Cascaded ac / dc converter having an intermediate circuit voltage matching converter and llc output converter and spread-spectrum operation by way of intermediate circuit voltage modulation

Abstract

According to a first aspect, the invention provides a device (200-1) for providing a stable DC voltage supply (220). The device (200-1) comprises a matching converter (206) that is electrically conductively connected or connectable, on an input side of the matching converter (206), to a DC voltage source (202, 204) or an AC voltage source (202), and comprises an LLC converter (100) that is electrically conductively connected or connectable, on an input side, to an output side of the matching converter (206). The LLC converter (100) is designed to provide a stable DC voltage supply (220) on an output side, wherein a DC voltage of the output-side stable DC voltage supply (220) is a function of a switching frequency of the LLC converter (100). The matching converter (206) comprises a control unit (208) that is designed to overlay an output DC voltage of the matching converter (206) with an AC voltage (218). An amplitude of the overlaid AC voltage (218) is less than the output DC voltage. A frequency of the overlaid AC voltage (218) is lower than the switching frequency of the LLC converter (100).

Description

[0001] Cascaded AC / DC converter with intermediate circuit voltage matching converter and LLC output converter and spread spectrum operation by means of intermediate circuit voltage modulation

[0002] The invention relates to a technology for stable DC voltage supply using an LLC converter (also known in technical terms as "LLC converter"). In particular, the invention comprises a device and a method in which a temporal clock jitter (technical term: jitter) of an LLC converter is generated in order to avoid narrowband peaks in the spectrum of the LLC converter.

[0003] LLC converters are increasingly being used in modern power supply devices (also known in technical terms as "power supplies") because they offer very high efficiency and a compact design. With the LLC converter type, the output voltage is changed by changing the switching frequency of the LLC converter. If the LLC converter is supplied with a stable, fixed input voltage (especially one with low voltage ripple), this results in a defined switching frequency of the LLC converter.

[0004] In LLC converters that are powered by a direct current (DC) or a three-phase (alternating current) voltage (AC) (possibly with an additional boost or buck converter between the DC or 3-phase input voltage and the LLC converter), the voltage at the LLC converter is conventionally so stable that the switching frequency of the LLC converter fluctuates only slightly. It is essentially a fixed frequency.

[0005] With regard to the conducted interference at the input and output of such an LLC converter, this results in the switching frequency of the LLC converter and its harmonics appearing as narrowband peaks in the spectrum. Because the frequency varies so little, the average value of these peaks is almost as high as their quasi-peak value. Although there is a significantly higher limit for the quasi-peak value than for the average value, e.g. a limit approximately 10 decibels (10 dB) higher or even higher, such stringent electromagnetic compatibility (EMC) measures must be taken that even the quasi-peak value is reduced below the limit for the average value. The effort required for this is high and is reflected in the device costs and size.

[0006] The conventional behavior described above is particularly evident with DC or three-phase device input voltage. With single-phase (1-phase) input voltage, the input voltage at the LLC converter is typically less stable, for example, with a large voltage ripple, and thus the switching frequency of the LLC converter is more variable, which is why the problem does not occur here or occurs to a lesser extent.

[0007] If the frequency of the LLC converter were to vary more, the quasi-peak and average values ​​would be lower because the energy would be distributed over a wider frequency range. Furthermore, the average value would then be significantly below the quasi-peak value, and as a result, less effort would be required for EMC measures. With other conventional converter types (e.g. flyback converters), this is achieved by deliberately jittering the switching frequency over time in order to generate a broader spectrum. Since the switching frequency is the manipulated variable for the output voltage in an LLC converter, this cannot be implemented in an analog way in a stable DC voltage supply. Changing the switching frequency of the LLC converter would disrupt the output voltage.

[0008] The invention is therefore based on the object of specifying a technology for stable DC voltage supply using an LLC converter, which is fed from a low-ripple input voltage, in particular a DC voltage or three-phase AC voltage with subsequent rectification. Alternatively or additionally, the object is to avoid narrowband peaks in the spectrum of an LLC converter with a low-ripple input voltage. Furthermore, alternatively or additionally, the object is to generate temporal clock jitter (technically known as jitter) in the switching frequency of an LLC converter without disturbing the output voltage of the LLC converter.

[0009] The problem or problems are solved by the features of the independent claims. Expedient embodiments and advantageous further developments of the invention are specified in the dependent claims.

