A wireless power transmission method for electric vehicles based on a TMR sensor

Abstract

The application provides a two-coil magnetic coupling resonance type wireless power transmission method based on a TMR sensor, which does not need to install an induction coil, but uses a double-layer TMR sensor array capable of reducing the influence of an interference magnetic field to perform magnetic field measurement. First, whether metal foreign matters exist in a charging position is judged, then whether coil mispositioning exists is detected, corresponding metal foreign matter coordinates and mispositioning distance are output, and a driver is helped to judge when to start charging, so that the problem that metal foreign matters and coil mispositioning result in low charging efficiency in the charging process of an electric vehicle at the present stage is solved. The application not only can well realize metal foreign matter detection and coil alignment functions, but also has the advantages of low cost, compact size, high sensitivity and the like, and has the value of popularization and application.

Description

Technical Field

[0001] This invention relates to the field of wireless power transmission and is used to solve the problems of metal foreign objects and coil misalignment during the wireless charging of electric vehicles by using a TMR sensor array. Background Technology

[0002] With the rapid development of smart grids, the structure of power grids is more complex than before. Electricity plays a crucial role in the normal operation and development of all sectors of society, placing higher demands on the stability of the power grid. To ensure power quality, it is essential to detect and monitor important parameters such as current, voltage, and power in the power grid in real time. Traditional electromagnetic current transformers have narrow bandwidths, small dynamic ranges, and cannot measure DC current, thus failing to meet the higher requirements of the power grid for current measurement. To achieve accurate and rapid measurement of various currents in the power system, new current sensors have become a new research hotspot. Among various new current sensors, miniaturization, intelligence, and low cost are the current mainstream development trends.

[0003] In the field of electric vehicle charging technology, there are currently three main methods: slow charging, fast charging, and battery swapping, all of which are essentially wired charging methods. Wired charging methods have drawbacks such as cumbersome operation, the charging stations and charging guns being prone to aging due to long-term exposure to outdoor environments, and the potential danger of electric shock in rainy weather and high-power fast charging situations. Therefore, wireless charging technology, which uses alternating electromagnetic fields instead of conductive wires to transmit energy, has emerged. Wireless power transfer refers to the technology of transferring electrical energy from the power source to the load without using connecting wires, but through other media in space. Wireless power transfer mostly uses electric fields, magnetic fields, microwaves, etc., as spatial transmission media. Wireless power transfer technology makes power transmission more flexible and avoids potential safety problems such as aging power lines and leakage. However, when the coils are misaligned, the energy transfer efficiency will decrease significantly. Therefore, it is necessary to align the transmitter and receiver in a timely manner to obtain high transmission efficiency and reduce unnecessary magnetic leakage.

[0004] In automotive current sensors, Hall effect current sensors combine the advantages of current transformers and shunts with a simpler structure, but they are susceptible to interference and are no longer suitable for the increasingly sophisticated and complex power supply environments of electric vehicles. TMR current sensors eliminate the need for temperature compensation when detecting current, reducing the total temperature drift from 1%~2% to 0.1%~0.2% in environments ranging from -40℃ to 85℃. As a new generation of magnetic sensing elements, compared to Hall effect devices, anisotropic magnetoresistance (AMR), and giant magnetoresistance (GMR), they offer advantages such as low energy consumption, low temperature drift, and high sensitivity, significantly improving the sensitivity and temperature characteristics of current detection. Therefore, they are being used to completely replace Hall effect sensors in the new generation of electric vehicle battery management systems. In practical applications, vehicle parking often involves certain errors. Therefore, for electric vehicle wireless charging systems, it is insufficient to consider only the transmission performance when the two coils are perfectly aligned; it is also necessary to consider situations where the two coils are misaligned or that metal foreign objects obstruct charging. To address this, this invention proposes an electric vehicle detection method in wireless power transfer (WPT) based on a TMR sensor, which includes coil positioning and metal foreign object detection functions. Summary of the Invention

[0005] The purpose of this invention is to provide a two-coil magnetically coupled resonant wireless power transfer system based on a TMR sensor, which aims to overcome the problems of low charging efficiency caused by interference from metal foreign objects and coil misalignment during electric vehicle charging, and to provide a new method for wireless charging systems of electric vehicles to improve current charging efficiency.

