Implementation method of current discontinuous soft switching based on switched inductor battery balancer

Abstract

The present invention proposes a method for implementing current intermittent soft switching based on a switched inductor battery balancer. This method is divided into three cases according to the voltage of the battery cells being balanced: no balancing is required between the battery cells, the first battery cell B1 transfers energy to the second battery cell B2, and the second battery cell B2 transfers energy to the first battery cell B1. The signal is modulated according to the modulation ratio to obtain a PWM signal for controlling the first switch tube S1 and the second switch tube S2. The method of the present invention enables all switches in the balancer to achieve soft switching and can adjust the current of the balancer inductor. Under the same balanced power, the current stress of the components in the balancer is reduced, and the efficiency of the balancer is greatly improved. In addition, the control of the balancer does not require the participation of the current feedback signal, eliminating the current sensor and saving the cost of the balancer. This method greatly enhances the market competitiveness of switched inductor lithium-ion battery balancers.

Description

Technical field

[0001] The present invention relates to the technical field of control of power electronic converters, in particular to a method for realizing current discontinuous soft switching based on a switching inductor battery equalizer. [Background Technology]

[0002] Lithium-ion batteries are widely used in daily production and life, such as in handheld portable power tools, laptop power supplies, smart microgrid energy storage systems, and electric vehicle power batteries. Due to differences in battery characteristics between individual cells, after repeated charge and discharge cycles, lithium-ion battery cells in series can experience inconsistent states of charge (SOC) and voltages. Long-term operation can lead to overcharge and overdischarge, adversely affecting the lifespan, capacity, and safety of the cells. SOC differences are often reflected in differences in cell voltage, making voltage balancing a must-have feature for lithium-ion battery packs used in series.

[0003] At present, lithium-ion battery balancers can be divided into energy-consuming type balancers and non-energy-consuming type balancers. The energy-consuming type balancer uses switch-controlled resistors to connect battery cells with higher SOC to ensure that the voltages of all battery cells tend to be consistent. This method is simple to control, low-cost, and easy to implement, but it has large losses and can easily cause safety hazards such as local overheating of the battery pack.

[0004] Non-energy-consuming balancers are further divided into active and passive balancers. Active balancers primarily use switching transistors to actively balance energy and voltage between battery cells. Common methods include switched capacitors and their derivative topologies, switched inductors and their derivative topologies, bidirectional CUK balancers, and bidirectional flyback balancers. However, these balancers incur significant losses in battery packs with a large number of series cells and high voltages.

[0005] Passive equalizers primarily achieve voltage balancing between battery cells through a rectifier circuit composed of transformer coils and diodes. The principle is that current always flows to the cell with the lowest voltage, so the cell with the lowest voltage always receives the most current distribution, causing its voltage to rapidly approach that of the cell with higher potential. Currently, the most commonly used topologies include a flyback equalizer with a multi-coil transformer, a single-secondary transformer + single-bridge-arm rectifier cascade equalizer, a single-secondary transformer + bridge rectifier cascade equalizer, and a slope voltage doubler rectifier equalizer. The flyback equalizer topology with a multi-coil transformer is relatively simple, but due to the characteristics of the flyback topology, it can only be used for voltage balancing of smaller power battery packs.

[0006] In recent years, switched-inductor battery balancers have developed improved cascaded balancing structures. While these cascaded balancers effectively accelerate the balancing speed between battery cells, the design methods, voltage, and current stresses of components such as switches and inductors at different levels are inconsistent, placing pressure on modularization and cost. While traditional switched-inductor battery balancers have a slow balancing speed, their circuit structure is simple and modularly scalable. In some battery packs with 3-4 cells in series, such as handheld portable power tool batteries and laptop batteries, switched-inductor balancers with energy transfer between adjacent cells still have strong application value. However, each switch in the balancer cannot fully achieve soft switching, or even if soft switching is achieved through current detection closed-loop control, the current stress of the device is too high, resulting in low balancer efficiency. This increases the difficulty of further application and promotion of the balancer.

[0007] Therefore, in a simple structure, the soft switching of all switching tubes is realized in the traditional switched inductor battery balancer, and the current stress of the device is reduced while the balancer processing power is the same, thereby improving the efficiency of the balancer. This can further expand the application scenarios of the traditional switched inductor battery balancer. A method for realizing current intermittent soft switching based on the switched inductor battery balancer is now proposed. [Summary of the invention]

[0008] The purpose of the present invention is to solve the problems in the prior art that the equalizer switch tube cannot achieve soft switching, the device current stress is large, the efficiency is low, and the control implementation cost is high, and a current intermittent soft switching implementation method based on a switching inductor battery equalizer is proposed.

