Patent Issued for Coupling-In and Coupling-Out of Power in a Branch of a DC Voltage Network Node Comprising a Longitudinal Voltage Source (USPTO 9774187)
By a News Reporter-Staff News Editor at Electronics Newsweekly -- SIEMENS AKTIENGESELLSCHAFT (Munich, DE) has been issued patent number 9774187, according to news reporting originating out of Alexandria, Virginia, by VerticalNews editors.
The patent's inventor is Eckel, Hans-Guenter (Rostock, DE).
This patent was filed on June 19, 2012 and was published online on September 26, 2017.
From the background information supplied by the inventors, news correspondents obtained the following quote: "Field of the Invention
"The invention relates to an apparatus for coupling in and coupling out power in a branch of a DC voltage network node comprising a longitudinal voltage source, which has means for coupling in or coupling out electric power.
"WO2010/115453A1 proposes voltage compensation in DC transmission networks. In said document, longitudinal voltage sources are introduced into DC transmission lines in order to keep the voltage in the DC networks within a permissible range at all points. By introducing the longitudinal voltage source, unavoidably energy is supplied to or conducted away from the DC system at this point. In accordance with WO2010/115453, this energy is drawn from a three-phase system provided or is drawn from the DC line itself by means of an additional device.
"The apparatus mentioned at the outset has the disadvantage that it severely limits the possibilities in respect of energy flow control.
"The object of the invention therefore consists in providing an apparatus of the type mentioned at the outset which can be used economically and flexibly for controlling a load flow at a network node."
Supplementing the background information on this patent, VerticalNews reporters also obtained the inventor's summary information for this patent: "The invention achieves this object by virtue of the fact that the means for coupling in and coupling out electric power are coupled to means for coupling in and coupling out electric power of a further apparatus for load flow control, which further apparatus is arranged in another branch of the same DC voltage network node. By virtue of the coupling to a plurality of apparatuses for load flow control, in particular via the DC voltage network node, it is possible to achieve load flow control in a flexible manner since the means for coupling in and coupling out electric power make it possible to use, in an expedient manner, electric power output by a longitudinal voltage source, for example, for any desired purpose. For example, the longitudinal voltage source can be designed for supplying a consumer or for feeding electrical energy from a source into the DC voltage network node. Instead of the consumer or the source, a power supply system can also be provided.
"However, the consumer may also at the same time be an energy store, for example a hydroenergy store, a mechanical store, an electrical or chemical energy store. If required, the consumer then becomes the energy source. The consumer can also be a conventional energy consumer, for example an industrial plant, a housing development or the like.
"For complete load flow control, the number of apparatuses according to the invention at a DC voltage network node can be one fewer than the number of branches of said network node. If, therefore, n is the number of branches of the DC voltage network node, the number m of apparatuses according to the invention which is required for complete load flow control is calculated in accordance with m=n-1.
"The apparatus according to the invention is intended for use in an HVDC network, wherein the coupling of a plurality of apparatuses via a low-voltage busbar is possible. This reduces the complexity involved in the power exchange considerably.
"The longitudinal voltage source can be connected to a low-voltage busbar designed for alternating current. In this case, low voltage means a voltage of a few kilovolts in contrast to the operating voltages of the branch of several hundred kilovolts.
"Within the context of one configuration, the longitudinal voltage source is connectable to a neutral point (ground potential) via a transverse current source.
"In particular, the DC voltage node can be connected to the neutral point via the transverse current source.
"In particular, the apparatus can have a transverse current source which is designed for connection to the neutral point. Alternatively, the apparatus can be designed for connection to the (for example one terminal or pole of the) transverse current source.
"Preferably, the transverse current source is connectable to the DC voltage network node.
"The transverse current source represents an option for the case where the total energy of the energy drawn by the longitudinal voltage sources and the energy fed by the longitudinal voltage sources is not equal to zero.
"One development consists in that the longitudinal voltage source is coupled to the AC system via a transverse current source or directly (for example via a transformer).
"A further development consists in that the longitudinal voltage source has at least one converter. For high-voltage direct-current (HVDC) transmission, so-called modular multilevel converters (MMCs) are used, whose basic module is a half-bridge comprising IGBTs and diodes, for example. This basic module is also referred to as submodule (also: converter module). It is known to connect a multiplicity of such submodules in series with one another in order to achieve HV strength.
"An additional development consists in that the longitudinal voltage source has at least one phase module comprising at least two phase module branches connected in series, wherein a center tap between the phase module branches is connectable to an AC voltage connection, in particular to a transformer.
"In particular, a plurality of phase modules can be connected in parallel with one another and thus realize a polyphase converter.
"A further configuration consists in that the longitudinal voltage source is connected in series with a mechanical switch, and a power switching unit is arranged in parallel with the longitudinal voltage source and the mechanical switch.
