Power supply system for a metal fabrication facility and method for operating a power supply system for a metal fabrication facility

Abstract

A power supply system for a metal fabrication facility having at least one electric arc furnace (EAF). The power supply system is connectable to an external power source for providing, powered by the external power source, a load power to one or more EAFs of the at least one EAF. The power supply system includes a first converter having a first front end, a first DC link, and a first inverter having a first determining unit configured for determining a first operating characteristic having information about a power quality of the load power. The power supply system includes a first feed forward data link. The power supply system includes a first power quality unit configured for improving the power quality of the load power, the first power quality unit comprising a first power quality unit controller. The first power quality unit controller is configured for receiving, through the first feed forward data link, a first reference signal, the first reference signal being based on the first operating characteristic, and is configured for controlling an operation of the first power quality unit based on the first reference signal.

Description

[0001] POWER SUPPLY SYSTEM FOR A METAL FABRICATION FACILITY AND METHOD FOR OPERATING A POWER SUPPLY SYSTEM FOR A METAL FABRICATION FACILITY

[0002] Field of the disclosure

[0003] The invention is in the area of power supply systems for metal fabrication facilities. Embodiments of the present invention relate to a power supply system for a metal fabrication facility and a method for operating a power supply system for a metal fabrication facility.

[0004] Technical Background

[0005] In electric grids and power supply systems, reactive and active power fluctuations can occur when the load voltage and load current vary. These fluctuations are, for example, visible in a light bulb and cause the light intensity in an incandescent light bulb to vary. When the frequency of these fluctuations is in the range where the human eye can detect them, the phenomena is termed as flicker. These fluctuations can be generated in industrial plants. In an industrial plant, the flicker is dependent on the load dynamics, the size of the load, the number of loads connected in parallel, the likelihood of coincident disturbances in relation to the strength of the grid. For a given load, the flicker is higher, when the grid fault level is lower.

[0006] Electric grid utility companies set flicker limits on how much a single consumer is allowed to emit into the grid. In addition, the IEC and IEEE define the allowed threshold limits for flicker and other power quality parameters, for example harmonics. The utility companies are getting more stringent concerning the power quality disturbances from the loads and are starting to lower the threshold values independent of the standards set by IEC and IEEE. As the grids are getting weaker and the industrial plants, for example electric arc furnaces, are getting larger, the plant operators are facing a significantly higher requirement in regard to power quality. This forces the consumers, for example electric arc furnace operators, to invest in better power quality mitigation equipment or into power supplies that by design minimize flicker at the point of their connection.

[0007] There is therefore a need for an improved power quality mitigation system. The present invention provides a power supply system for a metal fabrication facility and a method for operating a power supply system for a metal fabrication facility to address flicker and other power quality issues, such as power factor, harmonics, and voltage unbalance, more effectively.

[0008] Summary of the disclosure

[0009] Reference will now be made in detail to the various embodiments of the present disclosure, one or more examples of which are illustrated in the figures. Generally, only the differences with respect to individual embodiments are described. Each example is provided by way of explanation and is not meant as a limitation of the present disclosure. Features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet a further embodiment. It is intended that the description includes such modifications and variations.

[0010] In light of the above, a power supply system according to claim 1 and a method for operating a power supply system according to claim 12 is provided. Further aspects, advantages, and features are apparent from the dependent claims, the description, and the accompanying drawings.

[0011] The invention applies to industrial facilities, particularly metal fabrication facilities having at least one electric arc furnace, with transient behavior like phase asymmetry and dynamic random loading. The electric arc furnace (EAF) may be an AC arc furnace, a DC arc furnace, a submerged arc furnace, an open bath furnace, and / or a ladle metallurgy furnace (LMF). The industrial facilities, particularly the metal fabrication facilities, may further include any other fluctuating load, i.e. a load that can introduce fluctuations in a load power, and / or nonfluctuating load.

[0012] Throughout this description, a power quality of a load power is described. The load power may be a power provided by the power supply system to one or more loads, i.e. one or more EAFs of the metal fabrication facility. The power supply system may provide a first load power to a first load, a second load power to a second load and a n-th load power to a n-th load. The load power may be the total power received by the one or more loads from the power supply system. The load power may be the sum of the first load power, the second load power and the n-th load power. Particularly, the load power may describe multiple powers provided to the one or more loads, that are added up to the load power. The power quality of the load power may describe a quality of the load power. The power quality may be described by one or more power quality parameters. The power quality parameters may refer to quantities having information about a quality of an electric power provided, for example, by the power supply system according to the present invention. The power quality parameters may, for example, refer to flicker, harmonics, power factor, voltage unbalance, and / or any other quantity describing a quality of the electric power. Distortions in one or more of the power quality parameters can be caused by a load voltage, a load current, and / or a firing behavior of a converter, particularly, a firing angle, a firing pattern and / or a firing modulation. The power quality of a power provided by a power supply system, e.g. the power supply system according to the present invention, can be described by one or more of the power quality parameters.

[0013] Throughout this description multiple components of a same type, e.g. a first feed forward data link and a second feed forward data link, or a first power quality unit and a second power quality unit, are described. It is understood that the components of the same type are generally similar and / or identical. That is, unless otherwise indicated, when a feature is described for one component, e.g. the first feed forward data link, this applies to all components of the same type, e.g. the features are also described for the second feed forward data link. Further, the multiple components of the same type, e.g. a first feed forward data link and a second feed forward data link, or a first power quality unit and a second power quality unit, may generally be referred to by general terms, e.g. feed forward data links or power quality units. Unless otherwise indicated, it is intended that when describing features of or in relation to a component by using the general terms, e.g. feed forward data links or power quality units, these features are described for each component, e.g. the first feed forward data link and the second feed forward data link or the first power quality unit and the second power quality unit.

[0014] Throughout this description, different transformers are referred to, such as source transformers, power quality unit transformers, or arc furnace transformers. It is understood, that the transformers referred to throughout this description can be any suitable type of transformer, such as 2-winding transformers or 3 -winding transformers.

[0015] Power quality units can be used to improve a power quality of a power supply system, particularly a power quality of a power provided by the power supply system. For example, a STATCOM can be controlled, based on grid voltage measurements, to optimize a voltage waveform to be as close as possible to a sinewave and to adjust the phase angle between the voltage and current such that the phase angle is according to the needs for a power factor at a grid connecting point. The grid connecting point may be the point where the power supply system connects to the external power source. As the grid voltage must be measured prior to the control of the power quality unit being able to react, for example the power quality unit being a STATCOM, a time delay is introduced. This time delay increases the voltage distortion and limits the power quality improvement that the power quality unit can provide. By introducing a feed forward data link the control can be faster and more robust. The feed forward data link allows that the next loading and its characteristic can be transmitted to the power quality unit, for example being an active front end (AFE), a STATCOM and / or an energy storage system (ESS), where a suitable pulse pattern will be generated from an open loop control. Thereby, a faster, more accurate, and more robust control behavior of the power quality unit is enabled. Beneficially, the power quality improvement that the power quality unit provides can be enhanced. Particularly, the power quality of a load power, for example the load power provided by the power supply system according to the present invention, can be improved. Further, there is less risk of oscillations in the power provided by the power supply system.

