WO2020108959A1

WO2020108959A1 - Method for supplying electricity to the controller of an inverter, facility component, inverter and energy generation facility having such a facility component

Info

Publication number: WO2020108959A1
Application number: PCT/EP2019/080696
Authority: WO
Inventors: Tim Roesinger; Michael Krug; Andreas Kluger
Original assignee: Sma Solar Technology Ag
Priority date: 2018-11-30
Filing date: 2019-11-08
Publication date: 2020-06-04
Also published as: DE102018130453A1

Abstract

The application describes a method for supplying electricity to an inverter (1) through an AC voltage, wherein the inverter (1) has an AC voltage (AC) output (11) for connecting the inverter (1) to an AC voltage (AC) grid (21), a DC voltage (DC) input (12) for connecting the inverter (1) to a DC source (19), a DC-to-AC converter (2) for converting a DC voltage of the DC source (19) to an AC voltage, and a control unit (3) for controlling the DC-to-AC converter (2). The control unit (3) is connected to a switching unit (8) that is configured to supply the control unit (3) via the AC grid (21) connected to the AC output (11) in a first switching state, and to supply the control unit (3) via an auxiliary energy source (22) providing an AC voltage in a second switching state, which auxiliary energy source is disconnected from the AC output (11) in the second switching state of the switching unit (8). The inverter (1) furthermore has a grid monitoring unit (4) that is configured to detect a property of an AC voltage present in the AC grid (21). The method includes the method steps of: - operating the switching unit (8) in the second switching state when the AC voltage is not detected in the AC grid (21) or the property, detected by the grid monitoring unit (4), of the AC voltage prevailing in the AC grid (21) does not meet predefined criteria, and - operating the switching unit (8) in the first switching state when the property, detected by the grid monitoring unit (4), of the AC voltage prevailing in the AC grid (21) meets the predefined criteria. The application additionally discloses a facility component (17) suitable for performing the method and having an inverter (1) and a switching unit (8), an inverter (1) suitable for use within the facility component (17) and an energy generation facility (EEA) having at least one such inverter.

Description

METHOD FOR ELECTRICALLY SUPPLYING THE CONTROL UNIT OF A INVERTER,

PLANT COMPONENT, INVERTER AND POWER GENERATION PLANT WITH SUCH A PLANT COMPONENT

Technical field of the invention

The invention relates to a method for the electrical supply of an inverter with AC voltage, a system component designed to carry out the method with an inverter, an inverter suitable as a component of the system component, and an energy generation system, in particular a photovoltaic (PV) system, with at least one such system component

State of the art

In the future, larger regenerative energy generation plants (EEA) must be suitable for performing a black start. With such a black start, the EEA must be able to build up an AC voltage in a stand-alone grid, for example in a local stand-alone grid of the EEA, in order to synchronize the AC voltage with another AC voltage of another neighboring stand-alone grid in the event of a failure of the public energy supply network (EVN) and to keep it stable when interconnecting the two island grids.

A method for black starting a photovoltaic (PV) power plant with a plurality of inverters which can be connected to a local AC network is known from the document WO 2014/140281 A1. In this case, a first AC voltage is built up in the local AC network using a first inverter, which voltage is reduced compared to a nominal voltage of the local AC network. A second inverter is connected to the AC network after synchronization with the first AC voltage. After the second inverter has been switched on, a second AC voltage which is higher than the first AC voltage is then built up in the AC network. The AC voltage is built up in several stages with increasing amplitude of the AC voltage until the nominal voltage of the AC voltage in the local AC network is reached. The AC voltages built up in the first stage, possibly also in subsequent stages of the process, are opposite of the nominal voltage to ensure that the inverters connected to the local AC grid can operate below their respective power limits.

The known method is designed for inverters which supply themselves, but in particular their control unit, from a PV generator connected on the input side to the inverter. However, this property is often not given in conventional inverters, since this, in particular its control unit, is set up to be supplied from an AC voltage network connected to the output of the inverter.

US 2008 0284172 A1 describes a method for black starting a wind farm which is connected to an external energy supply network. The wind farm has a large number of wind energy plants and at least one auxiliary energy source which is switched on to a local AC network of the wind farm for the black start. During the black start - as usual - the wind turbines are supplied from the local AC network, via which the wind turbines are connected on the output side and via which, when the wind farm is operating properly, electrical power is fed into the public energy supply network connected to the wind farm. The auxiliary power source is dimensioned so that all other ohmic, capacitive and inductive loads connected to the internal AC voltage network can also be supplied. Especially in the case of extensive regenerative EEAs, a relatively large auxiliary energy source has to be provided here.

