Electric circuit arrangement and a method for a galvanically insulated, AC/DC sensitive differential-current measurement having high resolution

Abstract

An electric circuit arrangement and a measuring method for a galvanically insulated, AC/DC sensitive differential current measurement having a high resolution having: a toroid current transformer having at least one secondary winding for detecting a differential current; a driver circuit for powering the secondary winding; a first oscillator circuit for controlling the driver circuit and for generating a time-modulated binary oscillator signal having dwell times in a state 1 and a state 2; a second oscillator circuit for determining the corresponding dwell time in the states 1 and 2 in high resolution by means of a clock signal having a clock rate independent of the oscillator signal; an evaluation device for evaluating the dwell time; and a data interface for outputting a differential-current measuring value; the driver circuit and the second oscillator circuit each being realized as structurally individual, integrated circuits.

Claims

1. An electric circuit arrangement (2) for a galvanically insulated, AC/DC sensitive differential-current measurement, the electric circuit arrangement (2) comprising a toroid current transformer (4) having at least one secondary winding (6) for detecting a differential current (I.sub.d), a driver circuit (12) for powering the secondary winding (6), a first oscillator circuit (22) for controlling the driver circuit (12) and for generating a time-modulated binary oscillator signal (V) having dwell times (T.sub.h, T.sub.1) in a state 1 (S.sub.1) and a state 2 (S.sub.2), a second oscillator circuit (32) for determining the corresponding dwell time (T.sub.h, T.sub.1) in the states 1 and 2 in high resolution of smaller than 1 ns by means of a clock signal (C) having a clock rate independent of the oscillator signal (V), an evaluation device (42) for evaluating the dwell time (T.sub.h, T.sub.1), and a data interface (52) for outputting a differential-current measuring value (I.sub.m, I′.sub.m), the driver circuit (12) and the second oscillator circuit (32) each being realized as structurally individual, integrated circuits.

2. The electric circuit arrangement (2) according to claim 1, wherein the second oscillator circuit (32) consists of a closed series circuit of inverting elements having at least one back coupling (34).

3. The electric circuit arrangement (2) according to claim 1, wherein the evaluation device (42) is configurated as a digital circuit (44) for generating a differential-current measuring value (I.sub.m) from the dwell times (T.sub.h, T.sub.1).

4. The electric circuit arrangement (2) according to claim 1, wherein the data interface (52) is configured as an analog and/or digital signal for outputting the differential-current measuring value (I.sub.m, I′.sub.m).

5. A measuring method for a galvanically insulated, AC/DC sensitive differential-current measurement, the measuring method comprising the following steps: detecting a differential current (I.sub.d) by means of a toroid current transformer (4) having at least one secondary winding (6), powering the secondary winding (6) by means of a driver circuit (12) which is configured as a structurally individual, integrated circuit, controlling the driver circuit (12) and generating a time-modulated binary oscillator signal (V) having dwell times (T.sub.h, T.sub.1) in a state 1 (S.sub.1) and in a state 2 (S.sub.2) by means of a first oscillator circuit (22), determining the corresponding dwell time (T.sub.h, T.sub.1) in the states 1 and 2 (S.sub.1, S.sub.2) by means of a second oscillator circuit (32), which is realized as a structurally individual, integrated circuit, by generating a clock signal (C) having a clock rate which is independent of the oscillator signal (V) and causes a high temporal resolution of smaller than 1 ns, evaluating the dwell times (T.sub.h, T.sub.1) by means of an evaluation device (42), outputting a differential-current measuring value (I.sub.m, I′.sub.m) by means of a data interface.

6. The measuring method according to claim 5, wherein the clock signal (C) is generated by means of a closed series circuit of inverting elements having at least one back coupling (34).

7. The measuring method according to claim 5, wherein the differential-current measuring value (I.sub.m) is computed in the evaluation device (42) from the dwell times (T.sub.h, T.sub.1) by means of digital filtering algorithms.

8. The measuring method according to claim 5, wherein the differential-current measuring value (I.sub.m, I′.sub.m) is output as an analog and/or digital signal by means of the data interface (52).

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

(1) In the figures,

(2) FIG. 1 shows a magnetizing curve of a toroid current transformer in a schematic illustration;

(3) FIG. 2 shows a functional block diagram of the electric circuit arrangement according to the invention;

(4) FIG. 3 shows digital signal processing of the oscillator signal.

DETAILED DESCRIPTION

(5) FIG. 1 shows the passing through the magnetizing curve of toroid current transformer 4 (FIG. 2) in a schematic manner.

