Analysis and Simulation of Parallel DC-DC Converter fed Sonar Power Amplifiers Anu John, V. N. Panchalai, Preethi Thekkath

Transcription

1 SSN: SO 9:8 ertfed nternatonal Journal of nneern and nnoate Technoloy (JT) Volue 3, ssue 8, February 4 Analyss and Sulaton of Parallel DD onerter fed Sonar Power Aplfers Anu John, V. N. Panchala, Preeth Thekkath Abstract Parallel operaton of power aplfers as to deelop hher output power at low current stress. To proe the relablty of parallel connected conerter systes, the load current ust be dstrbuted aon the conerter odules. The total power delered at the output s the su of the nddual odule powers. n parallel operaton, the oltae across each odule wll be the sae and t s the current that decdes the aount of power delered to the load. By specfyn the requred output power fro each odule and known the load pedance, the requred output current can be calculated whch seres as the reference. The output current fro nddual odules are extracted and copared wth ther respecte reference current quantty to enerate the control snals. These control snals are used to swtch the DD conerter fed SONAR power aplfer. Thus, the output of the DD conerter s adjusted accordn to the reference current specfed and thereby the nput to the power aplfer ets adjusted. The feasblty of the proposed control s deonstrated by sulaton results. Sulaton s done usn MATAB/SMUNK. ndex Ters Dtal ontrol, DD onerter, Power Aplfer (PA), Pulse Wdth Modulaton (PWM).. NTRODUTON SONAR an underwater equalent of radar, explots acoustc enery for detecton, localzaton, trackn and classfcaton of underwater tarets. The ter sonar s an acrony for Sound Naaton and Rann. Sonar syste conssts of underwater transducers, frontend snal condtonn unts, snal processors, and dsplays. Sonar transducers transt acoustc power and pck up the echo returns or erely lsten to the underwater sounds, process the snal and prode nforaton about tarets on the dsplay unts. [] A typcal snal eneraton crcut whch conssts of a hh end processor enerates a snal wth partcular frequency, pulse lenth and pulse repetton rate. The snal s then en to the power aplfer for aplfcaton. The power aplfers n turn are connected to sonar transducers eleent whch enerally conssts of pezocrystals for exctaton. The power aplfer (PA) s a key eleent n transtter systes, aed to ncrease the power leel of the snal at ts nput up to a predefned leel requred for the transsson purposes. The power aplfers are usually proded the D supply they requre fro a swtch ode power supply. The swtch ode power supples used wll hae to tolerate aratons n ts nput supply whch s coon n shps, especally when lare loads are turned ON. Relable supply s of utost portance to sonar syste. An unrelable supply can daae whole syste s perforance and underne ts usefulness, especally durn crtcal war lke condtons. n power supply systes for hher power deand the parallel operaton of standard conerter odules s taken ore and ore nto consderaton. There are two reasons why conerters are operated n parallel. One s to prode ore current than aalable fro a snle unt and wll help to reduce the current ratn of the deces used. The second reason to connect unts n parallel s to prode a backup when one unt fals. Ths s also calledn redundancy. The parallel connecton offers seeral adantaes lke, proe syste relablty, enhance redundancy, reduce cost of deelopent, coer wde power rane, exstn systes extended easly []. The an proble occurrn wth the parallel operaton s the accurate dstrbuton of the total power to each odule to aod stress of a snle odule. The preous ethods to equalze the odules nductor currents are presented n lteratures [3][6].Ths paper dscusses control of current sharn n parallel connected DD conerter fed power conerter sonar aplfers usn