An electronic control device and method for reducing the multiple of the power frequency starting current of a motor

Abstract

The present invention relates to the technical field of power frequency starting of motors, and discloses an electric control device for reducing the power frequency starting current multiple of a motor, comprising an autotransformer step-down unit, a reactive compensation switching unit, a starting bypass conversion unit, and an integrated control system. The input end of the starting bypass conversion unit is connected to a power supply cabinet, and the output end is connected to the motor. One end of the autotransformer step-down unit is connected to the starting bypass conversion unit, and the other end is connected to the reactive compensation switching unit. The autotransformer step-down unit, the reactive compensation switching unit, and the starting bypass conversion unit are all connected to the integrated control system. The electric control device for reducing the power frequency starting current multiple of a motor provided by the present invention can achieve an extreme reduction in the starting current multiple of the motor under the power frequency starting mode by using the three units of the autotransformer step-down unit, the reactive compensation switching unit, and the starting bypass conversion unit in combination.

Description

Technical Field

[0001] The present invention relates to the technical field of power frequency starting of motors, and in particular to an electric control device and method for reducing a multiple of a power frequency starting current of a motor. Background Art

[0002] For a motor to rotate, sufficient kinetic energy must be supplied to overcome the resistance encountered during startup. Initially, the motor's speed is near zero. If the electrical energy applied to the motor cannot effectively convert the active component of mechanical energy required to propel the motor, the motor is effectively stalled. Its equivalent circuit is similar to a resistance circuit. If power is applied for too long, the motor's insulation will inevitably be damaged or even burn out.

[0003] Early motor soft-starters, limited by technical and cost constraints, mostly employed water resistance and reactance. With the maturation of semiconductor technology and the development of a comprehensive supporting industry chain, the cost of high-voltage solid-state soft-starters based on thyristors has been effectively controlled. They are gradually gaining market recognition for their ability to effectively limit the amplitude of starting current.

[0004] Whether it is water resistance and inductance, or the high-voltage solid-state soft start that is currently widely promoted in the market, the essence of its starting principle is to connect a certain resistance in series in the energy supply line on the stator side of the motor to limit the amplitude of the motor starting current and share the voltage at the stator end of the motor. The equivalent resistance in series will consume the actual output energy supplied by the power supply side during the starting process, so that the actual electric energy transmitted to the motor end is only a part of the power supply output, and the output capacity of the power supply end cannot be fully applied to the motor end.

[0005] Autotransformers, a traditional transformer with a unique structure, have been used in motor starting solutions for many years. However, due to their lack of significant cost advantages compared to similar reactors and their lack of significant attention to starting characteristics, they have not captured a significant market share, and their starting advantages have not been fully utilized. Unlike water resistance, reactance, and solid-state starting methods, which limit current amplitude and consume energy from the power supply, autotransformers perform an energy transfer function during the starting process. Eliminating the autotransformer's own electromagnetic conversion and transmission efficiency losses, they transfer the vast majority of the energy supplied by the power supply to the motor, resulting in significantly higher energy output than other soft-start methods. The power supply current of an autotransformer is proportional to the square of the transformation ratio, and the starting torque is proportional to the transformation ratio. Under the same motor specifications, load parameters, and power supply output conditions, the actual motor energy output is greater than with conventional soft-start methods. Conversely, for the same starting torque on the motor side, using an autotransformer with a step-down voltage reduction method results in lower starting current and less impact on the power grid. Summary of the Invention

[0006] The purpose of the present invention is to provide an electronic control device for reducing the multiple of the motor's industrial frequency starting current. By using three units, namely, an autotransformer step-down unit, a reactive compensation switching unit, and a starting bypass conversion unit, the starting current multiple of the motor under the industrial frequency starting mode can be reduced to the extreme.

