Method and device for the safe operation of an electrical machine

Abstract

A device for operating an electric machine using an inverter is described. The device is configured to determine, for a first cycle, an operating switching pattern for the operation of the switching group within the first cycle, which is designed to achieve a target operating point of the electric machine, as well as to determine a sequence of transition switching patterns for a sequence of successive cycles, which is designed to bring the electric machine from an actual operating point to a safe state.

Description

[0001] The invention relates to a method and a corresponding device that enable a gentle, safe operation of an electric machine.

[0002] An electrically powered vehicle comprises an electric drive motor that is powered by electrical energy from an electrical energy storage device. The alternating current for operating the drive motor can be generated by an inverter.

[0003] In the event of a safety-related incident, such as a vehicle accident, it may be necessary to bring the electric machine into a safe state where no critical voltages are present at its phase terminals. Bringing the electric machine into this safe state can place a relatively high load on components, particularly the switching elements of the inverter and / or on components, especially the magnets, of the electric machine itself. This necessitates designing the inverter and / or electric machine components to withstand a correspondingly high load.

[0004] This document addresses the technical challenge of enabling a particularly efficient and reliable design of an inverter and / or an electric (drive) machine.

[0005] The problem is solved by each of the independent claims. Advantageous embodiments are described, inter alia, in the dependent claims. It should be noted that additional features of a claim dependent on an independent claim, without the features of the independent claim itself or only in combination with a subset of the features of the independent claim, can constitute a separate invention independent of the combination of all features of the independent claim, which can be made the subject of an independent claim, a divisional application, or a subsequent application. This applies equally to technical teachings described in the description, which can constitute an invention independent of the features of the independent claims.

[0006] According to one aspect, a device for operating an electric machine by means of an inverter is described. The electric machine can be configured to power a motor vehicle. The inverter is configured to generate at least a suitable phase voltage for operating the electric machine by means of at least one switching group with one or more switching elements. A switching group can comprise a half-bridge with a high-side switching element and a low-side switching element. The individual switching elements can each comprise a transistor, e.g., a MOSFET or an IGBT.

[0007] The electric machine typically comprises three phases (or more). The inverter can include three switching groups for the corresponding three phases of the electric machine, each configured to generate a phase voltage for a corresponding phase of the electric machine.

[0008] The device is configured to determine an operating switching pattern for the switching group within a first cycle (from a sequence of successive first cycles), wherein the operating switching pattern is designed to achieve a target operating point of the electric machine. The operating switching pattern can be determined using a control system (e.g., a current control system) configured to acquire sensor data relating to the actual operating point of the electric machine and to determine the operating switching pattern based on this data. The operating switching pattern can then be used for the normal operation of the electric machine.

[0009] The device is configured to determine, for the first cycle and in addition to the operating switching pattern, a sequence of transition switching patterns for a sequence of (directly) successive cycles designed to bring the electric machine from its current operating point to a safe state. The sequence of (directly) successive cycles can begin with the respective first cycle or immediately following it.

[0010] The safe state can include an active short circuit (ACS) of several (especially all) phases of the electrical machine. Alternatively or additionally, the safe state can include: • a phase voltage that is less than a predefined voltage threshold (while the actual and / or target operating point of the electrical machine has a phase voltage that is greater than the voltage threshold, e.g., by a factor of 2 or more); and / or • a mechanical power output of the electric machine that is less than a predefined power threshold (while the actual and / or target operating point of the electric machine has a mechanical power output that is greater than the power threshold, e.g. by a factor of 2 or more greater than the power threshold).

[0011] In addition to the operating switching pattern, a sequence of transition switching patterns can be determined, which can be used to transition the electrical machine to a safe state when needed (i.e., in the event of a fault, or generally when a transition to a safe state is required). The sequence of transition switching patterns can be determined (predictively) based on a model, particularly a mathematical model, of the electrical machine. The sequence of cycles can, for example, comprise between 5 and 15 cycles. The individual cycles can each have a duration of, for example, 200 µs or less, particularly 100 µs or less.

[0012] By predictively determining a sequence of transition switching patterns, an efficient and reliable transition to the safe state can be achieved when needed, particularly without causing (significant) overshoots of one or more phase currents. This enables efficient design of the inverter and / or the electric machine. The transition to the safe state can also be achieved if the control system for operating the electric machine has failed completely or partially due to a fault.

