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Design and Implementation of an FPGA-Based Motor Control ICfor Permanent Magnet AC Servo MotorsY ing-Y u Tzou,Member, IEEE, and T ien-Sung KuoPower Electronics andM echatronics Control Lab.

Department of Electrical and Control Engineering, National Chiao TungUniversityAbstract- This paper presents the design and implementationof a motor control I C for permanent magnet ac (PM AC) servomotors using the field programmable gate arr ay (FPGA). Thispaper develops a hardware architecture for the digital controlof PM AC servo motors. T he proposed control structure hasalso been realized using FF'GAs from Xilinx Inc. All the controlfunctions, including the PWM waveform generation, currentcontrol, vector control, velocity control, and position controlhave been realized using FPGA based programmable logicgates. The constructed PM AC control I C includes 25,000 logicgates and is realized using 8-bit integer arithmetic.Experimental results are given to verify the implementedPMAC control IC.

I . INTRODUCTIONOwing to the rapid progress in motor control andmicroelectronics technologies, development in softwareservo and motor control I C will become a major trend [11-[7].Although most ac drives (ac servo drives or universal PWMinverters) in use today adopt microprocessor-based digitalcontrol strategy, the implementation of current control loopand PWM control are still tied to analog control circuitry.This kind of control scheme possesses the advantage of fastdynamic response, but suffers the disadvantages of complexcircuitry, limited functions, and difficulty in circuitmodification.The rapid development in high-performance, low-costDSP has encouraged research on digital control for ac drives.This control scheme has the advantages of simple circuitry,software control, and flexibility in adaptation to variousapplications. However, generating PWh4 gating signals andcurrent control loops require a high sampling rate to achievea wide bandwidth performance.The ASIC approach provides a rapid, low-costmanufacturing solution for ICs with special applications. Forsophisticated technology linked to a medium size marketingrequirement, it is an optimal solution. However, the longerlead time and higher setup cost for prototyping render itinappropriate for product development in the early stage.Since the 1980s, ASIC technology has given rise to severalnew specialized technologies, including mask-programmablegate array, cell-based IC (CBIC), programmable array logic(PA L), and field-programmable logic array (FPLA).With the advancement of the various technical aspectsof ASIC, three major categories have been categorized:CBIC, gate array, and programmable logic device (PLD).

This work was supported by National Science Council, Taipei,Taiwan, R.O.C. Project no. NSC86-2213-E-009-042.

PMAC Servo Motor

FPGA-based PMAC Control ICl l t t fI DSP-based Digital Controller

Fig. 1. Configuration of the DSP/FPGA controlled PWM inverter with anPM ac servo motor.The CBIC has the longest lead time with highest number ofgates, while the PL D allows the user to define the gateconnections but with a lowest number of gates. The fieldprogrammable gate array (FPGA) is a new PL D developedby Xilinx, Inc. [8]. The FPGA comprises thousands of logicgates and these logic gates are functional grouped together asa configurable logic block (CLB) to simplify higher levelcircuit design. The interconnections of the gates are definedby external S U M or ROM. The simplicity andprogrammabil ity of FPGA designate it as the most favorablechoice for prototyping an ASIC. The advent of FPGAtechnology has enabled rapid prototyping of digital systems.

11 SYSTEM DESIGN F THE PMAC CONTROL ICPM AC servo motor has become the major workinghorse in applications of precision automation equipment [9].In the paper, we have developed a new control structure forthe digital realization of vector-controlled PM ac servomotor. Fig. 1 shows the configuration of the PM AC controlIC incorporates with a digital signal processor for thepositioning control of aPM ac servo motor. TheDSP isusedfor the system initialization and parameter setting. A uto-tuning adaptive control can also be more easily implementedby employing such a control structure. Fig. 2 shows thedetailed control block diagram of the developed PM ACcontrol IC. T he PM AC control IC consists of a three-phasePWh4 waveform generator, a current controller in thestationary &-coordinate, a decoupling controller, a velocityloop controller, and a position loop controller. Keyparameters of the sub-controllers can be on-line adjusted byan external connected microcontroller.