tolerance band control. The sulaton of parallel DD conerter fed power aplfer s pleented n ths paper. The power aplfer crcut s ated usn unpolar PWM technque. These snals are external snals for the SONAR applcaton that are proded by an external atn crcut. Hence these snals are not aalable to prode the control to the power aplfer and thus we control the nput to the power aplfer. We control the atn to the DD conerter wth a feedback loop fro the output and obtan the requred current sharn property. MATAB/SMUNK sulatons are carred out to erfy the feasblty of the project.. RUT AND WORKNG OVRVW To control the output of the power aplfer, we can ether adjust the nput to the syste or we can adjust the duty cycle of the swtchn snals. For the SONAR applcaton, the PA swtchn snals are enerated fro an external source and are readly aalable as PWM snals. Hence, the only alternate aalable s to adjust the nput to the syste for the requred current sharn. We use a DD conerter at the nput sde of the PA for ths purpose whose atn s adjusted to produce the requred output at ts ternals that seres as the nput to the PA. Parallel syste s obtaned by connectn toether the output ternals of two slar odules. The syste conssts of control crcuts, nerter crcut or full brde crcut, dode brde crcut, power transforer and flter crcut. 96

2 SSN: SO 9:8 ertfed nternatonal Journal of nneern and nnoate Technoloy (JT) Volue 3, ssue 8, February 4 F.. rcut dara of one DD conerter fed sonar power aplfer The feedback fro the output s used to dre the DD conerter brde. The controlled output of DD conerter s then rectfed by a dode brde crcut and then fed to step up transforer to et the requred output leel. flter s used to reduce haronc content. The output of the transforer s then fed nto the power aplfer brde whose swtchn s controlled by externally enerated PWM snals. Ths nerter pulses are stepped up and fltered out to excte the transducer crystals. The total acoustc power radated by the projector s P, whch s less than the electrcal power suppled to t, Pe, and the rato of these s the projector effcency,. Thus, ncreasn Pe can result n ncreased power radated by the projector. Ths s acheed by a power aplfer crcut shown n F.. The power deeloped at the ternal s dependent on the supply oltae V n, the odulaton ndex a, the transforer turns rato N, the flter effcency etc. The PA brde s controlled by PWM snals that are external snals enerated fro a separate control card. Hence, we use a DD conerter crcut wth controllable swtches. The DD conerter s coposed of an nerter and a rectfer. The power aplfer s coposed of an nerter. The nerter conssts of a transforer and four power MOSFTs used as controllable swtches H,, H and. The transstors n each swtchn le are dren by nonoerlappn oltaes that are out of phase by 8. The axu duty cycle of the atetosource oltaes s slhtly less than 5%. The waefors of the ate to source oltaes should be nonoerlappn to aod crossconducton. The nddual ate control snal for the swtches are to be proded across the ate (base) and source (or etter) ternals of a partcular swtch. The ate control snals are low oltae snals referred to the source (etter) ternal of the swtch. For an nchannel GBT, when ate to source oltae s ore than threshold oltae for turnon, the swtch turns on and when t s less than threshold oltae the swtch turns off. The threshold oltae s enerally of the order of 5 olts but for qucker swtchn the turnon ate oltae antude s kept around 5 olts whereas turnoff ate oltae s zero or lttle neate (around 5 olts). The solaton transforers of the DD conerter and the power aplfer are not requred to store enery. ts anetzn nductance should be lare enouh to reduce the current throuh ths nductance. On the other hand, f the anetzn nductance s too lare, t requres a lare