1. Stator current and power factor optimization in an IPMSM for railway traction LOPEZ DE HEREDIA Amaia
application
Stator current and power factor optimization in an IPMSM
for railway traction application
A. Lopez-de-Heredia, C. Calleja, A. Lertxundi, A. Aranburu, T. Nieva
IKERLAN-IK4 TRAINELEC S. L.
Pº. J. M. Arizmendiarrieta, 2 - 20500 Poligono Katategi, 3 bis nº 1 - 20271
Arrasate-Mondragón, Spain Irura, Spain
Tel.: +34 / 943 71 24 00 Tel.: +34 / 943 69 08 70
Fax: +34 / 943 79 69 44 Fax: +34 / 943 69 09 12
alopezheredia@ikerlan.es, alerchundi@trainelec.com
http://www.ikerlan.es http://www.trainelec.com/
Aknowledgments
The authors gratefully acknowledge the support of the Centre for the Development of Industrial
Technology (CDTI) of the Spanish Ministry of Science, through the Strategic Consortium for
Technology Research, CENIT, called ECOTRANS.
Keywords
Traction Application, Permanent magnet motor, Rail vehicle, Control of drive
Abstract
The objective of this paper is to compare two control strategies aimed at optimizing stator current and
power factor in the constant torque operation zone on railway traction applications when interior
permanent magnet synchronous machines (IPMSM) are used. Both control strategies are the classical
“zero d-current”, which is used in most of industrial applications, and the Most Torque per Amp
(MTPA) technique, which optimizes the torque with the lowest current.
A simulation study has been carried out with different saliency interior permanent magnet syncronous
machines, in order to demonstrate that MTPA control strategy allows stator current and power factor
optimization, specially if high saliency IPMSM are used. Finally, experimental results with a full-scale
100kW prototype have been carried out, confirming the study fulfilled in simulation.
1. Introduction
At present, the squirrel cage induction machine is the preferred solution for railway traction applications
as it is considered a very robust and well-established technology. However, the cost reduction of
permanent magnets and the new quality and environmental requirements have made industry evolve
towards permanent magnet synchronous machines (PMSMs) and more and more train manufactures are
developing new traction units based on PMSMs [1] [2] [3] [4].
PMSMs provide high power density, high efficiency and small torque ripple. Besides, they are smaller
and lighter. Nevertheless, they also have some disadvantages: only one motor can be connected to an
inverter (which increases the final global cost value, even if their power is smaller) and additional
contactors are needed in order to isolate the induced voltage created by the rotating magnets from the
inverter in case of failure.
As it is well-known, radial PMSMs can be divided in two groups depending on the way the magnets are
buried. On the one hand, if permanent magnets are buried on the surface of the rotor, the machine is
called Surface PMSM (SPMSM). In this case, the machine has no saliency, so Ld=Lq (where Ld and Lq
are the longitudinal and transversal inductances respectively). On the other hand, if magnets are buried
inside the rotor, the machine is called Interior PMSM (IPMSM) and has a saliency effect, so Ld≠Lq. In
this case Lq is bigger than Ld. If the difference between the inductances is important (Lq-Ld), it is said
that the machine has big saliency. However, if the difference is small, the machine has low saliency.
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2. Stator current and power factor optimization in an IPMSM for railway traction LOPEZ DE HEREDIA Amaia
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In the IPMSM, besides the electromagnetic torque, the machine presents a reluctant torque effect, which
allows a higher torque. In addition, as magnets are inside the rotor, they are better protected against
demagnetization.
As it is well-known, the torque/speed diagram defines the working area of a drive. This characteristic
can be associated with the power/speed curve. As it is shown in Figure 1, in the first zone, the drive
works with constant torque and flux and the voltage increases with the rotating speed. Once a specific
speed is attained (base speed), the second zone starts reducing the torque value while power remains
constant due to the energy source voltage limitations. This second zone is called constant power
operation zone, where the magnetic field is reduced by injecting a flux component in opposite direction
to the magnet flux, maintaning a constant power value.
