electric vehicles

Abstract

This specification provides a technology for suppressing current fluctuations when transitioning from on-off control, including dead time, to fixed control of the inverter's switching elements in an electric vehicle in which two batteries are connected in parallel to the power receiving terminals. [Solution] For each SW cycle, the controller keeps the upper SW element on and the lower SW element off, switches the upper SW element off after a predetermined on-time has elapsed, switches the lower SW element on after a predetermined dead time has elapsed, and switches the lower SW element off after the time [switching cycle - dead time] has elapsed. When the difference in current between both batteries becomes equal to or less than the allowable current difference, the controller extends the on-time to [switching cycle - dead time x 2], then extends the SW cycle to an upper limit SW cycle while maintaining the relationship [on-time = switching cycle - dead time x 2], and then fixes the upper SW element on and the lower SW element off.

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to an electric vehicle, and more particularly to an electric vehicle that is equipped with a power receiving terminal and can charge a battery from an external power source and can supply battery power to an external device through the power receiving terminal. [Background technology]

[0002] An electric vehicle includes a battery, an inverter, and an electric motor. The inverter includes 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 technology 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 and charge the battery. For ease of explanation, hereinafter, "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. 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. [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] By connecting a device that consumes power instead of an external power source, an electric vehicle can also supply the device with battery power. When two batteries are connected in parallel, it is desirable that the current flowing in and out of each battery be equal, whether charging the batteries or supplying battery power to an external device. By using the inverter's switching elements and the motor's stator coil as voltage converters, the current flowing in and out of each battery can be made equal.

[0006] Now, let's consider a dual inverter configuration in which the first inverter is connected to one end of the stator coil and the second inverter is connected to the other end. The first battery and power receiving terminal are connected to the DC end (first DC end) of the first inverter, and the second battery is connected to the DC end (second DC end) of the second inverter. Power from the external power source is split between the first battery and the first inverter. Power flowing into the first inverter flows to the second inverter via the first inverter, stator coil, and second inverter. If a power-consuming device is connected to the power receiving terminal, power will flow in the opposite direction.

[0007] As mentioned above, an inverter has two switching elements connected in series, with a stator coil connected to the midpoint of the series connection. It is known that when one switching element is turned on and off at a predetermined duty cycle and the other switching element is turned on and off in reverse phase, this circuit functions as a bidirectional voltage converter. A dual inverter configuration can be used to step down the voltage from the first DC terminal (power receiving terminal) to the second DC terminal (second battery) using a first inverter and stator coil, and to step up the voltage in the reverse direction. Furthermore, a second inverter and stator coil can step down the voltage from the second DC terminal (second battery) to the first DC terminal (power receiving terminal), and to step up the voltage in the reverse direction. A dual inverter configuration can both step down or step up the voltage at the power receiving terminal and supply it to the second battery, and step down or step up the voltage of the second battery and supply it to the power receiving terminal. The first battery is directly connected to the power receiving terminal. Therefore, the above configuration using a dual inverter can adjust the voltage difference between the first DC end and the second DC end and make the currents flowing to the first battery and the second battery equal in both cases, when a power source is connected to the power receiving terminal (i.e., when current flows from the power receiving terminal to the battery) and when a device that consumes power is connected to the power receiving terminal (i.e., when current flows from the battery to the power receiving terminal).

[0008] A given PWM signal and its opposite-phase PWM signal are called complementary PWM signals. When two switching elements connected in series are driven with complementary PWM signals, a dead time is provided to prevent short circuits. The dead time is the period during which both switching elements are turned off when switching on and off. In the dual inverter configuration described above, two batteries are connected in parallel to the power receiving terminal, and a dual inverter circuit is connected between one battery and the power receiving terminal. The switching elements of the first or second inverter are driven to equalize the currents flowing into and out of the two batteries. Once the currents flowing into and out of the two batteries are equalized, the PWM control is switched to fixed control, in which the upper switching element is fixed on and the lower switching element is fixed off. If the dead time included in the PWM control is suddenly eliminated, large current fluctuations may occur. This specification provides a technology for suppressing current fluctuations when switching from PWM control, including dead time, to fixed control in an electric vehicle equipped with two batteries and a dual inverter. [Means for solving the problem]

[0009] The electric vehicle disclosed in this specification includes first and second batteries, a motor, first and second inverters, first and second current sensors, a power receiving terminal, a circuit selector, and a controller. The motor includes a stator coil. 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.

