A wireless charging system capable of achieving constant current - constant voltage and power expansion

Abstract

A wireless charging system capable of achieving constant current-constant voltage and power expansion, which relates to the field of wireless charging. The present invention is to solve the problem that during the entire charging process of the battery, the equivalent resistance of the battery changes greatly, making it difficult to achieve constant current and constant voltage output. In the constant current charging mode of the present invention, the two receivers can effectively share the energy transmitted by the transmitter, reducing the current stress on the diodes of each receiver. Moreover, finally, the two receivers are output in parallel, thereby increasing the output current and improving the power level, and can achieve zero voltage switching. In the constant voltage charging mode, only one receiver is used as the output, and the other receiver is used as the compensation for the output-side coil, which can achieve zero phase angle and improve the power transmission ability.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronic conversion, and particularly relates to a wireless charging system. Background Art

[0002] Wireless power transfer technology has currently received extensive attention in various fields such as electric vehicles, biomedicine, consumer electronics, and underwater channels. Compared with the traditional plug-in charging method, wireless power transfer technology transfers electrical energy to the load through a magnetic field without the need for complex wire connections. Therefore, wireless power transfer is more convenient and safe.

[0003] The usage time of an electric vehicle depends on the capacity of the power battery. A large-capacity battery is a basic requirement to ensure the long-distance driving of an electric vehicle. However, as the battery capacity increases, the time required to fully charge the battery will inevitably be extended, and the demand for fast charging will be increasing. In recent years, the wireless charging technology for electric vehicles has been continuously developing, and the wireless charging technology regarding power transfer capability is still a current research hotspot. However, due to the rated power of semiconductor components and the limitation of the installation space inside the electric vehicle, high-power wireless charging systems still face challenges. Currently, for a dual-coil wireless charging system with a single transmitter and a single receiver, if high-power output is to be achieved, it will increase the voltage or current stress on the diodes in the rectifier on the receiver, thereby increasing the cost. In addition, in practical applications, the battery of an electric vehicle has two charging stages, namely constant-current charging and constant-voltage charging. First, the battery is charged in the constant-current mode. During this process, the battery voltage continuously increases. When the battery voltage rises to a specified level, it switches to the constant-voltage mode to charge the battery. At this time, the charging current gradually decreases until it drops close to zero when the charging ends. During the entire charging process of the battery, the equivalent resistance of the battery changes very greatly. Therefore, it is actually difficult to design a wireless charging system with constant-current output and constant-voltage output. Moreover, in order to improve the charging efficiency and power transfer capability and reduce the switching loss, the input impedance of the inverter must be purely resistive or inductive throughout the charging process, so as to achieve zero phase angle or zero-voltage switching. Summary of the Invention

[0004] The present invention is to solve the problem that during the entire charging process of the battery, the equivalent resistance of the battery changes greatly, making it difficult to achieve constant-current and constant-voltage outputs. Now, a wireless charging system capable of achieving constant-current - constant-voltage and power expansion is provided.

[0005] A wireless charging system capable of achieving constant-current - constant-voltage and power expansion includes a transmitter and two receivers. The two receivers are connected in parallel to the load connection end in the constant-current operating mode. In the constant-voltage operating mode, one receiver is used for voltage compensation, and the other receiver is used for outputting voltage. There is mutual inductance between the coils of the transmitter and the two receivers pairwise.

[0006] Two compensation capacitors are connected in series on the coil of the transmitter, and a switch is connected in parallel across one of the compensation capacitors.

[0007] The receiver for voltage compensation includes: a compensation group coil, two compensation group diodes, two compensation group MOSFETs, and two compensation group capacitors. One compensation group diode and one compensation group MOSFET are connected in series to form a series group, and another compensation group diode and another compensation group MOSFET are connected in series to form another series group. The two series groups and one compensation group capacitor are all connected in parallel to the load connection terminal. The two ends of the compensation group coil are respectively connected to the connection points of the compensation group diode and the compensation group MOSFET in the two series groups. Another compensation group capacitor is connected in series with the compensation group coil. The two compensation group MOSFETs are both adjacent to the negative pole of the load.

