Apparatus and method for supplying power to or absorbing power from load

Abstract

There is provided an apparatus configured to supply power to or absorb power from a load (1) connected to a power system (2), the load being connected or connectable to a load conductor (3). The apparatus comprises: a power supply and / or absorption device (6) configured for selectively supplying power to or absorbing power from the load conductor (3); and a control unit (7) configured to control the power supply and / or absorption device (7). The control unit (7) is configured to determine a voltage reference value of the power supply and / or absorption device (6) based on at least one value indicative of a voltage of the load conductor (3) and a virtual impedance of the power supply and / or absorption device (6), and controlling the power supply and / or absorption device (6) to supply power to the load conductor (3) so as to supply power to the load (1) or to absorb power from the load conductor (3) so as to absorb power from the load (1) on the basis of the determined voltage reference value.

Description

Technical Field

[0001] The present invention relates to an apparatus configured to supply power to a load connected to a power system or absorb power from the load. Background Art

[0002] Power systems, e.g., power transmission and / or distribution systems and / or power grids, can be used to supply power to equipment in many industries. In this case, the power system can be referred to as a feed grid or system, and the equipment can be referred to as a load. At least in some industries, flicker in the voltage of the power system (i.e., rapid fluctuations in the voltage of the power system) and harmonic frequencies in the voltage of the power system generated by the load can be a problem. For example, in many electric arc furnace (EAF) steelmaking facilities, flicker in the voltage of the feed grid and the generation of harmonic frequencies or "harmonics" are a problem for the feed grid. Flicker can be reduced by measuring the EAF current and compensating for the harmonic frequencies and negative sequence currents in the voltage of the feed grid using devices such as static synchronous compensators (STATCOMs). In order to further improve the compensation for harmonic frequencies in the voltage of the feed grid, emphasis can be placed on compensating for low-order harmonics primarily generated by the EAF. Summary of the invention

[0003] Devices such as static synchronous compensators (STATCOMs) can be used to provide or absorb reactive power, thereby regulating the voltage at the connection point with a power system or a feeder grid. For example, for a STATCOM used in an electric arc furnace (EAF) application, two control methods can be run simultaneously. One control method can be so-called flicker control, which can work as an open-loop control and can offset any rapid changes in the load (e.g., EAF) current. Flicker control can compensate for reactive power, negative sequence current of the load, and some low-order harmonics that may be present in the voltage of the power system or feeder grid. Another control method can be power factor control, which can work as a closed-loop control and can compensate for the power factor of the connected power system or feeder grid. Power factor control can be based on sensing (or measuring) or calculating current of the power system or supply grid, which can give active power and reactive power at the connection point with the power system or feeder grid.

[0004] The flicker control algorithm may be intended to correct the negative sequence current of the load, which may produce flicker in the load current. However, harmonic compensation for low-order harmonics (e.g., harmonics below the 5th order) may be very limited. In order to improve low-order harmonic compensation, other control algorithms can be used. However, these other control algorithms may require that the device used to provide or absorb reactive power and thereby adjust the voltage at the connection point with the power system or the feeding grid (e.g., a device based on a STATCOM or a voltage source converter (VSC)) is relatively large, because a relatively large number of converter units may be required so that such a control algorithm can compensate for low-order harmonics. Examples of such other control algorithms are provided in WO 98 / 27476A1. However, increasing the size of the device by increasing the number of converter units typically increases the cost of the device, thereby also increasing the cost of the entire system.

[0005] In view of the above, one problem of the present invention is to provide means for compensating for any low-order harmonics produced by a load in the voltage of a grid or power system supplying the load (such as an EAF), while reducing or even avoiding the need to increase the size of the equipment for providing or absorbing reactive power and thereby regulating the voltage at the point of connection to the power system or supply grid.

[0006] In order to solve at least one of this and other problems, an apparatus and a method according to the independent claims are provided. Preferred embodiments are defined by the dependent claims.

[0007] According to a first aspect of the present invention, a device is provided. The device is configured to supply power to a load connected to a power system or absorb power from the load. The load is connected or can be connected to a load conductor. The power system can be connected or can be connected to the load conductor. The device includes a power supply and / or absorption device. The power supply and / or absorption device is connected to the load conductor. The power supply and / or absorption device is configured to selectively supply power to the load conductor or absorb power from the load conductor. The power supplied to the load conductor by the power supply and / or absorption device or the power absorbed from the load conductor is managed at least by a voltage reference value of the power supply and / or absorption device. The device includes a control unit, which is configured to control the power supply and / or absorption device, for example, to control the operation of the power supply and / or absorption device. The control unit is configured to obtain at least one value indicating the voltage of the load conductor. The control unit is configured to determine the voltage reference value of the power supply and / or absorption device based on at least one value indicating the voltage of the load conductor and the virtual impedance of the power supply and / or absorption device. The control unit is configured to control the power supply and / or absorption device to supply power to the load conductor so as to supply power to the load, or to absorb power from the load conductor so as to absorb power from the load, based on the determined voltage reference value. The virtual impedance of the power supply and / or absorption device is associated with the virtual reactance and the virtual resistance. The power supply and / or absorption device is configured so that the value of the virtual reactance is higher than the value of the reactance of the power supply and / or absorption device, and the value of the virtual resistance is smaller than the value of the virtual reactance.

