Ac current supply device for battery

Abstract

To provide an AC current supply device for improving deterioration of a battery by supplying AC current to the battery.SOLUTION: According to the present invention, an electrocrystallization reduction mode is operated in which alternating current is supplied to the battery to reduce the electrocrystallization material in the battery. This mode is operated in a higher battery temperature range than the conventional battery heating mode implemented for battery heating. The alternating current used in this dendrite reduction mode consists of a high-rate discharge current component supplied during short discharge periods and a low-rate charge current component supplied during long discharge periods. These discharge and charge periods are repeated alternately. In one example, the AC current supply circuit for supplying AC current to the battery has a smoothing capacitor in the motor drive circuit and a secondary coil of a step-down transformer that forms a closed loop circuit with the battery. In another example, the AC current supply circuit has multiple inductors that are charged in parallel and discharged in turn.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an alternating current supply device that improves battery deterioration by supplying an alternating current to a battery. [Background technology]

[0002] Secondary batteries such as lithium-ion batteries (LIBs) are widely adopted in electric propulsion systems such as electric vehicles. A high-voltage secondary battery consisting of multiple cells connected in series is called a battery or battery pack. A serious problem in electric propulsion systems is the long charging time of the battery. Rapid charging reduces this charging time. The rapid charging ability of the battery is very important for electric propulsion systems to obtain easy-to-use and excellent driving capabilities.

[0003] However, it is known that rapid charging causes carrier metals to deposit on the surface of the negative electrode of the battery. This deposition, called electrodeposition, causes the capacity degradation of the battery and so-called internal short circuit. To avoid these problems, the rate of the charging current during rapid charging is generally limited to a range that can avoid electrodeposition.

[0004] In particular, dendrites, known as typical electrodeposition, cause so-called thermal runaway accidents due to internal short circuits. Rapid charging of low-temperature batteries accelerates the formation of dendrites. Solid electrolytes, which are used instead of resin separators, suppress dendrites. However, solid electrolytes have the problem that dendrites grow along the grain boundaries of the solid electrolyte.

[0005] For this reason, battery heating technology is adopted to preheat cold batteries with temperatures below 0° C. This battery heating is terminated when the battery temperature reaches near 0° C. in order to reduce power consumption. However, it is difficult to heat an EV battery pack uniformly and quickly using an electric heater.

[0006] For this reason, various AC internal heating methods that supply AC current to the battery have been proposed, for example, in Non-Patent Document 1 and Non-Patent Document 2. These AC internal heating methods reduce temperature variations in the battery and heat the battery rapidly. However, AC internal heating methods have unresolved problems and have not yet been installed in electric vehicles.

[0007] One problem with the conventional AC internal heating method is that when a high-rate AC current is used to rapidly heat a battery, the electrodeposition described above is promoted. A high-rate AC current is composed of a high-rate charging current component and a high-rate discharging current component. The charging current component promotes electrodeposition, while the discharging current component eliminates electrodeposition. The promotion of electrodeposition by a high-rate AC current suggests that the increase in electrodeposition due to the charging current component exceeds the decrease in electrodeposition due to the discharging current component. For this reason, the rate of the AC current that can be used in the AC internal heating method must be limited to a range that does not cause electrodeposition.

[0008] Another problem with the conventional AC internal heating method is that the AC supply circuit requires high circuit cost, because the internal resistance of the battery is low, so a high rate AC current must be supplied to the battery to shorten the battery pre-heating time.

[0009] Therefore, in order to save power consumption, the AC supply circuit needs to temporarily store the power energy discharged from the battery until the next charging period. For this reason, the AC supply circuit needs to have a large inductor and / or a large capacitor capable of storing high power energy. However, the large inductor and the large capacitor are expensive.

[0010] For example, when 50A AC current is supplied to a 0.2 ohm battery, the battery generates 500W of electric heat. However, when the battery voltage is 400V, the battery must supply 20kW AC power to an external energy storage device.

[0011] Patent Document 1 proposes an AC internal heating method that utilizes a grid charger equipped in an electric vehicle (EV). The coil of a transformer built into the grid charger is used as an energy storage device. However, in order to use the transformer coil as an inductor for magnetic energy storage, it is necessary to add an expensive semiconductor power switching element.

[0012] Patent Document 2 proposes another AC internal heating method using a transformer. The AC current supply circuit adopted in Patent Document 2 is described with reference to FIG. 1. A battery E has, for example, a resistor R. The AC current supply circuit connected to the battery E has a transformer T, a switch S, and a diode D. The transformer T has a primary coil W1 and a secondary coil W2. The battery E forms a closed loop circuit for discharging together with the resistor R, the primary coil W1, and the switch S. Furthermore, the battery E forms a closed loop circuit for charging together with the resistor R, the diode D, and the secondary coil W2.

[0013] When the switch S is turned on, a discharge current Id flows through the discharge closed loop circuit. When the switch S is turned off, a charge current Ic flows through the charge closed loop circuit due to the magnetic energy stored in the inductance of the transformer T. As a result, the internal resistance R of the battery E is heated by the discharge current Id and the charge current Ic. The discharge period during which the discharge current Id flows through the primary coil W1 is determined by the on period of the switch S. The charge period during which the charge current Ic flows through the secondary coil W2 is determined by the off period of the switch S. The waveforms of the discharge current Id and the charge current Ic change depending on the number of turns of the primary coil W1 and the number of turns of the secondary coil W2.

[0014] Fig. 2 shows example waveforms of the discharge current Id and the charge current Ic. In Fig. 2, the discharge current Id has a higher average amplitude than the charge current Ic. The discharge period t1 is shorter than the charge period t2. However, Patent Document 2 does not explain that the example waveforms shown in Fig. 2 were intentionally selected for some reason, nor does it state the reason for such selection.

[0015] In conclusion, the conventional AC internal heating method, which is used instead of the conventional external electric heater, preheats a battery that has a temperature lower than the freezing point of water to near the freezing point. Therefore, a battery that has a temperature at room temperature where the battery can be charged and discharged well does not need to use the conventional AC internal heating method. Conversely, when a normal battery that has a temperature at room temperature is heated by the conventional AC internal heating method, overheating and deterioration of the battery are caused.

[0016] Patent Document 3 discloses an AC current supplying technology that is essentially different from the AC internal heating method for heating a low-temperature battery. This AC current supplying technology improves the solid-state state of a battery electrode by supplying an AC current to a non-low-temperature battery, for example. However, Patent Document 3 does not disclose anything about the waveform of the AC current or the circuit structure of the AC current supplying circuit. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] CN111181208B [Patent Document 2] US9,065,293B2 [Patent Document 3] US11,145,861B2 [Non-patent literature]

[0018] [Non-Patent Document 1] Applied Energy Volume 230, 15 November 2018, Pages 257-266: A low-temperature internal heating strategy without lifetime reduction for large-size automotive lithium-ion battery pack [Non-Patent Document 2] Applied Energy Volume 284, 15 February 2021, Pages 116-192: Effects of alternating current on Li-ion battery performance, Monitoring degrative processes with in-situ characterization tecniques Summary of the Invention

[0019] The first object of the present invention is to provide an AC current supply device for a battery that can reduce the above problems associated with battery charging. The second object of the present invention is to promote the spread of this AC current supply device for a battery by reducing the circuit cost.

[0020] According to a first aspect of the present invention, an electrodeposition reduction mode is implemented to reduce electrodeposition materials in a battery by supplying an AC current to the battery. In this electrodeposition reduction mode, an AC current is supplied to a battery having a temperature above a predetermined room temperature. Preferably, the predetermined room temperature is 20° C. On the other hand, the conventional AC internal heating method is implemented to increase the temperature of a cold battery that is essentially below 0° C. In this electrodeposition reduction mode, a charging period is set longer than a discharging period. Furthermore, the discharging current component has a higher average amplitude value than the charging current component. The discharging current component and the charging current component are supplied alternately to the battery. This makes it possible to reduce electrodeposition near the negative electrode.

[0021] This electrodeposition reduction effect will be further explained. The AC current supplied to the battery consists of a discharge current component supplied to the battery during the discharge period and a charge current component supplied to the battery during the charge period. The discharge current component and the charge current component are alternately supplied to the battery. It is generally known that the charge current component increases the amount of electrodeposited material, and the discharge current component reduces the amount of electrodeposited material. The AC current having the waveform adopted in the present invention has the effect of promoting the function of the discharge current component in reducing the amount of electrodeposited material. In a preferred embodiment, the discharge current component contains harmonics with a higher amplitude than the charge current component. This can promote the reduction of the electrodeposited material by the discharge current component.

[0022] In a preferred embodiment, the integral value of the AC current is set to approximately zero in the electrodeposition reduction mode. The approximately zero value includes less than 5% of the SOC of the battery. As a result, the decrease in the SOC of the battery due to the electrodeposition reduction mode performed immediately after the charging operation can be suppressed.

[0023] In a preferred embodiment, the electrodeposition reduction mode is started within 30 minutes after the end of the predetermined battery charging mode, thereby improving the electrodeposition reduction efficiency by the AC current. The predetermined battery charging operation preferably means a charging operation in which the SOC increases by 20% or more.

[0024] This effect is further explained. The battery charging operation deposits electrodeposited material on the surface of the negative active material of the battery. The new surface of the electrodeposited material formed on the surface of the negative active material is quickly covered by an inert layer such as an SEI film. However, when the inert layer is formed on the surface of the electrodeposited material, the effect of reducing the electrodeposited material by the discharge current component is reduced. This problem is largely solved by implementing the electrodeposition reduction mode immediately after the battery charging operation, which is the main cause of the electrodeposited material being formed on the surface of the negative active material. In particular, since the inert layer grown after the end of the charging operation is still thin, the alternating current can destroy the electrical insulation of this inert layer.

