STPM11_08 datasheet(35/45 Pages) STMICROELECTRONICS

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STPM11/12/13/14

Energy calculation algorithm

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i(t) = I

⋅ sin(tω+ ϕ); [Eq. 2 - see (6) in Figure 6]

can then be used to calculate. These digital signals are also used in two additional steps for

integration, obtaining:

dv/dt

→v(t) = V

⋅ sin tω; [Eq. 3 - see (7) in Figure 6]

[Eq. 4 - see (8) in Figure 6]

Now four signals are available. Combining (pairing) them by two multiplication steps two

results are obtained:

[Eq. 5 - see (9) in Figure 6]

[Eq. 6 - see (10) in Figure 6]

After these two operations, another stage another step involves the subtraction of p1 from

p2 and dividing the result by 2, to obtain the active power:

[Eq. 7 - see (11) in Figure 6]

In this way, the AC part

has been then removed from the instantaneous power.

In the case of current sensors like "Rogowski coils", which provide the rate of the

instantaneous current signal, the initial voltage signal differentiation stage is switched off. In

this case the signals coming from the A/D conversion and their consequent integrations are:

v(t) = V

⋅ sin (tω); [Eq. 8]

[Eq. 9]

[Eq. 10]

)

cos(

)

(

)

(

⋅

−

⋅

∫

i(t)

⋅

)

cos(

cos

)

(

)

(

⋅

−

⋅

−

⋅

∫

)

cos(

cos

)

(

)

(

)

(

⋅

−

⋅

cos

))

(

)

(

)

(

⋅

−

⎟

⎠

⎞

⎜

⎝

⎛

⋅

)

cos(

ωt

)

cos(

)

(

)

(

⋅

−

′

cos

)

(

)

(

⋅

−

⋅

∫

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