Control method and system for smooth stop of tower crane rotation mechanism after power failure

Abstract

The present application relates to the technical field of crane safety control, in particular to a control method and system for smooth stop of power-off of a rotary mechanism of a tower crane, which comprises: when unexpected power-off occurs, a battery is controlled to supply power to a brake of the rotary mechanism, an open state of the brake is maintained, a "smooth deceleration in power-off" state is entered, a frequency converter executes an operation of changing frequency from large to 0 according to deceleration time, and a timer is started immediately, within the timing time, an output voltage of the frequency converter is given to be reduced to 10%-20% of a voltage corresponding to a conventional setting pressure-frequency ratio, and after the timing time arrives, the voltage is restored to the voltage corresponding to the conventional setting pressure-frequency ratio; when it is detected that a bus voltage is lower than a certain threshold value and a current frequency is given to be reduced to be lower than a certain threshold value, a brake catch signal of the rotary mechanism brake is sent, and the rotary mechanism is stopped. The present application can smoothly decelerate from high speed to low speed and then catch the brake, thereby effectively avoiding the risk of collision caused by the tower crane rotary mechanism freely sliding through a large angle.

Description

Technical Field

[0001] This invention relates to the field of crane safety control technology, and more specifically to a control method and system for the smooth stopping of a tower crane's rotating mechanism when power is cut off. Background Technology

[0002] Tower cranes are commonly used in construction sites for building facilities. Many construction sites have temporary power lines that are poorly maintained, leading to frequent unexpected power outages. In other words, tower cranes often encounter unexpected power outages during operation.

[0003] Tower cranes generally have three working mechanisms: hoisting mechanism, luffing mechanism, and slewing mechanism. The hoisting and luffing mechanisms typically use mechanical brakes to abruptly stop the running motors, resulting in relatively low impact on the mechanisms. However, if the slewing mechanism's motor is suddenly stopped during operation, the high-speed rotating jib will exert a very large shearing impact force on the tower body, thereby affecting the crane's safety and lifespan.

[0004] Currently, there are two common practices in the industry when the tower crane's slewing mechanism loses power. One is not to brake, but to allow the tower crane to rotate freely and stop sliding. The advantage of this approach is that there is no shearing impact on the tower body caused by sudden braking, and the safety and lifespan of the tower body are not affected. However, the disadvantage is that the tower crane's slewing mechanism is no longer under control, and its free sliding angle is quite large, which may cause the tower crane's load or slewing boom to collide with adjacent buildings or tower cranes, posing a safety hazard. The second approach is to brake. Tower crane manufacturers must fully consider the mechanical impact caused by the sudden braking of the slewing mechanism when designing the tower crane, leaving sufficient mechanical design margin. This will increase the weight and manufacturing cost of the tower crane.

[0005] Therefore, how to enable the tower crane's rotating mechanism to smoothly decelerate from high speed to low speed and then engage the brake when it is rotating at medium to high speed and unexpectedly loses power, thereby effectively avoiding the risk of collision caused by excessive free sliding of the tower crane's rotating mechanism, is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the present invention provides a control method and system for the smooth stopping of the rotating mechanism of a tower crane when power is lost. When the rotating mechanism of the tower crane is rotating at medium and high speed and is unexpectedly powered off, it can smoothly decelerate from high speed to low speed and then apply the brake, thereby effectively avoiding the risk of collision caused by the tower crane rotating mechanism sliding too freely at an excessive angle.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a control method for smoothly stopping the rotating mechanism of a tower crane when power is lost, comprising the following steps:

[0009] When an unexpected power outage occurs, the normally open auxiliary contact of the main contactor of the tower crane slewing electrical control subsystem is received to control the battery to supply power to the brake of the slewing mechanism and keep the brake in the open state.

[0010] When the frequency converter receives the closing signal of the normally open auxiliary contact of the main contactor of the tower crane slewing electrical control subsystem during operation, it enters the "power-off smooth deceleration" state.

