IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 47, NO. 10, OCTOBER 2019 4473

Integrated 15-kV DC Trigger and Simmer PowerSupply for Light Sintering

Chan-Gi Cho , Ziyi Jia, Seung-Ho Song , Jae-Beom Ahn, and Hong-Je Ryoo

Abstract— An integrated full-bridge inverter circuit with fewercomponents and lower volume is proposed. The conventionallight sintering system uses several independent power supplies,each having an input voltage source and inverting component.However, the structure of the proposed circuit comprises onlyone full-bridge inverter with two separated transformers forapplying independent dc trigger and simmer output voltages. Theseparated transformers are considered to have the same operationswitching frequency because of the integrated inverter part.When designing the system, we considered not only matching theswitching frequency but also turning-on of the xenon flash lamp.Some of the considerations are as follows: no-load characteristicof the lamp at the initial moment, voltage-boosting effect of theparasitic inductance and capacitance, additional simmer outputcurrent path for continuous conduction, and dc trigger turn-offmoment when the 15-kV trigger output voltage changes the lampimpedance. Here, the successful results of the aforementionedconsiderations for applying the light sintering technology arepresented. The simulation and no-load experiment waveformsare consistent with the analysis of the effects of the parasiticinductance and capacitance. In addition, the waveforms show15- and 1.0-kV stable output voltages for the dc trigger andsimmer power supplies, respectively. Finally, the xenon flashlamp load is tested, and the integrated system is observed tobe functional for single or series-connected lamps.

Index Terms— AC–DC power conversion, trigger circuits, volt-age multipliers.

I. INTRODUCTION

THE light sintering technology, which is part of theprinted-electronics field, has been developed and applied

to various applications, including flexible inkjet printing,3-D printing, organic light-emitting diodes, and microstriparray antennas. Here, the light is generated by a xenonflash lamp, and it makes the ink material conductive. Thistechnology is advantageous in that the manufacturing processwith it is shorter compared to employing the normal thermalsintering technique and that it can be implemented by an

Manuscript received December 24, 2018; revised February 28, 2019;accepted April 2, 2019. Date of publication April 19, 2019; date of currentversion October 9, 2019. This work was supported in part by the Chung-AngUniversity Research Scholarship Grants in 2019 and in part by the HumanResources Program in Energy Technology of the Korea Institute of EnergyTechnology Evaluation and Planning (KETEP), granted financial resourcefrom the Ministry of Trade, Industry and Energy, South Korea, underGrant 20184030202270. The review of this paper was arranged by SeniorEditor R. P. Joshi. (Corresponding author: Hong-Je Ryoo.)

C.-G. Cho, Z. Jia, S.-H. Song, and J.-B. Ahn are with the Departmentof Energy Systems Engineering, Chung-Ang University, Seoul 06974, SouthKorea (e-mail: pon98095@cau.ac.kr).

H.-J. Ryoo is with the School of Energy Systems Engineering, Chung-AngUniversity, Seoul 06974, South Korea (e-mail: hjryoo@cau.ac.kr).

Color versions of one or more of the figures in this article are availableonline at http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TPS.2019.2909639

instantaneous energy irradiation, which does not damage thesubstrate [1]–[4].

To implement the light sintering technology, two or threeindependent power supplies are used for different roles. Theroles and characteristics of each power supply are briefly sum-marized as follows. The first power supply, known as “triggerpower supply,” generates a few tens of kilovolts output voltagefor the ionization of the xenon lamp. Its high output voltagecan be generated in various waveforms, such as pulse, ac,and dc waveforms [5]–[9]. Second, an auxiliary power supply,known as “simmer power supply,” is also used and has the roleof sustaining the ionized state of the lamp from the high outputvoltage of the trigger power supply. It prolongs the lifetimeof the xenon lamp by reducing the number of applied triggervoltages [10]–[12]. If the simmer power supply is not used,the trigger output voltage will be generated at every sinteringmoment. The last power supply is the main pulse power supplythat discharges the energy as pulse waveforms to the xenonflash lamp for changing the conductivity of used inks [13].

The described power supplies are selectively connected inseries or parallel for the implementation of the light sinteringtechnology [14], [15]. Although there are various conjunctionsbetween the power supplies, their operation sequence is simi-lar. First, the xenon flash lamp is ionized by the trigger voltage,and the lamp impedance drops. Then, the output power of thesimmer power supply sustains the ionized xenon gas conditionand ensures that the lamp remains in the turn-on condition.While the flash lamp is lit, the main pulse power supply appliesshort pulses to the lamp.

