CN114487827B - Motor starting locked-rotor detection method based on current variance - Google Patents
Motor starting locked-rotor detection method based on current variance Download PDFInfo
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- G—PHYSICS
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- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/02—Measuring effective values, i.e. root-mean-square values
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- G—PHYSICS
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Abstract
The invention discloses a motor starting locked-rotor detection method based on current variance, which realizes the accurate detection of whether a locked-rotor fault exists in a motor by detecting the current variance in a specific time window of the soft start of the motor and analyzing the current variance with the normal soft start current variance. The motor starting locked-rotor detection method provided by the invention takes the normal soft-starting current variance when the motor operation condition changes as a reference value, and can effectively improve the capability of the algorithm in adapting to different working condition environments, inhibiting parameter drift caused by motor aging and quickly detecting locked-rotor.
Description
Technical Field
The invention relates to the technical field of motors, in particular to a motor starting locked-rotor detection method based on current variance.
Background
The motor is widely used in various industries such as various machine tools, electric vehicles, high-speed rail locomotives, factory power equipment, water supply and drainage equipment, elevators, electric fans, air conditioners and the like as a power source. Due to the complex working conditions and imperfect protection measures of the motor, the motor rotor is often locked, for example, a transmission mechanism on the motor rotor is locked or a speed change gear is locked due to foreign matters or faults, an elevator transmission chain is locked, a belt of a transmission device is locked, a fluid medium of a water pump is frozen or silt is locked. Once the stalling occurs, the current of the motor rises sharply, which is far larger than the rated working current and even can reach dozens of times of the rated current. Huge electric current leads to motor consumption sharply to increase, and the inside temperature of motor rises fast, and motor coil insulated paint damages, leads to the inside short circuit of motor, and the electric current of the motor of further increase can arouse the conflagration even when serious. At present, the locked rotor detection technology provided in the existing literature generally adopts schemes of detecting the rotating speed of a motor, the counter electromotive force of the motor, the internal temperature of the motor, the current of the motor and the like. The locked rotor scheme is detected by adopting the rotating speed of the motor and the internal temperature of the motor, and a detection element needs to be added in the motor or on a rotating shaft, so that the structure of the motor is complex, the design and the manufacturing process of the whole motor are influenced, and the cost and the complexity are increased. The locked rotor is detected by adopting a counter electromotive force scheme, and on one hand, the rotating speed is calculated by an accurate and reliable mathematical model through the counter electromotive force; on the other hand, when the rotating speed is low, the value of the back electromotive force is small, the signal to noise ratio of the sampled data is not high, the sampled data is easily interfered by noise, a complex signal processing method is needed, and therefore a software algorithm is complex and the cost is high. The current detection locked rotor is adopted, and the locked rotor is widely used without changing the structure due to the aspect of data acquisition. However, in the existing scheme, the current peak value is often detected to judge whether the locked rotor occurs, and the locked rotor is compared with a motor locked rotor current reference value obtained by testing before leaving a factory, so as to judge whether the water pump has the start locked rotor. The scheme mainly has the following problems: firstly, locked-rotor current drift is caused by motor aging, difference of working environments and the like; and secondly, the judgment is only carried out by depending on the starting current peak value single-point parameter, so that misjudgment and failure can be caused, and the reliability, robustness and interference suppression capability of the judgment are reduced.
Disclosure of Invention
The invention aims to provide a motor starting locked-rotor detection method based on current variance. The invention has the advantages of accurate judgment, simple structure and low cost.
The technical scheme of the invention is as follows: a motor starting locked rotor detection method based on current variance comprises the following steps:
step one, when the motor is normally soft started, sampling period T is used s For interval pair motor current effective value
Sampling is performed, and an average value of the sampled data is calculated
Sum variance
Step two, when the motor is started to rotate and block, the sampling period T is used s For interval to effective value I of motor current soft (t) sampling and calculating the average of the sampled data
Sum variance S 2 ；
Step three, judging
If the current is less than or equal to the threshold eta, if not, the motor is determined to be normally soft-started, and if so, the step d is carried out;
step four, calculating
Judgment of
And if the value is larger than or equal to the threshold value theta, determining that the motor is started and blocked.
The motor starting locked-rotor detection method based on the current variance comprises the step IThe sampling process is to determine the effective value of the motor current
At the moment of occurrence of the maximum value of
Obtaining
Effective value of current in time
Form an array of
In the method for detecting the locked rotor during the motor starting based on the current variance, the sampling process in the second step is to determine the effective value I of the motor current soft (t) time of occurrence of maximum value
Obtaining
Effective value of current I in time soft (t) data, forming an array
According to the motor starting locked-rotor detection method based on the current variance, when a motor is normally and softly started, whether the running working condition of the motor changes or not is judged, sampling work is executed after the motor is determined not to be in abnormal conditions such as locked-rotor and other overload conditions, the soft start impedance is connected to a power line of the motor by a controller, and the motor starts to be softly started.