[0010] The power receiving terminal has a power receiving positive terminal and a power receiving negative terminal to which an external device that consumes or supplies power can be connected. The external device that supplies power is typically a power supply. The power receiving positive terminal is connected to the first positive terminal, and the power receiving negative terminal is connected to ground.

[0011] The first inverter includes 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. A 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.

[0012] The second inverter includes 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.

[0013] The circuit selector can select either a series mode or a parallel mode. In the series mode, the circuit selector connects the first negative terminal to the second positive terminal and connects the first DC terminal to the second DC terminal. In the parallel mode, the circuit selector connects the first negative terminal to ground and connects the second positive terminal to the second DC terminal and disconnects the first DC terminal from the second DC terminal.

[0014] The controller sets the circuit selector to series mode when driving the motor with high torque. The controller sets the circuit selector to parallel mode when an external device is connected to the power receiving terminal. When an external device is connected to the power receiving terminal, the controller executes the following process.

[0015] The controller sets the average value of the first measured current measured by the first current sensor and the second measured current measured by the second current sensor as the target value for the current flowing in and out of the second battery. The controller controls the switching elements of the two inverters so that the second measured current matches the target value. If the second measured current matches the target value, equal currents will flow in the first and second batteries.

[0016] (1) When a current flows from the first DC terminal to the second DC terminal and the second measured current is higher than the target value, or when a 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). The direction of the current is identified from the measurement value of the current sensor.

[0017] (1-1) The controller fixes the second upper switching element to ON and fixes the second lower switching element to OFF, thereby directly connecting the stator coil and the second DC terminal.

[0018] (1-2) The controller repeats a first on-off control for each switching period, holding the first upper switching element on and the first lower switching element off, switching the first upper switching element off while keeping the first lower switching element off after a predetermined on-time has elapsed, switching the first lower switching element on while keeping the first upper switching element off after a predetermined dead time has elapsed, and switching the first lower switching element on while keeping the first upper switching element off after a time equal to [switching period - dead time] has elapsed, and switching the first lower switching element off while keeping the first upper switching element off after a time equal to [switching period - dead time] has elapsed. This first on-off control causes the voltage at the second DC terminal to be lower than the voltage at the first DC terminal, regardless of the direction of current flow. When current is flowing from the first DC terminal to the second DC terminal, the current flowing into the second positive terminal decreases, thereby reducing the difference between the second measured current and the target value. When current is flowing from the second DC terminal to the first DC terminal, the current flowing out of the second positive terminal increases, thereby reducing the difference between the second measured current and the target value.

[0019] (1-3) When the difference between the second measured current and the target value becomes equal to or less than a predetermined allowable current difference, the controller extends the on-time to [switching period - dead time × 2], then extends the switching period to the upper limit switching period while maintaining the relationship [on-time = switching period - dead time × 2], and then transitions to first fixed control, which fixes the first upper switching element to on and the first lower switching element to off. Extending the switching period reduces the proportion of dead time in the switching period. This suppresses current fluctuations due to the loss of dead time when transitioning from first on-off control to first fixed control.

[0020] (2) When a 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 a 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).

[0021] (2-1) The controller fixes the first upper switching element to ON and fixes the first lower switching element to OFF, thereby directly connecting the stator coil and the first DC terminal.

[0022] (2-2) The controller repeats a second on-off control for each switching period, holding the second upper switching element on while holding the second lower switching element off, switching the second upper switching element off while holding the second lower switching element off after a predetermined on-time has elapsed, switching the second lower switching element on while holding the second upper switching element off after a predetermined dead time has elapsed, and switching the second lower switching element off while holding the second upper switching element off after a time equal to [switching period - dead time] has elapsed. This second on-off control causes the voltage at the second DC terminal to be higher than the voltage at the first DC terminal, regardless of the direction of current flow. When current is flowing from the first DC terminal to the second DC terminal, the current flowing into the second positive terminal increases, reducing the difference between the second measured current and the target value. When current is flowing from the second DC terminal to the first DC terminal, the current flowing out of the second positive terminal decreases, reducing the difference between the second measured current and the target value.

