PI controller will eliminate forced oscillations and steady state error resulting in operation of on -off controller and P controller respectively.

However, introducing integral mode has a negative effect on speed of the response and overall stability of the system.

PI controllers are very often used in industry, especially when speed of the response is not an issue.

A control without D mode is used when:

a) fast response of the system is not required

b) large disturbances and noise are present during operation of the process

c) there is only one energy storage in process (capacitive or inductive)

d) there are large transport delays in the system

It depends on the performance you are looking for.

The PI controller is good at DEVICE LEVEL for following a reference without any steady state error. It is popular because the gains can be tuned trial and error without using any analytical techniques. At System Level, for example a power oscillation damping controller, PI is not good.

It also depends on the complexity of the process which is being controlled.

PI controllers are usually used as single-input-single-output (SISO) controllers - although they can theoretically be extended to multiple-input-multiple-output (MIMO) structures.

The 'PI' part simply defines the structure of the controller - which can then be tuned using a number of ways (trial and error, analytically, optimisation techniques etc). For many systems, especially as the requirements of the controller become more complex, the PI structure will not be flexible enough on its own to form an adequate controller - no matter what tuning approach is used. It may be that it can simply be supplemented with filters and phase compensation blocks - or more complex controller structures may be required.

Another point to consider is what you want from the controller. As with all control design, you are looking to find the right balance of performance and robustness (and stability is a must-have in power systems). Correctly defining these requirements, and then testing your designed controllers will be the true test of whether PIs are good enough.

(as has previously been stated - for many applications they are).

PI controller will eliminate forced oscillations and steady state error resulting in operation of on -off controller and P controller respectively.

However, introducing integral mode has a negative effect on speed of the response and overall stability of the system.

PI controllers are very often used in industry, especially when speed of the response is not an issue.

A control without D mode is used when:

a) fast response of the system is not required

b) large disturbances and noise are present during operation of the process

c) there is only one energy storage in process (capacitive or inductive)

d) there are large transport delays in the system

Its entirely depends on the performance of system for different disturbances........ Based on response of the system and stabilty studies..we can design controller

Power systems are systems which are inherently fast and the current, voltage fluctuations are very fast. Hence, the ideal controller for these applications needs to have disturbance rejection properties and steady state error elimination.

Hence, PI is the preferred controller structure in such applications.

I think the principal reason for using PI or PID controllers was the very large experience of use for this controllers (50 years). Everybody knows how deal with this controllers, there is plenty information about them. How could you expect using "complex controllers" in power systems without enough proofs of your performance??

I agree "a PI controller can properly satisfy their requirements in many sections of power system studies". Please note that "many sections" is NOT equal to "all sections". In some complex cases, the complex controllers may be applied.

I also agree with Farid's comments on PI controller and PID controller.

(1) Only PID Control and Smith Predictor were listed in the “Leaders of the Pack” InTech’s 50 most influential industry innovators since 1774. Available from the following link.

http://www.isa.org/InTechTemplate.cfm?Section=Article_Index1&template=/ContentManagement/ContentDisplay.cfm&ContentID=28889

PID Control was listed twice (the dominant control method in the industrial applications) -- (1) John G. Ziegler and Nathaniel B. Nichols and classical PID Control; (2) Karl Johan Åström and modern PID Control (IEEE Medal of Honor, 1993)

http://en.wikipedia.org/wiki/IEEE_Medal_of_Honor

The next popular method is Smith Predictor: Otto J.M. Smith and Smith Predictor.

http://en.wikipedia.org/wiki/Otto_J._M._Smith

(2) A typical PID tuning procedure: (1) Use relay control to estimate the control model (or control plant); (2) Use Z-N formula to initialize Kp and Ki; (3) use trial and error to adjust Kp and Ki or other method such as iterative feedback tuning (IFT), internal model control (IMC), etc.

H. Hjalmarsson was elected to the Class of 2013 IEEE fellow last year due to his fundamental contribution to iterative feedback tuning. The key contribution of IFT is tuning controller parameters for those control model (or control plant) whose parameters are difficult to be identified relatively accurately, in other words, iterative feedback tuning was proposed to minimize a given quadratic cost function of the system output error and control effort, thus solving the controller tuning issues caused by plant uncertainty.

