There are many drawbacks to adjusting the speed of resistance change, and it is currently rarely used, only in certain transmission systems such as cranes, elevators, and trams that do not require high-speed adjustment or long-term operation. Time is at low speed. The range of field attenuation speed regulation is small, often combined with voltage regulation and speed regulation to increase the speed to a small range below the rated speed. Therefore, DC automatic speed regulation systems are usually based on voltage regulation and speed regulation. If necessary, two methods of voltage regulation and speed regulation are combined with field attenuation speed regulation.Adjusting the voltage of the armature power supply or changing the excitation current requires a special adjustable DC power supply. There are three widely used controllable DC power sources: (1))Rotary converter. This device consists of an AC motor and a DC generator to obtain adjustable DC voltage.(2) Static controllable rectifier (referred to as VM system). Static controllable rectifiers, such as mercury arc rectifiers and silicon controlled rectifiers, are used to generate adjustable DC voltage.(3) DC converter (pulse width modulation converter). Use a DC power supply or an uncontrolled rectifier power supply to generate an adjustable DC average voltage through DC interruption or pulse width modulation.In a rotary converter system, an AC generator drives a DC motor for conversion, and the generator supplies power to the DC motor. The DC motor requires speed regulation, and the excitation current regulation of the generator can change its output voltage, thereby regulating the speed of the motor. The change in the direction of excitation current will change the polarity of the output voltage and the direction of motor rotation, making it easy to achieve reversible operation of a universal system. The system requires a rotor converter unit, which includes at least two rotating motors with the same power as the governor and one excitation generator. It has many drawbacks of equipment, such as large size, high cost, low efficiency, and inconvenient location. Services. Due to outdated technology, it is not used.