A plot of the possible closedloop pole locations as some parameter varies from 0 to 1. Root locus technique in control system electrical4u. Note that while drawing the root locus of a system with a pi controller compensator, the stable openloop zero of the compensator will attract the. Design control systems using root locus the root locus method, developed by w. Problem of root locus design root locus design can locate poles only on the root locus. Pid compensators which add a zero at s0 and add zero, one, or two zeros, pulling the root locus left, speeding up the system.
In this method, the closedloop system poles are plotted against the value of a system parameter, typically the. This paper introduce the lead,lag,laglead compensator design of root locus using single composite matlab programme. A number of matlab function are developed for the compensator design method. Root locus for the compensated system of example the root locus for the equivalent compensated system is shown in the figure. Root locus is going out of favor as a practical tool because it gets really complicated by digital sampling models. Control systemsroot locus wikibooks, open books for an. A root locus stability criterion is discussed, which has the capability of handling more than one variable coefficient in the characteristic equation. Ppt root locus powerpoint presentation free to view id. Dec 08, 20 this video is the second in this series of videos that examine the graphical method of the root locus and its used in control system and design. Design of controller using root locus method notes edurev. Designing a pid controller using the root locus method duration. The minor loop is designed to change the open loop poles and open loop transientresponse. Design via root locus elec304alper erdogan 1 35 two approaches for feedback compensation 1. We exploit the properties of rootlocus to do a rough sketch.
The placement of the pole will determine the rate of which the zero is \cancelled as kincreases. A revision of root locus method with applications sciencedirect. The main idea of root locus design is to predict the closedloop response from the root locus plot which depicts possible closedloop pole locations and is drawn from the openloop transfer function. May 02, 2020 design of controller using root locus method notes edurev is made by best teachers of. The root locus is a graphical representation in sdomain and it is symmetrical about the real axis. It has since become a very popular tool for analysis and design of servomechanisms and control systems with rational transfer functions in general. Leadlag design, using root locus, is proposed for a class of linear systems. With this proposed approach, students can concentrate on the larger control system design issues, such as compensator selection and closedloop performance. This document is highly rated by students and has been viewed 261 times. Must be a singleinput and singleoutput siso system.
As the openloop gain, k, of a control system varies over a continuous range of values, the root locus diagram shows the trajectories of the closedloop poles of the feedback system. How to plot the root locus using matlab first thing you need to do is to enter the open loop transfer function or the equivalent state space then in the command window write rlocussys like the following example sketch the root locus of the following system. Therefore, lets explore the properties of root locus. Introduction to root locus islamic university of gaza. Root locus sketching rules negative feedback rule 1. Thought matlab can create root locus plots, it is still useful to sketch root locus plots by hand. This is because complex roots occur in conjugate pairs. After studying these materials, you should be able to create a root locus and use the locus to understand the closedloop system behavior given an openloop system and a feedback controller. Teaching the root locus technique with plots categorization in an. The shape of the locus can also give us information on design of a more complex leadlag, pid controller though that wasnt discussed here. This first short video explains the meaning of the. Rlocus analysis design nyu tandon school of engineering. The guiwindow for the root locus allows students to change the gain and also to move the compensator poles and zeros by clicking on them and dragging them to new locations. Root locus plot of dynamic system matlab rlocus mathworks.
With the leadcompensated transfer function in 4, the step response has an overshoot of 19. Consider compensation as adding poles and zeros to feedback section for the equivalent system. This fact can make life particularly difficult, when we need to solve higherorder equations repeatedly, for each new gain value. Hence, the ideal derivative compensator must contribute 225. Meeting design specs using root locus so far, we have lead compensators which cancel a pole and move it left, speeding up the root locus. What is the real world application of the root locus. A very basic executable file compiled via matlab and visual studio 2010 that will prompt you to give the numerator and denominator in an array format. A new method of plotting the rootloci is developed for the linear control system with delay in control or in state. Where are the zeros of the closedloop transfer function.
