A TMR current sensor and design method

Abstract

The application provides a TMR current sensor and a design method, which comprise a magnetic concentrating ring, a feedback coil, a TMR chip, a signal amplification loop, a temperature compensation circuit, a bias zero adjustment circuit and a power supply unit; the input end of the bias zero adjustment circuit is connected with the output end of the TMR chip, and the output end of the bias zero adjustment circuit is connected with the input end of the signal amplification loop; the output end of the signal amplification loop is connected with the feedback coil; the feedback coil is arranged around the magnetic concentrating ring, and the feedback coil, the TMR chip and the signal amplification loop form a closed loop feedback loop; when a current conductor to be measured passes through the magnetic concentrating ring, the feedback coil generates a magnetic field, the magnetic field direction of the magnetic field is opposite to the magnetic field direction generated by the current conductor to be measured, so that the TMR chip works in a zero magnetic field range. The TMR chip is arranged on the side far away from the magnetic concentrating ring of the air gap gap, so that the TMR chip can guarantee good output sensitivity, and the current measurement range of the sensor can be improved.

Description

Technical Field

[0001] This invention relates to the field of power equipment technology, and more specifically, to a TMR current sensor and its design method. Background Technology

[0002] With the development of smart grids and new power systems, higher requirements have been placed on current sensing technology. In addition to single DC, power frequency and inrush currents, complex transient current waveforms have appeared in the power grid, including inrush waveforms superimposed on DC waveforms, or inrush current waveforms superimposed on power frequency currents. It is difficult to meet the technical requirements of power system current measurement using existing single current sensors.

[0003] Traditionally used current sensors mainly include current transformers, Rogowski coils, shunts, Hall effect coils, and various magnetoresistive sensors. Current transformers are primarily used to measure power frequency currents, with a maximum frequency band of 10kHz. Rogowski coils are used to measure changing currents, with an upper frequency limit of up to 100MHz, but their low-frequency cutoff frequency is high, making them unsuitable for measuring DC currents. Shunts require disconnection from the original measurement circuit during measurement, and they generate heat under high current conditions, exhibiting a bandgap effect at high frequencies. Currently, commonly used magnetic sensors include Hall effect current coils, giant magnetoresistive sensors, and tunneling magnetoresistive sensors. Hall effect current coils are generally used to measure DC currents, with an upper frequency limit of up to 100MHz. With a frequency of 100kHz, it cannot measure impulse current. Giant magnetoresistive sensors have the advantages of wide measurement bandwidth and small size, but their magnetic field measurement range is narrow and cannot meet the requirements of large current measurement. In recent years, the application of tunnel magnetoresistive sensors has become more and more widespread. Compared with giant magnetoresistive sensors, their magnetic field measurement range is wider. However, whether it is giant magnetoresistive sensor or tunnel magnetoresistive sensor, the mature products at present are used to measure DC current and AC current. There is currently no mature magnetoresistive sensor product that can measure transient current. There is an urgent need to develop a tunnel magnetoresistive sensor that can measure transient current, so that a single current sensor can measure DC current to transient current.

[0004] Traditional tunnel magnetoresistive (TMR) current sensors often employ multiple TMR chips arranged in a ring. When a magnetic core structure is not used, if the TMR current sensor adopts a closed-loop feedback structure, multiple turns of feedback coils are required to achieve a good negative feedback effect. However, the more feedback coils there are, the larger the inductance and capacitance values ​​of the signal processing circuit become, which seriously affects the measurement bandwidth of the signal processing circuit, leading to distortion of the measurement waveform and severely affecting the measurement accuracy of transient current waveforms. When the TMR current sensor adopts a magnetic core structure, the TMR chip is usually placed at the air gap of the magnetic core opening. However, the magnetic field at the air gap of the magnetic ring is generally strong, and the TMR chip is prone to saturation, resulting in a very narrow measurement current range. Therefore, there is an urgent need to develop a TMR current sensor with a wide current amplitude measurement range and a measurement bandwidth that can cover DC to transient current. Summary of the Invention

[0005] In view of this, the present invention proposes a TMR current sensor and design method, aiming to solve the problem of inaccurate measurement results when existing TMR current sensors measure transient current.

[0006] In one aspect, the present invention proposes a TMR current sensor, comprising: a magnetic ring, a feedback coil, a TMR chip, a signal amplification circuit, a temperature compensation circuit, a bias zero-adjustment circuit, and a power supply unit; wherein,

[0007] An air gap notch is formed on the magnetic ring, and the TMR chip is disposed on the side of the air gap notch away from the magnetic ring;

[0008] The first branch of the power supply unit is connected to the power supply terminal of the temperature compensation circuit, and the output terminal of the temperature compensation circuit is connected to the power supply terminal of the TMR chip.

