When choosing a motor, how to choose power and torque?——Part three

(Part three)

Follow-up question: What if I use stepless speed regulation? In terms of motor output power and torque, what are the characteristics and differences between AC variable frequency speed regulation and DC speed regulation?

Answer: On AC variable frequency speed regulation and DC speed regulation 1: The development of frequency converter DC motor drive and AC motor drive have been born in the 19th century, with a history of more than 100 years, and has become the main driving device of power machinery . However, due to technical reasons, for a long period of time, AC motors (including asynchronous motors and synchronous motors) are used in the non-variable speed drive system, which accounts for about 80% of the entire electric drive system. The DC motor is basically used in the speed-controlled drag system.

However, it is well known that due to structural reasons, DC motors have the following disadvantages:

(1) The brushes and commutators need to be replaced regularly, maintenance is difficult, and the service life is short;

(2) Due to the commutation sparks of the DC motor, it is difficult to apply to harsh environments with flammable and explosive gases;

(3) The structure is complex , it is difficult to manufacture a DC motor with large capacity, high speed and high voltage.

Compared with DC motors, AC motors have the following advantages:

(1) Solid structure, reliable operation, easy maintenance;

(2) There is no commutation spark, and can be used in harsh environments with flammable and explosive gases;

(3) It is easy to manufacture large-capacity, high-speed and high-voltage AC motor.

Therefore, for a long time, people hope to replace the DC motor with a speed-adjustable AC motor in many occasions, and a lot of research and development work has been carried out on the speed control of the AC motor. However, until the 1970s, the research and development of the AC speed control system has not been able to get really satisfactory results, which limits the popularization and application of the AC speed control system. It is also for this reason that baffles and valves have to be used to adjust the wind speed and flow in the electric drive systems such as fans and water pumps that are widely used in industrial production and require speed control. This approach not only increases the complexity of the system, but also results in wasted energy.