Power supply facility

Abstract

Provided is a power supply facility comprising: a converter provided between a power system and a load, the converter converting AC power supplied from the power system side into power corresponding to the load and supplying the converted power to the load; and a control device that performs the supply of power to the load and also controls the operation of the converter so as to control at least one of the magnitude of reactive power flowing out to the power system side, the magnitude of AC voltage of the power system, and harmonics flowing out to the power system. Thus, a power supply facility capable of improving power supply quality with a simplified configuration is provided.

Description

Power supply equipment

[0001] An embodiment of the present invention relates to a power supply equipment.

[0002] There is a power supply equipment that converts the alternating current power supplied from the power grid into power according to the load and supplies the converted power to the load. The power supply equipment is used, for example, in arc furnaces and the like. In loads such as arc furnaces, there is a risk of degrading the power quality of the connected power grid due to reactive power, voltage fluctuations (voltage flicker), harmonics, etc. generated in response to the supply of power to the load. For this reason, in the power supply equipment, by providing reactive power equipment such as a reactive power compensation device (self-excited SVC, separately excited SVC, etc.), a harmonic filter, a power factor improvement capacitor, etc., the power quality on the power grid side is improved.

[0003] However, in a configuration that improves the power quality by reactive power equipment, there is a concern that the configuration of the power supply equipment becomes complicated, leading to an increase in the size of the equipment and the equipment cost. Therefore, in the power supply equipment, it is desired to improve the power quality with a simpler configuration.

[0004] Japanese Patent Application Laid-Open No. 2017-118600

[0005] An embodiment of the present invention provides a power supply equipment that can improve the power quality with a simpler configuration.

[0006] According to an embodiment of the present invention, there is provided a power supply equipment provided between a power grid and a load, including a converter that converts the alternating current power supplied from the power grid side into power according to the load and supplies the converted power to the load, and a control device that supplies power to the load and controls the operation of the converter so as to control at least any one of the magnitude of the reactive power flowing out to the power grid side, the magnitude of the alternating current voltage of the power grid, and the harmonics flowing out to the power grid.

[0007] According to an embodiment of the present invention, there is provided a power supply equipment that can improve the power quality with a simpler configuration.

[0008] This is a schematic block diagram of a power supply equipment according to the embodiment. This is a schematic block diagram of an example of a converter according to the embodiment. This is a schematic block diagram of an example of a control device according to the embodiment. This is a schematic block diagram of a modified version of the control device according to the embodiment. This is a schematic block diagram of a modified version of the control device according to the embodiment. This is a schematic block diagram of a modified version of the power supply equipment according to the embodiment. This is a schematic block diagram of a modified version of the power supply equipment according to the embodiment.

[0009] The embodiments will be described below with reference to the drawings. Note that the drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the ratio of the sizes of the parts, etc., are not necessarily the same as those of actual objects. Furthermore, even when representing the same part, the dimensions and ratios may be shown differently in different drawings. In this specification and in each drawing, elements similar to those described above are denoted by the same reference numerals, and detailed explanations are omitted as appropriate.

[0010] Figure 1 is a schematic block diagram showing a power supply system according to an embodiment. As shown in Figure 1, the power supply system 10 comprises a converter 12 and a control device 14. The converter 12 is installed between the power system 2 and the load, which is the arc furnace 4. Thus, the power supply system 10 is, for example, a power supply system for an arc furnace used in the arc furnace 4.

[0011] The converter 12 is connected to the power system 2 via, for example, a load system 6 and a transformer (not shown). The load system 6 is, for example, an in-house system within a factory where an arc furnace 4 is installed. The converter 12 converts the AC power supplied from the power system 2 via the transformer into power appropriate for the arc furnace 4, and supplies the converted power to the arc furnace 4.

[0012] The AC power of power system 2 is, for example, three-phase AC power. The power supplied to the arc furnace 4 is, for example, three-phase AC power. In other words, the arc furnace 4 is an AC arc furnace. The converter 12 converts the three-phase AC power supplied from power system 2 into another three-phase AC power suitable for the arc furnace 4, and supplies the converted three-phase AC power to the arc furnace 4. The converter 12 converts, for example, the AC voltage of power system 2 to the magnitude of the AC voltage suitable for the arc furnace 4. However, the AC power of power system 2 and the AC power of the arc furnace 4 are not limited to three-phase AC power, but may be any AC power.