A wind power installation is described in US 2012 0261917 A1, which has a diesel generator in order to initiate a black start in the event of a power grid failure to which the wind power installation can be coupled. To carry out the black start, the diesel generator provides a predetermined voltage at an output of the wind energy installation in order to imitate the operating state of the power grid. Furthermore, a wind farm with at least two wind turbines is disclosed.

The document US 2009 0160187 A1 discloses a method for operating a wind farm with a wind farm control system and at least two Wind turbines that are connected to each other via an internal network. The method includes determining a current power consumption of the wind farm and adjusting the power generation of at least one of the wind turbines so that the current values of power generation and power consumption of the wind farm are essentially the same. The utility model DE 21 2008 000 035 U1 describes a high frequency (HF) inverter for converting a direct voltage generated by at least one solar module via a DC / DC converter, an intermediate circuit and a DC / AC converter into an alternating voltage. The inverter is designed to supply consumers and / or to feed into a supply network. A grid monitoring unit monitors a status of the supply network and, depending on the status of the supply network, initiates a switchover of an operating mode of the inverter from a grid-connected operation to an island operation.

Object of the invention

The invention is based on the object of specifying a method for the electrical supply of an inverter with an AC voltage, with which the inverter can be supplied with electrical power in a particularly inexpensive and inexpensive manner. It is also an object of the invention to provide a system component suitable for carrying out the method and comprising the inverter, an inverter suitable for use within the system component, and an energy generation system with such a system component suitable for carrying out the method.

solution

The object is achieved according to the invention in a method of the type mentioned at the outset with the features of independent patent claim 1. The object of specifying a system component suitable for carrying out the method and comprising the inverter is achieved according to the invention with the features of independent claim 8. The object of specifying an inverter suitable for carrying out the method is achieved according to the invention with the features of independent claim 17. According to the invention, the task of specifying a power generation plant suitable for carrying out the method with such a plant component is achieved by the Features of independent claim 18 solved. Advantageous embodiments of the method are listed in dependent claims 2 to 7, advantageous embodiments of the system component in dependent claims 9 to 16 and an advantageous embodiment of the energy generation system in dependent claim 19.

Description of the invention

The method according to the invention is carried out with a system component which comprises an inverter and a switching unit. The switching unit can be integrated in the inverter. The method according to the invention aims at an electrical supply of the inverter with an alternating voltage. The inverter comprises an alternating voltage (AC) output for connecting the inverter to an alternating voltage (AC) network, a direct voltage (DC) input for connecting the inverter to a DC source, a DC / AC converter for converting one DC voltage applied to the DC input into an AC voltage and a control unit for controlling the DC / AC converter. The control unit is electrically connected to the switching unit. The switching unit is set up to supply the control unit via the AC network connected to the AC output in a first switching state and to supply the control unit via an auxiliary power source providing an AC voltage in a second switching state. The auxiliary power source is separated from the AC output of the inverter in the second switching state of the switching unit, so that a flow of power between the auxiliary power source and the AC output and between the auxiliary power source and an AC network connected to the AC output is prevented. The inverter also has a grid monitoring unit which is set up to detect a property of an AC voltage present in the AC grid. The process comprises the process steps:

Operating the switching unit in the second switching state when the AC voltage is not detected in the AC network or the detected property of the AC voltage prevailing in the AC network does not meet the criteria, and Operating the switching unit in the first switching state when the property of the AC voltage prevailing in the AC network, which property is detected by the network monitoring unit, meets the specified criteria.

The grid monitoring unit of the inverter can be designed as a separate component with a separate electrical supply. The network monitoring unit can be supplied together with the control unit in the first switching state of the switching unit via the AC network and in the second switching state of the switching unit via the auxiliary power source. Alternatively, the network monitoring unit can also be supplied via the control unit. In a further variant, the network monitoring unit can be designed as an integral part of the control unit and does not require a separate electrical supply for proper operation. The switching unit can be designed and set up to passively switch the switching unit to the second switching state and maintain the second switching state, and in particular without an explicit control signal.

Operating the switching unit in the first switching state can - but does not necessarily have to mean that the switching unit is operated in the first switching state permanently and for as long as the property of the AC voltage in the AC network that is detected by the network monitoring unit meets the specified criteria enough. Rather, it is sufficient that the switching unit is only operated in the first switching state for a limited period of time if the detected property of the AC voltage in the AC grid meets the specified criteria. For example, there may be a further period of time during which the property of the AC voltage prevailing in the AC network, which property is detected by the network monitoring unit, meets the specified criteria, but the switching unit is nevertheless not operated in the first switching state, but in a third switching state if appropriate. On the other hand, however, it applies that whenever the switching unit is operated in the first switching state, the detected property of the AC voltage prevailing in the AC network also meets the specified criteria. A corresponding consideration applies analogously to the operation of the switching unit in the second switching state. The switching unit can also be operated in the second switching state, but need not be permanent and as long as the AC voltage is not detected in the AC network or the detected property of the AC voltage prevailing in the AC network does not meet the specified criteria. Rather, a one-time and time-limited operation of the switching unit in the second switching state is sufficient, provided that at least one of the conditions named after the term “if” is met. For this reason, the term “if” within the process steps should not be understood in the sense of “exactly when” or “always when”.

