A low-voltage battery wireless charging system based on a three-coil structure

Abstract

The application provides a low-voltage battery wireless charging system based on a three-coil structure, which comprises a transmitting module and a receiving module; by switching the throw point of a single-pole double-throw switch in the transmitting module, the load can be switched between constant-current charging mode and constant-voltage charging mode. The primary side of the wireless charging system has two coils, and the secondary side has one coil. In the constant-current charging mode, the two coils on the primary side both act as transmitting coils, forming a series-series / series structure to transmit power to the secondary side; in the constant-voltage charging mode, one of the two coils on the primary side functions as an inductance compensation coil, forming an inductance-capacitance-capacitance / series structure, and the other acts as a transmitting coil to transmit energy to the secondary side. The system can realize constant-current and constant-voltage mode output, and through such a design, the output voltage is proportional to the coupling coefficient and the input voltage, a natural voltage reduction process is realized, and the system is very suitable for being used as a charging topology for low-voltage batteries.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of wireless power transmission, in particular to a low-voltage battery wireless charging system based on a three-coil structure. BACKGROUND

[0002] Wireless power transmission is to use the principle of electromagnetic induction to transmit energy from the transmitting coil to the receiving coil without electrical connection, which has the advantages of safety, convenience, reliability, etc. In recent years, WPT technology has developed rapidly, especially in the field of wireless charging of electric bicycles. Many companies are at the forefront of technology in the field of wireless charging of electric vehicles, and their products are gradually put into mass production. Therefore, the research on WPT for electric vehicles not only has academic significance, but also has strong social application value.

[0003] The widely used wireless charging system for electric vehicles generally uses a double-sided LCC topology as a compensation network. The transmitting coil end is buried underground, and the receiving coil end is placed in the vehicle. The parameters are designed according to the space in the vehicle, the transmission power level, the charging voltage of the load battery, and other conditions. Generally speaking, the mains is 220V alternating current, but the voltage of the electric vehicle battery is generally between 48-72V. Currently, a DC / DC conversion circuit is usually required to achieve voltage matching. This method not only increases the circuit cost and complexity, but also reduces the system efficiency.

[0004] Therefore, the market urgently needs a wireless charging topology scheme for electric vehicles that can achieve natural voltage reduction. SUMMARY

[0005] In view of the defects in the prior art, the purpose of the present application is to provide a low-voltage battery wireless charging system based on a three-coil structure, which can realize the switching of constant current (CC) and constant voltage (CV) modes through a single-pole double-throw switch, and the system has a natural voltage reduction process, which is very suitable for the charging needs of low-voltage batteries.

[0006] In a first aspect of the present application, a transmitting module of a low-voltage battery wireless charging system is provided, comprising:

[0007] The transmitting module comprises a connected DC power supply, a full-bridge inverter, a transmitting coil Lp, a second coil L1, a compensation capacitor Cp, a second capacitor C1, and a single-pole double-throw switch; wherein:

[0008] The input end of the full-bridge inverter is connected with a direct current power supply, and the output is a high-frequency alternating voltage; the transmitting coil Lp and the compensation capacitor Cp are connected in series, and the series connection is connected between the midpoints of the front bridge arm and the rear bridge arm of the full-bridge inverter; the throw point 1 of the single-pole double-throw switch is connected between the transmitting coil Lp and the compensation capacitor Cp, and a first loop is formed;

[0009] A second capacitor C1 and the throw point 2 of the single-pole double-throw switch are connected in sequence between the midpoints of the front bridge arm of the full-bridge inverter, and a second coil L1 is connected in series at the blade point of the single-pole double-throw switch, and then connected to the midpoint of the rear bridge arm, forming a second loop;

[0010] Through switching of the throw point 1 and the throw point 2 of the single-pole double-throw switch, the first loop and the second loop realize switching of the constant current mode and the constant voltage mode respectively.

[0011] In the second aspect of the present application, a receiving module of a low-voltage battery wireless charging system is provided, comprising a receiving coil L2, a compensation capacitor C2 and a rectifier bridge, the receiving coil L2 and the compensation capacitor C2 are connected in sequence between the midpoints of the two bridge arms of the rectifier bridge, forming a third loop, and the output end of the rectifier bridge is connected with a load.

