FR3163225A1 - Battery disconnect device with transistors and liquid cooling - Google Patents

Abstract

Electric Battery Disconnect Device with Transistors and Liquid Cooling Electric battery disconnect device comprising an input terminal (E) for connection to a terminal (201) of the battery, a current path (I) extending from the input terminal, and an output terminal (S) of the device for connection to a load (300), the current path comprising a first circuit (110) having at least two transistors (111, 112), each equipped with an internal diode and arranged in series with opposite conduction directions, the device further comprising a channel (400) through which a coolant can circulate, the channel being configured so that the power dissipated by said at least two transistors is removed by the coolant. Figure for the abstract: Fig. 1.

Description

Battery disconnect device with transistors and liquid cooling

The invention relates to devices for disconnecting an electric battery, for example batteries of electric or hybrid vehicles used to supply electrical energy to a powertrain.

Battery disconnect units, also known as BDUs (Battery Disconnect Units), are systems that allow the battery to be connected and disconnected from the electrical grid, particularly high-voltage grids. These devices protect electrical systems from overload, short circuit, overvoltage, and overcurrent conditions, which can originate in the battery, an inverter, an electric motor, or auxiliary systems.

A good level of protection is necessary to avoid the risk of fire or electrocution for users.

In an electric or hybrid vehicle operating on a high-voltage battery, the battery disconnect device is a specific subsystem which can be integrated separately or distributed into several subsystems in the vehicle so that protection is obtained as close as possible to certain critical systems of the vehicle (inverter, battery, charger, etc.).

Known solutions based on prior art may include a disconnect device integrated into a battery pack that primarily protects the inverter and a DC charger. Secondary devices may be provided in separate power distribution units (PDUs).

Other solutions based on the previous technique may include protection located directly in the battery pack, and other protections distributed, for example in one or more power distribution units.

As is known, the functions of disconnecting and connecting the battery are implemented by electromechanical contactors, fuses, or pyro-fuses.

These components are indeed well-suited for applications involving high power flows between the battery and power subsystems (inverter, charger). Considering their possible dimensions and optimizations, these components provide satisfactory safety functions, overload protection, and short-circuit protection.

That being said, these components have drawbacks. Their long-term durability (on a scale of approximately 15 years) is questionable. These devices can be affected by false positives; they can trigger unexpectedly without need.

These devices are also impacted by false negatives; they may not trigger when necessary, for example.

Another drawback of these components is their resistance to on-state current, which generates heat dissipation detrimental to the robustness and reliability of battery connection devices. Furthermore, battery disconnect devices can be sensitive to excessively high temperatures (momentary or prolonged) and can therefore be affected by their internal components.

Battery disconnect devices use two types of cooling for this purpose: free convection (the disconnect components and busbar dissipate heat into the air, which is then cooled), or indirect cooling where the components and busbars are interfaced with a cold plate via a thermal interface material, for example electrically insulating (usually referred to by the English acronym "TIM: Thermal Interface Material").

Therefore, there is a need for battery disconnection devices that do not have the disadvantages mentioned above.

To this end, the invention proposes a device for disconnecting (and reconnecting after disconnection) an electric battery, comprising a terminal intended to be connected to a terminal of the battery, a current path extending from the input terminal, and an output terminal of the device intended to be connected to a load,
the current path comprising a first circuit having at least two transistors each equipped with an internal diode and arranged in series (the input and output of the first circuit are on either side of the at least two transistors) and in two opposite directions of conduction,
the device further comprising a channel in which a coolant can circulate, the channel being configured so that the power dissipated by said at least two transistors is evacuated by the coolant.

Thus, the invention proposes not to use contactors, fuses or pyro-fuses, but to use at least two transistors in the device, at least in one of the branches going from one of the battery terminals to the load.

Transistors are particularly advantageous in that they can reversibly switch from the conducting state to the blocking state, and vice versa (therefore, disconnection and reconnection are possible).

