CN110266233B - Method and device for calculating initial rotating speed of asynchronous motor - Google Patents
Method and device for calculating initial rotating speed of asynchronous motor Download PDFInfo
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- CN110266233B CN110266233B CN201910556495.9A CN201910556495A CN110266233B CN 110266233 B CN110266233 B CN 110266233B CN 201910556495 A CN201910556495 A CN 201910556495A CN 110266233 B CN110266233 B CN 110266233B
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- 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
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Abstract
According to the method and the device for calculating the initial rotating speed of the asynchronous motor, after the direct current is injected into the motor, the initial rotating speed of the motor is calculated by extracting the frequency of the same-frequency alternating current component in the three-phase current of the motor, the whole calculation process does not involve the calculation of the stator voltage, so that the problem that the accuracy of the initial rotating speed of the motor calculated according to the stator voltage is too low due to the fact that the stator voltage is influenced by the dead zone of an inverter, the tube voltage drop and the resistance of the stator of the motor when the frequency of the stator of the motor is too low is solved, and the accuracy of calculating the initial rotating speed of the motor is improved.
Description
Technical Field
The invention relates to the technical field of wind power, in particular to a method and a device for calculating the initial rotating speed of an asynchronous motor.
Background
The asynchronous motor speed sensorless control system carries out speed estimation by utilizing easily detected physical quantities such as stator voltage, current and the like to replace a speed sensor, and has the advantages of low cost, small fault probability, no maintenance of the speed sensor and the like, so that the asynchronous motor speed sensorless control system is widely applied to the field of wind power. In the running process of the asynchronous motor speed sensorless vector control system, when the deviation between the actual initial rotating speed of the motor and the initial rotating speed set by the speed-sensorless vector control algorithm is too large, the starting failure can be caused, and even the service life of the motor and the mechanical system of the whole fan can be influenced by torque impact, so that the accurate calculation of the initial rotating speed of the motor is of great importance.
At present, direct current is generally injected into a motor to excite electrons to generate a rotor flux linkage, then the rotor flux linkage of the motor is estimated by using a voltage model, and the initial rotating speed of the motor is estimated according to the rotor flux linkage. However, when the frequency of the motor stator is too low, the stator voltage is also very low, the influence of the inverter dead zone, the tube voltage drop and the motor stator resistance on the stator voltage is great, and the influence of the inverter dead zone, the tube voltage drop and the motor stator resistance on the stator voltage is not considered in the stator voltage obtained through the reconstruction of the inverter duty ratio and the voltage, so that the error between the calculated stator voltage and the actual stator voltage is large. On the basis, the error between the rotor flux linkage estimated by using the voltage model and the actual rotor flux linkage is also large, so that the large error also exists between the initial rotating speed of the motor estimated according to the rotor flux linkage and the actual initial rotating speed of the motor.
Disclosure of Invention
In view of this, the invention provides a method and a device for calculating an initial rotation speed of an asynchronous motor, which further calculate the initial rotation speed of the motor by extracting the frequency of the common-frequency alternating-current component in the three-phase current of the motor, thereby improving the accuracy of the initial rotation speed of the motor.
In order to achieve the above object, the present invention provides the following technical problems:
a method for calculating the initial rotating speed of an asynchronous motor comprises the following steps:
injecting direct current into the motor;
extracting the frequency of the same-frequency alternating current component in the three-phase current of the motor;
and calculating the initial rotating speed of the motor according to the relationship between the current fluctuation frequency and the rotating speed of the motor.
Optionally, the method further includes:
judging whether the motor is in a long-time stop working state;
if the motor is in a long-time stop working state, injecting direct current into the motor;
and if the motor is in a short-time stop working state, executing the extraction of the frequency of the same-frequency alternating-current component in the three-phase current of the motor.
Optionally, the determining whether the motor is in a long-time stop working state includes:
judging whether the absolute values of the three-phase currents of the motor are not greater than preset values;
if any phase current is larger than the preset value, judging that the motor is in a short-time stop working state;
and if the number of the motor is not greater than the preset value, judging that the motor is in a long-time stop working state.
Optionally, before the determining whether the motor is in the long-time stop state, the method further includes:
controlling the inverter to output a duty ratio opposite to the duty ratio output last time;
outputting a zero voltage vector, and setting the identification step to be 1;
and starting a timer, wherein the timing duration is a first preset duration.