[0025] In a preferred embodiment, the operation period of the electrodeposition reduction mode has a positive correlation with the charge amount of the battery by the battery charging operation performed immediately before the electrodeposition reduction mode, thereby reducing the power loss due to the electrodeposition reduction mode.

[0026] In a preferred embodiment, the duration of the electrodeposition reduction mode is negatively correlated to the battery temperature detected immediately before the electrodeposition reduction mode, thereby reducing power loss due to the electrodeposition reduction mode.

[0027] In a preferred embodiment, when the battery is at a low temperature, a battery heating mode is performed before the start of the battery charging mode, thereby reducing the formation of electrodeposition due to the battery charging mode. Furthermore, according to this embodiment, the battery heating mode is performed using the same AC current supply circuit as the electrodeposition reduction mode performed after the battery charging mode is completed, thereby reducing the circuit cost.

[0028] In a preferred embodiment, the AC supply device is built into a battery charger, which simplifies the device configuration and makes it easy to start the electrodeposition reduction mode immediately after the battery charging mode.

[0029] In a preferred embodiment, the battery has a charging connector that can be connected to a connector of a charger, and the AC supply circuit has a connector that can be connected to the charging connector, thereby easily realizing the supply of AC to the battery.

[0030] In a preferred embodiment, the AC supply circuit includes a plurality of inductors and a switching circuit that connects the inductors to a battery. The battery discharges in parallel to each inductor. Each inductor charges the battery in turn. The discharging and charging operations are performed alternately. The discharging current contains more harmonic components than the charging current. As a result, the deposition of material in the battery can be reduced.

[0031] In a preferred embodiment, the switching circuit comprises a plurality of half bridges separately connected to the ends of the respective inductors. Each half bridge comprises an upper arm switch and a lower arm switch connected in series. One of the upper arm switch and the lower arm switch comprises a transistor. The other of the upper arm switch and the lower arm switch comprises a transistor or a diode. This can reduce circuit costs.

[0032] According to a second aspect of the present invention, an AC current supply circuit includes a step-down transformer for stepping down an AC voltage. A secondary AC voltage induced in a secondary coil of the step-down transformer is applied to a battery through a smoothing capacitor of a motor drive circuit.

[0033] In other words, the battery, the smoothing capacitor and the secondary coil form a closed loop circuit. This AC current supply device can implement an AC heating mode, a dendrite reduction mode and a residual charge discharge mode. The electrodeposition reduction mode includes a dendrite reduction mode and a residual charge discharge mode. Since this closed loop circuit uses the smoothing capacitor of the motor drive circuit, the circuit is very simple and the wiring structure is also very simple.

[0034] According to a preferred embodiment, the step-down transformer uses a transformer of an on-board charger installed in the electric propulsion system, thereby making it possible to reduce circuit costs.

[0035] According to a preferred embodiment, the on-board charger includes a grid-side converter, a step-down transformer, and a battery-side converter. The grid-side converter applies a high-frequency voltage to a grid-side coil of the step-down transformer, and the battery-side converter rectifies the high-frequency voltage applied from the battery-side coil of the step-down transformer and applies it to the battery. Preferably, the grid-side converter or the battery-side converter also functions as an oscillator of the AC supply device. [Brief description of the drawings]

[0036] [Figure 1]FIG. 1 is a schematic circuit diagram showing an AC current supply circuit that implements a conventional battery heating mode. [Diagram 2] 2 is a timing chart showing an example of an AC current waveform employed in the battery heating mode of FIG. 1. [Diagram 3] FIG. 4 is a schematic cross-sectional view for explaining a residual charge discharging mode in the first embodiment. [Figure 4] 4 is a timing chart showing an AC current waveform employed in the first embodiment. [Diagram 5] 5A to 5C are schematic cross-sectional views showing charge transfer during a charging period and a discharging period in the first embodiment. [Figure 6] FIG. 11 is a schematic cross-sectional view for explaining a discharge period in a dendrite reduction mode in the second embodiment. [Figure 7] FIG. 11 is a schematic cross-sectional view for explaining a charging period in a dendrite reduction mode in the second embodiment. [Figure 8] FIG. 11 is a block circuit diagram showing an AC current supply circuit according to a third embodiment. [Figure 9] 13 is a timing chart showing an AC current waveform employed in the third embodiment. [Figure 10] 4 is a flowchart for explaining an AC current supply mode in each of the above embodiments. [Figure 11] FIG. 13 is a block circuit diagram showing an AC current supply circuit according to a fourth embodiment. [Figure 12] FIG. 12 is a circuit diagram showing another example of the circuit shown in FIG. [Figure 13] FIG. 12 is a circuit diagram showing another example of the circuit shown in FIG. [Figure 14] FIG. 13 is a block circuit diagram showing an AC current supply circuit according to a fifth embodiment. [Figure 15] FIG. 15 is a circuit diagram illustrating the flux sum mode of the circuit shown in FIG. [Figure 16] FIG. 15 is a circuit diagram showing a magnetic flux difference mode of the circuit shown in FIG. [Figure 17] FIG. 13 is a circuit diagram showing an AC current supply circuit according to a sixth embodiment. [Figure 18]18 is a flowchart showing an example of control of the circuit in FIG. 17. [Figure 19] FIG. 13 is a schematic diagram showing an AC current supply circuit according to a seventh embodiment. [Figure 20] FIG. 20 is a circuit diagram showing an example of the circuit of FIG. 19. [Figure 21] 21 is a timing chart showing a schematic diagram of an AC current flowing through the circuit shown in FIG. 20. [Figure 22] FIG. 13 is a circuit diagram showing an AC current supply circuit according to an eighth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] The alternating current supply device of the present invention will be described with reference to several embodiments. The device has a mode of supplying alternating current to a battery consisting of a plurality of cells connected in series in order to suppress battery degradation. The alternating current supply mode includes an electrodeposition reduction mode in which an alternating current is supplied to a battery at room temperature, and a battery heating mode in which an alternating current is supplied to a battery at a low temperature. The electrodeposition reduction mode includes a residual charge discharge mode and a dendrite reduction mode. The residual charge discharge mode includes a discharge operation that dissipates charge on the surface of the negative electrode active material. The dendrite reduction mode includes a discharge operation that reduces dendrites growing from the negative electrode active material toward the positive electrode active material.

[0038] First Example The residual charge discharge mode is described with reference to Fig. 3. Fig. 3 shows the charge state near the negative electrode of a non-aqueous electrolyte type lithium ion cell 700. In Fig. 3, (A) shows the charge state during the charging period, (B) shows the charge state during the release period immediately after charging, and (C) shows the charge state during the discharging period immediately after charging.

[0039] 3 is a schematic cross-sectional view conceptually showing a cross section of a cell 700, and shows only an electrolyte 502, a negative electrode active material 503, and a negative electrode current collector 504 of the cell 700. The surface of the negative electrode active material 503 in contact with the electrolyte 502 is called an interface 505. The interface 505 has an SEI (Solid Electrolyte interface) coating (not shown). The separator, positive electrode active material, and positive electrode current collector of the cell 700 are omitted from the illustration.

[0040] The interface 505 is represented by a capacitor C2 and a resistor R0 connected in parallel. The negative electrode active material 503 is represented by an electrical resistor R3, and the capacitor C2 is represented as an electric double layer capacitor including an SEI film. The resistor R0 is represented as a leakage resistance of the SEI film. The resistor R0 and the electrical resistor R3 each include an ionic resistance component and an electronic resistance component. The ionic resistance component is related to the resistance to migration of lithium ions. The electronic resistance component is related to the resistance to migration of electrons.

[0041] In general, most of the resistor R0 is composed of an ionic resistance component. It is known that the electronic resistance component contained in the resistor R0 has a significantly higher electrical resistance value than the ionic resistance component. In FIG. 3, the resistor R0 is shown diagrammatically by an ionic resistance component R01 and an electronic resistance component R02 connected in parallel. The negative electrode active material 503 is composed of a carbon material such as graphite, soft carbon, or hard carbon. However, the negative electrode active material 503 may be a silicon anode or a metallic lithium anode.

[0042] The charge states of the cell 700 during the charging period, the release period, and the discharging period are described below. First, the charge state (A) during the charging period is described. A charging current is supplied to the cell 700. Lithium ions in the electrolyte 502 pass through the interface 505 and are inserted into the negative electrode active material 503. At the same time, electrons flow from the negative electrode collector 504 to the negative electrode active material 503. Some of the lithium ions that reach the interface 505 are not inserted into the negative electrode active material 503. As a result, electrons are supplied from the negative electrode collector 504 to the interface 505 through the negative electrode active material 503. This charges the capacitor C2.

[0043] Next, the charge state (B) during the open period will be described. During this open period, which starts immediately after the end of charging, the current flowing between the cell 700 and the external circuit becomes zero, and the voltage of the cell 700 becomes the so-called open voltage value. However, at the beginning of the open period, the capacitor C2 discharges through the ion transfer path and the electron transfer path. The ion transfer path has a resistance R01, and the electron transfer path has a resistance R02.

[0044] In discharging via the ion migration path, the lithium ions stored in the capacitor C2 diffuse into the negative electrode active material 503 through the resistor R01. In discharging via the electron migration path, the electrons stored in the capacitor C2 move to the electrolyte side surface of the capacitor C2 through the resistor R02. In other words, the electrons cross the SEI film. As a result, the lithium ions that have gained these electrons become metallic lithium.

