The 14th IFToMM World Congress, Taipei, Taiwan, October 25-30, 2015 DOI Number: 10.6567/IFToMM.14TH.WC.PS20.013

Thermal Analysis of the AFPM Motor with Air and Water Cooling Simulations

P. C. Chen1 Y. J. Cheng2

Industrial Technology Research Institute Industrial Technology Research InstituteChutung, Hsinchu, Taiwan Chutung, Hsinchu, Taiwan

itriA00256@itri.org.tw eric_cheng@itri.org.tw

Abstract: In the paper, the thermal analysis of the axial-fluxbrushless DC motor with air and water cooling simulations is performed to obtain the temperature distribution of the stator, rotor, and housing during operation. The simulation results are toserve as a reference for heat dissipation design of the electric motor. In order to accurately calculate the thermal loss of theAFPM motors, the finite element method is adopted here. Electromagnetic-thermal and fluid-thermal coupling analysis is performed using the ANSYS software. The copper loss and core loss were obtained from the simulation results of the AFPM motor by inputting the three phase current in the electromagnetic simulation. Then the surface convection coefficient were obtained from simulation results of the fluid field, and the copper and core losses were simultaneously inputted into the steady state thermal module for calculation. The temperature (less than 72C) of the stator in the electric motor with fins comparing with that in the electric motor without fins is greatly lowered. From the simulation results, the air and water coolings keep the motor temperature rise within the required value.

Keywords: Heat dissipation, Electric motor, Axial flux, Thermofluid Field

1. IntroductionAn axial flux permanent magnet (AFPM) motors with

pancake shape have been widely used in recent years due to their high torque density, modular and compact construction, high efficiency, reliability and easy integration with other mechanical components. The products with the special need for the axial compactness and high efficiency motors include cleaning robots, electric fans, electric vehicles, electric bicycles and so on. Besides, the advent of modern high energy permanentmagnet (PM) materials, such as NdFeB, has resulted in the rapid development of these types of machines. The high temperature rise of the AFPM motor may cause the magnetic degradation and further lead to the failure of the electric motor. Hence, the heat dissipation is extremely important for solving the problem. Here the air and water cooling are used to keep the temperature rise within the required value.

Thermal analysis of the electric motor has attracted Scientists’ attention in recent years. Vilar [1] proposed a lumped parameter thermal network model for the stationary single sided axial-flux permanent magnet motorin 2005. Huang [2] presented the thermal analysis of a high-speed motor with soft magnetic composite (SMC) in 2009. Mezani [3] presented a model for coupling electromagnetic and thermal phenomena in an induction motor. Gilson [4] set up a design strategy which is capable of optimizing both the electromagnetic as well as thethermal design of permanent magnet synchronous machines (PMSM) for aerospace actuation system in 2010.Staton [5] dealt with the formulations used to predict

convection cooling and flow in electric machines. For motor temperature rise prediction, Yabiku [6] outlined a set of useful calculations and design guidelines. Popescu [7]built a thermal model for a duplex three-phase induction machine for fault-tolerant applications in 2013. Kefalas [8]conducted a thermal investigation of a surface-mounted permanent-magnet synchronous motor designed for high-temperature aerospace actuation applications. In computational dynamics, Wang [9] developed a thermofluid model combining a lumped parameter heat transfer model and an air-flow model of a typical axial-field permanent-magnet (AFPM) machine. Jungreuthmayer [10] presented a comprehensive computational fluid dynamics (CFD) model of a radial flux permanent magnet synchronous machine with interior magnets. Boglietti [11] proposed an extended survey on the evolution and the modern approaches in the thermal analysis of electrical machines in 2009. In addition, thewater cooling of the AFPM machine has been studied in[12-14].

The proposed AFPM motor is shown in Fig. 1 and its schematic model with 30 stators and 60 coils is shown in Fig. 2. In order to enhance the torque of the AFPM motor,the stators are designed in the form of C shape and have transverse flux shown in Fig. 3. The topology of the C-shape stator and the rotor form two airgaps.

