TWI867614B - Charging and discharging device and method - Google Patents

Abstract

The present invention mainly provides a charging and discharging device and method, which adopts a supercapacitor to absorb the charging and discharging current generated by the discharge of the secondary battery when the secondary battery is discharged, so as to solve the technical problem that the solid electrolyte interface film of the negative electrode material deteriorates over time. The charging and discharging device and method of the present invention calculates the positive ion diffusion time of the secondary battery. By obtaining this positive ion diffusion time, the frequency of at least one pulse width modulation signal used to control the bidirectional DC/DC converter can be obtained. Furthermore, the charging and discharging device and method of the present invention does not charge and discharge the secondary battery with a fixed current, but charges and discharges the secondary battery with a quasi-sine wave signal as the charging and discharging current.

Description

Charging and discharging device and method

The present invention relates to a charging and discharging device and method, and in particular to a charging and discharging device and method that can delay the aging of a secondary battery, reduce the temperature rise during charging of the secondary battery, improve the charging efficiency, increase the service life of the secondary battery, and reduce the power consumption required for charging.

The charging and discharging devices of the prior art use a constant current to charge and discharge the secondary battery, and currently most secondary batteries are lithium batteries. However, the charging method of continuously injecting a fixed energy with a constant current can easily cause stress at the boundary of the positive electrode material particles inside the lithium battery, and cause the solid electrolyte interface film (SEI film) of the negative electrode material to deteriorate over time. In other words, the prior art method of using a constant current to charge and discharge the secondary battery will accelerate the aging of the entire lithium battery.

On the other hand, when the charging and discharging device of the prior art uses a fixed current to charge the secondary battery, the temperature rise of the secondary battery and the charging efficiency still have room for improvement. Furthermore, if the temperature rise of the secondary battery is too large, it will cause the electronic device to overheat and even affect the life of the electronic device; and the charging efficiency not only affects the temperature rise of the secondary battery during charging and discharging, but also affects the life of the secondary battery and the power consumption required for charging. Therefore, the industry still needs a charging and discharging device and method that can delay the aging of the secondary battery, reduce the temperature rise of the secondary battery charging, and improve the charging efficiency.

Based on the above purpose, the present invention provides a charging and discharging device, which is used to charge and discharge a secondary battery using a quasi-sine wave signal as a charging and discharging current. The charging and discharging device includes a digital signal processing circuit, a pulse width modulation signal generator, a bidirectional DC/DC converter, a mode conversion circuit and a super capacitor. The pulse width modulation signal generator is electrically connected to the digital signal processing circuit, the bidirectional DC/DC converter is electrically connected to the secondary battery and the pulse width modulation signal generator, the mode conversion circuit is electrically connected to the pulse width modulation signal generator and the bidirectional DC/DC converter, and the super capacitor is electrically connected to the mode conversion circuit. The digital signal processing circuit is used to calculate the positive ion diffusion time of the secondary battery. The pulse width modulation signal generator is used to generate at least one pulse width modulation signal, wherein the frequency of the pulse width modulation signal is inversely proportional to the positive ion diffusion time. The bidirectional DC/DC converter receives a DC power source and is controlled by the pulse width modulation signal to charge and discharge the secondary battery using a charge and discharge current, wherein the sine wave signal is composed of a plurality of step signals, the plurality of levels of the plurality of step signals are not completely the same, and the step time of each of the plurality of step signals is the positive ion diffusion time. The mode conversion circuit is used to conduct during the discharge period, so that the supercapacitor receives the charge and discharge current during the discharge period.

In one embodiment of the present invention, the positive ion diffusion time (represented by variable τ) is the square of the diffusion length (represented by variable L) provided by the secondary battery to the positive ions divided by the diffusion coefficient of the positive ions (represented by variable D), that is, τ=L ² /D, and the frequency of the pulse width modulation signal (represented by variable f) is the inverse of the positive ion diffusion time divided by twice the circumference of the circle, that is, f=1/(τ*2π).

In one embodiment of the present invention, the charging and discharging device further includes an AC/DC converter, wherein the AC/DC converter is electrically connected to the bidirectional DC/DC converter and is used to provide DC power to the bidirectional DC/DC converter.

