Electric vehicles

Abstract

To provide an electric vehicle capable of appropriately charging a high-voltage battery by a charger arranged in an electric path via a relay in parallel with a power control device.SOLUTION: When a high-voltage battery is charged by a charger, charging start time control is performed such that a closed state of a relay is maintained until a predetermined time elapses after the relay is switched to the closed state in response to connection of an external power supply. Further, the predetermined time is a threshold value determined in advance as a period in which charging of the high-voltage battery by the charger is actually started and a voltage of a battery cell increases. Thus, after the relay is switched to the closed state, switching of the relay to an open state is avoided or suppressed until charging of the high-voltage battery by the charger is actually started. Therefore, it is possible to appropriately charge the high-voltage battery by the charger disposed in an electric path via the relay in parallel with a power control device.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electric vehicle in which a high-voltage battery is charged with electric power supplied from an external power source. [Background technology]

[0002] A well-known electric vehicle includes an electric motor, a high-voltage battery for driving a vehicle having a plurality of battery cells connected in series, a power control device that controls the power exchanged between the high-voltage battery and the electric motor and that has a voltage converter that reduces the DC power from the high-voltage battery and supplies it to a low-voltage battery and vehicle accessories, a relay that switches between an open state that interrupts the electrical path between the high-voltage battery and the power control device and a closed state that connects the electrical path between the high-voltage battery and the power control device, a charger that charges the high-voltage battery with power supplied from an external power source, and a control device that controls the charging of the high-voltage battery. Patent Document 1 discloses an example of such a hybrid vehicle. Patent Document 1 discloses that the charger is connected to the high-voltage battery via a dedicated charging relay, not via a main relay (corresponding to the relay described above). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-104222 Summary of the Invention [Problem to be solved by the invention]

[0004] From a cost perspective, it is possible to eliminate the dedicated charging relay and place a charger in the electrical path via the main relay. Alternatively, when the voltage of the battery cells of the high-voltage battery drops below a predetermined abnormally low voltage, it is possible to switch the main relay to an open state to prevent power from being drawn from the high-voltage battery and to suppress a further voltage drop that could lead to a decrease in the durability of the battery cells. However, when an external power source is connected and the high-voltage battery is charged by a charger, the relay must be switched to a closed state. If the voltage converter is operated in conjunction with the relay being switched to a closed state, power will be drawn from the high-voltage battery. If the power drawn causes the battery cell voltage to drop below the predetermined abnormally low voltage, the main relay will be switched to an open state, preventing the charger from charging the high-voltage battery. In this case, the main relay will remain open due to the drop in battery cell voltage, preventing the charger from charging the high-voltage battery via the electrical path via the main relay, potentially preventing the battery cell voltage from being restored.

[0005] The present invention has been made against the background of the above circumstances, and its object is to provide an electric vehicle that can properly charge a high-voltage battery using a charger that is arranged in parallel with the power control device and in an electrical path via a relay. [Means for solving the problem]

[0006] The gist of a first invention is an electric vehicle including: (a) an electric motor; a high-voltage battery for driving a vehicle having a plurality of battery cells connected in series; a power control device that controls power exchanged between the high-voltage battery and the electric motor, the power control device having a voltage converter that steps down DC power from the high-voltage battery and supplies the stepped-down DC power to a low-voltage battery and vehicle accessories; a relay that is switchable between an open state that cuts off an electrical path between the high-voltage battery and the power control device and a closed state that connects the electrical path; a charger that charges the high-voltage battery with power supplied from an external power source; and a control device that controls charging of the high-voltage battery; (c) the control device operates the voltage converter in conjunction with switching of the relay to the closed state, (d) switches the relay to the open state when the voltage of the battery cell drops below a predetermined abnormally low voltage, and (e) when the high-voltage battery is charged by the charger, after switching the relay to the closed state in conjunction with connection of the external power source, performs charge start control so that the closed state of the relay is maintained until a predetermined period of time has elapsed during which charging of the high-voltage battery by the charger actually begins and the voltage of the battery cell increases. [Effects of the Invention]