[0008] An output group capacitor is connected in series on the coil of another receiver.

[0009] By adjusting the on or off states of the switch and the two compensation group MOSFETs, the switching between the constant voltage or constant current modes of the wireless charging system can be achieved.

[0010] Further, in the constant voltage mode of the wireless charging system, the switch is turned off, so that the compensation capacitor connected in parallel with the switch works. The two compensation group MOSFETs are turned on, so that the receiver for voltage compensation is disconnected from another receiver, and another receiver outputs voltage independently.

[0011] In the constant current mode of the wireless charging system, the switch is closed, so that the compensation capacitor connected in parallel with the switch does not work. The two compensation group MOSFETs are turned off, so that the two receivers output voltage in parallel.

[0012] Further, the above-mentioned transmitter includes: four transmitter group MOSFETs and a transmitter group coil.

[0013] The four transmitter group MOSFETs are connected in series in pairs to form two groups. The two groups are both connected in parallel across the power supply. The two ends of the transmitter group coil are respectively connected to the connection points of the two transmitter group MOSFETs in the two groups.

[0014] Further, the above-mentioned another receiver includes: an output group capacitor, an output group coil, and four output group diodes.

[0015] The four output group diodes are connected in series in pairs to form two diode groups. The two diode groups and the output group capacitor are all connected in parallel to the load connection terminal. The two ends of the output group coil are respectively connected to the connection points of the two output group diodes in the two diode groups.

[0016] A wireless charging system capable of achieving constant current - constant voltage and power expansion. In the constant current charging mode, the two receivers can effectively share the energy transmitted by the transmitter, reducing the current stress on the diodes of each receiver. Finally, the two receivers are output in parallel, thereby increasing the output current and improving the power level, and zero - voltage switching can be achieved. In the constant voltage charging mode, only one receiver is used as the output, and the other receiver is used as the compensation for the output - side coil, which can achieve zero phase angle and improve the power transmission ability. Description of the Drawings

[0017] Figure 1 Schematic diagram of the topological structure of a wireless charging system capable of achieving constant current - constant voltage and power expansion;

[0018] Figure 2 Topological structure diagram in the constant current working mode;

[0019] Figure 3 Equivalent circuit diagram in the constant current working mode;

[0020] Figure 4 Topological structure diagram in the constant voltage working mode;

[0021] Figure 5 Equivalent circuit diagram in the constant voltage working mode;

[0022] Figure 6 In the constant current working mode and I B Waveform diagrams, where (a) R B = 6Ω, (b) R B = 8Ω;

[0023] Figure 7 In the constant current working mode and Waveform diagrams, where (a) R B = 6Ω, (b) R B = 8Ω;

[0024] Figure 8 In the constant voltage working mode and V B Waveform diagrams, where (c) R B = 10Ω, (d) R B = 12Ω;

[0025] Figure 9 In the constant current mode, when R B changes from 6Ω to 8Ω and I B 、V B Waveform diagrams;

[0026] Figure 10 For R in constant voltage mode B When changing from 10Ω to 12Ω and I B , V B Waveform diagram;

[0027] Figure 11 It is a magnetic simulation modeling diagram. Specific implementation mode

[0028] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the scope of protection of the present invention. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0029] Refer to Figures 1 to 11 Specifically describe this implementation mode. A wireless charging system capable of realizing constant current - constant voltage and power expansion described in this implementation mode. The two receivers are connected in parallel with the load connection end in the constant current working mode. In the constant voltage working mode, one receiver is used as voltage compensation, and the other receiver is used to output voltage. There is mutual inductance between the coils of the transmitter and the two receivers pairwise.

