Multiple Load-Source Integration in a Multilevel Modular Capacitor Clamped DC-DC Converter Featuring Fault Tolerant Capability

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1 Muliple Load-Source Inegraion in a Mulilevel Modular Capacior Clamped DC-DC Converer Feauring Faul Toleran Capabiliy Faisal H. Khan, Leon M. Tolber The Universiy of Tennessee Elecrical and Compuer Engineering Knoxville, TN fkhan3@uk.edu, olber@uk.edu Absrac A mulilevel modular capacior clamped dc-dc converer (MMCCC will be presened in his paper wih some of is advanageous feaures. By virue of he modular naure of he converer, i is possible o inegrae muliple loads and sources o he converer a he same ime. The modular consrucion of he MMCCC opology provides ransformer like aps in he circui, and depending on he conversion raio of he converer, i becomes possible o connec several dc sources and loads a hese aps. The modulariy of he new converer is no limied o his ransformer like operaion, bu also provides redundancy and faul bypass capabiliy in he circui. Using he modulariy feaure, some redundan modules can be operaed in bypass sae, and during any faul, hese redundan modules can be used o replace a fauly module o mainain an uninerruped operaion. Thus, his MMCCC opology could be a soluion o esablish a power managemen sysem among muliple sources and loads having differen operaing volages. I. INTRODUCTION In auomoive applicaions, a high efficiency bi-direcional dc-dc converer is a key elemen o provide he power for he elecrical drive rain. For his applicaion, a jusified choice migh be a mulilevel capacior clamped dc-dc converer which can be operaed a a very high efficiency. One of he major advanages of he capacior clamped converer is ha i can aain very high efficiency even a parial loads [1], where i is he opposie for classical dc-dc converers wih an inducive energy ransfer mechanism. There are several differen ypes of mulilevel dc-dc converers ha have been previously developed [2-11]. The flying capacior mulilevel converer shown in [2][4] has some poenial feaures o be used in auomoive applicaions; however, i suffers from several limiaions [1]. A modular circui is advanageous over he non-modular srucure for several reasons. If he circui is modular, i is possible o disribue he oal power handling capabiliy among muliple modules used in he circui; hereby low volage/curren sress is experienced by individual semiconducor devices in he circui. In addiion, a modular circui could incorporae redundancy in he sysem ha yields some faul olerance properies of he circui. Using he modulariy, i is possible o localize any faul in he sysem, and he affeced module can be bypassed and anoher good module acivaed, and hus a coninuiy of operaion can be mainained. Moreover, he fauly module can be physically removed from he sysem, and can be repaired or replaced by anoher module. This feaure can faciliae easier mainenance and can obain higher mean ime beween failures (MTBF. This paper will presen some new feaures of he mulilevel modular capacior-clamped dc-dc converer (MMCCC ha was presened in [1]. One of he key feaures of he MMCCC opology is ha he circui can be considered as a dc ransformer having muliple aps where each module provides one inermediae volage node. Using his feaure of he circui, i becomes possible o connec several dc volage sources having differen magniudes simulaneously. Thus, he converer may eliminae he need of any power managemen uni ha is a requiremen for a sysem wih more han wo volage sources and loads. Moreover, i will also be shown how muliple loads can be conneced across he volage nodes so ha several volage oupus can be obained from he circui simulaneously. In secion II-IV, he new opology and he muliple load/source inegraion echnique will be presened along wih simulaion and experimenal resuls. Secion III will explain he dc ransformer acion of he converer, and secion V will presen he redundancy and faul bypass feaure of he converer. II. MMCCC TOPOLOGY The proposed 5-level MMCCC shown in Fig. 1 has an inheren modular srucure and can be designed o achieve any conversion raio. Each modular block has one capacior and hree ransisors leading o hree erminal poins. A modular block is shown in Fig. 2. The erminal is conneced o eiher he high volage baery or o he oupu of he previous sage. One of he oupu erminals is conneced o he inpu of he nex sage. The oher oupu erminal is conneced o he low volage side + baery erminal or load. In a flying capacior mulilevel dc-dc converer (FCMDC wih conversion raio of 5, he oal operaion akes 5 subinervals [1], and his is shown in Table 1. Only one chargedischarge operaion is performed in one sub inerval. Thus, he componen uilizaion becomes limied in his circui. For an N-level FCMDC circui, any capacior excep C 1 is uilized during only wo sub-inervals for a complee cycle (one sub inerval for charging, one for discharging and for he /07/$ IEEE. 361

