CN114900074A

CN114900074A - Start control method and device of asynchronous motor, frequency converter and storage medium

Info

Publication number: CN114900074A
Application number: CN202210558576.4A
Authority: CN
Inventors: 赵跃东; 汪利新
Original assignee: Beijing Hekang Xinneng Frequency Conversion Technology Co ltd
Current assignee: Beijing Hekang Xinneng Frequency Conversion Technology Co ltd
Priority date: 2022-05-20
Filing date: 2022-05-20
Publication date: 2022-08-12

Abstract

The invention discloses a starting control method and a starting control device for an asynchronous motor, a frequency converter and a storage medium, wherein the method comprises the following steps: controlling the frequency converter to output direct current to apply excitation current to a stator of the asynchronous motor; acquiring the 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 operate according to the starting mode. The method 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, so that the state of the motor does not need to be observed in the field manually and the corresponding starting mode is set for starting, the human resources are saved, and the problem of failed starting of the asynchronous motor caused by manual misoperation can be avoided.

Description

Start control method and device of asynchronous motor, frequency converter and storage medium

Technical Field

The invention relates to the technical field of motor control, in particular to a starting control method and device of an asynchronous motor, a frequency converter and a storage medium.

Background

At present, the mode of dragging the asynchronous motor to start through a frequency converter is as follows: the method comprises the following steps of starting at the lowest frequency, starting direct-current braking, starting speed tracking and the like, wherein 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 starting at the lowest frequency; when the asynchronous motor is in an idle state, the starting mode is direct current brake starting or rotating speed tracking starting and the like. However, in the related art, when determining the starting mode of the asynchronous motor, the starting mode is mainly manually implemented, for example, a field operator observes the state of the asynchronous motor, and then sets a corresponding starting mode according to the state of the asynchronous motor, so that the frequency converter is started according to the starting mode set by the operator.

Disclosure of Invention

The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. Therefore, a first object of the present invention is to provide a method for controlling starting of an asynchronous motor, which can automatically identify a state of the asynchronous motor, and determine a corresponding starting mode according to the state to control starting operation of the asynchronous motor, so that it is not necessary to manually observe the state of the asynchronous motor on site and set a corresponding starting mode for starting, thereby saving human resources and avoiding a problem of failed starting due to misoperation.

A second object of the invention is to propose another method for controlling the starting of an asynchronous machine.

A third object of the invention is to propose a computer-readable storage medium.

A fourth object of the present invention is to provide a frequency converter.

A fifth object of the present invention is to provide a start control device of an asynchronous motor.

A sixth object of the invention is to propose another starting control device for an asynchronous machine.

In order to achieve the above object, an embodiment of a first aspect of the present invention provides a method for controlling starting of an asynchronous motor, where the method includes: controlling the frequency converter to output direct current to apply excitation current to a stator of the asynchronous motor; acquiring the 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 operate according to the starting mode.

According to the starting control method of the asynchronous motor, the inverter is controlled to output direct current to apply exciting current to the stator of the asynchronous motor, the bus voltage of the inverter is obtained, the starting mode of the asynchronous motor is determined according to the bus voltage, 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 starting and running of the asynchronous motor, therefore, the state of the motor does not need to be observed in a manual site, the corresponding starting mode is set for starting, manpower resources are saved, and the problem that starting fails due to manual misoperation can be avoided.

According to one embodiment of the invention, controlling the frequency converter to output direct current comprises: acquiring any phase output current in three-phase output currents of a frequency converter; obtaining a current difference value between any phase output current and a corresponding target direct current; and performing PI regulation on the current difference value to enable the three-phase output current to be equal to the corresponding target direct current.

According to one embodiment of the invention, determining the starting mode of the asynchronous machine according to the bus voltage comprises: 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 that the starting mode is an idle starting mode; and if the application time of the excitation current is more than or equal to a first preset time and the bus voltage is less than a preset voltage, determining that the starting mode is a direct starting mode.

According to one embodiment of the invention, the method for determining the starting mode as the idle starting mode and controlling the asynchronous motor to start and operate according to the starting mode comprises the following steps: controlling the frequency converter to stop outputting direct current, and acquiring three-phase output voltage of the frequency converter; 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; and controlling the asynchronous motor to start according to the starting frequency, the starting voltage, the starting angle and the coasting direction, controlling the starting frequency to be kept unchanged, and adjusting the starting voltage until the output voltage of the frequency converter reaches the voltage corresponding to the starting frequency.

According to one embodiment of the invention, the three-phase output voltage comprises N groups, N is an integer greater than or equal to 4, and the starting frequency, the starting voltage, the starting angle and the coasting direction of the asynchronous motor are determined according to the three-phase output voltage, and the method comprises the following steps: aiming at each group of three-phase output voltages, acquiring the synthetic voltage and the rotation angle of the asynchronous motor under a two-phase static coordinate system according to the three-phase output voltages so as to obtain N synthetic voltages and N rotation angles; calculating the difference of the N rotating angles to obtain N-1 rotating angle differences; and determining the starting frequency, the starting voltage, the starting angle and the coasting direction of the asynchronous motor according to the N synthetic voltages, the N rotating angles and the N-1 rotating angle difference values.

According to one embodiment of the invention, determining the starting frequency, the starting voltage, the starting angle and the coasting direction of the asynchronous motor according to the N synthesized voltages, the N rotation angles and the N-1 rotation angle difference values comprises: when the sign of at least continuous N-2 rotation angle difference values in the N-1 rotation angle difference values is positive, determining that the coasting direction is positive, and the starting voltage is

If the signs of the N-1 rotation angle difference values are all positive or the signs of the 2 nd to the N-1 st rotation angle difference values are all positive, determining the starting frequency as

Starting angle theta _N +Δθ _N-1 Otherwise, determining the starting frequency as

Starting angle theta _N +Δθ _N-1 +2 π; when the sign of at least continuous N-2 rotation angle difference values in the N-1 rotation angle difference values is negative, determining that the coasting direction is negative, and the starting voltage is

When the coasting direction is negative, if the signs of the N-1 rotation angle difference values are all negative or the signs of the 2 nd to the N-1 st rotation angle difference values are all negative, determining that the starting frequency is

Starting angle theta _N +Δθ _N-1 -2 pi; under other conditions, determining that no idling direction exists, wherein 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 synthetic voltage, i belongs to [1, N ∈]，Δθ _N-1 Is the N-1 th rotation angle difference, theta _N And Ts is the control period of the frequency converter for the Nth rotation angle.

According to one embodiment of the invention, after the output voltage of the frequency converter reaches the voltage corresponding to the starting frequency, the asynchronous motor is controlled to normally operate.

