Constant power output wireless charging system and method with reconfigurable secondary side

Abstract

The invention belongs to the technical field of rotary steerable drilling, and relates to a constant power output wireless charging system and method with a reconfigurable secondary side, and the system comprises a high-frequency full-bridge inverter circuit, a primary side impedance matching network, a coupling coil, a secondary side impedance matching network, a secondary side topology switching network, and a rectification circuit. The input end of the high-frequency full-bridge inverter circuit is connected with a constant voltage source, the output end of the high-frequency full-bridge inverter circuit is connected with the input end of the primary impedance matching network, and the output end of the primary impedance matching network is connected with the input end of the secondary impedance matching network through a coupling coil. The positive electrode and the negative electrode of the secondary side impedance matching network are connected through the secondary side topology switching network, access and cut-out of the secondary side impedance matching network are achieved through opening and closing of the secondary side topology switching network, and the output end of the secondary side topology switching network is connected with the load through the rectifying circuit. Under the condition of system offset, switching between an S-S working mode and an S-LCC mode can be met, the design method is simple, and output is stable.

Description

Technical Field

[0001] The invention relates to a secondary-side reconfigurable constant-power output wireless charging system and method, belonging to the technical field of rotary steerable drilling. Background Art

[0002] Under rotating conditions, rotating electrical equipment has been widely used in oil and gas drilling, aerospace and other fields. Brushes and slip rings are the main equipment for wired power transmission under rotating conditions. However, this method has problems such as poor cable contact and easy generation of electric sparks, which reduces the reliability of power supply equipment and affects the performance of the system in actual operation. In recent years, WPT technology (Wireless Power Transfer Technology) has developed rapidly because of its advantages such as safety, convenience, reliability and flexibility compared with wired power transmission technology.

[0003] For the rotating WPT system, stable transmission power and high efficiency are key factors in evaluating the system. However, due to the randomness of the receiving side position, it is common in practical applications that the coupling structure is difficult to fully align. When the coupling coefficient error caused by the coupling structure offset exceeds a certain range, the output power of the rotating WPT system will drop sharply. In addition, due to the complex external use environment and high-speed rotation usage scenarios of the rotating equipment, the vibration and offset of the coupling structure will be further caused. Therefore, the rotating WPT system is required to have spatial freedom, that is, it can tolerate a certain degree of coupling structure offset, so as to have relatively stable transmission power. The application of rotating wireless power transmission technology not only improves the reliability of power transmission, but also greatly reduces the maintenance cost of system equipment.

[0004] In the prior art, coupling structures with opposite output characteristics are combined to make the changes in the total output current or voltage of the system offset each other within a certain range, thereby achieving overall constant output. However, in the prior art, there are problems such as the two sets of coupling topological structures influencing and interfering with each other, as well as system instability, current oscillation, frequency splitting, and low efficiency. Summary of the invention

[0005] In view of the above problems, the object of the present invention is to provide a secondary-side reconfigurable constant power output wireless charging system and method, which can meet the switching of SS working mode and S-LCC mode in the case of system offset, and has a simple design method and stable output.

[0006] To achieve the above-mentioned purpose, the present invention proposes the following technical scheme: a secondary-side reconfigurable constant power output wireless charging system, comprising: a high-frequency full-bridge inverter circuit, a primary-side impedance matching network, a coupling coil, a secondary-side impedance matching network, a secondary-side topology switching network and a rectifier circuit; the input end of the high-frequency full-bridge inverter circuit is connected to a constant voltage source, the output end of the high-frequency full-bridge inverter circuit is connected to the input end of the primary-side impedance matching network, the output end of the primary-side impedance matching network is connected to the input end of the secondary-side impedance matching network through the coupling coil, the positive and negative electrodes of the secondary-side impedance matching network are connected through the secondary-side topology switching network, the secondary-side impedance matching network is connected and switched out by opening and closing the secondary-side topology switching network, and the output end of the secondary-side topology switching network is connected to the load through the rectifier circuit.

