Diagnosis method for deposition of relay in battery circuit system for driving electric vehicle

Abstract

To more efficiently diagnose deposition of a relay SMRB provided for selectively conducting / cutting off between a battery Ba and a motor 3, and a relay DCR for connecting in parallel battery cell groups Ba1, Ba2 connected in series in the battery, in a battery circuit system 1 for driving an electric vehicle.SOLUTION: Diagnosis for deposition of a relay SMRB is performed by: giving, to the relay SMRB, a command to go into a cut off state while retaining the relay DCR in a conductive state after completion of driving of a motor in which a battery and an inverter are electrically connected or after completion of charging by an external charger at a DC output voltage not lower than an inter-terminal voltage of the battery, and determining whether or not the relay is cut off. Diagnosis for deposition of the relay DCR is performed by bringing the relay SMRB into the conductive state before driving of the motor or start of charging by the external charger, and determining whether or not the relay DCR is cut off.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a drive battery circuit system for an electric vehicle, and more particularly to a method for diagnosing the presence or absence of welding in a relay that switches between conductive and cut-off states in order to control a power transmission path in the battery circuit system. [Background technology]

[0002] In a circuit system for transmitting power from a battery to a motor in an electric vehicle (such as an electric vehicle or a plug-in hybrid vehicle), several relays are provided for switching the power transmission path, and it would be convenient to be able to diagnose whether or not the relays are operating normally, i.e., whether or not a fault in which the relay melts (a fault in which the relay remains connected) has occurred, without removing the relays from the circuit system. For example, Patent Document 1 discloses that, in a circuit system for transmitting power from a battery to a motor, if the battery and the motor are connected via one relay, if the relay melts, a continuous current will flow to the motor. Therefore, the battery and the motor are connected via two relays connected in series, and when one relay melts and cannot be cut off, the other relay can be cut off to prevent a continuous current flow to the motor. In this configuration, the circuit discloses that, in order to diagnose whether the relay is melted, priority is given to the contacts of the two relays to be turned on or off, and only one relay is diagnosed for the presence or absence of melting, thereby simplifying the circuit. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 06-237521 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, when the battery circuit system of an electric vehicle is configured to be capable of charging the battery with DC power from an external charger (such as a station), if the output voltage of the charger is lower than the terminal voltage of the battery, specifically, for example, if the terminal voltage of the battery is 800 V and the output voltage of the charger is 400 V, the charger cannot charge the battery. However, since a battery usually has a plurality of battery cells connected in series, when the output voltage of the charger is lower than the terminal voltage of the battery, it is considered to charge the battery by dividing the battery cells connected in series into a plurality of groups and connecting the groups of battery cells in parallel to the charger. In this case, the battery is provided with a circuit for switching the plurality of battery cells connected in series to a parallel connection, and as a part of the circuit, a relay is provided between the groups of battery cells connected in series to selectively switch between conduction and cut-off (see the embodiment section and drawings described later).

[0005] As described above, it is preferable that the relay provided between the groups of battery cells connected in series can be diagnosed for the presence or absence of welding at any time without removing it from the circuit, similar to the relay between the battery and the motor. In this regard, since the relay between the groups of battery cells is connected in series with the relay between the battery and the motor, it is not possible to diagnose the presence or absence of welding for these two relays at the same time. That is, when diagnosing one relay, the other needs to be in a conductive state. Also, it is preferable that each relay can be diagnosed for whether it is properly cut off, that is, for the presence or absence of welding, every time a command for a cut-off state is given after being made in a conductive state. However, for example, if one relay is diagnosed for the presence or absence of welding once and then made in a cut-off state, and then made in a conductive state again just to diagnose another relay, it becomes necessary to execute the diagnosis again, which makes the diagnostic process cumbersome and inefficient.

[0006] Thus, in consideration of the above-mentioned circumstances regarding diagnosing the presence or absence of welding of the relay between the battery and the motor and the relay between the battery cell groups, a main object of the present invention is to provide a configuration that more efficiently performs diagnosis for welding of a relay provided in a drive battery circuit system for an electric vehicle for selectively establishing / cutting conduction between the battery and the motor, and a relay interposed between the battery cell groups for switching a group of multiple battery cells connected in series within the battery to a parallel connection for charging by an external charger. [Means for solving the problem]

