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CA1304775C - Method and apparatus for the digital determination of the field angle of a rotating-field machine - Google Patents

Method and apparatus for the digital determination of the field angle of a rotating-field machine

Info

Publication number
CA1304775C
CA1304775C CA000566352A CA566352A CA1304775C CA 1304775 C CA1304775 C CA 1304775C CA 000566352 A CA000566352 A CA 000566352A CA 566352 A CA566352 A CA 566352A CA 1304775 C CA1304775 C CA 1304775C
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CA
Canada
Prior art keywords
value
stator
angle
vector
frequency
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
CA000566352A
Other languages
French (fr)
Inventor
Leonhard Reng
Thomas Schlegel
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Siemens AG
Original Assignee
Siemens AG
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Filing date
Publication date
Application filed by Siemens AG filed Critical Siemens AG
Application granted granted Critical
Publication of CA1304775C publication Critical patent/CA1304775C/en
Anticipated expiration legal-status Critical
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Classifications

    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02PCONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P21/00Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation
    • H02P21/14Estimation or adaptation of machine parameters, e.g. flux, current or voltage
    • H02P21/141Flux estimation
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02PCONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P21/00Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation
    • H02P21/06Rotor flux based control involving the use of rotor position or rotor speed sensors
    • H02P21/10Direct field-oriented control; Rotor flux feed-back control

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Control Of Ac Motors In General (AREA)
  • Control Of Eletrric Generators (AREA)
  • Measuring Magnetic Variables (AREA)

Abstract

ABSTRACT OF THE DISCLOSURE
An angle is calculated with high time resolution for the field angle of a rotating-field machine in order to control the rotating-field machine. Due to the inertia of the system, the speed of rotation of the field vector changes slowly. A
microprocessor reads the measured values of current and voltage only at a slow rate (tµ). The values are processed into the components of an EMF vector which is converted as to magnitude (?) and a discontinuously changing value (.omega.) for the frequency of a flux vector or the EMF vector. A hardware integrator (INT1) is coupled to the microcomputer and furnishes a quasi-continuously changing signal (?) for the field angle at a high computing rate under the control of the discontinuously changing value (.omega.) of the flux vector.

Description

~304775 METHOD AND APPARATUS FOR THE DIGITAL DETERMINATION OF THE FIELD
ANGLE OF A ROTATING-FIELD MACHINE
3 Field of the Invention 4 This invention relates to a method for determining an instantaneous field angle of a rotating field machine by 6 computing an electromotive force vector (EMF vector) from 7 values of the current and voltage of the stator of the machine, 8 and by means of integration of the EMF vector.

Related Art 12 In the interior of a rotating field machine (either a 1~ synchronous machine or an asynchronous machine) negative 14 feedback of the field angle takes place in accordance with its physical structure. In such a case the field of the machine, 16 in the steady-state situation, is proportional to the component 17 of the stator current vector that is parallel to the field.
18 The torque (which is physically: the vector product of the 19 field vector and the current vector) with a constant field is proportional to the component o' the stator current vector that 21 is perpendicular to the field. The individual winding currents 22 of the stator, the amplitude, frequency and phase of which can 2~ be impressed on the windings by a converter, can therefore be 2~ thought of as projections of a stator current vector given in a stator-oriented coordinate system. The field-oriented vector 26 components which define the field and the torque may be 27 generated from these projections through a transformation. If 28 the input variables of the converter are therefore computed 29 from a field-oriented reference vector for the machine currents and if this field-oriented reference vector is transformed into ,~

