Global Adaptative Output Feedback Control of Induction Motor With
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IEEE TRANSACTIONS ON AUTOMATIC CONTROL, VOL. 44, NO. 5, MAY 1999 967
Global Adaptive Output Feedback Controlof Induction Motors with Uncertain
Rotor ResistanceRiccardo Marino, Sergei Peresada, and Patrizio Tomei
Abstract— The authors design a global adaptive output feed-back control for a fifth-order model of induction motors, whichguarantees asymptotic tracking of smooth speed references on thebasis of speed and stator current measurements, for any initialcondition and for any unknown constant value of torque loadand rotor resistance.
The proposed seventh-order nonlinear compensator generatesestimates both for the unknown parameters (torque load androtor resistance) and for the unmeasured state variables (rotorfluxes); they converge to the corresponding true values underpersistency of excitation which actually holds in typical operating
conditions. In these cases the rotor flux modulus asymptoticallytracks desired smooth reference signals which allows the motorto operate within saturation limits (so that modeling assumptionsare met). As in field-oriented control, the control algorithmgenerates references for the magnetizing flux component and forthe torque component of stator current which lead to significantsimplifications for current-fed motors. Simulations show that theproposed controller is suitable for high dynamic performanceapplications. This is confirmed by experiments since the controlis robust with respect to modeling errors, sensors and actuatorsnoise, control discretization, and simplification. Experimentalcomparisons with a classical indirect field-oriented control ex-hibit a significant improvement of power efficiency when rotorresistance differs from its nominal value.
Index Terms— Adaptive nonlinear control, induction motor,
online parameter estimation, output feedback.
I. INTRODUCTION
INDUCTION motors are more reliable and less expensive
than those permanent magnet switched reluctance and d.c.
motors which are currently employed for high dynamic per-
formance applications; this is due to their simpler construction
since they have no brushes, no commutator, no permanent
magnet, and no windings in squirrel cage rotors.
On the other hand, the control of induction motors is rather
difficult. It is a highly coupled and nonlinear multivariable
problem with two control inputs (stator voltages) and two
output variables (rotor speed and flux modulus), required totrack desired reference signals. Since flux sensors are not
available, it is an output feedback problem in which the outputs
to be controlled do not coincide with measured outputs (speed
Manuscript received May 16, 1997; revised June 30, 1998. Recommendedby Associate Editor, J.-B. Pomet. This work was supported in part by MURST.
R. Marino and P. Tomei are with the Dipartimento di Ingegneria Elettronica,Universita di Roma “Tor Vergata,” 00133 Roma, Italy.
S. Peresada is with the Department of Electrical Engineering, Kiev Poly-technical Institute, Kiev 252056, Ukraine.
Publisher Item Identifier S 0018-9286(99)02825-1.
and stator currents). Moreover, there are uncertain critical
parameters: in addition to load torque, which is typically
unknown in all electric drives, in induction motors rotor
resistance is also largely uncertain since it may vary up to
100% during operations, due to rotor heating. In comparison,
the control of currently employed high dynamic performance
motors is much simpler; this is in fact one of the reasons for
their widespread use. However, the availability of low cost
powerful digital signal processors (requiring only 40 ns to ex-
ecute a simple instruction) and advances in power electronicsmake complex control algorithms now implementable even
for medium- and small-size induction motors which could
replace currently used motors, provided that high dynamic
performance in positioning and speed tracking along with
high-power efficiency are achieved; this motivates current
research efforts in induction motor control design.
Assuming that all state variables (including rotor fluxes) are
available from measurements and all parameters (including ro-
tor resistance) are known, the problem of controlling induction
motors was solved by the so-called field-oriented control [1],
[2] and, more recently, by the input–output linearizing control
[3] (see also [4] for a different feedback linearizing control and
[5] for a variable structure approach). As clarified in [6], bothfield-oriented and input–output linearizing controls make use
of nonlinear state-space change of coordinates and nonlinear
state feedback transformations to achieve different objectives.
