Method for operating an inverter, method for supplying energy to a local energy supply network, and inverter

Abstract

The invention relates to a method for operating an inverter (1) in an isolated operation, wherein the inverter (1) has at least two outputs (8a-c) for connecting external electrical conductors (L1, L2, L3), and the method has the following steps: i) outputting alternating voltages (U1, U2, U3), in particular alternating voltages which are phase-offset with respect to one another, at outputs (8a-c) which have been activated, each of the at least two outputs (8a-c) being assigned a priority level (A, B, C); ii) checking the inverter (1) with respect to an electrical overload; and iii) deactivating the output (8a-c) with the lowest priority level (A, B, C) at which one of the alternating voltages (U1, U2, U3) is output by terminating the output of the alternating voltage (U1, U2, U3) at said output (8a-c) if an electrical overload of the inverter (1) has been determined. The invention also relates to a method for supplying energy to a local energy supply network (2) and to an inverter (1).

Description

[0001] Method for operating an inverter, method for supplying energy to a local energy supply network and inverter

[0002] The invention relates to a method for operating an inverter in island mode, wherein the inverter has at least two outputs for connecting electrical outer conductors.

[0003] Furthermore, the invention relates to a method for supplying energy to a local energy supply network.

[0004] Furthermore, the invention relates to an inverter, preferably an inverter for a photovoltaic system, with at least two outputs for connecting electrical outer conductors and a control and / or regulating device.

[0005] In the event of a power failure, inverters can be used in island mode to supply local energy supply networks, such as building energy supply networks, with electrical energy. For this purpose, the inverters can be connected to an electrical energy storage device and / or an electrical energy supply device, such as a photovoltaic system. This means that loads connected to the local energy supply network, such as refrigerators, lighting, or heaters, can continue to operate even in the event of a power failure, at least for a while, ideally until the cause of the power failure has been rectified. However, if the electrical power required by the loads exceeds the available electrical power (overload), the inverters must stop operating. As a result, even essential loads are not supplied with electrical energy.However, it would be desirable to be able to continue operating certain consumers even in the event of an inverter overload.

[0006] It is known from the prior art to prioritize consumers connected to a local energy supply grid and, depending on the prioritization, to deactivate them if the inverter is overloaded or there is an energy deficit. Such a procedure is known, for example, in the emergency power supply systems described in EP 2 728 707 A2, DE 10 2019 112 270 A1 and DE 11 2010 005 914 T5. However, in order to deactivate individual consumers depending on their prioritization, a central control unit and distributed control units integrated in the consumers are required. In addition, a communication link to the consumers is necessary.

[0007] A method for controlling an emergency power supply is known from DE 199 35 754 B4. EP 0 275 633 A1 discloses a method for controlling a multi-phase motor.

[0008] In light of these statements, it is an object of the present invention to mitigate or even completely eliminate the disadvantages of the prior art. Preferably, the object of the present invention is to provide a method and an inverter of the type mentioned above that can at least partially maintain operation in the event of an inverter overload and can continue to supply certain consumers with electrical energy in a simple manner. Most preferably, a communication connection with the consumers should not be required.

[0009] This object is achieved by a method for operating an inverter in island operation according to claim 1, a method for supplying energy to a local energy supply network according to claim 14 and by an inverter according to claim 15.

[0010] According to the invention, the following steps are provided in a method for operating an inverter in island mode of the type mentioned at the outset: i) outputting alternating voltages which are in particular out of phase with one another at outputs which have been activated, wherein each of the at least two outputs is assigned a priority level; ii) checking the inverter for electrical overload; ill) deactivating that output with the lowest priority level at which an alternating voltage is output, by terminating the output of the alternating voltage at the output if an overload of the inverter has been detected.

