Journal of Power and Energy Engineering, 2014, 2, 103-112
Published Online April 2014 in SciRes. http://www.scirp.org/journal/jpee
http://dx.doi.org/10.4236/jpee.2014.24016
How to cite this paper: Nicolae, P.-M., Nicolae, I.-D. and Smărăndescu, I.-D. (2014) On Designing of the Main Elements of a
Hybrid-Electric Vehicle Driving System. Journal of Power and Energy Engineering, 2, 103-112.
http://dx.doi.org/10.4236/jpee.2014.24016
On Designing of the Main Elements of a
Hybrid-Electric Vehicle Driving System
Petre-Marian Nicolae, Ileana-Diana Nicolae, Ionuţ-Daniel Smărăndescu
Department of Electrical Engineering, Energetics and Aeronautics University of Craiova,
Faculty of Electrical Engineering, Craiova, Romania
Received December 2013
Abstract
The paper deals with the designing of an electric drive system used for hybrid electric vehicles.
The driving system is realized with an induction motor and a voltage source inverter. Specifically,
the application is for a series hybrid vehicle powered by electric storage batteries charged by
solar batteries. In the first part of the paper the designing of the electric storage batteries and of
the photoelectric system is presented. In the second part of the paper some aspects regarding the
designing of the induction motor are presented. Then some aspects concerning the voltage source
inverter designing are exposed.
Keywords
Hybrid Electric Vehicle; Drive System; Designing; Electric Storage Batteries; Photoelectric System;
Induction Motor; Voltage Source Inverter
1. Introduction
At present, the main problems facing humanity are pollution, as that produced by industrial activities and that
produced by motor vehicles, providing food for all mankind, as well as finding new solutions for the production
of energy, because conventional sources (non-renewable) and crude oil are running low.
According to [1-3], oil is a limited source of energy, and at the current rate of exploitation of oil resources
around the globe is expected to use this resource still about 46 years [4-5]. A possible solution to reduce the
consumption of oil could be the use of alternative drive systems as hybrid electric vehicles that use electric sto-
rage batteries [6-7].
The ever increasing traffic volume has produced high levels of carbon dioxide emissions from the conven-
tional gasoline and diesel-fueled vehicles, which will contribute to a substantial increase of pollution in the ma-
jor cities all over the world, causing heavy consequences to the communities [8-11].
It has been recognized that hybrid electric vehicles are the only viable solution in order to reduce air pollution,
in particular, in large urban areas. In a hybrid electric vehicle, the electric propulsion system is intended to pro-
vide advantages over conventional vehicles equipped with an internal combustion engine. With the help of the
electric drive, the life of the internal combustion engine can be optimized, which often means low fuel con-
sumption and low emissions.

P.-M. Nicolae et al.
104
In this context the induction motor offers weight and efficiency advantages over the more conventional DC
motors, besides its traditional advantages of robustness, low cost and well established manufacturing techniques.
These motors have comparable torque and efficiency, along with a rugged, durable design. They don’t have a
drag loss when the motor turns on and they don’t lose their efficiency during high speed or low torque condi-
tions. This makes them well suited for hybrid electric vehicles.
This work presents the design of a propulsion system for a series hybrid electric vehicle powered by an induc-
tion motor. For the operation of the hybrid electric vehicle, electric storage batteries charged by solar batteries
are used.
The used block diagram of the hybrid electric vehicle is depicted in Figure 1 [12].
The parameters of the chosen hybrid electric vehicle are:
• Rated power: Pn = 60 kW;
• Range: L = 75 km;
• Induction motor pole pairs: p1 = 1;
• Vehicle speed: v = 75 km/h.
2. Sizing of the Electric Storage Batteries
For the operation of the hybrid electric vehicle are used electric storage batteries charged by solar batteries [13].
Hybrid electric vehicle running time to a speed of 50 km/h and at a distance of 160 km is:
1
L
th
v
= =
(1)
The energy required to operate the hybrid electric vehicle at a power of 8 kW and with a running time of 1 h
is:
216
n
EP tMJ= ⋅=
(2)
To have this energy it can be used electric accumulators. To do this, one chooses an accumulator that has a
capacity C of 150 Ah:
4
150150 1150360054 10C AhAs== ⋅= ⋅=⋅
(3)
The energy stored in the accumulator is:
4
648 10
AE
ENUI tJ= ⋅⋅=⋅
(4)
The number of electric accumulators is:
30
n
AE AE
E
NEN = =
(5)
Figure 1. Structure and power flow diagram for a series hybrid electric
vehicle.