In this research, both the dc trigger and simmer powersupplies are addressed. Consequently, the integration of the dctrigger and simmer power supplies, which share a full-bridgeinverter for the implementation of light sintering, as shownin Fig. 1, is suggested. The inverter component of the dc trig-ger, which is needed only for the initial operation moment ofdriving the xenon lamp, is replaced by the integrated inverterpart of the simmer power supply. The integrated inverter partis connected to two transformers (TR1 and TR2), and eachtransformer is connected with the voltage multiplier circuit andoutput rectifying diodes. Thus, the sum of the dc trigger outputvoltage (Vout1) and simmer output voltage (Vout2) is appliedto the xenon flash lamp when the integrated power supplyturns on. If a specific voltage is reached, which depends onthe variation in the lamp length and diameter, the impedanceof the lamp is reduced. The controller detects this impedancechange (tionization), and subsequently, the magnetic contactor(MC) is closed to reduce the conducting loss of the diodesand generate the main pulse discharging path.

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4474 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 47, NO. 10, OCTOBER 2019

Fig. 1. Proposed integrated circuit of the dc trigger and simmer power supplies.

The xenon lamp driving system, which is typically com-prised of dc trigger and simmer with two independent inverterparts, is newly proposed to share a single inverter part forby the two power supplies. Thus, the proposed system hasadvantages such as a simplified circuit and reduced manufac-turing cost. In addition, the bypass current pass of the simmeroutput current is made to supply continuous current to thelamp. Furthermore, this paper also analyzes the experimentalphenomenon that the measured dc trigger output voltage ishigher than the theoretically calculated value and applies it asa voltage boost effect when designing the dc trigger powersupply.

To control both power supplies, the output voltage andcurrent of the simmer power supply are used as references.Therefore, the dc trigger output voltage is affected by thesimmer output values. This implies that there is a difficultyin generating an exact targeted output voltage of the trigger.This problem is solved by increasing the number of multiplierstages for ensuring the output voltage margin. In addition,when the xenon lamp is ionized (tionization), the transformerof the dc trigger power supply is disconnected from the full-bridge inverter to prevent unexpected problems.

Table I lists the specifications and parameters of the sug-gested integrated dc trigger and simmer power supply system.The design parameters are selected to achieve the target outputvoltage under a no-load condition because the xenon flashlamp shows a no-load characteristic at the initial moment.

This paper is organized as follows. Section II describes theimplementation considerations of the integrated dc trigger andsimmer power supply system. The operation principle of thepower supplies and analysis of the parasitic components aredealt with along with the equivalent circuit in Section III.The no-load experiment and actual xenon lamp test results forverifying the operation performance of the suggested commoninverter circuit system are given in Section IV. Section Vsummarizes the advantages of this system and experimentalresults.

TABLE I

SPECIFICATIONS AND PARAMETERS OF THE INTEGRATED DCTRIGGER AND SIMMER POWER SUPPLIES

II. CONSIDERATIONS FOR THE SUGGESTED INTEGRATED

DC TRIGGER AND SIMMER POWER SUPPLY

IMPLEMENTATION

For the proposed integrated circuit implementation, thereare additional requirements for driving the xenon flashlightsintering system. These considerations are summarized inSection II.

A. Simultaneous Operation Sequence at the Initial Momentfor Each Power Supply

The dc trigger and simmer power supply start simultane-ously when the full-bridge inverter switches work. This impliesthat the same switching frequency is used, and sufficientoutput voltage of the simmer power supply should be acquired.A high simmer output voltage, which is applied to the xenonlamp at the triggering moment, results in a stable sinteringsystem operation. Therefore, it is important to obtain a highoutput voltage rising rate for the simmer power supply toguarantee an adequate voltage margin.

CHO et al.: INTEGRATED 15-kV DC TRIGGER AND SIMMER POWER SUPPLY FOR LIGHT SINTERING 4475

B. No-Load Condition of the DC Trigger and SimmerPower Supply

The initial condition of the xenon lamp serves as a no-loadcondition because the high lamp impedance blocks the externalcurrent conduction through the lamp load. Therefore, the dctrigger and simmer power supplies should accomplish the tar-get output voltage under the no-load condition. To control theoutput voltage, the switching frequency starts at the maximumfrequency and slowly decreases until it reaches the referenceoutput voltage.

