Wireless charging system based on S-S-P compensation three-coil switching and control method

Abstract

The invention provides a wireless charging system based on S-S-P compensation three-coil switching and a control method, and the system comprises a DC power supply, a full-bridge high-frequency inverter, a resonance stage, a full-bridge rectifier and a load, and is characterized in that the resonance stage comprises a transmitting coil, a repeating coil, a receiving coil and a corresponding compensation capacitor; the transmitting coil and the primary side compensation capacitor are connected to the output end of the high-frequency inverter in series, the receiving coil and the first secondary side compensation capacitor are connected to the input end of the full-bridge rectifier in parallel, and the first secondary side compensation capacitor is further connected with a second secondary side compensation capacitor with a first circuit breaker in parallel. The relay coil and the first relay compensation capacitor form a series resonance circuit, and the first relay compensation capacitor is also connected in parallel with a second relay compensation capacitor with a second cut-out switch; the device has the advantages that the device can operate in a CC mode and a CV mode, system operation is maintained under ZPA, a system compensation element does not contain a compensation inductor and is more portable, and meanwhile the alternating current switch is located on the receiving side and is convenient to control.

Description

Technical Field

[0001] The present invention relates to wireless charging technology, and in particular to a wireless charging system and control method based on SSP compensation three-coil switching. Background Art

[0002] Wireless Power Transmission (WPT), also known as contactless power transmission, can be divided into different transmission types such as magnetic field, electric field, and microwave according to the different transmission media. It solves many limitations of traditional wired plug-in charging systems and has the advantages of safety, portability, and strong applicability. It has been widely used in technical fields such as electric vehicles, inspection drones, and consumer electronics. Typical lithium battery charging parameters are as follows: Figure 1 As shown in Figure 1, its main charging modes include constant current (CC) and constant voltage (CV). Initially, the battery charges in CC mode at a preset charging current. During the charging process, the voltage continuously increases. When the voltage reaches the preset charging voltage, the battery switches from CC mode to constant voltage mode. The current continuously decreases throughout the charging process, and the charging process ends when the charging current reaches a certain value. The battery's equivalent resistance gradually increases throughout the charging process. Therefore, the design of a WPT system requires consideration of the following two factors: First, to extend the battery's service life, the power battery should be charged using constant current and then constant voltage until the battery is fully charged. The converter then implements a stepwise constant current and constant voltage output. Second, to improve efficiency and avoid reactive power loss, the system's equivalent input impedance should be as purely resistive as possible. Therefore, it is crucial to charge the battery in both CC and CV modes and ensure that the system operates in the ZPA state in both CC and CV modes.

[0003] In existing research, many scholars have chosen a hybrid topology switching method and conducted in-depth research. Reference [1] introduced an additional relay coil, which is at the same level as the original transmitting and receiving coils, to avoid additional requirements for system space. Through a series of theoretical analysis and experimental verification, the study showed that without increasing the system volume, the three-coil structure WPT system improves the energy transmission distance and efficiency compared with the traditional two-coil WPT system. Reference [2] conducted an in-depth and comprehensive analysis of the three-coil structure WPT system and proposed a new parameter design method to achieve ZPA operation in CC and CV modes at two different switching frequency points. The system has the advantages of light receiver weight and compact structure, but the design process of its three-coil WPT system is complicated. Reference [3] proposed a switching topology based on three coils to achieve CC and CV output at 85kHz, but its structure not only contains compensation capacitors but also compensation inductors. The system has many compensation components and a complex structure, which is not conducive to the system's lightweight design criteria.

