Starting control methods, devices, frequency converters and storage media for asynchronous motors

Abstract

This invention discloses a starting control method, device, frequency converter, and storage medium for an asynchronous motor. The method includes: controlling the frequency converter to output DC current to apply excitation current to the stator of the asynchronous motor; acquiring the bus voltage of the frequency converter; determining the starting mode of the asynchronous motor based on the bus voltage; and controlling the asynchronous motor to start and run according to the starting mode. This method can automatically identify the state of the asynchronous motor and determine the corresponding starting mode to control the asynchronous motor to start and run, thus eliminating the need for manual on-site observation of the motor's state and setting the corresponding starting mode, saving manpower and avoiding the problem of asynchronous motor starting failure due to human error.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of motor control, and in particular to a starting control method and device of an asynchronous motor, a frequency converter and a storage medium. BACKGROUND

[0002] At present, the starting modes of the asynchronous motor driven by the frequency converter include the lowest frequency starting, DC braking starting and speed tracking starting, etc., and different states of the asynchronous motor correspond to different starting modes, for example, when the asynchronous motor is in a static state, the starting mode is the lowest frequency starting; when the asynchronous motor is in a coasting state, the starting mode is the DC braking starting or the speed tracking starting, etc. However, in the related art, the starting mode of the asynchronous motor is mainly realized by manual operation, for example, the state of the asynchronous motor is observed by the on-site operator, and then the corresponding starting mode is set according to the state of the asynchronous motor, so that the frequency converter starts according to the starting mode set by the operator. SUMMARY

[0003] The present application aims to at least solve one of the problems in the related art. To this end, the first object of the present application is to provide a starting control method of an asynchronous motor, which can automatically identify the state of the asynchronous motor and determine the corresponding starting mode according to the state to control the starting operation of the asynchronous motor, thereby saving human resources and avoiding the problem of starting failure caused by misoperation.

[0004] The second object of the present application is to provide another starting control method of an asynchronous motor.

[0005] The third object of the present application is to provide a computer-readable storage medium.

[0006] The fourth object of the present application is to provide a frequency converter.

[0007] The fifth object of the present application is to provide a starting control device of an asynchronous motor.

[0008] The sixth object of the present application is to provide another starting control device of an asynchronous motor.

[0009] To achieve the above objects, the first aspect of the present application provides a starting control method of an asynchronous motor, the method comprising: controlling a frequency converter to output a direct current to apply an excitation current to a stator of the asynchronous motor; acquiring a bus voltage of the frequency converter; determining a starting mode of the asynchronous motor according to the bus voltage; and controlling the asynchronous motor to start and run according to the starting mode.

[0010] According to the starting control method of the asynchronous motor, the DC current output by the frequency converter is controlled to apply the exciting current to the stator of the asynchronous motor, the bus voltage of the frequency converter is obtained, the starting mode of the asynchronous motor is determined according to the bus voltage, and the asynchronous motor is controlled to start and run according to the starting mode. The state of the asynchronous motor can be automatically identified, the corresponding starting mode is determined according to the state to control the asynchronous motor to start and run, so that the state of the motor does not need to be observed by artificial field observation and the corresponding starting mode is set for starting, human resources are saved, and the problem of starting failure caused by artificial misoperation can be avoided.

[0011] According to an embodiment of the present application, the control of the DC current output by the frequency converter comprises: obtaining any phase output current in the three-phase output current of the frequency converter; obtaining a current difference between the any phase output current and the corresponding target DC current; and performing PI adjustment on the current difference to make the three-phase output current equal to the respective corresponding target DC current.

[0012] According to an embodiment of the present application, the determination of the starting mode of the asynchronous motor according to the bus voltage comprises: if the application time of the exciting current is less than a first preset time and the bus voltage is greater than or equal to a preset voltage, determining that the starting mode is the inertia starting mode; and if the application time of the exciting current is greater than or equal to the first preset time and the bus voltage is less than the preset voltage, determining that the starting mode is the direct starting mode.

[0013] According to an embodiment of the present application, the determination of the starting mode as the inertia starting mode and the control of the asynchronous motor to start and run according to the starting mode comprises: controlling the frequency converter to stop outputting the DC current, and obtaining the three-phase output voltage of the frequency converter; determining the starting frequency, the starting voltage, the starting angle and the inertia direction of the asynchronous motor according to the three-phase output voltage; controlling the asynchronous motor to start according to the starting frequency, the starting voltage, the starting angle and the inertia direction, and controlling the starting frequency to remain unchanged and adjusting the starting voltage until the output voltage of the frequency converter reaches the voltage corresponding to the starting frequency.

[0014] According to an embodiment of the present application, the three-phase output voltage comprises N groups, N is an integer greater than or equal to 4, and the determination of the starting frequency, the starting voltage, the starting angle and the inertia direction of the asynchronous motor according to the three-phase output voltage comprises: for each group of three-phase output voltage, obtaining the resultant voltage and the rotation angle of the asynchronous motor in the two-phase stationary coordinate system according to the three-phase output voltage to obtain N resultant voltages and N rotation angles; performing difference calculation on the N rotation angles to obtain N-1 rotation angle differences; and determining the starting frequency, the starting voltage, the starting angle and the inertia direction of the asynchronous motor according to the N resultant voltages, the N rotation angles and the N-1 rotation angle differences.

[0015] According to one embodiment of the present application, the starting frequency, the starting voltage, the starting angle and the freewheeling direction of the asynchronous motor are determined according to N synthesized voltages, N rotation angles and N-1 rotation angle differences, comprising: when the sign of at least N-2 continuous rotation angle differences among the N-1 rotation angle differences is positive, determining that the freewheeling direction is positive, the starting voltage is wherein, if the sign of the N-1 rotation angle differences is all positive, or the sign of the 2nd to the N-1th rotation angle differences is all positive, determining that the starting frequency is the starting angle is θ N + Δθ N-1 , otherwise determining that the starting frequency is the starting angle is θ N + Δθ N-1 + 2π; when the sign of at least N-2 continuous rotation angle differences among the N-1 rotation angle differences is negative, determining that the freewheeling direction is negative, the starting voltage is wherein, when the freewheeling direction is negative, if the sign of the N-1 rotation angle differences is all negative, or the sign of the 2nd to the N-1th rotation angle differences is all negative, determining that the starting frequency is the starting angle is θ N + Δθ N-1 , otherwise determining that the starting frequency is the starting angle is θ N + Δθ N-1 - 2π; in other cases, determining that there is no freewheeling direction, the starting voltage is zero, the starting frequency is the lowest frequency of the asynchronous motor, and the starting angle is zero; wherein, Umodi is the ith synthesized voltage, i∈[1, N], Δθ N-1 is the N-1th rotation angle difference, θ N is the Nth rotation angle, and Ts is the control period of the frequency converter.

[0016] According to one embodiment of the present application, after the output voltage of the frequency converter reaches the voltage corresponding to the starting frequency, the asynchronous motor is controlled to run normally.

[0017] According to one embodiment of the present application, the starting mode is determined to be a direct starting mode, and the asynchronous motor is controlled to start running according to the starting mode, comprising: taking the lowest frequency of the asynchronous motor as the starting frequency of the asynchronous motor; controlling the asynchronous motor to start according to the starting frequency, and controlling the starting frequency to remain unchanged, and adjusting the output voltage of the frequency converter until the output voltage increases from zero to the voltage corresponding to the starting frequency.

[0018] According to one embodiment of the present application, after the output voltage of the asynchronous motor increases from zero to the voltage corresponding to the starting frequency, the asynchronous motor is controlled to run normally.

[0019] According to an embodiment of the present application, the normal operation of the asynchronous motor is controlled, including: gradually adjusting the starting frequency of the asynchronous motor according to a V / F curve until the starting frequency reaches a target frequency, wherein the voltage corresponding to the starting frequency is determined according to the V / F curve.

