DC-DC converter and method for operating DC-DC converter

Abstract

The invention relates to a DC-DC converter for transferring energy from a high-voltage network into a low-voltage network. For this purpose, a circuit configuration is used which can be operated either as an active clamp flyback converter or as an active clamp buck converter.

Description

TECHNICAL FIELD

[0001] The invention relates to a DC voltage converter, in particular a DC voltage converter for transferring energy between a high-voltage network and a low-voltage network. Furthermore, the invention relates to a method for operating a DC voltage converter. BACKGROUND

[0002] Completely or at least partially electrically driven vehicles usually have a so-called traction battery which provides electrical energy for driving the vehicle. Such traction batteries usually have an output voltage of several hundred volts, for example 400 volts. In addition, the vehicle has a so-called low-voltage network to which further loads, such as for example lighting devices, auxiliary drives, on-board computers or the like, are coupled. Here, the low-voltage network of the vehicle is usually fed with electrical energy from the high-voltage network. For this purpose, the voltage of the high-voltage network has to be converted to the voltage level of the low-voltage network. In addition, an electrical separation between the high-voltage network and the low-voltage network usually also has to be carried out.

[0003] The document DE 10 2016 220 679 A1 discloses a DC voltage converter and a method for operating a DC voltage converter with a so-called phase-shifted full-bridge DC voltage converter. The document inter alia proposes to reduce the number of lossy switching processes by suitably operating the DC voltage converter. SUMMARY

[0004] The invention discloses a DC voltage converter having the features of independent claim 1, in particular a DC voltage converter for transferring energy between a high-voltage network and a low-voltage network. Further advantageous embodiments are the subject of the dependent claims. Furthermore, the invention relates to a method for operating a DC voltage converter.

[0005] Correspondingly, it is provided that: A DC voltage converter for transferring energy between a high-voltage electrical system and a low-voltage electrical system. The DC voltage converter comprises an input connection, an output connection, a transformer, a first switching element, a third switching element, a fourth switching element, a fifth switching element and a capacitor. The input connection is designed for coupling to a first DC voltage electrical system, a first DC voltage source or a first DC voltage sink. The output connection is designed for coupling to a second DC voltage electrical system, a second DC voltage source or a second DC voltage sink. The transformer has a primary side and a secondary side. Between a first connection element of the input connection and a second connection element of the input connection there is coupled a series circuit consisting of the first switching element and the third switching element. There is coupled in parallel to the third switching element a series circuit consisting of the primary side or the primary winding of the transformer and the fourth switching element. There is coupled in parallel to the fourth switching element a series circuit consisting of the fifth switching element and the capacitor. Preferably the first connection element of the input connection is the positive connection pole of the input connection and the second connection element of the input connection is the negative connection pole of the input connection.

[0006] The present invention is based on the recognition that the low-voltage electrical system, preferably the second DC voltage electrical system, of an electric or hybrid vehicle is usually fed by means of energy from the high-voltage electrical system, preferably the first DC voltage electrical system. For this purpose, an electrical separation between the high-voltage electrical system and the low-voltage electrical system is usually required. Furthermore, the present invention is based on the recognition that the power and in particular the battery capacity of electrically driven vehicles also increases with the continuous further development of vehicles. In this respect, traction batteries with higher output voltages are also increasingly used. Therefore, for the coupling between the high-voltage electrical system and the low-voltage electrical system, a DC voltage converter with sufficient voltage strength is also required. It is therefore also desirable to have a DC voltage converter which can be used in as wide an input voltage range as possible.

[0007] The present invention is therefore based on the idea of taking this recognition into account and realizing a DC voltage converter which meets the above-mentioned requirements. For this purpose, the following invention realizes a circuit concept for a DC voltage converter for coupling a high-voltage electrical system to a low-voltage electrical system, which has a very simple circuit topology. The DC voltage converter can convert an input DC voltage to a predefined output DC voltage in a very large input voltage range. The circuit concept according to the invention can ensure sufficient voltage strength even with conventional component elements, in particular at high input voltages or input DC voltages. Due to the relatively simple circuit topology, the DC voltage converter can be realized particularly cost-effectively. Furthermore, the DC voltage converter according to the invention also only requires a relatively small installation space.

