The issue of stabilizing a time-delayed unstable processes is addressed in this article. It has been reported in literature that a P or PI controller can stabilize a first order delayed unstable (FODUS) process with theta/T <1 only. It is found that if a PD or PID controller is introduced into the system, this constraints of stabilizability can be relaxed to theta/T < 2. The effects of stable poles and zeros on this constraint of stabilizability are also investigated. Such a result can be used as guidelines for stabilizing an open loop unstable process by re-allocating the stable open-loop poles and zeros. References: 9
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