Current sensor

Abstract

To provide a current sensor with which it is possible to correct resistance values for detection with good accuracy.SOLUTION: A current detection unit 15 detects a detection object current using the terminal voltage of a shunt resistor 4 which is provided in series to a path in which the detection object current flows and a resistance value for detection that corresponds to the resistance value of the shunt resistor 4. A relay control unit 17 controls on / off of relays RL1, RL2 that are provided so as to be serially interposed in the path in which the detection object current flows. A resistance value correction circuit 18 calculates the resistance value of the shunt resistor 4 and corrects the resistance value for detection on the basis of a calculated resistance value that is the calculated resistance value of the shunt resistor 4. The current detection unit 15 detects the detection object current in a period in which the relays RL1, RL2 are on-controlled by the relay control unit 17. The resistance value correction circuit 18 calculates the resistance value of the shunt resistor 4 in a period in which the relays RL1, RL2 are off-controlled by the relay control unit 17.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a current sensor that detects a detected current by using a terminal voltage of a shunt resistor provided in series with a path through which the detected current flows and a detection resistance value corresponding to the resistance value of the shunt resistor.

Background Art

[0002] As disclosed in Patent Documents 1 and 2, in a conventional current sensor, a terminal voltage of a shunt resistor provided in series with a path through which a detected current flows is measured, and a current value of a measurement target is calculated based on the measured voltage value and a detection resistance value corresponding to the resistance value of the shunt resistor. In this case, since the resistance value of the shunt resistor changes due to aging deterioration or the like, it is necessary to correct the detection resistance value used for calculating the current value at any time. In the following description, the conventional current sensor disclosed in Patent Document 1 will be referred to as the first conventional technique, and the conventional current sensor disclosed in Patent Document 2 will be referred to as the second conventional technique.

[0003] In the first conventional technique, the detection resistance value is corrected as follows. That is, the first conventional technique includes a sub-resistor provided so that a detected current flows therethrough in the same manner as the shunt resistor during normal times, and a correction resistor provided so that the detected current does not flow therethrough during normal times. According to the above configuration, although the sub-resistor deteriorates in the same manner as the shunt resistor, the correction resistor hardly deteriorates. In the first conventional technique, during correction, the degree of deterioration of the sub-resistor, and thus the shunt resistor, is obtained by comparing the resistance values of the sub-resistor and the correction resistor, and the detection resistance value is corrected based on this.

[0004] In the second prior art, the detection resistance value is corrected as follows. Specifically, the second prior art has a configuration in which a correction current is passed from the interconnection node of the multiple shunt resistors, or a configuration in which an input terminal is provided in the central part of the shunt resistor and the correction current is passed from that input terminal. In the second prior art, the detection resistance value is corrected by measuring the terminal voltage of each resistor when the correction current is passed and calculating the individual resistance value based on the measurement result. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Domestic Specification No. 8779777 [Patent Document 2] U.S. Patent No. 10473724 [Overview of the project] [Problems that the invention aims to solve]

[0006] In both the first and second prior art, the configuration is such that current flows through the object being measured when each measurement is performed to correct the detection resistance value. Therefore, in the configurations of the first and second prior art, errors occur in each measurement due to the influence of noise generated in the object being measured, making it impossible to correct the detection resistance value accurately, and as a result, the accuracy of current detection may decrease. This noise-related problem is even more pronounced when the object being measured is a motor or power converter, which can generate relatively large amounts of noise. Thus, it was difficult to improve the accuracy of correcting the detection resistance value in the first and second prior art.

[0007] This invention has been made in view of the above circumstances, and its purpose is to provide a current sensor that can accurately correct the detection resistance value. [Means for solving the problem]

[0008] The current sensor described in claim 1 comprises a current detection unit (15), relays (RL1, RL2), a relay control unit (17), and a resistance value correction circuit (18). The current detection unit detects the current using the terminal voltage of a shunt resistor (4) provided in series with the path through which the current to be detected flows, and a detection resistance value corresponding to the resistance value of the shunt resistor. The relay is provided so as to be interposed in series with the path through which the current to be detected flows. The relay control unit controls the on / off state of the relay. The resistance value correction circuit calculates the resistance value of the shunt resistor and corrects the detection resistance value based on the calculated resistance value, which is the calculated resistance value of the shunt resistor.

[0009] In the above configuration, during the period when the relay is ON, a current equivalent to the current flowing through the device to be measured, i.e., the detected current, flows through the shunt resistor. Therefore, the current detection unit detects the detected current during the period when the relay control unit controls the relay to ON. In this way, the current detection unit can accurately detect the detected current based on the terminal voltage of the shunt resistor, i.e., the voltage drop across the shunt resistor.

[0010] Furthermore, in the above configuration, no current to be detected flows to the object being measured during the period when the relay is turned off. Therefore, the resistance correction circuit calculates the resistance value of the shunt resistor during the period when the relay control unit controls the relay to be turned off. In this way, the resistance correction circuit can perform measurements to calculate the resistance value of the shunt resistor when no current to be detected is flowing. As a result, the resistance correction circuit can perform the above measurements without being affected by various noises generated by the flow of the current to be detected, and as a result, it can correct the detection resistance value with high accuracy.

[0011] Claim 1The resistance correction circuit for the current sensor described herein comprises a correction resistor (5), a signal application unit (6), a first voltage detection unit (7), a second voltage detection unit (8), and a correction unit (16). The correction resistor is connected in series with the shunt resistor in a path different from the path through which the detected current flows, and has higher resistance accuracy than the shunt resistor. The signal application unit applies an AC signal to the series circuit of the shunt resistor and the correction resistor. The first voltage detection unit detects the terminal voltage of the shunt resistor when an AC signal is applied to the series circuit. The second voltage detection unit detects the terminal voltage of the correction resistor when an AC signal is applied to the series circuit. The correction unit calculates the resistance value of the shunt resistor based on the first voltage detection value, which is the terminal voltage detected by the first voltage detection unit, and the second voltage detection value, which is the terminal voltage detected by the second voltage detection unit, and corrects the detection resistance value based on the calculated resistance value, which is the calculated resistance value of the shunt resistor.

