DE102011079995B4 - Method for operating a drive unit - Google Patents

Abstract

Method for compensating for interharmonic torque excitations in a current intermediate circuit converter with an input or line-side converter (12) and an output or machine-side converter (14) and an intermediate circuit (16) with an inductance as an energy store when operating a drive unit (10) , wherein an average active power in the intermediate circuit (16) is dependent on a modulation level of the line-side or machine-side converter (12, 14), the modulation level being varied by a predetermined or predeterminable average level of modulation, with the intermediate circuit (16 ) an alternating power is impressed, the variation of the modulation level by the mean modulation level taking place on the basis of data stored in a control device (22) of the drive unit (10) in a multi-dimensional table, the data outside of a running time of the drive unit (10) were determined, and where a value for the actual variation during the running time of the drive unit (10) results on the basis of an access to at least one stored date of the network control angle and the machine control angle.

Description

The invention relates to a method for compensating for interharmonic torque excitations in an intermediate circuit converter when operating a drive unit.

In the intermediate circuit of a drive unit, in addition to direct voltage (intermediate circuit voltage) and direct current (intermediate circuit current), current and voltage harmonics with a multiple of the mains frequency or the machine-side frequency occur. Such harmonics usually occur in the range of six times the line or machine frequency and with decreasing amplitudes in the range of further multiples of six and the line or machine frequency, i.e. twelve, eighteen times, etc. line or machine frequency. This is due to the design of the respective converters and a six-pulse converter causes, for example, harmonics in the range of six, twelve, etc. mains or machine frequency. Such harmonics are called harmonics.

wobei f_N die netzseitige Frequenz oder Netzfrequenz und f_M die maschinenseitige Frequenz oder Maschinenfrequenz bezeichnet. Interharmonische sind dabei Oberschwingungen, die kein ganzzahliges Vielfaches einer netz- und/oder maschinenseitigen Grundschwingung f_N, f_M sind.The frequencies of the harmonics superimposed on the respective electrical power in the intermediate circuit (intermediate circuit power) result from the addition and subtraction of all combinations of the direct component and the harmonic frequencies in the intermediate circuit voltage and the intermediate circuit current $$\text{f}\_\text{k}=\text{n}*\text{f}\_\text{N}+/-\text{m}*\text{f}\_\text{M.}|\text{n},\text{m}=\mathrm{0,}\mathrm{6,}\mathrm{12,}\mathrm{..}$$

where f_N denotes the network-side frequency or network frequency and f_M the machine-side frequency or machine frequency. Interharmonics are harmonics that are not an integral multiple of a network-side and / or machine-side fundamental oscillation f_N, f_M.

Low-frequency interharmonics have proven to be particularly critical because they lead to torque excitations (electrical torque) in the respective machine, e.g. motor, generator, and can excite the mechanical natural frequencies of the mechanical part of the drive system or subsequent components, such as a shaft. Such mechanical natural frequencies are often in the range of ten to thirty Hertz. So-called interharmonic torque excitations (electrical torque) are usually relatively small, namely often less than approx. Two percent. Nevertheless, even such low torque excitations, due to the comparatively weak damping of the respective mechanical system, for example a shaft, can lead to relatively high excitations of the mechanical system, namely, for example, to relatively high shaft torsional moments. In the case of 6/6 pulse and 12/12 pulse arrangements, machine frequencies in the range of the mains frequency are particularly critical, i.e. if (at least approximately) f_M = f_N applies if the frequencies of the torque excitations (electrical torque) that occur are precisely the natural frequency of the mechanical part excite the drive system.

Different approaches have become known to deal with this problem. On the one hand, so-called fade-out frequency bands are provided in a speed setpoint channel. The machine can then only be operated stationary above or below a skip frequency band. The drive is driven dynamically through the frequencies covered by a skip frequency band. Due to the then only comparatively short excitation, the mechanical natural oscillation cannot develop. However, the fading out of individual frequency bands influences the dynamics of the drive and has a disruptive effect on the respective process in many applications. On the other hand, the EP 1 875 597 a method is proposed with which vibrations of the shaft torque at the torsion-critical point are to be spatially compensated for by means of a special regulation. For this purpose, the shaft torque is measured at the critical point with the help of strain gauges and a measured value obtained on this basis is used for the control. To implement such a control, however, precise knowledge of the shaft train and the associated mechanics is necessary.

From the specialist article "Compensation of Fluctuatin DC Link Voltage for Tranction Inveter Drive" by Z. Salam and C.j. Goodmann, published in "Power Electronics and Variable Speed Drives", 23-25 Sept. 1996, Conference Publication, a drive unit with line-side and motor-side converters and intermediate circuit is known, the mean effective power of which is achieved by adjusting the control of the machine-side converter a bill of exchange is charged.

An object of the invention is accordingly to provide a particularly favorable method for operating a drive system for compensating for interharmonic torque excitations in a current intermediate circuit converter and a drive system operating according to the method.

This object is achieved according to the invention with a method having the features of claim 1. For this purpose, in a method for operating a drive unit with an input or network-side converter and an output or machine-side converter and an intermediate circuit electrically located in between, an average effective power in the intermediate circuit is dependent on a modulation level of the network-side or machine-side converter, in particular that the modulation level is varied by a predetermined or predeterminable mean level of modulation and that an alternating power is impressed on the intermediate circuit by varying the level of modulation. The degree of modulation is varied within the framework of a control and not on the basis of a regulation, ie the essential variables on the basis of which the degree of modulation is varied are known and do not have to be determined during runtime Regarding relevant variables determined at runtime from the process.

The modulation of the modulation level by the mean level of modulation takes place on the basis of off-line determined data stored in a control device of the drive unit, a value for the actual variation during the runtime of the drive unit being obtained from access to at least one stored date.

