Genetic Algorithm Based Controller Optimisation For Non Linear Economics Essay

Most existent systems in our life are non-linear, which is really hard to plan suited accountants for as the parametric quantities are altering as the system runs. In this undertaking optimisation method to near the best reply is developed. And a new signifier of suited accountant for the systems is investigated by utilizing familial algorithm techniques. The simulation of the systems and optimisation of familial algorithm are implemented in the package, Matlab. The end product consequences from these Matlab simulations, which are the accountant parametric quantities, provide the systems a wider scope of operation conditions.

List of symbols




Military policeman




Rising clip



Settling clip



Integrated absolute mistake


Electromagnetic force








Undamped natural-frequency


Dumping factor



Steady province mistake


List of abbrevations


Electromagnetic suspension

Explosive detection system

Electrodynamic suspension


Familial algorithm


I wish to show my sincere and deepest gratitude and grasp to my supervisor, Dr. Rod Dunn for his priceless counsel, support and encouragement throughout the undertaking.

I would besides wish to thank Phd pupils, Chenghong Gu, Chenchen Yuan and Athony Gee for their proficient suggestions about Matlab.

Finally, I express my profound grasp to my girlfriend Ying Liu for her

encouragement, apprehension, and patience even during difficult times of this undertaking.


1. Introduction 1

1.1 Electromagnetic Levitation 1

1.2 Optimization: Familial Algorithm 2

2. Aims 4

3. Literature Review 5

3.1 Maglev Trains 5

3.2 Familial Algorithms ( GAs ) 6

3.3 Control Laws 8

4. Technical Content and Methodology 10

4.1 Physical system 10

4.2 The conventional algorithm for the non-linear magnetic levitation system 12

4.3 GA optimisation 16

5. Comparison of the two accountants 25

5.1 The standard fixed-parameter dynamic accountant 25

5.2 The GA optimized accountant 26

5.3 Compare the accountants 27

6. Decision 30

7. Further work 31

8. Mentions 32

Appendixs 34

List of figures

Figure 1: Electromagnetic Suspension System ( EMS ) aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦.5

Figure 2: Schematic of a standard familial algorithmaˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦.6

Figure 3: Closed-loop feedback control systemaˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦.8

Figure 4: The Performance steps obtained from a measure responseaˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦9

Figure 5: Physical theoretical account of unidimensional levitation systemaˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦..10

Figure 6: Actually physical relationship between Y and iaˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦11

Figure 7: The theoretical account of additive systemaˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦ … 13

Figure 8: The simplified theoretical account of control systemaˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦ … 14

Figure 9: Simplified theoretical account for the additive control systemaˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦14

Figure 10: The measure response in additive system for, andaˆ¦aˆ¦..

. aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦15

Figure 11: The theoretical account of control system ( Red: non-linear portion ; black: additive portion ) aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦ … … … 16

Figure 12: The measure response in the non-linear response, and aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦..16

Figure 13: The secret plan of the functionaˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦..18

Figure 14: The familial algorithm consequence 1aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦18

Figure 15: The familial algorithm consequence 2aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦19

Figure 16: The familial algorithm consequence 3aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦20

Figure 17: The best and intend fittingness value of each coevals aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦.20

Figure 18: The GA optimisation procedureaˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦.22

Figure 19: The mean and best fittingness of each generationaˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦23

Figure 20: System response for, and aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦ … 24

Figure 21: The steady province of the response for, and aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦ … 25

Figure 22: The steady province of the response for, andaˆ¦aˆ¦..25

Figure 23: The system response for, and ( input=0.05 ) aˆ¦aˆ¦26

Figure 24: The mean and best fittingness of each coevals ( input=0.05 ) aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦ … 27

Figure 25: The system response for =-96.89600246459612, = 0.27164377771365833 and =11.327052730175494aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦.27

Figure 26: The system response of the fixed-parameter accountant when input alterations

aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦ … … … … ..29

Figure 28: The system response for two accountants when inpu=0.02aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦.30

Figure 29: The system response for two accountants when inpu=0.05aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦.30

Figure 30: The simulink theoretical account for the GAaˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦..36

List of figures of tabular arraies

Table 1: Coefficients used in the considered systemaˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦ … 11

Table 2: The coveted accountant specification for measure responseaˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦ … 14

Table 3: Parameters used for running GAaˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦22

1. Introduction

1.1 Electromagnetic Levitation

In the existent universe, many systems are non-linear. To make suited accountants for them, some typical representative instances must be selected for the in-depth research. Therefore, the magnetic levitation system is chosen for this undertaking, since it is basically non-linear.

