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 and a second measurement path and a third measurement path including a battery, a positive / negative side insulation resistor and a capacitor; a reference resistor and a test switch; and a control unit that calculates a first reference value based on each charging voltage when the test switch is opened and the capacitor is charged, and calculates the insulation resistance with reference to a conversion map created corresponding to an electrostatic capacitance between a power line and a ground, wherein the control unit calculates a second reference value based on each charging voltage when the test switch is closed and the capacitor is charged for a shorter time, and estimates the electrostatic capacitance with reference to a predetermined test conversion map.

Description

Technical Field

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

[0002] In a vehicle such as a hybrid vehicle or an electric vehicle including an engine and an electric motor as a driving source, a battery equipped in a vehicle body is charged to generate propulsion using electric energy supplied from the battery. A power supply circuit associated with a battery is generally configured as a high-voltage circuit that handles a high voltage equal to or higher than 200 V. In order to ensure safety, the high-voltage circuit including the battery has a non-grounded configuration insulated from the vehicle body, which serves as a reference potential point for grounding.

[0003] In a vehicle equipped with a non-grounded high-voltage battery, a ground fault detection device is provided to monitor the insulation state (ground fault) between the vehicle body and the system provided with the high-voltage battery, specifically, the main power supply system from the high-voltage battery to the motor. As the ground fault detection device, a method using a capacitor called a flying capacitor has been widely used.

[0004] In order to obtain information about the insulation resistance, the flying capacitor type ground fault detection device selectively switches the measurement paths via a switch, each measurement path including the detection capacitor used as a flying capacitor, wherein the ground fault detection device performs V0 measurement, Vc1n measurement, and Vc1p measurement. Here, the V0 measurement is the measurement of the voltage corresponding to the voltage of the high voltage battery. The Vc1n measurement is the measurement of the voltage reflecting the influence of RLn as the insulation resistance on the negative side. The Vc1p measurement is the measurement of the voltage reflecting the influence of RLp as 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 from V0, Vc1n, and Vc1p that have been obtained through these measurements. The operation for calculation is complicated. Therefore, a conversion map that converts the insulation resistance using Vc1 / V0 (where Vc1=Vc1p+Vc1n) as a reference value is usually prepared in advance. The insulation resistance is then estimated based on the value of Vc1 / V0 that has been obtained through measurement with reference to the conversion map, and the occurrence of a ground fault is determined.

[0006] In any measurement of V0, Vc1n, and Vc1p, the charging voltage when the detection capacitor has been charged for a predetermined charging time Δtm is measured and set as a measurement value. The charging time Δtm is set to a value such that the detection capacitor is not fully charged, so as to determine a ground fault in a short time. On the other hand, in the case where the charging time Δtm is too short, the charging voltage decreases, and the detection accuracy decreases due to the influence of noise, etc. For this reason, the charging time Δtm is determined in consideration of the balance between the determination time and the detection accuracy, and the charging time Δtm may be, for example, about 1.2 seconds.

[0007] Incidentally, in order to remove high-frequency noise and stabilize operation, in many cases, capacitors called Y capacitors (line bypass capacitors) are connected between the positive and negative power lines of the high-voltage battery and the ground electrode. Note that in this specification, it is assumed that stray capacitance existing between the power line and the ground electrode is also included in the Y capacitor.

[0008] When the measurement path is switched, charges are exchanged between the Y capacitor and the detection capacitor. Therefore, the charge voltage of the detection capacitor may be affected by the Y capacitor, and the calculation accuracy of the insulation resistance may be reduced.

[0009] When the capacitance of the Y capacitor is known, the calculation accuracy of the insulation resistance can be prevented from being reduced by preparing a conversion map corresponding to the capacitance of the Y capacitor. However, the capacitance of the Y capacitor is unknown to the ground fault detection device and varies depending on the vehicle model, situation, etc.

[0010] Patent document JP2014-126382A describes preparing a plurality of conversion maps for each capacitance of a Y capacitor. A test mode is performed in a state where a reference resistor having a known resistance value is connected between a power line and a ground electrode so that a conversion map corresponding to the actual capacitance of the Y capacitor is selected.

[0011] Specifically, the insulation resistance is calculated in each conversion map using the reference value obtained in the test mode, and the conversion map that has obtained the value closest to the reference resistance is selected. Then, in actual measurement, the insulation resistance is calculated using the conversion map that has been selected in the test mode.

