1kVA UPS Block Diagram

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Just for clarifying myself -
1. How 390V dc will be obtained after PFC stage? As maximum input voltage is 264V AC (RMS), voltage after PFC stage should not cross 238v DC. I'm I right?
2. If it is 238V DC, how Buck converter will give output as 311v DC?
 


According to PFC handbook from On semiconductor, output voltage must be greater than maximum rectified input voltage. 264VAC x 1.414 = 373VDC which is lower than output voltage of 390VDC. If we select output voltage as 238VDC as maximum, then it will not work as PFC converter.

You can read here: https://www.onsemi.com/pub_link/Collateral/HBD853-D.PDF
 

Thanks Fethi...

Another query- Why Flyback converter is used as battery charger?
 

samEEEf said:
Thanks Fethi...

Another query- Why Flyback converter is used as battery charger?
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Since charging battery does not require powerful converter circuit. As i know, flyback can be used up to 250W and i will only charge three batteries. Also i have some kind of document that includes fully described step by step flyback converter design. I saw circuit there and it was very easy to implement. Thats all.
 

What kind of operation should i use in flyback converter for battery charging ? DCM, CCM or quasi resonant ?
 

DCM flybacks are usually the simplest and easiest to design. However, they have a poor utilization of the switching components, and therefore for power outputs larger than 15 or 25 watts, a CCM is preferable.
Quasi resonant go a step further in efficiency, but are more complex and thus used on the highest power.
 

Thnx. Very good answer. I need about 28W flyback converter for battery charging. I have fairchild flyback design documents and they are really good. So for 28W output, do i need to select CCM or quasi resonant right ?
 

Guys i have block diagram like this. I would like to ask a question. Do u think that it will work good when there is no electricity. I mean when there is AC line on grid, 390VDC will be appeared on bus, and when there is no AC line on grid, 350VDC will be appeared as i know. Do you think that it will work good during the transition in case of power cut. I always would like to see 220VAC at the output.

 

Do you think that it will work good during the transition in case of power cut. I always would like to see 220VAC at the output.
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It surely can with a suitable control scheme.

Personally I prefer PWM control algorithms that are varying the duty cycle according to the DC bus voltage, the method can be considered as bus voltage feed forward. In this case, the output voltage will be almost held constant during the transition without any feedback.
 

SPWM inverter will change its duty cycle between from 390VDC to 350VDC for constant AC output and i hope i will not see any change at the output. That is only thing i can do it for now.

Thnx a lot.
 

In detail, non-ideal output stage parameters (e.g. switching time, transistor voltage drop) will cause a certain voltage variation despite of bus voltage feedforward It should be in an acceptable range, however.
 
I would like to ask final question. I will use UC3825 for full bridge, is it good for full bridge applications ?
 

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