DE102011079995A1 - Method for operating drive system of e.g. engine, involves varying modulation depth of network-side or machine-side converters by average modulation depth of intermediate circuit, to supply alternating current power - Google Patents

Abstract

The method involves operating a drive system (10) having a beginning or network-side converter (12), a source or machine-side converter (14) and an electrically intervening intermediate circuit (16). The mean active power of the intermediate circuit is dependent on the modulation depth of network-side converter or machine-side converters. The modulation depth of network-side converter or machine side converters is varied by a predetermined average modulation depth of the intermediate circuit, for supplying alternating current (AC) power. Independent claims are included for the following: (1) a computer program stored in digital memory medium for operating drive system; and (2) a drive system.

Description

The invention relates to a method for operating a drive unit according to the preamble of claim 1.

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

The frequencies of the respective electrical power in the intermediate circuit (DC link power) superimposed harmonics result from addition and subtraction of all occurring combinations of the DC component and the harmonic frequencies in the DC link voltage and the DC link current f_k = n * f_N +/- m * f_M | n, m = 0, 6, 12, .. 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 integer multiples of a net and / or machine-side fundamental oscillation f_N, f_M.

Low-frequency interharmonics have proven particularly critical because they can lead to torque excitations (electrical torque) in the respective machine, for example motor, generator, and can excite the natural mechanical 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. Typically, so-called interharmonic torque excitations (electrical torque) are relatively small, often less than about two percent. Nevertheless, even such small 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 torsion torques. In the case of 6/6-pulse arrays and 12/12-pulse arrays, machine frequencies in the range of the line frequency are particularly critical, ie if (at least approximately) f_M = f_N, then the frequencies of the occurring torque excitations (electrical torque) are exactly the natural frequency of the mechanical part of the drive system.

To address this problem, different approaches have become known. On the one hand so-called Ausfendfrequenzbänder are provided in a speed setpoint channel. Stationary, the machine can then be operated only above or below a Ausblendfrequenzbands. The drive is dynamically driven through the frequencies encompassed by a blanking frequency band. Due to the then only comparatively short excitation, the mechanical natural vibration can not form. However, the blanking of individual frequency bands influences the dynamics of the drive and, in many cases, interferes with the respective process. On the other hand, in the EP 1 875 597 proposed a method by which oscillations of the shaft torque at the torsion critical point should be spatially compensated by a special regulation. For this purpose, the wave moment at the critical point is measured by means of strain gauges and a measurement value obtainable on this basis is used for the control. To realize such a regulation, however, a precise knowledge of the shaft train and the associated mechanics is necessary.

Accordingly, it is an object of the invention to provide a method of operating a drive system and a drive system operating according to the method which avoids the disadvantages outlined above or at least reduces their effects while being simple and efficient.

This object is achieved by 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 located therebetween electrically, wherein an average active power in the intermediate circuit of a Aussteuergrad of supply or machine-side power converter, provided that the Aussteuergrad is varied by a predetermined or predeterminable average Aussteuergrad and that the DC bus an alternating power is impressed by the variation of the Aussteuergrad. The variation of Aussteuergrades takes place in the context of a control and not based on a scheme, ie the essential variables on the basis of the variation of Aussteuergrades done are known and need not be determined at run time, while a possible control of a Aussteuergrades in this Regards relevant variables at runtime from the process.

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

A mean active power in the DC link can be with P = √3 · U1 · √6 / π · Id · cos (α) where U1 denotes the concatenated 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 output level (ast). By modulating the modulation level, an alternating power can be impressed in the DC link: ast (t) = ast_0 + ast_k * cos (2 * π * fk * t + φ_k).

In this case, ast_0 denotes a mean modulation level, ast_k a modulation amplitude of the modulation rate, f_k a modulation frequency, and φ_k a modulation phase angle.

The commutation power caused by the modulation is: P_k (t) = √3 · U1 · √6 / π · Id · ast_k · cos (2 · π · fk · t + φ_k)

By impressing one or more low-frequency interharmonics in the DC link power by modulating the control angle or the Aussteuergrads on the network or machine side certain occurring low-frequency interharmonic torque excitations in the machine are partially or fully compensated. As a result, any mechanical resonances that may have been excited in an overall system comprising the electric drive and the machine / work machine (eg compressor) are avoided or dampened.

