Automatic simulation system and method for dynamic characteristics of low-voltage contactor

Abstract

The invention provides an autonomous simulation system and method for dynamic characteristics of a low-voltage contactor. The system comprises a motion module, a circuit module and a finite element simulation module. The method comprises the following steps of: performing simulation calculation on the current position and the current current of the movable iron core of the contactor by using a finite element simulation module, transmitting data of the latest electromagnetic attraction suffered by the movable iron core of the contactor to a motion module, and transmitting a latest coil inductance value calculated according to a magnetic field to a circuit module. And the motion module calculates the displacement of the next time step according to the current resultant force and transmits the displacement to the finite element simulation module for real-time updating. And the circuit module calculates the current of the next time step according to the current inductance and current and outputs the current so as to carry out loop iteration of the next time step. According to the method, all possible coil current and movable iron core displacement do not need to be calculated once, so that the calculation efficiency is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of contactors, and in particular relates to an autonomous simulation system and method for dynamic characteristics of a low-voltage contactor. Background Art

[0002] In recent years, driven by my country's strategic goal of "carbon peak and carbon neutrality", the new energy industry has risen rapidly. As a key electrical equipment in the field of automatic control, contactors, which are economically efficient and effective, are widely used in power systems and new energy vehicle manufacturing. Therefore, the technological replacement of contactors is very frequent. If you want to design a new and reliable contactor, you need to simulate its dynamic characteristics. However, the current electromagnetic simulation software in China lacks in-depth research on the simulation module of the dynamic characteristics of the contactor. The dynamic characteristics of the contactor are usually simulated and calculated using the traditional interpolation method, which takes a long time to calculate and has poor flexibility. Summary of the invention

[0003] In order to solve the above problems, the present invention proposes an idea of ​​autonomous electromagnetic contactor simulation calculation. Through the independently developed algorithm module, a simulation method framework of circuit-motion-electromagnetic mechanism full coupling is designed, thereby achieving a contactor dynamic characteristics simulation method based on real-time calculation, which makes up for the defects of long simulation time and poor flexibility of contactor dynamic characteristics calculation based on interpolation method.

[0004] The technical solution adopted by the present invention to solve its technical problem is:

[0005] An autonomous simulation system for dynamic characteristics of a low-voltage contactor, comprising: a finite element simulation module, a circuit module, and a motion module;

[0006] The finite element simulation module is used to simulate and calculate the current position and current of the moving iron core of the contactor, and transmit them to the motion module and the circuit module respectively;

[0007] The motion module is used to calculate the displacement of the next time step according to the current position of the contactor moving iron core and transmit the displacement to the finite element simulation module for real-time update;

[0008] The circuit module is used to calculate the current of the next time step according to the current current and output it, so as to perform a cyclic iteration of the next time step.

[0009] Preferably, the circuit module is driven by a current source.

[0010] Preferably, the current source excitation can calculate the current without using components such as inductance, capacitance and resistance.

[0011] Preferably, the circuit module is driven by a non-current source.

[0012] Preferably, the non-current source excitation has a dynamic calculation process.

[0013] Preferably, the dynamic calculation process includes:

[0014] The latest electromagnetic attraction and the latest inductance are calculated through electromagnetic field equations;

[0015] If the simulation time is less than the specified deadline, the latest electromagnetic attraction and the latest current are substituted into the motion module and the circuit module respectively, and the latest position at the current moment is calculated according to the position of the contactor moving iron core at the previous moment. The latest current value is obtained by iterative solution according to the contactor coil current value at the previous moment and the voltage value at the current moment.

[0016] The latest current value and the latest position parameters of the contactor moving iron core are passed to the finite element simulation module again. The finite element simulation module updates the model according to the latest position of the contactor moving iron core and performs electromagnetic field simulation calculation according to the latest current value. The process is repeated until the simulation time is less than the specified deadline.

[0017] The present invention also provides a method for autonomous simulation of dynamic characteristics of a low-voltage contactor, the method comprising:

[0018] The finite element simulation module simulates and calculates the current position and current of the contactor moving iron core, and transmits them to the motion module and the circuit module respectively;

[0019] The motion module calculates the displacement of the next time step according to the current position of the contactor moving iron core and transmits the displacement to the finite element simulation module for real-time update;

[0020] The circuit module calculates the current of the next time step according to the current current and outputs it so as to perform a loop iteration of the next time step.

[0021] Preferably, the circuit module can be excited by a current source and can also be excited by a non-current source.

[0022] Preferably, the current source excitation can calculate the current without components such as inductance, capacitance and resistance.

[0023] Preferably, the non-current source excitation has a dynamic calculation process, including:

[0024] The latest electromagnetic attraction and the latest inductance are calculated through electromagnetic field equations;

[0025] If the simulation time is less than the specified deadline, the latest electromagnetic attraction and the latest current are substituted into the motion module and the circuit module respectively, and the latest position at the current moment is calculated according to the position of the contactor moving iron core at the previous moment. The latest current value is obtained by iterative solution according to the contactor coil current value at the previous moment and the voltage value at the current moment.