[0012] Reference List

[0013] Patent Literature

[0014] Patent Document 1: JP2014-126382A Summary of the invention

[0015] In the invention described in patent document JP2014-126382A, a known reference resistance is regarded as the insulation resistance in the test mode, and a conversion map that has obtained a value closest to the reference resistance is selected. However, what functions as the insulation resistance in the test mode is not only the reference resistance but also the composite resistance of the reference resistance, the insulation resistance RLn, and the insulation resistance RLp, and is also affected by the actual insulation resistance. In particular, as the actual insulation resistance decreases, the influence becomes greater.

[0016] In addition, in recent years, there are vehicles in which both high-voltage batteries and fuel cells are used. In such vehicles, the insulation resistance between the fuel cell and the ground is also added in parallel. Therefore, in the test mode, the difference between the insulation resistance and the reference resistance is further increased.

[0017] Therefore, the capacitance of the Y capacitor corresponding to the conversion map and having the obtained value closest to the reference resistance is not always close to the actual capacitance of the Y capacitor, and may adversely affect the calculation accuracy of the insulation resistance.

[0018] Therefore, an object of the present invention is to improve the estimation accuracy of the electrostatic capacitance between a power supply line and the ground in a flying capacitor type ground fault detection device.

[0019] In order to solve the above problem, the ground fault detection device in the present invention is the following ground fault detection device: 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, and the ground fault detection device includes:

[0020] a capacitor configured to operate as a flying capacitor;

[0021] a switch group, the switch group being 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 side insulation resistor and a capacitor, 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, the positive side insulation resistor is the insulation resistance between the positive side line of the battery and the ground;

[0022] a reference resistor and a test switch connected in series between the positive side line or the negative side line of the battery and the ground; and

[0023] a control unit configured to calculate a first reference value based on each charging voltage in a case where the test switch is turned off and the capacitor is charged for a first time in each of the first to third measurement paths, and the control unit configured to calculate the insulation resistance with reference to a conversion map that has been created, the conversion map being created corresponding to the electrostatic capacitance between the ground and the positive and negative side lines of the battery, wherein

[0024] The control unit calculates a second reference value based on each charging voltage when the test switch is closed and the capacitor is charged for a second time in each of the first measurement path to the third measurement path, the second time being shorter than the first time, and the control unit is configured to estimate the electrostatic capacitance with reference to a predetermined test conversion map.

[0025] According to the present invention, in a flying capacitor type ground fault detection device, it is possible to improve the estimation accuracy of the electrostatic capacitance between a power line and the ground. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a block diagram showing a configuration of a ground fault detection device according to an embodiment of the present invention;

[0027] Figure 2 is a diagram illustrating an example of a transformation mapping;

[0028] Figure 3 is a diagram illustrating the relationship between the charging time and the charging voltage of each capacitance of a Y capacitor;

[0029] Figure 4 is a diagram illustrating an example of a transformation map for a test pattern;

[0030] Figure 5 is a flow chart for describing the operation of the ground fault detection device in the test mode; and

[0031] Figure 6 is a flowchart for describing a ground fault determination process performed by the ground fault detection device.

[0032] Reference Mark List

[0033] 100 Ground fault detection device

[0034] 120 Control device

[0035] 130 Transformation Mapping (for measurement)

[0036] 140 Transformation Mapping (for testing)

[0037] 300 High Voltage Battery

[0038] 310 Load

[0039] 320 Fuel Cell

[0040] 330 Booster DETAILED DESCRIPTION

[0041] Embodiments of the present invention will be described in detail with reference to the accompanying drawings. Figure 1 1 is a block diagram showing a configuration of a ground fault detection device 100 according to an embodiment of the present invention. As shown in the drawing, the ground fault detection device 100 is a flying capacitor type device that is connected to a high voltage battery 300 and detects a ground fault of a system provided with the high voltage battery 300. Here, RLp represents an insulation resistance between the positive electrode side of the high voltage battery 300 and the ground, and RLn represents an insulation resistance between the negative electrode side of the high voltage battery 300 and the ground.

[0042] 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.

[0043] In addition, in the high-voltage system in the present embodiment, a fuel cell 320 is provided in addition to the high-voltage battery 300. The fuel cell 320 is connected in parallel with the high-voltage battery 300 through a booster 330. In the case where RLf represents the insulation resistance between the positive electrode side of the fuel cell 320 and the ground, the insulation resistance of the high-voltage system has a value obtained by synthesizing RLn, RLp, and RLf. Needless to say, the present invention is also applicable to a high-voltage system that does not include the fuel cell 320, a high-voltage system that includes the fuel cell 320 instead of the high-voltage battery 300, and the like.

