Power flow control module for use in a low-voltage local network

Abstract

Power flow control module (30) for use in an electrical network (12) and for adjusting the voltage and / or current in at least one line (20) of the network (12), comprising at least two module terminals (60, 62) for connection to the line (20) of the network (12), several switching elements (64), an energy storage device (68) and two energy terminals (70) for connection to an energy source (92), wherein the first module terminal (60) and the second module terminal (62) are configured to electrically connect the power flow control module (30) in series with the line (20);two of the switching elements (64) are connected in series and in parallel to the energy storage device (68), the switching elements (64) are connected as two half-bridges and are designed as transistors (66) or power transistors, the power flow control module (30) is connected such that it is at the potential of the line (20) of the network (12) and is galvanically isolated from an earth potential or another line of the network (12), the switching elements (64) are designed to increase or decrease the amplitude of the voltage in the line (20) in order to adjust the voltage, to shift the phase of the voltage, or to control the current flow in the line (20) accordingly, the power flow control module (30) has an AC part (32) and a DC part (34), the power flow control module (30) includes at least one galvanically isolated power supply unit (40) which is connected to the power terminals (70).

Description

The present invention relates to a power flow control module for use in electrical power networks, in particular AC networks with one or more phases, for adjusting the voltage and / or current in a line of the electrical power network, comprising at least two module connections for connection to the line of the electrical power network and at least two power connections for connection to a power source. In particular, the power flow control module can be used in low-voltage networks, for example local networks, medium-voltage networks, for example distribution networks, and high-voltage networks, for example transmission networks. The present invention offers particular advantages at low voltage levels in meshed networks, such as low-voltage local networks or medium-voltage distribution networks. The utilization of electrical power grids, particularly medium- and low-voltage networks, has been steadily increasing and constantly changing in recent years. This is due, on the one hand, to distributed power generation and decentralized power feed-in, for example, from solar power plants, and on the other hand, to the increased use of charging stations for electric vehicles. As a result, individual feeders of a local substation in a residential or industrial area can become overloaded. To avoid laying new lines with larger cross-sections and the associated excavation work, voltage regulation can be achieved, for example, through controllable local network transformers. However, these can only influence the load flow in the feeders to a very limited extent. EP 3 413 422, for example, proposes a local distribution substation with a three-winding transformer to feed two separate busbars, each from a separate low-voltage winding. This allows for responses to the power flow in the individual busbars. Another control module of this type is presented in US 2010 / 0 292 863 A1, which describes a control system for a thyristor-controlled series capacitor located in a high-voltage line. In this system, voltage and current values ​​are detected, processed in a nonlinear controller, and a control angle for driving thyristors is derived from these values. Alternatively, it is also known in the prior art to use variable-voltage transformers. However, these require more extensive modifications and an additional measuring unit to measure the voltage in the busbar of the low-voltage network and the current at the low-voltage network's feed point. A variable-voltage transformer cannot, however, provide selective control of individual supply lines. Low-voltage distribution networks are often designed as meshed structures to guarantee a high level of supply reliability. However, in such meshed networks, the current flows through the individual feeders cannot be controlled; instead, they adjust passively according to the load. It is common practice to use a mesh current controller to change the voltage level of a network feeder, i.e., to raise or lower the voltage amplitude. The energy for this is usually drawn from the network itself. If the voltage is changed in a network segment, the load can be distributed among the various feeders. For example, if the voltage is raised by a mesh current controller, less current flows into this segment from potentially other network nodes, and the main load is served via the feeder of the mesh current controller. Conversely, if the voltage is lowered, the main load is shifted to other connections.Thus, mesh current controllers prove to be an effective means of actively shifting the load within a mesh. This is achieved by the mesh current controller representing a voltage source in series with one or more phases, so that the current flows in the individual meshes, which cannot be controlled due to various loads, can be regulated via the individual inputs, which adjust passively depending on the load. However, the mesh current controllers known in the prior art require at least one power transformer for series coupling to provide a voltage between the conductor and ground potential and to change the voltage amplitude. Such transformers are very large, heavy, and expensive. They require a large amount of installation space, meaning they can no longer be housed in a standard switchgear cabinet or on a distribution network pole, as is common practice in the USA. Mesh current controllers also require additional transformers to supply power to the controller itself. Furthermore, it has been shown that while the transformers are well-suited for low frequencies, unwanted losses occur at higher frequency components. However, feeding in or drawing higher frequencies would allow for the compensation of unwanted distortions in the grid, such as harmonics, in order to improve grid quality. The known mesh regulators are not