• 전기학회논문지
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• 제59권2호
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• pp.262-266
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• 2010

During the restoration process of primary restorative transmission system, the over voltage may happen due to nonlinear interaction between the unloaded transformer and the transmission system. This over voltage is caused by harmonic resonance and can be prevented by damping loads that are connected before restoration process of primary restorative transmission system. But it is very difficult to predict the occurrence possibility of the harmonic resonance previously. This paper analyzes the relationship between the harmonic resonance and the amount of damping loads to prevent the harmonic resonance. This paper calculates the minimum amount of damping loads to prevent harmonic resonance while changing the length of primary restorative transmission line. And this paper confirmed that the amount of damping loads is not proportional to length of transmission line. The result of this paper will be used as important experiment data to predict the occurrence possibility of harmonic resonance previously.

• 전기학회논문지
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• 제62권7호
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• pp.913-917
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• 2013

During the restoration process of primary restorative transmission system, some over voltages may happen due to nonlinear interaction between unloaded transformers and transmission systems. These over voltages caused by harmonic resonance can be suppressed by inserting damping loads before energizing transformers. But it is very difficult to predict the occurrence possibility of harmonic resonance and complex simulation must be repeated to estimate the sufficient damping loads. This paper presents a damping loads prediction system to prevent harmonic resonance. Detailed analysis of the relationship between harmonic resonance and the amount of damping loads is discussed. The prediction system is developed using a curve fitting and a neural network based on this relationship. A curve fitting used a Gaussian function based on non-linear least square method and multi-layer back-propagation neural network is applied. The system is applied to primary restorative transmission lines in korean power system and the result showed satisfactory performance.

• Journal of Electrical Engineering and Technology
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• 제13권6호
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• pp.2335-2343
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• 2018

This paper proposes an optimal damping control algorithm of the DTI (Direct Two-level Inverter) to miniaturize and reduce the weight of auxiliary power supply for railway vehicles. The conventional auxiliary power supply for railway vehicles uses a DC-DC converter to maintain the inverter input power from the line voltage smoothly. The proposed topology does not use a DC-DC converter for reducing of manufacturing and maintenance costs. It also proposes a DTI topology removed damping resistors that generate ground signal noise in a certain period. At this time, a resonance phenomenon of DC-link voltage occurs due to variation of the inductive load, and a method of controlling the resonance phenomenon of DC-link voltage is required. In order to suppress the resonance phenomenon of the DC-link voltage, at a point before resonance occurs, this paper introduces an algorithm to suppress the resonance phenomenon of DC-link voltage by compensating the resonance component of the q axis voltage of the synchronous reference frame. The proposed algorithm verifies the effect through simulation and experiment.

• 한국생산제조학회지
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• 제23권1호
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• pp.56-63
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• 2014

This paper provides a comprehensive study on the Sommerfeld phenomena in an asymmetric rotor with a nonideal power supply. An analytical approach is employed by deriving the equations of motion in a nondimensional form. The system parameters, including the asymmetry, external and internal damping, and motor power, are chosen to find their effects on the characteristics of the Sommerfeld phenomena and critical behavior around resonance. Results show that the rotor asymmetry suppresses the Sommerfeld phenomena and helps pass through resonance if the asymmetry is small. However, it is observed that the opposite effects exist in case of a large asymmetry. It is also found that the effects of external damping on the Sommerfeld phenomena are similar to those of the asymmetry, whereas internal damping has less effects than external damping and the asymmetry. By performing numerical simulations, four types of critical behavior are identified from the viewpoints of the stability and the passage through resonance.

• 한국소음진동공학회논문집
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• 제22권4호
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• pp.352-357
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• 2012

The ground resonance instability of a helicopter with bearingless main rotor hub were investigated. The ground resonance instability is caused by an interaction between the blade lag motion and hub inplane motion. This instability occurs when the helicopter is on the ground and is important for soft-inplane rotors where the rotating lag mode frequency is less than the rotor rotational speed. For the analysis, the bearingless rotor was composed of blades, flexbeam, torque tube, damper, shear restrainer, and pitch links. The fuselage was modeled as a mass-damper-spring system having natural frequencies in roll and pitch motions. The rotor-fuselage coupling equations are derived in non-rotating frame to consider the rotor and fuselage equations in the same frame. The ground resonance instabilities for three cases where are without lead-lag damper and fuselage damping, with lead-lag damper and without fuselage damping, and finally with lead-lag damper and fuselage damping. There is no ground resonance instability in the only rotor-fuselage configuration with lead-lag damper and fuselage damping.

