An arc furnace current stabilizing system and arc furnace current stabilizing method

Abstract

The application relates to the technical field of arc furnace power supply, and discloses an arc furnace current stabilizing system and an arc furnace current stabilizing method, which comprises input rectifying units, a power regulating unit and an output current stabilizing unit which are electrically connected in sequence; the input rectifying units are used for converting alternating current into direct current; the power regulating unit is used for inverting the direct current into alternating current with adjustable frequency or amplitude; the output current stabilizing unit comprises a direct current stabilizing inductor and a current stabilizing bridge circuit, the current stabilizing bridge circuit comprises two alternating current ends, a positive direct current end and a negative direct current end, the two alternating current ends are connected to the power regulating unit and an arc furnace load respectively; the direct current stabilizing inductor is connected between the positive direct current end and the negative direct current end; the current stabilizing bridge circuit serves as a commutating bridge, so that the current flowing through the direct current stabilizing inductor is always direct current with the same direction; when the alternating current is zero or the current is suddenly changed, the direct current stabilizing inductor releases energy to the arc furnace load through the current stabilizing bridge circuit. The application can reduce the harmonic pollution of the grid side and improve the arc stabilizing performance.

Description

Technical Field

[0001] This application relates to the field of electric arc furnace power supply technology, and in particular to an electric arc furnace current stabilization system and method. Background Technology

[0002] As a crucial piece of equipment in the metallurgical industry, the stability and power quality of the power supply system for electric arc furnaces directly impact smelting efficiency and product quality. To improve arc stability, related technologies, such as the direct electric arc furnace with controllable current feeding disclosed in Chinese patent CN1057658C, employ an AC / DC controllable rectifier in conjunction with a smoothing reactor to provide DC power to the load. This scheme utilizes the DC reactor to smooth the current, improving arc stabilization performance to some extent. However, this type of regulation technology based on phase-controlled rectification (typically using thyristor SCRs) requires the rectifier to simultaneously perform the dual functions of AC-to-DC conversion and power / voltage regulation. During operation, the current is controlled by adjusting the conduction angle, inevitably generating a large amount of high-order harmonics on the grid side. Furthermore, the power factor significantly decreases during deep temperature control or arc initiation stages, causing grid pollution.

[0003] To address power quality issues on the grid side, flexible power supply solutions employing fully controllable devices have emerged in the industry. For example, Chinese patent CN109193655A discloses a flexible power supply device for an AC electric arc furnace, which uses AC-DC-AC conversion technology. Through the cooperation of rectifiers and inverters, it isolates the load from the grid and outputs AC power with adjustable frequency and amplitude, solving the problems of harmonic injection and low power factor.

[0004] However, the aforementioned flexible power supply solutions typically output AC power directly to the load. During electric arc furnace smelting, drastic changes in operating conditions frequently occur, such as short circuits caused by charge collapse or open circuits caused by arc extinction. Direct AC output still needs further improvement in suppressing drastic fluctuations in instantaneous current and maintaining the stability of continuous arc combustion.

[0005] Furthermore, in electric arc furnace power supply systems, whether DC or AC, reactors (inductors) are typically required in the circuit to limit short-circuit current and stabilize the arc. In traditional solutions, the reactor is directly connected in series in the AC power supply circuit. AC current flows through the reactor, generating significant eddy current and hysteresis losses in the iron core, leading to severe overheating, high energy consumption, and excessive size and weight. How to enable the reactor to operate with lower losses while maintaining its arc-stabilizing function is a problem that needs to be solved in this field.

[0006] In response to the aforementioned technologies, there is an urgent need for a power supply and current stabilization solution that balances power quality and arc stabilization performance. Summary of the Invention

[0007] To address the aforementioned technical problems, this application provides an electric arc furnace current stabilization system and a method for stabilizing the current of an electric arc furnace.

[0008] Firstly, this application provides a current stabilization system for an electric arc furnace, which adopts the following technical solution: An electric arc furnace current stabilization system includes an input rectifier unit, a power regulation unit, and an output current stabilization unit connected in sequence. The input rectifier unit is used to connect to the AC power grid and convert AC power into DC power. The power regulation unit receives DC power and inverts it into AC power with adjustable frequency or amplitude for supplying the electric arc furnace load. The output current stabilization unit is located in the power supply circuit between the power regulation unit and the electric arc furnace load, and includes a DC current stabilizing inductor and a current stabilizing bridge circuit. The current stabilizing bridge circuit includes two AC terminals, a positive DC terminal, and a negative DC terminal. The two AC terminals are respectively connected to the output terminal of the power regulation unit and the input terminal of the electric arc furnace load. The DC current stabilizing inductor is connected between the positive DC terminal and the negative DC terminal to form a DC inductance circuit. The current stabilizing bridge circuit acts as a commutation bridge, ensuring that the current flowing through the DC current stabilizing inductor is always a DC current in the same direction. When the AC current crosses zero or changes abruptly, the DC current stabilizing inductor releases energy to the electric arc furnace load through the current stabilizing bridge circuit.

[0009] By adopting the above technical solution, the input rectifier unit, power regulation unit, and output current stabilization unit constitute the power supply and current stabilization link. It eliminates the need for active power regulation or phase angle control using thyristors. Instead, it achieves power conversion and arc stabilization through a topological combination of "rectifier, inverter, current stabilization bridge, and DC current stabilization inductor," reducing grid-side harmonic pollution and improving low power factor conditions, thus mitigating adverse effects on the power grid. Simultaneously, the commutation effect of the current stabilization bridge circuit ensures the DC current stabilization inductor operates in DC mode, avoiding eddy current losses and hysteresis losses generated by AC current in the inductor core, reducing the inductor's own power consumption and heat generation. Meanwhile, the electric arc furnace load maintains AC power supply characteristics, ensuring the normal operation of the AC electric arc furnace.

[0010] Optionally, the current-regulating bridge circuit includes a diode bridge circuit or a controllable switch bridge circuit.

[0011] By adopting the above technical solutions, the diode bridge structure is simple and highly reliable. It can stably commutate the AC current in the power supply circuit, ensuring that the DC current in the DC current regulator always flows in the same direction, thus achieving basic arc stabilization function in conjunction with the DC current regulator. The diode bridge does not require additional control logic, reducing system complexity and cost, and its own power consumption is low, further ensuring the overall efficiency of the power supply system. The controllable switching bridge circuit further solves the problems of the diode bridge's inability to actively turn off and the uncontrollable freewheeling current, and achieves active management of inductor energy storage without increasing hardware costs.

[0012] Optionally, the current-regulating bridge circuit is a controllable switching bridge circuit, including at least one set of first switching branches that conduct during the positive half-cycle of AC current and at least one set of second switching branches that conduct during the negative half-cycle of AC current. The first switching branches and the second switching branches conduct alternately, so that the current flowing through the DC current-regulating inductor always maintains the same direction.

[0013] By adopting the above technical solution, a highly flexible current regulation architecture is constructed, which can switch between "fine current regulation mode" and "rapid protection mode" according to different smelting stages of the electric arc furnace: During the normal smelting stage, the system controls the alternating conduction timing of two sets of switching branches to adjust the energy storage level in the DC current regulating inductor and the timing of current replenishment to the load, thereby improving the stability of arc combustion and the accuracy of heat input; Under extreme conditions such as arc ignition, arc interruption, or severe load fluctuations, the system can actively construct a channel for dissipating inductor energy using controllable switching branches, taking into account both the regulation performance under normal operating conditions and the system safety under extreme operating conditions.

[0014] Optionally, the current-stabilizing bridge circuit includes a first bridge arm device, a second bridge arm device, a third bridge arm device, and a fourth bridge arm device. The first switching branch includes the first bridge arm device and the fourth bridge arm device located on the first diagonal of the bridge structure, and the second switching branch includes the second bridge arm device and the third bridge arm device located on the second diagonal of the bridge structure. The first bridge arm device and the second bridge arm device are both controllable switching devices, and the third bridge arm device and the fourth bridge arm device are either both controllable switching devices or both are uncontrollable rectifier devices.

[0015] By adopting the above technical solution and locking the controllability of the key bridge arms (first and second bridge arms), both fully controllable and semi-controllable schemes are realized. Regardless of the device used in the lower bridge arm, as long as the upper bridge arms (first and second bridge arms) have controllable switching functions, the on / off control of the forward and reverse circuits can be performed. This allows users to flexibly select the appropriate device based on their actual needs: when using fully controllable devices (full bridge), a double-frequency fast response and bidirectional energy flow capability can be obtained, suitable for high-precision alloy smelting; when using semi-controllable devices (half bridge), although hardware costs are reduced, the controllability of the upper bridge arm can still be utilized to forcibly shut off the reverse circuit during the negative half-cycle, and conduct only during faults to achieve protection. This design improves the system's configuration flexibility, meeting different cost and performance requirements while ensuring core current stabilization and protection capabilities.

[0016] Optionally, a control unit is also included. The control unit is connected to the input rectifier unit, the power regulation unit, and the output current stabilizing unit, respectively. The control unit is configured to: send a trigger signal to the controllable switching device in the first switch branch under normal operation and short-circuit conditions of the electric arc furnace load, and adjust the energy storage level in the DC current stabilizing inductor by controlling the conduction timing; and send a trigger signal to the controllable switching device in the second switch branch to turn it on under open-circuit conditions of the electric arc furnace load, so as to release the energy stored in the DC current stabilizing inductor.

