Wireless charging system for realizing unidirectional anti-offset by using symmetrical auxiliary receiving coil and duty ratio modulation

Abstract

The invention provides a wireless charging system for realizing unidirectional anti-offset by using symmetrical auxiliary receiving coils and duty ratio modulation. Cross coupling of a main coil and an auxiliary coil is eliminated by overlapping a group of symmetrical auxiliary coils and a main receiving coil; magnetic field decoupling of the main receiving coil and the auxiliary coil is realized through overlapping with the main receiving coil; the overlapping part of the auxiliary coil and the main receiving coil receives positive magnetic flux, the non-overlapping part receives negative magnetic flux, the positive magnetic flux and the negative magnetic flux in the area defined by the auxiliary coil are counteracted by adjusting the overlapping area and the non-overlapping area to a certain value, and therefore decoupling of the main receiving coil and the symmetrical auxiliary receiving coil is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless charging, and in particular relates to a wireless charging system that utilizes a symmetrical auxiliary receiving coil and duty cycle modulation to achieve unidirectional anti-drift. Background Art

[0002] At present, the charging of electric vehicles is mainly divided into two methods: wired charging and wireless charging. Wired charging is to physically connect the power supply to the car through a cable. The energy transmission is relatively stable and the technology development is relatively mature, but there are also limitations such as low charging flexibility and poor convenience. At the same time, the cable may be damaged or even broken due to external factors during the charging process, which poses a risk of electric shock. The wireless charging method transmits electrical energy from the power supply to the charging vehicle through a magnetic coupling structure, and magnetic isolation is achieved between the power supply and the car. There is no need to manually plug and unplug the cable, which has higher convenience, flexibility and safety than the wired charging method. However, there are still many problems with the wireless charging method. Among them, the misalignment between the transmitting and receiving coils during the parking process is one of the problems that need to be solved urgently. Under the traditional wireless charging coil structure, the offset of the transmitting coil and the receiving coil will cause a drastic change in the transmission mutual inductance, thereby causing fluctuations in the output voltage, reducing the wireless charging performance, and may also affect the service life of the electric vehicle battery. Summary of the invention

[0003] In view of the problems existing in the above-mentioned prior art, the present invention proposes a wireless charging system that realizes unidirectional anti-offset by using symmetrical auxiliary receiving coils and duty cycle modulation. A set of symmetrical auxiliary coils is added on the basis of the original receiving coil, and the cross-coupling between the main and auxiliary coils is eliminated by overlapping with the main receiving coil; at the same time, the auxiliary coil is connected to the half-bridge controlled rectifier circuit, and a duty cycle modulation strategy is added, and the voltage is jointly output after being connected in series with the original receiving circuit topology. Through the above method, the auxiliary coil can compensate for the change of the mutual inductance of the main coil during the offset process, thereby realizing the constant voltage output of the wireless charging system during the offset process, so that the system has anti-offset characteristics.

[0004] The technical solution adopted by the present invention to solve the technical problem is: A wireless charging system that achieves unidirectional anti-offset by utilizing symmetrical auxiliary receiving coils and duty cycle modulation, wherein a group of symmetrical auxiliary coils overlap with the main receiving coil to eliminate the cross coupling of the main and auxiliary coils; the magnetic field decoupling of the main receiving coil and the auxiliary coil is achieved by overlapping with the main receiving coil; the overlapping portion of the auxiliary coil and the main receiving coil receives positive magnetic flux, and the non-overlapping portion receives negative magnetic flux, and the positive and negative magnetic fluxes within the area enclosed by the auxiliary coil are offset by adjusting the size of the overlapping area and the non-overlapping area to a certain value, thereby achieving decoupling of the main receiving coil and the symmetrical auxiliary receiving coil.

[0005] Furthermore, through the two auxiliary coils, when the main receiving coil and the transmitting coil are relatively offset, the mutual inductance of the auxiliary receiving coil and the transmitting coil is utilized to compensate for the drop of the mutual inductance of the main receiving coil.

[0006] Furthermore, the auxiliary coil is connected to a half-bridge controlled rectifier circuit, and using a duty cycle modulation strategy, is connected in series with a main receiving circuit with a full-bridge uncontrolled rectifier to jointly output a voltage to achieve compensation for the change in mutual inductance of the main coil during the offset process by the auxiliary coil, thereby achieving a constant voltage output of the wireless charging system during the offset process.