[0020] To achieve the above object, the second aspect of the present application provides another starting control method of an asynchronous motor, the method comprising: determining that the asynchronous motor is in a coasting state, controlling a frequency converter to output a direct current to apply an exciting current to a stator of the asynchronous motor; after delaying for a second preset time, controlling the frequency converter to stop outputting the direct current, and acquiring a three-phase output voltage of the frequency converter; determining a starting frequency, a starting voltage, a starting angle and a coasting direction of the asynchronous motor according to the three-phase output voltage; and controlling the asynchronous motor to start according to the starting frequency, the starting voltage, the starting angle and the coasting direction, and keeping the starting frequency unchanged and adjusting the starting voltage until the output voltage of the frequency converter reaches the voltage corresponding to the starting frequency.

[0021] According to the starting control method of the asynchronous motor provided by the embodiment of the present application, for the coasting state of the asynchronous motor, the frequency converter is controlled to output a direct current to apply an exciting current to the stator of the asynchronous motor, and after delaying for a second preset time, the frequency converter is controlled to stop outputting the direct current, and the three-phase output voltage of the frequency converter is acquired, and the asynchronous motor is controlled to start according to the three-phase output voltage, so that the starting success rate of the asynchronous motor can be improved.

[0022] To achieve the above object, the third aspect of the present application provides a computer readable storage medium, which stores a starting control program of an asynchronous motor, and the starting control program of the asynchronous motor is executed by a processor to implement the starting control method of the asynchronous motor of the first aspect or the second aspect.

[0023] According to the computer readable storage medium provided by the embodiment of the present application, by using the starting control method of the asynchronous motor of the first aspect, the state of the asynchronous motor can be automatically identified, and the corresponding starting mode can be determined according to the state to control the asynchronous motor to start, so that the state of the motor does not need to be observed on site by human and the corresponding starting mode is set to start, human resources are saved, and the problem of starting failure caused by misoperation can be avoided; by using the starting control method of the asynchronous motor of the second aspect, the starting success rate of the asynchronous motor can be improved.

[0024] To achieve the above object, the fourth aspect of the present application provides a frequency converter, comprising: a memory, a processor and a starting control program of an asynchronous motor stored on the memory and executable on the processor, and when the processor executes the program, the starting control method of the asynchronous motor of the first aspect or the second aspect is implemented.

[0025] According to the present invention, the frequency converter, by adopting the asynchronous motor start-up control method of the first aspect embodiment, can automatically identify the state of the asynchronous motor and determine the corresponding start-up mode according to the state to control the asynchronous motor to start and run, thereby eliminating the need for manual on-site observation of the motor state and setting the corresponding start-up mode for start-up, saving manpower and avoiding the problem of start-up failure due to misoperation; by adopting the asynchronous motor start-up control method of the second aspect embodiment, the start-up success rate of the asynchronous motor can be improved.

[0026] To achieve the above objectives, a fifth aspect embodiment of the present invention provides a starting control device for an asynchronous motor, the device comprising: a first DC excitation module, used to control the inverter to output DC current to apply excitation current to the stator of the asynchronous motor, and to obtain the bus voltage of the inverter, and to determine the starting mode of the asynchronous motor based on the bus voltage; and a second starting module, used to control the asynchronous motor to start operation according to the starting mode.

[0027] According to an embodiment of the present invention, the asynchronous motor starting control device controls the inverter to output DC current through a first DC excitation module to apply excitation current to the stator of the asynchronous motor, obtains the bus voltage of the inverter, determines the starting mode of the asynchronous motor based on the bus voltage, and controls the asynchronous motor to start running through a first starting module according to the starting mode. It can automatically identify the state of the asynchronous motor and determine the corresponding starting mode to control the asynchronous motor to start running, thereby eliminating the need for manual on-site observation of the motor state and setting of the corresponding starting mode, saving manpower and avoiding the problem of starting failure due to misoperation.

[0028] To achieve the above objectives, a sixth aspect of the present invention provides another starting control device for an asynchronous motor. The device includes: a second DC excitation module, used to determine that the asynchronous motor is in a coasting state, control the inverter to output DC current to apply excitation current to the stator of the asynchronous motor, and control the inverter to stop outputting DC current after a second preset time delay; a coasting start module, used to acquire the three-phase output voltage of the inverter, and determine the starting frequency, starting voltage, starting angle, and coasting direction of the asynchronous motor based on the three-phase output voltage; and a coasting operation switching module, used to control the asynchronous motor to start according to the starting frequency, starting voltage, starting angle, and coasting direction, and control the starting frequency to remain unchanged and adjust the starting voltage until the output voltage of the inverter reaches the voltage corresponding to the starting frequency.

[0029] According to the asynchronous motor starting control device of the present invention, the asynchronous motor is determined to be in a coasting state by the second DC excitation module, the inverter is controlled to output DC current to apply excitation current to the stator of the asynchronous motor, and after a second preset time delay, the inverter is controlled to stop outputting DC current. The three-phase output voltage of the inverter is obtained by the coasting start module and the coasting operation switching module, and the asynchronous motor is started and run according to the three-phase output voltage, which can improve the starting success rate of the asynchronous motor.

[0030] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0031] Figure 1 A flowchart of an asynchronous motor start-up control method according to an embodiment of the present invention;

[0032] Figure 2 This is a schematic diagram of the sampling of the output voltage and output current of a frequency converter according to an embodiment of the present invention;

[0033] Figure 3 A flowchart illustrating the determination of the starting mode of an asynchronous motor according to an embodiment of the present invention;

[0034] Figure 4 This is a flowchart illustrating the control of an asynchronous motor starting in a coasting state according to an embodiment of the present invention;

[0035] Figure 5 This is a flowchart illustrating the control of an asynchronous motor starting in a coasting state according to another embodiment of the present invention;

[0036] Figure 6 A flowchart of an asynchronous motor start-up control method according to another embodiment of the present invention;

[0037] Figure 7 This is a block diagram of a starting control device for an asynchronous motor according to an embodiment of the present invention;

[0038] Figure 8 This is a block diagram of a starting control device for an asynchronous motor according to another embodiment of the present invention;

[0039] Figure 9 This is a block diagram of a starting control device for an asynchronous motor according to yet another embodiment of the present invention. Detailed Implementation

[0040] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0041] The following description, with reference to the accompanying drawings, outlines the starting control method, apparatus, frequency converter, and storage medium for an asynchronous motor according to embodiments of the present invention.

[0042] First aspect of the embodiment:

[0043] Figure 1 This is a flowchart of a starting control method for an asynchronous motor according to an embodiment of the present invention. (See reference...) Figure 1 As shown, the starting control method for this asynchronous motor may include the following steps:

[0044] Step S101: Control the inverter to output DC current to apply excitation current to the stator of the asynchronous motor.

[0045] Step S102: Obtain the bus voltage of the frequency converter.

[0046] Step S103: Determine the starting mode of the asynchronous motor based on the bus voltage.

[0047] Step S104: Control the asynchronous motor to start running according to the start mode.

[0048] Specifically, refer to Figure 2 As shown, the output terminal of the frequency converter is connected to the asynchronous motor M, used to drive the asynchronous motor M to start and run. When driving the asynchronous motor M to start and run, the frequency converter can first control the application of a certain value of DC current to the stator of the asynchronous motor M, so that the asynchronous motor M generates a stator magnetic field. If the asynchronous motor M is currently in a coasting state (that is, after the power supply to the asynchronous motor M is stopped, the asynchronous motor M is still rotating), the rotor of the asynchronous motor M will cut the stator magnetic field to generate an induced electromotive force (i.e., back electromotive force), and excite an induced current inside the rotor. This induced current causes the rotor to rotate and generate electricity, thereby causing the voltage of the frequency converter's bus capacitor C to rise. If the asynchronous motor M is currently in a stationary state, the asynchronous motor M will not generate electricity, and therefore will not cause the voltage of the frequency converter's bus capacitor C to rise. Therefore, after the frequency converter applies a certain value of DC current to the stator of the asynchronous motor M, the voltage of the bus capacitor C, i.e. the bus voltage, can be obtained. The state of the asynchronous motor M can be determined according to the change of the bus voltage. Different states correspond to different starting modes. Therefore, the corresponding starting mode can be determined based on the state of the asynchronous motor M. Then, the asynchronous motor M can be started and run according to the determined starting mode, so that the starting mode of the asynchronous motor M does not need to be manually confirmed.

