Development of an Ultra Low Speed Direct Driven Electrical Machine

Abstract:
Sustainable, efficient energy generation from hydropower can be achieved through the use of direct-driven generators. The construction and realization of a segmented direct drive for ultra low speed generator applications in harsh environmental conditions requires an unconventional solution approach. This paper focuses on a three phase permanentmagnet- synchronous machine (PMSM) where ferrite magnets and coils are arranged together in the stator, so that the rotor elements have only the function of the yoke. The design that is presented is based on the principle of Switched Flux Machines (SFM) and promises cost reduction and an improved assembly process due to the chosen configuration. Furthermore, it is shown how a high-resolution rotor position determination can be realized with only two simple and robust inductive sensors in generator operation. In order to avoid an expensive sensitive sensorsystem for direct detection of the rotor position, a state estimator was designed and successfully used to realize the field-oriented torque control. Finally, the electrical performance and efficiency achieved with the prototype is verified experimentally and compared with a conventional solution.