[0007] Further, the transmitting side is composed of a square wave inverter, an LCC compensation network and a transmitting coil connected in sequence; The receiving side is composed of a main receiving circuit and an auxiliary receiving circuit connected in series to a load; The main receiving circuit adopts an S-type compensation network and a full-bridge uncontrolled rectifier to output voltage; the main receiving coil is connected in series with a compensation capacitor to a full-bridge uncontrolled rectifier; The auxiliary receiving circuit adopts an S-type compensation network and two half-bridge fully-controlled rectifiers in parallel to output voltage; the two auxiliary receiving coils are respectively connected in series with compensation capacitors to connect the two half-bridge fully-controlled rectifiers.

[0008] Furthermore, the transmitting-side inverter realizes square wave inversion by injecting a driving signal with a duty cycle of 0.5 into four inverter switch tubes, wherein the first inverter switch tube S1 and the fourth inverter switch tube S4 are turned on at the same time, the second inverter switch tube S2 and the third inverter switch tube S3 are turned on at the same time, and the first inverter switch tube S1 and the fourth inverter switch tube S4 are complementarily turned on alternately with the second inverter switch tube S2 and the third inverter switch tube S3; by passing or cutting off the driving signal of the two bridge arms corresponding to the symmetrical auxiliary receiving coil to switch different working modes, voltage compensation for different transmitting and receiving coil offset conditions is realized.

[0009] Furthermore, the switching of different working modes realizes voltage compensation for different transmitting and receiving coil offset conditions, which is specifically divided into three working modes; When the transmitting coil and the receiving coil are facing each other, the wireless charging system works in mode 1. The two bridge arms of the auxiliary receiving circuit work simultaneously, and the driving signals of the two switch tubes in the same bridge arm are complementary and output in parallel. The main receiving circuit and the auxiliary receiving circuit are connected in series to output voltage to power the electric vehicle battery. When the receiving coil is offset to the left relative to the transmitting coil, the wireless charging system works in mode 2. Only the right bridge arm of the auxiliary receiving circuit works, the driving signal of the left bridge arm switch tube is turned off, and the driving signal of the right bridge arm switch tube is complementary; the mutual inductance of the right auxiliary receiving coil is greater than that of the left auxiliary receiving coil, and the left auxiliary receiving circuit current I R1is 0; the auxiliary receiving circuit is connected in series with the main receiving circuit to output a voltage, so that the voltage drop of the main receiving circuit is compensated by the voltage increase of the auxiliary receiving circuit; When the receiving coil is offset to the right relative to the transmitting coil, the wireless charging system works in mode 3; only the left bridge arm of the auxiliary receiving circuit works, the driving signal of the right bridge arm switch tube is turned off, and the driving signal of the left bridge arm switch tube is complementary; the mutual inductance of the left auxiliary receiving coil is greater than the mutual inductance of the right auxiliary receiving coil, and the current of the right auxiliary receiving loop I R2 is 0; the auxiliary receiving circuit is connected in series with the main receiving circuit to output a voltage, so that the voltage drop of the main receiving circuit is compensated by the voltage increase of the auxiliary receiving circuit.

[0010] Furthermore, by controlling the duty cycle of the complementary driving signal of the auxiliary rectifier bridge arm, the output voltage of the auxiliary receiving circuit is increased to achieve a constant voltage in the case of a unidirectional offset: The mutual inductance between the transmitting coil and the main receiving coil, and between the transmitting coil and the working auxiliary receiving coil is superimposed as the equivalent mutual inductance, and the output voltage is proportional to the equivalent mutual inductance; in the process that the duty cycle of the upper tube drive signal of the auxiliary receiving rectifier bridge arm gradually decreases from 0.5 and the lower tube drive signal remains complementary to the upper tube, the output voltage of the auxiliary receiving circuit is further increased; the overall output voltage when the equivalent mutual inductance of the magnetic coupling structure reaches the maximum value during the offset process is selected as the reference value, and the duty cycle of the upper tube drive signal of the working bridge arm at this time is adjusted in other offset cases, and the lower tube remains complementary, so as to raise the output voltage of the auxiliary receiving circuit, so that the overall output voltage rises to the reference value, and the stable output voltage of the wireless charging system under coil misalignment is realized.

[0011] Furthermore, when the wireless charging system is in working mode 1, the high level duration of the driving signal of the upper bridge arm switch tube of the auxiliary receiving circuit rectifier is shortened in the middle of the driving signal of the first inverter switch tube S1 and the fourth inverter switch tube S4 of the transmitting side inverter with the midline as the symmetrical axis, so that the system output voltage rises to be flush with the reference value; When the wireless charging system is in working modes 2 and 3, the same duty cycle modulation strategy is adopted; compared with working mode 1, the driving signal of the left bridge arm switch tube in working mode 2 is turned off, and the corresponding body diode is clamped; the driving signal of the right bridge arm switch tube in working mode 3 is turned off, and the corresponding body diode is clamped.