[0012] This configuration allows for a further improvement in the accuracy of correcting the detection resistance value compared to the first and second prior art. Specifically, in the first prior art, correction is not performed directly using the shunt resistor; instead, it is assumed that the sub-resistor degrades similarly to the shunt resistor, and the detection resistance value corresponding to the shunt resistor's resistance value is indirectly corrected using the sub-resistor. Therefore, in the first prior art, if the above assumption does not hold true, it becomes impossible to correct the detection resistance value accurately, which may result in a decrease in the accuracy of current detection. In the second prior art, it is necessary to provide multiple shunt resistors or to provide an input terminal in the center of the shunt resistor, which complicates the configuration. Furthermore, in the second prior art, the accuracy of correcting the detection resistance value largely depends on the accuracy of the correction current, making it difficult to sufficiently improve the accuracy of the correction.

[0013] In contrast, with the above configuration, the detection resistance value can be directly corrected using a shunt resistor, without having to indirectly correct it using a sub-resistor as in the first conventional technology. Furthermore, with the above configuration, there is no need to provide multiple shunt resistors or to provide an input terminal in the center of the shunt resistor, as in the second conventional technology, and only one shunt resistor is required, thus not complicating the overall configuration of the current sensor.

[0014] Furthermore, with the above configuration, the accuracy of calculating the calculated resistance value, and consequently the accuracy of correcting the detection resistance value, largely depends on the accuracy of the correction resistor's resistance value and the detection accuracy of the first and second voltage detection values. In this case, since the correction resistor has higher resistance accuracy than the shunt resistor, the accuracy of correcting the detection resistance value can be sufficiently improved. Therefore, with the above configuration, the excellent effect of being able to accurately correct the detection resistance value without complicating the overall configuration of the current sensor is obtained. [Brief explanation of the drawing]

[0015] [Figure 1] This figure schematically shows the configuration of the current sensor according to the first embodiment. [Figure 2] This figure shows a specific first configuration example of the signal application unit according to the first embodiment. [Figure 3] This figure shows a specific second configuration example of the signal application unit according to the first embodiment. [Figure 4] This figure shows a specific third configuration example of the signal application unit according to the first embodiment. [Figure 5] This figure shows a specific fourth configuration example of the signal application unit according to the first embodiment. [Figure 6] This figure shows specific configuration examples of each synchronous detection circuit according to the first embodiment. [Figure 7] This figure schematically shows the configuration of a current sensor according to a modified example of the first embodiment. [Figure 8] This figure schematically shows the configuration of the current sensor according to the second embodiment. [Figure 9]Figure showing an example of a specific switching pattern for each state by the state switching unit according to the second embodiment

Mode for Carrying out the Invention

[0016] Hereinafter, a plurality of embodiments will be described with reference to the drawings. In each embodiment, substantially the same configurations are denoted by the same reference numerals and description thereof is omitted. (First Embodiment) Hereinafter, the first embodiment will be described with reference to FIGS. 1 to 7.

[0017] <Overall Configuration> The current sensor 1 of the present embodiment shown in FIG. 1 is mounted on a vehicle such as an automobile, and detects a detected current which is the current flowing through the measurement target 2. As the measurement target 2, a motor, a battery, a power converter, etc. mounted on the vehicle are assumed. As the measurement target 2, a battery such as a main battery that supplies power to a drive unit for driving the vehicle or an accessory battery that supplies power to accessories of the vehicle, a power converter such as a DC / DC converter or an inverter, etc. are assumed. The power converter supplies power to a motor that generates a driving force for driving the vehicle, and constitutes the above-described drive unit together with that motor.

[0018] In this case, a load 3 is connected in series to the measurement target 2, and a loop circuit is formed by the measurement target 2, the load 3, and relays RL1 and RL2 described later. As the load 3, when the measurement target 2 is the above-described battery, for example, the above-described motor, the above-described power converter, an electric compressor, etc. are assumed. Also, as the load 3, when the measurement target 2 is the above-described power converter, for example, the above-described motor, etc. are assumed. In the present embodiment, the motor and the inverter which is a power converter are the measurement target 2. That is, in the present embodiment, at least one of a motor mounted on the vehicle and a power converter for supplying power to the motor is provided in the path through which the detected current flows.

[0019] The current sensor 1 comprises a shunt resistor 4, relays RL1 and RL2, a correction resistor 5, a signal application unit 6, a first voltage detection unit 7, a second voltage detection unit 8, and a control unit 9. One terminal of the shunt resistor 4 is connected to one terminal of the load 3 via relay RL1, and the other terminal is connected to ground, which is the reference potential of the circuit, and also to the low-potential side terminal of the object to be measured 2.

[0020] The other terminal of load 3 is connected to the high-potential terminal of the device to be measured 2 via relay RL2. In other words, shunt resistor 4 is provided in series with the path through which the detected current flows. Relays RL1 and RL2 are also provided so as to be interposed in series with the path through which the detected current flows. Current sensor 1 detects the detected current using the terminal voltage of the shunt resistor 4 provided in this manner and a detection resistance value corresponding to the resistance value of shunt resistor 4.

[0021] One terminal of the correction resistor 5 is connected to the signal application unit 6, and the other terminal is connected to one terminal of the shunt resistor 4. In other words, the correction resistor 5 is connected in series with the shunt resistor 4 in a path different from the path through which the detected current flows. In this case, since the detected current is a relatively large current, the resistance value of the shunt resistor 4 is relatively small, for example, on the order of μΩ.

[0022] On the other hand, since no relatively large detected current flows through the correction resistor 5, its resistance value is relatively large, for example, on the order of mΩ. Generally, it is difficult to accurately manufacture resistors with small resistance values, but it is relatively easy to accurately manufacture resistors with large resistance values. For this reason, in this embodiment, the resistance accuracy of the correction resistor 5 is sufficiently higher than that of the shunt resistor 4.

