In this system, the spindle of a 55KW vertical lathe is driven by a D32 75KW frequency converter, and a fast braking stop is realized through an external braking unit and braking resistor. Constant-speed cutting is achieved through open-loop vector control, and the speed variation caused by load changes is very small. The inverter is started through the control terminal, and the speed given is controlled by the 0-10V analog voltage signal of the control system. When the motor runs at 70Hz, the speed fluctuation is less than 1 rpm, and the current fluctuation is less than 1A, realizing precise speed control.