[0012] Furthermore, the working process is as follows: The working mode is switched according to the offset between the receiving coil of the electric vehicle and the transmitting coil of the wireless charging device to achieve stable voltage output and anti-offset effect; when the receiving coil is directly opposite to the transmitting coil, the system switches to working mode 1, the left and right auxiliary receiving coils work at the same time, and the duty cycle of the switch tubes on the left and right bridge arms is reduced according to the modulation strategy to increase the output voltage to the reference value; when the receiving coil is deviated to the left relative to the transmitting coil, the system switches to working mode 2, the right auxiliary coil receives and works, the left auxiliary coil receives and stops the driving signal and is clamped, and the duty cycle of the switch tube on the right bridge arm is reduced according to the modulation strategy to increase the output voltage to the reference value; when the receiving coil is deviated to the right relative to the transmitting coil, the system switches to working mode 3, the left auxiliary coil receives and works, the right auxiliary coil receives and stops the driving signal and is clamped, and the duty cycle of the switch tube on the left bridge arm is reduced according to the modulation strategy to increase the output voltage to the reference value.

[0013] Furthermore, the main receiving coil is a unipolar receiving coil.

[0014] Compared with the prior art, the outstanding features and optimizations of the present invention and its preferred embodiments include at least: (1) The present invention can maintain the same output voltage as that in the case of one-way misalignment of the transmitting and receiving coils during the charging process of the electric vehicle, thereby expanding the permissible range of one-way coil misalignment of the electric vehicle, achieving one-way anti-deviation, and improving the flexibility and convenience of wireless charging of electric vehicles.

[0015] (2) The proposed magnetic coupling structure only adds a pair of simple auxiliary receiving coils to the common unipolar receiving coil, and eliminates the cross-coupling between the auxiliary receiving coil and the main receiving coil by overlapping the auxiliary receiving coil, which simplifies the analysis difficulty and avoids the efficiency loss caused by cross-coupling. The scheme is simple.

[0016] (3) In the proposed topology, only a single auxiliary receiving coil and its corresponding circuit work in the event of an offset. Even in the absence of a driving signal, the voltage clamping of the other auxiliary receiving circuit can be achieved, thus avoiding the additional loss caused by the loop current generated when the other auxiliary receiving coil is not working.

[0017] (4) The proposed duty cycle modulation strategy can control the output voltage of the auxiliary circuit without generating reactive power, making the charging voltage more stable and beneficial to protecting the battery life of electric vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments: Figure 1 The receiving coil structure diagram proposed in the embodiment of the present invention: (a) the overall structure of the receiving coil; (b) the main receiving coil structure; (c) the symmetrical auxiliary receiving coil structure; Figure 2 The magnetic coupling structure diagram of the wireless charging system proposed in the embodiment of the present invention: (a) facing forward; (b) offset in the negative direction of the Y axis; (c) offset in the positive direction of the Y axis; Figure 3 This is a topology diagram of a voltage compensation type of LCC-S connected in series on the receiving side according to an embodiment of the present invention; Figure 4 This is a topological diagram of working mode 1 of the wireless charging system according to an embodiment of the present invention; Figure 5 This is a topological diagram of working mode 2 of the wireless charging system according to an embodiment of the present invention; Figure 6 This is a topology diagram of working mode 3 of the wireless charging system according to an embodiment of the present invention; Figure 7 1 is a diagram of the switch tube drive signal and the circuit modal analysis of each time period in the working mode 1 of the wireless charging system according to the embodiment of the present invention: wherein: (a) the modulation waveform of the system switch tube drive signal; (b) the circuit modal of the time period t0~t1 and t2~t3; (c) the circuit modal of the time period t1~t2; (d) the circuit modal of the time period t3~t4; Figure 8 1 is a diagram showing the switch tube drive signal and circuit modal analysis of each time period in the wireless charging system working mode 2 according to an embodiment of the present invention: (a) modulation waveform of the system switch tube drive signal; (b) circuit modalities in the time periods t0-t1 and t2-t3; (c) circuit modalities in the time period t1-t2; (d) circuit modalities in the time period t3-t4; Fig. 9 1 is a diagram of the switch tube drive signal and the circuit modal analysis in each time period of the wireless charging system working mode 3 according to an embodiment of the present invention: wherein: (a) the modulation waveform of the system switch tube drive signal; (b) the circuit modal in the time periods t0~t1 and t2~t3; (c) the circuit modal in the time period t1~t2; (d) the circuit modal in the time period t3~t4. DETAILED DESCRIPTION