This is based on the knowledge that a compensation of the interharmonics in those working points in which critical torsional natural frequencies are excited is usually sufficient. On the basis of this, a finding of this aspect of the invention is that the modulation amplitudes and the modulation phase angles are calculated in advance and are kept available for retrieval in tables or similarly suitable data structures. Depending on specific setpoints or measured values, the stored values can then be accessed and then the interharmonics resulting from these can be impressed.

With regard to the device, the stated object is achieved according to the invention with the features of the corresponding device claim (claim 7).

berechnen, wobei U1 die verkettete Netz- oder Maschinenspannung, Id den Zwischenkreisstrom und α den sogenannten Steuerwinkel des netz- bzw. maschinenseitigen Stromrichters bezeichnet.An average active power in the intermediate circuit can be achieved with $$\text{P.}=\surd 3*\text{U}1*\surd \mathrm{6th}/\mathrm{\pi }*\text{Id}*\text{cos}\left(\mathrm{\alpha }\right)$$

Calculate, where U1 denotes the linked network or machine voltage, Id the intermediate circuit current and α the so-called control angle of the network or machine-side converter.

The value cos (α) is generally referred to as the modulation factor (ast). By modulating the modulation level, an alternating power can be impressed in the intermediate circuit: $$\text{branch}\left(\text{t}\right)=\text{branch}\_0+\text{branch}\_\text{k}*\text{cos}\left(2*\mathrm{\pi }*\text{fk}*\text{t}+\mathrm{\phi }\_\text{k}\right).$$

Ast_0 denotes a mean modulation level, ast_k a modulation amplitude of the modulation level, fk a modulation frequency and φ_k a modulation phase angle.

The effective pendulum power caused by the modulation is: $$\begin{array}{l}\text{P.}\_\text{k}\left(\text{t}\right)=\surd 3*\text{U}1*\surd \mathrm{6th}/\mathrm{\pi }*\text{Id}*\text{branch}\_\text{k}*\\ \text{cos}\left(2*\mathrm{\pi }*\text{fk}*\text{t}+\mathrm{\phi }\_\text{k}\right)\end{array}$$

By impressing one or more low-frequency interharmonics in the intermediate circuit power by modulating the control angle or the modulation level on the network or machine side, certain low-frequency interharmonic torque excitations that occur in the machine are partially or completely compensated for. This means that they are electrically powered in an overall system and machine / working machine (eg compressor), possibly excited mechanical resonances are avoided or dampened.

Furthermore, by impressing one or more low-frequency interharmonics in the intermediate circuit power by modulating the control angle or the modulation level on the network or machine side, certain power fluctuations in the network caused by the network-side converter are partially or completely compensated for. This avoids or dampens the resonances excited in a supply network.

For this purpose, the intermediate circuit current harmonics and intermediate circuit voltage harmonics relevant for the interharmonic (s) to be compensated are calculated from the control angles of the line-side and machine-side converter, the existing impedances, the respective converter topology, the line and machine frequencies and the intermediate circuit current (setpoint or actual value) and from this the modulation amplitude ast_k and the modulation phase angle φ_k of the network or machine control angle are calculated in advance.

The main advantage of the approach according to the invention and the embodiments is that by varying the degree of modulation, it is avoided that torque excitations arise permanently or at least for longer periods of time, and that no extensive calculations or complicated measurements are required for varying the level of modulation during runtime are. Since such torque excitations take place, if at all, for very short periods of time, it is avoided that noticeable mechanical natural vibrations develop due to the torque excitations.

Advantageous refinements of the invention are the subject matter of the subclaims. References used here indicate the further development of the subject matter of the main claim through the features of the respective subclaim; they are not to be understood as a waiver of the achievement of an independent, objective protection for the combinations of features of the referenced subclaims. Furthermore, with regard to an interpretation of the claims in a more detailed specification of a feature in a subordinate claim, it must be assumed that such a restriction does not exist in the respective preceding claims.

In one embodiment of the method, it is provided that, in order to avoid extensive calculations or complicated measurement value recordings, the modulation level is varied by the mean level of modulation during runtime on the basis of a mathematical relationship stored in a control device of the drive unit, with a value for the actual variation occurring during the runtime of the drive unit results from the mathematical relationship and wherein the mathematical relationship is determined by one or more coefficients which are determined with regard to a possible low-frequency torque excitation of a work machine driven or drivable by the drive unit.

Alternatively or in addition, it is also possible to modulate the modulation level exactly or at least essentially in such a way that the alternating power thus impressed in the intermediate circuit compensates for any interharmonic motor swing power or mains swing power. Both the line-side converter (rectifier) and the machine-side converter (inverter) can be used for such compensation.

Both when using a stored mathematical relationship and when using stored data, there is a variation of the modulation level by a predetermined or predeterminable mean modulation level and, due to the variation of the modulation level, an alternating power is impressed in the intermediate circuit in the form of one or more interharmonics. Both approaches are based on properties of the drive system (device properties) and require knowledge of the drive system. However, knowledge of the (mechanical) properties of the drive train is not required.

The above-mentioned object is also achieved with a control device in or for a drive unit which operates according to the method as described here and below and for this purpose comprises means for carrying out the method. The invention is preferably implemented in software. The invention is thus, on the one hand, a computer program with program code instructions that can be executed by a computer and, on the other hand, a storage medium with such a computer program and finally also a control device or a drive unit, in whose memory such a computer program is loaded or loadable as a means for carrying out the method and its configurations .

By preventing the excitation of critical mechanical natural frequencies, skip bands for a speed setpoint can be dispensed with. The disadvantages of the fade-out bands are thus avoided. On the other hand, the above-mentioned adjustment of the interharmonics in the machine effective power also has the disadvantage of the dependence of the measurement of the interharmonics on aliasing effects, measurement value resolution effects and also changes in setpoints that cannot be neglected. These effects can also be avoided by the approach presented here and its embodiments, because there is no need to measure the values on which the approach from the prior art is based.

