Hybrid Drive Systems for Vehicles

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Karen Stevens
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1 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

2 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 Smaller Engine cylinder deactivation IC E Clutch Batt 1 5 IC E PE Clutch EM 1 GEAR Δ DIFF 2

3 Combustion On Demand Cylinder deactivation via free valve control Optimized efficiency Number of Cylinders in use Torque [Nm] Speed [rad/s] Torque [Nm] Speed [rad/s] Torque [Nm] Speed [rad/s] 3

4 Max efficiency.35 Blue=2-cylinder std, Red=2-cylinder COD Optimal Efficiency ICE Power [W] x1 4 Secondary Energy Storage selection Why electric? Efficient secondary energy converters (Electrical machines) Safe, quiet, flexible installation Increasing need for Auxilliary electric power High torque density of Electrical Mchines Up to 3 Nm/kg ICE: <2 Nm/kg 4

5 Secondary energy storage Hybridisation IC E EM PE Batt PE IC E Clutch EM GEAR Batt PE EM Δ DIFF Δ DIFF Series Parallell Energy Storage Systems Lund University, Sweden 5

6 How does a ery look? Design criteria Vehicle Performance Cost Operation 6

7 Driving the Hybrid by the Atoms Source: Uppsala University Technologies NiMH Li-ion Lead S.C. 7

8 Limiting Factors Durability NiMH Cost NiMH Weight Li-ion Cost Safety Charge Power Durability Lead Weight Maintenance S.C. Energy S.C. Initial Cost Performance Power Density S.C Effpower Pb- Acid NiMH Li-ion Energy Density 8

9 Relation to needs Power 1 kw 1 kw Propulsion Hybrid Hybrid Mode Mode Cranking Propulsion Electric Mode Mode Next NextGeneration Need Need Energy Battery Cell Properties All parameters are non-linear Strong dependance on SOC, temperature, current rate & direction, and history. No No Steady-State Operation! 9

10 Super Capacitor Cell Properties Fewer non-linear elements Strong dependance on SOC & temperature only Semi Steady-State Operation! Combined Energy Storage System Energy Density Battery Combined System SuperCaps Power Density 1

11 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 State of Charge Voltage Li-ion S.C. NiMH 1% State of Charge % 11

12 State of Health Temperature and Temperature Changes Charge and Discharge Properties Pure Electric Range State of Charge 2-5 individual cells in a ery system -- ALL need to be managed Management unit is needed SAFT data Mats Alaküla Mats Alaküla EHS 12

13 SAFT Lithium teknologi Mats Alaküla Mats Alaküla EHS Battery simulation model : 1 P i term P P η loss ch arg e = ( e = R e = 2 R = P P = P term ch arg e term + R i 2 ± P loss i ) i e 2 R = e 2 P + R i term + R i 2 P loss R e Pch arg e i P t e r m 13

14 Battery Simulation model : 2 2 Battery charge efficiency Efficiency Battery power [W].5 1 x1 5 Super Capacitors : 1 Low voltage -> series connection W = 1 2 C 2 C u C C system = # units 1 1 C unit 14

15 Supe Capacitors : 2 Size Capacitance Max electric specs Power density Energy density 22 liter / 15 kg 145 Farads 5 V / 6 A 29 W/kg 2.3 Wh/kg Fly wheel energy storage High speed rotating mass W mech = 1 2 J 2 ω wheel 15

16 Electric Motor Drive Systems Lund University, Sweden Torque and Power Torque = Force * radius on the shaft T = F * r Power = Torque*Speed on the shaft P = T * ω but, also Power = Voltage * Current on the electrical terminals P = U * I F r ω 16

17 Stator, Rotor and Airgap The stator is static (not moving) The rotor rotates The air gap seperates them Usually < 1 mm ω Hybrid Topologies Diesel Engine El Ma ch El. mach El. mac h Δ 17

18 Inner or Outer Rotor, Radial or Axial flux Inner rotor Radial flux Stator Rotor Stator Stator Stator End winding Outer rotor Radial flux Rotor Axial flux Stator Stator Rotor Distributed or Concentrated winding Axially shorter end winding Cheaper assembly Lower torque quality Longer end winding More expensive assembly Higher torque quality 18

