introduction to motor drives

1、PowerElectronicsIntroduction to Motor DrivesAutumn Semester, 2014-2015SUN Kai 孙凯Dept. of Electrical EngineeringChap.12Introduction to Motor DrivesOutlines12.1IntroductionWhy should we study motor drives?12.2Criteria for Selecting Drive ComponentsChap.12Introduction to Motor DrivesIntroductionMOTOR D

2、RIVESdeal withthe energy conversion from electric power to mechanical powerElectric PowerMechanical PowerMotorChap.12Introduction to Motor DrivesIntroductionWhyshouldwestudyMotorDrives?Chap.12Introduction to Motor DrivesIntroductionIndustrial ApplicationsCold rollingIrrigation anddrainageCNC machine

3、 toolsChap.12Introduction to Motor DrivesIntroductionApplications in TransportationsChap.12Introduction to Motor DrivesIntroductionApplications in TransportationsChap.12Introduction to Motor DrivesIntroductionApplications for ConsumersWashing MachinePCAir-conditionChap.12Introduction to Motor Drives

4、IntroductionWhyshouldwestudyMotorDrives? Motor drives are widely used in many industrial applications and also home appliances.Motor drives are used in a verywide power range, from a few watts to many thousands of kilowatts.Chap.12Introduction to Motor DrivesIntroductionWhy need we learnMotor Drives

5、 in Power Electronics?Chap.12Introduction to Motor DrivesIntroductionGeneral description of motor drive system In all drives where the speed and position are controlled, a power electronic converter is needed as an interface between the input power and the motor.Chap.12Introduction to Motor DrivesIn

6、troductionWhyneed welearn Motor Drives in Power Electronics?Control of motor drives is realizedthrough power electronics converters, which are the key elements in drive systems.Chap.12Introduction to Motor DrivesIntroductionMotor Drive Typesdc motor drives induction motor drivessynchronous motor dri

7、vesac motor drivesChap.12Introduction to Motor DrivesIntroductionThe basic control targets of motor drives arethe speed and position.Example Servo driveIn servo drives, the response time and theaccuracy with which the motor follows the speed and position commands are extremely important.Chap.12Intro

8、duction to Motor DrivesIntroductionHowever, in a large number of applications, theaccuracy and the response time of the motor to follow the speed command is not critical.Example Adjustable-speed drive in air-conditionChap.12Introduction to Motor DrivesCriteria for Selecting Drive Componentsu Match b

9、etween the motor and the loadu Thermal considerations in selecting the motoru Match between the motor and the power electronic converteru Servo drive control and current limitingu Current limiting in adjustable-speed drivesChap.12Introduction to Motor DrivesCriteria for Selecting Drive Components12.

10、2.1 Match between the motor and the load= J dwT - Tloaddt Prior to selecting the drive components, the load parameter and requirements such as the load inertia,maximum speed,speedrange and direction of motion must be available.Chap.12Introduction to Motor DrivesCriteria for Selecting Drive Component

11、s12.2.1 Match between the motor and the load= J dwT - Tloaddt As shown in the figure, the torque required by the load peaks during the acceleration and deceleration (assuming a purely inertial load).Chap.12Introduction to Motor DrivesCriteria for Selecting Drive Components12.2.1 Match between the mo

12、tor and the loadIn order to drive a rotating load, the motor and the loadmust be coupled directly or by some devices, such as gear, feed-screw（丝杠） and belt-pulley（皮带轮）.Tm= wL= qL= nm= awmqmTLnLand nL are thenmnumbers of teeth.Gear couplingChap.12Introduction to Motor DrivesCriteria for Selecting Dri

13、ve Components12.2.1 Match between the motor and the loadFeed-screw couplingTmvLwmxLqms2ps= ais the pitch of the feed screw.FLChap.12Introduction to Motor DrivesCriteria for Selecting Drive Components12.2.2 Thermal considerations in selecting the motor In electric machine, the electromagnetic torque

14、is proportional to the motor current, provided the flux in the air gap of the motor is kept constant.Chap.12Introduction to Motor DrivesCriteria for Selecting Drive Components12.2.2 Thermal considerations in selecting the motor The power loss PRin the winding resistance RM due to the motor current i

