Charging method

Abstract

To provide a charging method that can appropriately protect a battery.SOLUTION: A charging method is a method for specifying the frequency of a ripple current by analyzing the frequency of a current flowing in a battery during charging, calculating the magnitude of the ripple current before attenuation on the basis of the amount of attenuation of the current at the frequency, and determining the magnitude of the current to a value obtained by subtracting the magnitude of the ripple current before attenuation from a reference value.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a charging method.

Background Art

[0002] Regarding battery charging, for example, Patent Document 1 describes determining the ripple generated in the current flowing through the battery during charging.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The magnitude of the current during charging is controlled to a value obtained by subtracting the magnitude of the ripple current from a reference value based on, for example, the state of the battery so that the deterioration of the battery is suppressed. The ripple current is detected by a current sensor, but the detected value becomes smaller than the actual current value due to a noise removal filter incorporated in the current sensor. For this reason, the accuracy of current control becomes insufficient, and the battery may deteriorate. On the other hand, if a current sensor without a filter is used in combination, the accuracy can be improved, but problems of increased cost and size of the device occur.

[0005] Therefore, the present invention has been made in view of the above problems, and an object thereof is to provide a charging method capable of appropriately protecting a battery.

Means for Solving the Problems

[0006] The charging method of the present invention is a method of identifying the frequency of the ripple current by performing frequency analysis on the current flowing through the battery during charging, calculating the magnitude of the ripple current before attenuation based on the attenuation amount of the current at the frequency, and determining the magnitude of the current as a value obtained by subtracting the magnitude of the ripple current before attenuation from a reference value.

Advantages of the Invention

[0007] According to the present invention, the battery can be appropriately protected.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0009] (Configuration of Battery System) FIG. 1 is a configuration diagram schematically showing an example of a battery system of a vehicle V. The vehicle V includes a control device 1 including one or more ECUs (Electronic Control Units), a battery pack 2 as a power source, an inlet 3 for charging and discharging the battery pack 2, an inverter 4 for converting direct current into alternating current, and an electric motor (MG) 5 as a power source of the vehicle V. The battery pack 2 includes battery cells 20 as an example of a battery, a current sensor 21 for detecting a current value flowing through the battery cells 20, a voltage sensor 24 for detecting a voltage value of the battery cells 20, and a temperature sensor 25 for detecting the temperature of the battery cells 20. Detection values of the current sensor 21, the voltage sensor 24, and the temperature sensor 25 are output to the control device 1.

[0010] The control device 1 is a computer including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. The ECU 1 operates the CPU according to a program stored in the ROM. The control device 1 executes the charging method of this example.

[0011] The control device 1 controls the inverter 4. The inverter 4 converts a direct current into an alternating current by switching a plurality of switching elements such as MOS-FETs (Metal-Oxide-Semiconductor Field Effect Transistors). The control device 1 outputs a PWM (Pulse Width Modulation) signal with a duty ratio corresponding to the driving state of the vehicle V to the inverter 4.

[0012] Also, the control device 1 controls the charging of the battery cell 20. The battery cell 20 has a configuration in which, for example, a plurality of lithium ion batteries are connected in series. The battery cell 20 supplies DC power to the inverter 4. Thereby, the electric motor 5 is driven. The battery cell 20 is charged from an external charging stand 9.

[0013] The charging stand 9 is connected to the inlet 3 on the vehicle V side via a connector 90 of a charging cable (not shown). The inlet 3 is connected to the wiring between the battery pack 2 and the inverter 4. The charging stand 9 converts the AC power of the power system into DC power to charge the battery cell 20. The charging stand 9 converts power by switching a plurality of switching elements such as MOS-FETs.

[0014] When charging the battery cell 20, the control device 1 stops the operation of the inverter 4 and outputs a command value Icom of the current being charged to the charging stand 9. The charging stand 9 outputs a current Ic to the battery cell 20 according to the command value Icom. A ripple current is superimposed on the charging current Ic due to the switching operation of the charging stand 9.

[0015] The control device 1 calculates a command value Icom based on the detection values of the current sensor 21, the voltage sensor 24, and the temperature sensor 25. The current sensor 21 has a detection element 22 and a filter 23. The detection element 22 is, for example, a shunt resistor or a magnetic sensor element. The filter 23 is, for example, a low-pass filter that removes the noise contained in the current Ic. The ripple current is attenuated by the filter and becomes smaller than the actual ripple current.

[0016] Figure 2 is a waveform diagram showing an example of a ripple current. In Figure 2, the horizontal axis represents time, and the vertical axis represents current (A). The solid line indicates the actual current Ic, and the dotted line indicates the current Ic detected by the current sensor 21. The magnitude Ix of the actual ripple current is larger than the magnitude Idet of the ripple current detected by the current sensor 21. This is because the current Ic is attenuated by the filter 23 in the current sensor 21.

[0017] The control device 1 calculates the SOC (State Of Charge) of the battery cell 20 from the detection values of the current sensor 21, the voltage sensor 24, and the temperature sensor 25. The control device 1 calculates a reference value Iref of the current according to the SOC and temperature of the battery cell 20. The reference value Iref is the upper limit value of the magnitude of the current Ic. When the magnitude of the current Ic exceeds the reference value Iref, the deterioration and precipitation of the battery cell 20 progress.

[0018] The control device 1 may calculate the reference value Iref using, for example, map data stored in a memory (not shown). The map data shows the correlation between the SOC and temperature and the reference value Iref. Further, the control device 1 may calculate the reference value Iref in consideration of a predetermined offset value taking into account the delay time of the current control of the charging stand 9.

