Sunday, January 13, 2019

Interleaved Power Factor Correction


Power Factor we can define as the ratio between the useful (true) power (kW) to the total (apparent) power (kVA) consumed by a circuit. It is a measurement of how proficiently electrical power is converted into useful power which can be further use for output load.

More on Power Factor you can find in my previous article at below link;
"What is Power Factor and Why is it important?"

There are many methods for Power Factor Correction and Interleaved Power Factor Correction is one of them. Other Power Factor Correction methods you can find in my previous article at below link;
"Types of Power Factor Correction"


What is Interleaved Power Factor Correction?

A usual single-stage PFC controller design on a large inductor and requires extensive filtering to reduce high-frequency ripple. An alternative topology replaces the single PFC boost converter with a two interleaved converters each operating 180° out of phase.

This interleaved method very much reduces the high-frequency ripple of the input current and as well as the current into the output capacitor of the PFC pre-regulator. The arrangement of reduced ripple and lower average current in each phase allows use of a smaller inductor size and input – output capacitor as compare to single-phase design. Component size is one of the main reasons for implementing an Interleave PFC design.

Below figure shows,”Interleaved Transition Mode PFC using UCC28063”;

Interleaved Transition Mode PFC
Interleaved Transition Mode PFC using UCC28063
As we can see in the figure an interleaved PFC consists of a two boost converter sharing the same load capacitor. As we can see in the figure, if we have the same inductance for each boost converter, we can see that the energy stored by this PFC system is doubled.  An output power capability of this PFC system is determined by energy stored in the inductor. By an Interleaved PFC with much smaller inductor having lower inductance values for a given power rating, the output power can be generate same like single stage PFC.
     
Interleaved PFC arrangement consists of;
·     Two inductors; which is used for energy storage.
·      Load balancing controller; which is used to make sure energy should be distributed equally i.e. the load balancing controller balances the variation in inductance values or feedback circuits.
·       Feed-Forward controller; which control sudden input voltage changes.
·      Voltage error controller; the dc output voltage and corresponding reference are applied to this controller to avoid the load variations so that output voltage should not vary.
·      Current error controller; which controls phase and shape of the input current which is the sum of both the inductor current. The output of this controller is PWM which is used to drive MOSFETS.
·       Load balance loop; which controls current through both the inductor. It generate corrected PWM term, which is subtracted from first PWM to get the final duty cycle of the first boost converter, and it is added to second PWM to find out the balanced duty cycle of the second boost converter.
·      PI controller; which controls unbalanced current flowing through two inductors by regulating this error and by adjusting the MOSFETs duty cycles.

Interleaving power converters can lower conduction losses and improves the overall system efficiency.


Conclusion

Two double energy storing capacity of PFC system, "Interleaved Power Factor Correction" is the best method. Also, for high energy application by this method we can reduce the size of Inductor and capacitor.

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