Design and Performance Analysis of a Novel Fall-back Transverse-Flux Permanent Magnet Generator for Direct-Drive Wind Power Generation

Abstract

Advances in wind-generator technologies have enabled wind-energy conversion systems (WECS) to achieve remarkable growth among all renewable energy sources. Wind-generator technologies desires small dimensions, high-power-to-weight ratio, higher e ciency and controllability, as also installation feasibility and enable making choices in renewable power adaptation. Wind-power generation from wind-power plants (WPPs) employ either a direct-drive wind generator or a geared-drive wind generator concept. The direct-drive wind generator, better on multiple aspects among other generators, dominates wind-power generation today, despite a higher initial cost. Di erent types of direct-drive permanent magnet generators (DD-PMG), such as radial flux, axial flux and transverse flux PM machines, have been investigated and discussed in the literature. Various transverse flux permanent magnet generators (TFPMGs) have been classified in the literature as per number of stator sides, types of stator cores and permanent magnet arrangement. Conventional TFPMG brings in enhancement in comparison with other types of PM generators due to inherent characteristics of increasing power density without compromising the size of the generator. The inner-rotor surface-mounted TFPMG with singlesided U-shaped stator core is widely employed because of its high specific torque compared to radial flux and axial flux direct-drive PM generators, despite a complex manufacturing process. Various issues have been encountered with conventional TFPMGs as presented in the literature, e.g., flux distribution in a U-shaped stator core is uneven, and its inactive permanent magnet (PM) poles lead to high magnetic flux leakage. The flux pattern in such machines is multi-dimensional and to predict its performance through a magnetic equivalent reluctance circuit (MERC), an analytical model and validation through finite-element analysis (FEA) is essential. Their limitations in practical integration and large leakage fluxes deserve an analysis of such TFPMGs to widen the scope of research. This dissertation presents a novel fall-back transverse-flux permanent magnet generator (FB-TFPMG) suitable for direct-drive applications. In the proposed configuration, half the number of PMs (i.e., only active PMs) have been employed with the elliptical-shaped stator core and toroidal-shaped coil. This leads to immediate benefit of lower mass, better flux utilization and lower leakage fluxes. Highlighting the features of the proposed FB-TFPMG, the analytical model is derived using magnetic equivalent reluctance circuit (MERC) and its accuracy and reliability have been verified through FE analysis. Conventional TFPMG possesses a high cogging torque and it is important to observe the cogging torque of the proposed FB-TFPMG. A 3-dimensional (3-D) FEM analysis is used to find the cogging torque and compared with the conventional TFPMG. Outer rotor configurations, narrated in the literature, have an immediate merit of better cooling and are light weight in comparison with inner rotor configuration. The blades of the wind turbine have been bolted directly to the outer periphery of the drum, which reduce the net weight. An outer rotor FB-TFPMG is proposed, which is optimized through parametric sweep method using FEA. The performance of a novel FB-TFPMG is analyzed with inner and outer rotor configurations, under no-load and loaded conditions, using a 3D finite-element tool, and the results are presented in comparison with the conventional TFPMG. The results obtained through analytical model of FB-TFPMG have been validated by FE analysis. The results show improved outcome of the proposed topology in comparison with the conventional TFPMG. The FB-TFPMG with outer rotor design performance is compared with its conventional and inner rotor fall-back counterparts.