P.-M. Nicolae et al.
105
The energy of a battery is:
7.2
n
AE AE
E
E MJ
N
= =
. (6)
The Ag-Zn electric storage batteries disposal is depicted in Figure 2 [14].
3. Photoelectric System Sizing
Charging of the electric storage batteries is made from a solar cells system. These batteries will not give the
same energy throughout the day [15]. The surface of the solar battery for charging the electric storage batteries
is S = 20 m2. For a system of fixed and mobile solar panels, the power can be calculated as:
.
PUIno hours η = ⋅⋅⋅
(7)
For the fixed system the efficiency is η = 0.4 and for the mobile system η = 1.
The coordinates of the operation points from the operation characteristic of the batteries (Figure 3) are calcu-
lated as follows:
3
1
11 1
1 11
201 100.48000
100(100, 80)
/ 80
PW
PU VP
I PUA
= ⋅⋅⋅=
= ⇒

= =

(8)
Figure 2. Electric storage batteries disposal.
Figure 3. The operation characteristic of the batteries.

P.-M. Nicolae et al.
106
3
2
22 2
2 22
200.8 100.46400
90(90, 71.11)
/ 71.11
PW
PU VP
I PUA
=⋅⋅⋅=
= ⇒

= =

(9)
3
3
33 2
3 33
200.7 100.45600
80(80, 70)
/ 70
PW
PU VP
I PUA
=⋅⋅⋅=
= ⇒

= =

(10)
The energy given by the mobile system is:
123
80 1006360071.11 9023600708013600239E EEEMJ=++=⋅⋅⋅+ ⋅⋅⋅+⋅⋅⋅=
(11)
The energy of the fixed system is:
239 0.45107.55E MJ=⋅=
(12)
From these calculations it is observed that the mobile system provides more energy, because this system fol-
lows the sun and provides the maximum energy in the range of given hours.
4. Aspects Concerning Induction Motor Designing
The induction motor was designed considering the following rated data:
• Rated power: Pn = 60 kW;
• Rated voltage: Un = 230/400 V;
• Speed: nN = 2985 rot/min;
• Number of pole pairs: p1 = 1.
Further in the paper, the most representative parameters and results yielded from the induction motor design-
ing algorithm are exposed.
The rated current is given by:
3 cos
NN N
UI P ϕη ⋅⋅ ⋅⋅=
(13)
where cosφ = 0.85 and η = 0.91. In this case IN = 112 A.
Next, one determines the induction motor parameters. These are: the resistances R1 and R2, the inductances L1
and L2, the coupling inductance M, and the idling current I0 [16].
Determination of the internal resistance of the motor is calculated considering the power losses as:
12
0.13 ()
NN
P RRI⋅=⋅+ ⋅
(14)
It results that: R1 = R2 = 0.08 Ω.
The idle current is given by:
00.3 33.6 N
II A = ⋅=
(15)
The inductance is determined as:
01
N
U
LI
ω
=⋅
(1 6)
where ω1 = 314 rad/s. In this case, L = 0.021 H.
The coupling inductance is:
0.9ML= ⋅
(17)
In our case M = 0.0189 H.
Steady state equations of the induction motor are:
11
()
dq qr
URILI MI ω =⋅−⋅⋅+ ⋅
(18)
21
()
qddr
URILIMI ω =⋅+⋅⋅+ ⋅
(19)
1
0( )()
drqr q
RILI MI ωω =⋅− −⋅⋅+⋅
(2 0)

