AAON RQ SERIES, Manual

Page: 8 / 36

8
Introduction
This document provides instructions on how
the variable speed scroll compressor and
inverter drive are applied to a variable speed
compressor in a safe and reliable manner.
The variable speed scroll compressor will be
referred to throughout this document as the
“variable speed compressor” or the
“compressor”.
The inverter drive will be
referred to throughout this document as the
“ inverter drive ” or simply the “ drive ” .
Variable Speed Scroll Compressors
Product Description
The variable speed compressor has a speed
range of 900 (refer to operating envelope for
low speed operation) to 5000 revolutions per
minute and is intended for use in
commercial air conditioning, chiller, and
heat pump applications. The variable speed
scrolls utilize three-phase brushless
permanent magnet (BPM) motors. The
compressors have been qualified for use
with drives which have been developed and
qualified for BPM motor-compressors.
Compressor Motor
The brushless permanent magnet (BPM)
motor in the variable speed scroll consists of
a three-phase stator and a rotor embedded
with high energy permanent magnets. The
input voltage is a series of pulses of varying
frequency at 120 degree intervals between
phases.
Oil Pump
The variable speed scroll is equipped with
an oil pump to ensure an adequate supply of
oil to the bearing system throughout the
operating speed range of 900 to 5000 RPM.
Compressor Temperature Protection
A discharge line thermistor must be used to
protect the compressor. The drive will shut
down the compressor when the thermistor
temperature exceeds 275°F (135°C).
Oil Recovery
An oil recovery cycle is required if
compressor speed is below 1,800 rpm for 2
hours. When this occurs, the unit controls
will increase the compressor speed to 3,600
rpm for five minutes.
Motor Protection
The drive includes motor protection features
for the compressor. The drive sets the
maximum current limit, low voltage fold
back which allows the compressor to ride
through low voltage situations, which helps
keep the compressor running to avoid
nuisance trips.
Starting and Stopping Routine
The drive controls the starting and stopping
routine of the variable speed scroll. This
routine allows soft starting and controlled
stopping, an advantage over traditional on-
off control of fixed capacity units. Please
refer to Table 4 for an exact explanation of
the starting and stopping process.
The variable speed scroll compressor
incorporates a fluid brake design to help
mitigate reverse rotation during shutdown. A
momentary reverse rotation sound may be
heard.