[0023] During correction, when the detection resistance value correction described later is performed, the signal application unit 6 applies a pulse wave or sinusoidal AC signal to the series circuit of the shunt resistor 4 and the correction resistor 5. In other words, during correction, the signal application unit 6 applies the same AC signal to the shunt resistor 4 and the correction resistor 5. In this case, the signal application unit 6 is configured as a current source that supplies AC current to the series circuit from a power line 10 supplied with, for example, a +5V power supply voltage VDD. The operation of such a signal application unit 6 is controlled by the control unit 9. In other words, the control unit 9 can control the execution and cessation of the application of AC signals by the signal application unit 6.

[0024] The first voltage detection unit 7 detects the terminal voltage of the shunt resistor 4 when an AC signal is applied to the series circuit of the shunt resistor 4 and the correction resistor 5, and includes a first A / D converter 11 and a first synchronous detection circuit 12. In drawings such as Figure 1, the A / D converter is abbreviated as ADC. The first A / D converter 11 performs the following A / D conversion operation to detect the terminal voltage of the shunt resistor 4. That is, the first A / D converter 11 takes the signals from each terminal of the shunt resistor 4 as input and performs A / D conversion on each of these signals to output a digital signal corresponding to the difference in the terminal voltages of the shunt resistor 4, i.e., the terminal voltage of the shunt resistor 4. In this way, the digital signal output from the first A / D converter 11 is a signal corresponding to the signals at the terminals of the shunt resistor 4.

[0025] The first synchronous detection circuit 12 receives the digital signal output from the first A / D converter 11 and performs synchronous detection at the same frequency as the AC signal in the signal application unit 6 to extract the signal, and outputs the extracted signal to the control unit 9. The output signal of the first synchronous detection circuit 12 corresponds to the terminal voltage of the shunt resistor 4. In this way, during correction, the first voltage detection unit 7 is configured to detect the terminal voltage of the shunt resistor 4 based on the output signal of the first synchronous detection circuit 12, and outputs a signal representing the first voltage detection value, which is the detected value of that terminal voltage, to the control unit 9.

[0026] The first voltage detection unit 7 detects the terminal voltage of the shunt resistor 4 when no AC signal is applied to the series circuit of the shunt resistor 4 and the correction resistor 5, that is, under normal conditions, as follows. That is, under normal conditions, the first A / D converter 11 performs A / D conversion operation in the same way as during correction. In this case, the digital signal output from the first A / D converter 11 is output to the control unit 9 without being input to the first synchronous detection circuit 12. In other words, under normal conditions, the first voltage detection unit 7 detects the terminal voltage of the shunt resistor 4 based on the output signal of the first A / D converter 11, and outputs a signal representing the first voltage detection value, which is the detected value of that terminal voltage, to the control unit 9.

[0027] The second voltage detection unit 8 detects the terminal voltage of the correction resistor 5 when an AC signal is applied to the series circuit of the shunt resistor 4 and the correction resistor 5, and includes a second A / D converter 13 and a second synchronous detection circuit 14. The second A / D converter 13 performs the following A / D conversion operation to detect the terminal voltage of the correction resistor 5. That is, the second A / D converter 13 takes the signals from each terminal of the correction resistor 5 as input and performs A / D conversion on each of these signals to output a digital signal corresponding to the difference in the terminal voltages of the correction resistor 5, i.e., the terminal voltage of the correction resistor 5. In this way, the digital signal output from the second A / D converter 13 is a signal corresponding to the signals at the terminals of the correction resistor 5.

[0028] The second synchronous detection circuit 14 receives the digital signal output from the second A / D converter 13 and performs synchronous detection at the same frequency as the AC signal in the signal application unit 6 to extract the signal, which is then output to the control unit 9. The output signal of the second synchronous detection circuit 14 corresponds to the terminal voltage of the correction resistor 5. In this way, during correction, the second voltage detection unit 8 is configured to detect the terminal voltage of the correction resistor 5 based on the output signal of the second synchronous detection circuit 14, and outputs a signal representing the second voltage detection value, which is the detected value of that terminal voltage, to the control unit 9.

[0029] The control unit 9, together with the first voltage detection unit 7 and the second voltage detection unit 8, is configured as the same semiconductor integrated circuit, such as an ASIC. ASIC stands for Application Specific Integrated Circuit. The control unit 9 includes functional blocks such as a current detection unit 15, a correction unit 16, and a relay control unit 17. Each of these functional blocks is implemented in hardware.

[0030] The control unit 9 can be configured as a separate semiconductor integrated circuit from the first voltage detection unit 7 and the second voltage detection unit 8. For example, the control unit 9 can be configured as a microcomputer equipped with a CPU, RAM, ROM, etc. In this case, each of the above-mentioned functional blocks is realized by the CPU of the control unit 9 executing a computer program stored in ROM or the like to perform processing corresponding to the computer program; in other words, it is realized by software. In this case, at least a part of each functional block may be realized by hardware.

[0031] The current detection unit 15 detects the current to be detected using a signal corresponding to the terminal voltage of the shunt resistor 4 output from the first voltage detection unit 7 under normal conditions, and a detection resistance value corresponding to the resistance value of the shunt resistor 4. The detection resistance value is set based on the initial resistance value of the shunt resistor 4 actually used and is stored in the memory of the control unit 9. However, since the shunt resistor 4 is subjected to a relatively large current, the detected current, under normal conditions, its resistance value changes from its initial value due to aging and other factors.

[0032] Therefore, the detection resistance value described above is corrected as needed by the operation of the correction unit 16. During correction, the correction unit 16 calculates the resistance value of the shunt resistor 4 based on the signal representing the first voltage detection value output from the first voltage detection unit 7 and the signal representing the second voltage detection value output from the second voltage detection unit 8, and the correction resistance value corresponding to the resistance value of the correction resistor 5. The correction unit 16 corrects the detection resistance value based on the calculated resistance value, which is the calculated resistance value of the shunt resistor 4. For example, the correction unit 16 can correct the detection resistance value to match the calculated resistance value.

[0033] The correction resistance value described above is the initial resistance value of the correction resistor 5 actually used, and is pre-stored in the memory of the control unit 9. Since no current is normally drawn from the correction resistor 5, its resistance value hardly changes from its initial value due to aging or other factors. Thus, in the above configuration, the correction resistor 5, signal application unit 6, first voltage detection unit 7, second voltage detection unit 8, and correction unit 16 constitute a resistance value correction circuit 18 that corrects the detection resistance value.