[0007] According to the first aspect of the present invention, when the high-voltage battery is being charged by the charger, charging start control is performed so that the relay remains closed until a predetermined time has elapsed after the relay is switched to a closed state upon connection of an external power source. The predetermined time is a predetermined threshold value that represents the period during which the voltage of the battery cell increases after the charger actually starts charging the high-voltage battery. This prevents or suppresses the relay from being switched to an open state until the charger actually starts charging the high-voltage battery. Therefore, the high-voltage battery can be appropriately charged by the charger, which is connected in parallel to the power control device and in an electrical path via the relay. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating an example of a schematic configuration of a vehicle to which the present invention is applied; [Figure 2] This is a flowchart explaining the main control operations of the electronic control device, and is a flowchart explaining the control operations for properly charging the main battery by an AC charger placed in an electrical path via a main relay. [Figure 3] 3 is a diagram showing an example of a time chart when the control operation shown in the flowchart of FIG. 2 is executed. FIG. [Figure 4] This is a flowchart explaining the main control operations of the electronic control device, and is a flowchart explaining the control operations for appropriately charging the main battery by an AC charger placed in an electrical path via a main relay, and is an embodiment different from the flowchart of FIG. 2. [Figure 5] FIG. 10 is a diagram for explaining a comparative example to the present embodiment, showing an example in which the main relay is turned off when a BLOW is detected. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. [Example]

[0010] Fig. 1 is a diagram illustrating an example of a schematic configuration of an electric vehicle 10 to which the present invention is applied. In Fig. 1, the electric vehicle 10 is equipped with an electric motor MG that functions as a power source.

[0011] The electric motor MG is a known rotating electric machine, a so-called motor generator, that functions as a motor that generates mechanical power from electric power and as a generator that generates electric power from mechanical power. In the electric vehicle 10, the power from the electric motor MG is transmitted to the drive wheels via a power transmission device (not shown).

[0012] The electric vehicle 10 further includes a main battery 20, an AC charger 30, an in-vehicle charging cable 32, a charging inlet 34, a main relay 40, a power control unit 50, an auxiliary battery 60, vehicle accessories 62, and an electronic control device 70. FIG. 1 also illustrates an example of an electrical configuration related to the control of the electric motor MG and the main battery 20.

[0013] The main battery 20 is a high-voltage driving battery that is a chargeable and dischargeable DC power supply. The main battery 20 has a plurality of battery cells 22, and is a secondary battery such as a nickel-metal hydride battery pack or a lithium-ion battery pack in which the battery cells 22 are connected in series.

[0014] The AC charger 30 is connected to a charging inlet 34 via an in-vehicle charging cable 32. The charging inlet 34 is provided on the vehicle body so as to be connectable to a charging connector 104 of an external charging cable 102 connected to an external power source 100, which is a power source external to the electric vehicle 10. The charging inlet 34 is a terminal into which the charging connector 104 is inserted and through which power supplied from the external power source 100 is input. The charging inlet 34 is a charging port connected to the external power source 100. The AC charger 30 charges the main battery 20 with power supplied from the external power source 100. The AC charger 30 converts the alternating current supplied from the external power source 100 into direct current, and also boosts the voltage of the external power source 100 to a voltage equivalent to that of the main battery 20 to charge the main battery 20.

[0015] The main relay 40 is provided in the electrical path between the main battery 20 and the AC charger 30 and is a relay that connects and disconnects this electrical path. In other words, the main relay 40 is a relay that can be switched between an OFF state, which is an open state that disconnects the electrical path between the main battery 20 and the AC charger 30, and an ON state, which is a closed state that connects the electrical path. In other words, the AC charger 30 is connected to the main battery 20 via the main relay 40.

[0016] The power control unit 50 is connected to the main battery 20 via the main relay 40. In other words, the main relay 40 is provided in the electrical path between the main battery 20 and the power control unit 50 and is a relay that connects and disconnects the electrical path. In other words, the main relay 40 is a relay that can be switched between an OFF state, which disconnects the electrical path between the main battery 20 and the power control unit 50, and an ON state, which connects the electrical path. The AC charger 30 is arranged in parallel with the power control unit 50 and in the electrical path that is connected and disconnected to the main battery 20 by switching the main relay 40.

