Cirrus Logic CS5467 - Manual (Page 16)

CS5467
16 DS714F3
4.8 Power and Energy Results
The instantaneous voltage and current samples are
multiplied to obtain the instantaneous power (P1, P2)
(see
Figure 3 and 4 ). The product is then averaged over
N conversions to compute active power (P1
AVG
,
P2
AVG
).
Apparent power (S1, S2) is the product of RMS voltage
and current as shown:
Power factor (PF1, PF2) is active power divided by ap-
parent power as shown below. The sign of the power
factor is determined by the active power.
Wideband reactive power (Q1
WB
, Q2
WB
) is calculated
by doing a vector subtraction of active power from ap-
parent power.
Quadrature power (Q1, Q2) are sample rate results ob-
tained by multiplying instantaneous current (I1, I2) by in-
stantaneous quadrature voltage (V1Q, V2Q) which are
created by phase shifting instantaneous voltage (V1,
V2
) 90 degrees using first-order integrators. (See Fig-
ure 3 and 4 ). The gain of these integrators is inversely
related to line frequency, so their gain is corrected by
the Epsilon register, which is based on line frequency.
Reactive power (Q1
Avg
, Q2
AvG
) is generated by inte-
grating the instantaneous quadrature power over N
samples.
Active power (P1
AVG
, P2
AVG
), apparent power (S1, S2),
and reactive power (Q1
AVG
, Q2
AVG
) of the two channels
are summed up and then divided by 2. The calculation
results are placed in E
PULSE
, S
PULSE
, and Q
PULSE
reg-
isters which can be configured to drive energy pulse
outputs. (See
Figure 6 .)
V1
ACOFF
(V2
ACOFF
)
I1
ACOFF
(I2
ACOFF
)
P1
OFF
(P2
OFF
)
Figure 5. Low-rate Calculations
S V
RMS
I
RMS

=
PF
P
Active
S
------------------ =
Q
WB
S 2 P
Active
2 – =
P1
AVG
÷2
P2
AVG
E
PULSE
E
ACCM
+ × +
OVF=
S1
÷2
S2
S
PULSE
S
ACCM
+ × +
OVF=
Q1
AVG
÷2
Q2
AVG
Q
PULSE
Q
ACCM
+ × +
OVF=
PulseRate
( E1, E2, E3 )
Figure 6. Two-channel Power Summation