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IEEE TRANSACTIONS ON ENERGY CONVERSION, VOL. 19, NO. 4, DECEMBER 2004 715
Optimal Efficiency Control Strategy for InteriorPermanent-Magnet Synchronous Motor Drives
Abstract—In this paper, the problem of efficiency optimiza-
tion in vector-controlled interior permanent-magnet (PM) syn-
chronous motor drives is investigated. A loss model controller is
introduced that determines the optimal -axis component of the
stator current that minimizes power losses. For the implementa-tion of the suggested controller, the knowledge of the loss model
is not required since an experimental procedure is followed to
determine its parameters. Furthermore, it is shown that the loss
model of the interior PM motor can be used as a basis for deriving
loss minimization conditions for surface PM synchronous motors
and synchronous reluctance motors as well. Experimental results
of an interior PM motor are presented to validate the effective-
ness of the proposed method and demonstrate the operationalimprovements.
Index Terms—Losses, optimal control, optimization methods,permanent-magnet (PM) motors, variable-speed drives.
NOMENCLATURE
Stator resistance.
, - and -axis magnetizing inductances.
Stator leakage inductance.
Supply frequency.
Motor speed.
Stator voltage.
Air-gap voltage.
Air-gap magnetic flux.
Stator current.
, - and -axis components of stator current.
Magnetizing current.
, -and -axis components of magnetizing
current.
Equivalent excitation current of the perma-
nent magnet (PM).
Electromagnetic torque.
Total power losses.
Copper losses.
Iron losses.Stray losses.
Mechanical losses.
Iron loss coefficient.
Stray loss coefficient.
Mechanical loss coefficient.
Manuscript received January 3, 2003; revised July 31, 2003. Paper no. TEC-00296-2002.
The authors are with the Department of Electrical and Computer Engineering,Aristotle University of Thessaloniki, Thessaloniki GR-54 124, Greece (e-mail:[email protected]).
Digital Object Identifier 10.1109/TEC.2004.837282
I. INTRODUCTION
PERMANENT-MAGNET (PM) synchronous motor ad-
justable speed drives offer significant advantages over
induction motor drives in a wide variety of industrial appli-
cations (i.e., high-power density, high efficiency, improved
dynamic performance, and reliability) [1]. Since vector control
in PM synchronous motors provides fast dynamic response
with a less complex and nonparameter-dependent controller,
PM motor drives can be an attractive alternative choice [2].
Improvement of PM motor efficiency is a most important pri-
ority, especially in cases where drives are powered by a batterysource. Therefore, significant efforts are taken to improve their
efficiency. Since there are a great variety of PM motor configu-
rations, the efforts are mainly focused on the search for the op-
timum rotor structure [3]–[7]. However, efficiency can also be
improved by intervening in the motor operation principle with
automatic control techniques.
Several control methods have been proposed in order to
reduce the loss of PM motor drives and improve their perfor-
mance. The copper loss can be minimized by the maximum
torque-per-ampere current control [8]. In surface PM motor
drives, maximum torque-per-ampere current ratio is attained
by keeping the -axis component of the stator current equal to
zero ( ) [9], [10]. Since the “ control” prevents thedemagnetization of the PM, it is often employed in interior PM
motor drives. However, the current that provides maximum
torque-per-ampere current ratio in interior PM motor drives is
a function of the current and opposes the excitation field of
the PM [8]–[11].
Several attempts to minimize both copper and iron losses
have been recently presented [12]–[14]. However, the proposed
loss minimization conditions are complex and can only be
implemented using offline made lookup tables. Therefore,
a number of costly and time-consuming measurements are
required. A control method, described in [15], improves ef-
ficiency of PM motors and is implemented using a voltagesource inverter. The efficiency improvement is attained with
appropriate control of stator voltage in order to keep power
factor equal to unity. However, although the real-to-apparent
power ratio (kW/kVA) of the PM motor is maximized, power
losses are not minimized. An adaptive search controller for
interior PM motors was developed in [16]. Finally, an approach
that specifies the optimal -axis current for minimizing interior
PM motor losses was presented in [17].
This paper presents an optimal efficiency method for vector-
controlled interior PM synchronous motor drives. The loss
minimization is accomplished with a loss model controller that
is based on the optimal -axis current condition, as presented
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[9] S. A. Nasar, I. Boldea, and L. E. Unnewehr, Permanent Magnet, Reluc-
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[10] S. Morimoto, Y. Takeda, T. Hirasa, and K. Taniguchi, “Expansion of
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866–871, Sept./Oct. 1990.[11] B. J. Chalmers, L. Musaka, and D. F. Gosden, “Variable-frequency syn-
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[12] S. Morimoto, Y. Takeda, and T. Hirasa, “Loss minimization control of
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tron., vol. 41, pp. 511–517, Oct. 1994.[13] F. F. Bernal, A. Garcí a-Gerrada, and R. Faure, “Model-Based loss min-
imization for DC and AC vector-controlled motors including core satu-
ration,” IEEE Trans. Ind. Applicat., vol. IA-36, pp. 755–763, May/June
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[14] R. B. Colby and D. W. Novotny, “An ef ficiency-optimizing permanentmagnet synchronous motor drive,” IEEE Trans. Ind. Applicat., vol. 24,
pp. 462–469, May/June 1988.
