Electric current sensor

Abstract

To provide an electric current sensor that can be further miniaturized.SOLUTION: An electric current sensor 50 is provided with a bus bar 30, a coreless type first magnetic sensor 10 disposed on a front surface 30a side of the bus bar 30, and a coreless type second magnetic sensor 20 disposed on a back surface 30b side of the bus bar 30, and detects an electric current flowing in the bus bar 30 by differential detection of the output of the first magnetic sensor 10 and the output of the second magnetic sensor 20.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a current sensor. [Background technology]

[0002] Patent Document 1 discloses a current sensor that detects a current flowing in a measurement circuit. This current sensor has a circular magnetic core and a coil wound around the magnetic core. The measurement circuit is inserted into the magnetic core. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-148553 Summary of the Invention [Problem to be solved by the invention]

[0004] In the current sensor described above, the volume occupied by the magnetic core is dominant, which has led to a problem that there is a limit to how small the current sensor can be made.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a current sensor that can be made smaller. [Means for solving the problem]

[0006] The current sensor according to the present disclosure comprises a busbar, a coreless first magnetic sensor arranged on the front side of the busbar, and a coreless second magnetic sensor arranged on the back side of the busbar, and detects the current flowing through the busbar by differential detection of the output of the first magnetic sensor and the output of the second magnetic sensor. [Effects of the Invention]

[0007] According to the present disclosure, the current sensor can be made smaller. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a top view showing a configuration of a main part of a current sensor according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing the II-II cross section of FIG. [Figure 3] 1 is a circuit diagram showing a configuration of a current sensor according to a first embodiment. [Figure 4] 1 is a side view showing a schematic configuration of a current sensor according to a first embodiment. [Figure 5] FIG. 5 is a cross-sectional view showing the VV cross section of FIG. [Figure 6] FIG. 1 is a circuit diagram of a test device for evaluating a current sensor. [Figure 7] 10 is a graph showing the waveform of a voltage signal Vo1 of a current sensor of a comparative example together with the waveform of a reference current IL. [Figure 8] 4 is a graph showing the waveform of a voltage signal Vo output from the current sensor according to the first embodiment, together with the waveform of a reference current IL. [Figure 9] 4 is a graph showing the change over time of a voltage signal Vo when a current flowing through the current sensor according to the first embodiment is increased linearly. DETAILED DESCRIPTION OF THE INVENTION

[0009] Embodiment 1 A current sensor according to a first embodiment will be described. An inverter for driving a motor has a controller. The controller is configured to control the motor current to control the output torque of the motor. In order to control the motor current, the controller uses a current sensor to detect the current in the motor line. The current sensor according to this embodiment is provided in the controller of such an inverter.

[0010] FIG. 1 is a top view showing the configuration of a main part of a current sensor according to this embodiment. FIG. 2 is a cross-sectional view showing a cross section taken along line II-II of FIG. 1. As shown in FIGS. 1 and 2, a current sensor 50 includes a bus bar 30, a first magnetic sensor 10, a second magnetic sensor 20, and resin parts 40a and 40b. The bus bar 30 is formed in a flat plate shape. The bus bar 30 has a front surface 30a and a back surface 30b opposite to the front surface 30a. The front surface 30a and the back surface 30b are formed, for example, parallel to each other. The bus bar 30 has, for example, a linear planar shape that is long in one direction.

[0011] Both the first magnetic sensor 10 and the second magnetic sensor 20 are coreless magnetic sensors. The first magnetic sensor 10 is disposed on the front surface 30a of the bus bar 30, facing the front surface 30a with a gap therebetween. The second magnetic sensor 20 is disposed on the back surface 30b of the bus bar 30, facing the back surface 30b with a gap therebetween.

[0012] When viewed in a direction perpendicular to the surface 30a, the first magnetic sensor 10 and the second magnetic sensor 20 are arranged overlapping each other and facing each other with the bus bar 30 interposed therebetween.

[0013] Each of the first magnetic sensor 10 and the second magnetic sensor 20 has a Hall element therein. In Fig. 2, the position of the Hall element of the first magnetic sensor 10 is indicated by p1, and the position of the Hall element of the second magnetic sensor 20 is indicated by p2.

