ade7880 Analog Devices, Inc., ade7880 Datasheet - Page 53

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

Preliminary Technical Data
complement register with the MSB indicating the polarity of the
power factor. Each LSB of the APF, BPF and CPF registers
equates to a weight of 2
0x7FFF equating to a power factor value of 1. The minimum
register value of 0x8000 corresponds to a power factor of -1. If
because of offset and gain calibrations, the power factor is
outside the -1 to +1 range, the result is set at -1 or +1 depending
on the sign of the fundamental reactive power.
By default the instantaneous total phase active and apparent
powers are used to calculate the power factor and the registers
are updated at a rate of 8KHz. The sign bit is taken from the
instantaneous fundamental phase reactive energy measurement
on each phase.
Should a measurement with more averaging be required, the
ADE7880 provides an option of using the line cycle
accumulation measurement on the active and apparent energies
to determine the power factor. This option provides a more
stable power factor reading. This mode is enabled by setting
the PFMODE bit (bit 7) in the LCYCMODE register (Address
0xE702). When this mode is enabled the line cycle
accumulation mode must be enabled on both the active and
apparent energies. This is done by setting the xLWATT and
xLVA bits in the LCYCMODE register (Address 0xE702). The
update rate of the power factor measurement will now be an
integral number of half line cycles that can be programmed into
the LINECYC register (Address 0xE60C). For full details on
setting up the line cycle accumulation mode see the Line Cycle
Active Energy Accumulation Mode and Line Cycle Apparent
Energy Accumulation Mode sections.
Note that the power factor measurement is effected by the no
load condition if it is enabled – see No Load Condition section.
If the apparent energy no load is true, then the power factor
measurement is set to 1. If the no load condition based on total
active and reactive energies is true, the power factor
measurement is set at 0.
The ADE7880 also computes the power factor on the
fundamental and harmonic components based on the
fundamental and harmonic active, reactive and apparent
powers. See Harmonics calculations section for details.
HARMONICS CALCULATIONS
The ADE7880 contains a harmonic engine that analyzes one
phase at a time. Harmonic information is computed with a no
attenuation pass band of 2.8 KHz (corresponding to a -3dB
bandwidth of 3.3 KHz) and it is specified for line frequencies
between 45Hz and 66Hz. Neutral current can also be analyzed
simultaneously with the sum of the phase currents. Figure 57
presents a synthesized diagram of the harmonic engine, its
settings and its output registers.
-15
, hence the maximum register value of
Rev. PrE | Page 53 of 103
Theory of Operation
Let’s consider an nonsinusoidal ac system supplied by a voltage,
v(t) that consumes the current i(t). Then
where:
V
harmonic.
Φ
ω is the angular velocity at the fundamental (line) frequency f.
The ADE7880 harmonics calculations are specified for line
frequencies between 45Hz and 66Hz. The phase nominal
voltage used as time base must have an amplitude greater than
20% of full scale.
The number of harmonics N that can be analyzed within the 2.8
KHz pass band is the whole number of 2800/f. The absolute
maximum number of harmonics accepted by the ADE7880 is
63.
When the ADE7880 analyzes a phase, the following metering
quantities are computed:
-fundamental phase current rms: I
-fundamental phase voltage rms: V
-rms of up to 3 harmonics of phase current:
I
-rms of up to 3 harmonics of phase voltage:
V
- fundamental phase active power
- fundamental phase reactive power
-fundamental phase apparent power
-power factor of the fundamental
-active power of up to 3 harmonics:
Q
N
P
S =
P
P
x
pf
, I
k
1
1
x
x
k
y
1
, I
, V
, γ
1
=
=
y
=
=
=
, I
k
k
=
v
t i



y
V
V
V
are rms voltage and current, respectively, of each
V
V
) (
are the phase delays of each harmonic.
, V
z
) (
2800
1
sgn
, x,y,z=2, 3,…, N
1
x
t
1
y
I
I
I
I
1
I
f
1
=
z
1
x
=
, x,y,z=2, 3,…, N
y
cos
sin
( )
cos
∑
k
cos
Q
∞
∑
k
=



∞
=
1
1
1
I
, N≤63.
(
(
V
(
ϕ
ϕ
k
ϕ
(
ϕ
×
k
1
1
x
y
2
−
−
S
P
−
2
−
1
1
sin
γ
γ
γ
sin
γ
1
1
x
)
y
)
(
)
k
)
(kωt + φ
, x=2, 3,…, N
t ω
, y=2, 3,…, N
+
γ
k
)
k
)
1
1
ADE7880
(47)