Advising Page -- Control Systems

What is control?

Control systems make other systems do what we want them to do, without us having to do all the work. Examples of control systems in everyday life include the thermostat that regulates the temperature of a room and the cruise control that regulates the speed of a car. Typically, the core of a control system is an algorithm that computes the signal that must be applied at the input of a system so that its output follows certain reference values. Practical implementation involves a computer, a sensor (or sensors) that measures the output of the system, and an actuator (or actuators) that applies the required actions to the system. The actions may be physical forces, electrical signals, chemical products, or any other variables that affect the state of the system. A good introduction to control is available from the web site of the Control Systems Society. To become an expert in control, you should be comfortable with mathematics and computing. You should also be curious enough to study closely a variety of engineering applications.

Two modern applications of control theory are flight control and active noise control. In the X-29 aircraft shown below, the dynamic behavior is so unstable that a human pilot is unable to maintain steady flight without the feedback actions implemented by a flight control computer. In the worst flight condition of the X-29, an angular deviation from horizontal flight doubles every 0.12 seconds (the stabilization task is equivalent to the one required to balance a 17.4 inch stick on a finger). Computations are performed 40 times per second to provide adequate stabilization and control of the aircraft.

X-29 aircraft

The figure below shows an active noise control system for a turboprop aircraft. Here, the purpose of the control system is to reduce the noise in the cabin of the aircraft. The result is achieved by measuring the sound with microphones (shown in green) and generating cancelling sound waves using speakers (shown in red). The SAAB 2000 aircraft has 72 microphones and 36 speakers, so that the computer must deal with a large number of sensors and actuators. The control problem is quite different from the flight control application. There is no issue of stabilization of the system or of tracking of commands. The problem is purely one of disturbance rejection. In both cases, the control engineer designs the algorithm that is coded in the control computer so that the desired results are achieved.

Active noise control system

Control courses at the University of Utah

For undergraduate students, only ECE 3510 is required (with its prerequisites). Given the small number of control courses, we recommend that undergraduate students take as many of the courses as possible, as the schedule permits. Graduate students should also take all the graduate courses, as well as some of the undergraduate courses, depending on what is being offered. Courses in signal processing and communications are particularly relevant to control systems and should be considered in planning programs of study. Other related topics include analysis (mathematics), embedded systems (computer science), and human factors (psychology or mechanical engineering).

Useful web sites

www.ieeecss.org

Control Systems Society of IEEE (receive the e-mail newsletter for free by checking under "Publications")

www-control.eng.cam.ac.uk/extras/Virtual_Library/Control_VL.html

Control Engineering Virtual Library (links to societies, journals, research groups, ...)

www.jhu.edu/~signals

Demonstrations of systems & control concepts (from Johns Hopkins University)

www.engin.umich.edu/group/ctm

Control tutorials for Matlab (from Carnegie Mellon University and University of Michigan)

www.mathworks.com/products/control

Control Systems Toolbox, part of the Matlab products from Mathworks