[0045] Furthermore, some of the electrons that move from the negative electrode active material 503 to the surface of the SEI coating through the SEI coating combine with lithium ions in or on the SEI coating. As a result, some of the lithium ions stored in the capacitor C2 become metallic lithium that is liberated inside or on the SEI coating during the open period. This phenomenon is called electrodeposition during the open period.

[0046] Next, the charge state (C) during the discharge period that starts immediately after charging will be described. A discharge current is supplied to the cell 700. The lithium ions in the negative electrode active material 503 move to the electrolyte 502, and the electrons in the negative electrode active material 503 move to the negative electrode current collector 504. Thus, the cell 700 is discharged. Furthermore, the lithium ions stored in the capacitor C2 move to the electrolyte 502, and the electrons stored in the capacitor C2 return to the negative electrode active material 503. Thus, the capacitor C2 is also discharged.

[0047] From the above description, it can be understood that it is preferable to perform the discharging period immediately after the end of the charging period. In other words, it is preferable to shorten the open period. This can suppress electrodeposition during the open period. However, discharging immediately after charging reduces the remaining capacity of the battery. This embodiment solves this problem by implementing a residual charge discharging mode.

[0048] This residual charge discharging mode will be described with reference to FIG. 4. FIG. 4 is a timing chart showing an AC current Iac supplied to the cell 700. A residual charge reduction period (Tx) is placed immediately after the end of a charging period (Tcm). A charging current Icm is supplied to the cell 700 during the charging period (Tcm). The residual charge reduction period (Tx) is composed of a discharging period Td and a charging period Tc which are alternately repeated. A discharging pulse current Id is supplied to the cell 700 during the discharging period Td. A charging pulse current Ic is supplied to the cell 700 during the charging period Tc. In other words, the AC current Iac is composed of a discharging pulse current Id and a charging pulse current Ic which have the same pulse frequency. The discharging pulse current Id discharges the capacitor C2, and the charging pulse current Ic charges the capacitor C2.

[0049] In Fig. 4, the discharge pulse current Id consists of four pulse currents (Id1, Id2, Id3, and Id4) whose amplitudes gradually decrease. Similarly, the charge pulse current Ic consists of three pulse currents (Ic1, Ic2, and Ic3) whose amplitudes gradually decrease. The average amplitude of the discharge pulse current Id in the discharge period Td is set higher than the average amplitude of the charge pulse current Ic in the charge period Tc. However, the discharge period Td is set shorter than the charge period Tc.

[0050] Moreover, the integral value of the discharge current Id is approximately equal to the integral value of the charge current Ic. As a result, this residual charge discharging mode hardly reduces the State of Charge (SoC) of the cell 700. The discharge current Id and the charge current Ic can also adopt other current waveforms instead of the pulse current waveforms shown in FIG.

[0051] The effect of the residual charge discharge mode of this embodiment using the AC current waveform shown in FIG. 4 will be explained with reference to FIG. 5. FIG. 5 shows the charge state (A) during the charging period Tc and the charge state (C) during the discharging period Td. In the charge state (A) during the charging period Tc, lithium ions move from the electrolyte 502 to the negative electrode active material 503 through the resistor R0. Furthermore, the lithium ions charge the capacitor C2. In the charge state (C) during the discharging period Td, lithium ions move from the negative electrode active material 503 to the electrolyte 502 through the resistor R0. Furthermore, the lithium ions discharge the capacitor C2.

[0052] 4, the discharge pulse current Id contains more harmonic current components than the charge pulse current Ic. In other words, the AC current Iac flowing through the cell 700 is composed of a fundamental frequency component and a harmonic component. The harmonic component has a higher frequency than the fundamental frequency component.

[0053] The interface 505 is represented by an AC impedance consisting of a resistor R0 and a capacitor C2 connected in parallel. The AC impedance of the capacitor C2 is low for high-frequency current components and high for low-frequency current components. Therefore, the discharge pulse current Id flows through the capacitor C2 relatively more than the charge pulse current Ic. Conversely, the charge pulse current Ic flows through the resistor R0 relatively more than the discharge pulse current Id.

[0054] 5, the discharge current Id can be considered to be composed of the discharge current Ida flowing through the capacitor C2 and the discharge current Idb flowing through the resistor R0. Similarly, the charge current Ic can be considered to be composed of the charge current Ica flowing through the capacitor C2 and the charge current Icb flowing through the resistor R0. Due to the difference in harmonic components, the discharge current Ida increases relatively more than the charge current Ica.

[0055] Eventually, when the alternating current Iac having the current waveform shown in Fig. 4 is supplied to the cell 700, the capacitor C2 is discharged. As a result, the lithium ions stored in the capacitor C2 are returned to the electrolyte 502 by the alternating current Iac having the current waveform shown in Fig. 4.

[0056] Furthermore, the lithium ions pass through an interface 505 that is equivalent to the parallel connection of the capacitor C2 and the resistor R0. However, in the high frequency region, the lithium ions are slow to respond to the applied AC voltage. As a result, the resistance R0 becomes high in the high frequency region and low in the low frequency region. Therefore, the discharge current Id, which contains a relatively large amount of high frequency components, flows through the capacitor C2 more easily than the charge current Ic, which contains a relatively large amount of low frequency components. Ultimately, when the discharge current component Id contains a relatively large amount of high frequency components compared to the charge current component Ic, the discharge current component Id discharges the residual charge of the capacitor C2 well.

[0057] The effect obtained by the charging current Ic and the discharging current Id forming an alternating current is further explained. The charging current Ic increases the electrodeposition, and the discharging current Id decreases the electrodeposition. Therefore, the charging current Ic and the discharging current Id, which have different effects from each other, should be analyzed separately. The charging current Ic consists of a fundamental frequency component and a harmonic component. Similarly, the discharging current Id also consists of a fundamental frequency component and a harmonic component. The harmonic component of the discharging current Id has a higher amplitude than the harmonic component of the charging current Ic. In other words, the harmonic component of the discharging current Id has a higher power energy than the harmonic component of the charging current Ic. As a result, the fundamental component of the charging current Ic has a higher power energy than the fundamental component of the discharging current Id. High frequency currents flow more easily through the capacitors C1 and C2 than low frequency currents. Furthermore, high frequency currents flow less easily through the ion transport resistor R3. As a result, the discharging current Id, which has a richer harmonic component than the charging current Ic, can have a superior electrodeposition reduction effect.

[0058] Second Example The dendrite reduction mode will be described with reference to Figs. 6 and 7. Fig. 6 is a schematic cross-sectional view showing a charging state of one cell 700 of a non-aqueous electrolyte type lithium ion battery. An AC power source 600 supplies a charging current Ic to the cell 700. Fig. 7 is a schematic cross-sectional view showing a discharging state of the cell 700. The AC power source 600 supplies a discharging current Id to the cell 700. The AC current supplied to the cell 700 consists of a charging current Ic and a discharging current Id that are supplied alternately. The discharging current Id has a relatively high amplitude compared to the charging current Ic. The discharging period during which the discharging current Id is supplied to the cell 700 is relatively short compared to the charging period during which the charging current Ic is supplied to the cell 700. The integral value of the discharging current Id is approximately equal to the integral value of the charging current Ic.

[0059] The cell 700 has a positive electrode current collector 500, a positive electrode active material 501, an electrolyte 502, a negative electrode active material 503, and a negative electrode current collector 504. The electrolyte 502 is injected into the gap between the positive electrode active material 501 and the negative electrode active material 503. A separator (not shown) is inserted into the gap. The surface of the negative electrode active material 503 facing the gap is called the interface 505. A dendrite 703 grows from a partial area of ​​the negative electrode active material 503. However, FIG. 6 and FIG. 7 show a schematic shape of the dendrite 703. The surface of the positive electrode active material 501 facing the gap is called the positive electrode interface 506. Two current paths 701 and 702 are formed in the cell 700. The current path 701 that does not pass through the dendrite 703 is called the non-dendritic path. The current path 702 that passes through the dendrite 703 is called the dendritic path.

[0060] In the non-dendritic current path 701, the positive electrode active material 501 has an electric resistance R1, the electrolyte 502 has an electric resistance R2, the interface 505 has an electric resistance R0, and the negative electrode active material 503 has an electric resistance R3. The electric resistance R0 is called the interfacial resistance. The interface 505 has a capacitor C2 connected in parallel with the electric resistance RO. The capacitor C2 is called the interfacial capacitor.

[0061] In the dendritic current path 702, the positive electrode active material 501 has an electric resistance r1, the electrolyte 502 has an electric resistance r2, and the negative electrode active material 503 has an electric resistance r3. The surface of the dendrite 703 has an electric resistance r0 and a capacitor C1 connected in parallel. The electric resistance r0 is called the dendritic resistance, and the capacitor C1 is called the dendritic capacitor.

[0062] (Charge transfer during charging) First, the charge transfer of the non-dendritic current path 701 during the charging period is described with reference to FIG. 6. Lithium ions move in the order of the positive electrode active material 501, the electrolyte 502, the interface 505, and the negative electrode active material 503. Furthermore, electrons move from the negative electrode current collector 504 to the negative electrode active material 503. In this embodiment, the electrical resistance R3 of the negative electrode active material 503 is regarded as an ion transfer resistance. The interface 505 consists of an interface resistance R0 and an interfacial capacitor C2 connected in parallel. Therefore, as described in the first embodiment, the interfacial capacitor C2 is charged by lithium ions during the charging period.

