1. Electric motors KON-C2004 Mechatronics Basics Tapio Lantela, Nov 2nd, 2015

2. Applications

3. Power range From milliwatts to megawatts http://small-generator.com/buy/index.php?main_page=product_info&cPath=2&products_id=44&zenid=7am2ohqmufajn06bafie386007 http://www.dmaeuropa.com/Clients/Sulzer/News/tabid/3546/itemid/3334/Default.aspx

4. Speed range From a couple hundred rpm to hundreds of thousandsof rpm http://www.ebikes.ca/learn/hub-motors.html http://www.celeroton.com/en/products/motors.html

5. Electric motors DC -Brushed -Brushless AC -Synchronous Permanent magnet motor Field excitation Reluctance -Asynchronous (Induction) Squirrel cage Wound rotor

6. Force F Magnetic flux density B Current I Force F = B l I Torque T Radius r Torque T = 2rFcos(ϑ) Angle ϑ Current I Current -I Magnetic flux density B Force F Torque T = 2rF = 2NrB l I = K t I Stator Rotor Induced voltage = B l v = B l rω Induced voltage = 2NB l v =2NB l rω = K e ω Physics of a generic electric motor

7. DC motor working principle Simple two pole example In practise motors have three or more poles http://www.pcbheaven.com/wikipages/How_DC_Motors_Work/ https://en.wikipedia.org/wiki/Brushed_DC_electric_motor

8. Brushed DC motor construction http://www.electrical-knowhow.com/2012/05/classification-of-electric-motors.html

9. DC motor commutator

10. DC motor field generation Permanent magnet -Permanent magnet rotor (Brushless) -Permanent magnet stator (Brushed) Field coils(Brushed) -Series wound -Parallel (shunt) wound -Separately excited Material saturation limits field magnitude http://www.electrical4u.com/dc-servo-motors-theory-and-working-principle/

11. Electrical models of a DC motor Equivalent circuit Mathematical model http://ctms.engin.umich.edu/CTMS/index.php?example=MotorSpeed&section=SystemModeling

12. Mechanical models of an electric motor Physical model Mathematical model

13. Motor equations Input power P in = UI Electromagnetic torque T = K t I Output power P out = Tω Resistive loss in windigs P res = RI 2 Back electromagnetic force V bemf = K e ω

14. Time constants of a motor Winding inductance & resistance Rotor & load inertia

15. Power losses Resistive losses -Proportional to the square of the current (torque) -Resistance depends on temperature (0.4%/K) Core losses -proportional to the rotating speed Mechanical losses -Bearing friction proportional to the rotating speed -Damping (air etc.) proportional to the square of rotating speed Additional losses -Variable frequency drive harmonics etc.

16. Characteristics of a PMDC motor Maximum torque and efficiency are speed dependent

17. http://www.electrocraft.com/products/pmdc/DPP720/ Operating limits of a PMDC motor

18. Field weakening Reduce magnetic field flux density B -Smaller B -> smaller torque constant K t and BEMF constant K e -Smaller K t -> less torque -Smaller K e -> more angular velocity

19. Field weakening http://ecomodder.com/forum/showthread.php/bsfc-chart-thread-post-em-if-you-got-1466-26.html

20. Operating limits of a motor Temperature -Winding insulation melting temperature -Permanent magnet demagnetization temperature Voltage -Winding insulation breakdown voltage Mechanical strength -Rotor breakdown speed Commutation speed -Drive/controller speed

21. Source: Maxon corp. Characteristics of a DC motor Motor data Assigned power rating12 W 1 Nominal voltage12 V 2 No load speed12100 rpm 3 No load current155 mA 4 Nominal speed8060 rpm 5 Nominal torque10.1 mNm 6 Nominal current1.25 A 7 Stall torque31.3 mNm 8 Starting current3.47 A 9 Max. efficiency63 % 10 Terminal resistance3.46 Ω 11 Terminal inductance0.121 H 12 Torque constant9.02 mNm / A-¹ 13 Speed constant1060 rpm / V-¹ 14 Speed / torque gradient406 rpm / mNm -1 15 Mechanical time constant9.56 ms 16 Rotor inertia2.25 gcm²

22. Four quadrant operation

23. Brushed DC motor velocity control The torque is proportional to the current in the winding Current is controlled by voltage -Or usually with pulse width modulation, PWM -If the PWM frequency is high enough, the current stays almost constant (small fluctuations)

24. Brushed DC motor control Motor needs large currents -E.g. microcontroller signal not powerful enough for running the motor -A separate motor drive circuit controls the motor current according to the microcontroller signal One signal for PWM, one for direction M M

25. Brushless DC motor (BLDC) Permanent magnet rotor Stator with windings Commutating with integrated hall sensors and external electronics Almost service Withstands well short term overloading (heat is transported effectively from the stator into the environment) More complex control system

26. BLDC commutation http://www.mpoweruk.com/motorsbrushless.htm

27. AC motor Several types Asynchronous Synchronous Input voltage one or three phase sinusoidal AC voltage Only bearings need service Control with variable frequency drive http://www.pump-zone.com/topics/motors/ac-motors-part-two-three-phase-operation/page/0/1

28. AC field generation Three field coils (per pole) -120 °phase difference http://tdflashzone.net23.net/1_6_Physics-Flashes.html

29. Synchronous AC Permanent magnet AC motor is almost the same as BLDC.

30. Induction motor Conducting short circuited bars embeddes in steel frame Stator field induces current in the bars which causes torque http://www.nidec.com/en-IN/technology/motor/basic/00026/?prt=1

31. Rated values of an induction motor Rated values are for continuous duty -Rated voltage – winding insulation -Rated current – ohmic resistive losses -Rated field – magnetic saturation of the material -Rated power = T*omega For a dimensioning a motor for a variable load, it is possible to calculate an equivalent constant load or simulate the system

32. Motors for servo systems Many designs: DC (brushed or brushless), AC Integrated feedback sensors Ability to tolerate short term overloads Low inductance-> small electric time constant Low rotor inertial mass -> small mechanical time constant http://www.ustudy.in/node/5789 http://www.exlar.com/press_releases/1868

33. AC motor control Rotational speed is determined by the frequency of the input voltage Frequency is controlled with variable frequency drive/inverter (taajuusmuuttaja in Finnish) -Rectification of the three phase voltage to DC voltage -The rectified DC voltage is converted e.g. with pulse width modulation (PWM) to AC voltage with the needed frequency -The AC voltage is fed to one of the three coils of the stator according to the sensors of the control system.

34. small DC servo controller (8-30W) BIG AC servo controller (5-120kW) Source: www.maxonmotor.com and www.siemens.com Servo controllers Decentralised controllers

35. Summary Electric motors can be found anywhere and for any power rating They have excellent efficiency at proper loading conditions -Usually this means a large enough rpm Output power limited by temperature Motors can be overloaded for a short while Output rpm limited by voltage

36. Questions? More info on electric drives Advanced courses ELEC-E8407 - Electromechanics ELEC-E8405 - Electric Drives