[0019] In order to make the features and advantages of this patent more obvious and easy to understand, the following embodiments are specifically described in detail as follows: It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in this specification have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0020] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0021] The embodiment of the present invention specifically introduces the solution as follows: (1) Magnetic coupling structure of wireless charging system The receiving coil structure proposed by the present invention is as follows Figure 1 As shown, Figure 1 (a) is the overall structure of the receiving coil and the stacking method of the main receiving coil and the symmetrical auxiliary coil. Figure 1 (b) is the main receiving coil (common unipolar coil), Figure 1 (c) is the proposed symmetrical auxiliary coil (composed of two unipolar coils symmetrically along the midline). The two auxiliary coils on the left and right can achieve magnetic field decoupling between the main receiving coil and the auxiliary coil by overlapping with the main receiving coil at a certain distance. Figure 1 If the direction of the identification current is positive, a positive magnetic flux will be generated inside the main receiving coil and a negative magnetic flux will be generated outside. The overlapping part of the auxiliary coil and the main receiving coil receives the positive magnetic flux, and the non-overlapping part receives the negative magnetic flux. By adjusting the size of the overlapping area and the non-overlapping area to a certain appropriate value, the positive and negative magnetic fluxes inside the area enclosed by the auxiliary coil can be offset, thereby realizing the decoupling of the main receiving coil and the symmetrical auxiliary receiving coil.

[0022] The proposed magnetic coupling structure of the wireless charging system is as follows Figure 2 When the receiving coil is facing the transmitting coil (such as Figure 2 (a) shows that the mutual inductance between the main receiving coil and the transmitting coil is the largest. At this time, the mutual inductance between the symmetrical auxiliary receiving coil and the transmitting coil is much smaller, and the main power can be transmitted through the main receiving coil. Figure 2 (b) shows that during the gradual shift, the area facing the main receiving coil and the transmitting coil gradually decreases, and the mutual inductance between the main receiving coil and the transmitting coil rapidly decreases; at this time, the area facing the auxiliary receiving coil on the right side and the transmitting coil increases, and the mutual inductance between the auxiliary receiving coil on the right side and the transmitting coil gradually increases. This mutual inductance can be used to compensate for the drop in the mutual inductance of the main receiving coil, thereby achieving anti-shift in the misaligned direction. Similarly, when the receiving coil moves along the positive direction of the Y axis (such as Figure 2(c) shows that during the gradual shift, the mutual inductance between the main receiving coil and the transmitting coil decreases in the same trend; at this time, the area facing the left auxiliary receiving coil and the transmitting coil increases, and the mutual inductance between the left auxiliary receiving coil and the transmitting coil gradually increases. This mutual inductance can also be used to compensate for the drop in the mutual inductance of the main receiving coil, thereby achieving anti-shift in the misalignment direction.

[0023] (2) Wireless charging system circuit topology Based on the above magnetic coupling structure, the present invention proposes a receiving-side series LCC-S voltage compensation topology, such as Figure 3 The transmitting side of this topology consists of a square wave inverter, an LCC compensation network and a transmitting coil. V INV is the inverter DC input voltage, S1-S4 are the inverter switch tubes, L F is the series compensation inductor, C F is the parallel compensation capacitor, C T is the series compensation capacitor, L T is the self-inductance of the transmitting coil, I F , I T They are L F The receiving side of this topology is composed of the main receiving topology and the auxiliary receiving topology connected in series to the load. The main receiving topology uses an S-type compensation network and a full-bridge uncontrolled rectifier to output voltage, and the auxiliary receiving topology uses a symmetrical auxiliary receiving coil connected to an S-type compensation network and a half-bridge fully controlled rectifier to output voltage in parallel. L Rm , L R1 and L R2 are the self-inductance of the main receiving coil and the auxiliary receiving coils on the left and right sides, I Rm , I R1 and I R2 They are the corresponding branch currents, C Rm , C R1 and C R2 They are the series compensation capacitors for the main receiver and the auxiliary receivers on the left and right sides, D1-D4 are the diodes of the main receiver full-bridge uncontrolled rectifier, S 11 , S 12 and S 21, S 22 They are the switch tubes of the auxiliary receiving half-bridge fully controlled rectifiers on the left and right sides. C Om and C O12 They are the rectifier output filter capacitors of the main receiving topology and the auxiliary receiving topology respectively. R L Equivalent load resistance for charging electric vehicles, V Om , V O12 and V REC They are C Om , C O12 and R L Voltage across both ends. M TRm , M TR1 and M TR2 They are the mutual inductances of the transmitting coil and the main receiving coil, the left auxiliary receiving coil, and the right auxiliary receiving coil. The mutual inductance between the main receiving coil and the symmetrical auxiliary receiving coil can be ignored due to overlapping decoupling. The mutual inductance generated by the cross-coupling of the left and right auxiliary receiving coils can be simply decoupled by externally nesting the winding of another coil or adding a transformer to the dual-path auxiliary receiving loop, so it can also be ignored.

