Inverter operation method and inverter

Abstract

The present invention relates to a method of operating an inverter (100) with a DC input and an AC output, the DC input can be connected to a DC power source (10), the bridge branches (125) of the bridge circuit (110) can be connected to power chokes (L1ac, L1ac_a, L1ac_b, L2ac, L2ac_a, L2ac_b, L3ac, L3ac_a, L3ac_b), the AC output can be connected to an AC grid (20, 30) through a disconnect switch (GR), and the inverter (100) is designed to supply power to the AC grid (20, 30). The method comprises the steps of opening a disconnect switch (GR) and controlling semiconductor switches (T1, T2, T3, T4, T5, T6) of at least two bridge branches (125) of a bridge circuit (110), the bridge branches being connected on the AC side after at least one power choke (L1ac, L1ac_a, L1ac_b, L2ac, L2ac_a, L2ac_b, L3ac, L3ac_a, L3ac_b) such that a DC power source (10) connected to a DC input is loaded. The sum of currents flowing out of at least one of the at least two bridge branches (125) on the AC side corresponds to the sum of currents flowing into at least one other bridge branch of the at least two bridge branches (125) on the AC side. The invention further relates to an inverter.

Description

[Technical field]

[0001] This application relates to a method of operating an inverter with a DC input and an AC output, and to an inverter and its uses, which can be used to connect solar photovoltaic or certain other DC voltage sources to an AC grid. [Background technology]

[0002] In some situations, when operating an inverter, it is necessary to load a DC source that the inverter supplies power to the AC grid. The term AC grid is used to refer to, for example, an alternating current grid or an alternating voltage grid. The term DC can be used to refer to a direct current or a direct voltage, and accordingly, a DC source refers to a direct current source or a direct voltage source.

[0003] As an example, it is necessary to discharge a DC source, e.g. the input intermediate circuit of a hydrogen fuel cell or a PV (photovoltaic) system, within a certain time in the event of an AC grid failure or a controlled shutdown of the system. For this purpose, resistors can be connected at the output of the DC source for discharging. These resistors convert the residual energy from the fuel cell or intermediate circuit into heat. As the residual energy is usually very high, the resistors must be able to convert a large amount of energy and therefore become very large and expensive. In particular, these resistors represent an additional component, which means that the control and operation of the whole system becomes more complex.

[0004] PV inverters are usually started in the morning as soon as the DC voltage of the PV generators is high enough and the inverter is connected to the AC grid. There is a problem if the DC voltage is high enough, but the solar radiation is so low that the AC side grid connection causes the DC voltage to drop again quickly and the AC grid is disconnected immediately. This continuous switching operation has a negative effect on the useful life of the grid disconnection point, since it is usually designed for only a certain number of switching cycles. At this point, it is reasonable to start the AC grid connection only if not only sufficient DC voltage but also sufficient DC power is available. The same problem can occur with wind generators if sufficient power is not yet available.

[0005] In a two-stage inverter topology with a DC / DC converter upstream of the inverter bridge, the available power of the DC source can be determined by loading the DC source and charging the intermediate circuit of the two-stage inverter to a specific potential. The energy content of the charging process can be used to draw direct conclusions about the power availability of the DC source.

[0006] In single-stage topologies, the DC voltage of the DC power supply is primarily used as an indicator, however in this case this indicator may be unreliable since information about the rated current is missing.

[0007] Based on this, it is an object of the present application to provide an improved method for loading a DC power source connectable to an inverter and an improved inverter. Summary of the Invention

[0008] This object is achieved by a method with the features of independent claim 1. This object is further achieved by an inverter with the features of independent claim 12 and by the use of an inverter as claimed in claims 13 and 14. Advantageous embodiments of the method are set out in the dependent claims.

[0009] The inverter has a DC input for connecting to a DC power source and an AC output for connecting to an AC grid through a disconnect switch, and a bridge branch of a bridge circuit is connected to the AC output through a power choke. The AC output can be connected to the AC grid through a disconnect switch and disconnected from the AC grid through a disconnect switch. The inverter is designed to supply power provided from a DC power source to the AC grid. A method of operating the inverter includes the following steps: a) opening a shutoff switch; b) controlling semiconductor switches of at least two bridge branches of a bridge circuit, the bridge branches being connected after at least one power choke on the AC side such that a DC power source connected to the DC input is loaded.

