Ground fault detection device

Abstract

A ground fault detection device includes: a switch group configured to switch between a first measurement path including a battery and a capacitor, a second measurement path including a battery, a negative-side insulation resistor, and a capacitor, and a third measurement path including a battery, a positive-side insulation resistor, and a capacitor; and a control unit configured to calculate a reference value based on each charging voltage of the capacitor in each measurement path, and to calculate the insulation resistance with reference to a predetermined conversion map, wherein the conversion map includes a conversion map corresponding to the capacitance of the capacitor, and the control unit estimates the capacitance of the capacitor and refers to the conversion map corresponding to the estimated capacitance of the capacitor.

Description

Technical Field

[0001] The present invention relates to a ground fault detection device using a flying capacitor. Background Art

[0002] In vehicles such as hybrid vehicles and electric vehicles that include an engine and an electric motor as drive sources, a battery installed in the vehicle body is charged to generate propulsion using the electrical energy supplied from the battery. The power supply circuit associated with the battery is typically configured as a high-voltage circuit that handles high voltages equal to or higher than 200V. To ensure safety, the high-voltage circuit including the battery is insulated from the vehicle body and is ungrounded, with the vehicle body serving as a reference potential point for grounding.

[0003] Vehicles equipped with a non-grounded high-voltage battery are equipped with a ground fault detection device to monitor the insulation status (ground fault) between the vehicle body and the system housing the high-voltage battery, specifically the main power supply system from the high-voltage battery to the motor. A method utilizing a so-called flying capacitor as a ground fault detection device is widely used.

[0004] To obtain information about insulation resistance, a flying capacitor-type ground fault detection device selectively switches measurement paths via a switch. Each measurement path includes a detection capacitor serving as a flying capacitor. The ground fault detection device performs V0, Vc1n, and Vc1p measurements. V0 is a voltage measurement corresponding to the voltage of the high-voltage battery. Vc1n is a voltage measurement reflecting the influence of RLn, the insulation resistance on the negative side. Vc1p is a voltage measurement reflecting the influence of RLp, the insulation resistance on the positive side.

[0005] It is known that the insulation resistance obtained by combining the insulation resistance on the positive side and the insulation resistance on the negative side can be calculated based on V0, Vc1n, and Vc1p obtained through these measurements. The operation for the calculation is complicated. Therefore, a conversion map is usually prepared in advance that converts the insulation resistance using Vc1 / V0 (where Vc1=Vc1p+Vc1n) as a reference value. Then, the insulation resistance is estimated with reference to the conversion map based on the value of Vc1 / V0 obtained through the measurement, and the occurrence of a ground fault is determined.

[0006] When measuring any of V0, Vc1n, and Vc1p, the charge voltage after the detection capacitor has been charged for a predetermined charging time Δtm is measured and set as the measured value. The charging time Δtm is set to a value that does not fully charge the detection capacitor, allowing for a short ground fault detection time. On the other hand, if the charging time Δtm is too short, the charge voltage decreases, and detection accuracy deteriorates due to the influence of noise and other factors. Therefore, the charging time Δtm is determined in consideration of the balance between determination time and detection accuracy.

[0007] Reference List

[0008] Patent Literature

[0009] Patent Document 1: JP2017-78587A Summary of the Invention

[0010] A conversion map for obtaining insulation resistance from a reference value obtained from each measurement result of V0 measurement, Vc1n measurement, and Vc1p measurement can be calculated based on the capacitance of the detection capacitor, the value of the charging resistor provided on the measurement path, and the charging time Δtm.

[0011] The value of the charging resistor and the charging time Δtm can be set to substantially constant stable values. However, the capacitances of the respective detection capacitors vary greatly from one another and also vary under the influence of the surrounding environment such as temperature.

[0012] When the capacitance of the detection capacitor at the time of measurement changes from the capacitance of the detection capacitor set when the conversion map is created, the accuracy of the insulation resistance to be calculated may be reduced.

[0013] Therefore, an object of the present invention is to prevent a decrease in calculation accuracy of insulation resistance in a flying capacitor type ground fault detection device even when the capacitance of the detection capacitor changes.