Magnetic Fieldss have been found utile for a assortment of different applications of all time since they were discovered, and the figure is still turning. Many of today ‘s electrical applications contain engineerings that utilize magnetic Fieldss. Some such applications include electrical motors, cathode beam tubings and even magnetic levitated vehicles [ 1 ] . In this study, the work is chiefly related to the latter portion, viz. the electromagnetic levitation.

The usage of the electromagnetic levitation is assorted in different countries, e.g. research into merger reactors where magnetic levitation is used for commanding the highly hot plasma in the reactors. Another most of import use of our day-to-day life is the magnetic levitation train, which has been built in many developed states, such as United Kingdom, Germany, United State, Japan, etc. In some underdeveloped states like China, the magnetic levitation is under the commercial operation for the transit to the airdrome. The chief ground why it is wildly developed in recent old ages is that the magnetic levitation engineering provides the advantage of much smaller clashs when compared with the conventional wheel-rail train. There are two typical types of magnetic levitation engineerings: the electromagnetic suspension ( EMS ) and the Electrodynamic suspension ( EDS ) . The EMS uses the force yielded by the electromagnetic in the train to pull the path ; while the EDS uses the abhorrent force between the electromagnetisms on both path and train to raise the train from the rail. For the EDS, A major advantage of the abhorrent magnetic levitation systems is that they are of course stable – minor narrowing in distance between the path and the magnets creates strong forces to drive the magnets back to their original place, while a little addition in distance greatly reduces the force and once more returns the vehicle to the right separation [ 2 ] . No feedback control needed for the EDS. But the EMS systems have the built-in instability of the electromagnetic attractive force that brings about the hit. Therefore it should be monitored invariably and provided with smart accountant. However, one of the hard facets when it comes to magnetic levitation is the fact that magnetic Fieldss are non-uniform. In fact, they are extremely non-linear and the strength of a magnetic field non merely depends on the distance to the beginning but besides on the orientation of the field at the beginning and at the mark [ 1 ] .

In this undertaking, a unidimensional levitation system in the EMS magnetic levitation will be investigated. The standard magnetic levitation EMS systems need a fixed- parametric quantity dynamic accountant that keeps the train at a given tallness over the path. And the fixed-parameter dynamic accountant for the non-linear system is conventionally designed on the base of the additive estimate. However the additive estimate merely works under a rigorous restraint. If the existent status is out of scope of the restraints, the quality of accountant will go really hapless: larger wave-off or undershoot, longer settling clip and the fluctuation of the control response. Therefore, the parametric quantity of the accountant should be changed as the system moves frontward, and the accountant adjust the parametric quantities to guarantee the high quality of public presentation. But the complexness of the non-linear EMS system brings trouble of planing the standard accountant in the conventional manner. So, a new idea of utilizing evolutionary algorithm to accomplish the mark emerges at the right clip. The ground why the familial algorithm ( GA ) is used is explained in the citation from [ 3 ] : ” The evolutionary attack has proved peculiarly successful in jobs that are hard to formalize mathematically, and which are therefore non contributing to analysis. This includes systems that are extremely non-linear, that are stochastic, and that are ill understood ( control of which represents a ‘black art ‘ ) . Problems affecting the aforesaid categories of procedure tend to be hard to work out satisfactorily utilizing conventional methods ” .

1.2 Optimization: Familial Algorithm

In mathematics, computing machine scientific discipline and economic sciences, optimisation refers to taking the best component from some set of available options. And the classical optimisation thoughts normally based on an analytical method: utilizing some differentiable maps to depict the world, while most of the worlds seldom obey them. So some thoughts about development are put frontward to assist to optimise the complex jobs. Therefore, Genetic algorithm with the inductive nature will work out job as an development.