[0007] Furthermore, the coupling coil includes a first inductor, a second inductor and a third inductor, the first inductor and the second inductor are connected in series and connected to the output end of the primary impedance matching network, and the third inductor is connected to the input end of the secondary impedance matching network.

[0008] Furthermore, the first inductor is connected to the positive output terminal of the primary impedance matching network, and the second inductor is connected to the negative output terminal of the primary impedance matching network.

[0009] Furthermore, the primary impedance matching network includes a first capacitor, which is arranged at the positive electrode of the primary impedance matching network, an input end of which is connected to the high-frequency full-bridge inverter circuit, and an output end of which is connected to the first inductor.

[0010] Furthermore, the secondary side impedance matching network includes a second capacitor and a fourth inductor, the second capacitor is connected in series with the fourth inductor, and the second capacitor and the fourth inductor are both arranged at the positive electrode of the secondary side impedance matching network, and the secondary side topology switching network is arranged between the second capacitor and the fourth inductor.

[0011] Furthermore, the secondary side topology switching network includes a third capacitor and a switch, one end of the third capacitor is connected to the positive electrode of the secondary side impedance matching network, the other end is connected to one end of the switch, and the other end of the switch is connected to the negative electrode of the secondary side impedance matching network.

[0012] The present invention also discloses a secondary-side reconfigurable constant power output wireless charging method, which is used for any of the above-mentioned secondary-side reconfigurable constant power output wireless charging systems, and includes the following steps: the secondary-side topology switching network is a reconfigurable topology structure, and when the switch is disconnected, the reconfigurable topology structure operates in SS mode; when the switch is disconnected, the reconfigurable topology structure operates in SS mode, and when the switch is closed, the reconfigurable topology structure operates in S-LCC mode, and the output power of SS mode and S-LCC mode under a preset offset is obtained; according to the output power of SS mode and S-LCC mode under a preset offset, the reconfigurable topology structure is made to output constant power within a preset gain deviation Δ range, and it is judged whether it is necessary to switch between SS mode and S-LCC mode; according to the switching mode of the reconfigurable topology structure, the corresponding third capacitance value under different switching modes is calculated; according to the third capacitance value, the parameters of the constant power output wireless charging system are adjusted, so that the reconfigurable topology structure outputs constant power within the preset gain deviation Δ range, and the conversion between SS mode and S-LCC mode is completed under the action of the switch.

[0013] Furthermore, the output power P in the SS mode s for:

[0014]

[0015] The output power P in the S-LCC mode LCC for:

[0016]

[0017] Among them, U in is the input DC voltage; R is the resistance of the load; ω is the angular frequency; k is the coupling coefficient; L 1 is the first inductance; L 2 is the second inductor; L 3 is the third inductor; C 3 is the third capacitor.

[0018] Furthermore, the switching mode of the reconfigurable topology structure includes: the circuit is initially set to SS mode and switched to S-LCC mode. The variation range of the coupling coefficient is k min ~k max , where k min is the minimum coupling coefficient, k max is the maximum coupling coefficient. There is no offset in the initial state, and the coupling coefficient is k min , then P S Corresponding to P max At this time, the calculation formula of the third capacitor is:

[0019]

[0020] The circuit is initially set to S-LCC mode and then switched to SS mode. There is no offset in the initial state, and the coupling coefficient is k min , then P LCC Corresponding to P max , at this time the calculation formula of the third capacitor is:

[0021]

[0022] in,

[0023] Furthermore, the conversion method between the SS mode and the S-LCC mode is: determine whether the working mode needs to be switched, and if so, proceed to the next step; monitor the current of the switch branch to determine whether it is zero, if not, continue monitoring, and if it is zero, proceed to the next step; close the switch S and check whether the switch S is actually closed, if not, return to the previous step, and if so, start working in the S-LCC mode.

