DE102018220768A1 - Method for operating a motor system with an electrical machine and associated motor system - Google Patents

Abstract

The invention relates to a method for operating a motor system (1) with an electrical machine (3), a power driver circuit (2) for providing phase voltages (U, V, W) and a safety device (5) for interrupting phase string leads (4), which connect the power driver circuit (2) to phase strands (31) of the electrical machine (3), the following steps being carried out by means of a control unit (24) in the event of a fault: determining a speed of a rotor of the electrical machine (3), determining a rotor position range ( 11), in which a simultaneous interruption of the phase strand feed lines (4) is permitted, the determination being carried out on the basis of characteristic curves (18, 19) which, based on a simulation, estimate rotor position ranges (11) as a function of rotational speeds of the rotor of the electrical machine ( 3) Define, interrupt the phase strand leads (4) depending on the determined rotor position range (11) and a current rotor position by means of the safety device (5). The invention also relates to a motor system (1).

Description

The invention relates to a method for operating a motor system with an electrical machine and a motor system.

Electrical machines, which are designed as induction machines, are usually fed from a direct voltage source via power driver circuits, which can also be referred to as pulse inverters. The power driver circuits provide phase voltages to the electrical machine via phase strands. In the case of a three-phase electrical machine, a three-strand bridge circuit (also referred to as a B6 bridge) with power semiconductors, in particular metal-oxide-semiconductor field-effect transistors (MOSFETs), is often used.

In special applications, it is necessary to separate the electrical machine from the line driver circuit. If, for example, a short-circuit fault occurs in the power driver circuit, this can lead to a high current flow through one or more phase strands, which causes the electrical machine to become blocked or become stiff.

Critical applications are, for example, motor systems for steering support drives that provide a steering support force for steering systems. These drives can be designed as electronically commutated, multi-phase electrical machines. A blockage or a strong braking of the steering system must be avoided.

Monitoring circuits are usually provided which check the proper functioning of the power driver circuits and accordingly provide an error signal in the event of an error. In addition, isolating switches are provided in the phase strand feed line between the power driver circuit and the respective phase strand of the electrical machine. Since electro-mechanical switches, such as a relay or a contactor, are at risk of wear and are to be avoided in safety-relevant applications, isolating switches in the form of power semiconductors are usually provided, which can separate the phase string leads or switch with high resistance by means of appropriate control.

From the publication US 8,884,559 B2 A motor system is known which has a driver circuit for driving a plurality of phases on the electrical machine and a safety circuit which comprises isolating switches for each of the phase strands. With the aid of a safety control unit, each of the isolating switches is controlled in such a way that when a fault occurs, the semiconductor switching elements of the driver circuit are opened first and after a predetermined period of time the isolating switches of the safety circuit are opened. This can prevent the isolating switches of the safety circuit from being destroyed by a peak voltage.

In order to avoid blocking the electrical machine, in particular a steering assistance system, the phase currents can be interrupted with the aid of the isolating switch. The disconnectors are generally designed as semiconductor switches, but they are dimensioned such that they can only interrupt relatively small phase currents compared to the nominal current flow (nominal current) in the electrical machine. Particularly at a high temperature of the isolating switch, in particular the semiconductor switch, it can only interrupt a very low phase current. After the usual deactivation of the power driver circuit in the event of a fault, the induced voltages of the still rotating electrical machine can result in high current flows which exceed the separating capacity of the isolating switches, in particular semiconductor switches. When the electrical machine is still rotating after the occurrence of a fault, these currents pulse over the rotor position, so that a simultaneous interruption of the current flows in the phase strands is only possible during certain time windows.

In addition, there is often a problem that the phase currents cannot be measured when an error occurs in the power driver circuit itself. Therefore, at the time of the occurrence of an error, it is not known whether it is possible to open the disconnector, in particular the semiconductor switch, without endangering or destroying the disconnector.

The invention is based on the object of providing a method for operating a motor system with an electrical machine and a motor system in which an interruption of phase strand feed lines is possible in an improved manner.

The object is achieved by a method with the features of claim 1 and a motor system with the features of claim 9. Advantageous embodiments of the invention result from the subclaims.