In one embodiment of the present invention, the bidirectional DC/DC converter is a half-bridge circuit and includes a diode, a first switching transistor, a second switching transistor and a first inductor, wherein the pulse width modulation signal includes a first pulse width modulation signal and a second pulse width modulation signal. The anode of the diode receives a DC power source. The drain of the first switching transistor is electrically connected to the cathode of the diode, and the gate of the first switching transistor receives the first pulse width modulation signal. The drain of the second switching transistor is electrically connected to the source of the first switching transistor, and the gate of the second switching transistor receives the second pulse width modulation signal. One end of the first inductor is electrically connected to the drain of the second switching transistor.

In one embodiment of the present invention, the bidirectional DC/DC converter further includes a first capacitor and a second capacitor. The two ends of the first capacitor are electrically connected to the drain of the first switching transistor and the source of the second switching transistor, respectively. The two ends of the second capacitor are electrically connected to the other end of the first inductor and the source of the second switching transistor, respectively.

In one embodiment of the present invention, the mode conversion circuit includes a third switching transistor. The gate of the third switching transistor is controlled by a charge and discharge control signal, the drain of the third switching transistor is electrically connected to the drain of the first switching transistor, and the source of the third switching transistor is electrically connected to a super capacitor, wherein the mode conversion circuit generates a charge and discharge control signal according to at least one of the first pulse width modulation signal and the second pulse width modulation signal.

In one embodiment of the present invention, the secondary battery is a single-cell lithium battery.

In one embodiment of the present invention, the secondary battery is a lithium battery module comprising a plurality of single-cell lithium batteries connected in series.

In one embodiment of the present invention, the charging and discharging device charges the secondary battery with the charging and discharging current for a continuous charging period, then the charging and discharging device makes the charging and discharging current zero current for a continuous first rest period, then the charging and discharging device discharges the secondary battery with the charging and discharging current for a continuous discharging period, then the charging and discharging device makes the charging and discharging current zero current for a continuous second rest period.

Based on the above purpose, the present invention provides a charging and discharging method, which is used to charge and discharge a secondary battery using a quasi-sine wave signal as a charging and discharging current, and includes the following steps: calculating the positive ion diffusion time of the secondary battery; controlling a bidirectional DC/DC converter to charge the secondary battery using the charging and discharging current and continuing the charging period with at least one pulse width modulation signal, wherein the frequency of the pulse width modulation signal is inversely proportional to the positive ion diffusion time, and the supercapacitor and the secondary battery are separated from each other by a distance of 1000 m. ; using a pulse width modulation signal to control the bidirectional DC/DC converter so that the charge and discharge current is zero current and continues the first rest period; using a pulse width modulation signal to control the bidirectional DC/DC converter to use the charge and discharge current to discharge the secondary battery and continue the discharge period, so that the supercapacitor receives the charge and discharge current, wherein the supercapacitor and the secondary battery are electrically connected to each other; and, using a pulse width modulation signal to control the bidirectional DC/DC converter so that the charge and discharge current is zero current and continues the second rest period.

In short, the present invention provides a charging and discharging device and method, which solves the technical problems of the prior art that the secondary battery has a shorter service life, lower charging efficiency, and a larger temperature rise of the secondary battery during charging caused by the use of a fixed current to charge and discharge the secondary battery. It also has the technical effects of delaying the aging of the secondary battery, reducing the temperature rise of the secondary battery during charging, improving the charging efficiency, increasing the service life of the secondary battery, and reducing the power consumption required for charging.

11: AC/DC converter

12: Bidirectional DC/DC converter

13: Secondary battery

14: Pulse Width Modulation Signal Generator

15: Mode conversion circuit

16:Supercapacitor

17: Digital signal processing circuit

V _DC : DC power supply

I _CHR : Charge and discharge current

CTR1: First pulse width modulation signal

CTR2: Second pulse width modulation signal

L: First inductor

C _H : First capacitor

C _L : Second capacitor

S ₁ : First switch transistor

S ₂ : Second switch transistor

S ₃ : The third switching transistor

D:Diode

τ: positive ion diffusion time

T _R1 : First rest period

T _R2 : Second rest period

T _U : During charging

T _D : Discharge period

S41~S45: Steps

The attached figures are provided to enable a person having ordinary knowledge in the technical field to which the present invention belongs to further understand the present invention, and are incorporated into and constitute a part of the specification of the present invention. The attached figures show exemplary embodiments of the present invention, and are used together with the specification of the present invention to explain the principles of the present invention.

