Control method for slow variable power start-up of scraper conveyor

Abstract

A control method for slow variable-power start-up of a scraper conveyor includes: controlling the start-up of the motors at the head and tail of the scraper conveyor in four stages: In the first stage, the conveyor starts from zero speed and accelerates uniformly until the output torque of the head motor reaches a first torque threshold, at which point it enters the second stage; in the second stage, the conveyor moves at a uniform speed at the speed at which it entered the second stage, until the chain tension reaches a tension threshold, at which point it enters the third stage; in the third stage, the conveyor uses the speed at which it entered the third stage as the initial speed, gradually increasing acceleration, and then gradually decreasing acceleration until the output torque of the head motor reaches a second torque threshold, at which point it enters the fourth stage; and in the fourth stage, the conveyor moves at a uniform speed at the speed at which it entered the fourth stage. This method can reduce the number of chain tension peaks and the vibration frequency.

Description

Technical Field

[0001] This invention relates to the field of scraper conveyor equipment technology, and in particular to a control method for slow variable power start-up of a scraper conveyor. Background Technology

[0002] As the mining height of medium-thick coal seams continues to increase, the power of scraper conveyors is constantly increasing, the transportation distance is constantly lengthening, and the coal flow rate is significantly increasing, leading to a continuous increase in the risks of pressurization and heavy-load startup. In the past, the main startup methods for scraper conveyors under heavy load were CST reducers or valve-controlled hydraulic couplings. However, CST reducers have a complex system structure, a high failure rate, poor energy-saving effect, and are not suitable for long-term low-speed operation; while valve-controlled hydraulic couplings require periodic replacement of cooling water, resulting in high maintenance costs, and are not suitable for use in steeply inclined working faces or for long-term low-speed operation.

[0003] In subsequent developments, to address the shortcomings of CST reducers and valve-controlled hydraulic couplings, and to further ensure the safety of underground power grids and the service life of scraper conveyors, variable frequency soft starters are now widely adopted to reduce mechanical shock and starting current. However, due to factors such as frequent rock spalling in underground environments, starting scraper conveyors under load or even heavy load becomes more frequent and difficult. The starting torque of scraper conveyors under load or heavy load is generally greater than the rated working torque, significantly increasing the frequency of peak tension and oscillations in the scraper chain. This not only impairs the service life of the traction mechanism but also poses certain safety hazards. Summary of the Invention

[0004] In view of this, and to address the above shortcomings, it is necessary to propose a control method for slow variable power start-up of scraper conveyors to reduce the number of chain tension peaks and vibration frequency.

[0005] This invention provides a control method for slow variable power start-up of a scraper conveyor, comprising:

[0006] The starting process of the scraper conveyor is divided into four stages. The motors at the head and tail of the scraper conveyor are started according to the following four stages to achieve slow variable power start-up of the scraper conveyor.

[0007] in:

[0008] In the first stage, the machine starts from zero speed and accelerates uniformly, and enters the second stage when the output torque of the scraper conveyor head motor reaches the preset first torque threshold.

[0009] In the second stage, the machine moves at a constant speed at the speed when entering the second stage, and enters the third stage when the chain tension of the scraper conveyor reaches a preset tension threshold.

[0010] In the third stage, the initial speed at which the third stage is entered is used as the initial speed, and the acceleration is gradually increased from 0 to perform variable acceleration motion. When the output torque of the scraper conveyor head motor reaches a preset second torque threshold, the acceleration is gradually decreased to perform variable acceleration motion. And when the output torque of the scraper conveyor head motor reaches a preset third torque threshold, the fourth stage is entered. Wherein, the first torque threshold < the second torque threshold < the third torque threshold.

[0011] In the fourth stage, it moves at a constant speed, maintaining the speed it had when entering the fourth stage.

[0012] Preferably, the first torque threshold is 10% of the breaking tensile force of the scraper chain of the scraper conveyor.

[0013] Preferably, the second torque threshold is 15% of the breaking tensile force of the scraper chain of the scraper conveyor, and the third torque threshold is 30% of the breaking tensile force of the scraper chain of the scraper conveyor.

[0014] Preferably, the acceleration in the third stage satisfies the following condition: the acceleration just decreases to 0 when the output torque of the scraper conveyor head motor reaches a preset third torque threshold.