[0016] By knowing the loading of the EAF in advance, the expected power quality distortion, for example due fluctuation in the reactive power, i.e. AQ, or fluctuation in the active power, i.e. AP, harmonics, and / or voltage unbalance, can be calculated. Throughout this application the term flicker is referred to. Flicker describes a long-term integration of AQ and / or AP. Wherein long-term is with respect to the time scale of the fluctuations in the reactive power (AQ) and / or the active power (AP). Voltage variations can be caused by AQ and AP, which can result in flicker. By reducing AQ and AP, the voltage variations can be reduced, particularly the flicker can be reduced. Beneficially, the flicker in the load power provided by the power supply system can be improved, that is, the flicker can be minimized. Additionally, also the harmonics and other power quality parameters can be improved. Further, in conjunction with an ESS, advantageously also the active power fluctuation can be damped or absorbed. Specifically, on very weak grids and in island operation this will heavily improve the power quality. Advantageously, the improved power quality can result in increased production and / or reduced maintenance of the electric components powered by power supply system and / or the one or more EAFs powered by the power supply system.

[0017] To optimize the power quality improvement that a power quality unit, such as a STATCOM or an active front end (AFE) of a full converter, such as a solid state transformer (SST), a modular multilevel converter (MMC), a Matrix converter, and / or any other suitable type of full converter, can provide, a feed forward control is implemented in the power supply system according to the present invention. The power quality unit may improve the power quality by improving one or more power quality parameters, such as flicker, harmonics, power factor, and / or voltage unbalance. The power quality unit can be a grid forming converter interconnected with an ESS. The power quality units, such as the STATCOM and the load converters, can be based on various converter topologies based on switching semiconductors, such as fast switching force commutated semiconductors.

[0018] With modem converter topologies and modern semiconductors, higher effective switching frequencies can be achieved. This allows to improve power quality parameters, such as the reactive power, harmonics and / or voltage unbalances. Additionally, other power quality parameters can be improved. The power supply system according to the present invention allows to determine information about a power quality of the load. The power quality can be based on information about a load voltage, a load current and / or firing behavior of a converter. Particularly, the power quality can be described by one or more power quality parameters. The one or more power quality parameters can be based on information about a load voltage, a load current, and / or a firing behavior of the converters, particularly a firing angle, a firing pattern, and / or a firing modulation. This information can be used to determine what the load and the distortion is going to be in a subsequent cycle, i.e. determine the next firing pattern of the switching semiconductors of the power quality unit for the next switching cycle of the switching semiconductors of the power quality units. This information can be fed forward to the power quality units through the feed forward data links. Advantageously, the power quality units may react faster to distortions in the power quality. Therefore, an overall calculation of the expected distortion is possible and by adapting the modulating patterns, i.e. switching patterns, of the semiconductors, the aforementioned power quality parameters and others can be tackled, particularly in a faster manner.

[0019] In the past, with thyristor-based rectifiers and static var compensators (SVC), only the reactive power could be influenced. Advantageously, the present invention allows to improve power quality parameters, such as flicker, harmonics, active power factor, and / or voltage unbalance, resulting in an overall improvement in power quality. Advantageously, more power quality control objectives can be addressed. It is possible to focus on a single one power quality parameter or on various power quality parameters to improve the overall power quality of the load power. Also, the priorities between the control objectives can be set depending on the needs.

[0020] The power supply system according to the present invention is for a metal fabrication facility having at least one electric arc furnace. The electric arc furnace is typically controlled by power electronic converters, e.g. the first converter or the second converter. These converters can be located on a primary side, i.e. medium voltage (MV) side, or a secondary side, i.e. low voltage (LV) side, of a transformer, for example, of a furnace transformer. The converter can contain an active (AFE) or passive front end. The (AFE) can act as a power quality unit as described herein. A STATCOM can be provided as a power quality unit as described herein and can be connected in parallel to the converter. The determining units may communicate directly and very fast with the power quality unit controllers, particularly through the feed forward data links. In addition, ESS systems with grid forming converter interfaces may also be connected to the MV grid. The ESS may be linked via one or more feed forward data links to one or more of the converters, including the first converter and / or the second converter.

[0021] According to an aspect, a power supply system for a metal fabrication facility having at least one electric arc furnace (EAF) is provided. The power supply system is connectable to an external power source for providing, powered by the external power source, a load power to one or more EAFs of the at least one EAF. The power supply system includes a first converter having a first front end, a first DC link, and a first inverter having a first determining unit configured for determining a first operating characteristic having information about a power quality of the load power. The power supply system includes a first feed forward data link. The power supply system includes a first power quality unit configured for improving the power quality of the load power, the first power quality unit comprising a first power quality unit controller. The first power quality unit controller is configured for receiving, through the first feed forward data link, a first reference signal, the first reference signal being based on the first operating characteristic, and is configured for controlling an operation of the first power quality unit based on the first reference signal.

[0022] The first determining unit may be configured for determining the first operating characteristic in real time. The feed forward data links allow to feed forward the reference signals to the power quality unit controllers. The reference signals are based on the operating characteristic. The reference signals may correspond to the operating characteristic. By feeding forward the reference signal, the power quality unit controllers can know what will happen in advance. This allows to reduce a delay in the control and thus improve the performance of the power quality units. The delay in reaction time of the power quality units is dependent on a transfer speed of the feed forward data link. The feed forward data link needs to be fast to establish a fast communication between the converters and the power quality units. Particularly fast enough, such that the power quality units, for example being one of a STATCOM, an ESS and / or an AFE, can react to the fluctuation and / or distortions without any significant delay due to the information transmitted.

[0023] Reducing the delay in the control loop of the power quality unit is the target. A performance of the power quality unit can be improved by making a data communication through the feed forward data link faster. The power quality units, such as the STATCOM and the load converters, are based on various converter topologies based on switching semiconductors, such as fast switching force commutated semiconductors. The power quality unit can compensate fluctuations in the load power by switching the switching semiconductors. The switching semiconductors have a switching frequency. The necessary link speed of the feed forward data link can be determined based on the switching frequency of the switching semiconductors. Beneficially, the feed forward data link is faster than the switching frequency of the switching semiconductors of the power quality unit. In this case, after the operating characteristics, for example the first operating characteristic, is determined, the power quality unit, particularly the first power quality unit, will trigger the next time based on, i.e. the switching pattern of the semiconductors will be based on, the reference signal being based on said operating characteristic, particularly the first reference signals. Beneficially, this allows to improve the performance of the power quality unit, particularly this allows to ensure that the performance is as good as possible. For example, assuming a 10 kHz switching frequency of the semiconductor a link speed of not more than 50 ps is needed. That is, a reference signal, being based on an operating characteristic, is received, through a feed forward data link, within 50 ps by a power quality unit controller, after determining said operating characteristic. The faster the reaction of the converter is, the more precisely restoring the sine wave is possible. In embodiments, the power supply system is configured for the first power quality unit controller to receive the first reference signal within one switching period of a switching semiconductor of the first power quality unit after the first operating characteristic is determined by the first determining unit, particularly within half the switching period of the switching semiconductor.

[0024] The power supply system according to the present invention allows to feed forward reference signals for controlling an operation of the power quality units. The reference signals are based on operating characteristics having information about fluctuation in the load power. The reference signals may correspond to the operating characteristics. Advantageously, the power quality units can respond to disturbances in the power quality of the load power, for example, fluctuations in the active load power (AP) or reactive load power (AQ), harmonics, power factor, and / or voltage unbalance, in a faster manner. Particularly the response time may be primarily limited by the link speed of the feed forward data link and the switching frequency of the switching semiconductors. The power supply system allows to respond faster to distortions in the power quality of the load power. The faster response to the distortion in the power quality of the load power allows to improve a power quality of a load power provided by the power supply system according to the present invention. Beneficially, the power supply system according to the present invention allows to provide a load power with improved power quality.