TO RQ U E
Fig. 1: Torque/speed and power/speed curves.
Railway traction application most important requirements are: field weakening possibility to operate at
high speed, capability to cope with high catenary voltage variation, limitations on the converter
switching frequency in order to limit power looses and the wide range of possible existing applications:
trams, subways, suburban trains, high-speed trains, etc. Because of these characteristics, it is often said
that IPMSM is better suited for traction applications, where field weakening is required over a wide
speed range [5] [6].
However, the use of IPMSMs not only improves constant power operation zone, but also constant
torque operation zone if an appropriate control structure is used [6]. In the constant torque zone,
although most of industrial drives use the classical zero d-current control strategy [7] [8], the Most
Torque per Amp (MTPA) strategy is also often proposed as an alternative for IPMSM [9] [10].
The objective of this paper is to compare these two control strategies, zero d-current and MTPA, in the
constant torque operation zone for a railway application IPMSM. After a short explanation of both
control strategies, a simulation study has been carried out with different saliency interior permanent
magnet syncronous machines, in order to demonstrate that MTPA control strategy allows stator current
and power factor optimization, specially if high saliency IPMSM are used. Finally, experimental results
with a a full-scale 100kW prototype have been carried out, confirming the study fulfilled in simulation.
2. PMSM Control Strategy
The electric equations of stator voltage on a PMSM (d-q reference frame) are expressed as:
⎧ di d
⎪ V d = R s i d + L d dt − ω L q i q
⎪
⎨ , (eq. 1)
⎪ V = R i + L di q + ωϕ
⎪ q s q q PM + ω L d i d
⎩ dt
where Vd and Vq are the d and q axis stator voltages, id and iq are the d and q axis stator currents, Ld and
Lq are the d and q axis inductances, ω is the electrical speed and ϕ PM the permanent magnet flux.
Stator flux module ( ϕ S ) and electromagnetic torque (T) on a PMSM (d-q reference frame) can be
represented by the following mathematical equations:
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3. Stator current and power factor optimization in an IPMSM for railway traction LOPEZ DE HEREDIA Amaia
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3 (eq. 2)
T = . p .[ϕ PM .i q − ( L q − L d ).i d .i q ]
2
ϕS = ( L d .i d + ϕ PM ) 2 + ( L q .i q ) 2 (eq. 3)
where p are the pole pairs. As it can be seen, the electromagnetic torque expression is composed of two
terms: a magnetic component and a reluctant component. Figure 2 shows the vector representation of a
PMSM.
Fig. 2: Vector diagram of a PMSM.
where Is is the stator current module, the Vs is the stator voltage module and E is the electromotive
force (j ϕ PM ω).
Regarding the PMSMs control strategy, as it is typical in the constant torque operation zone in PMSM
traction applications [2] [3], a Field-Oriented Control (FOC) with space vector modulation is used (see
Figure 3).
Fig. 3: Block diagram of FOC control strategy in PMSM.
In the literature several authors highlight the advantages of controlling the drive with optimal values, in
other words, with the optimum stator current depending on the maximum torque (MTPA) [9] on the
constant torque operation zone or with Maximum Torque per Flux (MTPF) [11] or Maximum Torque
per Voltage (MTPV) [12] in the constant power operation zone. The most widespread technique is
Maximum torque per Ampere (MTPA), which permits to obtain the maximum torque with the
minimum available current, causing less heating on the drive and consequently, a better global
efficiency. In the following lines the classical zero-d current and the MTPA techniques are introduced.
2.1. Zero d-current control strategy
This control strategy is based on the principle that in the constant torque zone, and as the permanent
magnet flux is constant, id is made equal to zero and therefore torque is just proportional to iq,
simplifying the system (eliminating the reluctant torque, see equations 4 and 5) and reducing the
computational cost.
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3
T = . p .ϕ PM .i q (eq. 4)
2
ϕ S = ϕ PM 2 + ( L q .i q ) 2 (eq. 5)
This technique is very used in industry, because of its simplicity. The main disadvantage of this control
strategy is that with interior PMSM, the obtained torque is not optimized, as the reluctant torque is not
used.
