`
`PROPULSION SYSTEM DESIGN OF ELECTRIC VEHICLES
`
`Mehrdad Ehsani
`
`Fellow, IEEE
`
`Khwaja M. Rahman
`Student Member, IEEE
`
`Hamid A. Toliyat
`Member, IEEE
`
`Texas Applied Power Electronics Center
`Department of Electrical Engineering
`Texas A&M University
`College Station, TX 77843-3128
`Fax: (409) 845-6259
`to its self starting capability. However, soon after the
`introduction of electric starter for ICE early this century.
`despite being energy efficient and nonpolluting, EV lost the
`battle completely to ICE due to its limited range and
`inferior performance. Since
`then ICE has
`evolved,
`improved in design. and received wide spread acceptance
`and respect. Although this essentially being the case, EV
`interest never perished completely, and whenever there has
`been any crisis regarding the operation of ICE automobiles,
`we have seen a renewed interest for EV. The early air
`quality concerns in the 60’s and the energy crisis in the
`70’s have brought BVs back to the street again. However,
`the most
`recent environmental awareness and energy
`concerns have imposed,
`for
`the first
`time since its
`introduction, a serious threat to the use of ICE automobiles.
`Electric Vehicles
`offer
`the most promising
`solutions to reduce vehicular emission. Electric vehicles
`
`Abstract:
`
`There is a growing interest in electric vehicles due to
`environmental concerns. Recent efforts are directed toward
`
`developing an improved propulsion system for electric vehicle
`applications. This paper is aimed at developing the system design
`philosophies of electric vehicle propulsion systems. The vehicle‘s
`dynamics are studied in an attempt to find an optimal torque-
`speed profile for the electric propulsion system. This study
`reveals that the vehicle‘s operational constraints such as: initial
`acceleration and grade can be met with minimum power rating if
`the powertrain can be operated mostly in constant power region.
`Several examples are presented to demonstrate the importance of
`the constant power operation. Operation of several candidate
`motors in the constant power region are also examined. Their
`behaviors are compared, and conclusions are made.
`I. Introduction
`
`the present is a major
`The ICE automobile at
`source of urban pollution. According to figures released by
`the US Environmental
`Protection Agency
`(EPA).
`conventional ICE vehicles currently contribute 40-50% of
`ozone, 80-90% of carbon monoxide. and 50—60% of air
`toxins found in urban areas [1]. Besides air pollution, the
`other main objection regarding ICE automobiles is its
`extremely low efficiency use of fossil
`fire]. Hence,
`the
`problem associated with ICE automobiles are three fold.
`environmental, economical. as well as political. These
`concerns have forced governments all over the world to
`consider alternative vehicle concepts. The California Air
`Resource Board (CARB) is among the few who acted first
`through the declaration of the Clear Air Act of September,
`1990. This act requires that 52% of all vehicles sold in that
`state be either Low Emission Vehicles (LEV’s)— 48%, Ultra
`Low Emission Vehicles (ULEV’s)— 2%. or Zero Emission
`Vehicles (ZEV’s)- 2%, by the year of 1998 [2]. Similar
`measures are considered in other states and nations, as well.
`
`(EV) was
`The concept of Electric Vehicle
`conceived in the middle of previous century. After the
`introduction of internal combustion engine (ICE), EVs
`remained in existence side by side with ICE for several
`years. The energy density of gasoline is far more than what
`the electrochemical battery could offer. Despite this fact,
`the EV continued to exist, especially in the. urban areas due
`
`constitute the only commonly known group of automobiles
`that qualify as Zero Emission Vehicle (ZEV). These
`vehicles use an electric motor for propulsion, and batteries
`as electrical energy storage devices
`This paper presents the EV propulsion system
`design philosophies. The paper is organized as follows.
`Section II describes the design constraints and the variables
`for EV system. Design philosophies of EV propulsion
`systems are presented in sections 111. Section IV examines
`several most commonly used motors for EV system design.
`Section V compares our designed EV with the General
`Motors IMPACT. Summary and conclusions are presented
`in Section VI.
`
`11. Specifications of EV Propulsion System Design
`A. System Design Constraints
`Vehicle operation consists of three main segments.