Fig. 1. The photo of the proposed AFPM motor

Fig. 2. The schematic model of the AFPM motor

Fig. 3. The transverse flux stator of the AFPM motor with double air gaps

Table 1. Basic parameters of the AFPM motor with double air gaps

Effect axial length L (mm) 28.7

Outer diameter of rotor D (mm) 160

Aspect ratio L/D 0.18

Rated voltage (V) 110

Rated speed (rpm) 450

Rated output power (W) 400

Rotor core material NdFe35

Pole, Phase, Slot 40, 3, 30

2. The Simulation structure of thermal analysisThe simulation structure of the thermal analysis is

explained in this part. All the computation is completed in the ANSYS Workbench as shown in Fig. 4. The software ANSYS Maxwell is used to perform the 3D electromagnetic simulation. Besides, the software modules ANSYS Fluent and ANSYS Steady-State Thermal are used in the coupling calculation of fluid and thermal field.

ANSYS Workbench

Fluent Steady-State ThermalMaxwell 3D

Fig. 4. The simulation structure of the AFPM motor

A. The electromagnetic simulation of the AFPM motorThe 3D model of the AFPM motor for

electromagnetic simulation is shown in Fig. 5. To reduce the calculation time, the one tenth of the 3D full model of the AFPM motor is used through the advantage of symmetry. The B-H curve of the soft magnetic composite material is shown in Fig. 6. In addition, Fig. 7 indicates the driving circuit of the AFPM motor and the torque of the proposed electric motor is shown in Fig. 8. The copper and core losses of the AFPM motor are shown in Fig. 9 and Fig. 10.,respectively.

Fig. 5. The 3D model of the AFPM motor for electromagnetic simulation

0.00E+000 1.25E+004 2.50E+004 3.75E+004H (A_per_meter)

0.00

0.50

1.00

1.50

1.75

B (

tesl

a)

Fig. 6. The B-H curve of the soft magnetic composite material

Fig. 7. The driving circuit of the AFPM motor

Fig. 8. The torque of the AFPM motor

Rotor

StatorAir gap 1

Air gap 2

Coil 1

Coil 2Stator

Fig. 9. The copper loss of the AFPM motor

Fig. 10. The core loss of the AFPM motor

B. The air cooling simulation of the brushless DC motor

The simulation model of the AFPM motor with the two-hole shroud including the stators, coils, rotors, the housing, fins, and the shroud is shown in Fig. 11 and the air is ventilated by the fan at the outlet on the right side. The air cooling of the BLDC motor at various velocitiesfrom 0.1 m/s to 5 m/s is investigated. One of the simulation results is shown here. The inlet pressure is 1 atm and the outlet velocity is 5 m/s. The computational mesh for the air cooling simulation is shown in Fig. 12.The convection coefficients on the surface of the fin are computed and later will be applied to obtain the temperature distribution of the housing of the electric motor. Vilar [1] and Gilson [4] use 21.5 C and 24 C as the initial temperature respectively for the numerical simulation and the default value in ANSYS is 22 C.Hence, the initial temperature 22 C is adopted in this paper. Fig. 14 indicates the flow velocity distribution of the AFPM motor with the two-hole shroud and Fig. 15shows the temperature distribution of the housing. Additionally, the temperature distribution of the stators and coils of the AFPM motor with the two-hole shroudis shown in Fig. 16. In the simulation result of air cooling, the highest temperature of the stator in the electric motor without fins is generally greater than 100C.

Fig. 11. The simulation model of the AFPM motor with the two-hole shroud

Fig. 12. The mesh of the models for air cooling

Fig. 13. The mesh of the BLDC motor for the thermal

analysis

Fig. 14. The flow velocity distribution of the AFPM motor with the two-hole shroud

Fig. 15. The temperature distribution of the housing of the AFPM motor with the two-hole shroud

Fig. 16. The temperature distribution of the stators and coils of the AFPM motor with the two-hole shroud

C. The water cooling simulation of the AFPM motorFirst the 3D model of the AFPM motor for water cooling simulation is shown in Fig. 17. The inlet and the outlet are on the same side as shown in Fig. 18.The water cooling of the BLDC motor at various velocities is investigated. One of the simulation results of the water cooling is shown in Fig 19.