[0025] A further advantage compared to closed loop controls is, that closed loop controls generally introduce a delay, due to the time needed for the measurements and then applying the control algorithm, for example for a PI— Controller. This delay, may, in some cases introduce instabilities. Beneficially such instabilities are not seen in a feed forward control according to the present invention, resulting in a more stable operation of the power supply system according to the present invention.

[0026] The power supply system is connectable to an external power source for powering the power supply system. The external power source may be a traditional grid, a renewable energy-based grid, a fossil fuel based grid, a nuclear based grid, an island grid and / or any combination thereof. The power supply system may be powered entirely by a renewable energy system. The renewable energy system may comprise one or more renewable energy sources. The renewable energy system may comprise one or more energy storage systems to store energy produced by the renewable energy sources. The renewable energy source may be a solar energy source, a wind energy source, a geothermal energy source, a hydropower energy source, an ocean energy source, a bioenergy source, any other suitable renewable energy source, or any combination thereof.

[0027] The metal fabrication facility may be any type of metal fabrication facility having at least one electric arc furnace (EAF). The EAFs may be selected from the group consisting of an AC arc furnace, a DC arc furnace, an AC submerged arc furnace, a DC submerged arc furnace, an AC open bath furnace, a DC open bath furnace, and / or a ladle metallurgical furnace (LMF). The EAFs may be connected to the power supply system through one or more converters, for example, the first converter and / or the second converter. The LMF may be directly connected to the power supply system, particularly connected to the power supply system without a converter. The metal fabrication facility may comprise different types of EAFs, particularly different types of EAFs selected from the above group. The metal fabrication facility may comprise other loads that are not EAFs. The power supply system may provide a load power to one or more EAFs of the metal fabrication facility. The one or more EAFs may comprise electrodes. Particularly, each EAF may comprise one or more electrodes. The load power may be provided to the electrodes of the one or more EAFs. The load power may be distributed over the one or more EAFs, particularly over the electrodes of the one or more EAFs. The load power may correspond to the total power provided to the metal fabrication facility. The load power may correspond to the total power provided to the one or more EAFs, particularly correspond to the total power provided to the electrodes of the one or more EAFs. The power supply system may provide the load power to other loads of the metal fabrication facility that are not EAFs.

[0028] The power supply system includes a first converter. The first converter may be a load converter connected to an EAF. The first converter may be a power electronic converter. The first converter may be located on a primary side of a furnace transformer of an EAF, i.e. a MV side, or a secondary side of the furnace transformer of the EAF, i.e. a LV side.

[0029] The first converter comprises a first front end. The first front end may be a passive front end. The first front end may be an active front end. The active front end may be configured for compensating fluctuations in the load power. The active front end may be configured for improving a power quality performance. The active front end may act as a power quality unit as described herein. Particularly, the active front end may be a power quality unit.

[0030] The first converter comprises a first inverter and a first DC link. The first DC link is provided between the first front end and the first inverter. The first DC link is configured for receiving a DC current from the first front end. The first inverter may be a DC / AC inverter for converting the DC current received at the first DC link to an AC current that is provided to an EAF, particularly a load of the EAF. In other embodiments, instead of a DC / AC inverter, a DC / DC converter may be provided for converting the DC current received at the first DC link to a DC current that is provided to an EAF, particularly a load of the EAF.

[0031] The first inverter has a first determining unit. The first determining unit is configured for determining a first operating characteristic. The first determining unit may be configured for determining the first operating characteristic in real time. The first operating characteristic has information about a power quality of the load power. The first operating characteristic may have information about fluctuations in the load power. Particularly, the first operating characteristic may have information about fluctuations in a first load power provided to a first load. The first load power may be included in the load power and / or correspond to the load power. The first determining unit may be integral with the first inverter. The first determining unit may be a controller of the first inverter. The first determining unit may be configured for transmitting the first operating characteristic through the first feed forward data link to the first power quality unit. The first determining unit may be configured for determining the first reference signal based on the first operating characteristic. The first determining unit may be configured for transmitting the first reference signal through the first feed forward data link to the first power quality unit.

[0032] The first operating characteristic has information about a power quality of the load power. Particularly, about distortions in the power quality of the load power. The first operating characteristic may have information about fluctuations in the load power. The power quality may be defined by one or more power quality parameters, such as flicker, fluctuations in the reactive power and / or in the active power, power factor, and / or harmonics, particularly distortions in the power factor and / or the harmonics. The first operating characteristic may comprise information about one or more power quality parameters. The first operating characteristic may correspond to one or more power quality parameters. The first operating characteristic can be used to indicate what the load and the distortion is going to be in the next cycle. The first operating characteristic may be based on a load voltage, a load current, and / or a firing behavior of the first inverter, particularly a firing angle, a firing pattern, and / or a firing modulation. Particularly, the one or more power quality parameters may be based on the load voltage, the load current, and / or the firing behavior of the first inverter, particularly the firing angle, the firing pattern, and / or the firing modulation.

[0033] The first determining unit may determine the first operating characteristic in real time at the location of the first inverter. The location being the location of the first inverter in the electric network of the power supply system. At the time when the first determining unit detects the first operating characteristic, the fluctuations about which the first operating characteristic has information, may not yet have been detected by the first power quality unit. Particularly, the fluctuations may not have been received at the location of the first power quality unit in the electric network of the power supply system. The first operating characteristic and / or the first reference signal may be transmitted from the first determining unit to the first power quality unit controller through the first feed forward data link. The first reference signal may be received at the first power quality unit controller before the distortions in the power quality, upon which the first reference signal is based, are detected by the first power quality unit. The power supply system has the first feed forward data link. The first feed forward data link may connect the first determining unit to the first power quality unit for sending data from the first determining unit to the first power quality unit, particularly the first power quality unit controller. The first feed forward data link may be configured for sending any type of data. The first feed forward data link may be configured for sending the operating characteristics, particularly the first operating characteristic and / or reference signals, particularly the first reference signal. The first feed forward data link may send one or more operating characteristics and / or one or more reference signals at the same time. The first feed forward data link may include and / or be in communication with one or more further components. The first feed forward data link may be a single data link. The first feed forward data link may be composed of multiple data links forming the first feed forward data link. The first feed forward data link may have a first link speed. The first link speed describes a communication time for communicating data through the first feed forward data link. The first link speed may correspond to the communication time for communicating data, particularly an operating characteristic and / or a reference signal, from the first determining unit to the first power quality unit controller. The first link speed of the first feed forward data link may be less than a first switching period of the first switching semiconductors of the first power quality unit, particularly less than half the first switching period. The first power quality unit controller may receive the first reference signal within one first switching period after the first operating characteristic, upon which the said first reference signal is based, is determined.

[0034] The power supply system has a first power quality unit. The first power quality unit is configured for improving the power quality of the load power. Particularly, configured for compensating distortions in the power quality of the load power. The first power quality unit may be configured for compensating fluctuations in the load power quality. The first power quality unit may compensate fluctuations in the reactive load power and / or fluctuations in the active load power. Advantageously, the first power quality unit may be configured for compensating distortions in the power quality of the load power. Particularly, configured for compensating distortions in one or more power quality parameters, such as harmonics, active power, reactive power, voltage unbalance, and / or power factor. The first power quality unit may be configured for compensating distortions in the power quality of the load power by outputting a compensating power towards the external power source. The compensating power may be a reactive power, an active power, and / or a combination thereof. The compensating power can include opposite phase harmonics to compensate harmonics in the load power, particularly the first load power and / or the second load power. The first power quality unit may comprise first switching semiconductors, particularly first fast switching force commutated semiconductors. The first power quality unit may be based on a converter topology being based on switching semiconductors, particularly fast switching force commutated semiconductors. The first power quality unit may be operated, particularly for improving the power quality of the load power, by switching of the first switching semiconductors. The first switching semiconductors may have a first switching frequency and a first switching period. The first switching period may be the inverse of the first switching frequency. The first switching frequency may be more than 1 kHz and up to 100 kHz, particularly up to 1 MHz kHz. The first switching period may be the inverse of the switching frequency.

