CN108075707A - Based on the asynchronous machine Restart Method and system under V/f control models - Google Patents
Based on the asynchronous machine Restart Method and system under V/f control models Download PDFInfo
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- 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
- H02P23/00—Arrangements or methods for the control of AC motors characterised by a control method other than vector control
- H02P23/14—Estimation or adaptation of motor parameters, e.g. rotor time constant, flux, speed, current or voltage
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- 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
- H02P1/00—Arrangements for starting electric motors or dynamo-electric converters
- H02P1/16—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters
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- 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
- H02P25/00—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details
- H02P25/02—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the kind of motor
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- 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
- H02P2203/00—Indexing scheme relating to controlling arrangements characterised by the means for detecting the position of the rotor
- H02P2203/09—Motor speed determination based on the current and/or voltage without using a tachogenerator or a physical encoder
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- 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
- H02P2207/00—Indexing scheme relating to controlling arrangements characterised by the type of motor
- H02P2207/01—Asynchronous machines
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Abstract
The present invention discloses asynchronous machine Restart Method and system under a kind of control model based on V/f, it is under V/f control models, by synchronizing frequency from the descending continuous frequency sweep of highest frequency, based on asynchronous machine equivalent circuit, it provides under current frequency close to the stator voltage under field excitation branch line open circuit situation, and using the voltage by certain processing as stator given voltage, according to the situation of change of output current, judge synchronizing frequency whether close to motor actual motion frequency.When stator current is substantially reduced, judge synchronizing frequency close to motor actual motion speed, then given voltage is gradually risen to the control voltage of normal V/f by voltage gradient pattern, and then switches into normal V/f control models, entire start-up course is steady, no current overshoot.The method of the invention is without hardware circuit, it is not required that additional to increase current closed-loop PI controllers, versatility is stronger, and is easily achieved, and has preferable application prospect.
Description
Technical Field
The invention relates to the asynchronous motor control technology, in particular to a restarting method and a restarting system of an asynchronous motor based on a V/f control mode.
Background
In the field of asynchronous motor control, there may be occasions where the motor is started under a free rotation condition, such as a fan that rotates freely under the action of external wind power, and a free-sliding electric locomotive. Since the rotation speed of the controlled object is unknown at this time, if the controlled object is directly started, the rotation difference is too large, so that the overcurrent is caused, and the starting failure is caused.
For the motor with the speed sensor, the real rotating speed of the motor can be directly obtained through the speed sensor, and the motor is directly started under the condition that the rotating speed corresponds to the synchronous frequency. For a motor without a speed sensor, the real rotating speed of the motor needs to be indirectly acquired by a certain method, so that the running slip of the motor under a given frequency is in a controllable range, and then the normal control flow is switched, and the process is generally called rotating speed capturing restart in asynchronous motor control (called asynchronous motor restart for short).
Currently there are two main approaches to restart asynchronous motors:
one method is to add a hardware voltage capture circuit, a rotating motor can generate counter electromotive force at a stator port under the action of residual magnetism during short-time shutdown or residual magnetism generated by external given excitation, and the frequency of the counter electromotive force is judged through the hardware voltage capture circuit so as to acquire the current rotating speed of the motor. The method needs to add a hardware circuit, and the hardware cost of the system is increased.
One method is a software processing method, and is based on the operating characteristics of the asynchronous motor, namely the characteristic that the impedance of a rotor branch in an equivalent circuit of the asynchronous motor is remarkably increased when the synchronous speed of the motor is close to the rotating speed of the motor. By introducing a current closed-loop controller and adopting a frequency sweeping method, namely, the given synchronous frequency is swept step by step from large to small, when the synchronous frequency corresponding to the synchronous speed approaches to the actual rotating speed of the motor, the current is rapidly reduced, and the given frequency is judged to finish the capture of the motor speed. The method needs to add a current closed-loop PI regulator, and because of different motors of the control object and different change rates of the sweep frequency, the fixed PI value is difficult to ensure to adapt to all occasions.
Disclosure of Invention
In view of the above, it is desirable to provide a method and a system for restarting an asynchronous motor, which are highly versatile and easy to implement.
