Electrical Vehicles Dr.ir. Johan Driesen
overview • history • why drive “e” ? • what can be achieved ? • outlook
• technology – car types – drive system • motor • power electronics • control system
– energy storage/production – driving style
J.Driesen - Electrical Vehicles
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history: 1895-1910 • electric vehicles were the most promising drive technology end 1800’s: speed records, neater cars • combustion engine took over in early 1900’s: became more powerful, easy to take with cheap fuel J.Driesen - Electrical Vehicles
Janetzy Jamais Contente • first car ever to exceed 100 km/h – 24/04/1899 – 105.882 km/h – 2 electric motors in ‘aerodynamic’ car – driven by Camille Janetzy (B.) in Achères (Fr.) – named “Jamais Contente” J.Driesen - Electrical Vehicles
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history: 1905-1925 • gasoline vehicles take over completely: discovery of many oil wells drop fuel prices • mass production techniques introduced by Ford • short revivals: – Edison battery (NiFe) – WW I: oil shortage
• 1900 US car production: 1575 electric cars vs. 936 gasoline cars down to 4% in 1925 J.Driesen - Electrical Vehicles
history: after WW II • 60s: small ‘smog buster’ cars – GM 512, Ford Comuta (failed to sell: smog reduction incentive too limited)
• 1973: oil crisis – economical push to revive EV R&D as a mean to reduce oil dependence
• 80s: growing environmental concerns – Clean Air Acts (California) and other
• 90s: evolution in power electronics J.Driesen - Electrical Vehicles
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EV types • BEV: battery-electric vehicle – rechargeable batteries ONLY source (storage) of energy
• HEV: hybrid electric vehicle – electrical energy storage plus onboard means of power generation, which may be converted into electricity – additional diesel, gasturbine, fuel cell J.Driesen - Electrical Vehicles
noxious emissions • ‘zero-emission vehicle’ (ZEV) in fact does not exist ! • emissions MUST be considered over entire energy cycle, including power plants – reference: traditional combustion drive – battery vehicles need to be charged with electricity produced elsewhere: yet, in total only 1/10 of emissions – hybrid vehicles can reach 1/8 of emissions (just clean enough ?) J.Driesen - Electrical Vehicles
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emissions: detail • Full cycle (B)EV compared to CV – CO: -99%, HC: -97%, NOx: -92%, CO2: -50%
• EV emissions continuous; no peak emissions in ‘cold starts’ and short trips • hybrid emissions close to BEV levels: just clean enough • fuel cells: emissions almost eliminated J.Driesen - Electrical Vehicles
internal-combustion engine characteristics • internal combustion engine: bad efficiency characteristics • size determined by peak power • gears necessary • fuel efficiency: 18% (46 % electric) J.Driesen - Electrical Vehicles
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enhance efficiency • enhance efficient use of combustion engine – use a second drive (electric) to stay in point of maximum efficiency – size determined by peak power demand: shave the peak with electric motor – bring own energy source to produce (some of) the electricity
• different philosophies leading to hybrid cars
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HEV types • series HEV
• parallel HEV
– engine powers generator – generator charges batteries and/or supplies motor directly – purely electrical interface to drivetrain
– engine delivers mechanical energy to drivetrain directly – electric motor (generator) on drivetrain as well
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HEV types: power system architecture
J.Driesen - Electrical Vehicles
series HEV • ‘extend BEV with onboard charging’ • switch off engine (BEV mode) for short trips or to drive clean • energy production and driving are decoupled • simple mechanical drive (no gears) J.Driesen - Electrical Vehicles
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parallel HEV • keep engine in optimal operation • use motor while accelerating • use as generator while decelerating • engine can be very small • complex mechanical train
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alternative HEVs • fully decoupled
• series/parallel: complicated
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hybrid car layout
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Hybrid driving: starting
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Hybrid driving: driving
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Hybrid driving: Acceleration
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Hybrid driving: deceleration & braking