[0026] The latest current value and the latest position parameters of the contactor moving iron core are passed to the finite element simulation module again. The finite element simulation module updates the model according to the latest position of the contactor moving iron core and performs electromagnetic field simulation calculation according to the latest current value. The process is repeated until the simulation time is less than the specified deadline.

[0027] The present invention also discloses a computer storage medium, wherein the storage medium includes computer instructions, and when the computer is run on the computer, the computer executes any of the methods described above.

[0028] The present invention also discloses an electronic device, wherein the electronic device comprises: a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor implements any of the methods described above when executing the program.

[0029] The technical advantages of the present invention are as follows:

[0030] 1) At present, the interpolation method is mostly used in the dynamic simulation of contactors in China, but the interpolation method has the inherent defect of long calculation time. The dynamic simulation method based on real-time calculation of the present invention greatly speeds up the iterative calculation speed by combining real-time finite element calculation with circuit equations and motion equations, which makes up for this defect well;

[0031] 2) This invention deeply considers the influence of coil inductance on loop current, electromagnetic force and coil motion state under voltage source excitation, and builds a more accurate algorithm. This method is more accurate than the traditional interpolation method;

[0032] 3) The traditional interpolation method has the disadvantage of poor flexibility, and tedious fitting calculations need to be performed again after the circuit parameters are changed. The present invention can quickly iterate as usual when the initial conditions are changed through real-time parameter output and reading, which makes up for this defect well;

[0033] 4) The present invention establishes different circuit equations for different types of excitation sources, such as current source circuits, first-order voltage source circuits, second-order capacitor power supply circuits, second-order dual-winding voltage source circuits, etc., which are more comprehensive and applicable to most contactor coil circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1It is a general simulation logic diagram of contactor dynamic characteristics based on real-time calculation in one embodiment of the present invention;

[0035] Figure 2 A basic finite element one-dimensional schematic diagram of an embodiment of the present invention;

[0036] Figure 3 A basic finite element two-dimensional schematic diagram of an embodiment of the present invention;

[0037] Figure 4 A basic finite element three-dimensional schematic diagram of an embodiment of the present invention;

[0038] Figure 5 The overall flow chart of the contactor dynamic simulation current source excitation based on real-time calculation in one embodiment of the present invention;

[0039] Figure 6 The overall flow chart of non-current source excitation of contactor dynamic simulation based on real-time calculation in one embodiment of the present invention;

[0040] Figure 7 A flowchart of a motion module algorithm implementation in one embodiment of the present invention;

[0041] Figure 8 A flowchart of a circuit module algorithm implementation in one embodiment of the present invention;

[0042] Fig. 9 The current calculation results using different multiples of time constants as iteration steps in one embodiment of the present invention. DETAILED DESCRIPTION

[0043] The following will refer to the attached Figures 1 to 9 Specific embodiments of the present invention are described in detail. Although specific embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0044] It should be noted that certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that technicians may use different nouns to refer to the same component. This specification and claims do not use the difference in nouns as a way to distinguish components, but use the difference in the functions of the components as the criterion for distinction. As mentioned throughout the specification and claims, "including" or "comprising" is an open term, so it should be interpreted as "including but not limited to". The subsequent description of the specification is a preferred embodiment of the present invention, but the description is based on the general principles of the specification and is not intended to limit the scope of the present invention. The scope of protection of the present invention shall be determined by the attached claims.

[0045] To facilitate understanding of the embodiments of the present invention, further explanation will be given below by taking specific embodiments as examples in conjunction with the accompanying drawings, and each of the accompanying drawings does not constitute a limitation on the embodiments of the present invention.

[0046] The present invention provides an autonomous simulation system for dynamic characteristics of a low-voltage contactor, comprising: a finite element simulation module, a circuit module, and a motion module;

[0047] The finite element simulation module is used to simulate and calculate the current position and current of the moving iron core of the contactor, and transmit them to the motion module and the circuit module respectively;

[0048] The motion module is used to calculate the displacement of the next time step according to the current position of the contactor moving iron core and transmit the displacement to the finite element simulation module for real-time update;

[0049] The circuit module is used to calculate the current of the next time step according to the current current and output it, so as to perform a cyclic iteration of the next time step.

[0050] The present invention also provides a method for autonomous simulation of dynamic characteristics of low-voltage contactors. Figure 1 As shown: This method is jointly implemented by the motion module, circuit module and finite element simulation module. The circuit module and the motion module are implemented through independent compilation, and the algorithm is coupled with the finite element simulation module. The finite element simulation module is responsible for simulating and calculating the current position and current current of the contactor moving iron core using the finite element method, passing the latest electromagnetic suction data of the contactor moving iron core to the motion module, and passing the latest coil inductance value calculated based on the magnetic field to the circuit module. The motion module is responsible for calculating the displacement of the next time step based on the current combined force (electromagnetic suction + spring reaction force) and passing the displacement to the finite element simulation module for real-time update. The circuit module needs to calculate the current of the next time step based on the current inductance and current and output it for the next time step loop iteration.

[0051] It should be noted that the development logic of current source excitation and non-current source excitation is different for different circuit modules.