[0011] Advantageously, with the method according to the invention, consumers that are connected to a higher priority output of the inverter can continue to be supplied with electrical energy if there is an electrical overload of the inverter or of a supply device connected to the inverter, for example an electrical energy storage device or an energy generation device. At the same time, by deactivating the output with the lowest priority level, at which an alternating voltage is output, the overload of the inverter can be eliminated in many cases, so that alternating voltages and electrical currents at a predetermined level, i.e. according to a setpoint, can be output at the activated outputs. Deactivating an output means that no alternating voltage is output by the inverter at the deactivated output.Preferably, deactivated outputs are switched to a high-impedance state, as will be described further below. The method, in particular steps i), ii) and / or iii), can be carried out iteratively, so that alternating voltages are continuously output at activated outputs and further outputs can also be deactivated if an electrical overload still exists despite deactivation of the output with the lowest priority level at which an alternating voltage is output. The iterative execution of steps ii) and iii) can, in the event of a high electrical overload, also result in all outputs of the inverter being deactivated, so that no electrical alternating voltage is output at any of the outputs. An electrical overload can arise in particular because the consumers connected to the local energy supply network require more electrical power or...require more electrical energy than the inverter, an electrical energy storage device connected to the inverter and / or an electrical energy generation device can provide. Steps i), ii) and / or iii) can be carried out at least partially or entirely in an overlapping manner. In any case, the name of the steps does not necessarily specify their order in which they are carried out. Outputs of the inverter can be activated in particular by outputting an alternating voltage. In island operation, the inverter feeds into the local energy supply grid without the local energy supply grid being supplied by a higher-level public energy supply grid. In other words, the local energy supply grid is supplied exclusively by at least one inverter, or in one embodiment, several inverters.The inverter is therefore not guided by a voltage and / or a current in the local energy supply network in island operation. In a preferred embodiment, the local energy supply network is separated from the higher-level public energy supply network by a isolating switch in island operation. The inverter is designed to convert a direct voltage into an alternating voltage at the outputs. For this purpose, the inverter can have a direct voltage intermediate circuit, which can have one or more capacitors, and electrical switches that can be controlled by a switching pattern. The inverter has at least two, preferably at least three, in particular exactly three outputs for connection to outer conductors of a local energy supply network and is designed to output alternating voltages at the outputs, in particular voltages that are phase-shifted to one another.The alternating voltages are preferably offset from one another by 360 / n°, where n is the number of outputs of the inverter. The number of outputs is preferably n=3. An outer conductor, i.e. phase, of the local power supply network can be connected to each of the at least two outputs of the inverter. The level of the output alternating voltage is preferably substantially 230 V and has a frequency of preferably substantially 50 Hz. The inverter can also have a terminal for connection to a neutral conductor of the local power supply network. Each of the at least two outputs of the inverter is assigned a priority level. The priority levels can be in ascending order and thus specify a clear ranking. The priority levels can be in the form of natural numbers or letters, for example.The number of possible priority levels corresponds to the number of outputs of the inverter. Each priority level is preferably present only exactly once. Thus, in one embodiment of the invention, each output can be assigned a different priority level, so that the at least two outputs and thus the connected outer conductors of the local energy supply network are prioritized differently. In order to prioritize the outer conductors of the local energy supply network, they can be connected to an output with a priority level that has already been assigned, or the priority level of the outputs can be set after they have been connected to the outer conductors. In the first case, it is also possible for the priority levels to be fixed, i.e. unchangeable, for the outputs to be assigned. The inverter can be connected to the local energy supply network, to which the loads are in turn connected, via the at least two outputs.In step i), alternating voltages are output at outputs that have been activated. Preferably, at the start of the method, all of the at least two outputs of the inverter are activated, in particular substantially simultaneously, so that an alternating voltage is output at all of the at least two outputs. However, it is also possible to activate the outputs successively at time intervals at the start of the method. The inverter can be checked for electrical overload in step ii), for example, by measuring the output voltage at the at least two outputs or by measuring the intermediate circuit voltage of an intermediate circuit of the inverter, as will be described in more detail below. A measurement of the output currents is also possible. In step iii), the output with the lowest priority level, at which an alternating voltage is output, is deactivated.This means that loads connected to the deactivated inverter output are no longer supplied with electrical energy, thus reducing the electrical load. In many cases, this can eliminate the inverter overload. The outputs with a higher priority level, which continue to output an AC voltage, remain activated unless a further iteration of the process detects another electrical overload and the output with the lowest priority level, which is outputting an AC voltage, is deactivated again. By prioritizing the inverter outputs, the outer conductors of a connected local energy supply network, and therefore the loads, are prioritized.Less important loads can be connected to a common phase conductor that is connected to an outlet that has a low or the lowest priority level. Essential loads can be connected to a common phase conductor that is connected to an outlet that has a high or the highest priority level. By connecting the loads to such prioritized phase conductors or connecting the phase conductors to prioritized outlets, less important loads are switched off first in the event of an electrical overload. Essential loads, such as refrigerators and certain lamps, can continue to be supplied with electrical energy. The inverter can be, for example, an off-grid inverter or a hybrid inverter.In one embodiment of the invention it can be provided that before an output is deactivated in step iii) the setpoint for the intermediate circuit voltage or the output voltages at the activated outputs is reduced, for example to 90%. In some cases the overload can already be eliminated in this way, so that there is no need to deactivate an output. If an overload is therefore detected, the setpoint for the intermediate circuit voltage and / or the output voltages is first reduced. Only if the overload persists is the output with the lowest priority level, at which an alternating voltage is output, deactivated in this embodiment. The inverter is preferably designed as a three-phase inverter with three outputs, each for connecting an outer conductor.

[0012] According to an embodiment of the invention, the output with the highest priority level among the deactivated outputs can be reactivated after a predetermined period of time. If an electrical overload is subsequently detected again by comparing the electrical value with the threshold value, the output can be deactivated again in step iii).

[0013] In one embodiment of the invention, it is provided that steps i), ii) and iii) are continuously repeated. Steps i), ii) and iii) can be carried out at least partially in parallel. The continuous checking of the inverter with regard to electrical overload monitors the inverter or any connected supply device. Steps ii) and iii) can, for example, be carried out at regular intervals, for example with a frequency between 1 Hz and 100 Hz, in particular between 5 Hz and 70 Hz or between 10 Hz and 60 Hz. Steps i), ii) and iii) can be continuously repeated throughout the entire operation of the inverter. In a

[0014] According to an embodiment of the invention, steps i), ii) and iii) can be repeated or carried out, thereby monitoring the inverter or the supply device for overload, until, due to a persistent electrical overload, no more alternating voltage is output at any of the outputs of the electrical inverter, i.e. until the inverter is switched off or until the local energy supply network is reconnected to the higher-level public supply network.

[0015] In one embodiment of the invention, the inverter is checked for electrical overload by detecting an electrical variable, in particular an electrical voltage or an electrical current, of the inverter and comparing the electrical variable with a threshold value, and an overload is determined if the electrical variable falls below or exceeds the threshold value. The electrical variable can be detected by a measuring device, in particular one or more voltage and / or current measuring sensors. The threshold value can, for example, be a predetermined percentage of a target value for the electrical variable or of a maximum permissible value of the electrical variable. For example, the threshold value can be between 105% and 120%, in particular substantially 110%, of a rated current. The rated current can, for example, be an output current.In another embodiment, the threshold value can, for example, be between 80% and 95%, in particular substantially 90%, of a nominal voltage. The nominal voltage can, for example, be the intermediate circuit voltage or an output voltage at the outputs. Whether the threshold value is exceeded or not in order to check the inverter for electrical overload depends in particular on the type of electrical quantity. The wording “below or exceeds” does not necessarily imply that a range is provided for the electrical quantity, falling below or exceeding which means an overload of the inverter. If the electrical quantity is, for example, an electrical voltage, falling below the threshold value can mean an electrical overload.If the electrical quantity is, for example, an electric current, exceeding the threshold value may indicate an electrical overload. In one embodiment of the invention, as already described above, it may be provided that the setpoint value of the output voltages or the intermediate circuit voltage is reduced before an output is deactivated. In this case, the threshold value of the output voltages or the intermediate circuit voltage may correspond to the reduced setpoint value.