[0006] The technical solution provided by this invention is as follows:

[0007] A wireless power transfer method for electric vehicles based on a TMR sensor is available, capable of detecting metallic foreign objects and outputting their location coordinates, and identifying coil misalignment and outputting the coil offset direction and distance. The method includes the following steps:

[0008] Step 1: First, detect the presence of a metallic foreign object: By measuring the secondary magnetic field generated by the metallic foreign object under the excitation of the primary magnetic field of the coil, and using the single-point linear inversion positioning algorithm, the position coordinates of the metallic foreign object from the center of the TMR sensor array are derived. When there is a TMR sensor position output, it is considered that there is a metallic foreign object in the wireless power charging system, and the metallic foreign object is removed according to the position output; otherwise, proceed to the next step. The TMR sensor chip is installed at the center between the transmitting coil and the receiving coil, and is arranged in the middle of the transmitting coil and the receiving coil.

[0009] Step 2: Obtain the reference magnetic flux density when the two coils are aligned: Excite the receiving coil, and according to the parameters of different electric vehicle coil models, obtain the reference magnetic flux density B when the receiving coil is aligned with the transmitting coil in its plane using the Biot-Savart law.z1 ;

[0010] Step 3: Detect whether there is coil misalignment and calculate the misalignment distance: Obtain the TMR sensor output. If the magnetic flux density is not the reference magnetic flux density B... z1 Then, according to the Biot-Savart law, the misaligned magnetic flux density B of the coil can be calculated. z2 The misalignment direction is identified by the position output of the maximum sensor, and the coil misalignment magnetic flux density B is used to determine the direction of the misalignment. z2 Calculate the coil offset distance at this time and park the electric car;

[0011] Step 4: Determine whether to start wireless charging: Since the wireless charging efficiency will drop by more than 40% when the coil misalignment area reaches 50%, the threshold is set to the magnetic flux density when the misalignment area is 10%; when the magnetic flux density deviation value is less than the threshold, the wireless charging system is started.

[0012] The dual-layer ring sensor array contains 6 TMR sensors, with the inner TMR sensor ring having a radius of r and the outer TMR sensor ring having a radius of R.

[0013] The TMR sensors are evenly distributed on the inner and outer rings, with the magnetic sensing axis S direction tangent to the inner and outer rings, and the sensing directions of the inner and outer rings being opposite.

[0014] The TMR sensor's anti-interference function is defined by the magnetic field strengths along the magnetic sensitivity direction at the inner and outer magnetoresistive sensors, respectively:

[0015]

[0016] In the formula, H1 and H2 are the magnetic field strengths generated by the current I at the inner and outer magnetoresistive sensors; H ix The component of the interfering magnetic field in the sensor's sensitive direction is the same as the component of the interfering magnetic field in the sensor's sensitive direction. Since the inner and outer sensors are in opposite sensitive directions, the two sensors produce opposite output results due to the interference magnetic field. By adding the output results of the two sensors, the influence of the interference magnetic field can be approximately eliminated. When the receiving coil and the transmitting coil are aligned, the power transmission efficiency is the highest. Therefore, the TMR sensor double-layer array (2) is arranged between the two coil systems to measure the magnetic field changes caused by the presence of metal foreign objects or coil misalignment between the two coil systems, and output the corresponding position of the metal foreign object and the misalignment distance.

[0017] In step 2, the method for detecting and outputting the location coordinates of a metal foreign object, in order to obtain the output indicating the presence of a metal foreign object between the coils, firstly simplifies the metal foreign object model. When the measurement distance is approximately 2.5 times or more the size of the object being measured, a magnetic dipole model can be used to replace the magnetic object. Therefore, the metal foreign object is simplified to a magnetic dipole with a magnetic moment of m. Under the excitation of the primary magnetic field of the coil, the metal foreign object generates a secondary magnetic field with a magnitude of:

[0018]

[0019] in, The magnetic moment representing a metallic foreign object, The vector representing the metallic foreign object to the center of the TMR sensor array is further expressed as:

[0020] (1)

[0021] In step 2, the method for outputting the position coordinates of the metallic foreign object uses a magnetic gradient tensor, which is a second-order tensor composed of the rates of change of the three orthogonal components of the magnetic field vector in various directions in space, expressed as:

[0022]

[0023] The relationship between the magnetic field vector, magnetic gradient tensor, and distance vector is obtained through a single-point linear inversion positioning algorithm. Substituting (1) into the equation, the distance between the magnetic dipole and the center of the TMR sensor is calculated:

[0024] (2)