13047qS

1 the stator oriented coordinate system by a suitable 2 transformation, which represents a positive feedback with the 3 angle of the field vector with respect to the stator (i.e., the 4 "field angle"), a highly dynamic control of the torque and the flux can be achieved. It is beneficial to be able to determine 6 the field angle.
7 Such a control is described, for instance, in 8 "Siemens Forschungs-und Entwicklungsberichte 3", 1974, pages 9 327 to 332 where it is stated that the field angle is, in a first approximation, the angle of the stator voltage vector 11 phase-shifted by 90.
12 In "msr", I8 ap (1975), no. 12, pages 278 to 280, a 13 number of further methods for determining the field angle are 14 given. Unless Hall probes for directly measuring the field are used, machine models are used which compute the field angle 16 using physical equations and different measured variables.
17 Computing inaccuracies, as well as an incorrect setting of the 18 machine parameters in the computing model, however, may lead to 19 inaccurate calculated values of the field using the model. For different operating states, different machine models may be 21 more advantageous.
22 In the meantime, still further machine models, as 23 well as combinations of models, have been proposed. Thus, it 24 has been proposed in DE-OS 30 34 252 (U.S. Patent No.
4,447,787) to use an EMF detector which computes the EMF vector 26 from measured values of the stator current and the stator 27 voltage. In the steady state case, the magnitude of the flux 28 is proportional to the quotient of the magnitude and the 29 frequency of the EMF vector. In this case the direction of the EMF vector with respect to the direction of the field is phase 1 shifted by go. A more exact determination of the field in the 2 dynamic case is obtained by integrating the EMF vector.
3 However, the flux vector can also, in ways different from the 4 current and the rotor position, simulate the field excitation in the rotor. Since, for both flux vectors to agree, the 6 machine parameters (which for the EMF calculation are: the 7 stator resistance and the stray inductance) must be consistent, 8 it is proposed to form a control deviation from the deviation 9 of the two flux vectors calculated in the machine model (or EMF
vectors). This control deviation is leveled out by a 11 correction control. This correction control is accomplished by 12 correcting corresponding machine parameters with a correction-13 control output signal.
14 Such a balancing model furnishing the field angle requires a feedback loop which further requires a complex 16 structure and time consuming controls. This is troublesome, 17 particularly if AC variables are to be processed and leveled 18 out.
19 A particular problem is raised here by the presence of DC components in the measured actual value. Thus, for 21 instance, the measured values of current and voltage can have 22 DC components due to the inaccuracies of measuring 23 transformers, so that the EMF vector formed by the voltage 2~ vector which is itself derived after subtracting the ohmic and inductive voltage drops, is no longer, in the steady state 26 case, a vector with constant magnitude. If the stator oriented 27 components of the field vector are calculated by integration 28 from the corresponding EMF components, offset errors and other 29 computing errors of the integrators that are used can lead to further errors which are continuously further integrated. As a 1 result the model no longer operates in a stable state.
2 From DE-OS 34 18 573 (U.S. Patent No. ~,629,961), a 3 method is known in which, on the one hand, DC components in the 4 measurement errors are suppressed through a "weak" smoothing ~i.e., smoothing with a time constant which is large as 6 compared to the periods of the measurement value), but on the 7 other hand, are also corrected by a correction signal which is 8 ~ derived from a "volatile variable". This "volatile variable"
9 is a physical characteristic of the machine which assumes the value zero in the steady state. The model value for the 11 "volatile variable" is also calculated in the machine model 12 which is incorrect if the value calculated deviates from the 13 value zero. This non-zero model value determines the magnitude 14 of a correction vector. The direction of this correction vector i5 determined by shifting the incorrectly determined 16 model flux vector by a preset angle. .~s a rule, at least the 17 component of the model vector perpendicular to the incorrect 18 model value vector deviates from zero. The vectorial addition 19 of the correction vector to the EMF vector therefore requires at least one addition point for the addition of this component.
21 The integration of the stator-oriented components of 22 the EMF vector requires two AC voltage integrators which, when 23 implemented with a digital microcomputer, have only limited 24 resolution. In DE-OS 34 18 640 (U.S. Patent No. 4,626,761) it is proposed to transform the EMF vector, by means of a vector 26 rotator, into a rotating coordinate system and to subsequently 27 integrate the transformed vector. In the integration of a 28 vector in a rotating coordinate system, a rotary component must 29 be taken into account so that the transformed EMF components are composed with the mentioned correction signal and with the 13047~5 1 rotary component to form the input vector of a suitable 2 integration circuit. If the rotating coordinate system is 3 coupled to the field vector with rigid phases, the magnitude of 4 the actual field vector is always identical with its field-parallel component and the orthogonal component perpendicular 6 to the field has the value zero. Therefore, the corresponding 7 orthogonal component of the integrated vector is fed at the 8 output of the integration circuit to a zero-point controller.
9 The output signal of the zero-point controller represents the frequency of rotation of the coordinate system which, after a 11 further integration, supplies the transformation angle for the 12 vector rotator.
13 The corresponding circuit thus contains an additional 1~ control loop for forming the transformation angle, hut the frequency of rotation as well as the transformed components of 16 the EMF vector, the correction signal and the rotary EMF
17 components are now DC signals which are easier to integrate in 18 the microprocessor.
19 In DE-OS 34 18 641 (U.S. Patent No. 4,593,240) a circuit for the integration of the EMF vector is described 21 which likewise transforms the EMF vector (after suppression of 22 DC components) by means of a vector rotator into a rotating 23 coordinate system. The system of this reference is complicated 2~ in that the formation of the flux vector is performed with a total of two integrators and without a rotary EMF component and 26 without a control "transformation angle". Rather, according to 27 this system the magnitude of a field vector is formed through 28 the integration of the one transformed and corrected EMF
29 component. A divider furnishes, from the quotient of the other EMF component and the field vector magnitude, the field 130477~i 1 frequency. The second integrator determines the transformation 2 angle from the field frequency. The transformation angle then 3 corresponds to the field angle and the transformation frequency 4 corresponds to the field frequency.
A field angle determined in one of the above manners 6 is required for the phase control of the stator current in 7 order to assure the timely firing of the valves of a feeding 8 converter as a function of the field angle. Therefore, a 9 suitable device for determining the field must make available the instantaneous field angle as a steady-state or at least 11 quasi-steady actual value with high resolution (if possible, 12 only fractions of a degree). on the other hand, frequencies of 13 the winding currents, as required in many applications, can be 14 as high as 100 Hz. This requires that the instantaneous field angle must be read at a field determination device with a clock 16 frequency that is so high that a digital determination of the 17 field angle does not seem to be realizable.

