AC current supply device for battery

Abstract

To provide a battery alternating-current supply device capable of reducing electrocrystallization caused by battery charging.SOLUTION: An electrocrystallization reduction mode for operating a battery alternating-current supply device supplies an alternating current to a battery in order to reduce an electrocrystallization material in the battery and is operated within a battery temperature range higher than in a conventional battery heating mode performed for heating a battery. The alternating current used in the electrocrystallization reduction mode is composed of a high-rate discharge current component to be supplied in a short discharge period and a low-rate charge current component to be supplied in a long discharge period. The discharge period and the charge period are repeated alternately. An alternating-current supply circuit that supplies an alternating current to the battery has a step-down transformer. When a primary alternating-current voltage is applied to a primary coil of the step-down transformer, a secondary coil of the step-down transformer circulates a secondary alternating current to a closed loop circuit including the battery.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[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 composed of a plurality of cells connected in series is called a battery or a battery pack. The long charging time of the battery is a serious problem for electric vehicles. Therefore, the rapid charging ability of the battery is very important for the electric vehicle to obtain an excellent driving ability in terms of usability.

[0003] However, it is known that carrier metals are deposited on the surface of the negative electrode of the battery due to rapid charging. This deposition, called electrodeposition, causes capacity degradation of the battery and so-called internal short circuits. To avoid these problems, the rate of the charging current in rapid charging is generally limited within a range where electrodeposition can be avoided.

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

[0005] For this reason, a battery heating technique for preheating a cold battery having a temperature below 0°C is adopted. This battery heating is terminated when the battery temperature reaches near 0°C in order to reduce power consumption. However, it is difficult to uniformly and rapidly heat an EV battery pack with an electric heater.

[0006] Therefore, an AC internal heating method for supplying an alternating current to a battery has been proposed by, for example, Non-Patent Document 1 and Non-Patent Document 2. These AC internal heating methods reduce the variation in battery temperature and rapidly heat the battery. However, since this AC internal heating method has unsolved problems, it has not yet been equipped in electric vehicles.

[0007] One problem of the conventional AC internal heating method is that the electrodeposition described above is promoted by a high-rate alternating current. The high-rate alternating current consists of a high-rate charging current component and a high-rate discharging current component. The charging current component promotes electrodeposition, and the discharging current component eliminates electrodeposition. The promotion of electrodeposition by the high-rate alternating current suggests that the amount of increase in electrodeposition due to the charging current component exceeds the amount of decrease in electrodeposition due to the discharging current component. Therefore, the rate of the alternating current for which the AC internal heating method can be adopted must be limited to a range where no electrodeposition occurs.

[0008] Another problem of the conventional AC internal heating method is the high circuit cost of the alternating current supply circuit. This is because, since the internal resistance of the battery is low, the alternating current supply circuit needs to handle high-rate alternating current.

[0009] The alternating current supply circuit needs to temporarily store the electric energy discharged from the battery until the next charging period. For this reason, the alternating current supply circuit has a large inductor and / or a large capacitor capable of storing high electric energy. As a result, the alternating current supply circuit becomes expensive.

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

[0011] Patent Document 1 proposes an alternating current internal heating method that utilizes the 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, in order to utilize the coil of the transformer as an inductor, it is necessary to add expensive semiconductor elements. Furthermore, an increase in the inductance of the coil requires an increase in the weight and size of the transformer.

[0012] Patent Document 2 proposes another alternating current internal heating method using a transformer. The alternating current supply circuit adopted in Patent Document 2 will be described with reference to FIG. 1. The alternating current supply circuit connected to the battery E having the resistor R has a transformer T, a switch S, and a diode D. The transformer T, the primary coil W1, the switch S, and the resistor R of the battery E form a discharge closed loop circuit. Furthermore, the diode D, the secondary coil W2, and the resistor R of the battery E form a charging closed loop circuit. When the switch S is turned on, the discharge current Id flows through the discharge closed loop circuit. When the switch S is turned off, due to the magnetic energy stored in the inductance of the transformer T, the charging current Ic flows through the charging closed loop circuit. As a result, the internal resistor R of the battery E is heated by the discharge current Id and the charging current Ic. The discharge period during which the discharge current Id flows through the primary coil W1 is determined by the on period of the switch S. The charging period during which the charging current Ic flows through the secondary coil W2 is determined by the off period of the switch S. The waveforms of the discharge current Id and the charging current Ic change depending on the number of turns of the primary coil W1 and the number of turns of the secondary coil W2. Eventually, the transformer in Patent Document 2 functions only as a magnetic energy storage device in which the inductance of the primary coil stores the discharge energy of the battery and the inductance of the secondary coil releases the charging energy to the battery. Therefore, the weight and size of this transformer with high inductance increase.

[0013] FIG. 2 shows an example of waveforms of the discharge current Id and the charge current Ic shown in FIG. 1. 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 describe an explanation that the waveform example shown in FIG. 2 was intentionally selected for some reason and the reason for the selection.

[0014] Ultimately, all of the above-described alternating current internal heating methods are battery heating technologies that preheat the battery from a temperature lower than the freezing point of water to near this freezing point. Therefore, since a battery at room temperature has good charging operation and good discharging operation, a battery having a temperature higher than room temperature does not need to employ the alternating current internal heating method. Conversely, when heating a normal battery having a room temperature level by the conventional alternating current internal heating method, overheating of the battery and deterioration of the battery are caused.

[0015] Patent Document 3 discloses an alternating current supply technique different from the above-described alternating current internal heating method. This alternating current supply technique improves the solid state of the battery electrodes, for example, by supplying an alternating current to a non-low temperature battery. However, Patent Document 3 does not disclose anything about the waveform of the alternating current and the circuit structure of the alternating current supply circuit.

[0016] A battery deterioration detection technique using the alternating current impedance of a battery is widely used. This technique uses an alternating current supply circuit for supplying an alternating current to the battery. However, the idea of heating the battery or suppressing battery deterioration using an alternating current supply circuit for detecting alternating current impedance is not yet known. For example, Patent Document 4 proposes a technique for determining overcharge of an all-solid-state battery based on a change in alternating current impedance. However, Patent Document 4 does not disclose the specific circuit configuration of the alternating current supply circuit for detecting the alternating current impedance of the all-solid-state battery.

Prior Art Documents

Patent Documents

[0017]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non-Patent Document

[0018]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

[0019] The first object of the present invention is to provide an alternating current supply device for a battery capable of reducing electrodeposition due to battery charging. Further, the second object of the present invention is to promote the popularization of the alternating current supply device for a battery by cost reduction.

[0020] According to a first aspect of the present invention, an electrodeposition reduction mode is implemented in which an alternating current is supplied to a battery to reduce the electrodeposition material in the battery. This electrodeposition reduction mode supplies an alternating current to a battery having a temperature exceeding a predetermined room temperature. Preferably, this predetermined room temperature is 20°C. On the other hand, the conventional alternating current internal heating method is essentially implemented for raising the temperature of a cold battery lower than 0°C. According to this electrodeposition reduction mode, the charging period is longer than the discharging period. Further, the discharging current component has a higher average amplitude value than the charging current component. The discharging current component and the charging current component are alternately supplied to the battery. Thereby, the electrodeposition material near the negative electrode can be reduced.

[0021] This electrodeposition reduction effect is further explained. The alternating current supplied to the battery consists of a discharging current component supplied to the battery during the discharging period and a charging current component supplied to the battery during the charging period. The discharging current component and the charging current component are alternately supplied to the battery. Generally, it is known that the charging current component increases the electrodeposition material and the discharging current component decreases the electrodeposition material. The alternating current having the waveform adopted in the present invention has an effect of promoting the reduction of the electrodeposition material by the discharging current component.

[0022] In a preferred embodiment, the harmonics of the discharging current component have a higher average amplitude than the harmonics of the charging current component. Thereby, the reduction of the electrodeposition material by the discharging current component can be promoted. In a preferred embodiment, the integrated value of the alternating current in the electrodeposition reduction mode is made substantially zero. The above zero includes less than 5% of the SOC of the battery. As a result, the electrodeposition reduction mode implemented immediately after the charging operation can suppress the reduction of the SOC of the battery.

[0023] In a preferred embodiment, the electrodeposition reduction mode is started within 30 minutes after a predetermined battery charging mode ends. Thereby, the electrodeposition reduction efficiency by this alternating current is improved. The above predetermined battery charging operation preferably means a charging operation in which the SOC increases by 20% or more.

[0024] This effect is further explained. The battery charging operation deposits an electrodeposited material on the surface of the negative electrode active material of the battery. The new surface of the electrodeposited material formed on the surface of the negative electrode active material is rapidly covered by an inert layer such as an SEI film. However, when the inert layer is formed on the surface of the electrodeposited material, the reduction effect of the electrodeposited material due to the discharge current component decreases. This problem is improved by implementing an electrodeposition reduction mode immediately after the battery charging operation, which is the largest cause of the formation of the electrodeposited material on the surface of the negative electrode active material. In particular, since the inert layer grown after the completion of the charging operation is still thin, the alternating current can break the electrical insulation of this inert layer.

[0025] In a preferred embodiment, the operating period of the electrodeposition reduction mode has a positive correlation with the charge amount of the battery by the battery charging operation performed immediately before this electrodeposition reduction mode. Thereby, the power loss due to the electrodeposition reduction mode can be reduced. In a preferred embodiment, the operating period of the electrodeposition reduction mode has a negative correlation with the battery temperature detected immediately before this electrodeposition reduction mode. Thereby, the power loss due to the electrodeposition reduction mode can be reduced.

[0026] In a preferred embodiment, when the battery is at a low temperature, a battery heating mode is implemented before the start of the battery charging mode. Thereby, the electrodeposited material formed by the battery charging mode can be reduced. Further, according to this embodiment, this battery heating mode is implemented using the same alternating current supply circuit as the above-described electrodeposition reduction mode implemented after the end of the battery charging mode. Thereby, the circuit cost can be reduced.

