Hybrid compensation device for electric arc furnaces and method of application

Abstract

The mixed compensation device for arc furnace comprises a static reactive generator, a reactive compensation device filter, a high-power full-control IGBT, a control system based on an upper computer, a water cooling system, a disconnecting switch, a current transformer and a voltage sensor, and has a data acquisition unit, a data analysis unit and a control unit in the control system; and the application method of the mixed compensation device for arc furnace comprises three steps. The application solves the problem of response speed of the thyristor in the prior art, improves the voltage fluctuation suppression capability, solves the three-phase imbalance problem, realizes the SVG+FC mixed compensation, solves the harmonics generated by the arc furnace by the FC, simultaneously provides the compensation in the refining period, solves the over-compensation problem in the arc furnace tapping period, so that the SVG only operates in half load in the two time periods, is basically in idle operation in the refining period, the overall loss is greatly reduced, is only about 25%-30% of the SVG compensation, the loss is only about 10% of the traditional TCR type SVC, and the electric energy quality of the arc furnace steelmaking is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of electric arc furnace auxiliary equipment, in particular to a hybrid compensation device for an electric arc furnace and an application method thereof. Background Art

[0002] The electric arc furnace (EAF) is a type of power load with unique operational characteristics. The EAF (electric arc furnace) smelting process can be simply divided into the melting and refining phases. The arc furnace's power load fluctuates dramatically during the initial stages of metal melting (arc striking, perforation, and material collapse), while the load gradually stabilizes during the refining phase. Extensive analysis and engineering practice have shown that the maximum reactive power fluctuations in the arc furnace occur during the melting phase and during three-phase short circuits (caused by material collapse, which short-circuits the three conductors). During these periods, the power factor is very low, approximately 0.2, and the maximum load fluctuation is 1.5 to 3 times the rated capacity of the arc furnace's supporting transformer (specifically determined by system and arc furnace parameters). Rapid reactive power fluctuations can cause voltage fluctuations and flicker. Furthermore, as a nonlinear load, the EAF furnace generates harmonic currents, primarily of the 2nd to 7th order, during operation. Furthermore, because the EAF is an asymmetric load, the most severe condition is a two-phase short circuit with one phase open. Under these conditions, significant negative-sequence currents are generated, causing three-phase imbalance. This can adversely affect power supply lines and cause other electrical equipment to malfunction. Therefore, a solution is needed that can simultaneously address reactive power, harmonics, and negative-sequence currents during the EAF smelting process, while minimizing the adverse effects on power supply lines.

[0003] To overcome problems such as reactive power, harmonics, and negative sequence in the arc furnace smelting process, existing technologies employ compensation power supply technology for arc furnaces. Traditional compensation methods include filters (reactive power compensation devices, or FCs), TCR-type SVCs (nonlinear reactive power compensation devices), and SVGs. However, filters cannot dynamically track changing loads, resulting in under-compensation during the arc furnace melting period and over-compensation during steel tapping. As a result, the average power factor after compensation is only around 0.75. TCR-type SVCs also fail to achieve effective compensation due to the large losses of their phase-controlled reactors (thyristor-controlled reactors) and the slow response of their core thyristors. Although a simple static VAR generator (SVG) can solve the problem of voltage fluctuations, its harmonic control requires an active filtering solution. This consumes a large amount of equipment capacity and places high pressure resistance requirements on its power unit, requiring an increase in the number of series stages. The arc furnace has a long refining time, and the required reactive power accounts for half of the maximum reactive power fluctuation. SVG operates at full load during the melting and tapping periods. Therefore, SVG operates at half or full load for a long time while also dealing with harmonics. This results in significant operating losses and significant drawbacks in practical applications. Summary of the Invention

[0004] In order to overcome the technical limitations of the existing arc furnace compensation power supply, which has the disadvantages as described in the background, the present invention provides a hybrid compensation device and application method for arc furnaces that uses a high-power full-controller IGBT to realize reactive dynamic output power to the power input terminal of the arc furnace under the joint action of relevant mechanisms, solves the problem of response speed of the thyristor, and improves the ability to suppress voltage fluctuations. The main power supply circuit adopts angle connection and phase regulation in the control algorithm, which effectively solves the problem of unbalanced three-phase power supply. At the same time, it combines traditional FC and SVG to realize SVG+FC hybrid compensation to power the arc furnace, which can effectively solve the harmonics generated by the arc furnace, and at the same time provide power supply compensation during the refining period of the arc furnace, solve the problem of over-compensation during the steel-making period, and achieve the purpose of energy saving.

