{"id":528,"date":"2023-04-01T00:31:56","date_gmt":"2023-03-31T21:01:56","guid":{"rendered":"https:\/\/mohammadijoo.com\/blog\/?p=528"},"modified":"2024-05-30T23:15:56","modified_gmt":"2024-05-30T19:45:56","slug":"modern-control-versus-linear-control","status":"publish","type":"post","link":"https:\/\/mohammadijoo.ir\/en\/blog\/modern-control-versus-linear-control\/","title":{"rendered":"<strong>\u201cModern Control\u201d versus \u201cLinear Control\u201d<\/strong>"},"content":{"rendered":"\n<p style=\"text-align: justify\"> Control Engineering is an Interdisciplinary field which could be used in other engineering fields like \u201cMechanical Engineering\u201d, \u201cElectrical Engineering\u201d, \u201cAerospace Engineering\u201d, \u201cChemical Engineering\u201d and etc. There is no bachelor degree for control engineering in universities, but \u201cLinear Control\u201d course is a mandatory course in bachelor for all of above engineering fields. In this article, we first talk about control engineering in general and then we explain \u201cLinear Control\u201d and \u201cModern Control\u201d in two separate sections.<\/p>\n\n\n\n<!--more-->\n\n\n\n<p style=\"text-align: justify\"> If we want to describe \u201cControl Engineering\u201d in one paragraph, we could say, it is all about controlling some desired variable or state to reach to our desired situation. For example, you have governing dynamic equation of a powerplant and you want the \u201ctemperature\u201d of special part of plant to be exactly at some desired Degrees Celsius. I think it is obvious what the desired variable or state is (which is temperature) and what the desired situation is. The \u201ccontrol input\u201d could be \u201cheat\u201d that transferred among the piping which is controllable by us. Another example could be robots or vehicles. You have dynamic equation of motions and you want the robot or vehicle to be at a desired point or follow a desired path. Your control inputs are forces by actuators (usually electrical motors). In many times you need to observe your desired situation and if it is getting away from desired point, you need to tune control input. In this situation, we call it a control loop with feedback or in another word, a \u201cclosed loop control\u201d. Feedbacks like temperature of our desired part or location of robot or vehicle, is provided by sensors. Below diagram describes \u201cControl Engineering\u201d pretty well:<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large is-resized\"><img fetchpriority=\"high\" decoding=\"async\" width=\"1024\" height=\"414\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Modern_Control_Diagram1--1024x414.png\" alt=\"\" class=\"wp-image-851\" style=\"width:800px;height:auto\" srcset=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Modern_Control_Diagram1--1024x414.png 1024w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Modern_Control_Diagram1--300x121.png 300w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Modern_Control_Diagram1--768x311.png 768w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Modern_Control_Diagram1-.png 1249w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n<\/div>\n\n\n<div style=\"height:36px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p style=\"text-align: justify\"> However, like many other sciences, this field is not as easy as it seems to be. If the dynamic equation are linear differential equations, your job is easier. But many times, your dynamic equations are nonlinear and many \u201cNonlinear Control\u201d techniques developed for this purpose. Sometimes there are many disturbances or uncertainties in your dynamic model and you need to use \u201cAdaptive Control\u201d or \u201cRobust Control\u201d approaches in these situations. Sometimes, you even don\u2019t have the dynamic model of your system and you just know about your desired output and your control input. In these situations, you need to use \u201cSystem Identification\u201d approaches and you also could use \u201cFuzzy Controller\u201d or \u201cNeural Network Based Controller\u201d for this purpose. In the rest of this article, first we talk about \u201cLinear Control\u201d and then we talk about \u201cModern Control\u201d and its advantages over linear control. Other control methods need its own article in future.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Linear Control<\/strong> (Classic Control)<\/h3>\n\n\n\n<p style=\"text-align: justify\"> In linear control, we only study LTI systems which is abbreviation for \u201cLinear Time Invariant\u201d systems. It means dynamic equations of our system should be \u201cLinear\u201d and \u201cTime Invariant\u201d. We could write dynamic equations of system as below equation:<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large is-resized\"><img decoding=\"async\" width=\"1024\" height=\"73\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/1-1-1024x73.png\" alt=\"\" class=\"wp-image-800\" style=\"width:550px;height:auto\" srcset=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/1-1-1024x73.png 1024w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/1-1-300x21.png 300w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/1-1-768x55.png 768w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/1-1-1536x110.png 1536w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/1-1.png 