I can't comment on rikkitikki's suggestion which quotes a known amount of energy for switching a certain current and voltage and then using the ratio of current and voltage in your circuit to this standard value. I haven't seen it before but it doesn't seem to account for the actual switch transition time which will be different in different devices so I can't see how there can be a fixed amount of energy to switch a fixed voltage and current, unless I've missed something. About his conduction loss equation, it's right but if you just go by the datasheet value for Vce(sat), you won't get the right answer as that value was measured at Ic=800A
Correct, it is just a crude method. Switching loss estimation is based on the assumption that you do hard switching as fast as the device can go, and therefore the turn-on/off caracteristics of the device in the datasheet is typical and determining the actual on/off losses by different times. Taking in account for device variations and quite possibly the switching circuit complicates the calculation and perhaps it is better to use some margin in the estimation.
It all depends on how deep you want to go in your calculations, perhaps you have a good example how to calculate switching loss?
The example you state with max voltage/current * (toff+ton)* switching frequency is as you write grossly overestimating the loss, mainly because the current and voltage are never at maximum simultaneously but at some intermediate value during on/off switching. Hence using datasheet data for switching loss as I suggest.
When going resonant, it gets complicated...
Of course you need to use the Vce(sat) for the actual current and if you dont have it in the datasheet one needs to interpolate, or as you suggest build up a equation describion Vce(sat) as a function of Ic. You had a good example, there is quite a few articles on the net how to model this equation based on datasheet data. But for me it is simpler to use interpolate data from the Vce sat curves. Again, I estimate on the higher side to have some margin. Only if I discover that losses are huge it is motivated to recalculate in finer detail