Frequency converter control method based on state detection and load adaptive adjustment

Abstract

The invention relates to the technical field of coal mine mechanical equipment, and discloses a frequency converter control method based on state detection and load adaptive adjustment, which comprises the following steps: when a starting command is waited after a frequency converter is shut down, calling an event at the last moment and shutdown data to judge whether a control strategy is adjusted in next starting; after the frequency converter receives the starting command, the output rotating speed, the torque and the current value are monitored in real time to trigger abnormal starting identification; if the stator resistance changes, the identification parameters are stored, and then the normal starting mode is executed; if the stator resistance is abnormal, a frequency converter fault is output; if the stator resistance does not change, self-adaptive chain clamping identification is carried out according to the output rotating speed, the torque and the current value, self-adaptive adjustment is carried out on the frequency converter in the chain clamping state, and a normal starting mode is executed after chain clamping is removed. According to the invention, dynamic adjustment can be carried out according to load changes and specific abnormal conditions, so that the stability and reliability of equipment are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of coal mine mechanical equipment, and particularly relates to a frequency converter control method based on state detection and load adaptive adjustment. Background Art

[0002] Scraper conveyors are widely used in underground coal mines and other mines for transporting coal mine materials. Due to their complex working environment and large load fluctuations, especially during the startup process, abnormal working conditions such as difficult heavy-load startup, chain jamming, and chain breakage of the scraper chain often occur, resulting in the inability of the frequency converter to start smoothly, and in severe cases, the equipment may be damaged.

[0003] Currently, the abnormal working conditions commonly encountered by scraper conveyors include difficult startup, chain jamming, and chain breakage of the scraper chain. The occurrence mechanisms of the above abnormal working conditions are summarized as follows: Among them, difficult startup includes difficult heavy-load startup and difficult startup caused by parameter changes.

[0004] Difficult heavy-load startup - Since the output torque of conventional frequency converters is a fixed value and does not have the ability to adapt according to the load condition and the output capacity of the frequency converter, it is caused by insufficient output overload torque during startup; under heavy-load conditions, the torque limit value of the frequency converter can be adjusted short-term to meet the current heavy-load startup. How to obtain a suitable torque limit value to carry out the specified solution method, which not only meets the on-site heavy-load startup but also makes the output current value within the safe range of the IGBT.

[0005] Difficult startup caused by parameter changes - Generally, as the output cable of the coal mining face is cut during coal mining, the cut cable causes a change in the resistance value, and this resistance value is calculated in the stator resistance, directly affecting the failure of the closed-loop control of the frequency converter and ultimately resulting in difficult startup.

[0006] Chain jamming of the scraper chain - There are many factors causing chain jamming, such as large hard objects, anchor bolts, and mechanical structure damage. According to the output characteristics of the frequency converter after chain jamming, that is, the torque and current rise rapidly within a short time, but the speed is zero. At this time, the conventional frequency converter will detect the output current and trigger overcurrent protection and stop when the current rises to the overcurrent threshold. This method can only protect the frequency converter but cannot effectively identify the cause of overcurrent, because if the length of the external cable of the frequency converter changes, it will also cause abnormal startup and ultimately trigger overcurrent protection.

[0007] Chain breakage of the scraper chain - Chain breakage occurs under long-term overload or extreme tensile force conditions, resulting in fatigue of the scraper chain and ultimately breakage. When the chain breaks, the frequency converter needs to immediately make protection. If it cannot stop and protect in time, the chain breakage may cause damage to other components, such as chain troughs, sprockets, motors, etc. The damage of these components will increase the maintenance cost, and increase the cleaning difficulty and the time for resuming production, bringing great troubles to the maintenance.

[0008] Most of the inverter control strategies in the prior art are preset and cannot be dynamically adjusted according to the changes in the load and specific abnormal situations. Therefore, it is necessary to propose an inverter control strategy based on load self - adaptation for the special working environment of the scraper conveyor to improve the stability and reliability of the equipment. Summary of the Invention

[0009] In view of the above - mentioned deficiencies in the prior art, the present invention provides a frequency converter control method based on state detection and load self - adaptation adjustment.

[0010] In order to achieve the above - mentioned invention purpose, the technical solution adopted by the present invention is as follows: A frequency converter control method based on state detection and load self - adaptation adjustment, comprising the following steps: When waiting for a start command after the frequency converter stops, retrieve the events and shutdown data at the previous moment to determine whether to adjust the control strategy for the next start; if so, execute the heavy - load start mode to adjust the frequency converter parameters; otherwise, execute the normal start mode; After the frequency converter receives the start command, monitor the output speed, torque, and current values in real time to trigger abnormal start identification; if the stator resistance changes, store the identification parameters and then execute the normal start mode; if the stator resistance is abnormal, output a frequency converter fault; if the stator resistance does not change, perform adaptive chain - stuck identification based on the output speed, torque, and current values, perform adaptive adjustment on the frequency converter in the chain - stuck state, and execute the normal start mode after getting rid of the chain - stuck state.