[0007] According to the present invention, the above problem is solved by a method for diagnosing the presence or absence of welding of the first and second relays in a circuit system for transmitting power from a battery to a motor in an electric vehicle, the battery being configured such that two battery cell groups are selectively connected in series or parallel, the battery being chargeable by an external charger having a DC output voltage not lower than a terminal voltage of the battery and an external charger having a DC output voltage lower than a terminal voltage of the battery, the circuit system being provided with a first relay provided between the battery and an inverter controlling an operation of the motor and selectively conducting or interrupting conduction between the battery and the inverter, and a second relay provided between the two battery cell groups in the battery and selectively conducting or interrupting conduction between the two battery cell groups, a first diagnostic step in which, after the first relay and the second relay are in a conductive state and the driving of the motor in which the battery and the inverter are electrically connected is terminated or charging is terminated by an external charger having a DC output voltage not lower than a terminal voltage of the battery, a command is given to the first relay to switch to a cut-off state while keeping the second relay in a conductive state, and by determining whether the first relay is cut-off, the first diagnostic step diagnoses whether the first relay is welded; a second diagnostic process for diagnosing the presence or absence of welding of the second relay by bringing the first relay into a conductive state and determining whether the second relay is cut off or not, when the first relay is in a cut-off state and a command to bring the second relay into a cut-off state has been given, and before starting driving of the motor electrically connected between the battery and the inverter or charging by the external charger; This is achieved by a method comprising:

[0008] In the above configuration, the "electric vehicle" is a vehicle equipped with a battery that can be charged by an external charger, such as an electric vehicle or a plug-in hybrid vehicle. The "circuit system" of the present invention includes a circuit in which a battery, an inverter, and a motor are electrically connected in a normal manner and for charging the battery by an external charger, and is configured to selectively connect two battery cell groups in the battery in series or parallel so that the battery can be charged by either an external charger having a DC output voltage not lower than the terminal voltage of the battery or an external charger having a DC output voltage lower than the terminal voltage of the battery. The "battery cell group" is a group in which a plurality of battery cells are connected in series or parallel. The "external charger" may be a charger that is installed in a stand or the like and supplies DC power to a driving battery of the electric vehicle. In the above circuit system, the "first relay" is a relay that is provided between the battery and an inverter that controls the operation of the motor, and selectively connects or disconnects the battery and the inverter, thereby electrically connecting and disconnecting the battery and the inverter (and the motor). In order to prevent a voltage from being applied to the terminal portion (wire harness) of the electric wire in the battery connected to the inverter when the battery is electrically disconnected from the inverter, the first relay is provided on the battery side of the wire harness. On the other hand, the "second relay" is a relay provided between two battery cell groups in the battery to selectively connect or disconnect the two battery cell groups. When this relay is connected, the two battery cell groups are connected in series, and when this relay is disconnected, the two battery cell groups can be connected in parallel.

[0009] More specifically, the states of the first relay and the second relay in the above circuit system are as follows: first, when the motor is driven to run the vehicle, or when the battery is charged by an external charger having a DC output voltage not lower than the terminal voltage of the battery, the second relay is turned on to connect the two battery cell groups in series, and the first relay is turned on to electrically connect the battery to the connection terminal of the inverter or the external charger. When the battery is charged by an external charger having a DC output voltage lower than the terminal voltage of the battery (the motor is stopped), the first relay is turned on and the second relay is turned off. When the motor is stopped and charging of the battery by the external charger is not being performed, the first relay is turned off, whereby the battery is electrically disconnected from the connection terminal of the inverter and the external charger, and the second relay is also turned off to electrically disconnect the two battery cell groups.

[0010] In the above circuit system configuration, the diagnosis of the presence or absence of welding of the first relay and the second relay (hereinafter referred to as "welding diagnosis") may be performed by checking by any method whether or not each relay is in a conductive state when a cut-off command is given to the relay, and is preferably performed each time the relay is cut off after being turned on (because there is a possibility that a current flows and the relay will be welded each time the relay is turned on when the relay is turned on). Therefore, it is preferable that the welding diagnosis of the first relay and the second relay is performed each time both relays are cut off at the end of driving the motor or charging the battery by an external charger with a DC output voltage not lower than the terminal voltage of the battery, which causes both relays to be in a conductive state, and before each relay is turned on again. As already described, in the above circuit configuration, the first relay and the second relay are connected in series, so that when one relay is diagnosed for welding, the other relay needs to be in a conductive state. In other words, when it is confirmed that one relay is cut off and then a welding diagnosis is performed on another relay, the one relay that was previously confirmed to be cut off is placed in a conductive state. This means that it is not possible to perform a welding diagnosis on both relays when both relays are cut off.

