The invention relates to a local power supply installation according to the precharacterizing clause of Claim 1 . The invention also relates to an operating method for operating a local power supply installation.

Such a local power supply installation is used for a standby power supply, also called backup power supply, for an electrical installation, for example in a dwelling, when a supply from a power supply network to which the electrical installation is connected is interrupted, for example as a result of a failure in the power supply network. The local power supply installation monitors the power supply network and, in the event of a network failure, switches to a so-called stand-alone or island network operation. In this case, the local power supply installation disconnects the connection to the power supply network and switches on a standby power supply. The standby power supply may be fed from a storage unit, for example a rechargeable battery with appropriate power reserves, and thus forms a local stand-alone network. This standby power supply may be provided, for example, by an inverter which converts a DC voltage from a storage unit to an AC voltage. During stand-alone network operation, the power supply network is continuously monitored by the local power supply installation. As soon as the power supply network is available again, the local power supply installation switches back from stand-alone network operation to normal network operation again. In this case, the storage unit is then recharged.

The document EP 1 965 483 A1 describes such a local power supply installation. In this case, a local power generating unit, for example a photovoltaic installation, is extended by an inverter with a storage unit. The inverter is designed to monitor the power supply network, to disconnect the local power supply installation from the power supply network in the event of failure of the power supply network, and to form a local network autonomously. Various local power generating units can then be used in a modular fashion to feed power into this local network.

The power supply network is usually a public three-phase power supply network, although it may also be a regional power supply network. Such a regional power supply network could, for example, be fed from a continuously running electrictiy generator, wherein this generator does not need to be located at the same point as the electrical installation. The local electrical installations, for example in a dwelling or an industrial installation, are usually connected to a plurality of phases, in particular to all three phases, of the power supply network, in order to distribute the load caused by the consumers uniformly between the phases.

Usually, local power supply installations are single-phase installations, as a result of which, in the event of a network failure, only some loads, in particular the most important loads, may be supplied with power. Alternatively, a dedicated standby power supply is required for each phase.

There is a need for local power supply installations which do not need to have three-phase energy sources, such as diesel generators or a plurality of inverters, but are nevertheless able to supply power to the loads on all the phases in a local network in the event of failure of the power supply network.

One object of the present invention is therefore to provide an improved local power supply installation. A further object is to provide an operating method for a local power supply installation.

This object is achieved by a local power supply installation having the features of Claim 1 . It is also achieved by an operating method having the features of Claim 6. Developments and advantageous refinements are specified in the dependent claims.

According to a first aspect of the invention, the local power supply installation comprises the following: a multiphase transmission line for transmission of electrical power from a power supply network to a load arrangement, a disconnecting device, configured to separate the transmission line into two mutually electrically isolated sections when the disconnecting device is operated, a feeding section and an outgoing section; a network monitoring device connected to the feeding section of the transmission line and configured for monitoring a status of the power supply network; and a network former connected to the outgoing section of the transmission line via at least one phase. The local power supply installation is characterized by at least one connecting device connected to the outgoing section of the transmission line and configured to connect at least one phase in the outgoing section of the transmission line to another phase in the outgoing section of the transmission line to form a common phase.

The connections of the sections of the transmission line and of further functional units in the following designate electrically conductive connections. The term "disconnecting device" designates that both "normally-open" as well as "normally-closed" switches may be used. An electrical power supply network having at least two, three or more phases and a neutral conductor is referred to in the following text as a multiphase network, while a single-phase network means a network with one phase and one neutral conductor. A network former means a device which is designed to form a local power supply network by being able to predetermine a network voltage, a frequency and phase angle. Such a local network, which is isolated from a comprehensive power supply network, is also referred to as a stand-alone network and its operation is referred to as stand-alone network operation. The electrical energy which is required for this purpose is taken, for example, from a storage (battery), or from a generator which is driven by an internal combustion engine, by wind/water power, or in some other way. The network former may comprise a battery and an inverter. A monitoring device is used for monitoring an electrical network, with voltage, frequency and phase angle being determined, and with an existing status being derived therefrom. If all monitored parameters correspond to their rated values, within a predetermined tolerance range, the network status is referred to as being in the normal status. In the event of discrepancies therefrom, a fault status is detected, for example a network failure.

