Title of Invention

A METHOD AND OF AN APPARATUS FOR DIRECT TORQUE CONTROL OF PHASE MACHINE

Abstract

The present invention provides A method for direct torque control of a three-phase machine (1) which is fed from a multi-phase converter (2) through a harmonic filter (Lfi, Cfi) connected in between, which method comprises the following steps: (a) Calculation of an actual flux value yra,t from a converter output voltage ui,,,, and a correction variable which corresponds essentially to a voltage drop across a copper resistance of the stator of the three-phase machine; (b) Calculation of an actual torque value Tact from a current ii,,,, emitted by the converter and from the actual flux value Vract; (c) Comparison of the magnitude of the actual flux value yract and of the actual torque value Tact by means of a hysteresis controller (4) using a reference torque value Tref or a reference flux value yrref ; (d) Formation of an optimum control vector S (SA, SB, Sc) for the converter governed by the hysteresis controller (4) and the magnitude of the actual flux value Watt ; wherein (e) a current ift flowing through the filter and/or a filter output voltage uf1 are/is measured and (f) the reference flux value Wref and the reference torque value Tref before they are supplied to the hysteresis controller (4) are corrected on the basis of the current ifi flowing through the filter and/or on the basis of the filter output voltage ufi.

Full Text

The invention relates to a method and an apparatus for direct torque control of a three-phase machine. Discussion of Background Such a method and a corresponding apparatus are described in the article "Direkte Drehmomentregelung yon Drehstromantrieben" (Direct torque control of three-phase drives), ABB Technik 3/1995, pages 19-24. This method is based on so-called "direct self-control", as is described in EP-B1-0 179 356. The DTC method represents a simple, reliable and highly dynamic torque control method for three-phase machines. In principle, it comprises the following steps: Calculation of an actual flux value from a converter voltage Calculation of an actual torque value Comparison of the actual flux value and the actual torque value with corresponding reference values by means of a hysteresis controller. Formation of an optimum control vector for the switches in the converter on the basis of the hysteresis controller. In order to protect the machine against excessively steep voltage flanks, which may lead to damage to the insulations, it is desirable to connect a harmonic filter between the converter and the motor. A control method is specified, for example, in EP-A2-0 595 319 for a system of pulse-duration-modulated converters with a harmonic filter. The filter fl.G/03 9 capacitance ana tne niter inductance represent two integrators in control engineering terms. There is thus a 18 0° phase shift between the motor voltage and the converter voltage at the switching frequency, in the frequency band. This means that the signals required for the DTC method are present with an incorrect mathematical sign. Because of the 180° phase shift, caused by the harmonic filter, between the motor voltage and the converter voltage, the known DTC method can no longer be applied directly to an arrangement with a harmonic filter. In addition, disturbing oscillations occur because of the filter resonance. SUMMARY OF THE INVENTION Accordingly, one object of the invention is to provide a novel method and apparatus for direct torque control for a three-phase machine fed via a harmonic filter, which method manages as far as possible without major adaptation to already known methods and apparatuses. In addition, the oscillations caused by the filter are intended to be damped effectively. This object is achieved by the features of the first claim for a method of the type mentioned initially. The essence of the invention is thus that a current flowing through the filter and/or a filter output voltage are/is measured, and the reference flux value and the reference torque value are corrected on the basis of the measured voltage and/or of the measured current. The correction comprises a transformation of the filter output voltage into a first component at right angles to a stator flux and into a second component parallel to the stator flux as well as a reduction in the reference torque and flux values in proportion to the oscillating part of the filter output voltage. The oscillations caused by the harmonic filter can be effectively damped in this way. The components can be calculated in various ways. Instead of a filter output voltage, a filter current can also be measured, and a filter voltage can be calculated from this. These variants are the subject matter of dependent claims. In addition, an apparatus for carrying out a method according to the invention is also specified. Other exemplary embodiments result from