How Microgrids and DERs Can Maximize Sustainability and Resilience
Automation is an important consideration. Examples of automated subsystems include (Figure 1): n Generation within the microgrid, including a diverse range of DERs and CHP n Power distribution networks n BESS n Loads like HVAC systems and machines and motors in industrial facilities n Managing electric vehicle charging and vehicle-to-grid (V2G) connections n Microgrid controllers and switchgear n Interconnects to the utility grid for grid-connected installations
Grid-connected facilities have a single owner and are used to improve reliability in areas where the main grid is unreliable and power is necessary, or in cases where there are economic incentives for sheddable loads and other services from the microgrid owner. Use cases can include hospitals, data centers, continuous process manufacturing plants, and other high-availability buildings. Grid-connected communities have multiple energy users and producers connected to the main grid and managed as a single entity. Use cases include business or university campuses, villages, and small cities. These can have a diversity of energy users, producers, and storage facilities and can be the most complex to control. Sometimes microgrids are islands In addition to discussing the components of a microgrid, the DOE definition refers to microgrid operation in “both grid-connected and island-mode.” The definitions of those modes are straightforward, but implementation is more complex and is addressed in some IEEE standards.
of DERs with the power grid. IEEE 1547 is an evolving standard. Earlier versions of IEEE 1547 were designed for low DER penetration levels and did not consider the potential aggregate regional impact of DERs on the bulk power system. IEEE 1547-2018 added stricter requirements regarding voltage and frequency regulation and ride-through capability to help the reliability of the transmission system. More recently, the 1547a- 2020 amendment was added to
Microgrid categories Microgrids can be categorized by whether they are off-grid or grid- connected: Off-grid facility-led is the most common category. Use cases include remote areas not served by the commercial utility grid, like mines, industrial sites, mountain homes, and military bases. Off-grid community-led are also found in remote locations. Use cases include remote villages, islands, and communities. While facility-led microgrids are controlled by a single entity, community-led microgrids must cater to the needs of a group of users. They can require more complex command and control systems.
Figure 2: IEEE 2030.74 requires microgrid controllers to accommodate two steady-state conditions and four types of transitions between those states. (Image source: National Rural Electric Cooperative Association 2 )
accommodate abnormal operating performance.
n T1 , refers to a planned transition from grid connected to steady state island mode. Even when the utility grid is available, there may be economic or operational incentives to switch to island mode. In addition, this mode can support testing of microgrid operation. n T2 , is an unplanned transition from grid connected to steady state island mode. This is analogous to the operation of an uninterruptible power supply in a data center and is often used when the main grid fails. The microgrid seamlessly disconnects and operates as an independent power network. n T3 , refers to steady-state island reconnection to the utility grid. This is a complex technical procedure with a ‘grid-forming’ generator on the microgrid sensing the frequency and phase angle of the grid power
and exactly matching the microgrid with the main grid before reconnecting. n T4 , is a black start into steady- state island mode. In this case, the microgrid has gone down and must be isolated from the utility grid and restarted in island mode. This situation could occur because of an unexpected outage that the microgrid controller cannot
IEEE 2030.74 describes the functions of a microgrid controller in terms of two-steady state (SS) operating modes and four types of
transitions (T) (Figure 2): n SS1 , steady state grid-
connected mode, has the microgrid connected to the utility grid. The controller can use the components in the microgrid to provide services like peak shaving, frequency regulation, reactive power support, and ramp management to the grid. n SS2 , stable island mode, also called “islanding” mode, is when the microgrid is disconnected from the utility grid and operates in isolation. The controller is required to balance the loads and microgrid generation and energy storage services to maintain stable microgrid operation.
handle using a T2 stable transition, or it might be
necessary if the island does not have sufficient generation or energy storage reserve to continue to supply all the loads and must shut down all nonessential loads before bringing the generator online. In addition, any BESS on the microgrid must be at least partially recharged before being reconnected.
IEEE 1547-2018, Standard for Interconnecting Distributed
Resources with Electric Power Systems, details technical requirements for the interconnection and interoperability
Figure 1: Microgrids can include various DERs, CHP, and loads. (Image source: Schneider Electric)
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