[0063] Next, the charge transfer of the dendrite current path 702 during the charging period will be described with reference to FIG. 6. During the charging period shown in FIG. 6, lithium ions move in the order of the positive electrode active material 501, the electrolyte 502, and the dendrite 703. In this embodiment, the transfer of lithium ions from the dendrite 703 to the negative electrode active material 503 is ignored. As a result, electrons move from the negative electrode current collector 504 to the dendrite 703 through the negative electrode active material 503. In this embodiment, the electrical resistance r3 of the negative electrode active material 503 is regarded as an electron transfer resistance. The electrical resistance of the dendrite 703 made of metallic lithium is ignored. The surface of the dendrite 703 is represented by a dendrite resistance r0 and a dendrite capacitor C1 connected in parallel. The dendrite capacitor C1 is charged by lithium ions during the charging period.

[0064] (Charge transfer during discharge) Next, the charge transfer of the non-dendritic current path 701 during the discharge period will be described with reference to FIG. 7. Lithium ions move in the order of the negative electrode active material 503, the interface 505, the electrolyte 502, and the positive electrode active material 501. Similarly, electrons move from the negative electrode active material 503 to the negative electrode current collector 504. According to this embodiment, the electrical resistance R3 of the negative electrode active material 503 is considered to correspond to the ion transfer resistance. At the beginning of the discharge period, the interfacial capacitor C2 is discharged.

[0065] Next, the charge transfer of the dendritic current path 702 during the discharging period will be described with reference to Fig. 7. In the dendritic current path 702, metallic lithium on the surface of the dendrite 703 is converted to lithium ions, which are dissolved into the electrolyte 502 and then inserted into the positive electrode active material 501. Electrons accumulated on the dendrite 703 transfer to the negative electrode current collector 504 through the negative electrode active material 503. The electrical resistance r3 of the negative electrode active material 503 is regarded as an electron transfer resistance. During the discharging period, the dendritic capacitor C1 is discharged.

[0066] The difference between the non-dendritic path 701 and the dendritic path 702 will be explained. The electrical resistance R3 of the non-dendritic path 701 is composed of ion transfer resistance. On the other hand, the electrical resistance r3 of the dendritic path 702 is composed of electron transfer resistance. The ionic resistance R3 of the negative electrode active material 503 is relatively high compared to the electronic resistance r3 of the negative electrode active material 503. Furthermore, when the amplitude of the alternating current composed of the discharge current Id and the charge current Ic increases, the ionic resistance R3 of the negative electrode active material 503 increases. Furthermore, when the frequency of the alternating current increases, the ionic resistance R3 of the negative electrode active material 503 increases. In other words, the resistance value of the ionic resistance R3 has a positive correlation with the frequency of the alternating current. As a result, when the amplitude and / or frequency of the alternating current increases, the electrical resistance R3 increases relatively compared to the electrical resistance r3.

[0067] Therefore, the current flowing through the dendritic path 702 increases relatively in the high current and high frequency regions compared to the current flowing through the non-dendritic path 701 .

[0068] In this embodiment, the discharge current Id has a higher average amplitude than the charge current Ic, and also has a higher frequency. Therefore, the discharge current Id flows through the electrical resistance r3 relatively more than the electrical resistance R3. On the other hand, the charge current Ic flows through the electrical resistance R3 relatively more than the electrical resistance r3. Ultimately, the discharge current Id flows through the dendrite 703 more easily than the charge current Ic. As a result, the dissolution of the dendrite 703 caused by the discharge current Id flowing through the dendrite 703 exceeds the precipitation of the dendrite 703 caused by the charge current Ic flowing through the dendrite 703. Furthermore, according to this second embodiment, the dendrites can also be reduced by the residual charge reduction effect described in the first embodiment.

[0069] Third Example A third embodiment will be described with reference to Fig. 8. This embodiment discloses an AC current supply device for a battery that can economically realize the AC current supply to the battery employed in the first and second embodiments. This AC current supply device for a battery mounted on an electric vehicle circulates an AC current in a closed loop circuit consisting of a battery 1, a capacitor 2, and a secondary coil 5. The secondary coil 5 is wound around the core of a step-down transformer 13 together with a primary coil 8. A full bridge circuit 4, also called an H-bridge, applies an AC voltage to the primary coil 8.

[0070] The full-bridge circuit 4 is composed of four MOSFETs 41-44. The output terminal of a first half-bridge composed of the MOSFETs 41 and 42 is connected to one end of a primary coil 8. The output terminal of a second half-bridge composed of the MOSFETs 43 and 44 is connected to the other end of the primary coil 8 through a low-resistance element 81 for current detection. High-frequency noise current generated by the full-bridge circuit 4 is bypassed by a capacitor 80. The full-bridge circuit 4 is complementarily controlled by a PWM (pulse width modulation) method.

[0071] A low resistance element 81 for current detection detects a signal voltage Vs proportional to a primary current I1 supplied to the primary coil 8. A rectifier circuit 82 rectifies the signal voltage Vs. The rectifier circuit 82 includes a low-pass filter that outputs a low-frequency component VsL of the rectified voltage. A comparator 83 outputs a pulse voltage Vp1, which is a result of comparing the low-frequency component VsL with a reference voltage Vr1, to the controller 30. A comparator 84 outputs a pulse voltage Vp2, which is a result of comparing the low-frequency component VsL with a reference voltage Vr2, to the controller 30.

[0072] The pulse voltage Vp1 is at a high level when the low-frequency component VsL is lower than the reference voltage Vr1. The pulse voltage Vp2 is at a high level when the low-frequency component VsL is higher than the reference voltage Vr2. The controller 30 controls the gate drive signal voltages VG1-VG4 applied to the MOSFETs 41-44 from the gate drive circuit 85 based on the pulse voltages Vp1 and Vp2.

[0073] The gate drive circuit 85 pulse-width modulates the MOSFETs 41 and 44 from the point when the pulse voltage Vp2 shifts to a high level, and turns off the MOSFETs 42 and 43. The gate drive circuit 85 pulse-width modulates the MOSFETs 42 and 43 from the point when the pulse voltage Vp1 shifts to a high level, and turns off the MOSFETs 41 and 44.

[0074] Fig. 9 shows voltage and current waveforms of the device shown in Fig. 8. Time t1 is the timing when the pulse voltage Vp2 becomes high level. Time t2 is the timing when the pulse voltage Vp1 becomes high level. During a charging period Tc from time t1 to time t2, the secondary coil 5 supplies a charging current Ic to the battery 1. Similarly, during a discharging period Td from time t2 to time t1, the secondary coil 5 supplies a discharging current Id to the battery 1.

[0075] The MOSFETs 41 and 44 are controlled by a pulse width modulation method during the discharging period Td, which has a PWM duty ratio Dd. Similarly, the MOSFETs 42 and 43 are controlled by a pulse width modulation method during the charging period Tc, which has a PWM duty ratio Dc. The discharging PWM duty ratio Dd is approximately twice the charging PWM duty ratio Dc.

[0076] As a result, the discharge current Id flowing through the secondary coil 5 is approximately twice the charge current Ic. Because the charge current Ic is relatively low, the increase rate of the low-frequency component VsL output from the rectifier circuit 82 to the comparators 83 and 84 is relatively low during the charging period Tc. As a result, the charging period Tc is approximately twice the discharge period Td.

[0077] The total amount of discharged charge during the discharging period Td is approximately equal to the total amount of charged charge of the battery 1 during the charging period Tc. This suppresses changes in the SOC of the battery 1, and reduces the residual magnetic flux of the step-down transformer 13.

[0078] The full bridge circuit 4 controlled by the gate drive signal voltages VG1-VG4 applies a PWM voltage to the capacitor 80. The capacitor 80 absorbs high-frequency noise voltages including the PWM carrier voltage. According to this embodiment, the AC current I2 flowing through the secondary coil 5 is composed of a charging current Ic and a discharging current Id. The charging current Ic and the discharging current Id can each have a desired waveform. However, the circuit shown in FIG. 8 is only an example, and many circuit modifications are possible.

[0079] According to this embodiment, the average value of the discharge current Id during the discharge period Td is approximately twice as large as the average value of the charge current Ic during the charge period Tc. Furthermore, the battery charge period Tc is approximately twice as long as the battery discharge period. As a result, the integral value of the AC current I2 flowing through the battery 1 becomes approximately zero.

[0080] An example of the charging control of this device will be described with reference to the flowchart shown in Fig. 10. This charging control starts when the commercial grid or an external fast charger supplies charging power to the battery 1. This charging control includes a battery heating mode (S102), a standard charging mode (S108), and a fast charging mode (S112).

[0081] First, it is determined whether the temperature T of the battery 1 is lower than a predetermined threshold value Vth, for example 0° C. (S100), and if Yes, the battery heating mode (S102) is implemented.

[0082] According to the battery heating mode, the H-bridge 4 applies an AC voltage to the primary coil 8. The frequency of this AC voltage is, for example, 8000 Hz. This causes a high-rate secondary current to be supplied to the secondary coil 5. As a result, the battery 1 is heated.

[0083] Next, it is determined whether the temperature T of the battery 1 is higher than a predetermined threshold value Vth (S104). If No, the battery heating mode (S102) is continued, and if Yes, the battery heating mode is ended.

[0084] Next, it is determined whether or not the quick charging mode has been selected (S106). If the quick charging mode has not been selected, the standard charging mode is executed (S108). In this standard charging mode, an on-board charger (not shown) mounted on the electric vehicle is connected to an external grid. This on-board charger boosts the rectified grid voltage and supplies a charging current to the battery 1. Next, it is determined whether or not the SOC of the battery 1 has reached a predetermined level, and if Yes, the standard charging mode is terminated (S110).

[0085] If the quick charge mode is selected in step S106, the quick charge mode is executed (S112). In this quick charge mode, the battery 1 is connected to an external quick charger. Next, it is determined whether the SOC of the battery 1 has reached a predetermined level, and if Yes, the quick charge mode is terminated (S114).