(6) The magnetizing curve illustrates magnetic induction B in dependence of magnetic field strength H and in this instance consists of a linear section which extends between an upper and a lower saturation range.

(7) Starting from operating point AP predetermined by differential current I.sub.d (FIG. 2), an increasing current in the secondary winding (secondary current) first passes through the magnetizing curve in the direction of the positive saturation state. In operating point AP, the value of the current flowing in the secondary winding is zero so that operating point AP is only determined by differential current I.sub.d flowing on the supply side. The reaching of the saturation range is detected by an absolute measurement of the secondary current and by a comparison to a sufficiently high saturation threshold, which lies in the saturation range of the core material. If the secondary current exceeds this saturation threshold, the first oscillator circuit toggles. The polarity of the secondary winding is inverted and magnetic flux B in the core is driven out of the saturation range into the corresponding opposite saturation.

(8) Passing through the magnetizing curve makes apparent that the duration of an increasing/decreasing secondary current, i.e., dwell times T.sub.h, T.sub.1 (FIG. 3) depends on the position of operating point AP on the magnetizing curve. Knowledge of the zero point and the changeover points of the secondary current can therefore yield a time-modulated binary oscillator signal V (FIG. 3) having dwell times T.sub.h, T.sub.1 in a state 1 S.sub.1 and a state 2 S.sub.2 (FIG. 3).

(9) FIG. 2 shows a functional block diagram of electric circuit arrangement 2 according to the invention.

(10) Differential current I.sub.d (primary current) to be measured is detected by a toroid current transformer 4, which leads to a specific operating point AP being set on the magnetizing curve (FIG. 1).

(11) For passing through the magnetizing curve in both directions, toroid current transformer 4 comprises a secondary winding 6 which is powered by a driver circuit 12. Magnetic field strength H tied to the current flow in secondary winding 6 generates magnetic induction B in the core material.

(12) Driver circuit 12 is controlled by a first oscillator circuit 22, an oscillator signal V being computed in secondary winding 6 by evaluating the zero points and the flipflops of the secondary current.

(13) The passing of the magnetizing curve is thus mapped in dwell times T.sub.h, T.sub.1 (FIG. 3) having a state 1 S.sub.1 (high phase) and having a state 2 S.sub.2 (low phase), dwell times T.sub.h, T.sub.1 corresponding to the passed paths on the magnetizing curves being yielded in dependence of operating point AP prespecified by differential current I.sub.d.

(14) If, for example, operating point AP is close to the upper saturation point on the linear path section of the magnetizing curve as a consequence of a relatively high differential current I.sub.d, a shorter path is taken on the linear section when passing the magnetizing curve starting from the operating point than when the differential current is low—the resulting dwell time is shorter. As described above, oscillator signal V time-modulated in this manner therefore comprises dwell times T.sub.h, T.sub.1 of different durations in states 1 S.sub.1 and 2 S.sub.2 depending on the position of operating point AP and thus as a function of differential current I.sub.d.

(15) Corresponding dwell times T.sub.h, T.sub.1 are determined in a second oscillator circuit 32 in high resolution by means of a high-frequency clock signal C whose clock rate is several degrees larger than a basic frequency of oscillator signal V oscillating between states 1 S.sub.1 and 2 S.sub.2. Examinations have shown that a clock rate larger than 1 GHz and thus a high temporal resolution of smaller than 1 ns is possible.

(16) The clock impulses detected during corresponding dwell times T.sub.h, T.sub.1 are evaluated (counted) in an evaluation device 42 which provides a differential-current measuring value I.sub.m on the exit side proportional to differential current I.sub.d. Digitally available differential-current measuring value I.sub.m can be output directly in a digital format I.sub.m via data interface 52 and/or as an analog differential-current measuring value I′.sub.m by means of a D/A converter 54.

(17) FIG. 3 shows the digital signal processing of oscillator signal V in a functional block diagram.

(18) Dwell times T.sub.h, T.sub.1 of oscillator signal V in states 1 S.sub.1 and 2 S.sub.2 are quantized in second oscillator circuit 32 in high (temporal) resolution by means of a high-frequency clock signal C. For this purpose, second oscillator circuit 32 comprises a closed series circuit of inverting elements having at least one back coupling 34.

(19) Dwell times T.sub.h, T.sub.1 determined in this manner are evaluated in a downstream evaluation device 42 by means of a digital circuit 44, such as a microcontroller.

(20) At the output of evaluation device 42, a differential-current measuring value I.sub.m is available. Data interface 52 forwards digital differential-current measuring value I.sub.m directly and/or via a D/A converter 54 as an analog differential-current measuring value I′.sub.m.