[0030] The transmitter includes four MOSFET tubes (S 1 ~S 4 ), coil L 1 , compensation capacitor C 1 and compensation capacitor C k . The resistance R 1 is the internal resistance of coil L 1 . S 1 and S 2 are connected in series with each other to form a series group. S 3 and S 4 are connected in series with each other to form another series group. The two series groups are both connected in parallel at both ends of the power supply. One end of coil L 1 is connected to the connection point of S 1 and S 2 . The other end of coil L 1 is connected to the connection point of S 3 and S 4 . Compensation capacitor C 1 and compensation capacitor C k are connected in series with coil L 1 . A switch S is connected in parallel at both ends of compensation capacitor C k .

[0031] The receiver for output voltage (the first receiver) includes: four diodes (D 1 ~D 4 ), capacitor C 2 , capacitor C 4 and coil L 2 , and the resistance R 2 is the internal resistance of coil L 2 . D 1 and D 2 are connected in series with each other to form a diode group, and D 3 and D 4 are connected in series with each other to form another diode group. The two diode groups and capacitor C 4 are all connected in parallel with the load connection terminal. One end of coil L 2 is connected to the connection point of D 1 and D 2 , and the other end of coil L 2 is connected to the connection point of D 3 and D 4 . Capacitor C 2 is connected in series with coil L 2 .

[0032] The receiver for voltage compensation (the second receiver) includes: diode D 5 , diode D 7 , capacitor C 3 , capacitor C 5 , coil L 3 and two MOSFET transistors (S 5 and S 6 ). D 5 and S 5 are connected in series with each other to form a group, and D 7 and S 6 are connected in series with each other to form another group. The two groups and capacitor C 5 are all connected in parallel with the load connection terminal. One end of coil L 3 is connected to the connection point of D 5 and S 5 , and the other end of coil L 3 is connected to the connection point of D 7 and S 6 . D 6 and D 8 are the anti-parallel diodes inside S 5 and S 6 respectively. Capacitor C 3 is connected in series with coil L 3 .

[0033] By adjusting switch S and S 5 and S 6The conduction or cutoff of [the component] can achieve the switching between the constant voltage or constant current mode of the wireless charging system. Both working modes have soft-switching technology, and in the constant current working mode, the dual receivers can transfer more energy than the single receiver. Specifically:

[0034] When the wireless charging system operates in the constant voltage mode, the switch S is disconnected, causing the compensation capacitor C k to work, and the MOSFET transistors S 5 and S 6 to conduct, so that the receiver for voltage compensation is disconnected from the other receiver. The other receiver outputs voltage independently, and the input impedance is purely resistive, meeting the zero-phase angle characteristic, reducing the switching loss, and improving the power transmission ability.

[0035] When the wireless charging system operates in the constant current mode, the switch S is closed, making the compensation capacitor C k not work, and the MOSFET transistors S 5 and S 6 to cutoff. The diodes D 6 and D 8 work, enabling the two receivers to output voltage in parallel, increasing the output current, improving the power level, and making the input impedance of the inverter inductive, achieving zero-voltage switching.

[0036] In summary, the dual receivers can effectively share the energy transmitted by the transmitter with each other, that is, the currents on the two receivers are not very different, and the currents on the two receivers do not need to be very large. Finally, the two currents can be superimposed to increase the power level to a certain extent. Compared with the single receiver, the dual receiver has an additional energy transmission channel and also reduces the current stress on the diodes in the receiver.

[0037] According to the equivalent circuit of the constant current charging mode Figure 3 and the equivalent circuit of the constant voltage charging mode Figure 5 write the KVL equations and analyze the impedance network as follows:

[0038] The constant current mode is as follows:

[0039]

[0040] Among them, is the output voltage of the transmitter, and are the loop currents of the transmitter, the first receiver, and the second receiver respectively, j is the imaginary unit, ω is the operating frequency of the wireless charging system, L 1 、L 2 and L 3 are the coil L 1 、the coil L 2 and the coil L3 The inductance value of, C 1 , C 2 and C 3 are respectively the capacitance values of capacitor C 1 , capacitor C 2 and capacitor C 3 respectively, X 12 = jωM 12 , X 13 = jωM 13 , X 23 = jωM 23 , M 12 is the mutual inductance between coil L 1 and coil L 2 , M 13 is the mutual inductance between coil L 1 and coil L 3 , M 23 is the mutual inductance between coil L 2 and coil L 3 respectively, R B is the load resistance, R eq1 and R eq2 are respectively the equivalent AC load resistance values on the rectifiers in the first receiver and the second receiver.