[0009] The second branch of the power supply unit is connected to the power supply terminal of the signal amplification circuit; the input terminal of the bias zero-adjustment circuit is connected to the output terminal of the TMR chip; the output terminal of the bias zero-adjustment circuit is connected to the input terminal of the signal amplification circuit; and the output terminal of the signal amplification circuit is connected to the feedback coil.

[0010] The feedback coil is wound around the magnetic ring, and the feedback coil, the TMR chip, and the signal amplification circuit form a closed-loop feedback circuit. When the conductor under test passes through the magnetic ring, the feedback coil generates a magnetic field. The direction of the magnetic field is opposite to the direction of the magnetic field generated by the conductor under test, so that the TMR chip operates in the linear magnetic field range.

[0011] Furthermore, in the aforementioned TMR current sensor, the first end of the feedback coil is connected to the output end of the second-stage amplifier circuit in the signal amplification loop, and the second end of the feedback coil is connected in series with a current-limiting resistor and then grounded.

[0012] Furthermore, in the aforementioned TMR current sensor, the signal amplification circuit includes: a first-stage amplification circuit, a filter circuit, and a second-stage amplification circuit connected in sequence; wherein,

[0013] The output voltage of the TMR chip is connected to the input terminal of the first-stage amplifier circuit after being zeroed by the bias zeroing circuit. The output terminal of the first-stage amplifier circuit is connected to the input terminal of the second-stage signal amplifier circuit through the filter circuit.

[0014] Furthermore, in the aforementioned TMR current sensor, the width of the air gap notch on the magnetic ring is 5mm to 10mm.

[0015] Furthermore, in the aforementioned TMR current sensor, the distance between the TMR chip and the notch in the radial direction of the magnetic ring is 1-8 mm.

[0016] Furthermore, in the aforementioned TMR current sensor, the relative permeability of the magnetic ring is less than or equal to 10000.

[0017] Furthermore, in the aforementioned TMR current sensor, the number of turns of the feedback coil is less than or equal to 5 turns.

[0018] Furthermore, the aforementioned TMR current sensor also includes: a shielding housing; wherein,

[0019] The shielding shell has a cavity for accommodating the magnetic ring, the feedback coil, the TMR chip, the signal amplification circuit, the temperature compensation circuit, the closed-loop feedback circuit, and the power supply unit, so as to provide magnetic field shielding and electric field shielding.

[0020] Furthermore, the aforementioned TMR current sensor also includes: a conductor insulation fixing member; wherein,

[0021] The conductor insulation fixing member is sleeved inside the magnetic ring so that the conductor of the current to be measured passes perpendicularly through the center of the magnetic ring.

[0022] Furthermore, in the aforementioned TMR current sensor, the conductor insulation fixing component includes: an insulating post, a clip, and a retaining ring; wherein,

[0023] The insulating post is inserted inside the magnetic ring, and a through hole is provided in the middle of the insulating post for inserting the conductor of the current to be measured.

[0024] An annular groove is provided on the upper side of the insulating column, and the retaining ring is sleeved in the annular groove to be locked with the top of the magnetic ring.

[0025] The buckle is located at the bottom of the insulating post, and the buckle is provided with an annular flange for engaging with the bottom of the magnetic ring.

[0026] On the other hand, the present invention also proposes a design method for a TMR current sensor, comprising the following steps:

[0027] Step 1: Determine the saturation magnetic field value of the TMR chip based on the frequency range of the transient current generated by the conductor under test and the amplitude of the current under test.

[0028] Step 2: Determine the parameters of the magnetic ring based on the saturation magnetic field value of the TMR chip and the operating characteristics of the current conductor under test, set an air gap notch on the magnetic ring, and determine the placement position of the TMR chip relative to the magnetic ring.

[0029] Step 3: Determine the parameters of the feedback coil based on the maximum operating magnetic field value at the location of the TMR chip and the output voltage value of the TMR chip at this time;

[0030] Step 4: Design the bias zeroing circuit, signal amplification circuit, and temperature compensation circuit according to the characteristics of the TMR chip, and determine the type of power supply unit according to the signal amplification circuit and the temperature compensation circuit.

[0031] Step 5: Determine the closed-loop feedback circuit based on the saturation magnetic field value of the TMR chip, the parameters of the feedback coil, and the signal amplification circuit, so that the feedback coil generates a magnetic field with the opposite direction to the magnetic field generated by the conductor of the current under test, ensuring that the TMR chip operates in the linear magnetic field range.