[0086] When the standard charging mode or the rapid charging mode is completed, it is determined whether or not the external electrical load connected to the battery 1 has been turned on (S116). In other words, it is determined whether or not the battery 1 is supplying a high-rate discharge current to the external electrical load. When the battery 1 supplies a high-rate discharge current to the external electrical load, the residual charge stored in the capacitor in the battery 1 is consumed. Furthermore, dendrites formed by the charging current also dissolve into the electrolyte. Therefore, the dendrite reduction mode (S118) and the discharge mode for reducing residual charge (S120) are omitted.

[0087] When the standard charge mode or the rapid charge mode is ended, if the external electric load is not turned on, a dendrite reduction mode (S118) for reducing dendrites and a discharge mode (S120) for discharging residual charge are sequentially carried out. According to the dendrite reduction mode (S118), an AC current having a current waveform shown in Fig. 9 is supplied to the battery 1 immediately after the end of charging. According to the discharge mode (S120) for discharging residual charge, an AC current having a current waveform shown in Fig. 4 is supplied to the battery 1 immediately after the end of the dendrite reduction mode.

[0088] According to this embodiment, the battery heating mode (S102), the dendrite reduction mode (S118), and the residual charge discharge mode (S120) can be sequentially performed by using a common AC current supply device.

[0089] Fourth Example A fourth embodiment will be described with reference to FIG. 11. The electric propulsion system of this embodiment has a high-voltage battery 1, a smoothing capacitor 2, and a junction box 10. The high-voltage battery 1 is a lithium-ion battery with a rated voltage of about 400 V. The smoothing capacitor 2, which is made of a film capacitor with a capacitance of about 0.4 mF, is connected to a pair of DC power supply terminals of a motor drive circuit 20 that drives a traction motor of the EV. The motor drive circuit 20 includes a three-phase inverter. The motor drive circuit 20 may further include a boost chopper circuit for boosting the voltage of the smoothing capacitor 2.

[0090] The high-voltage battery 1 and the smoothing capacitor 2 are connected through a junction box 10. The junction box 10 houses a relay circuit 3, a grid charger 11, a DCDC converter 12, and a controller 30. The relay circuit 3 includes system relays 31 and 34, a pre-charge relay 32, a resistor 33, and safety relays 35 and 36.

[0091] The positive terminal B+ of the battery 1 is connected to the positive terminal C+ of the smoothing capacitor 2 through a relay 31. The negative terminal B- of the battery 1 is connected to the negative terminal C- of the smoothing capacitor 2 through a relay 34 and a secondary coil 5. The secondary coil 5 connects the negative terminal C- of the smoothing capacitor 2 to the system relay 34. The series-connected relay 32 and low resistor 33 are connected in parallel to the system relay 31. In order to precharge the smoothing capacitor 2, the relay 32 is turned on before the relay 31 is turned on.

[0092] A grid charger 11 that charges a battery 1 using grid power includes a grid-side converter 9, a transformer 13, and a battery-side converter 4A. The grid-side converter 9 includes a rectifier 93, a capacitor 92, and an oscillator 91.

[0093] The grid charging mode is initiated when the grid voltage is applied to the rectifier 93. In other words, the grid charging mode is executed after the rectifier 93 of the grid-side converter 9 is connected to the utility grid. Before the grid charging mode is initiated, the relays 31, 32, and 34 are turned off, and the relays 35 and 36 are turned on. According to the grid charging mode, the rectifier 93, which is configured as a diode full bridge, rectifies the single-phase grid voltage to charge the capacitor 92.

[0094] Capacitor 92 supplies DC power to oscillator 91, which is made up of a full-bridge inverter called an H-bridge. Oscillator 91 supplies high-frequency current to coil 7 of transformer 13. Four MOSFETs in H-bridge 91 are PWM-controlled to control the waveform of the high-frequency current.

[0095] The transformer 13 has three coils 5, 7, and 8A wound around a soft magnetic core 13A. The coils 5, 7, and 8A are magnetically coupled by the soft magnetic core 13A. When the oscillator 91 supplies a high-frequency primary current to the coil 7, the battery-side converter 4A as a rectifier rectifies the secondary voltage induced in the coil 8A. The battery-side converter 4A also consists of a full-bridge inverter called an H-bridge. The voltage rectified by the battery-side converter 4A is applied to the battery 1 through relays 35 and 36. In the end, the grid charger 11 can charge the battery 1 using the grid power. The transformer 13 is a step-down transformer.

[0096] The DC-DC converter 12 is composed of a battery-side converter 4B, a transformer 14, and a rectifier 61. The transformer 14 has coils 8B and 6 wound around a soft magnetic core 14A. The battery-side converter 4B, which constitutes an oscillator, applies a high-frequency voltage to the coil 8B. The secondary voltage induced in the coil 6 is rectified by the rectifier 61 and then applied to the low-voltage battery 60.

[0097] In addition to the grid charging mode, the controller 30 has a battery heating mode, which is implemented after the smoothing capacitor 2 is pre-charged. The battery heating mode is implemented when the temperature of the battery 1 is below a predetermined value. In the battery heating mode, a high frequency current circulating between the smoothing capacitor 2 and the battery 1 heats the battery 1.

[0098] The battery heating mode includes two modes: the first battery heating mode is called a battery-connected battery heating mode; the second battery heating mode is called a grid-connected battery heating mode.

[0099] First, the battery heating mode with battery connection will be described. Relays 35 and 36 are turned on, and the battery 1 applies the battery voltage to the battery-side converter 4A. Next, the battery-side converter 4A, which is driven as an oscillator, supplies a high-frequency current to the coil 8A. This induces a high-frequency secondary voltage in the coil 5, and the secondary current circulates in a closed loop circuit consisting of the battery 1, the coil 5, the relay 31, the smoothing capacitor 2, and the relay 34.

[0100] As a result, the battery 1 is efficiently heated by the resistive loss. For example, it is assumed that the internal resistance of the battery 1 is 0.1 ohms and the effective value of the high frequency current is 70 A. As a result, the battery 1 generates a resistive loss of about 490 W. This battery-connected battery heating mode can be implemented during periods when the propulsion motor is stopped and during periods when the propulsion motor is driven.

[0101] However, the battery heating power should be adjusted so that the sum of the high frequency power for the battery heating mode and the power for driving the motor does not exceed a predetermined level. The battery heating power is controlled by PWM control of the H-bridge as the battery side converter 4A. This battery heating mode is terminated when the temperature of the battery 1 reaches a predetermined value.

[0102] Next, the grid-connected battery heating mode will be described. This grid-connected battery heating mode can be implemented simultaneously with the grid charging mode described above, or can be implemented alone. When the battery heating mode and the grid charging mode are implemented together, the battery heating power is suitably controlled so that the current of the battery 1 does not exceed a predetermined value. The oscillator 91 of the grid-side converter 9 is PWM controlled to control the battery heating power.

[0103] First, the sole implementation of the grid-connected battery heating mode will be described. The relays 35 and 36 are turned off, and the relays 31 and 34 are turned on. The grid power rectified by the rectifier 93 is supplied to the oscillator 91. The oscillator 91 applies a primary high-frequency voltage to the coil 7. As a result, a secondary high-frequency voltage is induced in the secondary coil 5, and the battery 1 and the smoothing capacitor 2 are heated by the high-frequency current.

[0104] Next, the case where the grid-tied battery heating mode and the grid charging mode are simultaneously implemented will be described. When the grid-tied battery heating mode is implemented, the relays 35 and 36 are turned on. Capacitor 92 is charged by grid power rectified by rectifier 93. Oscillator 91 powered by capacitor 92 supplies high-frequency current to coil 7. As a result, the high-frequency voltage induced in secondary coil 5 heats battery 1. Furthermore, the secondary voltage induced in coil 8A is rectified by battery-side converter 4A, which serves as a rectifier. This charges battery 1.

[0105] The electrodeposition reduction mode can also be implemented by essentially the same control method as the battery heating mode described above. This electrodeposition reduction mode includes the residual charge discharge mode and the dendrite reduction mode described above. However, the battery heating mode is implemented when the battery temperature is lower than 0° C. On the other hand, the electrodeposition reduction mode is implemented when the battery temperature is higher than the lowest room temperature (e.g., 20° C.). Preferably, the electrodeposition reduction mode is implemented immediately after a charging operation.

[0106] Fig. 12 shows an example of one circuit of the battery-side converter 4A, the transformer 13, and the grid-side converter 9 shown in Fig. 11. In Fig. 12, a cross section of the transformer 13 is shown. Three coils 8A, 5, and 7 are wound around the central pole of a soft magnetic core 13A. The number of turns of the secondary coil 5 is preferably one turn.

[0107] The effect of this embodiment will be described. First, the transformer 13 of the grid charger 11 also serves as a step-down transformer of the AC current supply circuit. Furthermore, the battery-side converter 4A and the grid-side converter 9 of the grid charger 11 also serve as oscillators of the AC current supply circuit. Next, the effect of the inductance of the secondary coil 5 will be described. First, when the relays 31 and 34 are turned off, the so-called contact arc problem of the relays 31 and 34 becomes serious. This problem is solved by applying a secondary reverse voltage to the secondary coil 5 when the relays 31 and 34 are turned off. When the relays 31 and 34 are turned off, the battery-side converter 4A applies a primary reverse voltage to the primary coil 8A. As a result, a secondary reverse voltage is induced in the secondary coil 5. The direction of this secondary reverse voltage is opposite to the direction of the current flowing through the secondary coil 5. As a result, the adverse effect of the secondary coil 5 when the relays 31 and 34 are turned off is suppressed.

