Switching unit and backup system for a household network

Abstract

The invention describes a switching unit (1) for changing between network operation and island operation of a three-phase household network, having a first and a second positively driven relay (R1, R2), each having a control coil (A1, A2) and a number of normally open contacts (R1.1, R2.1, R1.4, R2.4) and a number of normally closed contacts (R1.2, R2.2, R1.3, R2.3). The terminals of the control coil (A2) of the second relay (R2) are connected in parallel with terminals of the control coil (A1) of the first relay (R1) via a first normally open contact (R1.1) of the first relay (R1). The switching unit (1) is provided for input-side connection to one of the phase terminals of a network terminal (4) and for output-side connection to a phase terminal of a household terminal (5). In a quiescent state, the second relay (R2) connects two of the phase terminals between the network terminal (4) and the household terminal (5) and, in a controlled state, connects the phase terminals of the household terminal (5) to one another. The invention also describes a backup system (10) having such a switching unit (1).

Description

[0001] Switching unit and backup system for a household network

[0002] Description

[0003] The invention relates to a switching unit between mains operation and island operation of a household network and a backup system for a household network with such a switching unit.

[0004] The constant availability of electrical energy to supply a household has become a natural part of everyday life. It is all the more disruptive or even dangerous when such a supply is interrupted due to a grid failure. For this reason, so-called backup systems exist that, in this case, ensure the household's supply from an energy storage device, such as a battery and / or a DC generator, particularly a solar generator. In the event of a grid failure, the household must first be disconnected from the grid before an island grid can be set up, for example using a voltage-regulating inverter. To ensure complete supply to all loads, it is common practice to use a single-phase inverter and connect the various phases of the household grid to one another.

[0005] For example, patent DE 10 2011 000 394 A1 describes a backup system in which, in the event of a grid failure, a control device uses a first relay to disconnect all phases of the grid from a consumer device, connects the phases of the consumer device with a second relay, and creates an island network with a network former. The first relay must be designed as a closed-circuit relay, and its control coil must therefore be permanently energized during grid operation to prevent the consumer device from being reconnected during island operation due to a fault that unintentionally interrupts the power supply to the first relay. The energy consumption of such a closed-circuit relay causes considerable additional costs for a backup system, even if it is not needed or almost never needed.

[0006] Furthermore, document DE 102012 023 424 A1 discloses a control device for a power distribution system in which separately controllable first and second electromechanical disconnectors are locked against simultaneous activation. In mains operation, the first disconnector connects a household to the grid, and in isolated operation, the second disconnector connects an output of a voltage-regulating inverter to the household. In isolated operation, the inverter is further disconnected from the grid via a third disconnector. The locking can be implemented by a mechanically interlocking coupling between the relays. In mains operation, the first disconnector is therefore activated.

[0007] Accordingly, it is the object of this invention to provide a switching unit or a backup system that enables a fault-safe switching between mains operation and island operation of a household network and has low energy consumption during mains operation.

[0008] This problem is solved by a switching unit having the features of independent claim 1, as well as a backup system with such a switching unit. Preferred embodiments of the backup system are the subject of the dependent claims.

[0009] A switching unit according to the invention for switching between mains operation and island operation of a three-phase household network comprises a first positively driven relay and a second positively driven relay, each having a control coil and a number of normally open contacts and a number of normally closed contacts. Terminals of the control coil of one of the two relays are connected in parallel with terminals of the control coil of the other relay via a first normally open contact of the other relay.The switching device has an input side with input connections, each of which is provided for connection to one of the phase connections of a mains connection, and an output side with output connections, each of which is provided for connection to a phase connection of a household connection, wherein a first output connection is connected to a first input connection via a first break contact of the first relay, and to a second output connection via a first connection path having a first make contact of the second relay, and to a third output connection via a first connection path having a second make contact of the second relay. Furthermore, the second output connection is connected to a second input connection via a first break contact, and the third output connection is connected to a third input connection via a second break contact.

[0010] By designing the first and second relays as positively driven relays, it can be ensured that interconnecting the phases of the household network and connecting the household network to the external network are mutually exclusive. This is because, in a positively driven relay, the switching contacts are mechanically rigidly connected to one another and can only be moved together. Due to their design, even with welded contacts, it is impossible for a normally closed contact and a normally open contact of the relay to be closed simultaneously. As a result, it is permissible to not energize the relays during mains operation, thus connecting the phases of the household network to the external network via normally closed contacts.

