SRM but this paper will deal with a new developed control strategy ..... Energy Optimization at 2000 rpm with DC-machine load torque T = 1.0 N m. I2100. 0 2050.
IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 31, NO. 5, SEPTEMBEWOCTOBER1995
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A New Energy Optimizing Control Strategy for Switched Reluctance Motors Philip Came Kjaer, Student Member, IEEE, Peter Nielsen, Student Member-, IEEE, Lars Andersen, Student Member, IEEE, and Frede Blaabjerg, Member, IEEE
Abstruct-This paper describes a new and machine-independent method to minimize the energy consumption of a speed controlled Switched Reluctance Motor (SRM). The control strategy is to vary the duty cycle of the applied dc voltage in order to obtain the desired speed quickly and when operating in steadyof the phase voltage to state vary the turn-on angle (ao,,) minimize the energy consumption. The power flow is measured in the dc-link and used to control the turn-on angle. Simulations carried out on a three-phase 614 pole SRM justify the algorithm and the physical implementation in a Siemens SAB 80C517A microcontroller is described. Measurements on two different load systems show it is possible to minimize the energy consumption on-line in a speed controlled Switched Reluctance Motor without losing the dynamic performance. A comparison with an ordinary mode-shift controlled SRM shows more than an 8% increase in overall efficiency for some operation points. The algorithm is fully applicable to other Switched Reluctance Motors at other power levels or with other pole configurations.
I. ~NTRODUCTION
T
HE Switched Reluctance Motor (SRM) experiences a revival due to improvements in power devices, lowcost microcontrollers and computer-aided design tools. In comparison with ac motors or commutated dc motors, the SRM is less expensive in production and design. It is also very suitable for high-speed applications. The disadvantages are the need for position feedback sensors, the produced torque-ripple, and the emitted acoustic noise when the stator and rotor attract each other. An important factor in electrical drives is high efficiency and low cost. Some papers have considered energy optimized control of ac machines like minimizing the energy consumption by adjusting the rotor slip frequency [l], [2] which gives a high dynamic performance. Another strategy is to minimize the energy consumption by measuring the dc-link current and voltage and in steady-state adjusting the voltage/frequency ratio [3]. Very few papers have considered such strategies for SRM but this paper will deal with a new developed control strategy based on a dc-link current measurement. Paper P C S D 95-32, approved by the Industrial Drives Committee of the IEEE Industry Applications Society for presentation at the 1994 IEEE Applied Power Electronics Conference and Exposition-APEC ’94, Orlando, FL, February 13-17. Manuscript released for publication March 27, 1995. P. C. Kjaer is with the SPEED Laboratory, Department of Electronics and Electrical Engineering, University of Glasgow, Glasgow 612 8LT, U.K. P. Nielsen is with the Transmission Division, Danfoss NS, DK-6300 Graasten, Denmark. L. Andersen is with Nilfisk N S , DK-2605 Brondby, Denmark. F. Blaabjerg is with the Department of Electrical Energy Conversion, Institute of Energy Technology, Aalborg University, DK-9220 Aalborg East, Denmark. IEEE Log Number 9412787.
