performance enhancement of evolutionary algorithm based

International Journal of Engineering, Management & Sciences (IJEMS)ISSN: 2348 –3733, Volume -1, Issue-9, September 2014

4 www.alliedjournals.com

Abstract— This paper aims to extend the knowledge about

the performance enhancement of cascaded multilevel inverter byusing heuristic optimization methods. For improving efficiencyof multilevel inverter, harmonics has to be eliminated. Toeliminate the harmonics, Selective Harmonics Elimination PulseWidth Modulation technique is used for a better power qualityoutput. This technique eliminates the pre-selected lower orderharmonics which are more dominant into the nature whilesatisfying the fundamental component of output voltage, but themajor issue is to solve the set of nonlinear harmonic equationsderived from Fourier analysis of the output waveform ofmultilevel inverter. Using Conventional approach to solve thoseequations does not guaranteed the optimal solution and maystuck in the local minima. Hence, Evolutionary optimizationalgorithms are used for solving those equation. Evolutionaryalgorithm consist a subset of evolutionary computation and theresults are obtained. Among of all a comparison is done betweensimulated annealing, Genetic Algorithm and multi objectivegenetic algorithm. Whereas, Evolutionary optimizationalgorithm are inspired by the biological process of evolution.Using those algorithm the main concern is to find the notchesangles for giving the gate pulse to the individual switches ofmultilevel inverter. Using all of the three algorithms data setsare collected for different modulation indexes and output areverified by results. Results also shows the comparison betweengenetic algorithm and multiobjective genetic algorithm forgetting the optimum results.

Index Terms— Genetic Algorithm (GA), Multilevel Inverter(MI), Selective harmonics elimination PWM (SHEPWM),Simulated Annealing(SA), Multi objective genetic algorithm(MOGA).

I. INTRODUCTION

Nowadays electricity plays an important role. For improvingthe efficiency of the power quality, harmonics has tobeeliminated. Achieving high power, high voltage situationand eliminate the harmonic components of the output voltagea single phase eleven level inverter in cascaded with equal DCsupply is designed. Multilevel inverters continue to receivemore and more attention because of their high voltageoperation capability, low switching losses, high efficiency

Manuscript received September 12, 2014.Rajat Sunia, Lecturer, Department of Electrical Engineering, Govt.

Polytechnic College, Chittorgarh , Rajasthan IndiaAbhishek Soni, Asst. Prof., Department of Electrical Engineering,

SwasthyaKalyan Technical Campus, Jaipur, Rajasthan ,India.Shifali Gupta, B.Tech Scholar, Poornima College of Engineering, Jaipur

, Rajasthan ,India.

and low output of electromagnetic interference (EMI). Thepreferred output of a multilevel inverter is combined byseveral sources of dc voltages. With an increasing number ofdc voltage sources, the inverter voltage waveform approachesa nearly sinusoidal waveform while using a low switchingfrequency scheme. This results in low switching losses, andbecause several dc sources are used to synthesize the totaloutput voltage, each experiences a lower dv/dt compared to asingle level inverter.Consequently the multilevel invertertechnology is a promising technology for high power electricdevices such as utility applications [1-4].Today, in many electric utility applications multilevel inverteris used such as flexible AC transmission system (FACTS)equipment [1], high voltage current lines [2], electrical drives[3], solar, generating system. Three types of multilevelinverters are used: diode clamped [4], flying capacitor [5],and cascaded H-bridge multilevel inverter with separate dcsources [6]. Referring to the literature reviews, the cascadedmultilevel inverter (CMI) with separated DC sources isclearly the most feasible topology for use as a powerconverter for medium & high power applications due to theirmodularization and extensibility.Improve the efficiency atinverter level, switching frequency techniques are used. Theyare categorized on the basis of high frequency and lowfrequency. To diminish the harmonic components from theoutput voltage of multilevel inverter various switchingstrategies are used, such as sinusoidal pulse width modulation(SPWM), Space vector pulse width modulation (SVPWM),Selective harmonics elimination PWM (SHEPWM),Optimized harmonic stepped waveform (OHSW) [7], [8].The other method is using a low pass filter in the output ofinverters to eliminate higher order harmonics. To eliminatethe lower order harmonics in multilevel inverter outputvoltage SHEPWM strategy is widely used. In this method theaim is to eliminate the lower order harmonics, while thefundamental component is retained. In this approach bysolving the n number of equations, (n-1) lower orderharmonics from the fifth order can be eliminated and thefundamental component gets satisfied. The nonlinearequations involve switching angles as unknown variables.Inthis paper we are using heuristic optimization methods. Thesemethods have also been introduced based on evolutionaryoptimization techniques. These methods involves continuesoptimization and combinational optimization problems.Evolutionary methods have advantage that the global minimais most of the time assured. These methods not only find the