[0011] When the frequency converter enters the "power-off smooth deceleration" state, it automatically decelerates and the frequency changes from large to 0 according to the deceleration time.

[0012] When the frequency converter enters the "power-off smooth deceleration" state, a timer is immediately started. During the timer period, the output voltage of the frequency converter is reduced to 10%-20% of the voltage corresponding to the normal voltage-frequency ratio. After the timer period is over, it is restored to the voltage corresponding to the normal voltage-frequency ratio.

[0013] When the bus voltage is detected to be below a certain threshold and the current frequency is reduced to below a certain threshold, a brake signal is issued to stop the rotating mechanism.

[0014] Furthermore, the timing time of the timer is set to the time it takes for the rotating mechanism motor to switch from electric to generator state after a power outage.

[0015] Furthermore, the timing interval of the timer is set to 1s-3s.

[0016] Furthermore, when the inverter's output voltage is set in the "power-off smooth deceleration" state, it is filtered by a low-pass filter.

[0017] Furthermore, the time constant of the low-pass filter is 500ms-1000ms.

[0018] Secondly, the present invention provides a control system for the smooth stopping of a tower crane's slewing mechanism upon power failure, comprising: a tower crane slewing electrical control subsystem and a power failure control subsystem; the tower crane slewing electrical control subsystem comprises: a main contactor, a frequency converter, and a slewing mechanism motor; mains power is connected to the frequency converter through the main contactor; the frequency converter is connected to the slewing mechanism motor; a brake is installed on the slewing mechanism motor;

[0019] The power failure control subsystem includes: a brake control module, a frequency converter frequency control module, and a frequency converter output voltage control module;

[0020] The power failure brake control module is used to control the battery to supply power to the brake and keep the brake open when an unexpected power failure occurs, after receiving the closing signal of the normally open auxiliary contact of the main contactor of the tower crane slewing electrical control subsystem.

[0021] The frequency control module of the inverter is used to enter the "power-off smooth deceleration" state when the inverter receives the normally open auxiliary contact closing signal of the main contactor of the tower crane slewing electrical control subsystem during operation; when the inverter enters the "power-off smooth deceleration" state, it automatically decelerates and performs the operation of changing the frequency from large to 0 according to the deceleration time.

[0022] The inverter output voltage control module is used to start a timer immediately when the inverter enters the "power-off smooth deceleration" state. During the timer period, the inverter output voltage is reduced to 10%-20% of the voltage corresponding to the normal voltage-frequency ratio. After the timer period is up, it is restored to the voltage corresponding to the normal voltage-frequency ratio.

[0023] The brake control module is used to issue a brake signal to stop the rotating mechanism when the bus voltage is detected to be lower than a certain threshold and the current frequency is reduced to be lower than a certain threshold.

[0024] Furthermore, the frequency converter has a built-in rectifier module, a filter module, and an inverter module; the rectifier module is connected to the main contactor; the inverter module is connected to the rotating mechanism motor; and the filter module is connected between the rectifier module and the inverter module.

[0025] Furthermore, the power supply of the brake is divided into two paths, one of which consists of a battery and a battery switch, and the other consists of a rectifier bridge and the secondary side of a transformer connected in series, with the primary side of the transformer connected to the mains power; a power switch is provided on the main power supply of the brake, and the power switch is controlled by the relay output interface of the frequency converter.

[0026] When an unexpected power outage occurs, the brake control module receives the normally open auxiliary contact closing signal of the main contactor and controls the battery switch to close. When the bus voltage is lower than a certain threshold and the current frequency setpoint is reduced to lower than a certain threshold, the brake control module controls the relay output interface of the frequency converter to disconnect, and the brake starts braking.

[0027] Furthermore, the timing time of the timer is set to the time it takes for the rotating mechanism motor to switch from electric to generator state after a power outage.