[0014] To solve the above problem, the ground fault detection device in the present invention is a ground fault detection device as follows: the ground fault detection device is connected to a non-grounded battery and is used to calculate the insulation resistance of a system including the battery. The ground fault detection device includes:

[0015] a capacitor configured to operate as a flying capacitor;

[0016] a switch group configured to switch between a first measurement path, a second measurement path, and a third measurement path; the first measurement path includes the battery and the capacitor; the second measurement path includes the battery, a negative insulation resistor, and the capacitor, the negative insulation resistor being the insulation resistance between the negative side line of the battery and ground; and the third measurement path includes the battery, a positive insulation resistor, and the capacitor, the positive insulation resistor being the insulation resistance between the positive side line of the battery and ground; and

[0017] a control unit configured to calculate a reference value based on each charging voltage of the capacitor in each of the first to third measurement paths, and the control unit configured to calculate the insulation resistance with reference to a predetermined conversion map, wherein

[0018] The conversion map includes a conversion map corresponding to the capacitance of the capacitor; and

[0019] The control unit estimates the capacitance of the capacitor and refers to the conversion map corresponding to the estimated capacitance of the capacitor.

[0020] According to the present invention, in a flying capacitor type ground fault detection device, even when the capacitance of the detection capacitor changes, it is possible to prevent a decrease in the calculation accuracy of the insulation resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a block diagram showing a configuration of a ground fault detection device according to an embodiment of the present invention;

[0022] Figure 2 A and Figure 2 B is a graph used to describe the change of the detection capacitor and the detection error;

[0023] Figure 3 is a flowchart for describing a ground fault determination operation of a ground fault detection device;

[0024] Figure 4 is a flowchart for describing a method for estimating the capacitance of a detection capacitor based on ambient temperature; and

[0025] Figure 5 A diagram for describing a method of estimating the capacitance of a detection capacitor through actual measurement.

[0026] Reference Mark List

[0027] 100 Ground fault detection device

[0028] 120 control device

[0029] 130 Detection capacitor capacitance estimation unit

[0030] 140 Conversion Mapping

[0031] 300 high-voltage battery

[0032] 310 load DETAILED DESCRIPTION

[0033] Embodiments of the present invention will be described in detail with reference to the accompanying drawings. Figure 1 is a block diagram illustrating the configuration of a ground fault detection device 100 according to an embodiment of the present invention. As shown in the figure, ground fault detection device 100 is a flying capacitor-type device that is connected to a high-voltage battery 300 and detects ground faults in a system equipped with high-voltage battery 300. Here, RLp represents the insulation resistance between the positive electrode side of high-voltage battery 300 and ground, and RLn represents the insulation resistance between the negative electrode side of high-voltage battery 300 and ground.

[0034] The high-voltage battery 300 is a battery for driving the vehicle to travel. The high-voltage battery 300 is configured with a rechargeable battery such as a lithium-ion battery, and drives a load 310 including, for example, an electric motor.

[0035] As shown in the figure, the ground fault detection device 100 includes a detection capacitor C1 operating as a flying capacitor and a control device 120 .

[0036] In addition, the ground fault detection device 100 includes four switches S1 to S4 around the detection capacitor C1 to switch the measurement path and control the charging and discharging of the detection capacitor C1. Each of these switches can be configured with an insulating switching element, such as an optical MOSFET.

[0037] Switch S1 has a first end connected to the positive power line and a second end connected to the anode of diode D1. The cathode of diode D1 is connected to the first end of resistor R1, and the second end of resistor R1 is connected to the first electrode of detection capacitor C1. Switch S2 has a first end connected to the negative power line, and a second end connected to the first end of resistor R2. The second end of resistor R2 is connected to the second electrode of detection capacitor C1.

[0038] A first end of switch S3 is connected to the first end of resistor R3 and the anode of diode D3, and a second end of switch S3 is connected to the first end of resistor R5, an analog input terminal of control device 120, and the first electrode of capacitor C2, whose second electrode is grounded. The cathode of diode D3 is connected to the first electrode of detection capacitor C1, the second end of resistor R3 is connected to the cathode of diode D2, and the anode of diode D2 is connected to the first electrode of detection capacitor C1. The second end of resistor R5 is grounded. A first end of switch S4 is connected to the second electrode of detection capacitor C1, and a second end of switch S4 is connected to the first end of resistor R4. The second end of resistor R4 is grounded.

