WO2023016836A1

WO2023016836A1 - Device for discharging an electric energy store of an electric apparatus

Info

Publication number: WO2023016836A1
Application number: PCT/EP2022/071498
Authority: WO
Inventors: Juergen Gerhart; Michael Rummel
Original assignee: Robert Bosch Gmbh
Priority date: 2021-08-11
Filing date: 2022-08-01
Publication date: 2023-02-16
Also published as: EP4385110A1; CN117678139A; DE102021208763A1

Abstract

Disclosed is a device (100) for discharging an electric energy store (10) of an electric apparatus, wherein: - the device (100) is designed to recognize a discharge event requiring that the electric energy store (10) be discharged within a specific time; - the device (100) is furthermore designed to activate the discharging operation of the electric energy store (10) by means of a discharging element (11); - in a discharge event, the discharging element (11) can be connected in parallel to the electric energy store (10).

Description

title

Device for discharging an electrical energy store of an electrical device

The invention relates to a device for discharging an electrical energy store of an electrical device. The invention also relates to a method for discharging an electrical energy store of an electrical device.

State of the art

A so-called "discharge function" must usually be implemented in electronic control units of vehicles that are operated in the electrical high-voltage (HV) network. This is used to discharge all electrical voltages in the control unit to less than 60V contact voltage in the event of a voltage failure of an electrical on-board network, a disconnection of the HV plug, in the event of an accident, etc.

There are basically two different ways of providing the named discharge function: a) Using a passive discharge unit (eg discharge resistor or discharge current sink) that is permanently connected to the HV power supply. If the electrical voltage of the control unit fails, e.g. B. by uncoupling the HV connector, the electronics are automatically discharged by the passive discharge unit. However, this variant has the disadvantage that when the HV voltage is present, a constant power loss (e.g. 5 watts) is generated by the passive discharge unit, which leads to the partial discharge of the HV battery and generates unnecessary heat loss. b) By means of an actively switched discharge unit: in this case the discharge is actively switched to the HV supply in the ECU and only generates the discharge when the discharge unit is switched on. This variant has the disadvantage that you cannot ensure the discharge in all situations, since you have to make an active decision to discharge. This is possible, for example, by controlling a microcontroller. However, if the power supply to the microcontroller fails or the microcontroller itself has a defect, it is no longer possible to activate the discharge.

Conventional discharge circuits are based on the active or passive discharge of the high-voltage voltage through a fixed ohmic resistor, which permanently (passively) or switched (actively) discharges the electrical high-voltage voltage via the buffer capacitor of the inverter. This is known, for example, from US 2017/0355267A1.

The electrical supply voltage is discharged to a lower voltage potential in an exponential curve in a defined period of time.

Disclosure of Invention

It is an object of the present invention to provide an improved device for discharging an electrical energy store of an electrical device.

According to a first aspect, the object is achieved with a device for discharging an electrical energy store of an electrical device:

- Wherein the device is designed to detect a discharge situation in which the electrical energy store has to be discharged within a defined time;

- Wherein the device is further designed to activate the discharging of the electrical energy store by means of a discharging element;

- In the event of discharge, the discharge element can be switched in parallel with the electrical energy store. This makes it possible to comply with a standard that stipulates, for example, that an electrical energy store of a control device must be discharged to contact voltage, in particular below 60V, within 5s.

According to a second aspect, the object is achieved with a method for discharging an electrical energy store of an electrical device, having the steps:

Recognizing a discharge case in which the electrical energy store has to be discharged; and

Discharging the electrical energy store by means of at least one discharge element, the discharge element being connected in parallel with the electrical energy store and being designed to discharge the electrical energy store in a defined time.

This provides a method with which an electrical energy store is discharged to a defined electrical voltage within a defined period of time.

Preferred embodiments of the device are subject of dependent claims.

A preferred embodiment is that the electrical energy store is designed as one or more buffer capacitors. More than one electrical energy store is preferably formed.

A preferred development of the device is characterized in that by comparing the measured voltage with a reference voltage, a decision is made as to whether a discharge situation is present, a discharge state being present when a measured voltage is less than a reference voltage. In this way a detection device is provided in the form of a sample and hold circuit.

