Wireless charging system capable of realizing constant current-constant voltage and power expansion

Abstract

The invention discloses a wireless charging system capable of realizing constant current-constant voltage and power expansion, and relates to the field of wireless charging. The invention aims to solve the problems that in the whole charging process of a battery, the equivalent resistance change of the battery is large, and constant-current and constant-voltage output is difficult to realize. In the constant-current charging mode, the double receivers can effectively share energy transmitted by the transmitter, the current stress of the diode on each receiver is reduced, and finally, the double receivers output in parallel, so that the output current is increased, the power level is improved, and zero-voltage switching can be realized. In a constant-voltage charging mode, only one receiver serves as output, the other receiver serves as compensation of the output side coil, a zero phase angle can be achieved, and the power transmission capacity is improved.

Description

Technical Field

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

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

[0003] The use time of electric vehicles depends on the capacity of the power battery. Large-capacity batteries are the basic requirement to ensure long-distance driving of electric vehicles. However, as the battery capacity increases, the time it takes to fully charge the battery will inevitably increase, and people's demand for fast full charging will become greater and greater. In recent years, the wireless charging technology of electric vehicles has been continuously developing. The wireless charging technology with power transmission capability is still a hot research topic, but due to the power rating of semiconductor components and the limitations of the internal installation space of electric vehicles, high-power wireless charging systems still face challenges. At present, the dual-coil wireless charging system with a single transmitter and a single receiver will increase the voltage or current stress of the diode in the rectifier on the receiver to achieve high power output, 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 constant current mode. During this process, the battery voltage continues to increase. When the battery voltage rises to a specified level, it switches to constant voltage mode to charge the battery. At this time, the charging current is gradually decreasing until it drops to near zero and the charging ends. During the entire charging process of the battery, the equivalent resistance of the battery changes 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 charging efficiency and power transmission capacity and reduce switching losses, the input impedance of the inverter must be purely resistive or inductive during the entire charging process to achieve zero phase angle or zero voltage switching. Summary of the invention

[0004] The present invention aims to solve the problem that during the entire charging process of the battery, the equivalent resistance of the battery changes greatly and it is difficult to achieve constant current and constant voltage output. A wireless charging system that can achieve constant current-constant voltage and power expansion is now provided.

[0005] A wireless charging system capable of realizing constant current-constant voltage and power expansion, comprising a transmitter and two receivers, wherein the two receivers are connected in parallel with a load connection terminal in a constant current working mode, and one receiver is used as a voltage compensation and the other receiver is used for outputting a voltage in a constant voltage working mode, and mutual inductance exists between coils of the transmitter and the two receivers;

[0006] 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;

[0007] 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;

[0008] The coil of the other receiver is connected in series with an output group capacitor;

[0009] 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.

[0010] Furthermore, 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;

[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, and the two compensation group MOSFET tubes are turned off, so that the two receivers output voltage in parallel.

[0012] Furthermore, the transmitter comprises: four transmitting group MOSFET tubes and a transmitting group coil,

[0013] 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.

[0014] Furthermore, the above another receiver comprises: 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 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.

[0016] The present invention discloses a wireless charging system that can realize constant current-constant voltage and power expansion. In constant current charging mode, dual receivers can effectively share the energy transmitted by the transmitter, reducing the current stress of the diode on each receiver. Finally, the dual receivers are output in parallel, thereby increasing the output current, improving the power level, and realizing zero voltage switching. In constant voltage charging mode, only one receiver is used as output, and the other receiver is used as compensation for the output side coil, which can achieve zero phase angle and improve power transmission capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic diagram of the topology of a wireless charging system capable of achieving constant current-constant voltage and power expansion;

[0018] Figure 2 This is the topological structure diagram under constant current working mode;

[0019] Figure 3 It is the equivalent circuit diagram under constant current working mode;

[0020] Figure 4 It is the topological structure diagram under constant voltage working mode;

[0021] Figure 5 It is the equivalent circuit diagram under constant voltage working mode;

[0022] Figure 6 In constant current working mode and I B The waveform diagram of R B =6Ω, (b) R B =8Ω;