[0017] By adopting the above technical solution, the control unit can accurately regulate the conduction timing of the controllable switching devices according to the real-time operating conditions of the electric arc furnace load. Under normal and short-circuit conditions, the first switch branch conducts to ensure stable main current delivery, and works with the DC current-regulating inductor to quickly suppress short-circuit current surges. Under open-circuit conditions, the second switch branch conducts as needed, providing a discharge path for the inductor to release energy and preventing high-voltage surges caused by sudden current interruptions. Compared to a commutator bridge without a control unit, this solution achieves closed-loop control with operating condition identification and accurate response, further improving arc stabilization reliability and system efficiency.

[0018] Optionally, the control unit is also configured to: monitor at least one operating parameter of the electric arc furnace load, and dynamically adjust at least one output characteristic of the power regulation unit according to the at least one operating parameter to intervene and control the electric arc, wherein the operating parameter includes arc voltage, arc current or arc impedance, and the output characteristic includes frequency, voltage amplitude or pulse width modulation duty cycle.

[0019] By adopting the above technical solutions and using dynamic matching and control of operating parameters and output characteristics, a control link adapted to the complex working conditions of the electric arc furnace is formed, which improves the system's responsiveness and control accuracy in response to the arc state.

[0020] Optionally, the input rectifier unit is a multi-pulse rectifier, including a 6-pulse rectifier, a 12-pulse rectifier, or a 24-pulse rectifier.

[0021] By adopting the above technical solutions, the multi-pulse rectifier can reduce the harmonic content on the grid side, improve the power factor, reduce pollution to the grid, and meet the high power quality requirements of the metallurgical industry for the power supply system. At the same time, it provides a stable DC input for the subsequent power regulation unit and ensures the overall operational stability of the system.

[0022] Optionally, the power regulation unit outputs AC power in the form of single-phase, three-phase, or six-phase AC power, and the output AC power type includes low-frequency AC power, power frequency AC power, or medium-frequency AC power, and the output AC power waveform includes sine wave or square wave.

[0023] By adopting the above technical solutions, the power regulation unit supports AC output with multiple phase numbers, frequencies and waveforms, which can adapt to the load requirements of electric arc furnaces of different power and types, thus improving versatility.

[0024] Optionally, a step-down transformer is also included, which is installed in the power supply circuit between the output current stabilizing unit and the electric arc furnace load.

[0025] By adopting the above technical solutions, the step-down transformer can adjust the output voltage of the output current stabilization unit to the appropriate range according to the rated voltage requirements of the electric arc furnace load, thus expanding the application scenarios of the system. At the same time, the step-down transformer can also play an electrical isolation role, reducing the impact of load-side faults on the front-end circuit and improving the overall safety and reliability of the system.

[0026] Secondly, the electric arc furnace current stabilization method provided in this application adopts the following technical solution: A current stabilization method for an electric arc furnace includes the following steps: S1. The AC power input from the AC grid is connected to the input rectifier unit and converted into DC power, which is then sent to the power regulation unit. S2. The DC power is converted into AC power that is compatible with the electric arc furnace load through the power regulation unit, and the AC power is delivered to the current stabilizing bridge circuit. S3. Use the current stabilizing bridge circuit to commutate the AC current in the power supply circuit so that the current in the DC current stabilizing inductor connected to the DC terminal of the current stabilizing bridge circuit is always a DC current in the same direction, while keeping the current on the electric arc furnace load an AC current. S4. When the AC current crosses zero, energy is released through the DC current stabilizer inductor and supplied to the electric arc furnace load through the current stabilizer bridge circuit to maintain continuous arc combustion. In short-circuit or open-circuit conditions, the energy storage and release characteristics of the DC current stabilizer inductor suppress sudden current changes in the electric arc furnace load.

[0027] By adopting the above technical solution, the AC power from the grid is first converted to DC power through the input rectifier unit, and then the AC power adapted to the load is generated by the power regulation unit. Subsequently, the DC current stabilizing inductor is made to work in DC mode through the commutation action of the current stabilizing bridge circuit. When the AC current crosses zero, the inductor releases energy to supplement the current to the load to maintain the stability of the electric arc, forming a "rectification-inversion-commutation current stabilization" link. The whole method does not rely on thyristors for active power regulation or phase angle control, avoiding grid-side harmonic pollution and power factor reduction. At the same time, the electric arc furnace load maintains AC power supply characteristics, and the inductor works in DC mode to reduce core loss. The operation is simple, the reliability is high, and the working stability of the electric arc furnace load can be improved.

[0028] In summary, this application includes at least one of the following beneficial technical effects: 1. By adopting the above technical solution, the input rectifier unit, power regulation unit, and output current stabilization unit constitute the power supply and current stabilization link. It does not rely on thyristors for active power regulation or phase angle control. Instead, it achieves power conversion and arc stabilization through a topological combination of "rectifier, inverter, current stabilization bridge, and DC current stabilization inductor". This avoids the problems of grid-side harmonic pollution and power factor reduction in the traditional thyristor active regulation mode. At the same time, the current stabilization bridge circuit acts as a commutation bridge, enabling the DC current stabilization inductor to operate in DC mode. While maintaining the AC power supply characteristics of the load, it reduces the eddy current loss and hysteresis loss of the inductor core and improves the overall system efficiency. 2. The current-stabilizing bridge circuit can use a diode bridge or a controllable switching bridge. The controllable switching bridge, through controllable switching devices and a control unit, can realize active management of the energy storage level of the DC current-stabilizing inductor and energy discharge protection under extreme conditions. It is suitable for complex conditions such as short circuit and open circuit, and the reliability of arc stabilization is improved compared with traditional solutions. 3. The power regulation unit supports AC output with multiple phase numbers, frequencies and waveforms. With the optional configuration of step-down transformer, it can be adapted to different types and power electric arc furnace loads. The solution is highly versatile and has a wide range of applications. At the same time, it adopts mature power electronic devices and topologies, taking into account both practicality and economy. Attached Figure Description

[0029] Figure 1 This is a structural block diagram of an electric arc furnace current stabilization system provided by relevant technologies; Figure 2 This is a structural block diagram of the electric arc furnace current stabilization system provided in the embodiments of this application; Figure 3 This is a structural diagram of the electric arc furnace current stabilization system provided in the embodiments of this application; Figure 4 This is a circuit structure diagram of the input rectifier unit and power regulation unit provided in the embodiments of this application; Figure 5 This is a circuit diagram of the output current stabilizing unit provided in an embodiment of this application; Figure 6 This is a structural diagram of another electric arc furnace current stabilization system provided in an embodiment of this application; Figure 7 This is another block diagram of an electric arc furnace current stabilization system provided in the embodiments of this application; Figure 8 This is a flowchart of the electric arc furnace current stabilization method provided in the embodiments of this application.

[0030] Explanation of reference numerals in the attached figures: 1. Input rectifier unit; 11. Transformer; 12. AC-DC rectifier module; 13. Filter capacitor; 2. Power regulation unit; 3. Output current stabilization unit; 31. DC current stabilizing inductor; 32. Current stabilizing bridge circuit; 4. Electric arc furnace load; 41. Top electrode; 42. Bottom electrode; 421. Bottom electrode plate; 422. Conductive vertical plate; 5. Input protection module; 6. Control unit. Detailed Implementation

[0031] The following combination Figures 1-8 This application will be described in further detail.

[0032] like Figure 1 The diagram illustrates a current stabilization system for an electric arc furnace provided in related technologies. This system employs thyristor phase-controlled rectification technology. Specifically, the AC grid (e.g., 10kV) is connected to a three-phase transformer via a circuit breaker and surge arrester. The transformer reduces the grid voltage to a level suitable for the low-voltage, high-current characteristics of the electric arc furnace, and then connects to a three-phase full-bridge rectifier module composed of thyristors to output DC power to the furnace load. In some existing technologies, to attempt current stabilization, an inductor (not shown in the diagram) is connected in series between the rectifier module and the load. However, the overall system still relies on thyristor phase-controlled regulation as the main control logic. This regulation logic adjusts the DC voltage by controlling the trigger conduction angle of the thyristors. When current adjustment is needed, the control unit sends a trigger pulse to the thyristors with a delay or advance, intercepting and rectifying a portion of the AC waveform. A larger conduction angle results in a higher output current, and vice versa. However, the system still faces some problems in practical applications. On the one hand, although it outputs DC power, it relies on "clipping" phase control regulation of AC waveform, which will inject a large number of low-order harmonics into the power grid. Moreover, the power factor is greatly reduced in the deep control state, requiring additional large-capacity reactive power compensation and filtering devices. On the other hand, the thyristor is a semi-controlled device that can only control conduction and cannot actively turn off. The trigger response is based on the AC voltage cycle. Even if a simple inductor is added, it is difficult to quickly suppress current surges. It cannot cope with extreme working conditions such as short circuit and open circuit of the electric arc furnace load 4, which can easily lead to electrode damage or arc extinction. It is difficult to meet the high-efficiency and stable smelting requirements of modern electric arc furnaces.

[0033] To address the shortcomings of the aforementioned traditional systems, this application discloses an electric arc furnace current stabilization system, which optimizes performance through a topology of "functional decomposition of each stage + upgrade of control devices".