According to the motor starting locked-rotor detection method based on the current variance, when the motor starting locked-rotor detection is carried out, the soft starting impedance is connected to the power line of the motor, and the current is always in a safe range when locked-rotor is ensured.
The motor starting locked-rotor detection method based on the current variance comprises the step four of judging
Whether the value is larger than or equal to the threshold value theta or not, if not, the motor is in a normal soft start state, whether the soft start timing is finished or not is judged, if so, the controller short-circuits soft start impedance on a power line of the motor, and the water pump enters a normal working procedure; otherwise, wait.
Compared with the prior art, the method and the device realize accurate detection on whether the motor has the locked rotor fault or not by detecting the current variance in the specific time window of the soft start of the motor and analyzing the current variance with the normal soft start current variance. The motor starting locked-rotor detection method provided by the invention takes the normal soft start current variance when the operation working condition of the motor changes as a reference value, and can effectively improve the capability of the algorithm in adapting to different working condition environments, inhibiting parameter drift caused by motor aging and quickly detecting locked-rotor. The hardware structure of the invention is simple, only the current data is sampled and analyzed, and the cost is low. In addition, the invention increases soft start impedance to effectively limit the start current, ensures that the current is always in a safe range during locked rotor, and ensures that the motor is safe and reliable; the method obtains the current variance in the soft start current window time as a judgment basis, has simple algorithm, can effectively reduce misjudgment, and improves the reliability and robustness of diagnosis and the capability of inhibiting interference. The invention obtains the variance of the soft starting current of the motor when the working condition changes (such as the change of the working environment, the aging of the motor and the like) as the reference of the locked-rotor detection, and can be self-adaptive to the locked-rotor current drift caused by the change of the motor working condition and parameters.
Drawings
FIG. 1 is a schematic diagram of a motor soft start circuit;
FIG. 2 is a graph of normal soft start current and speed time;
fig. 3 is a graph of soft-start current and speed time for a locked rotor fault.
Detailed Description
The invention is further illustrated by the following figures and examples, which are not to be construed as limiting the invention.
Example (b): a motor starting locked rotor detection method based on current variance comprises a motor normal soft start current variance obtaining algorithm and a motor starting locked rotor detection algorithm, wherein the motor normal soft start current variance obtaining algorithm comprises the following steps:
(1) Determine whether the operating condition of the motor has changed (e.g., operating environment changes and motor operating time is too long, resulting in aging, etc.)? If yes, entering the step (2); otherwise, the program exits without setting new parameters;
(2) After confirming that the motor is not in abnormal conditions such as locked rotor and other overload conditions, manually pressing a normal soft start current variance obtaining mode key, executing a soft start current variance obtaining program, and entering the step (3);
(3) The controller connects the soft start impedance to the power line of the motor, and the motor starts soft start. At the same time with a sampling period T s Starting the effective value of the motor current for the interval
Sampling is carried out;
(4) Determining
At the moment of occurrence of the maximum value of
(5) Obtaining
The current effective value data in time form an array
Calculating the mean value
Sum variance
(6) Will be provided with
Storing the motor rotor-locked rotor in a memory as a reference value of a motor starting locked rotor detection algorithm;
(7) The system displays that the soft start current variance is successfully updated and stops;
(8) The program exits;
the motor starting locked-rotor detection algorithm comprises the following steps:
(1) Entering a motor starting locked-rotor detection program;
(2) The controller connects the soft start impedance to the power line of the motor, and the motor starts soft start. Simultaneously with a sampling period T s Effective value I of motor current for interval start soft (t) sampling;
(3) Obtaining I soft Maximum value of (t)
And the moment of occurrence
(4) Obtaining
Within time I soft (t) value, composition of array
Calculating an array average
Sum variance
(5) Judgment of
(wherein η is setThresholds, for example: 0.1, 0.15)? If yes, entering the step (6); otherwise, entering the step (8);
(6) Calculating out
(7) Judgment of
(wherein
Is a positive number less than 1, for example: 0.8, 0.9)? If yes, entering the step (10); otherwise, entering step (8);
(8) Is the motor in a normal soft start state, does the soft start timing end? If yes, entering the step (9); otherwise, waiting;
(9) The controller shorts out the soft start impedance on the power line of the motor, the water pump enters a normal working procedure, and the step (11) is carried out;
(10) The controller cuts off the power supply of the motor, alarms that the motor is started and locked, and enters the step (11);
(11) The locked rotor detection program exits.