2 I in SR 1 I charge SB 2 SR 4 SB 5 SR 7 V C C C C HV + V C LV + LV - 1 Load - SR 2 SB 3 SR 5 SB 6 SB 1 SR 3 SB 4 SR 6 Fig. 1. The proposed 5-level MMCCC wih four modular blocks. remaining hree sub-inervals in one period, he componen is no used. The MMCCC opology can increase he componen uilizaion by performing muliple operaions a he same ime, which is shown in Table 1. The swiching sequence in he MMCCC circui works in a simpler way han he FCMDC converer. As here are only wo sub-inervals, wo swiching saes are presen in he circui. Swiches SR 1 o SR 7 in Fig. 1 are operaed a he same ime o achieve sae 1. In he same way swiches SB 1 o SB 6 are operaed simulaneously o make sae 2, and his gae signal sequence is shown in Fig. 3. The deail operaion of he MMCCC opology can be found in [1]. III. MULTIPLE LOAD-SOURCE INTEGRATION A. Source Inegraion The modular MMCCC opology can be used o inegrae muliple volage sources simulaneously o build a power managemen sysem among various volage sources. The 5-level MMCCC circui shown in Fig. 1 has 4 modules, and every module s inpu por creaes a volage node in he circui. Fig. 4 shows a 6-level MMCCC converer, and analyically compued volage levels generaed a nodes 1 o 6 are shown. This figure shows ha each node produces a ime varying dc volage wih an ac volage superimposed i. The ampliude of he ac volage swing is equal o 1 or. The volages a differen nodes are summarized in Table 2. TABLE 1. SWITCHING SCHEMES OF FCMDC AND THE MMCCC CIRCUIT. = CHARGING, = DISCHARGING FCMDC MMCCC Sub Operaions inerval No. 1 C 5 + C 1 2 C 5 C 4 + C 1 3 C 4 C 3 + C 1 4 C 3 C 2 + C 1 5 C 2 C 1 Sub Operaions inerval No. 1 C 5 + C 1 C 4 C 3 + C 1 C 2 C 1 2 C 5 C 4 + C 1 C 3 C 2 + C 1 Using his ime varying naure of hese node volages, some addiional volage sources can be conneced a hese nodes. Inherenly, he MMCCC circui is a bi-direcional converer and i can be used o manage he power flow beween and (Fig. 1 by conrolling he conversion raio (CR of he circui, and he number of acive levels presen in he circui governs he CR. The added funcionaliy of he muliple source inegraion can faciliae a sysem o inegrae up o 7 volage sources for a 6-level converer; which means 5 addiional volage sources a nodes 2 o 6 can be conneced. This feaure may be used o inegrae various kinds of energy sources such as solar cell, fuel cell, baery ec. having differen volages in he same sysem. Table 2 shows he simulaed values of he ime varying volages a differen nodes of he 6-level MMCCC circui for he wo saes presen in he circui. A sae 1, he volage a C SB 1 SR n V LB 0 T/2 T SR 1 SB 2 SB n 0 T/2 T Fig. 2. The unique modular block. Fig. 3. The gaing signal of he swiches in he MMCCC circui, i.e. here are only wo swiching saes presen in he circui. 362