1862w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n<\/div>\n\n\n<div style=\"height:24px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p style=\"text-align: justify\"> In above equation, we consider \u201cY\u201d variable as our output and \u201cX\u201d as our input variable and <img decoding=\"async\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/ql-cache\/quicklatex.com-66db6600bdb60c5d09023b8f743b5f28_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#32;&#89;&#94;&#123;&#40;&#110;&#41;&#125;&#32;\" title=\"Rendered by QuickLaTeX.com\" height=\"16\" width=\"31\" style=\"vertical-align: 0px;\"\/> is n-th derivative of Y and <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/ql-cache\/quicklatex.com-5bf58ae9d0d4484961fffee111666002_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#32;&#88;&#94;&#123;&#40;&#109;&#41;&#125;&#32;\" title=\"Rendered by QuickLaTeX.com\" height=\"16\" width=\"37\" style=\"vertical-align: 0px;\"\/> is m-th derivative of X and all of them are function of time. \u201cLinear\u201d condition means that X and Y and their derivatives should be linear (not polynomial, not a nonlinear function like cos, sin, etc) and \u201cTime Invariant\u201d condition means that coefficients of X and Y and their derivatives should be constants and not a function of time.<\/p>\n\n\n\n<p style=\"text-align: justify\"> The dominant approach in linear control for solving LTI systems, is \u201cLaplace Transform\u201d or \u201cS-domain\u201d. We take Laplace transform from our dynamic equations and the equations will transform from \u201ctime-domain\u201d to \u201cS-domain\u201d or \u201cfrequency-domain\u201d. The job of Laplace transform is to convert a differential equation system to a polynomial equation system and obviously working with polynomials are easier than differential equations. Rest of our analysis is in S-domain in \u201cLinear Control\u201d course.<\/p>\n\n\n\n<p style=\"text-align: justify\"> There are 2 visual approaches in linear control to make understanding of system better. They are \u201cSFG\u201d and \u201cTF\u201d approach. SFG stands for \u201csignal flow graph\u201d and TF stands for \u201ctransfer functions\u201d. In below pictures, the first chart is TF and the second chart is SFG.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"461\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Modern_Control_Diagram2--1024x461.png\" alt=\"\" class=\"wp-image-854\" style=\"width:688px;height:auto\" srcset=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Modern_Control_Diagram2--1024x461.png 1024w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Modern_Control_Diagram2--300x135.png 300w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Modern_Control_Diagram2--768x346.png 768w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Modern_Control_Diagram2-.png 1078w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n<\/div>\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"978\" height=\"545\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Modern_Control_Diagram3-.png\" alt=\"\" class=\"wp-image-856\" style=\"width:666px;height:auto\" srcset=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Modern_Control_Diagram3-.png 978w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Modern_Control_Diagram3--300x167.png 300w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Modern_Control_Diagram3--768x428.png 768w\" sizes=\"(max-width: 978px) 100vw, 978px\" \/><\/figure>\n<\/div>\n\n\n<div style=\"height:24px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p style=\"text-align: justify\"> The first step in linear control, is finding the transfer function from dynamic equations of system. The question is, what transfer function is? The transfer function of a system is defined as the ratio of Laplace transform of output to the Laplace transform of input where all the initial conditions are zero. T(S) = Transfer function of the system, C(S) = output and R(S) = input.<\/p>\n\n\n\n<p style=\"text-align: justify\"> There are many techniques to find transfer function not only from dynamic equations of system, but also from its visual representations that are SFG and TF block diagrams. One of these techniques is Mason\u2019s Rule. After finding the transfer function, we are ready to do control analysis of system or stability analysis or at the end, designing a linear controller for our system.<\/p>\n\n\n\n<p style=\"text-align: justify\"> First type of analysis, is finding characteristics of our system. We insert an input to system which is usually step function and then we find the properties of system like: \u201cDead Time\u201d, \u201cRise Time\u201d, \u201cPeak Time\u201d, \u201cPercent Overshoot\u201d, \u201cSettling Time\u201d, \u201cSteady-State Error\u201d and etc. A transfer function is like this:<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"147\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/2-1024x147.png\" alt=\"\" class=\"wp-image-811\" style=\"width:520px;height:auto\" srcset=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/2-1024x147.png 1024w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/2-300x43.png 300w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/2-768x110.png 768w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/2-1536x220.png 