[0028] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0029] This invention, based on the actual operating conditions of the tower crane's rotating mechanism, addresses the issue of a power outage during the initial deceleration phase of the power-off deceleration. Specifically, during the period before the motor transitions from motoring to generating power, the inverter's output voltage is rapidly reduced. This prevents excessive power consumption on the inverter's bus due to the motor's motoring state. During the transition, sufficient power is available to support the inverter's normal operation. Subsequently, during deceleration, the power generated by the motor's generating state powers the inverter, allowing the relay to continue operating. This enables the rotating mechanism to smoothly decelerate from high speed to low speed before engaging the brakes, effectively preventing collision risks caused by excessive free-slip angles of the tower crane's rotating mechanism. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0031] Figure 1 A flowchart of the control method provided by the present invention;

[0032] Figure 2 This is a schematic diagram of the structure of the control system provided by the present invention;

[0033] Figure 3 A simplified structural diagram of the tower crane slewing electrical control subsystem provided by this invention;

[0034] Figure 4 A schematic diagram of the power supply circuit structure of the brake provided by the present invention;

[0035] Figure 5 The waveform diagram of the tower crane slewing mechanism provided by the present invention decelerating from the highest speed to a stop under normal incoming power conditions;

[0036] Figure 6 The waveform diagram of the tower crane slewing mechanism provided by the present invention decelerating to a stop when the incoming power supply is cut off;

[0037] Figure 7 The waveform diagram provided by the present invention shows that when the tower crane slewing mechanism is decelerated to a stop at the same time as the incoming power supply is cut off after the method of the present invention is adopted. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] like Figure 1 As shown in the figure, an embodiment of the present invention discloses a control method for the smooth stopping of a tower crane's rotating mechanism after a power outage, comprising the following steps:

[0040] S1. When an unexpected power failure occurs, receive the normally open auxiliary contact closing signal of the main contactor of the tower crane slewing electrical control subsystem, and control the battery to supply power to the slewing mechanism brake to keep the brake open.

[0041] S2. When the frequency converter receives the closing signal of the normally open auxiliary contact of the main contactor of the tower crane slewing electrical control subsystem during operation, it enters the "power-off smooth deceleration" state.

[0042] S3. When the frequency converter enters the "power-off smooth deceleration" state, it automatically decelerates, and the frequency changes from high to 0 according to the deceleration time. The deceleration time is preset, and the deceleration time, or frequency change trend, is set according to the operating requirements of the tower crane under normal conditions. If it is set to a shorter time, the tower crane will decelerate from high speed to stop quickly; if it is set to a longer time, the tower crane will decelerate from high speed to stop slowly. This parameter does not change in the "power-off smooth deceleration" state.

[0043] S4. When the inverter enters the "power-off smooth deceleration" state, a timer is immediately started. During the timer period, the inverter's output voltage is reduced to 10%-20% of the voltage corresponding to the normally set voltage-frequency ratio. After the timer period is reached, it is restored to the voltage corresponding to the normally set voltage-frequency ratio. The timer period is set to the time it takes for the rotating mechanism motor to switch from motoring to generating mode after power failure, such as 1s-3s.

[0044] S5. When the bus voltage is detected to be lower than a certain threshold and the current frequency is reduced to be lower than a certain threshold, a brake signal is issued to stop the rotating mechanism.

[0045] Here, "bus voltage below a certain threshold" means that the inverter loses its external power supply after the incoming line is disconnected. In the state of smooth deceleration after power failure, it can only rely on the decelerated and generator motor to reverse charge the inverter's bus. However, this reverse charging will not continue indefinitely. Even after implementing this invention, the inverter will not be able to reverse charge after its speed drops below a certain value. At this point, the inverter's bus voltage will continue to drop until the inverter cannot work. This is because the power supply of the circuit board inside the inverter is supplied by the bus voltage. A brake signal needs to be issued before the inverter stops working to ensure that the brake can work and continue to stop the rotating mechanism.

[0046] The reasonable range of the threshold given by the current frequency is a parameter that can be set on site. For example, it can be set to 20% of the rated speed of the motor. This is because when the speed is below 20% of the rated speed, on the one hand, the motor may not be able to continue to generate electricity and the frequency converter may stop working. On the other hand, after the speed is below 20% of the rated speed, the impact of the brake on the entire tower is much less than when the brake is applied at the rated speed.

