Circuit arrangement for discharging at least one energy store charged to a high voltage

Abstract

The invention relates to a circuit arrangement for discharging at least one energy storage device (ES) charged to a high voltage in a motor vehicle, comprising: a discharge circuit (RD, TD; DC‑DC1, DC‑DC2) connected in parallel with the energy storage device (ES); an auxiliary microcontroller (MC1) for controlling the discharge circuit (RD, TD; DC‑DC1, DC‑DC2), the auxiliary microcontroller being capable of operating with a low voltage of 3‑5 volts; a first voltage supply circuit (SV1) for supplying the auxiliary microcontroller (MC1) with a low voltage of 3‑5 volts, the first voltage supply circuit being supplied with a voltage of 10‑15 volts by a buffer capacitor (C_Puffer); and a main microcontroller (MC2), the main microcontroller being configured to control the auxiliary microcontroller (MC1) for controlling the discharge circuit (RD, TD; DC‑DC1, DC‑DC2).

Description

Technical Field

[0001] The invention relates to a circuit arrangement for discharging at least one energy store in a motor vehicle which is charged to a high voltage, the circuit arrangement having a discharge circuit connected in parallel with the energy store. Background Art

[0002] Such a circuit arrangement is known from DE 10 2016 222 632 A1. In this document, before discharging an energy store charged to a high voltage, a short test discharge is first carried out by means of a timer, and in the process a voltage drop detector or a rate detector is used to check whether the energy store (here the intermediate circuit capacitor) is separated from the high-voltage battery and can therefore be discharged without the risk of excessive current flowing from the high-voltage battery. Only then is the discharge carried out under the control of the voltage drop detector. The timer and the voltage drop detector can be implemented in a microcontroller, wherein the microcontroller can be supplied with power via a buffer capacitor, which is charged from the energy store via a linear regulator.

[0003] In electric or hybrid vehicles, high-current lines are used to transfer electrical energy from the high-voltage battery to the electric traction motor or from the charging device to the high-voltage battery, to which high DC voltages of several hundred volts can be applied. In order to smooth out current peaks or to provide higher energy in a short period of time, energy stores (mostly in the form of intermediate storage capacitors) are connected to these high-current or high-voltage lines, which are then also charged to the high voltage.

[0004] The high-voltage battery is usually connected to the electrical circuit and the high-voltage line via switches (usually referred to as contactors), wherein the energy storage device on the electrical circuit side is connected to the high-voltage line.

[0005] If the vehicle is stationary for a longer period, undergoing inspection or repairs, or in the event of an accident, one or more energy storage devices must be discharged to a contact voltage of at least less than 60 V so that people are not exposed to high voltages.

[0006] The US Federal Motor Safety Standard (FMVSS) requires that under certain conditions, capacitors on high-voltage lines be discharged to less than 60 volts within 5 seconds.

[0007] However, the discharge circuit requires a voltage supply, which can be interrupted in the event of a vehicle accident, for example because a cable of the 12-volt vehicle battery breaks. When designing the discharge circuit, using high voltage for the voltage supply leads to complex insulation requirements and requires high-voltage-resistant and therefore expensive components. Summary of the invention

[0008] It is therefore an object of the present invention to specify a circuit arrangement for discharging at least one energy store in a motor vehicle which is charged to a high voltage, which circuit arrangement can be implemented in the low-voltage range and nevertheless has an accident-proof voltage supply.

[0009] This object is achieved by a circuit arrangement according to claim 1. Advantageous developments are specified in the dependent claims.

[0010] Therefore, the circuit arrangement according to the invention for discharging at least one energy storage device charged to a high voltage in a motor vehicle is formed by: a discharge circuit connected in parallel with the energy storage device; an auxiliary microcontroller for controlling the discharge circuit, the auxiliary microcontroller being operable with a low voltage of 3-5 volts; a first voltage supply circuit for supplying the auxiliary microcontroller with a low voltage of 3-5 volts, the first voltage supply circuit being fed with a voltage of 10-15 volts by a buffer capacitor; and a main microcontroller, the main microcontroller being configured to control the auxiliary microcontroller for controlling the discharge circuit.