[0025] In step 3, the method for identifying coil misalignment and outputting the coil offset direction and distance simplifies the transmitting coil to a coil with a radius of R. f The circular receiving coil is simplified to a circle with a radius of R. r The circle shape simplifies the TMR sensor array to a radius of R. s A circle, in which:

[0026]

[0027] To obtain the coil misalignment output, it is first necessary to obtain the magnetic field distribution under the condition of coil alignment:

[0028] (3)

[0029] in, This represents the vector from the origin Or1 of the receiving coil plane to a current element on the receiving coil. This represents the vector from the origin Or1 of the receiving coil plane to point P on the transmitting coil. This represents the vector from a current element on the receiving coil to point P on the transmitting coil; and Used for calculation ; express The angle between the y-axis and the y-axis; h is the perpendicular distance between the two coils;

[0030] According to the Biot-Savart law, we can obtain P(R) sMagnetic flux density of (0, h):

[0031] (4)

[0032] In step 3, the method for identifying coil misalignment and outputting the coil offset direction and distance considers the case of coil misalignment, where the receiving coil moves from Or1 (0,0,0) to Or2 (a,b,0):

[0033] (5)

[0034] From the above formula The length is calculated as follows:

[0035] (6)

[0036] Based on equations (4)-(6), the magnetic flux density along the z-axis is:

[0037] (7)

[0038] From equations (4) and (7), it can be seen that the magnetic flux density increases with the offset of the receiving coil. Therefore, the position of the maximum sensor output is used to identify the misalignment direction. The offset displacement determines the magnetic coupling strength, which is expressed as the average output of the total sensor:

[0039]

[0040] Where N S Given the number of coil turns and n as the number of sensors, the output of the largest TMR sensor is used to detect the misalignment direction and distance.

[0041] The beneficial effects of this invention are:

[0042] This invention proposes a two-coil magnetically coupled resonant wireless power transfer system based on TMR sensors. The system utilizes a dual-layer TMR sensor array to reduce the influence of interfering magnetic fields. By placing the TMR sensor array between the transmitting and receiving coils, magnetic field measurement is used to output a linear voltage, solving the problem of low charging efficiency caused by metal foreign objects and coil misalignment during current electric vehicle charging processes. Existing metal foreign object detection and coil alignment technologies often require the introduction of induction coils, magnetic induction tomography (MIT) technology, and compensation circuits, resulting in complex manufacturing and high costs. This invention uses only a dual array of six TMR sensors, which not only effectively achieves metal foreign object detection and coil alignment functions but also offers low cost, compact size, and high sensitivity, making it valuable for widespread application. Attached Figure Description

[0043] Figure 1This is a flowchart illustrating the construction of the two-coil magnetically coupled resonant wireless power transfer system based on a TMR sensor according to the present invention.

[0044] Figure 2 This is a physical model of a two-coil system and a TMR sensor, which is an embodiment of the present invention.

[0045] Figure 3 This is a schematic diagram of a multi-turn coil structure wound in a plane.

[0046] Figure 4 This is a schematic diagram of the TMR sensor array arrangement of the present invention.

[0047] Figure 5 The structure and equivalent circuit of the wireless power transmission system of the present invention are shown.

[0048] Figure 6 This is a schematic diagram showing the alignment of the transmitting coil and the receiving coil.

[0049] Figure 7 This is a schematic diagram showing the misalignment of the transmitting coil and the receiving coil.

[0050] Figure 8 This is a magnetic field distribution diagram of a metallic foreign object in an embodiment of the present invention, where the transmitting coil and receiving coil are aligned.

[0051] Figure 9 This is a diagram showing the change in mutual inductance between the transmitting and receiving coils at 0°, as simulated by the present invention.

[0052] Figure 10 This is a diagram showing the change in mutual inductance when the transmitting and receiving coils are misaligned by 45° according to the present invention. Detailed Implementation

[0053] Where appropriate, the same reference numerals are used in the specification to indicate the same features appearing in the embodiments.

[0054] A specific embodiment of a two-coil magnetically coupled resonant wireless power transfer system based on a TMR sensor is shown below. Figure 2 It includes the receiving coil 1, the TMR sensor array 2 and the transmitting coil 3, with the TMR sensor chip mounted on the PCB board at the center between the transmitting coil and the receiving coil.

[0055] The TMR sensor chip is a CT416 series current sensor, which supports 8 current ranges. The integrated current-carrying conductor can handle currents up to 65A and generate current measurements as a linear analog output voltage.

[0056] The transmitting and receiving coils are made of copper, and their operating frequency is 85kHz.

