DC voltage converter and method for operating a DC voltage converter

Abstract

A DC voltage converter and a method for operating a DC voltage converter. According to the invention, a correction variable which specifies a difference between the actual component values and idealized component values in the DC voltage converter is determined. For the determination of this correction variable, a predefined operating point can be set and subsequently this operating point can be modified until the DC voltage converter reaches the operating conditions which correspond to an expected value for the predetermined operating point.

Description

[0001] R. 416180

[0002] - 1 -

[0003] Description

[0004] title

[0005] DC-DC converter and method for operating a DC-DC converter

[0006] Technical field

[0007] The present invention relates to a DC-DC converter and a method for operating such a DC-DC converter. In particular, the present invention relates to an optimization of control parameters for a DC-DC converter.

[0008] background

[0009] DC-DC converters are capable of converting a DC voltage supplied at an input terminal into another DC voltage, possibly with a different voltage level, and supplying this at an output terminal. Furthermore, bidirectional DC-DC converters are known, which can transfer electrical power between two DC terminals in both directions. In particular, so-called galvanically isolated DC-DC converters are known, in which the two DC terminals are galvanically isolated from each other, for example, by means of a transformer or similar device.

[0010] Such DC-DC converters, especially galvanically isolated DC-DC converters, can be used, for example, to exchange electrical energy between a high-voltage network and a low-voltage network in an electric vehicle. Furthermore, DC-DC converters in an electric vehicle can also be used to convert a DC voltage supplied by an external energy source into a DC voltage. R. 416180

[0011] - 2 - convert, which is suitable for charging the internal energy storage, for example the traction battery of the electric vehicle

[0012] For example, the publication DE 10 2014 210 283 A1 describes a method for operating a vehicle electrical system with at least two voltage levels, which have different nominal voltages.

[0013] Disclosure of the invention

[0014] The present invention provides a DC-DC converter and a method for operating a DC-DC converter with the features of the independent claims. Further advantageous embodiments are the subject of the dependent claims.

[0015] Accordingly, the following is planned:

[0016] A method for operating a DC-DC converter, in particular a galvanically isolated DC-DC converter with a transformer. The method comprises a step for setting a predetermined operating point in the DC-DC converter. The predetermined operating point can be set, in particular, using initial control parameters. Furthermore, the method comprises a step for sensing an initial power output of the DC-DC converter at the set predetermined operating point. The method further comprises a step for comparing the sensed initial power output with an expected value for the power output at the predetermined operating point. Finally, the method comprises a step for adjusting the power output of the DC-DC converter to the expected value for the power output at the predetermined operating point.The transmission power can be regulated, in particular, by adjusting the control parameters. The procedure then includes a step to determine a correction value. The correction value can be determined by comparing the adjusted control parameters after the transmission power has been regulated to the expected value with the initial control parameters. Finally, the procedure includes step R. 416180.

[0017] - 3 - to control the DC voltage converter using the determined correction value.

[0018] Furthermore, the following is planned:

[0019] A DC-DC converter comprising a first DC input, a second DC input, a transformer, a first bridge circuit, a second bridge circuit, and a control unit. The first bridge circuit is arranged between the first DC input and a primary side of the transformer. The second bridge circuit is arranged between the second DC input and a secondary side of the transformer. The control unit is designed to execute the method according to the invention.

[0020] Advantages of the invention

[0021] The present invention is based on the understanding that the components used in electronic assemblies, and thus also in DC-DC converters, typically exhibit component tolerances in reality. Therefore, the actual component properties generally do not correspond exactly to the theoretical values ​​intended during the design and modeling of such an assembly. If, for example, the DC-DC converter is controlled based on idealized component values, the effects occurring in the actual DC-DC converter, such as voltage or current waveforms, may deviate, at least slightly, from the ideal theoretical values.

