• 전력전자학회:학술대회논문집
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• 전력전자학회 2000년도 전력전자학술대회 논문집
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• pp.493-497
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• 2000

A battery is the device that transforms the chemical energy into the direct-current electrical energy without a mechanical process. Unit cells are connected in series to obtain the required voltage while being connected in parallel to organize capacity for load current. Because the voltage drop down in one set of battery is faster than in two one it may result in the low efficiency of power converter with the voltage drop and cause the system shutdown. However when the system being shutdown. However when the system being driven in parallel a circular-current can be generated,. It is shown that as a result the new batteries are heated by over-charge and over-discharge and the over charge current increases rust of the positive grid and consequently shortens the lifetime of the new batteries. The difference between the new batteries and old ones is the amount of internal resistance. In this paper we can detect the unbalance current using the microprocessor and achieve the balance current by adjusting resistance of each set, The internal resistance of each set becomes constant and the current of charge and discharge comes to be balanced by inserting the external resistance into the system and calculating the change of internal resistance.

• Journal of Electrical Engineering and Technology
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• 제10권5호
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• pp.1989-2000
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• 2015

In this paper, digital peak current mode control for single phase H-bridge inverters is developed and implemented. The digital peak current mode control is achieved by directly controlling the PWM signals by cycle-by-cycle current limitation. Unlike the DC-DC converter where the output voltage always remains in the positive region, the output of DC-AC inverter flips from positive to negative region continuously. Therefore, when the inverter operates in negative region, the control should be changed to valley current mode control. Thus, a novel control logic circuit is required for the function and need to be analyzed for the hardware to track the sinusoidal reference in both regions. The problem of sub-harmonic instability which is inherent with peak current mode control is also addressed, and then proposes the digital slope compensation in constant-sloped external ramp to suppress the oscillation. For unipolar PWM switching method, an adaptive slope compensation in digital manner is also proposed. In this paper, the operating principles and design guidelines of the proposed scheme are presented, along with the performance analysis and numerical simulation. Also, a 200W inverter hardware prototype has been implemented for experimental verification of the proposed controller scheme.

• 설비공학논문집
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• 제2권3호
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• pp.243-255
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• 1990

The objective of this study is to present an efficient measurement method of the effective thermal diffusivity for the fibrous insulation material. The non-linear parameter estimation (NPE) method is adapted for this analysis because of its accuracy and its results are compared with those by other direct methods such as CTP, CHP and STD method. A experimental system is constructed with bell-jar vaccum chamber, diffusion pump, tube type furnace, control unit and data acquisition system included with A/D converter and IBM XT/AT personal computer. The typical results obtained from this study are as follows; 1) NPE method can be recommended as an useful and accurate method to measure the effective thermal diffusivity of insuation material because it is shown that the measurement error compared with those by other direct methods is reduced for standard material, NBS-1450b. 2) NPE method can minimize the effects of ill-measured temperature due to external disturbance, because the final value is found by point to point estimating. 3) NPE method dose not depend on the kinds of heat flux, since the surfac temperature are used to estimate the thermal diffusivity. 4) With NPE method, compared with the steady state method, a measuring time and a sample size could be reduced.

• Journal of Power Electronics
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• 제16권6호
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• pp.2338-2349
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• 2016

This paper presents an impedance-matching-based control scheme for the harmonic resonance damping of multiple grid-connected-converters (GCCs) with LCL filters. As indicated in this paper, harmonic resonance occurs if a GCC possesses an output impedance that is not matched with the rest of the network in some specific frequency bands. It is also revealed that the resonance frequency is associated with the number of GCCs, the grid impedance and even the capacitive loads. By controlling the grid-side current instead of the converter-side current, the critical LCL filter is restricted as an internal component. Thus, the closed-loop output impedance of the GCC within the filter can be configured. The proposed scheme actively regulates the output impedance of the GCC to match the impedance of the external network, based on the detected resonance frequency. As a result, the resonance risk of multiple GCCs can be avoided, which is beneficial for the plug-and-play property of the GCCs in microgrids. Simulation and experimental results validate the effectiveness of the proposed method.

