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Thermal Modelling of Electric Machines

Nguyễn Gia Hào

Academic year: 2023

Chia sẻ "Thermal Modelling of Electric Machines"


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This model allows us to estimate the randomness of the arrangement of the conductors in the coil. Compared to other methods, the thermal method with flat parameters is simple and attractive because it can provide an accurate representation of the thermal conditions in the machine. When calculating a single loss element, half of the losses must be used as a heat generator source.

There are potential benefits to be gained from knowing more about the behavior and effects of the heat generated in the machine during operation. Don't go near them, and some of the machine's potential is wasted.


The model is based on the PMSM machine at Chalmers, on which thermal measurements will be made in the future. However, water cooling does not ensure successful cooling of the end windings, which can be particularly problematic for machines with long end windings, e.g. In direct oil cooled machines, the oil is in direct contact with the internal parts of the machine and effective cooling of both the stator and the final winding body can be achieved.

A variety of work has been done and published on improvements in the electromagnetic design of various types of electrical machines to reduce losses, e.g. In order to improve the thermal behavior of electrical machines, a good knowledge of heat transfer in different parts of the machine is required.


Thermal conduction

In solid opaque bodies, thermal conduction is an important heat transfer mechanism because there is no net material flow in the process [23]. This gain is mainly due to conductive heat transfer through the wall that separates the air in the room from the outside air. Even in the electronics cooling process, conduction is a heat transfer mechanism used in every electronics design.

Even if a system is designed for convection cooling of the circuit boards, conduction is still the dominant heat transfer mechanism within the component devices and on the circuit board. For the one-dimensional plane wall shown in Figure I.4 with a temperature distribution T(x), the rate equation is expressed as The heat flux q" (W/m2) is the heat transfer rate in the x-direction per unit area perpendicular to the direction of transfer, and it is proportional to the temperature gradient, dT/dx, in this direction.

Figure I.3. Conduction in liquids and solids ascribed to molecules vibration (solids),  translational and rotational (liquids)
Figure I.3. Conduction in liquids and solids ascribed to molecules vibration (solids), translational and rotational (liquids)

Thermal Convection

Heat transfer by convection can be classified according to the nature of the flow into free or natural convection, the flow is caused by buoyancy forces arising from density differences caused by temperature changes in the fluid. An example is free convection heat transfer generated from hot components on a vertical array of printed circuit boards in still air, as shown in Figure I.6. For forced convection; the flow is caused by external factors such as a fan, pump or atmospheric winds.

An example of this is the use of a fan to provide forced convection air cooling of hot electrical components on printed circuit boards as shown in Figure I.6. Air movement due to temperature difference. a) Free convection on chips of electrical components. b) Forced convection on chips of electrical components. The approximate ranges of convection heat transfer coefficients are given in Table I.1 for both free and forced convection.

Figure I.5. Thermal Convection
Figure I.5. Thermal Convection

Thermal Radiation

Every material used in envelope construction has fundamental physical properties that determine their energy performance, such as conductivity, resistivity and thermal mass. With rotating machines, changes in the thermal properties of the materials used are minor and have little influence on the end result. Although electromagnetic-thermal interaction plays a critical role in the operation of electrical machines, it is often avoided to perform such a coupled simulation due to the complex modeling challenges and the computational cost of the problem.

In most cases, the thermal and electromagnetic domains can be separated easily and in a simple way in the simulation, since the electromagnetic phenomena are typically much faster than the thermal ones. Thermal effects are usually modeled as a "boundary condition" for the electromagnetic domain and temperatures of dependent components (eg: those that effect the conductivity) are only updated after modeling several electrical periods, or a few seconds of operation, or even a few minutes or hours. However, there are some problem types where the thermal effect can have a more direct and faster impact on the electromagnetic behavior of the system, eg: such as the case of direct online synchronous machine start-up transients.

Start-capable synchronous motors often experience large thermal stress in a short period of time - especially on the damper rods - during start-up. In the following, different approaches are presented and discussed for simulating the phenomena of synchronous ignition of the electromagnetic thermal coupling engine. Starting from a simple 2D model [1] and ending with the directly coupled 3D electromagnetic thermal model [2], the benefits and difficulties of the approaches are discussed and the results are presented.

Table I.2 gives the values of thermo physical properties of materials for a variety of materials.
Table I.2 gives the values of thermo physical properties of materials for a variety of materials.


Analogy between Heat Transfer and Electric Circuits

Just as an electrical resistance is associated with the conduction of electricity, a thermal resistance can be associated with the conduction of heat.