P.-M. Nicolae et al.
107
1
0( )()
qrdr d
RILI MI ωω =⋅+ −⋅⋅+⋅
(21)
Control of the algorithm takes into account the electromagnetic torque function in the form:
1() elmgdr qdqr
MpM IIII=⋅⋅ ⋅−⋅
(22)
The maximum of the function is analyzed by considering the method of Lagrange multipliers. One imposes a
maximum stator current:
22 22
16,307.2
dq N
III A+= =
(23)
For the stator flux Ψs one imposing a value closes to the magnetic saturation (Ψs=1.3 Wb) [17]:
2 22
()( )
sddrq qr
LIMILI MIΨ=⋅+⋅+⋅+⋅
(24 )
For the induction motor starting, the voltages Ud and Uq are written as:
11
()
ddq qr
UR ILIMI ω =⋅−⋅⋅+ ⋅
(25)
11
()
qq ddr
UR ILIMI ω =⋅+⋅⋅+ ⋅
(26)
and the following values are obtained: ω1 = 8.21 rad/s; Ud = 0.064 V; Uq = 9.626 V.
Hybrid electric vehicle operation at rated speed is given by:
400 ()
0( )
0( )()
0( )()
()
(2/ 60)3
dqqr
qd dr
drNqrq
qrNdrd
Nq drdqr
NN
RILI MI
RILIMI
RILIMI
RILIMI
MMII II
n
ω
ω
ωω
ωω
ωπ
=⋅−⋅ ⋅ +⋅

=⋅ +⋅⋅ +⋅

=⋅−− ⋅⋅+⋅

=⋅+− ⋅⋅+⋅

= ⋅⋅ −⋅

= ⋅⋅⋅

(27 )
and has the next results: Id = −31.409 A; Iq = 298.02 A; Iqr = −328.49 A; Idr = 32.253 A; MN = 13.331 Nm; ωN =
312.4 rad/s.
The obtained voltages are: Ud = 15.17 V; Uq = 25.36 V.
Regenerative braking of the hybrid electric vehicle is given by:
400 ()
0( )
0( )()
0( )()
()
dqqr
qd dr
drN qrq
qrN drd
Fq drdqr
RILI MI
RILIMI
RILIMI
RILIMI
MMII II
ω
ω
ωω
ωω
=⋅−⋅ ⋅ +⋅
=⋅ +⋅⋅ +⋅

=⋅−− ⋅⋅+⋅

=⋅+− ⋅⋅+⋅

= ⋅⋅ −⋅

(28)
The obtained results are:
7.557
306.76
273.54
4.262
14.36
d
q
qr
dr
F
IA
IA
IA
IA
M Nm
=

= −

=

= −

= −

(29)
5. Designing of the Voltage Source Inverter
5.1. Choosing the Power Electronics for the Converter
The designing of the VSI was performed in a MATLAB module and is based on the following rated data:
• Rotor AC line voltage: Uaclinerot = 400 V;

