Current measuring device with Hall sensor
By using a combination of a Hall sensor, an addition circuit, a subtraction circuit, and a voltage-controlled current source in the converter, combined with a ring coil power supply and a DC/DC converter, the problem of electromagnetic interference on the current measurement equipment in the converter is solved, and high-precision and interference-resistant current measurement is achieved, which is suitable for current measurement in the range of 400A to 10kA.
Patent Information
- Application Number
- CN202180051007.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Priority Date
- 2020-08-18
- Filing Date
- 2021-07-14
- Publication Date
- 2025-09-30
- Estimated Expiration
- 2041-07-14
AI Technical Summary
Existing current measurement equipment is susceptible to electromagnetic interference in converters, which affects measurement accuracy and reliability. In particular, it is difficult to achieve high-precision and interference-resistant current measurement in high-current environments.
At least two Hall sensors arranged on a circular track are used, combined with an addition circuit, a subtraction circuit and a voltage-controlled current source, a ring coil power supply device and a DC/DC converter, and an analog electronic circuit to eliminate offset and interference effects to achieve accurate current measurement.
It achieves high-precision measurement of DC and AC current in high current environments, reduces the impact of electromagnetic interference, and reduces power loss. It is suitable for compact current sensor design and meets the space and performance requirements of the converter.
Smart Images
Figure CN115917333B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a current measuring device for generating an output current proportional to a current to be measured. The present invention also relates to a current transformer having such a current measuring device. The present invention also relates to a method for measuring a current to be measured using such a measuring device or using such a current transformer. Background Art
[0002] Numerous current measuring devices are known today. Transformers can be used in a simple manner to measure alternating currents. The current to be measured, flowing through the primary winding, is transferred to the secondary side according to a transformation ratio corresponding to the turns ratio, where a correspondingly smaller current, which is of course proportional to the current to be measured, can be detected and evaluated using a measuring recorder.
[0003] Numerous other measurement methods and devices exist that utilize the magnetic field generated by the current to be measured. These methods and devices can be used to measure both AC and DC currents. A common characteristic of all these arrangements and methods is their extreme sensitivity to interference. Examples of interference include electromagnetic fields, which often occur in large electrical components such as electric drives. In converters, in particular, the high currents introduced can cause electromagnetic interference on current sensors. Furthermore, converter regulation relies on accurate measurement values from the current sensors for reliable and safe regulation, control, and protection of the converter.
[0004] Until now, a lot of space has been available in current transformers for current measurement. In this case, the current transformers are shielded by complex magnetic shields from the influence of external fields that may be generated by the operation of the current transformer. Summary of the Invention
[0005] The invention is based on the object of improving a current measuring device.
[0006] The object is achieved by a current measuring device for generating an output current proportional to a current to be measured, wherein the current measuring device comprises at least two Hall sensors arranged on a circular path, wherein the Hall sensors are oriented identically relative to the center point of the circular path, wherein the current measuring device has an adder circuit for adding the measurement signals of the Hall sensors, wherein the current measuring device has a subtractor circuit for cancelling an offset, wherein the current measuring device has a voltage-controlled current source, wherein the current measuring device has a power supply device with a toroidal coil for supplying the Hall sensors. The present invention is also achieved by a current transformer having such a current measuring device. Furthermore, the present invention is implemented by a method for measuring a current to be measured by means of such a current measuring device or by means of such a current transformer, wherein in a first step, the measurement signals of the Hall sensors are added by means of an adder circuit and a voltage proportional to the current to be measured is generated, wherein in a second step, an offset is subtracted from the voltage proportional to the current to be measured by means of a subtracter circuit, so that a reference voltage is obtained, wherein the voltage proportional to the current to be measured is referenced to a predetermined reference ground, wherein in a third step, an output current having a conversion ratio predetermined for the current to be measured is generated as a function of the reference voltage by means of a voltage-controlled current source.
[0007] Further advantageous embodiments of the invention are described in the dependent claims.
[0008] The present invention is also based on the discovery that current sensors, particularly for use in current transformers, can be improved by arranging their Hall sensors on a circular path, referred to as a circular line, for measuring the magnetic field generated by the current. The Hall sensors are arranged identically relative to the center point. In particular, the Hall sensors are oriented with their sensitive axes tangentially to the circular path.