[0012] Optionally, the rectifier bridge is a diode uncontrolled rectifier bridge.

[0013] In the third aspect of the present application, a low-voltage battery wireless charging system based on a three-coil structure is provided, comprising:

[0014] The transmitting module described above;

[0015] The receiving module described above;

[0016] Through switching of the throw point of the single-pole double-throw switch in the transmitting module, switching of the first loop for constant current charging of the load and the second loop for constant voltage charging of the load is realized.

[0017] Optionally, the primary side of the wireless charging system has two coils, i.e. the transmitting coil Lp and the second coil L1, and the secondary side has one coil, i.e. the receiving coil L2; in the constant current mode, the two coils in the primary side both serve as transmitting coils to transmit power to the secondary side; in the constant voltage mode, the second coil L1 in the primary side serves as a compensation inductor, and the other transmitting coil Lp serves as a transmitting coil to transmit energy to the secondary side.

[0018] Optionally, the coupling coefficient between the two coils in the primary side is zero, the transmitting coil Lp and the second coil L1 are decoupled, and the mutual inductance values between the two coils in the primary side and the one coil in the secondary side are equal.

[0019] Optionally, when the single-pole double-throw switch is connected to the 2th throw point, the compensation capacitor Cp and the transmitting coil Lp form a series loop, the second capacitor C1 and the second coil L1 form a second series loop, the energy is transmitted to the secondary side through the transmitting coil Lp and the second coil L1, and the system realizes the constant current output characteristic at this time.

[0020] Optionally, when the single-pole double-throw switch is connected to the 1th throw point, the compensation capacitor Cp and the transmitting coil Lp form a series loop, the second coil L1 is connected to the connection point of the compensation capacitor Cp and the transmitting coil Lp to form a second loop, and the second capacitor C1 is disconnected and does not work, the energy is transmitted to the secondary side through the transmitting coil Lp and the second coil L1, and the system realizes the constant voltage output characteristic at this time.

[0021] Optionally, in the constant current charging mode, the transmitting module forms two series loops, the transmitting module inverse output voltage v p is:

[0022]

[0023] The current i2 of the receiving coil L2 is:

[0024]

[0025] The output direct current I o is calculated as:

[0026]

[0027] The system has the CC output characteristic at this time.

[0028] Optionally, in the constant voltage charging mode, the currents on the two coils of the transmitting module are respectively:

[0029]

[0030] The alternating voltage v s of the receiving module is:

[0031]

[0032]

[0033] When , the above formula is simplified as:

[0034]

[0035] Further,

[0036]

[0037] The system has the characteristic of CV output, and the output voltage is proportional to the input voltage and the coupling coefficient.

[0038] Compared with the prior art, the low-voltage battery wireless charging system can realize CC and CV output, and provides a new solution for charging lithium batteries. Through such design, the output voltage is proportional to the coupling coefficient and the input voltage, realizing a natural voltage reduction process, and being very suitable for charging topology of low-voltage batteries. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 It is a low-voltage battery wireless charging system topology based on a three-coil structure in an embodiment of the application.

[0040] Figure 2 It is an equivalent circuit diagram of the WPT system in the CC mode in an embodiment of the application.

[0041] Figure 3 It is an equivalent circuit diagram of the WPT system in the CV mode in an embodiment of the application.

[0042] Figure 4 It is a coil decoupling and coupling mutual inductance design schematic diagram in an embodiment of the application. DETAILED DESCRIPTION

[0043] The application will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the application, but do not limit the application in any form. It should be noted that for those skilled in the art, without departing from the concept of the application, a number of changes and improvements can be made. These all belong to the protection scope of the application.

[0044] Figure 1 It is a low-voltage battery wireless charging system topology based on a three-coil structure in an embodiment of the application.

[0045] Referring to Figure 1 The left part of the figure is the transmitting module of the low-voltage battery wireless charging system, corresponding to the primary circuit of the low-voltage battery wireless charging system.

