PT symmetric wireless power transmission system for cardiac pacemaker and parameter design method

Abstract

The invention relates to the technical field of wireless electric energy transmission, and particularly discloses a PT symmetric wireless electric energy transmission system for a cardiac pacemaker and a parameter design method, and the system employs an S-0 topology of which a primary side is connected with an adjustable capacitor in series and a secondary side only comprises a coil and a load, and detects the voltage, current and zero phase angle frequency at the primary side in real time. Mutual inductance between coils is identified on line, and a capacitance value is adaptively adjusted according to the mutual inductance, so that the system always works in a PT symmetrical state. According to the system and the parameter design method, any compensation element of the secondary side is not needed, the implantation end is extremely simplified and miniaturized, meanwhile, high stability of output power and transmission efficiency in a wide coupling range is guaranteed, and the position robustness and the overall reliability of the wireless power supply system of the cardiac pacemaker are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of Wireless Power Transfer (WPT) technology, and more particularly to a PT-symmetric wireless power transfer system and parameter design method for cardiac pacemakers. Background Technology

[0002] Implantable pacemakers are key medical devices for treating heart diseases such as bradycardia, maintaining a normal heart rate through electrical pulse stimulation. Currently, pacemakers primarily rely on built-in lithium batteries for power, but these batteries have limited capacity and require surgical replacement once the power is depleted. This not only imposes an additional financial burden and surgical pain on patients but also carries potential risks such as surgical infection.

[0003] Wireless power transfer (WPT) technology offers a contactless power supply solution for implantable medical devices, potentially enabling long-term device operation and avoiding frequent replacement surgeries, thus possessing significant clinical value and application prospects. However, when applied to cardiac pacemakers, WPT systems must meet several stringent requirements:

[0004] 1) High positional robustness: Due to human breathing, daily activities, etc., the relative position between the inner and outer coils changes constantly, and the coupling coefficient (mutual inductance) changes accordingly. The system must be able to maintain stable and efficient power transmission over a wide coupling range.

[0005] 2) Miniaturization and weight reduction of the implant: The receiving end (secondary side) needs to be implanted in the body, and its size and weight must be as small as possible to reduce the burden on the patient and meet the implantation requirements.

[0006] 3) High efficiency and stability: Ensure sufficient power is delivered to the load while maintaining the highest possible efficiency.

[0007] Therefore, developing a WPT system that combines strong anti-deviation capability, compact secondary side structure, and high energy efficiency is a key technological challenge for realizing the clinical application of wireless power supply for cardiac pacemakers.

[0008] Existing technologies have proposed applying wireless power transmission systems based on the PT (potentially prismatic) symmetry principle to power implantable devices. This involves introducing active gain elements (saturated negative resistors) into the circuit to simulate the gain component of non-Hermitian Hamiltonian quantities, forming a conjugate unit with the loss component in the passive coil circuit that satisfies the PT symmetry condition. When the system operates in PT symmetry, it maintains high transmission efficiency even with changes in inter-coil coupling (corresponding to changes in transmission distance or offset). This characteristic makes it particularly suitable for applications sensitive to positional changes, such as wireless power supply for cardiac pacemakers.

[0009] In traditional PT-symmetric WPT system design, to achieve the required PT symmetry conditions and system performance (such as output power and efficiency), the ratio of the current amplitudes on the primary side to the secondary side ( This is a key parameter. In existing technologies, this current amplitude ratio is strictly limited by the self-inductance ratio of the primary and secondary coils. The square root of ), that is ( (Indicates proportional to).

[0010] To increase the system's transmission power or enhance its robustness (anti-offset capability) when the coupling coefficient changes, it is usually necessary to increase the current amplitude ratio, which corresponds to reducing the primary-secondary inductance ratio. Existing technologies mainly employ the following two hardware adjustment methods:

[0011] 1) Reduce the inductance of the primary coil ( This can be achieved by changing the geometry or number of turns of the primary coil. However, this method may weaken the magnetic field emission capability of the primary coil, reduce the coupling coefficient, and potentially shrink the effective transmission range.

