Comparative Analysis of Different Control Schemes for DC-DC Buck Converter

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1 ISSN (e): Volume, 08 Issue, 6 Jun 208 International Journal of Comutational Engineering Researh (IJCER) Comarative Analysis of Different Control Shemes for DC-DC Buk Converter Pranjal Kalita, Pushanjali Konwar 2, Mriganka Gogoi 3 Deartment of Eletrial and Eletronis Engineering, Assam Don Boso University,Azara, Guwahati 2 Assistant Professor, Deartment of Eletrial and Eletronis Engineering, Assam Don Boso University,Azara, Guwahati 2 Assistant Professor, Deartment of Eletronis and Communiation Engineering, Assam Don Boso University,Azara, Guwahati Corresondene Author: Pranjal Kalita ABSTRACT DC-DC onverter is some ower eletroni iruits that onvert the DC voltage from one level to another. They have a very large area of aliations ranging from omuting to ommuniation. They are widely used in aliane ontrol, transortations and high-ower transmission. Its inreasing demand is based on its aability of eletrial energy onversion. The basi toology of DC-DC onverter are Buk onverter and Boost onverter, other toologies are derived from this two basi toology. Mathematial modelling of both Buk onverter and Boost onverter is done. In this aer the mathematial modeling for buk onverter is erformed. Some of the ontrol shemes are summarized in this aer whih inludes Internal Model Control based PID ontrol and Geneti Algorithm based PID ontrol. Extensive simulation is arried out and the results are omared on the basis of transient arameters. KEYWORDS: Buk Converter, PID, IMC, Geneti Algorithm Date of Submission: Date of aetane: I INTRODUCTION The swith mode DC-DC onverter are the simlest ower eletroni iruit that effiiently onverts an unregulated DC voltage into a regulated DC voltage. Solid state devie suh as transistors and diodes are used as swithing ower sulies. They oerates as swith either in omletely ON or omletely OFF state. The energy storing elements suh as indutor and aaitor are used for energy transfer and works as a low ass filter. The Buk onverter and Boost onverter are the two fundamental toologies of swith mode DC-DC onverter whereas the other toologies are either buk-derived or boost-derived onverters. DC-DC onverters have a wide area of aliations. The drasti use of these onverters in alianes ontrol, teleommuniation equiment s, DC-motor drives, automotive, airrafts, et. inreases its interests in many fields. The analysis along the ontrol of swithing onverters are the main fator to be onsidered. Various ontrol shemes are used to ontrol the swith mode DC-DC onverter whih inludes Internal Model Control and Geneti Algorithm.. There are many advantages and disadvantages related to every ontrol methods. In this aer the following works are done: () Mathematial Modelling of the DC-DC Buk Converter is shown in setion III. (2) Internal Model Control sheme is imlemented in the Buk Converter transfer funtion is shown in setion V. (3) Imlementation of the Geneti Algorithm based PID ontrol for Buk Converter is shown in setion VI. II SWITCH MODE DC-DC CONVERTER: The swith mode DC-DC onverters are those whih onverts the unregulated DC voltage to a regulated DC voltage with high effiieny and flexibility. The different tyes of DC-DC onverters inludes buk onverter, boost onverter, buk-boost onverter, Cuk onverter, et. both buk onverter and boost onverter are the two Oen Aess Journal Page 3

2 fundamental toologies of swith mode DC-DC onverter whereas buk-boost onverter and Cuk onverter are the ombination of the two basi onverter toologies. DC-DC onverter usually oerates in two mode of oeration: ontinuous mode and disontinuous mode. In ase of ontinuous mode the urrent through the indutor never falls to zero whereas in ase of disontinuous mode the urrent through the indutor falls to zero as the swith is turned off. 2. Buk Converter: The buk onverter is shown in figure. It is the ste down onverter in whih a fixed high voltage is ste down to a desired low voltage level. It onsist of non-dissiative swith, indutor, aaitor. The swithes will oerate at the rate of PWM swithing frequeny. The ratio of ON time when the swith is losed to the entire swithing t eriod is known as the duty yle and is reresented as: ON and the outut voltage is ontrolled by varying T the duty yle. Figure: Basi Buk Converter In the first sub iruit state when the swith S is losed, the diode is reversed biased and the energy is transferred from the soure to the indutor and the urrent through the indutor gradually inreases during this time interval as shown in figure 2(a). In the next sub-iruit state when the swith S is losed, the soure is disonneted from the network. The diode will be forward biased and the urrent will flow through the freewheeling diode. During the seond time interval the urrent through the iruit dereases linearly as the energy in the indutor disharges as shown in the figure 2(b). Figure2: Buk Converter when (a) Swith is ON (b) Swith is OFF III MATHEMATICAL MODELING OF THE BUCK CONVERTER Swith On: When the swith is losed (ON-state) and diode is reverse biased, the indutor urrent L () aaitor voltage v () t and outut v () t are out i t, Oen Aess Journal Page 4

