Electric vehicle

Abstract

To prevent currents from flowing into a relay when connecting two batteries in parallel to supply electricity to the outside and then connecting the two batteries in series.SOLUTION: An electric vehicle is provided with a first relay through which a negative electrode end of a first battery to a positive electrode end of a second battery, a second relay through which the negative electrode end of the first battery is connected to the ground, a third relay through which the positive electrode end of the second battery is connected to a neutral point of a motor, and a fourth relay through which a positive electrode end of the first battery is connected to an electricity-supply positive electrode end. When the first relay is closed and the other relays are opened, two batteries are connected in series. When the first relay is opened and the other relays are closed, the two batteries are connected in parallel. The second battery is connected to an electricity supply terminal through a stator coil of the motor and an inverter. SW elements of the stator coil and the inverter function as booster circuits. When performing external electricity supply in a state where the batteries are connected in parallel, a controller drives the SW elements so that output voltages from the second battery become lower than output voltages from the first battery.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to an electric vehicle equipped with a battery and an electric motor, and more particularly to an electric vehicle capable of supplying power from an on-board battery to an external electric device. [Background technology]

[0002] Patent Document 1 discloses an electric vehicle equipped with a first battery and a second battery connected in series, an electric motor, and an inverter. The output power of the first battery and the second battery connected in series is converted to AC by the inverter and supplied to the electric motor. In the following, for ease of explanation, the "electric motor" will be referred to simply as the "motor."

[0003] It is known that a circuit consisting of a motor stator coil and an inverter switching element can be used as a voltage converter. The electric vehicle disclosed in Patent Document 1 is equipped with a relay that connects the connection point between the first and second batteries to the neutral point of the stator coil. By closing the relay and appropriately turning on and off the inverter switching element, power can be transferred between the first and second batteries. By appropriately turning on and off the inverter switching element, the output voltage of the second battery is boosted and applied to the first battery. In other words, power from the second battery is transferred to the first battery.

[0004] Patent Document 2 also discloses an electric vehicle having a first battery and a second battery. When driving the motor, the first battery and the second battery are connected in series. When charging the battery with an external power source, the first battery and the second battery are connected in parallel.

[0005] In the electric vehicle of Patent Document 2, the first battery and the second battery can be connected in parallel, and the electric power thereof can be supplied to an external electric device. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-120566 [Patent Document 2] Japanese Patent Application Publication No. 2019-118221 Summary of the Invention [Problem to be solved by the invention]

[0007] When a motor outputs a large torque, the first battery and the second battery are connected in series. As described above, when supplying battery power to an external electrical device, the first battery and the second battery may be connected in parallel. A relay is used to change the connection relationship between the first battery and the second battery. If a current flows through the relay when switching the relay from on to off, the relay may be damaged. This specification relates to an electric vehicle having two batteries, and prevents current from flowing through the relay that opens when the two batteries are connected in parallel to supply power to an external device and then switched to a series connection. [Means for solving the problem]

[0008] The electric vehicle disclosed in this specification includes first and second batteries, an inverter, a motor, power supply terminals, first, second, third, and fourth relays, and a controller. The first and second batteries have the same output voltage when fully charged. The positive terminal of the first battery is connected to the DC positive terminal of the inverter. The negative terminal of the second battery is connected to ground. The inverter includes a DC positive terminal, a DC negative terminal, and multiple AC terminals. The DC negative terminal is connected to ground. A series connection of an upper switching element and a lower switching element is connected in parallel between the DC positive terminal and the DC negative terminal. The inverter outputs AC from the AC terminal by alternately turning on and off the upper switching element and the lower switching element. The motor includes multiple stator coils, one end of each stator coil is connected to the respective AC terminal, and the other end of each stator coil is connected to a neutral point.

[0009] The power supply terminal has a positive power supply terminal and a negative power supply terminal to which an external electrical device is connected, and the negative power supply terminal is connected to ground. The first relay connects the negative terminal of the first battery to the positive terminal of the second battery. The second relay connects the negative terminal of the first battery to ground. The third relay connects the positive terminal of the second battery to the neutral point. The fourth relay connects the positive terminal of the first battery to the positive power supply terminal. When the motor is driven by the first and second batteries, the controller closes the first relay and opens the second, third, and fourth relays. The first and second batteries are connected in series.

