DE102018206280B4 - ELECTRICAL CONTACT DEVICE, METHOD FOR DETERMINING WEAK CONTACTS, BATTERY CHARGER, AND LOADING DEVICE FOR AN ELECTRIC VEHICLE - Google Patents

Abstract

The present invention relates to an electrical contact device having at least a first electrically conductive contact element and a second electrically conductive contact element, and at least one sensor for measuring the differential temperature between the two electrically conductive contact elements (105a, 105b), the sensor comprising Temperature difference conversion module (100), a thermally conductive material (110) arranged to connect the temperature difference conversion module (100) to the first electrical contact element (105a) and the second electrical contact element (105b), and wherein the temperature difference conversion module (100 ) is configured to measure the temperature difference between the first electrical contact element (105a) and the second electrical contact element (105b). In advantageous embodiments, the temperature difference conversion module provides an output voltage which is independent of the absolute temperature and linearly dependent on the temperature difference between the two electrically conductive contact elements (105a, 105b). A weak or a leakage current or leakage current leading contact of an electrical contact device can be identified from the polarity of the measured temperature difference.

Description

The present invention relates to an electrical contact device and a method for determining a weak electrical contact or leakage currents, as well as a battery charger provided therewith and a charging device for an electric vehicle.

Electric vehicles can be charged in different charging modes. These differ among other things in terms of safety devices, communication with the vehicle and charging power. For safety reasons, most car manufacturers choose the so-called Mode 3 charge. On the other hand, the charging mode 2 This charge modes are defined in the international standard IEC 61851-21: 2010 as follows: The Mode 3 charge is the safest way to charge a vehicle. It takes place at charging stations with a special charging device in accordance with IEC 61851, the so-called "Electrical Vehicle Supply Equipment" (EVSE), ie the charging infrastructure. The charger is installed in the vehicle. The charging station requires PWM communication, fault and overcurrent protection, shutdown and a specific charging socket.

Mode 2 charging is the safest alternative to Mode 3 charging when charging infrastructure is not available. Charging takes place from a standard household plug-in device (for example Schuko or CEE) with a control and protection function integrated in the charging cable. The charger is installed in the vehicle.

The requirements for the charging infrastructure for Mode 3 charging are clearly defined. In the case of Mode 2 charging, on the other hand, the connection is made using a household, industrial or “camping” connector. The use of normal household installations for the charging connection of electric vehicles harbors dangers that have not been fully taken into account by the previous solutions. The charging connections and their supply lines must be suitable for continuous currents of up to 16 A. In practice, however, this is not always guaranteed. There are still house installations without residual current protective devices and sockets, whose supply lines overheat dangerously due to insufficient cross-sections with this continuous load. The consequences can be serious. The user must be able to rely on the fact that the charging process is safe and reliable, because the vehicle is often charged overnight. Therefore, charging cables are for fashion 2 known, which different parameters beyond the requirements of the standard, such. B. monitor the temperature in the Schuko plug on the infrastructure side and thus make mode 2 charging considerably safer. For fashion 2 the IEC 61851 standard prescribes a mobile device for increasing the protection level (SPE-PRCD). In addition, a communication device (PWM module) with the vehicle is required for the power setting and to meet the safety requirements. These components are combined in a so-called "In-Cable Control and Protecting Device" (IC-CPD). The IC-CPD, which is permanently integrated in the charging cable, controls the protective conductor connection and transmits the upper charging current limit to the vehicle. In the event of a fault or a power failure, the charging process is interrupted immediately to protect the user and the electric vehicle. The intelligent IC-CPD also detects incorrect wiring of the socket on the infrastructure side and additionally checks the incoming protective conductor before charging begins.

The patent DE 102010050562 B3 discloses an apparatus for charging a vehicle drivable with electrical energy, the apparatus comprising at least one plug connectable to the vehicle to be charged, at least one power source and at least one cable for establishing an electrical connection between the plug and the power source and at least one means for cooling at least a part of the plug. According to the invention, at least one cooling circuit which is thermally connected to the plug is provided as the means for cooling, wherein the cooling circuit is closed even when the plug is disconnected from a vehicle to be charged up. In this way it can be ensured even with frequently repeated charging cycles that sufficient cooling of the charging plug takes place. Thus, for example, the charging plug can continue to be cooled between charges until a prescribed limit temperature is reached.

