• Journal of Electrical Engineering and Technology
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• v.6 no.3
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• pp.375-383
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• 2011

This paper describes a real-time hardware simulator for a grid-tied Permanent Magnet Synchronous Generator (PMSG) wind power system, which consists of an anemometer, a data logger, a motor-generator set with vector drive, and a back-to-back power converter with a digital signal processor (DSP) controller. The anemometer measures real wind speed, and the data is sent to the data logger to calculate the turbine torque. The calculated torque is sent to the vector drive for the induction motor after it is scaled down to the rated simulator power. The motor generates the mechanical power for the PMSG, and the generated electrical power is connected to the grid through a back-to-back converter. The generator-side converter in a back-to-back converter operates in current control mode to track the maximum power point at the given wind speed. The grid-side converter operates to control the direct current link voltage and to correct the power factor. The developed simulator can be used to analyze various mechanical and electrical characteristics of a grid-tied PMSG wind power system. It can also be utilized to educate students or engineers on the operation of grid-tied PMSG wind power system.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.7
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• pp.28-37
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• 2015

Owing to the variability of large-scaled wind power system, the development of wind farm management technologies and related compensation methods have been receiving attention. To provide an accurate and reliable output power, certain wind farm adopts a specified management system including a wind prediction model and grid expectation solutions for considering grid condition. Those technologies are focused on improving the reliability and stability issues of wind farms, which can affect not only nearby system devices but also a voltage condition of utility grid. Therefore, to adapt the develop management system, an expectation process about voltage condition of Point of Common Coupling should be integrated in operating system for responding system requirements in real-time basis. This paper introduce a grid imposing method for a real-time based wind farm management system. The expected power can be transferred to the power flow section and the required quantity about reactive power can be calculated through the proposed system. For the verification process, the gauss-seidel method is introduced in the Matlab/Simulink for analysing power flow condition. The entire simulation process was designed to interwork with PSCAD for verifying real power system condition.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.6
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• pp.1280-1285
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• 2011

Recently, due to the use of fossil fuels for electric power production, carbon emissions increased excessively. Thereby, in order to replace fossil fuels, many studies about fossil fuels such as solar and fuel cell energy source are progressing. Fuel cell system has high energy conversion efficiency. Also, fuel cell system is environmentally friendly system because the carbon emission is almost not occur. Therefore, the fuel cell system is considered as the core technology of in the fields of the future energy and environmental. Fuel cell system has an effect on distribution power system because another power source of other than large power plants. So, fuel cell system can be degradation reason of power quality in the power system. In this paper, we constructed the system for an assessment on harmonics effect. The system is composed with power source, harmonics generation and linear load, fuel cell system. we also performed assessment on harmonics effect in customer and the distributed power system during grid connection of residential fuel cell system. An assessment cases are divided into three. A Case 1 is state that residential load and fuel system are connected to grid, Case 2 is state that residential load and harmonics load are connected to grid, and Case 3 is state that all loads are connected to grid. As a output of fuel cell system is increase, analysis results based on assessment system showed that power quality became more aggravation as effect of harmonics.

• Journal of Power Electronics
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• v.18 no.3
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• pp.853-862
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• 2018

Frequency coupling in the phase domain is a recently reported phenomenon for phase locked loop (PLL) based three-phase grid-inverter systems. This paper investigates the mechanism and stabilization method for the frequency coupling to the stability of grid-inverter systems. Self and accompanying admittance models are employed to represent the frequency coupling characteristics of the inverter, and a small signal equivalent circuit of a grid-inverter system is set up to reveal the mechanism of the frequency coupling to the system stability. The analysis reveals that the equivalent inverter admittance is changed due to the frequency coupling of the inverter, and the system stability is affected. In the end, retuning the bandwidth of the phase locked loop is presented to stabilize the three-phase grid-inverter system. Experimental results are given to verify the analysis and the stabilization scheme.

• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.1
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• pp.41-50
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• 2014

The rising penetration of renewable energy resulted in the development of grid-connected large-scale power plants. Therefore, grid stabilization, which depends on the system-type or grid of each country, plays an important role and has been strengthened by different grid codes. With this background, VDE-AR-N 4105 for photovoltaic (PV) systems connected to the low-voltage grid and the German Association of Energy and Water Industries (BDEW) introduced the medium-voltage grid code for connecting power plants to the grid and they are the most stringent certifications. In this paper, an optimal control strategy scheme for three-phase grid-connected PV system is enhanced with VDE-AR-N 4105 and BDEW grid code, where both active/reactive powers are controlled. Simulation and experimental results of 100kW PV inverter are shown to verify the effectiveness of the proposed implemental control strategy.

• Journal of international Conference on Electrical Machines and Systems
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• v.2 no.4
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• pp.466-472
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• 2013

The paper presents a novel DC grid connection topology and control strategy for doubly-fed induction generator (DFIG) based wind power generation system. In order to achieve the wind power conversion, the stator side converter and the rotor side converter is used to implement the DFIG control based on the indirect air-gap flux orientation, and a DC/DC converter is used for the DFIG system to DC grid connection. The maximum power point tracking and DC voltage droop control can also be implemented for the proposed DFIG system. Finally, a 4-terminal DFIG-based multi-terminal DC grid system is developed by Matlab to validate the availability of the proposed system and control strategy.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.11
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• pp.2497-2506
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• 2010

Smart power grid is targeting to improve grid operation by integrating existing power IT technologies in the jeju smart grid field test. Real-time two-way communication and interoperability in power grid are essential to smart power grid. Adopting smart grid will increase security vulnerabilities in power grid by increasing the number of wireless sensors and the chances of the external exposure of communication networks. In addition, hackers can cause chaos in the power grid system with eavesdropping and forgery attacks in communication networks. Smart power grid is one of the most important systems in deploying smart grid, and it is important to design security system systematically since smart grid can be seriously damaged when problem occurs. In this paper, local and global smart grid security standard and security vulnerabilities in power grid are reviewed, and 2 level smart grid service model is proposed.

• Journal of the Korean Society of Industry Convergence
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• v.23 no.4_1
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• pp.559-567
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• 2020

As the renewable energy market grows, grid-connected inverters have been improving and expanding in several fields in recent years because energy conversion devices are the main components of solar systems. In this paper, a high-precision new grid-connected three-phase inverter system is proposed. The proposed system consists of a main inverter, a sub inverter and a transformer. The main inverter operates at a low switching frequency and high power and transmits power to the grid. A sub-inverter connected in series with the transmission line through a matching transformer operates at lower power than the main inverter to provide input values to the transformer. The transformer acts as a power supply according to the voltage compensation value. This study is based on the principle of operation of the UPFC(Unified Power Flow Controller) structure used to regulate power flow in AC transmission lines. The grid-connected inverter system proposed in this paper is implemented with high precision and high resolution. The proposed system was verified through its ability to enhance and ensure the safety of the proposed system through simulation and experiment.

• The Transactions of the Korean Institute of Power Electronics
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• v.20 no.1
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• pp.91-103
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• 2015

This paper investigates control algorithms for a doubly fed induction generator with a back-to-back three-level neutral-point clamped voltage source converter in a medium-voltage wind power system under unbalanced grid conditions. Negative sequence control algorithms to compensate for unbalanced conditions have been investigated with respect to four performance factors: fault ride-through capability, instantaneous active power pulsation, harmonic distortions, and torque pulsation. The control algorithm having zero amplitude of torque ripple indicates the most cost-effective performance in terms of torque pulsation. The least active power pulsation is produced by a control algorithm that nullifies the oscillating component of the instantaneous stator active and reactive power. A combination of these two control algorithms depending on operating requirements and depth of grid unbalance presents the most optimized performance factors under generalized unbalanced operating conditions, leading to a high-performance DFIG wind turbine system with unbalanced grid adaptive features.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.5
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• pp.1093-1101
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• 2017

Microgrid as a unit component consisting a smart grid is an isolated system, which has a decentralized power supply system. This paper proposes an electrical isolation of the microgrid from the utiliy grid based on a power conditioning system, and also proposes an operation method maintaining the isolated state efficiently using diverse distributed energy resources such as renewable energy sources and energy storage system. The proposed system minimizes the influence of the grid connection on the internal load though a phase detection and synchrnoization to the utiligy grid and the microgrid can be stable even if the grid is failed.