The invention provides an asynchronous motor restarting method based on a V/f control mode, which comprises the following steps:
s1, continuously sweeping the frequency of the synchronization from the highest frequency to a small frequency in a V/f control mode;
s2, calculating the stator voltage close to the open circuit condition of the excitation branch circuit under the current sweep frequency based on the model and the operating characteristics of the asynchronous motor;
s3, taking the stator voltage as a stator given voltage, and judging and obtaining the actual rotating speed of the motor according to the change condition of the output current;
and S4, gradually increasing the given voltage to the control voltage of the normal V/f through the voltage gradient mode, and switching into the normal V/f control mode.
The system for restarting the asynchronous motor based on the V/f control mode comprises the following functional modules:
the frequency sweeping module is used for continuously sweeping the frequency of the synchronous frequency from the highest frequency to a small frequency in a V/f control mode;
the open-circuit voltage determination module is used for calculating the stator voltage when the current sweep frequency is close to the open-circuit condition of the excitation branch circuit based on the model and the operating characteristics of the asynchronous motor;
the motor rotating speed acquisition module is used for judging and acquiring the actual rotating speed of the motor according to the change condition of the output current by taking the stator voltage as the stator given voltage;
and the voltage switching module is used for gradually increasing the given voltage to the control voltage of the normal V/f through the voltage gradient mode and then switching into the normal V/f control mode.
The invention relates to an asynchronous motor restarting method and system based on a V/f control mode, which continuously sweep frequency from maximum frequency to small in the V/f control mode, give stator voltage under the current frequency close to the open circuit condition of an excitation branch circuit based on an asynchronous motor equivalent circuit, use the voltage as stator given voltage after certain processing, and judge whether the synchronous frequency is close to the actual operation frequency of a motor according to the change condition of output current. When the stator current is obviously reduced, the synchronous frequency is judged to be close to the actual running speed of the motor, then the given voltage is gradually increased to the control voltage of the normal V/f through the voltage gradual change mode, and then the normal V/f control mode is switched to enter, the whole starting process is stable, and no current overshoot exists. The method does not need a hardware circuit, does not need to additionally increase a current closed-loop PI controller, has stronger universality, is easy to realize, and has better application prospect.
Drawings
FIG. 1 is a block flow diagram of a method for restarting an asynchronous motor based on a V/f control mode according to the present invention;
FIG. 2 is an equivalent circuit of a T-type asynchronous motor;
FIG. 3 is a flow chart illustrating the steps of a method for restarting an asynchronous motor based on a V/f control mode according to the present invention;
fig. 4 is a waveform of restart of the asynchronous motor at each speed stage.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail with reference to the accompanying drawings and embodiments, it being understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.
The invention provides an asynchronous motor restarting method based on a V/f control mode, as shown in figure 1, the asynchronous motor restarting method based on the V/f control mode comprises the following steps:
s1, continuously sweeping the frequency of the synchronization from the highest frequency to a small frequency in a V/f control mode;
s2, calculating the stator voltage close to the open circuit condition of the excitation branch circuit under the current sweep frequency based on the model and the operating characteristics of the asynchronous motor;
s3, taking the stator voltage as a stator given voltage, and judging and obtaining the actual rotating speed of the motor according to the change condition of the output current;
and S4, gradually increasing the given voltage to the control voltage of the normal V/f through the voltage gradient mode, and switching into the normal V/f control mode.
Wherein, the step S3 further includes the following sub-steps:
s31, correcting the stator voltage close to the open circuit condition of the excitation branch circuit to be used as the stator voltage given value under the current sweep frequency;
s32, when the rotating speed of the motor is close to the real rotating speed of the motor, the rotor branch impedance is increased and the stator current is obviously reduced due to the fact that the slip is reduced;
and S33, when the stator current value is smaller than the judgment threshold value, the synchronous frequency is considered to be close to the actual rotating speed of the motor, and rotating speed capture is further completed.
Specifically, the basic principle of the rotation speed capture of the asynchronous motor applied by the invention is analyzed as follows:
in an asynchronous motor control system without a speed sensor, the rotating speed of a motor cannot be directly obtained, and accurate obtaining of the real running speed of the motor is a premise for realizing normal restarting, so that the rotating speed of the motor needs to be indirectly obtained based on a model and running characteristics of the asynchronous motor.