While input–output linearization guarantees exact decoupling
so that speed and flux modulus can be independently controlled
with linear dynamics, field-oriented control achieves the same
properties only asymptotically, provided that the reference
for the flux modulus is constant. This is a disadvantage
especially in low power motors since at high speed, when the
flux modulus reference has to be lowered (flux weakening)
to operate the motor within the linear magnetic region and
without voltage saturation or varied for torque maximization
(see [7]), the speed tracking dynamics are perturbed.
Advances in nonlinear adaptive control (see for instance
[8]) allowed us to design in [6] an input–output state feedback
linearizing control which is adaptive with respect to both
load torque and rotor resistance. It is shown in [6] that
load torque and rotor resistance estimation errors converge to
zero in physical operating conditions. However, flux sensors
are typically not available in induction motors since they
reduce reliability and imply additional costs and technological
difficulties. Therefore, the design of state feedback controls is
0018–9286/99$10.00 © 1999 IEEE
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only a first step toward the solution of the output feedback
control of induction motors which points out two facts: high
tracking performance is achieved while rotor resistance is
estimated online; the resulting control is highly nonlinear but
implementable with available microprocessors. The currently
open problem, which is solved in this paper, is whether the
same results may be obtained without flux measurements.
Provided that rotor resistance is known, flux observers have
been studied in [9]–[11] and exponentially convergent flux
estimators are designed in [12] and [13]. They may be rather
sensitive with respect to rotor resistance variations. Exponen-
tially convergent flux observers have been tested in closed loop
in experiments and simulations providing flux estimates both
to field-oriented [14], [2], [15] and input–output linearizing
algorithms [16]–[20]. An independent line of research was
focused on the design of rotor resistance estimators starting
with [21] (see [22]–[28]), in which simplifying assumptions
are made including linear approximations and steady state
operations. More recently, an online nonlinear exponentially
convergent rotor resistance estimator and an adaptive flux
observer have been obtained in [29] which shows that bothrotor fluxes and rotor resistance may be estimated on line from
speed and stator current measurements. An output feedback
algorithm consisting of a flux observer which is adaptive
with respect to rotor resistance together with a state feedback
controller which is adaptive with respect to torque load is given
in [30]; however, the closed-loop behavior is only illustrated
by simulations since its stability is not proved in [30].
In fact, as far as nonlinear systems are concerned, replacing
state measurements by exponentially convergent state esti-
mates in global tracking controls does not yield, in general,
global output feedback tracking controls. This property, which
holds for linear systems, has to be independently established
for nonlinear ones. Therefore the output feedback control prob-lem for induction motors was addressed as such in [31]–[36],
assuming known rotor resistance. In [31] speed and flux
tracking are achieved by output feedback provided that the
initial conditions lie in a predetermined region. In the series
of papers [33]–[36], torque and flux tracking are globally
obtained by output feedback using a passivity approach. As
far as current-fed induction motors are concerned, an output
feedback controller is presented in [37] which is free of
singularities and experimentally gives high performance both
in speed and flux tracking: however, it is shown in [37]
that errors in rotor resistance reduce power efficiency since
higher currents are needed. Hence, it is proposed in [37] to
update the rotor resistance value used by the controller bya rotor resistance estimator; nevertheless, since no stability
proof has been obtained in [37] for the closed-loop system
with continuously updated rotor resistance, the design of a
global output feedback control which is adaptive with respect
to rotor resistance, is still an open problem. Very recently, an
adaptive output feedback position tracking controller is pro-
posed in [38]; position tracking is achieved despite unknown
inertia, load, and rotor resistance. The controller exhibits
a singularity when the magnitude of the estimated rotor
flux is zero and does not provide converging estimates for
rotor resistance and rotor flux so that the rotor flux tracking
objective (which is crucial to improve power efficiency) is not
fulfilled.
