Abstract

DC electric power distribution systems have higher efficiency, better current carrying capacity and faster response when compared to conventional AC systems. They also provide a more natural interface with many types of renewable energy sources. Furthermore, there are fewer issues with reactive power flow, power quality and frequency regulation, resulting in a notably less complex control system. All these facts lead to increased applications of DC systems in modern power systems. Still, design and operation of these systems imposes a number of specific challenges, mostly related to lack of mature protection technology and operational experience, as well as very early development stage of standards regarding DC based power infrastructure. This book provides an up-to-date overview of recent research activities in the control, protection and architectural design of a number of different types of DC distribution systems and microgrids. Practical requirements and implementation details of several types of DC distribution systems used in the real world industrial applications are also presented. Several types of coordinated control design concepts are shown, with concepts of stabilization being explained in detail. The book reviews the shortcomings and future developments concerning the practical DC system integration issues.

Abstract

Electric vehicle (EV) chargers can be controlled to support the grid frequency by implementing a standard-compliant fast primary frequency control (PFC). This study addresses potential effects on power systems due to control discreteness in aggregated EVs when providing frequency regulation. Possible consequences of a discrete response, as reserve provision error and induced grid frequency oscillations, are first identified by a theoretical analysis both for large power systems and for microgrids. Thus, an EV fleet management solution relying on shifting the droop characteristic for the individual EVs is proposed. The PFC is implemented in a microgrid with a power-hardware-in-the-loop approach to complement the investigation with experimental validation. Both the analytical and the experimental results demonstrate how the controller performance is influenced by the response granularity, and that related oscillations can be prevented either by reducing the response granularity or by applying appropriate shifts on the droop characteristics for individual EVs. This is an open access article published by the IET under the Creative Commons Attribution -NonCommercial License (http://creativecommons.org/licenses/by-nc/3.0/) Document type: Article