STPMC1 datasheet(71/77 Pages) STMICROELECTRONICS

71 / 77 page

STPMC1

Energy calculation algorithm

Doc ID 15728 Rev 6

71/77

10.3

Voltage and current RMS values calculation

The IRMS value is produced from 16-bit value of Equation 16:

Equation 49

The UiRMS is produced from stream and 16-bit value of Equation 15:

Equation 50

In case of non Rogowski sensor, the same dedicated RMS blocks produce some other

values, because input values for the blocks are changed.

Therefore, another RMS value, named IiRMS is produced from 16-bit value of Equation 25:

Equation 51

The URMS is produced from stream and 16-bit value of Equation 24:

Equation 52

10.4

Energy integration

The internal hard-wired DSP unit performs all the computations above in real time for a

power line in parallel by means of arithmetic blocks. Due to implementation of an integrator,

up/down counter or deviator, part of which is also an integrator in a feedback, additional

factors are introduced into computations. If we declare fMCLK as the measurement clock

frequency and M as number of possible values of some integrator, the following constant

factors can be defined:

Equation 53

kINT = 2 fMCLK / MINT = 2

kUD = 2 fMCLK / MUD = 2

kDIF = MDIF / 2 fMCLK = 2

-8

IRMSkLkINT =

∫

= B

UiRMSkD =

∫

= AkINT/

IiRMSkSkINT =

∫

= C/

URMSkD =

∫

= A

STPMC1 Datenblatt(PDF) 71 Page - STMicroelectronics