[0046] In some embodiments, the transmitting module of the low-voltage battery wireless charging system comprises a connected DC power supply, a full-bridge inverter, a first coil Lp, a second coil L1, a compensation capacitor Cp, a second capacitor C1, and a single-pole double-throw switch, wherein: the input of the full-bridge inverter is connected to the DC power supply, and the output is a high-frequency alternating voltage; the first coil Lp and the compensation capacitor Cp are connected in series, and the series connection is connected between the midpoints of the front bridge arm and the back bridge arm of the full-bridge inverter; the throw point 1 of the single-pole double-throw switch is connected between the first coil Lp and the compensation capacitor Cp, forming a first loop; the second capacitor C1 and the throw point 2 of the single-pole double-throw switch are connected in series between the midpoints of the front bridge arm of the full-bridge inverter, and the second coil L1 is connected in series at the blade point of the single-pole double-throw switch and then connected to the midpoint of the back bridge arm, forming a second loop; by switching the throw point 1 and the throw point 2 of the single-pole double-throw switch, the first loop and the second loop respectively realize the switching of the constant current mode and the constant voltage mode.

[0047] In a specific embodiment, the single-pole double-throw switch can use a relay, such as Figure 1 In the specific embodiment, the first coil Lp and the compensation capacitor Cp form a loop, the node 1 of the relay is connected at the connection point of the first coil Lp and the compensation capacitor Cp, the second coil L1 is connected to the blade end of the relay, and the node 2 of the relay is connected to the second capacitor C1, forming a second loop. By switching the node 1 or the node 2 of the relay, the CV or CC output characteristics can be realized, respectively.

[0048] In the above embodiment, the full-bridge inverter is composed of switch tubes S1-S4, the rectifier bridge is composed of diodes D1-D4, and RL is the load. The front bridge arm of the full-bridge inverter is composed of S1-S2, and the back bridge arm of the full-bridge inverter is composed of MOS tubes S3-S4. The first coil Lp and the compensation capacitor Cp are connected in series, one end of the series connection is connected between the front bridge arm S1 and S2, and the other end is connected between the back bridge arm S3 and S4. The second capacitor C1 and the throw point 2 of the single-pole double-throw switch are connected in series between the midpoints of the front bridge arm S1 and S2, and the second coil L1 is connected in series at the blade point of the single-pole double-throw switch and then connected to the midpoints of the back bridge arm S3 and S4.

[0049] Continuing to refer to the right side of Figure 1 , Figure 1 The receiving module of the low-voltage battery wireless charging system comprises a receiving coil L2, a compensation capacitor C2, and a rectifier bridge. The receiving coil L2 and the compensation capacitor C2 are connected in series between the midpoints of the two bridge arms of the rectifier bridge, forming a third loop, and the output of the rectifier bridge is connected to the load. Figure 1 In the above embodiment, the rectifier bridge is a diode uncontrolled rectifier bridge.

[0050] Referring to Figure 1As shown, a low-voltage battery wireless charging system based on a three-coil structure includes a transmitting module and a receiving module; the transmitting module and the receiving module adopt the above-mentioned circuit structure, and by controlling the switching of the throw point of the single-pole double-throw switch in the transmitting module, the first loop is switched to the constant current charging mode for the load, and the second loop is switched to the constant voltage charging mode for the load. That is, by using a single-pole double-throw switch (relay), the switching of the constant current (CC) mode and the constant voltage (CV) mode can be realized.

[0051] The wireless charging system formed in the above-mentioned embodiment has two coils in the primary side (i.e. the transmitting module) and one coil in the secondary side (the receiving module). In the constant current (CC) charging mode, both coils in the primary side act as transmitting coils, forming a series-series / series (SS / S) structure, and transmitting power to the secondary side; in the constant voltage (CV) charging mode, one of the two coils in the primary side acts as a compensation inductor, forming an inductor-capacitor-capacitor / series (LCC / S) structure, and the other acts as a transmitting coil, transmitting energy to the secondary side. The system can realize constant current and constant voltage mode outputs, and through such a design, the output voltage is proportional to the coupling coefficient and the input voltage, realizing a natural voltage reduction process, which is very suitable for charging topology of low-voltage batteries.

