Ultracapacitors and power electronic systems

Storing electrical energy, whether permanently or not, often involves storing it in electromagnetic or electrostatic form, as this is generally the simplest physical method. The aim is to recover this energy easily, with minimum losses, and in a very short time.

The arrival of supercapacitors with capacities well in excess of 1,000 F offers engineers new prospects, in particular the possibility of storing significant energy per element. For example, a supercapacitor with a capacity of 1,000 F and a voltage of around 2.5 V can store energy in excess of 3,000 J. And in a charge-discharge cycle with a period of 10 s, the power involved is of the order of a kilowatt, which is far from negligible in power electronics for a single storage element.

By way of comparison, a coil with an inductance of 0.1 H and a current of around 250 A would be needed to store the same energy. The volume and mass of this component would then be much greater than those of the supercapacitor, for equivalent stored energy.

What can we do with this energy? By recovering it easily and, above all, quickly, we can facilitate power exchanges in converters, provided we adapt their architecture.

By storing it for a long time, we have an emergency or back-up reserve that is all the more interesting because the self-discharge of supercapacitors is low.

The aim of this dossier is to present some possible prospects for the use of supercapacitors, based on their current characteristics in 2012.

To optimize charge – discharge cycles, and thus make the most of the large amount of energy stored, the environment of a supercapacitor battery must be adapted to the performance of its components. This is based on the characteristics supplied by the manufacturer. Today, this optimization is made possible by the use of suitable power converters, equipped with diodes and, above all, MOSFET or IGBT transistors.

Ultimately, the supercapacitor finds its place in many automated systems. Here are some typical examples.