Abstract:The pole placement with fractional-order PI?? controllers for time-delay systems is discussed by using the parameter space approach. The damping ratio angular sector region and the relative stability region in complex plane, which form a trapezoid region in the left-half of the complex plane, are mapped into the controller parameters space. Thus, the corresponding controller parameters can place all the closed-loop poles in the specified trapezoid region, and guarantee the performances of the closed-loop systems. Simulation results show that for appropriately selected parameters of the fractional-order PI?? controller, better system performances can be achieved with the fractional-order controller than withthe integer-order controller, and the superiority of fractional-order controllers is proved from the view point of the pole placement.