24-03-2012, 02:29 PM
Hybrid Active Power Filter
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Introduction
Active power filters (APF) have shown to be an effective
technology to eliminate harmonics and to compensate
nonlinear loads [1-3]. The shunt connection has been the
most studied topology, where the APF is connected in
parallel with the load. One of its traditional uses is the
elimination of current harmonics produced by loads which
generates such disturbances, this is HCS loads (Harmonic
Current Source) [4,5]. However, the parallel APF is not
suitable in situations where the load generates voltage
harmonics, HVS loads (Harmonic Voltage Source).
State Model of Hybrid Active Power Filter
Fig. 1 shows a three-phase circuit with a voltage source
that feeds a HCS type nonlinear load and a SAPPF hybrid
filter. The source impedance is constituted by a resistance
RS and an inductance LS. The active power filter is
connected in series with the source through a coupling
transformer. The passive filter is connected in parallel
with the load. It consists of two LC branches tuned to 5th
and 7th current harmonics.
Analysis of Different Compensation Strategies
In this section the state equations corresponding to the
strategies SCD, LVD and CVD are obtained. The different
developments allow the influence of each control strategy
on the system matrix to be analyzed.
A. Control strategy of source current detection
When the control strategy proportional to the source
current harmonics is applied, the voltage generated by the
APF is given by the expression
Conclusions
A system dynamic analysis has been carried out by means
of the state equations. It has allowed the design guidelines
for the APF control to be established.