[0014] Here, the distance between the Hall element of the first magnetic sensor 10 and the front surface 30a of the busbar 30 is defined as the distance D1 between the first magnetic sensor 10 and the front surface 30a. Also, the distance between the Hall element of the second magnetic sensor 20 and the back surface 30b of the busbar 30 is defined as the distance D2 between the second magnetic sensor 20 and the back surface 30b. In this case, the distance D1 and the distance D2 are equal (D1=D2).

[0015] The first magnetic sensor 10 has a power supply voltage terminal 11, a ground terminal 12, and an output terminal 13. A power supply voltage of, for example, DC 5V is applied to the power supply voltage terminal 11. The ground terminal 12 is connected to the ground. The output terminal 13 outputs a voltage signal Vo1 corresponding to the strength and direction of the magnetic field detected by the Hall element of the first magnetic sensor 10.

[0016] The first magnetic sensor 10 is held by a resin part 40a. The resin part 40a is attached to the front surface 30a side of the bus bar 30. The first magnetic sensor 10 is positioned relative to the bus bar 30 by attaching the resin part 40a holding the first magnetic sensor 10 to the front surface 30a side of the bus bar 30.

[0017] The resin part 40a has a container-like shape with an opening on the side opposite to the bus bar 30. A cover 41a is attached to the opening of the resin part 40a. Through holes are formed in the cover 41a. The power supply voltage terminal 11, the ground terminal 12, and the output terminal 13 are led out to the outside through the through holes in the cover 41a.

[0018] The second magnetic sensor 20 has a power supply voltage terminal 21, a ground terminal 22, and an output terminal 23. A power supply voltage of, for example, DC 5 V is applied to the power supply voltage terminal 21. The ground terminal 22 is connected to the ground. The output terminal 23 outputs a voltage signal Vo2 corresponding to the strength and direction of the magnetic field detected by the Hall element of the second magnetic sensor 20.

[0019] The second magnetic sensor 20 is held by a resin part 40b. The resin part 40b is attached to the rear surface 30b side of the bus bar 30. The second magnetic sensor 20 is positioned relative to the bus bar 30 by attaching the resin part 40b holding the second magnetic sensor 20 to the rear surface 30b side of the bus bar 30.

[0020] Resin part 40b has a container-like shape with an opening on the side opposite bus bar 30. Cover 41b is attached to the opening of resin part 40b. Through holes are formed in cover 41b. Power supply voltage terminal 21, ground terminal 22, and output terminal 23 are led out to the outside through the through holes in cover 41b.

[0021] 3 is a circuit diagram showing the configuration of a current sensor according to this embodiment. As shown in Fig. 3, the current sensor 50 further includes a differential detection unit 60 that performs differential detection between the output of the first magnetic sensor 10 and the output of the second magnetic sensor 20.

[0022] The differential detection unit 60 has an operational amplifier 61. An inverting input terminal 61a of the operational amplifier 61 is connected to the output terminal 13 of the first magnetic sensor 10 via a resistor 62a. The inverting input terminal 61a is also connected to the output terminal 61c of the operational amplifier 61 via a resistor 62b. A non-inverting input terminal 61b of the operational amplifier 61 is connected to the output terminal 23 of the second magnetic sensor 20 via a resistor 62c. The non-inverting input terminal 61b is also connected to ground via a resistor 62d.

[0023] A voltage signal Vo is output from the output terminal 61c of the operational amplifier 61 as a detection value of the current flowing through the bus bar 30. The voltage signal Vo is proportional to the difference (Vo2-Vo1) between the voltage signal Vo2 output from the second magnetic sensor 20 and the voltage signal Vo1 output from the first magnetic sensor 10.

[0024] Next, the principle of the current sensor according to this embodiment will be described. Fig. 4 is a side view showing a schematic configuration of the current sensor according to this embodiment. The left-right direction in Fig. 4 represents the longitudinal direction of the bus bar 30. Resin parts and covers are not shown in Fig. 4. Fig. 5 is a cross-sectional view showing the VV cross section of Fig. 4.

[0025] 4 and 5, when a direct current Ib flows along the longitudinal direction of the bus bar 30, a magnetic field is generated around the bus bar 30. When viewed in the direction of flow of the direct current Ib, the direction of the magnetic flux Φb is clockwise.

[0026] Since the distance between the first magnetic sensor 10 and the front surface 30a is equal to the distance between the second magnetic sensor 20 and the back surface 30b, the absolute value of the magnetic flux Φb detected by the first magnetic sensor 10 is equal to the absolute value of the magnetic flux Φb detected by the second magnetic sensor 20.