The fact that the AC voltage is not detected in the AC network can be understood to mean that the network monitoring unit is operating properly and therefore does not detect any AC voltage because there is no AC voltage with a voltage amplitude> 0V in the AC network. According to one exemplary embodiment, the switching unit can also be operated in the second switching state if the control unit detects or receives a failure / defect in the network monitoring unit. In this case, for example, the control unit can control a switching of the switching unit from the first to the second switching state. However, as explained below, the switching unit can be switched from the first to the second switching state passively and without explicit involvement of the control unit.

According to the invention, the term “operation” includes both active operation and passive operation. While the switching unit has to be acted upon in an active operation to maintain the respective switching state, this is not the case in a passive operation. Rather, the corresponding switching state is held by the switching unit on its own, in other words: the switching unit is left to its own devices, if necessary after an actively initiated switching operation, and has no further influence on the switching unit in the corresponding switching state. It is within the scope of the invention that each of the two switching states can be operated actively. Alternatively, it is also possible for only one of the two switching states to be operated actively while the other switching state is in each case is operated passively. Passive operation of the switching unit in the first or in the second switching state is also encompassed by the invention, but then a change from one switching state to the other switching state is actively carried out, for example similar to the function of a bistable relay. Operating the switching unit in the second switching state can also include switching the switching unit to the second switching state, optionally initially and once. The same applies to the operation of the switching unit in the first switching state.

The invention uses the effect that the AC voltage provided by the auxiliary energy source is not provided at the AC output of the inverter, but at a contact of the switching unit. The contact of the switching unit is separated from the AC output of the inverter - at least for a certain period of time. The auxiliary power source therefore does not have to supply energy to the AC network connected to the AC output of the inverter, including the impedances contained therein. This would be possible with a larger regenerative generation system with several inverters connected via a local island network, the control units of which are supplied via the AC output of the inverters, due to the impedances present in the local island network only with a comparatively high expenditure of energy. The auxiliary power source would therefore have to be designed correspondingly large. However, since, according to the invention, the auxiliary power source is now connected to the switching unit, which in its second switching state only supplies the control unit, and possibly other components of the inverter that use little energy, and in particular is not connected to the AC output of the inverter, the auxiliary power source does not have to be any more supply impedances connected in the local island network. For this reason, it is possible to design the auxiliary power source for a low nominal power and thus for a low cost. This is also the case if the control units of several inverters are simultaneously supplied by the auxiliary power source via the switching units assigned to the respective inverters or the auxiliary power source electrically supplies the control units of several inverters or a higher-level control system via the switching unit. The property detected by the grid monitoring unit can comprise several variables, for example the height of an amplitude and the frequency of an AC voltage prevailing in the AC grid. The predefined criteria in which the switching unit is operated in the first switching state can include at least one of the following criteria:

an amplitude Uo of the AC voltage prevailing in the AC network is - in particular at least for a predetermined first time period Atsw.i - within a predefined tolerance range around a nominal value Uo.nom for the amplitude of the AC voltage in the AC network,

- A frequency fo of the AC voltage is - in particular for a predetermined second period of time - within a predetermined tolerance range around a nominal value fo.nom for the frequency of the AC voltage in the AC grid.

Advantageous embodiments of the invention are specified in the following description and the subclaims, the features of which can be used individually and in any combination with one another.

In an advantageous embodiment of the method, a setting of the switching unit in the first switching state and / or the operation of the switching unit in the first switching state can be controlled via the network monitoring unit or via this in connection with the control unit. With the grid monitoring unit and possibly with the control unit for controlling the switching unit, components are used that are present in the inverter anyway. The additional components required are therefore limited to a controllable switching unit, but not its measured value-controlled control electronics, which can therefore further reduce the costs incurred.

It can also be regarded as advantageous that the switching unit is switched to the second switching state and in particular the switching unit is operated passively in the second switching state in the event of a mains failure of the AC network.

If only the detected properties of the AC voltage prevailing in the AC network does not meet the specified criteria, the switching unit can be switched to the second switching state and / or the switching unit can be operated can be controlled in the second switching state via the network monitoring unit or via this in connection with the control unit.

In a further advantageous embodiment of the method, in the second switching state of the switching unit, in addition to the control unit, at least one further component of the inverter can be selected from the group: fan, heater, AC switch, DC switch, and communication unit can be supplied by the auxiliary power source. The supply can take place via a supply unit connected to the switching unit, which may provide different voltages for operating the components from the AC voltage of the auxiliary energy source. The components are then connected to corresponding connections of the supply unit.