[0004] References:

[0005] [1]Yang L, Li

[0006] [2]L Yang,L.Ren,Y.Shi,M.Wang,et al.Analysis and Design of an S / S / P-Compensated Three-Coil Structure WPT System With Constant Current andConstant Voltage Output[J].IEEE Journal of Emerging and Selected Topics inPower Electronics,2023,11(3),pp:2487-2500;

[0007] [3] Geng Zhi, Wang Meng, Wang Can, et al. Research on three-coil constant current and constant voltage wireless charging system based on topology switching [J]. Journal of Power Supply, 2022. Summary of the Invention

[0008] In view of this, the primary purpose of the present invention is to provide a wireless charging system based on SSP compensation three-coil switching. The system can achieve CC and CV outputs in the ZPA state through different combinations of five compensation capacitors and two AC switches. The system does not require additional wireless communication modules and contains fewer compensation components, which reduces the system size and cost to a certain extent.

[0009] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0010] A wireless charging system based on SSP compensation three-coil switching includes a DC power supply, a full-bridge high-frequency inverter, a resonant stage, a full-bridge rectifier, and a load. The key features of the system are: the resonant stage includes a transmitting coil, a relay coil, a receiving coil, and corresponding compensation capacitors; the transmitting coil and the primary compensation capacitor are connected in series at the output of the high-frequency inverter; the receiving coil and the first secondary compensation capacitor are connected in parallel at the input of the full-bridge rectifier; a second secondary compensation capacitor with a first disconnect switch is also connected in parallel to the first secondary compensation capacitor; the relay coil and the first relay compensation capacitor form a series resonant circuit; a second relay compensation capacitor with a second disconnect switch is also connected in parallel to the first relay compensation capacitor;

[0011] When constant current output is required, the first circuit breaker is in an open state and the second circuit breaker is in a closed state;

[0012] When constant voltage output is required, the first circuit breaker is in a closed state, and the second circuit breaker is in an open state.

[0013] Optionally, in the constant current output state, the relay coil is in a non-resonant state.

[0014] Optionally, in a constant voltage output state, both the relay coil and the receiving coil are in a non-resonant state.

[0015] Optionally, the parameters of each component in the resonant stage are set to meet the following requirements:

[0016]

[0017] Among them: A and B are intermediate variables, ω is the system operating angular frequency, M PS is the mutual inductance between the transmitting coil and the receiving coil, M PT is the mutual inductance between the transmitting coil and the relay coil, M TS is the mutual inductance between the relay coil and the receiving coil, Z P is the transmitting coil L P And the primary compensation capacitor C P The equivalent impedance of the series resonant circuit, Z TV Relay coil LT and relay compensation capacitor C TV The equivalent impedance of the series resonant circuit is formed, and the relay compensation capacitor C TV is the equivalent capacitance when the first relay compensation capacitor is connected alone; Z TC Relay coil L T and relay compensation capacitor C TC The equivalent impedance of the series resonant circuit is formed, and the relay compensation capacitor C TC is the equivalent capacitance of the first relay compensation capacitor and the second relay compensation capacitor in parallel, Z S1 is the equivalent impedance of the receiving coil, Z S2V is the secondary side compensation capacitor C S2V Equivalent impedance, secondary side compensation capacitor C S2V is the equivalent capacitance when the first secondary compensation capacitor and the second secondary compensation capacitor are connected in parallel; Z S2C is the secondary side compensation capacitor C S2C Equivalent impedance, secondary side compensation capacitor C S2C It is the equivalent capacitance when the first secondary compensation capacitor is connected separately.

[0018] Optionally, in a constant current output state, the transmitting coil and the receiving coil are configured to be in a resonant state.

[0019] Optionally, in a constant voltage output state, the transmitting coil is configured to be in a resonant state.

[0020] Optionally, the relay coil and the receiving coil are arranged on a load device, and a charging voltage detection device, a charging current detection device and a control device are provided on the load device. When the charging voltage reaches a preset charging voltage, the control device changes the working state of the first circuit breaker and the second circuit breaker to achieve switching between constant current mode and constant voltage mode. When the charging current is less than a preset threshold, charging is stopped.

