Implementation of High Voltage Gain RS Cell- Based DC-DC Converter for Offshore Wind

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1 IJCTA, 1(2), 217, pp Inernaional Science Press Closed Loop Conrol of Sof Swiched Forward Converer Using Inelligen Conroller 147 Implemenaion of High Volage Gain RS Cell- Based DC-DC Converer for Offshore Wind B. Veeramuhu pandian* and P. UshaRani** Absrac : This paper proposed a new high-volage gain resonan swiched-capacior dc-dc converer for high-power offshore wind energy sysems. The proposed new dc-dc converer is characerized by he resonan swiching ransiions o achieve minimal swiching losses and maximum sysem efficiency. Here, he converer operaes a fifeen imes as high as he inpu volage wih a small device coun. Finally, he performance of he proposed converer is evaluaed wih he simulaion as well as experimenal resuls of a prooype sysem. Keywords : High volage gain, offshore wind energy, resonan swiched-capacior (RSC) converer, resonan swiching ransiions. 1. INTRODUCTION Offshore wind farms are growing rapidly because of heir comparaively more sable wind condiions han on-shore and land-based wind farms [1], [2]. Offshore 51-MW marine urbines are becoming more aracive for he wind power indusry [3], [4]. In paricular, hey increase he efficiency and reduce generaion cos, compared o previous wind urbine echnologies[5].i will increase sizes of he componen. Therefore, bulky and huge elecrical componens have high invesmen coss because of he mos difficul erecion and he equipmen ransporaion from he shore o he insallaion sies [6]. An opimal power conversion sysem should feaure high-power densiy, high efficiency, high reliabiliy, and low coss for high-power offshore wind energy applicaions. In his regard, high -volage dc (HVDC) ransmission promises a very flexible and efficien echnology for offshore wind farms ha requires power conversion sysems o sep-up and conrol he wind urbine oupu. A convenional HVDC sysem uses an AC line frequency (5/6 Hz) ransformer o boos he volage and AC-DC converers for recificaion and power flow conrol [7][9]. This echnology is robus and reliable, bu i causes a considerable increase in weigh and volume, which leads o higher insallaion cos. A high-power densiy can be obained by replacing he bulky 5/6-Hz ransformers wih high-frequency ransformers [1][12]. Bu, highfrequency ransformers wih large urn raios are difficul o design a high volages and mega power levels because of he enormous expense of he magneic maerial, core, and dialecic losses. To overcome he increasing power losses and mainain a high-power densiy, i is expeced ha large marine urbines will require a higher volage wih high-volage gain dc-dc conversion sysems o inerface wih he power ransmission neworks. Single-module dc-dc boos converers can heoreically achieve infinie volage conversion raios bu pracically, he maximum gain is limied by circui imperfecions, such as parasiic elemens and swich commuaion imes [13], [14]. Muliple-module boos converers have been proposed o achieve high conversion raios for applicaions o offshore wind farms [15]. Recenly, he common * Ph.D Scholar Deparmen of Elecrical & Elecronics Engineering J.N.N Insiue of Engineering, Chennai. Veesan9113@yahoo.com ** Professor Deparmen of Elecrical & Elecronics Engineering R.M.D Engineering College, Chennai. pusharani71@yahoo.com