[0027] In a preferred embodiment, an alternating current impedance detection mode for detecting the alternating current impedance of the battery is implemented using the alternating current supply circuit for implementing the electrodeposition reduction mode. As a result, the circuit cost of the alternating current supply circuit can be reduced. In a preferred embodiment, the electrodeposition reduction mode is controlled based on the alternating current impedance of the battery detected by the alternating current impedance detection mode. Thereby, the operation time and the alternating current power supply of the electrodeposition reduction mode can be appropriately managed.

[0028] In a preferred embodiment, this alternating current supply device is incorporated in a charger for charging a battery. As a result, the device configuration is simplified, and it becomes easier to start the electrodeposition reduction mode immediately after the battery charging mode.

[0029] In a preferred embodiment, the battery has a charging connector connectable to the charger connector, and the alternating current supply circuit has a connector connectable to the charging connector of this battery. Thereby, it is possible to easily supply an alternating current to the battery.

[0030] In a preferred embodiment, the alternating current supply circuit has a plurality of inductors and a switching circuit that connects these inductors to the battery. The battery discharges in parallel to each inductor. Each inductor charges the battery in turn. The discharging operation and the charging operation are performed alternately. As a result, the discharge current contains more harmonic components than the charging current.

[0031] In a preferred embodiment, the switching circuit consists of a plurality of half bridges separately connected to the ends of each inductor. Each half bridge consists of an upper arm switch and a lower arm switch connected in series. One of the upper arm switch and the lower arm switch consists of a transistor. The other of the upper arm switch and the lower arm switch consists of a transistor or a diode. Thereby, the circuit cost can be reduced.

[0032] According to a second aspect of the present invention, the alternating current supply circuit has a step-down transformer that steps down an alternating current voltage. The secondary alternating voltage induced in the secondary coil of the step-down transformer is applied to the battery through the smoothing capacitor of the motor drive circuit.

[0033] In other words, the battery, the smoothing capacitor, and the secondary coil form a closed-loop circuit. This alternating current supply device can implement an alternating current heating mode, a dendrite reduction mode, and a residual charge discharge mode. The electrodeposition reduction mode includes the dendrite reduction mode and the residual charge discharge mode. Thereby, circuit costs and wiring costs are reduced.

[0034] According to a preferred embodiment, this step-down transformer uses the transformer of an on-board charger equipped in an electric propulsion system. Thereby, circuit costs are reduced.

[0035] According to a preferred embodiment, this on-board charger has 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 the oscillator of the alternating current supply device.

[0036] According to a third aspect of the present invention, the alternating current supply circuit has a step-down transformer that steps down an alternating voltage. The battery has a first battery pack and a second battery pack that are substantially connected in parallel. The alternating current supply circuit includes an oscillator that supplies alternating current to the two battery packs through the step-down transformer. The step-down transformer has a first secondary coil connected in series with the first battery pack and a second secondary coil connected in series with the second battery pack. The first battery pack and the second battery pack are connected to each other through the first secondary coil and the second secondary coil connected in series. When the oscillator induces a secondary alternating voltage in the two secondary coils, the two secondary coils supply alternating current to the two battery packs.

[0037] In a preferred embodiment, two serially connected battery packs and two secondary coils form a closed loop circuit for the circulation of an alternating current. As a result, due to the two parallel-connected battery packs for improving reliability, the alternating current supply circuit can have a compact step-down transformer.

[0038] In a preferred embodiment, the first battery pack forms a first closed loop circuit with the smoothing capacitor of the motor drive circuit, and the second battery pack forms a second closed loop circuit with the smoothing capacitor of the motor drive circuit. The step-down transformer has a first secondary coil connected to the first closed loop circuit and a second secondary coil connected to the second closed loop circuit. The first secondary coil circulates a first alternating current in the first closed loop circuit, and the second secondary coil circulates a second alternating current in the second closed loop circuit. Due to the two parallel-connected battery packs for improving reliability, the alternating current supply circuit can have a compact step-down transformer. Furthermore, according to this embodiment, an alternating current waveform with an excellent electrolysis reduction effect can be adopted. Further, the oscillator can supply an alternating current to the other battery pack when one of the battery packs is disconnected.

Brief Description of the Drawings

[0039]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

Figure 20

Figure 21

Figure 22

Figure 23

Figure 24

Figure 25

Mode for Carrying Out the Invention

[0040] The alternating current supply device of the present invention will be described with reference to a plurality of embodiments. This device has a mode of supplying an alternating current to a battery composed of a plurality of cells connected in series in order to suppress battery deterioration. This alternating current supply mode includes an electrodeposition reduction mode of supplying an alternating current to a battery at normal temperature and a battery heating mode of supplying an alternating current to a battery at low temperature. The electrodeposition reduction mode consists of a residual charge discharge mode and a dendrite reduction mode. The residual charge discharge mode includes a discharge operation for eliminating the charge on the surface of the negative electrode active material. The dendrite reduction mode includes a discharge operation for reducing dendrites growing from the negative electrode active material toward the positive electrode active material. First Embodiment

[0041] The residual charge discharge mode will be described with reference to FIG. 3. FIG. 3 shows the state of charge in the vicinity of the negative electrode of a non-aqueous electrolyte type lithium ion cell 700. In FIG. 3, (A) shows the state of charge during the charging period, (B) shows the state of charge during the open period immediately after charging, and (C) shows the state of charge during the discharge period immediately after charging.

[0042] FIG. 3 is a schematic cross-sectional view conceptually showing a cross-section of the cell 700, and shows only the electrolyte 502, the negative electrode active material 503, and the negative electrode current collector 504 of the cell 700. The surface of the negative electrode active material 503 in contact with the electrolyte 502 is called an interface 505. The interface 505 has a SEI (Solid Electrolyte Interfphase) film (not shown). The illustration of the separator, the positive electrode active material, and the positive electrode current collector of the cell 700 is omitted.

[0043] The interface 505 is represented by a capacitor C2 and a resistor R0 connected in parallel. The negative electrode active material 503 is represented by an electrical resistance 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 resistance R3 each include an ion resistance component and an electron resistance component. The ion resistance component is related to the migration resistance of lithium ions. The electron resistance component is related to the migration resistance of electrons.

[0044] Generally, most of the resistor R0 consists of an ion resistance component. The electron resistance component included in the resistor R0 is known to have a much higher electrical resistance value compared to this ion resistance component. In FIG. 3, the resistor R0 is schematically shown by an ion resistance component R01 and an electron resistance component R02 connected in parallel. The negative electrode active material 503 is made of a carbon material member such as graphite, soft carbon, or hard carbon. However, the negative electrode active material 503 can also use a silicon anode or a metal lithium anode.

[0045] The charge states during the charging period, open circuit period, and discharging period of the cell 700 are described below. First, the charge state (A) during the charging period is described. A charging current is supplied to the cell 700. Lithium ions in the electrolyte 502 pass through the interface 505 and are inserted into the negative electrode active material 503. At the same time, electrons flow from the negative electrode current collector 504 to the negative electrode active material 503. A part of the lithium ions that reach the interface 505 is not inserted into the negative electrode active material 503. As a result, electrons are supplied from the negative electrode current collector 504 through the negative electrode active material 503 to the interface 505. Thereby, the capacitor C2 is charged.

[0046] Next, the charge state (B) during the open circuit period is described. In this open circuit period that starts immediately after the charging ends, the current flowing between the cell 700 and the external circuit becomes zero, and the voltage of the cell 700 becomes a so-called open circuit voltage value. However, at the initial stage of the open circuit period, the capacitor C2 discharges through the ion migration path and the electron migration path. The ion migration path has a resistor R01, and the electron migration path has a resistor R02.

[0047] In the discharge through the ion migration path, the lithium ions accumulated in the capacitor C2 diffuse into the negative electrode active material 503 through the resistor R01. In the discharge through the electron migration path, the electrons accumulated in the capacitor C2 move through the resistor R02 to the surface of the electrolyte side of the capacitor C2. In other words, the electrons cross the SEI film. As a result, the lithium ions that obtain these electrons become metallic lithium.

[0048] Furthermore, a part of the electrons that move from the negative electrode active material 503 to the surface of the SEI film through the SEI film combines with lithium ions inside or on the SEI film. As a result, a part of the lithium ions accumulated in the capacitor C2 becomes metallic lithium that is liberated inside or on the SEI film during the open period. This phenomenon is called the electrodeposition phenomenon during the open period.

[0049] Next, the state of charge (C) during the discharge period that starts immediately after charging is described. A discharge current is supplied to the cell 700. The lithium ions in the negative electrode active material 503 move to the electrolyte 502, and the electrons of the negative electrode active material 503 move to the negative electrode current collector 504. Therefore, the cell 700 is discharged. Furthermore, the lithium ions accumulated in the capacitor C2 move to the electrolyte 502, and the electrons accumulated in the capacitor C2 return to the negative electrode active material 503. Therefore, the capacitor C2 is also discharged.

[0050] From the above description, it is understood that it is preferable to perform the discharge period immediately after the end of the charging period. In other words, it is preferable that the open period is shortened. Thereby, electrodeposition during the open period can be suppressed. However, discharging immediately after charging reduces the remaining capacity of the battery. This embodiment solves this problem by executing the residual charge discharge mode.

[0051] This residual charge discharge mode will be described with reference to FIG. 4. FIG. 4 is a timing chart showing the alternating current Iac supplied to the cell 700. The residual charge reduction period (Tx) is arranged immediately after the end of the charging period (Tcm). The charging current Icm is supplied to the cell 700 during the charging period (Tcm). The residual charge reduction period (Tx) consists of alternatingly repeated discharge periods Td and charging periods Tc. The discharge pulse current Id is supplied to the cell 700 during the discharge period Td. The charging pulse current Ic is supplied to the cell 700 during the charging period Tc. In other words, the alternating current Iac consists of a discharge pulse current Id and a charging pulse current Ic having pulse frequencies equal to each other. The discharge pulse current Id discharges the capacitor C2, and the charging pulse current Ic charges the capacitor C2.

