high-efficiency bidirectional three-phase lcc resonant...

IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 34, NO. 1, JANUARY 2019 97

High-Efficiency Bidirectional Three-Phase LCCResonant Converter With a Wide Load Range

Suk-Ho Ahn , Member, IEEE, Sung-Roc Jang , Member, IEEE, and Hong-Je Ryoo , Member, IEEE

Abstract—This paper details the design and implementationof an efficient 4-kW bidirectional converter with a wide loadrange, based on a three-phase LCC resonant converter operatedin a continuous conduction model, which has a number ofadvantages pertaining to a bidirectional power supply. The voltageboost-up function yields a high voltage gain without increasingthe transformer turn ratio. The high switching frequency, whichis achievable by using the soft-switching condition and multiphaseoperation, decreases the output ripple and helps minimize the sizeof the output filter, as the requirement for a filter changes after thepower flow. Moreover, this reduction in the size of the filters yieldseconomic advantages. In addition, because of the synchronous rec-tifier operation employed during switching, the conduction loss inthe rectifier diode of the proposed converter is low. The direction ofthe output power can be changed easily, using phase control. Theimplemented power converter is connected to a 320-V rated gener-ator on one side and 28-V lead-acid batteries on the other side. Thefunctionality of the proposed converter is verified in experiments.We confirmed the high performance of the developed converterin terms of efficiency (92.2%), operable load range (0–12.5 A instep-up, and 0–142 A in step-down), and voltage ripple (0.05%).

Index Terms—Bidirectional dc–dc converter, LCC resonant con-verter, three-phase resonant converter.

I. INTRODUCTION

B IDIRECTIONAL dc–dc converters are widely used in var-ious battery charging and discharging applications, such asrenewable energy systems, ESS, UPS, and EV power converters.In general, these applications require high power density, highefficiency, and high reliability for bidirectional dc–dc convertersand generally require isolation for safety.

Manuscript received September 25, 2017; revised December 21, 2017 andFebruary 25, 2018; accepted March 4, 2018. Date of publication March 11, 2018;date of current version November 19, 2018. This work was supported in partby the Korea Electrotechnology Research Institute Primary Research Programthrough the National Research Council of Science and Technology funded bythe Ministry of Science, ICT, and Future Planning (MSIP) under Grant 18-12-N0101-28 and in part by the National Research Foundation of Korea fundedby the Korea Government (MSIP) under Grant NRF-2017R1A2B 3004855.Recommended for publication by Associate Editor A. Safaee. (Correspondingauthor: Hong-Je Ryoo.)

S.-H. Ahn is with the Accelerator Engineering Team, Pohang AcceleratorLaboratory, Pohang 37673, South Korea (e-mail:,[email protected]).

S.-R. Jang is with the Electric Propulsion Research Center, Korea Electrotech-nology Research Institute, Changwon 51543, South Korea, and also with theUniversity of Science and Technology, Daejeon 34113, South Korea (e-mail:,[email protected]).

H.-J. Ryoo is with the School of Energy Systems Engineering, Chung-AngUniversity, Seoul 06974, South Korea (e-mail:,[email protected]).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TPEL.2018.2815078

To meet these requirements, various isolation-type bidirec-tional dc–dc converter topologies have been proposed, and manyresearch results targeted at achieving high power density andhigh efficiency have been published [1]–[30].

The phase-shift-modulated dual active bridge (DAB) con-verter has been extensively researched because it has advantagessuch as simple structure, soft switching, and high efficiency [6]–[12]. This phase-shift-modulated DAB converter operates witha high efficiency if the voltage transfer ratio is identical dur-ing step-up and step-down operations. However, it is associatedwith problems of high reverse energy and turn-OFF loss, whichlower the efficiency of the total system. Thus, various controlmethods to improve the efficiency and performance of the DABconverter [12]–[17] and to reduce the reverse energy have beensuggested [13]–[17]. The resonant-type converters with an ad-ditional resonance circuit have been suggested to reduce theloss [18]–[26]. In addition, a multiphase DAB converter thatincreased output power and decreased output voltage ripplesby sharing the turn-OFF loss among multiple switches has beenproposed [27]–[30].