[0049] The above embodiments, by controlling the frequency converter to apply DC current to the asynchronous motor, obtaining the bus voltage of the frequency converter, and determining the starting mode of the asynchronous motor based on the bus voltage, can automatically identify the state of the asynchronous motor and determine the corresponding starting mode to control the asynchronous motor to start and run. This eliminates the need for manual on-site observation of the asynchronous motor's state and setting the corresponding starting method, saving manpower and avoiding the problem of starting failure due to misoperation.

[0050] In some embodiments of the present invention, controlling the DC current output of the frequency converter may include: acquiring the output current of any one of the three-phase output currents of the frequency converter; acquiring the current difference between the output current of any one phase and the corresponding target DC current; and performing PI (Proportion Integration) adjustment on the current difference so that the three-phase output current is equal to their respective target DC current.

[0051] For example, assuming the DC current setting of the inverter output is I_dcset, which can be 5% to 10% of the effective value of the rated current of the asynchronous motor M, then the target DC current corresponding to U of the inverter can be set to I_dcset, the target DC current corresponding to V to -0.5*I_dcset, and the target DC current corresponding to W to -0.5*I_dcset (when setting, the sum of the three-phase output currents of the inverter must be zero). (Reference) Figure 2 As shown, when controlling the DC output current of the frequency converter, a current sampling module can be set at the output terminal of the frequency converter. The current detection function module in the current sampling module collects the U-phase current Iu in the three-phase output current of the frequency converter, and obtains the current difference between the U-phase current Iu and the target DC current I_dcset corresponding to U. The current difference is then PI-regulated to adjust the three-phase output voltages Uu, Uv, and Uw of the frequency converter, thereby making the U-phase output current Iu = I_dcset, the V-phase output current Iv = -0.5*I_dcset, and the W-phase output current Iw = -0.5*I_dcset.

[0052] It should be noted that the W-phase current Iw in the three-phase output current of the frequency converter can also be acquired through the current detection function module in the current sampling module, and the current difference between the W-phase current Iw and the corresponding target DC current -0.5*I_dcset can be adjusted by PI to make the three-phase output current equal to their respective target DC current. Of course, PI adjustment can also be based on the V-phase current; the specific method is not limited here.

[0053] In the above embodiments, by using a closed-loop control method to control the DC current output of the frequency converter, the accuracy and stability of the output DC current can be guaranteed, thereby effectively improving the accuracy of determining the starting mode of the asynchronous motor.

[0054] In some embodiments of the present invention, determining the starting mode of the asynchronous motor based on the bus voltage may include: if the application time of the excitation current is less than a first preset time and the bus voltage is greater than or equal to a preset voltage, determining the starting mode as a coasting starting mode; if the application time of the excitation current is greater than or equal to the first preset time and the bus voltage is less than the preset voltage, determining the starting mode as a direct starting mode. It should be noted that the preset voltage is less than the bus voltage overvoltage protection value.

[0055] Specifically, assuming the application time of the excitation current is t, the first preset time is T_set, and the preset voltage is U_dcset, then when the application time t < the first preset time T_set, if the bus voltage Udc of the frequency converter is ≥ the preset voltage U_dcset, it is considered that the asynchronous motor M has generated electricity and sent it back to the frequency converter. Therefore, it can be determined that the asynchronous motor M is in a coasting state, and thus the starting mode of the asynchronous motor M is determined to be the coasting start mode. Afterwards, the frequency converter is controlled to stop outputting DC current, and the asynchronous motor M is started and run according to the coasting start mode. When the application time t < the first preset time T_set, if the bus voltage Udc of the frequency converter is ≥ the preset voltage U_dcset, then the asynchronous motor M is considered to have generated electricity and sent it back to the frequency converter. This indicates that the asynchronous motor M is in a coasting state. If the inverter's bus voltage Udc < preset voltage U_dcset at the preset time T_set, the excitation current continues to be applied until the application time t ≥ the first preset time T_set. If the inverter's bus voltage Udc < preset voltage U_dcset at this time, it is considered that the asynchronous motor M has not generated any power and sent it back to the inverter. Thus, it can be determined that the asynchronous motor M is in a stationary state (or the coasting frequency is extremely low). Therefore, the starting mode of the asynchronous motor M is determined to be the direct start mode. After that, the inverter is controlled to stop outputting DC current, and the asynchronous motor M is started and run according to the direct start mode.

[0056] As a concrete example, see reference Figure 3 As shown, determining the starting mode of an asynchronous motor may include the following steps:

[0057] Step S201: Control the frequency converter to apply a certain value of DC current to the stator of the asynchronous motor.

[0058] Step S202: Collect the bus voltage Udc and record the DC current application time t.

[0059] It should be noted that it can correspond Figure 2A voltage sampling module is installed on the bus capacitor C shown. This module collects the voltage of the bus capacitor C to obtain the bus voltage Udc. Assuming the control cycle of the frequency converter is Ts, the bus voltage Udc can be collected in each control cycle Ts, and the DC current application time t can be accumulated.

[0060] Step S203: Determine whether the bus voltage Udc has reached the preset voltage U_dcset. If yes, proceed to step S204; otherwise, proceed to step S206.

[0061] In step S204, the frequency converter stops outputting DC current.

[0062] Step S205: Determine that the starting mode of the asynchronous motor is the coasting start mode.

[0063] Step S206: Determine whether the applied time t has reached the first preset time T_set. If yes, proceed to step S207; otherwise, return to step S201 and continue to control the frequency converter to apply a certain value of DC current to the stator of the asynchronous motor.

[0064] In step S207, the frequency converter stops outputting DC current.

[0065] Step S208: Determine that the starting mode of the asynchronous motor is the direct start mode.

[0066] In the above embodiments, the starting mode of the asynchronous motor can be quickly and accurately determined based on the changes in the bus voltage, eliminating the need for manual on-site observation of the motor's status and setting the corresponding starting method. This saves manpower and avoids the problem of starting failure due to misoperation.

[0067] In some embodiments of the present invention, reference is made to Figure 4 As shown, the starting mode is determined to be coasting start mode. Controlling the asynchronous motor to start and run according to the starting mode may include:

[0068] Step S301: Control the frequency converter to stop outputting DC current and obtain the three-phase output voltage of the frequency converter.

[0069] Specifically, after determining that the starting mode of the asynchronous motor M is coasting start mode, the inverter stops outputting DC current. Since the asynchronous motor M is in a coasting state, it will generate a back electromotive force (EMF). Because the inverter's output is connected to the asynchronous motor M, the back EMF of the asynchronous motor M can be obtained by acquiring the inverter's three-phase output voltage. Therefore, the starting frequency, starting angle, starting voltage, and coasting direction of the asynchronous motor M can be calculated based on the back EMF. For example... Figure 2As shown, the U-phase output voltage Uu, V-phase output voltage Uv, and W-phase output voltage Uw of the inverter can be acquired through the voltage detection function module in the voltage sampling module at the output terminal of the inverter. During acquisition, the three-phase output voltage of the inverter can be acquired once within the first four or more control cycles Ts of the inverter after it stops outputting DC current, thereby obtaining at least four sets of three-phase output voltages.

[0070] Step S302: Determine the starting frequency, starting voltage, starting angle, and coasting direction of the asynchronous motor based on the three-phase output voltage.

[0071] Specifically, after obtaining at least four sets of three-phase output voltages from the frequency converter, the starting frequency, starting voltage, starting angle, and coasting direction of the asynchronous motor M can be determined based on these at least four sets of three-phase output voltages.

[0072] In some embodiments of the present invention, the three-phase output voltage includes N groups, where N is an integer greater than or equal to 4. Determining the starting frequency, starting voltage, starting angle, and coasting direction of the asynchronous motor based on the three-phase output voltage includes: for each group of three-phase output voltages, obtaining the composite voltage and rotation angle of the asynchronous motor in a two-phase stationary coordinate system based on the three-phase output voltages to obtain N composite voltages and N rotation angles; calculating the difference between the N rotation angles to obtain N-1 rotation angle differences; and determining the starting frequency, starting voltage, starting angle, and coasting direction of the asynchronous motor based on the N composite voltages, N rotation angles, and N-1 rotation angle differences.

[0073] Specifically, based on the three-phase output voltage of the asynchronous motor M, the combined voltage, rotation angle, and rotation angle difference of the asynchronous motor M can be calculated using the following formulas (1)-(3):

[0074]

[0075] Where Uui is the U-phase output voltage in the i-th group of three-phase output voltages, Uvi is the V-phase output voltage in the i-th group of three-phase output voltages, and Uwi is the W-phase output voltage in the i-th group of three-phase output voltages. αi Let U be the voltage component of the asynchronous motor on the α-axis in the i-th two-phase stationary coordinate system. βi Let Umodi be the voltage component of the asynchronous motor on the β axis in the i-th two-phase stationary coordinate system, where Umodi is the i-th composite voltage, 1≤i≤N, and N is the number of three-phase output voltage groups.

[0076]

[0077] Where θi is the i-th rotation angle, 1≤i≤N.

[0078] Δθi=θ(i+1)-θ(i) (3)

[0079] Where Δθi is the difference of the i-th rotation angle, θ(i+1) is the (i+1)-th rotation angle, and 1≤i<N.

[0080] To facilitate understanding, we will first use four sets of three-phase output voltages as an example. Assume that the four sets of three-phase output voltages obtained are Uu1, Uv1 and Uw1; Uu2, Uv2 and Uw2; Uu3, Uv3 and Uw3; Uu4, Uv4 and Uw4. Substituting the four sets of three-phase output voltages into the above formulas (1)-(3), we can calculate the four composite voltages Umod1, Umod2, Umod3 and Umod4 of the asynchronous motor M, the four rotation angles θ1, θ2, θ3 and θ4, and the three rotation angle differences Δθ1, Δθ2 and Δθ3. Then, through Table 1, we can determine the starting frequency, starting voltage, starting angle and coasting direction of the asynchronous motor M.

[0081] Table 1

[0082]

[0083]

[0084] As shown in Table 1, the coasting direction, starting frequency, starting angle, and starting voltage of the asynchronous motor M can be determined based on the rotation angle differences Δθ1, Δθ2, and Δθ3, the rotation angle θ4, the combined voltages Umod1, Umod2, Umod3, and Umod4, and the control cycle Ts of the frequency converter. It should be noted that when the signs of Δθ1 and Δθ3 are both positive and the sign of Δθ2 is negative, or when the signs of Δθ1 and Δθ3 are both negative and the sign of Δθ2 is positive, the coasting frequency of the asynchronous motor M is extremely low, and the asynchronous motor M can be considered to be in a stationary state. At this time, there is no coasting direction, and the starting frequency is the lowest frequency of the asynchronous motor M, with both the starting angle and starting voltage being zero.

[0085] It should be noted that the above description uses four sets of three-phase output voltages of the asynchronous motor M as an example. In other embodiments, five or more sets can also be used, and the principle is the same as that of four sets of three-phase output voltages.

[0086] Specifically, assuming there are N sets of three-phase output voltages, N-1 rotation angle differences, N rotation angles, and N composite voltages can be determined based on these N sets of three-phase output voltages. If at least N-2 consecutive rotation angle differences among the N-1 sets are positive, the coasting direction of the asynchronous motor M is determined to be positive; if at least N-2 consecutive rotation angle differences are negative, the coasting direction of the asynchronous motor M is determined to be negative; otherwise, the coasting direction of the asynchronous motor M is determined to be negative. Furthermore, when the coasting direction is positive, if all N-1 rotation angle differences are positive, or if the signs of the second to the (N-1)th rotation angle differences are all positive (i.e., the N-2 consecutive positive rotation angle differences are closer to the current moment), the starting frequency of the asynchronous motor M is determined to be... The starting angle is θ N +Δθ N-1 Otherwise, determine the starting frequency of the asynchronous motor M as follows: The starting angle is θ N +Δθ N-1 +2π; When the coasting direction is negative, if the signs of all N-1 rotation angle differences are negative, or the signs of all rotation angle differences from the 2nd to the N-1th rotation angle differences are negative (i.e., the N-2 consecutive rotation angle differences with negative signs are closer to the current moment), then the starting frequency of the asynchronous motor M is determined to be... The starting angle is θ N +Δθ N-1 Otherwise, determine the starting frequency of the asynchronous motor M as follows: The starting angle is θ N +Δθ N-1 -2π; otherwise, the starting frequency is the lowest frequency of the asynchronous motor M, and the starting angle is zero. Furthermore, when the coasting direction is positive or negative, the starting voltage of the asynchronous motor M is... When there is no coasting direction, the starting voltage of the asynchronous motor M is zero.

[0087] Step S303: Control the asynchronous motor to start according to the starting frequency, starting voltage, starting angle and coasting direction, and control the starting frequency to remain unchanged and adjust the starting voltage until the output voltage of the frequency converter reaches the voltage corresponding to the starting frequency.

[0088] Specifically, after determining the coasting direction, starting frequency, starting angle, and starting voltage of the asynchronous motor M, the asynchronous motor M can be started according to the determined starting frequency, starting angle, and starting voltage, and its rotation direction will be set to the determined coasting direction, that is, starting from the starting angle and rotating along the coasting direction at the starting frequency and starting voltage. Then, the starting frequency is kept constant while the starting voltage is adjusted until the inverter's output voltage reaches the voltage corresponding to the starting frequency. For example, the voltage corresponding to the starting frequency can be determined based on a pre-determined V / F curve (i.e., voltage-to-frequency ratio curve) of the asynchronous motor M. In other words, the asynchronous motor M can be controlled based on a pre-determined V / F curve. Furthermore, after the inverter's output voltage reaches the voltage corresponding to the starting frequency, the asynchronous motor is controlled to operate normally.

[0089] As a concrete example, see reference Figure 5 As shown, when the starting mode of the asynchronous motor M is determined to be coasting start mode, controlling the start-up and operation of the asynchronous motor according to the starting mode may include:

[0090] Step S401: Collect the three-phase output voltage of the frequency converter.

[0091] Step S402: Calculate the combined voltage Umodi, rotation angle θi, and rotation angle difference Δθi based on the three-phase output voltage, and count them.

[0092] Step S403: Determine if the count value i is greater than or equal to 4. If yes, proceed to step S404; otherwise, return to step S401.

[0093] Step S404: Determine the starting frequency, starting voltage, starting angle, and coasting direction of the asynchronous motor based on the combined voltage Umodi, rotation angle θi, and rotation angle difference Δθi.

[0094] Step S405: Control the asynchronous motor to start based on the starting frequency, starting voltage, starting angle, and coasting direction.

[0095] In the above embodiments, when the asynchronous motor is in a coasting state, the asynchronous motor's state is identified by applying a DC current. This DC current increases the rotor current of the asynchronous motor. After the DC current input to the asynchronous motor stops, the higher coasting speed increases the back electromotive force (EMF) of the asynchronous motor. This results in a higher back EMF relative to the noise voltage in the detection circuit and transmission cable. By setting up an analog processing circuit, interference noise can be effectively filtered out, ensuring the accuracy of the asynchronous motor's back EMF. Furthermore, by detecting the asynchronous motor's back EMF, i.e., the three-phase output voltage of the frequency converter, and determining the asynchronous motor's starting-related parameters based on the back EMF, the accuracy of the determined starting-related parameters is ensured. Then, the asynchronous motor is controlled to start according to the starting-related parameters, ensuring reliable starting and greatly improving the asynchronous motor's starting success rate.

[0096] In some embodiments of the present invention, the starting mode is determined to be a direct starting mode, and the asynchronous motor is controlled to start and run according to the starting mode, including: using the lowest frequency of the asynchronous motor as the starting frequency of the asynchronous motor; controlling the asynchronous motor to start according to the starting frequency and keeping the starting frequency unchanged; and adjusting the output voltage of the frequency converter until the output voltage increases from zero to the voltage corresponding to the starting frequency.

