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1、Implementation of a Current Controlled SwitchedReluctance Motor Drive Using TMS320F240APPLICATION REPORT: SPRA282Mohammed S Arefeen Automotive/Industrial ApplicationsDigital Signal Processing Solutions September 1998IMPORTANT NOTICETexas Instruments (TI) reserves the right to make changes to its pro

2、ducts or to discontinue any semiconductor product or service without notice, and advises its customers to obtain the latest version of relevant information to verify, before placing orders, that the information being relied on is current.TI warrants performance of its semiconductor products and rela

3、ted software to the specifications applicable at the time of sale in accordance with TIs standard warranty. Testing and other quality control techniques are utilized to the extent TI deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily perfor

4、med, except those mandated by government requirements.Certain application using semiconductor products may involve potential risks of death, personal injury, or severe property or environmental damage (“Critical Applications”).TI SEMICONDUCTOR PRODUCTS ARE NOT DESIGNED, INTENDED, AUTHORIZED, OR WARR

5、ANTED TO BE SUITABLE FOR USE IN LIFE-SUPPORT APPLICATIONS, DEVICES OR SYSTEMS OR OTHER CRITICAL APPLICATIONS.Inclusion of TI products in such applications is understood to be fully at the risk of the customer. Use of TI products in such applications requires the written approval of an appropriate TI

6、 officer. Questions concerning potential risk applications should be directed to TI through a local SC sales office.In order to minimize risks associated with the customers applications, adequate design and operating safeguards should be provided by the customer to minimize inherent or procedural ha

7、zards.TI assumes no liability for applications assistance, customer product design, software performance, or infringement of patents or services described herein. Nor does TI warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work rig

8、ht, or other intellectual property right of TI covering or relating to any combination, machine, or process in which such semiconductor products or services might be or are used.Copyright 1998, Texas Instruments IncorporatedTRADEMARKSTI is a trademark of Texas Instruments Incorporated.Other brands a

9、nd names are the property of their respective owners.CONTACT INFORMATIONUS TMS320 HOTLINE US TMS320 FAXUS TMS320 BBSUS TMS320 email(281) 274-2320(281) 274-2324(281) 274-2323ContentsIntroduction8Switched Reluctance Motor Configuration9Basic Principles of Operation11Converter Topologies13Con

10、trol Strategies15Voltage Controlled Drive15Current Controlled Drive16Controlling an SR motor using TMS320F24017Hardware Setup17Current and Voltage Sensing19Position Sensing20Commutation Sequence and Instants21Bi-directional Operation22Changing Conduction Angle23Current Regulation24Startup Operation2

11、4Brief Software Description26Experimental Results30References34Appendix A. Appendix B.Appendix C.Motor Specifications35Switched Reluctance Motor Drive code36Header Files64C240APP.H64SD_init.H69Appendix D. LINKER COMMAND FILE71Appendix E. C240tbed.cmd72FiguresStator and rotor configurations of SR mot

12、or (top) 4 phase 8/6 SR motor (bottom) 3 phase 6/4 SR motor9Inductance profile of an SR motor. (a) Variation of inductance with rotor position. (b) Phase current for motoring operation. (c) Phase current for generating operation.12Power Converter for a Current Controlled Switched Reluctance Motor Dr

13、ive14Voltage Controlled Switched Reluctance Motor Drive15Current controlled Switched Reluctance Motor Drive16Top view of TMS320F240 Evaluation Module18Top view of Motor Interface Board for TMS320F240-EVM18Top view of classical converter that plugs on to EVM motor interface board shown in Figure 619C

14、ounting four edges for every cycle of channels A/B20Rotor rotates 15mechanical degrees from nonaligned to aligned position22QEP configuration for bi-directional operation of the motor23Flowchart for startup operation27Current loop and QEP loop28Flowchart for ADC measurement.29Phase A current and vol

