CA1179775A - Apparatus for determining the rotor angle of a synchronous machine - Google Patents
Apparatus for determining the rotor angle of a synchronous machineInfo
- Publication number
- CA1179775A CA1179775A CA000399358A CA399358A CA1179775A CA 1179775 A CA1179775 A CA 1179775A CA 000399358 A CA000399358 A CA 000399358A CA 399358 A CA399358 A CA 399358A CA 1179775 A CA1179775 A CA 1179775A
- Authority
- CA
- Canada
- Prior art keywords
- signal
- angle
- flux
- rotor
- difference
- 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
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/34—Testing dynamo-electric machines
- G01R31/343—Testing dynamo-electric machines in operation
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P21/00—Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation
- H02P21/06—Rotor flux based control involving the use of rotor position or rotor speed sensors
- H02P21/10—Direct field-oriented control; Rotor flux feed-back control
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Control Of Ac Motors In General (AREA)
- Synchronous Machinery (AREA)
- Transmission And Conversion Of Sensor Element Output (AREA)
- Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Apparatus for determining the rotor angle of a synchronous machine relative to a fixed axis is disclosed. A field position sensor measures the voltage induced in the stator with the stator winding current off when the rotor winding current is turned on, and provides a rotating magnetic flux vector angular position to set an integrator to a starting value for rotor angle position. Thereafter the integrator integrates the rotary speed signal fed from a tachometer. A function former responds to the integrator sum of the initial rotor angle and the integrated rotary speed signal to provide a rotor angle signal for control of the machine. The disclosed apparatus provides simple, relatively inexpensive rotary angle measurement.
Apparatus for determining the rotor angle of a synchronous machine relative to a fixed axis is disclosed. A field position sensor measures the voltage induced in the stator with the stator winding current off when the rotor winding current is turned on, and provides a rotating magnetic flux vector angular position to set an integrator to a starting value for rotor angle position. Thereafter the integrator integrates the rotary speed signal fed from a tachometer. A function former responds to the integrator sum of the initial rotor angle and the integrated rotary speed signal to provide a rotor angle signal for control of the machine. The disclosed apparatus provides simple, relatively inexpensive rotary angle measurement.
Description
~ ~79~75 1. Field of the Invention This invention relates to an apparatus for determining the angular position relative to a ~fixed reference axis of the rotor axis of a synchronous machine by means of a tachometer.
2. Description of the Prior Art For precisc control of the torque or rotational speed of a synchron-ous machine, exact in-Eormation about the instantaneous position of the rotor is also often indispensable. T]lis is so, not only for starting the synchron-ous machine, but also for its continued operation. For instance, in order to maintain optimum rotor displacement angle when regulating the stator current, the accurate position of the rotor must be known. In general, a digital meter is used which, depending on the required precision, delivers signals on sev-eral (usually eight or ten) tracks which are coded according to the respective position of the meter. These meters are costly, however, and require accurate mechanical adjustments to adapt them to the rotor axis.
For the determination of rotational speed, simple tachometers (e.g.
tachogenerators or incremental digital tachometers) have been developed. For high accuracy in the determination of rotational speed, digital tachometers are most often used, the output signal of which consists of a pulse sequence with pulse intervals inversely proportional to the speed of rotation. These tacho-meters, however, give no information about the angle of rotation of the monit-ored shaft, i.e. the angle between thc rotor axis oE thc synchronolls machine and a fixed reference axis.
The inEormation on the instantaneous rotor angle is especially import-ant in field-oriented control, wherein a field detection device (such as dis-closed for example in German Offenlegungsschrift P 30 26 3~8 laid open on February ~, 1982) is used to determine the amplitude and angular position of l ~79~5 thc flux vector based on the motor currents and voltages. The motor current (i.e. the current supplied to the stator winding) and possibly the field cur-rent (i.e. the current supplied to the rotor winding) of the synchronous mach-ine are controlled so that the components normal to the flux vector (effective components) which determine the torque of the synchronous machine are control-led according to the given speed of rotation or torque, whereas the flux is maintained constant by control of t]le field current and motor current con~pon-ents parallel to the flux vector. I'he initial value of the flux angle (i.e.
the initial angle of the rotating magnetic field) can be determined as descri-bed in U.S. patent 4,119,893 of Bayer et al, issued October 10, 1978, for the start-up of a synchronous machine, by leaving the motor current turned off and calculating the flux angle from the voltage induced in the motor winding (i.e.
stator winding) when the field is connected.
The circuits used for determining the flux angle in this initial position-finding process and during the subsequent field-oriented operation utilize analog input signals and supply analog output signals. Thus, when using digital peripheral equipment (e.g. digital angle pulse generators), appropriate converters are necessary. Another difficulty is caused because such analog circuits contain integrators which are able to store a determined value for only a relatively short period of time.
SUM~IARY O~ TIIE INVENTION
It is an object of the present inventioTI to provide simple app.~ratus for determining the rotor angle o~ a synchronous IllaCIlille Wh:iCIl can easily be adapted to the charac-teristics of the particular circuitry used to control a synchronous machinc.
It is another ob;ject of the invention to provide al)paratus for clet-ermining the rotor angle of a synchronous mach;ne at reducecl e.Ypense for ana-log/digital and digital/analog converters.
~ ~ ~g~75 It is a further object of the invention to provide apparatus for determining the rotor angle of a synchronous machine with which it is possi~le to store the determined rotor angle for a prolonged time even at standstill or slow running of the synch-ronous machine.
