EP4158769A1

EP4158769A1 - Control device for an inverter, electric drive system and method for establishing a safe operating mode

Info

Publication number: EP4158769A1
Application number: EP21722858.4A
Authority: EP
Inventors: Daniel Raichle; Thomas Knorpp; Thomas Merkel; Volker Gilgenbach; Manfred Kirschner; Edwin Eberlein
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2020-05-25
Filing date: 2021-04-30
Publication date: 2023-04-05
Also published as: WO2021239386A1; CN115552787A; US20230246570A1; DE102020206478A1

Abstract

The present invention relates to establishing a rotational speed-dependent safe operating mode. For this purpose, two redundant control paths are provided and are each designed to establish either an active short-circuit or a freewheeling mode as the safe operating mode. In this way, even if one control path fails, a rotational speed-dependent safe operating mode can still be fully established.

Description

description

title

Control device for a power converter, electrical drive system and

Procedure for setting a safe operating state

The present invention relates to a control device for a converter, an electrical drive system and a method for setting a safe operating state in an electrical drive system.

State of the art

Electric drive systems are becoming increasingly important. In particular, electrical drive systems are found in wholly or at least partially electrically driven vehicles. For safety reasons, it is necessary to set a safe operating state in the event of an error, in particular in the event of an error in the control of the converter in such a drive system. An active short circuit or a so-called freewheel, for example, are known as such safe operating states.

In the event of an active short circuit, the phase connections of the electrical machine are electrically short-circuited by means of the switching elements in the converter. In the case of freewheeling, on the other hand, all switching elements of the converter can be opened so that the phase connections of the electrical machine are not electrically connected to one another.

The document DE 102011 081 173 A1 describes an operating state circuit for inverters and a method for setting operating states in an inverter. In this case, it is proposed in particular to switch to freewheeling as a safe operating state in the inverter if a speed of the electrical machine is less than a predetermined speed threshold value, and to switch the inverter to an active short circuit if the determined Speed of the electrical machine is greater than or equal to a predetermined threshold speed.

Disclosure of the invention

The present invention discloses a control device for a converter in an electric drive system, an electric drive system and a method for setting a safe operating state in an electric drive system with the features of the independent claims. Further advantageous embodiments are the subject of the dependent claims.

Accordingly, it is provided:

A control device for a converter in an electric drive system with a first control path and a second control path. The first control path and the second control path are each designed to set a safe operating state in the converter of the electrical drive system. The first control path comprises a first safety device. The first safety device is designed to determine a speed of the electrical machine of the electrical drive system. Furthermore, the first safety device is designed to use the determined speed of the electrical machine to set either an active short circuit or a freewheeling in the converter. The second control path comprises a second safety device. The second safety device is designed to determine the speed of the electrical machine in the electrical drive system. Furthermore, the second safety device is designed to use the speed of the electrical machine determined by the second safety device to set either an active short circuit or a freewheeling in the converter.

It is also provided: An electrical drive system with an electrical machine, a converter which is designed to control the electrical machine, and a control device according to the invention for the converter.

Finally, it is planned:

A method for setting a safe operating state in an electric drive system. The method comprises a first determination of a rotational speed of an electrical machine of the electrical drive system and a first setting of a safe operating state in the electrical machine by means of a first control path. The safe operating state is set using the determined speed. Depending on the determined speed, either an active short circuit or a freewheel is set in the converter of the electrical drive system. Furthermore, the method includes a second determination of a speed of the electrical machine of the electrical drive system and a second setting of a safe operating state in the electrical machine. The second determination of the speed and the second setting of the safe operating state takes place here by means of a second control path. Analogous to the first setting of the safe operating state, the second setting of the safe operating state also takes place using the determined speed, either an active short circuit or a freewheeling in the converter of the electrical drive system being set.