[0013] The individual switching patterns for a cycle can each comprise one or more pulses, each specifying the time (within the cycle) and / or the duration (within the cycle) for closing a switching element (in particular the high-side switching element or the low-side switching element) of the respective switching group during the cycle.

[0014] The device can be configured to determine an operating switching pattern and a sequence of transition switching patterns for each initial cycle and for all three (or more) switching groups of the inverter. Corresponding switching patterns for different phases can be identical, apart from a phase shift (e.g., of 120° each).

[0015] The device can be configured (for the respective first cycle) to check whether there is a requirement to bring the electrical machine into a safe state. In particular, it can check whether or not the electrical machine is faulty. The inverter can be operated in the first cycle according to the determined operating circuit pattern (without using the sequence of transition circuit patterns) to bring the electrical machine to its target operating point if it is determined that there is no requirement to bring the electrical machine into a safe state (in particular, that there is no electrical machine fault). On the other hand, the inverter can be operated in the sequence of successive cycles (starting with the respective first cycle) according to the determined sequence of transition circuit patterns (if necessary).(without using the operating circuit pattern) to bring the electrical machine (starting from the current operating state) into the safe state when it is determined that there is a requirement to bring the electrical machine into the safe state (in particular, that there is a fault in the electrical machine and / or that the transition to the safe state is requested (e.g. in response to an accident and / or in the event of a data communication failure)).

[0016] It is therefore possible to selectively use the determined operating switching pattern (to continue the normal operation of the electrical machine), or alternatively to use the sequence of transition switching patterns (to terminate the normal operation of the electrical machine in the event of a fault and to transfer the electrical machine to a safe state).

[0017] The device can be configured to determine, for each successive first cycle, an operating switching pattern for the operation of the switching group within that first cycle, and to determine a sequence of transition switching patterns for the sequence of successive cycles originating from that first cycle (in particular, for the sequence beginning with that first cycle). The sequence of transition switching patterns determined for each first cycle can be stored in a (secure) memory unit. Conversely, the sequence of transition switching patterns determined for each preceding first cycle can be deleted from the memory unit (and overwritten with the currently determined sequence of transition switching patterns).

[0018] Thus, (if necessary) only the most recently determined sequence of transition switching patterns can be stored in a memory unit to be available when needed for bringing the electric machine into a safe state. The memory unit can be separate from the device, if necessary, to ensure that the electric machine can still be brought into a safe state even if the device malfunctions. This allows for particularly safe operation of the electric machine.

[0019] The device can be configured to determine the sequence of transition switching patterns for successive cycles such that the sequence of transition switching patterns ends in a (safe) state in which (all) high-side switching elements of the three (in particular all) switching groups of the inverter or (alternatively) (all) low-side switching elements of the three (in particular all) switching groups of the inverter are permanently switched on (i.e., closed). For example, (optionally only) the last transition switching pattern in the sequence of transition switching patterns can cause the high-side switching elements or the low-side switching elements to remain permanently closed. The one or more preceding transition switching patterns can bring about one or more other states of the inverter (in particular to limit the phase currents). In this way, the AKS can be brought about in a particularly reliable and gentle manner.

[0020] The device can be configured to determine the sequence of transition switching patterns in such a way that during the entire transition to the safe state, • the phase currents of one or more phases of the electrical machine do not exceed a specific, predefined current threshold; the current threshold may correspond to the maximum value of the individual phase currents during the (normal) operation of the electrical machine; and / or • the sequence of transition circuit patterns has several different transition circuit patterns (e.g. two or more, or three or more, or four or more different transition circuit patterns).

[0021] According to another aspect, an inverter is described that includes the device described in this document.

[0022] According to another aspect, a (road) motor vehicle (in particular a passenger car or a truck or a bus or a motorcycle) is described that includes the device described in this document.

[0023] According to another aspect, a method for operating an electric machine (in particular, a drive motor of a motor vehicle) using an inverter is described. The method comprises, for a first cycle (from a sequence of successive first cycles), determining an operating switching pattern for the operation of the switching group within the first cycle, which is designed to achieve a target operating point of the electric machine, as well as determining a sequence of transition switching patterns for a sequence of successive cycles, which is designed to transition the electric machine from an actual operating point to a safe state.

