• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.5
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• pp.80-85
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• 2015

Recently, not only in the Middle East and Southeast Asia but in African area, too, industrial plant construction is being actually done. But unlike in Korea, a lot of them are small-scale isolated industrial plants. And because of the characteristics of industrial plants, induction motors' load forms a large part. The influence of stability resulted from the maneuver and operation of induction motors' load may lead to serious result in the isolated system. This study analyzed it through mathematical modeling on induction motors' maneuver phenomena in the isolated system, realized a case system with the E-TAP program, and simulated load follow performances according to the control variables of a generator inside the isolated system.

• Earthquakes and Structures
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• v.25 no.6
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• pp.399-415
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• 2023

In this study, we investigate the use of a negative stiffness tuned inerter damper system to improve the performance of a base-isolated structure. The negative stiffness tuned inerter damper system consists of a tuned inerter damper connected in parallel with a negative stiffness element. To find the optimal parameters for the base-isolated structure with negative stiffness tuned inerter damper system, we develop an optimization method based on performance criteria. The objective of the optimization is to minimize the superstructure acceleration response ratio, while ensuring that the base displacement response ratio remains below a specified target value. We evaluate the proposed method by conducting numerical analyses on an eight-story building. The structure is modeled using both a simplified 3-degree-of-freedom system and a more detailed story-by-story shear-beam model. Lastly, a comparative analysis using time history analysis is performed to compare the performance of the base-isolated structure with negative stiffness tuned inerter damper system with that of the base-isolated structure and base-isolated structure with tuned inerter damper systems. The results obtained from the comparative analysis show that the negative stiffness tuned inerter damper system outperforms the tuned inerter damper system in reducing the dynamic seismic response of the base-isolated structure. Overall, this study demonstrates that the negative stiffness tuned inerter damper system can effectively enhance the performance of base-isolated structures, providing improved seismic response reduction compared to other systems.

• Journal of applied mathematics & informatics
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• v.20 no.1_2
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• pp.557-567
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• 2006

This paper proves the invariability of reachable sets for the linear control system with positive isolated spectrum points in case where the principal operator generates $C_0-semigroup$ and derives the approximate controllability for the semilinear control system by using spectral operators with respect to isolated spectrum points.

• Structural Engineering and Mechanics
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• v.43 no.4
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• pp.527-543
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• 2012

This paper presents a response spectrum analysis procedure suitable for base isolated regular buildings subjected to near fault ground motions. This procedure is based on the fact that the isolation system may be treated separately since the superstructure behaves as a rigid body on well selected isolation systems. The base isolated building is decomposed into several single-degree of freedom systems, the first one having the total weight of the building is isolated while the remainder when superposed they replicate approximately the behavior of the superstructure. The response of the isolation system is governed by a response spectrum generated for a single isolated mass. The concept of the procedure and its application for the analysis of base isolated structures is illustrated with an example. The present analysis procedure is shown to be accurate enough for the preliminary design and overcomes the limits of applicability of the conventional linear response spectrum analysis.

• Journal of Power Electronics
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• v.8 no.1
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• pp.81-90
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• 2008

This paper presents an investigation of a voltage and frequency controller for an isolated asynchronous generator (IAG) driven. by a wind turbine and supplying 3-phase 4-wire loads to the isolated areas where a grid is not accessible. The control strategy is based on the indirect current control of the VSC (voltage source converter) using the frequency PI controller. The proposed controller consists of three single-phase IGBT (Insulated Gate Bipolar Junction Transistor) based VSC, which are connected to each phase of the IAG through three single phase transformers and a battery at their DC link. The controller has the capability of controlling reactive and active powers to regulate the magnitude and frequency of the generated voltage, harmonic elimination, load balancing and neutral current compensation. The proposed isolated system is modeled and simulated in MATLAB using Simulink and PSB (Power System Block-set) toolboxes to verify the performance of the controller.

• Earthquakes and Structures
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• v.16 no.4
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• pp.401-413
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• 2019

The concept of base isolation for equipment is well known. Its application in buildings and structures is rather challenging. Introduction of horizontal flexibility at the base helps in proper energy dissipation at the base level thus reducing the seismic demand of the super structure to be considered during design. The present study shows the results of a series of numerical simulation studies on seismic responses of secondary system (SS) housed in non-isolated and base-isolated primary structures (PS) including equipment-structure interactions. For this study the primary structure consists of two similar single bay three-store reinforced cement concrete (RCC) Frame building, one non-isolated with conventional foundation and another base isolated with Lead plug bearings (LPB) constructed at IIT Guwahati, while the secondary system is modeled as a steel frame. Time period of the base isolated building is higher than the fixed building. Due to the presence of isolator, Acceleration response is significantly reduced in both (X and Y) direction of Building. It have been found that when compared to fixed base building, the base isolated building gives better performance in high seismic prone areas.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.35 no.7
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• pp.165-170
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• 2019