Fig. 17. The 3D model of the AFPM motor for the water cooling simulation

Fig. 18. The 3D mesh of the water cooling channel of the AFPM motor

Fig. 19. The velocity vectors of the flow in the water cooling channel of the AFPM motor

3. ConclusionsAfter performing the above air cooling simulation of the

proposed AFPM motor with two-hole shroud, it indicates that the temperature near the outlet is higher than that near the inlet during the heat dissipation of the electric motor. In the simulation result of air cooling, it can be seen that the temperature (less than 72C) of the stator in the electric motor with fins comparing with that in the electric motor without fins is greatly lowered. Additionally, it also shows that the higher outlet velocity results in the lower temperature rise of the AFPM motor. As for the water cooling, the form of water cooling channel can provide an even temperature of the AFPM motor. From the simulation results, it demonstrates that the air and water coolings keep the motor temperature rise within the required value.

References [1] Vilar Z.W., Patterson D., and Dougal R.A. Thermal

analysis of a single sided axial flux permanent magnet motor. In IECON 2005. 31st Annual Conference of IEEE, pp. 2570–2574, 2005.

[2] Huang Y., Zhu J., and Guo Y. Thermal analysis of high-speed SMC motor based on thermal network and 3-D FEA with rotational core loss included. IEEE Trans. Magn., 45(10):4680–4683, 2009.

[3] Mezani S., Takorabet N., and Laporte B. A combined electromagnetic and thermal analysis of induction motors.IEEE Trans. Magn., 41(5):1572–1575, May 2005.

[4] Gilson G.M., Raminosoa T., Pickering S.J., Gerada C., and Hann D.B. A combined electromagnetic and thermal optimisation of an aerospace electric motor. In XIX International Conference on Electrical Machines - ICEM 2010, Rome, pp. 1-7, Sept. 6-8, 2010.

[5] Staton D.A. and Cavagnino A. Convection heat transfer and flow calculations suitable for electric machines

thermal models. IEEE Trans. Ind. Electron., 55(10):3509–3516, Oct. 2008.

[6] Yabiku R., Fialho R., Teran L., Ramos M.E., Jr., and Kawasaki N. Use of thermal network on determining the temperature distribution inside electric motors in steady-state and dynamic conditions. IEEE Trans. Ind. Applicat., 46(5):1787–1795, Sept./Oct. 2010.

[7] Popescu M., Dorrell D.G., Alberti L., Bianchi N., Staton D.A., and Hawkins D. Thermal analysis of duplex three-phase induction motor under fault operating conditions. IEEE Trans. Ind. Appl., 49(4):1523-1530, Jul./Aug. 2013.

[8] Kefalas T.D., and Kladas A.G. Thermal investigation of permanent-magnet synchronous motor for aerospace applications. IEEE Trans. Ind. Electron., 61(8):4404-4411, Aug. 2014.

[9] Wang R.J., Kamper M.J., and Dobson R.T. Development of a thermofluid model for axial field permanent-magnet machines. IEEE Trans. Energy Convers., 20(1):80–87, Mar. 2005.

[10]Jungreuthmayer C., Bäuml T., Winter O., Ganchev M.,Kapeller H., Haumer A., and Kral C. A detailed heat and fluid flow analysis of an internal permanent magnet synchronous machine by means of computational fluid dynamics. IEEE Trans. Ind. Electron., 59(12):4568–4578, Dec. 2012.

[11]Boglietti A., Cavagnino A., Staton D., Shanel M., Mueller M., and Mejuto C. Evolution and modern approaches for thermal analysis of electrical machines. IEEE Trans. Ind. Electron., 56(3):871-882, Mar. 2009.

[12]Caricchi F. and Crescimbini F. Axial-Flux Permanent-Magnet Machine with Water-Cooled IronlessStator. Proceedings of the IEEE Power Tech Conference, 1995, pp.98 -103, 1995.

[13]Caricchi F., Crescimbini F., and Di Napoli A. Prototype of innovative wheel direct drive with water-cooled axial-flux PM motor for electric vehicle applications, IEEE Applied Power Electronics Conference and Exposition, 1996. APEC '96. Conference Proceedings 1996, Eleventh Annual, Vol.2, pp.764–770, 1996.

[14]Odvářka E., Brown N.L., Mebarki A., Shanel M., Narayanan S., and Ondrůšek Č. Thermal modelling of water-cooled axial-flux permanent magnet machine. 5th IET International Conference on Power Electronics, Machines and Drives (PEMD 2010), pp.1–5, 2010.