[0097] In other words, when the starting mode of the asynchronous motor M is determined to be direct start mode, the lowest frequency of the asynchronous motor M is used as the starting frequency to control the start of the asynchronous motor M, and the starting frequency is kept constant. Simultaneously, the starting voltage of the asynchronous motor M is adjusted to gradually increase from zero until the output voltage of the frequency converter reaches the voltage corresponding to the starting frequency. For example, the voltage corresponding to the starting frequency can be determined based on a pre-determined V / F curve of the asynchronous motor M. That is, the asynchronous motor M can be controlled based on a pre-determined V / F curve. Furthermore, after the output voltage of the frequency converter reaches the voltage corresponding to the starting frequency, the asynchronous motor is controlled to operate normally.

[0098] In the above embodiments, when the asynchronous motor is stationary, the asynchronous motor is driven at the lowest frequency of the inverter so that its output voltage reaches the voltage corresponding to the lowest frequency, which can ensure the reliable start-up of the asynchronous motor.

[0099] In some embodiments of the present invention, controlling the normal operation of the asynchronous motor includes: gradually adjusting the starting frequency of the asynchronous motor according to the V / F curve until the starting frequency reaches the target frequency.

[0100] Specifically, after the asynchronous motor M starts and enters normal operation, the starting frequency of the asynchronous motor (i.e., the operating frequency of the asynchronous motor, which is also the output frequency of the frequency converter) can be gradually adjusted according to the predetermined V / F curve of the asynchronous motor M (which can be set according to the set time), while adjusting the output voltage of the frequency converter until the starting frequency reaches the target frequency.

[0101] In summary, the asynchronous motor starting control method according to embodiments of the present invention controls the output DC current of the frequency converter to apply excitation current to the stator of the asynchronous motor, obtains the bus voltage of the frequency converter, determines the starting mode of the asynchronous motor based on the bus voltage, and controls the asynchronous motor to start and run according to the starting mode. This method can automatically identify the state of the asynchronous motor and determine the corresponding starting mode to control its start-up, thus eliminating the need for manual on-site observation of the motor's state and setting of the corresponding starting method. This saves manpower and avoids starting failures due to misoperation. Furthermore, different starting modes correspond to different states, enabling the asynchronous motor to start successfully with a small starting inrush current in both stationary and coasting states. Simultaneously, since the asynchronous motor's state is identified by applying DC current, reliable starting in coasting state is guaranteed, significantly improving the starting success rate of the asynchronous motor in coasting state.

[0102] Second aspect of the embodiment:

[0103] Figure 6 This is a flowchart of a starting control method for an asynchronous motor according to another embodiment of the present invention. (See reference...) Figure 6 As shown, the starting control method for this asynchronous motor may include the following steps:

[0104] Step S501: Determine that the asynchronous motor is in a coasting state, and control the inverter to output DC current to apply excitation current to the stator of the asynchronous motor.

[0105] In step S502, after a second preset time delay, the inverter is controlled to stop outputting DC current, and the three-phase output voltage of the inverter is obtained.

[0106] Step S503: Determine the starting frequency, starting voltage, starting angle, and coasting direction of the asynchronous motor based on the three-phase output voltage.

[0107] Step S504: Control the asynchronous motor to start according to the starting frequency, starting voltage, starting angle and coasting direction, and keep the starting frequency unchanged and adjust the starting voltage until the output voltage of the frequency converter reaches the voltage corresponding to the starting frequency.

[0108] Specifically, when starting an asynchronous motor driven by a frequency converter, if the asynchronous motor is already in a coasting state, using a direct start mode to control its start can easily cause overvoltage or overcurrent in the frequency converter, leading to motor start-up failure. Therefore, for the coasting condition of asynchronous motors, related technologies often employ speed tracking start-up methods. For speed tracking start-up, a frequency search method is typically used. This method searches downwards from the highest frequency of the asynchronous motor, tracking the current to calculate the motor's coasting frequency using software or a combination of hardware. However, when the coasting direction of the asynchronous motor is opposite to the set direction, the frequency converter is prone to overvoltage or overcurrent, causing motor start-up failure. Simultaneously, during the search process, the frequency converter's output frequency may have a significant frequency and phase difference with the asynchronous motor's back electromotive force, making current closed-loop control extremely difficult and parameter adjustment challenging. This places high demands on on-site commissioning and user personnel, especially in cases where soft starting is used. In such cases, users often use a frequency converter with 40% of the motor's rated capacity to start the asynchronous motor under no-load conditions, making the frequency search method highly susceptible to overcurrent. Alternatively, the coasting frequency of an asynchronous motor can be determined by detecting its back electromotive force (EMF). However, this method is typically used for stopping the asynchronous motor for a short period of time. This is because when the stopping time exceeds the rotor time constant of the asynchronous motor, the back EMF signal becomes very weak and easily affected by interference signals, leading to incorrect calculation of the coasting frequency and thus causing the asynchronous motor to fail to start.

[0109] Based on this, for the coasting condition of the asynchronous motor, in the embodiments of the present invention, a certain value of DC current is applied to the stator of the asynchronous motor by controlling the frequency converter to generate a stator magnetic field. The rotor of the asynchronous motor will cut the stator magnetic field to generate an induced electromotive force and excite an induced current inside the rotor. This induced current causes the rotor to rotate and generate electricity, thereby causing the voltage of the bus capacitor of the frequency converter to rise. After a period of time, the frequency converter is controlled to stop applying a certain value of DC current to the stator of the asynchronous motor, and the back electromotive force of the asynchronous motor, i.e., the three-phase output voltage of the frequency converter, is detected for a short time. Then, the starting frequency, starting voltage, starting angle and coasting direction of the asynchronous motor are determined according to the three-phase output voltage. The asynchronous motor is started according to the starting frequency, starting voltage, starting angle and coasting direction, and the starting frequency is kept constant and the starting voltage is adjusted until the output voltage of the frequency converter reaches the voltage corresponding to the starting frequency.

[0110] It should be noted that this method can determine the coasting direction of the asynchronous motor, and control the motor's start-up based on this direction, thus avoiding start-up failures caused by the asynchronous motor's coasting direction not matching the set direction. Simultaneously, it can determine the asynchronous motor's starting frequency and starting voltage, and controlling the motor's start-up based on these parameters can prevent start-up failures caused by excessive differences in starting frequency and starting voltage. Furthermore, since the applied DC current increases the asynchronous motor's speed, the higher coasting speed after the DC current input stops can increase the asynchronous motor's back electromotive force. The back EMF of the asynchronous motor is relatively high compared to the noise voltage in the detection circuit and transmission cable. By setting up an analog processing circuit, interference noise can be effectively filtered out, ensuring the accuracy of the back EMF of the asynchronous motor. Therefore, by detecting the back EMF of the asynchronous motor, i.e., the three-phase output voltage of the frequency converter, and determining the relevant starting parameters of the asynchronous motor based on the back EMF, the accuracy of the determined relevant starting parameters of the asynchronous motor is ensured. Then, the asynchronous motor is controlled to start according to the relevant starting parameters, ensuring that the asynchronous motor can start reliably, greatly improving the starting success rate of the asynchronous motor, and avoiding starting failure due to weak back EMF signal.

[0111] In some embodiments of the present invention, controlling the DC current output of the frequency converter includes: acquiring the output current of any one of the three-phase output currents of the frequency converter; acquiring the current difference between the output current of any one phase and the corresponding target DC current; and performing PI adjustment on the current difference to make the three-phase output current equal to their respective target DC currents.

[0112] In some embodiments of the present invention, the three-phase output voltage includes N groups, where N is an integer greater than or equal to 4. Determining the starting frequency, starting voltage, starting angle, and coasting direction of the asynchronous motor based on the three-phase output voltage includes: for each group of three-phase output voltages, obtaining the composite voltage and rotation angle of the asynchronous motor in a two-phase stationary coordinate system based on the three-phase output voltages to obtain N composite voltages and N rotation angles; calculating the difference between the N rotation angles to obtain N-1 rotation angle differences; and determining the starting frequency, starting voltage, starting angle, and coasting direction of the asynchronous motor based on the N composite voltages, N rotation angles, and N-1 rotation angle differences.

