A variable topology anti-offset constant voltage and constant current self-switching wireless power transmission system

Abstract

A variable topology anti-deviation constant voltage and constant current self-switching wireless power transmission system, comprising: a direct current power supply, a high-frequency inverter circuit, a variable topology LCL / SP compensation circuit, a magnetic coupling mechanism rectifier circuit and a lithium battery equivalent load circuit connected in turn; the variable topology LCL / SP compensation circuit is that the primary side adopts an LCL type topology structure, and the secondary side adopts an SP type topology structure; a compensation capacitor is connected in parallel with a resonant capacitor in the SP type topology structure, and the compensation capacitor is controlled to be turned on or turned off by a switch, and is used for switching the working mode of the wireless power transmission system constant voltage or constant current. The variable topology control is used, wireless communication and complex control algorithm are not needed, the system structure is simplified, and the hardware cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of wireless power transmission technology, and more specifically to a variable topology anti-offset constant voltage and constant current self-switching wireless power transmission system. Background Technology

[0002] When wireless power transfer technology is applied to static charging of electric vehicles, it faces the challenge of dynamic changes in the battery's equivalent load. This necessitates that the wireless power transfer system possess excellent adaptability, capable of accommodating the "constant current-constant voltage" operating mode of lithium batteries, and ensuring its stability unaffected by load variations. Furthermore, during static charging, vehicle owners often fail to precisely align their vehicles with the ground-based transmitting coil, inevitably leading to misalignment between the transmitting and receiving coils. This coil misalignment not only reduces coupling between coils but also causes significant leakage inductance; simultaneously, it can also trigger detuning issues in the wireless power transfer system.

[0003] To ensure safety while achieving the fastest and most efficient charging and maximizing battery life, lithium batteries and other rechargeable batteries generally operate in a constant current output followed by a constant voltage output mode. Current methods for achieving constant voltage / constant current primarily include adding a DC / DC circuit on the secondary side, such as a BUCK circuit or BUCK-BOOST circuit. The disadvantage of this approach is that it increases the size and weight of the secondary receiver and reduces the system's output efficiency. Alternatively, closed-loop control can be added, such as phase-shift control or frequency modulation control. The disadvantage of this approach is that it requires additional wireless communication within the system, making the control strategy more complex. Summary of the Invention

[0004] To address the aforementioned technical issues, this technical solution provides a variable topology anti-offset constant voltage and constant current self-switching wireless power transmission system. It employs variable topology control, directly switching the system topology via a switch to adjust output characteristics. The control strategy is simple and intuitive, easy to implement and integrate, avoids additional wireless communication modules, and reduces system complexity and communication costs; effectively solving the technical problems.

[0005] This invention is achieved through the following technical solution:

[0006] A variable-topology anti-offset constant-voltage and constant-current self-switching wireless power transfer system includes: a DC power supply, a high-frequency inverter circuit, a variable-topology LCL / SP compensation circuit, a magnetic coupling mechanism rectifier circuit, and a lithium battery equivalent load circuit connected in sequence; the variable-topology LCL / SP compensation circuit has an LCL-type topology on the primary side and an SP-type topology on the secondary side; a compensation capacitor is connected in series with the resonant capacitor in the SP-type topology, and a switch controls the compensation capacitor to be turned on or off, which is used to switch the wireless power transfer system to constant-voltage output or constant-current output operating mode.

[0007] Furthermore, the switch is an AC switch, which consists of two IGBT transistors connected in reverse series.

[0008] Furthermore, the variable topology LCL / SP compensation circuit includes a primary-side compensation inductor L1 and a resonant capacitor C1 connected in parallel to form a first-stage loop, and the primary-side coil self-inductance L... p The primary side resonant capacitor C1 is connected in parallel to form the second-stage circuit; the coil self-inductance Ls of the secondary side, together with the series resonant capacitor C2 and the compensation capacitor C4, forms a series resonant path, and then forms a circuit with the secondary side resonant capacitor C3 connected in parallel, forming an SP series-parallel compensation structure; an AC switch S1 is connected in parallel above the compensation capacitor C4, and the switching between constant voltage and constant current modes is achieved by switching the AC switch S1.

