CN110880899A - Asynchronous motor load torque estimation method - Google Patents

Asynchronous motor load torque estimation method Download PDF

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Publication number
CN110880899A
CN110880899A CN201911195685.9A CN201911195685A CN110880899A CN 110880899 A CN110880899 A CN 110880899A CN 201911195685 A CN201911195685 A CN 201911195685A CN 110880899 A CN110880899 A CN 110880899A
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load torque
equation
formula
load
observer
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许小龙
王胜勇
卢家斌
王傲能
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Zhongye South (wuhan) Automation Co Ltd
Wisdri Wuhan Automation Co Ltd
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Zhongye South (wuhan) Automation Co Ltd
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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
    • 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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  • Power Engineering (AREA)
  • Control Of Electric Motors In General (AREA)

Abstract

Disclosed is an asynchronous motor load torque estimation method, comprising: establishing a mechanical motion equation of the asynchronous motor; transforming the mechanical equation of motion into an equation of state; constructing a reduced-order load torque observer according to the state equation; designing an expected pole according to the load torque observer, and observing a load torque value; verifying the feasibility of the load torque observer. The load torque estimated by the method is used for feedforward compensation, and the response speed of the system to the load disturbance can be improved.

Description

Asynchronous motor load torque estimation method
Technical Field
The invention discloses a method for estimating load torque of an asynchronous motor in engineering practice, which utilizes the estimated load torque to carry out feedforward compensation and improves the response speed of a system to load disturbance.
Background
In many application scenarios of the industrial frequency converter, the immunity is an important index of the control system, and the load disturbance is the most common disturbance source, so that it becomes the necessary performance of the high-performance industrial frequency converter to improve the immunity of the control system to the load disturbance. Particularly in the industrial fields of metallurgy, steel rolling and the like, as the processing technology has extremely high requirements on dynamic speed reduction, speed response and the like, the key point of the system is to improve the response speed of the driving system to load disturbance and enhance the disturbance resistance of the system.
The main idea for improving the response speed of the system to the load disturbance is to utilize the load torque to perform feedforward compensation. The key point of this concept is the acquisition of load torque. Since the direct measurement of the load torque is costly and has a slow response speed, the load torque is generally obtained by an indirect observation method. The load torque is observed by a commonly adopted reduced order observer, and the estimated load torque has low convergence speed due to the output of pure integration.
Disclosure of Invention
The invention discloses an asynchronous motor load torque estimation method, which improves the structure of a load torque observer, and compared with the traditional reduced-order load torque observer, the observation of the load torque is improved from the original integral to proportional plus integral, thereby effectively improving the observation convergence speed of the load torque, enhancing the compensation effect and improving the disturbance resistance of a system.
According to an aspect of an embodiment of the present invention, an asynchronous motor load torque estimation method includes:
step 1, establishing a mechanical motion equation of an asynchronous motor;
step 2, converting the mechanical motion equation into a state equation;
step 3, constructing a reduced load torque observer according to the state equation;
step 4, designing an expected pole according to the load torque observer, and observing a load torque value;
and 5, verifying the feasibility of the load torque observer.
Drawings
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Fig. 1 shows a block diagram of a reduced order load observer closed-loop observation method.
Fig. 2 shows torque waveforms at the time of sudden load addition and sudden load removal without using the load torque estimation function.
Fig. 3 is a waveform diagram showing torque waveforms at the time of sudden load addition and sudden load removal in the case where the load torque is obtained by the load torque observer method and feedforward compensation is performed.
Detailed Description
The invention discloses an asynchronous motor load torque estimation method, wherein the observation of load torque is improved from the original integral to proportion and integral, the observation convergence speed of the load torque is effectively improved, the compensation effect is enhanced, and the interference resistance of a system is improved. See steps 1-4 below.
Step 1: in the electric transmission, the motor provides electromagnetic torque to the load through the transmission shaft, the control of the load motion can be completed through controlling the electromagnetic torque on the motor transmission shaft, and according to the dynamics principle, a mechanical motion equation of the asynchronous motor is established:
Figure BDA0002294600750000021
Figure BDA0002294600750000022
in the formulae (1) and (2), TeIs an electromagnetic torque; j is the system moment of inertia; omegamIs the rotor mechanical angular velocity; bmIs the coefficient of friction; thetamIs a mechanical angle; t islIs the load torque.
Step 2: the equations (1) and (2) are written as the equation of state shown in the equation (3), wherein the sampling period of the controller is very small, and when the sampling frequency is very high, the load torque T can be approximately considered in one sampling periodlIs a constant value, i.e.
Figure BDA0002294600750000023
Figure BDA0002294600750000024
In the formula (3), the reaction mixture is,
Figure BDA0002294600750000025
u＝Te，C＝[1 0 0]，y＝θm。
and step 3: and (3) constructing a state equation of the load torque observer by adopting a reduced order method according to the formula (3):
Figure BDA0002294600750000026
in the formula (4), the reaction mixture is,
Figure BDA0002294600750000031
u＝Te，C＝[1 0]，y＝ωm；
constructing a reduced-order load torque observer shown in an equation (5):
Figure BDA0002294600750000032
wherein:
Figure BDA0002294600750000033
C＝[1 0]，u＝Te，
Figure BDA0002294600750000034
is an estimate of the state variable, y ═ ωm，K1＝[k1k2]T，k1And k2Is a feedback coefficient.
And 4, step 4: establishing a characteristic equation of the reduced-order load torque observer according to the formula (5): det (sI- (a-KC)) ═ 0, i.e.:
Figure BDA0002294600750000035
i is an identity matrix; matrices a, K, C are as above; s is a complex concept in the automatic control discipline, and is a convention complex variable.
Selecting proper K1The value to satisfy (A-KC) proper pole configuration to satisfy
Figure BDA0002294600750000038
Approaching the requirement of x, according to the desired pole αThe desired characteristic polynomial of the detector is:
s2-(α+β)s+αβ＝0 (7)
comparing equation (6) and equation (7), and neglecting the coefficient of friction bmAnd then:
Figure BDA0002294600750000036
from formula (5), formula (8) can be derived: the reduced order load torque observed value is:
Figure BDA0002294600750000037
fig. 1 shows a block diagram of a reduced order load observer closed-loop observation method. As shown in FIG. 1, the reduced order torque observer logic assigns a speed n and a feedback speed nobThe estimated load torque T is obtained by a PI controllerLobLoad torque TLobAnd electromagnetic torque TeSubtracting the difference and obtaining the feedback speed n through a first-order inertia linkobThereby constructing a closed loop control.
A comparative test was carried out on a tractor unit with an asynchronous machine rated at 7.5 kW. Fig. 2 shows torque waveforms at the time of sudden load addition and sudden load removal without using the load torque estimation function. Fig. 3 shows the effect of obtaining the load torque and performing the feed forward compensation using the load torque observer method.
As can be seen from comparison between fig. 2 and fig. 3, both the direct calculation method and the load torque observer method can reduce the speed drop when the load is suddenly applied and the speed rise when the load is suddenly removed. For example, without the load torque estimation function, the motor speed drops by 40rpm under the condition of sudden load; under the condition of sudden load release, the rotating speed of the motor is increased by 90 rpm. After load torque estimation and feedforward compensation are used, when loads with the same size are suddenly added, the falling amplitude of the rotating speed of the motor is 15-20 rpm; when the load is suddenly unloaded, the rising amplitude of the rotating speed of the motor is 60 rpm.
In addition, the load torque feed forward function can significantly reduce the settling time when the load changes. For example, without this function, the rotational speed recovery after a sudden load application takes about 0.4s, and the rotational speed recovery after a sudden load removal takes about 0.2 s; after the load torque feedforward is used, when the load with the same size is suddenly added, the rotating speed recovery time of the motor is 0.2s, and the rotating speed recovery time after the load is suddenly unloaded is 0.1 s. Therefore, after the load torque feedforward compensation function is applied, the response speed of the control system to the load change is obviously higher, and the immunity is obviously enhanced, which is shown in table 1.
TABLE 1 comparison of the results of the tests under the same conditions
Figure BDA0002294600750000041