[0052] For current source excitation, since the current is usually a function of time, the current can be calculated without the need for components such as inductors, capacitors, and resistors. At the initial moment, the time can be directly substituted into the current equation with respect to time to directly solve for the initial current.

[0053] In the subsequent iteration process, the latest current value is substituted into the electromagnetic field equation for calculation, and the latest electromagnetic suction force under the current displacement value of the moving iron core is obtained by solving. Then, it is determined whether the iteration time has exceeded the set total simulation time. If it exceeds, the simulation process ends. If it does not exceed, the latest electromagnetic suction force is passed to the motion module. The motion module calculates the displacement value within the simulation step, and the circuit module calculates the latest current value at the next moment. The latest current value and the latest displacement value of the moving iron core are passed to the finite element model again, the position of the finite element model is updated, and the electromagnetic field simulation calculation is performed according to the latest current value. This process is repeated until the simulation time t exceeds the set total simulation time T.

[0054] In one embodiment, the finite element pre-processing part includes the following steps:

[0055] 1. Regional Discreteness

[0056] Let the domain be Ω. In any finite element analysis, discretization of the domain is the first and most important step, because the way the domain is discretized will affect the computer memory requirements, calculation time and the accuracy of the numerical results. In this step, the entire domain is divided into many small domains, denoted by I (e=1,2,3,…,M), where M is the total number of subdomains. These subdomains are usually called elements. For one-dimensional domains that are actually straight lines or curves, the elements are usually short straight line segments that are connected to form the original line domain (see Figure 1 For two-dimensional regions, the cells are usually small triangles or rectangles (see Figure 2 In three-dimensional solutions, the domain can be divided into tetrahedrons, triangular prisms, or rectangular blocks (see Figure 3 ), where the tetrahedron is the simplest and most suitable unit for discretizing arbitrary volume regions.

[0057] In most finite element solutions, the problem is expressed in terms of unknown functions at the nodes associated with the element. For example, a linear line element has two nodes, one at each end; a linear triangle element has three nodes, one at each vertex; and a linear tetrahedron element has four nodes, one at each corner. A complete description of a node should include its coordinate values, local code, and global code. The local code of a node indicates its location in the element, while the global code indicates its location in the entire system.

[0058] 2. Select the interpolation function

[0059] The second step of finite element analysis is to select an interpolation function that can approximate the unknown solution in a unit. Usually, the interpolation function can be selected as a first-order (linear), second-order (quadratic), or high-order polynomial. Although high-order polynomials have higher accuracy, the formulas usually obtained are also more complicated. Therefore, simple and basic linear interpolation is still widely used. Once the order of the polynomial is selected, we can derive an expression for the unknown solution in a unit. Taking the e unit as an example, the following form is obtained:

[0060] (1)

[0061] Where n is the number of nodes in the cell; The trial function representing the unit; is the j-node in the cell value; is an interpolation function, whose characteristic is that it is not 0 only inside the unit e and is 0 outside the unit. e represents the matrix composed of interpolation functions; φ e Represents the matrix of trial functions for the cells.

[0062] 3. Establish the system of equations

[0063] A typical programming problem can be defined by the governing differential equations in the region Ω and the boundary conditions on the boundary Γ surrounding the region Ω. The differential equations can be expressed as:

[0064] (2)

[0065] in is the differential operator, f is the excitation or imposition function, is an unknown quantity. Boundary conditions include Dirichlet conditions and Norman conditions or more complex conditions. It is difficult to obtain analytical solutions to equations in engineering, so people seek various approximate methods to solve them, among which the most widely used are the Ritz method and the Galerkin method.

[0066] The system of equations solved using the Galerkin method is derived:

[0067] For formula (2), the residual weight of the e-th unit is:

[0068] (3)

[0069] Substituting equation (1) into equation (3):

[0070] (4)

[0071] Written in matrix form:

[0072] (5)

[0073] Among them, [K e ] is called the element stiffness matrix, {b e Since the expansion function associated with a node covers all units directly connected to the node, the relationship between local and global encoding can be used to expand (5) and then sum over each unit:

[0074] (6)

[0075] At this point, we set the residual {R}={0} and we get:

[0076] (7)

[0077] So it can be written as:

[0078] (8)

[0079] Here [K] can be called the overall stiffness matrix.

[0080] Before equation (8) can be solved, the required boundary conditions must be applied. There are two types of boundary conditions that often appear: the Dirichlet boundary condition, which gives the boundary conditions. The other type is the homogeneous Norman boundary condition, which requires that the boundary The normal derivative of is zero. The first type of boundary is a necessary boundary condition, which must be explicitly imposed in the calculation; the second type of boundary condition is usually implicitly satisfied automatically during the solution process. For this reason, the second type of boundary condition is often called a natural boundary condition.

[0081] It can be seen that there are actually three sub-steps in this step. First, the unit equation (5) is written by applying the Galerkin method. Second, the unit equation is summed over all units to obtain a system of equations. This process is called combination. Finally, boundary conditions are applied to obtain the final form of the system of equations. Note: In the process of implementing this calculation on a computer, these three sub-steps are usually not discrete. Instead, they are intertwined. The generation of the unit array and the imposition of boundary conditions usually occur in the combination process.

