AU2009309887A1

AU2009309887A1 - Device for feeding a consumer network with the electric power of a supply network

Info

Publication number: AU2009309887A1
Application number: AU2009309887A
Authority: AU
Inventors: Uwe Krebs; Jurgen Moser
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2008-10-27
Filing date: 2009-09-29
Publication date: 2010-05-06
Anticipated expiration: 2029-09-29
Also published as: CN102197562B; HK1159331A1; JP2012507253A; EP2347491A2; PT2347491T; WO2010049231A3; AU2009309887B2; DE102008053822B3; JP5363582B2; DK2347491T3; WO2010049231A2; EP2347491B1; CN102197562A

Description

PCT/EP2009/062622 - 1 2008P20964WOIN Description Apparatus for feeding a consumer network with the electrical power from a power supply system The invention relates to an apparatus for feeding a consumer network with electrical power from a power supply system, wherein the apparatus has a frequency converter which can be connected on the one hand to the power supply system and on the other hand to the consumer network. The invention also relates to a method for feeding a consumer network with electrical power from a power supply system. An apparatus such as this and a method such as this are already known from DE 10 2005 004 628 Al. The apparatus described there is intended for supplying power to marine vessels in harbor. Marine vessels in harbor are generally supplied with power by running diesel engines. However, the exhaust gases from the diesel engines lead to considerable environmental pollution in the harbor towns. The apparatus of the type in question allows power to be supplied from the land. A static frequency converter, by means of which the various systems can be coupled, is provided because the voltages, system frequencies, star-point treatments and the like generally differ between the land-based power supply system and the marine-vessel distribution system. Static converters have power semiconductors which allow currents and voltages to be converted. The already known apparatus has the disadvantage that high short-circuit currents cannot be fed into the marine vessel distribution system over a sufficiently long time period. The power semiconductor PCT/EP2009/062622 - 2 2008P20964WOIN valves in the frequency converter could otherwise be damaged or even destroyed. However, the short-circuit current must be fed in for a sufficiently long time to allow a short circuit in a marine vessel to be traced, to allow the faulty system part of the marine-vessel distribution system to be isolated from the rest of the marine-vessel distribution system. The object of the invention is therefore to provide an apparatus of the type mentioned initially and a method, by means of which even high short-circuit currents can be provided for the consumer network over a sufficiently long time period, thus allowing a short-circuit in the consumer network to be traced and to be deliberately isolated from the rest of the sound consumer network. The invention achieves this object by a switching unit, which is arranged in parallel with the frequency converter and is designed to bridge the frequency converter, and by control means, which are connected to the switching unit and are designed to operate the switching unit when it is found that a short-circuit current is flowing via the frequency converter. The invention furthermore achieves this object by a method for feeding a consumer network with the electrical power from a power supply system, wherein the power supply system is connected to the consumer network via a frequency converter and a switching unit which is designed to bridge the frequency converter, in which the current fed into the consumer network is monitored for a short-circuit criterion, with the switching unit being closed if the short-circuit criterion is fulfilled in order to bridge the frequency converter.

PCT/EP2009/062622 - 3 2008P20964WOIN According to the invention, a switching unit is provided connected in parallel to the frequency converter and allows the frequency converter to be bridged in the event of a short circuit. Control means are provided in order to identify or to find a short-circuit current which flows via the frequency converter, and are designed not only to identify the short circuit current on the basis of a predetermined short-circuit criterion but also to operate the switching unit. After operation of the switching unit, the short-circuit current also flows at least via the switching unit, which has an adequate current carrying capability for the short-circuit current. Moreover, for the purposes of the invention, the switching unit is a switching unit which closes so quickly that damage to the frequency converter as a result of the applied short-circuit current can be reliably avoided. For the purposes of the invention the frequency converter is preferably a static frequency converter. Static converters do not have any moving parts or components, but power semiconductor valves. For the purposes of the invention, the frequency converter may in principle have any desired topology. For example, the static frequency converter has a rectifier and an inverter, which are connected to one another on the DC voltage side. Rectifiers and inverters are very well known to a person skilled in the art in the field of power transmission and distribution, as a result of which there is no need to describe their design in detail at this point. In general, bridge circuits comprising so-called power semiconductor valves are used, with the power semiconductor valves being connected to a closed-loop control system and being movable by this closed-loop control system specifically from a blocking position, in which a current flow via the power semiconductor valve is interrupted, to an on position, in which current can flow via the power semiconductor valve.

