• Transactions on Electrical and Electronic Materials
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• v.15 no.6
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• pp.297-304
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• 2014

Due to the nonlinearity and complexity of the three-phase photovoltaic inverter, we propose an intelligent control based on fuzzy logic and the classical proportional-integral-derivative. The feedback linearization method is applied to cancel the nonlinearities, and transform the dynamic system into a simple and linear subsystem. The system is transformed from abc frame to dq0 synchronous frame, to simplify the state feedback linearization law, and make the close-loop dynamics in the equivalent linear model. The controls improve the dynamic response, efficiency and stability of the three-phase photovoltaic grid system, under variable temperature, solar intensity, and load. The intelligent control of the nonlinear characteristic of the photovoltaic automatically varies the coefficients $K_p$, $K_i$, and $K_d$ under variable temperature and irradiation, and eliminates the oscillation. The simulation results show the advantages of the proposed intelligent control in terms of the correctness, stability, and maintenance of its response, which from many aspects is better than that of the PID controller.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.25 no.7
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• pp.97-104
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• 2011

This paper presents modeling and control for the emerging IGBT converter-based high-voltage direct-current system (IGBT-HVDC). This paper adds to the representation of the IGBT-HVDC system in the dq-synchronous reference frame and its decoupled control scheme. Additionally, since the IGBT-HVDC is able to actively support the grid due to its capacity to control independently active and reactive power production, a reactive power control scheme is presented in order to regulate/contribute to the voltage at a remote location by taking into account its operational state and limits. The ability of the control scheme is assessed and discussed by means of simulations using ahybrid power system, which consists of a permanent magnetic synchronous-generator (PMSG) based wind turbine, an IGBT-HVDC, and a local load.

• Proceedings of the KAIS Fall Conference
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• 2010.11a
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• pp.66-69
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• 2010

본 논문에서는 태양광전원용 3상 인버터의 배전계통 연계시의 동특성을 이해하고 해석하기 위하여, dq좌표변환과 원하는 전압의 크기와 위상을 만들어 내기 위해 사용한 비례적분 제어기(Proportinal Controller : PI), 출력전류 제어를 위한 전류제어 알고리즘, 2상/3상 변환 및 인버터의 Sinusoidal PWM방식의 인버터 설계에 대한 이론적인 알고리즘을 제시하였다. 이를 바탕으로 PSCAD/EMTDC를 이용한 태양광발전의 모델링을 수행하여, Simulation 결과와 산술적 해석의 비교, 분석을 통하여 모델링의 유효성을 확인하였다.

• Proceedings of the KSR Conference
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• 1999.05a
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• pp.328-335
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• 1999

Three phase full bridge rectifier has been used to obtain dc voltage from three phase ac voltage source. The rectifier system has drawbacks that power factor is low and power flow is unidirectional. Therefore, when dc voltage increases due to regeneration of power the dynamic resister for dissipation of regeneration power must be installed. But three phase PWM converter can be controlled to operate with unity power factor and bidirectional power flow. Therefore when the PWM converter is used as do supply system, the dissipating resistor is not necessary. On this thesis, in order to design a controller having good performance, the hee phase PWM converter is completely modeled by using circuit DQ-transformation and thus a general and simple instructive equivalent circuit is obtained; the inductor set becomes a second order gyrator-coupled system and three phase inverter becomes a transformer as well. Under given phase angle(${\alpha}$) and modulation index(MI) of the three phase inverter, the dc and ac characteristics are obtained by analysis of the transformed equivalent circuit The validity of the equivalent circuit is confirmed through PSPICE simulation. And based on the dc and ac characteristics a controller with unity power factor is proposed.

• Proceedings of the KIEE Conference
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• 1993.07b
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• pp.764-766
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• 1993

A new static var compensator(SVC) system using three-level inverter is proposed for high voltage and high power applications. A general and simple model for the overall system is obtained using circuit DQ-transform and DC and AC analyses are achieved to characterize the open-loop system. Using the proposed model, a new control method which controls both the phase angle and modulation index of switching pattern simultaneously is suggested to provide fast response of SVC system without using independent voltage source. Finally, predicted results are verified by computer simulation.

• Journal of Power Electronics
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• v.18 no.6
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• pp.1879-1888
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• 2018

With power level of grid-connected converters rising, the switching frequency of the switching devices is commonly greatly reduced to improve its power capacity. However, this results in serious couplings of the dq current components, which leads to degradation of the static and dynamic performances of grid-connected converters and fluctuations of the reactive power in dynamic processes. In this paper, complex vector models under low switching frequency are established for an L/LCL grid-connected converter, and the relationship between the switching frequency and the coupling degree is analyzed. In addition, a series decoupling current control strategy is put forward. It is shown that the proposed control strategy can eliminate the couplings, improve the performances and have good robustness to parameter variations through static and dynamic characteristics analyses and a sensitivity analysis. Experimental and simulation results also verify the correctness of the theoretical analyses and the superiority of the proposed control strategy.

• Computers and Concrete
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• v.21 no.6
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• pp.717-726
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• 2018

Concrete pipelines are the most efficient and safe means for gas and oil transportation over a long distance. The use of nano materials and nono-engineering can be considered for enhancing concrete pipelines properties. the tests show that $SiO_2$ nanoparticles can improve the mechanical behavior of concrete. Moreover, severe hazard for pipelines is seismic ground motion. Over the years, scientists have attempted to understand pipe behavior against earthquake most frequently via numerical modeling and simulation. Therefore, in this paper, the dynamic response of underwater nanocomposite submerged pipeline conveying fluid is studied. The structure is subjected to the dynamic loads caused by earthquake and the governing equations of the system are derived using mathematical model via Classic shell theory and Hamilton's principle. Navier-Stokes equation is employed to calculate the force due to the fluid in the pipe. As well, the effect of external fluid is modeled with an external force. Mori-Tanaka approach is used to estimate the equivalent material properties of the nanocomposite. 1978 Tabas earthquake in Iran is considered for modelling seismic load. The dynamic displacement of the structure is extracted using differential quadrature method (DQM) and Newmark method. The effects of different parameters such as $SiO_2$ nanoparticles volume percent, boundary conditions, thickness to radius ratios, length to radius ratios, internal and external fluid pressure and earthquake intensity are discussed on the seismic response of the structure. From results obtained in this paper, it can be found that the dynamic response of the pipe is increased in the presence of internal and external fluid. Furthermore, the use of $SiO_2$ nanoparticles in concrete pipeline reduces the displacement of the structure during an earthquake.