[0023] (2-3) When the difference between the second measured current and the target value becomes equal to or less than a predetermined allowable current difference, the controller extends the on-time to [switching period - dead time x 2], then extends the switching period to the upper limit switching period while maintaining the relationship [on-time = switching period - dead time x 2], and then transitions to second fixed control, which fixes the second upper switching element to on and the second lower switching element to off. Extending the switching period reduces the proportion of dead time in the switching period. This suppresses current fluctuations due to the loss of dead time when transitioning from second on-off control to second fixed control.

[0024] By extending the switching period while maintaining the relationship [on time = switching period - dead time × 2], the ratio of dead time to on time (or switching period) is reduced. The effect of dead time becomes relatively small, and current fluctuations caused by the disappearance of dead time when transitioning from control with dead time (i.e., on-off control) to control without dead time (i.e., fixed control) are suppressed. Details and further improvements of the technology disclosed in this specification are described in the "Description of Embodiments" below. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a circuit diagram of an electric vehicle according to an embodiment of the present invention, showing the flow of current when driving a motor. [Figure 2] 2 is a circuit diagram of an electric vehicle according to an embodiment. FIG. 2 shows the current flow when charging two batteries with an external device. [Figure 3] These are diagrams illustrating the effect of extending the switching period. Figure 3(A) shows the relationship between the on time, dead time, and off time during on / off control. Figure 3(B) shows the relationship between the on time and dead time before extending the switching period, and Figure 3(C) shows the relationship between the on time and dead time after extending the switching period. DETAILED DESCRIPTION OF THE INVENTION

[0026] An electric vehicle 2 according to an embodiment will be described with reference to the drawings. FIG. 1 shows a circuit diagram of the electric vehicle 2. The 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 receiving terminal 50, and a controller 7. FIG. 1 also illustrates an external device 70 connected to the power receiving terminal 50, but the external device 70 is not connected to the power receiving terminal 50 in FIG. 1 . The external device 70 may be a power source that supplies power to the battery, or may be an electric device that consumes power from the battery. If the external device 70 is a power source, power flows from the external device 70 to the first battery 3 and the second battery 4 through the power receiving terminal 50, charging these batteries. If the external device 70 is a power consuming device, power is supplied from the first battery 3 and the second battery 4 to the external device 70 through the power receiving terminal 50. The controller 7 does not need to know in advance whether the external device 70 is a power supplying device or a power consuming device.

[0027] In the following, for the sake of simplicity, the "switching element" will be referred to as the "SW element" and the "switching frequency" will be referred to as the "SW frequency."

[0028] An axle (not shown) is connected to the output shaft of the motor 30. The motor 30 is driven by power from the first battery 3 and the second battery 4, which drives the electric vehicle 2. The motor 30 is a three-phase AC motor and has multiple stator coils 31. The thick arrows in FIG. 1 indicate the flow of current when the motor 30 is driven. The circuit selector 40 connects the first DC terminal 10p of the first inverter 10 to the second DC terminal 20p of the second inverter 20, and the first battery 3 and the second battery 4 are connected in series (the configurations of the circuit selector 40, the first inverter 10, and the second inverter 20 will be described later). Power from the first battery 3 and the second battery 4, which are connected in series, is supplied to the first inverter 10 and the second inverter 20. The DC power of the batteries is converted by the first inverter 10 and the second inverter 20 into AC power suitable for driving the motor 30, and is supplied to the motor 30 (the stator coil 31).

[0029] The configuration of the first inverter 10 will be described. The first inverter 10 has a first DC terminal 10p, three sets of first series-connected bodies 11a, 11b, and 11c, and a capacitor 15. The three sets of first series-connected bodies 11a, 11b, and 11c are connected in parallel between the first DC terminal 10p and ground 9. The ground 9 is common to the first inverter 10 and the second inverter 20.

[0030] Each of the three sets of first series-connected bodies 11a, 11b, and 11c includes a first upper switching element 12 and a first lower switching element 13 connected in series. The first upper switching element 12 is connected to the first DC end 10p, and the first lower switching element 13 is connected to the 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-connected bodies 11a, 11b, and 11c (the connection point between the first upper switching element 12 and the first lower switching element 13).

[0031] A free wheel diode is connected in anti-parallel to each of the first upper switching elements 12 and each of the first lower switching elements 13. The free wheel diode always passes a current from the ground 9 side to the first DC end 10p side. The free wheel diode may be an element separate from the first upper switching element 12 (first lower switching element 13), or may be a diode function included in the element of the first upper switching element 12 (first lower switching element 13).