[0009] Furthermore, the control strategy of the switch is as follows: in the initial stage of battery charging, switch S1 is closed, short-circuiting compensation capacitor C4, and the secondary circuit satisfies the series resonance condition to achieve constant current output; when the equivalent load of the lithium battery reaches the load transition resistance, switch S1 is opened, compensation capacitor C4 is connected to the circuit, changing the parameters of the secondary resonant network, so that the system switches to constant voltage output.

[0010] Furthermore, the coupling structure in the rectifier circuit of the magnetic coupling mechanism adopts a QR coil with resistance to lateral and longitudinal offset.

[0011] Furthermore, the QR coil consists of four rectangular coils arranged clockwise; all four rectangular coils are wound with Litz wire, each coil being 250mm long, 150mm wide, and 3.96mm thick, with a winding width of 40mm, a turn spacing of 8mm, and 5 turns; the QR coil has dimensions of 400mm × 400mm × 3.96mm and a transmission distance of 150mm; the magnetic core material is 420mm × 420mm × 10mm ferrite; the QR coil has an overall symmetrical structure of 400mm × 400mm, which helps maintain strong magnetic coupling even when there is a relative offset between the transmitting and receiving ends. All four rectangular coils are wound with Litz wire.

[0012] Furthermore, the QR coil magnetic coupling mechanism with anti-offset performance, constructed from the QR coils, has its primary and secondary coils facing each other, with their centers on the same central axis; first, the self-inductance L of the primary coil when no offset occurs is recorded. p and secondary self-sensing L s The value of the mutual inductance M between the coils is measured; the primary coil is kept stationary, and the secondary coil is moved 100mm along the positive X and Y axes respectively. The mutual inductance M and the primary self-inductance L are then measured at each movement. p and secondary self-sensing L s The value of .

[0013] Furthermore, the constant current output condition of the wireless power transfer system is as follows: ;

[0014] In the formula: L1 is the primary-side compensating inductance; C1 is the primary-side resonant capacitor; L p L is the self-inductance of the primary coil. s C1 is the self-inductance of the secondary coil; C2 is the series resonant capacitor of the secondary side; C3 is the parallel resonant capacitor of the secondary side. Here, ω is the system angular frequency; j is the imaginary unit.

[0015] The constant voltage output condition is: ;

[0016] ;

[0017] In the above formula: C4 is the secondary-side compensation capacitor; C 总 is the equivalent capacitance of C2 and C4 connected in series; M is the mutual inductance between the primary and secondary coils.

[0018] Furthermore, when the switch is closed, the system can achieve a constant current output independent of the load when the resonant network satisfies the parameter relationship of the constant current output condition; when the switch is open, a compensation capacitor C4 is connected to the resonant network, and the system can achieve a constant voltage output independent of the load when the resonant network satisfies the parameter relationship of the constant voltage output condition.

[0019] Furthermore, when switching between constant voltage and constant current operating modes in a wireless power transfer system, the switching point of the operating mode is the same as the switching point of the load resistance. The switching point of the load resistance refers to the critical load resistance value at which the output power is equal in both constant voltage and constant current operating modes; the expression for the load resistance switching point R0 is:

[0020] ;

[0021] In the above formula, C is the system angular frequency, and C3 is the parallel resonant capacitor on the secondary side.

[0022] Beneficial effects

[0023] The present invention proposes a variable topology anti-offset constant voltage and constant current self-switching wireless power transfer system, which has the following advantages compared with the prior art:

[0024] (1) The secondary-side compensation network of the present invention adopts an SP structure, enabling the system to achieve constant current output and constant voltage output at a fixed operating frequency. Only a combination unit of an AC switch and a parallel compensation capacitor is introduced on the secondary side. By controlling the on / off state of this switch, the two resonant topologies can be switched, thereby completing the conversion from constant current mode to constant voltage mode. This fundamentally meets the standardized charging curve requirement of "constant current first, then constant voltage" necessary for lithium battery charging. In addition, this scheme can automatically switch between constant current output and constant voltage output modes according to the battery state, adapt to the lithium battery charging curve, and improve charging efficiency and safety. It also introduces a "QR coil coupling structure", which has the ability to resist lateral and longitudinal offset, and can maintain stable power transmission even when the coil is offset. It does not require a complex wireless communication module between the primary and secondary sides, nor does it require the use of continuous adjustment strategies such as frequency conversion control or phase shift control, which greatly reduces the components of the main power circuit and control circuit, simplifies the system structure, and reduces hardware costs.

