Inter national J our nal of P o wer Electr onics and Dri v e System (IJPEDS) V ol. 11, No. 1, March 2020, pp. 466 476 ISSN: 2088-8694, DOI: 10.11591/ijpeds.v11.i1.pp466-476 r 466 Re view of multiport isolated bidir ectional con v erter interfacing r enewable and ener gy storage systems Arulmozhi S., Santha K. R. Department of Electrical and Electronics Engineeering, Sri V enkatesw ara Colle ge of Engineering, Sriperumb udur , Chennai, India Article Inf o Article history: Recei v ed Jun 13, 2019 Re vised Aug 7, 2019 Accepted Oct 22, 2019 K eyw ords: Bidirectional DC-DC con v erter Ener gy storage isolated Multi-port ABSTRA CT Multiport con v erters increasingly g ain prominance in the recent past to interf ace rene w able ener gy sources lik e photo v oltaic cells, fuel cells with the load. Ener gy stor - age elements lik e battery and supercapacitors play an important role as an additional and alternate sources in systems with primary intermittent rene w able ener gy sources. As these ener gy storage element’ s char ging and dischar ging c ycles are to be controlled, an isolated bidirectional con v erter topology with transformer is used. The g alv anic isolation pro vided by the high frequenc y ac link t ransformers in partly isolated and fully isolated topologies mak es these con v erters most preferrable in high po wer applications lik e electric v ehicles. A comprehensi v e re vie w is performed on v arious three port partly isolated topologies addressed by dif ferent research groups. The k e y contrib utions on soft switching for reducing switching losses and impro ving o v erall con v erter ef ficienc y with help of resonant elements are discussed. In addition, control strate gies for po wer flo w control with enhanced soft switching of partly isolated con v erters are highlighted. A summary of con v erter topologies is pro vided considering po wer rating, de vice count, soft switching resonant elements and ef ficienc y which gi v es an idea for selection of suitable topology for the desired system requirement. This is an open access article under the CC BY -SA license . Corresponding A uthor: Arulmozhi S., Department of Electrical & Electronics Engineering, Sri V enkatesw ara Colle ge of Engineering, Sriperumb udur , Chennai, India. Email: arulmozhi@svce.ac.in 1. INTR ODUCTION Rene w able sources such as Photo v oltaic (PV), Fuel cell(FC) and W ind ener gy g ains popularity in po wer generation due to the technology adv ancements and en vironmental concerns. In addition, inte gration of h ybrid po wer sources are increasing in recent days. By nature, intermittenc y and unpredictablity of rene w able sources and load highly demands inclusion of ener gy storage systems lik e battery , supercapacitors to meet the load requirement and also to impro v e the dynamic and steady state performance of the sources. Thus DC-DC con v erters are included to interf ace source, ener gy storing elements and load. Se v eral unidirectional con v erters are proposed to realise DC-DC po wer con v ersion and to meet necessary v oltage requirement of the load. In case of systems with ener gy storage, tw o indi vidual unidirectional con v erters are used to control it’ s char ging and dischar ging c ycles. Ho we v er , both char ging and dischar ging capability can be implemented in same topology to lessen the count of po wer electronic components. Thus bidirectional DC-DC con v erter manages po wer flo w between input source, ener gy stora g e el ements and load in addition to v oltage le v el con v ersion, control J ournal homepage: http://ijpeds.iaescor e .com Evaluation Warning : The document was created with Spire.PDF for Python.