According to one embodiment of the invention, the method for determining the starting mode as the direct starting mode and controlling the asynchronous motor to start and operate according to the starting mode comprises the following steps: taking the lowest frequency of the asynchronous motor as the starting frequency of the asynchronous motor; and controlling the asynchronous motor to start according to the starting frequency, controlling the starting frequency to keep unchanged, and adjusting the output voltage of the frequency converter until the output voltage is increased from zero to a voltage corresponding to the starting frequency.

According to one embodiment of the invention, the normal operation of the asynchronous motor is controlled after the output voltage of the asynchronous motor increases from zero to a voltage corresponding to the starting frequency.

According to one embodiment of the invention, the method for controlling the normal operation of the asynchronous motor comprises the following steps: and 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.

In order to achieve the above object, a second embodiment of the present invention provides a method for controlling starting of an asynchronous motor, the method including: determining that the asynchronous motor is in an idle state, and controlling the frequency converter to output direct current to apply excitation current to a stator of the asynchronous motor; after delaying the second preset time, controlling the frequency converter to stop outputting the direct current and acquiring the three-phase output voltage of the frequency converter; 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; and controlling the asynchronous motor to start according to the starting frequency, the starting voltage, the starting angle and the coasting direction, controlling the starting frequency to be kept unchanged, and adjusting the starting voltage until the output voltage of the frequency converter reaches the voltage corresponding to the starting frequency.

According to the starting control method of the asynchronous motor, aiming at the idle running state of the asynchronous motor, the frequency converter is controlled to output direct current so as to apply exciting current to the stator of the asynchronous motor, the frequency converter is controlled to stop outputting the direct current after delaying for the second preset time, the three-phase output voltage of the frequency converter is obtained, the asynchronous motor is controlled to start and run according to the three-phase output voltage, and the starting success rate of the asynchronous motor can be improved.

To achieve the above object, a third embodiment of the present invention provides a computer-readable storage medium, on which a start control program of an asynchronous motor is stored, the start control program of the asynchronous motor, when executed by a processor, implementing the start control method of the asynchronous motor of the foregoing first or second embodiment.

According to the computer-readable storage medium of the embodiment of the invention, by adopting the start control method of the asynchronous motor of the embodiment of the first aspect, the state of the asynchronous motor can be automatically identified, and the corresponding start mode is determined according to the state to control the start operation of the asynchronous motor, so that the state of the motor does not need to be observed on site manually and the corresponding start mode is set for starting, the human resources are saved, and the problem of start failure caused by misoperation can be avoided; by adopting the starting control method of the asynchronous motor in the embodiment of the second aspect, the starting success rate of the asynchronous motor can be improved.

In order to achieve the above object, a fourth aspect of the present invention provides a frequency converter, including: the present invention relates to a method for controlling the start of an asynchronous motor, and more particularly, to a method for controlling the start of an asynchronous motor, which includes a memory, a processor, and a start control program for an asynchronous motor stored in the memory and operable on the processor.

According to the frequency converter provided by the embodiment of the invention, by adopting the starting control method of the asynchronous motor in the embodiment of the first aspect, the state of the asynchronous motor can be automatically identified, and the corresponding starting mode is determined according to the state to control the starting operation of the asynchronous motor, so that the state of the motor does not need to be observed in a manual field and the corresponding starting mode is set for starting, the human resources are saved, and the problem of starting failure caused by misoperation can be avoided; by adopting the starting control method of the asynchronous motor in the embodiment of the second aspect, the starting success rate of the asynchronous motor can be improved.

In order to achieve the above object, a fifth embodiment of the present invention provides a start control device for an asynchronous motor, including: the first direct current excitation module is used for controlling the frequency converter to output direct current so as to apply excitation current to a stator of the asynchronous motor, acquiring bus voltage of the frequency converter and determining a starting mode of the asynchronous motor according to the bus voltage; and the second starting module is used for controlling the asynchronous motor to start and operate according to the starting mode.

According to the starting control device of the asynchronous motor, the first direct current excitation module controls the frequency converter to output direct current so as to apply excitation 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, the asynchronous motor is controlled to start and run according to the starting mode through the first starting module, the state of the asynchronous motor can be automatically identified, the corresponding starting mode is determined according to the state so as to control the starting and running of the asynchronous motor, therefore, the state of the motor does not need to be observed in a manual field, the corresponding starting mode does not need to be set for starting, manpower resources are saved, and the problem of starting failure caused by misoperation can be avoided.

In order to achieve the above object, a sixth aspect of the present invention provides a start control device for an asynchronous motor, the device including: the second direct current excitation module is used for determining that the asynchronous motor is in an idle running state, controlling the frequency converter to output direct current to apply excitation current to a stator of the asynchronous motor, and controlling the frequency converter to stop outputting the direct current after delaying for second preset time; the idling starting module is used for acquiring three-phase output voltage of the frequency converter and determining the starting frequency, the starting voltage, the starting angle and the idling direction of the asynchronous motor according to the three-phase output voltage; and the idling operation switching module is used for controlling the asynchronous motor to start according to the starting frequency, the starting voltage, the starting angle and the idling direction, controlling the starting frequency to be kept unchanged and adjusting the starting voltage until the output voltage of the frequency converter reaches the voltage corresponding to the starting frequency.

According to the start control device of the asynchronous motor, the second direct current excitation module determines that the asynchronous motor is in the idle running state, the frequency converter is controlled to output direct current to apply excitation current to the stator of the asynchronous motor, the frequency converter is controlled to stop outputting the direct current after delaying for the second preset time, the idle running starting module and the idle running switching module are used for obtaining three-phase output voltage of the frequency converter, the asynchronous motor is controlled to start and run according to the three-phase output voltage, and the start success rate of the asynchronous motor can be improved.

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.

Drawings

Fig. 1 is a flowchart of a start control method of an asynchronous motor according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of sampling of the output voltage and output current of a frequency converter according to one embodiment of the present invention;

FIG. 3 is a flow chart for determining a start mode of an induction motor according to one embodiment of the present invention;

FIG. 4 is a flow diagram for controlling the start of an asynchronous motor during a coasting condition in accordance with one embodiment of the present invention;

FIG. 5 is a flow chart for controlling the start of an asynchronous motor during a coasting condition according to another embodiment of the present invention;

fig. 6 is a flowchart of a start control method of an asynchronous motor according to another embodiment of the present invention;

fig. 7 is a block diagram of a start control apparatus of an asynchronous motor according to an embodiment of the present invention;

fig. 8 is a block diagram of a start control apparatus of an asynchronous motor according to another embodiment of the present invention;

fig. 9 is a block diagram of a start control apparatus of an asynchronous motor according to still another embodiment of the present invention.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.

The following describes a method and an apparatus for controlling starting of an asynchronous motor, a frequency converter, and a storage medium according to embodiments of the present invention with reference to the accompanying drawings.

In the first aspect:

fig. 1 is a flowchart of a start control method of an asynchronous motor according to an embodiment of the present invention. Referring to fig. 1, the start control method of the asynchronous motor may include the steps of:

and step S101, controlling the frequency converter to output direct current to apply excitation current to the stator of the asynchronous motor.

