03-07-2012, 02:47 PM
Harmonic Current Extraction Technique for Shunt Active Filter
Harmonic Extraction Process.ppt (Size: 2.79 MB / Downloads: 53)
Power Quality Issues in Supply System
Uses of Rectifier, Thyristors , converters and large number of low-power electric based appliance(nonlinear loads) create current and voltage disturbance in the ac mains.
These disturbances appears as:
Voltage drop
Shunt and Series Resonance,
Flicker
The main reason for these distortion : Harmonic current content produced by those non-linear loads and their presence in the supply side are the main re
Introduction to Active Filter
To reduce the harmonic current content in the ac mains various types of methods has been proposed like shunt and Series Active filters,shunt and series passive filters etc.
Study shows that use of active filter results in better performance for the mentioned purpose.
Active filters(AF) can compensate not only harmonis but also asymmetric currents.
There are many types of active filters .One type of Shunt Active filter that relies on three leg voltage source converter(VSC) will be discussed in the following.
Instantaneous Active and Reactive Current Component Method
In this method the harmonic currents are obtained from the instanteneous active and reactive current components ild and ilq of the nonlinear load.
First the stationary reference currents(ilα & ilβ ) are calculated from the line currents ili by the following equations:
Correlation Function Technique
Apparent power is divided into two orthogonal components:
Real power
Fictitious power
Reactive power
Deactive power
Auto correlation is done to calculate the RMS of current and voltage
Cross correlation is done calculate active power
This technique is good for reactive and distortion compensation
THD value comparison with other techniques:
P-Q: 5.5%
SRF: 1%
Correlation function :4.5%