DE102021214606A1 - current detection system - Google Patents

Abstract

The current detection system (2) comprises a busbar (9) which is connected (5) in a current path between a power supply (3) and a load. The busbar (9) includes a temperature-dependent resistor with a specific temperature coefficient. An amplifier (11) is designed to detect a voltage difference at a section of the busbar (9) caused by a current flow in the current path. The current detection system (2) comprises a temperature compensation circuit, the temperature compensation circuit acting as a temperature-dependent resistor with a temperature coefficient which has an opposite sign to the resistance of the busbar (9). A first input (C1) of a comparator (15) is connected directly or indirectly to a second terminal (S2) of the signal conditioning circuit (13). Furthermore, the current detection system (2) comprises a logic circuit arrangement (17) which is designed to control a state of a switch (7) arranged in the current path as a function of an output signal from the comparator (15).

Description

TECHNICAL AREA

The present disclosure relates to a current sensing system.

BACKGROUND

Accurate current measurement is essential to control energy flow and optimize efficiency in hybrid and electric vehicle powertrain subsystems such as traction inverters, on-board chargers, DC/DC converters, and battery management systems (BMS). After all, the subsystems mentioned above have to measure high currents - and at high voltages, usually in excess of 400 V. In recent years, the current used in these electronic devices has been increased to about 1 kA, for example. In this case, in order to ensure safety in the event of a circuit short circuit, it is necessary to control the short circuit current. Isolated current measurement is often used.

Various methods are available for isolated current measurements. Shunt methods with isolated amplifiers or isolated modulators are mainly used in hybrid and electric vehicles. However, the voltage drop across the shunt results in losses and corresponding heat generation. Therefore, the shunt resistor used for these purposes must have a low resistance value, for example 100 µΩ or less. Therefore, technical improvements are being made to shunt resistors to make them lighter/smaller and have lower resistance values while maintaining or even improving accuracy and drift characteristics.

An object of the present disclosure is to provide a current sensing system that is small in size and low in power loss and provides accurate overcurrent detection.

EXECUTIVE SUMMARY

The invention is defined by the independent claim. Advantageous embodiments of the invention are specified in the dependent claims.

In a first aspect, the present disclosure relates to a current sensing system. The current sensing system includes a bus bar connected in a current path between a power supply and a load.

A switch is arranged in the current path in order to disconnect the current path, in particular when an overcurrent is detected.

In at least one embodiment, the bus bar includes a copper alloy, wherein the copper alloy includes copper (Cu), nickel (Ni), and silicon (Si), or includes copper and silicon. Many high current applications involve Cu or CuNiSi busbars as current-carrying elements, and therefore a primary aspect of the disclosure is to use a section of the busbar as a current-sensing element. The use of a busbar instead of a separate shunt resistor offers the advantage that a separate shunt resistor or a Hall sensor can be dispensed with. This saves not only costs but also space and an additional loss of performance can be reduced to a minimum.

The current sensing system includes an amplifier having a first input and a second input and an output. The first input and the second input are connected to the busbar so that the amplifier is configured to detect a voltage difference or voltage drop across a portion of the busbar caused by a current flow in the current path.

In at least one embodiment, the amplifier comprises an isolated amplifier with galvanic isolation.

Because the bus bar includes a temperature dependent resistor with a specific temperature coefficient, the current sensing system includes signal conditioning circuitry. The signal conditioning circuit includes a first terminal and a second terminal and a temperature compensation circuit. The first connection is connected to the output of the amplifier. The temperature compensation circuit acts as a temperature dependent resistor with a temperature coefficient of opposite sign to the resistance of the busbar.

In at least one embodiment, the resistance of the bus bar includes a positive temperature coefficient.

The current sensing system includes a comparator having a first input and a second input, the first input of the comparator being directly or indirectly connected to the second terminal of the signal conditioning circuit.

