Hybridisatie van mijn machine - 07-06-2012_components-dc-example

the collective centre of the Belgian technological industry

Hybridisatie door energie-opslag in of nabij de machine

seminarie 07-06-2012

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[email protected]

mailto:[email protected]






© 2012 Sirris – FMTC – VUB www.sirris.be www.fmtc.be mobi.vub.ac.be

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Content

• Energy storage components• Inertial energy storage

(flywheel)• Hydro-pneumatic enrgy storage• Electric energy storage

• Batteries • Capacitors & supercaps

• Electric energy conversion• DC/DC & active control

• Example

07-06-2012


Kinetic energy storage flywheels

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Flywheels: Basics

• Kinetic Energy:

• Acceleration (w2>w1): energy stored in flywheel• Deceleration (w2<w1): energy is released• Typical: wmin = wdesign_max/2

• DOD = Depth of DischargeSOC = State of Charge SOC (%)= 100 – DOD(%)

•evolution of flywheels: • high speed• smaller volume & lower mass

flywheel Low speed High speed rpm <10000 15 000 – 100 000 technology mature recent Rotor Steel

(vmax≈300m/s) Composite fiber (vmax≈1000m/s)

Bearing Conventional (heat)

ceramic ; magnetic

Surrounding Air (air resistance) Vacuum Safety ! ! ! !

0 100 200 300 400 500 600 700 800 900 10000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Ekin/Ekin_max for nominal max speed wn=1000

0.250

0.502Ekin ( )

I wn2

wn

2

wn

2

DO

DS

OC

07-06-2012



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Flywheels: evolution to higher speed and smaller sizes

CCM (center for concepts in mechatronics)‘Autotram’ project (with Fraunhofer)

07-06-2012


Mechanical coupled flywheel

Test-setup for DriveTrain Control (DTC) testing (TU/e & mecHybrid)

©FlybridSystems

• Flywheel mechanical couped with drivetrain

• Outcoming shaft maintain vacuum for highspeed flywheels !!

• Brake energy recovery:

rpmflywheel rpmdriveshaft

CVT• No conversion needed to/from other

energy sources

• Control of energy flows with mechanical components (cvt/powersplit, clutches, …) is challenging for efficiency & comfort (shocks, response time… )


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Kinetic Energy Recovery System (KERS) in F1

07-06-2012

• regulation: max 60 kWatt , max 400kJoule/lap (i.e. boost of 60kWatt during 6.7s)

• F1 KERS from FlybridSystems• coupling to drivetrain via CVT (Torotrac)• total volume 13 litres • weight 25 kg (Flywheel 5 kg)• 30000-60000 rpm

• commercial mass production (Jaguar, end 2012/13)• 530 kJ (147 Wh) , 60 kW, < 40 kg• designed for 250000km lifetime

• project with Volvo & SKF• others:

• Zytec, Xtrac• Williams (electromechanical)

©FlybridSystems


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DriveTrain Innovations (NL):flywheel + ‘variomatic’ CVT+ planetary power split

• ‘Zero Inertia Driveline‘ (TU Eindhoven)• from ‘ecodrive’ project (late 90’s);

goal: decreased fuel consumption + emission• load levelling

Engine operates at optimal point flywheel = peak power unit

• Stop and Go regimes: uncouple & Shut down ICE at low speed

• spin-off DriveTrain Innovations (dtinnovations.nl)• Slower rpm, ‘classical’ technology

• mecHybrid project:• DTI+CCM+SKF+TU/e+Bosch+PunchPowertrain• develop lowcost flywheel system for small/medium cars• ‘small’ size (150kJ;30kW braking/10kW motoring)• Focus on energy management (DTC = DriveTrain Control)

07-06-2012


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Electromechanical flywheel‘mechanical capacitor’ , ’electromechanical battery’

• flywheel integrated with motor/generator unit (MGU)• permanent magnet motor or reluctance motor

size reduction at high rpm• power electronics

• connection to electric supply (grid or machine/vehicle DC-bus)

• mechanically uncoupled from machine/vehicle drivetrain• can be mounted at any position

• no shaft connection with exterior + easier to maintain vacuum

- thermal equilibrium of MGU in vacuum

• applications: • UPS-systems• automotive / transport

07-06-2012

15 kW motor (© Rosseta Technik)