[0008] According to a second aspect of the present invention, there is provided a method implemented in a device configured to supply power to a load connected to a power system or absorb power from the load. The load is connected or can be connected to a load conductor. The power system can be connected or can be connected to the load conductor. The device includes a power supply and / or absorption device. The power supply and / or absorption device is connected to the load conductor. The power supply and / or absorption device is configured to selectively supply power to the load conductor or absorb power from the load conductor. The power supplied to the load conductor by the power supply and / or absorption device or the power absorbed from the load conductor is managed by at least a voltage reference value of the power supply and / or absorption device. The method includes obtaining at least one value indicating the voltage of the load conductor. The method includes determining the voltage reference value of the power supply and / or absorption device based on at least one value indicating the voltage of the load conductor and the virtual impedance of the power supply and / or absorption device. The method includes controlling the power supply and / or absorption device to supply power to the load conductor so as to supply power to the load or to absorb power from the load conductor so as to absorb power from the load based on the determined voltage reference value. The virtual impedance of the power supply and / or absorption device is associated with a virtual reactance and a virtual resistance, wherein the power supply and / or absorption device is configured so that the value of the virtual reactance is higher than the value of the reactance of the power supply and / or absorption device, and so that the value of the virtual resistance is smaller than the value of the virtual reactance.

[0009] According to one or more embodiments of the present invention, a power supply and / or absorption device that can be directly connected to a load conductor can be considered to use a grid formation control to appear as a voltage source behind a virtual impedance. The virtual impedance of the power supply and / or absorption device can be used as described above to control the power supply and / or absorption device to supply power to the load conductor to supply power to the load, or to absorb power from the load conductor to absorb power from the load. This is done to compensate for any disturbance or voltage change in the voltage of the power system or the load conductor connected to the load, and to reduce or avoid any harmonics in the voltage of the power system that can be generated by the load, for example, low-order harmonics (such as harmonics below the 5th order). When the power supply and / or absorption device acts as a certain impedance on the load conductor, any change in the voltage of the load conductor may also cause the power supply and / or absorption device to provide a corresponding current. Therefore, this way of controlling the power supply and / or absorption device can remove some voltage changes in the voltage of the load conductor, thereby suppressing the voltage change of the voltage of the load conductor and any harmonics in the voltage of the power system that can be generated by the load.

[0010] Loads such as EAFs may generate not only characteristic harmonics, but also (e.g., primarily) relatively low frequency interharmonics. Interharmonics are of concern in many applications. By controlling power supply and / or absorption devices based on virtual impedance as described herein, characteristic harmonics and interharmonics may be suppressed.

[0011] By using the virtual impedance-based control of power supply and / or absorption equipment as described herein to reduce or avoid any harmonics in the voltage of the power system that may be generated by the load, the need to increase the size of the power supply and / or absorption equipment to achieve the capacity needed or required to compensate for the harmonics can be reduced or even avoided, so that the cost of the power supply and / or absorption equipment - and the cost of the entire system - can be kept relatively low.

[0012] As described herein, controlling power supply and / or sink devices based on virtual impedance may have a much lower response time than "conventional" voltage control (i.e., controlling the voltage of a power system by measuring the voltage and regulating the voltage of the power system to a certain voltage set point using a control loop mechanism that employs a controller that is a proportional-integral (PI) controller based on the measured voltage). By controlling power supply and / or sink devices based on virtual impedance as described herein, the power supply and / or sink devices may be treated as synchronous motors and provide rigidity to the power system. The greater the rigidity of the power system, the less impact any change in load will have on the voltage of the power system.

[0013] By controlling power sourcing and / or sinking devices based on virtual impedance as described herein, all phases may be controlled independently of each other.

[0014] The virtual reactance may be, for example, the sum of a selected percentage of the reactance of the power supply and / or absorption device and the reactance of the power supply and / or absorption device. The selected percentage of the reactance of the power supply and / or absorption device may be referred to as a margin, and may be, for example, in the range of 1% to 50% of the reactance of the power supply and / or absorption device.

[0015] In general, it may be desirable that the virtual reactance is as small as possible. For example, the virtual reactance may be such that, by means of the determined voltage reference value of the power supply and / or absorption device, the power supply and / or absorption device is able to supply power to and / or absorb power from the load conductor so as to keep the fluctuation of the voltage of the load conductor over a period of time compared to the average voltage level of the voltage of the load conductor below a selected threshold voltage fluctuation level while keeping the virtual reactance as small as possible. Preferably, the selected percentage of the reactance of the power supply and / or absorption device may be, for example, in the range between 1% and 20% of the reactance of the power supply and / or absorption device, more preferably between 1% and 10%.