And S102, acquiring the bus voltage of the frequency converter.

And step S103, determining the starting mode of the asynchronous motor according to the bus voltage.

And step S104, controlling the asynchronous motor to start and operate according to the starting mode.

Specifically, referring to fig. 2, the output end of the frequency converter is connected to the asynchronous motor M for dragging the asynchronous motor M to start and operate. When the asynchronous motor M is dragged to start and operate, the frequency converter can be controlled to apply a certain value of direct current to the stator of the asynchronous motor M to enable the asynchronous motor M to generate a stator magnetic field, if the asynchronous motor M is in an idle state (namely after the asynchronous motor M is stopped to supply power, the asynchronous motor M is still in a rotating state), the rotor of the asynchronous motor M cuts the stator magnetic field to generate induced electromotive force (namely counter electromotive force), induced current is excited in the rotor, the induced current enables the rotor to rotate to generate power generation energy, and therefore the voltage of a bus capacitor C of the frequency converter is increased; if the current asynchronous motor M is in a static state, the asynchronous motor M cannot generate power generation energy, and therefore the voltage of a bus capacitor C of the frequency converter cannot be increased. Therefore, after the frequency converter is controlled to apply a certain value of direct current to the stator of the asynchronous motor M, the state of the asynchronous motor M can be determined according to the change condition of the bus voltage by acquiring the voltage of the bus capacitor C, namely the bus voltage, and different states correspond to different starting modes, so that the corresponding starting mode can be determined based on the state of the asynchronous motor M, the asynchronous motor M is controlled to start and run according to the determined starting mode, and the starting mode of the asynchronous motor M does not need to be confirmed manually.

According to the embodiment, the direct current is applied to the asynchronous motor by controlling the frequency converter, the bus voltage of the frequency converter is obtained, the starting mode of the asynchronous motor is determined based on the bus voltage, the state of the asynchronous motor can be automatically identified, the corresponding starting mode is determined according to the state, the asynchronous motor is controlled to start and run, the state of the asynchronous motor does not need to be observed in a manual site, a corresponding starting mode is set for starting, manpower resources are saved, and the problem that starting fails due to misoperation can be solved.

In some embodiments of the present invention, controlling the frequency converter to output the direct current may include: acquiring any phase output current in three-phase output currents of a frequency converter; obtaining a current difference value between any phase output current and a corresponding target direct current; and performing PI (proportional integral) adjustment on the current difference value so as to enable the three-phase output current to be equal to the corresponding target direct current.

For example, assuming that the set value of the dc current output by the inverter is I _ dcset, which may be 5% to 10% of the rated current effective value of the asynchronous motor M, the target dc current corresponding to U of the inverter may be I _ dcset, the target dc current corresponding to V may be-0.5I _ dcset, and the target dc current corresponding to W may be-0.5I _ dcset (when set, the sum of the three-phase output currents of the inverter is zero). Referring to fig. 2, when controlling the inverter to output a dc current, a current sampling module may be disposed at an output end of the inverter, and a current detection function module in the current sampling module collects a U-phase current Iu in a three-phase output current of the inverter, obtains a current difference between the U-phase current Iu and a target dc current I _ dcset corresponding to U, and performs PI adjustment on the current difference to adjust three-phase output voltages Uu, Uv, and Uw of the inverter, so that the U-phase output current Iu of the inverter is I _ dcset, the V-phase output current Iv is-0.5I _ dcset, and the W-phase output current Iw is-0.5I _ dcset.

It should be noted that, a current detection function module in the current sampling module may also be used to collect a W-phase current Iw in the three-phase output current of the frequency converter, and perform PI adjustment on a current difference between the W-phase current Iw and a target dc current-0.5 × I _ dcset corresponding to W, so that the three-phase output current is equal to the respective corresponding target dc current. Of course, PI adjustment may also be performed based on the V-phase current, and is not limited herein.

According to the embodiment, the frequency converter is controlled to output the direct current in a closed-loop control mode, so that the accuracy and the stability of the output direct current can be ensured, and the accuracy of determining the starting mode of the asynchronous motor can be effectively improved.

In some embodiments of the present invention, determining the start mode of the asynchronous machine from 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 that the starting mode is an idle starting mode; and if the application time of the excitation current is more than or equal to a first preset time and the bus voltage is less than a preset voltage, determining that the starting mode is a direct starting mode. It should be noted that the preset voltage is smaller than the bus voltage overvoltage protection value.

Specifically, assuming that the application time of the excitation current is T, the first preset time is T _ set and the preset voltage is U _ dcset, when the application time T is less than the first preset time T _ set, if the bus voltage Udc of the frequency converter is greater than or equal to the preset voltage U _ dcset, the asynchronous motor M is considered to generate power generation energy and return the power generation energy to the frequency converter, so that the asynchronous motor M can be determined to be in an idle running state, the starting mode of the asynchronous motor M is determined to be an idle running starting mode, then the frequency converter is controlled to stop outputting direct current, and the asynchronous motor M is controlled to start and operate according to the idle running starting mode; when the application time T is less than the first preset time T _ set, if the bus voltage Udc of the frequency converter is less than the preset voltage U _ dcset, the excitation current is continuously applied until the application time T is more than or equal to the first preset time T _ set, if the bus voltage Udc of the frequency converter is less than the preset voltage U _ dcset at the moment, the asynchronous motor M is considered not to generate power generation energy and is returned to the frequency converter, so that the asynchronous motor M can be determined to be in a static state (or the idling frequency is extremely low), the starting mode of the asynchronous motor M is determined to be a direct starting mode, then the frequency converter is controlled to stop outputting the direct current, and the asynchronous motor M is controlled to start and operate according to the direct starting mode.

As a specific example, referring to fig. 3, determining the start mode of the asynchronous machine may include the steps of:

step S201, controlling the inverter to apply a constant dc current to the stator of the asynchronous motor.

Step S202, collecting bus voltage Udc, and recording the application time t of the direct current.

It should be noted that, a voltage sampling module may be provided corresponding to the bus capacitor C shown in fig. 2, and the voltage sampling module is used to collect the voltage of the bus capacitor C to obtain the bus voltage Udc. Assuming that the control period of the frequency converter is Ts, the bus voltage Udc can be collected in each control period Ts, and the application time t of the direct current is accumulated.

Step S203, determine whether the bus voltage Udc reaches the preset voltage U _ dcset. If so, step S204 is performed, otherwise step S206 is performed.

And step S204, stopping outputting the direct current by the frequency converter.

And step S205, determining the starting mode of the asynchronous motor to be an idle starting mode.

In step S206, it is determined whether the application time T reaches a first preset time T _ set. If so, executing step S207, otherwise, returning to step S201, and continuing to control the frequency converter to apply a certain value of direct current to the stator of the asynchronous motor.

