Research On Axial Flux Permanent Magnet Machine For Small-Scale Vertical-Axis Wind Power Application

With the growing concerns of the energy and environment issues, renewable energy is becoming the focus of the public. As one of the most matured technologies of the renewable energy industry, wind power is getting great attention from various governments and companies. Small-scale wind power system, with its high mobility and flexibility, has broad application prospects not only in the pastoral areas, fishing boats, islands and other remote areas, but also in cities and towns for public lighting and monitoring devices.Axial flux permanent magnet (AFPM) machines have the merits of compact structure and high torque density. Since the absence of stator core eliminates the cogging torque and stator coreloss, the double-rotor single-coreless-stator AFPM wind generator is able to start at a low torque and operate with high efficiency, and is a most suitable candidate for vertical-axis direct-drive wind power system. Because of the different structure from traditional radial flux machines,3-dimensional (3D) field analysis is needed for the AFPM machines, which brings difficulties in calculating the electromagnetic feature of the AFPM machines.By studying the basic theories and the flux distribution of AFPM machines, a segmental 2-dimensional (2D) finite-element method (FEM) is proposed. The method is to cut the AFPM machine in the radial direction into segments, and build up simplified 2D models to simulate the 3D flux distribution and calculate the back EMF of the machine, so as to improve the simulation efficiency. And then, an analytical method is presented based on the 2D model, and formulas of the flux density in the double-rotor single-coreless-stator AFPM machine is deduced. Besides, the coil factor for non-overlapping coil in slotless stator is also calculated, which provides a simplified method to design and optimize this kind of machine.3D FEM is also carried out to validate the accuracy of the two 2D methods.Finally, a prototype of double-rotor single-coreless-stator AFPM machine is manufactured and tested. Through the no-load test of the prototype, the segmental 2D FEM and 2D analytical method are confirmed to be both efficient and accurate. Load test and the temperature rise test indicate that the prototype has a satisfactory performance with high efficiency, low voltage regulation and low temperature rise. The prototype machine can be used for long-term stable operation.