[0057] The transmitting coil and receiving coil are both planar spirals, with the maximum outer diameter D of the transmitting coil. max The minimum inner diameter is 640mm. min 460mm, total number of turns N f It is 8; the maximum outer diameter of the receiving coil is D' max The minimum inner diameter is 340mm. min 260mm, total number of turns N s The value is 7; the coil diameter W is 4mm, the coil turn spacing L is 10mm; the vertical distance h between the two coils is 140mm;

[0058] The TMR sensor array uses a double-layer ring sensor array, with an inner layer sensor radius r of 300 mm and an outer layer sensor radius R of 550 mm. Three TMR sensors are evenly distributed in each layer, one group for the inner and one for the outer layers, for a total of three groups (201-203). The magnetic sensing axis S is tangent to the inner and outer rings, and the sensing directions of the inner and outer layers are opposite. The TMR sensor is located between the transmitting coil and the receiving coil, i.e., 70 mm from the transmitting coil.

[0059] The output of each TMR sensor can be expressed as a linear function:

[0060]

[0061] Among them, V c 5V DC power supply; S is sensor sensitivity; F s F is the sensitivity scaling factor; b The bias voltage factor can be obtained from the TMR sensor parameter table; B is the magnetic flux density to be measured; the output is amplified by an operational amplifier (OP). Finally, the sensor output is sampled by a data acquisition (DAQ) card and displayed in the LabVIEW interface.

[0062] The specific operation process of the specific embodiment is as follows: Figure 1 First, the presence of a metallic foreign object is detected. The secondary magnetic field generated by the metallic foreign object under the excitation of the primary magnetic field of the coil is measured, and the position coordinates of the metallic foreign object from the center of the TMR sensor array are derived by the single-point linear inversion positioning algorithm. When there is a TMR sensor position output, it is considered that there is a metallic foreign object in the wireless power charging system, and the metallic foreign object is removed according to the position output; otherwise, the next step is performed.

[0063] Secondly, the reference magnetic flux density under the aligned state of the two coils is obtained, and the receiving coil is excited. Based on the parameters of different electric vehicle coil models, the reference magnetic flux density B of the receiving coil when its plane is aligned with the transmitting coil is obtained by the Biot-Savart law. z1 ;

[0064] Next, detect whether there is coil misalignment and calculate the misalignment distance, obtain the TMR sensor output, and if the magnetic flux density is not the reference magnetic flux density B... z1 Then, according to the Biot-Savart law, the misaligned magnetic flux density B of the coil can be calculated. z2 The misalignment direction is identified by the position output of the maximum sensor, and the coil misalignment magnetic flux density B is used to determine the direction of the misalignment. z2 Calculate the coil offset distance at this time and park the electric car;

[0065] Finally, to determine whether to start wireless charging, since the wireless charging efficiency will drop by more than 40% when the coil misalignment area reaches 50%, the threshold is set to the magnetic flux density when the misalignment area is 10%; when the magnetic flux density deviation value is less than the threshold, the wireless charging system is started.

[0066] Furthermore, to obtain the output in the presence of a metallic foreign object between the coils, the model of the metallic foreign object is first simplified. When the measurement distance is more than 2.5 times the size of the object being measured, a magnetic dipole model can be used to replace the magnetic object; therefore, the metallic foreign object is simplified to a magnetic dipole with a magnetic moment of m. The metallic foreign object generates a secondary magnetic field under the excitation of the primary magnetic field of the coil, with the magnitude of:

[0067]

[0068] in, The magnetic moment representing a metallic foreign object, The vector representing the metallic foreign object to the center of the TMR sensor array can be further expressed as:

[0069] (1)

[0070] The magnetic gradient tensor is a second-order tensor composed of the rates of change of the three orthogonal components of the magnetic field vector in various directions in space, and is expressed as:

[0071]

[0072] The relationship between the magnetic field vector, magnetic gradient tensor, and distance vector is obtained through a single-point linear inversion positioning algorithm. Substituting (1) into the equation, the distance between the magnetic dipole and the center of the TMR sensor is calculated:

[0073] (2)

[0074] Furthermore, in the problem of coil misalignment, directly modeling a multi-turn planar coil using theory is often quite difficult; therefore, simplification of the multi-turn coil is necessary. This invention simplifies the transmitting coil to a coil with a radius of R. f The circular receiving coil is simplified to a circle with a radius of R. r The circle shape simplifies the TMR sensor array to a radius of R. sA circle, in which:

[0075]

[0076] To obtain the coil misalignment output, it is first necessary to obtain the magnetic field distribution under the condition of coil alignment:

[0077] (3)

[0078] in, This represents the vector from the origin Or1 of the receiving coil plane to a current element on the receiving coil. This represents the vector from the origin Or1 of the receiving coil plane to point P on the transmitting coil. This represents the vector from a current element on the receiving coil to point P on the transmitting coil; and Used for calculation ; express The angle between the y-axis and the y-axis; h is the vertical distance between the two coils.

