Electric automobile

Abstract

The present specification provides an electric vehicle. The present specification provides a technique for suppressing current fluctuations when transitioning from dead-time ON / OFF control of an SW element including an inverter to fixed control in an electric vehicle in which two batteries are connected in parallel to a power receiving / feeding terminal. The controller holds the upper SW element on and the lower SW element off for each SW cycle, switches the upper SW element to off after a predetermined on time has elapsed, switches the lower SW element to on after a predetermined dead time has elapsed, and switches the SW element to off after a time of [switching cycle-dead time] has elapsed. After the difference between the currents of the two batteries is equal to or less than an allowable current difference, the controller extends the ON time to [switching period-dead time * 2], then maintains the relationship [ON time = switching period-dead time * 2] and extends the SW period to an upper limit SW period, and thereafter fixes the upper SW element to be ON and fixes the lower SW element to be OFF.

Description

Technical Field

[0001] The technology disclosed in this specification relates to electric vehicles. In particular, it relates to an electric vehicle equipped with a power receiving terminal, capable of charging the battery with an external power source, and capable of supplying power from the battery to an external source via the power receiving terminal. Background Technology

[0002] Electric vehicles include a battery, an inverter, and an electric motor. The inverter has two switching elements connected in series, with the midpoint of the two switching elements connected to the stator coil of the electric motor. It is known that a circuit consisting of the stator coil of the electric motor and the switching elements of the inverter can be used as a voltage converter. Patent Document 1 discloses a technique in which an external power supply is connected to the neutral point of the stator coil, and the stator coil and the switching elements of the inverter are used as a boost circuit to boost the voltage of the external power supply to charge the battery. Hereinafter, for the sake of simplicity, "electric motor" will be simply referred to as "motor".

[0003] Furthermore, Patent Document 2 discloses an electric vehicle having a first battery and a second battery. In the case of a drive motor, the first battery and the second battery are connected in series. In the case of charging the batteries using an external power source, the first battery and the second battery are connected in parallel.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2005-184947

[0007] Patent Document 2: Japanese Patent Application Publication No. 2019-118221 Summary of the Invention

[0008] If an electric vehicle is connected to a power-consuming device instead of an external power source, it can also supply power from the battery to the device. When two batteries are connected in parallel, the current flowing into and out of each battery is preferably equal when charging the battery and when supplying power to the outside. This equalization of the current flowing into and out of the two batteries can be achieved by using the inverter's switching elements and the motor's stator coils as voltage converters.

[0009] Currently, a dual-inverter structure is envisioned, with a first inverter connected to one end of the stator coil and a second inverter connected to the other end. A first battery and a power supply terminal are connected to the DC terminal (first DC terminal) of the first inverter, and a second battery is connected to the DC terminal (second DC terminal) of the second inverter. Power from an external power source is distributed between the first battery and the first inverter. Power flowing through the first inverter flows through the first inverter, the stator coil, and the second inverter to the second inverter. Power flows in the reverse direction when a power-consuming device is connected to the power supply terminal.

[0010] As described above, the inverter has two switching elements connected in series, with a stator coil connected at the midpoint of the series connection. It is known that this circuit functions as a bidirectional voltage converter when one switching element is switched on and off with a predetermined duty cycle, and the other switching element is switched on and off in the opposite phase. In a dual-inverter structure, if a first inverter and stator coil are used, the voltage can be stepped down from the first DC terminal (power supply terminal) to the second DC terminal (second battery), and then stepped up in the reverse direction. Conversely, if a second inverter and stator coil are used, the voltage can be stepped down from the second DC terminal (second battery) to the first DC terminal (power supply terminal), and then stepped up in the reverse direction. In a dual-inverter structure, it is possible to supply voltage from the power supply terminal to the second battery by stepping down or stepping up the voltage, and to supply voltage from the second battery to the power supply terminal by stepping down or stepping up the voltage. The first battery is directly connected to the power supply terminal. Therefore, the above-described structure using dual inverters can adjust the voltage difference between the first DC terminal and the second DC terminal in either the case where the power supply terminal is connected to a power source (i.e., current flows from the power supply terminal to the battery) or the case where the power supply terminal is connected to a power-consuming device (i.e., current flows from the battery to the power supply terminal), so that the current flowing through the first battery and the second battery is equal.

[0011] The predetermined PWM signal and its inverse PWM signal are called complementary PWM signals. When driving two switching elements connected in series with complementary PWM signals, a dead time is set to prevent short circuits. Dead time refers to the period during which the two switching elements are turned off during the switching between on and off states. In the above dual-inverter structure, two batteries are connected in parallel to the power supply terminal, and a dual-inverter circuit is connected between one battery and the power supply terminal. The switching elements of the first or second inverter are driven so that the current flowing in and out of the two batteries is equal. If the current flowing in and out of the two batteries is equal, the control transitions from PWM control to fixed control, which keeps the upper switching element on and the lower switching element off. At this time, when the dead time included in the PWM control disappears instantaneously, there is a possibility of large current fluctuations. This specification provides a technique for suppressing current fluctuations when transitioning from PWM control including dead time to fixed control in an electric vehicle equipped with two batteries and dual inverters.