Top: 3000 rpm asyncronous motor

Down: 35000rpm permanent magnet motor (only rotor)


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Electromechanisch vliegwiel Rosseta Technik

07-06-2012

Type T3 lowcostLowpower (3-5-10-15kW)Low energy (~7sec @ max power)Classic technology (6000rpm),

Type T2 (orde 25 à 30 k€)Highpower (300-800W)High energy: 4kWh (14.4 MJ)New technology (25000rpm, vacuum)


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flywheel systems for UPS: Power-Thru (= ex Pentadyne)

pentadyne.com

• powerrating: 12sec @ 200kW (29sec @100kWatt) ~667Wh (805Wh)• carbon fiber composite flywheel cylinder 24kg (cabinet 590kg)

28Wh/kg (only rotor) 1.13Wh/kg (complete cabinet)• flywheel speed 52000 rpm; magnetic bearings• 250Watt nominal power consumption

07-06-2012


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flywheel systems for UPS: Vycon

• powerrating: model VDC: 30sec @ 100kW (max 215kW) ~833Wh model VDC-XE: 19sec @ 160 kW (max 300kW) idem• high grade steel flywheel (? kg) • flywheel speed 36000 rpm

07-06-2012


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Beaconpower : flywheel system for UPS & load levelling on grid

• model ‘Smart Energy 25 Flywheel’ • powerrating: 25kWh (15minutes @ 100kW)• composite rotor (glass & carbon)

?kg (~2m high ! )• flywheel speed 16000 rpm• unit contained in concrete bunker

powerplant NY: 15’ @ 20MWatt (consists of 200 Flywheel units)

07-06-2012


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Transport: electromechanical flywheel for trams (Citadis, NL)

CCM (center for concepts in mechatronics)

• load leveling• load flywheel during braking & low power

periods• unload during peak power requirements

• autonomy • No power supply over Erasmus bridge

(Rotterdam)• specs:

07-06-2012


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automotive electromechanical flywheels

• Williams F1:• 50000-100000 rpm; 40kg unit;• MLC Magnetically Loaded Composite

technology from Urenco (nuclear power) efficiency load/unload: 97-99%• Technical Center (Qatar) for development &

commercialisation of flywheel technology• prototype Porche911-GT3-R-hybrid

• flywheel 6à8sec@120kW; 40000 rpm• 2x60kW motors on front axle

07-06-2012

• KINERSTOR PROJECT (UK):

(William Hybrid Power, SKF, Torotrac, landrover, e.o.)

Goal: Mass market high speed

flywheel Cost of less than £1,000 Development of both electric

and mechanic flywheel


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automotive electromechanical flywheels

• Flybrid & Magneti Marelli• 530 kJ, 60 kW• System weight: 27 kg

07-06-2012

• Bosch (Motorsport) / Dynastore• 160000 rpm !!• allways dual contraspinning units• 750kJoule (208Wh) (set of 4)• MGU 60kW (8kg)

MGU

Control unitwater cooled


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Flywheels: + and -

+• State of Charge (SoC)• high energy & power density

• 3-10 Wh/kg (w.r.t. total weight)• 1000-3000 W/kg

• Low maintenance cost• Lifetime (order > 20 year) for big

non-mobile systems;automobile ? not proven yet

• Performance not influenced by: • Amount of cycles• Depth of discharge• Temperature or environment

• high round-trip-efficiency (load/unload)

07-06-2012

-• Purchase cost• Dedicated designs

• limited combinations of power & energy

• not sold/available as such• Standing losses• Safety issues• (Gyroscopic effect)

• for mobile applications• solve with 2 flywheels spinning

in opposite direction


Hydraulic energy storage


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Hydraulic energy storage: basic (‘hydro-pneumatic’ energy storage)

• Energy stored in accumulator•Most used: Piston and Bladder•Max press 350- 400 bar…500bar•preload pressure:

100 … 200 bar

•More energy/power needed ? accumulators in parallel

• Flow rates 5000- 45000 l/min 900 l/min(order of magnitude)

07-06-2012


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Hydraulic energy storageadvantages & disadvantages

+ high power density lifetime+ maintenance+ lower cost (ROI) ?