suitable for such tasks. Moreover, they are relatively inflexible and can only influence the fundamental frequency. Often, the voltages can only be varied in fixed, predetermined steps. While meshed networks are highly desirable for ensuring a high level of supply reliability, the current flows within the mesh cannot be controlled with various loads; instead, they adjust passively depending on the load. However, existing mesh current controllers, due to their electromechanical design and large transformers, are unsuitable for existing distribution cabinets and offer only rigid solutions that require re-parameterization after every switching operation in the network. Therefore, there is a need for smaller and more cost-effective solutions that can improve network quality and adjust load distribution in meshed local distribution networks. The present problem is solved by a power flow control module for use in an alternating current electrical power network, for example in a low-voltage local network, with the features of claim 1, and by a network segment of an electrical network with a line having the features of claim 18. In a first aspect, the invention relates to a power flow control module for use in an electrical network (AC power network, e.g., low-voltage distribution network) and for adjusting the voltage and / or current in a line of the network (e.g., low-voltage distribution network), comprising two module terminals for connection to the line of the network (e.g., low-voltage distribution network), several switching elements, an energy storage device, and two power connections for connection to a power source. The first module terminal and the second module terminal are configured to connect the power flow control module electrically in series with the line, so that the power flow control module is connected in series with the line. Two of the switching elements are connected in series with each other and simultaneously in parallel with the energy storage device.The power flow control module is configured so that it is at the potential of the network line and galvanically isolated from earth potential or any other line in the network, such as the low-voltage distribution network. In other words, the power flow control module is at the same potential as the line to which it is connected in series. The power flow control module therefore floats with the voltage in the line to which it is connected. For example, in European low-voltage networks with a frequency of 50 Hz and a peak voltage of approximately 325 V, the electrical potential of the power flow control module is relative to earth potential. The switching elements of the power flow control module are designed to increase or decrease the amplitude of the voltage in the line, shift the phase of the voltage, or introduce harmonics with specific frequencies, phases, and amplitudes. This adjusts the voltage in the line or controls the current flow accordingly. The power flow control module has the advantage of using only switching elements to inject the desired voltage difference into the line in series. Since the switching elements for the series injection and the power flow control module are designed to float with the mains voltage and therefore have no ground reference or connection to other lines or phases in a three-wire system, they only need to handle very low voltages. However, the switching elements must handle high currents, which is easily managed even at low voltages.Within the scope of the invention, it was recognized that it is highly advantageous to connect the power flow control module in a floating configuration with the mains voltage. The modules move with the voltage of their phase (line) and only establish a small voltage difference between the first module terminal and the second module terminal. One power flow control module is used for each line or conductor of a three-phase, three-wire system, i.e., connected in series with the line. The power flow control modules have no ground reference and are isolated from each other. Such a lack of ground reference, also referred to by those skilled in the art as galvanic isolation, can, within the meaning of the invention, also be a very high-impedance reference to ground or to other well-defined electrical potentials outside the power flow control module. Such a high-impedance reference should be at least 250 kΩ, preferably at least 1 MΩ, and particularly preferably at least 10 MΩ.Any currents from a power flow control module to earth or other electrical reference points outside the module are therefore negligible and cause no significant losses. Such resistances, sometimes referred to as "leakage resistances," can be created by discrete resistors or sensors, such as insulation monitoring sensors. Alternatively, (nearly) complete isolation can be used, which typically only involves leakage currents along (contaminated) surfaces or through insulators and gigaohm resistors (see, for example, the industry standard IEC 60664). Since the power flow control module operates only relative to the voltage between the first and second module connections and has no ground reference, it never experiences the total voltage amplitude, but only the maximum voltage difference to be set. Due to its floating module configuration, the switching elements can be low-voltage semiconductor components that can still conduct several hundred amperes of current in a very small space. Large power transformers for high power outputs (several hundred kVA), which provide high currents (greater than 100 A) and the required nominal voltage (e.g., greater than 220 V in distribution networks) relative to ground potential, are completely eliminated. In a preferred embodiment of the power flow control module, the voltage provided for changing the amplitude of the voltage in the line is at most one-third of the line's peak phase voltage. Preferably, the voltage provided is less than or equal to one-fifth of the peak phase voltage, and very preferably at most one-tenth. For low-voltage distribution networks, the voltage provided is at most 100 V, preferably at most 50 V, and particularly preferably at most 25 V. In further preferred embodiments, the voltage difference, and thus the voltage provided by the power flow control module, is at most 20 V, and very preferably at most 