[0007] The above technical objectives of the present invention are achieved through the following technical solutions: an electronic control device for reducing the power frequency starting current multiple of a motor, comprising an autotransformer step-down unit, a reactive compensation switching unit, a starting bypass conversion unit, and an integrated control system, wherein the input end of the starting bypass conversion unit is connected to a power supply cabinet, and the output end is connected to the motor, one end of the autotransformer step-down unit is connected to the starting bypass conversion unit, and the other end is connected to the reactive compensation switching unit, and the autotransformer step-down unit, the reactive compensation switching unit, and the starting bypass conversion unit are all connected to the integrated control system;

[0008] The autotransformer step-down unit is used to transfer the energy required during the motor starting process and limit the current impact amplitude during the starting process by reducing the voltage;

[0009] The reactive compensation switching unit is used to provide a large amount of reactive capacity required to establish a magnetic field and overcome the static torque of the motor during the motor starting phase;

[0010] The starting bypass conversion unit is used to control the autotransformer step-down unit to start working in the initial stage of motor starting to achieve motor step-down starting, and is also used to control the autotransformer step-down unit to stop working when the motor speed reaches a preset speed value or the motor starting current amplitude drops to a preset current amplitude, switching the motor from the step-down circuit to the rated voltage to achieve full speed operation of the motor;

[0011] The integrated control system is used to control the autotransformer step-down unit and the starting bypass conversion unit to perform actions, and to control the reactive compensation switching unit to be switched on or off.

[0012] Furthermore, the starting bypass conversion unit includes a primary-side bypass switch and a secondary-side switching switch. The autotransformer step-down unit is connected in series with the secondary-side switching switch and then connected in parallel at both ends of the primary-side bypass switch. The primary side of the autotransformer step-down unit is connected to the input end of the starting bypass conversion unit, the secondary side of the autotransformer step-down unit is connected to one end of the secondary-side switching switch, and the other end of the secondary-side switching switch is connected to the output end of the starting bypass conversion unit. The primary-side bypass switch and the secondary-side switching switch are both connected to the integrated control system.

[0013] Furthermore, the autotransformer step-down unit includes an autotransformer, a secondary-side current transformer, a servo drive system, a star-point short-circuiting switch, and a primary-side input switch. The secondary-side current transformer is connected to the secondary side of the autotransformer and is used to detect current changes on the secondary side of the autotransformer during motor step-down starting. The servo drive system is connected to the iron core of the autotransformer and is used to drag the iron core to move to adjust the tap voltage ratio on the secondary side of the autotransformer. The star-point short-circuiting switch is connected to the star point of the autotransformer, and the primary-side input switch is connected to the primary side of the autotransformer. The servo drive system, the star-point short-circuiting switch, and the primary-side input switch are all connected to the integrated control system.

[0014] Furthermore, the autotransformer step-down unit also includes a star-point side protection arrester and a secondary-side protection arrester, one end of the star-point side protection arrester is connected to the star point of the autotransformer, and the other end of the star-point side protection arrester is grounded, one end of the secondary-side protection arrester is connected to the secondary side of the autotransformer, and the other end of the secondary-side protection arrester is grounded.

[0015] Furthermore, the reactive compensation switching unit includes a secondary side voltage transformer, a reactive side current transformer and several compensation branches. The secondary side voltage transformer is connected to the secondary side of the autotransformer and is used to detect the voltage change on the secondary side of the autotransformer during the motor step-down starting process. The reactive side current transformer and several of the compensation branches are connected in series on the secondary side of the autotransformer, and several of the compensation branches are connected in parallel. The reactive side current transformer is used to detect the current change on the reactive side of the autotransformer.

[0016] Furthermore, the compensation branch includes a switching switch, a protective fuse, a protective lightning arrester, a reactive capacitor and a reactive discharge unit. One end of the switching switch is connected to the reactive side current transformer, and the other end is respectively connected to the protective fuse, the protective lightning arrester and the reactive discharge unit. The end of the protective lightning arrester away from the reactive side current transformer is grounded. The protective fuse is connected in series with the reactive capacitor and then in parallel at both ends of the reactive discharge unit. The reactive discharge unit is used to discharge the reactive capacitor after the compensation branch is cut off so that it is ready for next use.

[0017] Furthermore, the reactive compensation switching unit also includes a reactive detection controller, which is connected to the integrated control system. The reactive detection controller is respectively connected to several of the switching switches to control the closing or opening of the switching switches. The reactive detection controller is respectively connected to the secondary side current transformer, the secondary side voltage transformer and the reactive side current transformer to obtain the electrical quantity signal during the motor starting process and calculate the reactive power demand required for the motor starting process.

[0018] Furthermore, it also includes a human-machine display interface, which is connected to the reactive power detection controller and is used to display current data, voltage data and reactive power demand during the motor starting process.

