DC-DC converter

Abstract

A DC-DC converter includes a converter circuit including a switchable first circuit path in an on state during a first time interval and having at least a first switchable element and a second switchable element connected to each other in series, and including a second circuit path in an on state during a second time interval and having at least a first switchable element and a second switchable element connected to each other in series. The second circuit path is coupled to the first circuit path through the inductive element and maintains the conductive state for a second time interval that does not intersect the first time interval, wherein there is a time interval between the first time interval and the second time interval. The control device is configured to switch the first circuit path. A switchable freewheeling path is coupled in parallel with the inductive element, wherein the control device is configured to temporarily switch the switchable freewheeling path to a conductive state during a freewheeling interval during a time interval.

Description

Technical Field

[0001] The present invention relates to a DC - DC converter. The present invention particularly relates to semiconductor isolation for a DC - DC converter, and in some embodiments relates to fault protection measures for an isolated DC - DC converter based on semiconductor isolation. Background Art

[0002] One goal of current development is to implement a DC - DC converter using transistors. The prior art has proposed the possibility of involving semiconductor isolation, for example in the publication "New Cascaded Converter Topologies for Transformerless Galvanic Active Isolation", where such topologies are limited to using low voltages and low powers.

[0003] Known topologies cannot meet the requirements of continuously increasing operating voltage and power. On the one hand, in actual technical implementations, it is difficult to ensure the simultaneous turn - off of each transistor as required by the prior art. In addition, the coil current has built up before switching. During the switching process, this coil current may have an adverse effect on the circuit or even damage the circuit. For example, the potentials applied diagonally in two DC networks may be wrongly connected by diodes and transistors with delayed turn - off, which may cause sudden potential jumps in the two DC systems of the DC - DC converter and may generate large clock interference currents. On the other hand, it is possible that the two DC systems are directly diagonally connected to the corresponding other clock transistors. If a transistor cannot be turned off anymore due to a defect during operation, the isolation and potential separation are destroyed. This defect is particularly serious when the coil current has built up.

[0004] Therefore, what is desired is a DC - DC converter topology that can operate at high voltages and high powers and at the same time still allow a low noise level during operation. Summary of the Invention

[0005] Accordingly, an object of the present invention is to provide a DC - DC converter such that it can operate at high voltages and high powers and at the same time still ensure a low noise level during operation, that is, a low level of electromagnetic interference.

[0006] This problem is solved by the subject matter of the independent claims.

[0007] A core concept of the present invention is to recognize that a defined, in particular switchable, freewheeling path in parallel with the inductive element (coil) of a DC-DC converter enables the coil current to be absorbed and / or dissipated into the freewheeling path during a switching operation within a defined freewheeling interval, and thus into a circuit independent of the two DC links. This enables the switching elements of the DC link to be switched without problems, and at the same time it provides the possibility of dissipating the coil current in the event of a fault, namely via the ohmic resistance of the freewheeling path, which, in addition to high power and high voltage, also enables a low noise level to be achieved.

[0008] According to an embodiment, the DC-DC converter comprises a converter circuit having a switchable first circuit path which has at least a first switchable element and a second switchable element connected in series with each other, and the converter circuit has a second circuit path coupled to the first circuit path via an inductive element. The first circuit path is in a conducting state during a first time interval, and the second circuit path is in a conducting state during a second non-overlapping time interval, wherein there is a time interval between the end of the first time interval and the start of the second time interval, and / or, in particular taking into account the possible periodic driving of the elements, there is also a time interval between the end of the second time interval and the start of the first time interval. The DC-DC converter comprises a control device configured to switch the first circuit path and, in some dependent embodiments, also the second circuit path. Furthermore, a switchable freewheeling path coupled in parallel with the inductive element is provided, wherein the control device is configured to temporarily switch the switchable freewheeling path to a conducting state during a freewheeling interval within the duration of the time interval between the first time interval and the second time interval. This allows local freewheeling and / or enables the coil current to be dissipated during the freewheeling interval.

[0009] According to an embodiment, the second circuit path comprises at least a third switchable element and may also comprise a fourth switchable element connected in series therewith, for example in a manner similar or symmetric to the first circuit path. The control device may be configured to switch the third switchable element and / or the fourth switchable element. Another embodiment provides the use of a diode instead of the third switchable element or the fourth switchable element, which is switched passively by the flowing current or the existing potential.

[0010] According to an embodiment, the freewheeling path is in a bidirectional conducting state in the conducting state and / or in a bidirectional blocking state in the non-conducting state. This is particularly advantageous when semiconductor switches are used in the freewheeling path, since these switches may behave differently along different current flow directions.

[0011] According to an embodiment, the freewheeling path has at least one switching element that is in a bidirectional conducting state in the conducting state and in a bidirectional non-conducting state in the non-conducting state, and can be implemented by a mechanical switch, for example. As an alternative or in addition, the freewheeling path can have a first switching element that is in a unidirectional blocking state along a first direction of the freewheeling path in the non-conducting state. The freewheeling path includes a second switching element that is in a unidirectional blocking state along a second direction opposite to the freewheeling path in the non-conducting state. The first switching element and the second switching element are connected to each other such that in the non-conducting state, the freewheeling path is in a blocking state in the first direction and / or the second direction. This allows the two switching elements (such as semiconductor switches) to complement each other.

[0012] According to an embodiment focused thereon, the freewheeling path includes a first semiconductor switch and a second semiconductor switch that are anti-series coupled to each other, such as adjacent drain electrode terminals or collector electrode terminals. This makes it possible to overcome the different behaviors of semiconductor switches along different current flow directions while taking advantage of the advantages of semiconductor elements, such as fast switching frequency, small size, and good controllability. In such a configuration, the freewheeling path can also be configured by driving the semiconductor switch in a manner equivalent to a diode with a settable blocking direction between a bidirectional non-conducting state, a bidirectional conducting state, and a unidirectional conducting state for a specific first or second current direction. The unidirectional state can be used, for example, to prepare for current commutation from the first and second circuit paths to the freewheeling path. Refer to Figure 3a , Figure 4a , Figure 5a and Figure 6b , before the start of the freewheeling interval as time interval 54, the transistor of the freewheeling path can be configured or controlled to be in a unidirectional state, as described in detail in connection with Figure 3a .

[0013] According to an embodiment, the control device is configured to switch the freewheeling interval at the moment when the switchable element of the first circuit path switches to the blocking state and the second circuit path is in the blocking state. The freewheeling path allows the coil current to flow out, at least avoiding interference current as much as possible.

[0014] According to an embodiment, the control device is configured to extend the duration of the freewheeling interval compared to a previous freewheeling interval to reduce the switching frequency of the first circuit path and the switching frequency of the second circuit path within several switching cycles, and / or shorten the duration of the freewheeling interval compared to a previous freewheeling interval to increase the switching frequency of the first circuit path and the switching frequency of the second circuit path. This makes it possible to set the switching frequency independent of the operating point, thereby enabling different operating states.

[0015] According to an embodiment, the DC-DC converter includes a detection device which is coupled to a first circuit path and a second circuit path and is configured to detect a potential change between the first circuit path and the second circuit path. The control device is configured to at least partially terminate the switching of the first circuit path based on the potential change and terminate the switching of the switchable elements in the possible second circuit path. This makes it possible to prevent damage caused by continued operation using defective components.

[0016] According to an embodiment, the second circuit path includes at least a third switchable element and optionally also includes a fourth switchable element. The control device is configured to at least partially terminate the switching of the second circuit path based on the potential change as well.

[0017] According to an embodiment, the detection device includes an RC component having a resistance element and a capacitance element and is configured to detect the voltage drop across the resistance element and / or the capacitance element to detect the potential change. This makes it possible to detect the potential difference particularly simply and error-proof, which may indicate the loss of isolation ability of at least one circuit path.

[0018] According to an embodiment, the control device is configured to switch the switchable freewheeling path to the conducting state when a potential change is detected. This makes it possible to avoid further potential harmful interference currents.

[0019] According to an embodiment, the control device is configured to switch the first circuit path and / or the second circuit path to the blocking state when a potential change is detected. In other words, when an incorrect potential change is detected, the switching element is turned off or switched to the blocking state. This also makes it possible to avoid or at least reduce the current that may cause damage.

[0020] According to an embodiment, the control device is configured to control the DC-DC converter in at least one of a continuous mode, a discontinuous mode, a trapezoidal mode with coil current having alternating mathematical signs, and a limiting mode. This makes the DC-DC converter applicable to various applications.

[0021] According to an embodiment, the DC-DC converter includes a plurality of converter circuits and a corresponding plurality of detection devices, each detection device being coupled to one of the plurality of converter circuits for monitoring it. This makes it possible to perform converter circuit-specific monitoring, and the coupling to the plurality of converter circuits enables a small number of detection devices. Since a part of the plurality of converter circuits installed in the DC-DC converter can be monitored in combination by the detection device, while other converter circuits can be monitored individually or as a second group, these two designs can be easily combined with each other.

[0022] According to an embodiment, there is provided a DC-DC converter, wherein a potential change occurring in response to driving a switchable element in a first circuit path, a switchable element of a second circuit path in the second circuit path, or a switchable element in a freewheeling path clearly indicates that another element of the converter circuit is a defective element.

[0023] According to an embodiment, the DC-DC converter includes a plurality of converter circuits connected in parallel. The control device is configured to control the plurality of converter circuits with a time offset relative to each other such that at any given time, at most one path of a converter circuit is switched. The detection device is coupled to the plurality of converter circuits to clearly identify a potential change of each converter circuit.

