HIGH STEP-UP DC-DC CONVERTER FOR FUEL CELL POWERED RESIDENTIAL POWER GENERATION SYSTEM

Transcription

1 HIGH STEP-UP C-C CONVERTER FOR FUEL CELL POWERE RESIENTIAL POWER GENERATION SYSTEM 1 ANJALY TERESA CHERIAN, 2 SURYA NATARAJAN 1 Student, 2 Assstant Professor E-mal: teresa.anjaly@gmal.com, suryanatarajan@gmal.com Abstract- Ths paper presents a new hgh voltage boostng C-C converter topology ntended for resdental fuel cell power systems. The proposed system conssts of a hgh voltage boostng dc dc converter to boost the fuel cell voltage to 350 V dc and a pulse-wdth modulated nverter wth flter to convert the dc voltage to 240V ac. The operatng prncple of the dc-dc converter s based on bootstrap capactors or charge pumps and seres boost nductors. Furthermore, although three swtches are used, no solated gate drver s needed nstead one half-brdge gate drver and one low-sde gate drver s used. Accordngly, the proposed converter s easy n analyss and smple n mplementaton. Smulaton and expermental results are demonstrated. Keywords- Fuel cell, Boost Converter, Bootstrap capactor, Voltage Converson Rato. I. INTROUCTION II. SYSTEM ANALYSIS Increasng global polluton levels and depletng fossl fuel resources have ncreased concerns and propelled research towards renewable, clean and effcent energy. Fuel cells have been consdered as a hghly promsng alternatve for envronmentally frendly renewable energy generaton due to ther characterstcs of beng renewable, clean and effcent. A fuel cell powered resdental power generaton system typcally conssts of a fuel cell stack feedng a hgh voltage boostng dc-dc converter followed by an nverter to convert the dc voltage to 240V ac so as to power the resdental loads. A typcal fuel cell powered resdental power generaton system s shown n Fg.1. Fgure 1: Typcal Fuel Cell Powered Resdental Power Generaton System The output voltage of fuel cell s very low; hence C-C converter s requred to boost the low fuel cell voltage to a regulated hgher voltage C. Fnally a C/AC nverter, wth output flter cascade-connected, s used to obtan AC voltage feedng the load. As generally recognzed, the hgh-voltage boost converters are wdely used n renewable energy systems such as solar cell system, fuel cell system etc. For the fuel cell system, t needs the hgh-voltage boost converter to transfer the low voltage to the hgh voltage whch wll be transferred to the AC output voltage va the C-AC converter. A. Fuel Cell Fuel Cell s a devce that converts the chemcal energy contaned n a fuel, usually oxygen and hydrogen, electrochemcally nto electrcal energy. Of the dfferent modelng methods avalable, the fuel cell here s modeled based on the chemcal fundamentals. Based on Chemcal fundamentals [5], the output voltage of a sngle cell s gven by the followng equaton. V Where FC ENernst V act V Ohmc Vcon (1) Nernst VFC the output voltage of a sngle s s cell; E s the electrochemcal thermodynamc potental of the cell, V act s actvaton polarzaton loss, V Ohmc s the ohmc voltage drop and V con s the gas transportaton loss. B. C-C Converter Fgure2 shows the proposed hgh voltage boostng converter, contanng three MOSFET swtches S, S and S, two charge pump capactors C and C, three charge pump dodes, and, one output dode, two nductors L and L, one output capactor C, and one output resstor R. The nput voltage s sgnfed by V, the output voltage s represented by V, the voltages across C, C,, and are shown by V, V, V, and V, respectvely, and the currents flowng through L, L, C and C are denoted by,, and, respectvely. 71

