Method for operating an inverter, method for supplying energy to a local energy supply network, and inverter
Patent Information
- Application Number
- AU2025258424
- Authority / Receiving Office
- AU · AU
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2024-04-17
- Filing Date
- 2025-04-16
- Publication Date
- 2026-09-17
Smart Images
Figure 00000000_0000_ABST
Abstract
Description
The invention relates to a method for operating an inverter in an isolated operation, wherein the inverter has at least two outputs for connecting electrical phase conductors. The invention also relates to a method for supplying energy to a local energy supply network. Furthermore, the invention relates to an inverter, preferably an inverter for a photovoltaic system, with at least two outputs for connecting electrical phase conductors and a feed-forward and / or feedback control device. In the event of a power failure, inverters can be used in isolated operation to supply electrical energy to local energy supply networks, such as building energy supply networks. For this purpose, the inverters may be connected, for example, to an electrical energy storage device and / or an electrical energy supply device, such as a photovoltaic system. This allows consumers connected to the local energy supply network, such as refrigerators, lighting equipment or heating systems, to be operated even in the event of a power failure, at least for a certain period of time, ideally until the cause of the power failure has been remedied. However, if the electrical power required by the consumers exceeds the available electrical power (overload), the inverters must cease operation. As a result, even essential consumers 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. It is known from the prior art to prioritize consumers that are connected to a local energy supply network and, depending on the prioritization, to deactivate them if there is an overload of the inverter or an energy deficit. Such an approach 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 be able 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 required. 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 polyphase motor. In light of these statements, the object of the present invention is to alleviate 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 at the outset, which, in the event of an overload of the inverter, can at least partially maintain operation and can continue to supply certain consumers with electrical energy in a simple manner. It is particularly preferable that a communication link with the consumers is not required. This object is achieved by a method for operating an inverter in isolated 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. According to the invention, the following steps are provided in a method for operating an inverter in isolated operation of the type mentioned at the outset: i) outputting AC voltages, in particular AC voltages which are phase-offset with respect to one another, at outputs which have been activated, each of the at least two outputs being assigned a priority level; ii) checking the inverter for an electrical overload; and iii) deactivating the output with the lowest priority level at which an AC voltage is output by terminating the output of the AC voltage at the output if an overload of the inverter has been detected. 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 generating device. At the same time, by deactivating the output with the lowest priority level at which an AC voltage is output, the overload of the inverter can be eliminated in many cases, so that AC voltages and electric currents can be output at the activated outputs at a predetermined level, i.e., according to a setpoint. Deactivating an output means that no AC 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 AC voltages are continuously output at activated outputs and further outputs can also be deactivated if, despite deactivation of the output with the lowest priority level at which an AC voltage is output, an electrical overload is still present. In the event of a high electrical overload, the iterative execution of steps ii) and iii) can also lead to all outputs of the inverter being deactivated, so that an AC voltage is no longer output at any of the outputs. An electrical overload may arise, in particular, when the consumers connected to the local energy supply network require more electrical power or electrical energy than the inverter, an electrical energy storage device connected to the inverter and / or an electrical energy generating device can provide. Steps i), ii) and / or iii) may be carried out at least partially or entirely overlapping. In any case, the designation of the steps does not necessarily specify their order of execution. Outputs of the inverter can be activated, in particular, by outputting an AC voltage. In isolated operation, the inverter feeds into the local energy supply network without the local energy supply network being supplied by a higher-level public energy supply network. In other words, the local energy supply network is supplied exclusively by at least one inverter, or in one variant, by several inverters. In isolated operation, the inverter is therefore not guided by a voltage and / or a current in the local energy supply network. In a preferred embodiment, the local energy supply network is separated from the higher-level public energy supply network by a disconnector in isolated operation. The inverter is configured to convert a DC voltage into an AC voltage at the outputs. For this purpose, the inverter may have a DC voltage intermediate circuit, which may 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 phase conductors of a local energy supply network and is configured to output AC voltages at the outputs, in particular phase-offset relative to one another. The AC voltages are preferably offset from each other by 360 / n°, where n represents the number of outputs of the inverter. Preferably, the number of outputs is n=3. A phase conductor, i.e., phases, of the local energy supply network can be connected to each of the at least two outputs of the inverter. The level of the output AC voltage is preferably substantially 230 V and has a frequency of preferably substantially 50 Hz. The inverter may also have a terminal for connection to a neutral conductor of the local energy supply network. A priority level is assigned to each of the at least two outputs of the inverter. The priority levels may be in ascending order and thus specify a clear ranking. The priority levels may 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. Preferably, each