[0016] The virtual resistor may, for example, be such that the value of the virtual resistor is between 25% and 75%, preferably between 35% and 65%, more preferably between 45% and 55%, such as 50% or about 50%, of the value of the virtual reactance. The virtual resistor may control the extent and speed of transient attenuation following a disturbance in the power system. The virtual resistor may provide attenuation for approaching or reaching steady-state conditions following a disturbance in the power system. The selection of the value of the virtual resistor may depend on the characteristics of the load and may also depend on any one or more reactive power compensation devices other than the power supply and / or absorption devices, such as harmonic filters, which may be included in the apparatus. Loads with less attenuation may require a higher virtual resistor.

[0017] As previously described, the load may include, for example, an EAF (or EAF facility). However, the load is not limited thereto and may, in lieu of or in addition to the EAF (facility), include another or other type of load that may tend to generate low-order harmonics (e.g., below the 5th order harmonic) in the voltage of the power system or grid that supplies power to the load. For example, the load may include a cycloconverter or some type of relatively large motor.

[0018] There may be multiple loads connected to the power system. Each load may be connected or connectable to a load conductor.

[0019] The load conductors may include, for example, busbars or busbars. The power system may include, for example, a power transmission and / or distribution system. The power system may include, for example, a power grid, such as a transmission and / or distribution grid.

[0020] The voltage reference value may be determined by multiplying the sensed voltage of the load conductor by the virtual impedance. Controlling the power supply and / or sink device to supply power to or sink power from the load conductor based on the determined voltage reference value may include adjusting or controlling the voltage output by the power supply and / or sink device so that the output voltage meets or nearly meets the voltage reference value, for example, by comparing the voltage of the load conductor with the voltage reference value.

[0021] The virtual impedance of a power supplying and / or absorbing device is associated with a virtual reactance and a virtual resistance, for example, as components of the virtual impedance.

[0022] The power supplying and / or sinking device may be configured to have a selected or predefined virtual impedance such that the value of the virtual reactance is higher than the value of the reactance of the power supplying and / or sinking device and the value of the virtual resistance is lower than the value of the virtual impedance.

[0023] The reactance of the power supply and / or absorption device may consist of its "physical" reactance. In other words, the reactance of the power supply and / or absorption device may be the reactance of the power supply and / or absorption device caused by the reactance of individual elements or components of the power supply and / or absorption device.

[0024] As described above, the control unit is configured to obtain at least one value indicative of the voltage of the load conductor. The at least one value indicative of the voltage of the load conductor may for example be or have been measured or sensed by at least one sensor (e.g. at least one voltage transformer). The control unit may be connected to the at least one sensor to obtain the voltage of the load conductor (indicative of at least one value of the voltage). Such at least one sensor may be part of the device, and thus the device may include such at least one sensor.

[0025] In addition to controlling the power supply and / or absorption device based on virtual impedance as described herein, a flicker control algorithm or method can also be implemented in, for example, a control unit. To this end, the control unit can be configured to obtain multiple values ​​indicating the current of the load at different times within a period of time, and determine the current change of the load within the period of time based on the multiple values ​​indicating the current of the load at different times. The multiple values ​​indicating the current of the load at different times within a period of time can be, for example, or have been measured or sensed by at least one sensor (such as, at least one current transformer). The control unit can be connected to at least one sensor to obtain (indicate) multiple values ​​of the current of the load at different times. Such at least one sensor can be part of the device, so the device can include such at least one sensor. The control unit can be configured to further determine the voltage reference value of the power supply and / or absorption device based on the determined change of the current of the load within a period of time. The control unit can be configured to determine the voltage reference value of the power supply and / or absorption device based on the multiple values ​​indicating the current of the load at different times to reduce any fluctuation of the current of the load over a period of time compared to the average current level of the current of the load. With this configuration, the power supply and / or absorption device can offset any rapid changes in the load current (as mentioned above, this can be called flicker). This may be done in addition to attenuating any voltage variations in the voltage of the load conductors and any harmonics in the voltage of the power system that may be generated by the load by controlling the power supply and / or absorption devices based on the virtual impedance as described herein.

[0026] In some situations or applications, it may be difficult or even impossible to obtain (indicate) the value of the current of the load. For example, for some reasons, it may be difficult or even impossible to sense or measure the current of the load. In addition, as described above, there may be several loads connected to the power system, each of which may be connected or connectable to a load conductor. However, for some reasons, it may be difficult or even impossible to sense or measure the current of one or more loads. For example, it may be possible to sense or measure only the current of one of the loads, while the current of the other loads cannot be sensed. In this case, it may be difficult or even impossible to establish the load current for the flicker control algorithm or method. However, in this case, the virtual impedance-based control of the power supply and / or absorption device described herein can still be used.