The LCC resonant converter that operates in the continuousconduction mode (CCM) performs soft switching at zero volt-age and zero current during turn ON. Furthermore, it has a lowerconduction loss compared to the general resonant converter andcan reduce the turn-OFF loss because a relatively large losslesssnubber can be applied during turn OFF. For this reason, the LCCresonant converter has been applied in many industrial powersupply applications [31]–[35], and related analysis and designmethods have been researched [35]–[40]. Moreover, the LCCresonant converter is basically a series–parallel load resonantconverter and has the characteristics of a parallel resonant con-verter. Thus, it can change the voltage transfer ratio by changingthe resonance tank parameter without changing the transformerturn ratio [36]–[40].

In this study, we propose the three-phase LCC resonant con-verter with a bidirectional dc–dc converter topology. If the LCCresonant converter is applied to a three-phase bidirectional con-verter, it gives the advantage of using the above-mentioned loss-less snubber, which can reduce the turn-OFF loss, as a parallelresonant capacitor.

Furthermore, when the step-up and step-down operationshave different voltage transfer ratios due to battery voltage vari-ation because of the internal resistance of the battery resultingfrom the high current input/output of the battery load, the LCCresonant converter adopting the characteristics of a parallel loadresonant converter can be used to additionally connect a small

0885-8993 © 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.See http://www.ieee.org/publications standards/publications/rights/index.html for more information.

https://orcid.org/0000-0001-8567-3279https://orcid.org/0000-0001-5937-9068https://orcid.org/0000-0001-8657-7350mailto:[email protected]:[email protected]:[email protected]

98 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 34, NO. 1, JANUARY 2019

Fig. 1. Schematic of the proposed bidirectional three-phase LCC resonantconverter.

Fig. 2. Switching sequence for the step-down operation of the converter.

parallel resonance capacitor only during the step-up operationto compensate for the voltage transfer ratio. In addition, thefilter capacitance must be inevitably increased to minimize thevoltage ripples at the low voltage part, resulting in a low powerdensity. However, the bidirectional converter based on the pro-posed LCC resonant converter can achieve a high-power densityby minimizing the filter capacitance required in the multiphaseoperation.

Moreover, the proposed converter can reduce the conductionloss of rectifier diodes by operating the other switches (step-down and step-up) as synchronous rectifiers in the step-up andstep-down mode. Another advantage is that the direction ofoutput power can be easily switched through phase control. Thispaper explains in detail the implementation of the bidirectionalthree-phase LCC resonant converter and the principle of theoperation of the proposed converter, focusing on the efficiency,load range, ripples, and step load response.

II. OPERATIONAL PRINCIPLES OF THE PROPOSED CONVERTER

The proposed converter, which is shown in Fig. 1, is com-posed of twelve MOSFETs, three series resonant capacitors, threeseries resonant inductors, and three additional parallel resonantcapacitors. The three additional parallel resonant capacitors areonly operated in the step-up mode, to increase the voltage gainfrom the voltage boost function. Each inverter leg is operated asan LCC resonant converter in the CCM.

Fig. 3. Switching sequence for the step-up operation of the converter.

Fig. 4. Operation diagram for analysis of mode 1 of the step-down state.