Advantages of the invention

The present invention is based on the knowledge that, depending on a speed of the electrical machine in an electrical drive system, different safe operating states are advantageous. Therefore, a speed-dependent selection of the respectively suitable safe operating state can be advantageous. A further finding of the present invention is that, in the event of a fault in a conventional system, there may not be sufficient information about the speed of the electrical machine, or the speed information cannot be evaluated in a suitable manner. It is therefore an idea of the present invention to take this knowledge into account and to further improve the safety and reliability of an electric drive system, in particular for setting speed-dependent safe operating states. For this purpose, it is provided to implement a speed-dependent setting of safe operating states by means of two separate control paths. The two control paths here form two redundant control paths for a speed-dependent setting of safe operating states. In this way, the respectively suitable safe operating state can also be reliably set if an error occurs in one of the two control paths.

As a result of the redundant implementation of speed-dependent safe operating states, a suitable safe operating state can also be set if an error occurs in one of the two control paths. In this way it can be ensured, for example, that dangerous voltage increases in the electric drive system are avoided. The occurrence of undesirably high electrical currents can also be avoided by a suitable choice of the respective safe operating state. In addition, a redundant implementation of speed-dependent safe operating states can also prevent an operating state from being set which would possibly result in an undesirably high deceleration torque.

The redundant speed-dependent selection and setting of safe operating states thus leads to increased safety. In addition, dangerous voltage or current peaks can be avoided, which would lead to the destruction or at least premature aging of the components concerned.

According to one embodiment, the first safety device and / or the second safety device are designed to set an active short circuit in the converter if the determined speed of the electrical machine exceeds a first threshold value. Additionally or alternatively, the respective safety devices can set a freewheel if the determined speed of the electrical machine falls below a second threshold value. In particular, the second threshold value can be greater than the first threshold value. In this way, a hysteresis between the change from freewheeling and active short-circuit can be implemented. An active short circuit can lead to an active braking torque of the electrical machine. Such a braking torque can lead to strong deceleration, especially at low speeds, which can lead to loss of traction and thus dangerous driving situations in electric vehicles, for example. On the other hand, undesirably high voltage peaks can occur at higher speeds in freewheeling, which can lead to dangerous states within the drive system, in particular within the voltage converter.

According to one embodiment, the control device is designed to control a converter with a plurality of half bridges. As a rule, a half-bridge with an upper switching element and a lower switching element will be provided in the converter for each phase of an electrical machine. In this case, the first safety device and the second safety device can be designed to control the switching elements in the individual half bridges using phase currents in the corresponding phases in order to set a freewheel. In this way, it can be ensured that during the transition to freewheeling, even if there is no connection to an electrical energy source, such as the traction battery in an electric vehicle, there is no short-term overvoltage in the DC link capacitor of the converter. For example, the phase currents in the individual phases can be recorded and monitored. Thus, the individual switching elements can be activated at a zero crossing or near the zero crossing of the corresponding phase current, the activation for setting a freewheel including in particular opening the switching elements in the corresponding half bridge.

According to one embodiment, the first safety device and / or the second safety device are designed to control the switching elements in the individual half bridges using phase voltages in the corresponding phases in order to set an active short circuit. For example, the corresponding switching elements can be switched on at a phase angle at which the current would also be taken over in steady-state operation by the corresponding switching element. In this way, an excessive increase in the phase current with a correspondingly high load on the respective switch can be avoided. In particular, a recorded voltage-time area of the respective phase can be taken into account for determining a suitable point in time for controlling the respective switching elements. For example, the switching elements can be switched in a half-bridge when the voltage-time area of the corresponding phase reaches half of its maximum value. If necessary, it can be switched earlier as this has no influence due to the negative current direction.

According to one embodiment, the first safety device is designed to verify the determined speed of the electrical machine using the speed determined by the second safety device. The redundant detection of the speed of the electrical machine by means of the first safety device and the second safety device thus enables a functional test of the individual components during operation. In particular, for example, a malfunction of the speed determination can be realized by comparing the speeds determined in the safety devices. Of course, the second safety device can also verify the determined speed using the speed determined by the first safety device.

