STPM01_11 STMICROELECTRONICS [STMicroelectronics], STPM01_11 Datasheet - Page 47

• Manufacturer Part Number: STPM01_11
• Description: Programmable single phase energy metering IC with tamper detection
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

STPM01
8.24.2
(
Equation 11
Equation 12
[
The signals process flow will be the same as shown in the previous case, and even with the
formulas above, the result will be the same.
The absence of any AC component allows a very fast calibration procedure: it requires just
to set (using the internal device programming registers) the voltage and current sensor
conversion constants, using the effective voltage and current (V
provided by the device built-in communication port, avoiding the time-averaged readings of
the active power or need for line synchronization.
Reactive power
The reactive power is produced using the already computed signals. In case of shunt sensor
the voltage signal is derived while the current signal is not. A first computation is to multiply
DS value of integrated voltage channel with the value of integrated current channel, which
yields:
Equation 13
The second is to multiply filtered DS value of voltage channel with the value of filtered
current channel,
Equation 14
From the above results, Q1(t) is proportional to 1/
correct reactive power would result from the following formula:
Equation 15
Since the above computation would need significant additional circuitry, the Reactive Power
in the STPM01 is calculated using only the Q1(t) multiplied by
Q
Q
Q
V
) t
) t (
1
2
=
(
=
) t (
) t
=
1
2
∫
=
=
∫
⋅
( i
′
Q
∫
v
v
) t
v
1
) t (
′
t (
) t (
′
(
⋅
i )
) t
⋅
dt
⋅
dt
⋅
dt
ω
) t (
=
=
⋅
+
( I
=
( i
−
Q
) t
) t
V
V
ω
2
=
) t (
ω
( v
=
⋅
cos
cos
) t
⋅
−
ω
1
⋅
I
( I
⋅
ω
ω
=
) t
sin(
Doc ID 10853 Rev 8
t
t
=
VI
⋅
2
I
(
sin(
ω
sin
V
t
sin
ω
+
ϕ
t
ω
ϕ
+
) t
)
ϕ
⋅
)
⎛
⎜
⎝
−
=
ω
VI
I
2
ω
cos(
⋅
while Q2(t) is proportional to
ω
⋅
ω
(
sin
t
+
ϕ
ϕ
⎞
⎟
⎠
+
ω
=
sin(
RMS
, it means:
2
VI
ω
, I
2
ω
⋅
RMS
(
Theory of operation
sin
t
+
) readings
ϕ
ϕ
)
−
)
sin(
ω
2
. The
ω
t
+
47/60
ϕ
)
)