## 4 Results and Discussion
Figure 16: Flux density distribution of the proposed generator. (**a**) Symmetrical position, (**b**) lower side of the stator core, (**c**) upper side of the stator core. Figure 17: _Cont._  
* Moving torque The moving torque of the original generator and the moving torque of the proposed generator are depicted in Figure 18. The green line indicates the moving torque of the original generator and red lines indicate the moving torque of the proposed generator. Moving torque is produced because of the interaction between a magnetic field from the rotor circuit and another magnetic field from the stator circuit when the load current flows in the circuit. Due to the lowest THD of the proposed generator, the ripples in the moving torque are lower than the ripples in the original generator. The percentage of the ripple torque can be calculated by comparing the difference between the maximum and minimum torques to the average torque. From Figure 18, the calculated ripple torque of the proposed generator is 2.42% and this is 45.82% for the original generator. From the results, a good improvement of 94.72% in the torque ripple is obtained by the proposed generator. With the lowest torque ripple, the generator will rotate in a smooth performance, which can minimize the bearing fatigue. * Cogging torque  
Cogging torque is also known as detent torque, depicted in Figure 12.0 It appears in the permanent magnet machines as an interaction between the permanent magnets on the rotor core and the slots in the stator core. It happens when the stator windings are not energized. Cogging torque is an undesirable effect on permanent magnet generators as it can affect the self-starting capability of the generator, generate mechanical vibration, and produce acoustic noise. For small wind turbine generator applications, the cogging torque generated from the generator is expected to be low enough so that the aerodynamic power of the turbine in the start-up position can overcome it. The percentage of the cogging torque  
Figure 12.1 Voltage waveform and harmonic order; (**a**) original generator, (**b**) proposed generator, (c) harmonic order of original and proposed generators. Figure 12.2 Moving torque of original generator and proposed generator. factor is defined as the ratio of the peak-to-peak cogging torque to the average torque. From Figure 19, the calculated cogging torque factor for the original generator is 55.15% and this is 1.75% for the proposed generator. The results show a good improvement of 96.83% in term of the cogging torque factor, which will make the generator easier to rotate in the start-up position. * Output power  
The output power (\(P_{out}\)) of the original and proposed generators is shown in Figure 12.3 It is calculated as a product of the on-load terminal voltage (\(V_{t}\)), load current (\(I_{L}\)), power factor (\(\cos\varphi\)), and the number of the system phase (\(m_{1}\)). In this study, as the generator was simulated to be connected to a resistive load so that the phase difference between \(V_{t}\) and \(I_{L}\) is zero, this results in \(\cos\varphi\) equal to 1. From Figure 20, \(P_{out}\) of the original generator is 413, 91 watts, and is increased to 3.77 kW due to the effect of increasing \(m_{1}\) and adding the stator core. Due to the addition of two stator cores, an increase in the number of stator slots from 12 slots to 20 slots, and an increase in the volume of the permanent magnet to maintain the flux density in the stator teeth and stator yoke of around 1.5-2 T and 1.1-1.5 T, respectively, the axial length and diameter of the original generator are increased, which results in an increase in volume. Power density (\(P_{density}\)) is defined as a measure of \(P_{out}\) per volume of the generator. The calculated \(P_{density}\) for the original generator is 212.69 kW/m\({}^{3}\) and this is 457.51 kW/m\({}^{3}\) for the proposed generator.