The present invention relates to a current sensor for detecting an electrical current flow and to a method for detecting an electrical current flow. The invention furthermore relates to a charging control unit for controlling a charging procedure of a battery in a motor vehicle, in particular when charging an electric vehicle. However, the present invention can also be advantageously applied to any other type of direct current measurement.

Monitoring devices having universal-current-sensitive differential current sensors are used, inter alia, in transformerless solar or drive inverters. However, these sensors are also increasingly necessary in the charging infrastructure for electric vehicles or in charging apparatus in general. An important safety function of all these apparatus is the monitoring of the leakage current of the overall system, consisting of photo-voltaic modules or drives and the inverter or the mains connection and a battery.

A faulty system can be hazardous to persons or can cause fires, which is why the appropriate standards stipulate that the inverter or the apparatus itself must disconnect from the mains before it can become hazardous to persons or installations. Leakage currents are unintentional, and therefore uncontrollable, fault currents to earth and contain both direct and alternating current components. Universal-current- sensitive monitoring is therefore necessary, which contains a differential current sensor, the determined measured value of which is transmitted in the form of an output voltage to the control of the inverter and evaluated there.

In general, protective devices having universal-current-sensitive differential current sensors can be used wherever smooth or pulsating direct fault currents can occur, the magnitude of which is constantly greater than zero. Mains adapters or uninterrupted power supplies are mentioned as further examples.

To meet the applicable standards, such as Standard IEC 62752:2016 (Edition 1.0 2016-03), the charging of electric vehicles calls for universal-current-sensitive fault current monitoring to prevent electrical hazards when the car battery (DC) is connected to the domestic installation (AC). In this case, as in systems in general in which AC and DC networks are connected to one another, both direct-current and alternating-current fault currents can occur. Typically, only a circuit breaker of so-called type A is installed in the domestic installation, which can neither detect nor shut down the direct current fault. For the application involving charging an electric vehicle, the use of a so-called type B circuit breaker would be needed to also ensure the desired safety in the event of a direct current fault. By using a differential current sensor in a so-called "In-Cable Control- and Protecting Device" (IC-CPD), which is integrated in a fixed manner in the charging cable, or a wall box, the requirements regarding electrical safety and universal-current fault detection can be fulfilled, and with costs which are considerably reduced over those of a comparable type B circuit breaker. A conventional differential current sensor simultaneously monitors all currents flowing in the phases and in the neutral conductor and detects possible direct and alternating current faults. Depending on the application, in the event of a fault, the sensor can control the shut-down of the system automatically or signal to a superordinate control unit that the switching threshold has been exceeded. Excellent measuring precision is necessary since the fault currents to be measured are very small. Moreover, personal safety calls for the particularly rapid detection and subsequent shut-down of the overall system.

Known differential current sensors are based for example on an arrangement in which a magnetic core having an air gap is arranged around a conductor which is to be monitored. When a current is flowing, a magnetic field is induced, which is guided through the magnetic core. In known arrangements, a Hall element, which generates an output voltage depending on the magnetic field strength, is arranged in the air gap. A compensating winding, which is mounted on the magnetic core, can be provided to increase the measuring precision by electrically compensating the magnetic field generated by the current which is to be monitored and adjusting the zero position of the Hall sensor. The actual output signal represents the required current in the compensating winding. Alternatively, so-called GM sensors are also used, which detect the magnetic field via the GM R effect (giant magnetoresistance). It is furthermore known to use so-called flux gate sensors for measuring the magnetic field generated by the current flow. In the case of the latter method, a primary coil is wound around the magnetic core and controlled by an alternating current. An output signal, which is dependent on the current flow which is to be measured, is picked up by means of a secondary pickup coil. However, it is disadvantageous that the known differential current sensors for fault current detection, in particular when integrated in a charging cable, are too expensive and complex and have too high an energy consumption.

There is therefore a demand for a current sensor for detecting an electrical current flow which overcomes the disadvantages of the known solutions, whilst being safe and reliable and yet still economical to produce. This object is achieved by the subject matter of the independent claims. Advantageous embodiments of the present invention are the subject matter of the dependent claims.