• - Bestimmen einer Drehzahl eines Rotors der elektrischen Maschine,
• - Ermitteln eines Rotorlagebereichs, in dem ein gleichzeitiges Unterbrechen der Phasenstrangzuleitungen zugelassen wird, wobei das Ermitteln auf Grundlage von Kennlinien erfolgt, welche auf Grundlage einer Simulation geschätzte Rotorlagebereiche in Abhängigkeit von Drehzahlen des Rotors der elektrischen Maschine definieren,
• - Unterbrechen der Phasenstrangzuleitungen in Abhängigkeit des ermittelten Rotorlagebereichs und einer aktuellen Rotorlage mittels der Sicherheitseinrichtung.

In particular, a method is provided for operating a motor system with an electrical machine, a power driver circuit for providing phase voltages and a safety device for interrupting phase string leads that connect the power driver circuit to phase strands of the electrical machine, the following steps being carried out by means of a control unit in the event of a fault will:

• Determining a speed of a rotor of the electrical machine,
• Determining a rotor position range in which simultaneous interruption of the phase strand feed lines is permitted, the determination being carried out on the basis of characteristic curves which, on the basis of a simulation, define estimated rotor position ranges as a function of rotational speeds of the rotor of the electrical machine,
• - Interruption of the phase strand leads depending on the determined rotor position range and a current rotor position by means of the safety device.

• - Bestimmen einer Drehzahl eines Rotors der elektrischen Maschine,
• - Ermitteln eines Rotorlagebereichs, in dem ein gleichzeitiges Unterbrechen der Phasenstrangzuleitungen zugelassen ist, wobei das Ermitteln auf Grundlage von Kennlinien erfolgt, welche auf Grundlage einer Simulation geschätzte Rotorlagebereiche in Abhängigkeit von Drehzahlen des Rotors der elektrischen Maschine definieren,
• - Unterbrechen der Phasenstrangzuleitungen in Abhängigkeit des ermittelten Rotorlagebereichs und einer aktuellen Rotorlage mittels der Sicherheitseinrichtung.

Furthermore, a motor system is created, comprising an electrical machine, a power driver circuit for providing phase voltages, a safety device for interrupting phase string leads that connect the power driver circuit to phase strands of the electrical machine, and a control unit, the control unit being designed in this way, following in the event of a fault Follow steps:

• Determining a speed of a rotor of the electrical machine,
• Determining a rotor position range in which simultaneous interruption of the phase strand feed lines is permitted, the determination being carried out on the basis of characteristic curves which, on the basis of a simulation, define estimated rotor position ranges as a function of rotational speeds of the rotor of the electrical machine,
• - Interruption of the phase strand leads depending on the determined rotor position range and a current rotor position by means of the safety device.

One idea of the above method is to open the disconnector in the safety device at the same time within a time window in the event of a fault, i.e. switch off, while the amounts of all phase currents are less than a predetermined maximum amount for the phase currents. The maximum amount of phase currents corresponds to a phase current that can be safely interrupted by the isolating switch used without the isolating switch being damaged or malfunctioning due to the switching process.

The isolating switches are generally formed by semiconductor components, in particular as power MOSFETs, which due to their design have an inverse diode between a drain and source connection. If such a semiconductor component is switched to high impedance when there is a high current flow in an inductive load, there is a sharp rise in voltage between the drain and source connection, which can exceed a breakdown voltage depending on the level of the switched current. In the event of a voltage breakdown, the semiconductor component is generally destroyed.

If an error occurs in a power driver circuit during operation of the electrical machine, the power driver circuit is switched off. Due to the continued rotation of the rotor of the electrical machine due to the inertia or the action of external forces, phase currents arise in the phase strands due to induced voltages. If the induced voltages are greater in magnitude than the threshold voltages of the inverse diodes of the switching transistors in the power driver circuit and directed in such a way that the inverse diodes are brought into the conductive state, phase currents flow through the phase strands of the electrical machine.

In the event of a short circuit in a switching transistor of the power driver circuit connected to a high supply potential, the inverse diodes of the switching drivers of the power driver circuit are temporarily brought into the conductive state. The amplitude of the phase currents varies depending on the electrical position of the rotor. In a rotor position range, the phase currents in the phase strands are simultaneously low, that is to say lower than the maximum switching current, so that at one Rotor position within this rotor position range, the disconnectors can be switched off at the same time without a breakdown voltage occurring in one of the disconnectors. However, the rotor position range varies with the engine speed, the rotor position range, in which a simultaneous switch-off of the isolating switch is permitted, becomes smaller with increasing engine speed.

