Electromechanical transient simulation modeling method and device considering static load and storage medium

Abstract

The invention provides an electromechanical transient simulation modeling method and device considering a static load and a storage medium, and relates to the technical field of power system simulation. Static load frequency characteristics are considered, a power grid mathematical model is constructed, a generator set model is connected to a corresponding network node of a network, the generator set model is a generator set simulation model comprising a synchronous motor model, an excitation system model, a water turbine and a speed regulation system model, and load admittance is dynamically adjusted through frequency classification. According to the method, machine-network alternate solution is adopted, the convergence of original iterative calculation is not affected while the static load frequency characteristic is considered in electromechanical transient simulation of the power system, the calculation amount is not additionally increased, the calculation process is optimized, and the practicability and adaptability of the model are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power system simulation, and in particular to an electromechanical transient simulation modeling method, device and storage medium considering static load. Background Art

[0002] In a power system, the frequency characteristics are composed of the power-frequency characteristics of the generator set and the load. In electromechanical transient processes, the power-frequency characteristics of the load are of great significance to the system power balance and dynamic process.

[0003] In existing technology, four types of load models are commonly used in power system transient stability analysis: a constant impedance linear model; a nonlinear static model that accounts for voltage characteristics; a dynamic model that accounts for mechanical transients in induction motors; and a dynamic model that accounts for electromechanical transients in induction motors. When a constant impedance load model is used, it can be incorporated into the admittance matrix, with the corresponding diagonal elements modified. When solving the network equations, the injected current at the load nodes is set to zero. In this case, the load frequency characteristics are generally not considered.

[0004] When the load adopts a nonlinear model, there are two processing methods for the machine-grid interface: one is the iterative solution method. In each step of the calculation, the load node voltage is offset against the generator terminal voltage source. The load behavior and reactive power are calculated based on the load characteristics, and then the equivalent current injected into the network is obtained and substituted into the network equation for solution. If the obtained load node voltage is consistent with the predicted value, the calculation ends. Otherwise, it is iterated until convergence. However, when considering the load frequency characteristics, this method is difficult to achieve iterative convergence by predicting the frequency, and the amount of calculation will be greatly increased. The second is the Newton method, which solves the linear or nonlinear algebraic equations of the entire network by establishing the Jacobian matrix equation. However, for large-scale power systems, the joint solution will encounter the "curse of dimensionality" problem. Summary of the Invention

[0005] The main purpose of the present invention is to provide an electromechanical transient simulation modeling method, device and storage medium that takes static load into consideration, so as to solve the technical problems in the prior art that the iterative solution method for predicting voltage is difficult to converge, the amount of calculation is greatly increased, the "curse of dimensionality" occurs in large-scale systems, and the frequency characteristics are ignored, resulting in insufficient simulation accuracy.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is: a method for electromechanical transient simulation modeling considering static loads, comprising the following steps: S1: Considering the frequency characteristics of the static load, a mathematical model of the power grid is constructed. The mathematical model of the power grid is composed of the generator stator winding voltage equation after dq axis coordinate transformation and the n-node power grid node voltage equation; S2: The generator set is connected to the corresponding network node of the network, and a generator set simulation model is constructed. The generator set simulation model includes a synchronous motor model, an excitation system model, a turbine and a speed control system model. The generator set simulation model outputs a frequency in the simulation calculation at each time step; S3: Dynamically adjust the load admittance through frequency grading: preset multiple frequency levels, obtain the current frequency level as the load frequency, obtain the corresponding load power and equivalent impedance, and directly integrate them into the load node of the power grid to form a power grid simulation model. The power grid simulation model and the generator set simulation model are solved alternately by machine and network, and convergence judgment is performed until convergence is met.

