DE102023004903B3 - Method for operating an inverter - Google Patents

Abstract

The invention relates to a method for operating an inverter (100) for an electrical machine, in particular an electrically operated vehicle, wherein the inverter (100) is designed to be controllable in three stages and has at least one main current path (20) with at least two semiconductor switches (22, 24) and at least one neutral point path (30) opening into the main current path (20) with at least one semiconductor switch (32, 34). The neutral point path (30) is designed to provide output load currents at the load output (26) in a three-stage operation (1) which are smaller than the output load currents provided by the main current path (20) in a two-stage operation (2). The inverter (100) is converted from the three-stage operation (1) to the two-stage operation (2) and vice versa depending on at least one electrical load required by the electrical machine. The inverter (100) is controlled in a partial load range so that a mixed operation (3) between the three-stage operation (1) and the two-stage operation (2) is set.
The invention further relates to an inverter (100).

Description

The invention relates to a method for operating an inverter for an electrical machine, in particular an electrically operable vehicle, and to an inverter for an electrical machine, in particular an electrically operable vehicle, for carrying out such a method.

Two-stage inverters are usually used in battery-electric vehicles. Three-stage inverters are well known and have significant efficiency potential in electric drives. To increase the efficiency of the electric machine in the cycle-relevant area, a two-stage inverter can be expanded to a three-stage inverter, for example using a so-called T-branch, which then represents a version of a three-stage neutral-point-coupled inverter.

Three-stage inverters enable particularly efficient energy conversion, but require more semiconductor switches than currently used two-stage inverters.

The neutral point switches of the different three-stage structures with neutral point connection enable efficient partial load operation, but must be designed for the full current of the rated point for start-up with low control.

The DE 10 2021 003 941 B4 discloses the use of a controllable three- or multi-stage inverter for electric drive systems of motor vehicles, which can be operated in a three- or multi-stage operation and in a two-stage operation. A specially provided operating mode setting device sets the respective operating mode by controlling the power switches of the inverter in a suitable manner. The operating mode is set according to the overall efficiency of the entire drive system and thus not only on the basis of the electric machine and/or the inverter used. For the overall efficiency, in addition to the recorded phase current of the electric machine, other parameters and/or properties of the electric machine that influence the overall efficiency are also taken into account.

The genre-defining script DE 10 2013 202 649 A1 shows an optimized control of an inverter device, whereby the inverter device can be controlled alternatively in 2-level operation or in 3-level operation. By selecting the appropriate control method, the semiconductor losses in the inverter can be minimized and the thermal load on the components used can be controlled in a targeted manner. With such an operating method for an inverter, efficient and gentle inverter operation is possible even with low output voltages and highly inductive or capacitive loads.

In the publication of Kim and Lee in 2017 at the IEEE 3rd International Future Energy Electronics Conference and ECCE Asia on “Mode transition scheme for optimal efficient operation of a 3-level T-type inverter “ already suggests a general idea of mixed operation, even if it is implemented there for specific applications.

In the IEEE contribution by Wang, Zheng, Xu and Li from 2020, Volume 35 Issue 9 on “A Generalized Carrier-Overlapped PWM Method for Neutral-Point-Clamped Multilevel Converter “ describes a modulation method called COPWM (carrier overlapped pwm), which has an overlap range of the carrier voltage.

Also in the publication of the IEEE conference “European Conference on Power Electronics and Applications” from 2007 by Far, Radan and Far on “Introduction and evaluation of novel multi-level carrier-based PWM strategies using a generalized algorithm “ an overlap of the carrier voltages can be detected.

An object of the invention is to provide an improved method for efficiently operating an inverter for an electrical machine, in particular an electrically operated vehicle.

A further object is to provide an inverter for an electrical machine, in particular an electrically operated vehicle, for carrying out such an improved method.

The aforementioned objects are solved with the features of the independent claims.

Favorable embodiments and advantages of the invention emerge from the further claims, the description and the drawing.