[0017] The power control unit 50 includes a DC-DC converter 52, a boost converter 54, and an inverter 56. The power control unit 50 is a power control device that controls the power exchanged between the main battery 20 and the electric motor MG. The main battery 20 supplies stored power to the electric motor MG via the power control unit 50. In addition, the main battery 20 is supplied with power via the power control unit 50 as a result of power generation control, for example, regeneration control, of the electric motor MG.

[0018] The DCDC converter 52 is connected to the main battery 20 via the main relay 40. The DCDC converter 52 functions as a charging device that steps down the voltage of the main battery 20 to a voltage equivalent to that of the auxiliary battery 60 and charges the auxiliary battery 60. The DCDC converter 52 supplies the stepped-down power to the vehicle auxiliary devices 62, the electronic control device 70, etc. The auxiliary battery 60 is a low-voltage battery that supplies power to operate the vehicle auxiliary devices 62, the electronic control device 70, etc. The vehicle auxiliary devices 62 are, for example, auxiliary devices such as lamps and audio equipment. In this way, the DCDC converter 52 is a voltage converter that steps down the DC power from the main battery 20 and supplies it to the auxiliary battery 60 and the vehicle auxiliary devices 62.

[0019] The boost converter 54 is connected to the main battery 20 via the main relay 40. The boost converter 54 includes a reactor, a switching element, and the like (not shown). The boost converter 54 is a step-up / step-down circuit that has the function of boosting the voltage of the main battery 20 and supplying it to the inverter 56, and the function of reducing the voltage converted to DC by the inverter 56 and supplying it to the main battery 20.

[0020] The inverter 56 includes a switching element (not shown) and converts the DC current from the boost converter 54 into an AC current for driving the electric motor MG. The inverter 56 converts the AC current generated by the electric motor MG using regenerative braking into a DC current.

[0021] The electronic control device 70 is a controller including a control device that controls charging of the main battery 20. The electronic control device 70 is configured to include a so-called microcomputer equipped with, for example, a CPU, RAM, ROM, an input / output interface, etc. The electronic control device 70 performs various controls of the electric vehicle 10 by the CPU performing signal processing in accordance with a program stored in advance in the ROM while utilizing the temporary storage function of the RAM.

[0022] The electronic control device 70 is supplied with various signals (e.g., MG rotation speed Nmg, accelerator pedal opening θacc, brake-on signal Bon, battery temperature THbat, battery charge / discharge current Ibat, battery voltage Vbat, cell voltage Vcel, plug-in signal Pin, etc.) based on detection values ​​from various sensors (e.g., MG rotation speed sensor 80, accelerator pedal opening sensor 82, brake sensor 84, battery sensor 86, connection detection switch 88, etc.) provided in the electric vehicle 10.

[0023] The MG rotation speed Nmg is a signal that represents the rotation speed of the electric motor MG. The accelerator opening θacc is a signal that represents the magnitude of the driver's acceleration operation, and is a signal that represents the amount of accelerator operation by the driver. The brake-on signal Bon is a signal that indicates the state in which the brake pedal for operating the wheel brakes is being operated by the driver. The battery temperature THbat is a signal that represents the temperature of the main battery 20. The battery charge / discharge current Ibat is a signal that represents the current charged to the main battery 20 and the current discharged from the main battery 20. The battery voltage Vbat is a signal that represents the voltage of the main battery 20. The cell voltage Vcel is a signal that represents the voltage of each of the multiple battery cells 22. The plug-in signal Pin is a signal that indicates the state in which the charging connector 104 is connected to the charging inlet 34.

[0024] The electronic control unit 70 calculates the remaining charge SOC [%] based on, for example, the battery charge / discharge current Ibat and the battery voltage Vbat. The remaining charge SOC is the remaining charge of the main battery 20 and is a value indicating the state of charge of the main battery 20. The electronic control unit 70 calculates the chargeable power Win [W] and dischargeable power Wout [W] of the main battery 20 based on, for example, the battery temperature THbat and the remaining charge SOC.