[0039] The control device 120 is configured with a microcomputer or the like, and executes a program that has been incorporated in advance to perform various types of control required for the ground fault detection device 100. Specifically, the control device 120 controls switches S1 to S4 to switch measurement paths, and also controls charging and discharging of the detection capacitor C1.

[0040] The measurement circuits for V0, Vc1n, and Vc1p measurements are similar to those in the prior art. Specifically, during V0 measurement, switches S1 and S2 are turned on to charge detection capacitor C1. During Vc1n measurement, switches S1 and S4 are turned on to charge detection capacitor C1. During Vc1p measurement, switches S2 and S3 are turned on to charge detection capacitor C1.

[0041] Furthermore, control device 120 receives an analog level input corresponding to the charge voltage of detection capacitor C1 from an analog input terminal. This analog level serves as a measured value. Based on this measured value, a reduction in the insulation resistance of the system equipped with high-voltage battery 300 is detected. When the charge voltage of detection capacitor C1 is applied to the analog input terminal, switches S3 and S4 are closed. In this path, detection capacitor C1 is also discharged.

[0042] The above description relates to a basic circuit configuration widely used in flying capacitor type ground fault detection devices. However, flying capacitor type ground fault detection devices have various variations. The configuration of ground fault detection device 100 is not limited to the examples in the drawings.

[0043] In this embodiment, the control device 120 further includes a detection capacitor capacitance estimation unit 130 and a conversion map 140. For example, the detection capacitor capacitance estimation unit 130 can be configured by the control device 120 executing a predetermined program, and the conversion map 140 can be configured in a storage area included in the control device 120.

[0044] The detection capacitor capacitance estimation unit 130 is a block for estimating the current capacitance of the detection capacitor C1. The method for estimating the current capacitance of the detection capacitor C1 is not limited, and various methods may be used.

[0045] For example, the capacitance of a capacitor is often affected by temperature. Therefore, it is possible to use the thermometer TM131 (see Figure 1 ) measures the temperature around the detection capacitor C1 and calculates the change from the initial capacitance for estimation. Alternatively, the capacitance of the detection capacitor C1 can be estimated through actual measurement. For example, a charged detection capacitor C1 can be discharged for a predetermined time, and the capacitance can be calculated based on the change in the charging voltage before and after discharge. In this case, the thermometer TM131 can be omitted. The process for estimating the current capacitance of the detection capacitor C1 will be described later.

[0046] Conversion map 140 is a map used to convert reference values obtained from V0, Vc1n, and Vc1p measurements into insulation resistance values. Conversion map 140 is created to correspond to the capacitance of the detection capacitor. For example, capacitance can be categorized into multiple groups based on their size, and conversion map 140 can be created for each group. For each group, a capacitance representing that group is determined. For example, a capacitance representing the median value of a group defined by an upper and lower capacitance limit can be set.

[0047] The conversion map 140 can be calculated based on the capacitance of the detection capacitor C1, the value of the charging resistor (R1, R2) provided in the measurement path, and the charging time Δtm. Here, the value of the charging resistor and the charging time Δtm are fixed, and the capacitance of the detection capacitor C1 is changed according to the capacitance representing the group to create the conversion map 140 for each group. The conversion map 140 includes a standard conversion map 140 that has been created to correspond to the initial capacitance of the detection capacitor C1.

[0048] After calculating the reference value based on the V0, Vc1n, and Vc1p measurements, the control device 120 calculates the insulation resistance with reference to the standard conversion map 140 or the conversion map 140 corresponding to the estimated value of the current capacitance of the detection capacitor C1.

[0049] The ground fault detection device 100 in this embodiment calculates the insulation resistance by referring to the conversion map 140 corresponding to the estimated value of the current capacitance of the detection capacitor C1. Therefore, even when the capacitance of the detection capacitor changes, the calculation accuracy of the insulation resistance can be prevented from decreasing.

[0050] Here, we will refer to Figure 2 A and 2B describe the variation of the detection capacitor C1 and the detection error. Figure 2Figure A shows the change in reference values relative to insulation resistance when the capacitance of the test capacitor increases from an initial capacitance of b to capacitance of a and decreases to capacitance of c. As shown in the figure, the reference values for each capacitance differ between areas with low insulation resistance and areas with high insulation resistance, and these differences are particularly significant in areas with low insulation resistance.

