ADE7758 Analog Devices, ADE7758 Datasheet - Page 38

• Manufacturer Part Number: ADE7758
• Description: Poly Phase Multifunction Energy Metering IC with Per Phase Information
• Manufacturer: Analog Devices

ADE7758
If the active power of that phase is positive, no change is ma
to the sign of the reactive power. However, if the sign of the
active power is negative in that phase, the sign of its reactive
power is inversed before summing and creating VARCF pulses.
This mode should be used in conjunction with the absolute
value mode for active power (Bit 5 in the COMPMODE
register) for APCF pulses. Table 10 shows the effect of set
the ABS and SAVAR bits of the COMPMODE register.
The effects of setting the ABS and SAVAR bits of the
COMPMODE register results as follows when ABS = 1
and SAVAR = 1
If watt > 0
If watt < 0
The output
division registers before sending to the APCF pulse output.
Namely, VARCFDEN/VARCFNUM pulses are needed at the
DFC output before the VARCF pin outputs a pulse. Under
steady load conditions, the output frequency is directly
proportional to the total reactive power.
Figure 68 illustrates the energy-to-frequen
ADE7758. Note that the input to the DFC can be selected
between the total reactive power and total apparent power.
Therefore, the VARCF pin can output frequency that is
proportional to the total reactive power or total apparen
The selection is made by setting the VACF bit (Bit 7) in the
WAVMODE register. Setting this bit to logic high switches th
input to the total apparent power. The default value of this bit is
logic low. Therefore, the default output from the VARCF pin is
the total reactive power.
All other operations of th
of the active power frequency output (see the Active Power
Frequency Output section).
INPUT TO BVARHR
INPUT TO CVARHR
INPUT TO AVARHR
INPUT TO BVAHR
INPUT TO CVAHR
INPUT TO AVAHR
REGISTER
REGISTER
REGISTER
REGISTER
REGISTER
REGISTER
Figure 73. ADE7758 Reactive Power Frequency Output
from the DFC is divided down by a pair of fr
:
+
+
+
+
+
+
WAVMODE REGISTER
VACF BIT (BIT 7) OF
is frequency output are similar to that
0
1
APCF = Watts
VARCF = VAR
APCF = |Watts|
VARCF = -VAR
DFC
VARCFNUM[11:0]
VARCFDEN[11:0]
cy conversion in the
÷
÷
4
equency
t power.
ting
VARCF
de
Rev. A | Page 38 of 68
e
Line Cycle Reactive Energy Accumulation Mode
The line cycle reactive energy accumulation mode is activated
by setting the LVAR bit (Bit 1) in the LCYCMODE register. The
total reactive energy accumulated over an integer number of
zero crossings is written to the VAR-hr accumulation registers
after the LINECYC number of zero crossings has been detected.
The operation of this mode is similar to watt-hr accumulation
(see the Line Cycle Active Energy Accumulation Mode section).
When using the line cycle accumulation mode, the RSTREAD
bit (Bit 6) of the LCYCMODE register should be set to Logic 0.
APPARENT POWER CALCULATION
Apparent power is defined as the amplitude of the vector sum of
the active and reactive powers. Figure 74 shows what is typically
referred to as the power triangle.
There are two ways to calculate apparent power, namely the
arithmetical approach or the vectorial method. The arithmetical
method uses the product of the voltage rms value and current
rms value to calculate apparent power. Equation 22 describes
the arithmetical approach mathematically.
where S is the apparent power, and VRMS and IRMS are the
rms voltage and current, respectively.
The vectorial method uses the square root of the sum of the
active and reactive power, after the two are individually
squared. Equation 23 shows the calculation used in the vectorial
approach.
where S is the apparent power, P is the active power, and Q is
the reactive power.
S = VRMS × IRMS
S
=
P
2
+
Q
2
Figure 74. Power Triangle
ACTIVE POWER
APPARENT
POWER
(22)
(23)