1966
IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 44, NO. 6, NOVEMBER/DECEMBER 2008
A Scroll Compressor With a High-Performance
Induction Motor Drive for the Air Management of a
PEMFC System for Automotive Applications
Benjamin Blunier, Member, IEEE, Marcello Pucci, Member, IEEE,
Giansalvo Cirrincione, Member, IEEE, and Abdellatif Miraoui
Abstract—This paper proposes a technological solution with a
scroll compressor driven by a high-performance induction machine drive for the air management of proton exchange membrane
fuel cells (PEMFC) for automotive applications. The torque–speed
characteristics of a real scroll compressor have been measured
and then emulated by a brushless internal mounted permanent
magnets machine controlled in torque. This emulated scroll compressor has been driven by a field-oriented controlled induction
motor drive. The whole car model as well as the PEMFC have
been implemented by software on the same DSP which implements
the drive control algorithm; in this way, the hardware-in-the-loop
structure has been employed for emulating the behavior of a real
car including the electrical supply of the PEMFC. The whole
system has been tested with a classic European Driving Cycle. Two
experimental rigs have been setup, one for characterizing the scroll
compressor and the other for emulating the entire vehicle. The
experimental results have shown that the speed reference profile,
obtained during a urban driving cycle, is followed correctly, and
that the tank-to-wheel efficiency remains at quite high values
confirming the goodness of the proposed technological solution.
The hardware-in-the-loop approach of the experimental rig allows
tests to be performed to verify the operation in steady and transient states with low cost and reduced employment of the fuel cell
stack, with resulting increased durability.
Index Terms—Automotive applications, compressors for fuel
cells, fuel cell air management, high-performance motor drives.
I. I NTRODUCTION
T
HE AIR management in proton exchange membrane fuel
cells (PEMFC) systems for automotive applications plays
an important role for the overall performance of the entire
vehicle since it absorbs about 25% of the energy provided by
Paper MSDAD-08-07, presented at the 2007 Industry Applications Society Annual Meeting, New Orleans, LA, September 23–27, and approved
for publication in the IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS
by the Industrial Automation and Control Committee of the IEEE Industry
Applications Society. Manuscript submitted for review October 31, 2007
and released for publication March 6, 2008. Current version published
November 19, 2008.
B. Blunier and A. Miraoui are with FCLab-SeT Université de Technologie de Belfort-Montbéliard, 90010 Belfort Cedex, France (e-mail: benjamin.
blunier@utbm.fr; abdellatif.miraoui@utbm.fr).
M. Pucci is with the Institute on Intelligent Systems for Automation, 90100
Palermo, Italy (e-mail: marcello.pucci@ieee.org).
G. Cirrincione is with the Department of Electrical Engineering, University of Picardie-Jules Verne, 80025 Amiens, France (e-mail: g.cirrincione@
ieee.org).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TIA.2008.2006304
the fuel cell [1]. It is well known that the use of PEMFCs results
in the possibility of a working operation at a lower temperature
than other kinds of fuel cells, which makes it suitable for transport applications, in high power density and in a good tank-towheel efficiency. The literature lacks guidelines for the choice
of both the compressor to be adopted and the most suitable
electrical drive as well as the control strategy to be used for optimizing its performance [2]. As for the air compressor, the possibility of having high-pressure air results in higher efficiency,
lower weight, and lower humidification water for the membrane
in the PEMFC stack [3]–[5]. In general, the literature gives
experimental results as for the efficiency of the system only for
one working point, which is not the case in actual automotive
conditions where different working points occur, depending on
the path of the vehicle. Some comparative studies for PEMFC
system have been carried out over the past few years [1],
[6], [7], and they show that several kinds of compressors can
be employed, among which the turbocompressors (dynamical
compressors) and the positive displacement compressors (scroll
compressor, lobe compressor, screw compressor, etc.). Apart
from such key issues as efficiency, price, and reliability, these
papers also show that other requirements are necessary for fuel
cells in transport applications, as summarized below.
1) Pressure ratio: The pressure ratio should be around
1.5–3 bar depending on the fuel cell stack.
2) Oil content: The oil has to be prohibited because it is
detrimental for the fuel cell membrane.
3) Pressure ripple: No pressure ripple greater than 100–
200 mbar is allowed. A greater pressure ripple would
damage (perforate) the membrane.
4) Weight: Weight should be as low as possible.
5) Volume: Volume should be as small as possible.