[0024] Further embodiments are defined in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Preferred embodiments of the present invention will be explained below with reference to the drawings, wherein:

[0026] Figure 1 A schematic block diagram of a DC-DC converter according to an embodiment is shown;

[0027] Figure 2a A schematic block diagram of a DC-DC converter according to an embodiment is shown, wherein the switching elements of the freewheeling path are connected in anti-series with each other;

[0028] Figure 2b A schematic block diagram of a monitoring circuit according to an embodiment is shown;

[0029] Figure 3a An exemplary timing diagram on a matching time axis for driving the switching elements of a DC-DC converter in a TraCM operating mode is shown Figure 2a in;

[0030] Figure 3b A schematic description of a fault state table of a DC-DC converter in a trapezoidal mode is shown, which fault state can be detected within the scope of the embodiments;

[0031] Figure 3c - 3d A schematic curve of the voltage and current of a DC-DC converter in a fault state according to an embodiment is shown;

[0032] Figure 4a An exemplary timing diagram of drive signals of each switch in a continuous current mode CCM and a discontinuous current mode DCM and each switch in a freewheeling path is shown Figure 2a in;

[0033] Figure 4bSchematically depicts a fault state table of a DC-DC converter in continuous current mode, which fault states can be detected within the scope of the respective embodiments;

[0034] Figure 5a Schematically exemplarily shows drive signals of a switching element and a switching element of a freewheeling path according to an embodiment, as well as the coil current i of a negative coil current L of an exemplary schematic curve;

[0035] Figure 5b Schematically depicts a fault state table of a DC-DC converter in discontinuous current mode, which fault states can be detected within the scope of the respective embodiments;

[0036] Figure 6a Schematically shows a block diagram of a DC-DC converter according to an embodiment, wherein Figure 2a the switching element therein is replaced by a diode;

[0037] Figure 6b Shows, based on the description of Figure 3a and Figure 4a according to an embodiment, Figure 6a curves of the coil current and the gate electrode signal of the unidirectional variant;

[0038] Figure 6c Is a schematic illustration of the coil current in Figure 3a in the case of a variable freewheeling interval driven according to the invention;

[0039] Figure 6d Schematically depicts a fault state table of a DC-DC converter in unidirectional mode, which fault states can be detected within the scope of the respective embodiments;

[0040] Figure 7a - 7b Schematically shows a diagram for explaining the possibility of fault detection when the switching element of the freewheeling path of a DC-DC converter is turned off;

[0041] Figure 8a - 8b Schematically shows a diagram for explaining the possibility of fault detection when another switching element of the freewheeling path of a DC-DC converter is turned off;

[0042] Figure 9a - 9b Schematically shows a diagram for describing the possibility of fault detection when a second circuit path is turned on;

[0043] Figure 10a - 10b Schematically shows a diagram for describing the possibility of fault detection when a first circuit path is turned on; and

[0044] Figure 11 The example table showing the decomposition of the decision condition for fault detection or fault location based on the voltage drop in the DC-DC converter according to the present invention is shown. DETAILED DESCRIPTION

[0045] Before explaining the embodiments of the present invention in more detail with reference to the drawings below, it should be noted that elements, objects, and / or structures that are the same or have the same function, or elements, objects, and / or structures having the same effect in different drawings, have the same reference numerals, and thus the descriptions of these elements set forth in different embodiments may be exchanged with or applied to each other.

[0046] The embodiments described below are described in conjunction with a large number of details. However, the embodiments may also be implemented without these detailed features. In addition, for ease of understanding, block diagrams are used instead of detailed descriptions to describe the embodiments. In addition, as long as no clear description to the contrary is given, the details and / or features of each embodiment may also be combined with each other completely.

[0047] Figure 1 A schematic block diagram of a DC-DC converter 10 according to an embodiment is shown. The DC-DC converter 10 includes a converter circuit 12 having a first circuit path 14 and a second circuit path 16. The circuit path 14 includes a circuit path having switchable elements 181 and 182 connected in series with each other. These switchable elements include, for example, mechanical switches, but preferably include semiconductor switches, such as transistors, such as bipolar transistors, IGBTs, or MOSFETs. IGBTs and bipolar transistors generally do not conduct along the second direction, so they can be combined with diodes connected in antiparallel. In the case of MOSFETs, the diode can be implemented in whole or in part by a monolithic diode. The circuit paths 14 and 16 are coupled to each other through an inductive element, for example, through coupling points 241 and 242 of the first circuit path 14. The coupling points 241 and 242 are, on the one hand, between the switchable element 181 and the inductive element 22, and on the other hand, between the switchable element 182 and the inductive element 22. Each coupling point is cross-coupled to the switchable elements 184 and 183 respectively. The second circuit path 16 is formed, for example but not necessarily, by two switchable elements 184 and 183 connected in series with each other. It is pointed out here that the switchable elements 183 and 184 are not necessarily switchable, but other elements that change their conduction characteristics in the circuit may also be used, such as diodes that change their conductivity according to the corresponding current flow direction.

[0048] The DC-DC converter includes a control device 26, which is configured to switch at least the circuit path 14, for example, by adjusting the states of the switching elements 181 and 182 based on a control signal 28 from the control device 26. In the case where the switchable elements 183 and 184 are implemented or arranged in the circuit path 16, the control device 26 can also be configured to control these elements. However, for example, by using a diode according to the interpretation of Figure 6a The change of the second circuit path 16 between the conducting characteristic and the blocking characteristic due to the change of the direction of the applied voltage and / or current is also within the scope of the embodiments.

[0049] The DC-DC converter includes a switchable freewheeling path 32 coupled in parallel with the inductive element 22. The control device 26 is configured to temporarily switch the switchable freewheeling path 32 to the conducting state during the freewheeling interval for the freewheeling of the coil current, which may cause, for example, the center taps 241 and 242 to be short-circuited or at least connected to their own ohmic resistances. Thus, the current present in the inductive element 22 can be dissipated.

[0050] The switchable freewheeling path 32 includes a switchable element 33, which can be driven, for example, by the control device 26 and can be controlled in terms of at least unidirectional conductivity but preferably bidirectional conductivity. More than one switchable element can also be used, for example, to connect a plurality of unidirectionally controllable elements in inverse series with each other.

[0051] The DC-DC converter is configured such that the first circuit path is in the conducting state during a first time interval and the second circuit path is in the conducting state during a non-overlapping second time interval, where there is a time interval between the first time interval and the second time interval. Thus, as an alternative or in addition, a time interval can also be provided between the second time interval and the first time interval, or equivalently, a time interval can be provided between the second time interval and a further third time interval, in which control is performed in a manner corresponding to the first time interval, since the elements are driven periodically or in a periodically alternating manner where possible. This means that the fourth time interval after the third time interval can be controlled in the same manner as the second time interval. Exemplary timing diagrams are as shown in Figure 3a 、 Figure 4a 、 Figure 5a and Figure 6b It can be seen that the first time interval ends, for example, at time t2, and the second time interval starts at time t5, where, after time t2, a commutation period of approximately 100 ns to approximately 1000 ns can be waited until the freewheeling path 32 is in the conducting state in the freewheeling interval 54, which ends rapidly before the duration required for commutation.

[0052] This means that, after a time interval during which the circuit path 14 is in the conducting state and thus in the blocking state in at least one direction (preferably in both directions), but before the second circuit path 16 is in the conducting state, that is, as long as it (still) is in the blocking position, due to the active drive and / or due to the diode characteristic, the control device 26 is able to switch the freewheeling path to the conducting state, in particular before the second circuit path 16 is in the conducting state, at least in the relevant current flow direction, and switch the freewheeling path back to the blocking state. This achieves a situation in which, during the time interval, based on the freewheeling path, the current of the inductive element 22 can flow out, which can reduce the load on the components of the circuit path 14 and / or 16. The embodiment provides that at any moment, at most one of the two circuit paths 14 or 16 is in the conducting state.

[0053] Figure 2a FIG. shows a schematic block diagram of a DC-DC converter 20 according to an embodiment.

[0054] Compared with the DC-DC converter 10, the converter circuit 12' of the DC-DC converter 20 has additional details, including one or more phase circuits 341, 342, …, where the number of phase circuits can be at least 1, at least 2, at least 3 or more as required. Each phase circuit 34 can be connected in parallel with each other at the input end and the output end to shunt the total current flowing through the DC-DC converter, so as to keep the current load low in the corresponding components. As an alternative or supplement, it is possible to provide to keep the output current continuous and / or reduce the load on the capacitors of the DC-DC converter.

[0055] The switching elements 181 to 184 are, for example, MOSFET transistors or GaN-FETs and are denoted as S1, S2, S3, and S4. The coil current i L can flow through the inductive element 22 identified by the symbol L.

[0056] The DC link capacitor 361 on the first DC-DC converter side and the DC link capacitor 362 on the second DC-DC converter side are also shown, which are respectively denoted by C DC1 and C DC2 identified. For the DC link or the circuit path 14, the potentials and are shown by way of example. The DC link capacitor 361 is arranged between the potential and the potential . In a similar manner, the potentials and are shown. The DC link capacitor 362 is arranged between the potential and the potential .

[0057] A voltage U1 may exist on a first side of the DC-DC converter 20, and a voltage U2 may exist on a second side of the DC-DC converter 20. One of the two voltages U1 and U2 may be referred to as an input voltage, and the other may be referred to as an output voltage. The DC-DC converter 20 converts the voltage between the input voltage and the output voltage.

[0058] The freewheeling path 32’ coupled in parallel with the inductive element 22 includes, for example, two semiconductor switches 331 and 332 connected anti-series with each other, which are implemented, for example, in a MOSFET configuration and are identified by S FN and S FP identification.

[0059] This configuration enables a bi-directional blocking characteristic to be obtained based on the body diodes 381 and 382 and the open state of the conduction path in the case where both of the switchable elements 331 and 332 are switched to the blocking state. In the driving state, a bi-directional conduction path can be obtained by bypassing the body diodes 381 and 382.

[0060] It is possible to achieve a situation where, in the DC-DC converter 10 and the DC-DC converter 20, the freewheeling path 32 or 32’ is in a bi-directional conduction state in the conduction state and in a bi-directional blocking state in the non-conduction state. On the other hand, when only one semiconductor switch 331 or 332 is used, a unidirectional blocking state together with a bi-directional conduction state is achieved.