[0023] Figure 7 In constant current working mode and The waveform diagram of R B =6Ω, (b) R B =8Ω;

[0024] Figure 8 In constant voltage working mode and V B The waveform diagram of R B =10Ω, (d)R B =12Ω;

[0025] Fig. 9 R in constant current mode B Changing from 6Ω to 8Ω and I B 、V B Waveform diagram of

[0026] Fig.10 R in constant voltage mode B Changing from 10Ω to 12Ω and I B 、V B Waveform diagram of

[0027] Fig.11 Modeling diagram for magnetic simulation. DETAILED DESCRIPTION

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

[0029] Reference Figures 1 to 11 Specifically describe this embodiment. This embodiment describes a wireless charging system that can achieve constant current-constant voltage and power expansion. 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.

[0030] The transmitter includes four MOSFET tubes (S1~S4), coil L1, compensation capacitor C1 and compensation capacitor C k , resistor R1 is the internal resistance of coil L1. S1 and S2 are connected in series to form a series group, and S3 and S4 are connected in series to form another series group. Both series groups are connected in parallel at both ends of the power supply. One end of coil L1 is connected to the connection point of S1 and S2, and the other end of coil L1 is connected to the connection point of S3 and S4. Compensation capacitor C1 and compensation capacitor C k Connected in series with coil L1, compensation capacitor C k A switch S is connected in parallel at both ends.

[0031] The receiver for outputting voltage (first receiver) includes: four diodes (D1 to D4), capacitor C2, capacitor C4 and coil L2, and resistor R2 is the internal resistance of coil L2. D1 and D2 are connected in series to form a diode group, and D3 and D4 are connected in series to form another diode group. Both diode groups and capacitor C4 are connected in parallel to the load connection terminal. One end of coil L2 is connected to the connection point of D1 and D2, and the other end of coil L2 is connected to the connection point of D3 and D4. Capacitor C2 is connected in series with coil L2.

[0032] The receiver (second receiver) used as voltage compensation includes: diode D5, diode D7, capacitor C3, capacitor C5, coil L3 and two MOSFET tubes (S5 and S6). D5 and S5 are connected in series to form one group, and D7 and S6 are connected in series to form another group. Both groups and capacitor C5 are connected in parallel with the load connection end. One end of coil L3 is connected to the connection point of D5 and S5, and the other end of coil L3 is connected to the connection point of D7 and S6. D6 and D8 are anti-parallel diodes inside S5 and S6 respectively. Capacitor C3 is connected in series with coil L3.

[0033] By adjusting the on or off of switch S and S5 and S6, the wireless charging system can be switched between constant voltage and constant current modes. Both working modes have soft switching technology, and in constant current working mode, dual receivers can transmit more energy than single receivers. Specifically:

[0034] The wireless charging system works in constant voltage mode, and the switch S is disconnected, so that the compensation capacitor C k When the MOSFET tubes S5 and S6 are turned on, the receiver used as voltage compensation is disconnected from the other receiver. The other receiver outputs voltage independently, and the input impedance is purely resistive, which satisfies the zero phase angle characteristic, reduces switching losses, and improves power transmission capability.

[0035] The wireless charging system works in constant current mode, the switch S is closed, and the compensation capacitor C k When the inverter is not working, MOSFET tubes S5 and S6 are turned off, and diodes D6 and D8 are working, so that the two receivers output voltage in parallel, which increases the output current and the power level. The input impedance of the inverter is inductive, realizing zero voltage switching.

[0036] In summary, dual receivers can effectively share the energy transmitted by the transmitter, that is, the current difference between the two receivers is not large, and the current on the two receivers does not need to be very large. Finally, the superposition of the two currents can also increase the power level to a certain extent. Compared with a single receiver, dual receivers have an additional energy transmission channel, and also reduce the current stress of the diode in the receiver.