[0027] The magnetic flux Φb on the front surface 30a side of the busbar 30 is in the opposite direction to the magnetic flux Φb on the back surface 30b side of the busbar 30. As a result, the magnetic flux Φb detected by the first magnetic sensor 10 has an opposite sign to the magnetic flux Φb detected by the second magnetic sensor 20. The first magnetic sensor 10 and the second magnetic sensor 20 are installed so that the absolute values ​​of the magnetic flux Φb detected by each are equal and the positive and negative signs of the magnetic flux Φb detected by each are opposite.

[0028] Each of the first magnetic sensor 10 and the second magnetic sensor 20 detects not only the magnetic flux Φb due to the DC current Ib but also the magnetic flux due to magnetic noise from outside the current sensor 50. However, in the current sensor 50 of the present embodiment, the output of the first magnetic sensor 10 and the output of the second magnetic sensor 20 are differentially detected, so that the magnetic flux due to magnetic noise from outside the current sensor 50 is canceled out. Therefore, the current sensor 50 can accurately detect the DC current Ib flowing through the bus bar 30.

[0029] Next, the detection performance of the current sensor according to the present embodiment will be described in comparison with a current sensor of a comparative example. Fig. 6 is a circuit diagram of a test device used to evaluate the current sensor. In the test device shown in Fig. 6, a SiC-MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) or an IGBT (Insulated Gate Bipolar Transistor) is used for the high-side switching element Q1 and the low-side switching element Q2. A double-pulse test of the switching elements was performed using this test device, and the current flowing through the inductor L1 was measured at a measurement point MP.

[0030] First, the current at the measurement point MP was measured using the current sensor of the comparative example. In the current sensor of the comparative example, the physical arrangement of the bus bar 30, the first magnetic sensor 10, and the second magnetic sensor 20 is the same as the configuration shown in Figures 1 and 2. However, in the current sensor of the comparative example, the voltage signal Vo1 output from the first magnetic sensor 10 or the voltage signal Vo2 output from the second magnetic sensor 20 was detected using a single-ended method, and the current value was converted by calculation.

[0031] 7 is a graph showing the waveform of the voltage signal Vo1 of the current sensor of the comparative example together with the waveform of the reference current IL. The horizontal axis of the graph represents time (μs), and the vertical axis represents voltage (V) and current (A).

[0032] As shown in Figure 7, the voltage signal Vo1 output from the current sensor of the comparative example deviates significantly from the reference current IL, especially when switching elements Q1 and Q2. This indicates that the current sensor of the comparative example has no problems with DC current detection performance, but has problems with its dynamic characteristics during switching. The problems with the dynamic characteristics of the current sensor of the comparative example are thought to be caused by the influence of magnetic noise from outside the current sensor, for example, magnetic noise from inductor L1 in the test device shown in Figure 6.

[0033] Next, the current at measurement point MP was measured using current sensor 50 of the present embodiment. Figure 8 is a graph showing the waveform of voltage signal Vo output from the current sensor of the present embodiment together with the waveform of reference current IL. The horizontal axis of the graph represents time (μs), and the vertical axis represents voltage (V) and current (A).

[0034] 8, spike noise occurs in the voltage signal Vo output from the current sensor 50 of this embodiment when the switching element is turned on and off, but the deviation from the reference current IL during switching is significantly reduced compared to the current sensor of the comparative example. This shows that the dynamic characteristics during switching of the current sensor 50 of this embodiment are significantly improved compared to the current sensor of the comparative example.

[0035] 9 is a graph showing the change in voltage signal Vo over time when the current flowing through the current sensor according to this embodiment is linearly increased. The horizontal axis of the graph represents time (s), and the vertical axis represents voltage (V). Here, the current flowing through current sensor 50 is linearly increased from 0 A to 300 A over several tens of seconds. The voltage signal Vc in the graph is the output of the calibrated current sensor.

[0036] 9, the voltage signal Vo changes linearly, just like the voltage signal Vc. The increase in the voltage signal Vo per unit time is roughly equal to the increase in the voltage signal Vc per unit time. This indicates that the current sensor 50 has detection performance suitable for practical use.