[0035] The first power quality unit has a first power quality unit controller. The first power quality unit controller may be integral with the first power quality unit. The first power quality unit controller may be configured for controlling an operation of the first power quality unit. The first power quality unit controller may be configured for improving the power quality of the load power. The first power quality unit controller is configured for receiving the first reference signal. The first power quality unit controller receives the first reference signal through the first feed forward data link. The first power quality unit controller is configured for controlling an operation of the first power quality unit based on the first reference signal. The first power quality unit controller may have a first control speed. The first control speed may correspond to a time between the receiving the first reference signal at the first power quality unit controller and the controlling of the first power quality unit based on said first reference signal. The first control speed may be less than the first switching period, particularly less than half the first switching period.

[0036] The first power quality unit controller may determine a first control signal based on the first reference signal. The first power quality unit controller may determine a first control signal based on the first operating characteristic. The first power quality unit controller may control the operation of the first power quality unit based on the first control signal. The first reference signal may be the first control signal. The first control signal may comprise a first reference set point and the adjusting the operation of the first power quality unit may comprises adjusting a set point of the first power quality unit according to the first reference set point.

[0037] The first power quality controller may be configured to receive data from slow measurements. The first power quality controller may be configured for controlling an operation of the first power quality unit further based on data from the slow measurements. The first power quality unit controller may determine the first control signal based on data from the slow measurements. For example, a LMF that may have a load that is uncontrolled and thus only based on slow measurements. The first power quality unit controller may be configured to deliberately overcompensate a MV bus to achieve a unity power factor at the PCC.

[0038] An effectiveness of the compensating the fluctuations in the load power by the first power quality unit is dependent on a delay time between detecting of a first operating characteristic and the controlling an operation of the first power quality unit based on a first reference signal being based on said first operating characteristic. The delay time substantially corresponds to the sum of the first link speed and the first control speed. The delay time may be less than the first switching period. The delay time may be less than 1000ms, particularly less than 100 ms, particularly less than 50 ms, particularly less than 20 ms, particularly less than 10 ms. The delay time may be between 0.01 ps and 100 ms, particularly between 0.1 ps and 20 ms, particularly between 1 ps and 10 ms, particularly between 1 ps and 1 ms. Beneficially, the first link speed and the first control speed may be such that the first power quality unit controller may control the operation of the first power quality unit based on the first reference signal within one first switching period following the determination of the first operating characteristic. That is, upon determining the first operating characteristic, the next switching, i.e. firing, of the first switching semiconductors of the first power quality unit is based on the first reference signal that is based on said determined first operating characteristic.

[0039] In general, any power quality mitigation equipment can be interfaced via a fast forward link. The power quality units may be any suitable type of power quality unit. In some embodiments, the first power quality unit is one of a STATCOM, the first front end being an active front end (AFE), and / or an energy storage system (ESS). Further, the power quality unit may be a grid forming BESS. The power quality unit, particularly the power quality unit being a STATCOM, an AFE, and / or an ESS, can be of any converter topology suitable to correct power quality parameters based on switching semiconductors, particularly fast switching force commutated semiconductors. The power quality unit, particularly being one of a STATCOM, an AFE, and / or an ESS, may be connected directly to the grid or may connected to the grid through a transformer.

[0040] The power quality units may be provided for compensating reactive power. For example, a STATCOM can be controlled to optimize the voltage waveform to be as close as possible to a sinewave, to adjust the phase angle between the voltage and current according to the needs for a power factor at the grid connecting point, to provide flicker control, and / or to provide harmonics control. The feed forward data link beneficially improves the performance of the STATCOM for each of the control modes.

[0041] The power quality units may further be provided for compensating active power. Especially for weaker grids, active power swings have a higher impact on the power quality of load power. Active power fluctuations can contribute to flicker in the load power. In addition, in island operated grids, connected power sources based on rotating machines may suffer from premature aging due to the active power swings. By introducing a power quality unit configured for compensation active power, for example, an ESS system, the effects can be damped or eliminated. Beneficially, having a power quality unit configured for compensating active power may reduce premature aging by suppressing active power swings. By being able to compensate active power, a grid frequency can be stabilized within the limits of the available active power. This may be especially beneficial for island operated grids, as load variations may typically lead to frequency distortions. In some embodiments a power quality unit, for example the first power quality unit, may be an ESS system or a STACOM having an energy storage. The STATCOM having the energy storage can compensate fractions of active power. The power quality units may be any suitable type of power quality mitigation equipment or combination of such, that act to compensate for active power fluctuations drawn by the furnace.

[0042] In some embodiments, that can be combined with further embodiments described herein, the power supply system includes a second converter having a second front end, a second DC link, and a second inverter having a second determining unit for determining a second operating characteristic having information about the power quality of the load power. Particularly, the second operating characteristic may have information about fluctuations in a second load power provided to a second load. The second load power may be included in the load power. The load power may be the sum of the first load power and the second load power. The power supply system may include a second feed forward data link. The power supply system may include a second power quality unit configured for improving the quality of the load power, the second power quality unit comprising a second power quality unit controller configured for receiving, through the second feed forward data link, a second reference signal, the second reference signal being based on the second operating characteristic, and configured for controlling an operation of the second power quality unit based on the second reference signal. The second determining unit may determine the second operating characteristic in real time.

[0043] The second converter, particularly the second front end, the second DC link, and the second inverter having the second determining unit, the second feed forward data link, and the second power quality unit, particularly the second power quality unit controller are generally similar to the first converter, particularly the first front end, the first DC link, and the first inverter having the first determining unit, the first feed forward data link, and the first power quality unit, particularly the first power quality unit controller. Particularly, the features described above with respect to the first converter, particularly the first front end, the first DC link, and the first inverter having the first determining unit, the first feed forward data link, and the first power quality unit, particularly the first power quality unit controller also apply for the second front end, the second DC link, and the second inverter having the second determining unit, the second feed forward data link, and the second power quality unit, particularly the second power quality unit controller.

[0044] The second converter may be connected to a same EAF as the first converter. The second converter may be connected to an EAF different to the EAF to which the first converter is connected. The second converter may be same converter as the first converter. The second converter may be a different converter as the first converter. The second converter may be a thyristor or a direct inverter, such as a multilevel matrix converter or a multilevel converter.

[0045] The second power quality unit controller may determine a second control signal based on the second reference signal. The second power quality unit controller may control the operation of the second power quality unit based on the second control signal. The second reference signal may be the second control signal. The second control signal may comprise a second reference set point and the adjusting the operation of the second power quality unit may comprise adjusting a set point of the second power quality unit according to the second reference set point.

[0046] The second power quality unit may be different to the first power quality unit. The first power quality unit may be provided to improve the power quality by improving one or more power quality parameters. The second power quality unit may be provided to improve the power quality by improving one or more power quality parameters not improved by the first power quality unit or the same ones. The second power quality unit may be one of a STATCOM, the second front end being an active front end, or a grid forming energy storage system. The second power quality unit may be a synchronous condenser.