`These are, i) the initial acceleration, ii) cruising at vehicle
`rated speed, and iii) cruising at the maximum speed. These
`three operations provide the basic design constraints for the
`EV drivetrain. A drivenain capable of meeting these
`constraints will function adequately in the other operational
`regimes. Refinements to these basic design constraints are
`necessary for an actual commercial product, but those are
`beyond the scope of this paper. The objective here is to
`
`0-7803-2775-6/96 $4.00 © 1996 IEEE
`
`Page 1 of 7
`
`FORD 1436
`
`FORD 1436
`
`

`

`meet these constraints with minimum power. The variables
`defining the above design constraints are:
`(i) Vehicle rated velocity, v".
`(ii) Specified time to attain this velocity, tf.
`(iii) Vehicle maximum velocity, me .
`(iv) Vehicle mass, and other physical dimensions.
`B. System Design Variables:
`its electrical
`The main component of EV is
`powertrain. The electric propulsion design variables are:
`i) Electric motor power rating.
`ii) Motor rated speed.
`iii) Motor maximum speed.
`iv) The extend of constant power speed range,
`beyond the rated speed.
`v) Gear ratio between motor shaft and the wheel
`shaft (transmission).
`As mentioned earlier, the main design objective is
`to find the minimum drive weight, volume and cost that will
`meet the design constraints with minimum power.
`C. Road Load Characteristics
`
`The road load (F...) consists of rolling resistance
`(fm), aerodynamic drag (f1), and climbing resistance (f,,) [3].
`Fw = fr0 + f1 + fst
`(1)
`The rolling resistance (fm) is caused by the tire
`
`deformation on the road:
`
`(2)
`_
`fr0=f~m-g
`where f is the tire rolling resistance coefficient. It increases
`with vehicle velocity, and also during vehicle turning
`maneuvers. Vehicle mass is represented by m, and g is the
`gravitational acceleration constant.
`Aerodynamic drag, fl, is the viscous resistance of
`air acting upon the vehicle.
`(3)
`'
`r, = osgchw + v0)2
`where E, is the air density, Cw is the aerodynamic drag
`coefficient, A is the vehicle frontal area, v is the vehicle
`
`speed. and Va is the head wind velocity.
`positive
`(f,, with
`The
`climbing
`resistance
`operational sign) and the down grade force (f,, with
`negative operational sign) is given by
`f3, = m- g-sina
`where Otis the grade angle.
`The following assumptions will be made in the
`analysis prsented in the following sections, unless otherwise
`specified.
`
`(4)
`
`(i) velocity independent rolling resistance
`(ii) wro head wind velocity
`(iii) level ground
`These assumptions do not change the general trend
`of the solution and can be easily relaxed.
`The motive force F available from the propulsion
`system is partially consumed in overcoming the road load,
`Fw. The net
`force, F—Fw. accelerates the vehicle (or
`
`decelerates when Fw exceeds F). The acceleration is given
`by
`
`F — Fw
`
`a
`
`(5)
`
`km -m
`where kIn is the rotational inertia coefficient to compensate
`for the apparent increase in the vehicle’s mass due to the
`on-board rotating mass.
`III. EV System Design
`its
`The main component of EV drivetrain is
`electric motor. The electric motor in its normal mode of
`
`operation can provide constant rated torque up to its base or
`rated speed. At
`this speed,
`the motor reaches its rated
`power limit. The operation beyond the base speed up to the
`maximum speed is limited to this constant power region.
`The range of
`the constant power operation depends
`primarily on the particular motor type and its control
`strategy. However, some electric motors digress from the
`constant pOWer operation, beyond certain speed, and enter
`the natural mode before reaching the maximum speed. The
`maximum available torque in the natural mode of operation
`decreases inversely with the square of the speed. This range
`of operation is neglected in the analysis presented in this
`section. unless otherwise specified.
`It is assumed that the
`electric motor operates in the constant power region beyond
`the base speed and up to the maximum speed. Nevertheless,
`for some extremely high speed motors the natural mode of
`operation is an appreciable part of its total torque-speed
`profile. Inclusion of this natural mode for such motors may
`result in a reduction of the total power requirement. Of
`course, power electronic controls allow the motor
`to
`operate at any point in the torque speed plane, below the
`envelop defined by the mentioned limits. However, it is the
`profile of this envelop that is important in the motor drive
`selection and design.
