NHE 2487 Control Systems

1. Assignment Aims

Each student will design a stable liquid level control system.

Outcomes Assessed

1. Applying the scientific and mathematical principles, tools and notations to analyse and solve the given control engineering problems.

2. Determine the performance of the given system through the use of modelling techniques and MATLAB.

3. Demonstrate an awareness of developing technologies related to control systems.

4. Demonstrate creativity in the design of the given control system especially when designing phase lead and lag compensators.

2. Learning Outcomes:

Knowledge and Understanding:

1. Apply the underpinning scientific and mathematical principles, tools and notations proficiently in the analysis and solution of control engineering problems.

2. Analytically determine the performance of control systems through the use of modelling techniques and computer software.

Abilities:

3. Demonstrate an awareness of developing technologies related to control, and characterise modern control systems instrumentation.

4. Explain the limitations of mathematical and computer models relevant to control engineering.

5. Demonstrate creativity in the specification and design of a practical control system.

3. Assessment Brief

In a liquid level control system, an electric pump is used to pump liquid from a reservoir into a tank. The liquid flows out of the tank through an orifice at its bottom. The orifice is fitted with a manually operated flow valve having five (5) operating settings designated as “1”-“5” and represents an orifice area of 0%, 25%, 50%, 75% and 100% respectively. In addition, a level sensor is used to measure the height of liquid in the tank. It is desired to maintain the height of the liquid in the tank by controlling the flow rate of liquid into the tank, using an appropriate controller. Each student is expected to summarize his/her observations, including diagrams and attach relevant MATLAB scripts and plots where appropriate.

1. Draw the block diagram and derive the transfer function of the closed loop liquid level control system using a negative feedback [10%].

2. Design an appropriate controller to ensure the steady state error in the liquid level in the tank when it undergoes a step change is always less
than ±0.5%. The settling time and overshoot of the system response should also be less than 1.5 seconds and 5% respectively. You may assume the manually operated valve setting is at “position 2” and represents an orifice area of 25% [20%].

3. Using MATLAB, determine the time constant, settling time (2% criterion), rise time (10-90%) and steady state value of the level control system [15%].

4. Examine the stability of the closed loop level control system using the Bode stability criteria. Explain whether the system is stable or unstable in your answers [10%].

5. To ensure the level control system is safely operated, the phase margin of the closed loop system must be at least 120?. Design an appropriate compensator circuit to ensure the process is safely operated. Sketch an electronic circuit that could be used to implement your compensator design. Examine the effect of adding a compensator circuit on the response of the closed loop level control system? [35%].

6. General presentation of your solutions [10%]