EP3326286A1 - Method for operating a frequency converter and frequency converter - Google Patents

Method for operating a frequency converter and frequency converter

Info

Publication number
EP3326286A1
EP3326286A1 EP16751189.8A EP16751189A EP3326286A1 EP 3326286 A1 EP3326286 A1 EP 3326286A1 EP 16751189 A EP16751189 A EP 16751189A EP 3326286 A1 EP3326286 A1 EP 3326286A1
Authority
EP
European Patent Office
Prior art keywords
frequency converter
switching
pulse width
width modulation
activated
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP16751189.8A
Other languages
German (de)
French (fr)
Inventor
Fritz Witte
Thomas Petersen
Dirk Düsterberg
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Lenze Automation GmbH
Original Assignee
Lenze Automation GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Lenze Automation GmbH filed Critical Lenze Automation GmbH
Publication of EP3326286A1 publication Critical patent/EP3326286A1/en
Ceased legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
    • H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
    • H02M7/53875—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current with analogue control of three-phase output
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
    • H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
    • H02M7/53875—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current with analogue control of three-phase output
    • H02M7/53876—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current with analogue control of three-phase output based on synthesising a desired voltage vector via the selection of appropriate fundamental voltage vectors, and corresponding dwelling times
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P27/00—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage
    • H02P27/04—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage
    • H02P27/06—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters
    • H02P27/08—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters with pulse width modulation
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P27/00—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage
    • H02P27/04—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage
    • H02P27/06—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters
    • H02P27/08—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters with pulse width modulation
    • H02P27/14—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters with pulse width modulation with three or more levels of voltage
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/12—Arrangements for reducing harmonics from ac input or output
    • H02M1/123—Suppression of common mode voltage or current
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/44—Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P2209/00—Indexing scheme relating to controlling arrangements characterised by the waveform of the supplied voltage or current
    • H02P2209/13—Different type of waveforms depending on the mode of operation

Definitions

  • the invention relates to a method for operating a frequency converter, which is designed for driving a three-phase motor, and a frequency converter.
  • DE 101 49 270 A1 discloses a space-vector-based switching pattern for minimizing the neutral point voltage fluctuations in a three-phase machine operated on a DC voltage intermediate circuit converter.
  • the invention has for its object to provide a method for operating a frequency converter and a frequency converter available to reduce the fluctuations in the neutral point voltage compared with DE 101 49 270 A1 even further.
  • the invention achieves this object by a method according to claim 1 and a frequency converter according to claim 5.
  • the method is used to operate a frequency converter, for example in the form of a DC voltage intermediate converter.
  • the frequency converter is designed to control a three-phase motor or a three-phase machine.
  • the frequency converter conventionally has three half-bridges. Each of the three half-bridges conventionally has at least two switching means.
  • three phase voltages for the three-phase motor are generated by means of a pulse width modulation, wherein different switching patterns of the switching means are activated for pulse width modulation, set for different groups of switching patterns group-specific neutral point voltages or cause different groups of switching patterns group-specific neutral point voltages.
  • a pulse width modulation wherein different switching patterns of the switching means are activated for pulse width modulation, set for different groups of switching patterns group-specific neutral point voltages or cause different groups of switching patterns group-specific neutral point voltages.
  • a star point voltage is typically understood to mean a voltage which changes over time leads to undesired currents, in particular to leakage currents via mechanical bearings of the electric motor. This can be, for example, a voltage acting between the stator and the rotor. In the case of a star connection, the star point voltage can be the actual neutral point voltage.
  • the neutral point voltage may be, for example, a virtual or imaginary neutral point voltage, which can be calculated, for example, by triangular-star transformation in the case of a delta connection.
  • the neutral point voltage may be referred to as a common mode voltage.
  • the half bridges may each have a first state, during which an output of the respective half-bridge is connected to a positive intermediate circuit potential. The first state of each half bridge is denoted by "1.”
  • the half bridges each have a second state during which an output of the respective half bridge is connected to a negative DC link potential.
  • the at least one operating state only the following switching patterns are activated within a respective period of the pulse width modulation: either (100, 010, 001) or (01 1, 101, 110).
  • the switching patterns 100, 010, 001 belong to a first group of switching patterns and the switching patterns 01 1, 101, 110 belong to a second group of switching patterns, wherein the switching patterns within a group can be activated in any desired order.
  • the switching patterns 100, 010, 001 only one of the half bridges is always connected to the positive intermediate circuit potential at a time within a respective period of the pulse width modulation.
  • the switching pattern 01 1, 101, 1 10 only one of the half bridges is always connected to the negative DC link potential at a time within a respective period of the pulse width modulation. In this way, fluctuations in the neutral point voltage are avoided.
  • the maximum adjustable motor voltage is reduced compared to conventional driving methods.
  • a change of the group between successive periods of the pulse width modulation is typically avoided.