An exemplary embodiment of the invention is explained in more detail below with reference to the drawing. Objects or elements that correspond to one another are provided with the same reference symbols in all figures.

Figure list

• 1 a drive system with an input and output converter,
• 2 the intermediate circuit voltage and the feed currents without commutation,
• 3 the current path (left) and the equivalent circuit diagram (right) of a B6 bridge during a 60 ° interval,
• 4th the current path and the equivalent circuit diagram of a B6 bridge during commutation,
• 5 the vector image of a B6 bridge in α-β coordinates during commutation with the transition from one current space vector to the next and the associated voltage space vector,
• 6th the intermediate circuit voltage and the feed currents taking commutation into account,
• 7th the amplitudes of the 6-pulse voltage harmonics depending on the control angle and the overlap angle,
• 8th the amplitudes of the 12-pulse voltage harmonics depending on the control angle and the overlap angle,
• 9 the change in the commutation inductance Lw effective for the DC link harmonic currents.
• 10 a block diagram to illustrate a sequence for calculating the modulation modulation.

1 shows a schematically simplified drive system 10 with a line-side converter (line converter) 12th , for example a six-pulse line converter, a machine-side converter (machine converter) 14th , for example corresponding to a six-pulse line converter, an intermediate circuit electrically located in between 16 with a DC link inductance 18th and a machine connected on the output side, for example a motor 20th . A network frequency is shown with fN and a machine or motor frequency with fM. Other drive system configurations 10 , for example with a twelve-pulse line converter, twelve-pulse machine converter, two separate intermediate circuits, optionally with coupled intermediate circuit chokes, etc. are also conceivable.

For controlling and / or regulating the drive system 10 is a control unit 22nd with a processing unit 24 in the form of or in the form of a microprocessor and memory 26th intended. In the memory 26th are a control program 28 and data 30th stored for the control program. During the operation of the drive system 10 runs the processing unit 24 the control program 28 taking into account the data 30th and thereby causes the desired functionality of the drive unit 10 and indirectly the machine 20th .

To explain the online calculation of the compensation, the processes in a B6 thyristor bridge are considered as a possible embodiment of a converter.

The input current space vector of the B6 bridge can only assume six discrete states ( 5 ). Its length is proportional to the intermediate circuit current Id (= 2 / √3 * Id). The projection of the active current space vector into the R, S and T axes results in the temporal current curves in the phases R, S and T. The voltage space vector U1 describes the source voltage system of the network or the machine. The length of the pointer corresponds to the peak value of a phase voltage. The tension bridle pointer rotates at a constant angular velocity ω. The projection of the voltage space vector onto the currently effective one Current space vector is proportional to the time curve of the intermediate circuit voltage Ud. To do this shows 2 the intermediate circuit voltage Ud and the feed currents without commutation, where the control angle is shown with α.

A defined current path is always effective in a 60 ° interval. An in 3 The equivalent circuit diagram shown with source and impedance can be derived. The commutation inductance is designated there as Lk. It is made up of a network inductance and a transformer leakage inductance or corresponds to the leakage inductance of the machine. It corresponds approximately to the sub-transient leakage inductance of a synchronous machine.

Two phases are short-circuited during commutation. This changes the source voltage and the effective impedance of the equivalent circuit. 4th shows the current path and the equivalent circuit diagram of a B6 bridge during commutation and 5 the associated vector image in α-β coordinates during commutation. The radial arrows at a distance of 60 ° are the current space vector and here the transition from one current space vector to the next current space vector is shown. U1 is the voltage space vector. 6th shows the feed currents and the course of the resulting intermediate circuit voltage with the control angle α and overlap angle u.

In the present pointer image ( 5 ) the intermediate circuit current Id commutates from phase R to S. In phase T, the negative intermediate circuit current -Id flows. The commutation takes place in the phasor image on a line between the two active phasors, which results from the fact that the current in phase T remains constant. However, the transition does not take place uniformly over time, since the commutation voltage changes during the commutation. In the situation shown, the commutation voltage is U2-U1 and determines the direction of commutation. The projection of the voltage space vector onto the axis between R and S gives the intermediate circuit voltage during the commutation process under consideration. The level of the intermediate circuit voltage during commutation can reach a maximum of √6 / 2 * U_verk, compared to √2 * U_verk outside of the commutation.

• α: Steuerwinkel
• id: Zwischenkreisstrom [pu]
• ukTr: Kurzschlussspannung des Transformators [pu]

To calculate the voltage harmonics, an overlap angle u (see also 6th ), which results as follows: $$\text{u}=\text{acos}\left(\text{cos}\left(\mathrm{\alpha }\right)-\text{id}*\mathrm{\pi }*\text{ukTR}/3\right)$$

• α: control angle
• id: DC link current [pu]
• ukTr: short-circuit voltage of the transformer [pu]

mit: $$\text{Udi}=\surd 2*3/\mathrm{\pi }*\text{U}\_\text{verk}=\mathrm{1,35}*\text{U}\_\text{verk}$$

The DC component of the intermediate circuit voltage results as: $$\text{<figure-callout id="0" label="Ud" filenames="DE102011079995B4\_0042.png,DE102011079995B4\_0043.png" state="{{state}}">Ud</figure-callout>}0=\text{Udi}*\text{cos}\left(\mathrm{\alpha }\right)-\text{id}*\mathrm{\pi }/\mathrm{6th}*\text{ukTr}$$

with: $$\text{Udi}=\surd 2*3/\mathrm{\pi }*\text{U}\_\text{sell}=1.35*\text{U}\_\text{sell}$$

$$UbN\mathrm{,6}=2\cdot \left({\displaystyle \underset{\alpha }{\overset{\alpha +u}{\int }}\text{sin }6x\cdot \frac{\sqrt{3}}{2}\cdot \text{cos }xdx}+{\displaystyle \underset{\alpha +u}{\overset{\alpha +\frac{\pi }{3}}{\int }}\text{sin }6x\cdot \text{cos }\left(x-\frac{\pi }{6}\right)dx}\right)$$

und in komplexer Schreibweise als $$\underset{\_}{\text{UdN}\mathrm{,6}}=\text{UaN}\mathrm{,6}-\text{j UbN}\mathrm{,6}$$