3 Vg L RL. il vout dt RL V. i v dt L L L dv il iout dt g L out Figure3: Buk Converter when swith is ON The main differene among this model and the lossless model is that the outut voltage is not equal to the aaitane voltage. RR R vout il. v. vout R iout il. v. R Putting the value of v out and i out in the above equations we have: RR R V R i v dt L L g L L dv R il v dt C State sae reresentation when swith is ON R R L C R 0 0 RR R y x R L ' x x u OFF-State When the swith is oen (OFF-state) and diode is forward biased, the indutor urrent il () t, aaitor voltage v () t and outut voltage Vo () t are Oen Aess Journal Page 5

4 L R. i v dt di L L R. i v L dt L L dv il iout dt L L out out Figure 4: Buk Converter when swith is OFF The main differene among this model and the lossless model is that the outut voltage is not equal to the aaitane voltage. RR R vout il. v. vout R iout il. v. R Putting the value of v out and i out in the above equations we have: RR R R i v dt L L L dv R il v dt C State sae reresentation when swith is OFF RR R RL L 0 ' 0 0 x x u 0 C R 0 0 RR R y x R In the Buk Converter, A = A2, B2 = 0, C = C2. Finally, the average model in one swithing eriod is: Oen Aess Journal Page 6

5 R R L C R 0 0 RR R y x R L ' k x x u Control-to-outut transfer funtion From equation (xiii) the transfer funtion that relates the outut voltage when the duty yle is onstant and having a value of k is: ^ vout ( s) vout srr ^ () k ks L 2 R R s RC [ L] C s LC L L IV CONTROL TECHNIQUES USED IN DC-DC BUCK CONVERTER: In DC-DC onverter for a given inut voltage, the outut voltage an be ontrolled by ontrolling the ON or OFF duration of the swith. Pulse Width Modulation (PWM) is one of the method in whih ontrol iruit regulates the outut by varying the ON time of the swith and by fixing the swithing frequeny. When the onverter oerates in a losed loo mode with a ontroller rodues a ontrol signal whih is then omared with a arrier signal to generate a ulse that triggers the swith of the onverter. This results in a outut voltage from the onverter. V INTERNAL MODEL CONTROL BASED PID CONTROL The IMC onfiguration is designed for setting u a omarison between the roess and model outut to form a standard feedbak struture. Figure 5 shows the basi IMC imlementation in the roess transfer funtion. The transfer funtion for our Buk onverter is: ~ k ( s) g () s s 2 s Oen Aess Journal Page 7

6 ~ ~ ~ g ( s) g ( s) g ( s) ~ k ( s) g () s s 2 s ~ s q( s) g ( s) f ( s) k qs () g() s ~ q( s) g ( s) s 2 s g() s s( s) 2 s ( s) The transfer funtion for the PID ontroller is: 2 i ds is g() s k is Then the PID arameters based on IMC will be derived as: ~ g () s k ( s) s 2 s f() s k 2 2 ( s ) k ( ) s Table : IMC based PID arameters for Buk Converter i d 2 VI GENETIC ALGORITHM BASED PID CONTROL Geneti Algorithm generates solutions to otimization roblems using tehniques insired by natural evolution. Comared with other otimization tehniques, GA starts with an initial oulation ontaining a number of hromosomes where eah one reresents a solution of the roblem whih erformane is evaluated by a fitness funtion. Basially, GA onsists of three main stages: Seletion, Crossover and Mutation. The aliation of these three basi oerations allows the reation of new individuals whih may be better than their arents. This algorithm is reeated for many generations and finally stos when reahing individuals that reresent the otimum solution to the roblem. 6. Geneti Algorithm for Controller Design The following flow hart is neessary in order to design a PID Controller using Geneti Algorithm for Buk Converter: () Create a oulation of initial solution of arameters (K, K i & K d ). (2) Evaluation of objetive funtion. The objetive funtion is defined as: (3) Evaluation of fitness funtion. f ( ) The fitness funtion is defined as: (4) Generation of offsring. T f ( ) ( v v ) t0 ref o 2 (5) Relae the urrent oulation with the new oulation. Oen Aess Journal Page 8