Figure 1 is a schematic block diagram of a charging and discharging device of an embodiment of the present invention.

Figure 2 is a schematic circuit diagram of a charging and discharging device according to an embodiment of the present invention.

Figure 3 is a schematic waveform diagram of the charging and discharging current used by the charging and discharging device of the embodiment of the present invention.

Figure 4 is a schematic flow chart of the charging and discharging method of an embodiment of the present invention.

In order to help the examiner understand the technical features, content and advantages of the present invention and the effects it can achieve, the present invention is described in detail as follows with accompanying drawings and in the form of embodiments. The drawings used therein are only for illustration and auxiliary instructions, and may not be the true proportions and precise configurations after the implementation of the present invention. Therefore, the proportions and configurations of the attached drawings should not be interpreted to limit the scope of rights of the present invention in actual implementation.

The present invention mainly provides a charging and discharging device and method, which uses a supercapacitor to absorb the charging and discharging current generated by the discharge of the secondary battery when the secondary battery is discharged, so as to solve the technical problem that the solid electrolyte interface film of the negative electrode material deteriorates over time. Furthermore, when the secondary battery is a lithium battery, during the charging process of the lithium battery, the positive half-cycle current charging can embed/extract lithium ions from the active material to distribute more completely, and then the short-term discharge energy of the negative half-cycle current can reduce unnecessary chemical reactions to the solid electrolyte interface film of the negative electrode material, thereby reducing the temperature rise of the lithium battery during charging, thereby slowing down the battery aging and extending the battery life, and effectively improving the charging efficiency.

In addition, the charging and discharging device and method of the present invention also calculates the positive ion diffusion time of the secondary battery. By obtaining the positive ion diffusion time, the frequency of at least one pulse width modulation signal used to control the bidirectional DC/DC converter can be obtained. Furthermore, the charging and discharging device and method of the present invention does not charge and discharge the secondary battery with a fixed current, but uses a quasi-sine wave signal as the charging and discharging current to charge and discharge the secondary battery, wherein the quasi-sine wave signal is composed of a plurality of step signals, the plurality of levels of the plurality of step signals are not completely the same, and the step time of each of the plurality of step signals is the positive ion diffusion time.

Please note that supercapacitors are indispensable components for the implementation of the charging and discharging device and method of the present invention, and supercapacitors cannot be replaced by ordinary variable capacitors. The reason for using supercapacitors is the consideration of volume, capacitance and resistance. Since the capacitance and resistance cannot be too large or too small, only supercapacitors can be used. On the other hand, the capacitance and resistance of supercapacitors must be designed to be able to accept the amount of electricity during discharge, so the capacitance of supercapacitors is related to the specifications of battery discharge.

First, please refer to Figures 1 to 3. Figure 1 is a schematic block diagram of the charging and discharging device of the embodiment of the present invention, Figure 2 is a schematic circuit diagram of the charging and discharging device of the embodiment of the present invention, and Figure 3 is a schematic waveform diagram of the charging and discharging current used by the charging and discharging device of the embodiment of the present invention. The charging and discharging device of the embodiment of the present invention is used to charge and discharge the secondary battery 13 using a quasi-sine wave signal as the charging and discharging current I _CHR , and includes an AC/DC converter 11, a digital signal processing circuit 17, a pulse width modulation signal generator 14, a bidirectional DC/DC converter 12, a mode conversion circuit 15, and a super capacitor 16. The AC/DC converter 11 is electrically connected to the bidirectional DC/DC converter 12, the pulse width modulation signal generator 14 is electrically connected to the digital signal processing circuit 17, the bidirectional DC/DC converter 12 is electrically connected to the secondary battery 13 and the pulse width modulation signal generator 14, the mode conversion circuit 15 is electrically connected to the pulse width modulation signal generator 14 and the bidirectional DC/DC converter 12, and the super capacitor 16 is electrically connected to the mode conversion circuit 15.

