A large motor magnetic-thermal coupling model modeling and fast calculation method

Abstract

The patent proposes an improved method for analyzing and calculating the temperature field of large motors. It relates to the field of electromagnetic field and temperature field calculation of motors, and is suitable for temperature rise analysis of modern large motors. In order to ensure the safe and efficient operation of large motors under various working conditions, the electromagnetic performance and temperature rise of the motor under different working conditions need to be accurately and efficiently analyzed. The present application proposes a large motor magnetic-thermal coupling modeling and fast calculation method. The present application determines the specific structure of the large motor and the problem analysis, the structure is the stator and rotor core and coil under the large motor shell, the research problem analysis is electromagnetic performance and thermal performance, the physical field involved in the problem is electromagnetic field and temperature field, a dynamic magnetic network model, a thermal network model, a coupled equivalent magnetic network model and an equivalent thermal network model are established, and the established model is analyzed. The present application analyzes the specific problem according to the research, and ensures accurate and efficient analysis of the performance of the motor under different conditions.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of motor electromagnetic field and temperature field calculation, and relates to a large motor magnetic-thermal coupling model modeling and rapid calculation method. TECHNICAL BACKGROUND

[0002] Large induction motors are favored due to their relatively simple structure, high reliability, stable operation and other advantages. Generally speaking, low-speed large-capacity induction motors are often used to drive reciprocating compressors. Since the compression stages of the compressor vary, the driving motor often needs to be operated in short-time overload. Under the condition of overload operation, the temperature of the motor continues to rise because the heat generation rate exceeds the heat dissipation rate. If the temperature rise exceeds the safe temperature range of the motor, the insulation performance of the winding in the motor will decrease, the magnetic conductivity of the ferromagnetic material will decrease, the service life of the motor will be shortened, and in severe cases, insulation breakdown accidents will occur to damage the equipment. In order to ensure the safe and efficient operation of the motor under various operating conditions, the electromagnetic performance and temperature rise of the motor under different operating conditions need to be accurately and efficiently analyzed.

[0003] The current method for analyzing the temperature distribution in the induction motor is the equivalent thermal network model method and the fluid network-thermal network bidirectional coupling method. The loss distribution characteristics of the motor stator and rotor are calculated by the finite element method or numerical analysis method, and the equivalent thermal network model is established to obtain the temperature distribution. SUMMARY

[0004] The purpose of the present application is to analyze the temperature rise distribution of large motors using fluid network-thermal network analysis, but the fluid network-thermal network analysis method is suitable for steady-state analysis, while the motor is dynamic during operation. This method cannot accurately reflect the change of temperature rise with time. In view of the defects of this method, a large motor magnetic-thermal coupling model modeling and rapid calculation method is proposed. This method can analyze the electromagnetic performance and temperature rise of the motor under different operating conditions.

[0005] To achieve the above purpose, the technical solution proposed by the present application is as follows: a large motor magnetic-thermal coupling model modeling and rapid calculation method, comprising the following steps:

[0006] Step 1: Region division: the motor magnetic network model includes stator magnetic network model, rotor magnetic network model and air gap magnetic network model, and each region is divided into grids according to the magnetic field distribution of each component, and appropriate subdivision accuracy is selected;

[0007] Step 2: Establishing equivalent magnetic network model: according to the structural characteristics and magnetic distribution gradient of the large motor, the magnetic network model of the motor stator, rotor and air gap is constructed, and the model is connected to establish the equivalent magnetic network model according to the coupling relationship of each part;

[0008] Step 3: write the magnetic motive force equation set according to the equivalent magnetic network model, and calculate the magnetic density distribution of each area node;

[0009] Step 4: calculate the iron loss of each area according to the magnetic density distribution of each area node;

[0010] Step 5: calculate the copper loss of each area using a numerical analysis method;

[0011] Step 6: according to the thermal gradient distribution in the motor, divide the thermal nodes, calculate the thermal resistance of each area, and establish a thermal network model to solve the temperature rise of each node;

[0012] Step 7: magnetic-thermal coupling calculation: the core loss calculated using the magnetic network model and the copper loss calculated using the numerical analysis method are used as heat sources into the thermal network model to calculate the temperature rise of each node. If the temperature does not converge, recalculate the copper loss according to the influence of temperature on impedance, and repeat the above steps until the temperature meets the set convergence accuracy, that is, the target temperature is obtained;

[0013] Further, in the step 2, when establishing the transient equivalent magnetic network model, due to the normal operation of the motor, the magnetic flux path at the air gap changes due to the change of the relative position of the stator and the rotor, thereby affecting the size of the air gap permeance value. The air gap permeance matrix changes with the rotor position. The present application combines the characteristics of the induction motor being studied. For the air gap permeance between the stator and the rotor at any time, only the spatial included angle between the two tooth top center lines needs to be considered and solved according to the air gap permeance formula, so as to obtain the air gap permeance between any one stator tooth and any one rotor tooth at any rotor position at any time, that is, to establish a transient equivalent magnetic network model.

