Current detection devices, earth leakage breakers and earth leakage relays

Abstract

To detect a target current with high accuracy. [Solution] A current detection device comprising: a magnetic core surrounding a conductor through which a current to be detected flows; an excitation coil wound around the magnetic core; an oscillator circuit that generates a rectangular wave voltage by exciting the magnetic core; a current detection circuit that detects the current to be detected based on changes in the rectangular wave voltage; and a compensation circuit that compensates for offset errors in the oscillator circuit or the current detection circuit.

Description

[Technical field]

[0001] The present disclosure relates to a current detection device, an earth leakage circuit breaker, and an earth leakage relay. [Background technology]

[0002] A current detection device is known that includes an excitation coil wound around a magnetic core surrounding a conductor through which a measurement current flows, an oscillation circuit that generates a square wave voltage that inverts the direction of the excitation current supplied to the excitation coil when the magnetic core is in or near a saturated state, a current detection circuit that detects the measurement current based on a change in the duty of the square wave voltage output from the oscillation circuit, and a Zener diode that limits the amplitude of the square wave voltage to an amplitude range that suppresses the amplitude fluctuation of the square wave voltage due to temperature change. This current detection device compensates for the fluctuation of the current detection voltage output from the amplifier circuit due to the temperature dependency of the Zener diode by placing a thermistor in the amplifier circuit of the current detection circuit and changing the amplification factor of the amplifier circuit according to temperature (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-50921 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the conventional technology, there are cases where it is difficult to detect a current with high accuracy due to an offset error that exists in the oscillation circuit or the current detection circuit.

[0005] The present disclosure provides a current detection device, an earth leakage breaker, and an earth leakage relay capable of detecting a current with high accuracy. [Means for solving the problem]

[0006] The current detection device according to the first aspect is a magnetic core surrounding a conductor through which a current to be detected flows; an excitation coil wound around the magnetic core; an oscillator circuit that generates a square wave voltage by exciting the magnetic core; a current detection circuit that detects the target current based on a change in the square wave voltage; and a compensation circuit that compensates for an offset error of the oscillation circuit or the current detection circuit.

[0007] The earth leakage circuit breaker of the second aspect is A current detection device for detecting a target current flowing through a conductor; a breaker that breaks an electric circuit when the detected current is detected by the current detection device, The current detection device is a magnetic core surrounding a conductor through which a current to be detected flows; an excitation coil wound around the magnetic core; an oscillator circuit that generates a square wave voltage by exciting the magnetic core; a current detection circuit that detects the target current based on a change in the square wave voltage; and a compensation circuit that compensates for an offset error of the oscillation circuit or the current detection circuit.

[0008] The earth leakage relay of the third aspect is A current detection device for detecting a target current flowing through a conductor; a relay that outputs a contact when the detected current is detected by the current detection device, The current detection device is a magnetic core surrounding a conductor through which a current to be detected flows; an excitation coil wound around the magnetic core; an oscillator circuit that generates a square wave voltage by exciting the magnetic core; a current detection circuit that detects the target current based on a change in the square wave voltage; and a compensation circuit that compensates for an offset error of the oscillation circuit or the current detection circuit. Effect of the Invention

[0009] According to the present disclosure, a target current can be detected with high accuracy. [Brief description of the drawings]

[0010] [Figure 1] 1 is a diagram illustrating an example of a configuration of a current detection device according to a first embodiment. [Diagram 2] FIG. 2 is a diagram illustrating an example of an analog circuit configuration of an oscillator circuit. [Diagram 3] 3A and 3B are schematic diagrams illustrating an output voltage waveform of an oscillator circuit and a current waveform of an excitation coil. [Figure 4] 3A to 3C are characteristic diagrams illustrating the relationship between the magnetic field strength and magnetic flux density of a magnetic core and an example of the inductance characteristics of the magnetic core. [Diagram 5] 4 is a diagram illustrating an example of the relationship between the output voltage of the oscillation circuit and the current detection voltage of the current detection circuit during current detection; [Figure 6] 1A and 1B are schematic diagrams illustrating the influence of an offset error. [Figure 7] FIG. 2 is a diagram illustrating an example of an analog circuit configuration of a first amplifier circuit, a second amplifier circuit, a temperature compensation circuit, and an adjustment circuit. [Figure 8] 10A and 10B are schematic diagrams illustrating an example of switching of an operating current; [Figure 9] 4 is a diagram illustrating an example of a relationship between temperature and a temperature compensation circuit output. [Figure 10] FIG. 2 is a diagram showing an example of an analog circuit configuration of an absolute value circuit, a determination circuit, and an adjustment circuit. [Figure 11] 5 is a schematic diagram showing an example of the operation of the adjustment circuit; FIG. [Figure 12] FIG. 1 is a diagram illustrating a configuration example of an earth leakage breaker including a current detection device. [Figure 13] FIG. 1 is a diagram illustrating a configuration example of an earth leakage relay including a current detection device. [Figure 14] FIG. 2 is a diagram illustrating a configuration example of a filter circuit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present disclosure will be described. Note that "connection" is not limited to physical connection, and may include electrical connection. For example, connecting an object A to an object B is not limited to the case where the object A is conductively connected to the object B (e.g., at the same potential), but may include the case where the object A is conductively connected to the object B via the object C.