[0034] The relay control unit 17 controls the on / off state of relays RL1 and RL2. When the relay control unit 17 turns on relay RL1, it also turns on relay RL2, and when it turns off relay RL1, it also turns off relay RL2. In other words, the relay control unit 17 controls the on / off state of the two relays RL1 and RL2 in the same way. With this configuration, even if one of the two relays RL1 and RL2 is stuck in the on state, the power supply to the load 3 can be cut off by turning off the other relay, thereby increasing the safety of the vehicle. In this embodiment, two relays RL1 and RL2 are provided to enhance safety, but a configuration in which a single relay is interposed in series in the path through which the detected current flows may also be used.

[0035] The relay control unit 17 normally controls both relays RL1 and RL2 to be ON, and during correction, it controls both relays RL1 and RL2 to be OFF. Therefore, the current detection unit 15 detects the detected current during the period when relays RL1 and RL2 are controlled ON by the relay control unit 17. In addition, the resistance value correction circuit 18 calculates the resistance value of the shunt resistor 4 during the period when relays RL1 and RL2 are controlled OFF by the relay control unit 17.

[0036] <Specific configuration of the signal application section> Specific configurations of the signal application unit 6 include, for example, the first configuration example shown in Figure 2, the second configuration example shown in Figure 3, the third configuration example shown in Figure 4, and the fourth configuration example shown in Figure 5. [1] First configuration example As shown in Figure 2, the signal application unit 6a of the first configuration example includes a transistor 21, a signal generation unit 22, an operational amplifier 23, and the like. The transistor 21 is, for example, an N-channel MOSFET, whose drain is connected to the power line 10 via a correction resistor 5, and whose source is connected to ground via a shunt resistor 4. The signal generation unit 22 generates and outputs a pulse wave or sinusoidal wave signal having the same frequency as the AC current applied to the series circuit of the shunt resistor 4 and the correction resistor 5.

[0037] The output signal of the signal generation unit 22 is supplied to the non-inverting input terminal of the operational amplifier 23. The inverting input terminal of the operational amplifier 23 is connected to the drain of the transistor 21, and its output terminal is connected to the gate of the transistor 21. With the above configuration, the transistor 21 is driven by the operational amplifier 23, thereby applying an AC signal, which is an AC current, to the series circuit of the shunt resistor 4 and the correction resistor 5. In this way, the signal application unit 6a in the first configuration example is configured to drive an amplifier. In this case, the correction resistor 5 also functions as a current source for the signal application unit 6a.

[0038] [2] Second Configuration Example As shown in Figure 3, the signal application unit 6b of the second configuration example differs from the signal application unit 6a of the first configuration example shown in Figure 2 in that a resistor 24 is added. In this case, the drain of transistor 21 is connected to the power line 10 via resistor 24, and its source is connected to ground via correction resistor 5 and shunt resistor 4.

[0039] In the above configuration, as in the first configuration example, the transistor 21 is driven by the operational amplifier 23, thereby applying an AC signal, which is an AC current, to the series circuit of the shunt resistor 4 and the correction resistor 5. Thus, the signal application unit 6b in the second configuration example is amplifier-driven, similar to the signal application unit 6a in the first configuration example. In this case, the resistor 24 and transistor 21, which are provided separately from the correction resistor 5, function as current sources for the signal application unit 6b.

[0040] [3] Third Configuration Example As shown in Figure 4, the signal application unit 6c of the third configuration example differs from the signal application unit 6a of the first configuration example shown in Figure 2 in that it is equipped with a buffer 25 instead of an op-amp 23. In this case, the output signal of the signal generation unit 22 is supplied to the input terminal of the buffer 25. The output terminal of the buffer 25 is connected to the gate of the transistor 21. With the above configuration, the transistor 21 is driven by the buffer 25, thereby applying an AC signal, which is an AC current, to the series circuit of the shunt resistor 4 and the correction resistor 5. Thus, the signal application unit 6c of the third configuration example is configured to be buffer-driven.

[0041] [4] Fourth configuration example As shown in Figure 5, the signal application unit 6d of the fourth configuration example differs from the signal application unit 6b of the second configuration example shown in Figure 3 in that it is equipped with a buffer 25 instead of an op-amp 23. In this case, the output signal of the signal generation unit 22 is supplied to the input terminal of the buffer 25. The output terminal of the buffer 25 is connected to the gate of the transistor 21. With the above configuration, the transistor 21 is driven by the buffer 25, thereby applying an AC signal, which is an AC current, to the series circuit of the shunt resistor 4 and the correction resistor 5. Thus, the signal application unit 6d of the fourth configuration example is configured to be buffer-driven.

[0042] [5] Characteristics of each configuration example In the first and third configurations, the correction resistor 5 is positioned close to the power line 10 and the shunt resistor 4 is positioned close to ground, resulting in the first voltage detection unit 7 and the second voltage detection unit 8 detecting voltages at significantly different potentials. Therefore, while the first and third configurations are more prone to detection errors in the terminal voltages of the shunt resistor 4 and the correction resistor 5 compared to the second and fourth configurations, they have the advantage of reducing the number of components because the correction resistor 5 also serves as the current source for the signal application units 6a and 6c.

[0043] The second and fourth configurations have the disadvantage of having more components than the first and third configurations because they require a separate resistor 24 in addition to the correction resistor 5 to constitute the current source for the signal application units 6b and 6d. However, in the second and fourth configurations, both the correction resistor 5 and the shunt resistor 4 are positioned close to ground, so the first voltage detection unit 7 and the second voltage detection unit 8 detect voltages at similar potentials. Therefore, the second and fourth configurations have the advantage of being able to keep the detection error of the terminal voltages of the shunt resistor 4 and the correction resistor 5 smaller compared to the first and third configurations.

