Rotating speed tracking method of asynchronous motor and related assembly

Abstract

The invention discloses a rotating speed tracking method of an asynchronous motor and a related component, the asynchronous motor is excited according to a preset excitation frequency greater than the rated frequency of the motor, if the back electromotive force is detected, the current running speed and direction of the asynchronous motor can be directly calculated based on the back electromotive force, and if the back electromotive force is not detected, the current running speed and direction of the asynchronous motor are calculated. And if not, generating a reduced current excitation frequency based on the preset excitation frequency and the preset excitation frequency stepping value, that is, continuing to excite the asynchronous motor after the excitation frequency is reduced until the back electromotive force is detected. It can be seen that the preset excitation frequency set in the application is large, the slip ratio can be reduced when the rotor frequency is large, and if the back electromotive force is not detected, the excitation frequency is reduced step by step, so that it is ensured that excitation is carried out on the asynchronous motor within the whole excitation frequency range, and control over stable starting of the asynchronous motor is achieved.

Description

Technical Field

[0001] The present invention relates to the field of motor control, and in particular to a rotation speed tracking method of an asynchronous motor and related components. Background Art

[0002] In industrial applications, the start and operation of the motor is usually controlled by the inverter system. However, due to the inertia of the motor itself, the motor usually rotates freely at a certain speed before normal startup. When the motor speed and direction are unknown, directly starting the motor is prone to motor overcurrent or overvoltage failure. Therefore, before the motor starts, the motor speed needs to be tracked to obtain the motor speed and direction so that the motor can start smoothly.

[0003] In traditional speed tracking methods, a current with a continuously changing frequency is usually injected into the motor, and then the speed and direction are estimated based on the motor's response, or the motor's back electromotive force is detected through a hardware circuit.

[0004] However, the former solution requires real-time monitoring of motor parameters and the calculation is relatively complicated; the latter solution usually applies a specific low-frequency voltage to the motor. When the motor operating frequency is high, the motor slip is large, which may cause the bus voltage to increase or even an overvoltage fault. Summary of the invention

[0005] The purpose of the present invention is to provide a speed tracking method for an asynchronous motor and related components, wherein the preset excitation frequency is relatively large, and the slip rate can be reduced when the rotor frequency is relatively large. If the back electromotive force is not detected, the excitation frequency is reduced in a step-by-step manner, thereby ensuring that the asynchronous motor is excited within the entire excitation frequency range and realizing stable starting control of the asynchronous motor.

[0006] In order to solve the above technical problems, the present invention provides a speed tracking method of an asynchronous motor, comprising:

[0007] Setting a preset excitation frequency as the current excitation frequency, wherein the preset excitation frequency is greater than the rated frequency of the motor;

[0008] Exciting the asynchronous motor according to the current excitation frequency;

[0009] Determining whether a back electromotive force is induced on the stator coil of the asynchronous motor;

[0010] If not, generating a reduced current excitation frequency based on the preset excitation frequency and the preset excitation frequency step value, and returning to the step of exciting the asynchronous motor according to the current excitation frequency;

[0011] If so, the current running speed and direction of the asynchronous motor are calculated based on the back electromotive force, and the current running speed and the current running direction are used to control the start-up of the asynchronous motor.

[0012] Preferably, exciting the asynchronous motor according to the current excitation frequency comprises:

[0013] According to the current excitation frequency, the asynchronous motor is excited from a preset positive direction;

[0014] Determining whether a back electromotive force is induced on a stator coil of the asynchronous motor after the asynchronous motor is excited from the preset positive direction;

[0015] If yes, the step of calculating the current running speed and direction of the asynchronous motor based on the back electromotive force and controlling the start-up of the asynchronous motor based on the current running speed and direction is entered;

[0016] If not, exciting the asynchronous motor from a preset reverse direction according to the current excitation frequency;

[0017] Enter the step of determining whether back electromotive force is induced on the stator coil of the asynchronous motor.

[0018] Preferably, the asynchronous motor is excited from a preset reverse direction according to the current excitation frequency, comprising:

[0019] The current excitation frequency is inverted, and the asynchronous motor is excited according to the inverted current excitation frequency.

[0020] Preferably, after setting the preset excitation frequency as the current excitation frequency, the method further includes:

[0021] Determining an initial excitation number, and taking the initial excitation number as an actual excitation number;

[0022] After the asynchronous motor is excited according to the current excitation frequency, the method further includes:

[0023] Increasing the value of the actual number of excitation times;

[0024] The step of generating a reduced current excitation frequency based on the preset excitation frequency and the preset excitation frequency step value comprises:

[0025] The current excitation frequency is updated based on the preset excitation frequency, the preset excitation frequency step value, and the actual excitation times.