[0012] FIG. 1 is a configuration diagram showing an example of a current detection device according to the first embodiment. The current detection device 1 shown in FIG. 1 may be used as a detection means for detecting a current to be detected, such as a leakage current, in, for example, an earth leakage circuit breaker 100 (see FIG. 12) or an earth leakage relay 300 (see FIG. 13). Hereinafter, the current detection device 1 will be described as a current detection device applied to the earth leakage circuit breaker 100 or the earth leakage relay 300. Also, a current to be detected, such as a leakage current, will be collectively referred to as a "current to be detected" below. However, the use of the current detection device 1 is not limited to this. Configuration examples of the earth leakage circuit breaker 100 and the earth leakage relay 300 will be described separately with reference to FIG. 12 and FIG. 13.

[0013] The conductor 2 is an example of a conductor through which a current to be detected flows. The conductor through which a current to be detected flows is not limited to the conductor 2, and may be in another form such as a conductive conduit. The conductor 2 is, for example, a ground wire for grounding a power system in which the current detection device 1 is installed. Although FIG. 1 illustrates one conductor 2, the number of conductors 2 may be two or more. For example, the current detection device 1 may be a zero-phase current transformer that detects a difference current between a plurality of conductors.

[0014] Here, in a healthy state, the current I flowing through the conductor 2 is zero. However, in an abnormal state where a current leakage, earth fault, or the like occurs, the current I flowing through the conductor 2 does not become zero, and a minute current to be detected, for example, a current to be detected of about 15 mA to 500 mA, flows. A ring-shaped magnetic core 3 is disposed around this conductor 2. In other words, the conductor 2 is inserted into the magnetic core 3.

[0015] The magnetic core 3 is an annular magnetic member surrounding the conductive wire 2. An example of a material constituting the magnetic core 3 is a soft magnetic material such as an Fe-Ni based magnetic alloy. However, the material constituting the magnetic core 3 is not limited.

[0016] As the magnetic field acting on the magnetic core 3 becomes stronger, the magnetic flux density passing through the magnetic core 3 increases. When the magnetic field acting on the magnetic core 3 becomes even stronger and exceeds a predetermined value, the magnetic flux density passing through the magnetic core 3 stops changing. In other words, the magnetic core 3 becomes magnetically saturated.

[0017] The excitation coil 4 is wound around the magnetic core 3. The magnetic core 3 is inserted inside each winding portion that constitutes the excitation coil 4. When a DC or AC excitation current flows through the excitation coil 4, a magnetic field is generated inside the excitation coil 4. If the magnetic core 3 is not magnetically saturated, the magnetic flux density passing through the magnetic core 3 changes according to the change in the magnetic field generated inside the excitation coil 4. The number of turns, cross-sectional area, etc. of the excitation coil 4 are not limited.

[0018] The oscillator circuit 5 excites the magnetic core 3. The oscillator circuit 5 passes an excitation current that excites the magnetic core 3 through the excitation coil 4. The oscillator circuit 5 generates a square wave voltage Va by exciting the magnetic core 3. The oscillator circuit 5 generates a square wave voltage Va that reverses the direction of the excitation current supplied to the excitation coil 4 when the magnetic core 3 is in or near a saturated state. The square wave voltage Va output from the oscillator circuit 5 is supplied to a current detection circuit 6.

[0019] The current detection circuit 6 detects the current to be detected based on a change in the square wave voltage Va output from the oscillation circuit 5. For example, the current detection circuit 6 detects the current to be detected based on a change in the duty ratio of the square wave voltage Va output from the oscillation circuit 5.

[0020] The current detection circuit 6 includes a filter circuit 7 and a first amplifier circuit 8.

[0021] The filter circuit 7 removes high-frequency components from the square wave voltage Va output from the oscillation circuit 5. The filter circuit 7 operates, for example, as an integrator that removes high-frequency components from the square wave voltage Va. The filter circuit 7 generates a filter output voltage Vf as a voltage according to the duty ratio of the square wave voltage Va. When the square wave voltage Va is input to the filter circuit 7, a filter output voltage Vf, which is the square wave voltage Va from which the high-frequency components have been removed, is output from the filter circuit 7. A first amplifier circuit 8 is connected to the filter circuit 7.

[0022] The first amplifier circuit 8 outputs an output voltage Vout1, which is a signal obtained by amplifying, by a predetermined amplification factor, an input voltage (in this example, the filter output voltage Vf) corresponding to the square wave voltage Va. The output voltage Vout1 is an example of a first output voltage of the first amplifier circuit.

[0023] The current detection circuit 6 may include a temperature compensation circuit 9 that performs temperature compensation for an offset error e that the oscillator circuit 5, the filter circuit 7, the first amplifier circuit 8, the second amplifier circuit 10, etc. have. The temperature compensation circuit 9 is connected to, for example, an input portion of the first amplifier circuit 8. A detailed description of the temperature compensation circuit 9 will be given later.

[0024] The current detection circuit 6 includes a second amplifier circuit 10 having a function (operating current switching function) of switching a current value (operating current value) at which a detected current is determined to be an abnormal current. The second amplifier circuit 10 is connected to the output section of the first amplifier circuit 8.