[0012] 2) Increase the inductance of the secondary coil ( Alternatively, a compensation network can be introduced on the secondary side: directly adding a lumped inductance to the secondary side. Once the inductance value is fixed, the system characteristics are fixed and cannot be adjusted. A lumped capacitor can be connected in series on the secondary side: this adjusts the equivalent parameters to some extent through series resonance, but the main purpose is to construct resonant conditions, significantly altering the equivalent inductive reactance and thus significantly improving performance. The effect is limited. Therefore, both increasing the lumped inductance and the compensation capacitor will significantly increase the size, weight, and complexity of the secondary circuit. This is an unacceptable drawback for the highly integrated and space-constrained receiver of a cardiac pacemaker.

[0013] In addition, key performance parameters such as the system current amplitude ratio and critical coupling point are uniquely determined by hardware parameters such as coil self-inductance, compensation capacitor, and parasitic resistance. Once manufactured, they cannot be changed. When the patient's position, coil alignment, or output power requirements change, the system cannot make real-time and flexible adjustments to maintain optimal performance and cannot respond to dynamically changing needs or environments.

[0014] Furthermore, using lumped capacitors or complex compensation networks on the secondary side can cause parameter drift due to aging, temperature changes, or biological environmental corrosion, leading to system detuning, reduced transmission efficiency, and unstable output. Summary of the Invention

[0015] This invention provides a PT-symmetric wireless power transfer system and parameter design method for cardiac pacemakers. The technical problem it solves is: how to effectively reduce the volume of the secondary side while maintaining the high positional robustness of the PT-symmetric system, and at the same time avoid the detuning of the secondary side capacitor leading to a decrease in system energy efficiency.

[0016] To address the above technical problems, this invention provides a PT symmetrical wireless power transfer system for cardiac pacemakers, comprising a primary side and a secondary side, wherein the primary side includes an input voltage. A high-frequency inverter, a primary winding, and an adjustable capacitor connected in series with the primary winding. The secondary side includes a secondary coil and a load resistor. .

[0017] Preferably, the adjustable capacitor is determined by making the primary-side input impedance a pure resistance. The value of .

[0018] Preferably, the primary-side input impedance is a pure resistance that satisfies the following conditions: , The operating angular frequency of the system. , These are the self-inductances of the primary coil and the secondary coil, respectively. It is the square of the ratio of the secondary current amplitude to the primary current amplitude.

[0019] Preferably, and The relationship between them is satisfied: , This refers to the mutual inductance between the primary coil and the secondary coil.

[0020] Preferably, the adjustable capacitor The value is based on the mutual inductance between the primary coil and the secondary coil. The self-inductance of the primary coil The self-inductance of the secondary coil Secondary side parasitic resistance Load resistance and the expected critical coupling coefficient The square of the corresponding ratio of primary to secondary current amplitude Sure.

[0021] Preferably, the adjustable capacitor The value is set to .

[0022] Preferably, the mutual inductance between the primary coil and the secondary coil is... based on , , , , , , Sure, , These are the effective values ​​of the primary-side AC input voltage and the primary-side coil current under ZPA control, respectively. , These are the parasitic resistances of the primary and secondary sides, respectively. For load resistance, For the secondary coil inductance, The primary side ZPA control frequency.

[0023] Preferably, the mutual inductance between the primary coil and the secondary coil is... .

[0024] This invention also provides a parameter design method applied to the aforementioned PT symmetrical wireless power transfer system for a cardiac pacemaker, the key feature of which is that the method includes the following steps:

[0025] S1. Input initialization parameters, including system input voltage. Load resistance R L Primary coil inductance Primary parasitic resistance Secondary coil inductance Secondary side parasitic resistance Given an arbitrary initial capacitance value for the variable capacitor and the expected critical coupling coefficient and the square of the ratio of the primary and secondary current amplitudes. ;

[0026] S2. The effective value of the primary AC input voltage is detected through primary-side ZPA control. and the effective value of the primary coil current And read out the only ZPA frequency at this time. ;

[0027] S3, will , , , , , , Substitute the values ​​into the mutual inductance calculation formula to obtain the current mutual inductance value;

[0028] S4. The identified With initialization parameters , , , , Substituting into the variable capacitor calculation formula, we obtain the target value of the variable capacitor. ;

[0029] S5. Adjust the variable capacitor value to the target value. Then return to step S2.