[0009] Here, the Hall effect sensor is combined with an electronic system consisting of an energy supply, a summing circuit, a subtracting circuit, and a voltage-controlled current source to form a reliable, interference-insensitive, and compact current measuring device. For example, the components can be arranged on a printed circuit board in a space-saving manner.
[0010] For use in many power electronics systems, and also in systems for distributing electrical energy, it is advantageous or necessary for current sensors to be designed as current transformers. This means that the output signal of the current sensor is a current (the so-called secondary current) that is directly proportional to the measured current (primary current). Since this electronically generated secondary current typically reaches values of 1A to 5A and must meet very high requirements in terms of accuracy, frequency response, and robustness against external interference, namely very high magnetic fields, very high demands are placed on the corresponding electrical or electronic circuits.
[0011] A key innovation compared to known current sensors is the use of a toroidal coil for the power supply to generate the supply voltage for the Hall sensor. It has been shown that Hall sensors are typically fed with a voltage that differs from the supply voltage available to the current measuring device. The voltage required for the Hall sensor is generated by means of the power supply. It is important that this voltage does not affect the signal to be measured or the magnetic field associated with the current being measured. In this context, the toroidal coil plays a particularly advantageous role, enabling interference effects between the power supply and the Hall sensor to be avoided or substantially suppressed. Furthermore, the combination of the power supply with a very precise, potential-free, voltage-controlled current source that operates an operational amplifier and a B-type output stage allows for the creation of an interference-insensitive current measuring device suitable for measuring both direct currents and alternating currents according to the current transformer principle. The closed flux routing within the toroidal coil eliminates or at least substantially minimizes any mutual influence between the power supply and the measuring field. The combination of a potential-free, voltage-controlled current source based on an operational amplifier and a B-type transistor output stage enables particularly precise current measurement. Since the Type B output stage is not simply connected in series with the OPV-based voltage-controlled current source, but is optionally provided as a feedback device and thus an integral part of the OPV's control system, a very precise, potential-free, voltage-controlled current source is achieved, which has a very high power-bandwidth product and very good spatial distribution of power losses. This spatial distribution of power losses also allows the size of the circular Hall effect sensors on the circuit board to be reduced to a small size. This enables the creation of a sensor circuit board that can be installed in a space-saving manner in devices, such as converters, thereby meeting customer demands for increasingly smaller dimensions.
[0012] When setting up the magnetic field sensor, it is crucial that it be arranged along a circular line, preferably at uniform angular divisions. Furthermore, the orientation of the Hall effect sensors must be identical when viewed from the center of the circular line. To increase the sensitivity and, therefore, the accuracy of the current measuring device, the sensor's sensitive axis is preferably oriented tangentially to the circular line. An approximation to Ampere's law is generated from the individual signals of the magnetic field sensor via an analog electronic summing circuit, thereby generating a measurement voltage proportional to the current. In a subsequent step, an analog electronic subtraction circuit subtracts the existing offset, thereby referencing the measurement signal to a predetermined reference ground. This signal, or reference voltage, is then converted into an output current with a fixed conversion ratio to the measurement current via the voltage-controlled current source already described. This results in a purely electronic current transformer without active magnetic flux loops. The use of analog circuits eliminates dead time in the system, and the current measuring device operates precisely with respect to the current level and with no, or at least minimal, delay relative to the measurement signal.
[0013] It is particularly advantageous that the proposed current measuring device is suitable for measuring direct currents and alternating currents. Due to the magnetic field and saturation effects used there, previously known transformer converters for implementing the current transformer principle are only suitable for measuring alternating currents.
[0014] Due to their size and the components used, the described device and method are suitable for measuring currents in the order of 400 A to 10 kA.
[0015] Here, the power supply includes a DC / DC (direct current to direct current) converter. Compared to a linear regulator, the use of a DC / DC converter reduces power losses to approximately 30%, thus avoiding heat dissipation issues. Furthermore, the magnetic components required for the DC / DC converter can be incorporated into the current measuring device using a toroidal coil, without unacceptably affecting the magnetic field of the current being measured and, consequently, the measurement result. This results in an inexpensive, reliable, and precise current measuring device.