[0024] The technical solution of the present invention has at least the following technical effects or advantages:

[0025] 1. When the inductor of the wireless charging system is offset, the present invention can achieve a constant output power within an acceptable range through the impedance matching network of the primary side and the secondary side, thereby improving the stability and robustness of the system.

[0026] 2. The secondary side topology switching network can switch the system output mode through switch control. This switching circuit does not require auxiliary communication between the primary and secondary sides, and does not require the addition of additional frequency modulation and phase modulation control circuits, which reduces the complexity of the system and reduces manufacturing costs.

[0027] 3. The entire system of the present invention uses only one switch device, and performs equivalent optimization on some circuit components, thereby avoiding power loss caused by more switches or components, simplifying system design, and improving the overall efficiency of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 1 is a schematic diagram of the structure of a wireless charging system with constant power output and reconfigurable secondary side according to an embodiment of the present invention. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is described in detail through specific embodiments. However, it should be understood that the provision of specific embodiments is only for a better understanding of the present invention, and they should not be understood as limitations of the present invention. In the description of the present invention, it should be understood that the terms used are only for the purpose of description and cannot be understood as indicating or implying relative importance.

[0030] In order to solve the problems of mutual influence and interference between the two sets of coupled topological structures in the prior art, as well as the instability of the system, current oscillation, frequency splitting and low efficiency. The present invention proposes a secondary-side reconfigurable constant power output wireless charging system and method, including: a high-frequency full-bridge inverter circuit, a primary impedance matching network, a coupling coil, a secondary impedance matching network, a secondary topology switching network and a rectifier circuit; the high-frequency full-bridge inverter circuit is connected to a constant voltage source, the high-frequency full-bridge inverter circuit is connected to the primary impedance matching network, the primary impedance matching network is connected to the secondary impedance matching network through a coupling coil, the secondary topology switching network is connected to the secondary impedance matching network, and the secondary impedance matching network is connected to the load through a rectifier circuit; the secondary topology switching network includes a capacitor and a switch, and the switching of the secondary topology structure is realized by opening and closing the switch. It uses a switch to meet the system constant power output in the case of system offset, and the design method is simple and the output is stable. The scheme of the present invention is described in detail below with reference to the accompanying drawings through embodiments.

[0031] Embodiment 1

[0032] This embodiment discloses a secondary-side reconfigurable constant power output wireless charging system, such as Figure 1 As shown, it includes: a high-frequency full-bridge inverter circuit, a primary impedance matching network, a coupling coil, a secondary impedance matching network, a secondary topology switching network and a rectifier circuit; the input end of the high-frequency full-bridge inverter circuit is connected to a constant voltage source, the output end of the high-frequency full-bridge inverter circuit is connected to the input end of the primary impedance matching network, the output end of the primary impedance matching network is connected to the input end of the secondary impedance matching network through the coupling coil, the positive and negative electrodes of the secondary impedance matching network are connected through the secondary topology switching network, the secondary impedance matching network is connected and switched out by opening and closing the secondary topology switching network, and the output end of the secondary topology switching network is connected to the load through the rectifier circuit.

[0033] The coupling coil includes a first inductor L 1 , the second inductor L 2 and the third inductor L 3 , the first inductor L 1 and the second inductor L 2 connected in series and connected to the output end of the primary impedance matching network, the third inductor L 3 Connected to the input end of the secondary impedance matching network.1 The first inductor is connected to the positive output terminal of the primary impedance matching network, and the second inductor is connected to the negative output terminal of the primary impedance matching network. Figure 1 Medium 13 is the first inductor L 1 and the third inductor L 3 Mutual inductance, M 23 is the second inductor and the third inductor L 3 of mutual induction.

[0034] The primary impedance matching network includes a first capacitor C 1 , the first capacitor C 1 The positive electrode of the primary impedance matching network is set, and its input end is connected to the high-frequency full-bridge inverter circuit, and its output end is connected to the first inductor L 1 Connect the second inductor L 2 The output end is connected to the high frequency full-bridge inverter circuit.