[0016] In one embodiment of the invention, it is provided that the electrical variable is an electrical current, in particular an output current at one of the outputs (8a-c), a variable associated with the electrical current, an electrical intermediate circuit voltage of an intermediate circuit of the inverter, an electrical output voltage of at least one of the outputs of the inverter or a variable associated with the intermediate circuit voltage and / or the output voltage.

[0017] If the electrical variable is an intermediate circuit voltage of an intermediate circuit of the inverter, the threshold value can, for example, lie in the range between 70% and 98% of a setpoint, wherein the setpoint of the intermediate circuit voltage is preferably between 300 V and 1200 V, in particular between 600 V and 1200 V or between 650 V and 1000 V. The setpoints of the intermediate circuit voltage can depend on the parameters (for example the voltage or the frequency, etc.) of the respective supply network. If the electrical variable is an output voltage of at least one of the outputs of the inverter, the threshold value can, for example, be between 70% and 98% of a setpoint, wherein the setpoint of the output voltage is preferably between 200 V and 260 V, in particular substantially 230 V. The specified voltages represent effective values ​​and are related to a neutral conductor potential.It is particularly advantageous if the output voltages of all the inverter outputs are recorded as electrical quantities and compared with a threshold value, since the output voltages of the outputs are also used to regulate and / or control the inverter. A quantity related to the electrical current, the intermediate circuit voltage and / or the output voltage can, for example, be electrical power. The recorded or measured output voltages at the inverter outputs can essentially correspond to one of the output AC voltages, but they do not have to. The former is the case, for example, if the inverter is operated in normal operation, i.e. not in island operation, or if the inverter is not overloaded in island operation.The latter is the case, for example, if the output at which the output voltage is detected is deactivated. A voltage of 0 V or, as described in more detail below, an induced voltage at the deactivated output can then be detected as the output voltage. It is preferred if the priority levels can be assigned to the at least two outputs. For example, it can be provided that a user can assign a priority level to each output. The priority level can be assigned or changed, for example, when the inverter is put into operation for the first time or during ongoing operation. The priority level can preferably be set using an input interface, for example using buttons or a control panel. Setting by a computer via a data interface can also be provided.In an alternative embodiment of the invention, however, it can also be provided that each output is assigned a preferably unchangeable priority level and that by connecting the outer conductors of the local power supply network to the outputs, the priority levels are assigned to the outer conductors.

[0018] It is advantageous if each of the at least two outputs of the inverter is assigned a unique priority level that differs from the priority levels of the other outputs. This defines the order in which the outputs are deactivated if the inverter is overloaded.

[0019] In one embodiment of the invention, the inverter is connected to a local energy supply network, in particular to a building energy supply network, wherein the inverter supplies the local energy supply network. The building energy supply network can, for example, be an energy supply network of a house which is operated at a voltage of preferably substantially 230 V (effective value). The local energy supply network preferably has three outer conductors, to each of which consumers are connected. The local energy supply network can also have a neutral conductor. In one embodiment of the invention, several preferably identical inverters can feed into the local energy supply network and carry out the method according to the invention.Preferably, the inverter outputs that are connected to the same outer conductors of the local power grid are assigned the same priority levels, or the inverter outputs are prioritized in the same order with regard to their connection to the outer conductors. In other words, the corresponding inverter outputs are assigned the same priority levels. In this way, in the event of an electrical overload, those inverter outputs that are connected to the same outer conductor are deactivated in step iii). This avoids false detection of multi-phase loads. If several inverters feed into the local power grid, they can be operated in a master-slave configuration and communicate, for example, via a data connection.However, a data connection is not absolutely necessary, especially if the corresponding outputs of the inverters are assigned the same priority levels.

[0020] Preferably, the method comprises the following step: iv-a) reactivating the output with the highest priority level among the deactivated outputs when the overload which led to the deactivation of said output no longer exists.

[0021] The overload may no longer exist, for example, if a consumer has been disconnected from the local power supply network. Step iv-a) can be repeated as long as one or more outputs are deactivated. In one embodiment of the invention, the output can be activated manually. As already mentioned above, it is also possible for the output with the highest priority level among the deactivated outputs to be activated after a predetermined period of time, preferably for one or more periods. If an electrical overload is then detected again by comparing the electrical quantity with the threshold value, the output can be deactivated again. The determination of whether an overload exists can, as described above, be made by comparing an electrical quantity with a threshold value. In this context, reference is made to the above statements.Whether the overload still exists can be determined additionally or alternatively, for example, by calculating the power required by the connected loads. If the power required is still too high, the output is deactivated. The power calculation can be based on a measurement of the output currents and the output voltages during activation of the output with the highest priority level among the deactivated outputs. The specified time period for reactivating a deactivated output can, for example, be between 0.1 seconds and 30 seconds. It is also possible to provide several different specified time periods. For example, the specified time period after the first deactivation of an output in question can be 0.1 seconds for an initial period, which can be 5 seconds, for example.After the first time period has elapsed, the specified time period can be extended to, for example, 10 seconds, so that the output with the highest priority level among the deactivated outputs is reactivated every 10 seconds after the first time period has elapsed.

[0022] It is preferred if the method comprises the following step: iv-b) Reactivating the output with the highest priority level among the deactivated outputs if the inverter can provide a higher electrical output power and / or more electrical energy than was the case when the said output was deactivated. For example, the output with the highest priority level among the deactivated outputs can be activated if an energy generating device connected to the inverter provides the inverter with more electrical power and / or more electrical energy. This can be the case, for example, with a photovoltaic system if the sun is at a more favorable angle to the photovoltaic system or clouds have cleared, so that more solar radiation is converted into electrical energy per unit of time.Step iv-b ) can be repeated as long as one or more outputs are deactivated .