[0012] The electric vehicle disclosed in this specification includes a first / second battery, a motor, a first / second inverter, a first / second current sensor, a power supply terminal, a circuit selector, and a controller. The motor includes stator coils. The positive and negative terminals of the first battery are referred to as the first positive terminal and the first negative terminal, respectively, and the positive and negative terminals of the second battery are referred to as the second positive terminal and the second negative terminal, respectively. The first current sensor measures the current flowing in and out of the first battery, and the second current sensor measures the current flowing in and out of the second battery.

[0013] The power supply terminal has a positive and a negative terminal for connecting to an external device that consumes or supplies power. The external device supplying power is, typically, a power source. The positive terminal is connected to the first positive terminal, and the negative terminal is connected to ground.

[0014] The first inverter has a first DC terminal, a first upper switching element, and a first lower switching element. The first DC terminal is connected to the first positive terminal. The first upper switching element and the first lower switching element are connected in series between the first DC terminal and ground. The midpoint of the series connection of the first upper switching element and the first lower switching element is connected to one end of the stator coil.

[0015] The second inverter has a second DC terminal, a second upper switching element, and a second lower switching element. The second upper switching element and the second lower switching element are connected in series between the second DC terminal and ground. The midpoint of the series connection of the second upper switching element and the second lower switching element is connected to the other end of the stator coil.

[0016] The circuit selector can select either series or parallel mode. In series mode, the circuit selector connects the first negative terminal to the second positive terminal and the first DC terminal to the second DC terminal. In parallel mode, the circuit selector connects the first negative terminal to ground and the second positive terminal to the second DC terminal, disconnecting the first DC terminal from the second DC terminal.

[0017] When driving the motor with high torque, the controller sets the circuit selector to series mode. When an external device is connected to the power supply terminal, the controller sets the circuit selector to parallel mode. When an external device is connected to the power supply terminal, the controller performs the following processing.

[0018] The controller sets the average of the first measured current measured by the first current sensor and the second measured current measured by the second current sensor as a target value relative to the current flowing into and out of the second battery. The controller controls the switching elements of the two inverters in a manner that makes the second measured current match the target value. If the second measured current matches the target value, equal current flows through the first and second batteries.

[0019] (1) When the current flows from the first DC terminal to the second DC terminal and the second measured current is higher than the target value, and when the current flows from the second DC terminal to the first DC terminal and the second measured current is lower than the target value, the controller executes the following processes (1-1) to (1-3). In addition, the direction of the current is determined based on the measurement value of the current sensor.

[0020] (1-1) The controller fixes the second upper switching element to the ON position and the second lower switching element to the OFF position. Thus, the stator coil and the second DC terminal are directly connected.

[0021] (1-2) For each switching cycle, the controller repeatedly performs the first on / off control. In this first on / off control, the first upper switch element is kept on and the first lower switch element is kept off. After a predetermined on time, the first lower switch element is kept off as is, while the first upper switch element is switched off. After a predetermined dead time, the first upper switch element is kept off and the first lower switch element is switched on. After a time of [switching cycle - dead time], the first upper switch element is kept off and the first lower switch element is switched off. Through this first on / off control, regardless of the direction of current flow, the voltage at the second DC terminal is lower than the voltage at the first DC terminal. When current flows from the first DC terminal to the second DC terminal, the current flowing into the second positive terminal decreases, and the difference between the second measured current and the target value decreases. When current flows from the second DC terminal to the first DC terminal, the current flowing out of the second positive terminal increases, and the difference between the second measured current and the target value still decreases.

[0022] (1-3) After the difference between the second measured current and the target value becomes below a predetermined allowable current difference, the controller extends the turn-on time to [switching cycle - dead time × 2]. Then, maintaining the relationship [turn-on time = switching cycle - dead time × 2], the switching cycle is extended to the upper limit of the switching cycle. Afterward, it transitions to a first fixed control, fixing the first upper switching element to turn on and the first lower switching element to turn off. By extending the switching cycle, the proportion of dead time in the switching cycle is reduced. Current fluctuations caused by the disappearance of dead time when transitioning from the first turn-on / off control to the first fixed control are suppressed.

[0023] (2) When the current flows from the first DC terminal to the second DC terminal and the second measured current is lower than the target value, and when the current flows from the second DC terminal to the first DC terminal and the second measured current is higher than the target value, the controller executes the following processes (2-1) to (2-3).

[0024] (2-1) The controller fixes the first upper switching element to be on and the first lower switching element to be off. Thus, the stator coil and the first DC terminal are directly connected.

