Method and System for Extending the Life of a Converter Switch

Abstract

The present invention relates to a method for extending the lifespan of converter switches (Q1, Q2, Q3, Q4) in a system (10) comprising an energy source (PV) connected to a DC bus (DC+, DC-) and a DC / DC converter (12) having converter switches (Q1, Q2, Q3, Q4). The method includes determining a system state in which the power of the energy source (PV) is available and transmission via the DC / DC converter (12) and output to further participating devices on the DC bus (DC+, DC-) are not provided, and operating the DC / DC converter (12) during the determined system state such that power consumption occurs within the DC / DC converter (12) without power being transmitted via the DC / DC converter (12). The present invention also relates to a system comprising an energy source (PV) and a DC / DC converter having converter switches (Q1, Q2, Q3, Q4), and an energy generation system comprising such a system.

Description

Technical Field

[0001] The present application relates to a method for extending the life of a converter switch, and a system including a generator and a DC / DC converter having the converter switch.

Background Art

[0002] In an energy generation system, particularly a PV system (PV: photovoltaic power generation), a power converter including a clocked semiconductor switch, a so-called converter switch, is used. In the case of such a semiconductor switch, the life is shortened due to temperature fluctuations.

[0003] EP2600510A1 describes a method of controlling a power converter by a method in which, in addition to an output current, a current that does not affect the output current and simultaneously heats the converter switch to a predetermined target temperature is generated.

[0004] The present application is based on the problem of extending the life of the converter switch.

[0005] This object is achieved by a method including the configuration of claim 1, a system including the configuration of independent claim 8, and an energy generation system according to claim 14. Preferred embodiments are described in the dependent claims.

Summary of the Invention

[0006] In the system, an energy source, particularly a generator, is connected to a DC bus together with a DC / DC converter. The energy source is, for example, a PV generator. The DC / DC converter has a converter switch in the form of a semiconductor switch. The DC / DC converter is designed to transfer power, for example, from the DC bus to a DC energy storage device such as a battery or in the reverse direction. The DC storage device can be designed to receive and store electrical energy generated by the energy source, for example. The method for extending the life of the DC / DC converter switch is · A step of determining a system state in which power is available from an energy source and transmission via a DC / DC converter and output to further participating devices on the DC bus are not provided; · A step of operating the DC / DC converter during the determined system state such that power consumption occurs within the DC / DC converter without power being transmitted through the DC / DC converter; and it includes.

[0007] Accordingly, the determined system state is related to a system state in which transfer of electrical energy to a DC storage device via a DC / DC converter is not provided. For example, this may apply when the battery is already fully charged. Another participating device on the DC bus may be, for example, an inverter provided for transferring electrical energy from the DC bus to an AC network. The AC network may be, for example, an AC supply network. A further participating device on the DC bus may be, for example, an additional DC load. The DC bus usually has two conductors at different potentials, across which a DC bus voltage is applied.

[0008] Accordingly, by this method, during the determined system state, it becomes possible to operate the DC / DC converter such that power consumption occurs within the DC / DC converter without power being transmitted through the DC / DC converter, for example, by a circulating current flowing within the DC / DC converter. As a result, the converter switch is kept in a heated state compared to the non-active state. In this application, DC (direct current) refers to direct current / direct voltage. In this application, AC (alternating current) refers to alternating current / alternating voltage.

[0009] A system state in which power from an energy source is available but transmission via a DC / DC converter and output to further participating devices on the DC bus are not provided can be, for example, a state where the battery is already fully charged and the power currently available via an inverter connected to the DC bus is not being supplied to the AC network at all or at least not fully, and at the same time, no further participating devices on the DC bus for receiving electrical energy, such as further DC loads, are provided. In such a state, the electrical energy from the energy source may remain unused and available and can be used in the method according to the invention without inconvenience.

[0010] For a PV system, a period of good weather can be, for example, from the afternoon to the early evening of a sunny day, during which time the battery has already been charged by the PV generator earlier in the day and there is still solar radiation, so the PV generator can generate more electrical energy than it supplies to the DC bus. By this method, it becomes possible to determine such an operating state, and at the same time, the operation of a DC / DC converter through which energy is not transmitted (e.g., towards a DC storage device) via the DC / DC converter becomes possible. Rather, the DC / DC converter receives energy only to keep the converter switch warm through the flow of internal current within the DC / DC converter. Keeping the device warm is achieved by the flow of current within the DC / DC converter and the power consumption in the form of heat generated thereby.