Fig. 1, by means of radar graphs, shows that most of the
described compressors meet the requirements, with the exception of piston compressors and membrane compressors, which
are too bulky and heavy and also have a big pressure ripple.
The blowers (low pressure) have to be chosen for a lowpressure fuel cell, which is not, however, the case for automotive applications. Positive displacement compressors with
internal compression have to be preferred to those with external
compression (isochoric compression) because they offer a better efficiency. Usually, centrifugal compressors are employed
for the air management in PEMFC systems for automotive
0093-9994/$25.00 © 2008 IEEE
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BLUNIER et al.: SCROLL COMPRESSOR WITH A HIGH-PERFORMANCE INDUCTION MOTOR DRIVE
1967
technological solution which is not yet state of the art. It is
the adoption of a high-performance field-oriented controlled
(FOC) induction motor drive [2], with a commercial industrial
machine, connected with a scroll compressor, the use of which
is not wide spread in fuel cell systems for vehicular propulsion.
The whole system is driven by a classic European Driving
Cycle (EEC Directive 90/C81/01). An experimental rig has
been built for testing the system. The torque–speed characteristics of a real scroll compressor have been first measured, then
they have been emulated by a brushless IMPM controlled in
torque. This emulated scroll compressor has been driven by an
FOC induction motor drive. The whole car model, including the
PEMFC, has been implemented by software on the same DSP
where the drive control algorithm had been implemented; in
this way, a hardware-in-the-loop structure has been adopted to
emulate the behavior of the car including the electrical supply
of the PEMFC. This paper is organized as follows. Section II
describes the vehicle model and its components. Section III
explains the reasons for the choice of the induction motor drive
rather than IMPM motor drives. Section IV describes the experimental rig. Section V gives the simulation and experimental
results.
II. V EHICLE S YSTEM M ODEL
Fig. 1. Comparison between several kinds of compressors. (a) Centrifugal.
(b) Claw. (c) Lobe. (d) Membrane. (e) Piston. (f) Rotary vane. (g) Screw.
(h) Scroll. (i) Side channel. (j) Legend.
applications because they have the well-known advantage to
be very compact and light. However, they have to work at
a very high rotation speed (≥ 100 kr/min), which requires
the use of oil-free magnetic or gas bearings and an adequate
control. Centrifugal compressors have also the disadvantage
that their energy efficiency is high only in a reduced range of
mass flow and pressure [7], and they cannot work at constant
pressure, whatever the mass flow may be: At low values of
mass flow, the surge limit makes the compressor work at quite
low-pressure with low efficiency [3]. Many publications have
been issued about centrifugal compressors and their control
in PEMFC systems [8]. Moreover, these high speeds often
require properly designed and constructed electrical machines
to drive them. On the other hand, for medium power PEMFC
systems (below 20 kW), the efficiency achieved by centrifugal
compressors is not so good. It is in this power range that
these can be advantageously replaced by positive displacement
compressors like scroll compressors, which permit the system
to work at constant pressure and high efficiency over a wide
range of mass flow and do not have a zone of instability. In
addition, they allow the humidification to be embedded in the
compression system [9], [10], resulting in the elimination of
the humidifier and in a more compact and efficient system.
Finally, since they have a much lower rotational speed, offthe-shelf electrical machines, like induction machines or brushless internal mounted permanent magnets (IMPM) machines,
can be used in variable speed drives with high-performance
control strategies. From this standpoint, this paper proposes a
The fuel cell system for the vehicle consists of a cooling
system for taking away the heat generated by the stack, a
hydrogen supply stored in a high-pressure vessel, a humidifier
for humidifying the air at the cathode inlet and, in some system
configurations, the hydrogen at the anode side. One of the
most important and consuming subsystems is the air supply
composed mainly of the air compressor but also of the filters
and a valve at the cathode outlet. Fig. 2 shows the model of
vehicle system with a scroll compressor.
The fuel cell stack delivers a gross power (Pgross ) to the
car and auxiliaries. It is calculated from the required electrical
power of the car Pnet (based on the driving cycle) and the auxiliaries power (Paux ) of the fuel cell. The latter can be divided
into two main contributions: the electrical compressor power
(Pcomp ) and the constant auxiliary power (Pconst ) consumed
mainly by the cooling system and the humidifier
Pgross = Pnet + Pcomp + Pconst .
(1)
The compressor power Pcomp is measured: It is the electrical
power of the induction machine.