15 V.In many cases, the requirements for the power flow control module are such that the maximum voltage to be provided is at most 6% of the nominal voltage of the line with which the power flow control module is connected in series. Within the scope of the invention, it was recognized that, due to the use of the power flow control module as a floating module, this module can be designed as a power electronics solution. The power flow control module only needs to have a very low nominal power rating in order to still be able to operate a network segment of a low-voltage distribution network with very high power levels. In a preferred embodiment, the power flow control module comprises switching elements connected as half-bridges. According to the invention, two switching elements are connected as two half-bridges. Preferably, four switching elements are provided, preferably connected as two half-bridges. Both half-bridges are preferably connected in parallel to the energy storage device. According to the invention, the switching elements are designed as transistors or power transistors, low-voltage transistors, or preferably as microvoltage transistors. For example, field-effect transistors (FETs), such as low-voltage trench transistors with vertical current flow, as known from the automotive sector, can preferably be used. For low-voltage distribution networks, the switching elements are preferably designed as low-voltage silicon FETs. Alternatively, gallium nitride FETs or gallium nitride FETs on silicon substrates, for example with lateral current flow, can be used. For applications with higher voltages, such as medium-voltage distribution networks, the switching elements can also preferably be designed as silicon carbide FETs, preferably with blocking voltages above 200 V, particularly preferably above 600 V, and further preferably above 1700 V. As an alternative to silicon carbide FETs, insulated-gate bipolar transistors (IGBTs) can also be used in accordance with the invention. A preferred embodiment of the power flow control module provides that the phase of the AC voltage between the two module terminals connected to the line can be shifted. The power flow control module is preferably capable of shifting the phase in both the negative and positive directions, depending on the network requirements. In a preferred embodiment, the power flow control module is operated in a voltage-controlled manner. It is thus used in such a way that a voltage is added in series to the voltage prevailing in the network line. In this way, a voltage drop in a network line or network segment can be adjusted, so that the power quality can be easily restored or maintained. In an equally preferred embodiment, the power flow control module is used as a current-controlled voltage source. In this way, a current can be injected into the line in which the power flow control module is connected, so that the total current flowing in the line can be influenced as desired. For example, if the current flow in a segment or in a line of a mesh within a network segment is significantly higher than in a parallel line of the segment, the power flow controller can adjust the current in the corresponding line so that a nearly balanced current flows in both lines. In a preferred embodiment, the switching elements of the power flow control module are clocked. Preferably, clocking is achieved by means of pulse width modulation. The switching elements are preferably clocked at a switching rate of at least 10 kHz. When using silicon FETs with a blocking voltage below 200 V (preferably below 100 V) or silicon carbide FETs with a blocking voltage above 200 V (preferably above 600 V), the switching rate is preferably at least 20 kHz, and particularly preferably at least 50 kHz or 100 kHz. When using gallium nitride FETs, the switching rate is preferably at least 100 kHz, very preferably at least 250 kHz, and particularly preferably at least 500 kHz. With increasing switching rate, the need for mains filters, such as inductors, at module terminals decreases.When using a high switching rate, for example above 500 kHz, as achievable with gallium nitride FETs, but sometimes also with silicon carbide and silicon FETs, dedicated mains filters can preferably be completely omitted because the parasitic inductance of the line is sufficient to generate only minimal unwanted current ripple at these switching rates. In this embodiment, the parasitic inductances perform the function of mains filters. Another preferred embodiment of the power flow control module provides a power source connected to the power terminals. This power source is required to supply the necessary energy to increase the voltage in the network line. The power source can be, for example, a battery, preferably connected to the power terminals of the power flow control module via an intermediate DC-DC converter, a power supply unit, or another electrical power source. Within the scope of the invention, it was discovered that a power electronics solution for the power flow control module only needs to have very low nominal power ratings to still be able to generate very high power in the network line. It was further discovered that, through a clever circuit design, the locations with high voltage requirements within the power flow control module can be separated from those with high current requirements. This allows reactive power to be kept out of the circuit. The solution according to the invention eliminates the need for any (large and heavy) power transformers at the fundamental frequency. The power supply is shaped via the power electronics of the power flow control module, i.e., by the switching elements, and is supplied by a preferably modern power source. For example, a modern power supply technology can be used as the power source, preferably one that also provides compact galvanic isolation at the high frequency. According to the invention, the power flow control module therefore comprises at least one galvanically isolated power supply unit connected to the power connections. However, multiple power supplies may also be advantageous in some cases. The power supplies are preferably designed such that the intermediate circuit they form for the power flow control module can be maintained at very low voltages. These are, for example, at most