PI and PID controller design based on generalized stability boundary locus
Journal Name:
- Dicle Üniversitesi Mühendislik Fakültesi Mühendislik Dergisi
Keywords (Original Language):
Author Name | University of Author | Faculty of Author |
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Abstract (2. Language):
The paper introduces a generalized approach to
identify all stabilizing PI and PID controllers. For
this purpose, a stable first order plus dead time
(FOPDT) model is used to model higher order plant
transfer functions. In order to estimate the process
transfer function parameters, relay feedback
identification method given by Kaya and Atherton
(2001) is used. The identification method, assuming
no measurement errors and disturbances, results in
exact estimations. After obtaining the plant transfer
function model, normalized form of the process
transfer function model and controller is used to plot
stability boundary locus in , (T/ T ) c c i KK KK
plane for the PI controller and
(T / T), (T/ T ) c d c i KK KK plane for the PID
controller for a certain value of normalized dead
time, /T , where and T are, respectively,
the time delay and time constant of the FOPDT
model. By doing so, the need to compute the stability
boundary locus for different plant transfer functions
has been removed.
If the actual and the model transfer functions match
exactly, then the proposed approach will give exact
solutions. However, in the case of a mismatch
between the actual and the model transfer functions,
the approach will result in approximate solutions,
especially for the frequencies near the critical
frequency. Therefore, if the actual plant transfer
function is a higher order one, then, one must pay
attention with the points selected in the stability
region. Here two suggestions are provided in order
to ensure a stable closed loop response while
selecting the points to be used in determining PI and
PID controller parameters: 1) The points towards
the centre of the stability region must be selected. 2)
The stability region that corresponds to a previous
larger normalized dead time than the current
normalized dead time should be used.
The proposed approach can be extended to PID
controllers as well. For the all stabilizing PID
controller design the following procedure can be
used. In the controller design, it is more usual to
assume a controller gain and then to calculate the
remaining other two tuning parameters, namely, i T
and d T . Stability region in the
( (T/ T ), (T / T)) c i c d KK KK plane for a fixed value
of c KK can be obtained by using the stability
regions obtained in ( , (T / T)) c c d KK KK and
( , (T/ T )) c c i KK KK planes. Once the above cited
stability boundary locus are obtained, plotting
stability boundary locus in the
( (T/ T ), (T / T)) c i c d KK KK plane for different
values of normalized dead time ratios can be carried
out.
The proposed approach brings the advantage of not
requiring to plot the stability boundary locus each
time as the process transfer function changes, which
is the case for the so far reported studies in the
literature. Simulation examples are provided to
illustrate the usefulness of the proposed approach.
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Abstract (Original Language):
Bu çalışma, zaman gecikmeli kontrol sistemlerinin kararlılığı için tüm PI ve PID denetleyici
parametre değerlerinin hesaplanmasında genelleştirilmiş bir yaklaşım önermektedir. Bu
yaklaşımda yüksek mertebeden transfer fonksiyonlarının, birinci derece artı zaman gecikmeli
transfer fonksiyonları ile modellenmesi gerekir. Elde edilen model ve denetleyici transfer
fonksiyonları normalize edilerek PI denetleyici tasarımı için , (T/ T ) c c i KK KK düzleminde sınırlı
kararlılık bölgesi oluşturulur. Benzer şekilde PID denetleyici tasarımı için , (T / T) c c d KK KK ,
, (T/ T ) c c i KK KK ve (T / T), (T/ T ) c d c i KK KK düzlemlerinde sınırlı kararlılık bölgeleri
oluşturulur. PI ve PID denetleyici parametre değerleri, elde edilen sınırlı kararlılık bölgeleri ile
belirlenir. Bu yaklaşım sayesinde transfer fonksiyonunun her değişmesi ile sınırlı kararlılık
bölgelerinin yeniden oluşturulmasına ihtiyaç duyulmaz. Elde edilen genelleştirilmiş sınırlı kararlılık
bölgeleri ile tüm PI ve PID denetleyici parametre değerleri hesaplanabilir. Böylelikle bu yaklaşım
şimdiye kadar literatürde bildirilmiş çalışmalara göre avantaj sağlar. Önerilen yaklaşımın
kullanışlılığını açıklamak için örnek benzetimler verilmiştir.
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