A basic idea of the invention is to determine a rotor position range in which simultaneous interruption of the phase strand feed lines is based on characteristic curves. Estimated rotor position ranges are defined in the characteristic curves on the basis of a simulation as a function of the rotor speed of the electrical machine. For example, these can be two characteristic curves. One of the characteristic curves defines a start of a rotor position range as a function of the rotational speed of the electrical machine, the other of the characteristic curves accordingly defines an end of the rotor position range.

A rotor position range can be specified in particular in the form of an angle interval, defined by a start angle and an end angle.

The rotor position ranges defined by means of the characteristic curves are estimated according to the invention for individual speeds of the electrical machine by means of a simulation, wherein only static relationships between currents, the rotor position and the speed of the electrical machine are taken into account, i.e. the electrical machine is in the stationary, in particular steady state each simulated for a constant speed. The characteristic curves can be created point by point by simulation at different, in each case constant, speeds of the electrical machine.

The proposed method and the proposed motor system are based on the assumption that the current through a short-circuited MOSFET of the bridge circuit flows in a pulsating manner, but only in one direction depending on the direction of rotation of the motor.

In one embodiment it is provided that parameters are used in the simulation under which the maximum possible currents flow. The idea behind this is to simulate the worst-case scenario (“worst case scenario”) with the maximum possible currents and to estimate the characteristic curves on the basis of the results of this simulation. Since higher currents than those taken into account in the simulation cannot then occur, the interruption of the phase string leads always takes place at a safe point in time. One advantage is that the effort involved in simulating or identifying the characteristic curves can be significantly reduced, since only the maximum or minimum values for the parameters need to be taken into account. In particular, parameters of the electrical machine, resistances in the short-circuit current path and threshold voltages of the inverse diodes are selected accordingly.

For the parameters of the electrical machine, in particular a phase resistance is converted to the lowest possible operating temperature of the electrical machine and possibly reduced by a scatter value. In addition, in particular a maximum magnetic flux is converted to the lowest operating temperature of the electrical machine and possibly increased by a scatter value. For the inductors of the electrical machine, only the maximum and minimum values for the d and q components of the inductors are used, which result from the characteristic diagrams for all currents and operating temperatures of the electrical machine. The corresponding values can be found in the respective data sheets of the manufacturer of the electrical machine.

A resistance of the stator windings of the electrical machine and the behavior over temperature can also be found in the manufacturer's data sheet. The remaining resistances in the short-circuit current path (e.g. short-circuit point, phase switch, inverse diodes and the AC current paths of the power driver circuit) are set to zero, since in this case the currents become maximum. Thus, only the phase resistance of the electrical machine is taken into account in the simulation of all active resistances in the short-circuit current path.

The lowest possible value is used for the threshold voltages of the inverse diodes, since this enables the highest current through the inverse diode. The value corresponds to the value at a maximum permissible temperature of the semiconductor switch, in particular of the MOSFET. The value can be found in a manufacturer's data sheet.

In one embodiment it is provided that a speed signal depicting the speed of the electrical machine is delayed if a speed change rate is negative. In this way, dynamic effects can also be taken into account, such as a transient behavior of the current, as in the case of large braking gradients of the electrical machine can occur. By delaying the speed signal, a current value is only made available at a later point in time (ie delayed), so that the rotor position range is always determined with a larger value than the current value of the speed. In particular, it can be provided that a speed change rate is determined beforehand.

In a further embodiment it is provided that the interruption does not take place until a current decay time which is characteristic of the electrical machine has expired after an error. The characteristic current decay time of the electrical machine is the time it takes for a current to decay after the occurrence of a short circuit, that is to say after the current transients have decayed. The characteristic current decay time is also determined on the basis of the simulation. For this purpose, in particular a fault, in particular the short circuit of a switching transistor, with the motor speed zero and the maximum possible operating phase current of the motor is simulated and the time until the currents decay below the safe threshold value.

In a further embodiment it is provided that safety areas are taken into account in the simulation when estimating the rotor position areas. In other words, the rotor position range is reduced in that a safety value is added to an initial value of the rotor position range and a safety value is subtracted from an end value of the rotor position range. If the rotor position range is specified as an angular interval, an initial angle of the angular interval becomes correspondingly larger and an end angle of the angular interval correspondingly smaller.

In a further embodiment it is provided that the safety areas are taken into account as a function of the speed.

