ade7566 Analog Devices, Inc., ade7566 Datasheet - Page 60

• Manufacturer Part Number: ade7566
• Description: Single-phase Energy Measurement Ic With 8052 Mcu, Rtc, And Lcd Driver
• Manufacturer: Analog Devices, Inc.

ADE7566/ADE7569
APPARENT POWER CALCULATION
Apparent power is defined as the maximum power that can be
delivered to a load. V
current delivered to the load, respectively. Therefore, the apparent
power (AP) = V
phase angle between the current and the voltage.
Equation 28 gives an expression of the instantaneous power
signal in an ac system with a phase shift.
Figure 70 illustrates the signal processing for the calculation of
the apparent power in the ADE7566/ADE7569.
The apparent power signal can be read from the waveform register
by setting the WAVMODE register (0x0D) and setting the WFSM
bit in the Interrupt Enable 3 SFR (MIRQENH, 0xDB). Like the
current and voltage channel waveform sampling modes, the
waveform data is available at sample rates of 25.6 kSPS,
12.8 kSPS, 6.4 kSPS, or 3.2 kSPS.
v t
t i
p
p
( )
( )
( )
(
t
t
)
=
=
=
=
V
v
2
2
(
rms
t
V
I
)
rms
rms
I
rms
×
rms
t i
× I
sin(
sin( )
(
cos(
)
rms
rms
ω
ω
. This equation is independent from the
and I
t
θ
t
)
+
−
θ
V
)
rms
rms
are the effective voltage and
I
V
I
rms
rms
rms
cos(
CURRENT RMS SIGNAL – i(t)
VOLTAGE RMS SIGNAL – v(t)
0x1CF68C
0x1CF68C
2
ω
0x00
0x00
t
+
θ
)
Figure 70. Apparent Power Signal Processing
Rev. 0 | Page 60 of 136
(25)
(26)
(27)
(28)
VARMSCFCON
The gain of the apparent energy can be adjusted by using the
multiplier and by writing a twos complement, 12-bit word to the
VAGAIN register (VAGAIN[11:0]). Equation 29 shows how the
gain adjustment is related to the contents of the VAGAIN register.
For example, when 0x7FF is written to the VAGAIN register, the
power output is scaled up by 50% (0x7FF = 2047d, 2047/2
Similarly, 0x800 = –2047d (signed twos complement) and power
output is scaled by –50%. Each LSB represents 0.0244% of the
power output. The apparent power is calculated with the current
and voltage rms values obtained in the rms blocks of the
ADE7566/ADE7569.
Apparent Power Offset Calibration
Each rms measurement includes an offset compensation register to
calibrate and eliminate the dc component in the rms value (see the
Current Channel RMS Calculation section and Voltage Channel
RMS Calculation section). The voltage and current channels
rms values are then multiplied together in the apparent power
signal processing. Because no additional offsets are created in
the multiplication of the rms values, there is no specific offset
compensation in the apparent power signal processing. The
offset compensation of the apparent power measurement is
done by calibrating each individual rms measurement.
Output VAGAIN =
VAGAIN
⎛
⎜
⎝
Apparent
DIGITAL-TO-FREQUENCY
0x1A36E2
CONVERTER
APPARENT POWER
SIGNAL (P)
Power
TO
×
⎧ +
⎨
⎩
1
VAGAIN
2
12
⎫
⎬
⎭
⎞
⎟
⎠
12
= 0.5).
(29)