[0015] Preferably, in the third stage, the angular velocity of the head motor of the scraper conveyor is controlled according to the following formula:

[0016]

[0017] In the formula, ω(t) is the angular velocity of the scraper conveyor head motor at time t, ω0 is the angular velocity of the scraper conveyor head motor when the scraper conveyor is running stably, t1 is the time when entering the second stage, T is the acceleration period coefficient of the third stage, ω(t1) is the angular velocity of the head motor when it is moving at a constant speed in the second stage, and π is pi.

[0018] Preferably, the control method further includes:

[0019] The actual angular velocity of the scraper conveyor head motor is collected in real time.

[0020] The actual angular velocity is used to perform real-time feedback adjustment of the start-up control process of the scraper conveyor; wherein, the feedback adjustment method includes PID feedback adjustment.

[0021] Preferably, the head motor and tail motor of the scraper conveyor are controlled according to the four stages, and in the first stage, the head motor starts after the tail motor starts for a preset time.

[0022] Preferably, the method further includes:

[0023] The output torque of the head motor and tail motor of the scraper conveyor is output in real time.

[0024] The output power of the head motor and tail motor is determined based on the output torque of the head motor and tail motor, respectively.

[0025] Based on the output power of the head motor and tail motor, load power balance control is performed on the head motor and tail motor.

[0026] Preferably, the real-time output of the output torque of the scraper conveyor head motor and tail motor includes:

[0027] The motor parameters of the head motor and tail motor of the scraper conveyor are collected in real time.

[0028] The actual torque of the head motor and tail motor is calculated based on the motor parameters of the head motor and tail motor, respectively.

[0029] The output torque of the scraper conveyor head motor is obtained by using the actual torque of the head motor to adjust the preset torque of the given head motor; and,

[0030] The actual torque of the tail motor is used to adjust the preset torque of the tail motor to obtain the output torque of the scraper conveyor tail motor.

[0031] Preferably, the step of calculating the actual torque of the head motor and tail motor respectively based on the motor parameters of the head motor and tail motor includes:

[0032] The actual torque of the head motor and tail motor is calculated using the following formula:

[0033]

[0034] In the formula, i = 1 or 2, T e1 T represents the actual torque of the head motor of the scraper conveyor. e2 n represents the actual torque of the tail motor of the scraper conveyor. p L represents the number of pole pairs of a motor. m L represents the equivalent mutual inductance between the stator winding and the rotor winding. s Characterizing the transient self-inductance of the stator, L r Characterizing the rotor's equivalent self-inductance, Ψ r Characterizing the rotor flux linkage vector, Ψ s Characterizing the stator flux linkage vector, δ sr1 The load angle δ represents the motor at the head of the scraper conveyor. sr2 Characterizes the load angle of the tail motor of the scraper conveyor.

[0035] As can be seen from the above technical solution, in this embodiment of the invention, the starting process of the scraper conveyor is divided into four stages. A suitable operating speed and operating mode are set in each stage. After the corresponding output torque conditions and chain tension conditions are met between two adjacent stages, the stage transition is carried out, so that the speed change of the entire starting process is smoother, the starting current is smaller, and the mechanical impact is less. As a result, the number of peak scraper chain tension and the number of oscillations are greatly reduced, which improves the service life of the traction mechanism and also improves the safety of the scraper conveyor starting. Attached Figure Description

[0036] Figure 1 This is a speed variation curve of a scraper conveyor chain provided in an embodiment of the present invention.

[0037] Figure 2 This is a graph showing the acceleration change in the third stage, as provided in an embodiment of the present invention. Detailed Implementation

[0038] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Generally, the higher the input frequency, the higher the motor speed, because motor speed is directly proportional to the input frequency. However, the relationship between torque and input frequency is more complex. Under rated load conditions, the motor torque of a scraper conveyor drive motor usually remains constant when the input frequency changes. This is because the frequency converter automatically adjusts the motor's output torque to maintain rated load at different frequencies. Under non-rated load conditions, the motor torque gradually decreases as the input frequency increases. This is because the motor's response time is reduced at high frequencies, leading to a decrease in output torque. Therefore, under non-rated load conditions, torque compensation is usually required to maintain appropriate torque output. In summary, during the heavy-load start-up of a scraper conveyor, the relationship between input frequency and torque depends on the motor's load conditions and the start-up control strategy. Appropriate adjustments and compensations are needed under different load and frequency conditions to achieve the required speed and torque output.

[0040] Based on this, this solution proposes a control method for slow variable power start-up of scraper conveyors, which includes:

[0041] The starting process of the scraper conveyor is divided into four stages. The motors at the head and tail of the scraper conveyor are started according to the following four stages to achieve slow variable power start-up of the scraper conveyor.

