Power supply control device and overcurrent detection method

Abstract

A power supply control device 1 according to the present invention includes a current sensor 2 which has a magnetic sensor 4 that employs a magneto-resistive element to detect magnetism generated when a current to be measured flows through a bus bar, and which is capable of measuring the current to be measured, and a determining unit 7 for determining whether an overcurrent has flowed through the bus bar, wherein, the determining unit 7 measures an electric current increase time, which is the time taken for an output voltage of the current sensor 2 to increase from zero to a maximum value, and an electric current decrease time, which is the time taken for the output voltage of the current sensor 2 to decrease from the maximum value to zero, obtains an electric current increase / decrease time difference, which is the difference between the electric current increase time and the electric current decrease time, and determines whether an overcurrent has flowed through the bus bar on the basis of the electric current increase / decrease time difference, thereby making it possible to detect an overcurrent generated not only when the current sensor is functioning, but also when the current sensor is not functioning, without causing a decrease in the accuracy of the current sensor when measuring normal output.

Description

Power supply control device and overcurrent detection method

[0001] The present invention relates to a power supply control device that measures currents flowing through various devices to control a power supply system of a vehicle, and a method for detecting an overcurrent.

[0002] In recent years, power supply control devices equipped with current sensors that measure the currents flowing through various devices have been used to control the power supply systems of vehicles equipped with various devices. For example, Patent Document 1 describes a power supply control device that includes a switch control unit that opens a switch provided in an electrical path based on the determination result of an overcurrent determination unit in order to optimize measures when an overcurrent occurs. The power supply control device described in this document uses a current sensor to measure the value of the current flowing through an inverter and determine whether or not an overcurrent has occurred.

[0003] JP 2018-57244 A

[0004] The power supply control device described in Patent Document 1 requires the current sensor's current measurement range to be expanded to a range where overcurrents can be measured. However, expanding the current sensor's measurable range reduces the measurement accuracy for normal currents. Furthermore, the power supply control device in this document measures overcurrents that occur when the current sensor is functioning, and therefore cannot detect overcurrents caused by, for example, short circuits that occur during vehicle maintenance when the power supply control device is not in operation. Therefore, when the power supply control device is in an inoperative state before startup, it cannot detect overcurrents applied to various devices such as the power supply control device and inverter. Furthermore, even when the current sensor is in operation, depending on the sampling timing, it may not be able to detect momentary overcurrents. The present invention aims to provide a power supply control device that can detect overcurrents that occur when the current sensor is not in operation, as well as when the current sensor is in operation, without reducing the accuracy of the current sensor when measuring normal currents.

[0005] As a means for solving the above-described problems, the present invention has the following configuration: A power supply control device including a current sensor capable of measuring a current to be measured, the current sensor having a magnetic sensor that uses a magnetoresistance element to detect magnetism generated when a current to be measured flows through a bus bar, and a determination unit that determines whether an overcurrent has flowed through the bus bar, wherein the determination unit measures a current increase time, which is the time it takes for the output voltage of the current sensor to go from 0 to its maximum value, and a current decrease time, which is the time it takes for the output voltage of the current sensor to go from its maximum value to 0, calculates a current increase / decrease time difference, which is the difference between the current increase time and the current decrease time, and determines whether the overcurrent has flowed through the bus bar based on the current increase / decrease time difference.

[0006] When an overcurrent exceeding the rated current of the bus bar flows through the bus bar, a strong magnetic field is generated from the bus bar and applied to the magnetoresistive element. If the magnetic field is strong enough, the state of the magnetoresistive element changes, and hysteresis occurs, in which the changed state is maintained even after the magnetic field is removed. The hysteresis of the magnetic sensor can be measured as the difference in current increase and decrease time between the current increase and decrease time. Therefore, by calculating the difference in current increase and decrease time, it is possible to detect whether a strong magnetic field has been generated by the overcurrent flowing through the bus bar. Therefore, it is possible to determine whether an overcurrent has flowed through the bus bar based on the difference in current increase and decrease time.

[0007] The determination unit may output an external warning when it determines that the overcurrent has flowed through the bus bar. By outputting an external warning when an overcurrent has flowed through the bus bar, it is possible to notify a higher-level system or the like that a problem may have occurred in the power supply control device or a controlled device due to the overcurrent. This makes it possible to take measures such as inspection or repair to address problems that may arise due to the overcurrent.

[0008] The bus bar may further include a storage unit configured to store a threshold value of the current increase / decrease time difference that is used as a criterion by the determination unit to determine whether the current flowing through the bus bar is the overcurrent, and the determination unit may determine that the overcurrent has flowed through the bus bar when the calculated current increase / decrease time difference exceeds the threshold value. By storing the current increase / decrease time difference corresponding to hysteresis caused by the overcurrent flowing through the bus bar as a threshold value, it is possible to determine that an overcurrent has flowed when the calculated current increase / decrease time difference exceeds the threshold value.

