• The Transactions of the Korean Institute of Power Electronics
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• v.13 no.1
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• pp.46-54
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• 2008

In this paper, a low-cost impedance spectroscopy system(LCISS) suitable for modeling the electrochemical power sources such as fuel cells, batteries and supercapacitors is designed and implemented. Since the developed LCISS is composed of simple sensor circuits, commercial data acquisition board and LabVIEW software, a graphic language with powerful HMI(Human-Machine Interface), it is expected ta be widely used in substitution of the expensive EIS instruments. In the proposed system, the digital lock-in amplifier is adopted to achieve the accurate measurements even in the presence of the high level of noises. The developed hardware and software is applied to measure the impedance spectrum of the Ballard Nexa 1.2kW proton exchange membrane fuel cell stack and an equivalent impedance model is proposed based on the measurement results. The validity of the proposed equivalent circuit and the developed system is proven by the measurement of the ac power losses of the PEM fuel celt stack by the ripple current.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.21 no.6
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• pp.117-125
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• 2007

Recently, a fuel cell with low voltage and high current output characteristics is remarkable for new generation system. It needs both a DC-DC step-up converter and DC-AC inverter to be used in fuel cell generation system. Therefor, this paper, consists of an isolated DC-DC converter to boost the fuel cell voltage 380[VDC] and a PWM inverter with LC filter to convent the DC voltage to single-phase 220[VAC]. Expressly, The fuel cell system which it proposes DC-DC the efficient converter used PWM the phase transient control law and it depended to portion resonance ZVS switching, loss peek voltage and electric current of realization under make schedule, switching frequency anger and the switch reduction. And mind benevolence it sprouted 2 in stop circuit and it added and a direct current voltage and the electric current where the ingredient is reduced in load side ripple stable under make whom it will be able to supply. Besides the efficiency of 92[%]is obtained over the wide output voltage regulation ranges and load variations. Also, under make over together the result leads simulation and test, the propriety confirmation.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.49 no.1
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• pp.15-24
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• 2012

In this paper, we suggest the dynamic-response-free SMPS using a new high-resolution DPWM generator based on switched-capacitor delay technique. In the proposed system, duty ratio of DPWM is controlled by voltage slope of an internal capacitor using switched-capacitor delay technique. In the proposed circuit, it is possible to track output voltage by controlling current of the internal capacitor of the DPWM generator through comparison between the feedback voltage and the reference voltage. Therefore the proposed circuit is not restricted by the dynamic-response characteristic which is a problem in the existing SMPS using the closed-loop control method. In addition, it has great advantage that ringing phenomenon due to overshoot/undershoot does not appear on output voltage. The proposed circuit can operate at switching frequencies of 1MHz~10MHz using internal operating frequency of 100 MHz. The maximum current of the core circuit is 2.7 mA and the total current of the entire circuit including output buffer is 15 mA at the switching frequency of 10 MHz. The proposed circuit has DPWM duty ratio resolution of 0.125 %. It can accommodate load current up to 1 A. The maximum ripple of output voltage is 8 mV. To verify operation of the proposed circuit, we carried out simulation with Dongbu Hitek BCD $0.35{\mu}m$ technology parameter.

• The Transactions of the Korean Institute of Power Electronics
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• v.15 no.2
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• pp.103-110
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• 2010

In this paper, a new mode changeable asymmetric full bridge dc/dc converter is proposed to solve the freewheeling current problem of the conventional zero voltage switching(ZVS) phase shift full bridge(PSFB) dc/dc converter of low output voltage and high output current applications. The proposed converter is operated as an asymmetric full bridge converter when the duty cycle is less than 50% and active clamp full bridge converter when the duty cycle is greater than 50%. As a result, since its freewheeling current is eliminated, the conduction loss is lower than that of the conventional ZVS PSFB dc/dc converter. Moreover, ZVS of all power switches can be ensured along a wide load ranges and output current ripple is very small. Therefore, high efficiency of the proposed converter can be achieved. Especially since its operation mode is changed to the active clamp full bridge converter during hold up time and can be operated with 50~100% duty ratio, it can produce the stable output voltage along wide input voltage range. The operational principles, theoretical analysis and design considerations are presented. To confirm the operation, validity and features of the proposed converter, experimental results from a 1.2kW($400V_{dc}/12V_{dc}$) prototype are presented.

• Journal of Electrical Engineering and Technology
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• v.10 no.1
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• pp.165-175
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• 2015

Energy storage system has been widely applied in power distribution sectors as well as in renewable energy sources to ensure uninterruptible power supply. This paper presents a model predictive algorithm to control a bidirectional AC-DC converter, which is used in an energy storage system for power transferring between the three-phase AC voltage supply and energy storage devices. This model predictive control (MPC) algorithm utilizes the discrete behavior of the converter and predicts the future variables of the system by defining cost functions for all possible switching states. Subsequently, the switching state that corresponds to the minimum cost function is selected for the next sampling period for firing the switches of the AC-DC converter. The proposed model predictive control scheme of the AC-DC converter allows bidirectional power flow with instantaneous mode change capability and fast dynamic response. The performance of the MPC controlled bidirectional AC-DC converter is simulated with MATLAB/Simulink(R) and further verified with 3.0kW experimental prototypes. Both the simulation and experimental results show that, the AC-DC converter is operated with unity power factor, acceptable THD (3.3% during rectifier mode and 3.5% during inverter mode) level of AC current and very low DC voltage ripple. Moreover, an efficiency comparison is performed between the proposed MPC and conventional VOC-based PWM controller of the bidirectional AC-DC converter which ensures the effectiveness of MPC controller.

• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.1
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• pp.45-53
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• 2013

Fuel cell power system is one of the most promising energy source for the alternative energy because it has unique advantages such as high energy density, no power drop during operation, and feasible to make compact size. However, due to very low response time, fuel cell is difficult to correspond to drastic load changes and start-up operation. For solving these problem, fuel cell power system must include energy storage device such as Li-Poly battery or super capacitor. Therefore, bi-directional DC-DC converter must be required for this storage device and fuel cell-PCS control. This paper presents a design and modeling of the bi-directional DC/DC converter. Firstly, we present modeling the boost and buck mode of the bi-directional converter through both PWM switch model and state space averaging technique. Secondly, in order to minimize output ripple and transient response overshoot, we have two identical DC-DC converters interleaved and adopt two-loop voltage-current controller. The proposed bi-directional DC-DC converter's modeling method and control design have been verified with computer simulation and experimentation.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.14 no.4
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• pp.65-72
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• 2000

This paper proposes a Push type High Frequency DC-DC Converter using Zero Voltage Switching to reduce turn on and off loss at the switching instants. This paper has a advantage which is able to operating safely in load short, because DC reactor is connected with resonance reactor in order to supply a fixed safely in load short, because DC reactor is connected with resonance reactor in order to supply a fixed current with low ripple from DC power supply. The capacitor $(C_1, C_2)$ connected in switch are a common using as resonance capacitor and ZVS capacitor. The analysis of the proposed high frequency resonance DC-DC converter is generally described by using normallized parameter, and we has evaluated characteristic values which is needed to design a circuit. We conform a rightfulness of theoritical analysis by comparing a theoretical values and experimental values obtained from experiment using MOSFET as switching devices.

• Journal of Power Electronics
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• v.13 no.3
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• pp.369-380
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• 2013

Direct torque control based on space vector modulation (SVM-DTC) protects the DTC transient merits. Furthermore, it creates better quality steady-state performance in a wide speed range. The modified method of DTC using SVM improves the electrical magnitudes of asynchronous machines, such as minimizing the stator current distortions, the stator flux with electromagnetic torque without ripple, the fast response of the rotor speed, and the constant switching frequency. In this paper, the proposed method is based on two new control strategies for direct torque control with space vector modulation. First, fuzzy logic control is used instead of the PI torque and a PI flux controller to minimizing the torque error and to achieve a constant switching frequency. The voltages in the direct and quadratic reference frame ($V_d$, $V_q$) are achieved by fuzzy logic control. In this scheme, the switching capability of the inverter is fully utilized, which improves the system performance. Second, the close loop of stator flux estimation based on the voltage model and a low pass filter is used to counteract the drawbacks in the open loop of the stator flux such as the problems saturation and dc drift. The response of this new control strategy is compared with DTC-SVM. The experimental and simulation results demonstrate that the proposed control topology outperforms the conventional DTC-SVM in terms of system robustness and eliminating the bad outcome of dc-offset.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.1
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• pp.277-283
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• 2020

In a concentric magnetic gear, which replaces the teeth of a mechanical gear with a permanent magnet, the polar ratio of the magnet that determines the reduction ratio affects the behavior of the magnetic gear dramatically. This study analyzed the density of transmission torque, the efficiency of torque considering the solid loss, and the torque quality, including the cogging characteristics using finite element analysis. When the pole number on the driving side was changed from two to five, it was confirmed that there was an optimal pole ratio, in which the transmission torque was maximized. Because eddy current generation density is proportional to the magnetic field, the transmission efficiency also shows a similar tendency to the transmission torque density, and the efficiency is more than 95% at a low gear ratio. The cogging characteristics due to the interaction of the permanent magnets with the limited number of poles are inversely proportional to the least common multiple between the number of magnets on the drive side and the number of modulator teeth. A test model was built for the transmission torque evaluation.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.38 no.3
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• pp.40-46
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• 2001

In this paper, a novel low power full adder circuit comprising only 10 transistors is proposed. The circuit is based on the six -transistor CMOS XOR circuit, which generates both XOR and XNOR signals and pass transistors. This adder circuit provides a good low power characteristics due to the smaller number of transistors and the elimination of short circuit current paths. Layouts have been carried out using a 0.65 ${\mu}m$ ASIC design rule for evaluation purposes. The physical design has been evaluated using HSPICE at 25MHz to 50MHz. The proposed circuit has been used to build 2bit and 8bit ripple carry adders, which are used for evaluation of power consumption, time delay and rise and fall time. The proposed circuit shows substantially improved power consumption characteristics, about 70% lower than transmission gate full adder (TFA), and 60% lower than a design using 14 transistors (TR14). Delay and signal rise and fall time are also far shorter than other conventional designs such as TFA and TR14.