The software of controller uses design of F240 assembly language, block diagram is shown 3 times like the graph. The main program when the system works can handle other work, when timer 2 when producing cycle to interrupt, spark A/D sampling, collect sample and systematic set-point to be decreased next, the error inputs PID to control module, output PWM signal occupy sky comparing D, d sends PWM signal happening module, the PWM signal of generation is used at controlling the output of drive electric current.