Method for online evaluation of dynamic mutual inductance based on wireless power transfer system

Abstract

The application discloses a dynamic mutual inductance online evaluation method based on a wireless power transmission system, and is implemented according to the following steps: step 1: obtaining inherent parameters of the wireless power transmission system; step 2: setting a receiving coil side DC load voltage variation threshold and a load voltage variation time threshold, measuring the load voltage variation and the time interval of the detected voltage, so as to determine whether the receiving coil position is changed; step 3: if the receiving coil position is not changed, repeating step 2; if the receiving coil position is changed, detecting each phase circuit in turn, and obtaining the mutual inductance coefficient in combination with the inherent parameters in step 1; and step 4: according to the mutual inductance coefficient of each phase circuit obtained in step 3, the accuracy of the wireless power transmission system is evaluated. The method has the advantages of simple structure and convenient control, and can guarantee the online accurate estimation of the mutual inductance between the transmitting coil and the receiving coil when the receiving coil position is changed in the full-direction WPT system.

Description

Technical Field

[0001] This invention belongs to the field of radio transmission technology and relates to an online evaluation method for dynamic mutual inductance based on a wireless power transmission system. Background Technology

[0002] Wireless Power Transfer (WPT) is a technology that uses spatial electromagnetic fields, microwaves, or other media as energy carriers to transfer electrical energy from a power source to a device without direct contact via wires. It offers advantages such as on-demand charging, no direct contact required, and safety and reliability. Wireless power transfer is currently and will continue to be a hot research area, and it has already been applied in many fields (such as portable electronic devices, electric vehicles, medical devices, and the military). However, traditional wireless charging technologies typically use a "patch-on" charging method, requiring precise alignment of the receiving coil in the charging device with the transmitting coil on the charging pad, greatly limiting the flexibility of charging.

[0003] To improve charging flexibility, omnidirectional wireless power transfer (WPT) technology has emerged. This technology improves the coil structure and circuit topology of traditional "surface-mount" WPT technology, allowing charging devices to achieve greater flexibility during wireless charging. Among these, the omnidirectional WPT system based on three-phase orthogonal transmitting coils is widely studied due to its simple structure and ease of control. This system achieves wireless power transfer to the receiving coil at any position within a certain range by controlling the amplitude, phase, and frequency of the excitation current in the transmitting coil. However, existing omnidirectional WPT systems suffer from inefficient power transfer due to the misalignment of the transmitting and receiving coils. The root cause of this problem is the change in mutual inductance between the coils due to the misalignment, which directly affects the power transfer performance and consequently fails to provide stable and efficient power to the charging device.

[0004] Therefore, accurate estimation of the mutual inductance between the transmitting and receiving coils is a prerequisite for achieving efficient wireless power transmission. Existing mutual inductance estimation methods are either suitable for static mutual inductance estimation or are difficult and prone to large estimation errors for dynamic mutual inductance estimation. To address this, this invention proposes a high-precision online dynamic mutual inductance estimation method that meets the requirements for real-time online estimation of mutual inductance when the load location changes, laying the foundation for improving the efficiency of power transmission in WPT systems. Summary of the Invention

[0005] The purpose of this invention is to provide an online evaluation method for dynamic mutual inductance based on a wireless power transmission system, which solves the problems of high difficulty and large estimation error in existing dynamic mutual inductance estimation methods.

[0006] The technical solution adopted in this invention is a dynamic mutual inductance online evaluation method based on a wireless power transmission system. The wireless power transmission system is a multi-phase synchronous BUCK circuit, and the specific implementation is carried out according to the following steps: Step 1: Obtain the inherent parameters of the wireless power transfer system; Step 2: Set the threshold for DC load voltage change on the receiving coil side and the threshold for load voltage change time, measure the amount of load voltage change and the time interval of the detection voltage, thereby determining whether the position of the receiving coil has changed; Step 3: If the position of the receiving coil remains unchanged, repeat step 2; if the position of the receiving coil changes, sequentially test each phase of the circuit and obtain its mutual inductance coefficient by combining it with the inherent parameters from step 1. Step 4: Evaluate the accuracy of the wireless power transmission system based on the mutual inductance coefficient of each phase circuit obtained in Step 3.

[0007] The invention is further characterized by: The inherent parameters of a wireless power transfer system include LCC-compensated network inductance. L fi Equivalent resistance of receiving coil R RX Load resistance R L value.

