CN115313917A - Electric control device and method for reducing power frequency starting current multiple of motor - Google Patents

Abstract

The invention relates to the technical field of power frequency starting of motors, and discloses an electric control device for reducing the multiple of power frequency starting current of a motor. The electric control device for reducing the power frequency starting current multiple of the motor can realize the purpose of reducing the starting current multiple of the motor in a power frequency starting mode to the utmost extent by the matching use of the autotransformer voltage reduction unit, the reactive compensation switching unit and the starting bypass conversion unit.

Description

Electric control device and method for reducing power frequency starting current multiple of motor

Technical Field

The invention relates to the technical field of power frequency starting of motors, in particular to an electric control device and method for reducing the power frequency starting current multiple of a motor.

Background

The motor must provide sufficient kinetic energy to overcome the resistance encountered during starting of the motor. In the initial stage, the rotation speed of the motor is nearly zero, if the electric energy applied to the motor end cannot effectively convert the active component of the mechanical energy for pushing the motor to rotate, the motor is equivalent to be in a locked-rotor state, the equivalent circuit of the motor is in the same resistance mode, and once the energization time is too long, the phenomenon that the insulation of the motor is damaged or even burnt out is caused.

Early soft start of motors was limited by technical and cost constraints, mostly by water resistance and reactance. With the mature application of semiconductor technology and the perfection of a matched industrial chain, the cost of the high-voltage solid soft start taking the thyristor as the core is effectively controlled, and the high-voltage solid soft start can be gradually accepted by the market by the characteristics of effectively limiting the amplitude of the starting current and the like.

The starting principle of the high-voltage solid soft starter is that a certain resistance value is connected in series in an energy supply circuit on the side of a motor stator to play roles of limiting the starting current amplitude of the motor and sharing the voltage of the motor stator, and the series equivalent resistor consumes the actual output energy supplied by a power supply side in the starting process, so that the actual electric energy transmitted to the motor end is only one part of the power output, and the output capacity of the power supply end cannot be completely applied to the motor end.

Autotransformers have been used for years in motor starting schemes as a traditional transformer with a special structure. Since the cost is not significantly advantageous over the reactor having the common point, the starting characteristics thereof have not been paid sufficient attention, and the market rate has not been large, and the starting advantages thereof have not been sufficiently utilized. Different from a starting mode of limiting current amplitude and consuming energy supplied by a power supply side through water resistance, reactance and a solid state, the autotransformer plays a role in energy transfer in the starting process, removes electromagnetic conversion and transfer efficiency loss of the autotransformer, and can transfer most of energy supplied by the power supply side to a motor end, so that the actually obtained electric energy at the motor end is far higher than that of other soft starting modes. The current at the power supply side of the autotransformer is in direct proportion to the square of the transformation ratio, the starting torque is in direct proportion to the transformation ratio, the initial energy actually obtained by the motor is larger than that of a conventional soft starting mode under the condition that the parameter load of the motor and the output energy of the power supply end of the motor with the same specification are fixed, the starting current is smaller by adopting an autotransformer voltage reduction mode under the condition that the motor is reversely pushed to have the same starting torque, and the impact influence on a power grid is weaker.

Disclosure of Invention

The invention aims to provide an electric control device for reducing the power frequency starting current multiple of a motor, and the starting current multiple of the motor under the power frequency starting mode can be reduced to the utmost extent by matching three units, namely an autotransformer voltage reduction unit, a reactive compensation switching unit and a starting bypass conversion unit.

The technical purpose of the invention is realized by the following technical scheme: an electric control device for reducing the power frequency starting current multiple of a motor comprises an autotransformer voltage reduction unit, a reactive compensation switching unit, a starting bypass conversion unit and a comprehensive control system, wherein the input end of the starting bypass conversion unit is connected to a power cabinet, the output end of the starting bypass conversion unit is connected to the motor, one end of the autotransformer voltage reduction unit is connected with the starting bypass conversion unit, the other end of the autotransformer voltage reduction unit is connected with the reactive compensation switching unit, and the autotransformer voltage reduction unit, the reactive compensation switching unit and the starting bypass conversion unit are all connected with the comprehensive control system;

the autotransformer voltage reduction unit is used for transmitting energy required by the motor in the starting process and limiting the current impact amplitude in the starting process in a voltage reduction mode;

the reactive compensation switching unit is used for providing a large amount of reactive capacity required by establishing a magnetic field and overcoming the static moment of the motor in the starting stage of the motor;

the starting bypass conversion unit is used for controlling the autotransformer voltage reduction unit to work at the initial starting stage of the motor so as to realize the voltage reduction starting of the motor, and is also used for controlling the autotransformer voltage reduction unit to stop working when the rotating speed of the motor reaches a preset rotating speed value or the starting current amplitude of the motor is reduced to a preset current amplitude, so that the motor is switched to a rated voltage from a voltage reduction loop to run, and the full-speed running of the motor is realized;

and the comprehensive control system is used for controlling the autotransformer voltage reduction unit and the starting bypass conversion unit to execute actions and controlling the reactive compensation switching unit to be switched on or switched off.