Since the temperature dependence of the resistance of the busbar is at least partially compensated by the temperature compensation circuit, a fixed overcurrent threshold can be used for the comparator, since the tolerance for the resulting switch-off current is sufficiently small.

Furthermore, the current detection system includes a logic circuit arrangement, wherein the logic circuit arrangement is designed to control a state of the switch, which is arranged in the current path, depending on an output signal of the comparator.

In addition to the advantage that the busbar can be used as a detection element, the current detection system has the additional advantage that the temperature dependency of the detection element is compensated for by a cost-effective and fast hardware solution. There is no need to calculate complicated and time-consuming temperature compensation algorithms in a microcontroller.

In at least one embodiment according to the first aspect, the signal conditioning circuit comprises a first resistor, wherein the first resistor and the temperature compensation circuit are connected in series between the first terminal and a third terminal of the signal conditioning circuit and an intermediate node which is arranged between the first resistor and the temperature compensation circuit , is directly or indirectly connected to the second port.

In at least one embodiment according to the first aspect, the temperature compensation circuit comprises a resistor and a diode connected in series. The cathode of the diode is preferably connected directly or indirectly to the third terminal of the signal conditioning circuit. In particular, the diode includes a temperature-dependent resistor with a negative temperature coefficient. The diode can comprise a transistor which is connected in such a way that it acts or functions as a diode.

In at least one embodiment according to the first aspect, the diode is a silicon diode with a p-n junction. In particular, the diode does not include a Schottky barrier.

If the busbar uses a material with a negative temperature coefficient, a silicon carbide (SiC) Schottky barrier diode with a positive temperature coefficient can be used.

In at least one embodiment according to the first aspect, a ratio of a resistance value of the first resistor to a resistance value of the resistor of the temperature compensation circuit is equal to an amount of a ratio of a busbar value and a diode value, the busbar value being an increase in the amplified voltage drop of the busbar due to a temperature increase in a predefined represents a temperature range and the diode value represents a reduction in a forward voltage of the diode due to the temperature increase in the predefined temperature range. This allows the provision of a temperature-independent or less temperature-dependent output voltage at the second terminal.

In at least one embodiment according to the first aspect, the intermediate node between the first resistor and the temperature compensation circuit is connected to a voltage divider circuit, and an intermediate node of the voltage divider circuit is connected to the second terminal of the signal conditioning circuit. This allows the output signal level of the amplifier to be matched to a threshold voltage level of the comparator.

Furthermore, a second aspect of the present disclosure relates to a catalytic converter system for a vehicle, comprising a current detection system according to the first aspect and a catalytic converter, wherein the catalytic converter can be connected to a power supply via the bus bar.

Advantageous embodiments of the first aspect also apply to the second aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

It is to be understood that both the foregoing general description and the following detailed description are exemplary only, and are intended to provide an overview or framework for understanding the spirit and character of the claims. The accompanying drawings are included to provide a further understanding and are incorporated into this specification. The drawings illustrate one or more embodiments and together with the description serve to explain the principles and operation of the various embodiments.

In the figures, the same reference numbers are used for elements with essentially the same function, although these elements do not have to be identical in all details. The drawings are not necessarily to scale, but instead are designed to clearly illustrate the disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

Now, the present disclosure will be described in more detail below with reference to the accompanying drawings showing embodiments of the disclosure. However, the disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that the disclosure will fully convey the scope of the disclosure to those skilled in the art. While features of the present disclosure may be discussed below with respect to certain embodiments and figures, all embodiments of the present disclosure may include one or more advantageous features discussed herein. In other words, while one or more embodiments may be discussed as having certain advantageous features, one or more such features may also be used in accordance with the various embodiments of the disclosure discussed herein. Likewise, while example embodiments are discussed below in terms of device, system, or method embodiments, it should be understood that such example embodiments may be implemented in various devices, systems, and methods.