1536w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/2.png 1809w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n<\/div>\n\n\n<div style=\"height:24px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p style=\"text-align: justify\"> If we solve the polynomial of numerator of T(s), we find \u201cZero\u201ds of system and if we solve the polynomial in denominator of T(s), we find \u201cPole\u201ds of system. Most of our analysis in linear system is based on poles and zeros of transfer function of our system. In realistic and useful systems, we always have <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/ql-cache\/quicklatex.com-7d6449f4d7b7e7ca543b94016d1865af_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#32;&#110;&#32;&#92;&#103;&#101;&#113;&#32;&#109;&#32;\" title=\"Rendered by QuickLaTeX.com\" height=\"15\" width=\"49\" style=\"vertical-align: -3px;\"\/>.<\/p>\n\n\n\n<p style=\"text-align: justify\"> Sometimes we know our desired characteristics of system like \u201cSettling Time\u201d or \u201cPercent Overshoot\u201d and we also know the rank of our transfer function (highest degree of polynomial in denominators of transfer function) and then we place our poles and zeros somehow to reach our desired characteristics. In above mentioned case, we could tune our system components that means we can tune our transfer function, but in real world systems, we have a solid system or model of system is unknown and we need to tune our controller parameters to reach our desired characteristics. The main controllers we design in linear controller course are P controller, PD controller and PID controller which we describe later in this article.<\/p>\n\n\n\n<p style=\"text-align: justify\"> One important issue to discover about a system is \u201cstability\u201d of system in response to some inputs like step function or ramp function or etc. A system is \u201cstable\u201d if natural response of system to input tends to zero in finite time and If response tends to infinity, the system is \u201cunstable\u201d and if the response fluctuates, the system is \u201cboundary stable\u201d. If the response of system is bounded for bounded input, we call it \u201cBIBO stable\u201d or bounded-input bounded-output stable.<\/p>\n\n\n\n<p style=\"text-align: justify\"> One criterion for investigating of stability of a linear system is \u201cRouth-Hurwitz\u201d. In this criterion we just need to know about coefficients of \u201cCharacteristic Equation\u201d which is denominator of transfer function. We also can investigate stability by \u201cRoot Locus Graphs\u201d which is based on location of poles of closed loop system and some tuning parameters of closed loop system. If all poles of closed loop system are in left side of Root Locus Graph, then system is stable or in another word, real part of all poles of closed loop system must be negative.<\/p>\n\n\n\n<p style=\"text-align: justify\"> We can reach to our desired working condition of our system by designing \u201cController\u201d or \u201cCompensator\u201d for our system. As the number of controllers and compensators are infinite, the priority is with simplest one. There are 3 types of compensators: \u201cLead Compensator\u201d, \u201cLag Compensator\u201d and \u201cLead-Lag Compensator\u201d. Transfer function of a compensator is in this form:<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"839\" height=\"220\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/3.png\" alt=\"\" class=\"wp-image-815\" style=\"width:245px;height:auto\" srcset=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/3.png 839w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/3-300x79.png 300w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/3-768x201.png 768w\" sizes=\"(max-width: 839px) 100vw, 839px\" \/><\/figure>\n<\/div>\n\n\n<div style=\"height:24px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p style=\"text-align: justify\"> It is noteworthy that compensators are same as controllers but they are simplest ones. A linear compensator or controller in general form, is like below:<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"198\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/4-1024x198.png\" alt=\"\" class=\"wp-image-819\" style=\"width:316px;height:auto\" srcset=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/4-1024x198.png 1024w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/4-300x58.png 300w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/4-768x148.png 768w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/4.png 1190w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n<\/div>\n\n\n<div style=\"height:24px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"337\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Modern_Control_Diagram4--1024x337.png\" alt=\"\" class=\"wp-image-861\" style=\"width:768px;height:auto\" srcset=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Modern_Control_Diagram4--1024x337.png 1024w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Modern_Control_Diagram4--300x99.png 300w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Modern_Control_Diagram4--768x253.png 768w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Modern_Control_Diagram4-.png 1063w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n<\/div>\n\n\n<div