Method and device for operating a switching element of an inverter

Abstract

A device for operating an inverter is described. The device is configured to ensure that, during normal operation of the inverter, a switching element of the inverter is controlled with a control voltage that has an operating value. Furthermore, the device is configured to detect a special operating condition and to ensure that, during this special operating condition, the switching element of the inverter is controlled with a special value that is higher than the operating value.

Description

[0001] The invention relates to a method and a corresponding device for operating at least one switching element of an inverter.

[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 using an inverter.

[0003] The inverter is typically designed for all possible operating scenarios, including one or more (special) operating scenarios that occur relatively rarely. This can lead to relatively high costs for the inverter's components, especially the switching elements.

[0004] This document deals with the technical task of enabling a particularly efficient and reliable design of an inverter for the operation of an electrical (drive) machine.

[0005] The problem is solved by each of the independent claims. Advantageous embodiments are described, among other things, in the dependent claims. It should be noted that additional features of a patent claim dependent on an independent patent claim can form a separate invention, independent of the combination of all features of the independent patent claim, without the features of the independent patent claim or only in combination with a subset of the features of the independent patent claim, which invention 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 form an invention independent of the features of the independent patent claims.

[0006] According to one aspect, a device for operating an inverter is described. The inverter is designed to generate at least one corresponding phase voltage for operating an electrical machine using 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. The electrical machine can be designed to drive a motor vehicle.

[0007] The electric machine typically comprises three (or more) phases. The inverter may comprise three (or more) vector groups for the corresponding three (or more) 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 ensure that, during normal operation of the inverter, at least one specific switching element of the inverter (in particular all switching elements of the one or more switching groups of the inverter) is controlled with a control voltage having (in particular at most) an operating value. The maximum control voltage used during normal operation can thus have the operating value. The switching element can be designed for a nominal value of the (maximum) control voltage, and the operating value can be equal to or less than the nominal value. The control voltage can be applied to the control terminal, in particular to the gate, of the switching element (in particular to cause the switching element to become conductive and / or close).

[0009] The device can be configured to operate the inverter's switching group during normal operation of the inverter according to a temporal sequence of at least partially different switching patterns (for a corresponding sequence of cycles or modulation periods) in order to achieve a target operating point of the electrical machine. The individual switching patterns can be determined using a control system (e.g., a current control system) that is configured to acquire sensor data relating to the actual operating point of the electrical machine and, based thereon, to determine the respective switching pattern (for the respective cycle).

[0010] The individual switching patterns may each comprise one or more pulses, each indicating the time (within a cycle) and / or the duration (within the cycle) for the closing of a switching element (in particular the high-side switching element or the low-side switching element) of the respective switching group during the cycle.

[0011] The device is further configured to detect a special operating case. The special operating case can be an active short circuit of several phases of the electrical machine. Within the scope of the active short circuit, for example, it can be caused that in each switching group of the inverter, one switching element (e.g., the high-side switching element or the low-side switching element) is permanently closed. The device can thus be configured to keep the one or more switching groups of the inverter in a static switching state during the special operating case, in particular in order to transfer the electrical machine to a safe state.

[0012] A safe condition of the electrical machine can exist, for example, if • the one or more phase voltages are each smaller than a predefined voltage threshold (while the actual and / or target operating point of the electrical machine has one or more phase voltages that are each greater than the voltage threshold, e.g., by a factor of 2 or more greater than the voltage threshold); and / or • the mechanical power of the electrical machine is less than a predefined power threshold (while the actual and / or target operating point of the electrical machine has a mechanical power that is greater than the power threshold, e.g. a factor of 2 or more greater than the power threshold).

[0013] The device is further configured to ensure that, during the special operating case of the inverter, the switching element of the inverter (in particular, at least one switching element per switching group of the inverter) is controlled with a control voltage having a special value that is higher than the operating value, in particular 10% or more higher than the operating value. The device can, in particular, be configured to ensure that, during the special operating case, all switching elements of the inverter used to effect the active short circuit are each controlled with a control voltage having the (increased) special value.

[0014] The special value may be greater than, in particular by 10% or more, the nominal value for which the respective switching element was designed. On the other hand, the special value may be such that it does not exceed 1.3 times the nominal value.