[0009] The bus bar may further include a memory unit that stores a threshold value of the change in the current increase / decrease time difference, which is used as a criterion by the judgment unit to judge whether the current flowing through the bus bar is the overcurrent, and an initial value of the current increase / decrease time difference, and the judgment unit may calculate a change in the current increase / decrease time difference, which is the difference between the calculated current increase / decrease time difference and the initial value of the current increase / decrease time difference, and may determine that the overcurrent has flowed through the bus bar when the calculated change exceeds the threshold value.

[0010] Since the time lag between the current increase and decrease caused by an overcurrent in the bus bar may differ depending on the individual magnetic sensor, the amount of change from the initial value of the time lag between the current increase and decrease is calculated and used to determine the overcurrent. This eliminates the influence of individual differences, improving the accuracy of overcurrent determination.

[0011] a current increase time, which is the time it takes for the output voltage of the current sensor to change from 0 to its maximum value, and a current decrease time, which is the time it takes for the output voltage of the current sensor to change from its maximum value to 0, based on the measurement results of the current to be measured; a current increase / decrease time difference, which is the difference between the current increase time and the current decrease time, is calculated; and whether or not an overcurrent has flowed through the bus bar is determined based on the current increase / decrease time difference.

[0012] When the calculated current increase / decrease time difference exceeds a threshold, it may be determined that the overcurrent has flowed through the bus bar. A change in the current increase / decrease time difference, which is the difference between the calculated current increase / decrease time difference and an initial value of the current increase / decrease time difference, may be calculated, and when the calculated change exceeds a change threshold, it may be determined that the overcurrent has flowed through the bus bar.

[0013] Based on the measurement results of the current to be measured, the current increase time and current decrease time are measured, and by calculating the difference between these, the effect on the magnetic sensor of the magnetism generated when the current to be measured flows through the bus bar, can be determined. Therefore, the current increase / decrease time difference can be used to determine whether an overcurrent has flowed through the bus bar.

[0014] The current increase / decrease time difference or the change amount in the output voltage of the current sensor immediately after startup may be calculated. If the current increase / decrease time difference exceeds the threshold or the change amount exceeds the change amount threshold, a warning indicating that the overcurrent is likely to have flowed through the bus bar while the current sensor was stopped may be output. If it is determined that an overcurrent has flowed through the bus bar immediately after the current sensor was started, it is likely that the overcurrent flowed while the current sensor was stopped. Therefore, a warning indicating that the overcurrent is likely to have flowed while the current sensor was stopped is output externally. This warning can alert the worker to the possibility that an overcurrent may have flowed while the current sensor was stopped due to, for example, a short circuit caused by a work error during maintenance of the power supply control device. This makes it easier for the worker to select a more appropriate response.

[0015] According to the present invention, by calculating the current increase / decrease time difference that reflects the hysteresis of a magnetic sensor having a magnetoresistive effect element, it is possible to detect an overcurrent flowing through a bus bar without expanding the current measurement range of the current sensor to a range where an overcurrent can be measured. Therefore, it is possible to detect an overcurrent without reducing the accuracy of the current sensor. Furthermore, hysteresis occurs even when an overcurrent occurs momentarily or when an overcurrent flows when the current sensor is not functioning. Therefore, by calculating the current increase / decrease time difference, it is possible to reliably detect an overcurrent flowing through a bus bar.

[0016] 1 is a functional block diagram showing the configuration of a power supply control device according to an embodiment of the present invention; FIG. 2 is a cross-sectional view schematically showing the configuration of a magnetic sensor; FIG. 3 is a graph showing the difference between the presence and absence of hysteresis in the magnetic sensor with respect to the relationship between the primary current detected by the current sensor and the output voltage of the current sensor; FIG. 4 is a graph showing the difference between the presence and absence of hysteresis in the magnetic sensor with respect to the change over time in the voltage output from the current sensor; FIG. 5 is a graph showing the hysteresis of the current sensor caused by a strong magnetism; FIG. 6 is a graph showing the difference between the presence and absence of an offset in the magnetic sensor with respect to the relationship between the primary current detected by the current sensor and the output voltage of the current sensor; FIG. 7 is a graph showing the difference between the presence and absence of an offset in the magnetic sensor with respect to the change over time in the voltage output from the current sensor;

[0017] An embodiment of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a functional block diagram showing the configuration of a power supply control device 1 according to the present embodiment. As shown in the figure, the power supply control device 1 includes a current sensor 2 capable of measuring a current to be measured flowing through a bus bar, and a control unit 3 that controls the power supply control device 1.

