Power System

Abstract

To provide an electrical power system that can suppress relay disconnection due to erroneous determination.SOLUTION: In an electrical power system 1 provided with MOS-FETs 50 and 60 between a primary system A having a primary side storage battery 20 and a secondary system B having a secondary side storage battery 30, when there is a current change in a primary system A or a secondary system B and the slope of the current change is greater than or equal to a specified threshold, or when the slope of the current change is less than the specified threshold, in a case in which the absolute value of the current is equal to or greater than a predetermined threshold, it is determined that a ground fault has occurred, and the MOS-FETs 50 and 60 are disconnected. As a result, it is possible to accurately determine between the occurrence of a ground fault (abnormal state) and the change caused by the inrush current (normal state), and suppress the disconnection of the MOS-FETs 50 and 60 due to erroneous determination.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a power supply system, and more particularly to a measure for improving reliability in a power supply system that requires redundant power supplies. [Background technology]

[0002] Conventionally, there are known power supply systems that require power supply redundancy as installed in vehicles, etc., as disclosed in Patent Document 1. This type of power supply system includes a primary system having a primary storage battery and a secondary system having a secondary storage battery, and is configured to be able to supply power to an electrical load from each system.

[0003] Furthermore, in the power supply system disclosed in Patent Document 1, when a voltage drop in the primary system or the secondary system is detected, the relay between the systems is disconnected (shut off). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-192251 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the power supply system disclosed in Patent Document 1, the relay is disconnected when a drop in the voltage of the primary system or the secondary system is detected. Therefore, when voltage fluctuations occur due to alternator ripple or induced noise even under normal conditions, it may be erroneously determined that this is a ground fault, and the relay may be disconnected frequently.

[0006] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a power supply system that can suppress disconnection of a relay due to erroneous determination. [Means for solving the problem]

[0007] The solution of the present invention for achieving the above object is premised on a power supply system in which a system separation relay is provided between a primary system having a primary side storage battery and a secondary system having a secondary side storage battery. This power supply system includes a current detection means capable of detecting a current change in at least one of the systems, a ground fault determination unit that determines that a ground fault has occurred if the gradient of the current change detected by the current detection means is equal to or greater than a predetermined threshold, or if the gradient of the current change is less than the predetermined threshold and the absolute value of the current is equal to or greater than a predetermined threshold, and a control unit that causes the system separation relay to be disconnected when the ground fault determination unit determines that a ground fault has occurred. The current detection means includes a current sensor that detects a direction of current flow between the primary system and the secondary system, and a threshold value of a gradient of the current change for determining that a ground fault has occurred in the secondary system when the direction of the current flow is from the primary system to the secondary system, and a threshold value of the gradient of the current change for determining that a ground fault has occurred in the primary system when the direction of the current flow is from the secondary system to the primary system, are set to different values, and a threshold value of an absolute value of the current for determining that a ground fault has occurred in the secondary system when the direction of the current flow is from the primary system to the secondary system, and a threshold value of an absolute value of the current for determining that a ground fault has occurred in the primary system when the direction of the current flow is from the primary system to the secondary system, are set to different values. It is characterized by:

[0008] It should be noted that the phrase "when the gradient of the current change is less than a predetermined threshold value" here refers to a situation in which a current change is detected but the gradient of the current change is less than a predetermined threshold value, and a situation in which no current change is detected.

[0009] Due to the above-mentioned specific matters, if there is a current change in the primary system or the secondary system, and the gradient of the current change is equal to or greater than a predetermined threshold, it is determined that a ground fault has occurred, and the system isolation relay is disconnected. This threshold is set to a gradient greater than the gradient of the change in inrush current. Therefore, in the case of a current change due to an inrush current, the gradient of the current change is less than the threshold, and the system isolation relay is not disconnected. In this way, it is possible to quickly determine whether a ground fault has occurred (abnormal) or whether the change is due to an inrush current (normal), based on the gradient of the current change, and it is possible to prevent the system isolation relay from being disconnected (erroneous shutoff) due to an erroneous determination.

