From Research to Action

Advancing the Integrated Grid: Distributed Energy Resource Management Systems (DERMS)

By Dr. Gerald R. Gray, Dr. John Simmins, and Brian Seal Battery storage, solar and wind generation, as well as other distributed energy resources (DER) promise clean energy as well as grid stability benefits. Managing the growing penetration of these resources is becoming a challenge. Coordinated control of these resources depends on communication between back-office systems and devices. When Distributed Energy Resources (DER) were first being deployed at a scale to become interesting, they typically used inverters to convert direct current (DC) into AC that is synced with the grid. (Wind turbines convert ?wild? un-synched AC, to steady state DC, then do the AC conversion and syncing with the grid.) Various DER have clean energy benefits or work in combination resources such as wind/solar to mitigate the deleterious effects of unpredictable, variable generation. Additionally, while DER is often touted as a means to provide ancillary services on the grid to stabilize disruptions, the fact is at certain penetrations and locations, DER is the source of the disturbance. Enter the smart inverter. Beginning in 2008, the Electric Power Resource Institute (EPRI) led an initiative for the industry to define a common set of smart inverter functions. This was a very successful effort with international participation and manufacturers and utilities coming to agreement on what common functions were needed and practical given the state of the technology. Once a menu of standard functions was in place, standard protocols (languages) were developed to communicate settings and status data with the smart inverters. The resulting standard (IEC 61850-90-7) defines these functions and it has been successfully mapped to communication standards such as DNP3, SunSpec Modbus, and Smart Energy Profile 2 (SEP2). These developments have become the foundation upon which grid codes are being developed worldwide. In the context of DER, grid codes are the laws that dictate what is allowed to be connected to the grid. Grid codes are mandates that require certain grid-supportive characteristics and are put in place in order to enable the grid to support increasing levels of DER. In some cases, grid codes are created at the national level. The German medium and low voltage grid codes were among the first and most extensive examples of a national grid code. In the US, California is revising the state?s ?Rule 21? which is a code at the state level. Grid codes generally reference the standards, such as the IEC smart inverter standard and communication protocol standards. Such references benefit the manufacturers by providing more consistency in what is needed in the marketplace 1 . The next challenge to be addressed is how to manage the communication to all of these devices, especially as the number of deployed resources grows rapidly. The aggregate impact of many small DER, such as residential photovoltaic (PV) systems, is like that of large DER. Makers of distribution management systems (DMS) and utility control room operators typically do not want to view numerous small-scale DER on a device by device basis. They also do not want to view the numerous smart inverter functions and the detailed parameters involved with configuring each function. That level of control is too granular to be useful in the present distribution management environment where there are typically just a few control devices and basic on/off or up/down settings. The clear distinction between the many field devices with many functional capabilities and the control center need for simplicity creates a need for DER management systems, or DERMS. In view of this, EPRI began work with the US Department of Energy, National Institute of Standards and Technology, Smart Grid Interoperability Panel, and other entities in late 2012 to address this need. EPRI gathered a host of industry stakeholders to coalesce around a common set of use cases that are fitting for DER integration at the enterprise level. This body of work was aimed at addressing the needs for DMS integration of DER, including utilityto-aggregator interfaces and substation or feeder-level management of DER. The core set of use cases is based on the need to manage groups of DER, do maintenance on these groups (creating/deleting groups, adding or removing members), status monitoring of the group, dispatching of the group for real and reactive power, and forecasting of a group?s capabilities. ElectricEnergy T&D MAGAZINE I MAY-JUNE 2015 Issue 17

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