JOHNSON CONTROLS
112
FORM 160.84-OM1
ISSUE DATE: 9/21/2017
SECTION 4 - VSD OPERATION
The new Bus capacitor is the core of the power unit.
The new capacitor is made of a material that is much
more robust and has a longer lifetime than Bus capaci-
tors commonly used in the past. Also, this capacitor
contains all of the hardware required to mount all of
the other parts of the power unit.
The Harmonic filter operation is now part of the input
to the OSCD. This feature is no longer an option when
this OSCD is used with the YMC
2
chiller.
New special plastic cooling blocks were designed for
this OSCD. These plastic cooling blocks provide a light
weight solution by replacing heavy copper or alumi-
num cooling blocks, while providing direct liquid cool-
ing for the rectifier and inverter power modules. They
also provide a method for mounting the power module
assemblies to the bus capacitor within the power unit.
The power unit contains all of the items needed for the
output of the OSCD in a highly integrated, but modu-
lar design. On top of the bus capacitor is the laminated
bus structure and the gate driver board on the 0774 and
1278A amp design. The 0490, 0490A and 0612A amp
drives also have the laminated bus structure on top of the
bus capacitor or capacitors, but the gate driver boards
are mounted directly above the power modules. A power
supply board is located on the laminated bus structure on
the 0490, 0490A and 0612A amp power assemblies. The
rectifier and inverter assemblies are attached to each side
of the bus capacitor. The rectifier or inverter assemblies
can be replaced in the field.
Ease of maintenance is provided by using the commu-
nications link between the OptiView™ panel and the
OSCD. The cooling pumps and fans can be turned on
from the OptiView™ panel. This provides for a safer
annual coolant change. The programmed chiller full
load amps is now programmed from the OptiView
panel.
OPTISPEED COMPRESSOR DRIVE DETAILS
(0490 AND 0774 AMP DRIVES)
An electronic circuit breaker or disconnect switch con-
nects the three phase input power to input fuses and
then onto the AC line inductor, and input filter. See
Figure 36 on page 114. Three phase power continues
onto the rectifier power modules to the bus capacitor
to the inverter, then onto the output filter and the com-
pressor motor.
The AC line inductor provides isolation between the 3
phase power source and the input to the drive. The AC
line inductor improves the input current waveform so
that it appears more like a sine wave. The input filter
reduces the effects of the high frequency switching of
the rectifier and provides the inductance for boosting
the bus voltage above the peak of the line voltage.
The higher bus voltage is required for harmonic current
correction at the input of the OSCD, and to provide the
correct output voltage for high speed operation of the
compressor motor.
The AC to DC rectifier uses several power devices.
Each phase has one or more modules arranged in a par-
allel connection depending on the amount of input cur-
rent required. Each rectifier module contains 3 power
devices that are called the Upper, Lower, and Aux. de-
vice. All three devices are required to rectify and boost
the 3 phase input AC voltage into DC voltage in a mod-
ified new three-phase bridge configuration. The use of
the modified new three-phase bridge configuration in
the rectifier permits pre-charge of the DC Bus filter
capacitors when the chiller enters the start mode, and
provides a fast disconnect from the AC line when the
chiller enters the stopped mode. This new bridge con-
figuration also provides the harmonic filtering without
the need of separate power unit, precharge circuit, and
control board. Figure 38 on page 116 and Figure 42
on page 118.
The DC to AC inverter also uses several power devic-
es. Each phase has one or more modules arranged in a
parallel connection depending on the amount of output
current required. Each inverter module contains an Up-
per and Lower device. The Aux. device is not needed
in the inverter.
The permanent magnet motor used on the YMC
2
chiller
requires a near sine wave of voltage. Typically, drives
provide a pulse of voltage at the amplitude of the bus
voltage for a varying period of time. This waveform
is typically known as a square wave. This OSCD con-
tains a direct water cooled output filter.
A new drive logic board was designed to provide all
of the logic required to turn on and turn off all of the
power devices, turn on and off the cooling fans and
pumps, evaluate data from the input and output current
sensors, evaluate data about the input and output volt-
age, and communicated to the OptiView™ panel.
Other sensors and boards are used to convey informa-
tion back to the OSCD Logic board (See Figure 44 on
page 119), and provide safe operation of the OSCD.
Each power module contains a temperature sensor that
provides temperature information back to the OSCD
logic board. Two ambient temperature sensors ensure
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