A wireless power transmission frequency adaptive regulation method based on PT symmetry condition

Abstract

The application relates to a wireless power transmission frequency adaptive regulation method based on a PT symmetry condition, which comprises the following steps: determining the topological structure of a wireless power transmission system, the system comprising a transmitting end and a receiving end, the transmitting end comprising a transmitting coil and a series resonant capacitor, the receiving end comprising a receiving coil, a parallel resonant capacitor and a load, and the parallel resonant capacitor being connected in series with an external inductance; obtaining the coupling coefficient between the transmitting end and the receiving end; determining a critical coupling coefficient according to system parameters; judging whether the coupling coefficient is greater than the critical coupling coefficient, if yes, the PT symmetry condition is met, and energy transmission is carried out, if not, the external inductance is adjusted until the coupling coefficient is greater than the critical coupling coefficient, at this time, the PT symmetry condition is met, and energy transmission is carried out. The application can maintain the stability of power and efficiency when the coupling coefficient changes, and significantly improves the robustness of the system.

Description

Technical Field

[0001] This application relates to the field of wireless power transmission, and more specifically, to a wireless power transmission frequency adaptive control method based on PT symmetry conditions. Background Technology

[0002] Wireless power transfer technology utilizes magnetic coupling resonance to achieve contactless energy transfer, offering advantages such as safety, convenience, and durability. It has been widely applied in consumer electronics, medical implants, and wireless charging for electric vehicles. Its basic principle is to achieve efficient energy transfer from the power source to the load side through magnetic coupling between the transmitting and receiving coils. However, existing wireless power transfer systems generally suffer from a core problem: system performance is highly dependent on the coupling coefficient between the coils. When the relative position, spacing, or alignment of the transmitting and receiving ends changes, the coupling coefficient fluctuates, leading to a significant decrease in output power and transmission efficiency, thus severely impacting the system's stability and practicality.

[0003] To alleviate this problem, existing technologies have proposed several improvement methods. For example, maintaining frequency tracking of resonance by real-time detection of system parameters and adjustment of the operating frequency can improve performance to some extent, but it relies on complex detection and control circuits, resulting in limited response speed and high hardware costs. Maintaining impedance matching by introducing variable compensation networks or active matching circuits can also improve system adaptability, but the control strategy is complex and it is difficult to maintain stability over a wide coupling range. Improving effective coupling by adding a relay coil between the transmitter and receiver can enhance transmission capability, but it significantly increases the system size and cost, making it unsuitable for space-constrained applications such as automotive. In addition, there is an adaptive power control method that maintains stable output power by adjusting the transmitter power, which can offset the impact of coupling fluctuations to some extent, but often at the cost of reduced efficiency. Regarding compensation topologies, existing systems often use different structures such as SS, SP, PS, and PP to adapt to different application conditions, but these single compensation methods are still quite sensitive to fluctuations in the coupling coefficient, making it difficult to simultaneously achieve high efficiency and robustness.

[0004] In summary, existing methods are complex in structure, difficult to control, and have limited applicability. They still cannot simultaneously guarantee the stability of output power and transmission efficiency when the coupling coefficient changes. Summary of the Invention

[0005] To overcome at least one deficiency in the prior art, this application provides a wireless power transfer frequency adaptive control method based on PT symmetry conditions.

[0006] Firstly, a method for adaptive frequency control of wireless power transfer based on PT symmetry is provided, comprising: The topology of the wireless power transmission system is determined. The system includes a transmitter and a receiver. The transmitter includes a transmitting coil and a series resonant capacitor. The receiver includes a receiving coil, a parallel resonant capacitor, a load, and an external inductor. The load is connected in series with the external inductor and in parallel with the parallel resonant capacitor. Obtain the coupling coefficient between the transmitter and receiver. Determine the critical coupling coefficient based on system parameters. ; Determine the coupling coefficient Is it greater than the critical coupling coefficient? If so, the PT symmetry condition is met, and energy transfer occurs. If not, the external inductor is adjusted until the coupling coefficient is adjusted. Greater than the critical coupling coefficient At this point, the PT symmetry condition is satisfied, and energy transfer occurs.