[0022] For example, if switching operations of a semiconductor switching element are to be carried out during such a control, it may be desirable to preferably perform the switching operation at a voltage zero crossing or with the lowest possible electrical current flow. If the actual values ​​of components deviate from the values ​​underlying a control model, then R. 416180

[0023] - 4 - these or similar framework conditions may not be precisely adhered to. In conventional systems, therefore, a sufficient safety margin must be provided, for example, for the power to be switched, the power loss that will occur, or similar factors. This can lead to increased effort, higher costs, and greater requirements for the necessary installation space.

[0024] Based on this understanding, the present invention provides a concept that allows component tolerances in an electronic assembly such as a DC-DC converter to be taken into account. In particular, a concept is provided that enables parameter calibration to optimize the control in a DC-DC converter. This allows for improved control of the DC-DC converter. Specifically, the switching points of switching semiconductor switching elements can be adjusted to minimize losses occurring during switching operations, for example.

[0025] According to one embodiment, the initial control parameters for setting the predetermined operating point are determined using a model. In particular, this model can be determined based on tolerance-free values ​​for the components. Alternatively, the initial control parameters can, for example, be determined in advance and made available by means of a storage device or similar.

[0026] According to one embodiment, the predetermined operating point includes an operating point at which no electrical power is transferred through the DC-DC converter. Such an operating point, at which the switching elements of the DC-DC converter are controlled in such a way that no electrical power is transferred between the two DC terminals, is particularly well suited for determining any deviations that may exist between the actual component values ​​and the idealized values. R. 416180

[0027] - 5 -

[0028] According to one embodiment, the correction factor can be determined using at least two different operating points. For example, the two operating points can relate to different power transfers between the two DC terminals. Thus, for instance, in a bidirectional DC-DC converter, a first operating point can be selected at which electrical power is transferred in one direction. At a second, different operating point, electrical power can be transferred in the opposite direction. In addition to or as an alternative to one of the aforementioned operating points, the previously mentioned operating point at which no electrical power is exchanged between the two DC terminals is also possible.

[0029] According to one embodiment, the determined correction factor includes a correction factor for the turns ratio of a transformer provided in the DC-DC converter. By adjusting such a correction factor with respect to the turns ratio of the transformer, further component tolerances that influence the turns ratio between the two DC terminals can also be covered or taken into account. According to one embodiment, during operation of the DC-DC converter, particularly at the predetermined operating point, switching elements in bridge circuits of the DC-DC converter are controlled by pulse-width modulation. During this control of the DC-DC converter, a control angle can be applied to the switching elements in the bridge circuits using pulse-width modulation.In particular, the determined correction value can be incorporated when adjusting the control angle for pulse width modulated control.

[0030] According to one embodiment, an extended dead time is provided during the actuation phase for setting the predetermined operating point and / or during the adjustment of the transmission power to the expected value at at least one commutation in a half-bridge in one of the bridge circuits. By applying an extended dead time R. 416180

[0031] - 6 - during commutation, for example, it can be achieved that within this dead time electrical currents drop so low that a switching operation can be realized at zero voltage or in the range of zero voltage (this is called Zero Voltage Switching - ZVS).

[0032] According to one embodiment, the method can be executed during the initialization of the DC-DC converter. In particular, the method can be executed during a restart of the DC-DC converter. In this way, a new, suitable correction parameter can be determined during each such initialization or restart. This allows, for example, aging effects or similar factors to be taken into account.

[0033] According to one embodiment, the method can be executed regularly, that is, at regular intervals. Additionally or alternatively, it is also possible to execute the method after detecting a predetermined event, such as a temperature change or similar phenomenon. In this way, fluctuating operating conditions during the operation of the DC-DC converter can also be taken into account. In particular, component fluctuations resulting from such fluctuating operating conditions can also be considered.

[0034] The above embodiments and further developments can be combined with one another as appropriate. Further embodiments, further developments, and implementations of the invention also include combinations of features of the invention described previously or subsequently with regard to the exemplary embodiments, even if not explicitly mentioned. In particular, those skilled in the art will also add individual aspects as improvements or additions to the respective basic forms of the invention.

