Current Fed Full bridge converter

Archit · May 13, 2018

Hello people I am trying to make current fed full bridge DC/DC converter.
Specifications:
input voltage-30V to 45V
Output voltage 350V
Output Current 14A.
I have attached my LT-Spice file
Problems:
1-Simulation is slow
2-ripples in switch voltage.
3-Primary side voltage
Please tell where is the problem. Thanking in anticipation.

Edit. I changed the voltage source and inductor to constant current source. But switch voltage is still rising. and it still has ripples. Please help

alec_t · May 13, 2018

Welcome to ETO!
There is a lot of shoot-through current through the top and bottom FETs because of overlap in their Vgs drive waveforms. You need to avoid overlap and allow some dead-time.
The gate drive voltages are excessive and would fry the FETs in the real world.

Archit · May 13, 2018

alec_t said:
Welcome to ETO!
There is a lot of shoot-through current through the top and bottom FETs because of overlap in their Vgs drive waveforms. You need to avoid overlap and allow some dead-time.
The gate drive voltages are excessive and would fry the FETs in the real world.

Overlap has been done intentionally because there is a current source at the input.

Archit · May 13, 2018

alec_t said:
Welcome to ETO!
There is a lot of shoot-through current through the top and bottom FETs because of overlap in their Vgs drive waveforms. You need to avoid overlap and allow some dead-time.
The gate drive voltages are excessive and would fry the FETs in the real world.

Agreed. But it doesnt matter here in LT spice.

alec_t · May 13, 2018

I think the primary voltage build-up is due to the average current through L1 being non-zero.

Archit · May 13, 2018

alec_t said:
up is due to the average current through L1 being non-zero.

But average current through L1 is zero.

alec_t · May 13, 2018

LTS is telling me the average, over the 100mS sim interval, is ~180mA.

ronsimpson · May 13, 2018

I don't know what you are trying to build but this is a current fed full bridge boost circuit.
In your circuit: input is current I changed to voltage. ("current" = current in inductor)
Changed gate voltage from +/-30Vpk to +/-20V. (real world max voltage on G-S)
I also used a Pulse Voltage Source as input. This circuit wants to start up at zero volts. (initial condition problems)

Archit · May 13, 2018

alec_t said:
LTS is telling me the average, over the 100mS sim interval, is ~180mA.

Ok i i thought maybe it is not taking full.cycles.
What should I do?

alec_t · May 13, 2018

Archit said:
What should I do?

Investigate why there's slight asymmetry in the inductor current?

Archit · May 13, 2018

alec_t said:
LTS is telling me the average, over the 100mS sim interval, is ~180mA.[/Q

But for different cycles average is different. It is close to zero around 50mA if you neglect initial transitions.

Archit · May 13, 2018

ronsimpson said:
I don't know what you are trying to build but this is a current fed full bridge boost circuit.
In your circuit: input is current I changed to voltage. ("current" = current in inductor)
Changed gate voltage from +/-30Vpk to +/-20V. (real world max voltage on G-S)
I also used a Pulse Voltage Source as input. This circuit wants to start up at zero volts. (initial condition problems)

I got the problem.. Rising of switch voltage is because of the RCD clamp circuit. But if I remove this then the stress voltage is too high across the switches.
Please help to solve this issue.

Archit · May 13, 2018

alec_t said:
Investigate why there's slight asymmetry in the inductor current?

I got the problem.. Rising of switch voltage (Vds) is because of the RCD clamp circuit. But if I remove this then the stress voltage is too high across the switches.
Please help to solve this issue.

ronsimpson · May 13, 2018

This is not how you make a "current fed full bridge boost circuit".

Energy stored on L4 pushes your voltage up. Please remove it and see what happens.

Archit · May 13, 2018

ronsimpson said:
This is not how you make a "current fed full bridge boost circuit".

Energy stored on L4 pushes your voltage up. Please remove it and see what happens.

But That is the leakage inductance of the transformer. NO matter what I do It will be there practically.

Archit · May 13, 2018

ronsimpson said:
This is not how you make a "current fed full bridge boost circuit".

Energy stored on L4 pushes your voltage up. Please remove it and see what happens.

Also, If I remove it them , the current through the primary side is in KAmps range.

ronsimpson · May 13, 2018

Archit said:
KAmps range

I see 200A.

Your R7 is only 1000 ohms. It will not eat up all of the energy from L4.

Archit · May 13, 2018

ronsimpson said:
I see 200A.

But the spikes are going to 800A

ronsimpson · May 13, 2018

Archit said:
But the spikes are going to 800A

I give up. Where is there 800A?

ronsimpson · May 13, 2018

The "Constant Current" name comes from the constant current in L3.
Increased frequency, reduced the inductors/transformer size, New snubber, Use K1=0.995 for leakage inductance, changed D=0.64 to get 350V.

Current Fed Full bridge converter

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