[0061] Although the DC-DC converter 10 can be switched to a bi-directional conduction state and a bi-directional non-conduction state by a possible single switching element 33, in the DC-DC converter 20, there is provided: using a first switching element 331 and a second switching element 332, which are each in a unidirectional blocking state in different directions in the non-conduction state. The switching elements 331 and 332 are connected to each other such that in the non-conduction state, the freewheeling path is in a (i.e., bi-directional) blocking state in both directions. For this purpose, the switching element 331 and 332 are connected anti-series with each other.

[0062] Preferably in this regard, according to the implementation type of the semiconductor transistor, each semiconductor switch has adjacent drain electrode terminals or adjacent collector electrode terminals.

[0063] Regardless of the implementation of the freewheeling path 32', the implementation of the circuit path 16, and other developments according to the present invention, the DC-DC converter 20 may include a detection device 42 coupled to the circuit paths 14 and 16 and configured to detect a potential change between the circuit path 14 and the second circuit path 16. The control device 26 may consider such a potential change between the circuit paths 14 and 16 to terminate the switching of at least the first circuit path based thereon, that is, to terminate the switching of the switches 181 and / or 182. In one configuration of the circuit path 16 or its circuit path having switchable elements such as switchable elements 183 and 184, the control device 26 may also be configured to terminate the switching of these elements based on the detected potential change, where it is entirely possible to drive the safety state of the corresponding elements, such as the blocking state, and then maintain that state and then terminate further driving.

[0064] Such an embodiment solves another problem related to the prior art. On the one hand, the combined operation of the switchable freewheeling path and potential change detection solves the problem that during normal operation, the freewheeling path provides the possibility of ensuring a certain transition time for the current commutation between the active states of the switches S 1 / 2 and S 3 / 4 The switching elements S1 to S4 are turned off here to ensure isolation. Another problem solved is that the freewheeling path provides an energy release point decoupled from both sides for the energy stored in the coil, which is operable even after the failure detection of the switching elements. This means that isolation can still be ensured in the event of a simple failure.

[0065] In Figure 2a the description, the detection device 42 is coupled between the potential and the potential As an alternative, any other combination can also be selected, such as between the potential and the potential and between the potential and the potential or between the potential and the potential and the corresponding diagonal connection between them.

[0066] Based on the potential change, the control device 26 may be configured to switch the switchable freewheeling path 32' to the conducting state. The detection device 42 can also be used entirely in the DC-DC converter 10, where in the case of detecting a potential change, the switchable element 32 can be switched to the conducting state by the control device 26.

[0067] According to an embodiment of the detection device 42, it includes an RC component, which has a resistance element 44 identified by R1 and a capacitance element 46 identified by C1. The detection device 42 is configured to detect the voltage drop U across the resistance element 44 R1 and / or the voltage drop across the capacitance element 46 to detect a potential change. For example, the measuring device of the detection device or the corresponding measuring device of the control device 26 can be coupled to the detection device 42 or the elements 44 and / or 46 to detect a potential change.

[0068] In addition, in Figure 2a , for the DC-DC converter 20, an optional but advantageous enhancement is described with reference to the monitoring device 53. The monitoring device 53 can be configured to monitor the voltage drop across at least a part of the freewheeling path 32'. For example, the control device 26 can be configured to detect the fault state of the freewheeling path 32' based on the voltage drop or the information or signal 55 provided by the monitoring device 53. Based on this fault state, the control device 26 can at least partially terminate or prevent the switching of the first circuit path 14, for example as described in connection with the detection device 42. The monitoring device 53 can also be used in the DC-DC converter 10, for example in combination with the switchable element 33.

[0069] For this advantageous embodiment of the monitoring device 53, it has been recognized that monitoring the freewheeling path, in particular at least one of the switchable elements or each switchable element, can provide an indication of whether the operation of the freewheeling path is reliable or whether there is a fault here. Therefore, it has been recognized that depending on whether the switchable element 33, 331 or 332 is switched to the conducting state or the non-conducting state, a voltage drop significantly different from 0 (non-conducting state) is expected or a substantially short-circuit state with a low voltage drop is expected (conducting state). The monitoring device 53 can be configured to monitor this behavior according to the switching state of the freewheeling path and output a corresponding signal 55, which can be provided to the control device 26 so that based on the voltage drop, the fault state of the freewheeling path 32' can be detected, which enables at least partially terminating or adjusting the switching of the circuit path 14 based on this fault state.

[0070] In other words, the implementation of the monitoring device 53 enables the voltage monitoring circuit or the monitoring device 53 to be connected in parallel to the switching element S of the freewheeling circuit FP and S FN , which can detect the voltage across the switch during operation. Using the voltage monitoring circuit, the control device 26 can diagnose faults in the freewheeling circuit, for example based on the control signal and the detected voltage state.

[0071] Figure 2bShows a schematic block diagram of a voltage monitoring circuit 57 according to an embodiment, which voltage monitoring circuit can be at least part of the monitoring device 53 and is implemented or arranged twice, for example, in the DC-DC converter 20. For example, if both switchable elements 331 and 332 are to be monitored, each of the switchable elements 331 and 332 is monitored separately, and it is also possible to monitor only one of the elements.

[0072] According to an embodiment, the monitoring device 53 can be configured to take the voltage drop u of the freewheeling path 32 / 32’ FP and / or u FN and compare it with a constant or configurable reference value u Ref to provide a comparison result and provide the comparison result to the control device to detect a fault state. The reference value can be set by the control device 26 to vary over time, for example, or can be configurable, for example, according to the switching state of the DC-DC converter or at least one of its switching elements.

[0073] According to an embodiment, the voltage monitoring circuit 57 can be configured to compare the actual voltage drop across the switch element 33 (for example, the voltage u across the switch element 332 FP or the voltage u across the switch element 331 FN ) with a reference voltage u Ref The reference voltage can vary over time according to the drive state of the switch element 33. Based on this comparison and knowledge of the drive state, the control device 26 can detect whether the voltage drop corresponds to a target state or whether the detected conduction state or short circuit corresponds to a target state. A deviation from the target state can be interpreted as a fault state.

[0074] In other words, to avoid two main hazards during the operation of the DC-DC converter and reduce subsequent effects, the embodiment provides a combination of appropriate protection measures and corresponding detection methods and uses them for the topology to detect isolation faults. The protection measures can detect isolation faults that occur during operation and limit the impact to a small local circuit of the circuit by reducing or restricting the further operation of the DC-DC converter.

[0075] If the possibility of using several phase circuits 34 in the DC-DC converter 20 is applied, the embodiment provides that these phase circuits are driven with a time offset relative to each other, so that at any moment, at most one path of the converter circuit is switched. Since the switching of the path may cause the start or detectability of the potential difference at the detection device 42, it is also possible to detect which phase circuit 34 is defective based on time distinguishability. The detection device can be coupled to multiple converter circuits to clearly identify the potential changes in each converter circuit. Thus, for example, the detection device 42 can be contact-connected to the corresponding coupled potential points according to the selected parallel interconnection or and or This makes it possible to use one detection device to monitor several phase circuits 34.

[0076] As an alternative or supplement, for multiple converter circuits that are phase circuits 34, a corresponding multiple of detection devices 42 can be used, each detection device 42 being coupled to one of the multiple converter circuits for monitoring it. These can also be combined with each other such that different converter circuits or phase circuits are coupled to separate detection devices and other converter circuits or phase circuits are monitored in groups.

[0077] In the case where a potential change is detected by the detection device 42, as an alternative or supplement to setting the switching of one or more switchable elements in the circuit paths 14 and 16, the control device 26 can also be configured to switch the freewheeling path 32 to the conducting state.

[0078] Furthermore, the control device can be configured to disconnect the remaining switch elements that are operable among the switches S1 to S4, that is, to switch them to the blocking state. If one of these switch elements cannot be turned off due to a defect, the remaining three switches remain in the blocking state and thus ensure the isolation between the respective DC networks.

[0079] However, according to the embodiment, in the case where a potential change is detected, the control device 26 attempts to switch the circuit path 14 and / or the circuit path 16 to the blocking state, that is, to control the elements 181, 182, 183, and / or 184 to the off state as long as they are controllable and as long as they have no defects.

[0080] In other words, the embodiment makes it possible to introduce bidirectional switches into the DC-DC converter topology as predefined local freewheeling circuits or freewheeling paths and to introduce potential jump detection as a fault detection means. As Figure 2a shown. There are two DC networks 14 and 16 on the left and right respectively, and their voltages correspond to U1 and U2. Two DC link capacitors C connected to the respective DC networksDC1 and C DC2 It is possible to create two corresponding DC links for the circuit of the DC-DC converter. The current compensation coils 481 to 484 and the grounding devices 521 and 522, for example in the form of high-ohm resistors and grounding capacitors, can be regarded as standard designs of the DC-DC converter and the DC network.

[0081] Regarding the design of the topology, it is preferred to meet the operating conditions and because otherwise the shown DC-DC converter will lose its isolation ability between the two DC networks. The body diodes or freewheeling diodes of each switching element are the cause of this situation.

[0082] In this case, the converter circuit 12’ includes the main aspects of the embodiments of the present invention. It includes one or more phase circuits 34, detection means 42 and a control unit or control means 26. If multiple phase circuits are used in a multiphase application, the number of phase circuits 34 can be clock-synchronized in a staggered manner.

[0083] In the shown but non-limiting embodiment, each phase circuit 34 includes four switching elements S1, S2, S3, S4, a coil L and a bidirectional switch, a freewheeling path 32 or 32’ connected in parallel with the coil. In a possible embodiment, the freewheeling path 32’ includes two switching elements S connected in anti-series FP and S FN . The bidirectional switch is capable of blocking or conducting voltage and current from the selected direction or both directions by driving corresponding gate electrode signals.