[0011] Further, when retrieving the events and shutdown data at the previous moment to determine whether to adjust the control strategy for the next start, If the output torque is greater than the rated torque and the normal shutdown is without faults, execute the heavy - load start mode, increase the start torque, and at the same time increase the limit value of the start torque amplitude; If the output torque is less than or equal to the rated torque and the normal shutdown is without faults, execute the normal start mode.

[0012] Further, when monitoring the output speed, torque, and current values in real time to trigger abnormal start identification, Judge whether it satisfies that from the moment of receiving the start signal to the time T - 1S of allowing the long - time working current, and the real - time torque ≤ the real - time torque at the previous moment, and the real - time speed ≤ the rated speed / acceleration time × delay judgment time T - 1S × coefficient 80%; if so, trigger abnormal start identification; otherwise, do not trigger abnormal start identification.

[0013] Further, when triggering abnormal start identification, Inject a low - frequency signal, continuously collect voltage and current in multiple cycles, and calculate the average value of the stator resistance of the motor; When there are peaks or valleys in the current waveform, or the overcurrent threshold is directly triggered, or the sum of the three-phase identification currents is not zero, it is determined that the stator resistance is abnormal and the frequency converter fault is output.

[0014] Furthermore, when performing adaptive chain jamming identification based on the output speed, torque, and current values, it is judged whether the ratio of current to speed is greater than the set threshold and the motor slip rate approaches 1; if so, it is identified as the chain jamming state; otherwise, it is identified as the non-chain jamming state.

[0015] Furthermore, when performing adaptive adjustment on the frequency converter in the chain jamming state, the current and voltage values are detected in real time in the chain jamming state. When the current exceeds the set maximum current threshold, the current is limited to the maximum current threshold, and when the voltage exceeds the set maximum voltage threshold, the voltage is limited to the maximum voltage threshold.

[0016] Furthermore, when performing adaptive adjustment on the frequency converter in the chain jamming state, the acceleration time is dynamically adjusted by the following formula: Tacc(t)=Tmax / (1 + k×s(t)) where Tacc(t) is the acceleration time after dynamic adjustment, Tmax is the maximum acceleration time, k is the adjustment gain, s(t) is the slip rate, and t is the running time.

[0017] Furthermore, when performing adaptive adjustment on the frequency converter in the chain jamming state, the output frequency is dynamically adjusted by the following formula: F’(t)=f(t)-α×△I(t) where F’(t) is the output frequency after dynamic adjustment, f(t) is the real-time output frequency, α is the proportionality coefficient, △I(t) is the current change amount, and t is the running time.

[0018] Furthermore, when performing adaptive adjustment on the frequency converter in the chain jamming state, if the chain jamming state is not escaped, the direction given signal and the running given signal are received, the running given signal is transiently inverted, the received direction given signal is alternately inverted and output, and at the same time, the speed, torque, fault state, and current are monitored in real time, the maximum torque current value is calculated and output, and the torque limit current value is adaptively corrected according to the maximum torque that the chain of the scraper conveyor can withstand and the maximum temperature of the IGBT junction temperature.

[0019] Furthermore, when adaptively correcting the torque limit current value, the load torque at the last shutdown, the load current at the last shutdown, the current load torque, the current load current, the current torque limit value, the maximum torque limit value, the minimum torque limit value, and the increment coefficient for each adjustment are retrieved; Calculate the torque limit based on the last load torque and the current load condition: T_start=T_load+T_inertia Among them, T_start is the minimum torque required at startup, T_load is the load torque, and T_inertia is the dynamic inertia torque; If the current load torque is greater than the load torque at the last shutdown, the maximum torque limit value will be increased according to the incremental factor.

[0020] The present invention has the following beneficial effects: (1) The present invention realizes automatic identification of fault types between the frequency converter and the scraper conveyor, and implements targeted processing strategies by distinguishing between electrical and mechanical problems; (2) The present invention does not require human intervention. When the output cable length changes, the inverter automatically recognizes and performs identification operations; (3) The present invention can protect the scraper conveyor and prevent the inverter from continuously outputting large torque, which may cause the scraper conveyor to break or cause mechanical damage; (4) The present invention has accurate fault judgment and can accurately locate the fault without the aid of sensors other than the frequency converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The present invention is a flow chart of a frequency converter control method based on state detection and load adaptive regulation. DETAILED DESCRIPTION

[0022] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0023] like Figure 1 As shown, an embodiment of the present invention provides a frequency converter control method based on state detection and load adaptive adjustment, comprising the following steps S1 and S2: S1: When the inverter is waiting for the start command after stopping, the event and shutdown data of the previous moment are retrieved to determine whether the control strategy should be adjusted for the next start; if so, the heavy load start mode is executed to adjust the inverter parameters; otherwise, the normal start mode is executed; In an optional embodiment of the present invention, when step S1 retrieves the previous event and shutdown data to determine whether to adjust the control strategy at the next startup, If the output torque is greater than the rated torque and the normal stop is without fault, then the heavy-load starting mode is executed, the starting torque is increased, and at the same time, the limit value of the starting torque is amplified. If the output torque is less than or equal to the rated torque and the normal stop is without fault, then the normal starting mode is executed.