[0021] In addition, based on the above system, the present invention also proposes a control method for a wireless charging system based on SSP compensation three-coil switching, the key of which is to include the following steps:

[0022] S1: When the load needs to be charged, the control device controls the first circuit breaker to be in an open state and the second circuit breaker to be in a closed state, so that the load operates in a constant current mode;

[0023] S2: Detecting the charging voltage by the charging voltage detection device. When the charging voltage reaches a preset charging voltage, controlling the first disconnect switch to be in a closed state and the second disconnect switch to be in an open state by the control device, so that the circuit breaker operates in a constant voltage mode.

[0024] S3: The charging current detection device detects whether the charging current is less than a preset threshold value. When the charging current is less than the preset threshold value, the control device controls the load device to move out of the charging area and stop charging.

[0025] Due to the adoption of the above technical solution, the present invention has the following advantages:

[0026] The present invention can operate in both CC and CV modes, maintaining system operation under ZPA. The system's compensation components consist of only five compensation capacitors and no compensation inductors, making the system more portable. Furthermore, the proposed system's AC switch is located on the receiving side, eliminating the need for an additional wireless communication module. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings of the present invention are as follows:

[0028] Figure 1 This is a typical lithium battery charging characteristic curve;

[0029] Figure 2 This is the principle diagram of the three-coil structure WPT system proposed in this invention;

[0030] Figure 3 for Figure 2 Equivalent circuit diagram of

[0031] Figure 4 This is the equivalent circuit diagram of the three-coil WPT system in CC mode;

[0032] Figure 5 This is the equivalent circuit diagram of the three-coil WPT system in CV mode;

[0033] Figure 6 The curves of system transconductance gain and output phase angle changing with frequency under different resistance values;

[0034] Figure 7 The curves of system voltage gain and output phase angle changing with frequency under different resistance values;

[0035] Figure 8 The output current and voltage change curve with load in CC mode;

[0036] Figure 9 This is the curve of output current and voltage changing with load in CV mode. DETAILED DESCRIPTION

[0037] The present invention will be further described below with reference to the accompanying drawings and examples:

[0038] like Figure 2As shown, a wireless charging system based on SSP compensation three-coil switching includes a DC power supply, a full-bridge high-frequency inverter, a resonant stage, a full-bridge rectifier, and a load. The resonant stage includes a transmitting coil, a relay coil, a receiving coil, and corresponding compensation capacitors. The transmitting coil and the primary compensation capacitor are connected in series at the output end of the high-frequency inverter. The receiving coil and the first secondary compensation capacitor are connected in parallel at the input end of the full-bridge rectifier. A second secondary compensation capacitor with a first disconnect switch is also connected in parallel to the first secondary compensation capacitor. The relay coil and the first relay compensation capacitor form a series resonant circuit. A second relay compensation capacitor with a second disconnect switch is also connected in parallel to the first relay compensation capacitor.

[0039] When constant current output is required, the first circuit breaker is in an open state and the second circuit breaker is in a closed state;

[0040] When constant voltage output is required, the first circuit breaker is in a closed state, and the second circuit breaker is in an open state.

[0041] Combine Figure 2 It can be seen that the full-bridge HFI is composed of four power MOSFETs (Q1-Q4). The high-frequency inverter composed of Q1-Q4 can convert the DC voltage U D Converted into high-frequency AC fundamental voltage U I , transfers electrical energy to the coil. The resonant stage is composed of the transmitting coil L P , relay coil L T and receiving coil L S And the corresponding compensation capacitor. Among them, C P is the compensation capacitance of the transmitting coil, C T1 and C T2 is the compensation capacitance of the relay coil, C S1 and C S2 is the compensation capacitance of the receiving coil. M PT 、M PS 、M TS Represents the mutual inductance between the three coils, where the subscripts P, T, and S represent the transmitting coil, relay coil, and receiving coil respectively. P 、L T 、L S are the self-inductances of the coils. P 、R T 、R S The full-bridge rectifier consists of four Schottky diodes (D1-D4) and is installed on the receiver to convert the AC current in the receiving circuit into a DC current I L Output, for battery load R L Power supply. C DK1 and K2 are two control switches, which can switch the system between constant current mode and constant voltage mode by switching the switch states.