The SRM is usually voltage - controlled or current controlled. Voltage control means applying a phase voltage consisting of a chopped dc voltage with constant duty cycle D.The duty cycle is thus the control signal and no current control loop is used. In current control, the phase current is compared to a reference current and the phase voltage is controlled by a hysteresis control. The reference current is then the control signal. Apart from the duty cycle (or the reference current) and the angular speed, two other parameters determine the electromechanical torque production. These two are the turn-on angle aOnand the turn-off angle a O ~ which , are angles defined in relation to the rotor position of the SRM. A traditional control of the firing angles is presented in [4]-[ti]. The firing angles are moved in steps depending on the speed and the same firing angles are then used for a wide speed range. This control strategy is referred to as Mode-Shift Control. Few papers have treated optimized control of the SRM. Reference [4] treats microcomputer control of the SRM where the turn-on and turn-off angles are varied but not in the sense of optimizing the efficiency. In [5] the torque/current ratio is theoretical, maximized by adjusting the turn-off angle when the converter and the SRM operate in current control. Results are only validated by simulation and the efficiency is not optimized. Another paper 161 treats a simple energy optimization control scheme by adjusting both the turn-on and turn-off angle according to experimental obtained optimization points. The limits of this strategy are that it can only be used for one load condition at one specific speed and it is necessary to do many experiments. Another strategy is used in [7] concerning energy optimized control which is specially developed for high power SRM’s, where the number of transistor switchings in the converter is essential in order to reduce the converter losses, and this is used in an energy optimizing scheme. However, a detailed system knowledge is necessary to do this optimization. This paper suggests an energy optimizing (EO) control strategy for the SRM which is independent of machine parameters and where no measurements are necessary in order to perform the control. The strategy is based on an on-line adjustment of the turn-on angle in a voltage controlled closed-loop speed controlled SFW . First, the existence of an optimum turn-on angle, which minimizes the rim phase current (and thus the dc-link current) for constant load torque and speed is discussed. Next, a conventional control strategy for an SRM drive will be described. The new energy optimizing strategy will be explained and a
0093-9994/95$04.00 0 1995 IEEE
KJAER er al.: A NEW ENERGY OPTIMIZING CONTROL STRATEGY FOR SWITCHED RELUCTANCE MOTORS
\
i
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I
Stator
Rotor
1
1
Fig. 2. Idealized flux-linkage profile at constant current and at different rotor positions.
(b)
Fig. 1. Topology for SRh4-drive. (a) 6/4-pole SRM.(b) Converter topology, where A, B, and C are the phase windings.
detailed implementation given. Finally, different test results will be shown which are obtained on two different load systems. Especially, a comparison will be done between an ordinary control scheme and an energy optimization control scheme. (b)
(a)
11. MODELLING OF THE SRM
In order to develop an energy optimization strategy for an SRM, a dynamic model has been used. The characteristics of the SRM have been determined by the model developed in [ 111. The model has been the basis of a computer program, which simulates the instantaneous current i, the flux-linkage qh, the speed w, and the electromagnetic torque Tern. The produced electromagnetic torque can be described as
where Te, is the electromagnetic torque, i is the current in a phase, ?I, is the flux-linkage in the SRM, and B is the rotorposition. The torque calculated by (1) includes iron losses. Simulations have been used to determine rms current and torque production as functions of turn-on and turn-off angles as well as speed and duty cycle. Fig. 1 shows the profile of the 6/4-pole SRM and the converter used for control. A conventional converter is used for the SRM. Fig. 2 shows the idealized profile of the flux-linkage versus rotor position for a constant current, neglecting fringing. The optimum current should be rectangular and only cover the "positive" edge of the flux-linkage profile so only positive torque is produced, as described in (1). Due to back-EMF and limited rise-time of the current, the voltage must be applied to the machine phase windings earlier than the physical overlap cy1 to reach the desired value. As speed increases the turn-on angle aon should decrease, but depending on the duty cycle a negative torque may be produced according to (1) if significant current is present on the "negative" edge of the flux-linkage profile. This will reduce the efficiency of the SRM and increase the torque ripple. Therefore a control strategy should avoid the negative torque by adjusting the turn-off angles as a function of speed.
Fig. 3. Simulated average torque and rms phase current as a function of turn-on angle a,, and duty cycle D at speed of 1500 r/min. (a) Electromagnetic torque Tern. (b) RMS phase current I,,,.
Simulations have been carried out to investigate the relationship between the electromagnetic torque and the phase current. To illustrate how the average electromagnetic torque T,, and rms phase current I,,, depend on the turn-on angle and the duty cycle, simulation results are shown in Fig. 3. The speed is 1500 r/min with a fixed turn-off angle a,tf = 82' and a current limiter in the converter chopping at 30 A. Fig. 3 shows that the torque and current do not behave equally for changes in the turn-on angle and the duty cycle. Therefore, the current is not constant for any set of ( D , a O n ) that produces the same torque, and an optimum operating point can be expected, providing maximum efficiency. The power losses in the SRM are not only determined by the rms current but also the iron losses. The motor losses P,,,,can be characterized by ploss
= pcu
+ phy + Ped
(2)
where Ploss is the total power loss in motor, P,, is the copper losses, Phy are the hysteresis losses, and Ped are the eddy current losses. The copper losses are dependent on the rms current in the stator and are given by
Pcu= m . RSRM. I,,,2
(3)
where m is the number of stator poles and RSRM is the resistance in a stator pole winding. In a voltage controlled SRM, the rms phase current will increase as a function of the turn-on angle cyon and the conduction angle (aotf - cy,,). However, if aonis moved too close to aotf the desired torque will not be available.