The contribution of this paper is to design a global output
feedback control for induction motors which is adaptive with
respect to both load torque and rotor resistance and guarantees
asymptotic tracking of smooth speed references for any initial
condition of the closed-loop motor. The resulting control is
a seventh-order dynamic compensator which provides voltage
inputs on the basis of rotor speed and stator currents measure-
ments. The dynamic control algorithm generates estimates for
load torque, rotor resistance, and rotor fluxes that converge to
the corresponding true values under persistency of excitation,
which actually holds in physical operating conditions. The con-
trol also generates as internal signals stator current estimates
and an estimate for the rotor flux angle. When persistency
of excitation condition is satisfied the rotor flux modulus
asymptotically tracks desired smooth reference signals, so that
the motor operates within saturation limits at higher speed
and the modeling assumptions (linear magnetic circuits) are
met. As in classical field-oriented control, reference signals
both for the direct and the quadrature components of statorcurrents (in a frame attached to the estimated rotating flux
vector) are generated which are responsible for flux modulus
and speed tracking, respectively. Direct and quadrature current
errors are forced to zero so that simplified controls may be used
in current-fed machines relying on high gain current loops.
Simulations and experiments show converging estimates
both for rotor flux and for unknown parameters within 2 s
and very precise tracking of speed and flux modulus reference
signals, which are typically required in high-performance
applications in spite of sharp load torque variations and rotor
resistance uncertainties. Experiments confirm that since the
proposed control algorithm achieves rotor resistance estima-
tion and flux modulus tracking, an improved power efficiencyis obtained in comparison with a classical control scheme such
as the indirect field-oriented control.
II. ADAPTIVE OUTPUT FEEDBACK CONTROL DESIGN
A. Problem Statement
Assuming linear magnetic circuits, i.e., no magnetic satura-
tion, the dynamics of a balanced induction motor in a fixed
reference frame attached to the stator are given by the fifth-
order model (see for instance [6] for its derivation and [14]
and [39] for modeling assumptions)
(1)
in which the state variables are rotor speed , rotor fluxes
and stator currents ; the control inputs are
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MARINO et al.: GLOBAL ADAPTIVE OUTPUT FEEDBACK 971
We replace the unknown variables (recall that
are not measured) by the new error variables
(24)
so that the error equations (21) and (22) are expressed in new
coordinates as
(25)
The advantage of using the unknown variables instead
of relies on the fact that their dynamics no longer
depend on [compare (25) with (21)]. We now define some
of the yet undetermined terms in (17), (18), (22) as ( and
in (22) are still to be chosen)
(26)
with positive design parameter and estimates of
the unknown error variables
defined by (24). Note that the dynamics of
are yet to be defined. If converge to ,
they allow us to recover the rotor flux vector since
are known variables and is a known parameter. Hence, the
new variables may be viewed as rotor flux estimates.
Substituting (26) in (25), we obtain
(27)
We compute from (3), (17), (25), and (26) the dynamics of the
stator current tracking errors
(28)
with
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972 IEEE TRANSACTIONS ON AUTOMATIC CONTROL, VOL. 44, NO. 5, MAY 1999
(29)
In order to determine , the dynamics of the estima-
tion variables , and the feedback control inputs, we consider the function
(30)
in which are positive parameters and
are estimation errors. We define
with and to guarantee that is
chosen so that with the minimum value of
(assumed to be known). Alternatively, we may choose
and with the maximum value of (assumed to
be known). From (27) and (30), the time derivative of (30)
results in
(31)
We now consider the function
(32)
From (31), (27), and (28), its time derivative is
(33)
The terms , the feedback controls , and the
dynamics of are now chosen in order to force
to be negative semidefinite. Choosing the yet undetermined
terms in (22)
(34)
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MARINO et al.: GLOBAL ADAPTIVE OUTPUT FEEDBACK 973
we obtain
(35)
We finally define
(36)
(37)
so that (35) becomes
(38)
Equations (36), (37), (29), (22), (26), (34), (17), (18), and (2)
define a seventh-order dynamic feedback compensator, whose
state variables are , which generates
the control signals on the basis of the measurements
, the reference signals and their time deriva-
tives . In order to guarantee that for
every we modify the dynamics (37) according to
(39)
where is the smooth projection algorithm given in
[40] and defined in our case by
if
if and
otherwise
in which with the minimum
(known) value of and such that . The
initial condition in (39) is chosen so that . The
projection algorithm has the following properties:1) ;
2) is Lipschitz continuous;
3) ;
4) .