[0007] In one embodiment, the critical coupling coefficient The following formula is used to determine it:

[0008] in, The equivalent quality factor of the transmitting end. This is the equivalent quality factor at the receiving end.

[0009] In one embodiment, the equivalent quality factor of the transmitter. Equivalent quality factor of the receiving end for:

[0010] in, The resonant frequency of the system. For primary side inductance, The equivalent resistance of the power supply. For the primary side internal resistance, This is the equivalent resistance on the secondary side. For secondary side internal resistance, It is the secondary inductor.

[0011] Compared with the prior art, this application has the following beneficial effects: 1. This application can maintain the stability of power and efficiency when the coupling coefficient changes, which significantly improves the robustness of the system.

[0012] 2. This application maintains the simplicity of the compensation topology in terms of structure, and can be implemented by adding only an external inductor and a control strategy, without increasing the system complexity.

[0013] 3. This application achieves stable transmission solely through frequency modulation, avoiding the need for additional impedance matching circuits or relay coils, thus demonstrating high engineering feasibility. Compared to traditional fixed-frequency driving methods, it effectively maintains stable performance over a wide coupling range, making it more suitable for energy transmission needs under complex operating conditions. Attached Figure Description

[0014] This application can be better understood by referring to the description given below in conjunction with the accompanying drawings, which, together with the detailed description below, are incorporated in and form part of this specification. In the drawings: Figure 1 A flowchart of a wireless power transfer frequency adaptive control method based on PT symmetry conditions is shown. Figure 2 A circuit diagram of a wireless power transfer system is shown; Figure 3 The equivalent circuit on the secondary side is shown; Figure 4 A symmetrical equivalent circuit is shown; Figure 5 The transmission efficiency is shown as a function of the coupling coefficient. The curve of change; Figure 6 The output power as a function of the coupling coefficient is shown. The curve showing the change. Detailed Implementation

[0015] Exemplary embodiments of the present application will be described below with reference to the accompanying drawings. For clarity and brevity, not all features of the actual embodiments are described in the specification. However, it should be understood that many embodiment-specific decisions can be made in the development of any such actual embodiment to achieve the developer’s specific objectives, and these decisions may vary as the embodiments differ.

[0016] It should also be noted that, in order to avoid obscuring this application with unnecessary details, only the device structure closely related to the solution of this application is shown in the accompanying drawings, while other details that are not closely related to this application are omitted.

[0017] It should be understood that this application is not limited to the described embodiments by virtue of the following description with reference to the accompanying drawings. In this document, embodiments may be combined with each other, features may be substituted or borrowed between different embodiments, and one or more features may be omitted in one embodiment, where feasible.

[0018] This application provides a wireless power transfer frequency adaptive control method based on PT symmetry conditions. Figure 1A flowchart of an adaptive frequency modulation method for wireless power transfer based on PT symmetry conditions is shown. (See attached diagram.) Figure 1 The method mainly includes the following steps: Step S1: Determine the topology of the wireless power transmission system. The system includes a transmitter and a receiver. The transmitter includes a transmitting coil and a series resonant capacitor. The receiving end includes a receiving coil and a parallel resonant capacitor. Load and external inductor The load is connected in series with an external inductor and in parallel with a resonant capacitor; the load resistance is...

[0019] Figure 2 The circuit diagram of a wireless power transfer system is shown, based on an SP-type compensated topology. The mutual inductance between the transmitting and receiving coils is M, expressed using the coupling coefficient. express: (1) in, This is the primary inductance, i.e., the inductance of the transmitting coil. This is the secondary inductance, i.e., the inductance of the receiving coil.

[0020] Step S2: Obtain the coupling coefficient between the transmitter and receiver. Determine the critical coupling coefficient based on system parameters. .

[0021] Critical Coupling Coefficient The following formula is used to determine it: (2) in, The equivalent quality factor of the transmitting end. This is the equivalent quality factor at the receiving end.

