Designing fixed-order mixed μ robust controller for turbofan engine

After much research and discussion, we gradually came to forming the idea that a better controller - fixed-order mixed μ controller - can be designed for turbofan engines. One important factor for forming such an idea is that we, after much research, could prove the necessary existence conditions for an optimal fixed-order H_∞ controller; we give proof of these necessary existence conditions in this paper. We use homotopy algorithm for obtaining easily the solution of an optimal fixed order H_∞ controller. In this paper we propose and explain in much detail a new control strategy of obtaining fixed order mixed μ controller by incorporating fixed-order H_∞ controller into a mixed μ synthesis procedure. Compared with a full-order design, which brings several well-known disadvantages, our design of fixed-order mixed μ controller reduces controller complexity and achieves nearly the same robust performance levels. We applied our approach to the actual design of a fixed-order mixed μ controller for turbofan engine; simulation results show preliminarily that this actual design satisfies requirements on robust performance of controlled system.