[0018] The current sensor 2 has a magnetic sensor 4, which measures the magnetism generated when a current to be measured flows through the bus bar. The magnetic sensor 4 has a magnetoresistive element for detecting the magnetism. The control unit 3 has a timer 5, a memory unit 6, and a determination unit 7. The determination unit 7 determines whether an overcurrent has flowed through the bus bar.

[0019] The timer 5 is used to measure the time that the current to be measured flows through the bus bar, the time that has elapsed since power was turned on to the current sensor 2, etc. However, in measuring the time, the time may be obtained from a timer in a part other than the control unit 3 of the power supply control device 1 or in a device external to the power supply control device 1.

[0020] The storage unit 6 stores the threshold value used as the criterion for determining an overcurrent, the characteristics of the magnetic sensor 4, etc. However, the threshold value, the change amount threshold value, etc. may be acquired from a part other than the control unit 3 in the power supply control device 1 or an external device, etc. In this case, the storage unit 6 acquires the threshold value, etc. from a part other than the control unit 3 or an external device of the power supply control device 1.

[0021] The determination unit 7 measures a current increase time, which is the time it takes for the output voltage of the current sensor 2 to change from 0 to its maximum value, and a current decrease time, which is the time it takes for the output voltage of the current sensor 2 to change from its maximum value to 0. Then, the determination unit 7 calculates a current increase / decrease time difference, which is the difference between the current increase time and the current decrease time, and determines whether an overcurrent has flowed through the bus bar based on the current increase / decrease time difference.

[0022] The determination unit 7 can determine whether an overcurrent has flowed through the bus bar while the current sensor 2 was stopped, at the time of starting up the power supply control device 1. If it is determined that an overcurrent has flowed through the bus bar immediately after the start-up time, which is the time from when the power supply control device 1 is turned on until the current sensor 2 starts up, has elapsed, i.e., immediately after start-up, it is determined that an overcurrent has flowed between when the current sensor 2 was stopped and when it was started up.

[0023] "Immediately after startup" refers to the time when data for one cycle of the AC current output by the power supply control device 1 is acquired for the first time after startup. For example, if the current sensor 2 operates at a frequency of 1 Hz, it takes one second to acquire one cycle of data, so "immediately after startup" refers to the time one second has passed since the power supply control device 1 was started. The startup time of the current sensor 2 varies depending on the performance of the current sensor 2, but is very short, for example, about one millisecond. Therefore, it is not possible to determine whether an overcurrent flowed through the bus bar when the power supply control device 1 was started. However, if it is determined that an overcurrent flowed through the bus bar immediately after startup, it is highly likely that an overcurrent flowed at least between the time the current sensor 2 was stopped and the time it was started. Note that when the power supply control device 1 is installed in a vehicle, the time from when the vehicle's ignition switch is pressed to when the power supply control device 1 starts is usually about 30 seconds to one minute.

[0024] When an overcurrent flows through the bus bar, hysteresis occurs in the magnetic sensor 4. When comparing the current increase / decrease time difference of the output voltage of the current sensor 2 before and after the hysteresis occurs, the current increase / decrease time difference after the hysteresis occurs is larger. Therefore, the determination unit 7 can determine whether an overcurrent has flowed through the bus bar based on the calculated current increase / decrease time difference. For example, the determination unit 7 determines that an overcurrent has flowed through the bus bar when the calculated current increase / decrease time difference exceeds a threshold value. In this case, the determination unit 7 may determine the current value of the overcurrent flowing through the bus bar.

[0025] The determination unit 7 outputs a warning to the outside when it determines that an overcurrent has flowed through the bus bar. In addition to this warning, the current value may also be output to the outside. The warning indicates that an overcurrent has occurred, making it possible to inspect devices that may be causing problems due to the overcurrent and to take measures such as maintenance, repair, or replacement as necessary. This improves the reliability of the power supply control device 1 and the power supply system that is the object of control.

[0026] 2 is a cross-sectional view schematically showing the configuration of the magnetic sensor 4 included in the current sensor 2. The magnetic sensor 4 includes a magnetoresistive element 9, a feedback coil 10, and a magnetic shield 11, and detects magnetism generated when a current to be measured flows through the bus bar 8. However, instead of the magnetic sensor 4 shown in FIG. 2, a magnetic sensor including only the magnetoresistive element 9, or a magnetic sensor including the magnetoresistive element 9 and either the feedback coil 10 or the magnetic shield 11 may also be used.

[0027] The bus bar 8 is made of copper, brass, aluminum, or the like, and a current to be measured flows through the bus bar 8. When the current to be measured flows through the bus bar 8, a magnetic field is generated around the bus bar 8. In FIG. 2, the magnetic field generated around the bus bar 8 when the current to be measured flows is schematically shown by a dashed line. The magnetic sensor 4 measures the magnetic field around the bus bar 8 using a magnetoresistance effect element 9.

