STPM13 datasheet(36/46 Pages) STMICROELECTRONICS

36 / 46 page

Energy calculation algorithm

STPM11, STPM12, STPM13, STPM14

36/46

Doc ID 13167 Rev 8

Equation 16

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:

Equation 17

v(t) = V

⋅ sin (tω);

Equation 18

Equation 19

Equation 20

The signals process flow is the same as shown in the previous case, and even with the

formulas above, the result is the same.

The absence of any AC component allows a very fast calibration procedure. Averaging the

readings of several line periods is not needed. The active energy measurement is already

stable after one line cycle. Moreover the digital calibration allows saving time and space

compared to the hardware calibration made with resistor strings.

⎟

⎠

⎞

⎜

⎝

⎛

⋅

)

cos(

)

cos(

)

(

)

(

⋅

−

′

cos

)

(

)

(

⋅

−

⋅

∫

)

sin(

)

(

)

(

)

(

⋅

−

⋅

′

′′

∫

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