[0082] 4. Solve the system of equations

[0083] When the equation group (8) is solved, the following parameters are further calculated: capacitance, inductance, electromagnetic force, etc. Among them, in the case of solving the static magnetic field in three-dimensional space, the unknown quantity to be solved is the vector magnetic potential A. After the solution is completed according to the above method, the magnetic potential of each node is obtained [A] = [A x ,Ay ,A z ], post-processing is required to obtain the desired electromagnetic force and inductance.

[0084] like Figure 5 As shown, in one embodiment, the overall process of contactor dynamic simulation current source excitation based on real-time calculation includes the following steps:

[0085] The first step is to perform initialization, setting the current time t=0 and the current displacement x=x0.

[0086] The second step is to substitute the current time t into the circuit equation to obtain i(t), and then output the value of i in the form of a text file. For example, if a sinusoidal AC current source is required and it is a single-coil winding circuit, only the current amplitude i of the power supply needs to be given. m , frequency f and initial phase angle θ, we can program i(t)=i m *sin(2*pi*f*t+θ) directly calculates the current value at the current moment. If it is the initial moment, substitute t=0.

[0087] The third step is to read the current current and use the finite element method to calculate the electromagnetic field and the electromagnetic force F according to the current model. For example, the vector magnetic potential [A] = [A x ,A y ,A z ], the solution of the magnetic flux density B at this moment can be obtained by taking the curl of the vector magnetic potential A:

[0088] (9)

[0089] in and is the magnetic flux density and vector magnetic potential of the node numbered j. After obtaining the magnetic flux density of each node, take the arithmetic mean as the average magnetic flux density of the unit :

[0090] (10)

[0091] For a homogeneous medium, the electromagnetic force on the unit is f e It can be simplified to the gradient of energy density W:

[0092] (11)

[0093] For a uniform object in an electromagnetic field, the electromagnetic force on the whole object can be integrated and the discrete form is:

[0094] (12)

[0095] where f e is the unit force, V e is the unit volume. From this, we can get the calculation result of the electromagnetic force F that the moving iron core is subjected to at that moment.

[0096] The fourth step is to determine whether the current time t exceeds the specified deadline T. If not, the motion module algorithm reads the electromagnetic suction force F calculated in the third step, combines the spring reaction force with Newton's second law to calculate the displacement x of the moving iron core, and updates the current time to t+Δt; if exceeded, the algorithm ends.

[0097] In the fifth step, the geometric model is updated according to the displacement x of the moving iron core in the current time step, and the process returns to the second step for iteration, repeating the cycle.

[0098] For non-current source excitation, the circuit module is usually excited by a voltage source or other forms of excitation such as capacitor discharge. The coil current is not only a function of time, but also related to other factors. Therefore, the current value cannot be obtained directly, and needs to be obtained through continuous iteration and calculation within the current time step. During the iteration process, since the magnetic permeability of the contactor core is usually nonlinear, the coil inductance will also change with the change of the core saturation degree and the relative position of the moving core. Therefore, for the iteration process of the coil current, the inductance corresponding to the current moment needs to be calculated at each moment to ensure accurate calculation.

[0099] like Figure 6 As shown, in another embodiment, the overall process of non-current source excitation of contactor dynamic simulation based on real-time calculation includes the following steps:

[0100] The first step is to perform initialization: let the current time t=0, the current displacement x=x0, and the initial current i=0.

[0101] The second step is to calculate the electromagnetic field using the finite element method based on the current model and the current current i, and obtain the coil inductance L and the electromagnetic force F. For example, the vector magnetic potential [A] = [A x ,A y ,A z ], the solution of the magnetic flux density B at this moment can be obtained by taking the curl of the vector magnetic potential A:

[0102] (13)

[0103] in and is the magnetic flux density and vector magnetic potential of the node numbered j. After obtaining the magnetic flux density of each node, take the arithmetic mean as the average magnetic flux density of the unit :

[0104] (14)

[0105] For a homogeneous medium, the electromagnetic force on the unit is f e It can be simplified to the gradient of energy density W:

[0106] (15)

[0107] For a uniform object in an electromagnetic field, the electromagnetic force on the whole object can be integrated and the discrete form is:

[0108] (16)

[0109] where f e is the unit force, V e is the unit volume. From this, we can get the calculation result of the electromagnetic force F that the moving iron core is subjected to at that moment.

[0110] For example, according to the finite element pre-processing part, the vector magnetic potential [A] = [A x ,A y ,A z ]. The inductance L is usually calculated by dividing the magnetic flux of the coil by the current:

[0111] (17)

[0112] Where I is a known quantity, and the magnetic flux φ m If there are s volume elements passing through a certain cross section of the coil, and the formula and The average magnetic flux density of each volume element can be obtained, and the magnetic flux φ m It can be calculated as follows:

[0113] (18)

[0114] Among them, B i is the average magnetic flux density of the volume element passing through the cross section of the coil, S i is the projection area of ​​the i-th volume element passing through the coil cross section on the interface. Combining the above two equations:

[0115] (19)

[0116] From this, the calculation result of the coil inductance L can be obtained.

