• Journal of Power Electronics
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• v.10 no.5
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• pp.548-554
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• 2010

In this paper, a 1.5 kW Interior Permanent Magnet Synchronous Generator (IPMSG) with a power conditioner for the grid integration of a variable-speed wind turbine is developed. The power-conditioning system consists of a series-type 12-pulse diode rectifier powered by a phase shifting transformer and then cascaded to a PWM voltage source inverter. The PWM inverter is utilized to supply sinusoidal currents to the utility line by controlling the active and reactive current components in the q-d rotating reference frame. While the q-axis active current of the PWM inverter is regulated to follow an optimized active current reference so as to track the maximum power of the wind turbine. The d-axis reactive current can be adjusted to control the reactive power and voltage. In order to track the maximum power of the wind turbine, the optimal active current reference is determined by using a simple MPPT algorithm which requires only three sensors. Moreover, the phase angle of the utility voltage is detected using a simple electronic circuit consisting of both a zero-crossing voltage detecting circuit and a counter circuit employed with a crystal oscillator. At the generator terminals, a passive filter is designed not only to decrease the harmonic voltages and currents observed at the terminals of the IPMSG but also to improve the generator efficiency. The laboratory results indicate that the losses in the IPMSG can be effectively reduced by setting a passive filter at the generator terminals.

• Journal of the Korea Society of Computer and Information
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• v.12 no.3
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• pp.19-26
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• 2007

In recent rears. web portal system has received much attention as a user interface for the grid environment. Grid system uses symmetric key for authenticating user identity while the traditional portal system does a password-based authentication. Regarding this, many researches are progressing to integrate portal accounts with symmetric key. Specially. researches such as GAMA and PURSE are active and those focus on easy usability for users who familiar with password-based authentication. However the protection of data and resources is a critical issue in Grid environment, because those are shared through a wide-area network. In this paper, we suggest a new authentication mechanism which unify authentication mechanisms between portal system and grid service by using symmetric key. It will improve a security level in UI layer as much as in grid service.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.64 no.1
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• pp.18-22
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• 2015

When using a secondary battery in energy storage units, if the grid is in light duty the active power is stored so it can be used when the grid is in heavy duty. This makes possible for the load equalize and make the grid optimized. Recently the government is trying to propagate this technology. Depending on its capacity this kind of electric energy storage unit is used in adjusting the frequency, break up the energy peak in summer and winter, stabilize the energy output of renewable energy which can change unstably because of the environment. Which makes it possible to stabilize the grid. It is anticipated that market of 120 trillion won will be developed worldwide in 2030. Currently in Korea a steady supply is in progress. However because of stray electromagnetic waves some other electronics are malfunctioning. This paper covers the research in the method to detect the emission noise in small electric energy storage units using lithium secondary batteries and battery management system, Power conditioning systems with CIPSR standards. And the research of a more efficient method to measure such stray electromagnetic waves.

• The Transactions of the Korean Institute of Power Electronics
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• v.20 no.6
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• pp.526-533
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• 2015

A new algorithm is proposed for the estimation of equivalent grid impedance at the point of common coupling of a grid-tie inverter output. The estimated impedance parameter can be used for the improvement of the performance and the stability of the distributed generation system. The estimation error is inevitable in the conventional estimation method because of the axis rotation due to PLL. In the conventional estimation error, the d-q voltage and current are used for the calculation of the impedance with active and reactive current injections. Conversely, in the proposed algorithm, the negative sequence current is injected, and then the negative sequence voltage is measured for the impedance estimation. As the positive and negative sequence current controller is independent and the PLL is based on the positive sequence component only, the estimation of the equivalent impedance can be achieved with high accuracy. Simulation and experimental results are compared to validate the proposed algorithm.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.12
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• pp.1697-1704
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• 2017

As the power grid has been changed to a smart grid, existing power technologies are evolving into convergence technology through interdisciplinary research. According to the government policy to increase the proportion of renewable energy to 20% by 2030, the speed seems to be accelerating. This study analyzes the relationship between research technologies in order to grasp research trends of smart grid technology. To this end, we analyze the relationship between keywords extracted from topic modeling using social network analysis methodology. This is because, in the field where interdisciplinary research such as smart grid is active, each research topic is not independent, but research technologies emerging in one topic coexist in different topics, and linkage between research technologies can be important information. Therefore, this study can contribute to the analysis of research trend as it can be used as a package tool together with a topic modeling methodology.

