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 Electronic Theory and Principle Discussion of electrical theory, law, etc.

#1
03-13-2018
 ashiekh 20W User Join Date: Oct 2017 Location: Grand Junction, CO Posts: 1,431 Thanks: 53 Thanked 102 Times in 93 Posts
PFC thoughts

What current profile gives the best Power Correction Factor (the least losses)?

A sine wave in-sync with the voltage?

Last edited by ashiekh; 03-13-2018 at 06:38 PM.
#2
03-14-2018
 ridgid13579 Jun Fu capacitor advocate Join Date: Jan 2016 Location: Canada Posts: 780 Thanks: 26 Thanked 132 Times in 87 Posts

Quote:
 Originally Posted by ashiekh What current profile gives the best Power Correction Factor (the least losses)? A sine wave in-sync with the voltage?
Yes, when the current is in phase with the voltage, you will have a power factor of 1, which is the most ideal.

A resistive load (say a good old wire heater) should have a power factor of 1.
#3
03-14-2018
 ashiekh 20W User Join Date: Oct 2017 Location: Grand Junction, CO Posts: 1,431 Thanks: 53 Thanked 102 Times in 93 Posts

I tried a few current shapes, and so far none have beat the sine wave for losses. I even think I now have a proof of why the current needs to follow the voltage (for minimum losses), that works for all voltage shapes (not just sinusoidal); using ideas from functional analysis.

A strange exception to a resistive load being ideal:
Imagine a bulb whose filament resistance increases with temperature, it is pure resistive, but has higher resistance at high voltages, and so will have a non-sinusoidal current curve and so higher cable loses than an equal load with constant resistance.

Interestingly, the larger the primary capacitors, the worse the power factor issue (assuming no correction), due to reduced conduction angle; by the same reasoning the smaller the load the worse the power factor issue.
Attached Images
 conduction_angle[1].gif (6.0 KB, 5 views)

Last edited by ashiekh; 03-14-2018 at 08:05 PM.
#4
07-11-2018
 gdjacobs micro ATX User Join Date: Jul 2018 Location: Manitoba, Canada Posts: 10 Thanks: 0 Thanked 1 Time in 1 Post

Well, P = I dot V. If the objective is to minimize I while P and V are constant, obviously the phase between any components should be zero. Also, any harmonics from a non sinusoidal current waveform will be orthogonal to a sinusoidal voltage waveform and will have no contribution to the overall power output and be waste as well.

P = sum ( I_i V_j )
= sum ( |I_i| |V_j| int sin w_i t sin w_j t dt )
= |I_i||V_i| int sin w_i t sin w_i t dt
#5
07-11-2018
 ashiekh 20W User Join Date: Oct 2017 Location: Grand Junction, CO Posts: 1,431 Thanks: 53 Thanked 102 Times in 93 Posts

Nicely argued

Last edited by ashiekh; 07-11-2018 at 08:20 PM.

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