[0010] When an electric device is connected to the power supply terminal, the controller opens the first relay and closes the second, third, and fourth relays, and also turns on and off the lower switching element of the inverter so that the output voltage of the second battery is lower than the output voltage of the first battery, thereby boosting the voltage of the second battery and supplying it to the positive power supply terminal.

[0011] When power supply to an electrical device is terminated, if the voltage of the second battery is higher than the voltage of the first battery, current flows from the second battery to the first battery through the third relay. Opening the third relay at this time would damage the third relay. The technology disclosed in this specification utilizes a circuit consisting of a motor stator coil and an inverter switching element as a boost circuit. During external power supply, the first and second batteries are connected in parallel, and the battery output is supplied to an external electrical device through the power supply terminal. Since the output voltage of the second battery is increased by the boost circuit, more power is supplied to the external device from the second battery than from the first battery. As a result, when power supply is terminated, the output voltage of the second battery is lower than the output voltage of the first battery. If the inverter's upper switching element is open, no current flows from the first battery to the second battery. Therefore, when the third relay is opened to switch the two batteries from a parallel connection to a series connection, no current flows through the third relay, and the third relay is not damaged.

[0012] Details and further improvements of the technology disclosed in this specification are described in the following "Description of Embodiments of the Invention." [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a block diagram of an electric power system of an electric vehicle according to an embodiment (when driving a motor). [Figure 2] FIG. 2 is a block diagram of an electric power system of the electric vehicle according to the embodiment (when power is supplied to an external electric device). DETAILED DESCRIPTION OF THE INVENTION

[0014] An electric vehicle 2 according to the embodiment will be described with reference to the drawings. Fig. 1 shows a block diagram of the power system of the electric vehicle 2. The electric vehicle 2 according to the embodiment includes a driving motor 30, two batteries (a first battery 11 and a second battery 12), an inverter 20, a power supply terminal 50, four relays (a first relay 41, a second relay 42, a third relay 43, and a fourth relay 44), and a controller 60.

[0015] The electric vehicle 2 is driven by a motor 30. The output shaft of the motor 30 is connected to wheels 72 via a differential gear 71. An inverter 20 converts the DC power of the batteries 11, 12 into AC power suitable for driving the motor 30 and supplies it to the motor 30. A controller 60 determines a target output of the motor 30 based on the vehicle speed and accelerator opening, and controls the inverter 20 so that the output of the motor 30 follows the target output.

[0016] The motor 30 is a three-phase AC motor and includes three stator coils 31. One end of each of the three stator coils 31 (the left end of the coil in FIG. 1) is connected to a respective one of the AC terminals 20a of the inverter 20, and the other ends (the right end of the coil in FIG. 1) are connected to a neutral point 32.

[0017] The inverter 20 includes six switching elements and six diodes. Hereinafter, for ease of explanation, "switching elements" will be abbreviated as "SW elements." The inverter 20 includes three series-connected bodies (series-connected bodies 23u, 23v, 23w) each including an upper SW element 21 and a lower SW element 22. The three series-connected bodies 23u, 23v, 23w are connected in parallel between a DC positive terminal 20p and a DC negative terminal 20n of the inverter 20. The upper SW element 21 is connected to the DC positive terminal 20p, and the lower SW element 22 is connected to the DC negative terminal 20n. The midpoints 26 of the series-connected bodies 23u, 23v, 23w are connected to the respective AC terminals 20a of the inverter 20.

[0018] A diode 24 is connected in anti-parallel to each upper switching element 21, and a diode 25 is connected in anti-parallel to each lower switching element 22. The diode 24 associated with the upper switching element 21 has an anode connected to the midpoint 26 and a cathode connected to the DC positive terminal 20p. The diode 25 associated with the lower switching element 22 has an anode connected to the DC negative terminal 20n and a cathode connected to the midpoint 26. The diodes 24 and 25 allow current to flow from the DC negative terminal 20n side toward the DC positive terminal 20p side, but block current in the reverse direction.