[0008] The specific process of step 2 is as follows: Set the threshold value for DC load voltage variation on the receiving coil side according to the inherent parameters of step 1. σ and its load voltage change time threshold ζ The system monitors the DC load voltage on the receiving coil side in real time and determines the change in that load voltage. U out and the time interval of the detection voltage T ,in: (1) (2) In the formula, U out ( t 2) and U out ( t 1) The DC load voltages detected at the current sampling time t2 and the previous sampling time t1 are respectively the DC load voltages on the receiving coil side. U out Voltage amplitude; when U out ≥ σIf the time interval is too short, further determine the relationship between the time interval and the load voltage change time threshold; otherwise, repeat the above steps. T ≥ ζ When this happens, it is determined that the position of the receiving coil has changed.

[0009] Step 3 is as follows: First, the duty cycle of the first phase synchronization BUCK circuit is set to a fixed duty cycle between 0% and 100%, and the DC load voltage amplitude on the receiving coil side is measured. U out and the DC voltage amplitude output by the first phase synchronization BUCK circuit U buck1 The mutual inductance coefficient of the first phase is obtained through the mutual inductance model algorithm. M 1; Then, the duty cycle of the first phase synchronization BUCK circuit is set to 0, and after detecting that its output DC voltage amplitude drops to zero, the duty cycle of the second phase synchronization BUCK circuit is set to a fixed duty cycle between 0% and 100%, and the DC load voltage amplitude on the receiving coil side is detected. U out and the DC voltage amplitude output by the second phase synchronization BUCK circuit U buck2 The mutual inductance coefficient of the second phase is obtained through the mutual inductance model algorithm. M 2; Finally, following the detection process of the second phase, the mutual inductance coefficients of the remaining phase synchronization BUCK circuits are detected in sequence.

[0010] Before implementing step 3, the duty cycle of the synchronous BUCK circuit on the transmitting coil side needs to be set to 0 to ensure that there is no current input to the transmitting coil and the system output voltage is zero.

[0011] The mutual inductance model algorithm is as follows: (3) In the formula, M i Mutual inductance coefficient, U out The DC load voltage on the receiving coil side. R RX The equivalent resistance of the receiving coil, R rec_eq express Figure 2 The equivalent resistance at the dashed box in the circuit shown. L fi To compensate for network inductance, U i This refers to the port output voltage of each phase inverter. U bucki This is the output voltage of the synchronous BUCK circuit.

[0012] The derivation process of the mutual inductance model algorithm is as follows: The output voltage relationship of the synchronous BUCK circuit is as follows: (4) In the formula, D i For the first i The duty cycle of power switch 1 in the synchronous BUCK circuit. i =1, 2, ...; The inverter port input voltage can be obtained using Kirchhoff's voltage law. U i expression: (5) When designing an LCC compensation network, to ensure that the input transmitting coil current is not affected by load changes, the following design principles are typically followed: (6) (7) (8) No. i The induced electromotive force between the transmitting coil and the receiving coil is related to the mutual inductance and induced current between them, where the first... i The induced electromotive force corresponding to each transmitting coil to the receiving coil U TXi_RX and the receiving coil corresponds to the first i The induced electromotive force of each transmitting coil U RX_TXi They are respectively: (9) (10) In equations (9) and (10), I i , I 4 respectively represent the inflow of the first i The current in the transmitting coil and the current induced in the receiving coil; According to Kirchhoff's voltage law, the capacitance in the LCC compensation network can be calculated. C fi Port voltage: (11) The capacitance can be obtained by combining equations (5) to (11). C fi Port voltage: (12) It is known that the current in the transmitting coil is only generated by the inverter port output voltage. U i With compensation network inductanceL fi and system frequency ω The current in the transmitting coil can be obtained from this information: (13) According to Kirchhoff's voltage law, the receiving side can solve for: (14) In the formula, R rec_eq The equivalent resistance can be obtained from the impedance transformation of the full-bridge rectifier: (15) Extending equations (12) and (14) to a three-phase transmitting coil system yields the following equivalent circuit relationship for an omnidirectional WPT system: (16) The current of the receiving coil can be obtained from equation (16): (17) Equation (17) shows that the current in the receiving coil is inextricably linked to the mutual inductance of the three-phase transmitting coils and the current in the transmitting coil. To simplify the mutual inductance estimation model, it is assumed that only one transmitting coil operates at a time. i This work yields a simplified model for estimating mutual inductance coefficients: (18) As can be seen from equation (18), if the mutual inductance coefficient is estimated online using the above model, it is necessary to collect the high-frequency current of the receiving coil and the transmitting coil. However, the system frequency operates at hundreds of kilohertz, or even several megahertz or tens of megahertz, which increases the difficulty of mutual inductance coefficient identification and increases the system hardware cost.

