Countermeasures To Weaken High-order Harmonics Of Asynchronous Motors

Countermeasures to Weaken High-order Harmonics of Asynchronous Motors

The objective existence of the teeth and grooves of the iron core of the stator rotor of the motor, the unorthodox wave of the spatial distribution of the magnetic potential of the winding, and the uneven degree of saturation of the magnetic circuit system all lead to the existence of high-order harmonic magnetic fields in the air gap magnetic field of the motor to varying degrees. The high-order harmonic magnetic field will produce additional torque that is not conducive to the performance of the motor. One of the additional torque is asynchronous additional torque and the other is synchronous additional torque.

In the asynchronous additional torque, the fifth and seventh higher harmonic magnetic fields have a greater impact; the asynchronous additional torque will cause the torque characteristic curve of the motor to be distorted, and the starting performance of the motor will deteriorate. If the pole logarithm of a certain harmonic magnetic field established by a certain harmonic magnetic field of the stator to the rotor current is sensed, it is equivalent to the pole logarithm of another harmonic magnetic field, so at a certain speed, the two stator and rotor magnetic fields with equal pole logarithms rotate synchronously in space and are in a relatively stationary state. For this reason, a synchronous additional torque equivalent to a synchronous motor is generated; if the synchronous additional torque happens to occur in a specific state where the speed is zero, the motor may not be able to start.

In order to effectively weaken the impact of additional torque on motor performance, the necessary adjustments and controls are generally made from the basic starting point of reducing and eliminating high-order harmonics.

Stator or rotor chute is one of the more commonly used measures. Starting from the convenience of the manufacturing process, the rotor adopts chute mostly; especially in the electromagnetic noise control of the motor, the effect is significant. However, due to the use of chutes, the motor will have the consequences of deterioration of power factor and maximum torque due to the increase of leakage resistance. The adjustment of the air gap between the stator and the rotor is also a relatively easy measure to take. By adjusting the unevenness of the air gap between the stator and the rotor, or directly increasing the air gap between the two, it will also have a better effect; however, when this measure is taken, it will lead to the motor excitation current increases and the power factor deteriorates. Adverse effects.

In the motor design scheme, fractional groove windings are not used as much as possible; short-range and integer groove windings can be used to effectively avoid the fifth and seventh higher harmonics; reasonable selection of stator rotor groove cooperation can eliminate the impact of synchronous additional torque.