Int J Po w Elec & Dri Syst ISSN: 2088-8694 r 467 and increased lifetime of ener gy storage de vices. Isolation between po wer circuits are preferrable for safety reasons and hence to achie v e DC g alv anic isolation, transformers are included in the topologies. Thus intense researches are being carried out in de v elopment of ne w po wer electronic circuit topologies that interf aces solar PV , battery or supercapacitors and load with controlled po wer flo w between these ports [1–5]. The Bidirectional DC-DC con v erters (BDC) are operated in Boost mode (step up mode) and Buck mode (step-do wn mode) that controls po wer flo w both in forw ard and re v erse direction. The applications of such BDCs are e xtended in Electic V ehicles to char ge and dischar ge the batteries. Dual Acti v e Bridge (D AB) BDC topologies with a source port and a load port are deri v ed with bidirectional po wer flo w control [6–8]. Ho we v er , only tw o ports are controlled which leads to de v elopment of three port con v erter topologies to inte grate multi input and multi output ports with bidirectionality achie v ed in one or more ports. Based on the circuit configuration with or without g alv anic isolation pro vided by the transformer , these con v erters are cate gorized into partly / fully isolated con v erters and non-isolated con v erters respecti v ely . The design and analysis of v arious multiport topologies inte grating tw o or more sources are commonly found in literature. In this manuscript, a comprehensi v e re vie w of three port partly isolated bidirectional con v erters in recent decades are gi v en enhancing the researchers to de v elop man y no v el topologies for v arious applications. This paper gi v es an descripti v e analysis of e xisting multiport bidirectional con v erters listing its enhanced features and k e y contrib utions compared with other topologies. The or g anization of this manuscript is as follo ws: An o v ervie w and importance of bidirectional con v erter topologies are discussed in section 2. Section 3 deals with v arious isolated topologies highlighting the topology features and limitations. A com- parison of the topologies based on number of de vices, soft switching elements, its ef ficienc y are reported. In addition, the k e y contrib utions by the authors on achie ving soft switching of de vices and control techniques are also discussed follo wed with a brief summary in section 4. 2. O VER VIEW OF MUL TIPOR T BIDIRECTION AL CONVER TERS (MP-BDC) The traditional DC-DC con v erters in v olv e tw o ports namely the source and load port. The po wer changeo v er between the tw o ports either unidirectionally (con v entional con v erters) or bidirectionally (Bidirectional DC-DC Con v erter). Con v erters interf acing more than tw o ports are generally called multiport con v erters (MPC) in which the po wer con v ersion tak es place between an y tw o sources of the a v ailable sources. The primary source of the multiport con v erter is sized based on the a v erage load po wer consumption for a particular application instead of the peak po wer . The primary source o v ersizi ng is a v oided. In addition, the auxilliary storage serv es the purpose of acting as a back up ener gy source in case of main source f ailure and also impro v es the system dynamics. [9, 10] The input source port of the multiport con v erters is connected either to the rene w able ener gy sources lik e photo v oltaic system, fuel cells, wind ener gy or the ener gy storage systems lik e battery , supercapacitor or both [11]. The output load port is link ed to DC load. The ener gy con v ersion could be unidirectional or bidirectional between an y of these ports . The port v oltage, current or po wer is re gulated in each port for po wer flo w control. The phase shifting technique is basically emplo yed for po wer flo w control. The inductors in addition to transformer windings act as ener gy transfer elements for po wer e xchange. As per the la w of conserv ation of ener gy (po wer balance principle), in a system total po wer gener ated and total po wer consumed are equal. Ne glecting system loss, the source po wer is equal to all the po wer sunk in the ports e xpressed as in (1) where P x is positi v e for po wer sourcing from the port and ne g ati v e for po wer sinking into the port [9]. x = m + n X x =1 P x = 0 (1) Depending upon the source port po wer le v els compared with load port, the operating modes of three port con v erter are as follo ws [12]: Single Input - Dual Output (SI-DO) mode in whi ch input rene w able source supplies the load and surplus po wer from it char ges the ener gy storage elements. In Dual Input - Single Output (DI-SO) mode, po wer from both source and ener gy storage supplies the load to meet the load demand. The con v erter functions in Single Input - Single Output (SI-SO) mode is si milar to traditional tw o port DC-DC con v erter in the absence of rene w able input po wer . The load is supplied only by the ener gy storage system. In case of motor load operating in re generati v e braking mode, the braking po wer helps in char ging the ener gy storage element representing bidirectional po wer flo w in load port. Re vie w of multiport isolated bidir ectional... (Arulmozhi S.) Evaluation Warning : The document was created with Spire.PDF for Python.
