A Flyback Converter Fed Multilevel Inverter for AC Drives

Transcription

1 2016 IJRET olume 2 Iue 4 Print IN: Online IN : Themed ection: Engineering and Technology A Flyback Converter Fed Multilevel Inverter for AC Drive ABTRACT Teenu Joe*, reepriya R EEE Department, MG Univerity/RET, Kakkanad, Kerala,India Thi paper preent a flyback converter fed cacaded multilevel inverter drive having developed H-bridge. The DC upply required for the inverter i developed with a flyback converter with multiwinding at the econdary. An algorithm to determine the value of DC ource required for an N level inverter i alo propoed. Multilevel inverter topology wa developed in order to increae the number of output level and to reduce the number of power witche, driver circuit and the total cot of inverter. Both 7 level and 31 level inverter wa imulated and verified in MATLAB/imulink environment. The value of DC ource were made different to increae the output voltage level without increae in number of witche and voltage ource. Thi topology can be ued for high power motor. THD level of both the inverter are alo compared in thi paper. Keyword: Developed H-bridge, Multi-Level Inverter. I. INTRODUCTION The induction motor ha well-known advantage of imple contruction, reliability, ruggedne and low cot and ha found very wide indutrial application. Furthermore, in contrat to the dc motor, it can be ued in an aggreive or volatile environment ince there are no problem with parking and wear and tear. In the pat induction motor and ynchronou motor were employed mainly for contant peed application becaue variable peed application of thee drive are either too expenive or had very poor efficiency. But with the development of emiconductor converter employing thyritor,power tranitor, IGBT and GTO they are widely ued now a day. In thi paper a converter-inverter ection for AC drive application i explained. A converter ection will be ued to convert the input DC voltage into required DC. Motly inverter are ued to convert thi dc voltage into ac voltage at required voltage and frequency. o the mot crucial tep in the deign of a drive i the inverter ection. The converter ued i a flyback converter with a pecially deigned flyback tranformer having multiple winding o a to provide the required voltage for the inverter. The inverter ued for the drive i a multilevel inverter. The multilevel inverter have received more attention for their ability on high- power and medium voltage operation and becaue of other advantage uch a high power quality, lower order harmonic, lower witching loe, and better electromagnetic interference. Thee multilevel inverter will generate tepped voltage waveform by uing a number of dc voltage ource produced by the flyback converter. In thi paper, in order to increae the number of output voltage level and reduce the number of power witche, driver circuit, and the total cot of the inverter, a new topology of cacaded multilevel inverter i propoed. The magnitude of DC voltage i determined uing a new algorithm. Both 7 level and 31 level inverter i imulated in MATLAB/imulink and THD performance of both i compared. II. PROPOED YTEM Fig 1 and 2 how the propoed ytem for a even level and thirty one level inverter. A flyback converter i pecially deigned to produce multiple output. The flyback converter i a Buck-Boot converter with the inductor of Buck-Boot converter plit to form a flyback tranformer. A flyback tranformer i a multiwinding IJRET Received : 06 Augut 2016 Accepted : 11 Augut 2016 July-Augut 2016 [(2)4: ] 641

2 coupled inductor, unlike true tranformer. A flyback tranformer i ued a an energy torage device, where energy i tored in the air gap of the core. The inductor tranformer hould be deigned to minimie the leakage inductance, AC winding loe and core loe. WITCH ON: When the witch i cloed, input get connected to the ource. The primary current and magnetic flux increae toring energy in the tranformer. The diode i revere biaed a the voltage induced in econdary winding i negative. During thi period output capacitor upplie the load. WITCH OFF: When the witch i opened, primary current and magnetic field drop but the econdary voltage become poitive making the diode forward biaed. During thi period the energy from the tranformer core recharge the capacitor and upplie the load. Figure 1. chematic diagram of even level drive ytem. In recent year, indutrial application have begun to require higher power apparatu. ome medium voltage motor drive and utility application require medium voltage and megawatt power level. For a medium voltage grid, it i troubleome to connect only one power emiconductor witch directly. A a reult, a multilevel power converter tructure ha been introduced a an alternative in high power and medium voltage. The major ection of the drive are the converter, the inverter and control ection. Each ection of the propoed drive i explained in ection II.a,II.b, II.c. The operation of toring energy in the tranformer before tranferring to the output of the converter allow the topology to eaily generate multiple output with little additional circuitry. Tranformer can be claified by it primary econdary turn ratio, power ize and econdary winding. If the voltage drop acro witching MOFET and output diode i ignored, the volt*econd during the on time (Ton) hould be equal to the volt*econd during the off time (Toff ), in teady tate operation:. T. N. T (1) in on out Primary and econdary inductance i calculated by defining maximum econdary ripple current. econdary inductance i calculated a: p off L ( o dfw I )(1 D) f w (2) p 2 p L L N (3) Figure 2. chematic diagram of 31 level drive ytem A. Flyback Converter The flyback converter i equivalent to Buck-Boot converter with inductor plit to form tranformer. o the operating principle of both are imilar. Fig 3 how the operation of flyback converter during ON and OFF tate. MOFET election i baed on: The drain to ource breakdown of the MOFET ha to be greater than: N p d ( o df) i (4) N Total power lo On tate ource to drain reitance. Maximum allowed operating temperature. Gate threhold voltage. International Journal of cientific Reearch in cience, Engineering and Technology (ijret.com) 642

