• 전력전자학회:학술대회논문집
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• 전력전자학회 2004년도 전력전자학술대회 논문집(1)
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• pp.92-96
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• 2004

Islanding of PV systems can cause a variety of problems and must be prevented. However, if the real and active powers of RLC load and PV system are closely matched, islanding detection by passive methods becomes difficult. Active methods enables islanding detection by forcing the frequency of the voltage in the island to drift up/down. This paper shows the simulation and comparision by Matlab for the active methods.

• 전기의세계
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• 제26권3호
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• pp.73-75
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• 1977

A coupled-mode approach is used to analyze the interaction of the carrier wave in solid-state materials with the external slow electromagnetic wave. A general condition for an active coupling is derived. Gain characteristics is also examined as a function of operating frequency and thermal-to-drift veocity variations.

• 조명전기설비학회논문지
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• 제25권10호
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• pp.76-86
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• 2011

This paper proposes novel algorithm for anti-islanding of grid-connected photovoltaic(PV) inverter. The islanding of PV systems can cause a variety of problems such as deterioration in power quality and electric shock. To prevent islanding, many anti-islanding methods are researched. Typical methods of anti-islanding are active frequency drift(AFD) and active frequency drift positive feedback(AFDPF). However, the AFD has problem that widely exists non diction zone(NDZ). The AFDPF is a method that improves the AFD method and is detected islanding by changing the chopping fraction(cf). However, The AFDPF does not detect when cf is very small and does not satisfy the IEEE Std. 929-2000 when cf is very big. Therefore, this paper proposes novel anti-islanding method that is simple to implement using virtual resister. The anti-islanding method proposed in this paper is compared with conventional method. The validity of this paper is proved using this result.

• Journal of Power Electronics
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• 제18권5호
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• pp.1434-1447
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• 2018

The control design of inductive power transfer (IPT) systems has attracted a lot of attention in the field of wireless power transmission. Due to the high-order resonant networks and multiple loads in IPT systems, a simplified model of an IPT system is preferred for analysis and control design, and a controller with strong robustness is required. Hence, an active disturbance rejection control (ADRC) for IPT systems is proposed in this paper. To realize the employment of ADRC, firstly a small-signal model of an LC series-compensative IPT system is derived based on generalized state-space averaging (GSSA), then the ADRC is implemented in the designed IPT system. The ADRC not only provides superior robustness to unknown internal and external disturbances, but also requires few knowledge of the IPT system. Due to the convenient realization of ADRC, the designed IPT system retains its simple structure without any additional circuits. Finally, a frequency domain analysis and experimental results have validated the effectiveness of the employed ADRC, especially its robustness in the presence of frequency drifts and other common disturbances.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2008년도 추계학술대회 논문집
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• pp.64-67
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• 2008

To detect islanding mode when the grid is being tripped is a major safety issue in the Utility Interactive Distributed Generation (UIDG) system. In this paper, analytical design method is suggested for AFD & RPV method under IEEE929-2000 recommended islanding test condition. We have discussed that there is a same point. we injected reactive component of the current by AFD & RPV methods, but the current reference generated is other waveform. Possible if amount of reactive components in this methods are same each method, there is happened same rates frequency variation. To verify the validity of the analytical comparison, this paper presents simulation and experimental results from single phase, 3[kW] inverter for the transformerless UIDG system.

• E2M - 전기 전자와 첨단 소재
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• 제10권9호
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• pp.922-929
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• 1997

As the size of semiconductor devices shrinks in the horizontal as well as vertical dimension it is difficult to estimate the transport-velocity of electron because they drift in non-equilibrium with a few scattering. In this paper HYbrid Monte Carlo simulator which employs the drift-diffusion model for hole-transport and Monte Carlo model for electron-transport in order to reduce the simulation time and increase the accuracy as well has been developed and applied to analyze the electron-transport in InAlAs/InGaAs HBT which is attractive for an ultra high speed active device in high speed optical fiber transmission systems in terms of the velocity and energy distribution as well as cutoff frequency.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2009년도 정기총회 및 추계학술대회 논문집
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• pp.188-190
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• 2009