2.2 MTPA control strategy
With the maximum torque per ampere (MTPA) control strategy, the maximum torque with the
minimum total current is obtained. This current minimization improves the inverter operation, as there
are less power losses, and optimizes the machine efficiency [10]. In this case, d-axe current, id, is not
zero, and it has a negative value. Equations 6 to 9 present the mathematical representation of the torque
based on the stator current amplitude (Is) and the δ angle of the vector current so as to obtain the
position of the current vector that generates the maximum torque [9].
⎧ i d = − I s . sin δ (eq. 6)
⎨
⎩ i q = I s . cos δ
3 1 2
T = . p.[ϕ PM .I s . cos δ − .( Lq − Ld ).I s . sin 2δ ] (eq. 7)
2 2
The next step is to calculate the ‘sinβ’ value that gives the maximum torque for a specific current value.
Deriving the torque with respect to the δ angle and making it equal to 0, the required ‘sinδ’ is obtained.
This variable is positive so that id<0.
dT 2 2 (eq. 8)
= 0 = ( Lq − Ld ).I s − ϕ PM .I s . sin δ + 2( Lq − Ld ).I s . sin 2 δ
dδ
With:
2 2
− ϕ PM + ϕ PM + 8 ( L q − L d ) 2 .I s
sin δ = (eq. 9)
4 ( L q − L d ). I s
3. Simulation analysis
A simulation study has been carried out to compare both control strategies, zero d-current and MTPA,
for IPMSMs in the constant torque operation zone. As a case study a tram application has been
considered, with a 750V DC bus voltage, a traction inverter and a 100kW IPMSM. Two different
IPMSMs have been analyzed. The first one with low saliency, Lq=1.4*Ld, and the second one with high
saliency, Lq=2.8*Ld (see Table I). These values can be considered as typical for railway traction
applications [13] [14].
TABLE I.
SIMULATIONS MAIN PARAMETERS
Parameter Value
DC bus voltage 750V
Power (P) 100kW
Torque (T) 500Nm
Speed (ω) 2300rpm
PM Flux( ϕ PM ) 0.514Wb
IPMSM Lq=1.4*Ld
IPMSM 2 Lq=2.8*Ld
3.1. Calcul of MTPA current values
In MTPA control strategy, id and iq must be calculated in order to obtain the optimized stator current.
Using equation 7 and equation 9, the optimal current (in d and q axis is calculated. In order to avoid the
implementation of the complete table of calculations, which is quite hard from the computational load
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5. Stator current and power factor optimization in an IPMSM for railway traction LOPEZ DE HEREDIA Amaia
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point of view, an approximation to a thirth order polynomial is used. Figure 4 and 5 show how both
values (calculations and approximations) fix well for both low saliency machine (see Figure 4) and high
saliency machine (see Figure 5). The implementation of the MTPA control carried out with
approximated polynomials instead of the computational tables permits to minimize the complexity of
the control.
Iq table
0 180
Iq polynomial
Id table
Id polynomial 160
-5 140
120
Iq optimum (A)
-10
Id optimum (A)
100
80
-15
60
40
-20
20
0
0 50 100 150 200 250 300 350 400 450 500
-25
0 50 100 150 200 250 300 350 400 450 500 Tem reference (Nm)
Tem reference (Nm)
Fig. 4: Optimal id and iq currents depending on the demanding torque for low saliency machine.
Iq table
10
Id table 150 Iq polynomial
Id polynomial
0
-10
100
Iq optimum (A)
Id optimum (A)
-20
-30
50
-40
-50
0
-60 0 50 100 150 200 250 300 350 400 450 500
0 50 100 150 200 250 300 350 400 450 500 Tem reference (Nm)
Tem reference (Nm)
Fig. 5: Optimal id and iq currents depending on the demanding torque for high saliency machine.