3 6 V 6 V 5 V 4 V 3 V 2 ( HV R LV 6 / 5 4 / 5 4 / 3 2 / 3 2 / Fig. 4. The simulaion resuls of he inermediae node volages in a 6-level MMCCC circui. The volage magniude a any node prined in black is he value during sae 1, he value prined in gray is he volage magniude during sae 2. node 5 is 4, and during sae 2, he volage is 5. Thus, if an exernal volage source of ampliude 4 is conneced o node 2, i will conribue power along wih o he low volage side of he converer during sae 1. During sae 2, he volage a node 5 becomes 5, which is higher han he exernal source volage; hus he converer will no draw any power from he exernal source conneced a his node. In he same way, four oher volage sources can be conneced a nodes 2, 3, 4, and 6. While connecing muliple sources in he sysem, one issue needs o be considered o keep he oupu volage ripple he same as in he case when only is conneced o he sysem. TABLE 2. THE TIME VARYING NODE VOLTAGES OF A 6-LEVEL MMCCC CIRCUIT. Sae Acive Swiches V 6 V 5 V 4 V 3 V 2 1 S R1 -S R S B1 -S B To achieve his, he curren shared by he exernal sources mus be in phase wih he curren provided by. Table 1 shows ha he converer akes power from during sae 1 only. Thus, he addiional volage sources mus be conneced in he sysem in such a way ha hey provide power during sae 1 only. As menioned earlier, he magniude of an exernal volage source needs o be close o he lower value among he wo volage levels presen a any node, and his is required o bring a balance beween he volage a he node and he exernal source. Thus, if an exernal volage source needs o be conneced a node 6, is magniude needs o be close o 5. A node 6, he volage varies beween 6 and 5, and during sae 1, he volage is 6. Thus, i is no possible o connec a volage source a node 6 while keeping he oupu volage ripple unaffeced. For he same reason, node 4 and node 2 will no be suiable for inegraing a volage source in his 6-level converer. Fig. 5 shows he inegraion of wo exernal sources conneced a nodes 3 and 5, because hey share he load curren during sae 1 only. However, i is always possible o connec volage sources a any node, bu a compromise mus be made wih he oupu volage ripple. B. Load Inegraion The oher advanage of his inegraion feaure is he abiliy Load 53 Load 64 Load 42 HV V V 6 5 V 4 V 3 V 2 ( I V E5 V E3 R LV Fig. 5. The schemaic diagram of he inegraion of muliple sources and loads in a 6-level MMCCC circui. 363

o connec muliple loads a he same ime. Fig. 4 shows he no-load volages a differen nodes of he MMCCC circui.

This is rue for node 3 and 5 also. Thus, i is possible o connec a load in various ways beween hese in-phase nodes. Fig.

In he same way, he volage difference beween node 6 and 2 is 4. Thus, i is possible o connec muliple loads of 1, 2, and 4 simulaneously in a 6-level MMCCC circui. IV.

