• Journal of Communications and Networks
• /
• 제14권6호
• /
• pp.597-605
• /
• 2012

With the smart grid coming near, wide-area supervisory control and data acquisition (SCADA) becomes more and more important. However, traditional SCADA systems are not suitable for the openness and distribution requirements of smart grid. Distributed SCADA services should be openly composable and secure. Event-driven methodology makes service collaborations more real-time and flexible because of the space, time and control decoupling of event producer and consumer, which gives us an appropriate foundation. Our SCADA services are constructed and integrated based on distributed events in this paper. Unfortunately, an event-driven SCADA service does not know who consumes its events, and consumers do not know who produces the events either. In this environment, a SCADA service cannot directly control access because of anonymous and multicast interactions. In this paper, a distributed security framework is proposed to protect not only service operations but also data contents in smart grid environments. Finally, a security implementation scheme is given for SCADA services.

• Journal of Power Electronics
• /
• 제14권3호
• /
• pp.421-431
• /
• 2014

A DSP-based self-adaptive proportional-integral (PI) controller to control a DC-DC converter is proposed in this paper. The full-bridge topology is adopted here to obtain higher power output capability and higher conversion efficiency. The converter adopts the zero-voltage-switching (ZVS) technique to reduce the conduction losses. A parallel secondary active clamp circuit is added to deal with the voltage overshoot and ringing effect on the transformer's secondary side. A self-adaptive PI controller is proposed to replace the traditional PI controller. Moreover, the designed converter adopts the constant-current and constant-voltage (CC-CV) output control strategy. The secondary active clamp mechanism is discussed in detail. The effectiveness of the proposed converter was experimentally verified by an IGBT-based 10kW prototype.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2017년도 전력전자학술대회
• /
• pp.268-269
• /
• 2017

This paper presents an improved current control strategy for a three-phase grid-connected inverter under distorted grid conditions. Distorted grid condition is undesirable due to negative effects such as power losses and heating problem in electrical equipments. To enhance the power quality of distributed generation systems under such a condition, a modulated finite control set - model predictive control (MFCS-MPC) scheme will be proposed, in which the optimal switching signals of inverter are chosen by online basis using the principle of current error minimization. In addition, the moving average filter (MAF) is used to improve the phase-lock loop in order to obtain the harmonic-free reference currents on the stationary frame. The usefulness of the proposed MFCS-MPC method is proved by the comparative simulation results under different operating conditions.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2014년도 전력전자학술대회 논문집
• /
• pp.146-147
• /
• 2014

This paper presents an operation of the modular multilevel converter-high voltage direct current (MMC-HVDC) system as a Statcom to support the grid voltage. The advantage of the MMC-HVDC system is that it can control the active and reactive powers independently. The proposed control scheme will be designed by combining this performance and the control method of the Statcom. The grid voltage is regulated by the control of the reactive power, meanwhile the active power is controlled according to its applications. The simulation results based on the PSCAD/EMTDC simulation program will evaluate the effectiveness of the control scheme.

• 한국음향학회지
• /
• 제31권4호
• /
• pp.214-224
• /
• 2012

The objective of this paper is to design multichannel spherical loudspeaker array by considering various positioning methods such as Gaussian grid, Lebedev grid and packing method. For the spatial sound manipulation, which is to make desired sound field by controling multiple sound sources, the Kirchhoff-Helmholtz integral states that sound fields can be reproduced in terms of infinite control sources on the integral surface. But since we cannot control infinite number of sources for the implementation, we have to allocate finite number of sound sources which can approximately act as infinite number of sources. To manipulate sound field inside of a sphere (which is typical example of three dimensional array) by controlling sound sources on the surface, three methods of allocating sound sources, which are Gaussian grid, Lebedev grid and packing method, are reviewed. For each geometry, the performances of manipulation rendered by time-reversal operator and higher-order ambisonics are compared.

