Dc-dc converter and method for operating a dc-dc converter

Abstract

The invention relates to a DC-DC converter and to a method for operating a DC-DC converter, wherein rectification on the output side can be effected alternatively by means of a diode or a clocked switching element. According to the invention, a rapidly operating processing device is provided, which can adapt a controlled variable in the DC-DC converter according to the control of the switching element in order to compensate for the voltage drop across the diode or the switching element.

Description

[0001] Description

[0002] title

[0003] DC-DC converter and method for operating a DC-DC converter

[0004] Technical area

[0005] The present invention relates to a DC-DC converter and a method for operating a DC-DC converter.

[0006] background

[0007] DC-DC converters are used to convert one electrical direct voltage into another. A DC-DC converter can convert a DC voltage supplied at one input into another DC voltage whose magnitude is greater or less than the voltage at the input.

[0008] In addition, so-called galvanic isolating DC-DC converters are known, which can realize a galvanic isolation between electrical voltage at the input and electrical voltage at the output, for example by means of a transformer.

[0009] The document DE 20 2012 009 919 Ul, for example, describes a DC-DC converter in the form of a flyback DC-DC converter with a transformer for galvanic isolation between the input terminal and the output terminal.

[0010] Disclosure of the invention

[0011] The present invention provides a DC-DC converter and a method for operating a DC-DC converter having the features of the independent patent claims. Further advantageous embodiments are the subject of the dependent patent claims. Accordingly, it is provided:

[0012] A DC-DC converter with an input terminal, an output terminal, a transformer, a control circuit, a parallel circuit comprising a diode and a switching element, and a control device. The input terminal can be designed to be connected to a DC voltage source. The output terminal can be designed to be coupled to a DC voltage consumer or a DC voltage network. The transformer comprises a primary side, or a primary-side winding, and a secondary side, or a secondary-side winding. The control circuit is arranged between the input terminal and the primary side of the transformer. The parallel circuit comprising a diode and a switching element is arranged between a connection point of the secondary side of the transformer and a connection point of an output terminal. The switching element can in particular be a semiconductor switching element.The control device is designed to control the control circuit. In particular, the control circuit can be controlled using a controlled variable with a predetermined duty cycle. The control device further comprises a processing device. The processing device is designed to control the switching element between the transformer and the output terminal in a clocked manner in a first operating mode. Alternatively, the control circuit can not control the switching element in a second operating mode, so that the switching element is continuously open. The processing device is further designed to adapt the duty cycle for the controlled variable depending on the respective operating mode.

[0013] Furthermore, it is planned:

[0014] A method for operating a DC-DC converter. The DC-DC converter has a control circuit between an input terminal and a primary side of a transformer. Furthermore, the DC-DC converter has a parallel circuit consisting of a diode and a switching element between a secondary side of the transformer and an output terminal. The control circuit is designed to be controlled using a controlled variable with a predetermined duty cycle. In a first operating mode, the switching element between the secondary side of the transformer and the output terminal can be controlled in a clocked manner. Alternatively, in a second operating mode, the switching element between the secondary side of the transformer and the output terminal can be continuously open.The method for operating the DC-DC converter can adjust the duty cycle for the controlled variable for controlling the DC-DC converter depending on the respective operating mode. The adjustment can be carried out, in particular, by means of a processing device.

[0015] Advantages of the invention

[0016] In DC-DC converters, such as galvanically isolated bidirectional flyback DC-DC converters, a parallel circuit consisting of a diode and a switching element can be provided on the output side between a transformer and an output terminal instead of a pure rectifier diode. This switching element can be controlled in a clocked manner at sufficiently high currents. However, to prevent unwanted inverse energy flow at low currents, such a switching element is generally not clocked at low currents. This creates a relatively high voltage drop across the diode, for example, approximately 0.7 V. This voltage drop must be compensated by regulating the DC-DC converter.

[0017] Depending on the control speed in the DC-DC converter, short-term currents in the output voltage occur when switching between the clocked control and the continuous opening of the switching element.

[0018] It is therefore an idea of ​​the present invention to take this finding into account and to provide a concept for an optimized control of such a DC-DC converter, which eliminates or at least significantly reduces the voltage fluctuations when changing between the operating modes described above.