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IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 31, NO. 5 , SEF'TEMBEWOCTOBER 1995
Current waveforms a t n = 1500 rpm conetant shaft torque T , = 2.8 N m
1
I,,,&
=
k5 A
Fig. 4. Conventional fixed angle mode-shift control of SRM 30
40
SO
80
70
R o t o r positlon
BO
SO
100
['I
B
Fig 6. Two simuldted phase currents which produce the same average electromagnetic torque
-0
I
n, 90.) to avoid negative torque production. The approach used here does not adjust the turn-off angle cy,^ continuously because the influence on the efficiency is primarily affected by the turn-on %tr when the SRM Operates in This is validated later by experiments.
IV. ENERGYOPTIMIZING CONTROL STRATEGY In order to get an optimized operating point at all speeds and all loads, it is necessary to use the turn-on and turn-off angles as control parameters. The proposed strategy to minimize the power consumption is based on the principle shown in Fig. 7. Instead of measuring and using the rms phase current for an energy optimization, the dc-link current I d c is used. I d , reflects the active power fed into the converter. In order to minimize the total power consumption which includes both the converter and the SRM, the dc-link current is measured and the dc-link voltage is assumed to be constant. The ModeShift Control in Fig. 4 is substituted with a Floating Angle Control (FAC), where aOnfollows a first order function of speed determined by the optimum turn-on and turn-off angles at low and high speed. The turn-on and turn-off angles used in the FAC are given by n < 1400 r/min:
aon = 55"
n > 14001/inin:
aon = 55" -
n
< 3200 r/min:
n > 3200 r/min:
n - 1400 .3O0 3000
(6)
aoff = 82" aoff = 82" -
aon,min
= 25"
n - 3200 -30' 3000 aoff,min = 70"
(7) (8)
KJAER er al.: A NEW ENERGY OPTIMIZING CONTROL STRATEGY FOR SWITCHEDRELUCTANCE MOTORS
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EO Algorithm 1
I
!
%n I
I
OCoff
c
a off.&
a0n.h
Fig. 8. Floating Angle Control (FAC)-turn-on and turn-off angles. n l = 4400 r/min, nz = 3200 r/min, and n3 = 1400 r/min.
where n is the rotational speed, a,, is the turn-on angle, Q,R is the turn-off angle, aon,min is the minimum turn-on angle, and ( ~ , f f , ~ i minimum " turn-off angle. The functions for the firing angles can be explained by simulations. They can represent the firing angles which provide almost maximum efficiency. Achieved by experimental observations, the functions will only be an initial guess and can easily be machine and load-independent. Equations (6)-(8) can also be derived by the fact that a minimum conduction angle ( a o -~ a,,) is necessary to obtain maximum torque. At low speed, these firing angles are adequate. For speeds exceeding 1400 r/min, cy,, is adjusted due to the back-EMF to maintain full torque capability. The minimum turn-on angle aon,min is specified for high speed operation, to avoid negative torque production at the beginning of the conduction interval. In this paper, cy,^ is chosen relatively low initially and could be increased at lower speed. However, due to simplicity of the control algorithm a,tf is kept fixed below 3200 r/min and adjusted for higher speeds to avoid negative torque production. A minimum turn-off angle is specified in order to have a minimum conduction angle at higher speeds. Fig. 8 shows the turn-on and turn-off angles for the FAC as a function of speed. Another obvious initial guess for the turn-on angle as a function of speed could be that the current should reach a commanded value before the rotor moves into the magnetic overlap position ( a ~ The ) . turn-on angle can be given as in r71 L, . w Qon = -I, * ___ Q1 (9)
+
II PDc=UbcIDc I
Fig. 9. Flow chart for proposed energy optimized control of the Switched Reluctance Motor.