[0084] The freewheeling path 32 enables the possibility of creating in the circuit a local circuit in which the coil current i L can flow freely independently of the potential separation of the two circuit paths 14 and 16. All switching elements can be implemented independently of each other and are preferably semiconductor switches such as MOSFETs or GaN-FETs, and these advantageous embodiments are not restrictive.

[0085] It can be considered that the switching elements S1, S2 on the one hand and the switching elements S3 and S4 on the other hand belong to two switching groups, where within each group, the switching elements can be switched as synchronously or simultaneously as possible at the logic level, even if this may also involve time delays in the actual circuit design, for example due to component deviations or different cable lengths. For the sake of simplicity, the switching elements S1, S2 are also referred to here as grouped as 1 / 2 , and the switching elements S3, S4 are also referred to here as grouped as 3 / 4 .

[0086] During normal operation, the bidirectional switch can be activated by the switching elements S 1 / 2 and S 3 / 4 between each switching interval. During the activation interval, the coil current i L flows through the bidirectional switch into the freewheeling step or through the freewheeling path. This ensures a sufficient time interval, typically from a few hundred nanoseconds to microseconds, for confirming the turn-off of the switching elements S1, S2, S3, and S4, and eliminates or counteracts the diagonal connection caused by the unequal turn-off delays of the respective switching elements.

[0087] As a possibility for fault detection, a potential jump detection means or a detection device 42 monitors the potential jump between the two circuit paths 14 and 16. If a sudden potential jump occurs and persists or lasts for a period of time, such as a few hundred nanoseconds, during the corresponding activation of the gate electrode signal of the switching element, the control device 26 or the evaluation unit of the detection device 42 can detect a fault, such as a diagonal connection of the circuit path. Based on this, the protection method can be carried out as quickly as possible, particularly preferably, immediately and rapidly. This may include permanently turning on the bidirectional switch or the freewheeling path, that is, placing it in the conducting state, and turning off the switching elements S1, S2, S3, and S4 or switching them to the off state and keeping them permanently in the off state.

[0088] This protection measure according to the invention enables the influence of the faulty switching element to be restricted to a locally limited area. In the case of a fault in one of the switching elements S1 - S4, the remaining three or still operable switching elements can enable or maintain the isolation ability between the two DC systems. The current stored in the coil or the energy contained therein can be slowly released through freewheeling in the bidirectional switch.

[0089] The embodiment provides for diagnosing the faulty switching element, that is, the drive of the control device 26, using the mathematical sign of the potential jump and the gate electrode signal.

[0090] According to an embodiment, the control device of the DC - DC converter described herein is configured to control the DC - DC converter in at least one of a continuous mode CCM, a discontinuous mode DCM, a trapezoidal mode TraCM in which the mathematical sign of the coil current alternates, and a boundary mode BCM. The control device can be configured to operate or run one of a variety of operating types without change, or to switch between one or more operating types.

[0091] Figure 3a Elements S 1 / 2 and S 3 / 4 shown for driving the freewheeling path 32’ and the switching elements 331 and 332 (respectively by S FP and S FNAn exemplary timing diagram on the matching time axis t of the identification). The curve of the coil current I is also shown. L where the upper limit OG and the lower limit UG are also described.

[0092] To achieve low switching losses, the topology described herein can operate in trapezoidal current mode TraCM. Here, some or even all of the switching elements can operate in a soft switching mode or a so-called zero voltage switching (ZVS) mode. In Figure 3a the example shown, the current curves and gate electrode signals of the switching elements for obtaining TraCM are shown. It can be seen that the coil current i L is alternating in each switching period, which means that the current flow direction changes, so the freewheeling paths with bidirectional conduction and bidirectional blocking are advantageously applied.

[0093] A possible switching sequence is as follows:

[0094] The exemplary switching period starts at time t0. The switching element S FN is turned off, and the freewheeling step or freewheeling interval 540 defined by the switch S FP and S FN switched to the conducting state is terminated or aborted. The coil current i L now charges the junction capacitance of the switching element S FN and further flows through the diodes of the switching elements S1 and S2 into Figure 2a the DC link or U1 in.

[0095] The time intervals [t0, t1], [t2, t3], [t4, t5] and [t6, t7] can be considered as technically set dead times, which delay the turn-on of each switching element for the next step and take into account the fact that, at the same time, the junction capacitances of the switching elements are recharged by the coil current i L flowing in the appropriate direction for zero voltage switching.

[0096] In the time interval [t1, t2], the switching element S 1 / 2 is turned on; the coil current is accumulated using the DC link voltage U1 during this time interval.

[0097] At time t2, the switching element S 1 / 2 may be turned off. The coil current i L now flows through the switching elements S FP and S FN in the freewheeling step or freewheeling interval 541. Although the switching element S 1 / 2 is turned off simultaneously or with a slight delay (that is, not simultaneously), the active connection between the two circuit paths 14 and 16 is interrupted.

[0098] The time interval [t2, t4] can correspond to a freewheeling step or freewheeling interval 541; meanwhile, the switching elements S1, S2, S3, and S4 remain in the off or blocked state. During this period, the potential of the coil L or inductive element 22 is actively isolated from the two circuit paths.

[0099] At time t4, the switching element S FP can be turned off. The coil current i L now charges the junction capacitance of the semiconductor switch 332, and then the coil current i L flows through the diode of the switching element S 3 / 4 and enters the DC link U2 or the circuit path 16.

[0100] In the time interval [t5, t6], the switching element S 3 / 4 can be turned on; during this time interval, the coil current is dissipated using the DC link voltage U2.

[0101] At time t6, the switching element S 3 / 4 is turned off. Since at time t7, the element S FP is switched back to the on state, the coil current i L now flows through the switching elements S FP and S FN .

[0102] The time interval corresponds to a freewheeling step 542; meanwhile, the switching elements S1, S2, S3, and S4 remain in the off state. During this period, the potential of the coil L is actively isolated from the two circuit paths. By driving the anti-parallel switches, the freewheeling path can be configured to be in state 1) fully or bidirectionally conducting, 2) fully or bidirectionally blocked, 3) unidirectionally conducting in the first direction, and 4) unidirectionally conducting in the opposite second direction. The unidirectional conducting states 3) and 4) can be related to each other in terms of their polarities or can behave like a diode with a configurable blocking direction that can conduct current in the selected direction. In the case of the trapezoidal operation described in Figure 3a , this unidirectional conducting state is advantageously used to switch the freewheeling path to a diode with a varying blocking direction instead of a bidirectionally conducting state whenever possible. In the case of a positive coil current, the switching element S FN can be switched to the on state, and in the case of a negative coil current, the switching element S FP can be switched to the off state. Here, it can be considered that the freewheeling interval 54 lasts from the turn-off of the previous first or second circuit path until the turn-off of one of the bidirectional switches, since the start of the zero-voltage switching of the two circuit paths is considered to belong to the freewheeling step.

[0103] At a moment The next or subsequent switching period may occur; due to the switching sequence, the switching element continues to be driven. This means that repeated and / or periodic driving may occur. The first circuit path is in an on state during a first time interval between t1 and t2, and the second circuit path is in an on state during a non-overlapping second time interval between t5 and t6. Between the end of the first time interval and the start of the second time interval, and / or, especially considering the possible periodic driving of the components, between the end of the second time interval and the start of another time interval (during which the first circuit path is switched to the on state at a moment later, which may also be referred to as an updated first time interval or a third time interval), there may be time intervals (t5 - t2 and / or ), which can be used to switch the freewheeling path to the on state. The DC-DC converter can be driven periodically here, possibly with varying period durations.

[0104] Advantageously, the switching element S is turned off at the moment t2 1 / 2 after the switching element S is turned on FP and turned off at the moment t4 to abort the freewheeling step. In a practical implementation, the turning on of the switching element S FP can be carried out between the moment t7 of the last switching period and the moment t2. In particular, in order to reduce the conduction loss in the bidirectional switch during the freewheeling step and simplify the control logic, the switching element S FP can be kept in the on state between the moment t7 of the previous switching period and the moment t4 of the current switching period.

[0105] Due to the same principle, the switching element S FN must be turned on before the moment t6 when the switching element S 3 / 4 is turned off and turned off at the moment of the next switching period to abort the freewheeling step. In a practical implementation, the turning on of the switching element S FN can be carried out within the time interval [t3, t6]. In particular, in order to reduce the conduction loss in the bidirectional switch and the freewheeling path during the freewheeling step or keep it at a low level and simplify the control logic, the switching element S FN can be kept in the on state between the moment t3 of the current time period and the moment of the subsequent switching period.

[0106] In the trapezoidal current mode, the mathematical symbol of the alternating coil current i L is provided. The direction and power of energy transfer can be determined by the current upper limit i LOG and the current lower limit i LUGis defined by the value, where i LOG > 0, i LUG < 0.

[0107] In addition, Figure 3a shows curves of voltages U1 and U2 that can be provided as reference voltage u Ref to the voltage monitoring circuit 57 to monitor the operation of the freewheeling path. In Figure 3a it shows the voltages U1 and U2 for the voltages u FN and u FP monitored by the voltage monitoring circuit 57, where other reference voltages or thresholds may also be applicable for robust voltage drop / short circuit monitoring. The voltage monitoring circuit 57 can be configured to monitor one or both voltages across the switching elements S FP and S FN ; this value depends on the switching state.

[0108] In an example of normal operation, during the freewheeling steps in the time intervals [t3, t4] and [t7, t*0], the voltages u FP and u FN may be very low; this means that u FP ≈ 0 and u FN ≈ 0, where deviations within the inherent resistance and voltage drop of the components need to be considered. Since each switching element is capable of meeting the condition of zero voltage switching (ZVS) during the trapezoidal current operation, after the switching element is turned off by the coil current, the voltage can accumulate across the switching element; for this, see times t0 and / or t4. For example, at times t0, t2, t4, and t6, the corresponding switching elements are turned off and zero voltage switching is favorably driven. In this case, the voltages of different switching elements in the circuit may take complementary values, that is, if one increases, the other decreases.

