Loading on AC supply by full bridge diode rectifier

Thread Starter

Harry Hutchinson

Joined Jan 11, 2018
6
Hi all,
I'm new to the forum. I wondered if anyone could assist me.
I'm looking for information on the loading conditions that a rectifier puts on an AC source, better still if there is a transfer function for the bridge going from the rectified side through to the AC source.
All help gratefully received.
Regards, Harry
 

crutschow

Joined Mar 14, 2008
23,312
If the rectifier has a capacitor filter than the high peak currents from the rectifier generate an RMS current in the AC source that is nearly twice the DC output from the rectifier capacitor.
Thus, for example, transformers need to be derated at least 60% to generate a given DC output current from a rectifier filter.
 

Thread Starter

Harry Hutchinson

Joined Jan 11, 2018
6
If the rectifier has a capacitor filter than the high peak currents from the rectifier generate an RMS current in the AC source that is nearly twice the DC output from the rectifier capacitor.
Thus, for example, transformers need to be derated at least 60% to generate a given DC output current from a rectifier filter.
Hi AlbertHall

Thank you for this. Do you have a reference where I can read more about this?

Regards, Harry
 

AlbertHall

Joined Jun 4, 2014
8,330
Then that is more complicated. It depends on the impedance of the AC supply and on what is connected to the output of the rectifier.
 

Thread Starter

Harry Hutchinson

Joined Jan 11, 2018
6
If the rectifier has a capacitor filter than the high peak currents from the rectifier generate an RMS current in the AC source that is nearly twice the DC output from the rectifier capacitor.
Thus, for example, transformers need to be derated at least 60% to generate a given DC output current from a rectifier filter.

hi Crutschow,

Do you have a reference where I can read more about this?

A PWM current source inverter will be connected to the output of the bridge.

Regards, Harry
 

crutschow

Joined Mar 14, 2008
23,312
Here's a reference for rectifier circuits which gives the derating factors.
The basic problem is that the high peak currents drawn by the rectifier-filter at the peak of the AC waveform generate high I²R loss in the transformer winding (or AC source) resistance.
This causes the (effective) RMS transformer current to be much higher than the rectifier average DC output current (even though the average currents are the same in both).
 
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