[0010] The sum of the currents flowing out of at least one of the at least two bridge branches on the AC side corresponds to the sum of the currents flowing into at least one other of the at least two bridge branches on the AC side, which means that the sum of the currents flowing out of the bridge branches on the AC side corresponds to the sum of the currents flowing into the bridge branches on the AC side.

[0011] Thus, energy can be transferred between two or more bridge branches of the inverter in order to discharge the DC side with the resulting conversion losses. Such an inverter and the inverter operating in such a way allows the loading of DC sources that the inverter can feed into the AC grid. The load can be applied without the use of additional resistive components. This allows for a simpler and more cost-effective inverter design. Moreover, in this situation, it is possible to selectively load DC sources that the inverter can feed into the AC grid without the need to feed into the AC grid. The DC sources are loaded by drawing power from the DC sources and consuming it in the inverter. There is no need to consume power by additional components or feeding into the AC grid and / or by other components that can be connected to the AC output. For this purpose, the switching losses of the inverter, which amount to about 2% of the nominal power of the inverter if the efficiency of the bridge circuit is for example 98%, are used to realize self-consumption without connecting a load or sink on the AC side. However, it is possible to operate other existing consumers in the system, such as for example a fan. If the nominal power of the inverter is 100 kW, the discharge power will be 2 kW. This is a significant advantage over, for example, using a 2 kW resistor to discharge a DC voltage source.

[0012] This can be used, for example, for rapid discharge of charge storage systems on the DC side in the form of application of hydrogen fuel cell or PV systems in the event of a fault on the AC grid or in the form of application of a controlled shutdown of the hydrogen fuel cell or PV system.

[0013] The connection of the AC side of the at least two bridge branches of the bridge circuit downstream of the at least one power choke can be performed, for example, by closing a relay before step b). It is also possible that the connection of the AC side of the at least two bridge branches of the bridge circuit downstream of the at least one power choke already exists and no relay needs to be provided for this. To perform the method after disconnection from the grid, it is usually necessary to establish the connection of the bridge branches via a switching device such as a relay. In inverters with two or more parallel bridge branches per phase and operating, for example, in interleaved mode, the connection of the bridge branches downstream of at least one power choke of the parallel bridge branches already exists and the method can be performed using these parallel bridge branches without the use of additional relays. Nevertheless, in this case, one of the two or more parallel bridge branches per phase can alternatively also be connected to the bridge branch of the other phase via a relay.

[0014] In one embodiment, for example in a three-phase inverter having a bridge branch for each phase, for example two bridge branches can be connected together such that current flowing out of one bridge branch flows into the other bridge branch.

[0015] However, in one embodiment, for example, all three bridge branches of a three-phase inverter may be connected together such that, for example, the current flowing out of one bridge branch splits and flows into the other bridge branch, or the currents flowing out of two bridge branches are combined and flow into a third bridge branch.

[0016] In one embodiment of the method, the semiconductor switches for loading the DC power source connected to the DC input are controlled so that the inverter operates in voltage-controlled operation with zero voltage at the AC output. In such an embodiment, particularly when connecting bridge branches of all three phases of a three-phase system, the control of the semiconductor switches can be performed in the same way as in normal supply operation, and only the inverter has to be adjusted in voltage-controlled operation to a nominal value of zero output voltage, which corresponds to a short circuit present due to the connection of the bridge branches. When connecting a three-phase inverter in two phases and operating in voltage-controlled operation with zero output voltage, instead of the 120° phase shift that occurs in normal operation of a three-phase inverter, an additional 180° phase shift between the currents must be set in the method.

[0017] The bridge circuit for the three-phase inverter can be, for example, a B6 bridge circuit.

[0018] For example, in an embodiment with a single-phase inverter with an H4 or H5 bridge circuit having a total of two bridge branches, the two bridge branches may be connected together.