style=\"height:24px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p style=\"text-align: justify\"> If all of above coefficients are non-zero, we call above controller as \u201cPID\u201d controller which is abbreviation for Proportional-Integral-Derivative. If we only have <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/ql-cache\/quicklatex.com-c3f07c2ec2363bbfded909fa32645a20_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#32;&#75;&#95;&#112;&#32;\" title=\"Rendered by QuickLaTeX.com\" height=\"18\" width=\"22\" style=\"vertical-align: -6px;\"\/>, we call it P controller which is the simplest one and if have proportional and derivative terms, we call it PD controller as below:<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"902\" height=\"110\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/5.png\" alt=\"\" class=\"wp-image-822\" style=\"width:260px;height:auto\" srcset=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/5.png 902w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/5-300x37.png 300w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/5-768x94.png 768w\" sizes=\"(max-width: 902px) 100vw, 902px\" \/><\/figure>\n<\/div>\n\n\n<div style=\"height:24px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p style=\"text-align: justify\"> When we analysis our system in time domain, our input function is usually step function or ramp function or combination of some of them. If our input function is periodical like sinus function, we analysis our system in frequency domain. It could be shown that for a LTI system, if input is a sinus function, output is a sinus function as well but with different amplitude and phase. Frequency analysis has some advantages than time-domain analysis, for example:<\/p>\n\n\n\n<ul style=\"text-align: justify\">\n\n\n\n<\/ul>\n\n\n\n<p style=\"text-align: justify\"> There are 3 most important techniques in frequency analysis which are: \u201cBode Plot\u201d, \u201cNyquist Plot\u201d and \u201cNichols Plot\u201d. Each of these 3 methods needs its own description which could be find in any linear control text book. \u201cPhase Margin\u201d and \u201cGain Margin\u201d are two criteria for investigating stability of system in frequency analysis. Nyquist has also its own criterion for stability analysis in frequency domain.<\/p>\n\n\n\n<p style=\"text-align: justify\"> We also can design controller in frequency analysis using frequency parameters like \u201cGain Margin\u201d, \u201cPhase Margin\u201d, \u201cFrequency\u201d and etc. As we said already in frequency analysis, we don\u2019t need the mathematical model of plant and we can use \u201cBode Plot\u201d and \u201cNyquist Plot\u201d and \u201cNichols Plot\u201d in controller design.<\/p>\n\n\n\n<p style=\"text-align: justify\"> PID controllers are most frequently used linear controller, specially in industrial application and their pre-built module could be found in market. PID controllers could be used when we don\u2019t have mathematical model of plant and they can tune their parameters. By using Ziegler\u2013Nichols method, we can tune PID controller coefficients.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Modern Control<\/strong><\/h3>\n\n\n\n<p style=\"text-align: justify\"> In modern control, we talk about LTI systems like linear control and our system is in below form:<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"73\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/1-2-1024x73.png\" alt=\"\" class=\"wp-image-825\" style=\"width:568px;height:auto\" srcset=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/1-2-1024x73.png 1024w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/1-2-300x21.png 300w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/1-2-768x55.png 768w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/1-2-1536x110.png 1536w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/1-2.png 1862w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n<\/div>\n\n\n<div style=\"height:24px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p style=\"text-align: justify\"> But the main difference is that our analysis is in time domain instead of frequency domain or S-domain. The question is, why we didn\u2019t use time domain analysis in linear control at first place. The trick we used in linear control is that, we take Laplace transform from our system and convert a higher order differential equation to polynomial equation. In modern control we need a new trick and clearly, we don\u2019t work with above equation as it is.<\/p>\n\n\n\n<p style=\"text-align: justify\"> This time we convert a differential equation with degree of n (highest order of derivative in equation) to n separate differential equation with degree of 1. Solving differential equation with degree of 1 is very easy and its solution is taught in first lessons of \u201cOrdinary Differential Equations\u201d course in first semesters in bachelor degrees in engineering. Our new system of equation is in below form:<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"648\" height=\"249\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/6.png\" alt=\"\" class=\"wp-image-827\" style=\"width:182px;height:auto\" srcset=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/6.png 648w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/6-300x115.png 300w\" sizes=\"(max-width: 648px) 100vw, 648px\" \/><\/figure>\n<\/div>\n\n\n<div style=\"height:24px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p style=\"text-align: justify\"> In above equation, A, B, C and D are matrices and not scalar values. Therefore, if we expand above matrices equation, we will have n separate 1-degree differential equation. In above equation, x is state variables, u is input and y is output.