[0052] In FIG. 4, the discharge pulse current Id consists of four pulse currents (Id1, Id2, Id3, and Id4) whose amplitudes gradually decrease. Similarly, the charging 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 higher than the average amplitude of the charging pulse current Ic during the charging period Tc. However, the discharge period Td is set shorter than the charging period Tc.

[0053] Furthermore, the integrated value of the discharge current Id is approximately equal to the integrated value of the charging current Ic. As a result, this residual charge discharge mode hardly reduces the SoC (State of Charge) of the cell 700. The discharge current Id and the charging current Ic can also adopt other current waveforms instead of the pulse current waveforms shown in FIG. 4.

[0054] The effect of the residual charge discharge mode of this embodiment using the waveform shown in FIG. 4 will be described with reference to FIG. 5. FIG. 5 shows the state of charge (A) during the charging period Tc and the state of charge (C) during the discharging period Td. In the state of charge (A) during the charging period Tc, lithium ions move from the electrolytic solution 502 through the resistor R0 to the negative electrode active material 503. Further, the lithium ions charge the capacitor C2. In the state of charge (C) during the discharging period Td, lithium ions move from the negative electrode active material 503 through the resistor R0 to the electrolytic solution 502. Further, the lithium ions discharge the capacitor C2.

[0055] As shown in FIG. 4, the discharge pulse current Id contains more harmonic current components than the charge pulse current Ic. In other words, the alternating current Iac flowing through the cell 700 consists of a fundamental frequency component and a harmonic component. The harmonic component has a higher frequency than the fundamental frequency component.

[0056] The interface 505 is represented by an AC impedance composed of the resistor R0 and the capacitor C2 connected in parallel. The AC impedance of the capacitor C2 becomes low for the high-frequency current component and high for the low-frequency current component. Therefore, the discharge pulse current Id flows relatively through the capacitor C2 as compared with the charge pulse current Ic. Conversely, the charge pulse current Ic flows relatively through the resistor R0 as compared with the discharge pulse current Id.

[0057] Furthermore, in FIG. 5, the discharge current Id can be regarded as consisting of a discharge current Ida flowing through the capacitor C2 and a discharge current Idb flowing through the resistor R0. Similarly, the charge current Ic can be regarded as consisting of a charge current Ica flowing through the capacitor C2 and a charge current Icb flowing through the resistor R0. Due to the difference in the harmonic components, the discharge current Ida increases relatively more than the charge current Ica.

[0058] Ultimately, when the alternating current Iac having the current waveform shown in FIG. 4 is supplied to the cell 700, the capacitor C2 discharges. As a result, the lithium ions accumulated in the capacitor C2 return to the electrolytic solution 502 by the alternating current Iac having the current waveform shown in FIG. 4.

[0059] Furthermore, lithium ions pass through an interface 505 that is equivalent to a capacitor C2 and a resistor R0 connected in parallel. However, in the high-frequency region, the follow-up of lithium ions to the applied alternating voltage is delayed. As a result, the resistor R0 becomes high in the high-frequency region and low in the low-frequency region. Therefore, the discharge current Id containing relatively many high-frequency components is more likely to flow through the capacitor C2 than the charging current Ic containing relatively many low-frequency components. Eventually, when the discharge current component Id contains relatively more high-frequency components than the charging current component Ic, the discharge current component Id discharges the residual charge of the capacitor C2 well.

[0060] The effects obtained by the charging current Ic and the discharge current Id are further explained. The charging current Ic increases electrodeposition, and the discharge current Id decreases electrodeposition. Therefore, the charging current Ic and the discharge current Id having different effects on each other should be analyzed separately. The charging current Ic consists of a fundamental frequency component and a harmonic component. Similarly, the discharge current Id also consists of a fundamental frequency component and a harmonic component. The harmonic component of the discharge current Id has a higher amplitude than the harmonic component of the charging current Ic. In other words, the harmonic component of the discharge current Id has higher power energy than the harmonic component of the charging current Ic. High-frequency current is more likely to flow through the capacitors C1 and C2 than low-frequency current. Furthermore, high-frequency current is less likely to flow through the ion transport resistor R3. As a result, the discharge current Id having more harmonic components than the charging current Ic can have an excellent electrodeposition reduction function. Second Embodiment

[0061] The dendrite reduction mode will be described with reference to FIGS. 6 and 7. FIG. 6 is a schematic cross-sectional view showing the charged state of one cell 700 of a non-aqueous electrolyte type lithium ion battery. The AC power supply 600 supplies a charging current Ic to the cell 700. FIG. 7 is a schematic cross-sectional view showing the discharged state of this cell 700. The AC power supply 600 supplies a discharging current Id to the cell 700. The alternating current supplied to the cell 700 consists of the alternately supplied charging current Ic and discharging current Id. 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 integrated value of the discharging current Id is approximately equal to the integrated value of the charging current Ic.

[0062] The cell 700 has a positive electrode current collector 500, a positive electrode active material 501, an electrolyte 502, a negative electrode active material 503, and a negative electrode current collector 504. The electrolyte 502 is injected into the gap between the positive electrode active material 501 and the negative electrode active material 503. A separator (not shown) is inserted into the gap. The surface of the negative electrode active material 503 facing the gap is called an interface 505. A dendrite 703 is growing from a partial region of the negative electrode active material 503. However, FIGS. 6 and 7 show the schematic shape of the dendrite 703. The surface of the positive electrode active material 501 facing the gap is called a 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 a non-dendrite path. The current path 702 that passes through the dendrite 703 is called a dendrite path.

[0063] In the non-dendrite 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 an interface resistance. The interface 505 has a capacitor C2 connected in parallel with the electrical resistance RO. The capacitor C2 is called an interface capacitor.

[0064] 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 dendrite resistance, and the capacitor C1 is called the dendrite capacitor.

[0065] (Charge transfer during charging) First, the charge transfer in the non-dendrite current path 701 during the charging period will be described with reference to FIG. 6. Lithium ions move in the order of the positive electrode active material 501, the electrolyte 502, the interface 505, and the negative electrode active material 503. Further, electrons move from the negative electrode current collector 504 to the negative electrode active material 503. In this embodiment, the electrical resistance R3 of the negative electrode active material 503 is regarded as the ion migration resistance. The interface 505 consists of an interface resistance R0 and an interface capacitor C2 connected in parallel. Therefore, as described in the first embodiment, the interface capacitor C2 is charged by lithium ions during the charging period.

[0066] Next, the charge transfer in the dendrite current path 702 during the charging period will be described with reference to FIG. 6. During the charging period shown in FIG. 6, lithium ions move in the order of the positive electrode active material 501, the electrolyte 502, and the dendrite 703. In this embodiment, the movement of lithium ions from the dendrite 703 to the negative electrode active material 503 is ignored. As a result, electrons move from the negative electrode current collector 504 through the negative electrode active material 503 to the dendrite 703. In this embodiment, the electrical resistance r3 of the negative electrode active material 503 is regarded as the electron migration resistance. The electrical resistance of the dendrite 703 made of metallic lithium is ignored. The surface of the dendrite 703 is represented by a dendrite resistance r0 and a dendrite capacitor C1 connected in parallel. The dendrite capacitor C1 is charged by lithium ions during the charging period.

[0067] (Charge transfer during discharging) Next, the charge transfer of the non-dendritic current path 701 during the discharge period will be described with reference to FIG. 7. Lithium ions move in the order of the negative electrode active material 503, the interface 505, the electrolyte 502, and the positive electrode active material 501. Similarly, electrons move from the negative electrode active material 503 to the negative electrode current collector 504. According to this embodiment, the electrical resistance R3 of the negative electrode active material 503 is regarded as corresponding to the ion transfer resistance. At the initial stage of the discharge period, the interface capacitor C2 is discharged.

[0068] Next, the charge transfer of the dendritic current path 702 during the discharge period will be described with reference to FIG. 7. In the dendritic current path 702, the metallic lithium on the surface of the dendrite 703 is converted into lithium ions, eluted into the electrolyte 502, and then inserted into the positive electrode active material 501. The 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 regarded as the electron transfer resistance. During the discharge period, the dendrite capacitor C1 is discharged.

[0069] The difference between the non-dendritic path 701 and the dendritic path 702 will be described. The electrical resistance R3 of the non-dendritic path 701 consists of the ion transfer resistance. On the other hand, the electrical resistance r3 of the dendritic path 702 consists of the electron transfer resistance. The ion resistance R3 of the negative electrode active material 503 is relatively high compared to the electron resistance r3 of the negative electrode active material 503. Furthermore, when the amplitude of the alternating current composed of the discharge current Id and the charge current Ic increases, the ion resistance R3 of the negative electrode active material 503 increases. Furthermore, when the frequency of the alternating current increases, the ion resistance R3 of the negative electrode active material 503 increases. In other words, the resistance value of the ion resistance R3 has a positive correlation with the frequency of the alternating current. Eventually, when the amplitude and / or frequency of the alternating current increases, the electrical resistance R3 increases relatively compared to the electrical resistance r3.

[0070] Therefore, the current flowing through the dendritic path 702 increases relatively in the high current region and the high frequency region compared to the current flowing through the non-dendritic path 701.

[0071] In this embodiment, the discharge current Id has a higher average amplitude than the charging current Ic and, further, has a higher frequency. Therefore, the discharge current Id flows relatively through the electrical resistance r3 as compared with the electrical resistance R3. On the other hand, the charging current Ic flows relatively through the electrical resistance R3 as compared with the electrical resistance r3. Eventually, the discharge current Id is more likely to flow through the dendrite 703 as compared with the charging current Ic. As a result, the dissolution of the dendrite 703 due to the discharge current Id flowing through the dendrite 703 exceeds the precipitation of the dendrite 703 due to the charging current Ic flowing through the dendrite 703. Further, according to this second embodiment, the dendrite can also be reduced by the residual charge reduction effect described in the first embodiment. Third Embodiment

[0072] The 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 supply of an AC current to the battery employed in the first and second embodiments. This AC current supply device for a battery mounted on an electric vehicle circulates an AC current in a closed loop circuit including a battery 1, a capacitor 2, and a secondary coil 5. The secondary coil 5 is wound around the core of a step-down transformer 13 together with a primary coil 8. A full-bridge circuit 4, also called an H-bridge, applies an AC voltage to the primary coil 8.