The T-shaped equivalent circuit of the asynchronous motor is shown in figure 2: in the figure, the position of the upper end of the main shaft,is a voltage of a stator phase and is,is a stator phase current, RsIs stator resistance, RrIs rotor resistance, LsσFor stator leakage inductance, LrσFor rotor leakage inductance, LmIs an excitation inductance, s is the slip ratio of the asynchronous motor,n1the synchronous speed of the motor is shown, and n is the actual rotating speed of the rotor of the motor.
When the stator gives the synchronous frequency f, known from the equivalent circuit of the asynchronous motor1Corresponding to the synchronous speed n of the motor1(p is the number of pole pairs of the motor) and the actual rotating speed n of the motor are larger, because the slip is larger, the rotor resistance is far smaller than the excitation branch, the excitation branch is similar to an open circuit, and the relation between the stator voltage and the stator current is similar to the following:
wherein, UsσFor stator phase voltage effective value, U, under the condition of excitation branch being approximately open-circuitsIs the effective value of the stator phase voltage, IsIs the effective value of stator phase current, omega1For the electrical angular frequency (omega) of the motor1＝2πf1)。
When the synchronous frequency of the motor is close to the real rotating speed of the motor corresponding to the synchronous speed, the slip ratio is close to 0, the impedance of the rotor branch is obviously increased, the rotor branch is similar to an open circuit, and the relation between the stator winding voltage and the stator current of the asynchronous motor is similar to that:
wherein, UsmFor stator phase voltages in the case of an approximately open circuit of the rotor branchesEffective value
In the asynchronous motor, the exciting inductance value is far larger than the leakage inductance value of the stator and the rotor. Generally, under the same current value, when the sweep frequency of the asynchronous motor is corresponding to the synchronous speed and is close to the real rotating speed of the motor, the required voltage value is far larger than the voltage value U when the rotating difference value is largersm＞＞Usσ。
In other words, if the given voltage of the stator port is given according to the voltage value under the condition that the excitation branch is approximately open-circuit in the frequency sweeping stage, when the synchronous speed is close to the real rotating speed of the motor, the stator current of the motor can be greatly reduced.
The invention carries out the capture and restart of the rotating speed of the asynchronous motor based on the basic principle, namely, the voltage value of the port of the equivalent circuit is calculated when the excitation branch is approximately open-circuit under different sweep frequencies based on the resistance and the leakage inductance value of the stator and the rotor of the asynchronous motor. The value is used as a stator voltage given value under the current sweep frequency after correction, when the rotating speed of the motor is close to the real rotating speed of the motor, the rotor branch impedance is increased due to the fact that the slip is reduced, the stator current is obviously reduced, when the stator current value is smaller than a judgment threshold value, the synchronous frequency is considered to be close to the actual rotating speed of the motor, and then rotating speed capture is completed.
According to the basic principle of indirectly acquiring the rotating speed of the motor based on the model and the operating characteristics of the asynchronous motor, the method for realizing the restarting of the asynchronous motor comprises the following steps:
as shown in fig. 3, the whole process of restarting the asynchronous motor in the V/f control mode of the asynchronous motor is realized by the following stages:
stage 1: demagnetization waiting delay phase
The stage is to carry out a section of waiting time delay before wave generation, so that the overcurrent condition caused by the existence of the residual magnetism back electromotive force of the asynchronous motor is prevented when the controller is put into use. And after the time delay is finished, entering a sweep current rising stage.
And (2) stage: sweep voltage rise processing stage
In the phase, the initial value of current in the frequency sweep phase is set(this value is preferably the motor rated field current value ImNWhen the freely rotating motor speed may exceed the motor rated speed, this value may be suitably reduced) and the sweep start frequency f1_H(corresponding to the electrical angular frequency ω1_H＝2πf1_H) And calculating the stator voltage value U under the condition that the expected excitation branch is approximately opened (the slip is large) at the current value by the formula (1)sσ_H。
Gradually increasing the stator given voltage, observing the detected current value, and comparing the detected actual stator current value with the current initial value set in the frequency sweep stageWhen the difference is less than a certain threshold (preferably 1% of the rated current of the motor), after a certain time delay, recording the actually given sweep frequency voltage at the momentAnd entering a frequency sweeping phase.
