Since my job is related to led drivers and ballasts i get confused with some questions. I see that the capacitor that is placed after diode bridges decreases the power factor and when we remove it we can achieve a higher pf. So i think that our power factor is a leading pf.
How do you compensate leading power factor?
Also, why we know most of the loads as inductance loads?
and why do we just have capacitor banks, not inductors bank?
Best Answer
The capacitor in a power supply following the bridge rectifier is not causing a phase shift in the current. Instead, it is contributing to harmonic distortion of the current waveform, which is a different method of creating a poor power factor.
When you remove the capacitor, the conduction through the rectifier is more continuous. When you add the capacitor, the conduction now occurs only in short pulses at the peak of the voltage waveform.
Putting an inductor in parallel with such a load would solve nothing — you would now have a lagging current component PLUS a harmonic distortion component.
However, putting an inductor in series with such a load can have benefits. It will filter out the higher-frequency components of the harmonic distortion by forcing the rectifier diodes to switch on and off more slowly. Note that it will still cause a lag in the current relative to the voltage, but you can probably find a "sweet spot" value for the inductance that balances the two effects to create the best overall power factor.