Battery AC power supply

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 AC current supply device that improves battery degradation by supplying AC current to a battery. [Background technology]

[0002] Secondary batteries such as lithium-ion batteries (LIBs) are widely used 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 with electric propulsion systems is the long charging time of batteries. Fast charging reduces this charging time. The fast charging capability of batteries is very important for electric propulsion systems to achieve easy-to-use and excellent driving capabilities.

[0003] However, it is known that fast charging can cause carrier metals to deposit on the surface of the battery's negative electrode. This deposition, called electrodeposition, can lead to battery capacity degradation and internal short circuits. To avoid these problems, the charging current rate during fast charging is generally limited to a range that can avoid electrodeposition.

[0004] In particular, dendrites, known as typical electrodeposition, can 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, can 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 used to preheat cold batteries that have a temperature below 0°C. This battery heating is stopped when the battery temperature reaches near 0°C to reduce power consumption. However, it is difficult to heat an EV battery pack evenly 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 within 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 conventional AC internal heating methods is that when a high-rate AC current is used to rapidly heat a battery, the aforementioned electrodeposition is promoted. A high-rate AC current consists 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 AC current rate at which AC internal heating methods can be used 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 costs, 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 that can store high power energy. However, large inductors and large capacitors 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 uses a grid charger equipped in an electric vehicle (EV). The coil of the transformer built into the grid charger is used as an energy storage device. However, using the transformer coil as an inductor for magnetic energy storage requires the addition of an expensive semiconductor power switching element.

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

[0013] When switch S is turned on, a discharge current Id flows through the discharge closed loop circuit. When 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 transformer T. As a result, the internal resistance R of 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 switch S. The charge period during which the charge current Ic flows through the secondary coil W2 is determined by the off period of switch S. The waveforms of the discharge current Id and the charge current Ic change depending on the number of turns in the primary coil W1 and 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 provide any explanation as to why they were selected.

[0015] In other words, the conventional AC internal heating method, which is used instead of the conventional external electric heater, preheats a battery whose temperature is lower than the freezing point of water to near the freezing point. Therefore, the conventional AC internal heating method does not need to be used for a battery whose temperature is at room temperature, where the battery can be charged and discharged properly. Conversely, heating a normal battery whose temperature is at room temperature using the conventional AC internal heating method can cause the battery to overheat and deteriorate.

[0016] Patent Document 3 discloses an AC current supply technology that is essentially different from the AC internal heating method for heating low-temperature batteries. This AC current supply technology improves the solid-state state of battery electrodes by supplying AC current to, for example, a non-low-temperature battery. However, Patent Document 3 does not disclose anything about the waveform of the AC current or the circuit structure of the AC current supply 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 batteries that can reduce the above-mentioned problems associated with battery charging. The second object of the present invention is to promote the widespread use of this AC current supply device for batteries by reducing circuit costs.

[0020] According to a first aspect of the present invention, an electrodeposition reduction mode is implemented in which electrodeposition materials in a battery are reduced 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, this predetermined room temperature is 20°C. On the other hand, conventional AC internal heating methods are implemented to raise the temperature of a cold battery that is essentially below 0°C. In this electrodeposition reduction mode, the charging period is set longer than the discharging period. Furthermore, the discharging current component has a higher average amplitude than the charging current component. The discharging current component and the charging current component are alternately supplied to the battery. This reduces 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 supplied alternately to the battery. It is generally known that the charge current component increases the amount of electrodeposited material, while the discharge current component reduces the amount of electrodeposited material. The AC current having a waveform employed 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 electrodeposited material by the discharge current component.

[0022] In a preferred embodiment, the integral value of the AC current in the electrodeposition reduction mode is set to approximately zero. Here, "approximately zero" includes less than 5% of the battery's SOC. As a result, the decrease in the battery's SOC 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 initiated within 30 minutes after the end of the predetermined battery charging mode, thereby improving the electrodeposition reduction efficiency caused by the AC current. The predetermined battery charging mode preferably refers to a charging operation that increases the SOC by 20% or more.

