Computing unit for checking an overvoltage protection circuit for an electric machine, overvoltage protection circuit and power converter arrangement

Abstract

Computing unit designed to check an overvoltage protection circuit (200) for an electric machine (100), wherein the overvoltage protection circuit (200) comprises a series connection of at least two overvoltage protection assemblies (210, 220), wherein each of the at least two surge protection assemblies (210, 220) has a switching unit (215, 225) connected in parallel, so that by closing the switching unit (215, 225) the respective surge protection assembly (210, 220) is bypassed, wherein a first of the two surge protection assemblies (210, 220) comprises at least one surge protection element (211, 221, 222) and a second of the two surge protection assemblies (210, 220) comprises at least two surge protection elements (211, 221, 222), wherein each surge protection component (211, 221, 222) limits a voltage drop across it to a component voltage limit, wherein a first voltage tap (230a) is provided between two of the surge protection components (221, 222) of the second surge protection assembly, wherein a second voltage tap (231a) is provided between the two surge protection assemblies (210, 220), wherein the computing unit is set up: -- to detect a voltage applied to the overvoltage protection circuit (200) at two points, -- to switch the at least two switching units (215, 225) into at least two different switching configurations and to determine measured values ​​of a voltage applied to the voltage taps (230a, 231a) in each of the at least two different switching configurations, -- to compare at least two measured values ​​for each of the voltage taps (230a, 231a) with a corresponding reference value, which is determined depending on the voltage applied to the overvoltage protection circuit (200) and the component voltage limits, -- to determine the functionality of the overvoltage protection circuit (200) based on at least one comparison result.

Description

[0001] The present invention relates to a computing unit for checking an overvoltage protection circuit for an electric machine, an overvoltage protection circuit and a power converter arrangement. Background of the invention

[0002] Electric machines can be used to power a vehicle. A power converter (or inverter) is typically used to control or operate the electric machine, and in particular the phases of the stator winding. Typical electric machines have, for example, three, five, six, or even more phases. The power converter usually has a half-bridge for each phase, which in turn comprises two switching elements, such as MOSFETs, IGBTs, or other semiconductor devices. Furthermore, a control circuit may be provided to control the individual switching elements of the half-bridges; this could be, for example, a gate driver circuit. This allows, for example, a DC voltage supplied by an electrical system or a battery to be converted into an AC voltage for the stator winding.

[0003] The semiconductor switches, gate drivers, and any rotor field excitation circuitry are powered from the DC link. Therefore, overvoltage protection may be provided to prevent the DC link voltage from exceeding a certain limit.

[0004] A power converter can therefore have protective functions to safeguard the system against anomalous conditions such as overvoltage. If these protective functions detect a fault, a shutdown path can be activated to bring the system to a safe state. To prevent damage even during such a transition, additional fast-acting overvoltage protection can be provided to limit the voltage amplitude or spikes on the DC link. Diodes, such as suppressor diodes (TVS diodes) or Zener diodes, can be used for this purpose. Disclosure of the invention

[0005] Based on this prior art, a computing unit for checking an overvoltage protection circuit for an electric machine, an overvoltage protection circuit, and a power converter arrangement with the features of the independent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

[0006] The invention provides a simple and reliable method for verifying the functionality of an overvoltage protection circuit. If it is determined that the overvoltage protection circuit is not functioning, operation of the electrical machine can be prevented, for example, the output of alternating voltage to the electrical machine can be prevented or terminated. Specifically, the method is carried out in a state in which no alternating voltage is (yet) being output to or generated by the electrical machine, particularly before alternating voltage is output or generated. Conversely, if it is determined that the overvoltage protection circuit is functioning, operation of the electrical machine or a system containing it, such as a vehicle, can be started or continued.

[0007] The overvoltage protection circuit used within the scope of the invention has, in particular, two DC voltage terminals and is configured to limit the voltage between these two DC voltage terminals to a total voltage limit. For this purpose, it comprises a series connection of at least two overvoltage protection modules, wherein a switching unit is connected in parallel to each of the at least two overvoltage protection modules, such that closing the switching unit bypasses the respective overvoltage protection module. It can be provided that the bypass has a certain electrical resistance greater than zero in order to limit current flow through the switching unit. In one embodiment, the switching unit comprises a switching element, in particular a semiconductor switching element, e.g., a MOSFET or IGBT, and a resistive element for limiting current flow through the switching element.