[0024] In this embodiment, starting from the ready stage of the frequency converter (waiting for the start command after stopping), when the frequency converter receives the start instruction, by retrieving the events and stop data at the previous moment (the data includes values such as current, torque, and water-cooled plate temperature), the main controller of the frequency converter determines whether the control strategy needs to be adjusted for the next start.

[0025] The judgment logic is as follows: If Tout (output torque) ≤ Trated (rated torque) and the normal stop is without fault, then it is judged as light load, and the program segment ① (normal starting mode) is jumped to for the next start.

[0026] Program segment ① (normal starting mode): The normal torque limit value. Since there will be no large starting current for the next start, there will be no rapid junction temperature rise for the IGBT. Stop the external cooling water circulation to prevent temperature difference in the cavity from causing condensation on the water-cooled plate, and then wait for the start signal.

[0027] If Tout (output torque) > Trated (rated torque) and the normal stop is without fault, then it is judged as heavy load, and the program segment ② (heavy-load starting mode) is jumped to for the next start.

[0028] Program segment ② (heavy-load starting mode): Retrieve the Tout (output torque) at the stop moment. Since the frequency converter needs to overcome the inertia and resistance of the load to accelerate the load from the stationary state to the normal operating state for the next start. Its magnitude is usually larger than the torque during normal operation. To accelerate the load from the stationary state to the normal operating state. Its magnitude is usually larger than the torque at the stop. Therefore, the control system automatically adjusts the starting torque value for the next start. Generally speaking, the starting torque can be set to 1.5 to 2 times the rated torque.

[0029] While increasing the starting torque, the starting current will exceed the rated current. Under normal load operation conditions, to protect the frequency converter and the motor, the torque limit value is equal to the rated torque. Therefore, it is necessary to amplify the starting torque limit value to the required value to avoid the short-term torque peak during starting and prevent the inverter controller from protecting in advance. The starting torque Tstart is usually greater than or equal to the load torque Tload. The relationship between the starting torque and the stop torque is usually Tstart = C × Tload, where C is a coefficient, usually 1.5. This value varies slightly according to the control algorithm and load characteristics and can also be obtained in advance through testing.

[0030] In addition, due to the impact of current exceeding the rated current during the next startup, to prevent the IGBT from burning out due to junction temperature, the frequency converter controls the external cooling water tank to close with a time delay, and stops the cooling water when the temperature of the water-cooled plate approaches the water temperature. Then wait for the startup signal.

[0031] S2. After the frequency converter receives the startup command, it monitors the output speed, torque, and current values in real time to trigger abnormal startup identification; if the stator resistance changes, it stores the identification parameters and then executes the normal startup mode; if the stator resistance is abnormal, it outputs a frequency converter fault; if the stator resistance does not change, it performs adaptive stuck-chain identification based on the output speed, torque, and current values, performs adaptive adjustment on the frequency converter in the stuck-chain state, and executes the normal startup mode after getting rid of the stuck chain.

[0032] In an optional embodiment of the present invention, when step S2 monitors the output speed, torque, and current values in real time to trigger abnormal startup identification, it is judged whether it satisfies the condition that from the moment of receiving the startup signal to the time T - 1S of allowing long-time working current, and the real-time torque ≤ the real-time torque of the previous moment, and the real-time speed ≤ the rated speed / acceleration time × delay judgment time T - 1S × coefficient 80%; if so, it triggers abnormal startup identification; otherwise, it does not trigger abnormal startup identification.

[0033] When step S2 triggers abnormal startup identification, by injecting a low-frequency signal, continuously collect voltage and current in multiple cycles, and calculate the average value of the stator resistance of the motor; When there are peaks or valleys in the current waveform, or directly trigger the overcurrent threshold, or the sum of the three-phase identification currents is not zero, it is judged that the stator resistance is abnormal and a frequency converter fault is output.

[0034] When step S2 performs adaptive stuck-chain identification based on the output speed, torque, and current values, it is judged whether it satisfies the condition that the ratio of current to speed is greater than the set threshold and the slip ratio of the motor approaches 1; if so, it is identified as the stuck-chain state; otherwise, it is identified as the non-stuck-chain state.