[0024] Another aspect described is a software (SW) program. The SW program can be configured to run on a processor (e.g., on a vehicle's control unit) and thereby execute the procedure described in this document.

[0025] Another aspect describes a storage medium. This storage medium can include a software program configured to run on a processor and thereby execute the procedure described in this document.

[0026] It should be noted that the methods, devices, and systems described in this document can be used both alone and in combination with other methods, devices, and systems described in this document. Furthermore, any aspect of the methods, devices, and systems described in this document can be combined with one another in a variety of ways. In particular, the features of the claims can be combined with one another in a variety of ways. Features listed in parentheses are to be understood as optional features.

[0027] The invention will now be described in more detail using exemplary embodiments. Fig. 1a Exemplary components of a vehicle with an electric drive motor; Fig. 1b an exemplary inverter or converter for an electric machine of a vehicle; Fig. 2a an exemplary control loop for the operation of an electric machine; Fig. 2b an exemplary sequence of switching patterns for operating an inverter; and Fig. 3. A flowchart of an exemplary procedure for determining switching patterns for the operation of an inverter.

[0028] As stated at the outset, this document deals with enabling a particularly efficient and reliable design of an inverter and / or an electrical machine. In this context, it shows Fig. 1a Exemplary components of a vehicle 140, which includes an electric machine 103 for propelling the vehicle 140. The vehicle 140 can be a hybrid vehicle or a fuel cell electric vehicle (FCEV). The electric machine 103 is coupled to one or more wheels 141 of the vehicle 140 to drive the one or more wheels 141 and thus the vehicle 140. The electric machine 103 is operated with electrical energy from an electrical, in particular an electrochemical, energy storage device 130. The energy storage device 130 can be configured to provide a direct current at a specific direct voltage.

[0029] The vehicle 140 has an inverter 100, which is configured to generate phase voltages for the different phases of the electric machine 103 based on the DC voltage from the energy storage device 130. The inverter 100 can be operated by a (control) device 101.

[0030] Fig. Figure 1b shows an exemplary inverter 100, which is set up based on a vehicle electrical system voltage U. DC The inverter 100 generates phase voltages 111 (i.e., alternating voltages) for the coils of the stator of the electric machine 103 (e.g., the DC voltage of the energy storage device 130). The inverter 100 can have an intermediate circuit with an intermediate circuit capacitor 105, to which the on-board voltage U is applied. DC 110 is attached.

[0031] The inverter 100 comprises several switches or switching elements 102, 104, which, in the illustrated example, are arranged in a half-bridge (generally in a switching group) for each phase 121, 122, 123 (e.g., for three phases). The switching elements 102, 104 are controlled by the (control) device 101 to generate the phase voltages 111 for the electric machine 103. The individual phase voltages 111 and / or the resulting phase currents 112 can be supplied to the electric machine 103 via corresponding phase lines.

[0032] To operate the electric machine 103 at a specific operating point, e.g. at a specific speed and / or with a specific torque, it is possible, as exemplified in Fig. Figure 2a shows a control loop 200 (or a control system) that can be used, for example, to achieve certain target characteristics of the phase currents 112. For instance, a specific setpoint 202 can be specified for the phase currents 112. The setpoint 202 can be specified, for example, in a dq coordinate system or in an αβ coordinate system. The coordinate transformations are shown for simplification in Fig. 2a not shown.

[0033] Based on the control error 203 (which results from the setpoint 202 and the actual value of the phase currents 112), a control value 204 can be determined using a controller 201. The control value 204 can, for example, correspond to a specific voltage vector in the dq coordinate system or in the αβ coordinate system. From the voltage vector, a switching pattern for the operation of the inverter 100 can be determined using a modulation method. The inverter 100 can then be operated with the determined switching pattern to generate the phase voltages 111.

[0034] Using the control loop 200, operating switching patterns for the operation of the inverter 100 can be determined for a temporal sequence of modulation periods (generally cycles) that follow one another at a specific repetition rate or frequency (e.g., 10 kHz or more). The inverter 100 can then be operated in the sequence of modulation periods according to the respective determined operating switching pattern in order to set the target operating point of the electrical machine 103 corresponding to the setpoint 202.