3.2 Comparison between both control strategies and different saliency machines
Simulations have been carried out in the constant torque zone at a constant speed, 1000rpm, demanding
the nominal torque 500Nm. Therefore, a mecanical power around 50kW is demanded to the motor.
Next figure shows the torque variation (from 0Nm to 500Nm) and the DC bus voltage for the analyzed
four cases: both control strategies with low and high saliency IPMSMs. Left-side of Figure 6 (a and c)
shows zero d-current control strategy for both, low and high saliency machines and right-side of Figure
6 (b and d) shows MTPA control strategy for both, low and high saliency, machines. As it can be seen,
the four curves are almost equal and no differences can be identified. Thus, the same torque is obtained
whatever the control and the machine saliency is.
Torque Torque
600 600
400 400
Tem(Nm)
Tem(Nm)
Tem ref Tem ref
Tem Tem
200 200
0 0
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
time (s) time (s)
DC Bus Voltage DC Bus Voltage
800 800
780 780
Bus Voltage(V)
Bus Voltage(V)
760 760
740 740
720 720
700 700
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
time(s) time(s)
(a) (b)
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6. Stator current and power factor optimization in an IPMSM for railway traction LOPEZ DE HEREDIA Amaia
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Torque
Torque
600
600
400
Tem(Nm)
400
Tem(Nm)
Tem ref
Tem ref
Tem
200 Tem
200
0
0
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
time (s) time (s)
DC Bus Voltage DC Bus Voltage
800 800
780 780
Bus Voltage(V)
Bus Voltage(V)
760 760
740 740
720 720
700 700
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
time(s) time(s)
(c) (d)
Fig. 6. Torque and DC bus voltage for: (a) zero d-current control low saliency, (b) MTPA control low
saliency, (c) zero d-current control high saliency and (d) MTPA control high saliency machines.
Figure 7 shows d and q axis currents and the stator flux module for the analyzed four cases: both control
strategies with low and high saliency IPMSMs. Left-side of Figure 7 (a and c) shows zero d-current
control strategy for both, low and high saliency machines (note the negligible value of d current). Right-
side of Figure 7 (b and d) shows MTPA control strategy for both, low and high saliency machines. In
this case, a negative d-current is applied to the machine in order to obtain the same torque that in the
previous case but with a lower current (with the low saliency machine id=-19A and with high saliency
machine id=-43A). These values roughly match with the ones obtained in the analytical analysis (see
Figure 4 and 5). As it can be seen, the flux module is decreased in MTPA control, comparing with the
zero-d-current control, as the term Ld .id + ϕ PM is smaller (see equation 3). Besides, in high saliency
machines the flux module increases as the term Lq .iq is bigger (see equation 3).
Id Id
Id
50 50 Id filt
Id(A)
Id(A)
0 0
-50 Id -50
Id filt
-100 -100
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
time (s) time (s)
Iq Iq
200 200
150 150
100 100
Iq(A)
Iq(A)
Iq Iq
50 Iq filt 50 Iq filt
0 0
-50 -50
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
time (s) time (s)
Stator flux module Stator flux module
0.8 0.8
Fs mod Fs mod
Fs mod filt 0.7 Fs mod filt
0.7
Fs(Wb)
Fs(Wb)
0.6 0.6
0.5 0.5
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
time (s) time (s)
(a) (b)
Id Id
Id
50 50
Id filt
Id(A)
Id(A)
0 0
-50 -50
Id
Id filt -100
-100
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
time (s) time (s)
Iq Iq
200 200
150 150
100 Iq 100
Iq(A)
Iq(A)
Iq
Iq filt
50 50 Iq filt
0 0
-50 -50
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
time (s) time (s)
Stator flux module Stator flux module
0.8 0.8 Fs mod
Fs mod filt
0.7 0.7
Fs(Wb)
Fs(Wb)
0.6 Fs mod 0.6
Fs mod filt
0.5 0.5
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
time (s) time (s)
(c) (d)
Fig. 7. d and q axis currents and stator flux module for: (a) zero d-current control low saliency, (b)
MTPA control low saliency, (c) zero d-current control high saliency, (d) MTPA control high saliency.