The stator frequency and stator voltage at this stage are given by the following formula
Wherein,for stator voltage set-point in phase 2, τrIs a value of rotor time constantLrRotor inductance), KtFor adjusting the voltage rise rate (preferably 2), T, in this phase by a time coefficientsampleTo control the sampling time of the system.
In the formula (3), the increment of the stator voltage simultaneously considers the difference between the rotor time constant and the current and the given current, and the voltage rise can be combined with the current response of the motor by introducing the rotor time constant, so that the condition that the node voltage enters the next stage due to unstable voltage possibly caused by controlling the motor time constant to be different under fixed rising frequency is avoided. The introduction of the current difference value enables the closer the actual current is to the given current value, the smaller the voltage increment, and the situation of current overshoot is avoided.
And (3) stage: sweep frequency and rotation speed capturing stage
In the phase, the given frequency is swept from the starting high frequency of the phase 2 to the high frequency, the stator is given voltage, and the error of the motor parameter is considered, and the starting voltage of the actual sweep phase and the calculated voltage based on the equivalent circuit of the motor are combined to perform approximate geometric proportion.
The frequency and voltage of the sweep phase are given as follows:
wherein f is1 *For the given value of the sweep frequency in the third stage,for stator voltage set point in phase 3, UsσFor the current sweep frequency f calculated by equation (1)1 *The lower desired excitation branch approximates the value of the stator voltage in the open circuit (greater slip) condition.
When the sweep frequency is close to the real rotation speed of the motor corresponding to the synchronous speed, the stator current is reduced rapidly, and when the stator current is smaller than the judgment threshold delta ILWhen (Delta I)LThe value range can be set to 50% -10%, and the sweep current initial value is preferred here25%) of the current synchronous frequency is considered to be close to the real rotating speed of the motor, the speed capture is completed, and the normal process transition processing stage is jumped to.
At this stage, when the sweep frequency is lower than the capture lower limit frequency f1_L(preferably 5% of the rated frequency of the motor), the motor is considered to be static, and the system directly jumps to the 0-frequency starting process.
And (4) stage: transition processing stage from capture process to normal operation process
In the stage, given frequency is not changed, and output voltage value U corresponding to the frequency of a normal V/f curve is calculatedsAnd taking the voltage value as a target value, and gradually changing the voltage value to the voltage value in the sweep frequency stage. The voltage ramp formula is as follows:
when in useAnd then, finishing the transition process, jumping the system into a normal V/f control flow, and finishing the rotation speed capturing and restarting process of the asynchronous motor.
The restarting method of the asynchronous motor based on the V/F control mode is realized on a control platform taking a DSP control chip of TI company model F28335 as a main control chip, a 132kW three-phase alternating current asynchronous motor is adopted as a test platform, the rated voltage of the motor is 380V, the rated current 242A, 2 antipodes, the rated frequency is 50Hz, and the rated rotating speed is 1490 r/min. In the test, firstly, the motor is accelerated to a certain rotating speed and stably runs through a normal V/f control mode, then the controller is sealed to enable the controller to enter a free stop state, the motor is started in a rotating speed capturing and restarting mode, the actual rotating speed of the motor is observed through the encoder, and the actual current of the motor is obtained through the controller sampling circuit. The restart operation test is respectively carried out in three speed sections of high speed, middle speed and low speed of the motor, the given frequency, the motor speed, the motor current and the given voltage data in the whole process are recorded by the controller and are led into Matlab to draw process waveforms as shown in figure 4, wherein the speed base value is 1500r/min, and the frequency, the voltage and the current base value are rated values corresponding to the measured motor, wherein figure 4(a) shows a restart waveform diagram of the asynchronous motor in the high speed stage, figure 4(b) shows a restart waveform diagram of the asynchronous motor in the middle speed stage, and figure 4(c) shows a restart waveform diagram of the asynchronous motor in the low speed stage.
Test results show that the restarting method of the asynchronous motor based on the V/f control mode realizes normal restarting operation in high, middle and low frequency bands, the starting process is stable, and no current overshoot exists. The test results show the effectiveness of the method.