[0035] Brief description of the drawings

[0036] Further features and advantages of the invention are explained below with reference to the figures. Figure 416180 shows:

[0037] - 7 -

[0038] Fig. 1 : a schematic representation of a basic circuit diagram of a DC-DC converter according to one embodiment;

[0039] Fig. 2: a diagram illustrating the control concept in a DC voltage connection according to one embodiment;

[0040] Fig. 3: shows a flowchart as it may form the basis of a method for operating a DC voltage converter according to one embodiment.

[0041] Description of embodiments

[0042] Figure 1 shows a schematic representation of a basic circuit diagram of a DC voltage converter 1 according to one embodiment.

[0043] Although the present invention is described below by way of example based on one possible topology, the basic principle of the invention is not limited to this. Rather, this principle can also be applied to other suitable scenarios or topologies, independent of the technology. For example, instead of the full bridges described below, half bridges, in particular so-called stacked half-bridges, can also be provided as bridge circuits 30, 40, in order to implement functionalities such as inverters or rectifiers. Furthermore, a circuit arrangement can also be provided which, particularly at higher frequencies, is also operated at a resonant frequency and thus as one of the resonant circuit topologies. It is understood that the basic principle described below can also be transferred to any other suitable topology.

[0044] The DC-DC converter 1 comprises a first DC terminal 11, a second DC terminal 12, a transformer 20, a first bridge circuit 30, and a second bridge circuit 40. The first DC terminal 11 and the second DC terminal 12 can each have a positive and a negative terminal. DC networks, for example, can be connected to the two DC terminals 11 and 12. R. 416180

[0045] - 8 -

[0046] The transformer 20 comprises at least one primary side 21 and one secondary side 22. This transformer 20 provides galvanic isolation between the first DC voltage terminal 11 and the second DC voltage terminal 12. The first bridge circuit 30 is arranged between the first DC voltage terminal 11 and the primary side 21 of the transformer 20. Similarly, the second bridge circuit 40 is arranged between the secondary side 22 of the transformer 20 and the second DC voltage terminal 12.

[0047] The first bridge circuit 30 comprises two half-bridges 31 and 32. Each half-bridge 31 and 32 comprises two switching elements 31a and 31b, respectively, arranged in series. The two outer terminals of the two half-bridges 31 and 32 are connected to the corresponding terminals of the first DC input 11. The two connection points where the two switching elements 31a and 31b, respectively, are connected to each other are coupled to corresponding terminals on the primary side 21 of the transformer 20. A resonant element, for example a capacitor C1, can be provided between the connection points of the switching elements 31a and 31b, respectively, and the primary side 21 of the transformer 20.

[0048] The second bridge circuit 40 between the secondary side 22 of the transformer 20 and the second DC voltage terminal 12 is constructed analogously to the first bridge circuit 30. Accordingly, the first half-bridge 41 comprises two semiconductor switching elements 41a and 41b arranged in series. A connection point between the two semiconductor switching elements 41a and 41b is coupled to a terminal point of the secondary side 22 of the transformer 20.

[0049] Similarly, the second half-bridge 42 of the second bridge circuit 40 also comprises two semiconductor switching elements 42a and 42b arranged in series. A connection point between the two semiconductor switching elements 42a and 42b is coupled to another connection point on the secondary side 22 of the transformer 20. The two outer connections of the half-bridges 41 and 42 of R. 416180

[0050] - 9 - the second bridge circuit 40 are connected to corresponding connection points of the second DC voltage connection 12.

[0051] Between the secondary side 22 of the transformer and the second bridge circuit 40, another resonant element, for example a capacitor C2, can be provided.

[0052] Furthermore, a control unit 50 may be provided. This control unit 50 can generate the control signals for closing or opening the semiconductor switching elements 31a, 31b, 32a, 32b, 41a, 41b, 42a and 42b and make them available at the corresponding switching elements.