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] A hybrid compensation device for an electric arc furnace comprises a static VAR generator, a reactive compensation device filter, a full-controller IGBT, a control system based on a host computer, a water cooling system, an isolating switch, a current sensor, and a voltage sensor; the characteristic is that the power input end of the isolating switch is electrically connected to the power supply and then electrically connected in parallel with the power input end of the static VAR generator, the reactive compensation device filter, and the full-controller IGBT; the power output end of the static VAR generator, the reactive compensation device filter, and the full-controller IGBT is electrically connected to the power input end of the electric arc furnace; the two signal input ends of the control system are electrically connected to the signal output ends of the voltage sensor and the current sensor respectively, and the signal input ends of the voltage sensor and the current sensor are electrically connected to the power supply; the signal output end of the control system is electrically connected to the signal input end of the static VAR generator, the reactive compensation device filter, and the full-controller IGBT; the water cooling system is installed on the heating surface of the full-controller IGBT; the control system has a data acquisition unit, a data analysis unit, and a control unit software.

[0007] Furthermore, the connection mode of the full-controller IGBT adopts an H-type voltage source chain structure.

[0008] Furthermore, the static VAR generator SVG adopts a delta connection method.

[0009] The application method of the hybrid compensation device for an electric arc furnace is characterized in that it includes the following processes: S1: the data analysis unit uses the average load reactive power of the electric arc furnace during stable steelmaking to calculate the capacity of the reactive compensation equipment filter, and the voltage sensor and current sensor collected by the data acquisition unit output the arc furnace power supply voltage and current data to the control system, and the control unit controls the working mode of the reactive compensation equipment filter. The reactive compensation equipment filter provides average reactive power compensation for the power supply while filtering out the harmonics generated when the electric arc furnace is working. The reactive compensation equipment filter solves the power quality problem of the electric arc furnace during 80% of the working time; S2: when the load is zero during steelmaking in the electric arc furnace, the control unit controls the reactive generator to emit inductive reactive power to offset the capacity of the filter and not to reverse reactive power. When the electric arc furnace is short-circuited and reactive power is generated, the reactive power is generated. The generator emits capacitive reactive power, and the sum of its output capacity and the filter capacity is equal to the maximum reactive power required when the arc furnace starts to work; S3: When the arc furnace is running, the reactive power generator and the reactive power compensation device filter are all put into the power grid. The reactive power compensation device filter fixedly emits capacitive reactive power. The reactive power generator monitors the reactive power situation of the power grid in real time and samples the three-phase reactive current to the control subsystem of the reactive power generator. When the control subsystem receives the sampling signal, it outputs it to the data acquisition unit. The data analysis unit uses the instantaneous reactive power theory to analyze the reactive power demand of each phase, and then calculates the reactive power required for each phase, whether it is capacitive or inductive. Then the control unit triggers the full controller IGBT to work in phases, and solves the reactive power problem and the three-phase imbalance problem at the same time, ensuring the power quality of the arc furnace steelmaking.

[0010] Furthermore, the reactive generator only works when the electric arc furnace is tapping steel or when a short circuit occurs, and does not work at other times.

[0011] Furthermore, the connection method of the reactive power generator and the full-controller IGBT can solve the problem of three-phase reactive power and the problem of three-phase imbalance at the same time.

