Method and system for increasing useful life of converter switches

Abstract

The present application relates to a method for increasing the service life of converter switches (Q1, Q2, Q3, Q4) in a system (10) comprising an energy source (PV) attached on a DC bus (DC +, DC-) in common with a DC / DC converter (12) comprising the converter switches (Q1, Q2, Q3, Q4). The method comprises the following steps: determining a system state in which the electrical power of the energy source (PV) is available for which there is no transmission via the DC / DC converter (12) and no output to a further participant of the DC bus (DC +, DC-); during the determined system state, the DC / DC converter (12) is operated in such a way that loss power is generated in the DC / DC converter (12) without transferring power via the DC / DC converter (12). Furthermore, the application relates to a system (10) having an energy source (PV) and a DC / DC converter (12) having converter switches (Q1, Q2, Q3, Q4), and to an energy generation installation having such a system.

Description

Technical Field

[0001] The invention relates to a method for increasing the service life of a converter switch and to a system having a generator and a DC / DC converter having a converter switch. Background Art

[0002] Power converters are used in energy generation plants, in particular PV plants (PV: Photovoltaic), which can have clocked semiconductor switches, so-called converter switches. Temperature fluctuations in such semiconductor switches lead to a reduced service life.

[0003] EP 2 600 510 A1 describes a method in which an electrical power converter is controlled in such a way that, in addition to the output current, a current is generated which does not influence the output current and at the same time heats the converter switches to a predefined target temperature. Summary of the invention

[0004] The present application is based on the task of increasing the service life of a converter switch.

[0005] This object is achieved by a method having the features of claim 1 and by a system having the features of independent claim 8 and by a power generation plant according to claim 14. Preferred embodiments are given in the dependent claims.

[0006] In the system, an energy source, in particular a generator, is attached 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. For example, the DC / DC converter is configured to transfer electrical power from the DC bus to a DC energy storage, such as a battery, or in the opposite direction. For example, the DC storage can be configured to receive and store electrical energy generated by the energy source. The method for increasing the service life of a converter switch of a DC / DC converter has the following steps:

[0007] A system state is determined in which electrical power is available from the energy source, for which no transmission via a DC / DC converter and no output to other participants of the DC bus is provided.

[0008] During the determined system state, the DC / DC converter is operated in such a way that power loss occurs in the DC / DC converter, without power being transmitted via the DC / DC converter.

[0009] Ie the determined system state relates to a system state in which no transmission of electrical energy to the DC storage device via the DC / DC converter is provided. This can be the case, for example, if the battery is already fully charged. For example, a further participant of the DC bus can be an inverter which is provided for transmitting electrical energy from the DC bus into an AC network. For example, the AC network can be an AC supply network. For example, a further participant of the DC bus can be a further DC load. Typically, a DC bus has two conductors which are at different potentials and between which a DC bus voltage is applied.

[0010] That is, the method enables the DC / DC converter to be operated during the determined system state in such a way that power loss is generated in the DC / DC converter, for example, by a loop current flowing in the DC / DC converter, without power being transmitted via the DC / DC converter, so that the converter switch is kept in a state that is heated relative to the inactive state. In the present application, DC (English: Direct Current) means direct current / direct voltage. In the present application, AC (English: Alternating Current) means alternating current / alternating voltage.

[0011] For example, the system state in which the electrical power of the energy source is available for use, for which no transmission via a DC / DC converter is provided and no output to further participants of the DC bus is provided, may be a system state in which the battery is already fully charged, no feed-in of the power currently available into the AC network via an inverter attached to the DC bus is provided or at least not provided for complete feed-in, and at the same time no further participants of the DC bus, such as further DC loads, are provided to receive electrical energy. In such a state, the electrical energy of the energy source may be available in an unused manner and can be used for the method according to the invention without disadvantages.

[0012] In a good weather period of a PV system, for example on a sunny day, this can be from the afternoon to the evening, when the battery has already been charged earlier in the day by the PV generator and the PV generator can generate more electrical energy due to the solar radiation that is still present than is provided for supplying the DC bus. In this case, the method enables the determination of such an operating state and at the same time enables the operation of a DC / DC converter, in which no energy is transferred via the DC / DC converter (for example in the direction of a DC storage device), but rather the DC / DC converter only receives energy in order to keep the converter switches warm by means of an internal current flow in the DC / DC converter. In this case, the warming is achieved by means of a current flow in the DC / DC converter and the power loss in the form of heat generated thereby.