[0025] The second amplifier circuit 10 outputs an output voltage Vout2 which is a signal obtained by amplifying the output voltage Vout1 of the first amplifier circuit 8 with an amplification factor according to the operating current selected by an operating current selection switch (not shown). The output voltage Vout2 is an example of the second output voltage of the second amplifier circuit.

[0026] The current detection circuit 6 may include an adjustment circuit 11 that compensates for individual differences in offset error e that the oscillator circuit 5, the filter circuit 7, the first amplifier circuit 8, etc. have. The adjustment circuit 11 is connected to, for example, an input section of the second amplifier circuit 10. A detailed description of the adjustment circuit 11 will be given later.

[0027] The current detection circuit 6 includes an absolute value circuit 12 and a judgment circuit 13. The absolute value circuit 12 is connected to the output part of the second amplifier circuit 10. The judgment circuit 13 is connected to the output part of the absolute value circuit 12.

[0028] The absolute value circuit 12 outputs an output voltage Vout3 which is the absolute value of the output voltage Vout2 from the second amplifier circuit 10. The absolute value circuit 12 inverts and amplifies a signal that is equal to or lower than a reference voltage Vref, and outputs the amplified signal, for example.

[0029] The determination circuit 13 determines whether a current to be detected equal to or greater than the operating current value occurs based on the output voltage Vout2 (in this example, based on the output voltage Vout3 based on the output voltage Vout2). The determination circuit 13 determines whether a current to be detected equal to or greater than the operating current value occurs by, for example, comparing the output voltage Vout2 or the output voltage Vout3 with a threshold voltage Vth3. If the output voltage Vout2 or the output voltage Vout3 is equal to or greater than the threshold voltage Vth3, the determination circuit 13 determines that a current to be detected equal to or greater than the operating current value occurs. If the output voltage Vout2 or the output voltage Vout3 is less than the threshold voltage Vth3, the determination circuit 13 determines that a current to be detected equal to or greater than the operating current value does not occur. If the output voltage Vout2 or the output voltage Vout3 is equal to or greater than the threshold voltage Vth3, the determination circuit 13 outputs a determination output signal indicating that it has determined that a current to be detected equal to or greater than the operating current value occurs.

[0030] The current detection circuit 6 may include an adjustment circuit 14 that adjusts the judgment sensitivity of the judgment circuit 13. The adjustment circuit 14 is connected to, for example, an input unit of the judgment circuit 13. The adjustment circuit 14 compensates for fluctuations in the operating current value due to individual differences in the judgment sensitivity of the judgment circuit 13. The adjustment circuit 14 adjusts the judgment sensitivity of the judgment circuit 13, for example, by adjusting a threshold voltage Vth3 set in the judgment circuit 13. A detailed description of the adjustment circuit 14 will be given later.

[0031] Next, a specific example of the circuit configuration and an example of the operation of the current detection device according to the first embodiment will be described.

[0032] 2 is a diagram showing an example of an analog circuit configuration of the oscillator circuit 5. In the oscillator circuit 5, a threshold voltage Vth1 at a connection point E between the resistors 23 and 24 is supplied to the non-inverting input side of the operational amplifier 21. This threshold voltage Vth1 is expressed by the following formula (1), where R1 is the resistance value of the resistor 23, R2 is the resistance value of the resistor 24, and Va is the output voltage of the operational amplifier 21.

[0033] Vth1 = {R1 / (R1+R2)}Va (1) The operational amplifier 21 compares the threshold voltage Vth1 at the connection point E between the resistors 23 and 24 with the voltage Vd at the connection point D between the excitation coil 4 and the resistor 22, and outputs the comparison output from the output side as the output voltage Va shown in Figure 3(a).

[0034] Now, as shown in Fig. 3(a), when the output voltage Va on the output side of the operational amplifier 21 becomes high level at time t1, this high level output voltage Va is applied to the exciting coil 4. Therefore, an exciting current Iex according to the output voltage Va and the resistance value R12 of the resistor 22 is supplied to the exciting coil 4. At this time, as shown in Fig. 3(b), the exciting current Iex increases relatively steeply from time t1 when the output voltage Va rises, and then increases gently in a parabolic manner.

[0035] When the excitation current Iex is increasing in this manner, a threshold voltage Vth1 obtained by dividing the output voltage Va by the resistance value R1 of the resistor 23 and the resistance value R2 of the resistor 24 is input to the non-inverting input side of the operational amplifier 21. Meanwhile, the voltage Vd at the connection point D on the inverting input side of the operational amplifier 21 increases in accordance with the increase in the excitation current Iex of the exciting coil 4. Thereafter, when the excitation current Iex increases again sharply and the voltage Vd exceeds the threshold voltage Vth1 on the non-inverting input side at point F in FIG. 3(b) at time t2, the output voltage Va of the operational amplifier 21 is inverted to a low level as shown in FIG. 3(a).

[0036] In response to the inversion of the output voltage Va to a low level, the direction of the excitation current Iex flowing through the excitation coil 4 is reversed. The excitation current Iex initially decreases relatively steeply and then decreases parabolically, gradually decreasing.

[0037] When the excitation current Iex is decreasing in this manner, the threshold voltage Vth1 is a negative voltage lower than the reference potential because the output voltage Va is at a low level. Then, the voltage Vd at the connection point D on the inverting input side of the operational amplifier 21 decreases in response to the decrease in the excitation current Iex of the exciting coil 4, and when this voltage Vd falls below the negative threshold voltage Vth1 on the non-inverting input side at time t3, the output voltage Va of the operational amplifier 21 is inverted to a high level in the same manner as at time t1, as shown in FIG. 3(a).