[0012] Furthermore, in the process S1, in the application of the data analysis unit, in calculating the capacity of the reactive power compensation device filter, it is assumed that the arc furnace consumes inductive reactive power QEAF, and the reactive power compensation device filter FC filters out the harmonics generated by the arc furnace, while providing capacitive reactive power to the arc furnace QFC. When the arc furnace is operating in the melting period, the maximum inductive reactive power demand occurs, and the reactive power generator causes the arc furnace to generate capacitive reactive power, and QSVG+QFC=QEAF is taken. At this time, the reactive power generator only outputs -half capacity of the maximum impact arc furnace load. During the refining period, QFC is equal to QEAF. Although the reactive power generator also tracks the load for dynamic compensation, the reactive power generator output capacity is small during load fluctuations. When steel is tapped, QEAF is zero. At this time, the reactive power generator generates inductive reactive power, and QSVG is equal to QFC. In this way, the output capacity is reduced, so that QS=QSVG+QFC-QL=0.

[0013] Furthermore, in the process S3, the data analysis unit calculates and solves the problem of reactive power and three-phase imbalance. The active power between one phase is fully compensated by the reactive power between the other two phases. The reactive power is 1 / 1.732 times the active power. One phase is positive and the other phase is negative. That is, under the following interphase load, the three-phase active power balance formula is: When both reactive power and imbalance need to be compensated, the total reactive power required by this phase = reactive power demand of this phase + active power compensation demand of other phases, that is, when the three-phase power is as follows When the three-phase reactive power required for full compensation is: Due to the compensation of three-phase imbalance, the connection method of the reactive generator SVG needs to be delta-connected, and the three-phase imbalance can be solved by compensating reactive power in each phase.

[0014] Furthermore, in the control of the control unit, for the reactive generator, a constant reactive power control method is used, the data analysis unit detects the comprehensive current of the load arc furnace and the reactive compensation equipment filter, calculates the comprehensive reactive current of the load and the reactive compensation equipment filter, and the reactive current of the arc furnace is subtracted from the comprehensive reactive current and the negative is the reactive current set value controlled by the reactive generator. According to the fixed value of this reactive current, the full controller IGBT is triggered to turn on to achieve the reactive compensation effect of the arc furnace power supply.

[0015] Compared with the prior art, the beneficial effects of the present invention are: the present invention adopts a high-power full-controller IGBT to realize dynamic reactive output, solves the problem of response speed of the thyristor in the prior art, and improves the ability to suppress voltage fluctuations; the main circuit adopts angle connection, and the control algorithm adopts phase regulation, which effectively solves the problem of three-phase imbalance. At the same time, combined with the traditional FC, SVG+FC hybrid compensation is realized. FC solves the harmonics generated by the arc furnace and provides compensation during the refining period. SVG only needs to solve the instantaneous reactive impact and three-phase imbalance problems during the melting period, and solve the over-compensation problem during the steelmaking period. In this way, SVG only runs at half load in these two time periods, and basically runs at no load during the refining period. The overall loss is greatly reduced, only about 25%-30% of the SVG compensation, and its loss is only about 10% of the traditional TCR type SVC, ensuring the power quality of arc furnace steelmaking. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a block diagram of the architecture of a hybrid compensation device for an electric arc furnace. DETAILED DESCRIPTION

[0017] Figure 1As shown, the hybrid compensation device for an electric arc furnace includes a static VAR generator SVG, a reactive compensation device filter FC, a high-power full-controller IGBT, a control system based on a host computer (which can also provide monitoring and protection for the entire system and send relevant signals to the background), a water cooling system, an isolating switch, a current sensor, a voltage sensor, and other necessary power supply auxiliary equipment; the power input end of the isolating switch is connected to the power supply via a wire and then connected in parallel with the power input end of the static VAR generator SVG, the reactive compensation device filter FC, and the high-power full-controller IGBT via a wire; the power output end of the static VAR generator SVG, the reactive compensation device filter FC, and the high-power full-controller IGBT is connected to the power input end of the arc furnace via a wire; the control system The two signal input terminals and the signal output terminals of the voltage sensor and the current sensor are connected via wires respectively, and the signal input terminals of the voltage sensor and the current sensor are connected to the power supply via wires; the signal output terminal of the control system and the signal input terminals of the static VAR generator SVG, the reactive compensation device filter FC, and the high-power full-controller IGBT (which uses the carrier phase shift principle to achieve power supply regulation output) are connected via wires; the water cooling system is installed on the heating surface of the high-power full-controller IGBT (using deionized water to provide cooling for the power unit to ensure that the heat generated by the high-power full-controller IGBT is dissipated in time to avoid IGBT overheating and ensure the reliable operation of the power unit); the control system has a data acquisition unit, a data analysis unit and a control unit software. The wiring method of the high-power full-controller IGBT adopts an H-type voltage source chain structure (the power input terminal of the high-power full-controller IGBT is connected between the two phases AB\BC\CA of the three-phase electricity,