In an advantageous embodiment of the method, the auxiliary power source can be deactivated when the switching unit is operated in the first switching state, in particular when the switching unit has been operating in the first switching state for a certain period of time. For this purpose, the inverter can send a deactivation signal to the auxiliary energy source, which deactivates it. By deactivating a primary energy of the auxiliary energy source can be saved when its AC power is no longer required. This is the case, for example, when an AC voltage is already safely and in sufficient quality at the AC output of the inverter, e.g. because the AC voltage is generated by the inverter itself or by another inverter connected to the AC output of the inverter. The auxiliary power source can advantageously be designed as a mobile auxiliary power source, which is separated from the switching unit or from the inverter when the switching unit is operated in the first switching state or when the switching unit has been operating in the first switching state for a certain period of time becomes. A mobile auxiliary power source that is detachably connected to the inverter can be used in succession for several regenerative EEA. It is therefore only to be purchased once for the several EEA.

It can also be considered advantageous that the switching unit, provided that the AC voltage in the AC network meets the specified criteria, in particular depending on at least one state of the Auxiliary power source, operated for a period of time in a third switching state, which enables a power flow both between the control unit and the AC network and between the auxiliary power source and the AC network.

The auxiliary power source, which is connected to the inverter, in particular to its control unit, via the switching unit can comprise an auxiliary source inverter powered by a battery, an auxiliary source inverter powered by a PV module or a series connection of PV modules, or a diesel generator. Optionally, it is of course also possible for the auxiliary source inverter to be fed from a combination of at least one battery and at least one PV module. The auxiliary source inverter, if it is fed by at least one battery, can be designed as a bidirectionally operating auxiliary source inverter. Advantageously, the battery connected to the auxiliary source inverter can be formed by at least part of the battery that is also connected to the DC input of the inverter during normal operation. In the same way, the PV module connected to the auxiliary source inverter or the series connection of PV modules can comprise at least a part of the PV generator that is connected to its DC input during normal operation of the inverter. In this way, parts of the DC source, which is in any case connected to the DC input of the inverter, can be used for the black start without the need for additional components. It is not necessary for the battery or the PV module to be separate from the DC input of the inverter when it is connected to the auxiliary source inverter.

Especially in the case of a bidirectionally operating auxiliary source inverter, it can be advantageous if the switching unit is operated in a third switching state for a third period of time with an alternating voltage in the AC network that meets the specified criteria and which has a power flow between the control unit and the AC Network on the one hand and between the auxiliary power source and the AC network on the other hand. As a result, the battery can be charged via the (bidirectionally operating) auxiliary source inverter of the auxiliary power source from the AC grid. The switchover of the switching unit to the third switching state can be dependent in particular on a state of charge of the battery. A system component designed according to the invention for carrying out the method comprises an inverter for converting direct voltage into alternating voltage and a switching unit. The switching unit can be designed as a component of the inverter or as a separate component that is present outside a housing of the inverter. The inverter includes:

a direct voltage (DC) input for connecting the inverter to a DC source providing the direct voltage,

- an alternating voltage (AC) output for connecting the inverter to an alternating voltage (AC) network

a grid monitoring unit which is set up to detect a property of an AC voltage in the AC grid,

- a DC / AC converter, and

- A control unit for controlling the DC / AC converter.

The control unit of the inverter is electrically connected to the switching unit. The switching unit is designed and set up to supply the control unit in a first switching state of the switching unit via the AC network connected to the AC output of the inverter, and to supply the control unit in a second switching state of the switching unit via an auxiliary power source providing an AC voltage, which is separated from the AC output in the second switching state, so that a power flow between the auxiliary power source and the AC output, and a power flow between the auxiliary power source and an AC network connected to the AC output is prevented. Furthermore, the network monitoring unit of the inverter or the network monitoring unit in connection with the control unit is set up to operate the switching unit in the first or in the second switching state depending on the detected property of the AC voltage in the AC network. The advantages already explained in connection with the method result.

In one embodiment of the system component, the switching unit connected to the inverter can comprise a “normally-off” and / or a “normally-on” relay. In this way, the switching unit is able to assume a certain switching state on its own initiative and without external influence. This can advantageously be the second switching state. In an advantageous embodiment of the system component, the switching unit can be arranged in a housing of the inverter so that the inverter comprises the switching unit and the inverter is the system component. In one embodiment of the system component, the inverter can optionally have a connection for connecting the auxiliary power source, which is connected to a contact of the switching unit. In this case, the housing of the inverter does not have to be opened to connect the auxiliary power source to the switching unit. In a further embodiment of the system component, the inverter can have a further output which enables a power flow from the AC network or from the auxiliary energy source, which is mediated via the switching unit. Via the further output, further assemblies arranged outside a housing of the inverter and connected to the further output, for example a power plant control system, can be supplied either by the auxiliary power source or by the AC network, depending on the switching state of the switching unit. In one embodiment of the system component, the inverter can be set up not only to control the control unit in the second switching state of the switching unit, but also at least one of its components, for example a fan, an AC switch, a DC switch, a communication unit and / or to supply heating via the auxiliary energy source.