[0026] Preferably, after generating the reduced current excitation frequency based on the current excitation frequency and the preset excitation frequency step value, the method further comprises:

[0027] Determining whether the current excitation frequency is less than or equal to a preset minimum excitation frequency;

[0028] If yes, control the asynchronous motor to start according to the preset running speed and the preset running direction;

[0029] If not, return to the step of exciting the asynchronous motor according to the current excitation frequency.

[0030] Preferably, the step of exciting the asynchronous motor according to the current excitation frequency comprises:

[0031] Applying an excitation voltage to the asynchronous motor according to the current excitation frequency, and controlling the excitation voltage to increase from an initial voltage value at a preset speed;

[0032] In the process of increasing the excitation voltage, obtaining in real time a current excitation current corresponding to the current excitation voltage; the current excitation current is positively correlated with the current excitation voltage;

[0033] When the current excitation current is greater than the preset excitation current, the excitation voltage is maintained at the current excitation voltage until the single excitation stop condition is met and the current excitation is stopped.

[0034] Preferably, the method further comprises:

[0035] When the current excitation current is less than the preset excitation current, determining whether the current excitation voltage reaches the preset excitation voltage amplitude;

[0036] If not, the excitation voltage is controlled to continue to increase, and the process returns to the step of acquiring the current excitation current corresponding to the current excitation voltage in real time during the process of the excitation voltage increasing.

[0037] In order to solve the above technical problems, the present invention provides a speed tracking system for an asynchronous motor, comprising:

[0038] A frequency setting unit, used to set a preset excitation frequency as the current excitation frequency, wherein the preset excitation frequency is greater than the rated frequency of the motor;

[0039] An excitation unit, used for exciting the asynchronous motor according to the current excitation frequency;

[0040] A judging unit, used for judging whether a back electromotive force is induced on the stator coil of the asynchronous motor;

[0041] A frequency updating unit, for generating a reduced current excitation frequency based on the preset excitation frequency and the preset excitation frequency step value, and triggering the excitation unit when the back electromotive force is not detected;

[0042] A control unit is used to calculate the current running speed and direction of the asynchronous motor based on the back electromotive force when the back electromotive force is detected, and control the start-up of the asynchronous motor based on the current running speed and direction.

[0043] In order to solve the above technical problems, the present invention provides a speed tracking device for an asynchronous motor, comprising:

[0044] Memory for storing computer programs;

[0045] The processor is used to implement the steps of the speed tracking method of the asynchronous motor as described above when executing the computer program.

[0046] In order to solve the above technical problems, the present invention provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the asynchronous motor speed tracking method as described above are implemented.

[0047] The present invention provides a speed tracking method and related components for an asynchronous motor. The asynchronous motor is first excited according to a preset excitation frequency greater than the rated frequency of the motor. If a back electromotive force is detected, the current running speed and direction of the asynchronous motor can be directly calculated based on the back electromotive force. If no back electromotive force is detected, the reduced current excitation frequency is generated based on the preset excitation frequency and the preset excitation frequency step value, that is, the asynchronous motor is continued to be excited after the excitation frequency is reduced until the back electromotive force is detected. It can be seen that the preset excitation frequency set in the present application is relatively large, which can reduce the slip rate when the rotor frequency is relatively large, and if the back electromotive force is not detected, the excitation frequency is reduced in a step-by-step manner, thereby ensuring that the asynchronous motor is excited within the entire excitation frequency range and realizing the control of the stable start of the asynchronous motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0049] Figure 1 A schematic flow chart of a method for tracking the rotation speed of an asynchronous motor provided by the present invention;

[0050] Figure 2 A schematic diagram of an equivalent circuit structure of an asynchronous motor provided by the present invention;

[0051] Figure 3 A schematic diagram of an equivalent circuit of a motor under large slip provided by the present invention;

[0052] Figure 4 A schematic structural diagram of a speed tracking system for an asynchronous motor provided by the present invention;

[0053] Figure 5 A schematic structural diagram of a rotation speed tracking device for an asynchronous motor provided by the present invention. DETAILED DESCRIPTION

[0054] The core of the present invention is to provide a speed tracking method and related components for an asynchronous motor. The preset excitation frequency is set to be relatively large, which can reduce the slip rate when the rotor frequency is relatively large. If the back electromotive force is not detected, the excitation frequency is reduced in a step-by-step manner, thereby ensuring that the asynchronous motor is excited within the entire excitation frequency range and realizing stable starting control of the asynchronous motor.