[0007] In the preferred solution, the construction of the power grid mathematical model is specifically as follows: The generator adopts a fourth-order or third-order practical model, and the stator winding voltage equation is: (1); Where, and are the components of the stator winding voltage on the d and q axes, and The d and q axes are transient electromotive forces, and are the direct-axis and quadrature-axis transient reactances, and are the components of the stator current on the d and q axes, is the stator winding resistance; Convert to matrix form: (2); Transform the variables of the dq axis coordinates of the generator in the above equation into the variables of the dq axis coordinates of the nth generator, or transform it into the xy axis synchronous coordinate system, and the dq conversion matrix T is: ; Where δ is the rotor angle of the i-th generator set, that is, the angle of the rotor of generator set i relative to the rotor of generator set n; Multiplying the dq conversion matrix T on the left of equation (2) yields: (3); From equation (3), the voltage equation converted to the synchronous coordinate axis is: (4); The plural form of formula (4) is: (5); Where, To convert the stator winding voltage to the complex form on the synchronous coordinate axis, is the complex form of the stator current, is the complex form of the stator winding impedance, is the complex form of the stator winding potential on the synchronous coordinate axis; For the grid node voltage equation, is the admittance matrix, is the node voltage vector, The current vector is injected into the node, and the voltage equation of the n-node grid node is expressed as: (6); in, is the injected current of n nodes, 1~m are generator nodes, m~n are load nodes, ... is the voltage of n nodes, is the element in the node admittance matrix; Let the load admittance Y load =G+j*B, then the load admittance expression considering the load frequency characteristics is: (7); (8); Where Y load is the load admittance considering the load frequency characteristics, 、 and is the load static frequency characteristic coefficient, is the load conductance, is the load susceptance, is to set the frequency level, is the frequency level number; If the generator in equation (5) is connected to the i-th node of the network, substitute equation (5) into the i-th node equation in equation (6) and eliminate , perform the same treatment on each generator node, and compress the load nodes (m~n), and the following network equation is obtained: (9); The above formula can be abbreviated as: (10); in, is the equivalent admittance matrix of the processed power grid, is the equivalent electromotive force on the synchronous coordinate axis, Inject current vectors into grid nodes.

[0008] In the preferred solution, in step S3, multiple frequency levels are preset, including: Considering the load frequency characteristics, with the rated frequency as the center, the frequency difference between the preset levels is divided into multiple frequency levels; Detect the frequency of the current time step, make a judgment, and use the current frequency level as the current load frequency; The corresponding load power and equivalent impedance are calculated based on the current load frequency and incorporated into the load node of the power grid.

[0009] In a preferred embodiment, in S3, constructing a generator set simulation model includes: Construct a synchronous motor model for inputting the excitation electromotive force , and the machine-end current , obtain the stator winding potential in the synchronous coordinate system , the mathematical expression is: (11); in, and are the time constants respectively.

[0010] In the preferred solution, in said S3, constructing a generator set simulation model includes: constructing an excitation system model for inputting a terminal voltage u t , output excitation electromotive force E f , the mathematical expression is: (12); in, 、 、 ,and They are reference voltage and terminal voltage respectively; is the excitation electromotive force; is the saturation coefficient; 、 is the exciter gain and feedback gain; are the exciter time constant, feedback time constant, and field winding time constant; The terminal voltage u t , the expression is: (13); in, and are the x-axis component and y-axis component of the terminal voltage.

[0011] In the preferred solution, in said S3, constructing a generator set simulation model includes: constructing a turbine and speed control system model for inputting the electromagnetic torque at the machine end , speed control system control variable u0 or , output rotor angular frequency (or f), rotor angle , the mathematical expression is: (14); Where, is the time constant of water hammer effect; is the rotor angular frequency; is the given rotor angular frequency; is the damping coefficient; is the guide vane opening; is a given opening; is the moment of inertia; is the magnification; is the feedback coefficient; is the power coefficient; is the rotor angle; is the servo time constant; is the mechanical torque; is the electromagnetic torque;.

