Power converter for arc furnace power supply
The power converter system addresses arc furnace power quality issues by controlling AC power to DC and back, suppressing inrush currents and simplifying transformer design, thereby improving power quality and economic efficiency.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- TMEIC CORP (100 00)
- Filing Date
- 2024-10-30
- Publication Date
- 2026-05-15
AI Technical Summary
Arc furnace operations cause voltage flicker and inrush currents due to reactive power fluctuations and frequent breaker operations, leading to transformer saturation and increased size and cost.
A power converter system with a conversion circuit and control circuit that controls AC power to DC and back to AC, managing breaker states to suppress inrush currents and simplify transformer configuration.
Reduces transformer inrush currents, improves power quality, and simplifies transformer design, enhancing economic efficiency and power system stability.
Smart Images
Figure 2026079384000001_ABST
Abstract
Description
Technical Field
[0005] ,
[0004] , ,
[0001] Embodiments of the present invention relate to a power conversion device for an arc furnace power supply.
Background Art
[0002] In a steelmaking arc furnace, power is supplied from the power system through a furnace transformer. In arc furnace operation, the furnace breaker is frequently opened and closed during the melting process, such as when scrap is charged into the furnace, when the molten steel temperature is measured, or when overcurrent is detected. Also, in arc furnace operation, due to load fluctuations in the steelmaking arc furnace, fluctuations in lagging reactive power occur through the furnace transformer. This fluctuation may cause voltage flicker on the power system bus and the power system, deteriorating the power quality of the system.
[0003] For this reason, a power conversion device for an arc furnace power supply equipped with a forward converter and a reverse converter has been proposed. The power conversion device is connected to the power system bus by the forward converter, and the AC power of the power system bus is converted into DC power by the forward converter. Then, the power conversion device converts the DC power into AC power by the reverse converter and supplies power to the load equipment.
[0004] In an arc furnace facility to which a power conversion device for an arc furnace power supply is applied, the AC power on the load side becomes distorted due to the influence of reactive power generated from the arc furnace, but is once converted into DC power by the reverse converter of the power conversion device and then converted into AC power with reduced distortion by the forward converter. Therefore, the amount of reactive power flowing out to the power system bus and the power system can be suppressed, voltage flicker can be reduced, and the power quality of the power system can be improved.
[0005] Furthermore, in arc furnace equipment, when the furnace circuit breaker between the power system busbar and the furnace transformer is opened, magnetic flux dependent on the voltage phase at the time of opening remains in the transformer core. When the circuit breaker is closed again, if the excitation magnetic flux from when the power was applied is superimposed on the residual magnetic flux, the core may become magnetically saturated. When the magnetic flux density exceeds the saturation magnetic flux density, the excitation impedance decreases sharply, causing an excessive inrush current to flow into the furnace transformer. In arc furnace operation, the furnace circuit breaker is opened and closed frequently during the melting process, so the effect of this inrush current is significant. Therefore, furnace transformers require a robust structure that can withstand the overcurrent and electromagnetic force caused by the inrush current, which contributes to the increased size of furnace transformers and higher manufacturing costs.
[0006] Therefore, in arc furnace equipment, it is desirable to suppress the inrush current of the furnace transformer and to simplify the configuration of the furnace transformer. [Prior art documents] [Patent Documents]
[0007] [Patent Document 1] Japanese Patent Publication No. 2003-259655 [Overview of the project] [Problems that the invention aims to solve]
[0008] Embodiments of the present invention provide a power conversion device for arc furnace power supplies that suppresses the excitation inrush current of a furnace transformer and simplifies the configuration of the furnace transformer. [Means for solving the problem]
[0009] According to an embodiment of the present invention, a power converter for arc furnace power is used in an arc furnace facility comprising: an electrode that generates an arc discharge with a metal material; a furnace circuit breaker that switches between an closed state that enables the supply of AC power to the electrode and an open state that interrupts the supply of AC power to the electrode; and a furnace transformer provided between the furnace circuit breaker and the electrode. The power converter is provided between the power system and the furnace circuit breaker and comprises: a conversion circuit provided between the power system and the furnace circuit breaker; and a control circuit that controls the operation of the conversion circuit. The conversion circuit includes a forward converter that converts AC power supplied from the power system to DC power, and a forward converter that converts the DC power converted by the forward converter to AC power. An arc furnace power converter is provided, comprising: an inverse converter that converts AC power into electricity and outputs the converted AC power to the electrode side, wherein the control circuit comprises a converter control unit that controls the operation of the inverse converter, and the converter control unit receives input of a circuit breaker open command that instructs switching the furnace circuit breaker to the open state and a circuit breaker closed command that instructs switching the furnace circuit breaker to the closed state, and controls the operation of the inverse converter such that, in response to the input of the circuit breaker open command, the magnitude of the AC voltage output from the inverse converter is set to a predetermined value or less, and in response to the input of the circuit breaker closed command, the magnitude of the AC voltage output from the inverse converter is gradually increased from the predetermined value or less to a desired voltage. [Effects of the Invention]
[0010] A power conversion device for arc furnace power supplies is provided that suppresses the inrush current of the furnace transformer and simplifies the configuration of the furnace transformer. [Brief explanation of the drawing]
[0011] [Figure 1] This is a schematic block diagram showing an arc furnace system and a power converter for the arc furnace power supply according to the first embodiment. [Figure 2] This is a schematic block diagram showing an example of a conversion circuit according to the first embodiment. [Figure 3] This is a schematic block diagram showing an example of a control circuit according to the first embodiment. [Figure 4]This is a time chart schematically illustrating an example of the operation of a power converter according to the first embodiment. [Figure 5] This is a schematic block diagram showing a modified example of the conversion circuit according to the first embodiment. [Figure 6] This is a schematic block diagram showing an example of a control circuit according to the second embodiment. [Figure 7] This is a time chart schematically illustrating an example of the operation of a power converter according to the second embodiment. [Figure 8] This is a schematic block diagram showing an example of a control circuit according to the third embodiment. [Figure 9] This is a time chart schematically illustrating an example of the operation of a power converter according to the third embodiment. [Figure 10] This is a schematic block diagram showing an example of a control circuit according to the fourth embodiment. [Figure 11] This is a time chart schematically illustrating an example of the operation of a power converter according to the fourth embodiment. [Modes for carrying out the invention]
[0012] Each embodiment will be described below with reference to the drawings. Please note that the drawings are schematic or conceptual, and the relationships between the thickness and width of each part, as well as the ratios of the sizes of the parts, are not necessarily identical to those of reality. Furthermore, even when representing the same part, the dimensions and ratios may differ between drawings. In this specification and in each figure, elements similar to those described above are denoted by the same reference numerals, and detailed explanations are omitted as appropriate.
[0013] (First embodiment) Figure 1 is a schematic block diagram showing an arc furnace facility and a power converter for the arc furnace power supply according to the first embodiment. As shown in FIG. 1, the arc furnace facility 2 includes a furnace body 3, electrodes 4, a furnace transformer 5, a furnace breaker 6, and an arc furnace power supply power conversion device 10 (hereinafter referred to as the power conversion device 10).