[0108] Furthermore, the technique of inducing a secondary reverse voltage in the secondary coil 5 can be used to suppress the inrush current flowing through the smoothing capacitor 2 by turning on the pre-charge relay 32. First, by turning on relays 35 and 36, the battery-side converter 4A applies a primary reverse voltage to the coil 8A. This induces a secondary reverse voltage in the secondary coil 5. The direction of this secondary reverse voltage is a direction that reduces the inrush current flowing through the smoothing capacitor 2. This reduces the inrush current.

[0109] A variant of the transformer 13 and transformer 14 shown in Fig. 11 will be described with reference to Fig. 13. The soft magnetic core 15A of the transformer 15 shown in Fig. 13 has a first pole 101A, a second pole 101B, and a third pole 101C. The soft magnetic core 15A further has cross bars 101D, 101E, 101F, and 101G. Coils 5, 7, 8A are wound on the first pole 101A, and coils 6 and 8B are wound on the third pole 101C. The second pole 101B has no coil.

[0110] Thus, the magnetic flux of the coils 5, 7, and 8A flows through a closed loop magnetic path formed by the first pole 101A, the cross bar 101D, the second pole 101B, and the cross bar 101E. Similarly, the magnetic flux of the coils 6 and 8B flows through a closed loop magnetic path formed by the third pole 101C, the cross bar 101F, the second pole 101B, and the cross bar 101G.

[0111] 13 corresponds to the two transformers 13 and 14 shown in FIG 11. However, the soft magnetic core 15A of the transformer 15 is more compact than the soft magnetic cores 13A and 14A of the two transformers 13 and 14.

[0112] Fifth Example A fifth embodiment will be described with reference to Fig. 14. The electric propulsion system of this embodiment is similar to the electric propulsion system shown in Fig. 11. However, this embodiment uses one transformer 16 instead of the two transformers 13 and 14 shown in Fig. 11. Furthermore, this embodiment uses two coils 6A and 6B connected in series instead of the one coil 6 shown in Fig. 13.

[0113] The transformer 16 has six coils 5, 7, 8A, 8B, 6A, and 6B. The battery-side converter 4A is connected to the coil 8A, and the battery-side converter 4B is connected to the coil 8B. The two coils 6A and 6B connected in series are connected to a rectifier 61.

[0114] A positive terminal B+ of the high-voltage battery 1 is connected to a positive terminal C+ of the smoothing capacitor 2 through a relay 31. A negative terminal B- of the battery 1 is connected to a negative terminal C- of the smoothing capacitor 2 through a relay 34 and a coil 5. A three-phase inverter 20 for driving a motor is connected in parallel with the smoothing capacitor 2. A relay 32 and a low resistance element 33 are connected in series with each other and connected in parallel with the relay 31. The battery-side converters 4A and 4B are connected to the battery 1 through relays 35 and 36.

[0115] The coil 7 is connected to the electric grid through a grid-side converter 9. The grid-side converter 9 has an oscillator 91, a capacitor 92, and a rectifier 93 connected to the coil 7. The grid voltage is rectified by the rectifier 93. The rectified DC voltage charges the capacitor 92. The oscillator 91 converts the DC power of the capacitor 92 into high-frequency power and supplies it to the coil 7. In conclusion, the grid charger described above is formed by the grid-side converter 9, the coil 7, the coils 8A and 8B, and the battery-side converters 4A and 4B.

[0116] The battery 1 charges the low-voltage battery 60 through the battery-side converters 4A and 4B, the coils 8A and 8B, the coils 6A and 6B, and the rectifier 61. This operation is called a DCDC converter mode. The battery-side converters 4A and 4B, the coils 8A and 8B, the coils 6A and 6B, and the rectifier 61 form a DCDC converter for charging the low-voltage battery 6. The secondary voltage induced in the series-connected coils 6A and 6B is rectified by the rectifier 61. The rectifier 61 charges the low-voltage battery 60. The low-voltage battery 60, which has a rated voltage of 12 V, supplies control power to the controller 30.

[0117] Furthermore, the secondary coil 5 forms a closed loop circuit together with the battery 1 and the smoothing capacitor 2. The secondary voltage induced in the coil 5 causes a high-frequency current to circulate in this closed loop circuit.

[0118] The following describes the operation modes implemented by the controller 30. The controller 30 has a motor drive mode, a grid charging mode, a grid-connected battery heating mode, a battery-connected battery heating mode, and a DC-DC converter mode. These modes will be described in turn.

[0119] First, the grid charging mode will be described. First, relays 35 and 36 are turned on. When a rectifier 93 consisting of a diode bridge is connected to the 200 ACV electric grid, the rectifier 93 rectifies the grid voltage and charges a capacitor 92. An oscillator 91 connected to the capacitor 92 supplies a high frequency current to the primary coil 7.

[0120] As a result, the secondary voltage induced in the secondary coil 8A is rectified by the battery-side converter 4A and applied to the battery 1. Similarly, the secondary voltage induced in the secondary coil 8B is rectified by the battery-side converter 4B and applied to the battery 1. The secondary coils 8A and 8B have the same number of turns. Ultimately, the battery-side converters 4A and 4B as rectifiers charge the battery 1 in parallel.

[0121] Next, the grid-connected battery heating mode will be described. This grid-connected battery heating mode is implemented when the temperature of the battery 1 is low and the rectifier 93 is connected to the electric grid. First, the relays 31 and 34 are turned on. The rectifier 93 rectifies the grid voltage to charge the capacitor 92. The oscillator 91 connected to the capacitor 92 supplies a high-frequency current, for example, 8 kHz, to the primary coil 7. The secondary voltage induced in the secondary coil 5 causes a high-frequency current to flow in the closed loop circuit consisting of the coil 5, the battery 1, and the smoothing capacitor 2, and the battery 1 is heated. When the temperature of the battery 1 reaches a predetermined value, this grid-connected battery heating mode ends.

[0122] Next, the DCDC converter mode will be described. First, the relays 35 and 36 are turned on. In this DCDC converter mode, the battery-side converters 4A and 4B each operate as an oscillator. The battery-side converter 4A supplies a high-frequency current to the coil 8A, and the battery-side converter 4B supplies a high-frequency current to the coil 8B. The sum of the secondary voltages induced in the coils 6A and 6B is rectified by the rectifier 61 and applied to the low-voltage battery 60. The battery-side converters 4A and 4B are PWM-controlled according to the voltage of the low-voltage battery 60.

[0123] Next, the battery-connected battery heating mode will be described. The rectifier 93 is disconnected from the electric grid. First, the relays 31, 34, 35, and 36 are turned on. The battery-side converters 4A and 4B operating as oscillators supply high-frequency currents to the coils 8A and 8B, and a secondary voltage is induced in the secondary coil 5. As a result, the high-frequency current flows through a closed loop circuit consisting of the battery 1, the smoothing capacitor 2, and the coil 5, and the battery 1 is heated. Note that when the battery-connected battery heating mode and the motor driving mode are simultaneously performed, the high-frequency current is limited so that the maximum current flowing through the battery 1 is less than a predetermined threshold value.

[0124] According to this embodiment, both the battery-connected battery heating mode and the DCDC converter mode use the battery-side converters 4A and 4B as oscillators. Therefore, when the oscillators 4A and 4B supply primary current to the coils 8A and 8B, secondary voltages are induced in the coils 5, 6A, and 6B as secondary coils. In other words, the battery-connected battery heating mode and the DCDC converter mode are implemented simultaneously. However, it is preferable that the battery-connected battery heating mode and the DCDC converter mode are implemented independently, respectively. This problem is solved by adopting a special transformer 16 called a flux-switching transformer.

[0125] 15 and 16 are schematic cross-sectional views showing an example of the structure of the transformer 16. The soft magnetic core 16A has three poles 101A, 101B, and 101C, and four cross bars 101D, 101E, 101F, and 101G. The poles 101A, 101D, 101B, and 101E form a first closed magnetic circuit. The poles 101C, 101F, 101B, and 101G form a second closed magnetic circuit.

[0126] To avoid magnetic saturation, each of these closed magnetic circuits has a narrow air gap. Cross bars 101D and 101F magnetically short-circuit the upper ends of the three poles 101A, 101B, and 101C. Similarly, cross bars 101E and 101G magnetically short-circuit the lower ends of the three poles 101A, 101B, and 101C.

[0127] Coils 8A and 6A are wound around pole 101A, and coils 8B and 6B are wound around pole 101C. In other words, coils 8A and 6A are wound around the first closed magnetic circuit, and coils 8B and 6B are wound around the second closed magnetic circuit. However, coils 8A, 6A, 8B, and 6B are not wound around pole 101B, which is a common magnetic path of the first and second closed magnetic circuits.

[0128] The series connected coils 6A and 6B have equal turns. The coils 8A and 8B have equal turns. The coils 5 and 7 are wound around the pole 101B. The coil 5 preferably has one turn. In the transformer 16, the magnetic coupling between the coils 8A and 8B and the coil 5 is called the flux sum coupling, and the magnetic coupling between the coils 8A and 8B and the coils 6A and 6B is called the flux difference coupling.

[0129] 15 and 16, the battery-side converter 4A connected to the coil 8A is composed of an H-bridge having two legs 401 and 402. Similarly, the battery-side converter 4B connected to the coil 8B is composed of an H-bridge having two legs 403 and 404.