Optionally, before injecting the direct current into the motor, the method further includes:
the identification step is set to 2.
Optionally, before the extracting the frequency of the common-frequency alternating-current component in the three-phase current of the motor, the method further includes:
and starting a timer, wherein the timing duration is a second preset duration.
Optionally, the extracting the frequency of the common-frequency alternating-current component in the three-phase current of the motor includes:
sampling the same-frequency alternating-current components in the three-phase current of the motor at preset sampling frequency and sampling point number;
carrying out FFT analysis on the sampling current, the sampling frequency and the sampling point number, and calculating the rough frequency of the same-frequency alternating current component in the three-phase current of the motor;
setting current frequency precision, and calculating a frequency extraction interval corresponding to the current frequency precision according to the current frequency precision, the sampling frequency and the number of sampling points;
calculating the current amplitude corresponding to each frequency in the frequency extraction interval to obtain an amplitude array Amp [ k ]]And determining the array index k of the maximum current amplitude0；
According to the array subscript k of the coarse rate frequency, the current frequency precision and the maximum current amplitude0And the amplitude value array Amp [ k ]]And calculating the final frequency of the same-frequency alternating-current component in the three-phase current of the motor according to the maximum subscript of the motor.
Optionally, the FFT analysis of the sampling current, the sampling frequency, and the number of sampling points is performed to calculate a rough frequency of a common-frequency alternating current component in a three-phase current of the motor, and the calculation includes:
carrying out FFT analysis on the sampling current, the sampling frequency and the sampling point number to generate an FFT amplitude array FFTAmp [ Num ], wherein Num is the sampling point number;
determining an array subscript N of the maximum current amplitude values from FFTAmp [1] to FFTAmp [ Num/2], and calculating the rough frequency of the same-frequency alternating-current component in the three-phase current of the motor according to the subscript N, the sampling frequency and the number of the sampling points.
An apparatus for calculating an initial rotation speed of an asynchronous motor, comprising:
a current injection unit for injecting a direct current to the motor;
the frequency extraction unit is used for extracting the frequency of the same-frequency alternating current component in the three-phase current of the motor;
and the rotating speed calculating unit is used for calculating the initial rotating speed of the motor according to the relationship between the current fluctuation frequency and the rotating speed of the motor.
Optionally, the apparatus further comprises:
the state detection unit is used for judging whether the motor is in a long-time work-stopping state or not, and triggering the current injection unit if the motor is in the long-time work-stopping state; and if the motor is in a short-time stop working state, triggering the frequency extraction unit.
Optionally, the state detection unit is specifically configured to:
judging whether the absolute values of the three-phase currents of the motor are not greater than preset values;
if any phase current is larger than the preset value, judging that the motor is in a short-time stop working state;
and if the number of the motor is not greater than the preset value, judging that the motor is in a long-time stop working state.
Optionally, the apparatus further comprises:
a duty ratio output unit for controlling the inverter to output a duty ratio opposite to a duty ratio output last time;
the vector output unit is used for outputting a zero voltage vector and setting the identification step to be 1;
the first timing unit is used for starting a timer, the timing duration is a first preset duration, and the state detection unit is triggered after the timing is finished;
and the identification step setting unit is used for setting the identification step to be 2 before injecting the direct current into the motor.
Optionally, the apparatus further comprises:
and the second timing unit is used for starting a timer, the timing duration is a second preset duration, and the frequency extraction unit is triggered after the timing is finished.
Optionally, the frequency extracting unit includes:
the current sampling subunit is used for sampling the same-frequency alternating-current component in the three-phase current of the motor at a preset sampling frequency and sampling points;
the rough frequency calculation subunit is used for carrying out FFT analysis on the sampling current, the sampling frequency and the sampling point number and calculating the rough frequency of the same-frequency alternating-current component in the three-phase current of the motor;
the resolution interval calculation subunit is used for setting current frequency precision and calculating a frequency extraction interval corresponding to the current frequency precision according to the current frequency precision, the sampling frequency and the number of the sampling points;
a current amplitude value operator unit for calculating the current amplitude value corresponding to each frequency in the frequency extraction interval to obtain an amplitude value array Amp [ k ]]And determining the array index k of the maximum current amplitude0；
A final frequency calculation subunit for calculating a final frequency from the coarse frequency, the current frequency accuracy, and the array subscript k of the maximum current amplitude0And the amplitude value array Amp [ k ]]And calculating the final frequency of the same-frequency alternating-current component in the three-phase current of the motor according to the maximum subscript of the motor.