Furthermore, by impressing one or more low-frequency interharmonics in the DC link power by modulating the control angle or the Aussteuergrads on the network or machine side certain certain network side converter caused power oscillations in the network partially or completely compensated. This avoids or dampens the resonances excited in a supply network.

For this purpose, the relevant for the compensating (s) Interharmonische (s) relevant Zwischenkreisstromharmonischen and DC link voltage harmonics from the control angles of the network and machine-side converter, the existing impedances, the respective power converter topology, the network and machine frequencies and the DC link current (setpoint or actual value) is calculated 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 it is avoided by the variation of Aussteuergrads that permanently or at least for longer periods result in torque excitations, and that for the variation of the Aussteuergrades at runtime no extensive calculations or complicated measured value recordings required are. By such torque excitations take place at most during the shortest periods of time, it is avoided that form due to the torque excitations noticeable mechanical self-oscillation.

Advantageous embodiments of the invention are the subject of the dependent claims. This used backlinks point to the further development of the subject matter of the main claim by the features of the respective subclaim; they are not considered a waiver of achieving one to understand independent, objective protection for the feature combinations of the dependent claims. Furthermore, with a view to an interpretation of the claims in a closer specification of a feature in a subordinate claim, it is to be assumed that such a restriction does not exist in the respective preceding claims.

In one embodiment of the method, it is provided that to avoid extensive calculations or complicated measured value recordings at runtime, the variation of Aussteuergrads to the average Aussteuergrad due to a stored in a control device of the drive unit mathematical relationship, wherein a value for the actual variation at run time of the drive unit from the mathematical relationship, and wherein the mathematical relationship is determined by one or more coefficients determined with respect to a possible low-frequency torque excitation of a drive machine driven or drivable by the drive unit.

Alternatively or additionally, it is also possible to carry out the modulation of the modulation level exactly or at least substantially so that the alternating power impressed thereby into the intermediate circuit compensates for any interharmonic motor pendulum output or mains pendulum output. For such a compensation, both the line-side converter (rectifier) and the machine-side converter (inverter) come into consideration.

Alternatively to the modulation of the modulation rate on the basis of a stored mathematical relationship is also considered to make the variation of Aussteuergrads to the average Aussteuergrad due to stored in a control device of the drive unit, off-line determined data, with a value for the actual variation at run time the drive unit based on an access to at least one stored date results.

This approach is based on the recognition that normally a compensation of the internharmonic in those operating points in which critical torsion natural frequencies are excited, is sufficient. Based on this, a realization of this aspect of the invention is that the modulation amplitudes and the modulation phase angles are calculated in advance and stored in tables or similar suitable data structures for retrieval. Depending on specific setpoints or measured values, access to the stored values and then an impression of the resulting interharmonics can take place.

Both when using a stored mathematical relationship as well as the use of stored data results in a variation of Aussteuergrads by a predetermined or predeterminable average Aussteuergrad and due to the variation of the Aussteuergrads the impression of a change in performance in the intermediate circuit in the form of one or more Interharmonischer. Both approaches are based on properties of the drive system (device characteristics) and require knowledge of the drive system. On the other hand, knowledge of the (mechanical) properties of the powertrain 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 comprises means for carrying out the method. The invention is preferably implemented in software. The invention is therefore on the one hand also a computer program with program code instructions executable 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 means for carrying out the method and its embodiments ,

By preventing excitation of critical mechanical natural frequencies, it is possible to dispense with blanking bands for a speed setpoint. The disadvantages of Ausblendbänder are thus avoided. On the other hand, the above-mentioned adjustment of the interharmonics in machine performance has the disadvantage of a dependence of the measurement of the interharmonics of not negligible aliasing effects, Meßwertauflösungseffekten and setpoint changes. These effects can also be avoided by the approach presented here and its embodiments, since there is no need at all for the measurement of the values underlying the approach of the prior art.

An embodiment of the invention will be explained in more detail with reference to the drawing. Corresponding objects or elements are provided in all figures with the same reference numerals.

The or each embodiment is not to be understood as limiting the invention. Rather, numerous modifications and variations are possible within the scope of the present disclosure, for example, by combination or modification of individual in connection with the described in the general or specific description part and in the claims and / or drawings features or elements or method steps for the Skilled in terms of solving the problem are removable and lead by combinable features to a new subject or to new process steps or process steps.