[0028] The magnetoresistive element 9 functions as a magnetic detection element in the magnetic sensor 4. As the magnetoresistive element 9, for example, a giant magnetoresistive element (GMR element), an anisotropic magnetoresistive element (AMR element), or a tunneling magnetoresistive element (TMR element) may be used.

[0029] The feedback coil 10 is for magnetic balance and is provided between the magnetoresistive element 9 and the magnetic shield 11. A canceling current flows in the feedback coil 10 in the opposite direction to the current to be measured flowing through the bus bar 8. FIG. 2 shows a case where the current to be measured in the bus bar 8 flows from the front to the back of the page, and the canceling current in the feedback coil 10 flows from the back to the front of the page. The canceling current generates a canceling magnetic field in a direction that cancels out the current magnetism caused by the current to be measured, and this canceling magnetic field acts on the magnetoresistive element 9.

[0030] By increasing the canceling magnetic field, the detected voltage approaches zero, and the canceling magnetic field and current magnetism acting on the magnetoresistive element 9 are balanced, causing the detected voltage to fall below a predetermined value. At this time, the current flowing through the feedback coil 10 is detected as a measurement value of the current to be measured flowing through the bus bar 8.

[0031] The magnetic shield 11 may be, for example, a stack of multiple metal plates of the same shape. The provision of the magnetic shield 11 reduces external magnetic noise, thereby improving the measurement accuracy of the magnetic sensor 4.

[0032] As shown in Figure 2, the magnetic sensor 4 is arranged in the following order from the side closest to the bus bar 8: the magnetic shield 11, the feedback coil 10, and the magnetoresistive element 9. The magnetoresistive (MR, Magneto Resistance) magnetic sensor 4 having such a configuration has the characteristic that hysteresis increases when an overcurrent is detected. When the current to be measured flowing through the bus bar 8 is an AC current, the effect of hysteresis due to the overcurrent appears as a phase difference when an overcurrent flows. Therefore, an overcurrent can be detected by using the change in the phase difference in measurement from the initial state.

[0033] Factors that cause hysteresis in the magnetic sensor 4 due to the influence of a strong magnetic field generated by an overcurrent in the bus bar 8 include changes in the magnetization state in the magnetoresistive element 9 and residual magnetism in the magnetic shield 11.

[0034] The hysteresis of the magnetic sensor 4 is maintained even after an overcurrent flows through the bus bar 8, and therefore, the hysteresis of the magnetic sensor 4 can be used to detect afterward that an overcurrent has flowed through the bus bar 8. For example, even if an overcurrent flows through the bus bar 8 while the current sensor 2 (see FIG. 1) is not operating, the overcurrent can be detected based on the hysteresis of the magnetic sensor 4.

[0035] For example, when the power supply control device 1 is used to control a power supply system of a vehicle, maintenance work may be performed while the power supply system of the vehicle is stopped and the current sensor 2 is not operating. During such maintenance work, an overcurrent may flow through the bus bar 8 due to a work error.

[0036] Even if an overcurrent flows while the current sensor 2 is not operating, a magnetic field is generated around the bus bar 8 when the overcurrent flows through the bus bar 8. The generated magnetic field affects the magnetoresistive element 9 and the magnetic shield 11 of the magnetic sensor 4, just as it does when the current sensor 2 is operating. Therefore, hysteresis occurs in the magnetic sensor 4 due to the overcurrent. Therefore, by using the hysteresis of the magnetic sensor 4, it is possible to detect the overcurrent that has flowed through the bus bar 8 after the fact.

[0037] If it is determined that an overcurrent has flowed through the bus bar immediately after the current sensor 2 is started, the overcurrent has flowed through the bus bar while the current sensor 2 is stopped or at startup. Considering the time required for startup, it is more likely that the causative event that caused the overcurrent to flow occurred while the current sensor 2 is stopped than at the moment of startup. Therefore, if it is determined that an overcurrent has flowed through the bus bar 8 immediately after the current sensor 2 is started, the current sensor 2 outputs a warning during shutdown to the outside, indicating that an overcurrent may have flowed through the bus bar 8 while the current sensor 2 was stopped. By outputting this warning during shutdown to the outside, it is possible to notify the worker that an overcurrent may have flowed through the bus bar 8 due to a work error during maintenance work while the current sensor 2 was stopped.

[0038] Fig. 3A is a graph showing the relationship between the primary current detected by current sensor 2 and the voltage output from current sensor 2 when measuring an AC current as the current to be measured flowing through busbar 8. The current value of the primary current detected by current sensor 2 shown in Fig. 2 is obtained as the value of the current flowing through feedback coil 10 provided in magnetic sensor 4. Fig. 3B is a graph showing the change over time in the voltage output from current sensor 2 for Fig. 3A.