468 r ISSN: 2088-8694 The rene w able ener gy sources lik e photo v oltaic cells, fuel cells, wind mills can be inte grated to share the load with the help of po wer con v erters. As the rene w able sources are intermittent by nature and load demands are unpredictable, ener gy storage systems lik e battery and supercapacitors are included as an additional component. Also, in applications lik e electric v ehicles, the batteries and supercapacitors are the major input sources which are inte grated to share the load. The con v entional con v erters are being replaced with the multiport con v erters because of its compact design with better ef ficienc y . As ener gy storage elements under go char ging and dischar ging c ycle, the port that connects it should be bidirectional. The multi-port bidirectional con v erters are cate gorized into (i) Non-isolated, (ii) P artly-isolated and (iii) fully isolated con v erter depending on the connection between source, load and storage ports. The non- isolated multi-port DC-DC con v erter sho wn in Figure 1(a) are deri v ed from basic b uck, boost and b uck-boost con v erters. Due to the limitation of con v erter g ain, the v ol tage con v ersion ratio can be e xtended by using cou- pled inductor . The circuit emplo ys minimum po wer switches with no trans formers for g alv anic isolation and hence results in smaller size and higher po wer density . The partly-isolated and is o l ated multi-port bidirectional DC-DC con v erters emplo ys a high frequenc y (HF) transformer to isolate source ports and load port g alv anically a v oiding shock hazards. In addition, the v oltage con v ersion g ain of the con v erter is increased by proper choice of transformer turns ratio. The g alv anic transformers used in isolated and partly-isolated con v erters relati v ely limits po wer density and ef ficienc y due its increase in o v erall size and magnetic losses respecti v ely . The choice of modulation control strate gies and po wer m anagement systems helps in implementing these multi- port con v erters for the desired applications. A detailed re vie w of v arious partly-isolated multi- po r t bidirectional DC-DC con v erters are discussed belo w . 2.1. P artly-isolated multi-port bidir ectional DC-DC con v erter In partly-isolated multi-port bidirectional DC-DC con v erters, the source ports and bidi rectional ener gy storage ports will be connected directly and mostly , the load port wi ll be g alv anically isolated using transformers. In some cases, the bidirectional ener gy storage port and output ports wil l be connected without isolation and then interf aced to the source through a HF transformer . The general block diagram representing partly-isolated con v erters are gi v en in Figure 1(b) and 1(c). Figure 1. Structure of Multi-Port Con v erter (a) Non-Isolated T opology , (b) Fully Isolated T opology , (c) & (d) P artly-Isolated T opology T ype 1, T ype 2 respecti v ely A no v el three port full bridge con v erter for rene w able ener gy applications w as proposed in [13] is gi v en in Figure 2. It w as actually deri v ed from con v entional full bridge topology . The topology comprises tw o bidirec tional source ports and an isolated unidi rectional load port without including an y additi onal de vices. A wide range of source v oltage v ariation is allo wed by the con v erter . The po wer relationship between PV and load mak es the proposed con v erter to operate either in dual output mode (PV char ging battery and feeding the load) or dual input mode (PV and battery supplying load) or SISO mode (battery dischar ged to feed load Int J Po w Elec & Dri Syst, V ol. 11, No. 1, March 2020 : 466 – 476 Evaluation Warning : The document was created with Spire.PDF for Python.