priority level is present only exactly once. Thus, in one embodiment of the invention, each output may be assigned a different priority level, so that the at least two outputs and thereby the connected phase conductors of the local energy supply network are prioritized differently. In order to prioritize the phase conductors of the local energy supply network, they may be connected to an output with a priority level that has already been assigned, or the priority level of the outputs may be set after connection to the phase conductors. In the first case, it is also possible for the priority levels to be permanently assigned to the outputs, i.e., unchangeably. The inverter can be connected via the at least two outputs to the local energy supply network, to which in turn the consumers are connected. In step i), AC voltages are output at outputs that have been activated. Preferably, at the beginning of the method, all of the at least two outputs of the inverter are activated, in particular, substantially simultaneously, so that an AC voltage is output at all of the at least two outputs. However, it is also possible to activate the outputs successively at intervals at the beginning of the method. The inverter may be checked for an 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. It is also possible to measure the output currents. In step iii), the output with the lowest priority level, at which an AC voltage is output, is deactivated. As a result, consumers connected to the deactivated output of the inverter are no longer supplied with electrical energy, thus reducing the electrical load, which in many cases can lead to the elimination of the inverter overload. Those outputs with a higher priority level, at which an AC voltage continues to be output, remain activated, unless an electrical overload is again detected during a renewed iteration of the method and the output with the lowest priority level, at which an AC voltage is output, is again deactivated. By prioritizing the outputs of the inverter, the phase conductors of a connected local energy supply network and thus the consumers are prioritized. Less important consumers may be connected to a common phase conductor that is connected to an output to which a low or the lowest priority level is assigned. Essential consumers may be connected to a common phase conductor that is connected to an output to which a high or the highest priority level is assigned. By connecting the consumers to such prioritized phase conductors or by connecting the phase conductors to prioritized outputs, less important consumers are switched off first in the event of an electrical overload. Essential consumers, such as refrigerators and certain lamps, can continue to be supplied with electrical energy. The inverter may be, for example, an off-grid inverter or a hybrid inverter. In one embodiment of the invention, it may be provided that before deactivating an output 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, this may already eliminate the overload, so that there is no need to deactivate an output. Thus, if an overload is 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 AC voltage is output, deactivated in this embodiment. The inverter is preferably designed as a three-phase inverter with three outputs, each for connecting a phase conductor. In one 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 then again detected by comparing the electrical quantity with the threshold value, the output can be deactivated again in step iii). In one embodiment of the invention, it is provided that steps i), ii) and iii) are repeated continuously. Steps i), ii) and iii) can be carried out at least partially in parallel in terms of time. By continuously checking the inverter for an electrical overload, the inverter or any connected supply device is monitored. Steps ii) and iii) may be performed, for example, at regular intervals, for example, at 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) may be continuously repeated throughout the operation of the inverter. In one embodiment of the invention, steps i), ii) and iii) may be repeated or executed and the inverter or the supply device thereby monitored for an overload until, due to a sustained electrical overload, an AC voltage is no longer 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. In one embodiment of the invention, it is provided that the in verter is checked for electrical overload by an electrical quantity, in particular an electrical voltage or an electrical current, of the inverter being detected and the electrical quantity being compared with a threshold value, and an overload being detected when the electrical quantity falls below or exceeds the threshold value. The electrical quantity can be detected by a measuring device, in particular one or more voltage and / or current measuring sensors. The threshold value may, for example, be a predetermined percentage of a setpoint for the electrical quantity or a maximum permissible value of the electrical quantity. For example, the threshold value may be between 105 % and 120 %, in particular substantially 110 %, of a rated current. The rated current may be, for example, an output current. In another embodiment, the threshold value may be, for example, between 80 % and 95 %, in particular substantially 90 %, of a nominal voltage. The nominal voltage may be, for example, the intermediate circuit voltage or an output voltage at the outputs. Whether the threshold value is undershot or exceeded for checking the inverter with respect to electrical overload depends in particular on the type of electrical quantity. The phrase "falls 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. For example, if the electrical quantity is an electrical voltage, falling below the threshold value may mean an electrical overload. For example, if the electrical quantity is an electric current, exceeding the threshold value may mean an electrical overload. In one embodiment of the invention, as already described above, it can be provided that the setpoint 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. In one embodiment of the invention, it is provided that the electrical quantity is an electric current, in particular an output current at one of the outputs (8a-c), a quantity associated with the electric current, an electrical intermediate circuit voltage of an intermedi ate circuit of the inverter, an electrical output voltage of at least one of the outputs of the inverter or a quantity associated with the intermediate circuit voltage and / or the output voltage. If the electrical quantity is an intermediate