In a further embodiment it is provided that signal delays are taken into account in the simulation. In particular, these are signal delays that occur when a rotor position of the electrical machine is detected, for example in the case of a sensor system designed for this purpose, a signal age that arises from the transmission and processing of a signal, and a delay that arises when a hardware is activated. In particular, it is provided that the signal delay is taken into account in the respective security area.

In particular, it can be provided that a short circuit in a switching transistor of the power driver circuit is recognized as a fault.

In one embodiment it is provided that the safety device in each case has an isolating switch for each of the phase strand feed lines, the isolating switches being designed with semiconductor switches, in particular MOSFETs.

Parts of the control unit can be designed individually or in combination as a combination of hardware and software, for example as program code that is executed on a microcontroller or microprocessor.

• 1 eine schematische Darstellung eines Motorsystems mit einer Leistungstreiberschaltung, einer Sicherheitsschaltung und einer elektrischen Maschine;
• 2 ein schematisches Ablaufdiagramm einer Ausführungsform des Verfahrens zum Betreiben eines Motorsystems mit einer elektrischen Maschine;
• 3a eine schematische Darstellung eines zeitlichen Verlaufs von Phasenströmen zur Verdeutlichung der Bestimmung eines Rotorlagebereich bei einer niedrigen Drehzahl;
• 3b eine schematische Darstellung eines zeitlichen Verlaufs von Phasenströmen zur Verdeutlichung der Bestimmung eines Rotorlagebereich bei einer höheren Drehzahl;
• 4 eine schematische Darstellung von Kennlinien, welche Rotorlagebereiche in Abhängigkeit einer Drehzahl der elektrischen Maschine definieren;
• 5 eine schematische Darstellung einer Implementierung einer Verzögerung eines Drehzahlsignals;
• 6 eine schematische Darstellung einer Implementierung einer Ausführungsform des Verfahrens.

The invention is explained in more detail below on the basis of preferred exemplary embodiments with reference to the figures. Here show:

• 1 is a schematic representation of a motor system with a power driver circuit, a safety circuit and an electrical machine;
• 2nd a schematic flow diagram of an embodiment of the method for operating a motor system with an electrical machine;
• 3a a schematic representation of a time profile of phase currents to illustrate the determination of a rotor position range at a low speed;
• 3b a schematic representation of a time course of phase currents to illustrate the determination of a rotor position range at a higher speed;
• 4th a schematic representation of characteristic curves which define rotor position ranges as a function of a speed of the electrical machine;
• 5 a schematic representation of an implementation of a delay of a speed signal;
• 6 is a schematic representation of an implementation of an embodiment of the method.

In 1 is a schematic representation of an engine system 1 shown. The engine system 1 includes a power driver circuit 2nd for providing phase currents for an electrical machine 3rd . The electrical machine 3rd is designed as an electronically commutated electrical machine, such as a synchronous motor or the like. The electrical machine 3rd has several phase strands 31 on, which are connected as a star connection in the exemplary embodiment shown. In alternative embodiments, the phase strands 31 also be connected in a polygon.

The power driver circuit 2nd stands above a number of phase string leads 4th with the phase strands 31 of the electrical machine 3rd in electrical connection. The number of phase string leads 4th thus corresponds to the number of phases of the electrical machine 3rd . In the phase strand leads 4th is a safety device 5 provided a controlled electrical interruption of the phase strand leads 4th can make if an error occurs in the power driver circuit 2nd occured.

The power driver circuit 2nd is via a filter circuit 6 with a supply voltage U _DC between a high supply potential V _H and a low supply potential V _L connected. In the illustrated embodiment, the power driver circuit 2nd for the operation of a three-phase electrical machine 3rd educated. The power driver circuit 2nd can, for example, as shown, in the form of a B6 bridge circuit with a series circuit of two switching transistors assigned to the phase strands 21st which, for example, in the form of MOSFET transistors 22 are trained to be provided. The MOSFET transistors 22 have intrinsic inverse diodes due to their design 23 on that in a with respect to the voltage direction resulting from the arrangement of the switching transistors 21st results, opposite voltage can be permeable, ie with a negative voltage between the drain connection and the source connection of the switching transistors 21st , which exceeds a threshold voltage, a diode current flows from the source terminal to the drain terminal of the switching transistor in question 21st .

One between the two series-connected switching transistors 21st located node K1 , K2 , K3 is via a corresponding one of the phase string leads 4th with the respective phase strand 31 of the electrical machine 3rd connected to each through the power driver circuit 2nd provided phase voltage U , V , W to put on the electrical machine.

