Overview
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A universal motor is a motor that rotates on both direct and alternating
currents. A universal motor is used in home appliances and industrial machines
because these motors are robust and compact with a simple construction.
However, problems such as vibration and a reduction in starting torque
caused by the cogging torque occur as the size of the motor becomes smaller.
Evaluating the starting performance of a universal motor at the design
stage is necessary to resolve these problems.
This example presents the use of a magnetic field analysis to obtain the
speed versus time graph, the current waveform, and the torque versus time
graph for a universal motor. |
Speed vs. Torque Graph / Current Waveform / Torque vs. Time Graph
The speed versus time graph from when the motor starts to 0.4 seconds is
indicated in Fig. 1, the current waveform of the stator coil is indicated
in Fig. 2, and the torque versus time graph is indicated in Fig. 3.
The universal motor reaches a rotation speed of 6,000 rpm at approximately
0.35 seconds as indicated in Fig. 1. Furthermore, the larger the current
flowing through the stator coil is, the larger the torque becomes when
the motor is started. As the rotation speed increases, the current and
torque decrease. |
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