[0025] The electronic control device 70 outputs various command signals (e.g., a charge control command signal Scg for controlling the AC charger 30, a relay control command signal Srl for controlling the main relay 40, a motor control command signal Smg for controlling the motor MG, a DC-DC control command signal Sdc for controlling the DC-DC converter, etc.) to each device (e.g., the AC charger 30, the main relay 40, the power control unit 50, etc.) provided in the electric vehicle 10.

[0026] The electronic control device 70 includes an electric motor control unit 72, which is an electric motor control means, and a charge control unit 74, which is a charge control means, in order to realize various controls in the electric vehicle 10.

[0027] The motor control unit 72 controls the boost converter 54 and the inverter 56 to control the electric motor MG. For example, the motor control unit 72 converts DC current from the main battery 20 into AC current used by the electric motor MG. The motor control unit 72 drives the electric motor MG based on an output request value corresponding to the torque requested by the driver. The motor control unit 72 converts AC current from the electric motor MG into DC current used to charge the main battery 20. The motor control unit 72 causes the electric motor MG to function as a generator according to the required amount of regenerative braking.

[0028] The motor control unit 72 controls the DC-DC converter 52 to charge the auxiliary battery 60 and supply power to the vehicle auxiliary equipment 62 and the electronic control unit 70. The motor control unit 72 operates the DC-DC converter 52 in conjunction with the switching on of the main relay 40.

[0029] When the power supply to the electric vehicle 10 is turned on, the electric motor control unit 72 switches the main relay 40 on.

[0030] The charging control unit 74 determines whether the charging connector 104 is connected to the charging inlet 34 based on whether a plug-in signal Pin is present. When the charging control unit 74 determines that the charging connector 104 is connected to the charging inlet 34, it switches the main relay 40 on, and then drives the AC charger 30, causing the AC charger 30 to charge the main battery 20. In this way, when charging the main battery 20 with the AC charger 30, the charging control unit 74 switches the main relay 40 on when the external power source 100 is connected. In this embodiment, charging the main battery 20 with the AC charger 30, that is, charging the main battery 20 with the AC charger 30, is referred to as plug-in charging. The electric vehicle 10 is a vehicle capable of plug-in charging.

[0031] The charging control unit 74 switches off the main relay 40 when the cell voltage Vcel drops below the BLOW threshold Vcelf to prevent a decrease in the durability of the main battery 20, particularly the battery cells 22. BLOW indicates that the battery cells 22 are in an abnormally low voltage state. The BLOW threshold Vcelf is a predetermined threshold for determining whether the cell voltage Vcel is low enough to easily decrease the durability of the battery cells 22, i.e., a predetermined abnormally low voltage. For example, the charging control unit 74 determines whether the cell voltage Vcel is lower than the BLOW threshold Vcelf. If the charging control unit 74 determines that the cell voltage Vcel is lower than the BLOW threshold Vcelf, the charging control unit 74 establishes the BLOW condition. The charging control unit 74 determines whether the BLOW condition continues to be established for a detection determination time TMblow, i.e., whether a BLOW has been detected. If the charging control unit 74 determines that a BLOW has been detected, the charging control unit 74 switches off the main relay 40. The detection determination time TMblow is, for example, a predetermined threshold value for reliably determining that the cell voltage Vcel is less than the BLOW threshold value Vcelf.

[0032] During plug-in charging, the DC-DC converter 52 is activated in conjunction with the main relay 40 being switched on. The DC-DC converter 52 then reduces the cell voltage Vcel by carrying a load. As shown in the comparative example of FIG. 5 , if the cell voltage Vcel is close to the BLOW threshold Vcelf before plug-in charging begins, the DC-DC converter 52 may activate and cause the cell voltage Vcel to drop below the BLOW threshold Vcelf. Meanwhile, during plug-in charging, a charging command is output to the AC charger 30 when the main relay 40 is switched on. However, the AC charger 30 is not immediately activated. Plug-in charging does not begin until a predetermined preparation time for activating the AC charger 30 has elapsed. If the predetermined preparation time is longer than the detection determination time TMblow, BLOW is detected before plug-in charging actually begins and the cell voltage Vcel increases, causing the main relay 40 to be switched off (see FIG. 5 ). FIG. 5 is a diagram illustrating a comparative example of this embodiment, showing an example in which the main relay is turned off when BLOW is detected. The electric vehicle 10 is not connected to the main battery 20 via a dedicated charging relay, but is connected to the main battery 20 via the main relay 40, similar to the DC-DC converter 52. Therefore, if the main relay 40 is switched off, plug-in charging becomes impossible thereafter, and there is a risk that the cell voltage Vcel will not be able to recover.

