Minimization of cogging torque in a small axial-flux PMSG with a parallel-teeth stator

Abstract

A stator with a steel core is well suited for small, low speed PM machines, where core losses are much lower than copper losses. However, a slotted stator introduces cogging torque. A stator with parallel-teeth inherently lowers cogging torque but there is need to further reduce it. This is particularly important in wind generators since it raises the cut-in wind speed, thereby lowering the energy captured yield for a given installed capacity. Pulsating torques also produces noise and mechanical vibrations which accelerates the wear of the machine and its support structure. This paper presents some effective methods of minimizing cogging torque, which have minimal effects on the performance of the machine. Three PM rotor configurations were considered, which include: a pole-arc ratio of 0.80, alternating pole-arcs of 0.61 and 0.80, and skewed PM poles with a skew one slot-pitch. The 3 rotor configurations were simulated numerically using 3D Finite Element Analysis (FEA) and tested experimentally with the same stator. The machine topology with a rotor pole-arc ratio of 0.80 was used as the reference design. From the experimental results, the alternating pole-arcs effectively reduced coggingtorque by 73% whereas the skewed poles reduced it by 48%. The 3D-FEA and experimental cogging torque results are also comparable. The paper also compares cogging torque reduction techniques which are well suited for a parallel-teeth stator.Index Terms-Axial-Flux, Cogging torque, Finite element analysis, Parallel-teeth, Permanent Magnet, Ripple torque 978-1-4577-0541-0/11/$26.00 ©2011 IEEE

Detection of Static Eccentricities in Axial-Flux Permanent-Magnet Machines With Concentrated Windings Using Vibration Analysis

“…It employs the double-layer FSCW configuration, surface-mounted skewed magnet and parallel-cut stator teeth. The skewed magnets and parallel-cut teeth is used in [36] to reduce inherent cogging torque associated with PM machines by 70%; otherwise additional vibration due to excessive cogging may be induced. In this way, vibrations due to cogging were isolated.…”

“…The single-sided topology in [36] with parameters given in Table I is the prototype investigated in this paper using the experimental test-rig (Fig.3) developed for fault investigations in an AFPM machine in [37]. It employs the double-layer FSCW configuration, surface-mounted skewed magnet and parallel-cut stator teeth.…”

Detection of static eccentricity faults in AFPM machine with asymmetric windings using vibration analysis

“…2 nd , 4 th , 6 th … on close-circuit but the 2 nd ; the lowest is the most important to machine noise and vibration because of its much higher magnitude relative to others and its frequency of occurrence (usually below 1kHz) [16], [20]. On open circuit, the lowest mode is the greatest common divisor of the number of slots and poles [23]- [24]. Thus in a 10p/12s, 6p/10s, 18p/20s etc.…”

Conceptual Framework of Antecedents to Trends on Permanent Magnet Synchronous Generators for Wind Energy Conversion System

“…During the comparative analysis between alternating pole-arcs and skewing, the former effectively minimized the cogging torque closer to 70%, whereas it was only 50% by the latter and displayed minimal impacts on the performance of the machine. In terms of the performance of the machine, the alternating pole-arcs' topology had the maximum difference and the terminal voltage alongwith efficiency at a rated load was 8% and 2.5% respectively with the pole-arc ration of 0.80 [83]. Yong Pang (2011) considered Cogging torque as a vital parameter for designing a permanent-magnet machine which in turn has been investigated over the last few decades.…”