The control of the electrical machine 3rd is done using a control unit 24th that depend on an external target B the switching transistors according to a commutation scheme 21st controls and thereby opens or closes the phase voltages U , V , W for the individual phase strands 31 to generate and so certain phase currents in the electrical machine 3rd impress. The commutation can be based on a current (electrical) rotor position of the electrical machine 3rd done by using a rotor position sensor 26 provided rotor position signal 25th or is determined sensorless by measuring phase currents. A current speed can, for example, from the rotor position signal provided 25th be determined.

The security device 5 includes disconnector 51 , which can each be designed as a semiconductor switch in the form of a MOSFET transistor. The MOSFET transistors each have an inverse diode (also referred to as a body diode), via which a current flow greater than a predetermined threshold current is possible.

The control unit 24th is designed such that a short circuit fault in at least one of the switching transistors 21st the power driver circuit 2nd recognizable in a manner known per se. After detection of a short circuit fault, the power driver circuit 2nd switched off or the switching transistors 21st are no longer controlled.

• - Bestimmen einer Drehzahl eines Rotors der elektrischen Maschine 3,
• - Ermitteln eines Rotorlagebereichs, in dem ein gleichzeitiges Unterbrechen der Phasenstrangzuleitungen 4 zugelassen ist, wobei das Ermitteln auf Grundlage von Kennlinien 18, 19 erfolgt, welche auf Grundlage einer Simulation geschätzte Rotorlagebereiche in Abhängigkeit von Drehzahlen des Rotors der elektrischen Maschine 3 definieren,
• - Unterbrechen der Phasenstrangzuleitungen 4 in Abhängigkeit des ermittelten Rotorlagebereichs und einer aktuellen Rotorlage mittels der Sicherheitseinrichtung 5, wobei die Steuereinheit 24 die Sicherheitsrichtung 5 hierzu derart ansteuert, dass diese zum gewünschten Zeitpunkt die Trennschalter 51 gleichzeitig öffnet.

After detection of a short circuit fault in at least one of the switching transistors 21st leads the control unit 24th do the following:

• - Determining a speed of a rotor of the electrical machine 3rd ,
• - Determine a rotor position range in which a simultaneous interruption of the phase strand leads 4th is permitted, the determination based on characteristic curves 18th , 19th takes place, which on the basis of a simulation estimated rotor position ranges depending on the speed of the rotor of the electrical machine 3rd define,
• - Interrupting the phase string leads 4th depending on the determined rotor position range and a current rotor position by means of the safety device 5 , the control unit 24th the security direction 5 controls this in such a way that it switches the disconnectors at the desired time 51 opens at the same time.

In particular, it can be provided here that the simulation uses parameters under which the maximum possible currents flow. By using these "worst case parameters", the worst case scenario ("worst case scenario") with the maximum possible currents is always simulated, so that the rotor position ranges or characteristic curves estimated on the basis of the simulation always enable a safe interruption of the phase string leads.

It can also be provided that a speed signal depicting the speed of the electrical machine is delayed if a speed change rate is negative. In this way, current transients, such as those that occur with strong braking gradients, can be taken into account.

Provision can further be made for the interruption to take place only after a current decay time which is characteristic of the electrical machine has expired after an error.

In 2nd 10 is a schematic flow diagram of an embodiment of the method for operating an engine system 1 with an electric machine 3rd (see. 1 ) shown.

In a first step 100 it is checked whether there is a short circuit fault. If this is the case, proceed with process step 101 continue, otherwise the process step 100 executed again.

In process step 101 a speed of a rotor of the electrical machine is determined. This can be done, for example, with a sensor and evaluation device designed for this purpose.

In one step 102 a rotor position range in which simultaneous interruption of the phase strand feed lines is permitted is determined. The determination is carried out on the basis of characteristic curves which, on the basis of a simulation, define estimated rotor position ranges as a function of the speeds of the rotor of the electrical machine. The characteristics become independent of the execution of the process steps 100-103 in one process step 200 created by simulation of static or stationary states of the electrical machine and made available to the control unit. In other words, the control unit uses the characteristic curves to determine a start and an end of the rotor position range for those in the method step 101 certain speed of the electrical machine.

In the procedural step 103 The phase strand feed lines are interrupted simultaneously depending on the determined rotor position range and a current rotor position. This is done by means of the safety device, which is controlled accordingly by the control unit. Specifically, the safety device is controlled by the control unit in such a way that isolating switches of the safety device interrupt the phase strand feed lines at a point in time when the current rotor position lies within the determined rotor position range. For this purpose, the current rotor position is continuously compared with the determined rotor position area.