[0047] This invention requires that the bus voltage be below a certain threshold and the current frequency setting be reduced to below a certain threshold simultaneously. These two conditions mean that when the frequency converter can still work normally (corresponding to the bus voltage being above the aforementioned threshold), the impact of applying the brakes at a reasonable speed (corresponding to the frequency setting being reduced to a certain threshold) on the tower crane is reasonable. This reasonableness lies in the fact that it is much smaller on the tower body than the impact of applying the brakes at full speed.

[0048] Even more advantageously, when the inverter's output voltage is set in the "power-off smooth deceleration" state, it is filtered by a low-pass filter. The time constant of the low-pass filter is 500ms-1000ms.

[0049] like Figure 2 As shown, this embodiment of the invention also provides a control system for the smooth stopping of a tower crane's slewing mechanism in the event of a power outage, comprising: a tower crane slewing electrical control subsystem and a power outage control subsystem; the tower crane slewing electrical control subsystem includes: a main contactor, a frequency converter, and a slewing mechanism motor; mains power is connected to the frequency converter through the main contactor; the frequency converter is connected to the slewing mechanism motor; a brake is installed on the slewing mechanism motor;

[0050] The power failure control subsystem includes: a brake control module, a frequency converter frequency control module, and a frequency converter output voltage control module;

[0051] The power failure brake control module is used to control the battery to supply power to the brake and keep the brake open when an unexpected power failure occurs, after receiving the closing signal of the normally open auxiliary contact of the main contactor of the tower crane slewing electrical control subsystem.

[0052] The frequency control module of the frequency converter is used to enter the "power-off smooth deceleration" state when the frequency converter receives the normally open auxiliary contact closing signal of the main contactor of the tower crane slewing electrical control subsystem during operation; when the frequency converter enters the "power-off smooth deceleration" state, it automatically decelerates and performs the operation of changing the frequency from large to 0 according to the deceleration time.

[0053] The inverter output voltage control module is used to start a timer immediately when the inverter enters the "power-off smooth deceleration" state. During the timer period, the inverter output voltage is reduced to 10%-20% of the voltage corresponding to the normal voltage-frequency ratio. After the timer period is over, it is restored to the voltage corresponding to the normal voltage-frequency ratio.

[0054] The brake control module is used to issue a brake signal to stop the rotating mechanism when the bus voltage is detected to be lower than a certain threshold and the current frequency is reduced to be lower than a certain threshold.

[0055] Specifically, such as Figure 3 As shown, the frequency converter has a built-in rectifier module, filter module and inverter module; the three-phase mains power supply 1 is connected to the rectifier module 3 in the frequency converter 6 through the main contactor 2; the output of the rectifier module 3 is connected to the filter module 4, which can be an electrolytic capacitor; the output of the filter module 4 is connected to the inverter module 5, and the output of the inverter module 5 is connected to the rotating mechanism motor 7, which controls the rotating mechanism and the tower crane boom to rotate.

[0056] A brake 13 is installed on the rotating mechanism motor 7, such as Figure 4 As shown, the power supply for brake 12 is divided into two circuits. One circuit consists of battery 15 and battery switch 16, while the other circuit consists of rectifier bridge 17 and the secondary side of transformer 18 connected in series. The primary side of transformer 18 is connected to the mains power. The power supply voltage for brake 13 is typically 24V, therefore the DC voltage of battery 15 is 24V, and the voltage of transformer 18 is 48V. The primary side of transformer 18 is generally connected to one of the mains power supplies, which is not shown in the figure. A power switch 14 is installed on the main power supply circuit of brake 13, and the power switch 14 is controlled by the relay output interface 12 of frequency converter 6.