Optionally, the coarse frequency calculating subunit is specifically configured to perform FFT analysis on the sampling current, the sampling frequency, and the number of sampling points, and generate an FFT amplitude array FFTAmp [ Num ], where Num is the number of sampling points; determining an array subscript N of the maximum current amplitude values from FFTAmp [1] to FFTAmp [ Num/2], and calculating the rough frequency of the same-frequency alternating-current component in the three-phase current of the motor according to the subscript N, the sampling frequency and the number of the sampling points.
Compared with the prior art, the invention has the following beneficial effects:
the method for calculating the initial rotating speed of the asynchronous motor disclosed by the invention is characterized in that after direct current is injected into the motor, the initial rotating speed of the motor is calculated by extracting the frequency of the same-frequency alternating current component in the three-phase current of the motor, the whole calculation process does not relate to the calculation of the stator voltage, so that the problem that the initial rotating speed of the motor obtained by calculation according to the stator voltage is over-low in accuracy due to the fact that the stator voltage is influenced by an inverter dead zone, a tube voltage drop and the resistance of the stator of the motor when the frequency of the stator of the motor is over-low is solved, and the accuracy of calculating the initial rotating speed of the motor is improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
Fig. 1 is a schematic flow chart of a method for calculating an initial rotation speed of an asynchronous motor according to an embodiment of the present invention;
FIG. 2 is a block diagram illustrating initial rotation speed calculation control of an asynchronous motor based on a dq coordinate system according to an embodiment of the present invention;
FIG. 3 is a block diagram illustrating the calculation and control of the initial rotation speed of the asynchronous motor based on the α β coordinate system according to the embodiment of the present invention;
FIG. 4 is a schematic flow chart illustrating a current frequency extraction method according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of three-phase current waveforms of a 2.5Mw 2 antipodal three-phase asynchronous motor after 50A direct current is injected into the motor;
FIG. 6 is a schematic diagram of a frequency spectrum of a three-phase current of a 2.5Mw 2 antipodal three-phase asynchronous motor after the motor three-phase current is subjected to FFT analysis after being injected with 50A direct current;
FIG. 7 is a schematic flow chart illustrating another method for calculating the initial rotation speed of the asynchronous motor according to the embodiment of the present invention;
FIG. 8 is a schematic flow chart illustrating a method for calculating an initial rotation speed of an asynchronous motor according to an embodiment of the present invention;
fig. 9 is a schematic structural diagram of a device for calculating an initial rotation speed of an asynchronous motor according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The method for calculating the initial rotation speed of the asynchronous motor disclosed in this embodiment is applied to an asynchronous motor controller, and please refer to fig. 1, and specifically includes the following steps:
s101: injecting direct current into the motor;
referring to fig. 2, when the direct current needs to be injected, the current value to be injected is given as id ═ Idc, the angle required for the conversion of park and ipark is set to 0, at this time, the synchronously rotating dq coordinate system always coincides with the stationary α β coordinate system, and the injected current is the direct current in dq, α β, abc coordinates.
After direct current is injected, the motor is excited to generate rotor flux linkage, the amplitude of the alternating current component of the rotor flux linkage is exponentially attenuated along with the reciprocal of a rotor time constant, the frequency is rotor electrical angular frequency, and the rotor flux linkage is spatially represented as a magnetic field with the rotating speed being the rotating rotor electrical angular frequency. Because the motor stator is static, the rotating magnetic field can cut the stator winding to generate induced electromotive force with the same frequency, so that the current loop is disturbed with the same frequency, and finally, the three-phase current of the motor contains alternating current components with the same frequency. The initial speed of the motor can be obtained by extracting the frequency of the alternating current component of the current and then calculating.
It should be noted that, since the initial rotation speed calculation method of the asynchronous motor injects a direct current, the control method based on the α β coordinate system can also realize the initial rotation speed identification of the motor, and the initial rotation speed calculation control block diagram of the asynchronous motor based on the α β coordinate system is shown in fig. 3.
