DC electric drag and AC motor drag were born in the 19th century, which has a history of more than 100 years and has become the main driving device of power machinery. Due to the technical problems at that time, for a long time, the drag system that required speed control was basically a DC motor.
The following disadvantages of DC motors are due to structural reasons:
1. Due to the commutation spark of DC motor, it is difficult to apply the inverter to the harsh environment where flammable and explosive gases exist;
2. It is necessary to replace the brushes and commutators regularly, which is difficult to maintain and has a short life;
3. The structure is complex, and it is difficult to manufacture DC motors with large capacity, high speed and high voltage.
Compared with DC motors, AC motors have the following advantages:
1. There is no commutation spark, which can be applied to the harsh environment where there is flammable and flammable firestorm gas;
2. It is easy to manufacture AC motors with large capacity, high speed and high voltage;
3. Solid structure, reliable work, easy to maintain.
Because of this, the promotion and application of AC high-speed systems is limited. After the second oil crisis in the mid-70s of the 20th century and the development of electronic technology, the inverter technology of AC high-speed system has been developed at a high speed.
