Operating Modes Management

The main function of EMO-L is to manage the operating modes of the Microgrid, such as:

Connection with the grid.
Transitions between the voltage and frequency reference sources.
Operators interaction with the Microgrid - automatic and manual mode.

EMO-L can manage several islands in parallel, ensuring the interconnection or disconnection between islands are in specific operating conditions.

Transitions Sequence

EMO-L helps to manage the transitions from grid connected mode to islanded mode and vice versa. When moving from the grid connected mode to the island mode, the alternative energy source is started by the EMO-L and will become the voltage and frequency reference instead of the grid itself: either the GENSET or the BESS. In the Microgrid application terms, the reference alternative source is called the anchor source.

NOTE: EMO-L can disconnect a part of the Microgrid (island) if the Microgrid design and configuration allows it.

According to the feature embedded in the anchoring source, the transitions are either:

Open: the transition is achieved going through a stage where there is no voltage present on the island main busbar. This transition is applied when a grid loss event occurs.

On the current version of EMO-L, a predefined automatic sequence with generator or BESS as an anchor source and voltage source switching according to power or energy conditions is provided. Adaptation can be achieved by programming work to follow another source strategy when transition.
Close: no voltage interruption on the island main busbar occurs during the transition. This transition is used for energy sources synchronization or when it changes to the grid connected mode.

Transition from Grid Connected Mode to Islanded Mode

EMO-L enables the manual or forced transition from grid-connected mode to islanded mode.

EMO-L performs the following actions to accomplish this transition:

Action	Description
Topology management Monitor the grid availability	The Microgrid controller monitors and analyzes the grid electrical variables in real time (through a specific relay) to detect when the electrical conditions required to disconnect the Microgrid from the grid.
Automatic switch to island mode	As soon as the Microgrid controller identifies the grid power outage, it switches to islanded mode.
Load Shedding	The Microgrid controller initiates load shedding of a prioritized list of electrical loads. This action will adapt the loads’ current (and inrush currents in case of a blackstart) to power capabilities of the sources chosen to play as the voltage and frequency reference instead of the grid. In islanding sequence, EMO-L initiates the shed to preselected group of load: Shed Essential Load Shed Standard Load
DER management and control CSI to VSI Management	The Microgrid operator selects the alternative voltage and frequency reference energy resource for the island, according to the customer’s priorities. The Microgrid operator starts the alternative source, changing its operating mode if required. During the Grid outage, the switch from CSI to VSI is done based on the capability of the DER.

Transition from Islanded Mode to Grid Connected Mode

EMO-L is designed to provide the Microgrid structure with a stable transition from islanded mode to grid-connected mode by managing and controlling the stability of frequency and voltage and balancing the power generation and loads.

EMO-L enables reconnecting of the Microgrid to the utility grid. The voltage and frequency differences need to be detected and synchronized before reconnecting without disruption of the system power supply.

Action	Description
Topology management	The Microgrid controller manages grid connection and interaction to trigger the transition sequence toward the grid connected mode. Information is composed by grid availability and grid operator authorization to reconnect.
Automatic synchronization to the utility grid	The Microgrid controller manages and controls the re-synchronization to the utility grid. For the DERs, the utility grid becomes the frequency and voltage reference.
Main incomer breaker re-closing	Once the Microgrid frequency and voltage are in the acceptable range for t time, EMO-L initiates the sequence to close the main breaker through a synchro-check relay.
Load restoration	When grid is connected, EMO restores all the loads.

Microgrid Power Regulation in Grid Connected Mode

EMO-L performs the following actions during grid connected mode:

Action	Description
DER management Export management	The Microgrid controller controls and manages the generation sources within the Microgrid depending on the power demand. It also performs control actions to balance the generation and consumption in case of export or import of power to the grid. EMO-L prioritizes the usage of available renewable energy instead of other polluting sources. The Microgrid controller monitors the power exported at the utility point of connection in real time. When exported power exceeds a predefined threshold, the Microgrid controller loads the battery energy storage system if any, curtails the PV production.
Load sharing	Adjust active power (P) by control / command of distributed generation (sources, storage). Adjust reactive power (Q) by control/command of distributed generation (sources, storage).
BESS management	EMO-L monitors the energy SoC (battery state of charge) of the BESS. It manages and control the determined minimum and maximum SoC in order to increase or decrease PV production to avoid damage caused by BESS overcharging. The Microgrid controller manages the charge /discharge of the BESS according to the SoC level and the strategy defined by the energy management layer.

For more information on the regulations performed, see the following chapters:

Microgrid Power Regulation in Islanded Mode

EMO-L is designed to provide the Microgrid with stable conditions in islanded mode by managing and controlling the frequency and voltage and balancing the power generation and loads.