[0014] The furnace body 3 has a space capable of accommodating a metal material (e.g., scrap). The electrodes 4 generate an arc discharge between the metal material accommodated in the furnace body 3 based on the supplied AC power, thereby melting the metal material accommodated in the furnace body 3. More specifically, the arc furnace facility 2 is an AC arc furnace. The electrodes 4 are configured to be able to move up and down by a lifting mechanism (not shown) so as to maintain an appropriate distance required for the generation of arc discharge between the electrodes 4 and the metal material even when the height of the metal material changes due to melting.
[0015] The AC power supplied to the electrodes 4 is, for example, three-phase AC power. The arc furnace facility 2 has, for example, three electrodes 4 corresponding to each phase of the three-phase AC power. However, the AC power supplied to the electrodes 4 is not limited to three-phase AC power and may be any AC power. The configuration of the electrodes 4 may be any configuration capable of generating an arc discharge between the electrodes 4 and the metal material based on the supplied AC power.
[0016] The furnace breaker 6 is provided between the power conversion device 10 and the electrodes 4 (furnace transformer 5). The furnace breaker 6 switches between an on state that enables the supply of AC power to the electrodes 4 side and an open state that cuts off the supply of AC power to the electrodes 4 side. The furnace breaker 6 is switched from the on state to the open state, for example, at the timing required for operations such as charging the metal material into the furnace body 3 or measuring the molten steel temperature, and at the timing when an abnormality such as overcurrent detection is detected.
[0017] The furnace transformer 5 is installed between the furnace circuit breaker 6 and the electrode 4. The furnace transformer 5 transforms the voltage of the AC power supplied via the furnace circuit breaker 6 to a voltage corresponding to the electrode 4, and supplies the transformed AC power to the electrode 4. For example, the furnace transformer 5 steps down the voltage of the AC power supplied via the furnace circuit breaker 6 to a voltage corresponding to the electrode 4, and supplies the stepped-down AC power to the electrode 4.
[0018] Based on the alternating current power supplied from the furnace transformer 5, the electrode 4 generates an arc discharge between itself and the metal material housed in the furnace body 3, as described above, and melts the metal material housed in the furnace body 3.
[0019] The power converter 10 is installed between the power system PS and the furnace circuit breaker 6. The power converter 10 is connected to the power system PS via, for example, the power system busbar 7 and a receiving transformer (not shown in the figure). The receiving transformer steps down the voltage of the AC power supplied from the power system PS to a voltage corresponding to the arc furnace equipment 2 (power converter 10). The power converter 10 receives AC power from the power system PS side via the power system busbar 7 and the receiving transformer.
[0020] The power converter 10 converts the AC power supplied from the power system PS side into DC power, then converts the DC power back into AC power, and supplies the converted AC power to the furnace circuit breaker 6. The power converter 10 also changes the magnitude of the AC voltage supplied to the furnace circuit breaker 6 according to, for example, the processes of the arc furnace equipment 2. The AC power from the power system PS and the AC power supplied from the power converter 10 to the furnace circuit breaker 6 are, like the AC power supplied to the electrode 4, for example, three-phase AC power.
[0021] The power conversion device 10 comprises a conversion circuit 12 and a control circuit 14. The conversion circuit 12 is installed between the power system PS and the furnace circuit breaker 6. The conversion circuit 12 converts AC power supplied from the power system PS side to DC power, and converts DC power back to AC power. The conversion circuit 12 supplies the converted AC power to the furnace circuit breaker 6.
[0022] The control circuit 14 controls the operation of the conversion circuit 12. More specifically, the control circuit 14 controls the operation of the conversion circuit 12 to convert AC power to DC power, and also controls the operation of the conversion circuit 12 to convert DC power to AC power.
[0023] Furthermore, the control circuit 14 controls the operation of the furnace circuit breaker 6. The control circuit 14 controls the switching between the closed state and the open state of the furnace circuit breaker 6.
[0024] The power conversion device 10 further comprises an instrument transformer 16, an instrument current transformer 18, and an instrument transformer 20. The instrument transformer 16 detects the magnitude of the AC voltage supplied from the conversion circuit 12 to the furnace circuit breaker 6 (electrode 4 side) and inputs the detection result to the control circuit 14. The instrument current transformer 18 detects the magnitude of the AC current between the furnace circuit breaker 6 and the furnace transformer 5 and inputs the detection result to the control circuit 14. The instrument transformer 20 detects the magnitude of the AC voltage between the furnace circuit breaker 6 and the furnace transformer 5 and inputs the detection result to the control circuit 14. The control circuit 14 controls the operation of the conversion circuit 12 and the furnace circuit breaker 6 based on the detection results of the instrument transformer 16, the instrument current transformer 18, and the instrument transformer 20, for example.
[0025] The instrument transformer 16, instrument current transformer 18, and instrument transformer 20 are provided in the power conversion device 10 as needed and are optional. The instrument transformer 16, instrument current transformer 18, and instrument transformer 20 may also be components of, for example, the arc furnace equipment 2.
[0026] Figure 2 is a schematic block diagram showing an example of a conversion circuit according to the first embodiment. As shown in Figure 2, the conversion circuit 12 includes a forward converter 30 and a reverse converter 32. The conversion circuit 12 is, for example, a BTB (Back To Back) converter. The forward converter 30 converts AC power supplied from the power system PS side into DC power. The reverse converter 32 converts the DC power converted by the forward converter 30 back into AC power and supplies the converted AC power to the furnace circuit breaker 6. The reverse converter 32 also changes the magnitude of the AC voltage supplied to the furnace circuit breaker 6 according to the process of the arc furnace equipment 2.
[0027] The control circuit 14 controls the operation of the forward converter 30 and the reverse converter 32 of the conversion circuit 12. The control circuit 14 controls the conversion from AC power to DC power by the forward converter 30, and also controls the conversion from DC power to AC power by the reverse converter 32. In addition, the control circuit 14 controls the magnitude of the AC voltage output from the reverse converter 32 by controlling the operation of the reverse converter 32.
[0028] The forward converter 30 has multiple switching elements 30a, and converts AC power to DC power by switching the multiple switching elements 30a. The control circuit 14 controls the operation of the forward converter 30 by controlling the switching of the multiple switching elements 30a.
[0029] Similarly, the inverter 32 has multiple switching elements 32a, and converts DC power to AC power by switching the multiple switching elements 32a. The control circuit 14 controls the operation of the inverter 32 by controlling the switching of the multiple switching elements 32a.
[0030] The forward converter 30 is, for example, a three-phase full-bridge circuit in which six switching elements 30a are connected in a three-phase full-bridge configuration. Similarly, the reverse converter 32 is, for example, a three-phase full-bridge circuit in which six switching elements 32a are connected in a three-phase full-bridge configuration. However, the forward converter 30 and the reverse converter 32 are not limited to three-phase full-bridge circuits. The configuration of the forward converter 30 may be any configuration that enables conversion from AC power to DC power by switching multiple switching elements 30a. The configuration of the reverse converter 32 may be any configuration that enables conversion from DC power to AC power by switching multiple switching elements 32a.
[0031] Furthermore, the conversion circuit 12 further includes, for example, a charge storage element (not shown in the diagram). The charge storage element is provided between the forward converter 30 and the reverse converter 32, and suppresses voltage fluctuations of the DC power converted by the forward converter 30. This allows for a more stable supply of DC power from the forward converter 30 to the reverse converter 32.