[0032] A capacitor 15 is connected between the first DC terminal 10p and the ground 9. The capacitor 15 suppresses fluctuations in current / voltage caused by the on / off of the switching element.

[0033] The configuration of the second inverter 20 will be described. The second inverter 20 has a second DC terminal 20p, three sets of second series-connected bodies 21a, 21b, and 21c, and a capacitor 25. Each of the three sets of second series-connected bodies 21a, 21b, and 21c includes a second upper switching element 22 and a second lower switching element 23 connected in series. The other ends of the three stator coils 31 are connected to the midpoints of the three sets of second series-connected bodies 21a, 21b, and 21c (the connection points of the second upper switching element 22 and the second lower switching element 23). The configuration of the second inverter 20 is the same as that of the first inverter 10, so a detailed description will be omitted.

[0034] A first current sensor 5 is connected in series to the first battery 3, and a second current sensor 6 is connected in series to the second battery 4. The first current sensor 5 (second current sensor 6) measures the current flowing in and out of the first battery 3 (second battery 4). The measured values ​​of the current sensors 5 and 6 are sent to a controller 7. As will be described in more detail later, the controller 7 controls each switching element so that the measured values ​​of the current sensors 5 and 6 become equal.

[0035] The positive electrode of the first battery 3 (first battery positive terminal 3p) is connected to the first DC terminal 10p, and the negative electrode of the second battery 4 (second battery negative terminal 4n) is connected to the ground 9. The connection relationship between the negative electrode of the first battery 3 (first battery negative terminal 3n) and the positive electrode of the second battery 4 (second battery positive terminal 4p) is determined by the circuit selector 40. Next, the circuit selector 40 will be described.

[0036] 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 first battery negative terminal 3n and the second battery positive terminal 4p. The second switch 42 is connected between the first battery negative terminal 3n and ground 9. The third switch 43 is connected between the second battery positive terminal 4p and the second DC terminal 20p. The fourth switch 44 is connected between the first DC terminal 10p and the second DC terminal 20p.

[0037] The circuit selector 40 is controlled by the controller 7. The controller 7 sets the circuit selector 40 to either the series mode or the parallel mode. In the 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. In FIG. 1, the circuit selector 40 is set to the series mode. In the series mode, the first battery negative terminal 3n and the second battery positive terminal 4p are connected, and the first DC terminal 10p and the second DC terminal 20p are connected. Note that the first battery negative terminal 3n is disconnected from the ground 9, and the second battery positive terminal 4p is disconnected from the second DC terminal 20p.

[0038] In the parallel mode, the controller 7 opens the first switch 41 and the fourth switch 44 and closes the second switch 42 and the third switch 43. This causes the first battery negative terminal 3n to be connected to the ground 9, and the second battery positive terminal 4p to be connected to the second DC terminal 20p. The first battery negative terminal 3n is disconnected from the second battery positive terminal 4p, and the first DC terminal 10p is disconnected from the second DC terminal 20p.

[0039] When the controller 7 is to cause the motor 30 to output high torque, it sets the circuit selector 40 to the series mode. AC power is supplied to the first inverter 10 and the second inverter 20 from the series-connected first battery 3 and second battery 4. The thick arrows in FIG. 1 indicate the current flow at this time. The controller 7 supplies the second lower switching element 23 with a PWM signal (basic PWM signal) that is the same as that supplied to the first upper switching element 12, and supplies an inverted signal of the basic PWM signal to the first lower switching element 13 and the second upper switching element 22, thereby driving these switching elements on and off. This allows roughly twice as much current to flow through the motor 30 as when the motor 30 is driven by the first inverter 10 alone, causing the motor 30 to generate high torque.

[0040] When the motor 30 is to output a medium or low torque, the controller 7 sets the circuit selector 40 to the series mode and opens the fourth switch 44. The controller 7 fixes the second upper switching element 22 to ON, drives the first upper switching element 12 on and off with a predetermined basic PWM signal, and drives the first lower switching element 13 on and off with a signal obtained by inverting the basic PWM signal.

[0041] The electric vehicle 2 can connect an external device to the power receiving terminal 50. The external device 70 may be a power source that supplies power to the first battery 3 and the second battery 4, or may be a device that consumes the power of the first battery 3 and the second battery 4. Next, the processing of the controller 7 when the power receiving terminal 50 and the external device 70 are connected will be described.