Furthermore, the sixth harmonics of the intermediate circuit voltage on the network side (standardized to Udi) result as $$UaN\mathrm{,\; 6}=2\cdot \left({\displaystyle \underset{\alpha }{\overset{\alpha +u}{\int }}\text{cos}\mathrm{6th}x\cdot \frac{\sqrt{3}}{2}\cdot \text{cos}xdx}+{\displaystyle \underset{\alpha +u}{\overset{\alpha +\frac{\pi }{3}}{\int }}\text{cos}\mathrm{6th}x\cdot \text{cos}\left(x-\frac{\pi }{\mathrm{6th}}\right)dx}\right)$$

$$UbN\mathrm{,\; 6}=2\cdot \left({\displaystyle \underset{\alpha }{\overset{\alpha +u}{\int }}\text{sin}\mathrm{6th}x\cdot \frac{\sqrt{3}}{2}\cdot \text{cos}xdx}+{\displaystyle \underset{\alpha +u}{\overset{\alpha +\frac{\pi }{3}}{\int }}\text{sin}\mathrm{6th}x\cdot \text{cos}\left(x-\frac{\pi }{\mathrm{6th}}\right)dx}\right)$$

and in complex notation as $$\underset{\_}{\text{UdN}\mathrm{,\; 6}}=\text{UaN}\mathrm{,\; 6}-\text{j UbN}\mathrm{,\; 6}$$

In the following, complex quantities are always shown with an underscore, the conjugate complex quantities are also marked with an asterisk at the end.

The harmonic voltages calculated here are shown in the equivalent circuit diagrams 3 and 4th imprinted in Udq. The voltage determined here is not identical to the voltage measured at the intermediate circuit connections, e.g. the voltage measured on the line converter. The voltages differ in terms of voltage drops across the commutation inductances. The representations in 7th and 8th show the amplitudes of the voltage harmonics 6 * f1 [pu] and 12 * f1 [pu] based on Udi = 1.35 * Un depending on the control angle and the overlap angle u.

The calculation of the intermediate circuit current harmonics is generally carried out according to $$\underset{\_}{\text{Id},\mathrm{\nu }}=\underset{\_}{\text{Ud},\mathrm{\nu }}/\underset{\_}{\text{Zd},\mathrm{\nu }}.$$

LkN: Kommutierungsindktivität des Netzes
Ld: Zwischenkreisinduktivität
LkM: Kommutierungsindktivität des Motors wobei die Terme 2*LkN bzw. 2*LkM nicht ganz korrekt sind, denn während der Kommutierung ist der Wert 1,5*LkN bzw. 1,5*LkM. Die Berechnungen beziehen sich auf den Netzstromrichter, können aber entsprechend auch auf den Maschinenstromrichter übertragen werden.The effective intermediate circuit impedance Zd, v for a current intermediate circuit converter is made up as follows: $$\underset{\_}{\text{Zd},\mathrm{\nu }}=\mathrm{6th}\left(\text{fN}*\text{LkN}+\text{fM}*\text{LkM}\right)+\text{j}*\mathrm{\omega \nu }*\left(2*\text{LkN}+\text{Ld}+2*\text{LkM}\right),$$

LkN: commutation inductance of the network
Ld: DC link inductance
LkM: Commutation inductance of the motor whereby the terms 2 * LkN or 2 * LkM are not entirely correct, because during commutation the value is 1.5 * LkN or 1.5 * LkM. The calculations relate to the line converter, but can also be transferred to the machine converter accordingly.

$$\underset{\_}{\text{Ud}\mathrm{\nu },\mathrm{\mu }}=\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.\text{*j}*2*\mathrm{\pi }*\text{f}\mathrm{\mu }*\underset{\_}{\text{Lw},\mathrm{\nu }}*\underset{\_}{\text{Id},\mathrm{\mu }}$$

mit $$\text{Lw}\mathrm{,0}=2*\text{Lk}-0.5*\text{Lk}*3*\text{u}/\mathrm{\pi }$$

mit $$\underset{\_}{\text{Lw},\mathrm{\nu }}=-0.5*\text{Lk}*12/\mathrm{\pi }*\text{sin}\left(\mathrm{\nu }*\text{u}/2\right)$$

9 shows the change in the commutation inductance Lw (t) effective for the DC link harmonic currents. The harmonics Lw, v result from the Fourier analysis of the time course of Lw (t). A harmonic current with fµ causes a voltage drop of at the effective commutation inductance $$\underset{}{\text{Ud}}$$$$\underset{\_}{\mathrm{0,}\mathrm{\mu }}=\text{j}*2*\mathrm{\pi }*\text{f}\mathrm{\mu }*\text{Lw}\mathrm{,\; 0}*\underset{\_}{\text{Id},\mathrm{\mu }}$$

$$\underset{\_}{\text{Ud}\mathrm{\nu },\mathrm{\mu }}=\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.\text{* j}*2*\mathrm{\pi }*\text{f}\mathrm{\mu }*\underset{\_}{\text{Lw},\mathrm{\nu }}*\underset{\_}{\text{Id},\mathrm{\mu }}$$

with $$\text{Lw}\mathrm{,\; 0}=2*\text{Lk}-0.5*\text{Lk}*3*\text{u}/\mathrm{\pi }$$

with $$\underset{\_}{\text{Lw},\mathrm{\nu }}=-0.5*\text{Lk}*\mathrm{12th}/\mathrm{\pi }*\text{sin}\left(\mathrm{\nu }*\text{u}/2\right)$$

The occurring frequencies of this voltage drop are fµ and fv +/- fµ. Thus, for example, interharmonic voltage drops also occur over the effective commutation inductance of the line converter, which are caused by the harmonic currents Id, μ of the machine converter. The same applies to the voltage drops over the effective commutation inductance of the machine converter, which are caused by the harmonic currents of the line converter. These voltage drops in turn generate interharmonic intermediate circuit currents with fv +/- fµ.