[0032] A capacitor, for example, can be used as the charge storage element. In other words, the charge storage element is a smoothing capacitor. However, the charge storage element is not limited to a capacitor; any element capable of suppressing voltage fluctuations of the DC power converted by the forward converter 30 may be used. Furthermore, the charge storage element can be provided as needed and can be omitted. The charge storage element may be provided as appropriate, for example, depending on the circuit configuration of the conversion circuit 12.
[0033] Figure 3 is a schematic block diagram showing an example of a control circuit according to the first embodiment. Figure 4 is a time chart schematically illustrating an example of the operation of the power converter according to the first embodiment. As shown in Figure 3, the control circuit 14 includes a circuit breaker control unit 40 that controls the operation of the furnace circuit breaker 6, and a converter control unit 42 that controls the operation of the inverse converter 32.
[0034] The circuit breaker control unit 40 receives a circuit breaker open command instructing the switching of the furnace circuit breaker 6 to the open state, and a circuit breaker close command instructing the switching of the furnace circuit breaker 6 to the closed state. The circuit breaker open command and the circuit breaker close command are input to the circuit breaker control unit 40 (control circuit 14) from, for example, a higher-level controller of the arc furnace equipment 2. The circuit breaker open command and the circuit breaker close command may be generated within the control circuit 14 based on, for example, the detection of an overcurrent based on the detection result of the instrument current transformer 18, and the generated circuit breaker open command and circuit breaker close command may be input to the circuit breaker control unit 40. The method of inputting the circuit breaker open command and the circuit breaker close command to the circuit breaker control unit 40 is not limited to the above, and any method that allows the circuit breaker open command and the circuit breaker close command to be appropriately input to the circuit breaker control unit 40 may be used.
[0035] The circuit breaker control unit 40 has a control signal generation unit 40a. Based on the input circuit breaker open command and circuit breaker close command, the control signal generation unit 40a generates a control signal to switch between the closed state and the open state of the furnace circuit breaker 6, and inputs the generated control signal to the furnace circuit breaker 6.
[0036] As a result, the circuit breaker control unit 40 switches the closed state and the open state of the furnace circuit breaker 6 in response to the input circuit breaker open command and circuit breaker closed command. Specifically, the circuit breaker control unit 40 switches the furnace circuit breaker 6 from the closed state to the open state in response to the input of the circuit breaker open command (for example, timing t11 in Figure 4). Then, the circuit breaker control unit 40 switches the furnace circuit breaker 6 from the open state to the closed state in response to the input of the circuit breaker closed command (for example, timing t12 in Figure 4).
[0037] The converter control unit 42, like the circuit breaker control unit 40, receives input of circuit breaker open commands and circuit breaker close commands. The converter control unit 42 includes an output value calculation unit 42a and a control signal generation unit 42b. The output value calculation unit 42a calculates the magnitude of the AC voltage output from the inverse converter 32 based on the input circuit breaker open commands and circuit breaker close commands. In other words, the output value calculation unit 42a calculates the amplitude (amplitude command value) of the AC voltage output from the inverse converter 32 based on the input circuit breaker open commands and circuit breaker close commands.
[0038] The control signal generation unit 42b generates a control signal corresponding to the magnitude (amplitude) of the AC voltage calculated by the output value calculation unit 42a, and inputs the generated control signal to the inverter 32, thereby controlling the operation of the inverter 32 so that it outputs an AC voltage of the magnitude calculated by the output value calculation unit 42a. The control signal is, for example, a control signal for controlling the switching of multiple switching elements 32a of the inverter 32.
[0039] As shown in Figure 4, the output value calculation unit 42a reduces the magnitude of the AC voltage output from the inverter 32 to zero in response to the input of the circuit breaker open command (for example, at timing t11 in Figure 4). In other words, the output value calculation unit 42a reduces the amplitude of the AC voltage output from the inverter 32 to zero in response to the input of the circuit breaker open command.
[0040] Then, in response to the input of the circuit breaker closing command, the output value calculation unit 42a calculates the magnitude of the AC voltage output from the inverter converter 32 so as to gradually increase the magnitude of the AC voltage output from the inverter converter 32 from zero to a desired voltage (for example, at timings t12 to t13 in Figure 4).
[0041] The output value calculation unit 42a, for example, gradually increases the amplitude of the AC voltage output from the inverter 32 from zero to a desired magnitude (rated value) over a predetermined period in response to the input of the circuit breaker closing command, so that the amplitude of the AC voltage output from the inverter 32 reaches a desired magnitude (rated value) a predetermined period after the timing at which the input of the circuit breaker closing command is received. For example, in the example shown in Figure 4, the input of the circuit breaker closing command is received at timing t12, and the amplitude of the AC voltage output from the inverter 32 is gradually increased from zero so that the amplitude of the AC voltage output from the inverter 32 reaches the rated value at timing t13, a predetermined period later.
[0042] Thus, in the power converter 10 according to this embodiment, the converter control unit 42 controls the operation of the inverter converter 32 so as to set the magnitude of the AC voltage output from the inverter converter 32 to zero in response to the input of a circuit breaker open command, and to gradually increase the magnitude of the AC voltage output from the inverter converter 32 from zero to a desired voltage in response to the input of a circuit breaker close command. In other words, the converter control unit 42 controls the operation of the inverter converter 32 so as to set the magnitude of the AC voltage output from the inverter converter 32 to zero in synchronization with the switching of the furnace circuit breaker 6 to the open state, and to gradually increase the magnitude of the AC voltage output from the inverter converter 32 from zero to a desired voltage in synchronization with the switching of the furnace circuit breaker 6 to the closed state.
[0043] In the power converter 10 according to this embodiment, the power is applied starting from a voltage lower than the rated voltage, so the excitation flux superimposed on the residual magnetic flux of the core of the furnace transformer 5 can be suppressed. Therefore, the excitation inrush current when the furnace circuit breaker 6 is switched on can be suppressed.
[0044] In the arc furnace equipment 2, when the furnace circuit breaker 6 directly above the furnace transformer 5 is switched on, the excitation flux during energization superimposes on the residual magnetic flux of the core of the furnace transformer 5, potentially causing magnetic saturation of the core and inrush current (for example, 5 to 10 times the rated current) to flow into the furnace transformer 5. In the operation of the arc furnace equipment 2, it is common practice to switch on the furnace circuit breaker 6 for each charge, and furthermore, the furnace circuit breaker 6 is switched on and off during the energization of each charge for additional metal material charging, temperature measurement of molten steel, and composition confirmation. Therefore, there is a possibility that inrush current will flow several times for each charge of about one hour. If the furnace transformer 5 is made to have a robust structure that can withstand the overcurrent and electromagnetic force caused by the inrush current, there are concerns that the size of the furnace transformer 5 will increase and manufacturing costs will increase.
[0045] In contrast, the power converter 10 according to this embodiment can suppress the excitation flux superimposed on the residual magnetic flux of the core of the furnace transformer 5 when the furnace circuit breaker 6 is switched on, thereby suppressing the excitation inrush current. Therefore, the power converter 10 according to this embodiment can simplify the configuration of the furnace transformer 5. This eliminates the need for excessive overload capacity in the furnace transformer 5, thereby suppressing the need to increase the size of the furnace transformer 5 and the increase in manufacturing costs. Furthermore, for example, the lifespan of the furnace transformer 5 can be extended.