In the early 1960s Rechenburg ( 1965 ) conducted surveies at the Technical University of Berlin in the usage of an evolutionary scheme to minimise retarding force on a steel home base. Familial algorithms were used by Holland ( 1975 ) and his pupils at the University of Michigan in the late seventiess and early 1980s to analyze a scope of technology jobs. In peculiar, Goldberg ( 1983 ) used GAs to optimise the design of gas grapevine system [ 4 ] .These are numerically optimized algorithms which base themselves upon the forms of genetic sciences every bit good as development mechanisms found in natural home ground and living existences [ 5,6,7 ]

The rule of familial algorithm is simple. Within a population of persons ( solutions ) , some are fitter ( which means that they have higher fittingness ) to the environment than the others. Harmonizing to the theory of “ endurance of the fittest ” , the persons with higher fittingness are more likely to boom in the environment, therefore they have more chance to reproduce the following coevals. As each member of the following coevals inherits at least portion of its features from its two parents, the progeny of extremely fit parents have a higher chance of themselves being extremely fit than the progeny of less fit parents. The procedure is like a cringle that runs in nature and this procedure make the fittingness of the population addition as the figure of coevals rises [ 8 ] .

As the evolutional characteristic of GA, the hunt infinite of job with unsmooth bounds or information can be obtained by it. And a group of solutions are used from one time loop instead than a individual reply, which provide the optimisation a higher chance to make the optimal reply [ 8 ] . However, GA has some disadvantages:

Long clip needed to meet to a optimal point

No cogent evidence to guarantee the planetary lower limit found, but search country is reduced.

Unsuitable scene of GAs can take a premature convergence.

Examples about premature convergence ( planetary lower limit seeking ) and factors of convergence clip are illustrated in Chapter 4.3.1.

2. Aims

The aims of the undertaking are:

Make a suited theoretical account where the designed accountants can be applied, which may be a mathematical theoretical account or block diagrams for the control theory.

Obtain the parametric quantities and analyse them via the familial algorithm: to put up sensible fittingness map for the GA tool chest of Matlab.

Compare the new accountant with standard accountant in several facets, such as quality and operation scope.

3. Literature Reappraisal

3.1 Maglev Trains

The EMS attractive levitation system is shown in Fig. 2. Electromagnets ( called support magnets ) are attached to the train and powered by batteries on the train. There are spirals ( called stators ) built into the lower surface of the path ( called the guideway ) . The spirals are comprised of sheets of steel and spiral twists. When the electromagnets are switched on, the attractive force between the electromagnets and the spirals levitates the train. Guidance electromagnets are located on the side to maintain the train in place laterally [ 9 ] .

Figure 1: Electromagnetic Suspension System ( EMS ) [ 9 ]

To stabilise the levitation, a feedback system that utilizes spread detectors keeps the spreads between the train and the guideway at prescribed breadth. The spread detectors attached to the train contain oscillating circuits that induce eddy currents in the stators under the guideway. When the spread breadth alterations, common electromagnetic initiation between the spread detectors and the stators will bring forth characteristic signals in the oscillatory circuit. The signals are analyzed and used to modulate the power delivered to the electromagnets of the train, keeping the prescribed spread breadth [ 9 ] .

3.2 Familial Algorithms ( GAs )

Familial algorithms ( GAs ) are planetary, parallel, hunt and optimisation methods, founded on Darwinian rules [ Darwin, 1859 ] . It works with a population of possible solutions to a job. Each person within the population represents a peculiar solution to the job, by and large expressed in some signifier of familial codification. The population is evolved, over coevalss, to bring forth better solutions to the job. A conventional of the algorithm is shown in Figure 1 [ 3 ] .

Figure 2: Schematic of a standard familial algorithm [ 3 ]

The basic stairss of a GA shown above are described as below from [ 10 ] :

[ Start ] Generate random population of n chromosomes ( suited solutions for the job )

[ Fitness ] Evaluate the fittingness degree Fahrenheit ( x ) of each chromosome ten in the population

[ New population ] Create a new population by reiterating following stairss until the new population is complete

[ Selection ] Select two parent chromosomes from a population harmonizing to their fittingness ( the better fittingness, the bigger opportunity to be selected )

[ Crossover ] With a crossing over chance cross over the parents to organize a new progeny ( kids ) . If no crossing over was performed, offspring is an exact transcript of parents.

[ Mutation ] With a mutant chance mutate new offspring at each venue ( place in chromosome ) .

[ Accepting ] Place new offspring in a new population

[ Replace ] Use new generated population for a farther tally of algorithm

[ Test ] If the terminal status is satisfied, halt, and return the best solution in current population

[ Loop ] Go to step 2.

