Introduction of control engineering
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This document provides an introduction to control engineering. It discusses several key points: 1) Control engineering deals with designing systems to control dynamic processes and improve response speed, accuracy, and stability. This includes analyzing both classical and modern control methods. 2) Modern control engineering uses state-space and eigenvector approaches to model multi-input multi-output systems as sets of first-order differential equations. 3) Automatic control systems are commonly used, where a controlled variable is measured and compared to a setpoint to generate an output that achieves the desired result. This reduces costs and improves quality and productivity over manual control.
Introduction of control engineering
- 1. INTRODUCTION OF CONTROL ENGINEERING BY ASHVANI SHUKLA MANAGER(C&I) BGR ENERGY
- 2. BASIC INTRODUCTION • Control system engineering is the branch of engineering which deals with the principles of control theory to design a system which gives desired behavior in a controlled manner. Hence, this is interdisciplinary. Control system engineers analyze, design, and optimize complex systems which consist of highly integrated coordination of mechanical, electrical, chemical, metallurgical, electronic or pneumatic elements. Thus control engineering deals with diverse range of dynamic systems which include human and technological interfacing. • Control system engineering focuses on analysis and design of systems to improve the speed of response, accuracy and stability of system. The two methods of control system include classical methods and modern methods. The mathematical model of system is set up as first step followed by analysis, designing and testing.
- 3. CONTROL SYSTEM BLOCK DIAGRAM OF CONTROL SYSTEM DISTURBENCES INPUT OUTPUT MANIPULATED VARIABLES
- 4. • Modern control engineering deals with Multiple Input Multiple Output (MIMO) systems, State space approach, Eigen values and vectors etc. Instead of transforming complex ordinary differential equations, modern approach converts higher order equations to first order differential equations and solved by vector method. Automatic control systems are most commonly used as it does not involve manual control. The controlled variable is measured and compared with a specified value to obtain the desired result. As a result of automated systems for control purposes, the cost of energy or power as well as the cost of process will be reduced increasing its quality and productivity. •Historical Review of Control Engineering The application of Automatic control system is believed to be in use even from the ancient civilizations. Several types of water clock were designed and implemented to measure the time accurately from the third century BC, by Greeks and Arabs. But the first Automatic system is considered as the Watts Fly ball Governor in 1788, which started the industrial revolution. The mathematical modeling of Governor is analyzed by Maxwell in 1868. In 19th century, Leonhard Euler, Pierre Simon Laplace and Joseph Fourier developed different methods for mathematical modeling. The second system is
- 5. • Types of Control Engineering • Control engineering has its own categorization depending on the different methodologies used, which are as follows. • Classical Control Engineering : The systems are usually represented by using ordinary differential equations. In classical control engineering, these equations are transformed and analyzed in transformed domain. Laplace transform, Fourier transform and z transform are examples. This method is commonly used in Single Input Single Output systems. • Modern Control Engineering : In modern control engineering higher order differential equations are converted to first order differential equations. These equations are solved very similar to vector method. By doing so, many complications dealt in solving higher order differential equations are solved. These are applied in Multiple Input Multiple Output systems where analysis in frequency domain is not possible. Nonlinearities with multiple variables are solved by modern methodology. State space vectors, Eigen values and Eigen Vectors longs to this category. State Variables describe the input, output and system variables.
- 6. • Robust Control Engineering : In robust control methodology, the changes in performance of system with change in parameters are measured for optimization. This aids in widening the stability and performance, also in finding alternate solutions. Hence in robust control the environment, internal in accuracies, noises and disturbances are considered to reduce the fault in system. • Optimal Control Engineering : In optimal control engineering, the problem is formulated as mathematical model of process, physical constraints and performance constraints, to minimize the cost function. Thus optimal control engineering is the most feasible solution for designing a system with minimum cost. • Adaptive Control Engineering : In adaptive control engineering, the controllers employed are adaptive controllers in which parameters are made adaptive by some mechanism. The block diagram given below shows an adaptive control system. • Nonlinear Control Engineering : Non linear control engineering focuses on the non linearity’s which cannot be represented by using linear ordinary differential equations. This system will exhibit multiple isolated equilibrium points, limit cycles, bifurcations with finite escape time. The main limitation is that it requires laborious mathematical analysis. In this analysis the system is divided into linear part and non linear part. • Game Theory : In game theory, each system will have to reduce its cost function
- 7. •On Off Control Theory | Controller • Sometimes, the control element has only two position either it is fully closed or fully open. This control element does not operate at any intermediate position, i.e. partly open or partly closed position. The control system made for controlling such elements, is known as on off control theory. In this control system, when process variable changes and crosses certain preset level, the output valve of the system is suddenly fully opened and gives 100% output. • Generally in on off control system, the output causes change in process variable. Hence due to effect of output, the process variable again starts changing but in reverse direction. During this change, when process variable crosses certain predetermined level, the output valve of the system is immediately closed and output is suddenly reduced to 0%.