[0046] In the power converter 10 according to this embodiment, the power is first converted to DC power by the inverse converter 32 and then converted to AC power with suppressed distortion by the forward converter 30. This suppresses the amount of reactive power flowing out to the power system bus 7 and power system PS, reduces voltage flicker, and improves the power quality of the power system PS. Furthermore, as described above, the power converter 10 according to this embodiment suppresses the excitation inrush current and simplifies the configuration of the furnace transformer 5. Thus, the power converter 10 according to this embodiment can improve the power quality of the power system PS and improve the economic efficiency of the arc furnace equipment 2.
[0047] Furthermore, the magnitude of the AC voltage output from the inverter 32 when a circuit breaker closing command is received does not necessarily have to be zero. The magnitude of the AC voltage output from the inverter 32 when a circuit breaker closing command is received can be any voltage below a predetermined value that is lower than the desired voltage (rated voltage) and capable of appropriately suppressing the excitation flux superimposed on the residual magnetic flux of the core of the furnace transformer 5. Similarly, the magnitude of the AC voltage output from the inverter 32 when a circuit breaker opening command is received does not necessarily have to be zero. The magnitude of the AC voltage output from the inverter 32 when a circuit breaker opening command is received can be any voltage below a predetermined value. In other words, the converter control unit 42 should control the operation of the inverter 32 so that, in response to a circuit breaker opening command, the magnitude of the AC voltage output from the inverter 32 is below a predetermined value, and in response to a circuit breaker closing command, the magnitude of the AC voltage output from the inverter 32 is gradually increased from below a predetermined value to the desired voltage.
[0048] Furthermore, in the above embodiment, the control circuit 14 controls the switching between the closed and open states of the furnace circuit breaker 6. However, the control circuit 14 does not necessarily have to control the switching between the closed and open states of the furnace circuit breaker 6. The switching between the closed and open states of the furnace circuit breaker 6 may be controlled by another control device, such as a higher-level controller of the arc furnace equipment 2. The control circuit 14 only needs to be configured such that at least the converter control unit 42 receives inputs of circuit breaker open commands and circuit breaker closed commands and controls the magnitude of the AC voltage output from the inverter 32 in synchronization with the switching between the closed and open states of the furnace circuit breaker 6.
[0049] Figure 5 is a block diagram schematically showing a modified example of the conversion circuit according to the first embodiment. As shown in Figure 5, the conversion circuit 12a further includes a forward converter transformer 34 and a reverse converter transformer 36. The forward converter transformer 34 is installed between the power system PS (power system busbar 7) and the forward converter 30. The reverse converter transformer 36 is installed between the reverse converter 32 and the furnace circuit breaker 6.
[0050] In the conversion circuit 12a, the input and output voltages of the conversion circuit 12a can be adjusted by the forward converter transformer 34 and the reverse converter transformer 36. Therefore, compared to the conversion circuit 12 shown in Figure 2, the conversion circuit 12a can be more easily applied to any power system PS and any arc furnace load (such as electrodes 4 and furnace transformer 5). In addition, it is possible to easily adjust the withstand voltage and other parameters required for the forward converter 30 and reverse converter 32, thereby increasing the design flexibility of the forward converter 30 and reverse converter 32.
[0051] Alternatively, the system may be configured to provide only the forward converter transformer 34 and adjust only the magnitude of the input voltage, or to provide only the reverse converter transformer 36 and adjust only the magnitude of the output voltage. The forward converter transformer 34 and the reverse converter transformer 36 may be appropriately provided in the conversion circuit 12a as needed.
[0052] (Second embodiment) Figure 6 is a schematic block diagram showing an example of a control circuit according to the second embodiment. Figure 7 is a time chart schematically illustrating an example of the operation of the power converter according to the second embodiment. As shown in Figure 6, the circuit breaker control unit 40 in the control circuit 14a further includes a delay time setting unit 40b. Components that are substantially the same in function and configuration as those in the above embodiment are denoted by the same reference numerals, and detailed explanations are omitted.
[0053] The delay time setting unit 40b receives a circuit breaker open command. The delay time setting unit 40b sets a predetermined delay time for the input circuit breaker open command and processes the input circuit breaker open command to delay by the predetermined delay time. Then, the delay time setting unit 40b inputs the circuit breaker open command, which has been processed to delay by the predetermined delay time, to the control signal generation unit 40a. In other words, the delay time setting unit 40b is a delay circuit.
[0054] The control signal generation unit 40a generates a control signal to switch between the closed and open states of the furnace circuit breaker 6, similar to the embodiment described above, based on the circuit breaker closing command input from a higher-level controller and the circuit breaker opening command input from the delay time setting unit 40b, and inputs the generated control signal to the furnace circuit breaker 6.
[0055] As shown in Figure 7, in this example, the output value calculation unit 42a gradually reduces the magnitude of the AC voltage output from the inverter 32 in response to the input of the circuit breaker open command, thereby reducing the magnitude of the AC voltage output from the inverter 32 to zero over a predetermined time (for example, timings t21 to t22 in Figure 7). In other words, the output value calculation unit 42a gradually reduces the amplitude of the AC voltage output from the inverter 32 in response to the input of the circuit breaker open command, thereby reducing the amplitude of the AC voltage output from the inverter 32 to zero over a predetermined time.
[0056] Furthermore, in this case, the output value calculation unit 42a sets the frequency of the AC voltage output from the inverter 32 to a frequency higher than the rated frequency in response to the input of the circuit breaker open command. That is, in response to the input of the circuit breaker open command, the output value calculation unit 42a sets the frequency of the AC voltage output from the inverter 32 to a frequency higher than the rated frequency, while gradually reducing the magnitude of the AC voltage output from the inverter 32, thereby reducing the magnitude of the AC voltage output from the inverter 32 to zero over a predetermined time. This makes it possible to reduce the magnitude of the AC voltage output from the inverter 32 to zero at a faster rate. The rated frequency is, for example, the frequency during normal operation of the arc furnace equipment 2. The rated frequency is, for example, the same as the frequency of AC power in the power system PS.
[0057] However, the frequency used to reduce the magnitude of the AC voltage output from the inverter 32 may be the same as the rated frequency. The output value calculation unit 42a may, in response to the input of a circuit breaker opening command, set the frequency of the AC voltage output from the inverter 32 to the rated frequency and gradually reduce the magnitude of the AC voltage output from the inverter 32, thereby reducing the magnitude of the AC voltage output from the inverter 32 to zero over a predetermined time.
[0058] The output value calculation unit 42a, in response to the input of a circuit breaker closing command, gradually reduces the amplitude of the AC voltage output from the inverter 32 from a desired magnitude (rated value) to zero over a predetermined period, so that the amplitude of the AC voltage output from the inverter 32 becomes zero a predetermined period after the timing at which the circuit breaker opening command is received. For example, in the example shown in Figure 7, the input of the circuit breaker opening command is received at timing t21, and the amplitude of the AC voltage output from the inverter 32 is gradually reduced to zero so that the amplitude of the AC voltage output from the inverter 32 becomes zero at timing t22, a predetermined period later.