[0035] A switching pattern can each have a sequence of one or more switching pulses, where a switching pulse indicates the time and duration at which a switching element 102, 104 of a switching group of the inverter 100 is closed in order to connect the respective phase to the high-side voltage (e.g. +U). DC / 2) or with the low-side voltage (e.g. -U) DC / 2) to couple, and thus to generate a (possibly sinusoidal) phase voltage 111.

[0036] In the event of a fault, e.g., an accident involving vehicle 140, it may be necessary to bring the electric machine 103 into a safe state. A safe state can be achieved when the electric machine 103 generates only a relatively small torque (less than a torque threshold) and the voltage at the external electrical terminals of the electric machine 103 is not too high (i.e., less than a voltage threshold).

[0037] In particular, in the case of a permanent magnet electric machine (PMSM) 103, the inverter 100 can abruptly short-circuit all phase terminals of the electric machine 103 to bring the electric machine 103 into a safe state. This can be achieved by closing all high-side switching elements 102 or by closing all low-side switching elements 104. This measure can be referred to as an active short circuit (ACC). The ACC can be set abruptly and / or permanently by the inverter 100. This results in the electric machine 103 (which may be rotating) being unable to generate an electrical voltage at the phase terminals, and consequently generating no significant electrical power and therefore no significant mechanical conduction or torque.

[0038] The phase current 112 that establishes itself after the transient processes subside is typically smaller than the typical continuous phase current of the electric machine 103. On the other hand, the abrupt switching into the AKS can lead to a transient increase in the phase current 112 (e.g., up to 2 to 4 times the maximum permissible phase current). This short-term current can be a determining factor for the design of the inverter 100 and thus a determining factor for costs. Furthermore, this transient current can be a determining factor for the design of the excitation magnets of the electric machine 103 and thus a determining factor for costs.

[0039] If the transition to the AKS (Automatic Circuit Breaker) is not abrupt but controlled, the transient increase in phase current 112 (beyond the maximum permissible operating current) can be avoided. The controlled transition from the actual operating state of the electrical machine 103 to the safe AKS state can be achieved by gradually adjusting the operating point of the electrical machine 103 over a sequence of modulation periods. The voltage vectors and the corresponding switching patterns for the sequence of modulation periods can be determined using the control loop 200.

[0040] The transition to a safe state, particularly to the AKS state, primarily occurs in the event of a fault where it cannot be guaranteed that all components (e.g., current sensors, voltage sensors, computing resources, rotor position sensors, etc.) are available for the operation of control loop 200. A safe and / or reliable transition to the safe state should therefore be achieved with as few components of control loop 200 as possible, ideally without any of them.

[0041] The transition to the safe state, in particular to the AKS state, can be predictively calculated, for example cyclically, in each modulation period or cycle while the control system 200 is still in a known fault-free state, and the required sequence of switching operations of the inverter 100 can be stored in a protected and / or independent part of the (control) device 101. This protected part of the (control) device 101 can be activated in the event of a fault and can then independently execute the predicted sequence of switching operations for the inverter 100, resulting in the electrical machine 103 being brought into the safe state.

[0042] The sequence of switching operations can be calculated by using a machine model of the electric machine 103. Starting from the current operating state of the electric machine 103, the machine's state is then set, and in particular regulated, to a terminal voltage of 0V in several upcoming modulation periods or cycles. The necessary switching operations (or pulse patterns or switching patterns) of the inverter 100 are determined and stored. This pre-calculation can be performed for each cycle for which the regular pulse or switching pattern for the operation of the electric machine 103 is also calculated.

[0043] Fig. Figure 2b shows the operating switching pattern 221 determined for the first (e.g., current) cycle (i.e., modulation period) 211, which is used to set a specific target operating point of the electrical machine 103. The operating switching pattern 221 can be determined using the control loop 200. Furthermore, for a sequence of cycles 212 (which may directly follow the first cycle 211 or start with the first cycle 211), a corresponding sequence of transition switching patterns 222 can be determined, which can be used to transfer the electrical machine 103 to a safe state, in particular to the AKS state, in the event of a fault. The sequence of transition switching patterns 222 can be determined using a mathematical model of the electrical machine 103.

[0044] A similar procedure can be used for successive first cycles 211. An operating switching pattern 221 (for the intended and / or normal operation of the electrical machine 103) and a sequence of transition switching patterns 222 (for a possible transition to the safe state) can be determined for each cycle.