[0024] The transmitter-side inverter of this topology realizes square wave inversion by injecting a driving signal with a duty cycle of 0.5 into S1-S4, where S1 and S4 are turned on at the same time, S2 and S3 are turned on at the same time, and S1 and S4 complement and alternately turn on S2 and S3. By passing or cutting off the driving signal of the two bridge arms corresponding to the symmetrical auxiliary receiving coil, different working modes can be switched to realize voltage compensation for different offset conditions of the transmitting and receiving coils. Specifically, it can be divided into three working modes.

[0025] When the transmitting coil and the receiving coil are facing each other (such as Figure 2 (a) shows), the wireless charging system works in mode 1, and the topological working mode is shown in the figure Figure 4 As shown. At this time, the two bridge arms of the auxiliary receiving topology work simultaneously, and the switch tube S 11 , S 21 At the same time, S 21 , S 22 At the same time, S 11 With S 12 The driving signals are complementary, S 21 and S 22The driving signals are complementary. The mutual inductance between the two symmetrical auxiliary receiving coils and the transmitting coil is similar, corresponding to the parallel output of the two auxiliary receiving bridge arms. Finally, the auxiliary receiving topology and the main receiving topology are connected in series to output voltage to power the electric vehicle battery.

[0026] When the receiving coil is offset to the left relative to the transmitting coil (such as Figure 2 (b) shows that the wireless charging system works in mode 2, and the topological working mode is shown in the figure Figure 5 At this time, only the right bridge arm is working, and the switch tube S is turned off. 11 With S 12 The driving signal of the switch tube S 21 and S 22 The driving signals are complementary. As the receiving coil shifts to the left, the mutual inductance between the main receiving coil and the transmitting coil decreases, and the output voltage of the main receiving topology V Om The mutual inductance between the right auxiliary receiving coil and the transmitting coil increases, and the output voltage of the auxiliary receiving topology V O12 And because the mutual inductance of the right auxiliary receiving coil is greater than that of the left auxiliary receiving coil, the left auxiliary receiving bridge arm body diode is clamped, and the left auxiliary receiving loop current I R1 The auxiliary receiving topology is connected in series with the main receiving topology to output the voltage, so that the voltage drop of the main receiving topology is compensated by the voltage increase of the auxiliary receiving topology, thereby maintaining the overall output voltage of the system. V REC The fluctuation is affected by the offset and the fluctuation is reduced, achieving the effect of anti-offset.

[0027] When the receiving coil is offset to the right relative to the transmitting coil (such as Figure 2 (c) shows that the wireless charging system works in mode 3, and the topological working mode is shown in the figure Figure 6 As shown. At this time, only the left bridge arm is working, and the switch tube S 11 With S 12 The driving signals are complementary, turning off the switch tube S 21 and S 22 As the receiving coil shifts to the right, the mutual inductance between the main receiving coil and the transmitting coil decreases, and the output voltage of the main receiving topology V Om The mutual inductance between the left auxiliary receiving coil and the transmitting coil increases, and the output voltage of the auxiliary receiving topology V O12 And because the mutual inductance of the left auxiliary receiving coil is greater than that of the right auxiliary receiving coil, the body diode of the right auxiliary receiving bridge arm is clamped, and the current of the right auxiliary receiving loop I R2Similarly, by connecting the auxiliary receiving topology in series with the main receiving topology, the output voltage is compensated by the voltage increase of the auxiliary receiving topology, thereby maintaining the overall output voltage of the system. V REC The fluctuation is affected by the offset and the fluctuation is reduced, achieving the effect of anti-offset.