Property 4) implies that substituting (39) instead of (37) in
(35), we obtain instead of (38) the inequality
(40)
From (32) and (40), it follows that
are bounded for every . Their
bounds depend on the initial errors. Therefore,according to (36), and, consequently,
are bounded for every
. Hence, are bounded and therefore
are uniformly continuous. On the other hand,
integrating (40) we have
which implies by Barbalat’s lemma (see for instance [41] and
[8]) that
This shows that asymptotic speed tracking is achieved from
any initial condition provided that in (39). Moreover,
current estimation errors and current tracking errors
asymptotically tend to zero.
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D. Parameter Convergence
We now analyze under which conditions also
tend asymptotically to zero.
The error equations are
(41)
Whenever projection does not occur, i.e., , (41)
may be rewritten as
(42)
with and
the expressions shown at the bottom of the page.
Making the change of coordinates
with , from (42) we obtain
Since the structure of and is such that
setting
we finally have
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The radially unbounded function (32) may be written as
, whose time derivative is
. Since is skew-symmetric and recall-
ing the structure of and , we obtain , with
. From now on, using
the same arguments adopted in the proof of the persistency of
excitation Lemma B.2.3 in [8, p. 367] we can establish that
if persistency of excitation conditions are satisfied, i.e., thereexist two positive constants and such that
(43)
then the equilibrium point of system (42) is uni-
formly asymptotically stable and all trajectories tend asymp-
totically to zero.
If projection occurs, it is easy to see that the arguments in
the proof of [8, Lemma B.2.3] are still valid and, therefore,
we can conclude that if (43) holds then the equilibrium
point of system (41)is uniformly asymptotically stable and all trajectories tend
asymptotically to zero provided that . In summary,
if (43) is satisfied then, in addition to asymptotic speed
tracking:
1) since both and tend to zero, from (24)
it follows that rotor flux traking is achieved and, in
addition, the rotor flux vector is asymptotically oriented
with respect to the frame, i.e.,
2) since tend to zero, both rotor resistance and
torque load are asymptotically estimated, i.e.,
3) since tend to zero, the rotor flux vector is
asymptotically estimated: defining, according to (24)
(44)
we have in fact
III. CONTROL IMPLEMENTATION AND PERFORMANCE
A. Control Implementation
Let us first summarize the seventh-order dynamic feedback
control algorithm designed in Section II
(45)
with given in (26), (34) and
, given in (29).
The dynamic compensator (45) contains eight control pa-
rameters whose role may be eval-
uated by examining both the closed-loop error equations (41)and the corresponding function (32) with time derivative (40).
The parameters determine the rate of decay of
in (40) and directly affect [see (41)] the dynamics of
speed tracking error , current estimation errors and
current tracking errors , respectively. The parameter
determines the influence of speed tracking errors on the
other errors and is typically chosen much smaller than one.
The parameters and may be separately tuned using
(16), (9), and (13) so that has the desired transients.
The parameters and are the adaptation gains for
and , respectively. The smaller they are chosen, the
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slower the adaptations for and result. The parameter
is a weighting factor in the function
(32); the choice of depends on the interval of variation of
the uncertain parameter . The parameter should be the
last parameter to be tuned and should be chosen sufficiently
large so that the current error dynamics are much faster than
speed error dynamics while voltages are within saturation
limits. Of course, different tuning strategies should be followed
depending on sensor noise features, discretization strategies,
and other implementation issues.
