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putyn

Wed Nov 14 2012, 02:06PM

Registered Member #7927 Joined: Wed Nov 07 2012, 02:38PM
Location:
Posts: 2

hey everyone my name its vlad and im a student from Romania

im trying to build a digital PFC (very low power for didactic purpose) and ive found this pdf on google

and now im trying to find the topic where the pdf was posted because i have some questions and i would like to ask whoever posted it for some help

if someone could help me with finding the topic or maybe pointing me to some other resource (pdf/websites) describing low power pfc, i would greatly appreciate it

Thanks,
Vlad

hboy007

Fri Nov 16 2012, 11:29PM

Registered Member #1667 Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 374

I'm working on a similar project for low powers. I started with repurposing a UCC28019 CCM PFC boost controller but I want it to be done with a ÂµC.

Please keep this thread updated, I'd be glad to see your progress!

Marko

Sat Nov 17 2012, 12:33AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hey guys

I've also been researching this subject lately and've been reading through this article. I like how they used bang-bang control as a simple current regulation technique, and the microcontroller only provides reference voltage for it. If you use an mcu that has a built in DAC like xmega, it turns out even simpler because no PWM filtering is required; resolution and speed are also increased.

However, I've been researching this for high power levels, >10kW, and hence I'm not too satisfied with the variable frequency bang-bang control... I want to have fixed frequency PWM current mode control as the inner regulator, which has some problems of it's own. Ideally I'd implement it all using the microcontroller and it's PWM timer output - so I'd be glad to hear any suggestions regarding that ;)

Cheers,

Marko

putyn

Sat Nov 17 2012, 05:07PM

Registered Member #7927 Joined: Wed Nov 07 2012, 02:38PM
Location:
Posts: 2

hboy007 wrote ...

I'm working on a similar project for low powers. I started with repurposing a UCC28019 CCM PFC boost controller but I want it to be done with a ÂµC.

Please keep this thread updated, I'd be glad to see your progress!

that ic its similar to ir1150, irf has a nice application note describing how to properly design your PFC (application note an-1077 ) but the ir1150 its not manufactured anymore you can only source it from ebay

from a quick look at the datasheet TI also offers information on how to design the pfc also i can find in Romania and i dont have to wait 3-4 weeks for one bought from ebay - ill give it a try and see how it turns up

Marko wrote ...

Hey guys

I've also been researching this subject lately and've been reading through this article. I like how they used bang-bang control as a simple current regulation technique, and the microcontroller only provides reference voltage for it. If you use an mcu that has a built in DAC like xmega, it turns out even simpler because no PWM filtering is required; resolution and speed are also increased.

However, I've been researching this for high power levels, >10kW, and hence I'm not too satisfied with the variable frequency bang-bang control... I want to have fixed frequency PWM current mode control as the inner regulator, which has some problems of it's own. Ideally I'd implement it all using the microcontroller and it's PWM timer output - so I'd be glad to hear any suggestions regarding that ;)

Cheers,

Marko

i think an xmega its a bit of an overkill just to use it for a pfc - in the link i posted suggested that the task could be accomplished by an attiny15 (which its a modest mcu) - since my pfc if for didactic purpose and its low power (max 50W) i dont really care which control method it implements

anyway ill be looking at the UCC28019 ic to see if i can build something around it but if someone has any information about the posted link it would be great

putyn

Patrick

Sat Nov 17 2012, 05:26PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

you guys are going to a lot of trouble for PFC, a PFC IC is the way to go, a MCU has problems with digital and analog signal quality. CMRR and what not...

Marko

Sat Nov 17 2012, 07:50PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hey guys

anyway ill be looking at the UCC28019 ic to see if i can build something around it but if someone has any information about the posted link it would be great

What extra information do you require from this link? It shows the algorithm how to do PFC with a microcontroller. It only expect you to know to some extent how to design PID regulators and stabilie the control loops.. but if they told you that where'd be the didactic benefit :)

I'm not an expert in this field either, but as far as I remember there are two main types of active PFC used today:

1.) "Critical conduction mode" PFC which is actually discontinuous mode converter optimized for maximum inductor usage. Discontinuous operation is naturally pfc because it forces discrete energy packets to the output, making the input appear resistive. Regulator design is simpler in this case, but at disadvantage of having both very high inductor ripple current, requiring ferrite inductor, and high peak currents that result in high switch losses.
For these reasons such converters are usually reserved for low power, <500W or so (if you guys are looking for just 50W, then this may be your converter of choice..)

2.)"Continuous current mode" PFC's always work in continuous mode as the name says. They require some means of enforcing the input current to be sine and the inductor current continuous with little ripple. This is generally done in three steps:

a) There is an inner control loop that regulates the current based on external reference. This may be a PWM current mode regulator, or, like in this article, a simple hysteretic regulator made from a comparator with hysteresis. This regulator is completely independent from the rest of the system apart from receiving the reference signal (which in case of this article is provided by mcu PWM output).

b) The reference signal is received from a multiplier, which multiplies the outer control loop output with the input voltage waveform - this is the critical part where the current is forced to take sine shape.

c) Finally, this is all transparent to the outer control loop which is a classic voltage regulator, in this case implemented on a microcontroller.

I still have to decide how to implement the inner control loop in my case!

Cheers,

Marko

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