[0057] The battery switch 16 is controlled by the normally open auxiliary contact 8 of the contactor 2. That is, when the contactor 2 is engaged under normal mains power supply 1, the battery switch 16 is in the open circuit state. If the mains power supply 1 is interrupted, the contactor 2 will be disengaged, the normally open auxiliary contact 8 will be closed, and the battery switch 16 will be closed.

[0058] A digital input point 10 of the frequency converter is connected to a normally open auxiliary contact 8 of the contactor 2. That is, when the contactor 2 is engaged under normal mains power supply 1, the normally open auxiliary contact 8 is in an open circuit state. If the mains power supply 1 is de-energized, the contactor 2 will disconnect, and the normally open auxiliary contact 8 will close.

[0059] A digital or analog input point 11 of the frequency converter is connected to the operating handle 9 that controls the speed of the tower crane's slewing mechanism. The tower crane operator usually operates the operating handle 9.

[0060] When an unexpected power outage occurs, the brake control module receives the closing signal from the normally open auxiliary contact 8 of the main contactor 2 and controls the battery switch 16 to close, thereby switching the battery 15 to supply power to the brake 13 and keeping the brake 13 in the open state. When the bus voltage is lower than a certain threshold and the current frequency setpoint is reduced to below a certain threshold, the brake control module controls the relay output interface 12 of the frequency converter 6 to open, thereby controlling the power switch 14 to open, and the brake 13 to start braking, stopping the rotating mechanism motor 7.

[0061] To further verify the performance of the present invention, the following experiments were conducted.

[0062] Experiment 1: The tower crane slewing mechanism decelerates from its maximum speed to a stop under normal power supply conditions.

[0063] like Figure 5 The waveforms shown are from Experiment 1. The first row of the waveforms represents the motor speed, the second row represents the motor's output voltage (solid line) and current (dashed line), and the third row represents the inverter's bus voltage. The waveforms show that the motor accelerates from zero speed to its maximum speed, then begins to decelerate after approximately 28 seconds, reaching zero speed after approximately 41 seconds, for a total time of about 13 seconds. The bus voltage waveform also shows that the bus voltage did not rise during the initial deceleration at 28 seconds, but only began to rise after approximately 31 seconds as the motor entered generator mode. In other words, during the period from 28 to 31 seconds, the motor was still in motoring mode, and the inverter still needed to draw energy from the input power supply.

[0064] Experiment 2: When the tower crane is powered off, keep the brake of the rotating mechanism in the open position and send a deceleration and stop command to the frequency converter that controls the rotating motor, but do not perform timed control on the output voltage of the frequency converter.

[0065] like Figure 6 As shown, the waveform of the tower crane slewing mechanism in Experiment 2 decelerating to a stop when the incoming power supply is cut off is shown. The first line of the waveform is the speed waveform of the motor, the second line is the output voltage (solid line) and current waveform (dashed line) of the motor, and the third line is the bus voltage waveform of the frequency converter.

[0066] The waveforms show that the motor accelerates from zero speed to its maximum speed, then begins to decelerate after approximately 21 seconds, reaching zero speed after approximately 108 seconds, for a total time of about 87 seconds. The voltage and current waveforms in the second line show that although deceleration occurred simultaneously with the power supply interruption, the motor remained in an electric state during the initial deceleration phase. At this point, the electric energy supply relied solely on the residual energy on the inverter's bus capacitor, which is insufficient to support the motor's electric state energy demands under normal deceleration control. The bus voltage waveform in the third line shows a rapid drop in bus voltage, causing the inverter to enter an undervoltage fault state, resulting in zero output voltage and current. At this point, the slewing mechanism enters a free-sliding state without inverter drive, and the time taken to decelerate from maximum speed to zero is 6.7 times that of normal deceleration. Furthermore, the motor speed waveform in the first line shows a consistently slow and oscillating decrease in speed. This indicates that without the power-off deceleration state of the present invention, on the one hand, the free sliding of the tower crane boom will greatly increase the risk of collision with obstacles on the sliding trajectory, and on the other hand, the slewing mechanism of the tower crane will be in a state of strong mechanical vibration, which will affect the health of the entire mechanical structure of the tower crane.