[0055] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0056] Please refer to Figure 1 , Figure 1 A schematic flow chart of a method for tracking the rotation speed of an asynchronous motor provided by the present invention, the method comprising:

[0057] S11: Set the preset excitation frequency as the current excitation frequency, and the preset excitation frequency is greater than the rated frequency of the motor;

[0058] In the present application, it is taken into account that some asynchronous motors in the prior art will freely run at a certain speed before normal start due to their own inertia. At this time, if a speed sensor is not set, the speed of the asynchronous motor before normal start cannot be determined. If the speed of the free running of the asynchronous motor is ignored and the asynchronous motor is started according to the conventional zero-speed control, the asynchronous motor will have a large running slip, resulting in motor overcurrent or DC bus overvoltage fault, thereby causing the motor to fail to start. Therefore, under the working condition where a speed sensor is not set, how to track the speed of the asynchronous motor before starting, so as to ensure the smooth starting of the asynchronous motor, is a problem that needs to be solved urgently.

[0059] The existing hardware speed tracking method used for asynchronous motor speed tracking is to excite the asynchronous motor so that the stator coil of the asynchronous motor induces back electromotive force, and calculate the running speed and phase of the asynchronous motor based on the back electromotive force to achieve speed tracking. However, in the prior art, the excitation frequency when exciting the asynchronous motor is low, and if the rotor frequency is large at this time, according to , where s is the motor slip rate, is the excitation frequency, is the rotor frequency. It can be seen that when the difference between the excitation frequency and the rotor frequency is large, the motor slip rate is large. Please refer to Figure 2 , Figure 2 A schematic diagram of an equivalent circuit structure of an asynchronous motor provided by the present invention, wherein is the stator resistance of the single-phase winding of the asynchronous motor, is the stator leakage inductance of the motor, is the motor rotor leakage inductance, is the motor excitation inductance, is the motor rotor resistance, is the phase voltage applied to the stator winding, is the rotor phase current, is the excitation current. When the motor slip rate is large, the motor rotor resistance can be ignored, and Much greater than , Figure 2 Can be simplified to Figure 3 , Figure 3 This is a schematic diagram of an equivalent circuit of a motor under large slip provided by the present invention. It can be seen that the current will not flow into Where the excitation, excitation current Almost 0, so even if a higher voltage is applied to the stator side of the motor, it will not Magnetize so that Unable to store energy. When the end, the unstored energy The back electromotive force cannot be induced in the stator coil, resulting in failure to track the motor's running speed and direction. If the excitation frequency is too low, lower than the motor's running frequency, the motor may be in a generating state, which in turn causes the bus voltage to increase or even cause overvoltage problems.

[0060] Based on the above analysis, in order to achieve the induction of back electromotive force on the motor stator winding after the excitation is completed, it is necessary to reduce the motor slip rate and reduce the difference between the excitation frequency and the rotor frequency, so as to achieve the mutual inductance of the motor. Magnetize.

[0061] Therefore, in the present application, before the asynchronous motor is excited, a preset excitation frequency that is greater than the rated frequency of the motor is pre-set. Based on this, it can be ensured that when the motor rotor frequency is large, the slip rate of the motor is reduced, so that when the motor rotor frequency is large, the back electromotive force is induced in the stator coil, thereby determining the current operating parameters of the asynchronous motor, such as the current operating speed and direction.

[0062] S12: Excite the asynchronous motor according to the current excitation frequency;

[0063] In this step, if the asynchronous motor is excited for the first time, the current excitation frequency is the preset excitation frequency, that is, the asynchronous motor is firstly excited according to the preset excitation frequency. If, after the asynchronous motor is excited according to the preset excitation frequency, a back electromotive force is induced on the stator coil of the asynchronous motor, the current running speed and direction of the asynchronous motor can be directly calculated according to the back electromotive force, so as to control the start of the asynchronous motor based on the current running speed and direction. For example, when controlling the start of the asynchronous motor, the asynchronous motor starts running with the current running speed and direction as the initial running speed and direction.

