Introduction to Control Systems PDF

BATAAN PENINSULA STATE UNIVERSITY Module No. 1 INTRODUCTION TO CONTROL SYSTEMS CONTROL ENGINEERING ENGR. AIRA M. RAMOS, ECT ENGR. JAMES AARON O. RUBIANO, ECT College of Engineering and Architecture Introduction to Control Systems Page 1 of 10 Engr. Aira...

BATAAN PENINSULA STATE UNIVERSITY Module No. 1 INTRODUCTION TO CONTROL SYSTEMS CONTROL ENGINEERING ENGR. AIRA M. RAMOS, ECT ENGR. JAMES AARON O. RUBIANO, ECT College of Engineering and Architecture Introduction to Control Systems Page 1 of 10 Engr. Aira M. Ramos, ECT Engr. James Aaron O. Rubiano, ECT  BATAAN PENINSULA STATE UNIVERSITY Module 1: Introduction to Control Systems Module 1 deals with the understanding of how a control system works and its basic terminologies. Objectives of the Module: Upon the completion of this course, the student must be able to: 1. Know what is control system. 2. Differentiate closed loop and open loop control system. 3. Identify and know the functions of each component in a control system. 1.1 CONTROL SYSTEMS BASIC TERMINOLOGIES: System- A combination or arrangement of a number of different physical components to form a whole unit such that that combining unit performs to achieve a certain goal. Control- is a term that describes the process of forcing a system to behave in a desired way in order to achieve certain objective(s)/goal(s). The action to command, direct or regulate a system. Input- It is the signal or excitation supplied to a control system. Output- It is the actual response obtained from the control system. Disturbances- The signal that has adverse effect on the performance of a control system. Automation- The control of a process by automatic means. Introduction to Control Systems Page 2 of 10 Engr. Aira M. Ramos, ECT Engr. James Aaron O. Rubiano, ECT  BATAAN PENINSULA STATE UNIVERSITY Design- The process of conceiving or inventing the forms, parts, and details of system to achieve a specified purpose. Simulation- A model of a system that is used to investigate the behavior of a system by utilizing actual input signals. Optimization- The adjustment of the parameters to achieve the most favorable or advantageous design. Feedback Signal- A measure of the output of the system used for feedback to control the system. Negative feedback- The output signal is feedback so that it subtracts from the input signal. Block diagrams- Unidirectional, operational blocks that represent the transfer functions of the elements of the system. Signal Flow Graph (SFG)- A diagram that consists of nodes connected by several directed branches and that is a graphical representation of a set of linear relations. Specifications- Statements that explicitly state what the device or product is to be and to do. It is also defined as a set of prescribed performance criteria. Regulator: The control system where the desired values of the controlled outputs are more or less fixed and the main problem is to reject disturbance effects. Servo system: The control system where the outputs are mechanical quantities like acceleration, velocity or position. Stability: It is a notion that describes whether the system will be able to follow the input command. In a non-rigorous sense, a system is said to be unstable if its output is out of control or increases without bound. Introduction to Control Systems Page 3 of 10 Engr. Aira M. Ramos, ECT Engr. James Aaron O. Rubiano, ECT  BATAAN PENINSULA STATE UNIVERSITY Multivariable Control System: A system with more than one input variable or more than one output variable. Trade-off: The result of making a judgment about how much compromise must be made between conflicting criteria. Examples of Control: - Temperature Control - Pressure Control - Attitude Control of spacecrafts - Cruise Control - Human body implements sophisticated control strategies for various purposes such as body temperature regulation, hormone level control, etc. Control System - A system which consists of number of components connected together to perform a specific function in which the output us controlled by input. - is an interconnection of components forming a system configuration that will provide system response. These components are: - is a system that can command, direct or regulate itself or another system to achieve a certain goal. Plant- has one or more inputs and one or more outputs. It is a combination of process and actuator. The part or component of a system that is required to be controlled. Actuator- the device that causes the plant to provide output. Or simply, it provides the motive power to the plant. It is the device that causes the process to provide the output. It is the device that provides the motive power to the process. Introduction to Control Systems Page 4 of 10 Engr. Aira M. Ramos, ECT Engr. James Aaron O. Rubiano, ECT  BATAAN PENINSULA STATE UNIVERSITY Sensor- the device