[0024] This effect can be further explained by the following: Battery charging causes the deposition of electrodeposits on the surface of the negative electrode active material of a battery. The new surface of the electrodeposits formed on the surface of the negative electrode active material is quickly covered by an inert layer, such as an SEI film. However, when an inert layer forms on the surface of the electrodeposits, the effect of the discharge current component in reducing the electrodeposits is reduced. This problem can be largely solved by implementing the electrodeposition reduction mode immediately after the battery charging operation, which is the main cause of the electrodeposits forming on the surface of the negative electrode active material. In particular, because the inert layer grown after the end of the charging operation is still thin, AC 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 amount of charge 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 operating period of the electrodeposition reduction mode is negatively correlated with 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 battery charging mode is initiated. This reduces the formation of electrodeposits 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, which is performed after the battery charging mode is completed. This reduces circuit costs.

[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 this charging connector, thereby easily realizing AC supply 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 with 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, electrodeposition of material in the battery can be reduced.

[0031] In a preferred embodiment, the switching circuit comprises a plurality of half-bridges each connected to an end of each inductor. 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 reduces circuit costs.

[0032] According to a second aspect of the present invention, an AC current supply circuit includes a step-down transformer that steps 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, smoothing capacitor, and secondary coil form a closed loop circuit. This AC current supply device can perform AC heating mode, dendrite reduction mode, and residual charge discharge mode. The electrodeposition reduction mode includes dendrite reduction mode and residual charge discharge mode. Because 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] In a preferred embodiment, the step-down transformer uses a transformer of an on-board charger installed in the electric propulsion system, thereby reducing 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 the 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 serves as an oscillator of the AC current supply device. [Brief explanation of the drawings]

[0036] [Figure 1]FIG. 1 is a schematic circuit diagram showing a conventional AC current supply circuit that performs a battery heating mode. [Figure 2] 2 is a timing chart showing an example of an AC current waveform employed in the battery heating mode of FIG. 1. [Figure 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. [Figure 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. 10 is a schematic cross-sectional view illustrating a discharge period in a dendrite reduction mode according to a second embodiment. [Figure 7] FIG. 10 is a schematic cross-sectional view illustrating a charging period in a dendrite reduction mode according to a second embodiment. [Figure 8] FIG. 10 is a block circuit diagram showing an AC current supply circuit according to a third embodiment. [Figure 9] 10 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. 10 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. 10 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 the magnetic flux difference mode of the circuit shown in FIG. [Figure 17] FIG. 10 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 schematically showing 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 INVENTION

[0037] An AC supply device of the present invention will be described with reference to several embodiments. This device has a mode for supplying AC to a battery consisting of a plurality of cells connected in series to suppress battery degradation. The AC supply mode includes an electrodeposition reduction mode in which AC is supplied to a battery at room temperature and a battery heating mode in which AC is supplied to a battery at 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 will be explained with reference to Figure 3. Figure 3 shows the charge state near the negative electrode of a non-aqueous electrolyte type lithium ion cell 700. In Figure 3, (A) shows the charge state during the charging period, (B) shows the charge state during the open 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 illustrating a cross section of a cell 700, showing only the electrolyte 502, negative electrode active material 503, and negative electrode current collector 504 of the cell 700. The surface of the negative electrode active material 503 that contacts the electrolyte 502 is called the 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 not shown.

[0040] The interface 505 is represented by a parallel-connected capacitor C2 and resistor R0. 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 the 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] Generally, 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 schematically represented by an ionic resistance component R01 and an electronic resistance component R02 connected in parallel. The negative electrode active material 503 is made of a carbon material such as graphite, soft carbon, or hard carbon. However, the negative electrode active material 503 can also be a silicon anode or a metallic lithium anode.

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

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

[0044] During discharge via the ion migration pathway, lithium ions stored in capacitor C2 diffuse into the negative electrode active material 503 through resistor R01. During discharge via the electron migration pathway, electrons stored in capacitor C2 migrate to the electrolyte-side surface of capacitor C2 through 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 migrate from the negative electrode active material 503 to the surface of the SEI coating through the SEI coating bond with lithium ions in or on the SEI coating. As a result, some of the lithium ions stored in capacitor C2 become free metallic lithium in or on the SEI coating during the open-circuit period. This phenomenon is called electrodeposition during the open-circuit period.

