Increase motor power density by increasing speed

Maxon's airborne compressor motor with a speed of 20,000 rpm. The airborne refrigeration compressor supplied by UQM can also reach 8000 rpm.

The benefits of the high torque of the compressor motor are obvious. We can analyze it from a system perspective and a motor perspective.


1) System angle

With the complication of refrigeration compressors in daily life and industrial production, the demand for cooling capacity is also on the rise. In order to meet the demand for increased cooling capacity, the refrigeration compressor is required to increase the motor speed to achieve the purpose of increasing the heat of the refrigerant. Its inherent logic is:

As the compressor motor speed increases, the corresponding compressor operating speed also increases, and the refrigerant flow rate rises, resulting in an increase in cooling capacity.

This is an external system requirement to increase compressor speed. Of course, for the compressor system itself, the need for increased internal speed is derived from increased motor power density.

2) Motor angle

The formula for solving the back electromotive force of the motor armature is as follows:

When the rotational speed is higher, the smaller the dt, the larger the back electromotive force E0 of the armature reaction, and the stronger the armature reaction of the internal magnetic field for the permanent magnet motor. At the same time, the power density per unit volume of the motor is increased, and the size of the motor can be reduced, reducing the overall volume and weight of the compressor.

Whether the compressor motor used in the aircraft airborne compressor industry can radiate to other refrigeration compressor industries, taking advantage of this application case.

However, the problem of exposure is obvious at the same time as the compressor motor is speeded up. For example, the electromagnetic frequency of the motor will increase, the iron loss from the motor will increase, and the controller will switch frequently, resulting in an increase in current harmonics. And while the power density per unit volume of the motor increases, the heat dissipation of the motor is also a problem. There is also a large vibration speed of the electric drive system brought about by the high speed, and the NVH problem is highlighted. For the increase of iron consumption, it can be corrected by selecting high-performance silicon steel sheets during motor design. The problem of harmonic current can be adjusted from the controller angle to increase the switching frequency to optimize the current waveform. As for the solution of the NVH problem, we will focus on the following articles.

Reprinted from the network