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Hybrid City Bus Design
Evaluation Using System
Level Simulations
ISIE 2014, Istanbul, Turkey
Teemu Halmeaho, Pekka Rahkola, Jenni
Pippuri, and Kari Tammi
[email protected], +358 50 348 7902
VTT Technical Research Centre of Finland
211/12/2014 2
Objectives
Design hybrid bus (4th evolution version)
Study good (optimal) combination for power train (generator,
motor, battery)
Study vehicle performance on actual bus line (true loading)
Parameter study regarding to bus performance (*)
Bus weight
Motor torque
Regenerative braking under different friction conditions (*)
Regeneration capability
Bus stability
(*) = focus of this presentation and ISIE paper
311/12/2014 3
Bus specification – general
Serial hybrid powertrain (or range-extended electrical vehicle)
Model includes
Vehicle longitudinal dynamics
Drive (propulsion) motor-generator
Battery
Diesel-generator (range-extender)
Necessary power electronics for generator, energy storage and
drive motor
411/12/2014 4
Bus specification – detailed
Subsystem Parameter Value
Vehicle
Total massa, m10 000, 12 000, 14 000
kgb From CMc to FAc 3.0 mb From CMc to RAc 1.5 m
CMc height 1.0 m
Frontal area A 7.0 m2
Drag coefficient, Cd 0.4
Drive motorNominal torquea 660, 880, 1060 Nm
Nominal speed 1900 rpm
GeneratorNominal torque 310 Nm
Nominal speed 2200 rpm
Diesel engine Power 56 kW
Energy storageCapacity 0.74 kWh
Power 300 kW
DC-DC converter Efficiency 95 %
511/12/2014 5
Dynamic bus model
Mechanical domain
Longitudinal dynamics, Newtonian mechanics (rigid body)
Tyres, traction forces as a function of tyre slip
4-speed gearbox (!, 4 gear ratios + final drive)
Electrical domain
Permanent magnet (PM) drive motor & PM generator
Operated on linear range
dq model, no saturation
No field weakening needed to take into account
Energy storage, ultra capacitor
Resistance, no ageing
Power electronics
Field oriented control
Ideal switching
sind
dmgFF
t
vm dx
x
qqsddd
d iLRivt
iL
d
d
qdqdqafe iiLLiPT 2
3
rLer
r BTTt
J
d
d
611/12/2014 6
Electrical powertrain and control
Similar power electronics in generator model
Connected to DC bus with capacitor power electronics
Tool: Simulink/ Simscape
Results
811/12/2014 8
Energy saving estimation for varied bus weight
and propulsion motor generator torque
Mass: 10, 12, and 14 tonnes Max torque: 660, 860, and 1060 Nm
Nominal
case
Nominal
case
911/12/2014 9
Regenerative braking and stability
Rear wheel drive
Pure regenerative braking may be
unstable (no front brakes)
High gear always ensures stable
behaviour if mechanical front
brakes applied
Black curve: ideal brake force
distribution (front rear)
Stable below black curve for all
friction levels (front wheels
block first)
Vehicle deceleration ratio
z = a / g
1011/12/2014 10
Regeneration and stability
Energy regeneration works on dry
asphalt, no stability lost
Friction demand ~ 0.55 for rear wheel
braking with 1060 Nm motor generator
Friction demand ~ 0.3 for acceleration
Limited friction limited regeneration
Largest friction demand occurs at slow
speeds ~10 km/h
< 0: braking
Conclusions and future
work
11/12/2014 12
Conclusions
• Limited friction is real problem for busses operating in cold climate (and heavy rain)
• Slip control recommended for regenerative braking
• Front axle regeneration (and possibly four wheel drive) helps but increases cost
– Control of optimal front – rear distribution
• Parameters were fixed for electrical bus
• Commercial version is to be built
Future research work
• Lateral stability when cornering
• 3D mechanical model
TECHNOLOGY FOR BUSINESS