Hydrogen Fuel Cell and KERS Technologies For Powering Urban Bus

With Zero Emission Energy Cycle

National Scientific Seminar SIDT

POLITECNICO DI TORINO 14-15.09.2015

University of L’Aquila ITALY

D’Ovidio G., Masciovecchio C., Rotondale A.

1

Overview

Introduction

System project and objectives

Vehicle overview and technologies

Energy balance in solar-hydrogen cycle

Conclusions

2

Fuel consumption per bus

Transportation in urban areas significantly impacts on fuel consumption and environmental emissions. It accounted for about 2.3 gigatons / year of CO2 worldwide (almost 25% of carbon emissions of the whole transportation sector)

Introduction

Current electric buses with batteries represent the most common alternative to oil-fueled vehicles

If the batteries are charged with energy produced by thermoelectric plants, which burn fossil fuels, pollution is merely shifted from where the energy is used to where it is produced

Public transportation can play a primary role for emission reduction: at present, large urban transit buses with internal combustion motors are among the vehicles which pollute most

Batteries produce chemical pollution at the end of their life

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The electric energy generated from photovoltaic devices spread out in the urban area is used to feed the electrolyzer for hydrogen production

Integrated urban mobility with solar-hydrogen energy cycle

Accumulatore elettromeccanico

Cicli infiniti

Big sized buses

Batteries

disposal

Traffic

emission

Electric

Energy

Chemical

Energy

Solar Energy

Thermal

Energy

Tele- conditioning, hot water, etc

Efficient and sustainable

mobility

ELECTROLYSISH2 tankH2 cell

NOVEL PHOTOVOLTAIC

SYSTEMS

Mechanical

Energy

Small sizedHydrogen

urban vehicle(passengers and freight)

FESS

Urban Environment

NO

URBAN TRANSPORTATION NETWORK

Goals Fuel cell & FESSPower unit

To realize a sustainable public urban mobility by using buses with «zero» emission energy cycle without the use of chemical batteries for vehicle traction

The electric motors of buses are powered by hybrid units consisting of hydrogen fuel cells and kinetic energy storage systems

Photovoltaic device

Bus

Electrolyzer

4

Objectives

Vehicle overview

Fig. 1 Power and control configuration

The vehicle uses two or four in-wheel electric traction motors fed by a hybrid power unit consisting of a FC

connected to a pair of counter rotating KERS (Kinetic Energy Recover System)

The in-wheel motors (MT) are electrically supplied by the hybrid power unit

The motors operate as generators when control sets a negative acceleration of vehicle

The KERS are used to store the FC power (when no traction is required) and to recover the braking

energy in order to feed it back into the vehicle’s power system when it is required

5

Vehicle Power Train Technologies

Kinetic Energy Storage System (KERS)

In-wheel motor

Hydrogen fuel cell

Main power train components

Hyb

rid

po

we

r u

nit

Advantages

High efficiency of constant electric power output Wide energy output (depending on H2 vessel) No CO2 emission or chemical pollution

The torque is directly applied to the wheel No gearbox, differential, or drive shafts are required Reduction of space and weight on board the vehicle

High specific power density and high charge / discharge efficiency

Long active life (large number of cycles) Environmentally friendly (benign materials)

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Source: Flybrid® Flywheel Capacitor

Source: Protean Drive™

Features: • High power capability • Light weight and small size • Long system life

o High depths of discharge

o Wide temperature range o Severe stop start duty cycles • Truly green solution

o High efficiency storage and recovery o Low parasitic losses

Flywheel Energy Storage System

An electric motor generator is connected to the flywheel allowing DC energy to be stored or recovered. The electrical power is used to spin up the flywheel and when the power is turned off the flywheel continues to spin. To recover the kinetic power, the motor generator is used to generate electricity thereby slowing down the flywheel. Rotating at up to 60,000 rpm the very small flywheel can store enough energy to make a significant impact on vehicle performance and emissions.

EK = ½· J·2 =½·mf ·r2· k·2

Kinetic Energy Storage System Technology

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Max Energy

Source: Flybrid® Flywheel Capacitor

Type of KERS

Mechanical: it consists of a flywheel coupled to a fully mechanical

continuously variable transmission (MCVT) that is connected to a

rotating devices of car (i.e. wheels, crankshaft) permitting

mechanical power exchange with a flywheel storage system.

Electrical: it consists of a motor/generator that converts kinetic

energy into electric energy and vice versa. The electrical energy is

exchanged, by means a converter device, with batteries or

capacitors.

Electro-mechanical: it consists of a motor/generator

mechanically connected to a flywheel. The input/output

power are only electric type

1)

2)

3)

Au

tom

oti

ve

UP

S

(Un

inte

rru

pti

ble

Po

we

r Su

pp

ly)

8

Model of vehicle and its components

1. Vehicle

Where:

m is the efficiency of traction motor; FR is the wheel friction force, FS is the slope force (which could be positive or negative), FA is the air

resistance force, Fac is the acceleration force, m is the full mass of the vehicle, cr is the rolling coefficient, g is the gravity acceleration, is the

angle of terrain slope, ca is the drag coefficient, is the air density, Af is the vehicle frontal area and v is its speed.