[0027] In addition, the use of virtual impedance based control of power supply and / or absorption devices as described herein can facilitate or allow for the relaxation of requirements for any current sensing devices, for example, these devices can be installed in a feeder connecting a load (e.g., an EAF) to another or other component (such as a substation) and can be configured to sense the current of the load. Such current sensing devices can, for example, include current transformers, which may saturate when a load such as an EAF produces DC current. However, in this case, the virtual impedance based control of power supply and / or absorption devices as described herein can still be used.

[0028] In addition to controlling the power supply and / or sink device based on virtual impedance as described herein (and possibly flicker control as shown herein), a power factor control algorithm or method may also be implemented in, for example, a control unit. To this end, the control unit may be configured to obtain at least one value indicative of a current of the power system, and further determine a voltage reference value of the power supply and / or sink device based on at least one value indicative of the current of the power system. The control unit may be configured to determine the voltage reference value of the power supply and / or sink device based on at least one value indicative of the current of the power system and at least one value indicative of a voltage of a load conductor to increase the power factor of the load.

[0029] The current of the power system (at least one value indicative of the current) may be determined directly, for example by measuring or sensing the voltage of the power system (for example, using a sensor connected to the power system), or indirectly. For example, the current of the power system (at least one value indicative of the current) may be determined indirectly based on measuring or sensing the current of the power supply and / or sink device and the current of the load, for example, using one or more current transformers connected to the power supply and / or sink device and / or the load. The control unit may be connected to such one or more current transformers to obtain at least one value indicative of the current of the power system.

[0030] The power supply and / or absorption device may be based on a multi-level converter, a device based on a voltage source converter (VSC), and / or a static synchronous compensator (STATCOM), for example. A STATCOM may have a delta topology. However, a STATCOM is not limited thereto and may alternatively have, for example, a wye topology. A multi-level converter may include, for example, a three-level converter.

[0031] As previously described, the power supply and / or sink device may be directly connected to the load conductor. However, in another or other example implementation, the power supply and / or sink device may be indirectly connected to the load conductor (ie, through one or more intermediate components).

[0032] According to a third aspect of the present invention, there is provided a computer program comprising instructions which, when executed by one or more processors included in a control unit, cause the control unit to perform the method according to the second aspect of the present invention.

[0033] According to a fourth aspect of the present invention, there is provided a processor-readable medium having a computer program loaded thereon, wherein the computer program comprises instructions which, when executed by one or more processors included in or constituting a control unit, cause the control unit to perform the method according to the second aspect of the present invention.

[0034] According to a fifth aspect of the present invention, a system is provided. The system comprises a power system, a load connected to the power system, and a load conductor. The load is connected or connectable to the load conductor. The system comprises an apparatus according to the first aspect of the present invention, the apparatus being configured to supply power to the load or absorb power from the load.

[0035] The control unit may, for example, include any suitable central processing unit (CPU), microcontroller, digital signal processor (DSP), application specific integrated circuit (ASIC), field programmable gate array (FPGA), etc., or any combination thereof, or be composed of any combination thereof. The control unit may optionally be capable of executing software instructions stored in a computer program product (e.g., in the form of a memory). The memory may, for example, be any combination of a read-write memory (RAM) and a read-only memory (ROM). The memory may include a persistent storage device, such as a magnetic memory, an optical memory, a solid-state memory, or a remotely mounted memory, or any combination thereof.

[0036] Each or any one of the one or more processors may include, for example, a CPU, a microcontroller, a DSP, an ASIC, an FPGA, etc., or any combination thereof.

[0037] The processor-readable medium may, for example, include a digital versatile disk (DVD) or a floppy disk or any other suitable type of processor-readable device or processor-readable (digital) medium, such as but not limited to a memory, e.g., a non-volatile memory, a hard drive, a compact disk (CD), a flash memory, a magnetic tape, a universal serial bus (USB) storage device, a Zip drive, etc.

[0038] Other objects and advantages of the present invention are described below by exemplary embodiments. It should be noted that the present invention relates to all possible combinations of features described in the claims. Other features and advantages of the present invention will become apparent when studying the attached claims and the description herein. Those skilled in the art recognize that different features of the present invention can be combined to create embodiments other than those described herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Exemplary embodiments of the present invention will be described below with reference to the accompanying drawings.

[0040] Figure 1 is a schematic diagram of a system according to an embodiment of the present invention.

[0041] Figure 2 is a schematic flow chart of a method according to an embodiment of the present invention.