[0034] like Figure 2 and Figure 3As shown, the electric arc furnace current stabilization system of this application includes an input rectifier unit 1, a power regulation unit 2, and an output current stabilization unit 3 connected in sequence. The input rectifier unit 1 is used to connect to the AC power grid and convert AC power into DC power. The power regulation unit 2 receives DC power and is used to invert the DC power into AC power with adjustable frequency or amplitude. The output current stabilization unit 3 is set in the power supply circuit between the power regulation unit 2 and the electric arc furnace load 4, and includes a DC current stabilizing inductor 31 and a current stabilizing bridge circuit 32. The current stabilizing bridge circuit 32 has two AC terminals (points A and B) and a positive DC terminal (point C) and a negative DC terminal (point D). The two AC terminals are respectively connected to two nodes in the power supply circuit, and the DC current stabilizing inductor 31 is connected between the positive DC terminal and the negative DC terminal of the current stabilizing bridge circuit 32. The current on the electric arc furnace load 4 (including the top electrode 41) is maintained as an AC current, and the current stabilizing bridge circuit 32 acts as a commutation bridge, so that the DC current stabilizing inductor 31 always flows with a DC current in the same direction. When the alternating current crosses zero, the DC current stabilizer inductor 31 releases the stored magnetic field energy and replenishes the current to the electric arc furnace load 4 through the current stabilizer bridge circuit 32 to maintain the stability of the electric arc.

[0035] Specifically, in one embodiment, the input rectifier unit 1 may include a circuit breaker, a surge arrester, an AC-DC rectifier module (such as a 6-pulse rectifier, a 12-pulse rectifier, or a 24-pulse rectifier), a filter capacitor, and other modules. Unlike the "phase-controlled rectification" of traditional thyristors, the AC-DC rectification in this application is uncontrolled rectification. The current will completely follow the grid voltage waveform without clipping. Therefore, the current on the grid side is close to a sine wave with fewer harmonics, reducing grid-side harmonic pollution caused by "clipping" regulation. The power factor can approach 1, eliminating the need for additional large-capacity compensation devices. The power regulation unit 2 may include a DC-AC inverter module (such as an IGBT full-bridge inverter), a drive circuit, and a control board, etc. The IGBT is a full-bridge inverter. This controllable device can simultaneously control conduction and cutoff, accurately adjusting the amplitude, frequency, and phase of the output AC current. The adjustment process does not affect the current waveform on the grid side, replacing the traditional "passive clipping" regulation logic of thyristors and achieving "flexible power regulation." The response speed can reach the microsecond level. Compared to traditional current regulation relying on mechanically moving electrodes or SCR phase control (millisecond level), this application utilizes the high-frequency switching characteristics of IGBTs (microsecond level) combined with the smoothing effect of a DC inductor to quickly respond to the short-circuit / open-circuit trend of the electric arc furnace, thereby reducing flicker. The output current stabilization unit 3 may include a current stabilization bridge circuit 32 (such as a diode bridge, controllable switch bridge, or other commutation circuit) and a DC current stabilization inductor 31. The two AC terminals of the current stabilization bridge circuit 32 are connected across the power supply circuit, and the DC current stabilization inductor 31 is connected between the positive and negative DC terminals of the current stabilization bridge circuit 32. Through the commutation of the current-regulating bridge circuit 32, a DC current in the same direction always flows through the DC current-regulating inductor 31. The inductor core operates in a DC biased magnetic state, avoiding eddy current losses and hysteresis losses generated by AC current in the core, thus reducing inductor power consumption and heat generation. Simultaneously, when the AC current crosses zero, the DC current-regulating inductor 31 releases its stored energy to replenish the load current, maintaining arc stability. This can cope with sudden current changes during load short circuits / open circuits, solving the problem of poor arc stability in traditional systems.

[0036] Understandably, the combination of these modules upgrades and breaks down the traditional thyristor "phase-controlled rectification" function of "voltage regulation + rectification" and its crude current stabilization effect achieved only through an additional series inductor into three independent functional links: "clean rectification + flexible inversion + precise current stabilization". The power supply and current stabilization link composed of input rectification unit 1, power regulation unit 2 and output current stabilization unit 3 does not rely on the thyristor to passively adjust power and phase angle through phase-controlled rectification. Instead, it actively adjusts power parameters and achieves arc stabilization through the topology combination of "rectifier, inverter, current stabilization bridge and DC current stabilization inductor", relying on the flexible switching characteristics of IGBT fully controlled devices and the adaptive linkage of each unit's operating conditions. This design avoids the semi-controlled defects of thyristors and avoids grid-side harmonic pollution and power loss in the traditional thyristor active regulation mode. The problem of reduced current factor is addressed. Furthermore, compared to the coarse current stabilization of inductors in traditional systems, this application relies on the deep integration of the commutation function of the current-stabilizing bridge circuit 32 and the energy storage and release characteristics of the DC current-stabilizing inductor 31. The current-stabilizing bridge circuit 32 is connected across the power supply circuit, and through the commutation of the current, the DC current-stabilizing inductor 31 operates in DC mode, while the electric arc furnace load 4 maintains AC current. The DC current-stabilizing inductor 31 continuously stores magnetic field energy in DC operating mode, releasing energy to replenish the load current when the AC current crosses zero, maintaining continuous arc combustion. Combined with the accurate control of output power parameters by the power regulation unit 2, the arc stabilization accuracy is improved, simultaneously optimizing grid-side power quality and system efficiency. It can also be flexibly adjusted according to the power and arc stabilization requirements of the actual smelting scenario, forming an electric arc furnace power supply system adaptable to different operating conditions.

[0037] It should be noted that the current-regulating bridge circuit 32 in this application differs from the AC / DC controllable rectifier in a traditional DC electric arc furnace in terms of circuit function and control logic. Traditional AC / DC devices are directly connected to the power grid and rely on the phase-controlled regulation of the SCR to change the output voltage / current; that is, rectification and voltage regulation are combined, and the load receives DC power. In this application, however, the voltage amplitude and frequency regulation are handled by the preceding power regulation unit 2. The current-regulating bridge circuit 32 does not perform rectification or active power regulation; instead, it acts as a commutation bridge. Its two AC terminals are connected across the power supply circuit, maintaining AC current on the electric arc furnace load 4 while ensuring that a unidirectional DC current always flows through the DC current-regulating inductor 31 connected between its DC terminals through commutation. Even when using controllable devices, the controllable switch of the current-regulating bridge circuit 32 is mainly used to adjust the inductor's energy storage level or construct an energy discharge protection channel (such as open-circuit discharge), rather than for primary power regulation through waveform cutting as in traditional SCRs. This application improves power quality and current stability performance through an architecture design that decouples power regulation and current commutation.

[0038] like Figure 3As shown, in one embodiment, the electric arc furnace current stabilization system specifically includes an input rectifier unit 1, a power regulation unit 2, and an output current stabilization unit 3, which are connected in sequence. The high-voltage power grid is connected to the input rectifier unit 1 through an input protection module 5, which includes a circuit breaker and a surge arrester. The input rectifier unit 1 includes a transformer 11, an AC-DC rectifier module 12, and a filter capacitor 13. Specifically, the high-voltage power grid passes through the circuit breaker and multiple surge arresters in sequence to the multi-pulse transformer 11 (a combined transformer 11 composed of multiple windings in the figure). The transformer 11, as one of the modules of the input rectifier unit 1, converts the grid voltage into multi-phase staggered AC power, which is then connected to the AC-DC rectifier module 12 and the filter capacitor 13, thereby realizing the conversion of grid AC power to stable DC power. The input rectifier unit 1 is connected to the output of the power regulation unit 2 (the module marked "3H" in the figure, representing three-phase AC power). Preferably, the power regulation unit 2 is a full-bridge inverter, which converts the input DC power into AC power suitable for the three-phase electric arc furnace load 4. The output of the power regulation unit 2 is then connected to the output current stabilizing unit 3. The output current stabilizing unit 3 includes three sets of parallel current stabilizing bridge circuits 32 (each set in the figure is composed of rectifier diodes forming a commutation bridge) and DC current stabilizing inductors 31. The two AC terminals of the current stabilizing bridge circuits 32 (each set in the figure is composed of diodes forming a bridge circuit) are respectively connected across two nodes (points A and B) of each phase power supply circuit. The DC current stabilizing inductors 31 are connected between the positive DC terminal and the negative DC terminal (points C and D) of each current stabilizing bridge circuit 32. Through the commutation of the current stabilizing bridge circuits 32, the DC current in each DC current stabilizing inductor 31 always flows in the same direction, while the current on the electric arc furnace load 4 remains an AC current. When the AC current crosses zero, the DC current stabilizer inductor 31 releases the stored energy to replenish the current to the load, maintain the stability of the electric arc, and finally provide a stable AC power supply to the electric arc furnace load 4 (the power supply terminal at the bottom of the figure).

[0039] In the three-phase output structure of this embodiment, the electric arc furnace load 4 includes three top electrodes 41, which are respectively connected to three sets of output current stabilizing units 3. The three top electrodes 41 generate an electric arc between themselves and the molten pool. The current flows through the molten pool and forms a circuit between the three top electrodes 41. That is, at any given time, some electrodes act as current inflow terminals and others act as current outflow terminals. The currents from each electrode converge through the molten pool to form a circuit, eliminating the need for separate furnace bottom electrodes.

[0040] It should be noted that the multi-pulse transformer 11 used in this embodiment can flexibly select different pulse types according to the actual scenario. For small and medium-sized electric arc furnaces (smelting power below 50MVA), it is usually equipped with a 12-pulse rectifier module, which has a simple structure and low cost, and can meet the grid-side harmonic control requirements of conventional smelting. For large electric arc furnaces (smelting power exceeding 100MVA), a 24-pulse rectifier module can be used, which has stronger harmonic suppression capability (low-order harmonic content can be reduced to below 5%), and can match the grid access standard under high-power scenarios. For refining electric arc furnaces with extremely high power quality requirements, a 36-pulse rectifier combination can also be used to further reduce the grid-side distortion rate.