Figs. 2 and 3 show the switching sequences for the step-up and step-down operation state, respectively. In this section,operations of the converter in modes 1 and 2 of both the step-down state and the step-up state are explained. The other modeof the converter operation is similar to the explained mode. Inthe step-down mode, the switches in the step-up leg (S4, S5, S6,S4’, S5’, S6’) are synchronized and operated with the switchesin the step-down leg (S1, S2, S3, S1’, S2’, S3’) as a synchronousrectifier, to decrease conduction loss in the rectifier diode. In thestep-up mode, switches S7–S9 are turned ON to increase thevalue of the parallel resonant capacitor, for higher voltage gainfrom the voltage boost-up function. The switches in the step-down leg are also operated with the switches in the step-upleg switches, as a synchronous rectifier. However, in this modeof operation, the synchronous rectifier has a 120-degree phaseshift. With this switching sequence, the direction of the outputis changed. Detailed descriptions and principles of operation foreach state are discussed below.

Step-down mode 1: The operation diagram for this mode isshown in Fig. 4. The black line depicts the power flow direction,and the grey line expresses the direction of the free-wheelingcurrent. In this mode, switches S2 and S3’ are turned ON, and theinput current flows through these switches, the series resonantcapacitors Cs2, Cs3, and the series resonant inductor Ls2. Whenthe load current flows through D5 and D6’, switches S5 and S6’are turned ON as synchronous rectifiers, to decrease conductionloss in the rectifier diode. At the beginning of this mode, the

AHN et al.: HIGH-EFFICIENCY BIDIRECTIONAL THREE-PHASE LCC RESONANT CONVERTER WITH A WIDE LOAD RANGE 99



free-wheeling current flows through the lossless snubber capac-itor C1, S2, and the resonant tank. After C1 is fully discharged,the free-wheeling current flows through the antiparallel diodeD1 of switch S1.

Step-down mode 2: After switch S2 is turned OFF, the inputcurrent begins to flow through switch S1. The voltage acrossswitch S2 slowly increases, as a result of charging from thelossless snubber capacitor C2. This operation helps to decreasethe turn-OFF loss of the switch. Prior to the beginning of thismode, the voltage and current across switch S1 are almost zero,as a result of the free-wheeling current from mode 1. Thus,switch S1 is turned ON in the zero voltage zero current (ZVZC)condition. The input current flows through switches S1 and S3’,the series resonant capacitors Cs1, Cs3, and the series resonantinductor Ls3. In addition, at the beginning of this mode, the free-wheeling current flows through the lossless snubber capacitorC2’, S3’, and the resonant tank. After C2’ is fully discharged, thefree-wheeling current flows through the antiparallel diode D2’of switch S2’. When the load current flows through D4 and D6’,switches S4 and S6’ are turned ON as synchronous rectifiers.The operation diagram for this mode is shown in Fig. 5.

As mentioned above, the switches are turned ON under theZVZC condition and are turned OFF with low turn-OFF lossbecause of the lossless snubber capacitors. In the step-down

Fig. 7. Operation diagram for analysis of mode 1-1 of the step-up state.


operation, the switches in the step-up side are operated assynchronous rectifiers. Because of this operation, the proposedconverter has a high efficiency.

In the step-up mode, switches S7–S9 are always turned ON,to connect to the additional parallel resonant capacitors (Cp1–Cp3). Hence, these switches can be replaced by a relay. Theadditional parallel resonant capacitors help improve the voltageboost-up function.

Step-up mode 1: The operation diagrams for this mode areshown in Figs. 7 and 8. During this mode, switches S5 and S6’are turned ON, and the input current flows through these switchesand the series resonant inductor Ls2. The free-wheeling currentflows through the lossless snubber capacitor C4, S5, and theresonant tank. After C4 is fully discharged, the free-wheelingcurrent flows through the antiparallel diode D4 of switch S4.

In the 1-1 mode shown in Fig. 7, the resonant current flowsthrough the parallel resonant capacitors Cp1 and Cp2. The res-onant current rises rapidly, as it is influenced by the parallelresonant capacitor, which has a relatively small capacitance.The energy stored in the resonant inductor increases, due to therise in the resonant current. After charging, the voltage acrossthe parallel resonant capacitors Cp1 and Cp2 is clamped to theoutput voltage. Current flows through switches S2 and S3’ tothe load, as shown in Fig. 8.