In one aspect of the invent-ion, apparatus for determining the rotor angle of a synchronows machine includes a field position sensor, an integrator and a function former. The field position sensor is connected to determ-ine the angle of the rotating flux field relative to a fixed reference axis with the tor current off when the field current is turned on, based on measuring the voltage induced in the motor (i.e. voltage induced in the stator~. The inte-grator is connected to receive the field angle signal from the field position sensor and also a rotational speed-proportional signal from a tachometer. The function former is connected to develop a rotor angle signal that varies periodically with the output of the integrator.
In a preferred embodiment of the invention, described in greater detail below, the integrator is a digital up/down counter connected to receive the rotational speed-proportional signal from a conventional digital tachometer, and the function former is a read-only memory which is cyclically driven.
There have thus been outlined rather broadly certain objects, features and advantages of the invention in order that the detailed description that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional -features of the invention that will describe more fully hereina-fter. Those skilled in tllc art will appreciate that the conception on which this disclosure is based may readily be utili7ed as the basis for the designing of other arrangements for carrying out the purposes of this invent:ion. It is important, therefore, that ~'7~37~S
this disclosure be regarded as including all such equivalent arrangements that encompass the spirit and scope of the invention.
BRIEF DESCRIPTION OF THE DR~WINGS
Embodiments of the invention have been chosen for the purposes of illustration and description, and are shown in the accompanying drawings forming a part of the specification, wherein:
Figure 1 is a schematic view of one form of embodiment of the invention;
Figure 2 is a schematic view of a modified form of the embodiment of Figure l; and Figure 3 is a schematic view of another modified form of the embodiment of Figure 1.
Throughout the drawings, like elements are referred to by like numerals.
DESCRIPTION OF THE PREFERR~D E~BODIMENTS
Figure 1 shows a synchronous machine 1 which is supplied with a motor current (i.e. stator winding current) from a power supply, such as by means of an a.c. inverter. The motor voltage U at a terminal of the machine 1 is measured by means of a transformer 20 The machine 1 has a field winding 3 mounted on the rotor for setting up a magnetic flux field. A tachometer 4 coupled with the rotor shaft furnishes as its output 5 a speed-proportional signal n.
In accordance with the principles of the invention, a field position sensor is provided which measures during a short measurement time per:iod A t, the voltage U induced in the stator with the motor current turned off when thc field current is connected to the field winding 30 For this purpose, as shown in Figure 1, a time control unit 6 is pro-vided which separates the motor wind-ing and the field winding from their current sources by means of switches 7 ~md 8 -in response to a start pulse for initializing the position sensing proccss. After switch 8 has been closed, the motor voltage U induced by the connected field is measured by the voltage transformer 2. A computing circuit 9 develops a flux g~7~
angle signal from the voltage U which corresponds to the angle ~ of the rotat-ing magnetic field flux vector ~. This signal supplies the determined flux angle~ at the output 10 o-f the computing circuit 9 to the end of the measure-ment time period ~t (typically several milliseconds). The computing circuit 9 is constructed to supply this output 10 at the end of the measurement period, even though the other structural elements used in the computing unit 9, i.n particular the :intcgrators, are unable themselvcs to storc a valuc for a prolonged time.
The period ~t, therefore, is long enough to enable the computing circuit to detect the induced voltage U and the computed flux angle si.gnal, but short enough to prevent an alteration of the computed signal due to decay or drift of signal levels in the components, especially the integrators, used in the computing circuit.
The principles of operation of a position sensor of this type are disclosed in German Patent Application 26 35 965. The s-tructure of the comput-ing unit 9 may take the form of the circuit arrangement described, for example, in our Canadian Patent Application 381,414 filed July 9, 1981 and be used according to the teachings of this Canadian Patent Application for the field-oriented operation of the rotating field machine. For field-oriented operation, the motor current I is also measured and the computing unit 9 determines the amplitude ¦~¦ oE the :flux vector ~, in addition to information about thc ~flux angle ~. Determination of the flux amplitudc ~ is, ho~evel, llOt CssCllti.ll for the operation of thc present invention, and ~for thi.s roason the :respect-ive measurillg input 11 (see Fi.gure 1) for the motor currellt :[ and the respect-ive output line 12 oF the computillg unit 9 for the flux nmplitude ¦~¦ are indicated by dashed lines in Figures 1 and 2.
~ 17~775 The invention makes use of the assumption that during standstill of the unloaded machine, the rotor axis and the field axis coincide. The field angle relative to a given, fixed reference axis at the start-up of the synchro-nous machine can thus be used as a star~ting point for the determination of the rotor angle relative to the same fixed axis. This -value is obtained as the output signal 10 of the computing circuit 9.
The flux angle signal ~ developed at the output 10 of the computing circuit 9 is used to set an -integrator 13. A switch 14a which is actuated by the time control un:it 6 serves to connect the output 10 of the computing circuit 9 of the field position sensor to the integrator 13 at least at the end of the measurement period ~t. A switch 14b, which cooperates with the switch 14a in the manner of a change-over switch, connects the speed-proportional signal n output 5 of the tachometer 4 to the integrator 13 following the end of the measurement period ~t. Thus, following the end of the measurement period, the output of the integrator 13 has the value: ~ 0+ rnodtO
A function former circuit 15 develops a rotor angle signal ~ from the output of the integrator 13. For a flux vector ~ supplied by the computing circuit 9 in the form of polar coordinates, the flux angle signal ~ takes the form of the flux angle ~t itself, having a value lying between -~r and + ~. The rotor angle signal ~ developed by the function former 15 thus likewise varies between -~ and + ~ according to the rotor position. Tt will be appreciated by those skilled in the art that other functions may also be used tor the flux angle signal ~ and the rotor anglc signal ~ , clS discussed further below with reference to Figure 3, with the function former 15 sLIpplyillg a per-iodically varying -rotor angle signal ~\ , whose period changes accord-ing to the output signal of the integrator 13. One period of the output signal \ will then cor-~ 1~9775 respond in a two-pole machine to one rotor revolution; or more generally, in a 2p-pole machine, to the pth part of one rotor revolution.