[0073] The full-bridge circuit 4 is composed of four MOSFETs 41-44. The output terminals of the first half-bridge composed of the MOSFETs 41 and 42 are connected to one end of the primary coil 8. The output terminals of the second half-bridge composed of the MOSFETs 43 and 44 are connected to the other end of the primary coil 8 through a low-resistance element 81 for current detection. The high-frequency noise current generated by the full-bridge circuit 4 is bypassed by a capacitor 80. The full-bridge circuit 4 is complementarily controlled by a PWM (pulse width modulation) method.

[0074] The low-resistance element 81 detects a signal voltage Vs proportional to the primary current I1 supplied to the primary coil 8. The 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. The comparator 83 outputs a pulse voltage Vp1, which is a comparison result between the low-frequency component VsL and the reference voltage Vr1, to the controller 30. The comparator 84 outputs a pulse voltage Vp2, which is a comparison result between the low-frequency component VsL and the reference voltage Vr2, to the controller 30.

[0075] The pulse voltage Vp1 becomes high level when the low-frequency component VsL is lower than the reference voltage Vr1. The pulse voltage Vp2 becomes 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.

[0076] The gate drive circuit 85 performs pulse width modulation on the MOSFETs 41 and 44 and puts the MOSFETs 42 and 43 in a standby state from the time when the pulse voltage Vp2 shifts to the high level. The gate drive circuit 85 performs pulse width modulation on the MOSFETs 42 and 43 and puts the MOSFETs 41 and 44 in a standby state from the time when the pulse voltage Vp1 shifts to the high level.

[0077] FIG. 9 shows an example of waveforms of voltages and currents in FIG. 8. The time point t1 is the timing when the pulse voltage Vp2 becomes high level. The time point t2 is the timing when the pulse voltage Vp1 becomes high level. During the charging period Tc, which is the period from time point t1 to time point t2, the secondary coil 5 supplies a charging current Ic to the battery 1. Similarly, during the discharging period Td, which is the period from time point t2 to time point t1, the secondary coil 5 supplies a discharging current Id to the battery 1.

[0078] MOSFETs 41 and 44 are controlled by a pulse width modulation method during the discharge period Td. This pulse width modulation method has a PWM duty ratio Dd. Similarly, MOSFETs 42 and 43 are controlled by a pulse width modulation method during the charging period Tc. This pulse width modulation method has a PWM duty ratio Dc. MOSFETs 41 - 44 are pulse width modulated by, for example, a PWM carrier frequency of 40 kHz. On the other hand, the cycle frequency, which is the reciprocal of one cycle period consisting of one discharge period Td and one charging period Tc, is, for example, 5 kHz.

[0079] The discharge PWM duty ratio Dd is approximately twice that of the charge PWM duty ratio Dc. As a result, the discharge current Id flowing through the secondary coil 5 is approximately twice that of the charge current Ic. Since the charge current Ic is relatively low, the rate of increase of the low-frequency component VsL output to the comparators 83 and 84 by the rectifier circuit 82 is relatively low during the charging period Tc.

[0080] Ultimately, the charging period Tc is approximately twice that of the discharge period Td. The total amount of discharge charge during the discharge period Td is approximately equal to the total amount of charge of the battery 1 during the charging period Tc. Thereby, the change in the SOC of the battery 1 is suppressed, and the residual magnetic flux of the step-down transformer 13 is reduced.

[0081] 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 the high-frequency noise voltage including the PWM carrier voltage. According to this embodiment, the alternating current I2 flowing through the secondary coil 5 consists of the charge current Ic and the discharge current Id. The charge current Ic and the discharge current Id can each have a desired waveform. However, the circuit shown in FIG. 8 is an example, and numerous circuit modifications are possible.

[0082] According to this embodiment, the average value of the discharge current Id during the discharge period Td is approximately twice that of the average value of the charge current Ic during the charging period Tc. Furthermore, the battery charging period Tc is approximately twice that of the battery discharge period. As a result, the integrated value of the alternating current I2 flowing through the battery 1 becomes approximately zero.

[0083] One charging control example of this device will be described with reference to the flowchart shown in FIG. 10. This charging control is started when the commercial grid or an external rapid charger supplies charging power to the battery 1. This charging control includes a battery heating mode (S102), a standard charging mode (S108), and a rapid charging mode (S112).

[0084] 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). If Yes, the battery heating mode (S102) is implemented.

[0085] According to this battery heating mode, the H-bridge 4 applies an alternating voltage to the primary coil 8. The frequency of this alternating voltage is, for example, 8000 Hz. As a result, a high-rate secondary current is supplied to the secondary coil 5. Consequently, the battery 1 is heated.

[0086] Next, it is determined whether the temperature T of the battery 1 is higher than the predetermined threshold value Vth (S104). If No, the battery heating mode (S102) is continued. If Yes, the battery heating mode is terminated.

[0087] Next, it is determined whether the rapid charging mode has been selected (S106). If the rapid charging mode is not selected, the standard charging mode is executed (S108). In this standard charging mode, an in-vehicle charger (not shown) mounted on the electric vehicle is connected to the external grid. This in-vehicle 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 Yes, the standard charging mode is terminated (S110).

[0088] In step S106, when the rapid charging mode is selected, the rapid charging mode is executed (S112). In this rapid charging mode, the battery 1 is connected to an external rapid charging device. Next, it is determined whether the SOC of the battery 1 has reached a predetermined level. If Yes, the rapid charging mode ends (S114).

[0089] When the standard charging mode or the rapid charging mode ends, it is determined whether the external electrical load connected to the battery 1 is 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 accumulated in the capacitor in the battery 1 is consumed. Furthermore, the dendrites formed by the charging current also dissolve in the electrolyte. Therefore, the implementation of the dendrite reduction mode (S118) and the discharge mode for reducing residual charge (S120) is omitted.

[0090] When the standard charging mode or the rapid charging mode ends and the external electrical load is not turned on, the dendrite reduction mode (S118) for dendrite reduction and the discharge mode (S120) for residual charge discharge are sequentially implemented. According to the dendrite reduction mode (S118), an alternating current having the current waveform shown in FIG. 9 is supplied to the battery 1 immediately after the charging ends. According to the discharge mode (S120) for residual charge discharge, an alternating current having the current waveform shown in FIG. 4 is supplied to the battery 1 immediately after the end of the dendrite reduction mode.

[0091] According to this embodiment, by using a common alternating current supply device, the battery heating mode (S102), the dendrite reduction mode (S118), and the residual charge discharge mode (S120) can be sequentially implemented. Fourth Embodiment

[0092] The fourth embodiment will be described with reference to FIG. 11. The electric propulsion system of this embodiment has a high-voltage battery 1, a smoothing capacitor 2, and a connection box 10. The high-voltage battery 1 is a lithium-ion battery having a rated voltage of about 400V. The smoothing capacitor 2, which consists of a film capacitor having a capacitance of about 0.4 mF, is connected to a pair of DC power 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 can further include a boost chopper circuit for boosting the voltage of the smoothing capacitor 2.

[0093] The high-voltage battery 1 and the smoothing capacitor 2 are connected through the connection box 10. The connection box 10 houses a relay circuit 3, a grid charger 11, a DCDC converter 12, and a controller 30. The relay circuit 3 includes system relays 31 and 34, a precharge relay 32, a resistor 33, and safety relays 35 and 36.

[0094] The positive terminal B+ of the battery 1 is connected to the positive terminal C+ of the smoothing capacitor 2 through the relay 31. The negative terminal B- of the battery 1 is connected to the negative terminal C- of the smoothing capacitor 2 through the relay 34 and the secondary coil 5. The secondary coil 5 connects the negative terminal C- of the smoothing capacitor 2 and the system relay 34. The series-connected relay 32 and the low resistor 33 are connected in parallel with the system relay 31. To precharge the smoothing capacitor 2, the relay 32 is turned on before the relay 31.

[0095] The grid charger 11 that charges the battery 1 using grid power has a grid-side converter 9, a transformer 13, and a battery-side converter 4A. The grid-side converter 9 has a rectifier 93, a capacitor 92, and an oscillator 91.

[0096] When the grid voltage is applied to the rectifier 93, the grid charging mode is started. In other words, the grid charging mode is executed after the rectifier 93 of the grid-side converter 9 is connected to the commercial grid. Before the grid charging mode is started, the relays 31, 32, and 34 are turned off, and the relays 35 and 36 are turned on. According to the grid charging mode, the rectifier 93 composed of a diode full bridge rectifies the single-phase grid voltage to charge the capacitor 92.

[0097] The capacitor 92 supplies DC power to an oscillator 91 composed of a full-bridge inverter called an H-bridge. The oscillator 91 supplies a high-frequency current to the coil 7 of the transformer 13. The four MOSFETs of the H-bridge 91 are PWM-controlled for controlling the waveform of the high-frequency current.

[0098] The transformer 13 has three coils 5, 7, and 8A wound around a soft magnetic core 13A. The coils 5, 7, and 8A are magnetically coupled by the soft magnetic core 13A. When the oscillator 91 supplies a high-frequency primary current to the coil 7, the battery-side converter 4A as a rectifier rectifies the secondary voltage induced in the coil 8A. The battery-side converter 4A also consists of a full-bridge inverter called an H-bridge. The voltage rectified by the battery-side converter 4A is applied to the battery 1 through the relays 35 and 36. Eventually, the grid charger 11 can charge the battery 1 using the grid power. The transformer 13 is a step-down transformer.

[0099] The DCDC 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 forming 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.

[0100] In addition to the grid charging mode, the controller 30 has a battery heating mode. This battery heating mode is implemented after the smoothing capacitor 2 is pre-charged. This battery heating mode is implemented when the temperature of the battery 1 is less than a predetermined value. In this battery heating mode, a high-frequency current circulating between the smoothing capacitor 2 and the battery 1 heats the battery 1.

