How to achieve motor speed regulation without a frequency converter? When there was no Mitsubishi Inverter FR-A840 in the year, it was basically the world of DC motor speed control system. Apollo also used precise speed control system when landing on the moon, and even needed position positioning control. At that time, DC servo was used to complete it. Before the 1960s, when the thyristor was not born, the DC motor was used to speed the motor through the generator. By adjusting the excitation current of the generator, the output voltage of the generator can be controlled to control the speed of the DC motor. The speed control system can be seen in the early "Motor Drag" textbook, but it is only a clumsy focus, but the speed range is very wide, the torque is large, and it is stable and reliable. In addition, the theory of DC speed regulation is very mature, and the early electric This type of speed control system is used in cars.