the corresponding dependent claims. The advantage of the design according to the invention is that the three-phase machine can be protected by the use of a harmonic filter against excessively steep voltage flanks which can lead to damage to the insulation, and, nevertheless, that essential parts of the DTC method and of a corresponding apparatus can be used without any major change. In addition, oscillations caused by the filter can be damped effectively. Accordingly the present invention provides A method for direct torque control of a three-phase machine (1) which is fed from a multi-phase converter (2) through a harmonic filter (Lffl, Cfl]) connected in between, which method comprises the following steps: (a) Calculation of an actual flux value x^ from a converter output voltage uinv and a correction variable which corresponds essentially to a voltage drop across a copper resistance of the stator of the three-phase machine; (b) Calculation of an actual torque value Tact from a current ijnv emitted by the converter and from the actual flux value v^; (c) Comparison of the magnitude of the actual flux value \|/act and of the actual torque value Tact by means of a hysteresis controller (4) using a reference torque value Tref or a reference flux value \|/ref ; (d) Formation of an optimum control vector S_(SA, SB, Sc) for the converter governed by the hysteresis controller (4) and the magnitude of the actual flux value v|/act; wherein (e) a current if,i flowing through the filter and/or a filter output voltage u^ are/is measured and (f) the reference flux value \|/ref and the reference torque value Tref before they are supplied to the hysteresis controller (4) are corrected on the basis of the current igj flowing through the filter and/or on the basis of the filter output voltage u^. -4- Accordingly the present invention also provides an apparatus for direct torque control of a three-phase machine (1) which is fed from a multi-phase converter (2) through a harmonic filter (Lffl, Cfii) connected in between, comprising: (a) a torque controller (2), which calculates an actual flux value \j/aCt from a converter output voltage uinv and a correction variable which corresponds essentially to a voltage drop across a copper resistance of the stator of the three-phase machine; calculates an actual torque value Tact from a current iinv emitted by the converter (2) and by the actual flux value \j^ct; compares the magnitude of the actual flux value \|/act; and the actual torque value Tact by means of a hysteresis controller (4) with an externally predetermined reference torque value Tref and, respectively, a reference flux value i^ and forms an optimum control vector S (SA, SB, Sc) for the converter (2) governed by the hysteresis controller (4) and the actual flux value v|jract; wherein (b) current and voltage instruments are provided which measure a current if,i flowing through the filter and/or a filter output voltage u^, and (c) means are provided which correct the reference flux value \|/ref and the reference torque value Tref before they are supplied to the hysteresis controller on the basis of the current i^ flowing through the filter and/or the filter output voltage u^. BRIEF DESCRIPTION OF THE DRAWINGS A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: FIG. 1 shows a circuit arrangement with a three-phase machine fed from a converter via a harmonic filter; FIG. 2 shows a variant of FIG. 1; Fig. 3 shows a block diagram of an apparatus according to the invention, based on a first exemplary embodiment ; Fig. 4 shows a block diagram of an apparatus according to the invention, based on a second exemplary embodiment; Fig. 5 shows a block diagram of an apparatus according to the invention, based on a third exemplary embodiment; Fig. 6 shows a block diagram of an apparatus according to the invention, based on a fourth exemplary embodiment; Fig. 7 shows a block diagram of an apparatus according to the invention, based on a fifth exemplary embodiment. The designations used in the drawings and their meanings are listed in summary form in the List of Designations. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts through the several views used, Figure 1 shows a circuit arrangement with a three-phase machine 1 which is fed from a converter 2 via a harmonic filter comprising a three-phase network with filter inductances Lf-Q and filter capacitances Cfj_]_. The capacitances of the filter are combined to form a star point, which is not connected to the intermediate circuit. The intermediate circuit is represented by the intermediate-circuit capacitor C^. A DC voltage U^c is applied to the intermediate-circuit capacitor. A torque controller 3 is provided for torque control of the notor 1. This is fed, according to Figure 1, from the intermediate-circuit voltage UDC, from a current iinv smitted by the converter, and from a filter output