[0022] Equivalent quality factor of the transmitter Equivalent quality factor of the receiving end for: (3) in, The resonant frequency of the system. For primary side inductance, The equivalent resistance of the power supply. For the primary side internal resistance, This is the equivalent resistance on the secondary side. For secondary side internal resistance, It is the secondary inductor.

[0023] Step S3, determine the coupling coefficient Is it greater than the critical coupling coefficient? If so, then the PT symmetry condition (parity-time symmetry) is satisfied, and energy transfer occurs. If not, adjust the external inductor until the coupling coefficient is adjusted. Greater than the critical coupling coefficient At this point, the PT symmetry condition is satisfied, and energy transfer occurs.

[0024] external inductor As an adjustable element at the receiving end, its adjustment process relies on a real-time feedback mechanism. The inductor value is fine-tuned by controlling the current or voltage to ensure the system always maintains a symmetrical PT operating state. Specifically, the system calculates the coupling coefficient in real time by monitoring the input voltage and current, as well as the load voltage and current. When the coupling coefficient Less than the set critical coupling coefficient When this happens, the system will detect the resonant frequency shift and activate the external inductor adjustment mechanism.

[0025] The adjustment range is very small, typically a few hertz to tens of hertz, achieved by adjusting an external inductor. The inductance value is adjusted to restore the system's resonant frequency, keeping it within the PT symmetry region. The adjustment process does not cause drastic changes in the system frequency, ensuring stable power output and efficiency, and avoiding instability caused by excessive adjustment amplitude. In this way, the external inductor... The adjustment can quickly respond to changes in the coupling coefficient, maintain the system in a stable working state and efficiently transmit energy. Moreover, this adjustment method does not require complex circuit design or the addition of other compensation components, making the circuit structure simpler and the system more efficient and stable.

[0026] The following are Figure 2 The wireless power transmission system shown is analyzed in detail.

[0027] The resonant frequency of the primary side is expressed as: (4) in, The resonant frequency of the primary side. This refers to the primary side capacitance, i.e., the capacitance value of the series resonant capacitor. This is the primary inductor.

[0028] According to formula (4), the primary side capacitance The expression: (5) pass Figure 2 As can be seen, an external inductor is provided on the secondary side, which complicates the resonant design of the secondary side. Therefore, it is transformed into... Figure 3The equivalent circuit shown, in which the external inductor, parallel resonant capacitor, and load have undergone de-series transformation to reduce the number of circuit elements, has its parameters obtained through the following equations: (6) in, This is the equivalent resistance on the secondary side. For load resistance, The resonant frequency of the secondary side. For external inductance, It is a parallel resonant capacitor. This is the equivalent capacitance on the secondary side.

[0029] Power transfer performance is improved when the system operating frequency matches the secondary resonant frequency. The relationship between the secondary resonant frequency and the external inductor and capacitor is as follows: (7) Based on the aforementioned equivalent circuit, the equivalent parameters can be expressed as: (8) From the above formula, we can obtain: (9) (10) For simplicity, the system's resonant frequency : (11) In this embodiment, the receiving circuit is first subjected to equivalent processing. Figure 3 The equivalent resistance of the secondary side circuit shown can be obtained through series-parallel transformation. Equivalent capacitance of the secondary side This simplifies the circuit structure on the secondary side. Based on this, the primary and secondary sides are combined to form a symmetrical equivalent circuit, such as... Figure 4 As shown. This circuit includes a primary-side inductor. Primary side capacitor Primary side internal resistance and power supply equivalent resistance and secondary inductor Secondary equivalent capacitance Secondary side internal resistance Equivalent resistance of the secondary side The two are mutually inductive Coupling. According to Figure 4 The circuit shown can be used to derive the following system of equations by applying Kirchhoff's voltage law: (12) in, For primary side current, This is the secondary side current. It is the resonant frequency.

[0030] The equivalent circuit of the above equation can be transformed into: (13) in, The equivalent quality factor of the transmitting end. This is the equivalent quality factor at the receiving end.

