Introduction to Control System PDF

Introduction to Control System Ms. Chloe Laserna, ECT What is a system? What is a system? A system is an arrangement, set, or collection of things connected or related in such a manner as to form an entirety or whole. A system is an arrangement of physical components connected or related i...

Introduction to Control System Ms. Chloe Laserna, ECT What is a system? What is a system? A system is an arrangement, set, or collection of things connected or related in such a manner as to form an entirety or whole. A system is an arrangement of physical components connected or related in such a manner as to form and/or act as an entire unit. What is the definition of Control? The word control is usually taken to mean regulate, direct, or command. What is Control System? A control system is an arrangement of physical components connected or related in such a manner as to command, direct, or regulate itself or another system. Control System Control System  Control System Input Process Output  Control System Input Process Output The input is the stimulus, excitation or command applied to a control system, typically from an external energy source, usually in order to produce a specified response from the control system.  Control System Input Process Output This is the main part of the system where the input is used to produce a desired outcome or effect. It's essentially what you are trying to control.  Control System Input Process Output The output is the actual response obtained from a control system. It may or may not be equal to the specified response implied by the input.  Control System A control system may have several defined inputs and outputs. Sometimes, unwanted interference or noise can affect the system. These are usually considered separately in basic descriptions but need to be considered when examining the system closely. Why do we need Control System? Why do we need Control System? 1) Power Amplification 2) Telecommand 3) Convenience in input form 4) Automation What is a Control Subsystem? Control Subsystem Sometimes, a control system is just one part of a bigger system. When this happens, it’s called a subsystem or control subsystem. This is like a smaller piece or a specific function within a bigger machine or system. Inputs and Outputs in Control Subsystem Even within this larger system, the control subsystem has its own inputs and outputs, but these might be related to or controlled by the larger system’s internal workings. Guess who? Guess who?  Guess who? An electric switch is a manufactured control system, controlling the flow of electricity.  Guess who? A thermostatically controlled heater or furnace automatically regulating the temperature of a room or enclosure is a control system.  Guess who? A part of the human temperature control system is the perspiration system. Open-Loop and Closed Loop Control Subsystem Two general categories of control system. Open loop Closed loop  Control Action In control systems, this term refers to what the system does to achieve its goal. Even though the word "action" sounds like it means movement or change, it doesn't always involve something physical happening right away. Control Action Example: Think of a system where a missile is trying to hit a target. In this case, the control action is related to measuring the distance between the missile and the target. What is the Control Action in the given situation? What is the Control Action in the given situation? Is it measuring the distance or re-positioning the missle? Control Action Example: Think of a system where a missile is trying to hit a target. In this case, the control action is related to measuring the distance between the missile and the target. Distance is Not Action: Distance itself isn’t an action. It’s a measurement. But the system’s goal is to make this distance zero, which means moving the missile to hit the target. Control Action Example: Think of a system where a missile is trying to hit a target. In this case, the control action is related to measuring the distance between the missile and the target. Re-positioning the missle is the control action: The action here is implied because the system needs to adjust or move the missile to reduce the distance to zero. Even though measuring distance isn’t an action, it helps the system figure out what needs to be done (like moving the missile).  Control Action In control systems, "control action" might not always mean something is physically moving. Sometimes, it just involves measuring or assessing something (like distance) to guide the system towards its goal Open-loop An open-loop control system is one in which the control action is independent of the output.  Desired output Controller Actuator Process Output response Feedforward Path An open-loop control system is one in which the control action is independent of the output. Example: Toaster Washing Machine Traffic Light Printer Old Escalators Two outstanding features of open- loop control systems are: 1. Their ability to perform accurately is determined by their calibration. To calibrate means to establish or reestablish the input-output relation to obtain a desired system accuracy. 2. They are not usually troubled with problems of instability, a concept to be subsequently discussed in detail. Closed-loop A closed-loop control system is one in which the control action is somehow dependent on the output. Closed-loop Commonly called feedback control systems.  Feedforward Path Desired Error output Controller Actuator Process Actual response - Output Feedback Loop Sensor  Feedforward Path Desired Error output Controller Actuator Process Actual response - Output Feedback Loop Sensor *Positive Feedback (Regenerative) * Negative Feedback (Degenerative) A closed-loop control system is one in which the control action is somehow dependent on the output. Example: Aircon (Inverter) Flat Iron Microwave Oven Refrigerator Self Driving car Simple (+) More reliable (+) Easy to design (+) More resistant to disturbances (+) Cheap (+) Complex (-) Low maintenance (+) Requires Tuning (-) No feedback (-) Inaccurate (-)  Feedback Feedback is that characteristic of closed-loop control systems which distinguishes them from open-loop systems  Feedback - Feedback in a closed-loop system allows comparing the output with the input. - It enables the formation of appropriate control actions based on the output and input relationship. Characteristics of Feedback Characteristics of Feedback The presence of feedback typically imparts the following properties to a system. 1) Increased accuracy. For example, the ability to faithfully reproduce the input. 2) Tendency toward oscillation or instability. 3) Reduced sensitivity of the ratio of output to input to variations in system parameters and other characteristics. Characteristics of Feedback 4) Reduced effects of nonlinearities. 5) Reduced effects of external disturbances or noise. 6) Increased bandwidth. The bandwidth of a system is a frequency response measure of how well the system responds to (or filters) variations (or frequencies) in the input signal. Analog and Digital Control System  Analog and Digital Control Systems The signals in a control system, for example, the input and the output waveforms, are typically functions of some independent variable, usually time, denoted as “t”. A signal dependent on a continuum of values of the independent variable t is called a continuous-time signal or, more generally, a continuous-data signal or (less frequently) an analog signal. A signal defined at, or of interest at, only discrete (distinct) instants of the independent variable t (upon which it depends) is called a discrete-time, a discrete-data, a sampled- data, or a digital signal. Continuous-time control systems and Discrete- time control systems It is also called continuous-data control systems, or analog control systems, contain or process only continuous-time (analog) signals and components. It is also called discrete-data control systems, or sampled-data control systems, have discrete-time signals or components at one or more points in the system. GROUP ACTIVITY (Pass the Control System) Continuous-time control systems and Discrete-time control systems We note that discrete-time control systems can have continuous-time as well as discrete-time signals; that is, they can be hybrid. The distinguishing factor is that a discrete-time or digital control system must include at least one discrete-data signal. Also, digital control systems, particularly of sampled-data type, often have both open-loop and closed-loop modes of operation. The Control Systems Engineering Problem What is Analysis? Analysis is the investigation of the properties of an existing system.  What is Design Problem? The design problem is the choice and arrangement of system components to perform a specific task. Two Methods exist for design: 1) Design by analysis 2) Design by synthesis Two Methods exist for design: Design by analysis is accomplished by modifying the characteristics of an existing or standard system configuration, and design by synthesis by defining the form of the system directly from its specifications. Control System Models or Representation Three basic representations (models) of components and systems are used extensively in the study configuration and its components into a form amenable to analysis or design. of control systems: 1. Mathematical models, in the form of differential equations, difference equations, and/or other mathematical relations, for example, Laplace- and z-transforms 2. Block diagrams 3. Signal flow graphs