Performance Enhancement of EvolutionaryAlgorithm Based Multilevel Inverter: A

Comparative StudyRajat Sunia, Abhishek Soni , Shifali Gupta

Performance Enhancement of Evolutionary Algorithm Based Multilevel Inverter: A Comparative Study


solutions for infeasible M, where lower order harmonics canbe completely removed but also give the global minima toofor the optimal output. An evolutionary method provides theoptimum angles and can be used for any number of inverterlevels. GA is one of such heuristic optimization technique[14], [15] that has been used in the work. In addition Particleswarm optimization (PSO) method [16], Ant colonyoptimization [17] and Bee Algorithm [18] have also beenintroduced.In this paper GA is applied to solve nonlinear equationsobtained from SHE technique for obtaining switching angle.Result introduced the probability of reaching the globalminima has been compared without using the GA.Experimental results are presented to confirm the simulationresults.This paper is divided into following parts: Introduction,Multilevel Inverter, Evolutionary Optimization techniques,and Experimental results .

II. MULTILEVEL INVERTER

In this work cascaded type multilevel inverter is considered.In the multilevel inverter, we connect number of individualstogether. A single H-bridge is a three-level converter, as itsoutput waveform has three stepped waveform. The switchesin the inverter are turned on only at the fundamental frequencyand the voltage stress across the switches is only themagnitude of dc sources voltage. For an eleven level inverterfive dc source voltages are used for controllingthe fourH-bridges of the multilevel inverter. Each H-bridgehas fourIGBT. Each bridge is fed by separate sources. The fourswitches S1, S2, S3 and S4 are controlled to generate threediscrete outputs out V with levels Vdc, 0 and - Vdc. WhenS1and S4 are on, the output is Vdc; when S2 and S3 are on,the output is – Vdc; when either pair S1 and S2 or S3 and S4are on, the output is 0. Total output voltage is the sum of allthe individual voltage and symmetric with respect to neutralpoint. All the inverters can produce staircase output voltagewaveform as shown in fig2. The number of output phasevoltage levels in a cascaded multilevel inverter is 2N + 1,where N is the number of dc sources. For example, phasevoltage waveform for a 11-level cascaded inverter with threeisolated dc sources (N= 5) is shown in Fig. 2. Each H-bridgeunit generates a quasi-square waveform by phase-shifting theswitching timings of its positive and negative phase legs

Discrete,Ts = 5e-005 s.

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Figure 1. Eleven level inverter with five separate dc sources

III. SELECTIVE HARMONICS ELIMINITATION

The popular selective harmonic elimination methods provideus the opportunity to eliminate the lower order harmonics byselecting the more dominant harmonics. A eleven levelinverter waveform has five variables a1, a2, a3, a4 and a5,where Vdc1, Vdc2, Vdc3, Vdc4 and Vdc5 are assumed to beequal. By taking equal amplitude of all dc sources, the Fourierseries for a periodic function v0

v0(ωt)=a0 + (1)

For an odd quarter-wave symmetry waveform, a0 = 0, an = 0and

bn (2)

The Fourier series expansion of the output voltage for anotched waveform, will be written as

(3)