Claims (1)

1. A method of estimating load torque of an asynchronous machine, comprising:
step 1, establishing a mechanical motion equation of the asynchronous motor:
Figure FDA0002294600740000011
Figure FDA0002294600740000012
in the formulae (1) and (2), TeIs an electromagnetic torque; j is the system moment of inertia; omegamIs the rotor mechanical angular velocity; bmIs the coefficient of friction; thetamIs a mechanical angle; t islIs the load torque;
and 2, writing the formula (1) and the formula (2) into a state equation shown in the formula (3):
Figure FDA0002294600740000013
in the formula (3), the reaction mixture is,
Figure FDA0002294600740000014
u＝Te，C＝[1 0 0]，y＝θm。
and step 3: constructing a state equation of the load torque observer according to the formula (3):
Figure FDA0002294600740000015
in the formula (I), the compound is shown in the specification,
Figure FDA0002294600740000016
u＝Te，C＝[1 0]，y＝ωm；
constructing a load torque observer represented by equation (5):
Figure FDA0002294600740000017
wherein:
Figure FDA0002294600740000018
C＝[1 0]，u＝Te，
Figure FDA0002294600740000019
is an estimate of the state variable, y ═ ωm，K1＝[k1k2]T，k1And k2Is a feedback coefficient;
and step 4, establishing a characteristic equation det (sI- (A-KC)) of the reduced load torque observer as 0 according to the formula (5), namely:
Figure FDA0002294600740000021
selecting proper K1The value to satisfy (A-KC) proper pole configuration to satisfy
Figure FDA0002294600740000024
Approximating the requirement of x, the desired characteristic polynomial of the observer, according to the desired pole α, is:
s2-(α+β)s+αβ＝0 (7)
comparative formula (6)) And (7) and neglecting the coefficient of friction bmAnd then:
Figure FDA0002294600740000022
obtaining a reduced-order load torque observed value from equation (5) and equation (8):
Figure FDA0002294600740000023
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111733509A (en) * 2020-06-18 2020-10-02 常熟理工学院 Multi-machine cooperative intelligent control system for three-dimensional multilayer profiling weaving process
CN112953317A (en) * 2021-03-13 2021-06-11 无锡信捷电气股份有限公司 Load disturbance rapid suppression method based on observer

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103312255A (en) * 2013-06-18 2013-09-18 山东大学（威海） Method and device for controlling speed of permanent-magnet synchronous motor
CN108880370A (en) * 2018-07-03 2018-11-23 上海电机学院 The method for improving permanent magnet synchronous motor control performance

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103312255A (en) * 2013-06-18 2013-09-18 山东大学（威海） Method and device for controlling speed of permanent-magnet synchronous motor
CN108880370A (en) * 2018-07-03 2018-11-23 上海电机学院 The method for improving permanent magnet synchronous motor control performance

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
荀倩等: "基于负载转矩观测器的PMSM抗负载扰动控制策略", 《电工电能新技术》 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111733509A (en) * 2020-06-18 2020-10-02 常熟理工学院 Multi-machine cooperative intelligent control system for three-dimensional multilayer profiling weaving process
CN112953317A (en) * 2021-03-13 2021-06-11 无锡信捷电气股份有限公司 Load disturbance rapid suppression method based on observer

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