circuit voltage of an intermediate circuit of the inverter, the threshold value may, for example, be in the range between 70 % and 98 % of a setpoint value, wherein the setpoint value 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 may depend on the parameters (for example, the voltage or the frequency, etc.) of the respective supply network. If the electrical quantity is an output voltage of at least one of the outputs of the inverter, the threshold value may be, for example, between 70 % and 98 % of a setpoint value, wherein the setpoint value of the output voltage is preferably between 200 V and 260 V, in partic ular substantially at 230 V. The specified voltages represent RMS values and are based on a neutral conductor potential. It is particularly advantageous if the output voltages of all outputs of the inverter are detected as electrical quantities and compared with a threshold value, since the output voltages of the outputs are also used for the feedback control and / or feed-forward control of the inverter. A quantity associated with the electric current, the intermediate circuit voltage and / or the output voltage may be, for example, an electric power. The detected or measured output voltages at the outputs of the inverter may substantially correspond to one of the output AC voltages, but they do not have to. The former is the case, for example, when the inverter is operated in normal operation, i.e., not in isolated operation, or when there is no overload of the inverter in isolated operation. The latter is the case, for example, when the output at which the output voltage is detected is deactivated. In that case, a voltage of 0 V or, as described in more detail below, an induced voltage at the deactivated out put can be detected as the output voltage. It is preferred that the assignment of the priority levels to the at least two outputs be adjustable. For example, it may be provided that a priority level can be assigned to each output by a user. The assignment of the priority level may be made or changed, for example, during initial commissioning or during ongoing operation of the inverter. Preferably, the priority level can be set via an input interface, for example, via buttons or a control panel. Setting by a computer via a data interface may also be provided. In an alternative embodiment of the invention, however, it may also be provided that each output is assigned a preferably unchangeable priority level, and that the priority levels are assigned to the phase conductors by connecting the phase conductors of the local energy supply network to the outputs. 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 when the inverter is overloaded. 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 may be, for example, an energy supply network of a house that is operated with a voltage of preferably substantially 230 V (RMS value). The local energy supply network preferably has three phase conductors, to each of which consumers are connected. The local energy supply network may also have a neutral conductor. In one embodiment of the invention, a plurality of preferably identical inverters can also feed into the local energy supply network and carry out the method according to the invention. Preferably, those outputs of the inverters that are connected to the same phase conductors of the local energy supply network are each assigned the same priority levels, or the outputs of the inverters are prioritized in the same order with respect to their connection to the phase conductors. In other words, corresponding outputs of the inverters are assigned the same priority levels. In this way, in the event of an electrical overload, those outputs of the inverters that are connected to the same phase conductor are deactivated in step iii). This avoids error detections of polyphase loads. If multiple inverters feed into the local energy supply network, they can be operated in a master-slave network and communicate, for example, via a data connection. However, a data connection is not absolutely necessary, especially if the same priority levels are assigned to corresponding outputs of the inverters. It is preferred that the method includes the following step: iv-a) reactivating the output with the highest priority level among the deactivated outputs when the overload that led to the deactivation of said output is no longer present. The overload may, for example, no longer be present if a consumer has been disconnected from the local energy 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 that the output with the highest priority level among the deactivated outputs is activated after a predetermined period of time, preferably for one or more periods. If an electrical overload is then again detected by comparing the electrical quantity with the threshold value, the output can be deactivated again. The determination of whether an overload is present can be made, as described above, by comparing an electrical quantity with a threshold value. In this context, reference is made to the above statements. The determination of whether the overload is still present may additionally or alternatively also be made, for example, by calculating the required power of the connected consumers. If the required power 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 the activation of the output with the highest priority level among the deactivated outputs. The specified time period for reactivating a deactivated output may be, for example, between 0.1 seconds and 30 seconds. It is also possible for several different predetermined time periods to be provided. For example, the predetermined period of time after the first deactivation of a relevant output may be 0.1 seconds for a first period of time, which may be 5 seconds, for example. After the first period of time has elapsed, the specified time period may be extended and may be, 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 period of time has elapsed. It is preferred that the method includes the following step: iv-b) reactivating the output with the highest priority level among the deactivated outputs if inverters can provide a higher electrical output power and / or more electrical energy than was the case when 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 may be the case, for example, with a photovoltaic system when the sun is at a more favorable angle to the photovoltaic system or when clouds have dissipated, so that more energy from the 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. Not only single-phase consumers, such as typically lamps or televisions, but also polyphase consumers, such as