21 The present invention overcomes the difficulty 22 associated with applying a field angle to a phase control for 23 the stator current of a machine as described above. The 24 present invention selects from the multiplicity of known field angle determinations, a method suitable in view of digitizing 26 with high time resolution, and carries out this method with a 27 computing effort as simple as possible and with a suitable 28 choice of the interfaces between required computer building 29 blocks.
This problem is solved by a method for determining an 130~5 1 instantaneous field angle of a rotating-field machine in which 2 values for a current and voltage of the stator of the machine 3 are measured and a value for the frequency of the EMF vector is 4 calculated. This frequency value changes discontinuously at a slow rate.
6 A quasi-continuous angle signal for the field angle 7 is read from an integrator controlled by the discontinuously 8 changing value at a rate which is faster than the slow rate.
9 The method of the present invention may further include the steps of producing the magnitude of the EMF vector 11 and transforming the magnitude by division with the 12 discontinuous value of the frequency into a computed value for 13 the magnitude of the flux.
14 The calculation of the value of the frequency changing discontinuously is done by digitally differentiating a 16 direction angle of the EMF vector to form a value and 17 correcting deviations in this value by using a correction 18 signal, said correction signal which is produced by leveling a 19 deviation of the quasi-continuous angle signal from the direction angle with a time constant greater than the frequency 21 of rate. The value of frequency may be subsequently smoothed.
22 The step of measuring may include the step of 23 sampling the current and the voltage of the stator of the 24 machine to synchronously produce the EMF vector.
The method may further include calculating the EMF
26 vector in Cartesian coordinates, filtering out DC components of 27 the EMF vector, and calculating the frequency of the EMF vector 28 from the filtered components of the EMF vector.
29 The problem is also solved by a method for determining the instantaneous field angle of a rotating field 1 machine by calculating the EMF vector from values for the 2 stator current and the stator voltage of the machine, in which 3 the values for the stator current and the stator voltage and as 4 well as a fed-back value for the field angle are read into a calculation circuit at a slow rate and, stator-related 6 components of the EMF vector from the values for the stator 7 current and stator voltage and fed-back value are calculated.
8 In addition the components of said EMF vector are integrated 9 and a value for the frequency of said integrated EMF vector components is calculated, said value for the frequency changing 11 continuously the slow rate. The changing values for the 12 frequency are integrated by means of an integration circuit to 13 form an angle signal representing the field angle, and the said 1~ angle signal changes at a rate which is faster than the slow lS rate of reading in. The angle signal is used as the value for 16 the instantaneous field angle and also as a fed-back value for 17 the field angle.
18 A device suitable for this invention is a digital 19 device for determining a flux angle of a rotating field machine that includes a clock frequency transmitter and a 21 microprocessor that receives an output signal of the 22 transmitter as an input along with digital values representing 23 current and voltage. The microprocessor reads in the inputs at 2~ a slow rate and calculates a digital value for the frequency of the EMF vector and provides this calculation result as an 26 output. An integrator, external to the microprocessor has as 27 its input the output of the microprocessor. The integrator 28 calculates a quasi-continuous value for the field angle. An 29 additional clock transmitter controls the integrator to read out the field angle at a rate faster than the slow rate at which inputs are read into the microprocessor.
Another digital device for carrying out the inven-tion includes a clock frequency transmitter and a micro-processor which reads in digital values representative of stator current and voltage at a rate governed by the transmitter.
The microprocessor includes an EMF detector, a vector rotator to rotate the output of the EMF detector and an integrator that integrates the output of the vector rotator. Another integrator, external to the microprocessor calculates a quasi-continuous value for the field angle based on the output of themicroprocessor's integrator.
According to a broad aspect of the invention there is provided a method for determining an instantaneous field angle of a rotating-field machine having a stator, an EMF
vector being developed in the machine, comprising the steps of:
(a) measuring values for current and voltage of the stator of the machine;
(b) numerically calculating from said measured values a discontinuously changing value ~ for the frequency of the EMF
vector, said value ~ changing at a rate t~; and (c) reading, as the field angle, a quasi-continuous angle signal ~ from an integrator controlled by the discontinu-ously changing value ~ at a rate t~ which is faster than rate t,u ~
According to another broad aspect of the invention there is provided a method for determining the instantaneous field angle of a rotating field machine by calculating the EMF

vector from values for the stator current and the stator vol-tage of the machine, comprising the steps of: reading into a calculation circuit at a rate tu the values for the stator 1304'775 current and the stator voltage and a fed-back value for the field angle; and numerically calculating within said calculation circuit:
i) stator-related components of the EMF vector from said values for the stator current r said stator voltage and said fed-back value for the field angle; and ii) a value ~ for the frequency of a flux vector, said flux vector being calculated from said stator-related components of said EMF vector, said value ~ for the frequency changing at a rate t~, said value ~ being calculated in a microprocessor;
feeding said changing value ~ for frequency into an integration circuit, external to said microprocessor to form an angle signal ~ representing the field angle, said angle signal ~ changing at a rate of t~ which is faster than tu, and usiny said angle signal as the value for the instantaneous field angle and also using said angle signal as a fed-back value for the field angle.
According to another broad aspect of the invention there is provided a method for determining a field angle of a rotating-field machine having a stator and an EMF vector, comprising the steps of:
(a) measuring values for a current and voltage of the stator of the machine;
(b) numerically calculating from said measured values a discontinuously changing value ~ for the frequency of the EMF vector, said value ~ changing at a slow rate tu;
(c) reading a quasi-continuous angle signal ~ for the field angle from an integrator controlled by the discontinu-ously changing value ~ of a rate t~ which is faster than rate - 9a -13~4~7~;

tu;
(d) detecting the frequency of said field angle and if said frequency is greater than a threshold value repeating steps (a) to (d) and if ~he frequency of said field angle is equal to or less than said threshold performing the following steps (e) to (k);
(e) reading into a calculation circuit at a rate tu the values for the stator current and the stator voltage as well as a fed-back value for the field angle;
(f) numerically calculating stator-related components of the EMF vector from said values for the stator current, stator voltage and fed-back value, (g) integrating said stator-related components of the EMF vector;
(h) calculating a value for the frequency of said integrated stator-related components of the EMF vector said value ~ for the frequency changing at rate tu;
(i) integrating said changing value ~ for frequency by means of an integration circuit coupled to said calculating circuit to form an angle signal for the field angle, said angle signal changing at a rate of t~ which is faster than tu;
(j) using said angle signal as the instantaneous field angle and also using said angle signal as a fed-back value for the field angle, and (k) detecting a frequency of said angle signal, if said frequency is less than or equal to a threshold repeat steps (d) to (k) and if said frequency is greater than said threshold perform steps (a) to (d).
According to another broad aspect of the invention there is provided a digital device for determining a flux angle - 9b -` i3~4~77S

