Hydrogen Fuel Cell and KERS Technologies For Powering Urban Bus With Zero Emission Energy Cycle

Transcription

1 National Scientific Seminar SIDT University of L Aquila ITALY POLITECNICO DI TORINO Hydrogen Fuel Cell and KERS Technologies For Powering Urban Bus With Zero Emission Energy Cycle D Ovidio G., Masciovecchio C., Rotondale A. 1

2 Overview Introduction System project and objectives Vehicle overview and technologies Fuel consumption per bus Energy balance in solar-hydrogen cycle Conclusions 2

3 Introduction Transportation in urban areas significantly impacts on fuel consumption and environmental emissions. It accounted for about 2.3 gigatons / year of CO 2 worldwide (almost 25% of carbon emissions of the whole transportation sector) 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 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 Batteries produce chemical pollution at the end of their life 3

4 Integrated urban mobility with solar-hydrogen energy cycle Electrolyzer Solar Energy H 2 cell ELECTROLYSIS H 2 tank NOVEL PHOTOVOLTAIC SYSTEMS Electric Energy URBAN TRANSPORTATION NETWORK Chemical Energy Small sized Hydrogen urban vehicle (passengers and freight) Photovoltaic device Thermal Energy Tele- conditioning, hot water, etc Efficient and sustainable mobility Goals Batteries Traffic disposal emission NO Mechanical Energy Accumulatore FESS elettromeccanico Fuel cell & Cicli FESS infiniti Power unit Bus Big sized buses Urban Environment The electric energy generated from photovoltaic devices spread out in the urban area is used to feed the electrolyzer for hydrogen production The electric motors of buses are powered by hybrid units consisting of hydrogen fuel cells and kinetic energy storage systems Objectives To realize a sustainable public urban mobility by using buses with «zero» emission energy cycle without the use of chemical batteries for vehicle traction 4

5 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

6 Hybrid power unit Vehicle Power Train Technologies Main power train components Hydrogen fuel cell Advantages High efficiency of constant electric power output Wide energy output (depending on H2 vessel) No CO2 emission or chemical pollution Kinetic Energy Storage System (KERS) Source: Flybrid Flywheel Capacitor High specific power density and high charge / discharge efficiency Long active life (large number of cycles) Environmentally friendly (benign materials) In-wheel motor 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 Source: Protean Drive 6

7 Kinetic Energy Storage System Technology 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. E K = ½ J 2 =½ m f r 2 k 2 Max Energy 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 Source: Flybrid Flywheel Capacitor 7

8 UPS (Uninterruptible Power Supply) Automotive Type of KERS 1) 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. 2) 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. 3) Electro-mechanical: it consists of a motor/generator mechanically connected to a flywheel. The input/output power are only electric type 8

9 1.1 Power : Model of vehicle and its components 1. Vehicle P T (t)= 1/ m [(F R +F S +F A +F ac ] v(t)= 1/ m [m g (c r cos ± sen)+/2 c a A f v 2 (t)+ m dv(t)/dt] v(t) Where: m is the efficiency of traction motor; F R is the wheel friction force, F S is the slope force (which could be positive or negative), F A is the air resistance force, F ac is the acceleration force, m is the full mass of the vehicle, c r is the rolling coefficient, g is the gravity acceleration, is the angle of terrain slope, c a is the drag coefficient, is the air density, A f is the vehicle frontal area and v is its speed. 1.2 Energy : E T (t) = P T (t) dt PT ( t) dt PFC ( t) dt PG ( t) dt 0 0 E T 0 ( ) E ( ) E ( ) FC G where E T () is the traction energy, E FC () is the FC energy and E G () is the recovery braking energy in the cycle. where P T is the motor traction power, P FC is FC power and P G ( is the recovery braking power in the cycle. 2.1 Energy : E K = ½ J (t) Power losses: P L = E K 2. KERS E K = ½ J [ 2 max - 2 min] =½ m f r 2 k [ 2 max - 2 min] where m f 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 where is a constant so that the kinetic energy stored is reduced by 5% in one hour 3.1 Efficiency: η fc = cost 3.2 Hydrogen consumption: fc E E e ch and m H2 3. Fuel cell E H ch i m H2 Ee H fc i where E e is electrical energy supplied by FC, E ch is chemical energy of hydrogen, m H2 is hydrogen mass, and H i is lower heating value of hydrogen (119,9 MJ/kg). 9

10 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 Mass Kg 6.94 Rotor radius mm 90 2 KERS 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 10

11 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 11

12 Dynamic model 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 Fig. 1 Block diagram of dynamic model 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. 12

13 Results Vehicle speed and acceleration actually reached, compared to the ones imposed by the drive cycle 13

14 Results Power profiles of fuel cell, KERS and motors 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 14

15 Results Energy profiles of FC, KERS, traction motors and regenerative braking 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 15

16 Results: Flywheel performance 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) 16

17 Assumptions Ee m H2 H fc i Energy consumption 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) Electrical energy consumption for hydrogen production by electrolyzer 50 kwh/kg H2 Electric network Bus yearly travel (50,000 km) H 2 consumption for traction (Kg) Electric energy for H 2 production (MWh) Emission (tons CO 2 ) 24.7 Photovoltaic - Hydrogen specific consumption 53.6 km/kg H2 17

18 Standard technology Energy balance between consumption and production Silicon photovoltaic system Italian locations Average sum of solar irradiation per square meter 1.(kW/m 2 ) (*) Average annual electric energy production (kwh/kwp) (*) Power of photovoltaic plant (kwp) Photovoltaic plant foot-print (m 2 ) North (Milan) Centre (Rome) South (Palermo) (*) Solar radiation database; source: PVGIS) 18

19 Conclusions An integrated urban public system mobility based on solar-hydrogen cycle has been proposed and analyzed The main components of system have been technologically defined 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: Kg of hydrogen consumption for traction requirements MWh of electric energy for hydrogen production by electrolyzer - A photovoltaic plant of 32 kwp in Rome (standard technology) «Zero» emission energy cycle has been achieved without the use of electrochemical batteries for traction 19

20 Thank you for attention 20