ade7880 Analog Devices, Inc., ade7880 Datasheet - Page 43

• Manufacturer Part Number: ade7880
• Description: Polyphase Multifunction Energy Metering Ic With Harmonic Monitoring
• Manufacturer: Analog Devices, Inc.

Preliminary Technical Data
Sign of Active Power Calculation
The average active power is a signed calculation. If the phase
difference between the current and voltage waveform is more
than 90°, the average power becomes negative. Negative power
indicates that energy is being injected back on the grid. The
ADE7880 has sign detection circuitry for total active power
calculations. It can monitor the total active powers or the
fundamental active powers. As described in the Active Energy
Calculation section, the active energy accumulation is performed
in two stages. Every time a sign change is detected in the energy
accumulation at the end of the first stage, that is, after the energy
accumulated into the internal accumulator reaches the WTHR
register threshold, a dedicated interrupt is triggered. The sign of
each phase active power can be read in the PHSIGN register.
Bit 6 (REVAPSEL) in the ACCMODE register sets the type of
active power being monitored. When REVAPSEL is 0, the
default value, the total active power is monitored. When
REVAPSEL is 1, the fundamental active power is monitored.
Bits[8:6] (REVAPC, REVAPB, and REVAPA, respectively) in the
STATUS0 register are set when a sign change occurs in the
power selected by Bit 6 (REVAPSEL) in the ACCMODE
register.
Bits[2:0] (CWSIGN, BWSIGN, and AWSIGN, respectively) in
the PHSIGN register are set simultaneously with the REVAPC,
REVAPB, and REVAPA bits. They indicate the sign of the
The ADE7880 achieves the integration of the active power signal
in two stages (see Figure 49). The process is identical for both
total and fundamental active powers. The first stage
accumulates the instantaneous phase total or fundamental
active power at 1.024MHz, although they are computed by the
DSP at 8KHz rate. Every time a threshold is reached, a pulse is
generated and the threshold is subtracted from the internal
register.
The sign of the energy in this moment is considered the sign of
the active power (see Sign of Active Power Calculation section
v
A
i
A
APHCAL
AVGAIN
AIGAIN
CONFIG3[0]
CONFIG3[0]
HPFEN bit
HPFEN bit
HPF
HPF
CONFIG[0]
INTEN bit
Digital Signal Processor
LPF2
Figure 49. Total Active Energy Accumulation
APGAIN
Rev. PrE | Page 43 of 103
AWATTOS
Σ
2
:
power. When they are 0, the corresponding power is positive.
When they are 1, the corresponding power is negative.
Bit REVAPx of STATUS0 and Bit xWSIGN in the PHSIGN
register refer to the total active power of Phase x, the power type
being selected by Bit 6 (REVAPSEL) in the ACCMODE register.
Interrupts attached to Bits[8:6] (REVAPC, REVAPB, and
REVAPA, respectively) in the STATUS0 register can be enabled
by setting Bits[8:6] in the MASK0 register. If enabled, the IRQ0
pin is set low, and the status bit is set to 1 whenever a change of
sign occurs. To find the phase that triggered the interrupt, the
PHSIGN register is read immediately after reading the STATUS0
register. Next, the status bit is cleared and the
to high by writing to the STATUS0 register with the corresponding
bit set to 1.
Active Energy Calculation
As previously stated, power is defined as the rate of energy flow.
This relationship can be expressed mathematically as
Conversely, energy is given as the integral of power, as follows:
Total and fundamental active energy accumulations are always
signed operations. Negative energy is subtracted from the active
energy contents.
4
for details). The second stage consists of accumulating the
pulses generated at the first stage into internal 32-bit
accumulation registers. The content of these registers is
transferred to watt-hour registers, xWATTHR and
xFWATTHR, when these registers are accessed.
Power =
Energy
AWATT
=
dEnergy
∫
p
Σ
dt
( )
34
t
WTHR
dt
THRESHOLD
Accumulator
27
Internal
26
0
0
IRQ0 pin is returned
Σ
ADE7880
STATUS0[31:0]
REVAPA bit in
AWATTHR[31:0]
32 bit register
(23)
(24)