[0051] Figure 2 Figure B shows the detection error in the following case: Based on the reference values obtained in each case of capacitance a, capacitance b, and capacitance c, the insulation resistance is calculated using a standard conversion map corresponding to the initial capacitance b. In areas where the insulation resistance is low, the difference in the reference value depending on the capacitance is significant, and the ratio of the error to the true insulation resistance increases, and the detection error is extremely large. Theoretically, the error becomes zero at the resistance value Rt where the insulation resistance is equal to the charging resistance. However, when the insulation resistance becomes lower than this, the error suddenly increases and the calculation accuracy decreases.

[0052] In contrast, unless the insulation resistance decreases as low as the charging resistance, a change in the capacitance of the detection capacitor C1 does not significantly affect the calculation accuracy of the insulation resistance.

[0053] For this reason, in this embodiment, when there is a possibility of a decrease in insulation resistance, the current capacitance of the detection capacitor C1 is estimated, and the conversion map 140 corresponding to the estimated current capacitance of the detection capacitor C1 is referenced. On the other hand, when there is no possibility of a decrease in insulation resistance, the current capacitance of the detection capacitor C1 is not estimated, and the standard conversion map 140 is referenced.

[0054] Therefore, it is sufficient to prepare a conversion map 140 corresponding only to the region where the insulation resistance is reduced, in addition to the standard conversion map 140. Therefore, the storage area for the conversion map 140 in the control device 120 can be saved.

[0055] However, regardless of the possibility of insulation resistance reduction, the current capacitance of the detection capacitor C1 can be estimated, and the conversion map 140 corresponding to the estimated current capacitance of the detection capacitor C1 can be referenced. Therefore, the calculation accuracy of the insulation resistance can be further improved.

[0056] Next, we will refer to Figure 3 The ground fault determination operation performed by the ground fault detection device 100 having the above configuration is described with reference to a flowchart of FIG.

[0057] First, the switches S1 to S4 are controlled to be opened and closed, and V0, Vc1n, and Vc1p measurements are performed respectively (S101). Then, reference values are calculated based on V0, Vc1n, and Vc1p obtained by the measurements (S102).

[0058] Based on the V0, Vc1n, and Vc1p values obtained through measurement, it is determined whether there is a possibility of insulation resistance reduction (S103). As described above, when the insulation resistance is lower than the charging resistance, the error increases. Therefore, for example, the condition V0 < (Vc1n + Vc1p) can be considered an indication of insulation resistance reduction.

[0059] Therefore, in the case where it is determined that there is a possibility of insulation resistance reduction (S103: Yes), the detection capacitor capacitance estimation unit 130 estimates the current capacitance of the detection capacitor C1 (S104). The process for estimating the current capacitance of the detection capacitor C1 will be described later.

[0060] Next, the insulation resistance is calculated (S107) with reference to the conversion map 140 corresponding to the estimated capacitance of the detection capacitor C1 (S105). After the insulation resistance is calculated, a ground fault is determined based on whether the obtained insulation resistance is lower than a predetermined reference value (S108).

[0061] On the other hand, if it is determined that there is no possibility of insulation resistance reduction (S103: No), the insulation resistance is calculated with reference to the standard conversion map 140 (S106) (S107). After the insulation resistance is calculated, a ground fault is determined based on whether the obtained insulation resistance is lower than a predetermined reference value (S108).

[0062] Finally, an example of estimating the current capacitance of the detection capacitor C1 using the detection capacitor capacitance estimation unit 130 will be described. Figure 4 The flowchart describes the process of the estimation method based on detecting the ambient temperature of the capacitor C1.

[0063] In this method, the actual capacitance of the detection capacitor C1 at a reference temperature is measured before shipment of the ground fault detection device 100. For example, the actual capacitance of the detection capacitor C1 can be calculated by discharging the charged detection capacitor C1 for a predetermined time and measuring the change in the charging voltage before and after the discharge.

[0064] Then, together with the actual capacitance, the estimated capacitance of the detection capacitor C1 at each ambient temperature is actually measured or theoretically obtained, and the estimated capacitance is written as a capacitance table in a storage area in the control device 120, which can be referenced by the detection capacitor capacitance estimation unit 130. Instead of the capacitance table, a calculation formula or the like for calculating the current capacitance of the detection capacitor C1 according to the ambient temperature may be written.

