Knowing that;
Form factor= Rms/mean
Vrms=100 sin wt+30 sin 3 wt+20 sin 5 wt+15 sin 7 wt
How can I find the mean value?
See:
.
The mean over the whole period is zero. You might want to do the calculation over a half-period.
Like: \(mean=\frac{\int_0^{\pi/w}V(t)dt}{\int_0^{\pi/w}dt}\rightarrow\frac{w}{\pi}\int_0^{\pi/w}V(t)dt\)
