• Journal of Power Electronics
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• 제18권4호
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• pp.1235-1244
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• 2018

The application of shunt capacitor banks and underground cables typically induces resonance in power distribution systems. In this study, the propagation of resonance in a microgrid (MG) with inverter-based distributed generators (IBDGs) is investigated. If resonances are not properly damped, then the output current of the inverters may experience distortion via resonance propagation due to the adverse effect of resonances on MG power quality. This study presents a conceptual method for identifying resonances and related issues in multi-inverter systems. For this purpose, existing resonances are identified using modal impedance analysis. However, some resonances may be undetectable when this method is used. Thus, the resonances are investigated using the proposed method based on the frequency response of a closed-loop MG equivalent circuit. After analyzing resonance propagation in the MG, an effective virtual impedance damping method is used in the IBDG control system to damp the resonances. Results demonstrate the effectiveness of the proposed method in compensating for existing resonances.

• E2M - 전기 전자와 첨단 소재
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• 제8권1호
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• pp.27-34
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• 1995

The analysis of nonlinear equivalent circuit and the resonance characteristics of input current and output voltage were simulated, and their electrical properties are discussed in the transverse-type piezoelectric ceramic transformer. The nonlinear resonance characteristics of input current and output voltage showed by the thermal effect due to a higher driving current, the nonlinearity increased greatly as driving current increased. When load resistor was 100[M.ohm.], the nonlinear coefficient was -1.3. The nonlinear resonance curve of input current and output voltage for a variation of input voltage and load resistor agreed with the discussed theory. The output voltage increased nearly proportioned to input voltage when load resistors were below 50[M.ohm.], the voltage step-up ratio decreased when a load resistor was 100[M.ohm.] and their maximum value was 950.

• E2M - 전기 전자와 첨단 소재
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• 제9권1호
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• pp.24-29
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• 1996

A composite piezoelectric ceramic transducer is fabricated with three piezoelectric ceramic disk vibrators and two sheets of thin insulator. Its equivalent circuit is derived from the Mason's model of a thickness-driven piezoelectric vibrator. When the electric input near its fundamental resonance frequency is applied to the center vibrator and the output voltages across the left and the right vibrators are connected in series to the resistor loads, the load characteristics at resonance frequencies under the various resistor loads and the frequency characteristics near the resonance frequency without load are investigated. Furthermore, symbolic expressions for input impedances, voltage ratios, resonance frequencies, and bandwidths are derived. The data calculated from those symbolic expressions are agreed well with the measurement data.

• Journal of electromagnetic engineering and science
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• 제18권1호
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• pp.1-6
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• 2018

In this study, the analytic expression for the positive/negative $n^{th}-Mode$ resonance frequency of an N unit cell composite right-/lefthanded (CRLH) transmission line is derived. To explain the resonance mechanism of the $n^{th}$ mode, especially for the negative mode, the current distribution of the N unit cell CRLH transmission line is investigated with a circuit simulation. Results show that both positive and negative $n^{th}$ resonance modes have n times current variations, but their phase difference is $180^{\circ}$ as expected. Moreover, the positive $n^{th}$ resonance occurs at a high frequency, whereas the negative $n^{th}$ resonance transpires at a low frequency, thus indicating that the negative resonance mode can be utilized for a small resonator. The correlation between the slope of the dispersion curve and the bandwidth is also observed. In sum, the balanced condition of the CRLH transmission line provides a broader bandwidth than the unbalanced condition.

• 전자공학회논문지
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• 제50권4호
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• pp.73-80
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• 2013

본 논문에서는 전송선의 정확한 고주파 특성화를 위해 실험적 접근을 기반으로 한 회로모델을 제안한다. 측정 시 불가피하게 발생하는 공진현상으로 인하여 배선의 길이에 상응하는 공진주파수에서 특성 임피던스 및 전파상수를 정확히 결정하기 어렵다. 따라서 물리적 통찰 및 이론을 바탕으로 이러한 공진효과가 배제된 전송선 파라미터 결정 방법이 제시되었다. 또한 고속신호의 전파 특성화를 위해 실험적으로 결정된 파라미터를 사용한 고주파 회로모델이 제안되었다. 본 논문에서 제안한 주파수 종속 전송선 파라미터 모델은 측정을 통해 검증되었으며, 고속 신호의 전파 특성화에 유용하게 적용될 수 있다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.1273-1279
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• 2000

