Research On Control Method For Electrode Regulating System Of Electric Arc Furnace

The EAF (electric arc furnace) is a crucial equipment in the steelmaking process. The electrode regulating system plays an important role in improving electric power inputted to the furnace; reducing the cost of power consumption and shorting the duration of heating. So the control methods of electrode position become the primary research object of EAF control system. However the electrode regulator has been generally designed based on the linear arc resistance model for long, of which the control effect is actually not perfect. Therefore, the control strategy and controller designing of electrode regulating system are researched deeply based on the AC arc resistance model in the thesis.The models of the AC arc; three-phase power supply system and hydraulic system are firstly established according to analyses of the mechanism of EAF electrode control system. And these nonlinear models are approximately linearized to make it convenient to design the PID controller of electrodes. Then the control strategies of electrodes are simulated and analyzed by the nonlinear model. The results make out that the control strategy of constant impedance can weaken the three-phase coupling action and show us the characteristics of the two expressions of constant impedance control.Based on the characteristics of the modern EAF smelting craft, the whole smelting cycle is divided to two stages, which are melting stage and oxygenating stage. Within the melting stage electrode controller is desired to possess the characteristic of high-rapid response due to impact of scrap steel collapsing and so on, in which fuzzy controller is better than PID controller. Within the oxygenating stage the arc is more steady and high control precision is demanded, so PID controller is better than fuzzy controller. Finally the mix controller of PID and fuzzy control is proposed to make up the disadvantage that PID controller does not cope with the control requirements of regulation time and overshoot at the same time. In the mix controller of PID and fuzzy control the appropriate controller is selected to each smelting stage to get better control effect for electrode regulating system. It is settled effectively that in EAF smelting process different desires of high-rapid response and control precision are demanded to different stages. The results of computer simulation and application indicate that the control effect of the control method is satisfying.