Hybrid Drive Systems for Vehicles

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Chester Miles
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1 Hybrid Drive Systems for Vehicles L4 Alternative drive train Components

2 Drawback with conventional drivetrains Limited ability to optimize operating point No ability to regenerate braking power

3 Solutions Smaller Engine + Reach higher operating points - Still cannot regenerate Store energy in the vehicle mass - Speed variations - Still cannot regenerate Secondary energy storage + Selectable operating point (Pstorage = Pice Proad) + Can regererate - Expensive

4 Smaller Engine cylinder deactivation D IC E Clutch IC E Clutch EM GEAR DIFF Batt PE

5 Combustion On Demand Cylinder deactivation via free valve control

6 Optimized efficiency Number of Cylinders in use Torque [Nm] 0 0 Speed [rad/s] Torque [Nm] 0 0 Speed [rad/s] Torque [Nm] Speed [rad/s]

7 Optimal Efficiency Max efficiency 0.35 Blue=2-cylinder std, Red=2-cylinder COD ICE Power [W] x 10 4

8 Secondary Energy Storage Why electric? selection Efficient secondary energy converters (Electrical machines) Safe, quiet, flexible installation Increasing need for Auxilliary electric power High torque density of Electrical Mchines Up to 30 Nm/kg ICE: <2 Nm/kg

9 Secondary energy storage Hybridisation

10 Energy Storage Systems Industrial Electrical Engineering and Automation Lund University, Sweden

11 How does a battery look?

12 Design criteria Cost Vehicle Performance Operation Mats Alaküla EHS

13 Driving the Hybrid by the Atoms ECB Source: Uppsala University

14 Technologies NiMH Lead Li-ion S.C.

15 Limiting Factors Durability NiMH Weight Cost Charge Power Durability Lead Weight Maintenance Li-ion Cost Safety S.C. Energy Initial Cost

16 Power Density Performance S.C Li-ion Effpower NiMH Pb- Acid Energy Density

17 Power Relation to needs Propulsion Hybrid Mode Propulsion Electric Mode 100 kw 10 kw Cranking Next Generation Need Energy

18 Battery Cell Properties R = f(soc, T,I ) + OCV = f(soc, T,I ) + - C = f(soc, T,I ) Terminal Voltage - Losses All parameters are non-linear Strong dependance on SOC, temperature, current rate & direction, and history. No Steady-State Operation!

19 Super Capacitor Cell Properties R ohm = f(t, ω) L = f(t, ω) + C = f(u, T, ω) R leak = f(t) Terminal Voltage Losses - Fewer non-linear elements Strong dependance on SOC & temperature only Semi Steady-State Operation!

20 Energy Density Combined Energy Storage System Battery Combined System SuperCaps Power Density

21 Driving Criteria Power output/regeneration at a specific time Charge and Discharge Properties Cooling Issues Pure Electric Range Upcoming energy need (GPS, weather and traffic info, etc.) Factors Determined by: State of Function = State of Charge + State of Health

22 Voltage State of Charge Li-ion NiMH S.C. 100% State of Charge 0%

23 State of Health Temperature and Temperature Changes Charge and Discharge Properties Pure Electric Range State of Charge individual cells in a battery system ALL need to be managed Management unit is needed BMU (Battery Management Unit)

24 Mats Alaküla Mats Alaküla EHS SAFT data

25 Mats Alaküla Mats Alaküla EHS SAFT Lithium teknologi

26 Battery Lifetime : II Calculate the total converted energy as: Wconv=Wbatt*DoD/100*NoC And the battery cost per kwh converted energy as: SEKperkWh = CostPerkWh*Wbatt / Wconv CostPerkWh = 3000 [SEK]

27 Cost[SEK/kWh] Converted Energy [MWh] NoC Battery Lifetime : III Depth Of Discharge [%] Note! The total converted energy falls fast with increased DoD!!! The cost per converted kwh increases rapidly with increased DoD Depth Of Discharge [%] Depth Of Discharge [%]

28 Battery Lifetime : IV Assume that DoD is driven by a constant charge Power P charge 0 t P ch,ave then : DDoD P ch, ave W batt t SOC DDoD

29 [years] Battery Lifetime : V Battery Lifetime in Years, used 8h/day, 300 days/year The battery lifetime can be calculated as: DDoD P ch, ave W batt t Lifetime DoD Wbatt 2 NoC P 100 ch, ave DoD 2 NoC Pch, ave 100 W batt Now, plot the battery lifetime as a function of DoD and (P ch,ave /W batt ) Assume 8h/day, 300 days/year Pch,ave/Wbatt [1/h] DoD [%]

30 Battery Lifetime: Conclusions Deep discharge of a battery costs lifetime Best with less than 10 % DoD The battery may have a high power density BUT using it is expensive, i.e. a high power/energy ratio costs lifetime Best with an average battery power in the range 3 4 x the battery energy capacity.