[0010] Embodiments of the invention are described below with partial reference to the figures.

[0011] According to a first aspect, a device for a stable DC voltage supply is provided. The device comprises a matching converter, which is or can be electrically connected to a DC voltage source or to an AC voltage source on an input side of the matching converter. The device further comprises an LLC converter, which is or can be electrically connected to an output side of the matching converter on an input side. The LLC converter is designed to provide a stable DC voltage supply on an output side. A DC voltage of the stable DC voltage supply on the output side is a function of a switching frequency of the LLC converter. The matching converter comprises a control unit (in English and technical terms: controller), which is designed to superimpose an AC voltage on an output DC voltage of the matching converter (for example, a low-ripple DC voltage).The amplitude of the superimposed AC voltage is smaller than the output DC voltage of the matching converter. The frequency of the superimposed AC voltage is lower than the switching frequency of the LLC converter. The LLC converter can be a resonant converter. Alternatively or additionally, the LLC converter can include a transformer on the output side. A primary side of the transformer can be a primary inductance (LP, i.e., the larger output inductance) of the LLC converter. A leakage inductance (Ls) of the transformer can be the coupling inductance of the LLC converter.

[0012] Alternatively or additionally, the LLC converter can include a rectifier on the output side. The DC voltage of the stable DC power supply on the output side (which is a function of the LLC converter's switching frequency) can be this rectified (and optionally capacitively smoothed) DC voltage.

[0013] The LLC converter may include a circuit unit (also known as a regulator). The circuit unit of the LLC converter may generate the switching frequency of the LLC converter.

[0014] The stable DC voltage supply at the output side of the LLC converter may depend on the switching frequency of the circuit unit of the LLC converter.

[0015] The matching converter can comprise a boost converter (also: step-up converter), a buck converter (also: step-down converter) and / or a buck-boost converter (also: step-up / step-down converter).

[0016] Alternatively or additionally, the matching converter can comprise a flyback converter, a SEPIC converter (SEPIC is short for: Single Ended Primary Inductance Converter), a forward converter and / or a bridge converter. Further alternatively or additionally, the flyback converter and / or the SEPIC converter can be classified as a boost / buck converter. Further alternatively or additionally, the forward converter and / or the bridge converter can be designed and / or classified as a buck converter or boost / buck converter. For example, an output voltage can be higher than an input voltage by means of a transformer in a circuit of the forward converter and / or the bridge converter.

[0017] Furthermore, alternatively or additionally, the matching converter can comprise a, in particular bridgeless, rectifier, for example a Vienna rectifier. For example, the, in particular bridgeless, rectifier can be connected or connectable to the AC voltage source on the input side. The matching converter comprising a, in particular bridgeless, rectifier can provide a, for example, controllable, DC output voltage.

[0018] For example, a matching converter can comprise a rectifier, particularly a bridgeless one, for AC voltage sources and / or output voltages of the matching converter and / or the device comprising the LLC converter in the high power range, particularly greater than or equal to one kilowatt (1 kW). Alternatively or additionally, power factor correction (PFC) may be important and / or applied at high power levels. For example, conventional rectifiers that can be switched or connected in series between the AC voltage source and the input side of the matching converter are unsuitable for PFC at high power levels.

[0019] The DC voltage source on the input side of the matching converter may comprise a rectification of a three-phase AC voltage.

[0020] The frequency of the superimposed AC voltage can be a low-frequency AC voltage. Alternatively or additionally, the frequency of the superimposed AC voltage can be (in particular much or many times, for example by at least an integer multiple) lower than the switching frequency of the LLC converter and / or (in particular much, for example by an integer multiple) lower than a bandwidth of the circuit unit (also: the regulator) of the LLC converter. If the frequency of the superimposed AC voltage is (in particular much or many times, for example by at least an integer multiple) lower than the switching frequency of the LLC converter and (in particular much or many times, for example by at least an integer multiple) lower than the bandwidth of the circuit unit of the LLC converter, the output voltage, in particular, can be kept stable.

[0021] The amplitude of the (e.g. superimposed) alternating voltage can be a maximum absolute value of the (e.g. superimposed) alternating voltage.

[0022] By means of the superimposed alternating voltage, a temporal clock jitter (also: frequency jitter) of the LLC converter can be generated.