Auxiliary specification:

1. In instance of the doomed of the best chromosome from the last population, at least one best solution, which is called elitism, is copied without alterations to a new population.

2. There are several ways for the choices: Roulette Wheel choice, Rank choice, steady province choice and elitism, etc.

The information above provides a brief apprehension of GAs and what the working processs are. In an implement of GAs, the solution can be trapped in a premature convergence. And there are several methods to forestall this job [ 11-14 ] :

Hybrid familial algorithm: It is a synergism of evolutionary or any population-based attack with separate single acquisition or local betterment processs for job hunt, and the purpose is to maintain the diverseness of the population efficaciously.

Improve familial operators: To plan operators that involve the heuristic cognition, to increase ability of local searching.

Adjust the fittingness grading: In the early ( subsequently ) phase of GAs the fittingness of persons decently is narrowed ( broadened ) to keep the fluctuation of population.

Parallel familial algorithm. Through the multi-population parallel development, exchange information among different populations during the operation of a GA.

3.2.3Fitness map

In GAs the fittingness map is like a usher for the optimisation, suited fittingness map can assist the seeking engine find the country where the coveted consequences locate. Therefore the design of fittingness map is really important to the GA.

Harmonizing to [ 15 ] , as the map equips the ability of indicating the way of the searching of GA, an expressed fittingness map may either be non-existent or its calculation is prohibitively dearly-won. Normally in the consideration of the computational efficiency an approximated fittingness map is preferred instead than the precise description of development.

3.3 Control Laws

3.3.1 Closed-loop control system

A control system is a combination of different constituents that will make the coveted system response. A closed-loop control system consists of a accountant, the original system and a detector.

Figure 3: Closed-loop feedback control system

The analysis of control system is based on the additive system theory [ 16 ] , which means that the system in figure 3 should be a additive theoretical account for planing a accountant. The additive system theory for the analysis provides a good solution for the standard fixed-parameter accountant. But this method of analysis besides causes some restriction for system with built-in non-linearity.

3.3.2 Evaluation of quality of accountants

Resulted values of parametric quantities should be evaluated to choose the better pick for the accountant. The measure response is simulated in the Simulink and measured for the quality of the accountant. The public presentation measures that will be used in this undertaking are:

aˆ? Overshoot per centum ( Mp )

aˆ? Rise clip ( tr )

aˆ? Settling clip ( T )

aˆ? Integrated absolute mistake ( IAE )

An illustration of the public presentation steps is given in figure 4

Figure 4: The Performance steps obtained from a measure response. [ 1 ]

Overshoot is the maximal value minus the measure value divided by the measure value. Rise clip refers to the clip required for a signal to alter from a specified low value to a specified high value. Typically, these values are 10 % and 90 % of the measure tallness. The settling clip is the sum of clip elapsed from the measure was issued until the post-step system value is within 5 % of the steady-state value. The last public presentation step, the integrated absolute mistake, represents the country between the two signals, viz. the mention and the system response [ 1 ] .

4. Technical Content and Methodology

4.1 Physical system

4.1.1 Mathematical theoretical account

A unidimensional levitation system in the EMS magnetic levitation is used as an illustration.

Figure 5: Physical theoretical account of unidimensional levitation system

The magnetic force is approximately relative to the sum of square of quotient of current and distance of air spread, can be described as:

( 1 )

Where is the magnetic force between the railroad and the magnet, is the invariable of the equation, is the current in the spiral of electromagnet and is the tallness of air spread.

Denote the mass of the levitating object as m and the gravitation acceleration as g. By pretermiting the air clash, the kineticss of the levitating object can be obtained from Newton ‘s 2nd jurisprudence as:

. ( 2 )

. ( 3 )

In Laplace sphere, and this relationship among, and is indicated below, in figure 6.

Figure 6: Actually physical relationship between Y and I

For farther research on the magnetic levitation system, the coefficients used in the system are assumed and listed in table 1.




Unit of measurement

Current in the spiral at the balance point



Height of the air spread at the balance point



Acceleration of gravitation



Mass of the object



Table 1: Coefficients used in the considered system.

4.1.2 Premises

Equation ( 1 ) is obtained from the equation below:

[ 17 ] , where the coefficient, a, is assumed really little compared with. And the values of the coefficients in table 1 are besides estimated for the simulation in the Matlab.

