Current sensing system

TECHNICAL FIELD

The present disclosure relates to a current sensing system.

BACKGROUND

To control the flow of energy and optimize efficiency in powertrain subsystems of hybrid and electric vehicles, which include, for example, traction inverters, on-board chargers, DC/DC converters and battery management systems (BMS), precise current measurement is essential. After all, the aforementioned subsystems have to measure high currents - and at high voltages of typically over 400 V. In recent years, the current used in these electronic devices has been increased up to about 1 kA, for example. In this case, in order to ensure safety when the circuit is short-circuited, it is necessary to control the short-circuit current. Often an isolated current measurement is used.

There are various methods available for isolated current measurements.

Shunt-based methods with isolated amplifiers or isolated modulators are mainly used in hybrid and electric vehicles. However, the voltage drop across the shunt resistor results in losses and corresponding heating. Therefore, the shunt resistor used for this purpose is required to have a low resistance value of, for example, 100 pQ or less. Therefore, technical improvements to shunt resistors are being worked on so that they become lighter/smaller and have lower resistance values while maintaining or even improving accuracy and drift characteristics.

It is an object of the present disclosure to provide a current sensing system which has a small size and low power dissipation and provides precise overcurrent detection.

SUMMARY

The invention is defined by the independent claim. Advantageous embodiments of the invention are given in the dependent claims. According to a first aspect the present disclosure relates to a current sensing system. The current sensing system comprises a busbar connected in a current path between a power supply and a load.

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

In at least one embodiment the busbar comprises a copper alloy, wherein the copper alloy comprises copper (Cu), nickel (Ni) and silicon (Si), or comprises copper and silicon. Many of the high current applications include Cu or CuNiSi busbars as current carrying elements, therefore it is a main aspect of the disclosure to use a section of the busbar as current sensing element. Using a busbar instead of a separate shunt resistor provides the advantage that separate shunt resistor or hall sensor can be avoided. Thus, not only costs but also space can be saved, and additional power dissipation can be minimized.

The current sensing system comprises an amplifier with a first input and a second input and an output. The first input and the second input are connected to the busbar, such that the amplifier is configured to sense a voltage difference or voltage drop across a section of the busbar caused by a current flow in the current path.

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

As the busbar comprises a temperature dependent resistance with a specific temperature coefficient the current sensing system comprises a signal conditioning circuit. The signal conditioning circuit comprises a first terminal and a second terminal and a temperature compensation circuit. The first terminal is connected to the output of the amplifier. The temperature compensation circuit effects as a temperature dependent resistance with a temperature coefficient which has an opposite sign as the resistance of the busbar.

In at least one embodiment the resistance of the busbar comprises a positive temperature coefficient.

The current sensing system comprises a comparator with a first input and a second input, wherein the first input of the comparator is directly or indirectly connected to the second terminal of the signal conditioning circuit. As the temperature dependency of the resistance of the busbar is at least partly compensated by the temperature compensation circuit, a fixed overcurrent threshold for the comparator can be used as the tolerance for the resulting shut-OFF current is sufficiently small.

Furthermore, the current sensing system comprises a logic circuitry, wherein the logic circuitry is configured to control a state of the switch, which is arranged in the current path dependent on an output signal of the comparator.

The current sensing system has, besides the benefit that the busbar can be used as sensing element, the additional advantage that the temperature dependency of the sensing element is compensated by a low cost and fast hardware solution. It is not necessary 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 terminal.

In at least one embodiment according to the first aspect the temperature compensation circuit comprises a resistor and a diode connected in series. Preferably the cathode of the diode is directly or indirectly connected to the third terminal of the signal conditioning circuit. In particular, the diode comprises a temperature dependent resistance with a negative temperature coefficient. The diode may comprise a transistor which is wired such that it effects 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 comprise a Schottky barrier.

