• Structural Engineering and Mechanics
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• v.69 no.3
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• pp.307-315
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• 2019

This paper proposes a chattering-free sliding mode control (CFSMC) method for seismically excited structures. The method is based on a fuzzy logic (FL) model applied to smooth the control force and eliminate chattering, where the switching part of the control law is replaced by an FL output. The CFSMC is robust and keeps the advantages of the conventional sliding mode control (SMC), whilst removing the chattering and avoiding the time-consuming process of generating fuzzy rule basis. The proposed method is tested on an 8-story shear frame equipped with an active tendon system. Results indicate that the new method not only can effectively enhance the seismic performance of the structural system compared to the SMC, but also ensure system stability and high accuracy with less computational cost. The CFSMC also requires less amount of energy from the active tendon system to produce the desired structural dynamic response.

• Proceedings of the KIPE Conference
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• 2019.07a
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• pp.8-10
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• 2019

In this paper, a bidirectional three-phase push pull converter is analyzed for the high power, wide voltage range applications. From comparison analysis of two switching methods: PWM plus phase-shift (PPS) and dual-asymmetric PWM (DAPWM) with the effect of dead-time, the proposed hybrid control is aimed to reduce the circulating current under wide voltage range operation. Value of leakage inductance effect to the peak current value, current stress and conduction loss in facing the load variation. Trade-off between power range and slew rate of transformer current was analyzed for properly selecting value of the transformer leakage inductance. Experimental results from a 22-kW prototype are provided to validate the proposed concept.

• Journal of Power Electronics
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• v.19 no.3
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• pp.613-624
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• 2019

Digital current control techniques are an attractive option for DC-DC converters. In this paper, a digital predictive peak current control algorithm is presented for buck converters that allows the inductor current to track the reference current in two switching cycles. This control algorithm predicts the inductor current in a future period by sampling the input voltage, output voltage and inductor current of the current period, which overcomes the problem of hardware periodic delay. Under the premise of ensuring the stability of the system, the response speed is greatly improved. A real-time parameter identification method is also proposed to obtain the precision coefficient of the control algorithm when the inductance is changed. The combination of the two algorithms achieves adaptive tracking of the peak inductor current. The performance of the proposed algorithms is verified using simulations and experimental results. In addition, its performance is compared with that of a conventional proportional-integral (PI) algorithm.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.1
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• pp.584-596
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• 2019

This paper presents a Modified Adaptive Complementary Sliding Mode Control (MACSMC) system for the longitudinal motion control of the Fully-Submerged Hydrofoil Craft (FSHC) in the presence of time varying disturbance and uncertain perturbations. The nonlinear disturbance observer is designed with less conservatism that only boundedness of the derivative of the disturbance is required. Then, a complementary sliding mode control system combined with adaptive law is designed to reduce the bound of stabilization error with fast convergence. In particularly, the modified complementary sliding mode surface which contains the estimation of the disturbance can reduce the switching gain and retain the normal performance of the system. Moreover, a hyperbolic tangent function contained in the control law is utilized to attenuate the chattering of the actuator. The global asymptotic stability of the closed-loop system is demonstrated utilizing the Lyapunov stability theory. Ultimately, the simulation results show the effectiveness of the proposed approach.

• Journal of the Korean Society of Industry Convergence
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• v.24 no.4_1
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• pp.411-419
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• 2021

In this study, IGBT_Total_Loss and DIODE_Total_Loss were used to analyze the slope of the junction temperature for each section for temperature and duty variables in order to simply calculate the junction temperature of the power semiconductor (IGBT). As a result of the calculation, IGBT_Max_Junction_Temp and DIODE_Max_Junction_Temp form a proportional relationship with temperature for each duty. This simulation data shows that the power loss of a power semiconductor is calculated in a complex manner according to the current dependence index, voltage dependence index, and temperature coefficient. By applying the slope for each condition and section, the junction temperature of the power semiconductor can be calculated simply.

• International journal of advanced smart convergence
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• v.11 no.2
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• pp.53-58
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• 2022

In this paper, w-band frequency synthesizer was developed for frequency-modulated continuous wave (FMCW) radar sensors. To achieve a small size and high performance, We designed and manufactured w-band MMIC chips such as up-converter one-chip, multiplier, DA (Drive Amplifier) MMIC(Monolithic Microwave Integrated Circuit), etc. And interposer technology was applied between the W-band multiplier and the DA MMIC chip. As a result, the measured phase noise was -106.10 dBc@1MHz offset, and the frequency switching time of the frequency synthesizer was less than 0.1 usec. Compared with the w-band frequency synthesizer using purchased chips, the developed frequency synthesizer showed better performance.

• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.1
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• pp.9-17
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• 2022

The series-connected semiconductor devices structure is one way to achieve a high voltage rating. However, a problem with voltage imbalance exists in which different voltages are applied to the series-connected switches. This paper proposed a new voltage balancing technique that controls the turn-off delay time of the switch by adding one bipolar junction transistor to the gate turn-off path. The validity of the proposed method is proved through simulation and experiment. The proposed active gate driver not only enables voltage balancing across a variety of current ranges but also has a greater voltage balancing performance compared with conventional RC snubber methods.

• International Journal of Internet, Broadcasting and Communication
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• v.14 no.1
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• pp.1-9
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• 2022

Recently, a large number of cryptocurrencies and block chains have been continuously released. However, these cryptocurrencies and block chains are open to users without authorized verification and testing procedures, causing various reliability problems. Existing cryptocurrencies and blockchain test methods build a blockchain Testnet for a certain period of time by the developer without external verification by a third party, and after repeatedly self-testing and self-operating processes, commercialization is in progress by switching to the Mainnet. This self-verification method does not guarantee objectivity and publicness, and high reliability of customers cannot be realized. This study proposes a cryptocurrency and blockchain test interface and test control system as a third-party open test method.

• Journal of Surface Science and Engineering
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• v.55 no.4
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• pp.187-195
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• 2022

WO₃ thin films were synthesized by electrodeposition, and their electrochromic properties were investigated. The application of static voltage produced WO₃ films with a smooth, compact surface morphology, and the film thickness linearly increased with the application time. The thicker film showed a strong color contrast but a slow color-switching speed. High-temperature heat treatment exceeding 300 ℃ induced a phase transformation from an amorphous to a monoclinic structure and resulted in degraded electrochromic performance. Furthermore, the optimized WO₃ thin films demonstrated their potential application as electrochromic boards for writing and erasing letters using a simple modified 3D printer in a rapid, accurate process

• Kyungpook Mathematical Journal
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• v.63 no.3
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• pp.355-372
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• 2023

We make advances towards a structural characterisation of the signed graphs H for which the list switch H-colouring problem List-S-Hom(H) can be solved in polynomial time. We conjecture two different characterisations, the second refining the first, in the case that the graph H can be switched to a graph in which every negative edge is also positive. Using a recent proof of the first characterisations for reflexive signed graphs, by Bok et. al., we prove the second characterisation for reflexive signed graphs. We also provide several tools for reducing the problem to the bipartite case, and prove a full complexity dichotomy for a related problem.