[0044] Capacitors CYp and CYn, both referred to as Y capacitors, are connected between the positive side power line and the ground electrode and between the negative side power line and the ground electrode of the high voltage battery 300, respectively. Here, stray capacitance between the power line and the ground electrode is considered to be included in capacitors CYp and CYn. The capacitance values ​​of capacitors CYp and CYn are unknown.

[0045] 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. 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.

[0046] The switch S1 has a first end connected to the positive side power line and a second end connected to the anode side of the diode D1. The cathode side of the diode D1 is connected to the first end of the resistor R1, and the second end of the resistor R1 is connected to the first electrode of the detection capacitor C1. The switch S2 has a first end connected to the negative side power line and a second end connected to the first end of the resistor R2. The second end of the resistor R2 is connected to the second electrode of the detection capacitor C1.

[0047] The first end of the switch S3 is connected to the first end of the resistor R3 and the anode side of the diode D3, and the second end of the switch S3 is connected to the first end of the resistor R5, the analog input terminal of the control device 120, and the first electrode of the capacitor C2 whose second electrode is grounded. The cathode side of the diode D3 is connected to the first electrode of the detection capacitor C1, the second end of the resistor R3 is connected to the cathode side of the diode D2, and the anode side of the diode D2 is connected to the first electrode of the detection capacitor C1. The second end of the resistor R5 is grounded. The first end of the switch S4 is connected to the second electrode of the detection capacitor C1, and the second end of the switch S4 is connected to the first end of the resistor R4. The second end of the resistor R4 is grounded.

[0048] 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, respectively, and also controls charging and discharging of the detection capacitor C1.

[0049] The corresponding measurement circuits for V0 measurement, Vc1n measurement, and Vc1p measurement are similar to those in the prior art. That is, in V0 measurement, switches S1 and S2 are turned on to charge the detection capacitor C1. In Vc1n measurement, switches S1 and S4 are turned on to charge the detection capacitor C1. In Vc1p measurement, switches S2 and S3 are turned on to charge the detection capacitor C1.

[0050] In addition, the control device 120 receives an input of an analog level corresponding to the charging voltage of the detection capacitor C1 from the analog input terminal, wherein the analog level is used as a measured value. Based on such a measured value, a reduction in the insulation resistance of the system provided with the high-voltage battery 300 is detected. When the charging voltage of the detection capacitor C1 is applied to the analog input terminal, switches S3 and S4 are turned on. In this path, the detection capacitor C1 is also discharged.

[0051] The above description relates to a basic circuit configuration widely used in a flying capacitor type ground fault detection device. However, a flying capacitor type ground fault detection device has various modifications. The configuration of the ground fault detection device 100 is not limited to the example in the drawings.

[0052] In the present embodiment, the control device 120 further includes a measurement conversion map 130 for measurement and a test conversion map 140 for testing. The measurement conversion map 130 is a conversion map used in an actual ground fault detection process. The test conversion map 140 is a conversion map used in a test mode for estimating the capacitance of the Y capacitor. Two conversion maps are created for each capacitance of the Y capacitor. For example, the capacitance can be divided into a plurality of groups according to its size, and a conversion map can be created for each group.

[0053] In addition, the reference resistor Rref and the test switch Sr are connected in series with each other between the negative side power line and the ground. The resistance value of the reference resistor Rref is known, and the test switch Sr is switched to be closed by the control device 120 in the test mode. The reference resistor Rref and the test switch Sr can be connected between the positive side power line and the ground.

[0054] In the test mode, the combined resistance of each insulation resistance of RLp, RLn and RLf and the reference resistance Rref becomes the insulation resistance value at the time of the test. In this state, V0, Vc1n and Vc1p are measured to calculate the reference value. The reference value is applied to each test conversion map 140 that has been created for each capacitance of the Y capacitor, and the insulation resistance is calculated.

[0055] Then, among the insulation resistances that have been obtained, the capacitance of the Y capacitor corresponding to the conversion map assumed to be closest to the insulation resistance value at the time of the test is estimated as the actual capacitance of the Y capacitor. Then, in the actual ground fault detection process, the insulation resistance is calculated with reference to the measurement conversion map 130 corresponding to the capacitance of the Y capacitor that has been estimated.

[0056] Here, the prerequisite in the ground fault detection process is assumed. In a normal state where no ground fault occurs, the insulation resistance of each of RLp, RLn, and RLf is large enough. Assuming that the value in such a state is 4.8 MΩ, the combined insulation resistance (RLp / / RLn / / RLf) is 1.6 MΩ.