[0019] In addition, to achieve the above technical objectives, the present invention also provides an electronic control method for reducing the multiple of the power frequency starting current of a motor, the method comprising the following steps:

[0020] S1, when the power switch is closed, the autotransformer step-down unit is controlled by the starting bypass conversion unit to start working, and all reactive compensation switching units are put into operation at the same time. The autotransformer step-down unit completes the reduction of the starting voltage at the motor end and the transfer of the initial starting energy;

[0021] S2, controls the amplitude of the secondary voltage by dragging the core of the autotransformer through the servo drive system to adjust the motor starting current multiple;

[0022] S3, when the motor speed steadily increases, the power factor value of the motor is obtained through the reactive power detection controller, and the reactive power demand of the motor starting process is determined by combining the collected current and voltage amplitude changes;

[0023] S4, analyzing and calculating an optimal time node according to the reactive power demand, and cutting off the compensation branch of the reactive power compensation switching unit based on the optimal time node;

[0024] S5, when the motor speed reaches a preset speed value or the motor starting current amplitude reaches a preset current amplitude, all compensation branches are cut off;

[0025] S6, by starting the bypass conversion unit to control the autotransformer step-down unit to stop working, the motor is switched from the step-down circuit to the rated voltage to achieve full speed operation of the motor.

[0026] The beneficial effects of the present invention are:

[0027] 1. The electronic control device for reducing the multiple of the motor's industrial frequency starting current provided by the present invention can achieve the ultimate reduction of the starting current peak of the motor under the industrial frequency starting mode through the coordinated use of three units: an autotransformer step-down unit, a reactive compensation switching unit, and a starting bypass conversion unit. The autotransformer, which is the optimal energy transfer device under the industrial frequency mode, is used as the starting unit to maximize the utilization of energy at the power supply end, realize the current amplitude control under the industrial frequency starting mode of the motor, and maximize the reduction of the amplitude of energy obtained from the power grid side, thereby reducing the voltage fluctuation of the associated power grid, improving the reliability of the power supply of the upper transformer, and reducing the requirements for the capacity of the upper distribution network.

[0028] 2. Compared with the energy consumption characteristics of other soft starting methods, the autotransformer step-down unit only plays the role of voltage reduction and energy transfer, except for a very small part of the material's own electromagnetic loss. It can achieve the maximum effective transfer of electric energy from the power supply end to the motor end, avoiding the heat energy consumption under other power frequency starting methods and the harmonic pollution under variable frequency mode.

[0029] 3. By inputting reactive power into the reactive power compensation switching unit during the motor starting phase, the reactive power output of the autotransformer step-down unit can be reduced, thereby effectively increasing the active power output ratio of the power supply end. This reduces reactive power consumption on the grid side while controlling the effective load of the autotransformer within the rated range, maintaining good output linearity and matching the dynamic changing characteristics of reactive power demand during the motor starting phase.

[0030] 4. The electronic control method provided by the present invention for reducing the multiple of the motor's industrial frequency starting current estimates the optimal timing for capacitive reactive power removal by monitoring the balance algorithm of the reactive power and current and voltage amplitude changes during the motor starting process, gives accurate removal instructions, avoids the occurrence of reverse reactive power, and at the same time ensures the stability and controllability of the current amplitude switching on the grid side. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0032] Figure 1 This is a block diagram of a module of an electronic control device for reducing the multiple of the power frequency starting current of a motor according to the present invention;

[0033] Figure 2 This is a structural schematic diagram of an autotransformer step-down unit of an electronic control device for reducing the multiple of the power frequency starting current of a motor according to the present invention;

[0034] Figure 3 This is a schematic structural diagram of a reactive power compensation switching unit of an electronic control device for reducing the multiple of the power frequency starting current of a motor according to the present invention;

[0035] Figure 4 This is a schematic structural diagram of a starting bypass conversion unit of an electronic control device for reducing the multiple of the power frequency starting current of a motor according to the present invention;

[0036] Figure 5 This is an electrical schematic diagram of an electric control device for reducing the multiple of the power frequency starting current of a motor according to the present invention;

[0037] Figure 6 The present invention is a flow chart of an electric control method for reducing the multiple of the power frequency starting current of a motor.

