I'm trying to calculate the switching frequency of an IGBT (4MBI650VB-120R1-50) with only the datasheet. I know that it work approx at 7 to 12 kHz, but i don't know how to calculate the exact value from the datasheet. My first guess was to sum the turn-on time and the turn-off time and get the reciprocate of the sum, but the result is 456kHz sooo, i know thats wrong.

Thank you

 

Summing the maximum turn-on and turn-off times and taking the reciprocal gives the maximum frequency with no flat part to the output waveform. The output would look more or less like a triangle wave.
For efficient switching you probably want the total rise and fall times to be ≤5% of the waveform period (which would give a maximum switching frequency of about 23kHz if your original calculations were correct).
The lower the percentage, the better the switching efficiency, so you don't want to use a switching frequency higher than necessary.

 

The rough rule of thumb I have generally used for switching frequency limits is ~25% of the as calculated time if running under the lower 1/3 of the volt and or amp ratings derating down to ~ 5% at the upper end volt and or amp limits to keep them well with the devices SOA (Safe Operating Range) limits.

I've rebuilt many high powered switching power supplies for inverter power supply based welders and plasma cutters plus other higher powered commercial/industrial power supply units by replacing older lower volt and amp rated mosfets with newer higher capacity IGBT devices and found that using that rough rule I have never had a problem with the device swap outs. In most cases the heatsinks for those devices in those power supplies even ran cooler from the conversion.

The IGBTS may have had a higher forward drop voltage than the theoretical mosfet internal resistance calculated out as producing but given the faster smoother switching speeds plus often substantially superior voltage current and reverse conduction protection diode characteristics plus other various ratings they more than made up for the energy loss differences.