In this case, the present invention is based on the idea of detecting the magnetic field induced by a direct current flow by means of two acceleration sensors (also identified below as accelerometers). In this case, only one of the two acceleration sensors is magnetically active, whereas the other does not react to the magnetic field but is otherwise constructed identically. As is essentially known, miniaturised micromechanical acceleration sensors possess, for example, a movable electrode, which is mounted on the so-called seismic mass, and at least one fixed external electrode. A displacement of the seismic mass is detected via a change in capacitance between the movable electrode and the at least one fixed external electrode. According to the present invention, the seismic mass of the first acceleration sensor is magnetically inactive, whereas the seismic mass of the second acceleration sensor is magnetically active. Therefore, only the seismic mass of the second acceleration sensor reacts to a magnetic field, so that only the seismic mass of the second acceleration sensor is displaced by the induced magnetic field and causes a sensor signal. The first acceleration sensor is otherwise constructed identically, but is not sensitive to the magnetic field.

According to the present invention, a current sensor for detecting an electrical current flow comprises a magnetic core, which can be arranged around at least one electrical conductor so that an electrical current flow through the conductor generates a magnetic field that is guided in the magnetic core.

The current sensor has a first acceleration sensor having a movable first seismic mass, wherein the first acceleration sensor can be operated to generate a first sensor signal depending on a displacement of the first seismic mass. The current sensor further has a second acceleration sensor having a movable second seismic mass, wherein the second acceleration sensor can be operated to generate a second sensor signal depending on a displacement of the first seismic mass, wherein the first and the second acceleration sensor are arranged so that the first and the second seismic mass can at least partly be penetrated by the magnetic field guided in the magnetic core, and wherein the second seismic mass is provided with a magnetically active element, by means of which the second seismic mass is displaceable in response to the magnetic field guided in the magnetic core so that a difference between the first sensor signal and the second sensor signal forms an output signal depending on the electrical current flow through the conductor. Such an arrangement offers the advantage that, by calculating the difference, interferences from the environment, for example vibrations, thermal influences or the gravitational field, can be eliminated without difficulty. By using a highly sensitive magnetic field detector, costly coil windings that consume a great deal of energy become redundant.

In this case, the magnetic activation of the second seismic mass can take place in various ways. On the one hand, the second acceleration sensor can have a coil arrangement, which is arranged on the second seismic mass so that a second magnetic field is generated when the coil arrangement is energised. In the case of a micromechanically produced acceleration sensor, this can be, for example, a flat coil applied to the movable seismic mass. Alternatively or also additionally, the second acceleration sensor can also have a permanent magnetic element, which is arranged on the second seismic mass.

The advantage of the permanent magnetic element is that a current supply is not required for the magnetic activation of the second seismic mass. In contrast, the solution, which uses an excitation coil, is effective without using permanent magnetic materials which are expensive and unfamiliar to the production process, such as rare earth elements (e.g. neodymium or samarium). However, it is clear to the person skilled in the art that each of the two solutions for magnetic activation of the second seismic mass can be used equally and that a combination of a permanent magnetic material and a coil arrangement is also possible.

So that efficient suppression of the interferences can take place, the first and the second seismic mass should advantageously have an identical weight and only differ in terms of their magnetically inactive or magnetically active nature. According to an advantageous embodiment, the current sensor further comprises an evaluation device which is connected to the first and the second acceleration sensor to calculate an output signal of the current sensor from the first sensor signal and the second sensor signal. The evaluation device can advantageously be monolithically integrated together with the first and second acceleration sensor. However, a separate circuit arrangement can of course also be provided.