[0109] Due to this characteristic, the voltage across the switching element S FN should accumulate within the time interval [t0, t2]; in particular, the voltage u FN reaches the voltage U1 within the time interval [t1, T2]. At the switching element S FP , the voltage u FP should be high during the time interval [t4, t6], and in the time interval [t5, t6], the expected value can be provided, that is, the voltage u FP should approximately correspond to the voltage U2, where U1 and U2 are significantly different from 0, for example, from several hundred volts to several thousand volts (such as 400V to 800V or 1000V). For example, these values can represent the operating voltage of a DC-DC converter. The diode 61 in the detection device 57 (such as Figure 2bPrecisely generates a voltage block as shown; if the drain-source voltage Uds has substantially built up, the diode 61 isolates Uds from the voltage comparator. This makes the measurement range of the voltage comparator relatively small and precise.

[0110] Referring again to Figure 2b , which shows a possible embodiment as an example of the monitoring device 53. In this embodiment, the comparator 59 connects the switching voltage u FP or u FN to a reference voltage u Ref corresponding to the voltage state of the switching element for comparison. The reference voltage is preferably slightly greater than the voltage drop across the switching element caused by the coil current generated during normal operation. For example, considering an example of 5V to 15V.

[0111] The decision conditions can be understood as the interference frequency band and voltage in case of a fault. These depend on the size of the switch.

[0112] Since the operating voltage is significantly greater than the voltage in the conducting state, in an advantageous design, the reference voltage can be configured to be approximately 2 or 3 times the voltage drop across the switching element during normal operation.

[0113] This means that during normal operation, for example, the Uds of the switching element may be significantly lower than the reference voltage; in case of a fault, the diode 61 blocks U1 or U2 and the comparator 59 can also clearly detect the state using U FV explicitly.

[0114] The isolated voltage source can supply power to the components in the voltage monitoring circuit 57 and provides a voltage U FV for this purpose, that is, u Ref <U FV .

[0115] If the switching voltage u FP or u FN combines to u FP / N <U FV , the diode 61 becomes conducting. Thus, the switching voltage is compared with the reference voltage. As long as the switching element is turned on to be operable or current is conducted through the body diode or the freewheeling diode 38, the comparator 59 will transmit a logic signal "0" or zero as an indication of the voltage state of the low voltage. The voltage monitoring signal 55 and the target voltage state obtained through analysis can be used to diagnose short-circuit faults and open-circuit faults in the freewheeling circuit.

[0116] If the switching element in the freewheeling circuit cannot conduct current, this corresponds to an open-circuit fault. The coil current now directly commutates to the other side, and during the freewheeling step and time interval [t3, t4] or in which the switching voltage u FP or u FN has a high voltage state. Then, this fault is detected by the voltage monitoring circuit and transmitted to the control unit or control device 26.

[0117] For example, if the switching element in the freewheeling circuit cannot block the voltage, this corresponds to a short-circuit fault. After the exemplary time t4 or t0, the switching voltage u FP or u FN can no longer build up. In some embodiments, the control unit checks the voltage state of u FP and / or u FN at appropriate times, for example in the time interval [t1, t2], for example at time t1, or in the time interval [t5, t6], for example at time t5, to detect a short-circuit fault and avoid a short circuit between the freewheeling circuit and other switching elements.

[0118] Reference Figure 3b shows a fault detection method that can be implemented by the control device 26, where the term "open circuit" is used to describe an open-circuit fault and the term "short circuit" is used to describe a short-circuit fault.

[0119] The round brackets used in the time interval, such as (t4, t6], mean that the exact moment is excluded because at the start of the time interval, the switching element is currently off and the build-up of the switching voltage (u FN or u FP ) starts exactly at this moment. The transient switching voltage remains at a low voltage state at times t0 and t4, so the exact moment of measurement may not be appropriate. Therefore, embodiments of other operating modes, especially in the case of CCM or DCM, provide for measurement to be made only with a small delay after the switching element S 1 / 2 or S 3 / 4 has been turned on, because it can be expected that in these cases the switching voltage will only increase after S 1 / 2 or S 3 / 4 has been turned on.

[0120] The control device 26 can be configured to detect whether the output logic signal "1" or one, "0" or zero corresponds to the expected value respectively, and detect or identify a fault in the case of a deviation.

[0121] In the case where the control device 26 detects a fault, the control device 26 can abort the operation of the phase circuit and perform one or more of the protection measures described herein. In this case, the switching elements 331, 332, 333 and 334 (S1, S2, S3 and S4) can be turned off, for example, and the control signal for the freewheeling circuit can be kept on or turned on.

[0122] In the case of an open-circuit fault, the freewheeling circuit is inoperable, and the coil current i L Immediately after the switching elements (e.g., S1 and / or S2 or S3 and / or S4) on one side are turned off, it commutates to the other side through the body diodes or freewheeling diodes of the switching elements S3 and / or S4 or S1 and / or S2 and enters the capacitors 361 or 362. A higher voltage now acts across the switching elements of the freewheeling circuit, during which the incorrect voltage state can be detected by the monitoring device 53. As an example, Figure 3c shows the switching element S FP or the schematic curve of the open-circuit fault in 332. In the time interval [t3, t4], the voltage u FP has a higher voltage. Using the monitoring device 53, the fault is detected by the control device 26, and the phase circuit is turned off. Then, the coil current can be dissipated through the body diodes or freewheeling diodes of the switching elements S3 and S4 until it reaches zero. Figure 3d shows the scenario of a short-circuit fault; after the moment t4, S FP should be turned off, but due to the short-circuit fault, its voltage should not be accumulated. At the moment t5, the fault is detected by the control device 26 using the monitoring device 53, and the phase circuit is turned off. During this process, the coil current in the freewheeling circuit is slowly dissipated until it reaches 0.

[0123] In Figure 3a and Figure 4a the switching element S 3 / 4 is actively conducting during the time period between the moments t5 and t6. Figure 3a and Figure 4a The difference between the cycles of Figure 3a is that during the zero-voltage switching (ZVS), the coil current is automatically guided to the next step after the switching element has been turned off; see Figure 4a As shown in 3 / 4 the switching element S 3 / 4 is turned off at the moment t6. However, here, the coil current still flows in the positive direction, that is, the coil current still has a positive mathematical sign, so the coil current further passes through the body diode of S FP At the moment t7, the switching element S Figure 6a is turned on in the freewheeling circuit, and now the coil current commutates in the freewheeling circuit through hard switching. In the unidirectional variant described in conjunction with 1 / 2 this operation using the diode D

[0124] Figure 4a shows Figure 2a the switches of S1 - S4 and the freewheeling path 32' inLUG >0) CCM and discontinuous current mode (i LUG = 0) Exemplary timing diagram of drive signals during DCM. Although the TraCM mode is shown in Figure 3a where the coil current also flows in the negative direction, Figure 4a a conventional CCM mode comparable to the unidirectional variant is shown.

[0125] In continuous mode (CCM), the upper and lower current limits have the same mathematical sign during the switching period. Each switching operation here does not meet the criteria for zero voltage switching (ZVS), so some switching elements are switched using hard switching operations.

[0126] Figure 4a The curves of coil current i L for positive continuous coil current and gate electrode signals are shown. Compared with the Figure 3a trapezoidal current mode in FN the main difference is that zero voltage switching occurs in this case at the turn-off of switching element S 3 / 4 at time t0 and at the turn-off of switching element S L at time t6. Since the transient coil current i 1 / 2 still has a positive mathematical sign, it does not meet the criteria for capacitive commutation (zero voltage switching); after it is turned off, the coil current continues to flow through its diode. Then, current commutation occurs at the turn-on of switching element S FP at time t1 and at the turn-on of switching element S FN S 1 / 2 at time t7. Specifically, at time t1, switching elements S FP S 3 / 4 are switched by hard switching, and at time t7, switching elements S

[0127] In this mode, the fault detection method of the monitoring device 53 for open circuit faults and short circuit faults in S FP remains similar or the same as the method for the trapezoidal current mode; see Figure 3a - 3d in this regard. The deviation is that shortly after the switching elements S1, S2 or 181, 182 are turned on, short circuit faults in S FN are detected and checked, with a short delay of approximately 20 ns to 200 ns. Other delay values are also entirely possible. Figure 4b The table in shows the relevance of the fault detection method for this operating mode, which can be implemented based on using the voltage monitoring circuit 57 of the control device 26 or the monitoring device 53. In the event of a detected fault, the control device 26 can be configured to use or apply the same protection measures as those for the trapezoidal current mode TraCM.

[0128] For a negative continuous coil current, Figure 5a A schematic exemplary illustration of the drive signals of the switching elements S1 - S4 and the switching elements of the freewheeling path 32’ is shown, as well as an exemplary schematic curve of the coil current i L Here, hard switching occurs when the switching element S FN 、S 1 / 2 turns on at time t3 and when the switching elements S FP and S 3 / 4 turn on at time t5.

[0129] Figure 5b A table - based representation applicable to Figure 5a fault allocation is shown, and these faults can be recognized by the monitoring device 53. In this mode, the fault detection methods for open - circuit faults and short - circuit faults in S FN remain the same as those for the trapezoidal current mode. Shortly after the switching element S 3 / 4 or 183, 184 turns on, only the short - circuit faults in S FP or the switching element 332 are detected and checked, with a short delay of about 20 ns to 200 ns. Figure 5b The table in

[0130] shows the correlation of the fault detection method for this operating mode. For the detected faults, the same protection measures as in the trapezoidal mode can be used. FN For a continuously positive coil current, the switching element S FP can be permanently turned off; conversely, for a continuously negative coil current, the switching element S FN can be permanently turned off. In the case of a static implementation of the DC - DC converter, according to the embodiment, the corresponding element can also be replaced, for example, by a diode that switches according to the body diode of the replaced element. A possible control strategy for the control device can be configured such that the switching element 331 (denoted as S L ) can be immediately turned off when the coil current (denoted as i FP ) is positive (P), while the switching element 332 (denoted as S L ) can be immediately turned off when the coil current (denoted as i FP ) is negative (N), which is shown by the flags S FN . This means that if the coil current flows continuously in one direction (CCM), one of the two transistors 331 and 332 may also be excluded from the active control strategy, for example, because its freewheeling diode (in the case of the MOSFET body diode) can conduct current. Thus, the control logic can be simplified. InFigure 3a In the range 54 i In this case, the transistors 331 and 332 of the freewheeling path are turned on in an overlapping manner to optimize the lower conduction loss.

