Switching unit and standby power supply system for household power grid

Abstract

The invention relates to a switching unit (1) for switching between grid operation and islanding operation of a three-phase domestic grid, comprising a first and a second forced-guide relay (R1, R2), each having a drive coil (A1, A2) and a plurality of normally open contacts (R1.1, R2.1, R1.4, R2.4) and a plurality of normally closed contacts (R1.2, R2.2, R1.3, R2.3). The connection end of the drive coil (A2) of the second relay (R2) is connected in parallel with the connection end of the drive coil (A1) of the first relay (R1) via the first normally open contact (R1.1) of the first relay (R1). The switching unit (1) is designed to be connected on the input side to one of the phase connections of the network connection (4) and on the output side to the phase connection of the household connection (5). In a rest state, the second relay (R2) connects two of the phase connections between the network connection (4) and the home connection (5), and in a controlled state, the second relay (R2) connects the phase connections of the home connection (5) to each other. A backup power supply system (10) having such a switching unit (1) is also described.

Description

[0001] The present invention relates to a switching unit for switching between grid operation and islanded operation of a residential power grid, and a backup power system for a residential power grid having such a switching unit.

[0002] The continuous availability of electrical energy to power household loads has become an integral part of daily life. When this power supply is interrupted due to grid failures, it not only causes inconvenience but can also pose a danger. For this reason, so-called backup power systems exist, which ensure power supply to household loads in such situations from energy storage devices (e.g., batteries and / or DC generators, especially solar generators). When a grid failure occurs, household loads must first be disconnected from the grid before an islanded grid can be established, for example, through a voltage-regulating inverter. To ensure full power supply to all loads, single-phase inverters are known to be used, connecting the individual phases of the household grid to each other.

[0003] Therefore, patent document DE 10 2011 000 394 A1 discloses a backup power system in which a control device disconnects all phases of the power grid from the electrical equipment via a first relay in the event of a grid failure, connects the phases of the electrical equipment to each other via a second relay, and establishes an islanded grid via a grid construction device. Here, the first relay must be designed as a static current relay, so its drive coil must be continuously energized during grid operation to prevent reconnection of the electrical equipment during islanded operation due to a fault (unexpected power failure of the first relay). The energy consumption of such a static current relay would impose a significant additional cost on the backup power system, even if the system is never or almost never used.

[0004] Furthermore, document DE 10 2012 023 424 A1 discloses a control device for a power distribution system, wherein a first electromechanical disconnect switch and a second electromechanical disconnect switch, each capable of being driven independently, are interlocked to prevent simultaneous activation. In grid operation, the first disconnect switch connects the household load to the grid, and in islanded operation, the second disconnect switch connects the output of a voltage-regulating inverter to the household load. In islanded operation, the inverter remains disconnected from the grid via a third disconnect switch. The interlocking can be achieved through mechanical interlocking coupling between relays. Therefore, in grid operation, the first disconnect switch is controlled to conduct.

[0005] Therefore, the object of the present invention is to provide a switching unit and a backup power system that can perform fail-safe switching between grid operation and islanded operation of a household power grid, and has low energy consumption during grid operation.

[0006] This task is accomplished by a switching unit having the features of independent claim 1 and a backup power system having such a switching unit. A preferred embodiment of the backup power system is the subject of the dependent claims.

[0007] The switching unit according to the present invention for switching between grid operation and islanded operation of a three-phase household power grid includes a first forced-guided relay and a second forced-guided relay. The first and second forced-guided relays each have a drive coil and multiple normally open and multiple normally closed contacts. The connection terminal of the drive coil of one of the two relays is connected in parallel with the connection terminal of the drive coil of the other relay via the first normally open contact of the other relay. Here, the switching device has an input side and an output side. The input side has input connection terminals respectively configured for connection to one of the phase connection terminals of the grid connection terminal, and the output side has output connection terminals respectively configured for connection to the phase connection terminal of the household connection terminal. The first output connection terminal is connected to the first input connection terminal via the first normally closed contact of the first relay, and to the second output connection terminal via a first connection path having the first normally open contact of the second relay, and to the third output connection terminal via a first connection path having the second normally open contact of the second relay. Furthermore, the second output connection terminal is connected to the second input connection terminal via the first normally closed contact, and the third output connection terminal is connected to the third input connection terminal via the second normally closed contact.