• Journal of Power Electronics
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• 제18권5호
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• pp.1555-1566
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• 2018

Proportional capacitor-current-feedback active damping (AD) is a common damping method for the resonance of LCL-type grid-connected inverters. Proportional capacitor-current-feedback AD behaves as a virtual resistor in parallel with the capacitor. However, the existence of delay in the actual control system causes impedance in the virtual resistor. Impedance is manifested as negative resistance when the resonance frequency exceeds one-sixth of the sampling frequency ($f_s/6$). As a result, the damping effect disappears. To extend the system damping region, this study proposes a virtual resistor-inductor-capacitor (RLC) AD method. The method is implemented by feeding the filter capacitor current passing through a band-pass filter, which functions as a virtual RLC in parallel with the filter capacitor to achieve positive resistance in a wide resonance frequency range. A combination of Nyquist theory and system close-loop pole-zero diagrams is used for damping parameter design to obtain optimal damping parameters. An experiment is performed with a 10 kW grid-connected inverter. The effectiveness of the proposed AD method and the system's robustness against grid impedance variation are demonstrated.

• Journal of Power Electronics
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• 제18권4호
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• pp.1165-1177
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• 2018

This paper investigates the active damping of grid-connected LCL filter resonance using high-pass filter (HPF) of the grid current. An expression for such HPF is derived in terms of the filter components. This expression facilitates a general study of the actively damped filter behavior in the discrete time domain. Limits for the HPF parameters are derived to avoid the excitation of unstable open loop poles since such excitation can reduce both the damping performance and the system robustness. Based on this study, straightforward co-design steps for the active damping loop along with the fundamental current regulator are proposed. A numerical example along with simulation and experimental results are presented to verify the theoretical analyses.

• 조명전기설비학회논문지
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• 제27권1호
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• pp.76-84
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• 2013

The renewable energy sources is raising for use of grid connected systems, for which higher power quality requirements are being issued. A grid connected converter requires a LC-filter stage, this one is lightly damped for efficiency constraints. Hence, it is subject to resonance if excited by the converter current harmonics or pre-exciting grid voltage harmonics. In this paper, an active damping technique employing notch filter for damping of the resonance frequency is introduced. This technique doesn't need to additional sensors. In addition, it is simple to apply for various systems. Monitoring of the resonance frequency ensures the stable operation of the proper connection and disconnection of the grid. This paper proposes the estimating method of a resonant frequency to determine the cut-off frequency of the notch filter. This method is validated by both simulation and experimental results.

• Journal of Power Electronics
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• 제16권4호
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• pp.1587-1597
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• 2016

A novel active damping strategy for the LCL filter resonance is proposed using the grid current and the capacitor voltage. The proposed technique is deduced in the continuous time domain and a discussion for its discrete implementation is presented. According to the proposed technique, instability of the open loop system, which results in non-minimum phase behavior, can be avoided over wide range of resonant frequencies. Moreover, straightforward co-design steps for both the fundamental current regulator and the active damping loops can be used. A numerical example along with experimental results are introduced to validate the proposed strategy performance over wide range of resonant frequencies.

• 한국소음진동공학회논문집
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• 제12권10호
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• pp.766-772
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• 2002

In this investigation, experimental attempts were made to observe and determine the variations in elastic and damping properties of the PVC depending on the amounts of MBS added to the mixture, PVC/MBS, and also on the thicknesses of the specimens. An acoustic resonance technique was used for the tests In this investigation. It serves as a method to characterize properties of materials set in vibrational motions, which is initiated by low level stresses generated by externally supplied acoustic energy. Substantial variations were observed in the test results with the addition of the MBS to the PVC. It was found that the magnitudes of elastic constants decrease while the damping capacity improve when MBS rubber was added in the range up to 9 phr.