[0013] To solve the above problems, the fundamental frequency analysis method of the circuit is introduced. From the fundamental frequency analysis method, we can see that: (19) In the formula, U i_RMS For the first i Phase inverter output voltage U i The effective value of the fundamental voltage can be obtained, and the first... i RMS value of the current of each transmitting coil I i_RMS for: (20) Based on the voltage division principle of series circuits, the effective value of the input voltage at the port of the synchronous rectifier circuit on the receiving side can be obtained. U rec for: (twenty one) According to the fundamental frequency analysis method, the relationship between the effective value of the input voltage and the output DC voltage of the synchronous rectifier circuit is as follows: (twenty two) By combining equations (19) to (22), the mutual inductance model algorithm can be obtained: (3) In equation (3), U i For the first i Phase inverter port output voltage amplitude, U bucki For the first i Output voltage of the phase pre-stage synchronous BUCK circuit.

[0014] When the multiphase synchronous BUCK circuit obtains the mutual inductance coefficients, the fixed duty cycle is set to 70%.

[0015] The dynamic mutual inductance online estimation method of this invention estimates mutual inductance based on the DC voltage of the load on the receiving coil side, the DC voltage output of the front-stage BUCK circuit on the transmitting coil side, and the inherent parameters of the circuit. This method solves the problem of difficulty in online real-time estimation of mutual inductance changes caused by the movement of the receiving coil in an omnidirectional WPT system. This method does not require detection of high-frequency currents in the transmitting and receiving coils, and has the advantages of simple structure and convenient control. It can ensure accurate online estimation of the mutual inductance between the transmitting and receiving coils when the position of the receiving coil changes in an omnidirectional WPT system, which is beneficial for achieving real-time and efficient power transfer in an omnidirectional WPT system. Attached Figure Description

[0016] Figure 1 This is a schematic diagram showing the relative positions of the transmitting coil and the receiving coil of the WPT system based on a three-phase orthogonal transmitting coil in an embodiment of the present invention; Figure 2 This is the equivalent circuit diagram of the omnidirectional WPT system based on the three-phase LCC-S compensation network in this embodiment of the invention; Figure 3 The circuit equivalent diagram for a single phase in an omnidirectional WPT system; Figure 4 A flowchart for online estimation of dynamic mutual inductance for omnidirectional wireless power transfer systems; Figure 5 The output DC voltage waveform of the three-phase synchronous BUCK circuit during online mutual inductance estimation; Figure 6 The mutual inductance coefficient between transmitting coil 1 and receiving coil when the receiving coil is in position 1. M 1. Simulation estimation results; Figure 7The mutual inductance coefficient between transmitting coil 2 and receiving coil when the receiving coil is in position 1. M 2. Simulation estimation results (figures); Figure 8 The mutual inductance coefficient between transmitting coil 3 and receiving coil when the receiving coil is in position 1. M 3. Simulation estimation results (figures); Figure 9 The mutual inductance coefficient between transmitting coil 1 and receiving coil when the receiving coil is in position 2. M 1. Simulation estimation results; Figure 10 The mutual inductance coefficient between transmitting coil 2 and receiving coil when the receiving coil is in position 2. M 2. Simulation estimation results (figures); Figure 11 The mutual inductance coefficient between transmitting coil 3 and receiving coil when the receiving coil is in position 2. M 3. Simulation estimation results. Detailed Implementation

[0017] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0018] For ease of explanation, the wireless power transmission system in this application adopts a WPT system based on a three-phase quadrature transmitting coil. The basic parameters of the WPT system circuit are shown in Table 1.

[0019] Table 1 Basic Parameters of WPT System Circuit

[0020] A schematic diagram of the relative positions of the transmitting and receiving coils in a WPT system with three-phase quadrature transmitting coils is shown below. Figure 1 As shown, transmitting coil 1 is located in the XOY plane; transmitting coil 2 is located in the XOZ plane; transmitting coil 3 is located in the YOZ plane; and the receiving coil is located at the center of the transmitting coil, with an elevation angle of [missing information]. δ xy 、 Azimuth angle is .