[0019] Even in single-phase systems, the control of semiconductor switches for loading a DC source connected to the DC input can be performed in such a way that the inverter operates in voltage controlled operation with zero voltage at the AC output.

[0020] When connecting only two bridge branches of a three-phase or single-phase inverter, or when connecting only two parallel bridge branches of one phase, the semiconductor switches of the bridge branches can each be controlled to operate as a DC / DC converter. The DC voltage difference between the two bridge branches determines the current flowing through the connection between the bridge branches.

[0021] In one embodiment of the method, the degree of loading of the DC power source that can be connected to the DC input can be adjusted by controlling the semiconductor switch. In particular, the degree of loading can be adjusted by selecting the bridge branch in which the semiconductor switch is used in the method. For example, the adjustment of the load is possible by adjusting the current that flows when the two bridge branches are operated as a DC / DC converter via the voltage difference between the connected bridge branches. This can also be used to monitor a fuel cell, for example by recording the V(I,t) voltage characteristic.

[0022] Controlling a bridge branch as a DC / DC converter is also possible with three or more connected bridge branches.

[0023] For application of this method, the topology of the inverter bridge is not limited to the B6, H4, or H5 circuits described above, but may include any topology having at least two bridge branches. Instead of a half bridge, the bridge branches may have, for example, an NPC, also known as INPC, BSNPC, also known as TNPC, or ANPC topology.

[0024] The inverter has a DC input and an AC output and a bridge circuit with a controllable semiconductor switch. The DC input can be connected to a DC power source and the bridge circuit is connected to the AC output via a power choke. The AC output can be connected to an AC grid via a disconnect switch and the inverter is designed to feed the power provided by the DC power source to the AC grid. The inverter further has a control unit designed and configured to execute the aforementioned method. For this purpose, the control unit can be designed, for example, as a computing unit with a memory and a processor, and instructions corresponding to the method steps can be executed on the processor.

[0025] Such an inverter can be used, for example, to discharge a DC power source connected to the DC input, with the discharge power being up to the maximum power dissipation of the semiconductor switch.

[0026] Such an inverter may also be used, for example, to determine the power availability of a DC power source connected to the DC input.

[0027] In an application for determining DC side power availability of a DC power source, for example, a short term load up to the maximum power dissipation of the inverter can be applied to the DC power source and the load capacity of the DC power source can be determined from the determined current and voltage values. [Brief description of the drawings]

[0028] The invention of the present application is explained in more detail below with the aid of figures. [Figure 1] FIG. 1 shows a schematic of how an inverter operates. [Diagram 2] FIG. 2 shows a schematic diagram of an exemplary embodiment of an inverter with a DC source and an AC grid, as well as phase branches. [Diagram 3] FIG. 3 shows an exemplary embodiment of a bridge branch with a semiconductor switch. [Figure 4] FIG. 4 illustrates an exemplary embodiment of a three-phase bridge circuit. [Diagram 5] FIG. 5 illustrates an exemplary embodiment of a three-phase bridge circuit. [Figure 6] FIG. 6 illustrates an exemplary embodiment of a three-phase bridge circuit. [Figure 7] FIG. 7 illustrates an exemplary embodiment of a three-phase bridge circuit. [Figure 8] FIG. 8 illustrates an exemplary embodiment of a three-phase bridge circuit. [Figure 9] FIG. 9 illustrates diagrammatically the operation of the two bridge branches of FIG. [Figure 10] FIG. 10 illustrates an exemplary embodiment of a single phase bridge circuit. [Figure 11] FIG. 11 illustrates an exemplary embodiment of a single-phase bridge circuit.

[0029] In the various figures, identical or similar elements are designated with the same reference numerals. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] 1 shows a method of operating an inverter 100. The inverter 100 can be designed as single-phase or multi-phase, e.g., two-phase or three-phase, and can be connected to a single-phase, two-phase, or three-phase AC grid as appropriate. The method includes the following steps: a) The disconnect switch connecting the inverter to the AC grid opens. b) The semiconductor switches T1, T2, T3, T4, T5, T6 of at least two bridge branches 125 of the bridge circuit 110 are controlled such that the DC source 10 connected to the DC input of the inverter 100 is loaded.