[0042] For ease of analysis, this embodiment ignores the parasitic resistance of the compensation element and the high-order harmonic components in the circuit. I The effective value of can be calculated by formula (1):

[0043]

[0044] Equivalent AC resistance R eq It can be calculated by formula (2):

[0045]

[0046] Figure 3 The equivalent circuit diagram of the three-coil WPT system used in this embodiment is shown in Figure 2. According to Kirchhoff's voltage law (KVL), the loop equation of the three-coil WPT system can be obtained as follows:

[0047]

[0048] in:

[0049]

[0050] Where ω is the operating angular frequency of the system, which can be derived from formula (3):

[0051]

[0052] in:

[0053]

[0054] In order to reduce reactive input and improve system efficiency, it is necessary to implement ZPA operation. The input impedance Z I Considered as a pure resistor. For ease of calculation, define the input impedance Z of the system I is the input voltage U I With input current I I The ratio of , can be derived from equations (5) and (6):

[0055]

[0056] The following is an analysis of CC output and ZPA operation:

[0057] when Figure 2 When the control switch K1 is in the open state and K2 is in the closed state, the system can realize constant current mode charging and ZPA operation. Figure 4This is the equivalent circuit diagram of the three-coil WPT system in CC mode. Combined with the component distribution in the figure, we can get:

[0058]

[0059] Define the transconductance gain as the output current I O With input voltage U I The ratio of , can be deduced from formula (5):

[0060]

[0061] From the analysis of formula (9), we can see that when B = 0, the transconductance gain G(ωcc) of the proposed WPT system is proportional to the load R eq The system can work in CC output mode, which can be expressed as (10):

[0062]

[0063] By analyzing formula (10), it can be seen that according to the different resonance combinations in the three coil loops, there are four schemes shown in Table 1 that can make B=0. The specific situations of the resonance combinations of different coils in the three schemes are shown in Table 1.

[0064] Table 1 Resonance conditions of each coil loop in CC mode

[0065]

[0066] Taking Scheme 1 as an example, the resonance conditions in each coil are analyzed. When the transmitting coil loop and the receiving coil loop are resonant, and the relay coil loop is not resonant, equation (11) is satisfied:

[0067]

[0068] Substituting (11) into (7) can simplify the input impedance of the system in Scheme 1 to:

[0069]

[0070] Among them, ω CC_1 is the angular frequency when working under Scheme 1. By analyzing Equation (12), it can be seen that when Equation (13) is satisfied, the input impedance of the WPT system does not contain an imaginary part, and ZPA operation in CC mode can be achieved.

[0071]

[0072] Through the above analysis, when the system parameters are reasonably designed to satisfy Equations (10), (11), and (13), the WPT system can simultaneously achieve load-independent constant current output and ZPA operation under Scheme 1. The analysis methods for Schemes 2, 3, and 4 are similar to those for Scheme 1 and will not be repeated here.

[0073] Further analysis of CV output and ZPA operation:

[0074] when Figure 2 When the control switch K1 is in the closed state and K2 is in the open state, the system can realize constant current mode charging and ZPA operation. Figure 5 This is the equivalent circuit diagram of the three-coil WPT system in CC mode, where:

[0075]

[0076] Define voltage gain as output current U O With input voltage U I The ratio of , can be deduced from formula (5):

[0077]

[0078] From the analysis of formula (15), we can see that when A = 0, the voltage gain E(ωcv) of the proposed WPT system is proportional to the load R eq The system can work in CV output mode, which can be expressed as (16):

[0079]

[0080] Analysis of Equation (16) shows that, depending on the different resonant combinations of the three coil loops, there are two schemes shown in Table 2 that can achieve A = 0. The specific conditions of the resonant combinations of the different coils in the two schemes are shown in Table 2. The analysis methods for Schemes 1 and 2 in CV mode are similar to those for Scheme 1 in CC mode and are not repeated here.