The publication DE 102014111334 A1 relates to a charging connector for an electric vehicle having the following features: Contact pins for making a connector with a coupling and temperature sensors thermally coupled to the contact pins for detecting a temperature profile between the charging connector and the coupling. The document also discloses a charging cable with such a plug and a corresponding method for charging an electric vehicle.

The publication WO 02/013330 A1 refers to a connector comprising a housing having a plurality of longitudinally extending receptacles arranged therein Contacts which are formed in their free outer ends socket or sleeve-shaped for receiving contact pins, wherein at least one of the contacts is associated with a temperature sensor.

The patent DE 112007002307 B4 discloses a method of predicting at a connection terminal whether a normalized contact resistance value R _ter in units of ohms per millimeter is compatible with a permitted temperature increase ΔT in units of Kelvin, the permitted temperature increase ΔT representing a temperature increase up to a temperature standard of the connection terminal, the Connection terminal a male terminal with a wire crimping portion with which one end of a wire is crimped; a female terminal having a wire crimp portion with which one end of a wire is crimped; and a connection portion where the male and female terminals are connected to each other, wherein a contact resistance value of the entire connection terminal is a sum of a contact resistance value of the wire crimp portion of the male terminal, a contact resistance value of the wire crimp portion of the female terminal and a contact resistance value of the connection portion, and wherein a length of a contact portion is a sum of a length of the wire crimp portion of the male terminal, a length of the wire crimp portion of the female terminal, and a length of the connection portion; wherein the normalized contact resistance value R _{ter is} determined by dividing the contact resistance value of the entire connection terminal by the length of the contact portion; wherein a normalized wire resistance value R _{wire of} the wire is determined in units of ohms per millimeter, a current value I is specified in units of amperes, and wherein the compatibility is based on the relationship R _ter <ΔT / (752 × I ² ) - 3.7 × R _{wire is} predicted.

The Utility Model DE 202017102652 U1 discloses a mains voltage socket with a switched into a netzspannungsbeaufschlagten conductor switching contact for switching on and off the mains voltage socket, the mains voltage socket a measuring device for detecting the current flow and the applied voltage, a temperature measuring device for detecting the temperature of at least one of the connected by a to the mains voltage socket Plug contact of a power plug of an electrical load provided socket contact, an evaluation unit for evaluating the acquired measurement data and a signal path for transmitting the measurement data from the measuring devices to the evaluation has.

The present invention addresses two potential problems associated with a contact device, such as that used in charging an electric vehicle: the occurrence of weak contacts and the occurrence of leakage currents.

In each electrical system, part of the current flows through the protective conductor to earth. This current is generally referred to as leakage current. Leakage current mostly flows through the insulation surrounding the conductors. Leakage currents on electrical contacts are undesirable side effects of electrical circuits, and in particular of sockets, battery chargers or electric car chargers. Leakage occurs when an insulator is not ideal, that is, it has (low) electrical conductivity, or when the surface of an insulator conducts leakage current, especially when contaminants and / or moisture are present on the surface.

Insulation has both electrical resistance and capacitance - and conducts electricity in both ways. Due to the high resistance of the insulation, the level of the leakage current should be very low. However, if the insulation is old or damaged, the resistance decreases and higher current can flow. In addition, longer conductors have a higher capacitance, which leads to higher leakage current.

Leakage currents can also occur when free charge carriers spontaneously arise in the interior of semiconductors, which migrate through an applied electrical voltage in the semiconductor crystal. This can e.g. B. caused or increased by increased temperature or radiation.

Leakage current can cause unnecessary and intermittent tripping in circuits protected by RCCBs. In extreme cases, it can lead to a voltage increase in accessible and live parts.

Similar to the leakage currents described above, in the case of insulation faults, electric current flows through a given fault location (fault current).

