Learning digital control systems with a low-cost educational platform

Proceedings of 2005 CACS Automatic Control ConferenceTainan, Taiwan, Nov 18-19, 2005digital feedback controller is given to students suchthat they can modify the controller parameters andeven the controller structure [6] to see if the responsescoincide with the theoretical predictions. If not,double check of the software codes and theories canmake them more familiar with problem-solvingtechniques. Experimental results which compare theperformances of the servo control of dc motors withand without the anti-windup function are shown infigure 5. The robustness of the digital temperaturecontroller is shown via experimental results in figure 6by changing the amount of water in the water tank.Figure 5. The experimental results of digital servocontrol of DC motors with and without anti-windupfunction4. ConclusionsA low cost educational platform is devised in thispaper. It can be constructed for servo control of dcmotors and temperature control of a water tank forless than USD$ 50. Two experiments are devised tohelp students become familiar with the necessarycontrol theories and the corresponding softwareimplementation for the servo control of a dc motorand temperature control of a water tank. This canhelp encourage students to make their owneducational platform and learn to solve by themselvesmore practical digital control problems. To make theeducational platform more versatile, the USB portshould be used to increase the communication speedbetween the educational platform and the personalcomputer. This may be done with the help of theUSB interface device [11]. Moreover, the digitalsignal controller (dsPIC) provided by the MicrochipTechnology Inc. is another affordable choice ofmicro-controller for its fast computational speed andversatility. It is also easy to setup the developmentenvironment for the digital signal controller (dsPIC)without too much money.Figure 6. Robustness analysis of the digital PIDtemperature controller with and without anti-windupfunctionSince tuning of PID controller parameters may betedious in practice, techniques in auto-tuning ofcontroller parameters [2, 4] are introduced to studentsafter they successfully apply theories to design PIDcontrollers in both the problems. Because of thecomputational complexity, the self-tuning adaptivefeedback controller for servo control of dc motors byusing recursive least square (RLS) estimation can onlybe demonstrated in our dSPACE real time controlenvironment if the order of the reference model isgreater than or equal to 2. The student can stillimplement a convergent RLS algorithm on theeducational platform if the sampling frequency is nottoo high and a reference model of order 1 is used.Figure 7 shows the experimental results of asuccessful self-tuning adaptive feedback controller,whose reference model is of order 1. On the otherhand, the algorithm described in [5] for on-lineidentification of system parameters and auto-tuning ofPID controller parameters can be successfullyimplemented in the educational platform, because thedynamics for heat transfer in the temperature controlof a water tank is slow.Figure 7. The experimental results of a successfulself-tuning adaptive feedback controller, whosereference model is of order 15. References[1] D. S. Bernstein, “Enhancing undergraduatecontrol education,” IEEE Control SystemsMagazine, pp. 40-43, October 1999.[2] Y.-C. Chen and J. M. Naughton, “Anundergraduate laboratory platform for controlsystem design, simulation, and implementation,”IEEE Control Systems Magazine, pp. 12-20,June 2000.[3] G. F. Franklin, J. D. Powell, and A.Mami-Naeini, Feedback control of Dynamicsystems, 4 th edition, , chapter 2, Prentice-Hall,Inc., 2002.