Alpha Technologies XM3-HP Series - Technical Manual - Manual (Page 17)

17 017-882-B0-001 Rev. C2 (10/2013)
1.0
Introduction
1.2.2 Standby Operation
When the incoming AC line voltage drops or rises significantly or a complete power outage occurs,
the control logic’s line monitor activates standby operation. During the transfer from AC line to standby
operation, the battery powered inverter comes online as the isolation relay switches to prevent AC
power from back-feeding to the utility. The following changes also occur within the Power Supply:
• The isolation relay opens to disconnect the AC line from the primary winding of the ferroresonant
transformer.
• The control logic switches the inverter FETs on and off. This switching action converts the DC
battery current into AC current in the inverter windings of the ferroresonant transformer, providing
regulated power to the load.
• The control logic, which includes a microprocessor and other circuits to protect the inverter
FETs from overcurrent damage, monitors the condition of the batteries and the inverter during
standby operation. Since a prolonged AC line outage could severely discharge the batteries,
resulting in permanent damage, the control logic disables the inverter when the batteries drop
to a predetermined cutoff voltage.
• The XM3-HP offers two user-selectable EOD options based on either overall string voltage or
individual battery voltage. See Table 1-1 for battery specific EOD settings. Operation is defined
as follows:
• Battery String Voltage Mode which shuts off the inverter when the 36V bus voltage reaches
Low Battery Cutoff Voltage as seen at the inverter.
• Individual Battery Voltage Mode which shuts off the inverter when any battery in any string
(1-4) reaches Low Battery Cutoff Voltage.
• All units will factory default to Battery String Voltage Mode.
• Individual battery EOD will only be available (user-selectable) if individual battery voltages
are being sensed and present at logic card via the Smart AlphaGuard, DSM3 or other
approved status monitor card with individual battery voltage sensing.
• When set to Battery String Voltage Mode the “Low Battery Cutoff” (EOD) is not user adjustable
from the default. See Table 1-1 for more information.
• When set to individual Battery Voltage Mode the “Low Battery Cutoff” (EOD) will automatically
set to default values based on battery type (see Table 1-1). A secondary option is then
offered to the user for manually programming the “Low Battery Cutoff” (EOD), regardless
of battery type, within the range 1.65 to 1.80 V/C.
1.2 Theory of Operation
1.2.1 AC (Line) Operation
During AC Line operation, utility power is routed into the primary winding of the ferroresonant
transformer through the contacts of the transfer isolation relay. Simultaneously, in the inverter, power
is directed to the rectifier circuitry providing power for the control circuitry. The bidirectional inverter
also serves as a battery charger during line operation. The ferroresonant transformer and an AC
capacitor form the resonant tank circuit, which provides excellent noise and spike attenuation, output
short-circuit current-limiting, and output voltage regulation. The ferroresonant transformer produces
a quasi square wave output which resembles a rounded square wave.
When measuring the output voltage of ferroresonant transformers, use only a true RMS AC voltmeter. Non-
RMS reading meters are calibrated to respond to pure sine waves and do not provide an accurate reading when
measuring quasi square wave output.
NOTE:
1.0 Introduction, continued