Current measuring device

Abstract

Current measuring device (A), comprising: a shunt resistor (1) comprising a resistance element (3), a first electrode (5a) and a second electrode (5b) arranged at both ends of the resistance element (3); a pair of first and second voltage signal lines (L1, L2) connected to the shunt resistor (1), with the first voltage signal line (L1) connected to the first electrode (5a) and the second voltage signal line (L2) connected to the second electrode (5b); and a current measurement circuit for measuring a current using a signal through the pair of first and second voltage signal lines (L1, L2), wherein the pair of first and second voltage signal lines (L1, L2) is connected to an amplifier circuit (11) which includes the current measurement circuit for amplifying a voltage signal; wherein the second electrode (5b) of the shunt resistor (1) is connected to an output terminal of the inverter circuit connected between two switching elements of an inverter circuit, and a potential of the output terminal varies by switching the switching elements between a P-side and an N-side; wherein a third signal line (L3), which is distinct from the pair of first and second voltage signal lines (L1, L2) and originates from the second electrode (5b) of the shunt resistor (1), is connected to a common line (L4) of the current sensing circuit, which is connected to a voltage regulator (31) for the power supply of the amplifier circuit (11); wherein the shunt resistor (1) is designed separately from a substrate on which the amplifier circuit (11) is located; and wherein The current measurement circuit has a path (L12) along which common-mode noise generated by the switching of the switching elements flows from the third signal line (L3) through the voltage regulator (31) to a ground (GND), so that the third signal line (L3) reduces the influence of the common-mode noise on the pair of first and second voltage signal lines (L1, L2).

Description

Technical area

[0001] The present invention relates to a current measuring device. Current state of the art

[0002] A shunt resistor consists of two current terminals for applying a current to be measured and two signal output terminals or electrical wires for extracting a detection voltage signal (see, for example, JP 2014-142224 A).

[0003] Document CN 1 06 249 037 A describes a current detection circuit comprising: a shunt resistor; an amplifier; a first signal line connecting a first terminal of the shunt resistor to a first input terminal of the amplifier; a second signal line connecting a second terminal of the shunt resistor to a second input terminal of the amplifier; and a third signal line connecting the second terminal of the shunt resistor to the first power terminal of the amplifier.

[0004] Furthermore, document DE 10 2011 000 943 A1 discloses a current sensor that detects a current flowing through a wiring harness via a terminal of a battery, comprising: a resistor through which the current flows; a current detecting circuit that measures the current flowing through the resistor based on a potential difference between two positions along the direction in which the current flows through the resistor;a power supply circuit that supplies power to the current sensing circuit, and at least one capacitor connected to at least one of an input terminal and an output terminal of the power supply circuit to smooth an input / output voltage, wherein the resistor has a flat excitation path, and the capacitor is arranged in a region other than a projection plane of the excitation path on a board on which the current sensing circuit and the power supply circuit are mounted; Summary of the invention:Technical problem

[0005] As the current to be measured increases, it becomes necessary to reduce the value of the shunt resistor to reduce the losses caused by the shunt resistor. As a result, the shunt detection voltage also has a weaker signal level and is more likely to be affected by noise, which is not considered in JP 2014-142224 A.

[0006] In such a case, even weak common-mode noise, which was not considered a problem, is amplified by a high-sensitivity amplifier, making high-accuracy current detection impossible. Accordingly, there was the problem that in applications where common-mode noise becomes large, it is difficult to use a shunt resistor with a lower resistance value.

[0007] It is an object of the invention to provide a current measuring device capable of performing high-precision current detection by reducing the influence of common-mode noise. Solution to the problem

[0008] This is achieved according to the invention with a current measuring device having the features of claim 1. Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims.

[0009] According to the present invention, an additional terminal or electrical wire is additionally connected to a power supply line of an amplifier circuit. This makes it possible to suppress the influence of common-mode noise.

[0010] The current measuring device includes a shunt resistor having a resistance element, a first electrode, and a second electrode disposed at both ends of the resistance element; a pair of first and second voltage signal lines connected to the shunt resistor, the first voltage signal line being connected to the first electrode and the second voltage signal line being connected to the second electrode; and a current measuring circuit for measuring a current using a signal through the pair of first and second voltage signal lines.

