1. System/Plant/Process (Transfer function) Output Input The relationship between the input and output are mentioned in terms of transfer function, which is defined as the ratio between the Laplace transform of the output and the Laplace transform of the input. If the output is proportional to the input, the plant is called a linear system.

2. Controller Output PLANT/PROCESS Input Open-loop Controller Plant Output (Setpoint or reference value) An example of a block diagram of an open-loop control system. The term ‘open-loop’ comes from the fact that the output only depends on the inputs. This is a complete system by itself. The control system takes the input from the controller in order to produce output by the action of the plant.

3. The overall transfer function of the system is the product of individual transfer functions. In general, in open-loop configuration, mathematically, the overall transfer function of the composite system is given by the following formula.

4. Field-controlled DC motor Load Output speedDriving torqueDesired speed (set-point)Error Sensor (Tachometer) A closed-loop control system, on the other hand, uses input as well as some portion of the output to regulate the output. The closed-loop systems are also called feedback control systems. In feedback control the variable required to be controlled is measured. This measurement is compared with a given setpoint. If the error results, the controller takes this error and decides what action should be taken to compensate and hence to remove the error.

5. + - + - PLANT Load or disturbance Error Amplifier Control Systems + Controlled system Setpoint The closed-loop control schematic must have a plant which is to be controlled. The plant is referred to as the controlled system. The block that controls the plant (i.e., the controlled system) is called the controller. The controller is not a physical controller that you studied in the Chapter-8. It is a manipulation method that controls and regulates the output through feedback or closed-loop action. The algorithm of the manipulation can be implemented in a physical controller in order to achieve the objective, i.e., to regulate the output.

6. PLANT Feedback loop U(s) Y(s) U(s) Y(s) (a) (b) The equivalent transfer function of the feedback control system, shown in the figure- (b), is called closed-loop transfer function, which can be written as,

7. + - + - ON-OFF Controller PLANT From closed-loop control point of view there are commonly seven types of control actions which are considered as the most fundamental because the plant can adequately be controlled to attend the reachability point by designing appropriate controllers. On-off controller Proportional controller Integral controller Derivative controller PD controller PI controller PID controller On-off controller

8. ON-OFF Controller Dead-band On-off controller with hysteresis or dead-band The turn-ON and turn-OFF in case of ON/OFF controller in many situation are deliberately made to differ by a small amount, known as the hysteresis or dead-band, to prevent noise from switching the controller unnecessarily when the output is nearly the setpoint. The sensitivity of the On-Off controller depends on the hysteresis.

9. Proportional controller (K p ) Plant Output speedController Output Desired speed (set-point)Error Measured manipulated variable U(s) Y(s) E(s) Proportional Control means that the plant input is changed in direct proportion to the error, e(t). This controls the output so that the manipulated variable and the error has a proportional relation. The advantage of proportional controller is that it is relatively easy to implement. However, the disadvantage is that there always involves an offset in the output response causing difference between the set-point and the actual output.

10. Integral Controller Controller Output Desired speed (set-point) Error Feedback loop When the controller controls the output by integrating the error signal, then it is called an integral control action. The offset in the output, and hence the steady-state performance of the system can be improved by employing integral control action. But the integral action may lead to oscillatory output resulting poor stability.

11. Controller output Desired speed (set-point) Error Feedback signal + + + The transfer function of the PID controller is

12. Output INPUTS Intelligent control incorporates biological information processing method and Fuzzy theory. Biological information processing method includes Neural Network, Genetic Algorithm and Immune Network. At the core of the neural computation, there exist the concepts of distributed, adaptive, and nonlinear computing.

13. Input layerHidden layer Output layer All ANNs have a similar structure as far as topology is concerned. Some of the neurons interface the real world to receive its inputs, and other neurons provide the real world with the network’s outputs. Besides input layer and output layer there may be many middle layers, with a variable number of nodes, depending upon the task at hand.

14. R r R r 0 1 1 0.75 0.5 0.25 0 Degree Of Membership Uncertainties are of two types; stochastic uncertainty and fuzziness. Stochastic uncertainty has only two levels such as true or false. Where the event is not well defined, the outcome may be given by a quantity other than true or false, but rather fuzzy. There comes fuzzy logic. The outcome in presence of fuzziness is quantified by a degree of belief. FL system is called soft linguistic system.

15. System study Define the control functions Classical plant modeling Controller selection and Control algorithm System study Define the control functions Implement using FL Simulation, Testing, Refinement (a) (b) FL based strategy simplifies the design loop. This results in some significant benefits, such as reduced development time and simpler design.

16. A schematic diagram of a process is shown. The mathematical description is expressed as, Y = Output U = input N = Noise X = Process state variables P = Process parameters

17. Two main subtasks are involved within FDI techniques. Failure detection that indicates that something abnormal has happened in the system. Failure isolation is the ability to distinguish between specific faults and isolating the component that has failed.

18. Implementation of FDI is achieved mainly through statistical and model-based approach. Method that relies on a quantitative mathematical relation between the I/O is called model-based technique. Model-based fault detection depends only on the availability of a mathematical model of the plant.

19. 1011 Slot-1Slot-2Slot-3Slot-4 (Three pulses are generated in order to represent one pulse (Error correcting code) (a) (b) (c) Original digital Signal Noise introduced during transmission Distortion eliminator Output input Quantised level The digital control technology to some extend is immune to noise. The effect of noise can be efficiently reduced using error correcting codes or distortion eliminator.

20. Power converter PlantLoad Digital control Mechanical variables Position Speed Acceleration Torque Force, etc. Sensor Electrical variables Voltage Current Resistance Flux, etc. Sensor From implementation schematic an advanced digital control system in its basic nature can be seen as shown in the figure. Digital control technology makes it easy to implement state feedback and adaptive control.

21. Diagnostics and Prognostics Monitoring and Protection Status Display Storage Power circuit Interface System logic RTOS And Control Communication Data Acquisition and Processing Power converter drive signals Sensor signals Auxiliary functions A full-fledged advanced control system has to incorporate auxiliary functions such as display, storage, monitoring, protection, diagnostics and prognostics as illustrated above. The blocks drawn inside the dotted box shows the schematic diagram of a typical control implementation scenario.