適合冷凍空調系統之控制策略及其實現

Refrigeration and Air-conditioning System Adaptive Control Strategy and Implement

蔡貴義(Kuei-I Tsai)

《勤益學報》 25期 (2007/12) Pp. E-115-E-125

https://doi.org/10.6753/CYJ.200712.0003

摘要

傳統PID控制器，其比例、積分和微分動作皆在控制迴路順向路徑上進行，依設定點和輸出之間的偏差做修正動作，如此常導致微分的突變(derivative kick)。本文針對此問題，在實務上採用兩個市售泛用的PID控制器形成PI-PD架構，將PI控制器置於順向路徑、PD控制器置於回授路徑，如此可抑制微分突變的問題及抑制超越現象，進而達到空調制冷及制熱系統高精確度之控制性能。
本文以Smith預估器原理，利用辨識出之系統轉移函數推導出一簡易公式用來設計控制器，發現只要控制器設計得當，便可僅僅使用一個簡單市售的PID控制器，即可達到極爲精準之回授控制，非常適合冷凍空調系統之現場控制應用。經由電腦模擬及現場實測結果證明不論制冷或制熱系統在固定負載及變動負載的情況下，皆能符合工業要求的溫度追蹤性能，對系統干擾有甚佳之抑制特性，應用在油溫冷卻控制系統其精確度約可達±0.2℃。
一般工業控制爲了達到高精密度與高性能之要求，常需搭配電腦及數位信號處理器(DSP-based)來實現，因此有價格昂貴、維修不易、操作複雜之問題。本文所提冷凍空調系統之控制策略及其實現僅須利用市售泛用的PID控制器即可達到高精確度之控制，具有架構簡單、成本低廉且易於現場調控之優點，極適合工業應用之需求。

關鍵字

PI-PD控制 ； 時間延遲系統 ； 程序控制 ； Smith預估器

並列摘要

Generally, in the traditional PID controller, the proportion, integral and differential carry out in the forward loop. The modification is executed according to deviation between set point and output. This method will bring out the derivative kick. To resolve this problem, we used two commercial PID controllers to construct a double PID control system structure. In this control system, PT controller was put in forward loop, and the PD controller in feedback loop. It can suppress derivative kick and maximum overshoot. Then it can also attain high accuracy of heating and cooling system temperature control and has the low cost superiority.
In Smith predictor control section, we designed the controller by exploiting the identification system model and match with the simple formula derived in this thesis. We find out that so long as the controller design is appropriate, we can fulfill the accuracy control of feedback only by a simple market PID controller.
After those two kinds of control systems mentioned above are simulated and executed. The results show that they can provide the temperature tracing requirement of industry in the constant and variable load situation. They also have excellent system disturbance suppression property, and the precision of their temperature control may reach ±0.2℃ approximately In industry, in order to obtain high accuracy and high performance control, the controller is often handled with PC-based and DSP-based generally. But it has some trouble problem in this system, for example, high price, complex operation and difficult service. In paper , we develop two control methods (PT-PD strategy control, Smith predictor control) can fulfill high accuracy only by using market PID controllers. They have the merit of simple construction, low cost, and easy regulation. It meets the industrial application demand extremely.

並列關鍵字

PI-PD Strategy Control ； Time Delay System ； Process Control ； Smith Predictor