Design and Analyses of a Coreless-Stator Type Bearingless Motor/Generator for Clean Energy Generation and Storage Systems

摘要

There has been great progression in clean energy systems such as photovoltaic and wind energy as well as increasing interest in sea wave and tidal energy. Hydroelectric systems (especially small-scale) are also being refocused upon. These systems often require short-term energy storage so the flywheel is now attracting attention as a possible storage system. These systems are often in remote or inaccessible locations and are required to be low or maintenance-free with a long life cycle, or they are close to domestic dwellings. In either case they should have low vibration and acoustic noise. In addition, for an effective flywheel, the mechanical bearing losses and windage losses have to be low. In this paper the authors propose a bearingless drive system to satisfy the requirements above. The bearingless motor is being actively researched and developed around the world[1]. In this type of machine, the functions of the electric motor and magnetic rotor levitation are integrated so that the shaft is shorter and the number of inverters and controllers is less, hence the cost is reduced. The suspension and motor windings are wound together in the stator core so that the air-gap flux density distribution is unbalanced by the addition of the suspension and main motor fluxes; as a result, a suspension force is generated. A two-stage outer-rotor type of bearingless motor/generator for flywheel energy storage has already been proposed by the authors[2]. However, it was later concluded that the suspension force was insufficient to support the rotor using the topology proposed (a flywheel potentially has a very high centripetal force). It was found that the suspension force acting on the inner rotor was in the opposite to direction of the suspension force acting on the outer rotor. In order to avoid this, a new coreless-stator type of bearingless PM motor/generator is proposed here.