[0041] like Figure 4 As shown in one embodiment, a partial circuit structure diagram of the input rectifier unit 1 and the power regulation unit 2 is illustrated. The input rectifier unit 1 includes a three-phase full-bridge diode rectifier circuit (AC-DC rectifier module 12), which directly receives the three-phase AC input from the grid side and converts it into DC power. It works with the downstream filter capacitor 13 to achieve DC voltage filtering and regulation. The power regulation unit 2 includes a three-phase full-bridge inverter circuit composed of IGBTs, which inverts the input stable DC power into three-phase AC power (corresponding to output terminals L1, L2, and L3).

[0042] Understandably, diode rectifier circuits do not require phase control adjustment, ensuring that the grid-side current waveform is close to a sine wave from the source, with less harmonic pollution and a high power factor; while IGBT full-bridge inverter circuits have fast switching response speed, can accurately control the parameters of the output AC power, adapt to the power supply requirements of different electric arc furnace loads, and have a simple circuit topology, high reliability, and are easy to maintain and control costs in the later stages.

[0043] It should be noted that the inverter module of power regulation unit 2 is not limited to IGBT devices. In other embodiments, other fully controllable power electronic devices can be selected according to the actual scenario. For example, in the scenario of high-frequency low-power electric arc furnace, MOSFETs can be used as the main inverter device, which has a higher switching frequency and a simpler drive circuit. In the scenario of ultra-high voltage and high power, IGCTs (integrated gate commutator thyristors) can also be selected, which have stronger voltage and current tolerance and can adapt to more extreme power supply requirements. The selection of different devices can be flexibly adjusted according to the power, frequency and other parameters of the electric arc furnace, and all can achieve the flexible adjustment effect of fully controllable inverter.

[0044] It is understandable that the output parameters of the power regulation unit 2 can be flexibly adjusted according to the smelting requirements of the electric arc furnace. This parameter adjustment is achieved through modular expansion of the internal power topology, combination configuration of the converter arms, and adaptation of control strategies. In other embodiments, the number of AC phases output can be single-phase, three-phase, or six-phase, and can also be extended to multi-phase types such as twelve-phase or twenty-four-phase. Single-phase output is adapted to small-scale experimental electric arc furnaces through a single set of converter arms. Three-phase and six-phase outputs meet the conventional smelting requirements of small to medium-sized electric arc furnaces through modular splicing of 3 or 6 sets of arms. Multi-phase outputs such as twelve-phase and twenty-four-phase outputs are achieved through phase-shifting superposition of multiple sets of arms, specifically designed for ultra-large electric arc furnaces or special refining equipment, further reducing current pulsation after rectification and mitigating single-phase power loss. The system can handle multiple power device loads. The output AC power can be low-frequency, power frequency, or medium-frequency, and can be adjusted to high-frequency AC as needed. This is achieved by adjusting the switching frequency and drive timing of the power switching devices. Low-frequency and power frequency are commonly used in conventional melting processes, medium-frequency is suitable for high-efficiency refining scenarios, and high-frequency meets the precise temperature control requirements of special alloy melting. The output AC waveform can include sine waves and square waves, and can also be extended to customized waveforms such as triangular waves and pulse waves. This is achieved by modulating the duty cycle and phase of the power devices through the control circuit. Sine waves are suitable for high-precision smelting with stringent power quality requirements, square waves simplify circuit design and reduce costs, while triangular and pulse waves can match the specific needs of special electric arc heating processes. Through the modular configuration of the above hardware topology and the coordinated adjustment of the control strategy, flexible switching of output parameters can be achieved, enabling the system to more accurately match the operating characteristics of various electric arc furnaces and improve its versatility.

[0045] like Figure 5 The diagram shows the circuit structure of the output current stabilizing unit 3. In one embodiment, the current stabilizing bridge circuit 32 is a diode bridge circuit (composed of D1-D4), which utilizes the unidirectional conductivity of diodes and the full-bridge topology, along with the DC current stabilizing inductor 31, to achieve arc stabilization. The two AC terminals of the current stabilizing bridge circuit 32 are respectively connected to two nodes of the power supply circuit (labeled as node A and node B). The DC current stabilizing inductor 31 is connected between the positive DC terminal and the negative DC terminal of the current stabilizing bridge circuit 32 (labeled as node C and node D). The specific linkage logic is as follows: When the AC output of power regulation unit 2 is in the positive half-cycle (e.g., node A is positive and node B is negative): the load current flows through the electric arc furnace load 4 in the first direction (from node A through the load to node B); simultaneously, part of the current flows from node A to the positive DC terminal node C through diode D1, flows through DC current regulator inductor 31 to the negative DC terminal node D, and then flows back to node B through diode D3. At this time, DC current regulator inductor 31 stores magnetic field energy, and the current direction in the inductor is from the positive DC terminal to the negative DC terminal.

[0046] When the AC current switches to the negative half-cycle (e.g., node B is positive and node A is negative): the load current reverses direction and flows through the arc furnace load 4 in the second direction (from node B through the load to node A); simultaneously, part of the current flows from node B to the positive DC terminal through diode D4, through the DC current regulator 31 to the negative DC terminal, and then back to node A through diode D2. Thanks to the commutation effect of the diode bridge, the current direction in the DC current regulator 31 remains from the positive DC terminal to the negative DC terminal, exactly the same as in the positive half-cycle.

[0047] Therefore, although the direction of the current on the electric arc furnace load 4 changes alternately with the positive and negative half-cycles of the AC current (maintaining AC characteristics), the current in the DC current regulator 31 always maintains the same direction (DC state). This makes the iron core of the DC current regulator 31 work in a DC biased magnetic state, avoiding eddy current losses and hysteresis losses caused by repeated magnetization of the AC current in the iron core, and reducing the power consumption and heat generation of the inductor.

[0048] When the alternating current crosses zero: the voltage provided by the power regulation unit 2 is instantaneously zero, and a normal alternating arc is easily extinguished at this time. However, in this application, the magnetic field energy stored in the DC current-regulating inductor 31 does not disappear instantaneously. The inductor continues to maintain current flow, supplementing the current to the arc furnace load 4 through the diode bridge, helping to maintain the arc and thus improving the stability of the arc.

[0049] If the electric arc furnace load 4 is short-circuited (current surges): the self-inductance effect of the DC current regulator 31 will hinder the rapid rise of current (because the current in the inductor cannot change abruptly), weakening the impact amplitude of the short-circuit current through "energy storage", thus buying time for the front-end protection to act; if the electric arc furnace load 4 experiences arc interruption or zero crossing (impedance surges): in order to maintain the continuity of current, the DC current regulator 31 will generate an induced electromotive force, which is superimposed on the power supply voltage, increasing the success rate of breaking down the air gap between the electrode and the molten pool, thereby assisting the electric arc to reignite quickly and ensuring the continuity of the smelting process.

[0050] Understandably, diodes D1-D4, through bridge commutation logic, ensure that the AC current maintains its AC characteristics on the load while allowing the DC current regulator 31 to always operate with unidirectional current. The DC current regulator 31, relying on its energy storage / release characteristics, maintains the arc when the AC current crosses zero and suppresses current surges. The interaction between these two mechanisms maintains the AC power supply characteristics of the electric arc furnace load while ensuring the inductor operates in a low-loss DC state, simultaneously buffering sudden changes in extreme operating conditions. The diode bridge structure is simple and highly reliable; combined with the DC current regulator 31, it can achieve basic arc stabilization functionality without requiring additional control logic, reducing system complexity and cost.

[0051] It should be noted that the electric arc of an electric arc furnace has a typical negative resistance characteristic (i.e., the voltage decreases as the current increases). If a conventional constant voltage source is used for power supply, it is easy to cause the current positive feedback to run out of control. At this time, the current-regulating bridge circuit 32, through commutation, makes the DC current-regulating inductor 31 operate in a DC biased magnetic state. Unlike traditional AC-side series inductors, the magnetic field energy (E=0.5LI²) within the DC current stabilizer inductor 31 does not repeatedly build up and dissipate with the AC frequency crossing zero, but remains consistently at a high-energy baseline. This continuous high-energy magnetic field causes the inductor to exhibit a significant damping effect on the rate of change of current (di / dt), helping to suppress current runaway caused by negative resistance effects. Furthermore, the output current stabilization unit 3 of this application can also cope with charge collapse (short circuit). At the instant when scrap collapse causes an electrode short circuit, the DC current stabilizer inductor 31 generates a reverse induced electromotive force, hindering current abrupt changes and thus limiting the peak short-circuit current, providing time for the front-end IGBT (power regulation unit 2) to regulate. In addition, it also has the function of assisting arc reignition (circuit breaking / zero crossing). At the instant the AC output crosses zero or the arc breaks, the DC current stabilizer inductor 31 generates an induced electromotive force (L×di / dt) to maintain current continuity, which is superimposed on the power supply voltage, improving the success rate of arc breakdown and air gap reignition, and ensuring the continuity of the smelting process.

[0052] In one embodiment, the current-regulating bridge circuit is a controllable switching bridge topology circuit, including at least one set of first switching branches for forward conduction and at least one set of second switching branches for reverse conduction, with the two branches connected in parallel between the output terminal of the power regulation unit 2 and the electric arc furnace load 4.