[0013] The arc furnace 4 includes, for example, a furnace body, electrodes, an output transformer, and a furnace circuit breaker (all of which are not shown in the diagram). The furnace body has a space capable of accommodating metal material (e.g., scrap). The electrodes melt the metal material contained in the furnace body by generating an arc discharge between them and the metal material based on the supplied AC power. The electrodes are configured to be able to move up and down by a lifting mechanism (not shown in the diagram) so as to maintain an appropriate distance from the metal material necessary for generating an arc discharge, even when the height of the metal material changes due to melting.

[0014] The output transformer steps down the AC power supplied from the converter 12 and supplies the stepped-down AC power to the electrodes. The furnace circuit breaker switches between a state that allows AC power to be supplied to the output transformer (electrodes) and a state that cuts off the supply of AC power to the output transformer (electrodes).

[0015] In this way, the converter 12, more specifically, supplies the converted AC power to the electrodes of the arc furnace 4. In other words, the converter 12 supplies AC power to the arc furnace 4 to cause an arc discharge. The arc furnace 4 has, for example, three electrodes corresponding to each phase of three-phase AC power. The AC power supplied from the converter 12 to the arc furnace 4 can be set appropriately according to the configuration of the arc furnace 4.

[0016] The converter 12 includes a converter 20 and an inverter 22. The converter 12 is, for example, a BTB (Back-to-Back) converter. The converter 20 converts AC power supplied from the power system 2 into DC power. The inverter 22 converts the DC power converted by the converter 20 into AC power corresponding to the arc furnace 4 and supplies the converted AC power to the arc furnace 4. The inverter 22 also changes the magnitude of the AC voltage supplied to the arc furnace 4, for example, according to the process of the arc furnace 4.

[0017] The control device 14 controls the operation of the converter 12. More specifically, the control device 14 controls the operation of the converter 20 and the inverter 22 of the converter 12. The control device 14 controls the conversion from AC power to DC power by the converter 20, and also controls the conversion from DC power to AC power by the inverter 22. For example, the control device 14 controls the magnitude of the AC voltage output from the inverter 22 by controlling the operation of the inverter 22.

[0018] The power supply equipment 10 further includes, for example, a voltage detector 16, a current detector 17, and a voltage detector 18. The voltage detector 16 detects the magnitude of the AC voltage of the power system 2 and inputs the detection result to the control device 14. The voltage detector 16 detects, for example, the magnitude of the AC voltage of each phase of the three-phase AC power of the power system 2. The current detector 17 detects the magnitude of the AC current of the power system 2 and inputs the detection result to the control device 14. The current detector 17 detects, for example, the magnitude of the AC current of each phase of the three-phase AC power of the power system 2. The voltage detector 18 detects the magnitude of the DC voltage output from the converter 20 and inputs the detection result to the control device 14.

[0019] The control device 14 controls the operation of the converter 20 and inverter 22 of the converter 12 based on the detection results of the voltage detector 16, the current detector 17, and the voltage detector 18, respectively.

[0020] The control device 14 controls the operation of the converter 20 to convert AC power to DC power so that a predetermined amount of AC power is supplied to the arc furnace 4, and the amount of reactive power flowing out to the power system 2 is also predetermined.

[0021] The control device 14 controls the operation of the converter 20, for example, to output a DC voltage of substantially constant magnitude. This allows the operation of the converter 20 to be controlled to supply a predetermined magnitude of AC power to the arc furnace 4.

[0022] Power system 2 is connected, for example, to a converter 12 and a reactive power load 8. The reactive power load 8 is connected to load system 6, similar to the converter 12, and is connected to power system 2 via load system 6 and transformers. The reactive power load 8 is, for example, a secondary refining facility such as a ladle furnace that adjusts the composition of molten steel by heating the molten steel in the ladle with an arc discharge.

[0023] If the reactive power load 8 is a ladle furnace, then the reactive power load 8 is a lagging load. In this case, the control device 14 controls the operation of the converter 20 to supply leading reactive power to the power system 2 that is equal in magnitude to the lagging reactive power of the reactive power load 8. This makes it possible to substantially reduce the amount of reactive power flowing out to the power system 2. Alternatively, the control device 14 can control the operation of the converter 20 to supply leading reactive power to the power system 2 that is a predetermined amount smaller than the lagging reactive power of the reactive power load 8. This allows a predetermined amount of lagging reactive power to flow out to the power system 2. Furthermore, the control device 14 can control the operation of the converter 20 to supply leading reactive power to the power system 2 that is a predetermined amount larger than the lagging reactive power of the reactive power load 8. This also allows a predetermined amount of leading reactive power to flow out to the power system 2.