one-third of the network peak voltage, preferably at most one-fifth, more preferably at most one-tenth, and very preferably at most one-fifteenth. In low-voltage distribution networks, these are, for example, at most 100 V DC, preferably at most 60 V, more preferably at most 30 V, and very preferably at most 15 V. The galvanic isolation provided by the power supplies ensures that the power flow control module can float at the voltage present in the local distribution line to which it is connected in series. In other words, the electrical potential of the power flow control module always assumes the voltage present in the line. The floating of the power flow control modules, i.e., their oscillation in sync with the voltage prevailing in the connected line, has the added advantage that overvoltages are not a problem. This circuit also offers good protection against lightning strikes to the distribution network or local grid. Low-voltage local grids are sometimes very difficult to protect from lightning strikes. Medium-voltage lines, at least in rural areas, are implemented as overhead lines with closely spaced conductors. Underground lines of the low-voltage local grid are also affected, as local grid transformers transmit the voltage spikes that occur. Due to the lack of a ground reference for the power flow control module and the galvanic isolation of the electronic switching elements and the associated circuitry (electronic phase injection modules), as well as the lack of a potential reference between multiple power flow control modules, the modules follow every voltage change. In other words, they also follow voltage spikes from lightning strikes or other potential fluctuations. The power flow control module follows the potential spike, even if it reaches several thousand volts. Consequently, the voltage at any point on the power flow control module simultaneously increases by the ground voltage. The relevant voltage differences, or...However, differential voltages between the points within the power flow control module remain constant, so the power flow control module can still only be built with components with a significantly lower nominal voltage than the phase peak voltage, e.g. low-voltage components for local networks, i.e. low-voltage switching elements such as transistors, low-voltage capacitors, etc. Designing the power flow control modules exclusively with power electronics, specifically low-voltage components, offers the advantage of a very small size. For example, their dimensions are significantly smaller than those of a standard Eurocard circuit board. Due to their small size, large capacitive or inductive voltage differences cannot build up within the power flow control module, which could lead to damage. This is a further advantage of the power flow control modules according to the invention. Another preferred embodiment of the power flow control module comprises a power supply with a DC-DC converter, wherein the power supply is preferably fed from the low-voltage local network. Thus, no separate power connection or power source is necessary. Particularly preferably, the power supply is fed from the line to which the power flow control module is connected. In a further preferred embodiment, the DC-DC converter comprises an LLC circuit, as is known to those skilled in the art. A further preferred embodiment of the power flow control module according to the invention comprises a power supply including a rectifier circuit. For the purposes of this invention, a rectifier is any circuit capable of converting and / or exchanging energy between an AC voltage side with any number of phases and a DC voltage side with at least one DC link with one or more power flow directions. For example, a rectifier, an inverter, an active front end, or similar device could be used. Preferably, a unidirectional rectifier is used. Equally preferred is a power supply with a power factor correction (PFC) circuit. A power factor correction stage ensures, for example, a preferably uniform sinusoidal load on the AC side of the power supply.The power factor correction circuit can be designed, for example, as a boost power factor correction circuit (also called boost PFC) known to those skilled in the art, in conjunction with a rectifier, preferably a diode rectifier, or as a so-called bridgeless power factor correction circuit (bridgeless PFC), which usually already performs the function of a unidirectional rectifier with a mains current that is as sinusoidal as possible. According to the invention, the power flow control module has an AC part and a DC part. Another preferred embodiment of the power flow control module includes a heating resistor. This optional heating resistor can be used, for example, to consume energy. This occurs when the voltage difference multiplied by the current in the floating power flow control modules becomes negative, thus requiring energy to be drawn from the power flow control modules. The heating resistor can preferably be located within the power flow control module. An alternative and also preferred embodiment provides that the heating resistor can be arranged in the intermediate circuit upstream of a DC-DC converter. In another preferred embodiment, the power flow control module comprises a high-frequency transformer. Preferably, its frequency is at least 100 Hz, more preferably at least 400 Hz. In an equally preferred embodiment, the transformer operates at frequencies of at least 1 kHz, preferably at least 10 kHz, and very preferably at least 100 kHz. The choice of the transformer's operating frequency is left to the person skilled in the art, depending on the specific application and, for example, also depending on the frequency of the voltage used in the local distribution network. According to a further aspect, the invention relates to a power flow control system for regulating load distribution in a network or network segment, for example, a low-voltage local network, a medium-voltage distribution network, or a network segment of a low-voltage local network or medium-voltage distribution network, with a line. The power flow control system comprises a power flow control module, as described above, and a power source for supplying the power flow control module with energy in order to change or adjust the voltage in the line of the