Conatant electromagnetic torque traleetory n I 1500 rpm
for turn-on angle and dutyeyele
2
25
a5.
zo
Current trajectory corrcapondlng to
-3-; I
a o
I
0
e/.
(a)
(b)
Fig. 10. Simulated (aon,D)-trajectory for constant average torque T,, = 2.8 N m and constant speed n = 1500 r/min. (a) Torque trajectory. (b) Equivalent current trajectory.
where I, is the commandedwanted current, L , is the inductance in unaligned position, Vd, is the dc-link voltage, and w is the angular speed. The turn-off angle a,ff could similarly be determined by
The control strategy of the energy optimizer is: 1) The speed controller assures the desired speed by varying the duty cycle D at an initial turn-on angle and a fixed turn-off angle, which are both controlled by the FAC. 2) In steady-state, the load torque remains constant and the power flow is measured in the dc-link ( V d c , I&) by the
where I p h is the actual or maximum phase current and La is the inductance in aligned position. In (lo), it is assumed the converter applies negative voltage across the phase winding during turn-off. If a maximum current should be available to give the maximum torque, (6) can be calculated according to (9) and n1, n2, and n3 can be estimated according to the previous specifications.
3) The turn-on angle is initially changed Aa,, in either direction. 4) The speed controller changes the duty cycle D to reassure the desired speed. 5) When steady-state is reached again, a new set of (aOn,D) is obtained which exactly produces the necessary torque and gives a different power flow.
D
'
vdc
EO.
IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 31, NO. 5, SEPTEMBEWOCTOBER 1995
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MICRCK'ONT(:lLLER
S I E M E N S ?LIIC:
17A
..................................................................................................................
................................................................................................................
Fig. 11. Implementation of FAC and energy optimizing control of SRM. Sampled system response to step input from 1000 to 3000 rpm with hydraulic load
-
Erxorsy Optimiaor e a t 2000 rpm w l t h hydraullc load torque 0.6 N m POID
g :z cI
f
4
0
leeo
2
80
t
1
no an0 am PLO 900
10
"me
t [ma]
80
la0
,a0
zca
Tim- [m]
Fig. 12. Measured system response with speed controller by a step in reference speed from lMH)-3000 r/min.
Fig. 13. Measured values of power flow, tum-on angle, and speed with hydraulic system a\ load.
6) If the power flow has decreased, a,, is moved further in the same direction (the sign of Aa,, is unchanged). If the power flow has increased, the sign of Aa,, is changed. This is repeated until the change in power flow is too small to encourage any change in angle and the tum-on angle will alternate between two or three angles which all give the highest efficiency. Fig. 9 shows a flow chart of the energy optimizer algorithm. The time interval between two power flow measurements is determined by the time constants of the mechanical part of the system and the capability of the speed controller. The energy optimization principle is illustrated in Fig. 10 by simulations. By cutting the electromagnetic torque versus (aon,D ) curve at a constant torque (see Fig. 3(a)), a trajectory for (ao,,D) appears. The same trajectory implies an rms current corresponding to the constant torque, which is shown in Fig. 10(b). It can be seen that there exists a set of coordinates of (aon,D ) which defines the minimum rms-current and thereby a minimum power consumption. The optimum coordinates will move as a function of speed.
converter is 16 kHz. By means of a Hall sensor the dc-link current is measured and thus the energy optimization is realized. The speed is detected every 90' mechanical revolution and firing angles are calculated by interpolation in between a 30' position signal. A resolution of 1' is used for the firing angle control. Fig. 11 shows the implementation to control the SRM. In the following, all dynamical results are measured by the microcontroller and the efficiency is measured by a Voltech PM3000 Power Analyzer. VI. TEST RESULTS
All control parts are performed by a Siemens SAB 80C5 17A 8-b high-speed microcontroller. It receives position sensing signals from the motor and calculates speed and firing angles. The speed is calculated by the use of an edge-triggered timer. It produces firing pulses for all six power switches and also
Two load systems have been used for tests. One consists of a piston pump which circulates hydraulic oil in a closed pipe system. The olher load is a permanent magnet dc-machine, used for fast load changes and accurate load torque control. The sample time for the speed controller is 5 ms and the sample time for the Energy Optimizer is 2 s. Different tests are done to validate the proposed strategy. The tests are: 1) dynamic test of speed controller, 2 ) energy optimizing on piston pump load system, 3) validation of global minimum power consumption with dc machine load system, 4) influence from tum-on and tum-off angle adjustment, and 5 ) comparison between MSC and EO. The first test is done for validation of the speed controller. Fig. 12 shows it step response where the speed controller assures reference speed in about I50 ms, which is fast compared
performs the speed control. The switching frequency of the
to the time between two power flow samples.
