• Journal of international Conference on Electrical Machines and Systems
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• 제1권2호
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• pp.70-78
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• 2012

Due to the variable nature of renewable energy resources and power demand by consumers, it is difficult to operate a power system installed with only one type of renewable energy resource. Grid-based renewable generation may be the only solution to overcome this problem. The conventional approach based on a low-voltage converter with power frequency transformer is commonly employed for grid connection of offshore renewable energy systems. Because of the heavy weight and large size of the transformer, the system can be expensive and complex in terms of installation and maintenance. In this paper, an 11-kV series connected H-bridge (SCHB) multilevel voltage source converter (VSC) is proposed to achieve a compact and light direct grid connection of renewable energy systems. This paper presents the design, simulation and analysis of a five level (5L)-SCHB and an eleven level (11L)-SCHB VSC for 11-kV grid-based renewable energy systems. The performance, cost, modulation scheme and harmonic spectra of the converter are analyzed.

• 한국컴퓨터정보학회:학술대회논문집
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• 한국컴퓨터정보학회 2011년도 제44차 하계학술발표논문집 19권2호
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• pp.217-219
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• 2011

Smart Grid를 위해서 전기의 끊김없는 공급과 안전한 전기사용이 중요하다. Smart Grid에 사용되는 전기IT기기의 성능평가와 인증을 받기 위해서는 모듈 기준값, 모듈 성능값, 제품별 기능, 실험장비, 허용오차 등 실험 DataBase가 발생한다. 전기IT기기는, 기존의 존기기기에 IT와 통신기능을 융합하여 전기의 공급과 안전성을 강화시킨 제품이다. 본 논문에서는 Smart Grid DataBase 개발을 위한 전기IT기기들을 안전하게 관리하고, IT와 통신을 통한 인터넷 웹브라우저에서 접속할 수 있는 Java Servlet 기술을 이용한, 전기IT기기에 대한 평가기관 및 인증기관이 실시간으로 평가와 인증 자료를 관리 할 수 있도록 한다.

• Journal of Electrical Engineering and Technology
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• 제13권1호
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• pp.11-19
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• 2018

With the development of smart grid technology, it has become a hotspot to increase benefits of both residential users and electric power companies through demand response technology and interactive technology. In this paper, the game theory is introduced to the interaction between residential users and an electric company, making a mutually beneficial situation for the two. This paper solves the problem of electricity pricing and load shifting in the interactive behavior by building the game-theoretic process, proposing the interaction strategy and doing the optimization. In the simulation results, the residential users decrease their cost by 11% mainly through shifting the thermal loads and the electric company improves its benefits by 5.6% though electricity pricing. Simulation analysis verifies the validity of the proposed method and shows great revenue for the economy of both sides.

• 한국태양에너지학회 논문집
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• 제32권spc3호
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• pp.228-234
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• 2012

This paper presents the algorithm of the compensation of the grid current distortion caused by the grid voltage unbalance and distortion in 3-phase bi-directional DC to AC inverter. Usually 3-phase grid system has unbalance and distortion because of connecting 1-phase and non-linear load with 3-phase load using same input node. Controlling 3-phase inverter by general method under the unbalanced and distorted grid voltage, the grid current has distortion. This distortion of the grid current cause the grid voltage distortion again. So, it need to control the grid current balanced and non-distorted, even the grid voltage gets unbalanced and distorted. There are some complex method to compensate the gird current distortion. it sugest simple method to solve the problem. PSIM simulation is used to validate the proposed algorithm.

• 전력전자학회논문지
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• 제20권1호
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• pp.72-80
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• 2015

In distributed generation systems, a grid-connected inverter should operate with synchronization to grid voltage. Considering that synchronization requires the phase angle of grid voltage, a phase locked loop (PLL) scheme is often used. The synchronous reference frame phase locked loop (SRF-PLL) is generally known to provide reasonable performance under ideal grid voltage. However, this scheme indicates performance degradation under the harmonic distorted or unbalanced grid voltage condition. To overcome this limitation, this paper proposes a phase and harmonic detection method of grid voltage using fast Fourier transform (FFT). To reduce the calculation time of FFT algorithm, minimum sampling data is taken from the voltage measurement to determine the phase angle and the magnitude of harmonic components. An experimental test setup for a grid-connected inverter system has been constructed. By comparative simulations and experiments under various abnormal grid voltage conditions, the proposed scheme has been proven to effectively track the phase angle of the grid voltage.