[0035] The secondary impedance matching network includes a second capacitor C 2 and the fourth inductor L 4 , the second capacitor C 2 With the fourth inductor L 4 series, and the second capacitor C 2 and the fourth inductor L 4 Both are set at the positive pole of the secondary impedance matching network, and the secondary topology switching network is set between the second capacitor and the fourth inductor. 2 and the fourth inductor L 4 The second capacitor C 2 , the fourth inductor L 4 and the third inductor L 3 Series connection.

[0036] U in is the input voltage with angular frequency ω, I in is the output current, R is the equivalent load, U R and I o are the voltage and current across the equivalent load R, M 13 The first inductor L 1 and the second inductor L 3 The mutual impedance between 23 The second inductor L 2 and the third inductor L 3 According to the characteristics of the designed coil, the first inductor L 1 and the second inductor L 2 The mutual inductance between them can be ignored.

[0037] The secondary side topology switching network includes a third capacitor C 3 and switch S, the third capacitor C 3and the switch S in series, and connected to the secondary impedance matching network through two connection points, one of which is connected through the second capacitor C 2 Connected to the secondary impedance matching network; through the fourth inductor L 4 The other connection point is connected to the secondary impedance matching network and the rectifier circuit respectively. 3 One end is connected to the positive electrode of the secondary impedance matching network, the other end is connected to one end of the switch, and the other end of the switch is connected to the negative electrode of the secondary impedance matching network.

[0038] Embodiment 2

[0039] Based on the same inventive concept, this embodiment discloses a secondary-side reconfigurable constant power output wireless charging method, which is used in any of the above secondary-side reconfigurable constant power output wireless charging systems, comprising the following steps:

[0040] The S1 secondary side topology switching network is a reconfigurable topology structure. When the switch is disconnected, the reconfigurable topology structure works in SS mode; when the switch S is disconnected, the reconfigurable topology structure works in SS mode, and when the switch S is closed, the reconfigurable topology structure works in S-LCC mode, and the output power of the SS mode and the S-LCC mode under the preset offset condition is obtained;

[0041] Output power P in SS mode s for:

[0042]

[0043] Output power P in S-LCC mode LCC for:

[0044]

[0045] Among them, U in is the input DC voltage; R is the resistance of the load; ω is the angular frequency; k is the coupling coefficient; L 1 is the first inductance; L 2 is the second inductor; L 3 is the third inductor; C 3 is the third capacitor.

[0046] S2 determines whether it is necessary to switch between the SS mode and the S-LCC mode according to the output power of the SS mode and the S-LCC mode under the preset offset condition, so that the reconfigurable topology structure has a constant power output within a preset gain deviation Δ range;

[0047] According to the output power of SS mode and S-LCC mode under the preset offset condition, it can be known that as the coupling coefficient k value increases, the output power decreases, but due to different output power coefficients, the degree of output power reduction is also different. Therefore, if the parameters are properly selected, when the coupling coefficient k changes beyond the preset range, the secondary side topology structure is changed by switching the switch S to achieve the purpose of constant output power. Whether it is necessary to switch between SS mode and S-LCC mode is whether the coupling coefficient k exceeds the preset value.

[0048] Assume that the coupling coefficient varies within the range k min ~k max , where k min is the minimum coupling coefficient, k max is the maximum coupling coefficient. The relationship between the two is defined as k max =αk min (α>1). Assuming the acceptable output power deviation is Δ, P 0 is the set output power of the system. Define P max =(1+Δ)P 0 , P min =(1-Δ)P 0 , then the output power range is (1-Δ)P 0 ~(1+Δ)P 0 .

[0049]

[0050] The ratio of output power working in SS mode and S-LCC mode is:

[0051]

[0052] Among them, the coupling coefficient corresponding to the SS mode is k 1 , the coupling coefficient corresponding to the S-LCC mode is k 2 According to the output power formula, k min Corresponding to P max , k max Corresponding to P min .