[0019] To this end, the invention provides for a processing device in the control device of the DC-DC converter that can very quickly detect a change between the operating mode for the clocked activation of the switching element and the operating mode for the continuous opening of the switching element and then quickly adjusts a controlled variable in the DC-DC converter to compensate for voltage fluctuations in the output voltage. For example, the adjustment of the controlled variable in the DC-DC converter can be performed by the processing device, which also controls the activation of the output-side switching element.

[0020] With such a concept, when the operating mode changes between the clocked activation of the output-side switching element and the continuous opening of this switching element, the voltage drop across the diode arranged in parallel with the switching element can be compensated much faster than would be the case with a much slower reacting control loop based on the measured output voltage.

[0021] According to one embodiment, the processing device is designed to set the first operating mode or the second operating mode depending on an output current at the output terminal. For example, if the output current is below a predetermined threshold, the second operating mode can be set, thus allowing the switching element to remain permanently open. If the output current exceeds the predetermined threshold, the first operating mode can be set, thus allowing the switching element to be controlled in a clocked manner.

[0022] If necessary, a hysteresis for the output current switching threshold can be provided for switching between the first and second operating modes. This can prevent an inverse energy flow in the DC-DC converter at low output currents.

[0023] According to one embodiment, the processing device comprises a fast-operating processing unit. Such a fast-operating processing unit can, for example, comprise a multi-channel sequencer (MCS). This allows for particularly rapid response to changes in operating mode, and the controlled variable of the DC-DC converter can be adjusted quickly. This can reduce voltage fluctuations or disturbances in the output voltage.

[0024] According to one embodiment, the processing device is designed to adapt the duty cycle for the controlled variable in the second operating mode using a voltage drop across the diode between the transformer and the output terminal. If the voltage drop across the diode is known, the correspondingly higher voltage drop for the second operating mode can be adapted accordingly when adapting the controlled variable for controlling the DC-DC converter. In particular, a difference between the voltage drop across the diode when the switching element is open and a voltage drop across the switching element in the closed state can be taken into account when adapting the controlled variable.

[0025] According to one embodiment, the control device is designed to determine the duty cycle for the controlled variable for controlling the DC-DC converter using a setpoint value for the output voltage of the DC-DC converter, a measured value for the output voltage of the DC-DC converter, a setpoint current in the DC-DC converter, and / or a current current value of the DC-DC converter. This controlled variable or the duty cycle can be determined, in particular, at a first update rate. Furthermore, the processing device can be designed to adapt the determined duty cycle for the controlled variable for controlling the DC-DC converter at a second update rate. The second update rate can be higher or greater than the first update rate.In other words, the processing in the processing device takes place at a significantly higher or greater processing speed than the determination of the controlled variable in the control device.

[0026] According to one embodiment, the processing device is designed to detect an input voltage at the input terminal of the DC-DC converter. Furthermore, the processing device can be designed to adjust the duty cycle for the controlled variable using the sampled input voltage. In this way, rapid voltage fluctuations in the input voltage, such as voltage ripples or similar, can be well compensated and, if necessary, almost completely compensated for by the fast processing in the processing device.

[0027] According to one embodiment, the DC-DC converter is designed as a galvanically isolated flyback DC-DC converter. Accordingly, the inventive concept can further stabilize the output voltage. According to one embodiment, the DC-DC converter is designed as a bidirectional DC-DC converter. Such a voltage converter is capable of transmitting electrical energy in the opposite direction, from the terminal designated as the output terminal to the terminal designated as the input terminal, in addition to voltage conversion in the inventive operating mode.

[0028] The above embodiments and further developments can be combined with one another as desired, where appropriate. Further embodiments, further developments, and implementations of the invention also include combinations of features of the invention not explicitly mentioned above or described below with respect to the exemplary embodiments. In particular, those skilled in the art will also add individual aspects as improvements or additions to the respective basic forms of the invention.

[0029] Short description of the drawings

[0030] Further features and advantages of the invention are explained below with reference to the figures.

