Circuit arrangement and method for isolating a voltage source from at least one consumer

Abstract

Circuit arrangement (1) for isolating a voltage source (2) from at least one consumer (3), comprising at least one switching element (4), at least one control unit (6) controlling the switching element (4), at least one voltage source (2) and at least one current sensor (5) for detecting a current of the voltage source (2), wherein the control unit (6) is designed to initiate a disconnection process upon detection of a current (I) greater than a threshold value (S1), characterized in that the control unit (6) is designed to determine a currently maximum permissible current (I MAX ) of the voltage source (2), whereby the threshold value (S1) depends on the current maximum current (I MAX), wherein further threshold values (S2, S3) exist which are greater than the first threshold value (S1), wherein the separation process is carried out more quickly when the further threshold values (S2, S3) are exceeded.

Description

[0001] The invention relates to a circuit arrangement and a method for isolating a voltage source from at least one consumer.

[0002] For various reasons, it is necessary to disconnect a voltage source from at least one consumer. The term voltage source is generally understood to mean an electrical energy source, which should also include a current source, for example. For example, the voltage source must be switched off if a short circuit causes a short-circuit current to flow, which in extreme cases poses a fire hazard. Fuses, in particular safety fuses, are known for this purpose. These fuses are triggered when excessive current flows over a longer period of time. The disadvantage of safety fuses is that they are relatively large and not very flexible, and their disconnection is irreversible. As an alternative or in addition, functional disconnection elements are known which are controlled by a control unit in order to disconnect a voltage source under certain conditions.Functional isolating elements (hereinafter referred to as switching elements) can be, for example, relays, contactors, semiconductor switches (e.g., MOSFETs, IGBTs), but also controllable pyrotechnic isolating elements, which, in addition to functional / controlled isolating, can also provide (semi-)autonomous isolating. For this purpose, it is known to define a fixed threshold value that is greater than the maximum possible operating current of the voltage source, at which point the control unit initiates a isolating process but does not necessarily perform it, for example, because the current peak was only brief. This threshold value can also be referred to as the initialization threshold.

[0003] DE 10 2016 216 213 A1 discloses a circuit arrangement for isolating a voltage source from at least one load. The circuit arrangement is provided with at least one ammeter, which directly or indirectly measures at least a portion of the current supplied by the voltage source to the load via a network. The circuit arrangement is provided with control logic, which, depending on an output signal from the ammeter, actuates a switch via which the current supply via the network can be disconnected. A measuring device is also provided for measuring the state of the load, the output of which is connected to the control logic.The control logic actuates the switch based on the signals from the ammeter and the measuring device acting in parallel, allowing the current limit at which the electrical switch switches off to be dynamically adjusted to the measured state of the load. It is further provided that the voltage source is connected to a voltage monitor, the output signal of which is fed to the control logic, whereby the actuation of the switch by the control logic also depends on the output signal of the voltage monitor.

[0004] DE 10 2015 117 809 A1 discloses a method for operating a cable system, in particular for an on-board power system of a vehicle. The cable system for supplying electrical power to at least one consumer has at least one cable that connects a supply element to the at least one consumer. The output voltage at the supply element and the input voltage at the consumer are determined, and the power loss of the cable is determined from this.

[0005] DE 10 2017 205 612 A1 discloses a method for controlling a disconnecting device of an electrochemical energy storage device, wherein a temperature of the energy storage device is detected or determined and / or a charge level of the energy storage device is detected or determined based on a voltage. Furthermore, an internal resistance of the energy storage device is determined from the temperature and / or the charge level, and from this, and the voltage, a maximum possible short-circuit current is determined. Furthermore, a current flowing through the energy storage device is detected. The disconnecting device is activated if the calculated short-circuit current exceeds the disconnecting capability of the disconnecting device and the detected current is not plausible in a current operating state.

[0006] DE 10 2013 214 726 A1 discloses an arrangement for electrically protecting a first operating state in a power grid with a system-dependent, variable internal resistance of an energy source. The arrangement comprises a first protection device whose response behavior is insufficient to protect the power grid in a first operating state against a predefined load. Furthermore, the arrangement comprises a second protection device configured to protect the power grid against the load that occurs in the first operating state below the response behavior of the first protection device.