of a rotating field machine having a stator and a measuring device disposed between said stator and the digital device comprising:
a) a microprocessor receiving digital values representative of a current and a voltage of the stator of the rotating field machine as inputs, said microprocessor reading in said inputs at a slow rate t~ of a first clock signal, identifying an EMF vector from said inputs and calculating at said slow rate, a digital value for the frequency of said identified EMF vector;
b) an integrator, external to said microprocessor, having as an input said digital value for the frequency of a detected EMF vector, said integrator calculating a quasi-continuous value for the field angle that changes at a rate t~
faster than tp.
According to another broad aspect of the invention there is provided a digital device for determining a flux angle of a rotating field machine comprising:
a) means for producing a first clock signal;
b) a microprocessor receiving digital values representative of the current and voltage of the stator of the field machine as inputs, said microprocessor comprising:
i) means for detecting an EMF vector from said input digital values;
ii) means for rotating said detected EMF vector;
and ii.i) means for integrating said rotated detected EMF
vector to produce the digital value of the frequency of a flux vector at a rate of tu controlled by said first clock signal;
and -- 9c --1304~75 c) an integrator, receiving as an input said digital value for the frequency of the flux vector from the micro-processor, for calculating a quasi-continuous value for the field angle that changes at a rate t~ faster than tu.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates principle of a power section of a rotating field machine according to an embodiment of the present invention and of the control in a synchronous machine fed via an intermediate-link converter.
Figure 2 illustrates an embodiment of a processor module of Figure 1.
Figure 3 illustrates an embodiment of a structure for flux computation of Figure 2 for determination of the field angle for high frequencies.
Figure 4 illustrates an embodiment of a structure for flux computation of Figure 2 for determination of the field angle for lower frequencies.
DETAILED DESCRIPTION

-Figure 1 illustrates the use of a field angle - 9d -1 determination according to the present invention for impressing 2 the stator current in, for example, a synchronous machine. The 3 synchronous machine SM contains two winding systems, offset 4 relative to each other, ~hich are fed via an intermediate-link S converter. Each intermediate link converter consists of an 6 inverter (MSl and MS2 respectively) on the machine side which 7 is supplied via an intermediate link choke C1 and C2, 8 respectively) from an inverter (NS1 and NS2, respectively) 9 which is connected on the network side to a main supply network NM with a controlled intermediate circuit DC current. The 11 rotor winding of synchronous motor SM is fed from a rotating 12 excited device ER which is connected via a converter ES on the 13 exciter side to an auxiliary supply network NH.
14 The machine is regulated and the control of the converters takes place digitally. They are subdivided into 16 several function packets (FP) which are associated with 17 individual processor modules: namely, the function packets 18 FP-NS1 and FP-NS2 control the converters on the network side of 19 the synchronous machine (formed by NSl-Cl-MSl and NS2-C2-MS2, respectively) and the function packet FP-ES controls the 21 converter ES on the exciter side of the synchronous machine. A
22 universal processor module includes function packet FP-NC which 23 operates as a speed control as well as a function packet for 24 the sequence control of the entire procedure. Finally, peripheral subassemblies such as measured-value transmitters 26 and converters are associated with the individual processor 27 modules which include the function packets, arranged partially 28 on an interface module.
29 The two processor modules that have the function packets FP-NSl and FP-NS2 are of identical design and they have 1 the object of forming firing pulses for the valves of the 2 converters NSl and NS2 respectively on the network side in 3 order to control, by phase-gating, the current fed into the 4 respective DC intermediate circuit. Thereby, the amplitude of S the currents to be fed to the stator windings are controlled to 6 a value which is supplied by the module FP-NC and corresponds 7 to the desired torque. For this purpose, the interface 8 electronics contain voltage/frequency converters for 9 determining the actual current value, a rectifier with subsequent analog/digital conversion for forming the network 11 voltage as well as other components provided for the operation 12 of the network converter such as a hardware circuit (not shown) 13 to determine zero crossing of the current. The frequency and 14 digital conversions of the actual current values take place in the hardware (HW) of the module, while most of the software 16 functions of the module are shown schematically in Fig. 1.
17 Additional software functions not pertinent to this invention 18 are represented by SW.
19 In FP-NSl a current control IR furnishes a voltage reference value Ud* which is limited by a limiter BG1 to 21 permissible values. The voltage value is recalculated in a 22 linearizing stage LIN, that takes into consideration the 23 network voltage Un, into the control angle~ = cos l(Ud~/Un). A
24 control unit SS which is synchronized with the measured value of the instantaneous network voltage, makes the firing pulses 26 for the converter valves available.
27 The processor module including the function packet 28 FP-ES furnishes, as a function of the current reference¦i*~ the 29 exciter current reference value for the exciter current controller IER by means of a function generator FG. The output ~3~47'75 1 signal of IER is limited by a limiter BG2 and furnishes in a 2 control unit, the control signals for the converter ES on the 3 exciter side. Hardware components for voltage/frequency 4 conversion of the actual value of the exciter current in the converter ES, as well as proper hardware at the processor 6 module for frequency/digital conversion of the actual current 7 value, are provided in the portion designated HW.
8 These processor modules further form, like the 9 processor module with the functional packet FP-MS according to the invention, suitable monitoring quantities, acknowledgment 11 signals and call-back signals which are fed to the processor 12 module FP-NC. This latter msdule in turn provides start and 13 release signals to the function modules, controlling the 14 converters. It is shown separately in Fig. 1, that the module FP-NC transfers the field frequency as the actual speed 16 substitute value to a software building block NR for speed 17 control, by which the current reference value¦i*¦is formed.
18 The actual speed value is formed by a startup generator ~G from 19 a reference value n* which is entered by the operator. A
sequence control TC obtains its starting and stopping command 21 likewise from the operator, and furthermore, the operator can 22 enter the parameter values, adapted to the respective machine, 23 for control, for the selection of the mode of operation, and 24 other data as well. The sequence control TC thereby represents an interface between data to be entered by the operator and the 2~ control and regulation furnished by the manufacturer. In 27 addition, special operating characteristics, for instance, 28 speed, voltage, flux and EMF can be monitored here for assuring 29 adherence to given operating regions, and to initiate an orderly shutdown if necessary, in the event of impermissible i3~75 1 values for these operating characteristics.
2 Two-phase currents (iRl, iSl and iR2, iS2) 3 at least two interlinked voltages of a stator winding system 4 UsT and UTR are measured at the lead wires of each stator winding system, and are made available via a voltage/frequency 6 converter to the corresponding processor module FP-MS which 7 therefrom forms the digital measurement values as illustrated 8 in Fig. 2.
9 In Fig. 2, the operation of this processor module FP-MS is shown in greater detail, where the analog/digital 11 conversion, which is not the subject of the present invention, 12 is shown as a separate element distinct from the computing 13 operation of the processor proper. The entire control of the 14 converters MS2 and MS1 on the machine side of the converters NS2-C2-MS2 and NS1-C1-MSl is accomplished here by a computer 16 module which consists of the processor itself, FP-MS' and a 17 trigger module FT which uses hardware that is separate from 18 that of the processor itself. In the processor itself, FP-MS', 19 a control angle calculation A-CAL occurs first so as to fix the angle between the stator current vector to be impressed and the 21 EMF vector. This control angle can be calculated selectably 22 according to different parametric strategies. For instance, 23 one strategy might be operation with a fixed power factor, with 2~ a minimum quenching angle or it might be an angle given by field-oriented control, if desired, as compared with the flux 26 vector. The sequence control TC determines the choice of 27 strategies to be used. In the simplest case, a constant 28 control angle is given in order to always commutate the stator 29 current in the predetermined firing cycle of the converter valves on the machine side to the next winding when the EMF