(1700 €, 20 liter bladdertype)+ mature technology

- no really new technology- but: new applications

low energy density Size & weight for mobile

applications (passenger cars) thermal effects gas chamber (piston type -> standing

losses) (Leakage) Cost/efficiency of aggregates

07-06-2012

Light-weight carbon fibre reinforced accumulators


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Hydraulic energy storage: thermal aspect

07-06-2012

(example Hydac)


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Hydraulic energy storage Example: HyDrid

• Series hybrid• regeneration• load leveling

• Standard Car: 1450 kg• Accumulator: 20 liter

http://www.innas.com/

07-06-2012

https://www.fmtc.be/wiki/lib/exe/fetch.php?cache=cache&media=ensto_iwt_co:series-hydraulic.png


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• Goal: work in optimal operational condition of ICE• Also effective on highway !

07-06-2012

Hydraulic energy storage Example: HyDrid


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Hydraulic energy storage: UPS-van

•series hybrid• power density ~3000W/kg• energy density ~2Wh/kg

07-06-2012


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Hydraulic energy storage: commercial truck

• Bosch-Rexroth• parallel hydr.system:

• 500kg• 2 x32liter bladder

accumulator (210-330bar)• 250kWatt 500W/kg• 550kJoule(153Wh ) 0.3Wh/kg

(= Ekin of vehicle ~16ton @30km/h)

• fuel reduction 25%

07-06-2012


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Hydraulic energy storage : suppliers in automotive/transport sector• Bosch-Rexroth HRB (Hydraulic Regenerative Braking)• Eaton Corp: Hydraulic Launch Assist (HLA)• Parker Hannifin: RunWise Advanced Series • Hydraulic Hybrid Systems,LLC (HHS)

• light-duty vehicles• average price parallel system: $12,900

• Artemis Intelligent Power (Digital Displacement © system)• Hydac accumulators (+ calculator)

07-06-2012


Electric energy storage:

batteries capacitors supercaps (ultracaps)

http://upload.wikimedia.org/wikipedia/commons/e/e3/Maxwell_MC_and_BC_ultracapacitor_cells_and_modules.jpg


batterieslead acid

nickel based

lithium based

…

http://upload.wikimedia.org/wikipedia/commons/f/ff/UL20712.jpg


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Lead-acid batteries

07-06-2012

• simpel ‘vented’ VRLA advanced VRLA(VRLA = valve-regulated lead-acid)

• Specs• Low Energydensity (30-40 Wh / kg)• Self discharge 2 % / month• Small lifetime

• VRLA: 500-800 cycle• Vented: 1000-1500 cycles

• Efficiency 70-85 %• cheap (1kWh ~$250)

• Advanced VRLA (longer lifetime, higher power)• micro/mild hybrid (start-stop function in cars)• The Advanced Lead-Acid Battery Consortium (http://www.alabc.org

)

http://www.alabc.org/


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Ni-based batteries NiMH

• Used in hybrids• Toyota prius, Honda Insight, …

• Specs• E 80 Wh/kg• P 170-1000 W/kg• Standing losses 10 % month• Efficiency: 70-80 %

• Others• NiCd, NiZn

07-06-2012


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Lithium based batteries

07-06-2012

• A lot of different types• Li-ion based• Li-polymer based

• Different applications:• High power Li-batteries• High energy Li-batteries

• Specs• Broad power/energy range see table• Li: reactive element

• thermal monitoring/management

• expensive

May 2009 A. Burke


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NaNiCl - batteries (Zebra)

• Specs• good energy & power density

• E 100 -125 Wh/kg• P 150-180 W/kg

• Disadvantage:• High operating temp needed (270-330 °C)• Needs extra heating at shut down

• Good solution for intensively used vehicles

07-06-2012


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Lithium-Ion Capacitor (LIC)

• ‘Hybrid’ or ‘Pseudo’-capacitors• Ex.: JSR Micro (Leuven)

• Technology batteries and electrolytic capacitor• Positive electrode: reaction similar to battery• Negative electrode: Layer phenomena• higher energy density• Earlier stage of development

• Specs• Lifetime: +- 100 000 cycles• Less self-discharge (compared to supercaps)• Temperature window (better than batteries)• High cell voltage 3,8 V