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

[0047] From the above explanation, 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-circuit period. This can suppress electrodeposition during the open-circuit 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 discharge mode will be explained 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 arranged 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) consists of alternating discharge periods Td and charge periods Tc. 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 consists of a discharging pulse current Id and a charging pulse current Ic having 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 Figure 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 during the discharge period Td is set to be higher than the average amplitude of the charge pulse current Ic during the charge period Tc. However, the discharge period Td is set to be shorter than the charge period Tc.

[0050] Furthermore, 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 charge period Tc and the charge state (C) during the discharge period Td. In the charge state (A) during the charge period Tc, lithium ions move from the electrolyte 502 through resistance R0 to the negative electrode active material 503. The lithium ions then charge the capacitor C2. In the charge state (C) during the discharge period Td, lithium ions move from the negative electrode active material 503 through resistance R0 to the electrolyte 502. The lithium ions then 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 harmonic components. The harmonic components have frequencies higher than the fundamental frequency component.

[0053] The interface 505 is represented by an AC impedance consisting of a parallel connection of a resistor R0 and a capacitor C2. 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 relatively more through the capacitor C2 than the charge pulse current Ic. Conversely, the charge pulse current Ic flows relatively more through the resistor R0 than the discharge pulse current Id.

[0054] 5, the discharge current Id can be considered to consist 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 consist 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 waveform shown in Figure 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 waveform shown in Figure 4.

[0056] Furthermore, lithium ions pass through interface 505, which is equivalent to capacitor C2 and resistor R0 connected in parallel. However, in the high-frequency region, lithium ions are slow to respond to the applied AC voltage. As a result, 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 more easily through capacitor C2 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 effectively discharges the residual charge in capacitor C2.

[0057] The effects of the charging current Ic and the discharging current Id forming an AC current are further explained. The charging current Ic increases electrodeposition, while the discharging current Id reduces electrodeposition. Therefore, the charging current Ic and the discharging current Id, which have different effects, should be analyzed separately. The charging current Ic consists of a fundamental frequency component and harmonic components. Similarly, the discharging current Id also consists of a fundamental frequency component and harmonic components. The harmonic components of the discharging current Id have higher amplitudes than the harmonic components of the charging current Ic. In other words, the harmonic components of the discharging current Id have higher power energy than the harmonic components of the charging current Ic. As a result, the fundamental component of the charging current Ic has higher power energy than the fundamental component of the discharging current Id. High-frequency currents flow more easily through 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 the 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 the 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 alternately supplied. 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 includes 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. Dendrites 703 grow from a partial region of the negative electrode active material 503. However, FIGS. 6 and 7 show the schematic shape of the dendrites 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 electrical resistance R1, the electrolyte 502 has an electrical resistance R2, the interface 505 has an electrical resistance R0, and the negative electrode active material 503 has an electrical resistance R3. The electrical resistance R0 is called the interfacial resistance. The interface 505 has a capacitor C2 connected in parallel with the electrical resistance R0. The capacitor C2 is called the interfacial capacitor.

[0061] In the dendrite current path 702, the positive electrode active material 501 has an electrical resistance r1, the electrolyte 502 has an electrical resistance r2, and the negative electrode active material 503 has an electrical resistance r3. The surface of the dendrite 703 has an electrical resistance r0 and a capacitor C1 connected in parallel. The electrical 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 charging will be described with reference to FIG. 6. Lithium ions move in the following order: positive electrode active material 501, electrolyte 502, interface 505, and negative electrode active material 503. Electrons then move from negative electrode current collector 504 to negative electrode active material 503. In this example, the electrical resistance R3 of negative electrode active material 503 is considered to be the ion transfer resistance. Interface 505 consists of an interface resistance R0 and an interfacial capacitor C2 connected in parallel. Therefore, as described in the first example, interfacial capacitor C2 is charged by lithium ions during charging.

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

[0064] (Charge transfer during discharge) Next, charge transfer in the non-dendritic current path 701 during the discharging 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 discharging period, the interfacial capacitor C2 is discharged.

[0065] Next, charge transfer in the dendrite current path 702 during the discharge period will be explained with reference to FIG. 7. In the dendrite current path 702, metallic lithium on the surface of the dendrite 703 is converted into 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 move 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 considered to be the electron transfer resistance. During the discharge period, the dendritic capacitor C1 is discharged.