4.2 The conventional algorithm for the non-linear magnetic levitation system

4.2.1 Linear theoretical account design

Conventionally, the non-linear system is normally approximated as a additive system, and so a suited accountant is designed for the stableness of the system.

From equation ( 3 ) , the non-linear relationship among, and is obtained. However, the alteration in the tallness of air spread ( ) and the current ( ) is really little. As an estimate ( where and ) , the alteration in the magnetic force can consist the alterations, and, in a additive look, which is more suited in control jurisprudence. The derivation of it is described as:

When and: ( 4 )

And ( 5 )

Similarly, ( 6 )

Where and is the value of current and tallness of air spread severally at the balance place. At the balance,

( 7 )

( 8 )

Via the equation ( 8 ) , the equation ( 5 ) and ( 6 ) can be changed as:

( 9 )

And ( 10 )

Therefore the coefficients, and, are changeless. The additive system can be built on the base of the alterations of parametric quantities, , and. The additive system block is expressed in figure 7.

Figure 7: The theoretical account of additive system

4.2.2 Conventional accountant design

Once the additive system mold is set up, the accountant parts can be added to the additive system, which is described in figure 8.

Figure 8: The simplified theoretical account of control system

And the portion 1 and portion 2 of accountants in the figure above are the accountant and the sensor portion in figure 3 severally


With the theoretical account and matching coefficients in table 1, the control system is shown in figure 9.

Figure 9: Simplified theoretical account for the additive control system

The mark of the coveted accountant is to run into the specifications for the system in table 2.




Unit of measurement

Undamped natural-frequency



Muffling factor



Steady-state mistake



Table 2: The coveted accountant specification for measure response

In a conventional method, the unknown parametric quantities ( , and in figure 9 ) in the accountant parts could be obtained by computation:

The coveted transportation map for the control system from table 2:

( 11 )

The look for the simplification from figure 8:

( 12 )

Make =

( 13 )

And the theoretical account in figure 9 is simulated in Matlab with the parametric quantities in equation ( 13 ) . The input in the simulink is a step signal of 0.02, which starts at 1s. And the measure response is expressed below when dumping factor =0.5:

Figure 10: The measure response in additive system for, and

4.2.3 The consequences from the non-linear system

The procedure above returns a set of value of parametric quantities, which eventually is usage in the existent system. The estimate made as a additive system is the attack to the non-linear system. The figure below shows the full system with the non-linear constituents in ruddy.

Figure 11: The theoretical account of control system ( Red: non-linear portion ; black: additive portion )

The fake measure response is indicated in figure 12:

Figure 12: The measure response in the non-linear response, and

The corresponding public presentation steps for this accountant are Mp= 18.2966, T =1.9720s and IAE= 0.0992.

The accountants derived in traditional manner bring forth a good wave form for the measure response, but this solution can merely digest the little inputs. However, the conventional manner is still really of import for the accountant design.

4.3 GA optimisation

Compared with the traditional manner of obtain the parametric quantities in accountants, the GA can acquire the consequence without any linearization or algebraic operations. And an illustration for the basic familial algorithm is listed at first.

4.3.1 Local and planetary lower limit

In general instances, the end of optimisation is to happen the planetary minimum/maximum of the map in the hunt infinite, which is smaller/larger than the remainder of the value of map. However, many nonsubjective maps contain some local minima/maxima, which sometimes is difficult for making the planetary minimum/maximum because the optimisation some times is trapped in these local minima/maxima. The familial algorithm can work out this “ trap ” job by suited scene of the parametric quantities in the Matlab tool chest.

The map shown below has a local lower limit degree Fahrenheit ( x ) = -1 at x= 0, and a planetary lower limit degree Fahrenheit ( x ) = -1 – 1/e at x= 21.

( 14 )

Figure 13: The secret plan of the map

With the default scenes in the GA tool chest, the concluding consequence is shown below ( Figure 14 ) :

Figure 14: The familial algorithm consequence 1

The consequence is really near to the local lower limit at x=0, means that the GA is trapped in the local lower limit and the planetary lower limit is outside of the hunt infinite. And the premature convergence appears before the best consequence is obtained. To forestall this phenomenon, the diverseness of the population should be insured for the initial coevals of the development. The alteration is made: alter the initial scope from [ 0 ; 1 ] to [ 0 ; 20 ] .

