• Journal of Electrical Engineering and Technology
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• v.5 no.4
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• pp.614-622
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• 2010

This paper presents a control method, which reduces the pulsating torque and DC voltage problems of a doubly fed induction generator (DFIG)-based wind turbine system. To reduce the torque and power ripple, a current control scheme consisting of a proportional integral (PI) controller is presented in a positive synchronously rotating reference frame, which is capable of providing precise current control for a rotor-side converter with separated positive and negative components. The power theory can reduce the oscillation of the DC-link voltage in the grid-side converter. In this paper, the generator model is examined, and simulation results are obtained with a 3 kW DFIG-based wind turbine system to verify the proposed control strategy.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.643-647
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• 1996

The dynamic behavior of hydrostatic table is represented as the theoretical model, 1-dof, 2-dof rigid body spring-damper system, and finite element model. By the experimental and theoretical methods, the validity of these models and some other dynamic behaviors, such as the effects of unbalanced load and three dimensional motion, are investigated. To make easier to consider the dynamic behavior of hydrostatic table in design process, the stiffness and damping coefficients are calculated using the simple approximation method delived from the mass flow continuity condition, and compared with experimental results.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.3
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• pp.150-156
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• 1998

In this paper, a 3-DOF(Degree Of Freedom) rigid body model is developed for dynamic analysis of a hydrostatic table. The dynamic coefficients, stiffness and damping constant of each pad are calculated from the mass flow continuity condition. The validity of this model is examined in theoretical and experimental method. The dynamic behavior when mass unbalances and local variations of stiffness and damping of pads present is analyzed for real applications of hydrostatic table. Since the theoretical and experimental results show goof agreement. it can be said that the 3-DOF rigid body model is useful for the dynamic model of the table. The analysis reveals that the pitching motion is the dominant mode of vibration, It also reveals that unbalanced loads can increase amplitude of tilting motion and reduce natural frequencies and damping capacity of the hydrostatic table.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.213-214
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• 2014

This paper compares two instantaneous reactive power definitions in DFIG wind turbine with a back-to-back three-level neutral-point clamped voltage source converter under unbalanced grid conditions. In general, conventional definition of instantaneous reactive power is obtained by taking an imaginary component of complex power. The other definition of instantaneous reactive power can be developed based on a set of voltages lagging the grid input voltages by 90 degree. A complex quantity referred as a quadrature complex power is defined. Proposed definition of instantaneous reactive power is derived by taking a real component of quadrature complex power. The characteristics of two instantaneous reactive power definitions are compared using the ripple-free stator active power control algorithm in DFIG. Instantaneous reactive power definition based on quadrature complex power has a simpler current reference calculation control block. Ripple of instantaneous active and reactive power has the same magnitude unlike in conventional definition under grid unbalance. Comparison results of two instantaneous reactive power definitions are verified through simulation.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.291-292
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• 2014

The three-phase four-leg voltage source inverter (VSI) topology can be an interesting option for the three phase-four wire system. With an additional leg, this topology can achieve superior performance with unbalanced and/or nonlinear load. This paper proposes a new hybrid controller which combines PI controller and resonant controller in synchronous frame for three phase four leg inverter. The hybrid controller is simple in structure and easy to implement. The performance of proposed controller is verified by the experiments and compared with that of the conventional PI controller.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.417-420
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• 2005

This paper presents an analytical method to evaluate the dynamic behavior of the scroll compressor. Unbalanced forces and moments act on the compressor body because of the reaction forces acting on rotating components like the orbiting scroll, Oldham coupling ring, and the crank shaft. The vibration of the compressor is induced by the forces and the moments. In this paper, through modeling of the leakage flow, solving the forces from the equations of motion of the moving parts, the analysis of vibration of the compressor was performed. According to the operating condition, the variation of acceleration of the compressor body were calculated and compared.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2002.09a
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• pp.366-369
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• 2002

Subsurface biobarrier technology has potential applications to contain contaminated groundwater and/or to degrade toxic pollutants in groundwater. Most biobarrier studies were conducted under aerobic condition, however there were several obstacles to make aerobic condition. Thus, In this study, we examined biobarrier formation under denitrifying condition by using nitrate as an electron acceptor. Experiments were performed with a sand column inoculated with activated sludge from the nearby WWTP. The substrate medium was pumped to the sand column in an upflow mode. During the low substrate loading rate period, the extent of reduction rate in hydraulic conductivity was found similar throughout the column, and permeability became relatively stable after couple of days. However, during the high substrate loading rate period, the column demonstrated a gradient of permeability reduction, with the greatest reduction in sections nearest the column inlet. Rapid growth of microorganisms near the column inlet resulted in the unbalanced reduction of hydraulic conductivity throughout the sand column. As a result, at this denitrifying condition the thickness of biobarrier could be controlled by adjusting the medium conditions of microbial growth.

• Proceedings of the KIEE Conference
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• 2008.11b
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• pp.109-109
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• 2008

Neutral line current is analyzed by the neutral line CF in nonlinear load balanced and unbalanced conditions. The worst nonlinear load condition is nonlinear balanced load condition. and It is below CFNL=1.194 that a neutral line current could not excess the rated value.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.49 no.11
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• pp.720-728
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• 2000

This paper describes the calculation of the equivalent circuit parameters and the characteristic analysis of a capacitor-run type single-phase induction motor by means of the finite element method in coupled with the conventional equivalent circuit model. The circuit parameters of the stator are calculated form the lumped parameter and the slot leakage reactance of the rotor with the closed slot can be obtained by the use of slot pitch boundary condition. From the analysis result this combined equivalent circuit and finite element method which is used slot pitch boundary condition is compared with the experimental results, the validity of the method is proved.

• Proceedings of the KIPE Conference
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• 2000.07a
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• pp.752-755
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• 2000

This paper describes a new algorithm for active power filters which can be control source current symmetrically under unbalanced condition in power system. Positive sequency voltage is detected by symmetrical coordinate method and compensating reference current of active power filters is calculated using by accurate phase angle information of positive sequency voltage. The basic principle of the proposed method is described in detail and the conventional and proposed phase detecting methods are compared and discussed through the simulation results.