Int J Po w Elec & Dri Syst ISSN: 2088-8694 r 469 in the absence of PV source). Pulse W idth Modulation strate gy is implemented for smooth control of po wer flo w with impro v ed ef ficienc y . The adv antage of this topology is that po wer con v er sion is single stage with increased output v oltage between the ports. The stored ener gy in the transformer leakage inductor is utilized to achie v e Zero V oltage Switching (ZVS). Ho we v er , only the primary side switches are soft switched and secondary side diodes are hard switched. In spite of minimized switching losses, increase in conducti on losses results in reduced ef ficienc y which can be o v ercome by half bridge topology by reducing de vice count. Figure 2. Full Bridge Three Port Con v erter [13] Figure 3. Three port isolated con v erter with LCL resonant tank [14] Figure 4. FB-TPC T opology with PWM-SSPS control [15] Figure 5. FB-TPC T opology with V oltage Doubler circuit [16] The three port bidirectional DC-DC con v erter with tw o winding transformer inte grating PV cells and Battery output load port is proposed in [14] and is sho wn in Figure 3. In order to realize Zero-Current Switching (ZCS) for the main switch S 1 , resonant elements namely L-C-L (Inductor -Capacitor -Inductor) were included. The v oltage stress in main switch S 1 and the current stress di/dt v alue are reduced as a result of soft switching achie v ed by L-C-L resonant tank. The PV and load ports are unidirectional and the ener gy storage battery port is bidirectional. When the generated solar po wer is in e xcess of load demand, the con v erter operates in b uck mode and the surplus po wer char ges the battery . In case of Ppv < Pout, the con v erter w orks in boost mode to supply ener gy from char ged battery to satisfy t h e load requirement. In the absence of solar ener gy , the battery completely contrib utes the load demand as the con v erter manages to operate in boost mode. It has been observ ed that the LCL component reduces the v oltage stress and current stress by 45 % and 91 % respecti v ely . Ho we v er only the main switch S1 is soft switched and the remaining switches controlling battery bank are hard switched which results in o v erall increased losses. Also, the load port is unidirectional and hence this topology is not preferred for electric v ehicle applications under re generati v e braking mode. The limitations of primary side phase shift control (PSPS) lik e limited soft switching range, high conduction losses and high current ripple are o v ercome by proposing a no v el PWM - Secondary Side Phase Shift control (PWM-SSPS) as in [15, 17–19]. The proposed topology comprises of tw o bidirectional ports and an isolated port is gi v en in Figure 4. T w o interlea v ed Buck-Boost circuit inte grated wi th Full Bridge con v erter to eliminate the circulating current so that conduction los ses are reduced and hence resulting in impro v ed ef ficienc y in the range of 95 % to 97 % . A no v el topology proposed in [16] as in Figure 5 has similar primary side con v erter circuit, b ut secondary side with v oltage-doubler rectifier circuit. An or g anised approach for synthesizing three port con v erter is proposed using interlea ving bidirectional con v erter and bridgeless boost rectifier . The analysis is carried out in both continuous and discontinuous conduction modes of con v erter operation. PWM modulation control is emplo yed for primary side con v erter and phase shift control strate gy for secondary side con v erter . The v oltage stress and current ripple are highly reduced. ZVS is achie v ed for switches of both primary side and secondary side con v erters as result of PWM-SSPS t echnique. Ho we v er , the selection of high frequenc y inductor L f has a tradeof f between m aximum output and ef ficienc y for v arious load conditions. Re vie w of multiport isolated bidir ectional... (Arulmozhi S.) Evaluation Warning : The document was created with Spire.PDF for Python.
470 r ISSN: 2088-8694 Similar to the abo v e presented con v erter , a topology inte grating full bridge con v erter with tw o phase interlea v ed boost con v erter interf acing stand-alone PV sys tem with ener gy storage battery is proposed in [20, 21]. A center tapped secondary side transformer is used with a limitation of unidirectional load port as in Figure 6. The minimum curre n t ripple and better soft switching range are obtained with a trade-of f in choice of inductor v alue with dut y c ycle maintained at 0.5. Only PWM control is implement ed in the primary side con v erter circui t for mai ntaining the duty c ycle to the prescri bed v alue. Ho we v er the lim itation of center tapped circuit is o v ercome in [22] replacing with bridge type rectifier . The LLC resonant tank is included so that wide soft switching range, moderate circulating current and better po wer density can be obtained. In addition, the PWM and PFM modulation strate gy is implemented. In Figure 7, the duty c ycle D of S 1 , S 3 (the upper switch pairs) gi v en and switching frequenc y are the control v ariables for independent po wer flo w of each port and tight load re gulation of the output port. T o achie v e higher ef ficienc y , the duty c ycle and switching frequenc y are restricted to a relati v ely limited range. Ho we v er , v a lue of resonant elements are to be carefully chosen as it results in increased short circuit current and peak capacitor v oltage of resonant elements. Figure 6. FB-TPC T opology with bidirectional output port [20] Figure 7. TPC inte grated with interlea v ed boost con v erter and LLC tank [22] Figure 8. LLC-TPC using h ybrid full bridge structure [23] Figure 9. High ef ficienc y no v el three port isolated bidirectional