[0053] like Figure 6 As shown, in one embodiment, another electric arc furnace current stabilization system is disclosed. This differs from the aforementioned embodiment that uses diodes for passive commutation (…). Figure 5 In this embodiment, the output current stabilization unit 3 adopts a fully controlled bridge commutation circuit. By replacing diodes with controllable switching devices, the system can actively control the commutation timing and inductor energy storage level, which is suitable for smelting conditions with high requirements for arc stabilization accuracy and extreme working condition protection.

[0054] The current-regulating bridge circuit 32 consists of a full-bridge topology composed of four bridge arm devices: a first bridge arm device 321, a second bridge arm device 322, a third bridge arm device 323, and a fourth bridge arm device 324. All four bridge arm devices are controllable switching devices. The first bridge arm device 321 and the fourth bridge arm device 324 form the first switching branch, while the second bridge arm device 322 and the third bridge arm device 323 form the second switching branch. The conduction direction of the first switching branch is consistent with the current direction of the electric arc furnace load 4, while the conduction direction of the second switching branch is opposite to the current direction of the electric arc furnace load 4.

[0055] In the single-phase output structure of this embodiment, the electric arc furnace load 4 is equipped with only one top electrode 41. Therefore, a bottom electrode 42 needs to be set at the bottom of the electric arc furnace to form a complete DC current loop. The bottom electrode 42 includes a bottom electrode plate 421 and several conductive vertical pieces 422 disposed on the bottom electrode plate 421. The conductive vertical pieces 422 are vertically arranged and pass through the refractory material layer at the bottom of the furnace, with their tops in contact with the molten pool. The top electrode 41 is connected to the power regulation unit 2 through the output current stabilizing unit 3, and the bottom electrode plate 421 of the bottom electrode 42 returns to the power regulation unit 2. Thus, a complete closed loop is formed. The two AC terminals of the current stabilizing bridge circuit 32 are respectively connected to the two nodes of the power supply loop, and the DC current stabilizing inductor 31 is connected between the positive DC terminal and the negative DC terminal of the current stabilizing bridge circuit 32. During the positive half-cycle of the AC output from the power regulation unit 2, the load current flows along the first direction through the electric arc furnace load 4 (from the top electrode 41 through the electric arc, the molten pool, and the conductive vertical plate 422 to the bottom electrode plate 421). At the same time, the first bridge arm device 321 and the fourth bridge arm device 324 are turned on, and part of the current flows into the positive DC terminal through the first bridge arm device 321, flows to the negative DC terminal through the DC current stabilizer inductor 31, and then flows into the power supply circuit through the fourth bridge arm device 324. During the negative half-cycle of the AC output, the load current reverses direction and flows along the second direction through the electric arc furnace load 4 (from the bottom electrode plate 421 through the conductive vertical plate 422, the molten pool, and the electric arc to the top electrode 41). At the same time, the second bridge arm device 322 and the third bridge arm device 323 are turned on, and part of the current flows into the positive DC terminal through the third bridge arm device 323, flows to the negative DC terminal through the DC current stabilizer inductor 31, and then returns to the power supply circuit through the second bridge arm device 322. With the two half cycles alternating, the current on the electric arc furnace load 4 maintains AC characteristics, while the current in the DC current stabilizer inductor 31 always maintains the same direction.

[0056] It introduces a phase control regulation mechanism, and its specific working logic is as follows: Similar to a conventional diode bridge, when the power regulation unit 2 outputs AC power, the positive half-cycle is conducted by the first set of diagonal devices (first bridge arm device 321 and fourth bridge arm device 324), and the negative half-cycle is conducted by the second set of diagonal devices (second bridge arm device 322 and third bridge arm device 323). This ensures that both the positive and negative energy of the AC power are converted into DC power, maintaining twice the energy utilization rate of half-wave rectification.

[0057] Unlike diodes, which automatically conduct when a forward voltage is present, the conduction timing of the controllable switching device in this embodiment is controlled. By precisely adjusting the trigger delay angle (conduction angle) of the controllable switch within each half-wave, the system can control the magnitude and timing of the current flowing into the DC current-regulating inductor 31, thereby adjusting the energy storage level of the inductor. In high-current smelting mode, reducing the delay angle allows the switch to conduct earlier, increasing the energy storage of the inductor and enhancing the current replenishment capability at zero crossings to maintain the stability of high-power arcs. In low-current refining mode, increasing the delay angle allows the switch to conduct later, reducing the energy storage of the inductor and adapting to low-power smelting requirements. Furthermore, due to the use of a controllable switching device, the system can perform independent energy storage adjustment for each AC half-wave (i.e., the adjustment frequency is twice the AC frequency). This millisecond-level fast response capability allows the system to quickly compensate for fluctuations in the arc state, improving current regulation accuracy and dynamic response speed compared to uncontrollable diode solutions.

[0058] In yet another embodiment, the current-regulating bridge circuit 32 can also be configured as a semi-controlled bridge commutation circuit, see reference. Figure 6 In the circuit topology, among the four bridge arm devices, one of the two devices connected to each bridge arm is set as a controllable switch (e.g., keeping the first bridge arm device 321 and the second bridge arm device 322 as controllable switches), and the other two devices are set as uncontrollable rectifiers (e.g., the third bridge arm device 323 and the fourth bridge arm device 324 are uncontrollable rectifiers). For example, the two switches in the upper half of the bridge arm can be set as thyristors, and the two switches in the lower half can be set as diodes (or vice versa, depending on the specific control strategy). By controlling the conduction angle of the two controllable switches, the system can still continuously adjust the current and energy storage level in the DC current regulator inductor 31 to meet the power control requirements of the electric arc furnace at different smelting stages. When the AC voltage crosses zero, the two diodes in the circuit can automatically form a freewheeling circuit for the inductor, allowing the energy stored in the DC current regulator inductor 31 to be released to the load to replenish the zero-crossing current. This feature helps maintain the arc without adding an additional freewheeling diode. Compared to a fully controlled bridge, a semi-controlled bridge reduces the gate drive circuit and corresponding control logic by half, thereby reducing hardware costs and system complexity, and improving system reliability and cost-effectiveness. It is suitable for industrial applications that require moderate adjustment response speed but are sensitive to cost.

[0059] Understandably, a semi-controlled commutator bridge can only control the conduction time of controllable devices through gate signals. Since the diodes cannot be actively turned off, they are responsible for providing the freewheeling path. It is suitable for medium-power, unidirectional energy flow, and moderate control accuracy requirements in conventional smelting applications. The control logic is simple and the cost is low. On the other hand, a fully controlled commutator bridge is composed entirely of controllable switching devices (such as SCR, IGBT, GTO, etc.). All devices on the bridge arms can be independently controlled to turn on and off through gate signals. It can not only achieve a wide range of output voltage adjustment, but also complete active inversion (energy feedback to the grid). It is suitable for complex applications such as high-power, high-precision special alloy refining that require energy recovery.

[0060] It should be further explained that in this application Figure 6 The circuit architecture shown can achieve bidirectional asymmetric control characteristics, and its specific implementation varies depending on the type of device (fully controlled or partially controlled): When using Figure 6 In the fully controlled bridge rectifier circuit architecture shown, the four controllable switching devices are logically divided into two diagonal combinations with completely different functions.

[0061] Group 1 (Working Group): The first bridge arm device 321 and the fourth bridge arm device 324 (first switching branch) are defined as the "forward drive group." Their operating logic is as follows: Under normal smelting conditions, the control system only triggers the conduction of the first bridge arm device 321 and the fourth bridge arm device 324 during the positive half-cycle of the AC power supply. This group of devices establishes a charging channel for the inductor during the positive half-cycle of the AC power supply, while maintaining a positive half-cycle AC current on the load. The second bridge arm device 322 and the third bridge arm device 323 (second switching branch) are defined as the "reverse protection group." Their switching logic is as follows: During the normal drive phase, this group of devices remains off and does not participate in power supply. The control system only activates this group of devices when the system detects "extreme conditions" such as arc interruption, overcurrent, or the need for emergency discharge of inductor energy. At this time, the control system triggers the conduction of the second bridge arm device 322 and the third bridge arm device 323, constructing a controlled energy discharge channel to safely discharge excess energy accumulated in the DC current stabilizer inductor 31, preventing high-voltage breakdown of the front-end IGBT device.

[0062] Through this control allocation of "one dedicated driver and one dedicated protector", Figure 6 The fully controlled bridge is actually configured as a half-wave rectifier circuit with active inverter protection to achieve asymmetric bidirectional characteristics.

[0063] Similarly, under this mode, by selecting heterogeneous hardware components, an asymmetric architecture of a semi-controlled bridge circuit can also be achieved, realizing the physical separation of "operation" and "protection".

[0064] Similarly, the first switching branch is defined as the working group, and the second switching branch is defined as the protection group. The difference lies in that the first bridge arm device 321 and the second bridge arm device 322 are controllable switching devices, while the third bridge arm device 323 and the fourth bridge arm device 324 are uncontrollable rectifier devices. During the forward operation phase: the control system only triggers the first bridge arm device 321 during the positive half-cycle of the AC power supply. At this time, the current is output through the path of "first bridge arm device 321 (conducting) - fourth bridge arm device 324 (diode naturally conducting)," achieving unidirectional energy injection. During the negative half-cycle of this phase, the control system forcibly keeps the second bridge arm device 322 off, so the reverse loop is in the cut-off state and no output is generated.