EMO-L performs the following actions during islanded mode:

Action

Description

DER management

Power reserve (spinning reserve)

The Microgrid controller calculates the power balance of all energy sources in real time, taking into account of their operating mode, that is, forming or supporting type (e.g. rotating machine, grid-forming inverters) considering the capacity of the machine and the ongoing produced power.

The operator can configure the reserve ratio of power for the entire Microgrid.

Based on this ratio, EMO-L provides enough P/Q reserve by starting or stopping generators.

DER management

Load sharing

The Microgrid controller ensures Microgrid stability by maintaining the frequency and voltage within a predefined range by managing the active and reactive power production (P/Q) based on real-time measurements.

DER management

Energy source management

The Microgrid controller controls and manages the energy sources within the system according to power demand.

EMO-L manages the DER start or stop sequence priorities and set points based on customer strategies and needs.

EMO-L prioritizes the usage of available renewable energy instead of other polluting sources.

DER management and control

PV curtailment

BESS

Maintains the stability of the Microgrid even when the ratio of PV energy supply is too high.

The Microgrid controller curtails PV production when it detects an excess of the PV production.

EMO-L manages the storage of energy during PV production as well as the use of this stored energy when PV is not producing.

Load management

Load shedding

Load Restoration

The EMO-L sheds loads according to loads priorities when facing an unexpected loss of source.

The Microgrid controller has the ability (once it determines it is appropriated), to reconnect load feeders and re-energized by order of priority based on the loads previously shed. This ability must be initiated by the operator from the graphical user interface.

Fuel Saver - Genset as Anchor Resource

In the following example, EcoStruxure Microgrid Operation (EMO) strives to minimize the fuel consumption of the microgrid and uphold Genset operating at its minimum operating rate power, set by default at 30% of maximum load to avoid wet stacking of the fuel engine.

In Fuel Saver mode, regardless of the anchoring source, the fuel-based generator or BESS, the strategy of the feature is to reduce the fuel consumption and CO₂ emissions. The BESS is optional, saying the strategy considers the presence or not of the BESS. To prioritize the utilization of renewable assets, EMO-L maintains the Genset power at its minimum operating level as much as possible.

The total power demanded by the load(s) is greater than the power produced by the Genset when running at its minimum operating power:

Power produced from the PV is prioritized and maximized to satisfy the remaining demand of the loads. As sun is rising, the PV power slowly increases, causing the Genset power to decrease as the PV supports more of the loads.
If present and BESS SoC allows, the available excess power produced by the PV is used to charge the BESS. Genset is operating at P_{min Genset} (set by default to 30% but customizable from local HMI). PV power is still able to increase while maintaining Genset at this optimum level and using excess power to charge the BESS.
PV is curtailed to keep the Genset running at P_{min Genset} as BESS SoC reaches SoC _max, meaning excess PV power produced can no longer be used to charge the BESS and grid export is not allowed in the present use case (used as example).
PV power is reduced abruptly due to a cloud crossing, forcing the Genset to compensate by increasing its power production above P_{min Genset}.
The cloud has passed, and PV power availability increases abruptly (yellow dash line). EMO-L slowly increases the PV power with PV smoothing function until the Genset power is once again at P_{min Genset}.
Genset power is maintained at P_{min Genset} by curtailing the PV.
This stage is an example of behavior when the PV curtailment is not applied. The PV power increase up to its peak, forcing the genset to run below its minimal power rating. This strategy is applied when there is no BESS or if it is fully charged when present.
Steady state is reached.
Loads are increasing and the extract power is provided by the genset coming back to its minimal power rating.
As loads are still increasing, the excess power demand is then taken by the BESS discharging. If the power provided by the PV and Genset, operating at its minimum power, is insufficient to supply the loads, the BESS is discharged to close the gap, providing its SoC allows this. If still insufficient, the PV and the BESS not able to supply the remaining power, the Genset will operate above its minimum operating power to produce the remaining power required to satisfy the loads.
The loads decrease below the sum of the power of the PV and the genset. The Genset continues to run at its minimal power rating, no curtailment applied and the BESS is charged again. In the case where the power demanded by the loads is below the minimum operating power of the Genset, the PVs will be fully curtailed, and the BESS will be charged to maintain the Genset at minimumBESS operating power. If the BESS SoC is at its maximum and unable to be charged, the Genset power will then run below its minimum operating power.

Fuel Eraser - BESS as Anchor Resource

In the following example, EMO-L strives to not run the Genset as much as we can. This is the operating mode when a BESS with grid forming capability is present in the installation. In islanding event, prioritization is done on the BESS usage, if the BESS SoC allows it. And when the SoC reaches the lower limit, then the Genset is started and the microgrid goes to the fuel saver mode.