[0008] Furthermore, at least one of the at least two overvoltage protection assemblies comprises at least two overvoltage protection components, and each of the other at least two overvoltage protection assemblies comprises at least one overvoltage protection component, wherein each overvoltage protection component limits a voltage drop across it to a component voltage limit. In one embodiment, an overvoltage protection component comprises, or is itself, a diode, in particular a suppressor diode or Zener diode. Diodes with a breakdown voltage, such as Zener diodes or suppressor diodes, are particularly well suited for overvoltage protection, wherein the component voltage limit is determined by the breakdown voltage. The aforementioned overall voltage limit depends in particular on the component voltage limits involved and is, for example, their sum.

[0009] Furthermore, two voltage taps are provided between each pair of the overvoltage protection components, so that, depending on the switching states of the switching units, different voltage values ​​can be measured between the voltage tap and one of the DC voltage connections of the overvoltage protection circuit, in particular a ground connection.

[0010] To verify the functionality of the surge protection circuit, a voltage present at the surge protection circuit or between the DC voltage terminals is measured at several points. This voltage influences the voltage measurable at the voltage taps. The at least two switching units are switched in at least two different switching configurations, and the measured voltage at each of the voltage taps is determined or measured in each of the at least two different switching configurations and compared with a corresponding reference value, which is determined depending on the applied voltage and the component voltage limits.Based on the switching configuration, the component voltage limits, and the measured applied voltage, specific measured values ​​are expected for certain switching configurations (within tolerances), so that the functionality of the overvoltage protection circuit can be determined based on at least one comparative result. In general, the different switching configurations involve different permutations of the switching states of the switching units. The two voltage taps according to the invention can determine the functionality of the overvoltage protection circuit for each of the permutations. Should one of the voltage taps be defective, the functionality can be determined for a portion, approximately 80%, of the permutations using the other voltage tap.

[0011] The invention allows voltage spikes in the DC link to be limited to permissible values, preventing other safety mechanisms from being triggered prematurely, which would otherwise, for example, put the electric machine into a safe state (i.e., usually inoperative). Unnecessary downtime and outages can be reduced. The invention protects the electric machine's converter from overvoltage before a main safety mechanism is activated. The functionality of the overvoltage protection circuit can be easily checked before each start-up of the electric machine or the system containing it. The time required for the start-up test can be significantly reduced (due to point measurements).

[0012] In one embodiment, it is stipulated that the overvoltage protection circuit is inoperative if at least one measured value does not correspond to the corresponding reference value within a permissible tolerance. This occurs in particular if at least one component voltage limit does not correspond to the expected value, so that a defect or damage to at least one overvoltage protection component can be assumed. As already mentioned above, a (suitable) measure is then expediently taken, which is selected, for example, from stopping or...Terminating the commencement or ongoing operation of the electrical machine, preventing or terminating the energization of the electrical machine, issuing an error message, bringing the electrical machine into a safe state, or terminating the commencement or ongoing operation of a system in which the electrical machine is installed, such as a vehicle.

[0013] In one embodiment, it is stipulated that the overvoltage protection circuit is functional if at least one measured value from one or each of the two voltage taps corresponds to the associated reference value within a permissible tolerance. In this case, all component voltage limits correspond to the expected value.

[0014] In one embodiment, the surge protection circuit comprises exactly two surge protection modules. This allows surge protection to be achieved with very few components while simultaneously limiting the effort required for functional testing.

[0015] In one embodiment, the surge protection circuit comprises exactly three surge protection components. This approach also allows for surge protection to be achieved with very few components, while simultaneously limiting the effort required for functional testing and keeping the number of components subject to tolerances manageable.

[0016] In one embodiment, the surge protection circuit comprises exactly two surge protection assemblies, the first of which has exactly one surge protection component, and the second of which has exactly two surge protection components. This is an embodiment that has proven to be particularly practical and reliable.