A preferred development of the device is characterized in that a switch is switched, in particular cyclically, preferably for a first period of time. It is advantageous that a voltage is detected while the switch is switched. It is also advantageous that by comparing the measured voltage with a reference voltage, a decision is made as to whether a discharge case is present, a discharge state being present when the measured voltage is less than the reference voltage.

A further preferred development of the device provides for a switch to initiate rapid discharging of the electrical energy store to be activated when the event of discharge is detected.

A further preferred embodiment of the device is characterized in that a supply voltage is discharged to approximately 60 V, in particular less than 60 V, within 10 s, in particular 6 s, preferably approximately 5 s. This can easily be achieved, e.g. by means of an appropriately dimensioned resistor.

A further preferred embodiment of the device is characterized in that the electrical voltage is set at a reference capacitance by a switch controlled by a timer.

Another preferred embodiment of the device is characterized in that the timer is in the form of a bistable flip-flop or a programmable timer module.

A further preferred embodiment of the device is characterized in that it also has a suppression element which is designed to implement switch-on suppression of the switch. Diagnostic purposes for the device can advantageously be implemented in this way by means of a microcontroller which controls the suppression element.

A further preferred embodiment of the device is characterized in that it also has a passive discharge element in an electrically conductive connection with the reference capacitance. In this way, a defined comparison between the measurement voltage and the reference voltage is made possible, it being possible, for example, for a discharge characteristic of the reference capacitor to be monitored to be formed in a very defined manner. A further preferred embodiment of the device is characterized in that a two-stage voltage divider is provided for providing an electrical voltage for the comparator. In this way, a time constant for the reference capacitor can be set in an optimized manner.

A further preferred embodiment of the device is characterized in that the device is provided for discharging the electrical energy store of a control device in a defined manner.

A development is characterized in that the at least one electrical energy store is part of the electrical device. The electrical device is in particular a control device or is connected to such a device, in particular interacts, or the control device is part of the electrical device. The electrical device and/or the control device being used in particular in a vehicle. The electrical device and/or the control unit preferably serves to control an electrical high-voltage consumer, in particular a drive motor of the vehicle, an electric compressor, a fan, a pump or another supply device of the vehicle.

A development of the method is characterized in that a decision is made as to whether a discharge situation is present by comparing a measured voltage with a reference voltage. Furthermore, it is advantageous that a discharge state is present when the measured voltage is lower than the reference voltage.

A development of the method is characterized in that a switch is switched, in particular cyclically, preferably for a first period of time. It is advantageous that a voltage is detected while the switch is switched, in particular for a defined period of time, and that a decision is made by comparing the measured voltage with a reference voltage as to whether a discharge case is present, a discharge state being present when the measured voltage is smaller than the reference voltage. A further development of the method is characterized in that a switch for initiating rapid discharging of the electrical energy store is activated when the event of discharge is detected. Faster discharging takes place via the discharge element.

The invention is described in detail below with further features and advantages on the basis of several figures. Elements that are the same or have the same function have the same reference numbers therein. The figures are intended in particular to clarify the principles that are essential to the invention.

Device features disclosed result analogously from corresponding disclosed method features and vice versa. This means in particular that features, technical advantages and designs relating to the device for discharging an electrical energy storage device result from corresponding designs, features and technical advantages relating to the method for discharging an electrical energy storage device of an electrical device and vice versa.

In the figures shows:

1 shows a discharge curve that is monitored with the device when discharging the electrical energy store;

2 shows an embodiment of a device for discharging an electrical energy store;

3 shows a time profile of a control signal for providing an electrical reference voltage; and

4 shows a basic sequence of a method for discharging an electrical energy store of an electrical device;

5 shows a further embodiment of the discharge element; and

6 shows a further embodiment of the discharge element. Description of Embodiments

The present invention proposes an electronic circuit that makes it possible to activate a discharge of an electrical energy store without using a microcontroller or another control in a defined situation. This is achieved by using a sample-hold stage with a downstream comparator to monitor the HV input voltage of an electrical device. When the HV input voltage drops in a defined manner, a fast discharge circuit is activated, thus ensuring fast discharging in a defined manner, even if the control via a microcontroller fails.