voltage Uf -Q . In the variant according to Figure 2, a filter current ifn may also be measured instead of the filter output voltage Ufn- The converter 2 may be either a two-point invertor or a three-point invertor. Underlined variables in each case designate vectors in the following text. These may be transformed into vectors from the measured conductor currents or conductor voltages in the phases, using the known 120°/90° transformation. The torque controller 3 uses the measured variables as well as a reference flux value vj/ref and a reference torque value Tref to calculate an optimum control vector S{SJ^,S-Q,SQ) which is used for driving the switches in the converter 2. Figures 3-7 show block diagrams of various variants of torque controllers 3. That part of the regulator which is above the dashed line corresponds to the already known DTC controllers. The lower part comprises the adaptations according to the invention. In the following text, the fundamental principle of DTC control will be discussed briefly once again, and the problems on which the invention is based will be explained: In the DTC method, an actual flux value vj£act is calculated from a converter output voltage ulnv an The actual flux value is thus given by: ^act = uj_nv - Rsi.s)dt. The converter output voltage u-j_nv is in this case formed with the aid of a voltage forming element 8 from the intermediate-circuit voltage U-QQ and the actual control vector £!. An actual torque value Tact is subsequently formed from the calculated actual flux value vi/act and a current iinv emitted by the converter. The current iinv is obtained by measuring two phase currents and by transformation into a vector. The actual torque value Tact is obtained, finally, by forming the vector product of the current iinv and of the flux iHact • In addition, the magnitude Vact °f tne actual flux value }£act is also formed. Tact and v|/act are subsequently compared, by means of a hysteresis controller 4, with corresponding externally predetermined reference values Vref and Tref. The result of this comparison and the result of a vector assigner 12, which uses the actual flux value vj£act to determine an actual flux vector, are supplied to a logic circuit 13 which determines an optimum control vector S(S^,SB,SC) for the converter. However, if a harmonic filter is now connected between the converter and the motor as in the case of the invention, then, on the one hand, there is a 180° phase shift in the current and voltage at the switching frequency because of the double integration of the filter, so that the DTC method can no longer be applied directly. On the other hand, the filter causes resonant oscillations, which are intended to be damped. The known method and the known apparatus must therefore be adapted, as is described in the following text. The adaptation essentially comprises a current flowing through the filter and/or a filter output voltage being measured, and the reference flux value, or its magnitude, and the reference torque value being corrected on the basis of the measured filter variables. In particular, they are reduced in proportion to an oscillating part of the filter output voltage. There are various variants for calculating these oscillating disturbance variables: A first exemplary embodiment (Figure 3) comprises measurement of the filter output voltage on each phase and conversion, for example by means of addition, the product iinvLfil is subtracted from the actual flux value vj/act • A multiplier 5 and a subtractor 7 are provided for this purpose. In this way, a variable \gs is obtained, which corresponds to a stator flux. The voltage Uf±± is now split into a component ufild parallel to vus and into a component Uf-Qg at right angles to ij/s. A vector product forming element 9 and a scalar product forming element 10 are provided for this purpose, which multiply the voltage Ufa by v|is. The component uf iig is produced from the vector product, and the component uf-Qd from the scalar product. Ufiid represents just that proportion of the filter output voltage causing the oscillations and is therefore multiplied in a further multiplier 5 by the constant K^, is supplied to a limiter 6 and is subtracted from the reference flux value Mref i-n a subtractor 7. The oscillating part of Ufiiq must also be formed, in contrast. This is done according to Figure 3 by subtracting a constant value &-^Ls from ufilq- m ^n this case corresponds to the angular frequency of the stator flux. In the steady state, ufilq should correspond precisely to this value, so that the difference ufiiq=tu-vj/s thus corresponds just to the oscillating part Auf-Qg of Ufiig. This value is likewise multiplied in a multiplier 5 by a second constant K2, and is supplied to a limiter 6. Finally, the reference torque value is reduced by means of a further subtractor 7, using the output of this limiter 6. The essence