According to one aspect of the invention, a method for operating an inverter for an electrical machine, in particular an electrically operated vehicle, is proposed, wherein the inverter is designed to convert a direct voltage into an alternating voltage for driving the to convert the electrical machine connected to a load output of the inverter. The inverter is designed to be controllable in three stages and has at least one main current path with at least two semiconductor switches and at least one neutral point path leading into the main current path with at least one semiconductor switch.

The neutral point path is designed to provide output load currents at the load output in a three-stage operation that are smaller than the output load currents provided by the main current path in a two-stage operation. The inverter is converted from the three-stage operation to the two-stage operation and vice versa depending on at least one electrical load requested by the electrical machine. The inverter is controlled in a partial load range in such a way that a mixed operation between the three-stage operation and the two-stage operation is set.

When a load limit is exceeded, particularly at very high loads, the proposed method advantageously enables the semiconductor switches of the neutral point path to be relieved by means of a suitable modulation method of the inverter. When a load limit is exceeded, the system advantageously switches from three-stage operation to mixed operation. This allows the semiconductor switches of the neutral point path to be smaller while at the same time providing an advantage in partial load operation. Furthermore, depending on the electrical load required, the inverter can be switched between two-stage and three-stage operation. At full load, the inverter is then controlled exclusively in two-stage operation.

In this way, cost savings can be advantageously achieved by reducing the installed semiconductor area of the inverter without reducing the partial load efficiency.

The method can be used for three-stage neutral point inverters with any type of neutral point connection, for example so-called inverters with T-branch, NPC inverters or ANPC inverters. With a T-type inverter, a particularly large effect can be achieved with the help of the method according to the invention, although this can also have a positive influence on other types of inverter structures, in particular on the required semiconductor area.

According to the invention, the inverter is operated in a pulse width modulation method, wherein the semiconductor switches of the inverter are controlled by means of at least one carrier signal, in particular a periodic triangular signal, to define switching times, wherein in the two-stage operation the at least one carrier signal is compared with a predetermined setpoint signal, and wherein in the three-stage operation at least two carrier signals mirrored at a voltage zero point for two half-waves are compared with the predetermined setpoint signal. In the mixed operation, the at least two carrier signals are set to overlap in a predetermined overlap voltage range around the voltage zero point. In particular, one of the at least two carrier signals of one polarity can be scaled up to an overlap value of the other polarity, wherein a sum of the at least two overlap values results in the overlap voltage range. For this purpose, the carrier signals are advantageously stretched and not simply shifted.

In order to be able to compare the specified setpoint signal in three-stage operation, at least two carrier signals for two half-waves mirrored at a voltage zero point are used. The two carrier signals for two half-waves mirrored at a voltage zero point can also optionally be shifted in time by a period component, whereby the period component can be, for example, a quarter period.

According to the invention, the carrier signals are stretched beyond the voltage zero point. In the overlap voltage range, mixed operation can thus be advantageously set with a modulation of the inverter alternating between the two-stage and the three-stage modulation, while outside the overlap voltage range a quasi-normal three-stage modulation is used. A characteristic of the overlap voltage range sets the load on the semiconductor switches of the neutral point path.

According to the invention, the mixed operation can be set when the setpoint signal is in the overlap voltage range of the at least two carrier signals. The mixed operation in the overlap voltage range can thus advantageously relieve the load on the semiconductor switches of the neutral point path.

According to the invention, the overlap value is set dynamically during operation of the inverter. In this way, strong heating of the semiconductor switches of the neutral point path, which can have a negative impact on the service life, can be avoided.

According to an advantageous embodiment of the method, the three-stage operation can be set when the setpoint signal is outside the overlap voltage range of the at least two carrier signals. In this way, the semiconductor switches of the neutral point path can be relieved.

According to an advantageous embodiment of the method, an electrical load of the at least one semiconductor switch of the neutral point path can be adjusted by the overlap value. As a result, the electrical load can be advantageously adapted to the design values of the semiconductor switches of the neutral point path.

According to an advantageous embodiment of the method, a proportion of zero states in which the semiconductor switches of the neutral point path permanently carry current can be set via the overlap value. This allows the operation of the semiconductor switches of the neutral point path to be designed favorably.