In principle, the system component according to the invention can comprise a current-setting or a voltage-setting inverter. In a particularly preferred variant of the system component, the inverter can be set up for voltage-setting operation. The inverter of the system component can be designed as a photovoltaic (PV) inverter, the DC input of which is connected to a PV generator. Alternatively, the inverter of the system component can also be designed as a battery inverter, with its DC input being connectable or connected to a battery. The inverter can also have a plurality of DC inputs, of which one DC input can be connected to a PV generator and another DC input can be connected to a battery. An inverter according to the invention is designed and set up to be usable as an inverter of the system component. For this purpose, its control unit is designed to be connectable to a switching unit of the system component. This can be achieved, for example, via a connection on the housing of the inverter, which is electrically connected to the control unit, possibly with the interposition of the switching unit, and which is designed to supply the control unit electrically via an auxiliary power source that is connected to the connection and provides an AC voltage.

An energy generation system (EEA) according to the invention comprises a plurality of inverters and at least one system component according to the invention, the system component comprising at least one inverter from the plurality of inverters according to the invention, the control unit of which is connected to the switching unit of the system component. The EEA can be designed as a regenerative EEA, in particular as a photovoltaic (PV) system. In an advantageous embodiment, the EEA can have a power plant controller for controlling an operation of the plurality of inverters, which is also connected to the switching unit of the at least one system component and is designed and set up to be supplied via the auxiliary power source when the switching unit is operating in the second switching state will. The auxiliary power source in the second switching state is disconnected from an AC connection of the inverter assigned to the system component. The power plant controller is also set up to be supplied when the switching unit is operating in the first switching state via the AC network connected to the AC output of the inverter assigned to the system component. The power plant control can be designed as a separate component, which is arranged outside a housing of the inverter of the system component. In this case, the power plant controller can be connected to the further connection of the inverter assigned to the system component and can be electrically connected to the switching unit via this. As an alternative to this, the power plant control can also be arranged in a housing of the inverter of the system component and thus be an integral part of the inverter of the system component. Brief description of the figures

The invention is illustrated below with the aid of figures. Show from these

1 shows an embodiment of a system component according to the invention with an inverter and a switching unit;

2 shows a flowchart of the method according to the invention for the electrical supply of an inverter in one embodiment.

Description of features

1 illustrates an embodiment of a system component 17 according to the invention with an inverter 1 for converting a DC voltage into an AC voltage and a switching unit 8. The inverter 1 has a direct voltage (DC) input 12 to which a DC source 19 providing the direct voltage, for example a photovoltaic (PV) generator 15, is connected. As an alternative to this, the inverter 1 can also comprise a battery inverter, to whose DC input 12 a battery 16 is connected, which is illustrated in FIG. 1 in the form of symbols drawn in dashed lines. The inverter 1 has an alternating voltage (AC) output 11, via which power is exchanged with an alternating voltage (AC) network 21 connected to the AC output 11. The inverter 1 also includes a DC / AC converter 2, which converts the DC voltage present at the DC input 12 into an AC voltage, which is output at an output 13 of the DC / AC converter 2 and via a mains relay 6 to the AC output 11 of the inverter 1 is transmitted. A grid monitoring unit 4 serves to detect a property of the AC grid 21, for example a voltage amplitude Uo and or a frequency f of an AC voltage present in the AC grid 21, even when the grid relay 6 is open. For this purpose the network control unit 4 is connected to a line-side contact of the relay network ^'. 6 The inverter 1 further includes a control unit 3 for controlling the DC / AC converter. The switching unit 8 of the system component 17 is designed to supply the control unit 3 either via the AC output 11 or via an auxiliary energy source 22 which provides an AC voltage and is connected to a connection 18 of the inverter 1. In the switch position shown in FIG. 1 by a solid line, the switching unit 8 is in a first switching state in which the control unit 3 is supplied via the AC network 21 connected to the AC output 11. Power flows from the AC network 21 via a transformer 9, which transforms a nominal voltage of the AC network 21 to an alternating voltage suitable for supplying the control unit 3, via the circuit unit 8 to the control unit 3. In the case shown in FIG. 1 the power flowing from the AC network 21 via the switching unit 8 is first passed on to a supply circuit 5, which processes the incoming AC voltage for supplying further components of the inverter and forwards them to them. A fan 10 of the inverter 1 is shown as an example in FIG. 1 as further components of the inverter 1. The supply circuit 5 also supplies an external component 25 which is arranged outside the inverter 1. For this purpose, the external component 25 is connected to a further output 14 of the inverter 1 and connected to the supply circuit 5 via this. By way of example, the further component 25 is a power plant controller 20 for the superordinate control of a plurality of inverters within a regenerative EEA. In Fig. 1, a second switching state of the switching unit 8 is symbolized by a switch position shown in dashed lines. In the second switching state, there is a power flow from the auxiliary energy source 22 - here: as an example an auxiliary source inverter 24 fed by a battery 23a and / or by a PV module 23b (shown in dashed lines in FIG. 1) via the switching unit 8 to the control unit 3. In the second switching state of the switching unit 8, the supply circuit 5 also receives a power flow from the auxiliary energy source 22, which after preparation serves to supply the fan 10 and the external component 25. In the second switching state of the switching unit 8, a power flow between the auxiliary energy source 22 and the AC output 11 and between the auxiliary energy source 22 and the AC network connected to the AC output 11 is prevented.

