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參數(shù)資料
| 型號(hào)： | AD7751 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Energy Metering IC with On-Chip Fault Detection(高精度容錯(cuò)電子能量測(cè)量芯片) |
| 中文描述： | 電能計(jì)量IC片故障檢測(cè)（高精度容錯(cuò)電子能量測(cè)量芯片） |
| 文件頁數(shù)： | 10/16頁 |
| 文件大?。?/td> | 287K |
| 代理商： | AD7751 |
AD7751
10
PRELIM B1 1098
60°
Voltage
Current
Instantaneous
Power Signal
Instantaneous Real
Power Signal
V. I. Cos (60°)
2
Voltage
Current
Instantaneous
Power Signal
Instantaneous Real
Power Signal
2
V. I.
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. Figure 7 below displays the unity power factor condi-
tion and a dPF (Displacement Power Factor) = 0.5, i.e.,
current signal lagging the voltage by 60° . If we assume the
voltage and current waveforms are sinusoidal then the real
power component of the instantaneous power signal (i.e., the
dc term) is given by (V.I/2).Cos(60°).
Figure 7. dc component of Instantaneous Power Signal conveys
Real Power Information PF < 1
NONSINUSOIDAL VOLTAGE AND CURRENT
The real power calculation method also holds true for non
sinusoidal current and voltage waveforms. All voltage and
current waveforms in a 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.
∑
α
+
ω
+
=
0
h
h
0
)
t
.sin(h
V
.
V
v(t)
(1)
Where: v(t) is the instantaneous voltage, V
o
is the average
value, V
h
is the rms value of voltage harmonic h and
α
h
is the
phase angle of the voltage harmonic.
i(t)
I
2.
I .sin(h t
)
0
h
=
+
+
∑
β
(2)
Where:i(t) is the instantaneous current, I
o
is the dc component,
I
h
is the rms value of current harmonic h and
β
h
is the phase
angle of the current harmonic.
Using equations 1 and 2 the real power P can be expressed in
terms of its fundamental real power (P
1
) and harmonic real
power (P
H
).
P
P
P
H
=
+
1
where:
P
V I
1
1
1
=
=
φ
α
β
and
1
1
1
1
φ
(3)
P
V I
h
H
h
h
h
h
h
=
=
≠
∑
α
.
cos
φ
φ
β
1
(4)
As can be seen from equation 4 above, a harmonic real power
component is generated for every harmonic provided that
harmonic is present in both the voltage and current waveforms.
The Power Factor calculation has previously been shown to
be accurate in the case of a pure sinusoid, therefore the
harmonic real power must also correctly account for Power
Factor since it is made up of a series of pure sinusoids.
Note the input Bandwidth of the analog inputs is 3.5kHz with a
master clock frequency of 3.5795MHz.
Digital to Frequency Conversion.
As previously described the digital output of the Low Pass
Filter after multiplication contains the real power information.
However since this LPF is not an ideal "brick wall" filter
implementation, the output signal also contains attenuated
components at the line frequency and its harmonics ,i.e.,
Cos(h
.ω
.t) where h = 1,2,3,...etc. The dominating harmonic
will be at twice the line frequency, i.e., Cos(2
ω
.t) and this is
due the instantaneous power signal. Figure 8 shows the
instantaneous real power signal which still contains a significant
amount of instantaneous power information, i.e., Cos(2
ω
.t).
This signal is then passed to the digital to frequency converter
where it is integrated (accumulated) over time in order to
produce an output frequency. This accumulation of the signal
will suppress or average out any non dc components in the
instantaneous real power signal. The average value of a sinusoi-
dal signal is zero. Hence the frequency generated by the
AD7751 is proportional to the average real power. Figure 8
below shows the digital to frequency conversion for steady load
conditions, i.e., constant voltage and current.
MULTIPLIER
LPF
Σ
DIGITAL TO
FREQUENCY
F1
F2
FOUT
V
I
DIGITAL TO
FREQUENCY
V.I
2
frequency (rad/s)
Instantaneous Real Power Signal (frequency domain)
ω
2
ω
0
LPF to remove
Real Power
(dc term)
Cos(2
.t)
attenuated by
LPF
time
time
F1
FOUT
Σ
Figure 8. Real Power to Frequency Conversion
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AD7751AAN | 制造商:Analog Devices 功能描述: 制造商:Rochester Electronics LLC 功能描述:PRODUCT TO FREQUENCY CONV - Bulk |
| AD7751AAN-REF | 制造商:Analog Devices 功能描述: |
| AD7751AARS | 制造商:Rochester Electronics LLC 功能描述:PRODUCT TO FREQUENCY CONV - Bulk |
| AD7751ABRS | 制造商:AD 制造商全稱:Analog Devices 功能描述:Energy Metering IC With On-Chip Fault Detection |
| AD7751AN | 制造商:Rochester Electronics LLC 功能描述:PRODUCT TO FREQUENCY CONV - Bulk |
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