Time delay control and its applications

Time delay control (TDC) is to, intentionally and reasonably, use delay in controller to improve the system performances. It mainly consists of time delay filter (TDF), time delay observer (TDO), and time delay learning control (TDL). Time delay filter, using delay to attenuate or eliminate the damped exponential sinusoidal signals, is mainly applied to reduce the residual vibration of flexible structures. Time delay observer is a method of robust control that uses time delay to observe the uncertainties and disturbances. Time delay learning control, using delay to learn the periodic signal, is applied to track the periodic signal without error. Firstly, the concept of time delay control is presented in this paper to cover all the cases which delay is used in the controller (mainly for delay_free processes). Secondly, the research aim and main subjects of TDC are introduced. Thirdly, the current research situation and the applications are summarized. Lastly, some prospective subjects are proposed for reference.