(1/τ)。進一步地，正離子擴散時間為二次電池13提供給正離子之擴散長度(以變數L表示)的二次方除以正離子之擴散係數(以變數D表示)，即τ=L²/D，以及第一脈波寬度調變信號CTR1與第二脈波寬度調變信號CTR2的頻率為正離子擴散時間的一倒數除以兩倍的圓周率，即，f=1/(τ*2π)。 The AC/DC converter 11 is used to provide a DC power source V _DC to the bidirectional DC/DC converter 12. Furthermore, the AC/DC converter 11 converts the AC power supply of the AC signal into a DC power supply of the DC power source V _DC . The digital signal processing circuit 17 is used to calculate the positive ion diffusion time of the secondary battery 13. For example, when the secondary battery 13 is a single-cell lithium battery or a lithium battery module of multiple single-cell lithium batteries connected in series or in parallel, the positive ion diffusion time is the lithium ion diffusion time. The PWM signal generator 14 is used to generate a first PWM signal CTR1 and a second PWM signal CTR2, wherein the frequencies of the first PWM signal CTR1 and the second PWM signal CTR2 (represented by variable f) are inversely proportional to the positive ion diffusion time (represented by variable τ), that is, f

(1/τ). Furthermore, the positive ion diffusion time is the square of the diffusion length (represented by the variable L) provided by the secondary battery 13 to the positive ions divided by the diffusion coefficient (represented by the variable D) of the positive ions, that is, τ=L ² /D, and the frequency of the first pulse width modulation signal CTR1 and the second pulse width modulation signal CTR2 is the reciprocal of the positive ion diffusion time divided by twice the circumference of the circle, that is, f=1/(τ*2π).

The bidirectional DC/DC converter 12 receives a DC power source V _DC and is controlled by a first pulse width modulation signal CTR1 and a second pulse width modulation signal CTR2 to charge and discharge the secondary battery 13 using a charge and discharge current I _CHR . As shown in FIG3 , the quasi-sine wave signal is composed of a plurality of step signals, the plurality of levels of the plurality of step signals are not completely the same, and the step time of each of the plurality of step signals is the positive ion diffusion time. The mode conversion circuit 15 is used to conduct during the discharge period T _D , so that the supercapacitor 16 receives the charge and discharge current I _CHR during the discharge period T _D. Furthermore, the bidirectional DC/DC converter 12 can convert the DC power source V _DC into a DC/DC voltage, or reversely convert the voltage from the secondary battery 13 into a DC/DC voltage.

As shown in FIG3 , the bidirectional DC/DC converter 12 steps down the DC power source V _DC by controlling the first pulse width modulation signal CTR1 and the second pulse width modulation signal CTR2, and the generated charge and discharge current I _CHR is a positive half-cycle current, and the charge and discharge current I _CHR can charge the secondary battery 13 for a charging period T _U . Then, the bidirectional DC/DC converter 12 controls the first pulse width modulation signal CTR1 and the second pulse width modulation signal CTR2 to make the charge and discharge current I _CHR zero current for a first rest period T _R1 . Afterwards, the bidirectional DC/DC converter 12 boosts the secondary battery 13 through the control of the first pulse width modulation signal CTR1 and the second pulse width modulation signal CTR2, and the generated charge and discharge current I _CHR is a negative half-cycle current, and the secondary battery 13 is discharged to the supercapacitor 16 with the charge and discharge current I _CHR for a discharge period T _D . Then, the bidirectional DC/DC converter 12 controls the first pulse width modulation signal CTR1 and the second pulse width modulation signal CTR2 to make the charge and discharge current I _CHR zero current for a second rest period _TR2 . In this way, one charge and discharge operation is completed, and then the charge and discharge operation is repeated continuously until the secondary battery 13 is charged to a specific amount of electricity.