[0079] According to the Biot-Savart law, we can obtain P(R) s Magnetic flux density of (0, h):

[0080] (4)

[0081] Considering the case of coil misalignment, the receiving coil moves from Or1(0,0,0) to Or2(a,b,0):

[0082] (5)

[0083] From the above formula The length can be calculated as follows:

[0084] (6)

[0085] Based on equations (4)-(6), the magnetic flux density along the z-axis can be derived as follows:

[0086] (7)

[0087] From equations (4) and (7), it can be concluded that the magnetic flux density increases with the offset of the receiving coil, therefore the position of the maximum sensor output can be used to identify the misalignment direction. The offset displacement determines the magnetic coupling strength, which can be expressed as the average output of the total sensor:

[0088]

[0089] Where N SHere, n is the number of turns in the receiving coil, and n is the number of sensors. Therefore, the output of the largest TMR sensor can be used to detect the misalignment direction and distance.

[0090] During the simulation process, the mutual inductance between the transmitting coil and the receiving coil is calculated as follows:

[0091]

[0092] Where U2 is the open-circuit voltage of the receiving coil, I1 is the excitation current of the transmitting coil, and f is the system operating frequency.

[0093] Depend on Figure 8 It can be seen that in this specific implementation case, when there is a metallic foreign object at the operating frequency of 85kHz, the magnetic flux density distribution of the transmitting coil is more uneven. This is because the size of the transmitting coil is larger than that of the receiving coil, making it easier to capture the polarization field, and the influence of the metallic foreign object is more significant.

[0094] Depend on Figure 9 and Figure 10 It can be seen that as the coil misalignment distance increases, the mutual inductance between the transmitting coil and the receiving coil decreases, and the error between the simulation and experimental values ​​is small. When the misalignment distance increases from 0 to 250 mm, the mutual inductance decreases by 14.5 µH at a misalignment angle of 0° and by 14.8 µH at a misalignment angle of 45°. The impact of misalignment distance on charging efficiency is greater than that of misalignment angle.

Claims

1. A wireless power transfer method for electric vehicles based on a TMR sensor, characterized in that, The system can detect metallic foreign objects and output their location coordinates, as well as identify coil misalignment and output the coil offset direction and distance. It includes the following steps: Step 1: First, detect the presence of a metallic foreign object: By measuring the secondary magnetic field generated by the metallic foreign object under the excitation of the primary magnetic field of the coil, and using the single-point linear inversion positioning algorithm, the position coordinates of the metallic foreign object from the center of the TMR sensor array are derived. When there is a TMR sensor position output, it is considered that there is a metallic foreign object in the wireless power charging system, and the metallic foreign object is removed according to the position output; otherwise, proceed to the next step. The TMR sensor chip is installed at the center between the transmitting coil and the receiving coil, and is arranged in the middle of the transmitting coil and the receiving coil. Step 2: Obtain the reference magnetic flux density when the two coils are aligned: Excite the receiving coil, and according to the parameters of different electric vehicle coil models, obtain the reference magnetic flux density B when the receiving coil is aligned with the transmitting coil in its plane using the Biot-Savart law. z1 ; Step 3: Detect whether there is coil misalignment and calculate the misalignment distance: Obtain the TMR sensor output. If the magnetic flux density is not the reference magnetic flux density B... z1 Then, according to the Biot-Savart law, the misaligned magnetic flux density B of the coil can be calculated. z2 The misalignment direction is identified by the position output of the maximum sensor, and by the coil misalignment magnetic flux density B. z2 Calculate the coil offset distance at this time and park the electric car; Step 4: Determine whether to start wireless charging: Since the wireless charging efficiency will drop by more than 40% when the coil misalignment area reaches 50%, the threshold is set to the magnetic flux density when the misalignment area is 10%; when the magnetic flux density deviation value is less than the threshold, the wireless charging system is started. A dual-layer ring sensor array containing 6 TMR sensors, with the inner TMR sensor ring having a radius of r and the outer TMR sensor ring having a radius of R; The TMR sensors are evenly distributed on the inner and outer rings, with the magnetic sensing axis S direction tangent to the inner and outer rings, and the sensing directions of the inner and outer rings being opposite.