[0035] When step S2 performs adaptive adjustment on the frequency converter in the stuck-chain state, in the stuck-chain state, the current and voltage values are detected in real time. When the current exceeds the set maximum current threshold, the current is limited to the maximum current threshold, and when the voltage exceeds the set maximum voltage threshold, the voltage is limited to the maximum voltage threshold.

[0036] When step S2 performs adaptive adjustment on the frequency converter in the stuck-chain state, dynamically adjust the acceleration time through the following formula: Tacc(t)=Tmax / (1 + k×s(t)) Among them, Tacc(t) is the acceleration time after dynamic adjustment, Tmax is the maximum acceleration time, k is the adjustment gain, s(t) is the slip ratio, and t is the running time.

[0037] When step S2 performs adaptive adjustment on the frequency converter in the chain jamming state, dynamically adjust the output frequency through the following formula: F’(t)=f(t)-α×△I(t) Among them, F’(t) is the output frequency after dynamic adjustment, f(t) is the real-time output frequency, α is the proportionality coefficient, △I(t) is the current change amount, and t is the running time.

[0038] When step S2 performs adaptive adjustment on the frequency converter in the chain jamming state, if the chain jamming state is not escaped, then receive the direction given signal and the running given signal, transiently invert the running given signal, alternately invert the received direction given signal and output it, and at the same time, monitor the rotational speed, torque, fault state, and current in real time, calculate and output the maximum torque current value, and adaptively correct the torque limit current value according to the maximum torque that the chain of the scraper conveyor can withstand and the maximum temperature of the IGBT junction temperature.

[0039] When step S2 adaptively corrects the torque limit current value, retrieve the load torque at the last shutdown, the load current at the last shutdown, the current load torque, the current load current, the current torque limit value, the maximum torque limit value, the minimum torque limit value, and the increment coefficient for each adjustment; Calculate the torque limit according to the previous load torque and the current load condition: T_start=T_load+T_inertia Among them, T_start is the minimum torque required at startup, T_load is the load torque, and T_inertia is the dynamic inertia torque; If the current load torque is greater than the load torque at the last shutdown, increase the maximum torque limit value by the increment coefficient.

[0040] In the startup stage of this embodiment, when the frequency converter receives the startup signal, it jumps to the startup anomaly judgment program segment ③, executes the running command, and at the same time monitors the output rotational speed, torque, and current values in real time.

[0041] The judgment of the startup anomaly trigger conditions is as follows: (1) Between the start time of receiving the startup signal and the time T - 1S when the long-time working current is allowed (2) The real-time torque T ≤ the real-time torque T front at the previous moment (3) The real-time rotational speed ≤ the rated rotational speed / acceleration time × delay judgment time T - 1S × coefficient 80% After meeting the above conditions, trigger the abnormal state startup program segment ④.

[0042] In program segment ④, first, adjust the inverter setting parameters to the fast identification mode. In this mode, there is no need to rotate the motor, only the stator resistance is identified. By comparing the newly identified stator resistance with the previously identified stator resistance value, it is judged whether the winding is abnormal and whether the cable length has changed.

[0043] When the value of the motor stator resistance changes, the identification program segment ⑤ will be executed. (This program segment will judge three situations. The first is that the cable length change causes abnormal startup, then store the identification parameters and execute the normal startup command. The second is that the stator resistance value is abnormal, judge the motor winding or execute the algorithm steps of abnormal identification). The third is that the stator resistance value does not change, then jump to program segment ⑥.

[0044] Program segment ⑤ activates the static identification mode. Since only the stator resistance needs to be identified, this value can be obtained by injecting a low-frequency signal (the advantage of this is that the inductance effect can be ignored, and Ohm's law can still be followed, making it easier to calculate). The voltage and current are continuously collected within multiple cycles, and the average value R(measured) of the motor stator resistance is calculated. If the oscillation is severe and exceeds the normal value during the injection of the low-frequency signal during the identification process, it is judged as a problem with the peripheral cable or the motor, and the frequency converter reports a fault and gives maintenance suggestions. If the injection of the low-frequency signal is normal, the identification parameters are stored in the main board, used as identification parameter control calculations, and direct startup can be performed.

[0045] The main problems with the peripheral cable or the motor are disconnection and short circuit. When the frequency converter operates in the normal identification state, its current and voltage waveforms generally show a certain regularity and stability; Judgment conditions: When there is an inter-turn short circuit or an output cable short circuit in the motor, it causes sudden peaks or valleys to appear in the current waveform, or directly triggers the overcurrent threshold; When there is an open circuit, the sum of the three-phase identification currents is no longer zero, and the current of one or two open-circuited phases is zero.

