Method and compensation circuit for crosstalk compensation

Abstract

The invention relates to a method for crosstalk compensation for output signals (S L1 (t), S L2 (t)) of at least one low-power instrument transformer for measuring electrical quantities on at least two conductors (L1, L2), at least one of which causes crosstalk, wherein: - while a sinusoidal electrical quantity is fed in on one of the conductors (L1, L2), a crosstalk amplitude and a crosstalk phase angle of the low-power instrument transformer on the other conductor (L1, L2) is determined; - cross-coupling (Cr Cap ) at a phase angle of 90° (or -90°) is determined from the product of the measured crosstalk amplitude and the sine of the measured crosstalk phase angle for each low-power instrument transformer; - cross-coupling (Cr ind ) at a phase angle of 0° (or 180°) is determined from the product of the measured crosstalk amplitude and the cosine of the measured crosstalk phase angle for each low-power instrument transformer; - to form a compensated output signal (S L1comp (t), S L2comp (t)) of each low-power instrument transformer considered, the product of the electrical quantity on the other conductor (L1, L2) and the cross-coupling (Cr ind ) at a phase angle of 0° or 180° and the product of the electrical quantity phase-shifted by 90° on the other conductor (L1, L2) and the cross-coupling (Cr cap ) at the phase angle of +90° or -90° are subtracted from an uncompensated output signal (S L1 (t), S L2 (t)) of said low-power instrument transformer.

