STPMC1 datasheet(67/77 Pages) STMICROELECTRONICS

67 / 77 page

STPMC1

Energy calculation algorithm

Doc ID 15728 Rev 6

67/77

Energy calculation algorithm

For the purpose of simplicity the energy computation shown below is relative to only one

phase.

Given line voltage and current as:

Equation 12

u = U sin (

ω t)

i = I sin(

ω t + ϕ)

The voltage divider, AD converter and calibrator produce the value:

Equation 13

vu = u (R2/(R1+R2) (AU/VREF) kU = u kD = A sin (ω t)

The Rogowski coil preamplifier, AD converter and calibrator produce the value:

Equation 14

vi = - L (di/dt) (AI/VREF) kI = - I kL ω cos (ω t + ϕ) = - B ω cos (ω t + ϕ)

The 2nd stage internal integrations produce the values:

Equation 15

vui = ∫ vudt = - (A / ω) cos (ω t) kINT

Equation 16

vii =

∫ v

idt = - B sin (ω t + ϕ) kINT

From signs of vu and vui the base frequency of line can be produced:

Equation 17

ω / kINT = k / T

This result is used to compensate Eq. 41, Eq. 44, Eq. 45 and Eq. 54.

The frequency compensated values are:

Equation 18

vuic = ω / kINT vui = - A cos (ω t)

Equation 19

viic = ω / kINT vii = - B ω sin (ω t + ϕ)

The 3rd stage internal integrations and DC cancellations produce the values:

Equation 20

vuiic = ∫ vuicdt = - (A / ω) sin (ω t) kINT

Equation 21

viiic = ∫ viicdt = B cos (ω t + ϕ) kINT

STPMC1 Scheda tecnica(PDF) 67 Page - STMicroelectronics