In addition, the power supplies are designed to utilize thecurrent source characteristics to control the output currentwhen the lamp impedance is suddenly changed by the dctrigger output voltage. An LCC resonant converter operatingabove the resonant frequency region using the leakage induc-tance of the transformer is used as the current source powersupply.

C. Continuous Current Path for Sustaining the IonizedLamp State

When the lamp is triggered, the trigger voltage and simmervoltage are reduced steeply because of the reduction in thelamp impedance. Simultaneously, the simmer output currentstarts to flow to the lamp and sustains the ionized lamp state.Therefore, to sustain the ionized lamp gas, the simmer currentshould be conducted continuously. A bypass diode and MCare introduced to generate an additional current path. In termsof the conducting procedure, at the initial moment of thesystem, the simmer output current flows through the bypassdiode because the MC is open. After the controller detectsa certain simmer output current value, which corresponds tothe triggering, the MC is finally closed, and the simmer outputcurrent starts to flow continuously with the reduced conductingloss. In addition, the input line of the dc trigger transformer isalso disconnected when the MC is closed so that the voltagemultiplier part is completely separated from the integratedinverter part when the system operates.

III. ANALYSIS OF THE SUGGESTED INTEGRATED

POWER SUPPLY SYSTEM

The proposed power supplies are analyzed with an equiva-lent circuit and the simulation results to show the performanceof the system. For the dc trigger power supply, the result ofthe parasitic components is additionally analyzed.

A. DC Trigger Power Supply

A Cockcroft–Walton voltage multiplier is used to generatea few tens of kilovolts as a simple circuit. The target outputvoltage can be controlled by the turns ratio of the transformerused and number of multiplier stages. However, there is atradeoff relationship between the two control methods. If theturns ratio increases, the rated voltage value of the used diodeand capacitor will also increase. However, if the numberof stages increases, the loss increases so that there is adifference between the ideally calculated output voltage valueand measured value. The diode, capacitor, and turns ratio areselected by considering these conditions.

Fig. 2. Simulation results and operation mode circuits of the proposed dctrigger power supply. (a) Operation waveforms under the ideal condition.(b) Mode 1. (c) Mode 2. (d) Mode 3. (e) Mode 4.

In Fig. 2(a), the ideal operation waveform displays thecharging procedure. Here, the secondary voltage of TR1 asa pulse voltage (Vpulse), input current (iL), conducting current

4476 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 47, NO. 10, OCTOBER 2019

Fig. 3. Simulation results and schematic of the dc trigger power supply.(a) Operation waveforms with the parasitic components. (b) Schematic withthe parasitic capacitors of the diodes.

of the diodes (D6, D4, and D2) of each stage, and voltage ofthe capacitors (C1–C6) of each stage is shown. To analyze theideal operation mode clearly, the stage range of the multipliercircuit is simplified from 11-stage to three-stage, similar toFig. 2(b)–(e), because the charging principle is the same evenif the number of stages is decreased.

Mode 1 begins at the moment when Vpulse changes from anegative value to a positive value. As shown in Fig. 2(b), whileiL is conducted, capacitors C1, C3, and C5 are discharged andcapacitors C2, C4, and C6 are charged. Mode 2 starts whenthe voltage of C5 is equal to the voltage of C6 and currentpath changes from D6 to D4, as shown in Fig. 2(c). Mode 3begins when the voltage of C3 equals the voltage of C4 withdischarging C1 and charging C2. In Mode 4, the current doesnot conduct and waits until the next negative input voltage isapplied. Thereafter, the aforementioned mode is repeated inthe reverse direction for the negative input voltage.

Based on the aforementioned operation sequence, the outputvoltage of the dc trigger under the no-load condition isexpressed in the following equation [16], [17]:

Vout_trigger =m∑

n=1

VC2n = 2nVpulse (1)

where Vout_trigger is the sum of the even number capacitorvoltages, m represents the number of stages, and Vpulse is theinput voltage of the Cockcroft–Walton circuit.

However, unlike in the ideal operation mode analysis, thereexists a resonance between the leakage inductance of thetransformer and parallel parasitic capacitance of the diode.This resonance distorts the input voltage and current of thevoltage multiplier, as shown in Fig. 3(a). The distorted inputvoltage comprises the original input voltage (Vpulse) andadditionally generated voltage on the leakage inductor (VLr) so

Fig. 4. Graph for determining the optimized value of fop.

that the peak value of the transformer secondary-side voltageis increased. The voltage of the leakage inductor is generatedby the continuous resonant current. Although the ideal currentcannot conduct after the capacitors of the dc trigger arefully charged, in a realistic circuit, the resonant current flowsthrough the parallel parasitic capacitors of the diodes.