When the busbar uses a material, which has a negative temperature coefficient, a silicon carbide (SiC) Schottky barrier diode may be used which has a positive temperature coefficient. 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, wherein the busbar value represents an increase of the amplified voltage drop of the busbar due to a temperature increase in a pre-defined temperature range and the diode value represents an decrease of a forward voltage of the diode due to the temperature increase in the pre-defined temperature range. This allows to provide a temperature independent or less temperature dependent output voltage on 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 to adjust the output signal level of the amplifier to a threshold voltage level of the comparator.

Furthermore, according to a second aspect the present disclosure relates to a catalyst system for a vehicle, comprising a current sensing system according to the first aspect and a catalyst, wherein the catalyst is connectable via the busbar to a power supply.

Advantageous embodiments of the first aspect are also valid for 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 merely exemplary and are intended to provide an overview or framework to understand the nature and character of the claims. The accompanying drawings are included to provide a further understanding and are incorporated in this description. The drawings illustrate one or more embodiments, and together with the description serve to explain principles and operation of the various embodiments.

In the figures, the same reference signs are used for elements with essentially the same function, but these elements need not be identical in all details. The drawings are not necessarily drawn to scale but are configured to clearly illustrate the disclosure. DETAILED DESCRIPTION OF EMBODIMENTS

The present disclosure will now be described in greater detail hereinafter with reference to the accompanying drawings showing embodiments of the disclosure. The disclosure may, however, 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 relative to certain embodiments and figures below, all embodiments of the present disclosure can include one or more of the advantageous features discussed herein. In other words, while one or more embodiments may be discussed as having certain advantageous features, one or more of such features may also be used in accordance with the various embodiments of the disclosure discussed herein. In similar fashion, while exemplary embodiments may be discussed below as device, system, or method embodiments it should be understood that such exemplary embodiments can be implemented in various devices, systems, and methods.

It is understood that when an element is designated as “connected” or “coupled” to another element, it may be directly connected or coupled to the other element, or intermediate elements may be present. In contrast, when an element is designated as “directly connected” or “directly coupled” to another element, no intermediate elements are present.

Figure 1 shows an equivalent circuit diagram of an exemplary embodiment of the current sensing system and

Figure 2 shows an exemplary diagram of a resistance value of an exemplary busbar.

In Figure 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 3 may be a high voltage battery of an electric vehicle or a hybrid vehicle. The load 5 may be a resistive or inductive load of an electric vehicle or a hybrid vehicle.

The power supply 3 is electrically conductive connected via the switch 7 to the load

5. Therefore, there is a current path between the power supply 3 and the load 5 which can be disconnected by the switch 7, for example if an overcurrent is detected.

In the current path a busbar 9 is arranged. The busbar 9 is used as current sensing element for the current sensing system 2. The busbar 9 comprises a copper alloy, wherein the copper alloy comprises copper, Cu, nickel, Ni, and silicon, Si, or comprises Cu and silicon.

Copper alloy CuNiSi and copper alloy CuNi each comprises a temperature dependent resistance with a positive temperature coefficient. Therefore, a resistance value of the busbar 9 increases with increasing temperature.

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

In particular, a section of the busbar 9 with a pre-defined length is used in order to have a minimal resistance which causes a sufficient voltage drop such that the voltage drop can be sensed by the amplifier without too high measurement error.

Furthermore, the current sensing system 2 comprises an amplifier 11 comprising a first input A1 and a second input A2 and an output A3. The amplifier 11 is, for example a differential amplifier. The amplifier 11 is configured to sense a voltage difference across the busbar 9 caused by a current flow in the current path. In particular, the amplifier 11 is configured to sense a voltage difference or voltage drop across a section of the busbar 9 caused by a current flow in the current path. The amplifier 11 may comprise an operational amplifier.

The amplifier 11 may be an isolation amplifier providing electrical isolation.

In addition, the current sensing system 2 comprises a signal conditioning circuit 13. The signal conditioning circuit 13 comprises a first terminal S1 and a second terminal S2 wherein the first terminal S1 is connected to the output A3 of the amplifier 11 .