[0011] The pair of first and second voltage signal lines is connected to an amplifier circuit having the current measuring circuit for amplifying a voltage signal. The second electrode of the shunt resistor is connected to an output terminal of the inverter circuit connected between two switching elements of an inverter circuit, and a potential of the output terminal varies between a P-side and an N-side by switching the switching elements. A third signal line, different from the pair of first and second voltage signal lines and extending from the second electrode of the shunt resistor, is connected to a common line of the current measuring circuit, which is connected to a voltage regulator for supplying power to the amplifier circuit.

[0012] The shunt resistor is configured separately from a substrate on which the amplifier circuit is located. The current measuring circuit has a path along which common-mode noise generated by the switching of the switching elements flows from the third signal line through the voltage regulator to ground, so that the third signal line reduces the influence of the common-mode noise on the pair of first and second voltage signal lines.

[0013] A further development of the invention provides that the amplifier circuit has a GND terminal which is connected to the common line.

[0014] A further development of the invention provides that the amplifier circuit has a negative power supply terminal which is connected to the common line.

[0015] A further development of the invention provides that the shunt resistor carries out the current detection in a main circuit, such as an inverter circuit provided with a switching element.

[0016] A further development of the invention provides that the amplifier circuit has a resistor in a signal input part for each pair of first and second voltage signal lines.

[0017] A further development of the invention provides that the shunt resistor has a resistance value of no more than 0.1 mΩ. This is because the use of a low-ohm shunt resistor leads to a greater influence of noise. Beneficial effects of inventions

[0018] According to the present invention, it is possible to suppress the influence of common mode noise in current detection. Short description of the drawings

[0019] The invention is explained below with reference to the embodiments shown in the figures, without limiting the invention: Fig. 1(a) is a circuit diagram showing a configuration example of a current measuring device according to an embodiment of the present invention. Fig. 1(b) is a perspective view showing a configuration example of a shunt resistor of the current measuring device according to the embodiment of the present invention. Fig. 2 is a circuit diagram showing a configuration example of a current measuring device according to a second embodiment of the present invention. Fig. 3 is a circuit diagram showing a configuration example of a current measuring device according to a third embodiment of the present invention. Fig. 4 shows plan views and side views showing a configuration example of a shunt resistor in a current measuring device according to a fourth embodiment of the present invention. Fig. 5 shows a top view ( Fig. 5(a)) and a side view ( Fig. 5(b)), showing a configuration example of a shunt resistor in a current measuring device according to a fifth embodiment of the present invention. Fig. 6 shows an example of a circuit diagram of a current measuring device according to a sixth embodiment of the present invention. Fig. 7 shows an example of a circuit diagram of a current measuring device according to a seventh embodiment of the present invention, showing a circuit example in which, applied to an inverter circuit, a gate power supply is used as a power supply for a shunt signal amplifier. Description of the embodiments

[0020] In the following, the current measuring device according to embodiments of the present invention will be described with reference to the drawings. (First embodiment)

[0021] Fig. 1(a) is a circuit diagram showing a configuration example of a current measuring device A according to an embodiment of the present invention. Fig. 1(b) is a perspective view showing a configuration example of a shunt resistor 1 of the current measuring device according to the embodiment of the present invention.

[0022] As in Fig. 1(a) and Fig. As shown in Fig. 1(b), the shunt resistor 1 includes a resistance element 3 and a first electrode 5a and a second electrode 5b arranged at both ends of the resistance element 3.

[0023] Fig. 1 shows a butt joint structure in which, for example, an end face of the resistance element 3 and the end faces of the electrodes 5a, 5b abut each other; however, the butt joint structure is not limiting.

[0024] For example, plate material made of Cu-Ni-based, Cu-Mn-based, or Ni-Cr-based metals can be used as the material for the resistance element 3. Cu, for example, can be used as the electrode material for the connection parts 5. The shunt resistor 1 has a low resistance value of no more than 0.1 mΩ.

[0025] The electrodes 5a, 5b have holes 7a, 7b for mounting on a substrate, a bus bar, or the like, which are not shown. The electrodes 5a, 5b are provided, on the sides connected to the resistance element 3, with a first signal output terminal T1 and a second signal output terminal T2 extending vertically from their electrode surfaces. A third signal output terminal T3 is further provided near the second signal output terminal T2 and extends vertically from an electrode surface of the second electrode 5b.