[0101] This battery heating mode includes two modes. The first battery heating mode is called the battery-connected battery heating mode. The second battery heating mode is called the grid-connected battery heating mode.

[0102] First, the battery-connected battery heating mode will be described. Relays 35 and 36 are turned on, and the battery 1 applies a battery voltage to the battery-side converter 4A. Next, the battery-side converter 4A driven as an oscillator supplies a high-frequency current to the coil 8A. As a result, a high-frequency secondary voltage is induced in the coil 5, and the secondary current circulates in a closed-loop circuit composed of the battery 1, the coil 5, the relay 31, the smoothing capacitor 2, and the relay 34.

[0103] As a result, the battery 1 is efficiently heated due to its resistive loss. For example, assuming that the internal resistance of the battery 1 is 0.1 ohm and the effective value of the high-frequency current is 70 A. As a result, the battery 1 generates a resistive loss of approximately 490 W. This battery-connected battery heating mode can be implemented during the period when the propulsion motor is stopped and during the period when the propulsion motor is driven.

[0104] However, the battery heating power should be adjusted so that the sum of the high-frequency power for the battery heating mode and the power for motor drive does not exceed a predetermined level. The control of the battery heating power is implemented by PWM control of the H-bridge as the battery-side converter 4A. This battery heating mode ends when the temperature of the battery 1 reaches a predetermined value.

[0105] Next, the grid-connected battery heating mode is described. This grid-connected battery heating mode can be implemented simultaneously with the previously described grid charging mode, or can also be implemented independently. When the battery heating mode and the grid charging mode are implemented together, the battery heating power is preferably controlled so that the current of battery 1 does not exceed a predetermined value. The oscillator 91 of the grid-side converter 9 is PWM-controlled for the control of the battery heating power.

[0106] First, the independent implementation of the grid-connected battery heating mode is described. Relays 35 and 36 are turned off, and relays 31 and 34 are turned on. The grid power rectified by the rectifier 93 is supplied to the oscillator 91. The oscillator 91 applies a primary high-frequency voltage to the coil 7. As a result, a secondary high-frequency voltage is induced in the secondary coil 5, and battery 1 and the smoothing capacitor 2 are heated by the high-frequency current.

[0107] Next, the case of implementing the grid-connected battery heating mode and the grid charging mode simultaneously is described. When the grid-connected battery heating mode is implemented, relays 35 and 36 are turned on. The capacitor 92 is charged by the grid power rectified by the rectifier 93. The oscillator 91 powered from the capacitor 92 supplies a high-frequency current to the coil 7. As a result, the high-frequency voltage induced in the secondary coil 5 heats battery 1. Further, the secondary voltage induced in the coil 8A is rectified by the battery-side converter 4A as a rectifier. Thereby, battery 1 is charged.

[0108] The electrodeposition reduction mode can also be implemented by essentially the same control method as the previously described battery heating mode. This electrodeposition reduction mode includes the previously described residual charge discharge mode and dendrite reduction mode. However, the battery heating mode is executed 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 (for example, 20°C). Preferably, the electrodeposition reduction mode is implemented immediately after the charging operation.

[0109] FIG. 12 shows an example 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 schematically shown. The three coils 8A, 5, and 7 are wound around the central pole of the soft magnetic core 13A. The number of turns of the secondary coil 5 is preferably one turn.

[0110] The effects of this embodiment are described. First, the transformer 13 of the grid charger 11 also serves as a step-down transformer of the AC current supply circuit. Further, the battery-side converter 4A and the grid-side converter 9 of the grid charger 11 each also serve as an oscillator of the AC current supply circuit. Next, the influence of the inductance of the secondary coil 5 is 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. Thereby, a secondary reverse voltage is induced in the secondary coil 5. The direction of this secondary reverse voltage is opposite to the direction of the current flowing through the secondary coil 5. Thereby, the adverse effect of the secondary coil 5 when the relays 31 and 34 are turned off is suppressed.

[0111] Furthermore, the above 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 when the pre-charge relay 32 is turned on. First, by turning on the relays 35 and 36, the battery-side converter 4A applies a primary reverse voltage to the coil 8A. Thereby, a secondary reverse voltage is induced in the secondary coil 5. The direction of this secondary reverse voltage is the direction to reduce the inrush current of the smoothing capacitor 2. Thereby, the inrush current is reduced.

[0112] A modified form of the transformers 13 and 14 shown in FIG. 11 will be described with reference to FIG. 13. The soft magnetic core 15A of the transformer 15 shown in FIG. 13 has a first pole 101A, a second pole 101B, and a third pole 101C. The soft magnetic core 15A further has horizontal bars 101D, 101E, 101F, and 101G. The coils 5, 7, 8A are wound around the first pole 101A, and the coils 6 and 8B are wound around the third pole 101C. The second pole 101B has no coil.

[0113] Therefore, the magnetic fluxes of the coils 5, 7, 8A flow through a closed-loop magnetic path formed by the first pole 101A, the horizontal bar 101D, the second pole 101B, and the horizontal bar 101E. Similarly, the magnetic fluxes of the coils 6 and 8B flow through a closed-loop magnetic path formed by the third pole 101C, the horizontal bar 101F, the second pole 101B, and the horizontal bar 101G.

[0114] Ultimately, the transformer 15 shown in FIG. 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. Fifth Embodiment

[0115] The fifth embodiment will be described with reference to FIG. 14. The electric propulsion system of this embodiment is similar to the electric propulsion system shown in FIG. 11. However, this embodiment uses one transformer 16 instead of the two transformers 13 and 14 shown in FIG. 11. Further, this embodiment uses two coils 6A and 6B connected in series instead of the one coil 6 shown in FIG. 13.

[0116] 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 the rectifier 61.

[0117] The positive terminal B+ of the high-voltage battery 1 is connected to the positive terminal C+ of the smoothing capacitor 2 through the relay 31. The negative terminal B- of the battery 1 is connected to the negative terminal C- of the smoothing capacitor 2 through the relay 34 and the coil 5. The three-phase inverter 20 for motor drive is connected in parallel with the smoothing capacitor 2. The relays 32 and 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 the relays 35 and 36.

[0118] The coil 7 is connected to the electrical grid through the 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. Eventually, the aforementioned grid charger is formed by the grid-side converter 9, the coil 7, the coils 8A and 8B, and the battery-side converters 4A and 4B.

[0119] The battery 1 charges the low-voltage battery 60 through the battery-side converters 4A and 4B, the coils 8A and 8B, the coils 6A and 6B, and the rectifier 61. This operation is called the DCDC converter mode. The battery-side converters 4A and 4B, the coils 8A and 8B, the coils 6A and 6B, and the rectifier 61 form a DCDC converter for charging the low-voltage battery 6. The secondary voltage induced in the coils 6A and 6B connected in series is rectified by the rectifier 61. The rectifier 61 charges the low-voltage battery 60. The low-voltage battery 60 with a rated voltage of 12V supplies control power to the controller 30.

[0120] 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 circulates a high-frequency current in this closed-loop circuit.

[0121] The operating modes implemented by the controller 30 are described. 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 DCDC converter mode. These modes will be described in order.

[0122] First, the grid charging mode is described. First, the relays 35 and 36 are turned on. When the rectifier 93 composed of a diode bridge is connected to the electrical grid, 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 to the primary coil 7.

[0123] 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 equal turns values. Eventually, the battery-side converters 4A and 4B as rectifiers charge the battery 1 in parallel.

[0124] Next, the grid-connected battery heating mode is 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 electrical 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 through the closed-loop circuit composed of the coil 5, the battery 1, and the smoothing capacitor 2, and the battery 1 is heated. When the temperature of the battery 1 reaches a predetermined value, this grid-connected battery heating mode ends.

[0125] Next, the DCDC converter mode will be described. First, relays 35 and 36 are turned on. In this DCDC converter mode, the battery-side converters 4A and 4B each operate as an oscillator. The battery-side converter 4A supplies a high-frequency current to the coil 8A, and the battery-side converter 4B supplies a high-frequency current to the coil 8B. The sum of the secondary voltages induced in the coils 6A and 6B is rectified by the rectifier 61 and applied to the low-voltage battery 60. The battery-side converters 4A and 4B are PWM-controlled according to the voltage of the low-voltage battery 60.

[0126] Next, the battery-connected battery heating mode will be described. The rectifier 93 is disconnected from the electric grid. First, relays 31, 34, 35, and 36 are turned on. The battery-side converters 4A and 4B operating as oscillators supply high-frequency currents to the coils 8A and 8B, and a secondary voltage is induced in the secondary coil 5. As a result, a high-frequency current flows through the closed-loop circuit composed of the battery 1, the smoothing capacitor 2, and the coil 5, and the battery 1 is heated. When the battery-connected battery heating mode and the motor drive mode are simultaneously implemented, the high-frequency current is limited so that the maximum current flowing through the battery 1 is less than a predetermined threshold value.

[0127] According to this embodiment, both the battery-connected battery heating mode and the DCDC converter mode use the battery-side converters 4A and 4B as oscillators. Therefore, when the oscillators 4A and 4B supply a primary current to the coils 8A and 8B, a secondary voltage is induced in the coils 5, 6A, and 6B as secondary coils. In other words, the battery-connected battery heating mode and the DCDC converter mode are simultaneously implemented. However, it is preferable that the battery-connected battery heating mode and the DCDC converter mode be independently implemented. This problem is solved by adopting a special transformer 16 called a flux-switching type transformer.

[0128] Figs. 15 and 16 are schematic cross-sectional views showing one structural example of the transformer 16. The soft magnetic core 16A has three poles 101A, 101B, and 101C, and further has four horizontal bars 101D, 101E, 101F, and 101G. The pole 101A, the horizontal bar 101D, the pole 101B, and the horizontal bar 101E form a first closed magnetic circuit. The pole 101C, the horizontal bar 101F, the pole 101B, and the horizontal bar 101G form a second closed magnetic circuit.