[0023] Not only single-phase consumers, such as lamps or televisions, but also multi-phase consumers, such as a three-phase electric motor, can be connected to the local power grid. However, if individual outputs of the inverter and thus individual phase conductors of the local power grid are deactivated, damage to multi-phase consumers can occur. For this reason,

[0024] In one embodiment, it is provided that if a multi-phase load is electrically connected to at least two outputs of the inverter, all outputs of the inverter to which the multi-phase load is connected are deactivated, in particular after an electrical overload is detected. In one embodiment of the invention, it can be provided that a user can enter, for example via a button or a control panel, that a multi-phase load is connected to the local power supply network and, if an overload is detected, all outputs of the inverter to which the multi-phase load is connected are therefore deactivated. The deactivation preferably takes place after an overload has been detected. In one embodiment of the invention, all outputs of the inverter are deactivated if a multi-phase load is connected to the inverter.It is advantageous if the multi-phase load is detected by the inverter. If a multi-phase load is detected, a user does not have to inform the inverter that a multi-phase load is connected. The detection of a multi-phase load can take place, for example, by measuring an electrical variable at the at least two outputs of the inverter. In an exemplary embodiment, the multi-phase load is detected after at least one output of the inverter has already been deactivated by switching the at least one deactivated output to high impedance and measuring a voltage induced by the multi-phase load at the at least one deactivated output. For example, a voltage measuring sensor can be arranged at each of the at least two outputs for this purpose.In a particularly preferred embodiment of the invention, all outputs of the inverter are deactivated when a multi-phase load is detected. If no multi-phase load is connected to the local power grid, no voltage is induced in the at least one deactivated output. A measured voltage at a deactivated output therefore indicates the presence of a multi-phase load. High-impedance in this context preferably means that the electrical resistance between the deactivated output and a neutral conductor potential is at least 10 kΩ. Alternatively, it is possible to measure an induced current at the at least one deactivated output, wherein the at least one deactivated output is switched to low impedance. For this purpose, a current measuring sensor can be provided on each of the at least two outputs.A measured current at a deactivated output means the presence of a multi-phase load. In this context, low-resistance preferably means that the electrical resistance between the deactivated output and a neutral conductor potential is at most 10 Q, particularly preferably at most 1 Q. In a further embodiment, the presence of a multi-phase load can be detected before deactivating at least one output, for example by changing the amplitude and / or phase position of the output voltage at one output while the inverter is in operation. If a multi-phase load is connected to at least two outputs, a corresponding change in the output current at another output can be detected, which indicates a multi-phase load.

[0025] In one embodiment of the invention, a multi-phase load is detected when at least one output of the inverter is deactivated and a preferably induced voltage and / or a preferably induced current is measured at the at least one deactivated output of the inverter.

[0026] To avoid high induced currents in multi-phase loads, it is advantageous if the output in step iii) is switched to a high-impedance state upon deactivation. High-impedance in this context preferably means that the electrical resistance between the deactivated output and a neutral conductor potential is at least 10 kΩ.

[0027] In order to supply electrical consumers connected to the electrical power grid with electrical energy, it is advantageous if the inverter is supplied by an electrical energy storage device and / or an electrical energy generation device, in particular a photovoltaic system. For this purpose, the inverter can be connected to the electrical energy storage device or the electrical energy generation device. The electrical energy storage device can, for example, be an energy storage device with a storage capacity of at least 1 kWh.

[0028] The invention also relates to a method for supplying energy to a local energy supply network, in particular a building energy supply network, in the event of an undersupply by a public energy supply network, in particular in the event of a power failure, wherein the local energy supply network is initially connected to the public energy supply network via a disconnector and an inverter is connected to the local building energy supply network, the method comprising the following steps: a) detecting the undersupply of the local energy supply network by the public energy supply network; b) disconnecting the local energy supply network from the public energy supply network; c) operating an inverter according to a method for operating an inverter in island operation of the type described above.

[0029] An undersupply of the local energy supply network by the public energy supply network can be detected, for example, by a voltage dip and / or a frequency change in the voltage of the public energy supply network. The public energy supply network is preferably a public low-voltage or medium-voltage network. The local public energy supply network is connected to the local energy supply network via at least one isolating switch. With the aid of the at least one isolating switch, the local energy supply network can be separated from the public energy supply network. In particular, after the local energy supply network has been separated from the public energy supply network, an inverter can be operated in island mode according to the method described above for operating an inverter. In this way, the local energy supply network can be operated as an island network.

[0030] The invention also relates to an inverter, preferably an inverter for a photovoltaic system, with at least two outputs for connecting electrical outer conductors and a control and / or regulating device, wherein the control and / or regulating device is designed to output, in particular, alternating voltages that are phase-shifted with respect to one another, at outputs that have been activated, wherein each of the at least two outputs is assigned a priority level; to carry out a check for an electrical overload on the inverter; and to deactivate an output with the lowest priority level, at which an alternating voltage is output, by ending the output of the alternating voltage at the output if an overload of the inverter has been detected.

[0031] The advantages, effects and features described above in connection with the method for operating an inverter in island operation can also be applied to the inverter according to the invention. The inverter can be connected to external conductors of a local energy supply network. The control and / or regulating device can be formed, for example, by a microprocessor. The control and / or regulating device can be integrated into a housing of the inverter or be present as a separate control and / or regulating device. The control and / or regulating device can furthermore be designed to control and / or regulate the inverter in such a way that preferably phase-shifted alternating voltages are output at the outputs. Voltage measuring sensors can therefore be arranged at the at least two outputs.The voltage of a DC link can also be measured using a voltage measuring sensor. To assign priority levels to the outputs, the inverter can, for example, have at least one button or a control panel, such as a touch display. The priority levels can preferably be assigned to the inverter via a data connection. In particular, it can be provided that the priority levels can be set via a user interface. The user interface can, for example, be accessed in a browser or another application.