[0012] An electronic device comprising a memory and a processor; The memory is used to store computer programs; The processor is configured to implement the electromechanical transient simulation modeling method considering static loads when executing the computer program.

[0013] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the electromechanical transient simulation modeling method considering static loads.

[0014] The present invention provides an electromechanical transient simulation modeling method considering static loads. The method takes into account the frequency characteristics of the static loads, constructs a mathematical model of the power grid, connects a generator set model to a corresponding network node of the network, and is a generator set simulation model including a synchronous motor model, an excitation system model, a turbine, and a speed regulation system model. The load admittance is dynamically adjusted through frequency grading, and a machine-grid alternating solution is adopted. While considering the frequency characteristics of the static loads in the electromechanical transient simulation of the power system, the method does not affect the convergence of the original iterative calculation and does not increase the amount of calculation. The method optimizes the calculation process and improves the practicality and adaptability of the model. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will be further described below with reference to the accompanying drawings and examples: Figure 1 It is a flow chart of the electromechanical transient simulation modeling method of the present invention; Figure 2 It is a schematic diagram of the alternate solution calculation process of the machine-network simulation model of the present invention. DETAILED DESCRIPTION

[0016] Example 1 like Figure 1-2 As shown, a method for electromechanical transient simulation modeling considering static loads includes the following steps: S1: Considering the frequency characteristics of the static load, a mathematical model of the power grid is constructed. The mathematical model of the power grid is composed of the generator stator winding voltage equation after dq axis coordinate transformation and the n-node power grid node voltage equation.

[0017] S2: The generator set is connected to the corresponding network node of the network, and a generator set simulation model is constructed. The generator set simulation model includes a synchronous motor model, an excitation system model, a turbine and a speed control system model. The generator set simulation model outputs a frequency in the simulation calculation at each time step.

[0018] S3: Dynamically adjust the load admittance through frequency grading: preset multiple frequency levels, obtain the current frequency level as the load frequency, obtain the corresponding load power and equivalent impedance, and directly integrate them into the load node of the power grid to form a power grid simulation model. The power grid simulation model and the generator set simulation model are solved alternately by machine and network, and convergence judgment is performed until convergence is met.

[0019] In this embodiment, the frequency characteristics of the static load are taken into consideration, a mathematical model of the power grid is constructed, the generator is connected to the corresponding network node of the network, and a generator set simulation model including a mathematical model of the synchronous motor, a mathematical model of the excitation system, and a turbine and speed control system model is constructed. The load admittance is dynamically adjusted through frequency grading, and a machine-grid alternating solution is adopted. While considering the frequency characteristics of the static load in the electromechanical transient simulation of the power system, the convergence of the original iterative calculation is not affected, and the amount of calculation is not increased. This optimizes the calculation process and improves the practicality and adaptability of the model.

[0020] This embodiment introduces a frequency-dependent load admittance expression, setting multiple frequency levels based on the rated frequency to accurately reflect the system's actual frequency fluctuations. By matching the detected frequency level to the corresponding frequency level, the load power and equivalent impedance are accurately derived and incorporated into the grid load node, breaking through the limitations of traditional static load models.

[0021] In transient stability analysis, the general form of the mathematical model of the power system can be written as: ; Where x is the state variable of the system; U is the node voltage vector; I is the node injection current vector; x is the differential equation group describing the generator set or dynamic load; To describe the algebraic equations of the power grid, Y is the node admittance matrix.

[0022] The core of the power system electromechanical transient stability simulation calculation is to solve the above equations simultaneously or alternately. Based on the above technical ideas, this embodiment proposes a modeling method for considering the load frequency characteristics in power system electromechanical transient simulation. That is, in power system electromechanical transient simulation, the frequency characteristics of the load can be considered when using a static load model.

[0023] In step S1 , the grid mathematical model is composed of the generator stator winding voltage equation after dq axis transformation and the grid node voltage equation of n nodes.