07-06-2012


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Summary batteries

+• High energy densitiy• Low self discharge

07-06-2012

(VUB-Mobi econocap)

-• Limited lifetime (+- 1000 cycles)

• Depends on temperature• Depth of discharge

• Limited temperature range• More difficult to determine SOC

(+- constant voltage)• Power density (type dependigin)


capacitors supercaps/ultracaps

electrolytic capacitor

…


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Supercapacitors (EDLC): what & how

• EDLC = Electric (Electrochemical) Double Layer Capacitor• Principle:

• Charge separation (order of nanometers ) (d ↓)• Extension surface: ex. porous carbon (A↑)

07-06-2012

d A C

from Wikipedia

C~ 10’s F --. few kFC~ 10’s mF --. 10’s mF

http://upload.wikimedia.org/wikipedia/commons/8/83/Supercapacitor_diagram.svg

http://upload.wikimedia.org/wikipedia/commons/8/83/Supercapacitor_diagram.svg


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Supercapacitors facts

• Typical voltage cell: 2,5 - 2,7 V

Series connection required

• Tolerance on capacitance + series connection voltage balancing needed !• Different methods: passive & active• Modules with balancing commercially available

• Self-discharge

07-06-2012

Bron:VUB-mobi


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Supercaps: Still fork-lifts

07-06-2012


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Supercaps: Dana hybrid transmission

07-06-2012

Duty cycle

1 driving backward2 forward, at end empty carrier3 backward4 forward, at end load carrier

MGU

transmission (gear box)

balanced supercaps

inverter / MGU-drive


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Electrolytic capacitors

• lot of different types• Aluminum capacitors most relevant for energy storage

• capacity up to 20 mF• max voltage 400 à 500 V 2 in serie for industrial DC-bus

• lifetime: 1.000.000’s of cycles, BUT depends from: temperature T• Arrhenius approximation: lifetime halves every 10°C increase of

T

• amplitude ripple current IAC

• higher amplitude shorter lifetime• frequency of ripple current (frequency of load/unload)

• higher frequency higher lifetime• (smaller) effect of actual maximum voltage level

• Vmax higher lower lifetime

07-06-2012


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Electrolytic capacitors: lifetime

• strongly T and thus ESR-dependent (heating Q~ESR*IRMS2)

• ESR = Equivalent Series Resistance• ESR ⇗⇗ at low frequencies (<100Hz) Temp ⇗⇗ lifetime ⇘ ⇘

datasheets give data >50Hz or > 20Hz

much mechanical systems have cycles < 10Hz

07-06-2012

ESR-curves in data-sheet extrapolation for low frequencies


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Electrolytic capacitors: lifetime (cont’d)

• ‘End of Life’ when any of the following conditions is reached:• Core temp > 105 °C (85°C products)

> 120 °C (105°C products)• ESR > 2 x initial ESR• Capacitance change: decrease more than10 or 20% relative to initial value• Leakage current < initial limit

• Conclusion: • Design with low ESR !!! However forced cooling often necessary• Limit current in capacitors ‘oversizing’• Pay attention to balancing + limit inrush current at startup

+ safely unload capacitors at shutdown of the machine

• Remark concerning supercaps: same thermal problem, however• minor frequency dependency (ratio ESRDC / ESR1000Hz ≌ 2)

• mostly application with high power high currents forced cooling

07-06-2012


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Other capacitors

• Keramic capacitors: 4V-…-600V-…-50 kV• Small capacitance• Smaller lifetime (order of magnitude ~1000 hr)• Suited for high frequencies @ (very) high voltage

• Metallized film capacitors• higher voltage >1000 V no series connection required• Low capacitance (max. ~1000 mF)• high frequency/low energy

07-06-2012


other energy storage

components:pneumatic

superconducting magnetic energy storage

(SMES)

hydrogen (H2)

…

MDI Airpodaccumulator: 175l @350bar carbonfibre


Comparison of technologies


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Comparison of technologies (2)

07-06-2012

Energy Storage

type

Power densit

y

Energy densit

y

Cycle life

Safety assets

Typical load cycle

time

Know-ledge SoC

Temp.range / Temp

effect

Flywheel + + + Rupture Seconds-minutes

++ ++/+

Hydraulic ++ - + Leakage Seconds - minutes

+ ++/+

Pneumatic + - + ‘pressure vessle’

