Electric vehicle

Abstract

To provide an electric vehicle which has two batteries, and can efficiently charge the batteries even when the voltage of a second battery is lower than the voltage of a first battery.SOLUTION: An electric vehicle includes first / second batteries, a circuit selector and a controller. The circuit selector is a switch for switching the connection relationship between the two batteries, and selects one of a series state of connecting the negative electrode end of the first battery to the positive electrode end of the second battery, and a parallel state of connecting the negative electrode end of the first battery to the ground, and connecting the positive electrode end of the second battery to a neutral point. The controller controls the circuit selector so that the series state is selected when driving a motor. The controller controls the circuit selector so that the parallel state is selected when charging the batteries by an external power source, and turns upper SW elements of an inverter on / off so as to step down the voltage of the external power source and supply it to the second battery.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to an electric vehicle equipped with a battery and an electric motor, and more particularly to an electric vehicle that can charge its on-board battery using an external power source. [Background technology]

[0002] It is known that a circuit consisting of a stator coil of an electric motor and a switching element of an inverter can be used as a voltage converter. Patent Document 1 discloses a technology in which an external power supply is connected to the neutral point of the stator coil, and the stator coil and the switching element of the inverter are used as a boost converter to boost the voltage of the external power supply and charge a battery. Using this technology, a battery can be charged using an external power supply with a lower voltage than the battery itself. Hereinafter, for ease of explanation, charging a battery by transforming the voltage of an external power supply using a circuit combining an electric motor and an inverter will be referred to as "neutral point charging." Also, for ease of explanation, an "electric motor" will be simply referred to as a "motor."

[0003] Furthermore, Patent Document 2 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 batteries with an external power supply, the first battery and the second battery are connected in parallel. This technology also makes it possible to charge the batteries with an external power supply whose voltage is lower than the total voltage of the series-connected first battery and second battery. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-184947 [Patent Document 2] Japanese Patent Application Publication No. 2019-118221 Summary of the Invention [Problem to be solved by the invention]

[0005] If the voltage of the second battery is lower than the voltage of the first battery, the two batteries cannot be efficiently charged using either of the techniques disclosed in Patent Documents 1 and 2. This specification provides a technique that allows the two batteries to be efficiently charged using an external power source even when the voltage of the second battery is lower than the voltage of the first battery. [Means for solving the problem]

[0006] The electric vehicle disclosed in this specification includes first and second batteries, an inverter, a motor, a charging terminal, a circuit selector, and a controller.

[0007] The negative terminal of the second battery is connected to ground. The inverter has a DC positive terminal, a DC negative terminal, and multiple AC terminals. The DC positive terminal is connected to the positive terminal of the first battery. The DC negative terminal is connected to ground. An upper switching element and a lower switching element are connected in series 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 has multiple stator coils, one end of each stator coil is connected to a respective AC terminal, and the other end of each of the multiple stator coils is connected to a neutral point.

[0008] The charging terminal has a positive charging terminal and a negative charging terminal to which an external power source is connected, with the positive charging terminal connected to the DC positive terminal and the negative charging terminal connected to ground. The circuit selector is a switch that switches the connection state of the first battery and the second battery, and can select either a series state or a parallel state as follows: Series state: The negative terminal of the first battery is connected to the positive terminal of the second battery. Parallel state: The negative terminal of the first battery is connected to ground and the positive terminal of the second battery is connected to the neutral point.

[0009] The controller controls the circuit selector so that the first and second batteries are connected in series when the motor is driven by the first and second batteries, and the first and second batteries are connected in series between the DC positive and negative terminals of the inverter.

[0010] When an external power supply is connected to the charging terminal, the controller controls the circuit selector to establish a parallel state, and turns on and off the upper switching element of the inverter to step down the voltage of the external power supply and supply it to the second battery. The voltage of the external power supply is applied directly to the first battery.