[0024] In the preferred solution, a mathematical model of the power grid is constructed, specifically as follows: The generator adopts a fourth-order or third-order practical model, and the stator winding voltage equation is: (1); Where, and are the components of the stator winding voltage on the d and q axes, and The d and q axes are transient electromotive force, and are the direct-axis and quadrature-axis transient reactances, and are the components of the stator current on the d and q axes, is the stator winding resistance.

[0025] Convert to matrix form: (2); Transform the variables of the dq axis coordinates of the generator in the above equation into the variables of the dq axis coordinates of the nth generator, or transform it into the xy axis synchronous coordinate system, and the dq conversion matrix T is: ; Where δ is the rotor angle of the i-th generator set, that is, the angle of the rotor of generator set i relative to the rotor of generator set n.

[0026] Multiplying the dq conversion matrix T on the left of equation (2) yields: (3); From equation (3), the voltage equation converted to the synchronous coordinate axis is: (4); The plural form of formula (4) is: (5); Where, To convert the stator winding voltage to the complex form on the synchronous coordinate axis, is the complex form of the stator current, is the complex form of the stator winding impedance, is the complex form of the stator winding potential on the synchronous coordinate axis.

[0027] For the grid node voltage equation, is the admittance matrix, is the node voltage vector, The current vector is injected into the node, and the voltage equation of the n-node grid node is expressed as: (6); in, is the injected current of n nodes, 1~m are generator nodes, m~n are load nodes, ... is the voltage of n nodes, is the element in the node admittance matrix.

[0028] Let the load admittance Y load =G+j*B, then the load admittance expression considering the load frequency characteristics is: (7); (8); Where Y load is the load admittance considering the load frequency characteristics, 、 and is the load static frequency characteristic coefficient, is the load conductance, is the load susceptance, is to set the frequency level, is the frequency level number.

[0029] Through the above technical solution, the frequency characteristics of the static load are taken into account in the electromechanical transient simulation, without affecting the original iterative calculation convergence, without increasing the amount of calculation, and optimizing the calculation process.

[0030] If the generator in equation (5) is connected to the i-th node of the network, substitute equation (5) into the i-th node equation in equation (6) and eliminate , perform the same treatment on each generator node, and compress the load nodes (m~n), and the following network equation is obtained: (9); The above formula can be abbreviated as: (10).

[0031] in, is the equivalent admittance matrix of the processed power grid, is the equivalent electromotive force on the synchronous coordinate axis, Inject current vectors into grid nodes.

[0032] In the preferred solution, in step S3, multiple frequency levels are preset, including: Taking the load frequency characteristics into consideration, the frequency levels are divided into multiple levels with the rated frequency as the center and the difference between the frequency levels is preset.

[0033] Detect the frequency of the current time step, make a judgment, and use the current frequency level as the current load frequency.

[0034] The corresponding load power and equivalent impedance are calculated based on the current load frequency and incorporated into the load node of the power grid.

[0035] In this embodiment, as shown in formula (8), multiple frequency levels are set with the rated frequency as the center, and the level difference can be set to be small (0.01 is used in this embodiment). The frequency f of the simulation system at the current time step is detected, and the frequency level of the frequency is determined. The current frequency level is used as the load frequency, thereby obtaining the corresponding load power and equivalent impedance, which are incorporated into the load node of the power grid.

[0036] In the preferred solution, in step S3, constructing a generator set simulation model includes: Construct a synchronous motor model for inputting the excitation electromotive force , and the machine-end current , obtain the stator winding potential in the synchronous coordinate system , the mathematical expression is: (11).

[0037] in, and are the time constants respectively.

[0038] In the preferred solution, in step S3, a generator set simulation model is constructed, including: constructing a mathematical model of the excitation system for inputting the terminal voltage u t , output excitation electromotive force E f , the expression is: (12); in, 、 、 ,and They are reference voltage and terminal voltage respectively; is the excitation electromotive force; is the saturation coefficient; 、 is the exciter gain and feedback gain; are the exciter time constant, feedback time constant, and field winding time constant; The terminal voltage u t , the expression is: (13); in, and are the x-axis component and y-axis component of the terminal voltage.