[0008] According to an embodiment, the direct voltage converter comprises a rectifier. The rectifier is coupled to the secondary side or secondary winding of the transformer. Furthermore, the rectifier is designed to rectify the voltage applied at the secondary side of the transformer. The rectified voltage can then be provided at the output connection of the direct voltage converter. The rectification of the voltage at the secondary side of the transformer can be carried out in any manner by means of an active or passive rectifier. By means of the transformer and the subsequent rectification, an energy transfer from the high-voltage network into the low-voltage network can thus be realized with electrical separation.

[0009] According to an embodiment, the rectifier comprises a rectifying diode. As an alternative, the rectifier can also comprise a second switching element, preferably a semiconductor switch, in particular with a rectifying diode arranged in parallel to the semiconductor switch. In this case, the second switching element can be actively controlled, wherein the voltage at the secondary side of the transformer is rectified by means of the control of the second switching element. This active rectification by means of the second switching element can reduce the loss power and thus increase the efficiency. As an alternative, a particularly cost-effective rectification can be realized by means of the rectifying diode. Preferably, a series circuit consisting of the second switching element and the secondary side or secondary winding of the transformer is coupled between a first connection element and a second connection element of the output connection of the direct voltage converter. A simple circuit topology of the secondary side of the direct voltage converter is preferred. Preferably, the first connection element of the output connection is the positive connection pole of the output connection and the second connection element of the output connection is the negative connection pole of the output connection. If the rectifier comprises a second switching element, the direct voltage converter can preferably be operated bidirectionally.

[0010] According to an embodiment, the first switching element, the second switching element, the third switching element, the fourth switching element and / or the fifth switching element each comprise a semiconductor switch. In particular, a diode, in particular a so-called body diode, can be arranged in parallel to each semiconductor switch. The semiconductor switch can be, for example, a transistor, in particular a bipolar transistor with an insulated gate connection (IGBT). Of course, any other semiconductor switch, such as, for example, a MOSFET or a silicon carbide switch or a gallium nitride switch, is also possible.

[0011] According to an embodiment, the diode of the fifth switching element is arranged opposite to the diode of the first switching element. Preferably, the diode of the fifth switching element is oriented such that it prevents a current flow from the capacitor in the direction of the first connection element of the input connection when the fifth switching element is open. Preferably, the diode of the fifth switching element is oriented such that it prevents the capacitor from discharging via the closed fourth switching element. Preferably, the fifth switching element is then switched off and its diode is blocked. In this way, the discharge of the capacitor when the fifth switching element is open can be prevented.

[0012] According to an embodiment, the DC voltage converter comprises a control device. The control device can be designed to actuate the first switching element, the second switching element, the third switching element, the fourth switching element and / or the fifth switching element. Furthermore, if an active switching element, i.e. the second switching element, is provided in the rectifier of the DC voltage converter, the control device can also actuate this switching element of the DC voltage converter. In this way, the actuation of the individual switching elements can be synchronized in a targeted manner.

[0013] According to an embodiment, the control device is designed to open the third switching element and the fifth switching element and simultaneously to actuate the first switching element and the fourth switching element in a clocked manner in a first operating mode and / or to open the fourth switching element and to close the fifth switching element in a second operating mode. Furthermore, the first switching element and the third switching element can each be alternately actuated in a clocked manner in the second operating mode. In this way, a DC voltage conversion between a high-voltage side and a low-voltage side can be carried out on the basis of a so-called flyback converter, in particular an active-clamp flyback converter, in the first operating mode, and with the same circuit topology, the circuit can be operated as an active-clamp buck converter in a further operating mode. The DC voltage converter can thus be suitably actuated in a large voltage range.

[0014] Preferably, in the first operating mode, after the first and fourth switching elements have been switched off, the second, third and / or fifth switching elements are switched on after a dead time has elapsed. Advantageously, the losses due to the switching elements are thus reduced. Subsequently, the second, third and / or fifth switching elements are switched off or disconnected again. After a further dead time has elapsed, the cycle is restarted from the beginning with the switching on of the first and fourth switching elements.