As a result, the distorted input voltage of the multiplier cir-cuit generates a larger output voltage than the ideal dc triggeras with a voltage-boosting effect. Although, as a side effect,the additional heat problem should be considered for using thisboosted output voltage because the continuous current causesa temperature increase at the diodes and capacitors, the outputvoltage is increased by 30% compared with the ideal outputvoltage at the given switching frequency. Fig. 3(a) shows thesimulation result of the 30%-increased output voltage due tothe resonance.

B. Simmer Power Supply

The simmer power supply operates in a continuous con-duction mode for the modified LCC resonant converter. Theconverter uses SiC metal–oxide–semiconductor field-effecttransistors (MOSFETs) to increase the switching frequencyand replace the bulky resonant inductor with the leakageinductance of the transformer.

In the design of the LCC resonant converter, the trapezoidalapproximation method is used [18]. A parallel resonant fre-quency ( fop) of 280 kHz is determined by Fig. 4. This suggeststhat the peak current of the resonant inductor (ILs,peak) is lessthan 11.5 A and that 20% of the rated output power is achievedat thrice (Po,light) the rated switching frequency

tM2 = 4Ts − 3Top

8(2)

VCs,peak = ILs,peak × tM2

2Cs(3)

where tM2 is the time during which the resonant current isflat, Top is one cycle of the parallel resonant frequency, andCs is the series resonant capacitance.

Using (3), the value of the series resonant capacitor (Cs) canbe calculated using the peak voltage and current. Subsequently,

CHO et al.: INTEGRATED 15-kV DC TRIGGER AND SIMMER POWER SUPPLY FOR LIGHT SINTERING 4477

Fig. 5. Simulation results and schematic of the simmer power supply.(a) Operation waveforms under the no-load condition. (b) Schematic withthe additional components of the integrated circuit.

the parallel resonant characteristic impedance (Zop) by usingthe following equation, resonant inductance (31 μH), andparallel capacitance (10 nF) are also determined:

Zop = 2Vin + VCs.peak

ILs,peak. (4)

To apply the suggested integrated circuit for the implemen-tation of the light sintering technology, this power supplyshould generate a stable output voltage under the no-loadcondition until the impedance of the lamp is decreased bythe dc trigger output voltage. The reason is that a certainsimmer output voltage is required to accomplish successfullamp ionization. If the simmer output voltage is lacking,the lamp will only flash but without sustaining the ionizationcondition. Therefore, under the initial condition, the switchingfrequency is selected as the maximum value, which slowlydecreases to attain sufficient output voltage.

The simulation results of the no-load condition are presentedin Fig. 5(a), which shows the output voltage (Vout2), drain–source voltage of the main inverter switch (Vds), current ofthe main inverter switch (ids), and resonant current (iCs). The1.0-kV output voltage and zero-voltage turn-on are confirmedat the switching frequency of 270 kHz. The negative currentof the main inverter switch shows that the current flowsthrough the antiparallel diode under the zero-voltage condition.Although the MOSFET switch current conducts simultane-ously both the dc trigger and simmer circuits, the amount of

Fig. 6. Simulation results of the integrated dc trigger and simmer powersupply with the xenon lamp ionization moment at 0.5 ms.

resonant current of the simmer is a major factor determiningthe zero-voltage switching condition. This is because the dctrigger resonant current is comparatively small.

Fig. 5(b) also includes the block diode (Dblock), bypassdiode (Dbypass), and MC. These additional components haveroles in making the system operation stable. More specifically,the block diode protects the simmer power supply when themain high-voltage pulse is generated from the main powersupply. The bypass diode ensures an additional current path forcontinuously conducting the simmer output current. Finally,the MC turns on when the controller detects the specificvalue of the simmer output current required for reducing theconduction loss. Simultaneously, TR1 is also disconnectedfrom the inverter part to stop the operation of the dc triggerpower supply. Therefore, as the final step, the xenon flash lampis only connected to the simmer output port.