[0042] All the figures are schematic and not necessarily to scale and generally show only parts which are necessary in order to elucidate embodiments of the invention, wherein other parts may be omitted or merely suggested. DETAILED DESCRIPTION

[0043] The present invention will now be described below with reference to the accompanying drawings, in which exemplary embodiments of the present invention are shown. However, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments of the present invention described herein; rather, these embodiments are provided by way of example, so that this disclosure will convey the scope of the present invention to those skilled in the art.

[0044] Figure 1 is a schematic diagram of a system according to an embodiment of the present invention, the system comprising an apparatus according to an embodiment of the present invention.

[0045] according to Figure 1In the embodiment of the present invention shown, the system includes a power system 2, a transformer 4, a load 1 connected to the power system 2, and a load conductor 3. The load 1 may be connected to or can be connected to the load conductor 3 via a transformer 5. The transformer 5 may be omitted (the transformer 5 may be referred to as a load transformer). The power system 2 is connected or can be connected to the load conductor 3 via the transformer 4. The load conductor 3 may include, for example, a busbar or a busbar. The power system 2 may include, for example, a power transmission and / or distribution system. The power system 2 may include, for example, a power grid, such as a transmission and / or distribution grid. The load 1 may include, for example, an electric arc furnace (EAF), but is not limited thereto. The transformer 4 is connected between the power system 2 and the load 1, so according to one or more embodiments of the present invention, the transformer 4 may be referred to as (or include) a step-down transformer. The transformer 4 may be omitted.

[0046] like Figure 1 As shown, the load 1 may be connected to the load conductor 3 via a switch 8 , and the switch 8 may generally be closed (eg, causing the switch 8 to conduct current) when or whenever the load 1 is operating.

[0047] The system comprises an apparatus configured to supply power to or absorb power from a load 1 connected to a power system 2. The apparatus may be configured to supply power to the load 1 (eg in addition to any power supplied to the load 1 from the power system 2).

[0048] The apparatus comprises a power supply and / or absorption device 6. The power supply and / or absorption device 6 is connected to the load conductor 3 and is configured to selectively supply power to the load conductor 3 or absorb power from the load conductor 3. The power supplied to the load conductor 3 or absorbed from the load conductor 3 by the power supply and / or absorption device 6 is managed by at least a voltage reference value of the power supply and / or absorption device 6.

[0049] The arrangement comprises a control unit 7. The control unit 7 is configured to control the operation of the power supply and / or absorption device 6. The arrangement comprising the power supply and / or absorption device 6 and the control unit 7 is configured to supply power to or absorb power from the load 1 .

[0050] The power supply and / or absorption device 6 can be based on a multi-level converter, a device based on a voltage source converter (VSC), and / or a static synchronous compensator (STATCOM), for example. The STATCOM can have a delta topology, for example. However, the STATCOM is not limited thereto and can alternatively have, for example, a Y-shaped topology. The multi-level converter can, for example, include a three-level converter.

[0051] For example, in the case where the power supply and / or absorption device 6 is based on a STATCOM having a triangular topology, the power supply and / or absorption device 6 can be connected to the load conductor 3 at a corner point (e.g., a terminal) of the STATCOM configured in a triangular topology or via a conductor connected to the corner point.

[0052] The power supply and / or absorption device 6 can be directly connected to the load conductor 3, such as Figure 1 As shown, indirect connection to the load conductor 3 may also be possible (eg, via one or more intermediate devices or components).

[0053] The control unit 7 is configured to obtain at least one value indicating the voltage of the load conductor 3, and determine the voltage reference value of the power supply and / or absorption device 6 based on the at least one value indicating the voltage of the load conductor and the virtual impedance of the power supply and / or absorption device 6. The control unit 7 is configured to control the power supply and / or absorption device to supply power to the load conductor 3 so as to supply power to the load 1, or to absorb power from the load conductor 3 so as to absorb power from the load 1 based on the determined voltage reference value. The virtual impedance of the power supply and / or absorption device 6 is associated with a virtual reactance and a virtual resistance, for example, the virtual reactance and the virtual resistance are components of the virtual impedance. The power supply and / or absorption device is (or has been) configured so that the value of the virtual reactance is higher than the value of the reactance of the power supply and / or absorption device 6, and the value of the virtual resistance is smaller than the value of the virtual reactance.

[0054] The reactance of the power supply and / or absorption device 6 may be the "physical" reactance of the power supply and / or absorption device 6. In other words, the reactance of the power supply and / or absorption device may be the reactance of the power supply and / or absorption device 6 caused by the reactance of the various elements or components in the power supply and / or absorption device 6. For example, a STATCOM configured in a triangle topology may include three converter arms, each of which may include a plurality of converter units connected in series with a reactor, and may also include another or other components. In the case where the power supply and / or absorption device 6 is based on a STATCOM having a triangle topology, the reactor in a corresponding one of the converter arms may at least partially define the reactance of the power supply and / or absorption device 6. Similarly, in the case where the power supply and / or absorption device 6 is to be based on a STATCOM having a topology other than a triangle topology, any reactor in a corresponding one of the multiple converter arms of the STATCOM may at least partially define the reactance of the power supply and / or absorption device 6.