[0030] Furthermore, the mutual inductance calculation formula in step S3 is: The formula for calculating the variable capacitor in step S4 is: .

[0031] The present invention provides a PT-symmetric wireless power transfer system and parameter design method for cardiac pacemakers. Its core lies in employing an S-O topology with a series adjustable capacitor on the primary side and only a coil on the secondary side. By real-time detection of voltage, current, and frequency on the primary side to identify mutual inductance, the system adaptively adjusts the capacitor value, ensuring the system always operates in a PT-symmetric state. Its beneficial effects are:

[0032] 1) Fundamentally reduce the volume and complexity of the secondary side: Through the novel S-0 topology and PT symmetry mechanism, the requirement of any lumped capacitance or additional compensation network for the secondary side is completely eliminated, which greatly simplifies the receiver circuit and meets the core requirements of miniaturization and integration of the cardiac pacemaker implantation end.

[0033] 2) Achieve flexible and arbitrary adjustment of the current amplitude ratio: Without changing any hardware circuit structure or inductor parameters, the current amplitude ratio between the primary and secondary sides can be adjusted in real time and continuously by controlling the primary variable capacitor, thereby dynamically optimizing system performance.

[0034] 3) Improve the overall robustness and adaptability of the system: By using the critical coupling coefficient of the PT symmetrical system as an active design parameter, and by flexibly adjusting the current amplitude ratio, the system can adaptively adjust according to the actual coupling state (such as the degree of position offset), which significantly enhances the system's anti-offset capability and transmission stability over a wide coupling range, while avoiding the risk of performance degradation caused by detuning of secondary components.

[0035] Overall, the system and its parameter design method achieve stable output power and efficiency over a wide coupling range without requiring any compensation components on the secondary side. At the same time, it significantly simplifies the implantation end structure and improves the positional robustness and overall reliability of the wireless power supply for the cardiac pacemaker. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the circuit structure of the PT symmetrical wireless power transfer system for a cardiac pacemaker provided in an embodiment of the present invention;

[0037] Figure 2 This is a flowchart illustrating the parameter design of a PT symmetrical wireless power transfer system for a cardiac pacemaker, provided in an embodiment of the present invention.

[0038] Figure 3 This is a simulation waveform diagram of the primary and secondary currents of the system under a certain operating state in an embodiment of the present invention;

[0039] Figure 4 This is a schematic diagram of the mutual inductance identification results obtained by using the mutual inductance identification method at 10 different locations (corresponding to different mutual inductance values) in an embodiment of the present invention;

[0040] Figure 5 This is the corresponding embodiment of the present invention. Figure 4 The relative error distribution diagram of the mutual inductance identification results;

[0041] Figure 6 This is a simulation waveform diagram of the primary and secondary side voltage and current of the system at a certain position in an embodiment of the present invention;

[0042] Figure 7 This is a statistical chart of the simulation results of the system output power at 10 different locations in an embodiment of the present invention;

[0043] Figure 8 This is a statistical chart showing the simulation results of the system's transmission efficiency at 10 different locations in an embodiment of the present invention. Detailed Implementation

[0044] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. The embodiments are given for illustrative purposes only and should not be construed as limiting the present invention. The accompanying drawings are for reference and illustration only and do not constitute a limitation on the scope of patent protection of the present invention, because many changes can be made to the present invention without departing from the spirit and scope of the present invention.

[0045] The first embodiment of the present invention provides a PT symmetrical wireless power transfer system for a cardiac pacemaker, the circuit diagram of which is shown below. Figure 1 As shown, the system adopts an S-0 topology, meaning the primary side includes the input voltage. High-frequency inverter (whose output current is...) , The effective value is ), primary coil (inductance is Adjustable capacitor connected in series with the primary coil The secondary side includes the secondary coil (inductance is...) and load resistance . , , and These represent the primary and secondary currents and the primary and secondary parasitic resistances, respectively. , The effective value is represented as , , This refers to the mutual inductance between the primary and secondary coils.

[0046] according to Figure 1 The corresponding KVL equation is:

[0047]

[0048] in, This is the system's operating angular frequency.