[0021] The equivalent circuit diagram of the omnidirectional WPT system based on the three-phase LCC-S compensation network is as follows: Figure 2 As shown, where U dc The DC input voltage of the system. I dc This is the DC input current; U 1. U 2. U 3 represents the port output voltage of each phase inverter; U f1 , Uf2 , U f3 These represent the capacitance C in each LCC compensation network. f1 C f2 C f3 The port voltage; I f1 , I f2 , I f3 These represent the port output currents of each phase inverter; , , These represent the current flowing into each phase's transmitting coil; This represents the current induced in the receiving coil; U out For the DC load voltage on the receiving coil side of the system, I out This is the load current; Q bucki_1 , Q bucki_2 ( i= 1, 2, and 3) are the power switches for the three sets of synchronous BUCK circuits; Q i1 ~ Q i4 Power switches for three sets of single-phase bridge inverters; Q rec1 ~ Q rec4 For the power switch of the synchronous rectification circuit on the receiving side; C dc This is a DC power supply input filter capacitor. L buck1 、L buck2 、L buck3 These are the inductors of each phase synchronization BUCK circuit; U buck1 、U buck2 、U buck3 These are the output voltages of the phase synchronization BUCK circuits, respectively. L TX1 、L TX2 、L TX3 These are the inductances of the transmitting coils for each phase; L f1 、C f1 、C 1. The LCC compensation network that constitutes transmitting coil 1 Lf2 、C f2 、C 2 constitutes the LCC compensation network of transmitting coil 2. L f3 、C f3 、C 3 constitutes the LCC compensation network of transmitting coil 3; C 4 is the compensation capacitor for the receiving coil; R TX1 、 R TX2 、R TX3 These are the parasitic resistances of the transmitting coils for each phase; R RX This is the parasitic resistance of the receiving coil; R L This is the equivalent load resistance; R rec_eq The dashed line represents the equivalent resistance of the portion. M 1 、M 2 、M 3 represents the mutual inductance between the transmitting coil and the receiving coil of each phase; M 12 、 M 23 、M 13 This represents the mutual inductance between the transmitting coils of each phase.

[0022] Since the three-phase transmitting coils are orthogonal to each other, the cross-coupling between the transmitting coils can be ignored, therefore the mutual inductance between the three-phase transmitting coils is negligible. M 12 、M 23 、M 13 All can be equivalent to 0.

[0023] To simplify the calculation process, first use Figure 3 Analyze the single-phase circuit: The output voltage relationship of a synchronous BUCK circuit is known: (4) In the formula, D i For the first i The duty cycle of power switch 1 in the synchronous BUCK circuit. i =1, 2, 3.

[0024] The inverter port input voltage can be obtained using Kirchhoff's voltage law. U iexpression: (5) When designing an LCC compensation network, to ensure that the input transmitting coil current is not affected by load changes, the following design principles are typically followed: (6) (7) (8) No. i The induced electromotive force between the transmitting coil and the receiving coil is related to the mutual inductance and induced current between them, where the first... i The induced electromotive force corresponding to each transmitting coil to the receiving coil U TXi_RX and the receiving coil corresponds to the first i The induced electromotive force of each transmitting coil U RX_TXi They are respectively: (9) (10) In equations (9) and (10), I i , I 4 respectively represent the inflow of the first i The current in the transmitting coil and the current induced in the receiving coil.

[0025] According to Kirchhoff's voltage law, the capacitance in the LCC compensation network can be calculated. C fi Port voltage: (11) The capacitance can be obtained by combining equations (5) to (11). C fi Port voltage: (12) It is known that the current in the transmitting coil is only generated by the inverter port output voltage. U i With compensation network inductance L fi and system frequency ω The current in the transmitting coil can be obtained from this information: (13) According to Kirchhoff's voltage law, the receiving side can solve for: (14) In the formula, R rec_eq for Figure 2The equivalent resistance within the dashed box can be obtained from the impedance transformation of the full-bridge rectifier: (15) Extending equations (12) and (14) to a three-phase transmitting coil system yields the following equivalent circuit relationship for an omnidirectional WPT system: (16) The current of the receiving coil can be obtained from equation (16): (17) Equation (17) shows that the current in the receiving coil is inextricably linked to the mutual inductance of the three-phase transmitting coils and the current in the transmitting coil. To simplify the mutual inductance estimation model, it is assumed that only one transmitting coil operates at a time. i This work allows us to obtain a simplified model for estimating mutual inductance coefficients: (18) As shown in equation (17), if the mutual inductance coefficient is estimated online using the above model, it is necessary to collect the high-frequency current of the receiving coil and the transmitting coil. However, the system frequency is running at hundreds of kilohertz, or even several megahertz or tens of megahertz, which increases the difficulty of mutual inductance coefficient identification and increases the system hardware cost.