[0014] Further, in the step 4, the iron loss of each area is calculated according to the magnetic density distribution of each area node, and the internal magnetic field distribution gradient of the motor is also considered when calculating the iron loss.

[0015] Further, in the step 5, the influence of skin effect and proximity effect on winding copper loss should be considered; the skin effect is equivalent to reducing the area through which the current flows, indirectly increasing the resistance of the conductor, thereby increasing the loss of the conductor, reducing the efficiency of the motor, and increasing the temperature; when the distance between two conductors is close, the adjacent conductors are both connected with alternating current, and the adjacent conductors are both in the alternating magnetic field of each other. At this time, the current density distribution of each conductor will be affected by itself and the adjacent conductor, resulting in that the current density distribution of each conductor is different from that when it is connected with alternating current alone.

[0016] Furthermore, in steps 1 and 6, the stator magnetic network model is mainly divided into the stator yoke, stator teeth, slot leakage magnetic field, and stator winding. The rotor magnetic network model is mainly divided into the rotor yoke, teeth, slot leakage magnetic field, and rotor winding. When dividing the thermal network model, considering the magnetic-thermal distribution gradient within the motor, a common-region method is used to divide multiple thermal regions, such as the stator core thermal region, rotor core thermal region, winding thermal region, and air gap thermal region. Each thermal region has its own thermal characteristics, such as heat capacity. Attached Figure Description

[0017] Figure 1 This is a flowchart of an embodiment of the present invention;

[0018] Figure 2 This is a schematic diagram of a magnetic network model and some parts of it, as shown in the embodiment of the present invention.

[0019] Figure 3 This is a schematic diagram of a thermal network model and some parts of it, as shown in the embodiments of the present invention. Detailed Implementation

[0020] To make the purpose, technical solution, and advantages of this invention patent clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings.

[0021] This invention establishes a dynamic coupled magnetic-thermal network model of a large motor based on its structural characteristics and magnetic-thermal distribution gradient using a common-region method, taking into account the influence of transient electromagnetic processes on motor heating. Based on the interaction between the magnetic and thermal physical fields within the motor, the coupling solution parameters of the model are determined. An analytical method is employed to achieve rapid solution of the coupled model. Electromagnetic and thermal transient characteristic data of the motor under different operating conditions are stored on a host computer, enabling accurate and efficient analysis of the motor's electromagnetic performance and temperature rise.

[0022] This embodiment uses a specific large-capacity induction motor as an example. The embodiment is a 20-pole squirrel-cage rotor induction motor with 180 slots in the stator and 210 slots in the rotor. It is divided into three parts: stator, rotor, and air gap. The stator includes a yoke, stator teeth, stator slots, and stator windings. The stator windings adopt distributed windings with a pitch of 8 and 3 slots per pole per phase. The rotor includes a rotor yoke, rotor teeth, rotor slots, and rotor windings. The rotor windings adopt a squirrel-cage rotor.

[0023] As attached Figure 1 The flowchart shown consists of the following steps:

[0024] Step 1: Region Division. Based on the motor's topology, the motor is divided into six regions. For each region, the equivalent magnetic permeability is determined according to its geometry. Region 1 is the stator yoke, which is equivalent to a combination of two radial rectangular magnetic permeabilities and one tangential rectangular magnetic permeability. Region 2 includes the stator windings, stator slots, and winding section, which is equivalent to one radial magnetic permeability and one equivalent magnetomotive force source. Some leakage magnetic flux will pass through the slot closure in the stator slot section, thus it is equivalent to an "I"-shaped magnetic permeability structure formed by one radial rectangular magnetic permeability and four tangential rectangular magnetic permeabilities. Region 3 is the stator teeth, which is further refined to a "+"-shaped magnetic permeability structure composed of two radial rectangular magnetic permeabilities and two tangential rectangular magnetic permeabilities. Similarly, the equivalent magnetic permeability methods for Region 4 (rotor yoke), Region 5 (rotor windings), and Region 6 (rotor slots) are similar to those for the stator. Radial magnetic permeability G ser Tangential magnetic permeability G set The calculation formula is:

