Always wrong flying capacitor voltage when simulating a boost flying capacitor dc-dc converter

Question

Hi there,

I was trying to simulating a boost flying capacitor dc-dc converter with phase shift PWM in open loop. But the flying capacitor voltage has always been deviated from what it should be. But the output voltage is correct. I tried both directional and unidirection operations, but neither worked.

Also, it is weird that the model works fine if I change it to buck model. (The duty ratio was changed to buck mode also.) But in boost mode (with correct duty ratio), it always gave me wrong flying cap voltage.

Can anyone please help me check the attached model to see where I did wrong?

Many thanks!

Alex

-------

update

I tried different soler types and step sizes and got different results. I set output voltage to be 1300V. Sometimes I got 400V, sometimes I got 1000V. If the upper mosfets are changed to diodes, with a smaller step size the flying cap voltage is close to 650V. But then if the input voltage is changed to a different value, wrong flying cap voltage shows.

Also tried steady state analysis as a last resort (I knew it won't work) and gave me wrong result as well.

To me it looks like some kind accumulated error thats deviates the flying cap voltage to a stead state value different from what it should be.

Any input on a solution is greatly appreciated.

Comments

The steps to recreate your issue aren't exactly clear to me.  My recommendation is to simplify your circuit as much as possible by removing parasitics, device details, input filter, and so on to get down to the root of the issue.

If you post a more detailed guide comparing the expected results, observed results, and parameters your changing between simulations, we would be better positioned to help.

---

Thanks Bryan! Will do.