Further, the starting bypass conversion unit comprises a primary side bypass switch and a secondary side switch, the auto-transformer voltage reduction unit and the secondary side switch are connected in series and then connected in parallel at two ends of the primary side bypass switch, a primary side of the auto-transformer voltage reduction unit is connected with an input end of the starting bypass conversion unit, a secondary side of the auto-transformer voltage reduction unit is connected with one end of the secondary side switch, the other end of the secondary side switch is connected to an output end of the starting bypass conversion unit, and the primary side bypass switch and the secondary side switch are both connected with the integrated control system.

Furthermore, the autotransformer voltage reduction unit comprises an autotransformer, a secondary side current transformer, a servo drive system, a star point short-circuit switch and a primary side input switch, wherein the secondary side current transformer is connected to the secondary side of the autotransformer and used for detecting the current change of the secondary side of the autotransformer in the motor voltage reduction starting process, the servo drive system is connected with an iron core of the autotransformer and used for dragging the iron core to move so as to adjust the tap voltage ratio of the secondary side of the autotransformer, the star point short-circuit switch is connected with the star point of the autotransformer, the primary side input switch is connected to the primary side of the autotransformer, and the servo drive system, the star point short-circuit switch and the primary side input switch are connected with the comprehensive control system.

Furthermore, the autotransformer voltage reduction unit further comprises a star point side protection arrester and a secondary side protection arrester, one end of the star point side protection arrester is connected with a star point of the autotransformer, the other end of the star point side protection arrester is grounded, one end of the secondary side protection arrester is connected with the secondary side of the autotransformer, and the other end of the secondary side protection arrester is grounded.

Further, the reactive compensation switching unit comprises a secondary side voltage transformer, a reactive side current transformer and a plurality of compensation branches, wherein the secondary side voltage transformer is connected to the secondary side of the autotransformer and used for detecting the voltage change of the secondary side of the autotransformer in the motor voltage reduction starting process, the reactive side current transformer and the plurality of compensation branches are connected in series to the secondary side of the autotransformer and connected in parallel, and the reactive side current transformer is used for detecting the current change of the reactive side of the autotransformer.

Further, the compensation branch road includes fling-cut switch, protection fuse, protection arrester, reactive capacitance and reactive discharge unit, fling-cut switch's one end with idle side current transformer connects, the other end respectively with protection fuse, protection arrester and the reactive discharge unit connects, the protection arrester is kept away from idle side current transformer's one end ground connection, the protection fuse with the reactive capacitance connects in parallel after establishing ties at the both ends of reactive discharge unit, the reactive discharge unit is used for realizing after the compensation branch road amputates that reactive capacitance discharges in order to put into use next time.

Further, the reactive power compensation switching unit further comprises a reactive power detection controller, the reactive power detection controller is connected with the integrated control system, the reactive power detection controller is respectively connected with the plurality of switching switches and used for controlling the switching switches to be switched on or switched off, and the reactive power detection controller is respectively connected with the secondary side current transformer, the secondary side voltage transformer and the reactive side current transformer and used for acquiring an electric quantity signal in the starting process of the motor and calculating reactive power demand required by the starting process of the motor.

And the man-machine display interface is connected with the reactive power detection controller and is used for displaying current data, voltage data and reactive power demand in the starting process of the motor.

In addition, in order to achieve the above technical object, the present invention further provides an electric control method for reducing the power frequency starting current multiple of a motor, including the following steps:

s1, when a power switch is switched on, controlling the voltage reduction unit of the autotransformer to work by starting the bypass conversion unit, and simultaneously putting all the reactive compensation switching units into operation, wherein the voltage reduction unit of the autotransformer is used for reducing the initial voltage at the motor end and transmitting the starting initial energy;

s2, dragging an iron core of the autotransformer through a servo driving system to control the amplitude of secondary side voltage so as to adjust the starting current multiple of the motor;

s3, when the rotating speed of the motor is increased in a steady state, the power factor value of the motor is obtained through the reactive power detection controller, and the reactive power demand of the motor in the starting process is judged by combining the collected current and voltage amplitude changes;

s4, analyzing and calculating an optimal time node according to the reactive demand, and cutting off a compensation branch of the reactive compensation switching unit based on the optimal time node;

s5, when the rotating speed of the motor reaches a preset rotating speed value or the starting current amplitude of the motor reaches a preset current amplitude, cutting off all compensation branches;

and S6, controlling the step-down unit of the autotransformer to stop working by starting the bypass conversion unit, and switching the motor from the step-down loop to the rated voltage for running so as to realize the full-speed running of the motor.