[0038] In the figure, 1. Autotransformer step-down unit, 11. Autotransformer, 12. Secondary side current transformer, 13. Servo drive system, 14. Star point short-circuiter, 15. Primary side input switch, 16. Iron core, 17. Star point side protection arrester, 18. Secondary side protection arrester; 2. Reactive compensation switching unit, 21. Secondary side voltage transformer, 22. Reactive side current transformer, 23. Compensation branch, 231. Switch, 232. Protection fuse, 233. Protection arrester, 234. Reactive capacitor, 235. Reactive discharge unit, 24. Reactive detection controller; 3. Starting bypass conversion unit, 31. Primary side bypass switch, 32. Secondary side switching switch; 4. Integrated control system. DETAILED DESCRIPTION

[0039] The technical solutions of the present invention will be described clearly and completely below with reference to specific embodiments. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

[0040] See also Figure 1, an electric control device for reducing the multiple of the power frequency starting current of the motor, including an autotransformer step-down unit 1, a reactive compensation switching unit 2, a starting bypass conversion unit 3 and an integrated control system 4, the input end of the starting bypass conversion unit 3 is connected to the power cabinet, and the output end is connected to the motor, one end of the autotransformer step-down unit 1 is connected to the starting bypass conversion unit 3, and the other end is connected to the reactive compensation switching unit 2, the autotransformer step-down unit 1, the reactive compensation switching unit 2 and the starting bypass conversion unit 3 are all connected to the integrated control system 4; the autotransformer step-down unit 1 is used to transfer the energy required during the motor starting process and limit the current impact amplitude during the starting process by reducing the voltage. value; the reactive compensation switching unit 2 is used to provide a large amount of reactive capacity required to establish a magnetic field and overcome the static torque of the motor during the starting stage of the motor; the starting bypass conversion unit 3 is used to control the autotransformer step-down unit 1 to start working in the initial stage of motor starting to realize motor step-down starting, and is also used to control the autotransformer step-down unit 1 to stop working when the motor speed reaches a preset speed value or the motor starting current amplitude drops to a preset current amplitude, and switch the motor from the step-down circuit to the rated voltage to achieve full-speed operation of the motor; the integrated control system 4 is used to control the autotransformer step-down unit 1 and the starting bypass conversion unit 3 to perform actions, and to control the reactive compensation switching unit 2 to be put into operation or removed.

[0041] In a specific implementation, the motor requires a large amount of reactive power during the starting process, and sufficient reactive power needs to be obtained from the grid side to establish a magnetic field with the torque required for the motor to rotate. The autotransformer step-down unit 1 can maximize the energy obtained from the power supply end, and offset the large amount of inductive reactive power consumption in the initial stage of motor starting through the reactive power compensation switching unit 2, thereby further reducing the current amplitude obtained from the power supply end. When the speed of the motor reaches a certain limit, that is, the motor speed reaches the preset speed value, or the motor starting current amplitude drops to the preset current amplitude, the required reactive power drops sharply, and this is the opportunity to cut off the reactive power compensation switching unit 2 to ensure the normal operation of the motor.

[0042] It should be noted that compared with the energy consumption characteristics of other soft starting methods, the autotransformer step-down unit 1 only plays the function of stepping down and transferring energy, except for a very small part of the material's own electromagnetic loss, which can realize the maximum effective transfer of electric energy from the power supply end to the motor end, avoiding the heat energy consumption under other industrial frequency starting methods and harmonic pollution under the variable frequency mode. In other words, during the entire starting process, there is no situation where the semiconductor switch provides a large starting torque to cause harmonic pollution, and there is no heat accumulation on the starter caused by energy loss caused by other soft starting methods.

[0043] It should be understood that, by the reactive input of the reactive compensation switching unit 2 during the motor starting stage, the reactive output of the autotransformer step-down unit 1 can be reduced, thereby effectively improving the active power output ratio of the power supply end, reducing the reactive power grid side consumption, and controlling the effective load of the autotransformer 11 within the rated range, maintaining good output linearity, and matching the dynamic changing characteristics of the reactive power demand during the motor starting stage.

[0044] See also Figure 4 and Figure 5 The starting bypass conversion unit 3 includes a primary-side bypass switch 31 and a secondary-side switching switch 32. The autotransformer step-down unit 1 is connected in series with the secondary-side switching switch 32 and then connected in parallel at both ends of the primary-side bypass switch 31. The primary side of the autotransformer step-down unit 1 is connected to the input end of the starting bypass conversion unit 3, the secondary side of the autotransformer step-down unit 1 is connected to one end of the secondary-side switching switch 32, and the other end of the secondary-side switching switch 32 is connected to the output end of the starting bypass conversion unit 3. The primary-side bypass switch 31 and the secondary-side switching switch 32 are both connected to the integrated control system 4.