Switching angles has the constraints between 0 to 90 {0 ≤ α i<90} , because of quarter half wave symmetry characteristics,Even harmonics becomes zero and the triplen harmonics arealso absent since they will not show their effect in 3-phasebalanced systems. The general expression for an outputequations will equals to

, for fundamental (n=1)

Which can be shown as:+ +

= 5M+ +

= 0+ +

= 0+ +

= 0+ +

= 0 (4)Where M is the Modulation Index

International Journal of Engineering, Management & Sciences (IJEMS)ISSN: 2348 –3733, Volume -1, Issue-9, September 2014


IV. COMPARISIONBETWEEN DIFFERENTEVOLUTIONARY OPTIMIZATION TECHNIQUE

A. SIMULATED ANNEALING

Simulated annealing is the heuristic method based onthermodynamic free energy. It is the procedure of heating andcontrolled cooling of a material. Temperature andthermodynamic free energy affected by heating and cooling.It based on the concept of that obtaining good solution in afixed time that is acceptable, but it does not give best solution.

Table1. Data collection of firing angles with respect tomodulation index using simulated annealing

MI α1 α2 α3 α4 α5

1 21.42 28.66 58.25 60.92 80.85

Figure 2.. Output waveform of 11- level inverter by usingsimulated annealing

Figure 3.FFT Analysis of 11 level Inverter usingsimunnalannealing

B. GENETIC ALGORITHM

Genetic Algorithms are search and optimization techniquesbased on Darwin’s Principle of Natural Selection. Basicprinciple of GA is “Select the best Discard the Rest”. .Basically this algorithm is a set of instructions that is repeatedto solve a problem. Conceptually steps explained ahead areinspired by the biological processes of evolution (gradualworking or development). Also better solutions evolve fromprevious generations until a near optimal solution is obtained.”. A basic flowchart is shown in figure with the steps involvedin Genetic algorithm.

Table 2.Data collection of firing angles with respect tomodulation index using GA

MI α1 α2 α3 α4 α5

1 8.91 20.74 50.46 52.26 54.44

Figure 4. Output waveform of 11- level inverter by using GA

Figure 5.FFT Analysis of 11 level Inverter usingGA

C. MULTIOBJECTIVE GENETIC ALGORITHM

In a multi-objective optimization problem, multiple objectivefunctions need to be optimized simultaneously. There doesnot necessarily exist a solution that is best with respect to allobjectives because of incommensurability and conflictionamong objectives. There exist infinite number of optimalsolution which is called a pareto optimal.Table 3. Data collection of firing angles with respect to

modulation index using multiobjective genetic algorithmMI α1 α2 α3 α4 α5

1 12.88 31.82 42.37 64.33 84.19

Figure 6.Output waveform of 11- level inverter by using MultiObjective Genetic Algorithm (M=1)

Figure 7. FFT Analysis of 11 level Inverter using GeneticAlgorithm (M=1)

REFERENCES

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Performance Enhancement of Evolutionary Algorithm Based Multilevel Inverter: A Comparative Study