[0031] At least two bridge branches 125 are connected on the AC side downstream of at least one power choke L1ac, L1ac_a, L1ac_b, L2ac, L2ac_a, L2ac_b, L3ac, L3ac_a, L3ac_b. Thus, the semiconductor switches T1, T2, T3, T4, T5, T6 can be controlled such that the sum of currents flowing out of at least one of the at least two bridge branches 125 on the AC side corresponds to the sum of currents flowing into at least one other bridge branch of the at least two bridge branches 125 on the AC side. This means that the sum of currents flowing out of the bridge branches 125 on the AC side corresponds to the sum of currents flowing into the bridge branches 125 on the AC side.

[0032] Figure 2 shows such an inverter 100 configured for the method of Figure 1. The inverter 100 has a DC input and an AC output, with the DC input connected to a DC power source 10 and three phase branches 120, 130 of a bridge circuit 110 connected to the AC output. The AC output is connected to a three-phase AC grid 20, and the inverter 100 is designed to feed the power provided by the DC power source 10 to the AC grid 20. The inverter 100 has one phase branch 120, 130 for each phase of the AC grid 20.

[0033] Each phase branch 120, 130 has a bridge branch 125 and passive components such as inductors and capacitors. For connection to the AC output, each phase branch 120, 130 has one or more power chokes L1ac, L1ac_a, L1ac_b and a capacitor C1ac for connection to the center potential M of the DC source 10 or to the negative potential DC-. The phase branches 120, 130 can be designed as a monolithic phase branch 120 or as a phase branch 130 with several parallel phase branches 125, here for example two parallel phase branches 125. The parallel phase branches 125 are preferably operated using an interleaved method in which the semiconductor switches T1, T2, T3, T4, T5, T6 of the bridge branch 125 are clocked with an offset from each other.

[0034] Furthermore, the inverter 100 comprises a control unit 150 for controlling the semiconductor switches T1, T2, T3, T4, T5, T6 of the bridge branch 125.

[0035] It is possible to integrate additional DC / DC converters on the DC side of the inverter 100. For example, Si or SiC components designed as IGBTs or MOSFETs can be selected as power semiconductors for the semiconductor switches T1, T2, T3, T4, T5, T6. This method can be used for, for example, but not limited to, three-level 3L, two-level 2L, or multi-level topologies.

[0036] 3 shows possible topologies of the bridge branch 125. Shown are the TNPC topology, alternatively also referred to as the BSNPC topology, the INPC topology, alternatively also referred to as the (standard) NPC topology, the ANPC topology, as well as the arrangement of the semiconductor switches T1, T2, T3, T4, T5, T6 of a half-bridge HB, as used, for example, in a B6, H4 or H5 circuit.

[0037] 4 shows a three-phase bridge circuit 110 having monolithic phase branches 120 with relays R connecting the phases together. A disconnect switch GR for disconnecting the inverter 100 from the AC grid 20 is open. Each phase branch 120 has a bridge branch 125 and passive components such as power chokes L1ac, L2ac, L3ac and capacitors C1ac, C2ac, C3ac, and the bridge branch 125 is connected to the AC output through the power chokes L1ac, L2ac, L3ac. Each phase of the AC output can be connected to the AC grid 20 through a disconnect switch GR.

[0038] Possible energy flow 140 represents potential paths of loss generation for loading DC power supply 10. Load flow 140 occurs through one of relays R and is shown in this example between phase 1 and phase 2.

[0039] In this embodiment, a short circuit of the AC side of two phases of the inverter 100 is applied. For this purpose, the two AC phases are short circuited via a relay R after the power chokes L1ac, L2ac, and the semiconductor switches T1, T2, T3, T4, T5, T6 are controlled, for example, such that the system operates in DC / DC converter operation. Alternatively, the semiconductor switches T1, T2, T3, T4, T5, T6 can also be controlled such that two AC signals 180° out of phase are generated and the voltage of the AC output is adjusted to zero.