4 o connec muliple loads a he same ime. Fig. 4 shows he no-load volages a differen nodes of he MMCCC circui. Nodes 2-6 generae ime varying dc volages; however, a dc load canno be conneced beween any of hese nodes and ground. This figure shows ha he ime varying volage a node 2, 4, and 6 have he same phase. This is rue for node 3 and 5 also. Thus, i is possible o connec a load in various ways beween hese in-phase nodes. Fig. 5 shows how loads can be conneced beween nodes (6, 4, (5, 3, and (4, 2 o obain a consan dc volage across he loads. The volage difference beween wo adjacen in-phase nodes is 2. In he same way, he volage difference beween node 6 and 2 is 4. Thus, i is possible o connec muliple loads of 1, 2, and 4 simulaneously in a 6-level MMCCC circui. IV. EXPERIMENTAL RESULTS (a V 6 V 5 0 V ( 0 V (V 6 To verify he concep of inegraing muliple loads and sources in he circui, an experimenal seup was made, and he schemaic in Fig. 5 was followed. A 500 W 6-level MMCCC prooype shown in Fig. 6 was used. Three bench op power supplies were used as, V E5, and V E3, and a diode was used in series wih each volage source o proec he power supplies from reverse power flow. A 3 Ω load was used as R LV, and wo 24 Ω loads were used as Load 42 and Load 53. In addiion o hem, one 48 Ω load was used as a load conneced beween node 6 and 2. The main inpu volage was kep a 75 V. Fig. 7(a shows he no-load volages a HV (he cahode erminal of he diode conneced o, V 6 and V 5 nodes. Fig. 7(b shows he volages recorded a V 4, V 3, V 2, and nodes. These volages have he same variaions in phase and magniude found in he simulaion (shown in Fig. 4 and analyical compuaion. The volages a nodes 2-6 have a swing of 1. Thus, he volage a node 2 varies beween 12.3 V and 25 V. There was a small variaion found a HV node, hough i was supposed o be a consan value of 75 V obained from. This volage was measured a he converer board and no across he power supply erminals. Due o he volage drop across he curren sampling resisor and wire sray inducance, a small ripple was observed a his volage inpu por of he converer. Figs. 8 and 9 show how hree sources conneced o he converer can share he oal load curren simulaneously. For his experimen, a 3 Ω resisive load was conneced across he node and ground. This power sharing operaion was esed in wo seps. In he firs case, V E5 was kep less han 48 V and Fig. 6. The 500 W 6-level MMCCC prooype. 0 V (V 4 0 V (V 3 0 V (V 2 0 V ( (b Fig. 7. The experimenal resul of he node volages in a 6-level MMCCC circui a no-load condiion; (a volages, V 6, and V 5 (b volages V 4, V 3, V 2, and. The converer was operaed in down-conversion mode. V E3 was kep less han 24 V. During his ime, here was no power flow from hese wo sources, and his is shown in Fig. 8(a. In his sep, was kep a 75.8 V. When V E5 is varied o go beyond 48 V level, i sars o share he power delivered o he oupu side, and his is shown in Fig. 8(b. When V E5 reaches 52 V, i delivers he enire power o he load and no curren is drawn from he source. This is shown in Fig. 8(c. If is removed from he sysem, V E5 can provide he oal power o he load wih a volage lower han 52 V. This ime V 5 (before connecing V E5 decreases due o he absence of any curren injeced by, and a lower V E5 is required o flow he same curren o load as before when was presen. In he second case, V E3 was used o share he load curren. Fig. 9(a shows he siuaion when he magniude of V E3 was raised o V so ha i sars o share he load curren wih V E5. This ime, and V E5 were kep he same as hey were in case 1. When V E3 was raised o 30.7 V, i provided he enire power o he load, and power delivered by and V E5 became zero. This is shown in Fig. 9(b. However, if and V E5 are removed from he sysem, V E3 can deliver he oal power wih a volage less han 30.7 V. When he magniude of V E5 and V E3 were reduced, was back in operaion, and all V 4 V 3 V 2 364

(a (a (b (b (c Fig. 8. The experimenal resul of he inpu currens (2 A/div shared by hree sources (, V E5, and V E3 in Fig. 5. (a oal curren is provided by (75.8 V, (b curren is shared by and V E5 (51.

A 24 Ω load was conneced beween node 4 and 2 (Load 42, and a 3 Ω load (R LV was presen a node. The volages across hese loads are shown in Fig.

5 (a (a (b (b (c Fig. 8. The experimenal resul of he inpu currens (2 A/div shared by hree sources (, V E5, and V E3 in Fig. 5. (a oal curren is provided by (75.8 V, (b curren is shared by and V E5 (51.8 V, (c oal curren is provided by V E5 (52 V only. of hese hree dc sources shared he load curren. This is shown in Fig. 9(c. Fig. 10 explains he muliple load inegraion mehod in he sysem. A 24 Ω load was conneced beween node 4 and 2 (Load 42, and a 3 Ω load (R LV was presen a node. The volages across hese loads are shown in Fig. 10(a, and i can be seen ha he volage across Load 42 is almos 2. (c Fig. 9. The experimenal resul of he inpu currens (2A/div shared by hree sources (, V E5, and V E3 in Fig. 5. (a curren is shared by V E5 (52 V and V E3 (26.75 V, (b oal curren is provided by V E3 (30.7 V only, (c oal curren is shared by (75.9 V, V E5 (51.2 V, and V E3 (26.07 V. Fig. 10(b shows he load volages when R LV and Load 53 (24 Ω are presen in he circui. Like he Load 42, Load 53 also experiences a volage of approximaely 2. In Fig. 10(c, he load volage a he node and volage across Load 62 (48 Ω are shown, and volage across Load 62 was found o be almos 4 imes or. These experimens prove ha 3 differen 365

This unique feaure of he MMCCC opology enables an uninerruped operaion when here is a faul in any of he modules. When (a (b (c Fig. 10.

