Service manual

The control card logic
•
communicates via serial link with outside devices
such as personal computers or Programmable
Logic Controllers (PLC).
•
provides two voltage supplies for use from the
control terminals.
24 V DC is used for switching functions such as start, stop,
and forward/reverse. The 24 V DC supply also supplies 200
mA of power, which can partly be used to power external
encoders or other devices. A 10 V DC supply rated at 17
mA is also available for use with speed reference circuitry.
The analog and digital output signals are powered through
an internal frequency converter supply. The three power
supplies are isolated from one another to eliminate ground
loop conditions in the control input circuitry.
Two relays for monitoring the status of the frequency
converter are located on the power card. These relays are
programmable through parameter group 5-4
*
Relays. The
relays are Form C. These relays have one normally open
contact, and one normally closed contact on a single
throw. The contacts of the relay are rated for a maximum
load of 240 V AC at 2 Amps resistance.
The logic circuitry on the control card allows for adding:
•
option modules for synchronizing control
•
serial communications
•
additional relays
•
cascade pump controller
•
custom operating software
3.2.2
Logic to Power Interface
The logic to power interface isolates the high voltage
components of the power section from the low voltage
signals of the logic section. The interface consists of two
sections.
•
Power Card
•
Gate Driver
The control card handles much of the fault processing for
output short circuit and ground fault conditions. The
power card provides conditioning of these signals. Scaling
of current feedback and voltage feedback is accomplished
on the interface sections before processing by the control
card.
The power card contains a Switch Mode Power Supply
(SMPS). The SMPS provides the unit with 24 V DC, 16 V DC,
7 V DC, 6 V DC, and 3.3 V DC operating voltage. SMPS
powers the logic and interface circuitry. SMPS is supplied
by the DC bus voltage. The secondary SMPS provides
power to the logic circuitry with main input disconnected.
It can keep units with communication options live on a
network when the frequency converter is not powered
from the mains.
Circuitry for controlling speed of the cooling fans is also
provided on the power card.
3.2.3 Power Section
The DC coil is a single unit with two coils wound on a
common core. One coil resides in the positive side of the
DC bus and the other in the negative. The coil aids in the
reduction of mains harmonics.
The DC bus capacitors are arranged into a capacitor bank
along with bleeder and balancing circuitry.
The inverter section is made up of six IGBTs, commonly
referred to as switches. One switch is necessary for each
half phase of the three-phase power, for a total of six. The
six IGBTs are contained in three dual modules.
A Hall effect type current sensor is located on each phase
of the output to measure motor current.
Rectier
(SCR/Diodes)
Intermediate
circuit
Inverter
section (IGBTs)
130BC330.10
L1
L2
L3
T1
T2
T3
Illustration 3.2 Typical Power Section
3.3 Sequence of Operation
3.3.1 Rectifier Section
Depending on size of the frequency converters, the
rectifier section is built on either six or three diodes and
three thyristors.
Inrush current in units with a normal 6-diode rectifier is
limited with a simple PTC and relay circuit.
Phase controlling the thyristors (active inrush control)
limits the inrush current in units with diodes and thyristors.
Internal Frequency Converte...
VLT
®
HVAC Basic Drive Service Manual
24 MG90X202 - VLT
®
is a registered Danfoss trademark
3
3