[0025] (2-2) For each switching cycle, the controller repeatedly performs a second on / off control. In this second on / off control, the second upper switch element is kept on and the second lower switch element is kept off. After a predetermined on time, the second lower switch element is kept off as is, while the second upper switch element is switched off. After a predetermined dead time, the second upper switch element is kept off and the second lower switch element is switched on. After a time of [switching cycle - dead time], the second upper switch element is kept off and the second lower switch element is switched off. Through this second on / off control, regardless of the direction of current flow, the voltage at the second DC terminal is higher than the voltage at the first DC terminal. When current flows from the first DC terminal to the second DC terminal, the current flowing into the second positive terminal increases, and the difference between the second measured current and the target value decreases. When current flows from the second DC terminal to the first DC terminal, the current flowing out of the second positive terminal decreases, and the difference between the second measured current and the target value still decreases.

[0026] (2-3) After the difference between the second measured current and the target value becomes below a predetermined allowable current difference, the controller extends the turn-on time to [switching cycle - dead time × 2]. Then, maintaining the relationship [turn-on time = switching cycle - dead time × 2], the switching cycle is extended to the upper limit of the switching cycle. Afterward, it transitions to a second fixed control, fixing the second upper switching element to turn on and the second lower switching element to turn off. By extending the switching cycle, the proportion of dead time in the switching cycle is reduced. Current fluctuations caused by the disappearance of dead time when transitioning from the second turn-on / off control to the second fixed control are suppressed.

[0027] By maintaining the relationship [on-time = switching cycle - dead time × 2] and extending the switching cycle, the ratio of dead time to on-time (or switching cycle) is reduced. The impact of dead time is relatively smaller, and the current fluctuation caused by the disappearance of dead time when switching from control with dead time (i.e., on-off control) to control without dead time (i.e., fixed control) is suppressed. Detailed descriptions and further improvements to the technology disclosed in this specification are provided in the following "Specific Embodiments". Attached Figure Description

[0028] Figure 1 This is a circuit diagram of an electric vehicle according to an embodiment. Figure 1 This shows the flow of current when driving a motor.

[0029] Figure 2 This is a circuit diagram of an electric vehicle according to an embodiment. Figure 2 This shows the flow of current when charging two batteries using an external device.

[0030] Figure 3 This is a diagram illustrating the effect of extending the switching cycle. Figure 3 (A) shows the relationship between the lengths of the on-time, dead time, and off-time during on / off control. Figure 3 (B) shows the relationship between the turn-on time and the length of the dead time before extending the switching cycle. Figure 3 (C) shows the relationship between the turn-on time and the length of the dead time after extending the switching cycle. Detailed Implementation

[0031] Electric vehicle 2, an embodiment of which is described with reference to the accompanying drawings. Figure 1 The circuit diagram of electric vehicle 2 is shown. Electric vehicle 2 includes a first battery 3, a second battery 4, a first inverter 10, a second inverter 20, a motor 30, a circuit selector 40, a power supply terminal 50, and a controller 7. Figure 1 The text also depicts an external device 70 connected to the power supply terminal 50, but... Figure 1External device 70 is not connected to power supply terminal 50. External device 70 can be either a power source supplying power to the battery or an electrical device consuming battery power. When external device 70 is a power source, power flows from external device 70 to the first battery 3 and the second battery 4 via power supply terminal 50, charging these batteries. When external device 70 is a power-consuming device, power is supplied to external device 70 from the first battery 3 and the second battery 4 via power supply terminal 50. Controller 7 may not know in advance whether external device 70 is a power-supplying device or a power-consuming device.

[0032] For the sake of simplicity, "switching element" will be referred to as "SW element" and "switching frequency" will be referred to as "SW frequency".

[0033] An axle (not shown) is connected to the output shaft of motor 30. Motor 30 is driven by electricity from first battery 3 and second battery 4, thereby propelling electric vehicle 2. Motor 30 is a three-phase AC motor with multiple stator coils 31. Figure 1 The thick arrow indicates the current flow when driving motor 30. The first DC terminal 10p of the first inverter 10 and the second DC terminal 20p of the second inverter 20 are connected via circuit selector 40, and the first battery 3 and the second battery 4 are connected in series (the structure of circuit selector 40, the first inverter 10, and the second inverter 20 will be described later). The power from the series-connected first battery 3 and second battery 4 is supplied to the first inverter 10 and the second inverter 20. The DC power from the batteries is converted into AC power suitable for driving motor 30 by the first inverter 10 and the second inverter 20, and then supplied to motor 30 (stator coil 31).

[0034] The structure of the first inverter 10 is described below. The first inverter 10 has a first DC terminal 10p, three sets of first series connectors 11a, 11b, and 11c, and a capacitor 15. The three sets of first series connectors 11a, 11b, and 11c are connected in parallel between the first DC terminal 10p and ground 9. Furthermore, ground 9 is shared by the first inverter 10 and the second inverter 20.