The rotor angle ~ signal 16 supplied at the output of the function former 15 is delivered together with the ~ signal 10 and the ~ signal 12 to the control system of the synchronous machine.
Setting of the integrator 13 can be effected in a simple manner, in that the integrator 13 is arranged in a control loop which during the short measurement period ~t causes the flux angle which is to be set as the starting value for the integrator 13 to follow the actual flux angle determined by -the computing circuit 9. This is shown in the circuitry of Figure 2 which includes a regulator 17 to which the flux angle signal ~ is supplied as a nominal or reference value from the output 10 of the computing circuit 9, and to which the rotor angle signal ~ from the line 16 of the function former 15 is supplied as the actual value. A switch 18 actuated by a corresponding release signal serves to release the regulator 17 during the measurement period, while setting it to zero at other times, so that the connection between the flux angle signal ~ and the rotor angle sigral ~ is effected only during the measurement period. The output signal of the regulator 17 is supplied as an input to the integrator 13 throughout the entire measurement period by means of the change-over switch 14.
The time constant of the regulator 17 can be chosen very short, so that the rotation angle signal associated with the flux angle is very quickly set at thc output of the integrator 13 (viz. the output of the f~mction former 15) and is held there until the end of the measurement period, which can be chosen corres-pondingly short.
The arrangement shown in Figure 2 permits the omiss-ion of a separate time control unit 6 (see Figure 1), since compared with normal operation (switches ~ ~79775 7, 8 closed and regulator 17 set to zero by means of switch 18) during the measurement period only the switches 8 and 18 need be closed, with switch 7 opened and the change-over switch 14 set to the output of the regulator 17.
This arrangement of a memory in a control loop as in Fugure 2 is espeeially advantageous for use w-ith a non-pos-ition-coded digital taehometer.
In the embodiment of the :invention shown in Figure 3, a frequency con-verter 20 is connected at the output of the regulator 17. The con-verter 20 ser-ves to develop a sequence of pulses at a frequency proportional to the output signal of the regulator 17. This signal is then delivered to a digital up/down counter 21 which serves the funetion of the integrator 13 of Figures 1 and 2. The counting direetion of the counter 21 is determined by the sign of the output signal of the regulator 17 which is determined by the sign detecting element 19. The out-put signal and sign of the tachometer 4 are switehed as in the embodiments of Figures 1 and 2 by means of a ehange-over switch. At the end of the measurement period, the input of the eounter 21 is switehed by switeh 14e from the pulse sequenee of the frequency converter 20 to the digital pulse sequenee n on line 5a, and at the same time from the sign of the regulator 17 output by switeh 14d to the sign n on line 5b whieh eorresponds to the respeetive direetion of rotation of the rotor. A digital/analog eonverter 22 is provided, preferably after the funetion former, to convert the digital output of the eounter 21 to an analog signal for further processing. As the f~mction former in the embodiment ot Figure 3, it is advantageous to use a read-only menlory 23 eonnected between thc counter 21 and the eonverter 22 and whieh is eontrolled by the d-igital output signals of the counter 21. The memory addresses of the ROM 23 are accessed eyelieally, w;th one eyele representing the pth part of one rotor revolution.
This can be done, for example, by a preceding ring counter.
~ ~7~77~
Where the flux angle itself is uSed as the flux angle signal, the function former supplies a function that varies with the counter status of the counter 21 in saw-tooth fashion between - ~and + ~ . Those skilled in the art will appreciate that by appropriate programming of the ROM, however, it is possible to develop other function forms for the rotor angle signal~ For example, the rotor angle signal may consist of two separate signals which represent the sine and cosine, respectively, of an angle corresponding to the output signal of the -integrator.
The partially digitalized embod-iment of the ~invention shown in Figure 3 which uses a digital counter 21 as the integrator advantageously facilitates the setting of the starting value of the integrator, especially in those cases where the computing circuit 9 operates using analog input and output signals but the speed-proportional tachometer output signal n is in digital form. The final output of the control loop furnishes the flux angle as a digital starting value ~o to the integrator 210 The regulator 17, however, advantageously takes the form of an analog regulator. In particular, the regulator is one having proportional and integral components which enable the achievement of especially favorable relationships for the time constants of the control loop.
A special advantage of this form of control loop is that the flux angle ~ , which cannot be maintained constant throughout an unlimited time by the analog computing circuit 9, is stored digitally in the counter 21 at the end of the short measurement period, and :is thus available in the samc form everl a-t`tcr prolonged standstill of the machineO
As shown -in Figure 3, a computing circ-lit 25 is colmccted ahead ot thc regulator 17 to receive the fl~ angle signal and the rotor angle sigTnal, each in the form of two ~ignals representing each angle. The computing element 25 ~ 3.79775 f~mctions to develop a difference angle quantity which varies steadily in accordance with the difference ~ , corresponding to the difference between the two input angles. The difference angle quantity thus developed is supplied as the actual value :input 26 to the regulator 17. The value of-the developed difference angle quantity corresponding to L~r~ = O is connected to the regulator 17 as the nominal va:Lue input 27. Where the computing circuit 9 serves to supply the flux -vector (i.e~ the amplitude¦~y¦ and the angle ~) in polar coordinate form, and the function former ROM 23 supplies the angle ~ itself as the rotor angle signal, the computing element 25 comprises a simple subtraction stage. -.[t will be appreciated, however, that where other functions of ~ and ~ are used as the flux angle and rotor angle signals, the computing element 25 contains an angle difference determining element 30 for forming two quantities from the flux angle and rotor angle signals. The first quantity is proportional to the sine of the angle difference ~ and is connected to serve as the dividend input 31 of a divider element 32. The second quantity is proportional to the cosine of of the angle difference ~ and is connected by means of a threshold element 33 to serve as the divisor input 34 of the divider element 320 The threshold element is shown schematically in Figure 3 as a diode and functions to pass positive input signals (i.e. cos ~ ~ > O~ but blocks the passage of negative values, that is, for cos ~ < O the divisor input 34 has the value 0. Thus, in the range -~ /2 to +Tr/2, the divider element 32 has an output value which is proportional to sin ~ /cos a~ = tan a~; whereas for ~<rr/2 it has ~he valuc ~ x and for L~ ql~ +lr/2 it has thc value ~ . Thus~ thc output s:igna~L o-f the divider element 32 meets the general requirements ~for th( angle d:ifterellce determining element 25, ;.n that it represents a function wh:ich varics stead.ily in accordance with the angle L~. The nominal valuc :input 27 of the regulator ~ 17977~
17 is connected to receive the value tan ~' = O which corresponds to ~ d = O.
