Analyze the influence of heat generation of permanent magnet motor and its treatment

As a digital actuator, permanent magnet motor has been widely used in motion control systems. When the user uses a permanent magnet motor, he feels that the motor has a large amount of heat at work and he is skeptical. I wonder if this phenomenon is normal. In fact, heating is a common phenomenon of permanent magnet motors, but what kind of fever is normal, and how to minimize the permanent magnet motor heating it?

First of all, we must understand why the stepper permanent magnet motor generates heat.

For permanent magnet motors, the interior is made up of cores and winding coils. Windings have resistance, and power will produce losses. The loss is proportional to the square of the resistance and current. This is the copper loss we often say. If the current is not a standard DC or sine wave, it will also produce harmonic losses; the core has hysteresis The eddy current effect also produces losses in an alternating magnetic field. Its magnitude is related to material, current, frequency, and voltage. This is called iron loss. Both copper loss and iron loss are manifested as heat, which affects the efficiency of the motor. Stepping motors generally seek positioning accuracy and torque output, the efficiency is relatively low, the current is generally large, and the harmonic components are high, the frequency of the current alternating changes with the speed, so the stepper motor generally has a heating condition, and the situation is more general Severe AC motor.

In addition, the permanent magnet motor heating control within a reasonable range

The degree to which the permanent magnet motor heat is allowed depends on the internal insulation level of the motor. Internal insulation performance will be destroyed at high temperatures (above 130 degrees). So as long as the inside does not exceed 130 degrees, the motor will not be damaged, and the surface temperature will be below 90 degrees. Therefore, the stepper motor surface temperature is 70-80 degrees are normal. A simple temperature measurement method can be used with a thermometer, and it can also be roughly judged: You can touch for more than 1-2 seconds, not more than 60 degrees with your hand; you can only touch it with your hand, about 70-80 degrees; If it is more than 90 degrees, it can also be detected with a temperature gun.

Third, the permanent magnet motor heat changes with speed

With constant current drive technology, the stepper motor maintains a relatively constant current at both static and low speeds to maintain constant torque output. When the speed is high to a certain extent, the internal electromotive force of the motor increases, the current will gradually decrease, and the torque will also decrease. Therefore, the heat generated by the copper loss is related to the speed. Static and low temperatures are generally high, and high temperatures are low. However, the change in iron loss (although the percentage is small) is not always the case, and the whole heat of the motor is the sum of the two, so the above is just the general case.

Fourth, the impact of heat

Although permanent magnet motor heating does not generally affect the life of the motor, it does not need to be taken care of by most customers. However, severe fever can have some negative effects. For example, if the thermal expansion coefficient of each part of the internal part of the motor causes the structural stress change and the internal air gap to change slightly, it will affect the dynamic response of the motor, and the high speed will be easily out of step. Another example is the excessive heat generated by the motor, such as medical devices and high-precision test equipment. Therefore, the necessary control of the heating of the motor should be carried out.

Finally, reduce the heating of the stepper permanent magnet motor

To reduce fever is to reduce copper loss and iron loss. Reduce the copper loss in two directions, reducing the resistance and current, which requires the selection of the type of electric resistance as small as possible and the rated current of the motor is small, the two-phase motor, the motor can be used in series without the parallel motor. But this often contradicts the requirements of torque and high speed. For the selected motor, the automatic semi-flow control function and offline function of the driver should be fully utilized. The former automatically reduces the current when the motor is in a static state, and the latter simply cuts off the current. In addition, the subdivision driver has a near sinusoidal current waveform, less harmonics, and less heating of the motor. There are not many ways to reduce iron loss. The voltage level is related to it. Although the motor driven by high voltage will increase the high speed performance, it will also increase the heat generation. Therefore, we should choose the appropriate drive voltage level, taking into account the high speed, stability and heat, noise and other indicators.

More information about permanent magnet motors is available on the company website.