[0129] To avoid magnetic saturation, these closed magnetic circuits each have a narrow air gap. The horizontal bars 101D and 101F magnetically short-circuit the upper ends of the three poles 101A, 101B, and 101C. Similarly, the horizontal bars 101E and 101G magnetically short-circuit the lower ends of the three poles 101A, 101B, and 101C.

[0130] The coil 8A and the coil 6A are wound around the pole 101A, and the coil 8B and the coil 6B are wound around the pole 101C. In other words, the coil 8A and the coil 6A are wound around the first closed magnetic circuit, and the coil 8B and the coil 6B are wound around the second closed magnetic circuit. However, the coils 8A, 6A, 8B, and 6B are not wound around the pole 101B which is the common magnetic path of the first closed magnetic circuit and the second closed magnetic circuit.

[0131] The coils 6A and 6B connected in series have equal number of turns. The coils 8A and 8B have equal number of turns. The coils 5 and 7 are wound around the pole 101B. Preferably, the number of turns of the coil 5 is one turn. In the transformer 16, the magnetic coupling between the coils 8A and 8B and the coil 5 is called magnetic flux sum coupling, and the magnetic coupling between the coils 8A and 8B and the coils 6A and 6B is called magnetic flux difference coupling.

[0132] As shown in Figs. 15 and 16, the battery-side converter 4A connected to the coil 8A consists of an H-bridge having two legs 401 and 402. Similarly, the battery-side converter 4B connected to the coil 8B consists of an H-bridge having two legs 403 and 404.

[0133] A controller 30 having a flux sum mode, a mode, and a flux difference mode selects either flux sum coupling or flux difference coupling by switching the direction of the primary current supplied from the battery-side converter 4B to the coil 8B. By implementing the flux sum mode, flux sum coupling is selected, and by implementing the flux difference mode, flux difference coupling is selected. In both the flux sum mode and the flux difference mode, the first primary current I1A supplied from the battery-side converter 4A to the coil 8A has the same amplitude value and the same frequency value as the second primary current I1B supplied from the battery-side converter 4B to the coil 8B.

[0134] 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 each other. As a result, the direction of the magnetic flux F1 formed in the pole 101A by the coil 8A becomes upward, and the direction of the magnetic flux F2 formed in the pole 101C by the coil 8B also becomes upward. Therefore, the two magnetic fluxes F1 and F2 having the same waveform flow downward in the pole 101B.

[0135] According to this flux sum mode, a secondary voltage is induced in the coils 5 and 7. Since the coil 7 is connected to the oscillator 91, the influence of the secondary voltage induced in the coil 7 is ignored. Due to the secondary voltage induced in the coil 5, the battery heating mode is implemented. That is, this flux sum mode is adopted in the battery heating mode.

[0136] Furthermore, according to this flux sum mode, a secondary voltage is induced in coils 6A and 6B. However, coils 6A and 6B are connected to each other such that the sum of the secondary voltages of the serially connected coils 6A and 6B becomes zero. In other words, the secondary voltage applied by coil 6A to rectifier 61 is in the opposite direction to the secondary voltage applied by coil 6B to rectifier 61. As a result, the sum of the secondary voltages applied by coils 6A and 6B to rectifier 61 becomes zero, and the DC-DC converter mode is not implemented in the flux sum mode.

[0137] FIG. 16 shows the flow of current and flux in the flux difference mode. In this flux difference mode, the first primary current I1A supplied to coil 8A has a phase opposite to that of 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. By inverting the waveform of the second primary current I1B, the change from the flux sum mode to the flux difference mode is implemented. This change is easily implemented by the PWM control of the H-bridge 4B which is the battery-side converter.

[0138] The primary current I1B supplied by the H-bridge 4B shown in FIG. 16 to coil 8B has a waveform opposite to that of the primary current I1B supplied by the H-bridge 4B shown in FIG. 15 to coil 8B.

[0139] In the flux difference mode shown in FIG. 16, the first primary current I1A supplied to coil 8A forms a flux F1 in pole 101A, and the second primary current I1B supplied to coil 8B forms a flux F2 in pole 101C. Flux F1 and flux F2 have the same waveform. However, flux F1 flows upward through pole 101A, while flux F2 flows downward through pole 101C.

[0140] Ultimately, according to this flux difference mode, fluxes F1 and F2 having the same waveform flow in opposite directions within pole 101B. This means that the sum of the fluxes flowing within pole 101B becomes zero. Therefore, the secondary voltages induced in coil 5 and coil 7 each become zero.

[0141] Next, in this magnetic flux difference mode, magnetic fluxes F1 and F2 having the same direction flow through poles 101A and 101C. As a result, the sum of magnetic fluxes F1 and F2 induces secondary voltages in coils 6A and 6B, respectively. As a result, coils 6A and 6B apply secondary voltages in 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 the DCDC converter mode for transmitting DC power from battery 1 to battery 60.

[0142] The flow of magnetic flux in the grid charging mode described above is 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 causes magnetic flux F1 to flow through pole 101A and magnetic flux F2 to flow through pole 101C. In other words, half of the magnetic flux formed by coil 7 flows through pole 101A and the other half flows through pole 101C. Eventually, 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 becomes zero. Therefore, the DCDC converter mode is not implemented. Sixth Embodiment

[0143] The protection technology for relatively large-capacity batteries such as those for electric vehicles has been described by the above-described embodiments. However, the present invention is also effective for small-capacity batteries mounted in small electronic devices and small electric devices such as mobile phones, personal computers, electric drivers, vacuum cleaners, and electric bicycles.

[0144] An alternating current supply device for suppressing deterioration of a small battery will be described with reference to FIG. 17. Battery 1 built into a vacuum cleaner is a lithium ion battery composed of four cells 1A, 1B, 1C, and 1D connected in series. Battery 1 incorporates a battery management system 801 called BMS.

[0145] The charging terminals 821 and 822 of the battery 1 are connected to the charger 800. The charger 800 applies a charging voltage formed by rectifying grid power to the battery 1. The controller 30 controls the charging current Ic supplied from the charger 800 to the battery 1 based on the internal state of the battery 1. The charger 800 incorporates a DC power source and a switching regulator. This DC power source rectifies and steps down the grid voltage. The switching regulator supplies the charging current formed using the DC power received from this DC power source unit to the battery 1. The charger 800 controls battery charging by the well-known CCCV method.

[0146] Furthermore, a discharge circuit 830 is connected to the charging terminals 821 and 822 of the battery 1. This discharge circuit 830 consists of a MOSFET 802 and a discharge resistor 803 connected in series. When the MOSFET 802 is turned on, the battery 1 discharges through the discharge resistor 803.

[0147] After the battery charging is completed, the controller 30 executes an electrodialysis reduction mode. In this electrodialysis 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 sequentially performed consists of a charging period and a discharging period.

[0148] In one example, one cycle period is 200 μs, the charging period is 120 μs, and the discharging period is 60 μs. The transition periods respectively arranged between the charging period and the discharging period are 10 μs. The average value of the discharge current flowing during the discharging period is approximately twice the average value of the charging current flowing during the charging period. Preferably, the discharge circuit 830 is incorporated in the charger 800. According to this embodiment, the supply of an alternating current for suppressing battery deterioration can be realized by a simple circuit.

[0149] Next, a preferred control example of the charger 800 and the discharge circuit 830 by the controller 30 will be described with reference to the flowchart shown in FIG. 18. The discharge mode is the residual charge discharge mode described in FIGS. 3 to 5. The dendrite reduction mode is the mode described in FIGS. 6 and 7. The dendrite reduction mode and the discharge mode are essentially the same and have a current waveform as shown in FIG. 9, for example.

[0150] First, it is determined whether the constant current charging (CC) has ended (S200). Next, the amplitude, cycle period, and supply time of the alternating current to be supplied to the battery 1 are determined based on the content of the constant current charging (CC) (S202). Preferably, the average amplitude and supply time of the alternating current are positively correlated with the product of the amplitude and charging time of the charging current in the constant current charging (CC). Preferably, a map storing the relationship between the average amplitude and supply time of the alternating current and the product of the amplitude and charging time of the charging current is used.

[0151] Next, based on the determined specifications of the alternating current, the dendrite reduction mode is implemented (S204). Next, after the controller 30 determines the end of the dendrite reduction mode (S206), it 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 much larger than that 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 reduced well.

[0152] Next, it is determined whether the constant voltage charging (CV) mode has ended (S206), and if it has ended, the discharge mode (residual charge discharge mode) is executed (S208). Seventh Embodiment

[0153] One drawback of the apparatus 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 the conventional charger 800 that does not have the discharge circuit 830. A charge and discharge circuit 840 that can solve these drawbacks will be described with reference to FIG. 19.

[0154] FIG. 19 is a schematic diagram showing an alternating current supply device 901 that can be easily connected to the mobile phone 900. The mobile phone 901 has a female connector 902 as a charging terminal. The alternating current supply device 901 has a male connector 903 that can be inserted into the female connector 902.

[0155] FIG. 20 is a circuit diagram showing the charge and discharge circuit 840 incorporated in the alternating current supply device 901. Further, the alternating current supply device 901 also houses the controller 30. The male connector 903 having the same shape as the male connector of the charger 800 is connected to a pair of power lines 841 and 842 of the charge and 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 and discharge mode of the charge and discharge circuit 840, and then ends this charge and discharge mode after a predetermined time has elapsed. Thereby, the life of the battery incorporated in the mobile phone 900 can be extended. The charge and discharge circuit 840 can be incorporated in the charger 800 of the mobile phone.

[0156] The charge and discharge circuit 840 includes three half-bridges 811-813, two inductors 814 and 815, and the controller 30. The charge and discharge circuit 840 has a pair of power lines 841 and 842 that are detachably and individually connected to a pair of charging terminals 821 and 822 of the battery 1. The half-bridges 811-813 are respectively connected to the power lines 841 and 842.

[0157] 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.