low-voltage local network in its amplitude or to regulate the load distribution or the current flow in the line. According to a further aspect, the invention relates to an electrical network or AC power network, preferably a low-voltage distribution network, or a network segment of an electrical network, e.g., a low-voltage distribution network segment of a low-voltage distribution network. According to the invention, the network segment has one or three lines of a three-wire system, which are connected to a (distribution) network transformer and to which several consumers and / or (decentralized) power sources are connected. The network segment has a power flow control module for each line, which is preferably designed according to one of the aspects and embodiments described above and is connected in series in the line of the network, for example, of a low-voltage distribution network. In the network segment according to the invention, the power flow control module is connected to the network line via two module connections and comprises several switching elements, an energy storage device, and two power connections for a power source. The two switching elements of the power flow control module are connected in series and in parallel with the energy storage device. The switching elements are connected as two half-bridges and are designed as transistors or power transistors. The power flow control module has an AC section and a DC section. The power flow control module includes at least one galvanically isolated power supply unit, which is connected to the power connections. The power flow control module is connected such that it is at the potential of the line of the electrical network, e.g., a low-voltage distribution network, and is galvanically isolated from earth potential or any other line of the network.The power flow control module, with its switching elements, is designed to influence the voltage amplitude in the line, preferably increasing or decreasing it, in order to adjust the line voltage or to control the current flow in the line according to predefined requirements. This makes it easy to ensure network quality and supply quality in the local distribution network segment. Since the power flow control module is at the same potential as the line, only small voltages need to be supplied by the module to adjust the line voltage. This has the advantage that the switching elements can be designed as low-voltage switching elements or low-voltage transistors. However, they must be able to handle large currents, preferably greater than 500 A, at low voltages.Since the large currents are to be applied in combination with low voltages of less than 50 V, preferably less than 20 V, and very preferably less than 10 V, the power flow control module is very small overall and has a very low weight (less than 5 kg, preferably less than 1 kg, and very preferably less than 0.5 kg). It can therefore be installed in any conventional switchgear cabinet in a local distribution network. No further structural modifications are required. In particular, the use of large power transformers can be avoided, as can changes to the conductor cross-sections in the local distribution network segment to handle the higher loads. Instead, the voltage and current in the network segment according to the invention are adjusted within the desired ranges by using the power flow control module according to the invention. Preferred embodiments of the invention are defined in the dependent claims. It is understood that the features mentioned above and those to be explained below are applicable not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the present invention. Galvanic isolation is understood to mean either complete galvanic isolation, for example via a transformer or transfer transformer, or isolation via a resistance to earth of at least 250 kΩ (kilo-Ohm), preferably at least 1 MΩ (MegaOhm), very preferably > 10 MΩ. The invention is described and explained in more detail below with reference to some selected embodiments in conjunction with the accompanying drawings. Here, a low-voltage local distribution network is used as an example of a possible AC electrical network, without limiting the generality of local distribution networks. The figures show: Fig. 1 a schematic diagram of a network segment with a line and power flow control module; Fig. 2 a schematic diagram of an alternative network segment or local distribution network segment; Fig. 3 a detailed sketch of the network segment from Fig. 2; Fig. 4 a detailed sketch of an alternative embodiment of a network segment; Fig. 5 a further detailed sketch of an alternative embodiment of a local distribution network segment; Fig. 6 a further schematic diagram of a local distribution network segment; Fig. 7 a further detailed sketch of an alternative embodiment of a local distribution network segment; Fig.Fig. 8 shows an alternative local network segment with power flow control module and battery; Fig. 9 shows an alternative embodiment of the local network segment according to Fig. 8; and Fig. 10 shows an alternative embodiment of a local network segment with power flow control module. Fig. 1 shows a three-phase network segment 10 with three lines 20, where the network segment 10 is part of an electrical network 12. A local network segment 11 of a low-voltage local network 14 is shown here as an example. Each line 20 has a power flow control module 30 connected in series, comprising an AC section 32 and a DC section 34. Optional mains filters 36, which can be configured as inductors or as PI filters, are provided between the power flow control module 30 and the line 20. Each of the power flow control modules 30 is connected to a power supply 40, each of which has an isolating output. The power supplies 40 can be powered by any voltage source or energy source, whereby an AC portion 42 of the power supply 40 can be connected to an energy source (not shown) located at the terminals 46. The energy sources can be of different types. A connection exists between a DC part 44 of the power supply 40 and the DC part 34 of the power flow control module 30 via two conductors 48. Fig. 1 shows that the voltage at an input side 22 (referring to the power flow control module 30) has a different shape, i.e., a different amplitude, than the output