[0059] The delay time set by the delay time setting unit 40b in response to the circuit breaker open command is set to match a predetermined time for the output value calculation unit 42a to reduce the magnitude of the AC voltage output from the inverter 32. As a result, the circuit breaker control unit 40 switches the furnace circuit breaker 6 to the open state after the converter control unit 42 has reduced the magnitude (amplitude) of the AC voltage output from the inverter 32 to zero.
[0060] In this example, the output value calculation unit 42a calculates the magnitude of the AC voltage output from the inverter converter 32 in response to the input of the circuit breaker closing command, so that the magnitude of the AC voltage output from the inverter converter 32 is set to a desired voltage (for example, from timing t23 onwards in Figure 7). In other words, the output value calculation unit 42a calculates the amplitude of the AC voltage output from the inverter converter 32 in response to the input of the circuit breaker closing command, so that the amplitude of the AC voltage output from the inverter converter 32 is set to a desired magnitude (rated value).
[0061] Thus, in this example, the converter control unit 42 controls the operation of the inverter 32 so that, in response to the input of a circuit breaker open command, the magnitude of the AC voltage output from the inverter 32 is gradually reduced to zero over a predetermined time, and in response to the input of a circuit breaker close command, the magnitude of the AC voltage output from the inverter 32 is set to a desired voltage. In other words, the converter control unit 42 controls the operation of the inverter 32 so that, in synchronization with the switching of the furnace circuit breaker 6 to the open state, the magnitude of the AC voltage output from the inverter 32 is gradually reduced to zero over a predetermined time, and in synchronization with the switching of the furnace circuit breaker 6 to the closed state, the magnitude of the AC voltage output from the inverter 32 is set to a desired voltage.
[0062] As a result, in this example, when switching the furnace circuit breaker 6 to the open state, the residual magnetic flux remaining in the core of the furnace transformer 5 can be reduced. Therefore, even when the rated voltage is applied at the same time as the furnace circuit breaker 6 is re-closed by the circuit breaker closing command, the residual magnetic flux in the core of the furnace transformer 5 is small, which suppresses over-excitation of the core of the furnace transformer 5 and suppresses the generation of inrush current. As a result, in this example as well, the configuration of the furnace transformer 5 can be made simpler, similar to the embodiment described above. As with the embodiment described above, the power quality of the power system PS can be improved, and the economic efficiency of the arc furnace equipment 2 can be improved.
[0063] The target value for the magnitude of the AC voltage output from the inverter 32 when a circuit breaker open command is received does not necessarily have to be zero. The target value for the magnitude of the AC voltage output from the inverter 32 when a circuit breaker open command is received is lower than the desired voltage and can be a voltage below a predetermined value that can appropriately reduce the residual magnetic flux remaining in the core of the furnace transformer 5. The converter control unit 42 should control the operation of the inverter 32 so that, in response to the input of a circuit breaker open command, the magnitude of the AC voltage output from the inverter 32 is gradually reduced to below a predetermined value over a predetermined time.
[0064] (Third embodiment) Figure 8 is a schematic block diagram showing an example of a control circuit according to the third embodiment. Figure 9 is a time chart schematically illustrating an example of the operation of a power converter according to the third embodiment. As shown in Figure 8, in the control circuit 14b, the converter control unit 42 further includes a voltage phase storage unit 42c.
[0065] The voltage phase memory unit 42c receives the input of a circuit breaker open command, as well as the input of the detected value of the magnitude of the AC voltage between the furnace circuit breaker 6 and the furnace transformer 5, which is detected by the instrument transformer 20. In other words, the voltage phase memory unit 42c receives the detected value of the magnitude of the AC voltage on the primary side of the furnace transformer 5 (the primary voltage of the furnace transformer).
[0066] The voltage phase storage unit 42c stores the phase of the AC voltage on the primary side of the furnace transformer 5 at the time the circuit breaker open command was received, based on the input circuit breaker open command and the detected value of the magnitude of the AC voltage (for example, timing t31 in Figure 9). In other words, the voltage phase storage unit 42c stores the phase of the AC voltage on the primary side of the furnace transformer 5 when the furnace circuit breaker 6 is switched to the open state. If the AC voltage on the primary side of the furnace transformer 5 is a three-phase AC voltage, the voltage phase storage unit 42c stores the phase of each phase of the three-phase AC voltage. The voltage phase storage unit 42c then inputs the stored phases to the output value calculation unit 42a.
[0067] In this example, the output value calculation unit 42a sets the magnitude of the AC voltage output from the inverter 32 to zero in response to the input of the circuit breaker open command (for example, timing t31 in Figure 9).
[0068] In this example, when the output value calculation unit 42a receives a circuit breaker closing command, it calculates the magnitude of the AC voltage to be output from the inverter 32 based on the phase stored in the voltage phase storage unit 42c, so as to output an AC voltage that is in the same phase as when the furnace circuit breaker 6 is switched to the open state (for example, from timing t32 onwards in Figure 9).
[0069] Thus, in this example, the converter control unit 42 controls the operation of the inverter converter 32 so that, in response to the input of a circuit breaker open command, the magnitude of the AC voltage output from the inverter converter 32 is set to zero (below a predetermined value), and in response to the input of a circuit breaker close command, the inverter converter 32 outputs an AC voltage that is in phase with the same state as when the furnace circuit breaker 6 is switched to the open state, based on the phase stored in the voltage phase storage unit 42c. In other words, the converter control unit 42 controls the operation of the inverter converter 32 so that, in synchronization with the switching of the furnace circuit breaker 6 to the open state, the magnitude of the AC voltage output from the inverter converter 32 is set to zero (below a predetermined value), and in synchronization with the switching of the furnace circuit breaker 6 to the closed state, the inverter converter 32 outputs an AC voltage that is in phase with the same state as when the furnace circuit breaker 6 is switched to the open state, based on the phase stored in the voltage phase storage unit 42c.
[0070] As a result, in this example, when switching the furnace circuit breaker 6 to the closed state, the core of the furnace transformer 5 can be excited with a phase that is continuous with the phase when the furnace circuit breaker 6 is switched to the open state, relative to the magnetization curve of the core of the furnace transformer 5, thereby suppressing the generation of excitation inrush current. As a result, in this example as well, the configuration of the furnace transformer 5 can be made simpler, similar to the embodiment described above. As with the embodiment described above, the power quality of the power system PS can be improved, and the economic efficiency of the arc furnace equipment 2 can be improved.
[0071] (Fourth embodiment) Figure 10 is a schematic block diagram showing an example of a control circuit according to the fourth embodiment. Figure 11 is a time chart schematically illustrating an example of the operation of a power converter according to the fourth embodiment. As shown in Figure 10, the circuit breaker control unit 40 in the control circuit 14c further includes a residual magnetic flux calculation unit 40c and an closing phase angle calculation unit 40d.
[0072] The residual flux calculation unit 40c receives the input of a circuit breaker open command, as well as the detected value of the magnitude of the AC voltage between the furnace circuit breaker 6 and the furnace transformer 5, which is detected by the instrument transformer 20. In other words, the residual flux calculation unit 40c receives the detected value of the magnitude of the AC voltage on the primary side of the furnace transformer 5 (furnace transformer primary voltage).
