Dual-active bridge converter and method for operating a dual-active bridge converter

Description

[0001] The present invention relates to a method for operating a dual-active bridge converter. The present invention further relates to a dual-active bridge converter and a voltage converter arrangement with a dual-active bridge converter. State of the art

[0002] Dual-active bridge converters are bidirectional DC-DC converters with two semiconductor full bridges. Due to their compactness, dual-active bridge converters are particularly advantageous for applications with limited installation space. Furthermore, dual-active bridge converters also enable galvanic isolation between the two DC voltage sides. A detection method using dual-active bridge converters is known, for example, from EP 3 285 382 A1. A dual-active bridge converter and a method for operating a dual-active bridge converter are known from US 2019 / 148965 A1, in which the voltage specification of the secondary side is superimposed with a ripple component as a controlled variable, and the control of the dual-active bridge converter is carried out using the controlled variable superimposed with the ripple component, wherein the ripple component is a periodic variable.

[0003] When operating dual-active bridge converters, so-called deadtime effects can influence the controllability of the system. Deadtime can generally be understood as the time period between a signal change at the system input and a signal response at the system output. In the case of impressions, such as those used particularly in dual-active bridge converters, a deadtime corresponds to the time between the switching off of one switching element of the half-bridge and the switching on of the other switching element of the half-bridge. Such deadtimes occur for dual-active bridge converters in the transition region between hard-switching and soft-switching operation. This transition region is also referred to as the deadtime region. Disclosure of the invention

[0004] The present invention provides a method for operating a dual-active bridge converter, a dual-active bridge converter, and a voltage converter arrangement having the features of the independent patent claims. Further advantageous embodiments are the subject of the dependent patent claims. Accordingly, it is provided:

[0005] A method for operating a dual-active bridge converter, comprising a step for determining a controlled variable for the dual-active bridge converter. The method further comprises a step for superimposing a ripple component on the controlled variable, and a step for controlling the dual-active bridge converter using the controlled variable with the ripple component superimposed. Furthermore, it is planned:

[0006] A dual-active bridge converter with a control device. The control device is designed to determine a controlled variable for the dual-active bridge converter, superimpose a ripple component on the controlled variable, and control the dual-active bridge converter using the controlled variable with the ripple component superimposed. Finally, it is planned:

[0007] A voltage converter arrangement with at least one dual active bridge converter according to the invention. Advantages of the invention

[0008] The present invention is based on the finding that, in a dual-active bridge converter, in a transition region between hard-switching and soft-switching operation, dead times in the control of the switching elements in the dual-active bridge converter can lead to stagnation of the manipulated variable or to self-amplification of the manipulated variable. However, for reliable and stable control of the output variable of a dual-active bridge converter, a continuous and strictly monotonic characteristic curve of the controlled system is required.

[0009] It is therefore an idea of ​​the present invention to take this finding into account and to provide a control for a dual-active bridge converter which can counteract the dead time-related effects in the transition region between hard-switching operation and soft-switching operation of the dual-active bridge converter. For this purpose, the invention provides for the controlled variable for the dual-active bridge converter to be superimposed with an additional ripple component. This ripple component can be an alternating offset, for example a periodic signal. The frequency of the ripple can be selected in particular such that, on the one hand, the dual-active bridge converter can follow the ripple-related changes, but on the other hand, no significant ripple-related interference or fluctuations in the output variable of the dual-active bridge converter occur. The specific frequency orThe specific frequency range in which the ripple can move may therefore depend on the other operating parameters of the dual-active bridge converter.

[0010] By superimposing an additional ripple on the controlled variable for the dual-active bridge converter, the controlled variable is subjected to an offset, so that the dual-active bridge converter operates outside the deadtime range, at least temporarily, for each value of the controlled variable, also due to the superimposed ripple. To achieve this, a sufficiently large amplitude must be provided for the superimposed ripple.

[0011] In this way, it can be ensured that a strictly monotonic slope of the characteristic curve for the relationship between the controlled variable and the output variable is achieved even in the dead time range of the dual active bridge converter.

[0012] If this strategy is deployed across the entire operating range, precise knowledge of the specific position of the dead-time region of the dual-active bridge converter is not required. This allows for a high degree of robustness, particularly with regard to component tolerances.

[0013] According to one embodiment, the controlled variable comprises a setpoint for an output current of the dual-active bridge converter. In particular, the controlled variable can relate to a phase shift between the control on the input side and the output side of the dual-active bridge converter.

[0014] According to one embodiment, the ripple component comprises a periodic variable with a predetermined signal shape. The amplitude of the ripple component should be selected at least large enough to prevent stagnation of the manipulated variable when passing through the dead-time range.

[0015] According to one embodiment, the predetermined signal shape of the ripple component can comprise a rectangular signal waveform, a sinusoidal signal waveform, a triangular signal waveform, or a sawtooth signal waveform. Any other suitable signal waveforms are also possible. In particular, a rectangular signal waveform can be very easily implemented using a suitable digital signal. Furthermore, high-frequency interference components can be minimized, for example, using a sinusoidal signal waveform.