[0031] (14) To obtain the solution for the operating frequency, the determinant of formula (13) must be zero, as follows: (15) Decomposing (15) into real and imaginary parts, we get: (16) By considering two cases and Based on the above formula, the operating frequency can be determined as follows: (17) in It is the critical coupling coefficient, calculated as follows: (18) From the above formula, we can see that there are two regions: PT symmetrical working conditions ( ) and PT symmetry breaking condition ( First, the power transfer characteristics under symmetrical PT operating conditions are derived. When the PT is under symmetrical operating conditions: (19) Obtain the primary side current from (13) and (19). and load current Respectively with secondary side current The ratio: (20) (twenty one) Using (20) and (21), the ratio of input voltage to output voltage is obtained as follows: (twenty two) From (22), the output power and power transmission efficiency can be obtained, and then calculated using (23) and (24) respectively: (twenty three) (twenty four) Equations (23) and (24) show that, under PT symmetrical operating conditions, both output power and power transmission efficiency are related to the coupling coefficient. Irrelevant.

[0032] Next, the power transfer characteristics under PT symmetry breaking conditions (i.e., PT asymmetry operating conditions) are investigated. Using (16), the negative impedance under PT symmetry breaking conditions can be obtained in the following way: (25) Obtain the primary side current from (13) and (19). With secondary side current The ratio: (26) The ratio of the secondary current to the resistive load current is the same as in (21). Using (21) and (26), the ratio of the input voltage to the output voltage is obtained as follows: (27) From (27), the output power and power transmission efficiency can be calculated using (28) and (29) respectively: (28) (29) Equations (28) and (29) show that, under PT symmetry breaking, both output power and power transmission efficiency depend on k. Therefore, PT symmetry breaking should be avoided, and the critical coupling coefficient should be as small as possible.

[0033] In one specific embodiment, the wireless power transfer system based on PT symmetry conditions has its operating region limited to the PT symmetry state, i.e., the coupling coefficient is... Within the specified range, the system employs a transmitter-side series compensation and receiver-side parallel compensation (SP type) topology. Based on this, an adaptive frequency control strategy is introduced to achieve stable power and efficiency output by satisfying the PT symmetry condition. The transmitter outputs AC power, which is coupled to the receiver via a resonant network, realizing contactless energy transfer.

[0034] In this embodiment, the core idea of ​​the system is to utilize the parameter relationships under PT symmetry conditions to achieve a balanced state between the coupling coil and the load. When the PT condition is met, the system's characteristic equation has conjugate symmetric complex roots, the power transmission process is in the real-number spectrum region, the total input impedance of the system is purely resistive, and energy is transferred between the transmitter and receiver with minimal phase difference, thus achieving insensitivity of power and efficiency to coupling changes. The system uses a control module to detect the transmitter voltage, current, and phase information in real time, and performs adaptive frequency adjustment based on the calculated PT operating frequency. Since the coupling coefficient only changes slightly within the PT range during actual operation, the frequency adjustment range is narrow. The control algorithm employs a small-step, low-disturbance closed-loop to ensure stable operation of the system throughout the entire PT range.

[0035] In simulation verification, the coupling coefficient is selected. The analysis covered the range of 0.35 to 0.9, comparing the power and efficiency variations of "adaptive frequency control based on PT conditions" and "traditional fixed frequency control". Figure 5 The transmission efficiency is shown as a function of the coupling coefficient. The efficiency curve under PT conditions (solid blue line) remains stable at approximately 90%, with an overall fluctuation of no more than ±0.5%; while the traditional fixed-frequency curve (dashed orange line), although it varies with... The efficiency gradually increases, but significant fluctuations still exist throughout the entire PT region, with the peak-to-valley difference being significantly greater than that of the PT curve. This result indicates that, under operating conditions satisfying the PT conditions, the system efficiency is almost insensitive to coupling changes, exhibiting high stability and high repeatability.