[0045] By pre-calculating a sequence of transition switching patterns 222, a transient short-circuit current during the transition to the safe state can be reliably and functionally avoided. The transient short-circuit current is therefore no longer relevant for the design of the inverter 100 and / or the electric machine 103, leading to a cost reduction of the inverter 100 (smaller semiconductor area) and / or the electric machine 103 (reduced need for rare earth elements). Alternatively, the electric machine 103 can be efficiently designed for an increased torque density.

[0046] As explained above, a mathematical model of the electrical machine 103 can be used to determine the sequence of transition switching patterns 222. An exemplary model (for a permanent magnet synchronous machine) in the dq coordinate system comprises the following equations, Ud=rs∗id−Lq∗ω∗iq Uq=rs∗iq=Ld∗ω∗id+ω∗ΨPM Md=32∗p{ΨPM∗iq+(Ld−Lq)∗id∗iq} where U d and U q the phase voltages 111 and i d and i q The phase currents 112 of the electric machine 103 are in the dq coordinate system. L d and L q are inductances of the electrical machine 103, and r s ω is the ohmic resistance of the stator of the electric machine 103. ω is the (electrical) rotational speed of the electric machine 103. ψ PM is the magnetic flux of the permanent magnets of the electric machine 103, p is the number of pole pairs, and M d This is what the electric machine 103 produces, generating torque.

[0047] For a safe state, the absence of voltage to the electrical machine 103 can be specified, i.e., U d = 0 and U q = 0. Assuming r s The result is (approximately) = 0: iq=0 id=−ΨPMLd

[0048] From i q If it is equal to 0, it also follows that the torque M d = 0.

[0049] During a controlled transition to the safe state, the aforementioned values ​​for the d- and q-currents can be specified as setpoints 202. The control loop 200 then gradually, in a sequence of cycles 211, ensures that the safe state (with U) is reached. d = 0 and U q = 0) is reached.

[0050] In the pre-calculated transition to the safe state, the mathematical model of the electrical machine 103 can be used to determine step by step (for the sequence of cycles 212) the actual state of the electrical machine 103 in the respective cycle 212, based on this the voltage vector for the inverter 100 and based on this the transition switching pattern 222 for the respective cycle 212.

[0051] The final state can be achieved by closing all low-side switching elements 104 or all high-side switching elements 102 to keep the electrical machine 103 in a safe state.

[0052] Fig. Figure 3 shows a flowchart of a (possibly computer-implemented) method 300 for operating an electric machine 103 (in particular a synchronous machine) by means of an inverter 100. The electric machine 103 can be configured to drive a motor vehicle 140. The inverter 100 is configured to generate at least one corresponding phase voltage 111 for operating the electric machine 103 by means of at least one switching group with one or more switching elements 102, 104. Typically, the inverter 100 has at least or exactly three switching groups for generating corresponding phase voltages 111 for the different phases of the electric machine 103.

[0053] The procedure 300 can be repeated for a sequence of successive (first) cycles 211. For a first cycle 211 from the sequence of first cycles 211, the procedure 301 comprises determining an operating switching pattern 221 for the operation of the switching group within the first cycle 211, wherein the operating switching pattern 221 is designed to achieve a target operating point of the electrical machine 103. The target operating point can be defined, for example, by a specific torque and / or a specific speed of the electrical machine 103. The torque and / or speed are (significantly) greater than a torque threshold or a speed threshold (which apply to the safe state of the electrical machine 103).

[0054] Thus, an operating circuit pattern 221 can be determined, which is aimed at continuing to operate the electric machine 103 in normal operation.

[0055] The method 300 further comprises (for the first cycle 211) determining 302 a sequence of transition switching patterns 222 for a sequence of successive cycles 212 (e.g., for two or more, or three or more, or four or more cycles 212) designed to bring the electrical machine 103 into a safe state (where the torque is less than the torque threshold value) from the current operating point. The sequence of transition switching patterns 222 can be determined predictively and can be used only if necessary (possibly instead of the operating switching pattern 211) a fault in the electrical machine 103 is detected for the first cycle 211.

[0056] The present invention is not limited to the embodiments shown. In particular, it should be noted that the description and the figures are intended only to illustrate the principle of the proposed methods, devices, and systems by way of example.