[0039] 3A and 3B, the initial state before an overcurrent flows through the bus bar 8 is indicated by a dashed line, and the state after the overcurrent flows is indicated by a solid line. Note that to make it easier to understand the difference between the magnetic sensor 4 before and after the overcurrent flows, an ideal state before the overcurrent flows is shown.

[0040] As shown by the dashed line in Figure 3A, before an overcurrent flows through the busbar 8, the magnitude of the output is determined by the magnitude of the current. That is, the voltage output by the current sensor 2 at the same current value is the same when the output of the current sensor 2 reaches its maximum value from 0 and when the output of the current sensor 2 returns from its maximum value to 0. Therefore, in the graph shown by the dashed line in Figure 3A, the trajectory from point A1 to point A2 is the same as the trajectory from point A2 to point A3. Therefore, the current increase time T1A until the output reaches its maximum value from 0 is equal to the current decrease time T2A until the output returns from its maximum value to 0.

[0041] In contrast, as shown by the solid line in Figure 3A, the magnitude of the output from the current sensor 2 after an overcurrent flows through the bus bar 8 is determined not only by the magnitude of the current value, but also by the direction in which the current value changes. That is, even if the same current flows through the bus bar 8, the magnitude of the voltage output by the current sensor 2 differs depending on whether the direction in which the output changes is an increase or decrease. For this reason, in the graph shown by the solid line in Figure 3A, the trajectory from point B1 to point B2 when the current increases is different from the trajectory from point B2 to point B3 when the current decreases. Therefore, the current increase time T1B, which is the time it takes for the output to change from 0 to its maximum value, is different from the current decrease time T2B, which is the time it takes for the output to change from its maximum value to 0, and the current increase time T1A is longer than the current decrease time T2A.

[0042] As described above, when hysteresis occurs in the magnetic sensor 4, a zero-crossing error occurs in the output of the current sensor 2. As a result, a difference occurs between the current increase time T1B and the current decrease time T2B. Here, the zero-crossing error means that when the current value is 0 A, the output of the current sensor 2 differs depending on the direction in which the current value changes.

[0043] The determination unit 7 calculates the current increase time T1B and the current decrease time T2B, and detects an overcurrent by using the current increase / decrease time difference, which is the difference between the current increase time T1 and the current decrease time T2, to evaluate the magnitude of hysteresis of the magnetic sensor 4. That is, the determination unit 7 determines that an overcurrent has flowed through the bus bar 8 when the current increase / decrease time difference exceeds a threshold value.

[0044] The magnetic sensor 4 having the magnetoresistive element 9 has a feature that hysteresis increases when an overcurrent occurs in the bus bar 8. Therefore, when the current to be measured is AC, the effect of the increased hysteresis appears as a phase difference. Therefore, by measuring the change from the initial value of the phase difference, it is possible to detect that an overcurrent has flowed through the bus bar 8 as the current to be measured.

[0045] Regardless of whether the current sensor 2 is in operation or not, when an overcurrent flows through the bus bar 8, hysteresis occurs in the magnetic sensor 4. This means that the magnetic sensor 4 stores the fact that an overcurrent has flowed through the bus bar 8 as hysteresis. Therefore, the power supply control device 1 can extract the history of the effects of the overcurrent stored in the magnetic sensor 4 by calculating the current increase / decrease time difference. In other words, by measuring the current increase / decrease time difference that changes due to the hysteresis of the magnetic sensor 4 and comparing the current increase / decrease time difference with a threshold, it is possible to detect the occurrence of an overcurrent even after it has flowed. The threshold used to detect an overcurrent is determined taking into account the current increase / decrease time difference that occurs in the magnetic sensor 4 when an overcurrent flows through the bus bar 8.

[0046] 4 is a graph showing the hysteresis that occurs in the magnetic sensor 4 when a strong magnetic field is applied, and shows the effect on the magnetic sensor 4 of the magnetic field that occurs when an overcurrent flows through the bus bar 8. Specifically, the strength of the magnetic field applied to the magnetic sensor 4 is gradually increased, and the graph shows the results of measuring the hysteresis of the magnetic sensor 4 after the magnetic field is applied.

[0047] As shown in the figure, when an overcurrent flows as the current to be measured in the bus bar 8 and a strong magnetic field of 150 mT or more is applied, hysteresis occurs in the magnetic sensor 4. Note that the hysteresis of the magnetic sensor 4 caused by the strong magnetic field of 150 mT does not change even if an even stronger magnetic field is applied.