[0025] (2) By designing the QR coil in the coupling structure, the present invention improves the system’s ability to resist lateral and longitudinal offsets, and can make the mutual inductance decrease more gradually and the total coupling change less when the transmission distance or position changes, thus maintaining the stability of the system.

[0026] (3) The present invention can achieve a natural and smooth transition during the charging stage by calculating and setting the constant voltage and constant current mode switching point, effectively avoiding voltage or current surges that may occur during mode switching, eliminating the risk of battery damage and power circuit stress caused by sudden mode changes, and improving the safety and service life of the system. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the overall circuit of the present invention.

[0029] Figure 2 This is a schematic diagram of the QR coil in this invention.

[0030] Figure 3 This refers to the self-inductance of the primary coil of the QR coil offset in the preset X-axis direction in this invention.

[0031] Figure 4 This refers to the self-inductance value of the secondary coil of the QR coil offset in the preset X-axis direction in this invention.

[0032] Figure 5This refers to the self-inductance value of the primary coil of the QR coil offset in the preset Y-axis direction in this invention.

[0033] Figure 6 This refers to the self-inductance value of the secondary coil of the QR coil offset in the preset Y-axis direction in this invention.

[0034] Figure 7 This refers to the mutual inductance value between the QR coils offset in the preset X-axis direction in this invention.

[0035] Figure 8 This refers to the mutual inductance value between the QR coils offset in the preset Y-axis direction in this invention.

[0036] Figure 9 The output voltage and output current of the system in this invention before and after switching operating modes are given.

[0037] Figure 10 This refers to the output power of the system in this invention before and after switching operating modes. Detailed Implementation

[0039] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. The described embodiments are merely some embodiments of the present invention, and not all embodiments. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the design concept of the present invention should fall within the protection scope of the present invention.

[0040] Example 1:

[0041] like Figure 1 As shown, a variable topology anti-offset constant voltage and constant current self-switching wireless power transmission system includes: a DC power supply, a high-frequency inverter circuit, a variable topology LCL / SP compensation circuit, a magnetic coupling mechanism rectifier circuit, and a lithium battery equivalent load circuit connected in sequence.

[0042] The variable topology LCL / SP compensation circuit includes: the primary-side compensation inductor L1 and resonant capacitor C1 connected in parallel to form the first-stage loop, and the primary-side coil self-inductance L... p It is connected in parallel with the primary resonant capacitor C1 to form a second-stage circuit, thus forming an LCL-type topology.

[0043] The self-inductance Ls of the secondary coil, together with the series resonant capacitor C2 and the compensation capacitor C4, forms a series resonant path, which is then connected in parallel with the secondary resonant capacitor C3 to form a circuit, thus forming an SP series-parallel compensation structure. An AC switch S1 is connected in parallel above the compensation capacitor C4. The AC switch S1 is composed of two IGBT transistors connected in reverse series.

[0044] The constant voltage and constant current modes are switched by alternating AC switch S1. The switch controls the conduction or cutoff of the compensation capacitor, thus switching the wireless power transfer system between constant voltage and constant current output modes. The control strategy is as follows: During the initial stage of battery charging, switch S1 is closed, short-circuiting the compensation capacitor C4. The secondary circuit meets the series resonance condition, achieving constant current output. When the equivalent load of the lithium battery reaches the load transition resistance, switch S1 is opened, the compensation capacitor C4 is connected to the circuit, changing the parameters of the secondary resonant network, causing the system to switch to constant voltage output.

