speh hev parallel 2012
TRANSCRIPT
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PARALLEL HYBRID ELECTRIC VEHICLES:DESIGN AND CONTROL
Pierre Duysinx
Research Center in Sustainable AutomotiveTechnologies of University of Liege
Academic Year 2012-2013
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References R. Bosch. Automotive Handbook . 5th edition. 2002. Society
of Automotive Engineers (SAE)
C.C. Chan and K.T. Chau. Modern Electric Vehicle
Technology Oxford Science Technology. 2001. C.M. Jefferson & R.H. Barnard. Hybrid Vehicle Propulsion. WIT
Press, 2002.
J. Miller. Propulsion Systems for Hybrid Vehicles. IEE Power &Energy series. IEE 2004.
M. Ehsani, Y. Gao, S. Gay & A. Emadi. Modern Electric, HybridElectric, and Fuel Cell Vehicles. Fundamentals, Theory, andDesign. CRC Press, 2005.
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Outline Introduction
Control strategies
Maximum state-of-charge of peak power source strategy
Engine on-off strategy
Sizing of major components
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Introduction Parallel hybrid drivetrains allow both engine and electric traction
motor to supply their power to the driven wheels
Advantages of parallel hybrid electric vehicles vs series hybrid
Generator not necessary (save one component) Electric traction motor is smaller
Reduce the multiple conversions of energy from the engine to thedriven wheels Higher overall efficiency
Counterparts Control of parallel hybrids is more complex because of the
mechanical coupling between the ICE engine and the driven wheels Design methodology may be valid for only one particular
configuration
Design results for one configuration may be applicable for only aparticular given environment and mission requirements
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Introduction
Configuration parallel torque coupling hybrid electric drive train
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Introduction Design methodology of parallel hybrid drivetrains with torque
coupling which operate on the electrically peaking principle
Engine supplies its power to meet the base load operating at a
given constant speed on flat and mild grade roads or at an averageload of a stop-and-go drive pattern.
Electrical traction supplies the power to meet the peakingfluctuating part of the load.
This is an alternative option to mild hybrids
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Introduction In normal urban and highway driving, base load is much lower
than peaking load
Engine power rating is thus lower than electrical power rating
downsizing Because of better torque / speed characteristics of electric
traction motors (compared to engine) a single ratio transmissionfor traction motor is generally sufficient
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Introduction Objective of this lesson:
Design of parallel hybrid electric drivetrain with torque coupling
Design objectives: Satisfy the performance requirements (gradeability, acceleration,
max cruising speed, etc.)
Achieve high overall efficiency
Maintain battery state-of-charge (SOC) at a reasonable levels
during operation without charging from outside the vehicle Recover a maximum of braking energy
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Control strategies of parallel hybrid drive trains Available operation mode in parallel hybrid drive train;
Engine alone traction
Electric alone traction
Hybrid traction (engine + electric motor) Regenerative braking
Peak power source (batteries) charging mode
During operation, proper operation modes should be used to:
Meet the traction torque requirements
Achieve high level of efficiency
Maintain a reasonable level of SOC of PPS
Recover braking energy as much as possible
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Control strategies of parallel hybrid drive trains
Control level based on a two-level control scheme
Level 2: vehicle level = high level controller
Level 1: low level controller = subordinate controllers Engine, motor, brake, battery, etc.
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Control strategies of parallel hybrid drive
trains
Overall control scheme of the parallel hybrid drive train
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Control strategies of parallel hybrid drive trains Vehicle system level controller
Control commander
Assign torque commands to low level controllers (local or
component controllers) Command based on
Driver demand
Component characteristics and feed back information from components(torque, speed)
Preset control strategies
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Control strategies of parallel hybrid drive
trains Component controllers
Engine, motor, batteries, brakes, torque coupler, gear box,clutches, etc.
Control the components to make them work properly
Control operations of corresponding components to meetrequirements from drive train and prescribed values assigned bysystem controller
Vehicle system controller has a central role in operation of drive
train Full fill various operation modes with correct control commands to
each components
Achieve a high efficiency
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Maximum PPS state-of-charge strategy When vehicle is operating in a stop-and-go driving pattern,
batteries must deliver its power to the drive train frequently.PPS tends to be discharged quickly.
So maintaining a high SOC is necessary to ensure vehicleperformance
Max state-of-charge is an adequate option.