[0052] The two coils in the primary side are connected in series with two capacitors respectively, and the switching between the SS / S and LCC / S topologies is realized through a single-pole double-throw switch. The system realizes natural constant current output through the SS / S topology, and realizes natural constant voltage output through the LCC / S topology, to complete the CC and CV charging of the battery.

[0053] Figure 2 The equivalent circuit diagram of the WPT system in the CC mode in the above-mentioned embodiment of the application is shown.

[0054] When the single-pole double-throw switch is connected to node 2, the circuit forms Figure 2 The circuit diagram is shown. The transmitting coil Lp and the compensation capacitor Cp form a series circuit, and the second capacitor C1 and the second coil L1 form a second series circuit. Energy is transmitted to the secondary side through the transmitting coil Lp and the second coil L1. As can be seen from formula (3), the system can realize CC output characteristics at this time.

[0055] Specifically, the two primary side coils are connected in series with two capacitors respectively, and the switching of SS / S and LCC / S topologies is realized by a single-pole double-throw switch. The natural constant current output of the system is realized by the SS / S topology, and the natural constant voltage output is realized by the LCC / S topology to complete the CC and CV charging of the battery. The process requires that the coupling coefficient between the two primary side coils is zero to realize decoupling, and the mutual inductance value between the two primary side coils and the secondary side coil needs to be equal.

[0056] In the CC mode of the SS / S structure, the system circuit diagram is as shown in Figure 2 At this time, two series loops are formed in the primary side, and the primary side inverter output voltage vp is:

[0057]

[0058] The secondary side coil current i2 is:

[0059]

[0060] The output DC current Io can be further calculated as:

[0061]

[0062] It can be seen that the system has CC output characteristics at this time.

[0063] In the above formula, V i is the input DC voltage, j is the imaginary unit, ω is the angular frequency, M p2 is the mutual inductance between the transmitting coil L p and the receiving coil L2, M 12 is the mutual inductance between the second coil L1 and the receiving coil L2, i p , i1 and i2 are the currents on the transmitting coil Lp, the second coil L1 and the receiving coil L2 respectively; R Leq is the equivalent resistance of the secondary side uncontrolled rectifier bridge, I o is the DC current output by the system, I2 is the effective value of the secondary side receiving coil current i2, R1 and R p are the equivalent internal resistances of the coils L1 and L p , respectively. Figure 1 .

[0064] Figure 3 is the equivalent circuit diagram of the WPT system in the CV mode in the above embodiment of the application.

[0065] When the single-pole double-throw switch is connected to node 1, the circuit will form Figure 3The circuit diagram is shown. Cp and Lp form a series loop, and L1 connected at the joint of Cp and Lp forms a second loop. C1 is disconnected and does not function. Energy is transmitted to the secondary side through Lp and L1. According to formula (7), the system can realize CV output characteristics at this time.

[0066] Specifically, in the CV mode of the LCC / S structure, the system circuit diagram is shown. Figure 3 The single-pole double-throw switch is connected to the throw point 2 at this time, the compensation capacitor C1 is disconnected, and the primary side forms the structure of LCC. The currents on the primary side coils can be calculated as follows:

[0067]

[0068] The secondary side alternating voltage vs is:

[0069]

[0070] When , formula (5) can be simplified as:

[0071]

[0072] Further,

[0073]

[0074] It can be seen that the system has the characteristics of CV output, and the output voltage is proportional to the input voltage and the coupling coefficient. This shows that the system has a natural voltage reduction process and is suitable for use as a charging topology for low-voltage batteries.

