U.S. patent application number 12/617404 was filed with the patent office on 2010-03-04 for polyphase electric energy meter.
This patent application is currently assigned to Texas Instruments Deutschland GmbH. Invention is credited to Volker Rzehak.
Application Number | 20100052962 12/617404 |
Document ID | / |
Family ID | 39477692 |
Filed Date | 2010-03-04 |
United States Patent
Application |
20100052962 |
Kind Code |
A1 |
Rzehak; Volker |
March 4, 2010 |
POLYPHASE ELECTRIC ENERGY METER
Abstract
A polyphase electric energy meter comprises a microcontroller
with a front end that converts analog current input signals and
analog voltage input signals to digital current and voltage samples
for processing by the microcontroller. The front end includes
separate input channels, each for one of the current input signals
with a sigma-delta modulator followed by a decimation filter. The
front end further includes a common input channel for all voltage
input signals with a multiplexer, an analog-to-digital converter
and a de-multiplexer. The separate input channels and the common
input channel provide the digital current and voltage samples for
processing by the microcontroller.
Inventors: |
Rzehak; Volker; (Ergolding,
DE) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
US
|
Assignee: |
Texas Instruments Deutschland
GmbH
Freising
DE
|
Family ID: |
39477692 |
Appl. No.: |
12/617404 |
Filed: |
November 12, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11963546 |
Dec 21, 2007 |
|
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12617404 |
|
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Current U.S.
Class: |
341/143 ;
341/155 |
Current CPC
Class: |
G01R 21/133
20130101 |
Class at
Publication: |
341/143 ;
341/155 |
International
Class: |
H03M 3/00 20060101
H03M003/00; H03M 1/12 20060101 H03M001/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 5, 2007 |
DE |
10 2007 001 221.9 |
Claims
1-6. (canceled)
7. A polyphase analog front end comprising: a plurality of
programmable gain amplifiers (PGA), wherein each PGA is adapted to
receive a current signal; a multiplexer that is adapted to receive
a plurality of voltage signals; a plurality of sigma-delta
modulators, wherein each sigma-delta modulator is coupled to at
least one of the PGAs; an analog-to-digital converter (ADC) that is
coupled to the multiplexer; and a synchronizer that is coupled to
each of the sigma-delta modulators and to the ADC.
8. The polyphase analog front end of claim 7, wherein the polyphase
analog front end further comprises a decimation filter that is
coupled to each sigma-delta modulator.
9. The polyphase analog front end of claim 7, wherein the polyphase
analog front end further comprises a demultiplexer that is coupled
to the ADC.
10. A system comprising: a source having a plurality of phases; a
load that is coupled to each phase of the source; a plurality of
current transformers, wherein each transformer is coupled to at
least one of the phases; a plurality of voltage dividers, wherein
each voltage divider is coupled to at least one of the phases; a
microcontroller having an analog front end, wherein the analog
front end includes: a plurality of programmable gain amplifiers
(PGA), wherein each PGA is coupled to at least one of the
transformers; a multiplexer that is coupled to each of the voltage
dividers; a plurality of sigma-delta modulators, wherein each
sigma-delta modulator is coupled to at least one of the PGAs; an
analog-to-digital converter (ADC) that is coupled to the
multiplexer; and a synchronizer that is coupled to each of the
sigma-delta modulators and to the ADC.
11. The system of claim 10, wherein the system further comprises a
decimation filter that is coupled to each sigma-delta
modulator.
12. The system of claim 10, wherein the system further comprises a
demultiplexer that is coupled to the ADC.
Description
[0001] This application is a divisional of application Ser. No.
11/963,546, filed Dec. 21, 2007, which claims priority to German
Patent Application No. DE 10 2007 001 221.9, filed Jan. 5, 2007,
the entireties incorporated herein by reference.
[0002] The invention relates to a polyphase electric energy
meter.
BACKGROUND
[0003] In a typical three-phase electric energy meter current input
signals are derived from the three phases with current transformers
and voltage input signals are derived from the three phases with a
resistive voltage divider. The current and voltage input signals
are sampled and the current samples are multiplied with the voltage
samples to obtain electric energy samples which are cumulated to
provide an indication representative of consumed electric
energy.
[0004] In an advanced electric energy meter the current and voltage
input signals are converted to digital input samples for further
processing by a microcontroller. One straight-forward approach is
to use separate input channels, each for one of the three current
or voltage input signals and each with an analog-to-digital
converter (ADC). In this "synchronous" approach all input signals
are processed in parallel and synchronously. With high accuracy
requirements over a large dynamic range, e.g. smaller than 1% over
a range of 1:2000, high resolution (at least 16-bit) ADCs are
needed that are usually implemented with a sigma-delta modulator
followed by a decimation filter. While the approach promises to be
successful, it requires a large die space and is expensive. An
alternative approach is to use a single high resolution ADC with an
input multiplexer and an output de-multiplexer. In this
"sequential" approach the current and voltage input signals are
sequentially switched to the input of the ADC and the resulting
digital samples are corrected in phase to compensate for the delays
introduced by the sequential sampling. The sequential approach
needs less die space, but requires a complex analog-to-digital
converter to combine the high resolution requirements with the need
to multiplex through all current and voltage signals.
SUMMARY
[0005] The invention provides a polyphase electric energy meter
comprising a microcontroller with a front end that offers high
resolution at moderate die space requirements.