[0007] EP 1 600 337 B1 discloses a battery protection switch for disconnecting an electrical connection between the battery of a motor vehicle and a motor vehicle electrical system, comprising a semiconductor switch for connecting and disconnecting the battery and the motor vehicle electrical system as a function of an overcurrent and / or a crash signal. The semiconductor switch is designed for bidirectional current operation, with the semiconductor switch being switched on when the voltage of the electrical system is greater than the battery voltage. Preferably, the semiconductor switch is equipped with a current measuring function for monitoring the current flowing from the battery into the motor vehicle electrical system. A control device is also provided for evaluating the current measured by the semiconductor switch and for controlling the semiconductor switch to disconnect the electrical connection between the battery and the motor vehicle electrical system.The control device compares the current measured by the semiconductor switch with a specified limit value that can be adaptively adjusted.

[0008] The invention is based on the technical problem of improving a circuit arrangement for isolating a voltage source with regard to the response behavior and of providing a suitable method.

[0009] The solution to the technical problem results from a circuit arrangement having the features of claim 1 and a method having the features of claim 9. Further advantageous embodiments of the invention result from the subclaims.

[0010] For this purpose, the circuit arrangement for isolating a voltage source from at least one consumer comprises at least one switching element, at least one control unit controlling the switching element, at least one voltage source and at least one current sensor for detecting a current of the voltage source, wherein the control unit is designed to initiate a disconnection process upon detection of a current greater than a threshold value. The control unit is designed to determine a currently maximum permissible current of the voltage source as a function of at least one parameter of the voltage source, wherein the threshold value is set as a function of the currently maximum current. The currently maximum permissible current is understood to be a currently maximum permissible operating current. This means that the adaptation to the actual current conditions of the voltage source takes place dynamically, so that the circuit arrangement operates with correspondingly more sensitivity.In high-voltage systems, especially battery- or electrochemically operated high-voltage systems, a short-circuit current can vary by orders of magnitude depending on the conditions. A fixed threshold causes the circuit to respond too frequently if the threshold is too small, or too late if the threshold is too high. This is prevented by dynamic adaptation to the currently maximum permissible current. The switching element can be a relay, contactor, or semiconductor switch (e.g., MOSFET or IGBT). A preferred application is in a motor vehicle's traction system.

[0011] There are additional thresholds that are higher than the first threshold. When these thresholds are reached, the separation process can be carried out very quickly. These thresholds are preferably also set depending on the currently maximum permissible current. For example, the combination of threshold and switch-off time can be used to determine a fixed or dynamic melting integral (I 2 ·t) for overcurrent protection.

[0012] In one embodiment, the voltage source is at least one battery, wherein the at least one parameter of the voltage source is a state of charge of the battery (SOC) and / or a temperature of the battery and / or a state of aging of the battery (SOH) and / or a number of charging cycles. The first two parameters mentioned in particular have a significant influence on the maximum permissible current. If the battery is a lithium-ion battery, for example, the maximum permissible current must be limited at very low battery cell temperatures. The threshold value at which the disconnection process is initiated can then be reduced accordingly. In addition to the parameters mentioned, further parameters can also be taken into account.

[0013] In another embodiment, the threshold is determined by the currently maximum permissible current plus a current delta. This current delta can also be referred to as a robustness margin, which prevents the disconnection process from being incorrectly initiated too early.

[0014] In one embodiment, the current delta is a fixed absolute current value.

[0015] In an alternative embodiment, the current delta is a fixed percentage current value of the maximum permissible current, for example 10%.

[0016] In another alternative embodiment, the current delta depends on the vehicle's condition. For example, when charging a vehicle electrically, the current variance is smaller than during driving, where highly dynamic power requirements can occur. Accordingly, the current delta during charging can also be selected to be smaller than during driving (in absolute or percentage terms).

[0017] In another embodiment, a separate threshold value is assigned to each of the different current directions. This distinguishes whether the current flows out of or into the voltage source.

[0018] With regard to the procedural design, reference can be made in full to the preceding statements.

[0019] The invention is explained in more detail below using a preferred embodiment. The figures show: Fig. 1 a schematic representation of a circuit arrangement for isolating a voltage source from at least one consumer and Fig. 2 a representation of different threshold values.

