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윤재중(Jae-Jung Yun) 한국조명·전기설비학회 2020 조명·전기설비학회논문지 Vol.34 No.4
If some LEDs are shorted, overcurrent flows through an LED string consisting of multiple LEDs connected in series. In the LED driving circuit, a current regulator with semiconductor devices such as transistors can protect overcurrent but it generates heat in semiconductor devices, which can damage the LED driving circuit and LED string. In this paper, a novel LED short detection circuit is proposed to solve the LED short problem. The proposed circuit consists of an comparator and a MOSFET and operates in combination with a current regulator. It detects when the LED is shorted and then opens the transistor in current regulator so that the LED current does not flow. To verify the operation and effectiveness of the proposed circuit, a prototype of current regulator and short detection circuit was fabricated and tested by connecting to three LED strings. At LED diving voltage of 18V, The LED currents of all LED strings were 38.7mA∼39.1mA by the constant current operation of current regulators. When a LED is shorted in any LED string and the proposed circuit is not used, the collector-emitter voltage of the transistor in the current regulator was increased to 4.23V and the power consumption of 164.5mW is generated in the transistor. However, when using the proposed circuit, it protects the LED string and LED driving circuit by opening the transistor so that the LED current does not flow.
배터리 임피던스 변화를 반영한 확장 칼만 필터를 기반으로 한 배터리 SOC 추정에 관한 연구
이재형(Jae-Hyung Lee),김경환(Gyeong-Hwan Kim),윤재중(Jae-Jung Yun) 한국조명·전기설비학회 2021 조명·전기설비학회논문지 Vol.35 No.1
The state of charge(SOC) of battery should be accurately estimated because it is used as basic data for various functions of the battery management(BMS) as well as the remaining battery capacity. Extended Kalman Filter(EKF) based on a battery model is widely used as a real-time SOC estimation technique. However, the parameters of battery model are slightly different for each SOC section and changed by C-rate. As a result, if the battery parameters are used a fixed value, the accuracy of SOC estimation using EKF is decreased. In this paper, to improve the accuracy of the SOC estimation using EKF, the changes in battery parameters according to C-rate were analyzed for five SOC sections. Also, the accuracy of the SOC estimation according to the number of SOC sections was calculated by simulation. Experimental results show that the battery parameters reduce as C-rate increases. In addition, as the SOC decreased, the internal resistor R<SUB>i</SUB> and loss resistor R<SUB>d</SUB> increased, but the double layer capacitor C<SUB>d</SUB> decreased. Therefore, in order to increase the accuracy of SOC estimation using EKF, it is necessary to reflect the changes in battery parameters in each SOC section according to the C-rage. This was verified by simulation.
변압기의 파라미터 추출과 전기적 모델링 방법에 관한 연구
박준우(Jun-Woo Park),윤재중(Jae-Jung Yun) 한국조명·전기설비학회 2017 조명·전기설비학회논문지 Vol.31 No.5
The electric operation of a practical transformer, which is used in the various electric apparatus, is not easy to interpret, because it has some considerable parameters compared to a ideal transformer. In addition, although the commercial simulation tools provide electric models of a practical transformer for users, it is difficult to analyze intuitively the effects of the circuit performance caused by parameters of practical transformer such as a leakage inductance and mutual inductance. To solve these problems, this paper presents a method for parameter extractions and circuit modeling of a practical transformer. The equivalent model of a practical transformer by the suggested method consists of an ideal transformer model, two resistors, two leakage inductors, and a mutual inductor. The parameters for a practical transformer is extracted by open and short circuit analysis methods, and the electric model of an ideal transformer is made by solving the requirements. To verify the effectiveness of the equivalent model of a practical transformer, a test bed with two winding transformer is built. The Pspice model of a practical transformer was made of parameters extracted by a test bed, and a comparison between simulation and experiment results was given in this paper. As a result, the difference in the primary current and secondary current between simulated and experimental results is 1.2% and 1%, respectively.
