Method for calculating rotor time constant of an asynchronous motor driven by a frequency converter

Abstract

The application relates to the field of asynchronous motor control, in particular to a method for calculating the rotor time constant of an asynchronous motor driven by a frequency converter, which comprises the following steps: during the operation of the asynchronous motor, the three-phase voltage value and the three-phase current value of the asynchronous motor are sampled, and a voltage-current initial model is established according to the sampling results. The voltage equation of the asynchronous motor and the indirect magnetic field oriented vector control equation are used to perform Clark transformation on the voltage-current initial model, so that an adjustable model is obtained, the adjustable model is a model containing the rotor time constant and not containing the stator resistance; the error between the voltage-current initial model and the adjustable model is calculated, the error is adjusted by using proportional integral, and the rotor time constant of the asynchronous motor is obtained. The obtained result has better real-time effectiveness, avoids the precision error caused by factors such as temperature fluctuation and voltage fluctuation generated during the operation of the motor, and is also effective in the working scene of low-speed light load of the asynchronous motor.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of asynchronous motor control, in particular to a method for calculating rotor time constant of an asynchronous motor driven by a frequency converter. BACKGROUND

[0002] In current industrial production, frequency converters are widely used in various mechanical equipment such as fans, pumps, compressors, etc. Through accurate adjustment of the speed of asynchronous motors, frequency converters can realize optimal control of the production process and improve production efficiency and product quality. Since these devices usually have high requirements for the accuracy of asynchronous motor torque control, current frequency converter manufacturers usually integrate vector control algorithms into the main control chip of the frequency converter. This algorithm can decouple the control of motor current and magnetic field to achieve accurate control of motor torque. However, this current decoupling method is based on motor parameters, so the accuracy of motor parameter identification will directly affect the accuracy of frequency converter speed regulation and torque control.

[0003] The existing asynchronous motor parameter identification method has the following defects: if using no-load and locked-rotor experiments to obtain, the industrial site environment is very complex, which will make it difficult to implement the experiment. For the system of a motor controlled by a frequency converter, a set of offline identification programs can be executed by the controller before the motor is running to apply a specific excitation to the motor and detect the motor response to calculate the motor parameters, which is commonly known as motor parameter offline identification. However, in actual application, it is found that the motor parameters obtained by offline identification are difficult to guarantee the stability of control accuracy. SUMMARY

[0004] The technical problem to be solved by the present application is that the control accuracy of the existing frequency converter driven asynchronous motor is low.

[0005] The present application provides a method for calculating the rotor time constant of an asynchronous motor driven by a frequency converter, comprising the following steps:

[0006] During the operation of the asynchronous motor, the three-phase voltage and three-phase current of the asynchronous motor are sampled to obtain three-phase voltage values and three-phase current values;

[0007] A voltage-current initial model is established according to the three-phase voltage values and the three-phase current values;

[0008] The voltage-current initial model is subjected to Clark transformation using an asynchronous motor voltage equation and an indirect magnetic field oriented vector control equation to obtain an adjustable model, wherein the adjustable model is a model containing the rotor time constant and not containing the stator resistance;

[0009] The error between the voltage-current initial model and the adjustable model is calculated, and the error is adjusted using proportional integral to obtain the rotor time constant of the asynchronous motor.

[0010] Specifically, the voltage-current initial model is:

[0011]

[0012] wherein, F u s , i s ) is the voltage-current initial model, i a , i b , i c is the three-phase current value, u a , u b , u c is the three-phase voltage value.

[0013] Specifically, the step of performing Clarke transformation on the voltage-current initial model by using the asynchronous motor voltage equation and the indirect magnetic field oriented vector control equation comprises:

[0014] introducing the asynchronous motor voltage equation into the voltage-current initial model to obtain a decoupled model, by which the voltage-current initial model is converted into a decoupled model containing only current;

[0015] representing the decoupled model on a αβ coordinate system to obtain a two-phase model, αβ introducing the flux linkage equation in the αβ coordinate system into the two-phase model to obtain a flux linkage model, the coordinate system is a two-phase coordinate system, by which the decoupled model is further simplified to facilitate subsequent calculation.

[0016] introducing the indirect magnetic field oriented vector control equation into the flux linkage model to obtain the adjustable model.