[0024] Thus, the control device 14 controls the operation of the converter 20 (converter 12) to, for example, supply power to the arc furnace 4 and compensate for the reactive power of the reactive power load 8. In other words, the control device 14 controls the operation of the converter 12 to, for example, supply power to the arc furnace 4 (load) and to ensure that the amount of reactive power flowing out to the power system 2 is a predetermined amount.

[0025] The number of reactive power loads 8 connected to the power system 2 is not limited to one, but may be multiple. In this case, the control device 14 can, for example, control the operation of the converter 20 to supply reactive power to the power system 2 in an amount corresponding to the total amount of reactive power of the multiple reactive power loads 8. This makes it possible to compensate for the reactive power of the multiple reactive power loads 8.

[0026] Figure 2 is a schematic block diagram showing an example of a converter according to the embodiment. As shown in Figure 2, the converter 20 has a plurality of AC input terminals 30a to 30c, a pair of DC output terminals 31a and 31b, a plurality of switching elements 32a to 32f, and a plurality of rectifier elements 33a to 33f.

[0027] The converter 20 has, for example, three AC input terminals 30a to 30c corresponding to each phase of three-phase AC power. The converter 20 also has, for example, six switching elements 32a to 32f connected in a three-phase full bridge configuration, and six rectifier elements 33a to 33f connected in antiparallel to each of the six switching elements 32a to 32f.

[0028] The connection point between switching element 32a and switching element 32b is connected to AC input terminal 30a. The connection point between switching element 32c and switching element 32d is connected to AC input terminal 30b. The connection point between switching element 32e and switching element 32f is connected to AC input terminal 30c.

[0029] Furthermore, both ends of the series-connected switching elements 32a and 32b, both ends of the series-connected switching elements 32c and 32d, and both ends of the series-connected switching elements 32e and 32f are connected to a pair of DC output terminals 31a and 31b, respectively.

[0030] The converter 20 is connected to transformers, load systems 6, etc., via each AC input terminal 30a to 30c. The converter 20 receives AC power input from the power system 2 side via each AC input terminal 30a to 30c. The converter 20 converts the AC power supplied to each AC input terminal 30a to 30c into DC power by switching each switching element 32a to 32f, and outputs the converted DC power from a pair of DC output terminals 31a and 31b.

[0031] The converter 20 is, for example, a PWM rectifier circuit. Self-excited switching elements such as IGBTs and IEGTs are used for each switching element 32a to 32f. However, the configuration of the converter 20 is not limited to the above. The converter 20 may be, for example, a single-phase full-bridge circuit, a three-level converter such as an NPC (Neutral-Point-Clamped) type, or a multi-level converter such as an MMC (Modular Multilevel Converter) type. The configuration of the converter 20 can be any configuration that can convert AC power supplied from the power system 2 side into DC power by switching a plurality of switching elements 32a to 32f.

[0032] The inverter 22 has a pair of DC input terminals 40a and 40b, a plurality of AC output terminals 41a to 41c, a plurality of switching elements 42a to 42f, and a plurality of rectifier elements 43a to 43f.

[0033] The inverter 22 has, for example, three AC output terminals 41a to 41c corresponding to each phase of three-phase AC power. The inverter 22 also has, for example, six switching elements 42a to 42f connected in a three-phase full bridge configuration, and six rectifier elements 43a to 43f connected in antiparallel to each of the six switching elements 42a to 42f.

[0034] The connection point between switching element 42a and switching element 42b is connected to AC output terminal 41a. The connection point between switching element 42c and switching element 42d is connected to AC output terminal 41b. The connection point between switching element 42e and switching element 42f is connected to AC output terminal 41c.

[0035] Furthermore, both ends of the series-connected switching elements 42a and 42b, both ends of the series-connected switching elements 42c and 42d, and both ends of the series-connected switching elements 42e and 42f are connected to a pair of DC input terminals 40a and 40b, respectively.

[0036] The inverter 22 is connected to a pair of DC output terminals 31a and 31b of the converter 20 via a pair of DC input terminals 40a and 40b. The inverter 22 is also connected to the arc furnace 4 via AC output terminals 41a to 41c. The inverter 22 converts the DC power supplied from the converter 20 to the pair of DC input terminals 40a and 40b into AC power by switching the switching elements 42a to 42f, and outputs the converted AC power from the AC output terminals 41a to 41c.