Description

[0001] 2021PF09548 1 Description Method and compensation circuit for crosstalk compensation The invention relates to a method and a compensation circuit for crosstalk compensation, particularly in small-signal transducers. In instrument transformers according to IEC 61869, especially small-signal instrument transformers such as Rogowski coils and capacitive voltage sensors, crosstalk effects typically occur between adjacent conductors. This means, for example, that a Rogowski coil that is actually intended to measure the current in one of three phases also measures the current in the other two phases to a certain extent. This is undesirable. To prevent this, attempts can be made to design and shield the sensors in such a way that the crosstalk is as small as possible. Another possibility is to subsequently correct the measured signals mathematically.The invention is based on the object of specifying a novel method and a novel compensation circuit for crosstalk compensation for output signals of at least two small-signal converters. This object is achieved according to the invention by a method for crosstalk compensation for output signals of at least two small-signal converters having the features of claim 1 and by a compensation circuit for crosstalk compensation for output signals of at least two small-signal converters having the features of claim 6. Advantageous embodiments of the invention are the subject of the dependent claims. 2021PF09548 2 A method for crosstalk compensation for output signals of at least one small-signal converter for measuring an electrical quantity on at least two conductors, at least one of which causes crosstalk, is proposed.When a sinusoidal electrical quantity is applied to one conductor, a crosstalk amplitude and a crosstalk phase angle of the small-signal converter on the other conductor are determined. Furthermore, the crosstalk at a phase angle of +90° (or -90°) is determined from the product of the measured crosstalk amplitude and the sine of the measured crosstalk phase angle for each small-signal converter. Furthermore, the crosstalk at a phase angle of 0° (or 180°) is determined from the product of the measured crosstalk amplitude and the cosine of the measured crosstalk phase angle for each small-signal converter.According to the invention, to form a compensated output signal of each small-signal converter under consideration, the product of the electrical quantity on the other conductor and the crosstalk at a phase angle of 0° (or 180°) and the product of the electrical quantity on the other conductor, phase-shifted by 90°, and the crosstalk at a phase angle of +90° (or -90°) are subtracted from an uncompensated output signal of this small-signal converter. This method completely eliminates crosstalk. Multiple couplings can be accounted for using the appropriate mathematical matrix calculation methods. In one embodiment, the method is applied to several small-signal converters, each on a single conductor. In one embodiment, the crosstalk amplitude and the crosstalk phase angle of each small-signal converter are determined once, in particular during a routine test.2021PF09548 3 In one embodiment, the 90° phase-shifted output signal is generated by forming the time derivative of the respective output signal. In one embodiment, an integrator is provided for each conductor, wherein a signal tapped at an output of the integrator is used as the output signal of the respective conductor, wherein a signal tapped at an input of the integrator is used as the derivative. In one embodiment, a differentiator can be used to generate the derivative. According to one aspect of the present invention, a compensation circuit for crosstalk compensation for output signals of at least two measuring transducers, in particular small-signal transducers, for measuring an electrical quantity on one conductor each is proposed.The crosstalk amplitude and crosstalk phase angle of each transducer or small-signal transducer are known, for example by determining them once, especially when multiple crosstalks are correctly taken into account. This crosstalk is decomposed into a 0° (or 180°) and a 90° (or -90°) component as described above. The crosstalk at a phase angle of 0° or 180° is determined from the product of the measured crosstalk amplitude and the sine of the measured crosstalk phase angle for each transducer or small-signal transducer and is therefore known. The crosstalk at a phase angle of 0° or 180° is determined from the product of the measured crosstalk amplitude and the cosine of the measured crosstalk phase angle for each transducer or small-signal transducer and is therefore known.According to the invention, the compensation circuit is designed as analog and / or digital electronics for generating a compensated output signal from each considered measuring transducer or small-signal converter, which is configured to subtract from an uncompensated output signal of this measuring transducer or small-signal converter the product of the electrical quantity on the respective other measuring transducer or small-signal converter and the determined cross-coupling at a phase angle of 0° (or 180°) and the product of the 90° phase-shifted electrical quantity of the respective other measuring transducer or small-signal converter and the cross-coupling at a phase angle of +90° (or -90°). This compensation circuit completely eliminates crosstalk. In one embodiment, the compensation circuit comprises one element each for generating the 90° phase-shifted output signal by forming the time derivative of the respective output signal.In one embodiment, the element is designed as an integrator or as a differentiator. According to one aspect of the present invention, a measuring circuit is proposed, comprising at least two small-signal converters, each for measuring an electrical quantity on a respective conductor, and a compensation circuit as described above, wherein the small-signal converters are configured to use the time derivative of the signal to be measured. For example, the small-signal converters can use Rogowski coils with integrators. In small-signal converters that use sensors that output the time derivative of the signal to be measured (e.g., Rogowski coils), the time derivative is already present, making implementation particularly simple.The properties, features, and advantages of this invention described above, as well as the manner in which they are achieved, will become clearer and more easily understandable in connection with the following description of exemplary embodiments, which are explained in more detail in conjunction with a drawing. FIG. 1 shows a schematic view of a compensation circuit for output signals from two small-signal converters for measuring an electrical quantity. The sole FIG. 1 is a schematic view of a compensation circuit 1 for output signals from two small-signal converters for measuring an electrical quantity, in particular current or voltage, on a respective conductor L1, L2. The compensation circuit 1 serves to computationally compensate for the crosstalk between the two channels or conductors L1, L2.According to the invention, crosstalk is compensated for at phase angles of 0° (or 180°) and +90° (or -90°). The general mathematical equation is: ^^. ^^ ^ ^^^ ൌ ^^ ^ఠ௧ ^ ^ ^^ ^ ^^ ^ ൌ ^^^^ ^ ^^ ^ ൫ ^^ ^^^^ௗ ^ ^^ ^^ ^^^^^൯S L1 (t) is the current or voltage in a specific conductor, for example, conductor L1. Cr(t) is the overcoupling measured in another conductor, for example, conductor L2. Cr ind is an overcoupling with a phase angle of 0° (or 180°). Cr cap is an overcoupling with a phase angle of +90° (or -90°). A possible cause of the overcoupling Cr cap is the capacitive coupling of a current-proportional voltage in a Rogowski coil. The Cr indInduced voltage 2021PF09548 6 causes a current flow that induces a voltage via the coil's self-inductance. The adjacent conductor induces eddy currents in an expanded metal cage of a sensor ring. These generate a radial magnetic field that couples a voltage into the Rogowski coil's non-radial windings. During a measurement (routine test) of the small-signal converters, a crosstalk amplitude CTA and a crosstalk phase angle CTW are determined and provided to the user. The following applies before compensation during the measurement: The compensation device can be configured as analog or digital electronics to eliminate the overcoupling in an output signal S(t). A common, simple method is: That is, to form the compensated output signal ^^^ଶ^^^^ ^ ^^ ^ of the conductor L2 is from the uncompensated output signal ^^ ^ଶ^ ^^^ of the conductor L2 the product of the uncompensated output signal ^^ ^^ ^ ^^^ of the other conductor L1 and the measured crosstalk amplitude CTA. After compensation, the following applies: 90° 2021PF09548 7 In a method improved according to the invention, the following applies: That is, to form the compensated output signal ^^^ଶ^^^^ ^ ^^ ^ of the conductor L2 are from the uncompensated output signal ^^ ^ଶ ^ ^^^ of the conductor L2 the product of the electrical quantity ^^ ^^ ^ ^^^ on the other conductor L1 and the overcoupling ^^ ^^ ^^ௗ at a phase angle of 0° (or 180°) and the product of the electrical quantity phase-shifted by 90° ^^ ^^^^ ^ ^^ ^ on the other conductor L1 and the cross-coupling ^^ ^^^^^at a phase angle of +90° (or -90°). The cross-coupling ^^ ^^ ^^^At a phase angle of 0° or 180°, CTA is determined from the product of the measured crosstalk amplitude and the sine of the measured crosstalk phase angle. The crosstalk ^^ ^^ ^^ௗ At a phase angle of 0° or 180°, the crosstalk amplitude CTA is determined from the product of the measured crosstalk amplitude CTA and the cosine of the measured crosstalk phase angle CTW. After compensation, the following applies: ^^ ^ ^^ ^ ൌ ^^ ^ఠ௧ ൫ ^^ ^^^^ௗ ^ ^^ ^^ ^^^^^൯ െ ^^ ^^^^ௗ ^^ ^ఠ௧ െ ^^ ^^ ^^^^^ ^^ ^ఠ௧ ൌ 0 [8] This method completely eliminates crosstalk. However, it requires a 90° phase-shifted output signal. ^^ ^ ^^^ of the other conductor L1. This can be done, for example, by forming the time derivative ^^ ^^ ′^ ^^^ of the output signal ^^ ^^^ ^^^are generated. In small-signal converters that use sensors that use the time derivative of the signal to be measured (for example, Rogowski coils and integrators), this time derivative is already present and thus implementation is particularly simple. 2021PF09548 8 For example, an integration element 2.1, 2.2 can be provided for each channel or conductor L1, L2, with the output signal ^^ ^^ ^ ^^^, ^^ ^ଶ ^ ^^^ of the respective conductor L1, L2 after the integration term 2.1, 2.2 and the derivative ^^ ^^ ^^ ^ ^^^, ^^ ^^ ^ଶ^ ^^^ is tapped before the integration element 2.1, 2.2. The method according to the invention achieves significantly improved interference suppression. Multiple couplings can be taken into account using the mathematical matrix calculation methods described below. Three measuring transducers, for example, three small-signal transducers, measure the following output signals on three phases A, B, C or conductors, for example: ^^ ^^^^ These output signals result from the real currents taking into account the crosstalk Cr according to the following equation [9]: To determine the real currents from the measured currents, the inverse matrix is ​​used: For example, with 3.6% crosstalk in all three phases, the inverse matrix is: 1.0025 െ 0.0348 െ 0.0348 െ0.0348 1.0025 െ 0.0348 ൩

