Cogging Torque Minimization in Transverse Flux Permanent Magnet Generators using Two-step Axial Permanent Magnet Segmentation for Direct Drive Wind Turbine Application

Abstract

Transverse flux permanent magnet machines (TFPMs) are categorized as synchronous machines that benefit from having high value of torque density and capablity of accommodating high pole numbers. These characteristics make TFPMs suitable candidates for low-speed applications where high torque density value is requred such as direct drive wind turbine application. Despite the aforementioned advantages, TFPMs suffer from intrinsically high cogging torque value which is an important concern for wind turbine application. This paper focuses on axial PM segmentation technique to minimized cogging torque of TFPM topologies. Concept of the proposed method is discussed using analytical equations and optimum segmentaion angle is formulized. Non-linear magnetic equivalent circuit (MEC) is adopted where the PM segmentation, armature reaction, rotor transition and iron saturation effect are carefully modeled. The results of the MEC simulation are compared with the finite element method (FEM) results in terms of accuracy and computational time. The results from the analysis indicate that the proposed MEC method is almost ten times faster than FEM with reasonable level of precision. Taguchi method is adopted as a fast-response optimization method to improve the generator torque characteristics. The results show that the cogging torque has reduced by 97% with respect to the initial design while the average torque has only dropped by 8% which is an acceptable side effect due to the significant improvement in machine cogging torque.

A Review of Transverse Flux Machines Topologies and Design

“…Wind power (G) [15,17,26,[58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75][76][77]. Direct-drive wind generators are part of the so-called variable speed wind turbines.…”

“…In the design process, it is essential to optimize the PMs arc ratio for the arrays: using the same PM pieces size would not be always the good option to reduce the cogging torque [64]. The axial PMs segmentation, also named PMs skewing, is another well-known technique for TFMs [16,77] that imitates the slot skewing of classic electric machines.…”

“…Before the experimentation, to reduce the number of decision variables the Taguchi method can be applied [100], it consists of four stages [69]: identification of the design variables, develop the experimental matrix and conduct experiments, analysis, analysis of means. Taguchi method has been applied in some publications about TFMs [67,69,75,77,100]. For the function approximation, the Kriging method has been used [31,100,112], sometimes with variations [31].…”

Design and Optimization of the Dual-Stator Axial-Field Flux-Switching Permanent Magnet Motor with High-Torque Density and Low-cost

“…Different types of technology machines include axial and radial flux machines. Studies showed that axial flux machines (AFPM) have higher torque and power density (1)(2)(3), as well as efficiency (4-6). Axial field fluxswitching machines (AFFSPM) have limited torque density due to the location of PMs and coils, but still have higher torque and efficiency than radial flux machines and can reduce costs.…”

Design and Modeling of a High-Speed Permanent Magnet Synchronous Generator with a Retention Sleeve of Rotor

“…Two kinds of interior PM (IPM) and surface-mounted PM (SPM) machines are becoming candidates in highspeed applications. Figure 1 represents the most important advantages and disadvantages of the PMSGs [2][3][4][5][6]. In the last decade and along with the discovery of new PMs, these types of generators have drawn lots of attention, not only in academic papers but also in the power engineering world [7].…”