[0042] in:

[0043] In the first stage, the machine starts from zero speed and accelerates uniformly, and enters the second stage when the output torque of the scraper conveyor head motor reaches the preset first torque threshold.

[0044] In the second stage, the vehicle moves at a constant speed at the speed it entered in the second stage, and enters the third stage when the chain tension of the scraper conveyor reaches the preset tension threshold.

[0045] In the third stage, the initial speed at which the third stage is entered is used as the initial speed, and the acceleration is gradually increased from 0 to perform variable acceleration motion. When the output torque of the scraper conveyor head motor reaches the preset second torque threshold, the acceleration is gradually decreased to perform variable acceleration motion. And, when the output torque of the scraper conveyor head motor reaches the preset third torque threshold, the fourth stage is entered. Wherein, the first torque threshold < the second torque threshold < the third torque threshold.

[0046] In the fourth stage, it moves at a constant speed, maintaining the speed it had when entering the fourth stage.

[0047] In this embodiment, the scraper conveyor is controlled to start according to the speed change pattern of the above four stages during the start-up phase. The head motor is used as the control motor and the tail motor is used as the follower motor. This allows the scraper conveyor to maintain a smooth speed change during the start-up phase, minimizing mechanical and electrical shocks during the start-up phase under load or heavy load, and reducing the number of chain tension peaks and vibration frequency.

[0048] In one embodiment, the four stages of the scraper conveyor startup process can be given by the following set of calculations:

[0049]

[0050] In the formula, ω(t) is the angular velocity of the scraper conveyor head motor at time t, k represents the starting capability correction coefficient of the scraper conveyor, ω0 is the angular velocity of the scraper conveyor head motor when the scraper conveyor is running stably, t1 is the time of entering the second stage, t2 is the time of entering the third stage from the second stage, t3 is the time of entering the fourth stage from the third stage, T is the acceleration period coefficient of the third stage, ω(t1) is the angular velocity of the head motor when it is moving at a constant speed in the second stage, ω(t3) is the angular velocity of the head motor when it is moving at a constant speed in the fourth stage, and π is pi.

[0051] Where 0-t1 is the first stage, t1-t2 is the second stage, t2-t3 is the third stage, and t3 onwards is the fourth stage. Based on v=ωr, the chain speed curve v(t) of the scraper conveyor can be given, as follows: Figure 1As shown, r is the radius of the motor shaft.

[0052] Both the head motor and tail motor of the scraper conveyor are controlled in four stages. In the first stage, from 0 to t1, the head motor starts after the tail motor has been running for a preset time. This stage represents the initial start-up of the power unit, with the head motor starting slightly later than the tail motor, thus tightening the bottom chain of the scraper chain. Furthermore, in one embodiment, the first torque threshold is 10% of the breaking tension of the scraper chain. That is, when the output torque of the head motor reaches 10% of the breaking tension of the scraper chain, the second stage of startup begins.

[0053] During the second stage, t1-t2, which is a constant speed adjustment process, the variable frequency drive system pulls the chain to maintain a constant speed. During this stage, the chain is automatically tensioned, and the control system adjusts the chain tension. Once the chain tension reaches the preset value, the third stage of startup begins.

[0054] In the third stage, t2-t3, during the acceleration process, the output torque of the tail motor of the scraper conveyor follows the head motor, gradually increasing in speed. The starting acceleration gradually increases from zero, and the scraper chain speed increases accordingly. Then, when the output torque of the head motor reaches the preset second torque threshold, the starting acceleration is slowly reduced. Finally, when the output torque of the head motor reaches the preset third torque threshold, the fourth stage begins. The acceleration a(t) variation curve for this stage is shown below. Figure 2 As shown.

[0055] In one embodiment, the second torque threshold is 15% of the breaking tension of the scraper chain of the scraper conveyor, and the third torque threshold is 30% of the breaking tension of the scraper chain of the scraper conveyor. That is, when the output torque of the head motor reaches 15% of the breaking tension of the scraper chain, the acceleration begins to decrease slowly, and when the output torque of the head motor reaches 30% of the breaking tension of the scraper chain, the fourth stage is initiated.

[0056] Of course, it should be noted here that in the third stage, the acceleration should be reduced to 0 when the output torque of the scraper conveyor head motor reaches the preset third torque threshold.