According to one embodiment, the first control path is designed to be fed from a low-voltage side of the electric drive system. The second control path can be designed to be fed from a high-voltage side of the electric drive system. In this way, a high degree of independence between the two control paths can be achieved. For example, even in the event of a failure of the supply voltage on the low-voltage side and thus a complete failure of the first control path, a safe operating state, in particular a speed-dependent safe operating state, can still be set by means of the second control path.

According to one embodiment, the second safety device is designed to set the freewheel as a safe operating state, if a The intermediate circuit voltage of the converter falls below a predetermined first threshold voltage. In particular, freewheeling can be selected as the safe operating state even if an active short circuit should be selected on the basis of the determined speed. In this way, the intermediate circuit voltage can be increased by briefly setting the freewheeling and thus an energy supply of the second control path can be ensured.

According to one embodiment, the second safety device is designed to set the active short circuit as a safe operating state if the intermediate circuit voltage of the converter exceeds a predetermined second threshold voltage and the determined speed is greater than the first threshold value. In this way, dangerous excessive voltage increases on the intermediate circuit capacitor can be avoided. In particular, the second threshold voltage can be set in such a way that the intermediate circuit voltage is always lower than an electrical voltage of an energy source that can be connected to the intermediate circuit capacitor, for example the traction battery of an electric vehicle.

According to one embodiment, the second safety device is designed to determine the speed of the electrical machine during the active short circuit using forward voltages through the switching elements in the converter. In particular, the flow voltage of switching elements can be used here which set the active short circuit, that is to say which are closed during the active short circuit. The speed of the electrical machine can thus be determined on the high-voltage side without additional components.

According to one embodiment, the second safety device is designed to determine the speed of the electrical machine during freewheeling using at least two phase voltages of the electrical machine. In particular, at least two phase voltages can be evaluated in relation to a predefined reference potential. In this way, the speed of the electrical machine can be determined on the high-voltage side without additional components, even during freewheeling. The above configurations and developments can be combined with one another as desired, as far as this makes sense. Further refinements, developments and implementations of the invention also include combinations, not explicitly mentioned, of features of the invention described above or below with regard to the exemplary embodiments. In particular, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic forms of the invention.

Brief description of the drawings

Further features and advantages of the invention are explained below with reference to the figures. Show:

FIG. 1: a schematic representation of a block diagram of an electric drive system according to an embodiment;

FIG. 2: a schematic representation of the course of a braking torque over the speed during an active short circuit;

Figure 3: a schematic representation of a block diagram of a

Safety device for a control device according to one embodiment; and

FIG. 4: a flowchart on the basis of a method for setting a safe operating state according to an embodiment.

Description of embodiments

FIG. 1 shows a schematic representation of a block diagram of an electric drive system according to an embodiment. The electric drive system can be, for example, the electric drive system of a completely or at least partially electrically driven vehicle. The electric drive system can be powered by an electric energy store 1, for example a traction battery of an electric vehicle be fed. The energy provided by the electrical energy store 1 can be provided at the input connection of a converter arrangement 2, if necessary via a battery disconnect switch 1 a. The converter arrangement 2 can comprise, for example, an inverter 30 with a plurality of switching elements. For example, an intermediate circuit capacitor 31 can be provided at the input connection of the inverter 30. An output connection of the converter arrangement 2, in particular at the output connection of the inverter 30, can be connected to an electrical machine 3. The arrangement shown here with a three-phase electrical machine 3 serves only as an example for a better understanding. Of course, electrical machines 3 with any other number of electrical phases are also possible.

The inverter 30 can, for example, comprise a half-bridge with an upper switching element H1, H2, H3 and a lower switching element LI, L2, L3 for each phase of the electrical machine 3. During normal operational operation of the electrical drive system, the inverter 30, in particular the switching elements in the inverter 30, can be activated by means of activation signals from a control device in a first activation path 10. For this purpose, target value specifications and possibly also sensor signals from operating variables of the drive system can be received in the control device. On the basis of these setpoint specifications S and sensor values, the control device can generate suitable control signals for controlling the upper switching elements Hl, H2, H3 and the lower switching elements LI, L2 and L3.

