Fuel Cell systems can potentially replace every battery powered electric system, and furthermore, they can also do better, overcoming autonomy limits and be integrated in applications which can now be powered only through internal combustion engines.
In the field of generic, all-purpose applications, fuel cells need to be combined with battery storage and ultra capacitors (symbiotic hybrid mode) to effectively meet the varying load requirements of each specific application at the lowest price and the most responsive operating mode.
Femag intends to explore optimised integration of components and power aggregates, delivering an energy generator, closed, of small power, based on the integration of a fuel cell with a battery pack and super capacitors, for the flexible supply at variable power of small portable non automotive devices.
The FEMAG project targeted an energy generator based on the integration of a fuel cell (FC) with supercapacitors and eventually an ancillary battery pack, for the flexible supply at variable power of small portable non-automotive devices.
FEMAG proposed to develop a product which would be based on FCs, but would be combined with all the components required to make its application flexible, simple and able to satisfy not only the base power consumption, but also relative peaks of consumption of associated machines, within utilisation profiles prefixed at the design stage.
The main FEMAG generator goal was to avoid the FC to be forced to sustain highly dynamic load, since the variable power supply is one of the main reasons of the stack lifetime reduction.
The durability of polymer electrolyte membrane (PEM) FCs is a major barrier to the commercialisation of the stacks for transportation power applications and commercial viability depends on improving the durability of the FC components to increase system reliability and to reduce the system lifetime cost by reducing the stack replacement frequency.
The FEMAG architecture is able to convert the dynamic loads, typical of many applications, in stationary ones using ancillary power storage systems as supercapacitors and a backup battery, which supports the FC, and a intelligent DC/DC converter that manages intervention priority of FEMAG components in order that:
- the supercapacitors have the highest intervention priority in supplying the load and they are dimensioned, according to a specific application, in such a way that they have the capability to supply every power peak (e.g. start-ups) required by the load;
- the FC is the second component in order of priority to intervene and doesn't 'see' peak power requirements;
- the backup battery intervenes when the power demand exceeds the FC nominal power.
The project targeted the following overall objectives:
- define and test suitable design configurations for small and medium electric power systems based on PEMFC, realising two FEMAG generator prototypes for a wheelchair (300 W stack) and an AGV (1.5 kW stack);
- develop symbiotic hybrid modes to effectively meet the varying load requirements of each specific application at the lowest cost and the most responsive operating mode;
- identify adequate set of components for such systems (batteries, ultra capacitors and controllers);
The FEMAG methodology was based on the integration of commercial and pre-commercial devices and components, and targets high replicability as a main patrimony to be generated.
The aggregated FEMAG generator was designed around the criteria of minimising fuel cell rated power, entrusting to backup batteries and ultra capacitors the supply of power transients, and put the cell in the condition to work only at fixed power output, extending its life.
The project involved both experimental and computational optimisation of aggregated systems, and exploits experimental design to set up rigorous testing activities.
Experimental design was a very powerful and comprehensive methodology, allowing planning and carrying out experiments in such a way that maximum possible information is gained.
It was very useful in the investigation of several aspects in the course of knowledge acquisition from experimental data.
The technological goals of the programme were:
- to select the correct mix of technologies to support and enhance the FC based systems, in the various fields of application targeted;
- to manufacture a prototype system for each significant application chosen depending on the results of the scientific study;
- to validate the result of the scientific findings of the programme;
- to submit the innovation of the design to the end user industries and consequently enhance the potential use of the FC based system in a new and/or broader range of application;
- to obtain a parametric description of the economic savings obtainable by the new design in each of the applications.
The main achievements in relation to the above described objectives can be summarised as follows:
- The laboratory test bed has been developed for the FEMAG high energy. A complete prototype composed by the aforementioned items (1.5 kW ME-DEA FC, 6 58F/15 V Maxwell supercapacitors, 3 1000 Nl metal hydrides Treibacher tanks and the innovative DC/DC converter which manages the priority of intervention according to the FEMAG philosophy) has been prepared in the Labor laboratory with the collaboration of Tor Vergata researchers. A complete measurement system (pressure transducers, temperature sensors, a gas flow meter to measure the inlet hydrogen flow) has been designed to supervise all the dynamic variations of the operating conditions. Instead the low energy prototype has been designed to be assembled in the wheelchair on board in order to test the FEMAG generator functioning on field. Therefore, all the low energy generator components have been assembled in a case.
- An expert system has been realised by Molnet, based on the test-bench results and simulations by Simulink model. Two FEMAG generator systems are considered: the first is the architecture composed by the FC stack + SC pack + DC/DC converters, which is the one actually realised in the prototypes. The first architecture expert system has been modelled using experimental results obtained in the Labor laboratory. The second architecture is the complete, in which a backup emergency battery is integrated as well. Since the experimental results of the project were not enough to build a complete and comprehensive ES, they were complemented with the results of the Simulink model simulations.
- The experimental test bed of the FEMAG high energy prototype has been integrated. The measurement system is able to measure temperature, pressure and gas flow of hydrogen stream from the tanks to the anodic channel of the stack and inlet/outlet cooling water temperature in the tank cooling circuit in order to evaluate the heat produced when the tanks are charged, the heat consumed when the tanks are discharged. All the data of the cell are collected using the 'Electronic control unit' ECU and sensors integrated in the stack. The load profiles are imposed using an electronic load commanded by a Labview software designed and implemented by Labor.
- The FEMAG low energy prototype has been installed directly on a wheelchair. The complete system assembled has been inserted in a box and plugged in the wheelchair. The system has been teste