[0011] In one embodiment, the DC / DC converter includes a first half-bridge in which a first switch and a second switch are connected in series. The first switch and the second switch are preferably designed as semiconductor switches. The first switch and the second switch are converter switches of the DC / DC converter. The first half-bridge is disposed between the output terminals of the DC / DC converter. The output terminals are provided, for example, for connection to a DC storage device. The DC / DC converter further includes a second half-bridge in which a third switch and a fourth switch are connected in series. The third switch and the fourth switch are converter switches of the DC / DC converter and are preferably designed as semiconductor switches. The second half-bridge is disposed between the input terminals of the DC / DC converter connected to the DC bus. The central terminal of the first half-bridge and the second half-bridge are connected to each other via a choke. The central terminals of the first and second half-bridges are respectively disposed between the two switches. The choke is considered to be designed as an electrical choke, that is, an inductance. The first switch and the fourth switch have a common terminal and can be connected to, for example, one of the conductors of the DC bus.

[0012] In the case of such a DC / DC converter, in one embodiment of the method, during the determined system state, the second switch is permanently closed and the first switch is permanently open. Thereby, the flow of power through the DC / DC converter is effectively prevented. The third switch is clocked during the determined system state. Clocking means that the switch is controlled to open and close temporarily.

[0013] By controlling the switch in this way, electrical energy can be extracted from the DC network, passed as current in the DC / DC converter, and power consumption can be generated. Power consumption is generated by the flowing current, and the switch is heated by that power consumption. When the third switch is turned on, current flows through the third and second switches and the choke. When the third switch is open, current flows through the second and fourth switches. Depending on the switching state of the fourth switch, the current flows through the freewheel diode arranged in parallel with the fourth switch or through the closed fourth switch.

[0014] In one embodiment, the third and fourth switches are clocked to operate the DC / DC converter in the determined operating state. In a further embodiment, the third and fourth switches are clocked complementarily. Complementary clocking means that while the third switch is closed, the fourth switch is open, and vice versa. Since the desired current flow for heating the converter switch can also occur through the freewheel diode of the fourth switch, the fourth switch can be left open during the determined system state.

[0015] In one embodiment of the method, the third switch is clocked at a duty cycle such that it does not exceed the allowable nominal current of the DC / DC converter. For example, the third switch operates in a current control mode, opens when it exceeds the switch-off threshold below the nominal current, and closes again when the value falls below the switch-on threshold. In this method, since power is drawn from the DC network only when the third switch is closed, the current flowing through the DC / DC converter is determined by the duty cycle of the third switch. However, in the complementary clocking of the fourth switch, the fourth switch is clocked at a duty cycle corresponding in a complementary manner to the third switch.

[0016] In one embodiment of the method, the third switch is clocked at a duty cycle that depends on the temperature measured in the DC / DC converter. For example, the duty cycle can be selected such that a pre-settable target temperature in the DC / DC converter is aimed for. Also, in order to continue to achieve the desired heating of the converter switch, it is possible to increase the current in the determined system state at low temperatures within the DC / DC converter. For example, the above-mentioned switch-off threshold and / or switch-on threshold can be determined as a function of the measured temperature. Of course, the duty cycle also depends on other influencing factors such as the DC bus voltage.

[0017] Instead of, or in addition to, the temperature measured in the DC / DC converter, the clocking of the third switch or the power consumption generated by the method of the invention can be determined as a function of the temperature measured outside the DC / DC converter. For this purpose, the step of determining the system state includes the step of detecting the temperature of a component that is in thermal contact with the DC / DC converter but is not itself part of the DC / DC converter and whose temperature must not fall below a predetermined value. In one embodiment, this can be, for example, a battery that is charged and discharged via the DC / DC converter. Commonly used types of batteries have the characteristic that they cannot be charged, or should not be charged, below a critical charging temperature, even if discharging is possible at such low temperatures. Here, the generated power consumption can be used to raise the temperature of the battery in thermal contact with the DC / DC converter or to maintain it above a specified temperature. The power consumption can also be taken completely or partially from the battery, and for this purpose, the fourth switch can be clocked at an appropriate duty cycle.

