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FORM 160.00-O4
ISSUE DATE: 07/31/2019
This instruction is to be used in conjunction with the
Operation Instructions for YORK Centrifugal chillers
furnished with an optional OptiSpeed™ Compressor
Drive (OSCD).
OPTISPEED/HARMONIC FILTER COMPONENT
OVERVIEW
OptiSpeed Compressor Drive 270, 292, 351,
and 424 Hp (Low HP Model)
The YORK® OptiSpeed Compressor Drive (OSCD) is
a liquid cooled, transistorized, PWM inverter in a high-
ly integrated package. This package is small enough
to mount directly onto the chiller motor, and small
enough to be applied in many retrofit chiller applica-
tions. The power section of the drive is composed of
four major blocks: an AC to DC rectifier section with
an integrated pre-charge circuit, a DC bus filter sec-
tion, a three phase DC to AC inverter section and an
output suppression network.
An electronic circuit breaker with ground fault sens-
ing connects the AC line to an AC line inductor and
then to the DC converter. The line inductor will limit
the amount of fault current so that the electronic circuit
breaker is sufficient for protecting the OSCD. Input
fuses to the OSCD are no longer needed. The follow-
ing description of operation is specific for the 351 Hp
OSCD unless otherwise noted.
The AC to DC converter uses 3 Silicon Controlled
Rectifiers (SCRs) and 3 diodes. One SCR and one di-
ode are contained in each module. Three modules are
required to converter the 3 phase input AC voltage into
DC voltage. The modules are mounted on the bottom
of the liquid cooled heatsink. The use of the SCRs in
the converter permits pre-charge of the DC bus capaci-
tors when the chiller enters the prelube cycle, and it
also provides a fast disconnect from the AC line when
the chiller enters the coastdown cycle. At this time, the
OSCD is turned off, the SCRs in the converter are no
longer turned on and remain in a turned off condition
until the next pre-charge cycle. The DC bus capacitors
will start to discharge through the bleeder resistors.
When the chiller enters the prelube cycle, the OSCD is
commanded to pre-charge and the SCRs are gradually
turned on to slowly charge the DC bus capacitors. This
is called the pre-charge period, which last for 20-sec-
onds. At this time the SCRs are fully turned on. The
SCR Trigger board provides the turn on commands for
JOHNSON CONTROLS
SECTION 1 - GENERAL INFORMATION
the SCRs. The OSCD Logic board provides the com-
mand to the SCR trigger board when to precharge.
Although many of these parts are similar
to the parts used in previous Variable
Speed Drive (VSD) designs, these parts
are only compatible with drives having the
base part numbers included on the cover
of this form. Failure to use the correct
parts may cause major damage to these
and other components in the drive. For
example, the VSD logic board 031-02077-
000 used in this drive is not compatible
with 031-01433-000 logic board used in
previous designs. A new VSD logic board
was designed in 2006. The part number
of the new board is 031-02506-002. The
part number of the new board for the
575 VAC application is 031-02506-003.
The software is not interchangeable be-
tween the 575 VAC version and all other
applications. Also the software is not
interchangeable between the 031-01433,
031-02077, or the 031-02506 boards.
The DC Bus filter section of the drive consists of one
basic component, a series of electrolytic filter capaci-
tors. The capacitors provide a large energy reservoir
for use by the DC to AC inverter section of the OSCD.
The capacitors are contained in the OSCD Power Unit.
"Bleeder" resistors are mounted on the side of the
Power Unit to provide a discharge path for the stored
energy in the capacitors.
The DC to AC inverter section of the OSCD serves
to convert the DC voltage to AC voltage at the proper
magnitude and frequency as commanded by the OSCD
Logic board. The inverter section is actually composed
of one power unit. This power unit contains one very
fast switching transistor module mounted on the same
liquid cooled heatsink as the converter modules, the
DC Bus capacitors, and an OSCD Gate Driver board.
The gate driver board provides the turn on and turn off
commands to the output transistors. The OptiSpeed
Compressor Drive Logic board determines when the
turn on and turn off commands should occur. The gate
driver board is mounted directly on top of the transistor
module, and it is held in place with mounting screws
and soldered to the transistor module.
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