`In order to free up the motor speed from the
`vehicle speed, for design optimization. gearing between the
`motor shaft and the drive shaft is required. In our design,
`we will make the following assumptions.
`(i) single gear ratio transmission operation: power
`electronic control allows instantaneous matching of the
`available motor torque with the required vehicle torque, at
`any speed. Therefore, multiple gearing in order to match
`the motor torque-speed to the vehicle torque-speed is no
`longer a necessity.
`(ii) ideal loss free gear: without loss of generality.
`the gear losses can be incorporated at the end of analysis.
`The gear
`ratio and size will depend on the
`maximum motor speed, maximum vehicle speed, and the
`wheel radius. Higher maximum motor speed, relative to
`vehicle speed, means a higher gear ratio and a larger gear
`size. The selection criterion for the maximum motor speed
`will be further discussed later. The torque speed diagram of
`a typical motor is drawn in Fig. l, but in terms of tractive
`force and vehicular speed for different gear ratios. Notice
`
`Page 2 of 7
`
`FORD 1436
`
`FORD 1436
`
`

`

`
`
`form solution for the motor rated power Pm. The insight
`gained from the closed form solution is also valid for the
`more practical design involving running resistances.
`With these simplifying assumptions the governing
`differential equation reduces to:
`dvF
`a = E = ; (assuming km=1)
`
` o
`
`20
`
`so
`40
`Veticle Speed (mom
`
`so
`
`100
`
`Fig. 2. Typical torque-speed profile of electric motor in terms of
`tractive force and vehicular speed.
`
`solved with the
`This differential equation is
`previous boundary conditions and the force-speed profile of
`Fig. 2. The differential equation is integrated within the
`acceleration interval of O-vn, in O-tf Seconds, in order to get
`a closed form solution for the rated power Pm.
`v"
`t
`
`m g = jdt
`o F
`o
`The left hand side integral is broken into two parts, the O-
`vrm constant force operation and the vm-vn constant power
`operation
`
`(6)
`
`
`dv
`
`= tf
`
`(7)
`
`V“
`dv
`"'
`m! ——+ ml
`0 PIn / vrm
`V... Pm / v
`New solving for Pm, we get
`m
`P =—(v,2m+va)
`"‘
`2tf
`For minimum motor power, differentiating P... with
`respect to v,.ll and setting it to zero gives
`
`(8)
`
`v"n = 0
`This establishes a theoretical
`
`(9)
`limit for minimum
`
`motor power. For vm=0, the electric motor operates entirely
`in the constant power region. Therefore, if the motor is
`performing 0-v.,, in t, seconds in constant power alone, the
`power requirement is minimum. On the other hand. if the
`motor operates in the constant torque (force) region during
`the entire O‘tf period, we will have vm=vw. In this case, eq.
`(8) shows that
`the power requirement
`is twice that of
`
`now the electric motor base speed and maximum speed, in
`terms of the vehicle speed, depend on the gear ratio. A
`design methodology based on the three regions of operation
`will now be presented.
`A. Initial Acceleration:
`
`The force-velocity profile of a typical motor is
`redrawn once again in Fig. 2. In this figure, v,,..
`is the
`electric motor
`rated speed, v“, is the vehicle rated speed
`and vw is
`the vehicle maximum speed. The motor
`maximum speed must correspond to this vmx, after the gear
`ratio transformation.
`
`Wind Rams-11 imh
`
`0
`
`50
`
`100
`VendeSpecdmtpn)
`
`150
`
`200
`
`Fig. 1. Torque-speed diagram of an electrical motor in terms of
`tractive force and vehicular speed with gear size as the parameter.
`
`The range of operation for initial acceleration is 0-
`v”. For now, we will focus our attention only on this
`interval. For maximum acceleration the motor operates in
`constant rated force (torque), FW=Pmlvm up to the motor
`rated speed V“, and in constant power (PEPE/v) at speeds
`beyond the base speed, up to the vehicle rated speed vw.
`Here, Pm is the motor rated power. We assume vw>v.m. The
`wisdom of this assumption will become clear, shortly. The
`differential equation describing the performance of the
`system is given by eq.
