Calculation method for rotor time constant of asynchronous motor driven by frequency converter

Abstract

The invention relates to the field of asynchronous motor control, in particular to a method for calculating a rotor time constant of an asynchronous motor driven by a frequency converter, and the method comprises the steps: sampling a three-phase voltage value and a three-phase current value of the asynchronous motor in the operation process of the asynchronous motor, and building a voltage-current initial model according to a sampling result; performing Clark transformation on the voltage-current initial model by using an asynchronous motor voltage equation and an indirect field-oriented vector control equation to obtain an adjustable model which contains a rotor time constant and does not contain stator resistance; and calculating an error between the voltage-current initial model and the adjustable model, and adjusting the error by using proportional integral to obtain the rotor time constant of the asynchronous motor. The obtained result has better real-time effectiveness, precision errors caused by factors such as temperature fluctuation and voltage fluctuation generated in the operation process of the motor are avoided, and the method is also effective in a low-speed light-load working scene of the asynchronous motor.

Description

Technical Field

[0001] This application relates to the field of asynchronous motor control, and particularly to a method for calculating the rotor time constant of an asynchronous motor driven by an inverter. Background Art

[0002] In current industrial production, inverters are widely used in various mechanical equipment, such as fans, pumps, compressors, etc. By precisely adjusting the speed of the asynchronous motor, the inverter can achieve optimized control of the production process, improving production efficiency and product quality. Since these devices usually have high requirements for the accuracy of asynchronous motor torque control, current inverter manufacturers usually integrate vector control algorithms into the main control chip of the inverter. This algorithm can decouple and control the current and magnetic field of the motor to achieve precise control of the motor torque. And this current decoupling method is based on motor parameters, so the identification accuracy of motor parameters will directly affect the accuracy of the inverter's adjustment of the motor speed and torque control.

[0003] Existing asynchronous motor parameter identification methods have the following defects: If no-load and blocked-rotor experiments are used to obtain them, the industrial field environment is very complex, which will make the experiments difficult to implement. For a system where an inverter controls a motor, before the motor operates, a set of offline identification programs can be executed by the controller to apply specific excitation to the motor and detect the motor response to calculate the motor parameters, which is the so-called offline identification of motor parameters. However, in the actual application process, it is found that it is difficult to ensure the stability of control accuracy using the motor parameters obtained by offline identification. Summary of the Invention

[0004] The technical problem to be solved by this application is: The control accuracy of the existing asynchronous motor driven by an inverter is low.

[0005] This application provides a method for calculating the rotor time constant of an asynchronous motor driven by an inverter, including the following steps: During the operation of the asynchronous motor, sample the three-phase voltage and three-phase current of the asynchronous motor to obtain three-phase voltage values and three-phase current values; Establish a voltage-current initial model according to the three-phase voltage values and the three-phase current values; Perform Clarke transformation on the voltage-current initial model using the asynchronous motor voltage equation and the indirect field-oriented vector control equation to obtain an adjustable model, and the adjustable model is a model containing the rotor time constant and not containing the stator resistance; Calculate the error between the voltage-current initial model and the adjustable model, and use proportional-integral to adjust the error to obtain the rotor time constant of the asynchronous motor.

[0006] Specifically, the voltage-current initial model is: Among them, F ( u s , i s ) is the initial voltage-current model, i a , i b , i c are the three-phase current values, u a , u b , u c are the three-phase voltage values.

[0007] Specifically, the steps of performing the Clarke transformation on the initial voltage-current model by using the asynchronous motor voltage equation and the indirect field-oriented vector control equation include: Substitute the asynchronous motor voltage equation into the initial voltage-current model to obtain a decoupled model. Through this step, the initial voltage-current model is transformed into a decoupled model containing only current; Represent the decoupled model on the αβ coordinate system to obtain a two-phase model. Substitute the flux linkage equation in the αβ coordinate system into the two-phase model to obtain a flux linkage model. αβ The

[0008] coordinate system is a two-phase coordinate system. Through this step, the decoupled model is further simplified, facilitating subsequent calculations.

[0009] Substitute the indirect field-oriented vector control equation into the flux linkage model to obtain the adjustable model. , is the adjustable model, F is the initial voltage-current model.

[0010] Specifically, it is characterized in that the calculation result of the rotor time constant is: Among them, K p is the proportionality coefficient, K i is the integral coefficient, is the initial value of the rotor time constant, obtained by off-line identification, τ is the running time of the asynchronous motor.