In step S207, the inverter stops outputting the dc current.

And step S208, determining the starting mode of the asynchronous motor to be a direct starting mode.

In the embodiment, the starting mode of the asynchronous motor can be determined quickly and accurately according to the change condition of the bus voltage, the state of the motor does not need to be observed in a manual field, and a corresponding starting mode is set for starting, so that the manpower resource is saved, and the problem of starting failure caused by misoperation can be avoided.

In some embodiments of the present invention, referring to fig. 4, determining the start mode as the coasting start mode, and controlling the asynchronous motor to start according to the start mode may include:

and S301, controlling the frequency converter to stop outputting the direct current, and acquiring the three-phase output voltage of the frequency converter.

Specifically, after the start mode of the asynchronous motor M is determined to be the idle start mode, the frequency converter is controlled to stop outputting the direct current, the asynchronous motor M generates the back electromotive force because the asynchronous motor M is in the idle state, the back electromotive force of the asynchronous motor M can be obtained by collecting the three-phase output voltage of the frequency converter because the output end of the frequency converter is connected with the asynchronous motor M, and then the start frequency, the start angle, the start voltage and the idle direction of the asynchronous motor M are calculated according to the back electromotive force of the asynchronous motor M. As shown in fig. 2, the U-phase output voltage Uu, the V-phase output voltage Uv, and the W-phase output voltage Uw of the frequency converter may be collected through a voltage detection function module in a voltage sampling module at the output end of the frequency converter. During collection, the three-phase output voltages of the frequency converters can be collected once in the control period Ts of the first four or more frequency converters after the frequency converters stop outputting the direct current, so that at least four groups of three-phase output voltages are obtained.

And step S302, 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.

Specifically, after obtaining at least four sets of three-phase output voltages of the frequency converter, the starting frequency, the starting voltage, the starting angle, and the coasting direction of the asynchronous motor M can be determined according to the at least four sets of three-phase output voltages.

In some embodiments of the present invention, 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: aiming at each group of three-phase output voltages, acquiring the synthetic voltage and the rotation angle of the asynchronous motor under a two-phase static coordinate system according to the three-phase output voltages so as to obtain N synthetic voltages and N rotation angles; calculating the difference of the N rotating angles to obtain N-1 rotating angle differences; and determining the starting frequency, the starting voltage, the starting angle and the coasting direction of the asynchronous motor according to the N synthetic voltages, the N rotating angles and the N-1 rotating angle difference values.

Specifically, the composite voltage, the rotation angle, and the rotation angle difference of the asynchronous motor M may be calculated by the following equations (1) to (3) based on the three-phase output voltage of the asynchronous motor M:

wherein 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, Uwi is the W-phase output voltage in the i-th group of three-phase output voltages, U _αi Is the voltage component of the asynchronous motor on the alpha axis in the ith two-phase static coordinate system, U _βi The voltage component of the asynchronous motor on a beta axis under the ith two-phase static coordinate system is Umodi, the ith synthetic voltage is greater than or equal to 1 and less than or equal to N, and N is the number of groups of three-phase output voltages.

Wherein, theta i is the ith rotation angle, and i is more than or equal to 1 and less than or equal to N.

Δθi＝θ(i+1)-θ(i) (3)

Wherein, Delta theta i is the ith rotation angle difference, theta (i +1) is the (i +1) th rotation angle, and i is more than or equal to 1 and is less than N.

For convenience of understanding, the following description will be given taking four sets of three-phase output voltages as an example. Four sets of three-phase output voltages are assumed to be Uu1, Uv1 and Uw 1; uu2, Uv2, and Uw 2; uu3, Uv3, and Uw 3; uu4, Uv4 and Uw4, four groups of three-phase output voltages are substituted into the above equations (1) - (3), four composite voltages Umod1, Umod2, Umod3 and Umod4, four rotation angles θ 1, θ 2, θ 3 and θ 4 and three rotation angle differences Δ θ 1, Δ θ 2 and Δ θ 3 of the asynchronous motor M can be calculated, and then the starting frequency, the starting voltage, the starting angle and the coasting direction of the asynchronous motor M can be determined through table 1:

TABLE 1

As can be seen from table 1, the coasting direction, the starting frequency, the starting angle, and the starting voltage of the asynchronous motor M can be determined based on the rotation angle difference Δ θ 1, Δ θ 2, and Δ θ 3, the rotation angle θ 4, the combined voltage Umod1, Umod2, Umod3, and Umod4 of the asynchronous motor M, and the control period Ts of the frequency converter. It should be noted that when the signs of Δ θ 1 and Δ θ 3 are both positive and the sign of Δ θ 2 is negative, or when the signs of Δ θ 1 and Δ θ 3 are both negative and the sign of Δ θ 2 is positive, it is determined that the coasting frequency of the asynchronous motor M is extremely low, and it can be considered that the asynchronous motor M is in a stationary state, at this time, there is no coasting direction, the starting frequency is the lowest frequency of the asynchronous motor M, and the starting angle and the starting voltage are both zero.

It should be noted that, the above description is given by taking four groups of three-phase output voltages of the asynchronous motor M as an example, and in other embodiments, five or more groups may be adopted, and the principle of the three-phase output voltages is the same as that of the four groups of three-phase output voltages.

Specifically, assuming that there are N groups of three-phase output voltages, N-1 rotation angle difference values, N rotation angles, and N composite voltages may be determined based on the N groups of three-phase output voltages, wherein if a sign of at least N-2 consecutive rotation angle difference values among the N-1 rotation angle difference values is positive, it is determined that the coasting direction of the asynchronous motor M is positive; if it isIf the sign of at least continuous N-2 rotation angle difference values in the N-1 rotation angle difference values is negative, determining that the idling direction of the asynchronous motor M is negative; in other cases, the no-coasting direction of the asynchronous machine M is determined. Further, when the coasting direction is positive, if the signs of the N-1 rotation angle difference values are all positive, or the signs of the 2 nd to N-1 th rotation angle difference values are all positive (that is, the N-2 consecutive rotation angle difference values with positive signs are closer to the current time), it is determined that the starting frequency of the asynchronous motor M is equal to

Starting angle theta _N +Δθ _N-1 Otherwise, determining the starting frequency of the asynchronous motor M as

Starting angle theta _N +Δθ _N-1 +2 π; when the coasting direction is negative, if the signs of the N-1 rotation angle difference values are all negative, or the signs of the 2 nd to N-1 th rotation angle difference values are all negative (that is, the N-2 consecutive rotation angle difference values with negative signs are closer to the current moment), determining that the starting frequency of the asynchronous motor M is the same

Starting angle theta _N +Δθ _N-1 -2 pi; in other cases, the starting frequency is the lowest frequency of the asynchronous motor M, and the starting angle is zero. Further, 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.

