Flicker compensator

Abstract

To provide a low-cost flicker compensator which can be easily increased in power capacity.SOLUTION: A flicker compensator according to an embodiment comprises a line-communicated converter, a self-communicated converter, and a controller. The controller outputs a first control signal for controlling the line-communicated converter and a second control signal for controlling the self-communicated converter. The controller includes a first control unit for generating the first control signal and a second control unit for generating the second control signal. The first control unit calculates the reactive power fluctuation of a bus bar, and generates the first control signal so as to generate reactive power for canceling the reactive power fluctuation. The second control unit calculates the effective power fluctuation of the bus bar, and generates the second control signal so as to generate effective power for canceling the effective power fluctuation.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a flicker compensation device that suppresses voltage flicker that occurs in a steelmaking arc furnace. [Background technology]

[0002] In systems where steelmaking arc furnaces are connected, voltage flicker occurs due to fluctuations in reactive power caused by sudden load fluctuations. Consumers who use steelmaking arc furnaces as their loads connect flicker compensation devices to their systems in order to keep voltage flicker within the limits set by power suppliers.

[0003] In recent years, attempts to reduce fossil fuel consumption and achieve carbon neutrality have been made in many areas. Steel plants are also making concrete efforts to switch from blast furnaces to electric furnaces, and as a result, electric furnaces are being made larger in capacity.

[0004] Accordingly, flicker compensation devices are also required to have a larger power capacity, and there is an increasing demand for low-cost, high-performance flicker compensation devices. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6942618 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of an embodiment of the present invention is to provide a flicker compensation device that is low cost and can easily be made large in power capacity. [Means for solving the problem]

[0007] A flicker compensation device according to an embodiment of the present invention suppresses voltage flicker in a steelmaking arc furnace. The flicker compensation device includes an externally commutated converter (ECC) using thyristors as main switching elements and controlling the thyristors through phase control; a self-commutated converter (SCM) using self-extinguishing switching elements as main switching elements and controlling the self-extinguishing switching elements continuously in the time domain; and a control device that outputs a first control signal to the externally commutated converter and a second control signal to the SCM. The control device includes a first control unit that generates the first control signal and a second control unit that generates the second control signal. The first control unit detects the current and voltage of a bus supplying power to the steelmaking arc furnace, calculates reactive power fluctuations of the bus based on the current and voltage, and generates the first control signal to output reactive power that cancels the reactive power fluctuations. The second control unit detects the current and the voltage, calculates active power fluctuations of the bus based on the current and the voltage, and generates the second control signal to output active power that cancels the active power fluctuations, and the output power capacity of the externally excited converter is greater than three times the output power capacity of the self-excited converter in apparent power terms. [Effects of the Invention]

[0008] According to the embodiments of the present invention, it is possible to provide a flicker compensation device that is low cost and can easily have a large power capacity. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic block diagram illustrating a flicker compensation device according to an embodiment; [Figure 2] FIG. 2 is a schematic block diagram illustrating a control device that is a part of a flicker compensation device according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments will be described with reference to the drawings. The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc. are not necessarily the same as those in reality. Furthermore, even when the same part is shown, the dimensions and ratios may be different depending on the drawing. In the present specification and the drawings, elements similar to those described above with reference to the previous drawings are designated by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0011] FIG. 1 is a schematic block diagram illustrating a flicker compensation device according to an embodiment. As shown in Fig. 1, a flicker compensation device 1 according to the embodiment is connected to a bus 101 of an electric power system 100 via transformers 25 and 26, and is interconnected with the electric power system. Electrodes are connected to the bus 101 via a furnace transformer 21, and an arc discharge is formed between the electrodes and scrap charged into a steelmaking arc furnace 20, and the scrap is melted by the arc discharge.

[0012] A reactive power compensation device such as a capacitor equipment group 22 may be connected to the bus bar 101 to compensate for and adjust the reactive power flowing into the power system 100 and the decrease in power factor caused by the steelmaking arc furnace 20 and other power equipment.