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

[0038] The constant current mode is as follows:

[0039]

[0040] in, 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 an imaginary unit, ω is the operating frequency of the wireless charging system, L1, L2 and L3 are the inductance values ​​of coils L1, L2 and L3 respectively, C1, C2 and C3 are the capacitance values ​​of capacitors C1, C2 and C3 respectively, X 12 =jωM 12 , X 13 =jωM 13 , X 23 =jωM 23 , M 12 is the mutual inductance between coil L1 and coil L2, M 13 is the mutual inductance between coil L1 and coil L3, M 23 is the mutual inductance between coil L2 and coil L3, R B is the load resistance, R eq1 and R eq2 are the equivalent AC load resistance values ​​on the rectifier in the first receiver and the second receiver respectively.

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

[0042]

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

[0044]

[0045] When B=0,Z2=Z3=0:

[0046]

[0047] The output current in formula (4) It is independent of the resistance and realizes constant current output. 23 is a negative value, so the input impedance Z in It is inductive and achieves zero voltage switching.

[0048] The constant pressure mode is as follows:

[0049]

[0050] in, is the output voltage phasor of the first receiver, C k is the compensation capacitor C k Capacitance value.

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

[0052]

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

[0054]

[0055] When A′=0,Z2=Z3=0:

[0056]

[0057] In formula (8), the output voltage is independent of the resistance, achieving constant voltage output, and the input impedance Z in It is purely resistive and achieves zero phase angle.

[0058] All the equations listed are used to design and optimize the circuit parameters. The most critical point is that the constant current charging mode and the constant voltage charging mode in this example work at the same switching frequency and with the same set of parameters. When the embodiment switches to the constant voltage working mode, the impedance network Z1 in the constant current working mode is changed so that the changed impedance network is equal to the impedance Z1′ in the constant voltage working mode, thereby ensuring that the two working modes operate under the same set of parameters. In this embodiment, a compensation capacitor C is added. k To complete, the specific operations are as follows:

[0059]

[0060] The added compensation capacitance C can be calculated by formula (9): k The value of the compensation capacitor C is switched by the switch to the constant current working mode. k When not working and in constant voltage working mode, the compensation capacitor C k work, so that the two working modes can be switched under 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) show the resistance R B =6Ω and R B = Input voltage, input current, and output current I under 8Ω B Waveform diagram of output current I B The resistor R BIt is equal to 6Ω, and it is basically unchanged at 8Ω, which is constant at about 5.45A, realizing constant current output. Moreover, the input voltage is ahead of the input current, realizing zero voltage switching. In constant current working mode, Figure 7 They are the current waveforms of the first receiver and the second receiver. Figure 7 (a) Resistance R B When the current on the first receiver is 6Ω, The current on the second receiver is 4.39A. is 4.06A, when Figure 7 (b) Resistance R B When the current on the first receiver is 8Ω, The current on the second receiver is 4.89A. The first receiver and the second receiver share the energy transmitted by the transmitter, and the two receivers are connected in parallel to increase the output current and the output power. Compared with a single receiver, this embodiment increases the output power while reducing the current stress of the diode in the receiver.

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

[0065] Fig. 9 is the resistance R in constant current mode B Input voltage and input current change from 6Ω to 8Ω, I B and V B It can be seen that the present invention can achieve smooth switching, and the output current I B Before and after switching, the output voltage V B During the switching process, it gradually rises to meet the charging process of the electric vehicle battery. Fig.10 is the resistance R in constant voltage mode B Input voltage and input current change from 10Ω to 12Ω, I B and V B The waveform diagram. It can be seen from the figure that the output voltage V B It is also unchanged before and after switching, the output current I BThe slow decrease verifies the feasibility and practicability of the present invention in the wireless charging technology of electric vehicles.

[0066] Fig.11 This is a magnetic simulation modeling diagram of an embodiment of the present invention. The sizes of the coils L2 and L3 are exactly the same, both with 12 turns, and the coil L1 has 10 turns. The diameters of the excitation wires used in the three coils are all 3mm. The size of the ferrite used in the figure is 55mm*15mm*5mm. Fig.11 The inductance and mutual inductance used in this example can be designed by modeling in the manner described above, thereby verifying the reliability of the parameters in this example.

[0067] Although the present invention is 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. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that the features described in conjunction with a single embodiment may 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, It is 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, It is 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, It is 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, It is 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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