[0013] In one embodiment, the DC / DC converter comprises a first half-bridge having a series connection of a first switch and a second switch. Preferably, the first and second switches are implemented as semiconductor switches. The first and second switches are converter switches of the DC / DC converter. The first half-bridge is arranged between the attachment ends of the DC / DC converter on the output side. For example, the attachment end on the output side is set to be attached to a DC storage. In addition, the DC / DC converter has a second half-bridge having a series connection of a third switch and a fourth switch. The third and fourth switches are converter switches of the DC / DC converter and are preferably implemented as semiconductor switches. The second half-bridge is arranged between the attachment ends of the DC / DC converter on the input side and attached to the DC bus. The central attachment ends of the first half-bridge and the second half-bridge are connected to each other via a choke. The central attachment ends of the first half-bridge and the second half-bridge are arranged between the two switches respectively. The choke can be regarded as an electric choke, that is, it is implemented as an inductor. The first and fourth switches have a common attachment end, which can be connected to one of the conductors of the DC bus, for example.

[0014] Now, in one embodiment of the method, for such a DC / DC converter, during the determined system state, the second switch is permanently closed and the first switch is permanently opened. As a result, the power flow via the DC / DC converter is effectively inhibited. During the determined system state, the third switch is clocked. Clocking means that the switch is actuated in such a way that it is sometimes opened and sometimes closed.

[0015] By such actuation of the switch, it is possible to obtain electrical energy from the DC network and flow in the DC / DC converter as a current that generates power loss. Power loss is generated by the flowing current, and the switch is heated by the power loss. Here, in the case of the third switch being turned on, the current flows via the third and second switches and via the choke. In the case of the third switch being opened, the current flows via the second switch and the fourth switch. Depending on the switching state of the fourth switch, the current flows via a freewheeling diode (Freilaufdiode) arranged in parallel with the fourth switch or via a closed fourth switch.

[0016] In one embodiment, in order to operate the DC / DC converter, the third and fourth switches are clocked in the determined operating state. In another embodiment, the third and fourth switches are clocked in a complementary manner. Clocking in a complementary manner means that the fourth switch is open during the time period in which the third switch is closed and vice versa. It is also possible to keep the fourth switch open during the determined system state, since the desired current flow for heating the converter switch can also be achieved via the freewheeling diode of the fourth switch.

[0017] In one embodiment of the method, the third switch is clocked with a duty cycle such that the permitted nominal current of the DC / DC converter is not exceeded. For example, the third switch is operated in a current-regulated manner and, for example, is opened when a switch-off threshold below the nominal current is exceeded and is closed again when the switch-on threshold is less than. In the method, the current flowing through the DC / DC converter is determined by the duty cycle of the third switch, since electrical power is only drawn from the DC network when the third switch is closed. However, in the case of clocking the fourth switch in a complementary manner, the fourth switch is clocked with a corresponding duty cycle in a complementary manner to the third switch.

[0018] In one embodiment of the method, the third switch is clocked with a duty cycle that is dependent on the temperature measured in the DC / DC converter. For example, the duty cycle can be selected such that a target temperature that can be predetermined is sought to be reached in the DC / DC converter. It is also possible that, in the case of low temperatures in the DC / DC converter, the current flow is correspondingly increased in the determined system state in order to still achieve the desired heating of the converter switch. For example, the above-mentioned switch-off threshold and / or switch-on threshold can be determined as a function of the measured temperature. Here, the duty cycle can of course also be dependent on other influencing factors, for example, on the DC bus voltage.

[0019] Instead of or in addition to the temperature measured in the DC / DC converter, the clocking control of the third switch or the power loss generated by the method according to the invention can be determined based on the temperature detected outside the DC / DC converter. For this purpose, the determination of the system state includes the detection of the temperature of the following component: the DC / DC converter is in thermal contact with the component, but the component itself is not part of the DC / DC converter, and the temperature of the component should not drop below a predetermined value. In one embodiment, this can be, for example, a battery: the battery is charged and discharged via the DC / DC converter. Batteries of the type commonly used have the characteristics that the battery cannot or should not be charged at a temperature lower than a critical charging temperature, even if it can be discharged at such a low temperature. Here, the power loss generated can be used to increase the temperature of the battery in thermal contact with the DC / DC converter or to keep the temperature greater than the mentioned temperature. Here, the power loss can also be completely or partially obtained from the battery and for this purpose, the fourth switch can be clocked with a suitable duty cycle.