H. Hjalmarsson, M. Gevers, S. Gunnarsson, and O. Lequin, "Iterative feedback tuning: theory and applications," IEEE Control Systems Magazine, vol.18, no.4, Aug 1998, pp .26-41,

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=710876

By cooperating with his peer researchers including Stanford University researcher, H. Hjalmarsson integrated iterative feedback tuning with PID controller to solve controller tuning issues caused by plant uncertainty.

WK Ho, Y Hong, A Hansson, H Hjalmarsson, and JW Deng, "Relay auto-tuning of PID controllers using iterative feedback tuning," Automatica 39 (1), January 2003, pp. 149-157. Available from the following RG Link.

https://www.researchgate.net/publication/223504459_Relay_auto-tuning_of_PID_controllers_using_iterative_feedback_tuning

W.K. Ho, T.H. Lee, H.P. Han, and Y. Hong, "Self-Tuning IMC-PID Control with Interval Gain and Phase Margin Assignment," IEEE Transactions on Control Systems Technology, 9(3), May 2001, pp. 535-541. Available from the following RG Link.

https://www.researchgate.net/publication/3332273_Self-tuning_IMC-PID_control_with_interval_gain_and_phase_marginsassignment?ev=prf_pub

C.C. Hang, K.J. Astrom, and W.K. Ho, "Refinements of the Ziegler-Nichols tuning formula," IEE Proceedings on Control Theory and Applications, 138(2), March 1991, pp.111-118.

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=67610

This paper has been implemented by Maplesoft Inc. for MapleSim Control Design Toolbox

http://www.maplesoft.com/support/help/MapleSim/view.aspx?path=ControlDesign/GainPhaseMargin

K.J. Åström, T. Hägglund, C.C. Hang, and W.K. Ho, "Automatic tuning and adaptation for PID controllers - a survey," Control Engineering Practice, 1(4), August 1993, pp.699-714.

http://www.sciencedirect.com/science/article/pii/096706619391394C

K.J. Åström, C.C. Hang, P. Persson, and W.K. Ho, "Towards intelligent PID control," Automatica, 28(1), January 1992, pp.1-9.

http://www.sciencedirect.com/science/article/pii/000510989290002W

Control theorectic approaches have been applied to model the interactions between an overloaded SIP server and its upstream servers as a feedback control system in two different scenarios - round trip delay control (IEEE ICC 2011) and redundant retransmission ratio control (IEEE Globecom 2010).

Round-Trip Delay Control (RTDC, implicit SIP overload control) algorithm: Y. Hong, C. Huang, and J. Yan, "Design Of A PI Rate Controller For Mitigating SIP Overload," Proceedings of IEEE ICC, Kyoto, Japan, June 2011.

https://www.researchgate.net/publication/224249824_Design_of_a_PI_Rate_Controller_for_Mitigating_SIP_Overload

RTDC implicit SIP overload control algorithm has been recommended as White Paper by TechRepublic (CBS Interactive)

http://www.techrepublic.com/whitepapers/design-of-a-pi-rate-controller-for-mitigating-sip-overload/25142469

IEEE ICC 2011 presentation slides for RTDC implicit SIP overload control can be downloaded from the following RG link.

https://www.researchgate.net/publication/257945199_Round-Trip_Delay_Control_(RTDC)_For_Mitigating_SIP_Overload_(IEEE_ICC_2011_Slides)

Redundant Retransmission Ratio Control (RRRC, implicit SIP overload control) algorithm: Y. Hong, C. Huang, and J. Yan, "Mitigating SIP Overload Using a Control-Theoretic Approach," Proceedings of IEEE Globecom, Miami, FL, U.S.A, December 2010.

https://www.researchgate.net/publication/221284946_Miigating_SIP_Overload_Using_a_Control-Theoretic_Approach

RRRC implicit SIP overload control algorithm has been quickly adopted by The Central Weather Bureau of Taiwan for their early earthquake warning system.