According to an advantageous embodiment of the method, the control signals of the semiconductor switches of the neutral point path can be determined by comparing the at least two carrier signals with the setpoint signal and summing the comparison results. In this way, mixed operation with a combined two-stage and three-stage control of the inverter can be set up in a simple manner.

According to a further aspect of the invention, an inverter for an electrical machine, in particular an electrically operated vehicle, is proposed for carrying out a method, wherein the inverter can be converted from a three-stage operation to a two-stage operation and vice versa depending on at least one load required by the electrical machine. The inverter can be controlled in a partial load range so that a mixed operation between the three-stage operation and the two-stage operation can be set. Any three-stage inverter with a neutral point connection can benefit from the invention.

With the proposed inverter, the load on the semiconductor switches of the neutral point path can be reduced at full load by means of a suitable modulation method of the inverter. This allows the semiconductor switches of the neutral point path to be smaller while at the same time providing an advantage in partial load operation. Furthermore, depending on the electrical load required, the inverter can be switched between two-stage and three-stage operation.

In this way, cost savings can be advantageously achieved by reducing the installed semiconductor area of the inverter without reducing the partial load efficiency.

According to an advantageous embodiment, the inverter can comprise a T-type neutral point clamped inverter architecture, wherein a main current path has at least two series-connected semiconductor switches with a center tap, which are electrically connected to a positive and a negative operating voltage. The center tap is electrically connected to a load output. In this case, a neutral point path with at least one semiconductor switch is electrically connected to a neutral point of the positive and negative operating voltages and the center tap.

The inverter can advantageously be operated using the method described above, which provides for mixed operation with a combined two-stage and three-stage control of the inverter and thus allows efficient and service-saving operation.

Further advantages emerge from the following description of the drawings. The drawings show an embodiment of the invention. The drawings, the description and the claims contain numerous features in combination. The person skilled in the art will also expediently consider the features individually and combine them into further useful combinations.

• 1 eine Schaltungsanordnung eines Wechselrichters für eine elektrische Maschine, insbesondere eines elektrisch betreibbaren Fahrzeugs, für ein Verfahren nach einem Ausführungsbeispiel der Erfindung;
• 2 Sollwertsignal und Trägersignal für einen zweistufigen Betrieb des Wechselrichters nach 1;
• 3 Ansteuersignale des Wechselrichters beim zweistufigen Betrieb nach 2;
• 4 Sollwertsignal und Trägersignale für einen dreistufigen Betrieb des Wechselrichters;
• 5 Ansteuersignale des Wechselrichters beim dreistufigen Betrieb nach 4;
• 6 Sollwertsignal und Trägersignale für einen gemischten Betrieb des Wechselrichters nach einem Ausführungsbeispiel der Erfindung;
• 7 Ansteuersignale des Wechselrichters beim gemischten Betrieb nach 6;
• 8 einen zeitlichen Ausschnitt von Sollwertsignal und Trägersignalen aus 6;
• 9 einen zeitlichen Ausschnitt der Ansteuersignale nach 7;
• 10 Sollwertsignal und Trägersignale für einen gemischten Betrieb des Wechselrichters mit geänderten Überlappwerten;
• 11 Ansteuersignale des Wechselrichters beim gemischten Betrieb nach 10;
• 12 Sollwertsignal und Trägersignale für einen gemischten Betrieb des Wechselrichters mit geänderten Überlappwerten; und
• 13 Ansteuersignale des Wechselrichters beim gemischten Betrieb nach 12.

The following show:

• 1 a circuit arrangement of an inverter for an electrical machine, in particular an electrically operated vehicle, for a method according to an embodiment of the invention;
• 2 Setpoint signal and carrier signal for a two-stage operation of the inverter according to 1 ;
• 3 Control signals of the inverter in two-stage operation according to 2 ;
• 4 Setpoint signal and carrier signals for three-stage operation of the inverter;
• 5 Control signals of the inverter in three-stage operation according to 4 ;
• 6 Setpoint signal and carrier signals for a mixed operation of the inverter according to an embodiment of the invention;
• 7 Control signals of the inverter in mixed operation according to 6 ;
• 8 a temporal section of setpoint signal and carrier signals from 6 ;
• 9 a temporal section of the control signals after 7 ;
• 10 Setpoint signal and carrier signals for mixed operation of the inverter with modified overlap values;
• 11 Control signals of the inverter in mixed operation according to 10 ;
• 12 Setpoint signal and carrier signals for mixed operation of the inverter with modified overlap values; and
• 13 Control signals of the inverter in mixed operation according to 12 .