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Hybrid driving: charging
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Hybrid driving: stopping
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HEV: non-electrical parts • ‘engine’ with rotating output
• energy storage
– diesel: kept in optimal operation point – high-speed gasturbine
– batteries – flywheel – supercapacitors
• ‘engine’ with electrical output – fuel cell J.Driesen - Electrical Vehicles
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flywheel storage • major problem: gyroscopic effects – difficult to manoeuvre, overturn danger – use special fixture
J.Driesen - Electrical Vehicles
battery types • Pb-acid: cheap, low performance • NiCd: reliable, ‘memory effect’, environmental problems (Cd) • NaS, NaNiCl: operate above 300°C, dangerous, not flexible • NiZn: small number of load cycles
• NiMH, Li-Ion: high densities, long life, high charge/discharge rates, safe, no maintenance, pollution-free
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batteries: overview Properties of the main battery types. Pb-Acid
NiCd
NaNiCl
NiZn
NiMH
LiIon
specific energy [Wh/kg] 35 50 90 55 60 120 80 85 140 130 125 200 energy per volume [W/A] specific power 120 130 150 150 165 230 (*)[W/kg] cycle life (**) 800 3000 1500 300 > 600 600 operating temperature ambient ambient 300º C ambient ambient ambient (*) (**)
peak power density at 80% DOD (depth of discharge) over 30 s cycle life (80% of initial capacity)
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fuel cells • controlled oxidation reaction: direct conversion of chemical energy into electrical energy (DC) • run on pure H2 or H2-rich reformed methane, methanol, ethanol or gasoline • store gaseous fuel in pressure cylinder or metal hydride tank • higher efficiency than combustion-based: no Carnot-limit • different types, polymer electric membrane fuel cell (PEMFC) most promising J.Driesen - Electrical Vehicles
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fuel cell : PEMFC • • • • •
output power: 35 kW stack voltage: 50-55 V efficiency at rated load: 59 % efficiency at 20% load: 69 % operating temperature: 80°C
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pure battery EV • emissions are moved to (more efficient) power plants • need recharging stations • recharging = slow • recharge overnight (cheap power) • batteries are heavy and spacious • extremely silent J.Driesen - Electrical Vehicles
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true ZEV: solar challenge cars • regular race for photovoltaic powered cars: in Europe, Australia • extreme efficiencies required
J.Driesen - Electrical Vehicles
powering up • filling up a classical car with gasoline is the equivalent of an MW energy transfer • using an electrical cable: tens of kW (need several hours) • charge overnight: help load balancing • 2 systems: conductive, inductive
filling up a hybrid (trailer system)
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electrical motor types • DC machines: brush problems • induction machines with cage rotor • synchronous machine types – permanent-magnet machine, ‘brushless-DC’ – reluctance machine: simple but limited efficiency and performance, noisy – hybrid machines (mixed types, e.g. with additional cage): complicated design and construction J.Driesen - Electrical Vehicles
electrical motor location(s) • large central motor and mechanical distribution • motor per wheel – external motor – special motor design built-in wheel (direct drive) – 2- and 4-wheel drive schemes possible using fast (digital) control systems J.Driesen - Electrical Vehicles
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field weakening • higher speeds: induced voltages increase – need more insulation – power electronics must be capable to handle high voltages
• lower field or introduce ‘antifield’ • result: higher speed in exchange for lower torque, but keep power and losses constant • use for cruising: high speed on highway, but no more vigorous accelerations (‘overdrive’ gear) J.Driesen - Electrical Vehicles
DC-machine • simple to control, simple power electronics (DC/DC with choppers) • easy field weakening in shunt machines • maintenance of brush/collector • outperformed by all other motor types
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induction machines • special construction for use with inverter • advanced inverter and control, especially at low speeds • field weakening possible for cruising • significant rotor losses in cage: difficult to cool • limited efficiency J.Driesen - Electrical Vehicles