Figure 15: The familial algorithm consequence 2

The persons are in a wider initial scope, hence, the hunt infinite is extended. This clip the value returned from the GA is really closed to the planetary upper limit at x=21.

4.3.2 Elitism

From the illustration above, the optimisation converges early due to the loss of the familial fluctuation. The elitism is that several best persons from the last coevals are copied straight to the progeny, which evidently will take to a loss of diverseness of the following coevals. Consequently, a premature convergence would look in the loop of GA.

In the last illustration, when the figure of elitism is increased to 10 ( the population size is 20, half is copied as elitism ) , even with larger scope of initial population the development may be trapped in the local lower limit once more.

Figure 16: The familial algorithm consequence 3

The GA returns a point really near to the local lower limit, which indicates the premature convergence.

Figure 17: The best and intend fittingness value of each coevals

Figure 17 shows that the black ( best fittingness ) and bluish ( average fittingness ) converges in a degree for most of the coevalss. The elitisms lessening the fluctuation of the population.

However, the characteristic that increasing elitism causes premature convergence can be regarded as a good manner to make an expected consequence in sawed-off development period.

4.3.3 GA optimizes the accountants for non-linear magnetic levitation theoretical account

The conventional manner of planing the accountants in chapter 4.2 is to happen suited value of parametric quantities to fit the nonsubjective transportation map. Therefore the traditional thought needs a suited theoretical account or a formulized object. And particularly for the non-linear system of magnetic levitation system, “ little signal theoretical account ” of additive estimate works stably for the little input. However compared with those drawbacks of the conventional solutions, the GA can work out the jobs without deep apprehension of the system or the theory. Therefore the GA can calculate out the coveted coefficient without much information of the job, and the fittingness map is needed to state GA what sort of consequences is needed.

In GA, the fittingness provides an way for the optimisation. Therefore the puting up of the fittingness map is truly of import, which will impact the consequences significantly.

As the rating factors of the control public presentation, the steps of the response: wave-off ( Mp ) , settling clip ( T ) , rise clip ( tr ) and the integrated absolute mistake ( IAE ) , outputs an fitness value of the accountants. Obviously the smaller these steps are, the better of the control system is. Therefore, the fittingness map will consist the steps. For simplification of the fittingness map, the rise clip step is neglected in the fittingness map, since a shorter clip restraint for the subsiding clip means the value of the rise clip is little. The fittingness map ( degree Fahrenheit ) is approximately designed as:

( 15 )

Where, and are the different weightings for the three steps.

The same unidimensional magnetic levitation system will be used for optimisation, and the control theoretical account in figure 11 is besides the theoretical account designed in the Simulink of Matlab. The GA generated parametric quantities will be assigned to the accountant parts of K, h0 and h1.

Therefore the basic hint of the GA optimisation for the system is shown below in figure 18.

Measure 5: The persons are selected by GA, and the progeny is formed by the selected persons.

Measure 1: Original population is generated by the GA randomly

Measure 2: Value of persons are assigned to the parametric quantities in the accountant

Measure 3: The simulink processes the measure response for the corresponding parametric quantities.

Measure 4: , and of the response are obtained to give the fittingness of each person

Figure 18: The GA optimisation process

The stairss in figure 18 really are completed in the optimisation tool chest of Matlab. The GA is one of the convergent thinkers of the optimisation. The convergent thinker will name the fittingness map to return a value of the fittingness of the persons foremost, and so selects persons with better fittingness to reproduce the following coevals. And in the GA tool chest, the purpose of the optimisation is to happen the smallest value of the nonsubjective map, in other words, the smaller the value of the fittingness map, the fitter the accountant for the system response.

Many of the GA run-time parametric quantities used for this job are the same as the GA default values. Those default parametric quantities are summarized in table 3.

Representation type

Real values

Population size


Crossover chance


Mutation chance


Elite count


Table 3: Parameters used for running GA

The population size is set at 20 which provide an adequate figure of persons. The mutant chance of 0.8 ensures a sufficient commixture of the chromosomes. The mutant chance of 0.33, in fact, is the, where N is the figure of parametric quantities in one person which is 3 in the optimisation, and this value ensures that on mean one parametric quantity of each person will be mutated [ 1 ] .An elite count of 2 occupies 10 % of the population, which ensures that the best 10 per centums of the last coevals will be copied to the off spring.