[0047] The second feed forward data link may connect the second determining unit to the second power quality unit for sending data from the second determining unit to the second power quality unit, particularly the second power quality unit controller. The second feed forward data link may be configured for sending any type of data. The second feed forward data link may be configured for sending the second operating characteristic and / or the second reference signal. The second feed forward data link may include and / or be in communication with one or more further components. The second feed forward data link may have a second link speed. The second link speed may be equal to the first link speed. The second link speed may correspond to the communication time for communicating data from the second determining unit to the second power quality unit controller. The second link speed of the second feed forward data link may be less than a second switching period of second switching semiconductors of the second power quality unit, particularly less than half the second switching period. The second power quality unit controller may receive the second reference signal within one second switching period after the second operating characteristic, particularly within half a switching period, upon which the said second reference signal is based, is determined.

[0048] In some embodiments, that can be combined with other embodiments described herein, the power supply system includes a second converter having a second front end, a second DC link, and a second inverter having a second determining unit for determining a second operating characteristic having information about the power quality of the load power. The power supply system includes a third feed forward data link. The first power quality unit controller is configured for receiving, through the third feed forward data link, a third reference signal, the third reference signal being based on the second operating characteristic, and configured for controlling an operation of the first power quality unit based on the third reference signal. The second determining unit may determine the second operating characteristic in real time.

[0049] In some embodiments, the power supply system includes a second converter having a second determining unit for determining a second operating characteristic having information about the power quality of the load power. The power supply system includes a third feed forward data link. The first power quality unit controller is configured for receiving, through the third feed forward data link, a third reference signal, the third reference signal being based on the second operating characteristic, and configured for controlling an operation of the first power quality unit based on the third reference signal. The second determining unit may determine the second operating characteristic in real time. The second converter may be a thyristor or a direct inverter.

[0050] The third feed forward data link may connect the second determining unit to the first power quality unit for sending data from the second determining unit to the first power quality unit, particularly the first power quality unit controller. The third feed forward data link may be configured for sending any type of data. The third feed forward data link may be configured for sending the third operating characteristic and / or the third reference signal. The third feed forward data link may include and / or be in communication with one or more further components. The third feed forward data link may have a third link speed. The third link speed may be equal to the first link speed and / or the second link speed. The third link speed may correspond to the communication time for communicating data from the second determining unit to the first power quality unit controller. The third link speed of the third feed forward data link may be less than the first switching period of the first switching semiconductors of the first power quality unit, particularly less than half the first switching period. The first power quality unit controller may receive the third reference signal within one first switching period after the second operating characteristic, particularly within half a first switching period, upon which the said second reference signal is based, is determined.

[0051] The first power quality unit controller may be configured for controlling an operation of the first power quality unit based on the third reference signal. The first power quality unit controller is configured for controlling an operation of the first power quality unit based on the first reference signal and the third reference signal. The first power quality unit controller may determine a first control signal based on the first reference signal and the third reference signal. The first power quality unit controller may control an operation of the first power quality unit based on the first control signal.

[0052] In some embodiments, that can be combined with other embodiments described herein, the power supply system includes a fourth feed forward data link (FFi2), and a second power quality unit configured for improving the power quality of the load power, the second power quality unit including a second power quality unit controller configured for receiving, through the fourth feed forward data link, a fourth reference signal, the fourth reference signal being based on the first operating characteristic, and configured for controlling an operation of the second power quality unit based on the fourth reference signal.

[0053] The fourth feed forward data link may connect the first determining unit to the second power quality unit for sending data from the first determining unit to the second power quality unit, particularly the second power quality unit controller. The fourth feed forward data link may be configured for sending any type of data. The fourth feed forward data link may be configured for sending the fourth operating characteristic and / or the fourth reference signal. The fourth feed forward data link may include and / or be in communication with one or more further components. The fourth feed forward data link may have a fourth link speed. The fourth link speed may be equal to the first link speed, the second link speed and / or the third link speed. The fourth link speed may correspond to the communication time for communicating data from the first determining unit to the second power quality unit controller. The fourth link speed of the fourth feed forward data link may be less than the second switching period of the second switching semiconductors of the second power quality unit, particularly less than half the second switching period. The second power quality unit controller may receive the fourth reference signal within one second switching period after the first operating characteristic, particularly within half the second switching period, upon which the said fourth reference signal is based, is determined.

[0054] The second power quality unit controller may be configured for controlling an operation of the second power quality unit based on the fourth reference signal. The second power quality unit controller is configured for controlling an operation of the second power quality unit based on the second reference signal and the fourth reference signal. The second power quality unit controller may determine a second control signal based on the second reference signal and the fourth reference signal. The second power quality unit controller may control an operation of the second power quality unit based on the second control signal.

[0055] In some embodiments, that can be combined with further embodiments described herein, the power supply system includes a second feed forward data link. The second power quality unit controller is configured for receiving, through the second feed forward data link, a second reference signal, the second reference signal being based on the second operating characteristic, and configured for controlling an operation of the second power quality unit based on the second reference signal.

[0056] The power supply system may comprise one or more processing units for determining the reference signals. A first processing unit may be communicatively coupled to the first feed forward data link for receiving the first operating characteristic. The processing unit may determine the first reference signal based on the first operating characteristic and feed the first reference signal forward to the first power quality unit controller, particularly within the first link speed. Similarly, further processing units may be communicatively coupled to the second feed forward data link, the third feed forward data link, and / or the fourth feed forward data link. The same processing unit may be communicatively coupled to the first feed forward data link, the second feed forward data link, the third feed forward data link, and / or the fourth feed forward data link. The power supply system may comprise a single processing unit configured for determining the reference signals based on the corresponding operating characteristic. The processing unit may be communicatively coupled to each of the feed forward data links. In some embodiments, the power supply system comprises one or more processing units communicatively coupled to one or more of the feed forward data links for determining reference signals based on the corresponding operating characteristic.

[0057] While the above embodiments are described with two components of a same type, e.g. first converter and second converter, or first power quality unit and second power quality unit, it is understood that the above also applies in a similar manner to a plurality of components of the same type, e.g. a plurality of converters or a plurality of power quality units. The above description provided for two components of the same type applies accordingly to embodiments having a plurality of components of the same type. In some embodiments, that can be combined with other embodiments described herein, the power supply system includes a plurality of converters comprising the first converter, particularly comprising the second converter, each converter comprising a front end, a DC link, and an inverter having a determining unit for determining an operating characteristic; a plurality of feed forward data links comprising the first feed forward data link, particularly comprising the second feed forward data link, the third feed forward data link and / or the fourth feed forward data link; and a plurality of power quality units comprising the first power quality unit, particularly comprising the second power quality unit. Each of the power quality units has a power quality unit controller configured to receive a reference signal from one or more of the pluralities of feed forward data links, the reference signal being based on an operating characteristic, and configured for controlling an operation of the power quality unit based on the reference signal.

[0058] Preferably each of the power quality units is configured to receive, via the plurality of feed forward data links, one or more reference signals, the one or more reference signals being based on the operating characteristic of each of the plurality of converters. The metal fabrication facility may comprise several EAFs that can be operated at the same time and be connected in parallel to one point of common coupling (PCC). One or more power quality units, for example a STATCOM, may be used to compensate several furnaces. This can be achieved by providing several feed forward data links between the corresponding converters, particularly the determining units, associated with the several furnaces and the one or more power quality units, particularly the power quality unit controller. The converters and the power quality units may be operated in a master-follower configuration.

