Electrical system with current-consuming circuit for discharging a capacitor associated motor vehicle and method

The electrical system (100) includes: —a capacitor (C); —an electrical power supply device (102); —an electrical power receiving device (104); —a current-consuming electrical circuit (108) designed to consume a current (i) entering via a first interface terminal (BA) and exiting via a second interface terminal (BB). The electrical system (100) being designed such that the current-consuming electrical circuit (108) consumes the discharge current (i) when the electrical power supply device (102) is connected to the terminals of the capacitor (C).The current-consuming electrical circuit (108) includes a transistor (Q1) arranged such that the consumed current (i) enters via a current input terminal (C1) of the transistor (Q1) and exits via a current output terminal (E1) of the transistor (Q1), and in that the current output terminal (E1) is connected to a control terminal (B1) of the transistor (Q1) in order to stabilize the transistor (Q1).

TECHNICAL FIELD

The present invention relates to the discharging of a capacitor, in particular in the field of electric motor vehicles.

TECHNOLOGICAL BACKGROUND

The US patent published under the number U.S. Pat. No. 6,204,612 B1 describes a capacitor, to the terminals of which an electrical power module is intended to be connected. It additionally describes a current-consuming electrical circuit including a stabilized transistor, which is connected to the terminals of the capacitor. In this publication, the current-consuming electrical circuit is designed so as to be activated in order to consume a substantially constant discharge current when the power module is mechanically and electrically disconnected from the capacitor. Thus, the consumption of current discharges the capacitor so as to prevent electric shocks that could occur if an operator were to touch the capacitor. More specifically, the power module includes a conductor arranged so as to short a controlled switch in order to deactivate the current-consuming circuit. Thus, when the power module is disconnected, the conductor is disconnected from the controlled switch, causing the current-consuming electrical circuit to be activated. This solution has the drawback of requiring the presence of a mechanical element (the conductor) on the power-module side. Moreover, this solution does not allow the capacitor to be discharged while the power module is still mechanically in place but electrically disconnected from the capacitor, for example in the event of an electrical connection fault.

Additionally, it is known practice to connect a resistor to the terminals of a capacitor that is supplied with power by a high-voltage source in order to discharge the capacitor in the event that the high-voltage source is disconnected. This solution has the drawback that the resistor continuously consumes substantial current, even when this is not desired, that is to say when the high-voltage source is connected to the capacitor.

The aim of the invention is to at least partly overcome the abovementioned problems.

SUMMARY OF THE INVENTION

To this end, what is proposed is an electrical system including:a capacitor having two terminals;an electrical power supply device connected to the terminals of the capacitor;an electrical power receiving device connected to the terminals of the capacitor so as to receive the electrical power supplied by the electrical power supply device;a current-consuming electrical circuit having two interface terminals that are connected, respectively, to the terminals of the capacitor and being designed to consume a current entering via a first interface terminal and exiting via a second interface terminal,
the electrical system being designed such that the current-consuming electrical circuit consumes the current when the electrical power supply device is connected to the terminals of the capacitor,
the electrical system being characterized in that the current-consuming electrical circuit includes a transistor arranged such that the consumed current enters via a current input terminal of the transistor and exits via a current output terminal of the transistor, and in that the current output terminal is connected to a control terminal of the transistor in order to stabilize the transistor.

Optionally, the current-consuming electrical circuit includes a Zener diode connected between the current output terminal of the transistor and the control terminal of the transistor in order to stabilize the transistor.

Also optionally, the current-consuming electrical circuit includes a resistor connected between the control terminal of the transistor and the first interface terminal.

Also optionally, the current-consuming electrical circuit includes a resistor connected between the current input terminal of the transistor and the first interface terminal.

Also optionally, the current-consuming electrical circuit includes a resistor connected between the current output terminal and the second interface terminal.

Also optionally, the electrical power supply device is designed to apply a DC supply voltage.

Also optionally, the DC supply voltage is higher than 60 V, preferably higher than 300 V.

Also optionally, the electrical power supply device includes one of the following: a battery charger and a battery.

Also optionally, the electrical power receiving device includes one of the following: a battery, an inverter and a DC-to-DC converter.

An electrical system according to the invention is also proposed.

Throughout the preceding text, the current-consuming electrical circuit may be a passive circuit. This current-consuming electrical circuit may be supplied with electrical power exclusively via the two interface terminals, in particular by the capacitor that is to be discharged when the electrical power supply device is not operational. This electrical discharge circuit may moreover be devoid of any computing component, that is to say any component designed to run a computer program, such as a microcontroller or a microprocessor.