[0033] Plug-in charging starts after a predetermined preparation time has elapsed, and the cell voltage Vcel recovers as a result of plug-in charging, so the charging control unit 74 does not switch the main relay 40 off during the predetermined preparation time. Therefore, during plug-in charging, the charging control unit 74 determines whether a predetermined time TMf has elapsed after the main relay 40 was switched on in response to the connection of the external power source 100. The predetermined time TMf is a threshold value that is set in advance as a period during which the cell voltage Vcel increases after plug-in charging actually starts. After the main relay 40 is switched on in response to the connection of the external power source 100, the charging control unit 74 performs charging start control CNcs so that the main relay 40 remains on until the predetermined time TMf has elapsed.

[0034] Even if the charging control unit 74 detects BLOW during the predetermined time TMf, the charging control unit 74 performs the charge start control CNcs by not switching off the main relay 40. In other words, the charging control unit 74 performs the charge start control CNcs by prohibiting the main relay 40 from being switched off based on the BLOW threshold Vcelf. On the other hand, after the predetermined time TMf has elapsed, the charging control unit 74 ends the charge start control CNcs and allows the main relay 40 to be switched off based on the BLOW threshold Vcelf.

[0035] If the main battery 20 can withstand the drop in the cell voltage Vcel only during the predetermined time TMf until plug-in charging actually starts, the cell voltage Vcel will be restored thereafter.

[0036] FIG. 2 is a flowchart illustrating the main control operations of the electronic control device 70, which are executed repeatedly, for example, to properly charge the main battery 20 using the AC charger 30 disposed in the electrical path via the main relay 40.

[0037] 2, first, in step S10A (hereinafter, "step" will be omitted) corresponding to the function of the charging control unit 74, it is determined whether the charging connector 104 is connected to the charging inlet 34, i.e., whether it is inserted. If the determination in S10A is negative, the routine is terminated. If the determination in S10A is positive, the main relay 40 is switched on in S20A, corresponding to the function of the charging control unit 74. Next, in S30A, corresponding to the function of the motor control unit 72, the DC-DC converter 52 is operated. Next, in S40A, corresponding to the function of the charging control unit 74, it is determined whether the cell voltage Vcel is less than the BLOW threshold Vcelf. If the determination in S40A is positive, it is determined in S50A, corresponding to the function of the charging control unit 74, whether a BLOW has been detected. If the determination in S50A is negative, the routine returns to S40A. If the determination in S40A is negative or if the determination in S50A is positive, then in S60A, which corresponds to the function of the charging control unit 74, it is determined whether a predetermined time TMf has elapsed. If the determination in S60A is negative, then in S70A, which corresponds to the function of the charging control unit 74, switching off of the main relay 40 based on the BLOW threshold Vcelf is prohibited, thereby causing the charging start control CNcs to be executed. After execution of S70A, the process returns to S40A. If the determination in S60A is positive, then in S80A, which corresponds to the function of the charging control unit 74, the charging start control CNcs is terminated, and switching off of the main relay 40 based on the BLOW threshold Vcelf is permitted. During the period until the determination in S60A is positive, plug-in charging actually starts, and the cell voltage Vcel is restored.

[0038] FIG. 3 is a diagram showing an example of a time chart when the control operation shown in the flowchart of FIG. 2 is executed. FIG. 3 shows an example of a case where plug-in charging is performed when the cell voltage Vcel is near the BLOW threshold Vcelf. In FIG. 3, time t1 indicates the time when the charging connector 104 is inserted into the charging inlet 34. When the charging connector 104 is inserted into the charging inlet 34, charging control CNchg is executed. In charging control CNchg, the main relay 40 is switched on (see time t2), the DC-DC converter 52 is activated (see time t3), and plug-in charging actually starts after a predetermined preparation time has elapsed (see time t4). When the DC-DC converter 52 is activated, power is drawn from the main battery 20. At this time, if the cell voltage Vcel is near the BLOW threshold Vcelf, the cell voltage Vcel is reduced below the BLOW threshold Vcelf, and the BLOW condition is established. If the establishment of the BLOW condition continues for a detection determination time TMblow, BLOW is detected. In contrast, in this embodiment, the charge start control CNcs is executed until the predetermined time TMf has elapsed after the main relay 40 is switched on, and therefore the main relay 40 is prohibited from being switched off even if BLOW is detected. By the time the predetermined time TMf has elapsed, plug-in charging is actually started, thereby restoring the cell voltage Vcel. After the predetermined time TMf has elapsed, the charge start control CNcs is terminated (see time t5).

