DE102019203526A1 - Discharge device, electrical unit and discharge method - Google Patents

Abstract

The invention relates to a discharge device (4) for discharging an electrical network or an electrically operated unit (1), having a first discharge resistor (6) connected to the network voltage (U), to which a component (2, 3) of the network or to be discharged . The electrically operated unit (1) is connected, a discharge circuit (5) which has a second discharge resistor (7) and a controllable switching element (8), and a control circuit (13) assigned to the switching element (8) on the control connection side for connecting the second Discharge resistor (7) to the first discharge resistor (6) when the mains voltage (U) falls below a specified reference voltage (U).

Description

The invention relates to a discharge device for discharging an electrical network, in particular a high-voltage network, or an electrically operated unit of such a network. The invention also relates to such an electrical unit and to a discharge method.

In modern motor vehicles, components that are operated with a higher operating voltage value are usually used in parallel with the components operated with a voltage with a voltage value of 12 volts. In particular in vehicles with a purely electric drive or with a hybrid drive, such high operating voltages can exceed a value of 100 volts. In the automotive sector, voltage values of more than 60 volts are referred to as "high voltage (HV)". In particular, the electrical units operated with high voltage, typically electrical drive systems, which include, for example, a traction motor, a coolant or lubricant pump, an air conditioning compressor or the like, are integrated in a so-called “high voltage network”. Such a high-voltage network generally also includes at least one energy store (for example a capacitor), which is assigned to one or all of the electrical units of the high-voltage network. This serves for example to keep the operating voltage value required for the electrical unit or the electrical units constant.

For safety reasons, however, it is necessary that such high-voltage networks on the one hand be switched off and on the other hand, in particular, can be discharged. This is particularly the case when people can come into contact with the respective high-voltage network, or short-circuits can otherwise occur, for example during vehicle maintenance or repair or, under certain circumstances, in the event of an accident.

To enable an automatic discharge of, for example, a high-voltage capacitor as an energy store, either a purely passive resistive method or a circuit with controlling semiconductors (semiconductor switches) can be used (active discharge). Resistive methods have the disadvantage that a very high power loss is generated, or that the high voltage is only lowered to a harmless value after a very long time. Discharge circuits in which the discharge of the electrical unit or at least the associated energy storage device takes place reversibly via a controllable switch (semiconductor switch) as a power consumer, often fail because the semiconductor switches required for this are not approved or suitable for a desired linear operation.

In contrast, conceivable circuits with microcontrollers (controller controls) used to control the semiconductor switches are only functional if they work permanently without errors. In addition, circuits that also take voltage gradients into account require a high level of software complexity (software overhead). These circuits are also sensitive to voltage fluctuations or voltage pulses in load or idle mode.

From the EP 2 248 238 B1 a discharge circuit with a PTC resistor (resistor with positive temperature coefficient) is known, which is activated or deactivated by means of a switch designed as a transistor and is thermally coupled to this, the switchable resistor formed thereby being connected in parallel to a capacitor. The control connection of the transistor is fed from the mains voltage and controlled via a control circuit with a bipolar transistor, which in turn is controlled by a control unit. As soon as the transistor is switched on, the PTC resistor heated by it increases the resistance value, as a result of which the control voltage of the transistor is changed and the discharge current through the transistor and the PTC resistor is reduced.

The invention is based on the object of enabling the most reliable possible discharge of an electrical network or an electrically operated unit of such an electrical network. In particular, the highest possible discharge speed should be achieved with a low conduction loss.

This object is achieved according to the invention by a discharge device for active discharging with the features of claim 1. Furthermore, this object is achieved according to the invention by an electrically operated unit with the features of claim 9. In addition, the object is achieved according to the invention by a discharge method with the features of Claim 10. Advantageous and in part inventive embodiments and developments of the invention are set out in the subclaims and in the following description. The conjunction “and / or” here and in the following is to be understood in particular in such a way that the features linked by means of this conjunction can be designed both together and as alternatives to one another.

The discharge device according to the invention is used to discharge an electrical network, in particular a high-voltage network, or an electrically operated unit, which is preferably part of such a high-voltage network (on-board network) or includes one.

The discharge device has a first discharge resistor that is connected to the mains voltage. A component of the network or of the electrically operated unit to be discharged is connected to the first discharge resistor. The first discharge resistor is suitably connected between a positive pole and a negative pole of the mains voltage. The negative pole can also be a reference potential, e.g. B. Mass. The component to be discharged is in particular an (electrical) capacitor or a parallel connection of several capacitors or a capacitor bank.