[0158] 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 each transistor of the three half-bridges 811 - 813. This electrodeposition reduction mode is implemented after the charging operation from the charger 800 to the battery 1 is completed. After the charging operation of the charger 800 ends, a pair of output terminals of the charger 800 are disconnected from the charging terminals 821, 822 of the battery 1. Thereafter, a pair of power lines 841, 842 of the charge and discharge circuit 840 are connected to the charging terminals 821, 822 of the battery 1.

[0159] Figure 21 shows the discharge current Id and the charging current Ic flowing between the inductors 814 and 815 and the battery 1 in this electrodeposition reduction mode. The discharge period Td and the charging period Tc are arranged alternately in the electrodeposition reduction mode. First, the discharge period Td will be described. The transistors 811H, 812L, and 813H are turned on at time t1. As a result, the discharge current Id1 flowing through the inductor 814 increases, and the charging current Id2 flowing through the inductor 815 increases. The discharge current Id consists of the currents Id1 and Id2 simultaneously supplied from the battery 1 to the inductors 814 and 815. As a result, a predetermined discharge power energy is transported from the battery 1 to the inductors 814 and 815.

[0160] Next, the charging period Tc is described. The charging period Tc consists of a first charging period Tc1 and a second charging period Tc2 that are sequentially implemented. The first charging period Tc1 starts at time t2 and ends at time t3. The second charging period Tc2 starts at time t3 and ends at time t1. The discharging period Td starts at time t1 and ends at time t2. In the first charging period Tc1, transistors 811H and 812L are turned off. Thereby, the inductor 814 charges the battery 1 through diodes 811L and 812H. The charging current Ic1 is approximately equal to the discharging current Id1. The first charging period Tc1 ends when the transistor 811H is turned on. Thereafter, the freewheeling current circulates through the inductor 814, diode 812H, and transistor 811H. The current flowing through the inductor 815 in the first charging period Tc1 becomes the freewheeling current that circulates through the diode 812H and transistor 813H.

[0161] Next, the second charging period Tc2 is described. In the second charging period Tc2, the transistor 813H is turned off. Thereby, the inductor 815 charges the battery 1 through diodes 813L and 812H. This charging current Ic2 is approximately equal to the discharging current Id2. The second charging period Tc2 ends when the transistor 813H is turned on. Thereafter, the freewheeling current circulates through the inductor 815, diode 812H, and transistor 813H. The current flowing through the inductor 814 in the second charging period Tc2 becomes the freewheeling current that circulates through the diode 812H and transistor 811H.

[0162] FIG. 21 schematically shows an alternating current flowing between the battery 1 and the charge / discharge circuit 840. One cycle period Tcycle consists of one discharge period Td and one charge period Tc that are sequentially implemented. 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 sequence. Eventually, a discharge current Id that is approximately twice the charge current Ic flows during the discharge period Td, which is approximately half of the charge period Tc.

[0163] In FIG. 21, the fundamental frequencies of the discharge current Id and the charge current Ic are each equal to the reciprocal value of one cycle period Tcycle. The discharge current Id includes discharge harmonics, and the charge current Ic includes charge harmonics. The discharge harmonics and the charge harmonics each consist of frequency components that are integer multiples of the fundamental frequency. The discharge current Id within the discharge period Td has an average amplitude that is approximately twice that of the charge current Ic within the charge current Ic. However, the discharge harmonics within the discharge period Td can have an average amplitude that is even higher than twice that of the charge harmonics within the charge period Tc. In other words, in the high-frequency region, the discharge current Id is much higher than the charge current Ic. Therefore, the discharge current Id can have a relatively excellent effect of reducing the electroactive material compared to the charge current Ic.

[0164] A modified embodiment is described. The charge / discharge circuit 840 shown in FIG. 21 has two inductors 814 and 815 and three half-bridges 811 - 813. The charge / discharge circuit 840 can further have more sets each consisting of an additional inductor and an additional half-bridge. Each inductor is connected in series. For example, one end of this additional inductor is connected to the output end of the half-bridge 813, and the other end is connected to the output end of the additional half-bridge. Thereby, the discharge current Id can have an amplitude that is three times that of the charge current Ic. Furthermore, the charge period Tc can have a length that is three times that of the discharge period Td. As a result, the harmonic components included in the discharge current Id can be relatively increased even further compared to the harmonic components included in the charge current Ic. Eighth Embodiment

[0165] The eighth embodiment will be described with reference to FIG. 22. In this embodiment, the charge and discharge circuit 840 of the seventh embodiment shown in FIGS. 20 and 21 is used to supply an alternating current to an electric vehicle battery. The charge and discharge circuit including inductors 814 and 815 and half-bridges 811-813 has the same circuit configuration and the same operation as the charge and discharge circuit 840 shown in FIG. 20.

[0166] The circuit portion of FIG. 22 different from the charge and discharge circuit 840 shown in FIG. 20 will be described below. The high-voltage battery 1 supplies a direct current to an inverter 20 that drives an EV motor (not shown) through system switches 31 and 34. The smoothing capacitor 2 is connected in parallel with the inverter 20. The battery 1 applies the battery voltage to the three half-bridges 811-813.

[0167] 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.

[0168] The transformer 15 has a ferrite core 15A. The ferrite core 15A has three poles 101A, 101B, and 101C that are magnetically connected in parallel. The inductor 814 consists of a coil wound around the pole 101A. The coil 7 is wound around the pole 101B. The inductor 815 consists of a coil wound around the pole 101C. As shown in FIG. 22, the inductors 814 and 815 are wound in opposite directions to each other. The two coils forming the inductors 814 and 815 also each function as a secondary coil of the transformer 15. The three half-bridges 811-913 also function as a rectifier of the grid charger 9.

[0169] The operation of the circuit shown in FIG. 22 will be described. The charge and discharge circuit composed of inductors 814 and 815 and half-bridges 811-813 supplies an alternating current to the battery 1 during the period when the grid charger 9 is not performing the charging operation. Thereby, the battery heating mode and the electrodeposition reduction mode described above are implemented. In other words, when the oscillator 91 is not supplying a high-frequency current to the primary coil 7, the half-bridges 811-813 supply an alternating current to the battery 1.

[0170] The arrows shown in FIG. 22 indicate the direction of the alternating current supplied to the inductors 814 and 815. The magnetic flux F1 formed by the inductor 814 and the magnetic flux F2 formed by the inductor 815 flow in the same direction inside the core 15A. As a result, since the magnetic flux (F1 - F2) flowing through the pole 101B decreases, the alternating voltage induced in the coil 7 decreases.

[0171] 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 the switching operation for forming an alternating current. As a result, the half-bridges 811-813 operate as rectifiers. The high-frequency magnetic flux formed by the primary coil 7 flows in parallel to the inductors 814 and 815. As a result, the half-bridges 811-813 operated as rectifiers apply a rectified voltage to the battery 1. Thereby, the battery 1 is charged. The controller 30 controls the battery charging operation and the alternating current supply operation to the battery described above. According to this embodiment, since the grid charger 9 also serves as an alternating current supply circuit that supplies an alternating current to the battery 1, the circuit cost is reduced.

[0172] Ultimately, according to the electrodeposition reduction mode described above, by alternately supplying a high-frequency discharge current component and a low-frequency charging current component to the battery, the electrodeposited substance inside or on the SEI film is reduced. In other words, the discharge current component has a frequency spectrum shifted to the high-frequency side compared to the charging current component. Thereby, in addition to reducing the electrodeposited substance, the electrical characteristics of the surface of the negative electrode active material are improved.

[0173] A solid type, liquid type, or gel type electrolyte is employed in the battery. The electrical properties of the surface of the negative electrode active material in contact with these electrolytes are very important for the battery. The electrodeposition reduction mode of the present invention improves the electrical properties of the surface of the negative electrode active material by means of an alternating current having a frequency spectrum in which the discharge current Id is substantially higher than the charge current Ic. Furthermore, it can also be expected that the electrodeposition reduction mode realizes other effects such as reduction of the internal resistance of the battery. For example, it is expected to reduce the electrical resistance of this interface by expelling protons that have penetrated into the interface between the solid electrolyte and the negative electrode active material to the outside. Furthermore, it is expected to reduce the interface electrical resistance by reducing the thickness of the SEI film. Example 9

[0174] Example 9 will be described with reference to FIG. 23. This example discloses another economical alternating current supply circuit for supplying an alternating current to the battery. FIG. 23 is a circuit diagram showing this alternating current supply circuit and a DC power supply including the battery. This DC power supply has a pair of output terminals C+ and C− for supplying propulsion power to the drive motor of the electric propulsion device.

[0175] The battery essentially consists of a first battery pack 1A and a second battery pack 1B connected in parallel. The battery packs 1A and 1B each consist of a number of lithium ion battery cells connected in series. The cell voltage of each cell of the first battery pack 1A is detected by the first battery management system (BMS) 801, and the cell voltage of each cell of the second battery pack 1B is detected by the second battery management system (BMS) 802.

[0176] The first BMS 801 monitors the detected voltage value, detected temperature value, and detected current value of the first battery pack 1A. Further, the first BMS 801 performs a cell balancing operation to reduce the difference between the cell voltages of the first battery pack 1A. Similarly, the second BMS 802 monitors the detected voltage value, detected temperature value, and detected current value of the second battery pack 1B. Further, the second BMS 802 performs a cell balancing operation to reduce the difference between the cell voltages of the second battery pack 1B. The controller 30 that receives the detected signal determines abnormal events of the battery packs 1A and 1B.

[0177] The positive terminal of the first battery pack 1A is connected to the high-level output terminal C+ through the first secondary coil 5A and the first system relay 34A. Similarly, the positive terminal of the second battery pack 1B is connected to the high-level output terminal C+ through the second secondary coil 5B and the second system relay 34B.

[0178] The negative terminals of the battery packs 1A and 1B are connected to the low-level output terminal C- through the low-level system relay 31. The serially connected sub-relay 32 and the low-resistance element 33 are connected in parallel with the low-level system relay 31. As is well known, when the sub-relay 32 is turned on, the inrush current supplied from the battery packs 1A and 1B to a smoothing capacitor (not shown) is limited.

