frequency switching of the rectifier. The load inductor 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 drive, 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 power modules arranged in a
parallel connection, the number of modules depends on the amount of input current required for
the application. Each rectifier module contains two power devices that are called the Upper and
Lower device. These devices are required to rectify and boost the three-phase input AC voltage into
DC voltage in a three-phase bridge configuration. This new bridge configuration also provides the
harmonic filtering without the need of separate power unit, precharge circuit, and an additional
control board. See Figure 50.
The precharge of the drive is completed through a precharge and supply contactor, which are
controlled by the drive logic board. During the precharge period, the drive logic board commands
the precharge contactor to close for 12 seconds. During this time, the voltage increases across the
bus capacitors, and the current is limited by the precharge resistors. This 12 second period is called
the precharge time. After 12 seconds, a small relay closes, and causes the supply contactor to close.
Shortly after, the precharge contactor opens. The drive is now precharged and ready to run.
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 by the
application. Each inverter module contains an upper and lower device.
The permanent magnet motor used on the YVAM 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 output waveform typically looks like a square wave with varying widths to the pulse.
This type of wave form is a pulse width modulation (PWM). This drive contains a direct water-
cooled output inductor along with an output capacitor assembly to filter the voltage waveform
presented to the motor terminals. This filter reduces motor heating and improves the efficiency of
the compressor motor.
A new drive logic board was designed to provide the logic required to turn on and turn off the
rectifier and inverter 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 Control Center.
Other sensors and boards are used to convey information back to the drive logic board and provide
safe operation of the drive. See Figure 51. Each power module contains a temperature sensor that
provides temperature information back to the drive logic board. Two ambient temperature sensors
ensure that the internal temperature of the drive does not exceed a safe operation level. Three
current sensors monitor the output current from the drive power unit and this information is used
to protect the drive and motor from overcurrent conditions. Another three current sensors monitor
the input current to the drive to provide current limit, ground fault detection, and information for
the harmonic current filtering.
Harmonic filter benefits
The HYP model drive system now includes an input harmonic current filter and high frequency filter
trap designed to help buildings meet the IEEE Std 519 IEEE Recommended Practices and Requirements
for Harmonic Control in Electrical Power Systems. The harmonic filter provides a means to improve
the input current waveform drawn by the drive from the AC line. This reduces the possibility of
causing electrical interference with other sensitive electronic equipment connected to the same
power source, and reduces power loss in the customer’s switch gear and source transformer.
In addition, the power factor of the system with this harmonic filter corrects the drive’s input power
factor to nearly unity over the full load range of the product. Some passive filters may over correct
the power factor at lighter loads. Over-correcting the power factor can cause voltage ringing that
can affect or damage other equipment.
YVAM with OptiView Control Center130
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