• Journal of Power Electronics
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• v.19 no.6
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• pp.1554-1565
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• 2019

When grid voltage is unbalanced, the grid-connected output current and power of Virtual Synchronous Generators (VSGs) are distorted and quadratic. In order to improve the power quality of a grid connected to a VSG when the grid voltage is unbalanced, a comprehensive coordinated control strategy is proposed. The strategy uses the positive sequence current reference command obtained by a VSG in the balanced current control mode to establish a unified negative sequence current reference command analytical expression for the three objectives of current balance, active power constant and reactive power constant. In addition, based on the relative value of each target's volatility, a comprehensive wave function expression is established. By deriving the comprehensive wave function, the corresponding negative sequence current reference value is obtained. Therefore, the VSG can achieve the minimum comprehensive fluctuation under the premise that the three targets meet the requirements of grid connection, and the output power quality is improved. The effectiveness of the proposed control strategy is verified by simulation and experimental results.

• Proceedings of the KIPE Conference
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• 2004.07a
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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.

• Journal of Power Electronics
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• v.15 no.3
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• pp.819-829
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• 2015

This paper presents a shunt active power filter (SAPF) for compensating inter-harmonics and harmonics when inter-harmonics content is evident in the grid. The principle of inter-harmonics generation in the grid was analyzed, and the inter-harmonics effect on repetitive controllers was discussed in terms of control performance. Traditional repetitive controllers are not applicable in inter-harmonic compensation. Moreover, the effect of an ideal controller on harmonics signals was analyzed on the basis of the internal model principle. The repetitive controller was improved in the form of a basis function according to theoretical analysis. The finite-dimensional repetitive controller, which is also called the multiple-period repetitive controller, was designed for the control of multiple periodic signals. A selective harmonic compensation system was developed with SAPF. This system can be used to compensate harmonics and inter-harmonics in the grid. Finally, system control performance was verified by simulation and experimental results.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.508-514
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• 2005

This paper is concerned with the active vibration control of a grid structure equipped with piezoceramic sensors and actuators. The grid structure is a replica of the solar panel commonly mounted on satellites, which contains complex natural mode shapes. The multi input and multi output positive position feedback controller is considered as an active vibration controller for the grid structure. A new concept, the block-inverse technique, is proposed to cope with more modes than the number of actuators and sensors. This study also deals with the stability and the spillover effect associated with the application of the multi-input multi-output positive position feedback controller based on the block inverse technique. It was found that the theories developed in this study are capable of predicting the control system characteristics and its performance. The new multi-input multi-output positive position feedback controller was applied to the test structure using a digital signal processor and its efficacy was verified by experiments..

• Journal of Power Electronics
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• v.14 no.2
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• pp.369-382
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• 2014

A growing dynamic electrical demand has created an increasing interest in utilizing nonconventional energy sources like Photovoltaic (PV), wind power, etc. In this context, this paper focuses on the design and development of a composite power controller (CPC) in the decoupled double synchronous reference frame (DDSRF) combining the advantages of direct power control (DPC) and voltage oriented control (VOC) for a PV sourced grid connected inverter. In addition, a controller with the inherent active filter configuration is tested with nonlinear and unbalanced loads at the point of common coupling in both grid connected and autonomous modes of operation. Furthermore, the loss and reactive power compensation due to a non-fundamental component is also incorporated in the design, and the developed DDSRF model subsequently allows independent active and reactive power control. The proposed developed model of the controller is also implemented using MATLAB-Simulink-ISE and a Xilinx system generator which evaluate both the simulated and experimental setups. The simulation and experimental results confirm the validity of the developed model. Further, simulation results for the DPC are also presented and compared with the proposed CPC to further bring out the salient features of the proposed work.