that provides information about the output of the plant (not every control system is present). Controller- is the brain of the system. It may be a computer program, electrical or mechanical device, etc. The part or component of a system that controls the plant. Reference- is the desired outcome of the control system. Example 1: Manual control system for regulating the level of the fluid in a tank. Figure 1.1 The reference is the desired level of fluid that operator is instructed to maintain. The actuator is the valve that opens or closes the fluid flow out. The sensor is the visual of the operator. The controller is the operator. Introduction to Control Systems Page 5 of 10 Engr. Aira M. Ramos, ECT Engr. James Aaron O. Rubiano, ECT  BATAAN PENINSULA STATE UNIVERSITY Example 2: Magnetic Levitation. Figure 1.2 The reference is the position of the iron ball. The actuator is the electromagnet. The sensor is the gap sensor. The controller is the program in the computer. Types of Control System 1. Open Loop System- is a system that does not monitor its output. Open loop system cannot correct errors. A system that utilizes a device to control the process without using feedback. Thus the output has no effect upon the signal to the process. Figure 1.3 Block Diagram for an Open Loop System Introduction to Control Systems Page 6 of 10 Engr. Aira M. Ramos, ECT Engr. James Aaron O. Rubiano, ECT  BATAAN PENINSULA STATE UNIVERSITY ADVANTAGES OF OPEN LOOP SYSTEM: It is simple and economical. It is easier to construct. It is stable. DISADVANTAGES OF OPEN LOOP SYSTEM: It is inaccurate. The changes in the output are not corrected automatically. Example: Controlling the position of a missile launcher from a remote location. The input is the desired angular position of the missile launcher, and the control system consists of potentiometer, power amplifier, motor, gearing between the motor and missile launcher, and the missile launcher. Figure 1.3 2. Closed Loop System- is a system that monitors its output and makes corrections to reduce error. By monitoring, the output of the system can correct for disturbances. A system that uses a measurement of the output and compares it with the desired output. Introduction to Control Systems Page 7 of 10 Engr. Aira M. Ramos, ECT Engr. James Aaron O. Rubiano, ECT  BATAAN PENINSULA STATE UNIVERSITY Figure 1.4 Block Diagram of Closed Loop System ADVANTAGES OF CLOSED LOOP SYSTEM: It is accurate. It is less affected by noise. DISADVANTAGES OF CLOSED LOOP SYSTEM: The expenses will be much higher compared to open loop system. The system is more complicated. Feedback reduces the overall gain of the system. The main problem of closed loop system is its unstable output. Example: Controlling the position of a missile launcher from a remote location. Figure 1.5 Introduction to Control Systems Page 8 of 10 Engr. Aira M. Ramos, ECT Engr. James Aaron O. Rubiano, ECT  BATAAN PENINSULA STATE UNIVERSITY The previous example is modified by introducing a position feedback loop. Should an error exist, it is amplified and applied to a motor drive which adjusts the output-shaft position until it agrees with input-shaft position, and the error is zero. Example: Automobile steering control system. Figure 1.6 In this feedback control system: The reference is the desired path. The actuator is the steering mechanism. The sensor is the visual. The controller is the driver. The plant is the car. Introduction to Control Systems Page 9 of 10 Engr. Aira M. Ramos, ECT Engr. James Aaron O. Rubiano, ECT  BATAAN PENINSULA STATE UNIVERSITY COMPARISON BETWEEN OPEN-LOOP AND CLOSED-LOOP CONTROL SYSTEMS: It is a control system where its control action depends on both of its input signal and output response. NO. Open Loop Control System Closed Loop Control System 1 No feedback is given to the control system A feedback is given to the control system 2 Cannot be intelligent Intelligent controlling action 3 There is no possibility of undesirable Closed loop control introduces the system oscillation. possibility of undesirable system oscillation 4 The output will not vary for a constant In the system the output may vary for a input, provided the system parameters constant input, depending upon the remain unaltered. feedback 5 System output variation due to variation in System output variation due to variation in parameters of the system is greater and the parameters of the system is less. output very in an uncontrolled way. 6 Error detection is not present Error detection is present 7 Small bandwidth Large bandwidth 8 More stable Less stable or prone to instability 9 Affected by non-linearities Not affected by non-linearities 10 Very sensitive in nature Less sensitive to disturbances 11 Simple design Complex design 12 Cheap Costly Introduction to Control Systems Page 10 of 10 Engr. Aira M. Ramos, ECT Engr. James Aaron O. Rubiano, ECT