P.-M. Nicolae et al.
108
• Rotor rated current: Inrot = 112 A;
• Fundamental frequency: f = 25 Hz;
• Effective value of the rectified output voltage: Uef = 653.2 V;
• Rated current amplitude for the rotor:
2
namrot nrot
II= ⋅
= 158.4 A;
• Rated average current: Imed = 0.9∙Imed = 100.8 A;
• Ripple current, considering a peak of 5%: ILripple = 0.05∙Inamrot = 7.91 A.
5.2. Characteristic Parameters of the Voltage Source Inverter
The designing method is used for a wide range of engines and voltages. The sizing of the voltage source inverter
was made for a traction motor with the power of 60 kW and a voltage of 400 VAC. The maximum voltage that
the voltage source inverter can supply for the motor is determined by the main supply voltage.
Characteristic and functional parameters, from which the sizing of the voltage source inverter was performed,
are the following:
• Supplying voltage: Ua = 110 V (−30% ÷ +20%);
• Input filter parameters: Cf = 1000 μF; Lf = 3.96 mH;
• Operating frequency: fL = 2 kHz;
• Induction motor rated current: In = 112 A.
The simplified diagram of the inverter is depicted in Figure 4.
5.3. Calculation of the Conduction Time
Full conduction time t1 is determined from the condition that the average voltage at the motor terminals not to
exceed its rated voltage, respectively Un = 400 V.
For the switching period
3
1/0.0005 10
L
Tf s
−
= =⋅
and the supplying voltage Ua = 110 V, results:
3
1
0.0037 10
n
a
TU
ts
U
−
⋅
= =⋅
(30)
Changing of the voltage average value is achieved by changing the time length of the conduction, while
maintaining a constant switching period (corresponding to an operating frequency of 2 kHz).
5.4. Calculation of the Average Current through the IGBT
The average current through the static contactor is a fundamental criterion for choosing it. The average current
value is computed by mediation instantaneous values corresponding to a period:
00
11
sin( )
2
T
med Tn
IidtIt dt
T
π
ωω
π
== ⋅
∫∫
(31)
The current through the IGBT Iigbt is obtained with:
2n
igbt
I
I
π
⋅
=
(3 2 )
In this case, Iigbt = 38.98 A.
Since the induction motor is 60 kW/480 V, then the maximum current of the motor Imax is given by:
Figure 4. Voltage source inverter diagram.

P.-M. Nicolae et al.
109
max 1.5 n
II= ⋅
. (3 3)
In our case Imax = 129.90 A.
The average value corresponding to the maximum motor current is:
max
1
2
med
I
I
π
⋅
=
(34)
In this case, Imed1 = 58.47 A.
5.5. Network Filter Sizing
The network filter limits to a very large extent the switching surges and protects the equipment against net-
work’s short duration voltage variations. Short-term variations of the voltage applied to the equipment are
largely caused by instability of the galvanic connection between the sensors and the contact line [18].
Natural frequency of resonance (f0) for the filter is given by:
0
1
2
f
fLC
π
=⋅⋅
(35)
In this case, f0 = 79.97 Hz.
In order to not fall into the spectrum fn of the harmonics produced by the inverter, f0 must be lower than the
lowest operating frequency of the inverter, meaning f0 < fmin. Because fmin = f = 2 kHz and f0 = 79.97 Hz, the
above condition is satisfied.
5.6. Choosing the Switching Transistors
Depending on the parameters Imax and the rated voltage imposed, from the catalog of SEMIKRON manufacturer
of electronic components was chosen the following IGBT model: SKM900GA12E4 (SEMITRANS), which sa-
tisfies the conditions [19-20 ]:
maxmax log
900
cata
II A≤=
(36)
log 1200 a ncata
UU V≤=
(37)
5.7. Choosing and Verification of the Cooling System
The dissipation of the heat that is generated in the semiconductor during conduction is made via an aluminum
radiator that is cooled with forced air flow. Radiator sizing criteria is that the semiconductor junction tempera-
ture does not exceed the limit specified by the manufacturer, namely 175 °C under long-term.
The radiator is a subset of the equipment, with the aim of maintaining the temperature within limits for the
proper functioning of the equipment, especially IGBT.
The thermal effects of the electric current peak by conduction state represent the worst case during operation.
Other important computed parameters are:
• Switching losses of the transistor:
( )
52.37
medT
comTon offcom
ccref
I
P EEfW
I
= +⋅⋅=
(38)
• Conduction losses of the transistor:
1
216.48
condTCEsat cmed
t
P UIW
T
=⋅⋅=
(3 9)
• Average current through the antiparallel diode:
2 /3
00
11
sin( )
2
T
med Tn
IidtIt dt
T
π
ωω
π
= =⋅
∫∫
(40 )