The existing boundary conditions can be outlined as follows:

- Realization of "passive discharge" (slow discharging). This must be dimensioned in such a way that the HV voltage is discharged so quickly that a voltage drop can be reliably detected.

- If the HV voltage is switched off, the electrical energy storage device or devices are discharged via a passive discharge element 18 and the HV voltage drops quickly by a defined voltage level (e.g. 20V in 3.5 seconds).

1 shows a basic mode of operation of the proposed method. A time profile of an electrical supply voltage II can be seen. A permanent monitoring of AU/t1 is provided, with a comparison being carried out with a voltage reference value AUref. In the event that AU>AU _ref , a rapid discharge process (fast discharge) of the electrical energy store is activated.

As a result, rapid discharging of the electrical energy store 10 is supported, e.g. within 1 s. t1 can be dimensioned with 0.1 s, for example (factor 10 smaller than the rapid discharging). This enables rapid discharge faster than 5s, preferably within 4.6 - 4.7 s.

Figure 2 shows a device 100 for detecting a discharge case of an electrical energy store 10. Said electrical energy store 10 (DC link capacitor, DCL capacitor) can, for example, for buffering electrical Be arranged voltage in an electronic control unit of an electric vehicle, wherein the electrical supply voltage HV ⁺ 60V or more, in particular 200V, 400V, 800V or 1000V can be. One or more electrical energy stores 10 are conceivable.

In FIG. 2, the electrical energy store 10 is embodied as a buffer capacitor, for example. According to a preferred development, the electrical energy store is a buffer store or buffer elements or, in general, components of the electrical device that are designed to store electrical energy. In particular, the electrical energy store 10 can also be designed as one or more batteries, preferably as a secondary battery. The electrical energy store can also be a combination of a capacitor and a battery, in particular a secondary battery.

A two-stage voltage divider with a first voltage divider R1/R2 and a second voltage divider R3/R4 can be seen at the input of a comparator 15. The second voltage divider R3/R4 is only optional and is used to lower the electrical supply voltage HV ⁺ , which may be very high, to a level that is favorable for the comparator 15. A single-stage voltage divider with the two ohmic resistors R1, R2 would also be conceivable.

A discharge element 11 can be seen in the form of a constant ohmic resistance, for example, which is connected in series with a switch element 12 . If an impermissible drop or interruption of the supply voltage HV ⁺ or HV is detected; for example as a result of an accident, a technical maintenance operation, a cable fault, etc., the switch element 12 is closed and the electrical energy store 10 is thereby discharged “quickly” via the discharge element 11 in the form of the ohmic resistance.

A detection or trigger circuit of the device 100 that is suitable for this purpose is explained in more detail below.

A timer 13, which cyclically controls a switch 14, is used to alternately charge a reference capacitor Cref with a sample-hold stage, which provides the electrical reference voltage U _ref . A downstream comparator 15 can be seen, which compares the current measurement voltage Umess with a reference voltage _U ref , the measurement voltage being an image of the supply voltage HV ⁺ and the reference voltage _U ref normally having to be smaller than the electrical measurement voltage Umess. In this context, a “normal fair” is understood to mean a non-discharging situation of the electrical energy store 10 .

If the HV voltage HV ⁺ falls, the measurement voltage Umess falls below the reference voltage U _ref , as a result of which the rapid discharging of the electrical energy store 10 is activated. In this case, a logical electrical signal is output by the comparator 15, which is fed to an optional suppression element 16 (e.g. OR element), which is also controlled by a microcontroller (not shown) and is used to suppress switching on, e.g. for diagnostic purposes Device 100 to realize. An output signal of the suppression element 16 is fed to an inverter 17 which provides the correct polarity for a switch 12 driving control signal.