[0018] In an advantageous embodiment of the method, the system state is determined according to the voltage of the DC bus. The determined system state where no further consumption by the participating devices of the DC bus is provided and at the same time no power transmission via the DC / DC converter is provided can be determined according to the voltage of the DC bus. The voltage of the DC bus is determined, for example, by an inverter on the DC bus, a further load on the DC bus, and / or an energy source.

[0019] In a further embodiment of the method, the determination of the system state is instructed to the DC / DC converter by an input signal. This embodiment can be used, for example, when the system state is determined by a control device and then transmitted to the DC / DC converter, and the controller of the DC / DC converter controls the converter switch of the DC / DC converter according to the described method. The control device of the DC / DC converter can here be understood as part of the control device of the system. This embodiment can also be used when the system state is determined, for example, based on the voltage measurement on the DC bus, transmitted to the DC / DC converter, and then the controller of the DC / DC converter controls the converter switch according to the method. The control device can be a computing unit having at least a processor, a memory, and a communication interface.

[0020] The system includes an energy source and a DC / DC converter. The energy source and the DC / DC converter are each connected to a DC bus. The DC / DC converter has a converter switch that can be controlled to open and close for power conversion by the DC / DC converter. Further, a control device is provided that is designed and provided to execute one of the above methods. The control device can be arranged, for example, within the DC / DC converter and / or on another computing unit of the system. The control device can also be distributed and arranged across one or more additional computing devices of the DC / DC converter and the system, or arranged remotely from the system. The control device can also be designed to control the DC / DC converter and / or additional participating devices of the DC bus.

[0021] In one embodiment of the system, the first switch is thermally coupled to at least one of the second, third, and / or fourth switches. In this method, the current required to generate power consumption flows through the second, third, and fourth switches. Thus, they can be heated by power consumption. By coupling the first switch to the second, third, and / or fourth switches, the first switch can also be heated and its lifespan can be extended.

[0022] In one embodiment, the first switch is thermally coupled to a choke as a heat storage device. When this method is executed, the current that generates power consumption flows through the choke of the DC / DC converter. To heat the first switch, this switch is thermally coupled to a choke that functions as a heat storage device. This can cause heating of the first switch.

[0023] In one embodiment, the converter switch and the choke are thermally coupled to a common heat sink. The common heat sink ensures uniform heat exchange between the converter switch and the choke, and thus uniform heating of the converter switch can be achieved.

[0024] In one embodiment of the system, the energy source is a PV generator. The method is particularly advantageous for implementing a system with a PV generator, as the supply of power generated by the energy source to the grid may not be possible, or not desired, or at least not fully possible or desired when a system state is determined where there may be solar energy generated by the PV generator, and at the same time, the battery connected to the system is already fully charged or no further charging is provided. This solar energy is used to heat the converter switch, thus extending the life of the converter switch.

[0025] It is also conceivable to continuously or occasionally check whether the condition that no other use of the power used to heat the DC / DC converter is provided during the execution of the method according to the invention is still satisfied. Otherwise, the heating can be stopped or the power used for heating can be reduced.

[0026] In one embodiment of the system, the DC / DC converter comprises a first sub-converter and a second sub-converter. The two sub-converters are each connected to the DC bus on the input side. When the system state is determined, the two sub-converters are interconnected on the output side via an optional coupling switch such that the two sub-converters are of equal size but transmit power flows in opposite directions to each other. However, the sub-converters can also be permanently connected to each other on the output side without using a coupling switch. Due to the equal but opposite power flows, power consumption occurs within the sub-converters by the converter switches, and thus the converter switches are kept in a heated state. This occurs without overall power transfer of the DC / DC converter, i.e., without power being output via the output terminals of the DC / DC converter. Advantageously, when transmitting power via the DC / DC converter, the two sub-converters operate in parallel. This means that for transferring the total power across the DC / DC converter, both sub-converters are connected to the DC bus on the input side and both sub-converters are connected to the output terminals of the DC / DC converter on the output side. When the system state is determined, the output sides of the sub-converters are connected via a coupling switch such that power flows of equal magnitude and in opposite directions to each other are transmitted. Instead of the coupling switch, the sub-converters can also be permanently connected in parallel on the output side.

[0027] Furthermore, the present application relates to an energy generation plant comprising one of the above systems and an inverter connected to a DC bus for supplying power generated by an energy source to an AC network. The AC network is preferably an AC supply network.

Brief Description of the Drawings

[0028] Examples of the present application will be described in more detail below with reference to the accompanying drawings.

