Datasheet

STPMC1 Energy calculation algorithm
Doc ID 15728 Rev 7 71/77
10.3 Voltage and current RMS values calculation
The I
RMS
value is produced from 16-bit value of Equation 16 :
Equation 49
The Ui
RMS
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 Ii
RMS
is produced from 16-bit value of Equation 25 :
Equation 51
The U
RMS
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 f
MCLK
as the measurement clock
frequency and M as number of possible values of some integrator, the following constant
factors can be defined:
Equation 53
k
INT
= 2 f
MCLK
/ M
INT
= 2
8
k
UD
= 2 f
MCLK
/ M
UD
= 2
11
k
DIF
= M
DIF
/ 2 f
MCLK
= 2
-8
I
RMS
k
L
k
INT
=
∫
T
0
2
ii
dt
T
1
v
= B
2
1
Ui
RMS
k
D
=
∫
T
0
2
ui
dt
T
1
v
= Ak
INT
/ω
2
1
Ii
RMS
k
S
k
INT
=
∫
T
0
2
si
dt
T
1
v
= C/ω
2
1
U
RMS
k
D
=
∫
T
0
2
di
dt
T
1
v
= A
2
1