Second, the characteristics of variable frequency motor

1, the electromagnetic design The common for asynchronous motor, then design the performance parameters of the main consideration is overload ability, starting performance, efficiency and power factor. And frequency conversion motor, because of the critical slip inverse ratio in power supply frequency, can be in critical slip close to 1 direct start, therefore, overload ability and start performance is not too much to rotating joints consider, and to solve the key problem is how to improve motor to non sine wave power adaptability. The general way is as follows:
1) as the decrease of the stator and rotor resistance. Reduce stator resistance can reduce the fundamental wave copper loss, to make up for the high order harmonic cause copper consumption increase
2) to rotary union control the current of high order harmonic, need to appropriately increase motor inductance. But rotor slot leakage reactance larger the skin effect is big also, high harmonic copper loss and increase. Therefore, motor leakage reactance size mus
3) frequency conversion motor main magnetic circuit general design into unsaturated state, one is considered high order harmonic will deepen the magnetic circuit saturation, 2 it is to consider in low frequency, in order to enhance the output torque and increasing converter output voltage. 2, structure design To structure the design, main is also considering non-sinusoidal power characteristic of frequency conversion motor insulation structure, vibration and noise cooling way of influence, generally pay attention to the following questions:
1) insulation level, general for F or higher level, strengthen on insulation and turn insulation strength, especially to insulation impact resistance voltage ability.
2) the motor of the vibration and noise problem, should fully consider motor components and overall rigidity, trying to improve its natural frequency, to avoid and every force wave produce resonance phenomenon.
3) cooling way: generally USES forced air cooling, namely main motor cooling fan using independent motor drive.
4) prevent shaft current measures, the capacity of more than 160 kw motor should adopt bearing insulation measures. Mainly is easy to produce magnetic circuit asymmetry, also can produce shaft current, when other high frequency component produced by the current together effect, shaft current will increase greatly, leading to bearing damage, so generally take insulation measures.
5) to fiber optic rotary joint constant power variable frequency motor, when the speed more than 3000 / min, should use high temperature resistant special grease, to compensate for bearing temperature. Frequency conversion motor can be at 0. 1 hz - 130 hz range for the long term operation, common motor can be in: 2 pole for 20-65 hz range long-term operation. 4 pole for 25-75 hz range long-term operation. Six pole for 30-85 hz range long-term operation. Eight pole for 35-100 hz range long-term operation.