• Journal of Sensor Science and Technology
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• v.21 no.5
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• pp.379-384
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• 2012

This paper presents the power source of wireless sensor node (WSN) using supercapacitors and a solar cell. Supercapacitors have high lifetime cycling compared to that of batteries. Supercapacitors are connected in series to achieve higher voltage and a voltage balancing circuit is required to ensure that no individual cell goes overvoltage. We employ an active balancing circuit that draws minimal current by using transistors. A diode is connected in series with each supercapacitor. A new balancing circuit that equalize the cells-voltage reduces energy consumption of supercapacitors. Voltage of operating WSN is applied 2.2-3.3V by DC/DC converter and supercapacitor voltage 2.2-5.1V. Maximum operating time of wireless sensor node is about 16 hours in full charging.

• Korean Chemical Engineering Research
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• v.60 no.3
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• pp.363-370
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• 2022

In this paper, an estimation algorithm for state of charge (SOC) was applied using an equivalent circuit model (ECM) and an Extended Kalman Filter (EKF) to improve the estimation accuracy of the battery system states. In particular, an observer was designed to estimate SOC along with the aged capacity. In the case of the fresh battery, when SOC was estimated by Kalman Filter (KF), the mean absolute percentage error (MAPE) was 0.27% which was smaller than MAPE of 1.43% when the SOC was calculated by the model without the observer. In the driving mode of the vehicle, the general KF or EKF algorithm cannot be used to estimate both SOC and capacity. Considering that the battery aging does not occur in a short period of time, a strategy of periodically estimating the battery capacity during charging was proposed. In the charging mode, since the current is fixed at some intervals, a strategy for estimating the capacity along with the SOC in this situation was suggested. When the current was fixed, MAPE of SOC estimation was 0.54%, and the MAPE of capacity estimation was 2.24%. Since the current is fixed when charging, it is feasible to estimate the battery capacity and SOC simultaneously using the general EKF. This method can be used to periodically perform battery capacity correction when charging the battery. When driving, the SOC can be estimated using EKF with the corrected capacity.

• Journal of Electrical Engineering and Technology
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• v.10 no.1
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• pp.195-204
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• 2015

In this paper, the development of a cost-effective active power filter/uninterruptible power supply (APF/UPS) system with seamless mode transfer is described. The proposed scheme employs a pulse-width-modulation (PWM) voltage-source inverter and has two operational modes. First, when the source voltage is normal, the system operates as an APF, which compensates for the harmonics and power factor while boosting the DC-link voltage to be ready for the disturbance, without an additional DC charging circuit. A simple algorithm to detect the load current harmonics is also proposed. Second, when the source voltage is out of the normal range (owing to sag, swell, or outage), it operates a UPS, which controls the output voltage constantly by discharging the DC-link capacitor. Furthermore, a seamless transfer method for the single-phase inverter between the APF mode and the UPS mode is also proposed, in which an IGBT switch with diodes is used as a static bypass switch. Dissimilar to a conventional SCR switch, the IGBT switch can implement a seamless mode transfer. During the UPS operation, when the source voltage returns to the normal range, the system operates as an APF. The proposed system has good transient and steady-state response characteristics. The APF, charging circuit, and UPS systems are implemented in one inverter system. Finally, the validity of the proposed scheme is investigated with simulated and experimental results for a prototype APF/UPS system rated at 3 kVA.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.2
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• pp.54-62
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• 2009

The purpose of this study is to develop a piezo injector driver for common-rail direct injection diesel engines. In this research, we analyzed the electrical and mechanical characteristics of the piezo actuator through experiments. Current flow and charging voltage of the piezo injector are controlled by the PWM signal of variable duty ratio in order to realize both fast response and low peak current. The optimal switching duty ratio was designed by modeling and analyzing of the piezo driver circuit. In order to avoid resonance and unacceptably long settling time, appropriate frequency range of the PWM signal was derived based on the driver circuit model. The developed injector driver was validated by experiments under various fuel rail pressure, injection duration, and charging voltage.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.4
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• pp.506-511
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• 2011

In this paper, a rectenna for wireless power transmission at 900MHz is proposed. Rectenna is a device transforming RF power into DC power and it may consist of a antenna, rectifying and charging circuits. In this paper, we designed a slot antenna to receive 900MHz signal, a rectifying circuit of about 40% efficiency at 0dBm input, and a charging circuit to store a weak power signal and supply constant voltage to load. From the experiment using a RFID reader as a transmitter for 1W power, it was found that the proposed rectenna receiving about 0dBm power can supply 3.3V constant voltage to 50$k{\Omega}$ load during 280sec.

