Question { GNFC, 27609 }

The advantage of free wheeling diode in a Full Ware
rectifier is
-reduces the harmonics
-Supplies the voltage at negative vlotage

Answer

A Free Wheel Diode (FWD) at the output of a full wave rectifier will:




1) Increase DC voltage for a given firing angle due to the elimination of negative portions of the instantaneous dc waveform in a SCR phase controlled converter,




2) Will reduce the generated ripple voltage on the DC side of a SCR phase controlled converter due to same reason as in above, reducing the filtering requirements.




3) Will improve the input PF in an SCR phase controlled converter due to ending the input current waveform earlier by permitting internal free-wheeling.




However, the above will happen only if (a) the DC side has sufficient inductance either as filter or as part of load, (b) the firing angle is more than 30 deg for 3-phase, only after which the negative portion appears. Note that there will be no benefit in a diode rectifier since the FWD is always reverse-biased.




Also note that use of the FWD prevents operation of the SCR converter in inversion mode.