C. Integrated DC Trigger and Simmer Power Supply

Based on the aforementioned analysis, the integrated circuitis simulated and the result is shown in Fig. 6. The dc triggerand simmer output voltages increase up to the saturatedvoltage, which is determined by the switching frequency, turnsratio, and number of voltage multiplier stages. At 0.5 ms,the xenon lamp ionization is modeled as a resistor of 100 �so that the output voltages of both the dc trigger and simmerpower supplies drop. After the ionization occurs, the trans-former of the trigger (TR1) is disconnected. Thus, the triggerpower supply is disconnected from the common inverter part,and only the simmer power supply works for sustaining thedecreased impedance of the xenon flash lamp.

IV. EXPERIMENTAL RESULTS

The performance of the developed power supplies wascompared with the analysis results presented in Section IIIunder the no-load condition. Finally, under the xenon flashlamp load, the integrated dc trigger and performance of

4478 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 47, NO. 10, OCTOBER 2019

Fig. 7. Photographs of the developed power supplies and xenon flash lamp.(a) Implemented dc trigger power supply. (b) Implemented simmer powersupply. (c) Three serial xenon flash lamps.

TABLE II

MEASURING INSTRUMENTS USED IN THE EXPERIMENTS

the simmer power supplies, as well as the stable operation,were verified. Fig. 7 shows a photograph of the developeddc trigger, simmer power supply, and moment of the lampturn-on by the integrated circuit. The measuring instrumentsused in the experiments are tabulated in Table II along withthe manufacturer names, and the data of the used electroniccomponents and transformer core are tabulated in Table III.

A. DC Trigger Power Supply

The output voltage under the no-load condition andoperation waveforms of the voltage multiplier are shownin Fig. 8(a) and (b), respectively. The results are similar tothe simulation results so that the effect of the parasitic parallel

TABLE III

COMPONENTS DATA USED IN THE EXPERIMENTS

Fig. 8. Experimental waveforms of the dc trigger power supply. (a) Outputvoltage of the 11-stage Cockcroft–Walton circuit [100 ms/div]. (b) Operatingwaveforms of the dc trigger circuit with the parasitic components [2 μs/div].

capacitor of the diode on the Cockcroft–Walton voltage multi-plier circuit is apparent. The resonance between this parasiticcapacitor and the leakage inductor of the transformer (TR1)increases the peak voltage of the secondary side of thetransformer. The secondary-side voltage of TR1 includes boththe input rectangular voltage and sinusoidal voltage of theresonance. As a result, the increased peak voltage is used togenerate the final output voltage, 15 kV, which is larger thanthe calculated ideal voltage. The secondary-side output currentalso shows a resonant current, which conducts peak-to-peakat 1 A, continuously charging and discharging the voltage ofthe multiplier capacitors.

B. Simmer Power Supply

The operation waveforms of the no-load conditionat 270-kHz switching frequency are indicated in Fig. 9.The output voltage is controlled at 1.0 kV, and the peak value

CHO et al.: INTEGRATED 15-kV DC TRIGGER AND SIMMER POWER SUPPLY FOR LIGHT SINTERING 4479

Fig. 9. Experimental waveforms of the simmer power supply under theno-load condition [2 μs/div].

of the resonant current was 20 A, which is the same value asin the simulation result. The same waveforms show a zero-voltage turn-on similar to the simulation results. However,in terms of the turn-off moment, the main MOSFETs are openwhen the peak resonant current is conducted. This results inturn-off hard switching, but the loss is compensated by theadditional snubber capacitors.

In addition, the value of the resonant current is larger thanthe dc trigger input current. This shows that the soft switchingof the integrated inverter was predominantly determined by thesimmer resonant current.

C. Integrated DC Trigger and Simmer Power Supply

Fig. 10 shows the experimental results of the integrated dctrigger and simmer power supply system with actual singleand two- and three-series-connected xenon flash lamps. Theinitial operation procedure of the dc trigger and simmerpower supplies is indicated in Fig. 10(a), which is a resultof the single-lamp experiment. Both output voltages increasesimultaneously and the increase in the simmer output voltagestopped when 700 V is reached. However, the trigger outputvoltage continues to increase until the single lamp is ionized.The result of the lamp ionization appears as a voltage dropin the trigger output voltage because the ionization changesthe lamp impedance. Therefore, the simmer output currentincreases when the simmer output voltage decreases andsustains the ionized state of the lamp gas by its continuouscurrent, which is controlled as the reference value.

Regarding the roles of the aforementioned additional com-ponents, the bypass diode (Dbypass) generates another currentpath for the simmer output current when the output voltagedrops. The controller checks the value of the simmer outputcurrent and closes the MC. Simultaneously, the input line ofthe dc trigger power supply is disconnected so that the dctrigger completely turns off.