[0044] In the first and second configurations, which are amplifier-driven configurations, the drain voltage of the transistor 21 is controlled to a constant value by the operation of the op-amp 23. This has the advantage of improving the accuracy of the AC current applied to the series circuit of the shunt resistor 4 and the correction resistor 5 compared to the third and fourth configurations, which are buffer-driven configurations. On the other hand, the third and fourth configurations have the advantage of reducing the circuit size compared to the first and second configurations by using a buffer 25 instead of the op-amp 23.

[0045] <Specific configuration of each synchronous detection circuit> Specific configurations of the first synchronous detection circuit 12 and the second synchronous detection circuit 14 include, for example, the configuration shown in Figure 6. In this case, the AC signal, which is an AC current applied by the signal application unit 6 to the series circuit of the shunt resistor 4 and the correction resistor 5, is "Io·cos(ωt)", the resistance value of the correction resistor 5 is R1, and the resistance value of the shunt resistor 4 is R2. Here, ω is the angular frequency and t is time.

[0046] As shown in Figure 6, the first synchronous detection circuit 12 includes multipliers 31 and 32, low-pass filters 33 and 34, and an arithmetic unit 35. In this specification, the low-pass filter may be abbreviated as LPF. During correction, when an AC signal is applied to the series circuit of the shunt resistor 4 and the correction resistor 5, the digital signal output from the first A / D converter 11 is input to one of the input terminals of the multipliers 31 and 32 of the first synchronous detection circuit 12. This digital signal corresponds to the terminal voltage of the shunt resistor 4 during correction and can be expressed as "R2·Io·cos(ωt+φ2)".

[0047] A cosine wave signal "cos(ωt)" is input to the other input terminal of multiplier 31. A sine wave signal "-sin(ωt)" is input to the other input terminal of multiplier 32. As a result, the angular frequency ω signal is extracted as a DC component in the output signals of multipliers 31 and 32. The output signals of multipliers 31 and 32 are input to LPFs 33 and 34, respectively.

[0048] The output signal I2 of LPF33 is a low-frequency signal proportional to the common-mode component of the input signal, and the output signal Q2 of LPF34 is a low-frequency signal proportional to the quadrature-phase component of the input signal. The arithmetic unit 35 calculates the square root of the sum of the squares of signals I2 and Q2 and outputs a signal representing the result of the calculation. The output signal of the arithmetic unit 35 can be expressed as "R2·Io". The output signal of the arithmetic unit 35 becomes the output signal of the first synchronous detection circuit 12 and is supplied to the correction unit 16 of the control unit 9.

[0049] The second synchronous detection circuit 14 includes multipliers 36 and 37, low-pass filters 38 and 39, and an arithmetic unit 40. During correction, when an AC signal is applied to the series circuit of the shunt resistor 4 and the correction resistor 5, the digital signal output from the second A / D converter 13 is input to one of the input terminals of the multipliers 36 and 37 of the second synchronous detection circuit 14. This digital signal corresponds to the terminal voltage of the correction resistor 5 during correction and can be expressed as "R1·Io·cos(ωt+φ1)".

[0050] The other input terminal of multiplier 36 is input to a cosine wave signal "cos(ωt)". The other input terminal of multiplier 37 is input to a sine wave signal "-sin(ωt)". As a result, the angular frequency ω signal is extracted as a DC component in the output signals of multipliers 36 and 37. The output signals of multipliers 36 and 37 are input to LPFs 38 and 39, respectively.

[0051] The output signal I1 of LPF38 is a low-frequency signal proportional to the common-mode component of the input signal, and the output signal Q1 of LPF39 is a low-frequency signal proportional to the quadrature-phase component of the input signal. The arithmetic unit 40 calculates the square root of the sum of the squares of signals I1 and Q1 and outputs a signal representing the result of the calculation. The output signal of the arithmetic unit 40 can be expressed as "R1·Io". The output signal of the arithmetic unit 40 becomes the output signal of the second synchronous detection circuit 14 and is supplied to the correction unit 16 of the control unit 9.

[0052] The correction unit 16 obtains the value "R2 / R1" by dividing the output signal "R2·Io" of the first synchronous detection circuit 12 by the output signal "R1·Io" of the second synchronous detection circuit 14. Here, the resistance value R1 of the correction resistor 5 is a known value and is stored in advance in the memory of the control unit 9. Therefore, the correction unit 16 can calculate the current resistance value R2 of the shunt resistor 4, i.e., the calculated resistance value, by multiplying the value "R2 / R1" obtained as described above by the resistance value R1 that is stored in advance.

[0053] According to the embodiment described above, the following effects can be obtained. In the current sensor 1 of this embodiment, during the period when relays RL1 and RL2 are turned on, a current equivalent to the current flowing through the current to be measured 2, i.e., the detected current, flows through the shunt resistor 4. Therefore, the current detection unit 15 detects the detected current during the period when relays RL1 and RL2 are controlled to be turned on by the relay control unit 17. In this way, the current detection unit 15 can accurately detect the detected current based on the terminal voltage of the shunt resistor 4, i.e., the voltage drop across the shunt resistor 4.

[0054] Furthermore, in the current sensor 1 of this embodiment, no current to be detected flows to the measurement target 2 during the period when relays RL1 and RL2 are turned off. Therefore, the resistance value correction circuit 18 calculates the resistance value of the shunt resistor 4 during the period when relays RL1 and RL2 are controlled to be turned off by the relay control unit 17. In this way, the resistance value correction circuit 18 can perform measurements to calculate the resistance value of the shunt resistor 4 when no current to be detected is flowing. As a result, the resistance value correction circuit 18 can perform the above measurements without being affected by various noises generated by the flow of the current to be detected, and as a result, it can correct the detection resistance value with high accuracy.

[0055] In the first and second prior art, the current to be measured is connected in parallel between both terminals of the shunt resistor, which means that measurement errors may occur due to the impedance of the current to be measured. In contrast, in the current sensor 1 of this embodiment, the resistance value correction circuit 18 performs the measurement to calculate the resistance value of the shunt resistor 4 during the period when relays RL1 and RL2 are turned off by the relay control unit 17, that is, when the current to be measured 2 and load 3 are not connected in parallel between both terminals of the shunt resistor 4. Therefore, according to this embodiment, it is possible to perform the above measurement without being affected by the impedance of the current to be measured 2 and load 3, etc., and the measurement error is suppressed even more than in the first and second prior art, and as a result, the correction of the detection resistance value can be performed with even greater accuracy.