A. Fuel Cell Stack Model
Both for the simulation and the experimental tests, only a
static model of the PEMFC has been adopted, because the
variable time constant of the cell, depending on the so-called
“charge double layer” effect and due to the charge accumulation
on cell surfaces is a variable quantity ranging from about 0.5 s
to about 50 s which is much higher than the transient stator time
constant of the induction motor (6.2 ms in the motor under test);
this last time constant determines the dynamics of the stator
current control loop.
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IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 44, NO. 6, NOVEMBER/DECEMBER 2008
Fig. 2. Block diagram of the vehicle system.
The fuel cell is modeled and built from a single-cell static
characteristic [7]
Vc (j) = 1.031 − 2.45 × 10−4 j − 0.03 ln(j)
−2.11 × 10−5 exp(8 × 10−3 j)
(2)
where Vc and j (in milliamperes per square centimeter) are the
cell voltage and the current density, respectively.
The relation between the current density (j in amperes per
square centimeter), the stack current (I in amperes), the number
of cells (nc ), and the total surface active area (Stot in square
centimeters) is given by
j=
Inc
.
Stot
The fuel cell power is inferred from (2) and (3)
!
"
Inc
Pgross (I) = IV (I) = nc IVc
.
Stot
(3)
Fig. 3.
(4)
The design parameters are the number of cells nc for minimum desired voltage and Stot for the maximum power.
The simulated fuel cell contains 120 cells and a cell surface
area of 207 cm2 giving a maximal power of 13 kW which meet
the performance of the tested scroll compressor. The voltage
and power versus current characteristics of the stack are shown
in Fig. 3.
Because the voltage of fuel cells stack is low, a boost converter has to be added in order increase the dc voltage to 570 V.
B. Car Model
The scaled electrical power calculation of the car Pnet takes
into account the dynamics of the vehicle (dv/dt), its mass
(Mv ), the coefficient of friction (Cx ), the car front surface
(S), the rolling coefficient (Cr ), and the drive train efficiency
(ηd ). This model computes the electrical power necessary for
achieving the desired speed [11]
!
"
dv 1
1
2
+ ρair v SCx + Mv gCr .
Pnet = κ v Mv
(5)
ηd
dt
2
Fuel cell stack characteristics.
The power is reduced by a factor κ = 1/3 to adapt the power
to the maximum air flow rate of the tested scroll compressor.
C. Compressor Model
In the range of speed operation, the relation between the
variation of speed of the scroll and its torque is practically
instantaneous because of the internal compression which is
around 2 bar and very close to the fuel cell pressure operation to achieve maximum efficiency. This means that almost no external pressure compression exists, responsible for
the delay of the torque response. The compressor model is
therefore directly based on the experimental results shown in
Figs. 4 and 5.
The flow rate reference qair is calculated from the gross
power demand of the fuel cell system [7] on the basis of the
following equation:
qair = 3.57 × 10−7 λ
Pgross
Vc (j)
(6)
where λ is the air delivering stoichiometry (λ = 2).
The fuel cell current I (i.e., j) is obtained from a 2-D lookup
table (Pgross , I), and the single-cell voltage Vc (j) is calculated
from (2) and (3).
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BLUNIER et al.: SCROLL COMPRESSOR WITH A HIGH-PERFORMANCE INDUCTION MOTOR DRIVE
Fig. 4. Electrical power contour lines (in watts) of the scroll compressor and
working pressure line.
Fig. 5.
Relation between the speed and the air mass flow rate.
The compressor speed reference is obtained from the air
demand qair and the interpolated data shown in Fig. 5. The
corresponding torque is computed from Fig. 4 (taking into
account the compressor mechanical efficiency). As shown on
this figure, the pressure is kept at 2 bars during all the test when
it is possible: at low flow rates the scroll compressor cannot
work at 2 bars, and the pressure is maintained at its maximum
value.
III. I NDUCTION M OTOR D RIVE FOR THE A IR
M ANAGEMENT OF THE PEMFC S YSTEM
A. Choice of the Compressor Motor
Given the speed range of the drive required by the scroll
compressor, about 0–7000 r/min corresponding to the speed
range of the vehicle of 0–30 m/s of the urban vehicle under
study, a very important issue to be addressed is the choice of
the type and characteristics of the compressor motor. Among
the different solutions, an off-the-shelf induction machine drive
has been chosen here to drive the scroll compressor as it
has been done for the centrifugal compressor [12]. The main
alternative solution is a brushless permanent magnet drive, but
for centrifugal compressors, induction motors with high rated
frequencies (300 Hz) are generally a good alternative to them. It
1969
is well known that induction motors are better than permanent
magnet ones in terms of higher reliability, higher robustness,
and lower cost. On the contrary, induction motors exhibit
lower torque/volume and torque/weight ratios and increased
control algorithm complexity than the permanent magnet ones.