[0011] In consideration of the circumstances related to the welding diagnosis of the first relay and the second relay described above, in the present invention, as described above, the welding diagnosis of the first relay is performed by giving a command to the first relay to be cut off while keeping the second relay in a conductive state after completion of driving of the motor or charging by an external charger having a DC output voltage not lower than the terminal voltage of the battery, with both the first relay and the second relay in a conductive state, and confirming whether or not the first relay is cut off. On the other hand, the welding diagnosis of the second relay is performed by putting the first relay in a conductive state and confirming whether or not the second relay is cut off before the start of driving of the motor or charging by an external charger, with the first relay in a cut-off state and a command to the second relay to be cut off.

[0012] According to the above-mentioned configuration of the welding diagnosis of the first relay and the second relay, the welding diagnosis of the two relays can be performed more efficiently. That is, when driving of the motor or charging by an external charger is finished while both the first relay and the second relay are in a conductive state, it is necessary to stop continuous current supply to the motor and the inverter and to turn the first relay into an interrupted state to prevent electric shock in the wire harness between the battery and the inverter, so that the welding diagnosis of the first relay is performed using that opportunity, but since the welding diagnosis of the second relay requires the first relay to be returned to a conductive state in order to perform it, it is performed before the start of running of the electric vehicle or charging by an external charger, which is the next opportunity to turn the first relay into a conductive state. According to this configuration, the welding diagnosis of the two relays can be completed more efficiently without performing the troublesome process of returning another relay diagnosed as not being welded to a conductive state just for the welding diagnosis of one relay, and then returning the one relay to a conductive state when the other relay is turned into an interrupted state.

[0013] In the above welding diagnosis of the first relay and the second relay, whether or not the relay to be diagnosed has welding is diagnosed by determining whether or not the relay is certainly cut off when a command to turn the relay into a cut-off state is given to the relay. Specifically, for example, by monitoring the voltage of a smoothing capacitor provided between both terminals on the input side (battery side) of the inverter, it is possible to determine whether or not each relay is cut off. More specifically, as described later, when the smoothing capacitor is discharged (by cutting off the electrical connection between the battery and the inverter on the side opposite to the first relay) after the smoothing capacitor is discharged (by cutting off the electrical connection between the battery and the inverter on the side opposite to the first relay), when a cut-off command is given only to the first relay while both the first relay and the second relay are in a conductive state, the first relay is determined to be cut off because it is not conductive (even if the electrical connection between the battery and the inverter on the side opposite to the first relay is restored). Furthermore, when the first relay is cut off before the start of driving the motor or charging by an external charger with a DC output voltage not lower than the terminal voltage of the battery, and a cut-off command is given to the second relay, if the voltage of the smoothing capacitor remains at 0 V when a conduction command is given only to the first relay, the second relay is determined to be not conducting and cut off. This configuration is advantageous in that the welding diagnosis of each relay can be achieved using components that are normally provided in a circuit, without using an element dedicated to that purpose. Effect of the Invention

[0014] Thus, according to the method of the present invention, when a relay for selectively connecting / disconnecting battery cell groups is provided in the battery as well as a relay between the battery and the motor in a drive battery circuit system for an electric vehicle, each of the relays can be diagnosed for welding more efficiently. That is, the present invention performs a diagnosis for welding when the above two relays are connected or disconnected for the operation of the circuit, and does not require switching between connection and disconnection just for the purpose of the diagnosis for welding, and can be advantageously used in a circuit system configured to selectively connect two battery cell groups in a battery in series or parallel so that the battery can be charged by either an external charger with a DC output voltage not lower than the terminal voltage of the battery or an external charger with a DC output voltage lower than the terminal voltage of the battery.

[0015] Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a circuit diagram of a drive battery and a motor of an electric vehicle to which this embodiment is applied. [Explanation of symbols]

[0017] 1...circuit system, 2...battery-inverter wire harness, 3...motor, 4...inverter, 5...DC power charging circuit line, 6...external charger, 10, 11...smoothing capacitor, 13...bypass circuit, Ba...battery, Ba1, Ba2...battery cell group, SMRB, SMRG, SMRP, DCRG, DCRB, DCRNG, DCR, DCRN...relay BEST MODE FOR CARRYING OUT THEINVENTION

[0018] The present invention will now be described in detail with reference to some preferred embodiments thereof with reference to the accompanying drawings, in which like reference numerals indicate like parts.