of the method and of the apparatus according to the invention is thus based on the fact that the influence of the harmonic filter is included in the control system, in that those elements of the filter output voltage which cause the oscillations are first of all damped and a virtual converter flux and a converter moment, so to speak, are controlled as actual variables instead of directly controlling variables 915/030-which correspond to the " motor flux or motor moment upstream of the filter. A second exemplary embodiment (Figure 4) differs from the first in that the oscillating parts of the components ufii^ and Ufiiq are obtained by means of high-pass filtering. Two high-pass filters are provided for this purpose and are connected upstream of the multipliers 5, after the vector and scalar product formation 9, 10. In the case of a third exemplary embodiment (Figure 5) , a filter current ifii is measured instead of a filter output voltage ufii. Figure 5 is thus based on Figure 2. ifii is obtained, for example, by measuring two currents flowing through the filter capacitors Cfj_]_, and by converting these currents into a vector. Two currents are sufficient, since the sum of all the currents must be zero because of the star connection of the capacitors. The voltage Uf-Q across the capacitor can be calculated from the current ifii by means of limited integration. A limited integrator 15 is provided for this reason in Figure 5 at the input of ifii- Otherwise, the arrangement in Figure 5 corresponds to that in Figure 4. The variant according to Figure 3 can, of course, also be applied to the third exemplary embodiment. According to a fourth exemplary embodiment (Figure 6) , the integration can also be carried out after the scalar and vector product formation. Finally, Figure 7 shows an exemplary_ embodiment based on Figure 2, in which the integration for the component formation is carried out, on the one hand, before the scalar product formation 10 and, on the other hand, after the vector product formation 9. Since the current ifii should be parallel to ms from the start, the remaining part of a vector produc-represents just the element causing oscillations. The situation with the scalar product is the converse of this, since the voltage multiplied by the ms should result in zero here. For this reason, the voltage is calculated first for the scalar product formation, and not until after this for the vector product formation. The invention has the advantage that the known DTC method and the known DTC apparatus can also continue to be used essentially for an arrangement having a harmonic filter. The invention makes available an addition which is suitable for use with a harmonic filter and leaves the known part virtually undisturbed. An existing system can therefore be extended in a simple manner without having to dispense with the advantages of a harmonic filter. Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein. WE CLAIM: 1. A method for direct torque control of a three-phase machine (1) which is fed from a multi-phase converter (2) through a harmonic filter (Lfi], C^) connected in between, which method comprises the following steps: (a) Calculation of an actual flux value vj/act from a converter output voltage uinv and a correction variable which corresponds essentially to a voltage drop across a copper resistance of the stator of the three-phase machine; (b) Calculation of an actual torque value Tact from a current ijnv emitted by the converter and from the actual flux value \j/aCt; (c) Comparison of the magnitude of the actual flux value \|/act and of the actual torque value Tact by means of a hysteresis controller (4) using a reference torque value Tref or a reference flux value \|/ref ; (d) Formation of an optimum control vector S_(SA, SB, SC) for the converter governed by the hysteresis controller (4) and the magnitude of the actual flux value Yact ; wherein (e) a current im flowing through the filter and/or a filter output voltage Ufii are/is measured and (f) the reference flux value v|/ref and the reference torque value Tref before they are supplied to the hysteresis controller (4) are corrected on the basis of the current ifj flowing through the filter and/or on the basis of the filter output voltage Uffl. 2. The method as claimed in claim 1, wherein the reference flux value \j/ref and the reference torque value Tref are corrected in that: (a) a stator flux v^ is formed from a difference between the actual flux value v^ct and a product of the current ijnv emitted by the converter with an inductance L^ of the harmonic filter; (b) the stator flux \& is used to convert the filter output voltage u^ into a component uf,id parallel to the stator flux and into a component Ufiiq at right angles to the stator flux; (c) the reference flux value \(/ref is reduced by an amount proportional to the component UfiW, and the reference torque value Tref is reduced in proportion to an oscillating element Auqfii of the component Ufjiq. 