`(5) and is repeated here for
`convenience.
`
`dV
`a = — _
`
`F — Fw
`
`km ~m
`dt
`F is the motive force available from the propulsion
`system and Fw is the running resistance (road load). The
`boundary conditions are
`at t=0, vehicle velocity v=0.
`.
`at t=t;, vehicle velocity v=v,,,.
`To gain insight, we will solve eq. (5) under the most
`simplifying assumptions:
`i) The vehicle is on a level ground.
`ii) The rolling resistance is zero.
`iii) Aerodynamic drag is zero.
`we will relax these assumptions later for a more realistic
`solution. The above assumptions will result
`in a closed
`
`Page 3 of 7
`
`FORD 1436
`
`FORD 1436
`
`

`

`
`
`constant power Operation. The solid line curve of Fig. 3
`shows an example of the motor power
`requirements
`between these two extremes. Of course, operation, entirely
`in constant power regime,
`is not practically realizable.
`However,
`this theoretical discussion demonstrates that
`longer constant power range of operation will lower the
`motor power.
`Having discussed the simplified resistanceless
`case, we now solve the more realistic case, involving the
`running resistance. The vehicle differential equation (5) can
`
`120
`
`110
`
`§
`
`(KW) 8
`
`
`
`MotormienPower
`
`10
`
`20
`30
`40
`Motor Rated Speed Vrm (mph)
`
`50
`
`60
`
`Fig. 3. Acceleration power requirement as a function of
`motor rated speed. Solid line curve— resistanceless case,
`dashed curve- in the presence of road load.
`
`be solved under the same boundary conditions as before
`with the presence of the running resistance Fw.
`In this case.
`a closed form solution is feasible. However, the result is a
`
`transcendental equation involving rated motor power Pm,
`rated motor velocity vm,
`rated vehicle velocity v”,
`acceleration time tf, and all the other system constants, e.g.;
`vehicle ' mass m,
`rolling
`resistance
`coefficient
`f,
`aerodynamic drag coefficient Cw, etc. The resulting
`equation can be solved numerically for Pm for a specific
`motor rated velocity V“... using any standard root seeking
`method such as the secant method [4].
`Let’s assume that it is desired to obtain PIn for the
`following case
`- 0—26.82 m/s (0—60 mph) in 10 seconds.
`- vehicle mass of 1450 kg.
`- rolling resistance coefficient of 0.013.
`- aerodynamic drag coefficient of 0.29.
`- wheel radius of 0.2794 m (11 inch).
`- level ground.
`- zero head wind velocity.
`a plot of the resulting motor rated power vs. motor rated
`speed, in terms of vehicle speed,
`is shown in Fig. 3 (the
`dashed curve).
`Examination of Fig. 3 (the dashed curve) results in
`the following conclusions:
`
`i) Rated power versus vm. curve shows the same
`general trend of the resistanceless case.
`ii) Rated motor power requirement is minimum for
`continuous constant power operation (vm,=0).
`iii) Rated motor power is roughly twice that of
`continuous constant power operation for constant force
`(torque) operation (vn,=vm).
`remains close to its
`iv) Rated motor power
`minimum up to about 20 mph of rated motor speed and
`then grows rapidly.
`B. Cruising at Rated Vehicle Velocity.-
`A powertrain capable of accelerating the vehicle to
`the rated velocity v“, will always have sufficient cruising
`power at this speed. Hence, the constraint of cruising at
`rated vehicle speed is automatically met for the
`case of
`EV. Of course. cruising range is another issue, related to
`the battery design, which is outside the scope of this paper.
`However, minimizing power of the drive will help the
`battery size.
`C. Cruising at Maximum Vehicle Velocity:
`The power requirement
`to cruise at maximum
`vehicle speed can be obtained as
`
`Pvmax =(f,o+fst)-vm,(+f‘(v)-vmax
`(10)
`Since aerodynamic drag dominates at high speeds,
`this power
`requirement
`increases with the cube of
`maximum vehicle
`velocity.
