Sorry equation wrong (looked at the wrong cell in my excel sheet). I use
**broken link removed**
P = (1/3)*(V*I)*ts*F
Where P == power dissipated in that one switching event
V = peak voltage switching to/from
I = peak voltage switching into/out of
ts = switching time (in this case 50ns)
F = switching freq (in Hz)
its 1/3 due to the waveform of the voltage and the current changing at the same time (see assumptions)
v(t) = (-V/ts)*t
i(t) = (I/ts)*t
so integrate V*I by t over ts:
int( (-VI)/(ts^2)t^2,t,0,ts)
gives E = (1/3)*I*V*ts
so multipying by F will give you the power for all turn-ON (if that ts was the turn-ON time)
The assumptions made in this are
1) that the voltage falls/rises linearly (in practice it doesn't)
2) that the current rises/falls linearly (in practive it doesn't)
3) it neglects reverse-recovery of any freewheel diodes at turn-on
4) neglects any voltage overshoot due to stray inductance at turn off
4) neglects the delay in voltage falling w.r.t. current rising at turn-on & the delay with current falling w.r.t. voltage rising at turn-off
These assumptions are valid for low amp/voltage operation (you should be ok). Even at higher voltages and currents these assumptions can lead to a switching loss that, while not spot-on, isn't too far out.
mmm getting interesting, capturing the backEMF can be tricky and must be sync with your PWM and modulation depth (so you sample during periods of no switching). Still there is only two instances when you would go to the effort of trying to measure the BackEMF
1) space-vector modulation of a BLAC machine
2) a means to sense speed
#1 is bad, there are better ways to derive it indirectly
#2 alot of hassle, might as well strap an encoder disk and count pulses