The calculation of the interharmonic intermediate circuit currents and the resulting three-phase power is generally carried out according to (the interharmonic voltage drops in the mains and machine converters must be taken into account) $$\underset{\_}{\text{Id},\mathrm{\nu \mu }}=\left(\underset{\_}{\text{And},\mathrm{\nu \mu }}+\underset{\_}{\text{UMd},\mathrm{\nu \mu }}\right)/\underset{\_}{\text{Zd},\mathrm{\nu \mu }}$$

wobei auch hier wieder die Annahme von 2*LkN bzw. 2*LkM nicht ganz korrekt ist, denn während der Kommutierung ist der Wert 1,5*LkN bzw. 1,5*LkM (vgl. 9).The effective intermediate circuit impedance Zd, νµ for a current intermediate circuit converter is made up as follows $$\begin{array}{l}\underset{\_}{\text{Zd},\mathrm{\nu \mu }}=\mathrm{6th}\left(\text{fN}*\text{LkN}+\text{fM}*\text{LkM}\right)+\\ \text{j}*\left(\mathrm{\omega \nu \; +/-\; \omega \mu }\right)*\left(2*\text{LkN}+\text{Ld}+2*\text{LkM}\right),\end{array}$$

Here, too, the assumption of 2 * LkN or 2 * LkM is not entirely correct, because during commutation the value is 1.5 * LkN or 1.5 * LkM (cf. 9 ).

mit $$\text{f}\mathrm{\mu }=\mathrm{\mu }*\text{fN},\mathrm{\mu }=\mathrm{0,}-\mathrm{6,}+\mathrm{6,}-\mathrm{12,}+\mathrm{12,}\dots$$

The harmonics in the network power with ideally smoothed intermediate circuit current are calculated from the power in the substitute sources. Strictly speaking, this only applies outside of commutation, since the equivalent circuit is not power-invariant compared to the real circuit during commutation. If this commutation influence is neglected, the following applies: $$\underset{\_}{\text{PN}3\text{ph},\mathrm{\mu }}=\underset{\_}{\text{Pdq},\mathrm{\mu }}=\underset{\_}{\text{UdN},\mathrm{\mu }}*\text{Id}$$

with $$\text{f}\mathrm{\mu }=\mathrm{\mu }*\text{fN},\mathrm{\mu }=\mathrm{0,}-\mathrm{6,}+\mathrm{6,}-\mathrm{12,}+\mathrm{12,}...$$

mit $$\mathrm{\nu }=\mathrm{6,}\mathrm{12,}\dots$$

berechnen sich die Interharmonischen der Netzleistung aus: $$\underset{\_}{\text{PN}3\text{ph},\mathrm{\mu \nu }\mathrm{,1}}=\underset{\_}{\text{Pdq},\mathrm{\mu \nu }}=\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.*\underset{\_}{\text{UdN},\mathrm{\mu }}*\underset{\_}{\text{Id}\mathrm{\nu }*}$$

mit $$\text{f}\mathrm{\mu \nu }=\mathrm{\nu }*\text{fM}+/-\mathrm{\mu }*\text{fN},\mathrm{\nu },\mathrm{\mu }=\mathrm{6,}\mathrm{12,}\dots$$

These harmonics in the three-phase power result from the voltage harmonics of the own converter. However, if the intermediate circuit current contains harmonics Idv, which are caused by the machine converter, with: $$\text{f}\mathrm{\nu }=\mathrm{\nu }*\text{fM}$$

with $$\mathrm{\nu }=\mathrm{6,}\mathrm{12,}...$$

the interharmonics of the network power are calculated from: $$\underset{\_}{\text{PN}3\text{ph},\mathrm{\mu \nu }\mathrm{,1}}=\underset{\_}{\text{Pdq},\mathrm{\mu \nu }}=\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.*\underset{\_}{\text{UdN},\mathrm{\mu }}*\underset{\_}{\text{Id}\mathrm{\nu }*}$$

with $$\text{f}\mathrm{\mu \nu }=\mathrm{\nu }*\text{fM}+/-\mathrm{\mu }*\text{fN},\mathrm{\nu },\mathrm{\mu }=\mathrm{6,}\mathrm{12,}...$$

Another portion of the interharmonic network pendulum power results from the interharmonic intermediate circuit current Id, νµ and the intermediate circuit direct voltage Ud0: $$\underset{\_}{\text{PN}3\text{ph},\mathrm{\mu \nu }\mathrm{,\; 2}}=\text{<figure-callout id="0" label="Ud" filenames="DE102011079995B4\_0042.png,DE102011079995B4\_0043.png" state="{{state}}">Ud</figure-callout>}0*\underset{\_}{\text{Id},\mathrm{\nu \mu }*}$$

These two components must be added in the correct phase.

The interharmonics in the engine power can be calculated accordingly.

According to the approach according to the invention, it is now provided that one or more interharmonics of the mains or motor pendulum power is compensated for by corresponding modulation of the degree of modulation of one of the two converters. By compensating for one or more interharmonics of the motor swing power, the corresponding interharmonics in the air gap torque of the motor are also always compensated.

• 1.) Die interharmonische Motorpendelleistung wird mit dem netzseitigen Stromrichter kompensiert.
• 2.) Die interharmonische Motorpendelleistung wird mit dem maschinenseitigen Stromrichter kompensiert.
• 3.) Die interharmonische Netzpendelleistung wird mit dem netzseitigen Stromrichter kompensiert.
• 4.) Die interharmonische Netzpendelleistung wird mit dem maschinenseitigen Stromrichter kompensiert.

