Impact of PWM Control Frequency onto Efficiency of a 1 kW Permanent Magnet Synchronous Motor

The paper explains how to select the best PWM control frequency for specific Permanent Magnet Synchronous Motors (PMSM) to achieve its maximum efficiency. Examinations were carried out for a PMSM unit with the power of 1 kW, rated speed of 1000 rpm and rated torque of 6 Nm. The PWM frequency ranged from 4 kHz to 20 kHz with the increment of 1 kHz. Measurements were taken for each of the foregoing frequencies, for the load torques of 2 Nm, 4 Nm and 6 Nm and for the rotation speeds of 300 rpm, 500 rpm, 750 rpm, 1000 rpm and 1200 rpm to find out efficiency of the PMSM motor. The achieved results make it possible to properly adjust the PWM control frequency for each PMSM motor to operate the motor in the most efficient way and, in consequence, save energy consumed by that motor

Meteorological and biometeorological conditions in the Hornsund area (Spitsbergen) during the warm season

Meteorological and biometeorological conditions during the warm seasons (June-September) of 1979-2008 are described for the Hornsund area, Spitsbergen. The measurements were taken at four sites: at Hornsund, at the Hans Glacier (at its equilibrium line and in the firn section) and at the summit of Fugleberget. The variation of meteorological and biometeorological conditions was analysed in relation to altitude, distance from the sea and the ground type. In warm seasons, the air temperature at Hornsund was 2.2 °C higher on average than at the Hans Glacier (central section) and by 2.8 °C than at the Hans Glacier (firn section) and at Fugleberget. The average wind speed recorded at Hornsund was higher (0.6ms-1) than at the Hans Glacier and lower (0.9ms-1) than at Fugleberget. Four biometeorological indices were used: wind chill index (WCI), predicted insulation of clothing (Iclp), cooling power (H) and subjective temperature index (STI). The strongest thermal stimuli were observed on the Hans Glacier and in the upper mountain areas. The study has found a considerable degree of spatial variation between the meteorological elements investigated and the biometeorological indices in the Hornsund area. The impact of atmospheric circulation on meteorological elements and biometeorological indices is also presented. The mildest biometeorological conditions of the warm season found at Hornsund were associated with air masses arriving from the southwest and west

Magnetic structures of Ho5Rh4Ge10Ho_{5}Rh_{4}Ge_{10}

A powder diffraction measurement of $Ho_5Rh_4Ge_{10}$ is reported. This compound crystallizes in the tetragonal $Sc_5Co_4Si_{10}$-type structure (space group P4/mbm) in which the Ho atoms occupy three different sites. The neutron diffraction measurements indicate antiferromagnetic order with the Néel temperature $T_{N}$=7 K. Below $T_{N}$ an additional phase transition at 4.5 K connected with the change of the magnetic structure is observed. The Ho moments in 4(h) site form collinear order up to T_{N} while moments at 2(a) site form sine modulated structure. Determined experimentally magnetic structures are compared to the results of symmetry analysis