2. The method for wireless power transfer in electric vehicles based on a TMR sensor according to claim 1, characterized in that: The TMR sensor's anti-interference function is defined by the magnetic field strengths along the magnetic sensitivity direction at the inner and outer magnetoresistive sensors, respectively: In the formula, H1 and H2 are the magnetic field strengths generated by the current I at the inner and outer magnetoresistive sensors; H ix The component of the interfering magnetic field in the sensor's sensitive direction is the same as the component of the interfering magnetic field in the sensor's sensitive direction. Since the inner and outer sensors are in opposite sensitive directions, the two sensors produce opposite output results due to the interference magnetic field. By adding the output results of the two sensors, the influence of the interference magnetic field can be approximately eliminated. When the receiving coil and the transmitting coil are aligned, the power transmission efficiency is the highest. Therefore, the TMR sensor double-layer array (2) is arranged between the two coil systems to measure the magnetic field changes caused by the presence of metal foreign objects or coil misalignment between the two coil systems, and output the corresponding position of the metal foreign object and the misalignment distance.

3. The method for wireless power transmission in electric vehicles based on a TMR sensor according to claim 1, wherein in step 2, the method for detecting and outputting the location coordinates of a metallic foreign object is characterized in that: To obtain the output with a metallic foreign object between the coils, the model of the metallic foreign object is first simplified. When the measurement distance is more than 2.5 times the size of the object being measured, a magnetic dipole model can be used to replace the magnetic object. Therefore, the metallic foreign object is simplified to a magnetic dipole with a magnetic moment of m. The metallic foreign object generates a secondary magnetic field under the excitation of the primary magnetic field of the coil, the magnitude of which is: in, The magnetic moment representing a metallic foreign object, The vector representing the metallic foreign object to the center of the TMR sensor array is further expressed as: (1)。 4. The method for wireless power transmission in electric vehicles based on a TMR sensor according to claim 3, wherein the method for outputting the position coordinates of the metallic foreign object in step 2 is characterized in that: The magnetic gradient tensor is a second-order tensor composed of the rates of change of the three orthogonal components of the magnetic field vector in various directions in space, and is expressed as: The relationship between the magnetic field vector, magnetic gradient tensor, and distance vector is obtained through a single-point linear inversion positioning algorithm. Substituting (1) into the equation, the distance between the magnetic dipole and the center of the TMR sensor is calculated: (2)。 5. The method for wireless power transfer in electric vehicles based on a TMR sensor according to claim 4, characterized in that: In step 3, the method for identifying coil misalignment and outputting the coil offset direction and distance... The transmitting coil is simplified to a radius of R. f The circular receiving coil is simplified to a radius of R. r The circle shape simplifies the TMR sensor array to a radius of R. s A circle, in which: To obtain the coil misalignment output, it is first necessary to obtain the magnetic field distribution under the condition of coil alignment: (3) in, This represents the vector from the origin Or1 of the receiving coil plane to a current element on the receiving coil. This represents the vector from the origin Or1 of the receiving coil plane to point P on the transmitting coil. This represents the vector from a current element on the receiving coil to point P on the transmitting coil; and Used for calculation ; express The angle between the y-axis and the y-axis; h is the perpendicular distance between the two coils; According to the Biot-Savart law, we can obtain P(R) s Magnetic flux density of (0, h): (4)。 6. The method for wireless power transfer in electric vehicles based on a TMR sensor according to claim 5, characterized in that: In step 3, the method for identifying coil misalignment and outputting the direction and distance of coil offset is as follows: Considering the case of coil misalignment, the receiving coil is moved from Or1 (0,0,0) to Or2 (a,b,0): (5) From the above formula The length is calculated as follows: (6) Based on equations (4)-(6), the magnetic flux density along the z-axis is: (7) From equations (4) and (7), it can be seen that the magnetic flux density increases with the offset of the receiving coil. Therefore, the position of the maximum sensor output is used to identify the misalignment direction. The offset displacement determines the magnetic coupling strength, which is expressed as the average output of the total sensor: Where N S Given the number of coil turns and n as the number of sensors, the output of the largest TMR sensor is used to detect the misalignment direction and distance.

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