[0039] As described above, according to this embodiment, during plug-in charging, the charge start control CNcs is performed so that the main relay 40 remains on until the predetermined time TMf has elapsed after the main relay 40 is switched on in response to connection of the external power supply 100. This prevents or suppresses the main relay 40 from being switched off after the main relay 40 is switched on until plug-in charging actually starts. This allows the main battery 20 to be appropriately charged by the AC charger 30, which is arranged in parallel with the power control unit 50 and on an electrical path via the main relay 40.

[0040] Furthermore, according to this embodiment, the charge start control CNcs is performed by prohibiting the main relay 40 from being switched off based on the BLOW threshold Vcelf, thereby appropriately maintaining the main relay 40 in an on state until the predetermined time TMf has elapsed.

[0041] Furthermore, according to this embodiment, after the predetermined time TMf has elapsed, the charge start control CNcs is terminated and the main relay 40 is permitted to be switched off based on the BLOW threshold Vcelf. This appropriately suppresses a decrease in the durability of the battery cells 22.

[0042] Next, another embodiment of the present invention will be described. In the following description, parts common to the embodiments will be given the same reference numerals and the description thereof will be omitted. [Example]

[0043] During plug-in charging, even if the cell voltage Vcel is close to the BLOW threshold Vcelf, if the DC-DC converter 52 is not operated when the main relay 40 is switched on, the cell voltage Vcel is unlikely to drop below the BLOW threshold Vcelf.

[0044] In this embodiment, the charging control unit 74 performs the charge start control CNcs by not operating the DC-DC converter 52 when the main relay 40 is switched on. That is, the charging control unit 74 performs the charge start control CNcs by prohibiting the operation of the DC-DC converter 52 linked to the switching on of the main relay 40 by the electric motor control unit 72. Meanwhile, after the predetermined time TMf has elapsed, the charging control unit 74 ends the charge start control CNcs and releases the prohibition on the operation of the DC-DC converter 52. As a result, the electric motor control unit 72 operates the DC-DC converter 52 after the predetermined time TMf has elapsed.

[0045] If the auxiliary battery 60 can withstand the load caused by the vehicle auxiliary devices 62 and the like for the period until plug-in charging actually starts during the predetermined time TMf, the DC-DC converter 52 will then be activated.

[0046] 4 is a flowchart illustrating the main control operations of the electronic control unit 70, and is a flowchart illustrating the control operations for appropriately charging the main battery 20 by the AC charger 30 disposed in the electrical path via the main relay 40, and is executed repeatedly, for example. FIG. 4 is an embodiment different from the flowchart of FIG. 2.

[0047] 4, first, in S10B, which corresponds to the function of the charging control unit 74, it is determined whether the charging connector 104 is inserted into the charging inlet 34. If the determination in S10B is negative, the routine is terminated. If the determination in S10B is positive, the main relay 40 is switched on in S20B, which corresponds to the function of the charging control unit 74. Next, in S30B, which corresponds to the function of the charging control unit 74, operation of the DC-DC converter 52 linked to the switching on of the main relay 40 is prohibited, thereby executing the charging start control CNcs. Next, in S40B, which corresponds to the function of the charging control unit 74, it is determined whether a predetermined time TMf has elapsed. If the determination in S40B is negative, the routine returns to S30B. If the determination in S40B is positive, in S50B, which corresponds to the function of the charging control unit 74, the charging start control CNcs is terminated, and the prohibition on operation of the DC-DC converter 52 is lifted. Next, the DC-DC converter 52 is operated in S60B, which corresponds to the function of the electric motor control unit 72. Plug-in charging actually starts during the period until the determination in S40B above is affirmative.