15、s a large part of the total motor losses, which get into heat.P= RI 2RMrmsm2Itkk=I 2 k =1rmstperiodChap.12Introduction to Motor DrivesCriteria for Selecting Drive Components12.2.2 Thermal considerations in selecting the motor Because of the motor current being linearly proportional to the motor torq

16、ue, the rms value of the motor torque is,m2Itkk= k I 2P= k T 2T 2= k k =1T 2em,rms1rmsR2em,rmsem,rms1tperiod There are 5 kinds of losses within the motor that contribute to itsheating,= PR + PFW + PEH + Ps+ PstrayPlossFriction & windageEddy current & hysteresisMotor current rippleStray lossChap.12In

17、troduction to Motor DrivesCriteria for Selecting Drive Components12.2.2 Thermal considerations in selecting the motor In steady-state condition, the motor temperature rise is,DQ = Ploss RTH In general, the loss components other than PR within the motor increase with the motor speed. Therefore, the m

18、aximumallowable PRand the maximum continuous motor torque woulddecrease at higher speed, if the thermal resistance RTH remains constant.= PR + PFW + PEH + Ps+ PstrayPlosswmChap.12Introduction to Motor DrivesCriteria for Selecting Drive Components12.2.3 Match between the motor and the power electroni

19、c converteruIn general, the power electronic converter providesa controlled voltage to the motor in order to control the motor current and the electromagnetic torque produced by the motor.1)The current rating of the power electronicconverter must be selected based on the rms and the peak values of t

20、he torque that the motor is required to supply.Chap.12Introduction to Motor DrivesCriteria for Selecting Drive Components12.2.3 Match between the motor and the power electronic converter2) To be able to quickly control the motor current and its torque, the output voltagevof the power electronicconve

21、rter must be reasonably greater than the counter- emf e .Chap.12Introduction to Motor DrivesCriteria for Selecting Drive Components12.2.3 Match between the motor and the power electronic converter The magnitude of ein a motor increases linearly withthe motor speed, with a constant flux in the air ga

22、p of the motor. Hence, the voltage rating of the power electronic converter depends on the maximum motor speed with a constant air-gap flux.Chap.12Introduction to Motor DrivesCriteria for Selecting Drive Components12.2.3 Match between the motor and the power electronic converter3) The motor current

23、should be able to respond quickly to the load demand, thus requiring L to be small. The motor current ripple should be small to minimize motor loss and the torque ripple, which requiresL to be large.A reasonable compromise must be made in selecting the motor inductance and the switching frequency.di

24、= v - edtLChap.12Introduction to Motor DrivesCriteria for Selecting Drive Components12.2.4 Servo drive control and current limiting A very fast response to a sudden change in position or speed command would require a large peak torque and peak current.This may be prohibitive due to the cost of conve

25、rters. Theconverter currents need be limited by the controller through two ways, which are application dependent.Inner Current LoopChap.12Introduction to Motor DrivesCriteria for Selecting Drive Components12.2.4 Servo drive control and current limiting A very fast response to a sudden change in posi

26、tion or speed command would require a large peak torque and peak current.This may be prohibitive due to the cost of converters. Theconverter currents need be limited by the controller through two ways, which are application dependent.No Inner Current LoopChap.12Introduction to Motor DrivesCriteria f

27、or Selecting Drive Components12.2.5 Current limiting in adjustable-speed drives By providing ramp limiters, drive can be prevented from “triping” under sudden changes. The startup of induction motor by using VVVF (variable voltage variable frequency) control is an example of ramp limiters, which wil

28、l be introduced later.Chap.12Introduction to Motor DrivesReferences1)BooksMohan, Undeland, Robbins, Power Electronics, 3rd Edition, John Wiley & Sons, Inc., 2003.Philip T. Krein, Elements of power electronics, New York: Oxford University Press, 1998.B.K. Bose, 现代电力电子学与交流传动（英文版）,机械工业黄立培, 电动机控制, 清华大学2

29、)3)4)Chap.12Introduction to Motor DrivesReferencesJournals and ConferencesIEEE Transactions on Industrial ElectronicsIEEE Transactions on Power ElectronicsApplied Power Electronics Conference (APEC) IEEE Industrial Electronics Conference (IECON)IEEE Energy Conversion Congress and Exposition(ECCE)Chap.12Introduction to Motor DrivesVocabulary (1)1. motor2. motor drive3. adjustable-speed drive4. induction