[3] M. Hagiwara, K. Nishimura, and H. Akagi, “A medium voltagemotordrive with a modular multilevel PWM inverter,” IEEE Trans. PowerElectron., vol. 25, no. 7, pp. 1786–1799, Jul. 2010.[4] N. Hatti, K. Hasegawa, and H. Akagi, “A 6.6-kV transformer less motordrive using a five-level diode clamped PWM inverter for energy savings ofpumps and blowers,” IEEE Trans. Power Electron., vol. 24, no. 3, pp.796–803, Mar. 2009.[5] A. K. Sadigh, S. H. Hosseini, M. Sabahi, and G. B.Gharehpetian,“Double flying capacitor multicellconverterbasedon modified phase-shiftedpulse width modulation,” IEEE Trans. Power Electron., vol. 25, no. 6, pp.1517–1526, Jun. 2010.[6] A. Nami, F. Zare, A. Ghosh, and F. Blaabjerg, “A hybrid cascadeconverter topology with series-connected symmetrical and asymmetricaldiode clamped H-bridge cells,” IEEE Trans. Power Electron., vol. 26, no.1,pp. 51– 65, Jan. 2011.[7] A. Kaviani, S. H. Fathi, N. Farokhnia, and A. Ardakani, “PSO, aneffective tool for harmonics elimination and optimization in multilevelinverters,” in Proc. 4th IEEE Conf. Ind. Electron. Appl., May 25–27, 2009,pp. 2902– 2907.[8] W. Fei, X. Ruan, and B. Wu, “A generalized formulation of quarter-wavesymmetry SHE-PWM problems for multilevel inverters,” IEEE Trans. PowerElectron., vol. 24, no. 7, pp. 1758–1766, Jul. 2009.[9] M. T. Hagh, H. Taghizadeh, and K. Razi, “Harmonic minimization inmultilevel inverters using modified speciesbasedparticle swarmoptimization,” IEEE Trans. Power Electron., vol. 24, no. 10, pp. 2259–2267,Oct. 2009.[10] W. Fei, X. Du, and B.Wu, “Ageneralized half-wavesymmetrySHE-PWM formulation for multilevel voltage inverters,” IEEETrans. Ind. Electron., vol. 57, no. 9, pp. 3030–3038, Sep. 2010.[11] Z. Du, L. M. Tolbert, and J. N. Chiasson, “Active harmonic eliminationfor multilevel converters,” IEEE Trans. Power Electron., vol. 21, no. 2, pp.459–469, Mar. 2006.[12] M. G. Hosseini-Aghdam, S. H. Fathi, and G. B. Gharehpetian,“Elimination of harmonics in a multilevel inverter with unequal DC sourcesusing the homotopyalgorithm,” in Proc. IEEE Int. Symp. Ind. Electron., Jun.4–7, 2007, pp. 578–583.[13] R. Salehi, N. Farokhnia, M. Abedi, and S. H. Fathi, “Elimination of loworder harmonics in multilevel inverter using genetic algorithm,” J. PowerElectron., vol. 11, no. 2, pp. 132–139, Mar. 2011.[14] M. S. A. Dahidah and V. G. Agelidis, “Selective harmonic eliminationPWM control for cascaded multilevel voltage source converters: Ageneralized formula,” IEEE Trans. Power Electron., vol. 23, no. 4, pp.1620–1630, Jul. 2008.[15] R. Salehi, B. Vahidi, N. Farokhnia, and M. Abedi, “Harmonicelimination and optimization of stepped voltage of multilevel inverter bybacterial foraging algorithm,” J. Electr. Eng. Technol., vol. 5, no. 4, pp.545–551, 2010.[16] K. Sundareswaran, K. Jayant, and T. N. Shanavas, “Inverter harmonicelimination through a colony of continuously exploring ants,” IEEE Trans.Ind. Electron., vol. 54, no. 5, pp. 2558–2565, Oct. 2007.[17] M. Malinowski, K. Gopakumar, J. Rodriguez, andM. A. Perez, “Asurvey on cascaded multilevel inverters,” IEEE Trans. Ind. Electron., vol. 57,no. 7, pp. 2197–2206, Jul. 2010.[18] D. T. Pham, S.Otari, A. Adidy, M. Mahmuddin, andH.Al- Jabbouli,“Data clustering using the bees algorithm,” in Proc. 40th College Int. pour laRechercheenProductiqueInt. Manuf. Syst. Semin., 2007.[19] L. Ozbakir, A. Baykasoglu, and P. Tapkan, “Bees algorithm forgeneralized assignment problem,” Appl. Math.Comput.,vol. 215, pp.3782–3795, 2010.[20] N. Farokhnia, H. Vadizadeh, S. H. Fathi, and F. Anvariasl, “Calculatingthe formula of line voltage THD in multilevel inverter with unequal DCsources,” IEEE Trans. Ind. Electron., vol. 58, no. 8, pp. 3359–3372, Aug.2011.

performance enhancement of evolutionary algorithm based

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