[0015] Preferably, in the second operating mode, the second switching element is switched off and the first switching element is switched on. Further preferably, after the first switching element has been switched off and a dead time has elapsed, the second switching element is switched on, while the third switching element is switched on. Advantageously, the losses due to the second switching element are thus reduced. After a further dead time has elapsed, the cycle is restarted from the beginning with the switching on of the first switching element.

[0016] According to an embodiment, the input voltage at the input connection of the DC voltage converter for the actuation in the second operating mode is higher than the input voltage for the actuation in the first operating mode. The respective suitable operating mode for the DC voltage conversion can be selected, for example, by means of the control device for actuating the individual switching elements, preferably in dependence on the input voltage at the input connection.

[0017] Furthermore, the invention relates to a method for operating a DC voltage converter in a first or second operating mode. Herein, the first operating mode comprises the method steps of opening the third and fifth switching elements and simultaneously actuating the first and fourth switching elements in a clocked manner. The simultaneous actuation of the first and fourth switching elements in a clocked manner preferably means that the first and fourth switching elements are simultaneously switched on and subsequently switched off again in accordance with a clock pulse or signal given by the regulating unit, and are repeatedly switched on and off again in accordance with the clock pulse or signal. The second operating mode comprises the method steps of opening the fourth switching element and closing the fifth switching element and alternately actuating the first and third switching elements in a clocked manner. The alternating actuation of the first and third switching elements in a clocked manner preferably means that the first switching element is switched on and the third switching element is switched off in accordance with a clock pulse or signal given by the regulating unit, and subsequently the first switching element is switched off and the third switching element is switched on, and the first and third switching elements are repeatedly switched on and off again in a complementary manner in accordance with the clock pulse or signal. A dead time is preferably provided in the switching process, thereby preventing a short circuit between the connection elements of the input connection by the first and third switching elements.

[0018] The above-mentioned design solutions and refinements can be combined with one another arbitrarily, as far as this makes sense. Further design solutions, refinements and embodiments of the invention also include combinations of the features of the invention described previously or hereinafter with respect to the embodiments which are not explicitly mentioned. In particular, the person skilled in the art will add individual aspects here as improvements or supplements to the respective basic form of the invention. BRIEF DESCRIPTION OF DRAWINGS

[0019] Further features and advantages of the invention are explained below on the basis of the drawings. Herein: Figure 1 A block diagram of a DC voltage converter according to an embodiment is shown; Figure 2 A flow chart of a method for operating a DC voltage converter is shown. DETAILED DESCRIPTION

[0020] Figure 1A schematic diagram of a block diagram of a DC voltage converter 1 according to an embodiment is shown. The DC voltage converter 1 can be connected on the input side via an input connection 10, for example, to a first DC voltage grid 2, a first DC voltage source, a first DC voltage sink or a high-voltage grid. On the output side, the DC voltage converter 1 can be connected via an output connection 13, for example, to a second DC voltage grid 3, a second DC voltage sink, a second DC voltage source or a low-voltage grid. The DC voltage converter 1 can have, for example, an input connection 10 for coupling to a high-voltage grid. At this input connection 10, for example, electrical energy from a traction battery of an electrically driven vehicle can be supplied. At the input connection 10, a voltage, an input voltage U_in, is preferably applied. The DC voltage converter 1 can convert this input voltage U_in into a further DC voltage and supply this as an output DC voltage U_out at the output connection 13. If the input connection 10 is not already coupled in another way, for example, by a coupled DC voltage source 2, a first intermediate circuit capacitor (not shown in Figure 1 ) is preferably provided between the potential of a first connection element 11 and a second connection element 12 of the input connection 10.

[0021] In addition to the input connection 10 and the output connection 13, the DC voltage converter 1 also comprises a transformer T. The transformer T has a primary side Pri or primary winding and a secondary side Sek or secondary winding. Furthermore, the DC voltage converter 1 has, between the input connection 10 and the primary side Pri of the transformer T, four switching elements S1, S3, S4 and S5 and a capacitor C. A rectifier 40 is preferably provided on the secondary side of the DC voltage converter 1. The rectifier 40 is preferably used to rectify an applied alternating voltage generated at the secondary side Sek of the transformer. The rectifier 40 preferably comprises a switching element S2. The DC voltage converter 1 preferably has, between the output connection 13 and the secondary side Sek of the transformer T, the switching element S2.

