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This paper focuses on the matter of cogging torque reduction by combining various methods of cogging torque minimization. Due to the high costs of prototype construction, cogging torque is minimized during the design phase by using numerical methods, while computer simulations are used to find a magnetic circuit arrangement for which the cogging torque has the smallest possible value. Cogging torque occurs as a result of combined impact of the magnetic field of a permanent magnet located at rotor and stator with variable magnetic conductivity depending on an angle of rotation. It is a pulsating torque and occurs permanently during machine operation, impacting the operation of the entire device cooperating with the electric machine and causing vibrations, tension, and noise. It results in braking torque and subsequent power losses and leads to faster wear and tear of machine structural elements. High cogging torque values cause problems with rotational speed adjustment. In the case of electric generators used in wind power plants, it impedes the start-up of power plants at high wind speeds. Considering the above, the reduction of cogging torque in permanent-magnet machines is extremely important.

This paper presents the results of field calculations of cogging torque for a 12-pole torque motor with an 18-slot stator. A constant angular velocity magnet and the same size gap between n-1 magnets were assumed. In these conditions, the effect of change of the n-th gap between magnets on the cogging torque was tested. Due to considerable length of the machine the calculations were performed using a 2D model. The n-th gap for which the cogging torque assumed the lowest value was evaluated. The cogging torque of the machine with symmetrical magnetic circuit (the same size of gap between magnets) was compared to the one of the asymmetrical machine. With proper choice of asymmetry, the cogging torque for the machine decreased by four times.

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The paper presents a fan with DC brushless motor used to circulate air in the combustion chamber of a solid-fuel furnace. A way of constructing the permanent magnet motor using much less steel and copper than present motors has been shown. Thanks to the use of sensorless control, the control system of the motor is simple and allows for continuous speed control. It consumes much less energy than previous designs. The motor and control system can be applied in other fans. Wentylator do pieców na paliwa stałe Streszczenie. W pracy pokazano wentylator z bezszczotkowym silnikiem prądu stałego przeznaczony do nadmuchu powietrza do komory spalania w piecu na paliwa stałe. Pokazano konstrukcję silnika z magnesami trwałymi, na który zużyto znacznie mniej żelaza i miedzi w porównaniu z silnikiem dotychczas stosowanym. Dzięki zastosowaniu sterowania bezczujnikowego układ sterowania silnika jest prosty i umożliwia płynną regulację prędkości obrotowej. Nowy wentylator zużywa znacznie mniej energii niż wentylatory stosowane dotychczas. Taki silnik i układ sterowania może być stosowany w wentylatorach o innym przeznaczeniu.

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