Valve selection for compressor surge control

Abstract Surge is an aerodynamic flow instability which can lead to the catastrophic failure of the compressor system. One way to cope with this compressor flow instability is active control. For a laboratory-scale gas turbine installation, an active surge control system is proposed which consists of a plenum pressure sensor and a bleedhecycle valve. This work focuses on the selection of a control valve. More specifically, the required bandwidth and capacity of the valve are specified. To study the influence of the control valve on system behavior, simulations are done with the Greitzer model which describes the behavior of the nonlinear compression system during surge. This model is extended with a control valve model which accounts for the control valve dynamics and the effect of valve saturation. A linear static output feedback controller is used to stabilize the compression system around its nominal operating point. The main contributions of this study are the following. First, a systematic approach is presented to determine the required bandwidth and capacity of a control valve for active surge control. Second, an efficient control strategy is applied: one-sided control. In this control strategy, the control valve is nominally closed and only opens to stabilize the system in its nominal operating point. Third, a stability analysis of the constrained linearized compression system is presented. Using the bounded static output feedback controller, surge limit cycles are stabilized in the nominal operating point. Stable operation can be sustained in this point with zero control valve mass flow if disturbances are absent. From simulations, the minimal bandwidth and capacity of the control valve needed for stabilization are determined. Surge point mass flow is seen to reduce by approximately 15% with the applied one-sided control strategy. Furthermore, it is concluded that nonlinear flow curves of the control valve are unfavorable for active surge control. .