In the fault status of the power supply network, all the phases of the electrical installation are connected together to form a common phase on the load side, and these phases are also referred to in the following text as outgoing phases. Power from a network former is supplied to this common phase. In one possible embodiment this network formercomprises a single- phase inverter with a DC voltage source. This connection of the outgoing phases is cancelled, i.e. disconnected again, before switching back to network operation when the power supply network returns to the normal status.

The loads are usually single-phase appliances which are distributed between the outgoing phases, in order to achieve a uniform loading on the phases of an electrical installation. The connection of the outgoing phases in the event of a fault status in the power supply network results in all the loads being supplied, in contrast to an emergency power supply on only one phase. There is therefore no need for an additional multiphase generator for emergency operation.

In one embodiment of the invention, a control device is provided for controlling the connecting device, the disconnecting device and the network former. The control device can for example be connected for communication purposes to the network monitoring device and can use the output signals from this network monitoring device to control the connected switches and the connecting device in an appropriate time sequence.

In one advantageous embodiment of the invention, wherein the network former has a single-phase inverter for each outgoing phase, in the event of a network failure being detected, first of all all phases of the single-phase inverter are synchronized to one phase. That is to say the phase shift between the phases that usually exists (for example 120° in the case of three phases, 180° in the case of two phases) is eliminated before the outgoing phases are being connected. Before returning to network operation, the outgoing phases are firstly disconnected from each other again, followed by a process of the individual single-phase inverters being synchronized back to the previously existing phase shift, before being connected to the power supply network.

In this case, it is particularly advantageous that, when the outgoing phases are coupled during stand-alone network operation, the performance and in particular the overload capability of all the connected inverters are jointly available for operation of the loads, since the coupled outgoing phases are connected in parallel. Vice versa - depending on the power demand - it is possible to connect or disconnect inverters, for example, to save energy during low-load times (for example at night).

In a further embodiment, a local power generating unit, in particular a photovoltaic generator in connection with a photovoltaic inverter, is provided for feeding power into the transmission line. The local power generating unit can be connected to the feeding section of the transmission line or to the outgoing section of the transmission line. A local power generating unit can also be fed by other energy sources, such as wind or water power, fuel cells or internal combustion engines.

In this case, it is advantageously possible for the local power generating unit to be used both for feeding into the power supply network during network operation and for feeding into the outgoing phases in the event of a fault status of the power supply network.

The transmission line may be of three-phase design and the connecting device may be configured to connect all three phases in the outgoing section to form a common phase.

The network former may be of multiphase design, and the local power generating unit may be connected to one phase of the transmission line.

The local power supply installation may have a control device which is designed to operate the disconnecting device, the connecting device and the network former in order to form a stand-alone network in the outgoing section of the transmission line in a situation in which the network monitoring device detects a fault status in the power supply network. An operating method, for example for a local power supply installation as described above, which is connected on the one hand to a multiphase power supply network and on the other hand to a load arrangement with loads, has the following steps:

The power supply network is monitored and its status is determined. If a fault status is determined in the power supply network, the load arrangement is disconnected from the power supply network. In order to supply at least some of the loads, at least two phases of the load arrangement are connected in this way the loads are supplied from a network former via the phases which have been connected.

The status of the power supply network can also be monitored in order to disconnect the at least two phases of the load arrangement from each other after the power supply network has returned to the normal status, that is to say after the end of the fault status, and to reconnect the load arrangement to the power supply network, in order to supply the loads. In this case, the network former may be switched on or off as needed referring to the status of the power supply network.

In one particularly preferred embodiment of the operating method, in the fault status, all the phases of the load arrangement are connected together in order to supply all the loads.

In one embodiment, the power supply installation has a multiphase network former, which may comprise one inverter or a plurality of single-phase inverters, which are coupled to one another to provide a multiphase network with a phase shift between the phases. Referring to the operating method in this case, this phase shift is eliminated, i.e. the phases are synchronized, before the phases are connected. This means that, once the fault status has been detected in the power supply network, the phase angles are synchronized at such outputs of the network former, whose associated phases are to be connected.