For further explaining the technical solution of the present invention, fig. 1 shows the working principle of the soft start circuit of the motor as follows: when the system is in a standby state during power-on, output ports Out1 and Out2 are both at a low level. The controller detects the state of the keys in real time through a keyboard scanning program, and executes a normal soft start current variance obtaining algorithm after the fact that the keys are pressed in S1 is found. At this time, the controller enables the soft start timer to run for setting the soft start time. Meanwhile, the output port Out1 of the controller is at a high level, the coil of KM1 is electrified, the three-phase contact of KM1 is closed, and 380V three-phase alternating current is connected to the motor. Because Out2 is low level, the KM2 contact keeps an off state, the three-phase soft start impedance Z is connected in series on a power line, and the motor is in a soft start state. The controller acquires the time-varying relation of the current at the soft start stage by sampling the value of the current effective value detection circuit in real time through the AD (analog-to-digital) circuit
Until the soft start timing is finished. By applying current to the soft start phase
Analysis of, obtaining
Time of occurrence of peak
And window time
Inner part
Variance of (2)
And the reference value is used as a reference value for motor starting locked rotor identification and is stored in a memory of the processor. The reference value of the foundation
Under the existing condition, after the controller finds that S2 is pressed through a keyboard scanning program, the controller executes a motor starting locked rotor detection algorithm. The controller enables the soft start timer to run. Meanwhile, the output port Out1 of the controller is at a high level, the coil of the KM1 is electrified, the three-phase contact of the KM1 is closed, and 380V three-phase alternating current is connected to the water pump. Because Out2 is low level, the KM2 contact keeps an off state, the three-phase soft start impedance Z is connected in series on a power line, and the motor is in a soft start state. The controller samples the output value I of the current effective value detection circuit in real time through AD soft (t) obtaining I soft (t) time of occurrence of maximum value
Calculating window time
Inner I soft (t) variance
Further calculate the dimensionless quantity
By making a judgment
And a relationship with a set small positive threshold parameter theta (for example, theta is 0.8 or 0.9) so as to identify whether the motor is operated in a starting locked-rotor fault state. When it is satisfied with
When the motor is in a starting locked-rotor fault, the output port Out1 of the controller is at a low level, the coil of the KM1 is powered off, the three-phase contact of the KM1 is disconnected, and the motor is stopped and the locked-rotor fault is alarmed. Otherwise, the motor is in a normal starting state, and the state of the motor is continued until the soft start timing is finished. Once the soft start is finished, the output port Out2 of the controller is at a high level, the coil of the KM2 is electrified, the three-phase contact of the KM2 is closed, and the soft start state is finished to enter a full-voltage normal operation state. And no matter the controller executes a normal soft-start current variance obtaining algorithm or a motor start locked rotor detection algorithm, as long as the controller finds that S3 is pressed down, out1 and Out2 are low levels, and the controller is stopped immediately.
FIG. 2 is a graph showing the normal soft-start current and the time variation of the rotation speed, wherein the relevant parameters are described as follows:
is a relation curve of the normal soft start motor current along with the time t,
Is a curve of the normal soft start motor rotating speed with the time t,
Is composed of
Reaches the maximum value
Corresponding time, I N Rated current value of motor, NT s Observing window time for soft start data, N being the number of sampled data within the window time, T s Is a sampling period,
Is the soft start end time.
When the soft start is normal, the conditions of locked rotor and the like can not occur under the working condition of the motor. In fig. 1, at the start of soft start, the soft start current rapidly rises from zero to zero due to the small electromagnetic inertia of the motor circuit
But can be controlled due to the current limiting function of the soft start impedance connected in series on the power line of the motor
Is of a size satisfying
Wherein: alpha is a number greater than zero, and the specific value can be determined by actual conditions. By controlling the value of alpha, the synthetic starting torque of the motor can be ensured not to be too large or too small, and the normal soft start operation of the motor at certain acceleration is realized. In addition, the mechanical rotation inertia of the motor is far greater than the electromagnetic inertia of the circuit, so that
The motor speed is negligible. However, under the action of the resultant torque, the rotating speed of the motor is continuously increased, the counter electromotive force of the motor is also continuously increased, and the current is continuously increased
In that
And continues to decrease. Due to the continuous increase of the back electromotive force, so
In that
The degree of decline gradually decreases, and the curve gradually flattens. However, at observation window time
In the interior of the container body,
the curve changes significantly.