[0045] In a specific implementation, in the initial stage of motor starting, the integrated control system 4 controls the primary side bypass switch 31 to be disconnected and the secondary side switching switch 32 to be closed, so that the autotransformer step-down unit 1 is put into operation, thereby realizing the step-down starting of the motor; when the motor starting is completed, the integrated control system 4 controls the primary side bypass switch 31 to be closed and the secondary side switching switch 32 to be disconnected, so that the autotransformer step-down unit 1 stops working, and the motor is switched from the step-down circuit to the rated voltage to realize the full speed operation of the motor.

[0046] See also Figure 2 and Figure 5The autotransformer step-down unit 1 includes an autotransformer 11, a secondary-side current transformer 12, a servo drive system 13, a star-point short-circuiting 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 to detect the current change on the secondary side of the autotransformer 11 during the motor step-down starting process. The servo drive system 13 is connected to the iron core 16 of the autotransformer 11 and is used to drag the iron core 16 to move to adjust the tap voltage ratio on the secondary side of the autotransformer 11. The star-point short-circuiting switch 14 is connected to the star point of the autotransformer 11. The primary-side input switch 15 is connected to the primary side of the autotransformer 11. The servo drive system 13, the star-point short-circuiting switch 14, and the primary-side input switch 15 are all connected to the integrated control system 4. Preferably, the autotransformer step-down unit 1 also includes 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 to the star point of the autotransformer 11, and the other end of the star-point side protection arrester 17 is grounded, one end of the secondary-side protection arrester 18 is connected to the secondary side of the autotransformer 11, and the other end of the secondary-side protection arrester 18 is grounded.

[0047] It should be noted that the core component, the autotransformer 11, is used to transmit the energy required during the motor starting process and limit the current impact amplitude during the motor starting process by reducing the voltage; the peripheral current and voltage transformer is used to detect the change in the amount of electricity during the reduced-voltage starting process, providing a basic data judgment basis for system operation analysis; the deviation between the actual starting effect of the motor and the expected value can be controlled by the servo drive system 13 to control the movement of the iron core 16 of the autotransformer 11 to adjust the tap ratio and achieve adaptive regulation.

[0048] It should be understood that the primary and secondary sides of the autotransformer 11 share a common iron core 16 for energy transfer and magnetic field establishment. The change in the length of the iron core 16 in the winding can achieve a change in the secondary voltage ratio. The iron core 16 can achieve a change in the secondary side voltage of the autotransformer 11 unit under the drag of the servo drive system 13 and the precise servo positioning control, thereby achieving the starting current of the controlled motor to follow the change, and ultimately achieving the purpose of optimizing the grid voltage drop during the starting process.

[0049] In a specific implementation, the servo drive system 13 drags the core 16 of the autotransformer 11 to move, adjusting the tap ratio formed by the number of turns of the primary and secondary windings of the autotransformer 11. This difference in tap ratio reduces the amplitude of the secondary-side power frequency voltage, allowing the motor end to generate the torque required for rotation at a lower initial voltage, thereby reducing the starting current. This embodiment utilizes the servo drive system 13 to drag the core 16 to move to adjust the amplitude of the secondary-side voltage of the autotransformer 11, thereby achieving stepless adjustment of the voltage at the motor starting end, further satisfying the requirements for balanced control of the motor starting current multiple and the motor starting time.

[0050] Compared with the traditional form, the autotransformer 11 in this embodiment is adjusted from the original cast-type fixed tap ratio to a movable iron core 16. The change of the tap voltage ratio is achieved through the precise positioning and rapid response function of the servo drive motor. The brake system in the servo drive system 13 can stabilize the voltage ratio at a predetermined voltage value, and realize the current regulation by the change of voltage, thereby realizing the adjustment of the current size obtained from the power grid.

[0051] See also Figure 3 and Figure 5 The reactive compensation switching unit 2 includes a secondary-side voltage transformer 21, a reactive-side current transformer 22, and several compensation branches 23. The secondary-side voltage transformer 21 is connected to the secondary side of the autotransformer 11 and is used to detect voltage changes on the secondary side of the autotransformer 11 during the motor step-down starting process. The reactive-side current transformer 22 and several compensation branches 23 are connected in series on the secondary side of the autotransformer 11. Several compensation branches 23 are connected in parallel. The reactive-side current transformer 22 is used to detect current changes on the reactive side of the autotransformer 11.