V. IMPLEMENTATION
~
KJAER et al.: A NEW ENERGY OPTIMIZING CONTROL STRATEGY FOR SWITCHED RELUCTANCE MOTORS
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Energy O p t i m i z a t i o n a t 1500 rpm w i t h D C - m a c h i n e load torque T = 2.8 N m
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E n e r g y O p t i m i z a t i o n at 1000 rpm w i t h D C - m a c h i n e load torque T = 2 N m 1100 1050
c 1000 1 4 ..
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Time [m]
E n e r g y O p t i m i z a t i o n a t 2000 rpm with D C - m a c h i n e load torque T = 1.0 N m
E n e r g y O p t i m i z a t i o n a t 2000 rpm w i t h D C - m a c h i n e load torque T = 1.0 N m
(d)
2100 2050 2000
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80
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00
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(e)
Fig. 14. Measured values of power Row Pc,c, tum-on angle aon and speed n with a dc-mxhine as load. (a) n = 1000 dmin and T = 2.0 N . m. Initial -guess ann = 30'. (b) 71 = 1000 r/min and T = 2.0 N m. Initial guess ann ~.= 5.jo. (c) . . R = 1500 r/min and T = 2.8 N . m. Initial guess aon = 30O. (d) I I = 1500 r/min and T = 2.8 N . m. Initial guess aon = 54O. (e) R = 2000 dmin and T = 1 N . m. Initial guess aon = 30°. (f) I I = 2000 dmin and T = 1 N . m. Initial guess cy,, = 53'.
-
The next test shows the energy optimizer in operation. In Fig. 13, results are shown when the energy optimizer is used with the hydraulic load. Fig. 13 shows that the optimum turn-on angle is found in about 40 s (20 power flow samples). The search time will strongly depend on the initial turn-on angle and in many cases the optimum value will be reached quickly due to the Floating Angle Control. The power measurement is performed every 100 ms, but a filtered value is used only every 2 s in the energy optimizer. Fig. 13 shows also the change in turn-on angle and the resolution of 1" can be seen. The resolution can easily be increased by software if necessary. The speed is also measured and is kept constant by the controller.
~
Y
In the next tests, a dc machine has been used as load. This has been done to demonstrate the abilities of the energy optimizer with different types of load and different load torquespeed characteristics. It is also demonstrated that a global power minimum is found by the optimizer. Fig. 14 shows three different operating conditions with an active energy optimizer which is enabled after 10 s and with different initial guesses of the turn-on angles. For the six tests, the initial turn-on angles have been set very low or very high. This is a worst case situation (lowest efficiency) but it illustrates the EO principle very well. The optimizer finds in both cases almost the same optimum turn-on angle with a maximum variation of 3 O , and it is concluded that
IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 31. NO. 5, SEPTEMBEWOCTOBER 1995
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Turn-on angle fixed uon 75
70
-x
3 E
Mode Shlfl Control l
1
>
-
-
-
-
:
-
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_---
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4070
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---- 2000 rpm: a:
-3000
i .....................
a,
---
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39' I
75
Gained Efflclcncy by Enerw Optlmlration Control
80
Turn-off angle aoff
['I
(a) Turn-off angle fixed
ud,
(C) Fig. 16. Measured efficiencies for two control strategies of SRM. (a) Mode shift control. (b) Floating angle control with energy optimizer. (c) Absolute difference in efficiency for the two control strategies.