[0015] Thus, a device is described that, for a (relatively rare) special operating case, causes a (temporarily limited) increase in the control voltage for controlling one or more switching elements of the inverter, thereby reducing the conduction losses of the one or more switching elements and thus the thermal load on the inverter. As a result, an efficient design of the one or more switching elements of the inverter is possible (possibly without having to consider the special operating case in the design).

[0016] The device can be configured to ensure that the switching element is always controlled with a control voltage that has (at most or exactly) the operating value during normal operation. Furthermore, the device can be configured to ensure that the switching element is at least temporarily (e.g., at least during a predefined time period) controlled with a control voltage that has (at least or exactly) the special value during the special operating case. The predefined time period can correspond to the time period in which phase currents higher than a predefined current threshold are typically present during the special operating case. The current threshold can be equal to or greater than the maximum phase current during normal operation.

[0017] The increased control voltage can be used during the special operating mode to keep the switching element in the conductive state (possibly permanently). Due to the use of an increased control voltage (with the special value instead of the operating value), the on-resistance of the switching element can be reduced (compared to a situation where a control voltage with the operating value is used), thus reducing on-state losses.

[0018] During normal operation of the inverter, the control voltage can be generated using a voltage regulator (in particular a linear regulator) based on a supply voltage, wherein the supply voltage has a supply value that is typically higher than the operating value of the (maximum) control voltage. In other words, the (maximum) control voltage can be generated using a voltage regulator from a higher supply voltage (compared to the control voltage).

[0019] The device can be configured to cause the voltage regulator to be bypassed during the special operating case of the inverter in order to increase the control voltage from the operating value to the special value. For this purpose, the inverter can have a bypass element that allows the voltage regulator to be bypassed. As a result, the value of the control voltage can be increased in a particularly efficient and reliable manner (in particular, increased to the supply voltage value).

[0020] During normal operation of the inverter, the control voltage with the operating value can thus be generated based on a supply voltage with a specific supply value, and the device can be configured to ensure that during the special operating case of the inverter, the special value of the control voltage corresponds to the supply value of the supply voltage. This allows for a particularly efficient and reliable selective increase of the control voltage.

[0021] According to a further aspect, an inverter is described that comprises at least one switching group with one or more switching elements, wherein the switching group is configured to generate at least one corresponding phase voltage for the operation of an electrical machine. The inverter further comprises the device described in this document, which is configured to operate the inverter (in normal operation and in a special operating case).

[0022] According to a further aspect, a (road) motor vehicle (in particular a passenger car or a truck or a bus or a motorcycle) is described which comprises the device described in this document and / or the inverter described in this document.

[0023] According to a further aspect, a method for operating an inverter is described. The method comprises causing a switching element of the inverter to be controlled with a (maximum) control voltage having an operating value during normal operation of the inverter. Furthermore, the method comprises detecting a special operating case (in particular detecting that an active short circuit is to be performed), and causing the switching element of the inverter to be controlled with a (maximum) control voltage having a special value that is higher than the operating value, in particular 10% or more higher than the operating value, during the special operating case of the inverter (in particular during the active short circuit).

[0024] According to another aspect, a software (SW) program is described. The SW program can be configured to be executed on a processor (e.g., on a vehicle control unit) and thereby to carry out the method described in this document.

[0025] According to a further aspect, a storage medium is described. The storage medium can comprise a software program configured to be executed on a processor and thereby to carry out the method 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 aspects of the methods, devices, and systems described in this document can be combined in a variety of ways. In particular, the features of the claims can be combined in a variety of ways. Furthermore, features listed in parentheses are to be understood as optional features.

[0027] The invention will be described in more detail below using exemplary embodiments. Fig. 1a exemplary components of a vehicle with an electric drive motor; Fig. 1b shows an exemplary inverter or converter for an electrical machine of a vehicle; Fig. 2 an exemplary control circuit for a switching element of an inverter; and Fig. 3 a flowchart of an exemplary method for operating a switching element of an inverter.

[0028] As stated at the beginning, this document is concerned with enabling a particularly efficient and reliable design of an inverter. In this context, Fig. 1a shows exemplary components of a vehicle 140 having an electric machine 103 for driving the vehicle 140. The electric machine 103 is coupled to one or more wheels 141 of the vehicle 140 in order 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 with a specific direct voltage.