[0064] S13: Determine whether a back electromotive force is induced on the stator coil of the asynchronous motor;

[0065] Asynchronous motors, also known as induction motors, work on the principle of electromagnetic induction. In an asynchronous motor, the stator is the non-rotating part of the motor whose main task is to generate a rotating magnetic field. This rotating magnetic field is not achieved mechanically, but by passing an alternating current through several pairs of electromagnets, causing their magnetic pole properties to change cyclically, thus forming a seemingly rotating magnetic field. Excitation refers to the process of providing an additional magnetic field to the motor or generator. In asynchronous motors, excitation is usually achieved by applying a voltage to the stator coils. When current flows through the stator coils, a rotating magnetic field is generated. When the rotating magnetic field generated by the stator interacts with the rotor (usually a squirrel-cage rotatable conductor), the conductor bars in the rotor cut the magnetic lines of force of the stator magnetic field. According to the principle of electromagnetic induction, when a conductor moves in a magnetic field, an induced electromotive force is generated in the conductor. In an asynchronous motor, the movement of the rotor conductor bars cutting the magnetic lines of force of the stator magnetic field causes the generation of an induced electromotive force. The direction of this induced electromotive force is opposite to the direction of the externally applied power supply voltage, so it is called back electromotive force.

[0066] S14: If the back electromotive force is not induced on the stator coil of the asynchronous motor, a reduced current excitation frequency is generated based on the preset excitation frequency and the preset excitation frequency step value, and the step of exciting the asynchronous motor according to the current excitation frequency is returned.

[0067] If no back electromotive force is induced on the stator coil of the asynchronous motor after excitation, it may be because the rotor frequency of the asynchronous motor is relatively small at this time. Therefore, in order to obtain the back electromotive force, the present application reduces the excitation frequency, that is, reduces the current excitation frequency according to the preset excitation frequency and the preset excitation frequency step value until the back electromotive force is induced on the stator coil of the asynchronous motor.

[0068] Specifically, if the back electromotive force is not induced on the stator coil of the asynchronous motor after the asynchronous motor is excited according to the preset excitation frequency, the current excitation frequency is reduced and the asynchronous motor is excited again. If the back electromotive force is still not induced on the stator coil, the current excitation frequency is further reduced to excite the asynchronous motor. Based on this, the current excitation frequency is from large to small, and in the process of reducing the current excitation frequency, the entire excitation frequency range is traversed until the back electromotive force can be induced on the stator coil of the asynchronous motor. That is, no matter what operating state the asynchronous motor is in, the speed tracking can be achieved.

[0069] S15: If a back electromotive force is induced on the stator coil of the asynchronous motor, the current running speed and direction of the asynchronous motor are calculated based on the back electromotive force, and the asynchronous motor is controlled to start based on the current running speed and direction;

[0070] If back electromotive force is induced on the stator coil of the asynchronous motor, the rotating parts of the asynchronous motor, such as the speed and rotation direction of the rotor, can be determined based on the back electromotive force, thereby indirectly determining the current operating speed and direction of the asynchronous motor, so as to achieve speed tracking of the asynchronous motor and achieve stable control of the starting of the asynchronous motor.

[0071] In summary, the preset excitation frequency set in the present application is relatively large, which can reduce the slip rate when the rotor frequency is large. If the back electromotive force is not detected, the excitation frequency is reduced in steps, thereby ensuring that the asynchronous motor is excited within the entire excitation frequency range and realizing stable starting control of the asynchronous motor.

[0072] Based on the above embodiments:

[0073] As a preferred embodiment, exciting the asynchronous motor according to the current excitation frequency includes:

[0074] According to the current excitation frequency, the asynchronous motor is excited from the preset positive direction;

[0075] Determine whether a back electromotive force is induced on the stator coil of the asynchronous motor after the asynchronous motor is excited from a preset positive direction;

[0076] If yes, the process proceeds to the step of calculating the current running speed and direction of the asynchronous motor based on the back electromotive force, and controlling the start of the asynchronous motor based on the current running speed and direction;

[0077] If not, the asynchronous motor is excited from the preset reverse direction according to the current excitation frequency;

[0078] Enter the step of determining whether back electromotive force is induced in the stator coil of the asynchronous motor.

[0079] In this embodiment, it is considered that in an asynchronous motor, the excitation direction (i.e., the current direction of the stator winding) determines the direction of the rotating magnetic field. When three-phase alternating current is passed through the stator winding, a rotating magnetic field is generated. Therefore, when the asynchronous motor is excited, the asynchronous motor is first excited in a preset positive direction. If a back electromotive force can be induced on the stator coil after excitation from the preset positive direction, the speed can be directly tracked according to the back electromotive force and the asynchronous motor can be started. However, if the back electromotive force is not induced at this time, the current excitation frequency will not be changed, but the asynchronous motor will be excited from the preset reverse direction. If the back electromotive force can be induced at this time, the speed can be directly tracked according to the back electromotive force and the asynchronous motor can be started. However, if the back electromotive force still cannot be induced, the current excitation frequency will be reduced at this time.