[0037] This allows the AC power supplied from the power system 2 to be converted to DC power, then the DC power to be converted back to AC power, and the converted AC power to be supplied to the arc furnace 4. However, the configuration of the inverter 22 is not limited to the above, and can be any configuration that converts the DC power supplied from the converter 20 to a pair of DC input terminals 40a and 40b to AC power by switching a plurality of switching elements 42a to 42f, and supplies the converted AC power to the arc furnace 4. The inverter 22 may be, for example, a single-phase full-bridge circuit, a three-level converter such as an NPC (Neutral-Point-Clamped) type, or a multi-level converter such as an MMC (Modular Multilevel Converter) type.

[0038] Each switching element 42a to 42f can be a self-excited switching element such as an IGBT or IEGT. Each switching element 42a to 42f can be any element capable of appropriately converting DC power to AC power by switching.

[0039] Thus, self-excited switching elements are used for the multiple switching elements 32a to 32f of the converter 20 and the multiple switching elements 42a to 42f of the inverter 22. The converter 12 is, for example, a self-excited converter.

[0040] As shown in Figure 2, each converter 12 further includes, for example, a charge storage element 24. The charge storage element 24 is provided between the converter 20 and the inverter 22 and suppresses voltage fluctuations of the DC power converted by the converter 20. For example, a capacitor is used for the charge storage element 24. In other words, the charge storage element 24 is a smoothing capacitor. However, the charge storage element 24 is not limited to a capacitor, and may be any element capable of suppressing voltage fluctuations of the DC power converted by the converter 20.

[0041] The charge storage element 24 is provided, for example, between a pair of DC output terminals 31a and 31b of the converter 20 and between a pair of DC input terminals 40a and 40b of the inverter 22. As a result, the charge storage element 24 is charged based on the DC power output from the converter 20, and fluctuations in the voltage of the DC power converted by the converter 20 are suppressed by the charge storage element 24. However, the charge storage element 24 is provided as needed and can be omitted. The charge storage element 24 may be provided as appropriate, for example, depending on the circuit configuration of the converter 12.

[0042] The control device 14 transmits a control signal to the converter 20 and controls the switching of each switching element 32a to 32f of the converter 20, thereby controlling the conversion from AC power to DC power by the converter 20.

[0043] At this time, for example, the control device 14 controls the switching of each switching element 32a to 32f of the converter 20 so that the arc furnace 4 can be supplied with AC power of a predetermined magnitude and the magnitude of the reactive power flowing out to the power system 2 side becomes a predetermined magnitude. In other words, for example, the control device 14 controls the switching of each switching element 32a to 32f of the converter 20 so as to supply power to the arc furnace 4 and compensate for the reactive power of the reactive power load 8.

[0044] Further, the control device 14 transmits a control signal to the inverter 22 and controls the switching of each switching element 42a to 42f of the inverter 22, thereby controlling the conversion of DC power to AC power by the inverter 22. At this time, the control device 14 controls the magnitude of the AC voltage output from the inverter 22 by controlling the switching interval of each switching element 42a to 4

[0045] FIG. 3 is a block diagram schematically showing an example of the control device according to the embodiment. As shown in FIG. 3, the control device 14 includes, for example, a dq converter 51, a current controller 52, a DC voltage controller 53, a dq converter 54, adders 55 and 56, an inverse dq converter 57, and a control signal generator 58.

[0046] The AC current detection value of the power system 2 detected by the current detector 17 is input to the dq converter 51. The dq converter 51 performs dq conversion (Park conversion) on the AC current detection value, which is a three-phase AC current signal, to calculate an AC current d-axis signal and an AC current q-axis signal from the AC current detection value. The AC current d-axis signal represents the active current component of the AC current in the power system

[0047] 2. The AC current q-axis signal represents the reactive current component of the AC current in the power system 2. The dq converter 51 inputs the calculated AC current d-axis signal and AC current q-axis signal to the current controller 52.

[0047] The DC voltage controller 53 receives the DC voltage detection value detected by the voltage detector 18. Further, a command value (not shown) representing the magnitude of the DC voltage output from the converter 20 is input to the DC voltage controller 53. The DC voltage controller 53, for example, calculates the difference between the command value of the DC voltage and the DC voltage detection value, and performs proportional control or proportional integral control on the calculated difference, thereby bringing the DC voltage detection value closer to the command value of the DC voltage, and calculates the d-axis current command value representing the active current component output from the converter 20. Thereby, the operation of the converter 20 can be controlled so that the magnitude of the DC voltage output from the converter 20 becomes substantially constant according to the command value. The DC voltage controller 53 inputs the calculated d-axis current command value to the current controller 52.

[0048] The current controller 52 further receives a q-axis current command value representing the reactive current component output from the converter 20. The q-axis current command value is set to, for example, zero. Thereby, as described above, the magnitude of the reactive power flowing out to the power system 2 side can be made substantially zero. Further, for example, by setting the q-axis current command value to a predetermined value, a lag reactive power or a leading reactive power of a predetermined magnitude can be made to flow out to the power system 2 side.

