OptiSpeed compressor drive details (0490 and 0774 amp
drives)
An electronic circuit breaker or disconnect switch connects the three phase input power to input
fuses and then onto the AC line inductor, and input filter. See Figure 61. Three-phase power
continues onto the rectifier power modules to the bus capacitor to the inverter, then onto the
output filter and the compressor motor.
The AC line inductor provides isolation between the three-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 parallel connection depending on the amount of input current required. Each rectifier module
contains 3 power devices that are called the Upper, Lower, and Aux. device. All three devices are
required to rectify and boost the three-phase input AC voltage into DC voltage in a modified 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 configuration also provides the harmonic filtering without the need of separate
power unit, precharge circuit, and control board. See Figure 63 and Figure 67.
The DC to AC inverter also uses several power devices. 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 Upper 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 contains a direct water
cooled output inductor.
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 voltage, and communicated to
the OptiView panel.
Other sensors and boards are used to convey information back to the OSCD Logic board (see
Figure 69), 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 that the internal temperature of the OSCD does not exceed a safe
operation level. Three Current Transformers monitor the output current from the OSCD power
unit and are used to protect the drive and motor from overcurrent conditions. Another 3 Current
Transformers monitor the input current to the OSCD to provide current limit, ground fault
detection, and information for the harmonic current filtering.
OptiSpeed compressor drive details (0490A, 0612A, 0730A,
and 1278A amp drives)
The 0490A, 0612A, 0730A, and 1278A amp drives have the same basic function as the 0490 and 0774
amp drives, but the precharge of the drive is different.
The precharge is now completed through a precharge and supply contactor, which are control by
the drive logic board. During the precharge period the drive logic board commands the precharge
contactor to close for 12 s. During this time, the voltage increases across the bus capacitors, and
YMC
2
Mod B with OptiView Control Center
130
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