The control device in the first control path 10 can be, for example, a main computer which sends the required operating parameters during the operation of the electric drive system and generates the suitable control signals for controlling the inverter 30. Under certain circumstances, for example when a fault is detected in the electric drive system, it may be necessary to set a so-called safe operating state in the electric drive system, in particular in the inverter 30. This safe operating state can be a so-called freewheel, for example, in which all switching elements Hl, H2, H3 and LI, L2, L3 des Inverter 30 are open. Alternatively, a so-called active short circuit can be set as a safe operating state, in which the phase connections of the electrical machine 3 are electrically connected to one another by means of the upper switching elements Hl, H2, H3 or the lower switching elements LI, L2, L3.

As will be explained in more detail below, the selection of whether the safe operating state is set to freewheeling or active short-circuit can be established as a function of the current speed of the electrical machine 3. For this purpose, a first safety device 11 can be provided in the first control path 10, which device determines the speed of the electrical machine 3. This determined speed can be used to decide whether the active short circuit or the freewheel should be set as a safe operating state. For example, a threshold value can be set for the speed, and if the speed exceeds this threshold value, the active short circuit is set as the safe operating state. Below this threshold value, freewheeling can be set as a safe operating state. If the speed of the electrical machine 3 varies while a safe operating state is to be set, a hysteresis can be provided for the change between active short-circuit and freewheeling. In this case, a first threshold value nl can be provided, and when it is exceeded, there is a change from freewheeling to active short-circuit. Furthermore, a second threshold value n2 can be provided, which, if it is undershot, changes from the active short circuit to freewheeling. The speed for the first threshold value n1 can be smaller than the speed for the second threshold value n2.

FIG. 2 shows a schematic diagram for the course of a braking torque M of the electrical machine 3 as a function of the speed n during an active short circuit. As can be seen here, the active short circuit can cause a strong braking torque, especially at low speeds. Such a strong braking torque can, for example, lead to a loss of traction between the wheels and the road in electric vehicles. In order to avoid such dangerous driving situations, the active short-circuit is only set at higher speeds, while at lower speeds, the safe operating state is freewheeling is set. As further shown in FIG. 2, an above-described hysteresis can be provided between the speed for the first threshold value n1 and the speed for the second threshold value n2. When the safe operating state is set for the first time, either the first threshold value n1 or the second threshold value n2 can be used to decide whether the active short circuit or the freewheel should be set. In addition, any other approaches, for example with a speed in the range between n1 and n2, are basically also possible.

For the initial setting of a safe operating state in freewheeling or active short circuit as well as for the change between active short circuit and freewheeling, in particular the electrical voltages and currents in the inverter 30, in particular at the switching elements Hl, H2, H3, LI, L2, L3 can be taken into account will. In particular, a point in time can be provided for the opening or closing of the individual switching elements, which in a suitable manner avoids an excessive increase in electrical voltages and / or currents. For example, it can be advantageous to open a switching element at a zero crossing of the electrical current or at least near the zero crossing in order to avoid voltage peaks.

If only a first control path 10 is provided for controlling the inverter 30, the setting of the safe operating state and in particular the speed-dependent change between active short-circuit and freewheeling can only be implemented by the first safety device 11. Furthermore, an additional component can optionally be provided which, in the event of a complete failure of the first control path 10, sets a fixed, predetermined safe operating state, for example an active short circuit. In this case, however, if the first control path 10 fails, no speed-dependent setting of the safe operating state would be possible.

Therefore, in the electric drive system according to FIG. 1, a second control path 20 with a second safety device 21 is provided. This second safety device 21 can also determine the speed of the electrical machine 3 and, if necessary, in particular in the event of a fault, a speed-dependent, safe operating state in the converter arrangement 2, in particular in the inverter 30. The concept of the speed-dependent setting of a safe operating state largely corresponds to the previously described approach for setting the freewheeling or the active short-circuit as a function of the current speed of the electrical machine 3.