[0008] By implementing the first and second relays as forced-direction relays, it is possible to ensure that the phase connection (zusammenschalten) of the household power grid is mutually exclusive with the connection between the household power grid and the external power grid. This is because, in a forced-direction relay, the switch contacts are mechanically rigidly connected to each other and can only move together. Thus, even if the contacts are welded together, the structural limitations prevent the normally closed and normally open contacts of the relay from closing simultaneously.

[0009] Therefore, it is permissible to connect the phase of the household power grid to the external power grid without energizing the relay during grid operation, i.e., by using normally closed contacts.

[0010] In a first embodiment of the present invention, the connection terminal of the drive coil of the second relay is connected in parallel with the connection terminal of the drive coil of the first relay via the first normally open contact of the first relay. In this embodiment, the first relay switches first, and the switching of the second relay is contingent upon the correct switching of the first relay.

[0011] In a second embodiment of the invention, the connection terminal of the drive coil of the first relay is connected in parallel with the connection terminal of the drive coil of the second relay via a first normally open contact of the second relay. In this embodiment, the second relay switches first, and the switching of the first relay is contingent upon the correct switching of the second relay. Advantageously, the first connection path is additionally guided via the first normally open contact of the first relay, and the second connection path is additionally guided via the third normally open contact of the first relay. Since both connection paths extend via the normally open contacts of the two relays respectively, current can only flow through the connection paths after the two relays have switched correctly. That is, the output connection is only merged under the premise that the two relays have switched correctly.

[0012] In both implementations, a relay is preferably selected such that the switching time from the termination of relay actuation to the first opening of the relay's normally open contact is greater than the time interval between two consecutive zero crossings of the connected power grid, greater than 10 ms for a 50 Hz grid. Particularly preferably, the switching time is between two and ten times this time interval. This ensures that when switching back from islanded operation to grid operation, there is sufficient time for the voltage of the household power grid to drop below the desired residual voltage value before reconnection, thereby avoiding load spikes when the household power grid is reconnected to the existing grid.

[0013] In another aspect of the invention, the backup power system includes the aforementioned switching unit and a grid connection terminal having a phase connection end, each phase connection end being connected to one of the input connection terminals of the switching unit, wherein the grid connection terminal provides a grid monitoring signal indicating the availability of the connected grid. Furthermore, the backup power system includes a household connection terminal having a phase connection end, each phase connection end being connected to one of the output connection terminals of the switching unit. The AC output terminal of a single-phase inverter with a controller is connected to the first output connection terminal of the switching unit via an isolation relay. Here, the controller is configured to receive the grid monitoring signal and is connected to the connection terminal of the drive coil of the first relay, and is configured to drive the drive coil when the grid monitoring signal indicates a grid fault.

[0014] In a preferred embodiment, the controller is connected to the second normally open contact of the first relay to monitor the switching status of the first relay. This ensures that the inverter is activated only after the first relay has successfully completed its switching action. This allows for the identification of a fault in the first relay and prevents malfunctions in the backup power system. It should also be noted that if the first relay fails, the second relay will not switch at all, as its drive coil is connected to the first relay's drive coil via a normally open contact (which does not close when the first relay fails).

[0015] In another advantageous embodiment of the invention, the controller is configured to drive the drive coil of the first relay only after a first time delay following a power grid monitoring signal indicating a power grid failure, and to terminate the driving of the drive coil of the first relay only after a second time delay following a power grid monitoring signal indicating power grid restoration. Thus, brief power outages (e.g., lasting one or several seconds) do not lead to unintended activation of the backup power system, and only brief restoration of the power grid does not lead to unintended shutdown.

[0016] Preferably, the controller is also configured to close the isolation relay only after a third time delay, following the activation of the drive coil of the first relay, following a power grid failure, thereby creating an islanded grid in the household load via the inverter. This supports the controlled creation of an islanded grid in the household load because the third time delay eliminates residual voltage in the household grid.

[0017] Advantageously, the controller is configured to, upon grid restoration, first disconnect the isolating relay before ending the drive coil of the first relay, i.e., before reconnecting the phase of the household grid to the phase of the external grid, thereby ending the formation of an islanded grid. Successful disconnection of the inverter from the household grid can, of course, also be monitored by the inverter and set as a prerequisite for the reconnection of the phase of the household grid to the phase of the external grid.

[0018] The present invention will now be described with reference to the accompanying drawings, wherein: Figure 1 A first embodiment of a switching unit in a backup power system for a residential power grid according to the present invention is shown. Figure 2 Another embodiment of a switching unit in a backup power system for a residential power grid according to the present invention is shown, and Figure 3 A flowchart of a method for switching between grid operation and islanded operation of a residential power grid according to the present invention is shown.