[0020] In an advantageous embodiment of the method, the system state is determined as a function of the voltage of the DC bus. The system state to be determined, in which no acquisition via further participants of the DC bus and at the same time no power transmission via a DC / DC converter is provided, can be ascertained as a function of the voltage on the DC bus. The voltage on the DC bus is determined, for example, by an inverter on the DC bus, further loads on the DC bus and / or energy sources.

[0021] In another embodiment of the method, the determination of the system state is displayed to the DC / DC converter via an input signal. This embodiment can be applied, for example, if the system state is determined by a control device and then transmitted to the DC / DC converter, in which case the control unit of the DC / DC converter controls the converter switches of the DC / DC converter according to the described method. In this case, the control unit of the DC / DC converter can be understood as part of the control unit of the system. This embodiment can also be applied if, for example, the system state is determined based on a voltage measurement on the DC bus and transmitted to the DC / DC converter, in which case the control unit of the DC / DC converter then controls the converter switches according to the method. The control device can be a computing unit having at least one processor, a memory and a communication interface.

[0022] The system includes an energy source and a DC / DC converter. The energy source and the DC / DC converter are attached to the DC bus respectively. The DC / DC converter has a converter switch, which can be controlled to open and close in order to perform power conversion by the DC / DC converter. In addition, a control device is provided, which is established and arranged to implement a method in the above method. Here, the control device can be arranged in the DC / DC converter and / or can be arranged on another computing unit of the system. The control device can also be arranged in a distributed manner on one or more computing devices of the DC / DC converter and the other computing devices of the system or arranged away from the system. The control device can be additionally designed as another participant for controlling the DC / DC converter and / or the DC bus.

[0023] 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 the method, the current generated to generate power loss flows through the second, third and fourth switches. In other words, the switches can be heated by the power loss. By coupling the first switch to the second, third and / or fourth switch, it can be achieved that the first switch is also heated to increase its service life.

[0024] In one embodiment, the first switch is thermally coupled to a choke as a heat store. In this embodiment of the method, the current for generating the power loss flows through the choke of the DC / DC converter. In order to heat the first switch, the first switch is thermally coupled to the choke, which serves as a heat store. This also makes it possible to heat the first switch.

[0025] In one specific embodiment, the converter switch and the choke are thermally coupled to a common heat sink. Via the common heat sink, a uniform heat exchange between the converter switch and the choke can be ensured and thus a uniform heating of the converter switch can be achieved.

[0026] In one embodiment of the system, the energy source is a PV generator. The method is particularly advantageous for the implementation of a system with a PV generator, because if a system state is determined in which a grid feed-in or a complete grid feed-in of the power that can be generated by the energy source is not possible or is not desired and at the same time a battery attached to the system is already fully charged or no further charging is provided, then solar energy generated by the PV generator may be present. This solar energy can then be used to heat the converter switch and thus extend the service life of the converter switch.

[0027] It is also conceivable that during the implementation of the method according to the invention, it is continuously or occasionally checked whether the following condition is still met: no other application of the power for heating the DC / DC converter is provided. If this is not the case, the heating can be terminated or the power for heating can be reduced.

[0028] In one embodiment of the system, the DC / DC converter has a first and a second subconverter. The two subconverters are connected to the DC bus at the input side, respectively. In the case of determining the state of the system, it is set that the two subconverters are connected to each other at the output side via an optional coupling switch so that the power flows that are the same in magnitude but opposite to each other are transmitted by the two subconverters respectively. However, the subconverters can also be permanently connected to each other at the output side without a coupling switch. By the power flows that are the same in magnitude but opposite to each other, power loss is generated in the subconverter by the converter switch and the converter switch is therefore kept in a heated state. This is done without the total power transmission of the DC / DC converter, that is, when the electrical power is not output via the output attachment end of the DC / DC converter. Here, it is advantageously set that two subconverters are operated in parallel when transmitting power via the DC / DC converter. This means that in order to transmit the total power via the DC / DC converter, the two subconverters are attached to the DC bus at the input side, and the two subconverters are attached to the output attachment end of the DC / DC converter at the output side. In the determined system state, the output sides of the subconverters are then connected via the coupling switches in such a way that the subconverters each transmit power flows of equal magnitude but opposite to one another. As an alternative to the coupling switches, the subconverters can also be permanently connected in parallel on the output side.