6 kinds of loads having volages 1, 2, and 4 can be conneced simulaneously in he circui. V. REDUNDANCY AND FAULT BYPASS CAPABILITY To ake he full advanage of he modular srucure, i is fel necessary o inroduce redundancy in he circui. This unique feaure of he MMCCC opology enables an uninerruped operaion when here is a faul in any of he modules. When (a (b (c Fig. 10. The experimenal resul of he load volages conneced beween inermediae nodes. (a and V 42 ; and V 42 is wo imes, (b V 53 and, (c V 62 and ; and V 62 is 4 imes. V 42 0 V V 53 0 V V 62 0 V ransisor SB 1 in Fig. 2 is permanenly on and he oher wo ransisors are permanenly off, he module works as a bypass module. In his condiion, he module does no paricipae in he operaion of he converer and simply bypasses he curren hrough iself. During he normal operaion ha is defined as he acive sae, all hree ransisors in a module are conrolled by he proper gae-driving signal. Thus, any module can be operaed in eiher acive sae or bypass sae by acivaing appropriae conrol signals in a module. To ge some level of redundancy in he sysem, some modules are operaed in bypass sae and he remaining modules work in acive saes. When a faul is deeced inside any of he acive modules, he main board conrol circui deecs he locaion of he faul and sends a signal o he fauly module and hereby bypasses he module. However, o keep he conversion raio (CR unchanged, he conrol circui engages one of he redundan modules, which was in bypass sae so far. As a resul, an uninerruped operaion can be confirmed. The level of redundancy is applicaion specific, and depending on he applicaion of he converer, he number of redundan levels can be increased o any exen. Fig. 11 explains he redundancy and faul bypass operaion, and shows how he converer can wihsand a faul and coninue is normal operaion. A 3-level converer wih wo redundan modules is shown in Fig. 11. During normal operaion, module 1 and 2 work as acive modules, and module 3 and 4 work as bypass module. This is shown in Fig. 11(a. Fig. 11(b shows a siuaion where a faul has occurred in module 2. To keep he CR unchanged, he converer needs wo acive modules in he sysem. This ime, he conrol circui deecs he locaion of he faul and bypasses module 2. Then i engages module 3 in acive sae, which was in bypass sae so far. This is shown in Fig. 11(c. From his momen, module 1 and 3 work as acive modules, and module 2 and 4 work as bypass modules. A his poin, he presen sae of he circui is capable of handling one more faul which can be bypassed using module 4. Using he redundancy feaure, rue bi-direcional power managemen can also be esablished in he circui. Thus, i is possible o increase or decrease he number of levels and hereby he CR [1]. When a mulilevel converer is used o ransfer power beween wo volage sources, he direcion of power flow is governed by he raio of he wo volage sources (RVS and he CR. Unlike he RVS, he CR is usually an ineger value for capacior clamped converers, and when he CR is greaer han he RVS, he low volage source ransfers power o he high volage source. On he oher hand, a CR smaller han he RVS will force he converer o ransfer power from he high volage side o low volage side. However, depending on he baery condiion, RVS may change; and for a fixed CR, he power flow may change is direcion, even if i is no desired. In his siuaion, a variable CR could solve his problem, and in he MMCCC circui, he CR value can be changed by adding or subracing a level in he sysem. Thus, a 4-level converer can be operaed in eiher a 3 or 5 level configuraion only if i has redundan levels available, and rue bi-direcional power managemen can be 366