There are basically two options for modulating the modulation level (ast), namely compensation by the power converter on the line or machine side. In detail:

• 1.) The interharmonic motor pendulum power is compensated with the line-side converter.
• 2.) The interharmonic motor pendulum power is compensated with the converter on the machine side.
• 3.) The interharmonic mains pendulum power is compensated with the mains-side converter.
• 4.) The interharmonic mains pendulum power is compensated with the converter on the machine side.

In case 1, an intermediate circuit current is impressed, which compensates for the interharmonic motor power fluctuations (PM3Ph, νµ, 1 + PM3Ph, νµ, 2). $$\underset{\_}{\text{Id}\_\text{k},\mathrm{\nu \mu }}=\underset{\_}{-\left(\text{PM}3\text{Ph},\mathrm{\nu \mu }\mathrm{,1}+\text{PM}3\text{Ph},\mathrm{\nu \mu }\mathrm{,\; 2}\right)*}/\text{<figure-callout id="0" label="Ud" filenames="DE102011079995B4\_0042.png,DE102011079995B4\_0043.png" state="{{state}}">Ud</figure-callout>}0$$

mit $$\begin{array}{l}\underset{\_}{\text{Zd},\mathrm{\nu \mu }}=6\left(\text{fN}*\text{LkN}+\text{fM}*\text{LkM}\right)+\\ \text{ j}*\left(\mathrm{\omega \nu }-\mathrm{\omega \mu }\right)*\left(2*\text{LkN}+\text{Ld}+2*\text{LkM}\right),\end{array}$$

The DC link voltage required to be impressed in the line converter is $$\underset{\_}{\text{U.N.}\_\text{k},\mathrm{\nu \mu }}=\underset{\_}{\text{Id}\_\text{k},\mathrm{\nu \mu }}*\underset{\_}{\text{Zd},\mathrm{\nu \mu }}$$

with $$\begin{array}{l}\underset{\_}{\text{Zd},\mathrm{\nu \mu }}=\mathrm{6th}\left(\text{fN}*\text{LkN}+\text{fM}*\text{LkM}\right)+\\ \text{j}*\left(\mathrm{\omega \nu }-\mathrm{\omega \mu }\right)*\left(2*\text{LkN}+\text{Ld}+2*\text{LkM}\right),\end{array}$$

In case 4, an intermediate circuit current is impressed, which compensates for the interharmonic mains power fluctuations (PN3Ph, νµ, 1 + PN3Ph, νµ, 2). $$\begin{array}{l}\underset{\_}{\text{Id}\_\text{k},\mathrm{\nu \mu }}=-\left(\underset{\_}{\text{PN}3\text{Ph},\mathrm{\nu \mu }\mathrm{,1}*}+\underset{\_}{\text{PN}3\text{Ph},\mathrm{\nu \mu }\mathrm{,\; 2}*}\right)/\text{<figure-callout id="0" label="Ud" filenames="DE102011079995B4\_0042.png,DE102011079995B4\_0043.png" state="{{state}}">Ud</figure-callout>}0\\ \underset{\_}{\text{AROUND}\_\text{k},\mathrm{\nu \mu }}=\underset{\_}{\text{Id}\_\text{k},\mathrm{\nu \mu }}*\underset{\_}{\text{Zd},\mathrm{\nu \mu }}\end{array}$$

With $$\begin{array}{l}\underset{\_}{\text{Zd},\mathrm{\nu \mu }}=\mathrm{6th}\left(\text{fN}*\text{LkN}+\text{fM}*\text{LkM}\right)+\\ \text{j}*\left(\mathrm{\omega \nu }-\mathrm{\omega \mu }\right)*\left(2*\text{LkN}+\text{Ld}+2*\text{LkM}\right),\end{array}$$

$$\begin{array}{l}\underset{\_}{\text{UM}\_\text{k},\mathrm{\nu \mu }}/\underset{\_}{\text{Zd},\mathrm{\nu \mu }}*\text{Ud}0+\text{Id}0*\underset{\_}{\text{UM}\_\text{k},\mathrm{\nu \mu }}=-(\underset{\_}{\text{PM}3\text{Ph},\mathrm{\nu \mu }\mathrm{,1}}+\\ \underset{\_}{\text{PM}3\text{Ph},\mathrm{\nu \mu }\mathrm{,2}})\end{array}$$

$$\underset{\_}{\text{UM}\_\text{k},\mathrm{\nu \mu }}=-\left(\underset{\_}{\text{PM}3\text{Ph},\mathrm{\nu \mu }\mathrm{,1}}+\underset{\_}{\text{PM}3\text{Ph},\mathrm{\nu \mu }\mathrm{,2}}\right)/\left(\text{Ud}0/\underset{\_}{\text{Zd},\mathrm{\nu \mu }}+\text{Id}0\right)$$

In case 2, the modulation in the motor converter also generates an oscillation of the driving intermediate circuit voltage $$\underset{\_}{\text{Id}\_\text{k},\mathrm{\nu \mu }}*\text{<figure-callout id="0" label="Ud" filenames="DE102011079995B4\_0042.png,DE102011079995B4\_0043.png" state="{{state}}">Ud</figure-callout>}0+\text{<figure-callout id="0" label="Id" filenames="DE102011079995B4\_0042.png,DE102011079995B4\_0043.png" state="{{state}}">Id</figure-callout>}0*\underset{\_}{\text{AROUND}\_\text{k},\mathrm{\nu \mu }}=-\left(\underset{\_}{\text{PM}3\text{Ph},\mathrm{\nu \mu }\mathrm{,1}}+\underset{\_}{\text{PM}3\text{Ph},\mathrm{\nu \mu }\mathrm{,\; 2}}\right)$$

