Control Engineering is a branch of engineering that artificially modifies a system to ensure a desired behavior. A system can be mechanical, fluid, chemical, financial or even biological. Control engineering is a very broad discipline and is used in all fields of engineering.
Control systems can be found all around us, from your water kettle to the latest fighter aircraft, they are all artificially augmented.
Control Engineering – Augmenting our lives
Consider your home heating system. We all want a nice, stable temperature in our house during winter (say 24 degrees Celsius). By putting a heater (input) in our home (system/process) we can increase the temperature (output) of the house (see Fig.1). However, the main problem with this system is that the heater stays on even after exceeding the desired temperature of 24 degrees Celsius. This type of system is known as an open-loop system: the output has no influence on the system.
So, what can we do? We add feedback to the system…
By placing a thermostat (sensor) in the room, it is possible to monitor the room’s temperature. This information is then fed back to a computer which is programmed to control the heater. The heater is turned off when the desired temperature is reached. A system like this with a feedback loop is known as a closed-loop system (see Fig.2).
There are two types of closed loop system – negative feedback and positive feedback.
Negative feedback loops have the propensity of stabilising systems into a state of equilibrium, which is desirable in the loop diagram shown above, in order to maintain a constant temperature.
Positive feedback loops perform the opposite function and move a system out of equilibrium and into an increasingly unstable state.
From Fig.3, the advantage of a closed-loop system over an open-loop system is clear. At first this process may look simple, but the real challenge in control systems design is for the engineer to design the best controller using the best control design methodology.
So is that it? No, there’s more…
The above example is just one illustration of what a control system is. In fact, control engineering can be categorized into different fields depending on the methodology used to design the control system:
- Classical Control Engineering
- Modern Control Engineering
- Optimal Control Engineering
- Adaptive Control Engineering
- Nonlinear Control Engineering
These disciplines are so complex that they are usually taught in 2nd or 3rd year engineering as separate modules. However, for any person interested in control engineering, they should start with Classical Control.
What is Classical Control?
Classical control deals with single-input, single-output systems. The goal is to try to control only one variable (temperature in the above example) whereas Modern Control deals with multiple-input and multiple-output systems. The climate control system in your car is an example of modern control system design. The system uses a mixture of the humidifier, heater, and air-conditioner to maintain the temperature and humidity of the air at the most comfortable level for all passengers.
A note about the maths in Classical Control…
Systems are usually represented using Ordinary Differential Equations (ODE). These essentially show the relationship of a variable with respect to time. ODEs are intuitive. However, these need to be transformed from the time domain to the frequency domain using appropriate transforms: Laplace, Fourier, Z, etc. Frequency domain is more suited to design control systems.
So, to Conclude…
Control Engineering is the art of artificially augmenting systems to shape an output response. Systems can be simple or extremely complex, and depending on the system and its complexity, there are various control engineering domains that can be applied.