[0029] Furthermore, the present application relates to an energy generation facility having one of the above-described systems and an inverter, which is attached to a DC bus and is used to feed the power generated by the energy source into an alternating current network. Preferably, the alternating current network is an AC supply network. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Below, examples of the present application are explained in more detail by way of example with reference to the attached drawings. The drawings show:

[0031] Figure 1 A schematic diagram showing one embodiment of a system having an energy source and a DC / DC converter;

[0032] Figure 2 A method for increasing the service life of a converter switch is schematically illustrated;

[0033] Figure 3A schematic diagram of one specific embodiment of a system is shown, which has an energy source and a DC / DC converter.

[0034] In the drawings, the same reference numbers are used for the same or similar elements. DETAILED DESCRIPTION

[0035] exist Figure 1 Schematically shown in FIG. 1 is an embodiment of a system 10 comprising a DC bus DC+, DC-, to which an energy source PV with a voltage U_PV and a DC / DC converter 12 are attached. The DC bus DC+, DC- has two conductors DC+ and DC-, which are at different potentials. A DC bus voltage U_Bus is applied between the two conductors of the DC bus DC+, DC-. Attached to the DC bus DC+, DC- may be a DC / DC converter 12. Figure 1 . The further DC bus participant may be, for example, an inverter which may be provided for feeding the electrical power generated by the energy source PV into the AC supply network.

[0036] The DC / DC converter 12 is configured to obtain electrical power from the DC bus DC+, DC-, convert the electrical power and transmit the electrical power, for example, to the DC storage Bat attached to the output attachment terminals 12A+, 12A- of the DC bus, so that the power can be provided to the DC bus again at a later time point. The DC storage Bat has a voltage U_Bat between its attachment terminals. The DC / DC converter has a series connection of a first and a second semiconductor switch Q1, Q2 between its output attachment terminals 12A+, 12A-. A capacitor is arranged in parallel with the series connection of the first and second semiconductor switches Q1 and Q2. The DC / DC converter 12 has a series connection of a third and a fourth semiconductor switch Q3, Q4 between its input attachment terminals 12E+, 12E-. Between the input attachment terminals 12E+, 12E- of the DC / DC converter, a capacitor is arranged in parallel with the series connection of the third and fourth semiconductor switches Q3, Q4. The semiconductor switches Q1, Q2, Q3, Q4 correspond to the converter switches of the DC / DC converter 12 and can have an inherent freewheeling diode or a freewheeling diode is connected in antiparallel to the semiconductor switches. The two series connections 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 in the middle between the two switches via a choke D. An ammeter A is arranged in series with the choke D. The second switch Q2 and the fourth switch Q4 are connected to one another, for example by means of the conductor DC- of the DC bus.

[0037] Figure 2A method for increasing the service life of converter switches Q1, Q2, Q3, Q4 is schematically shown. Figure 1 or Figure 3 In the system 10 shown in FIG. 1 (which has a DC / DC converter 12 and an energy source PV, both of which are attached to a DC bus DC+, DC-), the electric energy generated by the energy source PV can be fed into the DC bus DC+, DC-. The energy source PV has a PV voltage U_PV present between its attachment terminals. The DC / DC converter 12 can obtain electric power from the DC bus DC+, DC-, and can output the electric power via its output attachment terminals 12A+, 12A-, for example, to a DC storage Bat.

[0038] In the method, the following system state is determined in step S1: in this system state, the electric power of the energy source PV is used by the DC bus DC+, DC-. Here, if the transmission of electric power via the DC / DC converter 12 is not set and at the same time the output of electric power to other participants of the DC bus DC+, DC- is not set, the system state is determined. Other participants of the DC bus DC+, DC- can be, for example, other DC loads (not shown) and / or inverters (not shown). The inverter can be set to, for example, feed electric power into the AC supply network. Now, the following state of the system can be generated: in this state, the energy source PV can generate electric power, but the transmission of the power that can be generated via the inverter is not set or at least not set to be fully transmitted. The reason for this situation can be, for example, a reason of management nature. At the same time, it is possible that the transmission to the DC storage Bat is not set, for example because the DC storage Bat is already full. This is an example of a system state determined in step S1.

[0039] Now, in step S2, after determining the system state, the DC / DC converter 12 is operated in such a way that power loss is generated in the DC / DC converter 12 without transmitting power via the DC / DC converter 12. As a result, the converter switches Q1, Q2, Q3, Q4 of the DC / DC converter 12 are kept in a heated state relative to the inactive state. The heated state is caused on the one hand by the switching process and by the current flowing in the DC / DC converter 12 and the power loss generated thereby.