[0179] The first secondary coil 5A and the second secondary coil 5B are wound around the magnetic core 13A of the step-down transformer 13. The primary coil 50 is wound around the magnetic core 13A. The oscillator 40 applies an alternating voltage to the primary coil 50. For example, the output terminals C+ and C- of the DC power supply apply the power supply voltage to the oscillator 40. As shown in FIG. 23, the two secondary coils 5A and 5B are wound in the same direction.

[0180] The operation of this DC power supply will be described. First, the dual mode in which two battery packs 1A and 1B are normal will be described. When relays 34A and 34B are turned on, battery pack 1A supplies load current I1 to an external load, and battery pack 1B supplies load current I2 to the external load. The load currents I1 and I2 are substantially equal. Further, the number of turns of secondary coils 5A and 5B is also equal. The DC magnetic flux formed in magnetic core 13A of step-down transformer 13 is proportional to the load current difference (I1 - I2). Therefore, magnetic saturation of magnetic core 13A is suppressed. The important point is that the total load current (I1 + I2) is hardly affected by the inductance of secondary coils 5A and 5B. As a result, when system relays 34A and 34B are turned off, the surge voltages of system relays 34A and 34B due to the inductance of secondary coils 5A and 5B can be reduced.

[0181] When the temperature of battery pack 1A or 1B is low, controller 30 executes a battery heating mode. In this battery heating mode, oscillator 40 applies an AC voltage to primary coil 50, and a primary AC current flows through primary coil 50. As a result, secondary AC voltages V2 are induced in secondary coils 5A and 5B, respectively. The sum of these secondary AC voltages V2 circulates a secondary AC current Iac in a closed loop circuit formed by battery pack 1A, secondary coil 5A, system relay 34A, system relay 34B, secondary coil 5B, and battery pack 1B. Thereby, battery packs 1A and 1B are heated. When battery pack 1A discharges AC current Iac, battery pack 1B is charged by AC current Iac. Conversely, when battery pack 1B discharges AC current Iac, battery pack 1A is charged by AC current Iac. Therefore, step-down transformer 13 does not need to have a high inductance for accumulating AC power energy.

[0182] Next, the single-sided mode that is implemented when either the battery pack 1A or 1B is defective will be described. When the battery pack 1A is defective, the controller 30 turns off the first system relay 34A. As a result, the battery pack 1B supplies the load current I2 to the motor drive circuit. On the other hand, when the battery pack 1B is defective, the controller 30 turns off the second system relay 34B. As a result, the battery pack 1A supplies the load current I1 to the motor drive circuit.

[0183] Immediately before the above-mentioned turn-off operation of the system relay 34A or 34B, it is preferable that the controller 30 commands the external load to reduce the load current (I1 + I2). Eventually, when either one of the two battery packs 1A and 1B is defective, the DC power supply can drive the external load. Of course, when both of the two battery packs 1A and 1B are defective, all of the system relays 31, 34A, and 34B are turned off. According to this embodiment, a compact battery heating circuit for a DC power supply that employs two battery packs 1A and 1B connected in parallel can be realized. Example 10

[0184] Example 10 will be described with reference to FIG. 24. This example discloses another economical AC current supply circuit for supplying an AC current to the battery. FIG. 24 is a circuit diagram showing this AC current supply circuit and a DC power supply including a battery. The DC power supply shown in FIG. 24 supplies a DC voltage for motor drive to the motor drive circuit 20. The smoothing capacitor 2 is connected in parallel with the motor drive circuit 20. The DC power supply shown in FIG. 24 has an essentially equal circuit configuration to the DC power supply shown in FIG. 23. The differences between the circuits of these two DC power supplies will be described below.

[0185] The characteristic of the DC power supply shown in FIG. 24 is that the second secondary coil 5B is wound in the opposite direction to the first secondary coil 5A compared to the DC power supply shown in FIG. 23. Therefore, when the oscillator 40 induces the first secondary AC voltage in the first secondary coil 5A, the second secondary AC voltage is induced in the second secondary coil 5B. The amplitudes of these two secondary AC voltages are essentially equal.

[0186] This DC power supply has essentially the same operation as the DC power supply of the ninth embodiment. When one of the two battery packs is defective, the controller 30 turns off the system relay connected in series with this defective battery pack. In order to reduce the surge voltage when the system relay is turned off, it is preferable to control the motor drive circuit 20. Further, immediately before the system relays 34A and / or 34B are turned off, the oscillator 40 can also induce a secondary voltage in the secondary coils 5A and 5B. This secondary voltage has a direction to reduce the load currents I1 and I2. Thereby, the surge voltage generated when the system relays 34A and / or 34B are turned off can be suppressed.

[0187] Next, the AC current supply operation for supplying an AC current to the battery packs 1A and 1B will be described. The battery pack 1A, the secondary coil 5A, the system relay 34A, the smoothing capacitor 2, and the system relay 31 form a first closed loop circuit. Similarly, the battery pack 1B, the secondary coil 5B, the system relay 34B, the smoothing capacitor 2, and the system relay 31 form a second closed loop circuit.

[0188] When the oscillator 40 supplies a primary AC current to the primary coil 50, the secondary coil 5A circulates a first secondary AC current Iac1 in the first closed loop circuit. Similarly, the secondary coil 5B circulates a second secondary AC current Iac2 in the second closed loop circuit.

[0189] The advantages of this embodiment will be described. First, since the DC power supply has two battery packs 1A and 1B connected in parallel, the motor drive circuit 20 can have high reliability. Further, the discharge current component and the charge current component included in the secondary alternating current can have different waveforms from each other. As a result, the electrodeposition reduction effect of the battery is improved. Example 11

[0190] Example 11 will be described with reference to FIG. 25. This example shows a mode of detecting the AC impedance of a battery using an AC current supply circuit for supplying an AC current to the battery. In FIG. 25, the battery 1 is connected in series with the secondary coil 5 of the step-down transformer 13. A battery management system 800 is connected to the battery 1. The battery 1 and the secondary coil 5 form a closed-loop circuit with a power storage device (not shown). The oscillator 40 supplies an AC primary current to the primary coil 50 of the step-down transformer 13. The step-down transformer 13 further has a current detection coil 51 for current detection. This current detection coil 51 is coupled to the primary coil 50 and the secondary coil 5 by a closed magnetic circuit. The AC impedance detection circuit 900 shapes the signal voltage induced in the current detection coil 51 and transmits it to the controller 30. The controller 30 has an AC impedance detection mode for detecting the AC impedance of the battery 1 based on the received signal voltage. Generally, this signal voltage is inversely proportional to the AC impedance of the battery 1. The controller 30 controls the oscillator 40 based on the detection signals of the BMS 800 and the AC impedance detection circuit 900.

[0191] Referring to the case of detecting overcharge of a battery based on the AC impedance of the battery, the features of this embodiment will be described. As a parameter adopted to determine the internal state of the battery such as overcharge, the AC impedance of the battery can have relatively higher detection accuracy than other known parameters such as the open-circuit voltage of the battery. This is because as the SOC increases, the migration resistance of lithium ions increases in the high-frequency region. However, since the impedance of the battery is very low, the signal voltage related to the AC impedance detected from the battery contains a lot of noise voltage. For example, the signal voltage obtained from the low-resistance element 81 for current detection shown in FIG. 8 contains a lot of resistive thermal noise voltage. Furthermore, the resistive thermal noise voltage of each switching element of the oscillator 4 also reduces the SNR of the signal voltage Vs.

[0192] This problem is well solved by adding a current detection coil 51 to the step-down transformer 13. Since the current flowing through the current detection coil 51 is very low, the increase in the size and weight of the step-down transformer 13 can be ignored. The turn ratio between the current detection coil 51 and the secondary coil 5 can be appropriately selected, but increasing the number of turns of the current detection coil 51 is effective in improving the SNR. It is easily understood that this current detection coil 51 can also be applied to the step-down transformer 13 shown in FIGS. 23 and 24. One current detection coil 51 detects the sum or difference of the secondary currents flowing through the two secondary coils 5A and 5B. Furthermore, battery degradation, SoC, and electrodeposition can also be detected based on the AC impedance of the battery detected by the AC impedance detection circuit 900 shown in FIG. 25. For example, as shown in FIGS. 6 and 7, the composite impedance of the negative electrode active material 503 consists of the parallel-connected electronic resistance r3 and ionic resistance R3. When the surface 505 of the negative electrode active material 503 is covered by a metallic lithium layer, the electronic resistance r3 decreases and the ionic resistance R3 increases. When the frequency of the alternating current increases, the ionic resistance R3 further increases. Eventually, the development of electrodeposition reduces the AC impedance of the battery in the high-frequency region.

[0193] Each of the above embodiments shows a preferred example of the present invention. However, the technical idea of the present invention should not be limited to these embodiments. For example, the electrolyte can be selected from any of a non-aqueous electrolyte, an all-solid electrolyte, and a semi-solid electrolyte.

Claims

In an AC current supply device for a battery, comprising an AC current supply circuit that supplies an AC current to the battery during an AC current supply period including alternately repeated discharge periods and charge periods, and a controller that controls the AC current supply circuit, the AC current includes a discharge current component supplied during the discharge period and a charge current component supplied during the charge period, the controller has an electrodeposition reduction mode in which the AC current is supplied to the battery when the temperature of the battery is higher than a predetermined room temperature, the discharge period is formed shorter than the charge period in the electrodeposition reduction mode, the discharge current component has a higher amplitude than the charge current component in the electrodeposition reduction mode, 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 component in parallel from the battery to the plurality of inductors, the switching circuit sequentially supplies the charge current component from the plurality of inductors to the battery. The AC current supply device for a battery is characterized by this.

2. the plurality of inductors are connected in series, the switching circuit consists of a plurality of half bridges connected to each inductor, each half bridge consists of an upper arm switch and a lower arm switch connected in series, one of the upper arm switch and the lower arm switch consists of a transistor, the other of the upper arm switch and the lower arm switch consists of a transistor or a diode. The AC current supply device for a battery according to Claim 1.

Images