[0048] For example, when the maximum output value of the current sensor 2 operating at 10 Hz is 2000 mV and the hysteresis is 4 mV, the time change (T2A-T2B in FIG. 3B) in the quarter sine wave (B2 to B3 in FIG. 3A) obtained by dividing the sine wave into four parts can be calculated using the following formula: 1 s / 10 / 360° × (90° / 2000 mV × 4 mV) = 50 μs

[0049] The peak of the quarter sine wave, which is the output for 90°, is 2000 mV, whereas as shown in Figure 3A, a displacement of the entire sine wave, i.e., full scale, occurs from the initial state at a current value of 0 A. Therefore, the change over time can be calculated using the above formula using the hysteresis value of 4 mV and the peak value of the quarter sine wave, 2000 mV.

[0050] When measuring AC current using the current sensor 2, the magnitude of the change over time due to hysteresis of the magnetic sensor 4 depends on the frequency. If the maximum value of the current sensor output is 2000 mV and the hysteresis is 4 mV, the relationship between frequency and change over time in a quarter sine wave is shown in the table below.

[0051] In the above example, when the current sensor 2 operates at 10 Hz, the change time of the current increase time T1B is +50 μs, and the change time of the current decrease time T2B is -50 μs. Therefore, the threshold value used to detect the flow of an overcurrent as the measured current of the bus bar 8 is calculated using the following formula: T1B - T2B = (T1A + 50 μs) - (T2A - 50 μs) = (T1A - T2A) + 100 μs. When T1A and T2A are equal, as shown by the dashed lines in Figures 3A and 3B, the threshold value is 100 μs. In this way, a threshold value determined based on the current increase / decrease time difference T1B - T2B that occurs in the magnetic sensor 4 when an overcurrent flows through the bus bar 8 can be used to detect an overcurrent.

[0052] 5A is a graph showing the relationship between the primary current detected by the current sensor 2 and the voltage output from the current sensor 2 when measuring an AC current as the current to be measured flowing through the bus bar 8. In the figure, the dashed line indicates the time before the offset occurs, and the solid line indicates the time after the offset occurs.

[0053] 5B is a graph showing the relationship between time and the voltage output from current sensor 2 before and after an offset occurs in magnetic sensor 4 included in current sensor 2. In the figure, the dashed line indicates the state before an offset occurs in magnetic sensor 4, and the solid line indicates the state after the offset occurs. The state before the offset occurs in FIGS. 5A and 5B is the same as the state before an overcurrent occurs in FIGS. 3A and 3B.

[0054] As shown in Fig. 5A, an offset may occur in the magnetic sensor 4 due to temperature changes, etc. However, if an offset occurs in the magnetic sensor 4, the current increase time T1C and the current decrease time T2C both increase by the same amount, as shown in Fig. 5B. Therefore, the current increase / decrease time difference (= T1C - T2C), which is the difference between the current increase time T1C and the current decrease time T2C, is not affected by the offset.

[0055] (Method of detecting overcurrent) Fig. 6 is a flowchart of the method of detecting overcurrent according to this embodiment. The flowchart shows a method of determining whether an overcurrent has flowed through the power supply control device 1. The power supply control device 1 is equipped with a current sensor 2 capable of measuring the current to be measured, and the current sensor 2 has a magnetic sensor 4 that detects magnetism generated when the current to be measured flows through the bus bar 8. The flowchart shown in the figure uses a predetermined magnitude of the current increase / decrease time difference H as a threshold value, and shows a case in which it is determined that an overcurrent has flowed through the bus bar 8 when the current increase / decrease time difference H exceeds the threshold value.

[0056] The overcurrent detection method includes a measurement step S1, an evaluation step S2, and a judgment step S3. In the measurement step S1, the current sensor 2 measures the current to be measured flowing through the bus bar 8. In the evaluation step S2, the control unit 3 calculates the hysteresis of the magnetic sensor 4 based on the measurement result of the measurement step S1. Then, in the judgment step S3, the judgment unit 7 determines that an overcurrent has flowed through the bus bar 8 if the hysteresis exceeds a threshold value.

[0057] The evaluation step S2 for evaluating hysteresis includes step S20 for determining the current increase time T1 and the current decrease time T2, and step S21 for determining the current increase / decrease time difference H. Step S20 uses the timer 5 to determine the current increase time T1, which is the time it takes for the output voltage of the current sensor 2 to go from 0 to its maximum value, and the current decrease time T2, which is the time it takes for the output voltage of the current sensor 2 to go from its maximum value to 0. Step S21 uses the determination unit 7 to determine the current increase / decrease time difference H, which is the difference between the current increase time T1 and the current decrease time T2.

[0058] The judgment step S3 includes steps S30 to S33. In step S30, the judgment unit 7 compares the current increase / decrease time difference H with a threshold value Ht. If the current increase / decrease time difference H is greater than the threshold value Ht (H>Ht, Yes in S31), it is judged in S32 that an overcurrent has flowed through the bus bar 8. In this case, the process proceeds to output step S4, in which the control unit 3 outputs a warning to the outside of the power supply control device 1, and the measurement of the overcurrent is terminated. If the current increase / decrease time difference H is equal to or less than the threshold value Ht (H≦Ht, No in S31), it is judged in S33 that an overcurrent is not flowing through the bus bar 8, and the overcurrent judgment is terminated.