[0046] In program segment ⑥, the chain jam is judged. If the motor resistance does not change, it is judged whether there is a chain jam. By real-time monitoring of parameters such as current, speed, and slip, the frequency converter can judge the possibility of a chain jam. Because when there is a chain jam, the motor load increases sharply, resulting in an increase in current, while the speed increase is limited, or the speed change rate decreases. Based on the above characteristics, the adaptive chain jam identification conditions are as follows: Condition 1: The frequency converter can use the ratio of current and speed to judge the chain jam problem. The ratio of current to speed is judged as: =I(t) / n(t); under normal circumstances, the ratio of current and speed should be stable. If the ratio increases significantly (for example, the current increases but the speed does not increase accordingly), it is satisfied.

[0047] When the chain is jammed, the motor is in a stalled state. Since the rotational speed n(t) of the motor approaches 0 at this moment but will not be 0, the rotational speed of the motor cannot catch up with the synchronous speed, resulting in the inability to generate rotational speed. Consequently, the current rises rapidly, and the ratio of current to rotational speed I(t) / n(t) will increase sharply. The judgment is as follows: (1) Obtain the current signal: Collect the current value at regular intervals.

[0048] (2) Obtain the actual rotational speed value: Synchronize with the current sampling period.

[0049] (3) Determine whether the ratio of current to rotational speed is abnormally high: Set a threshold, which is usually 5 - 7 times the rated current of the motor. When the ratio of current to rotational speed exceeds the threshold, the set flag 1 is output.

[0050] (4) Duration check: To prevent misjudgment caused by detection, according to the output set flag, continuously detect within the set time T. If the output set flag is always 1, it is judged as chain jamming.

[0051] Condition 2: For an induction motor, the slip S is closely related to the load. By detecting the increase in slip, the frequency converter can infer whether the motor is in a chain-jammed state because the slip will increase during chain jamming.

[0052] In the chain-jammed state, that is, when the motor is stalled, the slip of the motor at this time is 100%. The calculation is as follows: 1. The calculation formula for slip: The slip S is defined as: S = (ns - n) / ns; where ns is the synchronous speed (unit: rpm); n is the actual rotational speed of the motor (unit: rpm); Generally, the slip is close to 0 under no-load conditions and reaches approximately 10% - 15% under full-load conditions 2. Slip under the stalled state Since the rotational speed of the motor is 0 during stalling, that is, n = 0, the slip s is approximately: (Note: Most actual frequency converters are without speed sensors, and the rotational speed is deduced from the detected current and voltage. Due to problems such as the accuracy of current and voltage sensors, the detected rotational speed value approaches 0) Smax = (ns - 0) / ns = 1 At this time, the slip increases significantly, and it is judged as chain jamming.

[0053] If it is determined as chain jamming, it enters the program segment ⑦ chain-jammed operation mode. The chain-jammed operation mode is divided into two segments, namely program segment ⑧ and program segment ⑨. If the program segment ⑧ is completed and the chain jamming has not been resolved, it enters the program segment ⑨.

[0054] Adaptive adjustment of control strategy under the condition of the program segment ⑧ being stuck. The frequency converter needs to adjust the control strategy of the motor to gradually get rid of the stuck phenomenon. The following are several key adjustment strategies: (1)Limit current and voltage output: To reduce current impact and avoid motor damage, the frequency converter should actively limit the current and voltage output after detecting the stuck situation and smoothly adjust the load. This can be achieved by gradually reducing the voltage or current and slowing down the motor acceleration rate.

[0055] Current limit formula: I(t) = min(I(t), Imax) When the current I(t) exceeds the set maximum current threshold Imax, the frequency converter will limit the current to this threshold to avoid motor overload caused by excessive current.

[0056] Voltage limit formula: V(t) = min(V(t), Vmax) Similarly, when the motor load is too large, the frequency converter can limit the output voltage V(t) to avoid motor overload. By reducing the voltage, the output torque of the motor decreases, thereby reducing the load.

[0057] (2)Prolong the acceleration time: When detecting the stuck situation, the frequency converter can slow down the current peak and load impact by prolonging the acceleration time. This method can effectively reduce the current impact during the startup process and avoid the motor from bearing excessive load in a short time.

[0058] Acceleration time adjustment formula: Tacc(t)=Tmax / (1 + k×s(t)) Where: Tacc(t) is the dynamically adjusted acceleration time, Tmax is the maximum acceleration time, k is the control gain, which determines the amplitude of acceleration prolongation, and s(t) is the slip rate, which reflects the increase in load.

[0059] When the slip s(t) increases, the frequency converter will automatically increase the acceleration time Tacc(t) to make the motor accelerate more smoothly and avoid excessive current.

[0060] (3)Dynamically adjust the output frequency: The frequency converter can slow down the motor acceleration by adjusting the output frequency. By reducing the frequency, the frequency converter can effectively reduce the motor load and avoid the sudden increase in current and torque. At this time, the motor load is gradually released to avoid overload.

