EE357 Control System I - Lec B2 (2010W) - Introduction

1. EE357 Control System I - Lec B2 (2010W)- Introduction

2. Outline • What is a control system? • Open-loop control vs. Closed-loop (feedback) control • Development of control theory • A brief overview of EE357

3. What is a control system? • A general definition: “A control system is a device or set of devices to manage, command, direct or regulate the behavior of other devices or systems.” • A control (feedback) loop, including sensors, control algorithms and actuators, is arranged in such a fashion as to try to regulate a variable at a set point or reference value.

4. What is a control system? A typical (feedback) control system contains • Plant/process - object to be controlled • Controllers - devices that compute and generate control signals/actions • Actuators - devices that perform control actions • Sensors - devices that measure the output Control objectives - tasks, targets of control

5. Open-loop Control • The controller does not use measurement of system output being controlled when computing the control action, i.e. no feedback control action command input output controller process sensor Fig. 1. A block diagram representation of an open loop control

6. Closed-loop Control • Also called feedback control, the controlled system output is measured and being used for computing the control action. command input control action error output controller actuator process - sensor Fig. 2. A block diagram representation of a closed-loop control

7. Example 1. Room Temperature Control • Open-loop scheme: • no measurement for feedback • fixed control action • can’t adjust to unexpected changes from the system environment inlet vent heat furnace room temperature Switch (on/off)

8. Example 1. Room Temperature Control • Closed-loop scheme • thermostat: sensing plus control device • automatically adjust room temperature • can easily change room temp. as desired heat variation inlet heat room temp. desired temp. thermostat furnace room

9. Example 1. Room Temperature Control Fig. 3. Response of closed-loop room temp. control (ref. EE4629 notes, A. Lynch, 2006)

10. Example 2: Car Cruise Control Road grade • Control mechanism: compute the difference between the set speed and the actual speed; then open throttle according to the quantity of error speed desired speed Control unit Engine Car body speedometer Fig. 4. Bock diagram of closed-loop car speed control

11. Example 3: Human Balance System perturbation position (com) ankle, hip, foot brain body Sensors: eye, inner ear balance sys. & legs (pressure) Fig. 5. Block diagram of human balance control

12. Example 3: Human Balance System • Analogy of human balance control: • ankle, hip strategy: similar to inverted pendulum • step strategy: similar to inverted pendulum on a cart

13. Application and Theory • Control systems and feedback control concepts are everywhere: daily life, manufacture plant, aerospace industry, automotive industry, chemical, biomedical processes … … • The subject of control is multidisciplinary: engineering, mathematics, computer science, etc.

14. History: Primitive Phase • Float valve feedback regulator for water clock • time is determined by the outlet flow rate, which is determined by liquid level • liquid level is regulated by the float valve • sensing and actuation functions are integrated in the float valve mechanism (Ref. Dorf, 10th.)

15. History: Primitive Phase • Flyball Governor (Watt 1788) • Mile stone for industry revolution • Flyball feedback mechanism for the regulation of steam engine speed • Sensing and actuation are integrated in one mechanism (Ref. Dorf, 10th.)

16. History: Classical Phase • Analysis based on mathematical modeling • Analysis of Flyball governor based on nonlinear differential equations (Maxwell 1868) • Stability notions, stabilization • nonlinear stability (Lyapunov, 1890) • gyroscope/autopilot (Sperry, 1910) • PID control (Minorsky, 1922)

17. History: Classical Phase • Frequency domain methods for analysis and design • Nyquist plot, Bode diagram, feedback amplifier (Black, Bode, Nyquist at Bell lab) (1930’s - 50’s) • Key classical control methods • Routh-Hurwitz stability criterion, root locus, frequency response methods, Nyquist criterion • Graphical and hand computation • Suitable for SISO and low order systems

18. History: Modern Phase (1960 -) • Computer controlled system • State space modeling (based design) • Optimal control, Kalman filter • Communication systems, network based, distributed control systems (DCS)… Modern control uses state space modeling and can deal with MIMO and high order systems

19. Related Issues in Control System • Modeling: obtain mathematical models • Analysis: stability, time-domain specifications • Design: specify the structure and parameters of a controller to achieve the desired performance specifications • Implementation: analog filters, digital controllers, micro-controllers, PLC, DCS, etc.

20. EE 357 • Classical control methods and theories are covered in EE357, the first control course for EE students • Modeling: o.d.e, transfer function • Analysis: stability criteria, time-domain and frequency-domain system specification • Design: classical design tools based on several important system charts and plots Modern control is covered in EE460 and EE461.