Cogging Torque Reduction in Permanent-Magnet Brushless Generators for Small Wind Turbines

Abstract

We present the design optimization of the magnetic pole and slot design options that minimize the cogging torque of permanent-magnet (PM) brushless generators for small wind turbine generators. Most small windturbines use direct-driven PM generators which have the characteristics of low speed and high efficiency. Small wind-turbines are usually self-starting and require very simple controls. The cogging torque is an inherent characteristic of PM generators, and is mainly caused by the generator's geometry. The inherent the cogging torque can cause problems during turbine start-up and cut-in in order to start softly and to run a power generator even when there is little wind power during turbine start-up. Thus, to improve the operation of small turbines, it is important to minimize the cogging torque. To determine the effects of the cogging torque reductions, we adjust the slot opening width, slot skewing, mounting method of magnets, magnet shape, and the opening and combinations of different numbers of slots per pole. Of these different methods, we combine the methods and optimized the design variables for the most significant design options affecting the cogging torque. Finally, we apply to the target design model and compare FEA simulation and measured results to validate the design optimization.

Experimental evaluation of performance for micro wind turbines by using permanent magnets

“…Electromagnetic properties of PMSGs greatly depend on the number of slots per phase, shapes of PMs and slot width. (Chung and You 2015).…”

“…In recent years, PMSG usage in MWTs has become more and more common. PMSGs rotating at low speeds cause noise, vibration and cut-in speed problems in MWTs whereas PMSGs rotating at high speeds do not cause any serious problems (Bianchini et al 2014;Chung and You 2015). Under normal operating conditions, torque vibration is a result of interaction with air gap flux density high harmonics caused by stator winding and rotor PMs while the cogging torque is the result of interaction with the PMs and stator slots.…”

“…Their efficiency reaches up to 97% and they are direct-drive (Lebsir et al 2015). They are advantageous for their adaptable structure and simplicity in design, which makes them more preferable in small and medium power MWT applications (Daili et al 2015;Chung and You 2015). Because PMs employed in MWTs are constructed using rare-earth materials, PMSGs are slightly expensive compared to IGs (Petrow and Pyrhönen 2013).…”

An Analytical Method for Generating Determined Torque Ripple in Synchronous Machines with Surface Magnets by Harmonic Current Injection

“…In recent years, many publications have dealt with the reduction of the torque ripple of PMSM. Many good results have been achieved in this area through constructive modifications, like the distribution of the winding [4], single-layer winding or double-layer winding [5], magnetic pole, and anchor-slot design [6]. However, these methods are mostly limited to the reduction of the cogging torque.…”

An Analytical Method for Generating Determined Torque Ripple in Synchronous Machine with Interior Magnets by Harmonic Current Injection

“…Most of these methods use design features on the rotor or stator, and thus change the construction of the machine. There are many examples in the literature, including the distribution of the winding [7,8], an odd number of slots for the stator [9], using single-layer winding or double-layer winding [10], adjusting the magnetic pole and anchor-slot design [11], and other methods to improve the rotor or stator design [12][13][14][15][16][17][18]. Although most of the methods provide good results, most of them have to be applied in the conception phase of PMSMs, and are limited to the reduction of the cogging torque.…”