The dead time in a 3-phase grid connected inverter is a brief inverter during which all switches are turned off to avoid shoot through currents. It's typically added to prevent both upper and lower switches in a leg from being on simultaneously, which could cause a short circuit.

To calculate the dead time you need to consider the switching times of the power electronics devices like(IGBTs or MOSFETs) used in the inverter. The dead time is usually a fixed duration often specified by the manufacturer of the power devices.

Here's a basic formula:

Total dead time= individual dead time per switch × number of switches.