In a further embodiment of the operating method, after the disconnection of the at least two phases of the load arrangement, the phase angle at the outputs of the network former is first of all synchronized with corresponding phase angles in the power supply network. After this the load arrangement is reconnected to the power supply network, in order to ensure an uninterrupted transition between the stand-alone network supply and the supply from the power supply installation.

In comparison to the prior art, the local power supply installation according to the invention and the operating method according to the invention now make it possible to carry out an automatic transition between multiphase network operation and stand-alone network operation, which in the simplest case is fed from only one phase, in a simple manner, without any changes in the installation being required for the single-phase loads.

The invention will be explained in more detail in the following text with reference to exemplary embodiments and with the aid of figures, in which:

Figure 1 shows a general block diagram of a local power supply installation; Figure 1 a shows a block diagram of one embodiment of a network former for a local power supply installation as shown in Figure 1 ;

Figure 2 shows a block diagram of one exemplary embodiment of the local power supply installation;

Figure 3 shows a circuit diagram of the exemplary embodiment of the local power supply installation shown in Figure 2;

Figure 4 shows a circuit diagram of a further variant of the exemplary embodiment shown in Figure 2; and

Figure 5 shows a flowchart of a method.

Figure 1 illustrates a general block diagram of a local power supply installation 1 according to the invention.

The local power supply installation 1 has a multiphase transmission line 4 which can be subdivided by a disconnecting device 5, for example a mechanical switch, into a feeding section 6 and an outgoing section 7, for example when the disconnecting device 5 is operated. The sections 6 and

7 which have been subdivided in this way, they are electrically isolated and disconnected from one another. The transmission line 4 is intended to have three phases in this example.

The feeding section 6 of the transmission line 4 is electrically conductively connected to a power supply network 2, for example a public power supply network. The outgoing section 7 of the transmission line 4 is connected to a load arrangement 3. The individual loads are in general connected in a distributed manner to the multiphase transmission line 4, such that all the phases are loaded as uniformly as possible. A network monitoring device 8 is connected to the feeding section 6 of the transmission line 4 and is provided for monitoring a status of the power supply network 2. This status may be normal operation or a fault status. In the fault status, the power supply network 2 has, for example, failed or does not comply with its expectancy values, for example in voltage, frequency.

A network former 9 is connected on at least one phase to the outgoing section 7 of the transmission line 4. In addition, the outgoing section 7 of the transmission line 4 is connected to at least one connecting device 10. The connecting device 10 is designed to connect at least one phase to one other phase of the outgoing section 7 to form a common phase in the outgoing section 7. Figure 1 a shows one example of a network former 9. This network former 9 has a rechargeable battery 1 1 which is connected to an inverter 12. The inverter 12 uses the DC voltage from the battery 1 1 at its input to produce an AC voltage at its AC voltage output. The network former 9 may feed into one phase of the multiphase transmission line 4 or, as a multiphase inverter, may feed into a plurality of phases, or may consist of a plurality of possibly coupled inverters 12 with a common or respectively separate battery, in order to allow power to be supplied to all the phases of the transmission line 4. The network former 9 may also be a generator, which is driven by various power machines, for example an internal combustion engine, a fluid turbine, a wind power drive or the like.

The inverter 12 is a unit which is able to operate from the DC supply forming a network, that is to say to produce an AC voltage and thus to form a supply network and to supply the load arrangement. This is generally a bidirectional battery inverter, which is additionally also able to charge the batteries from the AC voltage side. In one embodiment, the local power supply installation 1 according to the invention has at least one separate local power generating unit (not shown here) which can be connected on the AC voltage side at any point to the transmission line 4 shown in Figure 1 .

The operation of the local power supply installation will be explained with reference to Figure 1 .

The power supply network 2 is monitored by the monitoring device 8. If a fault status is found, the disconnecting device 5 is operated, as a result of which the transmission line 4 is subdivided into the feeding section 6 and the outgoing section 7, that is to say the feeding section 6 and the outgoing section 7 are then electrically isolated from one another. The network former 9 is then activated in order to supply energy to the outgoing section 7, in order to supply the load arrangement 3. In addition, at least one phase is connected to another phase of the outgoing section 7 to form a common phase, by activation of the connecting device 10. This makes it possible to supply all the loads which are connected to the different, now connected phases. The power supply network 2 is further monitored, and when the normal status has returned and has been detected, the phases of the outgoing section 7 are disconnected from each other by deactivation of the connecting device 10. The disconnecting device 5 is then deactivated, as a result of which the sections 6 and 7 of the transmission line 4 are connected to one another again. The bidirectional inverter for the network former 9 can recharge the batteries. The load arrangement 3 can now be supplied from the power supply network 2 again.

