Research On Energy Feedback And Safe Brake Technoligy Of Downward Belt Conveyor

As an important transport equipment in the production process of coal mine, belt conveyor is widely used because of its strong ability of transport capacity and continuous transportation. With the deeper development of coal mining and improvement of mining technology, more and more high speed, long distance and large inclination angle downward belt conveyors are applied. Due to its special working condition, the driving motor often gets into the state of generating when the decline force of material exceeds running resistance. And because of huge braking energy it produced, it requires a high reliability of downward belt conveyor braking system. For a long time, the braking system of downward belt conveyor is the focus research of coal related experts and scholars. The core problem to study is how to deal with the braking energy.Traditional braking way of belt conveyor is to change the braking energy into temperature rise of braking system to consume energy, which always leads to excessive temperature rising and brake components loss easily, as well as energy waste. Therefore, the study of energy feedback brake system for the downward belt conveyor is of great importance, which can implement the safety brake and achieve energy recycle effectively. In this paper, by using theoretical research,combining simulation analysis and experimental verification, this paper is to realize the brake energy feedback of downward belt conveyor as much as possible under the condition of safe operation of conveyor, for the purpose of realizing energy feedback brake under the application of four quadrant frequency converter and the application of hydraulic soft braking system. It aims to enhance the economic benefits of coal enterprises and provides certain theoretical basis for the research of downward belt conveyor braking system.Based on the detailed analysis of the working principle and control mode of the four quadrant variable frequency feedback system, the energy conversion relation in the feedback process is obtained according to the energy conversion principle. Then, the mathematical model of energy feedback system is established in different coordinate, and the goal of energy feedback into power grid with unity power factor is achieved by the application of feed-forward decoupling and voltage and current double closed-loop control strategy in the process of energy feedback. Finally, the energy feedback system simulation model is built in Matlab/Simulink. According to the analysis of simulation results, it shows that the control strategy of feedback system is correct and effective.To solve braking problems in special conditions, which feedback brake system cannot deal with, strategies in each braking condition are studied in this paper, through analyzing the operating feature of downward belt conveyor and the characteristics of existing braking device characteristics. And a brakingstrategy of “feedback braking add hydraulic soft brake system” is studied,aiming to recycle as much as braking energy but less electrical equipment loss in heavy-load condition, enhancing working efficiency. To solve the braking problem of sudden power failure, it puts forward the application of hydraulic soft braking system. Then, in the Simulink and AMESim, each braking strategy of belt conveyor in two different working conditions are simulated and analyzed,and the results reveal the control law of the feedback braking system.Through the above research and combining the actual conditions, the downward belt conveyor simulation test bench is built. By designing the simulation test of regenerative braking system under no-load and heavy load respectively, the operation law of the two different load conditions are studied,and the voltage and feedback current are detected. Test results show that the application of regenerative braking technology in downward belt conveyor is proper to solve the energy feedback problems with high power factor and small harmonic pollution and performed a good control effect in the operating process.It embodies the necessity of "regenerative braking and soft braking co-system".The results also show that the application of four quadrant frequency converter has a good performance in soft start control. The application of soft braking system realizes safety brake of downward belt conveyor.