15、tage for a voltage controlled SR drive.30Phase A current is regulated 25 kHz PWM (2A/div.)31Expanded view of phase A current shown in Figure 16.32Phase A current during high speed operation of the motor33Figure 1.Figure 2.Figure 3.Figure 4.Figure 5.Figure 6.Figure 7.Figure 8.Figure 9.Figure 10.Figur

16、e 11.Figure 12.Figure 13.Figure 14.Figure 15.Figure 16.Figure 17.Figure 18.Implementation of a Current Controlled Switched Reluctance Motor Drive Using TMS320F240AbstractThe DSP controller TMS320F240 from Texas Instruments is suitable for a wide range of motor drives and power electronics applicatio

17、ns. TMS320F240 reduces chip count of a system by integrating most of the important power electronics peripherals on chip and thus increases system reliability and reduces system cost. This application note describes complete implementation of a current controlled Switched Reluctance Motor Drive usin

18、g TMS320F240.Implementation of a Current Controlled Switched Reluctance Motor Drive Using TMS320F2407SPRA282IntroductionThe Switched Reluctance motor (SR) drive is receiving renewed attention as a viable candidate for various adjustable speed and torque applications. Combining the unique features of

19、 an SR motor with its relatively simple and efficient power converter results in a motor drive that may be preferable for many applications compared to other ac or dc drive systems. The following are the main advantages of an SR motor drive:Simple and low-cost machine construction due to the absence

20、 of rotor winding and permanent magnets.?No shoot-through faults between the dc buses in the SR motor drive converter since each stator winding is connected in series with converter switching elements.?Unidirectional current required by the motor drive makes power electronics drive circuitry simple

21、and reliable.?Low rotor inertia and high torque/inertia ratio.Stator phases can be controlled independently. This makes SR drive more robust than other motor drives. Failure or loss of one of the stator phases does not prevent drive operation.SR motor can be operated in a harsh environment.?The main

22、 disadvantages of SR motor drives are the following:? High torque ripple.? Higher acoustic noise level than other motors.However, advanced motor design techniques and high performance algorithms are successfully addressing the above mentioned disadvantages and SR motor drives are becoming more and m

23、ore suitable for a wide range of applications.8Implementation of a Current Controlled Switched Reluctance Motor Drive Using TMS320F240SPRA282Switched Reluctance Motor ConfigurationThe switched reluctance motor (SR) is a doubly salient machine with independent phase windings on the stator and a solid

24、 laminated rotor. The stator windings on diametrically opposite poles are connected in series to form one phase of the motor.Figure 1 (a) and Figure 1 (b) shows a four phase 8/6 switched reluctance motor and a three phase 6/4 switched reluctance motor respectively. When a stator phase is energized,

25、the most adjacent rotor pole-pair is attracted towards the energized stator in order to minimize the reluctance of the magnetic path. Therefore, by energizing consecutive phases in succession it is possible to develop constant torque in either direction of rotation.Figure 1. Stator and rotor configu

26、rations of SR motor (top) 4 phase 8/6 SR motor (bottom) 3 phase 6/4 SR motor.Implementation of a Current Controlled Switched Reluctance Motor Drive Using TMS320F2409SPRA282Theoretically it is possible to have a number of stator and rotor pole combinations. However, certain combinations, such as 4/4

27、or 2/2, will have problems during start up operation. With a combinations like 2/2 or 4/4 it will be impossible to develop a starting torque with rotor and stator pole exactly aligned. Although, the configurations with higher number of stator/rotor pole combinations have less torque ripple and do no

28、t have the problem of starting torque, 6/4 or 8/6 combinations are typically used.A well designed Switched reluctance motor will minimize the core losses, will offer good starting capability, and will also minimize the unwanted effects due to varying flux distributions and saturation and to eliminat

29、e mutual coupling. The choice of the number of phases is open but increasing the number of phases would increase the number of power devices needed for power converter. Moreover, higher number of poles will decrease the maximum inductance ratio obtainable for a good torque per ampere. These practica

