ade7854 Analog Devices, Inc., ade7854 Datasheet - Page 30

• Manufacturer Part Number: ade7854
• Description: Poly Phase Multifunction Energy Metering Ic With Neutral Current Measurement
• Manufacturer: Analog Devices, Inc.

ADE7854
conditions will never be detected. Writing 0x0 to these registers
signifies the overvoltage or overcurrent conditions are
continuously detected and the corresponding interrupts are
triggered permanently.
As previously stated, the serial ports of the ADE7854 work on
32, 16 or 8-bit words. Similar to the register presented in Figure
17, OILVL and OVLVL registers are accessed as 32-bit registers
with 8 most significant bits padded with 0s.
PHASE COMPENSATION
As seen in Current Channel ADC and Voltage Channel ADC
chapters, the data path for both current and voltages is the
same. The phase error between current and voltage signals
introduced by the ADE7854 is negligible. However, the
ADE7854 must work with transducers that may have inherent
phase errors. For example, a current transformer (CT) with a
phase error of 0.1° to 3° is not uncommon. These phase errors
can vary from part to part, and they must be corrected to
perform accurate power calculations.
The errors associated with phase mismatch are particularly
noticeable at low power factors. The ADE7854 provides a
means of digitally calibrating these small phase errors. The
ADE7854 allows a small time delay or time advance to be
introduced into the signal processing chain to compensate for
the small phase errors.
The phase calibration registers (APHCAL[9:0], BPHCAL[9:0],
and CPHCAL[9:0]) are 10-bit registers that can vary the time
advance in the voltage channel signal path from +61.5 μs to
−374.0 μs, respectively. Negative values written to the PHCAL
registers represent a time advance, and positive values represent
a time delay. One LSB is equivalent to 0.976 μs of time delay or
time advance (clock rate of 1.024MHz). With a line frequency
of 60 Hz, this gives a phase resolution of 0.0211° (360° × 60
Hz/1.024 MHz) at the fundamental. This corresponds to a total
Rev. PrC| Page 30 of 71
correction range of −8.079° to +1.329° at 60 Hz. At 50Hz, the
correction range is -6.732° to +1.107° and the resolution is
0.0176°(360° × 50 Hz/1.024 MHz) .
Given a phase error of x degrees measured using the phase
voltage as the reference, then the corresponding LSBs are
computed dividing x by the phase resolution (0.0211°/LSB for
60Hz, 0.0176°/LSB for 50Hz). Only results between -383 and
+63 are acceptable. Numbers outside this range are not
accepted. If the result is negative, the absolute value is written
into PHCAL registers. If the result is positive, 512 is added to it
before writing the result into PHCAL.
Figure 38 illustrates how the phase compensation is used to
remove x=-1° phase lead in IA of the current channel from the
external current transducer (equivalent of 55.5μs for 50Hz
systems). To cancel the lead (1°) in the current channel of Phase
A, a phase lead must be introduced into the corresponding
voltage channel. Using expression (3), APHCAL is 57, rounded
up from 56.8. The phase lead is achieved by introducing a time
delay of 55.73 μs into the phase A current.
As previously stated, the serial ports of the ADE7854 work on
32, 16 or 8-bit words. As presented in Figure 37, APHCAL,
BPHCAL and CPHCAL 10-bit registers are accessed as a 16-bit
registers with 6 most significant bits padded with 0s.
yPHCAL
Figure 37. xPHCAL registers (x=A,B,C) are communicated as 16-bit registers
15
0000 00
=
⎧
⎪
⎪
⎨
⎪
⎪
⎩
phase
phase
10
_
Preliminary Technical Data
resolution
x
_
resolution
x
9
+
512
x ,
xPHCAL
x ,
≤
0
>
0
(6)
0