The embodiment of Figure 3, represents the case in which the computing circuit 9 of the position sensor develops a flux vector ~ in Cartesian vector component form, i.e.-~sin ~ ycos ~. These Cartesian vector components can be used directly as the flux angle signal, the function former ROM ~3 developing as the rotor angle signal, the functions sin ~ and cos ~ . In this event, the angle difference determining element 30 comprises a vector rotator. The Cartesian coordinates of the flux vector are received at two of the -vector rotator inputs and the s-in and cos of the rotor angle are received at two other vector rotator inputs. The vector rotator serves to rotate the reference system for the input vector by the input angle, and as shown in Figure 3 forms from the Cartesian coordinates ~ sin ~, ~ cos ~ the output quantities ~ sin ~ and ~cos ~ ~, where ~ ~ is given by ~ - ~ . The invention thus makes it possible, as described in reference to Figure 3, to set a digital counter which counts the digital pulses of a non-position-coded digital tach~meter to an initial starting value which corresponds to an angle given by its sine and cosine values. The rotor angle required for control of a synchronous machine can thus be made available as required, in analog form, with the addition of few electronic components other than those already required, such as the computing circuit 9, for control of the speed of rotation of the machine.
~ laving thus described the invention with particular reference to the preferred forms thereof, if will be obvious to those skilled in the a-rt to which the invention pertains, after understanding thc invent-ion, thilt va-rious ch.mges and modifications may be made therein without departing from the spirit .md scope of the invention as defined by the claims amended hereto. Tt will be appreciated that the selection, connection and layout of the v.lrious componen-ts of the described circuits may be varied to suit individual tastcs and require-ments.
For the determination of rotational speed, simple tachometers (e.g.
tachogenerators or incremental digital tachometers) have been developed. For high accuracy in the determination of rotational speed, digital tachometers are most often used, the output signal of which consists of a pulse sequence with pulse intervals inversely proportional to the speed of rotation. These tacho-meters, however, give no information about the angle of rotation of the monit-ored shaft, i.e. the angle between thc rotor axis oE thc synchronolls machine and a fixed reference axis.
The inEormation on the instantaneous rotor angle is especially import-ant in field-oriented control, wherein a field detection device (such as dis-closed for example in German Offenlegungsschrift P 30 26 3~8 laid open on February ~, 1982) is used to determine the amplitude and angular position of l ~79~5 thc flux vector based on the motor currents and voltages. The motor current (i.e. the current supplied to the stator winding) and possibly the field cur-rent (i.e. the current supplied to the rotor winding) of the synchronous mach-ine are controlled so that the components normal to the flux vector (effective components) which determine the torque of the synchronous machine are control-led according to the given speed of rotation or torque, whereas the flux is maintained constant by control of t]le field current and motor current con~pon-ents parallel to the flux vector. I'he initial value of the flux angle (i.e.
the initial angle of the rotating magnetic field) can be determined as descri-bed in U.S. patent 4,119,893 of Bayer et al, issued October 10, 1978, for the start-up of a synchronous machine, by leaving the motor current turned off and calculating the flux angle from the voltage induced in the motor winding (i.e.
stator winding) when the field is connected.
The circuits used for determining the flux angle in this initial position-finding process and during the subsequent field-oriented operation utilize analog input signals and supply analog output signals. Thus, when using digital peripheral equipment (e.g. digital angle pulse generators), appropriate converters are necessary. Another difficulty is caused because such analog circuits contain integrators which are able to store a determined value for only a relatively short period of time.
SUM~IARY O~ TIIE INVENTION
It is an object of the present inventioTI to provide simple app.~ratus for determining the rotor angle o~ a synchronous IllaCIlille Wh:iCIl can easily be adapted to the charac-teristics of the particular circuitry used to control a synchronous machinc.
It is another ob;ject of the invention to provide al)paratus for clet-ermining the rotor angle of a synchronous mach;ne at reducecl e.Ypense for ana-log/digital and digital/analog converters.
~ ~ ~g~75 It is a further object of the invention to provide apparatus for determining the rotor angle of a synchronous machine with which it is possi~le to store the determined rotor angle for a prolonged time even at standstill or slow running of the synch-ronous machine.
In one aspect of the invent-ion, apparatus for determining the rotor angle of a synchronows machine includes a field position sensor, an integrator and a function former. The field position sensor is connected to determ-ine the angle of the rotating flux field relative to a fixed reference axis with the tor current off when the field current is turned on, based on measuring the voltage induced in the motor (i.e. voltage induced in the stator~. The inte-grator is connected to receive the field angle signal from the field position sensor and also a rotational speed-proportional signal from a tachometer. The function former is connected to develop a rotor angle signal that varies periodically with the output of the integrator.
