Approaches to prove the rotor of the permanent magnet machine must be outside in order to improve the energy conversion process

Most of the electrical machines designed to have their stators on the outside and their rotors on the inside. However, it was noticed that the shaft fills a relatively high volume inside the machine without producing any torque. That means there is a wasted volume within the machine and this volume does not produce any torque. From this point of view, there are some trends in designing and building electrical machines to have their rotors outside the machine and their stators inside the machine. Here the example used for the machines using those designs is the permanent magnet (PM) machine, which is an electrical machines designed by the two different methods, inner and outer rotors to be used in many applications such as wind turbines and electric vehicle wheel motors. This paper is dedicated to prove that the external rotor permanent magnet machine is preferred for some significant reasons. The paper uses two approaches to demonstrate that. The first approach is using the geometrical volume of each machine to compare the torque capabilities in case of two possible topologies of the PM machines. The second approach is to compare the PM machine with another type of electrical machine, that has the same magnetic circuit topology and the rotor can be inside and outside as well.