[0049] The q-axis current command value is input to the control device 14 (current controller 52) via communication from an external device such as a higher-level controller, for example. The q-axis current command value may be manually input to the current controller 52 via, for example, an operation unit connected to the control device 14, or may be a preset constant value. The method of inputting the q-axis current command value to the current controller 52 may be any method that can appropriately input the q-axis current command value to the current controller 52.

[0050] The current controller 52 calculates the difference between the input d-axis current command value and the AC current d-axis signal, and performs proportional control or proportional integral control on the calculated difference, thereby bringing the AC current d-axis signal closer to the d-axis current command value, and calculates the control amount of the active component of the AC voltage output from the converter 20. The current controller 52 inputs the calculated control amount of the active component to the adder 55.

[0051] Furthermore, the current controller 52 calculates the difference between the input q-axis current command value and the AC current q-axis signal, and performs proportional control or proportional-integral control on the calculated difference to calculate the amount of control for the reactive component of the AC voltage output from the converter 20 in order to bring the AC current q-axis signal closer to the q-axis current command value. The current controller 52 inputs the calculated amount of control for the reactive component to the adder 56.

[0052] The dq converter 54 receives the AC voltage detection value of the power system 2 detected by the voltage detector 16. The dq converter 54 performs a dq conversion (Park conversion) on the AC voltage detection value, which is a three-phase AC voltage signal, to calculate the AC voltage d-axis signal and the AC voltage q-axis signal from the AC voltage detection value. The dq converter 54 inputs the calculated AC voltage d-axis signal to the adder 55 and the calculated AC voltage q-axis signal to the adder 56.

[0053] The adder 55 calculates the voltage command value of the active component of the AC voltage output from the converter 20 by adding the control amount of the active component to the AC voltage d-axis signal. The adder 55 inputs the calculated voltage command value of the active component to the inverse dq converter 57.

[0054] The adder 56 calculates the voltage command value of the reactive component of the AC voltage output from the converter 20 by adding a control amount of the reactive component to the AC voltage q-axis signal. The adder 56 inputs the calculated voltage command value of the reactive component to the inverse dq converter 57.

[0055] The inverse DQ converter 57 performs an inverse DQ conversion (inverse Park conversion) on the input active component voltage command value and reactive component voltage command value, thereby calculating the voltage command value of the three-phase AC voltage signal to be output from the converter 20 based on the active component voltage command value and reactive component voltage command value. The inverse DQ converter 57 inputs the calculated voltage command value of the three-phase AC voltage signal to the control signal generator 58.

[0056] The control signal generator 58 generates a control signal to control the operation of the converter 20 based on the input voltage command value. For example, the control signal generator 58 generates a pulse signal (PWM signal) as a control signal to switch the on and off states of the multiple switching elements 32a to 32f by comparing the voltage command value with a triangular wave carrier signal.

[0057] The control signal generator 58 inputs the generated control signal to the converter 20. This allows control of the power conversion operation by the converter 20. For example, in this example, by setting the q-axis current command value to zero, the magnitude of reactive power flowing from the converter 20 to the power system 2 can be made virtually zero, and the operation of the converter 20 can be controlled so that the magnitude of the DC voltage output from the converter 20 is substantially constant according to the DC voltage command value. However, the configuration of the control device 14 is not limited to the above, and may be any configuration that can appropriately control the operation of the converter 20.

[0058] As described above, the power supply equipment 10 according to this embodiment includes a converter 12. This allows the power supply equipment 10 to suppress fluctuations in reactive power generated by the arc furnace 4 through the power conversion operation of the converter 12, thereby preventing the outflow of reactive power fluctuations, voltage fluctuations, harmonics, etc., to the power system 2. Therefore, the power supply equipment 10 can reduce the need for reactive power equipment such as reactive power compensation devices, harmonic filters, and power factor correction capacitors. For example, reactive power equipment can be made unnecessary or its output capacity reduced. Furthermore, as shown in the example in Figure 2, if the converter 12 has a charge storage element 24, the charge storage element 24 can absorb the fluctuations in reactive power generated by the arc furnace 4, further suppressing the outflow of reactive power fluctuations, voltage fluctuations, harmonics, etc., to the power system 2.

