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Alternative Energy Storage System for Hybrid Electric Vehicles

Tobias Andersson, Jens Groot,

Helena Berg, Joachim Lindström, Torbjörn Thiringer

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Purpose and Method• Hybrid electric vehicle: demands on an efficient energy

storage system

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Energy Storage• Energy- and power density

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Supercapacitor

• Extremely high capacitance (kF)

• Low voltage (< 3 V)

d

AC

1000-2000m2/kg

5 Å

10-100 F/g

A.k.a Electrochemical Double Layer Capacitor (EDLC), Ultracapacitor, Electrochemical Capacitor (EC)

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Battery - Supercapacitor

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Simulation of the system

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Performance Parameters

• Reducing of RMS-current

• Reducing of power losses in battery

• Total energy efficiency

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Load Cycle (ECE15-L)

• Acceleration

• Constant velocity

• Regenerative braking

0 20 40 60 80 100 120 140 160 180 200-25

-20

-15

-10

-5

0

5

10

t[s]

P[W/kg]

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0 10 20 30 40 50 60 70 80 90 100-4000

-3000

-2000

-1000

0

1000

2000

t[s]

P[W]

EC PowerLoad PowerBattery Power

Control Strategy

• Low pass filtering

• Braking energy to EC

• Loading of EC

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Control Strategy

• Low pass filtering

• Braking energy to EC

• Loading of EC

0 10 20 30 40 50 60 70 80 90 100-4000

-3000

-2000

-1000

0

1000

2000

t[s]

P[W]

EC PowerLoad PowerBattery Power

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Test System

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Test System• EC

10 units 2.5V, 2600F /28 units 2.0V, 2700F

• Battery 50V / 100V, 60Ah NiMH

• DC/DC160 kW, 330A 2-quadrants DC/DC converter

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Results - simulations and experiment

• Battery, 100V

• EC, 56V

• Equal to car with the weight of 250 kg

0 20 40 60 80 100 120 140 160 180

-6000

-5000

-4000

-3000

-2000

-1000

0

1000

2000

3000

4000

t[s]

P[W]

Load Power Sim.Load Power Exp.Battery Power Exp.Battery Power Sim.

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Results - system performance

Performance Parameters Experiment Simulation Unit RMS battery current 56 55 % of reference case Power losses i battery 26 27 % of reference case Total energy efficiency 95 94 %

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Example-Simplified system for a city bus, 220kW

Battery 310 kgEC 280 kgDC/DC 90 kg

Total weight 680 kg

NiMH-battery + EC

Battery 1150 kgDC/DC 45 kg

Total weight 1195 kg

NiMH-battery

Weight reduction: 43 %

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Conclusions

Drawbacks Advantages• Weight reduction• Improved battery lifetime• Reduced temperature

dependency• EC could replace batteries

• Complexity• Difficult to estimate

the price• Not tested in full scale