Study On The Speed Control Strategy Of Permanent Magnet Direct-drive System For Mining Scraper Conveyor

The mining scraper conveyor is one of the 'three machine equipment'in the mechanized mining face,which is responsible for carrying coal,loading coal and unloading coal.The working status of scraper conveyor will directly affect the normal production of coal mining enterprises.The drive system is the core component of the scraper conveyor,and the main structure is 'asynchronous motor+(soft start device)+reducer'.Among them,the reducer not only increases the overall energy consumption of the transmission system,but also easily causes failure and running noise,thereby reducing the running stability and reliability of the transmission system.If a permanent magnet synchronous motor(PMSM)with low speed and high torque is used to directly drive the scraper conveyor,this type can directly eliminate the reducer in the transmission system,so it will bring some advantages,such as high running efficiency,good control performance,fast dynamic response,and so on.In addition,this transmission method can improve the stability and reliability of system operation,and it meets the development requirements of high power,high efficiency,high reliability and low failure of the mining scraper conveyor.At the same time,it will bring about energy-saving effects.However,due to the cancellation of the intermediate transmission mechanism,the vibration and shock of the load side will be directly transmitted to the motor shaft of the permanent magnet direct-drive system.There is a complex electromechanical coupling relationship between the mechanical structure of the mining scraper conveyor and the permanent magnet direct-drive system.The running characteristics of the scraper conveyor are intermittent operation,large starting torque,frequent starting and stopping,and large impact loads,which may cause problems such as parametric perturbation,large changes in load and inertia of permanent magnet direct drive systems,and these will seriously affect the stability of the speed control of the permanent magnet direct-drive system.For this reason,the speed stability control of permanent magnet direct-drive system for the mining scraper conveyor needs to be further studied,and it is a key subject to realize the successful application of permanent magnet direct-drive system to the scraper conveyor.This dissertation funded by the National Natural Science Foundation of China Joint Fund Project,combining with the load characteristics of the permanent magnet direct-drive system in actual working conditions,the theory of modeling,numerical simulation analysis,and experimental tests were used to conduct in-depth research on the speed control strategy of permanent magnet direct-drive system for mining scraper conveyor.The main contents of this paper are as follows:(1)Studying the dynamic model of scraper conveyor and the mathematical model of permanent magnet direct-drive system,the vector control model of permanent magnet direct-drive system under the load characteristics of scraper conveyor was constructed.Considering the time-varying load distribution and the polygon effect of the sprocket,the dynamic model of scraper conveyor was established based on the finite element model.Then,the mathematical model of permanent-magnet direct-drive system was established,and the vector control method i_d=0 was selected based on the analysis of vector control theory.On this basis,according to the coupling relation between the permanent magnet direct-drive system and the mechanical system of scraper conveyor,the the vector control model of the permanent magnet direct-drive system under the load characteristics of the scraper conveyor was built.Finally,the simulation results based on MATLAB/Simulink revealed the influence of load characteristics on the speed control of the permanent magnet direct-drive system.(2)Based on the equivalent parameter scaling principle and the inverse model load simulation strategy,the dynamic load simulation tracking method for the permanent magnet direct-drive system was proposed.By the analysis of the dynamic load simulation principle of the permanent magnet direct-drive system,the equivalent scaling principles of the actual system and the small scale simulation platform were proposed according to the similarity principle and the dimension analysis method.Based on the inverse model principle,the dynamic load simulation tracking method was designed,and the low-pass filter was used to reduce the noise interference caused by the speed differential term.Then,a small scale load simulation platform for the permanent magnet direct-drive system was built using a powder brake dynamometer,and the parameters of PMSM parameters was identified by off-line identification.Combined with the vector control model of permanent magnet direct-drive system under the load characteristics of scraper conveyor,the load characteristics simulation of the permanent magnet direct-drive system was realized,and it laied a foundation for the research on the speed control strategy of the permanent magnet direct-drive system.(3)Based on the nonlinear feedback control technology and integral sliding mode control,the speed controller of permanent magnet direct-drive system was designed.Considering the uncertainties and disturbances of the system model,a control model with output saturation of the permanent magnet direct-drive system was established,and designing a CNF speed controller for its nominal system by the nonlinear feedback control.Then,the rapidity and low overshoot of the control system were realized through the introduction of the nonlinear feedback parameter?_v which achieves the dynamic change of the damping ratio.Considering the uncertainty of the model parameters,the compensation control of the uncertainty part was realized by integrating the integral sliding mode control(ISM).Subsequently,the ISM_CNF speed controller was established by combining ISM and CNF control,it achieved a reduction in overshoot while improving system robustness.For the problem of chattering in sliding mode control,the soft switching function was used instead of the traditional switching function to reduce the chattering in the sliding mode control.Finally,based on the established small scale load simulation platform and load simulation method,the simulation and experimental comparison of the PI controller,CNF controller and ISM_CNF controller of the permanent magnet direct-drive system were carried out.It was verified that the designed ISM_CNF controller has no overshoot and better robustness.(4)Combined with the sliding mode load observer and the inertia online identification,an anti-disturbance compound speed controller for the permanent magnet direct-drive system was established.First,the influence of load perturbation on speed control of permanent magnet direct drive system was analyzed.Based on the traditional extended sliding mode load observer,combined with the advantages of both high-order sliding mode and non-singular terminal sliding mode,the second-order sliding mode load observer with fast convergence rate and no chattering was designed.Aiming at the influence of the inertial disturbance change on the load observer,a method based on variable gain coefficient model reference self-adaption was proposed to carry out online identification of the inertia.On this basis,based on nonlinear feedback integral sliding mode velocity controller,load disturbance observer and inertia online identification,an anti-disturbance compound control method for permanent magnet direct-drive system was proposed.Through simulation and experiment,the composite control strategy of permanent magnet direct-drive system has good anti-disturbance performance.The research results obtained in this paper have important guiding significance for the in-depth conducting the high-performance control of the permanent magnet direct-drive system of mining scraper conveyor,and laied the theoretical foundation for realizing the reliable and stable operation of the permanent magnet direct-drive system.It also provides technical support for the application of a permanent magnet direct-drive system for the mining scraper conveyor in the mechanized mining face.