On Implementation Possibilities of High-Voltage IGBTs in Resonant Converters

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1 On Implementation Possibilities of High-Voltage IGBTs in Resonant Convetes Andei Blinov and Dmiti Vinnikov Tallinn Univesity of Technology, Ehitajate tee 5, 986 Tallinn, Estonia Abstact. The conventional had switching half-bidge topology used as a olling stock auxiliay powe supply unit has limited switching fequency due to high powe losses in semiconductos. The study analyses LLC and LCC topologies in attempt to impove the pefomance of the convete and pesents a simulation of the opeation and an estimation of powe losses. Keywods: esonant convete, half bidge, powe losses. Intoduction Along with the development of 6.5 kv IGBT modules, complex applications managed by seies connection of numeous lowe voltage semiconductos could be simplified by eplacing them with a single 6.5 kv module, which would enable simple and eliable two-level half-bidge (HB) voltage-souce invete (VSI) topologies to be implemented fo the olling stock auxiliay powe units. This eseach focuses on an expeimental half-bidge convete ecently developed at Tallinn Univesity of Technology. This convete is based on two Infineon 2 A 6.5 kv IGBT modules (FZ2R65KF). Investigations have shown that the expeimental convete is capable of poviding equied pefomance within the whole ange of olling stock supply voltage of kv and a wide powe ange 5 kw []. The convete consists of pimay and seconday pats galvanically isolated by the high fequency tansfome. The pimay pat is a squae-wave twolevel half-bidge PWM invete and the seconday pat consists of a full-bidge ectifie and an LC filte. Such convetes (Fig. a) ae vey simple in contol and potection, have educed component count and povide good eliability. Main concens of this topology elate to paasitic oscillations afte IGBT tun-off (Fig. b) [2], high powe losses in semiconductos due to had switching and consequently, limited switching fequency (aound 2 khz) because of themal issues. This imposes inceased equiements on the passive components of the convete and associated cooling system. As a esult this leads to inceased pice and educed powe density of the convete. Seveal ways exist of how to impove the switching pocess of semiconducto switches in the HB invetes, which can be classified as asymmetical, auxiliay switch, and esonant convetes [3]. This howeve, equies inceased numbe of components including contolled switches. Due to inceased complexity the eliability is expected to be deceasing.

2 2 > 2 > > > T T 444 A. Blinov and D. Vinnikov Investigations of 6.5 kv IGBTs opeating in esonant topologies epot significant incease in efficiency [6, 7], howeve, the tansistos wee opeating in both zeo voltage switching (ZVS) and quasi- zeo cuent switching (ZCS) mode. (a) Fig.. Had-switched high-voltage half-bidge convete topology (a) and measued IGBT voltage and cuent wavefoms (b). This mode of opeation is had to achieve with wide input voltage and load vaiations. The following investigation focuses on the HB esonant convetes based on two 6.5 kv IGBT modules that equie minimum modifications to the hadswitched topology. (b) 2 Contibution to Value Ceation Moden high-voltage powe electonic applications elate to seveal fields, such as industial electical dives and taction as well as equipment fo powe geneation, tansmission and distibution. Thee ae tade-offs between size, complexity, eliability, cost and many othe paametes of the system. Evaluation of these factos is citical to achieve an optimum valuable design. This is often impossible without taking into account the most innovative technology achievements o without applying the available solutions to paticula needs. This aticle investigates the ways of optimisation of the expeimental convete in an attempt to ceate a moe valuable and innovative system. 3 Resonant Convete Types Resonant convetes ae an attactive altenative to taditional had-switched ones because of educed switching losses and the EMI due to the sinusoidal behaviou of the esonant cicuit. Such convetes (Fig. 2) could opeate at high fequencies to educe the size of thei eactive components. These convetes geneally featue the second o the thid ode esonant tank cicuit, i.e. the stoage tank consists of two o thee enegy stoage elements [8]. Resonant tanks can be divided into thee goups as