[0017] In one embodiment, the surge protection circuit has exactly two voltage taps, with the first being located between the two surge protection components of the previously described second surge protection assembly and the second being located between the two surge protection assemblies. The number of measuring points required for diagnostic purposes can be reduced to only two when using three surge protection components.

[0018] In one embodiment, the at least two different switching configurations are selected from a first switching configuration in which a first of the at least two switching units is closed (conducting) and a second of the at least two switching units is open (non-conducting), a second switching configuration in which the first of the at least two switching units is open and the second of the at least two switching units is closed, and a third switching configuration in which the first of the at least two switching units is open and the second of the at least two switching units is open. These configurations are easy to manufacture and cover a multitude of possible embodiments with regard to the number of surge protection assemblies and surge protection components.

[0019] In one design, nominal values, e.g., from datasheets, can be used for the component voltage limits. In such a case, the tolerances must be selected accordingly to account for component and temperature tolerances.

[0020] In one implementation, the component voltage limits of the surge protection devices are determined, for example, at the beginning of each procedure. This allows the necessary tolerances to be reduced and the result improved, or the accuracy increased. This determination can be based on calculations that specifically take the current temperature into account. As is well known, for example, the breakdown voltage of diodes depends on the current temperature.

[0021] In one embodiment, the current temperature is measured, for example using a temperature sensor, from which the current temperature of the surge protection components can be derived. It is advantageous to measure the temperature as close as possible to, or even directly on, the surge protection components. The component voltage limits are then determined based on the temperature.

[0022] A computing unit according to the invention, e.g., an integrated circuit (e.g., IC or ASIC), is configured, particularly by means of software and / or hardware, to perform the aforementioned steps. The at least two switching units can, in particular, also be part of the computing unit.

[0023] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.

[0024] The invention is schematically illustrated in the drawing using exemplary embodiments and is described below with reference to the drawing. Brief description of the drawings Fig. Figure 1 schematically shows an electrical machine with a power converter and overvoltage protection circuit according to an embodiment of the invention. Fig. Figure 2 schematically shows an overvoltage protection circuit according to an embodiment of the invention. Fig. Figure 3 shows an embodiment of the invention in a block diagram. embodiment(s) of the invention

[0025] Fig. Figure 1 shows a schematic and circuit diagram-like representation of an electric machine 100 with a power converter 140 and an overvoltage protection circuit 200 according to an embodiment of the invention. The electric machine 100 has, by way of example, a stator or stator winding 110 with three phases U, V, W, and a permanent magnet (and / or separately excited) rotor 120. It should be noted that the number of phases is not limiting and, for example, more than three phases, e.g., four, five, six, etc., can also be used. Furthermore, by way of example, a battery 130 is provided with a positive supply terminal B+ and a negative supply terminal B- (ground), to which the power converter 140 is connected. This can represent, by way of example, an on-board electrical system, e.g., of a plant or a vehicle. The overvoltage protection circuit 200 is connected between the positive and negative supply terminals.

[0026] The power converter 140 has three half-bridges 150 corresponding to the three-phase electric machine. One half-bridge is designated 153 as an example. Half-bridge 153 has a switch TW_H on one side of a positive terminal 161 (i.e., on the positive terminal side, highside), which is to be connected to the positive supply terminal B+, a switch TW_L on one side of a negative terminal 162 (i.e., on the negative terminal side, lowside), which is to be connected to the negative supply terminal B-, and a phase connection 163 (AC voltage connection) between the two switches TW_H and TW_L, which is to be connected to the phase W of the stator winding 110. The same applies to the other two half-bridges (without reference numerals). The switches can be, for example, designed as MOSFETs or IGBTs. An intermediate circuit capacitor C is also provided as an example between the positive terminal 161 and the negative terminal 162.

[0027] Furthermore, the power converter 140 has a control device 171, e.g. a driver circuit, by means of which the switches of the individual half-bridges (two switches per half-bridge) of the group 150 can be controlled, i.e. opened and closed.