[0053] By appropriately controlling the switching elements in the first bridge circuit 30 and the second bridge circuit 40, the energy transfer between the first DC voltage terminal 11 and the second DC voltage terminal 12 can be controlled. In particular, pulse-width modulated control can be provided for this purpose. In this case, the switching elements of the two bridge circuits 30 and 40 are controlled based on the same frequency for the pulse-width modulated control.

[0054] Figure 2 shows a schematic representation of a diagram illustrating the timing relationships for controlling the switching elements in the first bridge circuit 30 and the second bridge circuit 40. The upper diagram shows the voltage waveform between the two connection points of the switching elements in the first bridge circuit 30. If, in the two half-bridges 31 and 32, the two upper switching elements 31a and 32a are closed and the two lower switching elements 31b and 32b are open, or if the two upper switching elements 31a and 32a are open and the two lower switching elements 31b and 32b are closed, the voltage between the two connection points is at least approximately 0 volts. However, if, in the first half-bridge 31, the upper switching element 31a is open and the lower switching element 31b is closed, while in the second half-bridge 32, the upper switching element 32a is closed and the lower switching element R is closed, the voltage between the two connection points is approximately 0 volts.416180.

[0055] - 10 -

[0056] When 32b is open, a positive voltage is generated between the connection points, which corresponds approximately to the DC voltage at the first DC terminal 11. With a reversed circuit configuration of the two half-bridges 31 and 32, a negative voltage is generated between the two connection points, the magnitude of which also corresponds approximately to the DC voltage at the first DC terminal 11. With periodic control, a positive and a negative voltage pulse alternate with a time interval corresponding to the period T. The width of the voltage pulses is characterized by the parameter Alpha.

[0057] The corresponding curve for the second bridge circuit 40 is shown in the diagram below. The pulse width in the second bridge circuit 40 is characterized by the parameter Beta. The time offset between the pulses in the first bridge circuit 30 and the pulses in the second bridge circuit 40 is specified by the parameter Delta.

[0058] The output voltage level, the electrical power to be transferred, and the direction of energy transfer can all be adjusted by appropriately setting the parameters alpha, beta, and delta. Since the basic control principle for selecting these parameters is considered well-known, it will not be explained in detail here.

[0059] For the control of the switching elements 31a, 31b, 32a, 32b, 41a, 41b, 42a, 42b in the first bridge circuit 30 and the second bridge circuit 40 as described above, two switching states are possible for each of the half-bridges 31, 32, 41, 42. In the first switching state, the upper switching element 31a, 32a, 41a, or 42a is closed, and the corresponding lower switching element 31b, 32b, 41b, 42b is open. Alternatively, the upper switching elements 31a, 32a, 41a, 42a can be open, and the corresponding lower switching elements 31b, 32b, 41b, 42b can be closed. To prevent a possible short circuit between the connection points of the corresponding resistor R416180 during a change between these two switching states,

[0060] - 11 -

[0061] To avoid interference at DC terminal 11 or 12, a so-called dead time is provided for each switch. During this dead time, both switching elements of the corresponding half-bridge 31, 32, 41, 42 are open. In other words, when switching between the two switching states, the closed switching element is opened first, and after a predetermined dead time, the other switching element is then closed.

[0062] For controlling the switching elements 31a to 42b in the bridge circuits 30 and 40, the corresponding control signals are generally generated in the DC-DC converter 1 assuming idealized values ​​for the components used. In practice, however, these idealized values ​​cannot be precisely maintained due to manufacturing tolerances, aging effects, and fluctuations in operating conditions such as temperature changes. This can lead to deviations between the modeled behavior assumed for generating the control signals and the actual voltage and current conditions. Therefore, a method is described below by which these variations in component properties can be at least partially compensated.