[0049] Solving the KVL equation for the secondary side from equation (1), the ratio of the secondary current amplitude to the primary current amplitude is:

[0050]

[0051] Assumption (That is, the square of the ratio of the primary to secondary current amplitudes), the expression for the primary input impedance is:

[0052]

[0053] To achieve PT symmetry, the primary input impedance should be purely resistive, meaning it needs to satisfy:

[0054]

[0055] Solving equation (4) yields the corresponding parameter criteria for the adjustable capacitor:

[0056]

[0057] According to the parameter criterion given in equation (5), it is obvious Mutual induction Related, therefore must be identified .

[0058] The mutual inductance identification method used in this invention follows these steps: First, an arbitrary initial capacitance value is set. The corresponding resonant frequency is obtained by controlling the primary side using ZPA (Zero Phase Angle). Combined with the input impedance expression of the system under PT symmetry conditions. Only the main circuit voltage and current need to be measured to pass the formula. calculate :

[0059]

[0060] When the equation is satisfied When using the parameter criteria in the equation, the corresponding power and efficiency expressions of the PT-symmetric system at that point can be obtained, as shown in equation (7):

[0061]

[0062] According to the formula It can be seen that the newly proposed S-0 topology PT symmetric working mechanism enables the output power and transmission efficiency to be adjusted as desired, while also having strong position robustness.

[0063] Furthermore, the solution formula The parameter conditions that the critical coupling coefficient must satisfy can be derived, as shown in the equation. As shown:

[0064]

[0065] According to the formula It can be seen that the critical coupling coefficient is no longer limited to fixed electrical parameters, but can be adjusted as needed, breaking through the inherent EP point (Exceptional Point) constraint.

[0066] Based on the above analysis, embodiments of the present invention provide a system parameter design method, the design process of which is as follows: Figure 2 As shown, the steps include:

[0067] S1: Input initialization parameters, including system input voltage. Load resistance R L Primary coil inductance Primary parasitic resistance Secondary coil inductance Secondary side parasitic resistance Given an arbitrary initial capacitance value for the variable capacitor and the expected critical coupling coefficient and the square of the ratio of the primary and secondary current amplitudes. ;

[0068] S2: The effective value of the primary AC input voltage is detected through primary-side ZPA control. and the effective value of the primary coil current And read out the only ZPA frequency at this time. ;

[0069] S3: Will , , , , , , Substituting into the mutual inductance calculation formula shown in equation (6) The current mutual inductance value is calculated.

[0070] S4: The identified With initialization parameters , , , , Substituting into the variable capacitor calculation formula shown in equation (5) The target value of the variable capacitor is obtained. ;

[0071] S5: Adjust the variable capacitor value to the target value. Then return to step S2.

[0072] Using the above parameter design steps, the system always performs ZPA operation to realize a PT symmetric system, maintaining constant power output and stable transmission efficiency. The simulation verification is performed below.

[0073] To verify the effectiveness and correctness of the system and parameter design method proposed above, this embodiment uses the MATLAB numerical simulation platform to build a full circuit model of the system. The system simulation parameter settings are shown in Table 1.

[0074] Table 1 Simulation Data

[0075]

[0076] Based on the mutual inductance identification method proposed in the theoretical section, the obtained , Simulated waveforms such as Figure 3 As shown, the horizontal axis represents time ( / s), and the vertical axis represents the value ( / V, / A).

[0077] The mutual inductance identification results at 10 different locations are as follows: Figure 4 As shown, the corresponding relative error of mutual inductance identification is as follows: Figure 5 As shown. Based on mutual inductance identification, to comprehensively evaluate system performance, detailed energy efficiency simulation verification was performed at 10 different locations (corresponding to 10 different mutual inductance values). The simulated waveforms of the primary and secondary voltage and current at one of the locations are shown below. Figure 6 As shown (where u) s and i s (Representing the secondary-side induced voltage and current respectively), the output power results at 10 different locations are as follows: Figure 7 As shown, the efficiency results at 10 different locations are as follows: Figure 8 As shown, Figure 7 and Figure 8In this context, Mean represents the average value, Std Dev represents the standard deviation, and Range represents the range (the difference between the maximum and minimum values).