[0042] The power receiving terminal 50 has a power receiving positive terminal 50p and a power receiving negative terminal 50n. The positive terminal 70p of the external device 70 is connected to the power receiving positive terminal 50p, and the negative terminal 70n of the external device 70 is connected to the power receiving negative terminal 50n. The power receiving negative terminal 50n is connected to ground 9, and the power receiving positive terminal 50p is connected to the first battery positive terminal 3p and the first DC terminal 10p.

[0043] When the external device 70 is connected to the power receiving terminal 50, the controller 7 sets the circuit selector 40 to the parallel mode. The first battery 3 and the second battery 4 are connected in parallel 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 switching element 13 and the second lower switching element 23 off, and keeps the first upper switching element 12 and the second upper switching element 22 on. In this way, 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.

[0044] If the external device 70 is a power source that supplies power, current flows from the external device 70 to the first battery 3 and the second battery 4 through the power receiving terminal 50. The current flow at this time is indicated by the thick arrows in FIG. 2. The current supplied from the external device 70 branches at point A in FIG. 2 and flows to the first battery 3 and the second battery 4. However, the current flows from point A through the first inverter 10, the motor 30, and the second inverter 20 to the second battery 4.

[0045] If the external device 70 is a device that consumes power, current flows in the opposite direction to the thick arrow line in Figure 2. The current from the first battery 3 and the current from the second battery 4 join at point A in Figure 2 and flow to the external device 70.

[0046] When two batteries are connected in parallel, it is desirable that the current flowing in and out of each battery be equal, whether the batteries are being charged or the battery power is being supplied to an external device. By adopting the configuration shown in FIG. 2, the voltage ratio between the first DC terminal 10p and the second DC terminal 20p can be adjusted as desired, 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 in and out of the first battery 3 and the second battery 4 can be reduced. The mechanism behind this is briefly explained below.

[0047] When current flows as indicated by the thick arrow in FIG. 2, the second upper switching element 22 is kept on and the second lower switching element 23 is kept off. Complementary PWM signals are sent to the first upper switching element 12 and the first lower switching element 13. When the first upper switching element switches from on to off, the current from the first DC terminal 10p to the stator coil 31 is cut off. Instead, the self-induction of the stator coil 31 causes the charge in the capacitor 15 to flow to the stator coil 31 through the freewheeling diode associated with the first lower switching element 13. This operation causes the voltage at the second DC terminal 20p to drop below the voltage at the first DC terminal 10p. In other words, a step-down 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, the above-described step-down operation reduces the current flowing into the second battery 4, thereby increasing the current flowing into the first battery 3.

[0048] When current flows in the direction opposite to the thick arrow in FIG. 2, current flows from the second DC terminal 20p to the first DC terminal 10p through the second upper switching element 22 in the ON state and the freewheeling diode associated with the first upper switching element 12. That is, the voltage at the first DC terminal 10p becomes equal to the voltage at the second DC terminal 20p. When the first lower switching element 13 is turned 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 switching element 13 is switched from ON to OFF, the current to ground 9 is cut off, but the self-induction of the stator coil 31 causes the charge in the capacitor 25 to be absorbed through the freewheeling diode associated with the second lower switching element 23. The absorbed charge is pushed to the first DC terminal 10p. As a result, the voltage at the first DC terminal 10p becomes higher than the voltage at the second DC terminal 20p. That is, a voltage step-up operation is realized from the second DC terminal 20p toward the first DC terminal 10p. When the current output from the second battery 4 is less than the current output from the first battery 3, the voltage step-up operation increases the current output from the second battery 4, and the current output from the first battery 3 decreases accordingly.

[0049] The first upper switching element is fixed on, the first lower switching element is fixed off, and complementary PWM signals are sent to the second upper switching element 22 and the second lower switching element 23. Then, due to an operation similar to that described above, the voltage at the first DC terminal 10p becomes lower than the voltage at the second DC terminal 20p regardless of the direction of current flow. 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 the current flowing into the first battery 3 decreases accordingly. Furthermore, when the current output from the second battery 4 is greater than the current output from the first battery 3, the current output from the first battery 3 increases, and the current output from the second battery 4 decreases accordingly.

[0050] When the controller 7 supplies complementary PWM signals to the upper and lower switching elements, it provides a dead time during which both switching elements are turned off when switching on and off. This is to prevent a short circuit between the DC terminal and ground through the upper and lower switching elements.

