A performance improvement study of a permanent-magnet assisted synchronous motor used in washers

Everyday more, synchronous reluctance motors are becoming one of the most preferred type of electric motors used in different applications. Their simple, light and easily maintainable rotor structure have made many researches to continue their work on the optimization of the nowadays synchronous reluctance motors. Another issue considered in the area of motor design, is the use of permanent magnets in these motors. Such modification of synchronous reluctance machines has changed their performance drastically, resulting in another type of electric motor nowadays called as permanent magnet assisted synchronous reluctance motor. Permanent magnet assisted synchronous reluctance motors have become the comparable reluctance motors to the conventional induction and brushless DC motors, if not even replacing them in several industrial and home appliances. The complete structure of synchronous reluctance motors and permanent magnet assisted ones (PMaSynRM), is composed of a multiphase stator, similar to those of induction or permanent magnet synchronous motors. All of their advantages over other motors come from the special rotor structure, having no windings and simple structure. The special rotor structure includes flux barriers that guide the magnetic flux coming from the stator to flow from one to another pole of the rotor. Such flux guidance is possible due to the reluctance difference in different axes of the rotor. The low reluctance axis is called as the direct or d-axis, whereas the high reluctance axis is called as quadrature or q-axis. When currents flow in the stator, the magnetic flux coming into the rotor tends to pass through minimum reluctance, thus it tries to align the rotor axes accordingly. Thus, a rotating magnetic field induces a constant torque on the rotor trying to align by following it at the same rotating speed. The main purpose of the flux barriers is actually the minimization of reluctance in the d-axis and maximization of the reluctance in the q-axis. The inductance values on these axes would be vice-versa, meaning the d-axis inductance should be as high as possible, whereas the q-axis inductance should be as low as possible. In literature, there are many methods presented related to the optimization of inductance values of the synchronous reluctance motors. One way of doing this, is the positioning of permanent magnets inside the flux barriers in such way that they will decrease the q-axis inductance by opposing the flux on this axis, whereas they will increase the d-axis inductance by supporting the flux on this axis. Increasing the difference between the d- and q-axis inductances means that the motor of the same size will be able to induce larger torque than that without permanent magnets. Permanent magnets inside the flux barriers are placed in different configurations and sizes. The location of magnets and many other parameters related to the rotor design, including number of flux barriers and size of the segments are optimized when the performance of permanent magnet synchronous reluctance motor is to be improved. On the stator size, number of slots, slot shape and tooth shape are the parameters that are change during optimization of synchronous reluctance machines. On this thesis, the washer's sample motor taken from another thesis, is further optimized to get better performance on both washing and spinning mode operations. The optimization work is started with the decrease of the air-gap length without increasing the torque ripple too much. The effect of the distance between third rotor barriers is also observed to see whether the desired performance is possible with lower magnet volume compared to the sample motor. After the air-gap and the magnet location is defined, having in consideration the maximum slot fill factor, the stator yoke and tooth optimization is done such that the magnetic flux density in these parts remains under pre-defined limits. When general dimensions of the stator are defined, detailed optimization of the stator slot including slot shape, slot opening height and width are done to see whether they have effect on the performance of the motor. All of the analysis are simulated using finite element method solving software Maxwell 2D. After the optimized prototype is selected, it is produced and tested according to several electrical motor standards. Further, its thermal analysis is performed using Motor-CAD, and then compared to that of the sample motor to see the thermal advantages of the new prototype. Mechanical analysis of both the optimized prototype and the sample motor are performed in ANSYS Static Structural module to see the mechanical integrity of the rotor at high speed spinning mode operations.