Claims

[1] Device (101) for operating an electrical machine (103) by means of an inverter (100); wherein the inverter (100) is designed to generate at least one corresponding phase voltage (111) for the operation of the electrical machine (103) using at least one switching group with one or more switching elements (102, 104); wherein the device (101) is set up for a first cycle (211), - to determine an operating switching pattern (221) for the operation of the switching group within the first cycle (211), which is designed to bring about a desired operating point of the electrical machine (103); and - to determine a sequence of transition switching patterns (222) for a sequence of consecutive cycles (212) which is designed to transfer the electrical machine (103) from an actual operating point into a safe state. [2] Device (101) according to claim 1, wherein the device (101) is arranged - to determine the operating switching pattern (221) using a control system (200) which is designed to acquire sensor data relating to the actual operating point of the electric machine (103) and to determine the operating switching pattern (221) based thereon; and / or - to determine the sequence of transition switching patterns (222) based on a model, in particular a mathematical model, of the electrical machine (103). [3] Device (101) according to one of the preceding claims, wherein the device (101) is arranged - to check whether there is a requirement to transfer the electrical machine (103) to the safe state; - to operate the inverter (100) in the first cycle (211) according to the determined operating switching pattern (221) in order to effect the desired operating point of the electrical machine (103) if it is determined that there is no requirement to transfer the electrical machine (103) to the safe state; and - operate the inverter (100) in the sequence of consecutive cycles (212) according to the determined sequence of transition switching patterns (222) to transfer the electrical machine (103) to the safe state when it is determined that there is a request to transfer the electrical machine (103) to the safe state. [4] Device (101) according to one of the preceding claims, wherein the device (101) is arranged, for a sequence of successive first cycles (211) respectively, - to determine an operating switching pattern (221) for the operation of the switching group within the respective first cycle (211); and - to determine a sequence of transition switching patterns (222) for a sequence of successive cycles (212) starting from the respective first cycle (211). [5] Device (101) according to claim 4, wherein the device (101) is arranged - storing the sequence of transition switching patterns (222) determined for the respective first cycle (211) in a memory unit; and - to delete the sequence of transition switching patterns (222) determined for the respective preceding first cycle (211) from the memory unit. [6] Device (101) according to one of the preceding claims, wherein a switching pattern (211, 222) for a cycle (211, 212) comprises one or more pulses each indicating a time and / or a duration for the closing of a switching element (102, 104) of the switching group during the cycle (211, 212). [7] Device (101) according to one of the preceding claims, wherein the safe state comprises - an active short circuit of several phases of the electrical machine (103); - a phase voltage (111) which is less than a predefined voltage threshold; and / or - a mechanical power of the electric machine (103) which is less than a predefined power threshold value. [8] Device (101) according to one of the preceding claims, wherein - the electrical machine (103) comprises three phases; - the inverter (100) comprises three switching groups for the corresponding three phases of the electrical machine (103), each of which is designed to generate a phase voltage (111) for a corresponding phase of the electrical machine (103); and - the device (101) is configured to determine an operating switching pattern (221) and a sequence of transition switching patterns (222) for the first cycle (211) and for the three switching groups of the inverter (100). [9] Device (101) according to claim 8, wherein the device (101) is configured to determine the sequence of transition switching patterns (222) for the sequence of consecutive cycles (212) such that the sequence of transition switching patterns (222) ends in a state in which high-side switching elements (102) of the three switching groups of the inverter (100) or low-side switching elements (104) of the three switching groups of the inverter (100) are permanently switched on. [10] Device (101) according to one of the preceding claims, wherein - a cycle (211, 212) has a duration of 200µs or less, in particular 100µs or less; and / or - the sequence of cycles (212) comprises between 5 and 15 cycles (212). [11] Method (300) for operating an electrical machine (103) by means of an inverter (100); wherein the inverter (100) is designed to generate at least one corresponding phase voltage (111) for the operation of the electrical machine (103) using at least one switching group with one or more switching elements (102, 104); wherein the method (300) comprises, for a first cycle (211), - determining (301) an operating switching pattern (221) for the operation of the switching group within the first cycle (211), which is designed to effect a desired operating point of the electric machine (103); and - determining (302) a sequence of transition switching patterns (222) for a sequence of consecutive cycles (212) which is designed to transfer the electrical machine (103) from an actual operating point into a safe state.

Images