[0028] (3) Modulation strategy of auxiliary receiving rectifier in wireless charging system When the complementary driving signals of the auxiliary receiving rectifier bridge arms are set to a duty cycle of 0.5 in the three working modes, the output voltage of the auxiliary receiving rectifier often cannot accurately compensate the output voltage of the main receiving rectifier in the case of offset. Overcompensation will occur when the offset distance is small, and undercompensation will occur when the offset distance is large. Therefore, the present invention proposes a duty cycle modulation strategy for the auxiliary receiving topology, which controls the duty cycle of the complementary driving signal of the auxiliary rectifier bridge arm so that the output voltage of the auxiliary receiving topology rises to an appropriate value, thereby achieving voltage constancy in the case of unidirectional offset.

[0029] The topology proposed in the present invention is an LCC-S type compensation network, which has a constant voltage characteristic that is independent of the load. The mutual inductance between the transmitting coil and the main receiving coil, the transmitting coil and the working auxiliary receiving coil is superimposed as the equivalent mutual inductance, and the output voltage of the topology is proportional to the equivalent mutual inductance. In addition, in the process where the duty cycle of the upper tube drive signal of the auxiliary receiving rectifier bridge arm gradually decreases from 0.5 and the lower tube drive signal and the upper tube remain complementary, the output voltage of the auxiliary receiving topology can be further increased. Since the magnetic coupling structure proposed in the present invention will increase the equivalent mutual inductance first and then decrease during the offset process, the present invention selects the overall output voltage when the equivalent mutual inductance of the magnetic coupling structure reaches the maximum value during the offset process as the reference value, and adjusts the duty cycle of the upper tube drive signal of the working bridge arm at this time in other offset conditions, and the lower tube remains complementary, so that the output voltage of the auxiliary receiving topology can be raised, so that the overall output voltage rises to the reference value, and the voltage of the wireless charging system is output smoothly under the coil misalignment, and the effect of unidirectional anti-offset is achieved.

[0030] When the wireless charging system is in working mode 1, the driving signals of all switch tubes of the wireless charging system and the modal analysis of each period of the circuit are as follows: Figure 7 The upper arm of the auxiliary receiving topology rectifier is set as θ ( θ <180°), and t 0~ t 1 and t 2~ t3 duration is equal, that is, the high level duration of the upper tube drive signal is shortened to the middle of the symmetrical axis with the midline of the inverter S1 and S4 drive signals. This method can avoid the system from generating additional reactive power and keep the system efficiency at a high value. Through this duty cycle modulation strategy, the system output voltage can be raised to the same level as the reference value in this case.

[0031] When the wireless charging system is in working mode 2 and 3, the driving signals of all switch tubes of the wireless charging system and the modal analysis of each period of the circuit are as follows: Figure 8 , 9 As shown, the same duty cycle modulation strategy is adopted. Compared with working mode 1, the switch tube S in working mode 2 11 With S 12 The drive signal is turned off, and the corresponding body diode is clamped; in working mode 3, the switch tube S 21 With S 22 The driving signal is turned off and the corresponding body diode is clamped.

[0032] The present invention adds a symmetrical auxiliary receiving coil on the basis of a traditional unipolar receiving coil, increases the mutual inductance that can be used for offset compensation through the innovation of the magnetic coupling structure, realizes the compensation of the output voltage of the main receiving topology by the auxiliary receiving topology through the innovation of the circuit topology, and realizes accurate control of the output voltage compensation by adding a duty cycle modulation strategy, so that the output voltage of the wireless charging system remains basically unchanged when the coil is misaligned, thereby realizing unidirectional anti-offset.

[0033] The wireless charging system proposed in the embodiment of the present invention can switch the working mode according to the offset between the receiving coil of the electric vehicle and the transmitting coil of the wireless charging device to achieve stable voltage output and anti-offset effect. When the receiving coil is facing the transmitting coil, the system switches to working mode 1, the left and right auxiliary receiving work at the same time, and the duty cycle of the switch tubes on the left and right bridge arms is reduced according to the modulation strategy to increase the output voltage to the reference value; when the receiving coil is deflected to the left relative to the transmitting coil, the system switches to working mode 2, the right auxiliary receiving works, the left auxiliary receiving stops the driving signal and is clamped, and the duty cycle of the switch tube on the right bridge arm is reduced according to the modulation strategy to increase the output voltage to the reference value; when the receiving coil is deflected to the right relative to the transmitting coil, the system switches to working mode 3, the left auxiliary receiving works, the right auxiliary receiving stops the driving signal and is clamped, and the duty cycle of the switch tube on the left bridge arm is reduced according to the modulation strategy to increase the output voltage to the reference value.