Inventors have observed that power transistors can be used in place of electromechanical contactors, for example, because they perform the same function but with improved properties. In particular, semiconductor-based transistors have a response time on the order of hundreds of microseconds, compared to a response time of around 30 milliseconds for a contactor. Furthermore, transistors offer advantages over contactors in terms of power loss, lifespan, weight (60 g for a transistor versus approximately 200 g for an electromechanical relay), capacitance, vibration resistance, noise level, functionality, and efficiency.

Power transistors switch very quickly under a large load and can therefore ensure very good durability under highly variable current and cutoff profiles with reproducible performance.

That said, the inventors of this intervention have observed that the use of transistors results in greater heat dissipation. Losses can be three to five times higher, and therefore a specific cooling system is preferable.

Here, the suggestion is to use a cooling system that employs a coolant, rather than air. The coolant could be, for example, glycol-type.

Also, the two transistors are of the same type here (for example, if they are MOSFETs, they are both of the same conduction type N or P).

The arrangement of a transistor in a particular conduction direction is related to the structure of the transistor and the orientation of its internal diode. Here, the internal diodes of the two transistors are in opposite orientations, for example with the anode of the internal diode of one transistor connected to the anode of the internal diode of the other transistor, or the cathode of the internal diode of one transistor connected to the cathode of the internal diode of the other transistor.

Therefore, the direction of conduction of a transistor can be:
- drain to source for N-type field-effect transistors (the anode of the internal diode being connected to the source),
- source to drain for P-type field-effect transistors (the anode of the internal diode being connected to the drain).

Thus, the aforementioned at least two transistors can be connected in series with the source of one connected to the source of the other, or the drain of one connected to the drain of the other for field-effect transistors, regardless of the type of the two transistors (P or N).

The first circuit is therefore bidirectional.

For example, the load mentioned above that receives electrical energy from the battery can be a motor vehicle's powertrain. The electrical energy supplied to the powertrain can be called the discharge.

According to a particular embodiment, the battery terminal is the positive terminal, and wherein the device comprises a second circuit including at least one transistor arranged between an input terminal of the second circuit connected to a battery charging port, and an output terminal of the second circuit connected between the first circuit and the output terminal of the device (i.e. connected to the output terminal of the first circuit), said at least one transistor being provided with an internal diode and arranged in a direction of conduction from the input terminal of the second circuit to the output terminal of the second circuit (in other words, the anode of the internal diode of said at least one transistor is connected to the charging port).

The first circuit is located in the branch running from a battery terminal to the load. The second circuit is dedicated to protection during charging and is arranged between a battery charging port and a point located between the device's output terminal and the first circuit. The battery charging port may be intended to be connected to a charger that includes a rectifier.

According to a particular embodiment, the second circuit comprises, in the same package, at least two transistors arranged on one or more separate chips, connected in parallel and arranged between the input terminal of the second circuit and the output terminal of the second circuit, said at least two transistors being arranged according to said direction of conduction going from the input terminal of the second circuit to the output terminal of the second circuit.

According to a particular embodiment, the channel is further configured so that the power dissipated by said at least one transistor of the second circuit (or all the transistors of the second circuit) is evacuated by the coolant (for example the same liquid as the transistors of the first circuit, for the same channel).

It has been observed that the power from the charger may also require liquid cooling if a transistor is used. The channel can then be configured to allow this cooling (for example, by covering the casing of a transistor in the second circuit).

According to a particular embodiment, the device includes a processor configured to independently control the control electrodes of the transistors of the first circuit and the second circuit (if a second circuit is present).

In this particular embodiment, the control electrodes of the transistors (gate or base) each have their own connection to the processor.

According to a particular embodiment, one or more of said transistors of the first circuit or of the second circuit is mounted in a pin-shaped finned package, said pin-shaped fins extending into said channel.

A pin-shaped finned housing can be called by the Anglo-Saxon expression PINFIN, and allows good cooling of the transistor(s).

It can be noted that several transistors can be arranged in the same package, for example all the transistors of the first or second circuit.

According to a particular embodiment, at least one of said transistors of the first circuit or of the second circuit is mounted in a housing assembled on a metal plate by means of a layer of thermal interface material, the metal plate being in contact with the coolant in said channel.