[0032] Furthermore, in the above-described design method for the TMR current sensor, step 2 includes the following steps:

[0033] The material type of the magnetic ring is determined based on the saturation magnetic field value of the TMR chip;

[0034] Based on the rated current value of the conductor under test and the voltage value of the conductor, the minimum distance between the conductor under test and the magnetic ring is determined according to the insulation distance requirements, which corresponds to the minimum inner diameter value r of the magnetic ring;

[0035] The minimum outer diameter R of the magnetic ring and the width X of the air gap are determined based on the minimum inner diameter r and the material type of the magnetic ring.

[0036] The placement position of the TMR chip is determined based on the magnetic field uniformity requirements at the air gap notch of the magnetic ring and within a preset range outside the notch.

[0037] Furthermore, in the above-described design method for the TMR current sensor, step 3 includes the following steps:

[0038] Based on the maximum operating magnetic field value of the TMR chip at its location without a feedback coil and the output voltage value of the TMR chip at that time. U 1 ;

[0039] The maximum current-carrying capacity of the feedback coil conductor is determined based on the wire diameter of the feedback coil. I 1， Based on the output voltage U1 of the TMR chip and the maximum current carrying capacity of the feedback coil wire. I 1 The ratio determines the series resistance value of the feedback coil. R 1;

[0040] Based on the series resistance value of the feedback coil R 1. Gradually increase the number of turns in the winding coil and compare the time parameter difference between the output waveform of the TMR sensor and the measured waveform of the standard sensor. When the error between the two is close to 0, the corresponding number of turns N is the optimal parameter value.

[0041] The TMR current sensor in this invention uses a TMR chip positioned on the side of the air gap away from the magnetic ring. This ensures good output sensitivity of the TMR chip while preventing magnetic field saturation, thus improving the current measurement range of the sensor. The closed-loop feedback circuit ensures that the TMR chip operates near zero magnetic field, preventing magnetic saturation and guaranteeing good frequency response characteristics, enabling accurate measurement of transient currents. Attached Figure Description

[0042] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0043] Figure 1 This is a schematic diagram of the structure of the TMR current sensor provided in an embodiment of the present invention;

[0044] Figure 2 This is a schematic diagram illustrating the positional relationship between the TMR chip and the magnetic ring core in the TMR current sensor provided in this embodiment of the invention.

[0045] Figure 3 This is a schematic diagram of the closed-loop feedback circuit in the TMR current sensor provided in an embodiment of the present invention;

[0046] Figure 4 This is a system schematic diagram of the power supply unit in the TMR current sensor provided in an embodiment of the present invention;

[0047] Figure 5 A cross-sectional view of the insulating fixing member in the TMR current sensor provided in an embodiment of the present invention;

[0048] Figure 6 This is a schematic diagram of the retaining ring in the insulating fastener provided in an embodiment of the present invention;

[0049] Figure 7 A flowchart illustrating the design method of the TMR current sensor provided in an embodiment of the present invention. Detailed Implementation

[0050] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0051] Device Examples

[0052] See Figure 1 and Figure 2 The TMR current sensor of this invention includes: a magnetic ring 1, a feedback coil 2, a TMR chip 3, a signal amplification circuit, a temperature compensation circuit, a bias zero-adjustment circuit, and a power supply unit; wherein,

[0053] The magnetic ring 1 has an air gap notch 11, and the TMR chip 3 is located on the side of the air gap notch away from the magnetic ring 1. The first branch of the power supply unit is connected to the power supply terminal of the temperature compensation circuit. The output terminal of the temperature compensation circuit is connected to the power supply terminal of the TMR chip. The second branch of the power supply unit is connected to the power supply terminal of the signal amplification circuit. The input terminal of the bias zero-adjustment circuit is connected to the output terminal of the TMR chip. The output terminal of the bias zero-adjustment circuit is connected to the input terminal of the signal amplification circuit. The output terminal of the signal amplification circuit is connected to the feedback coil. The feedback coil is wound around the magnetic ring, and the feedback coil, the TMR chip, and the signal amplification circuit form a closed-loop feedback circuit. When the current conductor under test passes through the magnetic ring, the feedback coil generates a magnetic field. The direction of the magnetic field is opposite to the direction of the magnetic field generated by the current conductor under test, so that the TMR chip operates in the linear magnetic field range.

[0054] Specifically, the air gap 11 penetrates the magnetic ring body, forming a channel that runs through the hollow part of the magnetic ring and the outside of the magnetic ring. The air gap 11 on the magnetic ring enables the TMR chip to measure the magnetic field generated by the conductor under test, while also ensuring the shielding effect of the TMR current sensor and the sensitivity of the output signal.

[0055] The width X of the air gap notch 11 can be 5-10 mm, preferably 8 mm. This distance ensures that the operating magnetic field range of the TMR chip located outside the air gap is within its linear operating magnetic field range.

