通过调整PID的三个参数KP、TI、TD ，将系统的闭环特征根分布在 s 域的左半平面的某一特定域内，以保证系统具有足够的稳定裕度并满足给定的性能指标

-Ziegler-Nichols method for tuning PID controllers can be summarized as follows: Set the integral and derivative gains to zero and increase the proportional gain until the system just becomes unstable. Define this gain to be Kr and measure the period of oscillation, Tr.