a three-phase electric motor, can be connected to the local energy supply network. However, if individual outputs of the inverter and thus individual phase conductors of the local energy supply network are deactivated, damage to polyphase consumers may occur. For this reason, in one embodiment, it is provided that, when a polyphase load is electrically connected to at least two outputs of the inverter, all outputs of the inverter to which the polyphase load is connected are deactivated, in particular after an electrical overload has been 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 polyphase load is connected to the local energy supply network and, therefore, in the event of a detected overload, all outputs of the inverter to which the polyphase load is connected are 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 when a polyphase load is connected to the inverter. It is advantageous if the polyphase load is detected by the inverter. In the event that a polyphase load is detected, a user does not have to inform the inverter that a polyphase load is connected. The detection of a polyphase load may be carried out, for example, by measuring an electrical quantity at the at least two outputs of the inverter. In an exemplary embodiment, the polyphase 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 polyphase load at the at least one deactivated output. For example, a voltage measuring sensor may be arranged at each of the at least two outputs for this purpose. In a particularly preferred embodiment of the invention, it is provided that all outputs of the inverter are deactivated when a polyphase load is detected. If no polyphase load is connected to the local energy supply network, no voltage is induced in the at least one deactivated output. A measured voltage at a deactivated output thus indicates the presence of a polyphase load. In this context, high impedance preferably means that the electrical resistance between the deactivated output and a neutral conductor potential is at least 10 kQ. 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 a low impedance. For this purpose, a current measuring sensor may be provided at each of the at least two outputs. A measured current at a deactivated output indicates the presence of a polyphase load. In this context, low impedance preferably means that the electrical resistance between the deactivated output and a neutral conductor potential is at most 10 Q, more preferably at most 1 Q. In a further embodiment, the presence of a polyphase load can be detected before deactivating at least one output by, for example, changing the amplitude and / or phase position of the output voltage at an output during ongoing operation of the inverter. If a polyphase load is connected to at least two outputs, a corresponding change in the output current can be detected at another output, indicating a polyphase load. In one embodiment of the invention, a polyphase load is therefore 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. To avoid high induced currents with polyphase loads, it is advantageous if the output is switched to a high-impedance state during deactivation in step iii). In this context, high impedance preferably means that the electrical resistance between the deactivated output and a neutral conductor potential is at least 10 kQ. In order to be able to supply the electrical consumers connected to the electrical energy supply network with electrical energy, it is advantageous for the inverter to be supplied by an electrical energy storage device and / or an electrical energy generating device, in particular a photovoltaic system. For this purpose, the inverter may be connected to the electrical energy storage device or the electrical energy generating device. The electrical energy storage device may be, for example, an energy storage device with a storage capacity of at least 1 kWh. 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 net work 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 isolated operation of the type described above. An undersupply of the local energy supply network by the public energy supply network may be detected, for example, by a voltage dip and / or a frequency change of the voltage of the public energy supply network. The public energy supply network is preferably a public low- or medium-voltage grid. The local public energy supply network is connected to the local energy supply network via at least one disconnector. With the help of the at least one disconnector, the local energy supply network can be disconnected from the public energy supply network. In particular, after the local energy supply network has been disconnected from the public energy supply network, an inverter can be operated in isolated operation according to the method described above for operating an inverter. In this way, the local energy supply network can be operated as an isolated network. The invention also relates to an inverter, preferably an inverter for a photovoltaic system, with at least two outputs for connecting electrical phase conductors and a feed-forward and / or feedback control device, wherein the feed-forward and / or feed back control device is configured to output AC voltages, in particular AC voltages which are phase-offset with respect to one another, at outputs which have been activated, each of the at least two outputs being assigned a priority level; perform a check for an electrical overload on the inverter; and deactivate the output with the lowest priority level at which an AC voltage is output by terminating the output of the AC voltage at said output if an overload of the inverter has been detected. The advantages, effects and features described above in connection with the method for operating an inverter in isolated operation can also be transferred to the inverter according to the invention. The inverter can be connected to phase conductors of a local energy supply network. The feed-forward and / or feedback control device may be formed, for example, by a microprocessor. The feed-forward and / or feedback control device may be integrated into a housing of the inverter or may be provided as a separate feed-forward and / or feedback control device. The feed-forward and / or feedback control device may also be designed for the feed-forward control and / or feedback control of the inverter in such a way that preferably phase-shifted AC voltages are output at the outputs. Voltage measuring sensors can therefore be arranged at the at least two outputs. The voltage of a DC voltage intermediate circuit may also be detected by means of a voltage measuring sensor. In