Design of a State Space Controller for an Intercooled, Regenerated (ICR) Gas Turbine Engine
A multi-input, multi-output (MIMO) controller for an advanced gas turbine has been developed and tested using a computer simulation. The engine modeled is a two-and-one half spool gas turbine with both an intercooler and a regenerator. In addition, variable stator vanes are present in the free-power turbine. This advanced engine is proposed for future naval propulsion for both mechanical drive ships and electrical drive ships. The designed controller controls free-power turbine speed and turbine inlet temperature using fuel flow and angle of the stator vanes. The controller will also have four modes of operation to deal with over temperature and over speed conditions. An eight state reduced order controller was used with pole placement and LQR to arrive at control gains. Both these methods required considerable insight into the problem. This insight was provided by previous experience with controller design for a less complicated engine, and also by use of a polyhedral search model of the gas turbine engine. The difficulty with a MIMO controller was that both inputs affect both of the control variables. The classical resolution of this problem is to have one input control one variable at a fast time constant and the other input control the other variable at a slow time constant. The “optimal” resolution of this problem is analyzed using the transient curves and basic control theory.