There always exists a modelling error between system model and real system. Plant having a large modelling error or slowly time varying plant is hard to expect to have a good performance and robust stability with a controller based on nominal model. To make a controller designed with nominal model be effective on the real plant, we must design robust controller bearing the modelling error. Until now, it is well known that the $H_∞$ controller is excellent for an uncertain linear system. In this paper, based on recently developed TDC(Time Delay Controller), I propose the output feedback LSTDC(Loop Shaping Time Delay Controller) and $TDC/H_∞$ synthesis which optimize the LSTDC in view of $H_∞$. They can solve the robust stability problem of the TDC and have the better robust performance than the $H_∞$ control. Through analysis and simulations, an experiment, the proposal is justified.