[0032] The invention is described below with reference to figures, to which it is not intended to be limited. They show:

[0033] Fig. 1 shows an inverter connected to a local power grid, with only single-phase loads being connected to the local power grid;

[0034] Fig. 2 shows an inverter connected to a local power grid, with a multi-phase load also being connected to the local power grid;

[0035] Fig. 3 voltage curves;

[0036] Fig. 4 a flow chart

[0037] Fig. 5A-C show time profiles of output voltages, output currents and an intermediate circuit voltage according to a first example;

[0038] Fig. 6A-C show time courses of output voltages, output currents and an intermediate circuit voltage according to a second example;

[0039] Fig. 7A-C show time profiles of output voltages, output currents and an intermediate circuit voltage according to a third example;

[0040] Fig. 8A-C show time profiles of output voltages, output currents and an intermediate circuit voltage according to a fourth example; and Fig. 9A-C show time profiles of output voltages, output currents and an intermediate circuit voltage according to a fifth example.

[0041] Fig. 1 shows an inverter 1 which is connected to a local energy supply network 2 with three outer conductors L2, L2 and L3 and a neutral conductor N. The local energy supply network 2 can be, for example, the energy supply network of a building (not shown), for example a single-family home or an office building. The local energy supply network 2 is connected to a higher-level public energy supply network 4 via a multi-phase isolating switch 3 and is supplied via this during normal operation, i.e. when there is no undersupply due to a power failure. The inverter 1 can feed electrical energy E from an electrical energy storage device 5 and / or an energy generation device 6, which can be designed, for example, as a photovoltaic system 7, into the local energy supply network 2.For this purpose, the inverter 1 has a plurality of outputs 8a-c, to which the outer conductors L2, L2, L3 of the local power supply network 2 can be connected. The neutral conductor N can be connected to a terminal 50 of the inverter 1. The outputs 8a-c are each connected to electrical switches 9, for example IGBTs (Insulated-Gate Bipolar Transistors), of the inverter 1. The switches 9 are in turn connected to a DC voltage intermediate circuit 10, which has at least one capacitor 11 and to which an intermediate circuit voltage U. zis applied. In the illustration shown, two intermediate circuit capacitors 11 are provided, the connection point 53 of which is connected to the terminal 50. In one embodiment, the inverter 1 can also have one or more boost converters (not shown). By means of a switching pattern (not shown) for the switches 9, which can be predetermined by a control and / or regulating device 51, alternating voltages U2, U2, U3 can be generated at the outputs 8a-c, which are each phase-shifted by 120° to one another. With the aid of a measuring device 52a, the output voltages U a , Ub, U c measured at the outputs 8a-c and used for controlling and / or regulating the inverter 1 by the control and / or regulating device 51. In one embodiment of the invention, electrical currents I a , I b , I cat the outputs 8a-c using the measuring device 52a. With the help of a further measuring device 52b, the intermediate circuit voltage U z measured and also made available to the control and / or regulating device 51. During normal operation, the phase positions of the voltages Ui, U2, U3 output at the outputs 8a-c correspond to the respective voltages of the higher-level power supply network 2.

[0042] In Fig. 1, single-phase loads 12a, 12b are connected to the local power grid 2. In the illustration shown, the loads 12a, 12b are each connected to different phase conductors L2, L2, L3 and to the neutral conductor N. The loads 12a, 12b shown are lamps 12a and a refrigerator 12b.

[0043] In the event of a power outage 14 in the higher-level public power grid 4, the local power grid 2 can be supplied by the inverter 1, which draws the electrical energy E from the electrical energy storage device 5 and / or the energy generation device 6. The inverter 1 can thus be operated in isolated mode, supplying the local power grid 2 as an isolated grid. Before the inverter 1 feeds into the local power grid 2 in isolated mode, the grid is disconnected from the public power grid 4 by means of the isolating switch 3.

[0044] During island operation, it may happen that the loads 12a, 12b require more electrical power or more electrical energy E than can be provided by the inverter 1, the electrical energy storage device 5 and / or the energy generation device 6. In this case, an electrical overload occurs. In such a case, it is known from the prior art to completely deactivate the inverter 1 so that it does not output an alternating voltage Ui, U2, U2 at any of the outputs 8. This prevents damage to or malfunction of the loads 12a, 12b. Unfortunately, this means that all of the loads 12a, 12b are switched off.

[0045] However, consumers 12a, 12b of varying importance are typically connected to a local energy supply network 2. A refrigerator 12b or a lamp 12a in the basement of a building are generally more important in the event of a power outage than, for example, garden lighting, a hairdryer, or a games console.

[0046] According to the invention, it is therefore provided that each output 8a-c for an outer conductor L z , L2, L3 is assigned a priority level A, B, C and in the event of an overload of the inverter 1, the active output with the lowest priority level A, B, C, at which an alternating voltage Ui, U2, U2 is output, is deactivated. Before an output 8a-c is deactivated, the setpoint of the output voltages U a , Ub, U cbe reduced to eliminate the overload. If this does not work, output 8a-c can be deactivated with the lowest priority level A, B, C. The electrical overload can be detected by measuring an electrical value of the inverter 1, for example the measured intermediate circuit voltage U z , the measured output voltages U a , üb, U c , the electrical output currents I a , Ib, I c and / or related electrical voltages or currents are each compared with a corresponding threshold value. If the threshold value is exceeded or undershot, depending on the type of electrical quantity, an electrical overload can be assumed. The threshold value can, for example, depend on a setpoint for the electrical quantity. For example, if the measured intermediate circuit voltage U zis below an intermediate circuit voltage threshold value, which in one embodiment can be 90% of a setpoint value, an electrical overload can be detected. The same applies to the output voltages and an output voltage threshold value. If, for example, a measured output current is above an output current threshold value, which in one embodiment can be 110% of a setpoint value, an electrical overload can also be detected. In the example shown, A represents the highest priority level and C the lowest priority level. Consumers 12a connected to the output 8b with the lowest priority level C are therefore deactivated first in the event of an electrical overload, which in many cases can also eliminate the electrical overload.Consumers 12a, 12b connected to the outputs 8a, 8c with the next higher priority levels A, B will thus continue to be supplied with electrical energy E. Therefore, important consumers 12a, 12b, such as refrigerators 12b, are preferably connected to an outer conductor L3, L2, L3, which is connected to an output 8a, 8c of a high or the highest priority level A, B. Unimportant consumers 12a, 12b, such as garden lighting or circulation pumps for swimming pools, are preferably connected to an output 8a, 8b of a low or the lowest priority level B, C. If an electrical overload still exists after deactivation of the output 8b with priority level C, the steps described can be repeated and now the active output 8a with the lowest priority level B, at which an alternating voltage Ui, U3 is currently output, can be deactivated.This procedure may lead to the deactivation of all outputs 8a-c of inverter 1.