[0035] The three sets of first series connectors 11a, 11b, and 11c each have a first upper SW element 12 and a first lower SW element 13 connected in series. The first upper SW element 12 is connected to the first DC terminal 10p, and the first lower SW element 13 is connected to ground 9. One end of each of the three stator coils 31 is connected to the midpoint of each of the three sets of first series connectors 11a, 11b, and 11c (the connection point of the first upper SW element 12 and the first lower SW element 13).

[0036] A freewheeling diode is connected in anti-parallel to each of the first upper SW elements 12 and each of the first lower SW elements 13. The freewheeling diode always allows current to flow from the ground 9 side to the first DC terminal 10p side. The freewheeling diode can be a separate element from the first upper SW element 12 (first lower SW element 13), or it can function as a diode within the first upper SW element 12 (first lower SW element 13).

[0037] A capacitor 15 is connected between the first DC terminal 10p and ground 9. The capacitor 15 suppresses current / voltage fluctuations caused by the switching on and off of the SW component.

[0038] The structure of the second inverter 20 is described below. The second inverter 20 has a second DC terminal 20p, three sets of second series connectors 21a, 21b, and 21c, and a capacitor 25. Each of the three sets of second series connectors 21a, 21b, and 21c has a second upper SW element 22 and a second lower SW element 23 connected in series. The other ends of the three stator coils 31 are connected to the midpoints of each of the three sets of second series connectors 21a, 21b, and 21c (the connection points of the second upper SW element 22 and the second lower SW element 23). The structure of the second inverter 20 is the same as that of the first inverter 10, so detailed descriptions are omitted.

[0039] A first current sensor 5 is connected in series with the first battery 3, and a second current sensor 6 is connected in series with the second battery 4. The first current sensor 5 (second current sensor 6) measures the current flowing into and out of the first battery 3 (second battery 4). The measurements from current sensors 5 and 6 are sent to controller 7. As described in detail later, controller 7 controls each switching element in a manner that makes the measurements from current sensors 5 and 6 equal.

[0040] The positive terminal of the first battery 3 (positive terminal 3p) is connected to the first DC terminal 10p, and the negative terminal of the second battery 4 (negative terminal 4n) is connected to ground 9. The connection relationship between the negative terminal of the first battery 3 (negative terminal 3n) and the positive terminal of the second battery 4 (positive terminal 4p) is determined by the circuit selector 40. Next, the circuit selector 40 will be explained.

[0041] The circuit selector 40 includes a first switch 41, a second switch 42, a third switch 43, and a fourth switch 44. The first switch 41 is connected between the negative terminal 3n of the first battery and the positive terminal 4p of the second battery. The second switch 42 is connected between the negative terminal 3n of the first battery and ground 9. The third switch 43 is connected between the positive terminal 4p of the second battery and the second DC terminal 20p. The fourth switch 44 is connected between the first DC terminal 10p and the second DC terminal 20p.

[0042] The circuit selector 40 is controlled by the controller 7. The controller 7 sets the circuit selector 40 to either a series mode or a parallel mode. In series mode, the controller 7 closes the first switch 41 and the fourth switch 44, and opens the second switch 42 and the third switch 43. Figure 1 In this configuration, circuit selector 40 is set to series mode. In series mode, the negative terminal 3n of the first battery and the positive terminal 4p of the second battery are connected, and the first DC terminal 10p and the second DC terminal 20p are connected. Furthermore, the negative terminal 3n of the first battery is disconnected from ground 9, and the positive terminal 4p of the second battery is disconnected from the second DC terminal 20p.

[0043] In parallel mode, controller 7 opens switches 41 and 44 and closes switches 42 and 43. Consequently, the negative terminal 3n of the first battery is connected to ground 9, and the positive terminal 4p of the second battery is connected to the second DC terminal 20p. Furthermore, the negative terminal 3n of the first battery is disconnected from the positive terminal 4p of the second battery, and the first DC terminal 10p is disconnected from the second DC terminal 20p.

[0044] When the motor 30 outputs high torque, the controller 7 sets the circuit selector 40 to series mode. AC power is supplied to the first inverter 10 and the second inverter 20 from the series connection of the first battery 3 and the second battery 4. Figure 1 The thick arrow indicates the current flow at this time. Controller 7 provides the same PWM signal (basic PWM signal) provided to the first upper SW element 12 to the second lower SW element 23, and supplies the signal obtained by inverting the basic PWM signal to the first lower SW element 13 and the second upper SW element 22, thus turning these SW elements on and off. As a result, approximately twice the current flows into the motor 30 compared to the case where the motor 30 is driven only through the first inverter 10, and the motor 30 generates high torque.

[0045] Furthermore, when the motor 30 outputs medium or low torque, the controller 7 sets the circuit selector 40 to series mode and disconnects the fourth switch 44. The controller 7 keeps the second upper SW element 22 on, drives the first upper SW element 12 to turn on and off using a predetermined basic PWM signal, and drives the first lower SW element 13 to turn on and off using a signal obtained by inverting the basic PWM signal.

