Brushless DC motor is generally divided into two categories: DC motor with commutator and DC motor without commutator. DC motor is inferior to exchange motor in layout, price and protection function, but the speed regulation of exchange motor has not been satisfied for a long time, so DC motor has been widely used for its good control characteristics. Nowadays, although the achievements of speed regulation of exchange motors have been handled, it is necessary for equipment investors and reform to take a comparable long process. Exchange motor speed regulation has not been widespread, DC motor system is still in general use.

DC motor speed regulation system adopts constant DC voltage to supply DC motor, and adjusts speed by changing resistance in armature circuit. Such methods are simple, easy to manufacture, and inexpensive, but the drawbacks are that they are inefficient and have soft features that make it impossible to obtain a wider, war-slippery speed control. This method can only be applied to some places with low power and little request for speed regulation. This kind of control method can obtain a wider speed regulation scale, a smaller rate of change of speed war slippery speed regulation function. But the main problem of this method is that the system is heavy, with lots of land, low efficiency and hard training.

In recent years, with the rapid development of power electronics technology, the DC motor speed regulation system powered by thyristor converter has replaced the generator-motor speed regulation system, and its speed regulation function is far beyond the generator-motor speed regulation system. Especially with the rapid development of LSI and computer technology, the accuracy, static performance and reliability of DC motor speed regulation system have been improved greatly. The growth of IGBT and other high-power devices in power electronics technology is replacing thyristor, presenting a better DC speed regulation system.