permanent-magnet synchronous machine • same inverter, but slightly simpler control compared to induction machine • difficult flux weakening for cruising • temperature sensitive permanent magnets: reversible and irreversible demagnetisation • only significant stator losses • different designs J.Driesen - Electrical Vehicles
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motor types: examples • induction machine
• permanent magnet synchronous machine
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(switched) reluctance machine • synchronous machine without field winding nor permanent magnets • torque due to Xd/Xq difference • simple construction • noisy, vibrations
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direct wheel drives • usually PMSM with high number of poles, integrated into (four) wheels, special magnetic design • direct braking as well • difficult control to maintain synchronism between wheels, go through curves: ‘differential axle in software’ J.Driesen - Electrical Vehicles
motor cooling • use water cooling to prevent insulation damage and demagnetisation Water cooled HEV mini-van motor (ESAT/ELEN design)
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power electronic circuits • several base circuits necessary, with own (coordinated) control – DC/DC (chopping) with battery or fuel cell to deal with changing DC voltage level – AC/DC (active rectifier) with generator on diesel/gasturbine for rectification – DC/AC based on PWM for AC motor supply
• components: IGBTs • use special circuits to limit the (switching) losses and increase performance (high dynamism) • voltage as high as possible to minimize losses (500 V)
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electrical drive: scheme
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electrical drive: detail
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4-wheel direct drive control
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car control systems • implement control system in powerful digital signal processors (DSPs) • driver gives linear speed reference, but mimic feel of traditional gas pedal (nonlinear control of injected power/fuel) using digital filters • easy implementation of systems such as ABS, traction control and cruise control in DSP software J.Driesen - Electrical Vehicles
car operation • using advanced control and power electronics optimal performance (maximum torque) at every speed from 0 km/h to top speed • totally gearless (except some hybrids) • beyond ‘maximum torque speed’: cruising using controlled field weakening J.Driesen - Electrical Vehicles
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city driving cycle 300
T [Nm]
80
200
v [km/h] 60
100
50 0
40
0
30
1000
2000
3000
4000
5000
n [rpm]
6000
-100
20 10
-200
0 0
500
1000
1500
2000
t [s]
2500
standardized city driving cycle, based on measurements
-300
registered operating points in city driving cycle
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F3 on race track • typical driving cycle of F3 (Donington circuit, UK)
• electrical F3: comparable performance
J.Driesen - Electrical Vehicles
D. Howe: University of Sheffield
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regenerative braking • EV powertrains are reversible – motor becomes generator – batteries/flywheels are recharged
• 60% of energy spent in urban driving is used for inertia effects (acceleration) • braking/deceleration: recovery of about half of this energy could be possible J.Driesen - Electrical Vehicles
power system architecture design • typical design values – – – – – – – –
fuel economy: min. 35 km/l (3* better!) range: 612 km acceleration 0-100 km/h in 12 sec. max. speed 140 km/h 6.5 % climb at 90 km/h for 20 min. drive away in 5 sec., full power after 2 min. meet emission standards price of family sedan J.Driesen - Electrical Vehicles
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why drive electric ? • why ? – superior engine & driving performance – minimal emissions, clean(er)
• why not ? – weight (?) – complex maintenance (?) – price
J.Driesen - Electrical Vehicles
commercial (H)EVs • Traditional companies – – – – – – –
GM EV-1, S10 pickup Toyota Prius I & II, RAV4-EV Honda EV-plus, Insight Daimler Chrysler Epic Ford Ranger EV Nissan Altra, Tino ...
• EV-only companies – – – – –
Tzero Solelectrica Enova systems Orion …
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why doesn’t it sell (yet) ? • societal concerns: – pollution of environment – noise, dangerous petrochemicals
• personal concerns – cheap in investment and use – comfortable (e.g. noise)
• fail on price argument: electric vehicle are cars for “Greens with greens” J.Driesen - Electrical Vehicles
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