[0019] The upper switching element 21 and the lower switching element 22 are controlled by a controller 60. When the controller 60 alternately turns on and off the upper switching element 21 and the lower switching element 22, AC is output from the midpoints 26 of the series-connected bodies 23u, 23v, and 23w. The controller 60 drives the six switching elements so that three-phase AC is output from the three midpoints 26 with a phase difference of 120 degrees.

[0020] The batteries (first battery 11 and second battery 12) of the electric vehicle 2 can supply power to an external electric device 90. Therefore, the electric vehicle 2 is provided with a power supply terminal 50 for connecting the external electric device 90. A positive terminal (power supply positive terminal 50p) and a negative terminal (power supply negative terminal 50n) of the power supply terminal 50 can be connected to a positive terminal 90p and a negative terminal 90n of the external electric device 90, respectively. Note that FIG. 1 shows a state in which the electric device 90 is not connected to the power supply terminal 50. The power supply positive terminal 50p is connected to a positive terminal 11p of the first battery 11 via a fourth relay 44 (described later), and the power supply negative terminal 50n is connected to ground G.

[0021] The neutral point 32 of the motor 30 is connected to the positive terminal 12p of the second battery 12 via a third relay 43, which will be described later. When the third relay 43 is open, only the stator coil 31 is connected to the neutral point 32. When the motor 30 is driven, the third relay 43 is open.

[0022] The negative terminal 12n of the second battery 12 and the negative DC terminal 20n of the inverter 20 are also connected to the ground G. The ground G is a common ground for the entire power system for driving the electric vehicle 2.

[0023] The four relays 41, 42, 43, and 44 will now be described. The four relays 41, 42, 43, and 44 are switches that switch the connection relationship between the first battery 11 and the second battery 12. The first relay 41 is connected between the negative terminal 11n of the first battery 11 and the positive terminal 12p of the second battery 12. When the first relay 41 is closed, the negative terminal 11n is connected to the positive terminal 12p, and the first battery 11 and the second battery 12 are connected in series.

[0024] The second relay 42 is connected between the negative terminal 11n of the first battery 11 and ground G. When the second relay 42 is closed, the negative terminal 11n is connected to ground G. The third relay 43 is connected between the positive terminal 12p of the second battery 12 and the neutral point 32 of the motor 30. When the third relay 43 is closed, the positive terminal 12p of the second battery 12 is connected to the neutral point 32. The fourth relay 44 is connected between the positive terminal 11p of the first battery 11 and the DC positive terminal 20p of the inverter 20, and the positive terminal (feed positive terminal 50p) of the power supply terminal 50. When the fourth relay 44 is closed, the positive terminal 11p and DC positive terminal 20p are connected to the feed positive terminal 50p.

[0025] The four relays 41, 42, 43, and 44 are controlled by a controller 60. The controller 60 controls these relays to set the connection state of the first battery 11 and the second battery 12 to one of the following two states. (1) Series state: The first relay 41 is closed, and the second relay 42, the third relay 43, and the fourth relay 44 are open. At this time, the first battery 11 and the second battery 12 are connected in series, and the series connection of the first battery 11 and the second battery 12 is connected between the DC positive terminal 20p and the DC negative terminal 20n of the inverter 20. Also, at this time, only the stator coil 31 is connected to the neutral point 32 of the motor 30. (2) Parallel state: The first relay 41 is open, and the second relay 42, the third relay 43, and the fourth relay 44 are closed. At this time, the negative terminal 11n of the first battery 11 and the negative terminal 12n of the second battery 12 are connected to ground G, and the positive terminal 11p of the first battery 11 and the DC positive terminal 20p of the inverter 20 are connected to the power supply positive terminal 50p. In addition, the positive terminal 12p of the second battery 12 is connected to the neutral point 32. The positive terminal 11p of the first battery 11 is directly connected to the power supply positive terminal 50p, and the positive terminal 12p of the second battery 12 is connected to the power supply positive terminal 50p via the neutral point 32, the stator coil 31, the upper switching element 21, the diode 24, and the DC positive terminal 20p. The first battery 11 and the second battery 12 are connected in parallel.