[0022] The input connection 10 of the DC voltage converter 1 comprises a first connection element 11 and a second connection element 12. Between the first connection element 11 and the second connection element 12, an input DC voltage U_in can be supplied, for example. Between the first connection element 11 of the input connection 10 and the second connection element 12 of the input connection 10, a series circuit consisting of a first switching element S1 and a third switching element S3 is coupled. In parallel to the third switching element S3, a series circuit consisting of the primary side Pri of the transformer T and a fourth switching element S4 is coupled. In parallel to the fourth switching element S4, a series circuit consisting of a fifth switching element S5 and a capacitor C, i.e. a clamping capacitor, is coupled. The order of the fifth switching element S5 and the capacitor C within the series circuit parallel to the fourth switching element S4 is not important.

[0023] As already mentioned above, a rectifier 40 is provided between the secondary side Sek of the transformer T and the output connection 13 of the DC voltage converter 1. The rectifier 40 can be, for example, a passive diode, which is provided between the connection on the secondary side Sek of the transformer T and the connection element of the output connection 13. As an alternative, active rectification can also be carried out by means of a second switching element S2, in particular a semiconductor switching element, which is arranged between the connection on the secondary side Sek of the transformer T and the connection element of the output connection 13.

[0024] In order to operate the switching elements, in particular the first, third, fourth and / or fifth switching elements S1, S3-S5 and, if necessary, the second switching element S2 of the rectifier 40, a control device 50 can be provided. The operating principle and the switching sequence for operating the switching elements are explained in more detail below.

[0025] In the first operating mode, the DC voltage converter 1 can be operated, inter alia, as a so-called active-clamp flyback converter. The DC voltage converter is operated in the first operating mode preferably if the input voltage applied at the input connection is, for example, up to 500 V. Advantageously, the first operating mode is selected in the case of lower input voltages, in which the first operating mode all five switching elements are switched, preferably in order to reduce line losses. Furthermore, by means of the first operating mode, it is possible to keep the output voltage constant, even to increase the output voltage, even in the case of very low input voltages. The first and fourth switching elements S1 and S4 are switched on and off at the same time. If the first and fourth switching elements S1 and S4 are switched on, the transformer T is magnetized. The energy is stored, preferably, in the air gap of the core of the transformer. The second, third and fifth switching elements S2, S3 and S5 are switched off. In a next step, the first and fourth switching elements S1 and S4 are switched off. In a subsequent dead-time, all switching elements are switched off. The primary current flows from the transformer through the diode of the fifth switching element S5 into the capacitor C and continues to flow through the diode of the third switching element S3. In this dead-time, the secondary current flows through the diode of the second switching element S2 in the direction of the first connection element 14 of the output connection 13. The second, third and / or fifth switching elements S2, S3 and S5 are switched on, preferably, after this dead-time. Advantageously, the losses of the switching elements are minimized. Thus, the energy stored in the transformer is transferred onto the secondary side. Thereafter, the first, second, third, fourth and fifth switching elements are switched off, if this has not already been carried out. After a further dead-time, the cycle of the first operating mode is started again from the beginning. By adapting the frequency and / or the pulse width of the clock pulses or signals and thus the switching on and off of the first and fourth switching elements, it is possible here to regulate the energy transfer, in particular the output DC voltage U_out generated at the output connection 13. If the output connection is not already coupled in another way, for example by a coupled load element, a second intermediate circuit capacitor (not shown in Figure 1 ) is preferably provided between the potential of the first connection element 14 and the second connection element 15 of the output connection 13. This second intermediate circuit capacitor smoothes the generated pulsed secondary current.