[0029] The vehicle 140 has an inverter 100 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. 1b shows an exemplary inverter 100 which is configured to operate on the basis of a vehicle electrical system voltage U DC 110 (ie the DC voltage from the energy storage device 130) to generate phase voltages 111 (ie AC voltages) for the coils of the electric machine 103. The inverter 100 can have an intermediate circuit with an intermediate circuit capacitor 105, to which the vehicle electrical system voltage U DC 110 is applied.

[0031] The inverter 100 (or converter) comprises a plurality of switches or switching elements 102, 104, which in the illustrated example are each 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 can each comprise one or more transistors, in particular MOSFETs or IGBTs. The switching elements 102, 104 are controlled by the (control) device 101 to generate the phase voltages 111 for the electrical machine 103. The individual phase voltages 111 and the resulting phase currents 112 can be provided to the electrical machine 103 via corresponding phase lines.

[0032] In order to operate the electrical machine 103 (during normal operation) at a specific operating point, e.g., at a specific speed and / or with a specific torque, a control loop (or a control system) can be used, which can be used, for example, to effect specific target properties of the phase currents 112. For example, a specific target value can be specified for the phase currents 112. The target value can be specified, for example, in a dq coordinate system or in an αβ coordinate system of the electrical machine 103.

[0033] Based on the control error (which results from the setpoint and the measured actual value of the phase currents 112), a control value can be determined using a controller. The control value can, for example, correspond to a specific voltage vector in the dq coordinate system or in the αβ coordinate system. A switching pattern for operating the inverter 100 can be determined from the voltage vector 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, 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 respectively determined switching pattern in order to set the target operating point of the electric machine 103 corresponding to the target value.

[0035] A switching pattern can comprise a sequence of one or more switching pulses, wherein 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 supply the respective phase with the high-side voltage (e.g. +U DC / 2) or with the low-side voltage (e.g. -U DC / 2) and thus generate a (possibly sinusoidal) phase voltage 111.

[0036] It may be necessary to transfer the electric machine 103 to a safe state in the event of a fault, e.g., an accident involving the vehicle 140. The safe state may exist when the electric machine 103 only generates a relatively small torque (less than a torque threshold) and the external electrical terminals of the electric machine 103 do not have an excessively high voltage (which is thus less than a voltage threshold).

[0037] In particular, in the case of a permanently excited electrical machine (PSM) 103, all phase connections of the electrical machine 103 can be suddenly short-circuited by the inverter 100 in order to transfer the electrical machine 103 to the 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 (ACS). The ACS can be set suddenly and / or permanently by the inverter 100. This results in the (possibly rotating) electrical machine 103 being unable to generate any electrical voltage at the phase connections and, as a result, generating no significant electrical power and thus generating no significant mechanical conduction or torque.

[0038] Sudden switching in the AKS can lead to a transient increase in phase current 112 (e.g., up to 2 to 4 times the maximum permissible phase current). This temporarily increased current can lead to increased thermal stress on the switching elements 102, 104 of the inverter 100. Furthermore, this temporarily increased current can determine the design and thus cost of the inverter 100, particularly for the switching elements 102, 104 of the inverter 100.

[0039] A transistor, especially a MOSFET, can be influenced in its conduction behavior by the level of the control voltage used to switch the transistor. In particular, conduction losses can be reduced by increasing the control voltage. On the other hand, increasing the control voltage beyond the permissible nominal (control) voltage of the transistor (i.e., beyond the permissible nominal voltage for controlling the transistor) will, after a certain period of time, lead to damage to the transistor and / or a significant reduction in its service life.

[0040] For a rare special operating case (such as an AKS), such damage and / or lifetime reduction of a transistor can be accepted in order to reduce the forward losses occurring during the special operating case. Due to the rarity of such a special operating case, the lifetime reduction caused by increasing the control voltage can typically be neglected. On the other hand, increased cost efficiency can be achieved in the design of the switching elements 102, 104 of the inverter 100. If necessary, by increasing the control voltage, the one or more rarely occurring special operating cases can be disregarded in the design of the inverter 100.