S102: extracting the frequency of the same-frequency alternating current component in the three-phase current of the motor;
specifically, referring to fig. 4, the step of extracting the frequency of the common-frequency alternating-current component in the three-phase current of the motor specifically includes the following steps:
s401: sampling the same-frequency alternating-current components in the three-phase current of the motor at preset sampling frequency and sampling point number;
specifically, the sampling frequency is fs, the number of sampling points is Num, the frequency resolution is fs/Num, and the acquisition Time is Num/fs.
Because the amplitude of the rotor flux linkage alternating current component is exponentially attenuated, the current acquisition time cannot be too long, otherwise, the alternating current component of the current in the second half part of the acquired current is very small, the FFT analysis is not facilitated, and the resolution ratio and the sampling time are in contradiction. If Num is 1024 and the system sampling frequency fs is 2kHz, the acquisition Time is preferably 512 ms.
S402: carrying out FFT analysis on the sampling current, the sampling frequency and the number of sampling points, and calculating the rough frequency of the same-frequency alternating-current component in the three-phase current of the motor;
fft (fast fourier transform) is a fast algorithm for Discrete Fourier Transform (DFT).
Carrying out FFT analysis on the sampling current, the sampling frequency and the sampling point number to generate an FFT amplitude array FFTAmp [ Num ], wherein Num is the sampling point number;
determining an array subscript N of the maximum current amplitude values from FFTAmp [1] to FFTAmp [ Num/2], and calculating the rough frequency of the same-frequency alternating-current component in the three-phase current of the motor according to the subscript N, the sampling frequency and the number of the sampling points.
Coarse frequency fIThe current frequency accuracy at this time is only 1.953Hz, and the following process is performed to further improve the current frequency extraction accuracy.
S403: setting current frequency precision, and calculating a frequency extraction interval corresponding to the current frequency precision according to the current frequency precision, the sampling frequency and the number of sampling points;
setting the current frequency accuracy fmin，fminCan be arbitrarily small, provided that f is set heremin0.1Hz, the length Kmax of the frequency extraction interval is 2 fs/Num/fminWith a frequency extraction interval of [1,39 ═ 39]。
S404: calculating the current amplitude corresponding to each frequency in the frequency extraction interval to obtain an amplitude array Amp [ k ]]And determining the maximumArray subscript k of current amplitude0；
The current amplitude corresponding to each frequency in the frequency extraction interval can be regarded as an amplitude array Amp [ k ].
Find out array Amp [ k ] in turn]The lower label of medium amplitude maximum is k0。
S405: according to the array subscript k of coarse frequency, current frequency precision and maximum current amplitude0And amplitude array Amp [ k ]]And calculating the final frequency of the same-frequency alternating-current component in the three-phase current of the motor according to the maximum subscript of the motor.
The final precise current frequency is:
fIfinal＝fIfmin(k0-0.5Kmax)
fig. 5 shows the three-phase current waveform of the motor after the 2.5Mw 2 antipodal three-phase asynchronous motor is injected with 50A dc current, wherein the a-phase current has an average value of 50A and contains an ac component with attenuated amplitude.
Fig. 6 is a frequency spectrum diagram of current after FFT analysis of three-phase current of the motor, where a resolution of 2Hz is set for coarse analysis, and it is seen from the diagram that the amplitude is at most 8Hz, and the actual current frequency should be: since fl 60/Np 250/60/2 is 8.33Hz, the current frequency obtained directly from the FFT results will have a certain error, and the frequency extraction accuracy can be increased to any set value by the aforementioned high-accuracy frequency extraction method, so that the accuracy of the estimated initial rotation speed will be higher.
S103: and calculating the initial rotating speed of the motor according to the relationship between the current fluctuation frequency and the rotating speed of the motor.
Specifically, the initial rotation speed of the motor is calculated as follows:
wherein n is0Is the initial rotating speed of the motor,fIfinalthe frequency N of the same-frequency alternating current component in the three-phase current of the motor obtained in the steppThe number of pole pairs of the motor is shown.