[0006] Specifically, the polyphase electric energy meter of the
invention comprises a microcontroller with a front end that
converts analog current input signals and analog voltage input
signals to digital current and voltage samples for processing by
the microcontroller. The front end includes separate input
channels, each for one of the current input signals with a high
resolution analog-to-digital converter, preferably a sigma-delta
modulator followed by a decimation filter. The front end further
includes a common input channel for all voltage input signals with
a multiplexer, an analog-to-digital converter and a de-multiplexer.
The separate input channels and the common input channel provide
the digital current and voltage samples for processing by the
microcontroller.
[0007] The invention is based on the understanding that only the
current input signals, due to their possibly high dynamic range,
need an analog-to-digital conversion at a high resolution and that
the voltage input signals with their small dynamic range can be
sampled sequentially at a moderate resolution. Thus, for a
three-phase meter, only three high resolution are needed ADCs for
the three current input signals and a single ADC of a moderate
resolution for the voltage input signals.
[0008] In a preferred embodiment, the multiplexer has one input for
each voltage input signal and at least one additional input for an
auxiliary input signal such as a temperature signal or a battery
voltage signal. Since the voltage samples are taken at a moderate
rate, the multiplexer can be implemented with additional time slots
so that more than just the voltage input signals can be processed
in the single common input channel.
[0009] When an application requires the neutral current to be
measured in addition to the three live currents, the front end
comprises three of the separate input channels, each for one of
three current phases, and an additional separate input channel for
the neutral current input signal. Alternatively the multiplexed ADC
can be used if a reduction of accuracy for the conversion of the
neutral current is acceptable.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Further advantages and features of the invention will become
apparent from the following detailed description with reference to
the appended drawings, wherein:
[0011] FIG. 1 is a schematic block diagram of a microcontroller
incorporating a front-end; and
[0012] FIG. 2 is a block diagram of a polyphase electric energy
meter implemented with a microcontroller as illustrated in FIG.
1.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
[0013] The microcontroller 10 generally shown in FIG. 1 includes a
front-end 12 which has a plurality of analog inputs and a plurality
of digital outputs. The analog inputs are adapted to receive
external analog input signals and the digital outputs are internal
to the microcontroller for further processing therein.
[0014] With reference to FIG. 2, the front-end 12 includes three
parallel input channels, each with a fully differential
programmable gain amplifier PGA and a sigma-delta modulator
followed by a decimation low-pass filter. The differential inputs
of the amplifier PGA receive analog current input signals I.sub.A,
I.sub.B and I.sub.C, respectively, and the decimation filters
provide corresponding digital current output samples I.sub.AD,
I.sub.BD and I.sub.CD, respectively.
[0015] The front-end 12 further includes a multiplexer MUX with
four analog inputs receiving voltage input signals V.sub.A,
V.sub.B, V.sub.C and V.sub.N, respectively, and a number of further
optional inputs for application of auxiliary external or internal
signals. The output of multiplexer MUX is connected to the input of
an analog-to-digital converter ADC, the digital output of which is
connected to a de-multiplexer De-MUX. the de-multiplexer De-MUX
provides digital voltage samples V.sub.AD, V.sub.BD, V.sub.CD, and
V.sub.ND, respectively, and one or more optional parameter samples
P.
[0016] A block "Synchronization" in the front-end 12 synchronizes
operation of all sigma-delta modulators, of the multiplexer MUX and
de-multiplexer De-MUX, and of the ADC.
[0017] The electric energy meter is connected to the three phases
A, B and C of a three-phase power source 14 which feeds a
three-phase load 16. Specifically, each phase has an associated
current transformer CT.sub.A, CT.sub.B and CT.sub.C, respectively,
and a resistive voltage divider VD.sub.A, VD.sub.B and VD.sub.C,
respectively. In a well-known manner, the current transformers
CT.sub.A, CT.sub.B and CT.sub.C generate the current input signals
I.sub.A, I.sub.B and I.sub.C, and the voltage dividers VD.sub.A,
VD.sub.B and VD.sub.C provide the voltage input signals V.sub.A,
V.sub.B, V.sub.C. The neutral voltage signal V.sub.N is applied
directly to a corresponding input of the multiplexer MUX. Optional
input signals such as external parameters (temperature, battery
voltage, etc.) or internal analog signals are applied to further
inputs of multiplexer MUX.
[0018] In operation, the analog current and voltage input signals
are converted to digital samples for further processing by the
microcontroller. Specifically, the current input signals are
analog-to-digital converted at a high resolution (e.g., at least
16-bit resolution) in parallel and synchronously by the three
separate input channels, each with a programmable gain amplifier
and a sigma-delta modulator followed by a decimation filter. Thus,
three digital current samples I.sub.AD, I.sub.BD and I.sub.CD are
available at the output of the front-end 12. In turn, the voltage
input signals are sequentially applied to the ADC, which may have a
moderate resolution of, e.g., 12 bits, and corresponding digital
voltage samples V.sub.AD, V.sub.BD and V.sub.CD are available at
the outputs of the de-multiplexer De-MUX.
[0019] The digital current and voltage samples at the output of the
front-end 12 are further processed by the microcontroller by means
of software which accounts for the delays of the multiplexed
voltage samples.
[0020] In some applications, an additional input channel is
included with an associated further current transformer placed in
the neutral line. This additional input channel may be similar to
the three separate input channels and include a programmable gain
amplifier followed by a sigma-delta modulator and a low-pass
decimation filter.
[0021] Those skilled in the art to which the invention relates will
appreciate that the described embodiments are merely representative
embodiments and that there are variations of the described
embodiments and other embodiments within the scope of the claimed
invention.
* * * * *