[0113] In some embodiments of the present invention, determining the starting frequency, starting voltage, starting angle, and coasting direction of the asynchronous motor based on N combined voltages, N rotation angles, and N-1 rotation angle differences includes: determining the coasting direction as positive when at least N-2 consecutive rotation angle differences among the N-1 rotation angle differences have positive signs, and determining the starting voltage as... If the signs of all N-1 rotation angle differences are positive, or the signs of all rotation angle differences from the 2nd to the N-1th rotation angle differences are positive, then the starting frequency is determined as follows: The starting angle is θ N +Δθ N-1 Otherwise, determine the startup frequency as follows: The starting angle is θ N +Δθ N-1 +2π; When at least N-2 consecutive rotation angle differences out of N-1 rotation angle differences are negative, the coasting direction is determined to be negative, and the starting voltage is... Specifically, when the coasting direction is negative, if the signs of all N-1 rotation angle differences are negative, or the signs of all rotation angle differences from the 2nd to the N-1th rotation angle differences are negative, the starting frequency is determined to be... The starting angle is θ N +Δθ N-1 Otherwise, determine the startup frequency as follows: The starting angle is θ N +Δθ N-1 -2π; In other cases, the coasting direction is determined to be zero, the starting voltage is zero, the starting frequency is the lowest frequency of the asynchronous motor, and the starting angle is zero; where Umodi is the i-th composite voltage, i∈[1,N], Δθ N-1 For the (N-1)th rotation angle difference, θ N Let N be the Nth rotation angle, and Ts be the control cycle of the frequency converter.

[0114] In some embodiments of the present invention, the asynchronous motor is controlled to operate normally after the output voltage of the frequency converter reaches the voltage corresponding to the starting frequency.

[0115] In some embodiments of the present invention, controlling the normal operation of the asynchronous motor includes: gradually adjusting the starting frequency of the asynchronous motor according to the V / F curve until the starting frequency reaches the target frequency, wherein the voltage corresponding to the starting frequency is determined according to the V / F curve.

[0116] It should be noted that for details not disclosed in the second aspect embodiment of the asynchronous motor starting control method, please refer to the details disclosed in the first aspect embodiment of the asynchronous motor starting control method described above, which will not be repeated here.

[0117] According to the asynchronous motor starting control method of the present invention, when the asynchronous motor is in a coasting state, the method controls the inverter to output DC current to apply excitation current to the stator of the asynchronous motor, and after a second preset time delay, controls the inverter to stop outputting DC current, and obtains the three-phase output voltage of the inverter, and controls the asynchronous motor to start running according to the three-phase output voltage, which can improve the starting success rate of the asynchronous motor.

[0118] Third aspect of the embodiment:

[0119] In some embodiments of the present invention, a computer-readable storage medium is also provided, on which an asynchronous motor start-up control program is stored, which, when executed by a processor, implements the asynchronous motor start-up control method of the first aspect embodiment or the second aspect embodiment described above.

[0120] According to the computer-readable storage medium of the present invention, by employing the asynchronous motor start-up control method of the first aspect embodiment, the state of the asynchronous motor can be automatically identified, and the corresponding start-up mode can be determined according to the state for start-up operation. This eliminates the need for manual on-site observation of the motor state and setting of the corresponding start-up mode, saving manpower and avoiding the problem of start-up failure due to misoperation. By employing the asynchronous motor start-up control method of the second aspect embodiment, the start-up success rate of the asynchronous motor can be improved.

[0121] Fourth aspect of the embodiment:

[0122] In some embodiments of the present invention, a frequency converter is also provided, including: a memory, a processor, and an asynchronous motor start-up control program stored in the memory and executable on the processor. When the processor executes the program, it implements the asynchronous motor start-up control method of the first aspect embodiment or the second aspect embodiment described above.

[0123] According to the present invention, the frequency converter, by adopting the asynchronous motor start-up control method of the first aspect embodiment, can automatically identify the state of the asynchronous motor and determine the corresponding start-up mode for start-up operation based on the state, thereby eliminating the need for manual on-site observation of the motor state and setting the corresponding start-up mode, saving manpower and avoiding the problem of start-up failure due to misoperation; by adopting the asynchronous motor start-up control method of the second aspect embodiment, the start-up success rate of the asynchronous motor can be improved.

[0124] Fifth aspect of the embodiment:

[0125] Figure 7 This is a block diagram of a starting control device for an asynchronous motor according to an embodiment of the present invention. (Refer to...) Figure 7 As shown, the starting control device 700 for the asynchronous motor includes: a first DC excitation module 701 and a second starting module 702.

[0126] The first DC excitation module 701 is used to control the inverter to output DC current to apply excitation current to the stator of the asynchronous motor, obtain the bus voltage of the inverter, and determine the starting mode of the asynchronous motor according to the bus voltage; the first starting module 702 is used to control the asynchronous motor to start running according to the starting mode.

[0127] According to one embodiment of the present invention, the first DC excitation module 701 is specifically used to: acquire any one phase output current among the three phase output currents of the frequency converter; acquire the current difference between any one phase output current and the corresponding target DC current; and perform PI adjustment on the current difference so that the three phase output currents are equal to their respective corresponding target DC currents.

[0128] According to one embodiment of the present invention, the first DC excitation module 701 is specifically used to: if the application time of the excitation current is less than a first preset time and the bus voltage is greater than or equal to a preset voltage, determine the starting mode as coasting start mode and control the frequency converter to stop outputting DC current; if the application time of the excitation current is greater than or equal to the first preset time and the bus voltage is less than a preset voltage, determine the starting mode as direct start mode and control the frequency converter to stop outputting DC current.

[0129] According to one embodiment of the present invention, reference Figure 8 As shown, the first starting module 702 may include a coasting start unit 7021 and a coasting operation switching unit 7022. The coasting start unit 7021 is used to acquire the three-phase output voltage of the frequency converter when the first DC excitation module 701 determines that the starting mode is coasting start mode, and to determine the starting frequency, starting voltage, starting angle and coasting direction of the asynchronous motor according to the three-phase output voltage. The coasting operation switching unit 7022 is used to control the asynchronous motor to start according to the starting frequency, starting voltage, starting angle and coasting direction, and to control the starting frequency to remain unchanged and adjust the starting voltage until the output voltage of the frequency converter reaches the voltage corresponding to the starting frequency.

[0130] According to one embodiment of the present invention, the three-phase output voltage includes N groups, where N is an integer greater than or equal to 4. The coasting start unit 7021 is specifically used for: for each group of three-phase output voltage, obtaining the composite voltage and rotation angle of the asynchronous motor in the two-phase stationary coordinate system based on the three-phase output voltage to obtain N composite voltages and N rotation angles; calculating the difference between the N rotation angles to obtain N-1 rotation angle differences; and determining the starting frequency, starting voltage, starting angle, and coasting direction of the asynchronous motor based on the N composite voltages, N rotation angles, and N-1 rotation angle differences.

[0131] According to one embodiment of the present invention, the coasting start unit 7021 is specifically used to: determine the coasting direction as positive when at least N-2 consecutive rotation angle differences among N-1 rotation angle differences have positive signs, and set the start voltage as follows: If the signs of all N-1 rotation angle differences are positive, or the signs of all rotation angle differences from the 2nd to the N-1th rotation angle differences are positive, then the starting frequency is determined as follows: The starting angle is θ N +ΔθN-1 Otherwise, determine the startup frequency as follows: The starting angle is θ N +Δθ N-1 +2π; When at least N-2 consecutive rotation angle differences out of N-1 rotation angle differences are negative, the coasting direction is determined to be negative, and the starting voltage is... Specifically, when the coasting direction is negative, if the signs of all N-1 rotation angle differences are negative, or the signs of all rotation angle differences from the 2nd to the N-1th rotation angle differences are negative, the starting frequency is determined to be... The starting angle is θ N +Δθ N-1 Otherwise, determine the startup frequency as follows: The starting angle is θ N +Δθ N-1 -2π; In other cases, the coasting direction is determined to be zero, the starting voltage is zero, the starting frequency is the lowest frequency of the asynchronous motor, and the starting angle is zero; where Umodi is the i-th composite voltage, i∈[1,N], Δθ N-1 For the (N-1)th rotation angle difference, θ N Let N be the Nth rotation angle, and Ts be the control cycle of the frequency converter.