The beneficial effects of the invention are:

1. the electric control device for reducing the power frequency starting current multiple of the motor can realize the maximum reduction of the starting current peak value under the power frequency starting mode of the motor by matching the voltage reduction unit of the autotransformer, the reactive compensation switching unit and the starting bypass conversion unit, and realizes the maximum utilization of the energy of a power supply end by adopting the optimal energy transfer device under the power frequency mode of the autotransformer as the starting unit, thereby realizing the current amplitude control under the power frequency starting mode of the motor, maximally reducing the amplitude of the energy obtained from the power grid side, further reducing the voltage fluctuation of the associated power grid, improving the power supply reliability of a superior transformer and reducing the requirement on the capacity of a superior distribution network.

2. Compared with the characteristic that the autotransformer voltage reduction unit consumes energy in other soft starting modes, the autotransformer voltage reduction unit removes the electromagnetic loss of a material per se in a very small part, only plays a role in reducing voltage and transmitting energy, can realize the effective transmission of the electric energy of a power supply end to a motor end to the maximum extent, and avoids heating energy consumption in other power frequency starting modes and harmonic pollution in a frequency conversion mode.

3. The reactive output of the voltage reduction unit of the autotransformer can be reduced through the reactive input of the reactive compensation switching unit in the starting stage of the motor, so that the active power proportion of the energy output of the power supply end is effectively improved, the consumption of the reactive power grid side is reduced, meanwhile, the effective load of the autotransformer is controlled within a rated range, good output linearity is kept, and the characteristic of dynamic change of the reactive demand in the starting stage of the motor is matched.

4. The electric control method for reducing the power frequency starting current multiple of the motor estimates the optimal capacitive reactive power cutting time through a balance algorithm for monitoring the reactive power and the current and voltage amplitude value change in the starting process of the motor, gives an accurate cutting instruction, avoids the occurrence of reactive power in reverse feeding, and simultaneously ensures the stability and controllability of current amplitude value switching at the side of a power grid.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the description below are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a block diagram of an electrical control apparatus for reducing the power frequency starting current multiple of a motor according to the present invention;

FIG. 2 is a schematic structural view of an autotransformer voltage reduction unit of the electric control device for reducing the power frequency starting current multiple of the motor of the present invention;

FIG. 3 is a schematic structural diagram of a reactive compensation switching unit of the electric control device for reducing the power frequency starting current multiple of the motor of the invention;

FIG. 4 is a schematic structural diagram of a starting bypass converting unit of the electric control device for reducing the power frequency starting current multiple of the motor of the invention;

FIG. 5 is an electrical schematic of an electrical control apparatus for reducing the power frequency starting current multiple of a motor of the present invention;

fig. 6 is a schematic flow chart of an electric control method for reducing the power frequency starting current multiple of the motor according to the present invention.

In the figure, 1, an autotransformer voltage reduction unit, 11, an autotransformer, 12, a secondary side current transformer, 13, a servo drive system, 14, a star point short-circuit switch, 15, a primary side input switch, 16, an iron core, 17, a star point side protection lightning arrester, 18 and a secondary side protection lightning arrester; 2. the reactive compensation switching unit comprises a reactive compensation switching unit 21, a secondary side voltage transformer, 22, a reactive side current transformer, 23, a compensation branch circuit, 231, a switching switch, 232, a protection fuse, 233, a protection lightning arrester, 234, a reactive capacitor, 235, a reactive discharge unit, 24 and a reactive detection controller; 3. a startup bypass conversion unit 31, a primary side bypass switch 32, and a secondary side changeover switch; 4. and (4) a comprehensive control system.

Detailed Description

The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. It is to be understood that the described embodiments are merely a few embodiments of the invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without any inventive step, are within the scope of the present invention.