The discharge device also has a discharge circuit which has a second discharge resistor and a controllable switching element for connecting the second discharge resistor to the first discharge resistor. The switching element is expediently formed by a high-voltage-resistant, preferably a normally blocking, power transistor, in particular an IGBT or a SiCMOS or a GaN-FET. The discharge circuit has the first discharge resistor and preferably a series connection of the controllable switching element and the second discharge resistor, the second discharge resistor being suitably connected between the positive pole of the mains voltage and the drain connection of the switching element (power transistor), the source connection of which is connected to the negative pole or to the reference potential of the mains voltage.

In an advantageous embodiment, the series connection of the controllable switching element and the second discharge resistor is connected in parallel to the first discharge resistor. The component to be discharged is preferably connected in parallel to the first discharge resistor.

The discharging device also has a control circuit assigned to the switching element on the control connection side for switching on the second discharge resistor when the mains voltage falls below a predetermined voltage value. The control circuit is suitably designed as a comparator, the output of which is fed to the control input of the switching element. The control circuit is suitably supplied with a comparison voltage representing the mains voltage via a first input and a reference voltage via a second input.

In a particularly expedient embodiment, the first discharge resistor is designed as a voltage divider with a voltage tap, which is connected on the input side to the control circuit and which thus supplies the comparison voltage in a simple manner. The control circuit can thus be supplied with the mains voltage directly or via a voltage divider as a comparison voltage.

For diagnostic purposes, a measuring connection is preferably connected to the discharge circuit. This is preferably located between the controllable switching element and the second discharge resistor. Additionally or alternatively, a signal connection for activating the controllable switching element is routed to the control circuit.

In a discharging mode, the component to be discharged is connected to the negative pole or reference potential of the network voltage via the discharge circuit of the high-voltage network or the electrically operated unit. The discharge takes place via the parallel connection of the first and the second discharge resistor when this is connected to the first discharge resistor by means of the switching element. The resistance value of the second discharge resistor is preferably smaller than that of the first discharge resistor. In particular, the resistance value of the second discharge resistor is approximately 0.25 to 0.33 times (1/4 to 1/3) the resistance value of the first discharge resistor. The reason for this is that the second discharge resistor is preferably only switched on when the line voltage is comparatively low.

The electrically operated unit according to the invention is preferably part of a vehicle and in particular set up for high-voltage operation. The electrically operated unit is thus part of a high-voltage network described above or forms such a high-voltage network itself. The electrically operated unit according to the invention has the discharge device described above.

The discharge method according to the invention is used to discharge the electrical (high-voltage) network described above or the electrically operated unit described above. The preferably passive discharge method is carried out in particular automatically by means of the discharge device described above. In this case, the second discharge resistor is connected to the first discharge resistor by means of the discharge circuit when the mains voltage falls below the specified voltage value. As a result, the component to be discharged is discharged via the discharge circuit at a high discharge speed and thus in a particularly short time.

The advantages achieved with the invention are in particular that with the discharge circuit, in particular in comparison to a pure resistive discharge, a particularly low (continuous) power loss is achieved with a higher discharge speed at the same time. On the other hand, a possible software expenditure and a possibly required memory occupancy in a microcontroller are lower than with an active discharge. In addition, a thermal connection of the switching element, which is preferably designed as a controllable semiconductor switch, to a thermistor or the like is not required, which correspondingly reduces the circuit complexity and installation space and, with slowly increasing high voltage, the power loss, simplifies the discharge circuit and increases the reliability.

• 1 in einem schematischen Schaltbild eine Entladevorrichtung für eine elektrisch betriebene Einheit eines Fahrzeugs,
• 2 in Ansicht gemäß 1 ein weiteres Ausführungsbeispiel der Entladevorrichtung,
• 3 in einem Spannungs-Zeitdiagramm den Entladeverlauf mit normaler und verkürzter Zeitdauer bis zum Unterschreiten eines vorgegebenen Spannungswertes (Sicherheitsspannung), und
• 4 in einem Diagramm gemäß 3 den Spannungsverlauf bei beschleunigter Entladung mit zwei unterschiedlichen Refererenzspannungen (Spannungswerten).

Exemplary embodiments of the invention are explained in more detail below with reference to a drawing. Show in it:

• 1 In a schematic circuit diagram, a discharge device for an electrically operated unit of a vehicle,
• 2 in view according to 1 another embodiment of the unloading device,
• 3 in a voltage-time diagram the course of discharge with normal and shortened time until the voltage falls below a specified value (safety voltage), and
• 4th in a diagram according to 3 the voltage curve for accelerated discharge with two different reference voltages (voltage values).

Corresponding parts are always provided with the same reference symbols in all figures.

In 1 is a schematic block diagram of part of an electrical high-voltage network of an electrically operated unit 1 shown. The electrically operated unit 1 comprises as components an electric motor, not shown in detail, and an energy store for stabilizing an operating voltage value required for operating the electric motor. In the exemplary embodiment, the energy store is provided by a first capacitor 2 and a second capacitor connected in parallel to this 3 educated. To in certain cases the capacitors 2 , 3 To be able to discharge, the electrically operated unit 1 an unloader 4th on. The unloader 4th again has a discharge circuit 5 on that the capacitors 2 , 3 is connected in parallel.