[0019] The control device 1 determines the command value Icom as a value obtained by subtracting the ripple current from the reference value Iref. Since the magnitude Idet of the ripple current detected by the current sensor 21 is smaller than the actual magnitude Ix, there is a possibility that the current Ic exceeds the reference value Iref. Therefore, the control device 1 corrects the magnitude Idet of the ripple current to the magnitude Ix of the ripple current before attenuation based on the attenuation characteristics of the filter 23.

[0020] (Operation of the control device) FIG. 3 is a flowchart showing an example of the operation of the control device 1. First, the control device 1 determines whether the battery cell 20 is being charged by communicating with the charging stand 9 via, for example, the inlet 6 (step St1). If the battery cell 20 is not being charged (No in step St1), this process ends.

[0021] Also, when the battery cell 20 is being charged (Yes in step St1), the control device 1 calculates the reference value Iref (steps St2a, St3a) and corrects the magnitude Idet of the ripple current to the actual magnitude Ix (steps St2b to St7b). In this example, the calculation of the reference value Iref and the correction of the ripple current are performed simultaneously in parallel, but they may also be executed sequentially.

[0022] In calculating the reference value Iref, the control device 1 acquires the SOC and temperature of the battery cell 20 (step St2a). Next, the control device 1 calculates the reference value Iref from the SOC and temperature using map data or the like (step St3a).

[0023] Also, in correcting the ripple current, the control device 1 samples the current value detected by the current sensor 21 (step St2b). Next, the control device 1 performs a fast Fourier transform (FFT) process on each sampled current value (step St3b). Next, the control device 1 identifies the frequency of the ripple current based on the result of the FFT process (step St4b). Note that the FFT process is an example of frequency analysis.

[0024] FIG. 4(a) is a diagram showing an example of the current waveform detected by the current sensor 21. The control device 1 samples a predetermined number of current values Ps at regular time intervals Δt. The time interval Δt is determined, for example, according to the detection period of the ripple current and the desired number of samplings.

[0025] FIG. 4(b) is a diagram showing an example of the frequency spectrum of the current. The control device 1 obtains the amplitude of the current for each frequency by performing FFT processing on the sampled current values Ps. The control device 1 excludes the DC component of the current and identifies the frequency X at which the amplitude is maximum as the frequency of the ripple current. The frequency of the DC component is set in advance, for example, in the memory of the control device 1.

[0026] Referring again to FIG. 3, after identifying the frequency X of the ripple current, the control device 1 calculates a correction gain for the ripple current based on the attenuation characteristics of the filter 23 (step St5b). The data on the attenuation characteristics of the filter 23 is set in advance, for example, in the memory of the control device 1.

[0027] Next, the control device 1 calculates the magnitude Idet of the ripple current by analyzing the sampled current values Ps (step St6b). Next, the control device 1 corrects the magnitude Idet of the ripple current by the correction gain (step St7b). Thereby, the control device 1 calculates the magnitude Ix of the ripple current before attenuation by the filter 23.

[0028] FIG. 4(c) is a diagram showing an example of the attenuation characteristics of the filter 23. In FIG. 4(c), the horizontal axis represents the frequency (MHz), and the vertical axis represents the gain (dB). The filter 23 is, for example, a low-pass filter, which has a substantially constant gain regardless of the frequency in the low-frequency region, but has a lower gain as the frequency is higher in the high-frequency region.

[0029] The control device 1 obtains a gain Y corresponding to the frequency X of the ripple current from the attenuation characteristic data. The control device 1 calculates the reciprocal of the gain Y as the correction gain. For example, when the gain Y is 20 dB, the correction gain is 1 / 100. The control device 1 calculates the magnitude Ix of the ripple current before attenuation by multiplying the magnitude Idet of the ripple current by the correction gain.

[0030] Referring again to FIG. 3, the control device 1 subtracts the magnitude Ix of the ripple current from the reference value Iref to calculate a command value Icom (= Iref - Ix) (step St8). Thereby, the control device 1 can determine the command value Icom so as not to exceed the reference value Iref based on the actual magnitude Ix of the ripple current.

[0031] Next, the control device 1 outputs the command value Icom to the charging stand 9 (step St9). The charging stand 9 controls the switching operation so that the current Ic flowing through the battery cell 20 being charged approaches the command value Icom. The control device 1 operates in this way.

[0032] As described above, the control device 1 identifies the frequency X of the ripple current by performing frequency analysis on the current Ic flowing through the battery during charging, and calculates the magnitude Ix of the ripple current before attenuation based on the attenuation amount of the current Ic at the frequency X. The control device 1 determines the magnitude of the current Ic as a value obtained by subtracting the magnitude Ix of the ripple current before attenuation from the reference value Iref.

[0033] According to the above charging method, the control device 1 can control the current Ic to an appropriate command value Icom based on the ripple current before attenuation by the filter 23 of the current sensor 21. Therefore, it is possible to suppress deterioration of the battery cell 20 due to the current Ic exceeding the reference value Iref and appropriately protect the battery cell 20.

[0034] The above-described embodiments are preferred examples of the present invention. However, the present invention is not limited thereto, and various modifications can be made without departing from the gist of the present invention.

Description of Reference Numerals

[0035] 1 Control device, 2 Battery pack, 20 Battery cells, 21 Current sensor, 23 Filter, 9 Charging stand

Claims

**Claim 1** identifying the frequency of the ripple current by performing frequency analysis on the current flowing through the battery during charging, calculating the magnitude of the ripple current before attenuation based on the attenuation amount of the current at the frequency, determining the magnitude of the current as a value obtained by subtracting the magnitude of the ripple current before attenuation from a reference value, charging method.

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