Fig. 3 shows a graph of the soft start current and the time variation of the rotating speed in the locked rotor fault, and the relevant parameters in the graph are explained as follows: I.C. A soft (t) is a relation curve of the current of the soft start motor along with the time t during the locked rotor fault, n soft (t) is a relation curve of the rotating speed of the soft start motor along with the time t during the locked rotor fault,
Is I soft (t) reaches a maximum value
The corresponding time,
A stable value of locked-rotor fault current for soft start,
Is the maximum value of the current of the normal soft start motor, NT s Observing window time for soft start data, N being the number of sampled data within the window time, T s Is a sampling period,
Is the soft start end time.
When the motor is locked soft (t) is coincident with the time axis, and is held at zero, and its back electromotive force is zero. Because the electromagnetic inertia of the motor circuit is small, the current quickly rises from zero in soft start
Is timed to
Then slightly falls and quickly reaches the locked-rotor stable current
Due to normal soft start
The motor rotating speed is very small in time, so
And
the difference is small. As known from the equivalent circuit model of the motor, the leakage inductance and the excitation inductance in the model are very small, and the peak current of the soft start is realized when the motor is locked
And
the gap is also small. So that the method has the advantages that,
the difference in value of (a) is small. In the same way, the method for preparing the composite material,
and
the difference in (a) is also small. However, the waveforms shown in FIGS. 2 and 3 are at observation window times
And
in the interior of the container body,
the curve changes significantly, and I soft (t) does not vary significantly. The variance definition and the mathematical meaning show that the variance of the waveform with obvious change in a section of interval is large, and the variance of the waveform with unobvious change is small.
Comparing the waveforms of fig. 2 and 3, the normal soft start current of the motor can be seen
And soft start current I of locked rotor fault soft (t) in respective time windows
And
the variance within is very different. Thus, the current variance during the acquisition of the normal soft start phase
On the basis of serving as reference, solving the current variance s in the soft start stage of the actual working condition 2 And
by making a judgment
And a threshold value theta (wherein theta is a positive number smaller than 1, such as 0.8 and 0.9) to further judge whether the actual working condition is locked rotor, so that the locked rotor of the motor can be quickly detected and protected, and the motor can be improvedWorking life and safety.
In conclusion, the invention realizes the accurate detection of whether the motor has the locked rotor fault or not by detecting the current variance in the specific time window of the soft start of the motor and analyzing the current variance with the normal soft start current variance. The motor starting locked-rotor detection method provided by the invention takes the normal soft-starting current variance when the motor operation condition changes as a reference value, and can effectively improve the capability of the algorithm in adapting to different working condition environments, inhibiting parameter drift caused by motor aging and quickly detecting locked-rotor.
Claims (6)
1. A motor starting locked rotor detection method based on current variance is characterized in that: the method comprises the following steps:
step one, when the motor is normally soft started, sampling period T is used s For interval pair motor current effective value
Sampling is performed, and an average value of the sampled data is calculated
Sum variance
Step two, when the motor is started to rotate and is blocked to detect, the sampling period T is used in the same way s For interval to effective value I of motor current soft (t) sampling and calculating the average of the sampled data
Sum variance S 2 ；
Step three, judging
If the current value is less than or equal to the threshold eta, if not, determining that the motor is normally soft-started, and if so, entering the step d;
step four, calculating
Judgment of
And if the value is larger than or equal to the threshold value theta, determining that the motor is started and blocked.
2. The method for detecting locked rotor in motor starting based on current variance as claimed in claim 1, wherein: the sampling process in the step one is to determine the effective value of the motor current
At the time of occurrence of the maximum value of
Obtaining
Effective value of current in time
Form an array of
3. The method for detecting locked rotor in motor starting based on current variance as claimed in claim 1, wherein: the sampling process in the second step is to determine the effective value I of the motor current soft (t) time of occurrence of maximum value
Obtaining
Current in timeEffective value I soft (t) data, forming an array
4. The method for detecting locked rotor in motor starting based on current variance as claimed in claim 1, wherein: when the motor is normally and softly started, firstly judging whether the operation condition of the motor changes or not, and after confirming that the motor is not in the abnormal condition of locked rotor, executing sampling work, connecting the soft start impedance to a power line of the motor by using the controller, and starting the soft start of the motor.
5. The method for detecting locked rotor in motor starting based on current variance as claimed in claim 1, wherein: when the motor is started to rotate and is blocked, the soft start impedance is connected to a power line of the motor, and the current is always in a safe range when the motor is blocked.
6. The method for detecting locked rotor in motor starting based on current variance as claimed in claim 1, wherein: in the fourth step, judgment
Whether the value is larger than or equal to the threshold value theta or not, if not, the motor is in a normal soft start state, whether the soft start timing is finished or not is judged, if so, the controller short-circuits soft start impedance on a power line of the motor, and the water pump enters a normal working procedure; otherwise, wait.
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