The trigger voltage of the lamp depends on the lamp thick-ness and length. A long lamp length is associated with a hightrigger output voltage needed, and this is shown in Fig. 10 as6, 10, and 13 kV. Not only the trigger output voltage but alsothe simmer output voltage is increased by the lamp length.Therefore, the simmer output voltage is changed from 700 Vto 1.1 kV for the stable operation of the system.

Fig. 10. Operation waveforms of the actual xenon lamp experiments.(a) Single-lamp condition [5 ms/div]. (b) Two-series-connected lamp condition[5 ms/div]. (c) Three-series-connected lamp condition [10 ms/div].

V. CONCLUSION

In this paper, the xenon lamp driving system, which is com-prised of dc trigger and simmer generally using independentinverter part, is newly proposed to share one inverter part forby the two power supplies. The sharing of a single inverterpart effectively reduces the number of elements, volume, andmanufacturing cost and simplifies the circuit. In addition,the voltage boosting phenomenon of the dc trigger powersupply is analyzed and utilized to generate a 15-kV outputvoltage. In terms of the control, it should be considered thatthe same switching frequency is used for the two independentoutput voltages.

To verify the performance and characteristics of the inte-grated circuit, each dc trigger and simmer power supply is

4480 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 47, NO. 10, OCTOBER 2019

simulated and tested under a no-load condition. As a result,the same simulation and experimental results are measured.An actual xenon flash lamp is also experimented as a load forthe integrated system, and it is successfully lit using single andtwo- and three-series-connected lamps. Based on the success-ful experimental results, the performance and stable operationfor the implementation of the light sintering technology areverified.

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Chan-Gi Cho received the B.S. degree in infor-mation display engineering from Kyung-Hee Uni-versity, Seoul, South Korea, in 2016, and the M.S.degree from the Department of Energy Engineering,Chung-Ang University, Seoul, in 2018, where heis currently pursuing the Ph.D. degree with theDepartment of Energy Systems Engineering.

His current research interests include resonantconverters based on the lithium-ion battery and high-voltage pulse power system.

Ziyi Jia received the bachelor’s degree in materi-als science and engineering, energy and electronicmaterials from Chang’an University, Xi’an, China,in 2016, a one-year Korean language study fromKorea University, Seoul, South Korea, in 2017. Sheis currently pursuing the master’s degree with theDepartment of Energy System Engineering, Chung-Ang University, Seoul.

Her current research interests include the resonantconverter.

Seung-Ho Song received the B.S. degree in elec-trical engineering from Kwang-Woon University,Seoul, South Korea, in 2016. He is currently pur-suing the M.S. and Ph.D. degrees with the Depart-ment of Energy Engineering, Chung-Ang University,Seoul.

His current research interests include soft-switchedresonant converter applications and high-voltagepulsed-power supply systems.

Jae-Beom Ahn received the B.S. degree in elec-tronic engineering from Kookmin University, Seoul,South Korea, in 2019. He is currently pursuing theM.S. and Ph.D. degrees with the Department ofEnergy System Engineering, Chung-Ang University,Seoul.

His current research interests include power elec-tronics and high-voltage pulse power systems.

Hong-Je Ryoo (M’17) received the B.S., M.S.,and Ph.D. degrees in electrical engineering fromSungkyunkwan University, Seoul, South Korea,in 1991, 1995, and 2001, respectively.

From 2004 to 2005, he was a Visiting Scholarwith WEMPEC, University of Wisconsin–Madison,Madison, WI, USA. From 1996 to 2015, he wasa Principal Research Engineer with the ElectricPropulsion Research Division, Korea Electrotech-nology Research Institute, Changwon, South Korea,where he was a Leader of the Pulsed Power World

Class Laboratory, and the Director of the Electric Propulsion Research Center.From 2005 to 2015, he was a Professor with the Department of EnergyConversion Technology, University of Science and Technology, Daejeon,South Korea. In 2015, he joined the School of Energy Systems Engineering,Chung-Ang University, Seoul, where he is currently a Professor. His currentresearch interests include pulsed-power systems and their applications, as wellas high-power and high-voltage conversions.

Dr. Ryoo is an Academic Director of the Korean Institute of PowerElectronics, a Senior Member of the Korean Institute of Electrical Engineers,and the Vice President of the Korean Institute of Illuminations and ElectricalInstallation Engineers.