I think it depends on the duty cycle of PWM, in general the losses equal I^2R, but R depends on the on time to the period, i.e. if the switch is in on mode R=0(approximate) but if the switch is in off mode R=infinity.

Switching losses basically depends on number of switches devices used in the circuit, which can be detected by PWM duty cycle.

You can try to use the Thermal modules in the PSIM software

It would be very helpful for calculating the switching losses