用MATLAB程序软件完成临界比例带法对PID控制器的参数整定，并求出PID控制器的三个参数Kp，Ti，Td。最后绘制出参数整定前后的单位阶跃响应图进行比较。(The parameters of PID controller are adjusted by MATLAB software and the three parameters Kp, Ti and Td of PID controller are obtained. Finally, the unit step response di