[0010] Furthermore, even if the gradient of the current change is less than a predetermined threshold, if the absolute value of the current is equal to or greater than the predetermined threshold, it is determined that a ground fault has occurred, and the system isolation relay is disconnected. This threshold is set to a value greater than the absolute value of the current in the inrush current. Therefore, in the case of a current change due to an inrush current, the absolute value of the current is less than the threshold, and the system isolation relay is not disconnected. Therefore, even if the above-mentioned determination using the gradient of the current change cannot distinguish between the occurrence of a ground fault and an inrush current (when the current change is gradual), the determination using the absolute value of the current can accurately determine whether a ground fault has occurred (abnormal) or whether the change is due to an inrush current (normal), and it is possible to suppress disconnection of the system isolation relay due to erroneous determination. Effect of the Invention

[0011] In the present invention, in a power supply system equipped with a system isolation relay between a primary system and a secondary system, if there is a current change in the primary system or the secondary system and the gradient of the current change is equal to or greater than a predetermined threshold, or if the gradient of the current change is less than the predetermined threshold and the absolute value of the current is equal to or greater than a predetermined threshold, it is determined that a ground fault has occurred and the system isolation relay is disconnected. This makes it possible to accurately determine whether a ground fault has occurred (abnormal) or whether the change is due to an inrush current (normal), and to prevent the system isolation relay from being disconnected due to an erroneous determination. [Brief description of the drawings]

[0012] [Figure 1] 1 is an electrical block diagram showing a configuration of a power supply system according to an embodiment. [Diagram 2] FIG. 11 is a flowchart showing a procedure for controlling the isolation of a MOS-FET. [Diagram 3] 11 is a diagram illustrating an example of a relationship between a current change caused by a ground fault and a current change of an inrush current, and a ground fault determination gradient threshold value. FIG. [Figure 4]11 is a diagram showing an example of a relationship between a current change caused by a ground fault and a current change of an inrush current, and a ground fault determination current threshold value; FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this embodiment, the present invention will be described as being applied to a power supply system mounted on a so-called Maas (Mobility as a Service) vehicle. Note that the power supply system according to the present invention can also be applied to other types of vehicles and devices other than vehicles (devices equipped with a power supply system that requires power supply redundancy).

[0014] -Power supply system configuration- Fig. 1 is an electrical block diagram showing the configuration of a power supply system 1 according to this embodiment. As shown in Fig. 1, the power supply system 1 is configured such that a primary system (main system) A and a secondary system (redundancy system) B can be separated by two MOS-FETs (system separation relays, semiconductor switches) 50 and 60.

[0015] Specifically, the power supply system 1 includes a primary storage battery 20, a secondary storage battery 30, two MOS-FETs 50 and 60, various electrical loads (not shown), a generator, and the like.

[0016] The primary storage battery 20 is, for example, a lithium storage battery. In this case, an oxide containing lithium (lithium metal composite oxide) is used as the positive electrode active material of the primary storage battery 20, and specific examples include LiCoO2, LiMn2O4, LiNiO2, and LiFePO4. The positive electrode active material of the primary storage battery 20 is not limited to these. The negative electrode active material of the primary storage battery 20 is carbon, graphite, lithium titanate (for example, LixTiO2), and an alloy containing Si or Su. The negative electrode active material of the primary storage battery 20 is not limited to these. An organic electrolyte is used as the electrolyte of the primary storage battery 20. The primary storage battery 20 is configured by connecting a plurality of battery cells each composed of these electrodes in series.

[0017] The secondary storage battery 30 is, for example, a lead storage battery. In this case, lead dioxide (PbO2) is used as the positive electrode active material of the secondary storage battery 30, lead (Pb) is used as the negative electrode active material, and sulfuric acid (H2SO4) is used as the electrolyte. The positive electrode active material, negative electrode active material, and electrolyte of the secondary storage battery 30 are not limited to these. The secondary storage battery 30 is configured by connecting multiple battery cells, each of which is made up of these electrodes, in series.

[0018] Since both storage batteries 20, 30 are connected in parallel, when charging from a generator (not shown), if MOS-FETs 50, 60 are turned on, the generator's induced current flows into the storage battery with the lower terminal voltage. On the other hand, when supplying (discharging) power to an electrical load (not shown), if MOS-FETs 50, 60 are turned on when not generating power, the storage battery with the higher terminal voltage will be discharged to the electrical load.

[0019] The MOS-FETs 50 and 60 are disposed between the primary storage battery 20 and the secondary storage battery 30, and function as switching means for switching between the primary system A and the secondary system B between conduction (ON) and cutoff (OFF).