[0026] The current measuring device A includes an amplifier circuit (substrate) 11 connected to the shunt resistor 1 to amplify an output signal of the shunt resistor 1. The amplifier circuit 11 is provided with an analog isolation amplifier 27 with Δ-Σ conversion, which includes, for example, a photocoupler or a capacitive coupling capacitor.

[0027] The first signal output terminal T1 and the second signal output terminal T2 of the shunt resistor 1 are connected via wires L1, L2 to two input terminals T4, T5 of the amplifier circuit 11. Furthermore, the third signal output terminal T3 is provided and connected via a wire L3 to a negative power supply terminal T6, which is electrically connected to a common line L4 (GND 31) of the amplifier circuit 11. Preferably, the wires L1 and L2 are stranded wires.

[0028] In amplifier circuit 11, the input terminals T4, T5 are connected to the buffer amplifier 27 via resistors 21a, 21b. A capacitor 25 is arranged between the wires of the input terminals T4, T5. This makes it possible to suppress the intrusion of noise into the buffer amplifier 27 during normal operation. The buffer amplifier 27 has a positive power supply terminal connected to L5 (Vcc) and a negative power supply terminal connected to L4 (GND 31).

[0029] The shunt resistor 1 and the amplifier circuit 11 are connected by a 5-terminal system (5a, 5b, T1, T2, T3), where the common-mode noise passes through T3→L3→T6→L4 and drops to GND 31 on the amplifier circuit side. Accordingly, it is possible to reduce the influence of common-mode noise on the pair of voltage signal lines (wires L1, L2) connected to the amplifier circuit 11 provided in the current measuring device A for amplifying signals. (Second embodiment)

[0030] A current measuring device according to a second embodiment of the present invention will be described.

[0031] Fig. 2 is a circuit diagram showing a configuration example of the current measuring device A according to the present embodiment. In the Fig. In the training example shown in Figure 2, the shunt resistance 1 has a lower resistance than in Fig. 1 does not have the terminal T3. Instead, the wire L2 branches from the second signal output terminal T2 to the input terminal T5 of the amplifier circuit 11 and the wire L3 branches to the common line L4 (GND 31) from the terminal T2. With this design, it is also possible to achieve similar effects as in Fig. 1. Another special feature is that it is not necessary to provide Terminal T3. (Third embodiment)

[0032] A current measuring device according to a third embodiment of the present invention will be described.

[0033] Fig. 3 is a circuit diagram showing a configuration example of the current measuring device according to the present embodiment. Fig. The training example shown in Figure 3 differs from the one in Fig. 1 in that the amplifier circuit 11 (isolation amplifier 27) is supplied with a negative power supply Vee, and GND is provided separately from the power supply Vee. Terminal T6 is connected to GND of the amplifier circuit 11 (in this example, T6 is expressly referred to as the GND terminal). Wire L3 is connected to GND terminal T6.

[0034] In this way, the gain range on the minus side for the signal output is increased, which has the advantage of mitigating a reduction in the gain range due to the influence of common mode noise. (Fourth embodiment)

[0035] A current measuring device according to a fourth embodiment of the present invention will be described.

[0036] Fig. shows an example of a shunt resistor 91 in an ammeter according to the present embodiment, (a) in plan view, (b) in front view, and (c) in side view. The rear view is similar to the plan view (a). In the Fig. In the embodiment shown in Figure 4, the shunt resistor 91 includes a plurality of columnar resistance elements 93 arranged between two electrodes 91a, 91b arranged opposite each other. Each of the electrodes 91a, 91b has a through-hole 17a for attachment to a busbar or the like. Terminals T21 to T23 protrude laterally from the sides of the electrodes 91a, 91b. The shunt resistor makes it possible to implement a shunt resistor with a lower resistance. Fig. 4(d) shows an example where the shunt resistor 91 is connected to the Fig. 1. A terminal T21 as the first signal output terminal and a terminal T22 as the second signal output terminal are connected to the two input terminals T4, T5 of the amplifier circuit 11 via wires L1, L2, respectively. A terminal T23 as the third signal output terminal is connected via wire L3 to the negative power supply terminal T6, which is electrically connected to the common line L4 (GND 31) of the amplifier circuit 11. With this configuration, it is possible to more effectively reduce the influence of common-mode noise. (Fifth embodiment)

[0037] A current measuring device according to a fifth embodiment of the present invention will be described. Fig. 5 shows a top view ( Fig. 5(a)) and a side view ( Fig. 5(b)), showing a configuration example of the current measuring device (shunt module) according to the present embodiment.