~3(~477~;

1 vector or the flux vector reaches a predetermined position in 2 space.
3 The control angle~can advantageously be stored 4 temporarily in a separate hardware memory A-MEM so that it is still available for a controlled inverter operation in the 6 event of a failure of the processor module FP-MS. The trigger 7 module FT contains a comparison point to compare the control 8 angle~ with the field angle (corresponding to the phase shift 9 between the EMF vector and the field vector phase shifted by 90). In the event that they are equal, a subsequent control 11 stage ST forms the firing points in time directly, by which the 12 valves of the converters MSl and MS2 on the machine side are 13 fired according to a firing sequence fixed for one revolution 14 of the current vector.
The trigger building block FT thus requires the 16 instantaneous value of the field angle ~ , which must be 17 present for an exact control with high time resolution, i.e., 18 quasi-continuously. Of particular concern is the digital 19 formation of the field angle with high resolution.
For this purpose, a method is used which calculates 21 the EMF vector from the digitally available values for the 22 current and voltage of the machine stator, and determines 23 therefrom the instantaneous field angle, with at least one 24 integration being performed.
According to an embodiment of the invention, a value 26 for the frequency of the EMF vector ~J which changes at a slower 27 clock rate (i.e. "discontinuously") is calculated and, a value 28 changing at a faster rate is read out as a quasi-continuous 29 angle signal at the integrator which is arranged outside the microprocessor and is controlled by the discontinuous value.

~:~04~75 1 This present invention assumes that as a result of 2 the inertia of the machine, the flux vector and the speed of 3 rotation of the rotor change only relatively slowly. It is 4 therefore sufficient if, in a microprocessor, the current and voltage values are read in synchronously at a slower rate 6 adapted to the computing capacity of the processor. The 7 processor may form, in an EMF detector stage E-DET of Fig. 2, 8 the EMF vector _ which is present at the time t~Lof the 9 reading. A flux calculating stage F-CAL also of Fig. 2 determines the frequency which is obtained fram the motion of 11 the EMF vector resulting from the motion of the flux vector 12 relative to the respective read-in times t~ , t~, etc. or the 13 motion of the flux vector corresponding to this EMF vector.
1~ This frequency ~ is therefore a frequency value which changes at the slower read-in clock rate ("discontinuously") and from 16 which a field angle can be formed by in~egration. The field 17 angle changes continuously if an analog integrator is used or 18 changes quasi-continuously if an integrator INTl is used which 19 operates at a high operating rate.
Since the integrand of this integrator deviates only 21 insignificantly from the true flux frequency during the period 22 of read-in time t~, the values of the integral (angle 23 signal ~) deviate only insignificantly from the true field 2~ angle, which values are preset to the clock pulses t~ of the computing-clock transmitter of the integrator INTl. This 26 deviation can be corrected by feeding back the angle signal to 27 the microprocessor at a slow rate.
28 Advantageously, the reading in of the fed-back angle 29 signal into the microprocessor takes place synchronously with the reading of the current and voltage values, i.e., all read-~3047~75 1 in values are instantaneous values belonging to the s~me points 2 in time t~, so that no additional phase shifts occur thereby.
3 In the microprocessor, the frequency can then be readjusted so 4 that, for the reading-in times t~L , equality between the angle signal and the field angle discontinuously formed in the flux 6 computer F-CAL at these reading-in times is achieved. This is 7 described as synchronization. Since the feedback effect of the 8 angle signal increases with rising frequency, but on the other 9 hand, the flux calculation becomes more and more accurate at high frequencies, the synchronization may in some cases be 11 dispensed with completely or the correction control provided 12 for the synchronization can be equipped with a large time 13 constant.
14 Plane vectors must be described by two defining quantities. For the hardware integrator INTl, however, only 16 the derivative ~Jin time of the polar angle coordinate of the 17 calculated flux vector is required of the flux vector 18 calculated for the clock times t~L. In Fig. 2, the computing 19 stage F-CAL also computes the magnitude~ of the flux vector together with the frequency ~ from the microprocessor. The 21 magnitude 1~l is fed back to the sequence control TC for 22 monitoring purposes.
23 For describing the F~MF vector e, the orthogonal 24 Cartesian components e~ and e~ of the EMF vector in a stator-related coordinate system are used advantageously. The 26 currents and voltages required for the EMF calculation in a 27 stator winding system flow in windings which are shifted 120 2B relative to each other. Therefore, a coordinate transformation 29 of skewed coordinates which are associated with the three individual windings of a stator winding system into orthogonal 1 coordinates is necessary, which is known as a "three/two 2 conversion" or 120/90 conversion". It is immaterial at which 3 point in the input channel of the computing stage F-CAL this 4 conversion takes place. This conversion can be applied to the measurement values of the stator currents and stator voltages, 6 so that orthogonal components of the current vector and the 7 voltage vector can be fed to the EMF detector E-DET.
8 In Fig. 2 this conversion is performed at the output 9 of an offset control stage O-REG. This control stage is primarily advantageous when, through offset errors of the 11 preceding hardware (that is, the measuring stages and 12 analog/digital converters), the components of the EMF vector, 13 which are basically pure AC voltage quantities, have a DC
14 component. For the offset control, very weak smoothing is sufficient here, i.e., for instance, by means of a feedback 16 integrator, the time constant of which is large as compared to 17 the period of the reading times t~L , as is illustrated in the 18 functional block O-REG of Fig. 2.
19 EMF detector E-DET of Fig. 2 determines the EMF. It is sufficient in a machine with several stator winding systems, 21 to calculate the EMF vector in a single winding system by 22 subtracting from the voltage vector u of this winding system, 23 the ohmic voltage drop R.i, the ohmic resistance R of the 24 supply circuit and the ohmic voltage drop R.l corresponding to the current vector 1, as well as the inductive voltage drop 26 Ls.( ~ dt). That is, 28 e = u - Ri - L , ( i/dt) However, the individual stator winding systems are 1304~75 1 coupled inductively to each other so that, corresponding to a 2 coupling factor x, the inductive voltage drops belonging to the 3 stator current veGtor of the other winding system must be taken 4 into account. For the winding system (voltage vector u2, current vector i2) fed from the converter MS2 on the machine 6 side, the following vector equation is obtained.