[0059] In some embodiments, which can be combined with other embodiments described herein, the first operating characteristic is based on at least one of a load voltage, a load current, and / or a firing behavior of the first inverter, particularly a firing angle, a firing pattern and / or a firing modulation. The second operating characteristic is based on at least one of a load voltage, a load current, and / or a firing behavior of the second inverter, particularly a firing angle, a firing pattern and / or a firing modulation.

[0060] In some embodiments, the first power quality unit controller is configured for modifying, based on the first reference signal, a set point of the first power quality unit.

[0061] The reference signals may be determined based on the operating characteristics, particularly based on the power quality parameter. The operating characteristic, particularly the power quality parameter may be based on the load voltage, the load current, or the firing behavior of the converter, particularly the firing angle, firing pattern, and / or firing modulation. The first reference signal may, for example, include instructions for a set point of the first power quality unit. The second reference signal may, for example, include instructions for a set point of the second power quality unit.

[0062] Depending on the chosen switching frequency of the converters and the power quality unit controllers, there can be a deadtime before one of the two components can react on changes in power quality of the load power. In addition, if only basing a control of the power quality units on measurements and controllers, like a PI controller, there is a significant delay in the reaction of the controllers. The present invention uses the operation characteristics including the expected load power that will be established by the next firing of the converters as input to the power quality unit controller. Beneficially, a significant amount of deadtime and delays can be eliminated. The power quality units adjust their output power based on the data reference signal received from the feed forward link without having to wait for measurements and / or, for example, PI controllers to adjust the operation of the power quality units. The power quality unit can produce the opposite of the expected distortion in the power quality such that the distortion in the power quality is cancelled out. For example, the power quality can produce the opposite of the expected reactive power fluctuations and / or harmonics distortion, so that the reactive power and harmonics provided by the power quality unit cancel out, in summation, the reactive power fluctuations and / or harmonics distortions. Particularly, such that the distortion of the power quality of the load power would be zero, or any other value needed to fulfill the power quality requirements.

[0063] In some embodiments, the first converter and / or the second converter is a medium voltage (MV) or a low voltage (LV) converter. Particularly, any converter of the power supply system, including the first converter and / or the second converter, may be a medium voltage (MV) or a low voltage (LV) converter.

[0064] Additionally, model predictive control based on the to be expected load can be applied. Further, artificial intelligence (Al) and analysis of data can be implanted to react correctly on specific patterns of events, e.g. patterns detected in past operating times of the power supply systems. For example, events can be classified and the power quality unit controller can control the first power quality unit based on experience for similar events. Further, grid parameters, such as fault levels, can be measured on a permanent base and the reaction of the converter can take this parameter into consideration to provide an optimal response.

[0065] According to another aspect, a method for operating a power supply system for a metal fabrication facility having at least one electric arc furnace (EAF) is provided. The power supply system is connectable to an external power source for providing, powered by the external power source, a load power to one or more EAFs of the at least one EAF. The method includes determining a first operating characteristic in real time, the first operating characteristic having information about fluctuations in the load power, determining a first reference signal based on the first operating characteristic, feeding forward the first reference signal to a first power quality unit controller of a first power quality unit, and controlling an operation of the first power quality unit based on the first reference signal.

[0066] The first operating characteristic may have information about a power quality of a first load power provided to a first load. The first load power may be included in the load power and / or correspond to the load power.

[0067] In an embodiment, the method includes determining a second operating characteristics in real time, the second operating characteristics having information about the power quality of the load power, determining a second reference signal based on the second operating characteristic, feeding forward the second reference signal to a second power quality unit controller of a second power quality unit, and controlling an operation of the second power quality unit based on the second reference signal to improve the power quality of the load power.

[0068] In an embodiment, the method includes determining a second operating characteristics in real time, the second operating characteristics having information about the power quality of the load power, determining a third reference signal based on the second operating characteristic, feeding forward the third reference signal to the first power quality unit controller, and controlling an operation of the first power quality unit based on the third reference signal to improve the power quality of the load power. Particularly, the second operating characteristic may have information about a power quality of a second load power provided to a second load. The load power may correspond to the sum of the first load power and the second load power.

[0069] In an embodiment, the method includes determining a fourth reference signal based on the first operating characteristic, feeding forward the fourth reference signal to a second power quality unit controller of a second power quality unit, and controlling an operation of the second power quality unit based on the fourth reference signal to improve the power quality of the load power.

[0070] In an embodiment, the method includes determining a second reference signal based on the second operating characteristic, feeding forward the second reference signal to the second power quality unit controller, and controlling an operation of the second power quality unit based on the second reference signal to improve the power quality of the load power.

[0071] In an embodiment, the method includes determining the first operating characteristic comprises determining a load voltage information, a load current information and / or a firing angle information of a first inverter and / or wherein the determining the second operating characteristic comprises determining a load voltage information, a load current information and / or a firing angle information of a second inverter.

[0072] The power quality unit includes switching semiconductors having a switching frequency and a switching period. The switching frequency may be more than 1 kHz and up to 100 kHz, particularly up to 1 MHz. The switching period may be the inverse of the switching frequency. The controlling an operation of the first power quality unit based on the first reference signal may be within one switching period of determining the first operating characteristic upon which said first reference signal is determined. The operation of the power quality unit may be adjusted according to the first control signal in less than 50 ps, particularly less than 20 ps, more particularly less than 10 ps, after determining the first operating characteristic upon which the first control signal is based. In an embodiment, the operation of the power quality unit is adjusted according to the first reference signal in less than 50 ps after determining the first operating characteristic upon which the first reference signal is based.

[0073] In an embodiment, the power supply is according to embodiments described herein. The first operating characteristic is determined by the first determining unit, the first reference signal is feed forward through the first feed forward data link, and the operation of the first power quality unit (140A) is controlled by the first power quality unit controller.

[0074] Those skilled in the art will recognise additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings.

[0075] Brief description of the drawings

[0076] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be by reference to embodiments. The accompanying drawings relate to embodiments of the disclosure and are described in the following:

[0077] Fig. 1A is a schematic illustration of a power supply system for a metal fabrication facility.

[0078] Fig. IB is a schematic illustration of a power supply system for a metal fabrication facility.

[0079] Fig. 1C is a schematic illustration of a power supply system for a metal fabrication facility.

[0080] Fig. 2 is a schematic illustration of a power supply system for a metal fabrication facility.

[0081] Fig. 3 is a schematic illustration of a power supply system for a metal fabrication facility.

[0082] Fig. 4 is a schematic illustration of a method for operating a power supply system for a metal fabrication facility.

[0083] Detailed description of the drawings

[0084] Reference will now be made in detail to the various embodiments, one or more examples of which are illustrated in each figure. Each example is provided by way of explanation and is not meant as a limitation. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with any other embodiment to yield yet a further embodiment. It is intended that the present disclosure includes such modifications and variations.

[0085] Within the following description of the drawings, the same reference numbers refer to the same or to similar components. Generally, only the differences with respect to the individual embodiments are described. Unless specified otherwise, the description of a part or aspect in one embodiment can apply to a corresponding part or aspect in another embodiment as well.

[0086] Fig. 1 A is a schematic illustration of a power supply system 100 for a metal fabrication facility according to embodiments described herein. The metal fabrication facility has a first electric arc furnace 160 A. The power supply system 100 is connectable to an external power source 150 for providing, powered by the external power source 150, a load power to the first electric arc furnace 160A. The power supply system comprises a power supply bus 105 connectable to the external power source 150. The power supply bus 105 may be connectable to the external power source through a source transformer 155. The external power source may be connected to a high voltage (HV) side of the source transformer. The power supply bus 105 may be connected to a medium voltage (MV) side of the source transformer. The first electric arc furnace 160 A may be connected to the power supply bus 105.

