A Special Issue on Non-Bulk Generation
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By Farrokh Rahimi and Sasan Mokhtari
The electric power system is undergoing fundamental changes, due to a combination of factors. The most important of these factors are the increased penetration of distributed energy resources (DERs), the proliferation of grid-edge intelligent devices, and the increasing consumer/prosumer participation. The classical unidirectional patterns of power flow from bulk power generation through transmission and distribution grids to the end-use consumers is changing, because of the installation of active grid edge DERs and the provision of grid services from grid-edge assets. The classical information-flow pattern from field devices and meters to the utility central control systems and bulk power markets is complemented by routing of information in the opposite direction (in the form of price signals to consumers, and grid-edge devices and systems). Moreover, active consumer/prosumer production of electricity from local, privately owned resources (rooftop PV, etc.) is impacting the utility revenues, while, at the same time, it imposes operational issues for system operators in the form of reverse flows, voltage rise and so on. The classical seams between bulk power and distribution operations are getting blurred under the emerging Smart Grid/Grid Modernization. These changes require new business models and operational tools for the utilities to properly adapt. Changes in business models point to the need for new services, which utilities could offer to the increasingly savvy consumers/prosumers. The latter ones are, in turn, interested in transactive exchanges to derive maximum benefits from their investments in DERs and associated end-use control and communication technologies.
By Konstantinos Oikonomou, Masood Parvania, and Vijay Satyal
Electric energy storage (EES) represents one of the major components of grid modernization that provides various services for the enhancement of the reliability and the resiliency of the power grid. In the U.S., the potential benefits of EES have attracted the interest of policy makers and regulators at both the state and federal levels. As of June 2016, EES capacity in the U.S. was over 23 GW, out of which, 94 percent was pumped hydro systems and the remaining 6 percent was of the electrochemical type (lithium–ion, Nickel cadmium, sodium sulfur batteries), the electro mechanical type (compressed air, flywheels) and thermal storage units. In the western interconnection (WI), EES is identified as an asset critical to the improvement of the reliability of the system and as a complementary technology in the attempts to increase penetrations of variable renewable energy resources. More specifically, the additional intra-hour balancing capacity (from generators) that will be required to accommodate the variability of an expected 14.4 GW of additional wind integration between 2011 and 2020 is estimated at 1.53 GW. However, if these additional balancing services are to be provided by new energy storage plants, instead, the energy capacity would be about 0.58 GWh, or storage capable of providing electricity at the rated power capacity for about 20 minutes.
By Panayiotis (Panos) Moutis
Distribution Management Systems (DMS) have been at the center of attention since the mid-1990s as an extension of the Energy Management Systems (EMS) to the distribution networks (DNs). EMS, as computer applications (in most cases SCADA systems), were employed to robustly operate, manage, protect and monitor the transmission system and the central generation, due to the size and complexity of the infrastructure involved. That said, DMS had, at first, a very narrow range of functionalities, mainly of monitoring DNs and providing an interface with the overlying EMS. However, the ever-increasing penetration of Distributed Generation (DG) and the deregulation of energy markets changed this status. Nowadays, all major industrial companies such as ABB, General Electric, Siemens, Schneider and others, each offer their own DMS platform featuring numerous applications for the operation and control of DNs. In this sense, DMS are deployed widely, in order to facilitate the transition to the Transactive Energy paradigm.
By Qing-Chang Zhong
Power systems are going through a paradigm shift, due to the addition of numerous non-synchronous distributed generators and active loads connected through power electronic converters. This situation imposes unprecedented challenges to the frequency stability of power systems. Power electronic converters can be controlled to behave as virtual synchronous machines (also called “cyber synchronous machines”). Thus, a novel system architecture occurs with interfaces unified according to the synchronization mechanism of synchronous machines, which realizes the paradigm shift for power systems from centralized control to democratized interaction. This architecture enables all active players on the supply side, inside the network and on the load side, to offer continuous primary frequency control (PFC), reconfigurable virtual inertia and flexible droop control without delay, which improves the frequency stability of future power systems.
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