PCT/EP2009/062622 - 4 2008P20964WOIN The expedient control of the power semiconductor valves by the open-loop control unit or better, closed-loop control system, allows the desired conversion. By way of example, two-stage or three-stage converters, or else so-called multi-level converters, may be used for the purposes of the invention as rectifiers and inverters, which are also both jointly referred to as converters. The frequency converter is expediently designed for high voltages, and in particular for voltages between 1 kV and 52 kV. However, frequency converters which are designed for voltages above 52 kV can also be used for the purposes of the invention. The control means are expediently connected to the frequency converter and are designed to interrupt or to otherwise influence the frequency conversion of the frequency converter. According to this expedient further development, for example, the operation of the frequency converter is also interrupted by the switching unit, for example at the time when the frequency converter is bridged. The timing of the operation of the switching unit and the pulse inhibitor are matched to one another such that there is neither any interruption in the supply in the consumer network nor are currents at a different frequency superimposed at the same time. The control means are therefore either part of the closed-loop control system for the frequency converter, or are connected to it. Expediently, the control means thus apply a pulse inhibitor to the frequency converter when the switching unit is operated. For example, if the power supply system frequency is 50 Hz, but the consumer network in contrast uses a frequency of 60 Hz during normal operation, the consumer network is prevented from being connected directly to the 50 Hz power supply system, while the frequency PCT/EP2009/062622 - 5 2008P20964WOIN converter still feeds into the 60 Hz consumer network. This would result in undesirable disadvantages. The switching unit expediently comprises controllable power semiconductors. As already mentioned above, the switching unit has to switch sufficiently quickly to bridge the frequency converter before the rising short-circuit currents can damage the sensitive power semiconductor valves in the frequency converter. Since mechanical switches generally switch too slowly for this purpose, it is expedient to consider high-speed semiconductor switches for the purposes of the invention. The semiconductor switch or, to be more precise, power semiconductor switch, is, for example, connected via the gate connection of its power semiconductor to the control means. A simple control signal can therefore be used to allow the control means to switch the power semiconductor switch quickly from its interrupter position to its on position, and thus to switch it on. By way of example, the power semiconductors in the switching unit are thyristors. However, any desired switchable power semiconductors may be considered for the purposes of the invention which can be switched to be active from their off position to their on position and which are able to carry the short-circuit current required on the consumer side without being destroyed. In other words, the switchable power semiconductors have a sufficiently high current carrying capability to carry the short-circuit currents to be expected over the necessary time period without faults and destruction. According to one preferred refinement of the apparatus according to the invention, input measurement sensors are provided which are designed to detect electrical input measurement variables on the power supply system side of the frequency converter, and output measurement sensors are provided, which are designed to detect electrical PCT/EP2009/062622 - 6 2008P20964WOIN output measurement variables on the consumer network side of the frequency converter, wherein the control means are connected to the input measurement sensors and to the output measurement sensors and delay the operation of the switching unit until a selected input measurement variable and the corresponding output measurement variable are at the same phase. According to this advantageous refinement of the invention, consideration is given to the fact that the voltages in the power supply system and in the consumer network may be at different phases. In order to prevent uncontrolled equalizing currents from flowing when the frequency converter is bridged, the control means delay the operation of the switching unit until in-phase measurement variables are present on both sides of the frequency converter. The input measurement variables and output measurement variables are expediently respectively the input voltage and the output voltage, that