• 전력전자학회논문지
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• 제21권4호
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• pp.283-289
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• 2016

Islanding protection of a grid-connected photovoltaic (PV) inverter is a key function for standards compliance. Unintentional islanding results in safety hazards, reliability, and many other issues. Therefore, many anti-islanding schemes have been examined. However, existing anti-islanding schemes have poor power quality and non-detection zone issues. Moreover, most schemes have problems that deteriorate the performance of islanding detection under parallel operation. Therefore, this paper proposes a novel anti-islanding scheme that has negligible power quality degradation and has no non-detection zone and islanding detection under a parallel operation. Both simulation and experimental results validate the proposed scheme.

• 조명전기설비학회논문지
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• 제29권10호
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• pp.73-82
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• 2015

This paper proposes an ripple reduction algorithm and analyzes the effects of offset and scale errors generated by voltage sensor while measuring grid voltage in grid-tied single-phase inverters. Generally, the grid-connected inverter needs to detect the phase angle information by measuring grid voltage for synchronization, so that the single-phase inverter can be accurately driven based on estimated phase angle information. However, offset and scale errors are inevitably generated owing to the non-linear characteristics of voltage sensor and these errors affect that the phase angle includes 1st harmonic component under using SRF-PLL(Synchronous Reference Frame - Phase Locked Loop) system for detecting grid phase angle. Also, the performance of the overall system is degraded from the distorted phase angle including the specific harmonic component. As a result, in this paper, offset and scale error due to the voltage sensor in single-phase grid connected inverter under SRF-PLL is analyzed in detail and proportional resonant controller is used to reduce the ripples caused by the offset error. Especially, the integrator output of PI(Proportional Integral) controller in SRF-PLL is selected as an input signal of the proportional resonant controller. Simulation and experiment are performed to verify the effectiveness of the proposed algorithm.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1999년도 전력전자학술대회 논문집
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• pp.549-553
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• 1999

This paper describes a design method of grid-connected photovoltaic power generation systems with three phase inverter. A 3-phase 50kW photovoltaic power generation system including a DC/AC inverter is designed and made in order to investigate the system performance for grid connection. Also the control scheme of a three phase current-controlled PWM inverter is presented by using d-q transformation. The experimental waveforms show that the proposed system has stable behavior with an unit power factor in utility-interactive operation.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.279-281
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• 2005

In DC traction substation with 12-pulse diode rectifiers, the DC line voltage tends to rise above noload voltage because it can't absorb the regenerative power caused by electric brakes of train. To solve this problem, an IGBT regenerative inverter should be installed and thus recycles the surplus regenerative power by delivering it to the supply grid. In this paper, the DC traction substation equipped with a IGBT regenerative inverter is studied using computer simulation. Matlab/simulink is used to simulate the operation of regenerative inverter which injects the regenerative power into the supply grid and stabilizes the DC line voltage. It is confirmed that the high quality regenerative power is delivered to the supply grid thorough computer simulation.

• KEPCO Journal on Electric Power and Energy
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• 제7권1호
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• pp.101-105
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• 2021

Encouragement of DER from Korean government with several policies boosts DER installation in power system. When the penetration of DER in the grid is getting high, loss of generation with break-away of DER by abnormal grid conditions should be considered, because loss of high generation causes abnormal low frequency and additional operations of protection system. Therefore, KEPCO where is Korean power utility is preparing improvement in regulations for DERs connected to the grid to support abnormal grid conditions such as low and high frequencies or voltages. This is called 'Ride Through' because the requirement is for DER to maintain grid connection during required periods when abnormal grid conditions occur. However, it is not easy to have a test for ride through capability in reality because emulation of abnormal grid conditions is not possible in real power system in operation. Also, it is not easy to have a study on grid effect when ride through capability fails with the same reason. PHILs (Power Hardware In the Loop System) makes it possible to analyze power system and hardware performance at once. Therefore, this paper introduces PHILs test methods and presents verification of ride through capability especially for low voltage grid conditions.