In a preferred embodiment of the invention, described in greater detail below, the integrator is a digital up/down counter connected to receive the rotational speed-proportional signal from a conventional digital tachometer, and the function former is a read-only memory which is cyclically driven.
There have thus been outlined rather broadly certain objects, features and advantages of the invention in order that the detailed description that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional -features of the invention that will describe more fully hereina-fter. Those skilled in tllc art will appreciate that the conception on which this disclosure is based may readily be utili7ed as the basis for the designing of other arrangements for carrying out the purposes of this invent:ion. It is important, therefore, that ~'7~37~S
this disclosure be regarded as including all such equivalent arrangements that encompass the spirit and scope of the invention.
BRIEF DESCRIPTION OF THE DR~WINGS
Embodiments of the invention have been chosen for the purposes of illustration and description, and are shown in the accompanying drawings forming a part of the specification, wherein:
Figure 1 is a schematic view of one form of embodiment of the invention;
Figure 2 is a schematic view of a modified form of the embodiment of Figure l; and Figure 3 is a schematic view of another modified form of the embodiment of Figure 1.
Throughout the drawings, like elements are referred to by like numerals.
DESCRIPTION OF THE PREFERR~D E~BODIMENTS
Figure 1 shows a synchronous machine 1 which is supplied with a motor current (i.e. stator winding current) from a power supply, such as by means of an a.c. inverter. The motor voltage U at a terminal of the machine 1 is measured by means of a transformer 20 The machine 1 has a field winding 3 mounted on the rotor for setting up a magnetic flux field. A tachometer 4 coupled with the rotor shaft furnishes as its output 5 a speed-proportional signal n.
In accordance with the principles of the invention, a field position sensor is provided which measures during a short measurement time per:iod A t, the voltage U induced in the stator with the motor current turned off when thc field current is connected to the field winding 30 For this purpose, as shown in Figure 1, a time control unit 6 is pro-vided which separates the motor wind-ing and the field winding from their current sources by means of switches 7 ~md 8 -in response to a start pulse for initializing the position sensing proccss. After switch 8 has been closed, the motor voltage U induced by the connected field is measured by the voltage transformer 2. A computing circuit 9 develops a flux g~7~
angle signal from the voltage U which corresponds to the angle ~ of the rotat-ing magnetic field flux vector ~. This signal supplies the determined flux angle~ at the output 10 o-f the computing circuit 9 to the end of the measure-ment time period ~t (typically several milliseconds). The computing circuit 9 is constructed to supply this output 10 at the end of the measurement period, even though the other structural elements used in the computing unit 9, i.n particular the :intcgrators, are unable themselvcs to storc a valuc for a prolonged time.
The period ~t, therefore, is long enough to enable the computing circuit to detect the induced voltage U and the computed flux angle si.gnal, but short enough to prevent an alteration of the computed signal due to decay or drift of signal levels in the components, especially the integrators, used in the computing circuit.
The principles of operation of a position sensor of this type are disclosed in German Patent Application 26 35 965. The s-tructure of the comput-ing unit 9 may take the form of the circuit arrangement described, for example, in our Canadian Patent Application 381,414 filed July 9, 1981 and be used according to the teachings of this Canadian Patent Application for the field-oriented operation of the rotating field machine. For field-oriented operation, the motor current I is also measured and the computing unit 9 determines the amplitude ¦~¦ oE the :flux vector ~, in addition to information about thc ~flux angle ~. Determination of the flux amplitudc ~ is, ho~evel, llOt CssCllti.ll for the operation of thc present invention, and ~for thi.s roason the :respect-ive measurillg input 11 (see Fi.gure 1) for the motor currellt :[ and the respect-ive output line 12 oF the computillg unit 9 for the flux nmplitude ¦~¦ are indicated by dashed lines in Figures 1 and 2.
~ 17~775 The invention makes use of the assumption that during standstill of the unloaded machine, the rotor axis and the field axis coincide. The field angle relative to a given, fixed reference axis at the start-up of the synchro-nous machine can thus be used as a star~ting point for the determination of the rotor angle relative to the same fixed axis. This -value is obtained as the output signal 10 of the computing circuit 9.
The flux angle signal ~ developed at the output 10 of the computing circuit 9 is used to set an -integrator 13. A switch 14a which is actuated by the time control un:it 6 serves to connect the output 10 of the computing circuit 9 of the field position sensor to the integrator 13 at least at the end of the measurement period ~t. A switch 14b, which cooperates with the switch 14a in the manner of a change-over switch, connects the speed-proportional signal n output 5 of the tachometer 4 to the integrator 13 following the end of the measurement period ~t. Thus, following the end of the measurement period, the output of the integrator 13 has the value: ~ 0+ rnodtO
A function former circuit 15 develops a rotor angle signal ~ from the output of the integrator 13. For a flux vector ~ supplied by the computing circuit 9 in the form of polar coordinates, the flux angle signal ~ takes the form of the flux angle ~t itself, having a value lying between -~r and + ~. The rotor angle signal ~ developed by the function former 15 thus likewise varies between -~ and + ~ according to the rotor position. Tt will be appreciated by those skilled in the art that other functions may also be used tor the flux angle signal ~ and the rotor anglc signal ~ , clS discussed further below with reference to Figure 3, with the function former 15 sLIpplyillg a per-iodically varying -rotor angle signal ~\ , whose period changes accord-ing to the output signal of the integrator 13. One period of the output signal \ will then cor-~ 1~9775 respond in a two-pole machine to one rotor revolution; or more generally, in a 2p-pole machine, to the pth part of one rotor revolution.
