3 Internal Active Filter Operation
3.1 General
This section is intended to provide an operational overview
of the filter’s main assemblies and circuitry. With this
information, a repair technician should have a better
understanding of the unit's operation and aid in the
troubleshooting process.
3.2 Description of Operation
3.2.1 Introduction
The AAF consists of an inverter section (active) and an LCL
filter (passive). The inverter section actively compensates
for harmonic distortion on line power to maintain minimal
influence on the supply transformer load. The harmonic
suppression is designed to comply with customer
requirements and local standards. The LCL passive filter
section ensures trouble-free connection of the active
inverter section to line power, along with suppressing the
inverter switching frequency. In the filter section three
capacitors are located between two reactors to form an
LCL circuit. The LCL circuit is arranged in a common mode
(CM) and differential mode (DM) configuration. Connected
in series with the capacitors are three damping resistors to
ensure that the filter prevents resonance. Soft charge
circuitry limits the inrush current during power-up. The
control card along with the active filter control (AFC) card
provide the logic for controlling the active filter.
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130BX432
Figure 3.1 AAF Internal Circuitry
1
Line power option plate
6
Power module
2
HI (Lm) reactor
7
DC capacitors
3
Line power contactor
8
Damping resistors
4
Power card
9
AC capacitor
5
Inverter side reactor (Lc)
Table 3.1
3.2.2 Control Card
The primary logic element of the control card is a
microprocessor which supervises and controls all functions
of filter operation. In addition, separate PROMs contain
programmable parameters to provide the user with
customized control performance. These parameters are
programmed to enable the filter to meet application
requirements and to allow for changing the operational
characteristics of the filter. The programmed instructions
are then stored in an EEPROM which provides security
during power-down.
A custom integrated circuit generates a pulse width
modulation (PWM) waveform which is sent to the interface
circuitry located on the power card.
Another part of the control section is the local control
panel (LCP). This is a removable keypad/display mounted
on the front of the filter. The LCP provides the user
interface with the unit. All the filter's programmable
parameter settings can be uploaded into the EEPROM
located in the LCP. This function is useful for maintaining a
backup parameter set. It can also download programming
to the filter to restore programming to a repaired unit, or
to program multiple units by downloading from a
Internal Active Filter Oper...
VLT Advanced Active Filter AAF006 D and E Frames Service Manual
MG90Z122 - VLT
®
is a registered Danfoss trademark
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