[0023] The input voltage of the LLC converter can be changed (or manipulated) using the (especially small) superimposed AC voltage. Alternatively or additionally, the frequency of the LLC converter and its jitter need not only be visible in the input voltage. The clock frequency of the LLC converter can be observable and / or detectable in the input current and / or output current (and, for example, in the resulting voltage ripple on the input and output sides of the LLC converter), and / or in a transformer voltage of the LLC converter.

[0024] Due to the changing input voltage, the LLC converter can, or must, adjust its frequency (e.g., via the circuit unit; also known as a regulator). Jitter can thus be generated and / or originate directly in the LLC converter.

[0025] For example, an LLC converter can have an input DC voltage of 800 V (also: Vdc for DC voltage), an output DC voltage of 24 V (also: Vdc) and a switching frequency of 95 kHz. The input voltage can be increased to, for example, 815 V (also: Vdc) by means of the superimposed AC voltage (for example in a positive phase of the AC voltage). In order to maintain the output voltage at 24 V (also: Vdc), the circuit unit (also: regulator) of the LLC converter in this embodiment increases the switching frequency to, for example, 100 kHz. The input voltage can then be reduced to 785 V (also: Vdc) (for example in a negative phase of the AC voltage). In order to maintain the output voltage at 24 V (also: Vdc), the circuit unit (also: regulator) in this embodiment of the LLC converter reduces the switching frequency to, for example, 90 kHz.

[0026] The switching frequency of the LLC converter can be reflected in the input current and / or output current of the LLC converter. Alternatively or additionally, the switching frequency of the LLC converter can be reflected in the voltage across the transformer of the LLC converter.

[0027] With regard to electromagnetic compatibility (EMC), the switching frequency of the LLC converter can be observable (also: detectable or visible) in the (e.g., entire) device comprising the LLC converter. The switching frequency of the LLC converter can be transmitted, for example, through parasitic couplings to (e.g., all possible) locations, so that the switching frequency of the LLC converter can be detected both at the input and output sides of the device.

[0028] The circuit unit of the LLC converter can be designed to change the switching frequency in response to the AC voltage superimposed on the input DC voltage.

[0029] The output DC voltage of the matching converter can correspond to the input DC voltage of the LLC converter. The temporal clock jitter of the LLC converter can prevent, suppress, and / or broaden high peak values ​​in the frequency range of the LLC converter. Alternatively or additionally, high peak values ​​in the frequency range of the LLC converter can be distributed and / or smoothed over a frequency range broadened by the frequency of the superimposed AC voltage, rather than in a narrow frequency range of the switching frequency.

[0030] Due to the superimposed alternating voltage, a change in the level of the input-side DC voltage at the LLC converter and the change in the switching frequency can compensate each other in the circuit unit of the LLC converter in such a way that the output-side DC voltage supply of the LLC converter is stable.

[0031] By means of the device, an improved EMC of the LLC converter can be achieved with simple components and / or with a small size.

[0032] The DC voltage source may comprise an (e.g. three-phase) AC voltage source and a rectifier arranged between the (e.g. three-phase) AC voltage source and the input side of the matching converter.

[0033] The superimposed AC voltage can, for example, comprise a triangular voltage (also: triangular voltage), a sinusoidal voltage (also: sinusoidal voltage), a sawtooth voltage (also: sawtooth voltage), and / or a rectangular voltage (also: rectangular voltage). Alternatively or additionally, the superimposed AC voltage can comprise a trapezoidal voltage (also: trapezoidal voltage).

[0034] - The superimposed AC voltage, for example the triangular voltage and / or the sinusoidal voltage, can have a continuous waveform. The continuous waveform of the superimposed AC voltage can enable and / or improve a timely response of the circuit unit of the LLC converter. The device can further comprise two resistors that, when connected in series, form a voltage divider. The voltage divider can be connected between both poles of the output side of the matching converter and / or between both poles of the input side of the LLC converter. The control unit can be designed to regulate the output DC voltage of the matching converter depending on a voltage tapped at a node between the first resistor and the second resistor of the voltage divider.

[0035] The voltage tapped between the first resistor and the second resistor of the voltage divider can comprise an actual voltage (also: an actual value of the voltage).

[0036] The device may further comprise a signal generator that couples a control signal of the superimposed AC voltage into the tapped voltage. The coupling is optionally performed via a third resistor, which is electrically connected at a first terminal to the junction point between the first resistor and the second resistor of the voltage divider. The third resistor may be electrically connected to the signal generator at a second terminal.