$$\begin{array}{l}\underset{\_}{\text{AROUND}\_\text{k},\mathrm{\nu \mu }}/\underset{\_}{\text{Zd},\mathrm{\nu \mu }}*\text{<figure-callout id="0" label="Ud" filenames="DE102011079995B4\_0042.png,DE102011079995B4\_0043.png" state="{{state}}">Ud</figure-callout>}0+\text{<figure-callout id="0" label="Id" filenames="DE102011079995B4\_0042.png,DE102011079995B4\_0043.png" state="{{state}}">Id</figure-callout>}0*\underset{\_}{\text{AROUND}\_\text{k},\mathrm{\nu \mu }}=-(\underset{\_}{\text{PM}3\text{Ph},\mathrm{\nu \mu }\mathrm{,1}}+\\ \underset{\_}{\text{PM}3\text{Ph},\mathrm{\nu \mu }\mathrm{,\; 2}})\end{array}$$

$$\underset{\_}{\text{AROUND}\_\text{k},\mathrm{\nu \mu }}=-\left(\underset{\_}{\text{PM}3\text{Ph},\mathrm{\nu \mu }\mathrm{,1}}+\underset{\_}{\text{PM}3\text{Ph},\mathrm{\nu \mu }\mathrm{,\; 2}}\right)/\left(\text{<figure-callout id="0" label="Ud" filenames="DE102011079995B4\_0042.png,DE102011079995B4\_0043.png" state="{{state}}">Ud</figure-callout>}0/\underset{\_}{\text{Zd},\mathrm{\nu \mu }}+\text{Id}0\right)$$

The same applies to case 3: $$\underset{\_}{\text{U.N.}\_\text{k},\mathrm{\nu \mu }}=-\left(\underset{\_}{\text{PN}3\text{Ph},\mathrm{\nu \mu }\mathrm{,1}}+\underset{\_}{\text{PN}3\text{Ph},\mathrm{\nu \mu }\mathrm{,\; 2}}\right)/\left(\text{<figure-callout id="0" label="Ud" filenames="DE102011079995B4\_0042.png,DE102011079995B4\_0043.png" state="{{state}}">Ud</figure-callout>}0/\underset{\_}{\text{Zd},\mathrm{\nu \mu }}+\text{Id}0\right)$$

mit $$\text{fk}=\text{f}\mathrm{\nu }-\text{f}\mathrm{\mu },$$

The additional modulation depth and additional control angle are then calculated from UN k, νµ or UM k, νµ. The intermediate circuit voltage, e.g. on the line side, is calculated from: $$\begin{array}{l}\text{UdN},\text{q}\left(\text{t}\right)=\surd 2*3/\mathrm{\pi }*\text{U.N.}\_\text{sell}*(\text{BRANCH}\_0\\ +\text{BRANCH}\_\text{k}*\text{cos}\left(2*\mathrm{\pi }*\text{fk}*\text{t}+\mathrm{\phi }\_\text{k}\right))\end{array}$$

with $$\text{fk}=\text{f}\mathrm{\nu }-\text{f}\mathrm{\mu },$$

The amplitude of the component due to the degree of modulation is calculated as follows: $$\text{UdN}\_\text{k},\mathrm{\nu \mu }=\surd 2*3/\mathrm{\pi }*\text{U.N.}\_\text{sell}*\text{BRANCH}\_\text{k}$$

The amplitude AST_k of the degree of modulation is then calculated from the above equation.

The same applies to the machine side accordingly.

10 Finally and as a summary of the calculation steps explained above, shows a sequence for calculating the modulation of the modulation level. The flowchart relates, for example, to case 1, where the interharmonic motor pendulum power is compensated for with the line-side converter. In general, values are shown in the representation that are divided according to amount and phase by amount lines (||) or the symbol φ. General input values are a commutation inductance on the machine side 100 and a commutation inductance on the network side 102 , the intermediate circuit current Id 104 namely either its actual or nominal value, a machine control angle 106 and a mesh control angle 108 , where usually the network control angle 108 The result of a regulation is, as well as an effective intermediate circuit impedance 110 . This takes place (first function block 112 ) a calculation of the harmonics of the intermediate circuit voltage UdM on the machine side and (second function block 114 ) a calculation of the harmonics of the intermediate circuit voltage UdN on the network side. The respective results flow with magnitude and phase and the effective intermediate circuit impedance 110 into a calculation of the harmonics in the intermediate circuit current caused by the machine converter (third function block 116 ) and correspondingly in a calculation of the harmonics in the intermediate circuit current caused by the line converter (fourth function block 118 ) a. The results there flow according to amount and phase together with the network control angle 108 on the one hand and the machine control angle 106 on the other hand, in a calculation of the commutation voltage drop on the network side due to the current harmonics caused by the machine converter (fifth function block 120 ) or a calculation of the commutation voltage drop on the machine side due to the current harmonics caused by the line converter (sixth function block 122 ) a. These results are - according to amount and phase - together with the effective intermediate circuit impedance 110 used for calculating the interharmonics in the intermediate circuit current (seventh function block 124 ). This enables the calculation of the first component of the interharmonics of the engine power (eighth function block 126 ), with a direct component of the intermediate circuit voltage 128 is taken into account. The calculation of a second component of the interharmonics of the engine power (ninth function block 130 ) is based on the harmonics of the DC link voltage on the machine side and the harmonics in the DC link current caused by the line converter. The results are added according to amount and phase (tenth function block 132 ) and then with the quotient 134 from the effective intermediate circuit impedance 110 and the DC component of the intermediate circuit voltage 128 multiplied (eleventh function block 136 ). The result is the amount and phase of an intermediate circuit voltage oscillation to be modulated in the line converter, which is converted into a modulation level modulation according to amount and phase 138 is converted, so the modulation frequency fk and the modulation phase angle φ_k for the relationship introduced at the input to the modulation of the modulation level: $$\text{branch}\left(\text{t}\right)=\text{branch}\_0+\text{branch}\_\text{k}*\text{cos}\left(2*\mathrm{\pi }*\text{fk}*\text{t}+\mathrm{\phi }\_\text{k}\right).$$

The stored mathematical relationship in accordance with the terminology used at the beginning is the modulation of the modulation level shown above and in the following the in 10 summarized calculation steps according to the preceding explanations.

