Nonlinear Equivalent Circuit Model Of Electric Arc Furnace Load And Power Quality Control

As a typical nonlinear impact load,Electric Arc Furnace(EAF)grid-connected will cause power quality problems,such as harmonics and voltage fluctuation,which affects the safety and stability of the power grid and the operation of related equipment,and will bring harm to both suppliers and users.Therefore,it is very necessary to explore the equivalent circuit model of the nonlinear load of the EAF and take corresponding measures to control the power quality.Firstly,based on the nonlinear impact characteristics of the AC EAF load,this paper analyzes the operating overvoltage of the EAF system,puts forward its protective measures,and studies the power quality problems caused by the EAF load connected to the power grid,thereby obtaining corresponding suppression measures.Secondly,based on the nonlinear resistance model and chaotic model of EAF load,a new equivalent circuit model of AC EAF is obtained.According to the piecewise linear fitting method of U-I characteristic of EAF load,the equivalent circuit steady-state model of ac electric arc furnace load is obtained;On this basis,considering the arc variation characteristics and the chaotic characteristics of the EAF load,the equivalent circuit dynamic model of AC EAF load is obtained.Then,based on the AC EAF parameters of a steel plant and the circuit model of its power supply system,this paper simulates the steady-state model of the single-phase EAF load,and the results are consistent with the characteristics of the actual EAF load,thus verifying the rationality of the model;The dynamic model of three-phase EAF load is simulated,the results show that the harmonic distortion rate of 220 k V common bus(PCC)node voltage caused by EAF load is serious,up to11.26 %,and the voltage fluctuation of PCC node is also serious,up to 5.05 %,which is far beyond the national limit.Therefore,remedial measures must be taken.Finally,based on the consideration of the periodicity,randomness and chaos of the AC EAF load dynamic model,this paper proposes a power quality management scheme with static var compensator(SVC)installed.The parameters of SVC are designed,and the equivalent circuit model of AC EAF load containing SVC is built.The results show that the solution can well reduce the voltage total harmonic distortion rate of the PCC node to 1.11% and the voltage fluctuation to 1.73%,which are in line with national standards,and can effectively improve the voltage fluctuation and harmonics caused by the AC EAF load.