[0047] After an output 8a-c has been deactivated, it can be reactivated at intervals for one or more periods of the alternating voltage U3, U3, U3 to check whether the overload still exists. If this is not the case, the output 8a-c with the highest priority level among those deactivated can be reactivated. This can be repeated until all outputs are reactivated.

[0048] Fig. 2 shows a circuit diagram in which a multi-phase load 13, hereinafter also referred to as multi-phase consumer 13, is connected to the local energy supply network 2. The multi-phase consumer 13 can, for example, be an electric motor which represents a predominantly inductive load (see the inductances 15a, 15b, 15c). With the exception of the additional multi-phase consumer 13, the circuit diagram in Fig. 2 corresponds to the circuit diagram according to Fig. 1, which is why repetitions are omitted below. If a multi-phase consumer 13, in particular a three-phase consumer, is connected to the local energy supply network 2 and one of the outputs 8a-c of the inverter 1 is deactivated, damage can occur due to the asymmetrical voltage supply.It is therefore preferably provided that, when a multi-phase load 13 is connected to the local power supply network 2, those outputs 8a-c to which the multi-phase load 13 is connected, in particular all outputs 8a-c, are deactivated in the event of an electrical overload. For this purpose, in one embodiment of the invention, the presence of a multi-phase load 13 can be communicated to the inverter 1 by manual input. In a further embodiment, a multi-phase load 13 can be detected by measuring voltages Ui induced at already deactivated outputs 8a-c. n d and / or induced currents I ind The measurement of induced voltages Ui n d and / or induced currents lind can be measured using the measuring device 52a. In particular, induced voltages Uind are defined as voltages U a , Ub, U ccan be detected at deactivated outputs 8a-c and indicate a multi-phase load 13. Deactivated outputs 8a-c can be switched with high impedance (for measuring induced voltages Uind), preferably with a resistance value of at least 10 kΩ between the respective deactivated output 8a-c and the neutral conductor potential, or with low impedance (for measuring induced currents lind), preferably with a resistance value of maximum 1 Ω between the respective deactivated output 8a-c and the neutral conductor potential.

[0049] Fig. 3 shows an example of the measured voltages U a , Ub, U cat the outputs 8a-c when a multi-phase load 13 is connected to the local power grid 2. In the illustration shown, two of the three outputs 8 (outputs 8a, 8c) are activated and one output 8b is deactivated and switched to high impedance. It can be seen that a voltage Ui is present in the inductance L2 connected to the deactivated output 8b. nd Due to the fact that the output 8b is deactivated and does not output an alternating voltage U2, by measuring the voltage Ui n d the multi-phase load 13 can be detected.

[0050] Fig. 4 shows an exemplary sequence of the method according to the invention, as it can occur in the event of an overload of the inverter. Of course, other sequences of the method are also possible. In the event of a power failure 14 (block 100, see Fig. 1 and Fig. 2), the local power grid 2 is separated from the public power grid 4 by means of the isolating switch 3 (block 101). Subsequently, all outputs 8a-c of the

[0051] Inverter 1 is activated (block 102). Each output 8a-c is assigned a different priority level A, B, C. In step i), an alternating voltage Ui, U2, U3 is output at each activated output 8a-c (block 103). In step ii), a check is carried out to determine whether an electrical overload has occurred (block 104). If there is no electrical overload, the outputs 8a-c, which output an alternating voltage Ui, U2, U3, remain activated (branch 105, which returns to block 103). If an electrical overload has been detected (branch 106), in step iii) the active output 8a-c with the lowest priority level A, B, C, at which an alternating voltage Ui, U2, U3 is output, is deactivated by terminating the output of the alternating voltage Ui, U2, U3 at the output 8a-c (block 107). In a preferred embodiment of the invention, multiphase loads 13 are also deactivated, in particular by measuring induced voltages Ui nd or induced currents lind at deactivated outputs 8a-c are detected (block 108). If a multi-phase load 13 is detected (branch 109), preferably all outputs 8a-c of the inverter 1 are deactivated and the inverter 1 is thus switched off (block 110). If no multi-phase load 13 was detected, alternating voltages Ui, U2, U3 continue to be output at the (still) activated outputs 8a-c (see branch 111, which flows into branch 105). If the electrical overload has been eliminated, for example because loads 12a, 12b were removed from the local energy supply network 2 (step iv-a)), or the inverter 1 can provide a higher electrical output power and / or more electrical energy E because the energy generating device 4 can produce more electrical power orprovides energy E (step iv-b)), in block 112 the output 8a-c with the highest priority level A, B, C among the deactivated outputs 8a-c can be reactivated by outputting an alternating voltage Ui, U2, U3 at the said output 8 (block 112 or steps iv-a) and iv-b)). In one embodiment of the invention the output 8a-c with the highest priority level A, B, C among the deactivated outputs 8a-c can be reactivated in block 112 after a certain period of time, for example after 10 seconds. If an electrical overload is then detected again (step i)), in step iii) the said output can be deactivated again.