Based on the above method for restarting the asynchronous motor under the V/f control mode, the invention also provides a system for restarting the asynchronous motor under the V/f control mode, wherein the system for restarting the asynchronous motor under the V/f control mode comprises the following functional modules:
the frequency sweeping module is used for continuously sweeping the frequency of the synchronous frequency from the highest frequency to a small frequency in a V/f control mode;
the open-circuit voltage determination module is used for calculating the stator voltage when the current sweep frequency is close to the open-circuit condition of the excitation branch circuit based on the model and the operating characteristics of the asynchronous motor;
the motor rotating speed acquisition module is used for judging and acquiring the actual rotating speed of the motor according to the change condition of the output current by taking the stator voltage as the stator given voltage;
and the voltage switching module is used for gradually increasing the given voltage to the control voltage of the normal V/f through the voltage gradient mode and then switching into the normal V/f control mode.
Wherein, the motor speed acquisition module further comprises the following functional units:
the voltage correction unit is used for correcting the stator voltage close to the condition of an open circuit of the excitation branch circuit to be used as the given value of the stator voltage under the current sweep frequency;
the rotating speed pre-judging unit is used for enabling the rotor branch impedance to be increased and the stator current to be obviously reduced due to the fact that the slip is reduced when the rotating speed of the motor is close to the real rotating speed of the motor;
and the rotating speed determining unit is used for considering that the synchronous frequency is close to the actual rotating speed of the motor when the current value of the stator is smaller than the judgment threshold value, and further completing rotating speed capture.
The invention relates to an asynchronous motor restarting method and system based on a V/f control mode, which continuously sweep frequency from maximum frequency to small in the V/f control mode, give stator voltage under the current frequency close to the open circuit condition of an excitation branch circuit based on an asynchronous motor equivalent circuit, use the voltage as stator given voltage after certain processing, and judge whether the synchronous frequency is close to the actual operation frequency of a motor according to the change condition of output current. When the stator current is obviously reduced, the synchronous frequency is judged to be close to the actual running speed of the motor, then the given voltage is gradually increased to the control voltage of the normal V/f through the voltage gradual change mode, and then the normal V/f control mode is switched to enter, the whole starting process is stable, and no current overshoot exists. The method does not need a hardware circuit, does not need to additionally increase a current closed-loop PI controller, has stronger universality, is easy to realize, and has better application prospect.
The above apparatus embodiments and method embodiments are in one-to-one correspondence, and reference may be made to the method embodiments for a brief point of the apparatus embodiments.
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.
Those of skill would further appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the various illustrative components and steps have been described above generally in terms of their functionality in order to clearly illustrate this interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
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, read only memory, 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.
While the present invention has been described with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, which are illustrative and not restrictive, and it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (8)
1. A restarting method of an asynchronous motor based on a V/f control mode is characterized by comprising the following steps:
s1, continuously sweeping the frequency of the synchronization from the highest frequency to a small frequency in a V/f control mode;
s2, calculating the stator voltage close to the open circuit condition of the excitation branch circuit under the current sweep frequency based on the model and the operating characteristics of the asynchronous motor;
s3, taking the stator voltage as a stator given voltage, and judging and obtaining the actual rotating speed of the motor according to the change condition of the output current;
and S4, gradually increasing the given voltage to the control voltage of the normal V/f through the voltage gradient mode, and switching into the normal V/f control mode.
2. The V/f control mode-based asynchronous motor restarting method according to claim 1 wherein said step S3 further comprises the sub steps of:
s31, correcting the stator voltage close to the open circuit condition of the excitation branch circuit to be used as the stator voltage given value under the current sweep frequency;
s32, when the rotating speed of the motor is close to the real rotating speed of the motor, the rotor branch impedance is increased and the stator current is obviously reduced due to the fact that the slip is reduced;
and S33, when the stator current value is smaller than the judgment threshold value, the synchronous frequency is considered to be close to the actual rotating speed of the motor, and rotating speed capture is further completed.