Referring to fig. 1, an electric control device for reducing the power frequency starting current multiple of a motor comprises an autotransformer voltage reduction unit 1, a reactive compensation switching unit 2, a starting bypass conversion unit 3 and a comprehensive control system 4, wherein the input end of the starting bypass conversion unit 3 is connected to a power cabinet, the output end of the starting bypass conversion unit 3 is connected to the motor, one end of the autotransformer voltage reduction unit 1 is connected with the starting bypass conversion unit 3, the other end of the autotransformer voltage reduction unit is connected with the reactive compensation switching unit 2, and the autotransformer voltage reduction unit 1, the reactive compensation switching unit 2 and the starting bypass conversion unit 3 are all connected with the comprehensive control system 4; the autotransformer voltage reduction unit 1 is used for transmitting energy required in the starting process of the motor and limiting the current impact amplitude in the starting process in a voltage reduction mode; the reactive compensation switching unit 2 is used for providing a large amount of reactive capacity required by establishing a magnetic field and overcoming the static moment of the motor in the starting stage of the motor; the starting bypass conversion unit 3 is used for controlling the autotransformer voltage reduction unit 1 to work at the initial starting stage of the motor so as to realize the voltage reduction starting of the motor, and is also used for controlling the autotransformer voltage reduction unit 1 to stop working when the rotating speed of the motor reaches a preset rotating speed value or the starting current amplitude of the motor is reduced to a preset current amplitude, and the motor is switched to a rated voltage from a voltage reduction loop to run so as to realize the full-speed running of the motor; and the comprehensive control system 4 is used for controlling the autotransformer voltage reduction unit 1 and the starting bypass conversion unit 3 to execute actions and controlling the reactive compensation switching unit 2 to be switched on or switched off.

In a specific implementation, the amount of reactive power required by the motor during starting is large, and sufficient reactive power needs to be obtained from the power grid side to establish a magnetic field of torque required by the motor to rotate so as to realize the rotation of the motor. The autotransformer voltage reduction unit 1 can maximally acquire the energy of a power supply end, and a large amount of inductive reactive power consumption of the motor in the initial starting stage is counteracted through the reactive power compensation switching unit 2, so that the current amplitude acquired from the power supply end is further reduced, when the rotating speed of the motor reaches a certain limit value, namely the rotating speed of the motor reaches a preset rotating speed value, or the starting current amplitude of the motor is reduced to the preset current amplitude, the required reactive power amount is rapidly reduced, and therefore the reactive power compensation switching unit 2 is cut off at a time to ensure the normal operation of the motor.

It should be noted that, compared with the self energy consumption characteristics of other soft starting modes, the autotransformer voltage reduction unit 1 removes the electromagnetic loss of a very small part of the material, only plays the function of reducing voltage and transmitting energy, can realize the maximum and effective transmission of the power end electric energy to the motor end, and avoids the heating energy consumption under other power frequency starting modes and the harmonic pollution under a frequency conversion mode, that is, the situation that a semiconductor switch provides a larger starting torque to cause harmonic pollution does not exist in the whole starting process, and the heating aggregation of the energy loss on the starter caused by other soft starting modes does not exist.

It should be understood that the reactive output of the step-down unit 1 of the autotransformer can be reduced through the reactive input of the reactive compensation switching unit 2 in the motor starting stage, so that the active power ratio of the energy output of the power supply end is effectively improved, the consumption of the reactive power grid side is reduced, meanwhile, the effective load of the autotransformer 11 is controlled within the rated range, good output linearity is kept, and the characteristic of dynamic change of the reactive demand in the motor starting stage is matched.

Referring to fig. 4 and 5, the start bypass converting unit 3 includes a primary side bypass switch 31 and a secondary side switch 32, the autotransformer voltage reducing unit 1 and the secondary side switch 32 are connected in series and then connected in parallel to both ends of the primary side bypass switch 31, the primary side of the autotransformer voltage reducing unit 1 is connected to the input end of the start bypass converting unit 3, the secondary side of the autotransformer voltage reducing unit 1 is connected to one end of the secondary side switch 32, the other end of the secondary side switch 32 is connected to the output end of the start bypass converting unit 3, and both the primary side bypass switch 31 and the secondary side switch 32 are connected to the integrated control system 4.

In the specific implementation, at the initial stage of starting the motor, the comprehensive control system 4 controls the primary side bypass switch 31 to be switched off and the secondary side switch 32 to be switched on, so that the autotransformer voltage reduction unit 1 is enabled to work, and the voltage reduction starting of the motor is realized; after the motor is started, the comprehensive control system 4 controls the primary side bypass switch 31 to be closed and the secondary side switch 32 to be opened, so that the autotransformer voltage reduction unit 1 stops working, the motor is switched to a rated voltage from a voltage reduction loop to operate, and full-speed operation of the motor is realized.