[0026] When the motor 30 is driven by the first battery 11 and the second battery 12, the controller 60 controls the four relays 41, 42, 43, and 44 so that the first battery 11 and the second battery 12 are connected in series. The controller 60 then controls the inverter 20 so that three-phase AC flows through the AC terminal 20a. The thick arrows in Fig. 1 indicate the current flow when the motor 30 is driven in the series connection.

[0027] As described above, the electric vehicle 2 can supply power from the first battery 11 and the second battery 12 to an external electric device 90. The electric device 90 is connected to the power supply terminal 50. When supplying power to the electric device 90, the controller 60 controls the four relays 41, 42, 43, and 44 so that the first battery 11 and the second battery 12 are connected in parallel. FIG. 2 shows a circuit diagram of the parallel connection and the current flow at that time. The thick arrow indicates the current flow during power supply. The current from the first battery 11 flows directly to the power supply positive terminal 50p, and the current from the second battery 12 flows to the power supply positive terminal 50p via the stator coil 31 and the diode 24.

[0028] The first battery 11 and the second battery 12 have the same output voltage when fully charged. Because the first battery 11 and the second battery 12 are connected in parallel, power is supplied from each of the first battery 11 and the second battery 12 to the external electric device 90. However, the positive terminal 12p of the second battery 12 is connected to the power supply positive terminal 50p via the stator coil 31 and the diode 24. Therefore, the resistance between the positive terminal 12p and the power supply positive terminal 50p is greater than the resistance between the positive terminal 11p of the first battery 11 and the power supply positive terminal 50p. Therefore, while the power of the second battery 12 is being supplied to the electric device 90 as is, the power supplied from the first battery 11 exceeds the power supplied from the second battery 12. Therefore, the voltage of the first battery 11 is lower than the voltage of the second battery 12.

[0029] When power supply is terminated (when the external electric device 90 is disconnected from the power supply terminal 50), if the voltage of the first battery 11 is lower than the voltage of the second battery 12, current flows from the second battery 12 to the first battery 11 through the third relay 43, the stator coil 31, and the diode 24. If the third relay 43 is opened while current is flowing through it, the third relay 43 may be damaged. In other words, if the first battery 11 and the second battery 12 are switched from a parallel state to a series state immediately after power supply to the outside is terminated, the third relay 43 may be damaged. Damage to the third relay 43 accumulates each time the parallel state is switched to a series state immediately after power supply. In other words, the third relay 43 deteriorates each time the parallel state is switched to a series state immediately after power supply.

[0030] In the electric vehicle 2 of the embodiment, deterioration of the third relay 43 can be suppressed. When supplying power to the outside in the parallel state, the controller 60 utilizes the circuit of the stator coil 31 and the lower switching element 22 as a boost converter, and maintains a state in which the voltage of the second battery 12 is lower than the voltage of the first battery 11. When the controller 60 turns on the lower switching element 22 in the parallel state described above, current flows from the stator coil 31 to ground G, and magnetic energy is stored in the stator coil 31 at this time. When the controller 60 switches the lower switching element 22 from on to off, the magnetic energy of the stator coil 31 pushes out current through the diode 24. In other words, when the controller 60 appropriately turns on and off the lower switching element 22, the voltage of the second battery 12 is boosted and appears at the DC positive terminal 20p.

[0031] If the voltage appearing at the DC positive terminal 20p is higher than the voltage of the first battery 11, the second battery 12 will supply more power to the outside than the first battery 11. As a result, the remaining power of the second battery 12 will decrease faster than the first battery 11. There is a positive correlation between the remaining power and the output voltage of a battery. In other words, the lower the remaining power of a battery, the lower the output voltage of the battery. If the second battery 12 supplies more power to the outside than the first battery 11, the voltage of the second battery 12 will be lower than the voltage of the first battery 11.