In Figure 1, the inverter 1 is exemplarily designed as a three-phase inverter with three phase outputs. However, is also within the scope of the invention an inverter with a different number of phase outputs, for example a single-phase inverter possible. In addition, the inverter 1 can be designed as a multi-stage inverter and contain a DC / DC converter arranged between the DC input 12 and the DC / AC converter 2. The switching unit 8 is exemplarily arranged in a housing of the inverter 1 in FIG. 1. It is therefore an integral part of the inverter 1, which thus also forms the system component 17. However, this is not mandatory. In the context of the invention, it is also possible for the switching unit 8 to be arranged outside the inverter 1. In addition, the supply circuit 5 shown in FIG. 1 is not absolutely necessary, in particular not when the further components to be supplied - here the fan 10 and the external component 25 - are supplied with an alternating voltage of the same quality as that of the control unit 3 is needed.

2 shows a flowchart of the method according to the invention for the electrical supply of an inverter 1 in one embodiment. The method is explained below using the example of a black start of a regenerative energy generation system, here: a PV system, which has at least one - advantageously a plurality of inverters that operate in a voltage-setting manner. The EEA also has a system component 17, which is formed by way of example from an inverter 1 of the plurality of inverters and a switching unit 8. The aim of the black start is to build up an AC voltage in a local AC network of the EEA, which is disconnected from the public power supply network (EVN) during the black start. At the beginning of the black start, only a first inverter 1 is connected via its closed grid relay 6 to the local AC grid, hereinafter referred to as AC grid 21.

The method begins with method step S1, in which there is no AC voltage with an amplitude Uo> 0V in the AC network 21. In method step S2 it is queried whether a detection of an alternating voltage in the AC grid 21 by the grid monitoring unit 4 is possible. At the beginning of the black start, this is not the case, which is why the method branches to a step S3, in which the switching unit 8 is operated in the second switching state. For this purpose, the switching unit 8 can be selectively switched to the second state, if necessary by means of a power supply from the auxiliary energy source 22, provided that it is not already in the second switching state, for example because the switching unit 8 assumes the second switching state automatically or passively. In the following step S4, the auxiliary energy source 22 is started and operated, if this has not yet been done. It thus generates an AC voltage for supplying the control unit 3 of the inverter 1. By supplying the control unit 3 with electricity, it can control the DC / AC converter 2 of the inverter 1 to set an AC voltage with the nominal amplitude Uo.nom of the AC network 21 . Depending on the nominal power of the inverter 1, the alternating voltage can be generated directly with the nominal amplitude Uo.nom of the AC network 21. As an alternative to this, the AC voltage generated by the DC / AC converter 2 can also increase in steps to the nominal amplitude Uo.nom of the AC network 21, with further inverters 1 or 2 after each stage, as described in WO 2014/140281 A1 EEA can be added to the AC network 21. In this case, the inverter 1 sets a voltage amplitude Uo, which results from its nominal power and the impedance of the AC network 21. If the nominal amplitude Uo.nom or a power limit of the inverter 1 has been reached, the method branches back to step S2.

