US-12618872-B2 - Current sensing system

US12618872B2US 12618872 B2US12618872 B2US 12618872B2US-12618872-B2

Abstract

A current sensing system includes a busbar connected in a current path between a power supply and a load. The busbar includes a temperature dependent resistance with a specific temperature coefficient. An amplifier is configured to sense a voltage difference across a section of the busbar caused by a current in the current path. The current sensing system includes a temperature compensation circuit, wherein the temperature compensation circuit is effective as a temperature dependent resistance with a temperature coefficient which has a sign opposite from the resistance of the busbar. A first input of a comparator is directly or indirectly connected to a second terminal of the signal conditioning circuit. The current sensing system includes a logic circuitry, which is configured to control a state of a switch, which is disposed in the current path dependent on an output signal of the comparator.

Inventors

Laszlo Molnar
Octavian Luca

Assignees

Vitesco Technologies GmbH

Dates

Publication Date: 20260505
Application Date: 20221212
Priority Date: 20211217

Claims (14)

1 . A current sensing system, comprising: a busbar connected in a current path between a power supply and a load, said busbar having a temperature dependent resistance with a specific temperature coefficient; a switch is disposed in the current path; an amplifier having a first input, a second input and an output, said first input and said second input connected to said busbar, and said amplifier configured to sense a voltage difference across a section of said busbar caused by a current in the current path; a signal conditioning circuit having a first terminal, a second terminal and a temperature compensation circuit, said first terminal connected to said output of said amplifier, and said temperature compensation circuit acting as a temperature dependent resistance with a temperature coefficient having a sign opposite to the specific temperature coefficient of the temperature dependent resistance of said busbar; a comparator having a first input and a second input, said first input of said comparator directly or indirectly connected to said second terminal of said signal conditioning circuit; and logic circuitry configured to control a state of said switch disposed in the current path, in dependence on an output signal of said comparator.
2 . The current sensing system according to claim 1 , wherein: said signal conditioning circuit includes a first resistor and a third terminal; said first resistor and said temperature compensation circuit connected in series between said first terminal and said third terminal of said signal conditioning circuit; and an intermediate node is disposed between said first resistor and said temperature compensation circuit, and said intermediate node is directly or indirectly connected to said second terminal.
3 . The current sensing system according to claim 2 , which further comprises: a voltage divider circuit having an intermediate node connected to said second terminal of said signal conditioning circuit; said intermediate node disposed between said first resistor and said temperature compensation circuit being connected to said voltage divider circuit.
4 . The current sensing system according to claim 1 , wherein the resistance of the busbar includes a positive temperature coefficient.
5 . The current sensing system according to claim 1 , wherein said temperature compensation circuit includes a resistor and a diode connected in series.
6 . The current sensing system according to claim 5 , wherein said diode is a silicon diode with a p-n junction.
7 . The current sensing system according to claim 5 , wherein: a ratio of a resistance value of said first resistor to a resistance value of said resistor of said temperature compensation circuit is equal to an amount of a ratio of a busbar value and a diode value; the busbar value represents an increase of an amplified voltage drop of said busbar due to a temperature increase in a pre-defined temperature range; and the diode value represents a decrease of a forward voltage of said diode due to the temperature increase in the pre-defined temperature range.
8 . The current sensing system according to claim 1 , wherein said busbar includes a copper alloy, said copper alloy includes copper, nickel, and silicon, or said copper alloy includes copper and silicon.
9 . A catalyst system for a vehicle, the catalyst system comprising the current sensing system according to claim 1 , and a catalyst, said catalyst configured to be connected via said busbar to the power supply.
10 . A current sensing system, comprising: a busbar connected in a current path between a power supply and a load, said busbar having a temperature dependent resistance with a positive temperature coefficient; a switch is disposed in the current path; an amplifier having a first input, a second input and an output, said first input and said second input connected to said busbar, and said amplifier configured to sense a voltage difference across a section of said busbar caused by a current in the current path; a signal conditioning circuit having a first terminal, a second terminal and a temperature compensation circuit, said first terminal connected to said output of said amplifier, said temperature compensation circuit acting as a temperature dependent resistance with a temperature coefficient having a sign opposite to the positive temperature coefficient of the temperature dependent resistance of said busbar, and said temperature compensation circuit including a resistor and a diode connected in series, said diode being a silicon diode with a p-n junction; a comparator having a first input and a second input, said first input of said comparator directly or indirectly connected to said second terminal of said signal conditioning circuit; and logic circuitry configured to control a state of said switch disposed in the current path, in dependence on an output signal of said comparator.
11 . The current sensing system according to claim 10 , wherein: said signal conditioning circuit includes a first resistor and a third terminal; said first resistor and said temperature compensation circuit connected in series between said first terminal and said third terminal of said signal conditioning circuit; and an intermediate node is disposed between said first resistor and said temperature compensation circuit, and said intermediate node being directly or indirectly connected to said second terminal.
12 . The current sensing system according to claim 11 , which further comprises: a voltage divider circuit having an intermediate node connected to said second terminal of said signal conditioning circuit; said intermediate node disposed between said first resistor and said temperature compensation circuit being connected to said voltage divider circuit.
13 . The current sensing system according to claim 11 , wherein: a ratio of a resistance value of said first resistor to a resistance value of said resistor of said temperature compensation circuit is equal to an amount of a ratio of a busbar value and a diode value; the busbar value represents an increase of an amplified voltage drop of said busbar due to a temperature increase in a pre-defined temperature range; and the diode value represents a decrease of a forward voltage of said diode due to the temperature increase in the pre-defined temperature range.
14 . The current sensing system according to claim 11 , wherein said busbar includes a copper alloy, said copper alloy includes copper, nickel, and silicon, or said copper alloy includes copper and silicon.

Description

FIELD AND BACKGROUND OF THE INVENTION The present disclosure relates to a current sensing system. 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 μΩ 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 OF THE INVENTION 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 co