• International Journal of Computer Science & Network Security
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• 제22권4호
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• pp.1-12
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• 2022

In order to overcome the power fluctuation issues in photovoltaic (PV) smart grid-connected systems and the inverter nonlinearity model problem, an adaptive backstepping command-filter and a double second order generalized Integrators (DSOGI) controller are designed in order to tune the AC current and the DC-link voltage from the DC side. Firstly, we propose to present the filter mathematical model throughout the PV system, at that juncture the backstepping control law is applied in order to control it, Moreover the command filter is bounded to the controller aiming to exclude the backstepping controller differential increase. Additionally, The adaptive law uses Lyapunov stability criterion. Its task is to estimate the uncertain parameters in the smart grid-connected inverter. A DSOGI is added to stabilize the grid currents and eliminate undesirable harmonics meanwhile feeding maximum power generated from PV to the point of common coupling (PCC). Then, guaranteeing a dynamic effective response even under very unbalanced loads and/or intermittent climate changes. Finally, the simulation results will be established using MATLAB/SIMULINK proving that the presented approach can control surely the smart grid-connected system.

• 전기학회논문지
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• 제56권2호
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• pp.317-324
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• 2007

Most conventional hybrid systems using renewable energy sources have been applied for stand-alone operation, but Utility-interface may be an useful and viable option for hybrid systems. Grid-connected operation may have benefits such as reduced losses in power system distribution, utility support in demand side management, and peak load shaving. This paper addresses power control and dynamic performance of a grid-connected PV/wind/BESS hybrid system. At all times the PV way and the wind turbine are individually controlled to generate the maximum energy from given weather conditions. The battery energy storage system (BESS) charges or discharges the battery depending on energy gap between grid invertger generation and production from the PV and wind system. The BESS should be also controlled without too frequently repeated shifts in operation mode, charging or discharging. The grid inverter regulates the generated power injection into the grid. Different control schemes of the grid inverter are presented for different operation modes, which include normal operation, power dispatching, and power smoothing. Simulation results demonstrate that the effectiveness of the proposed power control schemes for the grid-interactive hybrid system.

• 한국정보통신학회논문지
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• 제17권5호
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• pp.1187-1195
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• 2013

태양광 인버터는 항상 태양전지 어레이의 최대 전력을 추종하며 동작해야 한다. 또한 태양광 인버터는 폭넓은 태양전지의 최대 전력점 전압과 관계없이 최대 전력점을 추종해야 한다. 태양전지의 전류리플이 발생한다면 최대 전력점 추종 기능이 저하되고 일사량 변동이나 최대 전력점 변동 시 정상적으로 추종하기 어려워진다. 이러한 문제점을 해결하기 위해 본 논문에서는 고효율의 새로운 최대 전력점 추종 알고리즘과 태양전지의 전류리플 감소 알고리즘을 제안하였다. 4KW급 계통연계형 태양광 인버터에 적용하여 실험한 결과 최대 전력점 추종 효율이 99.97%, 인버터 출력 효율은 97.5%, 인버터 전류의 고조파 총 왜곡률은 1.05%로 우수한 성능을 보였다. 또한 0.5초 동안 일사량을 100% -> 10%, 10% -> 100%로 급격히 변동하였을 때에도 안정된 최대 전력점 추종이 가능함을 알 수 있었다.

• Journal of Power Electronics
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• 제17권5호
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• pp.1278-1287
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• 2017

Inverters are widely used in distributed power generation and other applications. However, their lack of inertia and variable impedance may cause system instability and power transfer inaccuracy. This paper proposes a control scheme for a single phase voltage-controlled inverter with some grid-friendly characteristics. The proposed control algorithm enables the inverter to function as a voltage source with an inner output impedance in both the islanded and grid-connected modes. Virtual inertia and rotor equations are embedded in the PLL part. Thus, the frequency stability can remain. The inner output impedance can be adjusted freely, which helps to accurately decouple and transmit the output active and reactive power. The proposed inverter operates like a traditional synchronous generator. Simulations and experiments are designed and carried out to verify the proposed control strategy.

• 태양에너지
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• 제19권4호
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• pp.63-69
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• 1999

The conventional grid connected PV(Photovoltaic) system has a unstable output pattern due to its dependence on the weather condition, although solar-cell array averagely has a regular output characteristics to have a peak output nearly at noon. Therefore assuming the high density grid connection in the future, this unstable output pattern can be one of the main reasons to generate power disturbance such as voltage variation, frequency variation and harmonic voltage generation in low voltage distribution line. However general grid connected solar-cell system do not have functions to cope with these disturbances. Therefore this study proposed a advanced type grid connected PV system with functions to suppress output power fluctuation due to solar-cell array output variation and showed the levelling effect of fluctuation due to instantaneous array output variation.