For induction motors which allow for high gain current
loops the control may be greatly simplified as follows:
(46)
with obtained by setting in (17), (18),(22), (26), (34), (36), and (39)
(47)
B. Control Performance
We tested the proposed controller (45) both by simulations
and by experiments [using its simplified version (46), (47)] for
a three-phase single pole pair 0.6-kW induction motor (OE-
MER 7-80/C), whose parameters are listed in the Appendix
(see [29] for experimental and computed static speed-torque
characteristics). Since flux and torque measurements are not
available during the experiments, we first tested by simula-
tions how a typical flux modulus reference (including flux
weakening) is tracked and the role of torque in persistency of
excitation condition (43) when the controller (45) is used. We
then illustrate by experiments the robustness of the simplified
controller (46), (47) with respect to sensors noise, inaccura-
cies on mechanical and electrical parameters, control signals
distortions generated by the power inverter, control discretiza-
tion and truncation errors, inverter unmodeled dynamics, and
unmodeled saturation effects of the magnetic circuits. Finally,
we compare performances achieved by the proposed control
with those given by a classical indirect field-oriented control.
The proposed control algorithm (45) has been tested first
by simulation with the control parameters (all values are in SI
units):
. Recall that may be chosen
negative provided that is negative. All initial conditionsof the motor and of the controller are set to zero excepting
Wb and s , which is 50% greater
than the true parameter value s . The references
for speed and flux modulus along with the applied torque are
reported in Fig. 1. The flux reference starts from 0.01 Wb at
and grows up to the rated constant value 1.16 Wb;
field weakening starts at s. The speed reference is
zero until s and grows up to the constant value 100
rad/s; at s the speed is required to go up to the value
200 rad/s, while the reference for the flux is reduced to 0.5
Wb. A constant load torque (5.8 Nm, the rated value) which
is unknown to the controller is applied at s and reduced
to 0.5 Nm at s. Fig. 2 shows the time histories of speed,flux modulus, load torque estimate and , the estimate
of . The speed tracks tightly the reference even
though load torque sharply changes (at s and s),
since the load torque estimate quickly recovers the applied
unknown value. Also the estimate of converges within 1 s
to the true value. Note that the higher the torque is (see
Fig. 3), the larger the convergence rate for is. Persistency of
excitation condition (43) has been checked to hold. The flux
tracks its reference: there is, however, a coupling with speed
tracking at s and at s when speed is perturbed
by an unknown load torque. Fig. 3 shows the time histories of
torque, direct component of current estimation error, phase-
current, and phase- voltage. Currents and voltages are withinsaturation limits and reduced overshoots are noticed in torque
when unknown load torques are applied at s and
s. The current estimation errors tend rapidly to zero
after perturbations due to speed tracking errors.
The simplified control algorithm (46), (47) was then tested
experimentally with the control parameters values:
; the gains of the PI controllers (46) are
chosen so that a unit step reference is tracked with a settling
time of about 2.5 ms; all initial conditions of the controller
are set equal to zero excepting . The following typical
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Fig. 1. Reference signals and load torque in simulations.
Fig. 2. Speed, flux modulus, and parameter estimates in simulations.
operating conditions were experimentally tested: the unloaded
motor is required to reach the rated speed 100 rad/s with
acceleration 1000 rad/s in 140 ms starting from 0.5 s; during
the initial time interval s, the motor flux modulus
is driven from the initial value 10 Wb to its rated value
1.16 Wb, with flux speed 3.87 Wb/s; both speed and flux
reference signals (given in Fig. 4) are twice differentiable with
bounded second-order derivatives (the bounds are rad/s
and 38.7 Wb/s , respectively); after start-up a constant load
torque, equal to the rated value (5.8 Nm) is applied. Speed
measurements are provided by an optical incremental encoder
with 2000 lines per revolution, while current measurements
are filtered by low pass filters with cut off frequency equal
to 2.6 kHz and then converted by 12 bit A/D converters
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Fig. 3. Torque, ~
i
d
; i
a
; and u
a
in simulations.
