digital PFC control ?

[Adam Seychell]

It it feasible to implement active power factor correction using a low
cost microcontroller to digitally control the voltage loop ?
I have been reading information on the UC3854 PFC and it seemed that
there are a number of problems with the analog approach of voltage
outer loop control and these could be solved with simple DSP
techniques. Since voltage loop bandwidths are low, the sample rates
can be under 10 kHz. The PFC could be built from a conventional analog
average current mode control boost converter, where the line current
is programmed by the microcontroller/DAC. The micro would sample both
the line voltage and output voltage. If such PFC control were possible
then circuit complexity and cost would be less than the fully analog
technique.

 

[James Meyer]

can be under 10 kHz. The PFC could be built from a conventional analog
average current mode control boost converter, where the line current
is programmed by the microcontroller/DAC. The micro would sample both
the line voltage and output voltage. If such PFC control were possible
then circuit complexity and cost would be less than the fully analog
technique.

Except for the overhead needed for the A-D and D-A conversions.

Jim

 

[Ashish]

Hi!


I am sorry for causing all that misconception about PFC converter
control thru ASICs. The ASICs are just great and my UC3854 based unit
is working just fine.

No! you should not use a microcontroller for PFC control because
1. Even though sampling the DC voltage at 100Hz( synchronized to
zero-crossing of line voltage ) can give you great results. The uP are
pretty slow and you will end up with a large inductor due to low
switching frequency.
2. uP based system are not that easy to design and the whole unit will
be lot costlier that the unit build on ASIC.
3. Since I have a system working I can help you with the design. It
will not be that difficult.

 

[R.Legg]

The micro would sample both

the line voltage and output voltage. If such PFC control were possible
then circuit complexity and cost would be less than the fully analog
technique.

A mico is cheaper than an analog multiplier?

Count the transistors. Estimate the silicon real estate. Recalculate.

http://ece-www.colorado.edu/~pwrelect/pubarch/fast-pfc-apec02.pdf

RL

 

[Spehro Pefhany]

The micro would sample both

A mico is cheaper than an analog multiplier?

Count the transistors. Estimate the silicon real estate. Recalculate.

There's almost no market for analog multipliers, so the price is
astronomical.

* The B-B/TI MPY634 is $15+ in 100's.

* A PIC12F675 with 10-bit ADC is $1.26.

Of course the MPY634 can work at 10MHz. ;-)

Don't know if the old MC1495 is still made, I see a price of about $8
in 100's, but not from a real distributor.

Best regards,
Spehro Pefhany

 

[legg]

There's almost no market for analog multipliers, so the price is
astronomical.

* The B-B/TI MPY634 is $15+ in 100's.

* A PIC12F675 with 10-bit ADC is $1.26.

Of course the MPY634 can work at 10MHz. ;-)

Don't know if the old MC1495 is still made, I see a price of about $8
in 100's, but not from a real distributor.

Best regards,
Spehro Pefhany

How much is the multiplier inside a UC3854?

I don't think we're talking about small-scale integration here. We're
talking at least about an ASIC or PLD.

Then we're talking about package size and minimum pin count for the
same volume of product.

RL

 

[Spehro Pefhany]

How much is the multiplier inside a UC3854?

Good point, the chip is about the same price as the PIC, & there are
also inexpensive and accurate analog multipliers inside some energy
metering ASICs, IIRC.

Best regards,
Spehro Pefhany

 

[Klaus Vestergaard Kragelund]

Hi!


I am sorry for causing all that misconception about PFC converter
control thru ASICs. The ASICs are just great and my UC3854 based unit
is working just fine.

No! you should not use a microcontroller for PFC control because
1. Even though sampling the DC voltage at 100Hz( synchronized to
zero-crossing of line voltage ) can give you great results. The uP are
pretty slow and you will end up with a large inductor due to low
switching frequency.

We did it at my place of work. Saved a lot of circuits. The key is to keep
the inner loop current mode and analog, then there's no problem doing the
multiplying and the other stuff in the micro

Cheers

Klaus