3. The V/f control mode-based restart method for an asynchronous motor according to claim 1, wherein the frequency and voltage of the sweep phase are given as follows:
<mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <mrow> <msubsup> <mi>f</mi> <mn>1</mn> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>N</mi> <mo>+</mo> <mn>1</mn> <mo>)</mo> </mrow> <mo>=</mo> <msubsup> <mi>f</mi> <mn>1</mn> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>N</mi> <mo>)</mo> </mrow> <mo>-</mo> <mfrac> <msub> <mi>f</mi> <mi>N</mi> </msub> <msub> <mi>&tau;</mi> <mi>r</mi> </msub> </mfrac> <msub> <mi>T</mi> <mrow> <mi>s</mi> <mi>a</mi> <mi>m</mi> <mi>p</mi> <mi>l</mi> <mi>e</mi> </mrow> </msub> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msubsup> <mi>U</mi> <mi>s</mi> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>N</mi> <mo>+</mo> <mn>1</mn> <mo>)</mo> </mrow> <mo>=</mo> <msubsup> <mi>U</mi> <mrow> <mi>s</mi> <mi>H</mi> </mrow> <mo>*</mo> </msubsup> <mo>&times;</mo> <mfrac> <mrow> <msub> <mi>U</mi> <mrow> <mi>s</mi> <mi>&sigma;</mi> </mrow> </msub> <mrow> <mo>(</mo> <mi>N</mi> <mo>)</mo> </mrow> </mrow> <msub> <mi>U</mi> <mrow> <mi>s</mi> <mi>&sigma;</mi> <mo>_</mo> <mi>H</mi> </mrow> </msub> </mfrac> </mrow> </mtd> </mtr> </mtable> </mfenced>
wherein f is1 *For the given value of the frequency sweep frequency in the frequency sweep stage,for the given value of the stator voltage in the sweep frequency phase,Usσfor the current frequency f of the sweep1 *Stator voltage value, T, at which the desired excitation branch is approximately open-circuitsampleFor controlling the sampling time of the system, Usσ_HThe expected stator voltage value under the condition that the excitation branch is approximately open-circuit, N is the actual rotating speed of the motor rotor,for a given sweep voltage in practice, τrIs a rotor time constant value.
4. The V/f control mode-based restarting method for an asynchronous motor according to claim 3 wherein the voltage ramp formula is as follows:
<mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <mrow> <msubsup> <mi>f</mi> <mn>1</mn> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>N</mi> <mo>+</mo> <mn>1</mn> <mo>)</mo> </mrow> <mo>=</mo> <msubsup> <mi>f</mi> <mn>1</mn> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>N</mi> <mo>)</mo> </mrow> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msubsup> <mi>U</mi> <mi>s</mi> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>N</mi> <mo>+</mo> <mn>1</mn> <mo>)</mo> </mrow> <mo>=</mo> <msubsup> <mi>U</mi> <mi>s</mi> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>N</mi> <mo>)</mo> </mrow> <mo>+</mo> <mfrac> <msub> <mi>T</mi> <mrow> <mi>s</mi> <mi>a</mi> <mi>m</mi> <mi>p</mi> <mi>l</mi> <mi>e</mi> </mrow> </msub> <mrow> <msub> <mi>K</mi> <mi>I</mi> </msub> <msub> <mi>&tau;</mi> <mi>r</mi> </msub> </mrow> </mfrac> <msub> <mi>U</mi> <mrow> <mi>s</mi> <mi>&sigma;</mi> <mo>_</mo> <mi>H</mi> </mrow> </msub> </mrow> </mtd> </mtr> </mtable> </mfenced>
KIthe time coefficient is used for adjusting the voltage rising speed in the phase.
5. The asynchronous motor restarting system based on the V/f control mode is characterized by comprising the following functional modules:
the frequency sweeping module is used for continuously sweeping the frequency of the synchronous frequency from the highest frequency to a small frequency in a V/f control mode;
the open-circuit voltage determination module is used for calculating the stator voltage when the current sweep frequency is close to the open-circuit condition of the excitation branch circuit based on the model and the operating characteristics of the asynchronous motor;
the motor rotating speed acquisition module is used for judging and acquiring the actual rotating speed of the motor according to the change condition of the output current by taking the stator voltage as the stator given voltage;
and the voltage switching module is used for gradually increasing the given voltage to the control voltage of the normal V/f through the voltage gradient mode and then switching into the normal V/f control mode.