[0017] Specifically, the error between the voltage-current initial model and the adjustable model is: , F is the adjustable model, is the voltage-current initial model.

[0018] Specifically, the calculation result of the rotor time constant is:

[0019]

[0020] wherein, K pis a proportional coefficient, K i is an integral coefficient, is an initial value of the rotor time constant, obtained by offline identification, τ is the running time of the asynchronous motor.

[0021] Specifically, the step of bringing the asynchronous motor voltage equation into the voltage-current initial model comprises:

[0022] The asynchronous motor voltage equation is brought into the voltage-current initial model to obtain the decoupling model as follows:

[0023]

[0024] wherein,

[0025] ,

[0026] F ( u a , u b , u c , i a , i b , i c ) is the decoupling model ，i a 、 i b 、 i c is a three-phase current of the asynchronous motor, u a 、 u b 、 u c is a three-phase voltage of the asynchronous motor, R s is a stator resistance, φ a 、 φ b 、 φ c is a flux component, so it can be seen that the change of the stator resistance will not affect the calculation of the model of the present application when the motor is running stably. Especially in the case of low running speed of the asynchronous motor, the voltage of the stator resistance will decrease significantly, which will have a great influence on the running data of the asynchronous motor.

[0027] The asynchronous motor voltage equation is:

[0028] .

[0029] Specifically, the term "will" αβ The steps of substituting the flux linkage equations in the coordinate system into the two-phase model include:

[0030] Substituting the flux linkage equation into the two-phase model, we obtain the flux linkage model as follows:

[0031]

[0032] in, F ( u s , i s ) represents the magnetic flux linkage model. For the stator flux linkage vector in α Components on the axis, For the stator flux linkage vector in β Components on the axis, For the rotor flux vector in α Components on the axis, For the rotor flux vector in β Components on the axis, For the stator and rotor equivalent excitation inductance, For the stator equivalent self-inductance, i sα For stator current in α Components on the axis, i sβ For stator current in β Components on the axis, i rα For rotor current in α Components on the axis, i rβ For rotor current in β Components on the axis;

[0033] The magnetic flux linkage equation is:

[0034] .

[0035] Specifically, the step of substituting the indirect magnetic field orientation vector control equation into the flux linkage model includes:

[0036] Substituting the indirect magnetic field orientation vector control equation into the flux linkage model, the adjustable model is obtained as follows:

[0037]

[0038] in, For the adjustable model, L s’ is a stator transient inductance, and , is the rotor time constant, w s is a rotor angular frequency;

[0039] The indirect magnetic field oriented vector control equation is:

[0040]

[0041] wherein, w f is a slip angular frequency.

[0042] The present application has the following technical effects:

[0043] It is proposed that the control precision problem of the asynchronous motor is caused by the continuous change of the rotor time constant in the entire working process of the asynchronous motor, so that the rotor time constant of the asynchronous motor obtained by the corresponding relationship between the voltage-current initial model and the adjustable model will have better real-time effectiveness by sampling the three-phase voltage value and the three-phase current value of the asynchronous motor, avoiding the control precision error caused by using the fixed rotor time constant to control the motor when the rotor time constant changes due to factors such as temperature fluctuation and voltage fluctuation generated during motor operation;

[0044] The voltage-current initial model is subjected to Clark transformation through the asynchronous motor voltage equation and the indirect magnetic field oriented vector control equation, and the optimized model obtained only has a single unknown quantity of the rotor time constant, and the model does not contain the stator resistance, so that the model will not be disturbed by other parameters in the calculation process, such as the stator and rotor resistance, the stator and rotor leakage inductance and mutual inductance parameters, so that the model can be applied to the working scene of the low-speed light load of the asynchronous motor. BRIEF DESCRIPTION OF DRAWINGS

[0045] The above and other objects, features and advantages of the example embodiments of the present application will be readily understood through reading the detailed description of the example embodiments of the present application below, with reference to the accompanying drawings. In the drawings, several embodiments of the present application are shown by way of example and not limitation, and the same or corresponding reference numbers indicate the same or corresponding parts.