2 148 B. Veeramuhu pandian and P. UshaRani ypes of swiched-capacior (SC) converers are considered as an aracive soluion for meeing he requiremens, such as high-power densiy and conrol simpliciy. In [16] a resonan SC (RSC) converer was invesigaed, where an exra inducor was added o form a sinusoidal manner wih he capaciors o perform a sof swiching. In [17] a mulilevel RSC opology was proposed wih significan benefis, including a modular srucure, low-volage sress of he swiches, and reduced swiching loss. On he oher hand, a large number of capaciors, high passive componen losses, and ineviably large physical size of he converers have limied he use of hese opologies in high-volage gain offshore wind energy sysems. A 55kW (he oupu volage is hree imes he inpu volage) flying-capacior dc/dc converer was inroduced for hybrid elecric vehicles [18]. The major drawbacks are he nonmodular srucure, complicaed swiching scheme, and low-volage gain. An RSC volage Tripler an inerleaving capabiliy and high efficiency and Neverheless, i sill has several problems including he passive componen couns when a high-volage gain is required for high-power applicaions due o he low-volage conversion raio of he circui. To solve he problems lised previously, his paper presens a new high-gain RSC dc/dc converer for offshore wind energy sysems. The proposed converer combines he oupu of wo modular cells o reduce he device coun, oupu capaciance requiremens, and oal capacior power raing. The principle of a sof-swiching operaion and oupu volage analysis of he proposed converer are described in deail. The oupu capaciors are charged and discharged coninuously by an 18 phase shif wih respec o each oher o eliminae he oupu volage ripples wihou adding exra componens. In his paper, he series modular and cascade RSC configuraions are inroduced o increase he reliabiliy and reduce he conrol complexiy. These configuraions are verified by a simulaion and heir efficiency, volume, weigh, and device coun are compared wih a counerpar o highligh is advanages for high -volage and highpower offshore winds applicaions carried ou o evaluae he feasibiliy of he proposed converer. 2. TOPOLOGY A. Proposed RSC configuraion Fig. 1 shows he general block diagram of hree-phase generaed AC volage and an AC-DC converer in he fron-end of he proposed RSC converer. A large capacior is assumed o be used for energy sorage a he oupu of he ac-dc converer. The RSC converer consiss of hree modular cells which use a new arrangemen of he solid-sae swiches, diodes, capaciors, and inducors. B. Principle of he Proposed RSC Converer Operaion Fig. 2 presens a fifeen level RSC converer wih hree sages. The RSC converer is composed of six resonan capaciors (C r1, C r2, C r3, C rb1, C rb2 and C rb3 ), wo oupu filer capaciors (C o and C bo ), four resonan inducors (L r1, L r2, L r3, L rb1, L rb2 and L rb3 ), wo oupu resonan inducors (L o and L bo ), six diodes (D 1, D 2, D 3, D o, D b1, D b2,d b3 and D bo ), and four swiches (S 1, S 2, S b1, and S b2 ). In his paper, subscrips and b represen he corresponding variables o he circui componens a he op and boom cells, respecively. The swiches (S 1, S 2 ) and (S b1, S b2 ) are conrolled complemenarily wih a 5% duy cycle o minimize he conducion losses in he power devices and passive componens. Here, he following assumpions are made o simplify he analysis: 1. All he swiches, diodes, capaciors, and inducors are ideal. 2. The swiching frequency is less han he resonan frequency o achieve a zero-curren swiching (ZCS). 3. V s is an ideal dc volage source and he load is modeled by a pure resisor (R load ). Mode 1: In his firs mode S 1, S 2 and S 3 are on and S b1,s b2,s b3 and S b3 are mainaining off condiion. In his case D 1, D 2 and D 3 are forward bias condiion and D rb1, D rb2, D rb3 are reverse bias condiion so ha here is no curren flow hrough he lower boom of he circui. The upper side inducance and capaciance are sared o charging and anoher lower par swiches sar o discharging he energy o he load.

3 Implemenaion of High Volage Gain RS Cell- Based DC-DC Converer for Offshore Wind 149 THREE PHASE AC SUPPLY ACDC CONVERTER SWITCHED CELL LOAD PWM GENARATION FOR CONVERTER SWITCHED CELL BOTTOM MODULER CELL PWM PULSES FOR SWITCHED CELL Figure 1: Block diagram of he proposed RSC converer Top modular cell C o Swich-capacior-diode cell D1 D2 D3 L D Cr1 Cr2 Cr3 S1 Lr1 S2 Lr2 S3 Lr3 Vin V Load Crb1 Crb2 Crb3 Sb1 Lrb1 Sb2 Lrb2 Lrb3 Sb3 Lb Db Db1 Db2 Db3 Sage 1 Sage 2 Sage 3 Cb Boom modular cell Figure 2: Topology of he proposed RSC converer Mode 2: In his mode, he upper swich S 3 is on in his case D 3 is forward biased. The oher swiches kep off condiion so is sar o discharge he energy o he load o mainain he volage as consan.