[0065] When estimating the current capacitance of the detection capacitor C1, the ambient temperature of the detection capacitor C1 is acquired using the thermometer TM131 (S201). Then, the capacitance table written before shipment is referenced (S202), and the capacitance corresponding to the ambient temperature is estimated as the current capacitance of the detection capacitor C1 (S203).

[0066] Next, we will refer to Figure 5 This article describes a method for estimating the current capacitance of detection capacitor C1 through actual measurement. Here, a charged detection capacitor C1 is discharged for a predetermined time, and the current capacitance of detection capacitor C1 is calculated based on the change in charging voltage before and after discharge. This technique is described in JP2017-78587A, and only a brief overview will be provided.

[0067] As shown in the figure, when the detection capacitor C1 is charged between time t0 and time t1 and discharged between time t1 and time t2, the ratio of the charge voltage V2 at time t2 to the charge voltage V1 at time t1 depends on the capacitance of the detection capacitor C1. Note that the charging resistance is assumed to be known and constant.

[0068] To this end, the detection capacitor capacitance estimation unit 130 controls the opening and closing of switches S1 to S4, charges and discharges the detection capacitor C1 for a predetermined time, and measures the charge voltage V1 of the detection capacitor at the end of charging and the charge voltage V2 of the detection capacitor at the end of discharging. Then, based on the measured charge voltage and the resistance related to the discharge time, the current capacitance of the detection capacitor C1 is calculated.

[0069] Specifically, C1 =(t2-t1) / (Rd×ln(V2 / V1)) can be used for calculation, where Rd represents the resistance related to the discharge time.

[0070] As described above, the ground fault detection device 100 in this embodiment estimates the current capacitance of the detection capacitor C1 and calculates the insulation resistance with reference to the conversion map 140 corresponding to the estimated value. Therefore, even when the capacitance of the detection capacitor changes, it is possible to prevent a decrease in the calculation accuracy of the insulation resistance.

[0071] In this case, when there is no possibility of insulation resistance reduction, the standard conversion map 140 can be referenced without estimating the current capacitance of the detection capacitor C1. Therefore, the storage area of the conversion map 140 in the control device 120 can be saved.

Claims

1. A ground fault detection device, connected to a non-grounded battery and configured to calculate the insulation resistance of a system including the battery, the ground fault detection device comprising: a capacitor configured to operate as a flying capacitor; a switch group configured to switch between the first measurement path, the second measurement path, and the third measurement path; The first measurement path includes the battery and the capacitor; the second measurement path includes the battery, a negative side insulation resistor, and the capacitor, wherein the negative side insulation resistor is the insulation resistance between the negative side line of the battery and the ground; the third measurement path includes the battery, a positive side insulation resistor, and the capacitor, wherein the positive side insulation resistor is the insulation resistance between the positive side line of the battery and the ground; as well as a control unit configured to calculate a reference value based on each charging voltage of the capacitor in each of the first to third measurement paths, and the control unit configured to calculate the insulation resistance with reference to a predetermined conversion map, wherein The conversion map includes a conversion map corresponding to the capacitance of the capacitor and includes a standard conversion map; and The control unit estimates the capacitance of the capacitor and calculates the insulation resistance with reference to a conversion map corresponding to the estimated capacitance of the capacitor when it is determined that the insulation resistance is lower than a predetermined standard based on the calculated reference value; and calculates the insulation resistance with reference to the standard conversion map when it is determined that the insulation resistance is not lower than the predetermined standard.

2. The ground fault detection device according to claim 1, wherein: The conversion map corresponding to the capacitance of the capacitor is created within a range in which the insulation resistance is determined to be lower than the reference value of the predetermined standard.

3. The ground fault detection device according to claim 1 or 2, wherein: The control unit is configured to obtain an ambient temperature of the capacitor and estimate a capacitance of the capacitor based on the obtained ambient temperature.

4. The ground fault detection device according to claim 1 or 2, wherein: The control unit is configured to measure a charge voltage of the capacitor before and after discharging for a predetermined time, wherein the discharging is performed after charging the capacitor, and The control unit is configured to estimate the capacitance of the capacitor based on measured values of the charging voltage before and after discharging.

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