[0038] In the shunt module, the influence of self-inductance can be reduced by arranging the shunt resistor and the amplifier circuit substrate close to each other. However, if the shunt resistor and the amplifier circuit substrate are close to each other, the influence of heating of the shunt resistor on the amplifier circuit substrate becomes a problem.

[0039] The shunt resistor 1 comprises according to Fig. 5, the resistance element 3 and the electrodes 5a, 5b connected and fixed to both ends of the resistance element 3. The electrodes 5a, 5b are provided with through-holes 7a, 7b for fixing to a bus bar or the like. The electrodes 5a, 5b are provided with terminals T1, T2 for voltage take-off near parts thereof connected to the resistance element 3. An amplifier circuit substrate 71 is provided with circuit components, such as an isolating amplifier 15 for isolating a primary and a secondary side, and wires. The shunt resistor 1 and the amplifier circuit substrate 71 are arranged with a predetermined separation distance therebetween. The separation distance is maintained, for example, by a casing covering the amplifier circuit substrate 71, which is not shown.The wires L1, L2 connected to the terminals T1, T2 of the shunt resistor 1 are twisted together in a state of contact with or near the shunt resistor and then connected to the amplifier circuit substrate 71 to send voltage signals to the buffer amplifier 15. The terminal T2 extends vertically to a length such that it reaches and penetrates the amplifier circuit substrate 71 and is connected to GND of the amplifier circuit substrate 71.

[0040] With such a 5-terminal system, which uses electrical wires and the like for signal output, it is also possible to suppress the influence of common-mode noise. The voltage signal wires are made of stranded wires, which can reduce the influence of noise due to magnetic flux even when the shunt resistor 1 and the amplifier circuit substrate 71 are separated from each other. The 5-terminal system indicates the shunt resistor composed of the electrodes 5a, 5b for current flow, the terminals T1, T2 for voltage extraction, and the terminal T3 (or a wire branching from T1 or T2) for conducting noise to GND, and / or the formation of a current measuring device to which the shunt resistor is connected, and relates to the current measuring system according to the present invention. (Sixth Embodiment)

[0041] Fig. 6 shows an example of a circuit diagram of a current measuring device according to a sixth embodiment of the present invention. Fig. Figure 6 is an example of an inverter circuit for controlling a three-phase motor and illustrates a phase section of an inverter bridge circuit.

[0042] The Fig. The example shown in Figure 6, which is an example of applying a shunt current detector of the 5-terminal system to an inverter circuit, includes an inverter bridge section B and a current measuring device A provided with the shunt resistor 1 and the amplifier circuit 27. The inverter bridge section B includes gate drive circuits (43, 47) that respectively control a first gate integrated bipolar transistor (IGBT) 51 and a second IGBT 53, and gate power supply circuits (41, 46). The gate power supply circuits 41, 46 are controlled by a power supply regulator 45. The example is also provided with an inverter control circuit 28. The current measuring device A is equipped with the shunt resistor 1 and an isolation amplifier 37.

[0043] An output terminal TBu of the inverter bridge section B and a load-side motor are connected to terminals designated by the electrodes 5a, 5b of the shunt resistor 1 for applying the current to be measured.

[0044] As described above, the first signal output terminal T1 and the second signal output terminal T2 of the shunt resistor 1 for performing current detection in the inverter circuit provided with the switching elements are respectively connected to the two input terminals T4, T5 of the isolation amplifier 37 forming the amplifier circuit. The third signal output terminal T3 is connected to the common line L4 (GND 31) of the current measuring device A provided with the amplifier circuit. The symbols 29, 61 indicate a floating capacitance.