[0034] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0035] This patent is not limited to the above-mentioned optimal implementation mode. Anyone can derive other forms of a wireless charging system that uses a symmetrical auxiliary receiving coil and duty cycle modulation to achieve unidirectional anti-deviation under the inspiration of this patent. All equal changes and modifications made according to the scope of the patent application of the present invention should be covered by this patent.

Claims

1. A wireless charging system using symmetrical auxiliary receiving coils and duty cycle modulation to achieve unidirectional anti-drift, characterized in that: A set of symmetrical auxiliary coils overlaps the main receiving coil to eliminate the cross coupling between the main and auxiliary coils; The magnetic field decoupling of the main receiving coil and the auxiliary coil is achieved by overlapping with the main receiving coil; the overlapping part of the auxiliary coil and the main receiving coil receives positive magnetic flux, and the non-overlapping part receives negative magnetic flux. By adjusting the size of the overlapping area and the non-overlapping area to a certain value, the positive and negative magnetic fluxes inside the area enclosed by the auxiliary coil are offset, thereby achieving decoupling of the main receiving coil and the symmetrical auxiliary receiving coil.

2. The wireless charging system for realizing unidirectional anti-deviation by using symmetrical auxiliary receiving coils and duty cycle modulation according to claim 1, characterized in that: Through the two auxiliary coils, when the main receiving coil and the transmitting coil are relatively offset, the mutual inductance of the auxiliary receiving coil and the transmitting coil is utilized to compensate for the drop of the mutual inductance of the main receiving coil.

3. The wireless charging system for realizing unidirectional anti-deviation by using symmetrical auxiliary receiving coils and duty cycle modulation according to claim 1, characterized in that: The auxiliary coil is connected to a half-bridge controlled rectifier circuit, and uses a duty cycle modulation strategy to be connected in series with a main receiving circuit with a full-bridge uncontrolled rectifier to jointly output a voltage to achieve compensation of the auxiliary coil for the change in mutual inductance of the main coil during the offset process, thereby achieving a constant voltage output of the wireless charging system during the offset process.

4. The wireless charging system for realizing unidirectional anti-deviation by using symmetrical auxiliary receiving coils and duty cycle modulation according to claim 1, characterized in that: The transmitting side consists of a square wave inverter, an LCC compensation network and a transmitting coil connected in sequence; The receiving side is composed of a main receiving circuit and an auxiliary receiving circuit connected in series to a load; The main receiving circuit adopts an S-type compensation network and a full-bridge uncontrolled rectifier to output voltage; the main receiving coil is connected in series with a compensation capacitor to a full-bridge uncontrolled rectifier; The auxiliary receiving circuit adopts an S-type compensation network and two half-bridge fully-controlled rectifiers in parallel to output voltage; the two auxiliary receiving coils are respectively connected in series with compensation capacitors to connect the two half-bridge fully-controlled rectifiers.

5. The wireless charging system for realizing unidirectional anti-deviation by using symmetrical auxiliary receiving coils and duty cycle modulation according to claim 4, characterized in that: The transmitting-side inverter realizes square wave inversion by injecting a driving signal with a duty cycle of 0.5 into four inverter switch tubes, wherein the first inverter switch tube S1 and the fourth inverter switch tube S4 are turned on at the same time, the second inverter switch tube S2 and the third inverter switch tube S3 are turned on at the same time, and the first inverter switch tube S1 and the fourth inverter switch tube S4 are complementarily turned on alternately with the second inverter switch tube S2 and the third inverter switch tube S3; by passing or cutting off the driving signal of the two bridge arms corresponding to the symmetrical auxiliary receiving coil to switch different working modes, voltage compensation for different transmitting and receiving coil offset conditions is realized.

