Datasheet

STPM01 Theory of operation
Doc ID 10853 Rev 8 45/60
Equation 3
i(t) = I • sin (
ωt + ϕ);
where I is the peak current,
ω is related to the line frequency and ϕ is the phase difference
between voltage and current.
8.24.1 Active power
In the STPM01, after the pre-conditioning and the A/D conversion, the digital voltage signal
(which is dynamically more stable with respect to the current signal) is processed by a
differentiated stage which transforms:
Equation 4
v(t) → v’(t) = dv/dt = V
⋅ ω ⋅ cos ωt − [see Figure 28 - 5]
The resulted signal, together with the pre-processed and digitalized current signal:
Equation 5
i(t) = I
⋅ sin(ωt + ϕ); [see Figure 28 - 6]
are then available for the calculation process. These digital signals are also provided into
two additional stages which perform the integration of themselves, obtaining:
Figure 28. Active energy computation diagram