[0041] According to Equation (1), the relationship between voltage and current can be obtained:

[0042]

[0043] Among them, the expressions of A and B in Equation (2) are respectively:

[0044]

[0045] When B = 0, Z 2 = Z 3 = 0:

[0046]

[0047] The output current in Equation (4) is independent of the resistance, achieving a constant current output. In this embodiment, M 23 is negative, so the input impedance Z in is inductive, achieving zero-voltage switching.

[0048] The constant voltage mode is as follows:

[0049]

[0050] Among them, is the output voltage phasor of the first receiver, Ck For compensating capacitor C k 's capacitance value.

[0051] According to Equation (5), the relationship between voltage and current can be obtained:

[0052]

[0053] The expressions of A' and B' in Equation (6) are respectively:

[0054]

[0055] When A' = 0, Z 2 = Z 3 = 0:

[0056]

[0057] The output voltage in Equation (8) is independent of the resistance, achieving a constant voltage output, and the input impedance Z in is purely resistive, achieving a zero phase angle.

[0058] Utilize all the listed equation relationships to design and optimize the circuit parameters. The most crucial point is that in this example, the constant current charging mode and the constant voltage charging mode operate at the same switching frequency and with the same set of parameters. When switching to the constant voltage operating mode in this embodiment, by changing the impedance network Z 1 in the constant current operating mode, the changed impedance network is made equal to the impedance Z 1 ' in the constant voltage operating mode, thereby ensuring that the two operating modes run with the same set of numbers. In this embodiment, it is completed by adding a compensating capacitor C k as follows:

[0059]

[0060] The value of the added compensating capacitor C k can be calculated from Equation (9). Through switch switching, the compensating capacitor C k does not work in the constant current operating mode, and the compensating capacitor C k works in the constant voltage operating mode, so that the two operating modes can be switched and run with the same set of parameters.

[0061] Table 1

[0062]

[0063] In this embodiment, MATLAB / Simulink is used to experimentally verify the system of the present invention. First, in the constant current charging mode, Figure 6 Figures (a) and (b) in respectively show the resistor RB = 6 Ω and R B The input voltage, input current, and output current I under the condition of B R = 8 Ω. The output current I B When the resistance R B is equal to 6 Ω and 8 Ω, it is basically unchanged and remains at about 5.45 A, achieving constant current output. Moreover, the input voltage leads the input current, achieving zero voltage switching. In the constant current working mode, Figure 7 They are the current waveform diagrams of the first receiver and the second receiver respectively. In Figure 7 (a), when the resistance R B is 6 Ω, the current on the first receiver is 4.39 A, and the current on the second receiver is 4.06 A. When Figure 7 (b), when the resistance R B is 8 Ω, the current on the first receiver is 4.89 A, and the current on the second receiver is 3.57 A. The first receiver and the second receiver share the energy transmitted by the transmitter, and finally the two receivers are connected in parallel to output, increasing the output current and improving the output power. Compared with a single receiver, this embodiment reduces the current stress of the diode in the receiver while increasing the output power.

[0064] In the constant voltage charging mode, Figure 8 Figures (c) and (d) in B show the input voltage, input current, and output voltage V under the condition of B R = 12 Ω and R B = 10 Ω. The output voltage V B When the resistance R B is equal to 10 Ω and 12 Ω, it is basically unchanged and remains at about 51.4 V, achieving constant voltage output, and it is also at zero phase angle, improving the power output ability.