- 8. • As there is no output, the process variable again starts changing in its normal direction. When it crosses the preset level, the output valve of the system is again fully open to give 100% output. This cycle of closing and opening of output valve continues till the said on-off control system is in operation. A very common example of on-off control theory is fan controlling scheme of transformer cooling system. When transformer runs with such a load, the temperature of the electrical power transformer rises beyond the preset value at which the cooling fans start rotating with their full capacity. As the cooling fans run, the forced air (output of the cooling system) decreases the temperature of the transformer. When the temperature (process variable) comes down below a preset value, the control switch of fans trip and fans stop supplying forced air to the transformer. After that, as there is no cooling effect of fans, the temperature of the transformer again starts rising due to load. Again when during rising, the temperature crosses the preset value, the fans again start rotating to cool down the transformer. Theoretically, we assume that there is no lag in the control equipment. That means,
- 10. • But in practical on off control, there is always a non zero time delay for closing and opening action of controller elements. This time delay is known as dead time. Because of this time delay the actual response curve differs from the above shown ideal response curve. Let us try to draw actual response curve of an on off control system.
- 11. • Say at time T O the temperature of the transformer starts rising. The measuring instrument of the temperature does not response instantly, as it requires some time delay for heating up and expansion of mercury in temperature sensor bulb say from instant T1 the pointer of the temperature indicator starts rising. This rising is exponential in nature. Let us at point A, the controller system starts actuating for switching on cooling fans and finally after period of T2 the fans starts delivering force air with its full capacity. Then the temperature of the transformer starts decreasing in exponential manner. • At point B, the controller system starts actuating for switching off the cooling fans and finally after a period of T3 the fans stop delivering force air. Then the temperature of the transformer again starts rising in same exponential manner. N.B.: Here during this operation we have assumed that, loading condition of the electrical power transformer, ambient temperature and all other conditions of surrounding are fixed and constant.
- 12. • Control System | Closed Loop Open Loop Control System • When a number of elements are combined together to form a system to produce desired output then the system is referred as control system. As this system controls the output, it is so referred. Each element connected to the system has its own effect on the output. Definition of Control System • A control system is a system of devices or set of devices, that manages, commands, directs or regulates the behavior of other device(s) or system(s) to achieve desire results. In other words the definition of control system can be rewritten as A control system is a system, which controls other system. • As the human civilization is being modernized day by day the demand of automation is increasing accordingly. Automation highly requires control of devices. In recent years, control systems plays main role in the development and advancement of modern technology and civilization. Practically every aspects of our day-to-day life is affected less or more by some control system. A bathroom toilet tank, a refrigerator, an air conditioner, a geezer, an automatic iron, an automobile all are control system. These systems are also used in industrial process for more output. We find control system in quality control of products, weapons system, transportation systems, power system, space technology, robotics and many more. The principles of control theory is applicable to engineering and non engineering field both.