[0011] By using an auxiliary microcontroller which can be powered by a low voltage of 3-5 volts provided by the first voltage supply circuit, a relatively small buffer capacitor can be used to power the first voltage supply circuit, wherein even if the actual voltage source, i.e. the 12 volt vehicle battery, is no longer connected, the discharge circuit can still be kept running for the required time of 5 seconds, which is sufficient to discharge the energy storage device.

[0012] In a first embodiment, the discharge circuit is formed by a discharge resistor and a discharge transistor connected in series with the discharge resistor, wherein the auxiliary microcontroller is connected to the discharge circuit via a driver circuit.

[0013] This represents a very safe way of discharging, since the electrical energy stored in the energy store is converted into heat only by a discharge resistor which is connected in parallel with the energy store via a discharge transistor connected in series therewith, which can usually be carried out without any problems and without restrictions.

[0014] In an alternative second exemplary embodiment, the discharge circuit is formed by a DC-DC converter which is connected on the output side to the high-voltage battery and to an actuating control circuit which is connected to the auxiliary microcontroller.

[0015] This makes it possible in an advantageous manner not only to convert the electrical energy stored in the energy store into thermal energy but also to store it back in the high-voltage battery.

[0016] However, since in certain situations conditions may prevail in which sufficiently fast discharge is not possible due to recycling, the discharge circuit can advantageously also be formed by a discharge resistor and a discharge transistor connected in series therewith, which are connected in parallel with the DC-DC converter.

[0017] As a result, a safe discharge is then possible in any case, but without any energy recovery.

[0018] In order to charge the buffer capacitor which supplies the auxiliary microcontroller, the buffer capacitor can advantageously be connected to a second voltage supply circuit which, for operation, is connected to a permanent positive voltage terminal (so-called terminal 30 ) in the vehicle voltage grid.

[0019] The buffer capacitor is thus charged from the onboard voltage grid of the motor vehicle, wherein the auxiliary microcontroller can also be supplied directly from the onboard voltage grid if the cable is still intact after the accident.

[0020] In one development of the circuit arrangement, the high potential of the high voltage is connected to a monitoring circuit, which is connected to the auxiliary microcontroller and to the main microcontroller via a galvanic decoupling line.

[0021] The discharge current can thereby be monitored by both the auxiliary microcontroller and the main microcontroller.

[0022] In an advantageous embodiment of the circuit arrangement, the control lines between the main microcontroller and the auxiliary microcontroller are also galvanically decoupled. In this case, an optocoupler is used in one embodiment.

[0023] This makes it possible to achieve good decoupling between the low-voltage range, in which the main microcontroller must perform further tasks, and the high-voltage range, to which the auxiliary microcontroller is connected.

[0024] In an advantageous development, the discharge circuit can be formed by a further DC-DC converter which is connected on the output side to the low-voltage battery (terminal 30 ) and to a further control circuit which is connected to the auxiliary microcontroller.

[0025] Therefore, the energy stored in the energy storage device can be recovered not only into the high-voltage battery but also into the low-voltage battery.

[0026] In an advantageous embodiment of the circuit arrangement, the discharge transistor is an IGBT (Insulated Gate Bipolar Transistor), which is connected to a controlled driver circuit which is connected to the second voltage supply circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be explained in more detail below based on exemplary embodiments with the aid of the accompanying drawings.

