Design of semi-active battery-ultracapacitor hybrids

A design approach to battery-ultracapacitor semi-active hybrids for powering wireless sensing nodes is presented in the manuscript. The hybrid source, which is an enhancement of a passive topology, consists of an ultracapacitor assisted Li-ion battery, connected to the load via DC-DC converter. The system is controlled such that the DC-DC converter supplies a near-constant current to satisfy the average load demand while the ultracapacitor supplies the dynamic component of the load current. As a result, a high-energy battery can be used despite the load high-power demand spikes. In addition, the battery-load voltage matching is not required. It is shown that with the proposed control algorithm system performance is equivalent to the performance of a passive hybrid, employing a very high non-feasible capacitance value. In addition, the battery current is independent of the capacitor size which affects only the load voltage ripple. Extended simulation results are presented to demonstrate the approach feasibility.