[0009] To achieve the above objectives, the present invention proposes a method for implementing current discontinuous soft switching based on a switching inductor battery balancer. The method is implemented based on a switching inductor lithium-ion battery balancer. The switching inductor lithium-ion battery balancer includes two battery cells to be balanced: a first battery cell B1 and a second battery cell B2, two switching tubes: a first switching tube S1 and a second switching tube S2, and an inductor L0; the voltages of the first battery cell B1 and the second battery cell B2 are U B1 、U B2 The current flowing into the first battery cell B1 and the second battery cell B2 are i B1 、i B2 , the inductor current is i L , the inductance value of the inductor L0 is L; the method comprises the following steps:

[0010] S1. Judge U B1 、U B2 with U T The relationship between U T is the start-up voltage of the switching inductor lithium-ion battery balancer. B1-U B2 |≤U T When , the first switch tube S1 and the second switch tube S2 are all turned off, otherwise, enter step S2;

[0011] S2. Determine U again B1 、U B2 with U T relationship, when U B1 -U B2 >U T When U B2 -U B1 >U T When , go to step S4;

[0012] S3. Set the modulation ratio of the first switch S1 to D 1+ , the modulation ratio of the second switch tube S2 is D 2+ , the maximum inductor current i L_max for

[0013]

[0014] Where, T s is the switching cycle, and the inductor current decreases during the second switch tube S2 is (i L_max +x), then

[0015]

[0016] After the second switch S2 is turned off, the time it takes for the inductor current to rise from -x to 0 is ΔD + T s ,but

[0017]

[0018] Where U DF is the body diode conduction voltage drop of the switch tube. According to equations (1) to (3), the average value of the inductor current in this case is

[0019]

[0020] Then the average value of the inductor current in equation (4) is replaced by the current reference value I * Instead, get

[0021]

[0022] According to the relationship shown in formula (1) and formula (2), we can get

[0023]

[0024] Then proceed to step S5;

[0025] S4. Set the modulation ratio of the first switch S1 to D 1- , the modulation ratio of the second switch tube S2 is D 2- , the minimum inductor current i L_min for

[0026]

[0027] The inductor current rise during the first switch S1 on time period is (xi L_min ),but

[0028]

[0029] After the first switch S1 is turned off, the time it takes for the inductor current to drop from x to 0 is ΔD - T s ,but

[0030]

[0031] According to equations (7) to (9), the average value of the inductor current in this case is

[0032]

[0033] Then the average value of the inductor current in equation (10) is replaced by the current reference value I * Instead, get

[0034]

[0035] According to the relationship shown in formula (7) and formula (8), we can get

[0036]

[0037] Then proceed to step S5;

[0038] S5. According to the modulation ratio D 1+ 、D 2+ or D 1- 、D 2- The signal is modulated to obtain a PWM signal for controlling the first switch tube S1 and the second switch tube S2.

[0039] As an advantage, the current reference value I * Set to

[0040]

[0041] Among them, k v is the voltage loop control coefficient, I max is the maximum value allowed for the balancer inductor current.

[0042] As a preference, in step S3, U B1 -U B2 >U T When the energy of the first battery cell B1 flows to the second battery cell B2, the average value of the inductor current I L >0.

[0043] Preferably, in step S3, when the first switch tube S1 is turned on, the inductor current starts to increase from zero, and when the first switch tube S1 is turned off, the inductor current value is the maximum; then the second switch tube S2 is turned on, and the inductor current decreases. To achieve soft switching, the second switch tube S2 is turned off when the inductor current drops to -x.

[0044] Preferably, in step S3, after the second switch tube S2 is turned off, the inductor current rises from a negative value to 0 and remains at 0 for a period of time until the first switch tube S1 is turned on again after the next switching cycle starts.

[0045] As a preference, in step S4, U B2 -U B1 >U T When the energy of the second battery cell B2 flows to the first battery cell B1, the average value of the inductor current I L <0.

[0046] Preferably, in step S4, the second switch tube S2 is turned on first, and the first switch tube S1 is turned on later; when the second switch tube S2 is turned on, the inductor current begins to decrease from zero and becomes a negative value, and when the second switch tube S2 is turned off, the inductor current value is minimum; then the first switch tube S1 is turned on, and the inductor current increases from the negative minimum value; to achieve soft switching, the first switch tube S1 is turned off when the inductor current rises to x.