Show it

1 a drive system with an input and output converter,

2 the DC link voltage and the supply currents without commutation,

3 the current path (left) and the equivalent circuit diagram (right) of a B6 bridge during a 60 ° interval,

4 the current path and the equivalent circuit of a B6 bridge during a commutation,

5 the pointer image of a B6 bridge in α-β coordinates during commutation with the transition from one current space pointer to the next and the corresponding voltage space vector,

6 the DC link voltage and the supply currents taking into account the commutation,

7 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 effective for the DC link harmonic currents Kommutierungsinduktivität Lw.

10 a block diagram illustrating an operation for calculating the Aussteuergradmodulation.

1 schematically shows a simplified drive system 10 with a mains converter (mains converter) 12 , for example a six-pulse mains converter, a machine-side converter (machine converter) 14 , for example, according to a six-pulse power converter, an intermediate circuit located electrically therebetween 16 with a DC link inductance 18 and a machine connected on the output side, for example a motor 20 , A mains frequency is marked with fN and a machine or motor frequency with fM. Other configurations of the drive system 10 , For example, with twelve-pulse mains power converter, twelve-pulse machine converter, two separate DC buses, optionally with coupled DC chokes, etc. are also conceivable.

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

To explain the on-line calculation of the compensation, the operations in a B6 thyristor bridge are considered as a possible embodiment of a power converter.

The input current space pointer of the B6 bridge can only assume six discrete states ( 5 ). Its length is proportional to the DC link current Id (= 2 / √3 · Id). The projection of the active Current space pointers in the R, S and T axes yield the temporal current profiles in the phases R, S and T. The voltage space vector U1 describes the source voltage system of the network or of 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 on the currently effective current space vector is proportional to the time course of the intermediate circuit voltage Ud. In addition shows 2 the intermediate circuit voltage Ud and the supply currents without commutation, where α is the control angle.

At a 60 ° interval, a defined current path is always effective. This can be a in 3 derived equivalent circuit with source and impedance are derived. As Lk, the commutation inductance is designated there. It is composed of a network inductance and a transformer leakage inductance or corresponds to the stray inductance of the machine. It approximately corresponds to the subtransient leakage inductance of a synchronous machine.

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

In the present pointer image ( 5 ), the DC link current Id commutes from phase R to S. In phase T, the negative DC link current -Id. The commutation takes place in the pointer image on a line between the two active hands, which results from the fact that the current in the phase T remains constant. However, the transition does not occur evenly over time, since the commutation voltage changes during the commutation. The commutation voltage is in the illustrated situation U2-U1 and determines the direction of the commutation. The projection of the voltage space vector on the axis between R and S gives the DC link voltage during the considered commutation process. The height of the DC link voltage during commutation can reach a maximum of √6 / 2 · U_werk, compared to √2 · U_werk outside the commutation.

α:

Steuerwinkel

id:

Zwischenkreisstrom [pu]

ukTr:

Kurzschlussspannung des Transformators [pu]

To calculate the voltage harmonics, an overlap angle u (cf. 6 ), which is as follows: u = acos (cos (α) -id · π · ukTR / 3)

α:

control angle

id:

DC link current [pu]

ukTr:

Short-circuit voltage of the transformer [pu]

The DC component of the DC link voltage results as: Ud0 = Udi · cos (α) -id · π / 6 · ukTr with: Udi = √2 · 3 / π · U_werk = 1.35 · U_werk

und in komplexer Schreibweise als UdN, 6 = UaN, 6 – j UbN, 6 Next z. B. the sixth harmonic of the DC link voltage on the network side (normalized to Udi) as

and in complex notation as UdN, 6 = UaN, 6 - j UbN, 6

In the following, complex quantities are always shown with an underscore, and the conjugate complex quantities are additionally marked with a star at the end.

The harmonic voltages calculated here are reflected in the equivalent circuit diagrams 3 and 4 imprinted in Udq. The voltage determined here is not identical with the voltage at the DC link connections, eg. B. the mains converter, measured voltage. The voltages differ by voltage drops at the commutation inductances. The illustrations in 7 and 8th to show the amplitudes of the voltage harmonics 6 · f1 [pu] or 12 · f1 [pu] relative to Udi = 1.35 · Un depending on the control angle and the overlap angle u.