The process is then ended 104 .

It can be provided that parameters are used in the simulation under which the maximum possible currents flow. As a result, a rotor position range for a considered speed is always estimated on the basis of a maximum possible fault current. As a result, the estimated rotor position range shrinks compared to reality, where, for example, further resistances in the short-circuit current path are not equal to zero. Since only the current-maximizing parameters are used, the simulation and identification of the characteristic curves are simplified.

It can further be provided that a speed signal depicting the speed of the electrical machine is delayed if a speed change rate is negative. This is done in one step 101-a performed so the process steps 102 and 103 in this case be carried out on the basis of an already delayed speed signal.

Furthermore, it can be provided that the interruption does not take place until a current decay time that is characteristic of the electrical machine has expired after an error. The current decay time characteristic of the electrical machine is determined from the simulation.

It can further be provided that safety areas are taken into account in the simulation when estimating the rotor position areas. This will be done in process step 200 a start and an end of the rotor position ranges shifted, so that the rotor position ranges decrease, that is, the characteristic curves 18th , 19th (see. 4th ) move towards each other.

It can be further developed that the safety areas are taken into account as a function of speed.

Provision can also be made for signal delays to be taken into account in the simulation, such as occur, for example, in the case of speed detection and signal processing.

• - eine B6-Brücke mit Inversdioden (Body-Dioden) der Brücken-MOSFETs,
• - eine Sicherheitseinrichtung mit MOSFET-Trennschaltern mit zugehörigen Inversdioden (Body-Dioden)
• - eine Permanentmagnet-Synchronmaschine als elektrische Maschine,
• - eine Spannungsquelle (irrelevant für das Schätzen der Rotorlagebereiche)
• - ein DC-Filter (irrelevant für das Schätzen der Rotorlagebereiche)

The following is an example of a simulation of a short circuit in a high-side MOSFET of a phase to illustrate the invention U described in a B6 bridge. The simulation model comprises the following elements:

• a B6 bridge with inverse diodes (body diodes) of the bridge MOSFETs,
• - A safety device with MOSFET disconnectors with associated inverse diodes (body diodes)
• - a permanent magnet synchronous machine as an electrical machine,
• - a voltage source (irrelevant for estimating the rotor position ranges)
• - a DC filter (irrelevant for estimating the rotor position ranges)

The rotor position ranges are at constant speeds after a steady, i.e. especially static or steady state determined.

Rotor position ranges for the event of a short circuit of other MOSFETs in the B6 bridge as well as for an opposite direction of rotation can be determined with the help of a fixed rotor position offset using one for the short-circuited highside MOSFET of the phase U determined rotor position range can be determined.

Table 1 below shows values for the rotor position offset. Table 1: Offset depending on the phase (U, V, W), the potential side (HS = Highside, LS = Lowside) of the short-circuited MOSFET and the direction of rotation. (* In the case of a negative direction of rotation, a sign of a current rotor position must first be inverted before it is used for comparison with a rotor position area.) Direction of rotation HS U LS U HS V LS V HS W LS W positive 0 -π 2π / 3 -π / 3 -2π / 3 π / 3 negative* 0 -π -2π / 3 π / 3 2π / 3 π / 3

In 3a is a schematic representation of a time profile of phase currents 14 to clarify the determination of a rotor position range 11 shown at a low speed. The x axis 12 represents the time in s on the y-axis 13 are both the phase currents 14 in A as well as a phase angle or rotor position angle (electrical) in degrees. When the simulation starts, it starts at the beginning 15 of the rotor position area 11 assumed an initial angle of 0 ° and at the end 16 of the rotor position area 11 from an initial angle of 360 °. As soon as all phase currents 14 fall below a safe current threshold value, a rotor position angle coinciding with the associated time is the beginning 15 the rotor position range 11 set. The curve to start with 15 shows the course of a value for the beginning of the rotor position range 11 with progressive simulation. After all phase currents 14 have fallen below the current threshold, they will rise again in the next period. As soon as at least one of the phase currents 14 rises above a current threshold value, a rotor position angle coinciding with the associated point in time becomes the end 16 the rotor position range 11 set. The curve for the end 16 shows the course of a value for the end of the rotor position range 11 with progressive simulation. The rotor position area 11 coincides with a time window 17th , in which a safe interruption of the phase strand leads is possible. In the example shown, the rotor position range comprises an angular interval of 157 ° (electrical) to 44 ° (electrical).

