Self-Adaptive Switched Architecture for Ultra-Capacitors Storage

National audienceEnergy autonomy is a major barrier to the deployment of wireless sensors networks in many applications. Ambient energy harvesting and storage is a way to enhance this autonomy. Moreover, in some applications with harsh environment (extreme temperatures) or when a long service liftime is required, the use of batteries for storage is prohibited. Ultra-capacitor provide in this case a good alternative for a energy storage. This type of storage must comply with the following requirements: a sufficient voltage during the initial charge must be rapidly reached, a significant amount of energy should be stored and the unemployed residual energy must be minimised at discharge. To answer these apparently contradictory criteria, we propose a self-adaptive switched architecture consisting of a matrix of ultra-capacitors. The initial structure (series) allows a small capacitance to be connected to the source of energy (energy harvesting) at charge starting. The ultra-capacitors are then reconfigured. The final architecture (parallel) insures a maximal energy storage. This adaptive architecture enables a trade off between the charge time constant, the maximum voltage, the autonomy of the system and the maximum energy utilization rate