The DC link current harmonics are generally calculated Id, ν = Ud, ν / Zd, ν .

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 DC link impedance Zd, ν is composed as follows for a DC link converter: Zd, ν = 6 (fN * LkN + fM * LkM) + j * ων * (2 * LkN + Ld + 2 * LkM)

LKN:

Commutation of the network

ld:

intermediate-

LKM:

Commutation inductance of the motor

where the terms 2 · LkN and 2 · LkM are not completely correct, because during commutation the value is 1.5 · LkN or 1.5 · LkM. The calculations refer to the mains converter, but can also be transferred to the machine converter.

9 shows the change of the effective for the DC link harmonic currents Kommutierungsinduktivität Lw (t). The harmonics Lw, ν 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 Ud0, μ = j * 2 * π * fμ * Lw, 0 * Id, μ Udν, μ = ½ · j · 2 · π · fμ · Lw, ν · Id, μ with Lw, 0 = 2 · Lk - 0.5 · Lk · 3 · u / π
with Lw, ν = -0.5 · Lk · 12 / π · sin (ν · u / 2)

The occurring frequencies of this voltage drop are fμ and fν +/- fμ. Thus interharmonic voltage drops occur, for example, via the effective commutation inductance of the mains converter, which are caused by the harmonic currents Id, μ of the machine converter. The same applies to the voltage drops across the effective commutation inductance of the machine converter, the caused by the harmonic currents of the mains converter. These voltage drops in turn generate interharmonic DC link currents with fν +/- fμ.

The calculation of the interharmonic DC link currents and the resulting three-phase power is generally carried out (the interharmonic voltage drops in the line and machine converter must be taken into account) Id, νμ = ( UNd, νμ + UMd, νμ ) / Zd, νμ

The effective DC link impedance Zd, νμ is composed as follows for a current source converter Zd, νμ = 6 (fN * LkN + fM * LkM) + j * (ων +/- ωμ) * (2 * LkN + Ld + 2 * LkM), again, 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 ).

The harmonics in the network power with ideally smoothed DC link current are calculated from the power in the replacement sources. Strictly speaking, this applies only outside of the commutation since the equivalent circuit is not power invariant with respect to the real circuit during commutation. Neglecting this commutation influence, the following applies: PN3ph, μ = Pdq, μ = UdN, μ · Id with fμ = μ · fN, μ = 0, -6, +6, -12, +12, ...

These harmonics in the three-phase power result from the voltage harmonics of the own power converter. However, if the DC link current contains harmonics Idv caused by the machine converter, use: fν = ν · fM with ν = 6, 12, ...
calculate the interharmonics of the network performance: PN3ph, μν, 1 = Pdq, μν = ½ · UdN, μ · Idν * with fμν = ν · fM +/- μ · fN, ν, μ = 6, 12, ...

A further proportion of interharmonic mains power output results from the interharmonic DC link current Id, νμ and the DC link voltage Ud0: PN3ph, νμ, 2 = Ud0 · Id, νμ *

These two components must be added in the correct phase.

The interharmonics in the engine performance can be calculated accordingly.

According to the approach according to the invention, it is now provided that one or more interharmonics of the network or motor pendulum power is compensated by appropriate modulation of the Aussteuergrades one of the two power converters. By compensating for one or more interharmonics of the motor pendulum power, the corresponding interharmonics in the air gap moment of the motor are 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.

For modulation of Aussteuergrades (ast), there are basically two options, namely a compensation by the mains or machine-side converter. In detail:

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

In case 1, a DC link current is impressed which compensates for the interharmonic motor power excursions ( PM3Ph, νμ, 1 + PM3Ph, νμ, 2 ). Idk , νμ = - (PM3Ph, νμ, 1 + PM3Ph, νμ, 2) * / Ud0

The necessary einzuprägende DC link voltage in the power converter is UN k, k = Id νμ, νμ · Zd νμ With Zd, νμ = 6 (fN * LkN + fM * LkM) + j * (ων -ωμ) * (2 * LkN + Ld + 2 * LkM),

In case 4 a DC link current is impressed, which compensates the interharmonic network power surges ( PN3Ph, νμ, 1 + PN3Ph, νμ, 2 ). Id k, νμ = - ( PN3Ph, νμ, 1 * + PN3Ph, νμ, 2 * ) / Ud0 UM k, k = Id νμ, νμ · Zd νμ With Zd, νμ = 6 (fN * LkN + fM * LkM) + j * (ων -ωμ) * (2 * LkN + Ld + 2 * LkM),