According to an advantageous embodiment, the magnetic core has an air gap and the first acceleration sensor and the second acceleration sensor are arranged in the air gap. In particular through the integration of micromechanical systems at chip level, both accelerometers together with the evaluation electronics can be integrated on a chip and accommodated in the air gap of the magnetic core. This enables particularly economical production. For example, the magnetic core has an annular configuration and the air gap radially divides the magnetic core, wherein the first acceleration sensor and the second acceleration sensor are arranged radially offset from one another in the air gap. However, the magnetic core can also have any other suitable contour, for example a rectangular or even an irregularly-shaped configuration so long as the magnetic circuit is closed in a suitable manner and the magnetic field is guided sufficiently through the first and second acceleration sensor. The first and the second acceleration sensor are advantageously formed by microlectromechanical accelerometers. As already mentioned, the first and the second acceleration sensor can be formed as an integrated magnetic field detection unit which moreover also comprises evaluation electronics. However, two separate components can of course also be used. Each of the acceleration sensors can be based on the displacement of a resiliently suspended seismic mass, wherein the change in capacitance of one or more sides of the mass with respect to a stationary electrode is detected. Such an arrangement can be produced at particularly low cost.

According to the invention, the first acceleration sensor has at least one first fixed electrode for capacitively detecting the displacement of the first seismic mass and the second acceleration sensor has at least one second fixed electrode for capacitively detecting the displacement of the second seismic mass, wherein, in each case, corresponding counter electrodes are arranged on the seismic mass.

The magnetic core is advantageously produced from a magnetically soft (ferromagnetic) material with high relative permeability It is thus possible to achieve the most efficient possible amplification and guidance of the magnetic field generated by the current which is to be detected. Possible materials are, for example, alloys of iron, cobalt and/or nickel. The present invention can advantageously be used in a charging control unit for an electric vehicle. Such a charging control unit can be arranged for controlling a charging process of a battery in a motor vehicle. Alternatively, the present invention can be used particularly advantageously in a charging cable for connecting a battery of a motor vehicle to a voltage source, wherein the charging cable has a charging control unit with a monitoring device according to the invention. The present invention moreover relates to a method for detecting an electrical current flow, wherein the method comprises the following steps: arranging a magnetic core around at least one electrical conductor so that an electrical current flow through the conductor generates a magnetic field guided in the magnetic core, detecting a first sensor signal, which is generated by a first acceleration sensor having a movable first seismic mass, wherein the first acceleration sensor is arranged so that the first seismic mass is at least partly penetrated by the magnetic field guided in the magnetic core, and wherein the first sensor signal is generated depending on a displacement of the first seismic mass, detecting a second sensor signal, which is generated by a second acceleration sensor having a movable second seismic mass, wherein the second acceleration sensor is arranged so that the second seismic mass is at least partly penetrated by the magnetic field guided in the magnetic core, and wherein the second sensor signal is generated depending on a displacement of the second seismic mass, calculating a difference between the first sensor signal and the second sensor signal, wherein the second seismic mass is provided with a magnetically active element by means of which the second seismic mass is displaceable in response to the magnetic field guided in the magnetic core so that the difference between the first sensor signal and the second sensor signal forms an output signal depending on the electrical current flow through the conductor.

If the magnetic activation of the second seismic mass takes place via a coil arrangement which is arranged on the second seismic mass, the method further comprises the step of applying an electrical control current to the coil arrangement, which is arranged on the second seismic mass so that a second magnetic field is generated when the coil arrangement is energised. The second acceleration sensor alternatively or additionally has a permanent magnetic element, which is arranged on the second seismic mass. The current sensor according to the invention is particularly suitable for the differential current measurement described in the introduction. In this case, to carry out the differential current measurement, the magnetic core is arranged around at least two electrical conductors through which currents with different current directions flow.

For better understanding of the present invention, it is explained in more detail with reference to the exemplary embodiments illustrated in the following figures. In this case, the same parts are provided with the same reference numerals and the same component names. Furthermore, some features or feature combinations of the different embodiments shown and described can also represent solutions which are themselves independent, innovative or inventive. The figures show:

Fig. 1 a schematic illustration of a current sensor according to a first advantageous embodiment of the present invention;

Fig. 2 a schematic illustration of a first magnetic field detection device, which can be used in Fig. 1;

Fig. 3 a schematic illustration of a second magnetic field detection device, which can be used in Fig.

1; Fig. 4 a schematic illustration of a current sensor according to the present invention, operated as a differential sensor.

The present invention will explain the current sensor according to the invention in greater detail hereinafter, with reference to the figures and, in this case, in particular initially with reference to Figure 1.