The first control path 10 can be fed, for example, from a low-voltage network. Such a low-voltage network is, for example, a voltage supply that is separate from or independent of the energy source 1. In particular, the voltage level of the low-voltage network can be lower than the voltage level of a high-voltage network with the energy source 1, which feeds the electric drive system.

The second control path 20 can be fed, for example, from the high-voltage side of the electric drive system. In this way, even in the event of a failure or a fault on the low-voltage side of the electric drive system, a safe operating state can still be set by means of the second safety device 21 in the second control path 20.

FIG. 3 shows a schematic representation of a block diagram of a safety device 20 according to an embodiment. The safety device 21 can, for example, detect the electrical voltages U_ph at the phase connections of the electrical machine 3. A first evaluation device 22 can evaluate these phase voltages U_ph, in particular in freewheeling, and determine the speed of the electrical machine 3 using the phase voltage U_ph. Furthermore, the phase currents l_ph at the second safety device

21 are provided. For example, a second evaluation device

22 detect the phase currents l_ph and determine the speed of the electrical machine 3 on the basis of the phase currents l_ph. In particular, the speed can be determined on the basis of the phase currents l_ph in the active short circuit. The rotational speed determined by the first evaluation device 22 and / or the second evaluation device 23 can be made available to a processing device 25. The processing device 25 can thus determine a suitable safe operating state in each case as a function of the rotational speed and, if necessary, control the switching elements Hl, H2, H3, LI, L2, L3 in the inverter 30 accordingly.

If, during the safe operating state in the electric drive system, the electrical energy source 1 is disconnected from the converter arrangement 2 by opening the battery isolating switch la, the intermediate circuit capacitor 31 at the input of the inverter 30 can discharge over time, especially in the event of an active short circuit. There is thus the risk that if the intermediate circuit capacitor 31 is discharged too deeply, there is no longer sufficient energy available to supply the safety device 21 in the second control path 20. The safety device 21 can therefore monitor the intermediate circuit voltage U_ZK of the intermediate circuit capacitor 31 in the second control path 20. If the intermediate circuit voltage U_ZK at the intermediate circuit capacitor 31 falls below a predefined threshold voltage, it is possible to briefly switch to freewheeling even at high speeds. As a result, the intermediate circuit capacitor 31 can be charged further. However, in order to avoid an excessive increase in the electrical voltage at the intermediate circuit capacitor 31, especially at higher speeds, it is possible to switch back to the active short circuit when a second threshold voltage is exceeded. The second threshold voltage should preferably be lower than the electrical voltage that is provided by the electrical energy store 1. For example, a voltage can be selected as the voltage value for the change from active short circuit to freewheeling which corresponds to the pole wheel voltage in freewheeling at the switchover point for the speed-dependent safe state.

In order to increase the reliability of the electric drive system even further, the speed of the electric machine 3 determined by the first safety device 11 and the speed of the electric machine 3 determined by the second safety device 21 can be compared with one another during normal operation of the electric drive system. If a significant difference between the two determined speeds is detected, this can indicate a malfunction in at least one of the two safety devices. FIG. 4 shows a schematic representation of a flow chart for a method for setting a safe operating state in an electric drive system. The method can in principle comprise any steps, as have already been described above in connection with the electric drive system. Correspondingly, the electric drive system, in particular the control device, can also include any suitable components, as will be described below in connection with the method.

The method comprises two parallel steps S1 and S2. Step S1 is carried out by a first control path 10, and step S2 is carried out by a second control path 20. As already described above, the first control path 10 can be fed from a low-voltage network, and the second control path 20 can be fed from a high-voltage network. In step S1, a rotational speed of the electrical machine 3 is determined Sil. Then, in step S12, a safe operating state of the electrical machine can be set. The safe operating state can be set as a function of the speed, that is, using the determined speed. In particular, an active short circuit or freewheeling can be set in the converter of the electrical drive system as a function of the determined speed.