[0038] Therefore, the output voltage Va becomes a square wave voltage that repeats high and low levels as shown in Fig. 3(a), and the oscillator circuit 5 operates as an astable multivibrator. The excitation current Iex of the excitation coil 4 becomes a waveform that repeats increases and decreases as shown in Fig. 3(b).

[0039] Incidentally, the magnetic core 3 has a BH characteristic that indicates the relationship between the magnetic flux density B with a large squareness ratio and the magnetic field strength H as shown in Fig. 4(a), and has the nonlinear characteristics of a high permeability material. When the current in the conductor 2 is zero, the inductance L of the magnetic core 3 with this BH characteristic suddenly vanishes near the saturation current G as shown in Fig. 4(b). When a current I with a minute current value C that can be detected is generated in the conductor 2 that passes through the magnetic core 3, the LI characteristic in Fig. 4(b) shifts in the positive direction of the magnetic field strength H according to the current value C as shown by the dashed line, and the timing at which the inductance vanishes changes.

[0040] For this reason, the current at which the inductance saturates when the current is zero (G in Fig. 4) is made to match the current at which the direction of the excitation current Iex switches (F in Fig. 3). Then, the current at which the inductance saturates (J in Fig. 4) changes according to the current value C of the current I in the conductor 2, so the current at which the direction of the excitation current Iex switches (H in Fig. 3(b)) also changes in the same way.

[0041] The change in the current value at which the direction of the excitation current Iex switches causes a delay in the timing at which the voltage Vd at the connection point D exceeds the threshold voltage Vth1. As a result, the falling point of the output voltage Va output from the operational amplifier 21 is delayed as shown by the dashed line in Figure 3(a) in accordance with the current value C of the current I in the conductor 2. As a result, the duty ratio of the square wave output voltage Va (square wave voltage Va) changes in accordance with the current value C of the current I in the conductor 2.

[0042] The oscillator circuit 5 supplies the square wave voltage Va to a current detection circuit 6 that detects the duty ratio of the square wave voltage Va. The current detection circuit 6 removes high frequency components of the square wave voltage Va using a filter circuit 7, and outputs a filter output voltage Vf according to the duty ratio of the square wave voltage Va. The filter output voltage Vf is supplied to a first amplifier circuit 8 and amplified. In order to efficiently remove high frequency components from the square wave voltage Va, the filter circuit 7 is configured, for example, with a second or higher order active filter using an operational amplifier.

[0043] Next, the output voltage of the oscillator circuit and the current detection voltage of the current detection circuit will be described with reference to FIG.

[0044] When the current I in the conductor 2 is 0, the square wave voltage Va output from the oscillator circuit 5 has a duty ratio of 50%, as shown by the solid line in Fig. 5(a). On the other hand, when the current I in the conductor 2 is 0, the output voltage Vout1 output from the first amplifier circuit 8 maintains the reference voltage Vb (e.g., 0 V), as shown by the solid line in Fig. 5(b).

[0045] From this state, when a minute current I flows through the conductor 2, the square wave voltage Va output from the oscillator circuit 5 has a duty ratio that increases according to the current value C of the current I, as shown by the dotted line in Figure 5(a). As a result, the filter output voltage Vf is amplified by the first amplifier circuit 8, and the output voltage Vout1 becomes higher than the reference voltage Vb. The current detection circuit 6 can detect the minute current I by capturing this change in the output voltage Vout1.

[0046] 6 is a schematic diagram illustrating the influence of an offset error. An offset voltage Voff1 similar to that occurring when a current I flows through the conductor 2 even though the current I is zero may occur in the output voltage Vout1. The offset voltage Voff1 occurs in the output voltage Vout1 due to, for example, fluctuations in the output voltage (square wave voltage Va) of the oscillator circuit 5 and offset errors e inherent to electronic components such as the operational amplifiers used in the oscillator circuit 5, the filter circuit 7, and the first amplifier circuit 8.

[0047] When the reference voltage Vb of the circuit is set to 0, ideally the offset voltage Voff1 is 0, and the relationship between the current I flowing through the conductor 2 and the output voltage Vout1 of the first amplifier circuit 8 is as shown by the dashed line in Figure 6(a). However, due to the offset error e described above, the offset voltage Voff1 is not 0, and the relationship between the current I flowing through the conductor 2 and the output voltage Vout1 of the first amplifier circuit 8 shifts from the dashed line as shown by the solid line in Figure 6(a).

[0048] In order to simplify the circuit and adjustment by unifying the threshold voltage Vth3 used in the judgment circuit 13 at the subsequent stage, the current detection circuit 6 performs a process of inverting a signal below the reference voltage Vref using the absolute value circuit 12, and then performs judgment processing using a predetermined threshold voltage Vth3. Therefore, the relationship between the current I flowing through the conductor 2 and the output voltage Vout3 after absolute value processing is as shown in FIG. 6(b). In a state affected by the above-mentioned offset error e, an error occurs in the operating current compared to the operating current (Id+, Id-) in an ideal state, and the operating current value fluctuates due to the difference in the current flow direction even though the current value is the same (Id'+, Id'-). Furthermore, since the offset error e has temperature dependency, the operating current value fluctuates depending on the ambient temperature, and there is a risk of false detection or malfunction due to changes in ambient temperature.