[0011] Specifically, the step of substituting the asynchronous motor voltage equation into the voltage-current initial model includes: Substituting the asynchronous motor voltage equation into the voltage-current initial model to obtain the decoupling model as: Wherein, , F ( u a , u b , u c , i a , i b , i c ) is the decoupling model ，i a , i b , i c are the three-phase currents of the asynchronous motor, u a , u b , u c are the three-phase voltages of the asynchronous motor, R s is the stator resistance, φ a , φ b , φ c are the flux link components. It can be seen that when the motor is running stably, the change of the stator resistance will not affect the calculation of the model of the present invention. Especially when the running speed of the asynchronous motor is relatively low, the voltage of the stator resistance will drop significantly, which will have a great impact on the running data of the asynchronous motor.

[0012] The asynchronous motor voltage equation is: .

[0013] Specifically, the step of substituting the αβ flux link equation in the coordinate system into the two-phase model includes: Substituting the flux link equation into the two-phase model to obtain the flux link model as: Wherein, F ( u s ,i s ) is the flux linkage model, is the component of the stator flux linkage vector on the α axis, is the component of the stator flux linkage vector on the β axis, is the component of the rotor flux linkage vector on the α axis, is the component of the rotor flux linkage vector on the β axis, are the equivalent excitation inductances of the stator and rotor, is the equivalent self - inductance of the stator, 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; The flux linkage equation is: .

[0014] Specifically, the step of substituting the indirect field - oriented vector control equation into the flux linkage model includes: Substituting the indirect field - oriented vector control equation into the flux linkage model, the adjustable model obtained is: where, is the adjustable model, L s ’ is the stator transient inductance, and , is the rotor time constant, w s is the rotor angular frequency; The indirect field - oriented vector control equation is: where, w f is the slip angular frequency.

[0015] This application has the following technical effects: It is proposed that the control accuracy problem of the asynchronous motor is caused by the continuous change of the rotor time constant during the entire operation process of the asynchronous motor. Therefore, by sampling the three-phase voltage values and three-phase current values of the asynchronous motor, and then using the corresponding relationship between the voltage-current - initial model and the adjustable model, the rotor time constant of the asynchronous motor obtained will have better real-time effectiveness, avoiding the control accuracy error caused by using a fixed rotor time constant to control the motor when the rotor time constant changes due to factors such as temperature fluctuations and voltage fluctuations during the operation of the motor. Perform a Clarke transformation on the voltage-current initial model through the voltage equation of the asynchronous motor and the indirect field-oriented vector control equation. The optimized model obtained only has a single unknown quantity, the rotor time constant, and does not contain the stator resistance in the model, so that the model will not be interfered by other parameters during the calculation process, such as the stator and rotor resistances, stator and rotor leakage inductances, and mutual inductance parameters, etc., thereby enabling the model to be applicable to the working scenario of the asynchronous motor at low speed and light load. Brief Description of the Drawings

[0016] By reading the following detailed description with reference to the accompanying drawings, the above and other objects, features, and advantages of the exemplary embodiments of the present application will become readily understandable. In the drawings, several embodiments of the present application are shown in an exemplary rather than restrictive manner, and the same or corresponding reference numerals represent the same or corresponding parts.

[0017] Figure 1 It is a flowchart of a method for calculating the rotor time constant of an inverter-driven asynchronous motor according to an embodiment of the present application; Figure 2 It is a graph of the rotor time constant calculated by the method of the embodiment of the present application when the stator resistance changes; Figure 3 It is a graph of the rotor time constant calculated by the prior art when the stator resistance changes. Detailed Embodiments

[0018] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of 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 making creative efforts belong to the scope of protection of the present application.

[0019] It should be understood that when terms such as "first", "second", etc. are used in the claims, specification and drawings of the present application, they are only used to distinguish different objects and not to describe a specific order. The terms "comprising" and "including" used in the specification and claims of the present application indicate the presence of the described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or their combinations.

[0020] In an industrial site, when there is a problem of low motor control accuracy, after analysis by the inventors of the present application, it is found that the motor is controlled by an inverter equipped with a vector control algorithm. The implementation of this algorithm requires the rotor time constant of the motor. If no-load and locked-rotor experiments are used to obtain the rotor time constant, the industrial site environment is very complex, which will make the experiment difficult to implement. For a system in which an inverter controls a motor, before the motor operates, a set of offline identification programs can be executed by a controller to apply specific excitation to the motor and detect the motor response to calculate the motor parameters, which is usually referred to as offline identification of motor parameters. However, in the actual application process, it is found that it is difficult to ensure the stability of control accuracy using the motor parameters obtained by offline identification.

[0021] In view of this conclusion, the inventors of the present application believe that within the entire operating range of the motor, the rotor time constant value of the motor does not remain unchanged, but changes to a certain extent with the motor operating conditions. Therefore, directly using the rotor time constant obtained by offline identification for the control of the motor during the entire motor operation process will greatly reduce the control accuracy.