[0016] Since the entire circuit is exposed to very high magnetic fields and these should not be influenced by the power supply electronics, it is advantageous to design the coils required for the DC / DC converter as toroidal coils that are wound as evenly as possible.
[0017] Furthermore, the toroidal coil has a paramagnetic and / or diamagnetic core. By forming the toroidal coil with a paramagnetic and / or diamagnetic core, interference fields are further reduced and the accuracy of the measuring device is further improved. Although currents can also be measured with sufficient accuracy using ferromagnetic or ferrimagnetic core materials, the accuracy of current measurement can be further improved by using paramagnetic and / or diamagnetic cores. Furthermore, interference-free operation of the DC / DC converter is possible, which would otherwise be impaired by saturation effects of the ferromagnetic or ferrimagnetic core material. Therefore, by combining a ferromagnetic or ferrimagnetic core material with a DC / DC converter, a particularly reliable, interference-resistant, and accurate current sensor can be realized.
[0018] In one advantageous embodiment of the present invention, the current measuring device includes at least eight Hall sensors. Using eight Hall sensors has been shown to achieve a particularly good ratio of useful signal to interference signal. These eight Hall sensors are advantageously arranged at 45° intervals on a circular line, preferably on a printed circuit board. Even if the current to be measured does not extend through the center point of the circular line, the proposed device enables very precise current determination using multiple Hall sensors. The influence of interference variables, such as those caused by external magnetic fields, is thus very small, so that their influence on the measurement result is compensated by the summing circuit. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The present invention will be described and explained in more detail below based on the embodiments shown in the accompanying drawings. The accompanying drawings show:
[0020] Figure 1 Shows a circuit board with eight Hall sensors,
[0021] Figure 2 shows a converter, and
[0022] Figure 3 A simplified diagram for measuring with the aid of a current measuring device is shown. DETAILED DESCRIPTION
[0023] Figure 1 A current measuring device 1 is shown. Hall sensors 2 are arranged on a circuit board 5 along a circular path 21 around a midpoint M. In the exemplary embodiment, eight Hall sensors 2 are used. However, only at least two Hall sensors 2 are required to perform the measurement method using the proposed current measuring device. The more Hall sensors 2 used, the better the measurement results. Eight Hall sensors have proven to be a good compromise between high accuracy and a simple, inexpensive measuring device.
[0024] This allows the measurement of the current I through the area bounded by the circular path 21. In this embodiment, the circuit board 5 is designed as a disk to measure the current through the conductor 7 (not shown here), around which the circuit board 5 can be arranged. The eight Hall sensors 2 are oriented accordingly with respect to the center point M of the circular path 21. An orientation of the Hall sensors 2 with their sensitive axes tangential to the circular path 21 is particularly advantageous.
[0025] In this case, the eight Hall sensors 2 do not have to be distributed equidistantly on the circular trajectory 21. However, this allows accurate measurement of the current I even if the current does not flow through the center point M of the circular trajectory 21. As an output signal, the current measuring device 1 provides a current I proportional to the current I to be measured. Ausg The current is generated by an evaluation unit 6 , which comprises a power supply 10 , an adding circuit 11 , a subtracting circuit 12 and a voltage-controlled current source 13 .
[0026] In this case, the evaluation unit 6 can be arranged on the printed circuit board 5 with the Hall sensor 2 or can be located outside the printed circuit board 6 . Figure 2 The diagram shows a current transformer 4 with the proposed current measuring device 1 for measuring three currents. For this purpose, three circuit boards 5 are arranged around the corresponding conductors 7. For the sake of clarity, the Hall sensors 2 on the circuit boards 5 are not shown. In the exemplary embodiment shown, the evaluation unit 6 is located on the circuit boards 5 within the current transformer 4.
[0027] The circuit boards 5 are each connected to an evaluation unit 6 for transmitting the measurement signals 3 of the Hall sensors 2. This provides corresponding current measurement values with sufficient accuracy for regulating and protecting the current transformer 4. Furthermore, the current measuring device 1 is so robust that it can also be operated without special shielding measures, i.e., in an unshielded manner, within the interior of the current transformer 4 where electrical and / or magnetic interference fields can form.