[0039] In the preferred solution, in step S3, a generator set simulation model is constructed, including: constructing a turbine and speed control system model for inputting the electromagnetic torque at the machine end , speed control system control variable u0 or , output rotor angular frequency (or f), rotor angle , the mathematical expression is: (14); Where, is the time constant of water hammer effect; is the rotor angular frequency; is the damping coefficient; is the guide vane opening; is the moment of inertia; is the magnification; is the feedback coefficient; is the power coefficient; is the rotor angle; is the servo time constant.

[0040] like Figure 2 As shown, the schematic diagram of alternate solution calculation of the power grid simulation model and the generator set simulation model considering the static load frequency characteristics in this embodiment is shown in the figure below. After obtaining the node injection current vector matrix equation, it is input into the generator set simulation model to obtain the stator winding potential in the dq-axis synchronous coordinate system, that is, the load admittance is dynamically adjusted by frequency grading, the current frequency level is obtained as the load frequency, and the corresponding load power and equivalent impedance are obtained. After being directly incorporated into the load node of the power grid, a power grid simulation model is formed. The power grid simulation model and the generator set simulation model are solved alternately by machine and network, and convergence judgment is performed until convergence is met.

[0041] Example 2 Further described in conjunction with Example 1, an electronic device is provided, including a memory and a processor; Memory for storing computer programs.

[0042] The processor is configured to implement the electromechanical transient simulation modeling method considering static loads in embodiment 1 when executing the computer program.

[0043] A computer-readable storage medium stores a computer program. When the computer program is executed by a processor, the electromechanical transient simulation modeling method considering static loads in embodiment 1 is implemented.

[0044] The above embodiments are merely preferred technical solutions of the present invention and should not be construed as limiting the present invention. The scope of protection of the present invention shall be the technical solutions set forth in the claims, including equivalent alternatives to the technical features of the technical solutions set forth in the claims. In other words, equivalent alternatives and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. The electromechanical transient simulation modeling method considering static load is characterized by: The following steps are involved: S1: Considering the frequency characteristics of the static load, a mathematical model of the power grid is constructed. The mathematical model of the power grid is composed of the generator stator winding voltage equation after dq axis coordinate transformation and the n-node power grid node voltage equation; S2: The generator set is connected to the corresponding network node of the network, and a generator set simulation model is constructed. The generator set simulation model includes a synchronous motor model, an excitation system model, a turbine and a speed control system model. The generator set simulation model outputs a frequency in the simulation calculation at each time step; S3: Dynamically adjust the load admittance through frequency grading: preset multiple frequency levels, obtain the current frequency level as the load frequency, obtain the corresponding load power and equivalent impedance, and directly integrate them into the load node of the power grid to form a power grid simulation model. The power grid simulation model and the generator set simulation model are solved alternately by machine and network, and convergence judgment is performed until convergence is met.