[0031] Fig. 1: a schematic representation of a DC-DC converter according to a

[0032] embodiment;

[0033] Fig. 2: a schematic representation of a block diagram illustrating a control device for a DC-DC converter according to an embodiment; and

[0034] Fig. 3: a flow chart of a method for operating a

[0035] DC-DC converter according to one embodiment.

[0036] Description of embodiments

[0037] Figure 1 shows a schematic representation of a DC-DC converter 1 according to one embodiment. The DC-DC converter 1 can, for example, be a DC-DC converter implemented in the form of a so-called flyback DC-DC converter, in particular an isolating or galvanically isolating flyback DC-DC converter.

[0038] The DC-DC converter 1 comprises an input terminal 11 and an output terminal 12. For example, any DC voltage source (not shown) can be connected to the input terminal 11. On the output side, a DC voltage network or any DC voltage consumer can be connected. For example, the DC-DC converter 1 can convert an electrical DC voltage U_in provided at the input terminal 11 into another, for example, higher DC voltage U_out and provide this at the output terminal 12.

[0039] The DC-DC converter 1 further comprises a transformer 20. The transformer 20 has at least one primary-side winding 21 and one secondary-side winding 22.

[0040] The primary-side winding 21 is electrically coupled to the input terminal 11. A drive circuit 30 is provided between the primary-side winding 21 and the input terminal 11. This drive circuit 30 can be controlled, for example, by a control device 50. In particular, the drive circuit 30 can be controlled by the control device 50 with a drive signal according to a predetermined duty cycle. In addition to the embodiment shown in Figure 1 with two inductors and switching elements, the circuit concept of the drive circuit 30 can also be implemented differently if necessary.As is usual with flyback DC-DC converters, the control circuit 30 of the flyback DC-DC converter 1 is preferably designed such that a clocked switch, preferably a transistor or thyristor, is switched by means of the control device 50 with the control signal according to the predetermined duty cycle in order to convert a DC voltage applied to the input terminal 11 into an AC voltage applied to the primary-side winding 21.

[0041] The DC-DC converter 1 further comprises a rectifier circuit 40 between the secondary-side winding 22 and the output terminal 12. The rectifier circuit 40 is, as shown in Figure 1, implemented as a parallel circuit of a switching element 41 and a diode 42. This parallel circuit of the switching element 41 and the diode 42 is provided between a connection point of the secondary-side winding 22 and a connection point of the output terminal 12. The switching element 41 can be implemented, for example, as a semiconductor switching element in the form of a transistor, for example a MOSFET. Preferably, the parallel circuit of the switching element 41 and the diode 42 can be implemented in the form of a transistor with a body diode. Preferably, a first capacitor is connected between the two connection points of the output terminal 12 to smooth the applied DC voltage.

[0042] At a low output current at the output terminal 12, the switching element 41 can be continuously open. In this way, an inverse energy flow can be prevented. At higher output currents, the switching element 41 can be controlled in a clocked manner. In particular, the switching element 41 can be controlled at a frequency corresponding to the control of the control circuit 30. The clocked closing of the switching element 41 reduces the voltage drop across the parallel circuit comprising diode 42 and switching element 41 and thus the power loss occurring across this parallel circuit. At the same time, the output voltage U_out also increases in accordance with the reduced voltage drop if the control circuit 30 is controlled unchanged on the primary side.

[0043] For example, if the output current is above a predetermined threshold in a first operating mode, the switching element 41 can be controlled in a clocked manner, and if the output current is below a threshold in a second operating mode, the switching element 41 can be continuously open. If necessary, a hysteresis can be provided for the threshold of the output current between the changes between the two operating modes.

[0044] The switching element 41 can be controlled, for example, by a processing device 51 in the control device 30. Thus, the state of the switching element 41 and the associated operating state are always known in this processing device 51.

[0045] To compensate for the different voltage drops across the parallel circuit of diode 42 and switching element 41, the processing device 51 can adapt a controlled variable or a duty cycle of this controlled variable to control the control circuit 30 accordingly. For this purpose, for example, the controlled variable or the duty cycle can be adapted according to the voltage drop across diode 42 when switching element 41 is continuously opened in the second operating mode. If the system switches from the second operating mode back to the first operating mode, in which switching element 41 is controlled, the adaptation of the controlled variable or the duty cycle to compensate for the voltage drop across diode 42 can be omitted. Of course, any other suitable concepts for adapting the controlled variable or the duty cycle according to a change between the operating modes are also possible.