[0052] It should be noted that the large reactive compensation capacity provided by the reactive compensation switching unit 2 can offset the losses required to establish a magnetic field before the motor generates mechanical kinetic energy. This embodiment uses compensation on the low-voltage side of the autotransformer 11 to further improve the stability and reliability of the capacity linearity of the autotransformer 11. At the same time, the overload rate is effectively increased, line losses are reduced, and the service life of the equipment is extended.

[0053] Furthermore, the compensation branch 23 includes a switching switch 231, a protective fuse 232, a protective lightning arrester 233, a reactive capacitor 234 and a reactive discharge unit 235. One end of the switching switch 231 is connected to the reactive side current transformer 22, and the other end is respectively connected to the protective fuse 232, the protective lightning arrester 233 and the reactive discharge unit 235. The end of the protective lightning arrester 233 away from the reactive side current transformer 22 is grounded. The protective fuse 232 is connected in series with the reactive capacitor 234 and then connected in parallel at both ends of the reactive discharge unit 235. The reactive discharge unit 235 is used to discharge the reactive capacitor 234 after the compensation branch 23 is cut off in preparation for the next use.

[0054] In a specific implementation, multiple compensation branches 23 are set, and each compensation branch 23 is provided with a switching switch 231. By grouping the switching switches 231, a dynamic response can be achieved to the sharp drop in reactive power demand when the motor speed changes. As the motor speed changes, the reactive power compensation capacity actually invested is always matched with the required reactive power demand.

[0055] Furthermore, the reactive compensation switching unit 2 also includes a reactive detection controller 24, which is connected to the integrated control system 4. The reactive detection controller 24 is respectively connected to several switching switches 231, and is used to control the switching switches 231 to be closed or opened. The reactive detection controller 24 is respectively connected to the secondary side current transformer 12, the secondary side voltage transformer 21 and the reactive side current transformer 22, and is used to obtain the electrical quantity signal during the motor starting process and calculate the reactive power demand required for the motor starting process.

[0056] It should be noted that the reactive power detection controller 24 can sample the changing characteristics of reactive power during the starting process and provide data reference for the time point of cutting. The reactive power compensation switching unit 2 can capture the reactive power demand during the starting process through the reactive power detection controller 24 and control the switching switch 231 of the reactive power group to realize compensation of a large amount of reactive power demand in the motor starting state.

[0057] In the specific implementation, the reactive power demand of the motor starts gradually decreases as the motor speed increases. Through the data feedback from the reactive power detection controller 24 and the monitoring of the change amplitude of the secondary side current and voltage, the change characteristics of the torque and speed during the motor start-up process can be captured, and the power factor is calculated by comprehensively collecting the current and voltage signals. The integrated control system 4 of the equipment judges the change trend of the reactive power demand according to the power factor, and obtains the change point of the reactive power demand, thereby calculating the reasonable time to cut off the reactive compensation switching unit 2, giving accurate cutting instructions, and avoiding the occurrence of reverse reactive power.

[0058] Furthermore, it also includes a human-machine display interface, which is connected to the reactive power detection controller 24 and is used to display current data, voltage data and reactive power demand during the motor starting process.

[0059] In the specific implementation, the electrical power signal during the motor starting process is collected through the secondary side current transformer 12, the secondary side voltage transformer 21 and the reactive side current transformer 22, and transmitted to the reactive power detection controller 24. The reactive power detection controller 24 calculates the reactive power demand based on the acquired electrical power signal and feeds the data back to the human-machine display interface, which can perform real-time display monitoring and provide a data calculation basis for the reactive compensation switching unit 2 and the compensation branch 23 cut-off time point.

[0060] See also Figure 6 , Figure 6 The present invention is a flow chart of an electric control method for reducing the multiple of the power frequency starting current of a motor.

