1.1
Theory of Operation, continued
Fig. 1-2, Simplified Block Diagram
1.1.2 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 XM2-300HP:
The isolation relay opens to disconnect the AC line from the primary winding of
•
the transformer.
The control logic drives the inverter FETs on and off at line frequency. This
•
switching action converts the DC battery current into AC current in the inverter
windings of the 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 battery
and the inverter during standby operation. Since a prolonged AC line outage
would severely discharge the battery, resulting in permanent damage, the control
logic disables the inverter when the battery drops to approximately 10.5Vdc.
When acceptable AC line voltage returns, the power supply returns to AC line
operation after a 20 to 40 second lag. This delay lets the AC line voltage and
frequency stabilize before the control logic phase-locks the inverter’s output to the
utility input. The control logic then de-energizes the isolation relay, reconnects the AC
line to the primary of the transformer and disables (turns off) the inverter. This results
in a smooth, in-phase transfer back to utility power without interruption of service
to the load. The battery charging circuit then activates to recharge the battery in
preparation for the next power outage.
OUTPUT 1
OUTPUT 2
LRI
TRANSFORMER
INVERTER
BATTERY
INVERTER MODULE ASSEMBLY
POWER DISTRIBUTION BOARD
COAXIAL NETWORK
STATUS MONITORING
CONNECTION
OPTIONAL
COMMUNICATIONS
CARD AND
TRANSPONDER
OUTPUT
VOLTAGE TAP
SELECTOR
SERVICE
POWER INSERTER
(ALPHA SPI)
OPTIONAL SURGE PROTECTOR
REPLACEABLE PRIMARY POWER SUPPLY
OVERVOLTAGE PROTECTION
AC LINE DETECTION
AND CONTROL LOGIC
CIRCUITS
DUAL REMOTE
TEMPERATURE
SENSOR
SURGE PROTECTION
LRI CONTROL CIRCUIT
OUTPUT
CIRCUIT
BREAKER
14
017-877-B1-001 Rev. A