[0041] The control voltage of the control terminal (in particular the gate) of a switching element 102, 104 can thus be temporarily increased in the event of a certain (rare) special operating case (possibly depending on the particular special operating case). This voltage increase can be referred to as overdrive. For this purpose, as exemplified in Fig. 2, the voltage regulator (in particular the linear regulator) 203 for providing the control voltage 212 can be bridged in a particularly advantageous manner in order to provide the full supply voltage 211 as control voltage 212.

[0042] The (control) device 101 can thus be configured to ensure that, during normal operation of the inverter 100, an operating value of the control voltage 212 is used to control the individual switching elements 102, 104 of the inverter 100. On the other hand, in response to a detected special operating case, in particular in response to an AKS operating case, an increased special value of the control voltage 212 can be used to control at least some of the switching elements 102, 104 of the inverter 100. Thus, the conduction losses of the part of the switching elements 102, 104 can be reduced during the special operating case.

[0043] Following the special operating case, the operating value of the control voltage 212 can then be used again to operate the inverter 100 in normal operation.

[0044] Fig. 2 shows an exemplary control circuit 200 for controlling a switching element 102, 104 of the inverter 100. The control circuit 200 comprises a power supply 202 configured to provide a supply voltage 211 (with a specific voltage value, e.g., 22V, referred to in this document as the supply value). The control circuit 200 may comprise a voltage regulator (in particular, a linear regulator) 203 configured to generate the control voltage 212 with the operating value based on the supply voltage 211. The operating value may, for example, be 18V.

[0045] The (control) device 101 can cause the control voltage 212 to be applied to the control terminal of the switching element 102, 104 (in order to close the switching element 102, 104) or to be decoupled from the control terminal of the switching element 102, 104 (in order to open the switching element 102, 104) via a driver 201.

[0046] The control circuit 200 can comprise a bridging element 204 (e.g., with a switch) configured to bridge the voltage regulator 203 when needed, so that the value of the control voltage 212 substantially corresponds to the supply voltage 211. The (control) device 101 can be configured to cause the bridging element 204 to bridge the voltage regulator 203 when a special operating case occurs, thereby causing the control voltage 212 to be increased to a special value that corresponds to the (supply) value of the supply voltage 211. In this way, an increase in the control voltage 212 can be effected in a particularly efficient and reliable manner.

[0047] Fig.3 shows a flowchart of a (possibly computer-implemented) method 300 for operating an inverter 100. The inverter 100 can be configured to generate at least one corresponding phase voltage 111 for operating an electric machine 103 using at least one switching group with one or more switching elements 102, 104. The electric machine 103 can be a traction machine of a motor vehicle 140. 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.

[0048] The method 300 comprises causing 301 that, during normal operation of the inverter 100, a specific switching element 102, 104 of the inverter 100 (in particular all switching elements 102, 104 of all switching groups of the inverter 100) is controlled with a control voltage 212 that has (possibly at most) an operating value. The maximum control voltage can thus, if necessary, have the operating value during (the entire) normal operation. The operating value can correspond to the nominal voltage for which the specific switching element 102, 104 is designed. The normal operation of the inverter 100 can be directed to bringing about a target operating point of the electric machine 102 (e.g., with a target speed and / or with a target torque and / or with a target mechanical power).During normal operation of the inverter 100, the one or more switching groups can each be operated according to a temporal sequence of (changing) switching patterns.

[0049] Method 300 further includes detecting 302 a special operating case. For example, a fault and / or an accident (of the vehicle 140) can be detected. Based on this, it can be determined that a special operating case exists. In particular, it can be detected that an active short circuit of one or more phases of the electric machine 103 must be performed in order to transfer the electric machine 103 to a safe state.

[0050] Furthermore, the method 300 comprises causing 303 that, during the special operating case of the inverter 100, the switching element 102, 104 of the inverter 100 (possibly at least one switching element 102, 104 from each switching group of the inverter 100) is controlled with a control voltage 212 that has (possibly at most) a special value that is higher than the operating value, in particular 10% or more higher than the operating value. The special value can be above the nominal voltage of the switching element 102, 104. The maximum control voltage can thus have the special value during the (entire) special operating case.