• 1 zeigt ein Ersatzschaltbild eines Ausführungsbeispiels des Stromerfassungssystems und
• 2 zeigt ein beispielhaftes Diagramm eines Widerstandswerts einer beispielhaften Sammelschiene.

It should be understood that when an element is referred to as being “connected” or “coupled” to another element, it may be directly connected or coupled to the other element, or intervening elements may be present. Conversely, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.

• 1 shows an equivalent circuit diagram of an embodiment of the current detection system and
• 2 12 shows an example plot of a resistance value of an example busbar.

In 1 a high voltage system 1 and a current sensing system 2 are shown. The high voltage system 1 comprises a power supply 3, a load 5 and a switch 7. The power supply may be a high voltage battery of an electric vehicle or a hybrid vehicle. The load 5 can be a resistive or inductive load of an electric vehicle or a hybrid vehicle.

The power supply 3 is electrically conductively connected to the load 5 via the switch 7 . There is therefore a current path between the power supply 3 and the load 5, which can be separated by means of the switch 7, for example when an overcurrent is detected.

A busbar 9 is arranged in the current path. The bus bar 9 is used as a current detection element for the current detection system 2 . The bus bar 9 comprises a copper alloy, the copper alloy comprising copper, Cu, nickel, Ni, and silicon, Si, or comprising Cu and silicon.

The copper alloy CuNiSi and the copper alloy CuNi each include a temperature-dependent resistor with a positive temperature coefficient. Therefore, a resistance value of the bus bar 9 increases as the temperature increases.

In 2 an example plot of a resistance value of an example busbar 9 is shown. in the in 2 In the example shown, the resistance value increases by approximately 50% in the temperature range from -40 °C to +160 °C.

In particular, a section of the busbar 9 with a predefined length is used in order to have a minimum resistance that causes a sufficient voltage drop so that the voltage drop can be detected by the amplifier without excessively large measurement error.

Furthermore, the current detection system 2 includes an amplifier 11, which includes a first input A1 and a second input A2 and an output A3. The amplifier 11 is a differential amplifier, for example. The amplifier 11 is designed to detect a voltage difference at the busbar 9 caused by a current flow in the current path. In particular, the amplifier 11 is designed to detect a voltage difference or a voltage drop at a portion of the busbar 9 caused by a current flow in the current path. The amplifier 11 may include an operational amplifier.

Amplifier 11 may be an isolation amplifier that provides electrical isolation.

In addition, the current detection system 2 includes a signal conditioning circuit 13. The signal conditioning circuit 13 includes a first connection S1 and a second connection S2, the first connection S1 being connected to the output A3 of the amplifier 11.

The signal conditioning circuit 13 comprises a first stage with a temperature compensation circuit that acts or functions as a temperature dependent resistor with a temperature coefficient that has an opposite sign to the resistance of the busbar 9 . For example, when the resistance of the bus bar 9 has a positive temperature coefficient, the resistance of the temperature compensation circuit has a negative temperature coefficient.

For example, the temperature compensation circuit includes a resistor Rth and a diode D connected in series. The cathode of the diode D is preferably connected directly or indirectly to a lower potential than the cathode of the diode D. For example, the cathode of the diode D is connected directly or indirectly to a third connection S3 of the signal conditioning circuit 13, which is connected to a reference potential GND, for example ground. For example, the diode D is a silicon diode with a p-n junction.

In order not to greatly reduce the input resistance of the circuit for the signal through the diode D, the series connection of the diode D and the resistor Rth of the temperature compensation circuit is used. Preferably, the temperature compensation circuit is arranged in the vicinity of the busbar section so that the busbar section and the diode D have the same temperature as much as possible.

For example, the first stage of the signal conditioning circuit 13 includes a first resistor R1, the first resistor R1 and the temperature compensation circuit being connected in series between the first terminal S1 and a third terminal S3 of the signal conditioning circuit 13, and an intermediate node between the first resistor R1 and the Temperature compensation circuit is arranged, is directly or indirectly connected to the second terminal S2.