[0046] The electric vehicle 2 can connect an external device to the power supply terminal 50. The external device 70 can be either a power source that supplies power to the first battery 3 and the second battery 4, or a device that consumes power from the first battery 3 and the second battery 4. Next, the processing of the controller 7 when the power supply terminal 50 and the external device 70 are connected will be explained.

[0047] The power supply terminal 50 has a positive power supply terminal 50p and a negative power supply terminal 50n. The positive terminal 70p of the external device 70 is connected to the positive power supply terminal 50p, and the negative terminal 70n of the external device 70 is connected to the negative power supply terminal 50n. The negative power supply terminal 50n is connected to ground 9, and the positive power supply terminal 50p is connected to the positive terminal 3p of the first battery and the first DC terminal 10p.

[0048] When connecting an external device 70 to the power supply terminal 50, the controller 7 sets the circuit selector 40 to parallel mode. The first battery 3 and the second battery 4 are connected in parallel with respect to the external device 70. However, the first inverter 10, the motor 30 (stator coil 31), and the second inverter 20 are connected between the external device 70 and the second battery 4. The controller 7 keeps the first lower SW element 13 and the second lower SW element 23 disconnected, and keeps the first upper SW element 12 and the second upper SW element 22 connected. Thus, the external device 70 and the second battery 4 are directly connected. The first battery 3 is always directly connected to the external device 70.

[0049] When the external device 70 is a power source, current flows from the external device 70 to the first battery 3 and the second battery 4 via the power supply terminal 50. Figure 2 The thick arrow indicates the current flow at this moment. The current supplied from external device 70 is... Figure 2 The current flows from point A to the first battery 3 and the second battery 4. However, the current flows from point A to the second battery 4 via the first inverter 10, the motor 30, and the second inverter 20.

[0050] In the case that external device 70 is a power-consuming device, the current is calculated according to... Figure 2 The thick arrows flow in opposite directions. The current flowing from cell 1 (3) and the current flowing from cell 2 (4) are... Figure 2 The flow converges at point A and flows to external device 70.

[0051] When two batteries are connected in parallel, the current flowing into and out of each battery should preferably be equal, whether charging the batteries or supplying power to an external source. Figure 2 With this structure, the voltage ratio between the first DC terminal 10p and the second DC terminal 20p can be adjusted arbitrarily, whether current is flowing into or out of the battery. By adjusting the voltage ratio between the first DC terminal 10p and the second DC terminal 20p, the difference between the current flowing into and out of the first battery 3 and the current flowing into and out of the second battery 4 can be reduced. Its structure will be briefly explained.

[0052] In such Figure 2As indicated by the thick arrow, when current flows through, the second upper SW element 22 is kept on and the second lower SW element 23 is kept off. Complementary PWM signals are provided to the first upper SW element 12 and the first lower SW element 13. When the first upper SW element switches from on to off, the current from the first DC terminal 10p to the stator coil 31 is cut off. However, due to the self-induction of the stator coil 31, the charge of the capacitor 15 flows to the stator coil 31 through the freewheeling diode attached to the first lower SW element 13. Through this operation, the voltage at the second DC terminal 20p is lower than the voltage at the first DC terminal 10p. That is, a voltage reduction operation is achieved from the first DC terminal 10p to the second DC terminal 20p. When the current flowing into the second battery 4 is greater than the current flowing into the first battery 3, by performing the above-mentioned voltage reduction operation, the current flowing into the second battery 4 is reduced, and the current flowing into the first battery 3 increases accordingly.

[0053] In accordance with Figure 2 When current flows in the opposite direction to the thick arrow, the current flows from the second DC terminal 20p to the first DC terminal 10p via the second upper SW element 22 (on) and the freewheeling diode attached to the first upper SW element 12. That is, the voltage at the first DC terminal 10p is equal to the voltage at the second DC terminal 20p. When the first lower SW element 13 is on, one end of the stator coil 31 is connected to ground 9, and a large current flows through the stator coil 31. When the first lower SW element 13 switches from on to off, the current to ground 9 is cut off, but through the self-induction of the stator coil 31, the charge of the capacitor 25 is drawn away via the freewheeling diode attached to the second lower SW element 23. The drawn-away charge is pushed towards the first DC terminal 10p. As a result, the voltage at the first DC terminal 10p is higher than the voltage at the second DC terminal 20p. That is, a boost operation is achieved from the second DC terminal 20p towards the first DC terminal 10p. When the current flowing out of the second battery 4 is less than the current flowing out of the first battery 3, the current flowing out of the second battery 4 increases by performing the above-mentioned boost operation, and the current flowing out of the first battery 3 decreases accordingly.

