Brushless DC motor can be divided into two categories: DC commutator brushless DC motor. DC motor is better than AC motor in structure, price and maintenance performance, but AC motor drive control problem has not been solved satisfactorily for a long time, so the motor has been widely used for its good control performance. At present, although the speed control problem of AC motor has been solved, it takes a long time for people to reform the foundry equipment. AC motor speed control is not yet popular, DC motor system is still widely used.

The DC motor speed control system is powered by a DC motor with a constant DC voltage. First, the speed is achieved by changing the resistance in the armature circuit. This method is simple, easy to implement, easy to manufacture, low cost, but the disadvantages are low efficiency, soft mechanical characteristics, can not obtain a wide and smooth speed performance. This method is only suitable for occasions where there is no need for small power and variable speed ranges. The control method can obtain wide speed range, low speed change rate and smooth speed regulation performance. But the main drawback of this method is that the system has large weight, large area, low efficiency and difficult maintenance.

In recent years, with the rapid development of power electronics technology, the speed control system of DC motor powered by thyristor converter is replaced by electric generator. The speed performance is far beyond the speed control system of generator and motor. Especially with the rapid development of LSI technology and computer technology, the accuracy, dynamic performance and reliability of DC motor speed control system have been greatly improved. Power electronic technology such as high-power devices is replacing the development of thyristors, in which there is a better performance of DC speed control system.