  • the at least one operating state of the frequency converter can be set below a threshold speed of the electric motor. Above the threshold speed of the electric motor, switching patterns of any groups can be activated within a respective period of the pulse width modulation. Below the threshold speed usually forms no protective oil film in bearings of the electric motor, flow through the currents due to fluctuations in the neutral point voltage. In this speed range are therefore according to the invention Variations in the neutral point voltage are reduced or substantially completely avoided, whereby the reduced voltage adjustment range can be accepted in this speed range. Above the threshold speed, the protective oil film is usually formed, so that fluctuations in the neutral point voltage are more tolerable. It is understood that the switching can be carried out in dependence on the threshold speed taking into account a suitable hysteresis.
  • the threshold speed can be selected depending on the speed at which an oil film typically forms in bearings of the electric motor.
  • the threshold speed can be determined, for example, by tests on different types of motors / bearing types.
  • the threshold speed can be selected depending on the engine type or engine type. As an order of magnitude, the threshold speed may be, for example, in a range between 100 revolutions / minute to 1000 revolutions / minute.
  • the frequency converter according to the invention is designed to drive a three-phase motor and has three half-bridges, each with at least two switching means.
  • the frequency converter furthermore has a control unit, for example in the form of a microcontroller.
  • the control unit is designed to control the switching means in such a way that a method according to one of the preceding claims is carried out.
  • FIG. 1 shows a frequency converter which is designed to drive a three-phase motor, the frequency converter having three half bridges each having two switching means,
  • FIG. 2 shows various groups of switching patterns of the switching means and associated neutral point voltages
  • FIG. 3 shows a period of a pulse width modulation with a sequence of switching patterns of one
  • Fig. 1 shows a frequency converter 1, which is designed for driving a three-phase motor 2.
  • the frequency converter 1 has conventionally three half bridges B1, B2, B3.
  • the half-bridge B1 has two switching means S1, S2.
  • the half-bridge B2 has two switching means S3, S4.
  • the half-bridge B3 has two switching means S5, S6.
  • the half bridges are between a positive DC link potential UZK_P and a negative DC link potential UZK_N. looped, wherein a connection node of the switching means of a respective bridge (output aer bridge) with a phase connection U, V or W of the three-phase motor 2 is electrically connected.
  • UZK_P positive DC link potential
  • UZK_N negative DC link potential
  • the half bridges B1, B2, B3 each have a first state, during which an output of the respective half bridge B1, B2, B3 is connected to the positive intermediate circuit potential UZK_P, wherein the respective state of the half bridge B1, B2, B3 is denoted by 1 becomes.
  • the half bridges B1, B2, B3 each have a second state, during which an output of the respective half bridge B1, B2, B3 is connected to the negative intermediate circuit potential UZK_N, wherein the respective state of the half bridge B1, B2, B3 is denoted by 0.
  • Fig. 2 shows various groups G1 to G4 of switching patterns of the switching means S1, S2; S3, S4; S5, S6 and associated values of neutral point voltages US.
  • a threshold speed of the electric motor 2 within a respective period of a pulse width modulation (see also FIG. 3) only switching patterns are set either from group G2 or from group G3.
  • the threshold speed can be selected depending on the speed at which an oil film typically forms in bearings of the electric motor 2.
  • switching patterns of groups 2 or 3 are usefully used. A combined use of the switching patterns of groups 2 or 3 in successive or different periods is typically not provided in this speed range.
  • the upper speed range for example, from about 50% of the rated speed of the motor, within a respective period and / or in different (consecutive) periods, for example, only two groups directly adjacent to their neutral point voltage can be used, for example groups 2 and 3 , so that compared to the conventional operation, only 33% to 50% of the fluctuation of the neutral point voltage occurs.
  • the restriction to the switching pattern from the groups G2 and G3 can also be made dependent on other operating states or permanently.
  • 3 shows by way of example a PWM period TP of the pulse width modulation with a sequence of switching patterns 100, 010, 001 of the group G2 with identical neutral point voltage -UZK 6. It is understood that the switching patterns can also be generated in a different order, for example 001 , 010, 100, etc.
  • the sequence of switching patterns shown completely avoids fluctuations of the neutral point voltage. According to the invention, therefore, bearing currents due to fluctuations in the neutral point voltage can be largely avoided. This further reduces the spurious emission and fault currents significantly.
  • the adjustment range of the output voltage is reduced.
  • the current ripple in the motor phases which is present at low output voltages, can be used, for example, for wire break detection of a motor phase and for evaluation in the context of sensorless applications.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Control Of Ac Motors In General (AREA)
  • Inverter Devices (AREA)

Abstract

The invention relates to a method for operating a frequency converter which is designed for controlling a rotary current motor, wherein the frequency converter comprises three half-bridges, each having at least two switching means. The method comprises the steps of: - generating three phase voltages for the rotary current motor by means of pulse width modulation, wherein different switching patterns of the switching means are activated for pulse width modulation, wherein specific star point voltages are reached for different groups of switching patterns, - wherein only those switching pattern are activated in at least one operating state of the frequency converter within a respective period (TP) of the pulse width modulation, which reach an identical star point voltage.