- 13. • The main feature of control system is, there should be a clear mathematical relation between input and output of the system. When the relation between input and output of the system can be represented by a linear proportionality, the system is called linear control system. Again when the relation between input and output cannot be represented by single linear proportionality, rather the input and output are related by some non-linear relation, the system is referred as non-linear control system. Requirement of Good Control System • Accuracy: Accuracy is the measurement tolerance of the instrument and defines the limits of the errors made when the instrument is used in normal operating conditions. Accuracy can be improved by using feedback elements. To increase accuracy of any control system error detector should be present in control system. • Sensitivity: The parameters of control system are always changing with change in surrounding conditions, internal disturbance or any
- 14. • Noise: An undesired input signal is known as noise. A good control system should be able to reduce the noise effect for better performance. Stability: It is an important characteristic of control system. For the bounded input signal, the output must be bounded and if input is zero then output must be zero then such a control system is said to be stable system. Bandwidth: An operating frequency range decides the bandwidth of control system. Bandwidth should be large as possible for frequency response of good control system. Speed: It is the time taken by control system to achieve its stable output. A good control system possesses high speed. The transient period for such system is very small. Oscillation: A small numbers of oscillation or constant oscillation of output tend to system to be stable. •Types of Control Systems. •Open loop control system
- 15. • A control system in which the control action is totally independent of output of the system then it is called open loop control system. Manual control system is also an open loop control system. Fig - 1 shows the block diagram of open loop control system in which process output is totally independent of controller action. Practical Examples of Open Loop Control System • Electric Hand Drier – Hot air (output) comes out as long as you keep your hand under the machine, irrespective of how much your hand is dried. • Automatic Washing Machine – This machine runs according to the pre-set time irrespective of washing is completed or not. •
- 16. • Before I introduce you the theory of control system it is very essential to know the various types of control systems. Now there are various types of systems, we are going to discuss only those types of systems that will help us to understand the theory of control system and detail description of these types of system are given below: Linear Control Systems • In order to understand the linear control system, we should know the principle of superposition. The principle of superposition theorem includes two the important properties and they are explained below: • Examples of Linear Control System • Consider a purely resistive network with a constant dc source. This circuit follows the principle of homogeneity and additivity. All the undesired effects are neglected and assuming ideal behavior of each element in the network, we say that we will get linear voltage and current characteristic. This is the example of linear control system. Non-linear Systems • We can simply define non linear control system as all those system which do not follow the principle of homogeneity. In practical life all
- 17. • Examples of Non-linear System • A well known example of non-linear system is magnetization curve or no load curve of a dc machine. We will discuss briefly no load curve of dc machines here: No load curve gives us the relationship between the air gap flux and the field winding mmf. It is very clear from the curve given below that in the beginning there is a linear relationship between winding mmf and the air gap flux but after this, saturation has come which shows the non linear behavior of the curve or characteristics of the non linear control system.
- 18. • Analog or Continuous System • In these types of control system we have continuous signal as the input to the system. These signals are the continuous function of time. We may have various sources of continuous input signal like sinusoidal type signal input source, square type of signal input source, signal may be in the form of continuous triangle etc. Digital or Discrete System • In these types of control system we have discrete signal (or signal may be in the form of pulse) as the input to the system. These signals have the discrete interval of time. We can convert various sources of continuous input signal like sinusoidal type signal input source, square type of signal input source etc into discrete form using the switch. • Now there are various advantages of discrete or digital system over the analog system and these advantages are written below: • Digital systems can handle non linear control systems more effectively than the analog type of systems. • Power requirement in case of discrete or digital system is less as compared to analog systems. Digital system has higher rate of accuracy and can perform various complex computations easily as compared to analog systems. • Reliability of digital system is more as compared to analog system. They also have small and compact size. • Digital system works on the logical operations which increases their accuracy many times. • Losses in case of discrete systems are less as compared to analog systems in general.
- 19. • Single Input Single Output Systems • These are also known as SISO type of system. In this the system has single input for single output. Various example of this kind of system may include temperature control, position control system etc. Multiple Input Multiple Output Systems • These are also known as MIMO type of system. In this the system has multiple outputs for multiple inputs. Various example of this kind of system may include PLC type system etc. Lumped Parameter System • In these types of control systems the various active (resistor) and passive parameters (like inductor and capacitor) are assumed to be concentrated at a point and that’s why these are called lumped parameter type of system. Analysis of such type of system is very easy which includes differential equations. Distributed Parameter System • In these types of control systems the various active (resistor) and passive parameters (like inductor and capacitor) are assumed to be distributed uniformly along the length and that’s why these are called distributed parameter type of system. Analysis of such type of system is slightly difficult which includes partial differential equations.
- 20. •Block Diagrams of Control System • The block diagram is to represent a control system in diagram form. In other words practical representation of a control system is its block diagram. It is not always convenient to derive the entire transfer function of a complex control system in a single function. It is easier and better to derive transfer function of control element connected to the system, separately. The transfer function of each element is then represented by a block and they are then connected together with the path of signal flow. For simplifying a complex control system, block diagrams are used. Each element of the control system is represented with a block and the block is the symbolic representation of transfer function of that element. A complete control system can be represented with a required number of interconnected such blocks. In the figure below, there are two
- 21. • In addition to that, the diagram also shows there is a feedback path through which output signal C(s) is fed back and compared with the input R(s) and the difference between input and output E(s) = R(s) – C(s) is acting as actuating signal or error signal. • In each block of diagram, the output and input are related together by transfer function. Where, transfer function. • G(S) =C(S)/R(s) • where, C(s) is the output and R(s) is the input of that particular block. G(S) C(s) R(s)