A Method for Establishing a General Lumped-Parameter Thermal Network Model of an Electric Machine

Abstract

The present invention relates to the field of motor design. Specifically, it is a method for establishing a general lumped-parameter thermal network model of a motor. This method is based on the lumped-parameter modeling method of the heat transfer phenomenon of motor components, and uses lumped thermal resistance, thermal admittance, and lumped heat capacity parameters to describe the transient heat transfer and temperature change phenomena within and between motor components. By taking into account the anisotropy of the thermodynamic parameters of the motor component materials, this method gives the general formulas for lumped thermal resistance, lumped thermal admittance, and lumped heat capacity in different directions of the motor components. Combining the heat transfer characteristics between motor components, various connection methods of component thermal models are established. Finally, the establishment process of the general lumped-parameter thermal network model of the motor is given. The method for establishing the general lumped-parameter thermal network model of the motor in the present invention has clear ideas and simple operations. The method for establishing the general lumped-parameter thermal network model of the motor in the present invention has the advantages of high efficiency, general applicability, etc., and demonstrates superior performance.

Description

Technical Field

[0001] The present invention relates to the field of motor design, and specifically to a method for establishing a general lumped parameter thermal network model of a motor. Background Art

[0002] The demand for pursuing low-carbon emissions to address global warming is continuously driving society to shift from non-renewable fossil fuel energy to renewable new energy. In this process, the electrification of transportation has played an important role in this field, and motors play a core role in the electrification process of transportation in terms of electromechanical energy conversion. The further promotion of the electrification of transportation also places higher demands on the power density and efficiency of motors to continuously improve the performance indicators of motors and improve the comprehensive performance of motors under complex and variable working conditions. It is necessary to consider the complex coupling interaction mechanism between the electromagnetic field and the temperature field of the motor during the motor design stage, so as to accurately predict the performance of the motor and reduce the development cost of the motor.

[0003] Traditional motor temperature rise analysis tools include the finite element method and the computational fluid dynamics method. The finite element method is based on the accurate geometric model of the motor and can automatically calculate the heat conduction phenomenon of complex structures. The heat convection phenomenon is accounted for using a lumped convective heat transfer coefficient. The finite element method has high calculation accuracy, but it also depends on the accurate convective heat transfer coefficient and the empirical correction coefficient of the contact thermal resistance. At the same time, its calculation speed is slow, and it is difficult to integrate with the electromagnetic analysis of the motor to achieve electromagnetic-thermal coupling optimization. The computational fluid dynamics method directly uses the governing equations of fluid mechanics to calculate the flow field and temperature field inside the motor. This method can accurately account for the interaction and coupling between the flow field and the temperature field. However, currently, the computational fluid dynamics method cannot accurately capture the local flow field turbulence phenomenon. To improve the calculation accuracy of the fluid state as much as possible while reducing the calculation amount, a series of correction formulas are usually used to calculate the fluid motion equation, which will also introduce simulation errors in the fluid motion state. More importantly, even with a series of correction formulas introduced, the computational fluid dynamics method still has a huge calculation amount, which is unacceptable for the multi-field coupling performance optimization of motors. Therefore, it is of great significance to develop a motor temperature field analysis method with high calculation speed and high accuracy. Summary of the Invention

[0004] To solve the deficiencies mentioned in the above background art, the purpose of the present invention is to provide a method for establishing a general lumped parameter thermal network model of a motor, which can provide a set of general and efficient methods for establishing a lumped parameter thermal network model of motors with different topologies and sizes, and at the same time can also reduce the calculation amount of electromagnetic-thermal coupling analysis and design in the motor design process.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A method for establishing a general lumped parameter thermal network model of an electric machine, including establishing component geometry and material parameters, dividing component nodes, establishing component thermal models, defining the connection method of the thermal models of electric machine components, assembling the thermal models of electric machine components, and defining the heat exchange method between the electric machine and the outside. Among them, establishing component geometry and material parameters is used to define the key geometric parameters of electric machine components; dividing component nodes is used to define the node dimensions and numbers used in the component thermal model; establishing component thermal models is used to establish the thermal resistance matrix and heat capacity matrix of electric machine components; defining the connection method of the thermal models of electric machine components is used to define the connection relationship between different electric machine component nodes; assembling the thermal models of electric machine components is used to assemble the thermal models of electric machine components to form the overall thermal model of the electric machine; defining the heat exchange method between the electric machine and the outside is used to describe the heat exchange phenomenon between electric machine components and the external environment or cooling medium under different heat dissipation conditions

[0007] The method for establishing the general lumped parameter thermal network model of the electric machine specifically includes the following steps:

[0008] S1. Define the geometric parameters of the electric machine components. According to the geometric characteristics of the electric machine, give the axial, radial, and angular parameters in cylindrical coordinates, or the x, y, z-axis parameters in the Cartesian coordinate system, or the radius, azimuth angle, and zenith angle parameters in the spherical coordinate system; define the material parameters of the electric machine components, including heat transfer coefficient, specific heat capacity, mass density, etc.