[0011] In a first embodiment of the invention, the terminals of the control coil of the second relay are connected in parallel with the terminals of the control coil of the first relay via a first normally open contact of the first relay. In this embodiment, the first relay switches first, and switching of the second relay requires correct switching of the first relay.

[0012] In a second embodiment of the invention, the terminals of the control coil of the first relay are connected in parallel with the terminals of the control coil of the second relay via a first normally open contact of the second relay. In this embodiment, the second relay switches first, and switching of the first relay requires correct switching of the second relay. Advantageously, the first connection path is additionally routed via a first normally open contact of the first relay, and the second connection path is additionally routed via a third normally open contact of the first relay. Because both connection paths each extend via normally open contacts of both relays, current can only flow via the connection paths after both relays have switched correctly. The output terminals are therefore only connected together if both relays have switched correctly.

[0013] In both embodiments, relays are preferably selected in which the switching time between the loss of control of the relay and the first opening of a normally open contact of the relay is greater than the time interval between two consecutive zero crossings of the connected grid, greater than 10 ms for a 50 Hz grid. The switching time is particularly preferably between twice and ten times this time interval. This ensures that when switching back from island operation to grid operation, sufficient time elapses to allow the voltage of the household grid to drop below a desired residual voltage value before connecting to the grid, and thus to avoid a load peak when reconnecting the household grid to the connected grid.

[0014] In a further aspect of the invention, a backup system comprises the switching unit described above and a grid connection with phase connections, each connected to one of the input connections of the switching unit, wherein the grid connection provides a grid monitoring signal indicating the availability of a connected grid. Furthermore, the backup system comprises a household connection with phase connections, each connected to one of the output connections of the switching unit. A single-phase inverter with a controller is connected with its AC output to the first output connection of the switching unit via an isolating relay. The controller is configured to receive the grid monitoring signal and is connected to connections of the control coil of the first relay and is configured to control the control coil when the grid monitoring signal indicates a grid failure.

[0015] In a preferred embodiment, the controller is connected to a second normally open contact of the first relay in order to monitor the switching state of the first relay. This ensures that the inverter is only activated if the first relay switches successfully. A failure of the first relay is thus detected and a malfunction of the backup system is avoided. It should also be noted at this point that if the first relay fails, the second relay will not switch at all, since its control coil is connected to the control coil of the first relay via a normally open contact - which does not close if the first relay fails.

[0016] In a further advantageous embodiment of the invention, the controller is configured to activate the control coil of the first relay with a first time delay after the grid monitoring signal has indicated a grid failure, and to terminate the activation of the control coil of the first relay with a second time delay after the grid monitoring signal has indicated grid return. As a result, a brief grid failure, for example, lasting one or a few seconds, does not lead to an undesired activation of the backup system, and a brief grid return correspondingly does not lead to an undesired deactivation.

[0017] Preferably, the controller is further configured to close the isolation relay, thus creating an island grid in the household by the inverter, only after a third time delay after the activation of the control coil of the first relay after the mains failure. This supports the controlled creation of an island grid in the household, since the third time delay enables the reduction of remaining voltages in the household grid.

[0018] When the grid returns, the controller is advantageously configured to first open the isolation relay before terminating the activation of the control coil of the first relay, i.e., before reconnecting the household grid phases to the external grid phases, thus ending the islanding. The successful disconnection of the inverter from the household grid can, of course, also be monitored by the inverter and made a prerequisite for reconnecting the household grid phases to the external grid phases.

[0019] In the following, the invention is illustrated with the aid of figures, of which Fig. 1 shows a first embodiment according to the invention of a switching unit within a backup system for a household network,

[0020] Fig. 2 shows a further embodiment of a switching unit according to the invention within a backup system for a household network, and

[0021] Fig. 3 shows a flow chart for a method according to the invention for switching between mains operation and island operation of a household network.

[0022] Fig. 1 shows a first embodiment of a backup system 10 according to the invention with a switching unit 1, which switchably connects input connections R, S, T, intended for connection to phase connections of a three-phase power supply network, with output connections L1, L2, L3, intended for connection to phase connections of a household network. The phase connections are provided in a network connection 4. The network connection 4 further contains a network monitoring unit, which indicates the status of the power supply network by means of a network monitoring signal 6. This function can be fulfilled, for example, by an energy meter, but can also be implemented by a separate monitoring circuit. The household consumers are in turn distributed to the individual phase connections of the household network via a household connection 5.

