York VSD 292 Series Operation Manual page 14

SECTION 1 - GENERAL INFORMATION
The OSCD output suppression network is composed
of a series of capacitors and resistors. The job of the
suppressor network is to increase the time it takes for
the output voltage to switch as seen by the motor, and
reduce the peak voltage applied to the motor windings.
This network protects the compressor motor from prob-
lems commonly associated with PWM motor drives.
Other sensors and boards are used to provide safe oper-
ation of the OptiSpeed Compressor Drive. The transis-
tor module and heatsink have thermistors mounted on
them to provide temperature information to the OSCD
logic board. These sensors protect the OSCD from over
temperature conditions. A Bus Voltage Isolator board is
used to ensure that the DC bus capacitors are properly
charged. Three output current transformers protect the
OSCD and motor from over current conditions.
OptiSpeed Compressor Drive 385, 419, 503,
608, 658, 704, 790, 868, 882, 914, 917, 948, and
1055 Hp (High HP Model)
The high HP models' OSCDs function in the same
manner as the low HP models, and have the same ba-
sic components. The power requirements of these high
horsepower drives require more capacitors in the DC
Bus and 3 output transistor sections are needed. One
section is used for each output phase. Each transistor
module within the output transistor section contains
a thermistor, which is connected to the OSCD logic
board. The transistor gate driver board is mounted on
top of the transistor section in the same manner as the
low horsepower model, but it only contains 2 transis-
tor drivers. The modules and gate driver boards are not
interchangeable between the various models.
Harmonic Filter Option
The VSD model of OptiSpeed Compressor Drive
(OSCD) system may also include an optional harmon-
ic filter and high frequency trap designed to meet the
IEEE Std 519, "IEEE Recommended Practices and Re-
quirements for Harmonic Control in Electrical Power
Systems". The harmonic filter is offered as a means
to improve the input current waveform drawn by the
OSCD from the AC line, thus reducing the possibil-
ity of causing electrical interference with other sensi-
tive electronic equipment connected to the same power
source. An additional benefit of the optional harmonic
filter is that it will correct the system power factor to
nearly unity.
14
The power section of the Harmonic Filter is composed
of three major blocks: a pre-charge section, a three
phase inductor and a Filter Power Unit.
The pre-charge section contains pre-charge resistors, a
pre-charge contactor and a supply contactor. The pre-
charge network serves two purposes, to slowly charge
the DC bus capacitors associated with the Filter Power
Unit, and to provide a means of disconnecting the fil-
ter power unit from the AC line. When the chiller is
turned off, both contactors are de-energized and the fil-
ter power unit is disconnected from the AC line. When
the chiller starts to run, the pre-charge resistors are
switched into the circuit via the precharge contactor for
a fixed time period of 5 seconds. This permits the fil-
ter capacitors in the filter power unit to slowly charge.
After the 5-second time period, the supply contactor is
energized and the pre-charge contactor is de-energized,
permitting the filter power unit to completely charge.
Three power fuses connect the filter power compo-
nents to the AC line. Very fast semiconductor power
fuses are utilized to quickly disconnect the transistor
module from the power source if a catastrophic failure
were to occur on the DC bus of the filter power unit.
The three phase inductor provides some impedance for
the filter to "work against". It effectively limits the rate
of change in current at the input to the filter to a reason-
able level.
The Filter Power Unit is the most complicated power
component in the optional filter. Its purpose is to gen-
erate the harmonic currents required by the OSCD's
AC-to-DC converter so that these harmonic currents
are not drawn from the AC line. The Filter Power Unit
is identical to the OSCD's Power Unit in the 351 Hp
drive, except for 2 less capacitors in the filter capacitor
"bank", and a smaller transistor module and modified
gate driver board. The Harmonic Filter Gate Driver
board provides turn on and turn off commands as deter-
mined by the Harmonic Filter Logic board. "Bleeder"
resistors are mounted on the side of the Filter Power
Unit to provide a discharge path for the DC bus capaci-
tors.
Other sensors and boards are used to provide safe op-
eration of the harmonic filter. The transistor module
contains a temperature sensor that provides tempera-
ture information back to the Filter Logic Board. This
sensor protects the filter transistor module from over
temperature conditions. A Bus Isolator board is used to
ensure that the DC bus capacitors are properly charged
and the voltage is balanced. Two output current sensors
FORM 160.00-O4
ISSUE DATE: 07/31/2019
JOHNSON CONTROLS