In case 2, an additional oscillation of the driving intermediate circuit voltage is generated by the modulation in the motor converter Idk , νμ · Ud0 + Id0 · UMk , νμ = - ( PM3Ph, νμ, 1 + PM3Ph, νμ, 2 ) UM k, νμ / Zd, νμ · Ud0 + Id0 · UM k, νμ = - ( PM3Ph, νμ, 1 + PM3Ph, νμ, 2 ) UM k, νμ = - ( PM3Ph, νμ, 1 + PM3Ph, νμ, 2 ) / (Ud0 / Zd, νμ + Id0)

Likewise, for case 3: UN k, νμ = - ( PN3Ph, νμ, 1 + PN3Ph, νμ, 2 ) / (Ud0 / Zd, νμ + Id0)

From UN k, νμ or UM k, νμ the additional degree of modulation and additional control angle is calculated. The DC link voltage z. B. on the net side, calculated from: UdN, q (t) = √2 · 3 / π · UN_verk · (AST_0 + AST_k · cos (2 · π · fk · t + φ_k)) with fk = fν - fμ,

The amplitude of the component due to the modulation modulation is calculated as follows: UdN_k, νμ = √2 · 3 / π · UN_verk · AST_k

From the above equation, the amplitude AST_k of Aussteuergradmodulation is then calculated.

The same applies to the machine side accordingly.

10 Finally, and as a summary of the previously explained calculation steps, a sequence for calculating the modulation output modulation is shown. The flowchart exemplifies the case 1 where the interharmonic motor shuttle power is compensated with the grid side converter. In general, in the illustration, values which are divided according to amount and phase are represented by absolute values (||) 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 DC link Id 104 either its actual or setpoint, a machine control angle 106 and a network control angle 108 , where usually the network control angle 108 Result of a control is, as well as an effective DC link impedance 110 , In order to 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 DC link impedance 110 in a calculation of the harmonics in the DC link current caused by the machine converter (third function block 116 ) and corresponding to a calculation of the harmonics in the DC link current caused by the mains converter (fourth function block 118 ) one. 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 net 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 mains converter (sixth function block 122 ) one. These results, together with their magnitude and phase, together with the effective DC link impedance 110 used for calculating the interharmonic in the DC link current (seventh function block 124 ). Thus, the calculation of the first portion of the interharmonic engine power can be done (eighth function block 126 ), whereby still a DC component of the DC link voltage 128 is taken into account. The calculation of a second portion of the interharmonic engine power (ninth function block 130 ) takes place on the basis of the harmonics of the DC link voltage on the machine side as well as the harmonics in the DC link current caused by the mains converter. The results are added by amount and phase (tenth function block 132 ) and then with the quotient 134 from the effective DC link impedance 110 and the DC component of the DC link voltage 128 multiplied (eleventh function block 136 ). The result is the magnitude and phase of an intermediate circuit voltage oscillation to be modulated in the power converter, which is divided into an output and output modulation modulation 138 is converted, ie the modulation frequency fk and the modulation phase angle φ_k for the input introduced relationship to the modulation of Aussteuergrades: ast (t) = ast_0 + ast_k * cos (2 * π * fk * t + φ_k).

The stored mathematical relationship according to the terminology used here is the modulation of the modulation rate shown again above, and in addition the in 10 combined calculation steps according to the preceding embodiments.

It should be noted that apart from the results of the fifth and sixth functional block 120 . 122 whose calculations are based on the assumption of a negligible commutation, all other calculations can be performed quite accurately.

The alternative embodiment of the approach according to the invention, which is based on off-line compensation prediction, benefits from the recognition that compensation must be made only at critical engine frequencies resulting from the Campbell diagram of the drive. On the basis of this, it is proposed to store the necessary modulation amplitudes and phase angles, ie values for the modulation frequency fk and the modulation phase angle φ_k for the initially introduced relationship for the modulation of the modulation rate, in at least one table or an otherwise suitable data structure. The values can also be determined by means of a simulation because such a simulation emulates very well the commutation effects which have to be calculated analytically. Due to the offline pre-calculation, only a negligible calculation time load results at runtime.