[0080] After lowering the current excitation frequency, the asynchronous motor is still excited from the preset positive direction first. If the back electromotive force can be induced, the speed is tracked directly according to the back electromotive force and the start-up of the asynchronous motor is controlled. If the back electromotive force cannot be sensed, the asynchronous motor is excited from the preset reverse direction. If the back electromotive force can be sensed, the speed is tracked directly according to the back electromotive force and the start-up of the asynchronous motor is controlled. If the back electromotive force still cannot be sensed, the current excitation frequency is further reduced. In this cycle, the device induces the back electromotive force on the stator coil to track the speed of the asynchronous motor.

[0081] As a preferred embodiment, the asynchronous motor is excited from a preset reverse direction according to the current excitation frequency, including:

[0082] The current excitation frequency is inverted, and the asynchronous motor is excited according to the inverted current excitation frequency.

[0083] In this embodiment, when the asynchronous motor is excited from a preset positive direction, the excitation is directly performed based on the current excitation frequency, and when the asynchronous motor is excited from a preset reverse direction, the current excitation frequency is specifically reversed and the asynchronous motor is then excited.

[0084] Specifically, the inversion process is , is the current excitation frequency.

[0085] As a preferred embodiment, after setting the preset excitation frequency as the current excitation frequency, the method further includes:

[0086] Determine the initial excitation times, and take the initial excitation times as the actual excitation times;

[0087] After the asynchronous motor is excited according to the current excitation frequency, it also includes:

[0088] The actual number of excitations is incremented;

[0089] The reduced current excitation frequency is generated based on the preset excitation frequency and the preset excitation frequency step value, including:

[0090] The current excitation frequency is updated based on the preset excitation frequency, the preset excitation frequency step value and the actual excitation times.

[0091] In this embodiment, the actual number of excitations is set. When the asynchronous motor is not excited, the actual number of excitations is the initial number of excitations. If it is 0, that is, each time the asynchronous motor is excited once, the actual number of excitations is incremented. For example, each time the asynchronous motor is excited once, the value of the actual number of excitations is increased by one. Based on this, based on the preset excitation frequency and the preset excitation frequency step value, the current excitation frequency is reduced based on the actual number of excitations, so as to achieve a step-by-step reduction of the current excitation frequency, so as to improve the speed tracking efficiency of the asynchronous motor. Of course, the specific values ​​of the initial number of excitations and the increment processing are not limited in this application.

[0092] It should be noted that if the asynchronous motor is excited by switching from a preset positive direction to a preset reverse direction, there is no need to increment the actual number of excitations. That is, when the asynchronous motor is excited according to the same current excitation frequency, the actual number of excitations is only increased once regardless of whether it is from the preset positive direction or the preset reverse direction.

[0093] As a preferred embodiment, the current excitation frequency is updated based on the preset excitation frequency, the preset excitation frequency step value and the actual excitation times, including:

[0094] Based on the preset excitation frequency, the preset excitation frequency step value and the actual number of excitations, the current excitation frequency is updated using the result calculated using the first quantitative relationship, and the first quantitative relationship is:

[0095] ;

[0096] in, is the current excitation frequency, To preset the excitation frequency, is the actual excitation times, It is the preset excitation frequency step value.

[0097] When the current excitation frequency is reduced based on the actual number of excitations based on the preset excitation frequency and the preset excitation frequency step value, the actual number of excitations is first subtracted by 1, the difference is multiplied by the preset excitation frequency step value, and then the product is subtracted from the preset excitation frequency to determine the current excitation frequency.

[0098] For example, the initial value of the actual number of excitations is 1, the preset excitation frequency step value is 10Hz, and the preset excitation frequency is 60Hz. After the asynchronous motor is excited according to the preset excitation frequency, the value of the actual number of excitations is increased by 1. At this time, the value of the actual number of excitations is 2. If, under the preset excitation frequency, the back electromotive force cannot be induced on the stator coil of the asynchronous motor from both the preset positive direction and the preset reverse direction, the calculation process of calculating the current excitation frequency is: =60-(2-1)×10=50Hz. After the asynchronous motor is excited according to the current excitation frequency, i.e. 50Hz, the actual number of excitations is increased by one. At this time, the actual number of excitations is 3. If, at the current excitation frequency, the back electromotive force cannot be induced on the stator coil of the asynchronous motor from both the preset positive direction and the preset reverse direction, the calculation process for updating the current excitation frequency is: =60-(3-1)×10=40Hz, and continue in this way until the back electromotive force is induced on the stator coil of the asynchronous motor and the speed of the asynchronous motor is tracked.