[0018] A chain H-bridge consists of several single-phase converters (i.e., chain links) connected in series for each phase. The voltage level determines whether a large-capacity transformer is required for system integration. At voltages of 35kV and lower, no transformer is required, offering advantages such as modular design and compact size. The SVG static VAR generator utilizes delta connection (connecting each phase of the power supply or load end-to-end, with each connection point connected as the three phases of a three-phase power supply). The connection method for the SVG static VAR generator and the IGBT power controller utilizes instantaneous reactive power theory, which can simultaneously address three-phase reactive power issues and three-phase imbalance.

[0019] Figure 1As shown, the application method of the hybrid compensation device for arc furnace includes the following process: (1): the data analysis unit uses the average load reactive power of the arc furnace during steady steelmaking to calculate the capacity of the reactive compensation device filter FC (specifically, the existing arc furnace compensation is realized by a static reactive generator SVG, that is, the TCR+FC type. The reactive compensation device filter FC is designed according to the maximum reactive power demand, that is, the reactive power required to be compensated when the arc furnace has a short circuit. When the electric furnace is steadily steelmaking or tapping steel, the excess capacitive reactive power is offset by a thyristor-controlled reactor to achieve constant reactive power. In this way, the reactive compensation device filter FC with a large capacity is always connected to the power grid. Only the current in the reactor is 0 at the moment of short circuit. When the reactor is constantly working at a large current, the loss is large. Moreover, the reactor capacity of the static reactive generator SVG is the sum of the total capacity of the reactive compensation device filter FC. In order to solve the response speed and avoid harmonic saturation, this reactor must be air-core. The large-capacity air-core reactor will generate a large magnetic field interference. The present invention is to solve the above problem by using a large power A dynamic compensation device based on a fully-controlled IGBT replaces the existing thyristor-controlled reactor. Furthermore, while existing reactive power compensation filters (FCs) calculate their capacity based on the maximum impact reactive power at the moment of an arc furnace short circuit, the present invention calculates the capacity of the reactive power compensation filter (FC) based on the average reactive power during steady steelmaking. This improved capacity is approximately half that of traditional nonlinear reactive compensation devices, saving equipment costs. The absence of large reactors (the static VAR generator (SVG) reactor has only 3.5% the power of existing static VAR generator (SVC) reactors), minimizing the impact on the power supply quality of surrounding electrical equipment. During actual operation, the data acquisition unit collects arc furnace supply voltage and current data from voltage and current sensors, which are then output to the control system. The control unit controls the operating mode of the reactive power compensation filter (FC). The reactive power compensation filter (FC) provides average reactive power compensation while filtering out harmonics generated by the arc furnace during operation. This effectively addresses power quality issues during 80% of the arc furnace's operating time. (2) The voltage sensor and current sensor collected by the data acquisition unit output the arc furnace power supply voltage and current data to the control system. When the load is zero during the arc furnace tapping, the control unit controls the reactive power generator SVG to emit inductive reactive power to offset the capacity of the filter, ensuring that reactive power is not reversed (referring to the reactive power direction from the user side to the grid side). When the arc furnace is short-circuited, the reactive power generator SVG emits capacitive reactive power. The sum of its output capacity and the capacity of the reactive power compensation device filter FC is equal to the maximum reactive power required when the arc furnace starts to work. The reactive power generator SVG only works when the arc furnace is tapping or when there is a momentary short circuit. It does not work at other times, so the loss is small.(3): When the arc furnace is running, the reactive power generator SVG and the reactive power compensation device filter FC are all put into the power grid. The reactive power compensation device filter FC emits capacitive reactive power in a fixed manner. The reactive power generator SVG monitors the reactive power of the power grid in real time and samples the three-phase reactive current to the control subsystem of the reactive power generator SVG. When the control subsystem receives the sampling signal, it outputs it to the data acquisition unit. The data analysis unit uses the instantaneous reactive power theory (Steinmetz theory) to analyze the reactive power demand of each phase, and then calculates the reactive power required for each phase, whether it is capacitive or inductive. Then the control unit triggers the IGBT to work in phases, solving the reactive power problem and the three-phase imbalance problem at the same time, ensuring the power quality of the arc furnace steelmaking.