[0056] In this embodiment, the relative permeability of the magnetic ring is less than or equal to 10000, which ensures that the magnetic field at the air gap of the magnetic ring is not greater than the saturation magnetic field of the TMR chip, thereby improving the measurement current range of the TMR current sensor.

[0057] To ensure high sensitivity of the output signal of the tunnel magnetoresistive sensor, a two-stage signal amplification circuit is used in the signal processing loop. Specifically, the signal amplification loop includes a first-stage amplification circuit, a filter circuit, and a second-stage amplification circuit connected in sequence. The measurement signal from the TMR chip is zeroed by the bias zeroing circuit and then connected to the input terminal of the first-stage amplification circuit. The output terminal of the first-stage amplification circuit is connected to the input terminal of the second-stage amplification circuit through the filter circuit.

[0058] In this embodiment, the power supply terminals of both the first-stage and second-stage signal amplification circuits are connected to the second branch of the power supply unit to operate using the electrical energy provided by the power supply unit. The input terminal of the second-stage amplification circuit is connected to the output terminal of the filter circuit, which amplifies the power of the output signal of the first-stage signal amplification circuit.

[0059] The output signal of the TMR chip is amplified in two stages, with one path connected to the waveform measurement device and the other path connected to the feedback coil.

[0060] Preferably, the second-stage amplifier circuit uses a push-pull output circuit to avoid the signal amplification loop reducing the bandwidth of the sensor.

[0061] Combination Figure 1 and Figure 3 The TMR chip, signal amplification circuit, and feedback coil form a closed-loop feedback circuit. The voltage between the input terminal of the closed-loop feedback circuit and the current-limiting resistor is proportional to the current-carrying capacity of the conductor under test.

[0062] In this embodiment, a feedback magnetic field is generated by a feedback coil to counteract the external magnetic field, thereby reducing the actual working magnetic field of the sensor and making it work near zero magnetic field, thus improving the linearity and measurement range of the sensor. The magnitude of the feedback magnetic field is equal to the magnitude of the measured magnetic field, and its actual magnitude can be determined by the magnitude of the measured feedback current.

[0063] from Figure 3 As can be seen from this, when the current i1 of the conductor under test changes, the magnetic field strength inside the magnetic ring generates a corresponding variable ΔH. The TMR chip senses the change ΔH, and a corresponding differential change ΔV is generated between its output pins 2 and 4. The input A1 of ΔV generates an output voltage V1 (corresponding to ground potential) corresponding to ΔH.

[0064] V1 is phase-shifted and amplified by A1 to output A2. After power amplification, it is output to the feedback coil w to form a secondary ampere-turn coil w.i w i The generated feedback magnetic field balances with the measured magnetic field ΔH of i1, and the current-limiting resistor R is adjusted. B The resistance value can supply the output voltage V out The required value is reached, thereby generating the magnetic field corresponding to the feedback current i2.

[0065] More specifically, the first end of the feedback coil is connected to the output of the second-stage amplifier circuit in the signal amplification loop, and the second end of the feedback coil is connected in series with the current-limiting resistor.

[0066] In this embodiment, preferably, the number of turns of the feedback coil 2 is less than or equal to 5 turns. When the TMR chip is placed 5mm away from the outside of the air gap 11 of the magnetic ring, the closed-loop feedback effect can be achieved with only a few turns of the feedback coil. The introduction of the feedback coil 2 will increase the inductance and capacitance values ​​in the TMR current sensor circuit. Minimizing the number of turns of the feedback coil can reduce the influence of stray capacitance and stray inductance on the TMR current sensor and ensure the working bandwidth range of the signal processing circuit.

[0067] Continue reading Figure 1 Since TMR chips are sensitive to temperature, the addition of a temperature compensation circuit can ensure that TMR chips can operate within a wide temperature range.

[0068] See Figure 4 To avoid interference from the power supply system to the signal processing circuit, the power supply unit is powered by a 12V lithium battery. In this embodiment, after the power supply unit is powered by the 12V lithium battery, it is filtered and conditioned to convert it into multiple voltage signal outputs to power the temperature compensation circuit, the TMR chip, the first-stage signal amplification circuit, and the second-stage signal amplification circuit, respectively.

[0069] It is evident from the above that the TMR current sensor provided in this embodiment, by placing the TMR chip on the side of the air gap notch away from the magnetic ring, can ensure good output sensitivity of the TMR chip and avoid magnetic field saturation of the TMR chip, thereby improving the current measurement range of the sensor. The use of a closed-loop feedback circuit ensures that the TMR chip operates near the 0 magnetic field range, avoiding magnetic saturation of the TMR chip and ensuring good frequency response characteristics of the TMR current sensor, enabling accurate measurement of transient current.