Description

Verfahren zum Betreiben eines Frequenzumrichters und Frequenzumrichter  Method of operating a frequency converter and frequency converter
Die Erfindung betrifft ein Verfahren zum Betreiben eines Frequenzumrichters, der zum Ansteuern eines Drehstrommotors ausgebildet ist, und einen Frequenzumrichter. The invention relates to a method for operating a frequency converter, which is designed for driving a three-phase motor, and a frequency converter.
Aus der DE 101 49 270 A1 ist ein raumzeigerbasiertes Schaltmuster zur Minimierung der Sternpunktspannungsschwankungen bei einer an einem Gleichspannungszwischenkreisumrich- ter betriebenen Drehstrommaschine bekannt. DE 101 49 270 A1 discloses a space-vector-based switching pattern for minimizing the neutral point voltage fluctuations in a three-phase machine operated on a DC voltage intermediate circuit converter.
Der Erfindung liegt die Aufgabe zugrunde, ein Verfahren zum Betreiben eines Frequenzumrichters und einen Frequenzumrichter zur Verfügung zu stellen, die Schwankungen der Sternpunktspannung verglichen mit der DE 101 49 270 A1 noch weiter reduzieren. Die Erfindung löst diese Aufgabe durch ein Verfahren nach Anspruch 1 und einen Frequenzumrichter nach Anspruch 5. The invention has for its object to provide a method for operating a frequency converter and a frequency converter available to reduce the fluctuations in the neutral point voltage compared with DE 101 49 270 A1 even further. The invention achieves this object by a method according to claim 1 and a frequency converter according to claim 5.
Das Verfahren dient zum Betreiben eines Frequenzumrichters, beispielsweise in Form eines Gleichspannungszwischenkreisumrichters. Der Frequenzumrichter ist dazu ausgebildet, einen Drehstrommotor bzw. eine Drehstrommaschine anzusteuern. Der Frequenzumrichter weist her- kömmlich drei Halbbrücken auf. Jede der drei Halbbrücken weist herkömmlich mindestens zwei Schaltmittel auf. The method is used to operate a frequency converter, for example in the form of a DC voltage intermediate converter. The frequency converter is designed to control a three-phase motor or a three-phase machine. The frequency converter conventionally has three half-bridges. Each of the three half-bridges conventionally has at least two switching means.
Mittels des Frequenzumrichters werden drei Phasenspannungen für den Drehstrommotor mittels einer Pulsweitenmodulation erzeugt, wobei zur Pulsweitenmodulation verschiedene Schaltmuster der Schaltmittel aktiviert werden, wobei sich für verschiedene Gruppen von Schaltmustern gruppenspezifische Sternpunktspannungen einstellen bzw. verschiedene Gruppen von Schaltmustern gruppenspezifische Sternpunktspannungen bewirken. Insoweit sei auch auf die einschlägige Fachliteratur bzw. die DE 101 49 270 A1 verwiesen. By means of the frequency converter, three phase voltages for the three-phase motor are generated by means of a pulse width modulation, wherein different switching patterns of the switching means are activated for pulse width modulation, set for different groups of switching patterns group-specific neutral point voltages or cause different groups of switching patterns group-specific neutral point voltages. In that regard, reference is also made to the relevant specialist literature or DE 101 49 270 A1.
Erfindungsgemäß werden während mindestens eines Betriebszustands des Frequenzumrichters innerhalb einer jeweiligen (Grund-) Schaltperiode der Pulsweitenmodulation nur solche Schaltmuster aktiviert, die einer der Gruppen von Schaltmustern angehören, d.h. bei denen sich eine identische, gruppenspezifische Sternpunktspannung einstellt. Auf diese Weise kann eine Änderung der Sternpunktspannung aufgrund eines Schaltmusterwechsels vermieden werden. Unter einer Sternpunktspannung im Sinne der Erfindung wird typisch eine soicne öpannung verstanden, deren zeitliche Änderung zu unerwünschten Strömen führt, insbesondere zu Ableitströmen über mechanische Lager des Elektromotors. Dies kann beispielsweise eine Spannung sein, die zwischen Stator und Rotor wirkt. Im Falle einer Sternschaltung kann die Stern- punktspannung die tatsächliche Sternpunktspannung sein. Für andere Verschaltungen kann die Sternpunktspannung beispielsweise eine virtuelle oder gedachte Sternpunktspannung sein, die beispielsweise durch Dreieck-Stern-Transformation für den Fall einer Dreieckschaltung