In the figures, identical or similar components are numbered with identical reference symbols. The figures merely show examples and are not to be understood as limiting.

1 shows a circuit arrangement of an inverter 100 for an electrical machine, in particular an electrically operated vehicle, for a method according to an embodiment of the invention.

The inverter 100 is designed to convert a direct voltage 10, 12 into an alternating voltage 16 for driving the electrical machine connected to a load output 26 of the inverter 100. The inverter 100 is designed to be controllable in three stages and has at least one main current path 20 with at least two semiconductor switches 22, 24 and at least one neutral point path 30 with at least one semiconductor switch 32, 34. The neutral point path 30 opens into the main current path 20.

The main current path 20 of the 1 The circuit arrangement shown represents a so-called half-bridge of the inverter 100. Inverters 100 for three-phase electrical machines usually have three such half-bridges for controlling the electrical machines.

The inverter 100 comprises a so-called T-type neutral point clamped inverter architecture. A main current path 20 has at least two series-connected semiconductor switches 22, 24 with a center tap 36, which are electrically connected to a positive and a negative operating voltage 10, 12. The center tap 36 is electrically connected to the load output 26.

A neutral point path 30 with at least one semiconductor switch 32, 34 is electrically connected to a neutral point 14 of the positive and negative operating voltages 10, 12 and the center tap 36.

The neutral point path 30 is designed to provide output load currents at the load output 26 in a three-stage operation 1 which are smaller than the output load currents provided by the main current path 20 in a two-stage operation 2.

The inverter 100 can be converted from a three-stage operation 1 to a two-stage operation 2 and vice versa depending on at least one load required by the electrical machine. The inverter 100 can be controlled in a partial load range such that a mixed operation 3 between the three-stage operation 1 and the two-stage operation 2 can be set (in the 6 and 7 shown).

2 shows a setpoint signal 44 and a carrier signal 40 for a two-stage operation 2 of the inverter 100 according to 1 . 3 shows the associated control signals 60, 62, 64 of the inverter 100 in two-stage operation 2. The signals 44, 40, 60, 62, 64 are the same as in the other 4 to 13 each plotted as voltage U, scaled from -1 V to +1 V, as a function of time 70.

The inverter 100 is operated using a pulse width modulation method. The semiconductor switches 22, 24, 32, 34 of the inverter 100 are controlled by means of at least one carrier signal 40, 42, in particular a periodic triangular signal, to define switching times. The setpoint signal 44 for the desired control of the electrical machine is compared with one or more carrier signals 40, 42 to define the switching times of the semiconductor switches 22, 24, 32, 34.

In the 2 and 3 In the two-stage operation 2 shown, the carrier signal 40 is compared with the specified setpoint signal 44 (a sinusoidal signal) and the switching times for the two semiconductor switches 22, 24 of the main current path 20 are derived from this. This results in the 3 shown control signals 60, 62, 64 of the electrical machine.

4 shows setpoint signal 44 and carrier signals 40, 42 for a three-stage operation 1 of the inverter 100, while in 5 the corresponding control signals of the inverter 100 are shown.

In the 4 and 5 In the three-stage operation 1 shown, the two carrier signals 40, 42 mirrored at a voltage zero point 46 are compared for two half-waves with the specified setpoint signal 44 and the switching times for the two semiconductor switches 32, 34 of the neutral point path 30 and for the two semiconductor switches 22, 24 of the main current path are derived from this. This results in the 5 shown control signals 60, 62, 64 of the electrical machine.

