Datasheet

Data Sheet ADE7953
Rev. B | Page 25 of 72
SIGN OF ACTIVE POWER CALCULATION
The active power measurement in the ADE7953 is a signed
calculation. If the phase differential between the current and
voltage waveforms is more than 90°, the power is negative.
Negative power indicates that energy is being injected back
into the grid. The ACCMODE register (Address 0x201 and
Address 0x301) includes two sign indication bits that show the
sign of the active power of Current Channel A (APSIGN_A)
and Current Channel B (APSIGN_B). See the Sign Indication
section for more information.
ACTIVE ENERGY CALCULATION
As described in the Active Power Calculation section, power
is defined as the rate of energy flow. This relationship can be
expressed mathematically as shown in Equation 8.
d
t
dE
P 
(8)
where:
P is power.
E is energy.
Conversely, energy is given as the integral of power.

 Pdt E (9)
The ADE7953 achieves the integration of the active power
signal in two stages. In the first stage, the active power signals
are accumulated in an internal 48-bit register every 143 μs
(6.99 kHz) until an internal fixed threshold is reached. When
this threshold is reached, a pulse is generated and is accumu-
lated in 24-bit, user-accessible accumulation registers. The
internal threshold results in a maximum accumulation rate
of approximately 206.9 kHz with full-scale inputs. This process
occurs simultaneously on Current Channel A and Current
Channel B, and the resulting readings can be read in the 24-bit
AENERGYA (Address 0x21E and Address 0x31E) and
AENERGYB (Address 0x21F and Address 0x31F) registers.
Both stages of the accumulation are signed and, therefore,
negative energy is subtracted from positive energy.
This discrete time accumulation, or summation, is equivalent
to integration in continuous time. Equation 10 expresses this
relationship.












1
0
n
T
T P(nT)LimP(t)dtE (10)
where:
n is the discrete time-sampled number.
T is the sample period.
The discrete time sample period (T) for the accumulation
registers in the ADE7953 is 4.83 μs (1/206.9 kHz). This is
illustrated in Figure 46, which shows the energy register
roll-over rates with full-scale inputs.
0x000000
0
x7FFFF
F
0
x3FFFF
F
0x400000
0x800000
A
ENERGYx[23:0]
40.520.26 60.78
TIME (Seconds)
xWGAIN = 0x200000
xWGAIN = 0x400000
xWGAIN = 0x600000
0
9320-042
Figure 46. Energy Register Roll-Over Time for Active Energy
Note that the energy register contents roll over to full-scale
negative (0x800000) and continue to increase in value when the
power or energy flow is positive. Conversely, if the power is
negative, the energy register underflows to full-scale positive
(0x7FFFFF) and continues to decrease in value.
AENERGYA and AENERGYB are read-with-reset registers
by default. This means that the contents of these registers are
reset to 0 after a read operation. This feature can be disabled
by clearing Bit 6 (RSTREAD) of the LCYCMODE register
(Address 0x004).
The ADE7953 includes two sets of interrupts that are triggered
when the active energy register is half full (positive or negative)
or when an overflow or underflow condition occurs. The first
set of interrupts is associated with the Current Channel A active
energy, and the second set of interrupts is associated with the
Current Channel B active energy. These interrupts are disabled
by default and can be enabled by setting the AEHFA and
AEOFA bits in the IRQENA register (Address 0x22C and
Address 0x32C) for Current Channel A, and the AEHFB and
AEOFB bits in the IRQENB register (Address 0x22F and
Address 0x32F) for Current Channel B.