The discharge circuit 5 comprises a first discharge resistor 6th and a second discharge resistor 7th as well as a controllable switching element 8th . The first discharge resistor 6th is the capacitors 2 , 3 connected in parallel. The first discharge resistor 6th and the capacitors 2 , 3 are connected to a mains voltage U _N connected and connected between the positive pole (+) and the negative pole (-) of a high voltage (HV).

The switching element 8th and the second discharge resistor 7th are connected in series, i.e. form a series circuit. This is connected to the mains voltage U _N connected, the series circuit consisting of the second discharge resistor 7th and the switching element 8th is connected between the positive pole (+) and the negative pole (-) of the high voltage (+ HV, -HV). The switching element 8th is preferably a normally blocking, high voltage resistant n-channel FET (field effect transistor) with a drain connection (collector connection) 9 and with a source connection (emitter connection) 10 as well as with a gate connection (control connection) 11 . The drain connection (collector connection) 9 is across the second discharge resistor 7th connected to the positive pole (+) of the high voltage. The source connection (emitter connection) 10 is connected to the negative pole (-) of the high voltage. The negative pole of the high voltage can also be a reference potential, e.g. B. Mass.

Between the switching element 8th and the second discharge resistor 7th is a measuring connection 12 provided at which the drain voltage ( U _D ) of the switching element 8th as a measurement signal S _D can be tapped for diagnostic purposes.

The unloader 4th has a control circuit 13 on. In the exemplary embodiment, this is a comparator with a first (inverting) input 14th and with a second (non-inverting) input 15th as well as with an exit 16 connected to the gate connection (control connection) 11 of the switching element 8th is led. The control circuit 13 is connected to the positive pole (+) and the negative pole (-) of the high voltage (+ HV, -HV) to supply them.

When running after 1 is the first entrance 14th the control circuit 13 the mains voltage U _N as equivalent stress U _V fed. The control circuit 13 is via the second entrance 15th a reference voltage U _R fed. In addition, the control circuit 13 a control signal (activation signal) S _A to activate or deactivate the discharge circuit 5 are fed.

The control circuit 13 , which is preferably designed as a comparator, compares the inputs at its inputs 14th and 15th applied voltage values, ie the mains voltage U _N as equivalent stress U _V and the reference voltage U _R and shows at the exit 16 indicate, for example in binary or digital form, which input voltage is higher. When the line voltage U _N as equivalent stress U _V the Reference voltage U _R falls below, this is therefore greater than the mains voltage U _N , the control voltage approaches U _S at the exit 16 the positive supply voltage of the control circuit 13 , and the switching element 8th is switched on, ie the FET changes from the blocking to the conducting state.

By switching on the switching element 8th , so when the FET is turned on, the second discharge resistor becomes 7th the first discharge resistor 6th connected in parallel. Thus, the total resistance becomes smaller than the value of the first discharge resistance 6th (and also smaller than the sum of the values of the second discharge resistor 7th and the resistance of the conductive switching element 8th which is practically negligible). This accelerates the discharge process, ie the capacitors 2 , 3 are discharged faster and the time until reaching or falling below a safety voltage U _S , e.g. B. 60V is shortened accordingly.

In the 2 shown electrically operated unit 1 proves against those 1 a simplified provision of the equivalent stress U _V on. This is the first discharge resistor 6th as a voltage divider with two resistors 6a , 6b as well as in the exemplary embodiment with a third resistor 6c executed. Between the resistors 6a and 6b is a voltage tap 17th that goes to the control circuit 13 and this is the equivalent voltage U _V provides. The equivalent stress U _V is for example 2V to 3V.

Otherwise the in 2 shown electrically operated unit 1 after those 1 and also has an unloading device 4th with two capacitors 2 , 3 as well as with the discharge circuit 5 with the first discharge resistor and with the series connection of the second discharge resistor connected in parallel with this 7th and the controllable switching element 8th on to the capacitors connected in parallel 3 after switching on the second discharge resistor 7th to the resistors connected in series 6a , 6b , 6c with reduced discharge time t ₁ on the voltage value U _S to unload. Between the switching element 8th and the second discharge resistor 7th is also the measuring connection 12 intended for diagnostic purposes. The control circuit 13 the activation signal S _A are fed.