[0045] The coupling structure in the rectifier circuit of the magnetic coupling mechanism uses a QR coil with resistance to lateral and longitudinal offset. The QR coil consists of four rectangular coils arranged clockwise; for example... Figure 2 As shown. All four rectangular coils are wound with Litz wire. Each rectangular coil is 250mm long, 150mm wide, and 3.96mm thick, with a winding width of 40mm, a turn spacing of 8mm, and 5 turns. The QR coil has dimensions of 400mm × 400mm × 3.96mm and a transmission distance of 150mm. The core material is 420mm × 420mm × 10mm ferrite.

[0046] In the aforementioned QR coil magnetic coupling mechanism, the primary coil and the secondary coil face each other directly, and their centers are always on the same central axis.

[0047] Keeping the primary coil stationary, move the secondary coil 100mm along the positive X and Y axes respectively. First, record the primary self-inductance L of the coil when no displacement occurs. p and secondary self-sensing L s The values ​​of the coil mutual inductance M and the mutual inductance L between the coils are measured; then the mutual inductance M and the primary self-inductance L are measured during each movement. p and secondary self-sensing L s The value of .

[0048] As attached Figure 3-6 As shown, with a 100mm offset in both the X and Y axes, the self-inductance of the primary and secondary sides of the coil remains essentially unchanged. (See attached diagram.) Figure 7-8 As shown, the mutual inductance of the coils generally decreases under the offset in the X and Y axes, but the decreasing trend is relatively slow, which effectively enhances the system's resistance to lateral and longitudinal offset.

[0049] To analyze the transmission characteristics of the LCL / SP topology, an equivalent model of the LCL / SP wireless power transmission system is first established. Secondly, in the primary loop, Kirchhoff's theorem states that:

[0050] ;

[0051] In the formula: U inI is the input voltage; I1 is the primary input current; j is the imaginary unit; I p I is the primary-side output current. s L1 is the secondary input current; L1 is the primary compensation inductor; C1 is the primary resonant capacitor. The operating angular frequency; 0 represents the resonant angular frequency.

[0052] Further derivation yields:

[0053] ;

[0054] When the system operating angular frequency Equal to the resonant angular frequency At 0 o'clock, that is:

[0055] ;

[0056] The primary-side output current I of the system can be obtained. p for:

[0057] ;

[0058] Due to U in L p Since it is a fixed value, the primary-side output of the LCL / SP structure is a constant current output.

[0059] In the secondary loop, by Kirchhoff's theorem, we can obtain:

[0060] ;

[0061] In the formula: C2 and C3 are the series resonant capacitor and the parallel resonant capacitor on the secondary side, respectively; I L For output current; U out This is the output voltage.

[0062] Further derivation yields:

[0063] ;

[0064] (1) When the condition is met At that time, the output current I L for:

[0065] ;

[0066] At this point, the output current is only connected in parallel with the secondary resonant capacitor C3, the mutual inductance M, and the self-inductance L of the primary coil. p It is relevant to the load, but independent of the equivalent load R. The system can achieve constant current output regardless of the load.

[0067] (2) When the following conditions are met:

[0068] ;

[0069] Output voltage U out for:

[0070] ;

[0071] At this point, the output voltage is only related to the mutual inductance M and the self-inductance L of the primary coil. p The system can achieve constant voltage output independent of the load. By adding a switching module to the LCL / SP topology, a variable topology LCL / SP wireless power transfer system can be constructed, such as... Figure 1 As shown. Determine the constant current output conditions and constant voltage output conditions of the wireless power transfer system before and after the switch switching.

[0072] Constant current output condition: When AC switch S1 is closed, the primary-side LCL network of the system is in full resonance, i.e., the compensation inductor L1 and the self-inductance of the transmitting coil L1 are in perfect resonance. p Both resonate with the resonant capacitor C1. Simultaneously, the self-inductance L of the system's secondary coil... S Together with resonant capacitors C2 and C3, they form a series resonance, that is:

[0073] ;

[0074] In the formula: L1 is the primary-side compensating inductance; C1 is the primary-side resonant capacitor; L p L is the self-inductance of the primary coil. s C1 is the self-inductance of the secondary coil; C2 is the series resonant capacitor of the secondary side; C3 is the parallel resonant capacitor of the secondary side. ω is the system angular frequency; j is the imaginary unit.