4 15 B. Veeramuhu pandian and P. UshaRani Mode 3: In his mode, he boom swiches S b1, S b2, S b3 are conducs and s 1, s 2, s 3 are no conduced. In his case C r1, C r2, C r3, C rb1, C rb2 and C rb3, L rb1, L rb2 and L rb3 are charging.the boom inducance and capaciance ge sar o discharging. Mode 4: In his mode S 1, S 2 and S b3 are conducs and s b1, s b2 and s 3 are no conducs. The D 1, D 2, D 3, are forward biased and D b1, D b2, D b3 are reverse biased. The capaciance C r1, C r2 and C rb3 are charging and anoher capaciance is discharging he energy o mainain he oupu volage as consan. C D1 D2 L D Vs S1 Sb1 Cr1 Lr1 Crb1 Lrb1 S2 Sb2 Cr2 Lr2 Crb2 Lrb2 Lb Db I V Rload Db1 Db2 Cb ( a) C D1 D2 L D S1 Cr1 Lr1 Cr2 Lr2 I Vs Crb1 Crb2 V Rload Sb1 Lrb1 Lrb2 Lb Db Db1 Db2 Cb ( b)

5 Implemenaion of High Volage Gain RS Cell- Based DC-DC Converer for Offshore Wind 151 C D1 D2 L D S1 Cr1 Lr1 S2 Cr2 Lr2 I Vs Sb1 Crb1 Lrb1 Sb2 Crb2 Lrb2 Lb Db V Rload Db1 Db2 Cb () c Figure 3: Operaing modes of he -level RSC converer. (a) Mode I (b) Mode II and (c) Mode III Mode 6: In he final mode boom swiches are urn on and upper swiches are mainaining off condiion. In his case C rb1, L rb1, C rb2, L rb2, C rb3, L rb3 are charging and he upper capaciance and inducance are discharging he energy o mainain he oupu volage as consan. All he above modes of operaion diagrams are shown in fig3.through he fig3.we will know basic operaion of he proposed RSC cell based converer operaions and also derived expression for oupu volage and curren ec., Applying he charge balance principle o C leads o P ò = 2 d V æ P P ilo ö d d 3 4 () 2 ç V çè 3 ø V ò ò (1) Where P and V are he oupu power and oupu volage respecively. By ignoring he impac of he shor imes 1 2 and 3 4. Therefore, equaion 1 can be rewrien as P i Lo () = sin( r ) (2) V By applying he principle of charge balance o C r2 Ts/ 2 ò ( icr2( ) d = T s ò ilo() d (3) T/2 s Therefore,he resonan capacior and inducor currens and he oupu filer capacior currens of C o and C bo are P i Cr2 () = i Lr2 () = sin( r ) (4) V 2 P i Cr1 ( ) = i Lr1 () = 2 P sin( V r ) (5) i Cr () = ìï P í Ts/2 ìï P í T ï ïî V ï ïî V S /2 Ts (6)

6 152 B. Veeramuhu pandian and P. UshaRani Mode i Crb () = ìï P í ï ïî V I II III IV sin( r ) P Ts/2 ìï P í ï ïî V T S Ts (7) ( a) S & S b1 b2 ( b) S & S 1 2 i in () c P V ( d) ilr1 ilb il ilr2 ( e) () f ilrb1 ilrb2 (g) P V ( h) icb ic isb1 isb2 () i ZCS urn-off is1 is Figure 4: Key waveforms of he fifeen level RSC converer a he seady sae. (a) and (b) wiching paerns (c) Inpu curren (d) oupuinducor currens. (e) and (f) resonan inducor currens. (g) oupu capacior currens. (h) and (j) swich currens. 3. TECHNIQUES USED (i) Series-Modular Configuraions The series-modular configuraions are designed wih he specificaions such as inpu volage, oupu volage, and inpu power, used in simulaion. Therefore, hree modular cells A, B and C are designed for equal volage gains.the volage and curren sresses of he componens can be obained. (ii) Cascade Configuraions For he cascade configuraions, hree sages of he proposed RCS converer mus provide a volage gain. The volage and curren raings of he componens of he proposed converer. For he cascade ZCSRSC configuraion, seven sages are required o achieve a volage gain of 15. Each sage consiss of wo resonan

