Tuning of PID controllers for varying time-delay systems

PID controllers are used in industry in most applications. Usually, it is assumed that the system delay is constant. In this paper, tuning of PID controllers for time varying, including state-dependent delays is discussed. The approach used in the paper is simulation and optimization. The plant can be nonlinear, but the results are easier to compare with classical results for constant delay case, when the dynamics is linear and of first order. In fact, iterative feedback tuning could be applied for real systems instead of simulation.