ade7753 Analog Devices, Inc., ade7753 Datasheet - Page 22

• Manufacturer Part Number: ade7753
• Description: Active And Apparent Energy Metering Ic With Di/dt Sensor Interface
• Manufacturer: Analog Devices, Inc.

ADE7753
to V x I x t. The sinusoidal ripple in the Active Energy
calculation is also shown. Since the average value of a
sinusoid is zero, this ripple will not contribute to the energy
calculation over time. However, the ripple can be observed
in the frequency output, especially at higher output frequen-
cies. The ripple will get larger as a percentage of the
frequency at larger loads and higher output frequencies. The
reason is simply that at higher output frequencies the integra-
tion or averaging time in the Energy-to-Frequency conversion
process is shorter. As a consequence some of the sinusoidal
ripple is observable in the frequency output. Choosing a
lower output frequency at CF for calibration can significantly
reduce the ripple. Also averaging the output frequency by
using a longer gate time for the counter will achieve the same
results.
LINE CYCLE ENERGY ACCUMULATION MODE
In Line Cycle Energy Accumulation mode, the energy
accumulation of the ADE7753 can be synchronized to the
Channel 2 zero crossing so that active energy can be accumu-
lated over an integral number of half line cycles. The
advantage of summing the active energy over an integer
number of half line cycles is that the sinusoidal component
in the active energy is reduced to zero. This eliminates any
ripple in the energy calculation. Energy is calculated more
accurately and in a shorter time because integration period
can be shortened. By using the line cycle energy accumula-
tion mode, the energy calibration can be greatly simplified
and the time required to calibrate the meter can be signifi-
cantly reduced. The ADE7753 is placed in line cycle energy
accumulation mode by setting bit 7 (CYCMODE) in the
Mode register. In Line Cycle Energy Accumulation Mode
the ADE7753 accumulates the active power signal in the
LAENERGY register (Address 04h) for an integral number
of line cycles, as shown in Figure 39. The number of half line
cycles is specified in the LINECYC register (Address 1Ch).
The ADE7753 can accumulate active power for up to 65,535
half line cycles. Because the active power is integrated on an
integral number of line cycles, at the end of a line cycle energy
accumulation cycle the CYCEND flag in the Interrupt Status
register is set (bit 2). If the CYCEND enable bit in the
Interrupt Enable register is enabled, the IRQ output will also
go active low. Thus the IRQ line can also be used to signal
the completion of the line cycle energy accumulation. An-
other calibration cycle will start as long as the CYCMODE
bit in the Mode register is set. Note that the result of the first
E(t)
Figure 38 – Output frequency ripple
R S
T
4.
F
.
t
f
l
(1+ 2.
VIt
PRELIMINARY TECHNICAL DATA
VI
f
l
/ 8.9Hz)
U V
W
sin(4.
F
. . )
f t
l
–22–
calibration is invalid and should be ignored. The result of all
subsequent line cycle accumulation is correct.
From Equations 6 and 10.
where n is a integer and T is the line cycle period. Since the
sinusoidal component is integrated over a integer number of
line cycles its value is always zero.
T herefore:
Note that in this mode, the 16-bit LINECYC register can
hold a maximum value of 65,535. In other words, the line
energy accumulation mode can be used to accumulate active
energy for a maximum duration over 65,535 half line cycles.
At 60Hz line frequency, it translates to a total duration of
65,535 / 120Hz = 546 seconds.
POSITIVE ONLY ACCUMULATION MODE
In Positive Only Accumulation mode, the energy accumula-
tion is done only for positive power, ignoring any occurrence
of negative power above or below the no load threshold as
shown in Figure 40. The ADE7753 is placed in positive only
E
E
E(t)
Figure 39 – Energy Calculation in Line Cycle Energy Accu-
CHANNEL 2
(
t
FROM
ADC
)
Figure 40 – Energy Accumulation in Positive Only
0
nT
nT
VIdt
0
VI
VInT
LPF1
Active Energy
Active Power
dt
No-load
threshold
No-load
threshold
IRQ
0
Output from
LPF2
ZERO CROSS
DETECTION
1
PPOS
Accumulation Mode
VI
WDIV[7:0]
8
mulation Mode
f
9 .
PNEG
Interrupt Status Registers
CALIBRATION
2
LINECYC[14:0]
CONTROL
+
nT
0
+
PPOS
cos
2
PNEG PPOS
46
23
LAENERGY[23:0]
t f
dt
REV. PrF 10/02
PNEG
0
ACCUMULATE ACTIVE
ENERGY IN INTERNAL
REGISTER AND UPDATE
THE LAENERGY REGISTER
AT THE END OF LINECYC
LINE-CYCLES
0
(13)
(14)
(12)