8 - e = u2 - R12 _ Ls tdi2/dt + X dil/dt) This equation may also be implemented by E-DET. In 11 the example of Fig. 1, this vector equation in the form of two 12 scaler equations for the skewed-angle components of the vectors 13 are calculated.
14 Fig. 3 illustrates, an embodiment of flux calculation circuit F-CALl for the high frequency cases. The embodiment is 16 labelled F-CAL1. The dashed lines ~/S indicate here the 17 interface between the software-controlled microprocessor and 18 the hardware at its input and output. Vectors which are 19 represented by two signals corresponding to their definition quantities (according to Fig. 3, advantageously the Cartesian, 21 skewed angle or orthogonal components), are indicated as double 22 arrows. The structure of the EMF detector E-DET, as well as 23 that of the offset control O-REG can be chosen according to 24 Fig. 2. A Cartesian/polar converter K-P receives the EMF
vectors which are the outputs of offset control stage O-REG and 26 forms therefrom polar definition quantities. In the case of 27 orthogonal EMF control components e , e , the magnitude 28 signal is therefore -e = ~ e2 + e2~

~3~775 1 and the angle signal which changes discontinuously is 3 ~ = tan~1 te~ / ed ) The frequency of the EMF vector is derived using software with 6 a digital differentiator DIF which calculates the differential 7 quotient by the differential quotient g ~/d~
~
11 where ~and ~ I are the polar angle coordinates of the EMF
12 vectors belonging to the reading times t~ and t~_l ; T~ , 13 the period of the reading times and where TD is a time-14 normalizing constant adjusted to the time constant of the hardware integrator INT1 of the trigger building block FT of 16 Fig. 2. TD corresponds to the time-normalizing constant 17 corresponding to the nominal frequency.
lB A divider DIV1 forms therefrom the quotient e/~ as 19 the magnitude ~ of the calculated flux. The flux vector is physically the integral of the EMF vector. The integration, 21 however, can be avoided at high frequencies by replacing it 22 with the magnitude component of the flux vector by e/~ while 23 the angle coordinate is replaced by ~ + 90.
24 In the stationary state, this approximate determination of the flux vector with the determination of the 26 EMF magnitude and the EMF frequency is exact and it changes 27 only the dynamic state. In many applications, especially in 28 asynchronous machines, even computing errors such as are 29 caused, for instance, by rounding-off errors of the differentiation stage DIF can be tolerated without problem. In i30477S

1 other cases, however, it may be advantageous to follow the 2 differentiation stage DIF with a further smoothing member GL.
3 Thereby, however, a frequency-dependent phase error is 4 generated.
This phase error can be compensated by the provision 6 that the angle ~belonging to the respective reading times t~ is 7 synchronized with the angle~belonging to these points in time.
8 For this purpose, the correction control CR is provided, to 9 which the angle difference is fed and the output signal of which can be added to the output signal of the smoothing member 11 GL.
12 Since reading-in the current, voltage and angle 13 signal takes place synchronously, the identity between the 14 discontinuously calculated angle~ and the guasi-continuously calculated angle signal ~is ensured at these synchronous points 16 in time if the correction control CR is balanced. The hardware 17 integrator INTl thus serves as an interpolator for the 18 discontinuously calculated ~-values. Here, the differentiating 19 stage DIF is required in the microprocessor.
At lower frequencies it is often advantageous for the 21 calculation of the flux to use a structure with which an 22 integration of the EMF vector actually takes place, but no 23 differentiation is performed for forming the frequency ~J. To 24 this end it is merely necessary to switch, at a given limit of the frequency ~ to another program in the microproces~r for 26 the computation of the flux. For instance, if ~Jfalls below a 27 certain threshold the output of offset control stage O-Reg is 28 fed to the program F-CAL2 of Fig. 4. To the extent that with 29 this new flux calculation, the starting values of integrators or other computing elements are required, the values for the i30477~