[0073] The residual magnetic flux calculation unit 40c calculates the magnitude of the residual magnetic flux remaining in the core of the furnace transformer 5 when the furnace circuit breaker 6 is switched to the open state, based on the input circuit breaker open command and the detected magnitude of the AC voltage on the primary side of the furnace transformer 5. The residual magnetic flux calculation unit 40c calculates the magnitude of the residual magnetic flux remaining in the core of the furnace transformer 5 by, for example, integrating the magnitude of the AC voltage on the primary side of the furnace transformer 5. The residual magnetic flux calculation unit 40c inputs the calculation result of the magnitude of the residual magnetic flux to the switching phase angle calculation unit 40d.
[0074] The switching phase angle calculation unit 40d calculates the optimal phase of the AC voltage supplied to the furnace transformer 5 when switching the furnace circuit breaker 6 to the closed state, based on the magnitude of the residual magnetic flux calculated by the residual magnetic flux calculation unit 40c. The switching phase angle calculation unit 40d calculates the optimal switching phase according to the residual magnetic flux, for example, so that the excitation magnetic flux superimposed on the residual magnetic flux does not exceed the magnetic flux saturation level. The switching phase angle calculation unit 40d inputs the calculation result of the optimal phase to the control signal generation unit 40a.
[0075] The control signal generation unit 40a receives input of a circuit breaker open command, a circuit breaker close command, and the calculation result of the optimal phase, as well as input of the detected value of the magnitude of the AC voltage supplied to the furnace circuit breaker 6 from the conversion circuit 12 detected by the instrument transformer 16. In other words, the control signal generation unit 40a receives input of the detected value of the output voltage of the inverter 32.
[0076] The control signal generation unit 40a generates a control signal to switch the furnace circuit breaker 6 from the closed state to the open state in response to the input of a circuit breaker open command, and inputs the generated control signal to the furnace circuit breaker 6, thereby switching the furnace circuit breaker 6 from the closed state to the open state.
[0077] Then, upon receiving a circuit breaker closing command, the control signal generation unit 40a, based on the calculation result of the optimal phase and the detected value of the magnitude of the AC voltage, inputs a control signal to the furnace circuit breaker 6 (furnace transformer 5) at the timing when the phase of the AC voltage supplied from the conversion circuit 12 to the furnace circuit breaker 6 becomes the optimal phase, thereby switching the furnace circuit breaker 6 from the open state to the closed state.
[0078] In this example, the output value calculation unit 42a sets the magnitude of the AC voltage output from the inverter 32 to zero in response to the input of the circuit breaker open command (for example, at timing t41 in Figure 11).
[0079] In this example, the output value calculation unit 42a calculates the magnitude of the AC voltage output from the inverter 32 in response to the input of the circuit breaker closing command, so that the magnitude of the AC voltage output from the inverter 32 becomes the desired voltage (for example, from timing t42 onwards in Figure 11).
[0080] In this example, after a circuit breaker closing command is input and the inverter 32 starts outputting an AC voltage of the desired magnitude, the control signal generation unit 40a switches the furnace circuit breaker 6 from the open state to the closed state at the timing when the phase of the AC voltage supplied from the conversion circuit 12 (inverter 32) to the furnace circuit breaker 6 (furnace transformer 5) becomes the optimal phase (for example, timing t43 in Figure 11).
[0081] In this example, the circuit breaker control unit 40 switches the furnace circuit breaker 6 from the closed state to the open state in response to the input of a circuit breaker open command, and after receiving the input of a circuit breaker close command, switches the furnace circuit breaker 6 from the open state to the closed state at the timing when the phase of the AC voltage supplied from the conversion circuit 12 to the furnace circuit breaker 6 (furnace transformer 5) is at the optimal phase.
[0082] As a result, in this example, magnetic saturation of the core of the furnace transformer 5 due to the excitation flux superimposed on the residual flux can be suppressed, and the generation of excitation inrush current can be suppressed. As a result, in this example as well, the configuration of the furnace transformer 5 can be made simpler, similar to the embodiment described above. As with the embodiment described above, the power quality of the power system PS can be improved, and the economic efficiency of the arc furnace equipment 2 can be improved.
[0083] In this example, the converter control unit 42 does not necessarily have to reduce the magnitude of the AC voltage output from the inverter converter 32 to zero in response to the input of a circuit breaker open command. The converter control unit 42 may also control the operation of the inverter converter 32 so that it always outputs an AC voltage of a desired magnitude, regardless of whether the furnace circuit breaker 6 is closed or open. In this example, while AC power is being output from the inverter converter 32, the circuit breaker control unit 40 may be configured to control the timing of switching between the closed and open states of the furnace circuit breaker 6 (the phase of the AC voltage supplied to the furnace transformer 5).
[0084] This embodiment includes the following aspects. (Note 1) An electrode that generates an arc discharge between itself and a metal material, A furnace circuit breaker that switches between an "on" state, which enables the supply of AC power to the electrode side, and an "off" state, which interrupts the supply of AC power to the electrode side. A furnace transformer is provided between the furnace circuit breaker and the electrode, An arc furnace power converter is used in an arc furnace facility equipped with the following, and is installed between the power system and the furnace circuit breaker: A conversion circuit provided between the power system and the furnace circuit breaker, A control circuit for controlling the operation of the conversion circuit, Equipped with, The aforementioned conversion circuit is A forward converter that converts AC power supplied from the aforementioned power system into DC power, A reverse converter converts the DC power converted by the forward converter into AC power and outputs the converted AC power to the electrode side, It has, The control circuit includes a converter control unit that controls the operation of the inverse converter. The converter control unit receives inputs of a circuit breaker open command instructing the switching of the furnace circuit breaker to the open state and a circuit breaker close command instructing the switching of the furnace circuit breaker to the closed state, and controls the operation of the inverter so as to set the magnitude of the AC voltage output from the inverter converter to a predetermined value or less in response to the input of the circuit breaker open command, and to gradually increase the magnitude of the AC voltage output from the inverter converter from the predetermined value or less to a desired voltage in response to the input of the circuit breaker close command, in order to power the inverter.
[0085] (Note 2) The power converter for an arc furnace power supply according to Appendix 1, wherein the converter control unit gradually increases the amplitude of the AC voltage output from the inverse converter over a predetermined period from a predetermined value or less to the desired size in response to the input of the circuit breaker closing command, so that the amplitude of the AC voltage output from the inverse converter becomes a desired size a predetermined period after the timing of receiving the input of the circuit breaker closing command.
[0086] (Note 3) An electrode that generates an arc discharge between itself and a metal material, A furnace circuit breaker that switches between an "on" state, which enables the supply of AC power to the electrode side, and an "off" state, which interrupts the supply of AC power to the electrode side. A furnace transformer is provided between the furnace circuit breaker and the electrode, An arc furnace power converter is used in an arc furnace facility equipped with the following, and is installed between the power system and the furnace circuit breaker: A conversion circuit provided between the power system and the furnace circuit breaker, A control circuit for controlling the operation of the conversion circuit, Equipped with, The aforementioned conversion circuit is A forward converter that converts AC power supplied from the aforementioned power system into DC power, A reverse converter converts the DC power converted by the forward converter into AC power and outputs the converted AC power to the electrode side, It has, The control circuit includes a converter control unit that controls the operation of the inverse converter. The converter control unit receives a circuit breaker open command instructing the switching of the furnace circuit breaker to the open state and a circuit breaker close command instructing the switching of the furnace circuit breaker to the closed state, and controls the operation of the inverter so that, in response to the input of the circuit breaker open command, the magnitude of the AC voltage output from the inverter is gradually reduced over a predetermined time to a predetermined value or less, and in response to the input of the circuit breaker close command, the magnitude of the AC voltage output from the inverter is set to a desired voltage.
