A vector control method based on asynchronous motor excitation current control

Abstract

The present invention proposes a vector control method based on asynchronous motor excitation current control, which belongs to the field of asynchronous motor control technology. First, the active current setting and the excitation current setting are determined; second, the active current and the excitation current are calculated from the feedback current; third, the input voltage setting amplitude of the control power device is obtained; third, the main frequency of the input voltage of the control power controller is obtained; third, the input voltage adjustment frequency of the control power controller is obtained from the speed difference; finally, the power controller controls the motor running voltage according to the input voltage setting control output, thereby realizing the vector control of the asynchronous motor. By controlling the amplitude, frequency and speed difference frequency of the motor voltage, the desired slip is indirectly controlled, so that the rotating magnetic field generated by the stator current is orthogonal to the air gap rotating magnetic field generated by the rotor current, thereby realizing the vector control of the asynchronous motor. The problem of low control performance and complex control algorithm of asynchronous motors is solved.

Description

Technical Field

[0001] The present application relates to asynchronous motor control, and in particular to a vector control method based on asynchronous motor excitation current control, belonging to the technical field of asynchronous motor control. Background Art

[0002] Asynchronous motors are widely used in the field of drive control due to their simple structure and high reliability. Since the mathematical model of asynchronous motors has the characteristics of nonlinearity and strong coupling, especially the rotor parameters change with the operating conditions, it is difficult to accurately identify them, which makes it difficult to obtain the same control performance as synchronous motors. In order to improve the control performance of asynchronous motors, their control algorithms are complex and easily affected by parameter changes. Due to the wide application of asynchronous motors, it is of great practical significance to improve their control performance and high efficiency of operation. Summary of the invention

[0003] A brief overview of the present invention is provided below in order to provide a basic understanding of certain aspects of the present invention. It should be understood that this overview is not an exhaustive overview of the present invention. It is not intended to identify key or important parts of the present invention, nor is it intended to limit the scope of the present invention. Its purpose is merely to present certain concepts in a simplified form as a prelude to a more detailed description discussed later.

[0004] In view of this, in order to solve the technical problems of low asynchronous motor control performance and complex control algorithm in the prior art, the present invention provides a vector control method based on asynchronous motor excitation current control.

[0005] A vector control method based on asynchronous motor excitation current control comprises the following steps:

[0006] Step 1: Determine the active current setting and the excitation current setting;

[0007] Step 2: Calculate active current and excitation current from feedback current;

[0008] Step 3, obtaining a given amplitude of the input voltage of the control power device;

[0009] Step 4, obtaining the main frequency for controlling the input voltage of the power controller;

[0010] Step 5, obtaining the input voltage adjustment frequency of the control power controller according to the speed difference;

[0011] Step 6: The power controller controls the motor operating voltage according to the input voltage setting to achieve vector control of the asynchronous motor.

[0012] Preferably, the specific method for determining the active current and excitation current given in step one is to obtain the active current and excitation current by querying experimental data based on the speed given, the motor state detection current, and the speed n; the excitation current obtained by querying the experimental data is the excitation current given required by the control process determined according to the speed given; the active current given is determined by the speed controller based on the active current obtained by querying the experimental data and the real-time speed difference.

[0013] Preferably, the specific method of calculating the active current and the excitation current from the feedback current in step 2 is to detect the two-phase feedback current to calculate the active current and the excitation current.

[0014] Preferably, the specific method for obtaining the given amplitude of the input voltage of the control power device described in step three is to compare the active current and the excitation current with the given active current and the given excitation current and input them into the current controller to obtain the given amplitude of the input voltage of the control power controller.

[0015] Preferably, the specific method for obtaining the frequency of the input voltage of the control power controller described in step 4 is to determine the main frequency of the input voltage of the control power controller according to the speed setting.

[0016] Preferably, the specific method for the power controller described in step five to control the motor operating voltage according to the voltage given control output is to obtain the voltage given amplitude and the main frequency of the voltage from steps three and four as the control signal for controlling the inversion of the power controller; when the control motor speed target value and the speed given value reach a certain difference, determine the voltage regulation frequency that needs to be increased by the voltage given.

[0017] The beneficial effects of the present invention are as follows: The present invention determines the amplitude, frequency and speed difference frequency of the motor voltage by detecting and calculating the active current and excitation current of the asynchronous motor current, so as to control the desired operating speed of the system, so that the rotating magnetic field generated by the stator current is orthogonal to the air gap rotating magnetic field generated by the rotor current, thereby realizing the vector control of the asynchronous motor. The present invention uses the current response as the key control parameter, combines the operating characteristics of the asynchronous motor and the performance experimental data of the typical operating point of the motor as the control reference, so that the performance of the motor control system has the characteristic of being independent of the motor parameters. The technical problems of low asynchronous motor control performance and complex control algorithm existing in the prior art are solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0019] Figure 1 is a schematic diagram of the method flow chart;

[0020] Figure 2 It is the schematic diagram of control principle;