[0036] Figure 6 The output power as a function of the coupling coefficient is shown. The curves showing the changes are shown. The solid blue line represents the PT condition curve under adaptive frequency control, and the dashed orange line represents the traditional fixed frequency method. It can be seen that within the PT region (… Under PT conditions, the output power remains essentially constant, averaging approximately 3.6 kW, exhibiting only slight, smooth fluctuations; in contrast, the fixed-frequency curve, although generally varying with... The power output increases, but the fluctuation range is relatively large, with local undulations and slight discontinuities. This indicates that within the PT symmetry region, adaptive frequency control effectively suppresses power fluctuations caused by coupling changes, resulting in a more stable system output.

[0037] The results above demonstrate that the adaptive frequency control method based on PT symmetry proposed in this application can significantly reduce power and efficiency fluctuations within the PT region, enabling the wireless power transfer system to maintain stable energy transfer performance over a wide coupling range. Since this method only requires fine-tuning the frequency without altering the system topology or component parameters, it is simple to implement, has low control overhead, and is highly applicable. Both experiments and simulations show that when the system operates in the PT region, the output power fluctuation is less than 2%, and the transmission efficiency remains stable in the 89%–91% range. Compared to the traditional fixed-frequency method, the system's robustness and energy stability are significantly improved.

[0038] In summary, this embodiment demonstrates that a wireless power transfer system operating under PT-symmetric conditions can adaptively suppress changes in the coupling coefficient, exhibiting advantages such as simple structure, smooth control, and stable energy output. It is particularly suitable for applications requiring high-stability wireless power supply, including wireless charging for electric vehicles, power supply for medical implants, and fixed devices. Even considering only the PT region, this method fully demonstrates its core advantage in resisting coupling fluctuations, validating the theoretical feasibility and engineering applicability of this application.

[0039] This application maintains stable system output characteristics by adjusting the operating frequency in real time when the coupling coefficient fluctuates. Specifically: when the coupling coefficient decreases, the method of this application can suppress the decrease in output power and ensure that the power at the load end is maintained near the design value; when the coupling coefficient increases, the method can avoid a sharp decrease in efficiency or overload operation and ensure that the system maintains efficient transmission over a wide coupling range; compared with the traditional fixed frequency driving method, the method of this application can significantly reduce the output characteristic deviation under the same coupling fluctuation conditions.

[0040] When the vehicle's parking position shifts laterally or longitudinally, the vehicle's height changes, or the charging gap fluctuates, the method of this application ensures that the charging power and efficiency remain essentially constant through adaptive frequency regulation. During vehicle-to-grid interaction, when the electric vehicle acts as an energy feedback unit, the method of this application can also maintain stable power and efficiency in feedback power mode, avoiding grid-side fluctuations caused by coupling condition fluctuations. The method of this application is also applicable to occasions with high energy stability requirements, including rail transit, wireless charging for drones, and energy transmission for medical implants.

[0041] The above descriptions are merely various embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for adaptive frequency control of wireless power transfer based on PT symmetry, characterized in that, include: The topology of a wireless power transmission system is determined. The system includes a transmitter and a receiver. The transmitter includes a transmitting coil and a series resonant capacitor. The receiver includes a receiving coil, a parallel resonant capacitor, a load, and an external inductor. The load is connected in series with the external inductor and in parallel with the parallel resonant capacitor. Obtain the coupling coefficient between the transmitter and the receiver. ; Determine the critical coupling coefficient based on system parameters. ; Determine the coupling coefficient Is it greater than the critical coupling coefficient? If so, the PT symmetry condition is met, and energy transfer occurs. If not, the external inductor is adjusted until the coupling coefficient is adjusted. Greater than the critical coupling coefficient At this point, the PT symmetry condition is satisfied, and energy transfer occurs.

2. The method as described in claim 1, characterized in that, The critical coupling coefficient The following formula is used to determine it: in, The equivalent quality factor of the transmitting end. This is the equivalent quality factor at the receiving end.

3. The method as described in claim 2, characterized in that, Equivalent quality factor of the transmitter Equivalent quality factor of the receiving end for: in, The resonant frequency of the system. For primary side inductance, The equivalent resistance of the power supply. For the primary side internal resistance, This is the equivalent resistance on the secondary side. For secondary side internal resistance, It is the secondary inductor.

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