[0053] S3 calculates the third capacitance value corresponding to different switching modes according to the switching mode of the reconfigurable topology structure;

[0054] The switching modes of the reconfigurable topology include:

[0055] (1) The circuit is initially set to SS mode and switched to S-LCC mode. There is no offset in the initial state. At this time, the coupling coefficient is kmin, and PS corresponds to Pmax. As the coupling structure offsets, when the power drops to the switching point, the secondary impedance matching network is switched to the LCC topology through the switch.

[0056]

[0057] At this time, the third capacitor C 3 The calculation formula is:

[0058]

[0059] (2) The circuit is initially set to S-LCC mode and then switched to SS mode. There is no initial offset and the coupling coefficient is k min , then P LCC Corresponding to P max ,With the offset of the coupling structure, when the power drops to the switching point, the secondary side impedance matching network is switched to an S-type topology structure through the switch.

[0060]

[0061] At this time, the third capacitor C 3 The calculation formula is:

[0062]

[0063] in,

[0064] S4 adjusts the parameters of the constant power output wireless charging system according to the third capacitance value, so that the reconfigurable topology structure has a constant power output within a preset gain deviation Δ range, and completes the conversion between the SS mode and the S-LCC mode under the action of the switch.

[0065] The method for adjusting the parameters of the constant power output wireless charging system is:

[0066] The first capacitor C of the primary S-type impedance matching network 1 The value of is calculated by the following formula:

[0067]

[0068] The second capacitor C of the secondary side LCC impedance matching network 2 , the fourth inductor L 4 The value of is determined by the following formula:

[0069]

[0070] The conversion method between SS mode and S-LCC mode is:

[0071] S4.1 determines whether the working mode needs to be switched, and if so, proceeds to the next step;

[0072] S4.2 monitors the current of the switch branch to determine whether it is zero. If it is not zero, continue monitoring. If it is zero, proceed to the next step.

[0073] S4.3 Close switch S and check whether switch S is actually closed. If not, return to the previous step. If yes, start working in S-LCC mode.

[0074] For example, the method for switching from the SS mode to the S-LCC mode in this embodiment is specifically as follows:

[0075] The switch S is disconnected and operates in SS mode, and the load voltage is monitored by the control system on the secondary side;

[0076] Determine whether the working mode needs to be switched, if so, proceed to the next step;

[0077] Monitor the current of the switch branch to determine whether it is zero. If it is not zero, continue monitoring. If it is zero, proceed to the next step.

[0078] Close switch S and check whether switch S is actually closed. If not, return to the previous step. If yes, start working in S-LCC mode.

[0079] Combining the output power in the SS working mode and the S-LCC working mode, the reconfigurable topology structure has a constant power output characteristic within a preset gain deviation Δ range, and the conversion between the SS working mode and the S-LCC working mode is completed under the action of the switch S.

[0080] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0081] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0082] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0083] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation of the present invention can still be modified or replaced by equivalents, and any modification or equivalent replacement that does not deviate from the spirit and scope of the present invention should be included in the protection scope of the claims of the present invention. The above content is only a specific implementation of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or replacements within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A secondary-side reconfigurable constant power output wireless charging system, characterized in that: include: High-frequency full-bridge inverter circuit, primary impedance matching network, coupling coil, secondary impedance matching network, secondary topology switching network and rectifier circuit; The input end of the high-frequency full-bridge inverter circuit is connected to a constant voltage source, the output end of the high-frequency full-bridge inverter circuit is connected to the input end of the primary impedance matching network, the output end of the primary impedance matching network is connected to the input end of the secondary impedance matching network through the coupling coil, the positive and negative poles of the secondary impedance matching network are connected through the secondary topology switching network, the secondary impedance matching network is connected and disconnected by opening and closing the secondary topology switching network, and the output end of the secondary topology switching network is connected to the load through a rectifier circuit.

2. The secondary-side reconfigurable constant power output wireless charging system as claimed in claim 1, characterized in that: The coupling coil includes a first inductor, a second inductor and a third inductor, the first inductor and the second inductor are connected in series and connected to the output end of the primary impedance matching network, and the third inductor is connected to the input end of the secondary impedance matching network.