The choice of the induction motor has been made mainly on
the basis of criteria of reliability, robustness and cost. These
aspects have been preferred to the occupied volume and weight
which would have encouraged the use of the permanent-magnet
machine. However, as far as the motor efficiency is concerned,
some other aspects are to be taken into consideration. In respect
of this, it should be noted that, at low power levels, the fuel
cell (FC) stack is very inefficient. Typically, a reduction of
the demanded power to the FC from 12 to 5 kW decreases
correspondingly its efficiency from about 60% to about 30%
[13]. When the vehicle is idling or is running at low speed
(typical of urban cycles), no drive power is demanded to the
FC, but its compressor still requires power, even if at low load,
which makes the FC work with high losses and low efficiency,
with resulting reduction of the system efficiency. On the basis
of this last remark, even if an efficiency criterion would, in
general, suggest that a permanent magnet machine should be
employed because of the absence of losses in the rotor, in this
application, the reduction of the FC efficiency occurs mainly
when the compressor motor is slightly or not loaded, and
therefore, the increase of losses in the induction motor due to
the slip are not particularly significant. On the contrary, it would
be important to increase the efficiency of the compressor motor
drive when the FC presents a low efficiency. In this sense, highperformance induction motor drive control systems can easily
be integrated with suitable methodologies for the minimization
of motor losses (maximization of efficiency) [14], [15]. These
methodologies, which are based on the idea of properly reducing the reference flux of the drive at low load torque, permit
the losses to be significantly decreased particularly at low or
no load. Similar methodologies are not always well applicable
in permanent magnet motor drives, because of the well-known
difficulty in flux reduction. Thus, on the basis of the efficiency
criterion, the induction motor might be a good choice as well.
Given the type of the motor, another issue is the choice of the
motor characteristics. In general, if an electric traction motor
is present in the vehicle, it will impose the dc voltage level in
the 100–400 V; it means that both the inverter and motor design
and construction can follow standard industrial and commercial
practice [16]. If a scroll compressor is used, which implies a
speed range of the drive in a urban cycle of about 0–7000 r/min,
even a traditional induction motor designed for industrial frequency or slightly higher can be used, with no need of a specific
design (differently from the centrifugal compressor motor). A
traditional machine with 1 pole pair designed for industrial
frequency would permit the drive to work over the whole speed
range of 0–7000 r/min, some of which in field-weakening.
In this case, a two-pole-pair machine has been used for the
experimental tests because of its availability in the laboratory.
For this reason, in the experimental verification on the test rig,
the speed reference of the drive has been scaled of 1/2, so
that the results obtained with a two-pole-pair machine can be
referred to those obtainable with a one-pole machine.
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IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 44, NO. 6, NOVEMBER/DECEMBER 2008
Fig. 6. Block diagram of the FOC scheme for driving the scroll compressor.
B. Compressor Drive Control System
Since the compressor drive must track a speed reference
depending on the speed of the car, a high-performance control
technique has been chosen, the FOC. Particularly, a direct rotorflux-oriented FOC scheme (Fig. 6) has been adopted, where the
current control is performed in the rotor flux oriented reference
frame. In this case, the dc link is supplied by a PEMFC. On
the direct axis, a flux control loop commands the current loop,
and a voltage control loop commands the flux loop to permit
the drive to work automatically in the field weakening region
keeping the product between the rotor flux amplitude and rotor
speed absolute value constant. On the quadrature axis, a speed
loop controls the current loop. The speed reference of the drive
is computed in the hardware-in-the-loop structure on the basis
of the speed of an inverse car model based on the vehicle
dynamics which takes into account its mass, the coefficient
of friction, the car front surface, and the drive train efficiency
(Section II).
A decoupling circuit (Fig. 6) has been used to correctly
decouple the direct and quadrature current controls. All Proportional Integral (PI) controllers have been used in all the control
loops. An asynchronous space vector modulation with fPWM =
5 kHz has been used to command the inverter. This modulation
technique has been implemented by software in the same DSP
where the FOC algorithm has been implemented. The use of
such a control scheme permits the drive to follow the speed
reference with high performance, to provide the load torque
required by the scroll compressor, which has a nonlinear law
in respect with the speed of the drive itself, and finally to work
in the field weakening region when the car speed increases (see
the Appendix for the controller design). Since one of the most
expensive parts of a high-performance drive is the encoder, a
sensorless solution permitting the drive to work in a wide speed
range could be an interesting perspective [10], [17]–[19]. In this
case, a rotor flux estimator based on the rotor equations of the
induction motor in the rotor-flux-oriented reference frame (the
so-called “current model”) has been adopted. This choice has
been done for two reasons.