con v erter [24] The three port LLC resonant con v erter interf acing PV system, Battery with isolated output load port is proposed in [23]. In Figure 8, a h ybrid full bridge system is sho wn with a bidirectional battery port stabilizing the source ener gy with load requirements. The battery char ging and dischar ging is controlled by resonant current. The battery current direction remains same in a single switching period, hence increasing it’ s lifetime. Though the proposed topology has an adv antage of reduced ripple current, switching de vice count is increased. A wide range of ZVS for switches of primary s ide con v erter and ZCS for switches of secondary side con v erter is achie v ed with the help of LLC resonant tank. Ho we v er , the soft switching is diificult to achie v e in de vices which has lo w turn-of f current. The inclusion of LLC resonant tank for the dual acti v e bridge topologi es is proposed in [25, 26] which gi v es the importance and operation of LLC resonant tank with multi le v el topology . In addition, PW AM control and Synchronous control starte gies are implemented in addition to phase shift control strate gy . A no v el isolated three port topology as sho wn in Figure 9 with impro v ed boost flyback con v erter on the PV source side for stepping up the v oltage le v el is proposed in [24]. The v oltage stress on the transformer is reduced by a DC blocking capacitor on load port con v erter and current ripples in the battery are minimized by an auxiliary inductor on t he battery port, thus impro ving the battery lifetime. Compared to full bridge topology , the number of de vices are reduced which results in reduced cost and simple g ate control. Despite the achie v ement of impro v ed v oltage g ains in b uck and boos t modes of operation, soft switching of de vices has not been addressed by the author which is v ery much essential to impro v e the o v erall con v erter ef ficienc y . Int J Po w Elec & Dri Syst, V ol. 11, No. 1, March 2020 : 466 – 476 Evaluation Warning : The document was created with Spire.PDF for Python.
Int J Po w Elec & Dri Syst ISSN: 2088-8694 r 471 An impro v ed flyback-forw ard con v erter topology is proposed in [27] for standalone PV sys tems. PWM and phase shift control are used for better output re gulation and to achie v e MPPT in PV systems. In Figure 10, the main de vices S 1 and S 2 are made to operate either in interlea v ed mode when PV supplies both load and battery or as an acti v e clamp circuit when battery alone supplying load or as tw o b uck-boost con v erters controlled independently in the absence of load. The switches S 3 and S 4 operates either in synchronous rectifi- cation mode or as flyback con v erter . A feedback loop design scheme is implemented for controlling the output v oltage using phase shift method and PV v oltage using PWM control. Ho we v er con v erter ef ficienc y could ha v e been enhanced by introducing soft switching technique for all switching de vices. Also the test results re v ealed that the ripple is comparati v ely higher in battery current which may de grade its lifec ycle. Figure 10. Three port con v erter with impro v ed Flyback / F orw ard topology [27] Figure 11. 3 + 1 Multi port bidirectional con v erter [28] Figure 12. Multi-port DC-DC con v erter with coupled magnetic inductor [29] A no v el multi -port bidirectional DC-DC con v erter is proposed in [28] interf acing h ybrid ener gy storage system (HESS) lik e battery and supercapacitor . The topology gi v en in Figure 11 has tw o channel interlea ving Buck/Boost on both primary side ( battery) and secondary side with a high v oltage port (DC b us) and lo w v oltage port (Supercapacitor). In addition, filter capacitor on battery side forms an high v oltage port without an y input / output po wer and hence the proposed con v erter is named as 3+1 port Bidirectional con v erter . By e xtending ports, a no v el “n+(n-2)” multi port con v erter can be obtained. ZVS for battery side switches is atained by maintaining duty c ycle D 6 0.5 and by proper choice of filter inductance on DC b us side. The pro- posed con v erter has been realized mainly for DC - micro grid system with ener gy storage systems. Ho we v er , the e xperimental tests are being conducted ignoring fully char ged or dischar ged state of battery which has to be addressed. A multi-port bidirectional con v erter with tw o winding center tapped HF transformer as in Figure 12 is proposed in [29]. T w o multi phase con v erter is inte grated with an isolated DC-DC con v erter and the po wer flo w is go v erned by proper choice of phase angle dif ference in full bridge and duty c ycle. The impedance beha vior of magnetic components lik e primary inductance, secondary inductance and transformer with respect to con v erter functioning ha v e been addressed in detail. It has been found that the number of magnetic compo- nents and semiconducor switches are do wnsized compared to the pre v ailing con v erters. Ho we v er , the con v erter ef ficienc y could be impro v ed by implementing soft switching for all de vices with a penalty of including additional resonant elements. The summary of partly isolated topol ogies considered for discussion are gi v en in T able 1. The topolo- gies could be either partly isolated with 2 winding transformer isolating all source ports and a load port or fully isolated with 3 winding transformer pro viding isolation for indi vidual ports. The de vices are soft switched by including resonant elements in the circuit and the resonant topologies (LCL, LLC, LC) are listed. Re vie w of multiport isolated bidir ectional... (Arulmozhi S.) Evaluation Warning : The document was created with Spire.PDF for Python.