[0055] In the event that the power supply and / or absorption device 6 stops working, it can be disconnected from the load conductor 3 by switch 9, and when or whenever the power supply and / or absorption device 6 is working, switch 9 can normally be closed (for example, so that switch 9 conducts current).

[0056] The at least one value indicative of the voltage of the load conductor 3 can be or has been measured or sensed by at least one sensor, such as at least one voltage transformer. Figure 1 The embodiment of the present invention shown in the figure provides a sensor 13 including a voltage transformer for sensing the voltage of the load conductor 3. Figure 1 As shown, the control unit 7 may be connected to a sensor 13 in order to acquire the voltage of the load conductor 3 (indicating at least one value of the voltage). The sensor 13 may be part of the device, and thus the device may include the sensor 13.

[0057] according to Figure 1 In the illustrated embodiment of the invention, the control unit 7 comprises first, second, third, and fourth subunits 15 to 18, respectively.

[0058] The first subunit 15 takes as input the voltage of the load conductor 3 (indicating at least one value of the voltage) and Figure 1 In the embodiment of the invention shown, the input is provided by the sensor 13. Therefore, the first subunit 15 can obtain the voltage of the load conductor 3 (indicating at least one value of the voltage) from the sensor 13. The first subunit 15 implements the virtual impedance-based control of the power supply and / or absorption device 6, as described in the foregoing content in this part of the specification and other parts of this document. The first subunit 15 is configured to determine a first voltage reference value of the power supply and / or absorption device 6 based on the voltage of the load conductor 3 (indicating at least one value of the voltage) and the virtual impedance of the power supply and / or absorption device 6. The output of the first subunit 15 is the first voltage reference value, which is sent to the fourth subunit 18. The first voltage reference value may have a component corresponding to active power and a component corresponding to reactive power.

[0059] The second subunit 16 takes as input at least one value indicative of the current of the power system 2 and the voltage of the load conductor 3 (indicative of at least one value of the voltage). Figure 1 In the embodiment of the invention shown, the voltage of the load conductor 3 is provided by the sensor 13 (indicating at least one value of the voltage). Figure 1 In the embodiment of the invention shown, at least one value indicative of the current of the power system 2 is provided by a sensor 11, which may for example comprise a current transformer, such as Figure 1As described above, a current transformer may be connected to the power system 2. Thus, the current of the power system 2 may be determined directly (indicating at least one value of the current). For example, it may be determined indirectly based on measuring or sensing the current of the power supply and / or absorption device 6 and the current of the load 1. Figure 1 As shown, the control unit 7 can be connected to the sensor 11 to obtain the current of the power system 2 (indicating at least one value of the current). The sensor 11 can be part of the device, so the device can include the sensor 11. Therefore, the second subunit 16 obtains the current of the power system 2 from the sensor 11 (indicating at least one value of the current) and obtains the voltage of the load conductor 3 from the sensor 13 (indicating at least one value of the voltage). The second subunit 16 is configured to determine the second voltage reference value of the power supply and / or absorption device 6 based on the current of the power system 2 (indicating at least one value of the current) and the voltage of the load conductor 3 (indicating at least one value of the voltage) to increase the power factor of the load 1. The output of the second subunit 16 is the second voltage reference value, which is sent to the fourth subunit 18. The second voltage reference value may have (for example, only have) a component corresponding to reactive power. In this way, the second subunit 16 can implement a power factor control algorithm or method.

[0060] The third subunit 17 takes as input a plurality of values ​​indicating the current of the load 1 at different moments in a period of time. Figure 1 In the embodiment of the present invention shown, multiple values ​​indicating the current of the load 1 at different times within a period of time are provided by the sensor 12, which may include, for example, a current transformer, such as Figure 1 As shown, the current transformer can be connected to the load 1. Figure 1 As shown, the control unit 7 can be connected to the sensor 12 to obtain multiple values ​​of the current of the load 1 at different times within a period of time. The sensor 12 can be part of the device, so the device can include the sensor 12. Therefore, the third subunit 17 obtains multiple values ​​indicating the current of the load 1 at different times within a period of time from the sensor 12. The third subunit 17 is configured to determine the current change of the load 1 over a period of time based on the multiple values ​​indicating the current of the load 1 at different times, and determine the third voltage reference value of the power supply and / or absorption device 6 based on the determined change of the current of the load 1 during the period of time to reduce any current fluctuation of the current of the load 1 over a period of time compared to the average current level of the current of the load 1. The output of the third subunit 17 is a third voltage reference value, which is sent to the fourth subunit 18. The third voltage reference value can have a component corresponding to active power and a component corresponding to reactive power. In this way, the third subunit 17 can implement a flicker control algorithm or method.

