An assessment of ultra-capacitors as the power cache in Toyota THS-II, GM-Allision AHS-2 and Ford FHS hybrid propulsion systems

In this paper a brief history of the development paths leading to power split concepts is given. The power split architecture is used as the comparison platform because the global OEM's have converged to the electronic CVT in two different configurations, Toyota and Ford to the single epicyclic gear set, THS and FHS respectively and GM-Allison to the dual epicyclic gear set, AHS designs, each requiring 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