[0131] However, in order to reduce the conduction loss in the freewheeling step or simplify the control logic, a control strategy for the trapezoidal current mode can also be used to drive the bidirectional switching of the freewheeling path.

[0132] The discontinuous current mode can be a special continuous current mode in which one current limit is set to zero. The control method for the continuous current mode can also be used for the discontinuous current mode.

[0133] Figure 6a Fig. shows a schematic block diagram of a DC-DC converter 20' according to an embodiment. In terms of its design, it basically corresponds to the DC-DC converter 20, where the switching elements 183 and 184 of the DC-DC converter 20 are replaced by diode elements 561 and 562 respectively, and each diode element is arranged with respect to the potential in the blocking direction and This can be considered a unidirectional variant of the DC-DC converter 20 and can be used for special applications. In this variant, the switching element S 3 / 4 is replaced by the diode D 1 / 2 Although bidirectional energy transfer is not provided, this allows for material cost savings in terms of the switching element S 3 / 4

[0134] In this case, the operating principle of the unidirectional variant of the DC-DC converter 20' is the same as that of the continuous current mode or the discontinuous current mode in the bidirectional topology, so its control method can be directly applied. Since the switching element S 3 / 4 is replaced by the diode D 1 / 2 the corresponding gate electrode signals of Figure 4a and Figure 5a are no longer used.

[0135] Referring to Figure 3a , Fig. 4 and Figure 5a , the control device can be configured to switch the freewheeling interval 54 at the moment when the control device switches the circuit path 14 to the blocking state and the circuit path 16 is in the blocking state. In this case, the blocking state of the circuit path 16 can be actively maintained by appropriate driving of the control device, for example, implemented in the DC-DC converter 20. However, diodes are installed in the DC-DC converter 20'. These generally cannot be actively switched to the blocking state. However, since the freewheeling circuit or the freewheeling path 32' actively commutes the coil current, the diodes 561 and 562 have a blocking effect, so the circuit path 16 is in the blocking state. ​

[0136] In other words, in the unidirectional design, according to Figure 6a the topology of Figure 2a a sub-form of the variant according to 3 / 4 is formed. As with the bidirectional topology of the DC-DC converter 20, the switching elements S 3 / 4 are not activated, but rather their body diodes conduct the current. In terms of cost, S 1 / 2 can be replaced by a diode D for unidirectional applications, and the converter may still operate, for example, only in CCM mode and / or DCM mode, where the coil current is dissipated until it reaches zero. Otherwise, the topologies may be the same. The control method can likewise be the same as in the normal CCM mode (or DCM mode). Starting from Figure 4a in the topology according to Figure 6a only the control signal of the switch S 3 / 4 can be ignored, where it should be noted that especially at time t7, the coil current commutates in the freewheeling path only after S FP has been turned on.

[0137] Figure 6b Shows the curves of the coil current and the gate electrode signal for the unidirectional variant according to Figure 4a the description based on Figure 6a

[0138] An advantageous improvement of the embodiments described herein lies in the possibility of restricting the switching frequency of the DC-DC converter. According to the embodiment, the control device of the DC-DC converter according to the invention is configured to extend the duration of the freewheeling interval compared to the previous freewheeling interval in order to reduce the switching frequency of the DC-DC converter over several switching cycles. The switching frequency can be coupled in the circuit here, which may result in, for example, the diode being passively switched at the same frequency as the transistor, as Figure 6c shown.

[0139] Figure 6c Shows a possible effect of the embodiment in which the control device is configured to extend the duration of the freewheeling interval compared to the previous freewheeling interval in order to reduce the switching frequency of the first and second circuit paths over several switching cycles, and / or to shorten the duration of the freewheeling interval compared to the previous freewheeling interval in order to increase the switching frequency of the first and second circuit paths.

[0140] This enables the switching frequency to be set independently of the operating point, thereby enabling different operating states. This process is possible for both actively controllable elements in a second circuit path (such as, for example, the DC-DC converter 20) and passive switching elements (such as diodes) in a second circuit path (such as, for example, the DC-DC converter 20'). Thus, in each variant, the two circuit paths can be switched at the same matching frequency. For example, if the switching elements of the second circuit path are transistors, appropriate control signals can be used to drive them at the same switching frequency as the elements of the first circuit path. On the other hand, if at least one of the elements is implemented as a diode, it automatically switches passively between the conducting and blocking states at the same frequency.

[0141] Thus, the switching period T S can be shortened to the switching period T S * , and the frequency can be increased analogously. Figure 3a and / or Figure 6b the freewheeling intervals 540, 541, and 542 shown in * can likewise be shortened to obtain the shortened freewheeling intervals 540 * , 541 * and 542 * , which also directly affects the frequency of the current curve. When the freewheeling interval and / or the switching period T S is extended, a similar result is obtained.

[0142] As an alternative, compared to the previous freewheeling interval, the control device can shorten the duration of the freewheeling interval to increase the switching frequency of the DC-DC converter. In this regard, the control device can be configured to keep the duration of the freewheeling interval constant, or to shorten or increase the freewheeling interval according to the requirements of the switching frequency and adjust it over time.

[0143] Due to the build-up time and dissipation time of the coil current in the inductance element 22, the switching frequency implemented in the DC-DC converter topology may strongly depend on the operating state. For lower output powers, the switching frequency required according to the operating state may exceed the manageable frequency response of the control system, that is, exceed them. This may lead to problems or confusion in the control logic and increase EMC (electromagnetic compatibility) problems. In addition, the losses in the inductance element and / or other switching elements may increase, which is disadvantageous. To limit the switching frequency during operation, the duration of the freewheeling interval or freewheeling step can be actively adjusted (e.g., extended) in the control system. This includes shortening it when the extension is no longer necessary or advantageous due to a change in the operating state. Extending the duration of the freewheeling interval can keep the implemented complete switching duration long enough. In a specific embodiment, the extended duration of the freewheeling interval can be flexibly allocated, adjusted, and / or added in each initially provided freewheeling step.

[0144] The following refers to the possibilities for fault detection and possible protection methods, which are obtained using the switchable freewheeling path described herein and, where applicable, in cooperation with a detection device. For this purpose, reference is made to Figure 2a and Figure 6a the circuit topologies, in particular the voltage drop u across the resistor element 44 R1 , the potential on the circuit path and and the potential and and and

[0145] The possibilities for fault detection discussed herein are partly based on the findings outlined below. The occurrence of a voltage peak as the potential u R1 can be used by the control device as an indication or signal of a fault in the circuit. The detected potential change may be the reason for the control device to switch the circuit path 14 and / or the circuit path 16 to the blocking state.

[0146] In other words, when the switching element alloyizes due to excessive temperature, the accumulated coil current will further flow into the path, so the switching element will immediately lose its blocking ability and remain in the conducting state. If the converter now continues to operate, the two DC networks are connected by the faulty switching element and another diagonally placed switching element. Then, the converter loses isolation. This fault can be referred to as a diagonal connection in the topology.

[0147] To detect this fault and protect the isolation of the converter, the detection device 42 monitors the potential change between the two DC networks. When a diagonal connection occurs, the potential difference between the two circuit paths changes suddenly. Since the voltage across the capacitor C1 cannot change suddenly, the diagonal connection causes a suddenly changing voltage across the resistor R1 as a fault detection signal.

[0148] For example, if the switching elements S1 and S4 are wrongly connected, the potentials and are short-circuited. The potentials and suddenly instantaneously jump in the negative direction, and the potentials and jump in the positive direction. At this time, there is a negative possible transient voltage u R1 (0) across R1:

[0149]

[0150] The following may apply to the voltage curve:

[0151]

[0152] In another case, if the switching elements S2 and S3 are wrongly connected, the potentials and are short-circuited. The potentials and suddenly instantaneously jump in the positive direction, and the potentials and jump in the negative direction. At the same time, there is a positive possible transient voltage across R1:

[0153]

[0154] The following may apply to the voltage curve:

[0155]

[0156] Since during normal operation during switching, the junction capacitances of the switching elements are recharged, weak interference signals in the detection device 42 may also drop across the resistive element 44 or may be recognizable. To accurately and reliably detect the fault situation, according to the embodiment, the voltage pulse across the resistive element 44 is confirmed after a time delay t V associated with the switching operation. If the absolute value of the transient voltage u R1 (t V ) is even greater than the threshold value, this may be detected as a fault. For example, the threshold value can be defined as a value of at least 50%, at least 30% or up to 20%, and relative to the theoretical maximum value Lower or higher values. The threshold value enables interference signals that are not regarded as faults during normal operation to be detected, but actual fault situations can be reliably used as trigger conditions for the countermeasures described herein.

[0157] When switching the switching element during normal operation, the time delay t V Is preferably longer than the commutation period. The commutation period during normal operation is typically in the range between 100 ns and 1000 ns and can be understood as a kind of time upper limit or worst-case limit. Since in the case of no fault, any voltage pulse will dissipate during the commutation period, a longer duration t v Can be achieved. That is, the voltage level or potential that still exists after the expected decay of the voltage during the commutation period can be interpreted as a fault. This also shows that the detection at the start of the commutation period confirmed after time t v Can achieve reliable two-stage detection, but since the commutation period has passed, the detection only after time t v May be sufficient.