2 Fgure 2:Proposed hgh step-up converter The basc operatng prncple s based on charge pump prncple and boost nductors. Charge pumps use some form of swtchng devces to control the connecton of voltages to the capactor. For nstance, a two-stage cycle can be used to generate a hgher pulsed voltage from a lower-voltage supply. In the frst stage of the cycle, a capactor s connected across the supply, chargng t to that same voltage. In the second stage of the cycle, the crcut s reconfgured so that the capactor s n seres wth the supply to the load. Ignorng leakage effects, ths effectvely provdes double the supply voltage to the load (the sum of the orgnal supply and the capactor). There are 2 boost nductors namely L & L n the crcut confguraton whch are charged n parallel and dscharged n seres for boostng of the output voltage to the desred level. Thus the nput voltage, together wth energy stored n the two nductors along wth two charge pump capactors pump ther stored energy nto the output n seres thus boostng the voltage to the desred level.. Converter Analyss The varous assumptons taken for the analyss s gven as follows: 1) The blankng tmes between the swtches are Omtted. 2) The voltage drops across the swtches and dodes durng the turn-on perod are neglgble. 3) The voltages across capactors C b and C are e Assumed to be constant. beng turned on, s reverse based, but and are forward based, thereby causng C to be abruptly charged to V plus V, whereas due to S beng turned on, s reverse based, thereby causng C to be dscharged. At the same tme, the voltages across L and L are V plus V, thereby causng L and L to be magnetzed. Also, C releases energy to the output. The power flow durng ths mode s as shown n Fgure 3. In ths mode, the voltages across L and L, V and V, can be wrtten as Fgure 3:Power flow n mode1 Mode 2 [t t ]: urng ths mode swtches S and S are turned off, but S s turned on. ue to S beng turned on, dode s forward based, thereby causng C to be abruptly charged to V At the same tme, the nput voltage plus the energy stored n C plus the energy stored n L and L supples the load, thereby causng C to be energzed, C to be dscharged, and L and L to be demagnetzed. By dong so, the output voltage s boosted up, and s much hgher than the nput voltage. Accordng to the voltage-second balance, the voltages V and V, and V n ths mode can be expressed to be For the converter to be consdered, the PWM turn on types for three swtches and the voltages on the bootstrap capactors are tabulated n Table 1. TABLE 1 PWM TURN ON TYPES FOR SWITCHES AN VOLTAGES ON BOOTSTRAP CAPACITORS S S S V V 1- V 2V The analyss of the converter n contnuous conducton mode (CCM) wth Equal L1 to L 2 s explaned n two modes of operaton. Mode 1 [t t ]:urng ths mode, Swtches S and S are turned on, but swtch S s turned off. ue to S Fgure 5: Power flow n mode2. 72

3 Snce V and V are equal to V and 2V, respectvely, (2), (3), and (6) can be rewrtten to be (7) v v 2V L1 ON L2 ON V v 3V o L1 OFF vl2 OFF (8) By substtutng (7) nto (5) and (5), V and V can be rewrtten to be vl 1 OFF vl2 OFF 2V 1 vl 1 OFF vl2 OFF 2V 1 (9) (10) Fg.4 and Fg. 5 shows the key waveforms of the converter operated n contnuous conducton mode and the power flow n Mode 2 respectvely. sgnals are generated by comparng the snusodal reference sgnal and the trangular carrer sgnal. A PI control s also ncluded to regulate the output voltage of the nverter so as to power a resdental load. The feedback loop of the proposed converter s mplemented n the smulaton usng Proportonal Integral (PI) control method. The PI feedback control method adds postve correctons, removng the error from a system s controllable varable. PI feedback control method conssts of two actons the proportonal acton and the ntegral acton. Zegler-Nchols method s appled to desgn the PI controller. III. SIMULATION AN EXPERMENTAL RESULTS To valdate the above study, MATLAB/Smulnk platform has been used to smulate the proposed topology. The crcut s smulated for an nput voltage of 24V. The varous crcut parameters used for the smulaton s tabulated n Table 2. TABLE 2 CIRCUIT PARAMETERS Components Specfcaton L = L 170µH C 100 C 220µF C 680µF R 400 ohm The fuel cell s smulated usng MATLAB/Smulnk based on the chemcal fundamentals. Fgure 6 shows the smulnk model of the fuel cell. The fuel cell system s smulated for a sngle cell and then t s multpled for the 15 cells so as to obtan the desred nput voltage. Fgure 4: Key waveforms for CCM of converter The converter could also operate n dscontnuous conducton mode (CM) wth dfferent values of nductances. C. Inverter The dc-ac converter, also known as the nverter, converts dc power to ac power at desred output voltage and frequency. The dc power nput to the nverter s obtaned from the hgh voltage boostng dc-dc converter whch boosts the fuel cell voltage. In ths paper, snusodal pulse wdth modulaton technque s used to generate gatng pulses for the four swtches of the sngle phase nverter. The gatng Fgure 6: Smulnk Model of the fuel cell. Fgure 7:Smulnk Model of Inverter Subsytem 73

4 The nverter subsystem for generatng gatng sgnals to the nverter swtches s gven n Fg7. Fg.8 shows the Smulnk model for the complete system. The smulaton result of the converter as shown n Fgure 9 gves the waveforms of the nput voltage, gatng pulses to the swtches, voltage across the nductors and the current flowng through the nductor. The output voltage of the nverter after smulaton s shown n Fgure 10. S and a low sde gate drver FO3180 s used to drve swtch S.Fg. 12 to Fg. 14 shows the converter nput voltage,gatng sgnals to swtches S and S and output voltages respectvely as obtaned from CRO. Fgure 11: Hardware Setup Fgure 8: Smulnk Model of the System. Fgure 12: Input voltage Fgure 13:Gate pulse to swtch S 1 and S 3 Fgure 9:Smulaton Result for the converter. Fgure 10:Output Voltage of Inverter. The hardware setup of the converter s shown n Fg.11 The hardware crcut conssts of manly the converter crcut and the control crcut. The control for the converter s provded usng dspic30f2010. The converter crcut also conssts of the assocated gate drvng crcuts for the MOSFETS. The half brdge gate drver FAN7392 s used to drve swtches S and Fgure 14: Converter output voltage TABLE 3 COMPARISON WITH IFFERENT TOPOLOGIES Name of Converters Voltage Converson Rato Presented Topology Reference [10],Topology 3 (3+)/(1-) (3-)/(1-) 74

