Variable reluctance axial flux alternator incorporating air gap variation

摘要

The aim of this paper is to design and manufacture a generator that could be mounted on a fixture that allows the stator to move axially such that the air gap between the stator and the rotor can be varied. After considering an array of generator designs, an axial flux permanent magnet design was elected. This design is chosen because it is easier to manufacture and also potentially able to implement the required modifications for the air gap control. The generator comprises of a wooden disk rotor with embedded permanent magnets mounted on the shaft with bearings. The stator is also a wooden disk containing electroplated planar coils. Since the efficiency of the axial flux alternator is inversely proportional to the air gap to the fourth power, the goal of the assembly was to be able to achieve smallest air gap possible. To get a small air gap, it was necessary to have very sound alignment mechanism built into the design. As a result a design was produced that aligned itself as it was assembled. The necessary steps to calculate the output voltage and the entire stability of the system are also studied. The special type of construction adopted for this generator makes it unique. There are a few modifications which could improve the design. These modifications include enlarging the bulk head design and making it removable, revising the bearing configuration and using corrosion resistant materials for production model. The model presented in this paper uses motor screw mechanism for the variation in the air gap, while this will suffice for the present prototype, a real time implementation of such a mechanism would use a ball and spindle arrangement.