[0066] The difference between the non-dendritic pathway 701 and the dendritic pathway 702 will now be explained. The electrical resistance R3 of the non-dendritic pathway 701 is due to ion transfer resistance. On the other hand, the electrical resistance r3 of the dendritic pathway 702 is due to 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, as the amplitude of the AC current consisting of the discharge current Id and the charge current Ic increases, the ionic resistance R3 of the negative electrode active material 503 increases. Furthermore, as the frequency of the AC 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 is positively correlated with the frequency of the AC current. Consequently, as the amplitude and / or frequency of the AC current increase, the electrical resistance R3 increases relative 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 and a higher frequency than the charge current Ic. 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 residual charge reduction effect described in the first embodiment can also reduce dendrites.

[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 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 known as an H-bridge, applies an AC voltage to the primary coil 8.

[0070] The full-bridge circuit 4 is made up of four MOSFETs 41-44. The output terminal of the first half-bridge made up of MOSFETs 41 and 42 is connected to one end of the primary coil 8. The output terminal of the second half-bridge made up of MOSFETs 43 and 44 is connected to the other end of the primary coil 8 via 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 circuits 4 are controlled in a complementary manner by a PWM (pulse width modulation) method.

[0071] A low-resistance element 81 for current detection detects a signal voltage Vs proportional to the 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] From the point when the pulse voltage Vp2 shifts to high level, the gate drive circuit 85 pulse-width modulates the MOSFETs 41 and 44 and turns off the MOSFETs 42 and 43. From the point when the pulse voltage Vp1 shifts to high level, the gate drive circuit 85 pulse-width modulates the MOSFETs 42 and 43 and turns off the MOSFETs 41 and 44.

[0074] Figure 9 shows the voltage waveform and current waveform of the device shown in Figure 8. Time t1 is the timing when pulse voltage Vp2 becomes high level. Time t2 is the timing when pulse voltage Vp1 becomes high level. During a charging period Tc, which is the period 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, which is the period 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 pulse width modulation during the discharging period Td. This pulse width modulation has a PWM duty ratio Dd. Similarly, the MOSFETs 42 and 43 are controlled by pulse width modulation during the charging period Tc. This pulse width modulation has a PWM duty ratio Dc. The PWM duty ratio Dd for discharging is approximately twice the PWM duty ratio Dc for charging.

[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 rate of increase of the low-frequency component VsL output from the rectifier circuit 82 to the comparators 83 and 84 is relatively low during the charge period Tc. As a result, the charge 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 merely an example, and many circuit modifications are possible.

[0079] In this embodiment, the average value of the discharge current Id during the discharging period Td is approximately twice the average value of the charging current Ic during the charging period Tc. Furthermore, the battery charging period Tc is approximately twice the battery discharging 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 the result is Yes, the battery heating mode (S102) is implemented.

[0082] In this 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 supplies a high-rate secondary current 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 the rapid charging mode has been selected (S106). If the rapid charging mode has not been selected, the standard charging mode is executed (S108). In the standard charging mode, an on-board charger (not shown) installed in the electric vehicle is connected to an external grid. The on-board charger boosts the rectified grid voltage and supplies a charging current to the battery 1. Next, it is determined whether the SOC of the battery 1 has reached a predetermined level. If the result is 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 so, the quick charge mode is terminated (S114).

[0086] When the standard charge mode or the rapid charge mode ends, it is determined whether an external electrical load connected to the battery 1 has been turned on (S116). In other words, it is determined whether 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 within 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 ends, if the external electrical load is not turned on, a dendrite reduction mode (S118) for reducing dendrites and a discharge mode (S120) for discharging residual charge are sequentially performed. In the dendrite reduction mode (S118), an AC current having the waveform shown in Figure 9 is supplied to the battery 1 immediately after charging is completed. In the discharge mode (S120) for discharging residual charge, an AC current having the waveform shown in Figure 4 is supplied to the battery 1 immediately after the dendrite reduction mode ends.

[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 using a common AC power supply device.

[0089] Fourth Example A fourth embodiment will be described with reference to FIG. 11. The electric propulsion system of this embodiment includes 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 approximately 400 V. The smoothing capacitor 2, which is a film capacitor with a capacitance of approximately 0.4 mF, is connected to a pair of DC power supply terminals of a motor drive circuit 20 that drives the 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 DC-DC 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. A 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. In the grid charging mode, the rectifier 93, which is configured as a diode full bridge, rectifies the single-phase grid voltage and charges the capacitor 92.

