• Journal of Power Electronics
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• v.16 no.3
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• pp.861-871
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• 2016

With high penetration of renewable energies, power electronic transformers (PETs) will be one of the most important infrastructures in the future power delivery and management system. In this study, an isolated bidirectional modular multilevel DC/DC converter is proposed for PET applications. A modular multilevel structure is adopted as switching valves to sustain medium voltages to achieve modular design and high reliability. Only one high-frequency transformer is used in the proposed converter, which significantly simplifies the circuit and galvanic insulation design. A dual-phase-shift modulation strategy is proposed to regulate the output power and achieve a simple voltage balancing control. A down-scaled (2 kW/20 kHz) prototype is constructed to demonstrate the proposed converter and verify the control strategy. The experimental results comply with the theoretical analysis well, with the highest power efficiency reaching 97.6%.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.1
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• pp.49-57
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• 2016

A modular multilevel converter is widely adapted for a high-voltage direct current power transmission system. This study proposes a design methodology for a novel digital control that mitigates the negative effects caused by time delay, including communication transport delay for a modular multilevel converter. The modeling and negative effect of time delay are analyzed theoretically in a frequency domain, and its compensation methodology based on an inverse model is described fully with practical considerations. The proposed methodology is verified through several simulation results using a modular 21-level converter system.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.79-80
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• 2014

Voltage source multilevel module converter attracts more and more attention recently. The core component of the voltage source multilevel module converter is the valve based on IGBT. So the test circuit for the valve is very important, reliable test method can guarantee the converter valve design meet the operation requirement. This paper analyzes the valve voltage and current stress during the operation, and according to IEC standard test requirement, object, condition, introduces a kind of test circuit. Finally, through the simulation model, to verify the test circuit can provide the proper test condition for the voltage source multilevel module converter valve.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.10
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• pp.16-26
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• 2014

This paper proposes new 13-level inverter topology and DC/DC converter buck-boost structure topology for multilevel, compounding uni-directional and bi-directional switches, and proposes high-efficient multilevel inverter system in which the proposed two PCS(Power Conditioning System) was connected in series. In proposed multilevel inverter of forming a output 13-level phase voltage by using total 18 switching parts, Then bi-directional switch has a characteristic of reducing conduction loss and controlling the reactive power effectively by separating electrically from the neutral point. DC/DC converter for supplying in dependent 3 DC voltage to the proposed multi-level inverter generates 180-degree phase shifted PWM by the symmetrically combined structure of 2 buck-boost converter and twice switching frequency efficiency can be obtained, meanwhile, the converter can step up/down the output voltage and 20% output can be generated comparing the input voltage. This proposed system is verified with the simulation and laboratory test.

• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.1
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• pp.72-83
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• 2013

The paper proposes a new multilevel variable output voltage AC/DC Converter for power supply of power amplifiers used in underwater acoustic sensors. The proposed multilevel variable output voltage AC/DC Converter is composed of two parts. One as the input section is the high efficiency phase-shifted PWM full bridge DC-DC converter to get multiport power sources. The other as the output section is composed of two flying-capacitor 3-level DC-DC converters and a diode bridge circuit to get fast-response and multilevel variable output voltage for an envelope amplifier. Also the paper suggests the detailed circuit topology and design guideline of multilevel variable output voltage AC/DC converter. It also proposes the power balanced control method between 3-level converters and the voltage balanced algorithm for flying capacitors. Its characteristics should be verified by the detailed simulation results. It is anticipated that the proposed converter will be used very well for power amplifiers used in underwater acoustic sensors.

• Proceedings of the KIPE Conference
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• 2014.11a
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• pp.159-160
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• 2014

본 논문에서는 ${\Delta}$결선으로 구성된 Modular Multilevel Converter(MMC)에서 흐르는 전류가 매우 적은 경우 계통에 영향이 없이 셀 직류전압의 불평형을 제어할 수 있도록 영상분전류를 주입하는 방법을 제안하였고, 시뮬레이션을 통해 검증하였다.

• Journal of Power Electronics
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• v.19 no.4
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• pp.894-906
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• 2019

In this paper, a DC-DC converter is proposed based on the Cuk converter. The proposed converter has high efficiency and it can be used in multilevel DC-DC converters. A reduction of the inductors size in comparison to Cuk converter and a reduction in the inductors resistance negative effects on efficiency are the important points of the proposed converter. Its voltage ripple is reduced when compared to other converters. Its output voltage has a high quality and does not contain spikes. A theoretical analysis demonstrates the positive points of the proposed converter. The design and analysis of the converter are done in continues conduction mode (CCM). Experiments confirm the obtained theoretical equations. The proposed converter voltage gain is similar to that of a conventional Boost converter. As a result, they are compared. The comparison illustrates the advantages of the proposed converter and its higher quality. Furthermore, a prototype of the proposed converter and its combination with a 2x multiplier are built in the lab. Experimental results validate the analysis. In addition, they are in good agreements with each other.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.50 no.9
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• pp.459-466
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• 2001

This paper proposes a snubber circuit for flying capacitor multilevel inverter and converter. The proposed snubber circuit makes use of Undeland snubber as basic snubber unit. It has such an advantage of Undeland snubber used in the two-level inverter. Compared with conventional RCD/RLD snubber for multileve1 inverter and converter, the proposed snubber keeps such good features as fewer number of components, reduction of voltage stress of main switching devices due to low overvoltage, and improved efficiency of system due to low loss snubber. In this paper, the proposed snubber is applied to three-level flying capacitor inverter and this feature is demonstrated by computer simulation and experimental result.

• Journal of international Conference on Electrical Machines and Systems
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• v.2 no.2
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• pp.197-201
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• 2013

Cascaded H-bridge multilevel inverter requires independent DC voltage sources to produce multi output voltage levels. When it needs to generate more levels in the output voltage wave, the number of independent DC voltage sources usually limits its extension. To solve this problem, we propose a cascaded H-bridge multilevel inverter employing a front-end flyback converter for unifying input DC voltage sources. After theoretical analysis of the proposed circuit, we verify the validity of the proposed inverter using computer-aided simulations and experiments.

• Proceedings of the KIPE Conference
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• 2018.07a
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• pp.105-107
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• 2018

This paper presents a new hybrid multilevel converter topology, which consists of a combination of the series connected switched capacitor units with boost ability, and an H-bridge with T-type bidirectional switches. The proposed converter boosts the input voltage without any bulky inductors, and has the small number of components, which can make the size and cost of a power converter greatly reduced. The output filter size and harmonics are also reduced by the high quality multilevel output. In addition, there is no need for complicated methods to balance the capacitor voltage. Simulation and experimental results with a nine-level converter system are presented to validate the proposed topology and modulation method.