[0046] Figure 2 shows a schematic representation of a block diagram for explaining the concept of a control device 50 for a DC-DC converter 1 according to an embodiment.

[0047] For example, a voltage regulator 52 can be provided in the control device 50. This voltage regulator 52 can initially generate a first controlled variable. This first controlled variable can be generated, for example, based on a measured output voltage U_out of the DC-DC converter 1 and a predetermined setpoint U_setpoint for the DC-DC converter 1.

[0048] Furthermore, a current regulator 53 can be provided in the control device 50. This current regulator 53 can, for example, regulate or limit an electrical current in the DC-DC converter 1. To this end, the current regulator 53 can, for example, compare a detected electrical current in the DC-DC converter 1 with a target value and, if necessary, generate a second controlled variable. This second controlled variable can be superimposed on the first controlled variable by the voltage regulator 52. In this way, when the current regulator 53 is active, the voltage regulation can be modified, for example, to prevent excessive currents in the DC-DC converter 1.

[0049] Furthermore, a pilot control device 54 can be provided in the control device 50. This pilot control device 54 can generate a further controlled variable based on a setpoint U_setpoint for the output voltage and a measured input voltage U_in. This can, for example, provide an initial controlled variable so that the previously described voltage regulation only needs to regulate the remaining stabilization of the output voltage. Accordingly, the controlled variable from the pilot control device 54 and the first controlled variable from the voltage regulator 52 can be superimposed here as well.

[0050] The pilot control device 54 can detect the input voltage U_in at a relatively low sampling rate. Low-pass filtering or smoothing of the input voltage U_in can also be provided if necessary.

[0051] Furthermore, in the processing device 51 described above, the input voltage U_in can optionally be sampled at a relatively high sampling rate, for example, in the range of 10 kHz or more. This allows even rapid changes in the input voltage U_in, such as so-called voltage ripples or the like, to be detected. The processing device 51 can then adjust the controlled variable or the duty cycle for controlling the control circuit 30 according to the identified higher-frequency voltage fluctuations in the input voltage U_in. This allows further stabilization of the output voltage U_in.

[0052] Since the processing speed of the processing device 51 is significantly higher than the processing speed of the other components such as voltage regulator 52, current regulator 53 and / or pilot control device 54, the rapid adaptation of the controlled variable in the processing device 51 allows both the voltage fluctuations due to the high-frequency voltage components in the input voltage U_in and the variations when changing between the first operating mode and the second operating mode and the associated voltage drop at the parallel connection of switching element 41 and diode 42 to be compensated very quickly.

[0053] For example, the processing device 51 can be implemented by a fast-operating processing unit, such as a multi-channel sequencer. Of course, any other suitable fast-operating processing units are also possible.

[0054] Figure 3 shows a schematic representation of a flowchart underlying a method for operating a DC-DC converter 1 according to one embodiment. The method can be applied in particular to a previously described DC-DC converter 1. Therefore, all embodiments already described in connection with Figures 1 and 2 also apply to the method described below. Likewise, the previously described DC-DC converter 1 can comprise any components that may be required to implement the method described below.

[0055] The method for operating a DC-DC converter 1 can, for example, be applied to a DC-DC converter with the previously described circuit topology, in particular a parallel circuit comprising a diode 42 and a switching element 41 between the secondary side 22 of the transformer 20 and the output terminal 12. In the method, the control circuit 30 is controlled using a controlled variable with a predetermined duty cycle. In a first operating mode S 1 , the switching element 41 between the secondary side 22 of the transformer 20 and the output terminal is controlled in a clocked manner. In a second operating mode S 2 , the switching element 41 between the secondary side of the transformer and the output terminal is continuously open. Furthermore, in the method, the duty cycle for the controlled variable for controlling the DC-DC converter is adapted as a function of the respective operating mode by means of a processing device 51.For example, in a step S 2a, the controlled variable or the duty cycle can be adjusted in order to compensate for this voltage drop when the switching element 41 is continuously open.