[0094] Capacitor 92 supplies DC power to oscillator 91, which is a full-bridge inverter known as an H-bridge. Oscillator 91 supplies high-frequency current to coil 7 of transformer 13. The 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, acting as a rectifier, rectifies the secondary voltage induced in the coil 8A. The battery-side converter 4A also consists of a full-bridge inverter known as an H-bridge. The voltage rectified by the battery-side converter 4A is applied to the battery 1 through relays 35 and 36. Consequently, the grid charger 11 can charge the battery 1 using grid power. The transformer 13 is a step-down transformer.

[0096] The DC-DC converter 12 consists 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 acts as 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] This battery heating mode includes two modes: the first battery heating mode is called a battery-connected battery heating mode, and the second battery heating mode is called a grid-connected battery heating mode.

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

[0100] As a result, Battery 1 is efficiently heated due to its resistance loss. For example, assume that the internal resistance of Battery 1 is 0.1 ohms and the effective value of the high-frequency current is 70 A. As a result, Battery 1 generates a resistance loss of approximately 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 must 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 independently. 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 grid-connected battery heating mode will be described. Relays 35 and 36 are turned off, and relays 31 and 34 are turned on. Grid power rectified by rectifier 93 is supplied to oscillator 91. Oscillator 91 applies a primary high-frequency voltage to coil 7. As a result, a secondary high-frequency voltage is induced in secondary coil 5, and battery 1 and 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, 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 functions as a rectifier. As a result, battery 1 is charged.

[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 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 a 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 schematically. Three coils 8A, 5, and 7 are wound around the central pole of a soft magnetic core 13A. The secondary coil 5 preferably has one turn.

[0107] The effects of this embodiment will now be described. First, the transformer 13 of the grid charger 11 doubles as a step-down transformer for the AC current supply circuit. Furthermore, the battery-side converter 4A and the grid-side converter 9 of the grid charger 11 each double as an oscillator for 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. This induces a secondary reverse voltage 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. This suppresses the adverse effects of the secondary coil 5 when the relays 31 and 34 are turned off.

[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 the direction that reduces the inrush current flowing through the smoothing capacitor 2. This reduces the inrush current.

[0109] Modifications of the transformer 13 and transformer 14 shown in Figure 11 will be described with reference to Figure 13. The soft magnetic core 15A of the transformer 15 shown in Figure 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, and 8A are wound around the first pole 101A, and coils 6 and 8B are wound around the third pole 101C. The second pole 101B has no coil.

[0110] Therefore, the magnetic flux of coils 5, 7, and 8A flows through a closed loop magnetic path formed by the first pole 101A, cross bar 101D, second pole 101B, and cross bar 101E. Similarly, the magnetic flux of coils 6 and 8B flows through a closed loop magnetic path formed by the third pole 101C, cross bar 101F, second pole 101B, and 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 Figure 14. The electric propulsion system of this embodiment is similar to the electric propulsion system shown in Figure 11. However, this embodiment uses one transformer 16 instead of the two transformers 13 and 14 shown in Figure 11. Furthermore, this embodiment uses two coils 6A and 6B connected in series instead of the single coil 6 shown in Figure 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] The positive terminal B+ of the high-voltage 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 coil 5. A three-phase inverter 20 for driving the motor is connected in parallel with the smoothing capacitor 2. A relay 32 and a low-resistance element 33 connected in series are 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 summary, 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, coils 8A and 8B, coils 6A and 6B, and rectifier 61. This operation is called a DC-DC converter mode. The battery-side converters 4A and 4B, coils 8A and 8B, coils 6A and 6B, and rectifier 61 form a DC-DC 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 operating 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 explained. 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, acting 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 and charges 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, heating the battery 1. When the temperature of the battery 1 reaches a predetermined value, this grid-connected battery heating mode ends.

[0122] Next, the DC-DC converter mode will be described. First, the relays 35 and 36 are turned on. In this DC-DC 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 current 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, heating the battery 1. Note that when the battery-connected battery heating mode and the motor driving mode are simultaneously implemented, the high-frequency current is limited so that the maximum current flowing through the battery 1 is below a predetermined threshold.