[0051] Thus, in a relatively rare and / or time-limited special operating case, a temporary increase in the control voltage 212 can be effected in order to reduce the thermal load on one or more switching elements 102, 104 of the inverter 100 during the special operating case, and thus to efficiently prevent damage to the inverter 100, in particular to the one or more switching elements 102, 104 (even if the one or more switching elements 102, 104 were not designed for the special operating case).

[0052] The present invention is not limited to the embodiments shown. In particular, it should be noted that the description and 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 inverter (100); wherein the inverter (100) is designed to generate at least one corresponding phase voltage (111) for the operation of an electrical machine (103) using at least one switching group with one or more switching elements (102, 104); wherein the device (101) is configured, - to cause, during normal operation of the inverter (100), a switching element (102, 104) of the inverter (100) to be controlled with a control voltage (212) having an operating value; - to detect a special operating case; and - to ensure that during the special operating case of the inverter (100) the switching element (102, 104) of the inverter (100) is controlled with a control voltage (212) which has a special value which is higher than the operating value, in particular 10% or more higher than the operating value. [2] Device (101) according to claim 1, wherein - during normal operation of the inverter, the control voltage (212) is generated by a voltage regulator (201) based on a supply voltage (211); and - the device (101) is arranged to cause the voltage regulator (201) to be bridged during the special operating case of the inverter (100) in order to increase the control voltage (212) from the operating value to the special value. [3] Device (101) according to one of the preceding claims, wherein - during normal operation of the inverter, the control voltage (212) is generated with the operating value based on a supply voltage (211) with a specific supply value; and - the device (101) is arranged to ensure that during the special operating case of the inverter (100) the special value of the control voltage (212) corresponds to the supply value of the supply voltage (211). [4] Device (101) according to one of the preceding claims, wherein - the special operating case is an active short circuit of several phases of the electrical machine (103); and - the device (101) is designed to ensure that, during the special operating case, all switching elements (102, 104) of the inverter (100) which are used to effect the active short circuit are each controlled with a control voltage (212) which has the special value. [5] Device (101) according to one of the preceding claims, wherein - the switching element (102, 104) is designed for a nominal value of the control voltage (212); - the operating value is equal to or less than the nominal value; - the special value is greater than, in particular by 10% or more, the nominal value; and - the special value does not exceed 1.3 times the nominal value. [6] Device (101) according to one of the preceding claims, wherein - the electrical machine (103) comprises three or more phases; - the inverter (100) comprises three or more switching groups for the corresponding three or more 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 designed to ensure that during the special operating case of the inverter (100) in all three or more switching groups at least one switching element (102, 104) is controlled with a control voltage (212) which has the special value. [7] Device (101) according to one of the preceding claims, wherein - the switching element (102, 104) comprises at least one transistor, in particular a MOSFET; and / or - the control voltage (212) is applied to a control terminal, in particular to a gate, of the switching element (102, 104). [8] Device (101) according to one of the preceding claims, wherein the device (101) is arranged - during normal operation of the inverter (100), to operate the switching group of the inverter (100) according to a temporal sequence of at least partially different switching patterns in order to effect a desired operating point of the electrical machine (103); and - to keep the switching group of the inverter (100) in a static switching state during the special operating case, in particular in order to transfer the electrical machine (103) into a safe state. [9] Inverter (100) comprising - at least one switching group with one or more switching elements (102, 104) which is designed to generate at least one corresponding phase voltage (111) for the operation of an electrical machine (103); and - a device (101) according to one of the preceding claims, which is designed to operate the inverter (100). [10] Method (300) for operating an inverter (100); wherein the inverter (100) is designed to generate at least one corresponding phase voltage (111) for the operation of an electrical machine (103) using at least one switching group with one or more switching elements (102, 104); wherein the method (300) comprises, - causing (301) that during normal operation of the inverter (100) a switching element (102, 104) of the inverter (100) is controlled with a control voltage (212) having an operating value; - detecting (302) a special operating case; and - causing (303) that during the special operating case of the inverter (100) the switching element (102, 104) of the inverter (100) is controlled with a control voltage (212) which has a special value which is higher than the operating value, in particular 10% or more higher than the operating value.

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