Referring to fig. 2 and 5, the autotransformer voltage reduction unit 1 includes an autotransformer 11, a secondary side current transformer 12, a servo drive system 13, a star point short-circuit switch 14 and a primary side input switch 15, the secondary side current transformer 12 is connected to the secondary side of the autotransformer 11 and is used for detecting current change of the secondary side of the autotransformer 11 during the motor voltage reduction starting process, the servo drive system 13 is connected to an iron core 16 of the autotransformer 11 and is used for dragging the iron core 16 to move so as to adjust a tap voltage ratio of the secondary side of the autotransformer 11, the star point short-circuit switch 14 is connected to a star point of the autotransformer 11, the primary side input switch 15 is connected to the primary side of the autotransformer 11, and the servo drive system 13, the star point short-circuit switch 14 and the primary side input switch 15 are all connected to the integrated control system 4. Preferably, the autotransformer voltage reduction unit 1 further comprises a star point side protection arrester 17 and a secondary side protection arrester 18, one end of the star point side protection arrester 17 is connected with a star point of the autotransformer 11, the other end of the star point side protection arrester 17 is grounded, one end of the secondary side protection arrester 18 is connected with a secondary side of the autotransformer 11, and the other end of the secondary side protection arrester 18 is grounded.

It should be noted that the core component autotransformer 11 is used for transmitting energy required in the starting process of the motor, and limiting the current impact amplitude in the starting process of the motor in a voltage reduction mode; the peripheral current-voltage transformer is used for detecting the electric quantity change condition in the voltage reduction starting process and providing a basic data judgment basis for system operation analysis; the deviation of the actual starting effect of the motor from the expected value can be adjusted through controlling the movement of the iron core 16 of the autotransformer 11 through the servo driving system 13 to adjust the tap transformation ratio, so that the self-adaptive adjustment is realized.

It should be understood that the primary side and the secondary side of the autotransformer 11 share one iron core 16 for energy transfer and magnetic field establishment, the length change of the iron core 16 in the winding can realize the change of the secondary voltage transformation ratio, and the iron core 16 can realize the change of the secondary side voltage of the autotransformer 11 unit under the dragging and precise servo positioning control of the servo driving system 13, so as to realize the follow-up change of the starting current of the control motor, and finally achieve the purpose of optimally adjusting the grid voltage drop in the starting process.

In the specific implementation, the servo driving system 13 drags the iron core 16 of the autotransformer 11 to move, and the tap ratio formed by the number of turns of the primary winding and the secondary winding of the autotransformer 11 is adjusted, so that the reduction of the secondary side power frequency voltage amplitude is realized by utilizing the difference of the tap ratio, the motor end forms the torque required by rotation with lower initial voltage, and the reduction of the starting current is realized. In the embodiment, the secondary side voltage amplitude of the autotransformer 11 is adjusted by using the servo driving system 13 to drag the iron core 16 to move, so that the stepless adjustment of the starting end voltage of the motor is realized, and the requirements of motor starting current multiple and motor starting time balance control are further met.

Compared with the conventional form, in the autotransformer 11 of the present embodiment, the original cast fixed tap transformation ratio is adjusted to the movable iron core 16, the transformation ratio tap voltage ratio is changed by the precise positioning and fast response functions of the servo driving motor, the band-type brake system in the servo driving system 13 can stabilize the voltage transformation ratio at a predetermined voltage value, and the current adjustment is realized by the voltage change, so as to realize the adjustment of the current magnitude obtained from the power grid.

Referring to fig. 3 and 5, the reactive compensation switching unit 2 includes a secondary side voltage transformer 21, a reactive side current transformer 22 and a plurality of compensation branches 23, the secondary side voltage transformer 21 is connected to the secondary side of the autotransformer 11 and is used for detecting voltage change of the secondary side of the autotransformer 11 during the motor voltage reduction starting process, the reactive side current transformer 22 and the plurality of compensation branches 23 are connected in series to the secondary side of the autotransformer 11, the plurality of compensation branches 23 are connected in parallel, and the reactive side current transformer 22 is used for detecting current change of the reactive side of the autotransformer 11.

It should be noted that, the reactive compensation switching unit 2 provides a large-capacity reactive compensation capacity, so that the loss required for establishing a magnetic field before the motor does not form mechanical kinetic energy can be offset. In the embodiment, the mode of compensation at the low-voltage side of the autotransformer 11 is adopted, so that the stability and reliability of the linearity of the capacity of the autotransformer 11 can be further improved, the overload rate is effectively improved, the line loss is improved, and the service life of equipment is prolonged.

Further, the compensation branch 23 includes a switching switch 231, a protection fuse 232, a protection arrester 233, a reactive capacitor 234 and a reactive discharge unit 235, one end of the switching switch 231 is connected with the reactive side current transformer 22, the other end of the switching switch is respectively connected with the protection fuse 232, the protection arrester 233 and the reactive discharge unit 235, one end of the protection arrester 233, which is far away from the reactive side current transformer 22, is grounded, the protection fuse 232 and the reactive capacitor 234 are connected in series and then connected in parallel at two ends of the reactive discharge unit 235, and the reactive discharge unit 235 is used for realizing discharge of the reactive capacitor 234 after the compensation branch 23 is cut off so as to be put into use next time.