berechenbar ist. Die Sternpunktspannung kann alternativ auch als Gleichtaktspannung bezeichnet werden. Die Halbbrücken können jeweils einen ersten Zustand aufweisen, während dem ein Ausgang der jeweiligen Halbbrücke mit einem positiven Zwischenkreispotential verbunden ist. Der erste Zustand einer jeweiligen Halbbrücke wird mit„1 " bezeichnet. Die Halbbrücken können jeweils einen zweiten Zustand aufweisen, während dem ein Ausgang der jeweiligen Halbbrücke mit einem negativen Zwischenkreispotential verbunden ist. Der zweite Zustand einer jeweiligen Halbrücke wird mit„0" bezeichnet. Während des mindestens einen Betriebszustands werden innerhalb einer jeweiligen Periode der Pulsweitenmodulation nur folgende Schaltmuster aktiviert: entweder (100, 010, 001 ) oder (01 1 , 101 , 1 10). Die Schaltmuster 100, 010, 001 gehören zu einer ersten Gruppe von Schaltmustern und die Schaltmuster 01 1 , 101 , 1 10 gehören zu einer zweiten Gruppe von Schaltmustern, wobei die Schaltmuster innerhalb einer Gruppe in be- liebiger Reihenfolge aktivierbar sind. Für die Schaltmuster 100, 010, 001 ist innerhalb einer jeweiligen Periode der Pulsweitenmodulation zu einem Zeitpunkt immer nur genau eine der Halbbrücken mit dem positiven Zwischenkreispotential verbunden. Für die Schaltmuster 01 1 , 101 , 1 10 ist innerhalb einer jeweiligen Periode der Pulsweitenmodulation zu einem Zeitpunkt immer nur genau eine der Halbbrücken mit dem negativen Zwischenkreispotential verbunden. Auf die- se Weise werden Schwankungen der Sternpunktspannung vermieden. Allerdings reduziert sich die maximale stellbare Motorspannung im Vergleich zu herkömmlichen Ansteuerverfahren. According to the invention, during at least one operating state of the frequency converter within a respective (basic) switching period of the pulse width modulation only those switching patterns are activated which belong to one of the groups of switching patterns, ie in which an identical, group-specific neutral point voltage is established. In this way, a change in the neutral point voltage due to a switching pattern change can be avoided. In the sense of the invention, a star point voltage is typically understood to mean a voltage which changes over time leads to undesired currents, in particular to leakage currents via mechanical bearings of the electric motor. This can be, for example, a voltage acting between the stator and the rotor. In the case of a star connection, the star point voltage can be the actual neutral point voltage. For other interconnections, the neutral point voltage may be, for example, a virtual or imaginary neutral point voltage, which can be calculated, for example, by triangular-star transformation in the case of a delta connection. Alternatively, the neutral point voltage may be referred to as a common mode voltage. The half bridges may each have a first state, during which an output of the respective half-bridge is connected to a positive intermediate circuit potential. The first state of each half bridge is denoted by "1." The half bridges each have a second state during which an output of the respective half bridge is connected to a negative DC link potential. During the at least one operating state, only the following switching patterns are activated within a respective period of the pulse width modulation: either (100, 010, 001) or (01 1, 101, 110). The switching patterns 100, 010, 001 belong to a first group of switching patterns and the switching patterns 01 1, 101, 110 belong to a second group of switching patterns, wherein the switching patterns within a group can be activated in any desired order. For the switching patterns 100, 010, 001, only one of the half bridges is always connected to the positive intermediate circuit potential at a time within a respective period of the pulse width modulation. For the switching pattern 01 1, 101, 1 10, only one of the half bridges is always connected to the negative DC link potential at a time within a respective period of the pulse width modulation. In this way, fluctuations in the neutral point voltage are avoided. However, the maximum adjustable motor voltage is reduced compared to conventional driving methods.
Ein Wechsel der Gruppe zwischen aufeinanderfolgenden Perioden der Pulsweitenmodulation wird typischerweise vermieden. A change of the group between successive periods of the pulse width modulation is typically avoided.