[0059] In the power supply equipment 10 according to this embodiment, the power quality of the power system 2 connected to the arc furnace 4 can be improved with a simpler configuration compared to a configuration that includes reactive power equipment such as a reactive power compensation device and a harmonic filter. In the power supply equipment 10 according to this embodiment, for example, the need for reactive power equipment can be reduced, and while improving the power quality of the power system 2, increases in equipment costs and installation space can be suppressed.

[0060] Furthermore, in the power supply equipment 10 according to this embodiment, the control device 14 supplies power to the arc furnace 4 (load) and controls the operation of the converter 12 so that the amount of reactive power flowing out to the power system 2 is a predetermined amount. As a result, even when a reactive power load 8 is connected to the power system 2, the converter 12 can compensate for the reactive power of the reactive power load 8. For example, it is possible to suppress the need to install new reactive power equipment or increase the capacity of reactive power equipment in order to compensate for the reactive power of the reactive power load 8. Therefore, in the power supply equipment 10 according to this embodiment, even when a reactive power load 8 is connected to the power system 2, the power quality of the power system 2 to which the arc furnace 4 is connected can be improved with a simpler configuration.

[0061] Figure 4 is a schematic block diagram showing a modified example of the control device according to the embodiment. As shown in Figure 4, the control device 14a has a grid voltage controller 60. 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.

[0062] The system voltage controller 60 receives the AC voltage d-axis signal and AC voltage q-axis signal calculated by the dq converter 54. The system voltage controller 60 also receives the d-axis voltage command value and q-axis voltage command value for setting the magnitude of the AC voltage (effective value) of the power system 2 to a predetermined magnitude.

[0063] The system voltage controller 60 calculates the difference between the input d-axis voltage command value and the AC voltage d-axis signal, and also calculates the difference between the input q-axis voltage command value and the AC voltage q-axis signal. By performing proportional control or proportional-integral control on each of the calculated differences, it calculates a q-axis current command value to make the magnitude of the AC voltage of the power system 2 corresponding to the d-axis voltage command value and the q-axis voltage command value. The system voltage controller 60 inputs the calculated q-axis current command value to the current controller 52.

[0064] As a result, the control device 14a can supply power to the arc furnace 4 (load) and control the operation of the converter 12 so that the magnitude of the AC voltage (effective value) of the power system 2 becomes a predetermined magnitude.

[0065] In this way, the control device 14a supplies power to the arc furnace 4 (load) and controls the operation of the converter 12 so that the magnitude of the AC voltage (effective value) of the power system 2 becomes a predetermined magnitude. For example, the control device 14a supplies power to the arc furnace 4 (load) and adjusts the magnitude of the reactive power flowing out to the power system 2 so that the magnitude of the effective value of the AC voltage of the power system 2 becomes substantially constant.

[0066] Thus, the control device 14a may control the operation of the converter 12 so as to control the voltage value of the power system 2 and keep the voltage value constant. In this case as well, similar to the embodiment described above, the power quality of the power system 2 to which the arc furnace 4 is connected can be improved with a simpler configuration compared to a configuration that includes reactive power equipment such as a reactive power compensation device or a harmonic filter.

[0067] The control device 14a can suppress voltage fluctuations in the power system 2 caused by the reactive power of the reactive power load 8, even when the reactive power load 8 is connected to the power system 2. Furthermore, the control device 14a can suppress the voltage drop in the power system 2 associated with the supply of active power to the arc furnace 4, even when the power system 2 is a power system that is relatively vulnerable to load fluctuations.

[0068] Figure 5 is a schematic block diagram showing a modified example of the control device according to the embodiment. As shown in Figure 5, the control device 14b includes a high-pass filter 61, an arithmetic unit 62, and an adder 63.

[0069] The AC current d-axis signal calculated by the dq converter 51 is input to the high-pass filter 61. The high-pass filter 61 extracts the harmonic components superimposed on the AC current d-axis signal by attenuating the fundamental frequency component of the AC power of the power system 2 and suppressing the attenuation of components with frequencies higher than the fundamental frequency of the AC power of the power system 2. The high-pass filter 61 inputs the extracted harmonic component signal to the arithmetic unit 62.

[0070] The arithmetic unit 62 performs proportional control or proportional-integral control on the harmonic component signal input from the high-pass filter 61 to suppress the harmonic component superimposed on the AC current d-axis signal. The arithmetic unit 62 then calculates a correction value for the d-axis current command value, which is added to the d-axis current command value, from the harmonic component signal. The arithmetic unit 62 inputs the calculated correction value to the adder 63.

[0071] The adder 63 receives a correction value calculated by the arithmetic unit 62, as well as a d-axis current command value calculated by the DC voltage controller 53. The adder 63 corrects the d-axis current command value by adding the correction value to the input d-axis current command value, and inputs the corrected d-axis current command value to the current controller 52.