[0067] During normal operation, the inverter draws power from the three-phase AC power supply 1 through the rectifier bridge 3, converting it into DC power to charge the inverter module (bus capacitor) 4. The power required for the normal operation of the inverter 6 board is drawn from the bus capacitor 4. When the inverter 6 drives the motor to decelerate, if the motor 7 is in generator mode, the bus capacitor 4 will also be charged through the anti-parallel diodes inside the inverter module 5 of the inverter 6. In other words, the normal operation of the inverter board depends on whether there is power on the bus capacitor, and the amplitude of this voltage is required. The undervoltage fault is a software protection function designed to prevent the inverter board from operating normally if the bus voltage falls below a certain threshold. Once this protection function is triggered, the inverter will immediately stop operating, making it impossible to drive the motor, and the motor will not be able to enter generator mode.

[0068] This experiment emphasizes that, without the control of the method of this invention, when the incoming power supply is disconnected, the voltage of the bus capacitor can only be maintained by the motor decelerating into a generating state. However, for the tower crane's slewing mechanism, it does not immediately enter the generating state upon deceleration; there is a brief period of motoring. If this state cannot be successfully overcome, the energy on the bus capacitor will be rapidly depleted by the motor current in the motoring state, leading to an undervoltage fault and loss of control over the slewing mechanism. The method of this invention can successfully overcome this brief motoring state. During the overcoming process, the motor current is kept as low as possible to minimize the energy consumption on the bus capacitor, allowing the system to enter the generating state before the undervoltage point is reached. Once the generating state is successfully entered, the entire system can operate continuously.

[0069] Experiment 3: Using the method of this invention, the tower crane slewing mechanism is decelerated when the incoming power supply is cut off.

[0070] like Figure 7 The waveforms shown are from Experiment 3. The first row of the waveforms represents the motor speed, the second row represents the motor's output voltage (solid line) and current (dashed line), and the third row represents the inverter's bus voltage. The waveforms show that the motor accelerates from zero speed to its maximum speed, then begins to decelerate after approximately 22 seconds, reaching zero speed after approximately 36 seconds, for a total time of about 14 seconds. The voltage and current waveforms in the second row show that, simultaneously with the power supply interruption, the voltage and current drop significantly during the initial deceleration phase due to the method of this invention. This allows the energy of the bus electrolytic capacitor to sustain the motor until the generation state begins. Once generation begins, no further power from the input power supply is needed, as the electrical energy generated by the motor in generation mode is sufficient to support the motor's deceleration. When the motor decelerates to a low speed range, the bus voltage waveform shows that it gradually enters generation mode again. However, at this point, the motor speed is already very low, allowing for direct mechanical braking by controlling the holding brake. Through the method of this invention, it can be seen that, on the one hand, the boom can smoothly decelerate from the highest speed to the low speed range, which takes 1.08 times longer than normal deceleration. The increased sliding distance is negligible, and the risk of collision with obstacles on the running track is greatly avoided. On the other hand, the smoothness of the motor speed during the entire deceleration process is not much different from normal deceleration, that is, there is no excessive increase in mechanical vibration, and it will not affect the health of the tower crane's mechanical structure.

