Nowadays, the interest in the synchronous reluctance machines is growing up due to their several merits in comparison to other machine types. These machines offer high torque density with respect to the induction machines. Their torque density is slightly lower than permanent magnet synchronous machines even though the lower performance is compensated by a much cheaper rotor. Since synchronous reluctance machines do not induce voltage when the stator is not supplied, there are not short circuit currents and braking torques due to the electrical faults, e.g. they have high fault tolerant capability. In addition, synchronous reluctance machine has a robust structure, and a wide constant power speed range. For these aforementioned reasons, these machines are employed in several applications. However, there is a prominent defect of this kind of machines which is the low power factor. This defect is addressed by assisting the motor by permanent magnets within the flux barriers of the rotor leading to the permanent magnet assisted synchronous reluctance motor. In addition, these kinds of machines has high torque ripple. This is due to the high harmonic content in the magneto motive force which interacts with the rotor anisotropy. Several approaches are proposed to reduce the torque ripple, such as: (a) using skewed rotor, (b) adopting two different flux-barrier geometries in the same lamination, i.e., asymmetric rotor, (c) using equally spaced the flux-barrier ends along the rotor periphery, and (d) optimization approaches were applied to smooth the torque. The synchronous reluctance machine is becoming of great interest in the last years, due to two key reasons: (i) the increase of rare earth permanent magnet cost and (ii) the increasing request of high-efficiency machines. Therefore, the reluctance motor and the ferrite permanent assisted reluctance motor are becoming competitors of both surface-mounted permanent magnet machines and induction machines in many applications. Such motors are also becoming particularly interesting when the control is based on the sensor-less rotor position detection. Even if there is a great interest in this kind of machines, there is a few work about the analytical design of their rotor, e.g. about how to select the end barrier angles, designing the iron ribs, and designing the permanent magnet robust towards the demagnetization. In the majority of the cases the reluctance machine is analyzed by using finite element analysis. The results are precise and useful for achieving a specific geometry to be prototyped, but they refer to that particular solution and they lose generality. In other words, it is difficult to find general rules to design reluctance machines, since the analysis approach is focused on a single objective. During the manufacturing process, there are some manufacturing imprecision, such as mass unbalance, bearing tolerance, shaft bow, and etc., cause eccentricity fault. Eccentricity may cause magnetic and dynamic problems with additional vibrations, noises, and torque pulsations. Although the eccentricity faults in induction and permanent magnet motors are extensively investigated, there are a few publications on synchronous reluctance machines with eccentricity. It is important to study the effect of rotor eccentricity on these machines because of their high anisotropy and critical iron parts in the rotor (iron ribs). For the aim of designing the iron ribs thicknesses, the unbalanced magnetic force acting on theses ribs should be accurately estimated. Main contribution of the thesis This thesis aims to give an useful analytical approach for reaching a preliminary geometry of both synchronous reluctance and permanent magnet assisted synchronous reluctance motors, as starting point for a successive optimization. For more accurate design of the rotor iron ribs, the electro-magnetic force acting on the rotor, in different rotor eccentricity cases, are analytically computed. In addition, a comparative studies (analytically and FE) between the synchronous reluctance, permanent magnet assisted, and surface mounted permanent magnet machines, in different eccentricity cases, is carried out. Therefore, this thesis is divided into four main parts. At the first part, an analytical model based on the magnetic equivalent lumped network of the reluctance motor is discussed. This model studies the magnetic performance of the concentric synchronous reluctance motor. Then, this analytical model is adopted in order to study the impact of different eccentricity scenarios (static and dynamic eccentricity) on the reluctance motor. Different stator windings configurations (distributed and concentrated windings) and different rotor geometries (symmetric and asymmetric rotor) are considered. After that, the eccentric synchronous reluctance machine is compared with the eccentric permanent magnet assisted synchronous reluctance machine. The impact of the barrier dimensions, the rotor geometry, and the permanent magnet type is highlighted in this comparison. Furthermore, an analytical comparison between the reluctance motor and the surface mounted permanent magnet motor is carried out in different cases of eccentricity. The axial non uniform displacement of the rotor axis from the stator axis, at one end and both ends of the axis, are involved in this analytical comparison. The second part aims to achieve more realistic estimation of the electromagnetic forces acting on the rotor by considering the effect of stator slots and the magnetic voltage drop due to the actual B-H curve of the motor iron. The analytical model is developed for both eccentric and concentric synchronous reluctance motor. Then, an experimental validation of the analytical and FE analysis is carried out. At the third part, an analytical approach for designing the permanent magnet of the permanent magnet assisted reluctance motor is proposed. The width and the thickness are selected so as to achieve the desired no-load air-gap flux density and resist the demagnetization under the desired loading conditions, respectively. Both complete and simplified analytical analyses are discussed. In addition, the analytical approach is presented in both cases of neglecting and considering the rotor iron ribs. Then, from the previously mentioned three parts of this thesis, a rapid multi-objectives analytical approach is proposed to achieve the initial design of the synchronous reluctance and permanent magnet assisted synchronous reluctance motors. Finally, at the fourth part, a graphical user interface application for concentric and eccentric synchronous reluctance motor is developed. This application estimates stator and rotor scalar magnetic potential, air-gap flux density, electromagnetic torque, magnetic force acting on the rotor. The input parameters of this application are - the geometrical data of the stator and rotor, - the electric loading (kA/m), the electric load angle in (electric degree), - the rotor geometry type, e.g., symmetric or asymmetric rotor geometry, - number of flux-barriers per rotor pole, - eccentricity type or no eccentricity, e.g., healthy case, - the eccentricity value. Then, the user can run the application to estimate the magnetic performance of both concentric and eccentric synchronous reluctance motor.