The rotor angle ~ signal 16 supplied at the output of the function former 15 is delivered together with the ~ signal 10 and the ~ signal 12 to the control system of the synchronous machine.
Setting of the integrator 13 can be effected in a simple manner, in that the integrator 13 is arranged in a control loop which during the short measurement period ~t causes the flux angle which is to be set as the starting value for the integrator 13 to follow the actual flux angle determined by -the computing circuit 9. This is shown in the circuitry of Figure 2 which includes a regulator 17 to which the flux angle signal ~ is supplied as a nominal or reference value from the output 10 of the computing circuit 9, and to which the rotor angle signal ~ from the line 16 of the function former 15 is supplied as the actual value. A switch 18 actuated by a corresponding release signal serves to release the regulator 17 during the measurement period, while setting it to zero at other times, so that the connection between the flux angle signal ~ and the rotor angle sigral ~ is effected only during the measurement period. The output signal of the regulator 17 is supplied as an input to the integrator 13 throughout the entire measurement period by means of the change-over switch 14.
The time constant of the regulator 17 can be chosen very short, so that the rotation angle signal associated with the flux angle is very quickly set at thc output of the integrator 13 (viz. the output of the f~mction former 15) and is held there until the end of the measurement period, which can be chosen corres-pondingly short.
The arrangement shown in Figure 2 permits the omiss-ion of a separate time control unit 6 (see Figure 1), since compared with normal operation (switches ~ ~79775 7, 8 closed and regulator 17 set to zero by means of switch 18) during the measurement period only the switches 8 and 18 need be closed, with switch 7 opened and the change-over switch 14 set to the output of the regulator 17.
This arrangement of a memory in a control loop as in Fugure 2 is espeeially advantageous for use w-ith a non-pos-ition-coded digital taehometer.
In the embodiment of the :invention shown in Figure 3, a frequency con-verter 20 is connected at the output of the regulator 17. The con-verter 20 ser-ves to develop a sequence of pulses at a frequency proportional to the output signal of the regulator 17. This signal is then delivered to a digital up/down counter 21 which serves the funetion of the integrator 13 of Figures 1 and 2. The counting direetion of the counter 21 is determined by the sign of the output signal of the regulator 17 which is determined by the sign detecting element 19. The out-put signal and sign of the tachometer 4 are switehed as in the embodiments of Figures 1 and 2 by means of a ehange-over switch. At the end of the measurement period, the input of the eounter 21 is switehed by switeh 14e from the pulse sequenee of the frequency converter 20 to the digital pulse sequenee n on line 5a, and at the same time from the sign of the regulator 17 output by switeh 14d to the sign n on line 5b whieh eorresponds to the respeetive direetion of rotation of the rotor. A digital/analog eonverter 22 is provided, preferably after the funetion former, to convert the digital output of the eounter 21 to an analog signal for further processing. As the f~mction former in the embodiment ot Figure 3, it is advantageous to use a read-only menlory 23 eonnected between thc counter 21 and the eonverter 22 and whieh is eontrolled by the d-igital output signals of the counter 21. The memory addresses of the ROM 23 are accessed eyelieally, w;th one eyele representing the pth part of one rotor revolution.
This can be done, for example, by a preceding ring counter.
~ ~7~77~
Where the flux angle itself is uSed as the flux angle signal, the function former supplies a function that varies with the counter status of the counter 21 in saw-tooth fashion between - ~and + ~ . Those skilled in the art will appreciate that by appropriate programming of the ROM, however, it is possible to develop other function forms for the rotor angle signal~ For example, the rotor angle signal may consist of two separate signals which represent the sine and cosine, respectively, of an angle corresponding to the output signal of the -integrator.
The partially digitalized embod-iment of the ~invention shown in Figure 3 which uses a digital counter 21 as the integrator advantageously facilitates the setting of the starting value of the integrator, especially in those cases where the computing circuit 9 operates using analog input and output signals but the speed-proportional tachometer output signal n is in digital form. The final output of the control loop furnishes the flux angle as a digital starting value ~o to the integrator 210 The regulator 17, however, advantageously takes the form of an analog regulator. In particular, the regulator is one having proportional and integral components which enable the achievement of especially favorable relationships for the time constants of the control loop.
A special advantage of this form of control loop is that the flux angle ~ , which cannot be maintained constant throughout an unlimited time by the analog computing circuit 9, is stored digitally in the counter 21 at the end of the short measurement period, and :is thus available in the samc form everl a-t`tcr prolonged standstill of the machineO
As shown -in Figure 3, a computing circ-lit 25 is colmccted ahead ot thc regulator 17 to receive the fl~ angle signal and the rotor angle sigTnal, each in the form of two ~ignals representing each angle. The computing element 25 ~ 3.79775 f~mctions to develop a difference angle quantity which varies steadily in accordance with the difference ~ , corresponding to the difference between the two input angles. The difference angle quantity thus developed is supplied as the actual value :input 26 to the regulator 17. The value of-the developed difference angle quantity corresponding to L~r~ = O is connected to the regulator 17 as the nominal va:Lue input 27. Where the computing circuit 9 serves to supply the flux -vector (i.e~ the amplitude¦~y¦ and the angle ~) in polar coordinate form, and the function former ROM 23 supplies the angle ~ itself as the rotor angle signal, the computing element 25 comprises a simple subtraction stage. -.[t will be appreciated, however, that where other functions of ~ and ~ are used as the flux angle and rotor angle signals, the computing element 25 contains an angle difference determining element 30 for forming two quantities from the flux angle and rotor angle signals. The first quantity is proportional to the sine of the angle difference ~ and is connected to serve as the dividend input 31 of a divider element 32. The second quantity is proportional to the cosine of of the angle difference ~ and is connected by means of a threshold element 33 to serve as the divisor input 34 of the divider element 320 The threshold element is shown schematically in Figure 3 as a diode and functions to pass positive input signals (i.e. cos ~ ~ > O~ but blocks the passage of negative values, that is, for cos ~ < O the divisor input 34 has the value 0. Thus, in the range -~ /2 to +Tr/2, the divider element 32 has an output value which is proportional to sin ~ /cos a~ = tan a~; whereas for ~<rr/2 it has ~he valuc ~ x and for L~ ql~ +lr/2 it has thc value ~ . Thus~ thc output s:igna~L o-f the divider element 32 meets the general requirements ~for th( angle d:ifterellce determining element 25, ;.n that it represents a function wh:ich varics stead.ily in accordance with the angle L~. The nominal valuc :input 27 of the regulator ~ 17977~
17 is connected to receive the value tan ~' = O which corresponds to ~ d = O.