voltage at an output side 24. The voltages of the three phases are shown schematically. Fig. 2 differs from Fig. 1 in that the power supplies 40, which in principle can be powered from any possible source, are in this embodiment powered from the input side 22 of the network segment 10. Consequently, a conductor 49 is connected to the respective line 20 for each phase in order to supply the power supplies with energy. In the embodiments shown here according to Fig. 1 and Fig. 2, the power flow control modules 30 are connected in the line 20 such that they float at the voltage level of the lines 20. The power flow control modules are therefore at the respective voltage level of the line with which they are connected in series. Preferably, the power flow control modules 30 are designed to handle only small voltages, preferably voltages below 50 V, very preferably below 20 V, and particularly preferably below 15 V. On the other hand, it is possible to handle very high currents, typically currents greater than 500 A. The power supplies 40 provide galvanic isolation, allowing the power flow control modules 30 to float with the voltage in the lines 20. Therefore, the power flow control modules 30 have no ground reference and no connection to any phase or line 20 other than the one with which they are connected in series. Accordingly, the power flow control modules 30 move with the voltage in their line and therefore only need to handle a small voltage difference between the input and output of the modules.The power flow control modules 30 do not "see" the total voltage amplitude of the line 20, as they are positioned relatively between the input and output of the line 20. Only the maximum voltage difference to be set is relevant for them. Therefore, low-voltage switching elements, e.g., low-voltage semiconductor devices, can be used, which can still conduct several hundred amperes of current in a very small space. In addition to the three power supplies 40 shown here, i.e., one power supply 40 for each phase or line 20, a single power supply could also be used to power all three power flow control modules 30. However, galvanic isolation between the individual lines 20 must be present. Fig. 3 shows a detailed embodiment of a power flow control module 30 with a power supply 40 for a line 20 of the three-phase network segment 10, for example, a local distribution network segment 11. The power flow control module 30 is shown in detail. It comprises a first module terminal 60, which is connected to the line 20 at the input side 22, and a second module terminal 62, which is connected to the output side 24 of the line 20. The output side of the line 20 is not shown. A network filter 36 (e.g., an inductor) can be arranged between the line 20 and each of the respective module terminals 60 and 62. The power flow control module comprises several switching elements 64, which can be designed as low-voltage FETs (field-effect transistors), for example, as low-voltage silicon FETs.In the example shown here, the switching elements 64 are designed as transistors 66, with two transistors connected in series and in parallel to an energy storage device 68. The switching elements 64 are connected as two half-bridges. The switching elements can be clocked, preferably with a clock rate of at least 20 kHz, more preferably with at least 100 kHz, and most preferably with at least 250 kHz. Preferably, the switching elements 64 are transistors based on gallium nitride (GaN), with the advantage that the inductances 36 become very small (approximately proportional to the characteristic value of the switching rate, 1 / switching rate) or even the parasitic inductance of the lines (which also generate a small magnetic field around themselves, sufficient at a sufficient switching rate) is sufficient as a filter. The power supply 40 is connected to the power flow control module 30 via two power connections 70. In the embodiment shown here, the power supply includes a rectifier circuit 50, specifically a (unidirectional) rectifier 50b, which is fed from all three phases of the network segment 10 for a balanced load; in other words, it is connected to all three lines 20 of the network segment 10 or local network segment 11. The (unidirectional) rectifier circuit 50 is configured here as an active front end. It can handle high voltages (greater than 200 V) but only low currents (less than 50 A). Thus, the rectifier 50 of the power supply 40 contrasts with the power flow control module 30, which is designed to handle only low voltages (preferably less than 50 V) but high currents (over 500 A). In principle, the rectifier could be powered from only one phase. Furthermore, the power supply 40 preferably includes a power factor correction stage 52, a so-called PFC stage, on its AC side to ensure a uniform sinusoidal load. Additionally, the power supply includes a DC-DC converter 54, configured as an LLC circuit according to Fig. 3. The DC-DC converter must have at least one isolated output per power flow control module 30 for one line 20. Thus, the power supply used here is similar to typical power supplies. A mains filter 56, for example in the form of inductors, can also be provided on the AC side. Fig. 4 shows a modification of the power flow control module 30 with power supply 40. In the embodiment shown here, the PFC stage 52 is already integrated into the rectifier circuit 50 or a rectifier 50b and is not designed as a separate stage. In this case, the power supply again includes a DC-DC converter 54 to galvanically isolate the power flow control module 30 and make it ground-free, so that it is at the potential of line 20. The DC-DC converter 54 has a transformer 80, for example, a high-frequency transformer. In the embodiment shown in Fig. 5, the power supply 40, which is installed together with the power flow control module 30 in the local network segment 10, comprises a rectifier 50b and a DC-DC converter 54. A heating resistor 58, which can optionally be controlled, is arranged between the rectifier 50b and the DC-DC converter 54. The heating resistor 58 serves to draw energy from the network segment 10 and consume it. The heating element 58 is therefore an energy consumer. The DC-DC converter 54 of the power supply 40 in Figures 3, 4 to 5 includes, among other things, a transformer 80, which is