[0081] Table 2 Resonance conditions of each coil loop in CV mode

[0082]

[0083] According to the analysis of Table 1 and Table 2, by adjusting different combination states of the AC switch on the system receiving side, four modes can be used to achieve CC and CV charging characteristics at the same frequency point, as shown in Table 3.

[0084] Table 3 CC and CV charging characteristics of four modes

[0085]

[0086] This example uses Mode 1 in Table 3 as an example for subsequent parameter design and related simulation and experimental verification. Through the above theoretical derivation process, the constraints are iteratively calculated to obtain the compensation parameters of the system as shown in Equation (17).

[0087]

[0088] The designed system parameters can be shown in Table 4:

[0089] Table 4 Three-coil WPT system parameters

[0090]

[0091] In order to further understand the effect of the present invention, the following simulation experiment is used to verify:

[0092] Under different loads of 5Ω, 10Ω, 15Ω, and 20Ω, the system transconductance gain G(ωcc) and the inverter output voltage and current phase angle curves are as follows: Figure 6 As shown in Figure 2. Under different loads of 20Ω, 40Ω, 60Ω, and 80Ω, the system voltage gain E(ωcv) and the inverter output voltage and current phase angle curves are shown in Figure 2. Figure 7 shown.

[0093] By observation Figure 6 It can be seen that at a frequency of 85kHz, under different load conditions of 5Ω, 10Ω, 15Ω, and 20Ω, the system's transconductance G(ωcc) gain is the same, which can achieve a load-independent CC output characteristic. Moreover, under different resistance values, the phase angle of the inverter output voltage and current is 0, and the system meets the ZPA operation characteristics.

[0094] By observation Figure 7 It can be seen that at a frequency of 85kHz, under different load conditions of 20Ω, 40Ω, 60Ω, and 80Ω, the system voltage gain E(ωcv) is the same, which can achieve a load-independent CV output characteristic. Moreover, under different resistance values, the phase angle of the inverter output voltage and current is 0, and the system meets the ZPA operation characteristics.

[0095] Figure 8 and Figure 9 The following are the curves of the system's output current and output voltage changing with load when the system is running in CC and CV modes respectively. Figure 8 It can be seen that when the system operates in CC mode, the output current of the system is maintained at around 4A within a load range from 2Ω to 20 ohms, meeting the power supply requirements of the lithium battery CC mode.

[0096] observe Figure 9It can be seen that when the system operates in CV mode, the output current of the system is maintained at around 40V within a load range from 5Ω to 50 ohms, meeting the power supply requirements of the lithium battery CV mode.

[0097] From the above, it can be seen that the wireless charging system and control method based on SSP compensation three-coil switching proposed in this application can operate in both CC and CV modes, and both maintain system operation under ZPA. The system compensation elements have only 5 compensation capacitors and no compensation inductor, making the system more lightweight. At the same time, the AC switch of the proposed system is located on the receiving side and does not require the assistance of an additional wireless communication module. Finally, the proposed system was verified through simulation, and it was found that the proposed system can achieve a stable output of 4A and 40V, which can meet the charging requirements of lithium batteries. Therefore, during the control process, the system can follow the following steps:

[0098] S1: When the load needs to be charged, the control device controls the first circuit breaker to be in an open state and the second circuit breaker to be in a closed state, so that the load operates in a constant current mode;

[0099] S2: Detecting the charging voltage by the charging voltage detection device. When the charging voltage reaches a preset charging voltage, controlling the first disconnect switch to be in a closed state and the second disconnect switch to be in an open state by the control device, so that the circuit breaker operates in a constant voltage mode.

[0100] S3: The charging current detection device detects whether the charging current is less than a preset threshold value. When the charging current is less than the preset threshold value, the control device controls the load device to move out of the charging area and stop charging.