[0059] 7 is a flowchart of an overcurrent detection method according to Modification 1, which compares the hysteresis of the current sensor 2 during measurement with the initial hysteresis and determines that an overcurrent has occurred if the amount of change from the initial hysteresis is equal to or greater than a threshold. The overcurrent detection method shown in FIG. 7 differs from the overcurrent detection method shown in FIG. 6 in that it uses a change amount D from an initial value H0 instead of the current increase / decrease time difference H. That is, in the overcurrent detection method of Modification 1, the determination unit 7 calculates the change amount D from the initial value H0 of the current increase / decrease time difference H, and determines that an overcurrent has flowed through the bus bar 8 if the change amount D exceeds a change amount threshold Dt.

[0060] Explanation of the same parts as in the flowchart shown in Figure 6 will be omitted, and differences will be explained below. Determination step S3 in this modified example includes steps S34 to S38. In step S34, the determination unit 7 determines the amount of change D, which is the difference between the current increase / decrease time difference H and the initial value H0. Then, in step S35, the determination unit 7 compares the amount of change D with a change amount threshold Dt. The initial value H0 is a characteristic of the magnetic sensor 4 and is stored in the storage unit 6 (see Figure 1).

[0061] If the amount of change D is greater than the change amount threshold Dt (D>Dt, Yes in S36), it is determined in S37 that an overcurrent has flowed through the bus bar 8, an alarm is output to the outside in S4, and the overcurrent determination is terminated. If the amount of change D is equal to or less than the change amount threshold Dt (D≦Dt, No in S36), it is determined in S38 that an overcurrent has not flowed through the bus bar 8, and the overcurrent determination is terminated.

[0062] The initial value H0 of the initial current increase / decrease time difference H varies depending on the magnetic sensor 4. Therefore, in the modified example, in the determination step S3, instead of calculating the current increase / decrease time difference H and comparing it with the threshold value Ht, the amount of change D from the initial value H0 of the current increase / decrease time difference H is calculated and compared with the amount of change threshold Dt. Calculating the amount of change D removes the influence of the individual differences between the current sensors 2, thereby improving the accuracy of detecting that an overcurrent has flowed through the bus bar 8.

[0063] [Variation 2] FIG. 8 is a flowchart of an overcurrent detection method according to Variation 2. When a vehicle is stopped after operation and a power source such as an engine or motor is stopped, the current sensor 2 is also stopped, and essentially no current flows through the bus bar 8. However, as described above, when the vehicle is stopped for maintenance or inspection, an overcurrent may flow due to an operator's work error. In the example shown in the figure, if it is determined that an overcurrent has flowed through the current sensor 2 immediately after the current sensor 2 is started, a warning during the stoppage is output to the outside, indicating that an overcurrent may have flowed through the bus bar 8 while the current sensor 2 was stopped. Furthermore, if it is determined that an overcurrent has flowed through the current sensor 2 after the current sensor 2 is started, a warning is output to the outside, indicating that an overcurrent has flowed through the bus bar 8 while the current sensor 2 was operating.

[0064] 6 will be omitted, and only differences will be described below. Determination step S3 in Modification 2 includes steps S31 to S34. In step S34, the determination unit 7 determines whether it was determined that an overcurrent flowed through the bus bar 8 immediately after the current sensor 2 was activated. The predetermined time is a characteristic of the current sensor 2 and is stored in the storage unit 6 (see FIG. 1).

[0065] If it is determined that an overcurrent has flowed through the bus bar 8 immediately after the current sensor 2 is started (Yes in S34), it is determined that an overcurrent is likely to have flowed through the bus bar 8 while the current sensor 2 was stopped, and a warning indicating that the power supply sensor is stopped is output to the outside in S41, and the overcurrent determination is terminated. For example, a current increase / decrease time difference in the output voltage of the current sensor 2 immediately after start-up can be calculated, and if the current increase / decrease time difference exceeds a threshold, it can be determined that an overcurrent has flowed while the current sensor 2 was stopped or started. Alternatively, a change in the output voltage of the current sensor 2 immediately after start-up can be calculated, and if the change amount exceeds a change amount threshold, it can be determined that an overcurrent has flowed while the current sensor 2 was stopped or started. If it is determined that an overcurrent has flowed through the bus bar 8 after the current sensor 2 was started (No in S34), it is determined that an overcurrent has flowed through the bus bar 8 while the current sensor 2 was operating, and a warning indicating that the power supply sensor is operating is output to the outside in S42, and the overcurrent determination is terminated.