[0020] Moreover, the MOS-FETs 50 and 60 have a rectifying means in their internal structure. That is, the internal circuits of the MOS-FETs 50 and 60 are equivalent to a circuit in which the semiconductor switch units 52 and 62 and the parasitic diodes 51 and 61 are connected in parallel. The input signals to the gates of the semiconductor switch units 52 and 62 are controlled by an electronic control unit (ECU 80). That is, the on operation (energization operation) and off operation (cutoff operation, disconnection operation) of the MOS-FETs 50 and 60 are controlled so as to be switched by the ECU 80. With this configuration, for example, when the MOS-FETs 50 and 60 are in the on operation state, it is possible to take out the inrush current of the secondary system B from the primary side storage battery 20 of the primary system A. This makes it possible to relax the performance requirements of the power storage device, and to increase the options for reducing capacity and types of storage batteries.

[0021] The two MOS-FETs 50 and 60 are connected in series so that the parasitic diodes 51 and 61 are oriented in the opposite directions to each other. Therefore, when the two MOS-FETs 50 and 60 are turned off, the flow of current through the parasitic diodes 51 and 61 can be completely blocked.

[0022] Examples of the electric load include a car navigation system, an audio system, a headlight, and an air conditioner. The electric power generated by the generator is supplied to various electric loads and also to the primary storage battery 20 and the secondary storage battery 30. When the generator is not generating electric power, the electric power is supplied from the primary storage battery 20 and the secondary storage battery 30 to the electric loads. The amount of discharge from the primary storage battery 20 and the secondary storage battery 30 to the electric loads and the amount of charge from the generator to the primary storage battery 20 and the secondary storage battery 30 are adjusted by adjusting the set voltage and controlling the operation of the MOS-FETs 50 and 60 so that the SOC (State of charge) is within a range that does not cause overcharging or overdischarging.

[0023] Current sensors (current detection means) 91, 92 are respectively disposed on the positive electrode side of the storage batteries 20, 30. These current sensors 91, 92 detect the current values ​​in the storage batteries 20, 30. These current sensors 91, 92 are connected to the ECU 80 by signal lines 81, 82, and output detected current information to the ECU 80.

[0024] A current sensor (current detection means) 93 is disposed between the MOS-FETs 50, 60. This current sensor 93 detects the value and direction of a current (relay current) between the primary system A and the secondary system B. This current sensor 93 is connected to the ECU 80 by a signal line 83, and outputs detected current information to the ECU 80.

[0025] The ECU 80 is physically composed of a microprocessor that performs calculations, a ROM that stores programs for causing the microprocessor to execute various processes, a RAM that stores various data such as calculation results, and a backup RAM whose stored contents are maintained by a battery. The ECU 80 also has a certain level of instantaneous power failure resistance and will not be reset for a predetermined period of time even if the applied voltage falls below the guaranteed operating voltage. The ECU 80 realizes various functional units such as a ground fault determination unit 84 and a control unit 85 through the above-mentioned physical configuration.

[0026] The ground fault determination unit 84 acquires current information detected by each current sensor 91, 92, 93, and when a current change is detected, determines whether the gradient of the current change (amount of change in current value per unit time) is equal to or greater than a predetermined threshold (ground fault determination gradient threshold). This threshold is set in advance through experiments and simulations as a gradient greater than the gradient of the change in inrush current. If the gradient of this current change is equal to or greater than the predetermined threshold, it is determined that a ground fault has occurred. This determination of the presence or absence of a ground fault based on the gradient of the current change is intended to determine the presence or absence of a ground fault when a metal with low electrical resistance is applied to the terminal of the storage battery.

[0027] Furthermore, when the gradient of the current change is less than a predetermined threshold, the ground fault determination unit 84 determines whether the absolute value of the current is equal to or greater than a predetermined threshold (ground fault determination current threshold). This threshold is set in advance by experiment or simulation as a value greater than the absolute value of the current in the inrush current. This threshold is also set as a value that the ECU 80 will not reset based on the above-mentioned ground fault determination gradient threshold and the instantaneous power interruption tolerance. Also, when the absolute value of this current is equal to or greater than the predetermined threshold, it is determined that a ground fault has occurred. This determination of the presence or absence of a ground fault based on the absolute value of the current is intended to determine the presence or absence of a ground fault when a metal with high electrical resistance is applied to the electrical load end (when the voltage drops gradually).

[0028] When the ground fault determination unit 84 determines that a ground fault has occurred, the control unit 85 outputs a disconnection command signal to each of the MOS-FETs 50, 60 to disconnect each of the MOS-FETs 50, 60. This disconnects each of the MOS-FETs 50, 60, cuts off the current between the primary system A and the secondary system B, and prevents abnormal current propagation.