[0028] Figure 1 A first exemplary embodiment of a circuit arrangement is shown, which has a discharge circuit with a discharge resistor and a discharge transistor connected in series therewith, and

[0029] Figure 2 A second exemplary embodiment of a circuit arrangement is shown, which has a DC-DC converter which is connected on the output side to a high-voltage battery. DETAILED DESCRIPTION

[0030] Figure 1 An energy store ES is schematically shown, which is connected between two high-voltage lines, each with a high potential HV_DC+ and a low potential HV_DC-. The energy store ES can be formed by one or more capacitors, which are used either as smoothing capacitors for current and voltage peaks or, if necessary, to achieve higher load currents to support a high-voltage battery, to which the capacitors are connected via a protective switch (not shown).

[0031] In order to discharge the energy storage ES, Figure 1 In the embodiment shown, a series circuit consisting of a discharge resistor RD and a discharge transistor TD is connected in parallel with the energy storage ES, wherein the discharge transistor TD is designed as an IGBT (insulated gate bipolar transistor) with a substrate diode in the embodiment shown. The discharge transistor TD is controlled by a driver circuit TS, which is supplied by a 12 volt power supply, for example, on the one hand, and is connected to a low potential HV_DC- on the other hand. The driver circuit TS is itself controlled by an auxiliary microcontroller MC1 to discharge the energy storage ES, which is itself controlled by the main microcontroller MC2.

[0032] In the exemplary embodiment shown, the auxiliary microcontroller MC1 is supplied by a voltage source with a low voltage value of 5 volts and its reference potential connection is also at the low potential HV_DC- of the high-voltage line, since the auxiliary microcontroller MC1 is galvanically connected to the high-voltage part. The auxiliary microcontroller MC1 is controlled by the main microcontroller MC2 via an optocoupler and is therefore galvanically decoupled in order to isolate the main microcontroller MC2 from the high-voltage part of the circuit arrangement. The voltage level at the connection point of the discharge transistor TD and the discharge resistor RD is directly transmitted to the auxiliary microcontroller MC1 via a monitoring circuit and is also transmitted to the main microcontroller MC2 via a galvanically decoupled optocoupler in order to be able to monitor the switching on and off of the discharge transistor TD.

[0033] According to the invention, the 5 volt supply voltage of the auxiliary microcontroller MC1 is provided by a first voltage supply circuit SV1, which is itself supplied with 12 volts by a second voltage supply circuit SV2, which is assisted by a buffer capacitor C_puffer according to the invention so as to be able to provide the auxiliary microcontroller MC1 with the required 5 second supply voltage.

[0034] The second voltage supply circuit SV2 itself is powered by the 12-volt vehicle battery and is connected to the positive pole of the vehicle battery, the so-called permanent positive pole KL30, referred to as terminal 30. With regard to the reference potential, the second voltage supply circuit SV2 is located at the negative pole KL31 of the vehicle battery, referred to as terminal 31. The reference potential of the first voltage supply circuit SV1 and of the buffer capacitor C_puffer is the low potential HV_DC- of the high-voltage line, which requires that the second voltage supply circuit SV2 should be internally galvanically isolated.

[0035] Therefore, due to Figure 1 The design of the circuit arrangement according to the invention makes it possible to continue to supply auxiliary microcontroller MC1 with power via first voltage supply circuit SV1 at least for a predefined time, even if the battery cable is broken and therefore there is no longer any voltage at terminal 30 (KL30), because the buffer capacitor C_puffer is dimensioned sufficiently large to provide the energy required for this purpose.

[0036] exist Figure 2 0044 shows a further exemplary embodiment of a circuit arrangement according to the invention, wherein identical circuit components are provided with the same reference numerals.

[0037] and Figure 1 Unlike the exemplary embodiment of , the energy store ES arranged between the high-voltage line potentials HV_DC+ and HV_DC- is discharged by the auxiliary microcontroller MC1 and the main microcontroller MC2 via the DC / DC converter DC-DC1 when necessary, but the energy stored in the energy store ES is advantageously stored back in the high-voltage battery HVBatt.

[0038] The DC / DC converter DC-DC1 is controlled in a known manner by a control circuit Con1 , wherein the control circuit Con1 is controlled by an auxiliary microcontroller MC1 via a control signal EN_1 .