is to say the voltage which is respectively present in the consumer network and the voltage which is respectively present in the power supply system. Operation takes place, with the frequency converter therefore being bridged by the control means, only when the voltages in the power supply system and in the consumer network are in phase. Expediently, input connecting means are provided for connection of the apparatus to the power supply system, and possibly also output connecting means for connection of the apparatus to the consumer network. By way of example, a conventional transformer may be used as an input connecting means or output connecting means. By way of example, the short-circuit criterion is a simple threshold criterion, in other words the amplitude of the current is monitored on the consumer network or on the input power supply system side. If the amplitude of the current flowing via the frequency converter exceeds a predetermined threshold value PCT/EP2009/062622 - 7 2008P20964WOIN for a predetermined time period, the presence of a short circuit current is deduced. The amplitudes of short-circuit currents are many times greater than those of the normal rated current. By way of example, a short-circuit criterion would be satisfied if the measured measurement current exceeds a variable threshold value, which is expediently above the rated current. A further example of a short-circuit criterion according to the invention, in addition to the pure load current, that is to say in addition to the current fed into the consumer network from the frequency converter, comprises additionally monitoring the output voltage. The quotient of the measured voltage and the measured current represents an impedance. According to the example of a short-circuit criterion according to the invention, an impedance threshold value is defined for this impedance, whose undershooting is assessed as a short-circuit event or criterion. According to one expedient refinement of the method according to the invention, at least one electrical input variable is detected on the power supply system side of the frequency converter, and at least one electrical output variable is detected on the consumer network side of the frequency converter, and the phases of each input variable are compared with the phases of the corresponding output variable. Once the short-circuit criterion is satisfied, the switching unit is closed only when it is found that the input variable and the output variable are in phase, as has already been stated further above. According to a further refinement of the invention, a pulse inhibitor is applied to the frequency converter when the switching unit is operated. The pulse inhibitor 'causes the power bridging via the frequency converter to be interrupted. In other words, the frequency converter is switched off, thus reliably preventing damage to the sensitive PCT/EP2009/062622 - 8 2008P20964WOIN power semiconductors in the frequency converter. By way of example, the switching unit is operated and the pulse inhibitor set at the same time. Expediently, after bridging the frequency converter, the elapsing of a transmission time period and/or the absence of the short-circuit criterion is waited for, and only then is the pulse inhibitor of the frequency converter canceled, with the converter having been newly synchronized beforehand to the frequency previously found in the consumer network. Then, the switching unit is operated in order to cancel the bridging of the frequency converter. This allows simple recreation of the normal mode of operation of the apparatus, for example after the short circuit has been traced and disconnected. Once the bridging of the frequency converter has been canceled, the operating point before the short circuit is approached gradually again in the consumer network by closed-loop control of the frequency converter, for example by using a ramp function. By way of example, this may be the gradual production of a 60 Hz frequency in the consumer network, whose frequency briefly corresponded to the frequency of the power supply system after the bridging of the frequency converter, for example 50 Hz. The monitoring means expediently check whether energy is being produced in the consumer network, with the monitoring means preventing the operation of the switching unit if energy production is found in the consumer network. This is used to check whether the consumer network is a stand-alone network. For the purposes of this invention, stand-alone networks are distinguished by not having their own energy generator. If the consumer network is a stand-alone network, all of the short circuit power must therefore be applied by the frequency converter.

