1, electromagnetic design For ordinary asynchronous mot […]
1, electromagnetic design
For ordinary asynchronous motors, the main performance parameters considered during redesign are overload capability, startup performance, efficiency, and power factor. The variable frequency motor, because the critical slip ratio is inversely proportional to the power supply frequency, can be directly started when the critical slip rate is close to 1. Therefore, the overload capability and the starting performance do not need to be considered too much, and the key problem to be solved is how to improve the motor pair. The ability to adapt to non-sinusoidal power supplies. The method is generally as follows:
1) Reduce the stator and rotor resistance as much as possible.
Reduce the stator resistance to reduce the copper loss of the fundamental wave to compensate for the increase in copper consumption caused by higher harmonics
2) In order to suppress higher harmonics in the current, it is necessary to appropriately increase the inductance of the motor. However, the rotor slot leakage resistance is large, and the skin effect is also large, and the high-order harmonic copper consumption is also increased. Therefore, the size of the motor leakage resistance should take into account the reasonableness of the impedance matching within the entire speed regulation range.
3) The main magnetic circuit of the variable frequency motor is generally designed to be unsaturated. One is to consider the higher harmonics to deepen the saturation of the magnetic circuit, and the other is to increase the output voltage of the inverter in order to increase the output torque at low frequencies.