[0056] In the current sensor 1 of this embodiment, the resistance value correction circuit 18 for correcting the detection resistance value comprises a correction resistor 5, a signal application unit 6, a first voltage detection unit 7, a second voltage detection unit 8, and a correction unit 16. The correction resistor 5 is connected in series with the shunt resistor 4 in a path different from the path through which the detected current flows, and has higher resistance accuracy than the shunt resistor 4. The signal application unit 6 applies an AC signal to the series circuit of the shunt resistor 4 and the correction resistor 5.

[0057] The first voltage detection unit 7 detects the terminal voltage of the shunt resistor 4 when an AC signal is applied to the series circuit. The second voltage detection unit 8 detects the terminal voltage of the correction resistor 5 when an AC signal is applied to the series circuit. The correction unit 16 calculates the resistance value of the shunt resistor 4 based on the first voltage detection value, which is the terminal voltage detected by the first voltage detection unit 7, and the second voltage detection value, which is the terminal voltage detected by the second voltage detection unit 8, and corrects the detection resistance value based on the calculated resistance value, which is the calculated resistance value of the shunt resistor 4.

[0058] With this configuration, the detection resistance value can be directly corrected using the shunt resistor 4, without having to indirectly correct it using a sub-resistor as in the first conventional technology. Furthermore, with this configuration, there is no need to provide multiple shunt resistors or an input terminal in the center of the shunt resistor, as in the second conventional technology, and only one shunt resistor 4 is needed, thus not complicating the overall configuration of the current sensor 1.

[0059] Furthermore, with the above configuration, the accuracy of calculating the calculated resistance value, and consequently the accuracy of correcting the detection resistance value, largely depends on the accuracy of the resistance value of the correction resistor 5 and the detection accuracy of the first voltage detection value and the second voltage detection value. In this case, since the correction resistor 5 has higher resistance accuracy than the shunt resistor 4, the accuracy of correcting the detection resistance value can be sufficiently improved. Therefore, this embodiment provides the excellent effect of being able to accurately correct the detection resistance value without complicating the overall configuration of the current sensor 1.

[0060] In this case, the first voltage detection unit 7 includes a first synchronous detection circuit 12 that receives the signal from the terminals of the shunt resistor 4, performs synchronous detection at the same frequency as the AC signal to extract and output the signal, and detects the terminal voltage of the shunt resistor 4 based on the output signal of the first synchronous detection circuit 12. In this case, the second voltage detection unit 8 includes a second synchronous detection circuit 14 that receives the signal from the terminals of the correction resistor 5, performs synchronous detection at the same frequency as the AC signal to extract and output the signal, and detects the terminal voltage of the correction resistor 5 based on the output signal of the second synchronous detection circuit 14.

[0061] With this configuration, the terminal voltages of the shunt resistor 4 and the correction resistor 5 are detected by signals extracted through synchronous detection at the same frequency as the AC signal applied to the shunt resistor 4 and the correction resistor 5. Therefore, according to this embodiment, the detection accuracy of the first voltage detection value and the second voltage detection value is suppressed due to the influence of noise such as thermoelectric power and circuit offset, and as a result, the accuracy of the correction of the detection resistance value can be further improved.

[0062] The signal application unit 6 applies a pulse wave or sinusoidal AC signal to the series circuit of the shunt resistor 4 and the correction resistor 5. When the signal application unit 6 applies a sinusoidal AC signal, although the configuration for generating the AC signal, specifically the configuration of the signal generation unit 22, becomes more complex, it is possible to generate a signal that contains only the desired frequency components as an AC signal, thereby reducing the detection error of the first voltage detection value and the second voltage detection value, or in other words, improving the accuracy of the correction of the detection resistance value. On the other hand, when the signal application unit 6 applies a pulse wave AC signal, although there is a risk of errors in detecting the first voltage detection value and the second voltage detection value because the AC signal contains harmonic components, the configuration for generating the AC signal, specifically the configuration of the signal generation unit 22, can be simplified.

[0063] The following describes some modified examples of this embodiment. <Example of arrangement of shunt resistor 4> In this embodiment, the shunt resistor 4 was configured to be located on the low side of the device to be measured 2. However, the shunt resistor 4 only needs to be located in series with the path through which the detected current flows, and its arrangement can be changed as appropriate. For example, a modified configuration such as that shown in Figure 7 can be adopted for the arrangement of the shunt resistor 4.

[0064] As shown in Figure 7, in the modified configuration of the current sensor 41, one terminal of the shunt resistor 4 is connected to one terminal of the load 3 via relay RL1, and the other terminal is connected to the high-potential terminal of the object to be measured 2. In this case, the low-potential terminal of the object to be measured 2 is connected to ground, which is the reference potential of the circuit, and is also connected to the other terminal of the load via relay RL2. In other words, in this case, the shunt resistor 4 is located on the high side of the object to be measured 2. Even with this modified configuration, the same effects as in the embodiment can be obtained.

[0065] The resistance correction circuit 18 was configured to calculate the resistance value of the shunt resistor 4 during the period when relays RL1 and RL2 are turned off by the relay control unit 17. However, it is also possible to calculate the resistance value of the shunt resistor 4 during the period when relays RL1 and RL2 are turned on by the relay control unit 17. Therefore, the following modification can be adopted. In this modification, the current detection unit 15 detects the detected current during the period when relays RL1 and RL2 are turned on by the relay control unit 17, and the resistance correction circuit 18 calculates the resistance value of the shunt resistor 4. In addition, in this modification, the resistance correction circuit 18 calculates the resistance value of the shunt resistor 4 during the period when relays RL1 and RL2 are turned off by the relay control unit 17.