[0032] 1 and 2, electric vehicle 2 is equipped with voltage sensors 13 and 14, voltage sensor 13 measures the voltage of first battery 11, and voltage sensor 14 measures the voltage of second battery 12. The measured values ​​of voltage sensors 13 and 14 are sent to controller 60. When supplying power to the outside, controller 60 controls lower SW element 22 (i.e., boost converter) so that the voltage of second battery 12 is lower than the voltage of first battery 11.

[0033] If the voltage of the second battery 12 is lower than the voltage of the first battery 11 when the external power supply is terminated, no current flows through the third relay 43. When the two batteries 11, 12 are switched from a parallel state to a series state, no current flows through the third relay 43, and the third relay 43 is not damaged even when it is opened. Note that in the parallel state, a diode 24 is connected between the positive terminal 11p of the first battery 11 and the positive terminal 12p of the second battery 12, and the diode 24 prevents current from flowing from the first battery 11 to the second battery 12.

[0034] As described above, in the electric vehicle 2, even if the parallel connection is switched to the series connection immediately after two batteries are connected in parallel to supply power to an external electric device, the third relay will not be damaged.

[0035] Here are some points to note regarding the technology described in the embodiments. In this specification, the term "electric vehicle" may include a hybrid vehicle equipped with both a motor and an engine. The inverter 20 includes three low-side switching elements 22, but it is sufficient to drive at least one low-side switching element to boost the output voltage of the second battery 12.

[0036] When the first relay 41 and the fourth relay 44 are closed and the second relay 42 and the third relay 43 are opened, the electric vehicle 2 can supply power to the outside by connecting the two batteries 11 and 12 in series.

[0037] The electric vehicle 2 may also include a fifth relay that connects the positive terminal 12p of the second battery 12 to the DC positive terminal 20p of the inverter 20. When the second relay 42 and the fifth relay are closed and the other relays are opened, the two batteries 11 and 12 are connected in parallel between the DC positive terminal 20p and the DC negative terminal 20n of the inverter 20. In this case, the electric vehicle 2 can drive the motor 30 using the power of the two batteries 11 and 12 connected in parallel.

[0038] The electric vehicle 2 can also charge the batteries 11 and 12 by connecting an external DC power source to the power supply terminal 50.

[0039] Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives alone is technically useful. [Explanation of symbols]

[0040] 2: Electric vehicle 11: First battery 12: Second battery 13, 14: Voltage sensor 20: Inverter 21: Upper switch element 22: Lower switch element 23: Series connection body 24, 25: Diode 26: Neutral point 30: Motor 31: Stator coil 32: Neutral point 40: Circuit selector 41: First relay 42: Second relay 43: Third relay 44: Fourth relay 50: Power supply terminal 60: Controller 71: Differential gear 72: Wheel 90: Electric device G: Ground

Claims

[Claim 1] A first battery; a second battery whose output voltage when fully charged is the same as that of the first battery and whose negative terminal is connected to ground; an inverter including a DC positive terminal, a DC negative terminal, and a plurality of AC terminals, the DC positive terminal being connected to the positive electrode of the first battery and the DC negative terminal being connected to the ground, and outputting AC from the AC terminals by alternately turning on and off an upper switching element and a lower switching element connected in series between the DC positive terminal and the DC negative terminal; a motor including a plurality of stator coils, one end of each of the stator coils being connected to a respective one of the AC terminals and the other end of each of the stator coils being connected to a neutral point; a power supply terminal including a positive power supply terminal and a negative power supply terminal to which an external electric device is connected, the negative power supply terminal being connected to the ground; a first relay connecting a negative terminal of the first battery and a positive terminal of the second battery; a second relay connecting the negative terminal of the first battery to the ground; a third relay connecting the positive terminal of the second battery and the neutral point; a fourth relay connecting the positive terminal of the first battery and the positive terminal of the power supply; a controller that closes the first relay and opens the second, third, and fourth relays when the motor is driven by the first battery and the second battery, and that opens the first relay and closes the second, third, and fourth relays when the electric device is connected to the power supply terminal, and that turns on and off a lower switching element of the inverter so that the output voltage of the second battery is lower than the output voltage of the first battery, thereby boosting the voltage of the second battery and supplying it to the power supply positive terminal; An electric vehicle equipped with

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