The Flexible Power Supply System of AC Electric Arc Furnace Significance

The flexible power supply system for AC electric arc furnace is one of the core technologies for achieving green, efficient, and intelligent smelting in the steel industry. It is a complex system integrating electrical, metallurgical, automation, and artificial intelligence technologies. Through advanced power electronics technology, it achieves efficient control of irregular loads, significantly improving the EAF power factor and power quality.

The Significance of Flexible Power Supply Systems for AC Electric Arc Furnace

I. Why Does the EAF Need "Flexible Power Supply"?

Traditional steelmaking electric arc furnaces have relatively fixed power supply modes, while modern smelting processes have dynamically changing requirements:

1. Diversified Raw Materials: Extensive use of scrap steel, direct reduced iron, hot-pressed iron blocks, etc., with different melting characteristics.

2. Grid Constraints: Electric arc furnaces are "non-linear, impulsive loads," causing voltage flicker, harmonics, and other problems to the power grid. Active adaptation to grid requirements is necessary to avoid penalties or power rationing.

3. Process Optimization: Pursuing lower power consumption, electrode consumption, and shorter smelting time (Tap-to-Tap Time).

4. Energy Costs: Power output needs to be flexibly adjusted during peak and off-peak electricity periods to achieve economical electricity consumption.

II. Core Components of the Power Supply System

1. Sensing & Detection System:

• Electrical Parameters: Real-time monitoring of three-phase voltage, current, active/reactive power, power factor, harmonics, etc.

• Sound Intensity/Vibration Detection: Determining arc status (stable, short-circuit, open-circuit) and the effect of slag submersion in the furnace using furnace wall microphones or vibration sensors.

• Optical/Thermal Detection: Monitoring molten pool temperature and furnace wall hotspots using infrared thermography, high-speed cameras, etc.

• Chemical Analysis: Indirectly determining the molten pool reaction state through furnace gas analysis (CO, CO₂, O₂, etc.).

2. Advanced Control System:

• Core Brain: A model-based or artificial intelligence-based optimization controller.

• Traditional Model: Static/dynamic models based on energy balance and material balance.

• Intelligent Model: Applying expert systems, fuzzy logic, neural networks, machine learning, etc., to learn the optimal operating mode from massive amounts of historical data.

3. Actuators:

• Electrode Adjustment System: A fast and precise hydraulic or electromechanical servo system, directly executing power supply commands.

• On-Load Tap Changer/Thyristor Power Regulator: Adjusts the voltage level on the primary or secondary side of the transformer, changing the operating impedance.

• Static Var Compensator (SVC): Such as an SVC or more advanced SVG, used to dynamically compensate for reactive power and suppress flicker and harmonics; this is a key device for grid-friendly interaction.

• Auxiliary Energy Systems: Such as the linkage control of oxygen-burner and carbon powder injection systems.

III. In what aspects is "flexibility" reflected?

1. Flexibility of Power Input:

• Dynamic Power Optimization: Adjusts the active power setpoint in real time based on the smelting stage (well penetration, main melting, melting clearing, refining), furnace charge conditions, and grid electricity price.

• Constant Impedance vs. Constant Power Control: Intelligent switching of control modes; constant power may be used during the electric arc furnace melting period to accelerate melting, while constant impedance is used during the refining period to stabilize the arc.

2. Flexible Electrical Operating Points:

Optimized Operating Point: Within the allowable range of transformers and reactors, intelligently selects the optimal combination of secondary voltage and current (i.e., operating impedance) to maximize electrical efficiency, minimize grid interference, and reduce electrode consumption.

3. Flexible Interaction with the Grid:

• Demand-Side Response: Receives grid dispatch instructions and proactively reduces power during peak load periods ("peak shaving") and increases power during off-peak periods to provide ancillary services to the grid.

• Proactive Harmonic Mitigation: Actively injects compensating current through SVC/SVG and active filters to suppress harmonics within national standards.

4. Flexible Process Coordination:

• Linkage with Oxygen Blowing/Carbon Injection: Automatically optimizes oxygen blowing volume and carbon injection timing based on the power supply curve to create foamed slag, achieving efficient submerged arc heating and reducing radiative heat loss.

• Preventative Adjustment: Predicts "material collapse" or "arc interruption" through sound or vibration signals, and fine-tunes electrode positions in advance to maintain stability.

IV. Key Technologies

• Multi-objective real-time optimization algorithm: This algorithm aims to find the optimal or satisfactory solution among multiple conflicting objectives, including minimizing EAF power consumption, smelting time, grid impact, electrode consumption, and refractory erosion.

• Digital twin technology: This technology creates a virtual mirror image of each steelmaking electric arc furnaces, pre-simulating and optimizing power supply strategies in this virtual space before applying them to actual production.

• Big data & artificial intelligence: This technology utilizes machine learning to mine historical best-performing furnace data, forming an adaptive and self-learning power supply strategy model.

• Advanced power compensation technology: SVG (STATCOM) offers faster response and more accurate compensation than traditional SVC, providing the hardware foundation for ultra-high flexibility in power supply.

The flexible power supply system for AC electric arc furnace has evolved from simple "electrode lifting control" into a comprehensive intelligent platform that coordinates "energy-process-grid" optimization. It is not only a tool to improve the economic efficiency of the electric furnaces itself but also a key entry point for the steel industry to integrate into the new power system and achieve a green and low-carbon transformation.

Its ultimate goal is to achieve "the right input of precise energy at the right time and in the right way," thus realizing a safe, efficient, green, and economical ultimate production model.