[0047] Preferably, in step S4, after the first switch tube S1 is turned off, the inductor current drops from x to 0 and remains at 0 for a period of time until the second switch tube S2 is turned on again after the next switching cycle starts.

[0048] The present invention has the following beneficial effects: The method enables soft switching of all switches in a balancer and adjusts the current in the balancer's inductor. This reduces the current stress on the balancer's components at the same balanced power, significantly improving the balancer's efficiency. Furthermore, the balancer's control does not require a current feedback signal, eliminating the need for a current sensor and reducing balancer costs. This method significantly enhances the market competitiveness of switched-inductor lithium-ion battery balancers.

[0049] The features and advantages of the present invention will be described in detail through embodiments with reference to the accompanying drawings.

Brief Description of the Drawings

[0050] Figure 1 The circuit topology of the lithium-ion battery balancer based on the switched inductor;

[0051] Figure 2 This is the waveform of the lithium-ion battery balancer based on switching inductance when the current is continuous;

[0052] Figure 3 A switch inductor based lithium-ion battery balancer in U B1 -U B2 >U T Inductor current waveform when ;

[0053] Figure 4 A switch inductor based lithium-ion battery balancer in U B2 -U B1 >U T Inductor current waveform when ;

[0054] Figure 5 is a flow chart of the method of the present invention;

[0055] Figure 6 A current discontinuous soft switching control strategy for a lithium-ion battery balancer based on a switched inductor;

[0056] Figure 7 The current stress comparison curve between the method of the present invention and the traditional method;

[0057] Symbol names in the figure: B1—first battery cell, B2—second battery cell; U B1 —First battery cell voltage, U B2 - the voltage of the second battery cell; i B1 —First battery cell current, i B2 —second battery cell current; S1—first switch tube, S2—second switch tube; L0—inductor; i L —Inductor current; u GS1 —The driving signal of the first switch tube, u GS2 —Driving signal of the second switch tube; 1+ —U B1 -U B2 >U T When the switch tube S1 modulation ratio; D 2+ —U B1 -U B2 >U T The modulation ratio of the switch tube S2; D 1- —U B2 -U B1 >U T When the switch tube S1 modulation ratio; D 2- —U B2 -U B1 >UT The modulation ratio of the switch tube S2 is T s —Switching cycle; I * —Balancer inductor current reference value; U T —Equalizer turn-on voltage; k v —voltage loop control coefficient; I L_RMSp —The method disclosed in the present invention controls the equalizer inductor current; I L_RMSc —Traditional method to control the balancer inductor current. [Specific implementation method]

[0058] Based on the switch inductor lithium ion battery balancer circuit topology Figure 1 As shown, it is actually a buck-boost converter with bidirectional energy flow. When it is applied to the balancing of battery cells, if the strategy of complementary control of two switching tubes is adopted, the waveform of the inductor current is as follows Figure 2 As shown, Figure 2 At time t2, the inductor current is negative, and all the switches in the equalizer can achieve soft switching. However, if the average value of the inductor current needs to be adjusted, the inductor current waveform needs to be shifted downward, resulting in increased feedback power and increased current stress on the device at the same power. Therefore, the present invention proposes to make the inductor current waveform run at the voltage of the battery cell. Figure 3 or Figure 4 The waveform shown in Figure 1 is as follows: If there is no need to balance the battery cells, both switches are turned off and the inductor current remains zero.

[0059] The present invention proposes a method for realizing current intermittent soft switching of a switching inductor battery balancer. According to the voltage relationship between battery cells, the operating duty cycle of the first switch tube S1 and the second switch tube S2 is controlled respectively to realize the inductor current i in the balancer. L The average value I L The size of the inductor current i L The control of the instantaneous value at a specific moment achieves two control goals at the same time; the average value of the inductor current I L The benchmark value I * Set to

[0060]

[0061] Among them, k v is the voltage loop control coefficient, I max is the maximum value allowed for the average value of the balancer inductor current;

[0062] According to the voltage U between battery cells B1 、U B2 There are three situations in which the size of

[0063] I.|U B1 -U B2 |≤U T

[0064] When|U B1 -U B2 |≤U T When U T The start-up voltage of the lithium-ion battery balancer based on the switching inductor is that the energy between the two battery cells is close and no balancing is required, so the switching tubes S1-S2 are all turned off.