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7. Stator current and power factor optimization in an IPMSM for railway traction LOPEZ DE HEREDIA Amaia
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Figure 8 illustrates the u phase stator current of the IPMSMs. With the low saliency IPMSM, stator
current module decreases, but only slightly (from 162A to 159.1A). However, in the simulations carried
out with the high saliency IPMSM, the MTPA strategy improves considerably the stator current as it
allows a decrease of %11.85, from 162A to 142.8A. Therefore, it can be concluded that depending on
the level of saliency of the IPMSM, the current optimization achieved with MTPA control strategy is
more or less important.
Stator current: u phase Stator current: u phase
200 200
150 150
100 100
50 50
Stator current(A)
Stator current(A)
0 0
-50 -50
-100 -100
-150 -150
-200 -200
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
time (s) time (s)
(a) (b)
Stator current: u phase Stator current: u phase
200 200
150 150
100 100
50 50
Stator current(A)
Stator current(A)
0 0
-50 -50
-100 -100
-150 -150
-200 -200
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
time (s) time (s)
(c) (d)
Fig. 8. Stator currents for: (a) zero d-current control low saliency, (b) MTPA control low saliency, (c)
zero d-current control high saliency and (d) MTPA control high saliency.
Other aspect that is worth analyzing is the machine power factor. Table II shows the obtained power
factor for the simulated four cases. The table shows that with both types of machines (with low and high
saliency) the power factor is improved considerably when the MTPA control strategy is used.
Moreover, in a IPMSM with high saliency it does not make sense to use zero d-current strategy as the
machine power factor is very low (as the high reluctant torque is not used).
TABLE II.
POWER FACTOR OF DIFFERENT SIMULATIONS
Type of control Saliency Cos phi
Zero d-current Low 0.92
MTPA Low 0.96
Zero d-current High 0.75
MTPA High 0.93
4. Experimental results
The experimental tests have been carried out using a prototype composed of a traction inverter
(developed by IKERLAN-IK4 and TRAINELEC S.L) and a 100kW Leroy Somer commercial IPMSM
(see Figure 9).
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8. Stator current and power factor optimization in an IPMSM for railway traction LOPEZ DE HEREDIA Amaia
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Fig. 9. Traction inverter and IPMSM test bench.
Experimental tests have been accomplished using a whole traction conversion chain: A DC source,
emulating the 750 DC catenary, a three phase inverter, a 100kW IPMSM and an induction machine
connected to a three phase inverter as a load (see Figure 10).
Fig. 10. Block diagram of the whole traction conversion chain.
Due to power limitation of the DC source, experimental tests have been carried out at 1000rpm and
500Nm, around 50kW are demanded to the IPMSM (the same main characteristics and conditions as in
simulation). Table III shows the IPMSM main parameters, as it can be seen, the machine used for the
experimental tests has low saliency.
TABLE III.
IPMSM MAIN PARAMETERS
Parameter Value
Power (P) 100kW
Torque (T) 500Nm
Speed (ω) 2300rpm
PM Flux( ϕ PM ) 0.514Wb
IPMSM Lq=1.4*Ld
Next figure shows the torque variation (from 0Nm to 500Nm) and the DC bus voltage in traction
application for both control strategies: on the left-side the zero d-current control and on the right-side
the MTPA control. As it has been proved in the simulation study, both curves are roughly equal. In the
experimental test, the DC bus voltage decreases during the torque transient response due to the low
capacity of the DC source.
Torque Torque
600 600
500 500
400 400
Tem(Nm)
300 300
Tem(Nm)
200 200
100 100
0 0
-100 -100
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
time (s) time (s)
DC Bus Voltage DC Bus Voltage
800 800
780 780
760 760
Bus Voltage(V)
740 740
Bus Voltage(V)
720 720
700 700
680 680
660 660
640 640
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
tiempo (s) tiempo (s)
Fig. 11. Experimental tests: Torque and DC bus voltage with zero d-current control (left-side) and with
MTPA control (right-side) with a low saliency IPMSM.