[0026] To solve the above problems, the fundamental frequency analysis method of the circuit is introduced. From the fundamental frequency analysis method, we can see that: (19) In the formula, U i_RMS For the first i Phase inverter output voltage U i The effective value of the fundamental voltage can be obtained, and the first... i RMS value of the current of each transmitting coil I i_RMS for: (20) Based on the voltage division principle of series circuits, the effective value of the input voltage at the port of the synchronous rectifier circuit on the receiving side can be obtained. U rec for: (twenty one) According to the fundamental frequency analysis method, the relationship between the effective value of the input voltage and the output DC voltage of the synchronous rectifier circuit is as follows: (twenty two) By combining equations (19) to (22), the mutual inductance model can be obtained: (3) In equation (3),U i For the first i Phase inverter port output voltage amplitude, U bucki For the first i Output voltage of the phase pre-stage synchronous BUCK circuit.

[0027] Equation (3) yields an online estimation method for mutual inductance coefficients. This method significantly reduces the difficulty of online estimation of system mutual inductance, and only requires the output DC voltage of the synchronous BUCK circuit. U bucki and the DC load voltage on the receiving coil side of the system U out The detection process eliminates the need for additional sampling circuitry, reducing system hardware costs. Since the sampled values ​​are all DC voltage values, lacking high-frequency AC quantities, the online estimation of the mutual inductance coefficient exhibits low error and high accuracy. In practical system applications, the receiving coil side is typically a charging control system with Bluetooth or WLAN communication capabilities. Because the receiving coil moves relatively slowly, these communication technologies allow the DC load voltage data collected by the receiving coil side to be promptly transmitted to the transmitting coil side control system for mutual inductance estimation. This ensures voltage information exchange between the transmitting and receiving devices, guaranteeing the feasibility of this dynamic online mutual inductance estimation method.

[0028] A specific embodiment of the dynamic mutual inductance online evaluation method based on a wireless power transmission system provided by this invention is as follows: Figure 4 As shown, the specific implementation steps are as follows: Step 1: Determine the inherent parameters of the system, specifically the inductance of the LCC compensation network. L fi Equivalent resistance of receiving coil R RX Load resistance R L These values ​​are easily obtained when designing coils and compensation networks.

[0029] Step 2: Set the threshold for DC load voltage variation on the receiving coil side. σ and its load voltage change time threshold ζ The system monitors the DC load voltage on the receiving coil side in real time and determines the change in that load voltage. U out and the time interval of the detection voltage T ,in: (1) (2) In the formula, Uout ( t 2) and U out ( t 1) The DC load voltages detected at the current sampling time t2 and the previous sampling time t1 are respectively the DC load voltages on the receiving coil side. U out Voltage amplitude.

[0030] Determine the relationship between the change in DC load voltage on the receiving coil side and its load voltage change threshold. When U out ≥ σ Then, further determine the relationship between the time interval and the load voltage change time threshold. T ≥ ζ When this happens, it is determined that the position of the receiving coil has changed.

[0031] Step 3: Determine whether the position of the receiving coil has changed based on Step 2. If the position of the receiving coil has changed, then it is necessary to perform online estimation of the mutual inductance between each transmitting coil and receiving coil of the WPT system at the current position.

[0032] When performing online mutual inductance estimation, the system first sets the duty cycle of the synchronous BUCK circuit on the transmitting coil side to 0 to ensure that there is no current input to the three-phase transmitting coil and the system output voltage is zero.

[0033] To ensure the above operations are completed, the output voltage of the three-phase synchronous BUCK circuit needs to be detected. Once all output voltages are zero, the sequential detection process begins.