After the build-up of an AC voltage with the amplitude Uo with OV <Uo ^ Uo.nom, a detection of the AC voltage in the AC network 21 is possible in step S2. The method therefore branches to step S6, in which a property of the AC voltage in the AC network 21 - here: the amplitude Uo and a frequency f of the AC voltage - is detected by the network monitoring unit 4. In step S7, a query is made as to whether the detected property meets predetermined criteria. An allowed tolerance range of 20% around the nominal amplitude Uo.nom and around the nominal frequency fo.nom of the AC voltage of the AC grid 21 is given as an example in FIG. 2 as predetermined criteria. If the detected values of amplitude Uo and frequency f of the alternating voltage do not meet these criteria, the method branches back to step S3, the switching unit 8 still being operated in the second switching state. If, on the other hand, the amplitude Uo and the frequency f satisfy the specified criteria, the method branches to a step S8, in which it is checked whether the AC voltage in the AC network 21 is stable. It can be queried here, for example, whether the detected amplitude Uo for a predetermined first time period Atsw.i is within a predefined tolerance range around the nominal value Uo.nom of the amplitude of the alternating voltage Uo.nom. Alternatively or cumulatively, it can be queried whether the detected frequency f of the AC voltage has already been within a predetermined tolerance range around the nominal value for the frequency of the AC voltage fnom for a predetermined second time period. If the stability condition does not apply, the method branches back to step S6, in which the amplitude Uo and the frequency f of the AC voltage are again detected in the AC network 21. If, on the other hand, the stability condition is met, the method branches to step S9, in which the switching unit 8 is now operated in the first switching state. The operation of the switching unit 8 in the first switching state can also include that the switching unit 8 may be initially set to the first switching state. In the first switching state, the control unit 3 is supplied via the AC network 21 connected to the output 11 of the inverter 1. In a subsequent step S10, the auxiliary power source 22 is deactivated and the method ends with step S1 1.

In a further embodiment of the method, it is possible to operate the switching unit 8 between the method steps S8 and S9 for a certain period of time in a third switching state, which has both a power flow between the AC network 21 and the control unit 3 and a power flow between the AC network 21 and the auxiliary power source 22 allowed. The third switching state of the switching unit 8 enables the battery 24 of the auxiliary energy source 22 to be charged by the bidirectionally operating auxiliary source inverter 24 while the control unit 3 is supplied from the AC network 21 at the same time. Reference list

Inverter

DC / AC converter

Control unit

Network monitoring unit

Supply unit

Power relay

DC switch

Switching unit

transformer

Fan

AC output

DC input

exit

further exit

Photovoltaic (PV) generator

battery

Plant component

connection

DC source

Power plant control

AC grid

Auxiliary energy source

a battery

b PV module

Auxiliary inverter

Component -S1 1 process step

Claims

1. A method for the electrical supply of an inverter (1) with an alternating voltage, the inverter having an alternating voltage (AC) output (1 1) for connecting the inverter (1) to an alternating voltage (AC) network (21), a direct voltage (DC) - input (12) for connecting the inverter (1) to a DC source (19), a DC / AC converter (2) for converting a DC voltage from the DC source (19) into an AC voltage and a control unit (3) for controlling the DC / AC converter (2),

- The control unit (3) is connected to a switching unit (8) which is set up to supply the control unit (3) in a first switching state via the AC network (21) connected to the AC output (11) and to supply the control unit (3) in a second switching state via an auxiliary power source (22) which provides AC voltage and which is separated from the AC output (1 1) in the second switching state of the switching unit (8),

- The inverter (1) also has a grid monitoring unit (4) which is set up to detect a property of an AC voltage present in the AC grid (21),

with the steps:

- Operating the switching unit (8) in the second switching state when the AC voltage in the AC network (21) is not detected, or the property of the AC voltage (21) detected by the network monitoring unit (4) predetermined criteria not enough, and

- Operating the switching unit (8) in the first switching state when the property of the AC voltage (21) detected by the network monitoring unit (4) satisfies the specified criteria.

2. The method according to claim 1, wherein a switching of the switching unit (8) in the first switching state and / or the operation of the switching unit (8) in the first switching state via the network monitoring unit (4) or via this in connection with the control unit (3) is controlled.

3. The method according to claim 1 or 2, wherein in the second switching state of the switching unit (8) in addition to the control unit (3) at least one further Component of the inverter selected from the group: fan (10), heating, AC switch (6), DC switch (7), and communication unit is supplied by the auxiliary power source (22).

4. The method according to any one of the preceding claims, wherein the

Auxiliary power source (22) when the switching unit (8) is operated in the first switching state, in particular when the switching unit (8) has been operated in the first switching state for a certain period of time.

5. The method according to any one of the preceding claims, wherein the

Auxiliary power source (22) is designed as a mobile auxiliary power source which, when the switching unit (8) is operated in the first switching state, or when the switching unit (8) has been operated in the first switching state for a certain period of time, by the switching unit (8) or from the inverter (1).

6. The method according to any one of the preceding claims, wherein the predetermined criteria, in which the switching unit (8) is operated in the first switching state, comprise at least one of the following criteria:

- An amplitude Uo of the AC voltage prevailing in the AC network (21) is - in particular at least for a predetermined first time period Atsw.i - within a predefined tolerance range around a nominal value Uo.nom for the amplitude of the AC voltage in the AC network (21 ),

- A frequency fo of the AC voltage is - in particular for a predetermined second time period Atsw, 2 - within a predetermined tolerance range around a nominal value fo.nom for the frequency of the AC voltage in the AC network (21).