[0061] like Figure 6 As shown, the electronic control method proposed in this embodiment includes the following steps:

[0062] S1, when the power switch is closed, the autotransformer step-down unit 1 is controlled by the starting bypass conversion unit 3 to start working, and all reactive compensation switching units 2 are put into operation at the same time. The autotransformer step-down unit 1 completes the reduction of the motor end starting voltage and the transfer of the initial starting energy;

[0063] S2, controlling the amplitude of the secondary voltage by driving the core 16 of the autotransformer 11 through the servo drive system 13 to adjust the motor starting current multiple;

[0064] S3, when the motor speed steadily increases, the power factor value of the motor is obtained through the reactive power detection controller 24, and the reactive power demand of the motor starting process is determined in combination with the collected current and voltage amplitude changes;

[0065] S4, analyzing and calculating the optimal time node according to the reactive power demand, and cutting off the compensation branch 23 of the reactive power compensation switching unit 2 based on the optimal time node;

[0066] S5, when the motor speed reaches a preset speed value or the motor starting current amplitude reaches a preset current amplitude, all compensation branches 23 are cut off;

[0067] S6, by starting the bypass conversion unit 3 to control the autotransformer step-down unit 1 to stop working, the motor is switched from the step-down circuit to the rated voltage to achieve full speed operation of the motor.

[0068] In the specific implementation, the autotransformer 11 unit completes the reduction of the starting voltage at the motor end and the transfer of the initial starting energy. The precise positioning function of the servo drive system 13 can be used to drag the iron core 16 of the automatic transformer to move, 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 for establishing the magnetic field and overcoming the static torque requirement of the motor during the starting phase of the motor, so that the apparent power obtained from the power supply end is further reduced, which is specifically manifested in the further decrease in the starting current amplitude. The linearity of the starting current curve is better than the overall linearity before compensation. The starting bypass conversion unit 3 completes the full-voltage switching after the motor speed is increased and the current amplitude is reduced, so that the motor operates under the working conditions of the rated voltage of the industrial frequency.

[0069] At the initial start-up stage, the secondary circuit of the autotransformer 11 is prepared. When the power switch is closed, all the compensation branches 23 of the reactive compensation switching units 2 are put into operation to offset the need to establish a torque magnetic field for the motor to break the static inertia and rotate. When the motor speed rises steadily, the reactive power detection controller 24 monitors the power factor value of the motor, and combines the collected current and voltage amplitude changes to determine the reactive power demand during the motor starting process, and makes an optimal time node analysis and calculation, based on which the branch circuit of the reactive compensation unit is cut off; when the motor current approaches a steady state, the integrated control system 4 of the equipment issues a command to cut off all the compensation branches 23; the starting bypass unit switches the motor from the step-down circuit to the rated voltage to achieve full-speed operation of the motor, thereby completing the maximum energy transfer in the power frequency starting mode and reducing the amplitude of the starting current.

Claims

1. An electronic control device for reducing the power frequency starting current multiple of a motor, characterized by: The invention comprises an autotransformer step-down unit (1), a reactive power compensation switching unit (2), a starting bypass conversion unit (3) and an integrated control system (4); the input end of the starting bypass conversion unit (3) is connected to a power cabinet, and the output end is connected to a motor; one end of the autotransformer step-down unit (1) is connected to the starting bypass conversion unit (3), and the other end is connected to the reactive power compensation switching unit (2); the autotransformer step-down unit (1), the reactive power compensation switching unit (2) and the starting bypass conversion unit (3) are all connected to the integrated control system (4); The autotransformer step-down unit (1) is used to transmit the energy required during the motor starting process and limit the current impact amplitude during the starting process by reducing the voltage; The reactive compensation switching unit (2) is used to provide a large amount of reactive capacity required to establish a magnetic field and overcome the static torque of the motor during the motor starting phase; The starting bypass conversion unit (3) is used to control the autotransformer step-down unit (1) to start working in the initial stage of motor starting to achieve motor step-down starting, and is also used to control the autotransformer step-down unit (1) to stop working when the motor speed reaches a preset speed value or the motor starting current amplitude drops to a preset current amplitude, switching the motor from the step-down circuit to operate at the rated voltage, thereby achieving full-speed operation of the motor; The integrated control system (4) is used to control the autotransformer step-down unit (1) and the starting bypass conversion unit (3) to perform actions, and to control the reactive compensation switching unit (2) to be switched on or off; The starting bypass conversion unit (3) includes a primary-side bypass switch (31) and a secondary-side switching switch (32); the autotransformer step-down unit (1) and the secondary-side switching 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 step-down unit (1) is connected to the input end of the starting bypass conversion unit (3); the secondary side of the autotransformer step-down unit (1) is connected to one end of the secondary-side switching switch (32); the other end of the secondary-side switching switch (32) is connected to the output end of the starting bypass conversion unit (3); and both the primary-side bypass switch (31) and the secondary-side switching switch (32) are connected to the integrated control system (4); The autotransformer step-down unit (1) comprises an autotransformer (11), a secondary-side current transformer (12), a servo drive system (13), a star point shorting 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 to detect current changes on the secondary side of the autotransformer (11) during motor step-down starting; the servo drive system (13) is connected to the iron core (16) of the autotransformer (11) and is used to drag the iron core (16) to move so as to adjust the tap voltage ratio on the secondary side of the autotransformer (11); the star point shorting switch (14) is connected to the star point of the autotransformer (11); the primary-side input switch (15) is connected to the primary side of the autotransformer (11); the servo drive system (13), the star point shorting switch (14), and the primary-side input switch (15) are all connected to the integrated control system (4); The reactive compensation switching unit (2) comprises 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 to detect voltage changes on the secondary side of the autotransformer (11) during motor step-down starting; the reactive side current transformer (22) and a plurality of compensation branches (23) are connected in series on 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 to detect current changes on the reactive side of the autotransformer (11).