Also proposed is a method for discharging a capacitor having two terminals, including:when an electrical power supply device is connected to the terminals of the capacitor in order to apply a supply voltage across the terminals of the capacitor, a current-consuming electrical circuit having two interface terminals that are connected, respectively, to the terminals of the capacitor consumes a current entering via a first interface terminal and exiting via a second interface terminal;when the electrical power supply device is no longer in operation so as no longer to restrict a capacitor voltage present across the terminals of the capacitor, the current-consuming electrical circuit consumes the current in order to discharge the capacitor,
the method being characterized in that the current-consuming electrical circuit used in preceding steps includes a transistor arranged such that the consumed current enters via a current input terminal of the transistor and exits via a current output terminal of the transistor, and in that the current output terminal of the transistor is connected to a control terminal of the transistor in order to stabilize the transistor.

In one particular embodiment of the invention, the current-consuming electrical circuit used in the above-described steps of the discharge method further includes a Zener diode connected between the current output terminal of the transistor and the control terminal of the transistor in order to stabilize the transistor.

In another particular embodiment of the invention, the current-consuming electrical circuit used in the above-described steps of the discharge method further includes a resistor connected between the current input terminal of the transistor and the first interface terminal.

DETAILED DESCRIPTION

An electrical system100implementing the invention will now be described with reference toFIG.1.

The electrical system100firstly includes an electrical power supply device102that is provided with two electrical power supply terminals BC, BDacross which a supply voltage E is designed to be supplied. For example, the supply voltage E is substantially constant. Furthermore, in the example described, the power supply terminal BDis connected to an electrical ground of the electrical system100, and the power supply terminal BCis intended to be at the positive potential of +E V.

The electrical system100furthermore includes an electrical power receiving device104connected between the electrical power supply terminals BC, BDand designed to receive electrical power supplied by the electrical power supply device102.

The electrical system100furthermore includes a capacitor C having two terminals BE, BFthat are connected, respectively, to the electrical power supply terminals BC, BDand being designed for example to smooth the supply voltage E. Across its terminals BE, BF, the capacitor C has a capacitor voltage uCwhich is equal to the supply voltage E when the electrical power supply device102is operational.

The electrical system100furthermore includes a current-consuming electrical circuit108having two interface terminals BA, BBthat are connected, respectively, to the terminals BE, BFof the capacitor C so as to receive the capacitor voltage uC. The current-consuming electrical circuit108is designed to consume a current i entering via the first interface terminal BAand exiting via the second interface terminal BB.

The current-consuming electrical circuit108is intended in particular to discharge the capacitor C when the electrical power supply device102is not operational, for example when it is disconnected. This situation occurs for example, inFIG.1, when one of the connections connecting the electrical power supply terminals BC, BDto the interface terminals BA, BBis broken.

The current-consuming electrical circuit108includes a transistor Q1which has a current input terminal C1, a current output terminal E1and a control terminal B1. In the example described, the transistor Q1is a bipolar transistor which has a collector, an emitter and a base corresponding to the current input terminal C1, the current output terminal E1and the control terminal B1, respectively. The open or closed state of the transistor Q1is defined by a control voltage V1that is present between the control terminal B1and the current output terminal E1. Additionally, the current i flows through the transistor Q1by entering via the current input terminal C1and exiting via the current output terminal E1.

In the example described, the current-consuming electrical circuit108furthermore includes a resistor R1connected between the current input terminal C1and the interface terminal BA.

In the example described, the current-consuming electrical circuit108furthermore includes a resistor R2connected between the current output terminal E1and the interface terminal BB.

In the example described, the current-consuming electrical circuit108furthermore includes a resistor R4connected between the control terminal B1and the interface terminal BA.

In the example described, the current-consuming electrical circuit108furthermore includes a Zener diode D1connected between the control terminal B1and the interface terminal BB.

Thus, the current output terminal E1of the transistor Q1is connected to the control terminal B1of the transistor Q1through the resistor R2and the Zener diode D1in order to stabilize the transistor Q1.

The operation of the electrical system100will now be described with reference toFIG.2.

Initially, the electrical power supply device102is operational and supplies the supply voltage E, which has the value of 500 V in the example described. Generally, the supply voltage E is a “high voltage”, which means, in the automotive field, that it has a value greater than 60 V, preferably greater than 300 V.

Thus, the capacitor C is charged at the supply voltage E such that the capacitor voltage uCis equal to the supply voltage E.