[0117] The third step is to determine whether the current time t exceeds the specified cut-off time T. If not, the circuit module algorithm reads the current current i n , the current inductance L and other required parameters (such as the inductance L in the previous steplast ), calculate the next step current i n+1 At the same time, the motion module algorithm reads the current electromagnetic force F, calculates the displacement x of the moving iron core in combination with the spring reaction force, and updates the geometric model. Finally, the current time is updated to t+Δt; if it exceeds, the algorithm ends.

[0118] Step 4: Return to step 2 and iterate the loop.

[0119] In summary, for the dynamic calculation process under non-current source excitation, the latest electromagnetic attraction F and the latest inductance L are first calculated through the electromagnetic field equation. Subsequently, if the simulation time is less than the total simulation time, the latest electromagnetic attraction and the latest current are respectively substituted into the motion and circuit equation modules, and the latest position at the current moment is calculated according to the position of the contactor moving iron core at the previous moment. The latest current value is obtained by iterative solution based on the contactor coil current value at the previous moment and the voltage value at the current moment. Finally, the latest current value and the latest position parameters of the contactor moving iron core are passed to the simulation software again. The simulation software updates the model according to the latest position of the contactor moving iron core, and performs electromagnetic field simulation calculation according to the latest current value. This process is repeated until the simulation time t is less than the total simulation time T.

[0120] It is worth noting that there are differences in the position order of circuit equation iteration in the two different power supply models of non-current source excitation and current source excitation, but both need to ensure that each time corresponds to only one electromagnetic attraction, one contactor coil inductance value, one contactor coil current value and one moving iron core displacement value.

[0121] The purpose of building the motion module is to calculate the displacement and velocity changes of the model over time, so as to couple it with the finite element model and the circuit model. There are two main motion modes of the moving iron core of the contactor, one is linear translation motion, and the other is rotation motion around a fixed axis. Since the algorithm construction of these two motions is logically very similar, the following text will explain the case of linear motion.

[0122] In the first step, the algorithm script first reads the parameter information from the text file (obtained from the initial parameters given by the user and the parameters output by the previous iteration), imports the displacement, velocity, end time of the previous iteration, the specified maximum and minimum displacement values, time step, cutoff time and electromagnetic attraction of the previous iteration.

[0123] In the second step, before starting the iteration of the current time step, it is necessary to determine whether the moving iron core meets the motion conditions. If the direction of the resultant force on the moving iron core is positive, and the moving iron core has reached the maximum displacement in the positive direction, the algorithm determines that it cannot continue to move. The same applies to the negative direction. At this time, the algorithm should set the moving iron core speed to 0 and the displacement should also be set to 0.

[0124] The third step is to list the following according to Newton's second law:

[0125] (1.2)

[0126] Where a is the acceleration of the moving iron core / m·s -2 ; λ is the damping coefficient / N·s·m -1 ;v n is the speed of the moving iron core at the current time step / m·s -1 ;v n+1 The speed of the moving iron core in the next time step / m·s -1 ;x n is the displacement of the moving iron core at the current time step / m; x n+1 is the displacement of the moving iron core in the next time step / m; F f is the spring reaction force / N; F is the electromagnetic attraction force / N; Δt is the current time step; m is the mass of the moving iron core / kg.

[0127] Except for the spring reaction force, which is fitted by the script in the algorithm by the user inputting data points, the other parameters can be obtained from the text file. The spring reaction force is linearly related to the displacement. However, since the pre-set spring reaction force coordinate points are discrete, they usually cannot correspond to the current displacement. Therefore, the function of calculating the current spring reaction force must be fitted. Here, the first-order linear interpolation fitting method is used to express the reaction force as a function only about the displacement x:

[0128] (1.3)

[0129] Among them, x1 and x2 are the two displacement coordinate values ​​of the pre-set spring reaction force coordinate points that are closest to the current displacement, and F f (x1), F f (x2) represents the spring reaction force corresponding to these two displacement coordinates. X represents the displacement at the current moment. From this, we can fit F f After the algorithm completes this iteration and obtains new displacement data, it updates the current time and passes the displacement data to the finite element module, which should update the position of the model and proceed to the next iteration.

[0130] When setting the iteration conditions, the cutoff time may not be an integer multiple of the simulation step length. The following example illustrates how to deal with this situation. If the simulation step length is 0.3s and the total simulation time is 1s, when the simulation time reaches 0.9s, since the simulation time is less than the total simulation time of 1s, another iteration will be performed, and the final total simulation time will reach 1.2s. This not only exceeds the user's set length, but the extra 0.2s also causes more displacement of the contactor's moving iron core. In this regard, the algorithm will determine whether the current time exceeds the simulation termination time during the final processing. If it exceeds, it is necessary to calculate the excess time, correct the extra moving iron core displacement and moving iron core speed calculated during this period, and obtain the data at the simulation termination time.