40
45
50 Turn-on angle a m
55
['I
(b) Fig. 15. Influence on system efficiency by adjusting the turn-on and turn-off angles at different speeds and loads. (a) Fixed turn-on angle and variable turn-off angle. (b) Fixed turn-off angle and variable turn-on angle.
a global optimization point is estimated in all cases. Fig. 14 shows the actual speed during operation, and it can be seen that it remains constant when the optimizer is active. Previously it has been stated that the influence on the efficiency by adjusting the turn-on angle is much more dominant than the turn-off angle in voltage control and different tests are performed to validate this. Tests are performed at different speeds and different load torques. In Fig. 15(a), the efficiencies are shown when the turn-on angle is kept fixed and the turnoff angle is varied. The turn-on angle is varied according to the FAC-control specified in (6) and (7). Fig. 15(b) shows when the turn-off angle is kept fixed and the turn-on angle is varied. Where data points are missing, the converter is saturated (D = 1). Fig. 15 shows the efficiency is very dependent on the turnon angle while the adjustment of the turn-off angle does not change the efficiency significantly if it is chosen below 82' for the test conditions. However, it should also be stated that the freedom of changing the turn-on angle in voltage control is much higher than the turn-off angle, because the turn-off angle is dependent on the turn-on angle. The test results also show a small adjustment of the turn-off angle can give a small increase in efficiency, but then the energy optimization control strategy becomes much more complex because then there are two parameters in the optimization scheme.
Finally, an efficiency comparison of the Mode-Shift Controller and a Floating Angle Control with an energy optimizer is done. The SM4 runs with fixed torque at different speeds and the efficiencies are measured. The measured efficiencies include both the converter and the SRM. The measurement procedure has been that the SRM runs at one speed and one load for Mode-Shift Control, and after some time the control strategy has been changed to Energy Optimized Control and a new measurement is performed. This ensures comparative measurements. Fig. 16 shows the measured efficiencies for the two control strategies and their difference. Fig. 16 shows that a significant improvement can be obtained by using Floating Angle Control together with an energy optimizer compared with an ordinary Mode Shift Controller. In some operating points, 8% absolute efficiency are gained by using the proposed strategy. Fig. 16(b) shows also that an efficiency higher than 82% for the whole system can be obtained with the EO-control. VII. CONCLUSION A new control approach to minimize the power consumption of a voltage controlled Switched Reluctance Motor when it runs at steady-state has been introduced. It requires regular measurement of the power flow in the dc link, control of the turn-on angle a,,,, and a fixed turn-off angle a , as ~ a function of speed. An internal control loop with a speed controller, which uses the duty cycle of the applied phase voltage as a control parameter, assures the desired speed, regardless of the firing angles. The energy optimizer has no influence on the dynamic behavior of the SRM because it is only enabled during steady-state operation. It only requires the possibility to control the firing angles in a continuous way which is realized by an 8-b microcontroller and a stable and fast speed controller.
KJAER et al.: A NEW ENERGY OFTMIZING CONTROL STRATEGY FOR SWITCHED RELUCTANCE MOTORS
Tests have shown that an 8% increase in absolute efficiency can be obtained in some operation points by using an Energy Optimizing algorithm compared with an ordinary control scheme. The algorithm used for energy optimization is applicable to any Switched Reluctance Motor and the strategy also takes the characteristics of the converter into account.
1095
Philip Came Kjaer (S’91) was born in Montreal, Canada, in 1969. He received the M.Sc. degree in electrical engineering from Aalborg University, Denmark, in 1993, including one year at the Universite Catholique de Louvain-la-Neuve, Belgium. Since 1993, he has worked as a Research Assistant at the Department of Electronics and Electrical Engineering, University of Glasgow, Scotland. His research interests include control of electrical drives, applied nonlinear and optimal control, sensorless operation of electrical drives, and power electronics.
APPENDIX
MOTORRATINGS The data of the three-phase, 6/4 pole SRM used for tests are: dc-link voltage 80 V, rated current 25 A, rated power 1.0 kW, rated shaft torque 4N.m, rated speed 2500 r/min, max. speed loo00 r/min, and stator pole resistance R ~ R M0.3 R @25OC.
ACKNOWLEDGMENT The authors thank F. Jensen, Danfoss M s , for converter and switched reluctance motor design.
