H∞ loop shaping based low order structured robust controller design

Standard H_∞ loop shaping design has two drawbacks. The first is that it is difficult to select appropriate loop shaping weights, and the second is that the resulting controller is very complex. To resolve the two drawbacks, a low order structured robust controller design scheme is proposed. The scheme is based on fixed structure weight optimization and static H_∞ loop shaping controller synthesis. Giving control points of shaped plant singular value bounds and structure of controller, then controller with desired performance specifications and maximal robust stability margin can be derived via linear matrix inequality based iteration optimization. Third order robust controller for steam generator water level plant is designed using this method, and comparisons are made among the proposed method and other two H_∞ loop-shaping design schemes under different control condition, including step change of level reference, step change of steam flow rate and change of operation point. Simulation results show that the control system has good control performance, and its robust stability is better than the ones designed by other two schemes.