Abstract
This paper investigates the electromagnetic torque by considering back electromagnetic force (back-EMF) trapezoidal degrees of ironless brushless DC (BLDC) motors through the two-dimensional finite element method (2-D FEM). First, the change percentages of the electromagnetic torque with back-EMF trapezoidal degrees, relative to those of PMs without segments, are investigated on the premise of the same back-EMF amplitude. It is found that both PM symmetrically and asymmetrically segmented types influence back-EMF trapezoidal degrees. Second, the corresponding electromagnetic torque, relative to that of PMs without segments, is studied in detail. The results show that the electromagnetic torque can be improved or deteriorated depending on whether the back-EMF trapezoidal degree is lower or higher than that of PMs without segments. Additionally, the electromagnetic torque can easily be improved by increasing the number of PMs’ symmetrical segments. In addition, the electromagnetic torque in PMs with asymmetrical segments is always higher than that of PMs without segments. Finally, two ironless PM BLDC motors with PMs symmetrically segmented into three segments and without segments are manufactured and tested. The experimental results show good agreement with those of the 2-D FEM method. This approach provides significant guidelines to electromagnetic torque improvement without much increase in manufacturing costs and process complexity.
Highlights
With the merits of simple structure, easy control, fast transient response, and high efficiency, permanent magnet brushless DC (PM BLDC) motors have been widely used in different areas and applications, such as electric vehicles, energy storage flywheels, robots, household appliances, etc. [1–7]
Two ironless BLDC motor prototypes, one with PMs symmetrically segmented into three segments and the other without segments, are manufactured and tested to validate the simulated results
Symmetrical segmentations, it can be concluded that trapezoidal back-EMF can be easier obtained with the increase in the number of PM symmetrical segments
Summary
With the merits of simple structure, easy control, fast transient response, and high efficiency, permanent magnet brushless DC (PM BLDC) motors have been widely used in different areas and applications, such as electric vehicles, energy storage flywheels, robots, household appliances, etc. [1–7]. It has been proved in [16] that, in conditions of the same ideal square wave input currents and same back-EMF amplitudes, the electromagnetic torque with square back-EMF waveform is 15.5% higher than that with sinusoidal waveforms This indicates that the more trapezoidal degree the back-EMF has, the higher the load torque will be, and the lower the resulting torque ripple. In [17], a current optimization control method is proposed to reduce the torque ripple of PM. In [24], a second-order sensorless control strategy for a BLDC motor system with low inductance and nonideal back-EMF is adopted to improve the reliability of current commutation during high-speed operation and reduce the power consumption of high-speed steady-state operation. A method for improving the back-EMF trapezoidal degree by PM’s different segmentation types is proposed. Two ironless BLDC motor prototypes, one with PMs symmetrically segmented into three segments and the other without segments, are manufactured and tested to validate the simulated results
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