Fig. 4. Reference signals in experiments.
with conversion time of 50 s. A 32-bit DSP (AT&T 32C)
performs data acquisition, implements the control law using
an improved Euler integration algorithm with a sampling time
equal to 0.5 ms, and generates reference voltages for the power
inverter with symmetrical PWM and switching frequency of
15 kHz. The DSP is hosted by a PC which programs the DSP,generates smooth speed and flux modulus reference signals,
generates torque commands for a current controlled d.c. motor
(which is connected to the induction motor), and stores and
displays experimental data. We performed two experiments:
in the first one underestimates the correct value , i.e.,
; while in the second one is overestimated, i.e.,
. The closed-loop performance in the two cases
is documented in Figs. 5 and 6, respectively, in which speed
error , current estimation errors , estimated flux
modulus with given by (44), cur-
rents , voltage , and the normalized estimate
are given. In both cases speed errors are compatible with a
high-performance drive; estimated flux modulus converges to
the reference value and converges to 1 within 2 s; the
estimation of flux modulus and of depends on the torque
level (which may be evaluated from ). Finally, we performed
for comparison the same two experiments by using the indirectfield-oriented control (FOC), which is implemented by (46)
with
(48)
where is used in the last equation instead of the usual
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Fig. 5(a). Experimental ~ ! ( t ) ; (
^
2
d
( t ) +
^
2
q
( t ) )
1 = 2
; i
q
( t ) and i
d
( t ) with initial underestimated rotor resistance.
Fig. 5(b). Experimental u
q
; ^ ( t ) = ;
~
i
q
( t ) and ~
i
d
( t ) with initial underestimated rotor resistance.
estimated flux modulus. Comparing (48) with (47) we note that
(48) may be viewed as a simplification of (47) and therefore
the same tuning can be used ( with
and ) which guarantees satisfactory speed
tracking when in (48). The flux is estimated by the
observer (which is converging outside the magnetic saturation
region)
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Fig. 6(a). Experimental ~ ! ( t ) ; (
^
2
d
( t ) +
^
2
q
( t ) )
1 = 2
; i
q
( t ) and i
d
( t ) with initial overestimated rotor resistance.
Fig. 6(b). Experimental u
q
; ^ ( t ) = ;
~
i
q
( t ) and ~
i
d
( t ) with initial overestimated rotor resistance.
which makes use of the true value . The performance
achieved by FOC in the two cases are reported in Figs. 7 and
8; while the speed error is still satisfactory, the flux modulus
goes above the reference rated value when and
below when . In both cases higher currents
(when compared with the corresponding in Figs. 5 and 6)
are required to produce the rated torque: this is due to magnetic
saturation when and to low flux modulus when
. Experiments show that the controller proposed
in this paper gives improved transient performance and a
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Fig. 7. Experimental ~ ! ( t ) ; (
^
2
d
( t ) +
^
2
q
( t ) )
1 = 2
; i
q
( t ) and i
d
( t ) with FOC and underestimated rotor resistance.
Fig. 8. Experimental ~ ! ( t ) ; (
^
2
d
( t ) +
^
2
q
( t ) )
1 = 2
; i
q
( t ) and i
d
( t ) with FOC and overestimated rotor resistance.
power efficiency which is bigger than the one obtained by
the indirect field-oriented control (46), (48) with an inaccurate
rotor resistance estimate.