30、l issues limit stator and pole ratio to 6/4 or 8/6 in most applications of Switched Reluctance motor drives.10Implementation of a Current Controlled Switched Reluctance Motor Drive Using TMS320F240SPRA282Basic Principles of OperationThe phase voltage equation in a Switched reluctance motor can be wr

31、itten as:dl dtV = i R +Equation 1where, V is the dc bus voltage, i is the instantaneous phase current, R is the phase winding resistance and l is the flux linking the phase coil. Ignoring stator resistance, Equation 1 can also be written as:+ i dL(q) wL(q) diV =Equation 2dqdtwhere, w is the rotor sp

32、eed, q is the rotor angular position, and L(q) is the instantaneous phase inductance. The rate of flow of energy can be obtained by multiplying the voltage with current and can be written as:Li didtdL wVi =+ i 2Equation 3dqord 1 Li2 + 1 i2 dL wP =Equation 42dqdt 2The first term of the above equation

33、 represents the rate of increase in the stored magnetic field energy while the second term is the mechanical output. Thus, the instantaneous torque can be written as:1 i2 dLT(q, i)=Equation 52dq1 i2 dLT(q, i)=Equation 62dqImplementation of a Current Controlled Switched Reluctance Motor Drive Using T

34、MS320F240 11SPRA282Figure 2 shows an idealized inductance profile of an SR motor. In order to obtain motoring torque, phase current is switched on during the rising period of phase inductance. Generating operation or braking torque can be obtained by switching phase current during the decreasing per

35、iod of phase inductance. It is obvious from Figure 2 that in order to obtain optimum performance, switching of phase currents must be done accurately. This is why rotor position information (which can be obtained either by using position sensors or the position can be estimated by implementing posit

36、ion sensorless schemes) is always necessary to operate an SR motor drive. Rotor position information is fed back to the controller to determine the phase commutation sequence and instants.Figure 2. Inductance profile of an SR motor. (a) Variation of inductance with rotor position. (b) Phase current

37、for motoring operation. (c) Phase current for generating operation.12Implementation of a Current Controlled Switched Reluctance Motor Drive Using TMS320F240SPRA282Converter TopologiesSwitched reluctance motors do not require bi-directional current like other common ac motors. Therefore, unipolar con

38、verters are used as the power converter for SR motor drives. The converter topology for any specific SR motor depends on the motor construction as well as on the application. There are many types of converters available for different types of applications.Discussing all those converters is beyond th

39、e scope of this application note.Figure 3 shows the converter that is used in this application note. This particular converter is a modified version of a classical SR motor converter. The switches and diodes are rated for the supply voltage with any required safety factor. During motoring operation,

40、 both power switching devices are turned on for a particular phase. Pulse Width Modulation (PWM) can be obtained either by switching both or single power devices. At commutation, both power devices are turned off, and the phase gets defluxed quickly through the freewheeling power diodes. This conver

41、ter provides independent control for each phase and consequently phase overlap operation can be implemented easily. Two current sensors are available for phase current measurement. DC bus voltage and DC bus current can also be measured in order to implement advanced control techniques. These two var

42、iables (DC bus voltage and DC link current) are directly interfaced with TMS320F240 as shown in Figure 3.Implementation of a Current Controlled Switched Reluctance Motor Drive Using TMS320F24013SPRA282Figure 3. Power Converter for a Current Controlled Switched Reluctance Motor DrivePWM 5PWM 8ADC 2CH

43、 2ADC 1CH 3ADC 1CH 4PWM 3PWM 9PWM 7PWM 1ADC 2CH 314Implementation of a Current Controlled Switched Reluctance Motor Drive Using TMS320F240SPRA282Control StrategiesAn SR motor drive is controlled by proper positioning of the phase current pulses relative to the rotor position. The turn on timing and