Minutes (hours)

+ ++/-

(Super)caps

++ +/- ++ Chemicals

Fraction of seconds to

seconds

++ 0/-

battery - ++ -- Chemicals

Minutes to hours

- -/-


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Comparison of technologies (4)

07-06-2012

Hydraulic

SupercapsFlywheel

secondminute

hour

Positioning of energy storage devices in terms of energy density & power density (Ragone chart)


Electrical energy conversion (DC-converter)

[email protected]


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Content

• Introduction• Why dc/dc-converter• Market situation

• Topology DC-converter• basics• Interleaved multi-channel DC-converter

• DC-converter prototype in EnSto project

07-06-2012


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Typical electrical driveline

• Rectifier • Rectification electricity grid / dieselgenerator / …• High dc-bus voltage

• Depending on type of supply, country, …• Typical 550 V, 650 V (stationary applications)

• Several inverters + motors• Connected on dc-bus

• Brake chopper • dissipate energy when Vdc gets too high

• High dc-bus voltage• Depending on type of supply, country, …• Typical 550 V, 650 V (stationary applications)

• Energy saving store energy in supercaps

07-06-2012


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Compatibility: Supercaps DC-bus

• Voltage match DC-bus – Supercaps:• Supercaps require big voltage swings

to fully exploit energy• Energy exchange Voltage changes• Typical (maximum) voltage window: ½ Vmax to Vmax

• Limited voltage changes on DC-bus driveline (e.g. 550V to 750V)

• Number of cells • Low cell voltage supercaps: • typical max. 2.5 – 2.7 V • Put cells in series to match dc-bus

Not automatically matched with amount of energy!

• Interface needed to transform voltages• DC to DC converter• Also valid for battery systems or combined

07-06-2012


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Energy management

• Example: driveline with combustion engine + generator• cranes, cars,…

• Fuel + energy storage• Efficiency engine depends on load• Increase efficiency

1. Recuperate brake energy2. Operate in good working point

• control of powerflows needed• To obtain optimal efficiency• Implement Energy Management Strategy

• Energy management impossible without dc-converter

07-06-2012

Bron: http://www.innas.com


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Disadvantage dc-converter

• Extra component• Extra losses

• Losses when charging• Losses when discharging• Efficient dc-converter important

• Extra cost• Trade-off between

• more supercaps and dc-converter

07-06-2012

chargingdischarging


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dc-converter advantages & disadvantages

• Advantages• Control of powerflows

• Impossible without dc-converter (in series hybrid)• Allows optimisation of system efficiency (power management

strategies)• Downsizing supercaps possible

• Less cells required• Increased energydensity (vary voltage from Vmax to ½ Vmax)

• Protection (avoid peakcurrents in energy storage) • Disadvantages

• Extra losses: dc-converter with good efficiency is important• Extra cost: trade-off between more supercaps / efficiency gain

dc-converter

07-06-2012


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Market situation

• Used in automotive• Ex. Toyota Prius e.a.• Mainly in-house developments, not for sale

• Commercial products• A lot ‘off-the-shelf’ products in low voltage range

(range of 12 - 24 - 48 - …V)• High voltage dc-converters ?

• Rarely found off-the-shelf expensive, custom made(every application is different and has different specifications: voltages / currents / sizes / cost / targeted efficiencies)

07-06-2012

Study of DC-conversion in EnSto-project:• Gain knowhow in dc-converters / powerelectronics• Focus on high power / high voltages• Validate experimentally on set-up / prototype


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DC-converter basics

• Bidirectional DC-converter• 2 high frequent switches

• IGBTs / mosfets / …• With anti-parallel diode

• 1 inductor• filtercapacitors on both sides• Vdc>Vsc

• buck mode: power from high to low voltageboost mode: power from low to high voltage

• Example charging supercaps (buck mode)• Top switch on

• current inductor increases• Top switch off

• Bottom diode conducts• Current inductor decreases

• Current = Idc + Iripple

07-06-2012

1

2


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DC-converter topologies

• Different topologies exist (not detailed further)

• Interleaved multi-channel DC-DC converter most promising• Good efficiency and small volume

Source: Monzer Al Sakka, VUB, Comparison of 30KW DC/DC Converter topologies interfaces for fuel cell in hybrid electric vehicle