3 of the ix witche for the production of different voltage level. In thi table, 1 and 0 indicate the ON and OFF tate of the witche, repectively. From the table it i clear that if the value of the dc voltage ource are equal, the number of voltage level decreae to three. Therefore, the value of dc voltage ource hould be different to generate more voltage level without increaing the number of witche and dc voltage ource. Uing the baic even level higher level inverter can be developed. Figure 3. The on tate & off tate configuration of flyback converter B. Multilevel Inverter A new cacaded multilevel inverter topology i developed for propoed ytem. The even level inverter i obtained by adding two witche and one dc ource to the H-bridge. The propoed topologie are obtained by adding two unidirectional power witche and one dc voltage ource to the H-bridge inverter tructure. In other word, the propoed inverter are compried of ix unidirectional power witche ( a, b, L1, L2, and R 2 ) and two dc voltage ource ( L 1 and ). Thi topology i called developed H-bridge. TABLE 1: witching Table of even level inverter L1 L2 R 2 a b o L (L1+ ) L (L1+ ) The imultaneou turn-on of and (or and ) caue the voltage ource to hort-circuit. Therefore, the imultaneou turn-on of and (or and ) mut be avoided. In addition, and hould not turn on, imultaneouly. Table 1 how the witching tate The general topology conit of 2n dc voltage ource (n i the number of the dc voltage ource on each leg) and 4n + 2 unidirectional power witche. In the propoed general topology, the number of output voltage level ( ), number of witche ( ), number of dc voltage ource ( ) and the maximum magnitude of the generated voltage ( ) are calculated a follow: 2 2 n N 1 1 (5) tep N witch 4n 1 (6) N ource 2n (7) o, max Ln Rn (8) The variety of dc voltage ource and the value of blocking voltage of the witche have a ignificant effect in determining the cot of the inverter. The number of variety of the value of dc voltage ource ( ) and maximum blocking voltage of all the witche of the general topology ( a follow: ) i calculated N iety 2n var (9) 4( ) (10) block, n Ln Rn An algorithm i applied to determine the magnitude of dc voltage ource. The magnitude of the dc voltage ource of the propoed general multilevel inverter can be obtained a follow: j Lj 5 1 dc (11) International Journal of cientific Reearch in cience, Engineering and Technology (ijret.com) 643

4 j Rj 2* 5 1 dc (12) n1 o, max 3* 5 dc (13) For the even level inverter = 5 and = 10. The maximum output voltage of the converter will be 15. imilarly 31 level inverter i alo imulated. The imulation diagram and output voltage waveform i given Fig 5 and Fig 6 repectively. n1 block, n 12 * 5 dc (14) C. Control Unit for Multilevel Inverter The witching i done i uch a way that voltage rie from zero to peak and then to zero forming poitive half cycle and imilarly in the negative half cycle ine wave. The intant of each witching i determined by the equation: in 1 O t ( ) (15) m III. IMULATION & REULT In order to verify the performance of the propoed ytem imulation of prototype model of 7 level and 31 level ytem i done in MATLAB/ imulink environment. Alo the THD performance of 7 level and 31 level ytem are compared. In the proce of imulation load i aumed a R-L load with R = 100 Ω and L = 55mH. The converter voltage i elected a 100 with MOFET witching frequency 20kHz. Figure 4. imulation diagram of even level inverter THD analyi of 31 level and 7 level how leer THD i preent in 31 level. A the level increae the output waveform approache more and more to the ine. Fig 7 and Fig 8 how the THD reult of even level and 31 level repectively. Figure 5 (a). imulation diagram of 31-level inverter International Journal of cientific Reearch in cience, Engineering and Technology (ijret.com) 644

5 I CONCLUION In thi paper a drive ytem i propoed for medium voltage and high power application in indutrie. Uing the baic even level higher level inverter can be developed.. Here up to 31 level i imulated. The propoed ytem require leer no of witche driver circuit and dc voltage ource. Alo the circuit how THD reult :7-level THD = % and 31-level of 3.05% which i very important for a indutrial application. I. REFERENCE Figure 5(a) : imulation diagram of flyback converter of 31-level inverter. Figure 6: imulink reult of output waveform of 31 level inverter Figure 7: FFT window even level inverter,thd = 21.56%. [1] Ebrahim Babaei and omayeh Alilu, "A new general topology for cacaded multilevel inverter with reduced number of component baed on developed H-Bridge," IEEE Tran.Indutrial Electronic,ol.61, no.8 Aug [2] K. Wang and Y. Li,"oltage balancing and fluctuation uppreion method of floating capacitor in a new modular multilevel converter," IEEE Tran.Ind. Electron,vol. 60, no. 5, pp , May [3] J. Ebrahimi, E. Babaei, and G. B. Gharehpetian, "A new topology of cacaded multilevel converter with reduced number of component for high-voltage application," IEEE Tran. Power Electron, vol. 26, no. 11, pp , Nov [4] M. Narimani and G. Mochopoulo, "A novel ingle-tage multilevel type full-bridge converter," IEEE Tran. Power Electron.vol. no. 1, pp , Jan [5] M. Farhadi Kangarlu and E. Babaei, "A generalized cacaded multilevel inverter uing erie connection of ubmultilevel inverter," IEEE Tran. Power. Electron,vol. 28, no. 2, pp , Feb Figure 8: FFT window of thirty one level inverter,thd = 3.05% International Journal of cientific Reearch in cience, Engineering and Technology (ijret.com) 645