[0078] Figures 3 to 8 Simulation data shows that: at mutual inductance values ​​( Within the range of 12.637μH to 33.1μH, the system's output power remained stable at around 29.650W (standard deviation of only 0.175W), and the efficiency remained at around 85.940% (standard deviation of 0.415%).

[0079] Simulation results fully demonstrate that the system and parameter design method proposed in this embodiment can achieve excellent constant output characteristics under different mutual inductance (i.e., different offset distances), with output power fluctuation range less than 0.619W and efficiency fluctuation range less than 1.099%. This verifies the practicality and effectiveness of overcoming the critical coupling limitation of traditional PT symmetrical systems and significantly improving the system's anti-offset capability by adjusting the variable capacitor value to adjust the current amplitude ratio in real time without changing any hardware.

[0080] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A PT-symmetric wireless power transfer system for cardiac pacemakers, characterized in that: It includes a primary side and a secondary side, wherein the primary side includes the input voltage. A high-frequency inverter, a primary winding, and an adjustable capacitor connected in series with the primary winding. The secondary side includes a secondary coil and a load resistor. .

2. The PT symmetrical wireless power transfer system for a cardiac pacemaker according to claim 1, characterized in that: The adjustable capacitor is determined by making the primary-side input impedance a pure resistance. The value of .

3. The PT symmetrical wireless power transfer system for a cardiac pacemaker according to claim 2, characterized in that: The primary input impedance is a pure resistance and satisfies the following conditions: , The operating angular frequency of the system. , These are the self-inductances of the primary coil and the secondary coil, respectively. It is the square of the ratio of the secondary current amplitude to the primary current amplitude.

4. The PT symmetrical wireless power transfer system for a cardiac pacemaker according to claim 3, characterized in that, and The relationship between them is satisfied: , This refers to the mutual inductance between the primary coil and the secondary coil.

5. The PT-symmetric wireless power transfer system for a cardiac pacemaker according to any one of claims 1 to 4, characterized in that, Adjustable capacitor The value is based on the mutual inductance between the primary coil and the secondary coil. The self-inductance of the primary coil The self-inductance of the secondary coil Secondary side parasitic resistance Load resistance and the expected critical coupling coefficient The square of the corresponding ratio of primary to secondary current amplitude Sure.

6. The PT symmetrical wireless power transfer system for a cardiac pacemaker according to claim 5, characterized in that: Adjustable capacitor The value is set to .

7. The PT symmetrical wireless power transfer system for a cardiac pacemaker according to claim 4, characterized in that: The mutual inductance between the primary coil and the secondary coil is currently... based on , , , , , , Sure, , These are the effective values ​​of the primary-side AC input voltage and the primary-side coil current under ZPA control, respectively. , These are the parasitic resistances of the primary and secondary sides, respectively. For load resistance, For the secondary coil inductance, The primary side ZPA control frequency.

8. The PT symmetrical wireless power transfer system for a cardiac pacemaker according to claim 7, characterized in that: The mutual inductance between the primary coil and the secondary coil is currently... .

9. A parameter design method, applied to the PT symmetrical wireless power transmission system for a cardiac pacemaker as described in any one of claims 1 to 8, characterized in that, The method includes the following steps: S1. Input initialization parameters, including system input voltage. Load resistance R L Primary coil inductance Primary parasitic resistance Secondary coil inductance Secondary side parasitic resistance Given an arbitrary initial capacitance value for the variable capacitor and the expected critical coupling coefficient and the square of the ratio of the primary and secondary current amplitudes. ; S2. The effective value of the primary AC input voltage is detected through primary-side ZPA control. and the effective value of the primary coil current And read out the only ZPA frequency at this time. ; S3, will , , , , , , Substitute the values ​​into the mutual inductance calculation formula to obtain the current mutual inductance value; S4. The identified With initialization parameters , , , , Substituting into the variable capacitor calculation formula, we obtain the target value of the variable capacitor. ; S5. Adjust the variable capacitor value to the target value. Then return to step S2.

10. The parameter design method according to claim 9, characterized in that: The mutual inductance calculation formula in step S3 is: The formula for calculating the variable capacitor in step S4 is: .

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