[0026] In the second operating mode, the DC voltage converter 1 works as an electrically separated active-clamp buck converter. The DC voltage converter is preferably operated in the second operating mode if the input voltage applied at the input connection is for example higher than 500 V up to for example 1000 V or 1400 V. Advantageously, the second operating mode is selected in the case of higher input voltages, in which second operating mode only two or three switching elements are switched, preferably in order to reduce the switching losses. The second operating mode is suitable for higher input voltages, since in the second operating mode the output voltage cannot always be kept constant, preferably in the case of low input voltages. In this operating mode, the first switching element S1 and the third switching element S3 are alternately switched on and off at a frequency and / or pulse width to be determined and predefinable. The fourth switching element S4 is permanently switched off during the second operating mode. The fifth switching element S5 is permanently switched on during the second operating mode. As soon as the first switching element S1 is switched on, the transformer T is magnetized in the same direction as in flyback. Here, the primary winding or primary side Pri of the transformer and the capacitor C are connected in series. The input voltage U_in applied at the input connection 10 is thus distributed to the primary winding Pri of the transformer and the capacitor C. Advantageously, the voltage load of the transformer T is thereby minimized and kept low. It is thus advantageously not necessary for the second operating mode, despite the significantly higher input voltage, to take into account an increased insulation requirement for the transformer T compared to the first operating mode. The second and third switching elements S2 and S3 are switched off in this step. Subsequently, the first switching element S1 is switched off. In the following dead time, the primary current flows from the transformer through the closed fifth switching element S5 into the capacitor C and continues to flow through the diode of the third switching element S3. After this dead time, the third switching element S3 is switched on. The capacitor C is thus connected in parallel to the primary winding of the transformer, and the two components discharge to the secondary side of the transformer. The second switching element S2 and the third switching element S3 are preferably switched on at the same time. After a time or clock pulse taken and predefined by the regulating part, the third switching element and, if necessary, the second switching element are switched off. After a further dead time that follows, the cycle of the second operating mode starts again from the beginning. By adapting the frequency and / or pulse width of the clock pulse or signal and thus the alternating switching on and off of the first switching element S1 and the third switching element S3, it is possible here to regulate the energy transfer, in particular the output DC voltage U_out generated at the output connection 13.

[0027] In particular, because the rectifier 40 is implemented as a simple unidirectional rectifier, it is necessary for the configuration of the circuit arrangement of the DC voltage converter 1 that the transformer T is magnetized in each case in the same direction, not only in the first operating mode, but also in the second operating mode. The magnetization task is assumed by the first and fourth switching elements S1 and S4 in the first operating mode and by the first switching element S1 in the second operating mode. In both cases, the transformer T is then demagnetized when energy is transferred onto the secondary side Sek of the transformer T. This is done when the first and fourth switching elements S1 and S4 or the first switching element S1 are switched off and the fifth switching element S5 or its diode, respectively, is correspondingly switched on.

[0028] Advantageously, the first, third, fourth and fifth switching elements can be designed such that their respective blocking voltage corresponds to the maximum value of the input voltage to be applied. This advantage results from two different effects. On the one hand, it results from the use of two different topologies for different voltage ranges, namely the actively clamped flyback topology for low voltage ranges and the actively clamped buck topology for high voltage ranges. On the other hand, the advantage results from the special arrangement of the first, third, fourth and fifth switching elements, the capacitor and the primary side of the transformer on the primary side of the DC voltage converter.

[0029] In the second operating mode, in the active-clamp buck operation, the polarity of the voltage at the primary winding of the primary side Pri of the transformer T is reversed as the first switching element S1 is turned off. This voltage is equal or almost equal to the voltage at the capacitor C. However, the voltage at the capacitor C does not reverse its polarity. Therefore, the primary current continues to flow through the diodes of the fifth and third switching elements S5 and S3. The voltage drop through the diode of the third switching element S3 is very low and therefore almost negligible. Thus, the voltage at the connection point K between the first switching element S1, the primary side Pri of the transformer T and the third switching element S3 is almost 0 V when the first switching element S1 is turned off. As the maximum blocking voltage of the first switching element S1 the input voltage U_in applied at the input terminal 10 is obtained. The electrical circuit consisting of the primary winding of the primary side Pri of the transformer T, the capacitor C and the diodes of the third and fifth switching elements S3 and S5 has an almost 0 V voltage to the outside, because the sum of the reversed primary voltage at the primary side Pri of the transformer T and the voltage of the capacitor C is zero to the outside. When the first switching element S1 is turned on, the input voltage U_in applied at the input terminal 10 is higher than the third switching element S3. Thus, as the maximum blocking voltage for the third switching element S3 the input voltage U_in applied at the input terminal 10 is obtained. When the fourth switching element S4 is turned off, its maximum blocking voltage is limited or clamped to the maximum voltage of the capacitor C by the diode of the fifth switching element S5. When the fourth switching element S4 is turned on, as in the case in the first operating mode, the fifth switching element S5 is blocked. In this case, as the maximum blocking voltage of the switching element S5 also the maximum voltage of the capacitor C is obtained. In operation, the voltage at the capacitor C is significantly lower than the input voltage U_in applied at the input terminal 10. In the second operating mode, the first switching element S1 is preferably the main switch. The third switching element S3 is preferably the clamping switch in the second operating mode.