[0013] The power system 100 is a three-phase AC power system. The steelmaking arc furnace 20 is, for example, an AC arc furnace, and although not shown, it melts scrap by arc discharge using three electrodes connected to each phase of the three-phase AC power system.

[0014] The configuration of the flicker compensation device 1 will be described. The flicker compensation device 1 includes a self-commutated converter 27, an externally commutated converter 28, and a control device 29. The self-commutated converter 27 is connected to a bus 101 via an interconnection transformer 25. The externally commutated converter 28 is connected to the bus 101 via an interconnection transformer 26.

[0015] The self-excited converter 27 includes a self-extinguishing switching element. The self-extinguishing switching element is a switching element that can be turned on and off by a control signal, such as an IGBT or a MOSFET. For example, the self-excited converter 27 controls the on and off of the self-extinguishing switching element by a control signal generated by a PWM control circuit, and outputs desired current and voltage waveforms.

[0016] The externally commutated converter 28 includes a thyristor as a switching element. The thyristor is turned on by a gate signal, which is a control signal, and is turned off when the current flowing through the thyristor falls below the minimum cathode current. In other words, the thyristor is turned off when the AC voltage of the bus 101 crosses zero. The thyristor of the externally commutated converter 28 can output the desired reactive power through phase control using the generated gate signal.

[0017] The control device 29 is connected to the current transformer 23. The current transformer 23 detects the current flowing through the furnace transformer 21 and outputs the result to the control device 29. The control device 29 is connected to the potential transformer 24. The potential transformer 24 detects the voltage of the bus bar 101 and outputs the result to the control device 29.

[0018] The control device 29 is connected to each of the self-commutated converter 27 and the externally-commutated converter 28. The control device 29 generates a control signal for the self-commutated converter 27 based on the current signal output by the current transformer 23 and the voltage signal output by the potential transformer 24, and outputs the control signal to the self-commutated converter 27. The self-commutated converter 27 operates in accordance with the control signal.

[0019] The control device 29 generates a control signal for the separately excited converter 28 based on the current signal output by the current transformer 23 and the voltage signal output by the potential transformer 24, and outputs the signal to the separately excited converter 28. The separately excited converter 28 operates in accordance with the control signal.

[0020] In the flicker compensator 1 according to the embodiment, compensation for fluctuations in reactive power, which are one of the causes of voltage flicker, is performed by controlling the externally excited converter 28. Other causes of voltage flicker are compensated for by the self-excited converter 27. In this way, the flicker compensator 1 according to the embodiment operates so that the externally excited converter 28 and the self-excited converter 27 share the compensation load depending on the cause of voltage flicker.

[0021] In a steelmaking arc furnace, the majority of voltage flicker is caused by fluctuations in reactive power due to arc discharge. In the flicker compensation device 1 according to the embodiment, the output power capacity of the externally commutated converter 28 is sufficiently larger than the output power capacity of the self-commutated converter 27 in terms of apparent power (unit: VA). For example, the ratio of the output power capacity of the externally commutated converter 28 to the output power capacity of the self-commutated converter 27 is set to be larger than 3:1, preferably larger than 5:1.

[0022] The configuration of the control device 29 will be described. FIG. 2 is a schematic block diagram illustrating a control device that is a part of the flicker compensation device according to the embodiment. 2, the control device 29 has a first control unit 30 and a second control unit 31. The first control unit 30 generates a control signal for the externally excited converter 28. The second control unit 31 generates a control signal for the self-excited converter 27.

[0023] The first control unit 30 has a reactive power fluctuation calculation circuit 32, an output value calculation unit 33, and a control signal generation unit .