[0065] II.U B1 -U B2 >U T

[0066] At this time, the inductor current operating waveform corresponds to Figure 3 The waveform shown. Set the modulation ratio of the first switch S1 to D 1+ , the modulation ratio of the second switch tube S2 is D 2+ , the energy of the first battery cell B1 flows to the second battery cell B2, and the average value of the inductor current I L >0; When the first switch tube S1 is turned on ( Figure 3 At t0 in the middle), the inductor current starts to increase from zero, and when S1 is turned off ( Figure 3 At time t1), the inductor current is at its maximum; then the second switch S2 is turned on, and the inductor current decreases; in order to achieve soft switching, when the inductor current drops to -x ( Figure 3 At time t2, S2 is turned off. After S2 is turned off, the inductor current rises from a negative value to 0 and remains at 0 for a period of time until S1 is turned on again at the beginning of the next switching cycle. According to the above relationship, the maximum inductor current i L_max for

[0067]

[0068] Where, T s is the switching cycle, and the inductor current decreases during the second switch tube S2 is (i L_max +x), then

[0069]

[0070] After the second switch S2 is turned off, the time it takes for the inductor current to rise from -x to 0 is ΔD + T s ,but

[0071]

[0072] Where U DFis the conduction voltage drop of the body diode of the switch tube. According to equations (2) to (4), the average value of the inductor current in this case is

[0073]

[0074] In the control process, if we want to control the average value of the inductor current and the current value when the second switch tube S2 is turned off, we can use the current reference value I in formula (1) to replace the average value of the inductor current in formula (5) * Instead, get

[0075]

[0076] According to the relationship shown in formula (2) and formula (3), we can get

[0077]

[0078] III.U B2 -U B1 >U T

[0079] At this time, the inductor current operating waveform corresponds to Figure 4 The waveform shown. Set the modulation ratio of the first switch S1 to D 1- , the modulation ratio of the second switch tube S2 is D 2- , the energy of the second battery cell B2 flows to the first battery cell B1, and the average value of the inductor current I L <0; with U B1 -U B2 >U T The situation is different when the second switch tube S2 is turned on first and the first switch tube S1 is turned on later. When the second switch tube S2 is turned on ( Figure 4 At t0 in the middle), the inductor current begins to drop from zero and becomes negative. When S2 is turned off ( Figure 4 At time t1 in the middle), the inductor current is at its minimum; then the first switch tube S1 is turned on, and the inductor current increases from the negative minimum value; in order to achieve soft switching, when the inductor current rises to x ( Figure 4 At time t2, S1 is turned off. After S1 is turned off, the inductor current drops from x to 0 and remains at 0 for a period of time until S2 is turned on again at the beginning of the next switching cycle. According to the above relationship, the minimum inductor current i L_min for

[0080]

[0081] The inductor current rise during the first switch S1 on time period is (xi L_min ),but

[0082]

[0083] After the first switch S1 is turned off, the time it takes for the inductor current to drop from x to 0 is ΔD-T s ,but

[0084]

[0085] According to equations (8) to (10), the average value of the inductor current in this case is

[0086]

[0087] In the control process, if we want to control the average value of the inductor current and the current value at the time when the first switch tube S1 is turned off, we can use the current reference value I in formula (1) to replace the average value of the inductor current in formula (11) * Instead, get

[0088]

[0089] According to the relationship shown in formula (8) and formula (9), we can get

[0090]

[0091] The modulation ratio D obtained according to the above cases II and III is 1+ 、D 2+ or D 1- 、D 2- The signal is modulated to obtain a PWM signal for controlling the first switch tube S1 and the second switch tube S2.

[0092] Figure 5 The flowchart shown clearly describes the above solution process. Figure 5 The process shown is clear and can be easily implemented by DSP.

[0093] Figure 5 The duty cycle prediction control strategy for realizing soft switching does not need to detect the inductor current in the switched inductor balancer, which can further reduce the cost of the balancer.

[0094] Take U B1 >U B2 To ensure that the equalizer is Figure 3 The operating waveform shown must satisfy D 1+ +D 2+ +ΔD + ≤1, according to formula (4) and (6), we can get

[0095]

[0096] So we can get D 1+ The upper limit D 1+max.