[0028] In Fig. Figure 2 shows a schematic and circuit diagram-like embodiment of an overvoltage protection circuit, as used in an electrical machine, such as the electrical machine 100 according to Fig. 1. The overvoltage protection circuit has two DC voltage terminals 201, 202 and is designed to limit the voltage between these two DC voltage terminals to a total voltage limit. It comprises a series connection of, in the example shown, two overvoltage protection modules 210, 220, where the overvoltage module 210 has a suppressor diode 211 as its overvoltage protection component, and the overvoltage module 220 has a suppressor diode 221 and a suppressor diode 222 as its overvoltage protection components. Each of the suppressor diodes 211, 221, and 222 has a breakdown voltage, which defines a component voltage limit of the suppressor diode. The total voltage limit of the overvoltage protection circuit 200 is the sum of the three component voltage limits.

[0029] The overvoltage protection assembly 210 is a switching unit 215 and the overvoltage protection assembly 220 is a switching unit 225 connected in parallel. Each of the switching units 215, 225 can, in particular, have a switching element, for example in the form of a MOSFET, and a resistor connected in series with it to limit the current flow.

[0030] By closing or conducting the switching unit 215 or 225, the respective associated overvoltage protection assembly 210 or 220, more precisely the suppressor diodes 211 or 221 and 222, can be bypassed. The switching units 215 and 225 can be controlled via switching terminals 215a and 225a.

[0031] A first voltage tap is provided between the suppressor diodes 221 and 222, which in this example comprises a voltage measurement circuit 230 with an associated voltage sensor output 230a. A second voltage tap is provided between the overvoltage protection modules 210 and 220, which in this example comprises a voltage measurement circuit 231 with an associated voltage sensor output 231a. The voltage measurement circuits 230 and 231 can, for example, perform voltage division, amplification, smoothing, etc. It should be understood that the voltage tap can also be connected directly to the output 230a or 231a. It should be noted that the elements 215, 225, 230, and 231 can also be components of a computing unit configured for carrying out the method, meaning that the computing unit is directly connected to the series connection of the diodes via appropriate terminals.

[0032] One embodiment of the invention is described below with reference to the Fig. 2 and Fig. 3 described. In particular, an embodiment is described in which two different switching configurations are generated and measured.

[0033] In a first switching configuration, the first (upper) surge protection module 210 is bypassed by activating the switching unit 215, and the second (lower) surge protection module 220 is not bypassed. This allows the functionality and fault-free condition of the middle suppressor diode 221 and the lower suppressor diode 222 to be checked.

[0034] In a second switching configuration, the first overvoltage protection module 210 is not bypassed, and the second overvoltage protection module 220 is bypassed by activating the second switching unit 225. This allows the functionality and fault-free operation of the upper suppressor diode 211 to be tested.

[0035] For each circuit configuration, a voltage value at output 230a and a voltage value at output 231a are recorded and each compared to a reference value. If the measured value does not match the corresponding reference value within a tolerance, the overvoltage protection assembly is considered faulty and a corrective action is taken. This action may, for example, prevent the operation of the electrical machine and / or the operation of a system in which the electrical machine is installed, such as a vehicle. In particular, it may prevent the vehicle's internal combustion engine from being started.

[0036] The tables below show the measurable voltages for different circuit configurations and fault conditions. The states of the suppressor diodes are listed in the "Diode State" column and are designated as normal "N", non-conducting "O" (open), and permanently conducting "S" (short). "?" denotes any state.

[0037] The column “Switching configuration L / H” indicates the control state of the upper (H) and lower (L) switching unit, where “1” means that the switching unit is controlled and the corresponding overvoltage protection assembly is bypassed, and “0” means that the switching unit is not controlled and the corresponding overvoltage protection assembly is not bypassed.

[0038] VDC refers to the voltage applied between the DC terminals, measured at the beginning of the procedure. In a typical application in a vehicle, this might be, for example, 48 V. Vclamp_D1, Vclamp_D2, and Vclamp_D3 denote the respective component voltage limits of the suppressor diodes 211, 221, and 222, which in the example shown are set to 24 V, 13 V, and 16 V, respectively, resulting in a total voltage limit of 53 V. In this case, a tolerance of ± 4 V can be selected, for example. However, it should be emphasized that these numerical values ​​are purely illustrative and not intended to be restrictive.

