VYPER
™
VARIABLE SPEED DRIVE
INSTALLATION
100.200-IOM (SEP 13)
Page 17
damage the Vyper
™
and may also cause hazardous working
conditions for service and operating personnel.
INTERFERENCE WITH ELECTRONIC EQUIPMENT
RFI / EMI are acronyms for Radio Frequency Interference and
Electro Magnetic Interference. Any electronic device which
switches currents at high speed is capable of generating RFI
and EMI. Some typical sources are computers, light dimmers,
and motor speed controls.
RFI refers to electrical fields, which
are transmitted through the air. EMI refers to electrical cur-
rents, which are conducted in wiring connected to the device.
The Vyper
™
generates both RFI and EMI. Most RFI energy
generated by Vyper
™
is contained within it’s cabinet. The EMI
energy is conducted back in to the power line, and may be
capable of causing interference to other electronic equipment
that is powered by the same electrical distribution system.
VSDs are used successfully in many installations, which utilize
sensitive electronic equipment. However, in some highly
sensitive cases, there may be electronic equipment that is
affected by Vyper
™
originated EMI. For those cases, an op-
tional Harmonic Filter is recommended to reduce conducted
EMI levels by reducing current harmonics to limits defined by
the IEEE 519-1992 standard. The filter is located within the
Vyper
™
cabinet and is factory installed and tested. The filter
can also be retrofitted to an existing Vyper
™
.
The IEEE 519 filter is required on all hospital applications, and
is strongly recommended for any installation with sensitive
electronic equipment connected to the electrical distribution
system. The filter is also required whenever a local utility
places a limit on current distortion for an electronic device.
The IEEE 519 harmonic filter is filter is required where total
harmonic current distortion must be 8% or less.
SYSTEM OPERATING CONDITIONS
Refrigeration systems considered for Vyper
™
application
must be in good operating condition. A site survey should be
completed with the help of a trained Frick service technician.
The technician will review the condition of the equipment
and recommend actions that must be taken to ensure that
the equipment is in good operating condition. This survey
must be taken and required repairs made prior to the ap-
plication of the Vyper
™
.
PNEUMATIC CONTROLS
Pneumatic controls must be replaced with electronic controls
to be compatible with the Vyper
™
and the Quantum LX
™
control panel.
VYPER
™
SYSTEM OVERVIEW
The Frick Vyper
™
Variable Speed Drive is a liquid-cooled,
transistorized, PWM inverter in a highly integrated package.
This unit is factory designed to mount either remotely on a
stand or integrally to the compressor package. The power
section of the drive is composed of four major blocks:
• AC to DC rectifier section with integrated
precharge circuit
• DC link filter section
• Three-phase DC to AC inverter section
• Output suppression network
An electronic circuit breaker with ground fault sensing
connects the AC line to an AC line choke and then to the
DC converter. The line choke will limit the amount of fault
current so that the electronic circuit breaker is sufficient for
protecting the Vyper
™
input fuses. (See schematic, Figure 12)
THE AC TO DC SEMI-CONVERTER
uses 3 Silicon Controlled
Rectifiers (SCRs) and 3
diodes. One SCR and one diode are
contained in each module. Three modules are required to
covert the three-phase input AC voltage to DC voltage
(1SCR-3SCR). The modules are mounted on a liquid-cooled
heatsink. The use of the SCRs in the semiconverter con-
figuration permits precharge of the DC filter link capacitors
when the chiller enters the prelube cycle. It also provides fast
disconnect from the AC line. The SCR trigger board provides
the turn on and turn off commands for the SCRs. The Vyper
™
logic board provides commands to the SCR trigger board
during precharge.
THE DC LINK FILTER SECTION
of the drive consists of a
series of
electrolytic filter capacitors (C1-C6). These ca
-
pacitors provide a large energy reservoir for use by the DC
to AC inverter section of the Vyper
™
. The capacitors are
contained in the Vyper
™
Power Unit. “Bleeder” resistors
(RES1 and RES2) are mounted on the side of the Power Unit
to provide a discharge of the DC Link filter capacitors after
power is removed.
THE DC TO AC INVERTER SECTION
of Vyper
™
serves to
convert the DC voltage back to AC voltage at the proper
magnitude and frequency as commanded by the Logic board.
The inverter section is composed of one power unit. This
power unit is composed of very fast switching transistors
known as an Insulated Gate Bipolar Transistor (IGBT) module
(1MOD) mounted on the same liquid-cooled heatsink as the
semiconverter modules, the DC Link filter capacitors (C1-C6),
a semiconverter, and a Vyper
™
Gate Driver board. This board
provides the turn on, and turn off commands to the IGBT’s
output transistors. The Vyper
™
Compressor Drive Logic board
determines when the turn on, and turn off commands should
occur. The gate driver board is mounted directly on top of the
IGBT module, and it is held in place with mounting screws and
soldered to the module. This improves reliability by eliminating
the gate wires and their possible failure. In order to minimize
the parasitic inductance between the IGBT module and the
capacitor bank, copper plates which electrically connect the
capacitors to one another and the IGBT modules are connected
together using a “laminated bus” structure. This “laminated
bus” structure forms a parasitic capacitor which acts as a low
valued capacitor, effectively canceling the parasitic conduc-
tance of the copper plates. To further cancel parasitic induc-
tances, a series of small film capacitors (C7-C9) are connected
between the positive and negative plates at the IGBT module.
THE VYPER
™
OUTPUT SUPPRESSION NETWORK
is com-
posed of a series of capacitors (C10-C12) and resistors (3RES-
8RES). The job of the suppressor network is to reduce the
time it takes for the output voltage to switch as seen by the
motor. It also limits the peak voltage applied to the motor
windings, as well as the rate of change of motor voltage.
These are problems commonly associated with PWM motor
drives such as stator winding end turn failures and electrical
fluting of motor bearings.
Other sensors and boards are used to convey information
back to the Vyper
™
and provide safe operation of the variable
speed drive. The IGBT transistor module contains a thermis-
tor temperature sensor that provides temperature informa-
tion back to the logic board via the gate driver board. The AC
to DC semiconverter heat sink temperature is also monitored
using a thermistor temperature sensor (RT2). The uses the
three resistors on the board to provide a safe impedance
between the DC link filter capacitors located on the power