[0075] In the above formula, Z ref_1 is the equivalent impedance of the secondary side on the second coil L1 of the primary side, Z ref_p is the equivalent impedance of the secondary side on the transmitting coil Lp of the primary side, R Leq is the equivalent resistance of the uncontrolled rectifier bridge of the secondary side, ω is the angular frequency, v p is the output voltage of the transmitting module inverter, R1 and Rp are the equivalent internal resistances of the primary side coils L1 and Lp respectively, M p2 is the mutual inductance between the primary side coil Lp and the secondary side coil L2, M 12 is the mutual inductance between the primary side coil L1 and the secondary side coil L2, C p is the capacitance value of the compensation capacitor Cp, kp2 is the coupling coefficient between the coils Lp and L2, k12 is the coupling coefficient between the coils L1 and L2, L2 is the self-inductance of the receiving coil, L1 and L2 are the inductances of the second coil L1 of the primary side and the receiving coil L2 of the secondary side respectively, V i is the input DC voltage.

[0076] In addition, to meet the above CC and CV output conditions, let M p1 For the mutual inductance between the primary coil Lp and the secondary coil L1, the three-coil design of the primary and the secondary needs to meet the following conditions:

[0077] M p1 = 0, M p2 = M 12 (8)

[0078] That is, the two primary coils need to be completely decoupled, and the mutual inductance between the two primary coils and the secondary coil needs to be equal.

[0079] Figure 4 The above-mentioned embodiments of the present application are coil decoupling and coupling mutual inductance design schematic diagram. Referring to Figure 4 As shown, the two bottom partially overlapping coils are transmitting coils, and the two coils are the same size and have the same self-inductance. First, by adjusting the distance d1 between the centers of the two transmitting coils, zero coupling between the two coils is achieved, that is, the two coils are decoupled. After the primary coil is decoupled, the horizontal distance d2 between the center of the secondary coil L2 and the center of the primary coil Lp is adjusted so that the mutual inductance between L2 and Lp, L1 is equal. At this point, the coil decoupling and coupling coefficient design is completed.

[0080] In the above-mentioned embodiments of the present application, a single-pole double-throw switch can be used to switch between constant current (CC) and constant voltage (CV) modes, and the system has a natural voltage reduction process, which is very suitable for the charging needs of low-voltage batteries.

[0081] The specific embodiments of the present application have been described above. It should be understood that the present application is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essential content of the present application. In the case of no conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A transmitting module for a low-voltage battery wireless charging system, characterized in that, This includes a connected DC power supply, a full-bridge inverter, a transmitting coil Lp, a second coil L1, a compensation capacitor Cp, a second capacitor C1, and a single-pole double-throw switch, wherein: The input terminal of the full-bridge inverter is connected to a DC power supply, and the output is a high-frequency AC voltage. The transmitting coil Lp and the compensation capacitor Cp are connected in series and then connected between the midpoints of the front and rear bridge arms of the full-bridge inverter. The throwing point 1 of the single-pole double-throw switch is connected between the transmitting coil Lp and the compensation capacitor Cp to form the first circuit. A second capacitor C1 and the throwing point 2 of the single-pole double-throw switch are connected sequentially between the midpoints of the front arm of the full-bridge inverter. A second coil L1 is connected in series at the knife point of the single-pole double-throw switch and then connected to the midpoint of the rear arm to form a second circuit. By switching the throw point 1 and throw point 2 of the single-pole double-throw switch, the first circuit and the second circuit respectively realize the switching between constant current and constant voltage modes.

2. A low-voltage battery wireless charging system based on a three-coil structure, characterized in that, include: The transmitting module as described in claim 1; The receiving module corresponding to the transmitting module; By controlling the switching of the single-pole double-throw switch in the transmitting module, the switching between the constant current charging mode of the first circuit and the constant voltage charging mode of the second circuit for the load can be achieved.

3. The low-voltage battery wireless charging system based on a three-coil structure according to claim 2, characterized in that, The receiving module includes a receiving coil L2, a compensation capacitor C2, and a rectifier bridge. The receiving coil L2 and the compensation capacitor C2 are connected in series between the midpoints of the two arms of the rectifier bridge to form a third circuit. The output terminal of the rectifier bridge is connected to the load.

4. The low-voltage battery wireless charging system based on a three-coil structure according to claim 3, characterized in that, The rectifier bridge is a diode uncontrolled rectifier bridge.