[0087] (Note 4) The power converter for an arc furnace, as described in Appendix 3, wherein the converter control unit, in response to the input of the circuit breaker opening command, sets the frequency of the AC voltage output from the inverter to a frequency higher than the rated frequency, and gradually reduces the magnitude of the AC voltage output from the inverter, thereby reducing the magnitude of the AC voltage output from the inverter to a predetermined value or less over a predetermined period of time.
[0088] (Note 5) The control circuit includes a circuit breaker control unit that controls the operation of the furnace circuit breaker, The power converter for an arc furnace according to Appendix 3 or 4, wherein the circuit breaker control unit sets a predetermined delay time in response to the input circuit breaker open command, and after the converter control unit sets the magnitude of the AC voltage output from the inverse converter to less than or equal to the predetermined value, switches the furnace circuit breaker to the open state.
[0089] (Note 6) The power converter for an arc furnace power supply according to any one of the appendices 3 to 5, wherein the converter control unit gradually reduces the amplitude of the AC voltage output from the inverse converter from a desired magnitude to the predetermined value over a predetermined period in response to the input of the circuit breaker closing command, so that the amplitude of the AC voltage output from the inverse converter becomes less than or equal to a predetermined value after a predetermined period from the timing of receiving the input of the circuit breaker opening command.
[0090] (Note 7) An electrode that generates an arc discharge between itself and a metal material, A furnace circuit breaker that switches between an "on" state, which enables the supply of AC power to the electrode side, and an "off" state, which interrupts the supply of AC power to the electrode side. A furnace transformer is provided between the furnace circuit breaker and the electrode, An arc furnace power converter is used in an arc furnace facility equipped with the following, and is installed between the power system and the furnace circuit breaker: A conversion circuit provided between the power system and the furnace circuit breaker, A control circuit for controlling the operation of the conversion circuit, Equipped with, The aforementioned conversion circuit is A forward converter that converts AC power supplied from the aforementioned power system into DC power, A reverse converter converts the DC power converted by the forward converter into AC power and outputs the converted AC power to the electrode side, It has, The control circuit has a converter control unit that receives inputs of a circuit breaker open command instructing the switching of the furnace circuit breaker to the open state and a circuit breaker close command instructing the switching of the furnace circuit breaker to the closed state, and controls the operation of the inverse converter. The converter control unit receives the input of the circuit breaker open command and the input of a detected value of the magnitude of the AC voltage on the primary side of the furnace transformer, and has a voltage phase storage unit that stores the phase of the AC voltage on the primary side of the furnace transformer when the input of the circuit breaker open command is received. The converter control unit controls the operation of the inverter so that, in response to the input of the circuit breaker open command, the magnitude of the AC voltage output from the inverter is less than or equal to a predetermined value, and in response to the input of the circuit breaker close command, the inverter outputs an AC voltage that is in the same phase as when the furnace circuit breaker is switched to the open state, based on the phase stored in the voltage phase memory unit. This power converter is for an arc furnace.
[0091] (Note 8) An electrode that generates an arc discharge between itself and a metal material, A furnace circuit breaker that switches between an "on" state, which enables the supply of AC power to the electrode side, and an "off" state, which interrupts the supply of AC power to the electrode side. A furnace transformer is provided between the furnace circuit breaker and the electrode, An arc furnace power converter is used in an arc furnace facility equipped with the following, and is installed between the power system and the furnace circuit breaker: A conversion circuit provided between the power system and the furnace circuit breaker, A control circuit for controlling the operation of the conversion circuit, Equipped with, The aforementioned conversion circuit is A forward converter that converts AC power supplied from the aforementioned power system into DC power, A reverse converter converts the DC power converted by the forward converter into AC power and outputs the converted AC power to the electrode side, It has, The control circuit includes a circuit breaker control unit that controls the operation of the furnace circuit breaker, The circuit breaker control unit is, A circuit breaker open command that instructs the switching of the furnace circuit breaker to the open state, A circuit breaker closing command that instructs the switching of the furnace circuit breaker to the closed state, The detected value of the magnitude of the AC voltage on the primary side of the aforementioned furnace transformer, The detected value of the magnitude of the AC voltage supplied from the conversion circuit to the furnace circuit breaker, Upon receiving input, The circuit breaker control unit is, A residual magnetic flux calculation unit calculates the magnitude of residual magnetic flux remaining in the core of the furnace transformer when the furnace circuit breaker is switched to the open state, based on the circuit breaker open command and the detected magnitude of the AC voltage on the primary side of the furnace transformer. Based on the magnitude of the residual magnetic flux calculated by the residual magnetic flux calculation unit, the switching phase angle calculation unit calculates the optimal phase of the AC voltage supplied to the furnace transformer when switching the furnace circuit breaker to the closed state, It has, The circuit breaker control unit switches the furnace circuit breaker from the closed state to the open state in response to the input of the circuit breaker open command, and after receiving the input of the circuit breaker closed command, switches the furnace circuit breaker from the open state to the closed state at the timing when the phase of the AC voltage supplied from the conversion circuit to the furnace circuit breaker becomes the optimal phase, based on the detected value of the magnitude of the AC voltage supplied from the conversion circuit to the furnace circuit breaker.
[0092] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]
[0093] 2…Arc furnace equipment, 3…Furnace body, 4…Electrodes, 5…Furnace transformer, 6…Furnace circuit breaker, 7…Power system busbar, 10…Power converter for arc furnace power supply, 12, 12a…Conversion circuit, 14, 14a~14c…Control circuit, 16…Instrument transformer, 18…Instrument current transformer, 20…Instrument transformer, 30…Forward converter, 32…Inverse converter, 34…Transformer for forward converter, 36…Transformer for reverse converter, 40…Circuit breaker control unit, 40a…Control signal generation unit, 40b…Delay time setting unit, 40c…Residual magnetic flux calculation unit, 40d…Clocking phase angle calculation unit, 42…Converter control unit, 42a…Output value calculation unit, 42b…Control signal generation unit, 42c…Voltage phase memory unit, PS…Power system
Claims
1. An electrode that generates an arc discharge between itself and a metal material, A furnace circuit breaker that switches between an "on" state, which enables the supply of AC power to the electrode side, and an "off" state, which interrupts the supply of AC power to the electrode side. A furnace transformer is provided between the furnace circuit breaker and the electrode, An arc furnace power converter is used in an arc furnace facility equipped with the following, and is installed between the power system and the furnace circuit breaker: A conversion circuit provided between the power system and the furnace circuit breaker, A control circuit for controlling the operation of the conversion circuit, Equipped with, The aforementioned conversion circuit is A forward converter that converts AC power supplied from the aforementioned power system into DC power, A reverse converter converts the DC power converted by the forward converter into AC power and outputs the converted AC power to the electrode side, It has, The control circuit includes a converter control unit that controls the operation of the inverse converter. The converter control unit receives inputs of a circuit breaker open command instructing the switching of the furnace circuit breaker to the open state and a circuit breaker close command instructing the switching of the furnace circuit breaker to the closed state, and controls the operation of the inverter so as to set the magnitude of the AC voltage output from the inverter converter to a predetermined value or less in response to the input of the circuit breaker open command, and to gradually increase the magnitude of the AC voltage output from the inverter converter from the predetermined value or less to a desired voltage in response to the input of the circuit breaker close command, in order to power the inverter.