[0029]

Figure 1

Figure 2

Figure 3

[0030] In the figures, the same or similar elements are denoted by the same reference numerals. DETAILED DESCRIPTION OF THE INVENTION

[0031] FIG. 1 schematically shows an embodiment of a system 10 including an energy source PV having a voltage U_PV and a DC bus DC+, DC- to which a DC / DC converter 12 is connected. The DC bus DC+, DC- includes two conductors DC+ and DC- at different potentials. The DC bus voltage U_Bus exists between the two conductors of the DC bus DC+, DC-. Additional DC bus devices (not shown in FIG. 1) can be connected to the DC bus DC+, DC-. The additional DC bus participating device can be, for example, an inverter, which can be provided to supply the power generated by the PV energy source to an AC supply network.

[0032] The DC / DC converter 12 extracts power from the DC buses DC+ and DC-, converts it, and transfers it, for example, to the DC storage device Bat connected to the output terminals 12A+ and 12A-, and is designed such that this power can be used again on the DC bus later. There is a voltage U_Bat between the terminals of the DC storage device Bat. The DC / DC converter connects the first and second semiconductor switches Q1 and Q2 in series between its output terminals 12A+ and 12A-. A capacitor is arranged in parallel with the series connection of this first switch Q1 and the second switch Q2. Between the input terminals 12E+ and 12E- of the DC / DC converter 12, the third and fourth semiconductor switches Q3 and Q4 are connected in series. A capacitor is arranged in parallel with the series connection of the third switch Q3 and the fourth switch Q4 between its input terminals 12E+ and 12E-. The semiconductor switches Q1, Q2, Q3, and Q4 correspond to the converter switches of the DC / DC converter 12 and can have their own freewheel diodes or freewheel diodes are connected in anti-parallel to them. The two series circuits of the switches Q1, Q2 and Q3, Q4 correspond to the two half-bridges of the DC / DC converter 12. The two half-bridges are connected by an inductor D in the middle between the two switches. An ammeter A is arranged in series with the inductor D. The second switch Q2 and the fourth switch Q4 are connected to each other, for example, to the conductor DC- of the DC bus.

[0033] Figure 2 schematically shows a method for extending the lifetimes of the converter switches Q1, Q2, Q3, and Q4. In the system 10 shown as an example in Figure 1 or Figure 3, both the DC / DC converter 12 and the energy source PV are connected to the DC buses DC+ and DC-, and the electrical energy generated by the energy source PV can be supplied to the DC buses DC+ and DC-. The energy source PV has a PV voltage U_PV between its terminals. The DC / DC converter 12 can draw power from the DC buses DC+ and DC- and output it, for example, to the DC storage device Bat via its output terminals 12A+ and 12A-.

[0034] In this method, in step S1, a system state is determined in which the power from the energy source PV is available on the DC bus DC+, DC-. The system state is determined when power transmission via the DC / DC converter 12 is not provided and at the same time power output to further participating devices on the DC bus DC+, DC- is not provided. The further participating devices on the DC bus DC+, DC- can be, for example, additional DC loads (not shown) and / or inverters (not shown). The inverter can be designed, for example, to supply power to an AC supply network. Here, there is a possibility that a system state occurs in which the PV energy source can generate power, but the generated power is not transmitted at all or at least not completely via the inverter. This reason can be, for example, of a regulatory nature. At the same time, for example, there is also a possibility that transfer to the DC storage device Bat is not provided because the DC storage device Bat is already full. This is an example of the system state determined in step S1.

[0035] In step S2, after determining the system state, the DC / DC converter 12 is operated so that power consumption occurs within the DC / DC converter 12 without power being transmitted via the DC / DC converter 12. As a result, the converter switches Q1, Q2, Q3, Q4 of the DC / DC converter 12 are maintained in a heated state compared to the non-active state. The heated state is caused on the one hand by the switching operation and on the other hand by the current flowing through the DC / DC converter 12 and the power consumption thereby generated.

[0036] The system state determined in method step S1 can occur, for example, by measuring the voltage U_Bus of the DC bus DC+ and DC-. To operate the DC / DC converter 12 in step S2, the first switch Q1 can be permanently opened here. The second switch Q2 can be permanently kept closed. The third switch Q3 is clocked. For example, the fourth switch Q4 can be permanently kept open. It is also possible to close the fourth switch Q4 when the third switch Q3 is in the open state. Therefore, complementary clocking of the third and fourth switches Q3 and Q4 becomes possible. When the fourth switch Q4 is open while the third switch Q3 is closed, it is also possible that the clocking of the third switch Q3 and the fourth switch Q4 is not completely complementary. The possible clocking of the third switch Q3 is a duty cycle of 30 μs at a clock frequency of 100 Hz.