Step S303, controlling the asynchronous motor to start according to the starting frequency, the starting voltage, the starting angle and the coasting direction, controlling the starting frequency to be kept unchanged and adjusting the starting voltage until the output voltage of the frequency converter reaches the voltage corresponding to the starting frequency.

Specifically, after determining the coasting direction, the starting frequency, the starting angle, and the starting voltage of the asynchronous motor M, the asynchronous motor M may be controlled to start according to the determined starting frequency, the determined starting angle, and the determined starting voltage, and the rotation direction of the asynchronous motor M may be the determined coasting direction, that is, the asynchronous motor M starts to rotate from the starting angle along the coasting direction at the starting frequency and the starting voltage. Then, the starting frequency is controlled to remain unchanged, and the starting voltage is adjusted 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 may be determined according to a predetermined V/F curve (i.e., a voltage-to-frequency ratio curve) of the asynchronous motor M, that is, the asynchronous motor M may be controlled based on the predetermined V/F curve. And further, after the output voltage of the frequency converter reaches the voltage corresponding to the starting frequency, controlling the asynchronous motor to normally operate.

As a specific example, referring to fig. 5, when determining that the start mode of the asynchronous motor M is the idle start mode, controlling the asynchronous motor to start according to the start mode may include:

and S401, collecting the three-phase output voltage of the frequency converter.

In step S402, the combined voltage umod, the rotation angle θ i, and the rotation angle difference Δ θ i are calculated from the three-phase output voltages, and counted.

In step S403, it is determined whether or not the count value i is 4 or more. If yes, go to step S404, otherwise return to step S401.

And S404, determining the starting frequency, the starting voltage, the starting angle and the coasting direction of the asynchronous motor according to the synthesized voltage Umodi, the rotation angle theta i and the rotation angle difference delta theta i.

And step S405, controlling the asynchronous motor to start according to the starting frequency, the starting voltage, the starting angle and the coasting direction.

In the above embodiment, for the idle rotation state of the asynchronous motor, since the dc current is applied to the asynchronous motor when the state of the asynchronous motor is identified, the dc current increases the rotor current of the asynchronous motor, and after the dc current input to the asynchronous motor is stopped, the back electromotive force of the asynchronous motor can be increased based on a higher idle rotation speed, so that the back electromotive force of the asynchronous motor is higher than the noise voltage in the detection circuit and the transmission cable, the interference noise can be well filtered by setting the analog processing circuit, the accuracy of the back electromotive force of the asynchronous motor is ensured, and further, the accuracy of the determined start related parameters of the asynchronous motor is ensured by detecting the back electromotive force of the asynchronous motor, that is, the three-phase output voltage of the frequency converter, and determining the start related parameters of the asynchronous motor based on the back electromotive force, so as to control the start of the asynchronous motor according to the start related parameters, the starting method ensures that the asynchronous motor can be reliably started, and greatly improves the starting success rate of the asynchronous motor.

In some embodiments of the present invention, determining the start mode as a direct start mode, and controlling the asynchronous motor to start according to the start mode includes: taking the lowest frequency of the asynchronous motor as the starting frequency of the asynchronous motor; and controlling the asynchronous motor to start according to the starting frequency, controlling the starting frequency to keep unchanged, and adjusting the output voltage of the frequency converter until the output voltage is increased from zero to a voltage corresponding to the starting frequency.

That is, when the start mode of the asynchronous motor M is determined to be the direct start mode, the asynchronous motor M is controlled to start with the lowest frequency of the asynchronous motor M as the start frequency, and the start frequency is controlled to remain unchanged, while the start voltage of the asynchronous motor M is adjusted to gradually increase from zero until the output voltage of the inverter reaches the voltage corresponding to the start frequency. And further, after the output voltage of the frequency converter reaches the voltage corresponding to the starting frequency, controlling the asynchronous motor to normally operate.

In the above embodiment, when the asynchronous motor is in a static state, the asynchronous motor is driven at the lowest frequency of the frequency converter, so that the output voltage of the asynchronous motor reaches the voltage corresponding to the lowest frequency, and the asynchronous motor can be reliably started.

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

Specifically, after the asynchronous motor M is started, the asynchronous motor M enters a normal operation state, at this time, the start frequency of the asynchronous motor (i.e., the operation frequency of the asynchronous motor, i.e., the output frequency of the frequency converter) may be adjusted step by step (i.e., according to a set time) according to a predetermined V/F curve of the asynchronous motor M, and the output voltage of the frequency converter may be adjusted at the same time until the start frequency reaches a target frequency.

In summary, according to the start control method of the asynchronous motor of the embodiment of the invention, the inverter is controlled to output the direct current to apply the excitation current to the stator of the asynchronous motor, and the bus voltage of the inverter is obtained, and determining the starting mode of the asynchronous motor according to the bus voltage, controlling the asynchronous motor to start and operate according to the starting mode, automatically identifying the state of the asynchronous motor, determining the corresponding starting mode according to the state to control the asynchronous motor to start and operate, thereby saving human resources and avoiding the problem of starting failure caused by misoperation without observing the state of the motor in the field by manpower and setting a corresponding starting mode for starting, corresponding starting modes are provided aiming at different states, so that the asynchronous motor can be successfully started by small starting impact current in a static state and an idle state; meanwhile, because the mode of applying direct current to the asynchronous motor is adopted when the state of the asynchronous motor is identified, the asynchronous motor can be ensured to be reliably started in the idle state, and the starting success rate of the asynchronous motor in the idle state is greatly improved.

Embodiment of the second aspect:

fig. 6 is a flowchart of a start control method of an asynchronous motor according to another embodiment of the present invention. Referring to fig. 6, the start control method of the asynchronous motor may include the steps of:

step S501, determining that the asynchronous motor is in an idle state, and controlling the frequency converter to output direct current to apply excitation current to the stator of the asynchronous motor.

And step S502, after delaying the second preset time, controlling the frequency converter to stop outputting the direct current, and obtaining the three-phase output voltage of the frequency converter.

And step S503, 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.

And step S504, controlling the asynchronous motor to start according to the starting frequency, the starting voltage, the starting angle and the coasting direction, controlling the starting frequency to be kept unchanged, and adjusting the starting voltage until the output voltage of the frequency converter reaches the voltage corresponding to the starting frequency.

