Time delay limitations in control implementation

In this paper, the degrading effect of time delays in controlled system performances is revised, and some limitations based on the control effort are stated. This control effort is defined based on the shift of the open-to-closed loop poles. As digital control implies open-loop control in the intersampling time interval, digitally controlled open-loop unstable systems may become unstable as there is always a time delay in the updating of the control. Also, even if the open loop system is stable but a strong control action is required, a time delay may cause instability. In the paper, some bounds in the allowed time delay in the implementation of the control system to keep stable the controlled system are established. Some hints to design digital control systems under the presence of this delay are proposed.