[0061] Frequency adjustment formula: f(t) = f(t) - α×△I(t) Where: f(t) is the real-time output frequency, α is the proportional coefficient for frequency adjustment, and △I(t) is the current change amount.

[0062] When the current increases, the frequency converter will appropriately reduce the frequency to prevent the motor from accelerating too fast due to excessive load.

[0063] If the program segment ⑧ still cannot get rid of the jamming, then execute the program segment ⑨ S-curve operation mode. Give signals from the receiving direction and the running direction, and take the transient inversion of the running given signal. The received direction given signal is alternately inverted and output. At the same time, monitor the actual speed, actual torque, fault status, and actual current, and calculate the maximum torque current value. This value adaptively corrects the torque limit current value according to the maximum torque that the chain of the scraper conveyor can withstand and the maximum temperature of the IGBT junction temperature.

[0064] Controlling the output torque in the frequency converter is to control the torque current. First, calculate the required torque as follows: Approximate estimation formula: T_start = T_load + T_inertia; Where: T_start is the minimum torque required at startup, T_load is the load torque, which is confirmed according to the load at shutdown, and T_inertia is the dynamic inertia torque, which is related to the mass and acceleration of the motor. It can be calculated by the formula T_inertia = J ×Δω / Δt, where J is the load moment of inertia and Δω / Δt is the change rate of the difference between the initial speed and the final speed of the load divided by time.

[0065] After calculating the torque above, the relationship between the motor torque and the current can usually be expressed by the following formula: T = CT×Φ×Ia Where: T is the torque of the motor; CT is the torque constant, which is related to the structure of the motor; Φ is the main magnetic flux per pole; Ia is the armature current, that is, the torque current.

[0066] Substitute the known torque T, magnetic flux Φ, and torque constant CT, and solve for Ia to obtain the torque current.

[0067] The steps for adaptively correcting the torque limit current value are as follows: 1. Retrieve data, including the load torque T (last_shutdown_torque) at the last shutdown, the load current I (last_shutdown_current) at the last shutdown, the current load torque T (current_load_torque), the current load current I (current_load_current), the current torque limit value T (torque_limit), the maximum torque limit value T (max_torque_limit), the minimum torque limit value T (min_torque_limit), and the increment coefficient f (torque_adjustment_factor) for each adjustment.

[0068] 2. Calculate the torque limit according to the previous shutdown torque Tload and the current load condition (Reply: I don't understand the torque limit calculation here and the beginning part. This is a real-time adjustment and requires precise calculation. The calculation is as follows: First, calculate the starting torque Tstart, Tstart = Tload + △T, where △T is the additional torque generated by the short peak during the motor acceleration process to establish the magnetic field required for motor startup. Assume the startup time is t). Determine the change in the load torque. If the current load torque is greater than the load torque at the last shutdown, increase it by the increment coefficient, with the maximum not exceeding the maximum torque limit value T (max_torque_limit).

[0069] The calculation here is the same as the calculation of the maximum torque current above. Calculate the required torque as follows: Approximate estimation formula: T_start = T_load + T_inertia; Where: T_start is the minimum torque required during startup, and T_load is the load torque, which is confirmed according to the load at shutdown.

[0070] 1. T_inertia is the dynamic inertia torque, which is related to the mass and acceleration of the motor. It can be calculated by the formula T_inertia = J ×Δω / Δt, where J is the load moment of inertia, and Δω / Δt is the difference between the initial speed and the final speed of the load divided by the rate of change of time.

[0071] The method for incrementally adjusting the torque limit value based on the change in the load torque is as follows: Input: T_current: Current load torque T_last_shutdown: Load torque at the last shutdown T_limit_current: Current maximum torque limit value increment_factor: Increment coefficient used to determine the amount of torque increased each time T_limit_max: Preset maximum torque limit value Process: Initialization: Record the load torque T_last_shutdown at the last shutdown (this value is updated at each shutdown).

[0072] • Set the initial maximum torque limit value T_limit_current (this value is determined by the output capacity of the frequency converter).

[0073] 2. Compare the current load torque with the load torque at the last shutdown: • If T_current is greater than T_last_shutdown, proceed to the following steps; • Otherwise, keep T_limit_current unchanged and end the algorithm.

[0074] 1. Calculate the new maximum torque limit value: 1. Calculate the increment according to the increment factor increment_factor: delta_T = increment_factor (note: here increment_factor can directly represent the increased torque amount, which is a proportional coefficient and specifically depends on its set value).

[0075] 2. Calculate the new maximum torque limit value: T_limit_new = T_limit_current + delta_T.