[0039] The fault-free state is shown in row 1. Table 1 shows the measurable voltages of the first voltage tap for different circuit configurations and diode faults. Table 2 shows the measurable voltages of the second voltage tap for different circuit configurations and diode faults. Using Tables 1 and 2, the functionality of the overvoltage protection circuit can be determined for each permutation of switching states of the switching units by simultaneously reading the voltage tap measurements. In this way, the functionality of each of the suppressor diodes 211, 221, and 222 can be verified. Table 1: Measurable voltages of the first voltage tap for different circuit configurations and diode faults Diodenzustand Schaltkonfiguration L / H Spannung am Spannungsabgriffs 1 N-N-N(fehlerfrei) 1 / 0 Vdc - [Vclamp_D1 (24V) + Vclamp_D2 (13V)] 0 / 1 Vclamp_D3 (16V) 0 / 0 Vdc - [Vclamp_D1 (24V) + Vclamp_D2 (13V)] 2 N-N-S 1 / 0 0V 0 / 1 0V 0 / 0 0V 3 N-S-N 1 / 0 Vclamp_D3 (16V),wenn Vdc > Vclamp_D1 (24V) + Vclamp_D3 (16V)Vdc - [Vclamp_D1 (24V)],wenn Vdc < Vclamp_D1 (24V) + Vclamp_D3 (16V) 0 / 1 Vclamp_D3 (16V) 0 / 0 Vclamp_D3 (16V),wenn Vdc > Vclamp_D1 (24V) + Vclamp_D3 (16V)Vdc - [Vclamp_D1 (24V)],wenn Vdc < Vclamp_D1 (24V) + Vclamp_D3 (16V) 4 S-N-N 1 / 0 Vclamp_D3 (16V),wenn Vdc > Vclamp_D2 (13V) + Vclamp_D3 (16V)Vdc - [Vclamp_D2 (13V)],wenn Vdc < Vclamp_D2 (13V) + Vclamp_D3 (16V) 0 / 1 Vclamp_D3 (16V),wenn Vdc > Vclamp_D2 (13V) + Vclamp_D3 (16V)Vdc - [Vclamp_D2 (13V)],wenn Vdc < Vclamp_D2 (13V) + Vclamp_D3 (16V) 0 / 0 Vclamp_D3 (16V),wenn Vdc > Vclamp_D2 (13V) + Vclamp_D3 (16V) Vdc - [Vclamp_D2 (13V)],wenn Vdc < Vclamp_D2 (13V) + Vclamp_D3 (16V) 5 S-S-N 1 / 0 Vclamp_D3 (16V) 0 / 1 Vclamp_D3 (16V) 0 / 0 Vclamp_D3 (16V) 6 N-N-O 1 / 0 Vdc - [Vclamp_D1 (24V) + Vclamp_D2 (13V)] 0 / 1 Vdc - [Vclamp_D1 (24V) + Vclamp_D2 (13V)] 0 / 0 Vdc - [Vclamp_D1 (24V) + Vclamp_D2 (13V)] 7 O-N-N 1 / 0 0V 0 / 1 Vclamp_D1 (24V) 0 / 0 0V 8 O-N-O 1 / 0 0V 0 / 1 Vdc - [Vclamp_D2 (13V)] 0 / 0 0V 9 S-S-O 1 / 0 Vdc 0 / 1 Vdc 0 / 0 Vdc 10 O-S-O 1 / 0 0V 0 / 1 Vdc 0 / 0 0V 11 N-S-O 1 / 0 Vdc - [Vclamp_D1 (24V)] 0 / 1 Vdc 0 / 0 Vdc - [Vclamp_D1 (24V)] 12 S-N-O 1 / 0 Vdc - [Vclamp_D2 (13V)] 0 / 1 Vdc - [Vclamp_D2 (13V)] 0 / 0 Vdc - [Vclamp_D2 (13V)] 13 O-S-N 1 / 0 0V 0 / 1 Vclamp_D3 (16V) 0 / 0 0V Table 2: Measurable voltages of the second voltage tap for different circuit configurations and diode faults Diodenzustand Schaltkonfiguration L / H Spannung am Spannungsabgriff 1 N-N-N 1 / 0 Vdc-[Vclamp_D1 (24V)] 0 / 1 Vdc 0 / 0 Vdc-[Vclamp_D1 (24V)] 2 N-N-S 1 / 0 Vdc-[Vclamp_D1 (24V)] 0 / 1 Vclamp_D2 (13V) 0 / 0 Vdc-[Vclamp_D1 (24V)] 3 N-S-N 1 / 0 Vdc-[Vclamp_D1 (24V)] 0 / 1 Vclamp_D3 (16V) 0 / 0 Vdc-[Vclamp_D1 (24V)] 4 N-S-S 1 / 0 0V 0 / 1 0V 0 / 0 0V 5 S-N-N 1 / 0 Vdc 0 / 1 Vdc 0 / 0 Vdc 6 S-N-S 1 / 0 Vdc 0 / 1 Vdc 0 / 0 Vdc 7 S-S-N 1 / 0 Vdc 0 / 1 Vdc 0 / 0 Vdc 8 S-S-S 1 / 0 0V 0 / 1 0V 0 / 0 0V 9 N-N-N 1 / 0 Vdc-[Vclamp_D1 (24V)] 0 / 1 Vdc 0 / 0 Vdc-[Vclamp_D1 (24V)] 10 N-N-O 1 / 0 Vdc-[Vclamp_D1 (24V)] 0 / 1 Vdc 0 / 0 Vdc-[Vclamp_D1 (24V)] 11 N-O-N 1 / 0 Vdc-[Vclamp_D1 (24V)] 0 / 1 Vdc 0 / 0 Vdc-[Vclamp_D1 (24V)] 12 N-O-O 1 / 0 Vdc-[Vclamp_D1 (24V)] 0 / 1 Vdc 0 / 0 Vdc-[Vclamp_D1 (24V)] 13 O-N-N 1 / 0 0V 0 / 1 Vdc 0 / 0 0V 14 O-N-O 1 / 0 0V 0 / 1 Vdc 0 / 0 0V 15 O-O-N 1 / 0 0V 0 / 1 Vdc 0 / 0 0V 16 O-O-O 1 / 0 0V 0 / 1 Vdc 0 / 0 0V 17 S-S-S 1 / 0 0V 0 / 1 0V 0 / 0 0V 18 S-S-O 1 / 0 Vdc 0 / 1 Vdc 0 / 0 Vdc 19 S-O-S 1 / 0 Vdc 0 / 1 Vdc 0 / 0 Vdc 20 S-O-O 1 / 0 Vdc 0 / 1 Vdc 0 / 0 Vdc 21 O-S-S 1 / 0 0V 0 / 1 0V 0 / 0 0V 22 O-S-O 1 / 0 0V 0 / 1 Vdc 0 / 0 0V 23 O-O-S 1 / 0 0V 0 / 1 Vdc 0 / 0 0V 24 O-O-O 1 / 0 0V 0 / 1 Vdc 0 / 0 0V 25 N-S-O 1 / 0 Vdc-[Vclamp_D1 (24V)] 0 / 1 Vdc 0 / 0 Vdc-[Vclamp_D1 (24V)] 26 N-O-S 1 / 0 Vdc-[Vclamp_D1 (24V)] 0 / 1 Vdc 0 / 0 Vdc 27 S-N-O 1 / 0 Vdc 0 / 1 Vdc 0 / 0 Vdc 28 S-O-N 1 / 0 Vdc 0 / 1 Vdc 0 / 0 Vdc 29 O-S-N 1 / 0 0V 0 / 1 Vclamp_D3 (16V) 0 / 0 0V 30 O-N-S 1 / 0 0V 0 / 1 Vclamp_D2 (13V) 0 / 0 0V