[0070] To further reduce the operating magnetic field value of the TMR chip, the distance d between the TMR chip and the notch in the radial direction of the magnetic ring is 1-8 mm; preferably 5 mm.

[0071] In the above embodiments, the current-limiting resistor and the number of coil turns connected in series with the feedback coil need to be matched with the position of the conductor of the current to be measured from the TMR chip. Reducing the current-limiting resistor and increasing the number of coil turns can increase the magnitude of the reverse magnetic field of the feedback, and vice versa. The final effect is to make the TMR chip operate in the 0 magnetic field range and the current sensor have good measurement bandwidth.

[0072] To prevent the conductor of the current under test from becoming eccentric and affecting the measurement accuracy of the TMR current sensor, the above embodiments further include: a conductor insulation fixing member 4; wherein, the conductor fixing member is sleeved inside the magnetic ring to allow the conductor of the current under test to pass perpendicularly through the center of the magnetic ring.

[0073] For further details, please refer to [link / reference]. Figure 5 and Figure 6 The conductor insulation fixing component 4 includes: an insulating post 41, a buckle 42, and a retaining ring 43; wherein, the insulating post 41 passes through the interior of the magnetic ring 1, and the insulating post 41 has a through hole in the middle for passing through the conductor of the current to be measured; an annular groove 411 is provided on the upper side of the insulating post 41, and the retaining ring 43 is sleeved in the annular groove for locking with the top of the magnetic ring; the buckle 42 is located at the bottom of the insulating post 41, and an annular flange 421 is provided on the buckle 42 for locking with the bottom of the magnetic ring.

[0074] Specifically, the retaining ring 43 can be a ring structure with a notch along the radial direction.

[0075] The diameter D1 of the insulating post is slightly smaller than the inner diameter of the magnetic ring, the diameter D2 of the buckle is slightly larger than the inner diameter of the magnetic ring, the diameter D3 of the through hole is slightly larger than the diameter of the conductor to be tested, the inner diameter of the retaining ring is D1-2×H1 (depth of the annular groove), and the outer diameter of the retaining ring is slightly larger than D1.

[0076] The above embodiments further include: a shielding shell (not shown in the figure); wherein the shielding shell has a cavity for accommodating the magnetic ring, the feedback coil, the TMR chip, the signal amplification circuit, the temperature compensation circuit, the closed-loop feedback circuit, and the power supply unit.

[0077] Specifically, the magnetic ring, the feedback coil, the TMR chip, the signal amplification circuit, the temperature compensation circuit, the closed-loop feedback circuit, and the power supply unit are all placed inside the shielding shell to ensure the shielding effect of electric and magnetic fields.

[0078] Specifically, the shielding shell can be made of a composite material of metallic and ferromagnetic materials. Preferably, the shielding shell includes a permalloy layer and an aluminum alloy layer; wherein the permalloy layer is located in the inner layer and the aluminum alloy layer is located in the outer layer. The shape of the shielding shell can be determined according to the actual situation, and this embodiment does not impose any limitations on it. The shielding shell in this embodiment has both electrical and magnetic shielding functions.

[0079] In summary, the sensor of this invention adopts a magnetic ring structure with an air gap. To avoid saturation of the TMR chip, the TMR chip is placed at a predetermined distance from the outer diameter of the magnetic ring. This ensures good output sensitivity of the TMR chip while preventing magnetic field saturation, thus improving the current measurement range of the sensor. Temperature compensation control is implemented in the power supply stage to ensure that the TMR sensor can operate within a wide temperature range. The overall circuit adopts a closed-loop feedback structure to ensure that the TMR chip operates near zero magnetic field, avoiding magnetic saturation. Placing the TMR chip at a certain distance from the opening of the magnetic ring and adjusting the number of feedback coils ensures small stray capacitance and stray inductance, guaranteeing good frequency response characteristics of the TMR current sensor. A shielding shell composed of metal and magnetic materials is designed to protect the TMR chip from interference by external magnetic fields and to protect the signal processing circuit from interference by external electric fields.

[0080] Method Implementation Examples:

[0081] See Figure 7 On the other hand, the present invention also provides a design method for a TMR current sensor, comprising the following steps:

[0082] Step S1: Determine the saturation magnetic field value of the TMR chip based on the frequency range of the transient current generated by the conductor under test and the amplitude of the current under test.