3 On Implementation Possibilities of High-Voltage IGBTs in Resonant Convetes 445 Fig. 2. Genealised esonant convete topology and diffeent esonant tanks. seies (Fig. 2a), paallel (Fig. 2b) and seies-paallel. In tun, convetes with seiespaallel esonant tanks could be classified as LCC, and LLC (Figs. 2c and 2d, espectively). In esonant convetes egulation of output paametes is pefomed by vaying the IGBT switching fequency aound the esonance fequency of the convete [3]. A majo advantage of a seies-esonant convete is that the cuent in the powe devices deceases with a decease in the load, leading to highe efficiency. Howeve, thee ae difficulties in egulating the output voltage at light load opeation [9, ]. Since the studied convete must opeate with wide load vaiations, this topology is not consideed suitable. In contast to the seies-esonant convete, the paallelesonant convete can egulate the output voltage at no load by unning at a fequency above esonance. On the othe hand, such convetes have highe device cuent that is elatively independent of the load. This leads to high conduction losses in semiconducto and eactive components, deceasing the efficiency, especially at light loads. 4 LLC Resonant Convete LLC esonant convetes intoduce seveal advantages ove othe esonant convetes. These convetes equie a elatively naow vaiation of switching fequency to contol the output voltage; can opeate with a wide load ange and ZVS could be achieved ove the entie opeating ange. Moeove, the tansfome leakage and magnetizing inductances can be utilised as the esonant elements of the powe stage and, thus, educe the oveall pat count. In addition, the seies esonant capacito also povides DC blocking, favouable fo an isolation tansfome in the half-bidge configuation. The LLC convete has two esonant fequencies: L and C detemine the highe esonant fequency, while lowe esonant fequency is detemined by C and the seies inductance of L p and L. The chaacteistics of the convete ae dependent on the L /L p inducto atio. As L is educed, the lowe fequency needed at low voltage input deceases. In this case vaiations in the switching fequency within the opeating ange ae inceased, esulting in a complicated passive component design. On the othe hand, lage L will make the IGBT tun-off cuent highe,

4 446 A. Blinov and D. Vinnikov which inceases switching losses. Two esonant fequencies, f (LLC) and f 2(LLC) ae defined as follows [5]: Gain Gain (a) (b) Fig. 3. Genealised voltage gain vs. nomalised fequency at diffeent loads fo LLC convete (a) and LCC convete (b). f (LLC) =, () 2 π L C f 2(LLC) = 2 π ( L + L ) C p. (2) Since the load independent point (highe esonant fequency) is in the ZVS egion (Fig. 3a), the convete could be designed to opeate aound this point [, ]. High efficiency is achievable by applying lossless capacitive snubbes acoss the invete tansistos. The LLC convete does not equie an LC output filte used in taditional hadswitching HB convete. Only the capacito filte can be used, leading to a simple and lighte seconday pat. The equied capacitance value is estimated by C f =, (3) 4 U f R out sw(min) Load(min) whee U out is the output voltage ipple, f sw(min) is the minimum switching fequency, and R Load(min) is the minimum equivalent load esistance. 5 LCC Resonant Convete The seies-paallel convete, also efeed to as an LCC convete, aims at combining the advantages of the seies and the paallel convetes, at the same time educing o eliminating thei disadvantages. Similaly to the LLC, the LCC convete does not equie an LC output filte used in a taditional had-switching HB convete. The tansfome leakage inductance can be utilised as the esonant element L.

5 On Implementation Possibilities of High-Voltage IGBTs in Resonant Convetes 447 The low esonant fequency is detemined by a seies esonant tank L and C while the high esonant fequency is detemined by L and an equivalent capacitance of C and C p in seies. Two esonant fequencies, f (LCC) and f 2(LCC) ae defined as follows [2] f (LCC) =, (4) 2 π L C f 2(LCC) = 2 π L C C p p C + C. (5) The behaviou is dependent on the C /C p atio. As C p is educed, the convete esembles a seies convete and the uppe fequency needed at light loads inceases. On the othe hand, with an inceased C p the convete esembles a paallel convete and the ciculating cuent no longe deceases with the load [8]. Unlike in the case of the LLC convete, the load independent point (lowe esonant fequency) is in the ZCS egion, while in the ZVS egion (the highe esonant fequency) the convete is moe sensitive to changes in the load (Fig. 3b). Only the opeation above the uppe esonance will be consideed in the following as it is moe desiable fom the pactical point of view since the ZVS is povided fo the IGBTs, allowing the use of capacitive snubbes to educe tun-off losses. 6 Simulation Results and Loss Compaison Design of esonant components is always a compomise between load powe ange, opeating fequency, input voltage ange, ciculating enegy in the esonant cicuit etc. Fom the efficiency point of view the LLC convete is best to be opeated at the esonant fequency f (LLC). In this case the both ciculating enegy in the esonant netwok as well as the switching losses ae low. Since this opeating point is only achievable fo one given U in and load powe, the LLC esonant convete is usually designed aound f (LLC) fo a full load and maximum U in. With an incease in the load o a decease in the input voltage, the switching fequency is deceased to keep the output voltage egulated. Similaly, the LCC convete is usually designed aound f 2(LCC) fo a full load and minimum U in. The step-by-step analysis and design methods of LLC and LLC convetes wee pesented in a ange of publications [8-3] and ae beyond the scope of this pape. The values of the esonant tank components of both convetes ae selected so that thei switching fequency ange is simila and elatively naow (3 4 khz) and the isolation tansfome tuns atio is the same. The main paametes of the analysed convetes ae listed in Table. The input voltage and load powe ange as well as the output voltage values ae the same as fo the had-switched convete. Both convetes ae able to opeate with ZVS within desied conditions. The simulated wavefoms

