How LOMAC works

Definition

LOMAC (Load Operation Mode Advanced Control) is a plant control function that transfers a load bus between grid supply and supply formed by battery converters.

LOMAC:

• operates the grid-side switches (AC Control Switch and AC Control ATS points)
• confirms each switch position from its feedback input
• sets each converter to follow the grid or to form the bus
• runs every transfer as a fixed sequence, and does not start a forming converter until the grid side is confirmed open

A converter that disconnects itself from the grid acts as its own grid switch. A bus fed only by such converters can transfer with no separate switch.

Example Application

Site: grid connection, one battery converter, one contactor between the grid and the load bus.

On grid failure:

1. The converter disconnects by its own anti-islanding. The load bus is dead.
2. LOMAC confirms the grid is absent.
3. LOMAC opens the contactor and confirms it open from its feedback input.
4. LOMAC starts the converter forming the load bus.

On grid return:

1. LOMAC stops the converter.
2. LOMAC closes the contactor and confirms it closed.
3. The converter returns to following the grid.

Profiles

The LOMAC Profile setting on the load connection point sets what LOMAC aims for:

• On-grid priority: the load runs on the grid while the grid is available, and on the battery converters while it is not.
• Off-grid priority: the load runs on the battery converters while a forming level is eligible, and on the grid when none is.
• Disabled (holds position): LOMAC commands nothing and the bus stays where it is. Off grid, this also stops the return at Leave Off-grid Below.

The profile is a rule list, so it can follow a schedule. See Build a rule list.

Forming Levels

Each converter has a Forming Level setting. Converters with the same number switch together as one level. The highest level whose converters are all eligible, and that LOMAC can put on the load, forms the bus.

A converter that is not forming needs a state of charge at or above Enter Off-grid Above to be eligible. A forming converter stays eligible until its state of charge falls to Leave Off-grid Below. It also needs LOMAC Enabled on, Off-grid Permit at Permitted, and a driver that supports LOMAC.

Give two converters the same level only if they are wired to run in parallel. LoggerV does not check the parallel wiring.

A converter with LOMAC support and LOMAC Enabled off blocks off grid for its island. A LOMAC switch that cuts it off removes the block.

Site Protection

LOMAC is not a protection function. The site's interlocked grid switch and each inverter's anti-islanding protect people and the grid.

Location

On the Plant Control System page, open the three-dot menu on the plant control card and choose LOMAC. The Status tab shows the bus state, the target, the forming levels and any warning. The Timeline tab shows each transfer step by step. While a transfer runs, the plant control page shows the dialog LOMAC transfer in progress. Do not change plant settings.

The settings are on a LOMAC tab in each point's settings dialog. Turn on Edit from the Diagram menu, then double-click the point.

Permissions

• Viewer and higher: read the LOMAC dialog and the LOMAC tabs.
• Editor or higher, with the advanced role: change LOMAC settings, and use Reset fault, Evaluate now and Abort transfer.

This guide assumes How plant control works. To configure a site, see Set up and arm LOMAC. LOMAC statuses and settings field definitions defines every status and setting.