Comparative assessment of ultra-capacitors and advanced battery energy storage systems in PowerSplit electronic-CVT vehicle powertrains

The power split architecture has become the dejure "gold standard" of hybrid propulsion systems because the global OEM's have converged to the electronic-continuously variable transmission, or e-CVT in two different configurations. For Toyota and Ford the single epicyclic gear set, THS and FHS respectively e-CVT. For GM-Allison and others to the dual epicyclic gear set, AHS designs possessing 2-modes of operation. Regardless of architecture, power split transmissions require a pair of electric motor-generators in order to deliver their intended function. The power electronic architecture for the Toyota hybrid system, THS can be in either a battery unbuffered THS-I or battery buffered via a buck/boost converter as in THS-II. The GM-Allison advanced hybrid system, AHS is configured as a battery unbuffered configuration, but it could also be realized using the battery buffered configuration. Benefits of ultra-capacitor augmentation of the energy storage system in both unbuffered and buffered configurations are investigated