It can also be seen that the device 100 has an optional passive discharge element 18 . The optional passive discharge element 18 is embodied in the form of a resistor, for example. According to an alternative embodiment, it can also be designed as a current sink. A defined comparison between the measurement voltage Umess and the reference voltage U _ref is thus made possible, as a result of which, for example, a discharge characteristic of the reference capacitor C _ref to be monitored according to FIG. 1 can be formed in a very defined manner.

The optional passive discharge element 18 is preferably necessary in order to obtain a voltage drop in the event of discharge. The voltage drop requires activation of the "rapid discharge" via the discharge element 11 . The exact way it works is described below.

Furthermore, the optional passive discharge element 18 serves as a secondary discharge path, in particular when the device according to the invention fails. In particular, the discharge via the optional passive discharge element 18 takes place much more slowly, in particular in approximately 120 s or less. In particular, the optional passive discharge element 18 is a resistance, preferably with higher resistance value as the discharge element 11 . The resistance value is increased to keep the power loss low.

If no optional passive discharge element 18 is formed, the circuit activates the switch 12, in particular during the first time period t1. If the voltage falls below the reference voltage U _ref or if the voltage drop itself is greater than a defined value, the switch 12 remains closed . If no voltage drop is detected, the switch 12 is opened again. Closing to detect a voltage drop of the switch 12 is repeated cyclically. If there is a voltage drop, but this is less than the reference voltage Uref after the time t1, the switch 12 is opened again. Such a small voltage drop can occur in particular as a result of incorrect triggering, in particular due to voltage dips in the vehicle electrical system.

3 shows a time profile of an electrical control signal S for the switch 14. This shows a period t1 with a switch-on time tem in which the switch 14 is closed and with a switch-off time t _off in which the switch 14 is open. In this way, the reference capacitor C _ref is cyclically charged to the electrical reference voltage U _ref with the aid of the timer 13 .

As a result, the reference capacitor Cref is charged alternately with a sample hold stage in this way.

The first voltage divider R1, R2 provides the electrical reference voltage U _ref , the first voltage divider being dimensioned in such a way that it provides, for example, 90% of the measurement voltage Umess. This ensures that, under normal circumstances, the reference voltage U _ref is always smaller than the measurement voltage Umess. The reference capacitor Cref is always kept at the current measurement voltage Umess by the switch 14 cyclically controlled by the timer 13 . This occurs alternately with a predetermined time t1, with the electronic switch 14 bidirectionally carrying the charging/discharging current in the reference capacitor C _ref .

The second voltage divider R3, R4 can be used in order to use a comparator 15 for lower electrical voltages (eg max. 25V, with the voltage at R3 being approx. 5% of HV+ in a favorable design). In the case of discharge, the measured voltage Umess falls due to a discharge via "passive discharge", so the voltage U _ref tracks the measured voltage Umess for the switch-on time tem (e.g. with 0.2 x t1 , i.e. 20 ms). The "passive discharge" takes place in particular via the discharge element 18. During the switch-off time t _off , the measurement voltage Umess drops below the reference voltage U _ref and the comparator 15 switches. This leads to the activation of rapid discharging, as a result of which the electrical energy store 10 can be discharged very quickly (for example in about 1 second) to a defined voltage value, for example to <60V. Within the second time period t2, the rapid discharge then takes place via the discharge element 11. The profile is dependent on the discharge element 11. In particular, the profile is exponential if the discharge element includes a resistor or is designed as such. If, on the other hand, the discharge element 11 is in the form of a current sink, a linear profile results, with a preferably constant discharge current.

With a ratio of resistance values of the voltage divider R3, R4 of 1:20 (eg 20 kOhm: 400 kOhm) with an electrical voltage drop of 20 V, a difference of <1 V between Umess and U _ref can be detected (ok case).