[0099] As a preferred embodiment, after generating the reduced current excitation frequency based on the current excitation frequency and the preset excitation frequency step value, the method further includes:

[0100] Determine whether the current excitation frequency is less than or equal to the preset minimum excitation frequency;

[0101] If yes, the asynchronous motor is controlled to start according to the preset running speed and the preset running direction;

[0102] If not, return to the step of exciting the asynchronous motor according to the current excitation frequency.

[0103] Taking into account that when the excitation frequency is lower than the motor operating frequency, the motor may be in a power generation state, resulting in an increase in the bus voltage or even an overvoltage problem, a preset minimum excitation frequency is set in this embodiment. During the excitation of the asynchronous motor, if the current excitation frequency is reduced until it is reduced to the preset minimum excitation frequency, and the back electromotive force cannot be induced on the stator coil, then it can be considered that the asynchronous motor is in a stationary state or close to a stationary state. At this time, the asynchronous motor is directly controlled to start according to the preset operating speed and preset operating direction, that is, the asynchronous motor is controlled to start at zero speed and run according to the preset operating speed and preset operating direction.

[0104] As a preferred embodiment, the step of exciting the asynchronous motor according to the current excitation frequency includes:

[0105] Applying excitation voltage to the asynchronous motor according to the current excitation frequency, and controlling the excitation voltage to increase from an initial voltage value at a preset speed;

[0106] In the process of increasing the excitation voltage, the current excitation current corresponding to the current excitation voltage is obtained in real time; the current excitation current is positively correlated with the current excitation voltage;

[0107] When the current excitation current is greater than the preset excitation current, the excitation voltage is maintained at the current excitation voltage until the single excitation stop condition is met and the current excitation is stopped;

[0108] During the excitation process, the excitation voltage is controlled to increase from an initial voltage value, such as 0V, according to the current excitation frequency, and specifically increases at a preset speed. During the process of increasing the excitation voltage, the current excitation current corresponding to the current excitation voltage is obtained in real time, and it is determined whether the current excitation current is greater than the preset excitation current. If it is greater than the preset excitation current, the current excitation voltage is stopped from being increased, and the current excitation voltage is kept unchanged until the single excitation stop condition is met and the excitation is stopped. For example, starting from the current excitation voltage remaining unchanged until the preset single excitation time has passed, it can be considered that the single excitation stop condition is met and the excitation is stopped. The present application does not limit this, that is, each time the excitation is performed, after the current excitation current reaches the preset excitation current, the excitation voltage is kept for the preset single excitation time. After the preset single excitation time is reached, the excitation is completed, and the inverter performing the excitation is sealed.

[0109] It should be noted that the current excitation current in this application is the stator phase current. Excessive excitation current will cause excessive current impact on the components in the circuit. This impact may exceed the rated current carrying capacity of the component, causing the component to overheat, burn or degrade in performance. Especially for those components that are sensitive to current, such as power tubes, transformers, etc., excessive excitation current may cause serious damage, so it is necessary to set a preset excitation current.

[0110] As a preferred embodiment, the method further includes:

[0111] When the current excitation current is less than the preset excitation current, determining whether the current excitation voltage reaches the preset excitation voltage amplitude;

[0112] If not, the excitation voltage is controlled to continue to increase, and the process returns to the step of acquiring the current excitation current corresponding to the current excitation voltage in real time during the process of the excitation voltage increasing.

[0113] In order to avoid motor abnormality caused by excessive excitation voltage, a preset excitation voltage amplitude is set in this embodiment. During the process of increasing the excitation voltage, if the current excitation current has not been greater than the preset excitation current, and the current excitation voltage has not reached the preset excitation voltage amplitude, the excitation voltage will continue to increase; but if the current excitation voltage has increased to the preset excitation voltage, the excitation voltage will no longer be increased, but the current excitation voltage will be maintained for a preset single excitation time and then the excitation will be stopped. When controlling the excitation voltage to increase at a preset speed, the excitation voltage ramp time can be specifically set, that is, the excitation voltage increases from 0 and reaches the preset excitation voltage amplitude after the excitation voltage ramp time.