[0061] In the fourth subunit 18, the respective outputs from the first subunit 15, the second subunit 16, and the third subunit 17 may be combined (eg, summed) into a voltage reference value for the power supplying and / or absorbing device 6. Figure 1 As shown, the output of the fourth subunit 18 , ie the voltage reference value of the power supplying and / or absorbing device 6 , is sent to the power supplying and / or absorbing device 6 .

[0062] It should be understood that each of the second subunit 16 and the third subunit 17 is optional, and one or both of the second subunit 16 and the third subunit 17 can be omitted. In the case where both the second subunit 16 and the third subunit 17 are omitted, the fourth subunit 18 can also be omitted, wherein the output of the subunit 15 can be sent directly to the power supply and / or absorption device 6 instead of to the fourth subunit 18, as shown in FIG. Figure 1 In other words, in this case, the first voltage reference value output by the first subunit 15 can constitute the voltage reference value of the power supply and / or absorption device 6, which is sent to the power supply and / or absorption device 6, such as Figure 1 shown.

[0063] In case the third subunit 17 is omitted but the second subunit 16 is not omitted, the outputs from the first subunit 15 and the second subunit 16 may be sent to the fourth subunit 18, where they may be combined into a voltage reference value for the power supplying and / or absorbing device 6. The output of the fourth subunit 18, i.e. the voltage reference value for the power supplying and / or absorbing device 6, is sent to the power supplying and / or absorbing device 6. In this case, the sensor 12 may be omitted.

[0064] In case the second subunit 16 is omitted but the third subunit 17 is not omitted, the outputs from the first subunit 15 and the third subunit 17 may be sent to the fourth subunit 18, where they may be combined into a voltage reference value for the power supplying and / or absorbing device 6. The output of the fourth subunit 18, i.e. the voltage reference value for the power supplying and / or absorbing device 6, is sent to the power supplying and / or absorbing device 6. In this case, the sensor 11 may be omitted.

[0065] It should be understood that the control unit 7 including the first to fourth subunits 15 to 18 can be implemented in hardware and / or software. Each or any one of the first to fourth subunits 15 to 18 can be implemented in hardware and / or software.

[0066] Figure 2is a schematic flow chart of a method 30 according to an embodiment of the present invention. The method 30 is implemented in a device configured to supply power to a load connected to a power system or absorb power from the load. The load is connected or can be connected to a load conductor. The device includes a power supply and / or absorption device. The power supply and / or absorption device is connected to the load conductor. The power supply and / or absorption device is configured to selectively supply power to the load conductor or absorb power from the load conductor. The power supplied to the load conductor by the power supply and / or absorption device or the power absorbed from the load conductor by the power supply and / or absorption device is controlled by at least a voltage reference value of the power supply and / or absorption device.

[0067] The method 30 includes acquiring at 31 at least one value indicative of a voltage of a load conductor.

[0068] At 32 , a voltage reference value of the power supplying and / or sinking device is determined based on at least one value indicative of a voltage of a load conductor and a virtual impedance of the power supplying and / or sinking device.

[0069] At 33 , a power supply and / or sink device is controlled to supply power to the load conductors to supply power to the load, or to sink power from the load conductors to sink power from the load, based on the determined voltage reference value.

[0070] The virtual impedance of the power supply and / or absorption device is associated with a virtual reactance and a virtual resistance, wherein the power supply and / or absorption device is configured so that the value of the virtual reactance is higher than the value of the reactance of the power supply and / or absorption device, and so that the value of the virtual resistance is smaller than the value of the virtual reactance.

[0071] In summary, a device is provided, which is configured to supply power to a load connected to a power system or absorb power from the load, the load being connected or connectable to a load conductor. The device comprises: a power supply and / or absorption device, which is configured to selectively supply power to the load conductor or absorb power from the load conductor; and a control unit, which is configured to control the power supply and / or absorption device. The control unit is configured to determine a voltage reference value of the power supply and / or absorption device based on at least one value indicating a voltage of the load conductor and a virtual impedance of the power supply and / or absorption device, and to control the power supply and / or absorption device to supply power to the load conductor so as to supply power to the load, or to absorb power from the load conductor so as to absorb power from the load, based on the determined voltage reference value.

[0072] Although the present invention has been illustrated in the drawings and the foregoing description, such illustrations should be considered illustrative or exemplary rather than restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments may be understood and implemented by those skilled in the art in practicing the claimed invention through a study of the drawings, the present disclosure, and the appended claims. In the appended claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The fact that certain measures are cited in mutually different dependent claims does not mean that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be interpreted as limiting the scope.