<\/p>\n\n\n\n<p style=\"text-align: justify\"> As a simple example, consider below mechanical system which is a Mass-Spring-Damper model.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"430\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Mass-spring-damper-model--1024x430.png\" alt=\"\" class=\"wp-image-864\" style=\"width:482px;height:auto\" srcset=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Mass-spring-damper-model--1024x430.png 1024w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Mass-spring-damper-model--300x126.png 300w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Mass-spring-damper-model--768x323.png 768w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/Mass-spring-damper-model-.png 1359w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n<\/div>\n\n\n<div style=\"height:24px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p class=\"wp-block-paragraph\">The equation of this system is:<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"912\" height=\"104\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/7.png\" alt=\"\" class=\"wp-image-831\" style=\"width:272px;height:auto\" srcset=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/7.png 912w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/7-300x34.png 300w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/7-768x88.png 768w\" sizes=\"(max-width: 912px) 100vw, 912px\" \/><\/figure>\n<\/div>\n\n\n<div style=\"height:24px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p style=\"text-align: justify\"> This is a second-degree differential equation. How we convert it to 2 separate 1-degree differential equation??!!<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Our trick is as below. We put:<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"846\" height=\"88\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/8-1.png\" alt=\"\" class=\"wp-image-898\" style=\"width:256px;height:auto\" srcset=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/8-1.png 846w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/8-1-300x31.png 300w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/8-1-768x80.png 768w\" sizes=\"(max-width: 846px) 100vw, 846px\" \/><\/figure>\n<\/div>\n\n\n<div style=\"height:24px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p class=\"wp-block-paragraph\">So, our new system of equation is as below:<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"174\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/9-1024x174.png\" alt=\"\" class=\"wp-image-833\" style=\"width:476px;height:auto\" srcset=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/9-1024x174.png 1024w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/9-300x51.png 300w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/9-768x131.png 768w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/9.png 1494w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n<\/div>\n\n\n<div style=\"height:24px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p style=\"text-align: justify\"> As you see, above equation is a system of 1-degree equation. This form is also called, State-Space form and modern control is all about converting dynamic model of system to state-space form and then solve it.<\/p>\n\n\n\n<p style=\"text-align: justify\"> In above equation, our input or u(t) is F(t) and we have:<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"204\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/10-1024x204.png\" alt=\"\" class=\"wp-image-834\" style=\"width:384px;height:auto\" srcset=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/10-1024x204.png 1024w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/10-300x60.png 300w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/10-768x153.png 768w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/10.png 1274w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n<\/div>\n\n\n<div style=\"height:24px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p style=\"text-align: justify\"> Usually in motion equation, the x variable or location of system is important for us and we consider it as our output. Therefore, we have below equation for output variable:<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"234\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/11-1024x234.png\" alt=\"\" class=\"wp-image-835\" style=\"width:318px;height:auto\" srcset=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/11-1024x234.png 1024w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/11-300x69.png 300w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/11-768x176.png 768w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/11.png 1083w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n<\/div>\n\n\n<div style=\"height:24px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p class=\"wp-block-paragraph\">Thus, C and D matrices is as below:<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1007\" height=\"125\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/12.png\" alt=\"\" class=\"wp-image-836\" style=\"width:298px;height:auto\" srcset=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/12.png 1007w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/12-300x37.png 300w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/12-768x95.png 768w\" sizes=\"(max-width: 1007px) 100vw, 1007px\" \/><\/figure>\n<\/div>\n\n\n<div style=\"height:24px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p style=\"text-align: justify\"> After we convert our equation to state-space form, for solving them, we use linear algebra techniques. Therefore, solid background in linear algebra is a must for this course and modern control is teaching usually as a graduate course in universities.