[0054] The first upper SW element is fixed to be on, and the first lower SW element is fixed to be off, providing complementary PWM signals to the second upper SW element 22 and the second lower SW element 23. Thus, through an operation similar to the one described above, regardless of the direction of current flow, the voltage at the first DC terminal 10p is lower than the voltage at the second DC terminal 20p. When the current flowing into the second battery 4 is less than the current flowing into the first battery 3, the current flowing into the second battery 4 increases, and correspondingly the current flowing into the first battery 3 decreases. Conversely, when the current flowing out of the second battery 4 is greater than the current flowing out of the first battery 3, the current flowing out of the first battery 3 increases, and correspondingly the current flowing out of the second battery 4 decreases.

[0055] Furthermore, when the controller 7 provides complementary PWM signals to the upper and lower SW elements, it sets a dead time during which both SW elements are off when switching on and off. This is to prevent short circuits between the DC terminal and ground via the upper and lower SW elements.

[0056] After the difference in current between the first battery 3 and the second battery 4 becomes below a predetermined allowable current difference through on / off control of complementary PWM signals provided to the upper SW element and the lower SW element, the controller 7 switches to fixed control, fixing the upper SW element to on and the lower SW element to off. At this time, large current fluctuations may occur when the dead time instantaneously disappears.

[0057] The electric vehicle 2 of this embodiment, through the above-described operation, ensures that the current flowing into and out of the first battery 3 and the second battery 4 is equal, regardless of whether current flows from an external device to the battery or from the battery to an external device. Furthermore, it can suppress current fluctuations caused by the disappearance of dead time when transitioning from on / off control to fixed control. Its structure will be described in detail below.

[0058] When an external device 70 is connected to the power supply terminal 50, the controller 7 sets the circuit selector 40 to parallel mode. Furthermore, the controller 7 sets the average of the first measured current (i.e., the current flowing in and out of the first battery 3) measured by the first current sensor 5 and the second measured current (i.e., the current flowing in and out of the second battery 4) measured by the second current sensor 6 as a target value for the current flowing in and out of the second battery 4. The controller 7 then performs the aforementioned on / off control in a manner that makes the second measured current match the target value. The second measured current matching the target value means that the current flowing into the first battery 3 and the second battery 4 is equal.

[0059] When the difference between the second measured current and the target value falls below the allowable current difference, controller 7 switches from on-off control to fixed control. During the switchover to fixed control, controller 7 suppresses current fluctuations caused by the disappearance of the dead time through the following processing.

[0060] The following details the processing performed by the controller 7. First, (1) when the current flows from the first DC terminal 10p to the second DC terminal 20p and the second measured current is higher than the target value, and when the current flows from the second DC terminal 20p to the first DC terminal 10p and the second measured current is lower than the target value, the controller 7 performs the following processing (1-1) to (1-3).

[0061] (1-1) The controller 7 keeps the second upper SW element 22 always on and the second lower SW element 23 always off, regardless of the SW cycle. Through this process, the stator coil 31 and the second DC terminal 20p are directly connected.

[0062] (1-2) For each SW cycle, controller 7 keeps the first upper SW element 12 on and the first lower SW element 13 off. After a predetermined on-time, it keeps the first lower SW element 13 off as is and switches the first upper SW element 12 off. After a predetermined dead time, it keeps the first upper SW element 12 off and switches the first lower SW element 13 on. After a time of [switching cycle - dead time], it keeps the first upper SW element 12 off and switches the first lower SW element 13 off. This control is called the first on / off control. Furthermore, the SW cycle refers to the period of the PWM signal. The period from the on-time and dead time to [switching cycle - dead time] is the off-time (the time period when the first upper SW element 12 is off and the first lower SW element 13 is on). During the on-time, the first upper SW element 12 is on and the first lower SW element 13 is off. During the dead time, both the first upper SW element 12 and the first lower SW element 13 are disconnected.

[0063] Controller 7 repeatedly performs the first on / off control for each SW cycle. This first on / off control reduces the difference between the first and second measured currents. Furthermore, the first on / off control includes a dead time, eliminating the possibility of a short circuit between the first DC terminal 10p and ground 9. Figure 3 (A) shows the relationship between the turn-on time, turn-off time, and dead time at this time.

[0064] (1-3) After the difference between the second measured current and the target value becomes below the predetermined allowable current difference, the controller 7 extends the turn-on time to [SW cycle - dead time × 2]. Figure 3 (B) shows the relationship between the turn-on time and the dead time at this point. [Turn-on time + dead time × 2] equals the SW cycle, so the disconnection time disappears.

[0065] Controller 7 then maintains the relationship [on time = SW cycle - dead time × 2] and extends the SW cycle to the upper limit of the SW cycle. Controller 7 then transitions to a first fixed control that keeps the first upper SW element 12 always on and the first lower SW element 13 always off, regardless of the SW cycle.

[0066] Figure 3 (C) shows the relationship between the turn-on time and dead time after extending the SW cycle. For comparison... Figure 3 (B) and Figure 3 (C) shows that by extending the SW cycle, the proportion of dead time in the SW cycle is reduced. Therefore, the current fluctuation caused by the disappearance of dead time when switching from the first on / off control to the first fixed control is suppressed.