[0037] During the operation of step S2, when the third switch Q3 is closed, current flows through the choke D and the second switch Q2 to the third switch Q3. Then, when the third switch Q3 opens, the current can continue to flow back to the second switch Q2 through the switch Q4 and the choke D. Depending on the type of switch, the current flowing through the fourth switch Q4 is generated either through a freewheel diode arranged in anti-parallel to the fourth switch Q4 or a proprietary freewheel diode, or directly through the closed switch Q4 when the switch Q4 is closed. As a result, current does not flow through the output terminals 12A+ and 12A- of the DC / DC converter 12, but current flows through the third, second, and fourth switches Q3, Q2, and Q4. This flow of current causes power consumption and heats the converter switches Q1, Q2, Q3, and Q4. Since no direct current flows through the first switch Q1, the first switch Q1 can be heated, for example, through the choke D as a common heat storage device or a common heat sink for the choke D and the switches Q2, Q4, and Q3. However, it is also conceivable that the converter switch Q1 is installed in the module together with the converter switch Q2 and is thus already thermally coupled and heated with it.

[0038] In the system 10 shown in FIG. 3, the DC / DC converter 12 has two sub-converters 14, 16. The first sub-converter 14 and the second sub-converter 16 are each connected to the DC bus DC+, DC- on the input side. The input terminal 14E+ of the first sub-converter 14 and the input terminal 16E+ of the second sub-converter 16 are connected to the input terminal 12E+ of the DC / DC converter 12. The input terminal 14E- of the first sub-converter 14 and the input terminal 16E- of the second sub-converter 16 are connected to the input terminal 12E- of the DC / DC converter 12. The two sub-converters 14, 16 here also correspond to DC / DC converters. In normal operation, that is, when the DC / DC converter 12 draws power from the DC bus DC+, DC- and transfers it to the DC storage device Bat, the sub-converters 14, 16 are connected in parallel on the input side as shown in FIG. 3. On the output side, the DC / DC converter 12 has individual output terminals 12A+, 12A- for each of the sub-converters 14, 16, and a battery can be connected to each of those terminals. A coupling switch 18 can be optionally provided between the output terminals 14A+ and 16A+ and / or between the output terminals 14A- and 16A- to enable the sub-converters 14, 16 to be temporarily connected in parallel on the output side or to be separated from each other in a single-pole or full-pole manner on the output side. However, it is also conceivable to connect the output terminals 12A+, 12A- assigned to the sub-converters to the same battery, and thus permanently connect the sub-converters 14, 16 in parallel on the output side.

[0039] During the operation of step S2 of this method, the sub-converters 14 and 16 are here connected in parallel on the output side via an optional coupling switch, unless they are already permanently connected in parallel. The power output by one of the sub-converters 14 and 16 is of the same magnitude but is absorbed by the other sub-converters respectively, so power is not exchanged via the output terminals 12A+ and 12A- of the DC / DC converter 12. In the state of S2, power is absorbed via the input terminals 12E+ and 12E-, but the subsequent power flow is completely carried out within the DC / DC converter 12, and power is not exchanged via the output terminals 12A+ and 12A-.

Explanation of Signs

[0040] 10 System 12 DC / DC Converter 12A+, 12A- Output Terminals of the DC / DC Converter 12E+, 12E- Input Terminals of the DC / DC Converter 14 First Sub-Converter 14A+, 14A- Output Terminals of the First Sub-Converter 14E+, 14E- Input Terminals of the First Sub-Converter 16 Second Sub-Converter 16A+, 16A- Output Terminals of the Second Sub-Converter 16E+, 16E- Input Terminals of the Second Sub-Converter 18 Coupling Switch A Ammeter DC+, DC- DC Bus U_Bus DC Bus Voltage BAT Battery U_Bat Battery Voltage PV Energy Source U_PV PV Voltage D Choke Q1, Q2, Q3, Q4 Converter Switches

Claims

1. A method for extending the life of converter switches (Q1, Q2, Q3, Q4) in a system (10) comprising an energy source (PV) connected to a DC bus (DC+, DC−) and a DC / DC converter (12), wherein the DC / DC converter (12) comprises the converter switches (Q1, Q2, Q3, Q4), and the method comprises: Determining a system state in which power is available from the energy source (PV) and no transmission via the DC / DC converter (12) and output to further participating devices on the DC bus (DC+, DC−) is provided; Operating the DC / DC converter (12) during the determined system state such that power consumption occurs within the DC / DC converter (12) without power being transmitted through the DC / DC converter (12); A method comprising.