[0083] Specifically, the model of the TMR chip in the TMR current sensor is determined according to the amplitude and frequency range of the transient current to be measured. When the upper limit frequency of the measured current waveform is higher, the resistance value of the corresponding TMR chip should be smaller. While ensuring the frequency range meets the requirements, a chip with a large saturation magnetic field value and a high output sensitivity coefficient should be selected as much as possible. In this embodiment, the saturation magnetic field value is the maximum value of the linear magnetic field range.

[0084] Step S2: Determine the parameters of the magnetic ring based on the saturation magnetic field value of the TMR chip and the operating characteristics of the current conductor under test, set an air gap notch on the magnetic ring, and determine the placement position of the TMR chip relative to the magnetic ring.

[0085] Specifically, a magnetic ring can increase the operating range of the TMR chip's magnetic field and increase the chip's output voltage signal. The farther the TMR chip is from the magnetic ring, the weaker the magnetic field, allowing for a higher relative permeability of the magnetic ring. Conversely, if the TMR chip is close to the magnetic ring, for the same saturated magnetic field range, a magnetic ring with a lower relative permeability must be selected. In practice, when the measured current is constant, the magnetic field at a certain distance from the conductor can be calculated. Adding a magnetic ring increases the field strength due to its high permeability, but the magnetic field value cannot exceed the saturated magnetic field value of the TMR chip; otherwise, it will affect the chip's measurement accuracy. This allows us to determine the relative permeability of the magnetic ring and, consequently, its material type.

[0086] In practice, the relative permeability of the magnetic ring is determined based on the saturation magnetic field value of the TMR chip;

[0087] To reduce measurement errors, the magnetic ring should be made of a soft magnetic material with high initial permeability and easy demagnetization, with a relative permeability not exceeding 10000. Based on this, a suitable magnetic ring material is determined. The minimum distance between the conductor and the magnetic ring is determined according to the rated current value of the conductor under test, the voltage value of the conductor, and the required insulation distance. This corresponds to the minimum inner diameter value r of the magnetic ring. Based on the determined inner diameter value r and the type of magnetic ring material, the minimum outer diameter value R and the maximum opening size distance X required for a uniform magnetic field at the open air gap are calculated and analyzed in simulation software. The specific determination method is as follows:

[0088] 1) The larger the outer diameter R of the magnetic ring, the more uniform the magnetic field should be at the gap of the magnetic ring. However, considering the size limitation of the TMR current sensor, R should be minimized as much as possible. In the electromagnetic simulation calculation software, the outer diameter of the magnetic ring is first set to the initial value R0, and the corresponding opening size distance is set to the initial value X0. The outer diameter is gradually increased with the same step size. Under each corresponding size, the uniformity of the magnetic field at the air gap of the magnetic ring opening and at a certain distance away from the center of the conductor is recorded. The uniformity of the magnetic field is the deviation between the maximum magnetic field value and the minimum magnetic field value in the spatial region of interest. The smaller the deviation between the maximum magnetic field value and the minimum magnetic field value, the more uniform the magnetic field is. When the outer diameter of the magnetic ring is gradually increased, when the difference between the minimum magnetic field and the maximum magnetic field in this spatial region is less than 10%, the outer diameter of the magnetic ring at this time is taken as the minimum outer diameter.

[0089] 2) The wider the gap of the magnetic ring, the less uniform the magnetic field at the gap. However, the wider the gap, the stronger the magnetic field outside the gap. Therefore, the maximum gap width should be determined to ensure the uniformity of the magnetic field. First, set the opening gap size to 1 mm and gradually increase it in 1 mm increments. Once the difference between the minimum and maximum magnetic fields in the calculated area is greater than or equal to 10%, the opening gap at this time is determined as the final opening width X.

[0090] 3) Determine the placement position of the TMR chip based on the magnetic field uniformity requirements at the air gap notch of the magnetic ring and within a preset range outside the notch.

[0091] Specifically, to ensure the uniformity of the magnetic field at the air gap notch of the magnetic ring and within a preset range outside the air gap notch, the height of the magnetic ring can be set to 10mm, thus preventing the sensor size from becoming too large. This preset range refers to the area along the radial direction of the magnetic ring outside the notch. Preferably, the TMR chip is placed at a distance d = (1-8mm) from the notch in the radial direction of the magnetic ring. In this embodiment, when d = 5mm, the magnetic field at the location of the TMR chip is exactly at its saturation magnetic field value when the current conductor under test is at its maximum. This corresponds to the optimal position of the TMR chip, i.e., a distance of 5mm between the TMR chip and the air gap notch in the radial direction of the magnetic ring.

[0092] Step S3: Determine the parameters of the feedback coil based on the maximum working magnetic field value at the location of the TMR chip and the output voltage value of the TMR chip at this time.

[0093] Specifically, the parameters of the feedback coil include: wire diameter, number of turns, and series resistance value.

