Control Engineering
Control Engineering
Control Engineering is taught in the fourth and fifth year of the electrical engineering curriculum. In fourth year, the students mainly cover modelling, time domain and frequency domain analysis and stability analysis of linear control systems. In the fifth year of study, concepts like state space representation, digital control, proportional-integral-derivative (PID) controllers, nonlinear control systems and optimal control are covered.
Currently, the laboratory exercises are mainly Matlab based. We seek to enhance the teaching of these units by developing a laboratory exercise based on the Raspberry Pi to be undertaken by the fifth year students. The lab will cover the areas of Open loop and closed loop control, optimal control and digital control using a real life example, water tank level monitoring and filling.
The labs have been developed as follows
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Open and Closed Loop Control
In open loop control, the output has no effect on the control action i.e. the control action is totally independent of the output of the system. The output is neither measured nor fed back for comparison with the input. To each reference input, there corresponds a fixed operating condition and as a result the accuracy of the system depends on the calibration. Open loop control can be used, in practice, if the relationship between the input and output is known and if there are Ineither internal nor external disturbances. Open loop contro systems are simple in design and construction and easy to maintain. They are, however, inaccurate and unreliable
In closed loop control, the control action is somehow dependent on the output of the system. There is a comparison of the state of the output and the reference state. This property is known as feedback and is the main difference between open loop and closed loop systems. Feedback is the property of the system which permits the output to be compared with the reference input so that appropriate control action is formed. Closed loop control systems are more accurate and reliable but may be complex in design and suffer from instability.
In this lab, we demonstrate the two types of control in filliwng a water tank. In the first instance, no sensor is used to measure the level of water in the tank and the control action is therefore open loop. In the second instance, we use a level sensor (E-tape level sensor) to measure the current water level and generate a control signal based on the level. In both cases, we use Pulse Width Modulation in opening and closing a valve
Optimal Control
The objective of optimal control theory is to determine the control signal that will optimize (maximize or minimize) some performance criterion while at the same time satisfying the physical constraints of the system.
In this lab, the students will explore the optimal parameters for a PID controller designed to ensure the water level in a tank is maintained within an optimal range. The PID controller will be implemented in software and this will introduce the students to digital control concepts.
