The series motor has the advantages of high speed, small size, light weight and convenient speed regulation, so it is used as the power source in most electric tools. It is widely used in power tools, garden tools, kitchen appliances and other product fields based on its features such as wide adjustable speed range, large starting torque, simple maintenance and low cost. Single-phase series motors have frequent starting, high speed, large vibration, uneven load, etc., so higher requirements are put forward in terms of manufacturing quality.