5 Conventonal Boost Reference [12] Reference [10], Topology 1 Reference [10], Topology 2 V o / V /(1-) 2*/(1-) (1+)/(1-) 2/(1-) VOLTAGE CONVERSION RATIO Vs UTY CYCLE Proposed,type1 conventonal [12] [10],2 [10], Fgure 15: Smulaton result comparng dfferent Topologes On comparng dfferent topologes of C-C converters n Table 3 based on ther voltage converson rato, t s nferred that the proposed hgh voltage boostng C-C Converter provdes the hghest voltage converson rato. Ths comparson s shown n Fgure 15. CONCLUSION AN FUTURE ENHANCEMENT Ths paper has presented a new hgh step-up C/C converter wth pulse wdth modulated nverter usng a fuel cell at the nput. The topology s ntended for powerng the resdental load. The paper s focused on an example of the 100W hgh step-up C/C converter for resdental fuel cell power systems. The operatng prncple, system methodology and smulaton results are presented and analyzed. A complete power condtonng system for a fuel cell powered dstrbuted resdental power generaton system, ncludes a C-AC nverter followng the C-C converter to provde regulated AC supply power. Future work could nclude development of an economcal and effcent C-AC nverter whch would result n a complete power condtonng system for such an applcaton. REFERENCES [1] K. I. Hwu, C. F. Chuang, and W. C. Tu, Hgh Voltage-Boostng Converter n twenty-seventh Annual IEEE conf,appled Power Electroncs Conference and Exposton,Feb 2012 [2] H. Tao, J. L. uarte, and M. A. M. Hendrx, Lne-nteractve UPS usng a fuel cell as the prmary source, IEEE Trans. Ind. Electron., vol. 55, no. 8, pp , [3] K. I. Hwu and Y. T. Yau, Voltage-boostng converter based on charge pump and couplng nductor wth passve voltage clampng, IEEE Trans. Ind. Electron., vol. 57, no. 5, pp , [4] K. C. Tseng and T. J. Lang, Novel hgh-effcency step-up converter, IEE Proc. Electr. Power Appl., vol. 151, no. 2, pp , [5] Mng, LIU, ynamc Model of Proton Exchange Membrane Fuel Cell and Implementaton Tongj Unversty. IISB Conference Fraunhofer, Germany [6] W. L and X. He, A famly of solated nterleaved boost and buck converters wth wndng-cross-coupled nductors, IEEE Trans. Power Electron., vol. 23,no. 6, pp , [7] K-Bum Park, Hyun-Wook Seong, Hyoung-Suk Sm, Gun-Woo Moon and Myung-Joong Youn, Integrated boost-sepc converter for hgh step-up applcatons, IEEEPESC 08, pp , [8] Q. Zhao and F. C. Lee, Hgh-effcency, hgh step-up dc-dc converters, IEEE Trans. Power Electron., vol. 18, no. 1, pp , [9] E. H. Ismal, M. A. AI-Saffar and A. J. Sabzal, Hgh converson rato CC converters wth reduced swtch stress, IEEE Trans. Crcuts and Systems I: Regular Papers, vol. 55, no. 7, pp , [10] Lung-Sheng Yang, Tsorng-Juu Lang and Jann-Fuh Chen, Transformerless C-C converters wth hgh step-up voltage gan, IEEE Trans. Ind. Electron., vol. 56, no. 8, pp , [11] B. Axelrod, Y. Berkovch and A.Ionovc, Swtched-capactor/swtched nductor structures for gettng transformerless hybrd C-C PWM converters, IEEE Trans. Crcuts and Systems I: Regular Papers, vol. 55, no. 2, pp , [12] C. E. Slva, R. P. Bascope and. S. Olvera, Proposal of a new hgh voltage-boostng converter for UPS applcaton, IEEE ISIE 06, pp , [13] E. H. Ismal, M. A. AI-Saffar, A. J. Sabzal and A. A. Fardoun, A famly of sngle-swtch PWM converters wth hgh voltage-boostng converson rato, IEEE Trans. Crcuts and Systems I: Regular Papers, vol. 55, no. 4, pp , [14] K. I. Hwu and Y. T. Yau, KY converter and ts dervatves, IEEE Trans. Power Electron., vol. 24, no. 1, pp , [15] K. I. Hwu and Y. T. Yau, A KY boost converter, IEEE Trans. Power Electron., vol. 25, no. 11, pp ,