Some EPC GaN datasheets do not provide the Qoss and Eoss vs. vds curves so I digitized the Coss vs. vds and integrated it over vds to get the other two curves. I compared my calculated values from GaNs with Qoss and Eoss given in the datasheet with these values and while Qoss seems to match pretty well, Eoss was wrong by a factor of roughly 1.5. So my question is: What is the reason why in Eoss(vds) in the datasheets does not match with the integral of Qoss(vds) over vds? Is there anything that has to be considered within this integral calculation?
Your calculations for Qoss are correct. For Eoss, you need to make sure to use directly the formula for energy:
E_{OSS}(V) = \int^V_0{V^\prime C_{OSS}(V^\prime)}\cdot dV^\prime
This will yield a different result than using the formula:
E_{OSS}(V) = \int^V_0{Q_{OSS}(V^\prime)}\cdot dV^\prime
The two are the same only if Coss is constant, which is not the case…