T.Y. Chi, C.H. Chen, H.C. Chao, and S.Y. Kuo, "An Efficient Earthquake Early Warning Message Delivery Algorithm Using an in Time Control-Theoretic Approach", 2011.

http://link.springer.com/chapter/10.1007%2F978-3-642-23641-9_15#

http://www.ipv6.org.tw/docu/elearning8_2011/1010004798p_3-7.pdf

Short review and comments on this implicit SIP overload control algorithm by former IEEE TAC Associate Editor S. Mascolo:

L. De Cicco, G. Cofano, and S. Mascolo,"Local SIP Overload Control", Proceedings of WWIC, June 2013.

http://link.springer.com/chapter/10.1007%2F978-3-642-38401-1_16#

http://c3lab.poliba.it/images/2/2a/SipOverload_WWIC13.pdf

IEEE GLOBECOM 2010 presentation slides for RRRC implicit SIP overload control can be downloaded from the following RG link.

https://www.researchgate.net/publication/258555827_Mitigating_SIP_Overload_Using_a_Control-Theoretic_Approach

Journal paper (SIP Overload Control) not only conducts more theoretical analysis of Round trip delay control (RTDC) and Redundant retransmission ratio control (RRRC), but also discusses how to apply RTDC algorithm to mitigate SIP overload for both SIP over UDP and SIP over TCP (with TLS).

Y. Hong, C. Huang, and J. Yan, "Applying control theoretic approach to mitigate SIP overload", Telecommunication Systems, 54(4), 2013, pp. 387-404.

https://www.researchgate.net/publication/257667871_Applying_control_theoretic_approach_to_mitigate_SIP_overload

http://link.springer.com/article/10.1007/s11235-013-9744-8

Survey on SIP overload control algorithms: Y. Hong, C. Huang, and J. Yan, "A Comparative Study of SIP Overload Control Algorithms", IGI Global, 2012, pp. 1-20.

http://www.researchgate.net/publication/231609451_A_Comparative_Study_of_SIP_Overload_Control_Algorithms

http://www.igi-global.com/chapter/comparative-study-sip-overload-control/67496

Open-source SIP/VoIP project discussion archive

http://lists.sip-router.org/pipermail/sr-users/2013-April/077596.html

IETF-RFC "SIP Overload Control" discussion archive

http://www.ietf.org/mail-archive/web/sip-overload/current/msg00919.html

API-RCP(TCP Congestion Control):Y. Hong and O.W.W. Yang, "Design of Adaptive PI Rate Controller for Best-Effort Traffic in the Internet Based on Phase Margin," IEEE Transactions on Parallel and Distributed Systems, 18(4), April 2007, pp. 550-561.

http://www.researchgate.net/publication/3301176_Design_of_Adaptive_PI_Rate_Controller_for_Best-Effort_Traffic_in_the_Internet_Based_on_Phase_Margin

Review, comments, and extensive evaluation on API-RCP:

H. Zhou, C. Hu, and L. He, "Improving the Efficiency and Fairness of eXplicit Control Protocol in Multi-Bottleneck Networks", Elsevier Computer Communications, 36(10-11), June 2013, pp. 1193-1208.

http://www.sciencedirect.com/science/article/pii/S0140366413001059

(3) Control Theory developed in the twentieth century: 25 Seminal Papers (1932-1981) Selected by IEEE Control Society in 2000

http://www.wiley.com/WileyCDA/WileyTitle/productCd-0780360214,descCd-tableOfContents.html

http://ieeeexplore.com/xpl/bkabstractplus.jsp?bkn=5265919

IEEE Control Systems Award

http://en.wikipedia.org/wiki/IEEE_Control_Systems_Award

IFAC Giorgio Quazza Medal

http://www.ifac-control.org/awards/major-medals

4 co-authors of 25 Seminal Papers (1932-1981) awarded IEEE Medal of Honor (the highest IEEE award): Nyquist(1960), Kalman(1974), Bellman(1979), Astrom(1993).

http://www.ieee.org/about/awards/medals/medalofhonor.html

R.E. Bellman and K.J. Astrom, "On structural identifiability," Mathematical Biosciences, 7(3-4), 1970, pp. 329–339.

http://www.sciencedirect.com/science/article/pii/002555647090132X

Richard E. Bellman Control Heritage Award for US control systems engineers and scientists (US citizenship)

http://a2c2.org/awards/richard-e-bellman-control-heritage-award

Ragazzini's notable students are Rudolf Kalman (see Kalman filters), Eliahu Ibraham Jury (see Z-transform) and Lotfi Asker Zadeh (see Fuzzy sets and Fuzzy logic).

https://en.wikipedia.org/wiki/John_Ragazzini

K. Astrom, E.I. Jury, and R. Agniel, "A numerical method for the evaluation of complex integrals," IEEE Transactions on Automatic Control, vol.15, no.4, Aug 1970, pp.468-471.