[0057] In order to set the value of the reference resistance Rref to be lower than the normal insulation resistance, the value is set to 1350 kΩ here. In this case, when the reference resistance Rref is connected in the test mode, the combined resistance (RLp / / RLn / / RLf / / Rref) of the normal insulation resistance and the reference resistance is 736 kΩ. This value can be regarded as the maximum value of the insulation resistance value at the time of the test.

[0058] On the other hand, each insulation resistance varies according to various factors, and for example, any one of RLp, RLn, and RLf may be reduced to 3.0MΩ. In this case, the combined insulation resistance is 1.3MΩ. In the test mode, the combined resistance of the insulation resistance and the reference resistance is 668kΩ. It is assumed that this value is the minimum value of the insulation resistance value at the time of the test.

[0059] That is, in the test mode, it can be assumed that the insulation resistance value at the time of the test varies between 668 kΩ and 736 kΩ depending on the insulation resistance condition.

[0060] In addition, the range of the capacitance of the Y capacitor can be assumed to some extent for each vehicle model according to technical standards, etc. For example, it is assumed to vary between capacitance C1 and capacitance C9 (where C1<C9).

[0061] Figure 2 An example of a measurement conversion map 130 that has been created for each of the capacitances C1 to C9 is shown. In addition to the capacitance of the Y capacitor, a conversion map can also be obtained by calculating using the capacitance of the detection capacitor C1, the resistance in the measurement circuit, and the charging time. However, in the example of the figure, the charging time is set to the charging time Δtm in the actual ground fault detection process. As described above, the charging time Δtm is determined in consideration of the balance between the determination time and the detection accuracy, and the charging time Δtm may be, for example, about 1.2 seconds. In addition, the shaded area in the figure indicates 668kΩ to 736kΩ included in the variation range of the insulation resistance value at the time of the test.

[0062] For example, it is assumed that the reference value P12 is a reference value obtained by measuring V0, Vc1n and Vc1p in the test mode. In this case, the insulation resistance value of each capacitance of the Y capacitor varies in the range of 682kΩ to 736kΩ, and all insulation resistance values ​​fall within the variation range of the insulation resistance value during the test. Therefore, under this condition, the insulation resistance value closest to the insulation resistance value during the test cannot be selected, and the capacitance of the Y capacitor cannot be estimated.

[0063] By the way, if Figure 3 As shown in FIG. 1 , the rising speed of the charging voltage of the detection capacitor C1 is different depending on the capacitance of the Y capacitor. Specifically, as the capacitance of the Y capacitor becomes smaller, the rise becomes steeper. This difference significantly appears around the time tr indicated by the rectangular dotted line in the figure. The charging time Δtr is shorter than the charging time Δtm in the ground fault detection process, and can be set to, for example, about half, that is, about 600 milliseconds.

[0064] In order not to reduce the detection accuracy, the charging time Δtm cannot be shortened. Therefore, in the present embodiment, the charging time Δtr in the test mode is set to a value smaller than the charging time Δtm in the ground fault detection process. In the test mode, the accuracy of the reference value obtained is reduced by shortening the charging time Δtr. However, the insulation resistance calculated based on the reference value is distributed in a wide range and is conducive to estimating the capacitance of the Y capacitor.

[0065] Figure 4 An example of a test conversion map 140 that has been created for each of the capacitances C1 to C9 is shown. The capacitance C1 and the capacitance C9 are similar. Figure 2 The capacitance in the test is shown in FIG. 1 , but in the example of the drawing, the charging time is set to a charging time Δtr which is half of the charging time Δtm in the actual ground fault detection process. The shaded area in the drawing indicates 668 kΩ to 736 kΩ included in the variation range of the insulation resistance value at the time of the test.

[0066] For example, it is assumed that the reference value Q10 is a reference value obtained by measuring V0, Vc1n and Vc1p in the test mode when the charging time is Δtr. In this case, the insulation resistance value of each capacitance of the Y capacitor varies greatly within the range of 566kΩ to 888kΩ. This is because the charging time is shortened, and therefore the difference in the charging voltage corresponding to the capacitance of the Y capacitor occurs significantly.

[0067] Under the condition of shortened charging time, the insulation resistance value during the test changes significantly. Therefore, the capacitance of the Y capacitor corresponding to the insulation resistance value overlapping the variation range of the insulation resistance value during the test can be narrowed. Therefore, the estimation accuracy of the capacitance of the Y capacitor can be improved. Therefore, the conversion mapping suitable for the actual situation can be selected, and the calculation accuracy of the insulation resistance can also be improved.

