Active Control of Surge in Compressors Which Exhibit Abrupt Stall

Abstract : The present paper reports a study on the dynamic behaviour of a compression system based on a multi-stage centrifugal blower and provided with a device for the active suppression of surge instability. The control device includes a sensor of total pressure at the compressor inlet a proportional- derivative controller and an actuation valve at the plenum exit. A non-linear lumped- parameter model of the controlled compression system is presented. which considers also the time-lags in the compressor and actuator unsteady responses. The numerical simulation shows that: i) the predictions of control effectiveness provided by the non-linear model are rather different from the estimates of a linear approach mainly due to the abrupt stall which affects the compressor characteristics: ii) the present control device is capable of suppressing surge within almost the whole unstable operating range of the compressor with values of the proportional gain small enough to avoid actuator saturation (stroke- end occurrence); iii) the derivative component of the control law exerts a poor influence on the system stabilization and can be thus removed: iv) the proposed control strategy is effective over a wide range of stability parameter B which implies the possibility of suppressing surge also at the highest compressor speeds and when using large plenum volumes. On the basis of the numerical results, a practical control device has been designed. which consists of a transducer of differential pressure between plenum and compressor exit (equivalent to a sensor of compressor face total pressure, a butterfly throttle/actuation valve driven by a Stepper motor and a computer, provided with proper interfaces, for signal acquisition, data processing and motor control.