[0076] 2. Check whether the new maximum torque limit value exceeds the preset maximum value: 1. If T_limit_new is greater than T_limit_max, set T_limit_new to T_limit_max.

[0077] 2. Otherwise, keep the calculated value of T_limit_new.

[0078] 3. Update the maximum torque limit value: 1. Update T_limit_current to T_limit_new.

[0079] 4. Record the current load torque as the load torque at the next shutdown: 1. Assign the value of T_current to T_last_shutdown for use in the next algorithm run.

[0080] 5. End the algorithm: The algorithm ends and waits for the next run (when new load torque data is available, or after the system is shut down and restarted).

[0081] Through program segment ⑨, reverse reasoning and inertia are used to unjam the chain. At the beginning, the amplitude of the reverse operation is small to avoid additional damage to the motor and conveyor chain caused by excessive impact force. At this time, the frequency converter adopts S-shaped acceleration and deceleration curves to smooth the rise and fall of the motor speed. Then, gradually increase the time and amplitude of the reverse rotation to unjam it through the vibration of the chain; after each reverse operation, the frequency converter will judge whether the chain is unjammed according to the changes in current, torque and speed. If the current and torque return to normal, the system will call out this program segment and execute the normal start mode.

[0082] The frequency converter has acceleration and deceleration curves during operation (that is, the acceleration and deceleration are carried out according to the set slope). In the stop mode, automatic stop and decelerated stop can be selected. Automatic stop is used under normal circumstances, and it is modified to decelerated stop when entering this program segment. That is, decelerate from the current speed to 0, linearly ramp up and down according to the deceleration time, and achieve the effect of smooth starting speed.

[0083] This embodiment increases the reverse time, that is, the dead time, and the process is as follows: Set the initial forward rotation time (T_forward_init) and reverse rotation time (T_reverse_init).

[0084] Determine the increments of time and amplitude (delta_T and delta_A).

[0085] Set the upper limits of the forward and reverse rotation times (T_forward_max and T_reverse_max), and the upper limit of the amplitude (A_max).

[0086] 1) At the beginning of each cycle, check whether the current forward and reverse rotation times have reached the preset upper limits. If so, stop increasing the time, but the amplitude can still be adjusted (if the amplitude has not reached the upper limit).

[0087] 2) Update the forward and reverse rotation times and the operation amplitude according to the algorithm.

[0088] 3) Output the control parameters of the current cycle and send them to the frequency conversion main controller to execute the corresponding motor control.

[0089] 4) When both the forward and reverse rotation times reach the maximum values and the amplitude has also reached the upper limit, the algorithm stops iterating.

[0090] In this embodiment, the motor speed tends to zero in the case of chain jamming by judging the speed.

[0091] The rotational speed can be judged by the frequency, because the output rotational speed and the output frequency are in direct proportion.

[0092] The rotational speed is the synchronous speed minus the slip, that is, ωr = ω1 - ω2.

[0093] The slip of the motor is calculated according to the following formula ; "Slip = rotor resistance × stator torque current in vector control / flux reference value".

[0094] The synchronous speed can be calculated according to the following formula e = u s -r s i s -ω1L σ i s "Rotor back electromotive force = stator voltage - stator resistance voltage drop - stator leakage inductance electromotive force" The present invention is used for the control strategy of a frequency converter driving a scraper conveyor. The frequency converter can effectively identify the operating state of the scraper conveyor by monitoring parameters, and the state includes normal load operation.

[0095] The present invention is used for the control strategy of a frequency converter driving a scraper conveyor. The frequency converter monitors parameters to effectively identify the operating state of the scraper conveyor and adjusts the corresponding control strategy according to different states.

[0096] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, and the combination of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate a device for realizing the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0097] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured article including an instruction device, and the instruction device realizes the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0098] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus, so as to cause a series of operation steps to be performed on the computer or other programmable apparatus to generate a computer-implemented process, thereby the instructions executed on the computer or other programmable apparatus provide steps for realizing the functions specified in one process or a plurality of processes and / or blocks. Figure 1 one process or a plurality of processes and / or blocks Figure 1 and steps for realizing the functions specified in one block or a plurality of blocks.

[0099] In the present invention, specific embodiments are used to elaborate the principles and implementation manners of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the present invention.

[0100] Those of ordinary skill in the art will realize that the embodiments described herein are for helping the reader understand the principles of the present invention, and it should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those of ordinary skill in the art can make various other specific deformations and combinations without departing from the essence of the present invention according to the technical revelations disclosed in the present invention, and these deformations and combinations are still within the protection scope of the present invention.