[0068] In the example of the drawing, the capacitance of the Y capacitor can be specified as capacitance C5 or capacitance C6. In the actual ground fault detection process, measurement is performed with a charging time Δtm, and for the reference value that has been obtained, the insulation resistance can be obtained by referring to the measurement conversion map 130 corresponding to capacitance C5 or capacitance C6.

[0069] Next, the operation of the ground fault detection device 100 having the above configuration will be described. As a prerequisite, in the case where the charging time is the charging time Δtm, a measurement conversion map 130 is created for each capacitance of the Y capacitor, and in the case where the charging time is the charging time Δtr shorter than the charging time Δtm, a test conversion map 140 is created for each capacitance of the Y capacitor.

[0070] First, refer to Figure 5 The flowchart in describes the operation of the ground fault detection device 100 in the test mode. The test mode is controlled by the control device 120 and can be executed, for example, when starting the vehicle or based on a predetermined instruction.

[0071] In the test mode, the test switch Sr is closed to connect the reference resistor Rref ( S101 ).

[0072] In a state where the reference resistor Rref is connected, the switches S1 to S4 are controlled to be opened and closed, and V0, Vc1n and Vc1p are measured at a charging time Δtr, respectively (S102). The charging time Δtr is shorter than the charging time Δtm in the ground fault detection process.

[0073] Then, a reference value is calculated based on V0, Vc1n, and Vc1p obtained at the charging time Δtr (S103).

[0074] With respect to the calculated reference value, the capacitance of the Y capacitor is estimated with reference to the test conversion map 140 (S104). Specifically, the insulation resistance based on the reference value is calculated for each conversion map of each capacitance included in the test conversion map 140, and the capacitance corresponding to the insulation resistance overlapping the test insulation resistance range assumed at the time of the test is estimated as the capacitance of the Y capacitor.

[0075] Next, we will refer to Figure 6 The operation of the ground fault detection device 100 in the actual ground fault detection process is described with reference to the flowchart in FIG. The ground fault detection process is controlled by the control device 120 and can be appropriately performed, for example, while the vehicle is running.

[0076] During the ground fault detection process, the test switch Sr is turned off to disconnect the reference resistor Rref ( S201 ).

[0077] The switches S1 to S4 are controlled to be opened and closed, and V0, Vc1n, and Vc1p are measured at a normal charging time Δtm, respectively (S202).

[0078] Based on V0, Vc1n, and Vc1p which have been obtained at the charging time Δtm, a reference value is calculated (S203).

[0079] Referring to the measurement conversion map 130 corresponding to the capacitance of the Y capacitor that has been estimated in the test mode (S204), the insulation resistance based on the calculated reference value is calculated (S205).

[0080] Based on the calculated insulation resistance, ground fault determination is performed according to a given technical standard (S206).

[0081] As described above, in the ground fault detection device 100 of the present embodiment, the charging time in the test mode is shorter than the charging time in the actual ground fault detection process, so that the capacitance of the Y capacitor can be easily reduced and the estimation accuracy of the capacitance of the Y capacitor can be improved. Therefore, a conversion map suitable for the actual situation can be selected, and the calculation accuracy of the insulation resistance can also be improved.

Claims

1. A ground fault detection device, the ground fault detection device being connected to a non-grounded battery and used 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 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 side insulation resistor and the capacitor, 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, the positive side insulation resistor is the insulation resistance between the positive side line of the battery and the ground; A reference resistor and a test switch, wherein the reference resistor and the test switch are connected in series between the positive side line or the negative side line of the battery and the ground; as well as a control unit configured to calculate a first reference value based on each charging voltage in a case where the test switch is turned off and the capacitor is charged for a first time in each of the first to third measurement paths; and the control unit is configured to calculate the insulation resistance with reference to a conversion map that has been created corresponding to the electrostatic capacitance between each of the positive-side line and the negative-side line of the battery and the ground, wherein The control unit calculates a second reference value based on each charging voltage when the test switch is closed and the capacitor is charged for a second time in each measurement path from the first measurement path to the third measurement path, the second time being shorter than the first time, and the control unit is configured to estimate the electrostatic capacitance with reference to a predetermined test conversion map.

2. The ground fault detection device according to claim 1, wherein: the test conversion map indicates a resistance value of each of the electrostatic capacitances relative to the second reference value; and The control unit is configured to estimate the electrostatic capacitance based on a range of resistance values ​​to be assumed as a combined resistance of the insulation resistance and the reference resistance and a resistance value of each of the electrostatic capacitances relative to the second reference value.

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