In the arrangement shown, a current sensor 100 according to the present invention is arranged on an electrical conductor 102 so that a magnetic field induced around the conductor by a current flow I can be detected. The strength of the magnetic field gives information relating to the current strength of the current I flowing through the electrical conductor 102. The current sensor 100 has a magnetically soft magnetic core 104, illustrated schematically as an annulus. The magnetic core has an air gap 106 and forms an otherwise closed magnetic circuit around the electrical conductor 102. According to the invention, a magnetic field detection unit 108 is arranged in the air gap 106, which measures the magnetic field strength in the air gap 106.

As illustrated schematically in Figure 1, the magnetic field detection unit 108 according to the present invention comprises a first acceleration sensor 110 and a second acceleration sensor 112. The two acceleration sensors 110, 112 are formed by a micromechanical accelerometer, known per se, which each have a resiliently supported seismic mass. The displacement of each seismic mass is conventionally measured by means of a change in capacitance. To this end, the resiliently suspended seismic mass carries at least one first electrode, the capacitance of which is measured with respect to a corresponding counter electrode mounted in a fixed manner on the sensor. The two acceleration sensors 110, 112 can be realised for example as an integrated magnetic field detection unit 108 at chip level, evaluation electronics being likewise integrated in the chip.

The first acceleration sensor 110 is magnetically inactive and does not react to a magnetic field which may be present in the magnetic core 104. In contrast, the second acceleration sensor 112 is

magnetically active so that its seismic mass is displaced by a magnetic field present in the magnetic core 104. The displacement of the second seismic mass of the second acceleration sensor 112 results in a sensor signal, whilst the first acceleration sensor 110 does not deliver a magnetic-field-induced output signal. However, both acceleration sensors 110, 112 are subject to the same interfering environmental influences, such as temperature fluctuations and vibrations. These interference effects can be eliminated by calculating the difference between the output signals of the two acceleration sensors 110, 112, the first and the second seismic mass being identical in terms of weight. The standard evaluation of the differential signal takes place, for example, via a microcontroller connected downstream.

Figures 2 and 3 illustrate two different options for producing the magnetic activity according to the invention. Both options can be used alternatively, but also in combination with one another. As shown in Figure 2, the second acceleration sensor 112 can firstly have a coil arrangement 114 which is energised by means of a small current so that it creates a magnetic field at the second seismic mass. The coil arrangement 114 is applied to the second seismic mass so that, as a result of the magnetic field 116, a force Fl (as symbolised by the arrow 118) acts on the second seismic mass transversely to the magnetic field direction 116. The force Fl in turn results in a displacement of the seismic mass, which can be detected for example via a capacitive arrangement.

According to a further schematically illustrated embodiment (see Figure 3), the second seismic mass can, however, also be provided with a permanent magnetic element 115, for example a permanent magnetic coating, so that the second seismic mass is moved by the effect of a force F2 along the magnetic field lines 116, as symbolised by the arrow 120. Figure 4 schematically illustrates the application of the current sensor according to the invention for a differential current measurement, as is required, for example, for monitoring charging in an electric vehicle. In this case, the forward conductors 122 and the return conductors 124 of the current circuit which is to be monitored are guided through the magnetic core 104. If a differential current is flowing, a magnetic field occurs which, as explained above, results in a force Fl or F2 on the magnetically active seismic mass of the second acceleration sensor 112. The difference between the measured value of the first acceleration sensor 110, which has a non-magnetic seismic mass, and the measured value of the second acceleration sensor 112 represents the useful signal. Environmental influences, such as vibrations, the gravitational field and the like, are eliminated by the differential measurement. The standard evaluation of the useful signal advantageously takes place via a microcontroller connected downstream. The present invention offers the advantage that the construction of the measuring system is very simple and significant cost advantages arise as a result of integrated sensors and integrated evaluation electronics. Furthermore, a coil is not required on the magnetic core and the energy consumption of the measurement is considerably lower than that of known current sensor arrangements. This is particularly advantageous when applied to charging cables for electric vehicles.

In the above statements, it is always assumed that there are precisely two acceleration sensors.

However, it is clear to the person skilled in the art that a greater number of magnetically active and inactive acceleration sensors can also be provided if necessary, the signals of which are offset against each other.

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