[0065] Figure 9 is the waveform diagram of the input voltage and input current, I B and V B when the resistance R B varies from 6 Ω to 8 Ω in the constant current mode. It can be seen that the present invention can achieve smooth switching, and the output current I B is almost unchanged before and after the switching, and the output voltage V B gradually rises during the switching process, meeting the charging process of the electric vehicle battery. Figure 10 is the input voltage and input current, I B when the resistance RB and V B The waveform diagram of. It can be seen from the figure that the output voltage V B is also unchanged before and after switching, and the output current I B is slowly decreasing, verifying the feasibility and practicality of the present invention in the wireless charging technology of electric vehicles.

[0066] Figure 11 is the magnetic simulation modeling diagram in the embodiment of the present invention, L 2 and L 3 The coil sizes are exactly the same, both are 12 turns. The coil L 1 is 10 turns. The diameters of the exciting wires used for the three coils are all 3 mm. The size of the ferrite used in the figure is 55 mm * 15 mm * 5 mm. According to Figure 11 the method in, the inductance and mutual inductance values used in this example can be designed, thus verifying the reliability of the parameters in this example.

[0067] Although the present invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed, as long as they do not depart from the spirit and scope of the present invention defined by the appended claims. It should be understood that different dependent claims and the features described herein can be combined in a manner different from that described in the original claims. It should also be understood that the features described in connection with a single embodiment can be used in other described embodiments.

Claims

1. A wireless charging system capable of achieving constant current-constant voltage and power expansion, comprising a transmitter and two receivers, characterized in that: The two receivers are connected in parallel to the load connection terminal in the constant current working mode, one receiver is used as voltage compensation and the other receiver is used for output voltage in the constant voltage working mode, and mutual inductance exists between the coils of the transmitter and the two receivers; The transmitter coil is connected in series with two compensation capacitors, and a switch is connected in parallel at both ends of one compensation capacitor; The receiver as voltage compensation includes: a compensation group coil, two compensation group diodes, two compensation group MOSFET tubes and two compensation group capacitors, one compensation group diode and one compensation group MOSFET tube are connected in series to form a series group, another compensation group diode and another compensation group MOSFET tube are connected in series to form another series group, the two series groups and one compensation group capacitor are connected in parallel with the load connection end, the two ends of the compensation group coil are respectively connected to the connection points of the compensation group diodes and the compensation group MOSFET tubes in the two series groups, another compensation group capacitor is connected in series with the compensation group coil, and the two compensation group MOSFET tubes are adjacent to the negative electrode of the load; The coil of the other receiver is connected in series with an output group capacitor; By adjusting the switch and the on or off of the two compensation group MOSFET tubes, the wireless charging system can be switched between constant voltage mode and constant current mode.

2. A wireless charging system capable of achieving constant current-constant voltage and power expansion according to claim 1, characterized in that: In the constant voltage mode of the wireless charging system, the switch is disconnected, so that the compensation capacitor connected in parallel with the switch works, and the two compensation group MOSFETs are turned on, so that the receiver used as voltage compensation is disconnected from the other receiver, and the other receiver outputs voltage independently; In the constant current mode of the wireless charging system, the switch is closed, so that the compensation capacitor connected in parallel with the switch does not work, and the two compensation group MOSFET tubes are turned off, so that the two receivers output voltage in parallel.

3. A wireless charging system capable of achieving constant current-constant voltage and power expansion according to claim 1 or 2, characterized in that: The transmitter includes: four transmitting group MOSFET tubes and a transmitting group coil, The four emission group MOSFET tubes are connected in series in pairs to form two groups, and the two groups are connected in parallel at both ends of the power supply. The two ends of the emission group coil are respectively connected to the connection points of two emission group MOSFET tubes in the two groups.

4. A wireless charging system capable of achieving constant current-constant voltage and power expansion according to claim 3, characterized in that: The other receiver comprises: an output group capacitor, an output group coil and four output group diodes, The four output group diodes are connected in series in pairs to form two diode groups, the two diode groups and the output group capacitor are connected in parallel with the load connection end, and the two ends of the output group coil are respectively connected to the connection points of two output group diodes in the two diode groups.

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