[0051] When the difference in current between the first battery 3 and the second battery 4 becomes equal to or less than a predetermined allowable current difference due to on / off control that applies complementary PWM signals to the upper and lower switching elements, the controller 7 shifts to fixed control that fixes the upper switching element to on and the lower switching element to off. At this time, if the dead time disappears instantaneously, a large current fluctuation may occur.

[0052] The electric vehicle 2 of the embodiment, through the above operation, equalizes the current flowing into and out of the first battery 3 and the second battery 4, whether the current flows from an external device to the battery or from the battery to an external device. It also suppresses current fluctuations caused by the disappearance of dead time when transitioning from on-off control to fixed control. The mechanism for this is described in detail below.

[0053] When an external device 70 is connected to the power receiving terminal 50, the controller 7 sets the circuit selector 40 to the parallel mode. Then, the controller 7 sets the average value 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 the target value of the current flowing in and out of the second battery 4. Then, the controller 7 executes the on / off control described above so that the second measured current matches the target value. The fact that the second measured current matches the target value means that the currents flowing in the first battery 3 and the second battery 4 are equal.

[0054] When the difference between the second measured current and the target value becomes equal to or smaller than the allowable current difference, the controller 7 shifts from the on-off control to the fixed control. When shifting from the on-off control to the fixed control, the controller 7 suppresses the current fluctuation caused by the disappearance of the dead time by the process described below.

[0055] The following describes in detail the processing performed by the controller 7. First, (1) when a current flows from the first DC terminal 10p to the second DC terminal 20p and the second measurement current is higher than the target value, and when a current flows from the second DC terminal 20p to the first DC terminal 10p and the second measurement current is lower than the target value, the controller 7 performs the following processing (1-1) to (1-3).

[0056] (1-1) The controller 7 fixes the second upper switching element 22 to always ON regardless of the SW cycle, and fixes the second lower switching element 23 to always OFF. This process puts the stator coil 31 and the second DC end 20p in a directly connected state.

[0057] (1-2) For each SW cycle, the controller 7 keeps the first upper SW element 12 on and keeps the first lower SW element 13 off. After a predetermined on-time has elapsed, the controller 7 switches the first upper SW element 12 off while keeping the first lower SW element 13 off. After a predetermined dead time has elapsed, the controller 7 switches the first lower SW element 13 on while keeping the first upper SW element 12 off. After a time period of [switching cycle - dead time] has elapsed, the controller 7 switches the first lower SW element 13 on while keeping the first upper SW element 12 off. This control is referred to as first on-off control. The SW cycle refers to the period of the PWM signal. The off time (the time period during which the first upper SW element 12 is off and the first lower SW element 13 is on) is the period from when the on time and the dead time have elapsed until the time period of [switching cycle - dead time]. 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 off.

[0058] The controller 7 repeats the first on / off control for each SW cycle. The first on / off control reduces the difference between the first measured current and the second measured current. In addition, the first on / off control includes a dead time, so there is no risk of a short circuit between the first DC terminal 10p and ground 9. The relationship between the on time, off time, and dead time at this time is shown in FIG. 3(A).

[0059] (1-3) When the difference between the second measured current and the target value becomes equal to or less than a predetermined allowable current difference, the controller 7 extends the on-time to [SW cycle - dead time x 2]. The relationship between the on-time and the length of the dead time at this time is shown in Figure 3(B). Since [on-time + dead time x 2] is equal to the SW cycle, the off-time disappears.

[0060] The controller 7 then extends the SW cycle to the upper limit SW cycle while maintaining the relationship of [ON time = SW cycle - dead time × 2]. The controller 7 then transitions to first fixed control in which the first upper SW element 12 is always fixed to ON and the first lower SW element 13 is always fixed to OFF, regardless of the SW cycle.

[0061] Figure 3(C) shows the relationship between the on-time and the length of the dead time after the SW cycle is extended. As is clear from comparing Figure 3(B) and Figure 3(C), extending the SW cycle reduces the proportion of dead time in the SW cycle. Therefore, current fluctuations caused by the loss of dead time when transitioning from first on-off control to first fixed control are suppressed.

[0062] Next, the opposite situation to the above-mentioned (1) will be described. (2) When a current flows from the first DC terminal 10p to the second DC terminal 20p and the second measurement current is lower than the target value, and when a current flows from the second DC terminal 20p to the first DC terminal 10p and the second measurement current is higher than the target value, the controller 7 executes the following processes (2-1) to (2-3).