[0057] After time t3 in the fourth stage, this stage is a uniform motion process. The output torque of the scraper conveyor tail follows the motor of the head, and the drive system traction chain runs at a constant speed v0.

[0058] In one embodiment, to improve the control accuracy of the scraper conveyor, this solution may further include the following process:

[0059] Real-time acquisition of the actual angular velocity of the scraper conveyor head motor;

[0060] The start-up control process of the scraper conveyor is adjusted in real time using the actual angular velocity; the feedback adjustment method includes PID feedback adjustment.

[0061] In this embodiment, by continuously collecting the actual angular velocity of the head motor and feeding it back to the control system, the angular velocity is adjusted through closed-loop control, thereby further improving the control accuracy of the scraper conveyor.

[0062] Because the motor uses a direct-start method, the driving mechanical electrical system consumes a large current, forcing other systems to have lower current, affecting the normal operation of equipment in that current branch, and causing a power imbalance in the scraper conveyor, which may hinder its normal operation. Therefore, in one embodiment, load balancing control is considered for the start-up and operation of the scraper conveyor, which can be achieved in the following way:

[0063] S1: Real-time output of the output torque of the head motor and tail motor of the scraper conveyor;

[0064] S2: Determine the output power of the head motor and tail motor based on their respective output torques;

[0065] S3: Perform load power balance control on the head motor and tail motor based on their output power.

[0066] In one embodiment, step S1, when outputting the output torque of the head motor and tail motor of the scraper conveyor in real time, can be achieved in the following way:

[0067] Real-time acquisition of motor parameters for the head and tail motors of the scraper conveyor;

[0068] The actual torque of the head motor and tail motor is calculated based on their respective motor parameters.

[0069] The output torque of the scraper conveyor head motor is obtained by using the actual torque of the head motor to adjust the preset torque of the given head motor; and,

[0070] The output torque of the scraper conveyor tail motor is obtained by using the actual torque of the tail motor to adjust the preset torque of the given tail motor.

[0071] In this embodiment, the motor parameters of the head motor and tail motor may include the number of pole pairs, the equivalent mutual inductance between the stator winding and the rotor winding, the stator transient self-inductance, the rotor equivalent self-inductance, the stator and rotor flux linkage vectors, and the load angle. It should be noted that in this embodiment, the number of pole pairs, the equivalent mutual inductance between the stator winding and the rotor winding, the stator transient self-inductance, the rotor equivalent self-inductance, and the stator and rotor flux linkage vector parameters are consistent for both the head motor and the tail motor.

[0072] In one embodiment, the actual torque of the computer head motor and tail motor can be calculated using the following formula:

[0073]

[0074] In the formula, i = 1 or 2, T e1 T represents the actual torque of the head motor of the scraper conveyor. e2 n represents the actual torque of the tail motor of the scraper conveyor. p L represents the number of pole pairs of a motor. m L represents the equivalent mutual inductance between the stator winding and the rotor winding. s Characterizing the transient self-inductance of the stator, L r Characterizing the rotor's equivalent self-inductance, Ψ r Characterizing the rotor flux linkage vector, Ψ s Characterizing the stator flux linkage vector, δ sr1 The load angle δ represents the motor at the head of the scraper conveyor. sr2 Characterizes the load angle of the tail motor of the scraper conveyor.

[0075] After calculating the actual torques of the head motor and tail motor respectively, the calculated actual torques are used to adjust the given preset torque. The feedback adjustment method can be PID feedback adjustment, so as to make the output torque of the head motor and tail motor more accurate.

[0076] After obtaining the output torques of the head motor and tail motor, the output power of the head motor and tail motor in step S2 can be calculated using the following formula:

[0077]

[0078] In the formula, i = 1 or 2, which refer to the head motor and tail motor respectively, P1 represents the output power of the head motor, P2 represents the output power of the tail motor, ω1 represents the angular velocity of the head motor, and ω2 is the angular velocity of the tail motor.

[0079] In step S3, when performing power balance control on the head motor and tail motor, the load angle δ of the head motor and tail motor is adjusted. sr1 and δ sr2This ensures that the output power of the head motor and the tail motor are consistent, or that the output current of the head motor and the tail motor are consistent, thereby achieving power balance between the head motor and the tail motor, which in turn reduces the instantaneous starting current of the scraper conveyor and alleviates sudden torque changes.