[0020] In the Fig. 1 shows a circuit arrangement 1 for isolating a voltage source 2 from at least one consumer 3. The circuit arrangement 1 comprises two switching elements 4, which are preferably designed as relays. The switching elements 4 are functional isolating elements. The circuit arrangement 1 also has a current sensor 5 and a control unit 6, which controls the switching elements 4. The voltage source 2 is designed as a battery and consists of a plurality of battery cells 7, to which temperature sensors 8 and voltage sensors 9 are assigned, wherein the temperature and voltage data are fed to the control unit 6, for example via a bus system (not shown). The control unit 6 is designed, for example, as a battery management control unit and is able to use the data to determine an SOC and an SOH of the voltage source 2 and to record the number and duration of charging and discharging cycles. Based on characteristic curves orThe control unit determines a currently maximum permissible current from the battery using characteristic maps. The current level depends on a variety of parameters, although for the sake of simplicity, it is assumed below that these are primarily the SOC and the temperature T of the battery cells 7. At a time t1, the control unit 6 determines a state of charge SOC1 and a battery cell temperature T1 and uses these to determine a currently maximum permissible current I. MAX (T1, SOC1). At this current value I MAX (T1, SOC1) a current delta ΔI is then added and the sum value is stored as the current first threshold value S1 (T1, SOC1) (see also Fig. 2). S1 can be determined in real time or using look-up tables. If the current I from the battery then exceeds this first threshold value S1, this indicates a fault (e.g., a short circuit). If, for example, the first threshold value S1 is then exceeded for a specified period of time, the control unit 6 activates the switching elements 4 and disconnects the connection between the voltage source 2 and the load 3.

[0021] Assuming that S1 is not exceeded, the state of charge SOC2 and the temperature T2 are determined again at a time t2, whereby the battery cell temperature T2 has increased, for example, so that the currently maximum permissible current I MAX (T2, SOC2). Accordingly, a current first threshold value S1 (T2, SOC2) = I MAX (T2, SOC2) + ΔI, ie the first threshold S1 is dynamically adjusted to the currently maximum permissible current.

[0022] In the Fig. 2 is additionally an absolute maximum permissible current I MAX,absolut (maximum permissible operating current) is shown, which is permissible at optimal charge state and temperature and to which a first threshold value S 1,max Furthermore, further threshold values S2, S3 are shown, upon reaching which, for example, the control unit 6 performs the disconnection more quickly. It should be noted that the current deltas ΔI for the various first threshold values S1 do not have to be the same. List of reference symbols 1 Circuit arrangement 2 Voltage source 3 consumers 4 switching elements 5 Current sensor 6 Control unit 7 battery cells 8 temperature sensors 9 voltage sensors

Claims

[1] Circuit arrangement (1) for isolating a voltage source (2) from at least one consumer (3), comprising at least one switching element (4), at least one control unit (6) controlling the switching element (4), at least one voltage source (2) and at least one current sensor (5) for detecting a current of the voltage source (2), wherein the control unit (6) is designed to initiate a disconnection process upon detection of a current (I) greater than a threshold value (S1), characterized by that the control device (6) is designed in such a way that, depending on at least one parameter of the voltage source (2), a currently maximum permissible current (I MAX ) of the voltage source (2), whereby the threshold value (S1) depends on the current maximum current (I MAX), wherein further threshold values (S2, S3) exist which are greater than the first threshold value (S1), wherein the separation process is carried out more quickly when the further threshold values (S2, S3) are exceeded. [2] Circuit arrangement according to claim 1, characterized by that the voltage source (2) is at least one battery, wherein the at least one parameter of the voltage source (2) is a state of charge of the battery (SOC) and / or a temperature (T) of the battery and / or an aging state of the battery and / or a number of charging cycles. [3] Circuit arrangement according to claim 1 or 2, characterized by that the threshold value (S1) is the current maximum current (I MAX ) plus a current delta (ΔI). [4] Circuit arrangement according to claim 3, characterized by that the current delta (ΔI) is a fixed absolute current value. [5] Circuit arrangement according to claim 3, characterized bythat the current delta (ΔI) is a fixed percentage current value of the current maximum current (I MAX ) is. [6] Circuit arrangement according to claim 3, characterized by that the current delta (ΔI) depends on the vehicle condition of a motor vehicle. [7] Circuit arrangement according to claim 6, characterized by that the further threshold values (S2, S3) depend on the current maximum current (I MAX ) are specified. [8] Circuit arrangement according to one of the preceding claims, characterized by that the different current directions are each assigned their own threshold value (S1). [9] Method for isolating a voltage source (2) from at least one consumer (3), by means of at least one switching element (4), at least one control unit (6) controlling the switching element (4), at least one voltage source (2), wherein the control unit (6) initiates a disconnection process upon detection of a current (I) greater than a threshold value (S1), characterized by that the control unit (6) has a currently maximum permissible current (I MAX ) of the voltage source (2), whereby the threshold value (S1) depends on the currently maximum permissible current (I MAX ), wherein further threshold values (S2, S3) exist which are greater than the first threshold value (S1), wherein the separation process is carried out more quickly when the further threshold values (S2, S3) are exceeded.

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