[0066] According to the above modified example, the resistance value of the shunt resistor 4 can be calculated even during the period when relays RL1 and RL2 are ON. The calculation result of the resistance value of the shunt resistor 4 during the period when relays RL1 and RL2 are ON can be used as follows. That is, the accuracy of the resistance value calculation during the period when relays RL1 and RL2 are ON is lower than the accuracy of the resistance value calculation during the period when relays RL1 and RL2 are OFF, because the detected current flows through the object being measured 2.

[0067] Therefore, the above resistance value calculation result is not suitable for use in correcting the detection resistance value. However, it is possible to determine from the above resistance value calculation result whether or not the resistance value of shunt resistor 4 has changed significantly. Thus, according to this modified version, it is possible to determine whether or not a malfunction such as a break in the shunt resistor 4 has occurred using the above resistance value calculation result. In other words, according to this modified version, it becomes possible to diagnose malfunctions in shunt resistor 4, etc., during the period when relays RL1 and RL2 are turned on, thereby improving vehicle safety and ultimately contributing to the realization of functional safety.

[0068] (Second Embodiment) The second embodiment will be described below with reference to Figures 8 and 9. As shown in Figure 8, the current sensor 51 of this embodiment differs from the current sensor 1 of the first embodiment shown in Figure 1 in that it has a control unit 52 instead of a control unit 9. In addition to the functional blocks provided by the control unit 9, the control unit 52 has two functional blocks: a state signal input unit 53 and a state switching unit 54.

[0069] The status signal input unit 53 receives a status signal Sa supplied from outside the current sensor 51. The status signal Sa is a signal that represents the status of the motor and power converter assumed to be the measurement target 2 and load 3, that is, the motor mounted on the vehicle and the power converter for supplying power to the motor. Based on the status signal Sa input via the status signal input unit 53, the status switching unit 54 switches the state of the current sensor 51 to one of the first state, second state, or third state.

[0070] The first state is when the relay control unit 17 turns on relays RL1 and RL2, and the current detection unit 15 detects the current to be detected. The second state is when the relay control unit 17 turns on relays RL1 and RL2, the current detection unit 15 detects the current to be detected, and the resistance value correction circuit 18 calculates the resistance value of the shunt resistor 4. The third state is when the relay control unit 17 turns off relays RL1 and RL2, and the resistance value correction circuit 18 calculates the resistance value of the shunt resistor 4. In the third state, the resistance value correction circuit 18 also corrects the detection resistance value.

[0071] As for specific switching patterns for each state by the state switching unit 54, there are three patterns, for example, as shown in Figure 9. [1] Pattern 1 In the first pattern P1, the state switching unit 54 switches the state of the current sensor 51 to the first state when the state signal Sa indicates that the motor and power converter are being driven. The state in which the motor and power converter are being driven corresponds to the state in which the vehicle is being driven by a driver and the vehicle is in motion. Therefore, in Figure 9 and the following explanation, this state may be referred to as "driving and in motion".

[0072] Furthermore, in the first pattern P1, the state switching unit 54 switches the state of the current sensor 51 to the third state when the state signal Sa indicates that the power supply to the motor and power converter has been stopped. The state in which the power supply to the motor and power converter has been stopped corresponds to a state in which the vehicle is not being driven by the driver and the power supply to the components related to the vehicle's operation is turned off. Therefore, in Figure 9 and the following description, this state may be referred to as "power OFF". Note that in the first pattern P1, the state switching unit 54 does not switch the state of the current sensor 51 to the second state.

[0073] [2] Second pattern In the second pattern P2, the state switching unit 54 switches the state of the current sensor 51 to the second state when the state signal Sa indicates that the motor and power converter are running. Also in the second pattern P2, the state switching unit 54 switches the state of the current sensor 51 to the third state when the state signal Sa indicates that the power supply to the motor and power converter has been stopped.

[0074] [3] Third pattern In the third pattern P3, the state switching unit 54 switches the state of the current sensor 51 to the first state when the state signal Sa indicates that the motor and power converter are running. Also in the third pattern P3, the state switching unit 54 switches the state of the current sensor 51 to the second state when the state signal Sa indicates that the motor is stopped and the power converter is running.

[0075] The state in which the motor is stopped and the power converter is running corresponds to the state in which the vehicle is being driven by the driver and is also temporarily stopped. Therefore, in Figure 9, this state is represented as "driving and temporarily stopped". In the third pattern P3, the state switching unit 54 switches the state of the current sensor 51 to the third state when the state signal Sa indicates that the power supply to the motor and power converter has been stopped.

[0076] As described above, the current sensor 51 of this embodiment can switch to any of the following states based on a state signal Sa representing the state of the motor and power converter mounted on the vehicle: a first state in which relays RL1 and RL2 are turned ON and the detected current is detected; a second state in which relays RL1 and RL2 are turned ON, the detected current is detected and the resistance value of the shunt resistor 4 is calculated; and a third state in which relays RL1 and RL2 are turned OFF and the resistance value of the shunt resistor 4 is calculated.

[0077] With this configuration, based on the state of the vehicle at that time—specifically whether the vehicle is in operation and moving, in operation and stopped, or the vehicle's power is off—it becomes possible to switch to the most optimal of three states: a first state in which the detected current is detected, a second state in which the detected current is detected and the resistance value of the shunt resistor 4 is calculated with relatively low accuracy, and a third state in which the resistance value of the shunt resistor 4 is calculated with relatively high accuracy.

[0078] The state switching unit 54 can switch between the above states according to the first pattern P1, second pattern P2, and third pattern P3 described above. According to the first pattern P1, it is possible to stop the operation of the resistance value correction circuit 18 while driving, and as a result, the current consumption of the current sensor 51 can be reduced. According to the second pattern P2, it is possible to perform fault diagnosis regarding short-circuit failures of the shunt resistor 4, etc., while driving, and as a result, the safety of the vehicle can be improved.

[0079] According to the third pattern P3, it becomes possible to stop the operation of the resistance value correction circuit 18 while driving and while the vehicle is in motion, and it becomes possible to perform fault diagnosis regarding short-circuit failures of the shunt resistor 4 while driving and while the vehicle is stopped. As a result, although the effect is less than that of the first pattern P1, the effect of reducing the current consumption of the current sensor 51 is obtained, and although the effect is less than that of the second pattern P2, the effect of improving vehicle safety is obtained.