[0025]

[0026] In the formula: u is the core permeability, l is the axial length of the motor, R1 and R2 are the inner and outer radii of the stator yoke, θ is the mechanical angle corresponding to one slot of the stator, w1 and w2 are the inner and outer chord lengths of the sector permeability corresponding to one slot of the stator, and h is the tooth height.

[0027] Compared with traditional models, the model established in this invention fully considers the characteristics of leakage flux inside the motor and the obvious tooth saturation effect.

[0028] In this invention, the air gap of the induction motor is small, requiring high calculation accuracy, necessitating independent analysis of the air gap permeability model. A transient equivalent magnetic network model is established. During normal motor operation, the overlapping area between the stator and rotor teeth changes, altering the magnetic flux path in the air gap due to the change in the relative positions of the stator and rotor, thus affecting the magnitude of the air gap permeability. The permeability is maximized when the stator and rotor teeth are completely overlapping; when the two teeth are completely misaligned with no overlapping area, there is no magnetic flux flowing through both teeth simultaneously, i.e., no magnetic path connection, and the corresponding air gap permeability is 0. The air gap permeability G between the p-th stator tooth and the q-th rotor tooth is... p,q As the angle between the centerlines of the two teeth changes, the air gap permeability varies in [0, G]. max Variation within a certain range. Air gap permeability calculation formula:

[0029]

[0030] In the formula, γ, γ′ t γ t Angle variables are used to divide different intervals in order to determine the formula for calculating air gap permeability in different intervals.

[0031]

[0032] where u0 is air permeability, b st is the stator tooth tip width, b tmin is the smaller value of stator and rotor tooth width, δ is the air gap length, b ss is the stator slot opening width, b rt is the rotor tooth tip width, b sr is the rotor slot opening width, D si is the stator inner diameter, D ro is the rotor outer diameter, D ag is the arithmetic mean of the stator inner diameter and the rotor outer diameter, l is the motor axial length.

[0033] Step 2, according to the structural characteristics and magnetic distribution gradient of large motor, the magnetic network model of motor stator, rotor and air gap part is constructed, and the model is connected according to the coupling relationship of each part. As shown in the appendix Figure 2 , the node represents the magnetic potential of different areas, and the branch represents the magnetic circuit, and its magnetic resistance is related to the equivalent permeance; the nodes and permeance branches are numbered according to the order of stator magnetic network, rotor magnetic network and air gap magnetic network, and the motor has 2940 nodes, as shown in the appendix Figure 2 , the 1st and 2nd nodes are the stator yoke node numbers, the 3rd node is the stator tooth node number, the 4th node is the stator tooth tip node number, the 5th and 6th nodes are the stator slot body node numbers, and the 1st-1080th nodes are the node numbers of the stator magnetic network model; the 2551st node represents the first stator tooth, and the 2551st-2730th nodes are the stator tooth node numbers; the 1081st and 1082nd nodes are the rotor yoke node numbers, the 1083rd node is the rotor tooth node number, the 1084th and 1085th nodes are the rotor tooth tip node numbers, the 1086th and 1087th nodes are the rotor slot body node numbers, and the 1081st-2550th nodes are the node numbers of the rotor magnetic network model. The 2731st node is the first rotor tooth, and the 2731st-2940th nodes are the rotor tooth node numbers; on this basis, the initial permeance matrix G can be written.

[0034] Step 3, the magnetic potential source F in the dynamic magnetic network is written according to the current and winding turns of the stator and rotor, in the Ampere loop law, the difference of the magnetic motive force between adjacent teeth and slots is equal to the ampere-turns of the total current between them, the magnetic potential source of the stator and rotor is calculated, and the magnetic potential source matrix F s :

[0035] F s = [F D1 … F Dn F Z1 … F Zn ]

[0036] Where F Dn is the magnetic potential source on the nth tooth of the stator, F Zn is the magnetic potential source on the nth tooth of the rotor.

[0037] The node magnetic potential equation set of the dynamic magnetic network is established, and the node equation is as follows:

[0038]

[0039] Where G(i, j) is the magnetic conductance between nodes, U(i) is the magnetic potential of node i, and φ(i) is the magnetic flux of node i.