7. The method according to any one of the preceding claims, wherein the switching unit (8), provided that the AC voltage in the AC network (21) meets the predetermined criteria, is operated for a period of time in a third switching state, which has a power flow between the Control unit (3) and the AC network (21) and between the

Auxiliary power source (22) and the AC network (21) allows.

8. System component (17) with an inverter (1) for converting DC voltage to AC voltage, the inverter comprising

- A direct voltage (DC) input (12) for connecting the

Inverter (1) to a DC source (19) providing the DC voltage,

- an alternating voltage (AC) - output (1 1) for connecting the inverter (1) to an alternating voltage (AC) - grid (21)

a network monitoring unit (4) which is set up to detect a property of an AC voltage in the AC network (21),

- A DC / AC converter (2), and

- a control unit (3) for controlling the DC / AC converter (2),

characterized in that the system component (17) comprises a switching unit (8), and the control unit (3) is electrically connected to the switching unit (8), the switching unit (8) being designed and set up in a first switching state of the switching unit (8) to supply the control unit (3) via the AC network (21) connected to the AC output (1 1) and, in a second switching state of the switching unit (8), to supply the control unit (3) via an auxiliary power source that provides an AC voltage ( 22) to supply, which in the second switching state of the switching unit (8) is separated from the AC output (1 1), and

- The network monitoring unit (4), optionally in connection with the control unit (3), is set up to switch the switching unit (8) depending on the detected property of the AC voltage in the AC network (21) in the first or in the second switching state operate.

9. System component (17) according to claim 8, characterized in that the system component (17) is the inverter (1) and the inverter (1) comprises the switching unit (8), the inverter (1) optionally having a connection (18) for connecting the auxiliary power source (22).

10. System component (17) according to one of claims 8 and 9, characterized in that the switching unit (8) comprises a "normally-off" and / or a "normally-on" relay.

1 1. System component (17) according to any one of claims 8 to 10, characterized in that the inverter (1) has a further output (14) which has a power flow from the AC network (21) mediated via the switching unit (8). or the auxiliary power source (22), and via which further modules arranged outside a housing of the inverter (1), for example a power plant controller (20), can be supplied with electricity.

12. Plant component (17) according to one of claims 8 to 1 1, characterized in that the inverter (1) is set up, further of its components, for example a fan (10), an AC switch (6), a DC switch (7) to supply a communication unit and / or a heater in the second switching state of the switching unit (8) via the auxiliary power source (22).

13. System component (17) according to one of claims 8 to 12, characterized in that the inverter (1) is set up for a voltage-setting operation.

14. Plant component (17) according to one of claims 8 to 13, characterized in that the inverter (1) is designed as a photovoltaic (PV) inverter, whose DC input (12) can be connected to a PV generator (15) , or that the inverter (1) is designed as a battery inverter, the DC input (12) of which can be connected to a battery (16).

15. System component (17) according to any one of claims 8 to 14, characterized in that the switching unit (8) can be connected to an auxiliary power source (22) which is an auxiliary source inverter (24) fed by a battery (23a), one by comprises a PV module (23b) or a series connection of auxiliary source inverters (24) fed by PV modules (23b) or a diesel generator.

16. The system component (17) according to claim 15, wherein the battery (23a) connected to the auxiliary source inverter (24) is formed by at least part of the battery (16), which is in normal operation of the inverter (1) at its DC input (12) is connected, or wherein the PV module (23b) connected to the auxiliary source inverter (24) at least a part of the PV generator (15), which is connected to the DC input (12) of the inverter (1) during normal operation.

17. Inverter, characterized in that it is designed and set up to be used as an inverter (1) of the system component (17) according to one of claims 8 to 16.

18. Power generation plant (EEA), in particular photovoltaic (PV) plant, with a plurality of inverters, and at least one plant component (17) according to one of Claims 8 to 16, the plant component (17) comprising at least one inverter (1) from the Includes a majority of the inverters.

19. Power generation plant (EEA) according to claim 18, further comprising a power plant controller (20) for the superordinate control of an operation of the plurality of inverters, the power plant controller (20) being electrically connected to a switching unit (8) of the at least one plant component (17), and is set up

to be supplied when the switching unit (8) is operating in the second switching state via the auxiliary power source (22), which in the second switching state is separated from an AC output (1 1) of the inverter (1) assigned to the system component (17), and

to be supplied during operation of the switching unit (8) in the first switching state via the AC network (21), which is connected to the AC output (1 1) of the inverter (1) assigned to the system component (17).