preferably a high-frequency transformer. The high-frequency transformer is preferably implemented as a printed circuit board transformer or a flat transformer. The transformer can also be implemented as a planar transformer on printed circuit board technology. By using, for example, ferrite core materials, very high transformer frequencies can be achieved. The transmitted power increases linearly with frequency over a wide range (depending on the available space), thus enabling a very compact design in the power supplies. An alternative to using a heating element in the power supply is to design the power supplies 40 to be regenerative. In this way, energy accumulating in the floating power flow control modules 30 can also be "disposed of." The power supplies 40 accordingly absorb the power from the (floating) power flow control modules 30 and feed it back into the power supply's source, i.e., back into the network segment 10 or electrical network 14, or low-voltage local network. Fig. 6 shows a possible variant of regenerative power supplies, which is installed here in network segment 10 or local network segment 11. One possible variant of such regenerative power supplies 40 uses an active front end (AFE). However, this is not the only way to design a power supply 40 to be regenerative. Those skilled in the art will recognize that other regenerative power supply technologies could also be used.The invention does not exclude these power supply technologies, but rather incorporates them. As schematically shown in Fig. 6, the power supply 40 can comprise a rectifier circuit 50 (e.g., an inverter) and a galvanically isolated DC-DC converter 54, which is, for example, configured as an LLC stage. While the voltage ratio between input and output is generally difficult to control, this is not a problem for the present circuit and is sufficient. Alternatively, the DC-DC converter 54 can comprise a dual active bridge (DAB). Fig. 6 also shows that the power supply 40 has a rectifier circuit 50 and three DC-DC converters 54, one for each phase or line 20 of the distribution network segment 10. The power required to increase the voltage in phase 20 of network segment 10 is transmitted via the DC line 48. This power essentially consists of the added voltage difference multiplied by the current flowing in line 20. The required power is supplied by the DC-DC converter 54 and the rectifier circuit 50. At the junction between the rectifier circuit 50 and the DC-DC converters 54, a potentially pulsating DC voltage is present in the DC connection. This voltage depends on the size of the DC capacitor used. For example, it is greater than 400 V, but it can also be greater than 650 V or greater than 750 V. Fig. 7 shows the embodiments of the power supply 40 from Fig. 6 in detail with individual components, showing only a DC-DC converter 54 and a power flow control module 30 for one line 20. In a three-phase system, three galvanically isolated DC-DC converters must of course be used, one for each phase or for each power flow control module 30, or at least one DC-DC converter with an isolated output per phase or per power flow control module. The rectifier circuit 50 is designed here as a bidirectional active front end 51. This also allows energy to be fed back into the grid. Fig. 8 shows an embodiment of a power flow control module 30 with a battery 90 as the energy source 92 for the power flow control modules 30. In a three-phase system where three power flow control modules 30 are used, one per line 20, a single battery can be used. Simultaneously, the battery 90 can serve as a load to absorb energy and thus draw it from the system. The battery-based variant takes into account that both a voltage drop in a loop of an electrical network 12 (low-voltage local network 14) or in a network segment 10 (local network segment 11), and the need to limit the power input from weaker supply lines, are associated with a high power demand in the network segment. On the other hand, it considers that a voltage rise with an unexpectedly low load or with an unfavorably high feed-in, which can be caused, for example, by braking drives or solar panels, perfectly matches the requirements of a grid storage system. A battery thus makes it possible to forgo complicated and expensive, but potentially regenerative, power supplies. The battery 90 can be connected directly to the individual power flow control modules 30 (Fig. 8) or via a galvanically isolated additional DC DC converter 54 (Fig. 9). Preferably, one battery 90 with sufficient capacity, as provided in grid energy storage systems, is used per power flow control module 30. Energy exchange between individual batteries 90 is not necessary if the imbalances average out over time. Figure 10 shows another preferred embodiment of a power flow control module 30, which has multiple inputs and outputs, i.e., multiple first module terminals 60 and multiple second module terminals 62. In this case, the power flow control module 30 comprises multiple switching elements 64 or transistors 66 configured as half-bridges, e.g., FETs. In this case, the power flow control modules 30 can each operate as a "low-voltage energy router" and thus perform N-to-M routing. The power flow control modules 30 can distribute power like a switch between N inputs (first module terminal 60) and M outputs (second module terminal 62) by generating arbitrary voltage gradients between the MxN taps. This is preferably done within the intermediate circuit voltage levels of the series-connected power flow control modules 30, for example with a maximum of + / - 48 V at 48 V or a maximum of + / - 24 V at 24 V.Strictly speaking, due to the symmetry, the power flow control modules 30 no longer distinguish between inputs and outputs in this case (first module connection 60 and second module connection 62). This turns the compact power electronics mesh current controller, as described here, into a kind of gateway or router. However, it is also important here that there is still no galvanic connection to the other phases or lines 20, and especially no galvanic connection to earth potential. The inputs and outputs should also be very close to each other in phase. The power supply 40 preferably comprises a bidirectional active front end 51 as a rectifier circuit 50 or inverter and a DC-DC converter 54.

