A method of auto-tuning for PID controller based on the desired model is presented for the stable plant in this
paper. No model of controlled plants is needed by using the proposed method. The tuning of PID controller is formulated
by using the Maclaurin expansion. The model-free auto-tuning of PID controller is implemented during the open loop step
response. Simulation results show that the resulting PID controller is capable of enhancing the control performance for
high-order plant effectively, and the proposed method has a strong robustness even under noise condition.