The inverter 100 can be converted from the three-stage operation 1 to the two-stage operation 2 and vice versa depending on at least one electrical load required by the electrical machine.

According to the proposed method, the inverter 100 is controlled in a partial load range such that a mixed operation 3 between the three-stage operation 1 and the two-stage operation 2 is set.

6 shows setpoint signal 44 and carrier signals 40, 42 for a mixed operation 3 of the inverter 100 according to an embodiment of the invention, while in 7 the control signals 60, 62, 64 of the inverter 100 are shown in mixed operation 3. 8 shows a temporal section of setpoint signal 44 and carrier signals 40, 42 from 6 , while in 9 the corresponding temporal section of the control signals 60 is shown.

In the mixed operation 3, the two carrier signals 40, 42 are set to overlap in a predetermined overlap voltage range 50 around the voltage zero point 46. In this case, one of the at least two carrier signals 40, 42 of one polarity is assigned up to an overlap value 48, 49 (dashed lines in 8 ) of the other polarity, whereby a sum of the at least two overlap values 48, 49 results in the overlap voltage range 50.

The mixed operation 3 is set when the setpoint signal 44 is in the overlap voltage range 50 of the at least two carrier signals 40, 42 (dashed box in the 6 and 7 ), while the three-stage operation 1 is set when the setpoint signal 44 is outside the overlap voltage range 50 of the at least two carrier signals 40, 42 (solid boxes in the 6 and 7 ).

A proportion of zero states in which the semiconductor switches 32, 34 of the neutral point path 30 permanently carry current can be set via the overlap value 48, 49.

The control signals 60, 62, 64 of the semiconductor switches 32, 34 of the neutral point path 30 can be determined in a simple manner by comparing the at least two carrier signals 40, 42 with the setpoint signal 44 and summing the comparison results. This results, as can be seen from the 8 and 9 visible when the setpoint signal 44 is greater than the first carrier signal 40, a positive control signal 60 when the setpoint signal 44 is smaller than the second carrier signal 42, a negative control signal 60 and a control signal 60 of zero when the setpoint signal 44 is between the two carrier signals 40, 42.

An electrical load of the semiconductor switches 32, 34 of the neutral point path 30 can be set by the overlap value 48, 49. The overlap value 48, 49 can be set dynamically, in particular during operation of the inverter 100.

In the 10 and 11 An example with a relatively large overlap voltage range 50 is shown, while in the 12 and 13 an example with a relatively small overlap voltage range 50 is shown. The overlap values 48, 49 are shown in dashed lines.

As in the 11 and 13 As can be seen, the resulting control signals 60, 62, 64 differ greatly. In the 10 and 11 In the large overlap voltage range 50 shown, the proportion of mixed operation 3, where the setpoint signal 44 lies between the overlap values 48, 49, is large relative to the three-stage operation 1, while in the 12 and 13 In the small overlap voltage range 50 shown, the proportion of mixed operation 3 is very small due to the low overlap values 48, 49 relative to the three-stage operation 1.

The influence on the duration of the zero states of the control signals 60, 62, 64 is therefore dependent on the modulation. The larger the overlap voltage range 50, the less the semiconductor switches 32, 34 of the neutral point path 30 are loaded, since there is a greater degree of quasi-two-stage modulation and shorter zero intermediate states result.

Advantageously, the control signal 60 always belongs to the setpoint signal 40 and the control signals 62 and 64 belong to a respective setpoint signal (not shown) of the other two phases of a three-phase inverter. Each phase therefore has its own setpoint signal and a resulting control signal.

By applying the proposed method for operating the inverter 100 the semiconductor switches 32, 34 of the neutral point path 30 can be dimensioned smaller, which enables cost savings.