[0011] 0.0348 0.0348 1.0025Although the invention has been illustrated and described in detail by means of preferred embodiments, the invention is not limited by the disclosed examples 2021PF09548 9 and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

Claims

2021PF09548 10 Patent claims 1. Method for crosstalk compensation for output signals ( ^^ ^^ ^ ^^^, ^^ ^ଶ ^ ^^^) at least one small-signal converter for measuring electrical quantities on at least two conductors (L1, L2), at least one of which causes crosstalk, - wherein when a sinusoidal electrical quantity is fed into one of the conductors (L1, L2), a crosstalk amplitude and a crosstalk phase angle of the small-signal converter on the other conductor (L1, L2) are determined, - wherein an overcoupling ( ^^ ^^ ^^^ ^ at a phase angle of 90° (or -90°) is determined from the product of the measured crosstalk amplitude and the sine of the measured crosstalk phase angle for each small-signal converter, - where an overcoupling ( ^^ ^^ ^^ௗ^ at a phase angle of 0° (or 180°) is determined from the product of the measured crosstalk amplitude and the cosine of the measured crosstalk phase angle for each small-signal converter, - whereby to form a compensated output signal considered small signal converter from an uncompensated output signal ( ^^ ^^ ^ ^^^, ^^ ^ଶ ^ ^^^) of this small signal converter the product of the electrical quantity on the other conductor (L1, L2) and the coupling ^ ^^ ^^ ^^ௗ ) at a phase angle of 0° or 180° and the product of the electrical quantity on the other conductor (L1, L2) with a phase shift of 90° and the coupling ( ^^ ^^ ^^^) is subtracted at a phase angle of +90° or -90°.