`If
`this
`vehicle
`power
`requirement is greater than the motor power calculated
`previously (Pmu>Pm),
`then Pm“ will define the motor
`power rating. HOWever, in general Pm will dominate Pm,
`since modern vehicles are required to exhibit a high
`acceleration performance. As mentioned before,
`some
`extremely high speed motors usually have three distinct
`modes of operation. The initial constant torque operation,
`followed by a range of constant power operation, then to
`the maximum speed in natural mode (see Fig. 2). For such a
`motor it may be advantageous to use the entire constant
`power range for initial acceleration of the vehicle. The
`operation beyond that would be in the natural mode. This
`would allow a longer constant power operation in the initial
`acceleration. Consequently. the motor power requirement
`will be lower. This scheme will work provided the motor
`has adequate torque in natural mode to meet the constraints
`at the maximum vehicle speed. Otherwise some part of the
`constant power operation has to be used for the vehicle
`operation beyond the rated vehicle speed.
`V
`the
`Natural mode of motor operation is not
`preferred mode
`beyond
`the
`rated
`vehicle
`speed,
`unfortunately no control algorithm exists, presently,
`to
`operate some high speed motors entirely in constant power
`beyond their base speed. However, the natural mode,
`if
`included, can lower the overall power requirement. The
`speed at which the electric motor can enter the natural
`
`Page 4 of 7
`
`FORD 1436
`
`10
`
`FORD 1436
`
`

`

`(11)
`
`VN = Vmx
`
`mode and still meet the power requirement at maximum off between maximum motor speed and the gear size.
`vehicle speed is obtained from
`However,
`this tends to be more in favor of selecting a
`medium or high speed motors. For an extremely high speed
`motor, a sophisticated gear arrangement might be necessary
`for speed reduction. Planetary gear arrangement [5] could
`be th? choice,
`that
`is compact but allows high 5PM
`reductlon. Extended constant power range. on the other
`hand, will increase drive shaft torque and stress on the
`gear- Hence, another design tradeoff is involved between
`the gear stress and the extended constant power range. It
`can be seen from the results 0f table I that am” a certain
`point there is “0‘ any appreciable power reduction With
`extended constant power range. Any further extension of
`constant power range beyond this point will only adversely
`
`
`p
`"m“
`Pm
`Note that tile initial acceleration power is also a function of
`VN (extended Constant power ranger). Hence, vN and Pm have
`[0 be solved iteratively. Also, the gear ratio between the
`drive shaft and the motor shaft
`is to be determined by
`matching vN Willi the motor speed at which it enters the
`natural mode. More discussion about the natural mode of
`operation appears in section IV. The rest of the analysis is
`done assuming constant power operation beyond the base
`speed up to the maximum speed.
`The importance of extending the constant power
`speed range can be better understood by comparing the
`required motor power for different constant power speed
`ranges (as a multiple of its base speed). Table I shows an
`example of power requirement for several constant power
`ranges for the following case:
`i) Maximum motor speed is 10,000 rpm.
`ii) Maximum vehicle speed is 44.7 mls (100 mph).
`iii) Other system variables and constants are the
`same as the previous example.
`to match the
`ratio,
`Here,
`the required gear
`maximum motor speed to the maximum vehicle speed. for a
`wheel radius of 0.2794 in (11 inches),
`is 126.55. The
`results of Table I suggest an extended range of 4 to 6 times
`Fig. 4. Rated motor shaft torque as a function of maximum motor
`speed.
`the base motor speed in order to significantly lower the
`the gearing and drive shaft appreciably without
`’ affect
`motor POW." requirement. '
`.
`reducing the power requirement. This will set the upper
`Finally. we examine the effect of manmum motor
`limit of the extended range of the constant power operation.
`Speed and the extended constant power range 0" ‘h" overall
`Overall. the EV drive system design philosophy
`system pcrformancc- The power
`requirement
`is not a
`function of the motor maximum speed. Motor maximum can besummarized as:
`speed only affec“ the gear 5116- However, maximum speed
`i) Power requirement for acceleration decreases as
`
`
`
`Table 1: EV Power requirement as a function of constant power range.
`
`
`
`_—
`_———_——
`
`
`
`————unn
`
`the range of constant power operation increases. More
`has a pronounced effect on the rated torque of the motor.