[0021] Figure 3 To calculate the power factor angle diagram;

[0022] Figure 4 To obtain the voltage and current zero-crossing and peak values ​​corresponding to the phase difference;

[0023] Figure 5 It is the no-load power factor and current curve of the motor;

[0024] Figure 6 This is the motor load characteristic curve. DETAILED DESCRIPTION

[0025] In order to make the technical solutions and advantages in the embodiments of the present application more clearly understood, the exemplary embodiments of the present application are further described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than an exhaustive list of all the embodiments. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0026] Example 1, reference Figure 1-Figure 6 The present embodiment describes a vector control method based on asynchronous motor excitation current control, comprising the following steps:

[0027] Step 1: Determine the active current setting and the excitation current setting;

[0028] Step 2: Calculate active current and excitation current from feedback current;

[0029] Step 3, obtaining a given amplitude of the input voltage of the control power device;

[0030] Step 4, obtaining the main frequency for controlling the input voltage of the power controller;

[0031] Step 5, obtaining the input voltage adjustment frequency of the control power controller according to the speed difference;

[0032] Step 6: The power controller controls the motor operating voltage according to the input voltage setting to achieve vector control of the asynchronous motor.

[0033] Specifically, the current controller determines the voltage amplitude according to the given active current and the given excitation current; the speed setting determines the voltage main frequency; the motor speed and the speed setting difference determine the voltage regulation frequency to further control the active current and excitation current that meet the given speed requirements. That is, by controlling the voltage amplitude, frequency and speed difference frequency, the desired slip is indirectly controlled, so that the rotating magnetic field generated by the stator current is orthogonal to the air gap rotating magnetic field generated by the rotor current, thereby realizing the vector control of the asynchronous motor.

[0034] Figure 2 This is the control principle diagram of the asynchronous motor. The motor control links in the figure include speed comparison control, current feedback, operation status query, active current comparison, magnetic field current comparison, current control, power control output, and asynchronous motor.

[0035] The present invention uses the reactive current component of the current when the asynchronous motor is running as the excitation magnetic field control variable of the motor, called the excitation current component; the active current component is used as the motor torque control variable, called the torque current component, and indirectly controls the desired slip by controlling the voltage amplitude, frequency and slip frequency so that the rotating magnetic field generated by the stator current is orthogonal to the air gap rotating magnetic field generated by the rotor current, thereby realizing vector control of the asynchronous motor.

[0036] The minimum excitation current component determined by the voltage and frequency corresponding to the given motor speed obtained from the motor no-load test and load test is used as the initial given value i of the motor magnetic field control. Qref ; Torque control current according to active current i refs The output given value i is determined by the speed controller pref ; Detect the motor current and calculate the active current component i of the motor p and the excitation current component i Q The active current comparison value and the excitation current comparison value are combined to obtain the voltage and frequency control real-time value u from the current controller output value. ref ,u ref It is used as a modulation signal to control the output voltage of the power controller, thereby controlling the operation of the asynchronous motor.

[0037] Two methods for calculating active current and excitation current: 1. There are two zero-crossing points and two peak points in one cycle of AC voltage, twelve identifiable points for three-phase voltage, and twelve identifiable points for three-phase current. The phase difference and current amplitude corresponding to voltage and current can be obtained when the operating frequency is certain, and the active current component and excitation current component of the current can be calculated; 2. Detect the real-time current of two phases to calculate the power factor angle and current amplitude. The phase difference between voltage and current is equal to the power factor angle. According to the operating characteristics of the asynchronous motor, the phase difference between current and voltage is controlled by controlling the voltage and frequency, which is actually controlling the torque current component and the magnetic field current component of the asynchronous motor.

[0038] The motor speed and voltage, current, power factor angle and frequency parameters of the typical working condition of no-load operation with load only considering the rotation inertia of the electromechanical system are set to obtain the given speed n when the electromechanical system is running at no-load. ref The minimum excitation current component corresponding to voltage and frequency, and the given value of the magnetic field control current when the system is no-load dynamic control and the given speed changes.

[0039] Based on the voltage, frequency, minimum current and power factor angle corresponding to the speed of the motor under various working conditions obtained from the asynchronous motor type test, as well as the calculated active current component and excitation current component, data reference values ​​of the dynamic process of the motor load are given to achieve dynamic process control, and steady-state operation control is achieved based on the minimum control reference value of the excitation current.

[0040] The speed controller outputs the torque current component i pref , according to the motor working condition to control the motor excitation current component i Qref , the current controller that combines the control torque current component and the excitation current component outputs a modulation signal containing voltage amplitude and frequency to control the operation of the motor. When the motor speed target value and the speed setting value reach a certain difference, the speed difference determines the adjustment frequency of the output voltage setting that needs to be increased. Under the premise of meeting the control characteristics of the electromechanical system, the minimum excitation current control is achieved, thereby realizing the vector control of the asynchronous motor.

[0041] Specifically, detect the two-phase current i a and i c Depend on Figure 3 Calculate the maximum current I m and phase difference Get the active current component i P and the magnetic field current component i Q .