[0056] In summary, the present invention relates to a DC-DC converter and a method for operating a DC-DC converter, wherein output-side rectification can be achieved alternatively using a diode or a clocked switching element. A fast-operating processing device is provided, which can adjust a controlled variable in the DC-DC converter according to the control of the switching element in order to compensate for the voltage drop across the diode or the switching element.

Claims

Claims 1. DC-DC converter (1), comprising: an input terminal (11); an output terminal (12); a transformer (20) having a primary side (21) and a secondary side (22); a drive circuit (30) arranged between the input terminal (11) and the primary side (21) of the transformer (22); a parallel circuit comprising a diode (42) and a switching element (41), arranged between a connection point of the secondary side (22) of the transformer (20) and a connection point of an output terminal (12);and a control device (50) which is designed to control the control circuit (30) using a controlled variable with a predetermined duty cycle, wherein the control device (50) comprises a processing device (51) which is designed to control the switching element (41) between the transformer (20) and the output terminal (12) in a clocked manner in a first operating mode and not to control the switching element (41) in a second operating mode, and wherein the processing device (51) is designed to adapt the duty cycle for the controlled variable depending on the respective operating mode.; 2. DC-DC converter (1) according to claim 1, wherein the processing device (51) is designed to set the first operating mode or the second operating mode as a function of an output current at the output terminal (12).

3. DC-DC converter (1) according to claim 1 or 2, wherein the processing device (51) comprises a fast-operating computing unit, in particular a multi-channel sequencer.

4. DC-DC converter (1) according to one of claims 1 to 3, wherein the processing device (51) is designed to adapt the duty cycle for the controlled variable in the second operating mode using a voltage drop across the diode (42) between the transformer (20) and the output terminal (12).

5. DC-DC converter (1) according to one of claims 1 to 4, wherein the control device (50) is designed to determine the duty cycle for the controlled variable for controlling the DC-DC converter (1) using a setpoint value (U_setpoint) for the output voltage of the DC-DC converter (1), a measured value (U_out) for the output voltage of the DC-DC converter (1), a current setpoint value and / or a current current value of the DC-DC converter (1) at a first update rate, and wherein the processing device (51) is designed to adapt the determined duty cycle for the controlled variable for controlling the DC-DC converter (1) at a second update rate, wherein the second update rate is higher than the first update rate.

6. DC-DC converter (1) according to claim 5, wherein the processing device (51) is designed to detect an input voltage (U_in) at the input terminal (11) of the DC-DC converter (1) and to adapt the duty cycle for the controlled variable using the sampled input voltage (U_in).

7. DC-DC converter (1) according to one of claims 1 to 6, wherein the DC-DC converter (1) is designed as a galvanically isolating flyback DC-DC converter.

8. DC-DC converter (1) according to one of claims 1 to 7, wherein the DC-DC converter (1) is designed as a bidirectional DC-DC converter.

9. A method for operating a DC-DC converter (1), wherein the DC-DC converter (1) has a control circuit (30) between an input terminal (11) and a primary side (21) of a transformer (20), and a parallel circuit comprising a diode (42) and a switching element (41) is provided between a secondary side (22) of the transformer (20) and an output terminal (12), wherein the control circuit (30) is designed to be controlled using a controlled variable with a predetermined duty cycle, wherein in the method, in a first operating mode (S 1), the switching element (41) between the secondary side (22) of the transformer (20) and the output terminal (12) is controlled in a clocked manner, and in a second operating mode (S 2), the switching element (41) between the secondary side (22) of the transformer (20) and the output terminal (12) is open,and wherein in the method the duty cycle for the controlled variable for controlling the DC-DC converter (1) is adapted (S 2a) as a function of the respective operating mode by means of a processing device (51).

10. The method according to claim 9, wherein the adjustment (S 2a) of the duty cycle for the controlled variable is carried out as a function of the respective operating mode at a processing speed that is faster than a processing speed for determining the controlled variable with the duty cycle for controlling the control circuit.

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