On Research Of LNG Export Pressure Control System Based On Implicit Generalized Predictive Control Algorithm

In the modern industry and daily life, LNG export pressure control system has a wide range of applications. With the continuous development of industry, people have higher and higher demands on the pressure control of LNG. At the same time, the change of pressure in the industrial field is a changeable and complicated process. In the actual industrial field, the change of pressure is influenced by various factors, and the pressure control object generally has the characteristics of nonlinear, large inertia, disturbance factors and long time delay.This will put forward higher standards and requirements for the pressure control algorithm.With the development of science and technology, more and more advanced control technology has emerged. As it can overcome the shortcomings of the traditional control technology, it is widely used in industrial control. This paper studies the generalized predictive control algorithm, on the basis of this, the parameters of the control law are introduced, which makes the algorithm more real-time and fast,we call it an Implicit Generalized Predictive Control algorithm. We also establish the LNG export pressure control model based on Implicit Generalized Predictive Control algorithm. The effect of the PID algorithm and the Implicit Generalized Predictive algorithm for the pressure control is compared with the MATLAB simulation, the minimum system of STM32 and some peripheral circuits are established.We also design the pressure sampling circuit and proportional solenoid valve drive circuit, at the same time, Visual Studio-2010 and C# are used to design the pressure control system of LNG, which is convenient for the users to display and control the pressure. The paper’s main research work and innovation are as follows:1. Analysis and research of implicit generalized predictive control algorithm. In this paper,for the generalized predictive control algorithm,in order to solve the problem, we have to solve the problem of Diophantine equation on line.At the same time, it is necessary for us to calculate the inverse matrix, which makes the computation complexity.If the original model parameters of the system are directly identified, we have to solve the control law.It is necessary to find out the parameters of the controller, which can also extend calculating time and reduce the real-time performance of the controller. This will make practical application of the generalized predictive control algorithm is very unfavorable,so the direct identification of the control law parameters E、G、S is used in this paper. This will make Diophantine equation is not solved online, and it can help to reduce the calculating time. Based on this, the Implicit Generalized Predictive Control algorithm is developed.2.Modeling and Research of LNG export pressure control system based on Implicit Generalized Predictive Control algorithm.Because of the characteristics of LNG pressure control with time varying, uncertainty and large delay.It is not only the uncertainty of the control object, time variability, large delay, but also has the characteristics of large storage tank capacity, large gas consumption fluctuations, the air supply is not uniform, and the pressure control process in the presence of LNG by liquid into gas.So it is not up to the requirements of control by using the simple PID algorithm. Using the CARIMA model of Implicit Generalized Predictive Control algorithm, we construct the LNG export pressure control block diagram and Implicit Generalized Predictive Controller based on the Implicit Generalized Predictive Control algorithm.Through simulation, it is found that the LNG export pressure control is more perfect and stable for the pressure control.3.Hardware design of LNG export pressure control system. The design of the system based on the Implicit Generalized Predictive Control algorithm. STM32 is the core of the embedded controller Cortex-M3 in hardware. The STM32 minimum system is built. Based on this, the RS-485 communication interface circuit, pressure detection circuit, proportional solenoid valve drive circuit are designed. MODBUS-RTU protocol is used to realize the communication protocol. In order to achieve the stability of the communication and information transmission between system, according to the original protocol, the format of the control protocol is designed. At the same time, it also facilitates the real-time data display and data processing of LNG export pressure.4.Software design of the LNG export pressure control system. I mainly use visual studio-2010 development platform and C# language to develop, through the reference of other control system and operation of the user’s habits, I design the LNG export pressure control system, which mainly includes system settings interface, exit system interface, parameter setting interface, user interface, device settings interface, etc. I have achieved the function of monitoring and controlling of the executive machine of LNG export pressure control system, At the same time, the host computer to complete a variety of complex data processing.