<\/p>\n\n\n\n<p style=\"text-align: justify\"> We can summarize main differences between modern control and classic control (linear control) in this items:<\/p>\n\n\n\n<ul style=\"text-align: justify\">\n\n\n\n\n\n\n\n\n\n<\/ul>\n\n\n\n<p style=\"text-align: justify\"> There are multiple representation for a system like, \u201cOrdinary Differential Equations\u201d, \u201cState-Space\u201d, \u201cTransfer Function\u201d and \u201cSignal Flow Graph\u201d. In modern control course you learn how to convert a representation to another.<\/p>\n\n\n\n<p style=\"text-align: justify\"> For example, how could we extract state-space representation when we have transfer function of system?! For this purpose, there are 3 techniques: \u201cCanonical Decomposition\u201d, \u201cSeries Decomposition\u201d and \u201cParallel Decomposition\u201d.<\/p>\n\n\n\n<p style=\"text-align: justify\"> For solving state-space equation, we use linear algebra techniques, although many software packages like MATLAB, does this pretty well for us. Below is some step-by-step simple approach for solving state-space equation:<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"alignleft size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"78\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/13-1024x78.png\" alt=\"\" class=\"wp-image-837\" style=\"width:371px;height:auto\" srcset=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/13-1024x78.png 1024w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/13-300x23.png 300w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/13-768x58.png 768w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/13.png 1366w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n<\/div>\n\n\n<div style=\"height:7px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"alignleft size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"78\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/14-1024x78.png\" alt=\"\" class=\"wp-image-838\" style=\"width:368px;height:auto\" srcset=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/14-1024x78.png 1024w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/14-300x23.png 300w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/14-768x58.png 768w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/14.png 1372w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n<\/div>\n\n\n<div style=\"height:7px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"alignleft size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"69\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/15-1024x69.png\" alt=\"\" class=\"wp-image-839\" style=\"width:482px;height:auto\" srcset=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/15-1024x69.png 1024w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/15-300x20.png 300w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/15-768x52.png 768w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/15.png 1534w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n<\/div>\n\n\n<div style=\"height:7px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"alignleft size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"141\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/16-1024x141.png\" alt=\"\" class=\"wp-image-840\" style=\"width:417px;height:auto\" srcset=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/16-1024x141.png 1024w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/16-300x41.png 300w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/16-768x105.png 768w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/16.png 1296w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n<\/div>\n\n\n<div style=\"height:7px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"alignleft size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"140\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/17-1024x140.png\" alt=\"\" class=\"wp-image-841\" style=\"width:467px;height:auto\" srcset=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/17-1024x140.png 1024w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/17-300x41.png 300w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/17-768x105.png 768w, https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/uploads\/2024\/05\/17.png 1535w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n<\/div>\n\n\n<div style=\"height:24px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p style=\"text-align: justify\"> In above solution, when we want to calculate <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/ql-cache\/quicklatex.com-ef9901977871a3a9f0868a01213880db_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#32;&#101;&#94;&#65;&#32;\" title=\"Rendered by QuickLaTeX.com\" height=\"16\" width=\"18\" style=\"vertical-align: 0px;\"\/>, we are dealing with A as matric not a scaler, and also B appears in integral as a matric, that is why we need linear algebra techniques. There are many approaches for solving state-space equation like Cayley-Hamilton method. We also can use modal transform to convert our matrices in modal form or diagonal form and it makes solving equations easier and this is another linear algebra approach. We encourage readers to use modern control text books to know more about how to solve state-space equations.