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Hybrid High Energy Electrical Storage

Final Report Summary - HYHEELS (Hybrid High Energy Electrical Storage)

The overall goal of this project was to provide an UltraCap energy storage system for the use in hybrid and fuel cell vehicles, which satisfies all properties necessary to make an integrative component. Therefore, the development work comprised the optimisation of the electric properties of the basic cap, its combination into scalable modules with integrated power balancing within the modules, power prediction and the communication interface with the drivetrain.

The work programme consisted of two technical work packages (WPs) 1000 and 2000 for the development of the UltraCap modules and the UltraCap controller, and a WP 3000 concentrating on simulation and modeling as well as on testing and evaluation of the developed hardware.

After the kick-off meeting, several WP meetings took place to achieve a fine tuning of the project.

Within the project a newly cell / stack technology was developed and a new module was designed. The stack was made of one positive stack and one negative. On one side the positive electrode was connected to the lid and the other side to the bottom can. A plated connection was laser welded between the two cells to give a very low resistive connection for voltage measurement. A thermal shrink tube insulated the stack.

UltraCaps have become available on the market with restrictions regarding automotive applications when looking on maximum voltage and working temperature and packaging requirements. As the maximum voltage of a single capacitor is only 2.5 V, several capacitors had to be connected in serial to a module if higher supplying voltages were required. This made it necessary to develop an advanced UltraCap module packaging with optimised thermal behaviour, weight and cost. Furthermore, caused by different self-discharge of the single capacitors, the individual voltages of the module would be drifting away. Finally, the capacitor module would be mismatched in voltage. Battery systems would be usually overcharged to keep it balanced in charge and voltage. However, capacitors could not be overcharged. Therefore, special charge balancing systems were developed in the past. These charge-balancing systems exchanged the energy between the single capacitors in such a manner, that all capacitors achieved equal voltages.

The performance as well as the mechanical design of the controller ensured the reliable operation of the module and satisfied the future requirements of all automotive applications in this area.

New simulation models were developed to design and configure the UltraCap modules for different vehicles. The simulations were validated by experimental results.

The test platform at Vrije Universiteit Brussel was applied to verify the configuration the super capacitor based energy storages for passenger cars and heavy duty vehicles, with respect to the voltage variation, maximum charging / discharging current, power losses in speed cycles.

The driving cycle tests confirmed very good electrical stability even in the pre-series UltraCap modules. As a result, the super capacitor modules developed in the HYHEELs project were suitable for the automotive applications.

A Life cycle assessment (LCA) was done to compare the environmental impact of UltraCaps with batteries. The uncertainty analysis was performed through a Monte Carlo analysis. The UltraCap scored better than all the assessed battery technologies. The relatively low weight of the super capacitor and the high recyclability rate of its main material were the most important reasons for this.

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