ASHRAE OR-10-033-2010 Compensation of Manual Reset to Offset Thermal Loads Change for PID Controller《手动复位对PID控制器用偏离热负载的补偿》.pdf
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1、2010 ASHRAE 303ABSTRACTIn the heating, ventilating, and air-conditioning (HVAC)systems, Proportional-plus-integral (simply, PI) controllers areby far the most common control algorithm and this situation hasnot yet changed greatly. With a simple Proportional (P) control-ler, there would be an offset,
2、 which the operator could eliminateby the manual reset to compensate for thermal loads change. Theautomatic reset with an Integral (I) controller is absolutely neces-sary to make the control output be returned to the setpoint auto-matically. PI controller, however, often leads to a poorly dampedresp
3、onse. Proportional-plus-integral-plus-derivative (PID)controllers have been more desirable than PI controllers due tothe stabilizing effect of a Derivative (D) action. In practice,however, the D action has been frequently switched off for thesimple reason that it is difficult to tune properly. In so
4、me situa-tions, it might be possible to estimate thermal loads (or distur-bances) before they entered the plant. A typical example is acertain system for HVAC systems in which the outdoor thermom-eter detects sudden weather changes and the occupant roughlyanticipates thermal loads changes. Disturban
5、ces should be offsetby the compensation of the manual reset. This control strategycan be called a type of feed-forward control. The control schemewith lower (or no) I action may be interpreted as a PD controller.The thrust of this paper is to offset thermal loads before they affectthe control output
6、 and to confirm the effectiveness of compensa-tion of the manual reset. For the sake of comparison, simulationresults to demonstrate the validity of compensation method aresomewhat superior to those with a traditional PI controller.INTRODUCTIONAbout one hundred years ago, applying the thermostatand
7、the control valve to home heating controls, the automaticcontrol system has been initially realized. Since then, the heat-ing, ventilating, and air-conditioning (HVAC) systems havebeen considered from viewpoint of control engineering. Thecomplexity of multi-variable system, interacting system, anddi
8、stributed system are the common characteristics for anyprocess industries. The HVAC systems, however, have notbeen advanced compared to chemical and steel processes thatexploited the advantages of digital control (Hartman 2003).The HVAC systems have huge different characteristics incontrol engineeri
9、ng from chemical plants. One of the charac-teristics is that the equilibrium point (or the operating point)usually changes with disturbance such as outdoor tempera-ture, control input, and thermal loads etc. The change of theequilibrium point means the change of plant parameters. Thus,the HVAC contr
10、ol system is extremely difficult to obtain anexact mathematical model.Today, a variable air volume (VAV) system is universallyaccepted as means of achieving energy efficient and comfort-able building environment. While the VAV control strategiesprovide a high quality environment for building occupan
11、ts, theVAV system analysis rarely receives the attention it deserves.As a result, basic control strategies for the VAV system haveseen little significant change up to now (Hartman 2003).Recently, applying the model prediction control to theHVAC systems, the control performance has been highlyimprove
12、d by pursuing the perturbation of equilibrium point ofplant (Taira 2004). In this paper, recognizing the operatingpoint of control input and calculating the optimal control inputabout the perturbation for equilibrium point on next samplingtime, the control system gives better responses than the trad
13、i-tional feedback control systems.Compensation of Manual Reset to Offset Thermal Loads Changefor PID ControllerYuji Yamakawa Takanori Yamazaki, PhDKazuyuki Kamimura, PhD Shigeru Kurosu, PhDMember ASHRAEYuji Yamakawa is a graduate student in the Department of Information Physics and Computing at the
14、University of Tokyo, Tokyo, Japan.Takanori Yamazaki is a research associate in the Department of Mechanical Engineering at Oyama National College of Technology, Oyama,Japan. Kazuyuki Kamimura is a director in the Research & Development division, Yamatake Co., Ltd., Tokyo, Japan. Shigeru Kurosu is ad
15、irector at the Research Institute “Crotech,” Chikusei, Japan.OR-10-033 2010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2010, Vol. 116, Part 1. For personal use only. Additional reproduction, distribution, or tra
16、nsmission in either print or digital form is not permitted without ASHRAEs prior written permission. 304 ASHRAE TransactionsOne of the primary objectives of the HVAC systems is tomaintain the indoor temperature and humidity at the setpointvalues to provide a high quality environment for building occ
17、u-pants. Proportional-plus-integral (PI) controllers are by far themost common control algorithm and the situation has not yetchanged greatly. With a simple Proportional (P) controller, therewould be an offset (or a steady-state error), which the operatorcould eliminate by the manual reset to compen
18、sate for thermalloads change. The supply air flowrate (the control input) to theroom (the controlled plant) should offset thermal loads changeimposed on the room due to the function of an Integral (I) action.PI controller, however, often leads to a poorly damped response.Proportional-plus-integral-p
19、lus-derivative (PID) controllershave been more desirable than PI controllers due to the stabi-lizing effect of a Derivative (D) action. In practice, however, theD action has been frequently switched off for the simple reasonthat it is difficult to tune properly (Shilling 1963, Shinsky 1967,Takahashi
20、 1969).In some applications, thermal loads (or disturbances) canbe estimated in advance before they entered the plant. A typicalexample is a certain system for HVAC systems in which theoutdoor thermometer detects sudden weather changes and theoccupant roughly anticipates thermal loads changes. Distu
21、r-bances should be offset by the compensation of the manualreset. This control strategy can be called a type of feed-forwardcontrol. The control scheme with lower (or no) I action may beinterpreted as a Proportional-plus-derivative (PD) controller. Inthis paper, of special interest to us is how to m
22、ake the D actionmore effective for HVAC systems. At first, this paper proposesa compensation method of the manual reset to offset thermalloads before they affect the control output and confirms theeffectiveness of compensation.PLANT DYNAMICS AND CONTROL STRUCTUREDynamics of HVAC SystemTo explore the
23、 application of a PID controller to HVACsystem, we consider a single-zone environmental space cool-ing system, as shown in Figure 1. The system is composed ofa constant volume, single-zone air-handling unit (AHU oractuator), a PID controller, and an environmental space(controlled plant). With this s
24、ystem, the indoor temperature ofthe space () is measured with a thermometer (sensor). Theoutput signal from the sensor is amplified and then fed back tothe PID controller. Using the error defined as the differencebetween the setpoint value (r) and the measured value of thecontrolled variable (), the
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