<\/p>\n\n\n\n<p style=\"text-align: justify\"> For stability analysis in state-space form, when our system is in this form <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/mohammadijoo.ir\/en\/blog\/wp-content\/ql-cache\/quicklatex.com-45390f044115e0a7567b74faf4301109_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#32;&#92;&#100;&#111;&#116;&#123;&#88;&#125;&#32;&#61;&#32;&#65;&#32;&#88;&#40;&#116;&#41;&#32;\" title=\"Rendered by QuickLaTeX.com\" height=\"21\" width=\"88\" style=\"vertical-align: -5px;\"\/>, we first calculate \u201cEigen Values\u201d of matric A. In a stable system, real part of all eigen values is negative (less than zero). Another method for investigating stability of systems in state-space form, is \u201cLyapunov Method\u201d. In this approach, we only need differential equations of system and not the solution of dynamic equation. This approach is applicable to all linear and nonlinear systems and all time-variant and time-invariant systems.<\/p>\n\n\n\n<p style=\"text-align: justify\"> Another important concepts in modern control are \u201cControllability\u201d and \u201cObservability\u201d. Controllability is the relation between input and state variables and therefore A and B matrices are involved in Controllability Analysis. We call a system controllable, if we could design u(t) somehow that for each state variable x<sub>i<\/sub>, we can reach to our desired value for x<sub>i<\/sub> from an initial value of x<sub>i<\/sub>(0) in a finite time T. If a system is controllable:<\/p>\n\n\n\n<ul style=\"text-align: justify\">\n\n\n\n\n\n\n\n<\/ul>\n\n\n\n<p style=\"text-align: justify\"> Observability is the relation between output and state variables and therefore C and D matrices are involved in Observability Analysis. A LTI system is observable, if we could calculate each of state variable x<sub>i<\/sub>(t), only by knowing input u(t) and output y(t).<\/p>\n\n\n\n<p style=\"text-align: justify\"> There are some approaches to investigate controllability and observability of systems in state-space form. One of these approaches is Controllability and Observability \u201cGramian\u201d Matrices.<\/p>\n\n\n\n<p style=\"text-align: justify\"> We also can design controller for systems in state-space form. One of this controller design approaches is \u201cPole Placement\u201d. There are 3 methods for pole placement that are: \u201cState Feedback\u201d, \u201cAckerman Formula\u201d and \u201cSimilarity Transformation\u201d.<\/p>\n\n\n\n<p style=\"text-align: justify\"> In pole placement approach, we assume that all state variables are ready for feedback, but in real world systems, some state variables are not measurable. For this state variables, we need to design an estimator or observer. So, we need to design a \u201cfull state observer\u201d for our system or for only some state variables we can design \u201creduced order observer\u201d. The details of controller and observer design for state-space form systems, could be found in many text books of modern control.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Control Engineering is an Interdisciplinary field which could be used in other engineering fields like \u201cMechanical Engineering\u201d, \u201cElectrical Engineering\u201d, \u201cAerospace Engineering\u201d, \u201cChemical Engineering\u201d and etc. There is no bachelor degree for control engineering in universities, but \u201cLinear Control\u201d course is a mandatory course in bachelor for all of above engineering fields. In this article, we [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":539,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_post_was_ever_published":false},"categories":[6],"tags":[129,3,128,127],"class_list":["post-528","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-robotics-and-control-engineering","tag-classic-control","tag-control-engineering","tag-linear-control","tag-modern-control"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.9 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>\u201cModern Control\u201d versus \u201cLinear Control\u201d - Abolfazl Mohammadijoo&#039;s Blog<\/title>\n<meta name=\"description\" content=\"Control Engineering is an Interdisciplinary field which could be used in other engineering fields like \u201cMechanical Engineering\u201d, \u201cElectrical Engineering\u201d,\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/mohammadijoo.ir\/en\/blog\/modern-control-versus-linear-control\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"\u201cModern Control\u201d versus \u201cLinear Control\u201d - 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