Claims

1. A frequency converter control method based on state detection and load adaptive adjustment, characterized in that, It includes the following steps: When waiting for a start command after the frequency converter stops, retrieve the events and shutdown data at the previous moment to determine whether to adjust the control strategy for the next start; If so, execute the heavy-load start mode to adjust the parameters of the frequency converter; otherwise, execute the normal start mode; After the frequency converter receives the start command, monitor the output speed, torque, and current values in real time to trigger abnormal start identification; If the stator resistance changes, store the identification parameters and then execute the normal start mode; if the stator resistance is abnormal, output a frequency converter fault; if the stator resistance does not change, perform adaptive chaining identification based on the output speed, torque, and current values, perform adaptive adjustment on the frequency converter in the chaining state, and execute the normal start mode after getting rid of the chaining; 2. The frequency converter control method based on state detection and load adaptive adjustment according to claim 1, wherein, When retrieving the events and shutdown data at the previous moment to determine whether to adjust the control strategy for the next start, If the output torque is greater than the rated torque and the motor stops normally without faults, execute the heavy-load start mode, increase the starting torque, and at the same time increase the limit value of the starting torque; If the output torque is less than or equal to the rated torque and the motor stops normally without faults, execute the normal start mode.

3. A frequency converter control method based on state detection and load adaptive adjustment according to claim 1, characterized in that, When monitoring the output speed, torque, and current values in real time to trigger abnormal start identification, Judge whether it satisfies the condition between the start signal reception time and the allowable long-time working current time T - 1S, and the real-time torque ≤ the real-time torque at the previous moment, and the real-time speed ≤ the rated speed / acceleration time × delay judgment time T - 1S × coefficient 80%; if so, trigger abnormal start identification; otherwise, do not trigger abnormal start identification.

4. A frequency converter control method based on state detection and load adaptive adjustment according to claim 1, characterized in that, When triggering abnormal start identification, Inject a low-frequency signal, continuously collect voltage and current in multiple cycles, and calculate the average value of the stator resistance of the motor; When there are peaks or valleys in the current waveform, or directly trigger the overcurrent threshold, or the sum of the three-phase identification currents is not zero, judge that the stator resistance is abnormal and output a frequency converter fault.

5. A frequency converter control method based on state detection and load adaptive adjustment according to claim 1, characterized in that, When performing adaptive chaining identification based on the output speed, torque, and current values, Judge whether it satisfies the condition that the ratio of current to speed is greater than the set threshold and the slip rate of the motor approaches 1; if so, identify it as the chaining state; otherwise, identify it as the non-chaining state.

6. The frequency converter control method based on state detection and load adaptive adjustment according to claim 1, wherein, When performing adaptive adjustment on the frequency converter in the chaining state, In the chaining state, detect the current and voltage values in real time. When the current exceeds the set maximum current threshold, limit the current to the maximum current threshold. When the voltage exceeds the set maximum voltage threshold, limit the voltage to the maximum voltage threshold.

7. A frequency converter control method based on state detection and load adaptive adjustment according to claim 1, characterized in that, When performing adaptive adjustment on the frequency converter in the chaining state, Dynamically adjust the acceleration time through the following formula: Tacc(t)=Tmax / (1 + k×s(t)) Where, Tacc(t) is the dynamically adjusted acceleration time, Tmax is the maximum acceleration time, k is the adjustment gain, s(t) is the slip rate, and t is the running time.

8. A frequency converter control method based on state detection and load adaptive adjustment according to claim 1, characterized in that, When performing adaptive adjustment on the frequency converter in the chaining state, Dynamically adjust the output frequency through the following formula: F’(t)=f(t)-α×△I(t) Where, F’(t) is the dynamically adjusted output frequency, f(t) is the real-time output frequency, α is the proportional coefficient, △I(t) is the current change amount, and t is the running time.

9. A frequency converter control method based on state detection and load adaptive adjustment according to claim 1, characterized in that, When performing adaptive adjustment on the frequency converter in the stuck chain state, if the stuck chain state is not escaped, the direction given signal and the operation given signal are received, the operation given signal is transiently inverted, the received direction given signal is alternately inverted and output, and at the same time, the rotational speed, torque, fault state, and current are monitored in real time, the maximum torque current value is calculated and output, and the torque limit current value is adaptively corrected according to the maximum torque that the chain of the scraper conveyor can withstand and the maximum temperature of the IGBT junction temperature.

10. A frequency converter control method based on state detection and load adaptive adjustment according to claim 9, characterized in that, When adaptively correcting the torque limit current value, retrieve the load torque at the last shutdown, the load current at the last shutdown, the current load torque, the current load current, the current torque limit value, the maximum torque limit value, the minimum torque limit value, and the increment coefficient for each adjustment; Calculate the torque limit according to the previous load torque and the current load condition: T_start=T_load+T_inertia where, T_start is the minimum torque required at startup, T_load is the load torque, and T_inertia is the dynamic inertia torque; If the current load torque is greater than the load torque at the last shutdown, increase the maximum torque limit value by the increment coefficient.

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