order to assign priority levels to the outputs, the inverter may have, for example, at least one button or a control panel, for example, a touch display. Preferably, the priority levels may be assigned to the inverter via a data connection. In particular, it can be provided that the priority levels may be set via a user interface. The user interface may be accessed, for example, in a browser or another application. In the following, the invention is described with reference to figures, to which, however, it is not intended to be limited. In the drawings: Fig. 1 shows an inverter connected to a local energy supply network, with only single-phase consumers connected to the local energy supply network; Fig. 2 shows an inverter connected to a local energy supply network, with a polyphase consumer also connected to the local energy supply network; Fig. 3 shows voltage curves; Fig. 4 shows a flow chart; Figs. 5A-C show time profiles of output voltages, output currents and an intermediate circuit voltage according to a first example; Figs. 6A-C show time profiles of output voltages, output currents and an intermediate circuit voltage according to a second example; Fig. 7A-C show time profiles of output voltages, output currents and an intermediate circuit voltage according to a third example; Figs. 8A-C show time profiles of output voltages, output currents and an intermediate circuit voltage according to a fourth example; and Figs. 9A-C show time profiles of output voltages, output currents and an intermediate circuit voltage according to a fifth example. Fig. 1 shows an inverter 1 connected to a local energy supply network 2 with three phase conductors L1, L2 and L3 and a neutral conductor N. The local energy supply network 2 may be, for example, the energy supply network of a building (not shown), for example a single-family house or an office building. The local energy supply network 2 is connected via a polyphase disconnector 3 to a higher-level public energy supply network 4 and is supplied via this grid 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 generating device 6, which may be designed, for example, as a photovoltaic system 7, into the local energy supply network 2. For this purpose, the inverter 1 has several outputs 8a-c to which the phase conductors L1, L2, L3 of the local energy 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 Transistor), 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 UZ is 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 may also have one or more boost converters (not shown). By means of a switching pattern (not shown) for the switches 9, which can be specified by a feed forward and / or feedback control device 51, AC voltages U1, U2, U3 can be generated at the outputs 8a-c, each of which is phaseoffset by 120° relative to the others. With the aid of a measuring device 52a, the output voltages Ua, Ub, Uc at the outputs 8a-c can be measured and used for the feed-forward control and / or feedback control of the inverter 1 by the feedforward and / or feedback control device 51. In one embodiment of the invention, electric currents Ia, Ib, Ic at the outputs 8a-c can also be detected with the aid of the measuring device 52a. With the help of a further measuring device 52b, the intermediate circuit voltage UZ can be measured and likewise made available to the feed-forward and / or feedback control device 51. In normal operation, the phase positions of the voltages U1, U2, U3 output at the outputs 8a-c correspond to the respective voltages of the higher-level energy supply network 2. In Fig. 1, single-phase consumers 12a, 12b are connected to the local energy supply network 2. In the illustration shown, the consumers 12a, 12b are each connected to different phase conductors L1, L2, L3 and to the neutral conductor N. The consumers 12a, 12b shown are lamps 12a and a refrigerator 12b. In the event of a power failure 14 in the higher-level public energy supply network 4, the local energy supply network 2 can be supplied by the inverter 1, which obtains the electrical energy E from the electrical energy storage device 5 and / or the energy generating device 6. The inverter 1 can thus be operated in isolated operation, supplying the local energy supply network 2 as an isolated network. Before the inverter 1 feeds into the local energy supply network 2 in isolated operation, the local energy supply network is disconnected from the public energy supply network 4 by means of the disconnector 3. During isolated operation, it may happen that the consumers 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 generating device 6. In this case, there is an electrical overload. It is known from the prior art that in such a case the inverter 1 is completely deactivated, so that it does not output an AC voltage U1, U2, U3 at any of the outputs 8. This prevents damage to or malfunction of the consumers 12a, 12b. However, this has the disadvantage that all consumers 12a, 12b are switched off. However, consumers 12a, 12b of varying importance are typically connected to a local energy supply network 2. In the event of a power failure, a refrigerator 12b or a lamp 12a in the basement of a building are generally more important than, for example, garden lighting, a hair dryer, or a game console. According to the invention, it is therefore provided that each output 8a-c for a phase conductor L1, 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 AC voltage U1, U2, U3 is output, is deactivated. Before an output 8a-c is deactivated, the setpoint of the output voltages Ua, Ub, Uc can still be reduced in order to eliminate the overload. If this does not work, the output 8a- c with the lowest priority level A, B, C can be deactivated. The electrical overload may be detected by comparing an electrical quantity of the inverter 1, for example, the measured intermediate circuit voltage UZ, the measured output voltages Ua, Ub, Uc, the electrical output currents Ia, Ib, Ic and / or related electrical voltages or currents, each with a corresponding threshold value. If the threshold value, depending on the type of electrical quantity, is undershot or exceeded, an electrical overload can be assumed. The threshold value may, for example, depend on a setpoint value for the electrical quantity. For example, if the measured intermediate circuit voltage UZ is below an intermediate circuit voltage threshold value, which in one embodiment may 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. For example, if a measured output current is above an output current threshold, which in one embodiment may be 110 % of a setpoint value, an electrical overload can