[0114] Specifically, the implementation logic of the asynchronous motor speed tracking high-frequency excitation method is as follows:

[0115] Set the basic parameters of high-frequency excitation: preset excitation voltage amplitude , preset excitation frequency , preset excitation current , minimum excitation frequency , preset single excitation time , Excitation voltage ramp time and preset excitation frequency step value ;

[0116] Step 1: Calculate the maximum number of excitations n:

[0117] ;

[0118] Step 2: Determine whether the actual excitation times k is less than or equal to the maximum excitation times n. The initial value of k is 1. If k>n, jump to step 12; otherwise, go to step 3;

[0119] Step 3: Calculate the current excitation frequency :

[0120] ;

[0121] Step 4: Follow Start excitation, current excitation voltage From 0V to Increase to , and in Increased process judgment Is it greater than ,if > , Maintain the current value and do not increase it;

[0122] Step 5: Judgement Whether the maintenance time has been reached If it is reached, the excitation is stopped and the inverter is blocked.

[0123] Step 6: If back electromotive force is induced on the stator coil of the asynchronous motor, the operating frequency of the motor is calculated based on the back electromotive force, and the running direction of the motor is determined, and the process jumps to step 11; if no back electromotive force is induced, the process executes step 7;

[0124] Step 7: Reverse the actual excitation frequency, that is ;

[0125] Step 8: Follow Start excitation, current excitation voltage From 0V to Increase to , and in Increased process judgment Is it greater than ,if > , Maintain the current value and do not increase it;

[0126] Step 9: Judgement Whether the maintenance time has been reached If it is reached, the excitation is stopped and the inverter is blocked.

[0127] Step 10: If a back electromotive force is induced on the stator coil of the asynchronous motor, the operating frequency of the motor is calculated based on the back electromotive force, and the running direction of the motor is determined, and the process jumps to step 11. If no back electromotive force is induced, the value of the actual excitation times k is increased by 1 and the process returns to step 2.

[0128] Step 11: If residual magnetic excitation is successful, the inverter sets the starting frequency and running direction to the speed tracking to obtain the actual running frequency and direction of the motor before starting;

[0129] Step 12: = When the residual magnetism is not excited, it is considered that the motor is in a stationary state; the inverter starts according to the default parameters.

[0130] Please refer to Figure 4 , Figure 4 A schematic diagram of a speed tracking system for an asynchronous motor provided by the present invention, the system comprising:

[0131] A frequency setting unit 41, used to set a preset excitation frequency as the current excitation frequency, the preset excitation frequency being greater than the rated frequency of the motor;

[0132] An excitation unit 42, used to excite the asynchronous motor according to the current excitation frequency;

[0133] A judging unit 43, used to judge whether a back electromotive force is induced on the stator coil of the asynchronous motor;

[0134] The frequency updating unit 44 is used to generate a reduced current excitation frequency based on a preset excitation frequency and a preset excitation frequency step value when the back electromotive force is not detected, and trigger the excitation unit;

[0135] The control unit 45 is used to calculate the current running speed and direction of the asynchronous motor based on the back electromotive force when the back electromotive force is detected. The current running speed and the current running direction are used to control the start of the asynchronous motor.

[0136] For an introduction to the speed tracking system of the asynchronous motor provided by the present invention, please refer to the above method embodiment, and the present invention will not be described in detail here.

[0137] Please refer to Figure 5 , Figure 5 A schematic diagram of a speed tracking device for an asynchronous motor provided by the present invention, the device comprising:

[0138] A memory 51, used for storing computer programs;

[0139] The processor 52 is used to implement the steps of the above-mentioned method for tracking the rotation speed of the asynchronous motor when executing the computer program.

[0140] For an introduction to the speed tracking device for the asynchronous motor provided by the present invention, please refer to the above method embodiment, and the present invention will not be described in detail here.

[0141] The computer readable storage medium in the present invention stores a computer program, and when the computer program is executed by the processor 52, the steps of the speed tracking method of the asynchronous motor as described above are implemented.

[0142] For an introduction to the computer-readable storage medium provided by the present invention, please refer to the above method embodiment, and the present invention will not be repeated here.