[0130] The controller 30 having the flux sum mode and the flux difference mode selects either the flux sum coupling or the flux difference coupling by switching the direction of the primary current supplied from the battery side converter 4B to the coil 8B. The flux sum coupling is selected by implementing the flux sum mode, and the flux difference coupling is selected by implementing the flux difference mode. In both the flux sum mode and the flux difference mode, the first primary current I1A supplied from the battery side converter 4A to the coil 8A has the same amplitude value and the same frequency value as the second primary current I1B supplied from the battery side converter 4B to the coil 8B.

[0131] FIG. 15 shows the flow of current and magnetic flux in the flux-sum mode. In this flux-sum mode, the first primary current I1A supplied to the coil 8A has the same phase as the second primary current I1B supplied to the coil 8B. In other words, the first primary current I1A and the second primary current I1B have the same waveform. As a result, the direction of the magnetic flux F1 formed in the pole 101A by the coil 8A is upward, and the direction of the magnetic flux F2 formed in the pole 101C by the coil 8B is also upward. Therefore, the two magnetic fluxes F1 and F2 having the same waveform flow downward in the pole 101B.

[0132] According to this flux sum mode, secondary voltages are induced in coil 5 and coil 7. Since coil 7 is connected to oscillator 91, the effect of the secondary voltage induced in coil 7 is ignored. The secondary voltage induced in coil 5 implements the battery heating mode. That is, this flux sum mode is adopted in the battery heating mode.

[0133] Furthermore, according to this flux sum mode, secondary voltages are induced in the coils 6A and 6B. However, the coils 6A and 6B are connected to each other so that the sum of the secondary voltages of the series-connected coils 6A and 6B is zero. In other words, the secondary voltage applied to the rectifier 61 by the coil 6A is opposite to the secondary voltage applied to the rectifier 61 by the coil 6B. As a result, the sum of the secondary voltages applied to the rectifier 61 by the coils 6A and 6B is zero, and the DC-DC converter mode is not implemented in the flux sum mode.

[0134] FIG. 16 shows the current and flux flow in the flux difference mode. In this flux difference mode, the first primary current I1A supplied to the coil 8A has an opposite phase compared to the second primary current I1B supplied to the coil 8B. In other words, the first primary current I1A and the second primary current I1B have opposite waveforms. The change from the flux sum mode to the flux difference mode is performed by inverting the waveform of the second primary current I1B. This change is easily performed by PWM control of the H-bridge 4B, which is the battery side converter.

[0135] The primary current I1B supplied to the coil 8B by the H-bridge 4B shown in FIG. 16 has an inverse waveform to the primary current I1B supplied to the coil 8B by the H-bridge 4B shown in FIG.

[0136] 16, a first primary current I1A supplied to the coil 8A forms a magnetic flux F1 in the pole 101A, and a second primary current I1B supplied to the coil 8B forms a magnetic flux F2 in the pole 101C. The magnetic flux F1 and the magnetic flux F2 have the same waveform. However, the magnetic flux F1 flows upward through the pole 101A, while the magnetic flux F2 flows downward through the pole 101C.

[0137] As a result, according to this magnetic flux difference mode, magnetic fluxes F1 and F2 having the same waveform flow in opposite directions in pole 101B. This means that the sum of the magnetic fluxes flowing in pole 101B becomes zero. Therefore, the secondary voltages induced in coils 5 and 7 become zero.

[0138] Next, in this magnetic flux difference mode, magnetic flux F1 and magnetic flux F2 having the same direction flow through poles 101A and 101C. As a result, the sum of magnetic flux F1 and magnetic flux F2 induces secondary voltages in coils 6A and 6B, respectively. As a result, coils 6A and 6B apply secondary voltages of the same direction to rectifier 61. Rectifier 61 rectifies the sum of the secondary voltages of the two coils 6A and 6B and applies it to low-voltage battery 60. This magnetic flux difference mode is adopted in a DC-DC converter mode that transmits DC power from battery 1 to battery 60.

[0139] The flow of magnetic flux in the grid charging mode described above will be explained. The oscillator 91 supplies primary power to the coil 7. The coil 7 forms a magnetic flux sum coupling with the coils 8A and 8B. Therefore, the coil 7 wound around the pole 101B passes a magnetic flux F1 through the pole 101A and a magnetic flux F2 through the pole 101C. In other words, half of the magnetic flux formed by the coil 7 flows through the pole 101A, and the other half flows through the pole 101C. Ultimately, the rectifiers 4A and 4B charge the battery 1 in parallel. In this grid charging mode, the sum of the secondary voltages of the coils 6A and 6B connected in series becomes zero. Therefore, the DC-DC converter mode is not implemented.

[0140] Sixth Example Although the protection technology for a relatively large capacity battery such as that used in an electric vehicle has been described in the above embodiment, the present invention is also effective for small capacity batteries installed in small electronic devices and small electric devices such as mobile phones, personal computers, electric drivers, vacuum cleaners, and electric motorcycles.

[0141] An AC current supply device that suppresses deterioration of a small battery will be described with reference to Fig. 17. Battery 1 built into the vacuum cleaner is a lithium-ion battery consisting of four cells 1A, 1B, 1C, and 1D connected in series. Battery 1 has a built-in battery management system 801 called BMS.

[0142] Charging terminals 821 and 822 of the battery 1 are connected to a charger 800. The charger 800 applies a charging voltage formed by rectifying grid power to the battery 1. The controller 30 controls a charging current Ic supplied from the charger 800 to the battery 1 based on the internal state of the battery 1. The charger 800 has a built-in DC power supply and a switching regulator. This DC power supply rectifies and steps down the grid voltage. The switching regulator supplies a charging current formed by using the DC power received from this DC power supply unit to the battery 1. The charger 800 controls battery charging by the well-known CCCV method.

[0143] Furthermore, a discharge circuit 830 is connected to the charging terminals 821 and 822 of the battery 1. This discharge circuit 830 is made up of a MOSFET 802 and a discharge resistor 803 connected in series. When the MOSFET 802 is turned on, the battery 1 is discharged through the discharge resistor 803.

[0144] After the battery charging by the CCCV method is completed, the controller 30 executes the electrodeposition reduction mode. In the electrodeposition reduction mode, the controller 30 alternately performs the charging operation of the charger 800 and the discharging operation of the discharging circuit 830. One cycle period during which one charging operation and one discharging operation are performed in sequence consists of a charging period and a discharging period.

[0145] In one example, one cycle period is 200 μs, the charging period is 120 μs, and the discharging period is 60 μs. The transition periods arranged between the charging period and the discharging period are each 10 μs. The average value of the discharging current flowing during the discharging period is about twice the average value of the charging current flowing during the charging period. Preferably, the discharging circuit 830 is built into the charger 800. According to this embodiment, the prevention of battery deterioration by supplying AC current can be achieved with a simple circuit.

[0146] Next, a preferred example of control of the charger 800 and the discharge circuit 830 by the controller 30 will be described with reference to the flow chart shown in Figure 18. The discharge mode is the residual charge discharge mode described in Figures 3 to 5. The dendrite reduction mode is the mode described in Figures 6 and 7. The dendrite reduction mode and the discharge mode are essentially the same, and have current waveforms, for example, as shown in Figure 9.

[0147] First, it is determined whether constant current charging (CC) has ended (S200). Next, the amplitude, cycle period, and supply time of the AC current to be supplied to the battery 1 are determined based on the details of the constant current charging (CC) (S202). Preferably, the average amplitude and supply time of the AC current are positively correlated with the product of the amplitude and charge time of the charging current in the constant current charging (CC). Preferably, a map showing the relationship between the average amplitude and supply time of the AC current and the product of the amplitude and charge time of the charging current is used.

[0148] Next, the dendrite reduction mode is performed based on the determined AC current specifications (S204). Next, the controller 30 starts the constant voltage charging (CV) mode after judging the end of the dendrite reduction mode (S206). In other words, the dendrite reduction mode is performed before the constant voltage charging (CV) mode. The amount of electrodeposition in the constant current charging (CC) mode is far greater than the amount of electrodeposition in the constant voltage charging (CV) mode. Therefore, by performing the dendrite reduction mode before a thick SEI film is formed on the surface of the electrodeposited material, dendrites can be effectively reduced.

[0149] Next, it is determined whether the constant voltage charging (CV) mode has ended (S206), and if so, the discharging mode (residual charge discharging mode) is executed (S208).

[0150] Seventh Example One drawback of the device of the sixth embodiment is the power consumption and heat generation of the discharge circuit 830. Another drawback is that it is difficult to add the discharge circuit 830 to a conventional charger 800 that does not have a discharge circuit 830. A charge / discharge circuit 840 that can solve these drawbacks will be described with reference to FIG.

[0151] 19 is a schematic diagram showing an AC current supplying device 901 that can be easily connected to a mobile phone 900. The mobile phone 901 has a female connector 902 as a charging terminal. The AC current supplying device 901 has a male connector 903 that can be inserted into the female connector 902.

[0152] FIG. 20 is a circuit diagram showing a charge / discharge circuit 840 built into an AC current supply device 901. Furthermore, the AC current supply device 901 also houses a controller 30. A male connector 903 having the same shape as the male connector of the charger 800 is connected to a pair of power lines 841, 842 of the charge / discharge circuit 840. When the male connector 903 is connected to the female connector 902 of the mobile phone 900, the controller 30 starts the charge / discharge mode of the charge / discharge circuit 840, and then ends this charge / discharge mode after a predetermined time has elapsed. This makes it possible to extend the life of the battery built into the mobile phone 900. The charge / discharge circuit 840 can be built into the charger 800 of the mobile phone.

[0153] The charge / discharge circuit 840 includes three half bridges 811-813, two inductors 814 and 815, and a controller 30. The charge / discharge circuit 840 has a pair of power supply lines 841, 842 that are individually and detachably connected to a pair of charging terminals 821, 822 of the battery 1. The half bridges 811-813 are connected to the power supply lines 841, 842, respectively.