Peter Nielsen (S’93) was born in Taulov, Denmark, on August 17, 1968. He received the M.S. degree in electrical power conversion from the Institute of Energy Technology, Aalborg University, Denmark, in 1993. He started his Ph.D. project concerning direct converters for ac induction motor drives in August 1993. The project is supported by the Transmission Group, Danfoss A/S, and the Danish Academy of Technical Sciences. His research areas are in static converters. modulation technique, simulation, control of machines, and power devices. Mr. Nielsen received a DIFAN Award for his contribution to switched reluctance drives in 1994.
REFERENCES J. K. Pedersen and F. Blaabjerg, “An electrical car drive system using an energy-optimized control strategy based on an ac-machine and a microcontroller.” in Ilrh Inf. Elecrricul Vehicle Symp., Florence, 1992, pp. 12.03.1- 12.03.1 3. F. Blaabjerg and J. K. Pedersen, “An integrated high power factor three-phase ac-dc-ac converter for ac-machines implemented in one microcontroller.” in Proc. PESC ’93, 1993, pp. 285-292. J. C. Moreira, V. Blasko, and T. A. Lipo, “Low cost efficiency maximizer for an induction motor drive,’’ in Proc. IEEE fnd. Applicat. Soc. Annu. Meeting, 1989, pp. 42&431. T. J. E. Miller, C. Cossar, and D. Anderson, “A new control IC for switched reluctance motor drives,” Fifh fEE Int. Con$ Electrical Machines and Drives, London, 1991, pp. 331-335. R. Krishnan, X. Mang, and A. S. Bharadwaj, “Design and performance of a microcontrollerbased switched reluctance motor drive system,” Electric Machines and Power Syst., 1990, pp. 18:359-373. R. C. Becerra, M. Ehsani, and T. J. E. Miller, “Commutation of SR motors,” IEEE Trans. Power Electron., vol. 8, no. 3, pp. 257-263, 1993. B. K. Bose, T. I. E. Miller, P. M. Szczesny, and W. H. Bicknell, “Microcomputer control of switched reluctance motor,” IEEE Trans. fnd. Applicar., vol. 1A-22, no. 4,pp. 708-715, 1986. R. Orthmann and H. P. Schoner, ‘Turn-offangle control of switched reluctance motors for optimal torque out[offjput,” in Proc. EPE ’93, 1993, vol. 6, pp. 2&25. M. Stiebler and J. Ge, “A low voltage switched reluctance motor with experimentally optimized control,” in Pmc. ICEM ’92, part 2, pp. 532-536. D. A. Torrey and J. H. Lang, “Optimal-efficiency excitation of variablereluctance motor drives,” IEE Proc.-E, vol. B, vol. 138, no. 1, pp. 1-14, 1991.
[ l l ] T. J. E. Miller and M. McGilp, “Nonlinear theory of the switched reluctance motor for rapid computer-aided design,” IEE Proc., vol. 137, Pt. B, no. 6, pp. 337-347, Nov. 1990. [12] P. Materu and R. Krishnan, “Estimation of switched reluctance motor losses,” in Pmc. Ind. Applicat. Soc. Annu. Meefing, Oct. 1988, pp. 1 7 6 187.
Lars Andersen (S’93) was born in Hjsrring, Denmark, on March 26, 1969. He received the M.Sc. degree in electrical engineering from the Institute of Energy Technology, Aalborg University, Denmark, in 1993. He was a Teaching Assistent at Aalborg University from 1993 to 1994. He is now with NILFISK N S , Denmark, working as a Development Engineer in the Electrical Development Department. He is working with modelling and design of electrical motors, motor drives, and power electronics.
Frede Blaabjerg (S’90-M’91) was born in Erslev. Denmark, on May 6, 1963. He received the Msc.EE and Ph.D. degrees from the Institute of Energy Technology, Aalborg University, Denmark, in 1987 and 1995, respectively. He was employed at ABB-Scandia, Randers, from 1987 to 1988, and has been an Assistant Professor since 1992. His research areas are in power electronics, static power converters, ac drives, switched reluctance drives, modelling and characterization of power semiconductor devices, and finally simulation. Prof. Blaabjerg is a member of the European Power Electronics and Drives Association and the Industry Applications Society Industrial Drives Committee. In 1995, he received the Angelos Award for his contribution in modulation technique and control of electrical drives, as well as receiving a prize for being the “Annual Teacher” at Aalborg University.