P.-M. Nicolae et al.
110
23 60.42
4
n
med
I
IA
π
⋅⋅
= =
(41)
• Antiparallel diode switching losses:
()
8.73
medD
comDon offcom
ccref
I
P EEfW
I
= +⋅⋅=
(42)
One used data catalog for voltage drops at saturation. The total average power generated inside the case by a
module is:
257.92
TD
PP PW=+=
(43)
Total losses on all three phases [21]:
3 737.77
phase
PP W=⋅=
( 44)
Was made the preliminary selection of the radiator type P16_300_16B, with the technical characteristics spe-
cified in the catalog tab, cooled by an air flow produced by the fan type SK-Heat Sink P16_300_16B, with the
technical characteristics specified in the catalog of the manufacturer.
Junction over-temperature corresponding to the average power previously computed is checked within the
chosen cooling conditions:
0j th
TTT PR ∆= − =⋅
∑
(45)
The absolute temperature of the junction depends on the maximum ambient temperature specific to the tem-
perate climate: T0 = 40˚C.
The thermal resistances involved in this calculation are specified in the power transistor catalog, respectively
the radiator catalog:
• Thermal resistance junction—capsule for IGBT:
RthjcT = 0.035 K/W;
• Thermal resistance junction—capsule for diode:
RthjcD = 0.041 K/W ;
• Thermal resistance capsule—radiator:
Rthcr = 0.038 K/W;
• Thermal resistance of the radiator, at forced cooling with an air flow of 295 m3/h:
Rthr= 0.031˚C /W.
The average temperature of the junction is computed both for IGBT, and for antiparallel diode located in the
same capsule.
The general relation for calculating the junction temperature is:
0
()
jthjc thcr thr
TT PRRR= +⋅++
(46)
Junction temperature for IGBT is obtained with:
0
( )()
341.11 448.15
jTcomT condTthjcTthcrthr
TTPPRR R
KK
=+ +⋅ ++
= <
(47)
In this case TjT = (341.11 – 273.15) = 67.96˚C.
For the antiparallel diode, the junction temperature is computed with:
0
( )()
320.12448.15 .
jDcondD comDthjcDthcrthr
TTPPRR R
KK
=++ ⋅ ++
= <
(48)
In this case: TjD = 320.12 – 273.15 = 46.97˚C.
The results show that the cooling condition is fulfilled, namely:
175(448,15 )
j jad
TTC orK≤=°
( 49)

P.-M. Nicolae et al.
111
Results a factor of safety in heating of 67.96/175 = 0.388, which shows that the sizing of cooling conditions
has been rigorously made, without large reserves and so without undue consumption of materials and within a
minimum possible size.
For reliability an IGBT transistor was chosen with rated data higher than those considered to be adequate to
the rated data of the induction motor.
Evaluating the results obtained by the sizing methods is observed that an optimal configuration was used [22].
6. Conclusions
The paper was intended for a study on hybrid electric vehicle driving systems and on electric storage batteries
they use. The advantages of the electric drive system with the induction motor and voltage source inverter re-
vealed that it satisfies the requirements of the present application. The drive systems based on the induction mo-
tor will eliminate the most disadvantages of DC drive systems.
The results obtained from the designing algorithm of the induction motor show that an optimal configuration
was used.
In the paper was also presented a sizing algorithm for the power components of the voltage source inverter.
Choosing of the power semiconductor devices was made from the data catalog of a producer of electronic com-
ponents and the results obtained by computing were in good agreement with those from the catalog.
One can conclude that is possible to design propulsion system for a hybrid electric vehicle with the given
rated data for the specified application and the required performance.
Given that the conventional means of transport (with internal combustion engine) are the main source of
chemical and noise pollution on the planet, h ybrid electric transportation systems are a more viable alternative
for transporting people and goods.
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