Shear Force & Torque Current and Flux interact for tangential

accomplish about σ = 1-3 [N/m 2 ] in continuous operation and

torque density but high acceleration For the same torque, a

Assume 25 [N/m 2 ], and a desired torque of 1 Nm, AND that the

How long will the machine be to fulfill the torque requirement?

radius 2 *length Inertia ~ radius 4 *length Acceleration =

19 Shear Force & Torque Current and Flux interact for tangential force σ = Force/Unit area is a key figure A good design accomplish about σ = 1-3 [N/m 2 ] in continuous operation and 2..4 times more in transient operation σ 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 25 [N/m 2 ], and a desired torque of 1 Nm, AND that the stator outer diameter is.15.5 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 Length Radius High torque density but low acceleration 19

20 Eaton ISAM Short and Wide Concentrated winding PM motor from Hitachi Voith ExSAM Long and slender Induction motor from?? Probably very close to standard industrial good commonality 15 kw 52 motor or input shaft? Siemens 1FHX 2

21 Volvo/Renault/Mack/Nissan ISAM Short and Wide Mats Alaküla EHS ith w a d ll on le H aral P T CV Complex PM Machines Distributed windings 97 N/m2!!! Some Cars To Co yota mp l ex ISAM PM Motor Concentrated windings Mats Alaküla EHS 21

22 Generic Force Force Force = Flux density * Current * length (twice) Power Current Flux density = Force * Speed = Voltage * current Voltage = Force *speed / current = = Flux density * length * speed Lorentz force = current in magnetic field Linear movement from generic force 22

23 Rotating movement from generic force 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 23

24 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. Field Weakening : II [Nm] 25 [kw, V] Const torque Max torque Base speed Max voltage and power 6 Constant power [rpm] Max speed Field weakening ratio 1:4 24

Example from Toshiba Large Torque and High Efficiency Permanent Magnet

Al, EVS-22 Permanent Magnet Synchronous Machines Same as the generic machine

torque density 1...1 Nm/kg Compare to ICE 1.

25 Example from Toshiba Large Torque and High Efficiency Permanent Magnet Reluctance Motor for A Hybrid Truck - Masanori Arata et. Al, EVS-22 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. 25

The Induction Machine : I Same stator as the PMSM The rotor is a

magnetically Losses related to magnetization competes with losses

Robust construction Low cost Low/no maintenance Heavily

26 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 The Induction Machine : II Voltage and frequency proportional to speed, like PMSM 26

27 Comparison Electric Drives T max [Nm/kg] PM AC (IM) P continuous [kw/kg] Electrical machine losses Hysteresis losses Several types: Eddy current losses 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 [EtaEM,Tem,Wem] = CreateEMmap(Pem_max,wem_max,Tem_max) Electrical machine efficiency 1 5 Torque [Nm] Speed [rad/s] 8 27

28 The Traction motor efficiency Torque limit Torque [Nm] 1 5 Electrical machine efficiency 2 4 Speed [rad/s] 6 Power limit 8 Speed limit Power Electronics Needed to condition the ery voltage to the different electrical drives Use switching technology for high efficiency Conventional converters (like loudspeaker amplifiers) efficiency 25-6 % due to continuous control of the voltage. Switching means on/off control of voltage, leading to efficiency above 95 %. 28

29 1 Phase Pulse Width Modulation (PWM) +5 sa va Modulating wave Voltage reference Output voltage Three-phase Converters +Ud/2 id -Ud/2 sa va + ua - sb vb sc vc + uab - + ubc - - uca + + ub - vo Traction motor + uc - 29

30 Three-phase Pulse Width Modulation The voltages contain high harmonics that cause: Audible noise Torque ripple EMC problems ua r ef & tri 5 varef tri va va vo v ua u=va-v grundton 5 Hz Power Electronics Efficiency + V DC Several types of losses Switching losses Conduction losses v S I v S, i S V DC i S I v on p S P cond t on t cond t off t t T sw 3

31 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

Hybrid Drive Systems for Vehicles

Hybrid Drive Systems for Vehicles L4 Alternative drive train Components Mats Alaküla EHS Drawback with conventional drivetrains Limited ability to optimize operating point No ability to regenerate braking