[0023] In mains operation, the input terminals R, S, T of the three-phase power supply network are each electrically connected to one of the output terminals L1, L2, L3 via a first relay R1 and a second relay R2 via normally closed contacts R1.2, R2.2, R2.3, so that in mains operation no control of the control coils A1, A2 of the two relays R1, R2 is required and thus no corresponding power loss occurs.

[0024] To control the first relay R1, the terminals of the first control coil A1 are connected to a signal output of a controller 3 of a voltage-regulating inverter 2. The control coil A2 of the second relay R2 is connected in parallel with the control coil A1 of the first relay R1 via a first normally open contact R1.1 of the first relay R1. In this way, the switching state of the first relay R1 and the second relay R2 can be determined jointly by the controller 3 of the inverter 2, with the second relay R2 only being controlled when the first relay R1 switches correctly.

[0025] The second relay R2 is wired in such a way that in the idle state it connects two of the input terminals S, T with assigned output terminals L2, L3 and in the activated state it connects the assigned output terminals L2, L3 d with the remaining output terminal L1. For this purpose, two normally closed contacts R2.2, R2.3 are connected on one side to one of the input terminals S, T and on the other side to the assigned output terminals L2, L3. Furthermore, the output terminals L2, L3 are each connected to the remaining output terminal L1 via a normally open contact R2.1, R2.4. Because the second relay R2 is designed as a positively driven relay, it is impossible for one of the normally closed contacts R2.2, R2.3 and one of the normally open contacts R2.1, R2.4 to be closed at the same time.

[0026] The voltage-regulating inverter 2 is also connected to the output terminal L1 via an isolating relay 7. This enables the inverter 2, via its controller 3, to trigger the switching unit 1 via the signal output of the controller 3 upon receipt of a grid monitoring signal 6 indicating a grid failure, in order to disconnect the household grid from the power grid and connect all phases of the household grid to a common phase. The inverter 2 can then form a single-phase island grid, preferably initially with the isolating relay 7 open, and maintain this after the isolating relay 7 closes to supply the consumers of the household grid.

[0027] The first relay R1 has an optional normally open contact R1.4, which is connected to a signal input of the controller 3 and via which the controller 3 can verify the switching state of the first relay R1. In this way, the correct switching function of the first relay R1 can be monitored. This optional relay contact can also be designed as a normally closed contact and can also be located in the second relay R2 instead of the first relay R1.

[0028] Figure 1 shows an unused normally closed contact R1.3 in the first relay R1. This is not absolutely necessary, but rather demonstrates the fact that the two relays R1 and R2 can be constructed identically, which is often advantageous for cost reasons. Of course, different relay designs, including those with more or fewer unused contacts, are also conceivable. It is also conceivable to route the neutral conductor N, which is permanently connected between the household mains and the supply mains in Figure 1, via the normally closed contact R1.3 instead.

[0029] The switching unit according to Fig. 2 represents a further embodiment of the invention, which temporarily prevents possible short circuits between mains phases in the case of unfavorably short intervals between the switching times of the switching contacts of the positively driven relays, particularly when the time interval between the opening of a normally closed contact and the closing of a normally open contact is shorter than the time interval between two zero crossings of the mains voltage. In this embodiment, both the first relay R1 and the second relay R2 have an additional third normally open contact R1.5, R2.5, the use of which is explained below.

[0030] In this embodiment, the terminals of the second control coil A2 for controlling the second relay R2 are also connected to the signal output of the controller 3 of the voltage-regulating inverter 2. The control coil A1 of the first relay R1 is now connected in parallel with the control coil A2 of the second relay R2 via the third normally open contact R2.5 of the second relay R2, which is additional compared to the first embodiment. In this way, the switching state of the first relay R1 and the second relay R2 can be determined jointly by the controller 3 of the inverter 2, with the first relay R1 being controlled if and only if the second relay R2 has already switched correctly. This results in a delay between the switching times of the second relay R2, which switches earlier, and the switching times of the first relay R1, which switches later.It is preferred that such positively driven relays are selected in which a delay between the activation of the control coil and the resulting closing of the normally open contacts is ensured that is longer than the time between two consecutive voltage zero crossings of the supply network, 10 ms for a 50 Hz network.

