York OPTIVIEW Operation Manual page 143

FORM 160.78-O2
ISSUE DATE: 5/22/2017
OPTISPEED COMPRESSOR DRIVE AND
CHILLER OPERATION (490 AND 744 AMP
MODELS)
When the chiller enters a start command, the OSCD
is commanded to pre-charge, the Aux. power devices
are gradually turned on to slowly charge the DC bus
capacitors. This is called the pre-charge period, which
will last for 12-seconds. After the 12-second time peri-
od has expired, the AUX. power devices are gated fully
on. The OSCD logic board provides the turn on, and
turns off commands for the AUX. power devices dur-
ing precharge, and during normal running condition.
After precharge is complete the AUX. power device
will remain turned on for the duration of the run cycle.
During normal chiller run conditions the OptiView
panel provides a speed command to the OSCD. The
speed command must take into account minimum
speed command from the anti-surge control, and the
speed required by the leaving chilled liquid control.
The OSCD logic board will determine the proper turn-
on and turn-off commanded to the IGBT's to provide
the correct RPM.
When the chiller enters a normal stop command the
OSCD will continue to follow the speed command
from the OptiView panel. The OptiView panel begins
to unload the chiller. As the load and pressure across
the compressor starts to go down, the output speed of
the OSCD will go down. When the capacity control
devices (PRV or VGD and sometimes hot gas bypass
valve) reaches minimum load position, the OSCD will
start to decelerate the motor to 50 Hz. When 50 Hz is
reached all rectifier and inverter power devices will be
turned off except for the AUX. The OSCD will remain
in a precharge state for 60 seconds, and then the AUX.
is turned off. The DC link capacitors will start to dis-
charge through the bleeder resistors.
JOHNSON CONTROLS
OPTISPEED COMPRESSOR DRIVE AND
CHILLER OPERATION (0490A AMP MODEL)
When the chiller enters a start command, the OSCD
is commanded to pre-charge, the pre-charge contactor
will close and slowly charge the DC Bus capacitors
through the pre-charge resistors. This is called the
pre-charge period, which will last for 12-seconds. Af-
ter the 12-second time period has expired, the supply
contactor will close and the pre-charge contactor will
open. The supply and pre-charge contactors will re-
main in this state for the duration of the run cycle. The
OSCD logic board provides the commands for the sup-
ply and pre-charge contactors.
All models of HYP drives will control the motor in the
same manner for a normal stop command
SECTION 3 - VSD OPERATION
143
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