Research And Design Of Anti-surge Control Method For Centrifugal Compressor

Centrifugal compressors play a very important role in petrochemical industry.Most of the gas transportation and production need to pressurize the gas,so the normal operation of compression is related to the entire production.There is an unstable area in the entire operating range of the compressor.When the inlet flow of the compressor suddenly decreases,the compression system will enter an unstable state.If no intervention is taken at this time,the compressor will experience surge,which will cause the air flow inside the compressor to oscillate back and forth,and in severe cases will directly damage the compressor.It is necessary to predict the signs of surge in advance and control the flow to a safe line through the anti-surge system for the propose of preventing compressor surge in this paper,the following researches are made on the anti-surge method of compressor.（1）The return valve model and Greitzer are combined to establish a compressor anti-surge model.This method can not only ensure that the compressor load characteristics remain unchanged during the anti-surge control process,but also achieve accurate compressor flow control.In order to effectively control the system before the compressor surges,this thesis uses the attractor behavior prediction method to predict the compressor surge.When the compressor pressure fluctuates abnormally,the prediction device can send a control signal to the controller in advance to reduce the risk of deep surge of the compressor.（2）Since the compressor model parameters change with the working state,the compressor anti-surge system model is a second-order variable parameter system after linearization.The PID controller designed at the selected operating point can only accurately control the compressor in this state.In order to solve this problem,the adaptive PID controller is adopted in this paper,and the PID parameters are set as multivariate functions of the system state,which ensures that the system controller adapts to each state of the anti-surge system.The PID controller can overcome the input disturbance slowly,so the disturbance compensation device is designed for the situation that the input disturbance is measurable,and the double closed-loop PID control algorithm is designed for the situation that the input disturbance is unmeasurable,so that the controller can resist the input disturbance faster.（3）For the nonlinear system of compressor,feedback linearization transformation is considered to transform the nonlinear object of compressor into linear object.The traditional PD controller can effectively control the integral object,but in the actual system,there will be unmeasurable disturbance at the input of the converted system,which makes the converted system not a standard integral system,and PD controller will not be able to eliminate the static error.Therefore,this thesis uses sliding mode control rate to design the controller of linear system.The Greitzer lumped parameter model has a certain modeling error.In addition,unknown disturbances may occur in the flow and pressure state of the compressor.Therefore,a disturbance state observer is designed to observe the system error and disturbance.The disturbance can be effectively through disturbance compensation of the controller,thus effectively improves the anti-disturbance performance and robustness of the system.When the system is in an unstable state,the feedback linearization control method cannot be used to accurately linearize the system.In this paper,a backstepping control strategy is designed based on the results of Lyapunov stability analysis.The backstepping controller can directly adjust an unstable system to a stable state without considering the operating state of the system.To improve the anti-disturbance performance of the backstepping method,a disturbance compensation is added to the controller,which improves the system’s ability to resist state disturbances.（4）To combine the research content with industrial practice,based on OPTO 22 software,the anti-surge system of centrifugal compressor is implemented in engineering.Firstly,a surge prediction system based on attractor behavior prediction is designed.The system can monitor the pressure state of the compressor in real time.When the prediction device predicts that the pressure is abnormal,the system will switch to the automatic control mode.The discrete program of the backstep control law is written in the OPTO22 controller,which can quickly control the compressor object in Simulink to a steady state.Finally,the HMI interface is designed to realize the functions of real-time monitoring of compressor state,manual automatic mode switching and parameter setting of parameter controller.