[0132] According to one embodiment of the present invention, the first start-up module 702 may further include a normal operation unit 7023, which is used to control the asynchronous motor to operate normally after the output voltage of the frequency converter reaches the voltage corresponding to the start-up frequency.

[0133] According to one embodiment of the present invention, the first starting module 702 may include a direct starting unit 7024, which is used to take the lowest frequency of the asynchronous motor as the starting frequency of the asynchronous motor when the first DC excitation module 701 determines that the starting mode is the direct starting mode, and control the asynchronous motor to start according to the starting frequency, and control the starting frequency to remain unchanged, and adjust the output voltage of the frequency converter until the output voltage increases from zero to the voltage corresponding to the starting frequency.

[0134] According to one embodiment of the present invention, the first start-up module 702 may further include a normal operation unit 7023, which is used to control the asynchronous motor to operate normally after the output voltage of the asynchronous motor increases from zero to the voltage corresponding to the start-up frequency.

[0135] According to one embodiment of the present invention, the normal operation unit 7023 is specifically used to: gradually adjust the starting frequency of the asynchronous motor according to the V / F curve until the starting frequency reaches the target frequency, wherein the voltage corresponding to the starting frequency is determined according to the V / F curve.

[0136] It should be noted that for a description of the starting control device for asynchronous motors, please refer to the description of the starting control method for asynchronous motors; it will not be repeated here.

[0137] The asynchronous motor starting control device according to an embodiment of the present invention controls the inverter to output DC current through a DC excitation module to apply excitation current to the stator of the asynchronous motor and obtains the bus voltage of the inverter. The starting module determines the starting mode of the asynchronous motor based on the bus voltage and controls the asynchronous motor to start running according to the starting mode. It can automatically identify the state of the asynchronous motor and determine the corresponding starting mode to start running according to the state. Therefore, it is not necessary to manually observe the state of the motor on site and set the corresponding starting mode for starting, saving manpower and avoiding the problem of starting failure due to misoperation.

[0138] Sixth aspect of the embodiment:

[0139] Figure 9 This is a block diagram of a starting control device for an asynchronous motor according to an embodiment of the present invention. (Refer to...) Figure 9 As shown, the starting control device 800 of the asynchronous motor includes: a second DC excitation module 801, a coasting start module 802, and a coasting operation switching module 803.

[0140] The second DC excitation module 801 is used to determine that the asynchronous motor is in a coasting state, control the inverter to output DC current to apply excitation current to the stator of the asynchronous motor, and control the inverter to stop outputting DC current after a second preset time delay; the coasting start module 802 is used to obtain the three-phase output voltage of the inverter and determine the starting frequency, starting voltage, starting angle and coasting direction of the asynchronous motor according to the three-phase output voltage; the coasting operation switching module 803 is used to control the asynchronous motor to start according to the starting frequency, starting voltage, starting angle and coasting direction, and control the starting frequency to remain unchanged and adjust the starting voltage until the output voltage of the inverter reaches the voltage corresponding to the starting frequency.

[0141] In some embodiments of the present invention, the second DC excitation module 801 is specifically used to: obtain any one phase output current among the three phase output currents of the frequency converter; obtain the current difference between any one phase output current and the corresponding target DC current; and perform PI adjustment on the current difference so that the three phase output currents are equal to their respective target DC currents.

[0142] In some embodiments of the present invention, the three-phase output voltage includes N groups, where N is an integer greater than or equal to 4. The coasting start module 802 is specifically used for: for each group of three-phase output voltage, obtaining the composite voltage and rotation angle of the asynchronous motor in the two-phase stationary coordinate system based on the three-phase output voltage to obtain N composite voltages and N rotation angles; calculating the difference between the N rotation angles to obtain N-1 rotation angle differences; and determining the starting frequency, starting voltage, starting angle, and coasting direction of the asynchronous motor based on the N composite voltages, N rotation angles, and N-1 rotation angle differences.

[0143] In some embodiments of the present invention, the coasting start module 802 is specifically used to: determine the coasting direction as positive when at least N-2 consecutive rotation angle differences among N-1 rotation angle differences are positive, and set the start voltage to... If the signs of all N-1 rotation angle differences are positive, or the signs of all rotation angle differences from the 2nd to the N-1th rotation angle differences are positive, then the starting frequency is determined as follows: The starting angle is θ N +Δθ N-1 Otherwise, determine the startup frequency as follows: The starting angle is θ N +Δθ N-1 +2π; When at least N-2 consecutive rotation angle differences out of N-1 rotation angle differences are negative, the coasting direction is determined to be negative, and the starting voltage is... Specifically, when the coasting direction is negative, if the signs of all N-1 rotation angle differences are negative, or the signs of all rotation angle differences from the 2nd to the N-1th rotation angle differences are negative, the starting frequency is determined to be... The starting angle is θ N +Δθ N-1 Otherwise, determine the startup frequency as follows: The starting angle is θ N +Δθ N-1 -2π; In other cases, the coasting direction is determined to be zero, the starting voltage is zero, the starting frequency is the lowest frequency of the asynchronous motor, and the starting angle is zero; where Umodi is the i-th composite voltage, i∈[1,N], Δθ N-1 For the (N-1)th rotation angle difference, θ N Let N be the Nth rotation angle, and Ts be the control cycle of the frequency converter.

[0144] In some embodiments of the present invention, reference is made to Figure 9 As shown, the asynchronous motor start control device 800 also includes a normal operation module 804, which is used to control the asynchronous motor to operate normally after the output voltage of the frequency converter reaches the voltage corresponding to the start frequency.

[0145] In some embodiments of the present invention, the normal operation module 804 is specifically used to: gradually adjust the starting frequency of the asynchronous motor according to the V / F curve until the starting frequency reaches the target frequency, wherein the voltage corresponding to the starting frequency is determined according to the V / F curve.

[0146] It should be noted that for a description of the starting control device for asynchronous motors, please refer to the description of the starting control method for asynchronous motors; it will not be repeated here.

[0147] According to the asynchronous motor starting control device of the present invention, the asynchronous motor is determined to be in a coasting state by the second DC excitation module, the inverter is controlled to output DC current to apply excitation current to the stator of the asynchronous motor, and after a second preset time delay, the inverter is controlled to stop outputting DC current. The three-phase output voltage of the inverter is obtained by the coasting start module and the coasting operation switching module, and the asynchronous motor is started and run according to the three-phase output voltage, which can improve the starting success rate of the asynchronous motor.

[0148] It should be noted that the logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: an electrical connection having one or more wires (electronic device), a portable computer disk drive (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Alternatively, the computer-readable medium may be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in a computer memory.