[0124] According to this embodiment, both the battery-connected battery heating mode and the DC-DC 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 secondary coils 5, 6A, and 6B. In other words, the battery-connected battery heating mode and the DC-DC converter mode are implemented simultaneously. However, it is preferable to implement the battery-connected battery heating mode and the DC-DC converter mode independently. This problem is solved by employing a special transformer 16 called a flux-switching transformer.

[0125] 15 and 16 are schematic cross-sectional views showing an example 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 for the first and second closed magnetic circuits.

[0128] Coils 6A and 6B, which are connected in series, have the same number of turns. Coils 8A and 8B have the same number of turns. Coils 5 and 7 are wound around pole 101B. Preferably, coil 5 has one turn. In transformer 16, the magnetic coupling between coils 8A and 8B and coil 5 is called magnetic flux sum coupling, and the magnetic coupling between coils 8A and 8B and coils 6A and 6B is called magnetic flux difference coupling.

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

[0130] The controller 30, which has a flux sum mode and a 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. Implementing the flux sum mode selects the flux sum coupling, and implementing the flux difference mode selects the flux difference coupling. 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 and frequency 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, which have 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 negligible. 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, in 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 in direction 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 coil 8A has an opposite phase to the second primary current I1B supplied to 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 achieved by inverting the waveform of the second primary current I1B. This change is easily achieved 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 opposite 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 coil 8A forms a magnetic flux F1 in pole 101A, and a second primary current I1B supplied to coil 8B forms a magnetic flux F2 in pole 101C. The magnetic flux F1 and the magnetic flux F2 have the same waveform. However, the magnetic flux F1 flows upward through pole 101A, while the magnetic flux F2 flows downward through pole 101C.

[0137] Ultimately, in this magnetic flux difference mode, magnetic fluxes F1 and F2 having the same waveform flow in opposite directions within pole 101B. This means that the sum of the magnetic fluxes flowing within pole 101B is zero. Therefore, the secondary voltages induced in coils 5 and 7 are both 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 now be explained. Oscillator 91 supplies primary power to coil 7. Coil 7 forms a magnetic flux sum coupling with coils 8A and 8B. Therefore, coil 7 wound around pole 101B passes magnetic flux F1 through pole 101A and magnetic flux F2 through pole 101C. In other words, half of the magnetic flux generated by coil 7 flows through pole 101A, and the other half flows through pole 101C. Consequently, rectifiers 4A and 4B charge battery 1 in parallel. In this grid charging mode, the sum of the secondary voltages of coils 6A and 6B connected in series is zero. Therefore, the DC-DC converter mode is not implemented.

[0140] Sixth Example Although the above-described embodiments have been used to explain protection technology for relatively large-capacity batteries such as those used in electric vehicles, the present invention is also effective for small-capacity batteries used in small electronic devices and small electric appliances such as mobile phones, personal computers, power screwdrivers, electric vacuum cleaners, and electric motorcycles.

[0141] An AC power 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 a BMS.

[0142] Charging terminals 821 and 822 of battery 1 are connected to charger 800. Charger 800 applies a charging voltage formed by rectifying grid power to battery 1. Controller 30 controls the charging current Ic supplied from charger 800 to battery 1 based on the internal state of battery 1. Charger 800 incorporates a DC power supply and a switching regulator. This DC power supply rectifies and steps down the grid voltage. The switching regulator uses the DC power received from this DC power supply unit to generate a charging current, which is then supplied to battery 1. Charger 800 controls battery charging using the well-known CCCV method.

[0143] Furthermore, a discharge circuit 830 is connected to the charge 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 CCCV battery charging is completed, the controller 30 executes the electrodeposition reduction mode. In this electrodeposition reduction mode, the controller 30 alternately performs the charging operation of the charger 800 and the discharging operation of the discharge circuit 830. One cycle period, in which one charging operation and one discharging operation are performed sequentially, consists of a charging period and a discharging period.

[0145] In one example, one cycle period is 200 μs, the charge period is 120 μs, and the discharge period is 60 μs. The transition periods between the charge and discharge periods are each 10 μs. The average value of the discharge current flowing during the discharge period is approximately twice the average value of the charge current flowing during the charge period. Preferably, the discharge circuit 830 is built into the charger 800. According to this embodiment, battery degradation can be prevented by supplying AC current using a simple circuit.