In the concrete implementation, by arranging a plurality of compensation branches 23, each compensation branch 23 is provided with a switching switch 231, and the rapid reduction of the reactive power demand when the rotating speed of the motor changes can be dynamically responded by grouping and cutting off the switching switches 231, so that the actually input reactive power compensation capacity is always matched with the required reactive power demand along with the change of the rotating speed of the motor.

Further, the reactive power compensation switching unit 2 further includes a reactive power detection controller 24, the reactive power detection controller 24 is connected with the integrated control system 4, the reactive power detection controller 24 is respectively connected with the plurality of switching switches 231 for controlling the switching switches 231 to be turned on or turned off, and the reactive power detection controller 24 is respectively connected with the secondary side current transformer 12, the secondary side voltage transformer 21 and the reactive side current transformer 22 for obtaining an electric quantity signal in the starting process of the motor and calculating a reactive power demand required in the starting process of the motor.

It should be noted that the reactive power detection controller 24 can sample the reactive power variation characteristic in the starting process to provide data reference for the cut-off time point, and the reactive power compensation switching unit 2 can capture the reactive power demand in the starting process through the reactive power detection controller 24 and control the switching switch 231 for switching the reactive power group to act, so as to realize the compensation of a large amount of reactive power demand in the starting state of the motor.

In the concrete implementation, the reactive power demand of the motor starting is gradually reduced along with the increase of the rotating speed of the motor, the change characteristics of the torque and the rotating speed in the starting process of the motor can be captured through data fed back by the reactive power detection controller 24 and monitoring of the change amplitude of the secondary side current and voltage, the power factor is calculated through comprehensively collected current and voltage signals, and the comprehensive control system 4 of the equipment judges the change trend of the reactive power demand according to the power factor to obtain the change point of the reactive power demand, so that the reasonable opportunity of cutting off the reactive power compensation switching unit 2 is calculated, an accurate cutting-off instruction is given, and the occurrence of the reactive power reverse feeding condition is avoided.

Further, the system also comprises a human-computer display interface, wherein the human-computer display interface is connected with the reactive power detection controller 24 and is used for displaying current data, voltage data and reactive power demand in the starting process of the motor.

In the concrete implementation, an electric quantity signal in the starting process of the motor is collected through the secondary side current transformer 12, the secondary side voltage transformer 21 and the reactive side current transformer 22 and is transmitted to the reactive detection controller 24, the reactive detection controller 24 calculates a reactive demand according to the obtained electric quantity signal, and feeds back data to a human-computer display interface, so that real-time display monitoring can be carried out, and a data calculation basis is provided for the cutting time points of the reactive compensation switching unit 2 and the compensation branch 23.

Referring to fig. 6, fig. 6 is a schematic flow chart of an electric control method for reducing the power frequency starting current multiple of the motor according to the present invention.

As shown in fig. 6, the electric control method proposed by this embodiment includes the following steps:

s1, when a power switch is switched on, the starting bypass conversion unit 3 controls the autotransformer voltage reduction unit 1 to work, all the reactive compensation switching units 2 are put into operation at the same time, and the autotransformer voltage reduction unit 1 finishes the reduction of the initial voltage at the motor end and the transmission of starting initial energy;

s2, dragging the iron core 16 of the autotransformer 11 through the servo driving system 13 to control the amplitude of the secondary side voltage so as to adjust the starting current multiple of the motor;

s3, when the rotating speed of the motor is increased in a steady state, the reactive power detection controller 24 is used for acquiring the power factor value of the motor and judging the reactive power demand of the motor in the starting process by combining the collected current and voltage amplitude changes;

s4, analyzing and calculating an optimal time node according to the reactive demand, and cutting off a compensation branch 23 of the reactive compensation switching unit 2 based on the optimal time node;

s5, when the rotating speed of the motor reaches a preset rotating speed value or the starting current amplitude of the motor reaches a preset current amplitude, cutting off all the compensation branches 23;

and S6, the bypass conversion unit 3 is started to control the autotransformer voltage reduction unit 1 to stop working, and the motor is switched to operate under the rated voltage from the voltage reduction loop, so that the full-speed operation of the motor is realized.