[0094] To avoid the stray inductance and capacitance parameters of the feedback coil reducing the measurement bandwidth of the TMR current sensor, the number of turns in the feedback coil should be minimized. The number of turns is directly related to the relative permeability of the magnetic core and the position of the conductor being measured relative to the TMR chip. Higher relative permeability of the magnetic core requires fewer feedback turns; the closer the TMR chip is to the opening gap, the more feedback turns are needed. The specific implementation process for determining the number of feedback coil turns and the current-limiting resistor value is as follows:

[0095] a) First, determine the maximum operating magnetic field value of the TMR chip at its location without a feedback coil, and the output voltage value of the TMR chip at this time. U 1;

[0096] b) Determine the series resistance value of the feedback coil R 1. Determine the maximum current-carrying capacity of the feedback coil conductor based on the wire diameter of the feedback coil. I 1，Based on the output voltage U1 of the TMR chip and the maximum current carrying capacity of the feedback coil wire. I 1 The ratio determines the series resistance value of the feedback coil. R 1.

[0097] Specifically, to minimize the vertical height of the TMR current sensor, the diameter of the feedback coil should not be too large; the wire diameter should be selected to be within 0.5mm. When the wire diameter of the feedback coil is 0.5mm, the maximum current-carrying capacity of the feedback coil wire should be determined accordingly. I 1. Based on the output voltage of the TMR chip determined in step a), U Dividing 1 by I1 can preliminarily determine the series resistance value of the feedback coil. R 1. This corresponds to the minimum series resistance value. The smaller the series resistance value, the larger the current in the feedback coil circuit, and the fewer turns are required.

[0098] c) Based on the series resistance value of the feedback coil R 1. Using an experimental verification method, gradually increase the number of turns in the winding coil and compare the time parameter difference between the output waveform of the TMR sensor and the measured waveform of the standard sensor. When the error between the two is close to 0, the corresponding number of turns N is the optimal parameter value. Here, the standard sensor refers to a transient current shunt with accurate and reliable measurement values.

[0099] Step S4: Design a bias zeroing circuit, a signal amplification circuit, and a temperature compensation circuit based on the characteristics of the TMR chip, and determine the type of power supply unit based on the signal amplification circuit and the temperature compensation circuit.

[0100] Specifically, a suitable power source can be selected based on the actual application scenario, such as a 12V lithium battery.

[0101] Step S5: Determine a closed-loop feedback loop based on the saturation magnetic field value of the TMR chip, the parameters of the feedback coil, and the signal amplification circuit. This ensures that the feedback coil generates a magnetic field in the opposite direction to the magnetic field generated by the conductor carrying the current under test, guaranteeing that the TMR chip operates within the linear magnetic field range. For a specific design, refer to the system embodiment described above.

[0102] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A TMR current sensor, characterized in that, include: The system includes a magnetic ring, feedback coil, TMR chip, signal amplification circuit, temperature compensation circuit, bias zero-adjustment circuit, and power supply unit; among which, An air gap notch is formed on the magnetic ring, and the TMR chip is disposed on the side of the air gap notch away from the magnetic ring; The first branch of the power supply unit is connected to the power supply terminal of the temperature compensation circuit, and the output terminal of the temperature compensation circuit is connected to the power supply terminal of the TMR chip. The second branch of the power supply unit is connected to the power supply terminal of the signal amplification circuit; the input terminal of the bias zero-adjustment circuit is connected to the output terminal of the TMR chip; the output terminal of the bias zero-adjustment circuit is connected to the input terminal of the signal amplification circuit; and the output terminal of the signal amplification circuit is connected to the feedback coil. The feedback coil is wound around the magnetic ring, and the feedback coil, the TMR chip and the signal amplification circuit form a closed-loop feedback circuit. When the current conductor under test passes through the magnetic ring, the feedback coil generates a magnetic field. The direction of the magnetic field is opposite to the direction of the magnetic field generated by the current conductor under test, so that the TMR chip operates in the linear magnetic field range. The distance between the TMR chip and the notch in the radial direction of the magnetic ring is 1-8 mm; the relative permeability of the magnetic ring is less than or equal to 10000; the number of turns of the feedback coil is less than or equal to 5. The air gap notch penetrates the magnetic ring body, forming a channel that runs through the hollow part of the magnetic ring and the outside of the magnetic ring; the second-stage amplifier circuit adopts a push-pull circuit output to avoid the signal amplification circuit reducing the bandwidth of the sensor; the power supply unit is powered by a 12V lithium battery, and after filtering and conditioning, it is converted into multiple voltage signals to power the temperature compensation circuit, the TMR chip, the first-stage amplifier circuit and the second-stage amplifier circuit respectively.