3. The method as claimed in claim 2, wherein the oscillating element Aufflq of the component Ufiiq is produced from a difference between the component ufflq and the product tn"V|jfs of the stator flux vj/g and an angular frequency TO of the stator flux v^. 4. The method as claimed in claim 2, wherein the oscillating element Aufj]q of the component ufilq is produced by high-pass filtering of component ufflq" 5. The method as claimed in claim 4, wherein the component ufiid is also subjected to high-pass filtering. 6. The method as claimed in any one of claims 3 to 5, wherein (a) the current igi flowing through the filter is measured and (b) the filter output voltage u^ is produced by integration of the current ifa. 7. The method as claimed in any one of claims 2 to 6, wherein the filter output voltage Ufa is converted into the component Uflid parallel to the stator flux, and the component Uf,iq at right angles to the stator flux xj/g is converted by formation of the scalar product and vector product of uji and the stator flux vj/g. 8. An apparatus for direct torque control of a three-phase machine (1) which is fed from a multi-phase converter (2) through a harmonic filter (Lf,i, Cf,i) connected in between, comprising: (a) a torque controller (2), which calculates an actual flux value vj/act from a converter output voltage utav and a correction variable which corresponds essentially to a voltage drop across a copper resistance of the stator of the three-phase machine; calculates an actual torque value Tact from a current iinv emitted by the converter (2) and by the actual flux value v^; compares the magnitude of the actual flux value \|/act; and the actual torque value Tact by means of a hysteresis controller (4) with an externally predetermined reference torque value Tref and, respectively, a reference flux value \£.ef and forms an optimum control vector S (SA, SB, SC) for the converter (2) governed by the hysteresis controller (4) and the actual flux value \j^ct; wherein (b) current and voltage instruments are provided which measure a current iffl flowing through the filter and/or a filter output voltage UJH, and (c) means are provided which correct the reference flux value n/ref and the reference torque value Tref before they are supplied to the hysteresis controller on the basis of the current im flowing through the filter and/or the filter output voltage u^. -14- 9. The apparatus as claimed in claim 8, wherein the second means comprises: (a) a first multiplier (5) for forming a product of the current iinv emitted by the converter with an inductance Lf,i of the harmonic filter; (b) a first subtracter (7) which calculates a stator flux \j/s from a difference between the actual flux value \j/aCt and the product of the current ijnv emitted by the converter with the inductance Lfii of the harmonic filter; (c) a coordinate transformer (9, 10), which uses the stator flux vj/g to convert the filter output voltage u^ into a component ufiM parallel to the stator flux and a component Uf,iq at right angles to the stator flux; and (d) a reference value controller which reduces the reference flux value v£.ef by an amount proportional to the component Uf,id and reduces the reference torque value Tref in proportion to an oscillating element Auqfii of the component Uf,iq. 10. The apparatus as claimed in claim 9, wherein, both for the component Uf,id and for the component Ufnq, the reference value controller comprises in each case one multiplier (5) which multiplies the components by a first constant Kl or, respectively, by a second constant K2, in each case one limiter (6) connected downstream of the multipliers, and in each case one subtracter (7) connected downstream of the limiters (6), the subtracter assigned to the component uflM acting on the reference flux value v|/ref, and the subtracter assigned to the component Ufiiq acting on the reference torque value Tref. 11. A method for direct torque control of a three-phase machine substantially as herein described with reference to figures 3 to 7 of accompanying drawings. 12. An apparatus for direct torque control of a three-phase machine substantially as herein described with reference to figures 3 to 7 of accompanying drawings.

Documents:

0625-mas-97 abstract-duplicate.pdf

0625-mas-97 abstract.pdf

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0625-mas-97 claims-duplicate.pdf

0625-mas-97 claims.pdf

0625-mas-97 correspondence-others.pdf

0625-mas-97 correspondence-po.pdf

0625-mas-97 description (complete)-duplicate.pdf

0625-mas-97 description (complete).pdf

0625-mas-97 drawings-duplicate.pdf

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0625-mas-97 form-26.pdf

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0625-mas-97 others.pdf

0625-mas-97 petition.pdf