[0034] First, set the duty cycle of the first phase synchronization BUCK circuit to a fixed duty cycle between 0% and 100%, such as... Figure 5 As shown, in this embodiment, it is set to 70%, while the amplitude of the DC load voltage on the receiving coil side of the detection system is simultaneously detected. U out and the DC voltage amplitude output by the first phase synchronization BUCK circuit U buck1 The mutual inductance coefficient between transmitting coil 1 and receiving coil is estimated using equation (3). M 1, such as Figure 6 As shown; After the first set of mutual inductance coefficients is successfully estimated, the duty cycle of the first phase synchronization BUCK circuit is set to 0, and after detecting that its output DC voltage amplitude has dropped to zero, the duty cycle of the second phase synchronization BUCK circuit is set to a fixed duty cycle between 0% and 100%. Figure 5 As shown, in this embodiment, it is set to 70%; simultaneously, the detection system receives the DC load voltage amplitude on the coil side. Uout and the DC voltage amplitude output by the second phase synchronization BUCK circuit U buck2 The mutual inductance coefficient between the transmitting coil 2 and the receiving coil is estimated using equation (3). M 2, such as Figure 7 As shown; After the second set of mutual inductance coefficients is successfully estimated, the duty cycle of the second-phase synchronization BUCK circuit is set to 0. Furthermore, after detecting that its output DC voltage amplitude has dropped to zero, the duty cycle of the third-phase synchronization BUCK circuit is set to a fixed duty cycle between 0% and 100%. Figure 5 As shown, in this embodiment, it is set to 70%; simultaneously, the detection system receives the DC load voltage amplitude on the coil side. U out and the DC voltage amplitude output by the third phase synchronous BUCK circuit U buck3 The mutual inductance coefficient between the transmitting coil 3 and the receiving coil is estimated using equation (3). M 3, such as Figure 8 As shown.

[0035] Step 4: After estimating the mutual inductance coefficients between the three-phase transmitting coil and the receiving coil, the system returns to step 2 to perform a new round of detection process to check whether the position of the receiving coil has changed, and evaluates the accuracy of the wireless power transmission system based on the mutual inductance coefficients.

[0036] To verify the accuracy of the evaluation of this invention, the following experiment was designed to simulate and verify the results.

[0037] The dynamic mutual inductance estimation of the omnidirectional WPT system was simulated and verified in MATLAB. The simulation conditions were that the direction of the receiving coil was known, and the theoretical mutual inductance values ​​between each transmitting coil and the receiving coil were obtained through theoretical calculation and used for comparison and analysis with the estimated mutual inductance values. Table 1 shows the specific simulation parameters of the circuit.

[0038] When the receiving coil is set to position 1 (0.3m, 45°, 45°) in the simulation, the theoretical mutual inductance values ​​at position 1 are calculated according to the Neumann formula as follows: M 1 = 2.9627 μH M 2 = 2.3562 μH M = 2.3562μH. The above theoretical mutual inductance coefficient is written into the mutual inductance model in MATLAB as the transmitting coil and receiving coil model at position 1. At this time, according to steps 1 and 2, the voltage sampling stage is entered, and it is determined that the position of the receiving coil has changed from the previous position, and then the mutual inductance estimation stage is entered in step 3.

[0039] After proceeding to step 3, the three synchronous BUCK circuits operate sequentially, and the simulation results are as follows: Figure 5As shown, when the first phase synchronization BUCK circuit is working, the mutual inductance between the transmitting coil 1 and the receiving coil is estimated. M 1. Similarly, the mutual inductance between transmitting coil 2, transmitting coil 3 and receiving coil can be obtained respectively. M 2. M 3. Simulation results are as follows Figures 6-8 As shown. When only one phase of the synchronous BUCK circuit is working, the output voltage of the other two phases of the BUCK is zero. At this time, the estimated mutual inductance values ​​of these two phases tend to infinity. Therefore, when only one phase of the synchronous BUCK circuit is working, the estimated mutual inductance values ​​of the other two phases are set to 0, and finally only the estimated stable mutual inductance values ​​are retained. The estimated mutual inductance values ​​at position 1 are as follows: M 1e =2.943μH M 2e =2.330μH M 3e =2.332μH, such as Figures 6-8 As shown.