This particular design also allows for adequate cooling. It should be noted that one or more transistors can be arranged in the same package, for example, all the transistors of the first or second circuit. The metal plate is generally called a "cold plate." Several separate packages can be arranged on this plate.

According to a particular embodiment, at least one of said transistors of the first or second circuit is mounted in a housing assembled between two metal plates by means of two layers of thermal interface material, the two metal plates each being in contact with the coolant in said channel.

According to a particular embodiment, the device includes at least one current sensor arranged in series with a negative terminal of the battery, the current sensor having, once mounted in a system including the load and the battery, an accuracy less than or equal to plus or minus 2% and a bandwidth greater than 500kHz.

Such a current sensor can be made using a so-called "shunt" resistor.

According to a particular embodiment, the first circuit includes a damping circuit configured to allow conduction in both directions of conduction of the two transistors of the first circuit, connected in parallel to the two transistors of the first circuit.

The damping circuit can be referred to by the English term "snubber". This circuit allows for the management of current peaks.

According to a particular embodiment, the damping circuit of the first circuit comprises two branches connected together in parallel, each branch comprising, in series, a diode defining a direction of conduction specific to the branch, a resistor, and a capacitor.

In this particular embodiment, the diodes allow for one branch per direction of current conduction, to have a bidirectional damping circuit.

According to a particular embodiment, the second circuit includes a damping circuit configured to permit conduction in the direction of conduction from the input terminal of the second circuit to the output terminal of the second circuit, connected in parallel to said at least one transistor of the second circuit.

According to a particular embodiment, the damping circuit of the second circuit includes, in series, a diode defining the direction of conduction of the damping circuit, a resistor, and a capacitor.

FIG. 1 There FIG. 1 is a schematic representation of a device based on an example.

FIG. 2 There FIG. 2 represents a transistor in a finned, pin-shaped package.

FIG. 3 There FIG. 3 represents a transistor in a package mounted on a cold plate.

FIG. 4 There FIG. 4 represents a transistor in a package mounted between two plates.

FIG. 5 There FIG. 5 represents a damping circuit according to an example

FIG. 6 There FIG. 6 represents a damping circuit according to an example.

FIG. 7 There FIG. 7 shows yet another damping circuit according to an example.

On the FIG. 1 We have represented a system comprising a device 100 for disconnecting a battery 200 used for supplying electrical energy to a load 300.

Battery 200 can be an electric or hybrid vehicle battery used to power a powertrain (charge 300).

The 300 load can therefore be, for example, an electric or hybrid vehicle inverter used for vehicle traction and/or propulsion.

The battery, 200, has a positive terminal 201 and a negative terminal 202. In the illustrated example, the disconnect device is connected to the positive terminal. However, the invention is not limited to a disconnect device connected to the positive terminal of the battery and can be adapted for connection to the negative terminal of the battery.

The device includes an input terminal E, which is connected to the positive terminal 201 of the battery, and, in a current path leading to the load 300, a first circuit 110 comprising two transistors 111. The current path from the input to the output of the device carries a current denoted I in the figure. In the figure, the two transistors 111 and 112 are N-type MOSFET field-effect transistors (the invention also applies to P-type transistors), and preferably silicon carbide transistors, which are advantageous for high-power applications.

Transistor 111 is connected in the first direction of conduction, and the second transistor 112 is connected in the opposite direction of conduction with the two transistors in series.

Thus, the two sources 111S and 112S of these transistors are connected together here (alternatively, and not shown, the two drains 111D and 112D of these transistors are connected together). The figure shows the internal diodes of these transistors, with their anodes connected together.

The two gates 111G and 112G of these two transistors are controlled by a processor 130 of the device. It should be noted that the gate control of these transistors is implemented independently. As can be seen in the figure, each gate has a separate connection to the processor 130.

The device also includes a second circuit, 120 comprising a transistor 121 (here of type N, although the other type of conduction is conceivable by adapting the circuit) whose drain is connected to the output terminal of the device and the source to a PRC charging port (for example for connection to a rectifier).

