CS5463
VACoff
*
+
N
+
V
*
*
*
S
V
X
Σ
÷
÷
RMS
N
√
Σ
N
Σ
*
+
IACoff
*
X
QTRIG
*
X
Σ
-
√
+
+
*
PF
I
*
*
Inverse
I
X
X
Σ
RMS
N
√
E1
*
P
PulseRate
E2
*
X
Energy-to-pulse
off
E3
+
N
*
P
P
ACTIVE
÷
Σ
N
+
Σ
X
N
*
*
Q
QAVG
÷
N
*
DENOTES REGISTER NAME.
Σ
Figure 4. Power Calculation Flow.
provides a pulse output that is proportional to the reac-
tive power or apparent power. Output E3 can also be set
to display the sign of the voltage applied to the voltage
channel or the PFMON comparator output.
quadrature power (Q). The product is then averaged
over N conversions, utilizing the formula
N
Q
∑
N
n
=
n = 1
QAvg
The apparent power (S) is the combination of the active
power and reactive power, without reference to an im-
pedance phase angle, and is calculated by the CS5463
using the following formula:
------------------------
Fundamental active (P ) and reactive (Q ) power is cal-
F
F
culated by performing a discrete Fourier transform
(DFT) at the relevant frequency on the instantaneous
voltage (V) and current (I). Epsilon is used to set the fre-
quency of the internal sine (imaginary component) and
cosine (real component) waveform generator. The har-
S = VRMS × IRMS
monic active power (P ) is calculated by subtracting the
Power Factor (PF) is the active power (P
by the apparent power (S)
) divided
H
Active
fundamental active power (P ) from the active power
F
(P
).
Active
The peak current (I
) and peak voltage (V
) are
peak
peak
PActive
------------------
PF =
the instantaneous current and voltage, respectively,
with the greatest magnitude detected during the last
computation cycle. Active, apparent, reactive and fun-
damental power are updated every computation cycle.
S
The sign of the power factor is determined by the active
power.
4.4 Linearity Performance
The linearity of the V
power-factor power measurements (before calibration)
will be within ±0.1% of reading over the ranges speci-
fied, with respect to the input voltage levels required to
The CS5463 calculates the reactive power, Q
ing trigonometric identities, giving the formula
utiliz-
Trig
, I
, active, reactive and
RMS RMS
QTrig
=
S2 – PA2ctive
cause full-scale readings in the I
and V
regis-
RMS
RMS
ters. Refer to Accuracy Specifications on page 7.
Average reactive power, Q
is generated by averag-
Avg
ing the voltage multiplied by the current with a 90o phase
shift difference between them. The 90o phase shift is re-
alized by applying an IIR digital filter in the voltage chan-
nel to obtain quadrature voltage (see Figure 3). This
filter will give exactly -90o phase shift across all frequen-
cies, and utilizes epsilon (ε) to achieve unity gain at the
line frequency.
Until the CS5463 is calibrated, the accuracy of the
CS5463 (with respect to a reference line-voltage and
line-current level on the power mains) is not guaranteed
to within ±0.1%. (See Section 7. System Calibration on
page 36.) The accuracy of the internal calculations can
often be improved by selecting a value for the Cycle
Count Register that will cause the time duration of one
computation cycle to be equal to (or very close to) a
whole number of power-line cycles (and N must be
greater than or equal to 4000).
The instantaneous quadrature voltage (V ) and current
(I) samples are multiplied to obtain the instantaneous
Q
DS678PP1
15
CIRRUS [ CIRRUS LOGIC ]