2. The power conversion device for an arc furnace power supply according to claim 1, wherein the converter control unit gradually increases the amplitude of the AC voltage output from the inverse converter over a predetermined period from a predetermined value or less to the desired size in response to the input of the circuit breaker closing command, so that the amplitude of the AC voltage output from the inverse converter becomes a desired size a predetermined period after the timing of receiving the input of the circuit breaker closing command.
3. An electrode that generates an arc discharge between itself and a metal material, A furnace circuit breaker that switches between an "on" state, which enables the supply of AC power to the electrode side, and an "off" state, which interrupts the supply of AC power to the electrode side. A furnace transformer is provided between the furnace circuit breaker and the electrode, An arc furnace power converter is used in an arc furnace facility equipped with the following, and is installed between the power system and the furnace circuit breaker: A conversion circuit provided between the power system and the furnace circuit breaker, A control circuit for controlling the operation of the conversion circuit, Equipped with, The aforementioned conversion circuit is A forward converter that converts AC power supplied from the aforementioned power system into DC power, A reverse converter converts the DC power converted by the forward converter into AC power and outputs the converted AC power to the electrode side, It has, The control circuit includes a converter control unit that controls the operation of the inverse converter. The converter control unit receives a circuit breaker open command instructing the switching of the furnace circuit breaker to the open state and a circuit breaker close command instructing the switching of the furnace circuit breaker to the closed state, and controls the operation of the inverter so that, in response to the input of the circuit breaker open command, the magnitude of the AC voltage output from the inverter is gradually reduced over a predetermined time to a predetermined value or less, and in response to the input of the circuit breaker close command, the magnitude of the AC voltage output from the inverter is set to a desired voltage.
4. The power conversion device for an arc furnace power supply according to claim 3, wherein the converter control unit, in response to the input of the circuit breaker opening command, sets the frequency of the AC voltage output from the inverter to a frequency higher than the rated frequency, and gradually reduces the magnitude of the AC voltage output from the inverter, thereby reducing the magnitude of the AC voltage output from the inverter to a predetermined value or less over a predetermined time.
5. The control circuit includes a circuit breaker control unit that controls the operation of the furnace circuit breaker, The power conversion device for an arc furnace power supply according to claim 3, wherein the circuit breaker control unit sets a predetermined delay time in response to the input circuit breaker open command, and after the converter control unit sets the magnitude of the AC voltage output from the inverse converter to less than or equal to the predetermined value, switches the furnace circuit breaker to the open state.
6. The power conversion device for an arc furnace power supply according to claim 3, wherein the converter control unit gradually reduces the amplitude of the AC voltage output from the inverse converter from a desired magnitude to a predetermined value or less over a predetermined period in response to the input of the circuit breaker closing command, so that the amplitude of the AC voltage output from the inverse converter becomes less than or equal to a predetermined value after a predetermined period from the timing of receiving the input of the circuit breaker opening command.
7. An electrode that generates an arc discharge between itself and a metal material, A furnace circuit breaker that switches between an "on" state, which enables the supply of AC power to the electrode side, and an "off" state, which interrupts the supply of AC power to the electrode side. A furnace transformer is provided between the furnace circuit breaker and the electrode, An arc furnace power converter is used in an arc furnace facility equipped with the following, and is installed between the power system and the furnace circuit breaker: A conversion circuit provided between the power system and the furnace circuit breaker, A control circuit for controlling the operation of the conversion circuit, Equipped with, The aforementioned conversion circuit is A forward converter that converts AC power supplied from the aforementioned power system into DC power, A reverse converter converts the DC power converted by the forward converter into AC power and outputs the converted AC power to the electrode side, It has, The control circuit has a converter control unit that receives inputs of a circuit breaker open command instructing the switching of the furnace circuit breaker to the open state and a circuit breaker close command instructing the switching of the furnace circuit breaker to the closed state, and controls the operation of the inverse converter. The converter control unit receives the input of the circuit breaker open command and the input of a detected value of the magnitude of the AC voltage on the primary side of the furnace transformer, and has a voltage phase storage unit that stores the phase of the AC voltage on the primary side of the furnace transformer when the input of the circuit breaker open command is received. The converter control unit controls the operation of the inverter so that, in response to the input of the circuit breaker open command, the magnitude of the AC voltage output from the inverter is less than or equal to a predetermined value, and in response to the input of the circuit breaker close command, the inverter outputs an AC voltage that is in the same phase as when the furnace circuit breaker is switched to the open state, based on the phase stored in the voltage phase memory unit. This power converter is for an arc furnace.
8. An electrode that generates an arc discharge between itself and a metal material, A furnace circuit breaker that switches between an "on" state, which enables the supply of AC power to the electrode side, and an "off" state, which interrupts the supply of AC power to the electrode side. A furnace transformer is provided between the furnace circuit breaker and the electrode, An arc furnace power converter is used in an arc furnace facility equipped with the following, and is installed between the power system and the furnace circuit breaker: A conversion circuit provided between the power system and the furnace circuit breaker, A control circuit for controlling the operation of the conversion circuit, Equipped with, The aforementioned conversion circuit is A forward converter that converts AC power supplied from the aforementioned power system into DC power, A reverse converter converts the DC power converted by the forward converter into AC power and outputs the converted AC power to the electrode side, It has, The control circuit includes a circuit breaker control unit that controls the operation of the furnace circuit breaker, The circuit breaker control unit is, A circuit breaker open command that instructs the switching of the furnace circuit breaker to the open state, A circuit breaker closing command that instructs the switching of the furnace circuit breaker to the closed state, The detected value of the magnitude of the AC voltage on the primary side of the aforementioned furnace transformer, The detected value of the magnitude of the AC voltage supplied from the conversion circuit to the furnace circuit breaker, Upon receiving input, The circuit breaker control unit is, A residual magnetic flux calculation unit calculates the magnitude of residual magnetic flux remaining in the core of the furnace transformer when the furnace circuit breaker is switched to the open state, based on the circuit breaker open command and the detected magnitude of the AC voltage on the primary side of the furnace transformer. Based on the magnitude of the residual magnetic flux calculated by the residual magnetic flux calculation unit, the switching phase angle calculation unit calculates the optimal phase of the AC voltage supplied to the furnace transformer when switching the furnace circuit breaker to the closed state, It has, The circuit breaker control unit switches the furnace circuit breaker from the closed state to the open state in response to the input of the circuit breaker open command, and after receiving the input of the circuit breaker closed command, switches the furnace circuit breaker from the open state to the closed state at the timing when the phase of the AC voltage supplied from the conversion circuit to the furnace circuit breaker becomes the optimal phase, based on the detected value of the magnitude of the AC voltage supplied from the conversion circuit to the furnace circuit breaker.