[0030] In this application, the transformer is preferably always magnetized in the same direction and demagnetized in the same direction in both operating modes.

[0031] In the active-clamp flyback operation or in the first operating mode, as the maximum blocking voltage of the first and third switching elements S1 and S3 also the input voltage U_in applied at the input terminal 10 is obtained. The first and fourth switching elements S1 and S4 are preferably the main switches. The third and fifth switching elements S3 and S5 are preferably the clamping switches in the first operating mode.

[0032] In this application, the transformer is preferably always magnetized in the same direction and demagnetized in the same direction in both operating modes.

[0033] The described circuit arrangement for a DC voltage converter 1 can thus be used, for example, for traction batteries with a relatively low voltage level, for example up to 500 volts. For DC voltage conversion with a higher input voltage, for example more than 500 volts up to 800 or, if necessary, 1000 volts, the same DC voltage converter 1 can be operated in the second operating mode. A simple and cost-effective DC voltage conversion for input DC voltages in a large voltage range can thus be achieved with relatively little circuit expenditure.

[0034] It is further advantageous that, on the primary side of the DC voltage converter 1, two of the first, third, fourth and fifth switching elements are always arranged in series between the first connection element 1 1 of the input connection 10 and the second connection element 12 of the input connection 10. If one of the switching elements S1, S3, S4, S5 is short-circuited or damaged, the further series-connected switching element S1, S3, S4, S5 can block and advantageously prevent a short circuit of the input connection 10. An increased operating safety of the DC voltage converter 1 is advantageously achieved.

[0035] The secondary side of the preferred DC voltage converter comprises a sixth switching element S6. The sixth switching element S6 is preferably coupled between the connection element 14 or 15 and the end of the series circuit consisting of the secondary side Sek of the transformer T and the rectifier 40. Advantageously, a series circuit consisting of two switching elements S2, S6 is also obtained on the secondary side of the transformer. As described with respect to the primary side, an increased operating safety of the DC voltage converter 1 is thereby achieved, since in the event of damage to one of the switching elements on the secondary side, the switching element can continue to prevent a short circuit of the output connection 13. If the sixth switching element S6 is provided, a second intermediate circuit capacitor (not shown in Figure 1 is preferably coupled in parallel with the series circuit consisting of the secondary side Sek of the transformer T and the rectifier 40.

[0036] Advantageously, the transition from the first operating mode to the second operating mode or vice versa is performed during operation without interruption by means of suitable regulation and control.

[0037] Figure 2A flow chart of a method 100 for operating a DC voltage converter is shown. The method starts with step 105. Preferably, the DC voltage converter 1 is operated in a first operating mode or in a second operating mode depending on an input voltage U_in applied at the input terminal 10. The first operating mode comprises the following method steps: opening 110 the third switching element S3 and the fifth switching element S5 and simultaneously operating 120 the first switching element S1 and the fourth switching element S4 in a clocked manner. The second operating mode comprises the following method steps: opening 130 the fourth switching element S4 and closing the fifth switching element S5 and alternately operating 140 the first switching element S1 and the third switching element S3 in a clocked manner. The method ends with step 145.

[0038] Preferably, in the first operating mode, after switching off the first and fourth switching elements S1, S4, the second, third and / or fifth switching elements S2, S3, S5 are switched on after a dead time has elapsed. Advantageously, the losses due to the switching elements are thus reduced. Subsequently, the second, third and / or fifth switching elements S2, S3, S5 are switched off again. After a further dead time has elapsed, the cycle is restarted with the switching on of the first and fourth switching elements S1, S4.

