• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.1041-1044
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• 1992

A solar cell should be operated at the maximum output point on the I-V characteristic curve with constant current and constant voltage in order that the solar energy be fully utilized. According to, in this paper, we describes a controller which can track the maximum power point of a solar arry using current and voltage ripple variation of step up chopper system. The control circuit is desinged such that actual current and voltage are sensed directly from the solar cell array. These two signal are then holded sampling and multiplies by a single chip multiplier.

• Journal of the Korean Solar Energy Society
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• v.32 no.3
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• pp.26-32
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• 2012

A current compensation method to reduce the mismatch loss in PV systems is proposed as a way to increase the power generation efficiency. A dc-dc converter is used to supply currents to irregular modules in a PV string and is powered from the string output. The converter's voltage conversion ratio is adjusted so that all the modules in the string are operated at the maximum power point. The power rating and size of the converter can be reduced since only the current difference between the regular and irregular module may be supplied. The compensated string shows very little voltage mismatch compared to other regular strings. The validity of the proposed method is verified through a simulation and experiments in a prototype PV system.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.2
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• pp.279-284
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• 2011

Harmonic distortions in current waveform may cause significant problems in electric power system facility and operation. This paper presents an adaptive parameter estimation method to detect harmonic current components caused by nonlinear loads. In addition, a coordination strategy for multiple inverter-interfaced distributed generators to compensate the harmonic currents is discussed. The coordination strategy is realized by distributing the harmonic compensation participation index to individual distributed generators. The harmonic compensation participation index can be determined by the amount of remaining power generation capacity of each distributed generator. Simulation results based on switching-level inverter models show that the proposed harmonic detection method has good performance and the coordination strategy can improve harmonic problems efficiently.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1222-1223
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• 2007

This paper suggests a 6-pulse-shift converter with PWM current-source inverter based on buck-boost configuration to improve the efficiency and to reduce the switching frequency of inverter for photovoltaic generation system, the device can be operated as interface system between solar module system and power system grid without energy storage cell. the circuit has six current-source buck-boost converter which operate chopper part has one full bridge inverter which make a decision the polarity of AC output. Therefore, the proposed PWM power inverter has advantages such as the reduction of witching loss and realization of unity power factor operation. the theoretical backgrounds are discussed and the input-output characteristics for the implemented prototype inverter using TMS320F2812 are verified experimentally in this paper.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.29 no.1
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• pp.225-234
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• 2019

Bitcoin is a cryptocurrency with characteristics such as de-centralization and distributed ledger, and these features are maintained through a mining system called "proof of work". In the mining system, mining difficulty is adjusted to keep the block generation time constant. However, Bitcoin's current method to update mining difficulty does not reflect the future hash power, so the block generation time can not be kept constant and the error occurs between designed time and real time. This increases the inconsistency between block generation and real world and causes problems such as not meeting deadlines of transaction and exposing the vulnerability to coin-hopping attack. Previous studies to keep the block generation time constant still have the error. In this paper, we propose a machine-learning based method to reduce the error. By training with the previous hash power, we predict the future hash power and adjust the mining difficulty. Our experimental result shows that the error rate can be reduced by about 36% compared with the current method.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.22 no.1
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• pp.135-140
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• 2022

In addition to the stack that directly generates electricity by the reaction of hydrogen and oxygen, the fuel cell power generation system has a reformer that generates hydrogen from various fuels such as methanol and natural gas. It also consists of a power converter that converts the DC voltage generated in the stack into a stable AC voltage. The fuel cell output of such a system is direct current, and in order to be used at home, an inverter device that converts it into alternating current through a power converter is required. In addition, a DC-DC step-up converter is used to boost the fuel cell voltage to about 30~70V, which is the inverter operating voltage, to about 380V. The DC-DC step-up converter is a DC voltage variable device that exists between the fuel cell output and the inverter. Accordingly, since a constant output voltage of the converter is generated in response to a change in the output voltage of the fuel cell, the inverter can receive constant power regardless of the voltage change of the fuel cell. Therefore, in this paper, we discuss the detailed hardware design of the full-bridge converter, which is the main power source of the inverter that receives the fuel cell output voltage (30~70V) as an input and is applied to the grid among the members of the fuel cell power generation system.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.80-82
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• 2005

Distributed generation (IX;) plays an important role in the power system nowadays. Over-current relay, widely used in the DG protection, causes a wide outage section and long time delay. This paper proposes a DG protection technique to minimize the outage section. The proposed method uses three directional over-current relays with delay, which are connected to the point of common coupling. The method can minimize the outage section.

• Proceedings of the KIPE Conference
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• 2009.11a
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• pp.265-267
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• 2009

we proposed a grid connected peak load compensation system with high discharge current characteristics based on lithium polymer battery for development of the next generation power-station. The lithium polymer battery has faster discharge current characteristics than conventional battery, so that can compensate high active power demanded by load in a short time using the low capacity battery bank. Therefore, it is possible to control power leveling of grid by measuring storage energy of battery and active power which is needed from load. The validity of proposed system was verified through the simulation and experiment.

• Journal of Electrical Engineering and Technology
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• v.6 no.2
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• pp.255-262
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• 2011

This paper proposes a grid-tied power conditioning system for fuel cell, which consists of three-phase current-fed DC-DC converter and three-phase PWM inverter. The three-phase current-fed DC-DC converter boosts fuel cell voltage of 26-48 V up to 400 V with zero-voltage switching (ZVS) scheme, while the three-phase PWM(Pulse Width Modulation) inverter controls the active and reactive power supplied to the grid. The operation of the proposed power conditioning system with fuel cell model is verified through simulations with PSCAD/EMTDC software. The feasibility of hardware implementation is verified through experimental works with a laboratory prototype with 1.2 kW proton exchange membrane (PEM) fuel cell stack. The proposed power conditioning system can be commercialized to interconnect the fuel cell with the power grid.

• Journal of Power Electronics
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• v.14 no.6
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• pp.1293-1302
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• 2014

A flyback inverter using voltage sensorless maximum power point tracking (MPPT) for photovoltaic (PV) AC modules is presented. PV AC modules for a power rating from 150 W to 300 W are generally required for their small size and low price because of the installation on the back side of PV modules. In the conventional MPPT technique for PV AC modules, sensors for detecting PV voltage and PV current are required to calculate the PV output power. However, system size and cost increase when the voltage sensor and current sensor are used because of the addition of the auxiliary circuit for the sensors. The proposed method uses only the current sensor to track the MPP point. Therefore, the proposed control method overcomes drawbacks of the conventional control method. Theoretical analysis, simulation, and experiment are performed to verify the proposed control method.