[0022] Therefore, the embodiments of the present application provide a method for calculating the rotor time constant of an asynchronous motor driven by an inverter. In this embodiment, the asynchronous motor used is connected to the inverter to form an inverter - asynchronous motor system. The nameplate parameters of the asynchronous motor are shown in the following table: Nameplate Parameter Table of Asynchronous Motor The inverter in this embodiment is equipped with a vector control algorithm. The data given in the nameplate parameter table is input into the vector control algorithm for parameter self-learning, and then the output power of the inverter is gradually increased to 50 Hz and the output voltage is gradually increased to 380 V. The phase-locked function of the inverter is started. At this time, the asynchronous motor is soft-started. When the operating state of the asynchronous motor is stable, referring to Figure 1 the following steps, the rotor time constant of the asynchronous motor is calculated: Step S1, during the operation of the asynchronous motor, sample the three-phase voltage and three-phase current of the asynchronous motor to obtain three-phase voltage values and three-phase current values; Step S2, establish a voltage - current initial model based on the three-phase voltage values and three-phase current values; Step S3: Perform a Clarke transformation on the voltage-current initial model using the asynchronous motor voltage equation and the indirect field-oriented vector control equation to obtain an adjustable model, which is a model containing the rotor time constant and not containing the stator resistance. Step S4: Calculate the error between the voltage-current initial model and the adjustable model, and use proportional-integral to adjust the error to obtain the rotor time constant of the asynchronous motor.

[0023] In step S1, connect the P10.1 and P10.2 pins of the voltage transformer to the voltage input terminal of the asynchronous motor, measure the voltage between any one of the three-phase alternating currents A, B, and C of the asynchronous motor and the N line. At the same time, use three current sensors to sample the currents of phases A, B, and C respectively, and adjust the sampling timing by setting the register to ensure the simultaneity of the sampled three-phase current values and three-phase voltage values. According to the sampling results, establish the following voltage-current initial model: where, F ( u s , i s ) is the voltage-current initial model, i a , i b , i c are the three-phase current values, u a , u b , u c are the three-phase voltage values.

[0024] In step S3, the steps of performing a Clarke transformation on the voltage-current initial model using the asynchronous motor voltage equation and the indirect field-oriented vector control equation include: Substitute the asynchronous motor voltage equation into the voltage-current initial model to obtain a decoupled model. Through this step, the voltage-current initial model is transformed into a decoupled model containing only current. Express the decoupled model on the αβ coordinate system to obtain a two-phase model. Substitute the flux linkage equation in the αβ coordinate system into the two-phase model to obtain a flux linkage model. αβ The

[0025] coordinate system is a two-phase coordinate system. Through this step, the decoupled model is further simplified for subsequent calculations.

[0026] 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.

[0027] In this embodiment, it is characterized in that the calculation result of the rotor time constant is: wherein, K p is the proportionality coefficient, K i is the integral coefficient, is the initial value of the rotor time constant, obtained by offline identification, τ is the running time of the asynchronous motor.

[0028] In this embodiment, the steps of substituting the asynchronous motor voltage equation into the voltage-current initial model include: Substituting the asynchronous motor voltage equation into the voltage-current initial model, the decoupled model obtained is: wherein, , F ( u a , u b , u c , i a , i b , i c ) is the decoupled model ，i a , i b , i c are the three-phase currents of the asynchronous motor, u a , u b , u c are the three-phase voltages of the asynchronous motor, R s is the stator resistance, φ a , φ b , φ c are the flux link components; The asynchronous motor voltage equation is: 。

[0029] In this embodiment, the steps of substituting the flux linkage equation in the coordinate system into the two-phase model include: αβ Substituting the flux linkage equation into the two-phase model, the obtained flux linkage model is: Substituting the flux linkage equation into the two-phase model, the obtained flux linkage model is: Among them, F ( u s , i s ) is the flux linkage model, is the component of the stator flux linkage vector on the α axis, is the component of the stator flux linkage vector on the β axis, is the component of the rotor flux linkage vector on the α axis, is the component of the rotor flux linkage vector on the β axis, are the equivalent excitation inductances of the stator and rotor, is the equivalent self-inductance of the stator, 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; The flux linkage equation is: 。

[0030] In this embodiment, the steps of substituting the indirect field-oriented vector control equation into the flux linkage model include: Substituting the indirect field-oriented vector control equation into the flux linkage model, the obtained adjustable model is: Among them, is the adjustable model, L s ’ is the stator transient inductance, and , is the rotor time constant, w s is the rotor angular frequency; The indirect field-oriented vector control equation is: Among them, w f is the slip angular frequency.

[0031] When the asynchronous motor operates stably for 1 s, 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. The rotor time constant of the asynchronous motor is calculated respectively by using the method provided in this embodiment and the prior art (MRAS method) closest to the method provided in this embodiment, and Figure 2 and Figure 3 are obtained. It can be seen that Figure 3 the rotor time constant has a deviation at 1 s, while Figure 2 the accuracy of the rotor time constant result will not be affected by the stator resistance.