With a ratio of resistance values of the voltage divider R1, R2 with 90 kOhm: 10 kOhm (90%) and a reference capacitance C _ref at 5*tau in 20 msec, a capacitance value of the reference capacitor Cref results as follows:

Cref= Tau/R = 1/5 x 0.02s/10kOhm = 400nF (1)

Tau ... time constant of the reference capacitor C _re f

If the reference voltage U _ref is greater than a voltage across the resistor R3 of the second voltage divider, the reference capacitor C _ref is discharged via R2+R3 || R1 (approx. 27 kOhm). This results in:

5 x Tau = Cref x R = 400 nF x 27 kOhm = 54 ms (OK case) (2)

Timer 13 can be implemented using various standard circuits, e.g. as a bistable flip-flop, programmable timer module, etc. In the event of voltage dips on the HV line, rapid discharging must not be incorrectly activated for several timer cycles (e.g. max. 5×t1), because the discharge resistor 11 can then be thermally overloaded due to the rapid discharging. The discharge resistor 11 is therefore designed in such a way that it can discharge the electrical energy store 10 within, for example, 1s.

When an electronic device with the device 100 is switched on, the “fast discharge” could be incorrectly activated due to an undefined voltage level in the electronic device HV circuit. To do this, the fast discharge signal could be suppressed by the microcontroller. As a rule, however, this is permissible because a "fast discharge" when switching on the electrical device can usually be accepted for a short time.

Diagnostic options result from a back measurement and a comparison of Uref and Umess, as well as monitoring the on/off time of the timer 13. In addition, cyclic monitoring of the rapid discharging can be carried out by activation via the microcontroller. A test of the comparator 15 and the activation of “fast discharge” can be carried out by feeding in a test voltage for the reference voltage, which is greater than the measurement voltage Umess.

It goes without saying that all the aforementioned numerical values and dimensioning information are merely examples. The electrical energy store 10 can be provided, for example, to buffer an electrical operating voltage in an electronic control unit of an electric vehicle.

However, other applications are also conceivable, in which an electrical voltage of an electrical energy store 10 is to be discharged in a defined manner. A capacitance value of the electrical energy store 10 can be specified, for example, by EMC specifications or other relevant standards.

The proposed device 100 can be used in all HV devices that require the electronics to be discharged, e.g. in an e-compressor, which implements an electrically controlled compressor for the purpose of air conditioning the interior of a vehicle.

4 shows a basic sequence of a proposed method. In a step 200, a discharge case in which the electrical energy store 10 has to be discharged is detected.

As described above, the detection takes place by means of the optional passive discharge element 18 or by switching the switch 12, in particular cyclically.

In a step 210, the electrical energy store 10 is discharged by means of at least one discharge element 11, the discharge element 11 being connected in parallel with the electrical energy store 10 and being designed to discharge the electrical energy store 10 to a defined voltage value in a defined time.

According to a development of the invention, the discharge element 11 is designed as a current sink. Corresponding discharge elements are shown in FIGS.

The discharge element 11 according to FIG. 5 has a depletion MOS FET. In addition, the discharge element 11 may include a resistor R5. The resistor is arranged between the source S and the gate G of the depletion MOSFET. By connecting the gate G and source S through the resistor R5, a negative gate-source voltage UGS is generated, so that the depletion MOS FET can be used as a constant current sink with a defined current according to its characteristic. In particular in the case of large currents, preferably greater than 100mA, the resistor R5 could also be omitted. Correspondingly, the gate G and the source S of the depletion MOSFET would then be connected directly to one another. A level of the electrical current results from dividing the threshold voltage of the depletion MOS FET by a resistance value of the resistor R5. The diode shown as an example in Figure 5 represents a parasitic element of the depletion MOSFET.

FIG. 6 shows a further embodiment of a discharge element 11 with bipolar transistors T1, T2, which are connected within a current-limiting circuit known per se. In this case, an electric current is generated by means of the resistor R5 determined, with a current flow through the transistor T1 being monitored. An electrical voltage drop across R5 increases in the event of an increasing electrical current through the transistor T1. As soon as the voltage across the resistor R5 reaches a defined voltage limit value, in particular 0.65V, the transistor T2 begins to conduct, with the transistor T2 diverting electrical current from the base of T1 and conducting it to ground. This reduces the collector current of the transistor T1 and keeps the electrical voltage across the resistor R1 constant at a defined value, in particular at approx. 0.7 V.

