Charging system and charging method for secondary batteries

Abstract

When controlling the charging of a secondary battery by detecting the ripple current with a current sensor, this prevents excessive restriction of the charging current when ripple current is detected. [Solution] The secondary battery charging system includes a current sensor that measures the current flowing through the secondary battery, and a control device that controls the charging of the secondary battery by referring to the measured value of the current sensor during charging of the secondary battery. The current sensor includes a magnetic current sensor. The charging control includes setting an allowable charging current value during charging of the secondary battery. If a ripple is detected from the measured value of the magnetic current sensor, and the detected ripple current value is greater than or equal to a predetermined current value, the charging current value is set using the detected ripple current value.

Description

Technical Field

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[0001] The present disclosure relates to a charging technique for secondary batteries.

Background Art

[0002] Japanese Patent No. 7149543 discloses a system that charges a secondary battery with AC power supplied from a commercial power supply system using a charger. A ripple component may be superimposed on the output power of the charger. The ripple voltage (minute voltage fluctuation) pulsates the voltages of a plurality of cells constituting the secondary battery. If the pulsation of the cell voltage becomes large, it may exceed the maximum allowable voltage of the cell. Therefore, the conventional system estimates the ripple voltage of each cell based on the total voltage of the plurality of cells and the internal impedance of each cell. The conventional system also cuts off the inflow of the charging current from the charger to the secondary battery when the estimated ripple voltage of each cell exceeds the allowable voltage range.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the conventional system, the inflow of the charging current is cut off because the ripple component contained in the charging current has an adverse effect on the cell. For example, when the secondary battery is a lithium-ion battery, the ripple current flowing into the lithium-ion battery may deposit lithium.

[0005] Conventional systems estimate the ripple voltage of each cell during charging and interrupt charging accordingly. However, it is also possible to directly detect the ripple component in the charging current and interrupt charging. In this case, the detection of the ripple current is performed using a current sensor. If a ripple current is detected, charging control is performed to prevent the ripple current from flowing into the secondary battery.

[0006] However, since ripple current is a high-frequency current, there is a problem when detecting ripple current using a shunt resistor type current sensor. Specifically, when ripple current occurs, the characteristic of the shunt resistor, where the increase in impedance due to the skin effect amplifies the frequency of the shunt voltage, may cause a larger ripple current to be detected than it actually is. This could lead to excessive limiting of the charging current in charge control.

[0007] One objective of this disclosure is to provide a technology that can suppress excessive restriction of the charging current when a ripple current is detected, in a case where the ripple current during charging of a secondary battery is detected by a current sensor and charging control is performed accordingly. [Means for solving the problem]

[0008] The first aspect of this disclosure is a charging system for a secondary battery, which has the following features: The charging system includes a current sensor for measuring the current flowing through the secondary battery, and a control device that controls the charging of the secondary battery by referring to the measured value of the current sensor during charging of the secondary battery. The current sensor includes a magnetic current sensor. The charging control includes setting a maximum chargeable current value that is permitted during the charging of the secondary battery. If a ripple is detected from the measurement value of the magnetic current sensor, and the detected ripple current value is equal to or greater than a predetermined current value, the rechargeable current value is set using the detected ripple current value.

[0009] The second aspect of this disclosure is a method for charging a secondary battery, which has the following features. The charging method includes measuring the current flowing through the secondary battery using a current sensor, and during the charging of the secondary battery, a control device controlling the charging of the secondary battery by referring to the measured value of the current sensor. The current sensor includes a magnetic current sensor. The charging control includes setting a maximum chargeable current value that is permitted during the charging of the secondary battery. If a ripple is detected from the measurement value of the magnetic current sensor, and the detected ripple current value is equal to or greater than a predetermined current value, the rechargeable current value is set using the detected ripple current value. [Effects of the Invention]

[0010] Unlike shunt-resistance current sensors, magnetic current sensors have the characteristic that the frequency of the magnetic field input to the sensor element is attenuated due to the skin effect. Therefore, from the standpoint of accurate detection of ripple current, magnetic sensors are superior to shunt-resistance sensors. This disclosure focuses on this point. Specifically, according to this disclosure, ripple is accurately detected from the measured value of a magnetic current sensor. If the detected ripple current value is greater than or equal to a predetermined current value, the detected ripple current value is used to set the allowable chargeable current value during charging of the secondary battery. Therefore, it is possible to prevent excessive restriction of the charging current when ripple current is detected. [Brief explanation of the drawing]