[0052] The deactivation of outputs 8a-c due to overload is explained below using the time curves of the output voltages U a , üb, U c , the output currents I a , I b , I cand the intermediate circuit voltage U z illustrated in more detail. The abscissas of Fig. 5a-9C each describe a time t in seconds. The ordinates of Fig. 5A, 6A, 7A, 8A and 9A each describe time courses of output voltages U a , U b , U c in volts. The ordinates of Fig. 5B, 6B, 7B, 8B and 9B describe the time courses of output currents I a , I b , I c in amperes. The ordinates of Fig. 50, 60, 70, 80 and 90 describe the time profiles of the intermediate circuit voltages U z in volts .

[0053] In Fig. 5A-C it can be seen that at the outputs 8a-c alternating voltages U z , U z, U3 are output. In the example shown, it is assumed that 3.7 kW of power is available and can be accessed from inverter 1. Output 8a has been assigned the lowest priority 0. Output 8b has been assigned the highest priority A. Output 8c has been assigned the medium priority B.

[0054] At time T o A power of 3 kW is drawn at the outputs 8a-c by connected single-phase loads 12a, 12b. At time T z Another large single-phase consumer 12a, 12b, for example a resistive consumer such as a hotplate with a power requirement of 1.5 kW, is connected to the output 8a with the lowest priority 0, so that a total power requirement of 4.5 kW exists, which would exceed the available power of 3.7 kW. It can be seen that this results in an overload of the inverter 1 and the intermediate circuit voltage Uz collapses. The current I a at output 8a increases due to the existing power requirement of 4.5 kW - for example to twice the amount (as shown).

[0055] Subsequently, in one embodiment of the invention, the setpoint value for the output voltages U a , Ub, U c at outputs 8a-c to 90% in order to possibly eliminate the overload of inverter 1. This reduces the output voltage from 230 V (effective value, corresponding to an amplitude value of approximately 325 V) to 209 V (effective value, corresponding to an amplitude value of approximately 292 V). However, in the diagram shown, the current I a at output 8a remains high - and also the intermediate circuit voltage U z remains below its setpoint U Z d - The previously increased current I a at output 8a is achieved by reducing the setpoint for the output voltages Ua , üb, U c in the case of a resistive load, the load is reduced by approximately 10%. The required power is reduced in this case by approximately 19%. This reduction in electrical power is not sufficient, which is why the intermediate circuit voltage U z still below its target value U z d remains . The reduction of the setpoint for the output voltages U a , üb, U c therefore does not lead to the desired result. This means that this measure prevents the intermediate circuit voltage from rising to the setpoint and deactivates at least one output 8a-c.

[0056] Subsequently, at time T2, the output 8a is deactivated (step iii of the method according to the invention) since the lowest priority C has been assigned to the output 8a.

[0057] Deactivating output 8a eliminates the overload of inverter 1. Outputs 8b and 8c can therefore remain active. The setpoint of the voltages üb and U c at the outputs 8b, 8c can therefore be increased to 100% again, as can be seen in Fig. 5A. The intermediate circuit voltage U z rises back to the setpoint U zd or settles on it or stabilizes at the setpoint. After deactivation of the output 8a, in a preferred variant of the invention, the output 8a can be reactivated after a predetermined time period of, for example, 10 seconds, in order to check whether the overload is still present (see Fig. 6A-C). It would of course also be possible for more power to be made available by an electrical energy storage device 5 and / or an energy generation device 6. Therefore, after the predetermined time period has elapsed, an output voltage U a output . To check whether the overload of inverter 1 is still present , the output voltage U afrom the time T3 for one or more periods at the output 8a. In a variant of the invention, as already explained in more detail above, an electrical variable of the inverter 1 can be compared again with a corresponding threshold value in order to determine whether the overload of the inverter 1 still exists or whether it has ceased. In another variant, it can be determined by calculating the electrical power whether the overload of the inverter 1 still exists. The electrical power can be determined in particular by measuring the electrical currents I output at the outputs. a , I b , I c and multiply by the respective electrical voltage U a , üb, U cbe determined. If the available power - in this case 3.7 kW as mentioned above - is not exceeded, the output 8a can be activated again. If, on the other hand, an overload is detected again, i.e. the power exceeds the available power while the output 8a is switched on, the output 8a is deactivated again. This is shown in Fig. 6A-C. The output 8a remains deactivated for the remainder of the period shown in Fig. 6A-C. However, the output 8a can be activated again to check once more, as described, whether the overload still exists. This process can be repeated at regular intervals, for example every 10 seconds.

[0058] The case in which the overload has been eliminated after the deactivation of the output 8a is shown in Fig . 7A-C . It can be seen that the output 8a is activated at time T3 and subsequently remains activated due to the elimination of the overload . It can be seen that the output 8a is activated at time T3 and the output voltages U a , Ub, U c do not need to be reduced or the intermediate circuit voltage U z does not fall below the limit set for overload. Therefore, no overload is detected and output 8a remains activated.

[0059] Fig. 8A-C shows the case where connecting a single-phase load 12a, 12b to one output 8a-c can lead to deactivation of another output 8a-c in the event of an overload. In Fig. 8A-C, the highest priority A is assigned to output 8a, the medium priority B, and the lowest priority C to output 8c. The load 12a, 12b is connected to output 8a at time T2, which leads to deactivation of output 8c at time T2, whereby the overload can be eliminated because the required power is therefore below the available power of 3.7 kW.

[0060] Fig. 9A-C describe the case in which a multiphase load 13 is connected to the inverter 1. At time T2, an additional load 12a, 12b is connected to the output 8a. Since a reduction of the setpoint for the output voltage U a , üb, U cIf the overload is not eliminated, output 8c with the lowest priority C is deactivated at time T2. Output 8c is switched to high impedance.