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current controllespeed controller decoupling controller

Fig 2 Control block diagram of theP M A C motor control I C

COORDINATORTRANSFORMATION

CURRENT LOOP

Fig. 3. Detailed functional block diagram of the P M A C motor control ICFig. 3 shows the detailed block diagram for the circuitdesign of the PM AC motor control IC . This control IC issynthesized using modular circuit design methodology. Itconsists of three circuit modules: a current loop controller, avelocity-loop and decoupling controller, and a position loopcontroller. T here are a lot of control registers for parameterssetting and status feedback. Fig. 4depicts the external circuitinterface and functional block diagram of the PMAC motorcontrol IC. This PMAC control IC consists of a command

register and a status register for parameter setting and statusmonitoring. To simplify the interface circuit, commands tothese registers are routed through a common data bus anddecoded by a command mode decoder. Control parameterscan be set by externally connected hardware, such as AIDconverters, digital switches, or a microprocessor.In the design of a motor control IC, there are manyfactors needs to take into considerations, such as simplicity,flexibility, and complexity of the circuit design. In practical

applications, the motor control IC should provide easyinterface with conventional microprocessor and, therefore,needs a computer interface. One major design goal in thedesign of a high-performance motor control IC is to relievethe microprocessor from time consuming computationaltasks such as PWM signal generation, delay-timecompensation, and high sampling-rate current control.Fig. 5 shows the functional block diagram for thecoordinate synchronization in vector control of ac motors.The synchronization angle control register is used to providean offset angle for the orthogonalization of stator and rotorflux vector. The rotor flux of a PM AC motor is fixed to therotor and its position can be detected from an initialorientation test. The rotor flux of an induction motor can beestimated via a rotor flux model of the machine and it needsmore complicated computation. The provision of thiscontrol register has an advantage for its future expansion inapplication to the vector control of induction motors.

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WW OE D7 D6 DS D4 0 3 D2 D DO A4 A3 A2 AI All

E.._.......___.

Pulse A B fm

Fig. 4.Circuit connection and block diagram of the PMAC control I C

jr--P

t t 0 L - b

MACHINICAL ANGLE f,

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Table I. Control registers of the PMAC motor ICI symbol range description0- 127 proportional gain for CLCKCPTcs

FcarKSP

-255 sampling period for current loop,corresponding to28 psec - 10 psecPWM carrier frequency(78431HZ-308 Hz)proportional gain for VLC

-2550 - 127

I 8 sl 1 0 -249 I synchronization(0- 2 x 0 ITable 11. Realization of function modules

KsitTss

1 I function I flip-flop 1unction modules

0- 127 integral gain for VLCsamplingperiod of VLC1 - 31 (0- 31 .TCS)

description value unit

I 64-phase PWM generatorcurrent loop i nterrupt timer I 31

39.37 I mA Irotating coordinate converter

2-axis to 3-axis converter

I 91 I 39 IIynchronization angle andII sin/cos reference eenerator

generator460 074 0

current loop controller

In the given example, the sampling period of the current loopcontroller isset at 50 psec, the same as the PWM switchingperiod. The rise time for the current response is about 500psec. Fig. 8shows the steady-state current response of thecurrent vector trajectory in dq-plane. Some related data forthe experimental verif ication are listed in Table111Decoupling control plays a most important role in thetorque control of an lac motor. The designed PMAC ICprovides a synchronization angle control register to adjustthe phase between the controlled stator current vector and therotor flux vector. Fig. 9shows the experimental results of thespeed responses at different decoupling angles. Experimentalresults show a detuned vector control will lead to systemunstable.

Table 111. Testing condition

268speed detector

1 dc-linkvoltage I I 1 1switching frequency 19.61 kHzCL C sampling Deriod p sec

current limit

37

I mSecHz I1LC samplingperiod 1 1I BW of the low-pass fil ter I 3quadrature decoder

Fig. 10 shows the speed responses of the PM AC servomotor when the control parameters of the velocity loopcontroller (VLC) are set at different values. Theproportional-integral control with 8-bit integer arithmetic isemployed in the realization of the speed regulator.Experimental results illustrate the effect in tuning of thecontrol parameters. Fig. 11shows the velocity and positionresponses of a PM ac servo motor using the constructedPMAC control IC.A K cv=60

3

080604 ~

velocity loop controllerreadwrite interface

analoddigital interface

KC

278 8151 200122 92

_ _ _ __ -secFig. 6. Block diagram of the DSP/FPGA based A C motor control system 0 0002 0004 0006 0 008 001( 4

AIV . EXPERIMENTALERIFICATION 10806

04020

.o 2- 04 -sec~- _ _ I _ _ _ -0 0002 0004 0006 0008 001

(b)

The constructed PMAC has been incorporated with asingle-chip digital signal processor (TMS320C14) forexperimental verification. Fig. 6shows the block diagram ofthe DSPBPGA based AC motor control system. Fig. 7 showsthe step responses of the current control loop at differentcontrol parameterg. In the tuning of the control parameters r ( u r y q r wfor the current loop controller, the rotor has been locked toeliminate the back emf effect. The control registers of thePMAC IC can be adjusted interactively via the data busbetween the p m c C and its incorporated microcontroller. Fig 7 Experimental results of the step current response with rotor locked,(a) &axis, and (b) q-axis.

