| As main equipment in steel-making industry, the AC electric arc furnace has been widely paid more and more attention. However, the electric arc furnace is a kind of classic impact load and may yield serious power quality problems, due to its widely application in the power system. In this dissertation, on basis of modeling a precise and practical arc model, the power quality problem caused by electric arc furnace load is systematically analyzed, and governed by employing STATCOM. The main work is as follows:1. A novel steelmaking AC electric arc furnace model is proposed, in which the parameter is a function of arc length in time domain. The original AC electric arc model is modified by analyzing its resistance characteristics, wherein, arc admittance is used as the state variable, and a model parameter estimation method is presented. The proposed model has merits of clear physics meaning and simple parameter estimation method, which is suitable for various electric arc furnaces with different tonnage design and parameter specification, and is verified by the model comparison analysis.2. An electrical system simulation model is built up with a real 100t AC electric arc furnace, and the power quality problems such as three-phase unbalance, harmonic, voltage fluctuation and flicker are analyzed under random variation of the arc length. The electric arc furnace load is in state of three-phase unbalance when three-phase arc lengths are not equal. Wherein, when a phase arc length is changed, the voltage and current associated to this phase arc length will change in a maximum amount, meanwhile the phase current change will result in heavy influence on the other two phase currents. Furthermore, when the electric arc furnace operates in melting stage, each phase harmonic current on the bus will seriously exceed the GB, while the electric arc furnace at refining period will cause relatively a little harmonic pollution to the power grid. The reactive shocks, voltage fluctuation and flicker to the power grid caused by electric arc furnace are analyzed through theoretical estimation method, by comparing it with the practical simulation, which illustrates that a severe reactive power shock will occur, and the maximum voltage fluctuation value will exceed over the limit in GB, when the three-phase electrodes of electric arc furnace operate in the condition of grounding short-circuit. The above results show that the proposed modified electric arc furnace model has high precision and is suitable for the power quality analysis.3. A reactive power compensation scheme with STATCOM is proposed for power supply system of electric arc furnace. The modified id-iq current detection method is used to detect harmonic and reactive current, and the hysteresis current tracking control strategy is proposed to synthesize the controller. Considering the actual electric arc furnace power supply system, main circuit parameters of the STATCOM are calculated, and the STATCOM is in-parallel connected to 35kV side of the system, in order to suppress the harmonics and compensate the reactive power. When the STATCOM works in the system, the amplitude of system bus harmonic current at melting stage decreases greatly, which is controlled under the limit of GB, and the three-phase unbalance is also obviously improved. The power factor at steady state is improved up to 0.99, and will be not less than 0.6 even if the maximum reactive shock occurs. The above simulation results further show the effectiveness of the proposed reactive power compensation scheme with STATCOM.
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