The control terminal B1of the transistor Q1is charged through the resistor R4such that the transistor Q1is in the closed (on) state. Thus, a non-zero current i flows from the interface terminal BAto the interface terminal BBthrough the transistor Q1. Since the transistor Q1is stabilized, the current i is substantially constant, even in the case of a fluctuation in the supply voltage E, and has a value of 5 mA in the example illustrated. In general, the current i preferably has a value of more than 1 mA.

At a time t0, the electrical power supply device102transitions to the non-operational state, for example by being disconnected from the rest of the electrical system100.

Thus, the consumption of the current i results in the capacitor C being discharged and hence the capacitor voltage uCdropping. Since the transistor Q1is stabilized, the current i flowing through it is substantially constant (slightly decreasing, in fact), at a distinctly higher level than would be the case if it were discharged into a simple resistor. Specifically, in this latter case, the current would decrease exponentially and hence very quickly in the first moments following the disconnection of the electrical power supply device102. Thus, since the current i consumed remains at a high level, close to the level before time to, the capacitor voltage uCdrops rapidly.

Preferably, the components are chosen such that the capacitor C is discharged to less than 60 V in less than 60 seconds (time t1inFIG.2).

By virtue of the transistor Q1being stabilized, it is possible to size the current-consuming electrical circuit108such that the starting current i (i.e. before t0, when the electrical power supply device102is operational) is small, in any case smaller than when using a discharge resistor. Thus, in the electrical system100, the losses arising from the consumption of the current i while the electrical power supply device102is operational are lower than when a resistor is used.

Furthermore, at a time t2, when the capacitor voltage uCbecomes too low to keep the transistor Q1stabilized, the current-consuming device108“collapses”, i.e. it is no longer capable of keeping the current i substantially constant and this current decreases very rapidly. This collapse is of no consequence since the desired discharging of the capacitor (uC<60 V) has already been achieved.

Furthermore, in accordance with the foregoing, it will be understood that the current-consuming electrical circuit108is a passive circuit, which means both that it is designed to be supplied with electrical power exclusively via the two interface terminals BA, BB, in particular by the capacitor C when the electrical power supply device102is not operational and that it does not include any computing component, that is to say any component designed to run a computer program, such as a microcontroller or a microprocessor.

An electric motor vehicle300will now be described with reference toFIG.3.

The electric motor vehicle300includes a charger302designed to be connected to an electrical network and to provide a DC voltage.

The electric motor vehicle300furthermore includes a high-voltage battery304designed to be charged by the charger302.

The electric motor vehicle300furthermore includes a capacitor C1inserted between the charger302and the high-voltage battery304.

The electric motor vehicle300furthermore includes an inverter306designed to supply AC voltages on the basis of the DC voltage from the high-voltage battery304.

The electric motor vehicle300furthermore includes a capacitor C2inserted between the high-voltage battery304and the inverter306.

The electric motor vehicle300furthermore includes an electric motor308designed to be supplied with electrical power by the inverter306and to drive wheels of the electric motor vehicle300.

The electric motor vehicle300furthermore includes a DC-to-DC converter310designed to supply a low voltage on the basis of the high voltage supplied by the high-voltage battery304.

The electric motor vehicle300furthermore includes a capacitor C3inserted between the high-voltage battery304and the DC-to-DC converter310.

The electric motor vehicle300furthermore includes a low-voltage battery312designed to be charged by the DC-to-DC converter310. The low-voltage battery312serves for example to supply electrical power to accessories of the electric motor vehicle300.

The current-consuming electrical circuit108described with reference toFIG.1may be used for each of the capacitors C1, C2, C3. Thus, depending on the capacitor concerned, the electrical power supply device102thus includes one of the following: the charger302and the high-voltage battery304, and the electrical power receiving device includes one of the following: the high-voltage battery304, the inverter306and the DC-to-DC converter310.

The present invention is not limited to the embodiment described above, but rather is defined by the claims below. Indeed, it will be obvious to a person skilled in the art that it can be modified.

For example, one or other of the resistors R1and R2could be omitted.

Additionally, the Zener diode D1could be replaced with a resistor.

Moreover, each of one or more resistors R1, R2and R4is preferably a resistor having a resistance that varies little with temperature, for example varying at most by 100 millionths of an ohm per degree Celsius between 0° C. and 150° C.

Moreover, the terms used in the claims should not be understood as being limited to the elements of the embodiment described above, but rather should be understood as covering all equivalent elements that a person skilled in the art is able to infer from his or her general knowledge.

In particular, the term “electric motor vehicle” also covers the case of hybrid motor vehicles including both an electric motor and a combustion engine for driving the wheels.