When the axial flow fan is started, the current of the motor will be 5-6 times higher, which will not only endanger the service life of the motor and consume more electricity. The system software sets aside a certain capacity on the motor model selection in the design scheme. The speed of the motor is fixed and will not change, but in the whole process of practical application, it should sometimes run at a lower or higher rate. Therefore, it is necessary to terminate DC frequency conversion renewal. Soft starter can be used for motor soft start, after changing the machine and equipment to type the working voltage rate to reach the goal of environmental protection and energy saving speed change, and can show the machine equipment over-current, overvoltage, load and other maintenance functions. It can be used for ventilation and ventilation in metallurgical industry, chemical plant, light industry, food, pharmaceutical equipment, industrial equipment and industrial buildings. If the shell is removed, it can also be used as a self-contained cooling fan, or a long exhaust pipe can be spaced in series to develop the air pressure in the pipeline. Axial flow fan characteristics: small and medium axial flow fan: low functional loss, fast heat discharge, low noise, green environmental protection and so on. Because small use analogy is extensive. The large and medium-sized axial flow fan has the characteristics of simple structure, stable and firm, low noise, large exhaust volume and wide coverage of function selection.