1 flux ~, the EMF e and the frequency 6~ can be taken from the old 2 prog~am F-CALl into the new program F-CAL2, as is indicated in 3 Fig. 3 by corresponding outputs of the program section F-CALl.
4 Vice versa, a corresponding starting value for the S differentiation stage DIF as well as the value zero can be 6 preset for the correction control CR when swit~hing back to the 7 program section ~-CAL1.
8 No further timing problems arise when switching over 9 since the hardware integrator INT1 can run unsynchronized for one or more computing cycles required for calculating the 11 discontinuous frequency value ~.
12 According to Fig. 4, the method for determining the 13 instantaneous field angle at lower frequencies utilizes a 14 calculation of the EMF vector (program section E-DET) which can be followed by an offset control stage O-REG. The program 16 section F-CAL2 follows and contains at least one integration 17 stage INT2 which is in addition to the hardware integrator INTl 18 of the trigger building block FT of Fig. 2.
19 In this method also, the values for the stator current and stator voltage are likewise read into the 21 microprocessor at a slower rate and with a fed-back value for 22 the field angle are read-in synchronously. From them, the 23 stator-related components e~ , e~ of the EMF vector and 24 therefrom, by means of a first integration, a value L~, changing discontinuously at a slower rate for the frequency of the flux 26 vector (integrated EMF vector), is calculated. This 27 discontinuous value ~is integrated in the hardware integrator 28 INTl of FT to form a faster-changing angle signal ~ for the 29 field angle ("second integration") and the angle signal is taken off on the one side as the value of the instantaneous 1 field angle and is scanned on the other hand as a fed-back 2 value for the field angle.
3 Advantageously, the read-in values are converted in 4 the microprocessor, by means of the offset-control stage O-REG
into smoothed stator-related orthogonal components of the EMF
6 vector. In a vector rotating stage VD of F-CAL2, these 7 orthogonal components are subjected to a coordinate 8 transformation with the fed-back value of the field angle as 9 the transformation angle. The transformation angle is converted here advantageously into its angle functions cos ~, 11 sin ~ since the vector transformation then consists of only 12 four multiplications and two additions.
13 In contrast to the stator-related orthogonal 14 com~onents of the EMF vector, which represent AC signals, the transformed orthogonal components are now represented by DC
16 voltage signals, the integration of which does not require a 17 high working cycle.
18 Advantageously, a correction vector is vectorially 19 added in a damping stage DAMP to the transformed vector, corresponding to the German Offenlegungsschriften 34 18 573, 34 21 18 640, and 34 18 641, mentioned at the outset.
22 From these publications the structure of suitable 23 integration stages INT2 can also be seen.
2~ In Fig. 4, an integration stage INT2 realized in software is indicated which requires only a single integrator 26 for forming the flux magnitude ~, while the discontinuous 27 frequency value is formed by means of a division stage.
28 This form of the integration stage INT2 therefore 29 does not require a differentiation stage for determining, from the components of the transformed EMF vector, the discontinuous 130~

l value ~, which must be entered as the integrand into the 2 h~rdware inteqrat~r INTl.

Claims (13)

1. A method for determining an instantaneous field angle of a rotating-field machine having a stator, an EMF vector being developed in the machine, comprising the steps of:
(a) measuring values for current and voltage of the stator of the machine;
(b) numerically calculating from said measured values a discontinuously changing value .omega. for the frequency of the EMF vector, said value .omega. changing at a rate tµ; and (c) reading, as the field angle, a quasi-continuous angle signal ? from an integrator controlled by the discontinu-ously changing value .omega. at a rate t? which is faster than rate tµ.
2. The method of claim 1, wherein the step of calculat-ing the discontinuously changing value .omega. comprises the steps of:
numerically calculating and digitally differentiat-ing a direction angle ? of the EMF vector to form a value .omega.';
producing a correction signal by leveling a deviation of the quasi-continuous angle signal ? from the direction angle ? with a time constant greater than the frequency of rate tµ; and forming said discontinuously changing value .omega. by using said correction signal to correct deviations in said value .omega.'.
3. The method of claim 2, further including subsequent-ly smoothing said value of the frequency .omega.' obtained by the digital differentiation.
4. The method of claim 2 wherein:

said step of measuring comprises a step of synchron-ously sampling the current and the voltage of the stator of the machine;
said step of calculating the discontinuously chang-ing value .omega. is performed in a microprocessor and comprises feeding said value .omega. to a control input of an integrator, said integrator being external to said microprocessor;
said step of producing said correction signal com-prises a step of feeding back said quasi-continuous angle signal ? from said integrator; and said step of feeding back said quasi-continuous angle signal ? is synchronized to said step of sampling the current and the voltage of the stator.
5. The method of claim 1, further comprising the steps of producing the magnitude e, of the EMF vector and trans-forming said magnitude e, by division with the discontinuous value .omega., into a computed value ? for the magnitude of the flux.
6. The method of claim 1, further comprising the steps of:
calculating the EMF vector in Cartesian coordinates;
filtering out DC components of the EMF vector; and calculating the frequency of the EMF vector from the filtered components of the EMF vector.
7. A method for determining the instantaneous field angle of a rotating field machine by calculating the EMF vector from values for the stator current and the stator voltage of the machine, comprising the steps of:
reading into a calculation circuit at a rate tµ