[0040] 5 shows a three-phase bridge circuit 110 with phase branches 130 in an interleaved topology. The isolating switches GR are open to isolate the inverter 100 from the AC grid 20. Each phase of the phase branch 130 has parallel sub-phases 1a, 1b, 2a, 2b, 3a, and 3b. Each sub-phase has a respective bridge branch 125 and passive components, such as power chokes L1ac_a, L1ac_b, L2ac_a, L2ac_b, L3ac_a, and L3ac_b, and capacitors C1ac, C2ac, and C3ac, and the bridge branch 125 is connected to the AC output via the power chokes L1ac_a, L1ac_b, L2ac_a, L2ac_b, L3ac_a, and L3ac_b. Each phase of the AC output can be connected to the AC grid 20 via the isolating switches GR.

[0041] Relay R may be optionally used in three-phase bridge circuit 110 of FIG. 5. However, the method may also be practiced here without relay R. Possible energy flows 140 represent potential paths of loss generation for loading DC power supply 10. In the illustrated example, load flow 140 occurs without relay R. Load flow 140 could occur directly, for example, through the connection point of sub-phase 1a and sub-phase 1b.

[0042] Alternatively, a possible energy flow 140 as shown in FIG. 4, for example via an optional relay R between phase 1 and phase 2, is also possible in the three-phase bridge circuit 110 according to FIG.

[0043] 6 shows an embodiment with a three-phase bridge circuit 110 with a monolithic phase branch 120, where all three phases are connected via two relays R. Control of the semiconductor switches T1, T2, T3, T4, T5, T6 in the bridge branch 125 is performed in such a way that power is supplied to the AC side short circuit, allowing energy flow 140.

[0044] In this embodiment, a three-phase AC-side short circuit is applied to the inverter 100. For this purpose, the three AC phases are short circuited after the power chokes L1ac, L2ac, L3ac via the relay R, and the semiconductor switches are controlled to synchronize the system to the short circuit. Alternatively, the bridge branch can be operated as a DC / DC converter.

[0045] 7 shows an embodiment of a three-phase bridge circuit 110 with an interleaved phase branch 130, where all three phases, and therefore also the sub-phases, are connected via two relays R. Control of the semiconductor switches T1, T2, T3, T4, T5, T6 in the bridge branch 125 is performed in such a way that power is supplied to the AC-side short circuit, allowing an energy flow 140. Alternatively, the bridge branch can again be operated as a DC / DC converter.

[0046] FIG. 8 shows an embodiment of a three-phase bridge circuit 110 with interleaved phase branches 130. The three-phase inverter 100 has two respective sub-phases, for example in an ANPC topology in interleaving. The bridge branches 125 are designed, for example, in an ANPC topology, and no relays R are provided between the phases in this exemplary embodiment. Thus, the inverter 100 has two bridge branches for each of the three phases, which are connected in parallel on both the AC and DC sides. Optionally, the inverter 100 can have even more sub-phases per phase.

[0047] The AC grid 20 can be disconnected from the inverter 100 via a disconnect switch GR.

[0048] A method of operating the inverter 100 of FIG. 8 includes, for example, the following steps. a) Isolation switch GR is opened to isolate inverter 100 from AC grid 20. As a result, sub-phases 1a and 1b, sub-phases 2a and 2b, and sub-phases 3a and 3b are connected in parallel with each other. b) Switching the operating method of the AC side of the phase from AC current control to DC current control or voltage control: The semiconductor switches T1, T2, T3, T4, T5, T6 of the bridge branch 125 are controlled in such a way that the bridge branch 125 connected to the power chokes L1ac_a, L1ac_b, L2ac_a, L2ac_b, L3ac_a, L3ac_b and the capacitors C1ac, C2ac, C3ac performs the function of a DC / DC converter (Figure 9).

[0049] Fig. 9 shows this exemplarily on the basis of phases 1a and 1b. The adjustment of the power losses and therefore also the determination of the desired DC power for a safe and reliable AC grid connection and / or the desired discharge power of the DC source can be performed via the current I resulting from the difference between the voltages Vc1 and Vc2, which are set as the nominal values ​​of the output voltages of the two DC / DC converters.