In particular, a ratio of a resistance value of the first resistor R1 to a resistance value of the resistor Rth of the temperature compensation circuit is equal to an absolute value of a ratio of a busbar value and a diode value, the busbar value representing an increase in the amplified voltage drop of the busbar 9 due to a temperature increase in a predefined temperature range and the Diode value represents a reduction in a forward voltage of the diode D due to the temperature rise in the predefined temperature range.

For example, the amplified bus voltage drop shows a 1.48V increase due to a temperature change from -40°C to 160°C, and the diode forward voltage shows a 0.436V decrease. Thus, the absolute value of the ratio of the busbar value and the diode value is RatioBD=1.48/0.436=3.44.

In order to generate a constant voltage drop at the intermediate node between the first resistor R1 and the temperature compensation circuit, the ratio between the first resistor R1 and the resistance Rth of the temperature compensation circuit must be RatioBD=3.44.

Optionally, the signal conditioning circuit 13 for adjusting a voltage level comprises a second stage with a voltage divider circuit with a third resistor R3 and a fourth resistor R4, and the intermediate node between the first resistor R1 and the temperature compensation circuit is connected to the voltage divider circuit and an intermediate node of the voltage divider circuit between the third Resistor R3 and the fourth resistor R4 is connected to the second connection S2 of the signal conditioning circuit 13 . The voltage divider circuit scales the first stage output voltage to a predefined threshold voltage level of a subsequent comparator 15.

The first resistor R1, the temperature compensation circuit resistor Rth, the third resistor R3 and the fourth resistor R4 may each comprise one or more resistive elements.

The comparator 15 comprises a first input C1 and a second input C2, the first input C1 of the comparator 15 being connected directly or indirectly to the second terminal S2 of the signal conditioning circuit 13. The predefined threshold voltage can be applied to the second input C2 of the comparator 15 .

The current detection system 2 comprises a logic circuit arrangement 17 which is designed to control a state of the switch 7 arranged in the current path depending on an output signal of the comparator 15 .

The logic circuitry 17 may include a set-reset latch 171, e.g 7 to put include. The logic circuitry 17 may include a microcontroller 173 configured to reset the set-reset latch 171 and provide a control signal to the AND gate 175 so that the switch 7 can be closed again after an overcurrent is detected and the fault condition is removed .

The effect of temperature compensation can be seen in the results summarized in Tables 1-3. Table 1 and Table 2 show simulation results, while Table 3 shows measurement results. Table 1 shows a minimum and maximum detection current that can be detected by the current detection system 2 under typical conditions, e.g. B. with typical parameters, and with a threshold voltage of the comparator 15 of 600 mV in the temperature range from -40 °C to +160 °C was detected. The difference between the minimum detection current and a maximum detection current is about 114 A without temperature compensation and only 12 A with temperature compensation. Table 1 Simulation results typical temperature range -40 °C to 160 °C Without temperature compensation With temperature compensation Delta detection [A] 114 12 I detection min [A] 240.9 302 I detection max [A] 355.6 314

Table 2 shows the minimum and maximum detection current that can be drawn by the current detection system 2 under worst-case conditions, e.g. B. with worst-case parameters, and with a threshold voltage of the comparator 15 of 600 mV in the temperature range from -40 °C to +160 °C. the differential The difference between the minimum detection current and a maximum detection current is about 139 A without temperature compensation and only 54 A with temperature compensation. Table 2 Simulation results worst case temperature range -40 °C to 160 °C Without temperature compensation With temperature compensation Delta detection [A] 139 54 I detection min [A] 232 282 I detection max [A] 371 336

Table 3 shows a minimum and maximum detection current detected by the current detection system 2 with a threshold voltage of the comparator 15 of 600 mV in the temperature range from -40°C to +160°C. With temperature compensation, the difference between the minimum detection current and a maximum detection current is about 15 A. Table 3 Measurement results Temperature range -40 °C to 160 °C With temperature compensation Delta detection [A] 15 I detection min [A] 309 I detection max [A] 324

Thus, the temperature compensation causes the tolerance for the resulting turn-off current to be sufficiently small and the system efficiency can be improved.