[0080] The modules or units in the device of this invention can be merged, divided, and deleted according to actual needs. The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the invention. Those skilled in the art will understand that implementing all or part of the processes of the above embodiments and making equivalent changes according to the claims of this invention still fall within the scope of the invention.

Claims

1. A control method for slow variable power start-up of a scraper conveyor, characterized in that, include: The starting process of the scraper conveyor is divided into four stages. The motors at the head and tail of the scraper conveyor are started according to the following four stages to achieve slow variable power start-up of the scraper conveyor. in: In the first stage, the machine starts from zero speed and accelerates uniformly, and enters the second stage when the output torque of the scraper conveyor head motor reaches the preset first torque threshold. In the second stage, the machine moves at a constant speed at the speed when entering the second stage, and enters the third stage when the chain tension of the scraper conveyor reaches a preset tension threshold. In the third stage, the initial speed at which the third stage is entered is used as the initial speed, and the acceleration is gradually increased from 0 to perform variable acceleration motion. When the output torque of the scraper conveyor head motor reaches a preset second torque threshold, the acceleration is gradually decreased to perform variable acceleration motion. And when the output torque of the scraper conveyor head motor reaches a preset third torque threshold, the fourth stage is entered. Wherein, the first torque threshold < the second torque threshold < the third torque threshold. In the fourth stage, it moves at a constant speed at the speed it entered the fourth stage. The acceleration in the third stage satisfies the following condition: the acceleration decreases to 0 exactly when the output torque of the scraper conveyor head motor reaches a preset third torque threshold; and the angular velocity of the scraper conveyor head motor is controlled according to the following formula: ； In the formula, Let be the angular velocity of the scraper conveyor head motor at time t. The angular velocity of the head motor during stable operation of the scraper conveyor is given by t1, where t1 is the moment of entering the second stage, and T is the acceleration period coefficient of the third stage. The angular velocity of the head motor during the uniform motion in the second stage. Pi; The head motor and tail motor of the scraper conveyor are controlled according to the four stages, and in the first stage, the head motor starts after the tail motor starts for a preset time.

2. The control method for slow variable power start-up of a scraper conveyor according to claim 1, characterized in that, The first torque threshold is 10% of the breaking tensile force of the scraper chain of the scraper conveyor.

3. The control method for slow variable power start-up of a scraper conveyor according to claim 2, characterized in that, The second torque threshold is 15% of the breaking tensile force of the scraper chain of the scraper conveyor, and the third torque threshold is 30% of the breaking tensile force of the scraper chain of the scraper conveyor.

4. The control method for slow variable power start-up of a scraper conveyor according to claim 1, characterized in that, The control method further includes: The actual angular velocity of the scraper conveyor head motor is collected in real time. The actual angular velocity is used to perform real-time feedback adjustment of the start-up control process of the scraper conveyor; wherein, the feedback adjustment method includes PID feedback adjustment.

5. The control method for slow variable power start-up of a scraper conveyor according to claim 1, characterized in that, The method further includes: The output torque of the head motor and tail motor of the scraper conveyor is output in real time. The output power of the head motor and tail motor is determined based on the output torque of the head motor and tail motor, respectively. Based on the output power of the head motor and tail motor, load power balance control is performed on the head motor and tail motor; The real-time output of the output torque of the head motor and tail motor of the scraper conveyor includes: The motor parameters of the head motor and tail motor of the scraper conveyor are collected in real time. The actual torque of the head motor and tail motor is calculated based on the motor parameters of the head motor and tail motor, respectively. The output torque of the scraper conveyor head motor is obtained by using the actual torque of the head motor to adjust the preset torque of the given head motor; and, The actual torque of the tail motor is used to adjust the preset torque of the tail motor to obtain the output torque of the scraper conveyor tail motor. The step of calculating the actual torque of the head motor and tail motor respectively based on the motor parameters of the head motor and tail motor includes: The actual torque of the head motor and tail motor is calculated using the following formula: ； In the formula, i = 1 or 2, Characterizes the actual torque of the head motor of the scraper conveyor. Characterizes the actual torque of the tail motor of the scraper conveyor. Characterizing the number of pole pairs of a motor, Characterizing the equivalent mutual inductance between the stator winding and the rotor winding. Characterizing the transient self-inductance of the stator, Characterizing the rotor's equivalent self-inductance, Characterizing the rotor flux linkage vector, Characterizing the stator flux linkage vector, Characterizing the load angle of the head motor of the scraper conveyor. Characterizes the load angle of the tail motor of the scraper conveyor.

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