[0011] According to the above configuration, the voltage of the external power supply is applied directly to the first battery, and the voltage of the external power supply is stepped down and applied to the second battery. Even if the voltage of the second battery is lower than the voltage of the first battery, the two batteries can be charged efficiently.

[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. 1 is a block diagram of a power system of an electric vehicle according to an embodiment (when charging a battery). 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 circuit selector 40, a charging terminal 50, 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 AC end 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. 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, and 23w) each including an upper SW element 21 and a lower SW element 22. The three series-connected bodies 23u, 23v, and 23w are connected in parallel between the DC positive terminal 20p and the 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. A midpoint 24 of each of the series-connected bodies 23u, 23v, and 23w is connected to each of the AC terminals 20a of the inverter 20. A diode is connected in antiparallel to each of the upper SW element 21 and the lower SW element 22. The diode allows current to flow from the ground G side toward the DC positive terminal 20p side.

[0018] 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 24 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 24 with a phase difference of 120 degrees.

[0019] The batteries (first battery 11 and second battery 12) of the electric vehicle 2 can be charged by an external power supply 90. Therefore, the electric vehicle 2 is provided with a charging terminal 50 for connecting the external power supply 90. The positive terminal (positive charging terminal 50p) and negative terminal (negative charging terminal 50n) of the charging terminal 50 can be connected to the positive terminal 90p and negative terminal 90n of the external power supply 90, respectively. Note that FIG. 1 shows a state in which the external power supply 90 is not connected to the charging terminal 50.

[0020] The charging positive terminal 50p is connected to the DC positive terminal 20p of the inverter 20, and the charging negative terminal 50n is connected to ground G. When an external power source is not connected to the charging terminal 50, the charging terminal 50 is in an open state. When the electric vehicle 2 is running, no external power source is connected, and the charging terminal 50 does not affect the flow of current during running. The negative terminal 12n of the second battery 12 and the DC negative terminal 20n of the inverter 20 are also connected to ground G. Ground G is a common ground for the entire power system used to drive the electric vehicle 2.

[0021] The circuit selector 40 is a switch that switches the connection relationship between the first battery 11 and the second battery 12. The circuit selector 40 includes a first switch 41, a second switch 42, and a third switch 43. The first switch 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 switch 41 is closed, the negative terminal 11n is connected to the positive terminal 12p. The second switch 42 is connected between the negative terminal 11n of the first battery 11 and ground G. When the second switch 42 is closed, the negative terminal 11n is connected to ground G. The third switch 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 switch 43 is closed, the positive terminal 12p is connected to the neutral point 32.

[0022] The circuit selector 40 is controlled by the controller 60. The controller 60 controls the circuit selector 40 to set the connection state of the first battery 11 and the second battery 12 in one of the following two ways. (1) Series state: The first switch 41 is closed, and the second switch 42 and the third switch 43 are opened. 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. At this time, the neutral point 32 of the motor 30 is held in an open state. (2) Parallel state: The first switch 41 is opened, and the second switch 42 and the third switch 43 are closed. At this time, the negative terminal 11n of the first battery 11 is connected to ground, and the positive terminal 12p of the second battery 12 is connected to the neutral point 32.

[0023] The positive terminal 11p of the first battery 11 is always connected to the DC positive terminal 20p of the inverter 20, and the negative terminal 12n of the second battery 12 is always connected to the ground G.

[0024] When the motor 30 is driven by the first battery 11 and the second battery 12, the controller 60 controls the circuit selector so that the first battery 11 and the second battery 12 are connected in series. Then, the controller 60 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 series.

[0025] As described above, the electric vehicle 2 can charge the first battery 11 and the second battery 12 using the external power supply 90. When charging the batteries, the external power supply 90 is connected to the charging terminal 50. When charging the batteries 11, 12 using the external power supply 90, the controller 60 controls the circuit selector 40 so that the first battery 11 and the second battery 12 are connected in parallel. Figure 2 shows a circuit diagram of the parallel state and the current flow at that time. The thick arrow indicates the current flow during charging. Part of the output current from the external power supply 90 flows to the positive terminal 11p of the first battery 11, and the remainder flows to the DC positive terminal 20p of the inverter 20.