[0149] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0150] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0151] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0152] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0153] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method of starting control of an asynchronous motor, characterized in that, The method comprises: controlling the frequency converter to output a direct current to apply an exciting current to a stator of the asynchronous motor; obtaining a bus voltage of the frequency converter; determining a starting mode of the asynchronous motor according to the bus voltage; controlling the asynchronous motor to start running according to the starting mode; determining the starting mode of the asynchronous motor according to the bus voltage comprises: if an application time of the exciting current is less than a first preset time and the bus voltage is greater than or equal to a preset voltage, determining that the starting mode is a slow-revving starting mode; if the application time of the exciting current is greater than or equal to the first preset time and the bus voltage is less than the preset voltage, determining that the starting mode is a direct starting mode; determining that the starting mode is the slow-revving starting mode, and controlling the asynchronous motor to start running according to the starting mode comprises: controlling the frequency converter to stop outputting the direct current, and obtaining a three-phase output voltage of the frequency converter; determining a starting frequency, a starting voltage, a starting angle and a slow-revving direction of the asynchronous motor according to the three-phase output voltage; controlling the asynchronous motor to start according to the starting frequency, the starting voltage, the starting angle and the slow-revving direction, and controlling the starting frequency to remain unchanged and adjusting the starting voltage until an output voltage of the frequency converter reaches a voltage corresponding to the starting frequency; the three-phase output voltage comprises N groups, N is an integer greater than or equal to 4, and determining the starting frequency, the starting voltage, the starting angle and the slow-revving direction of the asynchronous motor according to the three-phase output voltage comprises: for each group of three-phase output voltage, obtaining a resultant voltage and a rotation angle of the asynchronous motor in a two-phase stationary coordinate system according to the three-phase output voltage to obtain N resultant voltages and N rotation angles; performing difference calculation on the N rotation angles to obtain N-1 rotation angle differences; determining the starting frequency, the starting voltage, the starting angle and the slow-revving direction of the asynchronous motor according to the N resultant voltages, the N rotation angles and the N-1 rotation angle differences; determining the starting frequency, the starting voltage, the starting angle and the slow-revving direction of the asynchronous motor according to the N resultant voltages, the N rotation angles and the N-1 rotation angle differences comprises: When at least N-2 consecutive ones of the N-1 rotational angle difference values are positive, the freewheeling direction is determined to be positive, and the start voltage is , wherein, if all of the N-1 rotational angle difference values are positive, or if the second rotational angle difference value to the N-1th rotational angle difference value are all positive, the start frequency is determined to be , and the start angle is , otherwise the start frequency is determined to be , and the start angle is ; When at least N-2 consecutive ones of the N-1 rotational angle difference values are negative, the freewheeling direction is determined to be negative, and the start voltage is , wherein, when the freewheeling direction is negative, if all of the N-1 rotational angle difference values are negative, or if the second rotational angle difference value to the N-1th rotational angle difference value are negative, the start frequency is determined to be , and the start angle is , otherwise the start frequency is determined to be , and the start angle is ; in other cases, determining that there is no slow-revving direction, the starting voltage is zero, the starting frequency is a lowest frequency of the asynchronous motor, and the starting angle is zero; wherein Umodi is the i-th resultant voltage, i∈[1, N], is the N-1th rotation angle difference, is the Nth rotation angle, and Ts is the control period of the frequency converter.

2. The method of claim 1, wherein, controlling the frequency converter to output a direct current comprises: obtaining any phase output current of three-phase output current of the frequency converter; obtaining a current difference between the any phase output current and a corresponding target direct current; performing PI adjustment on the current difference to make the three-phase output current equal to the respective corresponding target direct current.

3. The method of claim 1, wherein, After the output voltage of the frequency converter reaches the voltage corresponding to the starting frequency, the asynchronous motor is controlled to run normally.

4. The method of claim 1, wherein, determining that the starting mode is the direct starting mode, and controlling the asynchronous motor to start running according to the starting mode comprises: taking the lowest frequency of the asynchronous motor as the starting frequency of the asynchronous motor; controlling the asynchronous motor to start according to the starting frequency, and controlling the starting frequency to remain unchanged and adjusting an output voltage of the frequency converter until the output voltage increases from zero to a voltage corresponding to the starting frequency.

5. The method of claim 4, wherein, controlling the asynchronous motor to run normally after the output voltage of the asynchronous motor increases from zero to the voltage corresponding to the starting frequency.

6. The method according to claim 3 or 5, characterized in that, controlling the asynchronous motor to run normally includes: adjusting the starting frequency of the asynchronous motor according to a V / F curve until the starting frequency reaches a target frequency, wherein a voltage corresponding to the starting frequency is determined according to the V / F curve.

7. A starting control method of an asynchronous motor, characterized by, The method includes: determining that the asynchronous motor is in a coasting state, controlling the frequency converter to output a direct current to apply an exciting current to a stator of the asynchronous motor; after delaying for a second preset time, controlling the frequency converter to stop outputting the direct current, and acquiring a three-phase output voltage of the frequency converter; determining a starting frequency, a starting voltage, a starting angle and a coasting direction of the asynchronous motor according to the three-phase output voltage; controlling the asynchronous motor to start according to the starting frequency, the starting voltage, the starting angle and the coasting direction, and controlling the starting frequency to remain unchanged and adjusting the starting voltage until an output voltage of the frequency converter reaches a voltage corresponding to the starting frequency. The three-phase output voltage includes N groups, N is an integer greater than or equal to 4, and determining the starting frequency, the starting voltage, the starting angle and the coasting direction of the asynchronous motor according to the three-phase output voltage includes: for each group of three-phase output voltage, acquiring a resultant voltage and a rotation angle of the asynchronous motor in a two-phase stationary coordinate system according to the three-phase output voltage to obtain N resultant voltages and N rotation angles; performing difference calculation on the N rotation angles to obtain N-1 rotation angle differences; determining the starting frequency, the starting voltage, the starting angle and the coasting direction of the asynchronous motor according to the N resultant voltages, the N rotation angles and the N-1 rotation angle differences. determining the starting frequency, the starting voltage, the starting angle and the coasting direction of the asynchronous motor according to the N resultant voltages, the N rotation angles and the N-1 rotation angle differences includes: When at least N-2 consecutive ones of the N-1 rotational angle difference values are positive, the determination is that the coasting direction is positive, and the start voltage is , wherein, if all of the N-1 rotational angle difference values are positive, or if the second rotational angle difference value to the N-1th rotational angle difference value are all positive, the determination is that the start frequency is , and the start angle is , otherwise the determination is that the start frequency is , and the start angle is ; When at least N-2 consecutive ones of the N-1 rotational angle difference values are negative, the freewheeling direction is determined to be negative, and the start voltage is , wherein, when the freewheeling direction is negative, if all of the N-1 rotational angle difference values are negative, or if the second rotational angle difference value to the N-1th rotational angle difference value are negative, the start frequency is determined to be , and the start angle is , otherwise the start frequency is determined to be , and the start angle is ; in other cases, determining that there is no coasting direction, the starting voltage is zero, the starting frequency is a lowest frequency of the asynchronous motor, and the starting angle is zero; wherein Umodi is the ith synthesized voltage, i∈[1, N], is the Nth rotation angle difference, is the Nth rotation angle, and Ts is the control period of the frequency converter.

8. A computer-readable storage medium, characterized in that, a storage medium having stored thereon an asynchronous motor starting control program, which, when executed by a processor, implements the asynchronous motor starting control method according to any one of claims 1-6 or implements the asynchronous motor starting control method according to claim 7.

9. A frequency converter, characterized in that includes: a memory, a processor and an asynchronous motor starting control program stored on the memory and executable on the processor, and when the processor executes the program, the asynchronous motor starting control method according to any one of claims 1-6 is implemented, or the asynchronous motor starting control method according to claim 7 is implemented.

10. A starting control device of an asynchronous motor that implements the starting control method of the asynchronous motor according to any one of claims 1 to 6 or the starting control method of the asynchronous motor according to claim 7, characterized by The device includes: The first direct current excitation module is configured to control a variable frequency converter to output a direct current to apply an excitation current to a stator of an asynchronous motor, acquire a bus voltage of the variable frequency converter, and determine a starting mode of the asynchronous motor according to the bus voltage. The first starting module is configured to control the asynchronous motor to start running according to the starting mode.

11. A starting control device of an asynchronous motor, which implements the starting control method of the asynchronous motor according to any one of claims 1 to 6, characterized by The device comprises: The second direct current excitation module is configured to determine that the asynchronous motor is in a coasting state, control the variable frequency converter to output a direct current to apply an excitation current to the stator of the asynchronous motor, and control the variable frequency converter to stop outputting the direct current after a second preset time delay. The coasting starting module is configured to acquire a three-phase output voltage of the variable frequency converter, and determine a starting frequency, a starting voltage, a starting angle and a coasting direction of the asynchronous motor according to the three-phase output voltage. The coasting running switching module is configured to control the asynchronous motor to start according to the starting frequency, the starting voltage, the starting angle and the coasting direction, and control the starting frequency to remain unchanged and the starting voltage to be adjusted until the output voltage of the variable frequency converter reaches a voltage corresponding to the starting frequency.

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