[0072] As a result, the control device 14b can control the operation of the converter 12 to supply power to the arc furnace 4 (load) and suppress the outflow of harmonics into the power system 2. This allows the converter 12 to compensate for harmonics in the power system 2 caused by the reactive power of the reactive power load 8, even when a reactive power load 8 is connected to the power system 2. For example, it is possible to suppress the need to install new reactive power equipment or increase the capacity of reactive power equipment in order to compensate for harmonics. Therefore, even when a reactive power load 8 is connected to the power system 2, the control device 14b can improve the power quality of the power system 2 to which the arc furnace 4 is connected with a simpler configuration compared to a configuration that includes reactive power equipment such as a reactive power compensation device or a harmonic filter.

[0073] In this way, the control device supplies power to the arc furnace 4 (load) and controls the operation of the converter 12 (converter 20) to control at least one of the following: the magnitude of reactive power flowing out to the power system 2, the magnitude of the AC voltage (effective value) of the power system 2, and the harmonics flowing out to the power system 2. This makes it possible to omit reactive power equipment or reduce the capacity of reactive power equipment, and to improve the power quality of the power system 2 to which the arc furnace 4 is connected with a simpler configuration.

[0074] Figure 6 is a schematic block diagram showing a modified example of the power supply equipment according to the embodiment. As shown in Figure 6, in the power supply equipment 10a, the voltage detector 16a detects the magnitude of the AC voltage of the reactive power load 8 and inputs the detection result to the control device 14. Then, the current detector 17a detects the magnitude of the AC current of the reactive power load 8 and inputs the detection result to the control device 14.

[0075] In this example, the control device 14 controls the operation of the converter 12 based on the detection results of the voltage detector 16a, the current detector 17a, and the voltage detector 18. For example, the control device 14 supplies power to the arc furnace 4 (load) according to the magnitude of the reactive power flowing from the reactive power load 8 to the power system 2, and controls the operation of the converter 12 to control at least one of the magnitude of the reactive power flowing to the power system 2, the magnitude of the AC voltage (effective value) of the power system 2, and the harmonics flowing into the power system 2. Thus, the detection point for reactive power (reactive current) may be on the power receiving side or on the load side.

[0076] Figure 7 is a schematic block diagram showing a modified example of the power supply equipment according to the embodiment. As shown in Figure 7, in the power supply equipment 10b, the inverter 22 is omitted in the converter 12b. In this example, the power supplied to the arc furnace 4b is DC power. In other words, the arc furnace 4b is a DC arc furnace. The converter 12b converts, for example, the three-phase AC power supplied from the power system 2 side into DC power corresponding to the arc furnace 4b, and supplies the converted DC power to the arc furnace 4b.

[0077] Thus, the arc furnace is not limited to an AC arc furnace, but may also be a DC arc furnace. In other words, the load connected to the power supply equipment is not limited to an AC load, but may also be a DC load. In this case as well, in the same manner as in each of the embodiments described above, the power supply quality of the power system 2 to which the arc furnace 4b is connected can be improved with a simpler configuration by controlling the operation of the converter 12b (converter 20) to supply power to the arc furnace 4b (load) and to control at least one of the magnitude of reactive power flowing out to the power system 2, the magnitude of the AC voltage (effective value) of the power system 2, and the harmonics flowing out to the power system 2. The load connected to the power supply equipment is not limited to an arc furnace, but may be any load.

[0078] The converter configuration is not limited to the above, and may be any configuration capable of supplying power to the load and controlling at least one of the following: the magnitude of reactive power flowing out to power system 2, the magnitude of the AC voltage (RMS value) of power system 2, and the harmonics flowing out to power system 2. When supplying AC power to the load, the converter may be a direct conversion circuit capable of directly converting AC power to another AC power without going through DC power, such as a matrix converter or a cycloconverter.

[0079] This embodiment includes the following aspects: (Note 1) A power supply system comprising: a converter provided between a power system and a load, which converts AC power supplied from the power system into power corresponding to the load and supplies the converted power to the load; and a control device that supplies power to the load and controls the operation of the converter to control at least one of the magnitude of reactive power flowing out to the power system, the magnitude of the AC voltage of the power system, and the harmonics flowing out to the power system.

[0080] (Note 2) The power supply equipment described in Note 1, wherein the control device supplies power to the load and controls the operation of the converter so that the amount of reactive power flowing out to the power system is a predetermined amount.