[0019] Figure 1 A first embodiment of a backup power system 10 according to the present invention, having a switching unit 1, is shown. This switching unit 1 is switchably connected to input terminals R, S, T configured for connection to phase connections of a three-phase power grid and output terminals L1, L2, L3 configured for connection to phase connections of a household power grid. Phase connections are provided in a grid connection terminal 4. The grid connection terminal 4 also includes a grid monitoring unit that indicates the state of the power grid by means of a grid monitoring signal 6. This function can be implemented, for example, by an electricity meter, but can also be implemented by its own monitoring circuitry. Household loads are distributed to the respective phase connections of the household power grid via household connection terminals 5.

[0020] During grid operation, the input terminals R, S, and T of the three-phase power grid are electrically connected to the output terminals L1, L2, and L3 via the first relay R1 and the second relay R2 through normally closed contacts R1.2, R2.2, and R2.3, respectively. This eliminates the need to drive the drive coils A1 and A2 of the two relays R1 and R2 during grid operation, thus preventing any corresponding power loss.

[0021] The connection terminal of the first drive coil A1 is connected to the signal output terminal of the controller 3 of the voltage regulating inverter 2 to drive the first relay R1. The drive coil A2 of the second relay R2 is connected in parallel with the drive coil A1 of the first relay R1 via the 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 jointly determined by the controller 3 of the inverter 2, wherein the second relay R2 is only driven when the first relay R1 switches correctly.

[0022] The second relay R2 is connected in the following manner: in the static state, it connects two of the input terminals S and T to the associated output terminals L2 and L3; in the driven state, it connects the associated output terminals L2 and L3 to the remaining output terminal L1. For this purpose, the two normally closed contacts R2.2 and R2.3 are connected to one of the input terminals S and T on one side, and to the associated output terminals L2 and L3 on the other side. Furthermore, the output terminals L2 and L3 are connected to the remaining output terminal L1 via normally open contacts R2.1 and R2.4, respectively. By designing the second relay R2 as a forced-direction relay, the simultaneous closure of one of the normally closed contacts R2.2 and R2.3 and one of the normally open contacts R2.1 and R2.4 is prevented.

[0023] The voltage regulating inverter 2 is also connected to the output connection terminal L1 via the isolation relay 7. This allows the inverter 2, through its controller 3, to trigger the drive of the switching unit 1 via the signal output of the controller 3 when it receives a grid monitoring signal 6 indicating a grid fault, thereby separating the household grid from the power supply grid and merging all phases of the household grid into a common phase. Subsequently, the inverter 2 can form a single-phase islanded grid. Preferably, the single-phase islanded grid is first formed when the isolation relay 7 is open, and the single-phase islanded grid is maintained after the isolation relay 7 is closed to supply power to the household appliances.

[0024] The first relay R1 has an optional normally open contact R1.4, which is connected to the signal input terminal of the controller 3. The controller 3 can verify the switching state of the first relay R1 via this normally open contact. 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.

[0025] exist Figure 1 In the diagram, an unused normally closed contact R1.3 is shown in the first relay R1. This contact is not essential but serves to indicate that the two relays R1 and R2 can be designed with the same structure, which is often advantageous for cost reasons. Of course, different relay designs with more or fewer unused contacts can also be considered. It is also possible to consider... Figure 1 The neutral line N, which is fixedly connected between the household power grid and the power supply grid, is now guided by the normally closed contact R1.3.

[0026] according to Figure 2 The switching unit, according to another embodiment of the invention, avoids brief short circuits that may occur between grid phases when unfavorable short intervals occur between the switching times of the switching contacts of the forced-guide relay, particularly when the time interval between the opening of the normally closed contact and the closing of the normally open contact is less than the time interval between the two zero-crossing points of the grid voltage. In this embodiment, both the first relay R1 and the second relay R2 have additional third normally open contacts R1.5 and R2.5, the purpose of which will be explained below.

[0027] Furthermore, in this embodiment, the connection terminal of the second drive coil A2 used to drive the second relay R2 is also connected to the signal output terminal of the controller 3 of the voltage regulating inverter 2. Now, the drive coil A1 of the first relay R1 is connected in parallel with the drive coil A2 of the second relay R2 via the third (added compared to the first embodiment) normally open contact R2.5. In this way, the switching states of the first relay R1 and the second relay R2 can be jointly determined by the controller 3 of the inverter 2, wherein the first relay R1 is only driven after the second relay R2 has been correctly switched. This results in a delay between the switching time of the first relay R2 (switched first) and the switching time of the first relay R1 (switched later). Preferably, this forced-guided relay is selected, where the delay between the driving of the drive coil and the resulting closing of the normally open contact is ensured to be longer than the time interval between two consecutive zero-crossing points of the power grid (10ms for a 50Hz grid).