472 r ISSN: 2088-8694 T able 1. Summary of partly isolated multi port topologies Ref P aper T opology Input/Output ports their v olt- age le v els f sw Rating T ransformer connections Resonant Elements De vice Count Bi- directional Ports A v erage [13] FBTPC PV - 38 to 76V , Battery - 26 to 38V , R load - 42V , 180W 100kHz 180W 2 winding transformer n = 5:14 L m L lk C 0 4M, 4D Battery port 94 % [14] P artly iso- lated TPC PV -22V , Battery- 7.5V , R load -50V , 25W 100- 170kHz 100W 2 winding transformer n = 5:14 LCL 3M, 4D Battery port 94.5 % [15] FB- interlea v ed TPC PV - 30 to 40V , Battery - 64 to 80V , R load - 100V 100kHz 600W 2 winding transformer n = 6:8 L f L 1 L 2 6M, 2D Battery port 95 to 97 % [22] FB- interlea v ed TPC PV - 65 to 115V ,500W Battery - 165 to 200V , R load - 360V 74 - 100kHz 500W 2 winding transformer n = 25:45 L r L m C r 4M, 4D Battery port 94 to 96 % [23] Hybrid FB-LLC interlea v ed TPC Battery - 150V , R load - 60 - 100V 100kHz 1kW 2 wi nding transformer n = 1:4 LCL 6M (4 +2), 4D Battery port – [24] TPC wit h impro v ed boost flyback con v erter PV - 20 to 26V ,Battery - 24V , R load - 200V 50kHz 500W 2 winding transformer n = 1:3 – 4M, 2D Battery , load port 94.2 to 97.6 % [27] Isolated TPC with impro v ed flyback forw ard con v erter Battery - 12V , R load - 80V 20kHz 250W 2 winding transformer with coupled inductor – 4M, 2D Battery port 90 to 91.3 % [28] Multi port con v erter with in- terlea ving b uck-boost Battery - 40 to 56.4V , Superca- pacitor - 150 to 300V R load - 400V 20kHz 500W 2 wi nding transformer n = 1 : 3.1 L r C r 8M Battery and superca- pacitor port – [29] Multi port con v erter with coupled inductor Port A to D - 40V , 200V , 16V , 80V 40kHz 1.5kW 2 winding center tap, n = 1 : 5 - 8M Port A and B 90 to 94 % *FB - Full Bridge, TPC - Threeport Con v erter , M - MOSFET , D - Diode The po wer de vices are soft swit ched to curtail the switching losses and enhance the ef ficienc y [30]. Zero V oltage Switching (ZVS) and Zero Current Switching (ZCS) either during turn on or turn of f interv al can be achie v ed by proper choice of resonant tank elements lik e inductor and capacitor . Dif ferent resonant tank configurations are de v eloped lik e series or parallel LC tank, LLC tank, LCC tank. Also, the interlea v ed b uck/boost con v erter circuitss are added to enhance better ef ficienc y . The k e y contrib utions of soft switching techniques and elements in the considered topologies are listed in T able 2. Int J Po w Elec & Dri Syst, V ol. 11, No. 1, March 2020 : 466 – 476 Evaluation Warning : The document was created with Spire.PDF for Python.