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A wireless charging system based on SSP compensation three-coil switching, comprising a DC power supply, a full-bridge high-frequency inverter, a resonant stage, a full-bridge rectifier and a load, characterized in that: The resonant stage includes a transmitting coil, a relay coil, a receiving coil and a corresponding compensation capacitor, the transmitting coil and the primary compensation capacitor are connected in series at the output end of the high-frequency inverter, the receiving coil and the first secondary compensation capacitor are connected in parallel at the input end of the full-bridge rectifier, a second secondary compensation capacitor with a first disconnect switch is also connected in parallel to the first secondary compensation capacitor, the relay coil and the first relay compensation capacitor form a series resonant circuit, and a second relay compensation capacitor with a second disconnect switch is also connected in parallel to the first relay compensation capacitor; When constant current output is required, the first circuit breaker is in an open state, and the second circuit breaker is in a closed state; When constant voltage output is required, the first circuit breaker is in a closed state, and the second circuit breaker is in an open state.

2. The wireless charging system based on SSP compensation three-coil switching according to claim 1 is characterized in that: In the constant current output state, the relay coil is in a non-resonant state.

3. The wireless charging system based on SSP compensation three-coil switching according to claim 1 is characterized in that: In the constant voltage output state, both the relay coil and the receiving coil are in a non-resonant state.

4. The wireless charging system based on SSP compensation three-coil switching according to claim 1 is characterized in that: The parameter settings of each component in the resonant stage meet the following requirements: Among them: A and B are intermediate variables, ω is the system working angular frequency, M PS is the mutual inductance between the transmitting coil and the receiving coil, M PT is the mutual inductance between the transmitting coil and the relay coil, M TS is the mutual inductance between the relay coil and the receiving coil, Z P The transmitting coil L P And the primary compensation capacitor C P The equivalent impedance of the series resonant circuit is Z TV For the relay coil L T and relay compensation capacitor C TV The equivalent impedance of the series resonant circuit is formed, and the relay compensation capacitor C TV is the equivalent capacitance when the first relay compensation capacitor is connected alone; Z TC For the relay coil L T and relay compensation capacitor C TC The equivalent impedance of the series resonant circuit is formed, and the relay compensation capacitor C TC is the equivalent capacitance of the first relay compensation capacitor and the second relay compensation capacitor in parallel, Z S1 is the equivalent impedance of the receiving coil, Z S2V is the secondary compensation capacitor C S2V Equivalent impedance, secondary compensation capacitor C S2V Z is the equivalent capacitance when the first secondary compensation capacitor and the second secondary compensation capacitor are connected in parallel; S2C is the secondary compensation capacitor C S2C Equivalent impedance, secondary compensation capacitor C S2C It is the equivalent capacitance when the first secondary compensation capacitor is connected separately.

5. The wireless charging system based on SSP compensation three-coil switching according to claim 2 is characterized in that: In the constant current output state, the transmitting coil and the receiving coil are configured in a resonant state.

6. The wireless charging system based on SSP compensation three-coil switching according to claim 3 is characterized in that: In the constant voltage output state, the transmitting coil is configured in a resonant state.

7. The wireless charging system based on SSP compensation three-coil switching according to any one of claims 1 to 6, characterized in that: The relay coil and the receiving coil are arranged on the load device, and the load device is provided with a charging voltage detection device, a charging current detection device and a control device. When the charging voltage reaches a preset charging voltage, the control device changes the working state of the first circuit breaker and the second circuit breaker to realize the switching between the constant current mode and the constant voltage mode. When the charging current is less than a preset threshold value, charging is stopped.

8. A control method for a wireless charging system based on SSP compensation three-coil switching as claimed in claim 7, characterized in that: The following steps are involved: S1: When the load needs to be charged, the control device controls the first circuit breaker to be in an open state and the second circuit breaker to be in a closed state, so that the load operates in a constant current mode; S2: Detecting the charging voltage by the charging voltage detection device, and when the charging voltage reaches the preset charging voltage, controlling the first circuit breaker to be in a closed state and the second circuit breaker to be in an open state by the control device, so that the first circuit breaker works in a constant voltage mode; S3: The charging current detection device detects whether the charging current is less than a preset threshold value. When the charging current is less than the preset threshold value, the control device controls the load device to move out of the charging area and stop charging.

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