Figure 2 shows a block diagram of a further exemplary embodiment of the local power supply installation 1 according to the invention.

In this case, the local power supply installation 1 is provided with a control device 15, which is functionally connected to the network monitoring device 8, to the disconnecting device 5, to the network former 9 and to the connecting device 10. This is in each case indicated by double-headed arrows with the aim of illustrating that the control device 15 not only controls the respective functional units, but can also receive information from them. By way of example, the control device 15 may also be integrated in the network former 9, the connecting device 10 or the network monitoring device 8.

Figure 3 shows a circuit diagram of the exemplary embodiment of the local power supply installation 1 according to the invention as shown in Figure 2.

The local power supply installation 1 is used to ensure power is supplied to at least one load arrangement 3 having at least one load V1 , V2, V3, after failure of the power supply network 2.

The local power supply installation 1 comprises at least one network former 9 with an inverter 12 and a battery 1 1 , a network monitoring device 8, a control device 15, a connecting device 10 and a disconnecting device 5. On the AC voltage side, the inverter 12 is, for example, connected to the outgoing phase L1 ' and to the outgoing neutral conductor N'.

The network monitoring device 8 is connected to the feed phases L1 , L2 and L3 and to the feed neutral conductor N of the power supply network 2, and measures the network voltage between these feed phases L1 , L2 and L3, and with respect to the feed neutral conductor N. Furthermore, the network monitoring device 8 determines the instantaneous phase angle of the feed phases L1 , L2 and L3. The phase angles and network voltage are transmitted to the control device 15 continuously or on request by the control device 15.

In this case, the disconnecting device 5 is a contactor having four normally- open contacts, to which the feed phases L1 , L2, L3 and the feed neutral conductor N, and the outgoing phases L1 ', L2', L3' and the outgoing neutral conductor N', are connected.

By way of example the at least one load arrangement 3 consists of single- phase loads V1 , V2, V3 which are each connected between an outgoing phase L1 ', L2', L3' and the outgoing neutral conductor N'. For example, if this is a building installation, in which there are, of course, a plurality of single-phase loads, then these are distributed between the outgoing phases L1 ', L2', L3' such that the load is distributed as uniformly as possible, that is to say the outgoing phases L1 ', L2', L3' are uniformly loaded.

In this case, the connecting device 10 is in the form of a contactor. In this case, a first contact set is used for connection of the outgoing phases L1 ' and L2'. A second contact set connects the outgoing phases L1 ' and L3'. The connecting device 10 is in this case activated by switching on a contactor for making the contact sets. The control inputs of the contactor in the connecting device 10 and the disconnecting device 5 are connected to the control device 15, and are controlled by it.

Figure 4 shows a circuit diagram of a further variant of the exemplary embodiment shown in Figure 2. In this variant, the network former 9 is of three-phase design, with three single-phase inverters 12 each producing one phase with a phase shift between them, and being connected to a common battery 1 1 . Furthermore, three local power generating units 16 are each also provided for one phase. Such local power generating units 16 may, for example, consist of inverters with a further DC voltage source at their input, for example a photovoltaic installation. These inverters are designed for feeding into an existing network, that is to say only when this network is present and is within the selected limits is the feed inverter connected to the network, feeding power into it. It is also possible, of course, to provide only one such local power generating unit 16 for feeding into only one phase.

In this case, the switching members transfer switch 18, feed enable switch 19 and reference enable switch 20 are used as disconnecting devices. These switching means are each designed for three phases and a neutral conductor. The connecting device 10 may be provided by a dedicated contactor, as shown in Figure 3, or uses a common switching member, for example contact sets on the transfer switch 18.