3. The secondary-side reconfigurable constant power output wireless charging system as claimed in claim 2, characterized in that: The first inductor is connected to the positive output terminal of the primary impedance matching network, and the second inductor is connected to the negative output terminal of the primary impedance matching network.

4. The secondary-side reconfigurable constant power output wireless charging system as claimed in claim 2, characterized in that: The primary impedance matching network includes a first capacitor, which is arranged at the positive electrode of the primary impedance matching network, an input end of which is connected to a high-frequency full-bridge inverter circuit, and an output end of which is connected to a first inductor.

5. The secondary-side reconfigurable constant power output wireless charging system according to any one of claims 1 to 4, characterized in that: The secondary side impedance matching network includes a second capacitor and a fourth inductor, the second capacitor is connected in series with the fourth inductor, and the second capacitor and the fourth inductor are both arranged at the positive electrode of the secondary side impedance matching network, and the secondary side topology switching network is arranged between the second capacitor and the fourth inductor.

6. The secondary-side reconfigurable constant power output wireless charging system as claimed in claim 5, characterized in that: The secondary side topology switching network includes a third capacitor and a switch, one end of the third capacitor is connected to the positive electrode of the secondary side impedance matching network, the other end is connected to one end of the switch, and the other end of the switch is connected to the negative electrode of the secondary side impedance matching network.

7. A secondary-side reconfigurable constant power output wireless charging method, characterized in that: A wireless charging system with a reconfigurable secondary side and constant power output as claimed in any one of claims 1 to 6, comprising the following steps: The secondary side topology switching network is a reconfigurable topology structure. When the switch is disconnected, the reconfigurable topology structure works in SS mode; when the switch is disconnected, the reconfigurable topology structure works in SS mode, and when the switch is closed, the reconfigurable topology structure works in S-LCC mode, and the output power of SS mode and S-LCC mode under preset offset conditions is obtained; According to the output power of the SS mode and the S-LCC mode under the preset offset condition, the reconfigurable topology structure is made to output constant power within the preset gain deviation Δ range, and it is determined whether it is necessary to switch between the SS mode and the S-LCC mode; According to the switching mode of the reconfigurable topology structure, calculating the third capacitance value corresponding to different switching modes; According to the third capacitance value, the parameters of the constant power output wireless charging system are adjusted so that the reconfigurable topology structure can output constant power within a preset gain deviation Δ range, and the conversion between the SS mode and the S-LCC mode is completed under the action of the switch.

8. The secondary-side reconfigurable constant power output wireless charging method according to claim 7, characterized in that: The output power P in SS mode s for: The output power P in the S-LCC mode LCC for: Among them, U in is the input DC voltage; R is the resistance of the load; ω is the angular frequency; k is the coupling coefficient; L1 is the first inductor; L2 is the second inductor; L3 is the third inductor; C3 is the third capacitor.

9. The secondary-side reconfigurable constant power output wireless charging method according to claim 8, characterized in that: The switching mode of the reconfigurable topology structure includes: The circuit is initially set to SS mode and switched to S-LCC mode. There is no offset in the initial state, and the coupling coefficient is k min , then P S Corresponding to P max , at this time the calculation formula of the third capacitor is: The circuit is initially set to S-LCC mode and then switched to SS mode. There is no offset in the initial state, and the coupling coefficient is k min , then P LCC Corresponding to P max , at this time the calculation formula of the third capacitor is: in, 10. The secondary-side reconfigurable constant power output wireless charging method according to claim 7, characterized in that: The conversion method between the SS mode and the S-LCC mode is: Determine whether the working mode needs to be switched, if so, proceed to the next step; Monitor the current of the switch branch to determine whether it is zero. If it is not zero, continue monitoring. If it is zero, proceed to the next step. Close switch S and check whether switch S is actually closed. If not, return to the previous step. If yes, start working in S-LCC mode.

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