[0146] Next, a preferred example of control of the charger 800 and discharge circuit 830 by the controller 30 will be described with reference to the flowchart 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 such as those 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 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 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 implemented based on the determined AC current specifications (S204). Next, after determining that the dendrite reduction mode has ended (S206), the controller 30 starts the constant voltage charging (CV) mode. In other words, the dendrite reduction mode is implemented before the constant voltage charging (CV) mode. The amount of electrodeposition in the constant current charging (CC) mode is significantly greater than the amount of electrodeposition in the constant voltage charging (CV) mode. Therefore, by implementing 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 supply 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 supply 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. The AC current supply device 901 also houses a controller 30. A male connector 903, which has 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 mobile phone charger 800.

[0153] The charge / discharge circuit 840 comprises 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 consists of an upper arm transistor 811H and a lower arm diode 811L connected in series. The half bridge 812 consists of an upper arm diode 812H and a lower arm transistor 812L connected in series. The half bridge 813 consists 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 terminal of the half bridge 811 is connected to one end of the inductor 814. The output terminal of the half bridge 812 is connected to the other end of the inductor 814 and one end of the inductor 815. The output terminal 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 the transistors 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 supply 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, discharge periods and charge periods 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 amount of 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 sequentially. During the first charging period, transistors 811H and 812L are turned off. This causes inductor 814 to charge battery 1 through diodes 811L and 812H. The charging current Ic1 is approximately equal to the discharging current Id1. This first charging period ends when transistor 811H is turned on. Thereafter, a freewheeling current circulates through inductor 814, diode 812H, and transistor 811H. Similarly, the current flowing through inductor 815 becomes a freewheeling current circulating through diode 812H and transistor 813H.

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

[0159] FIG. 21 schematically shows 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 performed sequentially. The length of the charge period Tc is approximately twice the length of the discharge period Td. 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 will now be described. The charge / discharge circuit 840 shown in Figure 21 has two inductors 814 and 815 and three half-bridges 811-813. The charge / discharge 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 this additional inductor is connected to the output terminal of 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 be three times as long as the discharge period Td. As a result, the harmonic components contained in the discharge current Id can be further increased relatively compared to the harmonic components contained in the charge current Ic.

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

[0163] The circuit parts of Figure 22 that differ from the charge / discharge circuit 840 shown in Figure 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] Transformer 15 has ferrite core 15A. Ferrite core 15A has three poles 101A, 101B, and 101C magnetically connected in parallel. Inductor 814 consists of a coil wound around pole 101A. Coil 7 is wound around pole 101B. Inductor 815 consists of a coil wound around pole 101C. As shown in FIG. 22, inductors 814 and 815 are wound in opposite directions. Each of the two coils making up inductors 814 and 815 also functions as a secondary coil of transformer 15. Three half-bridges 811-913 also function as rectifiers for grid charger 9.

[0166] The operation of the circuit shown in Fig. 22 will now be described. The charge / discharge circuit, consisting of inductors 814 and 815 and half bridges 811-813, supplies AC current to the battery 1 during periods 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 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 formed by inductor 814 and magnetic flux F2 formed by inductor 815 flow in the same direction within core 15A. As a result, the 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 rectifiers. The high-frequency magnetic flux generated by the primary coil 7 flows in parallel through the inductors 814 and 815. As a result, the half-bridges 811-813 operating as rectifiers 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, as described above. According to this embodiment, the grid charger 9 also functions as an AC current supply circuit that supplies AC current to the battery 1, thereby reducing circuit costs.

Claims

1. 1. An AC current supply device for a battery, comprising: an AC current supply circuit that supplies AC current to a 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 electrodeposition of the battery in a predetermined room-temperature environment, 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 from the battery to the plurality of inductors in parallel; The AC current supply device for a battery, wherein the switching circuit supplies the charging current from the plurality of inductors to the battery in sequence.

2. An AC current supply device for a battery, comprising: an AC current supply circuit that supplies AC current to a battery during an AC current supply period consisting of alternating 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 electrodeposition of the battery in a predetermined room-temperature environment, the AC current supply circuit includes a step-down transformer and an oscillator that applies an AC voltage to a primary coil of the step-down transformer; a 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 AC current supply device for a battery, wherein the controller controls the oscillator to circulate the AC current through the closed loop circuit.

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