[0028] Furthermore, in this embodiment, the electrical connections between output terminals L2 and L3 and the output terminal L1 to which the inverter 2 is connected are now guided by the series connection of two normally open contacts, which are arranged on different relays in the two relays R1 and R2. Therefore, the electrical connection path between output terminals L2 and L1 now extends via normally open contacts R1.5 and R2.1, while the electrical connection path between output terminals L3 and L1 is guided via normally open contacts R1.1 and R2.4. By selecting the delay between driving the drive coil and the resulting closing of the normally open contacts, it is ensured that when the household power grid is disconnected from the power grid, the output terminals L2 and L3 are first disconnected from the input terminals S and T. At this time, the normally open contacts R1.1 and R1.5 of the first relay R1 are still open, so that even if the normally open contacts R2.1 and R2.4 of the second relay R2 are closed, the arc that may occur between the normally closed contacts R2.2 and R2.3 of the second relay R2 will not cause the corresponding input terminals S and T connected to the power grid to short-circuit with each other.

[0029] The additional electrical connection between the switching contacts of the two relays R1 and R2 is implemented in the same manner in both embodiments.

[0030] Figure 3 A flowchart illustrating an implementation of a method for operating a home power grid is shown. In an initial state, the home power grid is connected to an external power grid via a switching unit. In this state, the first relay R1 and the second relay R2 are in a stationary state, i.e., no current flows, and therefore the phases are connected via the normally closed contacts of the relays. In a first step S0, a fault in the external power grid is identified. This fault can be detected, for example, by an energy meter integrated into the grid connection or by other known monitoring devices. The grid fault is transmitted to the inverter controller via a grid monitoring signal. Alternatively, the identification of external grid faults can also be performed directly by the inverter, for example, by monitoring the grid voltage and / or grid frequency at the inverter's connection point, thus eliminating the need to transmit a grid monitoring signal.

[0031] In the second step S2, a predetermined first waiting time is waited for, and then in the third step S3, the switching unit is driven by the inverter controller, thereby changing the relay of the switching unit from a static state to an active state. The purpose of this waiting time is to avoid direct switching to emergency power supply in the event of a brief power failure, thus avoiding unnecessary switching processes for the switching unit. Therefore, a waiting time between 10 seconds and several minutes can be selected here, such as one minute, two minutes, or three minutes.

[0032] In step S4, with the isolation relay open, the inverter generates an AC voltage conforming to the grid specifications. This AC voltage is preferably generated synchronously with the phase of the external grid prior to the fault. Then, before the isolation relay closes in step S5, a second predetermined waiting time is waited for, thus allowing the inverter to supply power to the household grid as long as the grid fault persists. Here, a waiting time within a few seconds (e.g., 5 or 10 seconds) is sufficient to release any residual voltage that may exist on the phases of the household load and safely place the equipment in a power-off state.

[0033] Step S6 involves waiting for the power grid to be restored. Therefore, before this point, the method will remain at step S6 (if the power grid has not been restored, it will proceed along the negative branch of step S6), and the inverter will maintain the operation of the home power grid.

[0034] When grid recovery is detected via grid monitoring signals (positive branch of step S6), in step S7, a third waiting time is first waited for the possibility of a brief grid recovery followed by another failure. In this case, it is best to continue supplying power to the household grid via the inverter. Subsequently, only after the third waiting time has elapsed is the inverter's isolation relay disconnected in step S8, thereby ending the inverter's power supply to the household grid. The third waiting time can be in the range of minutes, such as 2 minutes, 5 minutes, or 10 minutes. Subsequently, in step S9, a fourth waiting time is waited for the household grid's electrical appliances to enter a defined quiescent state from which they can be faultlessly re-powered. Instead of the predetermined fourth waiting time, the voltage of the household grid can be compared with a predetermined threshold, and step S9 ends when it falls below the threshold.

[0035] In the final tenth step S10, the drive of the relay in the switching unit is terminated, causing the relay to return to a stationary state. This disconnects the phase connections of the household power grid before the individual phases of the external and household power grids are reconnected. From this point onward, the household appliances are once again powered by the external power grid.