[0024] The reactive power fluctuation calculation circuit 32 calculates reactive power having a phase that cancels fluctuations in the reactive power of the bus 101, based on the current signal output by the current transformer 23 and the voltage signal output by the voltage transformer 24. The output value calculation unit 33 calculates the magnitude of the reactive power output by the reactive power fluctuation calculation circuit 32. The control signal generation unit 34 generates a control signal for phase control so that the reactive power is generated to cancel fluctuations in the reactive power of the bus 101.

[0025] The second control unit 31 has an active power fluctuation calculation circuit 35, a distortion current calculation circuit 36, a negative-sequence voltage calculation circuit 37, an output value calculation unit 38, and a control signal generation unit 39. The active power fluctuation calculation circuit 35 calculates reactive power having a phase that cancels fluctuations in the reactive power of the bus 101. The distortion current calculation circuit 36 ​​calculates a current value so as to cancel the distortion current of the bus 101. The negative-sequence voltage calculation circuit 37 calculates a voltage value so as to cancel the negative-sequence voltage of the bus 101. The output value calculation unit 38 calculates an output value so as to cancel the active power fluctuation, the distortion current, and the negative-sequence voltage, respectively. The control signal generation unit 39 generates a control signal for PWM control, for example, based on these.

[0026] In the control device 29, by using vector control technology such as DQ conversion of the current signal and voltage signal, the power in the bus 101 can be decomposed into reactive power, active power, distortion current, and negative-phase voltage, and a control signal can be generated to cancel each of them.

[0027] All of the active power fluctuation calculation circuit 35, the distortion current calculation circuit 36, and the negative-phase voltage calculation circuit 37 may be provided, or one or more of them may be selected and provided depending on the occurrence status of voltage flicker in the steel-making arc furnace 20.

[0028] The effects of the flicker compensation device 1 according to the embodiment will be described. The flicker compensation device 1 according to the embodiment includes an externally commutated converter 28. A control device 29 has a reactive power fluctuation calculation circuit 32, and generates a control signal to cancel fluctuations in the reactive power of the steelmaking arc furnace 20, and outputs the control signal to the externally commutated converter 28. Therefore, the externally commutated converter 28 can reduce fluctuations in reactive power, which is the main cause of voltage flicker in the steelmaking arc furnace 20.

[0029] The separately-commutated converter 28 employs a phase control method using a thyristor or the like. As is well known, thyristors can easily be made to handle large currents and withstand high voltages, and by using thyristors as the main switching elements to configure the separately-commutated converter 28, a large-capacity converter can be realized at low cost with a small number of parts.

[0030] In the case of an AC arc furnace, fluctuations in active power, the generation of distorted current, and the generation of negative-phase voltage flowing to the bus 101 can cause voltage flicker. As the capacity of the steelmaking arc furnace 20 increases, the causes of voltage flicker can also become more diverse in DC arc furnaces. In the case of the externally excited converter 28, phase control is performed for each AC cycle, making it difficult to control the current and voltage waveforms continuously.

[0031] In the flicker compensator 1 according to the embodiment, the self-excited converter 27 uses IGBTs, MOSFETs, or the like as self-extinguishing switching elements, and can continuously generate any appropriate current and voltage waveforms on the time and phase axes by applying vector control techniques such as DQ conversion. The control device 29 includes an active power fluctuation calculation circuit 35, a distortion current calculation circuit 36, and a negative-phase-sequence voltage calculation circuit 37. This allows the flicker compensator 1 to appropriately control the current and voltage waveforms injected into the bus 101 on the time and phase axes so as to reduce active power fluctuations, distortion currents, and negative-phase-sequence voltages. Therefore, voltage flicker can be suppressed in large-capacity steelmaking arc furnaces, regardless of whether they are AC arc furnaces or DC arc furnaces.

[0032] In the steelmaking arc furnace 20, the main cause of voltage flicker is fluctuations in reactive power, and among the causes of voltage flicker, those caused by active power fluctuations, distortion current, and negative-phase voltage are sufficiently small compared to the magnitude of the reactive power output by the flicker compensator 1. Therefore, the output power capacity of the self-commutated converter 27, which operates to suppress these, can be made sufficiently smaller than the output power capacity of the externally commutated converter 28. This makes it possible to realize a low-cost, large-capacity, and highly functional flicker compensator 1.