[0040] The magnetic flux density B(i, j) between nodes is calculated, and the formula is as follows:

[0041]

[0042] B(i, j) is the magnetic flux density between node i and node j, G(i, j) is the branch magnetic conductance between node i and node j, U n (i) and U n (j) are the node magnetic potentials, and S is the area.

[0043] At different transient time points, the magnetic density distribution of each area node is calculated by solving the non-linear matrix equation set through successive over-relaxation iteration method according to the equivalent magnetic network model and the magnetic potential equation set. In each time step, the magnetic conductivity and other parameters are updated, and the calculation is repeated until the set transient time range is reached to obtain the magnetic density under different time states. The magnetic density data of different areas at different transient times obtained in the equivalent magnetic network calculation are sorted and brought into the formula, and the core loss of each area is calculated.

[0044] Step 4, according to the generation mechanism of core loss, the core loss is divided into hysteresis loss, eddy current loss and abnormal loss. For the yoke core loss, the magnetic density data of the yoke is substituted into the corresponding formula for calculation; for the tooth core loss, the tooth magnetic density data is also substituted into the formula for calculation. The core loss calculation formula is as follows:

[0045] P Fe = P h + P c + P e

[0046] Where P h is the hysteresis loss, P c is the eddy current loss, and P e is the abnormal loss.

[0047] The calculated core loss of each part, such as the stator yoke core loss and the rotor yoke core loss, is taken as the heat source in the corresponding equivalent thermal network model division area.

[0048] In step 5, the copper loss is calculated using numerical analysis method, which is mainly generated by the rotor winding and the stator winding, while considering the influence of skin effect and proximity effect on the copper loss of the induction motor winding. In the calculation process, first, the current excitation of the winding is applied, and the copper loss at this time is calculated. According to the temperature rise, the winding resistance is updated, and the copper loss is recalculated as a new heat source to be brought into the thermal network for calculation, until the thermal network temperature change is less than the preset threshold, the iteration is terminated, otherwise continue iteration.

[0049] The copper loss calculation formula is:

[0050] P cu =mI 2 R

[0051] In the formula, m is the number of phases, I is the effective value of phase current, and R is the resistance of each phase winding.

[0052] The copper loss of the stator and rotor winding is obtained by numerical calculation, and the power value at different transient time is recorded as the heat source in the winding area, which participates in the subsequent thermal analysis together with the core loss heat source.

[0053] In step 6, according to the structure characteristics and thermal distribution gradient of the motor, the thermal network model is constructed by comprehensively considering the regional coupling relationship with the magnetic network model, as shown in the appendix Figure 3 The node represents the temperature of the thermal zone, and the branch represents the thermal resistance. Node 1 is the node number of the stator core thermal zone; node 2 is the node number of the stator winding thermal zone; node 3 is the node number of the stator slot wedge thermal zone, each region contains a heat capacity; different regions have different heat sources, such as the copper loss of the stator winding part at node 2, and the core loss of the stator core thermal zone at node 1; nodes 1-1080 represent the 1-180 stator teeth; nodes 1081-1920 represent the 210 rotor teeth; among them, node 1081 is the node number of the rotor bar thermal zone, node 1082 is the node number of the rotor core thermal zone, and nodes 1921-2130 are the air gap nodes.

[0054] The equivalent thermal network model of each part is constructed, the initial temperature distribution of thermal analysis is set, and the heat source power value is substituted into the thermal network model according to the characteristics of each region; such as the magnetic loss of nodes 1 and 2 in the magnetic network model, which corresponds to the regional heat source of node 1 region in the thermal network model, the temperature rise at node 1 of the thermal network model is solved; the rest is calculated by this method, and the loss is brought into the thermal network model as a heat source; at the same time, the influence of the heat capacity of each region needs to be considered, so as to store the transient temperature rise data.

[0055] For each region inside the motor, a heat balance equation is written according to Fourier heat conduction law. A difference method (such as finite difference method, finite element method, etc.) is used for numerical solution to calculate the temperature change of each thermal region at different transient times. In each time step, the heat source power is updated (because the copper loss changes with temperature change, and the core loss may also change with temperature to a certain extent), and the calculation is repeated until the set transient time range is reached to obtain the temperature change curve with time.

