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LC filter for a single phase full wave bridge rectifier

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pssd994

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We designed a single phase AC(50Hz) to DC converter with a full wave half controlled SCR-Diode bridge rectifier and LC filter on DC side. The LC filter is mainly to limit output ripple. In addition to attenuate ripple which we calculate at full load; we intend to maintain good voltage regulation from no load to full load.

So we wanted to explore swinging choke option where inductance changes with load current (low current-high inductance; high current-low inductance) so that our system acts as a choke fed filter at no/light load condition & capacitor fed filter at full load thereby maintaining output nearly constant from no load to full load.

But we got to know from the manufacturer that a swinging choke only has a range of inductance change for a given change of current. Our current range from no load to full load is too much of a change and the real inductance will never coincide. Instead, we can add a resistor in series with the choke but will make up the loss.

Please suggest any other method to have good ripple attenuation along with good voltage regulation with a LC filter?
WhatsApp Image 2017-11-25 at 10.45.38 PM.jpeg

I have seen people also doing as below.

WhatsApp Image 2017-11-25 at 10.45.38 PM (1).jpeg
 

Transformer sizing for AC-DC Power converter

While designing a transformer for AC-DC power converter (SCR full wave half controlled thyristor-diode bridge rectifier) with DC output power of 240W @24VDC, we picked up a transformer with rating of 600VA, 230/40VAC to account for output voltage regulation, losses in rectifier & choke of a DC LC filter.

But gradually loading the power converter to 10A drops my output voltage to as low as 21V and even my regulator couldn't help it

Is my transformer not sufficiently rated?

My circuit schematic is as below
WhatsApp Image 2017-11-25 at 10.45.38 PM.jpeg

Transformer name plate details: Rating: 600VA Primary voltage / Current: 230V AC / 2.6A
Secondary voltage / current: 40V AC / 15A Frequency - 1-Phase Insulation class-F
 
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Hi,

What about "switching" fixed inductances?
What about a step down converter?
Nowadays one uses a primary switched SMPS.

Klaus
 

But gradually loading the power converter to 10A drops my output voltage to as low as 21V and even my regulator couldn't help it.
Missing information. How much is the transformer voltage actually dropping in this load case? What's the inductor DC voltage drop?
I would expect that the controlled rectifier can still achieve > 24V@10A load with 100% duty cycle. There may be a problem of suitable phase angle control.

- - - Updated - - -

Referring to the first post, I really don't know what a "swinging choke" is meaned to be. In my view it's a classical controlled rectifier design (stuff that was already aged during my study 30 years ago). By design, the rectifier commutation changes from discontinuous mode at low currents to continuous mode at higher currents. Take it as is.
 

Hi,

With perfect 40V RMS rectifier input, 2 x 0.7V rectifier loss, perfect (no loss) inductance, 100% ON and perfect capacitor I expect:
* at no load:
40V x sqrt(2) - 1.4V = 55.2V (independent of inductance value)

* at full load (continous conducting)
40V x sqrt(2) x 0.6366 - 1.4V 34.6V

If you see less than this, then you will have some loss. Most likely the inductance.
Find out it's DC resistance.

Klaus
 

Re: Transformer sizing for AC-DC Power converter

But gradually loading the power converter to 10A drops my output voltage to as low as 21V and even my regulator couldn't help it

Please tell us more about the inductor. What is the nature of the load? Motor or a lamp?
 

Re: Transformer sizing for AC-DC Power converter

Please tell us more about the inductor. What is the nature of the load? Motor or a lamp?

Inductor is normal DC choke rated at full load. Load is resistive in nature.
 

I am baffled; did you check the suggestions made in #5 by KlausST? LC value should approx correspond to 100Hz- perhaps L is too high and C is too low?
 

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