6. The wireless charging system for realizing unidirectional anti-deviation by using symmetrical auxiliary receiving coils and duty cycle modulation according to claim 5, characterized in that: The switching of different working modes realizes voltage compensation for different transmitting and receiving coil offset conditions, which is specifically divided into three working modes; When the transmitting coil and the receiving coil are facing each other, the wireless charging system works in mode 1. The two bridge arms of the auxiliary receiving circuit work simultaneously, and the driving signals of the two switch tubes in the same bridge arm are complementary and output in parallel. The main receiving circuit and the auxiliary receiving circuit are connected in series to output voltage to power the electric vehicle battery. When the receiving coil is offset to the left relative to the transmitting coil, the wireless charging system works in mode 2. Only the right bridge arm of the auxiliary receiving circuit works, the driving signal of the left bridge arm switch tube is turned off, and the driving signal of the right bridge arm switch tube is complementary; the mutual inductance of the right auxiliary receiving coil is greater than that of the left auxiliary receiving coil, and the left auxiliary receiving circuit current I R1 is 0; the auxiliary receiving circuit is connected in series with the main receiving circuit to output a voltage, so that the voltage drop of the main receiving circuit is compensated by the voltage increase of the auxiliary receiving circuit; When the receiving coil is offset to the right relative to the transmitting coil, the wireless charging system operates in mode 3; Only the left bridge arm of the auxiliary receiving circuit works, the driving signal of the right bridge arm switch tube is turned off, and the driving signal of the left bridge arm switch tube is complementary; the mutual inductance of the left auxiliary receiving coil is greater than the mutual inductance of the right auxiliary receiving coil, and the current of the right auxiliary receiving loop I R2 is 0; the auxiliary receiving circuit is connected in series with the main receiving circuit to output a voltage, so that the voltage drop of the main receiving circuit is compensated by the voltage increase of the auxiliary receiving circuit.

7. The wireless charging system for realizing unidirectional anti-deviation by using symmetrical auxiliary receiving coils and duty cycle modulation according to claim 6, characterized in that: By controlling the duty cycle of the complementary driving signal of the auxiliary rectifier bridge arm, the output voltage of the auxiliary receiving circuit is increased to achieve a constant voltage in the case of unidirectional offset: The mutual inductance between the transmitting coil and the main receiving coil, and between the transmitting coil and the working auxiliary receiving coil is superimposed as the equivalent mutual inductance, and the output voltage is proportional to the equivalent mutual inductance; in the process that the duty cycle of the upper tube drive signal of the auxiliary receiving rectifier bridge arm gradually decreases from 0.5 and the lower tube drive signal remains complementary to the upper tube, the output voltage of the auxiliary receiving circuit is further increased; the overall output voltage when the equivalent mutual inductance of the magnetic coupling structure reaches the maximum value during the offset process is selected as the reference value, and the duty cycle of the upper tube drive signal of the working bridge arm at this time is adjusted in other offset cases, and the lower tube remains complementary, so as to raise the output voltage of the auxiliary receiving circuit, so that the overall output voltage rises to the reference value, and the stable output voltage of the wireless charging system under coil misalignment is realized.

8. The wireless charging system for realizing unidirectional anti-deviation by using symmetrical auxiliary receiving coils and duty cycle modulation according to claim 7, characterized in that: When the wireless charging system is in working mode 1, the high level duration of the driving signal of the upper bridge arm switch tube of the auxiliary receiving circuit rectifier is shortened in the middle of the driving signal of the first inverter switch tube S1 and the fourth inverter switch tube S4 of the transmitting side inverter with the midline as the symmetrical axis, so that the system output voltage rises to the same level as the reference value; When the wireless charging system is in working modes 2 and 3, the same duty cycle modulation strategy is adopted; compared with working mode 1, the driving signal of the left bridge arm switch tube in working mode 2 is turned off, and the corresponding body diode is clamped; the driving signal of the right bridge arm switch tube in working mode 3 is turned off, and the corresponding body diode is clamped.

9. The wireless charging system for realizing unidirectional anti-deviation by using symmetrical auxiliary receiving coils and duty cycle modulation according to claim 8, characterized in that: The specific working process is: The working mode is switched according to the offset between the receiving coil of the electric vehicle and the transmitting coil of the wireless charging device to achieve stable voltage output and anti-offset effect; when the receiving coil is directly opposite to the transmitting coil, the system switches to working mode 1, the left and right auxiliary receiving coils work at the same time, and the duty cycle of the switch tubes on the left and right bridge arms is reduced according to the modulation strategy to increase the output voltage to the reference value; when the receiving coil is deviated to the left relative to the transmitting coil, the system switches to working mode 2, the right auxiliary coil receives and works, the left auxiliary coil receives and stops the driving signal and is clamped, and the duty cycle of the switch tube on the right bridge arm is reduced according to the modulation strategy to increase the output voltage to the reference value; when the receiving coil is deviated to the right relative to the transmitting coil, the system switches to working mode 3, the left auxiliary coil receives and works, the right auxiliary coil receives and stops the driving signal and is clamped, and the duty cycle of the switch tube on the left bridge arm is reduced according to the modulation strategy to increase the output voltage to the reference value.

10. The wireless charging system for realizing unidirectional anti-deviation by using symmetrical auxiliary receiving coils and duty cycle modulation according to claim 1, characterized in that: The main receiving coil is a unipolar receiving coil.

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