The root locus is one of the major topics covered in an. We have also seen that feedback can change pole locations in the system. The idea of a root locus can be applied to many systems where a single parameter k is varied. In case of the system with delay in control, the rootlocus plot starts from. It can be observed that as increases, the steady state errors decrease assuming systems asymptotic stability, but the maximum percent overshoot increases. Aka put in the transfer functions numerator coefficients and denominator coefficients in descending order, and will output a root locus plot. The points that are part of the root locus satisfy the angle condition. From given specifications determine the damping ratio. If damping ratio alone is given then draw the root locus and draw line from origin at an angle to intersect the root locus, the point of intersection is the dominant pole measure angle contributed by each pole. The value of the parameter for a certain point of the root locus can be obtained using the magnitude condition. We can choose a value of s on this locus that will give us good results. Ppt design control systems using root locus techniques.
If damping ratio alone is given then draw the root locus and draw line from origin at an angle to intersect the root locus, the point of intersection is the dominant pole measure angle contributed by each pole and zero. State space root locus sketching rules negative feedback rule 1. Design of control systems cascade root locus design this is the first lecture devoted to the control system design. To show potential pitfalls of this method, consider the two systems g1s and g2s. Pdf a rootlocus technique for linear systems with delay. The purpose of compensator design generally is to satisfy both transient and steadystate speci. In the root locus design approach presented here, these two tasks are approached separately.
A unified approach for teaching root locus and bode. The method cannot change the root locus and locate poles desired locations if they are outside the existing root locus. Root locus elec304alper erdogan 1 1 lecture 1 root locus. This video is the second in this series of videos that examine the graphical method of the root locus and its used in control system and design. Introduction root locus the root locus of an openloop transfer function kgs is a plot of the locations locus of all possible closed loop poles with proportional gain k and unity feedback from the root locus we can select a gain such that our closedloop system will perform the way we want k gs openloop trans. Article information, pdf download for teaching the root locus technique with plots.
The best spot to select is usually the largest gain which results in a fast system with low error, that meets your design criteria such as no more than 20% overshoot in the step response ndsu root locus in the z. Each plot starts at a location equal to the location of a root of the plant transfer function. Consequently, the root locus plot will be symmetric about the real axis rule 2. As we change gain, we notice that the system poles and zeros actually move around in the splane. Modern control lec 04 analysis and design of control. In this chapter, let us discuss how to construct draw the root locus. From given specifications determine the damping ratio and the natural frequency. Example the root loci start at the poles and at the zeros.
Then by adding zeros andor poles via the controller, the root locus can be modified in order to achieve a desired closedloop response. Zac sutton explains the properties of a root locus and how to draw them. Ppt design via root locus powerpoint presentation free. In my approach to root locus design, the purpose of compensator design using root locus methods generally is to establish a speci. With the advent of the personal computer and the availability of faster processors, a suitable technique to be used in a personal computer is the rootlocusplotting. The purpose of compensator design using root locus methods generally is to establish a speci. Root locus techniques are used infrequently in the design of tachometer and acceleration feedback compensation, for feedback control systems. The solution to this problem is a technique known as root locus graphs. The rootlocus design method problems and solutions for section 5. The proposed algorithm set of rules and equations does not.
Draw the root locus of the given open loop uncompensated system with k1. The gain at the design point, which is k1kf from figure 9. Root locus design root locus design is a common control system design technique in which you edit the compensator gain, poles, and zeros in the root locus diagram. Lead and lag root locus design application center maplesoft. This worksheet shows how systems with multiple free parameters can be analyzed. In control theory and stability theory, root locus analysis is a graphical method for examining how the roots of a system change with variation of a certain system parameter, commonly a gain within a feedback system. Ensuring stability for an open loop control system, where hs csgs, is straightforward as it is sufficient merely to use a controller such that the cascade csg. Chapter 9 design via root locus linkedin slideshare. Using rootlocus ideas to design controller we have seen how to draw a root locus for given plant dynamics. First design the minor loop then design the major loop.