likewise be detected. In the example shown, A represents the highest priority level and C represents the lowest priority level. Therefore, consumers 12a connected to the output 8b with the lowest priority level C are 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 thus continue to be supplied with electrical energy E. Therefore, important consumers 12a, 12b, such as refrigerators 12b, are preferably connected to a pahse conductor L1, L2, L3 that is connected to an output 8a, 8c of a high or the highest priority level A, B. Unimportant consumers 12a, 12b, such as garden lights 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 is still present after deactivation of the output 8b with priority level C, the described steps can be repeated and now the active output 8a with the lowest priority level B, to which an AC voltage U1, U3 is currently being output, can be deactivated. This procedure can lead to the deactivation of all outputs 8a-c of the inverter 1. After an output 8a-c has been deactivated, it can be reactivated at intervals for one or more periods of the AC voltage U1, U2, U3 to check whether the overload is still present. If this is not the case, the output 8a-c with the highest priority level among the deactivated ones can be reactivated. This can be repeated until all outputs are reactivated. Fig. 2 shows a circuit diagram in which a polyphase load 13, hereinafter also referred to as a polyphase consumer 13, is connected to the local energy supply network 2. The polyphase consumer 13 may be, for example, an electric motor that represents a predominantly inductive load (see the inductances 15a, 15b, 15c). With the exception of the additional polyphase consumer 13, the circuit diagram of Fig. 2 corresponds to the circuit diagram of Fig. 1, which is why repetitions are omitted in the following. If a polyphase 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 unbalanced voltage supply. It is therefore preferably provided that, if a polyphase consumer 13 is connected to the local energy supply network 2, in the event of an electrical overload, those outputs 8a-c to which the polyphase consumer 13 is connected, in particular all outputs 8a-c, are deactivated. For this purpose, in one embodiment of the invention, the inverter 1 can be informed of the presence of a polyphase consumer 13 by manual input. In a further embodiment, a polyphase consumer 13 can be detected by measuring induced voltages Uind and / or induced currents Iind at already deactivated outputs 8a-c. The measurement of induced voltages Uind and / or induced currents Iind can be carried out using the measuring device 52a. In particular, induced voltages Uind can be detected as voltages Ua, Ub, Uc at deactivated outputs 8a-c and indicate a polyphase load 13. Deactivated outputs 8a-c can be switched to high impedance (for the measurement of induced voltages Uind), preferably with a resistance value of at least 10 W between the respective deactivated output 8a-c and the neutral conductor potential, or to low impedance (for the measurement of induced currents Iind), preferably with a resistance value of a maximum of 1 Q between the respective deactivated output 8a-c and the neutral conductor potential. Fig. 3 shows an example of the course of measured voltages Ua, Ub, Uc at the outputs 8a-c when a polyphase consumer 13 is connected to the local energy supply network 2. In the illustration shown, two of 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 Uind is induced in the inductance L2 connected to the deactivated output 8b. Due to the fact that the output 8b is deactivated and does not output any AC voltage U2, the polyphase load 13 can be detected by measuring the voltage Uind. Fig. 4 shows an exemplary sequence of the method according to the invention, as it may 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, cf. Fig. 1 and Fig. 2), the local energy supply network 2 is disconnected from the public energy supply network 4 by means of the disconnector 3 (block 101). Subsequently, all outputs 8a-c of the inverter 1 are activated (block 102). Each output 8a-c is assigned a different priority level A, B, C. In step i), an AC voltage U1, U2, U3 is output at each activated output 8a-c (block 103). In step ii), a check is made to determine whether there is an electrical overload (block 104). If there is no electrical overload, the outputs 8a-c that output an AC voltage U1, U2, U3 remain activated (branch 105, which leads back 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 AC voltage U1, U2, U3 is output, is deactivated by terminating the output of the AC voltage U1, U2, U3 at the output 8a-c (block 107). In a preferred embodiment of the invention, polyphase consumers 13 are also detected, in particular by measuring induced voltages Uind or induced currents Iind at deactivated outputs 8a-c (block 108). If a polyphase consumer 13 is detected (branch 109), preferably all outputs 8a-c of the inverter 1 are deactivated and the inverter 1 is thereby switched off (block 110). If no polyphase load 13 has been detected, AC voltages U1, U2, U3 continue to be output at the (still) activated outputs 8a-c (see branch 111, which leads to branch 105). If the electrical overload has ceased, for example because consumers 12a, 12b have been removed from the local energy supply network 2 (step iv-a)), or because the inverter 1 can provide a higher electrical output power and / or more electrical energy E because the energy generating device 4 is providing more electrical power or energy E (step iv-b)), then, 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 AC voltage U1, U2, U3 at said output 8 (block 112 or steps iv-a) and iv-b)). In one embodiment of the invention, in block 112, the output 8a-c with the highest priority level A, B, C among the deactivated outputs 8a-c can be reactivated after a certain period of time, for example after 10 seconds. If an electrical overload is then detected again (step i)), said output can be deactivated again in step iii). In the following, the deactivation of outputs 8a-c due to an overload is illustrated in more detail using the time profiles of the output voltages Ua, Ub, Uc, the output currents Ia, Ib, Ic, and the intermediate circuit voltage UZ. The abscissae of Figs. 5a-9C each represent a time t in seconds. The ordinates of Figs. 5A, 6A, 7A, 8A, and 9A each describe the time profiles of output voltages Ua, Ub, Uc in volts. The ordinates of Figs. 5B, 6B, 7B, 8B and 9B each describe time profiles of output currents Ia, Ib, Ic in amperes. The ordinates of Figs. 5C, 6C, 7C, 8C and 9C each describe time profiles of intermediate circuit voltages UZ in volts. In Fig. 5A-C, it can be seen that AC voltages U1, U2, U3 are output at the outputs 8a-c. In the example shown, it is assumed that 3.7 kW of power is available from inverter 1 and can be drawn. The lowest priority C was assigned to output 8a. The highest priority A was assigned to output 8b. The medium priority B was assigned to output 8c. At time T0, a power of 3 kW is drawn at the outputs 8a-c by connected single-phase consumers 12a, 12b. At time T1, another large single-phase consumer 12a, 12b, for example a resistive consumer such as a hot plate with a power requirement of 1.5 kW, is connected to the output 8a with the lowest priority C, so that there is a total power requirement of 4.5 kW, 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 Ia at output 8a increases due to the present power demand of 4.5 kW - for example, to twice the value (as shown). Subsequently, in one embodiment of the invention, the setpoint for the output voltages Ua, Ub, Uc at the outputs 8a-c can be reduced to 90 % in order to possibly eliminate the overload of the inverter 1 in this way. This reduces the output voltage from 230 V (RMS value, corresponds to an amplitude value of approx. 325 V) to 209 V (RMS value, corresponds to an amplitude value of approx. 292 V). However, in the illustration shown, the current Ia at output 8a remains high - and the intermediate circuit voltage UZ also remains below its setpoint UZ_d. The previously increased current Ia at output 8a is reduced by approximately 10 % by reducing the setpoint for the output voltages Ua, Ub, Uc in the case of a resistive consumer. In this case, the drawn power is reduced by approximately 19 %. This reduction in electrical power is not sufficient, which is why the intermediate circuit voltage UZ continues to remain below its setpoint UZ_d. The reduction of the setpoint value for the output voltages Ua, Ub, Uc therefore does not lead to the desired result. This means that, as a result of this measure, the intermediate circuit voltage does not rise to the setpoint value and at least one output 8a-c is deactivated. Subsequently, at time T2, output 8a is deactivated (step iii of the method according to the invention), since the lowest priority C was assigned to output 8a. By deactivating output 8a, the overload of inverter 1 is eliminated. The outputs 8b, 8c can therefore remain activated. The setpoint of the voltages Ub, Uc at the outputs 8b, 8c can therefore be increased again to 100 %, as can be seen in Fig. 5A. The intermediate circuit voltage UZ also rises again to the setpoint value UZ_d or settles at this value or stabilizes at the setpoint value. After deactivation of output 8a, in a preferred variant of the invention, output 8a can be reactivated after a predetermined period of time of, for example, 10 seconds, in order to check whether the overload is still present (see Figs. 6A-C). Of course, it would also be possible for more power to be provided by an electrical energy storage device 5 and / or an energy generating device 6. Therefore, after the specified period of time has elapsed, an output voltage Ua is again output at output 8a. To check whether the overload of the inverter 1 is still present, the output voltage Ua can be output at the output 8a for one or more periods from the time T3. In one variant of the invention, as already explained in more detail above, an electrical quantity of the inverter 1 can again be compared with a corresponding threshold value in order to determine whether the inverter 1 is still overloaded or whether the overload has ceased. In another variant, it can be detected by calculating the electrical power whether the overload of the inverter 1 is still present. The electrical power can be determined, in particular, by measuring the electrical currents Ia, Ib, Ic output at the outputs and multiplying them by the respective electrical voltage Ua, Ub, Uc. If the available power - in the present case 3.7 kW as mentioned above - is not exceeded, output 8a can be reactivated. If, on the other hand, an overload is again detected, i.e. the power exceeds the available power while output 8a is switched on, output 8a is again deactivated. This is shown in Figs. 6A-C. Output 8a remains deactivated for the remainder of the period shown in Figs. 6A-C. However, output 8a can be reactivated to check once more, as described, whether the overload is still present. This process may be repeated at regular intervals, for example, every 10 seconds. The case where the overload has ceased after deactivation of output 8a is shown in Fig. 7A-C. It can be seen that the output 8a is activated at time T3 and then 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 Ua, Ub, Uc do not have to be reduced or the intermediate circuit voltage UZ does not fall below the limit value specified for overload. As a result, no overload is detected and output 8a remains activated. Fig. 8A-C shows the case where a connection of a single-phase consumer 12a, 12b to an output 8a-c can lead to a 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 is assigned to output 8b, and the lowest priority C is assigned to output 8c. The consumer 12a, 12b is connected to the output 8a at time T1, which leads to a deactivation of the output 8c at time T2, whereby the overload can be eliminated because the required power is thereby below the available power of 3.7 kW. Figs. 9A-C describe the case where a polyphase load 13 is connected to the inverter 1. At time T1, an additional consumer 12a, 12b is connected to output 8a. Since a reduction of the setpoint for the output voltage Ua, Ub, Uc does not eliminate the overload, the output 8c with the lowest priority C is deactivated at time T2. Output 8c is switched to high impedance. However, it is found that an induced voltage Uind with a 50 Hz component and a smaller amplitude can be measured at output 8c, which is an indication that a polyphase load is connected to the inverter. Subsequently, at time T3, all outputs 8a-c of the inverter 1 are deactivated to prevent damage to the polyphase load 13. The deactivation of all outputs 8a-c may take place simultaneously or sequentially, in particular according to the assigned priority levels. In the latter case, the deactivation of only one further output 8a-c may already suffice, for example, if only one two-phase consumer is connected and the overload of the inverter 1 can be eliminated by deactivating the two outputs 8a-c to which the two-phase consumer is connected. As described above, after a predetermined period of time, one or more outputs 8a-c can be reactivated to check whether the overload of the inverter 1 is still present.