Some of the information non mentioned in the Table 3, such as the scope of, and, are based on some information about the item of the job, and will be illustrated in the farther execution. Implementation and consequences

Harmonizing to the conventional computation of the accountants in chapter 4.2.2, the consequences of the optimisation will be in the scope around the old value: , and. And the spheres around them are infinite for the refinement of the old consequences. Therefore the scenes of the scopes of the parametric quantities are defined as: , and. With these scenes, the GA generates the optimized parametric quantities measure by measure.

Figure 19: The mean and best fittingness of each coevals

The figure above shows the fittingness of each coevals, the black points are the best fittingness of each coevals, and the bluish one means the average value of the population in each coevals. At about first 20 loops, the black points sit at the underside, which means that some of the persons have obtained a good fittingness ; while the public presentation of the whole population is non that good, since the blue points spread in the part of high fittingness value ( hapless control public presentation ) .

The concluding consequences generated by GA are:

( 16 )

And for the corresponding parametric quantities, the system response is illustrated in figure 20

Figure 20: System response for, and

The steps of the response are: Mp=1.5056, ts = 1.3600s and IAE= 0.0963 Analysis and treatment

It can be seen that these three steps going smaller, compared with the conventional consequence. The wave form shows a better response figure with no undershoot smaller wave-off and shorter subsiding clip. However the consequence generated by the GA really does non settle in the 0.04 as the conventional accountant does. Mathematically, the transportation map for the new accountants developed by GA can non run into mark of the zero steady-state mistake. The figure 20 will demo the existent steady province of the response for, and:

Figure 21: The steady province of the response for, and

Figure 22: The steady province of the response for, and

The figure 21 is a image that zoomed into the country of 4.9s-5.0s in clip and 0.0398m-0.0402m in supplanting. The bluish line ( ) is the response wave signifier and the ruddy line ( ) is the degree of 0.04m.In figure 22, the steady province of the response is settling down at 0.04 as the ruddy line covers the bluish line. In contrast, the GA optimisation can bring forth a accountant at the cost of non-zero steady-state mistake. Nevertheless, the wave-off, settling clip and incorporate absolute mistake are refined much better. Therefore the GA optimisation is still a really good solution with some tolerance of the non-zero steady province.

5. Comparison of the two accountants

5.1 The standard fixed-parameter dynamic accountant

The standard fixed-parameter dynamic accountant is obtained by the conventional solution, and this accountant is built on the base of the additive estimate for the non-linear system. In other words, merely when the little signal is taken as the input, the additive estimate can come into consequence. In the simulation in chapter 4, the input is a step signal of 0.02 that is really little. Once the input additions, the fake response of the fixed parametric quantity accountant will be non good as ever.

The value of step signal additions from 0.02 to 0.05, and parametric quantity is fixed at, and. The response of the standard accountant is shown below:

Figure 23: The system response for, and ( input=0.05 )

The relevant steps are: Mp=43.8349, ts = 2.9460s and IAE=0.1099. And compared with the public presentation when the input peers 0.02, the alteration of the steps implies that the control public presentation deteriorates.

5.2 The GA optimized accountant

While with the aid of GA, the optimisation can bring forth a accountant for the input alteration. Use the same scenes for the tool chest in Matlab as old one, the fittingness altering in each coevals is shown below:

Figure 24: The mean and best fittingness of each coevals ( input=0.05 )

The best fittingness returns the corresponding values of three parametric quantities: =

-96.89600246459612, = 0.27164377771365833 and=11.327052730175494.

These values are assigned back to the accountants, and the system response is simulated in the simulink and shown in figure 25.

Figure 25: The system response for =-96.89600246459612, = 0.27164377771365833 and =11.327052730175494

Then the public presentation of the response is measured, and the steps are listed: Mp=2.1736, ts=1.4860s and IAE=0.0957. And the steady province value of supplanting is 0.0697, hence the ratio of steady province mistake is ( 0.07-0.0697 ) /0.07*100 % =0.4286 % , which is closed to zero.

