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Using AC Coupling
5.0 Using the MS-PAE Series in an AC Coupled Application
This section covers the use of MS-PAE Series inverter/chargers in an AC coupled system.
5.1 What is an AC Coupled System
Many homeowners utilize renewable energy (e.g., PV, wind, etc.) by installing high ef fi ciency,
battery-less, grid-tie inverter systems to offset their power consumption from the utility grid.
However, during a utility power outage, the grid-tie inverter normally stops operating. This can
cause considerable frustration as the homeowner realizes that the critical loads in the home (e.g.,
refrigerator, lights, water pump, etc.) are no longer powered, and all the energy produced by the
renewable energy source is being wasted while the utility power is out.
In an AC coupled system, since all the energy sources and loads are connected directly to the
AC side, an option would be to install a bi-directional battery-based inverter, such as the MS-PAE
Series. The MS-PAE Series would allow the existing battery-less, grid-tie inverter to continue
operating during a power outage; thereby, continuing to utilize the renewable energy to power
the home’s critical loads—all from the AC side. However, in an AC coupled system—during a utility
power outage—the utility grid is not available to export any excess power that is generated. This
means there may be more power produced than the critical loads can consume, causing this
excess current to be pushed back through the output of the inverter into the battery bank. Since
this is not the normal path for the inverter to control incoming current, it is unable to regulate the
battery voltage, providing the possibility that the battery voltage will rise and cause damage to
your batteries. However, the MS-PAE Series inverter includes a “frequency shift” feature that can
be used to regulate the battery voltage by changing its output frequency.
5.2 Frequency Shift Feature
The frequency shift feature—when enabled—causes the output frequency of the MS-PAE Series
inverter ( ≥ Version 6.0) to change based on the inverter’s battery voltage. If the battery voltage
begins rising, the output frequency starts decreasing; as the battery voltage returns to its correct
voltage level, the frequency increases.
In an AC coupled system, the MS-PAE Series inverter is optimized to work with Magnum Energy’s
MicroGT500
1
grid-tie inverter to regulate the battery voltage. During a utility power interruption, if
the battery voltage begins to rise above the custom-absorb voltage level, the output frequency of
the MS-PAE Series will start shifting down. The MicroGT500 grid-tie inverter responds by decreasing
its output current to avoid overcharging the battery. As the battery voltage falls, the MS-PAE Series
frequency starts shifting back up allowing the MicroGT500 inverter to gradually provide more
current so that the battery can return to its custom-absorb voltage level. The response time and
whether the frequency continues to shift down or start shifting back up depends on how fast the
battery voltage rises or returns to the custom-absorb voltage level.
Note
1
: If you are using a grid-tie inverter other than the MicroGT500, you may need to use an additional
primary battery management system to ensure the batteries are not overcharged. This may require
you to install a diversion controller and a load capable of absorbing the majority of the expected surplus
energy. Options include: 1) a DC diversion controller and DC resistance loads; 2) AC diversion using AC
resistance loads driven by DC controlled relays; or, 3) Sensata’s AC Load Diversion controller (ACLD-40).
5.3 Con fi guring a Remote to work in an AC Coupled System
A remote control (ME-RTR, ME-ARC, or ME-RC) is required and must be con fi gured in order for
the MS-PAE inverter to work optimally in an AC coupled system—as described below:
1. Enable Frequency Shift: Under the SETUP button, set the
Battery Type menu setting to “Custom”.
2. Turn off Search mode: Adjust the SETUP button’s Search Watts menu setting to “OFF”.
3. Turn off Parallel Threshold (ME-RTR only): Adjust the SETUP button’s Inverter Threshold to
Start Parallel menu setting to “OFF”.
4. Ensure the MS-PAE is set to automatically accept grid power when available (ME-ARC and ME-
RTR only): Adjust the CTRL button’s AC In Control menu setting to “Auto Connect”.