[0131] After the motion equation calculation is completed, the displacement of the moving iron core at the current moment may exceed the range of the maximum positive displacement or the maximum negative displacement. This not only does not meet the moving iron core displacement range set by the user, but may also cause the moving iron core component to overlap with other components of the model, resulting in an error in the overall simulation. Therefore, it is necessary to compare the moving iron core displacement result after the current step length calculation with the maximum positive displacement and the maximum negative displacement set by the user. If the moving iron core displacement is greater than the maximum positive displacement, its displacement value is reset to the maximum positive displacement value; if the moving iron core displacement is less than the maximum negative displacement, its displacement value is reset to the maximum negative displacement value, and the moving iron core speed in both cases is reset to 0.

[0132] like Figure 7 As shown, in another embodiment, the motion module algorithm implementation process includes the following steps:

[0133] In the first step, the iterative algorithm obtains the electromagnetic suction force F, the displacement x of the moving iron core in the previous step and other parameter information from the finite element module and the text file saved in the previous iteration.

[0134] The second step is to determine whether the current motion condition is met in combination with the spring reaction force. If it is at the maximum positive displacement and the resultant force is in the positive direction, or at the maximum negative displacement and the resultant force is in the negative direction, the motion condition is not met, the displacement remains unchanged, the speed is set to 0, the update time is t+Δt, and finally jump to the fourth step; if the motion condition is met, jump to the third step.

[0135] The third step is to write the motion equation according to Newton’s second law, calculate the displacement x and velocity v at the next moment under the current force, and update the time to t+Δt.

[0136] The fourth step is to post-process the calculated data and correct the overflowed displacement data.

[0137] The fifth step is to change the position of the moving iron core according to the calculated x data and update the geometric model.

[0138] The purpose of building the circuit module is to calculate the size of the coil current, and then couple it with the finite element module and motion module algorithms. After the algorithm reads the parameters in the text file (different circuit types have different calculation methods, but the overall logic is the same), the algorithm script of the circuit module can perform iterative calculations.

[0139] The circuit module algorithm implementation flow chart is as follows Figure 8 As shown, after the algorithm obtains the necessary circuit parameter information, if the set time step is found to be too long, the algorithm will refine the time step to pursue high-precision calculation. The current finally obtained through iteration will be passed to the finite element module and the motion module for subsequent inductance calculation and electromagnetic attraction calculation. Exemplarily, the circuit module algorithm implementation process includes the following steps:

[0140] In the first step, the iterative algorithm obtains the inductance L and the current i in the previous step from the finite element module and the text file saved in the previous iteration. n And other parameter information.

[0141] The second step is to divide the specified time step Δt by Δm based on the circuit time constant, and set m=0 at the current moment.

[0142] The third step is to determine whether the segmentation time step Δm is less than the time step to be segmented Δt. If Δm is less than Δt, the segmentation step Δm is used as the time step to calculate the current i using the fourth-order Runge-Kutta method. n+1 , and update the time m=m+Δm; if Δm is greater than Δt, use Δt as the time step to perform the above Runge-Kutta method iteration and then jump to the fifth step.

[0143] The fourth step is to determine whether the iterative calculation of the current time step has been completed, that is, m is greater than Δt. If m is less than Δt, it is not completed, and return to the third step to continue the iterative calculation; if m is greater than Δt, it is completed, and post-processing is performed to correct the overflowed time step.

[0144] The fifth step is to save the calculated current value in a local text file and then pass it to the finite element module.

[0145] For the case where the current source is used as the excitation, the current source is directly connected in series with the contactor coil, and the circuit module algorithm can be solved by the current analytical method; the case where the capacitor discharge and the voltage source are used as the excitation is different. The algorithm script of the circuit module does not take the method of directly writing the circuit analytical formula to calculate the current. Although this method is relatively simple, the main magnetic circuit of the coil is generally composed of nonlinear ferromagnetic materials, so the value of the coil inductance will change with the change of current (the change of the saturation degree of the ferromagnetic material). At the same time, there are critical damping, overdamping and underdamping in the second-order circuit. The formula method cannot guarantee the correct analysis for each case. According to the first-order circuit voltage source, the second-order circuit capacitor discharge and the second-order circuit voltage source, the present invention compiles the circuit equation iteration program under different situations and adopts the fourth-order Runge Kutta method to iteratively solve.

[0146] For certain circuit parameters, directly using the simulation time step given by the user for iterative calculations may lead to large errors. Therefore, this circuit module iteration program needs to divide the relatively long simulation time step given by the user in advance. Although the iterative calculation steps are increased, the iterative process is only performed within the circuit module algorithm, and the calculation speed is fast, without the need for additional static simulation links. For circuits with different parameters, the most universal way to determine the iteration step is to determine it through the time constant of the circuit. In order to determine the feasibility of this solution, tests were carried out using time constants of different multiples as the iteration step. A circuit case with a 10V DC voltage source, a 0.3Ω resistor, and a 1.8H coil inductance was used to illustrate the circuit. The time constant of this circuit is 6, and it iterates from 0s to 24s. The test results are as follows Fig. 9 As shown:

[0147] This case uses 5 different time steps, namely 3 times the time constant, 2.5 times the time constant, 2 times the time constant, 1 time constant and 0.1 times the time constant. Obviously, it can be seen that as the iteration step decreases, the simulation results are getting closer and closer to the accurate curve, and 1 time constant is already relatively accurate as a step. Therefore, when determining whether the specified iteration step is too large, it is feasible to use 1 time constant as a reference standard. When dividing, the time constant can also be divided into integer multiples of 10 as the iteration time step.