5.3 Compare the accountants

The information of public presentation from chapter 4.2, 4.3, 5.1 and 5.2 is in the tabular array below:

No. of row


Military policeman

T ( s )



Fixed-parameter accountant






GA generated accountant






Fixed-parameter accountant






GA generated accountant





Table 4: The public presentation of the accountants under different inputs

5.3.1 Comparison of each accountant ‘s public presentation when input varies Comparison of the fixed-parameter accountant at different input

From Row 1 and 3 in table 4:

The wave-off ( Mp ) at input=0.05 additions to more than twice of the value when input=0.02.

The subsiding clip ( T ) is extended for about 1 2nd

The integrated absolute mistake ( IAE ) grows over 10 %

Figure 26: The system response of the fixed-parameter accountant when input alterations

In figure 26, the fixed-parameter accountant become worse when input additions. Comparison of the GA accountant at different input

From Row 2 and 4:

The three steps maintain about the same when the input is 0.02 or 0.05, which means the quality of public presentation about keeps the same.

Figure 27: The system response of the GA generated accountant when input alterations

In figure 27, both of the two curves settle down at approximately 1.5s, and in a really little wave-off. Quality of the GA accountants remains the same good degree as input varies.

5.3.2 Comparison between the two accountants

By comparing Row 1with 2 or 3 with 4, all the value of Mp, T and IAE of the GA generated accountant is smaller than the fixed-parameter accountant. And the 2 figures below are the response for the two accountants with different input.

Figure 28: The system response for two accountants when inpu=0.02

Figure 29: The system response for two accountants when inpu=0.05

Therefore, the comparing in the figure 28 and 29 demonstrates that the fixed-parameter accountant performs worse than the GA generated accountant whenever input equals 0.02 or 0.05, since the fixed-parameter accountant has inaccuracy of the additive estimate for big signal input.

6. Decision

Through the comparing, the GA produces a accountant of higher quality for the given magnetic levitation system than the conventional solution. Without the restraints of the additive estimate theoretical account, the new accountant yielded by a GA responses the mention input rapidly with less wave-off and quiver. Meanwhile, the new accountant generates different parametric quantities as the input size is altering, to guarantee the high quality of system response. However the cost of the high quality of GA generated accountant is the really little growing of the steady-state mistake. Normally the steady-state mistake should be tolerant for the implement, as in the illustration of this undertaking the steady province mistake ratio is merely 0.4286 % , because the new accountant can settle down much quicker to a degree with a really little steady-state mistake when the criterion accountant is still in quiver of an unacceptable scope. But in this undertaking, the scope of variables that GA searches for the best consequence is based on the value of parametric quantities in fixed-parameter accountants. In other words, the conventional method aids GA to cut down the interval where the best reply lies. If the GA method is expected to happen the suited parametric quantities without an estimated sphere, the fittingness map would be more complicated with some more “ ushers ” in it. The “ ushers ” mean the modus operandis in the Matlab codification that can assist the GA to contract the scope that the possible replies locates and happen the optimum. And some “ ushers ” are already used in the fittingness map of this undertaking and the item of it is shown in Appendixs.

In decision, GAs can construct accountants of better public presentation, and the application of the GA method is wider than the conventional one, since the response can stay in a really stable degree and unswayed by the alteration of mention input.

7. Further work

In this undertaking, many efforts are completed to the aid the GA tool chest to happen the consequences. The chief attempts are spent to construct suited fittingness map. However, as a GA is an evolutionary method, any plans, which guide the GA to happen the way to the best consequence, are deserving utilizing even non precise. But excessively unsmooth way will misdirect GAs, the loops would takes an unexpected clip to meet to a suited fittingness point. To better these inaccurate guiding codifications of the system will shorten clip of optimisation.

On the other manus, the burdening map of the fittingness map, which is shown in equation ( 15 ) , should be built in a more accurate manner. In the equation, = + , the value of each weighting for three steps is set by intuitions. And the undertaking consequences indicate that the values in the weightings are effectual. Due to the limited clip of proving in undertaking, the sensitivity of the fittingness map to the weightings can non be confirmed. Therefore some other farther work will concentrate on the more precise weightings for the fittingness map.

Hypothetically, a fast moving magnetic levitation train is utilizing the GA method to bring forth altering parametric quantities to command the distance of the air spread between the train and railroad, the consequence of parametric quantities should be derived in really short clip in the consideration of safety of the whole system. Therefore, any mechanism for bettering optimisation quality and processing-time of GAs is possible work for the future implement of GA in magnetic levitation or some other scientific discipline Fieldss.