31 Other technologies? Lithium batteries comes in a number of siblings Lithium-Manganese Oxide or Lithium Nickel Oxide or Lithium Cobolt Oxide or Lithium Iron Phosphate Most of these are considered thermally unsafe since the oxygen is easily released in case of cell abuse The only alternative, up to now, that is considered thermally stable is Lithium Iron Phosphate Watch : Material Average Voltage Gravimetric Capacity LiCoO2 3.7 V 140 mah/g LiMnO2 4.0 V 100 mah/g LiFePO4 3.3 V 120 mah/g Li2FePO4F 3.6 V 115 mah/g

Toshiba SCiB? New Lithium chemistry? Toshiba calls it SCiB Claims 90 % recharge in 5 minutes and 5000 Cycles life 90 % in 5 minutes means (0.9/(5/60)) = 10.8 in Power/EnergyCapacity ratio.

32 Toshiba SCiB? New Lithium chemistry? Toshiba calls it SCiB Claims 90 % recharge in 5 minutes and 5000 Cycles life 90 % in 5 minutes means (0.9/(5/60)) = 10.8 in Power/EnergyCapacity ratio. A 10 kwh battery would be possible to recharge with 108 kw charging power without damage 2.4*4.2/1000/0.150 = kwh/kg normal Nominal Voltage Nominal Capacity Size 2.4 V 4.2 Ah Approx. 62 x 95 x 13mm Weight Approx. 150 g

33 Cost[SEK/kWh] Converted Energy [MWh] [years] NoC Toshiba vs LiFePo Battery Lifetime in Years, used 8h/day, 300 days/year Depth Of Discharge [%] Depth Of Discharge [%] Pch,ave/Wbatt [1/h] DoD [%] Depth Of Discharge [%]

34 Battery simulation model : I P term ( e batt R batt i batt ) i batt e batt i batt R batt i 2 batt i batt e 2 R batt batt e 2 R batt batt 2 P R term batt P P loss ch arg e batt R P batt term ch arg e P P term i 2 batt P loss e b a t t P l o s s R b a t t P c h a r g e i b a t t P t e r m

35 Efficiency Battery Simulation model : II 2 Battery charge efficiency Battery power [W] x 10 5

36 Super Capacitors : I Low voltage -> series connection 1 W C u 2 C 2 C C system # units 1 1 C unit

37 Supe Capacitors : II 30 ton, 50 km/h = ½*m*v^2 = 0.82 kwh 0.82/ = 355 kg

Fly wheel energy storage High speed rotating mass A flywheel made of steel and carbon fibre that rotated at over 60,000 RPM inside an evacuated chamber The flywheel casing featured containment to

38 Fly wheel energy storage High speed rotating mass A flywheel made of steel and carbon fibre that rotated at over 60,000 RPM inside an evacuated chamber The flywheel casing featured containment to avoid the escape of any debris in the unlikely event of a flywheel failure The flywheel was connected to the transmission of the car on the output side of the gearbox via several fixed ratios, a clutch and a Continuously Variable Transmission 60 kw power transmission in either storage or recovery 400 kj of usable storage A total system weight of 25 kg A total packaging volume of 13 liters kwh/kg W mech 1 2 J 2 wheel

39 Electric Motor Drive Systems Industrial Electrical Engineering and Automation Lund University, Sweden

40 Torque and Power Torque = Force * radius on the shaft T = F * r Power = Torque*Speed on the shaft P = T * F r but, also Power = Voltage * Current on the electrical terminals P = U * I

41 Stator, Rotor and Airgap The stator is static (not moving) The rotor rotates The air gap seperates them Usually < 1 mm

42 Hybrid Topologies Diesel Engine El Ma ch D El. mac h El. mach

43 Rotor Stator Rotor Inner or Outer Rotor, Radial or Axial flux Inner rotor Radial flux Outer rotor Radial flux Axial flux Stator Stator Rotor Stator Stator End winding Stator

44 Distributed or Concentrated winding Axially shorter end winding Cheaper assembly Lower torque quality Longer end winding More expensive assembly Higher torque quality

45 Shear Force & Torque Current and Flux interact for tangential force s = Force/Unit area is a key figure s A good design accomplish about s = [N/m 2 ] in continuous operation and 2..4 times more in transient operation

Length Form Factor Low torque density but high acceleration For the same torque, a machine

of 1000 Nm, AND that the stator outer radius is 0.15 0.5 meter.

