https://support.industry.siemens.com/cs/document/103526819/single-and-multi-loop-controller-structures-(cascade-control)-with-pid_temp?dti=0&lc=en-US    (P32)

原文：Using the D-fraction of the PID controller results in a higher control activity, i.e. a “more agitated” control value signal. Since for cascaded control the control value signal is transferred to the subsequent controller as setpoint value, using the D-fraction does not always make sense here.

串级控制系统中，外环控制器使用PID与使用PI相比为什么就没有意义？

串级控制系统中，外环不能用PID只有内层可以使用吗？