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Fig. 8.(a) phase current, and (b) current vector trajectories in dq-plane.Experimental results of the current responses in steady-state,

0 ni =2020 L10

_ _ - -- sec0 002- - - - 0--4 0 06 0 08 01Fig. 9.control decoupling angles.Experimental results of the speed responses at different vector

0 04- _006 -~se c0 08

Fig. I O . Experimental results of the speed responses under different controlparameter settings.

V. CONCLUSIONThis paper has presented a complete realization of thevector control of a permanent- 3agnet ac servo motor usingthe state-of-art FPGA technology. The position, velocity,torque, and current control of the PM ac servo motor can allbe realized by using the programmable logic arrays. In thispaper, we have designed an 8-bit PMAC motor control ICusing about 25,000 gate counts. PM AC Experimental resultshave shown the feasibility in design of advanced motorcontrol IC using programmable gate arrays. The constructedPM AC IC provides a systematic and simple solution fohigh-performance ac servo drives. The designed PMAC ICcan be incorporated with a general-purpose microcontrollerto provide a simple, compact, low-cost, and effectivesolution for high-performance ac drives. Given that aneconomical manufacturing cost can be achieved, it isbelieved that such PM AC control ICs will become keycomponents in motor drives of the future.

REFERENCES[ l ] E. Kappos, D. J . Kinniment, P. P. Acarnley, and A . G. J ack, Design oan integrated circuit control ler for brushless DC drives, IEE 4th h t

Con$ Power Electron. and Variable-Speed Drives, pp. 336-341, 1990[2] M . G. Egan, J . M. Murphy, E. J . Heffeman, S . U. Lidholm, and M LMcGrath, An ASI C-based PWM waveform generator for AC motocontrol applications, IEEE International Symposium on Circuits andSystems. Proceedings, vol. 2, pp. 1369-72, 1988.[3] T. C. Green, M. Mirkazemi-Moud, J . K. Goodfellow, and B. WWil li ams, Field-programmable gate-arrays and semi-custom designsfor sinusoidal and current-regulated PWM, IEE Colloquiumon ASITechnology or Power Electronics Equipment, pp. 411-4, 1992.[4] D. J . K inniment, E. Kappos, andP. P . Acarnley, Experience of the usof ASIC methods in amotor control application, IEE Fifth EuropeanConference on Power Electronics and Applications, vol. 5, pp. 458463, 1993.[ 5 ] J . Pasanen, P. J ahkonen, S. J . Ovaska, 0.Vainio, H. Tenhunen, Aintegrated digital motion control unit, IEEE Transactions oInstrumentation and Measurement,vol. 40, no. 3, pp. 654-657, 1991.[6] E. B. Patterson, D. M orley, C. G. Oswald, and P. G. Holmes, Totadigital ASIC control for an induction motor drive, IEE Col loquium oASIC Technologv or Power Elecr,,,,its Equipment, pp. 2/14, 1992.[7] D. R. Woodward, D. C. Levy, and R. G. Harley, An FPGA baseconfigurable 110 system for AC drive controllers, Proceedings IEEInternational Conference on Computer Design: VLSI in Computeand Processors (Car.N0.94CH35712), pp. 424-142, 1994.[SI Xilinx, The Programmable Gate Array Data Book, Xilinx Inc., SaJose, CA , 1992.[9] T. M. Jahns, M otion control with permanent-magnet ac machines,IEEEProc.,vol. 82, no. 8, pp. 1241-1252, Aug. 1994.[10]0gasawara, H. Akagi, and A. Nabae, The generalized theory oindirect vector control for ac machines, IEEE Trans. Ind. Appl., vo24, no. 3, pp. 470-478, May/J une1988.

Fig. 11. Experimental results of a PM ac servo motor using the constructedPMAC motor control IC, (a) velocity response to a step command, and (b)position response to aramp command

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