[0087] The power supply system 100 includes first converter 110A. The first converter 110A has a first front end 120 A, a first DC link 125 A, and a first inverter 130A having a first determining unit 135A. As shown in Fig. 1A, the first converter 110A is provided on a primary side, i.e. a MV side, of an arc furnace transformer 165 A of the EAF 160 A. In further embodiments, the first converter 110A may be provided on a secondary side, i.e. a low voltage (LV) side, of the arc furnace transformer 165 A, as exemplarily shown in Fig. IB. The first converter 110A may be connected to the power supply bus 105. The first front end 120A is shown as a passive front end in Fig. 1 A. In other embodiments, the first front end 120A may be an active front end. The first electric arc furnace 160 A may be connected to the power supply bus 105 through the first converter 110A and a first arc furnace transformer 165 A.

[0088] The power supply system 100 includes a first power quality unit 140 A being a STATCOM. In other embodiments, the first power quality unit 140 A may be a grid forming EES or a synchronous condenser. The first power quality unit 140 A includes a first power quality unit controller 145 A. The first power quality unit 140 A may be connected to the power supply bus 105. The fist power quality unit 140A may be connected indirectly to the power supply bus 105. For example, the first power quality unit 140 A may be connected through a first power quality unit transformer (not shown) to the power supply bus 105. The first power quality unit 140 A may be provided in parallel to the first converter 110A. The first power quality unit may be configured to compensate fluctuations in the load power. The first power quality unit may provide reactive power, active power, and / or a combination thereof to the power supply bus 105. Particularly, a positive or negative reactive power, a positive or negative active power, and / or a combination thereof. The power provided by the first power quality can include opposite phase harmonics to compensate harmonics in the load power, particularly the first load power and / or the second load power.

[0089] The power supply system 100 includes a first feed forward data link FFn. The first feed forward data link FFn may connect the first determining unit 135 A to the first power quality unit controller 145 A for sending data from the first determining unit 135 A to the first power quality unit controller 145 A. The first power quality unit controller may receive the first reference signal through the first feed forward data link FFn.

[0090] Fig. 1C is a schematic illustration of a power supply system according to embodiments described herein. The power supply system according to Fig. IB is similar to the power supply system in Fig. 1 A. Instead of the first power quality system 145A being a STATCOM as in Fig. 1A, the first power quality system 145A in Fig. 1C is the first front end of the first converter 110A being an active front end.

[0091] The power supply system 100 of any one of Figs. 1 A, IB and 1C may include a processing unit 170. The processing unit 170 may be communicatively coupled to the first feed forward data link FFn. The processing unit 170 may receive the first operating characteristic from the first feed forward data link FFn and determine the first reference signal. The processing unit 170 may feed the first reference signal forward to the first power quality unit controller 145 A.

[0092] Fig. 2 is a schematic illustration of a further power supply system 100 according to embodiments described herein. The first converter 110A has an active front end being the first power quality unit 140A. The first converter 110A is provided on a primary side, i.e. a MV side, of a first arc furnace transformer 165 A. The power supply system 100 includes a second converter HOB having a second front end 120B, a second DC link 125B, and a second inverter I 30B having a second determining unit 135B. The second converter HOB is provided on a secondary side, i.e. a LV side, of a second arc furnace transformer 165B. The second front end is a passive front end. A second EAF 160B is connected to the power supply bus 105 through the second converter 110B and the second arc furnace transformer 165B. The power supply system 100 includes a second power quality unit 140B having a second power quality unit controller. The second power quality unit 140B is a STATCOM. In other embodiments, the second power quality unit 140B may be a grid forming EES or a synchronous condenser. The second power quality unit 140B may be directly connected to the power supply bus 105. The second power quality unit 140B may be connected indirectly to the power supply bus 105. For example, the second power quality unit 140B may be connected through a second power quality unit transformer 147B to the power supply bus 105. The second power quality unit 140B may be provided in parallel to the first converter and / or the second converter.

[0093] The power supply system 100 includes a first feed forward data link FFn. The first feed forward data link FFn may connect the first determining unit 135 A to the first power quality unit controller 145 A for sending data from the first determining unit 135 A to the first power quality unit controller 145 A. The first power quality unit controller may receive the first reference signal through the first feed forward data link FFn.

[0094] The power supply system 100 includes a second feed forward data link FF22- The second feed forward data link FF22 may connect the second determining unit 135B to the second power quality unit controller 145B for sending data from the second determining unit 135B to the second power quality unit controller 145B. The second power quality unit controller may receive the second reference signal through the second feed forward data link FF22.

[0095] The power supply system 100 includes a third feed forward data link FF2I. The third feed forward data link FF2I may connect the second determining unit 135B to the first power quality unit controller 145 A for sending data from the second determining unit 135B to the first power quality unit controller 145 A. The first power quality unit controller may receive the third reference signal through the third feed forward data link FF2I.

[0096] The power supply system 100 includes a fourth feed forward data link FFi2. The fourth feed forward data link FFi2may connect the first determining unit 135 A to the second power quality unit controller 145B for sending data from the first determining unit 135 A to the second power quality unit controller 145B. The second power quality unit controller may receive the fourth reference signal through the fourth feed forward data link FFi2.

[0097] The processing unit 170 can receive one or more operating characteristics from the feed forward data links to determine one or more reference signals. The one or more reference signals may be provided to the power quality units through the corresponding feed forward data links. For example, the processing unit may receive the second operating characteristic, the third operating characteristic, and the fourth operating characteristic. The processing unit may determine the second reference signal, the third reference signal, and the fourth reference signal. The processing unit 170 may feed the second reference signal to second power quality unit 140B through the second feed forward data link FF22. The processing unit 170 may feed the third reference signal to the first power quality unit 140 A through the third feed forward data link FF21. The processing unit 170 may feed the fourth reference signal to the second power quality unit 140B through the fourth feed forward data link FF12.

[0098] Fig. 3 is a schematic illustration of a power supply system 100 according to embodiments described herein. The power supply system has a plurality of converters (110A, HOB, HON) including the first converter (110A) and the second converter (110B). Each converter (110 A, HOB, HON) has a front end (120A, 120B, 120N), a DC link (125A, 125B, 125N), and an inverter (130A, 130B, 130N) having a determining unit (135A, 135B, 135N) for determining an operating characteristic.

[0099] The power supply system 100 includes a plurality of feed forward data links (FFibFFi2, FFiM, FF2bFF22, FF2M, FFNi, FFN2, FFNM) including the first feed forward data link (FFn), particularly including the second feed forward data link (FF22), the third feed forward data link (FF2I), and / or the fourth feed forward data link (FFn).

[0100] The power supply system includes a plurality of power quality units (140A, 140B, 140M) including the first power quality unit (140 A), particularly including the second power quality unit (140B). Each of the power quality units (140A, 140B, 140M) has a power quality unit controller (145 A, 145B, 145M) configured to receive a reference signal from one or more of the pluralities of feed forward data links (FFn, FFi2, FFiM, FF2bFF22, FF2M, FFNbFFN2, FFNM). Each converter of the plurality of converters (110A, 110B, 11 ON) may be connected to each power quality unit of the plurality of power quality units (140 A, MOB, MOM), by a respective feed forward data link of the plurality of feed forward data links (FFn, FFn, FFiM, FF2bFF22, FF2M, FFN1, FFN2, FFNM)

[0101] Fig. 4 is a schematic illustration of a method 400 for operating a power supply system for a metal fabrication facility having at least one electric arc furnace. The power supply system is connectable to an external power source for providing, powered by the external power source, a load power to one or more EAFs of the least one EAF. The power supply system may be according to embodiments described herein. At step 410 a first operating characteristic is determined in real time. The first operating characteristic has information about a power quality of the load power. Particularly, the first operating characteristic may have information about fluctuations in the load power.