Computer aided design of lead compensator using root locus. The root locus need to find the values of a and b15 10 5 0 5252015105 0 5 10 15 20 25 real axis i m a g a x i sb c a j5. In the previous lectures we laid the groundwork for design techniques based on root locus analysis. Since kf is the reciprocal of the compensator zero, kf 0. Direct expressions for ogata leadlag design method using root locus. Because the open loop poles and zeros exist in the sdomain having the values either as real or as complex conjugate pairs. The root locus of a feedback system is the graphical representation in the complex splane of the possible locations of its closedloop poles for varying values of a certain system parameter. Now in order to determine the stability of the system using the root locus technique we find the range of values of k for which the complete performance of the system will be satisfactory and the operation is stable. Lec30 compensator design using root locus plots duration. Choose the zero to be at 10 to attract the root locus towards it. We include a variable gain k in a unityfeedback con.
Now, we choose a kfor which the root locus will cross into the desired region. Design via root locus elec304alper erdogan 1 1 lecture. As a conceptual thought model and as long as linear theory remains the paradigm of choice, the root locus does a really good job of. The root locus plot indicates how the closed loop poles of a system vary with a system parameter typically a gain, k. Set up the following characteristic equations in the form suited to evanss rootlocus method. Meeting design specs using root locus bison academy. Design by rootlocus method the rootlocus approach to design is very powerful when the specifications are given in terms of timedomain quantities, such as the damping ratio and undamped natural frequency of the desired dominant closedloop poles, maximum overshoot, rise time, and settling time. Design via root locus elec304alper erdogan 1 1 lecture 1. Do the zeros of a system change with a change in gain. Vast literature on these subjects can be found, for example in refs. In control theory and stability theory, root locus analysis is a graphical method for examining.
Compensator design to improve transient performance using. Ppt root locus powerpoint presentation free to view. A unified procedure for discretetime root locus and bode design. Root locus examples erik cheever swarthmore college. Craig 4 the root locus plot is a plot of the roots of the characteristic equation of the closedloop system for all values of a system parameter, usually the gain. The interactive root locus tool lslnr plots the root locus in one window and the closed loop step response in another window. In chapter 10, we learnt the benefits of knowing where the poles and the zeros lie in the splane.
Evans, is widely used in control engineering for the design and analysis of control systems. Root locus 2 root locus observations because we have a 3rdorder system, there are 3 separate plots on the root locus, one for each root. From given specifications determine the damping ratio and the natural frequency find the dominant pole. The poles on the root locus plot are denoted by x and the zeros are denoted by o. Oct 24, 2011 thought matlab can create root locus plots, it is still useful to sketch root locus plots by hand. Now desing the lag compensator part use sse for the design of the lag compensator parameters let then. The steps to design the lead compensator are with root locus are. May 25, 2012 the steps to design the lead compensator are with root locus are. Manually plotting a root locus recall step response. In this method, the closedloop system poles are plotted against the value of a system parameter, typically the openloop transfer function gain.
The root locus rl method was developed in 1948 independently by walter r. A unified approach for teaching root locus and bode compensator design conference paper in proceedings of the american control conference 1. We can choose it to be 40 to give the zero ample time to act to bring the root locus towards the left. Pdf computer aided design of lead compensator using root. Root locus elec304alper erdogan 1 7 real axis segments which parts of real line will be a part of root locus. Generic compensators cs are used in such situations in order to change the existing root locus.
The program, rlocsugui, takes loop gain as input and then applies and visually demonstrates all of the rules that are typically used to sketch the plot by hand. More elaborate techniques of controller design using the root locus are available in most. In this post we will deal with lag compensator design with time domain specifications and using the root locus technique. Design via root locus using the systems poles and the pole and zero of the ideal integral compensator, the summation of angles to the design point is 225. This is also known as root locus technique in control system and is used for determining the stability of the given system. We emphasised the useful information on the system stability and performance which may be extracted from the knowledge of the position of the poles. The root locus is obviously a very powerful technique for design and analysis of control systems, but it must be used with some care, and results obtained with it should always be checked.
1226 42 1389 771 276 1044 1079 943 550 805 1275 1401 1042 1190 1042 238 1191 373 921 898 16 1302 692 939 134 1399 131 291 748 479 1318 1030 1222