[0049] Therefore, as shown in FIG. 1, the current detection device 1 of the first embodiment is equipped with an adjustment circuit 11 that compensates for individual differences in the offset error e, and a temperature compensation circuit 9 that temperature compensates for the offset error e, thereby performing highly accurate current detection.

[0050] The adjustment circuit 11 and the temperature compensation circuit 9 are examples of a compensation circuit that compensates for an offset error of an oscillation circuit or a current detection circuit. The compensation circuit of the current detection device 1 according to the first embodiment includes both the adjustment circuit 11 and the temperature compensation circuit 9, but may include only one of the adjustment circuit 11 and the temperature compensation circuit 9.

[0051] FIG. 7 is a diagram showing an example of an analog circuit configuration of the first amplifier circuit 8, the second amplifier circuit 10, the temperature compensation circuit 9, and the adjustment circuit 11.

[0052] The first amplifier circuit 8 amplifies an input voltage (in this example, a filter output voltage Vf) according to the duty ratio of the square wave voltage Va. The first amplifier circuit 8 is an inverting amplifier circuit including resistors 33, 34, 35, and 36 and an operational amplifier 31. The filter output voltage Vf (an example of an input voltage corresponding to the square wave voltage Va) is input to an inverting input terminal of the operational amplifier 31. A temperature compensation circuit 9 for compensating for the temperature characteristic of the above-mentioned offset error e is connected to a non-inverting input terminal of the operational amplifier 31.

[0053] The temperature compensation circuit 9 performs temperature compensation for the offset voltage included in the output voltage Vout2 of the second amplifier circuit 10. The temperature compensation circuit 9 adjusts the reference voltage of the first amplifier circuit 8 according to temperature, thereby reducing the offset voltage included in the output voltage Vout2 of the second amplifier circuit 10 to zero. The temperature compensation circuit 9 includes a voltage divider circuit that divides the power supply voltage (V+, V-) using a thermistor 40 and resistors 37, 38, and 39.

[0054] The second amplifier circuit 10 amplifies the output voltage Vout1 of the first amplifier circuit 8. The second amplifier circuit 10 is an inverting amplifier circuit including resistors 41, 42, 44, feedback resistors 49, 50, 51, and an operational amplifier 32. The output voltage Vout1 is input to an inverting input terminal of the operational amplifier 31. An adjustment circuit 11 is connected to a non-inverting input terminal of the operational amplifier 32 to adjust for individual differences in the offset error e of the current detection device 1.

[0055] The adjustment circuit 11 adjusts the reference voltage of the second amplifier circuit 10 to reduce the offset voltage included in the output voltage Vout2 of the second amplifier circuit 10 to zero. The adjustment circuit 11 includes a voltage divider circuit that divides the power supply voltage (V+, V−) using resistors 45, 46 and a variable resistor 47.

[0056] The current detection circuit 6 includes, as an operating current switching function, a switching circuit 43 that switches the gain of the second amplifier circuit 10. The switching circuit 43 includes a switch 48 and feedback resistors 49, 50, and 51 to switch the gain of the second amplifier circuit 10 to different values.

[0057] 8 is a schematic diagram illustrating an example of switching of the operating current. As shown in FIG. 8, the switching circuit 43 sets the amplification factor of the second amplifier circuit 10 so that the output voltage Vout2 of the second amplifier circuit 10 at each set operating current value is the same. This allows the downstream determination circuit 13 to perform a determination operation using the same (common) threshold voltage Vth3. The switching circuit 43 switches the amplification factor of the second amplifier circuit 10 by selecting a feedback resistor to be connected from feedback resistors 49, 50, and 51 using a switch 48 in accordance with a switching signal (e.g., an operation signal by a user) from outside the current detection device 1.

[0058] Next, the compensation operation for the offset error e will be described.

[0059] First, in Fig. 7, the adjustment circuit 11 adjusts the individual difference of the offset error e of the current detection device 1 at room temperature (for example, 25°C). For example, the adjustment circuit 11 adjusts the reference voltage of the non-inverting input terminal of the operational amplifier 32 so that the same voltage as the voltage obtained by converting the offset voltage included in the output voltage Vout2 into the input voltage of the operational amplifier 32 is applied to the non-inverting input terminal of the operational amplifier 32. The voltage obtained by converting the offset voltage included in the output voltage Vout2 into the input voltage of the operational amplifier 32 is a value obtained by dividing the output voltage Vout2 by the amplification factor of the second amplifier circuit 10. In this example, the adjustment circuit 11 applies a voltage obtained by dividing the power supply voltage (V+, V-) by resistors 45, 46 and a variable resistor 47 to the non-inverting input terminal of the operational amplifier 32. This makes it possible to compensate for the individual difference of the offset error e of the current detection device 1.

[0060] The adjustment circuit 11 adjusts the reference voltage of the non-inverting input terminal of the operational amplifier 32 by adjusting the resistance value of the variable resistor 47 according to, for example, a switching signal from outside the current detection device 1 (for example, an operation signal by a user).