3 illustrates the shortened discharge time when the second discharge resistor is connected 7th . The voltage curve (U (t)) over time t is shown. After the initially passive resistive discharge, the additional discharge at the point in time can be recognized t ₀ triggered to which the reference voltage U _R is fallen below. The dashed curve B shows the purely passive (resistive) discharge over the time t, in which the safety voltage (the voltage value) only reaches the time t ₂ U _S is achieved. However, due to the connection of the second discharge resistor 7th to the first discharge resistor 6th , according to curve A with a shortened discharge time, the safety voltage Us already at the earlier point in time t ₁ reached.

4th again illustrates the shortened discharge time when the second discharge resistor is connected 7th providing two thresholds with different reference voltages U _R1 and U _R2 . Again, the voltage curve (U (t)) is shown over time t. It becomes recognizable after initially passive resistive discharge when falling below the first, higher reference voltage U _R1 the additional discharge at the time t ₀₁ triggered. When the equivalent stress U _V at the time t ₀₂ the value of the second, lower reference voltage U _R2 reaches or falls below, the discharge is further accelerated. The point in time is recognizable t ' ₁ to which the safety voltage (the voltage value) U _S is reached, even before the point in time t ₁ out 3 .

The subject matter of the invention is not limited to the exemplary embodiments described above. Rather, further embodiments of the invention can be derived from the above description by a person skilled in the art. In particular, the individual features of the invention described on the basis of the various exemplary embodiments and their design variants can also be combined with one another in other ways.

For example, a GaN-FET or an IGBT (insulated-gate bipolar transistor) or a CMOS (complementary metal-oxide semiconductor), e.g. B. a SiCMOS can be used.

List of reference symbols

1

electrically operated unit

2

first capacitor

3

second capacitor

4th

Unloading device

5

Discharge circuit

6th

first discharge resistor

6a, b, c

resistance

7th

second discharge resistor

8th

Switching element / MOSFET

9

Drain / collector connection

10

Source / emitter connection

11

Gate / control connection

12

Measuring connection

13

Control circuit / comparator

14th

first entrance

15th

second entrance

16

output

17th

Voltage tap

S _A

Control / activation signal

S _D

Measurement signal

U _N

Mains voltage

U _R

Reference voltage

U _S

Safety voltage

U _V

Equivalent stress

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 2248238 B1 [0006]

Claims (10)

Discharge device (4) for discharging an electrical network or an electrically operated unit (1), comprising - a first discharge resistor (6) connected to the network voltage (U _N ), to which a component (2, 3) of the network or the electrically operated unit (1) is switched on, - a discharge circuit (5) which has a second discharge resistor (7) and a controllable switching element (8), and - a control circuit (13) assigned to the switching element (8) on the control connection side for switching on the second Discharge resistor (7) to the first discharge resistor (6) when the mains voltage (U _N ) falls below a predetermined reference voltage (U _R ). Unloading device (4) after Claim 1 , characterized in that the control circuit (13) is designed as a comparator, the output (16) of which is fed to the control input (11) of the switching element (8). Unloading device (4) after Claim 1 or 2 , characterized in that the control circuit (13) is fed a reference voltage (U _V ) representing the mains voltage (U _N ) via a first input (14) and the reference voltage (U _R ) is fed via a second input (15). Unloading device (4) according to one of the Claims 1 to 3 , characterized in that the first discharge resistor (6) is designed as a voltage divider (6a, 6b, 6c) with a voltage tap (17) which is connected on the input side to the control circuit (13). Unloading device (4) according to one of the Claims 1 to 4th , characterized in that the first discharge resistor (6) is connected between a positive pole and a negative pole of the mains voltage (U _N ), and / or that the component (2, 3) to be discharged is connected in parallel to the first discharge resistor (6). Unloading device (4) according to one of the Claims 1 to 5 , characterized in that the discharge circuit (8) is designed as a series connection of the controllable switching element (8) and the second discharge resistor (7), and / - or that the discharge circuit (8) is connected in parallel to the first discharge resistor (6). Unloading device (4) according to one of the Claims 1 to 6th , characterized in that a measuring connection (12), preferably for system diagnosis, is led to the discharge circuit (5), in particular between the controllable switching element (8) and the second discharge resistor (7), and / or that to the control circuit (13 ) a control signal (S _A ) for activating the controllable switching element (8) is performed. Unloading device (4) according to one of the Claims 1 to 7th , characterized in that the switching element (8) is formed by a power transistor, preferably an FET, in particular a normally blocking n-channel FET, and / or that the component (2, 3) to be discharged is formed by a capacitor bank or at least one capacitor is formed. Electrically operated unit (1) for a vehicle, which the unloading device (4) according to one of the Claims 1 to 8th includes. Discharge method for discharging an electrical network or an electrically operated unit (1) by means of the discharge device (4) according to one of the Claims 1 to 9 , the second discharge resistor (7) being connected to the first discharge resistor (6) by means of the discharge circuit (5) when the mains voltage (U _N ) falls below a predetermined reference voltage (U _R ).

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