In 3b is a schematic representation of a time profile of phase currents 14 over time to clarify the determination of a rotor position range 11 shown at a higher speed. The reference symbols denote the same features and terms as in 3a . Since the speed of the electrical machine compared to that in 3a shown situation is significantly increased, the flowing phase currents also increase 14 . The determined rotor position range is correspondingly reduced with the same current threshold value 11 since the beginning 15 and the end 16 are closer together and a time window 17th , in which a safe interruption of the phase strand feed lines is possible, has decreased. In the example shown, the rotor position range comprises an angular interval from 276 ° (electrical) to 334 ° (electrical).

In 4th is a schematic representation of characteristic curves 18th , 19th shown which rotor position ranges 11 depending on the speed of the electrical machine. On the x axis 12 the speed of the electrical machine is shown on the y-axis 13 a rotor position angle (electrical) is shown in rad. The characteristics 18th , 19th were determined as part of a simulation of the temporal course of the phase currents for speeds from 0 to a maximum speed (normalized to 1), as described, for example, in FIGS 3a and 3b are shown. The characteristic 18th was from the values for the beginning of the respective rotor position range 11 and the characteristic 19th from the values for the end of the respective rotor position range 11 certainly. The characteristic curves repeat due to the periodicity 18th , 19th each other 2π or every 360 °. Based on these characteristics 18th , 19th can a rotor position range for a certain speed 11 can be determined in which a safe interruption of the phase strand feed lines is possible.

The characteristics of this example deliver a rotor position range of 360 ° up to a speed of 0.06 (on a standardized scale), i.e. in this speed range all phase currents for each rotor position are below the safe current. Up to a speed of 0.95 (on a standardized scale), this example provides a valid rotor position range, i.e. there is an area in which a reliable interruption of the phase strand leads is possible. Above a speed of 0.95 (on a standardized scale) there is no currentless state at all or the current is always too high, so that safe interruption is not possible.

However, it should be noted that an interruption in the range up to a speed of 0.06 (on a standardized scale) may only take place when current transients have subsided. For this purpose, it is provided that the interruption does not take place until a current decay time which is characteristic of the electrical machine has expired after an error. For this purpose, for example, the expiry of a timer (timer) is checked after the occurrence of an error, in particular a short circuit. An interrupt can only be carried out after the timer has expired.

Furthermore, it can be provided that a speed change rate of the speed of the electrical machine is determined, a speed signal depicting the speed of the electrical machine being delayed, provided that the determined speed change rate is negative (cf. 5 ).

Furthermore, the characteristics 18th , 19th in the 4th to recognize that a transition from a speed of 0 to a 360 ° rotor position range is abrupt. In order to rule out a faulty reaction to measurement errors in a speed signal, this can be taken into account by means of a positive speed markup (offset) in the speed signal. The speed surcharge must be taken into account accordingly at the maximum speed up to which an interruption is possible. In the simulation example described, the speed value at 0.95 (on a standardized scale) is reduced by the speed mark-up where there is a valid rotor position range.

In 5 a schematic representation of a time-discrete implementation of a delay in a speed signal is shown. The delay is achieved by means of a delay element 7 first order achieved. The delay element 7 first order is designed in such a way that a delay only in the case of negative gradients in the amount of a speed signal 71 works. This is done in one step 300 an amount of the speed signal 71 educated. An output signal 72 will be in one step 301 delayed from the delayed output signal 72 the amount of the speed signal 71 subtracted and then this signal in one step 302 multiplied by a factor. Then the amount of the speed signal 71 added and the respective larger value of the amount of the speed signal 71 or the signal processed in this way in step 303 determined and as an output signal 72 provided. Through the implementation shown, current transients that can occur with large braking gradients can be sufficiently taken into account.

In 6 a schematic representation of an implementation of an embodiment of the method is shown. In one step 400 becomes the amount of a speed signal 71 educated. A speed surcharge is added to this amount 73 added. This signal is then processed in one step using a low-pass filter 401 delayed.

Based on the delayed speed and the static characteristics 18th , 19th (see also 4th ) after a short-circuit of a bridge MOSFET, a start and an end of a rotor position range can be determined.

