load rejection, and leading phase operation.

[0184] Step 2.4: Verify and calibrate the generator model;

[0185] Compare and verify the results obtained from the generator model calculation with the operating data of the actual generator under the corresponding working conditions (such as on-site meter measurement data, etc.). If there is a deviation, analyze the cause and adjust the model parameters or optimize the model; ensure that the model can accurately simulate the entire physical process of the generator, so that it can accurately and real-time simulate the dynamic and static behavior of the generator under various operating conditions and different loads, consistent with the actual situation on site.

[0186] By combining the hydraulic turbine model and generator model constructed above and their synergy, the overall operating characteristics of the unit can be simulated and analyzed more accurately based on electromechanical transient theory.

[0187] Step 3: Construct a dynamic simulation system based on the power grid model and unit model based on electromechanical transient theory, and perform accident and fault prediction for the power grid-unit based on electromechanical transient theory;

[0188] Based on electromechanical transient theory, the dynamic process of the power system is described by the state space equation:

[0189]

[0190] in, It represents the time derivative of the state variable x. The function f() is a nonlinear function that reflects the dynamic characteristics of the system. Its specific form is determined according to the mathematical model of each component under the electromechanical transient principle and the coupling relationship between them. The parameters u and f represent the input variable and the fault disturbance term respectively.

[0191] When the fault disturbance term f≠0, that is, a fault occurs, an additional disturbance term caused by the superimposed fault is required; for example, when a short circuit fault occurs, a term corresponding to the injected current at the short circuit point is introduced into the network equation. The corresponding additional term is determined according to the different fault types, so that the state space equation becomes:

[0192]

[0193] Where Δf is the additional impact function caused by the fault, which is related to the fault type (determined by the fault disturbance term f) as well as the current state variable x, input u and system parameter θ.

[0194] Step 3.1: Initialization phase;

[0195] Based on the actual power system topology and component parameters (including generators, transformers, transmission lines, circuit breakers, disconnectors, grounding switches, load nodes, busbars, etc.), the initial values ​​of system parameters θ are determined. Specifically, these include the rated power, synchronous reactance, and moment of inertia of each generator; the capacity, ratio, and short-circuit impedance of the transformer; the resistance, reactance, susceptance, and length of the line; the operating time and blocking logic parameters of switchgear such as circuit breakers; and the initialization of the active and reactive load setting parameters of the load nodes. This provides the basic conditions for the subsequent system dynamic simulation and fault injection stages.

[0196] Set the value of the initial state variable x, such as the initial speed and voltage of each generator, so that it is in a state corresponding to a certain stable operating condition;

[0197] Set the input variable u to the control input information corresponding to the initial working condition:

[0198] The fault identification variable f′ is initialized to 0, indicating that the system is in normal operation and has no faults;

[0199] Step 3.2: Fault injection phase, corresponding to the case where f′≠0;

[0200] Failures caused by natural occurrence or equipment defects: f′ = 1;

[0201] According to the specific fault type to be simulated (such as line short circuit, generator failure, etc.), the corresponding fault parameters are set through the trainer station, the fault identification variable f′ is modified to 1, and the specific form of the corresponding additional influence function Δf is determined (for example, for a short circuit fault, the short circuit point location, short circuit impedance and other parameters are determined, and then the impact on the network equation is obtained). The disturbance caused by the fault is superimposed on the state space equation through the additional influence function Δf, and the change of the system state variable x is calculated;

[0202] Fault caused by human error: f′=2;

[0203] When simulating operator misoperations in the dynamic simulation system (such as accidentally pulling a switch or misadjusting equipment parameters), the system detects the misoperation in real time, immediately changes the fault identification variable f′ to 2, and determines the corresponding additional impact function Δf based on the fault mechanism corresponding to the misoperation (for example, pulling a switch incorrectly will change the network topology, so the network admittance matrix needs to be adjusted accordingly). This additional impact is superimposed on the state space equation, and the changes in the system state variable x are tracked in real time.

[0204] Step 3.3: Dynamic simulation stage;

[0205] The state space equation containing fault additional terms is solved by numerical calculation methods (such as improved Euler method, Runge-Kutta method, etc.) The solution is solved and the calculation is gradually carried out according to the set time step Δt to obtain the value of the system state variable x at different times, thereby simulating the dynamic change process of the system after the fault occurs. The change of the state variable x in this process will be reflected in the changes of physical quantities such as generator speed, voltage, and line current.