[0011] [Figure 1] This figure illustrates a configuration particularly relevant to a charging system according to an embodiment of the present disclosure. [Figure 2] This is a conceptual diagram explaining the epidermal effect. [Figure 3] This figure shows an example of the frequency characteristics of the shunt voltage. [Figure 4] This figure shows an example of the frequency characteristics of a magnetic field input to a magnetic current sensor. [Figure 5] This flowchart shows the processing flow for charging control of a secondary battery, which is particularly relevant to the embodiment. [Figure 6]It is a diagram showing an example of the relationship between the battery current and the minimum value and the average value over 10 milliseconds of the sampling current.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. However, the structures and the like described in the following embodiments are not necessarily essential to the present disclosure, unless specifically stated or clearly specified by principle.

[0013] 1. Charging System for Secondary Battery The charging system for the secondary battery according to the embodiment is a system for charging the secondary battery mounted on a vehicle. The vehicle on which the secondary battery is mounted is, for example, a vehicle capable of plug-in charging with electric power supplied from an external power source (external power supply) outside the vehicle. Examples of such vehicles include plug-in hybrid vehicles (PHV (Plug-in Hybrid Vehicle) and PHEV (Plug-in Hybrid Electric Vehicle)).

[0014] FIG. 1 is a diagram for explaining a configuration particularly related to the charging system according to the embodiment. In FIG. 1, an external power source 10, a power storage system 20, and a motor 30 are depicted. The external power source 10 is, for example, a household single-phase 100V AC power source or a single-phase 200V AC power source. The external power source 10 includes a charger 11 and a connector 12.

[0015] The charger 11 is a device for performing rapid charging of the secondary battery. For example, the charger 11 includes a boost / buck converter and various relays (not shown). The charger 11 performs rapid charging in response to a charging permission signal from the power storage system 20. During rapid charging of the power storage system 20, the charger 11 outputs a DC current according to the chargeable current value Itag[t] from the power storage system 20.

[0016] The power storage system 20 is a system mounted on a vehicle. In the example shown in FIG. 1, the power storage system 20 includes a charging lid 21, a power line 22, a secondary battery 23, a current sensor 24, and a control device 25.

[0017] The charging lid 21 is a part where the connector 12 is inserted. The power line 22 connects the charging lid 21 and the secondary battery 23. The power line 22 supplies the direct current received from the charger 11 through the connector 12 to the secondary battery 23. The secondary battery 23 is a power storage device for driving the motor 30. The secondary battery 23 is composed of a secondary battery such as a nickel-hydrogen battery or a lithium-ion battery. For example, the secondary battery 23 is composed of a stack in which a plurality of cells of about 1 to 5 V are stacked.

[0018] The current sensor 24 detects the current (battery current) Ib flowing through the secondary battery 23. The current sensor 24 includes two types of current sensors: a shunt resistance type and a magnetic type. The former includes, for example, a shunt resistance and a sensor IC. The former also measures the battery current Ib by amplifying the voltage (shunt voltage) generated at both ends of the shunt resistance inserted in the current path with an amplifier and processing it with the sensor IC. The latter measures the battery current Ib by measuring the magnetic field generated when the current flows. The latter includes a core type and a coreless type. The core type sensor inserts the sensor IC into the gap of the magnetic core and measures the magnetic field around the current path through the magnetic core. The coreless type sensor directly measures the magnetic field generated by the current drawn into the sensor IC.

[0019] The control device 25 is a computer that performs various controls in the vehicle. The control device 25 includes computer hardware such as a processor and memory, and operates according to the installed software such as the OS (Operating System) and application programs. The various controls performed by the control device 25 include charging control of the secondary battery 23. In the charging control of the secondary battery 23, the allowable current value during charging of the secondary battery 23 (i.e., the chargeable current value Itag) is set, and this is output to the charger 11.

[0020] Motor 30 drives a vehicle equipped with an energy storage system 20. Motor 30 is supplied with power from a secondary battery 23. Motor 30 converts the power supplied from the secondary battery 23 into rotational energy to rotate the wheels. Motor 30 may also be composed of a motor generator. In this case, motor 30 also operates as a generator. When operating as a generator, motor 30 converts regenerative energy during vehicle deceleration into electricity and stores it in the secondary battery 23. Multiple motors 30 may be provided on the vehicle.