6. The V/f control mode-based asynchronous motor restarting system according to claim 5 wherein the motor speed acquisition module further comprises the following functional units:
the voltage correction unit is used for correcting the stator voltage close to the condition of an open circuit of the excitation branch circuit to be used as the given value of the stator voltage under the current sweep frequency;
the rotating speed pre-judging unit is used for enabling the rotor branch impedance to be increased and the stator current to be obviously reduced due to the fact that the slip is reduced when the rotating speed of the motor is close to the real rotating speed of the motor;
and the rotating speed determining unit is used for considering that the synchronous frequency is close to the actual rotating speed of the motor when the current value of the stator is smaller than the judgment threshold value, and further completing rotating speed capture.
7. Asynchronous motor restart system according to claim 5 based on V/f control mode characterized in that the frequency and voltage of the sweep phase are given as follows:
<mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <mrow> <msubsup> <mi>f</mi> <mn>1</mn> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>N</mi> <mo>+</mo> <mn>1</mn> <mo>)</mo> </mrow> <mo>=</mo> <msubsup> <mi>f</mi> <mn>1</mn> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>N</mi> <mo>)</mo> </mrow> <mo>-</mo> <mfrac> <msub> <mi>f</mi> <mi>N</mi> </msub> <msub> <mi>&tau;</mi> <mi>r</mi> </msub> </mfrac> <msub> <mi>T</mi> <mrow> <mi>s</mi> <mi>a</mi> <mi>m</mi> <mi>p</mi> <mi>l</mi> <mi>e</mi> </mrow> </msub> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msubsup> <mi>U</mi> <mi>s</mi> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>N</mi> <mo>+</mo> <mn>1</mn> <mo>)</mo> </mrow> <mo>=</mo> <msubsup> <mi>U</mi> <mrow> <mi>s</mi> <mi>H</mi> </mrow> <mo>*</mo> </msubsup> <mo>&times;</mo> <mfrac> <mrow> <msub> <mi>U</mi> <mrow> <mi>s</mi> <mi>&sigma;</mi> </mrow> </msub> <mrow> <mo>(</mo> <mi>N</mi> <mo>)</mo> </mrow> </mrow> <msub> <mi>U</mi> <mrow> <mi>s</mi> <mi>&sigma;</mi> <mo>_</mo> <mi>H</mi> </mrow> </msub> </mfrac> </mrow> </mtd> </mtr> </mtable> </mfenced>
wherein f is1 *For the given value of the frequency sweep frequency in the frequency sweep stage,for stator voltage set-point in sweep-frequency phase, UsσFor the current frequency f of the sweep1 *Stator voltage value, T, at which the desired excitation branch is approximately open-circuitsampleFor controlling the sampling time of the system, Usσ_HThe expected stator voltage value under the condition that the excitation branch is approximately open-circuit, N is the actual rotating speed of the motor rotor,for a given sweep voltage in practice, τrIs a rotor time constant value.
8. The V/f control mode-based restart system for an asynchronous motor according to claim 7, wherein the voltage ramp formula is as follows:
<mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <mrow> <msubsup> <mi>f</mi> <mn>1</mn> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>N</mi> <mo>+</mo> <mn>1</mn> <mo>)</mo> </mrow> <mo>=</mo> <msubsup> <mi>f</mi> <mn>1</mn> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>N</mi> <mo>)</mo> </mrow> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msubsup> <mi>U</mi> <mi>s</mi> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>N</mi> <mo>+</mo> <mn>1</mn> <mo>)</mo> </mrow> <mo>=</mo> <msubsup> <mi>U</mi> <mi>s</mi> <mo>*</mo> </msubsup> <mrow> <mo>(</mo> <mi>N</mi> <mo>)</mo> </mrow> <mo>+</mo> <mfrac> <msub> <mi>T</mi> <mrow> <mi>s</mi> <mi>a</mi> <mi>m</mi> <mi>p</mi> <mi>l</mi> <mi>e</mi> </mrow> </msub> <mrow> <msub> <mi>K</mi> <mi>I</mi> </msub> <msub> <mi>&tau;</mi> <mi>r</mi> </msub> </mrow> </mfrac> <msub> <mi>U</mi> <mrow> <mi>s</mi> <mi>&sigma;</mi> <mo>_</mo> <mi>H</mi> </mrow> </msub> </mrow> </mtd> </mtr> </mtable> </mfenced>
KIthe time coefficient is used for adjusting the voltage rising speed in the phase.
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