Shark - new motor design concept for energy saving-applied to Switched Reluctance Motor

The aim of this thesis is to document and promote a relatively new concept of designing electrical machine with improved efficiency, without using more or better material. The concept, called Shark, consists in replacing the cylindrical air gap by a non-linear shape obtained by translating specific geometrical pattern on the longitudinal axis of the electrical machine. This shape modification increases the air gap area and thus the energy conversion, taking place in the machine. Whilst other methods of improving the efficiency consider the use of more and/or better magnetic material and/or optimisation of the magnetic circuit of the radial cross-section of the machine, the proposed method makes use of the longitudinal cross-section of the machine.

In spite of a few reports claiming the improvement of the efficiency by applying the optimisation of the longitudinal cross-section, none analysis of various air gap shapes and of their influence on the magnetic performance has been reported. Due to a simple geometry, the Switched Reluctance Machine has been selected for demonstration of the Shark principle.

Initially, linear and finite element analysis are considered. They provide the basic knowledge of the manner in which various Shark air gap, having different dimensions, influence the energy conversion in the machine. The saturation mechanisms, specific to each Shark profile are analysedand optimum Shark profile and its dimensions are selected for implementation in a demonstration machine.

Due to the lack of quick analysis tools, an analytical model of the Shark Switched Reluctance Machine is also proposed in this thesis. This model is conceived by modifying one of the existing models of cylindrical air gap Switched Reluctance Machines, such as to account for the presence of the Shark profiles in the air gap.

The calculations are verified by measurement on two demonstration machines, having cylindrical and Shark air gaps. The measurement proved the theory right and measurement of efficiencies proved that the Shark air gap improves the efficiency of a specified machine by two to four % point with respect to a corresponding cylindrical air gap machine. Furthermore, the two Switched Reluctance Machines are compared with other motor technologies such as Induction Motor and Brushless DC Motor.

Analysis of the forces produced in the Shark SRM reveals particular aspects, adding some difficulties to assembly the Shark motor. However, the latest assembly technologies provide solution for a simplified assembly of a Shark machine.

Calculations of economical aspects demonstrate a small difference in saving between the Shark Switched Reluctance Motor and the Brushless DC Motor considered in this project.