JOHNSON CONTROLS
137
SECTION 3 - VSD OPERATION
FORM 160.78-O2
ISSUE DATE: 5/22/2017
3
passed, a small relay will close, and cause the supply
contactor to close. Shortly, after this time the precharge
contactor will open. The drive is now precharged and
ready to run. All of the precharge faults will remain the
same as when the Aux. power device is used to pre-
charge the drive.
The 0490A amp drive contains only one power as-
sembly. It is very similar to the assembly used on the
490 amp drive. The power assembly contains 1 bus ca-
pacitor, with 6 power devices attached to both of the
outer faces of the bus capacitor. A pair of power de-
vices share a gate driver board. A power supply board
mounted on top of the power assembly provides power
to the gate driver boards.
Harmonic Filter Benefits
The OptiSpeed Compressor Drive (OSCD) system is
designed to meet the IEEE Std 519 -1992, “IEEE Rec-
ommended Practices and Requirements for Harmonic
Control in Electrical Power Systems”. 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 custom-
er’s switch gear.
In addition, the input power factor of the OSCD is
nearly unity.
Harmonic Filter General Information
The Harmonic Filter is no longer an option for this
style of OSCD. The function of the Harmonic Filter is
now integrated into the input of the OSCD. The input
rectifier has fast switching transistors instead of SCR’s
and diodes. The OSCD can now control the input cur-
rent waveform to a near sine wave shape by controlling
how the rectifiers are turned on and off. The Harmonic
Filter of the past injected harmonic current into the in-
put of the OSCD to correct the current waveform.
Since the Harmonic Filter is basically the input to
the OSCD there is no need for the additional, pre-
charge, power unit, Harmonic Filter logic board, and
contactors for the harmonic filter of yesterday. The
Harmonic Filter does not require its own pre-charge
time, thus allowing the chiller to start or restart sooner.
This is an important benefit to many customers. The
reductions in parts counts will improve the reliability
of the OSCD, and ease of repair.
A line inductor is still needed to limit the rate of change
in the input current. Without the line inductor the input
current cannot be properly controlled and harmonic
currents would be generated.
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