[0067] Next, the opposite situation to (1) above will be explained. (2) When the current flows from the first DC terminal 10p to the second DC terminal 20p and the second measured current is lower than the target value, and when the current flows from the second DC terminal 20p to the first DC terminal 10p and the second measured current is higher than the target value, the controller 7 performs the following processes (2-1) to (2-3).

[0068] (2-1) The controller 7 keeps the first upper SW element 12 always on and the first lower SW element 13 always off, regardless of the SW cycle. Through this process, the stator coil 31 and the first DC terminal 10p are directly connected.

[0069] (2-2) For each SW cycle, controller 7 keeps the second upper SW element 22 on and the second lower SW element 23 off. After a predetermined on time, it keeps the second lower SW element 23 off as is and switches the second upper SW element 22 off. After a predetermined dead time, it keeps the second upper SW element 22 off and switches the second lower SW element 23 on. After a time of [switching cycle - dead time], it keeps the second upper SW element 22 off and switches the second lower SW element 23 off. This control is called the second on / off control. The states of the second upper SW element 22 and the second lower SW element 23 during the on time, off time, and dead time are the same as in (1).

[0070] Controller 7 repeatedly performs the second on / off control for each SW cycle. Through the second on / off control, the difference between the first measured current and the second measured current is reduced. Similar to case (1), the second on / off control includes a dead time, so there is no possibility of a short circuit between the second DC terminal 20p and ground 9.

[0071] (2-3) After the difference between the second measured current and the target value becomes below a predetermined allowable current difference, the controller 7 extends the turn-on time to [SW cycle - dead time × 2]. The controller 7 then maintains the relationship [turn-on time = SW cycle - dead time × 2] and extends the SW cycle to the upper limit of the SW cycle, and then switches to a second fixed control that keeps the second upper SW element 22 always on and the second lower SW element 23 always off, regardless of the SW cycle.

[0072] The effects of the processes (2-1) to (2-3) are the same as those of the processes (1-1) to (1-3). Through the processes (2-1) to (2-3), equal currents flow through the first battery 3 and the second battery 4, and the current fluctuations caused by the disappearance of the dead time when the control switches from on to off to fixed are suppressed.

[0073] Furthermore, both the first fixed control and the second fixed control keep the first upper SW element 12 and the second upper SW element 22 always fixed in the ON state, regardless of the SW cycle, and keep the first lower SW element 13 and the second lower SW element 23 always fixed in the OFF state, regardless of the SW cycle. That is, the first fixed control and the second fixed control are in the same state.

[0074] As described above, the electric vehicle 2 utilizes the inverter's SW element and the motor's stator coils to ensure that current flows equally into the first battery 3 and the second battery 4. Furthermore, the electric vehicle 2 can suppress current fluctuations when transitioning from on / off control with dead time to fixed control without dead time.

[0075] Here are some structural features of the electric vehicle 2. The electric vehicle 2 includes a first inverter 10, a second inverter 20, and a motor 30. The motor 30 includes multiple stator coils 31. The first inverter 10 includes multiple first series connectors 11a, 11b, and 11c, which are series-connected bodies of a first upper SW element 12 and a first lower SW element 13. In each series connector, the first upper SW element 12 is located on the side closer to the first DC terminal 10p, and the first lower SW element 13 is located on the side closer to the ground 9. The midpoint of each of the multiple first series connectors 11a, 11b, and 11c is connected to one end of each stator coil 31.

[0076] The second inverter 20 includes multiple second series connectors 21a, 21b, and 21c, which serve as series connectors for the second upper SW element 22 and the second lower SW element 23. In each series connector, the second upper SW element 22 is located on the side closer to the second DC terminal 20p, and the second lower SW element 23 is located on the side closer to the ground 9. The midpoint of each of the multiple second series connectors 21a, 21b, and 21c is connected to the other end of each stator coil 31.

[0077] Notes relating to the techniques described in the embodiments. The techniques disclosed in this specification are applicable not only to electric vehicles without an engine, but also to hybrid vehicles that have a battery, a motor, and an engine. That is, "electric vehicle" in this specification only needs to have a motor and a battery for driving, and may also include hybrid vehicles.

[0078] In this embodiment, the controller 7 simultaneously and alternately turns all upper SW elements and lower SW elements on and off during the on / off control. The controller 7 may also turn one or two upper SW elements and their corresponding lower SW elements on and off, while keeping the remaining upper SW elements and lower SW elements off.

[0079] The permissible current difference is set as a tolerance that treats the first and second measuring currents as substantially equal.

[0080] The performance of battery 3 (first battery) and battery 4 (second battery) is basically the same (same output voltage). However, due to manufacturing errors, differences in the degree of degradation, etc., their characteristics are slightly different. Therefore, when battery 3 and battery 4 are connected in parallel to an external device, the current flowing through them may sometimes be different. Furthermore, the difference in characteristics between battery 3 and battery 4 is slight, so by simply setting a slight voltage difference between the first DC terminal 10p and the second DC terminal 20p, the current flowing into each battery can be adjusted. Additionally, the voltage of the external device is the same as the voltage of the first / second batteries.