2. The electronic control device for reducing the power frequency starting current multiple of a motor according to claim 1, characterized in that: The autotransformer step-down 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 to the star point of the autotransformer (11), and the other end of the star point side protection arrester (17) is grounded, one end of the secondary side protection arrester (18) is connected to the secondary side of the autotransformer (11), and the other end of the secondary side protection arrester (18) is grounded.

3. The electronic control device for reducing the power frequency starting current multiple of a motor according to claim 1, characterized in that: The compensation branch (23) comprises a switching switch (231), a protective fuse (232), a protective lightning arrester (233), a reactive capacitor (234) and a reactive discharge unit (235). One end of the switching switch (231) is connected to the reactive side current transformer (22), and the other end is respectively connected to the protective fuse (232), the protective lightning arrester (233) and the reactive discharge unit (235). One end of the protective lightning arrester (233) away from the reactive side current transformer (22) is grounded. The protective fuse (232) is connected in series with the reactive capacitor (234) and then connected in parallel to the two ends of the reactive discharge unit (235). The reactive discharge unit (235) is used to discharge the reactive capacitor (234) after the compensation branch (23) is cut off so as to prepare for next use.

4. The electronic control device for reducing the power frequency starting current multiple of a motor according to claim 3, characterized in that: The reactive power compensation switching unit (2) further includes a reactive power detection controller (24), the reactive power detection controller (24) being connected to the integrated control system (4), the reactive power detection controller (24) being respectively connected to a plurality of switching switches (231) for controlling the switching switches (231) to be closed or opened, and the reactive power detection controller (24) being respectively connected to the secondary side current transformer (12), the secondary side voltage transformer (21) and the reactive side current transformer (22) for obtaining an electrical quantity signal during the motor starting process and calculating the reactive power demand required for the motor starting process.

5. The electronic control device for reducing the power frequency starting current multiple of a motor according to claim 4, characterized in that: It also includes a human-machine display interface, which is connected to the reactive power detection controller (24) and is used to display current data, voltage data and reactive power demand during the motor starting process.

6. An electric control method for reducing the power frequency starting current multiple of a motor, the method being used in the electric control device for reducing the power frequency starting current multiple of a motor as claimed in any one of claims 4 to 5, characterized in that: The method comprises the following steps: S1, when the power switch is closed, the autotransformer step-down unit (1) is controlled to start working through the starting bypass conversion unit (3), and all reactive compensation switching units (2) are put into operation at the same time, and the autotransformer step-down unit (1) completes the reduction of the starting voltage at the motor end and the transfer of the initial starting energy; S2, controlling the amplitude of the secondary side voltage by driving the iron core (16) of the autotransformer (11) through the servo drive system (13) to adjust the motor starting current multiple; S3, when the motor speed steadily increases, the power factor value of the motor is obtained through the reactive power detection controller (24), and the reactive power demand of the motor starting process is determined in combination with the changes in the collected current and voltage amplitudes; S4, analyzing and calculating an optimal time node according to the reactive power demand, and cutting off the compensation branch (23) of the reactive power compensation switching unit (2) based on the optimal time node; S5, when the motor speed reaches a preset speed value or the motor starting current amplitude reaches a preset current amplitude, all compensation branches (23) are cut off; S6, by starting the bypass conversion unit (3) to control the autotransformer step-down unit (1) to stop working, the motor is switched from the step-down circuit to operate at the rated voltage, and the full speed operation of the motor is achieved.

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