[0071] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0072] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A control system for the smooth stopping of a tower crane's rotating mechanism upon power failure, characterized in that, include: Tower crane slewing electrical control subsystem and power failure control subsystem; The tower crane slewing electrical control subsystem includes: a main contactor, a frequency converter, and a slewing mechanism motor; mains power is connected to the frequency converter through the main contactor; the frequency converter is connected to the slewing mechanism motor; a brake is installed on the slewing mechanism motor; The power failure control subsystem includes: a brake control module, a frequency converter frequency control module, and a frequency converter output voltage control module; The brake control module is used to control the battery to supply power to the brake and keep the brake open when an unexpected power failure occurs, after receiving the closing signal of the normally open auxiliary contact of the main contactor of the tower crane slewing electrical control subsystem. The frequency control module of the inverter is used to enter the "power-off smooth deceleration" state when the inverter receives the normally open auxiliary contact closing signal of the main contactor of the tower crane slewing electrical control subsystem during operation; when the inverter enters the "power-off smooth deceleration" state, it automatically decelerates and performs the operation of changing the frequency from large to 0 according to the deceleration time. The inverter output voltage control module is used to immediately start a timer when the inverter enters the "power-off smooth deceleration" state. During the timer period, the inverter output voltage is reduced to 10%-20% of the voltage corresponding to the normally set voltage-frequency ratio. After the timer period is reached, it is restored to the voltage corresponding to the normally set voltage-frequency ratio. The timer period is set to the time it takes for the rotating mechanism motor to switch from the motor state to the generator state after the power is off. The brake control module is used to issue a brake signal to stop the rotating mechanism when the bus voltage is detected to be lower than a certain threshold and the current frequency is reduced to be lower than a certain threshold.

2. The control system for the smooth stop of the tower crane's rotating mechanism upon power failure according to claim 1, characterized in that, The frequency converter has a built-in rectifier module, filter module and inverter module; the rectifier module is connected to the main contactor; the inverter module is connected to the rotating mechanism motor; the filter module is connected between the rectifier module and the inverter module.

3. The control system for the smooth stop of the tower crane's rotating mechanism upon power failure as described in claim 1, characterized in that, The power supply for the brake is divided into two circuits. One circuit consists of a battery and a battery switch, while the other circuit consists of a rectifier bridge and the secondary side of a transformer connected in series. The primary side of the transformer is connected to the mains power. A power switch is installed on the main power supply circuit of the brake, and the power switch is controlled by the relay output interface of the frequency converter. When an unexpected power outage occurs, the brake control module receives the normally open auxiliary contact closing signal of the main contactor and controls the battery switch to close. When the bus voltage is lower than a certain threshold and the current frequency setpoint is reduced to lower than a certain threshold, the brake control module controls the relay output interface of the frequency converter to disconnect, and the brake starts braking.

4. A control method for the smooth stopping of a tower crane's rotating mechanism upon power failure, characterized in that, A control system for the smooth stop of a tower crane's rotating mechanism after a power outage, as described in any one of claims 1-3, comprises the following steps: When an unexpected power outage occurs, the normally open auxiliary contact of the main contactor of the tower crane's slewing electrical control subsystem is closed, and the battery is used to supply power to the slewing mechanism brake to keep the brake open. When the frequency converter receives the closing signal of the normally open auxiliary contact of the main contactor of the tower crane slewing electrical control subsystem during operation, it enters the "power-off smooth deceleration" state. When the frequency converter enters the "power-off smooth deceleration" state, it automatically decelerates, and the frequency changes from large to 0 according to the deceleration time. When the frequency converter enters the "power-off smooth deceleration" state, a timer is immediately started. During the timer period, the output voltage of the frequency converter is reduced to 10%-20% of the voltage corresponding to the normally set voltage-frequency ratio. After the timer period is reached, it is restored to the voltage corresponding to the normally set voltage-frequency ratio. The timer period is set to the time for the rotating mechanism motor to switch from motoring to generating mode after power failure. When the bus voltage is detected to be below a certain threshold and the current frequency is reduced to below a certain threshold, a brake signal is issued to stop the rotating mechanism.

5. The control method for smoothly stopping the rotating mechanism of a tower crane when power is cut off, as described in claim 4, is characterized in that... The timer's timing interval is set to 1-3 seconds.

6. The control method for smoothly stopping the rotating mechanism of a tower crane when power is cut off, as described in claim 4, is characterized in that... When the inverter's output voltage is set to the "power-off smooth deceleration" state, it is filtered by a low-pass filter.

7. The control method for smoothly stopping the rotating mechanism of a tower crane when power is cut off, as described in claim 6, is characterized in that... The time constant of the low-pass filter is 500ms-1000ms.

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