Step-up mode 2: This mode begins after switch S5 is turnedOFF and the input current starts to flow through switch S4. Thevoltage across switch S5 increases slowly, as a result of chargingfrom the lossless snubber capacitor C5. This operation helps todecrease turn-OFF loss in the switch. Prior to the beginning ofthis mode, the voltage and current across switch S4 are almostzero, as a result of the free-wheeling current. Thus, S4 is turnedON under the ZVZC condition. The input current flows throughS4 and S6’, and free-wheeling current flows through S5’ andS6’. The influence of the parallel resonant capacitors (Cp2, Cp3)on the resonant current in this mode is shown in Fig. 9. The loadcurrent flows through switches S2 and S3’, as shown in Fig. 10.

III. IMPLEMENTATION OF A 4-KW BIDIRECTIONAL CONVERTER

A prototype of the proposed 4-kW converter was built, forverifying the functionality of the device as a bidirectional powersupply. Table I shows the required specifications for the step-down operation, and Table II shows the required specificationsfor the step-up operation of the prototype. These specificationswere used in the implementation of the prototype. The 4-kWbidirectional power supply prototype is connected to a generatoras the step-up side load and lead-acid batteries as the step-downside load. The rated voltage of the load batteries is 28 V, and thevoltage of the load generator is 320 V.

TABLE ISPECIFICATIONS FOR THE STEP-DOWN OPERATION OF THE CONVERTER

Input voltage 320 V ± 16 VTransient voltage (during a 3-second period afterswitching)

260–360 V

Maximum input current 16 A (4 kW (28 V, 143 A)Instantaneous maximum output power (during a1.5-second period after switching)

5 kW (179 A)

Efficiency at rated operation >90%Output voltage variation range for 100% step loadresponse

24–29.5 V

Settling time for 100% step load response 90%Output voltage variation range for 100% step loadresponse

280–350 V

Settling time for 100% step load response 90%). The specificationfor the step load response of the prototype bidirectional powersupply is shown in Fig. 11. A stable output is required from thepower supply, within 3 seconds of switching, against a 100%step load.


Fig. 12. PSpice model of the bidirectional three-phase LCC resonant converter.

TABLE IIIDESIGNED PARAMETERS OF THE CONVERTER

Component Value

Series resonant capacitors (Cs1–Cs3) 4 µFHV snubber capacitors (C1–C3’)/parallel resonant capacitors 3.3 nFLV snubber capacitors (C4–C6’)/parallel resonant capacitors 1.5 µFTransformer turn ratio 4:22Resonant inductor (leakage inductance) 0.8 µHAdditional resonant capacitors (Cp1–Cp3) 47 nFHV filter capacitor 15 µFLV filter capacitor 150 µF

Fig. 13. Simulation waveforms for the step-down operation mode with a4-kW rated load.

The size and weight of the implemented 4-kW bidirectionalpower supply are less than 450 mm × 500 mm × 250 mmand 55 kg. The schematic of the power supply, which is usedas a PSpice simulation model, is shown in Fig. 12. The designparameters of the power supply are shown in Table III.

Figs. 13 and 14 show the simulation result waveforms forthe voltages at both ends of the switch, switch current, andgate signals under the rated load condition of 4 kW. As with

Fig. 14. Simulation waveforms for the step-up operation mode with a4-kW rated load.

the general characteristics of the LCC resonant converter, thedesigned converter naturally performs soft switching at zerovoltage and zero current conditions as current flows throughthe switch by resonance after the turn-ON gate signal is appliedand the current flows through the parallel diodes in the switchat the time of turn ON. Furthermore, at the time of turn OFF,the voltages at both ends of the switch are slowly increased bythe lossless snubber capacitor (HV switch; 3.3 nF; LV switch1.5 µF) connected in parallel in the switch, thus reducing theturn-OFF loss.