Der mindestens eine Betriebszustand des Frequenzumrichters kann unterhalb einer Schwellen- drehzahl des Elektromotors eingestellt werden. Oberhalb der Schwellendrehzahl des Elektromotors können innerhalb einer jeweiligen Periode der Pulsweitenmodulation Schaltmuster beliebiger Gruppen aktiviert werden. Unterhalb der Schwellendrehzahl bildet sich in der Regel kein schützender Ölfilm in Lagern des Elektromotors, über die Ströme aufgrund von Schwankungen der Sternpunktspannung fließen. In diesem Drehzahlbereich werden daher erfindungsgemäß Schwankungen der Sternpunktspannung reduziert bzw. im Wesentlichen vollständig vermieden, wobei in diesem Drehzahlbereich der reduzierte Spannungsstellbereich in Kauf genommen werden kann. Oberhalb der Schwellendrehzahl hat sich der schützende Ölfilm in der Regel gebildet, so dass Schwankungen der Sternpunktspannung tolerierbarer sind. Es versteht sich, dass das Umschalten in Abhängigkeit von der Schwellendrehzahl unter Berücksichtigung einer geeigneten Hysterese erfolgen kann. Die Schwellendrehzahl kann in Abhängigkeit davon gewählt werden, ab welcher Drehzahl sich typisch ein Ölfilm in Lagern des Elektromotors bildet. Die Schwellendrehzahl kann beispielsweise über Versuche an verschiedenen Motorentypen/Lagertypen ermittelt werden. Die Schwellendrehzahl kann motorentypabhängig oder moto- rentypunabhängig gewählt werden. Als eine Größenordnung kann die Schwellendrehzahl beispielsweise in einem Bereich zwischen 100 Umdrehungen/Minute bis 1000 Umdrehungen/Minute liegen. The at least one operating state of the frequency converter can be set below a threshold speed of the electric motor. Above the threshold speed of the electric motor, switching patterns of any groups can be activated within a respective period of the pulse width modulation. Below the threshold speed usually forms no protective oil film in bearings of the electric motor, flow through the currents due to fluctuations in the neutral point voltage. In this speed range are therefore according to the invention Variations in the neutral point voltage are reduced or substantially completely avoided, whereby the reduced voltage adjustment range can be accepted in this speed range. Above the threshold speed, the protective oil film is usually formed, so that fluctuations in the neutral point voltage are more tolerable. It is understood that the switching can be carried out in dependence on the threshold speed taking into account a suitable hysteresis. The threshold speed can be selected depending on the speed at which an oil film typically forms in bearings of the electric motor. The threshold speed can be determined, for example, by tests on different types of motors / bearing types. The threshold speed can be selected depending on the engine type or engine type. As an order of magnitude, the threshold speed may be, for example, in a range between 100 revolutions / minute to 1000 revolutions / minute.
Der erfindungsgemäße Frequenzumrichter ist zum Ansteuern eines Drehstrommotors ausgebildet und weist drei Halbbrücken mit jeweils mindestens zwei Schaltmitteln auf. Der Frequenzum- richter weist weiter eine Steuereinheit auf, beispielsweise in Form eines Mikrocontrollers. Die Steuereinheit ist dazu ausgebildet, die Schaltmittel derart anzusteuern, dass ein Verfahren nach einem der vorhergehenden Ansprüche ausgeführt wird. The frequency converter according to the invention is designed to drive a three-phase motor and has three half-bridges, each with at least two switching means. The frequency converter furthermore has a control unit, for example in the form of a microcontroller. The control unit is designed to control the switching means in such a way that a method according to one of the preceding claims is carried out.
Die Erfindung wird nachfolgend detailliert unter Bezugnahme auf die Zeichnungen beschrieben. Hierbei zeigen: Fig. 1 einen Frequenzumrichter, der zum Ansteuern eines Drehstrommotors ausgebildet ist, wobei der Frequenzumrichter drei Halbbrücken mit jeweils zwei Schaltmitteln aufweist, The invention will be described in detail below with reference to the drawings. 1 shows a frequency converter which is designed to drive a three-phase motor, the frequency converter having three half bridges each having two switching means,
Fig. 2 verschiedene Gruppen von Schaltmustern der Schaltmittel und zugehörige Sternpunktspannungen und Fig. 3 eine Periode einer Pulsweitenmodulation mit einer Abfolge von Schaltmustern einer 2 shows various groups of switching patterns of the switching means and associated neutral point voltages, and FIG. 3 shows a period of a pulse width modulation with a sequence of switching patterns of one
Gruppe mit identischer Sternpunktspannung.  Group with identical neutral point voltage.
Fig. 1 zeigt einen Frequenzumrichter 1 , der zum Ansteuern eines Drehstrommotors 2 ausgebildet ist. Der Frequenzumrichter 1 weist herkömmlich drei Halbbrücken B1 , B2, B3 auf. Die Halbbrücke B1 weist zwei Schaltmittel S1 , S2 auf. Die Halbbrücke B2 weist zwei Schaltmittel S3, S4 auf. Die Halbbrücke B3 weist zwei Schaltmittel S5, S6 auf. Die Halbbrücken sind zwischen ein positives Zwischenkreispotential UZK_P und ein negatives Zwischenkreispotential UZK_N ein- geschleift, wobei ein Verbindungsknoten der Schaltmittel einer jeweiligen Brücke (Ausgang aer Brücke) mit einem Phasenanschluss U, V bzw. W des Drehstrommotors 2 elektrisch verbunden ist. Insoweit sei auch auf die einschlägige Fachliteratur verwiesen. Fig. 1 shows a frequency converter 1, which is designed for driving a three-phase motor 2. The frequency converter 1 has conventionally three half bridges B1, B2, B3. The half-bridge B1 has two switching means S1, S2. The half-bridge B2 has two switching means S3, S4. The half-bridge B3 has two switching means S5, S6. The half bridges are between a positive DC link potential UZK_P and a negative DC link potential UZK_N. looped, wherein a connection node of the switching means of a respective bridge (output aer bridge) with a phase connection U, V or W of the three-phase motor 2 is electrically connected. In that regard, reference is also made to the relevant specialist literature.