PCT/EP2009/062622 - 9 2008P20964WOIN However, if the consumer network has an energy generator, for example if a marine-vessel generator in the consumer network has not yet been switched off, the short-circuit current can be provided by the generator without this loading the frequency converter. In this case, there is no need to bridge the frequency converter. According to this advantageous refinement of the invention, a determination is accordingly made as to whether the consumer network is a stand-alone network, and bridging of the frequency converter by the control means is prevented if this is not the case. In addition to three-phase applications, the invention extends expressly to arrangements with any desired number of phases. Further expedient assignments and advantage of the invention are the subject matter of the following description of exemplary embodiments of the invention with reference to the figure of the drawing, in which: The figure schematically illustrates one exemplary embodiment of the apparatus according to the invention. The figure shows a schematic illustration of one exemplary embodiment of the apparatus 1 according to the invention. The apparatus 1 comprises a frequency converter 2 and a switching unit 3, which is designed to bridge the frequency converter 2 and is arranged in a three-phase parallel branch 4 in parallel with the frequency converter 2. For clarity reasons, the figure illustrates only one phase. The three short lateral strokes on the illustrated phase are, however, intended to indicate that the illustrated exemplary embodiment of the apparatus according to the invention is a three-phase apparatus. In principle, however, PCT/EP2009/062622 - 10 2008P20964WOIN the apparatus according to the invention may have any desired number of phases. In each phase of the parallel branch 4, the switching unit 3 has two power semiconductor valves 5 which are connected back-to-back in parallel and, for example, each have a series circuit or else only a single power semiconductor module, such as an IGBT, a GTO or a single thyristor. The frequency converter 2 has a converter which is operated as a rectifier 6, and a converter which is operated as an inverter 7, with the rectifier 6 and the inverter 7 being connected to one another via a DC voltage link 8. An open-loop control unit 9, which comprises the control means as described initially, is used for closed-loop control and protection of the converters 6, 7 and for tripping the power semiconductors 5 of the switching unit 3. The apparatus according to the invention is connected to a power supply system 12, which carries a 50 Hz AC voltage, via an input transformer 10 as an input connecting means and via an output transformer 11 as an output connecting means. In the case illustrated in the figure, the consumer network 13 is a distribution system in a relatively large marine vessel which is in harbor. In this case, the marine vessel distribution system 13 is connected to the land-based power supply system 12 via the frequency converter 2. The frequency converter is therefore required to convert the 50 Hz voltage from the power supply system 12 to the 60 Hz voltage for the marine vessel distribution system 13. For closed-loop control of the frequency conversion and of the power transmission, as well as the operation of the switching unit 3, the open-loop control unit 9 is PCT/EP2009/062622 - 11 2008P20964WOIN connected to input current sensors 14 on the power supply system side and to output current measurement sensors 15 arranged in the marine vessel distribution system 13. Furthermore, the open-loop control unit 9 is connected to input voltage measurement sensors 16 on the power supply system side and to output voltage measurement sensors 17 arranged in the marine vessel distribution system 13. If all the generators in the marine vessel have been switched off, the marine vessel distribution system is a stand-alone network. In this case, a short-circuit current has to be provided solely by the frequency converter 2. In order to prevent the frequency converter being switched off too quickly for fault identification, the open-loop control unit 9 uses the input measurement sensors 14 and the output current measurement sensors 15 to monitor the amplitude of the current flowing via the frequency converter 2. If the open-loop control unit finds that a short-circuit criterion is satisfied, for example if the measured current is less than a previously defined current threshold value implemented in the open-loop control unit 9, or an impermissible undershooting of the impedance in the consumer network 13 is found, the open-loop control unit 9 operates the switching unit 3 and applies a pulse inhibitor to the frequency converter 2. The short-circuit current now flows exclusively via the parallel branch 4. In order to avoid uncontrolled equalizing currents, the control unit 9 does not switch the switching unit 3 on, however, until the voltages which occur on both sides of the switching unit are at the same phase angle. For this purpose, the control unit 9 compares the phases on the power supply system side of the voltage Uon, which are detected by means of the input voltage network sensors 16, with the voltages Uoff on the consumer network side, which are detected by means of the output voltage measurement sensors 17. In the exemplary embodiment, a 50 Hz power supply system feeds a 60 Hz consumer network. The phases of said voltages are therefore automatically the same every 100 ms. Only when the voltages on PCT/EP2009/062622 - 11a 2008P20964WOIN the input side and output side of the frequency converter 2 are the same in this way PCT/EP2009/062622 - 12 2008P20964WOIN is the switching unit 3 operated, with the frequency converter 2 therefore being bridged, and with a pulse inhibitor at the same time being applied to the frequency converter 2. The short-circuit current then flows exclusively via the switching unit 3, thus preventing damage to the sensitive semiconductor components in the frequency converter 2. The consumer network 13 adopts the frequency of the power supply system 12 once the frequency converter has been bridged. After a short-circuit time period has elapsed, during which the protective devices, which are not illustrated in the figure, in the consumer network 13 in the marine vessel trace and disconnect the short circuit, the open-loop control unit 9 identifies the absence of the short-circuit criterion, by evaluation of the signals from the connected sensors 15 and 17. The open-loop control unit 9 synchronizes the inverter 7 to the frequency in the consumer network 13, and cancels the pulse inhibitor on the frequency converter 2. The frequency converter 2 then feeds the consumer network 13 in synchronism with the switching unit 3. Only after this has occurred is the switching unit 3 switched to its interrupt position, as a result of which power is now supplied exclusively via the frequency converter 2. Finally, after the switching unit 3 has been switched off, the closed-loop control for the inverter 7 ensures that a 60 Hz AC voltage is gradually restored in the consumer network 13, with the aid of a so-called ramp function.