[0158] According to a preferred embodiment of the present invention, the time constant τ of the RC component of the detection device 42 is configured such that at the delayed time t v The voltage u R1 That has dropped across the resistor element 44 after V (t v ) Can still be correctly detected and distinguished from noise; for example, the time constant can be configured to be three times the time delay, that is, τ = 3·t

[0159] In particular, false potential jumps may preferably occur or only at the end of the freewheeling step or when the switching element is turned on after the freewheeling step. Therefore, a non-operating switching element can be diagnosed based on the activated gate electrode signal. According to the switching sequence, this switching element should be turned off at the start of the last freewheeling step.

[0160] Figure 6d Shows an exemplary table-based representation of fault detection. For example, an optional monitoring device 53 and a control device 56 can be used for fault detection. For Figure 6a And 6b Variants, the above-described fault detection methods for CCM or DCM modes with positive coil current can be used. The deviation may be that shortly after the switching element S FP Or 332 is turned off, after a short delay, S FPShort - circuit faults in. In this case, the short delay can have a value, for example, between 50 ns and 200 ns, where, in particular, larger values are also possible, especially with respect to longer time delays, as in other embodiments. However, it is acceptable here that a corresponding interfering or disruptive current will flow. To this end, it is noted that this delay for detection (i.e., the detection delay) does not necessarily have a specific value or range, but the time delay can be determined, designed, or set according to the short - circuit capability of the switching element. Some switching elements or MOSFETs may allow short - circuits up to 1 μs, but other switching elements may allow shorter short - circuits.

[0161] Figure 6d The table in shows the relevance of the fault - detection method. In the event of a detected fault, the control device 26 can turn off the switching elements S1, S2 or 181, 182 and keep the control signal of the free - wheeling circuit on.

[0162] The embodiments related to fault detection described herein are understood to mean that the target value of the voltage drop across the monitored element has a first value in the conducting state of the free - wheeling path and a second value different from the first value in the non - conducting state. The control device can be configured to detect the fault state based on the deviation of the actual voltage drop from the first value in the conducting state and / or from the second value in the non - conducting state, which can be performed, for example, based on the binary value output by the comparator of the voltage - monitoring circuit.

[0163] Figure 7a and Figure 7b shows the fault detection when turning off the switching element S FP Here, the fault detection is triggered at the turn - off gate - electrode signal edge of the switching element S FP If the switching element S1 ( Figure 7a ) is defective, the diagonal connection will generate a negative voltage signal in the detection device 42. If the switching element S2 ( Figure 7a ) is defective, the diagonal connection will generate a positive voltage signal in the detection device 42.

[0164] To filter out the interference from the re - charging junction capacitance, it should be at the set delay time t VInternal confirmation of a fault detection signal, the delay time typically lasting from a few hundred ns to a few thousand ns. This means that the control device can be configured to detect a potential change again with a delay time of up to 800 ns, up to 500 ns or up to 200 ns and use it for checking purposes. If the fault detection signal is still active after the delay, the fault is confirmed and, simultaneously or in response thereto, the fault protection is activated. Thus, the switching elements S1, S2, S3, S4 are turned off and the switching elements in the bidirectional switch or freewheeling path are permanently turned on. The diagonal connection is thus disrupted. The other three switching elements enable continued isolation to be maintained and the energy stored in the coil 22 is released into the bidirectional switch. This phase circuit 34 of the DC / DC converter needs to be deactivated. The fault detection signal can be used to detect a fault in the switching element S1 or S2.

[0165] Thus, the voltage signal 58 that still appears after the delay time t V itself is already able to detect the presence of a fault state. The fault detection can be configured differently. During normal operation of the DC-DC converter, voltage drops may occur in the detection device 42 during the durations t2 and t5, see for example Figure 3a and Figure 4a . However, these depend on the short time periods and the commutation periods of the switching elements such that they decay after a suitably set duration t v . Thus, checking at time t4 + t v whether the corresponding potential or voltage signal 58 still exists or even exists at all can provide information indicating that the voltage signal was not triggered by normal operation but by a fault in the DC-DC converter. On the one hand, this may trigger countermeasures to achieve: switching the freewheeling path to the conducting state and / or switching the switches S1 and S2 or S1 to S4 (if they are still operational) to the off state, and on the other hand, it can also be used for fault analysis, as described in connection with Figure 11 . However, in the DC-DC converter, it is also possible that, due to normal operation, the amplitude of the voltage signal 58 is much lower than the theoretically possible level, which means that, as an alternative or in addition to taking into account the time t v , a threshold decision regarding the voltage signal 58 can also be implemented by the detection device 42 and / or the control device 26 to determine whether the detected pulse or voltage curve should be regarded as a fault, which can be applied to the rising edge and / or the falling edge and as an alternative or addition to evaluating only one or both of the two edges.

[0166] As will be explained below, taking into account the time of occurrence and taking into account the mathematical sign of the voltage signal 58, it is also possible to locate the faulty component. According to an embodiment, there is provided a DC-DC converter in which a potential change occurring in response to the driving of a switchable element to be driven (e.g., one of switches 181-184 and / or switch 331 or 332 or a switchable element to be driven in circuit path 14, circuit path 16, and / or the freewheeling path) is explicitly indicated as a defect of another element of the converter circuit.

[0167] In Figure 8a and Figure 8b by way of example, the fault detection at the turn-off of the switching element S FN is illustrated. The fault detection here is triggered at the turn-off gate electrode signal edge of the switching element S FN . If the switching element S3 ( Figure 8a ) is defective, the diagonal connection generates a positive voltage signal in the detection device 42. If the switching element S4 ( Figure 8b ) is defective, the diagonal connection generates a negative voltage signal in the detection device 42. If, according to Figure 7a - 7b and after confirming the delay t V the fault detection signal remains active, the fault is confirmed. The fault protection is immediately activated so that the switching elements S1, S2, S3, S4 are turned off and the switching elements in the bidirectional switch are permanently turned on. The fault detection signal can be used to detect a fault in the switching element S3 or S4.

[0168] Figure 9a and Figure 9b by way of example, the fault detection at the turn-on of the switching element S 3 / 4 is illustrated. The fault detection here is triggered at the turn-on gate electrode signal edge of the switching element S 3 / 4 . If the switching element S1 ( Figure 9a ) is defective, the diagonal connection generates a negative voltage signal in the detection device 42. If the switching element S2 ( Figure 9b ) is defective, the diagonal connection generates a positive voltage signal in the detection device 42. If, according to Figure 7a - 7b and Figure 8a - 8b and after confirming the delay t v the fault detection signal remains active, the fault is confirmed. The fault protection is immediately activated so that the switching elements S1, S2, S3, S4 are turned off and the switching elements in the bidirectional switch are permanently turned on. The fault detection signal can be used to detect a fault in the switching element S1 or S2.

[0169] Figure 10a and Figure 10b by way of example, the switching element S 1 / 2Fault detection upon connection. The fault detection here is triggered at the rising edge of the connection gate electrode signal of the switching element S 1 / 2 . If the switching element S3 ( Figure 10a ) is defective, the diagonal connection will generate a positive voltage signal in the detection device 42. If the switching element S4 ( Figure 10b ) is defective, the diagonal connection will generate a negative voltage signal in the detection device 42. If the fault detection signal (as described in conjunction with Figure 7a - 7b , Figure 8a - 8b and Figure 9a - 9b ) remains active after being confirmed with a delay t v , a fault is confirmed in one possible embodiment. The fault protection is immediately activated, causing the switching elements S1, S2, S3, S4 to be turned off and the switching elements in the bidirectional switch to be permanently connected. The fault detection signal can be used to detect faults in the switching elements S3 or S4.

[0170] For the unidirectional variant of the DC-DC converter described herein, the diodes D1 and D2 or 561 and 562 in the fault detection can correspond to the switching elements S3 and S4 or 183 and 184. One difference may be that the coil current here does not have a negative mathematical sign and is therefore positive or has a zero value.

[0171] Figure 11 An example of a breakdown table of decision conditions for fault detection or fault location based on the voltage signal 58 and the operating mode of the DC-DC converter and the time within the circuit period is shown. For rows 1 - 8 of the table, column 621 indicates which event triggers the voltage signal 58. In rows 1 and 2, this is the turn-off of switch S FP or 332. In rows 3 and 4, this is the turn-off of switch S FN or 331. In rows 5 and 6, this is the turn-on of the switching element S 3 / 4 , that is, the turn-on of switches 183 and 184. Rows 7 and 8 indicate the turn-on of the switching element S 1 / 2 or 181 and 182. Referring to the timing diagram in Figure 3a , rows 1 and 2 are related to time t4, rows 3 and 4 are related to time t0 or , rows 5 and 6 are related to time t5, and rows 7 and 8 are related to time t1.

[0172] Referring to column 622, each of these paired assignments in rows 1 / 2, 3 / 4, 5 / 6, and 7 / 8 is distinguished according to whether the voltage signal 58 has a negative or positive mathematical sign, that is, whether u R1 < 0 or u R1 > 0 exists.

[0173] Column 623 combines it with the detection of the mathematical sign of the coil current, and column 625 indicates the operating state TraCM, CCM, or DCM in which the DC-DC converter operates.

[0174] Column 624 indicates which switching elements should be considered defective or have failed.

[0175] Since the diagonal connection only occurs when a switching element fails, the voltage signal 58 will not be activated or recognized during normal operation. Therefore, Figure 11 the eight fault detection cases shown in the table of can be monitored simultaneously and in parallel in the control system.

[0176] Similarly, from Figure 11 the table of combined with Figure 3a it can be clearly seen that as long as it is ensured that Figure 3a the respective moments indicated in do not overlap, the converter circuits driven with phase offsets related to each other can transmit corresponding distinct signals or corresponding distinct information at different times.