[0065] Extreme protection phase: When the system detects a load-side voltage surge, arc interruption, or an emergency power discharge requirement, the control system actively triggers the second bridge arm device 322 to conduct during the negative half-cycle. At this time, the reverse current forms a loop through "second bridge arm device 322 (conducting) - third bridge arm device 323 (diode naturally conducting)". This loop utilizes the negative voltage polarity of the AC power supply and the superposition of the inductor back EMF, or forms a low-impedance discharge path, thereby achieving the protection function.

[0066] Understandably, this application utilizes a bidirectional controllable switch branch to construct a highly flexible power regulation architecture, capable of switching between "fine current stabilization mode" and "fast protection mode" according to different smelting stages of the electric arc furnace. During normal smelting, the system can employ a full-wave or half-wave phase control strategy to independently control the firing angle of the positive and negative half-cycles of the AC power supply, thereby achieving continuous adjustment of the output current and improving the stability of arc combustion and the accuracy of heat input. Under extreme conditions such as arc ignition, arc extinguishing, or severe load fluctuations, the system can utilize the controllability of the reverse branch to switch to asymmetric logic, actively constructing a reverse discharge or inverter channel. This not only solves the problems of the diode commutation bridge's inability to actively turn off and the uncontrollable freewheeling current, but also achieves clamping and feedback of arc overvoltage energy without increasing hardware costs, balancing regulation performance under normal operating conditions with system safety under extreme conditions. By locking the controllability of the key bridge arms (first and second bridge arms), both fully controllable and semi-controllable schemes are achieved. Regardless of the device used in the lower bridge arm, as long as the upper bridge arms (first and second bridge arms) have controllable switching functions, the on / off control of the forward and reverse circuits can be performed. This allows users to flexibly select the appropriate device based on their actual needs: when using fully controllable devices (full bridge), a double-frequency fast response and bidirectional energy flow capability can be obtained, suitable for high-precision alloy smelting; when using semi-controllable devices (half bridge), although hardware costs are reduced, the controllability of the upper bridge arm can still be utilized to forcibly shut off the reverse circuit during the negative half-cycle, and conduct only during faults to achieve protection. This design improves the system's configuration flexibility, meeting different cost and performance requirements while ensuring core current stabilization and protection capabilities.

[0067] In one embodiment, the selection of controllable switching devices includes, but is not limited to, power electronic devices such as thyristors (SCR), insulated gate bipolar transistors (IGBT), gate turn-off thyristors (GTO), integrated gate commutated thyristors (IGCT), and power MOSFETs. The selection can be made according to the current stabilization system of the electric arc furnace with different power levels and control precision. Among them, the control bridge with SCR has strong impact resistance, while the control bridge with IGBT has high-frequency switching characteristics, which can achieve more precise current and voltage regulation. Switching devices such as SCR and IGBT are mature power electronic devices with strong compatibility and high reliability, which can meet the high current and high voltage operating requirements of the electric arc furnace system, thereby improving the practicality and scalability of the solution.

[0068] In one embodiment, the electric arc furnace current stabilization system further includes a step-down transformer connected in series between the output current stabilization unit 3 and the electric arc furnace load 4 (not shown in the figure).

[0069] Understandably, the step-down transformer can adjust the output voltage of the output current stabilizing unit 3 to a suitable range according to the rated voltage requirements of the electric arc furnace load 4, thus expanding the application scenarios of the system. At the same time, the step-down transformer can also play an electrical isolation role, reducing the impact of load-side faults on the front-end circuit and improving the overall safety and reliability of the system.

[0070] It should be noted that the newly added step-down transformer in this embodiment differs from the functional step-down transformer 11 on the front-end grid side. The step-down transformer is designed for voltage adaptation and safety protection requirements in special smelting scenarios: the front-end grid side transformer 11 reduces the high-voltage grid voltage (e.g., 10kV / 35kV) to the adaptation input voltage (e.g., 380V / 690V) of the power regulation unit 2, providing a safe operating voltage for power electronic devices such as inverters; while the step-down transformer set between the output current stabilization unit 3 and the electric arc furnace load 4 is mainly used in specific scenarios, such as when the electric arc furnace load 4 is a small-capacity, high-precision precision... When smelting furnaces (such as laboratory-grade special alloy refining furnaces and small electrode furnaces), their rated operating voltage (such as 110V / 220V) is lower than the conventional output voltage (380V±5V) of the power regulation unit 2. At this time, the voltage after rectification of the output current stabilization unit 3 can be reduced to the rated voltage range of the load through the step-down transformer, so as to avoid problems such as excessive arc and electrode burnout caused by voltage mismatch. In addition, in the multi-electrode group power supply scenario of large electric arc furnaces, the independent voltage regulation of different electrodes can be realized by setting the turns ratio of multiple step-down transformers to meet the heating needs of different areas of the molten pool and improve the uniformity of smelting.

[0071] Furthermore, this step-down transformer complements the hardware architecture of the power regulation unit 2 and the output current stabilization unit 3 mentioned above. The power regulation unit 2 performs coarse adjustment of the frequency and amplitude of the AC power, the output current stabilization unit 3 completes current stabilization and pulsation suppression, and the step-down transformer undertakes the final voltage adaptation and electrical isolation functions, improving the voltage regulation accuracy of the entire system. At the same time, through electromagnetic isolation, it blocks the transmission of abnormal signals such as arcing and short-circuit faults on the load side to the front-end power regulation unit 2 and the input rectifier unit 1, preventing the damage to the front-end devices caused by the spread of faults.

[0072] like Figure 7 As shown, in one embodiment, the electric arc furnace current stabilization system further includes a control unit 6, which is connected to the input rectifier unit 1, the power regulation unit 2, and the output current stabilization unit 3, respectively. The control unit 6 is configured to: Under normal operation and short-circuit conditions of the electric arc furnace load 4, a trigger signal is sent to the controllable switching device in the first switch branch to adjust the output current; under open-circuit conditions of the electric arc furnace load 4, a trigger signal is sent to the controllable switching device in the second switch branch to turn it on, so as to discharge the energy stored in the DC current regulator in the second switch branch.

[0073] It is understandable that in medium to large-scale industrial DC electric arc furnace / welding machine scenarios (such as...) Figure 6 The circuit shown employs four bridge arm devices, at least two of which are controllable switching devices forming a current-stabilizing bridge. When the molten pool in the furnace is melting normally, the control unit 6 keeps the first bridge arm device 321 on to maintain power supply. If the molten pool material is accidentally short-circuited, the control unit 6 will extend the conduction time of the first bridge arm device 321, causing the current to rise slowly, which, in conjunction with the DC current-stabilizing inductor 31, buffers the short-circuit current. When the electrode lifts, causing the load to open, the control unit 6 switches the second bridge arm device 322 on, forming an energy discharge and freewheeling circuit for the DC current-stabilizing inductor 31. The smooth release of energy stored in the DC current-stabilizing inductor 31 prevents sudden current interruption and prevents high-voltage surges caused by sudden current changes from damaging the front-end power devices.

[0074] Understandably, control unit 6 can accurately regulate the conduction timing of controllable switching devices based on the real-time operating conditions of the electric arc furnace load. Under normal and short-circuit conditions, the first switch branch conducts to ensure stable main current delivery, working in conjunction with the DC current-regulating inductor to quickly suppress sudden changes in short-circuit current. Under open-circuit conditions, the second switch branch conducts as needed, providing a discharge path for the inductor to release energy and preventing high-voltage surges caused by sudden current interruptions. Compared to a commutator bridge without a control unit, this solution achieves closed-loop control with operating condition identification and accurate response, further improving arc stabilization reliability and system efficiency.

[0075] In one embodiment, the control unit 6 is further configured to: monitor at least one operating parameter of the electric arc furnace load 4 in real time, including arc voltage, arc current, or arc impedance; and dynamically adjust at least one output characteristic of the AC power output by the power regulation unit 2 according to the above operating parameters, including frequency, voltage amplitude, or pulse width modulation duty cycle, so as to realize rapid intervention in the arc reignition process or closed-loop precise control of smelting power. By means of dynamic matching and regulation of operating parameters and output characteristics, a precise control link adapted to the complex working conditions of the electric arc furnace is formed, thereby improving the system's response timeliness and control accuracy to the arc state.

[0076] Specifically, such as Figure 7 As shown, the input terminals of the control unit 6 are electrically connected to the input rectifier unit 1, the power regulation unit 2, the output current stabilizing unit 3, and the electric arc furnace load 4, respectively. The input rectifier unit 1 also includes a current detection unit (not shown in the figure), which is used to collect current data from the grid side and the rectifier module in real time to provide a basis for on / off control. The power regulation unit 2 also includes a status feedback interface (not shown in the figure), which is used to provide feedback on the conduction status of the inverter switching transistor and the real-time parameters (frequency, amplitude, etc.) of the output AC power. The output current stabilizing unit 3 also includes a voltage / current sampling terminal (not shown in the figure), which is used to collect the amplitude of the unidirectional current after rectification and the voltage data of the load side. The electric arc furnace load 4 is configured with an operating parameter monitoring node (not shown in the figure), which is used to capture the main smelting parameters such as arc voltage, arc current, and arc impedance.

[0077] Based on the module configuration in the above embodiments, the connection links of the control unit 6 are as follows: The input terminal of the control unit 6 is connected to the current detection module of the input rectifier unit 1, the status feedback interface of the power regulation unit 2, the voltage / current sampling terminal of the output current stabilization unit 3, and the operating parameter monitoring node of the electric arc furnace load 4, respectively. The output terminal is connected to the controllable switching device of the input rectifier unit 1, the inverter switching tube drive terminal of the power regulation unit 2, and the controllable switching device of the output current stabilization unit 3, forming a closed-loop control link of "monitoring-decision-control".