[0046] Figure 1 is a flow chart of a method for calculating the rotor time constant of an asynchronous motor driven by a frequency converter according to an embodiment of the present application;

[0047] Figure 2 is a graph of the rotor time constant calculated by the method of the present embodiment when the stator resistance changes;

[0048] Figure 3is a rotor time constant diagram calculated by the prior art when the stator resistance changes. DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0050] It should be understood that when the terms "first", "second", etc. are used in the claims, the specification and the drawings of the present application, they are only used to distinguish different objects, and are not used to describe a specific order. The terms "include" and "contain" used in the specification and claims of the present application indicate the existence of the described features, whole, steps, operations, elements and / or components, but do not exclude the existence or addition of one or more other features, whole, steps, operations, elements, components and / or sets thereof.

[0051] In an industrial site, when the problem of low motor control accuracy occurs, the present inventors found after analysis that the motor is controlled by a frequency converter loaded with a vector control algorithm. The line of sight of this algorithm needs the rotor time constant of the motor. If the rotor time constant is obtained by using no-load and locked-rotor experiments, the industrial site environment is very complex, which will lead to the difficulty of implementing the experiment. For the system of the motor controlled by the frequency converter, before the motor works, a set of offline identification program can be executed by the controller to apply a specific excitation to the motor, detect the motor response and calculate the motor parameters, that is, the so-called offline identification of motor parameters. However, in the actual application process, it is found that the motor parameters obtained by using offline identification are difficult to guarantee the stability of control accuracy.

[0052] In view of this conclusion, the present inventors believe that in the entire working range of the motor, the rotor time constant value of the motor does not remain unchanged, but changes with the working condition of the motor. Therefore, directly using the rotor time constant obtained by offline identification for the control of the motor in the entire motor operation process will greatly reduce the control accuracy.

[0053] Therefore, the embodiment of the present application provides a calculation method of rotor time constant of an asynchronous motor driven by a frequency converter. In the embodiment, the asynchronous motor is connected with the frequency converter to form a frequency converter-asynchronous motor system, and the nameplate parameters of the asynchronous motor are shown in the following table.

[0054] Nameplate parameter table of asynchronous motor

[0055]

[0056] The frequency converter in the embodiment is equipped with a vector control algorithm, data given by a nameplate parameter table is input into the vector control algorithm for parameter self-learning, then output power of the frequency converter is gradually increased to 50Hz, output voltage is gradually increased to 380V, a phase-locked function of the frequency converter is started, at this time the asynchronous motor is soft-started, when the asynchronous motor is in a stable running state, the step of calculating the rotor time constant of the asynchronous motor is referred to Figure 1 .

[0057] Step S1, during the running of the asynchronous motor, three-phase voltage and three-phase current of the asynchronous motor are sampled to obtain three-phase voltage values and three-phase current values;

[0058] Step S2, a voltage-current initial model is established according to the three-phase voltage values and the three-phase current values;

[0059] Step S3, the voltage-current initial model is subjected to a Clarke transformation by using an asynchronous motor voltage equation and an indirect magnetic field oriented vector control equation to obtain an adjustable model, the adjustable model being a model containing the rotor time constant and not containing the stator resistance;

[0060] Step S4, an error between the voltage-current initial model and the adjustable model is calculated, the error is adjusted by using a proportional integral to obtain the rotor time constant of the asynchronous motor.

[0061] In step S1, the P10.1 and P10.2 pins of the voltage transformer are connected with voltage input ends of the asynchronous motor, voltage between any one of three-phase alternating currents A phase, B phase and C phase of the asynchronous motor and N line is measured, meanwhile, three current sensors are used to sample currents of the A phase, the B phase and the C phase, sampling time is adjusted by setting a register to ensure simultaneity of the sampled three-phase current values and three-phase voltage values, according to the sampling results, the following voltage-current initial model is established:

[0062]

[0063] wherein, F ( u s , i s ) is the voltage-current initial model, i a , i b , i c is the three-phase current value, u a , u b , u c is the three-phase voltage value.

[0064] In step S3, the step of Clarke transformation of the voltage-current initial model by using the asynchronous motor voltage equation and the indirect field-oriented vector control equation includes:

[0065] The asynchronous motor voltage equation is brought into the voltage-current initial model to obtain a decoupling model, and the voltage-current initial model is converted into the decoupling model containing only currents by this step;

[0066] The decoupling model is represented on a two-phase model in a αβ coordinate system to obtain a flux linkage model, αβ the flux linkage equation in the αβ coordinate system is brought into the two-phase model to obtain the flux linkage model,

[0067] The indirect field-oriented vector control equation is brought into the flux linkage model to obtain an adjustable model.