[0042]

[0043] when i a +2i c ≠0 hours

[0044] We can get:

[0045]

[0046]

[0047] Find:

[0048]

[0049] when i a ≠0,

[0050] Find:

[0051]

[0052]

[0053] Figure 4To obtain the voltage and current zero-crossing and peak values ​​of the phase difference, take phase A as an example, within the electrical resolution cycle, we can get Figure 4 The phase difference is calculated by the time difference Δt between the voltage zero-crossing point, the peak point and the current zero-crossing point and the peak point.

[0054]

[0055] Where ω=2πf, f is the voltage frequency.

[0056] When the motor is running, f has a strict corresponding relationship with the speed of the air gap rotating magnetic field.

[0057] Corresponding to the above calculation of active current component and excitation current component, the accuracy of the numerical values ​​can also be verified by detecting the calculation results of the current and voltage phase difference.

[0058] Specifically, the frequency value is determined by the speed setting to determine the main frequency and the difference between the given speed and the speed feedback value Δn=n ref -n determines the adjustment frequency Δf.

[0059]

[0060] Where p is the number of pole pairs. When Δn is less than the desired speed error 1.5e n When Δf takes effect, e n To satisfy the absolute error value between the system speed given value and the motor running speed value.

[0061] The operation status query link includes the experimental data of the motor's typical operating conditions under no-load and load conditions, such as Figure 5 The figure shows the no-load power factor and current curve at rated frequency. Figure 6 The motor load characteristic curve is drawn based on the experimental data at rated voltage and rated frequency. In actual operation control, this link includes the experimental data of the motor's typical working conditions. Since the experimental data is collected under various working conditions of the motor, the experimental data implicitly includes the changes in the motor parameters with the operating state reflected in the current response information, so the given motor control reference value controls the dynamic adjustment and steady-state operation of the motor without relying on the changes in the motor parameters.

[0062] The running status query link outputs the excitation current given value i according to the speed given Qref Control the motor magnetic field during dynamic and steady-state operation. Output active current i refs Give the speed controller as a control motor dynamic process adjustment i pref When the excitation current reaches the minimum and the motor is able to run stably, the vector control of the asynchronous motor is realized.

[0063] Specifically, Figure 2The meaning of the parameters in are:

[0064] n ref Speed ​​setting;

[0065] i Motor status detection current;

[0066] nMotor status detection speed;

[0067] i p Active current;

[0068] i pref Active current given;

[0069] i Qref Excitation current given;

[0070] i Q Excitation current;

[0071] Δn real-time speed difference;

[0072] SVR speed controller;

[0073] AVR current controller;

[0074] Δf adjusts the frequency;

[0075] u ref Voltage given;

[0076] f main frequency.

[0077] Although the present invention has been described according to a limited number of embodiments, it will be apparent to those skilled in the art, with the benefit of the above description, that other embodiments may be envisioned within the scope of the invention thus described. In addition, it should be noted that the language used in this specification is selected primarily for readability and teaching purposes, rather than for explaining or defining the subject matter of the present invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the present invention is illustrative, not restrictive, with respect to the scope of the present invention, which is defined by the appended claims.

Claims

1. A vector control method based on asynchronous motor excitation current control, characterized in that: The following steps are involved: Step 1: Determine the active current setting and the excitation current setting; Step 2: Calculate active current and excitation current from feedback current; Step 3, obtaining a given amplitude of the input voltage of the control power device; Step 4, obtaining the main frequency for controlling the input voltage of the power controller; Step 5, obtaining the input voltage adjustment frequency of the control power controller according to the speed difference; Step 6: The power controller controls the output motor operating voltage according to the input voltage setting to realize the vector control of the asynchronous motor; The specific method for determining the active current and the excitation current given in step 1 is to obtain the active current and the excitation current from the speed given, the motor state detection current, and the speed query experimental data; the excitation current obtained by querying the experimental data is the excitation current given required by the control process determined according to the speed given; The speed controller determines the active current given by the active current obtained from the query experimental data and the real-time speed difference; The specific method of obtaining the given amplitude of the input voltage of the control power device in step 3 is to compare the active current and the excitation current with the given active current and the given excitation current and input them into the current controller to obtain the given amplitude of the input voltage of the control power controller; The specific method of the power controller in step five controlling the motor operating voltage according to the voltage given control output is to obtain the voltage given amplitude and the main frequency of the voltage from steps three and four as the control signal for controlling the inversion of the power controller; when the control motor speed target value and the speed given value reach a certain difference, determine the voltage regulation frequency that needs to be increased by the voltage given.

2. The method according to claim 1, characterized in that: The specific method of calculating the active current and the excitation current from the feedback current in step 2 is to detect the two-phase feedback current to calculate the active current and the excitation current.

3. The method according to claim 2, characterized in that The specific method of obtaining the frequency of the input voltage of the control power controller in step 4 is to determine the main frequency of the input voltage of the control power controller according to the speed setting. 。

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