This kind of driving mode has the function of speed regulation, which is generally used in large-scale vertical roller mill which requires speed regulation.

Advantages: good soft starting performance, linear controllable speed curve when starting, linear controllable speed curve when stopping, good electric braking performance, stepless speed change, excellent controllable performance, closed-loop control, high reliability.

Disadvantages: the price is very expensive, the silicon controlled rectifier system is complex, the electric control equipment covers a large area, the power factor is low, the DC motor has slip ring, the brush is worn, the maintenance workload is large, there is no explosion-proof type at present, so it can not be used in the coal mine.