[0021] 2. Characteristics of the current sensor The inclusion of a shunt resistor type current sensor in the current sensor 24 enables measurement of the battery current Ib, taking advantage of the low error characteristics of the shunt resistor. However, when charging the secondary battery 23 from the external power supply 10, the characteristics of the shunt resistor may hinder accurate measurement of the battery current Ib. This issue will be explained with reference to Figures 2 and 3.

[0022] Figure 2 is a conceptual diagram illustrating the skin effect. When a direct current flows through a wire, the current distribution inside the wire is uniform. However, when an alternating current flows through a wire, the current concentrates on the surface of the wire, and the flow of current becomes more difficult as you move from the surface towards the center. This phenomenon is the skin effect. The skin effect also becomes more pronounced as the frequency of the alternating current increases. In other words, high-frequency alternating current flows along the surface of the wire and hardly flows through the center of the wire.

[0023] When a ripple component is superimposed on the output power of the charger 11 during charging from an external power source 10, the skin effect caused by this ripple component increases the frequency of the charging current flowing into the secondary battery 23. Therefore, in current detection using a shunt resistor type current sensor, the increase in impedance due to the skin effect amplifies the frequency of the shunt voltage. Figure 3 shows an example of the frequency characteristics of the shunt voltage. As can be seen from Figure 3, the frequency of the shunt voltage increases in the high-frequency range of the charging current (ripple current).

[0024] The challenges encountered when charging from an external power source 10 are also anticipated when charging from the motor 30. Specifically, when the motor 30 operates as a generator, a ripple current is generated in proportion to the motor 30's output (torque × rotational speed), and the frequency of this ripple current increases with the rotational speed of the motor generator. Therefore, when charging from the motor generator, the increase in impedance due to the skin effect may amplify the frequency of the shunt voltage.

[0025] In contrast, magnetic current sensors have the characteristic that the frequency of the magnetic field input to the sensor IC is attenuated due to the skin effect. Figure 4 shows an example of the frequency characteristics of the magnetic field input to a magnetic current sensor. As can be seen from Figure 4, in a magnetic current sensor, the frequency of the magnetic field input to the sensor IC decreases in the high-frequency range of the charging current (ripple current). This is because, due to the skin effect, the higher the frequency of the alternating current that is concentrated on the surface side of the conductor (busbar), the more the magnetic field near the sensor IC is attenuated.

[0026] 3. Charging control Thus, from the standpoint of accurately detecting ripple current, the magnetic type is superior to the shunt resistor type. Therefore, in this embodiment, the measured value of the battery current Ib by the magnetic current sensor is used for charging control of the secondary battery 23. In other words, in this embodiment, the ripple current is detected using the magnetic measurement value of the battery current Ib measured by the current sensor 24, without using the shunt resistor measurement value, and the rechargeable current value Itag[t] is calculated. For various controls other than charging control of the secondary battery 23, the measured value of the shunt resistor type is used as appropriate.

[0027] Figure 5 is a flowchart showing the processing flow of the charging control of the secondary battery 23, which is particularly relevant to the embodiment. The routine shown in Figure 5 is repeatedly executed by the processor of the control device 25, for example, when the processor of the control device 25 sends a charge permission signal to the external power supply 10 (i.e., when plug-in charging is performed). The routine shown in Figure 5 is also repeatedly executed by the processor of the control device 25 while the motor 30 is operating as a generator.

[0028] In the routine shown in Figure 5, the battery current Ib is first sampled (step S11). Specifically, the battery current Ib is detected at 1ms intervals for 10ms. The detected battery current Ib is represented as Ib_1ms[0],···,Ib_1ms

[10] (Ib_1ms[0]-

[10] ).

[0029] Following the processing in step S11, the processing in step S12 is performed. In the processing in step S12, the minimum value Ib_1ms_min among the battery currents Ib_1ms[0],...,Ib_1ms

[10] detected in the sampling in step S11 is calculated, and the 10ms average value Ib_10ms(average(Ib_1ms[0]-

[10] )) of these battery currents Ib_1ms[0],...,Ib_1ms

[10] is calculated.