[0097]

[0098] When the duty cycle is obtained by formula (15), the waveform of the inductor current is as follows: Figure 2 As shown, it shows the unification of the disclosed method of the present invention and the traditional equalizer control strategy. It can be seen from formula (5) that the duty cycle D 1+ The larger the inductor current I L (Indicator of balancing speed) The larger the value, the faster the balancing speed. Limited by the rated power of the equalizer, it is necessary to specify I L The maximum value I Lmax ,but

[0099]

[0100] Substituting equation (15) into equation (16), we get the quadratic equation of the inductance value, and finally get

[0101]

[0102] in,

[0103] Therefore, when the switching frequency of the balancer is known, the maximum mean value of the inductor current I during the balancing process is determined. Lmax After the instantaneous minimum value, the inductance value is designed by formula (17); during operation, according to Figure 5 After the operating duty cycle of the switch tube is obtained by the method shown, the driving signal waveform obtained by signal modulation can ensure that the equalizer operates in the current DCM. The corresponding control block diagram is shown in Figure 6 As shown by Figure 6 It can be seen that the output of the voltage loop is used as the current reference, but current feedback is not adopted in the strategy. Instead, the inductor current is tracked according to the proposed algorithm.

[0104] An important performance indicator of the equalizer is efficiency. Achieving soft switching and lower effective current values ​​of the device under the same power conditions can greatly improve efficiency. Figure 3 、 Figure 4 The DCM operation strategy shown is the same as Figure 2 The waveforms of the traditional control methods shown can both achieve soft switching. The following comparison focuses on the device current stress of the two methods. In a balancer, the effective value of the inductor current is an important indicator of the balancer's efficiency.

[0105] according to Figure 3 The inductor current function of the three modes is used to obtain the effective value of the inductor current, and we get

[0106]

[0107] and Figure 2 The effective value of the inductor current corresponding to the waveform shown is

[0108]

[0109] Where x c 、D 1c 、D 2c They are the inductor current value for achieving soft switching, the modulation ratio of the switch tube S1, and the modulation ratio of the switch tube S2.

[0110] According to equations (18) and (19), at the same inductor current mean value I L Under the condition of , we can get the effective current curves of the two control strategies, as shown in Figure 7 As shown. According to the actual situation of the battery cell, Figure 7 The maximum voltage difference between the monomers is 0.1V. The figure shows U B1 = The effective current curves of the three cases of 2.9V, 3.2V and 3.6V show that: when the inductor current average value I L In the case of a smaller current, the DCM soft switching scheme disclosed in the present invention has an effective current value I L_RMSp Obviously higher than the effective current value I of the traditional solution L_RMSc As the battery cell voltage increases, I L_RMSp with I L_RMSc The difference becomes larger; as the current I L As the rated value approaches, the difference between the two becomes smaller and closer. Since the effective value of current is directly related to the loss, including line loss, inductor copper loss, switch tube heating, etc., the DCM soft switching scheme disclosed in the present invention has obvious advantages in high-efficiency conversion. The main reason for the above advantages is that the operating duty cycle of the traditional current continuous soft switching strategy is limited by the battery cell voltage. In order to reduce the current I L , the minimum value of the current (x in formula (19) c value) moves down synchronously, causing the effective value of the current to remain basically unchanged; while the current intermittent soft switching strategy is based on the required current I L The size of the switch tube duty cycle is obtained to ensure the current value of the soft switch -x at different I L Therefore, the effective value of current and the average value of current are basically linearly related.

[0111] In summary, the current intermittent soft switching implementation method disclosed in the present invention realizes the soft switching of all switching tubes in the equalizer, and can effectively reduce the current stress of the devices in the equalizer under the same balanced power conditions, greatly improving the efficiency of the equalizer; and this method does not use current feedback to participate in the control, eliminating the cost of the current sensor and reducing the cost of the equalizer; the above characteristics increase the market competitiveness of the lithium-ion battery balancer based on the switched inductor.

[0112] The above embodiments are intended to illustrate the present invention, not to limit the present invention. Any solution that is a simple transformation of the present invention falls within the protection scope of the present invention.

