Strong stabilization of MIMO systems with restricted zeros in the unstable region

The strong stabilization problem (i.e., stabilization by a stable feedback controller) is considered for a class of finite dimensional linear, time-invariant, multi-input multi-output plants. It is assumed that the plant satisfies the parity interlacing property, which is a necessary condition for the existence of strongly stabilizing controllers. Furthermore, the plant class under consideration has no restrictions on the poles, on the zeros in the open left-half complex plane, on the zeros at the origin or at infinity; but only one finite positive real zero is allowed. A systematic strongly stabilizing controller design procedure is proposed that applies to any plant in the class, whereas alternative approaches may work for larger class of plants but only under certain sufficient conditions. The freedom available in the design parameters may be used for additional performance objectives although the only goal here is strong stabilization. In the special case of single-input single-output plants in the class considered, the proposed stable controllers have order one less than the order of the plant.