Study On Single-phase Low Frequency Power Supply Conversion System Of 300T Electroslag Furnace

Electroslag furnace is a special smelting equipment for the production of electroslag ingots in the field of metallurgy.It often uses single-phase alternating current power supply.With the different tonnage of the furnace body,the current demanded from several thousands to tens of thousands of amps.The traditional electroslag furnace has to use the power frequency power supply directly because of the limitations of the conventional inverter output current.Since the distributed inductance can not be ignored,the power factor is mostly below 0.8 by this kind of power supply mode,it is a serious waste of electrical energy.Due to the single-phase power supply,the three-phase balance cannot be guaranteed,causing distortion of the power grid waveform and causing serious harmonic pollution.Under the situation in which modern industry promotes energy conservation and emission reduction,this paper adopts an AC-AC frequency conversion scheme from power frequency three-phase to low-frequency single-phase.This design reduces the frequency of the power supply in order to reduce the pressure drop of the inductive reactance and increase the power factor.The article against the technical difficulty of low-frequency power,this paper designs a single-phase low-frequency power supply conversion system for single-phase 300 T electroslag furnace with 10.8MW output and 1~5Hz output in order to improve the power factor of the power supply system and reduce the harmonic pollution.the large number of thyristors,steel rectifier cabinet due to eddy current heating and expanding the output current capacity and other issues is considered,the basic topology of the main circuit is selected as a double anti-star inverse in parallel with the balance reactor AC-AC inverter circuit after comparison.In order to reduce the influence of the harmonics injected into the grid current and the fluctuating frequency of the grid voltage during system operation,the transformer design a 24 pulse rectifier transformer.The combination of on-load voltage regulator coarse adjustment and thyristor fine adjustment enables precise control of the output voltage and current to ensure that the system has a higher power factor under different operating conditions.All-digital,phase-adaptive trigger control board with DSP and CPLD as the core unit is used to ensure simultaneous generation of multiple pulses.The whole system has also designed perfect voltage/current signal detection and processing circuit,protection circuit and monitoring circuit.Finally,the software and hardware design are simulated and debugged to verify the correctness and feasibility of the design results.It is further confirmed that reducing the frequency of the electric slag furnace power supply voltage can improve the power factor and reduce the energy waste.