1) The current model is sensitive mainly to the rotor resistance variation at increasing slip speed of the machine
caused by the load torque, differently from the “voltage
model” which is sensitive to the stator resistance variations at low speed. Many parts of the drive speed cycle are
at very low speed, and this justifies choice of the current
model.
2) The current model in the rotor-flux-oriented reference
frame performs a closed-loop integration, while the
voltage model requires an open-loop integration with
consequent problems that can be overcome by suitable
solution [20].
Since the correct field orientation of the drive adopting such
a flux model depends on the correct knowledge of the rotor time
constant, the drive has been integrated with a online rotor time
constant estimator [21].
IV. E XPERIMENTAL R IG
An experimental rig has been devised for the experimental
assessment of the methodology. First, a scroll compressor has
been experimentally characterized to retrieve the speed versus
torque curve (extracted from Fig. 4) and the air mass flow
rate versus speed (Fig. 5). Fig. 7(a) shows a photograph of
the scroll compressor under study. This experimental rig has
been built to test the performance and control laws of positive
displacement compressors in an automated way. Afterward, the
speed versus torque characteristics has been emulated by a
torque controlled high-performance FOC PMSM drive. In this
way, the PMSM drive behaves exactly as the scroll compressor
in the whole speed range. There are at least three reasons for
using an emulator of the scroll compressor instead of using the
scroll itself. The first is a practical reason: The electrical drive
on which the control is experimentally implemented, and the
scroll test setup is located in different laboratories of different
universities (France and Italy). The emulator permits therefore
to work on the scroll compressor in one place without having it
at disposal. The second is that, by using a controlled PMSM
instead of the scroll compressor, the tests can be performed
safely, in presence of the protections on the PMSM system
and the induction motor drive, avoiding any possible damage of
the scroll compressor. This is useful particularly for the initial
configuration and tuning of the system. The third is that the
same system can be used in the future for emulating different
kinds of compressors. The system in Fig. 7(b) presents thus
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BLUNIER et al.: SCROLL COMPRESSOR WITH A HIGH-PERFORMANCE INDUCTION MOTOR DRIVE
1971
TABLE I
PARAMETERS OF THE INDUCTION MOTOR
of the PEMFC (see Section II-A) has been adopted for the
experimental verification of the method.
The drive test set up consists of [22]:
1) a three-phase induction motor with parameters shown in
Table I;
2) a frequency converter which consists of a three-phase
diode rectifier and a 7.5-kVA three-phase voltage source
inverter (VSI) for supplying the induction motor;
3) a brushless IMPM machine drive for loading the induction machine;
4) a frequency converter which consists of a three-phase
diode rectifier and a 8-kVA three-phase VSI for supplying
the IMPM;
5) a dSPACE card (DS1103) with a PowerPC 604e at
400 MHz and a floating-point DSP TMS320F240.
Fig. 7. Test benches. (a) Photograph of the scroll compressor test bench
(Laboratory of Université de Technologie de Belfort-Montbéliard, France).
(b) Photograph of the test setup (Istituto di Studi sui Sistemi Intelligenti
per l’Automazione, Consiglio Nazionale delle Ricerche, Electrical Drives
Laboratory, Italy).
Fig. 7(b) shows a photograph of the test setup. The output
digital-to-analog channel of the DSP gives the torque reference
to the IMPM drive in real time on the basis of the scroll
compressor model implemented on the DSP itself. In this way,
the IMPM drive behaves exactly as the scroll compressor in the
whole speed range.
The flux estimator and the whole FOC control algorithm
have been implemented on the DSP at a sampling frequency of
fc = 10 kHz. The car model, the PEMFC model, and the scroll
compressor model have been implemented at a lower sampling
frequency, which is in this case 1 kHz.
V. R ESULTS
two motors, one is the induction machine which is under test
for varying its capability to drive the scroll compressor, and
the second is the PMSM whose function is simply to emulate
the scroll compressor (in perspective any kind of compressor).