The embodiment of Figure 3, represents the case in which the computing circuit 9 of the position sensor develops a flux vector ~ in Cartesian vector component form, i.e.-~sin ~ ycos ~. These Cartesian vector components can be used directly as the flux angle signal, the function former ROM ~3 developing as the rotor angle signal, the functions sin ~ and cos ~ . In this event, the angle difference determining element 30 comprises a vector rotator. The Cartesian coordinates of the flux vector are received at two of the -vector rotator inputs and the s-in and cos of the rotor angle are received at two other vector rotator inputs. The vector rotator serves to rotate the reference system for the input vector by the input angle, and as shown in Figure 3 forms from the Cartesian coordinates ~ sin ~, ~ cos ~ the output quantities ~ sin ~ and ~cos ~ ~, where ~ ~ is given by ~ - ~ . The invention thus makes it possible, as described in reference to Figure 3, to set a digital counter which counts the digital pulses of a non-position-coded digital tach~meter to an initial starting value which corresponds to an angle given by its sine and cosine values. The rotor angle required for control of a synchronous machine can thus be made available as required, in analog form, with the addition of few electronic components other than those already required, such as the computing circuit 9, for control of the speed of rotation of the machine.
~ laving thus described the invention with particular reference to the preferred forms thereof, if will be obvious to those skilled in the a-rt to which the invention pertains, after understanding thc invent-ion, thilt va-rious ch.mges and modifications may be made therein without departing from the spirit .md scope of the invention as defined by the claims amended hereto. Tt will be appreciated that the selection, connection and layout of the v.lrious componen-ts of the described circuits may be varied to suit individual tastcs and require-ments.
Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Apparatus for determining the rotor angle of a synchronous machine relative to a fixed reference axis, using a rotational speed-proportional signal supplied by a tachometer, comprising:
a field position sensor for measuring within a short time period the voltage induced in the stator with the motor current off when the field current is turned on, for developing a flux angle signal corresponding to the angle of the magnetic flux vector of the machine, and for storing the developed signal at least until the end of the time period;
an integrator connected at least at the end of the time period to receive the flux angle signal from the field position sensor for setting the integrator at the end of the time period to an initial value correponding to the flux angle signal, and connected after the end of the measurement period to receive and integrate the rotational speed-proportional signal from the tacho-meter; and a function former, connected to receive the sum of the initial value and the integrated rotational speed-proportional signal from the integrator, for developing a rotor angle signal that varies periodically with the integrator output.
a field position sensor for measuring within a short time period the voltage induced in the stator with the motor current off when the field current is turned on, for developing a flux angle signal corresponding to the angle of the magnetic flux vector of the machine, and for storing the developed signal at least until the end of the time period;
an integrator connected at least at the end of the time period to receive the flux angle signal from the field position sensor for setting the integrator at the end of the time period to an initial value correponding to the flux angle signal, and connected after the end of the measurement period to receive and integrate the rotational speed-proportional signal from the tacho-meter; and a function former, connected to receive the sum of the initial value and the integrated rotational speed-proportional signal from the integrator, for developing a rotor angle signal that varies periodically with the integrator output.
2. Apparatus as defined in claim 1, further comprising a regulator connected during the time period to receive the flux angle signal and the rotor angle signal as inputs and to supply an output signal during the time period to the integrator.
3. Apparatus as defined in claim 2, for determining the rotor angle, using a speed-proportional signal supplied by a non-position-coding digital tachometer, further comprising a frequency converter connected between the regulator and the integrator; wherein the integrator comprises a digital up/
down counter whose counting direction is determined by the sign of the regulator output signal; and also comprising a digital-to-analog converter connected at the output of one of the integrator and function former.
down counter whose counting direction is determined by the sign of the regulator output signal; and also comprising a digital-to-analog converter connected at the output of one of the integrator and function former.
4. Apparatus as defined in claim 3, wherein the function former comprises a read-only memory cyclically driven at a period of one rotor revolution; and wherein the digital-to-analog converter is connected to receive the output of the function former.
5. Apparatus as defined in any of claims 2-4, further comprising a computing circuit connected to receive the flux angle signal and the rotor angle signal for forming a difference angle signal which varies steadily as a function of the difference between the values of the flux angle and the rotor angle; wherein the regulator is connected to receive the difference angle signal as an actual value input and to receive a signal representing the value of the difference angle signal for equal flux and rotor angles as a reference value input.