Claims

1. A method for implementing current discontinuous soft switching based on a switched inductor battery balancer. The method is implemented based on a switched inductor lithium-ion battery balancer. The switched inductor lithium-ion battery balancer includes two battery cells to be balanced: a first battery cell B1 and a second battery cell B2, two switching transistors: a first switching transistor S1 and a second switching transistor S2, and an inductor L0. The voltages of the first battery cell B1 and the second battery cell B2 are U B1 、U B2 The current flowing into the first battery cell B1 and the second battery cell B2 are i B1 、i B2 , the inductor current is i L , the inductance value of the inductor L0 is L; it is characterized in that, The method comprises the following steps: S1. Judge U B1 、U B2 with U T The relationship between U T is the start-up voltage of the switching inductor lithium-ion battery balancer. B1 -U B2 |≤U T When , the first switch tube S1 and the second switch tube S2 are all turned off, otherwise, enter step S2; S2. Determine U again B1 、U B2 with U T relationship, when U B1 -U B2 >U T When U B2 -U B1 >U T When , go to step S4; S3. Set the modulation ratio of the first switch S1 to D 1+ , the modulation ratio of the second switch tube S2 is D 2+ , the maximum inductor current i L_max for Where, T s is the switching cycle, and the inductor current decreases during the second switch tube S2 is (i L_max +x), then After the second switch S2 is turned off, the inductor current continues to flow through the body diode of the switch S1, and the time it takes for the inductor current to rise from -x to 0 is ΔD + T s ,but Where U DF is the body diode conduction voltage drop of the switch tube. According to equations (1) to (3), the average value of the inductor current in this case is Then the average value of the inductor current in equation (4) is replaced by the current reference value I * Instead, get According to the relationship shown in formula (1) and formula (2), we can get Then proceed to step S5; S4. Set the modulation ratio of the first switch S1 to D 1- , the modulation ratio of the second switch tube S2 is D 2- , the minimum inductor current i L_min for The inductor current rise during the first switch S1 on time period is (xi L_min ),but After the first switch S1 is turned off, the time it takes for the inductor current to drop from x to 0 is ΔD - T s ,but According to equations (7) to (9), the average value of the inductor current in this case is Then the average value of the inductor current in equation (10) is replaced by the current reference value I * Instead, get According to the relationship shown in formula (7) and formula (8), we can get Then proceed to step S5; S5. According to the modulation ratio D 1+ 、D 2+ or D 1- 、D 2- The signal is modulated to obtain a PWM signal for controlling the first switch tube S1 and the second switch tube S2.

2. The method for implementing current discontinuous soft switching based on a switched inductor battery equalizer according to claim 1, characterized in that: The current reference value I * Set to Among them, k v is the voltage loop control coefficient, I max is the maximum value allowed for the balancer inductor current.

3. A method for implementing current discontinuous soft switching based on a switched inductor battery equalizer according to claim 1 or 2, characterized in that: In step S3, U B1 -U B2 >U T When the energy of the first battery cell B1 flows to the second battery cell B2, the average value of the inductor current I L >0.

4. The method for implementing current discontinuous soft switching based on a switched inductor battery equalizer according to claim 3, wherein: In step S3, when the first switch S1 is turned on, the inductor current starts to increase from zero. When the first switch S1 is turned off, the inductor current reaches its maximum value. Then, the second switch S2 is turned on, and the inductor current decreases. To achieve soft switching, the second switch S2 is turned off when the inductor current drops to -x.

5. The method for implementing current discontinuous soft switching based on a switched inductor battery equalizer according to claim 4, characterized in that: In step S3 , after the second switch tube S2 is turned off, the inductor current rises from a negative value to 0 and remains at 0 for a period of time until the first switch tube S1 is turned on again after the next switching cycle starts.

6. A method for implementing current discontinuous soft switching based on a switched inductor battery equalizer according to claim 1 or 2, characterized in that: In step S4, U B2 -U B1 >U T When the energy of the second battery cell B2 flows to the first battery cell B1, the average value of the inductor current I L <0.

7. The method for implementing current discontinuous soft switching based on a switched inductor battery equalizer according to claim 6, characterized in that: In step S4, the second switch S2 is turned on first, and the first switch S1 is turned on later; When the second switch tube S2 is turned on, the inductor current begins to decrease from zero and becomes negative. When the second switch tube S2 is turned off, the inductor current value is minimum. Then the first switch tube S1 is turned on, and the inductor current increases from the negative minimum value. To achieve soft switching, the first switch tube S1 is turned off when the inductor current rises to x.

8. The method for implementing current discontinuous soft switching based on a switched inductor battery equalizer according to claim 7, characterized in that: In step S4 , after the first switch tube S1 is turned off, the inductor current drops from x to 0 and remains at 0 for a period of time until the second switch tube S2 is turned on again after the next switching cycle starts.

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