Another problem with electrical contact devices is the possible occurrence of insufficient electrical contact between two interconnected contact elements, e.g. B. due to the oxidation of contact pins. Such a bad contact corresponds to an increased electrical resistance, which leads to increased heat generation at load current.

It is also known to monitor the temperature at individual contact elements and to modify or cancel the charging process when a limit value is exceeded.

However, the problem often arises that a high absolute temperature at a single contact element does not necessarily have to be an indication of a leakage current or an insufficient electrical contact, and the charging process may therefore be modified or terminated unnecessarily early. This problem occurs in particular when the contact device is in an environment in which high temperatures already exist under normal operating conditions.

The object on which the present invention is based is therefore to provide an electrical contact device which can be safely monitored for leakage currents, fault currents or faulty electrical contact, but can still be operated with sufficient power even under higher ambient conditions ,

This object is achieved by the subject matter of the independent claims. Advantageous further developments are the subject of the dependent claims.

The present invention is based on the idea of identifying leakage currents or insufficient contact in an electrical contact device via the generated temperature difference between at least two contact elements.

Temperature increases occur e.g. after switching on when a device is warming up. However, this temperature increase is equally distributed and not relevant for leakage currents. On the other hand, an electrical contact on which leakage occurs is warmer than contacts without leakage, so that the measurement of temperature differences between the contacts can reveal finite temperature differences and thus leakage currents.

In this case, a distinction can be made between leakage currents and an insufficient contact input in an electrical contact device in that an insufficient contact only when there is a load current, but a leakage current without load current leads to increased heat generation.

In particular, in charging devices for electric vehicles, which are operated in a domestic garage and therefore are poorly secured, securing mechanisms of the contact device are particularly important.

In particular, the present invention relates to an electrical contact device with at least a first electrically conductive contact element and a second electrically conductive contact element, and at least one sensor for measuring the differential temperature between the two electrically conductive contact elements. The sensor comprises a temperature difference conversion module and a thermally conductive material which is arranged such that it connects the temperature difference conversion module to the first electrical contact element and to the second electrical contact element. The temperature difference conversion module is configured to measure the temperature difference between the first electrical contact element and the second electrical contact element.

In advantageous embodiments, the temperature difference conversion module comprises a Peltier element. A Peltier element is an electrothermal transducer that, based on the Peltier effect, generates a temperature difference when the current flows through or a current flow when the temperature differs (Seebeck effect). Peltier elements can be used both for cooling and - if the current direction is reversed - for heating.

The basis for the Peltier effect is the contact of two semiconductors that have a different energy level (either p- or n-type) in the conduction bands. If you conduct a current through two contact points of these materials, one behind the other, thermal energy must be absorbed at one contact point so that the electron enters the higher energy band of the neighboring one Semiconductor material arrives, consequently it cools down. At the other contact point, the electron falls from a higher to a lower energy level, so that energy is given off in the form of heat.

Since n-doped semiconductors have a lower energy level in the conduction band, cooling takes place at the point at which electrons pass from the n-doped to the p-doped semiconductor (technical current flow, i.e. from p-doped to n-doped semiconductor).

A Peltier element consists of two or more small cuboids, each made of p- and n-doped semiconductor material (e.g. bismuth telluride or silicon germanium), which are alternately connected at the top and bottom by metal bridges. The metal bridges also form the thermal contact surfaces and are insulated by a foil or a ceramic plate. Always two different cuboids are connected so that they form a series connection. The electrical current supplied flows through all the cuboids one after the other. Depending on the current strength and direction, the upper connection points cool down while the lower ones heat up. The current thus pumps heat from one side to the other and creates a temperature difference between the plates.

The most common form of Peltier elements consists of two mostly square plates of alumina ceramic with an edge length of 5 mm to 90 mm and a distance of 1 mm to 5 mm, between which the semiconductor cuboids are soldered. The ceramic surfaces are provided for this purpose on their facing surfaces with solderable metal surfaces.

If you cool the warm side z. B. by means of an attached heat sink with fan, the cooling side is even colder. Depending on the element and current, the temperature difference between the two sides can be up to approx. 70 Kelvin for single-stage elements.