[0026] It is known that the combination of the switching element of the inverter 20 and the stator coil 31 of the motor 30 can be used as a voltage converter. When the lower switching element 22 of the inverter 20 is held off and the upper switching element 21 is appropriately turned on and off, the inverter 20 and the stator coil 31 function as a step-down converter, and the voltage of the DC positive terminal 20p is stepped down and appears at the neutral point 32. As shown in Fig. 2, in the parallel state, the positive terminal 90p of the external power supply 90 is connected to the DC positive terminal 20p, and the positive terminal 12p of the second battery 12 is connected to the neutral point 32 via the third switch 43 of the circuit selector 40.

[0027] When the controller 60 appropriately turns on and off the upper switching element 21, the voltage of the power from the external power supply 90 is stepped down and supplied to the second battery 12. The second battery 12 is charged with the stepped-down power from the external power supply 90.

[0028] An external power supply 90 is directly connected to the first battery 11. The first battery 11 is charged by the output voltage of the external power supply 90.

[0029] Charging in the electric vehicle 2 of this embodiment is advantageous when the output voltage of the second battery 12 is lower than the output voltage of the first battery 11. That is, during charging, the electric vehicle 2 can apply the output voltage of the external power supply 90 to the first battery 11, and can apply a lower voltage obtained by stepping down the output voltage of the external power supply 90 to the second battery 12. By appropriately adjusting the duty ratio of the PWM signal provided to the upper switching element 21, the voltage at the neutral point 32, i.e., the voltage applied to the second battery 12, can be adjusted. Even if the output voltage of the second battery 12 is lower than the output voltage of the first battery 11, the electric vehicle 2 can charge the second battery 12 at a voltage appropriate for charging the second battery 12. By adjusting the voltage applied to the second battery 12, the ratio between the charging current supplied to the first battery 11 and the charging current supplied to the second battery can be appropriately adjusted. That is, the electric vehicle 2 can efficiently charge two batteries (the first battery 11 and the second battery 12).

[0030] 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. When charging the second battery 12 using the inverter 20 and the motor 30, all three upper switches 21 may be used, or only one or two upper switches 21 may be used.

[0031] In the circuits of Figures 1 and 2, current sensors and voltage sensors appropriately placed at various locations are omitted from the illustration.

[0032] When the voltages of the first battery 11 and the second battery 12 are equal, the upper switching element 21 is kept on. Then, the voltage of the external power supply 90 is applied as is to the second battery 12. The first battery 11 and the second battery 12 are charged at the same voltage.

[0033] 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]

[0034] 2: Electric vehicle 11: First battery 12: Second battery 20: Inverter 21: Upper switch element 22: Lower switch element 23: Series connection body 24: Neutral point 30: Motor 31: Stator coil 32: Neutral point 40: Circuit selector 41: First switch 42: Second switch 43: Third switch 50: Charging terminal 60: Controller 71: Differential gear 72: Wheels 90: External power supply G: Ground

Claims

[Claim 1] A first battery; a second battery having a negative terminal 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 terminal 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 charging terminal including a positive charging terminal and a negative charging terminal to which an external power supply is connected, the positive charging terminal being connected to the DC positive terminal and the negative charging terminal being connected to the ground; a circuit selector for switching a connection relationship between the first battery and the second battery, the circuit selector selecting either a series state in which the negative terminal of the first battery is connected to the positive terminal of the second battery, or a parallel state in which the negative terminal of the first battery is connected to the ground and the positive terminal of the second battery is connected to the neutral point; a controller that controls the circuit selector to establish the series state when the motor is driven by the first battery and the second battery, and controls the circuit selector to establish the parallel state when the external power supply is connected to the charging terminal, and also turns on and off an upper switching element of the inverter to step down the voltage of the external power supply and supply it to the second battery; An electric vehicle equipped with

Images