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9. Stator current and power factor optimization in an IPMSM for railway traction LOPEZ DE HEREDIA Amaia
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Figure 12 shows d and q axis currents and stator flux module for both control strategies (on the left-side
the zero d-current control and on the right-side the MTPA control). In this case, although the machine
has low saliency, differences can be identified between the curves: in MTPA control id current is equal
to -20A, while in zero d-current control id is equal to zero. In the iq current, the difference is very small
(iq current is decreased from 160A to 157A), and therefore the difference is negligleable. In MTPA
control, the stator flux module is also slighlty reduced, from 0.563Wb to 0.544Wb.
Stator current: d axis Stator current: d axis
Is d
80 80
Is d filt Is d
60 60
Is d filt
40 40
20 20
Id(A)
Id(A)
0 0
-20 -20
-40 -40
-60 -60
-80 -80
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
time (s) time (s)
Stator current: q axis Stator current: q axis
200 200
150 150
100 100
Iq(A)
Iq(A)
50 50
0 0
-50 -50
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
time (s) time (s)
Stator flux module Fs mod Stator flux module
0.65 Fs mod filt 0.65
Fs mod
Fs mod filt
0.6 0.6
Fs mod(Wb)
Fs mod(Wb)
0.55 0.55
0.5 0.5
0.45 0.45
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
time (s) time (s)
Fig. 12. Experimental tests: d and q axis currents and stator flux module with zero d-current control
(left-side) and with MTPA control (right-side) with a low saliency IPMSM.
Finally, Figure 13 shows the u phase stator current for both control strategies: left-side, zero d-current
control, and right-side, MTPA control. As the machine has low saliency, both curves are quite similar.
Stator current: u phase Stator current: u phase
200 200
150 150
100 100
50 50
Stator current(A)
Stator current(A)
0 0
-50 -50
-100 -100
-150 -150
-200 -200
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
time (s)
time (s)
Fig. 13. Experimental tests: U phase stator current with zero d-current control (left-side) and with
MTPA control (right-side) with a low saliency IPMSM.
Table IV shows the power factor obtained with both control strategies. As it is shown in the simulation
study, power factor is improved considerably using MTPA control strategy.
TABLE IV.
POWER FACTOR OF DIFFERENT EXPERIMENTAL TESTS
Type of control Saliency Cos phi
Zero d-current Low 0.91
MTPA Low 0.95
Experimental tests have confirmed the results obtained in simulation. In low saliency machines,
although the MTPA control strategy only optimizes slightly stator currents, it improves considerably the
machine power factor.
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10. Stator current and power factor optimization in an IPMSM for railway traction LOPEZ DE HEREDIA Amaia
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5. Conclusions
In this paper two different control strategies, Most Torque Per Amp (MTPA) and zero d-current, are
compared from the point of view of Interior PMSM stator current and power factor optimization on a
railway traction application.
A simulation study has been carried out to compare both control strategies in the constant torque
operation zone. As a case study a tram application has been considered, with a 750V DC bus voltage, a
traction inverter and a 100kW IPMSM. Two different IPMSMs have been analyzed. The first one with
low saliency and the second one with high saliency. The simulation study has concluded that with a low
saliency IPMSM the advantage of using MTPA techniques is limited to the power factor improvement.
However, with high saliency IPMSM, not only power factor but also stator currents are optimized.
The experimental tests have been carried out using a prototype composed of a traction inverter and a
100kW commercial IPMSM. This IPMSM has low saliency, and therefore the simulation study carried
out with the low saliency machine has been validated experimentally, showing the improvement on the
power factor.
6. References
[1] A. Jöckel and H.-J Knaak, “Intra Ice-A Novel Direct Drive System for Future High Speed Trains”, ICEM
Conference 2002.
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EPE 2011 - Birmingham ISBN: 9789075815153 P.10