"The longitudinal voltage source can be used by way of example as follows. It is firstly used as commutation voltage when, for example, short-circuit currents are intended to be interrupted. First, a high current rise and/or an excessively high current over a specific duration is detected. Then, a tripping signal is transmitted to a tripping unit of the mechanical switch in the continuous current path. At the same time, the power semiconductor switches of the power semiconductor unit in the switching path are switched on. Finally, a back-emf is generated, which generates a circulating current in the mesh formed from the continuous current path and the switching current path, which circulating current is in opposition to the short-circuit current to be switched in the continuous current path. The longitudinal voltage source actively generates a back-emf, for example. As a deviation from this, the longitudinal voltage source, as in the document mentioned at the outset, is realized as an auxiliary electronic switch. An IGBT or IGCT with a freewheeling diode which is parallel in opposition, for example, is suitable as auxiliary electronic switch. It goes without saying that it is also possible for a plurality of series-connected auxiliary electronic switches which are arranged back-to-back in series to be used. The switching-off of the auxiliary switch can be equated to the application of a back-emf, which acts in opposition to the current flow in the continuous current path. The current is commutated into the switch-off branch by means of the longitudinal voltage source, with the result that the mechanical switch is opened at zero current. The actual interruption of the short-circuit current takes place in the power switching unit.
"Within the scope of the invention, the longitudinal voltage source can in principle have any desired design. However, particular advantages are considered to be that the longitudinal voltage source has at least one submodule, which is provided with an energy store and a power semiconductor circuit, wherein each submodule has means for coupling in and coupling out electric power. If a plurality of submodules of this type is provided, these submodules are connected in series with one another.
"Advantageously, each submodule has a half-bridge circuit. Such half-bridge circuits are provided with a power semiconductor circuit, which consists of a series circuit comprising two power semiconductor switches, wherein the series circuit is connected in parallel with an energy store, for example a unipolar storage capacitor. The potential point between the two power semiconductor switches of the series circuit is connected to a first connection terminal, wherein a pole of the energy store is connected to a second connection terminal of the submodule.
"If required, a freewheeling diode in opposition is connected in parallel with the power semiconductor switches. Possible power semiconductor switches are, for example, IGBTs or IGCTs. By virtue of the half-bridge circuit, either the energy store voltage U.sub.C which forms as a voltage drop across the energy store or else a zero voltage can be generated at the connection terminals of each submodule. In accordance with this advantageous development, the longitudinal voltage source can therefore actively generate a back-emf in only one direction.
"Thus, half-bridge circuits are particularly suitable when the direction of the back-emf to be impressed is known.
"In order to be able to build up a voltage in both directions, however, submodules which have a full-bridge circuit are advantageous. These submodules are also connected in series, with the result that the longitudinal voltage source consists of a series circuit of submodules. The submodules having a full-bridge circuit are each provided with two series circuits comprising two power semiconductor switches, wherein the potential point between the two power semiconductor switches connected in series of the first series circuit is connected to the first connection terminal, and the potential point between the two power semiconductor switches of the second series circuit is connected to the second connection terminal. Both series circuits are connected in parallel with an energy store. Overall, the full-bridge circuit thus has four power semiconductor switches. If required, a freewheeling diode is again connected in parallel, in opposition, with each of these power semiconductor switches. Owing to this circuit arrangement, either the energy store voltage U.sub.C which forms as a voltage drop across the energy store, a zero voltage or else the inverse energy store voltage -U.sub.C can be generated at the connection terminals of each submodule. Therefore, with a series circuit of such full-bridge submodules, back-emfs are built up in both directions, wherein the maximum back-emf is dependent on the number of submodules. By using pulse width modulation during the actuation of the power semiconductor switches, the back-emf can be varied quasi continuously between the maximum positive and the maximum inverse energy store voltage.
"Expediently, an AC voltage in the low-voltage range can be generated by the means for coupling in and coupling out electric power. The AC voltage has the advantage that it can easily be coupled, for example, inductively and in a cost-effective manner to other means for coupling in and coupling out electric power generating AC voltage.
"In accordance with an expedient development in this regard, the means for coupling in and coupling out electric power have at least one series circuit comprising two power semiconductor switches which can be switched on and off and a coil, said series circuit being connected in parallel with the energy store. The coil is connected at one of its terminals to the potential point between the power semiconductor switches of said series circuit. In accordance with a development in this regard, at least one capacitor is also used in addition to a coil. It is also possible for two series circuits in the form of a hard-switched full-bridge to be used, wherein the potential points between the two power semiconductor switches of the two series circuits are connected to different terminals of the coil.
"Expediently, the coil is inductively coupled to a coil of a longitudinal voltage source of a further apparatus according to the invention which is arranged in another branch of the DC voltage network node. This inductive coupling takes place via individual transformers, for example. The individual transformers have secondary windings, which are connected to the low-voltage busbar. It is also possible to arrange all of the coils on a common transformer.
"The invention likewise relates to a mains voltage node (DC voltage network node) having branches, wherein an apparatus in accordance with the present invention is arranged in at least two branches.
"Expediently, the means for coupling in and coupling out electric power of the at least two apparatuses in accordance with the invention are coupled to one another via a low-voltage busbar. The low-voltage busbar is designed for AC voltages, for example."
For the URL and additional information on this patent, see: Eckel, Hans-Guenter. Coupling-In and Coupling-Out of Power in a Branch of a DC Voltage Network Node Comprising a Longitudinal Voltage Source. U.S. Patent Number 9774187, filed June 19, 2012, and published online on September 26, 2017. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=9774187.PN.&OS=PN/9774187RS=PN/9774187
Keywords for this news article include: Energy, Electronics, Semiconductor, Electric Power, SIEMENS AKTIENGESELLSCHAFT.
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