7 i HV i LV i HV i LV R LV R LV (a (b i HV i LV Good module in acive sae Fauly module R LV 4 3 (c 2 1 Good module in bypass sae Indicaion of bypass operaion Fig. 11. The redundancy and faul wihsand capabiliy of he converer, (a a hree level converer running a normal operaing mode wih wo redundan modules (3 and 4, (b a faul occurred in module 2, (c module 2 wen ino bypass mode and replaced by module 3. esablished. For a finer conrol on he CR, he duy raio of he gae drive signal may be changed, and i becomes possible o ge a more precise conrol of he curren. This can be considered as a fuure work a his poin. VI. CONCLUSIONS A new opology of modular mulilevel dc-dc converer has been proposed, and he muliple load/source inegraion echnique has been presened and verified hrough experimens. The es resuls show ha several volage sources can be conneced o he differen nodes of he circui, and load power requiremen can be miigaed by hose volage sources in a combined fashion. Thus, i becomes possible o ge variable conversion raio from he circui, and a complee power managemen proocol can be esablished among various volage sources. Moreover, he circui can generae differen load volages simulaneously, and his feaure makes i possible o obain various oupu volages from a wide inpu volage range. Thus, his feaure simply helps o consider he MMCCC converer as a dc ransformer having muliple aps o connec muliple loads and dc sources a he same ime. In addiion o his feaure, he modular naure of he MMCCC opology can be successfully used o ge redundancy and faul bypassing capabiliy in he sysem. This feaure can increase he reliabiliy of he sysem and decreases he down ime of he converer. Above all, he circui is capable of bidirecional power handling, and all hese feaures make he MMCCC opology a suiable candidae in various applicaions. [3] F. Zhang, F. Z. Peng, Z. Qian, Sudy of Mulilevel Converers in DC- DC Applicaion, IEEE Power Elecronics Specialiss Conference (PESC, pp , June [4] F. Z. Peng, F. Zhang, Z. Qian, A Novel Compac DC-DC Converer for 42V Sysems, IEEE Power Elecronics Specialiss Conference (PESC, pp , June [5] K. D. T. Ngo, R. Webser, Seady-Sae Analysis and Design of a Swiched-Capacior DC-DC Converer, IEEE Transacions on Aero. and Elec. Sysems, vol. 30, no. 1, pp , Jan [6] W. Harris, K. Ngo, Power Swiched-Capacior DC-DC Converer, Analysis and Design, IEEE Transacions on Aero. and Elec. Sysems, vol. 33, no. 2, pp , April [7] S. V. Cheong, H. Chung, A. Ioinovici, Inducorless DC-o-DC Converer wih High Power Densiy, IEEE Transacions on Indusrial Elecronics, vol. 41, no. 2, pp , April [8] O. Mak, Y. Wong, A. Ioinovici, Sep-up DC Power Supply Based on a Swiched-Capacior Circui, IEEE Transacions on Indusrial Elecronics, vol. 42, no. 1, pp , Feb [9] C. K. Tse, S.C. Wong, M. H. L. Chow, On Lossless Swiched- Capacior Power Converers, IEEE Transacions on Power Elecronics, vol. 10, no. 3, pp , May ] E. Bayer, Opimized Conrol of he Flying -Capacior Operaing Volage in Gear-Box Charge Pumps, - The Key Facor for a Smooh Operaion, IEEE Power Elecronics Specialiss Conference (PESC, pp , June [11] R. D. Middlebrook, Transformerless DC-o-DC Converers wih Large Conversion Raios, IEEE Transacions on Power Elecronics, vol. 3, no. 4, pp , Ocober ACKNOWLEDGEMENT We would like o hank Oak Ridge Naional Laboraory for supporing his work hrough UT-Baelle conrac no REFERENCES [1] Faisal H. Khan, Leon M. Tolber, A Mulilevel Modular Capacior- Clamped DC-DC converer, IEEE Indusry Applicaions Annual Meeing (IAS, Oc [2] Z. Pan, F. Zhang, F. Z. Peng, Power Losses and Efficiency Analysis of Mulilevel DC-DC Converers, IEEE Applied Power Elecronics Conference (APEC, pp , March

Modular Capacitor Clamped DC-DC Converter Featuring Fault Tolerant Capability

Multiple Load-Source Integration in a Multilevel Modular Capacitor Clamped DC-DC Converter Featuring Fault Tolerant Capability Faisal H. Khan, Leon M. Tolbert The University of Tennessee Electrical and