[0075] Constant voltage output condition: When AC switch S1 is open, the primary-side LCL network of the system is in full resonance. Simultaneously, the secondary-side compensation capacitor C3 and the mutual inductance M form an equivalent reactance resonance, and the resonant capacitor C2, compensation capacitor C4, and the secondary coil self-inductance L... S This constitutes a series resonance, that is:

[0076] ;

[0077] ;

[0078] In the above formula: C4 is the secondary-side compensation capacitor; C 总 is the equivalent capacitance of C2 and C4 connected in series; M is the mutual inductance between the primary and secondary coils.

[0079] The parameters of the variable topology LCL / SP wireless power transfer system are the self-inductance L of the primary and secondary sides of the coil when no offset occurs, as recorded in the above measurements. p L sThe results are calculated based on the mutual inductance M between the coils and the aforementioned constant voltage and constant current output conditions.

[0080] The wireless power transfer operating mode switching point is also known as the load resistance switching point. The load resistance switching point refers to the critical load resistance value at which the output power is equal in both constant voltage and constant current operating modes.

[0081] ;

[0082] In the formula: P out-cc Output power in constant current operating mode; P out-cv The output power is in constant voltage operating mode; R is the equivalent value of the load resistance after being transformed by the rectifier circuit.

[0083] Taking the remaining system parameters as constants and the equivalent load resistance R as a variable, then:

[0084] ;

[0085] The equivalent load R includes the secondary rectifier circuit, therefore the load inflection point R0 after the rectifier circuit can be determined as:

[0086] ;

[0087] The control strategy of the switching module is as follows: In the initial stage of battery charging, switch S1 is closed, short-circuiting compensation capacitor C4, and the secondary circuit satisfies the series resonance condition to achieve constant current output; when the switch is closed, if the resonant network satisfies the parameter relationship of the constant current output condition, the system can achieve constant current output independent of the load.

[0088] When the equivalent load of the lithium battery reaches the load transition resistance value, switch S1 is opened, and compensation capacitor C4 is connected to the circuit, changing the parameters of the secondary resonant network and causing the system to switch to constant voltage output. When the switch is open, compensation capacitor C4 is connected to the resonant network. When the parameters of the resonant network meet the constant voltage output conditions, the system can achieve constant voltage output independent of the load.

[0089] As attached Figure 9 As shown, in the initial charging stage, with the switch closed, the wireless power transfer system is in a constant current state. The equivalent resistance of the lithium battery continuously increases, the system output current remains essentially constant, and the output voltage continues to increase. At 0.1s, the equivalent resistance of the lithium battery reaches the load inflection point, the switch opens, and the system enters a constant voltage mode. The equivalent load of the lithium battery continues to increase, but the output voltage only increases by 2.44V, with a deviation of only 5.35%.

[0090] As attached Figure 10As shown, at 0.1s, the equivalent load of the lithium battery reaches the load inflection point, and the switch is activated. Before the switch, the system output power was 149W, and after the switch, the system output power was 150.4W, with a fluctuation of only 0.9%, which basically achieved a smooth transition when switching working modes.

[0091] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered by the present invention.

Claims

1. A variable topology anti-offset constant voltage and constant current self-switching wireless power transfer system, characterized in that: include: The circuit consists of a DC power supply, a high-frequency inverter circuit, a variable topology LCL / SP compensation circuit, a magnetic coupling mechanism rectifier circuit, and a lithium battery equivalent load circuit connected in sequence. The variable topology LCL / SP compensation circuit has an LCL-type topology on the primary side and an SP-type topology on the secondary side. A compensation capacitor is connected in series with the resonant capacitor in the SP-type topology, and a switch controls the compensation capacitor to turn on or off, which is used to switch the constant voltage output or constant current output working mode of the wireless power transmission system.

2. The variable topology anti-offset constant voltage and constant current self-switching wireless power transmission system according to claim 1, characterized in that: The switch is an AC switch, which consists of two IGBT transistors connected in reverse series.