[0040] It is evident that the functionality of the overvoltage protection circuit 200 can be determined quickly and easily using the illustrated embodiment.

[0041] In step 310, the voltage Vdc between the positive and negative supply voltage terminals B+ and B- is first determined.

[0042] In an optional step 320, a temperature is determined from which a temperature T of the suppressor diodes can be derived. For example, a temperature sensor can be placed on the circuit board on which the suppressor diodes are arranged, either near the suppressor diodes or in thermal contact with one or more of them.

[0043] Fig.Figure 3 shows a block diagram illustrating steps that can occur, for example, in the processing unit. In step 330, the respective component voltage limits Vclamp_D1, Vclamp_D2, and Vclamp_D3 are determined based on the measured temperature T. The following relationship, for example, can be used: Vclamp(T)=Vclamp(25°C)×(1+αT×(T−25K)) with α = 0.08% and Vclamp(25°C): Breakdown voltage at 25°C

[0044] In step 340, the first switching unit 215 is closed (state "1") and the second switching unit 225 is opened (state "0").

[0045] After a sufficient waiting period, step 350, of for example a minimum of 50 microseconds, which corresponds to three times the output filter time constant of the voltage measurement circuit 230, the voltage applied to the outputs 230a, 231a is measured in step 360.

[0046] In step 370, the measured voltage is compared with a reference value, which is determined based on the measured applied voltage (step 310) and the specified component voltage limit (step 330) (see Table 1 and 2, respectively). If either of the two values ​​of a voltage tap does not match within a permissible tolerance (branch "0"), the procedure is terminated in step 430, and the electrical machine and / or the system it contains is brought to a safe state.

[0047] If the values ​​of both voltage taps match within the tolerance range, branch “1”, the process continues with step 380, in which the first switching unit 215 is opened (state “0”) and the second switching unit 225 (state “1”) is closed.

[0048] After a sufficient waiting period of, for example, a minimum of 50 microseconds, step 390, which corresponds to three times the output filter time constant of the voltage measurement circuits 230, 231, the voltage applied to the outputs 230a, 231a is measured in a step 400.

[0049] In step 410, the measured voltage is compared with a reference value, which is determined based on the measured applied voltage (step 310) and the specified component voltage limit (step 330) (see table). If the two values ​​do not match within a permissible tolerance (branch "0"), the procedure is terminated in step 430, and the electrical machine and / or the system it contains is brought to a safe state.

[0050] If the values ​​match within the tolerance limits, branch “1”, the process continues with step 410, in which the overvoltage protection circuit is assessed as functioning, and optionally a corresponding measure is taken, which consists in particular of enabling subsequent operation.