Die Halbbrücken B1 , B2, B3 weisen jeweils einen ersten Zustand auf, während dem ein Aus- gang der jeweiligen Halbbrücke B1 , B2, B3 mit dem positiven Zwischenkreispotential UZK_P verbunden ist, wobei der jeweilige Zustand der Halbbrücke B1 , B2, B3 mit 1 bezeichnet wird. Die Halbbrücken B1 , B2, B3 weisen jeweils einen zweiten Zustand auf, während dem ein Ausgang der jeweiligen Halbbrücke B1 , B2, B3 mit dem negativen Zwischenkreispotential UZK_N verbunden ist, wobei der jeweilige Zustand der Halbbrücke B1 , B2, B3 mit 0 bezeichnet wird. Fig. 2 zeigt verschiedene Gruppen G1 bis G4 von Schaltmustern der Schaltmittel S1 , S2; S3, S4; S5, S6 und zugehörige Werte von Sternpunktspannungen US. The half bridges B1, B2, B3 each have a first state, during which an output of the respective half bridge B1, B2, B3 is connected to the positive intermediate circuit potential UZK_P, wherein the respective state of the half bridge B1, B2, B3 is denoted by 1 becomes. The half bridges B1, B2, B3 each have a second state, during which an output of the respective half bridge B1, B2, B3 is connected to the negative intermediate circuit potential UZK_N, wherein the respective state of the half bridge B1, B2, B3 is denoted by 0. Fig. 2 shows various groups G1 to G4 of switching patterns of the switching means S1, S2; S3, S4; S5, S6 and associated values of neutral point voltages US.
In der Gruppe G1 weisen alle Brücken B1 , B2, B3 den Zustand 1 auf, d.h. die Schaltmittel S1 , S3, S5 sind geschlossen und die Schaltmittel S2, S4 und S6 sind geöffnet. Es ergibt sich eine Sternpunktspannung US von UZK/2. In der Gruppe G2 weisen zwei der Brücken B1 , B2 und B3 den Zustand 1 auf und eine der Brücken B1 , B2 und B3 den Zustand 0 auf. Es ergibt sich eine Sternpunktspannung US von UZK/6. In group G1, all bridges B1, B2, B3 are in state 1, i. the switching means S1, S3, S5 are closed and the switching means S2, S4 and S6 are open. The result is a neutral point voltage US of UZK / 2. In the group G2, two of the bridges B1, B2 and B3 have the state 1 and one of the bridges B1, B2 and B3 has the state 0. The result is a neutral point voltage US of UZK / 6.
In der Gruppe G3 weisen zwei der Brücken B1 , B2 und B3 den Zustand 0 auf und eine der Brücken B1 , B2 und B3 den Zustand 1 auf. Es ergibt sich folglich eine Sternpunktspannung US von -UZK/6. In der Gruppe G4 weisen alle Brücken B1 , B2, B3 den Zustand 0 auf, d.h. die Schaltmittel S1 , S3, S5 sind geöffnet und die Schaltmittel S2, S4 und S6 sind geschlossen. Es ergibt sich eine Sternpunktspannung US von -UZK/2. In group G3, two of the bridges B1, B2 and B3 have the state 0 and one of the bridges B1, B2 and B3 has the state 1. Consequently, a neutral point voltage US of -UZK / 6 results. In group G4, all bridges B1, B2, B3 have the state 0, i. the switching means S1, S3, S5 are opened and the switching means S2, S4 and S6 are closed. The result is a neutral point voltage US of -UZK / 2.
Erfindungsgemäß werden unterhalb einer Schwellendrehzahl des Elektromotors 2 innerhalb einer jeweiligen Periode einer Pulsweitenmodulation (siehe auch Fig. 3) nur Schaltmuster ent- weder aus Gruppe G2 oder aus Gruppe G3 eingestellt. Die Schwellendrehzahl kann in Abhängigkeit davon gewählt werden, ab welcher Drehzahl sich typisch ein Ölfilm in Lagern des Elektromotors 2 bildet. According to the invention, below a threshold speed of the electric motor 2 within a respective period of a pulse width modulation (see also FIG. 3), only switching patterns are set either from group G2 or from group G3. The threshold speed can be selected depending on the speed at which an oil film typically forms in bearings of the electric motor 2.
Die Schwankungen der Sternpunktspannung, d.h. auch der Spannung zwischen Stator und Rotor, kann zerstörend wirken, wenn diese Spannung über die mechanischen Lager kurzge- schlössen wird, wobei sich in den tribologischen Kontaktflächen der Lager hohe öiromaicnien einstellen können, welche die Kontaktflächen des Lagers kurzfristig verschweißen können. Diese Verschweißungen werden beim Weiterdrehen aufgerissen und führen zur Zerstörung der Oberfläche des mechanischen Lagers. Dies betrifft im besonderen Maße den Stillstand und den Betrieb bei langsamen Drehfrequenzen, da sich hier noch kein geschlossener isolierender Schmierfilm aufbauen kann und es daher in diesem Betriebsbereich zu leitfähigem metallischen Kontakt kommen kann. The fluctuations of the star point voltage, ie also the voltage between stator and rotor, can have a destructive effect if this voltage is short-circuited via the mechanical bearings. be closed, which can adjust in the tribological contact surfaces of the bearing high öiromaicnien that can weld the contact surfaces of the bearing in the short term. These welds are torn open during further rotation and lead to the destruction of the surface of the mechanical bearing. This particularly relates to the standstill and the operation at slow rotational frequencies, since here can not build a closed insulating lubricant film and therefore it can come in this operating range to conductive metallic contact.