A new concept of piezoelectric smart panels for noise reduction in wide band frequencies is proposed and their possibility is experimentally investigated. The proposed panels are based on active and passive methods. They use piezoelectric smart structure technology for active noise reduction at low band frequencies and passive sound absorbing materials for mid-range of noise frequencies. To prove the concept of piezoelectric smart panels, an acoustic measurement experiment was performed. The smart panels exhibit a good noise reduction in middle and high frequency ranges due to the mass effects of absorbing materials or/and the air gap. The use of piezoelectric smart panel renders noise reduction large at resonance frequency. Another concept of smart panel that uses piezoelectric damping is experimentally investigated. Since piezoelectric dampings can reduce vibration and noise at resonance frequencies with simple shunt circuit, they have merits in terms of economy and simplicity. Dissipated energy method(DEM) is adopted to tune the shunt circuit precisely in piezoelectric dampings. Noise reduction at multiple resonance frequencies is demonstrated.

• Journal of Power Electronics
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• 제11권1호
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• pp.97-104
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• 2011

This paper proposes a new alternating current driving method for highly capacitive loads such as plasma display panels or piezoelectric actuators, etc. In the proposed scheme, a current balance transformer, which has two windings with the same turn-ratio, provides not only a resonance inductance for energy recovery but also a current balance among all of the switching devices of the driver for current stress reduction. The smaller conduction loss than conventional circuits occurs due to the dual conduction paths which are parallel each other in the current balance transformer. Also, the leakage inductances of the transformer are utilized as resonant inductors for energy recovery by the series resonance to the capacitive load. Furthermore, the resonance contributes to the small switching losses of the switching devices by soft-switching operation. To confirm the validity of the proposed circuit, prototype hardware with a 12-inch mercury-free flat fluorescent lamp is implemented. The experimental results are compared with a conventional energy-recovery circuit from the perspective of luminance performances.

• 센서학회지
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• 제26권4호
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• pp.245-250
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• 2017

A novel method to implement a birdcage-type receiving coil sensor for use in a magnetic resonance imaging(MRI) system has been demonstrated employing a flexible printed circuit board (FPCB) fabrication technique. Unlike the conventional methods, the two-dimensional shape of the coil sensor is first implemented as a FPCB and then it is attached to the surface of a cylindrical supporting structure to implement the three-dimensional birdcage-type coil sensor. The proposed method is very effective to implement object-specific MRI coil sensors especially for small animal measurements in research and preclinical applications since the existing well-developed FPCB-based techniques can easily meet the requirements on accuracies and costs during coil implement process. The performances of the coil sensor verified through $^1H$ 1.5T MRI measurements for small animals and it showed excellent characteristics by providing a high spatial precision and a high signal-to-noise ratio.

• Journal of international Conference on Electrical Machines and Systems
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• 제3권4호
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• pp.465-471
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• 2014

This paper proposes a new switching algorithm for an active clamp snubber to improve the efficiency of a module integrated converter system. This system uses an active clamp method for the snubber circuit for the efficiency and reliability of the system. However, the active clamp snubber circuit has the disadvantage that system efficiency is decreased by switch operating time because of heat loss in resonance between the snubber capacitor and leakage inductance. To address this, this paper proposes a new switching algorithm. The proposed algorithm is a technique to reduce power consumption by reducing the resonance of the snubber switch operation time. Also, the snubber switch is operated at zero voltage switching by turning on the snubber switch before main switch turn-off. Simulation and experimental results are presented to show the validity of the proposed new active clamp control algorithm.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2000년도 전력전자학술대회 논문집
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• pp.1-5
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• 2000

This paper deals with the modeling and analysis of the high voltage flyback transformer (HVFBT) often utilized in small-sized high voltage DC power supplies. The parasitic capacitance of th HVFBT with the large turns of the secondary winding causes the undesirable parasitic resonance in the transient state which produces the high current stress and limits the switching frequency of the converter. In order to analyze this phenomenon the equivalent circuit model including the parasitic capacitance is derived and the frequency characteristics are provided. The parasitic resonance in the switching states is also investigated based on this equivalent circuit model. The derived model and analysis is finally validated through the SPICE simulation and experiments.