[0019] Circuit system configuration The method of the present embodiment is applied to a circuit system 1 as shown in FIG. 1 , that is, a circuit system that is mounted on an electric vehicle, a plug-in hybrid vehicle, or other such motor-driven vehicle, and that transmits drive power from a battery Ba that can be charged from an external charger 6 that outputs DC power, such as a station, to a drive motor 3 via an inverter 4, in which a relay SMRB that selectively establishes / cuts conduction between the battery Ba and the inverter 4 and a DC power charging circuit line 5, and a relay DCR that selectively establishes / cuts conduction between two battery cell groups Ba1, Ba2 in the battery Ba.

[0020] More specifically, in the illustrated circuit system 1, when the motor 3 is driven, the battery Ba is used with all the battery cell groups Ba1 and Ba2 connected in series and the sum of their inter-terminal voltages, for example, a voltage of 800 V. On the other hand, when charging the battery Ba, the circuit can be switched so that the battery cell groups Ba1 and Ba2 can be connected in series or in parallel to the DC power charging circuit line 5 to which the external charger 6 is connected, so that charging is possible both when the output voltage of the external charger 6 is not lower than the inter-terminal voltage of the battery Ba (the sum of the inter-terminal voltages of the battery cell groups Ba1 and Ba2) (high-voltage charging, for example, 800 V) and when it is lower than the inter-terminal voltage of the battery Ba (low-voltage charging, for example, 400 V). Specifically, when the battery Ba is electrically connected to the inverter 4 and the DC power charging circuit line 5, the relays SMRB, SMRG (or SMRP), DCRB, and DCRG are turned ON (conductive state), whereas when the battery cell groups Ba1 and Ba2 are connected in series to the DC power charging circuit line 5, the relay DCR is turned ON and the relays DCRNG, DCRNB, and DCRN are turned OFF (disconnected state), and when the battery cell groups Ba1 and Ba2 are connected in parallel to the DC power charging circuit line 5, the relay DCR is turned OFF and the relays DCRNG, DCRNB, and DCRN are turned ON (in this case, the battery cell group Ba1 is directly connected to the external charger 6, and the battery cell group Ba2 is connected to the external charger 6 via the inverter 4 and the neutral point 3a of the coil of the motor 3). A smoothing capacitor 10 is provided between both terminals on the battery side of the inverter 4, and a smoothing capacitor 11 is provided between the neutral point 3a of the motor coil and the ground wire, and a voltage sensor is provided to monitor the respective voltages.In addition, both terminals of battery Ba are connected to the inverter 4 (and motor 3) via a wire harness 2, and in order to prevent electric shock due to the battery voltage remaining applied to the wire harness 2 when electrically disconnecting the battery Ba from the motor, the relays SMRB, SMRG (or SMRP), DCRNG, and DCRNB that disconnect the battery Ba from the motor are all provided on the battery side of the wire harness 2 (as shown in the figure, a configuration 7 for charging the battery by a charger AC that outputs AC power may also be provided).

[0021] Diagnosis of welding of relay SMRB and relay DCR As already mentioned, the relay SMRB between the battery Ba and the inverter 4 and the DC power charging circuit line 5, and the relay DCR between the battery cell groups Ba1 and Ba2 may become welded when they are in a conductive state and a current is flowing through them. Therefore, it is preferable that each relay is diagnosed for welded every time it is turned from ON to OFF, that is, diagnosed for whether it is ON despite the OFF command being given. In this regard, since the relays SMRB and DCR are connected in series, when one relay is diagnosed for welded, the other needs to be ON. In addition, when diagnosing two relays for weldedness, if one relay is diagnosed as not welded and then the other relay is turned ON just to diagnose the other relay for weldedness, a welded diagnosis is required again when the relay is turned OFF, which makes the process cumbersome (the diagnostic process may be repeated more than necessary). Furthermore, when the battery Ba is electrically disconnected from the inverter 4, in order to prevent electric shock in the wire harness 2, it is preferable to turn off the relay SMRB directly connected to the wire harness 2 as quickly as possible. However, even if the relay DCR in the battery Ba is not turned off, as long as the relay SMRB is turned off, there is no effect on the potential in the wire harness 2.

[0022] In consideration of the above circumstances, in this embodiment, at the end of motor driving or high voltage charging, in which relays SMRB and DCR are switched from ON to OFF, relay DCR is kept ON and a welding diagnosis of relay SMRB is performed, and immediately before the start of motor driving or high voltage charging, in which relays SMRB and DCR are switched from OFF to ON, relay SMRB is turned ON and a welding diagnosis of relay DCR is performed, thereby more efficiently achieving a welding diagnosis of two relays without switching one relay OFF / ON just for the welding diagnosis of another relay. The welding diagnosis of the two relays may be performed as follows.