Im unteren Drehzahlbereich, beispielsweise bis ca. 50% der Nenndrehzahl des Motors, werden daher nur Schaltmuster einer der Gruppen genutzt, so dass keine Lagerströme auftreten. Bei einem dreiphasigen System kommen sinnvollerweise Schaltmuster der Gruppen 2 oder 3 zum Einsatz. Ein kombinierter Einsatz der Schaltmuster der Gruppen 2 oder 3 in aufeinanderfolgenden bzw. unterschiedlichen Perioden ist in diesem Drehzahlbereich typisch nicht vorgesehen. In the lower speed range, for example up to about 50% of the rated speed of the motor, therefore, only switching pattern of one of the groups are used, so that no bearing currents occur. In the case of a three-phase system, switching patterns of groups 2 or 3 are usefully used. A combined use of the switching patterns of groups 2 or 3 in successive or different periods is typically not provided in this speed range.
Im oberen Drehzahlbereich, beispielsweise ab ca. 50% der Nenndrehzahl des Motors, können innerhalb einer jeweiligen Periode und/oder in unterschiedlichen (aufeinanderfolgenden) Perio- den beispielsweise nur zwei von ihrer Sternpunktspannung unmittelbar benachbarte Gruppen zum Einsatz kommen, beispielsweise die Gruppen 2 und 3, so dass gegenüber dem konventionellen Betrieb nur 33% bis 50% der Schwankung der Sternpunktspannung auftritt. In the upper speed range, for example, from about 50% of the rated speed of the motor, within a respective period and / or in different (consecutive) periods, for example, only two groups directly adjacent to their neutral point voltage can be used, for example groups 2 and 3 , so that compared to the conventional operation, only 33% to 50% of the fluctuation of the neutral point voltage occurs.
Es versteht sich, dass die Beschränkung auf die Schaltmuster aus den Gruppen G2 und G3 auch abhängig von anderen Betriebszuständen oder dauerhaft vorgenommen werden kann. Fig. 3 zeigt exemplarisch eine PWM-Periode TP der Pulsweitenmodulation mit einer Abfolge von Schaltmustern 100, 010, 001 der Gruppe G2 mit identischer Sternpunktspannung -UZK 6. Es versteht sich, dass die Schaltmuster auch in einer anderen Reihenfolge erzeugt werden können, beispielsweise 001 , 010, 100 usw. Die gezeigte Abfolge von Schaltmustern verhindert Schwankungen der Sternpunktspannung vollständig. Erfindungsgemäß können folglich Lagerströme aufgrund von Schwankungen der Sternpunktspannung weitgehend vermieden werden. Dies reduziert weiter die Störemission und Fehlerströme deutlich. Der Stellbereich der Ausgangsspannung ist jedoch reduziert. It is understood that the restriction to the switching pattern from the groups G2 and G3 can also be made dependent on other operating states or permanently. 3 shows by way of example a PWM period TP of the pulse width modulation with a sequence of switching patterns 100, 010, 001 of the group G2 with identical neutral point voltage -UZK 6. It is understood that the switching patterns can also be generated in a different order, for example 001 , 010, 100, etc. The sequence of switching patterns shown completely avoids fluctuations of the neutral point voltage. According to the invention, therefore, bearing currents due to fluctuations in the neutral point voltage can be largely avoided. This further reduces the spurious emission and fault currents significantly. The adjustment range of the output voltage is reduced.
Aufgrund der geringeren Fehlerströme, die ein Auslösen eines Fehlerstromschalters verhindern, ist die Verwendung der Erfindung beispielsweise in Büroanwendungen (Kopierer, etc.) und in der Medizintechnik (Antrieb eines Krankenbetts, etc.) möglich. Der bei kleinen Ausgangsspannungen vorhandene Stromripple in den Motorphasen Kann Dei- spielsweise zur Drahtbruch-Erkennung einer Motorphase und zur Auswertung im Kontext von sensorlosen Anwendungen verwendet werden. Due to the lower fault currents that prevent the triggering of a fault current switch, the use of the invention, for example, in office applications (copiers, etc.) and in medical technology (drive a hospital bed, etc.) is possible. The current ripple in the motor phases, which is present at low output voltages, can be used, for example, for wire break detection of a motor phase and for evaluation in the context of sensorless applications.