It should be noted that, considering the speed range of the
scroll compressor drive, the induction machine drive is operated in field weakening since a speed above the rated one
(1500 r/min) is required, while the PMSM drive (which emulate
the scroll compressor) works always within the rated speed
(3000 r/min), and therefore, there is no problem of demagnetization. The model of the scroll compressor as well as the
whole car model including the PEMFC has been implemented
by software on the same DSP where the drive control algorithm
had been implemented; in this way, a hardware-in-the-loop
structure has been adopted to emulate the behavior of the car
including the electrical supply of the PEMFC. A static model
A. Simulation Results
The proposed scroll compressor-based system supplied by
the PEMFC has been tested first in numerical simulation in
Matlab-Simulink environment. The parameters of the simulated induction machine, VSI inverter, scroll compressor,
and PEMFC are those of the experimental rig described in
Section IV. The sampling frequency of the control scheme
has been set equal to 10 kHz for both control schemes. The
models of the FOC drive with its flux observer, the PEMFC, and
the vehicle dynamics have been created for this purpose (see
Section II). The European Driving Cycle (one urban followed
by one extraurban) has been adopted to test the behavior of
the drive. Since the adopted working cycle makes the machine
work in the field weakening region, the value of the load torque
required by the scroll compressor has been limited to 4 N · m,
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IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 44, NO. 6, NOVEMBER/DECEMBER 2008
the 200 rad/s. Both in transient and steady-state conditions, the
dynamics of the speed loop is high, with hardly distinguishable
curves of the reference and measured speed; the drives thus
works correctly with the driving cycle. Fig. 11 shows the net
and gross power Pnet , Pgross , qair , and the PEMFC voltage provided by the fuel cells stack during the same test. It also shows
the global efficiency of the systems (tank-to-wheel efficiency).
B. Experimental Results
Fig. 8. Car speed during the driving cycle (simulation).
Fig. 9. Rotor flux amplitude, scroll compressor torque during the driving cycle
(simulation).
which is close to the torque limit value which can be provided
by the induction machine under test at the maximum speed
during the aforementioned test cycle. Fig. 8 shows the car speed
in the European Driving Cycle.
This is very challenging cycle from the point of view of the
compressor drive. As a matter of fact, it can be observed that the
drive speed reference ranges from zero speed during some time
intervals to very low speed (1.97 rad/s) in other time intervals
up to 197 rad/s in field weakening region.
Figs. 9 and 10 show wavefoms of the rotor flux amplitude,
the scroll torque with the corresponding electromagnetic torque
provided by the induction machine, and finally the reference
and measured speed of the drive. They show that above
150 rad/s, the control system automatically reduces the rotor
flux amplitude, as expected. The electromagnetic torque produced by the induction machine is always equal to the scroll
compressor torque excepted when a speed transients required
by the machine. The speed curves show that the drive correctly
works in the whole speed range from very low speed up to
The experimental verification of the scroll compressor drive
has been carried out on the test setup described in Section IV.
As in the simulation test, the standard European Driving Cycle
has been adopted. Since this working cycle makes the machine work in the field weakening region, also in this case
the value of the load torque has been limited to 4 N · m.
Fig. 12 shows the car speed in the European Driving Cycle,
as implemented on the DSP. Figs. 12–14 show the corresponding wavefoms of the rotor flux amplitude, the scroll torque
(IMPM torque), and the reference and measured speed of the
drive, respectively. They show that above 150 rad/s, the control
system automatically reduces the rotor flux amplitude. The
load torque produced by the IMPM corresponds to that of the
scroll compressor, with the aforementioned limit of 4 N · m
in field weakening. The speed curves show that the induction
motor drive correctly works in the whole speed range from very
low speed up to the 200 rad/s. Both in transient and steadystate conditions, the speed loop dynamics is high, and the
drives works correctly with the European Driving Cycle. This
is particularly interesting, since the drive cycle requires varying
speed ranging from zero up to 200 rad/s at varying speed load
torques.
Fig. 15 shows the speed controller error ωrref − ωr related
to the speed curve in Fig. 14. It can be observed that the
tracking error is always in average close to zero, apart from
some spikes. These spikes are all in correspondence of the step
variations of the reference speed, and the maximum instantaneous tracking error is about 8 rad/s in correspondence to the
transient from about 190 rad/s (in field weakening region) to
about 100 rad/s. In all the other working conditions, both in
steady state and in slow transients, the instantaneous tracking error is basically zero. This behavior can be justified on
the basis of the following considerations. From linear control
theory, it is well known that a PI controller permits a zero
steady-state tracking error only for constant references. For
higher order references, a nonnull steady-state error is to be
expected.