본 연구에서는 독립운전 검출기법의 능동적 기법 중 AFDPF 기법을 IEEE Std 929-2000에 제시된 독립운전 시험 조건하에서 위상동기기법 영점검출방식(Zero Crossing PLL)을 적용하여 독립운전 시 chopping fraction에 따른 PCC(Point of Common Coupling)의 주파수 변동 특성을 PSIM을 통하여 분석하였다

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 B
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• pp.1705-1707
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• 2005

This paper proposes a novel active frequency drift(AFD) method for the islanding prevention of grid-connected photovoltaic inverter. To detect the islanding phenomenon of grid-connected photovoltaic(PV) inverters concerning about the safety hazards and the damage to other electric equipments, many kinds of anti-islanding methods have been presented. Among them, AFD method using chopping fraction(cf) enables the islanding detection to drift up(or down) the frequency of the voltage during the islanding situation. However, the performance of the conventional AFD methods, which have a certain value of cf only, is inefficient and difficult to design the appropriate cf value analytically to meet the limit of harmonics. In this paper, the periodic chopping fraction based on an AFD method is proposed. This proposed method shows the analytical design value of cf to meet the test procedure of IEEE Std. 929-2000 with the power quality and islanding detection time. To verify the validation of the proposed method, the islanding test results are presented. It is confirmed that the proposed method has not only less harmonic distortion but also good performance of islanding detection compare with the conventional AFD method.

• Journal of Power Electronics
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• 제16권2호
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• pp.760-768
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• 2016

Three-phase grid-connected inverters are widely applied in the fields of new energy power generation, electric vehicles and so on. Islanding detection is necessary to ensure the stability and safety of such systems. In this paper, feature recognition technology is applied and a novel islanding detection method is proposed. It can identify the features of inverter systems. The theoretical values of these features are defined as codebooks. The difference between the actual value of a feature and the codebook is defined as the quantizing distortion. When islanding happens, the sum of the quantizing distortions exceeds the threshold value. Thus, islanding can be detected. The non-detection zone can be avoided by choosing reasonable features. To accelerate the speed of detection and to avoid miscalculation, an active islanding detection method based on feature recognition technology is given. Compared to the active frequency or phase drift methods, the proposed active method can reduce the distortion of grid-current when the inverter works normally. The principles of the islanding detection method based on the feature recognition technology and the improved active method are both analyzed in detail. An 18 kVA DSP-based three-phase inverter with the SVPWM control strategy has been established and tested. Simulation and experimental results verify the theoretical analysis.

• Journal of Electrical Engineering and Technology
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• 제3권4호
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• pp.528-537
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• 2008

Primary frequency control(PFC) has the ability to regulate short period random variations of frequency during normal operation conditions and also to respond rapidly to emergencies. However, during the past decade, numerous significant sized blackouts occurred worldwide that resulted in serious economic losses. Therefore, the conclusion has been reached that the ability of the current PFC to meet an emergency is poor, and security of power systems should be improved. An alternative to enhance the PFC and thus security is to store excessive amounts of energy during off-peak load periods in efficient energy storage systems for substituting the primary control reserve. In this sense, superconducting magnetic energy storage(SMES) in combination with a static synchronous compensator(STATCOM) is capable of supplying power systems with both active and reactive powers simultaneously and very rapidly, and thus is able to enhance the security dramatically. In this paper, a new concept of PFC based on incorporating a STATCOM-SMES is presented. A complete detailed model is proposed and a new control scheme is designed, comprising an enhanced frequency control scheme, and a fully decoupled current control strategy in d-q coordinates with a novel controller to prevent dc bus capacitors voltage drift/imbalance. The performance of the proposed control schemes is validated through digital simulation carried out using MATLAB/Simulink.