The structural damage caused by earthquake to the upper structure of seismic base-isolated system can be suppressed effectively because it is designed to concentrate the input energy on the seismic isolation floor. Further, the response acceleration of seismic base-isolated system can be greatly reduced compared to the seismic structure because of the long period, which means that the design shear force of the seismic base-isolated system can be reduced appropriately. However, when the design shear force is determined to be reduced, the design stiffness will decrease, and the response acceleration will increase oppositely. Therefore, for finding the extent to which the design shear force of the upper structure can be reduced, this paper considered the seismic base-isolated structure as the analytical model and proposed the design shear force reduction factor of the base-isolated structure through the dynamic response analysis, while considering the decrement effect of response acceleration. The research result shows that the response acceleration of the isolated the upper structure can be reduced by 50%~70% of the seismic structure under the same design conditions, and the design shear force can be reduced by up to 40%. By increasing the design stiffness over to 1.8 times of the original design value, the design shear force can be reduced to the same extent as the response acceleration can be reduced compared to the seismic structure.

• Journal of Power Electronics
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• v.9 no.6
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• pp.874-883
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• 2009

This paper deals with an integrated voltage and frequency (VF) controller for isolated asynchronous generators (IAG) driven by a constant power pico-hydro uncontrolled turbine feeding three-phase four-wire loads. The proposed VF controller is used to control the frequency and voltage of an IAG with load leveling. Such a VF controller is also known as an integrated electronic load controller (IELC) which is realized using an isolated star/polygon transformer with a voltage source converter (VSC) and a battery at its DC bus. The proposed generating system with a VFC is modeled and simulated in MATLAB along with Simulink and Simpower system (SPS) toolboxes. The simulated results are presented to demonstrate the performance of an isolated asynchronous generator feeding three-phase four-wire loads with neutral current compensation.

• Smart Structures and Systems
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• v.3 no.3
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• pp.385-403
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• 2007

The effectiveness of the newly developed smart passive control system employing a magnetorheological (MR) damper and an electromagnetic induction (EMI) part for seismic protection of base isolated structures is numerically investigated. An EMI part in the system consists of a permanent magnet and a coil, which changes the kinetic energy of the deformation of an MR damper into the electric energy (i.e. the induced current) according to the Faraday's law of electromagnetic induction. In the smart passive control system, the damping characteristics of an MR damper are varied with the current input generated from an EMI part. Hence, it does not need any control system consisting of sensors, a controller and an external power source. This makes the system much simpler as well as more economic. To verify the efficacy of the smart passive control system, a series of numerical simulations are carried out by considering the benchmark base isolated structure control problems. The numerical simulation results show that the smart passive control system has the comparable control performance to the conventional MR damper-based semiactive control system. Therefore, the smart passive control system could be considered as one of the promising control devices for seismic protection of seismically excited base isolated structures.

• Structural Engineering and Mechanics
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• v.24 no.3
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• pp.375-393
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• 2006

Under high velocity, pulse type near source earthquakes semi-active control systems are very effective in reducing seismic response base isolated structures. Semi-active control systems can be classified as: 1) independently variable stiffness, 2) independently variable damping, and 3) combined variable stiffness and damping systems. Several researchers have studied the effectiveness of independently varying damping systems for seismic response reduction of base isolated structures. In this study effectiveness of a combined system consisting of a semi-active independently variable stiffness (SAIVS) device and a magnetorheological (MR) damper in reducing seismic response of base isolated structures is analytically investigated. The SAIVS device can vary the stiffness, and hence the period, of the isolation system; whereas, the MR damper enhances the energy dissipation characteristics of the isolation system. Two separate control algorithms, i.e., a nonlinear tangential stiffness moving average control algorithm for smooth switching of the SAIVS device and a Lyapunov based control algorithm for damping variation of MR damper, are developed. Single and multi degree of freedom systems consisting of sliding base isolation system and both the SAIVS device and MR damper are considered. Results are presented in the form of nonlinear response spectra, and effectiveness of combined variable stiffness and variable damping system in reducing seismic response of sliding base isolated structures is evaluated. It is shown that the combined variable stiffness and variable damping system leads to significant response reduction over cases with variable stiffness or variable damping systems acting independently, over a broad period range.