Claims

Patentansprüche claims
1 . Verfahren zum Betreiben eines Frequenzumrichters (1 ), der zum Ansteuern eines Drehstrommotors (2) ausgebildet ist, wobei der Frequenzumrichter (1 ) drei Halbbrücken (B1 , B2, B3) mit jeweils mindestens zwei Schaltmitteln (S1 , S2; S3, S4; S5, S6) aufweist, wobei das Verfahren die Schritte aufweist: 1 . Method for operating a frequency converter (1) designed to drive a three-phase motor (2), wherein the frequency converter (1) has three half-bridges (B1, B2, B3) each having at least two switching means (S1, S2; S3, S4; S5 , S6), the method comprising the steps of:
Erzeugen von drei Phasenspannungen für den Drehstrommotor (2) mittels einer Pulsweitenmodulation, wobei zur Pulsweitenmodulation verschiedene Schaltmuster der Schaltmittel (S1 , S2; S3, S4; S5, S6) aktiviert werden, wobei verschiedene Gruppen von Schaltmustern (G1 , G2, G3, G4) spezifische Sternpunktspannungen (US) bewirken,  Generating three phase voltages for the three-phase motor (2) by means of pulse width modulation, different switching patterns of the switching means (S1, S2, S3, S4, S5, S6) being activated for pulse width modulation, different groups of switching patterns (G1, G2, G3, G4 ) cause specific neutral point voltages (US),
dadurch gekennzeichnet, dass characterized in that
in mindestens einem Betriebszustand des Frequenzumrichters (1 ) innerhalb einer jeweiligen Periode (TP) der Pulsweitenmodulation nur solche Schaltmuster aktiviert werden, die eine identische Sternpunktspannung bewirken.  In at least one operating state of the frequency converter (1) within a respective period (TP) of the pulse width modulation only those switching patterns are activated which cause an identical neutral point voltage.
2. Verfahren nach Anspruch 1 , dadurch gekennzeichnet, dass 2. The method according to claim 1, characterized in that
die Halbbrücken (B1 , B2, B3) jeweils einen ersten Zustand aufweisen, während dem ein Ausgang der jeweiligen Halbbrücke (B1 , B2, B3) mit einem positiven Zwischenkreispoten- tial (UZK_P) verbunden ist, der mit 1 bezeichnet wird, und jeweils einen zweiten Zustand aufweisen, während dem ein Ausgang der jeweiligen Halbbrücke (B1 , B2, B3) mit einem negativen Zwischenkreispotential (UZK_N) verbunden ist, der mit 0 bezeichnet wird, wobei in dem mindestens einen Betriebszustand innerhalb einer jeweiligen Periode der Pulsweitenmodulation nur folgende Schaltmuster aktiviert werden: entweder (100, 010, 001 ) oder (01 1 , 101 , 1 10).  the half bridges (B1, B2, B3) each have a first state, during which an output of the respective half bridge (B1, B2, B3) is connected to a positive DC link potential (UZK_P), which is denoted by 1, and one each second state, during which an output of the respective half-bridge (B1, B2, B3) is connected to a negative DC link potential (UZK_N), which is denoted by 0, wherein activated in the at least one operating state within a respective period of the pulse width modulation, only the following switching pattern either: (100, 010, 001) or (01 1, 101, 1 10).
3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass 3. The method according to claim 1 or 2, characterized in that
der mindestens eine Betriebszustand des Frequenzumrichters unterhalb einer Schwellendrehzahl des Elektromotors (2) eingestellt wird.  the at least one operating state of the frequency converter is set below a threshold speed of the electric motor (2).
4. Verfahren nach Anspruch 3, dadurch gekennzeichnet, dass 4. The method according to claim 3, characterized in that
oberhalb der Schwellendrehzahl des Elektromotors (2) innerhalb einer jeweiligen Periode (TP) der Pulsweitenmodulation Schaltmuster beliebiger Gruppen (G1 , G2, G3, G4) aktiviert werden.  above the threshold speed of the electric motor (2) within a respective period (TP) of the pulse width modulation switching patterns of any groups (G1, G2, G3, G4) are activated.
5. Frequenzumrichter (1 ), der zum Ansteuern eines Drehstrommotors (2) ausgebildet ist, aufweisend: drei Halbbrücken (B1 , B2, B3) mit jeweils mindestens zwei Schaltmitteln (0 i , Ö ; 00, ö^t; S5, S6), und 5. frequency converter (1), which is designed for driving a three-phase motor (2), comprising: three half bridges (B1, B2, B3) each having at least two switching means (0i, Ö; 00, ö ^ t, S5, S6), and
eine Steuereinheit (3), die dazu ausgebildet ist, die Schaltmittel (S1 , S2; S3, S4; S5, S6) derart anzusteuern, dass ein Verfahren nach einem der vorhergehenden Ansprüche ausgeführt wird. a control unit (3) which is designed to control the switching means (S1, S2; S3, S4; S5, S6) in such a way that a method according to one of the preceding claims is carried out.
EP16751189.8A 2015-07-20 2016-07-19 Method for operating a frequency converter and frequency converter Ceased EP3326286A1 (en)

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