07-06-2012


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Hig

h V

olta

ge

Low

Vol

tage

(sup

erca

ps)

Interleaved multi-channel DC-converter

• Multi-channel ? • multiple buck-boost converters in parallel• total current is split in different branches

• Interleaved ? • The currents of each branch are shifted from

each other• Origin of name ‘interleaved’• Ex. 3 branches each current shifted 1/3 of the

period

Ex. 3 branches

07-06-2012


61

Advantages of splitting in multiple branches

• Increased efficiency• Reduction of conduction losses (Ri2) in inductors, IGBTs, diodes

• Average currents per branch decrease (current splitted in N branches)

• Size inductors decreases• Current splitted in N branches

• Rough approximation: • Volume inductor ~ related to energy in inductor =

• Total energy in coils:

Energy and thus total inductor volume proportional with 1/N Reduction in size and price

07-06-2012


62

Advantages: effect of interleaving

• Effect of interleaving• Reduction ripple current at energy storage• Output ripple current reduction + increased frequency of ripple• To get the same input and output ripples:

Smaller filtercapacitors needed (compared to 1 branch converter

07-06-2012

Hig

h V

olta

ge

Low

Vol

tage

(sup

erca

ps)


63

Summary advantages of interleaved converter

• Good efficiency feasible• Small filters needed (capacitors, inductors)

• Small volume and weight, reduced price• Faster dynamic response (faster transients currents possible)

• Modular system• More power needed? Extra branches can be ‘added’ to the

system• No need to redesign inductors etc. again from scratch

07-06-2012


64

Prototype DC-converter

• Specifications• Possible to charge and discharge supercaps• Voltages

• Low voltage (supercaps): 300 - 650 V @ 360A (≈ 110 – 230 kW)• High voltage (DC-bus): up to 800 V

• Weight / size• Less relevant, stationary application

• High efficiency

• Realisation Together with member company Bluways

07-06-2012


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Realisation

• Design with 3 branches• efficiency measurements

• Shows efficiency of 97-98 %ca. 1% lower at half current

Efficiency depends on:• Voltage level and voltageratio• Current level• Switching frequency Efficiency maps created

• Issues: • temperature in coils• noise

3 inductors6 IGBTs (watercooled)

+ drivers

Controller/Interfacing etc.

07-06-2012


66

Conclusion

• DC-converter• Working prototype

• Issues identified and tackled• Good efficiencies are obtained

• Allows to implement power management strategies• Prototype product

• Further development done by bluways• Commercial product now successfully put on market

07-06-2012


67

Ongoing work

• Other inductor configurations• Coupled inductors• Mutual coupling between branches can lead to material/price-

reduction

• Efficiency• Efficiency can still be improved at lower currents by selecting

number of branches ifo load

07-06-2012


Voorbeeld van elektrische energieopslag bij machine met

harmonische cyclische beweging


69

Elektrische energie-opslag: technologie

07-06-2012

Electrolytic capacitors→ Small energy density (indication: around 0,5 Wh/kg)→ Very high lifetime possible (10 year and more / 100 millions of cycles possible)→ high voltage per cell (typical 400V, up to >1000V for some types);→ capacity per cell: 100 mF < C < 10’s mF Super-capacitors→ High power density, low energy density Orders of magnitude: 5 Wh/kg, 6 kW/kg (depending on efficiency) at cell level)→ High lifetime possible (500 000-1 000 000 cycles).→ low voltage per cell (typical 2.7V);→ capacity per cell typical 10's F < C < few kF

Batteries→ high energy and energy density; rather low power characteristics (at cell level 50-150-200...400 Wh/kg possible depending on the batterytype)→ Short lifetime (order of magnitude 500-2000 cycles for full charge/discharge)→ low voltage per cell (typical 1.2 à 3.5 V)


70

Elektrische energie-opslag: topologie

07-06-2012

DC-Bus + Storage technology (Energy storage directly on DC-bus)→ 'passive' configuration

DC-Bus + DC/DC-Converter + Storage technology (Energy storage coupled to DC-bus via DC/DC converter)

More difficult to indicate when to use and when not to use DC/DC-converter. Some guidelines:

