Research On Reactive Power Compensation And Harmonic Suppression Of Electric Arc Furnace

The electric arc furnace(EAF),as an important equipment in modern steelmaking industry,is widely used in the metal smelting industry.However,the operation of EAF will reduce the power factor of the load system and cause the power quality problems like voltage fluctuation and flicker.The basic reason for the load fluctuation of EAF is that the random changes of arc length lead to a complicated variation of arc voltage and current.Therefore,based on the electric characteristics of EAF,a synthetical compensator is used which is composed of active power filter(APF)and thyristor switching capacitor(TSC)to comprehensive treatment of power quality problems caused by EAF.It is practically significant to realize the comprehensive treatment of reactive power and harmonics wave in power grid.Firstly,the establishment process of time-varying resistance model of AC arc is expounded.Then the reactive power compensation principle and circuit structure of TSC and APF are introduced.When TSC compensates EAF in a way of arge capacity and stepwise reactive power,it requires lower precision.Hence,a fuzzy control method to switch is proposed and considers the voltage and reactive power as the switching criterion of TSC.However,APF can realize fast and continuous reactive power compensation and harmonic suppression of which requires higher precision and faster response speed.Therefore,the i_p-i_q method is used which is based on instantaneous reactive power theory to detect the reactive power reference current,while the control system using the current direct control.At last,the controller based on fuzzy PI control method is designed.The introduction of APF makes the integrated compensation system with higher steady-state precision and dynamic response speed.At the same time,it can also filter the harmonic current generated by the load,reduce the reactance rate of series reactance in TSC and the economic cost.The simulation models of TSC/APF and EAF are builded respectively by using MATLAB/Simulink.The simulation results show that in a certain extend,the time-varying resistance model of the AC arc can reflect the voltage and current characteristics of EAF.TSC can achieve large reactive power compensation,but the voltage and current of the load system can not be kept in the same phase.TSC can also produces harmonics current.APF can filter the harmonic current of load system quickly and efficiently.As a result,when the TSC+APF compositive compensator put into the EAF load system,the harmonic current of the system is greatly reduced.The current and voltage of the system remain in the same phase and the power factor stays at about 1 in 0.05s.The effect of fast,accurate and stable compensation and suppression is realized.