Fig. 15 shows the control block diagram of the designed powersupply. The error signal is output through the PI controller forthe real voltage/current and reference voltage current measuredthrough the voltage divider and the direct-current current trans-former. If this signal is input through the frequency modulationIC, a frequency to control the output is formed. This frequencysignals have the range of 420 kHz to 1.8 MHz, which is sixtimes larger than the actual switching frequency. This signalis input to the clock of a 3-bit Johnson-Counter and outputs aswitching frequency signal (70–300 kHz) that has a phase dif-ference of 120°. The switching frequency signals are divided


Fig. 15. Control block diagram of the bidirectional three-phase LCC resonantconverter.

Fig. 16. Experimental waveforms of the power supply during the step-downoperation with a 4-kW load [time scale: 5 µs/div.; resonant current, 10 A/div.;HV MOSFET (step-up) Vds , 200 V/div.; LV MOSFET (step-down) Vds , 20 V/div.;output current (LV), 50 A/div.].

through the analog control switch, and the gate signals with theforms of Figs. 2 and 3 are input to the gate driver circuit of eachswitch. As in [31]–[35], the designed gate drive circuit of thepower system operates the LCC resonant converter using a gatedriver with zero voltage detection feature, and turn ON is onlyperformed when the current flows through the parallel diode ofthe switch at the time of operating the synchronous rectifier.

IV. EXPERIMENTAL RESULTS

In this section, results of experiments performed using the4-kW bidirectional power supply based on the proposed con-verter, to verify its functionality and that it satisfies the opera-tional requirements detailed in Tables II and III, are discussed.

Fig. 16 shows experimental waveforms of voltage and currentduring the step-down operation with a 4-kW rated load resistor.As shown in Fig. 16, the peak of the resonant current is about18 A, and the switching frequency is 70 kHz. During the step-down operation, the MOSFET switches on the step-up side are alsooperated as synchronous rectifiers, to decrease their conductionloss. Because of this operation, the total measured efficiency ofthe power supply is 92.2%. Fig. 17 shows experimental currentand voltage waveforms during the step-down operation withno load. The peak of the resonant current is about 3 A, andthe switching frequency is 298 kHz. Thus, we verified that the

Fig. 17. Experimental waveforms of the power supply during the step-downoperation with no load [time scale: 5 µs/div.; resonant current, 20 A/div.; HVMOSFET (step-up) Vds , 200 V/div.; LV MOSFET (step-down) Vds , 20 V/div.;output current (LV), 50 A/div.].

Fig. 18. Experimental waveforms of the power supply during the step-upoperation with a 4-kW load [time scale: 5 µs/div.; resonant current, 20 A/div.;HV MOSFET (step-up) Vds , 200 V/div.; LV MOSFET (step-down) Vds , 20 V/div.;output current (HV), 2 A/div.].

implemented bidirectional power supply can be operated withhigh efficiency in the step-down mode, and with a wide rangeof loads, from no-load to a 4-kW rated load.

Figs. 18 and 19 show experimental waveforms during thestep-up operation. As shown in Fig. 18, the peak of the resonantcurrent, measured at the step-down side of the transformer, is21 A, and the switching frequency is 68 kHz.

At the beginning of the resonance condition, the current in-creases rapidly because of the additional parallel resonant ca-pacitor. Hence, the resonant current has a low crest factor, whichdecreases the conduction loss. Fig. 19 shows experimental wave-forms during the step-up operation under the no-load condition.In this case, the peak of the resonant current, measured at thestep-down side of the transformer, is 10 A, and the switchingfrequency is 203 kHz. We also verified that the power supplycan be operated with a wide load range in the step-up mode.

