Flyback converter help please.

Hi,

I will try to explain my problem first.

I am trying to simulate a flyback dcdc converter with the following spec, Vin-min = 80V, Vin-max = 122V, Vout=58V, Iout = 6A. I am using a calculation to define the parameters of the transformer mainly. I followed the following steps,

1. Pin = Pout/eff

2. Iav-min = Pin/Vin-min and Iav-max = Pin/Vin-max

3. Ipk = (2*Pout)/ (Vin-min * Dmax), Dmax is set to .5 as that what i found typical for most previous literatures

4. Lpri = (Vin-min * Dmax)/(Ipk * fsw)

5. Np/Ns = (Vin-min * Dmax)/(Vout *(1-Dmax))

6. Ls = Lpri/(Np/Ns)^2

I have a simple RCD clamp for the MOSFET and output capacitor. I sensed the voltage from the output of the load which is set to 9.8Ohm(Vout/Iout) and tried to control the gate of the MOSFET. However, no luck. Changed the PI controller 1000 times but still the output remains 32V all the time.

My question would be:

1. What i am missing here?

2. I am not 100% confident on the calculation of the turn ratio (there are 1000 of formulas around, i just picked the easy one that does not involve magnetics!) and secondary inductance.

3. I was trying to simulate the system in PSIM and it is asking for a parameter called Lm , i.e., magnetizing inductance in addition to primary and secondary inductance. Does anybody know how to calculate Lm. I found some papers talking about the effect of Lm on the circuit performance. But some papers just ignore it.

Can anybody here give me some clue so that i can investigate further? It seems like there are 100 formulas and none of them matches with one another.

Thanks
Arif