Therefore, according to the method for calculating the initial rotating speed of the asynchronous motor disclosed by the embodiment, after the direct current is injected into the motor, the initial rotating speed of the motor is calculated by extracting the frequency of the same-frequency alternating current component in the three-phase current of the motor, the whole calculation process does not involve the calculation of the stator voltage, so that the problem that the accuracy of the initial rotating speed of the motor calculated according to the stator voltage is too low due to the fact that the stator voltage is influenced by the dead zone of the inverter, the tube voltage drop and the resistance of the stator of the motor when the frequency of the stator of the motor is too low is solved, and the accuracy of calculating the initial rotating speed of the motor is improved.
When the motor is in a short-time stop working state, the flux linkage of the motor is not completely attenuated, and when residual magnetism exists, the initial rotation speed of the motor can be calculated more quickly and accurately by using the residual magnetism without causing large torque impact, on the basis, please refer to fig. 7, this embodiment discloses another method for calculating the initial rotation speed of the asynchronous motor, and firstly, S701 is executed: judging whether the motor is in a long-time stop working state;
if the motor is in the long-time stop working state, executing S702: injecting direct current into the motor;
if the motor is in the short-time stop working state, executing S703: and extracting the frequency of the same-frequency alternating current component in the three-phase current of the motor.
Specifically, whether the motor is in a long-time stop working state is judged by judging whether the absolute values of the three-phase currents of the motor are not larger than preset values.
If any phase current is larger than the preset value, judging that the motor is in a short-time stop working state;
and if the number of the motor is not greater than the preset value, judging that the motor is in a long-time stop working state.
By judging whether the motor is in a long-time stop working state or not, the problem that the service lives of the motor and a mechanical system are influenced by large torque impact caused by accidentally injecting current when the motor is in a short-time stop working state, namely, a flux linkage is not attenuated is solved, and the stability and the safety of the operation of the motor are ensured.
Further, in order to accurately judge whether the motor is in a long-time stop operation state and accurately extract the frequency of the same-frequency alternating-current component in the three-phase current of the motor, the embodiment discloses another method for calculating the initial rotating speed of the asynchronous motor.
Referring to fig. 8, in execution S804: before judging whether the motor is in a long-time stop state, executing the following operations:
s801: and controlling the inverter to output a duty ratio opposite to the duty ratio output last time.
Specifically, if the duty ratio output by the inverter last time is 1, the duty ratio output this time is 0, and if the duty ratio output by the inverter last time is 0, the duty ratio output this time is 1, so that the problem that the service life of the power tube is shortened because the upper bridge arm short circuit or the lower bridge arm short circuit is adopted each time due to the fact that the duty ratios output each time are the same is solved.
S802: the zero voltage vector is output and the identification step is set to 1.
The state identification Step determines whether the actual duty ratio is from the current loop control output or is a fixed value of 0 or 1, thereby controlling whether the motor is in a three-phase stator short-circuit state or a current loop control state.
The identification step is set to 1, and the three-phase duty ratio signals are all equal to 0 or 1.
S803: and starting a timer to determine whether the timing time reaches a first preset time, such as 10 ms.
When the timing time reaches a first preset time, the three-phase current of the motor is relatively stable, and at the moment, whether the motor is in a long-time stop working state or not can be accurately judged by judging whether the absolute values of the three-phase current of the motor are all larger than a preset value or not.
Accordingly, S805: the identification step is set to 2, and direct current is injected into the motor.
By setting the identification step to be 2, the motor is controlled to be in a current loop control state, so that direct current can be conveniently injected into the motor subsequently.
In executing S807: extracting the frequency of the same-frequency alternating current component in the three-phase current of the motor, and executing the following steps before:
s806: and starting a timer to determine whether the timing time reaches a second preset time, such as 50 ms.
When the timing duration reaches a second preset duration, the same-frequency alternating-current components in the three-phase current of the motor are relatively stable, and at the moment, the frequency of the same-frequency alternating-current components in the three-phase current of the motor can be accurately extracted.
Based on the method for calculating the initial rotation speed of the asynchronous motor disclosed in the above embodiments, this embodiment correspondingly discloses a device for calculating the initial rotation speed of the asynchronous motor, please refer to fig. 9, and the device includes:
a current injection unit 901 for injecting a direct current to the motor;
the frequency extraction unit 902 is used for extracting the frequency of the same-frequency alternating-current component in the three-phase current of the motor;
and a rotating speed calculating unit 903, configured to calculate an initial rotating speed of the motor according to a relationship between the current fluctuation frequency and the rotating speed of the motor.
