Hello guys. I am working on PSFB converter and I want to be sure and see zero voltage transient(ZVT). I need to add a capatiance between drain and source in mosfet to ensure resonance with leakage inductance of primer winding.
When I add a thermal model of a mosfet , is it included Coss parameter ?
as second option, When I connect a capacitance paralell to mosfet , the simulation doesnt work. I connected a series resistance to capacitance to prevent this but is this a good solution to model a Coss capacitance If yes, what should the resistance value be for optimal performance?
What are your thoughts ?
Hi mazers26, Does this post help answer your question: Soft switching implementation in a DAB converter - #5 by Munadir_Ahmed .
Let me know if you still have any open questions. Also, sharing a model would help clarify what is happening when you say “the simulation doesn’t work.”
Hello,
Firstly, If I work without Coss capacitances , mosfets ensure the ZVS in any primer current. However, ZVS cant be ensured in any primer current therocially . There is a critical value of primer current to ensure ZVS . Thus, the simulation is not accurate at all. I mean my first clear question is how can I observe the ZVS in this circumstances.
Second option , connecting a paralell coss capaticance to mosfets . In this case , When a gate signal is high and if the primer current is under the critical value to get in ZVS , mosfets current go to peak instantly then stabilize.
like that.
I dont understand that why these peak currents happen ?
This is my full bridge structure and those capacitance are supposted to be Coss and I have to connect a series resistance each of them . Otherwise , simulation goes to error like the image below
I wonder that Why mosfet current goes to peak to high values when I connect capactiance under critical value of primer current for ZVS ? and how can I observe thermal charasteristic in this situtaion
Please see my responses below:
Firstly, If I work without Coss capacitances […] this circumstances.
You are absolutely right, without modeling the resonating capacitor you will not be able to observe the ZVS functionality.
Second option , connecting a paralell coss […] then stabilize.
Hard to tell what is going on without a PLECS model. What I will say is if you don’t achieve ZVS and turn on the FET you are effectively shorting a capacitor (Coss) across a very small resistor (Rdson). For example, if your Rdson is 1mOhm and you have 1V then the instantaneous current would be 1000A with a decay defined by the Rdson*Coss time constant.
This is my full bridge structure […] to error like the image below
Please see the following description of the error you are experiencing: What does the error message "state/source dependence" mean? | Plexim
I wonder that Why mosfet […] thermal charasteristic in this situtaion
A potential solution might be the one I proposed in this comment on that thread I had sent you earlier: Soft switching implementation in a DAB converter - #7 by Munadir_Ahmed . Effectively having a single configuration to model both ZVS and thermals may not be a feasible option.