TCI HGA Manual - Manual (Page 16)

16
Product Description
HarmonicGuard Active filter
The HarmonicGuard Active filter is an active harmonic filter designed and developed by TCI to relieve
the power distribution system of the issues associated with harmonic currents that flow within the
power distribution network caused by non-linear loads. The typical configuration can be found in
Figure 3.1.
The topology of the bus-applied (three phase, three wire) HGA consists of major components or
modules:
Component 1 is made up of two current transformers (CTs) installed on phases A and C of the AC bus
that is to be acted upon by the filter. The purpose of the CTs are to supply information to the HGA
regarding the integrity of the composite AC bus current with regard to the distortion (non-sinusoidal
waveform) and displacement power factor relative to the AC bus voltage. These signals will result in
the HGA injecting currents that will return the AC line current to near sinusoidal shape and at unity
power factor. Note that the CTs are located outside the HGA enclosure.
Component 2 is the HGA input circuit breaker (optional). This is provided to protect the HGA for
destructive over current conditions if a malfunction occurs within the HGA circuitry. It also provides a
convenient disconnect means and field wiring point for the installer of the filter equipment.
Components 3 and 4 are the high frequency converter inductors. These inductors provide the proper
inductance to the power converter.
Component 5 is the power electronic converter module. The Power converter module (PCM) is the
heart of the HarmonicGuard Active filter and is what differentiates the HGA from other types of
harmonic mitigation. The PCM provides several highly complex electronic functions controlled by the
on board DSP controller. The PCM continuously senses the AC bus line voltage and currents,
processes the information at “nearly real time” by means of the instructions resident within the DSP
program code, properly controls the six IGBT’s to operate in a safe manner that injects current into the
AC bus grid that ensures the AC bus current is sinusoidal and near unity power factor. Power converter
contains a pre-charge circuit which consists of two SCRS and two pre-charging resistances which
control the inrush current.