[0020] Figure 1 As shown, in the process (1), in the application of the data analysis unit, the capacity of the reactive compensation device filter FC is calculated. It is assumed that the arc furnace consumes inductive reactive power QEAF. The reactive compensation device filter FC is used to filter out the harmonics generated by the arc furnace and provide capacitive reactive power QFC to the arc furnace. When the arc furnace is working in the melting period, the maximum inductive reactive power demand appears. At this time, the reactive generator SVG causes the arc furnace to generate capacitive reactive power, and takes QSVG+QFC=QEAF. At this time, the reactive generator SVG only outputs half the capacity of the maximum impact load of the arc furnace; during the refining period, QFC is almost equal to QEAF. Although the reactive generator SVG also tracks the dynamic compensation of the arc furnace load, the output capacity of the reactive generator SVG is very small during the load fluctuation process; when the arc furnace steel is discharged, QEAF Almost zero. At this time, the reactive power generator SVG generates inductive reactive power, and QSVG is almost equal to QFC. In this way, the output capacity of the reactive power generator SVG is also about half of that of the traditional compensation method. Therefore, it can be guaranteed that: QS=QSVG+QFC-QL=0 (the overall loss is greatly reduced).

[0021] Figure 1 As shown in the figure, in process (2), the data analysis unit calculates and solves the problem of reactive power and three-phase imbalance. The three-phase unbalanced load involved is based on the principle of susceptance compensation. The principle of susceptance compensation is that the active power between a certain phase of the electrical equipment can be fully compensated by the reactive power between the other two phases. The reactive power is 1 / 1.732 times the active power. One phase is positive and the other phase is negative. That is, under the following interphase load, the three-phase active power balance formula on the system side is: In actual situations, when both reactive power and imbalance need to be compensated, the total reactive power required by this phase = reactive power demand of this phase + active power compensation demand of other phases. That is, when the three-phase interphase power is as follows When , the three-phase reactive power required for full compensation is: To compensate for three-phase imbalance, the SVG wiring method requires delta connection. This three-phase imbalance can be resolved by providing reactive power compensation on a per-phase basis. The control unit utilizes a constant reactive power control method for the reactive power generator (SVG). The data analysis unit detects the combined current between the load arc furnace and the reactive power compensation device filter (FC) (typically obtained by subtracting the grid current from the reactive power generator (SVG) current). It then calculates the combined reactive current between the load and the reactive power compensation device filter (F). The difference between the target (arc furnace) reactive current and the combined reactive current is taken as the negative of the difference, which represents the reactive current setpoint for the reactive power generator (SVG). This set reactive current triggers the IGBT to conduct, achieving the desired reactive power compensation effect for the arc furnace power supply.