[0040] The system state that can be determined in method step S1 can be realized, for example, by measuring the voltage U_Bus of the DC bus DC+, DC-. In order to operate the DC / DC converter 12 in step S2, the first switch Q1 can now be permanently opened. The second switch Q2 can be permanently kept closed. The third switch Q3 is clocked. The fourth switch Q4 can be permanently opened, for example. It is also possible that if the third switch Q3 is in an open state, the fourth switch Q4 is closed. That is, the third and fourth switches Q3 and Q4 can be clocked in a complementary manner. If the fourth switch Q4 is opened at the time when the third switch Q3 is closed, the third and fourth switches Q3 and Q4 can also be clocked in an incompletely complementary manner. A possible clocking control of the third switch Q3 is a switch-on duration of 30μs at a clocking frequency of 100Hz.

[0041] In the operation in step S2, now, in the case of a closed third switch Q3, the current flows via the third switch Q3 via the choke D and the second switch Q2. Then, if the third switch Q3 is opened, the current can continue to flow back to the second switch Q2 via the choke D via the switch Q4. Here, depending on the type of switch, the current flow via the fourth switch Q4 can be achieved either via a freewheeling diode that is arranged in reverse parallel to the fourth switch Q4 or inherently, or, if the switch Q4 is closed, it can be achieved directly via the closed switch Q4. As a result, a current flow is generated via the third, second and fourth switches Q3, Q2, Q4, while the current does not flow via the output attachment terminals 12A+, 12A- of the DC / DC converter 12. Power loss is generated by this current flow, and the converter switches Q1, Q2, Q3, Q4 are heated via this power loss. Since there is no direct current flow via the first switch Q1, the latter can be heated, for example, via the choke D as a common heat store or a common heat sink with the choke D and the switches Q2, Q4, Q3. However, it is also conceivable that the converter switch Q1 is mounted together with the converter switch Q2 in a module and is thus already thermally coupled to the converter switch Q2 and heated.

[0042] exist Figure 3In the system 10 shown in , the DC / DC converter 12 has two subconverters 14, 16. The first subconverter 14 and the second subconverter 16 are connected to the DC buses DC+, DC- on the input side, respectively. The input attachment terminal 14E+ of the first subconverter 14 and the input attachment terminal 16E+ of the second subconverter 16 are connected to the input attachment terminal 12E+ of the DC / DC converter 12. The input attachment terminal 14E- of the first subconverter 14 and the input attachment terminal 16E- of the second subconverter 16 are connected to the input attachment terminal 12E- of the DC / DC converter 12. Here, the two subconverters 14, 16 also correspond to DC / DC converters. In normal operation, that is, when the DC / DC converter 12 draws electrical power from the DC buses DC+, DC- and transmits it to the DC storage Bat, the subconverters 14, 16 are connected in parallel on the input side, as shown in FIG. Figure 3 As shown in . On the output side, the DC / DC converter 12 has separate output attachment terminals 12A+, 12A- for each subconverter 14, 16, and batteries can be attached to the output attachment terminals respectively. Optionally, a coupling switch 18 can be provided between the output attachment terminals 14A+ and 16A+ and / or between the output attachment terminals 14A- and 16A-, so as to enable temporary parallel connection of the subconverters 14, 16 on the output side or to separate these subconverters from each other in a unipolar or omnipolar manner on the output side. However, it is also conceivable that the output attachment terminals 12A+, 12A- assigned to the subconverters are connected to the same battery and thus the subconverters 14, 16 are also permanently connected in parallel on the output side.

[0043] During the execution of step S2 of the method, if the subconverters are not permanently connected in parallel anyway, the subconverters 14, 16 are now connected in parallel on the output side via the optional coupling switch, wherein the electrical power output by one of the subconverters 14, 16 is identical in magnitude, but is received by the other subconverter in each case, so that no electrical power is exchanged via the output terminals 12A+, 12A- of the DC / DC converter 12. Although electrical power is received via the input terminals 12E+, 12E- in the state S2, the further power flow runs completely within the DC / DC converter 12 and no electrical power is exchanged via the output terminals 12A+, 12A-.