[0050] 10 shows a bridge circuit 110 in an H4 topology of a single-phase inverter 100. The phase branches 120 of the H4 topology are the same as the phase branches 120 of the three-phase B6 bridge circuit. The bridge branch 125 is designed as a half-bridge and is connected to the AC output via the power chokes L1ac and L2ac, which can be connected to the AC grid 30 via the disconnect switch GR. The phase branch 120 can be connected via a relay R to implement this method, in particular to achieve self-consumption.

[0051] In the lower part of Fig. 10, a load flow 140 for implementing the method, in particular for achieving self-consumption, is shown as an example for a single-phase H4 topology with a relay R connecting the two phases. The disconnect switch GR is open and the load flow 140 can be realized between the half-bridges T1 / T2 and T3 / T4 via the relay R. The control of the semiconductor switches T1, T2, T3, T4 of the bridge branch 125 is performed by operating the bridge branch 125 in conjunction with the power chokes L1ac and L2ac, similar to the control of Figs. 4, 8 and 9. The capacitors C1ac and C2ac operate as a DC / DC converter or the bridge branch 125 operates as an inverter bridge, whose output voltage is adjusted to zero according to an existing short circuit.

[0052] Fig. 11 shows an example of a load flow 140 for implementing a method for achieving self-consumption, in particular for a single-phase H5 topology with a relay R for connecting the two phases. The disconnect switch GR is open and the load flow 140 can be realized between the half-bridges T1 / T2 and T3 / T4 via the relay R. The control of the semiconductor switches T1, T2, T3, T4, T5 of the bridge branch 125 is performed here similarly to the control of Figs. 4, 8 and 9, by connecting the power chokes L1ac and L2ac and the capacitors C1ac and C2ac to operate the bridge branch 125 as a DC / DC converter or by operating the bridge branch 125 as an inverter bridge, whose output voltage is regulated to zero according to an existing short circuit.

[0053] List of codes 10 DC power supply 20 AC Grid, Polyphase 30 AC Grid, Single Phase 100 Inverter 110 Bridge circuit 120 Phase Branch, Monolithic 125 Bridge Branch 130 Phase Branching, Interleaving 140 Energy Flow 150 Control Unit GR cutoff switch R Relay Capacitance of C1ac, C2ac, C3ac capacitors L1ac, L1ac_a, L1ac_b, L2ac, L2ac_a, L2ac_b, L3ac, L3ac_a, L3ac_b Power Choke a) and b) Method steps DC+ Positive DC potential DC- Negative direct current potential M center potential AC Alternating current voltage, alternating current L1, L2, L3 AC Grid Conductors N AC grid neutral conductor I current VC1, VC2 voltage T1, T2, T3, T4, T5, T6 Solid State Switches

Claims

1. A method for operating an inverter (100) having a DC input and an AC output, comprising: The DC input can be connected to a DC power source (10), and the bridge branch (125) of the bridge circuit (110) is connected to the DC power source (10) through power chokes (L1ac, L1ac_a, L1ac_b, L2ac, L2ac_a, L2ac_b, L3ac, L3ac_a, L3ac_b), and the AC output can be connected to an AC grid (20, 30) through a disconnect switch (GR), and the inverter (100) is - opening said isolation switch (GR); - controlling semiconductor switches (T1, T2, T3, T4, T5, T6) of at least two bridge branches (125) of said bridge circuit (110), said bridge branches being connected behind at least one power choke (L1ac, L1ac_a, L1ac_b, L2ac, L2ac_a, L2ac_b, L3ac, L3ac_a, L3ac_b) on the AC side such that a DC power source (10) connected to said DC input is loaded; a power supply system for supplying power to said AC grid (20, 30) comprising the steps of: a sum of currents flowing out of at least one of the at least two bridge branches (125) on the AC side corresponds to a sum of currents flowing into at least one other of the at least two bridge branches (125) on the AC side.