the values for the stator current and the stator voltage and a fed-back value for the field angle; and numerically calculating within said calculation circuit;
i) stator-related components of the EMF vector fro said values for the stator current, said stator voltage and said fed-back value for the field angle; and ii) a value .omega. for the frequency of a flux vector, said flux vector being calculated from said stator-related components of said EMF vector, said value .omega. for the frequency changing at a rate tµ, said value .omega. being calculated in a microprocessor;
feeding said changing value .omega. for frequency into an integration circuit, external to said microprocessor to form an angle signal ? representing the field angle, said angle signal ? changing at a rate of t? which is faster than tµ, and using said angle signal as the value for the instantaneous field angle and also using said angle signal as a fed-back value for the field angle.
8. The method of claim 7, further comprising the steps of:
converting said read-in values of said stator cur-rent and stator voltage into smoothed stator-related orthogonal components of the EMF vector;
subjecting said orthogonal components to a coor-dinate transformation using said fed-back value of the field angle as the transformation angle; and integrating said transformed orthogonal components by means of a first integrator to determine said changing value .omega. of the frequency.
9. The method of claim 8, further comprising the steps of:
calculating a correction vector from an output of said first integration; and vectorially adding said correction vector to said EMF vector subjected to the coordinate transformation.
10. A method for determining a field angle of a rotat-ing-field machine having a stator and an EMF vector, comprising the steps of:
(a) measuring values for a current and voltage of the stator of the machine;
(b) numerically calculating from said measured values a discontinuously changing value .omega. for the frequency of the EMF vector, said value .omega. changing at a slow rate tµ;
(c) reading a quasi-continuous angle signal ? for the field angle from an integrator controlled by the discon-tinuously changing value .omega. of a rate t? which is faster than rate tµ;
(d) detecting the frequency of said field angle and if said frequency is greater than a threshold value repeat-ing steps (a) to (d) and if the frequency of said field angle is equal to or less than said threshold performing the follow-ing steps (e) to (k);
(e) reading into a calculation circuit at a rate tµ the values for the stator current and the stator voltage as well as a fed-back value for the field angle;
(f) numerically calculating stator-related com-ponents of the EMF vector from said values for the stator current, stator voltage and fed-back value, (g) integrating said stator-related components of the EMF vector;
(h) calculating a value for the frequency of said integrated stator-related components of the EMF vector said value .omega. for the frequency changing at rate tµ;
(i) integrating said changing value .omega. for frequency by means of an integration circuit coupled to said calculating circuit to form an angle signal for the field angle, said angle signal changing at a rate of t? which is faster than tµ;
(j) using said angle signal as the instantaneous field angle and also using said angle signal as a fed-back value for the field angle; and (k) detecting a frequency of said angle signal, if said frequency is less than or equal to a threshold repeat steps (d) to (k) and if said frequency is greater than said threshold perform steps (a) to (d).
11. A digital device for determining a flux angle of a rotating field machine having a stator and a measuring device disposed between said stator and the digital device comprising:
a) a microprocessor receiving digital values representative of a current and a voltage of the stator of the rotating field machine as inputs, said microprocessor reading in said inputs at a slow rate t of a first clock signal, identifying an EMF vector from said inputs and calculating at said slow rate, a digital value for the frequency of said identified EMF vector;
b) an integrator, external to said microprocessor, having as an input said digital value for the frequency of a detected EMF vector, said integrator calculating a quasi-continuous value for the field angle that changes at a rate t? faster than tµ.
12. The device of claim 10, further comprising:
means for feeding said quasi-continuous value back to said microprocessor; and means for sampling said quasi-continuous value synchronously with sampling of the values for the stator current and the stator voltage.
13. A digital device for determining a flux angle of a rotating field machine comprising:
a) means for producing a first clock signal;
b) a microprocessor receiving digital values representative of the current and voltage of the stator of the field machine as inputs, said microprocessor comprising:
i) means for detecting an EMF vector from said input digital values;
ii) means for rotating said detected EMF vector;
and iii) means for integrating said rotated detected EMF
vector to produce the digital value of the frequency of a flux vector at a rate of tµ controlled by said first clock signal;
and c) an integrator, receiving as an input said digital value for the frequency of the flux vector from the microprocessor, for calculating a quasi-continuous value for the field angle that changes at a rate t? faster than tµ.
CA000566352A 1987-05-12 1988-05-10 Method and apparatus for the digital determination of the field angle of a rotating-field machine Expired - Fee Related CA1304775C (en)

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DE3715854 1987-05-12
DEP3715854.6 1987-05-12

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JPH02168886A (en) * 1988-12-19 1990-06-28 Meidensha Corp Variable speed driving controller for rotary electric machine
NL1029659C2 (en) * 2005-08-02 2007-02-05 Atlas Copco Airpower Nv Processor unit for measurement data from e.g. compressor motor, comprises measurement sensor interface connected to general purpose processor with real time control system

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DE2833542C2 (en) * 1978-07-31 1980-09-25 Siemens Ag, 1000 Berlin Und 8000 Muenchen Rotary field machine drive, consisting of a converter-fed rotary field machine, in particular a synchronous machine and a converter control for the self-clocked, in particular field-oriented operation of this machine, with two identical AC voltage integrators and a method for operating the rotary field machine drive
DE3034252A1 (en) * 1980-09-11 1982-04-15 Siemens AG, 1000 Berlin und 8000 München DEVICE FOR FIELD-ORIENTED OPERATION OF A CONVERTER-DRIVEN ASYNCHRONOUS MACHINE
DE3138557A1 (en) * 1981-09-28 1983-04-07 Siemens AG, 1000 Berlin und 8000 München METHOD FOR IMPROVING THE MACHINE FLOW OF A ROTARY FIELD MACHINE, AND CIRCUIT ARRANGEMENT FOR IMPLEMENTING THE METHOD
DE3460506D1 (en) * 1983-05-27 1986-09-25 Siemens Ag Method and apparatus to derive the flux vector of an induction machine from the stator current and the stator voltage, and application thereof
NO851324L (en) * 1984-05-18 1985-11-19 Siemens Ag PROCEDURE AND APPARATUS FOR AA DETERMINE A TRIANGLE-MACHINE FLUCH VECTOR.
DE3418573A1 (en) * 1984-05-18 1985-12-05 Siemens AG, 1000 Berlin und 8000 München METHOD AND DEVICE FOR STABILIZING THE LOCATION CURVE OF A VECTOR FORMED BY INTEGRATION

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FI881947A (en) 1988-11-13
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FI881947A0 (en) 1988-04-26
DE3868689D1 (en) 1992-04-09

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