A unified approach to closed-loop plant identification and direct controller reduction

Closed loop output error identification algorithms and recently developed algorithm for direct closed loop estimation of reduced order controllers [3, 5] despite their diversity have in fact a unifying basic ground which will be enhanced. The paper also will explore the interaction between closed loop plant model identification and direct estimation in closed loop of reduced order controllers. The following problem will be addressed: what closed loop plant model identification should be used when a criterion for direct controller reduction is given? An illustrative application example is given in a companion paper [7].