Int J Po w Elec & Dri Syst ISSN: 2088-8694 r 473 T able 2. K e y contrib utions on soft switching range Ref. P aper Soft switched de vice K e y contrib utions [13] T urn on and turn of f ZVS of all switches Leakage inductance, filter inductance and output capacitors along with magnetising inductance are used to accomplish ZVS of the switches. [14] ZCS of switch S 1 in LCL con v erter T o achie v e soft switching, the optimal range for Q f actor is 1.5 to 5 and selected v alue is 3.7 for nominal load with allo w able current ripple of 5 % . MPPT algorithm with frequenc y modul ation method is realized for soft switching of the de vice S 1 by fixing its on time. [15] ZVS of primary side switches high frequenc y inductor L f , inductor current L 1 , L 2 , input output po wer and dead time has to be properly designed [22] ZVS - primary side switches (MOSFETs) turn-on and ZCS - secondary side diodes o v er full operating range ZVS is related to resonant current I lr and boost inductor currents I b 1 and I b 2 with condition f n (normalized switching frequenc y) = 1, and D = D min and the the range for ZVS could be impro v ed by proper design of leakage inductance L lk [23] ZVS on primary side MOSFET and ZCS on secondary side rectifier diodes ZVS of l o wer de vice (M6) in le g B is dif ficult b ut still achie v eable based on the design v alue of magnetizing inductor and parasitic capacitance v alue in addition to the switching interv al dead time. [28] ZVS on primary side MOSFETs Soft switching achie v ed for phase shift angle ranging from 0.5* to - 0.5* with duty c ycle = 0.5, with a condi tion of i min i Lr 2 (min) and i max i Lr 2 (max) for ZVS of all DC b us side switches for full load range. 2.2. Contr ol strategy The output v oltage g ain and po wer re gulation between the ports are achie v ed by control v ariabl es lik e duty ratio, phase shift angle and switching frequenc y . Re vie w on the control strate gies using pulse width modulation and phase shift techniques are discussed as follo ws. A three port topology interf acing battery and supercapacitor with load is discussed in [31] which is deri v ed from [32]. The dynamic performance of battery is impro v ed because of the supercapacitor sharing the load during sudden changes. The bidirectional po wer flo w between the ports is achie v ed in addition to soft switching of main de vices by emplo ying phase shift control strate gy . This technique has also been discussed in [33–37], Ho we v er the solution for high current stress and limited soft switching range under light load conditions are not addressed. Pulse width modulation with phase shift control (PWMPS) technique in [38] helps to v anquish the dra wbacks of con v entional phase shift control technique. Ho we v er , the phase shift control results in higher current stress in switches and narro w limited ZVS range for mismatch in the input and output v oltage amplitudes. The abo v esaid limitations are subdued by PWMPS technique. The adv antages are reduced current stress, conduction losses, switching losses of semiconductors with a wider ZVS range. Similar PWMPS control technique to Dual Acti v e Bridge topology is implemented as in [39]. The reacti v e po wer algorithm for optimizing the reacti v e and a v erage output po wer is de v eloped to in v estig ate in detail so that the reacti v e po wer is considerably reduced compared to PS technique. An asymmetrical duty c ycle control is proposed in [40] in which the duty c ycle is v aried for the input side bridge de vices and i s fix ed to a v alue of 0.5 for the load side bridge switches. This control technique helps in achie ving wide ZVS range, reduced peak and rms current, impro v ed ef ficienc y due to reduced rms losses. The isolated topology with LCLC resonant tank is proposed in [41] which discuss in detail the role of resonant tank in achie ving high ef ficienc y of 96.9 % . The notable contrib utions by the authors on control strate gy for v arious topologies are listed in T able 3. Re vie w of multiport isolated bidir ectional... (Arulmozhi S.) Evaluation Warning : The document was created with Spire.PDF for Python.