[0063] During such a calibration process, an operating point can first be set which, assuming idealized properties of the components in the DC-DC converter 1, establishes a specific operating state, for example, realizing a predetermined energy transfer between the first DC terminal 11 and the second DC terminal 12. Alternatively, an operating point can be set in the DC-DC converter 1 at which, assuming idealized components, no energy transfer occurs between the first DC terminal 11 and the second DC terminal 12. For this purpose, the phase angles alpha and beta, as well as the parameter delta for the pulse-width modulated control of the switching elements 31a to 42b, can be adjusted accordingly. R. 416180

[0064] - 12 -

[0065] The energy flow through the DC-DC converter 1 can then be measured, for example, using suitable sensor data such as current and voltage measurements. If the actual energy flow deviates from the desired target value based on these measurements, this could be due, for example, to a discrepancy between the actual values ​​of the components in the DC-DC converter 1 and the assumed idealized values.

[0066] The control signal in the DC-DC converter 1 can then be adjusted within a control system such that the desired energy flow is actually achieved, for example, no energy transfer between the first DC terminal 11 and the second DC terminal 12. Once this control objective is reached, and especially once it is stably achieved, a deviation can be determined from the discrepancy between the control parameters used to actually realize the desired operating state and the originally assumed parameters, assuming idealized components. Based on this deviation, a correction parameter, in particular a correction factor, can then be determined.For example, such a correction factor can relate to a deviation between the idealized assumed transfer ratio of a transformer 20 in the DC-DC converter 1 and the actual transfer ratio required based on the control system to achieve the desired operating ratio. Thus, by integrating the deviations or component tolerances in the DC-DC converter 1 for a corrected transfer ratio, the control system can be determined accordingly during the operational use of the DC-DC converter 1. Since any errors in the voltage measurement are also included in the ratio, these deviations can be corrected as part of this ratio. It is irrelevant for the control or adaptation whether the deviation results from a voltage measurement error or a deviation in the transfer ratio. R. 416180.

[0067] - 13 -

[0068] Although the operating state in which as little electrical power as possible is transferred between the first DC terminal 11 and the second DC terminal 12 has proven advantageous for determining the correction parameter or a corrected transfer ratio, other operating conditions can also be set in principle, in which the idealized control parameters are compared with the control parameters actually required to achieve the desired operating state. It is also possible, for example, to repeat the described procedure for several different operating points and thus further optimize the correction parameter(s).

[0069] The described procedure can be performed, for example, when starting or restarting the DC-DC converter. It can also be performed, for example, when reinitializing the DC-DC converter. Thus, suitable correction parameters are determined again after each iteration of the described procedure. This also allows for the compensation of any aging effects or similar factors that may occur.

[0070] Furthermore, it is also possible to perform such a recalculation of correction parameters regularly during the operation of the DC-DC converter, for example, during scheduled breaks in power transmission or similar events, or after predetermined trigger events. For instance, fluctuations due to temperature effects can also be taken into account in this way. The procedure can be initiated, for example, when a temperature change in the DC-DC converter exceeds a predefined absolute or relative threshold.

[0071] Figure 3 shows a flowchart of a method for operating a DC-DC converter 1 according to one embodiment. The method can, in principle, include any steps that have already been carried out in connection with the previously described DC-DC converter 1. Similarly, the previously described DC-DC converter 1 can also include any components or elements R. 416180.

[0072] - 14 - include how they are suitable for implementing the procedure described below.

[0073] The procedure can include a step S1 for setting a predetermined operating point in the DC-DC converter 1. The operating point can be set, in particular, using initial control parameters. Subsequently, in step S2, an initial power output of the DC-DC converter 1 at the set predetermined operating point can be recorded. In step S3, the recorded power output is compared with an expected value for the power output at the predetermined operating point. Then, in step S4, the power output of the DC-DC converter can be adjusted to the expected value. For this purpose, predefined control parameters, based on which the control signals are determined, can be varied until the expected operating point is reached.