[0061] However, it turns out that an induced voltage U 2nd with a 50 Hz component and smaller amplitude can be measured at the output 8c, which is an indication that a multi-phase load is connected to the inverter. Subsequently, at time T3, all outputs 8a-c of the inverter 1 are deactivated in order to avoid damage to the multi-phase load 13. The deactivation of all outputs 8a-c can take place simultaneously or one after the other, in particular according to the assigned priority levels. In the latter case, it may be sufficient to switch off just one additional output 8a-c, for example if only one two-phase load is connected and the overload of the inverter 1 can be eliminated by deactivating the two outputs 8a-c to which the two-phase load is connected.As described above, after a predetermined period of time, one or more outputs 8a-c can be activated again to check whether the overload of the inverter 1 still exists.

Claims

Patent claims:

1. Method for operating an inverter (1) in island operation, wherein the inverter (1) has at least two outputs (8a-c) for connecting electrical outer conductors (Lx, L2, L3) and the method comprises the following steps: i) outputting alternating voltages (Ui, U2, U3) which are in particular phase-shifted with respect to one another at outputs (8a-c) which have been activated, wherein each of the at least two outputs (8a-c) is assigned a priority level (A, B, C); ii) checking the inverter (1) for an electrical overload; iii) deactivating that output (8a-c) with the lowest priority level (A, B, C) at which one of the alternating voltages (Ui, Ui, U3) is output, by terminating the output of the alternating voltage (Ui, Ui, Ui) at this output (8a-c) when the electrical overload of the inverter (1) has been detected.

2. Method according to claim 1, characterized in that steps i), ii) and iii) are continuously repeated.

3. Method according to claim 1 or 2, characterized in that the inverter (1) is checked for electrical overload by detecting an electrical variable, in particular an electrical voltage or an electrical current, of the inverter (1) and comparing the electrical variable with a threshold value, and the electrical overload of the inverter (1) is determined if the electrical variable falls below or exceeds the threshold value.

4. Method according to claim 3, characterized in that the electrical quantity is an electrical current, in particular an output current at one of the outputs (8a-c), a quantity associated with the electrical current, an electrical intermediate circuit voltage (U z ) of an intermediate circuit (10) of the inverter (1), an electrical output voltage (U a , Ub, U c ) at least one of the outputs (8a-c) of the inverter (1) or a device connected to the electrical intermediate circuit voltage (U z ) and / or the output voltage.

5. Method according to one of claims 1 to 4, characterized in that an assignment of the priority levels (A, B, C) to the at least two outputs is adjustable.

6. Method according to one of claims 1 to 5, characterized in that each of the at least two outputs (8a-c) of the inverter (1) is assigned a unique priority level (A, B, C) which differs from the priority levels (A, B, C) of the other outputs (8a-c).

7. Method according to one of claims 1 to 6, characterized in that the inverter (1) is connected to a local energy supply network (2), in particular to a building energy supply network, and supplies the local energy supply network (2).

8. Method according to one of claims 1 to 7, characterized by the step iv-a) reactivating that output (8a-c) with the highest priority level (A, B, C) among the deactivated outputs (A, B, C) when the overload which led to the deactivation of the output (8a-c) no longer exists.

9. Method according to one of claims 1 to 8, characterized by step iv-b) reactivating the output (8a-c) with the highest priority level (A, B, c) among the deactivated outputs (8a-c) if the inverter (1) can provide a higher electrical output power and / or more electrical energy (E) than was the case when the output (8a-c) was deactivated.

10. Method according to one of claims 1 to 9, characterized in that when a multi-phase load (13) with the at least two outputs (8a-c) of the inverter (1) are electrically connected, all outputs (8a-c) of the inverter to which the multi-phase load (13) is connected are deactivated, in particular after an electrical overload has been detected, preferably wherein the multi-phase load (13) is detected.

11. The method according to claim 10, characterized in that the multi-phase load (13) is detected when at least one output (8a-c) of the at least two outputs (8a-c) of the inverter (1) is deactivated and a preferably induced voltage (Ui n d) and / or a preferably induced current (lind) is measured at the at least one deactivated output (8a-c) of the inverter (1).

12. Method according to one of claims 1 to 11, characterized in that the output (8a-c) is switched to a high-impedance state during deactivation in step iii).

13. Method according to one of claims 1 to 12, characterized in that the inverter (1) is supplied by an electrical energy storage device (5) and / or an electrical energy generation device (6), in particular a photovoltaic system (7).

14. Method for supplying energy to a local energy supply network (2), in particular a building energy supply network, in the event of an undersupply by a public energy supply network (4), in particular in the event of a power failure (14), wherein the local energy supply network (2) is initially connected to the public energy supply network (4) via a disconnector (3) and an inverter (1) is connected to the local building energy supply network (2), the method comprising the following steps: a) detecting the undersupply of the local energy supply network (2) by the public energy supply network (4); b) disconnecting the local energy supply network (2) from the public energy supply network (4); c) operating the inverter (1) according to a method according to claims 1 to 13.

15. Inverter (1), preferably inverter for a photovoltaic system (7), with at least two outputs (8a-c) for connecting electrical outer conductors (L2, L2, L3) and a control and / or regulating device (51), characterized in that the control and / or regulating device (51) is designed to output, in particular, mutually phase-shifted alternating voltages (Ui, U2, U3) at outputs (8a-c) that have been activated, wherein each of the at least two outputs (8a-c) is assigned a priority level (A, B, C); to carry out a check for electrical overload on the inverter; and to deactivate an output (8a-c) with the lowest priority level, at which one of the alternating voltages (Ui, U2, U2) is output, by stopping the output of the alternating voltage (U2, U2, U2) at the output (8a-c) when the electrical overload of the inverter (1) has been detected.

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