5. The low-voltage battery wireless charging system based on a three-coil structure according to claim 3, characterized in that, The transmitting module has two coils, namely the transmitting coil Lp and the second coil L1, and the receiving module has one coil, namely the receiving coil L2. In constant current charging mode, both primary coils serve as transmitting coils to transmit power to the secondary side. In constant voltage charging mode, the second coil L1 of the two primary coils serves as inductance compensation, and the other transmitting coil Lp serves as the transmitting coil to transmit energy to the secondary side.

6. The low-voltage battery wireless charging system based on a three-coil structure according to claim 5, characterized in that, When the single-pole double-throw switch is connected to throw point 2, the compensation capacitor Cp and the transmitting coil Lp form a series circuit, and the second capacitor C1 and the second coil L1 form a second series circuit. Energy is transferred to the secondary side through the transmitting coil Lp and the second coil L1, and the system achieves constant current output characteristics at this time.

7. The low-voltage battery wireless charging system based on a three-coil structure according to claim 5, characterized in that, When the single-pole double-throw switch is connected to throw point 1, the compensation capacitor Cp and the transmitting coil Lp form a series circuit. A second coil L1 is connected at the connection point of the compensation capacitor Cp and the transmitting coil Lp to form a second circuit. The second capacitor C1 is disconnected and has no effect. Energy is transferred to the secondary side through the transmitting coil Lp and the second coil L1. At this time, the system achieves constant voltage output characteristics.

8. The low-voltage battery wireless charging system based on a three-coil structure according to claim 5, characterized in that, The coupling coefficient between the two coils of the transmitting module is zero, the transmitting coil Lp and the second coil L1 are decoupled, and the mutual inductance between the two coils of the transmitting module and one secondary coil of the receiving module is equal.

9. The low-voltage battery wireless charging system based on a three-coil structure according to claim 5, characterized in that, In constant current charging mode, the transmitting module forms two series circuits, and the transmitting module inverter output voltage v p for: The current i2 of the receiving coil L2 is: Calculate the output DC current I o for: The system now has CC output characteristics; In the above formula, V i It is the input DC voltage, j is the imaginary unit, ω is the angular frequency, and M is the input DC voltage. p2 For transmitting coil L p Mutual inductance between the receiving coil L2 and the receiving coil L2, M 12 For the mutual inductance between the second coil L1 and the receiving coil L2, i p i1 and i2 are the currents in the transmitting coil Lp, the second coil L1, and the receiving coil L2, respectively; R Leq I is the equivalent resistance of the uncontrolled rectifier bridge on the secondary side. o I1 is the DC output current of the system, I2 is the effective value of the secondary receiving coil current i2, and R1 and R2 are the DC output current of the system. p They are coils L1 and L respectively. p The equivalent internal resistance.

10. The low-voltage battery wireless charging system based on a three-coil structure according to claim 5, characterized in that, In constant voltage charging mode, the current i in the transmitting coil Lp and the second coil L1 of the transmitting module is... p i1 and i1 are respectively: AC voltage v of the receiving module s for: when When the above formula is simplified to: Furthermore, The system has the characteristic of CV output, and the output voltage is proportional to the input voltage and the coupling coefficient; In the above formula, Z ref_1 Z is the equivalent impedance of the secondary side on the second coil L1 of the primary side. ref_p R is the equivalent impedance of the secondary side on the primary side transmitting coil Lp. Leq The equivalent resistance of the uncontrolled rectifier bridge on the secondary side is ω, where ω is the angular frequency and v is the angular frequency. p The inverter output voltage of the transmitting module is given by R1 and Rp, which are the equivalent internal resistances of the primary coils L1 and Lp, respectively. M p2 M is the mutual inductance between the primary coil Lp and the secondary coil L2. 12 C is the mutual inductance between the primary coil L1 and the secondary coil L2. p This is the capacitance value of the compensation capacitor Cp, kp2 is the coupling coefficient between coils Lp and L2, k12 is the coupling coefficient between coils L1 and L2, L2 is the self-inductance of the receiving coil, L1 and L2 are the inductances of the second primary coil L1 and the secondary receiving coil L2, respectively, and V i It is the input DC voltage.

Images