Transistor 121 is configured to carry current from the charging port PRC to the branch carrying current I. Specifically, transistor 121, via its drain 121D, is connected between the output terminal S and the first circuit. The source 121S of this transistor is connected to the charging port PRC. The anode of the internal diode of transistor 121 is connected to the charging port.

The second circuit also includes, in parallel with transistor 121, another transistor 121’ arranged in the same direction of conduction, transistor 121’ is optional, and is used for applications where the power requires the paralleling of several transistors.

In fact, transistors 121 and 121’ can be transistors arranged in the same package, present on one or more separate semiconductor chips.

This is also the case for transistors 111 and 112 which can include one or more semiconductor chips in one or more packages.

In fact, a transistor shown in the figure can be implemented using a plurality of individual transistors, formed on one or more semiconductor chips. It should be noted that the number of chips per package allows for fine-tuning the possible power output. The number of packages connected in parallel allows for coarser adjustment of the possible power output.

The first circuit electrically isolates battery 200 from the load 300. To achieve this, the gates of transistors 111G and 112G can be controlled by processor 130, particularly when processor 130 detects, using a sensor, a situation requiring the blocking of current I. For example, a current sensor comprising a resistor 140 in series with the battery, connected to terminal 202 of the battery, can be used to detect short circuits. A voltage sensor 141 is connected across resistor 140, which is itself connected to processor 130. In this case, the resistor is a shunt resistor. This configuration allows for an accuracy of ±2% and a bandwidth exceeding 500 kHz.

The use of a resistor allows for precise and rapid detection of a rise in current level, which should lead to a blocking of the transistors.

The invention is not limited to the use of a shunt resistor and covers other equally efficient sensors.

The second 120 circuit is useful for protecting the rest of the circuit from a problem with the battery charger.

The transistors in the first circuit may require special cooling. This may also be the case for the transistors in the second circuit. We will now describe the possible cooling methods.

There FIG. 2 This is a cross-sectional view of transistor 111, and more specifically a cross-sectional view of package 111B, which houses the transistor 111 chip. Package 111B is a PINFIN type, with fins extending directly into a channel 400 through which a coolant circulates. It should be noted that package 111B can contain other semiconductor chips, for example, the chip(s) of transistor 112. FIG. 3 This is a cross-sectional view of a variant in which a package 111B' of transistor 111 is mounted on a metal plate 500 by means of a layer of thermal interface material (preferably electrically insulating). It can be noted that several packages can be assembled on the plate 500, which is in contact with the channel 400 through which a coolant flows.

There FIG. 4 is a cross-sectional view of another variant in which a 111B'' package of transistor 111 is mounted between two 500'' metal plates, by means of a layer of thermal interface material (preferably electrically insulating). The two 500'' metal plates are in contact with the channel 400 coolant.

It can be noted that the 111B case of the FIG. 2 is the most suitable for high power, followed by the 111B' box, then the 111B'' box.

There FIG. 5 Figure 125 shows a damping circuit mounted on transistor 121 in the second circuit. Specifically, the damping circuit 125 is connected in parallel to the source and drain of transistor 121. It has one branch and is configured to allow conduction from the transistor's drain to its source. This branch includes a diode 126 whose anode is connected to the source of transistor 121, a resistor 127, and a capacitor 128 whose terminal is connected to the drain of transistor 121.

There FIG. 6 Figure 115B shows a damping circuit connected in parallel to the two transistors 111 and 112 of the first circuit. More precisely, the damping circuit has two branches, each associated with a direction of conduction. The first branch, 115A, has a diode 116A in series with a resistor 117A and a capacitor 118A. The anode of diode 116A is connected to the drain of transistor 111, and capacitor 118A has one terminal connected to the drain of transistor 112. The second branch, 115B, has a diode 116B in series with a resistor 117B and a capacitor 118B. The anode of diode 116B is connected to the drain of transistor 112, and capacitor 118B has one terminal connected to the drain of transistor 111.

There FIG. 7 shows an alternative to the damping circuit of the FIG. 6 .