[0078] In one embodiment, coordinated control of output frequency and voltage amplitude based on arc voltage parameters can also be achieved. When the control unit 6 detects a sudden drop in arc voltage (indicating the risk of arc extinction), it will quickly link the power adjustment unit 2 to perform adjustment operations. On the one hand, the power adjustment unit 2 will increase the frequency of the output AC power from the power frequency (50Hz or 60Hz) to the intermediate frequency range (1kHz-10kHz). This intermediate frequency range can avoid the power grid resonance band under the power frequency. Power frequency resonance is prone to arc current harmonic distortion, which increases the difficulty of reignition after arc extinction. Intermediate frequency power supply can make the ionization state of arc plasma more stable and reduce the reignition interval after arc extinction. On the other hand, the power adjustment unit 2 will be controlled to increase the voltage amplitude of the output AC power, enhance the electric field strength between the electrode and the molten pool, accelerate the formation of arc plasma to promote arc reignition, and shorten the follow current interval through the controllable switching device of the output current stabilizing unit 3 to ensure that the arc recovers quickly within 3-5 power cycles and prevent the sudden drop in molten pool temperature from affecting the smelting uniformity.

[0079] Understandably, the aforementioned collaborative control method can accurately capture subtle changes in the arc state and quickly intervene to adjust it. It optimizes the response speed of arc reignition through the linkage of frequency and voltage amplitude, and suppresses current fluctuations with the help of the output current stabilization unit 3, thereby reducing the risk of smelting interruption caused by arc extinction, ensuring the stability and uniformity of the molten pool temperature field, and thus improving the quality consistency of the smelted product. At the same time, it reduces electrode wear and energy waste caused by frequent arc extinction and restart, taking into account both process stability and operational economy.

[0080] It should be noted that in this embodiment, shortening the freewheeling interval by using the controllable switching device of the output current stabilizing unit 3 is different from the discharge function objective under open circuit conditions. Under open circuit conditions, when the electrode separates from the molten pool, causing the load circuit to be physically disconnected, an independent discharge circuit is formed by the inductor and the controllable switch / diode to achieve stable energy discharge, avoid high-voltage surges caused by sudden current interruption that could damage the front-end devices, and maintain the pre-excitation state of the inductor. However, shortening the freewheeling interval when the arc voltage drops sharply is to allow the energy stored in the DC current stabilizing inductor 31 to be fed back to the arc circuit more quickly, avoiding plasma dissipation, and buffering instantaneous current fluctuations to prevent the critical condition from further deteriorating into a short circuit.

[0081] In one embodiment, coordinated control based on arc current parameter regulation and pulse width modulation duty cycle can also be achieved. When the control unit 6 detects in real time that the arc current continuously exceeds the preset safety threshold (such as reaching 120%-150% of the rated operating current, indicating that the load is close to the short-circuit critical state, at which time the loop impedance drops sharply due to the bridging of the molten pool material, the collapse of the furnace charge, etc., and the current shows an uncontrolled upward trend), it will quickly execute a two-dimensional regulation operation through the closed-loop control link. On the one hand, it will link the power regulation unit 2 to control the pulse width modulation duty cycle (PWM duty cycle) of its inverter switching transistor to decrease from 60%-80% in conventional smelting to 30%-50%, by shortening the single The effective power supply time within the cycle is reduced, the average power output to the load is decreased, and the continuous increase of current is suppressed. On the other hand, the synchronous linkage output current stabilizing unit 3 performs duty cycle reduction regulation on its first type of controllable switching device (such as the first bridge arm device 321 or the fourth bridge arm device 324, which are switches whose conduction direction is consistent with the load current), shortens the single conduction time, and, in conjunction with the energy storage characteristic of the DC current stabilizing inductor 31 that "current cannot change abruptly", limits the magnetic energy stored in the inductor to a safe range, avoids the concentrated release of magnetic energy to form an inrush current, and thus suppresses the current peak from exceeding the device tolerance threshold (such as the maximum on-state current of the power switch tube and the rated carrying current of the electrode).

[0082] It is understandable that the collaborative control scheme in the above embodiments, through the dual protection logic of "power source current limiting and current stabilization peak suppression," can not only quickly respond to abnormal surges in arc current and achieve timely and accurate closed-loop current stabilization control, but also reduce the mechanical impact and electrothermal damage of inrush current on core components such as electrodes, power switching tubes, and transformers, thereby extending equipment lifespan and reducing maintenance costs; at the same time, it prevents circuit overcurrent protection triggering or equipment shutdown due to current runaway, ensuring the continuity of the smelting process; furthermore, compared with the control method in traditional technologies that relies solely on a single module of power regulation unit 2 to perform current limiting, this application constructs a "power regulation" system... The unique hardware combination of Unit 2 and Independent Output Current Stabilizer Unit 3, by adding Output Current Stabilizer Unit 3 which includes controllable switching devices and DC current stabilizer inductor 31, forms a dual active control mechanism of "source current limiting and back-end peak suppression". With the coordinated adjustment of pulse width modulation duty cycle (power adjustment unit 2) and controllable switch conduction duty cycle (output current stabilizer unit 3), it not only achieves a dual improvement in the accuracy of current suppression and response speed, but also reduces the current surge and high voltage surge problems under the traditional single current limiting method through the inductor energy storage buffer and controllable freewheeling function of Output Current Stabilizer Unit 3, thus taking into account equipment safety, process stability and operational reliability.

[0083] It should be noted that this embodiment prioritizes current limiting control over direct circuit disconnection. This is because current overruns (approaching short-circuit thresholds) in electric arc furnace smelting scenarios are mostly transient process short circuits caused by charge collapse or molten metal droplet bridging, rather than fault-related short circuits requiring emergency power disconnection, such as electrode breakage or furnace leakage. These transient short circuits typically last only tens to hundreds of milliseconds. Directly disconnecting the circuit would, on the one hand, cause the arc to extinguish instantly, resulting in a sudden drop in molten pool temperature, disrupting the continuity of the smelting process, and even leading to problems such as furnace lining cracking and accelerated electrode wear due to drastic temperature changes. On the other hand, components in the system, such as the DC current regulator inductor 31 and transformer leakage inductance, have the characteristic that "current cannot change abruptly." Direct power disconnection would cause the inductor to instantly release its stored magnetic energy, generating a reverse high-voltage surge far exceeding the device's tolerance, breaking down core power electronic devices such as power switching transistors and thyristor current bridges, causing permanent equipment damage.

[0084] By employing a dual flexible control mechanism—reducing the pulse width modulation duty cycle of the power regulation unit 2 and shortening the on-time of the controllable switch of the output current stabilization unit 3—output power can be limited at the source, while the energy storage buffer effect of the inductor can be used to smoothly suppress current peaks, allowing the system to weather the momentary short circuit without interrupting smelting. Only when the current over-limit duration exceeds a preset safety threshold (e.g., 500ms), and a fault short circuit is identified, will the control unit 6 trigger the ultimate protection mechanism, disconnecting the main controllable switch of the input rectifier unit 1 and cutting off the power supply.

[0085] In one embodiment, coordinated control of the output frequency and pulse width modulation duty cycle based on the arc impedance parameter can also be achieved. When the control unit 6 detects in real time that the arc impedance is continuously higher than the preset process threshold (indicating that the molten pool material shows a solidification trend or the arc length increases due to electrode lifting, at which time the equivalent impedance of the circuit increases, which can easily lead to a decrease in arc power, arc jitter, or even the risk of arc extinction), it will perform a two-dimensional coordinated control operation through the closed-loop control link. On the one hand, it dynamically controls the power adjustment unit 2 to reduce the frequency of its output AC power from the medium frequency range (1kHz-10kHz) of conventional smelting. Adjusting to the low-frequency-medium-frequency sub-range (500Hz-1kHz), the low-frequency-medium-frequency power supply mode can extend the existence time of the arc plasma, improve the rigidity and stability of the arc, and enhance the penetration depth of the arc into the molten pool, preventing heat dissipation caused by the increase in arc length. On the other hand, the pulse width modulation duty cycle of the power adjustment unit 2 is adjusted simultaneously, increasing the duty cycle from the conventional 60%-80% to 80%-90%, increasing the effective power supply time per unit cycle, compensating for the power loss caused by the increase in impedance from the power output end, and ensuring that the melting power is always maintained within the preset process range.

[0086] Understandably, the aforementioned collaborative control scheme, through the regulation logic of "reducing frequency to stabilize the arc and increasing the duty cycle to compensate for power," not only solves the problems of poor arc stability and insufficient heat caused by increased arc impedance, but also improves the current overload problem caused by simply increasing power. At the same time, it ensures the uniformity of the molten pool temperature field and prevents smelting quality defects caused by local solidification of materials. Compared with the traditional fixed frequency and duty cycle control method, its dynamic adaptation to impedance changes further enhances the system's adaptability to complex smelting conditions, taking into account both process stability and energy utilization efficiency.