474 r ISSN: 2088-8694 T able 3. K e y contrib utions on control strate gy Ref. P aper control strate gy K e y contrib utions [13] Pulse W idth Modulation (PWM) duty c ycle of switching de vices are determined based on minimizing L m of the transformer [15, 19] PWM and Secondary side phase shift control Phase shift angle in the range of (0 - 90) ; free wheeling stage circulating currents are eliminated; the rectifier v olt- age stresses are also suppressed [22] PWM and PFM f s and duty c ycle are controlle d with D=0.5 and induc- tor ratio m for g ain characteristics. F or minimizing input current ripple, design v alues are duty c ycle D = 0.5, phase shift = [23] Phase shift control Fundamental Harmonic Approximation method to deter - mine v oltage g ain by maintaining condition of D1 +D2 = 0.5 [28] Phase shift control phase shift angle is fix ed to 3. CONCLUSION The intention of this paper is to pro vide a detailed re vie w of the multi-port partial isolated bidirec- tional DC-DC con v erter topologies. The present trend in interf acing rene w able source with ener gy storage system sho ws clearly an increasing demand for high performance DC-DC con v erters with bidirectional po wer transfer capability . The details of e xisting multi-port con v erter topologies interf acing rene w able photo v oltaic source, ener gy storing battery , supercapacitor and load are discussed. The char ging and dischar ging of batter - ies, supercapacitors are controlled by implementing phase shift or pulse width modulated control techniques. Based on the discussions in this paper , it is clear that g alv anic isolation by transformer in both partly isolated and fully isolated three port con v erter topologies are preferred for bidirectional po wer flo w control of ener gy storage elements with higher po wer ratings.The soft switching of the po wer de vices are achie v ed by including LC, LLC resonant tank elements and thus impro ving the o v erall con v erter ef ficienc y as the switching losses are minimised. The k e y contrib utions by v arious authors on achie ving zero v oltage switching during turn on or turn of f and contrib utions in implementing control strat e g y for po wer flo w control are listed. This paper clearly e xhibits the scope for de v eloping no v el bidirect ional DC-DC con v erter topologies with additional input rene w able source ports or h ybrid ener gy storing systems. REFERENCES [1] M. Jain, M. Daniele, and P . K. Jain, “ A bidirectional DC-DC con v erter topology for lo w po wer applica- tion, ” IEEE T r ansactions on P ower Electr onics , v ol. 15, no. 4, pp. 595–606, 2000. [2] F . Z. Peng, H. Li, G.-J. Su, and J. S. La wler , “ A ne w ZVS bidirectional DC -DC con v erter for fuel cell and battery application, ” IEEE T r ansactions on power electr onics , v ol. 19, no. 1, pp. 54–65, 2004. [3] K. Sun, L. Zhang, Y . Xing, and J. M. Guerrero, “ A distrib uted control strate gy based on DC b us signaling for modular photo v oltaic generation sys tems with battery ener gy storage, ” IEEE T r ansactions on P ower Electr onics , v ol. 26, no. 10, pp. 3032–3045, 2011. [4] M. Ka vitha, V . Elanang ai, S. Jayaprakash, and V . Balasubramanian, “De v elopment of re generati v e brak- ing concept for electric v ehicle enhanced wit h bidirectional con v erter , ” International J ournal of P ower Electr onics and Drives , v ol. 9, no. 4, pp. 1584–1590, 2018. [5] A. Hatami, M. R. T ousi, P . Bayat, and P . Bayat, “Po wer management strate gy for h ybrid v ehicle using a three-port bidirectional DC-DC con v erter , ” in Electrical Engineer ing (ICEE), 2015 23r d Ir anian Confer - ence on . IEEE, 2015, pp. 1498–1503. [6] A. K. Jain and R. A yyanar , “PWM control of dual acti v e bridge: Comprehensi v e analysis and e xperimen- tal v erification, ” IEEE T r ansactions on P ower Electr onics , v ol. 26, no. 4, pp. 1215–1227, 2011. [7] R. Naayagi and A. F orsyth, “Bidirectional DC-DC con v erter for aircraft electric ener gy storage systems, ” 2010. [8] B. Zhao, Q. Song, W . Li u, and Y . Sun, “Ov ervie w of dual-acti v e-bridge i solated bidirectional DC-DC Int J Po w Elec & Dri Syst, V ol. 11, No. 1, March 2020 : 466 – 476 Evaluation Warning : The document was created with Spire.PDF for Python.
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