Specifically, when the asynchronous motor is dragged by the frequency converter to start and operate, if the asynchronous motor is already in an idling state, if the asynchronous motor is controlled to start in a direct start mode, overvoltage or overcurrent of the frequency converter is easily caused, and the asynchronous motor is easily started to fail. For the rotation speed tracking starting mode, there is usually a frequency searching method, in which the coasting frequency of the asynchronous motor is calculated by searching downward from the highest frequency of the asynchronous motor, by tracking the current, using software or combining hardware. However, when the coasting direction of the asynchronous motor is opposite to the set direction, the frequency converter is easy to generate overvoltage or overcurrent, which causes the starting failure of the asynchronous motor; meanwhile, in the searching process, the output frequency of the frequency converter may have a larger frequency difference and phase difference with the back electromotive force of the asynchronous motor, the current closed loop is extremely difficult, the parameter adjustment is difficult, the requirements on field debugging personnel and using personnel are high, especially for the working condition of utilizing the soft start of the frequency converter, at this time, a user usually adopts a small horse-drawn cart mode, the frequency converter with the rated capacity of 40 percent of the motor capacity is used for starting the asynchronous motor in a no-load mode, and at this time, the overcurrent is extremely easy to occur by using a frequency searching method. In addition, the coasting frequency of the asynchronous motor can also be determined by detecting the back electromotive force of the asynchronous motor, but this method is usually used for stopping the asynchronous motor in a short time, because when the stopping time exceeds the rotor time constant of the asynchronous motor, the signal of the back electromotive force of the asynchronous motor is very weak and is easily affected by the interference signal, so that the coasting frequency of the asynchronous motor is calculated incorrectly, and the starting of the asynchronous motor fails.

Based on the above, aiming at the idle running working condition of the asynchronous motor, in the embodiment of the invention, a certain value of direct current is applied to the stator of the asynchronous motor by controlling the frequency converter, so that the asynchronous motor generates a stator magnetic field, the rotor of the asynchronous motor cuts the stator magnetic field to generate induced electromotive force, induced current is excited in the rotor, the induced current enables the rotor to rotate to generate power generation energy, and the voltage of a bus capacitor of the frequency converter is increased, after a period of time, the frequency converter is controlled to stop applying a certain value of direct current to the stator of the asynchronous motor, the counter electromotive force of the asynchronous motor, namely the three-phase output voltage of the frequency converter, is detected immediately in a short time, the starting frequency, the starting voltage, the starting angle and the idle running direction of the asynchronous motor are determined according to the three-phase output voltage, and the starting frequency, the starting voltage, the starting angle and the idle running direction of the asynchronous motor are controlled to be started, and controlling the starting frequency to be kept unchanged and adjusting the starting voltage until the output voltage of the frequency converter reaches the voltage corresponding to the starting frequency.

It should be noted that the idling direction of the asynchronous motor can be determined by the method, and the starting operation of the asynchronous motor is controlled according to the idling direction, so that the starting failure caused by the inconsistency between the idling direction of the asynchronous motor and the set direction can be avoided; meanwhile, the starting frequency and the starting voltage of the asynchronous motor can be determined, the asynchronous motor is controlled to start and operate based on the starting frequency and the starting voltage, and starting failure caused by overlarge difference between the starting frequency and the starting voltage can be avoided; meanwhile, the applied direct current can increase the rotating speed of the asynchronous motor, so that after the direct current is stopped being input to the asynchronous motor, the back electromotive force of the asynchronous motor can be improved based on higher idle rotating speed, the back electromotive force of the asynchronous motor is higher relative to the noise voltage in the detection circuit and the transmission cable, the interference noise can be well filtered by arranging the analog processing circuit, the accuracy of the back electromotive force of the asynchronous motor is ensured, therefore, the accuracy of the determined starting related parameters of the asynchronous motor is ensured by detecting the back electromotive force of the asynchronous motor, namely the three-phase output voltage of the frequency converter, and determining the starting related parameters of the asynchronous motor based on the back electromotive force, the starting of the asynchronous motor is further controlled according to the starting related parameters, the asynchronous motor can be reliably started, and the starting success rate of the asynchronous motor is greatly improved, the starting failure caused by weak back electromotive force signals is avoided.

In some embodiments of the present invention, controlling the frequency converter to output a direct current comprises: acquiring any phase output current in three-phase output currents of a frequency converter; obtaining a current difference value between any phase output current and a corresponding target direct current; and performing PI regulation on the current difference value to enable the three-phase output current to be equal to the corresponding target direct current.

In some embodiments of the present invention, determining the starting frequency, the starting voltage, the starting angle, and the coasting direction of the asynchronous motor according to the N combined voltages, the N rotation angles, and the N-1 rotation angle difference values comprises: when the sign of at least continuous N-2 rotation angle difference values in the N-1 rotation angle difference values is positive, determining that the coasting direction is positive, and the starting voltage is

Wherein, if the signs of the N-1 rotation angle difference values are all positive or the 2 nd rotationThe sign of the rotation angle difference value to the N-1 rotation angle difference value is positive, and the starting frequency is determined to be

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

In some embodiments of the present invention, controlling the normal operation of the asynchronous motor comprises: and 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.

It should be noted that, for details that are not disclosed in the embodiment of the second aspect of the start control method for an asynchronous motor, please refer to details that are disclosed in the embodiment of the first aspect of the start control method for an asynchronous motor, and detailed description thereof is omitted here.

According to the starting control method of the asynchronous motor, aiming at the condition that the asynchronous motor is in the idle running state, the frequency converter is controlled to output direct current to apply exciting current to the stator of the asynchronous motor, the frequency converter is controlled to stop outputting the direct current after delaying for the second preset time, three-phase output voltage of the frequency converter is obtained, the asynchronous motor is controlled to start and run according to the three-phase output voltage, and the starting success rate of the asynchronous motor can be improved.

Embodiment of the third aspect:

in some embodiments of the present invention, there is also provided a computer-readable storage medium on which a start control program of an asynchronous motor is stored, the start control program of the asynchronous motor, when executed by a processor, implementing the start control method of the asynchronous motor of the foregoing first aspect embodiment or second aspect embodiment.

According to the computer-readable storage medium of the embodiment of the invention, by adopting the start control method of the asynchronous motor of the embodiment of the first aspect, the state of the asynchronous motor can be automatically identified, and the corresponding start mode is determined according to the state to carry out start operation, so that the state of the motor does not need to be observed on site manually and the corresponding start mode is set to carry out start, thereby saving human resources and avoiding the problem of start failure caused by misoperation; by adopting the starting control method of the asynchronous motor in the embodiment of the second aspect, the starting success rate of the asynchronous motor can be improved.

Embodiment of the fourth aspect:

in some embodiments of the present invention, there is also provided a frequency converter, including: the present invention relates to a method for controlling the start of an asynchronous motor, and more particularly, to a method for controlling the start of an asynchronous motor, which includes a memory, a processor, and a start control program for an asynchronous motor stored in the memory and operable on the processor.

According to the frequency converter provided by the embodiment of the invention, by adopting the starting control method of the asynchronous motor in the embodiment of the first aspect, the state of the asynchronous motor can be automatically identified, and the corresponding starting mode is determined according to the state to carry out starting operation, so that the state of the motor does not need to be observed on site manually and the corresponding starting mode is set to carry out starting, the human resources are saved, and the problem of starting failure caused by misoperation can be avoided; by adopting the starting control method of the asynchronous motor in the embodiment of the second aspect, the starting success rate of the asynchronous motor can be improved.