It should be noted that apart from the results of the fifth and sixth function blocks 120 , 122 whose calculations are based on the assumption of negligible commutation, all other calculations can be carried out quite precisely.

The alternative embodiment of the approach according to the invention, which is based on an offline precalculation of the compensation, benefits from the knowledge that the compensation only has to take place at critical machine frequencies that result from the Campbell diagram of the drive. Based on this, it is proposed to store the necessary modulation amplitudes and phase angles, i.e. values for the modulation frequency fk and the modulation phase angle φ_k for the relationship introduced at the beginning for the modulation of the modulation level, in at least one table or another suitable data structure. The values can also be determined by means of a simulation, because such a simulation very well reproduces the commutation effects, which are analytically complex to calculate. Due to the offline forecast, there is only a negligible amount of computing time at runtime.

• - Netzspannung
• - Netzkurzschlussleistung
• - Netzfrequenz
• - Maschinenfluss
• - Motorfrequenz
• - Maschinenstrom
• - Steuerwinkel des Maschinenstromrichters
• - Steuerwinkel des Netzstromrichters

The working points considered result from the Campell diagram. The following temporal and operational dependencies of the modulation amplitude and phase result from:

• - Mains voltage
• - network short-circuit power
• - grid frequency
• - machine flow
• - motor frequency
• - machine power
• - Control angle of the machine converter
• - Control angle of the line converter

Some of these dependencies can be assumed to be constant at the respective operating point. This includes the short-circuit power, the mains frequency, as it has only a low tolerance, and the machine frequency, since the compensation is only effective in a narrow frequency range. The variables described are not all independent of each other, e.g. the mains voltage results from all other variables. Because the remaining quantities are independent of each other, it must be an n-dimensional table. The number of table elements depends on the possible range of variation of the individual sizes.

A multidimensional table is then formed with all non-constant, independent variables, in particular the network control angle and the machine control angle. During operation, the modulation level is varied by the mean level of modulation based on the data stored in this table. The data was outside of a running time of the drive unit 10 determined and a value for the actual variation is obtained at the runtime of the drive unit 10 based on access to at least one date stored in this table. Intermediate values can be determined in a manner known per se by interpolation.

During the runtime of the drive system 10 A quick access to the table (s) on the basis of the respective data and on the basis of which it is possible to read out the modulation amplitudes and phase angles stored in the table at the positions specified by the data is readily possible.

Both proposed approaches relate to a machine- and motor-specific voltage vector and their phase, so that the difference between these pointers forms the reference system to which the modulation relates.

The or each table or an implementation of the in 10 The calculation scheme shown is stored in a memory 26th ( 1 ) the control device 22nd ( 1 ) and the table is essentially stored as data 30th for the control program 28 and the calculation scheme essentially as a software implementation of the calculation steps included therein, that is to say as part of the control program 28 . The processing unit 24 , the memory 26th , as well as the control program 28 and / or the data 30th are the means to carry out the procedure.

In summary, a central aspect of the description presented here can be briefly summarized as follows: A method for operating a drive unit is described 10 with an input or line-side converter 12th and an output or machine-side converter 14th and an intermediate circuit electrically located in between 16 specified, with an average active power in the intermediate circuit 16 from a modulation level of the line-side or machine-side converter 12th , 14th is dependent, in which the modulation level is varied by a predetermined or predeterminable mean modulation level and in which the intermediate circuit by varying the modulation level 16 an alternating power is impressed, so that a compensation of undesired interharmonics results with the impressed alternating power.

Claims (6)

Method for compensating for interharmonic torque excitations in a current intermediate circuit converter with an input or line-side converter (12) and an output or machine-side converter (14) and an intermediate circuit (16) with an inductance as an energy store when operating a drive unit (10) , wherein an average active power in the intermediate circuit (16) is dependent on a modulation level of the network-side or machine-side converter (12, 14), the degree of modulation being varied by a predetermined or predeterminable mean degree of modulation, whereby an alternating power is impressed on the intermediate circuit (16) by varying the modulation level, wherein the variation of the modulation level by the mean modulation level takes place on the basis of data stored in a control device (22) of the drive unit (10) in a multidimensional table, wherein the data were determined outside of a running time of the drive unit (10) and wherein a value for the actual variation during the running time of the drive unit (10) results from an access to at least one stored date of the network control angle and the machine control angle. Procedure according to Claim 1 , the variation of the modulation level by the mean level of modulation taking place on the basis of a mathematical relationship stored in a control device (22) of the drive unit (10), a value for the actual variation during the running time of the drive unit (10) being obtained based on the mathematical relation and whereby the mathematical relationship is determined by one or more coefficients which are determined with regard to a possible low-frequency torque excitation of a machine (20) driven or drivable by the drive unit (10). Procedure according to Claim 2 , the mathematical relationship causing a periodically alternating variation of the modulation level by the mean level of modulation. Computer program with program code means to carry out all the steps of any of the Claims 1 until 3 to be carried out when the program is executed on a control device (22) for a drive unit (10). Digital storage medium with electronically readable control signals which can interact with a control device (22) for a drive unit (10) in such a way that a method according to one of the Claims 1 until 3 is performed. Drive unit (10) with an input or network-side converter (12) and an output or machine-side converter (14) and an intermediate circuit (16) electrically located in between, with an average active power in the intermediate circuit (16) depending on a modulation level of the network or machine-side converter (12, 14) is dependent, and with a control device (22) with a memory (26) in the a computer program after Claim 4 is loaded.

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