[0068] In this embodiment, the error between the voltage-current initial model and the adjustable model is: , is the adjustable model, F is the voltage-current initial model.

[0069] In this embodiment, the calculation result of the rotor time constant is:

[0070]

[0071] wherein, K p is a proportional coefficient, K i is an integral coefficient, is an initial value of the rotor time constant, which is obtained by offline identification, τ is the running time of the asynchronous motor.

[0072] In this embodiment, the step of bringing the asynchronous motor voltage equation into the voltage-current initial model includes:

[0073] The asynchronous motor voltage equation is brought into the voltage-current initial model to obtain a decoupling model:

[0074]

[0075] wherein,

[0076] ,

[0077] F ( u a , ub , u c , i a , i b , i c () is a decoupling model ，i a , i b , i c This represents the three-phase current of the asynchronous motor. u a , u b , u c This refers to the three-phase voltage of the asynchronous motor. R s For stator resistance, φ a , φ b , φ c For magnetic flux linkage components;

[0078] The voltage equation for an asynchronous motor is:

[0079] .

[0080] In this embodiment, αβ The steps for substituting the flux linkage equations in the coordinate system into the two-phase model include:

[0081] Substituting the flux linkage equation into the two-phase model, we obtain the flux linkage model as follows:

[0082]

[0083] in, F ( u s , i s () represents the magnetic flux linkage model. For the stator flux linkage vector in α Components on the axis, For the stator flux linkage vector in β Components on the axis, For the rotor flux vector in α Components on the axis, For the rotor flux vector in β Components on the axis, For the stator and rotor equivalent excitation inductance, For the stator equivalent self-inductance, i sα For stator current inα the component on the axis, i sβ the component on the axis, β the component on the axis, i rα the component on the axis, α the component on the axis, i rβ the component on the axis, β the component on the axis,

[0084] the flux linkage equation is:

[0085] .

[0086] In the embodiment, the step of bringing the indirect field-oriented vector control equation into the flux linkage model comprises:

[0087] the adjustable model is obtained by bringing the indirect field-oriented vector control equation into the flux linkage model,

[0088]

[0089] wherein, the adjustable model, L s ’ the stator transient inductance, and , the rotor time constant, w s the rotor angular frequency;

[0090] the indirect field-oriented vector control equation is:

[0091]

[0092] wherein, w f the slip angular frequency.

[0093] When the asynchronous motor is stably running to 1s, a step signal is sent to the asynchronous motor through the frequency converter, so as to increase the resistance value of the stator resistance of the asynchronous motor, and the rotor time constant of the asynchronous motor is calculated by using the method provided in the embodiment and the prior art (MRAS method) closest to the method provided in the embodiment, respectively, to obtain the results of Figure 2 and Figure 3 It can be seen that, Figure 3 the rotor time constant of the asynchronous motor in the embodiment has a deviation at 1s, and the accuracy of the rotor time constant result of the asynchronous motor in the embodiment is not affected by the stator resistance. Figure 2

[0094] ​While the present specification has shown and described a number of embodiments of the present application, it is to be understood that those skilled in the art will be able to devise numerous alterations, modifications and equivalents of the embodiments that are within the spirit and scope of the present application without departing from the intended spirit and scope of the present application. It is to be understood that all the terms and expressions used herein are meant to be interpreted in an illustrative way and are not to be interpreted in a limiting sense.

[0095] The above are preferred embodiments of the present application, and are not intended to limit the protection scope of the present application, therefore: all equivalent changes made on the structure, shape, principle of the present application should be covered within the protection scope of the present application.