2. The electromechanical transient simulation modeling method considering static load according to claim 1 is characterized in that: The construction of the power grid mathematical model is specifically as follows: The generator adopts a fourth-order or third-order practical model, and the stator winding voltage equation is: （1）； Where, and are the components of the stator winding voltage on the d and q axes, and The d and q axes are transient electromotive force, and are the direct-axis and quadrature-axis transient reactances, and are the components of the stator current on the d and q axes, is the stator winding resistance; Convert to matrix form: （2）； Transform the variables of the dq axis coordinates of the generator in the above equation into the variables of the dq axis coordinates of the nth generator, or transform it into the xy axis synchronous coordinate system, and the dq conversion matrix T is: ； Where δ is the rotor angle of the i-th generator set, that is, the angle of the rotor of generator set i relative to the rotor of generator set n; Multiplying the dq conversion matrix T on the left of equation (2) yields: （3）； From equation (3), the voltage equation converted to the synchronous coordinate axis is: （4）； The plural form of formula (4) is: （5）； Where, To convert the stator winding voltage to the complex form on the synchronous coordinate axis, is the complex form of the stator current, is the complex form of the stator winding impedance, is the complex form of the stator winding potential on the synchronous coordinate axis; For the grid node voltage equation, is the admittance matrix, is the node voltage vector, The current vector is injected into the node, and the voltage equation of the n-node grid node is expressed as: （6）； in, is the injected current of n nodes, 1~m are generator nodes, m~n are load nodes, ... is the voltage of n nodes, is the element in the node admittance matrix; Let the load admittance Y load =G+j*B, then the load admittance expression considering the load frequency characteristics is: （7）； （8）； Where Y load is the load admittance considering the load frequency characteristics, 、 and is the load static frequency characteristic coefficient, is the load conductance, is the load susceptance, is to set the frequency level, is the frequency level number; If the generator in equation (5) is connected to the i-th node of the network, substitute equation (5) into the i-th node equation in equation (6) and eliminate , perform the same treatment on each generator node, and compress the load nodes (m~n), and the following network equation is obtained: (9)； The above formula can be abbreviated as: （10）； in, is the equivalent admittance matrix of the processed power grid, is the equivalent electromotive force on the synchronous coordinate axis, Inject current vectors into grid nodes.

3. The electromechanical transient simulation modeling method considering static load according to claim 2 is characterized in that: In step S3, multiple frequency levels are preset, including: Considering the load frequency characteristics, with the rated frequency as the center, the frequency difference between the preset levels is divided into multiple frequency levels; Detect the frequency of the current time step, make a judgment, and use the current frequency level as the current load frequency; The corresponding load power and equivalent impedance are calculated based on the current load frequency and incorporated into the load node of the power grid.

4. The electromechanical transient simulation modeling method considering static load according to claim 1 is characterized in that: In S3, a generator set simulation model is constructed, including: Construct a synchronous motor model for inputting the excitation electromotive force , and the machine-end current , obtain the stator winding potential in the synchronous coordinate system , the mathematical expression is: （11）； in, and are the time constants respectively.

5. The electromechanical transient simulation modeling method considering static load according to claim 1, characterized in that: In the above S3, the generator set simulation model is constructed, including: constructing an excitation system model for inputting the terminal voltage u t , output excitation electromotive force E f , the mathematical expression is: （12）； in, 、 、 ,and They are reference voltage and terminal voltage respectively; is the excitation electromotive force; is the saturation coefficient; 、 is the exciter gain and feedback gain; are the exciter time constant, feedback time constant, and field winding time constant; The terminal voltage u t , the expression is: （13）； in, and are the x-axis component and y-axis component of the terminal voltage.

6. The electromechanical transient simulation modeling method considering static load according to claim 1, characterized in that: In said S3, a generator set simulation model is constructed, including: constructing a turbine and speed control system model for inputting the electromagnetic torque at the machine end , speed control system control variable u0 or , output rotor angular frequency (or f), rotor angle , the mathematical expression is: (14)； Where, is the time constant of water hammer effect; is the rotor angular frequency; is the damping coefficient; is the guide vane opening; is the moment of inertia; is the magnification; is the feedback coefficient; is the power coefficient; is the rotor angle; is the servo time constant.

7. An electronic device, characterized in that: including memory and processor; The memory is used to store computer programs; The processor is configured to implement the electromechanical transient simulation modeling method considering static loads according to any one of claims 1 to 6 when executing the computer program.

8. A computer-readable storage medium, characterized in that The storage medium stores a computer program, and when the computer program is executed by a processor, the electromechanical transient simulation modeling method considering static loads according to any one of claims 1 to 6 is implemented.

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