However, Fig. 18 in Appendix, which draws the Bode
diagram of the closed loop transfer function of the speed
loop, shows that 3-dB bandwidth of the speed loop is about
128 Hz. On the contrary, Fig. 16, which draws the drive
speed reference and its spectrum obtained with the fast Fourier
transform (FFT), shows that the maximum frequency content
of the speed reference waveform is within 1 Hz. It means that
inside the frequencies of the reference speed, the gain of the
speed loop is always one, and therefore, the speed controller
can deal with the time variations of the speed reference required
by the scroll compressor drive. Furthermore, if the mechanical
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BLUNIER et al.: SCROLL COMPRESSOR WITH A HIGH-PERFORMANCE INDUCTION MOTOR DRIVE
1973
Fig. 10. Reference and measured drive speed during the driving cycle (simulation).
Fig. 11. Net power provided by the supply during the driving cycle (simulation). (a) PEMFC voltage. (b) Air mass flow. (c) Gross and net power. (d) Tank-towheel efficiency.
damping factor of the rotor is considered nonnull (as it is in the
real case), the open-loop transfer function from the output of
the speed controller to the measured speed has not poles in the
origin (system of type 0). This means that, adopting a speed PI
controller, it presents a zero steady-state tracking error to a step
reference and a nonnull tracking error to a ramp reference. In
the ideal case, with zero mechanical damping factor (in a wellconstructed machine it is close to zero), it would be a system of
type 1, and thus, it would present a zero steady-state tracking
error also to speed ramp reference. For the above reasons, if
the slow transient of the reference speed are considered linear
(they are either ramps or constant values, which is not far from
the actual variation), the steady-state tracking error for a ramp
input, which is constant with a PI controller, can be computed
as 1/Kv where Kv = lims→0 sGω , with Gω the open-loop
transfer function of the speed loop. In the case under hand, Kv
is 55.4 dB, and therefore, the theoretical steady state tracking
error for a ramp is 0.017 rad/s, which is negligible.
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1974
IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 44, NO. 6, NOVEMBER/DECEMBER 2008
Fig. 12. Car speed in the standard driving cycle (experiment).
Fig. 15.
Speed controller error ωrref − ωr .
Fig. 13. Rotor flux amplitude, scroll compressor torque during the European
Driving Cycle (experiment).
Fig. 16.
Drive speed reference and its spectrum obtained with the FFT.
Fig. 14. Reference and measured speed of the drive (experiment).
VI. C ONCLUSION
This paper presents experimentally the advantages of using a high-performance induction motor drive connected to
a scroll compressor for the air management of PEMFC in
automotive applications. The use of a scroll compressor has the
advantage that it can be controlled at constant pressure, unlike
centrifugal compressors. Moreover, the lower rotational speed
of such compressors makes the use of induction motor drive
possible, which results in higher robustness, lower cost, and
higher reliability than those obtainable with other technological
solutions (for example, centrifugal compressors plus permanent
magnet motors). The torque–speed characteristics of a real
scroll compressor have been measured and then emulated by
a brushless IMPM machine controlled in torque. This emulated
scroll compressor has been driven by a FOC induction motor
drive. The whole car model as well as the PEMFC have been
implemented by software on the same DSP which implements
the drive control algorithm; in this way, the hardware-in-theloop structure has been employed for emulating the behavior of
a real car including the electrical supply of the PEMFC. The
whole system has been tested with a classic European Driving
Cycle. The experimental results have shown that the speed
reference profile ranging from zero speed to very low speed up
to 200 rad/s in field weakening region, obtained during a urban
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BLUNIER et al.: SCROLL COMPRESSOR WITH A HIGH-PERFORMANCE INDUCTION MOTOR DRIVE
1975
The control design of the current loop is the same on both
axes. It is however particularly important, for the application
under study, the tuning of the speed controller, since the speed
profile of the compressor drive is composed of some constant
and time varying parts and correspondingly the load torque
presents variations with the rotor speed. Fig. 17 shows the
Bode diagram of the closed loop transfer function of the current
loop. A 3-dB bandwidth of 100 Hz has been set. For security
reasons, the current control has been tuned overdamped to avoid
potential damaging of the machine. Fig. 18 shows the Bode
diagram of the closed loop transfer function of the speed loop.
A 3-dB bandwidth of 128 Hz has been achieved.
R EFERENCES
Fig. 17. Bode diagram of the current closed-loop transfer function.