Claims

1. A method of calculating the rotor time constant of an asynchronous motor driven by a frequency converter, characterized in that, The method comprises the following steps: During the operation of the asynchronous motor, three-phase voltage and three-phase current of the asynchronous motor are sampled to obtain three-phase voltage values and three-phase current values; An initial voltage-current model is established according to the three-phase voltage values and the three-phase current values; The initial voltage-current model is subjected to Clark transformation by using an asynchronous motor voltage equation and an indirect magnetic field oriented vector control equation to obtain an adjustable model, wherein the adjustable model is a model containing a rotor time constant and not containing a stator resistance; An error between the initial voltage-current model and the adjustable model is calculated, and the error is adjusted by using a proportional integral to obtain a rotor time constant of the asynchronous motor; The step of subjecting the initial voltage-current model to Clark transformation by using the asynchronous motor voltage equation and the indirect magnetic field oriented vector control equation comprises: The asynchronous motor voltage equation is brought into the initial voltage-current model to obtain a decoupling model; The decoupling model is represented in αβ A two-phase model is obtained in the coordinate system, and αβ Substituting the flux linkage equation in the coordinate system into the two-phase model yields the flux linkage model. The indirect magnetic field oriented vector control equation is brought into the flux linkage model to obtain the adjustable model; The step of bringing the indirect magnetic field oriented vector control equation into the flux linkage model comprises: The indirect magnetic field oriented vector control equation is brought into the flux linkage model to obtain the adjustable model as follows: wherein, is the adjustable model, L s ’ is the stator transient inductance, and , is the rotor time constant, w s is the rotor angular frequency, i s is the vector resultant of the two components of the stator current on the α axis and β axis, is the rotor equivalent self-inductance, is the stator and rotor equivalent excitation inductance, is the rotor time constant; The indirect magnetic field oriented vector control equation is as follows: wherein w f is the slip frequency, is the component of the rotor flux vector in the α axis, is the component of the rotor flux vector in the β axis, i sα is the component of the stator current in the α axis, i sβ is the component of the stator current in the β axis.

2. The method of claim 1, wherein the rotor time constant of the variable frequency drive-fed asynchronous motor is calculated by, The initial voltage-current model is as follows: wherein F u s , i s ) is the voltage-current initial model, i a , i b , i c is the three-phase current value, u a , u b , u c is the three-phase voltage value.​ 3. The method of claim 1, wherein the rotor time constant of the variable frequency drive-fed asynchronous motor is calculated by: an error between the voltage-current initial model and the adjustable model is: wherein, e is the error, is the adjustable model, F is the voltage-current initial model.

4. A method of calculating the rotor time constant of an asynchronous motor driven by a frequency converter according to claim 1, characterized in that, The calculation result of the rotor time constant is as follows: wherein, is the rotor time constant, K p is a proportional coefficient, K i is an integral coefficient, is an initial value of the rotor time constant and is obtained by offline identification, τ is the operating time of the asynchronous machine, e is the error between the voltage-current initial model and the adjustable model.

5. The method of claim 1, wherein the method further comprises: The step of bringing the asynchronous motor voltage equation into the initial voltage-current model comprises: The asynchronous motor voltage equation is brought into the initial voltage-current model to obtain the decoupling model as follows: Wherein, ， F u a u b u c i a i b i c is the decoupling model ，i a i b i c is the three-phase current value u a u b u c is the three-phase voltage value R s is the stator resistance φ a φ b φ c is the flux component I is the vector sum of the three-phase current values w is the rotational angular velocity of the asynchronous machine t is the operating time of the asynchronous machine​​​​​​​​​​​​ The asynchronous motor voltage equation is as follows: 。 6. The method of claim 1, wherein the method further comprises: Said αβ The step of incorporating the flux linkage equations in the coordinate system into the two-phase model comprises: The flux linkage equation is brought into the two-phase model to obtain the flux linkage model as follows: wherein F u s i s is the magnetic chain model, is the component of the stator magnetic chain vector on the α axis, is the component of the stator magnetic chain vector on the β axis, is the component of the rotor magnetic chain vector on the α axis, is the component of the rotor magnetic chain vector on the β axis, is the equivalent excitation inductance of the stator and rotor, is the equivalent self-inductance of the rotor, i sα is the component of the stator current on the α axis, i sβ is the component of the stator current on the β axis, i rα is the component of the rotor current on the α axis, i rβ is the component of the rotor current on the β axis, L s is the equivalent self-inductance of the stator, i s is the vector resultant of the two components of the stator current on the α axis and on the β axis;​​ The flux linkage equation is as follows: 。

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