2. The TMR current sensor according to claim 1, characterized in that, The first end of the feedback coil is connected to the output of the second stage amplifier circuit in the signal amplification loop, and the second end of the feedback coil is connected in series with a current-limiting resistor and then grounded.

3. The TMR current sensor according to claim 1, characterized in that, The signal amplification circuit includes: a first-stage amplification circuit, a filter circuit, and a second-stage amplification circuit connected in sequence; wherein... The output voltage of the TMR chip is connected to the input terminal of the first-stage amplifier circuit after being zeroed by the bias zeroing circuit. The output terminal of the first-stage amplifier circuit is connected to the input terminal of the second-stage amplifier circuit through the filter circuit.

4. The TMR current sensor according to claim 1, characterized in that, The width of the air gap notch on the magnetic ring is 5mm to 10mm.

5. The TMR current sensor according to claim 1, characterized in that, Also includes: Shielding enclosure; wherein, The shielding shell has a cavity for accommodating the magnetic ring, the feedback coil, the TMR chip, the signal amplification circuit, the temperature compensation circuit, the closed-loop feedback circuit, and the power supply unit, so as to provide magnetic field shielding and electric field shielding.

6. The TMR current sensor according to claim 1, characterized in that, Also includes: Conductor insulation fasteners; among which, The conductor insulation fixing member is sleeved inside the magnetic ring so that the conductor of the current to be measured passes perpendicularly through the center of the magnetic ring.

7. The TMR current sensor according to claim 6, characterized in that, The conductor insulation fixing component includes: an insulating post, a clip, and a retaining ring; wherein... The insulating post is inserted inside the magnetic ring, and a through hole is provided in the middle of the insulating post for inserting the conductor of the current to be measured. An annular groove is provided on the upper side of the insulating column, and the retaining ring is sleeved in the annular groove to be locked with the top of the magnetic ring. The buckle is located at the bottom of the insulating post, and the buckle is provided with an annular flange for engaging with the bottom of the magnetic ring.

8. A design method for a TMR current sensor as described in any one of claims 1 to 7, characterized in that, Includes the following steps: Step 1: Determine the saturation magnetic field value of the TMR chip based on the frequency range of the transient current generated by the conductor under test and the amplitude of the current under test. Step 2: Determine the parameters of the magnetic ring based on the saturation magnetic field value of the TMR chip and the operating characteristics of the current conductor under test, set an air gap notch on the magnetic ring, and determine the placement position of the TMR chip relative to the magnetic ring. Step 3: Determine the parameters of the feedback coil based on the maximum operating magnetic field value at the location of the TMR chip and the output voltage value of the TMR chip at this time; Step 4: Design the bias zeroing circuit, signal amplification circuit, and temperature compensation circuit according to the characteristics of the TMR chip, and determine the type of power supply unit according to the signal amplification circuit and the temperature compensation circuit. Step 5: Determine the closed-loop feedback circuit based on the saturation magnetic field value of the TMR chip, the parameters of the feedback coil, and the signal amplification circuit, so that the feedback coil generates a magnetic field with the opposite direction to the magnetic field generated by the conductor of the current under test, ensuring that the TMR chip operates in the linear magnetic field range.

9. The design method of the TMR current sensor according to claim 8, characterized in that, Step 2 includes the following steps: The minimum distance between the conductor under test and the magnetic ring is determined based on the rated current value of the conductor, the voltage value of the conductor, and the insulation distance requirements. This distance corresponds to the minimum inner diameter value r of the magnetic ring. The minimum outer diameter R of the magnetic ring and the width X of the air gap are determined based on the minimum inner diameter r and the material type of the magnetic ring. The placement position of the TMR chip is determined based on the magnetic field uniformity requirements at the air gap notch of the magnetic ring and within a preset range outside the notch.

10. The design method of the TMR current sensor according to claim 8, characterized in that, Step 3 includes the following steps: When no feedback coil is set on the magnetic ring, determine the maximum working magnetic field value at the location of the TMR chip and the output voltage value U1 of the TMR chip at this time; The maximum current-carrying capacity I1 of the feedback coil wire is determined based on the wire diameter of the feedback coil, and the series resistance value R1 of the feedback coil is determined based on the ratio of the output voltage value U1 of the TMR chip to the maximum current-carrying capacity I1 of the feedback coil wire. Based on the series resistance value R1 of the feedback coil, the number of turns of the winding coil is gradually increased. The time parameter difference between the output waveform of the TMR sensor and the measured waveform of the standard sensor is compared. When the error between the two is close to 0, the corresponding number of turns N of the winding is the optimal parameter value.

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