[0036] Reference tag list 1 Switching Unit 2 Inverter 3 Controllers 4. Power grid connection terminal 5 Home Connector 6. Power Grid Monitoring Signals 7. Isolation Relay 10. Backup power system Relays R1 and R2 Normally open contacts R1.1, R1.4, R1.5 Normally open contacts R2.1, R2.4, R2.5 Normally closed contacts R1.2 and R1.3 Normally closed contacts R2.2 and R2.3 R, S, T input terminals L1, L2, L3 output connection terminals Steps S1–S10.

Claims

1. A switching unit (1) for switching between grid operation and islanded operation of a three-phase household power grid, the switching unit comprising: A first forced-guided relay (R1) and a second forced-guided relay (R2) each have a drive coil (A1, A2) and multiple normally open contacts (R1.1, R2.1, R1.4, R2.4) and multiple normally closed contacts (R1.2, R2.2, R1.3, R2.3). The connection terminal of the drive coil (A1, A2) of one of the relays (R1, R2) is connected in parallel with the connection terminal of the drive coil (A1, A2) of the other relay (R1, R2) via the first normally open contact (R1.1, R2.5) of the other relay (R1, R2). The switching unit (1) has an input side and an output side. The input side has input connection terminals (R, S, T) respectively configured to be connected to one of the phase connection terminals of the power grid connection terminal (4). The output side has output connection terminals (L1, L2, L3) respectively configured to be connected to the phase connection terminal of the household connection terminal (5). The first output connection terminal (L1) is connected to the first input connection terminal (R) via the first normally closed contact (R1.2) of the first relay (R1), and to the second output connection terminal (L2) via a first connection path having the first normally open contact (R2.1) of the second relay (R2), and to the third output connection terminal (L3) via a second connection path having the second normally open contact (R2.4) of the second relay (R2). The second output terminal (L2) is connected to the second input terminal (S) via the first normally closed contact (R2.2), and the third output terminal (L3) is connected to the third input terminal (T) via the second normally closed contact (R2.3).

2. The switching unit (1) according to claim 1, wherein The connection terminal of the drive coil (A2) of the second relay (R2) is connected in parallel with the connection terminal of the drive coil (A1) of the first relay (R1, R2) via the first normally open contact (R1.1) of the first relay (R1, R2).

3. The switching unit (1) according to claim 1, wherein The connection terminal of the drive coil (A1) of the first relay (R1) is connected in parallel with the connection terminal of the drive coil (A2) of the second relay (R2) via the first normally open contact (R2.5) of the second relay (R2).

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

5. The switching unit (1) according to any one of the preceding claims, wherein, The relays (R1, R2) have a switching time between the termination of the drive to the relay and the first opening of the normally open contact of the relay, and the switching time is greater than the time interval between two consecutive zero crossings of the voltage of the connected power grid.

6. A backup power system (10), comprising: The switching unit (1) according to any one of the preceding claims. A grid connection terminal (4) has a phase connection end, which is respectively connected to one of the input connection terminals (R, S, T) of the switching unit (1), wherein the grid connection terminal provides a grid monitoring signal (6), which indicates the availability of the connected grid. A household connection terminal (5) has a phase connection end, which is respectively connected to one of the output connection terminals (L1, L2, L3) of the switching unit (1). A single-phase inverter (2) having a controller (3), wherein the inverter (2) is connected to the first output connection terminal (L1) of the switching unit (1) via an isolation relay (7) through its AC output terminal, and The controller (3) is configured to receive the power grid monitoring signal (6) and is connected to the connection terminal of the drive coil (A1, A2) of the other relay (R1, R2), and is configured to drive the drive coil (A1, A2) when the power grid monitoring signal (6) indicates a fault in the power grid.

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

8. The backup power system (10) according to claim 6 or 7, wherein, The controller (3) is configured to: After the power grid monitoring signal (6) indicates the power grid fault, the drive coils (A1, A2) of the other relays (R1, R2) are activated only after a first time delay. After the power grid monitoring signal (6) indicates that the power grid has been restored, the driving of the drive coils (A1, A2) of the other relays (R1, R2) ends only after a second time delay.

9. The backup power system (10) according to claim 8, wherein, The controller (3) is configured to close the isolation relay (7) after a third time delay following the power grid failure and after driving the drive coils (A1, A2) of the other relays (R1, R2).

10. The backup power system (10) according to claim 8, wherein, The controller (3) is configured to, when the power grid is restored, first disconnect the isolation relay (7) before ending the drive coil (A1, A2) of the other relay (R1, R2).

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