nuber of turns and s physcally lare. deally, the dc coponent of the current throuh the anetzn nductance s zero. A coupln capactor ay be added n seres wth the prary wndn to achee zero dc coponent of the current throuh the anetzn nductance and thus reoe an balance of the anetc core. The fullbrde conerter s well suted to hhpower applcatons, usually fro.5kw to seeral klowatts. t offers the hhest power leels aon all conerters. n ery hhpower applcatons, nsulated ate bpolar transstors thyrstors, or MOSFTcontrolled thyrstors are used as swtchn deces. n addton, two or ore power swtchn deces ay be connected n parallel to ncrease current capablty of eery swtch and output power leels [7]. The brde rectfer s suted for hh output oltae applcatons because the oltae stress of the dodes s V n /n, whch s half of the transforer centertapped rectfer. Ths rectfer s not sutable for lowoltae applcatons because two dodes conduct when two swtches are ON, and the total forward oltae across the two dodes ay becoe coparable wth the output oltae, resultn n low effcency. [8][]. SMUATON AND RSUTS MATAB/Sulnk odel of the parallel DD conerter fed power aplfer s shown n F.. They are connected n parallel for hher power ratn. The desn paraeters for the sulaton crcut are en n the Table. The flter s desned for a cut off frequency of 5 Hz. t wll allow all the frequences below 5 Hz to pass throuh and reject all the hh frequences. The desn s erfed usn MATAB bode plot shown n F. 3. 3dB pont n the antude plot es the cutoff frequency alue. The desned alue of cutoff frequency 5Hz s obtaned at the 3dB pont and hence we can conclude that the desned flter s satsfyn the paraeters. 97

3 Phase (de) Mantude (db) A. Reference urrent alculaton SSN: SO 9:8 ertfed nternatonal Journal of nneern and nnoate Technoloy (JT) Volue 3, ssue 8, February 4 The control snals are enerated by coparson of the power aplfer output current wth a reference current as shown n Table. n the proposed DD conerter fed power aplfer, the control snals enerated are used to control the swtchn of the DD conerter to pleent proper current sharn. The control snals for the power aplfer are externally enerated and hence the user has no access to t. The antude of the reference current specfed deternes what percentae of the total requred power has to be shared between the parallel odules. The total output power requred and the nddual odule powers are oerned by the follown equaton, P total P P () Where, P s the power output of odule and P s the power output of odule. P P R R f odule has to enerate P Watts of power and odule P Watts, then the RMS currents to be to be produced s calculated fro () and (3) as below, P P R R The reference s specfed as the peak alue of current to be produced. t s calculated fro (4) and (5) as below, ref ref Thus, the equatons (6) and (7) e the alues of the reference current. STP () (3) (4) (5) (6) (7) TAB. Sulaton Syste and Desn Paraeters nput supply 3 V D SUPPY Output power W Output frequency 5 Hz PA swtchn frequency, f s 5 khz Dc/dc conerter transforer turns rato PA transforer turns rato.9 Dcdc flter alues =.nh, =.pf PA flter alues f =7.5H, f =.375µF oad pedance ΩΩ 3 db Pass Band utoff frequency=5 Hz Bode Dara Frequency (Hz) Stop Band F. 3. MATAB/Sulnk bode dara of flter transfer functon TAB. ONTRO AGORTHM OF TH DD ONVRTR SWTHNG ref act H on, off ref < act on, H off ref act H on, off ref < act on, H off DD ONVRTR BRDG [D] [D] POWR AMPFR BRDG [AA] D [] D3 [A] P [] P3 [] [4] [3] D SUPPY [BB] D [DD] D4 T A B RTFR [B] P [D] P4 T3 [V4] f [V] f R [V3] DD ONVRTR BRDG POWR AMPFR BRDG [] D5 [GG] D7 [D3] A [A] P5 [] P7 [] f [5] [D] [FF] D6 [HH] D8 T B RTFR [B] P6 [D] P8 T4 [V] f Requred Total Power Dscrete, Ts = e6 s.. Requed RMS urrents poweru Requed Power fro odule Requred power fro odule R n n Out Out Requred Peak urrents 4.47 [RF] [RF] [AA] [BB] [] Out Out n [] [] [FF] [GG] Out Out n [] [A] [] [B] Out Out n [DD] n [RF] [HH] n [RF] [D] GNRATON OF URRNT RFRN FDBAK ONTROR FDBAK ONTROR PWM SGNAS TO POWR AMPFR F.. MATAB/Sulnk odel of the DD conerter fed power aplfer [4] 98