Further, as shown in FIG2 , the bidirectional DC/DC converter 12 is a half-bridge circuit and includes a diode D, a first switching transistor S ₁ , a second switching transistor S ₂ and a first inductor L. The anode of the diode D receives a DC power source V _DC . The drain of the first switching transistor S ₁ is electrically connected to the cathode of the diode D, and the gate of the first switching transistor S ₁ receives a first pulse width modulation signal CTR1 modulation signal. The drain of the second switching transistor S ₂ is electrically connected to the source of the first switching transistor S ₁ , and the gate of the second switching transistor S ₂ receives a second pulse width modulation signal CTR2. One end of the first inductor L is electrically connected to the drain of the second switching transistor S ₂ . The DC power source V _DC is input to the drain of the first switching transistor S _1. When the first switching transistor S ₁ is turned on, the second switching transistor S ₂ is turned off, and vice versa. In addition, in conjunction with the setting of the first inductor L, the diode D, the first switching transistor S ₁ , the second switching transistor S ₂ and the first inductor L realize the function of DC/DC voltage conversion. In one embodiment, the first pulse width modulation signal CTR1 and the second pulse width modulation signal CTR2 are two independent signals, but the present invention is not limited to this. For example, in other embodiments, the second pulse width modulation signal CTR2 is a signal generated after inverting the first pulse width modulation signal CTR1.

Furthermore, in this embodiment, the bidirectional DC/DC converter 12 further includes a first capacitor C _H and a second capacitor C _L . Two ends of the first capacitor C _H are electrically connected to the drain of the first switching transistor S ₁ and the source of the second switching transistor S ₂ , respectively. Two ends of the second capacitor C _L are electrically connected to the other end of the first inductor L and the source of the second switching transistor S _2, respectively. Furthermore, the mode conversion circuit 15 includes a third switching transistor S ₃ . The gate of the third switching transistor _S3 is controlled by the charge and discharge control signal, the drain of the third switching transistor _S3 is electrically connected to the drain of the first switching transistor _S1 , and the source of the third switching transistor _S3 is electrically connected to the super capacitor 16, wherein the mode conversion circuit 15 generates the charge and discharge control signal according to at least one of the first pulse width modulation signal CTR1 and the second pulse width modulation signal CTR2. For example, the mode conversion circuit 15 has a logic circuit to generate the charge and discharge control signal according to at least one of the first pulse width modulation signal CTR1 and the second pulse width modulation signal CTR2. The mode conversion circuit 15 is used to isolate the supercapacitor 16 and the secondary battery 13 from each other during the charging period T _U , and is used to electrically connect the supercapacitor 16 and the secondary battery 13 during the discharging period T _D , so that the supercapacitor 16 receives the charge and discharge current I _CHR generated by the discharge of the secondary battery 13 .

Next, please refer to Table 1, which shows the actual data of charging and discharging UF553450Z Sanyo single-cell lithium battery using the above-mentioned charging and discharging device and the fixed current method of the prior art. From Table 1, it can be seen that the charging efficiency is significantly improved and the temperature rise during charging is significantly reduced by adopting the method of the present invention, so it can be proved that the above-mentioned technical effects of the present invention and the present invention have indeed solved the technical problems encountered by the prior art.

Next, please refer to Table 2, which is the actual data of charging and discharging multiple UF553450Z Sanyo single-cell lithium batteries in series using the above-mentioned charging and discharging device and the fixed current method of the prior art. From Table 2, it can be seen that the charging efficiency is significantly improved and the temperature rise during charging is significantly reduced by adopting the method of the present invention. Therefore, it can be proved that the above-mentioned technical effects of the present invention and the present invention have indeed solved the technical problems encountered by the prior art, and the present invention can be used for higher voltage charging and discharging applications, such as charging piles for electric vehicles.

Next, please refer to FIG. 4, which is a schematic flow chart of the charging and discharging method of an embodiment of the present invention. This charging and discharging method is used to charge and discharge the secondary battery using a quasi-sine wave signal as the charging and discharging current, and includes the following steps. First, in step S41, the positive ion diffusion time of the secondary battery is calculated. Then, in step S42, at least one pulse width modulation signal is used to control the bidirectional DC/DC converter to use the charging and discharging current to charge the secondary battery and continue the charging period, wherein the frequency of the pulse width modulation signal is inversely proportional to the positive ion diffusion time, and the mode conversion circuit is turned off to isolate the supercapacitor and the secondary battery from each other.