Optionally, the apparatus further comprises:
the state detection unit is used for judging whether the motor is in a long-time work-stopping state or not, and triggering the current injection unit if the motor is in the long-time work-stopping state; and if the motor is in a short-time stop working state, triggering the frequency extraction unit.
Optionally, the state detection unit is specifically configured to:
judging whether the absolute values of the three-phase currents of the motor are not greater than preset values;
if any phase current is larger than the preset value, judging that the motor is in a short-time stop working state;
and if the number of the motor is not greater than the preset value, judging that the motor is in a long-time stop working state.
Optionally, the apparatus further comprises:
a duty ratio output unit for controlling the inverter to output a duty ratio opposite to a duty ratio output last time;
the vector output unit is used for outputting a zero voltage vector and setting the identification step to be 1;
the first timing unit is used for starting a timer, the timing duration is a first preset duration, and the state detection unit is triggered after the timing is finished;
and the identification step setting unit is used for setting the identification step to be 2 before injecting the direct current into the motor.
Optionally, the apparatus further comprises:
and the second timing unit is used for starting a timer, the timing duration is a second preset duration, and the frequency extraction unit is triggered after the timing is finished.
Optionally, the frequency extracting unit 902 includes:
the current sampling subunit is used for sampling the same-frequency alternating-current component in the three-phase current of the motor at a preset sampling frequency and sampling points;
the rough frequency calculation subunit is used for carrying out FFT analysis on the sampling current, the sampling frequency and the sampling point number and calculating the rough frequency of the same-frequency alternating-current component in the three-phase current of the motor;
the resolution interval calculation subunit is used for setting current frequency precision and calculating a frequency extraction interval corresponding to the current frequency precision according to the current frequency precision, the sampling frequency and the number of the sampling points;
a current amplitude value operator unit for calculating the current amplitude value corresponding to each frequency in the frequency extraction interval to obtain an amplitude value array Amp [ k ]]And determining the array index k of the maximum current amplitude0；
A final frequency calculation subunit for calculating a final frequency from the coarse frequency, the current frequency accuracy, and the array subscript k of the maximum current amplitude0And the amplitude value array Amp [ k ]]And calculating the final frequency of the same-frequency alternating-current component in the three-phase current of the motor according to the maximum subscript of the motor.
Optionally, the coarse frequency calculating subunit is specifically configured to perform FFT analysis on the sampling current, the sampling frequency, and the number of sampling points, and generate an FFT amplitude array FFTAmp [ Num ], where Num is the number of sampling points; determining an array subscript N of the maximum current amplitude values from FFTAmp [1] to FFTAmp [ Num/2], and calculating the rough frequency of the same-frequency alternating-current component in the three-phase current of the motor according to the subscript N, the sampling frequency and the number of the sampling points.
The device for calculating the initial rotating speed of the asynchronous motor disclosed by the embodiment calculates the initial rotating speed of the motor by extracting the frequency of the same-frequency alternating-current component in the three-phase current of the motor after injecting the direct current into the motor, and the whole calculation process does not relate to the calculation of the stator voltage, so that the problem that the accuracy of the initial rotating speed of the motor obtained by calculation according to the stator voltage is too low due to the fact that the stator voltage is influenced by an inverter dead zone, a tube voltage drop and the resistance of the stator of the motor when the frequency of the stator of the motor is too low is solved, and the accuracy of calculating the initial rotating speed of the motor is improved.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
It is further noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in Random Access Memory (RAM), memory, Read Only Memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (9)
1. A method for calculating the initial rotating speed of an asynchronous motor is characterized by comprising the following steps:
injecting direct current into the motor;
extracting the frequency of the same-frequency alternating current component in the three-phase current of the motor;
calculating the initial rotation speed of the motor according to the relationship between the current fluctuation frequency and the rotation speed of the motor,
the method for extracting the frequency of the same-frequency alternating current component in the three-phase current of the motor comprises the following steps:
sampling the same-frequency alternating-current components in the three-phase current of the motor at preset sampling frequency and sampling point number;
carrying out FFT analysis on the sampling current, the sampling frequency and the sampling point number, and calculating the rough frequency of the same-frequency alternating current component in the three-phase current of the motor;
setting current frequency precision, and calculating a frequency extraction interval corresponding to the current frequency precision according to the current frequency precision, the sampling frequency and the number of sampling points;
calculating the current amplitude corresponding to each frequency in the frequency extraction intervalObtaining the value of the amplitude array Amp [ k ]]And determining the array index k of the maximum current amplitude0；
An array subscript k according to the coarse frequency, the current frequency accuracy, the maximum current amplitude0And the amplitude value array Amp [ k ]]And calculating the final frequency of the same-frequency alternating-current component in the three-phase current of the motor according to the maximum subscript of the motor.
