Apportioning and mitigation of losses in a Flywheel Energy Storage system

A typical Flywheel Energy Storage (FES) system consists of a flywheel, an electrical machine and bidirectional converter/controller. Between the flywheel (which stores the energy) and the load (which consumes the energy) there are different systems like, electrical machine and bi-directional power converter. A portion of extracted energy from the flywheel is dissipated as loss in these devices before it is delivered to the load. These losses can be categorized as mechanical losses (drag, Bearing friction), electrical losses (hysterisis, eddy current, copper) and power converter losses (switching, conduction). Magnitude of these losses depends on the operating conditions like, motor speed, dc bus voltage, switching frequency, load current etc. It is necessary to find out the sources of these losses and quantify them, which will help us to adopt suitable loss mitigation techniques. One such system was built, tested; various sources of losses are found out and quantified. Also the tests were conducted to find the performance parameters such as backup time, boost converter gain at various loads, energy efficiency etc and the results are presented.