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Maximum PPS state-of-charge strategy
Various operation modes based on power demand
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Maximum PPS state-of-charge strategyElectric Motor alone propelling mode:
If the vehicle speed is below a presetvalue Veb, a vehicle speed below which
the engine cannot operate properly insteady state
Electric motor alone supplies power tothe driven wheels
Engine is shut down or idling
,
0
0
0
e
Lm
t m
m
PPS d
m
PP
P
P
P
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Maximum PPS state-of-charge strategyHybrid propelling mode:
Load demand such as A is greater thanthe engine power
Both engine and motor have to delivertheir power to the wheels simultaneously
Engine operates at its max efficiency lineby controlling the throttle to produce Pe
Remaining power is supplied by the
electric motor
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Maximum PPS state-of-charge strategyHybrid propelling mode:
Engine operates at its max efficiency lineby controlling the throttle to produce Pe
Remaining power is supplied by theelectric motor
,
,
( ) 0
0
0
opt
e e
L e t e
m
t m
mPPS d
m
P P v R
P P
P
PP
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Maximum PPS state-of-charge strategyBatteries / PPS charging mode:
When the power demand is less than thepower produced by engine in its optimum
operation line (as in point B) When batteries are below their max SOC
Engine is operating in optimum line
Motor works as a generator and covertsthe extra power of engine into electro
power stored in batteries
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Maximum PPS state-of-charge strategyBatteries / PPS charging mode:
, ,
,
( ) 0
0
0
opt
e e
Lm e t e m m
t e
PPS c m
P P v R
PP P
P P
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Maximum PPS state-of-charge strategyEngine alone propelling mode:
When load power demand (point B) isless than power engine can produce while
operating on its optimum efficiency line When PPS has reached its maximum SOC
Engine alone supplies the poweroperating at part load
Electric motor is off
,
0
0
L
et e
m
PPS
PP
P
P
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Maximum PPS state-of-charge strategyRegenerative alone braking mode:
When braking demand power is less thanmaximum regeneration capability of
electric motor (point D) Electric motor is controlled to work as a
generator to absorb the demand power
, 0m braking L t m m
PPS c m braking
P P
P P
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Maximum PPS state-of-charge strategyHybrid braking mode:
When braking demand power is greaterthan maximum regeneration capability of
electric motor (point C) Electric motor is controlled to provide its
maximum braking regenerative power
Mechanical brakes provide the remainingpart
max 0m braking m braking m
PPS c m braking
P P
P P
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Maximum PPS state-of-charge strategy
Flowchart of max SOC of PPS strategy
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On-off control strategy Similar strategy to the one used in series hybrid drive train
Engine on-off strategy may be used in some operation
conditions
With low speed and moderate accelerations
When engine can produce easily enough extra power to recharge
quickly the batteries
Engine on-off is controlled by the SOC of PPS or batteries
When SOC reaches its max level, engine is turned off andvehicle is propelled in electric motor only mode
When SOC reaches again its low level, engine is turned on and
propelled by the engine in PPS charging mode until max SOC is
reached
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On-off control strategy When SOC reaches its max level,
engine is turned off and vehicle is
propelled in electric motor only
mode
When SOC reaches again its low
level, engine is turned on and
propelled by the engine in PPS
charging mode until max SOC is
reachedIllustration of thermostat control
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Design of parallel hybrid components Key parameters
Engine power
Electric motor power
Gear ratio of transmissions Batteries or peak power sources
Great influence on vehicle performances and operationefficiency
Design methodology
Preliminary choice based on performance requirements
Accurate selection with detailed simulations
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Illustrative design example Design specification
M=1500 kg
f = 0,01 Re=0,279 m Cx= 0,3 S=2 m
Transmission ratio efficiency: t,e=0,9 t,m=0,95
Performance specifications
Acceleration time (0 to 100 km/h): 10 +/- 1 s
Maximum gradeability: 30% @ low speed and 5% @ 100 km/h
Maximum speed 160 km/h
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Power rating of engine Engine should supply sufficient power to support vehicle
operation at normal constant speed on both flat or mild graderoad without the help of PPS
Engine should be able to produce an average power that islarger than load power when operating in a stop-and-go pattern
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Power rating of engine Operating on highway at constant speed on flat road or mild
grade road
Illustrative example
V=160 km/h requires 42 kW
With a 4 ratio gear box
Engine allows driving
road at 5 % at 92 km/h in gear 4
road at 5 % at 110 km/h in gear 3
, ,
1( sin )
2
res
e xt e t e
P VP m g f S C V mg
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Power rating of engine Engine is able to supply the average power requirement in stop-
and-go driving cycles
The average power depends on the degree of regenerationbraking.
Two extreme cases: full and zero regenerative braking:
Full regenerative braking recovers all the energy dissipated inbraking and can be calculated as above
No regenerative braking, average power is larger so that whenpower is negative, third term is set to zero.
2
0 0
1 1 1
2
T T
ave x
dV
P m g f SC V Vdt m dtT T dt
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Power rating of engine
Instantaneous and average power with full andregenerative braking in typical driving cycles
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Power rating of engine Average power of engine must be greater than average power
load.