Figs. 20 and 21 show the results of output voltage ripplemeasurements performed during the step-down and step-up op-eration. During the step-up operation with a rated resistor load,the measured output voltage ripple is 0.5 V peak-to-peak. Inthe step-down operation with a rated resistor load, the measured


Fig. 19. Experimental waveforms of the power supply during the step-upoperation with no load [time scale: 5 µs/div.; resonant current, 20 A/div.; HVMOSFET (step-up) Vds , 200 V/div.; LV MOSFET (step-down) Vds , 20 V/div.].

Fig. 20. Experimental waveforms of the output voltage ripple during the step-down operation [time scale: 5 µs/div.; resonant current, 20 A/div.; HV MOSFET(step-up) Vds , 200 V/div.; output current, 20 A/div.; output voltage (ac), 1V/div.].

Fig. 21. Experimental waveforms of the output voltage ripple during the step-up operation [time scale: 5 µs/div.; resonant current, 20 A/div.; HV MOSFET(step-up) Vds , 200 V/div.; output current, 5 A/div.; output voltage (ac), 2 V/div.].

output voltage ripple is 1 V peak-to-peak. We expect the outputvoltage ripple to decrease if the power supply is operated with areal load (generator and batteries), instead of the rated resistorsused in the detailed experiments, as the implemented bidirec-tional power supply is designed to reduce ripples through the

Fig. 22. Measured output power with respect to switching frequency.

Fig. 23. Experimental waveforms of the step load response during the step-down operation (time scale: 100 ms/div.; resonant current, 20 A/div.; LV MOSFETVds , 20 V/div.; output current, 5 A/div.; output voltage, 100 V/div.).

multiphase operation (three-phase) with a high switching fre-quency (70–200 kHz), without increasing the number of com-ponents in the output filter.

Fig. 22 shows the measured output power with respect to theswitching frequency during the step-down operation with a 28 Voutput and the step-up operation with a 320 V output.

To measure the step load response characteristic of the powersupply, the load is suddenly disconnected and reconnected usinga circuit breaker, during a 4-kW rated operation. As shown inFig. 23, which depicts the results of step load response experi-ments performed in the step-down operation, the power supplycan be operated with output voltage fluctuations below 1 V, whenthe load is rapidly disconnected and reconnected. The measuredsettling time with a 100% step load is below 10 ms. The re-sponse of the output voltage satisfies the system requirementsshown in Table II, where voltage fluctuations of less than 9.6 Vfor a 320 V output are satisfactory. Fig. 24 shows the resultsof step load response experiments performed during the step-upoperation. The power supply can be operated with output volt-age fluctuations below 1.4 V, which settle within 10 ms. Thesecharacteristics also satisfy the step load response requirementsdetailed in Table I. We posit that in comparison to the resultsobtained with the purely resistive load, an improved response


Fig. 24. Experimental waveforms of the step load response during the step-upoperation (time scale: 100 ms/div.; resonant current, 20 A/div.; LV MOSFET Vds ,20 V/div.; output current, 5 A/div.; output voltage, 100 V/div.).

Fig. 25. Result of efficiency measurement.

will be observed with a real load, due to the capacitors of thegenerator and the batteries.

Finally, Fig. 25 shows the result of efficiency measurementof the implemented bidirectional power supply, during the step-down and step-up operation. From this image, it can be seenthat the maximum efficiency measured is 92.2% during the step-down operation with a 28 V output and 91.7% during the step-upoperation with a 320 V output. Thus, it has been verified that abidirectional power supply based on the converter proposed inthis paper can be operated with high efficiency. We have alsodemonstrated that the proposed converter is suitable for use asa bidirectional power supply.