• Journal of international Conference on Electrical Machines and Systems
• /
• 제3권2호
• /
• pp.169-175
• /
• 2014

This paper presents an improved direct power control (DPC) strategy for grid-connected voltage source inverter (VSI) under unbalanced and harmonic grid voltage conditions. Based on the mathematic model of VSI with the negative sequence, 5th and 7th harmonic voltage components consideration, a PI controller is used in the proposed DPC strategy to achieve the average output power regulation. Furthermore, vector PI controller with the resonant frequency tuned at the two times and six times grid fundamental frequency is adopted to regulate both negative and harmonic components, and then two alternative targets of the balanced/sinusoidal current and smooth active/reactive output power can be achieved. Finally, simulation results based on MATLAB validate the availability of the proposed DPC strategy.

• Journal of Electrical Engineering and Technology
• /
• 제12권2호
• /
• pp.549-558
• /
• 2017

DC distribution has several differences compared to AC distribution. DC distribution has a higher efficiency than AC distribution when distributing electricity at the same voltage level. Accordingly, power can be transferred further with low-voltage DC. In addition, power flow in a DC grid system is produced by only a voltage difference in magnitude. Owing to these differences, operation of a DC grid system significantly differs from that of an AC system. In this paper, the power flow problem in a bipolar-type DC grid with unbalanced load conditions is organized and solved. Control strategy of energy storage system on a slow time scale with power references obtained by solving an optimization problem regarding the DC grid is then proposed. The proposed strategy is verified with computer simulations.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2007년도 추계학술대회 논문집
• /
• pp.108-111
• /
• 2007

Phase angle in grid-connected inverter is important information for current control. When different loads are connected to PCC(Point of Common Coupling) of grid, distorted grid voltage is taken place by load utility generating distorted current. Especially, in case the grid voltage is distorted by low order frequency such as $3^{rd}$, $5^{th}$ harmonic, phase angle of PLL output is distorted. This paper analyze problem of current THD(Total Harmonic Distortion) due to distorted phase angle by distorted grid voltage, and propose control method compensating this problem. Also, it‘s validity is verified by simulation and experiment.

• 전력전자학회논문지
• /
• 제26권4호
• /
• pp.294-297
• /
• 2021

A grid voltage estimation method for modular plug-in active power decoupling (APD) circuits is proposed in this study as direct replacements of electrolytic capacitors. Since modular plug-in APD circuits cannot have additional grid voltage sensors and should be operated independently without information exchange with the front-end converter, it is impossible to obtain the phase information of the grid directly. Therefore, the proposed method uses the second-order harmonic component of the DC-link voltage to estimate the grid voltage necessary to control the APD circuit. By employing the proposed method, the concept of modular plug-in APD circuits can be realized and implemented without direct detection of the grid voltage. The experimental results based on hardware-in-the-loop simulation (HILS) validate the effectiveness of the proposed control method.

• 한국정보과학회논문지:시스템및이론
• /
• 제31권3_4호
• /
• pp.152-159
• /
• 2004

그리드는 기존의 컴퓨팅 환경을 대체하는 새로울 환경으로 각광받고 있다. 그러나 그리드가 원천적으로 가지고 있는 이질적인 특성으로 인한 사용상의 복잡함 때문에 일반 사용자가 사용하기 어렵다. 본 논문에서는 그리드 안경에서 사용자에게 편리하고 향상된 작업 환경을 제공하고 효율적인 작업의 수행을 돕는 JCML(Job Control Markup Language)과 편집기에 대해 소개한다. JCML은 기존의 글로버스에서 사용하는 RSL을 향상시킨 작업 제어 언어이다. JCML은 표준 XML 문서 형식으로 설계되어 그리드 서비스와의 데이타 호환성을 제공하며, 작업의 표현과 의존성 정보를 표시하기 위해 GXL(Graph eXchange Language)을 이용한 그래프 방식으로 노드와 에지를 사용하여 두 노드간의 의존성을 표현한다. 그리고 JCML 편집기는 사용자가 직관적으로 이해할 수 있도록 GUI 기반의 비주얼 환경을 제공하며, 끌어다 놓기와 같은 간단한 조작만으로도 복잡한 작업 지시를 수행할 수 있도록 구성되었다.