Claims
Patent claims:
1. A method for operating an inverter (1) in an isolated operation, wherein the inverter (1) has at least two outputs (8a-c) for connecting electrical phase conductors (L1, L2, L3), and the method comprises the following steps:i) outputting AC voltages (U1, U2, U3), in particular AC 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) for an electrical overload; andiii) deactivating the output (8a-c) with the lowest priority level (A, B, C) at which one of the AC voltages (U1, U2, U3) is output by terminating the output of the AC voltage (U1, U2, U3) at said output (8a-c) if an electrical overload of the inverter (1) has been detected.
2. The method according to claim 1, characterized in that stepsi), ii) and iii) are repeated continuously.
3. The method according to claim 1 or 2, characterized in thatthe inverter (1) is checked for electrical overload byan electrical quantity, in particular an electrical voltage or an electrical current, of the inverter (1) being detected andthe electrical quantity being compared with a threshold value, and the electrical overload of the inverter (1) being detected when the electrical quantity falls below or exceeds the threshold value.
4. The method according to claim 3, characterized in that theelectrical quantity isan electric current, in particular an output current at oneof the outputs (8a-c),a quantity associated with the electric current,an electrical intermediate circuit voltage (UZ) of an intermediate circuit (10) of the inverter (1),an electrical output voltage (Ua, Ub, Uc) of at least one ofthe outputs (8a-c) of the inverter (1) ora quantity associated with the electrical intermediatecircuit voltage (UZ) and / or the output voltage.
5. The method according to any 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. The method according to any 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) that differs from the priority levels (A, B, C) of the other outputs (8a-c).
7. The method according to any one of claims 1 to 6, characterized in that the inverter (1) is connected to a local energysupply network (2), in particular to a building energy supply network, and supplies the local energy supply network (2).
8. The method according to any one of claims 1 to 7, characterized by the step ofiv-a) reactivating the output (8a-c) with the highest priority level (A, B, C) among the deactivated outputs (A, B, C) when the overload that led to deactivation of the output (8a-c) is no longer present.
9. The method according to any one of claims 1 to 8, characterized by the step ofiv-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. The method according to any one of claims 1 to 9, characterized in that when a polyphase load (13) is electrically connected to the at least two outputs (8a-c) of the inverter (1), all outputs (8a-c) of the inverter to which the polyphase load (13) is connected are deactivated, in particular after an electrical overload is detected, preferably wherein the polyphase load (13) is detected.
11. The method according to claim 10, characterized in that the polyphase 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 (Uind) and / or a preferably induced current (Iind) is measured at the at least one deactivated output (8a-c) of the inverter (1).
12. The method according to any one of claims 1 to 11, characterized in that the output (8a-c) in step iii) is switched to a high-impedance state during deactivation.
13. The method according to any one of claims 1 to 12, characterized in that the inverter (1) is supplied by an electricalenergy storage device (5) and / or an electrical energy generating device (6), in particular a photovoltaic system (7).
14. A method for supplying energy to a local energy supply network (2), in particular a building energy supply network, in theevent 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 supplynetwork (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. An inverter (1), preferably an inverter for a photovoltaic system (7), with at least two outputs (8a-c) for connecting electrical phase conductors (L1, L2, L3) and a feed-forward and / or feedback device (51), characterized in that the feed-forward and / or feedback control device (51) is configured tooutput AC voltages (U1, U2, U3), in particular AC 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);perform a check for an electrical overload on the inverter;anddeactivate the output (8a-c) with the lowest priority levelat which one of the AC voltages (U1, U2, U3) is output by terminating the output of the AC voltage (U1, U2, U3) at said output (8a-c) if an electrical overload of the inverter (1) has been detected.