In a first transitional status from the normal status of the power supply network 2 to the fault status, once the feed enable switch 19 and the reference enable switch 20 have been opened, the second and third outgoing phases L2', L3' are synchronized to the first outgoing phase L1 ' by the control device 15 synchronizing the phases of the associated inverters 12 to the outgoing phase L1 '. In this first transitional status, there is no power failure for the load arrangement 3 since each outgoing phase L1 ', L2', L3' is supplied by a network former 9. The synchronization of the outgoing phases L2', L3' which is carried out in this case cannot be perceived by the loads V1 , V2, V3 connected thereto if this is done in a fixed time period which must not be too short and is in the region of several 100 ms. When the phase angle of the outgoing phases L1 ', L2', L3' is the same, the connecting device 10 is activated in the manner described above. In the embodiment in which a common contactor (not shown) is used for the transfer switch 18 and the connecting device 10, the local power generating unit 16 is connected, and the phases are connected at the same time.

In this variant with three single-phase inverters as network formers 9 and in the local power generating unit 16, this results in the particular advantage that the overload capability of all the connected inverters 12 is jointly available for the operation of the loads V1 , V2, V3, since, when the outgoing phases L1 ', L2', L3' are connected, the loads V1 , V2, V3 are connected in parallel by means of the connecting device 10.

In this case, the inverters 12 can be connected and/or disconnected individually as required in order, for example, to reduce losses and to save energy during low-load times.

In a second transitional status from the fault status of the power supply network 2 to the normal status, the connecting device 10 is first of all deactivated, as a result of which the inverters 12 are no longer connected in parallel and must be individually synchronized back to the feed phases L1 , L2, L3 of the power supply network 2. Measured values from the network monitoring device 8 are used for this purpose. After synchronization back, the feed enable switch 19 and the reference enable switch 20 are closed again. In the case of the variant of the invention shown in Figure 4, a three-phase local power generating unit 16 in the normal case feeds into the feeding section 6 via the feed enable switch 19. In the event of a fault, the feed into the local stand-alone network is provided via a transfer switch 18 after successful disconnection of the local stand-alone network from the power supply network 2, and the described synchronization and connection of the outgoing phases 7.

Figure 5 shows a flowchart of a method according to the invention for operation of a local power supply installation 1 .

After a start in a step S1 , the network monitoring device 8 monitors the power supply network 2 for the network voltage and the phase angle in the normal status. This continues until a fault status occurs, for example a network failure (j).

Then, in a step S2, the disconnecting device 5 and the inverter 12 in the network former 9 are activated in a first transitional status. In the case of the variant shown in Figure 4, that is to say when there are at least two single-phase inverters 12, each of which is connected to one outgoing phase L1 ', L2', L3', all the inverters 12 are synchronized to one phase.

In a further step S3, the connecting device 10 is activated for connection of the outgoing phases L1 ', L2', L3'.

In step S4, the power supply network 2 is monitored further by means of the network monitoring device 8.

As soon as it is found that this network has returned to the normal status (j), the phase connection is cancelled in a second transitional status in a step S5, by deactivating the connecting device 10.

In a step S6, synchronization of the inverter or inverters 12 back to the values of the power supply network 2 then takes place and, finally, the deactivation, that is to say closing, of the disconnecting device 5. A jump is then made back to step S1 . The invention is not restricted to the exemplary embodiments described above, but can be modified within the scope of the attached claims.

For example, the connecting device 10 may also have manual switching elements added to it (not illustrated), such that coupling is prevented for individual phases or for all of the phases, or a control process is carried out by the control unit 10 such that it is permanently open, thus preventing a phase connection. It is also feasible when a local power generating unit 16 is connected, to use network monitoring of the local power generating unit 16 as the network monitoring device 8.

The network monitoring device 8 and the control device 15 may both be integrated in a local power generating unit 16 and in the network former 9.

List of reference symbols

1 Local power supply installation

2 Power supply network

3 Load arrangement

4 Transmission line

5 Disconnecting device

6 Feeding section

7 Outgoing section

8 Network monitoring device

9 Network former

10 Connecting device

1 1 Battery

12 Inverter

15 Control device

16 Local power generating unit

18 Transfer switch

19 Feed enable switch

20 Reference enable switch

L1 ...3 Feed phases

L1 '...3' Outgoing phases

N Feed neutral conductor

N' Outgoing neutral conductor

S1 ... 6 Method step

V1 ... 3 Load