[0154] The half bridge 811 is composed of an upper arm transistor 811H and a lower arm diode 811L connected in series. The half bridge 812 is composed of an upper arm diode 812H and a lower arm transistor 812L connected in series. The half bridge 813 is composed of an upper arm transistor 813H and a lower arm diode 813L connected in series. It is also possible to add a transistor connected in parallel with the diode.

[0155] The output end of the half bridge 811 is connected to one end of the inductor 814. The output end of the half bridge 812 is connected to the other end of the inductor 814 and one end of the inductor 815. The output end of the half bridge 813 is connected to the other end of the inductor 815. The controller 30 executes the electrodeposition reduction mode by switching each transistor of the three half bridges 811-813. This electrodeposition reduction mode is implemented after the charging operation from the charger 800 to the battery 1 is completed. After the charging operation is completed, the pair of output terminals of the charger 800 are disconnected from the charging terminals 821, 822 of the battery 1. Then, the pair of power lines 841, 842 of the charge / discharge circuit 840 are connected to the charging terminals 821, 822 of the battery 1.

[0156] In this electrodeposition reduction mode, the discharge period and the charge period are alternately arranged. First, the discharge period will be described. The transistors 811H, ​​812L, and 813H are turned on. This increases the discharge current Id1 flowing through the inductor 814, and increases the charge current Id2 flowing through the inductor 815. As a result, a predetermined discharge power energy is transferred from the battery 1 to the inductors 814 and 815.

[0157] Next, the charging period will be described. This charging period consists of a first charging period and a second charging period that are performed in sequence. In the first charging period, the transistors 811H and 812L are turned off. This causes the inductor 814 to charge the battery 1 through the diodes 811L and 812H. The charging current Ic1 is approximately equal to the discharging current Id1. This first charging period ends when the transistor 811H is turned on. After that, a freewheeling current circulates through the inductor 814, the diode 812H, and the transistor 811H. Similarly, the current flowing through the inductor 815 becomes a freewheeling current circulating through the diode 812H and the transistor 813H.

[0158] Next, the second charging period is described. In this second charging period, the transistor 813H is turned off. This causes the inductor 815 to charge the battery 1 through the diodes 813L and 812H. The charging current Ic2 is approximately equal to the discharging current Id2. This second charging period ends when the transistor 813H is turned on. After that, a freewheeling current circulates through the inductor 815, the diode 812H, and the transistor 813H.

[0159] FIG. 21 shows a schematic diagram of an AC current flowing between the battery 1 and the charge / discharge circuit 840. One cycle period Tcycle consists of a discharge period Td and a charge period Tc that are sequentially performed. The length of the charge period Tc is approximately twice the length of the discharge period Td. The two inductors 814 and 815 are simultaneously connected in parallel to the battery 1 during the discharge period Td. During the charge period Tc, the two inductors 814 and 815 are connected to the battery 1 in turn. As a result, a discharge current Id that is approximately twice the charge current Ic flows during the discharge period Td, which is approximately half the charge period Tc.

[0160] A variation is described. The charging / discharging circuit 840 shown in Fig. 21 has two inductors 814 and 815 and three half-bridges 811-813. The charging / discharging circuit 840 can further have more sets of additional inductors and additional half-bridges, respectively. Each inductor is connected in series.

[0161] For example, one end of the additional inductor is connected to the output terminal of the half bridge 813, and the other end is connected to the output terminal of the additional half bridge. This allows the discharge current Id to have three times the amplitude of the charge current Ic. Furthermore, the charge period Tc can have three times the length of the discharge period Td. As a result, the harmonic components contained in the discharge current Id can be further relatively increased compared to the harmonic components contained in the charge current Ic.

[0162] Eighth Example The eighth embodiment will be described with reference to Fig. 22. This embodiment utilizes the charge / discharge circuit 840 of the seventh embodiment shown in Fig. 20 and Fig. 21 to supply AC current to a battery for an electric vehicle. The charge / discharge circuit consisting of inductors 814 and 815 and half bridges 811-813 has the same circuit configuration and operates in the same manner as the charge / discharge circuit 840 shown in Fig. 20.

[0163] The circuit parts of Fig. 22 that differ from the charge / discharge circuit 840 shown in Fig. 20 are described below. A high-voltage battery 1 supplies DC current to an inverter 20 that drives an EV motor (not shown) through system switches 31 and 34. A smoothing capacitor 2 is connected in parallel with the inverter 20. The battery 1 applies a battery voltage to three half-bridges 811-813.

[0164] The grid charger 9 has an oscillator 91, a capacitor 92, and a rectifier 93. This grid charger 9 is essentially the same as the charger 9 shown in Fig. 11. The oscillator 91 supplies high frequency power to the coil 7 of the transformer 15. This transformer 15 is essentially the same as the transformer 15 shown in Fig. 13.

[0165] The transformer 15 has a ferrite core 15A. The ferrite core 15A has three poles 101A, 101B, and 101C that are magnetically connected in parallel. The inductor 814 is composed of a coil wound around the pole 101A. The coil 7 is wound around the pole 101B. The inductor 815 is composed of a coil wound around the pole 101C. As shown in FIG. 22, the inductors 814 and 815 are wound in opposite directions. Each of the two coils that make up the inductors 814 and 815 also functions as a secondary coil of the transformer 15. The three half bridges 811-913 also function as a rectifier for the grid charger 9.

[0166] The operation of the circuit shown in Fig. 22 will be described. The charge / discharge circuit consisting of the inductors 814 and 815 and the half bridges 811-813 supplies AC current to the battery 1 during a period when the grid charger 9 is not performing a charging operation. This allows the battery heating mode and electrodeposition reduction mode described above to be implemented. In other words, when the oscillator 91 is not supplying a high-frequency current to the primary coil 7, the half bridges 811-813 supply AC current to the battery 1.

[0167] 22 indicate the direction of AC current supplied to inductors 814 and 815. Magnetic flux F1 generated by inductor 814 and magnetic flux F2 generated by inductor 815 flow in the same direction in core 15A. As a result, magnetic flux (F1-F2) flowing through pole 101B decreases, and the AC voltage induced in coil 7 decreases.

[0168] When the grid charger 9 is connected to the commercial grid and the oscillator 91 supplies a high-frequency current to the primary coil 7, the half bridges 811-813 stop switching to generate an AC current. As a result, the half bridges 811-813 operate as a rectifier. The high-frequency magnetic flux generated by the primary coil 7 flows in parallel to the inductors 814 and 815. As a result, the half bridges 811-813 operated as a rectifier apply a rectified voltage to the battery 1. This charges the battery 1. The controller 30 controls the battery charging operation and the AC current supply operation to the battery described above. According to this embodiment, the grid charger 9 also functions as an AC current supply circuit that supplies an AC current to the battery 1, thereby reducing circuit costs.

Claims

1. In an AC current supply device for a battery, comprising: an AC current supply circuit that supplies an AC current to the battery during an AC current supply period consisting of alternately repeated discharge periods and charge periods; and a controller that controls the AC current supply circuit, the controller has a battery heating mode in which the AC current is supplied from the AC current supply circuit to the battery in order to raise the temperature of the battery in a predetermined low-temperature environment, and an electrodeposition reduction mode in which the AC current is supplied from the AC current supply circuit to the battery in order to suppress the electrodeposition phenomenon of the battery in a predetermined room-temperature environment. The AC current supply device for a battery is characterized by this.

2. The predetermined low-temperature environment includes an environment in which the temperature of the battery is lower than the freezing point of water, The predetermined room-temperature environment includes a predetermined environment in which the temperature of the battery is higher than the freezing point of the water. The AC current supply device for a battery according to Claim 1.

3. The AC current has a discharge current component supplied during the discharge period and a charge current component supplied during the charge period, The discharge period is formed shorter than the charge period in the electrodeposition reduction mode, The discharge current component has an amplitude higher than that of the charge current component in the electrodeposition reduction mode. The AC current supply device for a battery according to Claim 1.

4. The discharge current component and the charge current component each have a fundamental frequency component and a harmonic component, The harmonic component of the discharge current component has an amplitude higher than that of the harmonic component of the charge current component in the electrodeposition reduction mode. The AC current supply device for a battery according to Claim 1.

5. The integrated value of the AC current is essentially zero in the electrodeposition reduction mode. The AC current supply device for a battery according to Claim 1.

6. The electrodeposition reduction mode is started immediately after the end of a predetermined battery charging mode. The AC current supply device for a battery according to Claim 1.

7. The AC current supply circuit is incorporated in a charger that charges the battery with grid power. The AC current supply device for a battery according to Claim 1.

8. The AC current supply circuit has a connector that can be connected to a charging connector of the battery for connecting to a charger that charges the battery with grid power. The AC current supply device for a battery according to Claim 1.

9. The AC current supply circuit includes a plurality of inductors and a switching circuit that connects the plurality of inductors to the battery. The switching circuit supplies the discharge current in parallel from the battery to the plurality of inductors. The switching circuit supplies the charging current to the battery from the plurality of inductors in sequence. The AC current supply device for a battery according to claim 1. **Claim 10** The AC current supply circuit has a step-down transformer and an oscillator that applies an AC voltage to the primary coil of the step-down transformer. The secondary coil of the step-down transformer forms a closed-loop circuit together with the battery and a smoothing capacitor. The smoothing capacitor is connected to a motor drive circuit powered by the battery. The controller circulates the AC current through the closed-loop circuit by controlling the oscillator. The AC current supply device for a battery according to claim 1.

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