[0102] At step 420 a first reference signal is determined based on the first operating characteristic. At step 430 the first reference signal is fed forward to a first power quality unit controller of a first power quality unit.

[0103] At step 440 an operation of the first power quality unit is controlled based on the first reference signal to improve the power quality of the load power.

[0104] While the foregoing is directed to embodiments, other and further embodiments may be devised without departing from the basic scope, and the scope is determined by the claims that follow.

Claims

Claims1. A power supply system (100) for a metal fabrication facility having at least one electric arc furnace (160A, 160B), EAF, the power supply system (100) connectable to an external power source (150) for providing, powered by the external power source, a load power to one or more EAFs of the at least one EAF (160A, 160B), the power supply system comprising: a first converter (110A) having a first front end (120A), a first DC link (125A), and a first inverter (130A) having a first determining unit (135 A) configured for determining a first operating characteristic having information about a power quality of the load power; a first feed forward data link (FFn); and a first power quality unit (140 A) configured for improving the power quality of the load power, the first power quality unit (140A) comprising a first power quality unit controller (145 A) configured for receiving, through the first feed forward data link (FFn), a first reference signal, the first reference signal being based on the first operating characteristic, and configured for controlling an operation of the first power quality unit (140 A) based on the first reference signal.

2. The power supply system of claim 1, wherein the first power quality unit (140A) is one of a STATCOM, the first front end (110A) being an active front end, or an energy storage system.

3. The power supply system of any one of claims 1 through 2, comprising: a second converter (HOB) having a second front end (120B), a second DC link (125B), and a second inverter (130B) having a second determining unit (135B) for determining a second operating characteristic having information about the power quality of the load power; a second feed forward data link (FF22); anda second power quality unit (140B) configured for improving the power quality of the load power, the second power quality unit (140A) comprising a second power quality unit controller (145B) configured for receiving, through the second feed forward data link (FF22), a second reference signal, the second reference signal being based on the second operating characteristic, and configured for controlling an operation of the second power quality unit (140B) based on the second reference signal.

4. The power supply system of any one of claims 1 through 2, comprising: a second converter (HOB) having a second front end (120B), a second DC link (125B), and a second inverter (130B) having a second determining unit (135B) for determining a second operating characteristic having information about the power quality of the load power; and a third feed forward data link (FF2I); wherein the first power quality unit controller (145A) is configured for receiving, through the third feed forward data link (FF2I), a third reference signal, the third reference signal being based on the second operating characteristic, and configured for controlling an operation of the first power quality unit based on the third reference signal.

5. The power supply system of any one of claims 1 through 2 and 4, comprising: a fourth feed forward data link (FFi2); and a second power quality unit (140B) configured for improving the power quality of the load power, the second power quality unit (140A) comprising a second power quality unit controller (145B) configured for receiving, through the fourth feed forward data link (FFi2), a fourth reference signal, the fourth reference signal being based on the first operating characteristic, and configured for controlling an operation of the second power quality unit based on the fourth reference signal.

6. The power supply system of claim 5 being dependent on claim 4, comprising a second feed forward data link (FF22), wherein the second power quality unit controller (145B) is configured for receiving, through the second feed forward data link (FF22), a second reference signal, the second reference signal being based on the second operating characteristic, and configured for controlling an operation of the second power quality unit based on the second reference signal.

7. The power supply system of any one of claims 1 through 6, comprising one or more processing units (170) communicatively coupled to one or more of the feed forward data links (FFn, FFn, FF2bFF22) for determining reference signals based on the corresponding operating characteristic.

8. The power supply system of any one of claims 1 through 7, comprising: a plurality of converters comprising the first converter, particularly comprising the second converter, each converter comprising a front end, a DC link, and an inverter having a determining unit for determining an operating characteristic; a plurality of feed forward data links comprising the first feed forward data link, particularly comprising the second feed forward data link, the third feed forward data link, and / or the fourth feed forward data link; and a plurality of power quality units comprising the first power quality unit, particularly comprising the second power quality unit, wherein each of the power quality units has a power quality unit controller configured to receive a reference signal from one or more of the pluralities of feed forward data links, the reference signal being based on an operating characteristic, and configured for controlling an operation of the power quality unit based on the reference signal.

9. The power supply system of any one of claims 1 through 8, wherein the first operating characteristic is based on at least one of a load voltage, a load current, and a firing behavior of the first inverter (130A) and / or wherein the second operating characteristic is based on at least one of a load voltage, a load current, and a firing behavior of the second inverter (130B).

10. The power supply system of any one of claims 1 through 8, wherein the first power quality unit controller is configured for modifying, based on the first reference signal, a set point of the first power quality unit.

11. The power supply system of any one of claims 1 through 10, wherein the first converter and / or the second converter is a medium voltage (MV) or a low voltage (LV) converter.

12. A method for operating a power supply system (100) for a metal fabrication facility (160 A, 160B) having at least one electric arc furnace, EAF, the power supply system connectable to an external power source (150) for providing, powered by the external power source (150), a load power to one or more EAFs of the at least one EAF (160A, 160B), the method comprising: determining a first operating characteristic in real time, the first operating characteristic having information about a power quality of the load power; determining a first reference signal based on the first operating characteristic; feeding forward the first reference signal to a first power quality unit controller of a first power quality unit; and controlling an operation of the first power quality unit based on the first reference signal to improve the power quality of the load power.

13. The method of claim 12, comprising: determining a second operating characteristics in real time, the second operating characteristics having information about the power quality of the load power; determining a second reference signal based on the second operating characteristic; feeding forward the second reference signal to a second power quality unit controller of a second power quality unit; and controlling an operation of the second power quality unit based on the second reference signal to improve the power quality of the load power.

14. The method of claim 12, comprising: determining a second operating characteristics in real time, the second operating characteristics having information about the power quality of the load power; determining a third reference signal based on the second operating characteristic; feeding forward the third reference signal to the first power quality unit controller; and controlling an operation of the first power quality unit based on the third reference signal to improve the power quality of the load power.

15. The method of any one of claim 12 and 14, comprising: determining a fourth reference signal based on the first operating characteristic; feeding forward the fourth reference signal to a second power quality unit controller of a second power quality unit; andcontrolling an operation of the second power quality unit based on the fourth reference signal to improve the power quality of the load power.

16. The method of any one of claims 14 and 15, comprising: determining a second reference signal based on the second operating characteristic; feeding forward the second reference signal to the second power quality unit controller; and controlling an operation of the second power quality unit based on the second reference signal to improve the power quality of the load power.

17. The method of any one of claims 12 through 16, wherein the determining the first operating characteristic comprises determining a load voltage, a load current, and a firing behavior of the first inverter and / or wherein the determining the second operating characteristic comprises determining a load voltage, a load current and / or a firing behavior of a second inverter.

18. The method of any one of claims 12 through 17, wherein the operation of the power quality unit (130) is adjusted according to the first reference signal in less than 50 ps after determining the first operating characteristic upon which the first reference signal is based.

19. The method of any one of claims 12 through 19, wherein the power supply system is according to any one of claims 1 through 11, particularly wherein: the first operating characteristic is determined by the first determining unit (135A); the first reference signal is feed forward through the first feed forward data link (FFn); andthe operation of the first power quality unit (140A) is controlled by the first power quality unit controller (145A).

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