7 Implemenaion of High Volage Gain RS Cell- Based DC-DC Converer for Offshore Wind inducors, wo resonan capaciors, wo oupu filer capaciors, and four diodes.for all he configuraions, each swich or diode is comprised of several series and parallel-conneced devices o wihsand he raed curren and volage. The swiching frequency, inducances, and resonan capacior values are he same as hose in he simulaion for boh RSC and ZCSRSC converers. The oupu filer capaciors are considered larger han he resonan capaciors in he ZCSRSC configuraions.the suiable high-power capaciors and inducors wih heir weighs and sizes are seleced from AVX, GS-ESI, and REO.These converers are compared based on he following feaures : (i) oal number of devices; (ii) passive componen weighs and volumes and (iii) losses. 4. SIMULATION RESULTS Developing resonan swiched capacior cell based dc-dc converer for 15-level wih series modular configuraion echn ique is simulaed in MATLAB Simulink for performance analysis. The proposed converer simulaion circui and oupu waveform are shown in fig, 5, 6, 7and fig. 8. C 153 ST1 From D1 From1 ST2 D2 From5 ST3 D3 Discree, 5e-5s Powergui PULSE GENERATION 3 DC Source 1 S1 From3 Cr1 Lr1 S2 From2 5B2 Cr2 Lr2 S3 From6 Cr3 Lr3 L Mulimeer D LOAD Scope Sb1 Crb1 Sb2 Crb2 5B3 Crb3 Db Lrb1 Lrb2 Sb3 Lrb3 Lb Db1 Db2 Db3 C1 Figure 5: Proposed Sysem Simulaion Circui 5. CONCLUSION In his projec, RSC cell-based dc-dc converer wih a high volage gain is proposed for offshore wind energy applicaions. The sof-swiching acion is provided by he resonan condiion of he circui. Therefore, he swiching losses are minimal in boh ON and OFF insans, and he power densiy of he sysem can be enhanced by increasing he swiching frequency. Oupu filer capacior volages are phase shifed by 18 wih respec o each oher o eliminae he oupu volage ripples wihou adding exra componens. The proposed series-modular and cascade RSC configuraions have he inheren advanage of being readily applicable o mulisage power swiching converers. Concepual comparisons of he

8 154 B. Veeramuhu pandian and P. UshaRani proposed converer o a counerpar show ha he proposed converer is well suied for high-volage and high-power offshore wind applicaions requiring a high-power densiy and high efficiency. Finally, he operaion and performance of he proposed converer are verified wih experimens on a 15-level converer prooype. Y-axis Y-axis.4 Y-axis-Inpu volage in V; X-axis-Time in ms Figure 6: Proposed Sysem Inpu Volage Waveform X-axis X-axis Y-axis-Inpu Curren in A; X-axis-Time in ms Y-axis 2 Figure 7: Proposed Sysem Inpu Curren Waveform Y-axis-Oupu Volage in V; X-axis-Time in ms X-axis Figure 8: Proposed Sysem Oupu Volage Waveform

9 Implemenaion of High Volage Gain RS Cell- Based DC-DC Converer for Offshore Wind 155 POWER CIRCUIT MAIN CIRCUIT CONTROL CIRCUIT Figure 9: Proposed Hardware circui Figure 1: Proposed Hardware Circui Inpu Volage Figure 11: Proposed Hardware Circui Oupu Volage

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