2. The method according to claim 1, wherein during the determined operating state, the DC / DC converter (12) is operated such that a circulating current flowing through the converter switches (Q1, Q2, Q3, Q4) is generated within the DC / DC converter (12).

3. The DC / DC converter (12) comprises a first half-bridge in which a first switch (Q1) and a second switch (Q2) arranged between the output side terminals (12A+, 12A−) of the DC / DC converter (12) are connected in series, and a third switch (Q3) and a fourth switch (Q4) arranged between the input side terminals (12E+, 12E−) of the DC / DC converter (12) connected to the DC bus (DC+, DC−) are connected in series. A second half-bridge, wherein the central terminals of the first half-bridge and the second half-bridge are connected to each other via a choke (D), and the second switch (Q2) has a common terminal with the fourth switch (Q4). The method according to claim 1 or 2, wherein the DC / DC converter (12) permanently closes the second switch (Q2) and permanently opens the first switch (Q1) during the determined system state, while the third switch (Q3) is clocked.

4. The method according to claim 3, wherein the third switch (Q3) and the fourth switch (Q4) are clocked, in particular complementary clocked.

5. The clocking of the third switch (Q3), in particular the complementary clocking of the third switch (Q3) and the fourth switch (Q4), is performed with a duty cycle such that the nominal current allowed by the DC / DC converter (12) is not exceeded, according to the method of claim 3 or 4.

6. The clocking of the third switch (Q3), in particular the complementary clocking of the third switch (Q3) and the fourth switch (Q4), is performed with a duty cycle selected such that the temperature measured in the DC / DC converter (12) is controlled to a target temperature, according to the method of any one of claims 3 to 5.

7. The determination of the system state is performed according to the voltage of the DC bus (DC+, DC-), according to the method of any one of claims 1 to 6.

8. The step of determining the system state includes the step of detecting the temperature of the components in thermal contact with the DC / DC converter (12), according to the method of any one of claims 1 to 7.

9. The determination of the system state is instructed to the DC / DC converter (12) by an input signal, according to the method of any one of claims 1 to 8.

10. A system (10) comprising an energy source (PV) and a DC / DC converter (12) with converter switches (Q1, Q2, Q3, Q4) commonly connected to a DC bus (DC+, DC-), and provided with a control device designed to execute the method of any one of claims 1 to 9.

11. The first switch (Q1) is thermally coupled to at least one of the second switch, the third switch, and / or the fourth switch (Q2, Q3, Q4), according to the system of claim 10.

12. The first switch (Q1) is thermally coupled to the choke (D) as a heat storage device, according to the system of claim 10 or 11.

13. The converter switches (Q1, Q2, Q3, Q4) and the choke (D) are thermally coupled to a common heat sink, according to the system of any one of claims 10 to 12.

14. The energy source (PV) comprises a PV generator, according to the system of any one of claims 10 to 13.

15. The DC / DC converter (12) includes a first sub-converter (14) and a second sub-converter (16). The first sub-converter (14) and the second sub-converter (16) are each connected to the DC bus (DC+, DC−) on the input side (14E+, 14E−, 16E+, 16E−). When the system state is determined to be in a state of parallel connection on the output side, since they are designed to transmit power flows in opposite directions with equal magnitudes, the converter switches (Q1, Q2, Q3, Q4) of the first sub-converter (14) and the second sub-converter (16) are kept in a heated state without full power transmission of the DC / DC converter (12). The system according to any one of claims 10 to 14.

16. The system according to claim 15, wherein the system is configured to achieve a parallel connection state on the output side via a coupling switch (18) disposed between the output terminals (14A+, 14A−, 16A+, 16A−).

17. An energy generation plant comprising the system (10) according to any one of claims 10 to 16 and an inverter connected to the DC bus (DC+, DC−) for supplying the power generated by the energy source (PV) to an AC network.

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