Claims

[1] Computing unit designed to check an overvoltage protection circuit (200) for an electric machine (100), wherein the overvoltage protection circuit (200) comprises a series connection of at least two overvoltage protection assemblies (210, 220), wherein each of the at least two surge protection assemblies (210, 220) has a switching unit (215, 225) connected in parallel, so that by closing the switching unit (215, 225) the respective surge protection assembly (210, 220) is bypassed, wherein a first of the two surge protection assemblies (210, 220) comprises at least one surge protection element (211, 221, 222) and a second of the two surge protection assemblies (210, 220) comprises at least two surge protection elements (211, 221, 222), wherein each surge protection component (211, 221, 222) limits a voltage drop across it to a component voltage limit, wherein a first voltage tap (230a) is provided between two of the surge protection components (221, 222) of the second surge protection assembly, wherein a second voltage tap (231a) is provided between the two surge protection assemblies (210, 220), wherein the computing unit is set up: -- to detect a voltage applied to the overvoltage protection circuit (200) at two points, -- to switch the at least two switching units (215, 225) into at least two different switching configurations and to determine measured values ​​of a voltage applied to the voltage taps (230a, 231a) in each of the at least two different switching configurations, -- to compare at least two measured values ​​for each of the voltage taps (230a, 231a) with a corresponding reference value, which is determined depending on the voltage applied to the overvoltage protection circuit (200) and the component voltage limits, -- to determine the functionality of the overvoltage protection circuit (200) based on at least one comparison result. [2] Computing unit according to claim 1, which is further configured to determine the functionality of the overvoltage protection circuit (200) using at least one comparison result: to determine that the overvoltage protection circuit (200) is not functioning if at least one measured value for each of the voltage taps (230a, 231a) does not agree with the corresponding reference value within a permissible tolerance. [3] Computing unit according to claim 2, which is further configured to perform an action when it is determined that the overvoltage protection circuit (200) is not functioning. [4] Computing unit according to one of the preceding claims, which is further configured to determine the functionality of the overvoltage protection circuit (200) using at least one comparison result: to determine that the overvoltage protection circuit (200) is functioning if all measured values ​​within a permissible tolerance match the associated reference value. [5] Computing unit according to one of the preceding claims, which is further configured to select the at least two different switching configurations from a first switching configuration in which a first of the at least two switching units (215, 225) is closed and a second of the at least two switching units (215, 225) is open, a second switching configuration in which the first of the at least two switching units (215, 225) is open and the second of the at least two switching units (215, 225) is closed, and a third switching configuration in which the first of the at least two switching units (215, 225) is open and the second of the at least two switching units (215, 225) is open. [6] Computing unit according to one of the preceding claims, further configured to determine the component voltage limits of the surge protection components (211, 221, 222). [7] Computing unit according to the preceding claim, further equipped to: -- to determine a temperature, -- to determine the voltage limits of the surge protection components (211, 221, 222) as a function of temperature. [8] Computing unit according to one of the preceding claims, wherein the overvoltage protection element (211, 221, 222) comprises a diode, in particular a suppressor diode or Zener diode. [9] Computing unit according to one of the preceding claims, which is configured to perform a check of an overvoltage protection circuit (200) with only one functional voltage tap in the event of a defective voltage tap. [10] Overvoltage protection circuit (200) for an electric machine (100), comprising a series connection of at least two overvoltage protection assemblies (210, 220), wherein each of the at least two surge protection assemblies (210, 220) has a switching unit (215, 225) connected in parallel, so that by closing the switching unit (215, 225) the respective surge protection assembly (210, 220) is bypassed, wherein a first of the two surge protection assemblies (210, 220) comprises at least one surge protection element (211, 221, 222) and a second of the two surge protection assemblies (210, 220) comprises at least two surge protection elements (211, 221, 222), wherein each surge protection component (211, 221, 222) limits a voltage drop across it to a component voltage limit, wherein a first voltage tap (230a) is provided between two of the surge protection components (221, 222) of the second surge protection assembly, wherein a second voltage tap (231a) is provided between the two surge protection assemblies (210, 220). [11] Power converter arrangement comprising a power converter circuit (140) with two DC voltage terminals (161, 162) and a plurality of AC voltage terminals (163), an overvoltage protection circuit (200) connected between the two DC voltage terminals, and a computing unit according to the preceding claim, wherein the overvoltage protection circuit (200) comprises a series connection of at least two overvoltage protection assemblies (210, 220), wherein each of the at least two surge protection assemblies (210, 220) has a switching unit (215, 225) connected in parallel, so that by closing the switching unit (215, 225) the respective surge protection assembly is bypassed, wherein a first of the two surge protection assemblies (210, 220) comprises at least one surge protection element (211, 221, 222) and a second of the two surge protection assemblies (210, 220) comprises at least two surge protection elements (211, 221, 222), wherein each surge protection device (211, 221, 222) limits a voltage drop across it to a voltage limit, wherein a first voltage tap (230a) is provided between two of the surge protection components (221, 222) of the second surge protection assembly, wherein a second voltage tap (231a) is provided between the two surge protection assemblies (210, 220). [12] Power converter arrangement according to claim 11, wherein the overvoltage protection circuit (200) comprises a series connection of exactly two overvoltage protection assemblies (210, 220). [13] Power converter arrangement according to claim 12, wherein a first surge protection assembly (210) comprises exactly one surge protection element (211), and a second surge protection assembly (220) comprises exactly two surge protection elements (221, 222). [14] Power converter arrangement according to one of claims 11 to 13, wherein the overvoltage protection circuit (200) has exactly two voltage taps (230a, 231a). [15] Power converter arrangement according to claims 13 and 14, wherein the first voltage tap (230a) is between the two surge protection components (221, 222) of the second surge protection assembly (220) and the second voltage tap (231a) is arranged between the two surge protection assemblies (210, 220).

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