[0066] 8 outputs a different warning to the outside depending on whether it is determined in step S32 that an overcurrent has flowed through the bus bar 8 immediately after the activation of the current sensor 2 or later. This allows the worker to know whether the overcurrent has flowed through the bus bar 8 while the current sensor 2 is stopped or while the current sensor 2 is activated, enabling the worker to take more appropriate measures depending on the assumed cause.

[0067] Although FIG. 8 shows an embodiment in which steps S34, S41, and S42 are performed after step S32 in FIG. 6, steps S34, S41, and S42 may be performed after step S37 in FIG.

[0068] The embodiments disclosed in this specification are illustrative in all respects and are not limited to these embodiments. The scope of the present invention is defined by the claims rather than by the description of the above-described embodiments alone, and is intended to include all modifications within the meaning and scope of the claims.

[0069] The present invention is useful as a power supply control device that measures the current to be measured flowing through various devices and controls the power supply system of a vehicle, for example.

[0070] 1: Power supply control device 2: Current sensor 3: Control unit 4: Magnetic sensor 5: Timer 6: Storage unit 7: Determination unit 8: Bus bar 9: Magnetoresistance effect element 10: Feedback coil 11: Magnetic shield H: Current increase / decrease time difference H0: Initial value Ht: Threshold value D: Amount of change Dt: Amount of change threshold T1, T1A, T1B, T1C: Current increase time T2, T2A, T2B, T2C: Current decrease time

Claims

1. A power supply control device comprising: a current sensor capable of measuring a current to be measured, the current sensor having a magnetic sensor that uses a magnetoresistance element to detect the magnetism generated when a current to be measured flows through a bus bar; and a judgment unit that judges whether an overcurrent has flowed through the bus bar, wherein the judgment unit measures a current increase time, which is the time it takes for the output voltage of the current sensor to go from 0 to its maximum value, and a current decrease time, which is the time it takes for the output voltage of the current sensor to go from its maximum value to 0, calculates a current increase / decrease time difference, which is the difference between the current increase time and the current decrease time, and judges whether an overcurrent has flowed through the bus bar based on the current increase / decrease time difference.

2. The power supply control device according to claim 1, wherein the determination unit outputs an external warning when it determines that the overcurrent has flowed through the bus bar.

3. A power supply control device as described in claim 1, further comprising a memory unit that stores a threshold value of the current increase / decrease time difference that serves as a criterion for the judgment unit to judge whether the current flowing through the bus bar is an overcurrent, and the judgment unit judges that the overcurrent has flowed through the bus bar when the calculated current increase / decrease time difference exceeds the threshold value.

4. A power supply control device as described in claim 1, further comprising a memory unit that stores a threshold value of the change in the current increase / decrease time difference that is used as a criterion for the judgment unit to judge whether the current flowing through the bus bar is an overcurrent or not, and an initial value of the current increase / decrease time difference, wherein the judgment unit calculates a change in the current increase / decrease time difference, which is the difference between the calculated current increase / decrease time difference and the initial value of the current increase / decrease time difference, and when the calculated change exceeds the change threshold value, judges that the overcurrent has flowed through the bus bar.

5. A method for detecting an overcurrent, comprising the steps of: measuring the current to be measured flowing through the bus bar with a current sensor capable of measuring the current to be measured, the current sensor having a magnetic sensor that uses a magnetoresistance element to detect the magnetism generated when the current to be measured flows through the bus bar; measuring a current increase time, which is the time it takes for the output voltage of the current sensor to go from 0 to its maximum value, and a current decrease time, which is the time it takes for the output voltage of the current sensor to go from its maximum value to 0, based on the measurement result of the current to be measured; determining a current increase / decrease time difference, which is the difference between the current increase time and the current decrease time; and determining whether or not an overcurrent has flowed through the bus bar based on the current increase / decrease time difference.

6. The method for detecting an overcurrent according to claim 5, further comprising the step of determining that the overcurrent has flowed through the bus bar when the calculated current increase / decrease time difference exceeds a threshold value.

7. A method for detecting an overcurrent as described in claim 5, further comprising: calculating an amount of change in the current increase / decrease time difference, which is the difference between the calculated current increase / decrease time difference and an initial value of the current increase / decrease time difference; and determining that the overcurrent has flowed through the bus bar when the calculated amount of change exceeds a change amount threshold.

8. A method for detecting an overcurrent as described in claim 6 or 7, further comprising: determining the current increase / decrease time difference or the amount of change in the output voltage of the current sensor immediately after startup; and, if the current increase / decrease time difference exceeds the threshold value or the amount of change exceeds the change amount threshold value, outputting a warning indicating that there is a high possibility that the overcurrent flowed through the bus bar while the current sensor was stopped.

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