In the specific implementation, the autotransformer 11 unit completes the reduction of the initial voltage of the motor end and the transmission of the starting initial energy, and can drag the iron core 16 of the autotransformer to move through the precise positioning function of the servo driving system 13, and further control the amplitude of the secondary side voltage to adjust the starting current multiple; the reactive compensation switching unit 2 provides a large amount of reactive capacity required by a magnetic field building and overcoming the static moment of the motor at the starting stage of the motor, so that the apparent power obtained from a power supply end is further reduced, the specific expression is in the form of further reduction of the starting current amplitude, the linearity of a starting current curve is better than the whole linearity before compensation, and the starting bypass conversion unit 3 completes the full-voltage switching after the rotation speed of the motor is increased and the current amplitude is reduced, so that the motor works under the working condition of power frequency rated voltage.

The secondary circuit of the autotransformer 11 is prepared at the initial stage of starting, the compensation branches 23 of all reactive compensation switching units 2 are put into when the power switch is switched on, the compensation branches are used for offsetting the requirement that the motor breaks through the establishment of a torque magnetic field required by the static inertia rotation, when the rotating speed of the motor is stably increased, the power factor value of the motor is monitored through the reactive detection controller 24, the reactive demand quantity of the motor in the starting process is judged by combining the change of the collected current and voltage amplitude values, and the optimal time node analysis calculation is made, so that the branch circuit of the reactive compensation unit is cut off according to the situation; when the current of the motor approaches a steady state, the comprehensive control system 4 of the equipment sends a command to cut off all the compensation branches 23; the motor is switched to the rated voltage from the voltage reduction loop to run through the starting bypass unit, full-speed running of the motor is achieved, maximum energy transfer under a power frequency starting mode is further completed, and the amplitude of starting current is reduced.

Claims (9)

1. The utility model provides an electrically controlled device for reducing motor power frequency starting current multiple which characterized in that: the starting device comprises an autotransformer voltage reduction unit (1), a reactive compensation switching unit (2), a starting bypass conversion unit (3) and a comprehensive control system (4), wherein the input end of the starting bypass conversion unit (3) is connected to a power cabinet, the output end of the starting bypass conversion unit is connected to a motor, one end of the autotransformer voltage reduction unit (1) is connected with the starting bypass conversion unit (3), the other end of the autotransformer voltage reduction unit is connected with the reactive compensation switching unit (2), and the autotransformer voltage reduction unit (1), the reactive compensation switching unit (2) and the starting bypass conversion unit (3) are all connected with the comprehensive control system (4);

the autotransformer voltage reduction unit (1) is used for transmitting energy required in the starting process of the motor and limiting the current impact amplitude in the starting process in a voltage reduction mode;

the reactive compensation switching unit (2) is used for providing a large amount of reactive capacity required by establishing a magnetic field and overcoming the static moment of the motor in the starting stage of the motor;

the starting bypass conversion unit (3) is used for controlling the autotransformer voltage reduction unit (1) to work at the initial starting stage of the motor so as to realize voltage reduction starting of the motor, and is also used for controlling the autotransformer voltage reduction unit (1) to stop working when the rotating speed of the motor reaches a preset rotating speed value or the starting current amplitude of the motor is reduced to a preset current amplitude, and switching the motor from a voltage reduction loop to a rated voltage for running so as to realize full-speed running of the motor;

and the comprehensive control system (4) is used for controlling the autotransformer voltage reduction unit (1) and the starting bypass conversion unit (3) to execute actions and controlling the reactive compensation switching unit (2) to be switched on or switched off.

2. The electric control device for reducing the power frequency starting current multiple of the motor according to claim 1, wherein: the starting bypass conversion unit (3) comprises a primary side bypass switch (31) and a secondary side switch (32), the autotransformer voltage reduction unit (1) and the secondary side switch (32) are connected in series and then connected in parallel at two ends of the primary side bypass switch (31), the primary side of the autotransformer voltage reduction unit (1) is connected with the input end of the starting bypass conversion unit (3), the secondary side of the autotransformer voltage reduction unit (1) is connected with one end of the secondary side switch (32), the other end of the secondary side switch (32) is connected to the output end of the starting bypass conversion unit (3), and the primary side bypass switch (31) and the secondary side switch (32) are both connected with the comprehensive control system (4).

3. The electric control device for reducing the power frequency starting current multiple of the motor as claimed in claim 1, wherein: the autotransformer voltage reduction unit (1) comprises an autotransformer (11), a secondary current transformer (12), a servo drive system (13), a star point short-circuit switch (14) and a primary side input switch (15), wherein the secondary current transformer (12) is connected to the secondary side of the autotransformer (11) and used for detecting current change of the secondary side of the autotransformer (11) in the motor voltage reduction starting process, the servo drive system (13) is connected with an iron core (16) of the autotransformer (11) and used for dragging the iron core (16) to move so as to adjust a tap voltage ratio of the secondary side of the autotransformer (11), the star point short-circuit switch (14) is connected with a star point of the autotransformer (11), the primary side input switch (15) is connected to the primary side of the autotransformer (11), and the servo drive system (13), the star point short-circuit switch (14) and the primary side input switch (15) are connected with the comprehensive control system (4).