44、the total conduction period determines torque, efficiency and other performance characteristics.At low speed, phase current builds up very quickly after turn-on due to the negligible back-EMF, and the current must be limited by either controlling the average voltage or regulating the current level.V

45、oltage Controlled DriveIn low-performance drives, where precise torque control is not a critical issue, fixed-frequency PWM voltage control with variable duty-cycle provides the simplest means of controlling an SR motor. A highly efficient, variable speed drive having a wide speed range can be achie

46、ved with SR motor by using voltage PWM with closed loop position control only. Figure 4 shows a block diagram of such a system. The angle controller generates the turn-on and turn-off angles for a phase, i.e., determines the conduction period, depending on the instantaneous rotor position. The duty-

47、cycle is changed according to the voltage command signal. A speed feedback loop can be added on the outside as shown in the figure for a good speed control.Figure 4. Voltage Controlled Switched Reluctance Motor DriveImplementation of a Current Controlled Switched Reluctance Motor Drive Using TMS320F

48、24015SPRA282Current Controlled DriveFigure 5 shows a torque controlled switched reluctance drive. The torque command is executed by regulating the current in the inner loop as shown in the Figure 5. The reference current I* for a given operating point is determined from the load characteristics. The

49、 controller needs current feedback information from each of the motor phases. Current controlled SR drive provides fast motor response.Figure 5. Current controlled Switched Reluctance Motor Drive16Implementation of a Current Controlled Switched Reluctance Motor Drive Using TMS320F240SPRA282Controlli

50、ng an SR motor using TMS320F240The DSP controller TMS320F240 of Texas Instruments is capable of controlling an SR motor. This application note presents a complete current controlled SR motor drive implemented using TMS320F240. TMS320F240 has nine independent PWM channels, providing maximum flexibili

51、ty for SR motor control. Built- in Quadrature Encoder Pulse (QEP) module makes encoder interfacing to TMS320F240 simple. Quadrature pulses A and B can directly be connected to a TMS320F240 by configuring Capture pins 1 and 2 as QEP input pins. TMS320F240 as dual ADC module with eight channels in eac

52、h ADC. Therefore, phase currents can be read simultaneously. Two variables can be converted in 6.6 mS.A current controlled SR motor drive is implemented by using Evaluation Module (EVM) for TMS320F240 interfaced with a motor interface board and power converter board. Motor interface and power conver

53、ter boards are designed by Spectrum Digital.Figure 5 shows the converter used SR drive. The following sections describe all major components of the above mentioned hardware setup.Hardware SetupThe SR drive was implemented using three boards. The first board, as shown in Figure 6, is the evaluation m

54、odule for TMS320F240 introduced by Texas Instruments. The second board, the motor interface board, introduced by Spectrum Digital, plugs into TIs EVM board. This motor interface board has all the drivers for power MOSFETs, current/voltage sensing circuitry, QEP input port, over current protection ci

55、rcuitry, user interface LEDs and user input DIP switch. Figure 7 shows the top view of motor interface card. The power converter board, introduced by Spectrum Digital, plugs into the interface board. The converter board, as shown in Figure 8, has all power MOSFETs, current sensing resisters, and hea

56、t sink. The following sections describe major blocks of this hardware setup.Implementation of a Current Controlled Switched Reluctance Motor Drive Using TMS320F240 17SPRA282Figure 6. Top view of TMS320F240 Evaluation Module.Figure 7. Top view of Motor Interface Board for TMS320F240-EVM18Implementati

57、on of a Current Controlled Switched Reluctance Motor Drive Using TMS320F240SPRA282Figure 8. Top view of classical converter that plugs on to EVM motor interface board shown in Figure 6.Current and Voltage SensingDifferent currents and voltages can be sensed for control purposes. In this particular implementation, phase currents are sensed to implement current controlled SR motor drive.TMS320F240 has a dual ADC that enables a user to simultaneously sample/hold and convert two variables. Total time required for this