Here, the damping circuit has two branches, each associated with a direction of conduction. The first branch, 115A, contains a diode 116A in series with a resistor 117A and a capacitor 118A. Here, the cathode of diode 116A is connected to the drain of transistor 112, and capacitor 118A has one terminal connected to the drain of transistor 111. The second branch, 115B, contains a diode 116B in series with a resistor 117B and a capacitor 118B. The cathode of diode 116B is connected to the drain of transistor 111, and capacitor 118B has one terminal connected to the drain of transistor 112.

In addition, resistor 119A connects branch 115A to ground, and resistor 119B connects branch 115B to ground. This alternative has the advantage of improving the switch-off response time. It should be noted that in one variation, resistors 119A and 119B can each be replaced by a varistor (less expensive than power resistors).

Claims (13)

Device for disconnecting an electric battery, comprising an input terminal (E) intended to be connected to a terminal (201) of the battery, a current path (I) extending from the input terminal, and an output terminal (S) of the device intended to be connected to a load (300),
the current path comprising a first circuit (110) having at least two transistors (111, 112) each equipped with an internal diode and arranged in series and in two opposite directions of conduction,
the device further comprising a channel (400) in which a coolant can circulate, the channel being configured so that the power dissipated by said at least two transistors is evacuated by the coolant. Device according to claim 1, wherein the battery terminal is the positive terminal (201), and wherein the device comprises a second circuit (120) comprising at least one transistor arranged between an input terminal of the second circuit connected to a battery charging port, and an output terminal of the second circuit connected between the first circuit and the output terminal of the device, said at least one transistor being provided with an internal diode and arranged in a direction of conduction from the input terminal of the second circuit to the output terminal of the second circuit. Device according to claim 2, wherein the second circuit comprises, in the same package, at least two transistors arranged on one or more separate chips, connected in parallel and arranged between the input terminal of the second circuit and the output terminal of the second circuit, said at least two transistors being arranged according to said direction of conduction going from the input terminal of the second circuit to the output terminal of the second circuit. Device according to claim 2 or 3, wherein the channel is further configured so that the power dissipated by said at least one transistor of the second circuit is evacuated by the coolant. Device according to any one of claims 1 to 4, comprising a processor (130) configured to independently control the control electrodes of the transistors of the first circuit and the second circuit. Device according to any one of claims 1 to 4, wherein one or more of said transistors of the first circuit or of the second circuit is mounted in a pin-shaped finned housing (111B), said pin-shaped fins extending into said channel. Device according to any one of claims 1 to 6, wherein at least one of said transistors of the first circuit or of the second circuit is mounted in a housing (111B’) assembled on a metal plate by means of a layer of thermal interface material, the metal plate being in contact with the coolant in said channel. Device according to any one of claims 1 to 7, wherein at least one of said transistors of the first or second circuit is mounted in a housing (111B’’) assembled between two metal plates by means of two layers of thermal interface material, the two metal plates each being in contact with the coolant in said channel. Device according to any one of claims 1 to 5, comprising a current sensor (140, 141) arranged in series with another terminal of the battery, configured to have in use with the battery and load an accuracy less than or equal to plus or minus 2% and a bandwidth greater than 500kHz. Device according to any one of claims 1 to 9, wherein the first circuit comprises a damping circuit (115) configured to permit conduction in both directions of conduction of the two transistors of the first circuit, connected in parallel to the two transistors of the first circuit. Device according to claim 10, wherein the damping circuit of the first circuit comprises two branches connected together in parallel, each branch comprising, in series, a diode (116A, 116B) defining a direction of conduction specific to the branch, a resistor (117A, 117B) and a capacitor (118A, 118B). Device according to any one of claims 1 to 11, wherein the second circuit comprises a damping circuit (125) configured to permit conduction in the direction of conduction from the input terminal of the second circuit to the output terminal of the second circuit, connected in parallel to said at least one transistor of the second circuit. Device according to claim 12, wherein the damping circuit of the second circuit comprises, in series, a diode (126) defining the direction of conduction of the damping circuit, a resistor (127) and a capacitor (128).