However, the brushes and commutators are worn for a long time, and at the same time, there is a huge current change during commutation, which is very easy to generate sparks. The commutator and brushes limit the capacity and speed of the DC motor, which makes the speed regulation of the DC motor encountered. bottleneck. For the brushless DC motor, only the input voltage is ostensibly controlled during speed regulation, but the self-controlled frequency conversion speed regulation system of the motor (the brushless DC motor itself has a rotor position signal acquisition device such as a rotor position detector, and the rotor of this device is used The position signal to control the commutation time of the variable voltage variable frequency speed control device) automatically controls the frequency according to the variable voltage, which is almost the same as the DC (brush) motor, which is very convenient.