[0016] According to one embodiment, the ripple component has a fixed, predetermined frequency. The selection of a suitable frequency may depend on the other operating characteristics of the dual-active bridge converter. In particular, the predetermined frequency should be sufficiently high to avoid fluctuations in the output of the dual-active bridge converter.

[0017] According to one embodiment, the frequency of the ripple component can be varied within a predetermined frequency range. In particular, the frequency can be varied periodically within the predetermined frequency range. By varying the frequency of the ripple component, further interference effects can be eliminated or at least reduced.

[0018] According to one embodiment, the amplitude of the ripple component can be adjusted using a current value of the controlled variable. For example, the amplitude can be increased in a range within or within a predetermined range around the expected deadtime range in the transition between hard-switching and soft-switching operation of the dual-active bridge converter. Accordingly, the amplitude of the ripple component can be reduced in ranges farther away from the expected deadtime range. Furthermore, any other schemes for adjusting the amplitude of the ripple component are of course also possible.

[0019] According to one embodiment of the voltage converter arrangement, the voltage converter arrangement can comprise multiple dual-active bridge converters. In such a case, the controlled variable of the individual dual-active bridge converters can be superimposed with different ripple components. In particular, individual characteristics, such as the ripple frequencies or the ripple signal shapes, can be different for the individual dual-active bridge converters.

[0020] 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. Short description of the drawings

[0021] Further features and advantages of the invention are explained below with reference to the figures. These show: Figure 1: a schematic representation of a basic circuit diagram of a dual-active bridge converter, as it is based on an embodiment of the present invention; Figure 2: schematic voltage curves during operation of a dual-active bridge converter; Figure 3: a schematic representation of an output current and the underlying controlled variable during operation of a dual-active bridge converter according to an embodiment; and Figure 4: a flowchart as it is based on a method for operating a dual-active bridge converter according to an embodiment. Description of the embodiments

[0022] Figure 1shows a schematic representation of a dual-active bridge converter 1 according to an embodiment. A primary side comprises a first half-bridge with two switching elements M1p and M2p, as well as a second half-bridge with two switching elements M3p and M4p. A secondary side 20 also comprises two half-bridges with the switching elements M1s to M4s. Between the primary side and the secondary side, a transformer region 30 comprises a first primary-side inductance L1p, a second primary-side inductance L2p, and a secondary-side inductance L1s. On the primary side, an input voltage V_p is provided, which is converted by the dual-active bridge converter 1 into a secondary-side output voltage V_s. A control device 40 can be provided to control the switching elements M1p to M4p and M1s to M4s. In addition to the Figure 1In addition to the embodiment of a dual-active bridge converter 1 shown, the principle of the present invention described below can also be applied in principle to any other suitable DC-DC converters. In particular, the inventive superposition of a control variable with a ripple component can also be applied to further variations of dual-active bridge converters. Such variations include, in particular, for example, voltage converters which have only a half-bridge with a split input capacitor on the primary side and / or secondary side. Furthermore, multilevel configurations of the transistors for increasing the input voltage or smoothing the transformer voltages are also possible. Furthermore, one or more of the inductors of the coupling network can be omitted if necessary, or a secondary side shunt inductance can be implemented.

[0023] Figure 2shows a schematic representation of the voltage sequences when operating the dual active bridge converter 1. As in the upper part of Figure 2 As shown, a pulse-shaped voltage waveform is provided by the primary-side switching elements M1s to M4s, wherein the duration of a pulse is predetermined by a first phase angle a. Voltage pulses result on the secondary side, wherein the duration of the secondary-side pulses is predetermined by a second phase angle b. A third phase angle d is determined by a temporal shift between the center points of the voltage pulses on the primary side and the secondary side. In particular, the third phase angle d can be varied, for example, as a controlled variable for an output current of the dual-active bridge converter 1.

[0024] With a continuous increase of the controlled variable, in particular of the third phase angle d, a stagnation of the output variable, in particular of the output current, occurs in a dead time range during the transition between the soft-switching operation and the hard-switching operation of the dual active bridge converter 1.

[0025] To counteract this effect and achieve the most strictly monotonic increase possible over the dead time range, the controlled variable d can be superimposed with an additional ripple component. This ripple component can be a periodic signal with a predetermined frequency, for example. In this way, the controlled variable d will fluctuate periodically with the amplitude of the superimposed ripple. For example, if the controlled variable d has a value D and the amplitude of the superimposed ripple component is designated A, the dual active bridge converter 1 is operated with a controlled variable in the range D ± A. If the amplitude A of the ripple component is selected to be sufficiently large, it can be ensured for each value of the controlled variable d that the controlled variable d lies at least temporarily outside the dead time range.In this way, a strictly monotonic increase of the output variable can be achieved over the entire control range, particularly in the dead time range, even if it is reduced.