Claims

Power flow control module (30) for use in an electrical network (12) and for adjusting the voltage and / or current in at least one line (20) of the network (12), comprising at least two module terminals (60, 62) for connection to the line (20) of the network (12), several switching elements (64), an energy storage device (68) and two energy terminals (70) for connection to an energy source (92), wherein the first module terminal (60) and the second module terminal (62) are configured to electrically connect the power flow control module (30) in series with the line (20);two of the switching elements (64) are connected in series and in parallel to the energy storage device (68), the switching elements (64) are connected as two half-bridges and are designed as transistors (66) or power transistors, the power flow control module (30) is connected such that it is at the potential of the line (20) of the network (12) and is galvanically isolated from an earth potential or another line of the network (12), the switching elements (64) are designed to increase or decrease the amplitude of the voltage in the line (20) in order to adjust the voltage, to shift the phase of the voltage, or to control the current flow in the line (20) accordingly, the power flow control module (30) has an AC part (32) and a DC part (34), the power flow control module (30) includes at least one galvanically isolated power supply unit (40) which is connected to the power terminals (70). Power flow control module according to claim 1, characterized in that the voltage provided by the power flow control module (30) for changing the amplitude of the line (20) is at most one third of the nominal network peak voltage, preferably at most one fifth, very preferably at most one tenth, further preferably at most one fifteenth, particularly preferably at most one twentieth. Power flow control module according to claim 1 or 2, characterized in that the voltage provided by the power flow control module (30) for changing the amplitude of the line (20) is at most 100 volts in magnitude, preferably at most 50 volts, very preferably at most 25 volts, further preferably at most 20 volts, particularly preferably at most 15 volts. Power flow control module according to one of the preceding claims, characterized in that the transistors (66) or power transistors are designed as low-voltage transistors or as micro-voltage transistors, very preferably as low-voltage trench transistors. Power flow control module according to one of the preceding claims, characterized in that at least one of the switching elements (64) comprises at least one field-effect transistor, preferably made of silicon, silicon carbide, gallium nitride or gallium nitride on a silicon substrate. Power flow control module according to one of the preceding claims, characterized in that the power flow control module (30) can shift the phase between the two module terminals (60, 62) which are connected to the line (20), preferably both in the negative direction and in the positive direction. Power flow control module according to one of the preceding claims, characterized in that the power flow control module (30) is operated in a voltage-controlled manner or is used as a current-controlled voltage source. Power flow control module according to one of the preceding claims, characterized in that the switching elements (64) are clocked, preferably by means of pulse width modulation (PWM). Power flow control module according to one of the preceding claims, characterized in that the switching elements (64) are clocked at a switching rate of at least 20 kHz, preferably at least 100 kHz, particularly preferably at least 250 kHz. Power flow control module according to the preceding claim, characterized in that the energy source (92) which is connected to the energy terminals (70) is a battery (90) which is preferably connected to the energy terminals (70) by means of an intermediate DC-DC converter (54). Power flow control module according to the preceding claim, characterized in that the power supply (40) comprises a DC-DC converter (54) and is supplied from the electrical network (12), preferably connected to the line (20), wherein the DC-DC converter (54) preferably comprises an LLC circuit. Power flow control module according to claim 10 or 11, characterized in that the power supply (40) comprises a rectifier circuit (50), preferably a unidirectional rectifier, and preferably a power factor correction circuit. Power flow control module according to claim 10 or 11, characterized in that the power supply (40) is at least one bidirectional active front end (51). Power flow control module according to one of the preceding claims, characterized in that the power flow control module (30) comprises a heating element (58), preferably a heating resistor. Power flow control module according to one of the preceding claims, characterized in that the power flow control module (30) comprises a high-frequency transformer (80) whose frequency is at least 400 Hz, preferably at least 1 kHz, very preferably at least 10 kHz, further preferably at least 100 kHz, further preferably at least 300 kHz, particularly preferably at least 600 kHz. Power flow control module according to one of the preceding claims, characterized in that the power flow control module (30) comprises an intermediate circuit, wherein the voltage of the intermediate circuit is at most 100 volts dc, preferably at most 60 volts dc, more preferably at most 30 volts dc, particularly preferably at most 15 volts dc. Power flow control system for controlling the load distribution in an electrical network (12) or in a network segment (10) of an electrical network (12) with at least one line (20), comprising a power flow control module (30) according to one of the preceding claims and an energy source (92) for supplying the power flow control module (30) with energy to change or adjust the voltage in the line (20) in its amplitude. Network segment (10) of an electrical network (12) with a line (20) connected to a network transformer and to which several consumers and / or feed-in sources are connected, and with a power flow control module (30) according to one of the preceding claims, which comprises two module connections (60, 62) connected to the line (20) of the network (12), several switching elements (64), an energy storage device (68) and two energy connections (70) for connection to an energy source (92), wherein the first module connection (60) and the second module connection (62) are connected to the line (20) such that the power flow control module (30) is electrically connected in series with the line (20); two of the switching elements (64) are connected in series and in parallel with the energy storage device (68);the switching elements (64) are connected as two half-bridges and are designed as transistors (66) or power transistors; the power flow control module (30) is connected such that it is at the potential of the line (20) of the electrical network (12) and is galvanically isolated from an earth potential or any other line of the network (12); the switching elements (64) are designed to increase or decrease the amplitude of the voltage in the line (20) in order to adjust the voltage, to shift the phase of the voltage, or to control the current flow in the line (20) accordingly; the power flow control module (30) has an AC section (32) and a DC section (34); the power flow control module (30) includes at least one galvanically isolated power supply unit (40) which is connected to the power terminals (70).

Images