[0039] Preferably, in the second operating mode, the second switching element S2 is switched off while the first switching element S1 is switched on. Further preferably, after switching off the first switching element S1 and after a dead time has elapsed, the second switching element S2 is switched on while the third switching element S3 is switched on. Advantageously, the losses due to the second switching element S2 are thus reduced. After a further dead time has elapsed, the cycle is restarted with the switching on of the first switching element S1.

[0040] In summary, the present application relates to a DC voltage converter for transferring energy from a high-voltage grid into a low-voltage grid. For this purpose, a simple circuit configuration is proposed which can alternatively be operated as an active-clamp flyback converter or as an active-clamp buck converter.

Claims

1. A DC voltage converter (1) for transferring energy between a high voltage network (HV) and a low voltage network (LV), having: an input connection (10) designed for coupling to a first DC voltage network (2); an output connection (13) designed for coupling to a second DC voltage network (3); a transformer (T) having a primary side (Pri) and a secondary side (Sek); a capacitor (C); a first switching element (SI), a third switching element (S3), a fourth switching element (S4) and a fifth switching element (S5); a series circuit consisting of the first switching element (SI) and the third switching element (S3) is connected between a first connection element (11) of the input connection (10) and a second connection element (12) of the input connection (10); wherein, in parallel to the third switching element (S3), a series circuit consisting of the primary side (Pri) of the transformer (T) and the fourth switching element (S4) is connected; wherein, in parallel to the fourth switching element (S4), a series circuit consisting of the fifth switching element (S5) and the capacitor (C) is connected.

2. The DC voltage converter (1) according to claim 1, having a rectifier (40) coupled to the secondary side (Sek) of the transformer (T) and designed for rectifying a voltage applied at the secondary connection (Sek) of the transformer (T). The rectifier (40) comprises a rectifying diode or a second switching element (S2) designed for rectifying a voltage applied at the secondary connection (Sek) of the transformer (T). The first switching element (SI), the third switching element (S3), the fourth switching element (S4) and / or the fifth switching element (S5) each comprise a semiconductor switch having a body diode. The body diode of the fifth switching element (S5) is arranged opposite to the body diode of the first switching element (SI).

6. The DC voltage converter (1) according to any one of claims 1 to 5, having a control device (50) designed for actuating the first switching element (SI), the second switching element (S2), the third switching element (S3), the fourth switching element (S4) and / or the fifth switching element (S5). wherein The control device (50) is designed, in a first operating mode, for opening the third switching element (S3) and the fifth switching element (S5) and simultaneously actuating the first switching element (SI) and the fourth switching element (S4) in a clocked manner, and / or is designed, in a second operating mode, for opening the fourth switching element (S4), closing the fifth switching element (S5) and actuating the first switching element (SI) and the third switching element (S3) in a clocked manner, respectively, alternately. The control device (50) is designed, in a first operating mode, for opening the third switching element (S3) and the fifth switching element (S5) and simultaneously actuating the first switching element (SI) and the fourth switching element (S4) in a clocked manner, and / or is designed, in a second operating mode, for opening the fourth switching element (S4), closing the fifth switching element (S5) and actuating the first switching element (SI) and the third switching element (S3) in a clocked manner, respectively, alternately. ​ ​ 3. The DC voltage converter (1) of claim 2, wherein ​ 4. The direct voltage converter (1) according to any of claims 1 to 3, wherein ​ 5. The DC voltage converter (1) of claim 4, wherein ​ ​ 7. The DC voltage converter (1) according to claim 6, wherein ​ ​ 8. The DC voltage converter (1) according to the preceding claim, wherein The value of the input voltage (U_in) at the input connection (10) for the actuation in the second operating mode is higher than the value of the input voltage (U_in) for the actuation in the first operating mode.

9. A method (100) for operating a DC voltage converter according to any one of claims 1 to 8 in a first operating mode or in a second operating mode, wherein The first operating mode comprises the following method steps: opening (110) the third switching element (S3) and the fifth switching element (S5); simultaneously actuating (120) the first switching element (S1) and the fourth switching element (S4) in a clocked manner; wherein the second operating mode comprises the following method steps: opening (130) the fourth switching element (S4) and closing the fifth switching element (S5); alternately actuating (140) the first switching element (S1) and the third switching element (S3) in a clocked manner.

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