PT (t)= 1/m [(FR+FS+FA+Fac]·v(t)= 1/m [m·g·(cr·cos ± sen)+/2·ca··Af·v2(t)+ m·dv(t)/dt]· v(t)

ET(t) = PT(t)·dt

1.2 Energy :

1.1 Power :

)()()( GFCT EEE where ET() is the traction energy, EFC() is the FC energy and EG() is the recovery braking energy in the cycle.

dttPdttPdttP GFCT )()()(000

where PT is the motor traction power, PFC is FC power and PG( is the recovery braking power in the cycle.

2. KERS

EK = ½ · J · (t)2

2.1 Energy :

EK = ½· J·[2max -

2min] =½·mf ·r

2· k·[2max -

2min]

where mf is the rotor mass, r is the rotor radius, k is the inertial constant which is dependent on rotor shape, max and min are the maximum and minimum values of angular speed, respectively

PL = · EK

2.2 Power losses:

3. Fuel cell

where is a constant so that the kinetic energy stored is reduced by 5% in one hour

ηfc = cost 3.1 Efficiency:

3.2 Hydrogen consumption: ifc

eH

H

Em

2and

E

E

ch

efc

i

chH

H

Em

2

where Ee is electrical energy supplied by FC, Ech is chemical energy of hydrogen, mH2 is hydrogen mass, and Hi is lower heating value of hydrogen (119,9 MJ/kg).

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Vehicle features

Fig. 1 Concept of Hybus

Hybus 4 WD version Unit

Carrying capacity # Pass. 21

Length mm 6155

Height mm 2950

Width mm 2035

Tare Kg 2,500

Pay load Kg 1,470

Full mass Kg 3,970

Power train components

# Component Unit

2 KERS

Mass Kg 6.94

Rotor radius mm 90

Rotor speed rpm 14,000-45,000

Max energy MJ 0.49

Peak power of motor/generator

kW 21

1 Fuel cell Power kW 7

4 Traction motor Peak power kW 11

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Urban drive cycle model

A route cycle consisting of three sub-cycles, each equal to the European urban drive cycle

(ECE), but with different road slopes, was considered in order to design the power-train

components of vehicle

Fig. 1 Urban drive cycle

Each sub-cycle is characterized as follows:

A distance of about 1041 m

A variable slope profile: the first part is flat, the second and the third parts have a negative and positive constant

grade of 2%, respectively

A bus stopping (30 sec) for passengers transfer so that average bus stop distances of about 500 m are obtained

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Fig. 1 Block diagram of dynamic model

Dynamic model

1 2 3 4 5

1. The hybrid power unit (HPU) feeds power to the motors according to their own physical limits and losses. The motors

provide torque to the wheels as a function of the available power.

2. The acceleration and the speed of the vehicle are managed by the controller to meet the requirements of the route

cycle at best. The power consumed and the speed actually achieved by the vehicle are determined.

A proper control logic block has been defined and used for calculating the power that the

vehicle must produce to meet the drive cycle requirements

Vehicle

Path slopes

Drive Cycle

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Vehicle speed and acceleration actually reached, compared to the ones imposed by the drive cycle

Results

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The downsized FC provides the constant power of 7 kW

The KERS handles the transient loads by storing or releasing power

When the motor power request is zero the FC recharges the KERS

Results

Power profiles of fuel cell, KERS and motors

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The energy needed to complete the full route cycle is 3.8 MJ of which 2.5 are provided by

the KERS.

The KERS recovers, through the regenerative braking, about 30 % of the total energy

needed for traction

Results

Energy profiles of FC , KERS , traction motors and regenerative braking

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Flywheel speed vs. cycle time

The flywheel operates with a rotational speed in the range 14,00045,000 rpm

The speed of the flywheel increases during charge (storing energy) and decreases

during discharge (losing energy)

Results: Flywheel performance

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ifc

eH

H

Em

2

Hydrogen consumption of the vehicle

Ee is the electrical energy of FC ηfc is the FC efficiency Hi is the lower heating value of hydrogen (119,9 MJ/kg)

Energy consumption

Hydrogen specific consumption

53.6 km/Kg H2

Bus yearly travel (50,000 km)

H2 consumption

for traction

(Kg)

Electric energy

for H2

production

(MWh)

Emission

(tons CO2)

Electric network 933

46.6 24.7

Photovoltaic -

Electrical energy consumption for hydrogen production by electrolyzer

50 kWh/Kg H2

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Assu

mp

tio

ns

Energy balance between consumption and production

Silicon photovoltaic system

Italian

locations

Average sum of

solar irradiation

per square meter

1.(kW/m2) (*)

Average annual

electric energy

production

(kWh/kWp) (*)

Power of

photovoltaic

plant

(kWp)

Photovoltaic

plant

foot-print

(m2)

North (Milan) 1680

1280 36.5 202

Centre (Rome) 1950 1460 32.0 178

South (Palermo) 2040 1530 30.5 169

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Sta

nd

ard

te

ch

no

log

y

(*) Solar radiation database; source: PVGIS)

Conclusions

The electric bus powertrain components (hydrogen fuel cell, KERS and traction motors) have been modeled for the European urban drive cycle.

The energy balance for a yearly travel of 50,000 km shows: - 933 Kg of hydrogen consumption for traction requirements - 46.6 MWh of electric energy for hydrogen production by electrolyzer - A photovoltaic plant of 32 kWp in Rome (standard technology)

An integrated urban public system mobility based on solar-hydrogen cycle has been proposed and analyzed

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The main components of system have been technologically defined

«Zero» emission energy cycle has been achieved without the use of electrochemical batteries for traction

Thank you for attention

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