Magnetic Field Modelling of an Ironless Wind Power Microgenerator

Microgeneration wind turbines often have starting problems due to cogging torque. Since small turbines for urban use are often located near or on top of buildings, they are subjected to a lower level the wind speed and to a more turbulent wind. The wind turbine presented in this digest is rated at only 1 kW; to increase the wind speed through the turbine, a diffuser is proposed. This can increase the speed in about 30% and improve the power coefficient $C_{w}$ by about 70 %. The rotor is integrated into the turbine by fixing the turbine blade tips to an outer rotor ring which avoids shading by a centre rotor hub [1]. This ensures that the turbine reaches rated speed in less time and with greater regularity, i.e. it improves the starting. The turbine micro generator has an induced volts-per-phase of 94 V at 450 rpm. It is formed from a rotor with 100 surface mounted magnetic poles with no back iron, and an ironless three-phase stator. The inner diameter of the rotor is 1500 mm and determined by the length of the blades. The outer diameter of the rotor is 1546 mm. Each magnetic pole measures 30×40×5 mm (w×1×h). The outer diameter of the micro generator is 1554 mm. The pole pitch is very small due to the pole pair number and the diameters of the rotor. Therefore, the permanent magnets poles do not need to be arc shaped and rectangular shapes can be employed. Fig. 1 presents a view of the wind turbine with the electrical generator, the blades, and the diffuser.