[0148] It should be pointed out that the segmentation of small steps is not based on the simulation time step set by the user, but on the time constant. Therefore, when the iterative calculation is performed using the small step after segmentation, an additional step of post-processing of the calculation data should be performed. For example, if the simulation time step is 0.5s, the small step after segmentation is 0.2s, and the actual time of the simulation time step after normal iteration is 0.6s, which does not match the user-set value. Therefore, similar to the post-processing of the previous motion module, this situation requires the additional 0.1s iteration step to be corrected, and the time step is changed to 0.1s in the last iteration to ensure that the current result is the result after 0.5s. Only by modifying in this way can the actual simulation time step set by the user be obtained.

[0149] Based on the above discussion, this patent designs iterative algorithms for current source circuits, first-order voltage source circuits, second-order capacitor power supply circuits, and second-order voltage source dual-winding circuits.

[0150] 1 Current source circuit

[0151] The solution of the current source circuit is relatively simple. As mentioned above, the present invention has built three calculation algorithms for current source excitation, namely direct current, alternating current and custom current. When current source excitation is used, since the current flows directly through the coil, the coil current can be solved directly through the current source analytical formula instead of iteration. In the case of direct current, the coil current i(t) is equal to the power supply current is; in the case of alternating current source, the circuit module algorithm will obtain the current simulation time in the parameter transfer step before the start of iteration, and the current value can be obtained by substituting the current simulation time into the expression of alternating current; for custom current, according to the one-to-one corresponding time-current coordinate point input by the user, find the two time points t1 and t2 that are closest to the current simulation time t, and the currents i(t1) and i(t2) corresponding to the time points. The coil current value i(t) of the current step can be solved by formula (1.4). This solution method is almost the same as the idea of ​​the spring reaction force on the contactor mentioned above, and both use the interpolation method to fit the curve.

[0152] (1.4)

[0153] 2 First-order voltage source circuit

[0154] As mentioned above, for the first-order voltage source circuit, the present invention has built six solution algorithms under different excitations, including DC voltage, AC voltage, square wave voltage, triangular wave voltage, custom voltage waveform (periodic), and custom voltage waveform (non-periodic). The circuit elements of the first-order circuit are composed of power supply, coil resistance, and coil inductance. Since the coil of the contactor is usually a nonlinear ferromagnetic material, at the same time, the proportion of the air magnetic circuit becomes smaller and smaller during the closing process of the moving iron core. Therefore, the coil inductance value is not constant. It will change with the change of current and the spatial position of the moving iron core. The circuit equation of the first-order circuit is shown in formula (1.5):

[0155] (1.5)

[0156] in It represents the magnetic flux linked with the coil; u is the voltage provided by the voltage source; i is the current of the circuit; R is the total resistance of the line; L is the current inductance value.

[0157] By simplifying the equations in (1.5), we can obtain:

[0158] (1.6)

[0159] In summary, the coil inductance changes with the change of current and the distance between the moving and static cores. The inductance value L is obtained through finite element simulation. For dL / dt, the current inductance L is subtracted from the inductance L at the previous moment. last , and then divided by the time step Δt, we can approximate the current inductance change rate dL / dt. After sorting, we can get the common first-order differential equation expression as follows:

[0160] (1.7)

[0161] The coefficients of the independent variable i and its derivative in the first equation in formula (1.7) have been determined, and the differential equation can be solved by numerical calculation method. The present invention adopts the fourth-order Runge-Kutta method for solution, and the following is the iterative expression of this method:

[0162] (1.8)

[0163] Among them, i n is the current after the nth time step iteration, u is the power supply voltage value at the current moment, R is the total resistance of the circuit, L n is the inductance at the nth time step, L n-1 is the inductance at the n-1th time step, and Δt is the time step.

[0164] 3 Second-order capacitor power supply circuit

[0165] When a charging capacitor is used to power the contactor coil, the circuit elements of the second-order circuit are composed of the coil inductance, the total circuit resistance, and the capacitor power supply. According to Kirchhoff's law, the circuit equation satisfies the formula:

[0166] (1.9)

[0167] Among them, u C Indicates capacitor voltage / V; u L Indicates the inductor voltage / V.

[0168] Transforming equation (1.9) into a differential equation about the independent variable i yields:

[0169] (1.10)

[0170] Where C is the capacitance value.

[0171] Similar to the first-order circuit, the second-order circuit is also solved by the fourth-order Runge-Kutta method. Formula (1.10) needs to be organized into an iterative form to transform the second-order differential equation into the joint solution of two first-order differential equations. The formula is as follows:

[0172] (1.11)

[0173] Among them, y1 represents the coil current; y2 represents the first-order derivative of the coil current.