IV. CONCLUSION
We have designed for the fifth-order model (1) of an
induction motor with constant load torque a seventh-order
nonlinear adaptive control (45) which, on the basis of rotor
speed and stator currents measurements, guarantees asymptotic
tracking of smooth speed references for any initial condition
and for any unknown constant value of load torque and rotor
resistance. Under persistency of excitation condition (43), we
have shown that smooth rotor flux modulus reference signals
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982 IEEE TRANSACTIONS ON AUTOMATIC CONTROL, VOL. 44, NO. 5, MAY 1999
are asymptotically tracked while the rotor flux vector tends to
coincide with the -axis of the frame, achieving the
so-called field orientation; both unknown parameters (rotor
resistance and load torque) and the rotor flux vector are
asymptotically estimated. The control algorithm structure leads
to a straightforward simplification for current-fed motors given
by (46), (47).
Simulations of typical operating conditions show accurate
tracking of speed and flux modulus smooth reference signals
usually required in high-performance applications in spite
of load torque perturbations and rotor resistance variations,
converging estimates of uncertain parameters and unmeasured
state variables within 2 s. The simplified version (46), (47) of
the controller was experimentally tested and compared with the
classical indirect field-oriented control (46), (48); simulation
results were confirmed showing robustness with respect to
sensor noise, unmodeled dynamics and saturation effects,
inverter distortions, parameter inaccuracies, control discretiza-
tion, and simplification. Moreover, improved power efficiency
and transient performance are documented in comparison with
the classical indirect field-oriented control algorithm whenrotor resistance differs from its nominal value.
APPENDIX
MOTOR PARAMETERS
Rated power 600 W.
Rated speed 1000 rev/min.
Rated torque 5.8 Nm.
Rated frequency 16.7 Hz.
Excitaton current 2 A.
Rated current 4 A.
Stator resistance
Rotor resistanceMutual inductance H.
Rotor inductance H.
Stator inductance H.
Motor-load inertia kg m .
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Riccardo Marino was born in Ferrara, Italy, in1956. He received the degree in nuclear engineeringand the M.S. degree in systems engineering fromthe University of Rome “La Sapienza,” in 1979and in 1981, respectively, and the D.Sc. degree insystem science and mathematics from WashingtonUniversity, St. Louis, MO, in 1982.
Since 1984 he has been with the Department of
Electronic Engineering at the University of Rome“Tor Vergata” where he is currently a Professor of systems theory. He is the author, with P. Tomei, of
Nonlinear Control Design (Englewood Cliffs, NJ: Prentice-Hall, 1995). Hisresearch interests include theory and applications of nonlinear control.
Sergei Peresada was born in Donetsk, Ukraine, onJanuary 14, 1952. He received the Diploma of Elec-trical Engineer from Donetsk Polytechnical Institutein 1974 and the Candidate of Sciences degree inelectrical engineering from the Kiev PolytechnicalInstitute, Ukraine, 1983.
From 1974 to 1977 he was a Research Engineer inthe Department of Electrical Engineering, Donetsk Polytechnical Institute. Since 1977 he has beenwith the Department of Electrical Engineering, Kiev
Polytechnical Institute, where he currently is anAssociate Professor. From 1985 to 1986 he was a Visiting Professor in theDepartment of Electrical and Computer Engineering, University of Illinois,Urbana-Champaign. His research interests include applications of modern con-trol theory (nonlinear control, adaptation, VSS control) in electromechanicalsystems, model development, and control of electrical drives and internalcombustion engines.
Patrizio Tomei was born in Rome, Italy, on June 21,1954. He received the “dottore” degree in electronicengineering in 1980 and the “dottore di ricerca”degree in 1987, both from the University of Rome“La Sapienza.”
He currently is an Associate Professor of Adap-tive Systems at the University of Rome “Tor Ver-gata.” He is coauthor of the book Nonlinear Control
Design (Englewood Cliffs, NJ: Prentice-Hall, 1995)with R. Marino. His research interests include adap-tive control, nonlinear control, robotics, and control
of electrical machines.