AC Coupling Guide

XW Pro switches to back-up and powers the critical load panel to support the loads.
Thus, the XW Pro forms the grid to keep the PV inverters operating. The XW Pro switch-
over to back-up is almost instantaneous. In some cases, the PV inverter does not detect
the transition and continues to operate without interruption. If the PV inverter detects the
switch over, it will disconnect and then reconnect after re-qualifying the grid formed by
the XW Pro, according to its settings.
Surplus Power in Off-Grid/Backup Modes
The most critical element of AC coupling is the use of the surplus power that the PV
system produces when operating in off-grid or backup mode. The surplus power is the
power that is not used by the loads. For instance, if the PV inverter produces 4 kW and
the load is 1 kW, there is a surplus of 3 kW.
Figure 2Off-Grid/Back-Up Mode and Surplus Power
If there is more power being generated than can be consumed by the loads, the surplus
power will flow to the XW Pro and will be converted to DC power which flows into the
battery. Once the battery approaches full charge, power generation by the PV inverter
must be curtailed to maintain the balance between generation and consumption. As the
battery bank approaches full charge or its charge voltage, charge SOC, or current limits,
XW Pro curtails PV inverter generation by raising the AC output frequency, causing
compatible PV inverters to reduce their power output. This is called Frequency Shift
power curtailment.
NOTICE
RISK OF EQUIPMENT DAMAGE
Follow all instructions related to AC-coupled PV sizing, battery sizing, and charge settings
in the following sections of this document.
Failure to follow these instructions can result in equipment damage.
Introduction XW Pro AC Coupling Solutions Guide
990-6421 This manual is intended for use by qualified personnel 9