4 H Voltae (V) H Voltae (V) Voltae (V) Voltae (V) urrent (A) urrent (A) urrent (A) B. Generaton of Gatn Pulses SSN: SO 9:8 ertfed nternatonal Journal of nneern and nnoate Technoloy (JT) Volue 3, ssue 8, February 4 The DD conerter brde s dren by snals obtaned fro the feedback loop. The reference current s ade to follow the actual odule currents as shown n F. 4. The reference current s calculated fro the power requreent of each odule. PWM wth Unpolar oltae swtchn technque uses two nerted sne waes as odulatn snals for the two les of the nerter. Here, the les of the full brde nerter are controlled separately by coparn V tr wth V control and V control, respectely as shown n F. 5. Unpolar SPWM oltae odulaton type s selected because ths ethod offers the adantae of effectely doubln the swtchn frequency of the nerter oltae, thus akn the output flter saller, cheaper and easer to pleent.. Output Waes For the alues en n Table and for a load pedance of Ω, let us specfy that each of the odules supply the total power of W equally, e, each odule supply W. As per the desn en n secton A, the rs reference current s 3.6A and peak s 4.47A for each odule. The current waefors n F. 6 show that, the actual current enerated fro each odule equals the reference specfed. The oltae waefors n F. 7 show that, the oltae across each ternal s the sae. Hence, the proble of the unt wth the 5 hher output oltae supplyn all the current untl t reaches ts current lt settn could be aoded. The Power waefors n F. 8 show that, each odule enerates the aount of power specfed. Thus, fro the aboe analyss t s clear that the nddual odules can be ade to operate at desred power by specfyn the reference current to the controller. URRNT FROM MODU Peak=4.8A RMS=3.A.5.5 URRNT FROM MODU.5 3 Peak=4.8A RMS=3.A.5.5 TOTA OUTPUT URRNT.5 3 Peak=9.8A RMS=6.9A Actual urrent Reference urrent F. 4. Generaton of swtchn pulses DD onerter (a) oparson of reference and actual current (b) Gatn pulses to H Vcontrol Vcontrol Vtr F. 5. Generaton of PWM swtchn pulses for PA (a) oparson of Reference and ontrol Snals (b) Gatn Pulses to H (c) Gatn Pulses to (d) Gatn Pulses to H (e) Gatn Pulses to F. 6. MATAB/Sulnk waefor of current for a power of W (a) urrent fro odule (b) urrent fro odule (c) Total output current POWR AMPFR NVRTR VOTAG (NONFTRD) TOTA OUTPUT VOTAG 5 5 RMS=363.8V OUTPUT VOTAG FROM PA 5 5 RMS=363.8V OUTPUT VOTAG FROM PA 5 5 RMS=363.8V F. 7. MATAB/Sulnk waefor of oltae for a power of W (a) Nonfltered PWM output fro transforer ternal (b) Voltae of odule (c) Voltae of odule (d) Total output oltae 99

5 Power (W) Power (W) Power (W) SSN: SO 9:8 ertfed nternatonal Journal of nneern and nnoate Technoloy (JT) Volue 3, ssue 8, February 4 OUTPUT POWR Power=W OUTPUT POWR TOTA OUTPUT POWR Power=W Power=W F. 8. MATAB/Sulnk waefor of power output of W (a) Power output of odule (b) Power output of odule (c) Total power output ) onstant supply, Varyn oad, onstant reference current A. Sulaton Analyss 3) Varyn supply, Varyn oad, onstant An analyss s done for the results obtaned for the reference current follown condtons, ) onstant supply, Varyn oad, Varyn reference current F. 9. Plot shown actual current follown reference current wth aryn load F.. Plot shown constant current wth aryn load