Embodiment of the fifth aspect:

fig. 7 is a block diagram illustrating a start control apparatus for an asynchronous motor according to an embodiment of the present invention, and referring to fig. 7, a start control apparatus 700 for an asynchronous motor includes: a first direct current excitation module 701 and a second start module 702.

The first direct current excitation module 701 is used for controlling the frequency converter to output direct current so as to apply excitation current to a stator of the asynchronous motor, acquiring bus voltage of the frequency converter, and determining a starting mode of the asynchronous motor according to the bus voltage; the first starting module 702 is used for controlling the asynchronous motor to start and operate according to a starting mode.

According to an embodiment of the present invention, the first dc excitation module 701 is specifically configured to: acquiring any phase output current in three-phase output currents of a frequency converter; obtaining a current difference value between any phase output current and a corresponding target direct current; and performing PI regulation on the current difference value to enable the three-phase output current to be equal to the corresponding target direct current.

According to an embodiment of the present invention, the first dc excitation module 701 is specifically configured to: if the application time of the excitation current is less than the first preset time and the bus voltage is greater than or equal to the preset voltage, determining that the starting mode is an idle starting mode, and controlling the frequency converter to stop outputting the direct current; and if the application time of the excitation current is more 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, and controlling the frequency converter to stop outputting the direct current.

According to an embodiment of the present invention, referring to fig. 8, the first starting module 702 may include an idle starting unit 7021 and an idle operation switching unit 7022, where the idle starting unit 7021 is configured to obtain a three-phase output voltage of the frequency converter when the first dc excitation module 701 determines that the starting mode is the idle starting mode, and determine a starting frequency, a starting voltage, a starting angle, and an idle direction of the asynchronous motor according to the three-phase output voltage; the idling operation switching unit 7022 is configured to control the asynchronous motor to start according to the starting frequency, the starting voltage, the starting angle, and the idling direction, and control the starting frequency to remain unchanged and adjust the starting voltage until the output voltage of the frequency converter reaches a voltage corresponding to the starting frequency.

According to an embodiment of the present invention, the three-phase output voltage includes N groups, where N is an integer greater than or equal to 4, and the coasting start unit 7021 is specifically configured to: aiming at each group of three-phase output voltages, acquiring the synthetic voltage and the rotation angle of the asynchronous motor under a two-phase static coordinate system according to the three-phase output voltages so as to obtain N synthetic voltages and N rotation angles; calculating the difference of the N rotating angles to obtain N-1 rotating angle differences; and determining the starting frequency, the starting voltage, the starting angle and the coasting direction of the asynchronous motor according to the N synthetic voltages, the N rotating angles and the N-1 rotating angle difference values.

According to an embodiment of the present invention, the coasting start unit 7021 is specifically configured to: when the sign of at least continuous N-2 rotation angle difference values in the N-1 rotation angle difference values is positive, determining that the coasting direction is positive, and the starting voltage is

According to an embodiment of the present invention, the first starting module 702 may further include a normal operation unit 7023, configured to control the asynchronous motor to normally operate after the output voltage of the frequency converter reaches a voltage corresponding to the starting frequency.

According to an embodiment of the present invention, the first starting module 702 may include a direct starting unit 7024, configured to, when the first dc excitation module 701 determines that the starting mode is the direct starting mode, use the lowest frequency of the asynchronous motor as a starting frequency of the asynchronous motor, control the asynchronous motor to start according to the starting frequency, control the starting frequency to be constant, and adjust the output voltage of the frequency converter until the output voltage increases from zero to a voltage corresponding to the starting frequency.

According to an embodiment of the present invention, the first starting module 702 may further include a normal operation unit 7023 for controlling the asynchronous motor to normally operate after the output voltage of the asynchronous motor is increased from zero to a voltage corresponding to the starting frequency.

According to an embodiment of the present invention, the normal operation unit 7023 is specifically configured to: and 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.

It should be noted that, for the description of the start control device of the asynchronous motor, please refer to the description of the start control method of the asynchronous motor, which is not described herein again.

According to the starting control device of the asynchronous motor, the direct current excitation module is used for controlling the frequency converter to output direct current so as to apply excitation current to the stator of the asynchronous motor, the bus voltage of the frequency converter is obtained, the starting module is used for determining the 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, the state of the asynchronous motor can be automatically identified, the corresponding starting mode is determined according to the state to start and run, therefore, the state of the motor does not need to be observed manually on site and the corresponding starting mode does not need to be set to start, human resources are saved, and the problem of starting failure caused by misoperation can be avoided.

Embodiment of the sixth aspect:

fig. 9 is a block diagram illustrating a start control apparatus of an asynchronous motor according to an embodiment of the present invention, and referring to fig. 9, the start control apparatus 800 of the asynchronous motor includes: a second dc excitation module 801, a coasting start module 802, and a coasting operation switching module 803.

The second direct current excitation module 801 is configured to determine that the asynchronous motor is in an idle state, control the frequency converter to output a direct current to apply an excitation current to a stator of the asynchronous motor, and control the frequency converter to stop outputting the direct current after delaying for a second preset time; the idling starting module 802 is configured to obtain a three-phase output voltage of the frequency converter, and determine a starting frequency, a starting voltage, a starting angle, and an idling direction of the asynchronous motor according to the three-phase output voltage; the idling operation switching module 803 is configured to control the asynchronous motor to start according to the starting frequency, the starting voltage, the starting angle, and the idling 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.

In some embodiments of the present invention, the second dc excitation module 801 is specifically configured to: acquiring any phase output current in three-phase output currents of a frequency converter; obtaining a current difference value between any phase output current and a corresponding target direct current; and performing PI regulation on the current difference value to enable the three-phase output current to be equal to the corresponding target direct current.

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, and the coasting start module 802 is specifically configured to: aiming at each group of three-phase output voltages, acquiring the synthetic voltage and the rotation angle of the asynchronous motor under a two-phase static coordinate system according to the three-phase output voltages so as to obtain N synthetic voltages and N rotation angles; calculating the difference of the N rotating angles to obtain N-1 rotating angle differences; and determining the starting frequency, the starting voltage, the starting angle and the coasting direction of the asynchronous motor according to the N synthetic voltages, the N rotating angles and the N-1 rotating angle difference values.

In some embodiments of the present invention, the coasting start module 802 is specifically configured to: when the sign of at least continuous N-2 rotation angle difference values in the N-1 rotation angle difference values is positive, determining that the coasting direction is positive, and the starting voltage is

In some embodiments of the present invention, referring to fig. 9, the start control apparatus 800 of the asynchronous motor further includes a normal operation module 804, configured to control the asynchronous motor to normally operate after the output voltage of the frequency converter reaches a voltage corresponding to the start frequency.