Problem is more difficult than in series hybrid because engine is
coupled to the driven wheels Engine rotation speed varies with vehicle speed
Engine power varies with rotation speed and vehicle speed
Calculate the average power that the engine can produce withfull throttle during the driving cycle
0
1( / , )
T
ave e eP P v R i dtT
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Power rating of engine
Average power of a 42 kW engine
42 kW Engine is OK
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Design of electric motor power capacity Electric motor function is to supply peak power to drive train
Design criteria: provide acceleration performance and peakpower demand in typical drive cycles
Difficult to directly design motor power for prescribedacceleration performance
Methodology
Provide good estimates first in a preliminary approach
Final design with detailed simulations
Assumption to calculate initial estimates Steady state load (rolling resistance, areo drag) handled by engine
while dynamic load (acceleration) handled by motor
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Design of electric motor power capacity Acceleration related to the torque output of the electric motor
Power rating
Illustrative example Passenger car Vmax=160 km/h, Vb=40 km/h, Vf=100 km/h
ta (0 100km/h)=10 s, =1,04
, ,m t m t m
e
T i dvm
R dt
2 2,2
m f b
t m a
mP V V
t
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Design of electric motor power capacity
Illustrative example
Passenger car Vmax=160 km/h, Vb=40 km/h, Vf=100 km/h
ta (0 100km/h)=10 s, =1,04
Pm= 74 kW
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Design of electric motor power capacity The approach overestimates the
motor power, because the engine hassome remaining power to acceleratethe vehicle also
Average remaining power of theengine used to accelerate the vehicle
Depends on gear ratio, so that itvaries with engaged gear box andincreases with gear box
,
1( )
a
i
t
e accel e rest
a i
P P P dt
t t
Engine remaining power: 17 kW
Pm=74 17 = 57 kW
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Design of electric motor power capacity When power rating of engine and electric motor are initially
designed, more accurate calculations have to be carried out toevaluate the vehicle performances:
Max speed Gradebility
Acceleration
Gradebility and max speed can be obtained from the diagram oftractive effort and resistance forces vs speed
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Design of electric motor power capacityIllustrative example
At 100 km/h, gradeabiltiy
of 4,6% for engine aloneand 18,14% for hybridmode
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Design of electric motor power capacityIllustrative example
Acceleration performance
for 0-100 km/h: ta=10,7 s
d=167 m
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Transmission designTransmission ratio for electric motor
Because electric motor supplies peak power and because it hasa high torque at low speed, a single ratio transmission between
motor and the driven wheels is generally sufficient to producehigh torque for hill climbing and acceleration
Transmission ratio for engine
Multi gear transmission between engine and wheels can
enhance the vehicle performances
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Transmission designMulti gear transmission ratio between engine and wheels
(+) Increase remaining power of the engine and vehicleperformance (acceleration and gradebility)
(+) Energy storage can be charged with the large engine power (+) Improve vehicle fuel economy because the engine operates
closer to its optimal speed
(-) More complex system
(-) Heavier and larger
(-) Complicated automatic gear shifting control
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Design of batteries and PPS Batteries and PPS are sized according to power and to energy
capacity criteria
POWER CAPACITY Battery power must be greater than the input electric power of
the electric motor
max
mPPS
m
PP
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Design of batteries and PPSENERGY CAPACITY
Related to energy consumption in various driving patterns(mainly full load acceleration and typical driving cycles)
Evaluate energy required from the PPS and from the engineduring acceleration period
Illustrative example:
Energy from batteries 0,3 kWh
0
at mPPS
m
PP dt
0
ate eP P dt
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Design of batteries and PPSENERGY CAPACITY
Energy capacity must meet the energy requirements duringdriving pattern in drive cycles
For a given control energy strategy charging and dischargingpower of energy storage can be obtained from simulation
Generally energy consumption (and capacity sizing) isdominated by full load acceleration
0 00
( )at
PPS c PPS dE P P dt
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Design of batteries and PPS
Simulation results for FTP75 urban driving cycle
Max energychange: 0,11 kWh
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Design of batteries and PPS Not all energy stored can be used to deliver power to the drive
train
Batteries: low SOC will limit power output and reduce efficiencybecause of internal resistance increase
Ultracapacitors: low SOC results in low voltage and affects theperformances
Flywheels: low SOC is low flywheel velocity and low voltage atelectric machine to exchange port
Only part of the stored energy can be available for use
Part available is given by a certain percentage of its SOC
min max,E SOC SOC
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Design of batteries and PPS Energy capacity of the energy storage
Illustrative example
E= 0,3 kWh
SOCmax-SOCmin=0,3
Ecap= 1 kWh
max
max min
cap
EE
SOC SOC
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Accurate simulation When major components have been designed, the drive train
has to be simulated
Simulation on typical drive train brings useful information:
Engine power Electric motor power
Energy changes in energy storage
Engine operating points
Motor operating points
Fuel consumption
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Accurate simulation
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Accurate simulation