2. Method according to claim 1, wherein the crosstalk amplitude and the crosstalk phase angle of each small-signal converter are determined once, in particular during a routine test.

3. Method according to claim 1 or 2, wherein the 90° phase-shifted output signal ( ^^ ^^ ^^ ^ ^^^, ^^ ^^ ^ଶ ^ ^^^) by forming 2021PF09548 11 a temporal derivative ( ^^ ^^ ′^ ^^^, ^^ ^ଶ ′^ ^^^) of the respective output signal ( ^^ ^^ ^ ^^^, ^^ ^ଶ ^ ^^^) is generated.

4. Method according to claim 3, wherein an integration element (2.1, 2.2) is provided for each conductor (L1, L2), wherein the output signal ( ^^ ^^ ^ ^^^, ^^ ^ଶ ^ ^^^) of the respective conductor (L1, L2) a signal tapped at an output of the integration element (2.1, 2.2) is used, wherein as derivative ( ^^ ^^ ′^ ^^^, ^^ ^ଶ′^ ^^^) a signal tapped at an input of the integration element (2.1, 2.2), in particular the output signal ( ^^ ^^) phase-shifted by 90° ^^ ^ ^^^, ^^ ^^ ^ଶ ^ ^^^).

5. The method according to claim 3, wherein a differentiator is used to generate the derivative.

6. Compensation circuit (1) for crosstalk compensation for output signals ( ^^ ^^ ^ ^^^, ^^ ^ଶ ^ ^^^) at least one small-signal converter for measuring an electrical quantity on at least two conductors (L1, L2), at least one of which causes crosstalk, - wherein a crosstalk amplitude and a crosstalk phase angle of each small-signal converter are known, - wherein the crosstalk ( ^^ ^^ ^^^ ^ at a phase angle of 90° or -90° is known from the product of the measured crosstalk amplitude and the sine of the measured crosstalk phase angle for each small signal converter, - where the overcoupling ( ^^ ^^ ^^ௗ^ at a phase angle of 0° or 180° is known from the product of the measured crosstalk amplitude and the cosine of the measured crosstalk phase angle for each small-signal converter, - wherein the compensation circuit (1) is designed as an analogue or digital electronics for forming a compensated output signal ( ^^^^^^^^ ^ ^^ ^ , ^^^ଶ^^^^ ^ ^^ ^ ) of each small signal converter under consideration and is configured to operate from an uncompensated output signal ( ^^ ^^ ^ ^^^, ^^ ^ଶ ^ ^^^) of this small signal converter the product of the electrical quantity on the other conductor (L1, L2) and the coupling 2021PF09548 12 ^ ^^ ^^ ^^ௗ ) at a phase angle of 0° or 180° and the product of the electrical quantity on the other conductor (L1, L2) which is phase-shifted by 90° and the coupling ( ^^ ^^ ^^^) at a phase angle of +90° or -90°.

7. Compensation circuit (1) according to claim 6, comprising one element each for generating the 90° phase-shifted output signal ( ^^ ^^ ^^ ^ ^^^, ^^ ^^ ^ଶ ^ ^^^) by forming the time derivative ( ^^ ^^ ′^ ^^^, ^^ ^ଶ ′^ ^^^) of the respective output signal ( ^^ ^^ ^ ^^^, ^^ ^ଶ ^ ^^^).

8. Compensation circuit (1) according to claim 7, wherein the element is designed as an integration element (2.1, 2.2) or as a differentiator.

9. Measuring circuit, comprising at least two small-signal converters for measuring an electrical quantity on a respective conductor (L1, L2) and a compensation circuit (1) according to one of claims 6 to 8, wherein the small-signal converters are configured to measure the time derivative ( ^^ ^^ ′^ ^^^, ^^ ^ଶ ′^ ^^^) of the signal to be measured, in particular the 90° phase-shifted output signal ( ^^ ^^ ^^ ^ ^^^, ^^ ^^^ଶ ^ ^^^).

10. Measuring circuit according to claim 9, wherein the small-signal converters are arranged for use with Rogowski coils with integrators or wherein the small-signal converters are designed as capacitors with displacement current measurement, as C-dividers or RC dividers.

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