[0056] Under different operating conditions, the temperature rise of the motor is dynamic, and the dynamic component heat capacity should be considered.

[0057] The heat capacity C refers to the heat absorbed when the temperature of an object rises by 1°C, reflecting the dynamic rise of the temperature of the object. The formula is as follows:

[0058] C D = cvp

[0059] C D is the equivalent heat capacity of each partition, c is the specific heat capacity of the sub-region, v is the volume of the sub-region, and p is the density of the sub-region.

[0060] Under different states, the temperature rise of the motor is dynamic. The dynamic component heat capacity should be considered to construct the heat balance equation under the dynamic state as follows:

[0061]

[0062] G is the thermal resistance matrix, T(t) is the node temperature rise matrix, C is the heat capacity matrix, and P(t) is the heat source matrix.

[0063] Step 7, magnetic-thermal coupling calculation: the core loss calculated using the magnetic network model and the copper loss calculated using the numerical analysis method are used as heat sources to substitute into the thermal network model to calculate the node temperature rise T i If the temperature does not converge, the copper loss is recalculated according to the influence of temperature rise on impedance, and the above steps are repeated until the temperature meets the set convergence accuracy, as follows:

[0064]

[0065] T i+1 is the temperature obtained by the i+1 iteration, T i is the temperature obtained by the i iteration, and ε is the convergence accuracy. If the convergence accuracy is met, the temperature is considered to be the target temperature.

[0066] In summary, the present application proposes a large motor magnetic-thermal coupling model modeling and fast calculation method, which ensures accurate and efficient analysis of the performance of the motor under different states, is clear in organization and easy to operate, and effectively improves the calculation efficiency.

Claims

1. A large motor magnetic-thermal coupling model modeling and fast calculation method, comprising the following steps: Step 1: Region division: the motor magnetic network model includes a stator magnetic network model, a rotor magnetic network model, and a gap magnetic network model, each region is divided into a grid, and the magnetic field distribution of each component is selected as the basis to select the appropriate subdivision accuracy; Step 2: Establishing an equivalent magnetic network model: according to the structural characteristics and magnetic distribution gradient of the large motor, the magnetic network model of the motor stator, rotor and gap is constructed, and the model is connected according to the coupling relationship of each part to establish an equivalent magnetic network model; Step 3: According to the equivalent magnetic network model, the magnetic motive force equation set is written, and the node magnetic density distribution of each region is calculated; Step 4: According to the node magnetic density distribution of each region, the core loss of each region is calculated; Step 5: Using numerical analysis method, the copper loss of each region is calculated; Step 6: According to the thermal gradient distribution in the motor, the thermal nodes are divided, the thermal resistance of each region is calculated to establish a thermal network model to solve the temperature rise of each node; Step 7: Magnetic-thermal coupling calculation: the core loss calculated by the magnetic network model and the copper loss calculated by the numerical analysis method are used as heat sources to be substituted into the thermal network model to calculate the temperature rise of each node. If the temperature does not converge, the copper loss is recalculated according to the influence of temperature rise on impedance, and the above steps are repeated until the temperature meets the set convergence accuracy, that is, the target temperature is considered.

2. The method of claim 1, wherein step 2 is characterized by: When establishing the equivalent magnetic network model, due to the normal operation of the motor, the magnetic flux path at the air gap changes due to the change of the relative position of the stator and rotor, thereby affecting the size of the air gap permeance value; Combined with the characteristics of the motor studied, for the air gap permeance between the stator and the rotor at any time, only the spatial angle between the two tooth top center lines needs to be considered and solved according to the air gap permeance formula, the air gap permeance between any one stator tooth and any one rotor tooth at any rotor position at any time can be obtained, and the equivalent magnetic network model can be established.

3. The method of claim 1, wherein step 4 is characterized by: The equivalent magnetic network model is established, and the node magnetic density of each region is obtained. When calculating the core loss, the internal magnetic field distribution gradient of the motor is also considered.

4. The method of claim 1, wherein step 5 is characterized by: When calculating the copper loss of the stator and rotor, the influence of skin effect and proximity effect on the winding copper loss is considered.

5. The method of claim 1, wherein step 1 is characterized by: The stator magnetic network model region division is mainly divided into stator yoke, stator tooth, slot body leakage magnetic part and stator winding part, and the rotor magnetic network model region division is mainly divided into rotor yoke, tooth, slot body leakage magnetic part and rotor winding part.

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