• The Transactions of the Korean Institute of Power Electronics
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• v.14 no.6
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• pp.514-521
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• 2009

This paper deals with a new overvoltage snubber for a diode-clamped 3-level IGBT inverter. Usually most power converters use snubber circuits to protect the switching devices from voltage spike. However, it is difficult for the diode-clamped multi-level converter to be protected from voltage spike with overvoltage snubber since the series connection of the switching devices. To solve the problem the characteristic of a overvoltage snubber for a DC-DC converter is analyzed, and a new snubber for a diode clamped 3-level inverter is proposed. The performance of the proposed snubber is verified through experiments.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.21 no.4
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• pp.123-127
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• 2021

Millimeter-wave tracking radars should be operated in various environmental restrictions, thus they demand more computing power and smaller size compared to conventional tracking radars. This paper presents the design and implementation of the compact power supply for millimeter-wave tracking radar applications. To meet requirements of low voltage/high current and voltage accuracy for FPGA/DSP digital circuits, Point of Load (POL) converters are used in order to enhance power density and system efficiency. LDO (Low Dropout) is applied for the output voltage under the light load condition, then the single-input-multi-output power supply with max power of 375 W and 8 outputs is developed. The proposed power supply achieves output voltage accuracy of ±2 % and noise level of <50 mVpp % under full load conditions.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.5
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• pp.88-95
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• 2009

This paper is the research on the development of power conversion system for the fuel cell. In composing the DC/DC converters which have high boost voltage ratio, unlike the conventional method a new multi DC/DC converter system is proposed that the diode and the condenser and the reactor can be reduced by connecting the secondary side output of the transformer. In this system the rectifier part and the filter part of the secondary side in the power transformer that is connecting in series are composed into a single module, which is the strong advantage and the number of level can be easily increased. A new variable shift phase switching method is also suggested that it makes possible to reduce the output voltage ripples in the proposed system. All the factors mentioned above have been verified through simulations and experiments, and the proposed converter is considered very useful in the demanded load which requires a wide of the output.

• Journal of Power Electronics
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• v.19 no.4
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• pp.922-933
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• 2019

The arm inductance (AI) of a modular multilevel converter (MMC) affects both the fault and circulating current magnitudes. In addition, it has an impact on the inverter efficiency and harmonic content. In this study, the AI of a three-phase MMC is optimized in a novel way in terms of DC voltage utilization, harmonics and efficiency. This MMC has 10 submodules (SM) per arm and the power circuit topology of the SM is a half-bridge. The optimum AI is adopted and verified in an MMC that has 100 SMs per arm. Then the phase shift (PS) and phase disposition (PD) pulse width modulation (PWM) methods are investigated for better DC voltage utilization, efficiency and harmonics. It is found that similar performances are obtained for both modulation techniques in terms of DC voltage utilization. However, the total harmonic distortion (THD) of the PS-PWM is found to be 0.02%, which is slightly lower than the THD of the PD-PWM at 0.16%. In efficiency calculations, the switching and conduction losses for all of the semiconductor are considered separately and the minimum efficiency of the 100-SM based MMC is found to be 99.62% for the PS-PWM and 99.64% for the PD-PWM with the optimal value of the AI. Simulation results are verified with an experimental prototype of a 6-SM based MMC.

• Journal of Power Electronics
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• v.18 no.2
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• pp.558-572
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• 2018

In addition to its modular nature, a Hybrid Modular Multilevel Converter (HMMC) assembled from half-bridge and full-bridge sub-modules, is able to block DC faults with a minimum number of switching devices, which makes it attractive for high power applications. This paper introduces a control strategy based on the Root-Least Square (RLS) algorithm to estimate the capacitor voltages instead of using direct measurements. This action eliminates the need for voltage transducers in the HMMC sub-modules and the associated communication link with the central controller. In addition to capacitor voltage balancing and suppression of circulating currents, a fault tolerant control unit (FTCU) is integrated into the proposed strategy to modify the parameters of the HMMC controller. On advantage of the proposed FTCU is that it does not need extra components. Furthermore, a fault detection unit is adapted by utilizing a hybrid estimation scheme to detect sub-module faults. The behavior of the suggested technique is assessed using PSCAD offline simulations. In addition, it is validated using a real-time digital simulator connected to a real time controller under various normal and fault conditions. The proposed strategy shows robust performance in terms of accuracy and time response since it succeeds in stabilizing the HMMC under faults.

• Journal of Energy Engineering
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• v.14 no.1
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• pp.37-45
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• 2005

The fuel cell system is one of very useful energy sources. The system has advantages as renew-able and environmental sources. To obtain AC electricity from fuel cells, inverters are necessary. A multilevel converter is used as an inverter for a high power fuel cell system. Through harmonic analysis, it is shown that the harmonic components and THD increase while fundamental component decreases as voltage sag increases. To solve the voltage sag problems, three different approaches are investigated in this paper; installation of a boost converter at the fuel cell output, control of pulse widths, and use of ultracapacitors. The proposed three approaches are analyzed and compared using simulation and experimental results.