[0061] The adjustment circuit 11 monitors the difference (offset voltage) between the output voltage Vout2 and the reference voltage when the current I flowing through the conductor 2 is zero, and adjusts the variable resistor 47 so that the difference becomes zero. At this time, the amplification factor set in the second amplifier circuit 10 may be any value. However, setting a higher amplification factor increases the value of the output voltage Vout2, and therefore the effect of the resolution of the measuring device that monitors the difference (offset voltage) between the output voltage Vout2 and the reference voltage becomes less noticeable.

[0062] Next, the temperature compensation circuit 9 adjusts the reference voltage of the non-inverting input terminal of the operational amplifier 31 so that a voltage equal to the voltage obtained by converting the offset voltage included in the output voltage Vout2 into the input voltage of the operational amplifier 31 is applied to the non-inverting input terminal of the operational amplifier 31. The voltage obtained by converting the offset voltage included in the output voltage Vout2 into the input voltage of the operational amplifier 31 is a value obtained by dividing the offset voltage included in the output voltage Vout2 by the amplification factor of the first amplifier circuit 8 and the amplification factor of the second amplifier circuit 10. The temperature compensation circuit 9 adjusts the reference voltage of the non-inverting input terminal of the operational amplifier 31 to cancel out the influence of the temperature characteristics of the offset error e and set the offset voltage included in the output voltage Vout2 to zero.

[0063] Fig. 9 is a diagram illustrating the relationship between temperature and the output of the temperature compensation circuit. As shown in Fig. 9, the temperature compensation circuit 9 adjusts the reference voltage of the non-inverting input terminal of the operational amplifier 31 so that a voltage equal to the offset error Vout2' converted into the input voltage of the operational amplifier 31 is applied to the non-inverting input terminal of the operational amplifier 31. The temperature compensation circuit 9 cancels the offset error e by the voltage generated by the temperature compensation circuit 9 so that the voltage approximately matches the temperature dependency of the offset error e measured in advance.

[0064] Here, the first amplifier circuit 8, the temperature compensation circuit 9, the second amplifier circuit 10, and the adjustment circuit 11 can be arranged in any order (even if the order of arrangement is changed), which has the effect of reducing the offset error e. However, in order to simplify the operation of switching the amplification factor of the second amplifier circuit 10, it is preferable that the temperature compensation circuit 9 is arranged on the input side (input section) of the first amplifier circuit 8, and the adjustment circuit 11 is arranged on the input side (input section) of the second amplifier circuit 10. The temperature compensation circuit 9 and the adjustment circuit 11 are arranged on the signal transmission path between the oscillation circuit 5 and the second amplifier circuit 10.

[0065] Specifically, the temperature compensation circuit 9 and the adjustment circuit 11 are arranged in front of the second amplifier circuit 10 having the gain switching function (operating current switching function). If the temperature compensation circuit 9 and the adjustment circuit 11 are arranged in the rear of the gain switching function, the offset error in the adjustment stage will change every time the gain is set, depending on the gain of the second amplifier circuit 10. This requires that the adjustment amount be changed every time the gain is switched, which causes inconveniences such as providing an additional adjustment mechanism in the temperature compensation circuit section and adjusting the offset error by the adjustment mechanism every time the gain is switched. Therefore, in order to simplify the circuit and adjustment, it is preferable to arrange the temperature compensation circuit 9 and the adjustment circuit 11 in front of the second amplifier circuit 10 having the gain switching function.

[0066] Since it is preferable to make the sensor output (output voltage) as high as possible in the stage preceding the adjustment circuit 11, amplification processing is performed in advance by a first amplifier circuit 8 having a fixed amplification factor. The variable resistor 47 used in the adjustment circuit 11 is easily affected by external noise such as radiated noise, and is prone to voltage fluctuations. Therefore, by setting (amplifying) the offsetting voltage level high in advance, highly accurate adjustment of the offset error e is achieved.

[0067] For example, when the amplification factor of the first amplifier circuit 8 is G1 and the amplification factor of the second amplifier circuit 10 is G2, when the operating current value (setting 1 in Figure 8) at which the total amplification factor Gtotal = G1 x G2 is the lowest, G2 = 1 and Gtotal is set to G1.

[0068] Next, an operation for compensating for fluctuations in the determination sensitivity of the determination circuit 13 due to individual differences in the current detection device 1 will be described.

[0069] The judgment sensitivity varies depending on the magnetic characteristics of the magnetic core 3 and the accuracy of the electronic components used in the signal processing. Therefore, in the case of a small operating current that requires particularly sensitive current detection, i.e., a high amplification factor, this variation cannot be ignored and leads to a deterioration in detection accuracy. Therefore, the adjustment circuit 14 adjusts the threshold voltage Vth3 for each current detection device 1 to compensate for the variation due to individual differences in the current detection device 1.

[0070] FIG. 10 is a diagram showing an example of an analog circuit configuration of an absolute value circuit, a determination circuit, and an adjustment circuit.

[0071] The absolute value circuit 12 receives the output voltage Vout2 of the second amplifier circuit 10. The absolute value circuit 12 converts the output voltage Vout2 into an output voltage Vout3 obtained by positively inverting a negative value lower than a reference voltage Vref. The absolute value circuit 12 generates the output voltage Vout3, which is the absolute value of the output voltage Vout2.