V. CONCLUSION

In this paper, a bidirectional three-phase LCC resonant con-verter with high output voltage gain is presented, which is appli-cable to bidirectional power supplies. The proposed converterhas the general advantages of LCC resonant converters operat-ing in the CCM, especially when used as a bidirectional powersupply. The voltage boost-up function yields a high voltage gainwithout increasing the transformer turn ratio. The high switch-ing frequency, resulting from the soft-switching condition andmultiphase operation, can decrease the output ripple and helpminimize the size of the output filter, as the requirement for afilter changes after the power flow, which yields certain eco-nomic advantages. The conduction loss in the rectifier diode of

the proposed converter is low due to the synchronous rectifieroperation. The direction of the output power can be changedeasily through phase control. We demonstrated the high perfor-mance of the proposed converter, with respect to a wide operableload range, a low output voltage ripple, and an efficient step re-sponse characteristic. The operational principle of the proposedconverter was also explained. The design and implementationof a 4-kW bidirectional power supply, based on the proposedconverter, was presented. During experiments, one side of thepower supply was connected to a 320-V rated generator, and theother side was connected to 28-V rated lead-acid batteries.

Finally, the developed bidirectional power supply was testedwith a resistor load. We observed a maximum efficiency of92.2%, during the step-down operation and 91.7% in the step-up operation, and a controllable load range of 0–28 V, in thestep-down operation and 0–320 V in the step-up operation. Theoutput voltage ripple was 1 V in the step-down operation and1.4 V in the step-up operation. Thus, we verified that the pro-posed converter topology can be used effectively for a highvoltage gain bidirectional power supply.

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Suk-Ho Ahn (M’11) received the B.S. degree fromIncheon National University, Incheon, South Korea,in 2009, and the Ph.D. degree from the University ofScience and Technology, Daejeon, South Korea, in2015, both in electrical engineering.

In 2016, he was a Postdoctoral Research Fellowwith the Korea Electrotechnology Research Institute,Changwon, South Korea. Since 2016, he has beena Staff Scientist with the Department of Accelera-tor R&D, Pohang Accelerator Laboratory, Pohang,South Korea. His research interests include high-

voltage, high-power converter, and solid-state pulsed power modulator.

Sung-Roc Jang (M’11) was born in Daegu, SouthKorea, in 1983. He received the B.S. degreefrom Kyungpook National University, Daegu, SouthKorea, in 2008, and the M.S. and Ph.D. degrees inelectrical engineering from the University of Scienceand Technology, Daejeon, South Korea, in 2011.

Since 2011, he has been with the KoreaElectrotechnology Research Institute, Changwon,South Korea, as a Senior Researcher with the ElectricPropulsion Research Center. In 2015, he became anAssistant Professor with the Department of Energy

Conversion Technology, University of Science and Technology. His current re-search interests include high-voltage resonant converters and solid-state pulsedpower modulators and their industrial applications.

Dr. Jang was a recipient of the Young Scientist Award at the 3rd Euro-Asian Pulsed Power Conference in 2010, and the IEEE Nuclear Plasma ScienceSociety Best Student Paper Award at the IEEE International Pulsed Power Con-ference in 2011.

Hong-Je Ryoo (M’17) received the B.S., M.S.,and Ph.D. degrees in electrical engineering fromSungKyunkwan University, Seoul, South Korea, in1991, 1995, and 2001, respectively.

From 2004 to 2005, he was a Visiting Scholar forhis postdoctoral study with the Wisconsin ElectricMachines and Power Electronics Consortium, Uni-versity of Wisconsin-Madison, Madison, WI, USA.During 1996–2015, he was with the Korea Elec-trotechnology Research Institute, Changwon, SouthKorea, where he joined the Electric Propulsion Re-

search Division, as a Principal Research Engineer, in 2008, and was a Leader ofthe Pulsed Power World Class Laboratory. He was a Professor with the Depart-ment of Energy Conversion Technology, University of Science and Technology,Daejeon, South Korea. In 2015, he joined the School of Energy Systems Engi-neering, Chung-Ang University, Seoul, South Korea, where he is currently anAssociate Professor. His current research interests include pulsed-power sys-tems and their applications, as well as high-power and high-voltage conversions.

Dr. Ryoo is a Member of the Korean Institute of Power Electronics and theKorean Institute of Electrical Engineers.

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