[0177] For multiphase applications, the phase circuit 34 can preferably be clock-synchronized in a staggered manner. In this case, the switching operations in the phase circuit 34 are distributed in chronological order, and thus, a common detection device 42 for multiple phase circuits for fault detection is possible. In particular, the freewheeling steps or freewheeling intervals obtained using the bidirectional switches of the freewheeling paths 32 or 32' provide the possibility of adjusting the phase offset and switching frequency between multiple phases. Therefore, according to the embodiment, the provided control device switches the different phase circuits 34 of the DC-DC converter 20 or 20' individually and adjusts its switching frequency, for example, by adjusting the duration of the freewheeling interval as described herein, for example, to keep the moments related to the fault detection according to Figure 11 from intersecting with each other in time.

[0178] As an alternative or supplement, several phase circuits can be combined and monitored only in groups, or each phase circuit 34 can be coupled to its own detection device 42, which means that an alternating clock between the phase circuits 34 is no longer necessary. The detection device 42 is preferably connected to the corresponding and mutually different circuit paths 14 and 16 on both sides. If different coupling points are used instead of the illustration shown, the R1 mathematical sign of may change, which can easily be taken into account in fault detection.

[0179] Embodiments provide a DC-DC converter having fault protection measures for one or more transistors failing. These DC-DC converters connect two different DC networks and implement unidirectional or bidirectional energy transfer therebetween. Due to semiconductor-based potential isolation (pseudo-isolation), the converter achieves transformerless isolation. In particular, it can be ensured that in the case of a simple fault, the converter can maintain or sustain its isolation ability between the two DC networks. The fault detection method according to the embodiments described herein is advantageous here, and the protection measures can be used together with corresponding protection circuits.

[0180] Although some aspects have been described in connection with a device, it goes without saying that these aspects also constitute a description of the corresponding method, which means that the blocks or components of the device should also be understood as corresponding method steps or features of method steps. Similarly, aspects described in connection with method steps or as method steps also represent a description of the corresponding blocks or details or features of the corresponding device.

[0181] According to specific implementation requirements, embodiments of the present invention can be implemented in hardware or software. A digital storage medium can be used to perform this implementation, such as a floppy disk, DVD, Blu-ray disc, CD, ROM, PROM, EPROM, EEPROM or flash memory, hard disk drive or another magnetic or optical memory storing electronic readable control signals that interact with or are capable of interacting with a programmable computer system, thereby performing the corresponding method. Therefore, the digital storage medium can be computer-readable. Thus, some embodiments according to the present invention include a data carrier that contains electronic readable control signals capable of interacting with a programmable computer system, thereby performing one of the methods described herein.

[0182] Generally, embodiments of the present invention can be implemented as a computer program product including program code, where when the computer program product runs on a computer, the program code has the function of performing one of the methods. For example, the program code can also be stored on a machine-readable carrier.

[0183] Other embodiments include a computer program for performing one of the methods described herein, where the computer program is stored on a machine-readable carrier.

[0184] Therefore, in other words, an embodiment of the method according to the present invention is a computer program that includes program code for performing one of the methods described herein when the computer program runs on a computer. Thus, another embodiment of the method according to the present invention is a data carrier (or digital storage medium or computer-readable medium) on which a computer program for performing one of the methods described herein is recorded.

[0185] Accordingly, another embodiment of the method according to the present invention is a data stream or signal sequence representing a computer program for performing one of the methods described herein. The data stream or signal sequence may be configured, for example, to be transmitted via a data communication connection (e.g., over the Internet).

[0186] Another embodiment includes a processing device, such as a computer or a programmable logic component, which is configured or adapted to perform one of the methods described herein.

[0187] Another embodiment includes a computer having installed thereon a computer program for performing one of the methods described herein.

[0188] In some embodiments, a programmable logic component (e.g., a field programmable gate array, FPGA) may be used to perform some or all of the functions of the methods described herein. In some embodiments, the field programmable gate array may interact with a microprocessor to perform one of the methods described herein. Generally, in some embodiments, these methods are performed by any hardware device. This may be general-purpose hardware, such as a computer processor (CPU), or hardware specific to the method, such as an ASIC.

[0189] The above embodiments merely illustrate the principles of the present invention. It will be apparent to those skilled in the art that modifications and variations of the arrangements and details described herein are obvious. Accordingly, the intention of the present invention is to be limited only by the scope of the following claims, and not by the specific details set forth in the description and explanation of the reference embodiments herein.

Claims

1. A DC-DC converter, comprising: A converter circuit (12) including a switchable first circuit path (14) that is in an on state during a first time interval and has at least a first switchable element (181) and a second switchable element (182) connected in series therewith, and including a second circuit path (16) that is coupled to the first circuit path (14) through an inductive element (22) and is in an on state during a second time interval that does not intersect with the first time interval, wherein there is a time interval between the first time interval and the second time interval; A control device (26) configured to switch the first circuit path; A switchable freewheeling path (32; 32'), coupled in parallel with the inductive element (22), wherein the control device (26) is configured to temporarily switch the switchable freewheeling path (32; 32') to an on state during the time interval within a freewheeling interval (54).

2. The DC-DC converter according to claim 1, wherein the second circuit path (16) includes a third switchable element (183) and a fourth switchable element (184); wherein the control device (26) is configured to switch the third switchable element (183) and the fourth switchable element (184).

3. The DC-DC converter according to claim 1, wherein the freewheeling path (32; 32') is in a bidirectional conduction state in the on state and / or in a bidirectional blocking state in the non-on state.

4. The DC-DC converter according to claim 3, wherein the freewheeling path (32; 32') includes at least one switching element (33) that is in a bidirectional conduction state in the on state and in a bidirectional non-conduction state in the non-on state; or wherein the freewheeling path includes a first switching element (331) and a second switching element (332), the first switching element (331) being in a unidirectional blocking state along a first direction of the freewheeling path (32') in the non-on state; and the second switching element (332) being in a unidirectional blocking state along a second direction opposite to the freewheeling path (32') in the non-on state; wherein the first switching element (331) and the second switching element (332) are connected to each other such that the freewheeling path (32; 32') is in a blocking state in the first direction and / or the second direction in the non-on state.

5. The DC-DC converter according to claim 1, wherein the freewheeling path (32') includes a first semiconductor switch (331) and a second semiconductor switch (332) anti-serially coupled with the first semiconductor switch (331), such as adjacent drain electrode terminals or collector electrode terminals.

6. The DC-DC converter according to claim 1, wherein the control device (26) is configured to Extend the duration of the freewheeling interval (54) compared to a previous freewheeling interval (54) to reduce the switching frequency of the first circuit path (14) and optionally the switching frequency of the second circuit path (16) over several switching cycles; and / or Shorten the duration of the freewheeling interval (54) compared to the previous freewheeling interval (54) to increase the switching frequency of the first circuit path (14) and the switching frequency of the second circuit path (16).

7. The DC-DC converter according to claim 1, wherein the first switchable element and / or the second switchable element comprises a semiconductor switch.

8. The DC-DC converter according to claim 1, comprising a detection device (42) coupled to the first circuit path (14) and the second circuit path (16) and configured to detect a potential change (58) between the first circuit path (14) and the second circuit path (16); wherein the control device (26) is configured to at least partly terminate the switching of the first circuit path based on the potential change (58).

9. The DC-DC converter according to claim 8, wherein the detection device (42) comprises an RC component having a resistance element R (44) and a capacitance element C (46) and is configured to detect a voltage drop across the resistance element (44) and / or the capacitance element (46) to detect the potential change (58).

10. The DC-DC converter according to claim 9, wherein the control device (26) is configured to switch the switchable freewheeling path (32, 32') to the conducting state upon detection of a potential change (58).

11. The DC-DC converter according to claim 8, wherein the control device (26) is configured to switch the first circuit path (14) and / or the second circuit path (16) to the blocking state upon detection of a potential change (58).

12. The DC-DC converter according to claim 1, comprising a monitoring device (53) configured to monitor the voltage drop across at least part of the freewheeling path, wherein the control device (26) is configured to detect a fault state of the freewheeling path (32') based on the voltage drop; and at least partly terminate the switching of the first circuit path (14) based on the fault state.

13. The DC-DC converter according to claim 12, wherein the monitoring device is configured to compare the voltage drop across the switchable elements (331, 332) of the freewheeling path with a constant or configurable reference value to provide a comparison result and provide the comparison result to the control device to detect the fault state.

14. The DC-DC converter according to claim 12, wherein the target value of the voltage drop has a first value in the conducting state of the freewheeling path; and a second value different from the first value in the non-conducting state, wherein the control device (26) is configured to detect the fault state based on a deviation of an actual voltage drop from the first value in the on-state and / or from the second value in the off-state.

15. The DC-DC converter according to claim 1, comprising a plurality of converter circuits (12) connected in parallel; wherein the control device (26) is configured to drive the plurality of converter circuits (12) with a time offset relative to each other such that at any given time, at most one converter circuit path is switched; and wherein the detection device (42) is coupled to the plurality of converter circuits (12) to unambiguously identify a potential change (58) in each of the converter circuits (12).

16. The DC-DC converter according to claim 1, wherein the control device (26) is configured to control the DC-DC converter in at least one of a continuous conduction mode CCM, a discontinuous conduction mode DCM, a trapezoidal mode TraCM with alternating current mathematical signs, and a boundary conduction mode BCM.

17. The DC-DC converter according to claim 1, comprising a plurality of converter circuits (12) and a corresponding plurality of detection devices (42), each of the detection devices (42) being coupled to one of the plurality of converter circuits (12) to monitor it.

18. The DC-DC converter according to claim 1, wherein a potential change (58) occurring in response to driving a switchable element (181, 182) in the first circuit path, a switchable element (183, 184) of the second circuit path in the second circuit path (16), or the switchable freewheeling path (32; 32') unambiguously indicates that another element of the converter circuit (12) is a defective element.

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