Robust controller design for simultaneous control of throttle pressure and megawatt output in a power plant unit

This paper presents an application of H_∞ and μ-synthesis controller design methods to a coal-fired power generation unit and compares the closed loop performance and robustness of H_∞ and μ-synthesis control laws with those of an H₂ control law. All three controller synthesis procedures are applied to a two-input two-output plant model which has time delay, differential part, colored noise output disturbance, and sensor noise disturbance. Application of the procedures to the model shows that when the shape of the closed loop control signals of all three designs is closely matched, in the low frequency range the μ-synthesis and H_∞ control laws have robustness much better than that of H₂ control law, while providing adequate robustness in the high frequency range. H_∞ control law gives the best performance, and H₂ - the worst of the three designs, exhibiting the largest overshoot. The balancing procedure permits significant reduction of the order of the controllers without degradation in performance and robustness. The comparative evaluation of three designs shows that in power plant control problem H_∞ and μ-synthesis designs provide much more consistent and convenient performance/robustness trade-off than H₂ design.