[0040] Therefore, the relative error precision between the estimated mutual inductance value at location 1 and the theoretical value is: (twenty three) (twenty four) (25) As can be seen from the relative error of mutual inductance calculated by equations (23) to (25), this mutual inductance estimation method has high accuracy in estimating the mutual inductance between the receiving coil at position 1 and each transmitting coil.

[0041] To further verify the mutual inductance estimation method, the receiving coil was moved to position 2 (0.3m, 30°, 60°). At this point, the theoretically calculated mutual inductance values ​​were respectively... M 1 = 3.2594 μH M 2 = 2.1032 μH M 3 = 1.2946 μH. The simulation yielded the following estimated mutual inductance values ​​at position 2: M 1e =3.233μH M 2e =2.086μH M 3e =1.286μH, such as Figures 9-11 As shown.

[0042] Therefore, the relative error accuracy between the estimated mutual inductance at position 2 and the theoretical value is: (26) (27) (28) As can be seen from the relative error of mutual inductance calculated by equations (26) to (28), this mutual inductance estimation method also has high accuracy in estimating the mutual inductance between the receiving coil at position 2 and each transmitting coil.

[0043] Therefore, the above simulation results demonstrate that the dynamic mutual inductance estimation method used in this invention has high accuracy, which lays a solid foundation for the efficiency optimization control of the omnidirectional WPT system.

Claims

1. A method for online evaluation of dynamic mutual inductance in a wireless power transmission system, wherein the wireless power transmission system is a multi-phase synchronous BUCK circuit, characterized in that, Follow these steps: Step 1: Obtain the inherent parameters of the wireless power transfer system; Step 2: Set the threshold for DC load voltage change on the receiving coil side and the threshold for load voltage change time, measure the load voltage change and the time interval of the detection voltage, and thus determine whether the position of the receiving coil has changed; Step 3: If the position of the receiving coil remains unchanged, repeat step 2; if the position of the receiving coil changes, sequentially test each phase circuit and obtain its mutual inductance coefficient by combining it with the inherent parameters from step 1, specifically: First, the duty cycle of the first phase synchronization BUCK circuit is set to a fixed duty cycle between 0% and 100%, and the amplitude of the DC load voltage on the receiving coil side is measured. U out and the DC voltage amplitude output by the first phase synchronization BUCK circuit U buck1 The mutual inductance coefficient of the first phase is obtained through the mutual inductance model algorithm. M 1; Then, the duty cycle of the first phase synchronization BUCK circuit is set to 0, and after detecting that its output DC voltage amplitude drops to zero, the duty cycle of the second phase synchronization BUCK circuit is set to a fixed duty cycle between 0% and 100%, and the DC load voltage amplitude on the receiving coil side is detected. U out and the DC voltage amplitude output by the second phase synchronization BUCK circuit U buck2 The mutual inductance coefficient of the second phase is obtained through the mutual inductance model algorithm. M 2; Finally, following the detection process of the second phase, the mutual inductance coefficients of the remaining phase synchronization BUCK circuits are obtained by sequentially detecting them. The mutual inductance model algorithm is as follows: （3） In the formula, M i Mutual inductance coefficient, U out The DC load voltage on the receiving coil side. R RX The equivalent resistance of the receiving coil, R rec_eq This represents the equivalent resistance on the receiving side. L fi To compensate for network inductance, U i This refers to the port output voltage of each phase inverter. U bucki The output voltage of the synchronous BUCK circuit is denoted by i, where i is the i-th phase circuit. i =1, 2, ...; Step 4: Evaluate the accuracy of the wireless power transmission system based on the mutual inductance coefficient of each phase circuit obtained in Step 3.

2. The method for online evaluation of dynamic mutual inductance based on a wireless power transmission system according to claim 1, characterized in that, The inherent parameters of the wireless power transmission system include LCC-compensated network inductance. L fi Equivalent resistance of receiving coil R RX Load resistance R L value.

3. The method for online evaluation of dynamic mutual inductance based on a wireless power transmission system according to claim 1, characterized in that, The specific process of step 2 is as follows: Set the threshold value for DC load voltage change on the receiving coil side according to the inherent parameters of step 1. σ and its load voltage change time threshold ζ The system monitors the DC load voltage on the receiving coil side in real time and determines the change in that load voltage. U out and the time interval of the detection voltage T ,in: （1） （2） In the formula, U out ( t 2) and U out ( t 1) The DC load voltages detected at the current sampling time t2 and the previous sampling time t1 are respectively the DC load voltages on the receiving coil side. U out Voltage amplitude; when U out ≥ σ If the time interval is too short, further determine the relationship between the time interval and the load voltage change time threshold; otherwise, repeat the above steps. T ≥ ζ When this happens, it is determined that the position of the receiving coil has changed.

