Will PMSM Demagnetize After Long-Term Operation?

Demagnetization is an inherent concern in the application of permanent magnet synchronous motors. Will permanent magnet motors lose magnetism after prolonged service? We will briefly discuss this topic below.

The permanent magnets fitted inside PMSM possess mediocre thermal stability. Deficient design expertise or improper operating conditions can both trigger deterioration of the magnets' magnetic properties. Mild demagnetization impairs overall motor performance, while severe cases render the motor inoperable. Temperature and electric current constitute the two core factors governing magnet performance. The motor is highly susceptible to performance degradation when operating in high-ambient-temperature surroundings or generating excessive internal temperature rise. In addition, overcurrent operation also serves as a major contributor to magnetic attenuation.

Demagnetization occurring during motor operation falls into two categories: reversible demagnetization and irreversible demagnetization, which are closely tied to the magnet's recoil line. When the motor runs under load, the magnetic characteristics of the permanent magnet alter to varying degrees; after the load is removed, these magnetic traits partially recover. The recoil line is listed as a key technical parameter in all permanent magnet performance datasheets.

Reversible magnetic loss is unavoidable during PMSM operation. However, the extent to which magnetic flux can fully revert to its original baseline state is directly determined by the intrinsic material properties of the permanent magnet itself.

Irreversible magnetic loss refers to permanent degradation where magnetic properties fail to bounce back to their original levels even after temperature cools down. One type of irreversible loss can be remedied via re-magnetization to restore the motor's rated performance. The other form is permanent and irreparable, such as microstructural transformations within the magnet caused by high-temperature oxidation.

Therefore, for well-designed and properly deployed permanent magnet motors, the operating point of the permanent magnet merely fluctuates along its recoil line under demagnetizing fields induced by normal current and temperature. Under such conditions, irreversible demagnetization will not occur. Conversely, improper design or operation will result in varying degrees of permanent performance decline.

To summarize whether a PMSM will suffer demagnetization over years of use, two decisive factors come into play. The first is the inherent design standard of the motor assembly itself. The second - an equally critical determinant - lies in effective regulation of the motor's operational state to prevent demagnetization triggered by excessive current or extreme temperature spikes.