[0032] Although this specification has shown and described multiple embodiments of the present application, it is obvious to those skilled in the art that such embodiments are provided only by way of example. Those skilled in the art will think of many changes, alterations, and alternative ways without departing from the spirit and idea of the present application. It should be understood that various alternative solutions to the embodiments of the present application described herein can be adopted in the process of practicing the present application.

[0033] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereby. Therefore, all equivalent changes made according to the structure, shape, and principle of the present application should be covered within the protection scope of the present application.

Claims

1. A method for calculating the rotor time constant of an asynchronous motor driven by a frequency converter, characterized in that: The following steps are involved: During the operation of the asynchronous motor, the three-phase voltage and three-phase current of the asynchronous motor are sampled to obtain the three-phase voltage value and the three-phase current value; Establishing a voltage-current initial model according to the three-phase voltage values ​​and the three-phase current values; Using the asynchronous motor voltage equation and the indirect field oriented vector control equation, the voltage-current initial model is subjected to Clarke transformation to obtain an adjustable model, wherein the adjustable model is a model containing a rotor time constant and excluding a stator resistance; 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.

2. The method for calculating the rotor time constant of an inverter-driven asynchronous motor according to claim 1, characterized in that: The voltage-current initial model is: in, 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 for calculating the rotor time constant of an inverter-driven asynchronous motor according to claim 1, characterized in that: The step of performing Clarke transformation on the voltage-current initial model by using the asynchronous motor voltage equation and the indirect field oriented vector control equation comprises: Substituting the asynchronous motor voltage equation into the voltage-current initial model to obtain a decoupling model; The decoupled model is represented as αβ The two-phase model is obtained in the coordinate system. αβ Substituting the flux equation in the coordinate system into the two-phase model, a flux model is obtained; The indirect magnetic field oriented vector control equation is substituted into the flux linkage model to obtain the adjustable model.

4. The method for calculating the rotor time constant of an inverter-driven asynchronous motor according to claim 1, characterized in that: The error between the voltage-current initial model and the adjustable model is: ,in, e is the error, is the adjustable model, F is the voltage-current initial model.

5. The method for calculating the rotor time constant of an inverter-driven asynchronous motor according to claim 1, characterized in that: The calculation result of the rotor time constant is: in, is the rotor time constant, K p is the proportionality coefficient, K i is the integration coefficient, is the initial value of the rotor time constant and is obtained by offline identification, τ is the running time of the asynchronous motor, e is the error between the voltage-current initial model and the adjustable model.

6. The method for calculating the rotor time constant of an inverter-driven asynchronous motor according to claim 3, characterized in that: The step of bringing the asynchronous motor voltage equation into the voltage-current initial model comprises: Substituting the asynchronous motor voltage equation into the voltage-current initial model, the decoupling model is obtained as follows: in, ， 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 magnetic flux component; I is the vector synthesis value of the three-phase current value, w is the angular velocity of the asynchronous motor, t is the running time of the asynchronous motor. The asynchronous motor voltage equation is: 。 7. The method for calculating the rotor time constant of an inverter-driven asynchronous motor according to claim 3, characterized in that: The αβ The steps of bringing the magnetic flux equation in the coordinate system into the two-phase model include: Substituting the flux equation into the two-phase model, the flux model is obtained as follows: in, F ( u s , i s ) is the magnetic flux model, is the stator flux vector α The weight on the axis, is the stator flux vector β The weight on the axis, is the rotor flux vector α The weight on the axis, is the rotor flux vector β The weight on the axis, is the equivalent excitation inductance of the stator and rotor, is the rotor equivalent self-inductance, i sα The stator current is α The weight on the axis, i sβ The stator current is β The weight on the axis, i rα is the rotor current in α The weight on the axis, i rβ is the rotor current in β The weight on the axis, L s is the stator equivalent self-inductance, i s The stator current is α Axis and β The vector resultant of two components on an axis; The magnetic flux equation is: 。 8. The method for calculating the rotor time constant of an inverter-driven asynchronous motor according to claim 3, characterized in that: The step of bringing the indirect magnetic field oriented vector control equation into the flux linkage model comprises: Substituting the indirect magnetic field oriented vector control equation into the flux linkage model, the adjustable model is obtained as follows: in, 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 The stator current is α Axis and β The vector resultant of the two components on the axis, is the rotor equivalent self-inductance, is the equivalent excitation inductance of the stator and rotor, is the rotor time constant; The indirect magnetic field oriented vector control equation is: in, w f is the slip angular frequency, is the rotor flux vector α The weight on the axis, is the rotor flux vector β The weight on the axis, i sα The stator current is α The weight on the axis, i sβ The stator current is β Components on the axis.

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