Coupling via DC/DC-Converter allows for: → different (independent) voltage levels for energy storage components and drive DC-powerline → energy management ('active' control of the power flows) Control of power flows allows for fully use of potential of capacitor (deeper discharge possible),

implement strategy (maximize energy recuperation, load leveling), better control of battery SOC... Choosing a dc-dc converter will be cost effective when having a big package of supercaps. → for small packages it is more difficult to say if a dc-dc converter is cost effective. (trade-off between price of the supercap package and price dc-converter)

Combination of technologies: Following topologies have been identified: DC-Bus + Batteries + Super-capacitorsDC-Bus + Batteries + DC/DC-Converters + Super-capacitorsDC-Bus + High energy batteries + DC/DC converter + High power batteries


71

Elektrische energieopslag:

workflow

07-06-2012

• Workflow bij gebruik van cellen (electrolytische capaciteiten, supercaps of batterijcellen) voor energieopslag, direct gekoppeld aan DC-bus.

• Indien men de werkspanning kan kiezen (bij gebruik van DC-omvormer, of bij een apart systeem van MGU gekoppeld op aandrijflijn met vermogensomzetter), dan de gekozen spanningsrange toepassen (Vmax, Vmin).

• Keuze technologie-topologie (eerste stap): bij machines met frequente cycli => capaciteiten (batterij meestal geen optie wegens lage levensduur en/of beperkte stromen (vermogen)


72

cyclische beweging (kinetische energie)

07-06-2012

Theoretical power needs for mechanism• Basisgegevens

• vermogenspiek ≌32 kW• energie ≌2200 Joule• frequentie: ≌ 5Hz• grid: 3x380V~;

DC-bus: 600…max800V

• doel: ‘negatief’ vermogen recupereren

• Oplossing (na enkele iteraties): technologie:

electrolytische capaciteiten (20mF, 400V max) (2 in serie, 5 parallel)

topologie: passief (zonder DC/DC converter)


73

cyclische beweging: simulatie

• werkelijke vereiste & recupereerbare vermogens: rendementen frequentiesturing, motor, tandwieloverbrenging mechanische verliezen in systeem (wrijving) efficiëntie capaciteiten

Werkelijke vermogens & energieën: 4100 Joule vereiste energie per cyclus ; 1200 Joule gerecupereerd

(29%) vereist vermogen uit net: > 60kW piek;

07-06-2012


74

cyclische beweging: levensduur capaciteiten

• invloedsfactoren:stroom ⇗ levensduur ⇘frequentie ⇘ levensduur ⇘ (specs. datasheets slechts > 10 of

20Hz)spanning over caps. ⇗ levensduur ⇘temperatuur ⇗ levensduur ⇘ (10°⇗ halveren levensduur !)

• levensduurschatting meer dan 10 jaar op basis van specificaties datasheets (levensduur i.f.v. Temp bij

ref.spanning) vereist (benaderende) berekening Temp i.f.v. stroom (IRMS)

vereist kennis van ESR-waarde i.f.v. frequentie !! in datasheets slechts boven 10, 20 of 50 Hz mechanische systemen lagere frequentie !!

correctie i.f.v. werkelijk optredende maximale spanning over capaciteit

Opmerking: puur energetisch reeds voldoende met 1 tak van 2 capaciteiten in serie omwille van levensduur en max spanning (<750V) tot 5 takken gekomen

(meestal oversizing nodig bij electrolythische caps omwille van levensduur) 07-06-2012


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cyclische beweging: tot slot…

• pay-back: kostprijs capaciteit: ±€95 *10 €950 energie-recuperatie: 6kW gemiddeld (5*1200 Joule/seconde)

6kW*8u/dag*5dag/week*52weken/jaar* € 0.15/kWh = €1872 payback ongeveer half jaar

• alternatieven: supercaps of batterij => te veel cellen nodig in serie en/of DC-

convertor zowiezo veel duurder• verdere opmerkingen:

• mogelijke strategie (mits DC/DC converter en actieve controle over vermogensstromen; hier niet uitgevoerd): load levelling

energie in capaciteiten niet onmiddelijk benutten, maar op moment van piekvermogen

• belang van rendementen (vb motor) werkt in 2 richtingen !!

07-06-2012


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Dank u !! Vragen ??

07-06-2012