[0206] Step 3.4: Result output and analysis;

[0207] Based on the calculated values ​​of the system state variable x at different moments, the corresponding phenomenon information is output, such as generating brief information (including a brief description of the fault occurrence time, location, type, etc.), updating the equipment status (which equipment is tripped, locked, etc.), changing the light display (reflecting fault alarms, etc.), updating the monitoring screen display (visual display of each component's operating parameters), and presenting the change curve of the main equipment operating parameters, etc., so that it is consistent with the fault phenomenon and action conditions in actual production;

[0208] Observe the operation of the operator (this can be the actual operator operating on the simulation system or a preset operation strategy simulation) to handle the fault, modify the input variable u again according to the operation situation (such as adjusting the generator output, switching the switch, etc.), continue dynamic simulation, and judge whether the operation can alleviate the impact of the fault or restore the normal operation of the system. If the handling is inappropriate, continue to observe the changes in the system state to see if it will cause the fault to expand. The whole process must also ensure that it is consistent with the accident handling process in actual production;

[0209] "Improper handling" here refers to situations where, during the operator's response to a fault, misjudgment, operational errors, or inappropriate control strategy settings lead to failure to effectively isolate the fault area, suppress the spread of disturbances, or restore system stability, potentially leading to more serious secondary faults. Examples include incorrectly closing or opening circuit breakers, untimely load shedding, excitation system control imbalances, and failure of frequency or voltage over-limit control. The simulation system dynamically evolves to track these operational outcomes, thereby assessing the system's safety margin and reliability during incident response.

[0210] Through the accident fault model constructed above, various accident fault conditions and their handling processes in the power system can be simulated more comprehensively and accurately based on electromechanical transient theory.

[0211] The above description is merely a preferred embodiment of the present disclosure and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in the embodiments of the present disclosure is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also encompass other technical solutions formed by any combination of the above-mentioned technical features or their equivalents without departing from the above-mentioned inventive concept. For example, a technical solution formed by mutually replacing the above-mentioned features with (but not limited to) technical features with similar functions disclosed in the embodiments of the present disclosure.