Claims

1. An apparatus (1) for feeding a consumer network (13) with electrical power from a power supply system (12), wherein the apparatus (1) has a frequency converter (2) which can be connected on the one hand to the power supply system (12) and on the other hand to the consumer network (13), characterized by a switching unit (3), which is arranged in parallel with the frequency converter (2) and is designed to bridge the frequency converter (2), and by control means (9), which are connected to the switching unit (3) and are designed to operate the switching unit (2) when it is found that a short-circuit current is flowing via the frequency converter (2).

2. The apparatus (1) as claimed in claim 1, characterized in that the control means (9) are connected to the frequency converter (2) and are designed to interrupt or to otherwise influence the frequency conversion of the frequency converter (2).

3. The apparatus (1) as claimed in claim 1 or 2, characterized in that the switching unit (3) comprises controllable power semiconductors (5).

4. The apparatus (1) as claimed in one of the preceding claims, characterized by - input measurement sensors (14, 16), which are designed to detect electrical input measurement variables (Iin, Uin) on the power supply system side of the frequency converter (2), and - output measurement sensors (15, 17), which are designed to detect PCT/EP2009/062622 - 14 2008P20964WOIN electrical output measurement variables (Iout, Uout) on the consumer network side of the frequency converter (2), - wherein the control means (9) are connected to the input measurement sensors (14, 16) and to the output measurement sensors (15, 17) and delay the operation of the switching unit (3) until a selected input measurement variable (Uin) and the corresponding output measurement variable (Uout) are at the same phase angle.

5. The apparatus (1) as claimed in one of the preceding claims, characterized by input connecting means (10) for connection of the apparatus to the power supply system and/or output connecting means (11) for connection of the apparatus to the consumer network.

6. The apparatus (1) as claimed in one of the preceding claims, characterized in that the frequency converter (2) has converters (6, 7) which are connected to one another on the DC voltage side, with each converter (6, 7) having controllable power semiconductor valves.

7. A method for feeding a consumer network (13) with the electrical power from a power supply system (12), wherein the power supply system (12) is connected to the consumer network (13) via a frequency converter (2) and a switching unit (3) which is designed to bridge the frequency converter (2), in which the current fed into the consumer network (13) is monitored for a short-circuit criterion, with the switching unit (3) being closed if the short-circuit criterion is fulfilled in order to bridge the frequency converter (2).

8. The method as claimed in claim 7, characterized in that PCT/EP2009/062622 - 15 2008P20964WOIN - at least one electrical input variable Uin is detected on the power supply system side of the frequency converter (2), and at least one electrical output variable Uou 1 t is detected on the consumer network side of the frequency converter (2), - the phases of the input variable Uin are compared with the phase of the output variable Uou 1 t, and - once the short-circuit criterion is satisfied, the switching unit (3) is closed only when it is found that the input variable Uin and the output variable Uut are in phase.

9. The method as claimed in claim 7 or 8, characterized in that after operation of the switching unit (3), the frequency converter (2) has a pulse inhibitor applied to it.

10. The method as claimed in one of the preceding claims 9, characterized in that - after bridging the frequency converter (2), the absence of the short-circuit criterion is waited for, - the frequency converter (7) is synchronized to the frequency of the consumer network (13), - only then is the pulse inhibitor of the frequency converter (2) canceled, and - then the switching unit (3) is operated in order to cancel the bridging of the frequency converter (2).

11. The method as claimed in one of claims 8 to 11, characterized in that monitoring means check whether energy is being produced in the consumer network (13), with the monitoring means preventing the operation of the switching unit (3) if energy production is found in the consumer network (13).