Analysis of continuously variable transmission for flywheel energy storage systems in vehicular application

Energy storage devices are an essential part of hybrid and electric vehicles. The most commonly used ones are batteries, ultra capacitors and high speed flywheels. Among these, the flywheel is the only device that keeps the energy stored in its original form i.e. mechanical energy. In order to connect the flywheel with the vehicle drive line, a suitable means is needed which would allow the flywheel to vary its speed continuously, in other words a continuously variable transmission (CVT) is needed. To improve the efficiency and range of the variators, a power spilt CVT (PSCVT) is one of the suitable options. This paper discusses the kinematics of PSCVT used to connect the flywheel to the driveline. The characteristic equations of the PSCVT have been derived for various types of PSCVT including the power recirculating and the multi regime type in both directions of power flow. An example of a PSCVT for a flywheel energy storage system (FESS) is computed using the derived equations. Finally the results, including powers and efficiencies for different types are compared