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=1099492

"To control theorists, Nyquist is no doubt best known as the inventor of the Nyquist diagram, defining the conditions for stability of negative feedback systems. This has become a foundation stone for control theory the world over, applicable in a much wider range of situations than that for which it was orignally enunciated." Hendrik W. Bode, Harvard University, USA, 1977.

http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1101666

Biography of Harry Nyquist, University of Cambridge, UK, 2003

"Between 1920 and 1940 he published a series of papers on research in telecommunications which are arguably the most outstanding set of scientific contributions since Newton (apart from Einstein!)."

http://babylon.acad.cai.cam.ac.uk/students/study/engineering/engineer03l/cenyquist.htm

http://babylon.acad.cai.cam.ac.uk/students/study/engineering/engineer03l/ceframes.htm

K.J. Åström, "Harry Nyquist (1889-1976): A Tribute to the Memory of an Outstanding Scientist," Royal Swedish Academy of Engineering Sciences, 2003.

American Society of Mechanical Engineers (ASME) Nyquist Lecturer Award

https://www.asme.org/about-asme/get-involved/honors-awards/unit-awards/nyquist-lecturer

8 wonderful presentations in control symposium "Paths Ahead in the Science of Information and Decision Systems", Massachusetts Institute of Technology (MIT), USA, November 12 – 14, 2009.

http://paths.lids.mit.edu/papers_mitter.html

Panel on Future Directions in Control, Dynamics, and Systems, Richard M. Murray (chair), California Institute of Technology, April 2002

http://www.cds.caltech.edu/~murray/cdspanel/

R. Murray, K. Astrom, S. Boyd, R. Brockett, and G. Stein, "Future Directions in Control in an Information-Rich World," IEEE Control Systems Magazine, 23(2), April 2003, pp.20-33.

http://www.stanford.edu/~boyd/papers/cds_panel.html

To celebrate the golden anniversary, IFAC Automatica will publish in the 50th volume throughout the year, special survey/overview papers, on selected topics, some tracing the history on some mature topics and areas, others focusing on newly emerging areas, with forecasts into the future. The survey paper published by the 1st issue provides an overview of the developments in the control field from its early days.

K.J. Astrom and P.R. Kumar, "Control: A Perspective," Automatica, 50(1), January 2014, pp. 3-43.

http://www.sciencedirect.com/science/article/pii/S0005109813005037

Article Design of Adaptive PI Rate Controller for Best-Effort Traffi...

Article Self-tuning IMC-PID control with interval gain and phase mar...

Conference Paper Mitigating SIP Overload Using a Control-Theoretic Approach.

Article Relay auto-tuning of PID controllers using iterative feedback tuning

Conference Paper Design of a PI Rate Controller for Mitigating SIP Overload

Article A Comparative Study of SIP Overload Control Algorithms

Article Applying control theoretic approach to mitigate SIP overload

Data Round-Trip Delay Control (RTDC) For Mitigating SIP Overload ...

Data Mitigating SIP Overload Using a Control-Theoretic Approach

I think that the use of PI controllers in industry is because they are simple and robust. I have worked with Electric Arc Furnaces and their automatic control device was just a P controller, because was more important that this device were working without stops that have an accurate movement of the furnace's electrodes or have a complex control device that will require continuos regulations or fixing of their variables, pieces, etc.

It should be noted that the concept of the PI controller includes various structures with different properties. Especially controllers with two degrees of freedom 2-DOF can flexibly shape the characteristics of the control system.

Its not really what researchers think it is what is actually used / implemented in practice. You will find a gap between research and practice particularly as the former assume no liability. In practise a "PI" controller is a typical basic entity but in reality we have saturation, hysteresis, non-symmetry, anti-windup etc and many other practical and operational specific issues that must be accounted for in the control of power systems as Yang Hong above notes.

most of the electric drives use PI controllers.Can any one tell me why PI and why not PID?