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When we want to correction power factor of a motor(inductive load) its simply can done by adding an capacitor in parallel with the motor but its not possible to correction power factor of an capacitive load such as LED lamp by adding an coil in series and have to use a special circuit to do that, why?

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ Hint: For the inductive load if you don't add a parallel capacitor to correct power factor what does the current look like? Now for an LED load what does the current look like? \$\endgroup\$ – Warren Hill Mar 15 '17 at 21:31
  • \$\begingroup\$ leading & lagging \$\endgroup\$ – M.A.K Mar 15 '17 at 21:33
  • \$\begingroup\$ If it were just a case of leading and lagging then you could use a parallel L or C to correct power factor but LEDs and CFLs don't draw a sinusoidal current. At least not the ones I have seen. \$\endgroup\$ – Warren Hill Mar 15 '17 at 21:38
  • \$\begingroup\$ A series reactance will reduce the voltage across the load. \$\endgroup\$ – Chu Mar 15 '17 at 22:32
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An LED lamp is a non-linear load not a capacitive load. Non-linear loads cause current waveform distortion. The distortion has the effect of adding harmonic currents to the load current. Harmonic currents do not transmit power, so they have the same effect as reducing the power factor. However harmonic currents can not be compensated using conventional power factor correction techniques. Harmonic filters are required.

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The smaller voltage ripple cap current translates into larger peak/avg pulse which contains harmonics and inherent poor power factor.

enter image description here

The peak current appears to be in phase with peak voltage but not continuous making it not correctable with a passive compensation. Active PFC is used in new power supplies >100W to meet new stds.

There are many variations of offline LED lamps which induce Switched currents unless with high active PFC circuit. enter image description here

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