An auxiliary LQG/LTR robust controller design for cogeneration plants

A robust controller is designed to reduce the sensitivity of the frequency and the extraction steam pressure to the disturbance imposed on a cogeneration plant by using the LQG/LTR (linear quadratic Gaussian/loop transfer recovery) methodology. The natural frequency of the generator swing is analyzed to determine the frequency band of the disturbance due to the variation in load and utilized as a design specification for the LQG/LTR controller. The singular-value Bode diagram of the sensitivity transfer function matrix is shaped to reduce disturbance effects on the power system frequency and steam pressure according to the design specification. The high order LQG/LTR controller is reduced to a low order controller and implemented in a nonlinear cogeneration plant model. Simulation shows the performance of the LQG/LTR controller in disturbance rejection.