[0080] Furthermore, the resistance value of the shunt resistor 4 can be calculated when the power is off using any of the first pattern P1, second pattern P2, and third pattern P3. Therefore, the resistance value of the shunt resistor 4 can be calculated with higher accuracy using any of the first pattern P1, second pattern P2, and third pattern P3, without being affected by noise generated in the motor and power converter, and as a result, the correction of the detection resistance value can be performed with even greater accuracy.

[0081] (Other embodiments) It should be noted that the present invention is not limited to the embodiments described above and shown in the drawings, and can be arbitrarily modified, combined, or expanded without departing from its essence. The numerical values ​​and other figures shown in each of the above embodiments are illustrative examples and are not limiting.

[0082] The specific configuration of the signal application unit 6 is not limited to the configurations described in each of the above embodiments, and any configuration that can apply an AC signal to the series circuit of the shunt resistor 4 and the correction resistor 5 is acceptable. For example, it can be configured as a voltage source that supplies an AC voltage to the series circuit of the shunt resistor 4 and the correction resistor 5.

[0083] The specific configuration of the first synchronous detection circuit 12 is not limited to the configuration described in each embodiment above, and any configuration that can take the signal from the terminal of the shunt resistor 4 as input, perform synchronous detection at the same frequency as the AC signal, extract the signal, and output it is acceptable. The specific configuration of the second synchronous detection circuit 14 is any configuration that can take the signal from the terminal of the correction resistor as input, perform synchronous detection at the same frequency as the AC signal, extract the signal, and output it is acceptable.

[0084] This disclosure is described in accordance with the embodiments, but it is understood that this disclosure is not limited to such embodiments or structures. This disclosure also includes various modifications and variations within the equivalence. In addition, various combinations and forms, as well as other combinations and forms that include only one, more, or fewer of those elements, fall within the scope and concept of this disclosure. [Explanation of Symbols]

[0085] 1, 41, 51...Current sensor, 4...Shunt resistor, 5...Correction resistor, 6...Signal application unit, 7...First voltage detection unit, 8...Second voltage detection unit, 11...First A / D converter, 12...First synchronous detection circuit, 13...Second A / D converter, 14...Second synchronous detection circuit, 15...Current detection unit, 16...Correction unit, 17...Relay control unit, 18...Resistance value correction circuit, 53...Status signal input unit, 54...Status switching unit, RL1, RL2...Relays.

Claims

1. A current detection unit (15) detects the current to be detected using the terminal voltage of a shunt resistor (4) provided in series with the path through which the current to be detected flows and a detection resistance value corresponding to the resistance value of the shunt resistor. A relay (RL1, RL2) is provided in series with the path through which the detected current flows, A relay control unit (17) that controls the on / off state of the relay, A resistance value correction circuit (18) calculates the resistance value of the shunt resistor and corrects the detection resistance value based on the calculated resistance value of the shunt resistor, Equipped with, The current detection unit detects the current to be detected during the period when the relay is turned ON by the relay control unit. The resistance value correction circuit calculates the resistance value of the shunt resistor during the period when the relay is turned off by the relay control unit. The aforementioned resistance value correction circuit is A correction resistor (5) is connected in series with the shunt resistor in a path different from the path through which the detected current flows, and has higher resistance accuracy than the shunt resistor. A signal application unit (6) applies an AC signal to the series circuit of the shunt resistor and the correction resistor, A first voltage detection unit (7) detects the terminal voltage of the shunt resistor when the AC signal is applied to the series circuit, A second voltage detection unit (8) detects the terminal voltage of the correction resistor when the AC signal is applied to the series circuit, A correction unit (16) calculates the resistance value of the shunt resistor based on the first voltage detection value, which is the terminal voltage detected by the first voltage detection unit, and the second voltage detection value, which is the terminal voltage detected by the second voltage detection unit, and corrects the detection resistance value based on the calculated resistance value, which is the calculated resistance value of the shunt resistor. A current sensor equipped with the following features.

2. The resistance value correction circuit calculates the resistance value of the shunt resistor even during the period when the relay is turned ON by the relay control unit. The current sensor according to claim 1, wherein the resistance value of the shunt resistor calculated during the period in which the relay is controlled to be ON is not used to correct the detection resistance value, but is used for fault diagnosis to determine whether or not an open circuit has occurred in the shunt resistor.

3. The path through which the detected current flows is provided with at least one of a motor mounted on the vehicle and a power converter for supplying power to the motor. A status signal input unit (53) that inputs status signals representing the status of the motor and the power converter, A state switching unit (54) that switches to one of the first state, second state, and third state based on the state signal input via the state signal input unit, Equipped with, The first state is a state in which the relay control unit turns on the relay and the current detection unit detects the current to be detected. The second state is a state in which the relay control unit turns on the relay, the current detection unit detects the current to be detected, and the resistance value correction circuit calculates the resistance value of the shunt resistor. The third state is a state in which the relay control unit turns off the relay, and the resistance value correction circuit calculates the resistance value of the shunt resistor. The current sensor according to claim 1, wherein the resistance value of the shunt resistor calculated during the period in which the relay is controlled to be ON is not used to correct the detection resistance value, but is used for fault diagnosis to determine whether or not an open circuit has occurred in the shunt resistor.

4. The state switching unit is, If the status signal indicates that the motor and the power converter are in operation, switch to the first state. The current sensor according to claim 3, which switches to the third state when the state signal indicates that the power supply to the motor and the power converter has been stopped.

5. The state switching unit is, If the status signal indicates that the motor and the power converter are in operation, switch to the second state. The current sensor according to claim 3, which switches to the third state when the state signal indicates that the power supply to the motor and the power converter has been stopped.

6. The state switching unit is, If the status signal indicates that the motor and the power converter are in operation, switch to the first state. If the status signal indicates that the motor is stopped and the power converter is running, switch to the second state. The current sensor according to claim 3, which switches to the third state when the state signal indicates that the power supply to the motor and the power converter has been stopped.

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