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

The considered operating points result in each case from the Campell diagram. The following temporal and operational dependencies of the modulation amplitude and phase of:

• - mains voltage
• - Network short-circuit power
• - Mains frequency
• - Machine flow
• - Motor frequency
• - Machine power
• - Control angle of the machine converter
• - Control angle of the mains converter

Of these dependencies, some are considered to be constant at each operating point. This includes the short-circuit power, the line frequency, since it has only a small tolerance, and the machine frequency, since the compensation is effective only in a narrow frequency range. The sizes described are not all independent of each other, eg. B. results in the mains voltage from all other sizes. Because of the independence of the remaining sizes must be an n-dimensional table. The number of table elements depends on the possible range of variation of the individual sizes.

Then a multidimensional table is formed with all non-constant, independent variables, in particular the network control angle and the machine control angle. In operation, the modulation level is varied by the average modulation rate on the basis of the data stored in this table. The data was outside a runtime of the drive unit 10 determined and a value for the actual variation results at runtime of the drive unit 10 by accessing at least one date stored in this table. Intermediate values can be determined by interpolation in a manner known per se.

At runtime of the drive system 10 It is readily possible to quickly access 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.

Both proposed approaches each relate to a machine- and engine-specific voltage vector and their phase, so that the difference of these pointers forms the reference system to which the modulation refers.

The or each table or implementation of the in 10 Calculation schemes shown in a memory 26 ( 1 ) of the control device 22 ( 1 ) and stored the table essentially as data 30 for the control program 28 and the calculation scheme essentially as a software implementation of the computation steps involved, ie as part of the control program 28 , The processing unit 24 , the memory 26 , as well as the control program 28 and / or the data 30 are thereby means for carrying out the method.

In summary, a central aspect of the description presented here can be briefly summarized as follows: It is a method for operating a drive unit 10 with an input or mains side converter 12 and an output or machine side power converter 14 and an intermediate circuit between them 16 indicated, with an average active power in the DC link 16 from a modulation level of the mains or machine-side converter 12 . 14 is dependent, in which the Aussteuergrad is varied by a predetermined or predeterminable average Aussteuergrad and in which by the variation of Aussteuergrads the intermediate circuit 16 an alternating power is impressed, so that the impressed alternating power results in a compensation of unwanted interharmonics.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1875597 [0005]

Claims (7)

Method for operating a drive unit ( 10 ) with an input or power converter ( 12 ) and an output or machine-side converter ( 14 ) and an intermediate circuit ( 16 ), where an average active power in the DC link ( 16 ) of an output level of the mains or machine-side converter ( 12 . 14 ), characterized in that the Aussteuergrad is varied by a predetermined or predeterminable average Aussteuergrad and that by the variation of Aussteuergrads the intermediate circuit ( 16 ) an alternating power is impressed. Method according to claim 1, wherein the variation of the modulation rate by the average modulation degree due to a control device ( 22 ) of the drive unit ( 10 ), wherein a value for the actual variation at runtime of the drive unit ( 10 ) and wherein the mathematical relationship is determined by one or more coefficients which, with regard to a possible low-frequency torque excitation, are determined by one of the drive unit (s). 10 ) driven or drivable machine ( 20 ). The method of claim 2, wherein the mathematical relationship causes a periodically alternating variation of the Aussteuergrads about the average Aussteuergrad. Method according to claim 1, wherein the variation of the modulation rate by the average modulation degree due to in a control device ( 22 ) of the drive unit ( 10 stored data, whereby the data is stored outside of a run time of the drive unit ( 10 ) and wherein a value for the actual variation at runtime of the drive unit ( 10 ) based on an access to at least one stored date. Computer program with program code means for carrying out all the steps of any one of claims 1 to 4, when the program is stored on a control device ( 22 ) for a drive unit ( 10 ) is performed. Digital storage medium with electronically readable control signals, which can be used with a control device ( 22 ) for a drive unit ( 10 ) can cooperate, that a method according to any one of claims 1 to 4 is carried out. Drive unit ( 10 ) with an input or power converter ( 12 ) and an output or machine-side converter ( 14 ) and an intermediate circuit ( 16 ), where an average active power in the DC link ( 16 ) of an output level of the mains or machine-side converter ( 12 . 14 ) and with a control device ( 22 ) with a memory ( 26 ) in which a computer program according to claim 5 is loaded.

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