Series Circuits

Parallel Circuit


Series-Parallel Network Reduction

  • Combined Convection and Radiation

In this case, using the analogy between thermal and electrical network would simplify the analysis. To simplify the thermal networks, the thermal resistors are combined in series and parallel to arrive at a simplified analysis. In most real-world cases under investigation, heat is transferred through more than one mode;

So let's use a radiative heat transfer to express the radiative heat transfer, q rad, as a linear function of the temperature difference between the surface temperature and the liquid temperature. Now it is time to define how the radiation heat transfer coefficient can be obtained (I.17). In the above equation, Te is used to express the envelope temperature as this is the more common case.

But in most cases the fluid adjacent to the surface has the same temperature as the case temperature. Significant reductions in the hot spot temperature of the winding have been achieved, which is promising for the thermal management of electrical machines and also the resulting efficiency, especially in high performance applications. Electromagnetic-thermal coupling in electrical machine simulation is a very important research topic with strong academic and industrial interest.

The simulation of the direct online starting of a synchronous machine provides a good basis of comparison for different calculation methods. To validate this approach, we propose to establish the equivalent thermal diagram of the actuator. The next chapter is devoted to the implementation of the model and the identification of these parameters and the simulation of the thermal behavior of the actuator.




The losses in the machine then increase due to the injection of current harmonics and the temperature rises even more than during normal operation. In this context, a study of the thermal behavior of the motor's permanent magnets is useful to combat the problems already mentioned and to consider its impact on the design and traction control system. This article attempts to address the issue of developing tools for modeling and simulating the axial flux behavior of a permanent magnet electrothermal actuator (PMAF) dedicated to electrical traction.

Our objective requires the development of models for the various components used in the actuator: coil, rotor, stator...etc. The models developed must allow wind to account for the electrical behavior but also the thermal behavior of components.




Où λi est la conductivité thermique de l'isolant, Si est la section transversale de l'isolant et Ei est l'épaisseur de l'isolant. = Où λi est la conductivité thermique de l'isolant, Si est la section transversale de l'isolant et Ei est l'épaisseur de l'isolant.



The iron losses are located in the center of gravity of the head and stator teeth. The thermal model of the PMSMAF transient structure can be represented by a similar electrical network, as described in Figure II.6. The expressions for the thermal resistances are derived from the solution of the equation for the thermal boundary regions.

Where λ is the thermal conductivity, the heat exchange section is set, and Φt is the total heat flow that is exchanged, and E is the thickness of the heat exchange. Where; λcu is the thermal conductivity of copper, Scu is the section of the coil and Ecu is the thickness of copper. Where λi is the thermal conductivity of the insulator, Si is the cross section of the insulation and Ei is the thickness of the insulation.

Where h is the heat transfer coefficient, we choose h = 30W.K-1.m (natural ventilation) and Gender is the outer surface of the actuator. Where q is the quality factor of the sheets, Mcs is the mass of the stator yoke and the magnetic induction is Bcs in the stator yoke. Where Mds is the mass of the stator teeth and Bd is the magnetic induction in the stator teeth.

Where R is the resistance of the stator winding, it is expressed by the following relationship: The thermal model developed for the different components of the car was importantly implemented in MATLAB SIMULINK to estimate the temperatures of the materials. This figure shows that the temperature of the copper and insulation is reduced to the critical value of 70°C.

This makes it possible to calculate the operating temperature of the component with a precision of a few degrees (temperature of the magnetic material and temperature of the windings). The operation of the latter provided protection engine running on missions urban traffic data type.

Table II.1. The geometric dimensions of the PMSMAF
Table II.1. The geometric dimensions of the PMSMAF


NEJI : "Conception d'un moteur synchrone à aimants permanents à flux axial pour véhicule électrique" ; INNORPI, Brevet d'invention n° TN2013/0240, juin 2013. NEJI : "Design of an Axial Flux Brushless DC Motor with Concentrated Winding for Electric Vehicles", Journal of Electrical Engineering (JEE), Volume Edition : 2, pp. TOUNSI, "Modélisation et optimisation de la motorisation et de l'autonomie d'un véhicule électrique", thèse de doctorat 2006, Ecole Nationale d'Ingénieurs de Sfax (Tunisie).

Hình ảnh

Figure I.1. Conduction convection and radiation modes of heat transfer
Figure I.2. Conduction heat transfer as diffusion of energy due to molecular activity
Figure I.3. Conduction in liquids and solids ascribed to molecules vibration (solids),  translational and rotational (liquids)
Figure I.4. One- Dimensional heat transfer (diffusion of energy)

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