[0063] (2-1) The controller 7 fixes the first upper switching element 12 to always ON regardless of the SW cycle, and fixes the first lower switching element 13 to always OFF. This process puts the stator coil 31 and the first DC end 10p in a directly connected state.

[0064] (2-2) For each SW cycle, the controller 7 holds the second upper SW element 22 on and the second lower SW element 23 off, and after a predetermined on-time has elapsed, switches the second upper SW element 22 off while keeping the second lower SW element 23 off, and after a predetermined dead time has elapsed, switches the second lower SW element 23 on while keeping the second upper SW element 22 off, and after a time of [switching cycle-dead time] has elapsed, switches the second lower SW element 23 off while keeping the second upper SW element 22 off. This control is referred to as 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 the case of (1).

[0065] The controller 7 repeats the second on / off control for each SW cycle. The second on / off control reduces the difference between the first measured current and the second measured current. As in the case of (1), the second on / off control includes a dead time, so there is no risk of a short circuit between the second DC terminal 20p and ground 9.

[0066] (2-3) When the difference between the second measured current and the target value becomes equal to or less than a predetermined allowable current difference, the controller 7 extends the ON time to [SW cycle - dead time × 2]. The controller 7 then extends the SW cycle to the upper limit SW cycle while maintaining the relationship [ON time = SW cycle - dead time × 2], and then transitions to second fixed control in which the second upper SW element 22 is fixed to always ON and the second lower SW element 23 is fixed to always OFF regardless of the SW cycle.

[0067] The effects of the processes (2-1) to (2-3) are the same as those of the processes (1-1) to (1-3). The processes (2-1) to (2-3) allow equal currents to flow through the first battery 3 and the second battery 4, and suppress current fluctuations caused by the elimination of dead time when switching from on-off control to fixed control.

[0068] In both the first fixed control and the second fixed control, the first upper switching element 12 and the second upper switching element 22 are fixed to be always on regardless of the SW cycle, and the first lower switching element 13 and the second lower switching element 23 are fixed to be always off regardless of the SW cycle. In other words, the first fixed control and the second fixed control are in the same state.

[0069] As described above, the electric vehicle 2 uses the inverter's switching elements and the motor's stator coil to ensure that current flows evenly between the first battery 3 and the second battery 4. Furthermore, the electric vehicle 2 can suppress current fluctuations when transitioning from on-off control that includes dead time to fixed control without dead time.

[0070] Some of the structural features of the electric vehicle 2 are listed below. The electric vehicle 2 includes a first inverter 10, a second inverter 20, and a motor 30. The motor 30 includes a plurality of stator coils 31. The first inverter 10 includes a plurality of first series-connected bodies 11a, 11b, and 11c, each of which is a series-connected body of a first upper switching element 12 and a first lower switching element 13. In each series-connected body, the first upper switching element 12 is located closer to the first DC end 10p, and the first lower switching element 13 is located closer to ground 9. The midpoint of each of the plurality of first series-connected bodies 11a, 11b, and 11c is connected to one end of the corresponding stator coil 31.

[0071] The second inverter 20 includes a plurality of second series-connected bodies 21a, 21b, and 21c, each of which is a series-connected body of a second upper SW element 22 and a second lower SW element 23. In each series-connected body, the second upper SW element 22 is located closer to the second DC end 20p, and the second lower SW element 23 is located closer to the ground 9. The midpoint of each of the plurality of second series-connected bodies 21a, 21b, and 21c is connected to the other end of the corresponding stator coil 31.

[0072] Here are some points to note regarding the technology described in the examples. The technology disclosed in this specification can be applied not only to electric vehicles that do not have engines, but also to hybrid vehicles that have a battery, a motor, and an engine. In other words, the term "electric vehicle" in this specification refers to any vehicle that has a motor and a battery for driving, and can also include hybrid vehicles.

[0073] In the embodiment, the controller 7 alternately turns on and off all the upper and lower switching elements simultaneously in the on / off control. The controller 7 may also turn on and off one or two upper switching elements and their corresponding lower switching elements, and keep the remaining upper and lower switching elements off.

[0074] The allowable current difference is set to a tolerance that allows the first measured current and the second measured current to be considered substantially equal.