[0143] It should also be noted that, in this specification, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0144] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for tracking the rotation speed of an asynchronous motor, characterized in that: include: Setting a preset excitation frequency as the current excitation frequency, wherein the preset excitation frequency is greater than the rated frequency of the motor; Exciting the asynchronous motor according to the current excitation frequency; Determining whether a back electromotive force is induced on the stator coil of the asynchronous motor; If not, generating a reduced current excitation frequency based on the preset excitation frequency and the preset excitation frequency step value, and returning to the step of exciting the asynchronous motor according to the current excitation frequency; If so, the current running speed and the current running direction of the asynchronous motor are calculated based on the back electromotive force, and the current running speed and the current running direction are used to control the start-up of the asynchronous motor.

2. The method for tracking the speed of an asynchronous motor according to claim 1, characterized in that: Exciting the asynchronous motor according to the current excitation frequency includes: According to the current excitation frequency, the asynchronous motor is excited from a preset positive direction; Determining whether a back electromotive force is induced on a stator coil of the asynchronous motor after the asynchronous motor is excited from the preset positive direction; If yes, the step of calculating the current running speed and direction of the asynchronous motor based on the back electromotive force and controlling the start-up of the asynchronous motor based on the current running speed and direction is entered; If not, exciting the asynchronous motor from a preset reverse direction according to the current excitation frequency; Enter the step of determining whether back electromotive force is induced on the stator coil of the asynchronous motor.

3. The method for tracking the speed of an asynchronous motor according to claim 2, wherein: According to the current excitation frequency, the asynchronous motor is excited from a preset reverse direction, including: The current excitation frequency is inverted, and the asynchronous motor is excited according to the inverted current excitation frequency.

4. The method for tracking the speed of an asynchronous motor according to claim 1, characterized in that: After setting the preset excitation frequency as the current excitation frequency, it also includes: Determining an initial excitation number, and taking the initial excitation number as an actual excitation number; After the asynchronous motor is excited according to the current excitation frequency, the method further includes: Incrementing the actual number of excitations; The step of generating a reduced current excitation frequency based on the preset excitation frequency and the preset excitation frequency step value comprises: The current excitation frequency is updated based on the preset excitation frequency, the preset excitation frequency step value, and the actual excitation times.

5. The method for tracking the speed of an asynchronous motor according to claim 1, wherein: After generating the reduced current excitation frequency based on the current excitation frequency and the preset excitation frequency step value, the method further includes: Determining whether the current excitation frequency is less than or equal to a preset minimum excitation frequency; If yes, control the asynchronous motor to start according to the preset running speed and the preset running direction; If not, return to the step of exciting the asynchronous motor according to the current excitation frequency.

6. The method for tracking the speed of an asynchronous motor according to any one of claims 1 to 5, characterized in that: The step of exciting the asynchronous motor according to the current excitation frequency comprises: Applying an excitation voltage to the asynchronous motor according to the current excitation frequency, and controlling the excitation voltage to increase from an initial voltage value at a preset speed; In the process of increasing the excitation voltage, obtaining in real time a current excitation current corresponding to the current excitation voltage; the current excitation current is positively correlated with the current excitation voltage; When the current excitation current is greater than the preset excitation current, the excitation voltage is maintained at the current excitation voltage until the single excitation stop condition is met and the current excitation is stopped.

7. The method for tracking the speed of an asynchronous motor according to claim 6, characterized in that: The method further comprises: When the current excitation current is less than the preset excitation current, determining whether the current excitation voltage reaches the preset excitation voltage amplitude; If not, the excitation voltage is controlled to continue to increase, and the process returns to the step of acquiring the current excitation current corresponding to the current excitation voltage in real time during the process of the excitation voltage increasing.

8. A speed tracking system for an asynchronous motor, characterized in that: include: A frequency setting unit, used to set a preset excitation frequency as the current excitation frequency, wherein the preset excitation frequency is greater than the rated frequency of the motor; An excitation unit, used for exciting the asynchronous motor according to the current excitation frequency; A judging unit, used for judging whether a back electromotive force is induced on the stator coil of the asynchronous motor; A frequency updating unit, configured to generate a reduced current excitation frequency based on the preset excitation frequency and the preset excitation frequency step value when the back electromotive force is not detected, and trigger the excitation unit; A control unit is used to calculate the current running speed and the current running direction of the asynchronous motor based on the back electromotive force when the back electromotive force is detected, and the current running speed and the current running direction are used to control the start-up of the asynchronous motor.

9. A speed tracking device for an asynchronous motor, characterized in that: include: Memory for storing computer programs; A processor is used to implement the steps of the speed tracking method of an asynchronous motor as described in any one of claims 1 to 7 when executing a computer program.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of the method for tracking the rotation speed of an asynchronous motor as claimed in any one of claims 1 to 7 are implemented.

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