The inverse of the Peltier effect is the Seebeck effect. It is thus possible to generate a voltage and / or an electric current by producing a temperature difference between the two sides of a Peltier element (thermoelectric generator). This is the effect that is used to advantage in the present invention. The voltage results in an output signal which is independent of the absolute temperature and linearly dependent on the temperature difference between the two contact elements, between which the Peltier element is arranged. The temperature difference can thus be determined from the voltage via a corresponding calibration.

In addition, the generated electrical voltage can be used, for example, to supply an evaluation circuit with current at least partially. However, it should be noted here that thermoelectric elements available today only have a relatively low efficiency (17% of the theoretically highest possible efficiency, the Carnot efficiency).

In an advantageous embodiment, the Peltier element comprises two galvanically insulated ceramic plates, which are connected to the thermally conductive material. As a result, the Peltier element is isolated against possible leakage currents via the conductive material. In an advantageous embodiment, each bismuth telluride block generates an output voltage of 0.4 mV / K.

In advantageous embodiments of the invention, the evaluation circuit is designed so that it determines from the sign of the output voltage, which contact has the higher temperature. This has the advantage that the leakage current can be precisely located.

In some embodiments of the invention, the temperature difference conversion module indicates a voltage independent of the absolute temperature but linearly dependent on the temperature difference between the two electrical contacts. The linear relationship is advantageous in that it allows a simple method of converting the voltage values to temperature values.

As noted above, the temperature differential measurements are to be used to find leakage currents, fault currents, or insufficient high contact resistance electrical contacts. Therefore, the above-mentioned stress is a measure of contact quality.

In an advantageous embodiment, the sensor supplies an output voltage that is independent of the absolute temperature and linearly dependent on the temperature difference between the two electrically conductive contact elements. This has the advantage that the sensor can be calibrated very easily.

In an advantageous embodiment, the contact device has an electrical detection and evaluation unit that can be operated to evaluate the output signal of the sensor as a measure of a contact quality of the first and second contact elements. This has the advantage that it allows the contact quality of the contact device to be checked via the temperature measurement. This invention therefore also relates to a method in which a contact element which has a leakage current, a fault current or a weak contact is identified from the polarity of the measured temperature difference.

In advantageous embodiments of the electrical contact device, the Peltier element comprises a plurality of bismuth telluride blocks which are connected in series. By connecting a large number of bismuth telluride blocks in series, the value range of the Peltier element can be made almost arbitrarily large.

In advantageous embodiments, the electrical contact device comprises a third contact element, the energy for operating the evaluation circuit being provided by the temperature difference conversion module. This makes it possible to extend the principle to three-phase plugs and to make sensible use of the energy that is released when the evaluation circuit is operated, and thus to minimize the energy consumption of the contact device.

The present invention also relates to a battery charger comprising an electrical contact device as described above. This embodiment has the advantage that possible leakage currents can be identified during charging of the battery.

The present invention also relates to a charging station for an electric car, comprising a charging cable and an electrical contact device as described above, the contact device being configured to make electrical contact between the charging cable and the operating circuit of a car.

• 1 eine Kontaktvorrichtung gemäß einer vorteilhaften Ausführungsform der vorliegenden Erfindung;
• 2 eine schematische Darstellung einer Kontaktvorrichtung gemäß einer zweiten vorteilhaften Ausführungsform der vorliegenden Erfindung.

For a better understanding of the present invention, this will be explained in more detail using the exemplary embodiments shown in the following figures. The same parts are provided with the same reference numerals and the same component names. Furthermore, some features or combinations of features from the different embodiments shown and described can also represent independent, inventive or inventive solutions. Show it:

• 1 a contact device according to an advantageous embodiment of the present invention;
• 2 is a schematic representation of a contact device according to a second advantageous embodiment of the present invention.

The invention will now be described with reference to the figures beginning with 1 ,

1 shows an electrical contact device 102 according to a first advantageous embodiment of the present invention. The contact device 102 has a first contact pin 105a and a second contact pin 105b on. The contact device 102 is for example a charging plug for an electric vehicle. The associated housing and the connecting lines are not shown in the figures.

The electrical contact device 102 according to the present invention comprises a Peltier element 100 on which over a thermally conductive material 110 with the two pins 105a . 105b connected is.