Next, in step S43, the bidirectional DC/DC converter is controlled by the pulse width modulation signal so that the charge and discharge current is zero current and continues the first rest period. Then, in step S44, the bidirectional DC/DC converter is controlled by the pulse width modulation signal so that the charge and discharge current is used to discharge the secondary battery and continues the discharge period, and the mode conversion circuit is turned on so that the supercapacitor receives the charge and discharge current, wherein the supercapacitor and the secondary battery are electrically connected to each other. Then, in step S45, the bidirectional DC/DC converter is controlled by the pulse width modulation signal so that the charge and discharge current is zero current and continues the second rest period. After step S45, go back to step S42 and restart another charging and discharging operation.

As can be seen from the above description, the charging device and method provided by the present invention have the technical effects of delaying the aging of secondary batteries, reducing the temperature rise during charging of secondary batteries, improving charging efficiency, increasing the service life of secondary batteries, and reducing the power consumption required for charging. Because the charging device and method provided by the present invention have the above technical effects, the number of secondary batteries to be replaced can be reduced, the service life of secondary batteries can be increased, and the number of secondary batteries to be manufactured and replaced can be reduced, thereby reducing the carbon emissions caused by manufacturing more secondary batteries. On the other hand, the improvement of the charging efficiency of secondary battery charging means that charging and discharging can have less power consumption, achieving the effect of energy saving and carbon reduction. In general, the charging device and method provided by the present invention are in line with the current sustainable development trend of countries around the world to achieve net zero carbon emissions, and have considerable economic benefits and practicality.

The above-mentioned embodiments are only for illustrating the technical ideas and features of the present invention. Their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it accordingly. They cannot be used to limit the patent scope of the present invention. In other words, all equivalent changes or modifications made according to the spirit disclosed by the present invention should still be covered by the patent scope of the present invention.

11: AC/DC converter

12: Bidirectional DC/DC converter

13: Secondary battery

14: Pulse Width Modulation Signal Generator

15: Mode conversion circuit

16:Supercapacitor

17: Digital signal processing circuit

Claims (10)