[0022] Figure 1 As shown, through all the above technical solutions, the present invention uses a high-power fully-controlled IGBT to achieve dynamic reactive power output, solving the response speed problem of thyristors in the prior art and improving the ability to suppress voltage fluctuations. The main circuit adopts angle connection and the control algorithm adopts phase regulation, which effectively solves the problem of three-phase imbalance. At the same time, combined with the traditional FC, SVG+FC hybrid compensation is realized. FC solves the harmonics generated by the arc furnace and provides compensation during the refining period. SVG only needs to solve the instantaneous reactive power impact and three-phase imbalance problems during the melting period and solve the overcompensation problem during the tapping period. In this way, SVG only operates at half load during these two time periods and basically runs at no load during the refining period. The overall loss is greatly reduced to only about 25%-30% of the compensation of SVG and its loss is only about 10% of the traditional TCR-type SVC, thus ensuring the power quality of arc furnace steelmaking.

[0023] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

Claims

1. A hybrid compensation device for an electric arc furnace, comprising a static VAR generator, a VAR compensation device filter, an IGBT controller, a host computer-based control system, a water cooling system, an isolating switch, a current sensor, and a voltage sensor; characterized in that: The power input end of the isolating switch is electrically connected to the power supply and then electrically connected in parallel with the power input end of the static VAR generator, the reactive compensation device filter, and the full controller IGBT; the power output end of the static VAR generator, the reactive compensation device filter, and the full controller IGBT is electrically connected to the power input end of the arc furnace; the two signal input ends of the control system are electrically connected to the signal output ends of the voltage sensor and the current sensor respectively, and the signal input ends of the voltage sensor and the current sensor are electrically connected to the power supply; the signal output end of the control system is electrically connected to the signal input end of the static VAR generator, the reactive compensation device filter, and the full controller IGBT; the water cooling system is installed on the full controller IGBT. The heating surface of BT; the control system has a data acquisition unit, a data analysis unit and a control unit software; the application method of the hybrid compensation device for the electric arc furnace includes the following process, S1: the data analysis unit uses the average load reactive power of the electric arc furnace during stable steelmaking to calculate the capacity of the reactive compensation device filter, the voltage sensor and current sensor collected by the data acquisition unit output the arc furnace power supply voltage and current data to the control system, the control unit controls the working mode of the reactive compensation device filter, the reactive compensation device filter provides average reactive compensation for the power supply while filtering out the harmonics generated when the electric arc furnace is working, and the reactive compensation device filter solves the power quality problem during the working time of 80% of the electric arc furnace; S2: When the load is zero during steel tapping, the control unit controls the reactive power generator to generate inductive reactive power to offset the filter capacity and prevent reactive power from being reversed. When the arc furnace experiences a short circuit, the reactive power generator generates capacitive reactive power. The sum of its output capacity and the filter capacity equals the maximum reactive power required at the initial start of the arc furnace operation. S3: When the arc furnace is operating, the reactive power generator and the reactive power compensation device filter are both connected to the grid. The reactive power compensation device filter generates capacitive reactive power at a fixed rate. The reactive power generator monitors the reactive power status of the grid in real time and samples the three-phase reactive current to the reactive power generator's control subsystem. Upon receiving the sampled signal, the control subsystem outputs it to the data acquisition unit. The data analysis unit uses instantaneous reactive power theory to analyze the reactive power demand for each phase. It then calculates the reactive power required for each phase and determines whether it is capacitive or inductive. The control unit then triggers the fully-controlled IGBTs in phase by phase, simultaneously resolving the reactive power issue and three-phase imbalance, ensuring the power quality for arc furnace steelmaking.

2. The hybrid compensation device for an electric arc furnace according to claim 1, characterized in that: The wiring method of the full-controller IGBT adopts an H-type voltage source chain structure.

3. The hybrid compensation device for an electric arc furnace according to claim 1, characterized in that: The static VAR generator SVG adopts delta connection.