The long and slender machine will accelerate faster Torque ~ radius 2 *length Inertia ~

46 Length Form Factor Low torque density but high acceleration For the same torque, a machine can be either short and wide, or long and slender Assume [N/m 2 ], and a desired torque of 1000 Nm, AND that the stator outer radius is meter. How long will the machine be to fulfill the torque requirement? The long and slender machine will accelerate faster Torque ~ radius 2 *length Inertia ~ radius 4 *length Acceleration = Torque/Inertia ~ 1/radius Radius High torque density but low acceleration

47 Eaton ISAM Short and Wide Concentrated winding PM motor from Hitachi

48 Voith ExSAM Long and slender Induction motor from?? Probably very close to standard industrial good commonality 150 kw 520 motor or input shaft? Siemens 1FHX

49 Volvo/Renault/Mack/Nissan ISAM Short and Wide

50 Complex PM Machines Distributed windings N/m 2!!! Some Cars ISAM PM Motor Concentrated windings

* length (twice) = Force * Speed = Voltage * current

51 Generic Force Force Flux density Lorentz force = current in magnetic field Current Force Power = Flux density * Current * length (twice) = Force * Speed = Voltage * current Voltage = Force *speed / current = = Flux density * length * speed

52 Linear movement from generic force

53 Rotating movement from generic force

54 Conclusions on force and movement The same generic circuit accomplish both linear and rotating movement. One phase is not enough for continuos force Qualitative: Voltage ~ Speed Current ~ Force

55 Field Weakening : I Remember: Voltage ~ flux density * speed Torque ~ flux density * current Power ~ speed*torque = voltage*current The required voltage hits the roof at some speed. What to do, to increase speed beyond? Answer: Reduce flux density Consequences: The voltage requirement is kept constant, as desired The torque capability drops as the flux density. The power is kept constant, since the speed increases in the same rate as the torque drops with increasing speed.

56 Base speed Max speed [rpm] Field Weakening : II [Nm] 250 [kw, V] 200 Field weakening ratio 1: Max voltage and power 50 0 Const torque Constant power

57 Example from Toshiba Large Torque and High Efficiency Permanent Magnet Reluctance Motor for A Hybrid Truck - Masanori Arata et. Al, EVS-22

58 Permanent Magnet Synchronous Machines Same as the generic machine Voltage and frequency proportional to speed Current proportional to torque High torque density Nm/kg Compare to ICE Nm/kg High efficiency Up to 97% Higher efficiency, higher torque density and more expensive than other machines Due to the permanent magnets.

59 The Induction Machine : I Same stator as the PMSM The rotor is a short circuited cage The rotor current must be induced magnetically Losses related to magnetization competes with losses due to torque generation. Robust construction Low cost Low/no maintenance Heavily standardized for industrial applications

60 The Induction Machine : II Voltage and frequency proportional to speed, like PMSM

61 Comparison Electric Drives T max [Nm/kg] AC (IM) PM P continuous [kw/kg]

62 Electrical machine losses Several types: Copper losses (Ri 2 ) Iron losses (k 1 *f*b 2 + k 2 *(f*b) 2 ) Windage losses (surface speed) Other friction losses Approximately calculated by Hysteresis losses Eddy current losses [EtaEM,Tem,Wem] = CreateEMmap(Pem_max,wem_max,Tem_max) Electrical machine efficiency Torque [Nm] Speed [rad/s]

63 The Traction motor efficiency Torque limit Electrical machine efficiency Power limit Torque [Nm] Speed [rad/s] Speed limit

64 Power Electronics Needed to condition the battery voltage to the different electrical drives Use switching technology for high efficiency Conventional converters (like loudspeaker amplifiers) efficiency % due to continuous control of the voltage. Switching means on/off control of voltage, leading to efficiency above 95 %.

65 1 Phase Pulse Width Modulation (PWM) sa va Modulating wave Voltage reference Output voltage

66 Three-phase Converters +Ud/2 id 0 sa va sb vb sc vc -Ud/2 + uab - + ubc - - uca ua ub uc - - vo - Traction motor

67 Three-phase Pulse Width Modulation The voltages contain high harmonics that cause: Audible noise Torque ripple EMC problems ua r ef & tri va vo v0 0 varef va tri ua u=va-v0 grundton 50 Hz

68 Power Electronics Efficiency Several types of losses Switching losses Conduction losses v S, i S V DC i S I 0 v S v on t + V DC p S I 0 P cond t on t cond t off t T sw

69 Power Electronic Efficiency Mostly depending on the ratio Output voltage DC link voltage Almost constant over wide operating range Can be represented by a constant, e.g. 0.97

Hybrid Drive Systems for Vehicles. Drawback with conventional drivetrains

Hybrid Drive Systems for Vehicles L4 Alternative drive train Components Drawback with conventional drivetrains Limited ability to optimize operating point No ability to regenerate braking power 1 Solutions