6 448 A. Blinov and D. Vinnikov Convete Table. Main paametes of the compaed convetes. Switching fequency (f sw, khz) Tansfome tuns atio (N s/n p) C (µf) C p (µf) L (mh) L p (mh) L f (mh) C f (mf) Had-switched LLC LCC Uce(T), [V] Uce(TT), [V] Ic(TT), [A] Ic(TT), [A] U(T_p), [V] U(T_p), [V] 2K 2K K K -2K -2K I(T_p), [A] I(T_p), [A] 4 U(D2), [V] 4 U(D2), [V] I(D2), [A] Time (s) (a) 4 2 I(D2), [A] Time (s) Fig. 4. Main simulation wavefoms of LLC (a) and LCC (b) convetes (U in =3V, P out =3kW). (b) of LLC and LCC convetes opeating at nominal conditions ae shown in Figs. 4a and 4b, espectively. Simulations show that the tun-off cuent of IGBT as well as peak cuent of the ectifie diodes is essentially highe in the LCC convete (Fig. 5). The estimated invete IGBT powe loss in the studied solutions is pesented in Fig. 6. The simulations of LLC and LCC convetes include the IGBT loss eduction duing the tun-off with the snubbe capacitos. Since eductions in the IGBT tun-off powe loss by help of capacitive snubbes have been epoted to be lowe than expected due to inceased cuent tail duation and could vay between diffeent IGBTs, the appoximate aveage eduction of 5% [4-7] is consideed in this pape. It should be mentioned that in eal convetes, the powe losses could be distinctly highe than the simulated values due to additional powe dissipation of passive components and the output ectifie. Despite opeating with highe switching fequency than the had-switched convete, the esonant LLC convete is able to povide essential (up to 57%) eduction of invete losses. On the contay, the powe losses of the LCC convete ae highe, especially at highe input voltages. This situation could be impoved by adjusting C /C p atio. As a downside, the opeation fequency ange will incease.

7 On Implementation Possibilities of High-Voltage IGBTs in Resonant Convetes 449 Fig. 5. IGBT tun-off cuent vs. load powe of the consideed convetes (U in =3 V). (a) (b) (c) Fig. 6. Single IGBT module powe loss estimation vs. output powe at diffeent input voltages in had-switched (a), LLC (b) and LCC (c) convetes. 7 Conclusions Implementation of esonant convetes instead of the had switching half-bidge topologies seems to be an attactive way of impoving the efficiency of the powe convete. Both LLC and LCC convetes can delive low noise and ZVS of the invete switches ove the whole ange of opeation conditions. Fom the two, the LCC convete design equies additional adjustments in ode to educe switching losses. This will esult in a wide egulation fequency ange, making design moe challenging. On the contay, the LLC convete pefomance seems advantageous due to lowe powe losses with a simila egulation fequency ange. On the othe hand, the additional complexity of the topology, its contol and potection as well as possible eduction in obustness eliability may not ovecome the advantages it bings. The futhe eseach will focus on investigations of HB topology with phaseshifted synchonous ectifie, which seems an advantageous altenative since it does not equie any modifications in the invete pat. Acknowledgement. This eseach wok has been suppoted by Estonian Ministy of Education and Reseach (Poject SF46s), Estonian Science Foundation (Gant ETF82) and Estonian Achimedes Foundation (poject - Doctoal School of Enegy and Geotechnology II ).