2. 2. The method of claim 1 , The inverter (100) is designed to supply power to a single-phase or polyphase AC grid (20, 30), The inverter (100) has at least two parallel bridge branches (125) for each phase, which are connected on the AC side downstream of at least one power choke (L1ac_a, L1ac_b, L2ac_a, L2ac_b, L3ac_a, L3ac_b), The semiconductor switches (T1, T2, T3, T4, T5, T6) of the bridge branch (125) are controlled to load the DC power source (10) connected to the DC input; A method according to claim 1, characterized in that said bridge branch (125) is specifically designed for operation in an interleaved mode.

3. In the method according to claim 1, 13. The method of claim 12, wherein the connection of the AC side of the at least two bridge branches (125) of the bridge circuit (110) downstream of the at least one power choke (L1ac, L1ac_a, L1ac_b, L2ac, L2ac_a, L2ac_b, L3ac, L3ac_a, L3ac_b) is performed by closing a relay (R).

4. 4. The method of claim 3, The inverter (100) is designed to supply power to a three-phase AC grid (20); The inverter (100) has at least one bridge branch (125) for each phase; a first bridge branch (125) from a first phase and a second bridge branch (125) from a second phase are connected to each other on an AC side downstream of the at least one power choke (L1ac, L1ac_a, L1ac_b, L2ac, L2ac_a, L2ac_b, L3ac, L3ac_a, L3ac_b), 13. The method of claim 12, wherein the semiconductor switches (T1, T2, T3, T4, T5, T6) are controlled such that a current flowing out of the first bridge branch (125) flows into the second bridge branch (125).

5. 4. The method of claim 3, The inverter (100) is designed to supply power to a three-phase AC grid (20); The inverter (100) has at least one bridge branch (125) for each phase; three bridge branches (125) are connected to each other on the AC side downstream of the at least one power choke (L1ac, L1ac_a, L1ac_b, L2ac, L2ac_a, L2ac_b, L3ac, L3ac_a, L3ac_b); 4. The method according to claim 3, wherein the semiconductor switches (T1, T2, T3, T4, T5, T6) are controlled in such a way that the current flowing out of at least one bridge branch (125) of one phase is split and flows into at least one bridge branch (125) of each of the other two phases, or the current flowing out of at least one bridge branch (125) of each of the two phases is combined and flows into at least one bridge branch (125) of a third phase.

6. The method of claim 1, wherein the inverter (100) is designed to supply power to a single-phase AC grid (30).

7. The method according to claim 1, CHARACTERIZED IN THAT semiconductor switches (T1, T2, T3, T4, T5, T6) for loading the DC power source (10) connected to the DC input are controlled in such a way that the inverter (100) operates in voltage controlled operation where the voltage of the AC output is zero.

8. The method according to claim 1, 10. A method according to claim 9, wherein the degree of loading of said DC power supply (10) connected to said DC input is adjustable by controlling said semiconductor switches (T1, T2, T3, T4, T5, T6).

9. The method of claim 5, wherein the bridge circuit (110) is a B6 bridge circuit.

10. The method according to claim 6, The method according to claim 1, wherein the bridge circuit (110) is an H4 bridge circuit or an H5 bridge circuit.

11. The method according to claim 1, The method of claim 1, wherein each of said bridge branches (125) has a TNPC, INPC, or ANPC topology.

12. An inverter (100) comprising a DC input and an AC output and a bridge circuit (110) with controllable semiconductor switches (T1, T2, T3, T4, T5, T6), wherein the DC input can be connected to a DC power source (10), a bridge branch (125) of the bridge circuit (110) is connected to the AC output via power chokes (L1ac, L1ac_a, L1ac_b, L2ac, L2ac_a, L2ac_b, L3ac, L3ac_a, L3ac_b), and the AC output can be connected to an AC grid (20, 30) via a disconnect switch (GR), the inverter (100) being designed to supply power to the AC grid (20, 30), The inverter (100) is characterized in that it comprises a control unit (150) designed and arranged to carry out the method according to any one of claims 1 to 11.

13. Use of the inverter (100) of claim 12 for discharging a DC power source (10) connected to the DC input.

14. Use of the inverter (100) of claim 12 for determining power availability of a DC power source (10) connected to the DC input.

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