Switching unit and backup system for a household network

Abstract

Described is a switching unit (1) for switching between mains operation and island operation of a three-phase domestic network, comprising a first and second positively driven relay (R1, R2), each with 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 to 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). The switching unit (1) is designed for input connection to one of the phase terminals (R, S, T) of a mains connection (4) and for output connection to one phase terminal (L1, L2, L3) of a domestic connection (5).In a resting state, the second relay (R2) connects two of the phase terminals between the mains connection (4) and the household connection (5), and in a controlled state, it connects the phase terminals (L1, L2, L3) of the household connection (5) together. A backup system (10) with such a switching unit (1) is also described.

Description

[0001] 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.

[0002] 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.

[0003] 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.

[0004] 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.

[0005] 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.

[0006] 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 the second relay are connected in parallel with terminals of the control coil of the first relay via a first normally open contact of the first relay.The switching device has an input side with input terminals, each provided for connection to one of the phase terminals of a mains connection, and an output side with output terminals, each provided for connection to a phase terminal of a household connection. A first output terminal is connected to a first input contact via a first break contact of the first relay, to a second output contact via a first break contact of the second relay, and to a third output contact via a second break contact of the second relay. Furthermore, the second output contact is connected to a second input contact via a first break contact, and the third output contact is connected to a third input contact via a second break contact.

[0007] By designing the first and second relays as positive-guided 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 positive-guided relay, the switching contacts are mechanically rigidly connected to each other and can only be moved together. Due to their design, even with welded or corroded contacts, it is impossible for a normally closed contact and a normally open contact of the relay to be closed simultaneously.

[0008] As a result, it is permissible not to energize the relays during mains operation, i.e. to connect the phases of the household network with the external network via normally closed contacts.

[0009] 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.

[0010] In a preferred embodiment, the controller is connected to a second normally open contact of the first relay in order to monitor switching 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.

[0011] 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 restoration. 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 restoration correspondingly does not lead to an undesired deactivation.

[0012] 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.

[0013] 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.

[0014] In the following, the invention is illustrated by means of figures, of which Fig. 1 shows an embodiment of a switching unit according to the invention within a backup system for a household network, and Fig. 2 shows a flowchart for a method according to the invention for switching between mains operation and island operation of a household network.

[0015] Fig. Figure 1 shows an inventive embodiment of a backup system 10 that switchably connects phase terminals R, S, T of a three-phase power supply network to phase terminals L1, L2, L3 of a household network. The phase terminals R, S, T are provided in a network connection 4. The network connection 4 further contains a network monitoring unit that indicates the status of the power supply network using a network monitoring signal 6. This function can be fulfilled, for example, by an energy meter, but can also be implemented by a dedicated monitoring circuit. The household's loads are, in turn, distributed to the individual phase terminals L1, L2, L3 of the household network via a household connection 5.

[0016] In mains operation, the phase connections R, S, T of the three-phase power supply network are each electrically connected to one of the household phases L1, L2, L3 via a first relay R1 and a second relay R2 via break 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.

[0017] 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.

[0018] The second relay R2 is wired in such a way that, in the idle state, it connects two of the phase terminals S, T of the power supply network to the associated phase terminals L2, L3 of the household network. When energized, it connects the associated phase terminals L2, L3 of the household network to the remaining phase terminal L1 of the household network. For this purpose, two normally closed contacts R2.2, R2.3 are each connected on one side to one of the phase terminals S, T of the power supply network and on the other side to the associated phase terminals L2, L3 of the household network. Furthermore, the phase terminals L2, L3 of the household network are each connected to the remaining phase terminal L1 of the household network via a normally open contact R2.1, R2.4e. The design of the second relay R2 as a positively driven relay prevents one of the normally closed contacts R2.2, R2.3 and one of the normally open contacts R2.1, R2.4 from being closed at the same time.

[0019] The voltage-regulating inverter 2 is also connected to the phase connection L1 of the household grid 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 interconnect 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.

[0020] 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.

[0021] In the Fig. Figure 1 shows an unused normally closed contact R1.3 in the first relay R1. This is not absolutely necessary, but merely demonstrates 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.

[0022] In Fig.Figure 2 shows a flowchart for one embodiment of a method for operating a household grid. In an initial state, the household grid is connected to the external grid 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 established via the closed break contacts of the relays. In a first step S0, a failure of the external grid is detected. This can be done, for example, by an electricity meter integrated into the grid connection or by other known monitoring devices. The grid failure is transmitted to the inverter controller via a grid 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.

[0023] 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.

[0024] 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.

[0025] Step S6 involves waiting for the grid to return, so that the method 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.

[0026] If a returning mains supply is detected by the grid monitoring signal (branch with a plus sign at step S6), a seventh step S7 initially waits for a third waiting period in case the mains supply only returns briefly and then immediately fails again. In this case, it is better to supply the household grid continuously via the inverter. Only after the third waiting period has elapsed is the inverter's isolation relay opened in an eighth step S8, which stops the inverter supplying the household grid. The third waiting period can be in the range of minutes, for example 2 minutes, 5 minutes or 10 minutes. A ninth step S9 then waits for a fourth waiting period so that the consumers in the household grid can enter a defined idle state from which they can be supplied again without errors.

[0027] 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. List of reference symbols 1 switching unit 2 off-grid inverters 3 Control 4 Mains connection 5 household connection 6 Network monitoring signal 7 isolating relays 10 Backup system S1 - S10 step QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2011 000 394 A1

[0003]

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 (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), wherein the switching unit (1) has an input side with input terminals, each provided for connection to one of the phase terminals (R, S, T) of a mains connection (4), and an output side with output terminals, each provided for connection to a phase terminal (L1, L2, L3) of a household connection (5), wherein a first output terminal is connected via a first break contact (R1.2) of the first relay (R1) to a first input contact, via a first break contact (R2.1) of the second relay (R2) to a second output contact, and via a second break contact (R2.4) of the second relay (R2) to a third output contact, and wherein the second output contact is connected to a second input contact via a first normally closed contact (R2.2) and the third output contact is connected to a third input contact via a second normally closed contact (R2.3). [2] Backup system (10), comprising: - the switching unit (1) according to claim 1, - a mains connection (4) with phase connections (R, S, T), each connected to one of the input connections 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 (L1, L2, L3), each connected to one of the output connections 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 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) of the first relay (R1) and is configured to control the control coil (A1) when the grid monitoring signal (6) indicates a failure of the grid. [3] Backup system (10) according to claim 2, wherein the controller (3) is connected to a second normally open contact (R1.4) of the first relay (R1) to monitor switching of the first relay (R1). [4] Backup system (10) according to claim 2 or 3, wherein the controller (3) is arranged to - to control the control coil of the first relay (R1) with a first time delay after the network monitoring signal (6) has indicated a network failure, and - stop the activation of the control coil of the first relay (R1) with a second time delay after the mains monitoring signal (6) has indicated a return of the mains. [5] Backup system (10) according to claim 4, wherein the controller (3) is configured to close the isolating relay (7) with a third time delay after actuation of the actuation coil of the first relay (R1) after the mains has failed. [6] Backup system (10) according to claim 4, 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 of the first relay (R1).

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