[15] Y. Nakamura, T. Kudo, F. Ishibashi, and S. Hibino, “High-ef ficiency
drive due to power factor control of a permanent magnet synchronous
motor,” IEEE Trans. Power Electron., vol. 10, pp. 247–253, Mar. 1995.
[16] S. Vaez and M. A. Rahman, “An on-line loss minimization controller for
interior permanent magnet motor drives,” IEEE Trans. Energy Conver-
sion, vol. 14, pp. 1435–1440, Dec. 1999.
[17] C. Mademlis and N. Margaris, “Loss minimization in vector-controlled
interior permanent-magnet synchronous motor drives,” IEEE Trans. Ind.
Electron., vol. 49, pp. 1344–1347, Dec. 2002.[18] P. C. Krause, Analysis of Electric Machinery. New York: McGraw-Hill, 1986.
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MADEMLIS et al.: OPTIMAL EFFICIENCY CONTROL STRATEGY FOR INTERIOR PM SYNCHRONOUS MOTOR DRIVES 723
[19] V. B. Hosinger, “Performance of polyphase permanent magnet ma-chines,” IEEE Trans. Power App. Syst., vol. PAS-99, pp. 1510–1518,July/Aug. 1980.
[20] S. A. Nasar, Handbook of Electric Machines. New York: McGraw-Hill, 1987.
[21] F. Fernández-Bernal, A. Garcí a-Cerrada, and R. Faure, “Determinationof parameters in interior permanent-magnet synchronous motors withiron loss without torque measurement,” IEEE Trans. Ind. Applicat., vol.
37, pp. 1265–1272, Sept./Oct. 2001.[22] C. Mademlis, J. Xypteras, and N. Margaris, “Loss minimization in sur-face permanent-magnet synchronous motor drives,” IEEE Trans. Ind.
Electron., vol. 47, pp. 115–122, Feb. 2000.[23] I. Boldea, Reluctance Synchronous Machines and Drives. Oxford,
U.K.: Clarendon Press, 1996, pp. 26–30.
Christos Mademlis (S’96–A’00–M’04)was bornin Arnea Chalkidikis,Greece,on February 7, 1964. He received the Diploma degree in electrical engineering(Hons.) and the Ph.D. degree in electrical machines from the Aristotle Univer-sity of Thessaloniki, Thessaloniki, Greece, in 1987 and 1997, respectively.
Since 1990, he hasbeen with theElectrical Machines Laboratory, Departmentof Electrical and Computer Engineering, Aristotle University of Thessalonikias a Research Associate. He was recently appointed as a Lecturer in the sameDepartment. His research interests are in the areas of electrical machines and
drives, especially in machines design and control optimization.
Iordanis Kioskeridis was born in Thessaloniki, Greece, on January 29, 1965.He received the Diploma degree in electrical engineering and the Ph.D. degreein asynchronous motors loss minimization from Aristotle University of Thessa-loniki, Thessaloniki, Greece, in 1989 and 1994, respectively.
Currently, he is with the Technological Educational Institute of Thessaloniki,where he teaches power electronics andelectrical machines.From 1995to 2000,he was Superintendent Engineer with the Natural Gas Project in the North Sec-tion of Greece. His research activities include power-electronic converters, con-
trol, and modeling of adjustable speed drives.
Nikos Margaris (M’00) was born in Athens, Greece, on February 10, 1949. Hereceived the Diploma in physics, the Postgraduate degree in electronics and thePh.D. degree in automatic control from the Aristotle University of Thessaloniki,Thessaloniki, Greece, in 1972, 1975, and 1982, respectively.
Since 1977, he has been with the Electrical and Computer Engineering De-partment, Aristotle University of Thessaloniki, teaching graduate and postgrad-uate courses in electronics, automatic control, power electronics, and circuittheory. From 1992to 1994, he wasthe Director of the Electronics and ComputerDivision and from 1993 to 1995, he was the Vice President of the Electrical andComputer Engineering Department. His current research interests include theloss minimization in variable and constant speed drives, the study of nonlinearoscillations, the analysis and design of switch mode dc-dc converters, and the