[0023] (1) Diagnosis of SMRB relay welding Referring to FIG. 1, while the motor is being driven or high-voltage charging is being performed, relays SMRB, SMRG, and DCR are ON. When the motor is driven or high-voltage charging is finished, relay SMRG is first turned OFF, and furthermore, motor 3 is driven to discharge smoothing capacitor 10 until it reaches 0V (if smoothing capacitor 10 is not discharged, it is determined that relay SMRG is welded). After that, an OFF command is given to relay SMRB, and relay SMRP that conducts circuit 13 in parallel with relay SMRG is turned ON (circuit 13 and relay SMRP are circuit elements that are usually provided to precharge smoothing capacitor 10). In this state, if the voltage of smoothing capacitor 10 remains at 0V, relay SMRB is not conductive, and it is diagnosed that welding has not occurred. On the other hand, when the voltage of smoothing capacitor 10 increases, relay SMRB is determined to be conductive, and it is diagnosed that welding has occurred. After such a diagnosis, an OFF command is given to relay DCR and relay SMRP.

[0024] (2) Diagnosis of relay DCR welding When neither the motor is driven nor the battery is charged, the relays SMRB, SMRG, and SMRP are OFF (whether these relays are welded or not is diagnosed at the end of the motor drive or high-voltage charging. If they are welded, the motor drive or high-voltage charging will not start), and the OFF command is given to the relay DCR. In this state, when the motor drive or high-voltage charging starts, the relays SMRB and SMRP are turned ON without giving an ON command to the relay DCR. Then, if the relay DCR is in the OFF state, the battery cell groups Ba1 and Ba2 are not connected, so the smoothing capacitor 10 is not charged. On the other hand, if the relay DCR is welded, the battery cell groups Ba1 and Ba2 are connected in series, and the voltage of the smoothing capacitor 10 rises, so that it is possible to diagnose whether the relay DCR is welded or not. If it is determined that the relay DCR is not welded and is normal, the relay DCR is turned ON and the smoothing capacitor 10 is precharged. After that, the relay SMRG is turned ON and the relay SMRP is turned OFF, and the motor drive or high voltage charging begins.

[0025] If the relay is diagnosed as welded in the above-mentioned relay welding diagnosis, the system will be stopped from operating.

[0026] According to the configuration of the present embodiment described above, in a circuit system provided with a relay SMRB between the battery Ba and the inverter 4 and the DC power charging circuit line 5, and a relay DCR between the battery cell groups Ba1 and Ba2, a specific processing procedure is provided for executing a welding diagnosis of these two relays. According to the present embodiment, there is no need to remove the relay from the circuit to perform a welding diagnosis of the relay, and the welding diagnosis can be performed by simply monitoring the voltage of a smoothing capacitor normally provided in the circuit while operating the state of the relay, which is advantageous in that no special element is required for the diagnosis.

[0027] The above description has been given in relation to the embodiment of the present invention, but it will be apparent to those skilled in the art that many modifications and changes can be easily made thereto, and that the present invention is not limited to the embodiment exemplified above, but can be applied to various devices without departing from the concept of the present invention.

Claims

[Claim 1] A method for diagnosing the presence or absence of welding of the first and second relays in a circuit system for transmitting power from a battery to a motor in an electric vehicle, the battery being configured such that two battery cell groups are selectively connected in series or parallel, the battery being chargeable by an external charger having a DC output voltage not lower than a terminal voltage of the battery and an external charger having a DC output voltage lower than a terminal voltage of the battery, the circuit system being provided with a first relay provided between the battery and an inverter controlling an operation of the motor and selectively conducting or interrupting between the battery and the inverter, and a second relay provided between the two battery cell groups in the battery and selectively conducting or interrupting between the two battery cell groups, a first diagnostic step in which, after the first relay and the second relay are in a conductive state and the driving of the motor in which the battery and the inverter are electrically connected is terminated or charging is terminated by an external charger having a DC output voltage not lower than a terminal voltage of the battery, a command is given to the first relay to switch to a cut-off state while keeping the second relay in a conductive state, and by determining whether the first relay is cut-off, the first diagnostic step diagnoses whether the first relay is welded; a second diagnostic process for diagnosing the presence or absence of welding of the second relay by bringing the first relay into a conductive state and determining whether the second relay is cut off or not, when the first relay is in a cut-off state and a command to bring the second relay into a cut-off state has been given, and before starting driving of the motor electrically connected between the battery and the inverter or charging by the external charger; The method includes:

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