[0048] As described above, according to this embodiment, similarly to the above-described first embodiment, during plug-in charging, the charge start control CNcs is performed so that the main relay 40 is maintained in an on state until the predetermined time TMf has elapsed after the main relay 40 is switched on in response to the connection of the external power supply 100. Therefore, the same effects as those of the above-described first embodiment can be obtained.

[0049] Furthermore, according to this embodiment, the charge start control CNcs is performed by prohibiting the operation of the DC-DC converter 52. As a result, the main relay 40 is appropriately maintained ON until the predetermined time TMf has elapsed.

[0050] Furthermore, according to this embodiment, after the predetermined time TMf has elapsed, the charge start control CNcs is terminated and the prohibition on the operation of the DC-DC converter 52 is lifted. This appropriately suppresses a decrease in the durability of the auxiliary battery 60.

[0051] Although the embodiments of the present invention have been described in detail above with reference to the drawings, the present invention can also be applied to other embodiments.

[0052] For example, in the above-described embodiment, if a determination to detect BLOW is not made, the main relay 40 is not switched off based on the BLOW threshold Vcelf, and the main relay 40 is maintained on. The charge control unit 74 may perform the charge start control CNcs by not determining whether the cell voltage Vcel is less than the BLOW threshold Vcelf or whether BLOW has been detected.

[0053] In the above-described embodiment, the predetermined time TMf may be set to a time equivalent to a predetermined preparation time for driving the AC charger 30.

[0054] In the above-described embodiments, the electric vehicle may be a so-called plug-in hybrid vehicle that includes an engine and an electric motor and can charge a high-voltage battery with electric power supplied from an external power source.

[0055] It should be noted that the above is merely one embodiment, and the present invention can be embodied in various forms with various modifications and improvements based on the knowledge of those skilled in the art. [Explanation of symbols]

[0056] 10: Electric vehicle 20: Main battery (high voltage battery) 22: Battery cell 30: AC charger (charger) 40: Main relay (relay) 50: Power control unit (power control device) 52: DC-DC converter (voltage converter) 60: Auxiliary battery (low voltage battery) 62: Vehicle auxiliary equipment 70: Electronic control device (control device) 100: External power supply MG: Electric motor

Claims

1. An electric vehicle comprising: an electric motor; a high-voltage battery for driving in which a plurality of battery cells are connected in series; a power control device that controls power exchanged between the high-voltage battery and the electric motor, the power control device having a voltage converter that steps down DC power from the high-voltage battery and supplies the power to a low-voltage battery and vehicle accessories; a relay that is switchable between an open state that interrupts an electrical path between the high-voltage battery and the power control device and a closed state that connects the electrical path; a charger that charges the high-voltage battery with power supplied from an external power source; and a control device that controls charging of the high-voltage battery, the charger is arranged in parallel with the power control device and in an electrical path that is connected and disconnected to the high-voltage battery by switching the relay, The control device The voltage converter is operated in conjunction with the switching of the relay to the closed state, When the voltage of the battery cell drops below a predetermined abnormally low voltage, the relay is switched to the open state. When the high-voltage battery is charged by the charger, the relay is switched to the closed state in response to the connection of the external power source, and then charging start control is performed so that the relay is maintained in the closed state until a predetermined time has elapsed as a period during which the voltage of the battery cell increases after the charger actually starts charging the high-voltage battery. An electric vehicle characterized by:

2. 2. The electric vehicle according to claim 1, wherein the control device performs the charge start control by prohibiting the relay from switching to the open state based on the predetermined abnormally low voltage.

3. 3. The electric vehicle according to claim 2, wherein the control device terminates the charge start control after the predetermined time has elapsed, and permits the relay to be switched to the open state based on the predetermined abnormally low voltage.

4. 2. The electric vehicle according to claim 1, wherein the control device performs the charge start control by prohibiting operation of the voltage converter.

5. 5. The electric vehicle according to claim 4, wherein the control device terminates the charge start control and activates the voltage converter after the predetermined time has elapsed.

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