[0074] In step S5, a correction value is then determined by comparing the adjusted control parameters after the transmission power has settled to the expected value with the initial control parameters. This correction value could, for example, be a correction factor or a corrected transmission ratio, in particular a corrected transmission ratio of transformer 20 in the DC-DC converter 1. Deviations in the voltage measurement can be part of the correction factor.

[0075] Finally, in step S6, the DC-DC converter can be controlled using the determined correction parameter.

[0076] In summary, the present invention relates to a DC-DC converter and a method for operating a DC-DC converter. It is provided that a correction factor is determined which specifies a deviation between the actual component values ​​and idealized component values ​​in the DC-DC converter. For determining this correction factor, a predetermined operating point can be set, and this operating point can then be maintained for as long as necessary. R. 416180

[0077] - 15 - be modified until the DC voltage converter achieves operating conditions that correspond to an expected value for the predetermined operating point.

Claims

R. 416180 - 16 - Claims 1. Method for operating a DC voltage converter (1), comprising the steps: Setting (S1) a predetermined operating point in the DC-DC converter (1) using initial drive parameters; Detection (S2) of a first transmission power of the DC voltage converter (1) at the set predetermined operating point; Comparing (S3) the first transmission power with an expected value for the transmission power at the predetermined operating point; Adjusting (S4) the transmission power of the DC-DC converter (1) to the expected value for the transmission power at the predetermined operating point by adjusting the control parameters; Determine (S5) a correction value by comparing the adjusted control parameters after adjusting the transmission power to the expected value with the initial control parameters; and Controlling (S6) the DC voltage converter (1) using the determined correction value; 2. Method according to claim 1, wherein the initial control parameters are determined using a model, in particular a model based on tolerance-free components. R. 416180 - 17 - 3. Method according to claim 1 or 2, wherein the predetermined operating point comprises an operating point at which no electrical power is transferred through the DC-DC converter.

4. Method according to any one of claims 1 to 3, wherein the correction quantity is determined using at least two different predetermined operating points.

5. Method according to any one of claims 1 to 4, wherein the determined correction parameter comprises a correction parameter for a transformation ratio of a transformer (20) in the DC voltage converter (1).

6. Method according to one of claims 1 to 4, wherein the determined correction quantity comprises a correction quantity for a transformation ratio of a transformer (20) and the primary-side and secondary-side voltage sensing in the DC-DC converter (1).

7. A method according to any one of claims 1 to 6, wherein, during the operation of the DC-DC converter (1) at the predetermined operating point, pulse width modulated control of switching elements (31a, 31b, 32a, 32b, 41a, 41b, 42a, 42b) in bridge circuits (31, 32, 41, 42) of the DC-DC converter (1) is performed, and wherein the control of the DC-DC converter (1) using the correction parameter comprises adjusting a control angle in the pulse width modulated control of the switching elements (31a, 31b, 32a, 32b, 41a, 41b, 42a, 42b) in the bridge circuits (31, 32, 41, 42).

8. Method according to claim 7, wherein an extended dead time is provided during the setting (S1) of the predetermined operating point and / or during the adjustment (S4) of the transmission power to the expected value for a commutation in at least one half-bridge (31 , 32, 41 , 42) of at least one bridge circuit (30, 40). R. 416180 - 18 - 9. Method according to any one of claims 1 to 8, wherein the method is carried out during an initialization of the DC voltage converter (1), in particular during a restart of the DC voltage converter (1).

10. Method according to any one of claims 1 to 9, wherein the method is executed at regular intervals and / or after the detection of a predetermined event.

11. DC-DC converter (1) comprising a first DC-DC terminal (11); a second DC-DC terminal (12); a transformer (20) comprising a primary side (21) and a secondary side (22); a first bridge circuit (30) arranged between the first DC-DC terminal (11) and the primary side (21) of the transformer (20); a second bridge circuit (40) arranged between the second DC-DC terminal (12) and the secondary side (22) of the transformer (20); and a control device (50) configured to perform a method according to any one of claims 1 to 10.

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