[0009] S2. Divide the electric machine components into a series of nodes according to the accuracy requirements of temperature calculation. To ensure the accuracy in different spatial dimensions, the division fineness in different spatial dimensions should be given;

[0010] S3. Comprehensively consider the node fineness of the electric machine components in the spatial dimension, calculate the lumped thermal resistance and lumped heat capacity parameters in different spatial dimensions; consider all nodes of the electric machine components and establish the thermal resistance and heat capacity matrices of the electric machine components;

[0011] For a certain electric machine component, the lumped thermal resistance R in a certain direction is expressed as

[0012]

[0013] where L represents the heat transfer path length of a certain electric machine component in a certain direction, A represents the heat transfer cross-sectional area of a certain electric machine component in a certain direction, and k represents the heat transfer coefficient of a certain electric machine component in a certain direction.

[0014] For a certain electric machine component, the lumped heat capacity in a certain direction is expressed as

[0015] C = Mc p #(2)

[0016] where M represents the mass of a certain electric machine component, and c p represents the specific heat capacity of a certain electric machine component.

[0017] Considering that the node dimension of a certain motor component in a certain direction is l, and the node dimensions in the other two directions are m and n, for a certain motor component, the lumped thermal resistance of the motor component in this direction is expressed as

[0018]

[0019] Considering that the node dimension of a certain motor component in a certain direction is l, and the node dimensions in the other two directions are m and n, for a certain motor component, its lumped heat capacity in this direction is expressed as

[0020]

[0021] For a certain motor component, its lumped admittance in a certain direction is the reciprocal of the lumped thermal resistance in this direction.

[0022] S4. Define the connection method of the motor component thermal model. Considering the contact thermal resistance between different components, connect it in series to the heat transfer path between components, such as the slot insulation paper and its gap between the winding and the silicon steel sheet, the gap between the outer circle of the stator silicon steel sheet and the machine shell, etc.

[0023] S5. Define the overall assembly of the motor thermal model and the external heat exchange method. According to the connection method between motor components, assemble the thermal models of each motor component to form the overall motor thermal model. Considering the external heat exchange method of the motor, add its external heat exchange conductance at the nodes where there is heat exchange between the motor and the external environment or the cooling medium; consider the convective heat transfer coefficient of the motor at the air gap and add the air gap convective heat transfer conductance.

[0024] For a certain motor component, if its heat transfer form is convective heat transfer, then its convective heat transfer resistance is

[0025]

[0026] where k cov is the convective heat transfer coefficient, and A cov is the convective heat transfer cross-sectional area.

[0027] For a certain motor component, its convective heat transfer conductance is the reciprocal of the convective heat transfer resistance.

[0028] Furthermore, the motor parameters in step one are applicable not only to radial motors but also to axial motors.

[0029] Furthermore, the thermal model connection methods in step four are mainly the following three types, namely, full connection of the edge nodes of different components; full connection of some edge nodes of different components; one-to-one connection of the edge nodes of different components.

[0030] Further, for the thermal model connection method in the fourth step, considering that the heat transfer phenomenon between components generally occurs at the edges of the components, this method generally uses the edge nodes of the components to connect the component thermal models.

[0031] Further, the external heat exchange method in the fifth step is a generalized motor cooling method. As long as the heat transfer phenomenon involving heat transfer from the motor components to the external environment or the cooling medium is involved, it falls into the external heat exchange phenomenon here. The external heat exchange methods here include, but are not limited to, natural cooling, air cooling, water cooling, oil cooling and other cooling methods.