Rotor positions for a start and an end of the determined rotor position area are then in step 402 compared with a current rotor position. For this purpose, a rotor position signal 74 an (electrical) rotor position provided, which in step 404 is adapted to a phase affected by the short circuit and a current direction of rotation (see Table 1). If the current rotor position lies in the determined rotor position range, a corresponding signal is provided.

If the current rotor position lies within the rotor position range and if a current decay time has elapsed after a short circuit, which takes into account the decay of current transients, then an interrupt signal is generated 76 generated to interrupt the phase strand leads simultaneously. For this purpose, an expiry signal is generated after a short circuit by means of a timer 75 generated and logically with the comparison signal of the step 402 compared in an AND logic. If all the requirements are met, the interrupt signal is given 76 generated and made available to the safety device which interrupts the phase strand leads.

Reference symbol list

1

Engine system

2nd

Power driver circuit

3rd

electrical machine

4th

Phase strand feed

5

Safety device

6

Filter circuit

7

Delay element

11

Rotor position range

12

X axis

13

y axis

14

Phase current

15

Beginning of the rotor position area

16

End of the rotor position range

17th

Time window

18th

Characteristic curve for the beginning of the rotor position range

19th

Characteristic curve for the end of the rotor position range

21st

Switching transistor

22

MOSFET transistor

23

Inverse diode

24th

Control unit

25th

Rotor position signal

26

Rotor position sensor

31

Phase strand

51

Disconnector

71

Speed signal

72

Output signal of the delay element

73

Speed markup

74

Rotor position signal

75

Expiry signal

76

Interrupt signal

100-104

Procedural steps

200

Process step (simulation)

300-303

Procedural steps

400-404

Procedural steps

B

Target

U

Phase voltage

V

Phase voltage

W

Phase voltage

U _DC

Supply voltage

V _L

Supply potential

V _H

Supply potential

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included 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

• US 8884559 B2 [0006]

Claims (10)

Method for operating a motor system (1) with an electrical machine (3), a power driver circuit (2) for providing phase voltages (U, V, W) and a safety device (5) for interrupting phase string leads (4) which connect the power driver circuit ( 2) connect to phase strands (31) of the electrical machine (3), the following steps being carried out by means of a control unit (24) in the event of a fault: - Determining a speed of a rotor of the electrical machine (3), - Determining a rotor position area (11) in which a simultaneous interruption of the phase strand feed lines (4) is permitted, the determination being carried out on the basis of characteristic curves (18, 19) which, based on a simulation, estimate rotor position areas (11) as a function of the rotational speed of the Define the rotor of the electrical machine (3), - Interrupting the phase strand feed lines (4) as a function of the determined rotor position area (11) and a current rotor position by means of the safety device (5). Method according to one of the preceding claims, characterized in that the simulation uses parameters under which the maximum possible currents flow. Procedure according to Claim 1 or 2nd , characterized in that a speed signal (71) depicting the speed of the electrical machine (3) is delayed if a speed change rate is negative. Method according to one of the preceding claims, characterized in that the interruption takes place only when a current decay time which is characteristic of the electrical machine (3) has expired after an error. Method according to one of the preceding claims, characterized in that in the simulation, safety areas are taken into account when estimating the rotor position areas (11). Procedure according to Claim 5 , characterized in that the safety areas are taken into account depending on the speed. Method according to one of the preceding claims, characterized in that signal delays are taken into account in the simulation. Method according to one of the preceding claims, characterized in that a short circuit in a switching transistor (21) of the power driver circuit (2) is detected as an error. Motor system (1) comprising: an electrical machine (3), a power driver circuit (2) for providing phase voltages (U, V, W), a safety device (5) for interrupting phase strand feed lines (4) which connect the power driver circuit (2) to phase strands (31) of the electrical machine (3), and a control unit (24), the control unit (24) being designed to carry out the following steps in the event of an error: - Determining a speed of a rotor of the electrical machine (3), - Determining a rotor position area (11) in which a simultaneous interruption of the phase strand feed lines (4) is permitted, the determination being carried out on the basis of characteristic curves (18, 19) which, based on a simulation, estimate rotor position areas (11) as a function of the rotational speed of the Define the rotor of the electrical machine (3), - Interrupting the phase strand feed lines (4) as a function of the determined rotor position area (11) and a current rotor position by means of the safety device (5). Motor system (1) after Claim 9 , characterized in that the safety device (5) in each case has a disconnector (51) for each of the phase strand feed lines (4), the disconnectors (51) being designed with semiconductor switches.

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