The signal conditioning circuit 13 comprises a first stage with a temperature compensation circuit, which effects or acts as a temperature dependent resistance with a temperature coefficient which has an opposite sign as the resistance of the busbar 9. For example, if the resistance of the busbar 9 has a positive temperature coefficient the resistance of the temperature compensation circuit has a negative temperature coefficient.

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

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

For example, the first stage of 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 the third terminal S3 of the signal conditioning circuit 13 and an intermediate node, which is arranged between the first resistor R1 and the temperature compensation circuit, 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 amount of a ratio of a busbar value and a diode value, wherein the busbar value represents an increase of the amplified voltage drop of the busbar 9 due to a temperature increase in a pre-defined temperature range and the diode value represents an decrease of a forward voltage of the diode D due to the temperature increase in the pre-defined temperature range.

For example, the amplified busbar voltage drop has an increase of 1 .48 V due to temperature change from -40 degC to 160 degC and the diode forward voltage has a decrease of 0.436V. Thus, the amount of the ratio of the busbar value and the diode value is RatioBD=1 .48/0.436=3.44. In order to create 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 resistor Rth of the temperature compensation circuit needs to be RatioBD=3.44.

Optionally, for adjusting a voltage level the signal conditioning circuit 13 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 terminal S2 of the signal conditioning circuit 13. The voltage divider circuit is scaling the first stage output voltage to a pre-defined threshold voltage level of a successive comparator 15.

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

The comparator 15 comprises a first input C1 and a second input C2, wherein the first input C1 of the comparator 15 is directly or indirectly connected to the second terminal S2 of the signal conditioning circuit 13. On the second input C2 of the comparator 15 the pre-defined threshold voltage may be applied.

The current sensing system 2 comprises a logic circuitry 17 configured to control a state of the switch 7, which is arranged in the current path dependent on an output signal of the comparator 15.

The logic circuitry 17 may comprise a set-reset latch 171 , for example a SR NAND latch, which provides a state of the output signal of the comparator 15 to a higher logic and an AND-gate 175, which is configured to set the state of the switch 7. The logic circuitry 17 may comprise a microcontroller 173 which is configured to reset the set-reset latch 171 and to provide a control signal to the AND-gate 175, so that after an overcurrent has been detected and the fault condition has been cleared, the switch 7 can be closed again.

The effect of the temperature compensation can be seen in the results summarized in Tables 1 to 3. Table 1 and Table 2 show simulation results, wherein Table 3 shows measurement results. Table 1 shows a minimum and maximum detection current detected by the current sensing system 2 under typical conditions, e. g. with typical parameters, and with a 600 mV threshold voltage of the comparator 15 in the temperature range from -40 degC to +160 degC. The difference between the min. detection current and a max. detection current is about 114 A without temperature compensation and only 12 A with temperature compensation.

Table 1

Table 2 shows the minimum and maximum detection detected current by the current sensing system 2 under worst case conditions, e. g. with worst case parameters, and with a 600 mV threshold voltage of the comparator 15 in the temperature range from -40 degC to +160 degC. The difference between the min. detection current and a max. detection current is about 139 A without temperature compensation and only 54 A with temperature compensation.

Table 2

Table 3 shows a minimum and maximum detection current detected by the current sensing system 2 with a 600 mV threshold voltage of the comparator 15 in the temperature range from -40 degC to +160 degC. With temperature compensation the difference between the min. detection current and a max. detection current is about 15 A.

Table 3

Thus, the temperature compensation effects that the tolerance for the resulting shut-OFF current is sufficiently small and system efficiency can be improved.

REFERENCE SIGNS

1 high voltage system

2 current sensing 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 amplifier

A3 amplifier output

C1 , C2 input of comparator

C3 output of comparator

D diode

GND reference potential

R1 first resistor

R3 third resistor

R4 fourth resistor

Rth resistor of temperature compensation circuit

S1 , S2, S3 terminal of the signal conditioning circuit