A charging and discharging device is used to use a sine wave signal as a charging and discharging current (I _CHR ) to charge and discharge a secondary battery (13), comprising: a digital signal processing circuit (17) for calculating a positive ion diffusion time (τ) of the secondary battery (13); a pulse width modulation signal generator (14) electrically connected to the digital signal processing circuit (17) for generating at least one pulse width modulation signal (CTR1, CTR2), wherein a frequency of the pulse width modulation signal (CTR1, CTR2) is inversely proportional to the positive ion diffusion time (τ); a bidirectional DC/DC converter (12) electrically connected to the secondary battery (13) and the pulse width modulation signal generator (14) for receiving a DC power source (V _DC ), controlled by the pulse width modulation signal (CTR1, CTR2), to use the charge and discharge current (I _CHR ) to charge and discharge the secondary battery (13), wherein the sine wave signal is composed of a plurality of step signals, the plurality of levels of the plurality of step signals are not completely the same, and the step time of each of the step signals is the positive ion diffusion time (τ); a mode conversion circuit (15), electrically connected to the pulse width modulation signal generator (14) and the bidirectional DC/DC converter (12); and a super capacitor (16), electrically connected to the mode conversion circuit (15), wherein the mode conversion circuit (15) is used to charge and discharge the secondary battery (13) during a discharge period ( _TD ) is turned on so that the super capacitor (16) receives the charge and discharge current (I _CHR ) during the discharge period (T _D ). A charging and discharging device as described in claim 1, wherein the positive ion diffusion time (τ) is the square of a diffusion length (represented by variable L) provided by the secondary battery (13) to a positive ion divided by a diffusion coefficient (represented by variable D) of the positive ion, that is, τ=L ² /D, and the frequency (represented by variable f) of the pulse width modulation signal (CTR1, CTR2) is the inverse of the positive ion diffusion time (τ) divided by twice pi, that is, f=1/(τ*2π). The charging and discharging device as described in claim 1 further includes: an AC/DC converter (11) electrically connected to the bidirectional DC/DC converter (12) for providing the DC power (V _DC ) to the bidirectional DC/DC converter (12). The charging and discharging device as claimed in claim 1, wherein the bidirectional DC/DC converter (12) is a half-bridge circuit and comprises: a diode (D), an anode of which receives the DC power source (V _DC ); a first switching transistor (S ₁ ), a drain of which is electrically connected to a cathode of the diode (D), and a gate of which receives a first pulse width modulation signal (CTR1) included in the pulse width modulation signal (CTR1, CTR2); a second switching transistor (S ₂ ), a drain of which is electrically connected to the first switching transistor (S ₁ ) has a source, a gate thereof receives a second pulse width modulation signal (CTR2) included in the pulse width modulation signal (CTR1, CTR2); and a first inductor (L) has one end electrically connected to the drain of the second switching transistor ( _S2 ). A charging and discharging device as described in claim 4, wherein the bidirectional DC/DC converter (12) further comprises: a first capacitor (C _H ) whose two ends are electrically connected to the drain of the first switching transistor (S ₁ ) and a source of the second switching transistor (S ₂ ) respectively; and a second capacitor (C _L ) whose two ends are electrically connected to the other end of the first inductor (L) and the source of the second switching transistor (S ₂ ) respectively. A charging and discharging device as described in claim 5, wherein the mode conversion circuit (15) includes: a third switching transistor ( _S3 ), a gate of which is controlled by a charging and discharging control signal, a drain of which is electrically connected to the drain of the first switching transistor ( _S1 ), and a source of which is electrically connected to the supercapacitor (16), wherein the mode conversion circuit (15) generates the charging and discharging control signal according to at least one of the first pulse width modulation signal (CTR1) and the second pulse width modulation signal (CTR2). A charging and discharging device as described in claim 1, wherein the secondary battery (13) is a single-cell lithium battery. A charging and discharging device as described in claim 1, wherein the secondary battery (13) is a lithium battery module in which a plurality of single-cell lithium batteries are connected in series. A charging and discharging device as described in claim 1, wherein the charging and discharging device charges the secondary battery (13) with the charging and discharging current (I _CHR ) for a charging period (T _U ), then the charging and discharging device makes the charging and discharging current (I _CHR ) zero current for a first rest period ( _TR1 ), then the charging and discharging device charges the secondary battery (13) with the charging and discharging current (I _CHR ) for the discharging period ( _TD ), then the charging and discharging device makes the charging and discharging current (I _CHR ) zero current for a second rest period ( _TR2 ). A charging and discharging method is used to charge and discharge a secondary battery (13) using a sine wave signal as a charging and discharging current (I _CHR ), comprising: calculating a positive ion diffusion time (τ) of the secondary battery (13); controlling a bidirectional DC/DC converter (12) using at least one pulse width modulation signal (CTR1, CTR2) to use the charging and discharging current (I _CHR ) to charge the secondary battery (13) for a charging period ( _TU ), wherein a frequency of the pulse width modulation signal (CTR1, CTR2) is inversely proportional to the positive ion diffusion time (τ), and a super capacitor (16) and the secondary battery (13) are isolated from each other; the pulse width modulation signal (CTR1, CTR2) is used to control the bidirectional DC/DC converter (12) so that the charge and discharge current (I _CHR ) is zero current and continues for a first rest period ( _TR1 ); the pulse width modulation signal (CTR1, CTR2) is used to control the bidirectional DC/DC converter (12) to use the charge and discharge current (I _CHR ) to discharge the secondary battery (13) and continue for a discharge period ( _TD ) so that the super capacitor (16) receives the charge and discharge current (I _CHR ), wherein the super capacitor (16) is electrically connected to the secondary battery (13); and the pulse width modulation signal (CTR1, CTR2) is used to control the bidirectional DC/DC converter (12) so that the charge and discharge current (I _CHR ) is zero current and continues for a second rest period ( _TR2 ).

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