In some embodiments of the present invention, the normal operation module 804 is specifically configured to: and 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.

It should be noted that the logic and/or steps represented in the flowcharts or otherwise described herein, such as an ordered listing of executable instructions that can be considered to implement logical functions, can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. For the purposes of this description, a "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of the computer-readable medium would include the following: an electrical connection (electronic device) having one or more wires, a portable computer diskette (magnetic device), a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). Additionally, the computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via for instance optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner if necessary, and then stored in a computer memory.

It should be understood that portions of the present invention may be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, the various steps or methods may 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, any one or combination of the following techniques, which are known in the art, may be used: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, an application specific integrated circuit having an appropriate combinational logic gate circuit, a Programmable Gate Array (PGA), a Field Programmable Gate Array (FPGA), or the like.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

Although embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are exemplary and not to be construed as limiting the present invention, and that changes, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims

1. A start control method of an asynchronous motor, characterized in that the method comprises:

controlling the frequency converter to output direct current to apply excitation current to a stator of the asynchronous motor;

acquiring the 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 operate according to the starting mode.

2. The method of claim 1, wherein controlling the inverter to output a direct current comprises:

acquiring any phase output current in three-phase output currents of the frequency converter;

obtaining a current difference value between the output current of any phase and a corresponding target direct current;

and performing PI regulation on the current difference value to enable the three-phase output current to be equal to the respective corresponding target direct current.

3. The method of claim 1, wherein determining a starting mode of the asynchronous machine based on the bus voltage comprises:

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 that the starting mode is an idle starting mode;

and 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 that the starting mode is a direct starting mode.

4. The method of claim 3, wherein determining the start mode as a coasting start mode, controlling the asynchronous machine to start operation according to the start mode comprises:

controlling the frequency converter to stop outputting the direct current, and acquiring a three-phase output voltage of the frequency converter;

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;

and controlling the asynchronous motor to start according to the starting frequency, the starting voltage, the starting angle and the coasting direction, controlling the starting frequency to be kept unchanged, and adjusting the starting voltage until the output voltage of the frequency converter reaches the voltage corresponding to the starting frequency.

5. The method of claim 4, wherein the three-phase output voltages comprise N groups, N being an integer greater than or equal to 4, and wherein determining the starting frequency, starting voltage, starting angle, and coasting direction of the asynchronous motor based on the three-phase output voltages comprises:

aiming at each group of three-phase output voltages, acquiring the synthetic voltage and the rotation angle of the asynchronous motor under a two-phase static coordinate system according to the three-phase output voltages so as to acquire N synthetic voltages and N rotation angles;

calculating the difference of the N rotating angles to obtain N-1 rotating angle differences;

and determining the starting frequency, the starting voltage, the starting angle and the coasting direction of the asynchronous motor according to the N synthetic voltages, the N rotating angles and the N-1 rotating angle difference values.

6. The method of claim 5, wherein determining a starting frequency, a starting voltage, a starting angle, and a coasting direction of the asynchronous motor from the N resultant voltages, the N rotational angles, and the N-1 rotational angle difference values comprises:

when the sign of at least continuous N-2 rotation angle difference values in the N-1 rotation angle difference values is positive, determining that the coasting direction is positive, and the starting voltage is

Wherein if the signs of the N-1 rotation angle difference values are all positive, or the signs of the 2 nd to the N-1 st rotation angle difference values are all positive, determining the starting frequency as

The starting angle is theta _N +Δθ _N-1 Otherwise, determining the starting frequency as

The starting angle is theta _N +Δθ _N-1 +2π；

When the sign of at least continuous N-2 rotation angle difference values in the N-1 rotation angle difference values is negative, determining that the coasting direction is negative, and the starting voltage is

The starting angle is theta _N +Δθ _N-1 -2π；

Under other conditions, determining that no idling direction exists, wherein 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 synthetic voltage, i belongs to [1, N ∈]，Δθ _N-1 Is the N-1 th rotation angle difference, theta _N And Ts is the control period of the frequency converter for the Nth rotation angle.

7. The method according to claim 4, characterized in that the asynchronous machine is controlled to operate normally after the output voltage of the frequency converter reaches the voltage corresponding to the starting frequency.

8. The method of claim 3, wherein determining the start mode as a direct start mode, controlling the asynchronous machine to start operation according to the start mode comprises:

taking the lowest frequency of the asynchronous motor as the starting frequency of the asynchronous motor;

and controlling the asynchronous motor to start according to the starting frequency, controlling the starting frequency to keep unchanged, and adjusting the output voltage of the frequency converter until the output voltage is increased from zero to a voltage corresponding to the starting frequency.

9. The method according to claim 8, characterized in that the asynchronous motor is controlled to operate normally after the output voltage of the asynchronous motor increases from zero to a voltage corresponding to the starting frequency.

10. The method according to claim 7 or 9, wherein controlling the normal operation of the asynchronous machine comprises:

and 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.

11. A start control method of an asynchronous motor, characterized in that the method comprises:

determining that the asynchronous motor is in an idle state, and controlling a frequency converter to output direct current to apply excitation 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 obtaining a three-phase output voltage of the frequency converter;

12. A computer-readable storage medium, characterized in that a start control program of an asynchronous motor is stored thereon, which when executed by a processor implements the start control method of an asynchronous motor according to any one of claims 1 to 10, or implements the start control method of an asynchronous motor according to claim 11.

13. A frequency converter, comprising: memory, a processor and a start control program for an asynchronous machine stored on the memory and executable on the processor, the processor implementing a start control method for an asynchronous machine according to any one of claims 1-10 or implementing a start control method for an asynchronous machine according to claim 11 when executing the program.

14. A start control device of an asynchronous motor, characterized in that the device comprises:

the first direct current excitation module is used for controlling the frequency converter to output direct current so as to apply excitation current to a stator of the asynchronous motor, acquiring bus voltage of the frequency converter and determining a starting mode of the asynchronous motor according to the bus voltage;

and the first starting module is used for controlling the asynchronous motor to start and operate according to the starting mode.

15. A start control device of an asynchronous motor, characterized in that the device comprises:

the second direct current excitation module is used for determining that the asynchronous motor is in an idle running state, controlling the frequency converter to output direct current to apply excitation current to a stator of the asynchronous motor, and controlling the frequency converter to stop outputting the direct current after delaying for second preset time;

the idling starting module is used for acquiring three-phase output voltage of the frequency converter and determining starting frequency, starting voltage, starting angle and idling direction of the asynchronous motor according to the three-phase output voltage;

and the idling operation switching module is used for controlling the asynchronous motor to start according to the starting frequency, the starting voltage, the starting angle and the idling direction, controlling the starting frequency to be kept unchanged and adjusting the starting voltage until the output voltage of the frequency converter reaches the voltage corresponding to the starting frequency.