[0081] (Note 3) The power supply equipment according to Note 1 or 2, wherein the control device supplies power to the load and controls the operation of the converter so that the magnitude of the AC voltage of the power system becomes a predetermined magnitude.

[0082] (Note 4) The power supply equipment according to any one of Notes 1 to 3, wherein the control device supplies power to the load and controls the operation of the converter in order to suppress the outflow of harmonics into the power system.

[0083] (Note 5) The power supply equipment according to any one of Notes 1 to 4, further comprising: a voltage detector that detects the magnitude of the AC voltage of the power system and inputs the detection result to the control device; and a current detector that detects the magnitude of the AC current of the power system and inputs the detection result to the control device, wherein the control device controls the operation of the converter based on the detection results of the voltage detector and the current detector.

[0084] (Note 6) The power supply equipment according to any one of Notes 1 to 4, further comprising: a voltage detector that detects the magnitude of the AC voltage of a reactive power load connected to the power system together with the converter and inputs the detection result to the control device; and a current detector that detects the magnitude of the AC current of the reactive power load and inputs the detection result to the control device, wherein the control device controls the operation of the converter based on the detection results of the voltage detector and the current detector.

[0085] (Note 7) The power supply equipment according to any one of Notes 1 to 6, wherein the load is an AC load, the converter comprises a converter that converts AC power supplied from the power system to DC power, and an inverter that converts the DC power converted by the converter to AC power corresponding to the load and supplies the converted AC power to the load, and the control device supplies power to the load and controls the operation of the converter to control at least one of the magnitude of reactive power flowing out to the power system, the magnitude of the AC voltage of the power system, and the harmonics flowing out to the power system.

[0086] 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 and in the scope of the invention and its equivalents as described in the claims.

[0087] 2...Power system, 4, 4b...Arc furnace, 6...Load system, 8...Reactive power load, 10, 10a, 10b...Power supply equipment, 12, 12b...Converter, 14, 14a, 14b...Control device, 16, 16a...Voltage detector, 17, 17a...Current detector, 18...Voltage detector, 20...Converter, 22...Inverter, 24...Charge storage element, 30a-30c...AC input terminal, 31a, 31b...DC output terminal, 32a-32f...Switching element, 33a-33f...Rectifier element, 40a, 40b...DC input terminal, 41a-41c...AC output terminal, 42a-42f...Switching element, 43a-43f...Rectifier element, 51...DQ converter, 52...Current controller, 53...DC voltage controller 54...dq converter, 55, 56...adder, 57...inverse dq converter, 58...control signal generator, 60...system voltage controller, 61...high-pass filter, 62...arithmetic unit, 63...adder

Claims

1. A power supply system comprising: a converter installed between a power system and a load, which converts AC power supplied from the power system into power corresponding to the load and supplies the converted power to the load; and a control device that supplies power to the load and controls the operation of the converter to control at least one of the magnitude of reactive power flowing out to the power system, the magnitude of the AC voltage of the power system, and the harmonics flowing out to the power system.

2. The power supply equipment according to claim 1, wherein the control device supplies power to the load and controls the operation of the converter so that the amount of reactive power flowing out to the power system is a predetermined amount.

3. The power supply equipment according to claim 1, wherein the control device supplies power to the load and controls the operation of the converter so that the magnitude of the AC voltage of the power system becomes a predetermined magnitude.

4. The power supply equipment according to claim 1, wherein the control device supplies power to the load and controls the operation of the converter to suppress the outflow of harmonics into the power system.

5. The power supply equipment according to claim 1, further comprising: a voltage detector that detects the magnitude of the AC voltage of the power system and inputs the detection result to the control device; and a current detector that detects the magnitude of the AC current of the power system and inputs the detection result to the control device, wherein the control device controls the operation of the converter based on the detection results of the voltage detector and the current detector.

6. The power supply equipment according to claim 1, further comprising: a voltage detector that detects the magnitude of the AC voltage of a reactive power load connected to the power system together with the converter and inputs the detection result to the control device; and a current detector that detects the magnitude of the AC current of the reactive power load and inputs the detection result to the control device, wherein the control device controls the operation of the converter based on the detection results of the voltage detector and the current detector.

7. The power supply equipment according to claim 1, wherein the load is an AC load, the converter comprises a converter that converts AC power supplied from the power system to DC power, and an inverter that converts the DC power converted by the converter to AC power corresponding to the load and supplies the converted AC power to the load, and the control device supplies power to the load and controls the operation of the converter to control at least one of the magnitude of reactive power flowing out to the power system, the magnitude of the AC voltage of the power system, and the harmonics flowing out to the power system.

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