• Journal of Power Electronics
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• v.9 no.5
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• pp.726-735
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• 2009

This paper presents a Bidirectional High-Frequency Link (BHFL) inverter that utilizes the Deadbeat controller. The main features of this topology are the reduced size of the inverter and fewer power switches. On the secondary side of the transformer, the active rectifier employs only two power switches, thus reducing switching losses. Using this configuration, the inverter is capable of carrying a bidirectional power flow. The inverter is controlled by a Deadbeat controller, which consists of the inner current loop, outer voltage loop and a feedforward controller. Additional disturbance decoupling networks are employed to improve the system's robustness towards load variations. A 1-kVA prototype inverter has been constructed and the Deadbeat control algorithm is experimentally verified. The experimental results show that the inverter has high efficiency (91%) with low steady state output voltage total harmonics distortion (1.5%).

• Journal of Power Electronics
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• v.11 no.1
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• pp.74-81
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• 2011

The cutoff frequency of the output LC filters of PWM inverters limits the control bandwidth of the converter system while it attenuates voltage ripples that are caused by inverter switching activities. For a selected cutoff frequency of an output LC filter, an infinite number of L-C combinations is possible. This paper analyses the characteristics of output LC filters for PWM inverters terms of the L-C combinations. Practical circuit conditions such as no-loads, full resistive-loads, and inductive-load conditions are considered in the analysis. This paper proposes a LC filter design method for PWM inverters considering both the voltage ynamics and he inverter stack size. An experimental PWM inverter system based on the proposed output LC lter design uideline is built and tested.

• Proceedings of the KIPE Conference
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• 1997.07a
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• pp.111-115
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• 1997

This Paper is concerned on developing DC-DC converter using ZVS-FB-PWM Converter. The converter output is 28V and regulated by phase shift control methode. MOSFET is used by the main switching device and high frequency transfomer is made for operating at 300㎑ switching frequency. When the load vary widely, converter's ZVS characteristic is expressed by experiment result.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10b
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• pp.743-748
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• 1998

As nation's infrastructure is getting old, nondestructive evaluation of existing structures and construction quality control are getting important. In this thesis, flaw detection techniques of concrete members with asphalt using impact echo test were introduced. This techniques are based on stress wave propagation. In this field impact echo test, As load is gradually increased, frequency is increased. From this change of frequency through impact echo test, we can detect that the crack of bridge ascends and what the depth of crack is.

• Proceedings of the KIPE Conference
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• 2015.11a
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• pp.149-150
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• 2015

This paper presents narrowband voltage controller for large capacity UPS system with low switching frequency. The proposed controller is repetitive controller applicable to low sampling. The controller reduces the control error for nonlinear load and improve efficiency. The proposed controller is verified through the experiment using 40kW UPS inverter.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.1
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• pp.26-32
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• 2007

This study was carried out fusion-welded butt joints in SWS 490A high strength steel subjected to tensile test that load-deflection curve. The windowed or short-time Fourier transform(WFT or STFT) makes possible for the analysis of non-stationary or transient signals into a joint time-frequency domain and the wavelet transform(WT) is used to decompose the acoustic emission(AE) signal into various discrete series of sequences over different frequency bands. In this paper, for acoustic emission signal analysis to use a continuous wavelet transform, in which the Gabor wavelet base on a Gaussian window function is applied to the time-frequency domain. A wavelet transform is demonstrated and the plots are very powerful in the recognition of the acoustic emission features. As a result, the technique of acoustic emission is ideally suited to study variables which control time and stress dependent fracture or damage process in metallic materials.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2005.05a
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• pp.342-348
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• 2005

This study was carried out fusion-welded butt joints in SWS 490A high strength steel subjected to tensile test that load-deflection curve. The windowed or short-time Fourier transform (WFT or SIFT) makes possible for the analysis of non-stationary or transient signals into a joint time-frequency domain and the wavelet transform (WT) is used to decompose the acoustic emission (AE) signal into various discrete series of sequences over different frequency bands. In this paper, for acoustic emission signal analysis to use a continuous wavelet transform, in which the Gabor wavelet base on a Gaussian window function is applied to the time-frequency domain. A wavelet transform is demonstrated and the plots are very powerful in the recognition of the acoustic emission features. As a result, the technique of acoustic emission is ideally suited to study variables which control time and stress dependent fracture or damage process in metallic materials.

• Journal of Power Electronics
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• v.19 no.2
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• pp.580-590
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• 2019

The concept of virtual synchronous generators (VSGs) is a valuable means for improving the frequency stability of microgrids (MGs). However, a great virtual inertia in a VSG's controller may cause power oscillation, thereby deteriorating system stability. In this study, a small-signal model of an MG with two paralleled VSGs is established, and a control strategy for maintaining a constant inertial time with an increasing active-frequency droop coefficient (m) is proposed on the basis of a root locus analysis. The power oscillation is suppressed by adjusting virtual synchronous reactance, damping coefficient, and load frequency coefficient under the same inertial time constant. In addition, the dynamic load distribution is sensitive to the controller parameters, especially under the parallel operation of VSGs with different capacities. Therefore, an active power increment method is introduced to improve the precision of active power sharing in dynamic response. Simulation and experimental is used to verify the theoretical analysis findings.

• Journal of the Korean Society for Railway
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• v.11 no.5
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• pp.477-481
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• 2008

This paper dealt with a detection method of series arc existence which is a symptom of electric fires in low-voltage system. The proposed detection circuit consists of a high-pass filter with a low cut-off frequency of 3kHz to attenuate power frequency voltage by 80 dB and an active band-pass filter with a center frequency of 4kHz to detect only the series arc signals. The performance of the circuit was evaluated in a phase-controlled incandescent lamp as a non-linear load and an inverted-fed induction motor as a high frequency load by using the arc generator specified in UL1699. From the experimental results, it was confirmed that the proposed method solved the detection error, which is being the most problem, by discriminating the series arc signal even in non-linear and high frequency loads.

• 제어로봇시스템학회:학술대회논문집
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• 1993.10a
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• pp.1172-1177
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• 1993

Dynamic characteristics of a hydraulic power supply are studied theoretically and computationally. The transfer function between the supply pressure and the load flow is derived considering relief valve dynamics, accumulator dynamics, and flow line dynamics. Frequency responses and time responses are obtained in many conditions using the transfer function and nonlinear mathematical model respectively.