[0174] From the formula, it can be concluded that if you want to use the Runge-Kutta method to solve the capacitor discharge of the second-order circuit, you need to know the two initial values ​​of the current and the first-order derivative of the current over time. Due to the existence of the coil inductance, according to the circuit switching law, the initial value of the current is 0 when the circuit is connected, and the initial voltage of the capacitor is all applied to both ends of the coil inductance. Therefore, the initial value of the first-order derivative of the current over time is the ratio of the initial voltage of the capacitor to the coil inductance. At this point, the complete iterative expression for solving the current of the second-order circuit can be written, as shown in formula (1.12).

[0175] (1.12)

[0176] Where R is the total resistance of the circuit (in Ω), C is the power supply capacitance (in F), and L is the current coil inductance (in H). y1(n) and y2(n) represent the values ​​of y1 and y2 after the nth iteration of the practice step, and y1(n+1) and y2(n+1) represent the values ​​of y1 and y2 after the n+1th iteration of the practice step.

[0177] Each iteration of the capacitor discharge in a second-order circuit requires two initial values, namely the current and the first-order derivative of the current with time. The variables that the finite element simulation module can pass to the circuit module algorithm are the current, the initial voltage of the capacitor, and the coil inductance. However, only the initial value of the first-order derivative of the current with time can be calculated through the initial voltage of the capacitor and the coil inductance. Therefore, after each time step iterative calculation is completed, the algorithm not only needs to output the current value, but also needs to save the latest value of the first-order derivative of the current with time within the step, so that it can be called during the next iteration of the circuit equation.

[0178] 4 Second-order voltage source dual winding circuit

[0179] The second-order voltage source dual-winding circuit refers to a circuit in which the excitation is a voltage source and two coil windings are connected in parallel. Ignoring the mutual inductance effect between the two windings, Kirchhoff's law can be listed as follows:

[0180] (1.13)

[0181] Among them, L1 and L2 are the inductance values ​​of the two coil windings at the current moment, I1 and I2 are the current current values ​​of the two coil windings, R1 and R2 are the resistance values ​​of the branches where the two coil windings are located, and R L is the load resistance value.

[0182] The above formula is organized into the expression of differential equation. Considering the similarity of the solution expressions of I1 and I2, only the differential equation of I2 is listed here, as shown in formula (1.14).

[0183] (1.14)

[0184] Finally, formula (1.14) is transformed into the joint solution of two differential equations according to the idea of ​​formula (1.12). At this point, the complete iterative expression for solving the voltage source double-winding second-order circuit can be written, as shown in formula (1.15):

[0185] (1.15)

[0186] Where R is the total resistance of the circuit (in Ω), C is the power supply capacitance (in F), and L is the current coil inductance (in H). y1(n) and y2(n) represent the values ​​of y1 and y2 after the nth iteration of the practice step, y1(n+1) and y2(n+1) represent the values ​​of y1 and y2 after the n+1th iteration of the practice step, and u is the voltage at the current moment.

[0187] The above general description of the invention involved in the present invention and the description of its specific implementation methods should not be understood as limiting the technical solutions of the invention. Based on the contents disclosed by the present invention, those skilled in the art can add, reduce or combine the disclosed technical features in the above general description and / or specific implementation methods (including examples) without violating the constituent elements of the invention involved, to form other technical solutions within the protection scope of the present invention.

Claims

1. An autonomous simulation system for dynamic characteristics of low-voltage contactors, characterized in that: The system comprises: a finite element simulation module, a circuit module, and a motion module; The finite element simulation module is used to simulate and calculate the current position and current of the moving iron core of the contactor, and transmit them to the motion module and the circuit module respectively; The motion module is used to calculate the displacement of the next time step according to the current position of the contactor moving iron core and transmit the displacement to the finite element simulation module for real-time update; The circuit module is used to calculate the current of the next time step according to the current current and output it, so as to perform a cyclic iteration of the next time step.

2. The system according to claim 1, characterized in that Preferably, the circuit module is driven by a current source.

3. The system according to claim 2, characterized in that The current source excitation can calculate the current without components such as inductance, capacitance and resistance.

4. The system according to claim 1, characterized in that The circuit module is excited by a non-current source.

5. The system according to claim 4, characterized in that The non-current source excitation has a dynamic calculation process.

6. A method for autonomous simulation of dynamic characteristics of low-voltage contactors, characterized in that: The method comprises: The finite element simulation module simulates and calculates the current position and current of the contactor moving iron core, and transmits them to the motion module and the circuit module respectively; The motion module calculates the displacement of the next time step according to the current position of the contactor moving iron core and transmits the displacement to the finite element simulation module for real-time update; The circuit module calculates the current of the next time step according to the current current and outputs it so as to perform a loop iteration of the next time step.

7. The method according to claim 6, characterized in that The circuit module can be excited by a current source or by a non-current source.

8. The method according to claim 7, characterized in that The current source excitation can calculate the current without components such as inductors, capacitors and resistors.

9. A computer storage medium, characterized in that The storage medium includes computer instructions, which, when executed on a computer, enable the computer to execute the method according to any one of claims 6 to 8.

10. An electronic device, characterized in that: The electronic device comprises: a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor implements the method according to any one of claims 6 to 8 when executing the program.

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