[0029] -MOS-FET isolation control- Next, a description will be given of the control of disconnection of the MOS-FETs 50, 60 in the power supply system 1 configured as described above. Fig. 2 is a flow chart showing the procedure of the control of disconnection of the MOS-FETs 50, 60. This flow chart is repeatedly executed at predetermined time intervals while the power supply system 1 is operating, for example, by turning on the IG switch of the vehicle.

[0030] First, in step S1, it is determined whether or not there has been a change in the currents detected by the current sensors 91, 92, and 93.

[0031] If there is no change in the current and the result of step S1 is NO, the process proceeds to step S8. On the other hand, if there is a change in the current and the result of step S1 is YES, the process proceeds to step S2. In step S2, the direction of the current flow is determined based on the current information detected by the current sensors 91, 92, and 93. Specifically, it is determined whether the direction of the current flow is from the primary system A to the secondary system B.

[0032] If the direction of current flow is from the primary system A to the secondary system B and the determination in step S2 is YES, the process proceeds to step S3. In this case, there is a possibility that a ground fault has occurred in the secondary system B. In step S3, a threshold value of the gradient of the current change for determining whether a ground fault has occurred (ground fault determination gradient threshold) di1 and a threshold value of the absolute value of the current for determining whether a ground fault has occurred (ground fault determination current threshold) I1 are set.

[0033] On the other hand, if the direction of current flow is from the secondary system B to the primary system A and the result of step S2 is NO, the process proceeds to step S4. In this case, there is a possibility that a ground fault has occurred in the primary system A. In step S4, a threshold value of the gradient of the current change for determining whether a ground fault has occurred (ground fault determination gradient threshold) di2 and a threshold value of the absolute value of the current for determining whether a ground fault has occurred (ground fault determination current threshold) I2 are set.

[0034] After setting each threshold value in this manner, the process proceeds to step S5, where the gradient of the current change detected by the current sensors 91, 92, and 93 (the amount of current change per unit time: di / dt) is calculated.

[0035] Then, the process proceeds to step S6, where it is determined whether the gradient of the current change (di / dt) is equal to or greater than the threshold of the gradient of the current change. That is, if the direction of the current flow is from the primary system A to the secondary system B, the threshold of the gradient of the current change di1 is compared with the gradient of the detected current change (di / dt). On the other hand, if the direction of the current flow is from the secondary system B to the primary system A, the threshold of the gradient of the current change di2 is compared with the gradient of the detected current change (di / dt).

[0036] Then, if the gradient of the current change (di / dt) is equal to or greater than the set threshold value of the gradient of the current change and the result of the determination in step S6 is YES, the process proceeds to step S7, in which a disconnection command signal is output to each of the MOS-FETs 50, 60, causing each of the MOS-FETs 50, 60 to be disconnected.

[0037] FIG. 3 is a diagram showing an example of the relationship between the current change caused by a ground fault (see the solid line in the diagram) and the current change of the inrush current (see the dashed line in the diagram) and the ground fault judgment gradient threshold (see the dashed line in the diagram). This FIG. 3 shows a case where the gradient of the current change caused by a ground fault is relatively large. As shown in this FIG. 3, the gradient of the current change caused by a ground fault is larger than the gradient of the current change of the inrush current. Then, by setting the threshold to an intermediate value between the gradients of these current changes, if the gradient of the current change is equal to or greater than the threshold, a YES judgment is made in step S6, and the MOS-FETs 50 and 60 are disconnected in step S7. This cuts off the current between the primary system A and the secondary system B, and prevents abnormal current propagation.

[0038] On the other hand, if the gradient of the current change is less than the set threshold value of the gradient of the current change and the result of the determination in step S6 is NO, the process proceeds to step S8. In this step S8, it is determined whether or not the absolute value of the detected current is equal to or greater than the set threshold value of the absolute value of the current. That is, if the direction of the current flow is from the primary system A to the secondary system B, the threshold value I1 of the absolute value of the current is compared with the absolute value of the detected current. On the other hand, if the direction of the current flow is from the secondary system B to the primary system A, the threshold value I2 of the absolute value of the current is compared with the absolute value of the detected current.

[0039] Then, if the absolute value of the detected current is equal to or greater than the set threshold value of the absolute value of the current and the result of the determination in step S8 is YES, the process proceeds to step S7, in which a disconnection command signal is output to each of the MOS-FETs 50, 60, causing each of the MOS-FETs 50, 60 to be disconnected.