7 (6) Terminate the rogram if termination riterion is reahed; else go to ste 2. VII RESULTS: In this work, more emhasis is given for imroving the dynami resonse of the DC-DC buk onverter by identifying roer ontroller arameter. The following dynami arameters are onsidered in this work. i) Rise Time ii) Settling Time iii) Peak Overshoot In order to examine the effetiveness of the roosed algorithm, extensive simulation and exerimental studies have been arried out on the losed loo system of Buk onverter. 7. Resonse Based on IMC based PID ontroller: Figure 6: Resonse of Buk Converter based on GA-PID Control 7.2 Resonse Based on GA based PID ontroller: Figure 7: Resonse of Buk Converter based on GA-PID Control Oen Aess Journal Page 9

8 Transient Resonse of the Buk Converter based on two ontrol shemes: Sl.No Transient Parameters GA PID Control IMC-PID Control Settling Time.44 X X Peak Time Rise Time Overshoot VIII CONCLUSION The design of ontroller for the buk onverter is ereived as an otimization task and the ontroller onstants are estimated through different ontrol algorithms. Initially the designs of PID ontroller arameters for the buk onverter were designed based on Internal Model Control (IMC)) and later the results are omared with Geneti Algorithm (GA). By observing the rise time, settling time, eak overshoot from the resonse urves whih are obtained by using the ontroller arameters of two different ontrol shemes it an be onluded that GA based arameter gives good and robust resonse omared to IMC. REFERENCES []. Mohan N., Undeland T. M. and Robbins W. P., Power Eletronis - Converters, Aliations, and Design (3rd Edition), ed: John Wiley and Sons. [2]. Rashid M.H., Power Eletronis: Ciruits, Devies and Aliations vol. (3rd Edition), Prentie Hall (2003) [3]. Forsyth A.J. and Mollov S.V, Modelling and ontrol of DC-DC onverters, Power Engineering Journal, 2, , (998) [4]. M. Ahmed, M. Kuisma, K. Tolsa, P. Silventoinen, Standard Proedure for Modeling the Basi Three Converters (Buk, Boost, and Buk-boost) With PID Algorithm Alied, Proeedings of XIII-th International Symosium on Eletrial Aaratus and Tehnologies, SIELA 2003, May, 2003, Plovdiv, Bulgaria, : 5-2. [5]. Nanda R Mude, Prof. Ashish Sahu, Adative Control Shemes For DC- DC Buk Converter, International Journal of Engineering Researh and Aliations, Vol. 2, Issue 3, May-Jun 202, [6]. Shyama M, P.Swaminathan, Digital Linear and Nonlinear Controllers for Buk Converter, International Journal of Soft Comuting and Engineering (IJSCE), Volume2, Issue-, Marh 202, [7]. Chun T. Rim, Gyu B. Joung, and Gyu H. Cho, Pratial Swith Based State-Sae Modeling of DC-DC Converters with All Parasitis, IEEE Transations on Power Eletronis Vol 6 Otober (99) [8]. P. Wood, General theory of swithing ower onverters, in IEEE Power Eletronis Seialists Conf Re., 979, [9]. C. T. Rim, G. B. Joung, and G. H. Cho, A state sae modeling of non-ideal d-d onverters, in IEEE Power Eletronis Seialists Conf Re., 988, [0]. Kinattingal Sundareswaran and V. T. Sreedevi, Boost onverter ontroller design using Queen-bee-assisted GA, IEEE Transations on industrial eletronis, vol. 56, no. 3, Marh []. G. Seshagiri Rao, S. Raghu, N. Rajasekaran, Design of Feedbak Controller for Boost Converter Using Otimization Tehnique, International Journal of Power Eletronis and Drive System (IJPEDS), Vol. 3, No., Marh 203,. 7~28 [2]. Jun Zhang, Henry Shu-Hung Chung, Wai-LUN Lo, S.Y.Ron Hui, Imlementation tehnique For Design of swithing Regulators Using Geneti Algoritham, IEEE Transations on ower eletronis, vol. 6, no. 6, November 200 Pranjal Kalita Comarative Analysis of Different Control Shemes for DC-DC Buk Converter. International Journal of Comutational Engineering Researh (IJCER), vol. 08, no. 06, 208, Oen Aess Journal Page 20