[0072] The absolute value circuit 12 includes two operational amplifiers 61 and 62, diodes 64 and 65, and resistors 66 to 70. The operational amplifier 61 outputs a sensor signal lower than a reference voltage as 0 (reference voltage), and inverts and outputs a signal higher than the reference voltage. Next, the operational amplifier 62 adds the signal from the operational amplifier 61 and the output voltage Vout2 from the second amplifier circuit 10 at a voltage ratio of 2:1, and then inverts and amplifies the result and outputs it. Through this operation, the output voltage Vout3 is generated as a sensor output obtained by inverting a negative sensor output lower than the reference voltage to a positive one.

[0073] The determination circuit 13 includes a comparator 63. The determination circuit 13 compares the output voltage Vout3 with a predetermined threshold voltage Vth3, and outputs a determination output signal that is at a high level when the output voltage Vout3 is equal to or higher than the threshold voltage Vth3, and is at a low level when the output voltage Vout3 is less than the threshold voltage Vth3.

[0074] The adjustment circuit 14 includes a voltage division circuit that divides the power supply voltage (V+, V-) using a variable resistor 74 and resistors 72, 73. The adjustment circuit 14 adjusts the threshold voltage Vth3 by dividing the power supply voltage (V+, V-) using the variable resistor 74 and resistors 72, 73, thereby compensating for individual differences in the judgment sensitivity of the current detection device 1, as shown in FIG.

[0075] Fig. 11 is a schematic diagram showing an example of the operation of the adjustment circuit. The dashed line represents the case of ideal sensor output. The solid line represents the case where the sensor output is not ideal due to the magnetic characteristics of the magnetic core 3 or the precision of the electronic components used in the signal processing. The adjustment circuit 14 adjusts the threshold voltage to Vth3', thereby causing the judgment circuit 13 to perform the judgment process at the target operating current (Id+, Id-).

[0076] The adjustment circuit 14 flows a target operating current beforehand, for example, at the time of shipping from a factory, and while monitoring the output of the determination circuit 13, gradually increases the threshold voltage Vth3 from a state in which no current is detected until it is determined that a current is detected.

[0077] As a method for compensating for the variation in sensor output sensitivity due to individual differences, in addition to adjusting the threshold as in the illustrated embodiment, a method of compensating by externally adjusting the amplification factor is also conceivable. However, as described above, it is not desirable to place a mechanism that varies the amplification factor in front of the temperature compensation circuit 9 and adjustment circuit 11 that compensate for the offset error. Under such constraints, in order to compensate for the variation in sensor output sensitivity with a simple circuit, the circuit configuration of the present disclosure is desirable.

[0078] With the above configuration, it is possible to realize a current detection device that can easily switch the operating current and detect DC current at low cost without depending on the ambient temperature. The adjustment of the adjustment circuit 11 and the adjustment of the adjustment circuit 14 may be performed, for example, at the time of shipment from the factory.

[0079] 12 is a diagram showing a configuration example of an earth leakage circuit breaker including a current detection device. The earth leakage circuit breaker 100 includes the current detection device 1 and a breaker means 200. The breaker means 200 is a breaker mechanism that breaks the electric circuit 15 when a current to be detected, such as a leakage current, is detected by the current detection device 1. The breaker means 200 breaks the electric circuit 15 based on a determination output signal from the current detection device 1.

[0080] The interrupting means 200 is, for example, an actuator that is connected to the current detection circuit 6 of the current detection device 1 and operates to interrupt the electric circuit 15 in response to the determination output signal. The interrupting means 200 may also include an electromagnetic contactor or the like that opens and closes the electric circuit 15. Furthermore, the interrupting means 200 may be an electronic circuit or the like that includes a semiconductor switching element. However, the configuration of the interrupting means 200 is not limited to these.

[0081] 13 is a diagram showing an example of the configuration of an earth leakage relay equipped with a current detection device. Earth leakage relay 300 includes current detection device 1 and relay 301. Relay 301 performs contact output when a current to be detected, such as a leakage current, is detected by current detection device 1. Relay 301 issues a contact output to the outside of earth leakage relay 300, for example, based on a determination output signal from current detection device 1. Breaking means 200 provided outside earth leakage relay 300 breaks the electric circuit when it receives the contact output.

[0082] Fig. 14 is a diagram showing a configuration example of the filter circuit 7. The filter circuit 7 generates a filter output voltage Vf as a voltage corresponding to the duty ratio of the square wave voltage Va. Fig. 14 shows an example in which the filter circuit 7 is an active filter using an operational amplifier 85. This active filter is a Sallen-Key type secondary low-pass filter having a non-inverting circuit configuration consisting of resistors 81 and 82, capacitors 83 and 84, and the operational amplifier 85. The filter circuit 7 is not limited to this configuration.

[0083] As described above, the embodiment has been described, but the above embodiment is presented as an example, and the present invention is not limited to the above embodiment. The above embodiment can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims.