• International Journal of Computer Science & Network Security
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• 제21권4호
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• pp.255-263
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• 2021

Smart grid is a fully-automated, bi-directional, power transmission network based on the physical grid system, which combines sensor measurement, computer, information communication, and automatic control technology. Blockchain technology, with its security features, can be integrated with Smart Grids to provide secure and efficient power management and transmission. This paper dicusses the deployment of Blockchain technology in Smart Grid. It presents application areas and protocols in which blockchain can be applied to in securing smart grid. One application of each area is explored in detail, such as efficient peer-to-peer transaction, lower platform costs, faster processes, greater flexibility in power generation to transmission, distribution and power consumption in different energy storage systems, current barriers obstructing the implementation of blockchain applications with some level of maturity in financial services but concepts only in energy and other sectors. Wide range of energy applications suggesting a suitable blockchain architecture in smart grid operations, a sample block structure and the potential blockchain technicalities employed in it. Also, added with efficient data aggregation schemes based on the blockchain technology to overcome the challenges related to privacy and security in the smart grid. Later on, consensus algorithms and protocols are discussed. Monitoring of the usage and statistics of energy distribution systems that can also be used to remotely control energy flow to a particular area. Further, the discussion on the blockchain-based frameworks that helps in the diagnosis and maintenance of smart grid equipment. We have also discussed several commercial implementations of blockchain in the smart grid. Finally, various challenges have been discussed for integrating these technologies. Overall, it can be said at the present point in time that blockchain technology certainly shows a lot of potentials from a customer perspective too and should be further developed by market participants. The approaches seen thus far may have a disruptive effect in the future and might require additional regulatory intervention in an already tightly regulated energy market. If blockchains are to deliver benefits for consumers (whether as consumers or prosumers of energy), a strong focus on consumer issues will be needed.

• Journal of Power Electronics
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• 제16권4호
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• pp.1578-1586
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• 2016

A power quality improvement scheme for grid connected inverters, even in the presence of the disturbances in grid voltages due to harmonic distortions and three-phase imbalance, is presented for distributed generation (DG) power systems. The control objective is to force the inverter currents to follow their references with robustness even under external disturbances in grid voltages. The proposed scheme is realized by a disturbance observer (DOB) based current control scheme. Since the uncertainty in a system can be effectively canceled out using an estimated disturbance by the DOB, the resultant system behaves like a closed-loop system consisting of a disturbance-free nominal model. For experimental verification, a 2 kVA laboratory prototype of a grid connected inverter has been built using a digital signal processor (DSP) TMS320F28335. Through comparative simulations and experimental results under grid disturbances such as harmonic distortion and imbalance, the effectiveness of the proposed DOB based current control scheme is demonstrated.

• Journal of Power Electronics
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• 제18권3호
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• pp.757-765
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• 2018

This paper deals with the instability and resonant phenomena in distribution systems with multiple grid-connected inverters with an LCL output filter. The penetration of roof-top and other types of small photovoltaic (PV) grid-connected systems is rapidly increasing in distribution grids due to the attractive incentives set forth by different governments. When the number of such grid-connected inverters increases, their interaction with the distribution grid may cause undesirable effects such as instability and resonance. In this paper, a grid system with several grid-connected inverters is studied. Since proportional-resonant (PR) controllers are becoming more popular, it is assumed that most inverters use this type of controller. An LCL filter is also considered at the inverters output to make the case as realistic as possible. A complete modeling of this system is presented. Consequently, it is shown that such a system is prone to instability due to the interactions of the inverter controllers. A modification of PR controllers is presented where the output capacitor is virtually decreased. As a result, the instability is avoided. Simulation results are presented and show a good agreement with the theoretical studies. Experimental results obtained on a laboratory setup show the validity of the analysis.

• Journal of Electrical Engineering and Technology
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• 제11권4호
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• pp.839-847
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• 2016

Energy recovery battery testing systems (ERBTS) have been widely used in battery manufactures. All the ERBTS are connected in parallel which forms a special and complicated micro-grid system, which has the shortcomings of low energy recovery efficiency, complex grid-connected control algorithms issues for islanded detection, and complicated power circuit topology issues. To solve those shortcomings, a DC micro-grid system is proposed, the released testing energy has the priority to be reutilized between various testing system within the local grid, Compared to conventional scheme, the proposed system has the merits of a simplified power circuit topology, no needs for synchronous control, and much higher testing efficiency. The testing energy can be cycle-used inside the local micro-grid. The additional energy can be recovered to AC-grid. Numerous experimental comparison results between conventional and proposed scheme are provided to demonstrate the validity and effectiveness of the proposed technique.

• Journal of Power Electronics
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• 제15권5호
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• pp.1286-1294
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• 2015

Capacitor current feedback active damping is extensively used in grid-connected converters with an LCL filter. However, systems tends to become unstable when the digital control delay is taken into account, especially in low switching frequencies. This paper discusses this issue by deriving a discrete model with a digital control delay and by presenting the stable region of an active damping loop from high to low switching frequencies. In order to overcome the disadvantage of capacitor current feedback active damping, this paper proposes a modified approach using grid current and converter current for feedback. This can expand the stable region and provide sufficient active damping whether in high or low switching frequencies. By applying the modified approach, the active damping loop can be simplified from fourth-order into second-order, and the design of the grid current loop can be simplified. The modified approach can work well when the grid impedance varies. Both the active damping performance and the dynamic performance of the current loop are verified by simulations and experimental results.