[0075] The first battery 3 and the second battery 4 basically have the same performance (same output voltage). However, there are slight differences in their characteristics due to manufacturing errors and differences in the degree of deterioration. Therefore, when the first battery 3 and the second battery 4 are connected in parallel to an external device, the current flowing through them may differ. Furthermore, because the difference in the characteristics of the first battery 3 and the second battery 4 is slight, the current flowing through each battery can be adjusted by providing a slight voltage difference between the first DC terminal 10p and the second DC terminal 20p. Furthermore, the voltage of the external device is the same as that of the first and second batteries.

[0076] The expression "holding an SW element on" is equivalent to the expression "closing an SW element," which means electrically connecting devices connected to each end of the SW element. The expression "holding an SW element off" is equivalent to the expression "opening an SW element," which means electrically disconnecting devices connected to each end of the SW element.

[0077] 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]

[0078] 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: Capacitor 20: Second inverter 30: Motor 31: Stator coil 40: Circuit selector 50: Power receiving terminal 70: External device

Claims

[Claim 1] a motor having a stator coil; a first battery having a first positive terminal and a first negative terminal; Grand and a second battery having a second positive terminal and a second negative terminal connected to the ground; a first current sensor that measures current flowing into and out of the first battery; a second current sensor that measures current flowing into and out of the second battery; a power receiving terminal including a power receiving positive terminal and a power receiving negative terminal to which an external device that consumes or supplies power can be connected, the power receiving positive terminal being connected to the first positive terminal and the power receiving negative terminal being connected to the ground; a first inverter including a first DC 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 DC terminal and the ground, wherein a midpoint of a series connection of the first upper switching element and the first lower switching element is connected to one end of the stator coil; a second inverter including a second DC terminal and a second upper switching element and a second lower switching element connected in series between the second DC terminal and the ground, the second inverter having a midpoint of the series connection of the second upper switching element and the second lower switching element connected to the other end of the stator coil; a circuit selector for selecting either a series mode in which the first negative terminal is connected to the second positive terminal and the first DC terminal is connected to the second DC terminal, or a parallel mode in which the first negative terminal is connected to the ground and the second positive terminal is connected to the second DC terminal and the first DC terminal is disconnected from the second DC terminal; a controller that sets the circuit selector to the parallel mode when the external device is connected to the power receiving terminal; It is equipped with when the external device is connected to the power receiving terminal, the controller sets an average value 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 in and out of the second battery; (1) When a current flows from the first DC terminal to the second DC terminal and the second measurement current is higher than the target value, and when a current flows from the second DC terminal to the first DC terminal and the second measurement current is lower than the target value, (1-1) fixing the second upper switching element to ON and fixing the second lower switching element to OFF; (1-2) Repeating a first on / off control for each switching period, in which the first upper switching element is held on and the first lower switching element is held off, and after a predetermined on-time has elapsed, the first upper switching element is switched off while holding the first lower switching element off, and after a predetermined dead time has elapsed, the first upper switching element is switched on while holding the first lower switching element off, and after a time of [switching period-dead time] has elapsed, the first upper switching element is held off and the first lower switching element is switched off, (1-3) when the difference between the second measured current and the target value becomes equal to or less than a predetermined allowable current difference, extend the on-time to [switching period-dead time x 2], then extend the switching period to an upper limit switching period while maintaining the relationship [on-time = switching period-dead time x 2], and then transition to first fixed control in which the first upper switching element is fixed to on and the first lower switching element is fixed to off; (2) When a current flows from the first DC terminal to the second DC terminal and the second measurement current is lower than the target value, and when a current flows from the second DC terminal to the first DC terminal and the second measurement current is higher than the target value, (2-1) fixing the first upper switching element to ON and fixing the first lower switching element to OFF; (2-2) For each switching period, a second on / off control is repeated, in which the second upper switching element is held on and the second lower switching element is held off, and after a predetermined on-time has elapsed, the second upper switching element is switched off while holding the second lower switching element off, and after a predetermined dead time has elapsed, the second upper switching element is switched on while holding the second lower switching element off, and after a time of [switching period-dead time] has elapsed, the second upper switching element is held off and the second lower switching element is switched off, (2-3) When the difference between the second measured current and the target value becomes equal to or less than a predetermined allowable current difference, the on-time is extended to [switching period−dead time×2], and then the switching period is extended to an upper limit switching period while maintaining the relationship [on-time=switching period−dead time×2], and thereafter, transition is made to second fixed control in which the second upper switching element is fixed to on and the second lower switching element is fixed to off. Electric car.

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