[0045] In Fig. 6, L12 indicates common-mode noise, which is generated because the potential at the output terminal TBu varies greatly due to the switching of the IGBTs to the P-side or N-side. The common-mode noise L12 of the inverter bridge section B flows from the output terminal TBu to the shunt resistor and then from the third signal output terminal T3 to GND of the current measuring device A. Thus, a system is assumed in which a common line 33 of the amplifier circuit 11 is wired through the shunt resistor 1 via a different path than the signal output line, causing the common-mode noise current of the signal output terminal TBu to flow to GND. Accordingly, it is possible to perform current detection with the influence of the common-mode noise reduced. (Seventh Embodiment)

[0046] Fig. 7 shows an example of a circuit diagram of a current measuring device according to a seventh embodiment of the present invention. Fig.7 is an example of an inverter circuit for driving a three-phase motor and illustrates a phase section of an inverter bridge circuit. In the circuit example, a gate power supply is used to supply power to the shunt signal amplifier (isolation amplifier 37). In this case, there is the advantage of being able to bypass noise to the output terminal TBu with respect to noise in shunt signals (signals at terminals T1, T2) due to current fluctuations of the gate power supply. In particular, when a charge pump type voltage regulator is used to power the amplifier circuit, noise may increase due to the pulsed current of the power supply. In such a case, it is helpful to use the 5-terminal system of the present invention, as in the present example.

[0047] In the above embodiments, the configurations shown in the drawings and the like are not limitative and may be changed as needed as long as the effects of the present invention can be achieved. Other changes may also be made as needed without departing from the scope of the present invention.

[0048] The constituent elements of the present invention may be selectively adopted or not adopted, and an invention provided with the selected configurations is also included in the present invention. Industrial applicability

[0049] The present invention can be used in a current measuring device. LIST OF REFERENCE SYMBOLS A current measuring device. 1 shunt resistor 3 resistance element 5a First electrode (electrode) 5b Second electrode (electrode) 11 Amplifier circuit 21a resistance 21b resistance 31 GND L1 wire (stranded wire) L2 wire (stranded wire) L3 wire L4 Joint Management T1 First signal output connection T2 Second signal output connection T3 Third signal output terminal T4 input connection T5 input connection

Claims

[1] Current measuring device (A), comprising: a shunt resistor (1) having a resistance element (3), a first electrode (5a) and a second electrode (5b) arranged at both ends of the resistance element (3); a pair of first and second voltage signal lines (L1, L2) connected to the shunt resistor (1), the first voltage signal line (L1) being connected to the first electrode (5a) and the second voltage signal line (L2) being connected to the second electrode (5b); and a current measuring circuit for measuring a current using a signal through the pair of first and second voltage signal lines (L1, L2), wherein the pair of first and second voltage signal lines (L1, L2) is connected to an amplifier circuit (11) having the current measuring circuit for amplifying a voltage signal; wherein the second electrode (5b) of the shunt resistor (1) is connected to an output terminal of the inverter circuit connected between two switching elements of an inverter circuit, and a potential of the output terminal varies by switching the switching elements between a P-side and an N-side; wherein a third signal line (L3) different from the pair of first and second voltage signal lines (L1, L2) and extending from the second electrode (5b) of the shunt resistor (1) is connected to a common line (L4) of the current measuring circuit, which is connected to a voltage regulator (31) for supplying power to the amplifier circuit (11); wherein the shunt resistor (1) is designed separately from a substrate on which the amplifier circuit (11) is present; and wherein the current measuring circuit has a path (L12) along which a common-mode noise generated by the switching of the switching elements flows from the third signal line (L3) through the voltage regulator (31) to a ground (GND), so that the third signal line (L3) reduces an influence of the common-mode noise on the pair of first and second voltage signal lines (L1, L2). [2] A current measuring device according to claim 1, wherein the amplifier circuit (11) has a negative power supply terminal connected to the common line (L4). [3] Current measuring device according to claim 1, wherein the amplifier circuit (11) has a GND terminal connected to the common line (L4). [4] A current measuring device according to claim 1, wherein the amplifier circuit (11) has a resistor in a signal input section for each pair of first and second voltage signal lines (L1, L2). [5] Current measuring device according to claim 1, wherein the shunt resistor (1) has a resistance value of not more than 0.1 mΩ.

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