Claims

1. A method for constructing an integrated model of power grid and generator set based on electromechanical transient theory, characterized in that: The following steps are involved: Step 1: Construct a power grid model based on electromechanical transient theory; Step 1.1: Determine the basic components and topology of the power grid system and obtain the topology of the power grid; Step 1.2: Set component parameters; The component parameters specifically include: generator parameters, transformer parameters, line parameters, circuit breaker, disconnector, and grounding switch parameters; Step 1.3: Establish a power flow calculation model; The power flow calculation model is based on Kirchhoff's law, and its goal is to solve the voltage amplitude U of each bus in the power grid. i and phase angle θ i And the power flow of each branch; for a power grid with n buses, its power flow equation is expressed in polar coordinate form as follows: (1) Active power balance equation: Among them, P Gi is the active power injected by the generator connected to bus i, P Li is the active power consumed by the load connected to bus i, G ij and B ij are the conductance and susceptance elements in the node admittance matrix, θ j is the voltage phase angle of bus j; (2) Reactive power balance equation: Among them, Q Gi is the reactive power injected by the generator connected to bus i, Q Li is the reactive power consumed by the load connected to bus i; By iteratively solving the active power balance equation and the reactive power balance equation, the power flow distribution of the power grid under normal operating conditions is obtained, and then the static characteristics of the power grid are analyzed; Step 1.4: Establish a short-circuit calculation model; For a three-phase short-circuit fault, the short-circuit current at the short-circuit point is assumed to be I k , the short-circuit impedance is Z k , according to Ohm's law, the short-circuit current calculation formula is obtained, and the short-circuit calculation model is obtained: Among them, U c is the calculated voltage at the short-circuit point; Step 1.5: Construct a calculation model for electromechanical transient processes; The generator rotor motion equation is expressed as: Where ω is the angular velocity of the generator rotor, ω s is the synchronous angular velocity, T m is the mechanical torque input by the prime mover, T e is the electromagnetic torque output by the generator, H is the inertia time constant, and δ is the power angle of the generator rotor; Step 1.6: Build a power grid model based on electromechanical transient theory and perform simulation. Step 1.7: Verify and calibrate the constructed power grid model based on electromechanical transient theory; The equipment operating parameters obtained during power flow calculation and transient simulation, including bus voltage, frequency, line active power, reactive power, and the dynamic changes of current over time, are compared and analyzed with actual on-site operating data to verify the accuracy of the power grid model and complete calibration through parameter correction. Step 2: Construct a unit model based on electromechanical transient theory; Step 2.1: Build a turbine model; Based on the turbine's operating and regulation characteristics, including the operating characteristic curve, runaway operating condition curve, force characteristics, and the nonlinear relationship between head, flow, and guide vane opening, a turbine model covering the water diversion system and the water discharge system is established; The turbine output power P is expressed as a function of the head H, flow rate Q, and efficiency η, and is modeled using the following expression: P=ρgQHη Where ρ is the density of water and g is the acceleration due to gravity; The relationship between the turbine torque, power and speed is: P=Mω=M·2πn, so M represents the mechanical torque on the turbine output shaft. The water head H, flow Q, speed n, and guide vane opening a are described by the turbine characteristic curve, which can be expressed in the form of a function: H=f1(Q,n,a) Q=f2(H,n,a) n=f3(H,Q,a) a=f4(H,Q,n) Among them, functions f1 to f4 are corresponding relationships obtained by fitting the actual turbine characteristic test data or querying the characteristic curve; Step 2.2: Build the generator model; Specifically, a set of electromechanical transient differential equations is used to describe the generator characteristics, including the generator rotor motion equations, voltage and current equations, and the mathematical model of the excitation system; The generator rotor motion equation: Wherein, J is the moment of inertia of the generator rotor; The voltage-current equation: Among them, E q 、E d are the quadrature axis and direct axis potentials of the generator respectively; U q 、U d are the quadrature-axis and direct-axis components of the generator terminal voltage respectively; I q , I d are the quadrature-axis and direct-axis components of the stator current respectively; R a is the stator winding resistance; X q 、X d are the direct-axis synchronous reactance and quadrature-axis synchronous reactance of the generator respectively; The mathematical model of the excitation system: Among them, T f is the time constant of the excitation system, E f is the excitation voltage, U ref is the reference voltage of the excitation system, K e is the magnification of the excitation system; Step 2.3: Collect data; Substitute the obtained parameter values ​​into step 2.2 to construct a complete set of electromechanical transient differential equations. During the actual simulation or analysis process, numerical calculation methods are used to solve the electromechanical transient differential equations to obtain the changes in the generator operating parameters at different times, thereby simulating the operating characteristics of the generator under various operating conditions. Step 2.4: Verify and calibrate the generator model; Compare and verify the results calculated by the generator model with the operating data of the actual generator under the corresponding working conditions. If there is any deviation, analyze the cause and adjust the model parameters or optimize the model; Step 3: Construct a dynamic simulation system based on the power grid model and unit model based on electromechanical transient theory, and perform accident and fault prediction for the power grid-unit based on electromechanical transient theory; Based on electromechanical transient theory, the dynamic process of the power system is described by the state space equation: in, represents the time derivative of the state variable x, the function f() is a nonlinear function that reflects the dynamic characteristics of the system, and the parameters u and f represent the input variable and the fault disturbance term respectively; When the fault disturbance term f≠0, that is, a fault occurs, it is necessary to superimpose the additional disturbance term caused by the fault so that the state space equation becomes: Among them, Δf is the additional impact function caused by the fault, which is related to the fault type as well as the current state variable x, input u and system parameter θ.

2. The method for constructing a power grid and unit integrated model based on electromechanical transient theory according to claim 1, characterized in that: The step 1.6 specifically includes the following steps: Step 1.6.1: Switching operation simulation; Based on actual operating rules and the interlocking and interlocking relationships between various switchgear, program logic is written to simulate the equipment's action sequence and state changes during the switching operation, as well as the impact on power flow, voltage, current distribution, and electrical characteristics of the network structure system; Step 1.6.2: Calculate network topology; Real-time monitoring of changes in the connection status of each component in the power grid, updating the network topology, and regenerating the basic structured data of the node admittance matrix, branch admittance information, and network connectivity; Step 1.6.3: Simulate the operation of relay protection and automatic devices; According to the operating principles and setting values ​​of different protection devices, when a fault or abnormal operation occurs in the power grid, it is determined whether the protection device should operate, and its operating behavior and the action logic of the subsequent automatic device are simulated. At the same time, the system parameters of the power grid's operating status, power flow distribution, node voltage, electrical equipment status and network topology are updated.