Analogously, step S2 comprises a step S21 for determining the rotational speed of the electrical machine and a step S22 for setting a safe operating state. Here, too, the safe operating state can be set using the speed determined in step S21, with either a free-wheeling or an active short-circuit being able to be set as the safe operating state, depending on the speed.

In summary, the present invention relates to the setting of a speed-dependent safe operating state. For this purpose, two redundant control paths are provided, each of which can set either an active short circuit or a freewheel as a safe operating state, depending on the speed. In this way, a speed-dependent safe operating state can still be set completely even if a control path fails.

Claims

Expectations

1. Control device for a converter (30) in an electrical drive system, with a first control path (10) and a second control path (20), each of which is designed to set a safe operating state in a converter (30) of the electrical drive system, wherein the first control path (10) comprises a first safety device (11) which is designed to determine a speed of an electrical machine (3) of the electrical drive system and using the determined speed of the electrical machine (3) either an active short circuit or a Set freewheeling in the converter (30); and wherein the second control path (20) comprises a second safety device (21) which is designed to determine the speed of the electric machine (3) of the electric drive system and either an active short circuit using the determined speed of the electric machine (3) or to set a freewheel in the converter (30).

2. Control device according to claim 1, wherein the first safety device (11) and / or the second safety device (21) are designed to set an active short circuit in the converter (30) if the determined speed of the electrical machines (3) has a exceeds the first threshold value (nl), and to set a freewheel if the determined speed of the electrical machine (3) falls below a second threshold value (n2).

3. Control device according to claim 1 or 2, wherein the control device is designed to control a converter (30) with a plurality of half bridges, and wherein the first safety device (11) and / or the second safety device (21) are designed for setting a freewheeling switching elements (LI, L2, L3, Hl, H2, H3) in the individual half bridges using phase currents in the corresponding To control phases.

4. Control device according to one of claims 1 to 3, wherein the control device is designed to control a converter (30) with several half bridges, and wherein the first safety device (11) and / or the second safety device (21) are designed for setting an active short circuit to control the switching elements (LI, L2, L3, Hl, H2, H3) in the individual half bridges using phase voltages in the corresponding phases.

5. Control device according to one of claims 1 to 4, wherein the first safety device (11) is designed to verify the determined speed of the electrical machine (3) using the speed determined by the second safety device (20).

6. Control device according to one of claims 1 to 5, wherein the first control path (10) is designed to be fed from a low-voltage side of the electric drive system and the second control path (20) is designed to be fed from a high-voltage side of the electric drive system will.

7. Control device according to one of claims 1 to 6, wherein the second safety device (21) is designed to set the freewheel as a safe operating state if an intermediate circuit voltage of the converter (30) falls below a predetermined first threshold voltage.

8. The control device of claim 7, wherein the second safety device is designed to set the active short circuit as a safe operating state if an intermediate circuit voltage of the converter is a exceeds the predetermined second threshold voltage and the determined speed is greater than the first threshold value.

9. Control device according to one of claims 1 to 7, wherein the second safety device (21), which is designed to determine the speed of the electrical machine (3) during the active short circuit using forward voltages through switching elements in the converter (30) .

10. Control device according to one of claims 1 to 9, wherein the second safety device (21), which is designed to determine the speed of the electrical machine (3) during freewheeling under at least two phase voltages of the electrical machine (3).

11. An electric drive system, comprising: an electric machine (3); a converter (30) which is designed to control the electrical machine (3); and a control device according to any one of claims 1 to 10.

12. Procedure for setting a safe operating state in an electric drive system, with the steps:

Determining (Sil) a speed of an electrical machine (3) of the electrical drive system and setting (S12) the safe operating state in the electrical machine (3) by means of a first control path (10), the setting (S12) of the safe operating state using the determined Speed sets either an active short circuit or a freewheeling in a converter (30) of the electrical drive system; and or

Determining (S21) a rotational speed of the electric machine (3) of the electric drive system and setting (S22) a safe operating state in the electric machine (3) by means of a second control path (20), the Setting (S22) the safe operating state using the determined speed sets either an active short circuit or a freewheel in a converter (30) of the electrical drive system.