외부전극 형광램프의 암흑구동 불량 개선을 위한 저 가격 장치에 관한 연구
김명환(Myung-Hwan Kim),윤재중(Jae-Jung Yun) 한국조명·전기설비학회 2018 조명·전기설비학회논문지 Vol.32 No.2
LCD backlight which uses the external electrode fluorescent lamps (EEFLs) connected in parallel has a problem that some lamps are not turned on during the initial drive in the dark state. To solve this problem, the conventional method uses lights emitted from LEDs which are driven by an electric circuit consists of a DC power source and several passive and active components, because LED lights can help the lamps to turn on easily. This paper proposes a new low-cost device for improving the dark drive failure of EEFLs without a DC source and an electric circuit. The proposed device consists of a LED, a diode, and a metal line and is installed on the PCB board which is used to drive EEFLs connected in parallel. The operation principle is to drive LEDs with the induced LED driving voltage on the floating metal line of the proposed device from the high voltage and high frequency EEFL driving voltage. To verify the operation of the proposed device, it is tested on a 42-inch LCD backlight which driven by the inverter producing the EEFL driving voltage having the operating frequency of 45kHz and rms value of 1000Vrms. As a result of the experiment, the LED lights were emitted simultaneously with the initial lighting of the LCD backlight by the proposed device and the measured LED current was 2.4mArms in the case of the metal pattern of 3mm width and 250mm length.
GaN FET 기반 플라이백 컨버터를 이용한 능동 셀 밸런싱의 성능 향상
최영훈(Young-Hoon Choi),윤재중(Jae-Jung Yun) 한국조명·전기설비학회 2022 조명·전기설비학회논문지 Vol.36 No.2
In a battery module with multiple cells in series, the efficiency of the cell balancing circuit is very important because it is related to the balancing time and energy usage. This paper proposes a high efficiency active cell balancing circuit that can transfer energy from module to cell. The proposed balancing circuit consists of a flyback converter for transferring energy and bidirectional switches for selecting a weak cell. In order for the proposed circuit to have high efficiency, the flyback converter uses GaN FETs with excellent electrical characteristics and operates in DCM(Discontinuous Conduction Mode) for soft switching. To verify the performance of the proposed circuit, a 5W GaN FET based flyback converter was built and cell balancing experiments was performed. This was compared to a MOSFET based balancing circuit. Experimental results show that the proposed circuit improves maximum efficiency by 8.6%, reduces cell balancing time by 10%, and reduces cell balancing energy loss by 16% compared to the MOSFET-based circuit.
센서 오차를 고려한 전류 적산과 확장 칼만 필터 방법의 배터리 SOC 추정 성능 비교에 관한 연구
정대웅(Dea-Ung Jeong),송하나(Ha-Na Song),윤재중(Jae-Jung Yun) 한국조명·전기설비학회 2020 조명·전기설비학회논문지 Vol.34 No.5
Coulomb counting(CC) and Extended Kalman Filter(EKF) methods are most commonly used to estimate the state of charge(SOC) of a battery. However, the SOC estimation accuracy of these two methods is affected by the sensor error because these methods estimate SOC based on the voltage and current information measured by the sensor. This paper compared and analyzed the effect of the voltage and current sensor errors on the SOC estimation accuracy of the Coulomb counting(CC) and Extended Kalman Filter(EKF) methods. To verify the effect of the voltage and current sensor errors, on the SOC estimation accuracy, the above two methods were tested at the voltage sensor error of 1% ∼ 3%, and the current sensor error of 3% when the battery SOC discharged 100% to 0%. In the Coulomb counting(CC) method, the accumulation of current sensor errors degraded the SOC estimation accuracy. Also, in the Extended Kalman Filter(EKF) method, it was confirmed that the voltage sensor error degraded the SOC estimation accuracy more than the current sensor error. The simulation results show the importance of sensor filter design and sensor fault detection in SOC estimation. estimation.