Claims

1. A device, the device being configured to supply power to a load (1) connected to a power system (2) or absorb power from the load, the load being connected or connectable to a load conductor (3), the device comprising: a power supply and / or absorption device (6) connected to the load conductor and configured to selectively supply power to or absorb power from the load conductor, wherein the power supplied to or absorbed from the load conductor by the power supply and / or absorption device is governed by at least a voltage reference value of the power supply and / or absorption device; and A control unit (7), the control unit (7) being configured to control the operation of the power supply and / or absorption device, the control unit being further configured to: obtaining at least one value indicative of a voltage of the load conductor; determining a voltage reference value of the power supplying and / or absorbing device based on the at least one value indicative of the voltage of the load conductor and a virtual impedance of the power supplying and / or absorbing device; and Based on the determined voltage reference value, controlling the power supply and / or absorption device to supply power to the load conductor so as to supply power to the load, or to absorb power from the load conductor so as to absorb power from the load; wherein the virtual impedance of the power supply and / or absorption device is associated with a virtual reactance and a virtual resistance, wherein the power supply and / or absorption device is configured such that the value of the virtual reactance is higher than the value of the reactance of the power supply and / or absorption device, and such that the value of the virtual resistance is smaller than the value of the virtual reactance.

2. The device according to claim 1, wherein: The virtual reactance is the sum of a selected percentage of the reactance of the power supply and / or absorption device and the reactance of the power supply and / or absorption device, and the selected percentage of the reactance of the power supply and / or absorption device is in the range of 1% to 50% of the reactance of the power supply and / or absorption device.

3. The device according to claim 1 or 2, wherein: The virtual reactance enables the power supply and / or absorption device to supply power to or absorb power from the load conductor through the determined voltage reference value of the power supply and / or absorption device, thereby keeping any fluctuation of the voltage of the load conductor compared to the average voltage level of the voltage of the load conductor over a period of time below a selected threshold voltage fluctuation level while keeping the virtual reactance as small as possible.

4. The device according to any one of claims 1 to 3, wherein: The virtual resistance is such that the value of the virtual resistance is between 25% and 75% of the value of the virtual reactance.

5. The device according to any one of claims 1 to 4, wherein: The control unit is further configured to: obtaining a plurality of values ​​indicative of a current of the load at different moments in time over a period of time; determining a change in the current of the load over the period of time based on the plurality of values ​​indicative of the current of the load at the different moments in time; as well as A voltage reference value of the power supplying and / or absorbing device is determined further based on the determined change of the current of the load within the period of time.

6. The device according to claim 5, wherein: The control unit is configured to determine a voltage reference value of the power supplying and / or sinking device based on the plurality of values ​​indicative of the current of the load at the different moments in time to reduce any fluctuations of the current of the load compared to an average current level of the current of the load over a period of time.

7. The device according to any one of claims 1 to 6, wherein: The control unit is further configured to obtain at least one value indicative of a current of the power system and to determine a voltage reference value of the power supplying and / or sinking device further based on the at least one value indicative of a current of the power system.

8. The device according to claim 7, wherein: The control unit is configured to determine a voltage reference value of the power supplying and / or absorbing device based on at least one value indicative of a current of the power system and at least one value indicative of a voltage of a load conductor to increase a power factor of the load.

9. The device according to any one of claims 1 to 8, wherein: The power supplying and / or absorbing devices are based on multi-level converters, devices based on voltage source converters VSC, and / or static synchronous compensators STATCOM.

10. The device according to any one of claims 1 to 9, wherein: The power supplying and / or absorbing device is directly connected to the load conductor.

11. A method (30) implemented in a device configured to supply power to or absorb power from a load (1) connected to a power system (2), the load being connected or connectable to a load conductor (3), the device comprising a power supply and / or absorption device (6) connected to the load conductor and configured to selectively supply power to or absorb power from the load conductor, wherein: The power supplied to or absorbed from the load conductor by the power supply and / or absorption device is managed at least by a voltage reference value of the power supply and / or absorption device, the method comprising: acquiring (31) at least one value indicative of a voltage of the load conductor; determining (32) a voltage reference value of the power supplying and / or absorbing device based on at least one value indicative of a voltage of the load conductor and a virtual impedance of the power supplying and / or absorbing device; and Based on the determined voltage reference value, controlling (33) the power supply and / or absorption device to supply power to the load conductor so as to supply power to the load, or to absorb power from the load conductor so as to absorb power from the load; wherein the virtual impedance of the power supply and / or absorption device is associated with a virtual reactance and a virtual resistance, wherein the power supply and / or absorption device is configured such that the value of the virtual reactance is higher than the value of the reactance of the power supply and / or absorption device, and such that the value of the virtual resistance is smaller than the value of the virtual reactance.

12. A computer program comprising instructions which, when executed by one or more processors comprised in a control unit (7), cause the control unit to perform the method according to claim 11.

13. A system comprising: Power system (2); A load (1), wherein the load (1) is connected to the power system; a load conductor (3), wherein the load is connected or connectable to the load conductor; and The device according to any one of claims 1 to 10, the device being configured to supply power to the load or absorb power from the load.

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