• Proceedings of the KIEE Conference
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• 2002.07a
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• pp.551-553
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• 2002

The cubicle type GIS rated at 25.8kV has been designed and manufactured by Jinkwang E&C eacently with their own technologies and KERI's assistances. The C-GIS has been tested to check the design capability for reference before conducting the type test. The operating characteristics test, short time withstand current and peak withstand current test, basic short circuit test duty T60 for preconditioning test, cable charging current switching test, capacitor bank current switching test, basic short circuit test duty T100s and T100a, single phase earth fault test, double earth fault test has been conducted. The test results show that the design and the manufacturing of the C-GIS has an enough capability to pass through the type test except the occurrence of 2 NSDDs in the cable charging current switching test and the instability of opening time at the minimum operating voltage. The problems shown in the tests will be improved soon and the successful pass will be expected in the following type test.

• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1612-1614
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• 1994

Modulators Installed in PLS(Pohang Light Source) Linac are composed of a DC high voltage section, a charging section and a discharging section. PFN is charged by a resonant charging mechanism, and discharged by a switching device through the primary of the pulse transformer connected to a load. Charged PFN voltage must be well regulated to obtain stable output pulse voltage at the load. For this purpose, DCHV is controlled by a SCR controller with feedback signal, and PFN voltage is regulated by a De-Q'ing circuit. The full power operation test shows the pulse voltage regulation within ${\pm}0.13%$ with SCR feedback control alone, and within ${\pm}0.08%$ together with De-Q'ing. This paper describes the design concept and operational characteristics of the De-Q'ing circuit.

• Progress in Superconductivity and Cryogenics
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• v.23 no.4
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• pp.44-48
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• 2021

In order to obtain ultra-high resolution MRI images, research and development of 11 T or higher superconducting magnets have been actively conducted in the world, recently. The high-temperature superconductor (HTS), first discovered in 1986, was very limited in industrial application until mid-2010, despite its high critical current characteristics in the high magnetic field compared to the low-temperature superconductor. This is because HTS magnets were unable to operate stably due to the thermal damage when a quench occurred. With the introduction of no-insulation (NI) HTS magnet winding technology that does not burn electrically, it could be expected that the HTS magnets are dramatically reduced in weight, volume, and cost. In this paper, a 6 T-class NI HTS magnet for basic characteristic analysis was designed, and a distributed equivalent circuit model of the NI coils was configured to analyze the charging current characteristics caused by excitation current, and the charge delay phenomenon and loss were predicted through the development of a simulation model. Additionally, the critical current of the NI HTS magnets was estimated, considering the magnetic field, its angle and temperature with a given current. The loss due to charging delay characteristics was analyzed and the result was shown. It is meaningful to obtain detailed operation technology to secure a stable operation protocol for a 6T NI HTS magnet which is actually manufactured.

• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.2
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• pp.141-149
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• 2021

In the field of electric vehicles and AGVs, wireless power transfer (WPT) charging systems have been developed recently because of its convenience, reliability, and positive environmental impact due to cable and cord elimination. In this study, we propose a WPT charging system using a single stage AC-DC converter that can be reduced in size and weight and thus can ensure convenience. The proposed single-stage AC-DC converter can control a wide output voltage (36-54 VDC) within coupling ranges by using the variable link voltage applied to the WPT resonant circuit through phase-shifted modulation at a fixed switching frequency. Moreover, the input power factor and total harmonic distortion can be improved by using the proposed converter. A 1 kW prototype that can operate with an air gap range of 40-50 mm is fabricated and validated through experimental results and analysis.

• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.4
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• pp.277-284
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• 2021

A single and three phase-compatible single-stage EV charger without electrolytic capacitor is proposed in this study. DC battery-charging current is inherently guaranteed in the three-phase grid due to three output currents with a phase shift of 120° between each other. The proposed EV charger can provide a DC battery charging current for the single-phase grid through the integrated active power decoupling circuit without using additional switches. The proposed EV charger ensures ZVS turn-on of all switches with wide grid and battery voltage ranges. The 11 kW prototype of the proposed EV charger demonstrates a peak efficiency of 97.01% and a power density of 5.58 kW/L.