[0030] Following the processing in step S12, the processing in step S13 is performed. In the processing in step S13, the ripple current Ib_ripple is calculated. The ripple current Ib_ripple is calculated as the absolute value of the difference between the minimum value Ib_1ms_min calculated in step S12 and the average value Ib_10ms over 10 m seconds (|Ib_1ms_min-Ib_10ms|). An example of the relationship between the battery current Ib, the minimum value Ib_1ms_min, and the average value Ib_10ms over 10 m seconds is shown in Figure 6.

[0031] Following the processing in step S13, the processing in step S14 is performed. In the processing in step S14, it is determined whether the ripple current Ib_ripple calculated in the processing of step S13 is greater than or equal to a predetermined current value Ibk. The predetermined current value Ibk is a value that has been set in advance as the error equivalent value of the magnetic current sensor.

[0032] If the result of step S14 is positive, it is determined that a ripple has been detected, and the process in step S15 is performed. In the process in step S15, the chargeable current value Itag[t] is set using the following formula (1). Itag[t]=Ilim[t]'+Itag_OFFSET[t]+Ib_ripple[t]...(1) In equation (1), the current value Ilim[t]' is a value set according to the charging performance of the secondary battery 23, and the current value Itag_OFFSET[t] is a value set according to the sensor error, etc. The current value Ib_ripple[t] is a value calculated in the process of step S13. Note that the sign of each current value is treated as negative for charging current and positive for discharge current.

[0033] If the result of step S14 is negative, it is determined that no ripple was detected, and the process in step S16 is performed. In the process in step S16, the chargeable current value Itag[t] is set using the following formula (2). Itag[t]=Ilim[t]'+Itag_OFFSET[t]...(2)

[0034] 4. Effects According to the embodiment described above, in the charging control of the secondary battery 23, ripple is accurately detected using the battery current Ib measured by a magnetic current sensor. When the detected ripple current Ib_ripple is greater than or equal to a predetermined current value Ibk, the chargeable current value Itag is set using the detected ripple current Ib_ripple. Therefore, it is possible to suppress the occurrence of malfunctions that occur when controlling the charging of the secondary battery 23 using the battery current Ib measured by a shunt resistor type current sensor. [Explanation of symbols]

[0035] 10…External power supply, 11…Charger, 12…Connector, 20…Charging system, 21…Charging lid, 22…Power line, 23…Rechargeable battery, 25…Control device, 30…Motor, Ib…Battery current, Ib_ripple…Ripple current, Itag…Chargeable current value

Claims

1. A rechargeable battery system, A current sensor for measuring the current flowing through the secondary battery, The system includes a control device that controls the charging of the secondary battery by referring to the measured value of the current sensor while the secondary battery is being charged, The current sensor includes a magnetic current sensor, The charging control includes setting a maximum chargeable current value that is permitted during the charging of the secondary battery. If a ripple is detected from the measurement value of the magnetic current sensor, and the detected ripple current value is equal to or greater than a predetermined current value, the rechargeable current value is set using the detected ripple current value. A charging system for secondary batteries characterized by the following:

2. If a ripple is detected from the measurement value of the magnetic current sensor, and the detected ripple current value is less than a predetermined current value, the rechargeable current value is set without using the detected ripple current value. A charging system for a secondary battery according to feature 1.

3. The current sensor further includes a shunt resistor type current sensor, The measured value of the aforementioned shunt resistance current sensor is not used for ripple detection. A charging system for a secondary battery according to claim 1 or 2.

4. The magnetic current sensor is either a core-type current sensor having a magnetic core or a coreless type current sensor without a magnetic core. A charging system for a secondary battery according to claim 1 or 2.

5. A method for charging a rechargeable battery, The current flowing through the secondary battery is measured using a current sensor, The control device controls the charging of the secondary battery by referring to the measured value of the current sensor while the secondary battery is being charged, The current sensor includes a magnetic current sensor, The charging control includes setting a maximum chargeable current value that is permitted during the charging of the secondary battery. If a ripple is detected from the measurement value of the magnetic current sensor, and the detected ripple current value is equal to or greater than a predetermined current value, the rechargeable current value is set using the detected ripple current value. A method for charging a secondary battery, characterized by the following features.

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