`specifically, as the ratio of the vehicle rated speed to motor
`An example of this is illustrated in the surface plot of Fig.
`rated speed increases.
`4. Low speed motors with extended constant power speed
`ii) The gear ratio between the electric motor and
`range have a much higher rated shaft torque. Consequently,
`the drive shaft is determined by the motor and’ vehicle
`they need more iron to support this higher flux and torque.
`Furthermore, higher torque is associated with higher motor maximum speeds.
`the
`cruising at
`for
`requirement
`and power electronics currents. This will also impact the
`iii) Power
`power converter
`silicon size
`and conduction losses. maximum vehicle speed is obtained directly from the road
`Extended speed range, however,
`is necessary for initial
`resistance at maximum speed.
`In general,
`this power
`acceleration as well as for cruising intervals of operation.
`requirement will be
`lower than the initial acceleration
`Therefore, the rated motor shaft torque can only be reduced
`power requirement.
`through picking a high speed motor. This would however
`iv) High speed motors would be more favorable
`affect the gear ratio. A good design is the result of in trade
`for EV application, in general.
`
`Page 5 of 7
`
`FORD 1436
`
`11
`
`FORD 1436
`
`

`

`
`
`the BLDC motor makes it appear inferior to the induction
`IV. Electric Propulsion Systems for EV Design
`An electric propulsion system comprises of three motor, despite its high power factor and high efficiency.
`main elements: power electronic converter, motor, and its
`The extremely high speed operation of the SRM and its
`controller. This section is devoted to examining several
`relatively longer constant power range helps it to overcome
`most commonly used motors
`for EV propulsion. The
`some of the difficulty associated with its lower power factor
`importance of extended speed range, under constant power
`operation. Furthermore, the SRM converter is simpler and
`operation of electric motors in EV system design was
`easier to control.
`Table II: Motor data.
`
`
`
`RatedSnd m m—a—
`8750
`
`—m_ 12.25
`
`20000
`123
`Rest in Natural Mode
`
`established in the previous section. This mode of operation
`V. Comparison of our Designed EV and General
`is referred to as field weakening, from its origin in do motor
`Motors IMPACT.
`drives. Therefore, this section will concentrate mainly on
`In this section an EV prototype is discussed. The
`the field weakened extended speed operation of the EV
`actual design specifications of this vehicle are compared
`motors. A more detailed study of these motors for EV
`with our theoretical design of the same vehicle, based on
`propulsion application is presented in [6].
`the ideas presented in this paper. The EV is the General
`
`Table III: Rated power and converter volt-ampere requirements for the motors of
`Table ll for pica] EV - u-lication.
`
`
`
`- Vehicle Rated Speed of 26.82 m/s (60 mph).
`- Required acceleration of 26.82 this
`in 10
`
`seconds.
`
`Motor corporation IMPACT car.
`Design Example
`We present a design example of some most General Motors Electric Vehicle IMPACT
`commonly used motors in the constant power region. This
`General Motors announced the first version of its
`example will help clarify the capabilities of these motors
`electric vehicle, IMPACT. in January, 1990. Over the years
`for vehicle applications.
`there have been several modifications of the IMPACT. The
`EV data:
`following are the most
`recent
`specifications of
`the
`IMPACT. We have included only those features which are
`pertinent to this study.
`Performance:
`0—26.82 m/s
`
`(0-60 mph) acceleration in 8.5
`
`- Vehicle maximum speed of 44.7 m/s (100 mph).
`- Vehicle mass of 1450 kg.
`T0p speed of 35.76 m/s (80 mph).
`- Rolling resistance coefficient of 0.013.
`Dimensions:
`- Aerodynamic drag coefficient of 0.29.
`Frontal area 2.2578 m2.
`- Frontal Area of 2.13 ml.
`Drag coefficient 0.19.
`- Wheel radius of 0.2794 in (11 inch).
`Curb weight 1347.17 kg.
`- level ground.
`Design Features:
`.
`- zero head wind.
`102.16 kW three phase induction motor.
`The motor data are shown in Table II. The motor
`lGBT power inverter module— 102 kW.
`data chosen are for the commercially available samples of
`High speed rated 205/50 R15 tires.
`these motors.