[0033] In this way, a flicker compensation device can be realized that is low cost and can easily be made large in power capacity.

[0034] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0035] 1...Flicker compensation device, 20...Steel-making arc furnace, 21...Furnace transformer, 22...Capacitor equipment group, 23...Current transformer, 24...Instrument transformer, 25, 26...Transformer, 27...Self-commutated converter, 28...Separately-commutated converter, 29...Control device, 30...First control unit, 31...Second control unit, 32...Reactive power fluctuation calculation circuit, 33, 38...Output value calculation unit, 34, 39...Control signal generation unit, 100...Power system, 101...Bus

Claims

1. A flicker compensation device for suppressing voltage flicker in a steelmaking arc furnace, a separately excited converter using a thyristor as a main switching element and controlling the thyristor by phase control; a self-excited converter that uses a self-extinguishing switching element as a main switching element and controls the self-extinguishing switching element continuously in the time domain; a control device that outputs a first control signal to the externally excited converter and a second control signal to the self-excited converter; Equipped with the control device includes a first control unit that generates the first control signal and a second control unit that generates the second control signal; The first control unit detecting a current and a voltage of a busbar supplying power to the steelmaking arc furnace; Calculating a reactive power fluctuation of the bus based on the current and voltage; generating the first control signal to output reactive power that cancels the reactive power fluctuation; The second control unit is detecting the current and the voltage; Calculating an active power fluctuation of the bus based on the current and the voltage; generating the second control signal to output an active power that cancels the active power fluctuation; A flicker compensation device in which the output power capacity of the externally excited converter is greater than three times the output power capacity of the self-excited converter in apparent power conversion.

2. A flicker compensation device for suppressing voltage flicker in a steelmaking arc furnace, a separately excited converter using a thyristor as a main switching element and controlling the thyristor by phase control; a self-excited converter that uses a self-extinguishing switching element as a main switching element and controls the self-extinguishing switching element continuously in the time domain; a control device that outputs a first control signal to the externally excited converter and a second control signal to the self-excited converter; Equipped with the control device includes a first control unit that generates the first control signal and a second control unit that generates the second control signal; The first control unit detecting a current and a voltage of a busbar supplying power to the steelmaking arc furnace; Calculating a reactive power fluctuation of the bus based on the current and voltage; generating the first control signal to output reactive power that cancels the reactive power fluctuation; The second control unit is detecting the current and the voltage; calculating a distortion current of the bus bar based on the current and the voltage; generating the second control signal to output an output current that cancels the distortion current; A flicker compensation device in which the output power capacity of the externally excited converter is greater than three times the output power capacity of the self-excited converter in apparent power conversion.

3. A flicker compensation device for suppressing voltage flicker in a steelmaking arc furnace, a separately excited converter using a thyristor as a main switching element and controlling the thyristor by phase control; a self-excited converter that uses a self-extinguishing switching element as a main switching element and controls the self-extinguishing switching element continuously in the time domain; a control device that outputs a first control signal to the externally excited converter and a second control signal to the self-excited converter; Equipped with the control device includes a first control unit that generates the first control signal and a second control unit that generates the second control signal; The first control unit detecting a current and a voltage of a busbar supplying power to the steelmaking arc furnace; Calculating a reactive power fluctuation of the bus based on the current and voltage; generating the first control signal to output reactive power that cancels the reactive power fluctuation; The second control unit is detecting the current and the voltage; calculating a negative-phase-sequence voltage of the bus based on the current and the voltage; generating the second control signal to output an output voltage that cancels the negative-phase voltage; A flicker compensation device in which the output power capacity of the externally excited converter is greater than three times the output power capacity of the self-excited converter in apparent power conversion.

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