[0087] In one embodiment, coordinated control based on the fusion of multiple parameters including arc voltage, arc current, and arc impedance can also be achieved to meet the high-precision process requirements of special alloy refining. When the control unit 6 synchronously collects the three parameters of arc voltage, arc current, and arc impedance through the operating parameter monitoring node of the electric arc furnace load 4 and performs real-time data fusion analysis, differentiated control strategies will be implemented for two typical operating conditions: If the arc voltage fluctuation reaches ±5% and the arc current synchronously oscillates periodically, it is determined to be an unstable arc condition. This state will lead to uneven heat distribution in the molten pool, affecting the compositional uniformity of the special alloy. At this time, the control unit 6 prioritizes the linkage with the power adjustment unit 2, first adjusting the voltage amplitude of the output AC power to calibrate it to the reference voltage range set by the process, providing stable basic energy support for the arc; then, it performs fine-tuning of the output frequency (such as dynamic adjustment within ±50Hz in the mid-frequency range of 1kHz-10kHz) to optimize the ionization state of the arc plasma, changing the arc shape from divergent to concentrated, and improving the directional penetration capability of heat.

[0088] If the arc impedance is continuously increasing and the arc current decreases synchronously, it is determined that the melt pool material is not sufficiently melted. This condition is mostly caused by excessively low local temperature in the melt pool and material solidification bridging. At this time, while maintaining a stable arc voltage, the control unit 6 increases the pulse width modulation duty cycle of the power regulation unit 2 to increase the effective output power per unit cycle and compensate for the power loss caused by the increased impedance. At the same time, it links the output current stabilizing unit 3 to control its controllable switching devices to maintain a high-frequency on / off mode. In conjunction with the energy storage characteristics of the DC current stabilizing inductor 31, it suppresses high-frequency current pulsation, ensuring that the power input to the melt pool is stable and controllable, and realizing precise closed-loop power control in the special alloy refining process.

[0089] Understandably, in this embodiment, the multi-parameter fusion and collaborative control scheme breaks through the limitations of traditional single-parameter regulation. Through the linkage analysis of voltage, current, and impedance, it can accurately identify the state of the arc and molten pool under complex refining conditions. Its hierarchical regulation logic of first calibrating energy and then optimizing the morphology, stabilizing voltage and compensating for power, and suppressing high-frequency pulsation not only ensures the stability of the arc and the accuracy of power, but also reduces the risk of current overload or arc extinction caused by single-parameter adjustment. It improves the compositional uniformity and mechanical property consistency of special alloy refining, and meets the process requirements of high-precision smelting.

[0090] like Figure 8 As shown in the embodiments, this application also discloses a current stabilization method for an electric arc furnace, including the following steps: S1. The AC power input from the AC power grid is connected to the input rectifier unit 1 and converted into DC power, which is then sent to the power regulation unit 2. S2. The DC power is converted into AC power that is compatible with the electric arc furnace load 4 through the power regulation unit 2, and the AC power is delivered to the current stabilizing bridge circuit 32. S3. The current stabilizing bridge circuit 32 is used to commutate the AC current in the power supply circuit so that the current in the DC current stabilizing inductor 31 is always a DC current in the same direction, while keeping the current on the electric arc furnace load 4 an AC current. S4. When the AC current crosses zero, the stored magnetic field energy is released through the DC current stabilizer inductor 31 and supplied to the electric arc furnace load 4 through the current stabilizer bridge circuit 32 to maintain the continuous combustion of the electric arc. When the electric arc furnace load 4 is short-circuited or open-circuited, the energy storage and release characteristics of the DC current stabilizer inductor 31 are used to suppress the current change of the electric arc furnace load 4.

[0091] It is understood that the electric arc furnace current stabilization method of this application first converts the AC power from the grid to DC power through the input rectifier unit 1, then inverts the AC power through the power regulation unit 2 to generate AC power adapted to the load, and then uses the commutation effect of the current stabilizing bridge circuit to make the DC current stabilizing inductor work in DC mode. When the AC current crosses zero, the inductor releases energy to supplement the current to the load to maintain arc stability, forming a "rectification-inversion-commutation current stabilization" link. The electric arc furnace load maintains AC power supply characteristics, and the inductor works in DC mode to reduce core losses. The whole method does not rely on thyristors for active power regulation or phase angle control, thus avoiding grid-side harmonic pollution and power factor reduction problems from the root. At the same time, it achieves efficient arc stabilization through the energy storage and release characteristics of the inductor. It is simple to operate, highly reliable, and can significantly improve the working stability of the electric arc furnace load.

[0092] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A current stabilization system for an electric arc furnace, characterized in that, It includes an input rectifier unit (1), a power regulation unit (2), and an output current stabilizer unit (3) that are connected in sequence. The input rectifier unit (1) is used to connect to the AC power grid and convert AC power into DC power; The power regulation unit (2) receives the DC power and inverts the DC power into AC power with adjustable frequency or amplitude to supply the electric arc furnace load (4). The output current stabilizing unit (3) is set in the power supply circuit between the power regulating unit (2) and the electric arc furnace load (4), including a DC current stabilizing inductor (31) and a current stabilizing bridge circuit (32); the current stabilizing bridge circuit (32) includes two AC terminals, a positive DC terminal and a negative DC terminal, the two AC terminals are respectively connected to the output terminal of the power regulating unit (2) and the input terminal of the electric arc furnace load (4); the DC current stabilizing inductor (31) is connected between the positive DC terminal and the negative DC terminal to form a DC inductance circuit; the current stabilizing bridge circuit (32) acts as a commutation bridge so that the current flowing through the DC current stabilizing inductor (31) is always a DC current in the same direction; when the AC current crosses zero or the current changes abruptly, the DC current stabilizing inductor (31) releases energy to the electric arc furnace load (4) through the current stabilizing bridge circuit (32).

2. The electric arc furnace current stabilization system according to claim 1, characterized in that, The current-stabilizing bridge circuit (32) includes a diode bridge circuit or a controllable switch bridge circuit.

3. The electric arc furnace current stabilization system according to claim 2, characterized in that, The current-stabilizing bridge circuit (32) is a controllable switch bridge circuit, including at least one first switch branch that is turned on during the positive half-cycle of AC power and at least one second switch branch that is turned on during the negative half-cycle of AC power. The first switch branch and the second switch branch are turned on alternately so that the current flowing through the DC current-stabilizing inductor (31) always remains in the same direction.

4. The electric arc furnace current stabilization system according to claim 3, characterized in that, The current-stabilizing bridge circuit (32) includes a first bridge arm device (321), a second bridge arm device (322), a third bridge arm device (323), and a fourth bridge arm device (324); the first switching branch includes a first bridge arm device (321) and a fourth bridge arm device (324) located on the first diagonal of the bridge structure, and the second switching branch includes a second bridge arm device (322) and a third bridge arm device (323) located on the second diagonal of the bridge structure. The first bridge arm device (321) and the second bridge arm device (322) are both controllable switching devices, and the third bridge arm device (323) and the fourth bridge arm device (324) are either controllable switching devices or uncontrollable rectifier devices.

5. The electric arc furnace current stabilization system according to claim 4, characterized in that, It also includes a control unit (6), which is connected to the input rectifier unit (1), the power regulation unit (2) and the output current stabilizing unit (3) respectively. The control unit (6) is configured as follows: Under normal operation and short-circuit conditions of the electric arc furnace load (4), a trigger signal is sent to the controllable switching device in the first switch branch, and the energy storage level in the DC current stabilizer inductor (31) is adjusted by controlling the conduction timing; When the electric arc furnace load (4) is open, a trigger signal is sent to the controllable switching device in the second switch branch to turn it on, so as to release the energy stored in the DC current stabilizer inductor (31).

6. The electric arc furnace current stabilization system according to claim 5, characterized in that, The control unit (6) is also configured to: monitor at least one operating parameter of the electric arc furnace load (4) and dynamically adjust at least one output characteristic of the power regulation unit (2) according to at least one of the operating parameters to intervene and control the electric arc, wherein the operating parameter includes the electric arc voltage, electric arc current or electric arc impedance, and the output characteristic includes frequency, voltage amplitude or pulse width modulation duty cycle.

7. The electric arc furnace current stabilization system according to claim 1, characterized in that, The input rectifier unit (1) is a multi-pulse rectifier, including a 6-pulse rectifier, a 12-pulse rectifier or a 24-pulse rectifier.

8. The electric arc furnace current stabilization system according to claim 1, characterized in that, The power regulation unit (2) outputs AC power with the following phases: single-phase, three-phase, or six-phase; AC power type: low-frequency AC, power frequency AC, or medium-frequency AC; and AC power waveform: sine wave or square wave.

9. The electric arc furnace current stabilization system according to claim 1, characterized in that, It also includes a step-down transformer, which is installed in the power supply circuit between the output current stabilizing unit (3) and the electric arc furnace load (4).

10. A method for stabilizing the current of an electric arc furnace, characterized in that, Includes the following steps: S1. The AC power input from the AC power grid is converted into DC power and sent to the power regulation unit (2) by connecting the input rectifier unit (1). S2. The power regulation unit (2) converts the DC power into AC power that is compatible with the electric arc furnace load (4) and delivers the AC power to the current-stabilizing bridge circuit (32). S3. The AC current in the power supply circuit is reversed by the current stabilizing bridge circuit (32) so that the current in the DC current stabilizing inductor (31) connected to the DC terminal of the current stabilizing bridge circuit (32) is always a DC current in the same direction, while keeping the current on the electric arc furnace load (4) an AC current. S4. When the AC current crosses zero, energy is released through the DC current stabilizer inductor (31) and current is supplied to the electric arc furnace load (4) through the current stabilizer bridge circuit (32) to maintain continuous arc combustion. In the case of short circuit or open circuit, the energy storage and release characteristics of the DC current stabilizer inductor (31) are used to suppress the current change of the electric arc furnace load (4).

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