Design an axial flux brushless direct current motor and comparison with a radial flux brushless direct current motor

Need and dependence on electrical energy and electrical motors that constitute one of the fundamental of electrical equipment are increasing with a growing world population. The necessity of the new designs which have compact and multitasking are also increased. These type of systems require various electronic components and electrical motors that must exist and work together in a narrow space. Increasing the number of used electrical motors, energy requirement with the attitudes toward compact system reveal the constraints that are high efficiency, low volume and low weight in electrical motors. Electrical motors excited by permanent magnets come into prominence with the ability to satisfy the requirements of efficiency, volume and weight. With the simplest explanation, the usage of permanent magnets on rotor instead of electromagnets in conventional motors gives rise to lower weight and losses, and hence, it improves the volumetric power density (W/m3) and efficiency. The permanent magnets brushless motors can provide requirements on efficiency, volume and weight with these superior advantages. The permanent magnet brushless direct current (BLDC) motor that comes to fore with some outstanding features, is one of the permanent magnet motors. BLDC motors are classified according to flux path in the motor; these are radial flux and axial flux BLDC motors. In this thesis, instead of a radial flux motor used in a washing machine, an axial flux motor was designed with higher power density, lower volume and less weight. Later on, axial and radial flux motors are compared. Before starting the axial flux motor design, analysis of a radial flux motor already used in a washing machines is completed. Radial flux BLDC motor has 24 slots, 4 poles, ferrite type permanent magnets on the rotor, rated operation at 530 min-1 speed and 1,2 Nm shaft torque. Before starting the axial motor design, two dimensional model of radial flux motor was set up by using the mechanical and electrical specifications taken from the manufacturer. Two dimensional model was created in a package software programme that made analysis and calculations according to the finite element method (FEM). The radial motor was analysed and accuracy of 2 dimensional FEM motor model was proven by comparing FEM results with radial flux motor test results and rated values. Axial flux motor can be classified according to a number of rotor and stator used in motor topologies. Designed axial flux motor is low power motor; this is because axial flux motor was designed as an alternative to the radial flux motor used in low power washing machine applications. In low power applications and under the volume, weight and cost constraints, the best choice of axial flux BLDC motor configuration is single sided topologies which are comprised of one stator and one rotor. After specifying the axial flux motor topology, using the basic sizing equations for single sided motor that is deduced from literature, an analytical algorithm was created using MATLAB®. This algorithm designed for single sided axial flux BLDC according to maximum power density for a different number of poles. Axial flux motors were designed by using developed MATLAB® algorithm for a different number of poles, to provide same nominal operation performance with radial flux 530 min-1 speed and 1,2 Nm shaft torque. The same materials such as stator, rotor laminations, ferrite permanent magnet and copper conductor were used while designing the axial flux motor to make a proper comparison of radial and axial flux motors. Under the cost, manufacturability and power density conditions, the optimum motor design was chosen for a proper number of poles, out of designed axial flux motors with a different number of poles, and then the basic sizing and electrical design of axial motor were done. Thus, the analytical design of the axial flux motor were completed. The analytically designed axial flux motor has 12 slots, 8 poles, 3 phase stator windings and surface mounted magnets on the rotor. 3 dimensional model of axial flux motor is required in order to do FEM analysis. Contrary to the radial motor, a large change in axial axis and axial path of magnetic flux in axial motor made three dimensional model and analysis mandatory. The same FEM based package program used in the radial analysis were used in axial flux BLDC motor analysis too. The quarter model of the axial motor was set up in order to decrease simulation time and memory usage. The quarter model contained 4 slots and 2 poles. Thus, taking advantage of symmetry, more simulations with shorter times were done. FEM analysis were performed by using the quarter three dimensional axial flux BLDC motor model, the results were compared with analytical results and the design was confirmed. Later on, axial and radial flux motors' analytically calculated efficiency, volume, weight and cost data were added on FEM results and detailed comparisons of these motors were given. Radial and axial flux BLDC motors were compared under the power density, torque density, volume, total weight, efficiency and pulsation on the shaft torque headings. The comparison results show that designed axial flux motor has 68,8% higher power density, 209,6% higher torque density, 40,6% lower volume, 67,6% less weight and 54,3% lower cost versus radial flux motors. Besides, the efficiency of the axial flux motor increased 31,9% according to radial flux motors, from 52,67% to 69,5%. Thus, the targets at the starting of design such as higher power density and lower volume and less weight were performed successfully also the designed axial motor has higher efficiency. The basic reason why axial flux motor has higher power and torque density, lower volume and less weight than radial flux motor, was less used materials in the axial flux motor design. When the amount of used materials in radial and axial flux BLDC motor were investigated, it can be clearly seen that the amount of ferrite permanent magnets used in both axial flux and radial flux motors were nearly the same. However, the amount of used ferromagnetic material in the rotor, stator laminations located in axial and radial flux motors was higher more than 3 times at radial flux motor than axial flux. This huge difference is due to the utilization of the ferromagnetic material. The used ferromagnetic material used both radial and axial flux motors began to saturation about 2T. In radial flux motor, ferromagnetic materials used very low levels of magnetic flux density that gave rise to low utilization of the ferromagnetic material. Besides, axial flux motor used ferromagnetic material at near knee area in B-H curve that caused the higher utilization of ferromagnetic material. The better utilisation reduced the amount of required ferromagnetic material. Lower ferromagnetic material provided a reduction on motor volume and weight, and also an improvement on power and torque density. While the ratio of utilization on the ferromagnetic material was increasing along with the iron losses composed of hysteresis and eddy losses. In addition, required amount of copper conductor decreased in axial flux motor compare to radial flux motor due to the decreasing winding turn length of the compact structure result of axial flux motor. If the examination of losses is continued: Even though axial flux motors number of phase turns went up, stator phase resistance was lower than radial flux motor. Because, the compact structure of axial flux motors gave rise to a lot smaller turn length according to radial motors. Both of radial and axial flux phase currents were close to each other; therefore, the smaller phase resistance caused lower copper losses that occurred in axial flux motor. As a result, even iron losses increased in axial flux motor, the copper losses that has bigger value and more impact on motor efficiency, was lower in axial flux motor, the axial flux BLDC motor efficiency was higher than radial flux BLDC motor. In terms of motor torque pulsations, the radial flux reference motor had 55%, the preliminary designed axial flux motor had 72% torque pulsation. Later on, magnet pole arc to pole pitch ratio was changed while keeping used magnet volume constant and axial flux motor torque pulsation was decreased to 27,5%. The comparisons revealed that the design goals accomplished and axial flux motor surpassed in each comparison aspects; as a result, the axial flux BLDC motor has proved to be a suitable motor that can be used in washing machine applications.