2. The method of claim 1, further comprising:
judging whether the motor is in a long-time stop working state;
if the motor is in a long-time stop working state, injecting direct current into the motor;
and if the motor is in a short-time stop working state, executing the extraction of the frequency of the same-frequency alternating-current component in the three-phase current of the motor.
3. The method of claim 2, wherein determining whether the motor is in a long-term shutdown state comprises:
judging whether the absolute values of the three-phase currents of the motor are not greater than preset values;
if any phase current is larger than the preset value, judging that the motor is in a short-time stop working state;
and if the number of the motor is not greater than the preset value, judging that the motor is in a long-time stop working state.
4. The method of claim 2, wherein prior to said determining whether the motor is in a long-stop state, the method further comprises:
controlling the inverter to output a duty ratio opposite to the duty ratio output last time;
outputting a zero voltage vector, and setting the identification step to be 1;
and starting a timer, wherein the timing duration is a first preset duration.
5. The method of claim 4, wherein prior to said injecting a direct current into the electric machine, the method further comprises:
the identification step is set to 2.
6. The method of claim 4, wherein before the extracting the frequencies of the co-frequency alternating current components in the three-phase current of the motor, the method further comprises:
and starting a timer, wherein the timing duration is a second preset duration.
7. The method according to claim 1, wherein the FFT analysis of the sampling current, the sampling frequency and the number of sampling points to calculate the coarse frequency of the co-frequency ac component in the three-phase current of the motor comprises:
carrying out FFT analysis on the sampling current, the sampling frequency and the sampling point number to generate an FFT amplitude array FFTAmp [ Num ], wherein Num is the sampling point number;
determining an array subscript N of the maximum current amplitude values from FFTAmp [1] to FFTAmp [ Num/2], and calculating the rough frequency of the same-frequency alternating-current component in the three-phase current of the motor according to the subscript N, the sampling frequency and the number of the sampling points.
8. An apparatus for calculating an initial rotation speed of an asynchronous motor, comprising:
a current injection unit for injecting a direct current to the motor;
the frequency extraction unit is used for extracting the frequency of the same-frequency alternating current component in the three-phase current of the motor;
the rotating speed calculating unit is used for calculating the initial rotating speed of the motor according to the relation between the current fluctuation frequency and the rotating speed of the motor;
the frequency extraction unit is specifically configured to:
sampling the same-frequency alternating-current components in the three-phase current of the motor at preset sampling frequency and sampling point number;
carrying out FFT analysis on the sampling current, the sampling frequency and the sampling point number, and calculating the rough frequency of the same-frequency alternating current component in the three-phase current of the motor;
setting current frequency precision, and calculating a frequency extraction interval corresponding to the current frequency precision according to the current frequency precision, the sampling frequency and the number of sampling points;
calculating the current amplitude corresponding to each frequency in the frequency extraction interval to obtain an amplitude array Amp [ k ]]And determining the array index k of the maximum current amplitude0；
An array subscript k according to the coarse frequency, the current frequency accuracy, the maximum current amplitude0And the amplitude value array Amp [ k ]]And calculating the final frequency of the same-frequency alternating-current component in the three-phase current of the motor according to the maximum subscript of the motor.
9. The apparatus of claim 8, further comprising:
the state detection unit is used for judging whether the motor is in a long-time work-stopping state or not, and triggering the current injection unit if the motor is in the long-time work-stopping state; and if the motor is in a short-time stop working state, triggering the frequency extraction unit.
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