Fig. 18. Bode diagram of the closed-loop transfer function of the speed loop.
driving cycle, is followed correctly and that the tank-to-wheel
efficiency remains at quite high values confirming the goodness
of the proposed technological solution. Future work will deal
with the application of intelligent control techniques to improve
the reliability and reduce the cost of such this application.
A PPENDIX
C ONTROL S YSTEM D ESIGN
The design of the control system has been done by means
of the frequency analysis (Bode diagrams). Since a decoupling
circuit (feedforward control) has been adopted, the direct and
quadrature axis controls can be considered completely decoupled. The controller design on the two axes can be therefore
performed separately. The following design criteria have been
followed:
1) a significant stability margin (at least 45◦ );
2) a bandwidth as high as possible;
3) a steady-state error as low as possible also for a first-order
reference input.
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Benjamin Blunier (S’07–M’07) received the Ph.D.
degree in science engineering from the Université
de Technologie de Belfort-Montbéliard (UTBM),
Belfort, France, in 2007.
Since 2007, he has been an Associate Professor at
UTBM in the research field of fuel cells, particularly
in regard to their modeling and air management.
Dr. Blunier is a member of the IEEE Industry
Applications Society.
Marcello Pucci (M’03) received the “Laurea” and
Ph.D. degrees in electrical engineering from the University of Palermo, Palermo, Italy, in 1997 and 2002,
respectively.
In 2000, he was a Host Student with the Institut
of Automatic Control of the Technical University of
Braunschweig, Braunschweig, Germany, working in
the field of control of ac machines, with a grant from
Deutscher Akademischer Austauscdienst—German
Academic Exchange Service. From 2001 to 2007, he
was a Researcher with the Section of Palermo of the
Institute on Intelligent Systems for the Automation, Palermo, where he has been
a Senior Researcher since 2008. His current research interests include electrical
machines, control, diagnosis and identification techniques of electrical drives,
intelligent control, and power converters.
Dr. Pucci is a member of the Editorial Board of the Journal of Electrical
Systems.
Giansalvo Cirrincione (M’03) received the
“Laurea” degree in electrical engineering from
the Politecnico di Torino, Turin, Italy, in 1991, and
the Ph.D. degree, with the congratulations of the
jury, from the Laboratoire d’Informatique et Signaux
de l’Institut National Polytechnique de Grenoble,
Grenoble, France, in 1998.
He spent a year of postdoctoral research with
the Department SISTA, Leuven University, Leuven,
Belgium, in 1999. Since 2000, he has been an Assistant Professor with the University of Picardie-Jules
Verne, Amiens, France. His current research interests include neural networks,
data analysis, computer vision, brain models, and system identification.
Abdellatif Miraoui was born in Morocco in 1962.
He received the M.Sc. degree from Haute Alsace
University, Mulhouse, France, in 1988, and the Ph.D.
degree and Habilitation to Supervise Research from
Franche Comté University, Besançon, France, in
1992 and 1999, respectively.
He was an Associate Professor of electrical machines with Franche Comté University. He is with
Université de Technologie de Belfort–Montbéliard
(UTBM), Belfort, France, where since 2000, he has
been a Full Professor of electrical engineering (electrical machines and energy) and where, since 2001, he has been the Director
of the Electrical Engineering Department. He is the Head of the “Energy
Conversion and Command” Research Team (38 researchers in 2007) and the
Editor of the International Journal on Electrical Engineering Transportation.
He is the author of over 40 journal and 80 conference papers and the author
of the first textbook in French about fuel cells Pile à Combustible: Principes,
Technologies Modélisation et Application (Fuel Cells: Basic Principles, Technologies, Modeling and Applications) (Ellipses-Technosup, France, 2007). He
is also a Scientific Responsible for the column “Electrical Machines” of the
important French industrial review Techniques de l’Ingénieur. His research
interests include fuel-cell energy, integration of ultracapacitor in transportation, design and optimization of permanent magnet machines, and electrical
propulsion/traction.
Dr. Miraoui is a member of several international journals and conference
committees. He is a member of the IEEE Power Electronics, IEEE Industrial
Electronics, and IEEE Vehicular Technology Societies. He was the recipient of
a Doctor Honoris Causa from Cluj-Napoca Technical University, Cluj-Napoca,
Romania. In 2007, he received the high distinction from the French Higher
Education Ministry of “Chevalier dans l’Ordre des Palmes Académiques.” He
was also distinguished as an Honorary Professor by the University of Brasov,
Romania, Romania.
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