Cheol-Hee Yoo

Hardware-in-the-loop simulation of DC microgrid with Multi-Agent System for emergency demand response

This paper presents the real-time hardware-in-the-loop simulation (HILS) of DC microgrids containing multiple distributed resources (DRs) such as a battery energy storage system, a small distributed generator and a smart DC load. The power grid and the DRs are developed in the real-time simulation software, specifically Opal-RT RT-LAB software. The controllers of the DRs are developed as hardware devices using AVR microcontroller named as ATMega-128. The simulation model and hardware devices are integrated in the HILS framework. Each controller of the DRs acts as an intelligent agent that can communicate and cooperate with the coordinator and other agents. Emergency demand response problems are applied to the HILS setup for the performance verification.

A new phase drift anti-islanding method for grid-connected inverter system

Islanding phenomenon of grid-connected photovoltaic (PV) power generation system refer to their independent operation when the utility is disconnectied. Since the islanding phenomenon causes significant hazards to personnel and equipment, PV power generation systems are required to detect and prevent the islanding operation. The islanding detection meethods can be classified into two categories : passive and active methods. If the power mismatch of real and reactive power of between the load and renewable power generation systems are small, the detecting accuracy of passive methods might be lowered. On the other hand, active methods can allegedly deteriorate power quality. This paper proposes a novel anti-islanding method that enables islanding detection by using current command with phase difference. The proposed method is able to not only reduce the non-detection zone (NDZ) but also minimize power quality deterioration. To confirm the validity of the proposed method, this paper presents simulation results, it was recognized that the whole procedure, from removal of the grid to system shutdown, was completed within 0.5 seconds.

Development of Pilot Plant for Distributed Intelligent Management System of Microgrids

This paper describes the development of the pilot plant of distributed intelligent management system for a microgrid. For optimal control and management of microgrids, intelligent agents area applied to the microgrid management system. Each agent includes intelligent algorithms to make decisions on behalf of the corresponding microgrid entity such as distributed generators, local loads, and so on. To this end, each agent has its own resources to evaluate the system conditions by collecting local information and also communicating with other agents. This paper presents key features of the data communication and management of the developed pilot plant such as the construction of mesh network using local wireless communication techniques, the autonomous agent coordination schemes using plug-and-play functions of agents and contract net protocol (CNP) for decision-making. The performance of the pilot plant and developed algorithms are verified via real-time microgrid test bench based on hardware-in-the-loop simulation systems.

The RMS current stress reduction technique in link capacitor of two-stage AC/DC converter

The RMS (Root Mean Square) current reduction technique for the link capacitor of two-stage PFC (power factor correction) AC/DC converter is proposed. Although there exist various factors for optimizing the link capacitor, the RMS current stress is one of the most important factors to determine the capacitor size. To reduce the RMS current of the link capacitor, the main concept of the proposed method is by adding the small C-L-L-C filter around the link capacitor. Namely, the front C-L filter and rear L-C filter of proposed C-L-L-C filter can effectively reduce the RMS currents entering into and coming out of the link capacitor by filtering out the switching current components, respectively. Especially, since the crossover frequency of proposed filter is very far from that of the PFC converter, the proposed filter has hardly any effect on the dynamics of the AC/DC converter and thus, makes it easy to design the overall system controller. To confirm the validity of proposed filter, the theoretical analysis, design considerations, and experimental verification are presented.

Rule-based Coordination Algorithms for Improving Energy Efficiency of PV-Battery Hybrid System

This paper presents effective design schemes for a photovoltaic (PV) and battery hybrid system that includes state-of-the-art technologies such as maximum power point tracking scheme for PV arrays, an effective charging/discharging circuit for batteries, and grid-interfacing power inverters. Compared to commonly-used PV systems, the proposed configuration has more flexibility and autonomy in controlling individual components of the PV-battery hybrid system. This paper also proposes an intelligent coordination scheme for the components of the PV-battery hybrid system to improve the efficiency of renewable energy resources and peak-load management. The proposed algorithm is based on a rule-based expert system that has excellent capability to optimize multi-objective functions. The proposed configuration and algorithms are investigated via switching-level simulation studies of the PV-battery hybrid system.