[0031] Furthermore, in this embodiment the electrical connections between the output terminals L2 and L3 and the output terminal L1, to which the inverter 2 is connected, are now made up of a series connection of two normally open contacts each, which are arranged on different ones of the two relays R1, R2. The electrical connection path between the output terminals L2 and L1 now extends via the normally open contacts R1.5 and R2.1, and the electrical connection path between the output terminals L3 and L1 is made via the normally open contacts R1.1 and R2.4. The above-described selection of the delay between the activation of the control coil and the resulting closing of the normally open contacts ensures that when the household mains is disconnected from the supply network, the output terminals L2 and L3 are the first to be disconnected from the input terminals S and T, and the normally open contacts R1.1 and R1.5 of the first relay R1 are still open at this time, so that any arc that may occur between the normally closed contacts R2.2 and R2.3 of the second relay R2 cannot short-circuit the input terminals S and T connected to the corresponding phases of the supply network, even if the normally open contacts R2.1 and R2.4 of the second relay R2 close.

[0032] The other electrical connections between the switching contacts of the two relays R1, R2 are designed in the same way in both embodiments. Fig. 3 shows a flow chart for one embodiment of a method for operating a household network. In an initial state, the household network is connected to the external network via the switching unit. In this state, the first relay R1 and the second relay R2 are in the idle state, i.e. de-energized, so that the connection of the individual phases is made via the closed break contacts of the relays. In a first step S0, a failure of the external network is detected. This can be done, for example, by an electricity meter integrated into the network connection or by other known monitoring devices. The failure of the network is transmitted to the inverter control system via a network monitoring signal.Alternatively, the failure of the external grid can also be detected directly by the inverter, for example by monitoring the grid voltage and / or grid frequency at a connection point of the inverter, thus eliminating the need to transmit a grid monitoring signal.

[0033] In a second step S2, a predefined initial waiting period is observed before, in a third step S3, the inverter controller activates the switching unit, causing the switching unit's relays to switch from the idle state to the activated state. This waiting period serves to prevent direct switching to an emergency power supply in the event of a brief power failure, thus avoiding unnecessary switching operations by the switching unit. Therefore, a waiting period between 10 seconds and several minutes can be selected, for example, one, two, or three minutes.

[0034] In a fourth step S4, the inverter initially generates a grid-compliant alternating voltage with the isolation relay open, which can preferably also be generated synchronously with the phase of the external grid before the outage. A second predefined waiting period is then waited for before the isolation relay is closed in a fifth step S5, whereby the inverter takes over supplying the household grid for the duration of the power outage. A waiting period of a few seconds, for example, 5 or 10 seconds, is sufficient to allow any residual voltages on the household phases to dissipate and to safely shut down devices.

[0035] Step S6 involves waiting for the grid to return, so the process remains in the sixth step S6 until this time (branch with a minus sign at step S6 if the grid has not yet returned) and the household grid is maintained by the inverter. If a returning grid is detected by the grid monitoring signal (branch with a plus sign at step S6), a third waiting period is initially waited for in a seventh step S7 in case the grid only returns briefly and then fails again immediately. In this case, it is better to supply the household grid continuously through the inverter. Only after the third waiting period has elapsed is the inverter's isolation relay opened in an eighth step S8, thereby ending the supply of the household grid by the inverter. The third waiting period can be in the range of minutes, for example 2 minutes, 5 minutes, or 10 minutes.Subsequently, in a ninth step S9, a fourth waiting period is observed so that the consumers of the household grid can enter a defined idle state from which they can be supplied again without failure. Instead of a predefined fourth waiting period, the voltage of the household grid can also be compared with a predefined threshold, and the ninth step S9 is terminated if the voltage falls below the threshold.

[0036] In a final tenth step S10, the control of the relays of the switching unit is terminated, so that they return to the idle state. This removes the interconnection of the phases of the household network before reconnecting the individual phases of the external network and the household network. From this moment on, the consumers of the household network are again supplied via the external network.