4. The application method of the hybrid compensation device for an electric arc furnace according to claim 1, characterized in that: The process includes the following steps: S1: the data analysis unit uses the average load reactive power of the arc furnace during steady steelmaking to calculate the capacity of the reactive compensation device filter; the voltage sensor and current sensor collected by the data acquisition unit output the arc furnace power supply voltage and current data to the control system; the control unit controls the working mode of the reactive compensation device filter; the reactive compensation device filter provides average reactive power compensation for the power supply while filtering out harmonics generated by the arc furnace during operation; the reactive compensation device filter solves the power quality problem during 80% of the arc furnace's working time; S2: When the load is zero during steel tapping, the control unit controls the reactive power generator to generate inductive reactive power to offset the filter capacity and prevent reactive power from being reversed. When the arc furnace experiences a short circuit, the reactive power generator generates capacitive reactive power. The sum of its output capacity and the filter capacity equals the maximum reactive power required at the initial start of the arc furnace operation. S3: When the arc furnace is operating, the reactive power generator and the reactive power compensation device filter are both connected to the grid. The reactive power compensation device filter generates capacitive reactive power at a fixed rate. The reactive power generator monitors the reactive power status of the grid in real time and samples the three-phase reactive current to the reactive power generator's control subsystem. Upon receiving the sampled signal, the control subsystem outputs it to the data acquisition unit. The data analysis unit uses instantaneous reactive power theory to analyze the reactive power demand for each phase. It then calculates the reactive power required for each phase and determines whether it is capacitive or inductive. The control unit then triggers the fully-controlled IGBTs in phase by phase, simultaneously resolving the reactive power issue and three-phase imbalance, ensuring the power quality for arc furnace steelmaking.

5. The application method of the hybrid compensation device for an electric arc furnace according to claim 4, characterized in that: The reactive power generator only works when the arc furnace is tapping steel or when there is a momentary short circuit, and does not work at other times.

6. The application method of the hybrid compensation device for an electric arc furnace according to claim 4, characterized in that: The connection method of the reactive power generator and the full controller IGBT can solve the problem of three-phase reactive power and the problem of three-phase imbalance at the same time.

7. The application method of the hybrid compensation device for an electric arc furnace according to claim 4, characterized in that: In process S1, the data analysis unit calculates the capacity of the reactive power compensation device filter, assuming that the arc furnace consumes inductive reactive power QEAF. The reactive power compensation device filter FC filters out harmonics generated by the arc furnace and provides capacitive reactive power QFC to the arc furnace. When the arc furnace is operating in the melting phase, the maximum inductive reactive power demand occurs. The reactive power generator generates capacitive reactive power, and QSVG + QFC = QEAF. At this time, the reactive power generator only outputs half the capacity of the maximum impact arc furnace load. During the refining phase, QFC equals QEAF. Although the reactive power generator also tracks the load for dynamic compensation, the reactive power generator output capacity is small during load fluctuations. During steel tapping, QEAF is zero. At this time, the reactive power generator generates inductive reactive power, and QSVG equals QFC. This reduces the output capacity, making QS = QSVG + QFC - QL = 0.

8. The application method of the hybrid compensation device for an electric arc furnace according to claim 4, characterized in that: In process S3, the data analysis unit calculates and solves the reactive power problem and three-phase imbalance. The active power between one phase is fully compensated by the reactive power between the other two phases. The reactive power is 1 / 1.732 times the active power. One phase is positive and the other phase is negative. That is, under the following interphase load, the three-phase active power balance formula is: When both reactive power and imbalance need to be compensated, the total reactive power required by the phase = the reactive power demand of the phase + the active power compensation demand of other phases. That is, when the three-phase power is as follows: When the three-phase reactive power required for full compensation is: Due to the compensation of three-phase imbalance, the connection method of the reactive generator SVG needs to be delta-connected, and the three-phase imbalance can be solved by compensating reactive power in each phase.

9. The application method of the hybrid compensation device for an electric arc furnace according to claim 4, characterized in that: In the control of the control unit, for the reactive power generator, a constant reactive power control method is used. The data analysis unit detects the comprehensive current of the load arc furnace and the reactive compensation equipment filter, calculates the comprehensive reactive current of the load and the reactive compensation equipment filter, and the difference between the reactive current of the arc furnace and the comprehensive reactive current is taken as the negative of the reactive current set value controlled by the reactive generator. According to the set value of this reactive current, the IGBT of the full controller is triggered to turn on to achieve the reactive compensation effect of the arc furnace power supply.

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