[0028] Figure 3 A simplified diagram of a method for measuring a current I by means of a current measuring device 1 is shown. To avoid repetitions, reference is made to Figure 1 and Figure 2 Description of and reference numerals introduced therein. Figure 1 The structure of the embodiment of the present invention further comprises eight Hall sensors 2 for detecting the current I. The Hall sensors 2 are supplied with electrical energy by a power supply 10. The measurement signals 3 of the Hall sensors 2 are fed to an adder circuit. The adder circuit adds the measurement signals and generates therefrom a voltage U that is proportional to the current to be measured. An offset is subtracted from the voltage U by means of a subtraction circuit 12. The resulting voltage is then related to a predetermined reference ground. This is also referred to as reference ground, so that the voltage is referred to as a reference voltage U. refThe voltage is then fed to a voltage-controlled current source 13, which converts the reference voltage U ref Converted to output current I Ausg , which is proportional to the current to be measured I. In this case, the adding circuit 11 , the subtracting circuit 12 and the voltage-controlled current source 13 can also be supplied with electrical energy from the power supply device 10 .
[0029] In summary, the present invention relates to a current measuring device for generating an output current proportional to a current to be measured. In order to improve the current measuring device, it is proposed that the current measuring device comprises at least two Hall sensors arranged on a circular trajectory, wherein the Hall sensors are oriented uniformly relative to the center point of the circular trajectory, wherein the current measuring device has an adding circuit for adding the measurement signals of the Hall sensors, wherein the current measuring device has a subtracting circuit for eliminating an offset, wherein the current measuring device has a voltage-controlled current source, wherein the current measuring device has a power supply device with a toroidal coil for powering the Hall sensors, wherein the power supply device (10) comprises a DC / DC converter, wherein the toroidal coil has a paramagnetic and / or diamagnetic core. The present invention also relates to a converter having such a current measuring device. The present invention also relates to a method for measuring a current to be measured by means of such a current measuring device or by means of such a current transformer, wherein the measurement signals of the Hall sensors are added by means of an adder circuit and a voltage proportional to the current to be measured is generated, wherein an offset is subtracted from the voltage proportional to the current to be measured by means of a subtracter circuit, so that a reference voltage is obtained, wherein the voltage proportional to the current to be measured is referenced to a preset reference ground, and wherein an output current having a conversion ratio preset for the current to be measured is generated as a function of the reference voltage by means of a voltage-controlled current source.
Claims
1. A current measuring device (1) for generating an output current (I) proportional to a current to be measured (I) Ausg ),in, The current measuring device (1) comprises at least two Hall sensors (2) arranged on a circular track (21), wherein the Hall sensors (2) are aligned with respect to a center point (M) of the circular track (21), wherein the current measuring device (1) has an adding circuit (11) for adding the measurement signals (3) of the Hall sensors (2), wherein the current measuring device (1) has a subtraction circuit (12) for eliminating an offset, wherein the current measuring device (1) has a voltage-controlled current source (13), wherein, for powering the Hall sensors (2), the current measuring device (1) has a power supply (10) with a toroidal coil, wherein the power supply (10) comprises a DC / DC converter, wherein the toroidal coil has a paramagnetic and / or diamagnetic core.
2. The current measuring device (1) according to claim 1, wherein The voltage-controlled current source (13) is formed at the base of an operational amplifier having a B-type transistor output stage.
3. The current measuring device (1) according to claim 1 or 2, wherein The current measuring device (1) has at least eight Hall sensors (2).
4. A current transformer (4) having a current measuring device (1) according to any one of claims 1 to 3.
5. A method for measuring a current (I) to be measured, using a current measuring device (1) according to any one of claims 1 to 3 or by means of a current transformer (4) according to claim 4, wherein: In a first step, the measurement signals (3) of the Hall sensors (2) are added by means of an adding circuit (11) and a voltage (U) proportional to the current to be measured is generated, wherein in a second step, an offset is subtracted from the voltage (U) proportional to the current to be measured by means of a subtracting circuit (12), thereby obtaining a reference voltage (U ref ), wherein the voltage (U) proportional to the current to be measured is based on a preset reference ground, wherein, in the third step, according to the reference voltage (U ref ) generates an output current (I) with a conversion ratio preset for a current (I) to be measured by means of a voltage-controlled current source (13) Ausg ).