As schematically in 1 shown, has the Peltier element 100 a plurality of first and second bismuth telluride blocks connected in series 104 . 106 on. The bismuth telluride blocks 104 . 106 of the Peltier element 100 are alternated by electrically conductive bridges 120 that are made of metal, for example. Always two different cuboids are connected so that they form a series connection. Of course, any other suitable material, such as silicon germanium, can be used in place of the bismuth telluride.

The metal bridges 120 at the same time form the thermal contact surfaces and the series connection of the first and second bismuth telluride blocks 104 . 106 is between galvanically insulating plates 130 embedded. The galvanically insulating plates 130 are advantageously made of a thermally highly conductive material, such as a ceramic. A first and a second connection cable 108a . 108b grab those from the Peltier element 100 generated voltage.

The Peltier element 100 is according to the invention via a heat-conducting material 110 with the first contact pin 105a and the second contact pin 105b connected. In this way, heat development occurring at the contact pins can be imparted to the bismuth telluride blocks with the least possible time delay 104 . 106 of the Peltier element 100 be directed. Thermally conductive materials are often metals and therefore also electrically conductive. Therefore, leakage currents could also flow in the thermally conductive material of the present invention. The Peltier element is therefore according to the invention 100 over the two galvanically insulating ceramic plates 130 against the thermally conductive materials 110 electrically isolated.

Now lies a temperature difference between the first and second contact pins 105a . 105b before, generates the Peltier element 100 an electrical voltage applied to the ends of the two connection cables 108a . 108b is applied. These electrically conductive bridges 120 are connected to an evaluation unit (not shown in the figures).

The evaluation unit determines a temperature difference which corresponds to the voltage generated by the Peltier element 100 at the ends of the two connection cables 108a . 108b is issued. By evaluating the polarity of the voltage, it can be determined according to the invention which of the two contacts 105a . 105b is faulty or has a leakage current because the higher temperature is measured at this contact.

Furthermore, the voltage between the cable ends can optionally be used to at least partially supply power to the evaluation unit.

2 shows a further advantageous embodiment of the electrical contact device according to the present invention. The electrical contact device 202 , which is shown here only schematically, may for example be a three-phase connector, as it is needed for charging electric vehicles. The electrical contact device 202 has correspondingly three electrically conductive contact pins 105a . 105b . 105c on. In 2 are these pins 105a . 105b . 105c shown schematically as arranged in a row. Of course, the contact pins 105a . 105b . 105c be arranged arbitrarily to form each required connector face. Furthermore, it is also not necessary that the contact pins 105a . 105b . 105c have identical dimensions.

The electrical contact device 202 has a first Peltier element 100a and a second Peltier element 100b on which with a thermally conductive material 110 with a first contact pin 105a , a second contact pin 105b and a third contact pin 105c are connected.

About the Peltier elements 100a . 100b can show temperature differences between the first contact pin 105a and the second contact pin 105b , as well as between the second contact pin 105b and the third contact pin 105c be measured. Then the contact pin can be used via the polarities of the output signals 105a . 105b . 105c identify who has a leakage current or an increased contact resistance. The leakage current or the increased contact resistance affect the contact pin 105a . 105b . 105c which has the highest temperature.

The present invention thus makes it possible to measure the temperature difference between two contact pins, mainly in power applications, and to identify a weak contact via the temperature increase when the current flows.

According to the invention, a thermoelectric generator (TEG), in particular a Peltier element, which is used as a generator, is used which generates a linear voltage which is only dependent on the temperature difference on the two sides. The measured voltage is positive or negative, depending on which of the two contact pins has the higher temperature. The temperature difference can thus provide information about which of the two contact pins may have an excessively high contact resistance or a leakage current. According to the present invention, a Peltier element is used which has bismuth telluride blocks, each of which provides an output voltage of approximately 0.4 mV / Kelvin and is connected in series in order to generate a higher output voltage overall. Typically, these blocks are mounted between alumina ceramic plates, which are good electrical insulators but at the same time have high thermal conductivity. Advantageously, such TEG elements are small in size, so that the arrangement according to the present invention can be installed in a household connector.