`'Clearly, more specific motors can be
`the same
`Our propulsion system is
`to meet
`designed for vehicle applications, but such data were not
`performance specifications as that of IMPACT. In light of
`available for this paper. Based on the vehicle data.
`the
`the design methodologies presented in section III and the
`powerequirement to cruise at the maximum speed is 41 kW.
`electric propulsion system performance analysis presented
`The motor power for acceleration and converter volt—
`in section IV, we pick an induction motor with maximum
`ampere (VA) requirement for each motor are
`shown in
`speed of 14000 rpm and the rated speed of 3500 rpm
`Table 111.
`The extended constant power range available from (extended constant power range of 1:4). A comparison of
`the induction motor clearly makes it highly favorable for
`our design EV with that of General Motors IMPACT is
`vehicle application. The limited constant power range of
`presented in Table IV. The cogent result of this exercise is
`
`seconds.
`
`Page 6 of 7
`
`FORD 1436
`
`12
`
`FORD 1436
`
`

`

`that our motor power rating for this vehicle is only 73 kW.
`as compared to the 102 kW motor in the prototype. This
`demonstrates
`the importance of
`the design approach
`presented in this paper.
`VI. Conclusions
`A design methodology for EV propulsion systems
`is presented based on
`the vehicle dynamics. This
`methodolo
`is aimed at findin the 0 ti
`_ peed
`gy
`g
`p mal torque 8
`profile for the electric powertrain. The design is to meet the
`operational constraints with minimum power requirement.
`The study reveals that
`the extended constant power
`operation is important for both the initial acceleration and
`
`The design methodology of this paper was applied
`to an actual EV to demonstrate its benefits. Clearly the
`detailed design of a vehicle propulsion system is more
`complicated
`than
`in our
`examples. However,
`this
`methodology can serve as the foundation of the detailed
`design.
`
`Refm
`in the clean air act",
`[l] A. Alison. “Searching for perfect fuel
`Conference Proceedings of Environmental Vehicles, 94, pp. 61-87,
`mm ,m 19%
`for BV and HEV". NIST
`s. Barsony,
`‘1nfrastructure needs
`Wort-shop on Advanced Comments for Electric and Hybrid
`E’w’i‘ "mm" W ”flrcdu‘embmflv MD- 0““ 1993-
`
`[2]
`
`Table IV: Comparison of General Motor EV. IMPACT and our designed EV.
`The rotational inertia constant km=l.l.
`Our Desi :u H EV
`General Motor IMPACT
`
`
`Rand Motor
`Gear Ratio
`Rated Motor
`Gear Ratio
`Rated Motor
`Rated Drive
`Rated Motor
`Rated Drive
`Power (kW)
`Torque (N-
`Shaft Torque
`Power (kW)
`Torque (N-
`Shaft Torque
`m
`-m
`m)
`-m
`
`
`
`
`
`
`————_-fi--IE_-Z§-
`
`
`
`cruising intervals of operation. The more the motor can
`-
`-
`operate in constant power. the less the acceleration power
`”WWW” W1“ be.
`.
`.
`_
`Several types of motors are studied rn this context.
`is concluded that
`It
`the
`induction motor has clear
`nrsh
`advantages for BY, at the present. B
`less .dc mom.” must
`be capable of high speeds to be competitive wrth the
`induction motor. The switched reluctance motor may be
`superior to both of these motors. for vehicle application,
`both in size and cost. However. more design and evaluation
`data is needed to verify this possibility.
`
`iii “me1'"! "Wthfibobefl 30x30? germ“)!- 1936-
`a!
`A.
`ston an
`.
`inowitz.
`m nurse in
`runen'c
`Analysis. 2nd e¢.New ‘101k. M 3 w Hill. 1 978.
`[51 A. G. Edman. G. N. Sandor. Mechanism Design: Analysis and
`Synthesis. Vol. 1, New me, Prentice-Hall, 1984.
`I: A-Tfiatfilérxmm nlndM. Wm?” yypgg
`eectric
`y '
`' e appications."
`u ing:
`t
`International Conference on Power Electronics, Oct. 10-14. Seoul,
`Rom.
`
`[6]
`
`Page 7 of 7
`
`FORD 1436
`
`13
`
`FORD 1436
`
`