[0084] In this embodiment, the controller or control circuit is an electronic circuit such as a central processing unit (CPU), a field programmable gate array (FPGA), or an application specific integrated circuit (ASIC). The controller or control circuit may be a computer having a memory and a processor. The controller or control circuit may perform various control operations described in this specification by executing a program such as an instruction code stored in the memory, or by being a circuit designed for a specific application. [Explanation of symbols]

[0085] 1 Current detection device 2 conductors 3. Magnetic Core 4 Excitation coil 5 Oscillator Circuit 6 Current detection circuit 7 Filter Circuit 8 First Amplifier Circuit 9 Temperature compensation circuit 10 Second amplifier circuit 11 Adjustment circuit 12 Absolute Value Circuit 13 Judgment circuit 14 Regulating circuit 15 Electric circuit 43 Switching Circuit 100 Earth Leakage Circuit Breaker 200 Cutting means 300 Earth Leakage Relay 301 Relay

Claims

1. a magnetic core surrounding a conductor through which a current to be detected flows; an excitation coil wound around the magnetic core; an oscillator circuit that generates a square wave voltage by exciting the magnetic core; a current detection circuit that detects the target current based on a change in the square wave voltage; a compensation circuit that compensates for an offset error of the oscillation circuit or the current detection circuit; the current detection circuit includes an amplifier circuit; the compensation circuit includes an adjustment circuit that adjusts an input voltage of the amplifier circuit to adjust an offset voltage included in an output voltage of the amplifier circuit; The current detection circuit includes a switching circuit that switches the amplification factor of the amplifier circuit by a switching signal.

2. A current detection device as described in claim 1, wherein the switching signal is a signal from outside the current detection device.

3. A current detection device as described in claim 1, wherein the switching signal is a signal from a user.

4. A current detection device as described in claim 1, wherein the switching circuit includes a switch that switches the amplification factor in accordance with the switching signal.

5. The amplifier circuit includes an operational amplifier, The current detection device according to claim 1 , wherein the switching circuit switches the amplification factor by selecting a feedback resistor connected to the operational amplifier in accordance with the switching signal.

6. A current detection device as described in claim 1, wherein the input voltage is a reference voltage of the amplifier circuit.

7. The current detection device of claim 1, wherein the adjustment circuit adjusts the input voltage using a variable resistor.

8. the current detection circuit includes a filter circuit that generates a voltage according to a duty ratio of the rectangular wave voltage; The current detection device according to claim 1 , wherein the amplifier circuit amplifies an output voltage of the filter circuit.

9. The current detection device according to claim 1 , wherein the compensation circuit includes a temperature compensation circuit that temperature compensates the offset voltage.

10. 10. The current detection device according to claim 9, wherein the temperature compensation circuit adjusts a reference voltage of the amplifier circuit to temperature compensate for the offset voltage.

11. The current sensing device of claim 10 , wherein the temperature compensation circuit includes a thermistor that adjusts the reference voltage.

12. The amplifier circuit includes a first amplifier circuit that outputs a first output voltage in response to the square wave voltage, and a second amplifier circuit that outputs a second output voltage in response to the first output voltage, The current detection device according to claim 9 , wherein the temperature compensation circuit and the adjustment circuit adjust an offset voltage included in the second output voltage.

13. The temperature compensation circuit adjusts an offset voltage included in the second output voltage by adjusting an input voltage of the first amplifier circuit according to temperature; The current detection device according to claim 12 , wherein the adjustment circuit adjusts an input voltage of the second amplifier circuit to adjust an offset voltage included in the second output voltage.

14. The current detection circuit includes: a determination circuit for determining occurrence of the target current based on an output voltage of the amplifier circuit; The current detection device according to claim 1 , further comprising: an adjustment circuit that adjusts a determination sensitivity of the determination circuit.

15. a magnetic core surrounding a conductor through which a current to be detected flows; an excitation coil wound around the magnetic core; an oscillator circuit that generates a square wave voltage by exciting the magnetic core; a current detection circuit that detects the target current based on a change in the square wave voltage; a compensation circuit that compensates for an offset error of the oscillation circuit or the current detection circuit; the current detection circuit includes an amplifier circuit; The compensation circuit includes a temperature compensation circuit that performs temperature compensation for an offset voltage included in the output voltage of the amplifier circuit.

16. A current detection device for detecting a target current flowing through a conductor; a breaker that breaks an electric circuit when the detected current is detected by the current detection device, The current detection device is a magnetic core surrounding a conductor through which a current to be detected flows; an excitation coil wound around the magnetic core; an oscillator circuit that generates a square wave voltage by exciting the magnetic core; a current detection circuit that detects the target current based on a change in the square wave voltage; a compensation circuit that compensates for an offset error of the oscillation circuit or the current detection circuit; the current detection circuit includes an amplifier circuit; the compensation circuit includes an adjustment circuit that adjusts an input voltage of the amplifier circuit to adjust an offset voltage included in an output voltage of the amplifier circuit; The current detection circuit includes a switching circuit that switches the amplification factor of the amplifier circuit by a switching signal.

17. A current detection device for detecting a target current flowing through a conductor; a relay that outputs a contact when the detected current is detected by the current detection device, The current detection device is a magnetic core surrounding a conductor through which a current to be detected flows; an excitation coil wound around the magnetic core; an oscillator circuit that generates a square wave voltage by exciting the magnetic core; a current detection circuit that detects the target current based on a change in the square wave voltage; a compensation circuit that compensates for an offset error of the oscillation circuit or the current detection circuit; the current detection circuit includes an amplifier circuit; the compensation circuit includes an adjustment circuit that adjusts an input voltage of the amplifier circuit to adjust an offset voltage included in an output voltage of the amplifier circuit; The current detection circuit includes a switching circuit that switches the amplification factor of the amplifier circuit by a switching signal.

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