[0032] Advantages of the present invention:

[0033] 1. By using the method for establishing the general lumped parameter thermal network model of the motor provided by the present invention, the lumped parameter thermal model of the motor can be established efficiently, and the thermal network models of motors with different topologies and different types all follow the unified thermal network model establishment framework;

[0034] 2. By using the method for establishing the general lumped parameter thermal network model of the motor provided by the present invention, there is no need to pay attention to the complex node definition and parameter assignment process of the thermal network matrix in the motor components and between components during the motor design process. Only the top-level settings of the motor thermal model need to be concerned, such as geometric parameters, component contact methods, etc., which has the characteristics of intuitiveness and easy implementation;

[0035] 3. By using the method for establishing the general lumped parameter thermal network model of the motor provided by the present invention, the established motor thermal model can be conveniently coupled with the motor electromagnetic model, and the electromagnetic-thermal coupling design of the motor can be realized at the initial design stage of the motor. It can not only accurately predict the motor performance, but also ensure the operation stability and safety of the designed motor. Description of the drawings

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings;

[0037] Figure 1 is the flow chart for establishing the general lumped parameter thermal network model of the motor involved in the present invention;

[0038] Figure 2 is the motor topology in the embodiment of the present invention, where 1 - rotating shaft, 2 - rotor core, 3 - permanent magnet, 4 - flat wire winding, 5 - stator core;

[0039] Figure 3 is the distribution of thermal resistance, heat capacity, temperature and thermal power under the steady state of the motor thermal circuit in the embodiment of the present invention;

[0040] Figure 4 is the correlation coefficient matrix of different components of the motor in the embodiments of the present invention. The maximum value of 1 represents the minimum thermal resistance, and the minimum value of 0 represents the maximum thermal resistance;

[0041] Figure 5 is the comparison between the predicted results of the end winding temperature rise under rated conditions in the embodiments of the present invention and the predicted results of commercial software;

[0042] Figure 6 is the comparison between the predicted results of the effective winding temperature rise under rated conditions in the embodiments of the present invention and the predicted results of commercial software;

[0043] Figure 7 is the comparison between the predicted results of the permanent magnet temperature rise under rated conditions in the embodiments of the present invention and the predicted results of commercial software. Detailed implementation manners

[0044] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0045] A method for establishing a general lumped parameter thermal network model of a motor, as Figure 2 shown, the analyzed components of the motor are typical common components in the motor, such as the stator, rotor, and winding. There is an air gap between the stator and the rotor; the winding of the motor is a 7-layer flat wire structure, and all are embedded in the motor stator.

[0046] The motor involved in this example uses a three-phase symmetrical AC winding. In addition, the technology involved in the present invention is not only applicable to this type of winding, but also applicable to single-phase, multi-phase, and asymmetric motor windings.

[0047] The technology involved in the present invention is not only applicable to this type of motor, but also applicable to all equipment involving electromechanical energy conversion, such as all rotating and translational mechanical devices.

[0048] This example will analyze the method for establishing a lumped parameter thermal network model of this type of motor, which includes the following steps:

[0049] S1. Define the geometric structure parameters of the motor stator, rotor, and winding, including geometric positions, winding slot fill factors, etc.; define the material physical properties of the stator, rotor, and winding, including mass density, specific heat capacity, thermal conductivity, etc.; calculate their volumes according to the geometric parameters of the motor stator, rotor, and winding; calculate their masses according to the component volumes and material mass densities; calculate their lumped heat capacity parameters according to the component specific heat capacities.

[0050] S2. According to the temperature calculation accuracy requirement, divide the motor components into a series of node grids; for the motor yoke, set one node; for the motor teeth, to improve the temperature calculation accuracy, set 7 nodes along the radial direction; for the motor winding, set 7 nodes along the radial direction, corresponding to the stator tooth nodes respectively; for the motor rotor, set three layers of core nodes and permanent magnet nodes; for the motor air gap, set one node; for the motor housing, set one node.

[0051] S3. According to the node distribution of the motor components, calculate the lumped thermal resistance and heat capacity parameters corresponding to different nodes inside the components; considering the node spatial distribution of the motor components, establish the corresponding lumped thermal resistance and lumped heat capacity matrices.

[0052] S4. Establish the thermal model connection methods of different motor components. The motor teeth and yoke are connected radially; there is a tangential thermal connection between the motor teeth and the motor winding; there is a thermal connection between the radial adjacent air gap nodes of the motor teeth and winding and the motor air gap; there is a thermal connection between the motor air gap and the rotor; there is a thermal connection between the rotor permanent magnet and the rotor core; there is a thermal connection between the motor housing and the stator; in addition, there is a contact thermal resistance between the winding and the motor stator, and there is a contact thermal resistance between the housing and the motor stator.