[0026] Figure 3 illustrates this relationship and presents a temporal variation of the output variable in the form of an output current I, as well as the underlying controlled variable d. The ripple component superimposed on the controlled variable d is greatly simplified here and shown at a very low frequency. This low frequency serves only to improve understanding. In practice and during operation, however, a significantly higher frequency is generally selected for the superimposed ripple.

[0027] Area I in Figure 3 indicates the hard-switching range, range III the soft-switching range and range II the dead-time range in the transition between the hard-switching and soft-switching ranges.

[0028] As in Figure 3 As can be seen, there is no stagnation of the output variable I in the dead time range between the first and second dashed lines. For comparison, the course of the output variable I* is shown in dashed lines, which would be the basis of the controlled variable d without superimposed ripple.

[0029] As already explained, the ripple component can be formed as a periodic signal with a fixed frequency. Alternatively, it is also possible to vary the frequency of the ripple within a specified frequency range. For example, the frequency can periodically increase and / or decrease within the specified frequency range. A sinusoidal variation of the ripple frequency within the specified frequency range is also possible. Of course, any other principles for varying the frequency of the ripple component within a specified frequency range are also possible.

[0030] The ripple component superimposed on the controlled variable d can have any signal shape. In particular, rectangular, triangular, sawtooth, or sinusoidal ripple components are possible.

[0031] The amplitude of the ripple component can, for example, be kept constant across the entire control range. Furthermore, the amplitude of the ripple component can also be varied if necessary. For example, it is possible to increase the amplitude of the ripple component within the expected dead-time range. However, any other schemes for adjusting the amplitude of the ripple component are also fundamentally possible. In particular, the amplitude of the ripple component should always be selected to be at least large enough so that, even within the dead-time range, the dead-time range can be at least partially exited by superimposing the controlled variable d with the ripple component.

[0032] The previous explanations described the control principle for a circuit arrangement with a single dual-active bridge converter 1. Furthermore, it is fundamentally possible to apply this principle to circuit arrangements with multiple dual-active bridge converters connected in parallel. In particular, in a circuit arrangement with multiple dual-active bridge converters connected in parallel, the ripple component superimposed on the controlled variables can be selected differently for each dual-active bridge converter.

[0033] Figure 4shows a schematic representation of a flowchart underlying a method for operating a dual-active bridge converter 1 according to one embodiment. The method can, in principle, comprise any steps as previously described in connection with the dual-active bridge converter 1. Similarly, the previously described dual-active bridge converter can also comprise any components to implement the method described below.

[0034] In a first step, a controlled variable d for the operation of the dual-active bridge converter 1 can be determined. This determination can, for example, comprise receiving the controlled variable from an external control device. Additionally or alternatively, it is also possible to determine the controlled variable d based on one or more further setpoints and / or measured values. In step S2, the determined controlled variable d can be superimposed with a ripple component. The options already explained above apply to the ripple component that is superimposed on the controlled variable d. Finally, in step S3, the dual-active bridge converter 1 can be controlled using the controlled variable d with the ripple component superimposed.

[0035] In summary, the present invention relates to the control of a dual-active bridge converter. In particular, it is provided to superimpose an additional ripple component on a controlled variable for the dual-active bridge converter and to control the dual-active bridge converter with a combination of the controlled variable and the additional ripple component.

Claims

1. Method for operating a dual-active-bridge converter (1), having the steps of: ascertaining (S1) a phase angle as a control variable (d) for the dual-active-bridge converter (1); superimposing (S2) the control variable (d) with a ripple component; and controlling (S3) the dual-active-bridge converter (1) by using the control variable (d) superimposed with the ripple component, wherein the ripple component comprises a periodic variable having a predetermined signal shape.

2. Method according to Claim 1, wherein the predetermined signal shape comprises a rectangular signal characteristic, a sinusoidal signal characteristic, a triangular signal characteristic or a sawtooth signal characteristic.

3. Method according to either of Claims 1 and 2, wherein the ripple component has a fixed predetermined frequency.

4. Method according to one of Claims 1 to 3, wherein a frequency of the ripple component is periodically varied within a predetermined frequency range.

5. Method according to one of Claims 1 to 4, wherein an amplitude of the ripple component is set using a present value of the control variable (d).

6. Dual-active-bridge converter (1) having a control device (40) which is designed to ascertain a phase angle as a control variable (d) for the dual-active-bridge converter (1), to superimpose the control variable (d) with a ripple component, and to control the dual-active-bridge converter (1) by using the control variable (d) superimposed with the ripple component, wherein the ripple component comprises a periodic variable having a predetermined signal shape.

7. Voltage-converter arrangement having at least one dual-active-bridge converter (1) according to Claim 6.

8. Voltage-converter arrangement according to Claim 7, wherein the voltage-converter arrangement comprises a plurality of dual-active-bridge converters (1), and wherein the control variables (d) of the individual dual-active-bridge converters (1) are superimposed with different ripple components.