6 SSN: SO 9:8 ertfed nternatonal Journal of nneern and nnoate Technoloy (JT) F.. Plot shown constant current wth aryn supply Volue 3, ssue 8, February 4 F. 9 shows that the reference current s decreased wth ncreasn load. Ths araton n reference current s fed as nput to the controller whch controls the atn to the DD conerter thereby akn the actual current to follow the reference. F. shows that the current reference s kept constant and the load pedance s ared. The aratons at the output load do not cause the actual current to deate fro the reference. F. shows that the current reference s kept constant and the nput oltae s ared. The aratons at the supply oltae do not cause the actual current to deate fro the reference. V. ONUSON The proposed sonar syste fnds applcaton anly for underwater naaton and surellance. lan uses nclude deternaton of water depth, appn the ocean floor, locatn arous objects n the ocean, deternn the characterstcs of ocean botto, and een fsh fndn. Sulaton of parallel connected DD conerter fed power aplfer odules s dscussed n the paper. The parallel connecton offers seeral adantaes lke, proe syste relablty, enhance redundancy, reduce cost of deelopent, coer wde power rane, exstn systes extended easly. The accurate dstrbuton of the total power to each odule s done usn tolerance band current control ethod. The power aplfer s a class D aplfer whch s also known as the swtchn aplfer. t offers hh effcency copared to the lnear power aplfer. ontrol of PA usn DD conerter swtches prodes relable operaton to the syste. Analytcal, sulaton results of the power aplfer hae been presented. RFRNS [] Technoloes for sonar systes Technoloy Focus Bulletn of Defense Research and Deelopent Oranzaton, Vol. 8 No. 4,pp., Auust. [] M. Jordan, U397 load share splfes parallel power supply desn, Untrode Applcaton note U9. [3] S.uo, Z. Ye, R. n, and F. ee, A classfcaton and ealuaton of paralleln ethods for power supply odules, PS 99 proc., ol., June 999, PP. 998 [4] B. T rn and M. M Joanoc, Analyss, Desn and perforance ealuaton of Droop current sharn ethod, AP proc, ol., Feb., pp. 354 [5] V. J Thottuel and G. Verhese, Stablty analyss of parallel D/D conerters wth acte current sharn, PS 96 proc., ol., june 996, pp. 886 [6] R. H Wu, T. Kohaa, Y. Kodera, T. Nnoa, and F. hara, load current sharn control for parallel operaton of DtoD conerters, PS 93 proc., June 993, pp. 7 [7] M. K. Kazerczuk Fullbrde PWM D D onerter n Pulsewdth Modulated D D Power onerters, John Wley & Sons, td Dayton, Oho, USA, 8, pp [8] B. R. n and.h. hao A New ZVS D/D onerter wth Three APWM rcuts Trans. On ndustral lect., VO.6,NO.,October 3 [9] J.W. K, H.S. ho, and B. H. ho A Noel Droop Method for onerter Parallel Operaton eeetrans.s on Power lect., VO. 7, NO., January [] S. hae, Y. Son, S. Park, and H. Jeon Dtal urrent Sharn Method for Parallel nterleaed D D onerters Usn nput Rpple Voltae Trans. On ndustral nforatcs,vol. 8,No. 3, Auust [] Jaber A. A.Qahouq,. Huan, and D. Huard Sensor less urrent Sharn Analyss and Schee for Multphase onerters Trans. On Power lect., Vol. 3, No. 5, Septeber 8 [] Ned Mohan. T. M. Undeland and W. P. Robbns, Power lectroncs: onerters, Applcatons and Desn, 3, Thrd edton, John Wley and Sons. AUTHOR S PROF Anu John receed the BTech. deree n lectrcal and lectroncs nneern fro TocH nsttute of Scence and Technoloy, Arakkunna, Kerala, nda n. urrently workn towards the MTech. deree n Power electroncs at TocH nsttute of Scence and Technoloy (under the ochn Unersty), Arakkunna, Kerala, nda. V. N. Panchala receed hs B deree n lectrcal and lectroncs nneern fro Reonal nneern ollee, Truchrappall and MTech n lectrcal nneern fro T, Madras n the year 996 and 8 respectely. He s an assocate eber of the nsttuton of nneers nda (AM). urrently he s workn as a Scentst D wth Naal Physcal and Oceanoraphc aboratory, Koch. Preeth Thekkath s currently workn as Professor n lectrcal and lectroncs nneern departeent at TocH nsttute of Scence and Technoloy, Arakkunna, Kerala, nda.