[0040] FIG. 4 is a diagram showing an example of the relationship between the current change caused by a ground fault (see the solid line in the diagram) and the current change of the inrush current (see the dashed line in the diagram) and the ground fault determination current threshold (see the dashed line in the diagram). FIG. 4 shows a case where the gradient of the current change caused by a ground fault is relatively small, and it is difficult to distinguish between the occurrence of a ground fault and an inrush current by the determination using the gradient of the current change described above. As shown in FIG. 4, the absolute value of the current caused by a ground fault is greater than the absolute value of the inrush current. Then, by setting the threshold to a value intermediate between the absolute values ​​of these currents, if the absolute value of the current is equal to or greater than the threshold, a YES determination is made in step S8, and the MOS-FETs 50 and 60 are disconnected in step S7. This cuts off the current between the primary system A and the secondary system B, and prevents abnormal current propagation.

[0041] On the other hand, if the absolute value of the detected current is less than the set threshold value of the absolute value of the current and the result of the NO judgment in step S8 is NO, the process proceeds to step S9, in which a disconnection command signal is not output to each of the MOS-FETs 50, 60, and the connection state of each of the MOS-FETs 50, 60 is maintained.

[0042] The above operations are repeated.

[0043] -Effects of the embodiment- As described above, in this embodiment, in the power supply system 1 provided with the MOS-FETs 50 and 60 between the primary system A and the secondary system B, if there is a current change in the primary system A or the secondary system B and the gradient of the current change is equal to or greater than a predetermined threshold, or if the gradient of the current change is less than the predetermined threshold and the absolute value of the current is equal to or greater than a predetermined threshold, it is determined that a ground fault has occurred and the MOS-FETs 50 and 60 are disconnected. This makes it possible to distinguish between the occurrence of a ground fault and an inrush current, and to prevent disconnection of the MOS-FETs 50 and 60 due to erroneous determination. As a result, for example, the number of times the secondary storage battery 30 is charged and discharged can be reduced, and the life of the secondary storage battery 30 can be extended.

[0044] In addition, while the power supply system in Patent Document 1 requires an inductance, this embodiment does not require an inductance by using MOS-FETs 50 and 60. This makes it possible to simplify the configuration of the entire power supply system 1 (reducing size and weight) and reduce costs.

[0045] -Other embodiments- The present invention is not limited to the above-described embodiment, and all modifications and applications encompassed within the scope of the claims and equivalents thereto are possible.

[0047] Furthermore, the above-mentioned threshold value setting based on the direction of current may be based on other conditions in addition to the direction detected by the current sensors 91, 92, and 93.

[0048] In addition, in the above embodiment, the ground fault determination gradient threshold is a fixed value, but the ground fault determination gradient threshold may be switched to a smaller value when the gradient of the current change detected by the current sensors 91, 92, and 93 is large. This makes it possible to more quickly determine whether a ground fault has occurred (abnormal) or whether the change is due to an inrush current (normal). [Industrial Applicability]

[0049] The present invention is applicable to a power supply system mounted on a vehicle that requires power supply redundancy. [Explanation of symbols]

[0050] 1 Power System 20 Primary storage battery 30 Secondary storage battery 50,60 MOS-FET (system isolation relay) 80 ECU 84 Earth fault determination unit 85 Control Unit 91, 92, 93 Current sensor (current detection means) A Primary system B Secondary system

Claims

[Claim 1] A power supply system including a system separation relay between a primary system including a primary side storage battery and a secondary system including a secondary side storage battery, a current detection means capable of detecting a current change in at least one of the systems; a ground fault determination unit which determines that a ground fault has occurred when a current change is detected by the current detection means and the gradient of the current change is equal to or greater than a predetermined threshold, or when the gradient of the current change is less than the predetermined threshold and the absolute value of the current is equal to or greater than a predetermined threshold; A control unit that disconnects the system isolation relay when the ground fault determination unit determines that a ground fault has occurred, the current detection means includes a current sensor that detects a direction of a current flow between the primary system and the secondary system, a threshold value of the gradient of the current change for determining that a ground fault has occurred in the secondary system when the direction of the current flow is from the primary system to the secondary system, and a threshold value of the gradient of the current change for determining that a ground fault has occurred in the primary system when the direction of the current flow is from the secondary system to the primary system, are set to different values; and a threshold value of the absolute value of the current for determining that a ground fault has occurred in the secondary system when the direction of the current flow is from the primary system to the secondary system, and a threshold value of the absolute value of the current for determining that a ground fault has occurred in the primary system when the direction of the current flow is from the secondary system to the primary system, are set to different values.

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