3. The method for constructing a power grid and unit integrated model based on electromechanical transient theory according to claim 1, characterized in that: The step 2.1 specifically includes the following steps: Step 2.1.1: Collect data; Collect data on the prototype turbine's operating characteristic curves, runaway operating curves, and related force characteristics; Step 2.1.2: Establish a basic relationship model; Based on the relationship between the turbine's torque, power, and speed, mathematical expressions are constructed between the operating parameters of head, flow, efficiency, speed, torque, and guide vane opening; Step 2.1.3: Fit the characteristic curve relationship; Using the data collected in step 2.1.1, determine the specific function expressions, i.e., functions f1 to f4, through data fitting methods; Step 2.1.4: Consider dynamics and calibrate the model; Taking into account the dynamic factors of dynamic torque, rotational inertia, head change, water flow inertia, guide vane adjustment lag, and damping torque, the dynamic characteristics of the turbine model are improved so that it can accurately reflect the parameter changes of the turbine in the dynamic process; using the operating characteristic curve of the prototype unit, the turbine model data is corrected by three-dimensional interpolation to improve the model accuracy and ensure that the system parameter changes are consistent with the simulation prototype.

4. The method for constructing a power grid and unit integrated model based on electromechanical transient theory according to claim 1, characterized in that: The step 2.2 specifically includes the following steps: Step 2.2.1: Establish a mathematical model of the generator; According to the physical principles of the generator and electromechanical transient theory, select the rotor motion equation, voltage and current equations, and the mathematical model of the excitation system, and determine the variables and parameters involved in the equations; Step 2.2.2: Get parameter values; Obtain the parameters required to build the generator model, including: moment of inertia, mechanical torque, and electromagnetic torque in the rotor motion submodel; stator resistance, synchronous reactance, potential, and quadrature and direct axis components of current in the voltage and current submodel; and excitation time constant, gain, excitation voltage, and reference in the excitation system submodel.

5. The method for constructing a power grid and unit integrated model based on electromechanical transient theory according to claim 1, characterized in that: The step 3 specifically includes the following steps: Step 3.1: Initialization phase; Determine the initial values ​​of system parameters θ based on the actual power system topology and component parameter configuration; specifically, the rated power, synchronous reactance, and moment of inertia of each generator; the capacity, ratio, and short-circuit impedance of the transformer; the resistance, reactance, susceptance, and length of the line; the operating time and blocking logic parameters of switchgear such as circuit breakers; and the initialization of the active and reactive load setting parameters of the load nodes; Set the value of the initial state variable x so that it is in a state corresponding to a certain stable operating condition; Set the input variable u to the control input information corresponding to the initial working condition: The fault identification variable f′ is initialized to 0, indicating that the system is in normal operation and has no faults; Step 3.2: Fault injection phase, corresponding to the case where f′≠0; Failures caused by natural occurrence or equipment defects: f′ = 1; According to the specific fault type to be simulated, the corresponding fault parameters are set through the trainer station, the fault identification variable f′ is modified to 1, and the specific form of the corresponding additional influence function Δf is determined. The disturbance caused by the fault is superimposed on the state space equation through the additional influence function Δf, and the change of the system state variable x is calculated. Fault caused by human error: f′=2; When simulating operator misoperation in the dynamic simulation system, the dynamic simulation system detects the misoperation in real time, immediately changes the fault identification variable f′ to 2, and determines the corresponding additional impact function Δf based on the fault mechanism corresponding to the misoperation. This additional impact is superimposed on the state space equation, and the change process of the system state variable x is tracked in real time. Step 3.3: Dynamic simulation stage; The state space equation with fault additional term is solved by numerical calculation method. Solve the problem and gradually advance the calculation according to the set time step Δt to obtain the value of the system state variable x at different times, thereby simulating the dynamic change process of the system after the fault occurs; Step 3.4: Result output and analysis; According to the calculated values ​​of the system state variable x at different times, the corresponding phenomenon information is output to make it consistent with the fault phenomenon and action conditions in actual production; Observe the operation of the operator to handle the fault, modify the input variable u again according to the operation situation, continue dynamic simulation, and judge whether the operation can alleviate the impact of the fault or restore the normal operation of the system. Otherwise, continue to observe the changes in the system status to see whether it will cause the fault to expand.

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