8 45 A. Blinov and D. Vinnikov Refeences. Jalakas, T., Vinnikov, D., Laugis, J.: Development of 5-kW Isolated DC/DC Convete with High-Voltage IGBTs, Compatibility in Powe Electonics, CPE '7, pp. --6, (27) 2. Blinov, A. Jalakas, T., Vinnikov, D., Janson, K.: Switch-Off Behaviou of 6.5 kv IGBT Modules in Two-Level Voltage Souce Invete, Scientific Jounal of Riga Technical Univesity: Powe and Electical Engineeing, vol. 27, pp , (2) 3. Aydemi, M.T., Evan, F.: Opeation pinciples of a switched capacito snubbe cicuit suggested fo half-bidge DC DC convetes, Intenational Jounal of Electonics, Vol. 96, No., pp , (29) 4. Coccia, A., Canales, F., Rinike, H.R., Knapp, G., Kalbematten, M., Baldinge, M., Babosa, P.: Vey high pefomance AC/DC/DC convete achitectue fo taction powe supplies, Powe Electonics and Applications, 3th Euopean Confeence, EPE '9. pp. --, 8-, (29) 5. Lin, B.R., Hou, B.R: Implementation of a seies esonant convete with seies-paallel connection, 6th IEEE Confeence on Industial Electonics and Applications (ICIEA), pp , (2) 6. Lindenmulle, L., Alvaez, R., Kleinichen, P., Benet, S.: Chaacteization of a 6.5 kv / 5A IGBT module in a seies esonant convete, Enegy Convesion Congess and Exposition (ECCE), IEEE, pp , (2) 7. Weigel, J., Ag, A.N.S., Hoffmann, H.: High voltage IGBTs in medium fequency taction powe supply, 3th Euopean Confeence on Powe Electonics and Applications, EPE '9, pp. --, (29) 8. Bataseh, I., Liu, R., Otiz-Conde, A., Yacoub, A., Sii, K.: Steady state analysis and pefomance chaacteistics of the LLC-type paallel esonant convete, Powe Electonics Specialists Confeence, PESC '94 Recod., 25th Annual IEEE, pp vol., (994) 9. Yang, B., Lee, F.C., Zhang, A.J., Guisong, H: LLC esonant convete fo font end DC/DC convesion, Applied Powe Electonics Confeence and Exposition, APEC 22. Seventeenth Annual IEEE, pp vol. 2, (22). Cavalcante, F.S.: High Output Voltage Seies-Paallel Resonant DC-DC Convete fo Medical X-Ray Imaging Applications, D.Sc. thesis, pp , (26). LLC esonant half-bidge convete design guideline, STMicoelectonics Application note AN245, Octobe, (27) 2. Steigewald, R.L.: A Compaison of Half-bidge esonant convete topologies, IEEE Tansactions on Powe Electonics, vol. 3, no. 2, (988) 3. Jung, J.H, Kwon, J.G.: Theoetical analysis and optimal design of LLC esonant convete, Powe Electonics and Applications, 27 Euopean Confeence, pp.--, (27) 4. Naayagi, R.T., Shuttlewoth, R., Fosyth, A.J.: Investigating the effect of snubbe capacito on high powe IGBT tun-off, Electical Enegy Systems (ICEES), 2 st Intenational Confeence, pp , (2) 5. Fujii, K., Koellenspege, P., De Doncke, R.W.: Chaacteization and Compaison of High Blocking Voltage IGBTs and IEGTs Unde Had- and Soft-Switching Conditions, IEEE Tansactions on Powe Electonics, vol. 23, no., pp , (28) 6. Song, B.M., Zhu, H., Lai, J.H., Hefne, A.R.: Switching chaacteistics of NPT- and PT-IGBTs unde zeo-voltage switching conditions, Industy Applications Confeence, Thity-Fouth IAS Annual Meeting. Confeence Recod of the 999 IEEE, vol., pp , (999) 7. Petteteig, A., Lode, J., Undeland, T.M.: IGBT tun-off losses fo had switching and with capacitive snubbes, Industy Applications Society Annual Meeting, Confeence Recod of the 99 IEEE, pp vol. 2, (99)

Design of an LLC Resonant Converter Using Genetic Algorithm

Design of an LLC Resonant Convete Using Genetic Algoithm H. H. Nien, C. K. Huang, S. K. Changchien, C. H Chan Dept. of Electical Engineeing, Chienkuo Technology Univesity E-mail: nien@ctu.edu.tw Dept,