[0037] List of reference symbols

[0038] 1 switching unit 2 inverters

[0039] 3 Control

[0040] 4 Mains connection

[0041] 5 Household connection

[0042] 6 Network monitoring signal

[0043] 7 Isolating relay 10 Backup system

[0044] R1 , R2 relay

[0045] R1.1 , R1.4, R1.5 normally open contact

[0046] R2.1 , R2.4, R2.5 Normally open contact R1.2, R1.3 Normally closed contact R2.2, R2.3 Normally closed contact R, S, T Input connection L1 , L2, L3 Output connection

[0047] S1 - S10 step

Claims

Patent claims:

1. Switching unit (1) for switching between mains operation and island operation of a three-phase household network, comprising: a first positively driven relay (R1) and a second positively driven relay (R2), each having a control coil (A1, A2) and a number of normally open contacts (R1.1, R2.1, R1.4, R2.4) and a number of normally closed contacts (R1.2, R2.2, R1.3, R2.3), wherein terminals of the control coil (A1, A2) of one of the two relays (R1, R2) are connected in parallel with terminals of the control coil (A1, A2) of the other relay (R1, R2) via a first normally open contact (R1.1, R2.5) of the other relay (R1, R2), wherein the switching unit (1) has an input side with input terminals (R, S, T), each of which is designed for connection to one of the phase terminals of a Mains connection (4) are provided, and an output side with output terminals (L1, L2, L3), each for connection to a phase terminal of a household connection (5) are provided, wherein a first output terminal (L1) is connected to a first input terminal (R) via a first break contact (R1.2) of the first relay (R1) and is connected to a second output terminal (L2) via a first connection path having a first make contact (R2.1) of the second relay (R2) and to a third output terminal (L3) via a second connection path having a second make contact (R2.4) of the second relay (R2), and wherein the second output terminal (L2) is connected to a second input terminal (S) via a first break contact (R2.2) and the third output terminal (L3) is connected to a third input terminal (T) via a second break contact (R2.3).

2. Switching unit (1) according to claim 1, wherein the terminals of the control coil (A2) of the second relay (R2) are connected in parallel with the terminals of the control coil (A1) of the first relay (R1) via a first normally open contact (R1.1) of the first relay (R1, R2).

3. Switching unit (1) according to claim 1, wherein the terminals of the control coil (A 1 ) of the first relay (R 1 ) are connected in parallel with the terminals of the control coil (A2) of the second relay (R2) via a first normally open contact (R2.5) of the second relay (R2).

4. Switching unit (1) according to claim 3, wherein the first connection path is additionally routed via a first normally open contact (R1.1) of the first relay (R1) and the second connection path is additionally routed via a third normally open contact (R1.5) of the first relay (R1).

5. Switching unit (1) according to one of the preceding claims, wherein the relays (R1, R2) have switching times between the cessation of control of the relays and the first opening of a normally open contact of the relays, which are greater than the time interval between two consecutive zero crossings of the voltage of a connected network.

6. Backup system (10), comprising: - the switching unit (1) according to one of the preceding claims, - a mains connection (4) with phase connections, each connected to one of the input connections (R, S, T) of the switching unit (1), the mains connection providing a mains monitoring signal (6) indicating the availability of a connected mains, - a household connection (5) with phase connections, each connected to one of the output connections (L1, L2, L3) of the switching unit (1), - a single-phase inverter (2) with a controller (3), wherein the inverter (2) with an AC output is connected to the first output terminal (L1) of the switching unit (1) via an isolating relay (7), and wherein the controller (3) is configured to receive the grid monitoring signal (6) and is connected to terminals of the control coil (A1, A2) of the other relay (R1, R2) and is configured to control the control coil (A1, A2) when the grid monitoring signal (6) indicates a failure of the grid.

7. Backup system (10) according to claim 6, wherein the controller (3) is connected to a second normally open contact (R1.4) of the first relay (R1) in order to monitor a switching state of the first relay (R1).

8. Backup system (10) according to claim 6 or 7, wherein the controller (3) is configured to - to control the control coil (A1, A2) of the other relay (R1, R2) with a first time delay after the network monitoring signal (6) has indicated a network failure, and - stop the activation of the control coil (A1, A2) of the other relay (R1, R2) with a second time delay after the mains monitoring signal (6) has indicated a return of the mains.

9. Backup system (10) according to claim 8, wherein the controller (3) is configured to start the backup system with a third time delay after activation of the control coil (A1, A2) of the other relays (R1, R2) to cause the isolating relay (7) to close after the mains failure.

10. Backup system (10) according to claim 8, wherein the controller (3) is configured to first open the isolating relay (7) upon return of the mains before terminating the activation of the control coil (A1, A2) of the other relay (R1, R2).

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