[0039] In an extension of this alternative circuit arrangement, Figure 2 It is also indicated in FIG. 2 that a further DC / DC converter DC-DC2 can be provided, via which the energy store ES can be discharged into a low-voltage battery NVBatt (the low-voltage battery being a conventional 12-volt vehicle battery).

[0040] The further DC / DC converter DC-DC2 is here controlled by a further control circuit Con2 which is itself controlled by the auxiliary microcontroller MC1 via a further control signal EN_2 .

[0041] Both the high voltage battery HVbatt and the low voltage battery NVbatt can be connected by the control circuit Con1 or the further control circuit Con2 via corresponding connections HV_BCN_Sense or LV_BCN_Sense so that the control circuits Con1 , Con2 have access to the charge state of the battery in order to be able to control the discharge into the respective battery accordingly.

[0042] Figure 2 Not shown in the figure by adding Figure 1 This circuit arrangement is extended by a discharge circuit, ie a series circuit of a discharge resistor and a discharge transistor, in order to be able to discharge the energy store ES in any case if the battery cannot be used as a recovery device.

Claims

1. A circuit arrangement for discharging at least one energy storage device (ES) charged to a high voltage in a motor vehicle, comprising: a discharge circuit connected in parallel with the energy storage device (ES); an auxiliary microcontroller (MC1) for operating the discharge circuit, the auxiliary microcontroller being capable of operating at a low voltage of 3-5 volts; a first voltage supply circuit (SV1) for supplying a low voltage of 3-5 volts to the auxiliary microcontroller (MC1), the first voltage supply circuit being fed with a voltage of 10-15 volts by a buffer capacitor (C_Puffer); as well as a main microcontroller (MC2) which is designed to control an auxiliary microcontroller (MC1) for controlling the discharge circuit, The discharge circuit comprises a DC-DC converter (DC-DC1), which is connected to a high-voltage battery (HVBatt) on the output side and to a control circuit (Con1) for controlling the DC-DC converter, and the control circuit is connected to the auxiliary microcontroller (MC1).

2. The circuit arrangement according to claim 1, wherein the discharge circuit further comprises a discharge resistor and a discharge transistor connected in series with the discharge resistor, the discharge resistor and the discharge transistor being connected in parallel with the DC-DC converter (DC-DC1).

3. The circuit arrangement according to claim 2, wherein the buffer capacitor (C_Puffer) is connected to a second voltage supply circuit (SV2) for charging, and the second voltage supply circuit (SV2) is connected to a permanent positive voltage terminal (KL30) in the onboard voltage network of the motor vehicle for operation.

4. A circuit arrangement according to any one of claims 1 to 2, wherein the high potential (HV_DC+) of the high voltage to which the energy storage device (ES) is charged is connected to a monitoring circuit, the monitoring circuit being connected to the auxiliary microcontroller (MC1) and connected to the main microcontroller (MC2) via a galvanic decoupling line. 5 . The circuit arrangement as claimed in claim 1 , wherein the control lines between the main microcontroller ( MC2 ) and the auxiliary microcontroller ( MC1 ) are galvanically decoupled.

6. A circuit arrangement according to any one of claims 1 to 2, wherein the discharge circuit further comprises an additional DC-DC converter (DC-DC2), which is connected to a low-voltage battery (NVBatt) on the output side and to an additional control circuit (Con2) for controlling the additional DC-DC converter, and the additional control circuit (Con2) is connected to the auxiliary microcontroller (MC1).

7. The circuit arrangement according to claim 3, wherein the discharge transistor (TD) is an IGBT which is connected to a driver circuit (TS) for driving the IGBT, and the driver circuit (TS) is connected to the second voltage supply circuit (SV2).

8. The circuit arrangement as claimed in claim 4, wherein the current decoupling line is formed by an optocoupler.

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