Unlike conventional temperature sensors, the output voltage of the TEG is independent of the absolute ambient temperature, requires only two connecting wires and there is no need for compensation or measurement of the ambient temperature.

The accuracy of the differential measurement is only a function of the physical properties of the TEG material and its low impedance also advantageously simplifies the design of the signal amplifiers. If the evaluation circuit is also arranged directly in the connector, it can also be avoided that interference signals are coupled into the signal processing.

The present invention thus makes it possible to monitor the contact quality or the wiring of a connector or a charging connection, even if the ambient temperature is high or very low. The polarity of the voltage indicates which of the contact pins has the higher temperature. By using more than one Peltier element in a connector, arrangements with more than two contact elements, for example with a three-phase system, can also be monitored. With this arrangement, the weak contact can be identified by comparing the polarity and the value of two sensors.

Although it was always assumed in the above explanations that the contact device according to the invention comprises contact pins between which a temperature difference is monitored, it is of course clear to a person skilled in the art that the solution according to the invention for any type of electrical contact elements, that is to say also for. B. sockets, press-in connections or soldered connections can be applied.

LIST OF REFERENCE NUMBERS

numeral description 100, 100a, 100b Temperature difference conversion module; thermoelectric generator, Peltier element 102, 202 Electrical contact device 104 First bismuth telluride block 105a, 105b, 105c Electrically conductive contact element 106 Second bismuth telluride block 108a, 108b connection cable 110 thermally conductive material 120 Electrically conductive bridge 130 Galvanically insulated plates

Claims (12)

Electrical contact device with at least a first electrically conductive contact element (105a) and a second electrically conductive contact element (105b), and at least one sensor (100a) for measuring the differential temperature between the two electrically conductive contact elements (105a, 105b), the sensor comprising : a temperature difference conversion module (100), a thermally conductive material (110) which is arranged such that it connects the temperature difference conversion module (100) to the first electrical contact element (105a) and to the second electrical contact element (105b), and wherein the temperature difference conversion module (100) is configured to measure the temperature difference between the first electrical contact element (105a) and the second electrical contact element (105b). Electric contact device according to Claim 1 wherein the temperature difference conversion module (100) comprises a Peltier element. Electrical contact device according to Claim 2 , wherein the Peltier element comprises two galvanically insulated ceramic plates (130) which are connected to the thermally conductive material (110). Electrical contact device according to one of the preceding claims, wherein the temperature difference conversion module (100) is designed such that it supplies an output voltage which is independent of the absolute temperature and linearly dependent on the temperature difference between the two electrically conductive contact elements (105a, 105b). Electrical contact device according to one of the Claims 2 to 4 , wherein the Peltier element (100) comprises a plurality of bismuth telluride blocks which are connected in series. Electric contact device according to Claim 5 Each bismuth telluride block is designed to produce an output voltage of 0.4 mV / K. Electrical contact device according to one of the preceding claims, further comprising an evaluation circuit which is connected to the temperature difference conversion module (100). Electric contact device according to Claim 7 , wherein the evaluation circuit is designed such that it determines from the sign of the output voltage, which contact has the higher temperature. Electrical contact device according to one of Claims 7 or 8th further comprising a third contact element (105c), wherein the energy for operating the evaluation circuit is provided by the temperature difference conversion module (100). wherein a second sensor (100b) is configured to measure the temperature difference between the second contact element (105b) and the third contact element (105c). A battery charger comprising an electrical contact device according to one of the preceding claims. A charging device for an electric vehicle, comprising: a charging cable, an electrical contact device (102, 202) according to one of the Claims 1 to 9 wherein the contact device (102, 202) is configured to make electrical contact between the charging cable and the operating circuit of the electric vehicle. A method of identifying weak contact in an electrical contact device (102, 202) according to one of the Claims 1 to 9 , wherein a temperature difference between at least a first and a second contact element (105a, 105b, 105c) is measured and a contact element (105a, 105b, 105c), which has a weak contact, a fault current or a leakage current, from the polarity of the measured temperature difference is identified in the presence of a load current.

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