6. Apparatus as defined in any of claims 2-4, further comprising a computing circuit connected to receive the flux angle signal and the rotor angle signal for forming a difference angle signal which varies steadily as a function of the difference between the values of the flux angle and the rotor angle; wherein the regulator is connected to receive the difference angle signal as an actual value input and to receive a signal representing the value of the difference angle signal for equal flux and rotor angles as a reference value input, and wherein the computing circuit comprises a difference deter-mining element which forms first and second quantity signals based on the flux angle and the rotor angle signals, the first quantity signal being proportional to the sine and the second quantity signal being proportional to the cosine of the difference between the flux angle and the rotor angle; and a divider con-nected to receive the first quantity signal as a dividend input; and a thres-hold element connected to deliver the second quantity signal as a divisor input to the divider for positive values and to deliver a zero value as the divisor input for negative values of the cosine of the difference between the flux angle and the rotor angle; the output of the divider being connected as an input to the regulator.
7. Apparatus as defined in any of claims 2-4, further comprising a computing circuit connected to receive the flux angle signal and the rotor angle signal for forming a difference angle signal which varies steadily as a function of the difference between the values of the flux angle and the rotor angle; wherein the regulator is connected to receive the difference angle signal as an actual value input and to receive a signal representing the value of the difference angle signal for equal flux and rotor angles as a reference value input, wherein the computing circuit comprises a difference determining element which forms first and second quantity signals based on the flux angle and the rotor angle signals, the first quantity signal being proportional to the sine and the second quantity signal being proportional to the cosine of the difference between the flux angle and the rotor angle;
and a divider connected to receive the first quantity signal as a dividend input; and a threshold element connected to deliver the second quantity signal as a divisor input to the divider for positive values and to deliver a zero value as the divisor input for negative values of the cosine of the difference between the flux angle and the rotor angle; the output of the divider being corrected as an input to the regulator, and wherein the flux angle signal developed by the field position sensor represents the Cartesian vector components of the magnetic flux vector; the rotor angle signal developed by the function former represents the values of the sine and cosine of the angle corresponding to the sum received from the integrator and the difference determining element comprises a vector rotator.
and a divider connected to receive the first quantity signal as a dividend input; and a threshold element connected to deliver the second quantity signal as a divisor input to the divider for positive values and to deliver a zero value as the divisor input for negative values of the cosine of the difference between the flux angle and the rotor angle; the output of the divider being corrected as an input to the regulator, and wherein the flux angle signal developed by the field position sensor represents the Cartesian vector components of the magnetic flux vector; the rotor angle signal developed by the function former represents the values of the sine and cosine of the angle corresponding to the sum received from the integrator and the difference determining element comprises a vector rotator.
8. Apparatus as defined in any of claims 2-4, wherein the regulator comprises an analog regulator having proportional and integral components.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP3112010.5 | 1981-03-26 | ||
| DE19813112010 DE3112010A1 (en) | 1981-03-26 | 1981-03-26 | DEVICE FOR DETERMINING THE ROTATOR ANGLE OF A SYNCHRONOUS MACHINE |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1179775A true CA1179775A (en) | 1984-12-18 |
Family
ID=6128395
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000399358A Expired CA1179775A (en) | 1981-03-26 | 1982-03-25 | Apparatus for determining the rotor angle of a synchronous machine |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0061647B1 (en) |
| JP (1) | JPS57173757A (en) |
| AT (1) | ATE11832T1 (en) |
| BR (1) | BR8201712A (en) |
| CA (1) | CA1179775A (en) |
| DE (2) | DE3112010A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102017215633A1 (en) * | 2017-09-06 | 2019-03-07 | Zf Friedrichshafen Ag | Method and device for angle determination for a rotary field machine |
| CN114448319B (en) * | 2022-04-08 | 2022-06-17 | 华中科技大学 | Permanent magnet synchronous motor parameter identification method, device, equipment and storage medium |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1273686B (en) * | 1960-02-20 | 1968-07-25 | Siemens Ag | Measuring transducer for recording the rotor angle of synchronous machines |
| AT234836B (en) * | 1960-09-24 | 1964-07-27 | Oerlikon Maschf | Device for detecting the pole wheel angle of a synchronous machine |
| DE2353594C2 (en) * | 1973-10-25 | 1975-10-09 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Method and arrangement for determining the rotor angle of a synchronous machine |
| JPS50158817A (en) * | 1974-06-14 | 1975-12-23 | ||
| DE2635965C3 (en) * | 1976-08-10 | 1979-01-18 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Circuit arrangement and method for forming an electrical quantity which is proportional to a flux component in a rotating field machine |
| JPS547042A (en) * | 1977-06-17 | 1979-01-19 | Hitachi Metals Ltd | Anticorrosive structure of iron metal system chain |
| JPS555035A (en) * | 1978-06-26 | 1980-01-14 | Hitachi Ltd | Brushless motor starting system |
| 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 |
-
1981
- 1981-03-26 DE DE19813112010 patent/DE3112010A1/en not_active Withdrawn
-
1982
- 1982-03-16 DE DE8282102121T patent/DE3262271D1/en not_active Expired
- 1982-03-16 EP EP82102121A patent/EP0061647B1/en not_active Expired
- 1982-03-16 AT AT82102121T patent/ATE11832T1/en not_active IP Right Cessation
- 1982-03-19 JP JP57044464A patent/JPS57173757A/en active Pending
- 1982-03-25 CA CA000399358A patent/CA1179775A/en not_active Expired
- 1982-03-25 BR BR8201712A patent/BR8201712A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| DE3112010A1 (en) | 1982-10-07 |
| EP0061647A1 (en) | 1982-10-06 |
| DE3262271D1 (en) | 1985-03-28 |
| JPS57173757A (en) | 1982-10-26 |
| EP0061647B1 (en) | 1985-02-13 |
| ATE11832T1 (en) | 1985-02-15 |
| BR8201712A (en) | 1983-02-22 |
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