3. A variable topology anti-offset constant voltage and constant current self-switching wireless power transmission system according to claim 1 or 2, characterized in that: The aforementioned variable topology LCL / SP compensation circuit includes a primary-side compensation inductor L1 and a resonant capacitor C1 connected in parallel to form the first-stage circuit, and the primary-side coil self-inductance L... p The primary side resonant capacitor C1 is connected in parallel to form the second-stage circuit; the coil self-inductance Ls of the secondary side, together with the series resonant capacitor C2 and the compensation capacitor C4, forms a series resonant path, and then forms a circuit with the secondary side resonant capacitor C3 connected in parallel, forming an SP series-parallel compensation structure; an AC switch S1 is connected in parallel above the compensation capacitor C4, and the switching between constant voltage and constant current modes is achieved by switching the AC switch S1.

4. The variable topology anti-offset constant voltage and constant current self-switching wireless power transmission system according to claim 3, characterized in that: The control strategy of the switch is as follows: In the initial stage of battery charging, switch S1 is closed, short-circuiting compensation capacitor C4, and the secondary circuit satisfies the series resonance condition to achieve constant current output; when the equivalent load of the lithium battery reaches the load switching resistance, switch S1 is opened, compensation capacitor C4 is connected to the circuit, changing the parameters of the secondary resonant network, so that the system switches to constant voltage output.

5. The variable topology anti-offset constant voltage constant current self-switching wireless power transmission system according to claim 1, characterized in that: The coupling structure in the rectifier circuit of the magnetic coupling mechanism adopts a QR coil with resistance to lateral and longitudinal offset.

6. The variable topology anti-offset constant voltage constant current self-switching wireless power transmission system according to claim 5, characterized in that: The QR coil consists of four rectangular coils arranged clockwise; all four rectangular coils are wound with Litz wire.

7. A variable topology anti-offset constant voltage constant current self-switching wireless power transmission system according to claim 5 or 6, characterized in that: The QR coil magnetic coupling mechanism with anti-offset performance, constructed from the aforementioned QR coils, has its primary and secondary coils facing each other, with their centers on the same central axis. First, record the primary self-inductance L of the coil when no offset occurs. p and secondary self-sensing L s The value of , and the value of the mutual inductance M between the coils; Keeping the primary coil stationary, move the secondary coil 100mm along the positive X and Y axes respectively, and then measure the mutual inductance M and the primary self-inductance L at each movement. p and secondary self-sensing L s The value of .

8. The variable topology anti-offset constant voltage and constant current self-switching wireless power transmission system according to claim 1, characterized in that: The constant current output condition of the wireless power transmission system is: ； In the formula: L1 is the primary-side compensating inductance; C1 is the primary-side resonant capacitor; L p L is the self-inductance of the primary coil. s C1 is the self-inductance of the secondary coil; C2 is the series resonant capacitor of the secondary side; C3 is the parallel resonant capacitor of the secondary side. Here, ω is the system angular frequency; j is the imaginary unit. The constant voltage output condition is: ； ； In the above formula: C4 is the secondary-side compensation capacitor; C 总 is the equivalent capacitance of C2 and C4 connected in series; M is the mutual inductance between the primary and secondary coils.

9. A variable topology anti-offset constant voltage and constant current self-switching wireless power transmission system according to claim 8, characterized in that: When the switch is closed, the system can achieve a constant current output independent of the load when the resonant network satisfies the parameter relationship of the constant current output condition. When the switch is open, a compensation capacitor C4 is connected to the resonant network, and the system can achieve a constant voltage output independent of the load when the resonant network satisfies the parameter relationship of the constant voltage output condition.

10. A variable topology anti-offset constant voltage constant current self-switching wireless power transmission system according to claim 9, characterized in that: When switching between constant voltage and constant current operating modes in a wireless power transfer system, the switching point of the operating mode is also the switching point of the load resistance. The switching point of the load resistance refers to the critical load resistance value at which the output power is equal in both constant voltage and constant current operating modes; the expression for the load resistance switching point R0 is: ； In the above formula, C is the system angular frequency, and C3 is the parallel resonant capacitor on the secondary side.

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