4. The method for online evaluation of dynamic mutual inductance based on a wireless power transmission system according to claim 1, characterized in that, Before implementing step 3, the duty cycle of the synchronous BUCK circuit on the transmitting coil side needs to be set to 0 to ensure that there is no current input to the transmitting coil and the system output voltage is zero.

5. The method for online evaluation of dynamic mutual inductance based on a wireless power transmission system according to claim 1, characterized in that, The derivation process of the mutual inductance model algorithm is as follows: The output voltage relationship of the synchronous BUCK circuit is as follows: （4） In the formula, D i For the first i The duty cycle of power switch 1 in the synchronous BUCK circuit. i =1, 2, ...; U dc This refers to the DC input voltage of the system. The inverter port input voltage can be obtained using Kirchhoff's voltage law. U i expression: （5） in, Output current to the ports of each phase inverter; The parallel compensation capacitor C of each LCC compensation network fi The port voltage; When designing an LCC compensation network, to ensure that the input transmitting coil current is not affected by load changes, the following design principles are typically followed: （6） （7） （8） in, L TXi The inductance of each phase's transmitting coil; The inductance of the receiving coil, These are the series compensation capacitors for each LCC compensation network. C 4 is the compensation capacitor for the receiving coil; No. i The induced electromotive force between the transmitting coil and the receiving coil is related to the mutual inductance and induced current between them, where the first... i The induced electromotive force corresponding to each transmitting coil to the receiving coil U TXi_RX and the receiving coil corresponds to the first i The induced electromotive force of each transmitting coil U RX_TXi They are respectively: （9） （10） In equations (9) and (10), I i , I 4 respectively represent the inflow of the first i The current in the transmitting coil and the current induced in the receiving coil; According to Kirchhoff's voltage law, the parallel compensation capacitors in the LCC compensation network can be determined. C fi Port voltage: （11） in, This represents the parasitic resistance of each phase's transmitting coil; The capacitance can be obtained by combining equations (5) to (11). C fi Port voltage: （12） It is known that the current in the transmitting coil is only generated by the inverter port output voltage. U i With compensation network inductance L fi and system frequency ω The current in the transmitting coil can be obtained from this information: （13） According to Kirchhoff's voltage law, the receiving side can solve for: （14） in, This is the parasitic resistance of the receiving coil; In the formula, R rec_eq The equivalent resistance on the receiving side is obtained through impedance transformation of the full-bridge rectifier: （15） in, R L Equivalent load resistance Extending equations (12) and (14) to a three-phase transmitting coil system yields the following equivalent circuit relationship for an omnidirectional WPT system: （16） The current of the receiving coil can be obtained from equation (16): （17） Equation (17) shows that the current in the receiving coil is inextricably linked to the mutual inductance of the three-phase transmitting coil and the current in the transmitting coil. To simplify the mutual inductance model, it is assumed that only one transmitting coil is working at any given time. i This work yields a simplified model for estimating mutual inductance coefficients: （18） By introducing the fundamental frequency analysis method of the circuit, it can be seen that: （19） In the formula, U i_RMS For the first i Phase inverter output voltage U i The effective value of the fundamental voltage can be obtained simultaneously. i RMS value of the current of each transmitting coil I i_RMS for: （20） Based on the voltage division principle of series circuits, the effective value of the input voltage at the port of the synchronous rectifier circuit on the receiving side can be obtained. U rec for: （21） According to the fundamental frequency analysis method, the relationship between the effective value of the input voltage and the output DC voltage of the synchronous rectifier circuit is as follows: （22） By combining equations (19) to (22), the mutual inductance model algorithm can be obtained: （3） In equation (3), U i For the first i Phase inverter port output voltage amplitude, U bucki For the first i Output voltage of the phase-preceding synchronous BUCK circuit.

6. The method for online evaluation of dynamic mutual inductance based on a wireless power transmission system according to claim 1, characterized in that, When the multiphase synchronous BUCK circuit obtains the mutual inductance coefficients, the fixed duty cycle is set to 70%.

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