Process Identification And PID Parameters Auto-tuning Theory And Application In HVAC System

The PID control is the most common control algorithm. PID control is widely applied on process control system. The main reason is its relatively simple structure, which can be easily understood and implemented in practice and that many sophisticated control strategies are based on it. The tuning of PID controllers, usually done by seasoned engineers and technicians, is laborious and time-consuming. Furthermore, because the real processes are different in dynamics, and have time delay and nonlinearity, the tuning of PID sometimes becomes very difficult. As a result, many regulators are in practice poorly tuned, so it is important to study auto-tuning PID control.With the development of society and economy, the requirements of people for the quality of habitation are higher and higher. The buildings have been from the simple shelter to the comfort, health, energy-saving, automatic and intelligent green buildings. And the corresponding building energy consumption also increased annually. The cost of HVAC systems for the energy in the total building energy consumption is of 3 0% - 5 0%, and showed an increasing trend. Therefore, in the international energy increasingly scarce, the HVAC system control study is of great practical significance and value. HVAC system control system of the research focus on various internal loop controller design and optimization. A good control method can not only meet the people's demands on the environment and comfort but also achieve energy conservation purposes. Concluding remarks, the main contents of thesis can be summarized as follows:1. Summary of success/failure for relay feedback test for common difficult dynamic processes in HVAC systems.The process identification and controller tuning based on relay feedback tests are widely used, so it is very important for the tests are of success or failure. We studied the relay feedback tests for difficult dynamic processes common in HVAC system such as process with time delay, RHP zero and Open-loop unstable systems and summarized the heuristics the successor failure of a relay feedback tests for such processes. So it laid a good foundation for the process identification and controller tuning based on relay feedback.2. Proposed a HVAC engineering oriented multivariable process identification method.Compared with Single-inputs single-outputs (SISO) systems. It is more complicated and difficult for the control on MIMO systems. A HVAC engineering oriented multivariable process identification method for TITO process in HVAC system is proposed. By two set-point change tests, the frequency response in the range of interest corresponding toπphase lag are estimated; and the parameters of transfer function matrix are identified by matching the model in the frequency domain. The proposed identification method only requires response data of process input and output, and no prior knowledge of the process dynamics is needed. The proposed method requires no prior knowledge of the process, and that the method can be extended to multivariable process. The typical Simulation examples are given to show both effectiveness and practicality of the identification method.3. Propose a PID parameters auto-tuning arithmetic for integral processes.A simple and practical auto-tuning method of PID controller for integral processes is proposed and a successful application in the HVAC pilot plant system is made. The method first identify model for the processes. Then, PID controllers are designed based on robustness specification. PID tuning adopts two feedback loop structure and controller design method based on robustness specification, which can overcome the structural limitation of conventional PID controller. Finally tuning formulas for PID controller with setpoint weighting are obtained through structural simplicity. Simulation examples show the effectiveness and practicability of proposed auto-tuning method.4. A Handset intelligent auto-tunner is implemented based on PIC18f452.With present PID auto-tuning method, a Handset intelligent auto-tunner based on PIC18f452 is implemented. It is small, easy to take and can save a lot of time for engineers to tune the PID controllers so as to increase efficiency greatly. The controller is applied to practical industrial process. In the control on VAV System of HVAC, the PID controller for air supply control Loop of main pipeline was tuned by the Handset auto-tunner, which gives the PID parameters quickly and arrived at a good control effect. Currently the product is preparing to apply for a patent.5. A PID auto-tuning system based on INTERNET is developed on Visual C++ and JAVA development platform.Industrial Ethernet is a new control system structure based on network. Industrial Ethernet with TCP/IP protocol has only a communication protocol in whole network and satisfies the demand of various parts in control system. Furthermore, industrial Ethernet is easily connected to Internet, so it can implement the seamless connection between enterprise information network and industrial control network. Combining the automatic tuning technique with internet, a PID auto-tuning system with independent intellectual property rights is developed based on internet.Finally, a conclusion is made and the future research directions are Proposed in this field.