For symmetrical inverter operation, this also necessarily results in a symmetrical overlap area and thus equal overlap values 48, 49.

list of reference symbols

1

three-stage operation

2

two-stage operation

3

mixed operation

10

positive direct current

12

negative DC voltage

14

neutral point

16

alternating current

20

main current path

22

semiconductor switches

24

semiconductor switches

26

load output

30

neutral point path

32

semiconductor switches

34

semiconductor switches

36

center tap

40

carrier signal

42

carrier signal

44

setpoint signal

46

voltage zero point

48

overlap value

49

overlap value

50

overlap voltage range

60

control signal

62

control signal

64

control signal

70

Time

100

inverter

Claims (7)

Method for operating an inverter (100) for an electrical machine, in particular an electrically operated vehicle, wherein the inverter (100) is designed to convert a direct voltage (10, 12) into an alternating voltage (16) for driving the electrical machine connected to a load output (26) of the inverter (100), wherein the inverter (100) is designed to be controllable in three stages and has at least one main current path (20) with at least two semiconductor switches (22, 24) and at least one neutral point path (30) opening into the main current path (20) with at least one semiconductor switch (32, 34), wherein the neutral point path (30) is designed to provide output load currents at the load output (26) in a three-stage operation (1) which are smaller than the output load currents provided by the main current path (20) in a two-stage operation (2), wherein the inverter (100) is designed to provide output load currents at the load output (26) in a three-stage operation (1) depending on at least one electrical load requested by the electrical machine is transferred from the three-stage operation (1) to the two-stage operation (2) and vice versa, wherein the inverter (100) is controlled in a partial load range such that a mixed operation (3) between the three-stage operation (1) and the two-stage operation (2) is set, characterized in that the inverter (100) is operated in a pulse width modulation method, wherein the semiconductor switches (22, 24, 32, 34) of the inverter (100) are controlled by means of at least one carrier signal (40, 42), in particular a periodic triangular signal, to define switching times, wherein in the two-stage operation (2) the at least one carrier signal (40, 42) is compared with a predetermined setpoint signal (44), wherein in the three-stage operation (1) at least two carrier signals (40, 42) mirrored at a voltage zero point (46) for two half-waves with the predetermined setpoint signal (44), wherein in the mixed operation (3) the at least two carrier signals (40, 42) are set to overlap in a predetermined overlap voltage range (50) around the voltage zero point (46), in particular wherein one of the at least two carrier signals (40, 42) of one polarity is scaled up to an overlap value (48, 49) of the other polarity, wherein a sum of the at least two overlap values (48, 49) results in the overlap voltage range (50), wherein the mixed operation (3) is set when the setpoint signal (44) is within the overlap voltage range (50) of the at least two carrier signals (40, 42) and the overlap value (48, 49) is set dynamically during ongoing operation of the inverter (100). procedure according to claim 1 , whereby the three-stage operation (1) is set when the setpoint signal (44) is outside the overlap voltage range (50) of the at least two carrier signals (40, 42). procedure according to claim 1 or 2 , wherein an electrical load of the at least one semiconductor switch (32, 34) of the neutral point path (30) is adjusted by the overlap value (48, 49). Method according to one of the preceding claims, wherein a proportion of zero states in which the semiconductor switches (32, 34) of the neutral point path (30) permanently carry current is set via the overlap value (48, 49). Method according to one of the preceding claims, wherein control signals (60, 62, 64) of the semiconductor switches (32, 34) of the neutral point path (30) are determined by comparing the at least two carrier signals (40, 42) with the desired value (44) and summing the comparison results. Inverter (100) for an electrical machine, in particular an electrically operated vehicle, for carrying out a method according to one of the preceding claims, wherein the inverter (100) can be converted from a three-stage operation (1) to a two-stage operation (2) and vice versa depending on at least one load required by the electrical machine, wherein the inverter (100) can be controlled in a partial load range such that a mixed operation (3) between the three-stage operation (1) and the two-stage operation (2) can be set. inverter to claim 6 , comprising a T-type neutral point clamped inverter architecture, wherein a main current path (20) has at least two series-connected semiconductor switches (22, 24) with a center tap (36) which are electrically connected to a positive and a negative operating voltage (10, 12), wherein the center tap (36) is electrically connected to a load output (26), wherein a neutral point path (30) with at least one semiconductor switch (32, 34) is electrically connected to a neutral point (14) of the positive and negative operating voltages (10, 12) and the center tap (36).

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