[0037] As described above, the current sensor 50 according to this embodiment includes the bus bar 30, the first magnetic sensor 10, and the second magnetic sensor 20. The first magnetic sensor 10 is disposed on the front surface 30a side of the bus bar 30. The second magnetic sensor 20 is disposed on the back surface 30b side of the bus bar 30. The first magnetic sensor 10 and the second magnetic sensor 20 are both coreless magnetic sensors. The current sensor 50 is configured to detect the current flowing through the bus bar 30 by differentially detecting the output of the first magnetic sensor 10 and the output of the second magnetic sensor 20.

[0038] According to this configuration, the first magnetic sensor 10 and the second magnetic sensor 20 are both coreless magnetic sensors that do not have a magnetic core, and therefore the current sensor 50 can be made smaller and lighter.

[0039] Furthermore, with this configuration, current is detected by differential detection between the output of the first magnetic sensor 10 arranged on the front surface 30a of the bus bar 30 and the output of the second magnetic sensor 20 arranged on the back surface 30b of the bus bar 30, thereby canceling out external magnetic noise. This improves the detection accuracy of the current sensor 50. In other words, with this configuration, the current sensor 50 can be made smaller and lighter while maintaining its detection accuracy.

[0040] Furthermore, with this configuration, the shape of the busbar 30 can be flexibly changed to match the structure of the inverter, thereby increasing the degree of freedom in installing the current sensor 50 and allowing the current sensor 50 to be installed in inverters with a variety of structures.

[0041] In the current sensor 50 according to this embodiment, when viewed in a direction perpendicular to the surface 30a of the bus bar 30, the first magnetic sensor 10 and the second magnetic sensor 20 are arranged to overlap each other.

[0042] According to this configuration, the magnetic noise detected by the first magnetic sensor 10 and the magnetic noise detected by the second magnetic sensor 20 can be made substantially equal, so that the magnetic noise can be more reliably canceled out by differential detection.

[0043] In the current sensor 50 according to this embodiment, the distance D1 between the first magnetic sensor 10 and the front surface 30a of the bus bar 30 and the distance D2 between the second magnetic sensor 20 and the rear surface 30b of the bus bar 30 are equal.

[0044] According to this configuration, when a current flows through the bus bar 30, the absolute values ​​of the magnetic fluxes detected by the first magnetic sensor 10 and the second magnetic sensor 20 are equal to each other. Therefore, the detection accuracy of the current sensor 50 can be improved.

[0045] The current sensor 50 according to this embodiment further includes a resin part 40a and a resin part 40b. The resin part 40a is configured to hold the first magnetic sensor 10 and to be attached to the bus bar 30. The resin part 40b is configured to hold the second magnetic sensor 20 and to be attached to the bus bar 30.

[0046] According to this configuration, the resin part 40a can position the first magnetic sensor 10 relative to the bus bar 30, and the resin part 40b can position the second magnetic sensor 20 relative to the bus bar 30. Therefore, the distances D1 and D2 can be ensured more accurately. [Explanation of symbols]

[0047] 10 first magnetic sensor, 11 power supply voltage terminal, 12 ground terminal, 13 output terminal, 20 second magnetic sensor, 21 power supply voltage terminal, 22 ground terminal, 23 output terminal, 30 bus bar, 30a front surface, 30b back surface, 40a, 40b resin parts, 41a, 41b cover, 50 current sensor, 60 differential detection unit, 61 operational amplifier, 61a inverting input terminal, 61b non-inverting input terminal, 61c output terminal, 62a, 62b, 62c, 62d resistors, p1, p2 positions of Hall elements.

Claims

1. A bus bar (30); a coreless first magnetic sensor (10) arranged on the surface (30a) side of the bus bar; a second magnetic sensor (20) of a coreless type arranged on the rear surface (30b) side of the bus bar; Equipped with a current sensor that detects a current flowing through the bus bar by differential detection of an output of the first magnetic sensor and an output of the second magnetic sensor;

2. The current sensor according to claim 1 , wherein the first magnetic sensor and the second magnetic sensor are arranged to overlap each other when viewed in a direction perpendicular to the surface of the bus bar.

3. 3. The current sensor according to claim 1, wherein a distance (D1) between the first magnetic sensor and the front surface of the bus bar is equal to a distance (D2) between the second magnetic sensor and the back surface of the bus bar.

4. The current sensor according to claim 3 , further comprising resin parts (40 a, 40 b) that hold the first magnetic sensor and the second magnetic sensor and that are attached to the bus bar.

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