fs6611 Fortune Semiconductor Corporation, fs6611 Datasheet - Page 12

• Manufacturer Part Number: fs6611
• Description: Energy Metering Ic With Impulse Output
• Manufacturer: Fortune Semiconductor Corporation

Rev. 1.1
13. Detail Description
13.1 Theory of Operation
The two ADCs digitize the voltage signals from the
current and voltage transducers. These ADCs are
16-bit
oversampling rate of 895 kHz. This analog input
structure greatly simplifies transducer interfacing by
providing a wide dynamic range for direct connection
to the transducer and also by simplifying the
anti-aliasing filter design. A programmable gain
stage in the current channel further facilitates easy
transducer interfacing.
The real power calculation is derived from the
instantaneous multiplication of the current and
voltage signals. In order to extract the real power
component
instantaneous real power signal is a low pass filter
output. Fig5 illustrates the instantaneous real power
signal.
instantaneous real power for non-sinusoidal current
and voltage waveforms at all power factors. All
signal processing is carried out in the digital domain
for superior stability over temperature and time.
Fig5
The low frequency output of the FS6611 is
generated
information. This low frequency inherently means a
long accumulation time between output pulses. The
output frequency is therefore proportional to the
average real power. This average real power
information can, in turn, be accumulated (e.g., by a
counter) to generate real energy information.
Because of its high output frequency and shorter
integration time, the CF output is proportional to the
instantaneous real power. This is useful for system
calibration purposes that would take place under
i (t), v( t)
V
V
V
V
2 P
2 N
1 N
1 P
Signal Flow Diagram
second
This
x 1 , x8 , x1 6 , x 3 2
by
(i.e.,
P G A
i (t ) & v( t ) S ig n al
I ns t a nt a n e o us
accumulating
scheme
order
the
A DC
A DC
Time
DC
sigma-delta
V ×
correctly
P( t)
2
I
component),
this
In s ta n t a ne o u s R e a l
DS P
P o we r Sig n a l
real
calculates
with
power
Time
CF
the
F1
F2
an
steady load conditions.
13.2 Power Factor Considerations
The method used to extract the real power
information from the instantaneous power signal (i.e.,
by low pass filtering) is still valid even when the
voltage and current signals are not in phase. Fig6
displays the unity power factor and a power factor =
0.5 conditions, i.e., current signal lagging the voltage
by 600. If we assume the voltage and current
waveforms
component of the instantaneous power signal (i.e.,
the DC term) is given by:
Fig6
Conveys Real Power Information (PF
13.3 Non-sinusoidal Voltage and Current
The real power calculation method also holds true
for non-sinusoidal current and voltage waveforms.
All voltage and current waveforms in practical
applications will have some harmonic content. Using
the Fourier Transform, instantaneous voltage and
current waveforms can be expressed in terms of
their harmonic content.
V×I
2
×
This is the correct real power calculation.
cos(60
DC Component of Instantaneous Power Signal
V× I
0V
0
0V
2
)
are
Instantaneous
Power Signal
V( t)
Instantaneous
Power Signal
 × I


V( t)
V
sinusoidal,
2
60



0
Real Power Signal
×
Instantaneous
I( t)
cos
Real Power Signal
≦
Instantaneous
I(t)
1)
( )
the
60
0
real
FS6611
power
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