• 전기학회논문지
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• 제57권12호
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• pp.2173-2178
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• 2008

A doubly-fed induction generator(DFIG) system has been widely used in the modem wind turbines due to variable-speed operation, high efficiency and small converter size. It is well known that an inter-turn fault of a generator is very difficult to be detected. The DFIG system uses a wound rotor induction machine so that the magnetizing current of the generator can be fed from both the stator and the rotor. This paper proposes a protection algorithm for a DFIG using the d-q equivalent circuit in the time domain. In the case of a DFIG, the voltages and currents of the rotor side as well as the voltages and currents of the stator are available. The proposed algorithm estimates the instantaneous(i.e., converted into the stationary frame) induced voltages from the rotor and the stator sides. If the difference between the two estimated induced voltages exceeds the threshold, the proposed algorithm detects the inter-turn fault. The algorithm can detect a inter-turn fault of a winding. The performance of the proposed algorithm is validated using a PSCAD/EMTDC simulator under inter-turn fault conditions and normal operating conditions such as an external fault and the change of the wind speed.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권1호
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• pp.25-34
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• 2017

The concentric dual-buoy Wave Energy Converter (WEC), which consists of external buoy (hallow-cylinder) with toroidal appendage and cylindrical internal buoy within the moon-pool is suggested in this research and its performance in various wave conditions is studied. The Linear Electric Generator (LEG), consisting of a permanent magnet and coils, is used as a direct Power Take-Off (PTO) system. To maximize the electrical energy extracted from the PTO system, the relative heave motions between the dual buoys must be highly amplified by the multiple resonance phenomena of dual-buoy and internal-fluid motions. The high-performance range can be widened by distributing those natural frequencies with respect to the peak frequency of the wave spectrum. The performance of the newly developed dual-buoy WEC was measured throughout the systematic 1:5.95-model test in regular and irregular waves conducted in a wave tank at Seoul National University. The model-test results are also validated by an independently developed numerical method.

• 전기전자학회논문지
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• 제21권3호
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• pp.260-263
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• 2017

다종의 CPU를 기반으로 ADC와 DC-DC 변환기를 포함하며 2M-byte의 SRAM이 내장된 SoC가 제안되었다. CPU 코어는 12-bit MENSA 코어, 32-bit Symmetric Multi-core 프로세서, 16-bit CDSP로 구성된다. 외부 SDRAM 메모리를 제거하기 위해 내부의 2M-byte SRAM을 설계하였으나 SRAM 블록들이 넓은 영역에 분포하여 기생 성분에 의해 속도가 저하되므로 SRAM을 작게 분할하여 레이아웃 하였다. 설계된 SoC는 55nm 공정으로 개발되었으며 속도는 200MHz이다.

• 한국해안·해양공학회논문집
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• 제28권4호
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• pp.250-255
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• 2016

부유식 진자형 파력발전 장치의 실해역 설치를 위한 예인 시 예상항로의 조류 및 풍속, 유의 파고 등의 모든 환경자료를 수집 및 분류 분석하여 위험구간에 대해 검토하였다. 이를 위하여 기상청 및 국립 해양조사원의 자료들을 수집하였으며 이들 분류 검토된 자료들을 토대로 구조물에 작용하는 외력에 대해 계산하였다. 또한 ANSYS를 이용하여 복합 환경하중이 작용할 때의 FEM 해석에 기초한 상기 부유식 진자형 파력발전 장치의 안전 여부를 확인하였다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2005년도 춘계종합학술대회
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• pp.804-807
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• 2005

본 논문에서는 Digital IF(Intermediate Frequency) 기술을 이용한 Up/Down 변환기를 설계하고, 이에 대한 성능을 평가 하였다. Digital IF 기술을 사용하는 이유는 passive 소자로 구성되어진 IF 주파수 영역은 고정되어진 한 주파수 밖에 사용하지 못하지만, Digital IF로 구성되어지면 보드의 외형적인 변경 없이 다양한 통신 주파수 영역에서 유연성 있게 사용이 가능하게 된다. 이러한 구성은 기존의 아날로그 헤테로다인 방식에 비하여 높은 유연성을 가지며, 우수한 성능향상을 보여준다.

• Journal of Power Electronics
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• 제11권3호
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• pp.271-278
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• 2011

This paper presents a LLC resonant controller IC for secondary side control without external active devices to achieve low profile and low cost LED back light units. A gate driving transformer is adopted to isolate the primary side and the secondary side instead of an opto-coupler. A new integrated dimming circuitry is proposed to improve the dynamic current control characteristic and the current density of a LED for the brightness modulation of a large screen LCD. A dual-slope clock generator is proposed to overcome the frequency error due to the under shoot in conventional approaches. This chip is fabricated using 0.35 ${\mu}m$ BCD technology and the die size is $2{\times}2\;mm^2$. The frequency range of the clock generator is from 50 kHz to 500 kHz and the range of the dead time is from 50 ns to 2.2 ${\mu}s$. The efficiency of the LED driving circuit is 97 % and the current consumption is 40 mA for a 100 kHz operation frequency from a 15 V supply voltage.