Frequency converter is used to control AC motor, DC speed governor is used to control DC motor, the two are not one thing, but the use is close. Generally, DC motor is used in high power (above 50KW). The advantage of DC motor is that it has high output power, stable operation and good speed control performance. It is difficult for AC motor to meet this requirement.

Because of the continuous development of frequency converter technology, the speed regulation and output power of AC motor have been gradually improved, so if the engineering reform design is carried out now, the frequency converter can be used to drive AC motor instead of DC speed regulator to drive DC motor, which is not very different from direct DC motor. The application of AC variable frequency speed regulation in speed regulation can save energy by saving excess wastage intelligently, but the precise control of torque can not be achieved. Although the current variable frequency speed regulation has vector control, in AC speed regulation, the armature current and excitation current are coupled, which can not be accurately controlled. That is to say, using modern control theory, through vector conversion, the coupling armature current and excitation current in AC motors are decoupled, so as to control them. It is the principle of simulation DC speed regulation. DC speed regulation does not involve frequency conversion. The armature and excitation of DC speed regulation are not coupled and separated, so that the armature current and excitation current can be accurately controlled. But it is very difficult to achieve DC speed control characteristics at present. Therefore, DC speed regulation is still widely used in industries requiring high torque, such as rolling mills, papermaking, cranes and so on.

DC governor is used in DC motor, DC speed regulation is relatively simple, direct control of excitation circuit can be. AC speed regulation uses frequency converter, it is the device that converts the power frequency to any frequency. AC speed regulation can be realized by voltage regulation or frequency converter, and the design price of frequency converter is low. So now many speed regulation occasions use the way of frequency converter instead of DC speed regulation.