How Microgrid works

The controller decides on its own, about once per second, which mode the site is in. This page explains the modes and what happens at every transition. The thresholds named here are set in the microgrid settings; the values between brackets are the defaults.

A complete outage in seven steps. Watch who forms the grid: blue for the grid, green for the battery, pink for the generator.

Operating modes

Mode	What it means
On grid	The site is connected to the public grid. The battery follows the grid and runs the normal control strategy.
On grid with generator	On the grid, with the generator supporting the site. Only when generator support with the grid present is allowed.
Grid fault, still coupled	The grid is outside its window, but the site is not yet separated from it.
Islanded	The site is separated from the grid and the battery forms the grid.
Islanded with generator	Island operation, with the generator supporting the battery.
Generator forms the grid	The generator forms the grid; the battery follows and charges.
Grid back, waiting for release	The grid is stable again, the site still runs as an island until the reconnection is released.
Returning to the grid	The reconnection procedure is running.
Switching between modes	A transition between two modes is in progress.
Fault	The microgrid logic stopped in a fault and no longer switches modes on its own. An incident is raised.

On the grid

• The controller watches the grid voltage and frequency. The grid counts as usable inside the grid window (207 to 253 V, 49.5 to 50.5 Hz).
• The battery keeps an island reserve (50 %): on the grid it does not discharge below this state of charge, so energy is ready for an outage. Only holding the grid import limit may use the reserve. The controller tops it up from the grid at any price. Set it to 0 to turn it off.

From the grid to island operation

When the grid leaves its window, the controller opens the grid breaker and switches the battery inverter to grid forming. The site then has its own grid. With the EMS performing the transfer, the switchover costs a short interruption.

In island operation

• Power reserve (10 %): the controller keeps this share of the available power free to absorb a sudden load.
• Load shedding: below the load shedding SOC (30 %), the controller starts shedding loads in the order of the load shedding priorities. Critical loads are never shed.
• PV: by default the PV inverters stay online with a limited setpoint, so they never produce more than the site and the battery can absorb. Alternatively the PV is disconnected from the AC bus. See PV while islanded.

The generator takes over

1. The battery reaches the start threshold

   Below the generator start SOC (20 %), the controller starts the generator. The battery keeps forming the grid while the generator runs up.

2. The generator forms the grid

   Once the generator is ready, it forms the grid and the battery switches to grid following. The generator powers the site and charges the battery. The procedure panel shows what the controller waits for.

3. The battery reaches the stop threshold

   Above the generator stop SOC (90 %), the controller stops the generator again, after its minimum runtime, and the battery takes over.

By default the generator only runs in island operation. With Generator support with the grid present it may also support the site on the grid, for example to shave a peak.

The grid returns

When the grid stays inside its window for the grid stable time (60 s), the site enters Grid back, waiting for release. In manual mode a user releases the reconnection; in automatic mode the controller reconnects after a delay. The procedure is described in Grid reconnection.