Influence of lamination iron core size on magnetic properties of motor

27 Dec 2023
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Modern society needs a lot of energy, especially clean energy and adaptable electricity. The largest consumer of electricity is the electric motor, which uses more than 57.3 percent of its electricity. Motors are divided into industrial, commercial and home applications, and improving motor efficiency is an effective way to quickly achieve energy saving. The electronic power equipment realizes the bidirectional energy conversion between energy, energy storage and distribution network. They use IGBT, SiC and GaN semiconductors to enable power conversion electronics and motor controllers to operate at high frequencies.
On the other hand, in inverter-controlled switching operations, secondary loops are created in the hysteresis curve, which increases core losses. Although there are some researches on the magnetic properties of motor with inverter excitation at home and abroad, the influence of iron core size on the magnetic properties of motor is still unclear. Under normal circumstances, if the soft magnetic material is the same under sinusoidal excitation, the iron core size does not affect the measured magnetic properties, because the excitation current waveform is controlled, so that the magnetic flux density obtained by time integration of the induced voltage on the secondary side becomes a sine wave. However, under inverter excitation, unlike sine wave excitation, the waveform of the excitation current is not controlled, so the resulting output waveform will be distorted.
Professor Kyyoul Yun and his team at Gifu University have done a lot of research on the influence of core size on the magnetic properties of motors. In a recent study, they measured the effect of iron core size on magnetic properties of lamellar toroidal motors by keeping the cross-sectional area and turns of the lamellar iron core unchanged under sine excitation and inverter excitation, changing only the input voltage V, and keeping the carrier frequency and regulation mode constant.
They found that under inverter excitation, the hysteresis cycle width of small, medium and large annular iron core is 205.1, 248.4 and 273.1 A/m, respectively, while under inverter excitation, the secondary loop width of small, medium and large annular iron core is increased by 73.1, 96.1 and 123.5 A/m, respectively. Under the excitation of the inverter, the iron loss values of small, medium and large samples are 6.05, 9.58 and 11.62 W/kg, respectively. Compared with the iron loss of each annular iron core under sinusoidal excitation, the iron loss of small, medium and large annular core under inverter excitation increases by 124.9%, 256.1% and 332.0% respectively.
These findings suggest that the larger the iron core, the higher the voltage and iron loss required, that is, the more energy required to excite a larger ring iron core. This is because compared with other iron cores, the magnetic flux density of large toroidal iron cores varies more per unit time, resulting in larger eddy currents. Therefore, the eddy current loss of large annular iron cores is greater than that of other cores.
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