4. The electric control device for reducing the power frequency starting current multiple of the motor according to claim 3, wherein: the autotransformer voltage reduction unit (1) further comprises a star point side protection arrester (17) and a secondary side protection arrester (18), one end of the star point side protection arrester (17) is connected with a star point of the autotransformer (11), the other end of the star point side protection arrester (17) is grounded, one end of the secondary side protection arrester (18) is connected with a secondary side of the autotransformer (11), and the other end of the secondary side protection arrester (18) is grounded.

5. The electric control device for reducing the power frequency starting current multiple of the motor as claimed in claim 3, wherein: reactive compensation switching unit (2) include secondary side voltage transformer (21), reactive side current transformer (22) and a plurality of compensation branch road (23), secondary side voltage transformer (21) are connected the secondary side of auto transformer (11) for detect the motor step-down start-up in-process the voltage variation of auto transformer (11) secondary side, reactive side current transformer (22) and a plurality of compensation branch road (23) are established ties the secondary side of auto transformer (11), a plurality of compensation branch road (23) parallel connection, reactive side current transformer (22) are used for detecting the current variation of auto transformer (11) reactive side.

6. The electric control device for reducing the power frequency starting current multiple of the motor according to claim 5, wherein: the compensation branch circuit (23) comprises a switching switch (231), a protection fuse (232), a protection arrester (233), a reactive capacitor (234) and a reactive discharge unit (235), one end of the switching switch (231) is connected with the reactive side current transformer (22), the other end of the switching switch is respectively connected with the protection fuse (232), the protection arrester (233) and the reactive discharge unit (235), one end, far away from the reactive side current transformer (22), of the protection arrester (233) is grounded, the protection fuse (232) and the reactive capacitor (234) are connected in series and then connected in parallel at two ends of the reactive discharge unit (235), and the reactive discharge unit (235) is used for achieving discharge of the reactive capacitor (234) after the compensation branch circuit (23) is cut off so as to be put into use for the next time.

7. The electric control device for reducing the power frequency starting current multiple of the motor as claimed in claim 6, wherein: reactive power compensation switching unit (2) still include reactive power detection controller (24), reactive power detection controller (24) with integrated control system (4) are connected, reactive power detection controller (24) respectively with a plurality of switching switch (231) are connected, are used for control switching switch (231) are closed or break off, reactive power detection controller (24) respectively with secondary side current transformer (12) secondary side voltage transformer (21) and reactive side current transformer (22) are connected for acquire the electric quantity signal of motor start-up in-process and calculate the required reactive demand of motor start-up process.

8. The electric control device for reducing the power frequency starting current multiple of the motor according to claim 7, wherein: the reactive power detection system is characterized by further comprising a human-computer display interface, wherein the human-computer display interface is connected with the reactive power detection controller (24) and is used for displaying current data, voltage data and reactive power demand in the starting process of the motor.

9. An electric control method for reducing the power frequency starting current multiple of a motor is characterized by comprising the following steps:

s1, when a power switch is switched on, the autotransformer voltage reduction unit (1) is controlled to work by starting the bypass conversion unit (3), all the reactive compensation switching units (2) are simultaneously put into operation, and the autotransformer voltage reduction unit (1) is used for reducing the initial voltage at the motor end and transmitting the starting initial energy;

s2, dragging an iron core (16) of the autotransformer (11) through a servo driving system (13) to control the amplitude of secondary side voltage so as to adjust the starting current multiple of the motor;

s3, when the rotating speed of the motor is increased in a steady state, the power factor value of the motor is obtained through the reactive power detection controller (24), and the reactive power demand of the motor in the starting process is judged by combining the change of the collected current and voltage amplitude;

s4, analyzing and calculating an optimal time node according to the reactive demand, and cutting off a compensation branch (23) of the reactive compensation switching unit (2) based on the optimal time node;

s5, when the rotating speed of the motor reaches a preset rotating speed value or the starting current amplitude of the motor reaches a preset current amplitude, all the compensation branches (23) are cut off;

and S6, the step-down unit (1) of the autotransformer is controlled to stop working by starting the bypass conversion unit (3), and the motor is switched to operate under rated voltage from the step-down loop, so that full-speed operation of the motor is realized.

Images