For Central Air Conditioning, Pid Parameter Tuning Instrument Developed

The PID control is relatively simple in structure, convenient in parameter tuning, which can be easily understood and implemented in practice. So many sophisticated control strategies are based on it. At present, the supply air pressure loop and the temperature of chilling water loop are controlled by this method. Due to the change of outdoor temperature and indoor cooling/heating load, the controlling process is characterized by time variable. So the PID parameters should be tuned by itself during a certain time to meet new demands. 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 poorly tuned in practice, so it is important to study auto-tuning PID control.In this thesis, the classical PID control method and parameter tuning method are studies based on step response, and a portable PID parameter tuning equipment is developed. The experimental equipment, the practicability of the portable PID parameter tuning equipment is testified in the experimental equipment. So it is utilized in parameter tuning to raise the control quality of HVAC system.In sectionⅠ, the operating principle and major control loop of variable air volume HVAC are introduced including their development and status of research in this area. This section also give a brief introduction of PID parameter tuning methods, its development and some products of this kind produced both home and abroad.In sectionⅡ, PID control algorithm and several classical parameter tuning methods are studied. A detailed analysis is made in the time-domain based parameter tuning method. The value ofρis worked out when the control performance isoptimized by simulative analyses. Through the simulative experiments of several parameter tuning methods, the results show that the time-domain based parameter tuning method have sound control quality, and provides a reliable technical basis for the development of portable parameter tuning equipment.In sectionⅢ, the hardware and software designs of portable PID parameter tuning equipment are introduced. Characterized by high performance and low power waste, the PIC micro processor is used as core processing unit of the portable parameter tuning equipment. The functions of parameter tuning of the PID controller are achieved by software design. The advantages of the designed equipment are compact in structure and convenient in use.In sectionⅣ, the designed equipment is tested in the supply air pressure loop of HVAC to tune the indoor temperature. The results show that the designed PID parameter tuning equipment is feasible. It can be utilized in parameters tuning to raise the control quality of HVAC system. Besides, the practical control experiment on HVAC suggests that the equipment is well worth developing and popularizing.At last, it is discussed that the limitation of the portable PID parameter tuning equipment and the prospect of further exploration in this field.