It is advantageous that the discharge takes place with a discharge element, which is designed as a current sink, in particular according to one of the two previous statements, with a constant current.

In particular, in accordance with FIG. 2, a substantially more linear course of the voltage results in the time period t2.

According to a development, the passive discharge element is also designed as a current sink according to one of the embodiments above.

The person skilled in the art can also implement embodiments of the invention that are not disclosed or only partially disclosed without departing from the core of the invention.

Claims

Expectations

1. Device (100) for discharging an electrical energy store (10) of an electrical device:

- Wherein the device (100) is designed to detect a discharge situation in which the electrical energy store (10) must be discharged in a defined time;

- Wherein the device (100) is further designed to activate the discharging of the electrical energy store (10) by means of a discharging element (11);

- In the event of discharge, the discharge element (11) can be connected in parallel with the electrical energy store (10).

2. Device according to claim 1, characterized in that the electrical energy store is designed as a buffer capacitor.

3. Device (100) according to one of the preceding claims, characterized in that by comparing a measured voltage (Umess) with a reference voltage (U _ref ) a decision is made as to whether a discharge case is present, a discharge state being present when the measured voltage (Umess) is smaller than the reference voltage (U _ref ).

4. Device (100) according to one of the preceding claims, characterized in that a switch (12) is switched, in particular cyclically, preferably for a first time period (t1), and that a voltage (Umeas) is detected while the switch ( 12) is connected, and that by comparing the measured voltage (Umeas) with a reference voltage (U _ref ) a decision is made as to whether a discharge situation is present, with a discharge state being present when the measured voltage (Umeas) is less than the reference voltage (U _re f) is. Device (100) according to one of the preceding claims, characterized in that upon detection of the event of discharge, a switch (12) for initiating rapid discharging of the electrical energy store (10) via the discharge element (11) is switched. Device according to one of the preceding claims, characterized in that a supply voltage is discharged to approximately 60 V or less within 10 s, in particular 6 s, preferably approximately 5 s. Device according to one of the preceding claims, characterized in that the electrical voltage at a reference capacitance (Cref) is set by a switch (14) controlled by a timer (13). Device (100) according to Claim 6, characterized in that the timer (14) is designed as a bistable flip-flop or as a programmable timer module. Device (100) according to one of the preceding claims, further comprising a suppression element (16) which is designed to implement switch-on suppression of the switch (12). Apparatus (100) according to any one of the preceding claims, further comprising a passive discharge element (18) in electrically conductive communication with the reference capacitance. Device (100) according to one of the preceding claims, characterized in that a two-stage voltage divider (R1, R2, R3, R4) is provided for providing an electrical voltage for the comparator (15). Device (100) according to one of the preceding claims, characterized in that the device (100) is provided for discharging the electrical energy store (10) of a control device in a defined manner. - 17 - Method for discharging an electrical energy store (10) of an electrical device (200), comprising the steps:

Recognizing a discharge case in which the electrical energy store (10) must be discharged; and

Discharging the electrical energy store (10) by means of at least one discharge element (11), the discharge element (11) being connected in parallel with the electrical energy store (10) and being designed to discharge the electrical energy store (10) to a defined voltage value within a defined time . Method according to the preceding claim, characterized in that a decision is made by comparing the measured voltage (Umeas) with a reference voltage (U _ref ) as to whether a discharge case is present, a discharge state being present when the measured voltage (Umeas) is smaller than the reference voltage (U _re f). Method according to one of Claims 13 to 14, characterized in that a switch (12) is switched, in particular cyclically, preferably for a first time period (t1), and that a voltage (Umeas) is detected while the switch (12) is switched , and that by comparing the measured voltage (Umeas) with a reference voltage ( _Uref ), a decision is made as to whether a discharge situation is present, with a discharge state occurring when the measured voltage (Umeas) is less than the reference voltage ( _Uref ) is. Method according to one of Claims 13 to 15, characterized in that when the event of discharge is detected, a switch (12) for initiating rapid discharging of the electrical energy store (10) via the discharge element (11) is switched.