ADE7854AACPZ View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'ADE7854AACPZ' PDF : 96 Pages View PDF
ADE7854A/ADE7858A/ADE7868A/ADE7878A
Data Sheet
first stage, that is, after the energy accumulated into the internal
accumulator reaches the WTHR register threshold, it triggers a
dedicated interrupt. Read the sign of each phase active power
using the PHSIGN register.
Bit 6 (REVAPSEL) in the ACCMODE register sets the type
of active power being monitored. Setting REVAPSEL to 0,
the default value, monitors the total active power. Setting
REVAPSEL to 1 monitors the fundamental active power.
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; these bits indicate the sign of the
power. When these bits are set to 0, the corresponding power is
positive; when they are set to 1, the corresponding power is
negative.
Bit REVAPx in the STATUS0 register and Bit xWSIGN in the
PHSIGN register refer to the total active power of Phase x, the
power type that is selected by Bit 6 (REVAPSEL) in the
ACCMODE register.
Interrupts attached to Bits[8:6] (REVAPC, REVAPB, and REVAPA,
respectively) in the STATUS0 register are enabled by setting
Bits[8:6] in the MASK0 register. When enabled, the IRQ0 pin is
set low, and the status bit is set to 1 when a change of sign occurs.
To find the phase that triggered the interrupt, after reading the
STATUS0 register, immediately read the PHSIGN register. Next,
writing to the STATUS0 register with the corresponding bit set to
1 clears the status bit and returns the IRQ0 pin to high.
Active Energy Calculation
As previously stated, power is defined as the rate of energy flow.
This relationship is expressed mathematically as
Power dEnergy
(29)
dt
Conversely, energy is the integral of power, expressed as follows:
Energy = p(t) dt
(30)
Total and fundamental active energy accumulations are always
signed operations. Negative energy is subtracted from the active
energy contents. The ADE7854A/ADE7858A/ADE7868A/
ADE7878A achieve the integration of the active power signal in
two stages (see Figure 71). The process is identical for both total
and fundamental active powers. The first stage is accomplished
inside the DSP: every 125 μs (8 kHz frequency) the instantaneous
phase total or fundamental active power accumulates into an
internal register. Upon reaching a threshold, a pulse is generated
at the processor port, 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 the Sign of Active
Power Calculation section). The second stage occurs outside the
DSP and consists of accumulating the pulses generated by the
processor into internal 32-bit accumulation registers. When
these registers are accessed, the content of these registers
transfers to the watt-hour registers, xWATTHR and
xFWATTHR (see Figure 70).
WTHR[47:0]
ACTIVE POWER
ACCUMUL ATION
IN DSP
DSP
GENERATED
PULSES
1 DSP PULSE = 1LSB OF WATTHR[31:0]
Figure 70. Active Power Accumulation Inside the DSP
IA
APHCAL
VA
HPFDIS
[23:0]
DIGITAL
INTEGRATOR AIGAIN
HPF
HPFDIS
[23:0]
AVGAIN
HPF
AWGAIN AWATTOS
LPF2
ACCUMULATOR
WTHR[47:0]
AWATT
DIGITAL SIGNAL PROCESSOR
24
Figure 71. Total Active Energy Accumulation
Rev. C | Page 50 of 96
REVAPA BIT IN
STATUS0[31:0]
AWATTHR[31:0]
32-BIT
REGISTER
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