Integrated Transmission and Distribution Control

Abstract

Printed in the United States of America Available to DOE and DOE contractors from the Office of Scientific and Technical Information, P.O. Box 62, Oak Ridge, TN 37831-0062; ph: (865) 576-8401 fax: (865) 576-5728 email: reports@adonis.osti.gov Available to the public from the National Technical Information Service, U.S. Department of Commerce, 5285 Port Royal Rd., Springfield, VA 22161 ph: (800) 553-6847 fax: (703) 605-6900 email: orders@ntis.fedworld.gov online ordering: http://www.ntis.gov/ordering.htmThis document was printed on recycled paper. Executive SummaryDistributed, generation, demand response, distributed storage, smart appliances, electric vehicles and renewable energy resources are expected to play a key part in the transformation of the American power system. Control, coordination and compensation of these smart grid assets are inherently interlinked. Advanced control strategies to warrant large-scale penetration of distributed smart grid assets do not currently exist. While many of the smart grid technologies proposed involve assets being deployed at the distribution level, most of the significant benefits accrue at the transmission level. The development of advanced smart grid simulation tools, such as GridLAB-D, has led to a dramatic improvement in the models of smart grid assets available for design and evaluation of smart grid technology. However, one of the main challenges to quantifying the benefits of smart grid assets at the transmission level is the lack of tools and framework for integrating transmission and distribution technologies into a single simulation environment. Furthermore, given the size and complexity of the distribution system, it is crucial to be able to represent the behavior of distributed smart grid assets using reduced-order controllable models and to analyze their impacts on the bulk power system in terms of stability and reliability.The objectives of the project were to: Develop a simulation environment for integrating transmission and distribution control,  Construct reduced-order controllable models for smart grid assets at the distribution level,  Design and validate closed-loop control strategies for distributed smart grid assets, and  Demonstrate impact of integrating thousands of smart grid assets under closed-loop control demand response strategies on the transmission system.More specifically, GridLAB-D, a distribution system tool, and PowerWorld, a transmission planning tool, are integrated into a single simulation environment. The integrated environment allows the load flow interactions between the bulk power system and end-use loads to be explicitly modeled. Power system interactions are modeled down to time intervals as short as 1-second.Another practical issue is that the size and complexity of typical distribution systems makes direct integration with transmission models computationally intractable. Hence, the focus of the next main task is to develop reduced-order controllable models for some of the smart grid assets. In particular, HVAC units, which ...

Transmission and Distribution (T&D) Quasi-Static Co-Simulation: Analysis and Comparison of T&D Coupling Strength

“…The integration of largely single-phase roof-top PVs at the distribution-level necessitates the analysis of unbalanced loading conditions on the interconnected TS, thus, calling for a detailed three-phase TS modeling and power flow analysis [22]. Second, many of the co-simulation tools do not include a mathematical model for T&D interactions and they mostly couple T&D systems using a non-iterative/loosely coupled (LC) protocol where the boundary values at T&D coupling points are sequentially exchanged without allowing for convergence at each timestep [12]- [15]. The LC co-simulation methods are accurate only when the changes in the DS loading characteristics, both the load unbalances and demand variability, are slower than the simulation time-step at which the two systems are solved, and the solutions are exchanged; otherwise, they introduce simulation errors [22].…”

“…Owing to the need for capturing T&D interactions, lately, increasing efforts have been put forward to develop simulation tools capable of combined T&D modeling and analysis. The existing frameworks can be broadly categorized as (1) standalone T&D system models [9]- [11], and (2) T&D cosimulation platforms [12]- [20].…”

“…The co-simulation interface shown in Fig. 1 calculates R T and R D as defined in (11) and (12) subject to (7) and (9). Then it is compared with the predefined tolerance .…”

Combined Transmission and Distribution State-Estimation for Future Electric Grids

“…The proposed approach for combined T&D ACSE is dependent on the underlying combined T&D models. There is active research on development of such combined T&D models [8], [9], [10], [11] [12]; however, most of the research focus has been on building models for solving planning problems rather than state estimation that requires optimization and inclusion of measurement data. These models, when combined, represent transmission and distribution grids with a mix of positive sequence and three-phase network components.…”

Dynamic Co-Simulation Methods for Combined Transmission-Distribution System With Integration Time Step Impact on Convergence

“…Here, generally there are no dynamics involved. The second category [4][5][6], is to integrate the controls and communications into the steady state power flows for energy management and market clearance. In this category, the dynamics of the system are related to hourly or daily load and generation profiles.…”