In most of the electrified transportation systems, where only batteries are utilized as energy storage system, usually batteries are tailored for the power rather than energy. Present technologies do not provide a battery proficient of high enough power densities without over-sizing it. Moreover, battery lifetime can diminish drastically if it is subjected to instantaneous charge/discharge pulses or fast fluctuating currents. This results in increasing the size, cost and size of the battery pack or shortening the battery life and thermal runaway problems.
In order to provide more efficient propulsion, without sacrificing the performance, increasing the fuel consumption, and over-sizing the battery, more than one energy storage devices with complementary characteristics can be used in electric traction systems. In a hybrid ESS, proper power budgeting based on the specific characteristics of energy sources would result in higher efficiency, longer life time of energy sources, as well as reducing their size and cost. The energy sources should be able to store, supply, recapture high power pulses and supply the steady demands of the vehicle. A hybrid topology composed of a high power density component such as an ultra-capacitor (UC) and high energy density component such as a rechargeable battery offers a compromise of both.
The research team at the Power Electronics, Energy Harvesting and Renewable Energies Laboratory (PEHREL) is investigating various system-level technologies to facilitate introduction of hybrid energy storage systems (HESS) to transportation and energy industries. These include:
(a) Innovative bidirectional dc/dc converters,
(b) Unique methods for optimal sizing the hybrid energy storage systems, and
(c) Novel supervisory online/offline time-domain/frequency-domain power and energy decoupling methods.
This research has applications in electric vehicles, plug-in hybrid electric vehicles, electric ships, more electric aircrafts, as well as high-power density mobile and stationary micro-grids.