[0053] S5. According to the motor component thermal model and the defined thermal model connection methods, assemble the motor thermal model to form the motor total lumped thermal resistance matrix and lumped heat capacity matrix; according to the motor cooling method, set the external heat exchange method. In this example, the motor is oil-cooled, including spray cooling and housing oil duct cooling. Set the convective heat transfer coefficient at the motor housing, the end winding, and the rotor surface, and at the same time update the motor lumped admittance matrix and lumped thermal resistance matrix.

[0054] S6. According to the established lumped parameter thermal network model of the motor, refer to the operating conditions of the motor, calculate the motor losses corresponding to the conditions, and based on the lumped parameter thermal network model, calculate the relationship between the motor temperature and time.

[0055] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed.

Claims

1. A method for establishing a general lumped parameter thermal network model of an electric machine, characterized in that, it includes the definition of component geometric parameters and material parameters, the division of component nodes, the establishment of component thermal models, the definition of the connection method of the thermal models of electric machine components, the general assembly of the thermal models of electric machine components, and the definition of the heat exchange method between the electric machine and the outside. Among them, the definition of component geometric parameters and material parameters is used to define the key geometric parameters of electric machine components; the division of component nodes is used to define the node dimension and number used in the component thermal model; the establishment of component thermal models is used to establish the lumped thermal resistance matrix, lumped thermal admittance, and lumped heat capacity matrix of electric machine components; the definition of the connection method of the thermal models of electric machine components is used to define the connection relationship between different electric machine component nodes; the general assembly of the thermal models of electric machine components is used to assemble the thermal models of electric machine components to form the overall thermal model of the electric machine; the definition of the heat exchange method between the electric machine and the outside is used to describe the heat exchange phenomenon between electric machine components and the external environment or cooling medium under different heat dissipation conditions; specifically including the following steps: S1. Define the geometric parameters of the motor components. According to the geometric characteristics of the motor, give the axial, radial, and angular parameters in cylindrical coordinates, or the x , y , z axis parameters in Cartesian coordinates, or the radius, azimuth angle, and zenith angle parameters in spherical coordinates; define the material parameters of the motor components, including the heat transfer coefficient, specific heat capacity, and mass density; S2. According to the accuracy requirements of temperature calculation, divide the electric machine components into a series of nodes. To ensure the temperature calculation accuracy in different spatial dimensions, the division fineness in different spatial dimensions is given; S3. Considering the node fineness in the spatial dimension of the electric machine components comprehensively, calculate the lumped thermal resistance and lumped heat capacity parameters of the nodes in different spatial dimensions; considering all nodes of the electric machine components, establish the lumped thermal resistance, lumped thermal admittance, and lumped heat capacity matrix of the electric machine components; S4. Define the connection method of the thermal models of electric machine components. Considering the contact thermal resistance between different components, connect it in series to the heat transfer path between components, including the slot insulating paper and its voids between the winding and the silicon steel sheet, and the gap between the outer circle of the stator silicon steel sheet and the machine shell; S5. General assembly of the electric machine thermal model and definition of the heat exchange method between the electric machine and the outside. According to the connection method between electric machine components, assemble the thermal models of each electric machine component to form the overall thermal model of the electric machine. Considering the heat exchange method between the electric machine and the outside, add the external heat exchange thermal admittance at the nodes where there is heat exchange between the electric machine and the external environment or cooling medium.

2. A method for establishing a general lumped parameter thermal network model of an electric machine according to claim 1, characterized in that, this method is applicable to the establishment of thermal network models of electric machine type electrical equipment, as well as electrical equipment such as transformers and reactors.

3. A method for establishing a general lumped parameter thermal network model of an electric machine according to claim 1, characterized in that, this method can establish thermal network models for electric machines with different structures and different topological parameters. The electric machines include electrically excited machines, permanent magnet machines, asynchronous machines, magnetic field modulation machines, and other special electric machines.

4. A method for establishing a general lumped parameter thermal network model of an electric machine according to claim 1, characterized in that, the different cooling methods of the electric machine are represented by the external heat transfer coefficient. The external heat exchange methods include oil cooling, water cooling, natural cooling, and air cooling.

5. A method for establishing a general lumped parameter thermal network model of an electric machine according to claim 1, characterized in that, this method is applicable to the establishment of one-dimensional, two-dimensional, and three-dimensional electric machine thermal network models.

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