Petko Petkov, Da Wei Gu and Mihail Konstantinov

SLICOT Working Note 2001-7: December 2001.

In this expository paper we show the application of some of the SLICOT routines in the robust control analysis and design of a disk drive servo system. An uncertainty model of the system plant is first derived which contains eleven uncertain parameters including four resonance frequencies, four damping coefficients and three rigid body model parameters. Three controllers for the uncertain system are designed using, respectively, the techniques of H_inf mixed sensitivity design, H_inf loop shaping design procedure (LSDP) and mu-synthesis method. With these controllers the closed-loop system achieves robust stability and in the cases of H_inf and mu-controllers the closed loop system practically achieves robust performance. A detailed comparison of the frequency domain and time domain characteristics of the closed-loop system with the three controllers is conducted. Further, model reduction routines have been applied to find a reasonably low order controller based on the mu-synthesis design. This reduced order controller maintains the robust stability and robust performance of the closed-loop system. Simulations of the nonlinear sampled-data servo system with the low order controller have been included as well, which confirms the practical applicability of the controller obtained.