Reference List

1

high voltage system

2

current detection system

3

power supply

5

load

7

Switch

9

busbar

11

amplifier

13

signal conditioning circuit

15

comparator

17

logic circuitry

171

latch

173

microcontroller

175

AND gate

A1, A2

input of the amplifier

A3

amplifier output

C1, C2

input of the comparator

C3

Comparator output

D

diode

GND

reference potential

R1

first resistance

R3

third resistance

R4

fourth resistance

Rth

Temperature compensation circuit resistance

S1, S2, S3

Connection of the signal conditioning circuit

Claims (9)

Current sensing system (2) comprising: - a busbar (9) connected in a current path between a power supply (3) and a load (5), a switch (7) being arranged in the current path and the busbar (9) having a temperature-dependent resistor with a specific temperature coefficient includes, - an amplifier (11) comprising a first input (A1) and a second input (A2) and an output (A3), the first input (A1) and the second input (A2) being connected to the busbar (9). are so that the amplifier (11) is designed to detect a voltage difference caused by a current in the current path at a section of the busbar (9), - a signal conditioning circuit (13) comprising a first terminal (S1) and a second terminal (S2) and a temperature compensation circuit, wherein the first terminal (S1) is connected to the output (A3) of the amplifier (11) and the temperature compensation circuit as temperature-dependent resistor with a temperature coefficient which has an opposite sign to the resistance of the busbar (9), a comparator (15) with a first input (C1) and a second input (C2), the first input (C1) of the Comparator (15) is connected directly or indirectly to the second terminal (S2) of the signal conditioning circuit (13), and - a logic circuit arrangement (17), wherein the logic circuit arrangement (17) is designed to control a state of the switch (7), which is arranged in the current path, depending on an output signal of the comparator (15). Current detection system (2) according to claim 1 , wherein the signal conditioning circuit (13) comprises a first resistor (R1), wherein the first resistor (R1) and the temperature compensation circuit are connected in series between the first terminal (S1) and a third terminal (S3) of the signal conditioning circuit (13) and a Intermediate node, which is arranged between the first resistor (R1) and the temperature compensation circuit, is connected directly or indirectly to the second terminal (S2). Current detection system (2) according to claim 1 or 2 , wherein the resistance of the busbar (9) comprises a positive temperature coefficient. Current detection system (2) according to one of Claims 1 until 3 , wherein the temperature compensation circuit comprises a resistor (Rth) and a diode (D) connected in series. Current detection system (2) according to claim 4 , where the diode (D) is a silicon diode with a pn junction. Current detection system (2) according to one of claims 2 until 5 , wherein the intermediate node between the first resistor (R1) and the temperature compensation circuit is connected to a voltage divider circuit and an intermediate node of the voltage divider circuit is connected to the second terminal (S2) of the signal conditioning circuit (13). Current detection system (2) according to one of Claims 4 until 6 , wherein a ratio of a resistance value of the first resistor (R1) to a resistance value of the resistor (Rth) of the temperature compensation circuit is equal to an amount of a ratio of a bus bar value and a diode value, the bus bar value increasing the amplified voltage drop of the bus bar (9) due to a temperature rise in a predefined temperature range and the diode value represents a reduction in a forward voltage of the diode (D) due to the temperature increase in the predefined temperature range. Current detection system (2) according to one of Claims 1 until 7 , wherein the busbar (9) comprises a copper alloy, wherein the copper alloy comprises copper, Cu, nickel, Ni, and silicon, Si, or comprises copper and silicon. Catalytic converter system for a vehicle, comprising a current detection system (2) according to any one of Claims 1 until 8th and a catalytic converter, wherein the catalytic converter can be connected to a power supply (3) via the bus bar (9).

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