[0081] The expression "keep SW components on" is equivalent to "keep SW components closed," meaning that the devices connected to the respective ends of SW components are electrically connected. The expression "keep SW components off" is equivalent to "keep SW components off," meaning that the devices connected to the respective ends of SW components are electrically disconnected.

[0082] The specific examples of the present invention have been described in detail above, but these are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples described above. The technical elements described in this specification or drawings are technically useful individually or in various combinations, and are not limited to the combinations described in the claims at the time of application. Furthermore, the technology illustrated in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives is itself technically useful.

[0083] (Symbol Explanation)

[0084] 2: Electric vehicle; 3, 4: Battery; 5, 6: Switch; 7: Controller; 9: Ground; 10: First inverter; 12, 13, 22, 23: Switching elements (SW elements); 15, 25: Capacitors; 20: Second inverter; 30: Motor; 31: Stator coil; 40: Circuit selector; 50: Power supply terminal; 70: External device.

Claims

1. An electric vehicle, comprising: a motor including a stator coil; a first battery including a first positive terminal and a first negative terminal; a ground; a second battery including a second positive terminal and a second negative terminal connected to the ground; a first current sensor that measures a current flowing to and from the first battery; a second current sensor that measures a current flowing to and from the second battery; a power reception and supply terminal including a power reception and supply positive terminal connectable to an external device that consumes or supplies electric power and a power reception and supply negative terminal connected to the ground; a first inverter including a first direct current terminal connected to the first positive terminal, and including a first upper switching element and a first lower switching element connected in series between the first direct current terminal and the ground, a midpoint of a series connection of the first upper switching element and the first lower switching element being connected to one end of the stator coil; a second inverter including a second direct current terminal, and including a second upper switching element and a second lower switching element connected in series between the second direct current terminal and the ground, a midpoint of a series connection of the second upper switching element and the second lower switching element being connected to the other end of the stator coil; a circuit selector that selects either a series mode in which the first negative terminal is connected to the second positive terminal and the first direct current terminal is connected to the second direct current terminal, or a parallel mode in which the first negative terminal is connected to the ground, the second positive terminal is connected to the second direct current terminal, and the first direct current terminal is disconnected from the second direct current terminal; and a controller that sets the circuit selector to the parallel mode when the external device is connected to the power reception and supply terminal, sets an average of a first measured current measured by the first current sensor and a second measured current measured by the second current sensor as a target value of a current flowing to and from the second battery when the external device is connected to the power reception and supply terminal, in a case where the current flows from the first direct current terminal to the second direct current terminal and the second measured current is higher than the target value, or in a case where the current flows from the second direct current terminal to the first direct current terminal and the second measured current is lower than the target value, fixes the second upper switching element to be on and the second lower switching element to be off (1-1), repeatedly performs a first on-off control in which the first upper switching element is kept on and the first lower switching element is kept off, the first lower switching element is kept off as it is after a predetermined on time elapses and the first upper switching element is switched to be off, the first upper switching element is kept off and the first lower switching element is switched to be on after a predetermined dead time elapses, the first upper switching element is kept off and the first lower switching element is switched to be off after [switching period - dead time] elapses (1-2), and sets the circuit selector to the series mode when the external device is disconnected from the power reception and supply terminal. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (1-3) after the difference between the second measured current and the target value becomes equal to or lower than a predetermined allowable current difference, the on time is extended to [switching period - dead time x 2], then the relationship of [on time = switching period - dead time x 2] is maintained and the switching period is extended to an upper limit switching period, and thereafter the control is shifted to the first fixed control in which the first upper switching element is fixed to be on and the first lower switching element is fixed to be off, (2) in the case where the current flows from the first DC terminal to the second DC terminal and the second measured current is lower than the target value, and the case where the current flows from the second DC terminal to the first DC terminal and the second measured current is higher than the target value, (2-1) the first upper switching element is fixed to be on and the first lower switching element is fixed to be off, (2-2) for each of the switching periods, the second on-off control is repeated, in which the second upper switching element is maintained to be on and the second lower switching element is maintained to be off, after a predetermined on time elapses, the second lower switching element is maintained to be off as it is and the second upper switching element is switched to be off, after a predetermined dead time elapses, the second upper switching element is maintained to be off and the second lower switching element is switched to be on, after a time of [switching period - dead time] elapses, the second upper switching element is maintained to be off and the second lower switching element is switched to be off, (2-3) after the difference between the second measured current and the target value becomes equal to or lower than a predetermined allowable current difference, the on time is extended to [switching period - dead time x 2], then the relationship of [on time = switching period - dead time x 2] is maintained and the switching period is extended to an upper limit switching period, and thereafter the control is shifted to the second fixed control in which the second upper switching element is fixed to be on and the second lower switching element is fixed to be off.

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