[0044] Reference numerals list

[0045] 10 System

[0046] 12 DC / DC Converter

[0047] Output connection for 12A+, 12A- DC / DC converters

[0048] 12E+, 12E- DC / DC converter input connection terminal

[0049] 14 First Subconverter

[0050] 14A+, 14A- Output connection terminal of the first sub-converter

[0051] 14E+, 14E- Input connection terminal of the first subconverter

[0052] 16 Second subconverter

[0053] 16A+, 16A- Output connection terminal of the second sub-converter

[0054] 16E+, 16E- Input connection of the second subconverter

[0055] 18 Coupling switch

[0056] A Current meter

[0057] DC+, DC-DC bus

[0058] U_Bus DC bus voltage

[0059] Bat Battery

[0060] U_Bat Battery voltage

[0061] PV Energy Source

[0062] U_PV PV voltage

[0063] D Choke

[0064] Q1, Q2, Q3, Q4 converter switches

Claims

1. A method for increasing the service life of a converter switch (Q1, Q2, Q3, Q4) in a system (10), the system comprising an energy source (PV) which is attached to a DC bus (DC+, DC-) together with a DC / DC converter (12), the DC / DC converter comprising the converter switch (Q1, Q2, Q3, Q4), wherein: The method comprises the following steps: determining a system state in which electrical power from the energy source (PV) is available for use, for which no transmission via the DC / DC converter (12) and no output to further participants of the DC bus (DC+, DC-) is provided, During the determined system state, the DC / DC converter (12) is operated in such a way that power loss occurs in the DC / DC converter (12) without power being transmitted via the DC / DC converter (12).

2. The method according to claim 1, wherein: During a determined system state, the DC / DC converter (12) is operated in such a way that a loop current is generated within the DC / DC converter (12) which flows via the converter switches (Q1, Q2, Q3, Q4).

3. The method according to claim 1 or 2, wherein: The DC / DC converter (12) comprises a first half-bridge and a second half-bridge, the first half-bridge having a series connection of a first switch (Q1) and a second switch (Q2), the first switch and the second switch being arranged between attachment terminals (12A+, 12A-) on the output side of the DC / DC converter (12), the second half-bridge having a series connection of a third switch (Q3) and a fourth switch (Q4), the third switch and the fourth switch being arranged between attachment terminals (12E+, 12E-) on the input side of the DC / DC converter (12) and attached to the DC bus (DC+, DC-), wherein the central attachment 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) and the fourth switch (Q4) have a common attachment terminal, Therein, during the determined system state, the DC / DC converter (12) permanently closes the second switch (Q2) and permanently opens the first switch (Q1), 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 in a complementary manner.

5. The method according to claim 3 or 4, wherein: The third switch (Q3) is clocked, in particular the third switch (Q3) and the fourth switch (Q4) are clocked complementary with such a pulse duty factor that a permissible nominal current of the DC / DC converter (12) is not exceeded.

6. The method according to claim 3, 4 or 5, wherein: The third switch (Q3) is clocked, in particular the third switch (Q3) and the fourth switch (Q4) are clocked complementary, with a duty cycle selected such that a temperature measured in the DC / DC converter (12) is regulated to a target temperature.

7. A method according to any one of the preceding claims, wherein: The system status is determined based on the voltage of the DC bus (DC+, DC-).

8. A method according to any one of the preceding claims, wherein: The determination of the system state includes detecting the temperature of a component with which the DC / DC converter (12) is in thermal contact.

9. A method according to any one of the preceding claims, wherein: The determination of the system state is indicated to the DC / DC converter (12) via an input signal.

10. System (10), comprising an energy source (PV) and a DC / DC converter (12), the DC / DC converter comprising converter switches (Q1, Q2, Q3, Q4), the energy source and the DC / DC converter being jointly attached to a DC bus (DC+, DC-), the system comprising a control device, which is established and arranged for implementing a method according to any of the above claims.

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

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

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

14. A system according to any one of claims 10 to 13, wherein: The energy source (PV) is a PV generator.

15. A system according to any one of claims 10 to 14, wherein: The DC / DC converter (12) comprises a first subconverter (14) and a second subconverter (16), wherein the first subconverter and the second subconverter are respectively connected to the DC bus (DC+, DC-) on the input side (14E+, 14E-, 16E+, 16E-), and the first subconverter and the second subconverter are configured to transmit power flows of the same magnitude but opposite to each other in a state of parallel connection on the output side when the system state is determined, so that the converter switches (Q1, Q2, Q3, Q4) of the first and second subconverters (14, 16) are kept in a heated state without the total power transmission of the DC / DC converter (12).

16. The system of claim 15, wherein: The system is designed to achieve a parallel connection state on the output side via a coupling switch (18) arranged between the output terminals (14A+, 14A-, 16A+, 16A-).

17. An energy generation facility, comprising a system (10) according to any one of claims 10 to 16 and an inverter, the inverter being attached to a DC bus (DC+, DC-) and used to feed the power generated by an energy source (PV) into an AC current network.

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