[0037] The superimposed AC voltage can be coupled to the control unit of the matching converter via the voltage divider for actual value detection of the voltage on the input side of the LLC converter.

[0038] Alternatively or additionally, an analog coupling of the control signal (signal coupling) of the superimposed alternating voltage can be enabled by means of the third resistor.

[0039] The signal generator can also be electrically connected to one of the two poles on the output side of the matching converter and / or one of the two poles on the input side of the LLC converter. Alternatively or additionally, the signal generator can be arranged outside the matching converter. Alternatively or additionally, the control signal of the superimposed AC voltage can be added to the voltage tapped via the voltage divider.

[0040] The summation of the voltages on the input side of the control unit can include an analog and / or digital coupling of the control signal (in short: signal coupling).

[0041] The control unit can be configured to regulate the output DC voltage of the matching converter depending on an actual voltage. The signal generator can couple a control signal of the superimposed AC voltage into the actual voltage. Optionally, the control signal can be added to an actual value in the control unit.

[0042] Alternatively or additionally, the control unit can be configured to regulate the output DC voltage of the matching converter depending on a target voltage. The signal generator can couple a control signal of the superimposed AC voltage into the target voltage. Optionally, the control signal can be summed to a constant target value in the control unit.

[0043] The device may comprise the signal generator coupling to the desired voltage and / or the signal generator coupling to the actual voltage.

[0044] The addition of the superimposed alternating voltage to the constant setpoint in the control unit can include an analog and / or a digital coupling of the control signal (in short: signal coupling).

[0045] The superposition of the output voltage of the matching converter with the alternating voltage can comprise an analog signal coupling and / or a digital signal coupling in the control unit. A frequency of the voltage at the input side of the matching converter can comprise zero Hertz (Hz) for a direct voltage source. Alternatively or additionally, a frequency of the voltage at the input side of the matching converter (before its rectification) can be between 50 Hz and 60 Hz for an input-side (e.g. three-phase) alternating voltage source with a subsequent rectifier. Furthermore, alternatively or additionally, a frequency of the voltage at the input side of the matching converter (before its rectification) can be between 100 Hz and 1000 Hz, in particular 400 Hz, for an (e.g. aircraft) on-board electrical system.

[0046] The frequency of the superimposed AC voltage can be between 0.5 Hz and 2 Hz, for example, in the case of an AC voltage source with a rectifier on the input side of and / or in the matching converter. In particular, the frequency of the superimposed AC voltage can be 1 Hz.

[0047] Alternatively or additionally, the frequency of the superimposed AC voltage may be (e.g. a little or slightly) higher than 2 Hz, for example in the case of a DC voltage source on the input side of the matching converter.

[0048] An input-side (e.g., three-phase) AC voltage source can, for example, comprise an AC voltage amplitude of 400 volts (V) to 500 V. Alternatively or additionally, an input-side DC voltage of the matching converter can, for example, comprise between 12 V and 800 V. For example, the AC voltage of an input-side (e.g., three-phase) AC voltage source can be rectified before entering the matching converter.

[0049] The output DC voltage of the matching converter can be at least an integer multiple of the amplitude of the superimposed AC voltage, for example, at least three times to at least 40 times. Alternatively or additionally, the output DC voltage of the matching converter can be 800 V. Furthermore, alternatively or additionally, the amplitude of the superimposed AC voltage can be between 10 V and 20 V.

[0050] According to a second aspect, a method for providing a stable DC voltage supply is provided. The method comprises a step of adjusting a DC voltage from a DC voltage source or adjusting an AC voltage from an AC voltage source using a matching converter. The method further comprises a step of superimposing an AC voltage on an output DC voltage of the matching converter, wherein an amplitude of the superimposed AC voltage is smaller than an output DC voltage of the matching converter. The method further comprises a step of converting (also: transforming) the output DC voltage of the matching converter, superimposed with the AC voltage, using an LLC converter.The LLC converter is configured to provide a stable DC voltage supply on an output side, wherein a DC voltage of the stable DC voltage supply on the output side is a function of a switching frequency of the LLC converter. According to the method, a frequency of the superimposed AC voltage is lower than the switching frequency of the LLC converter. The method further comprises the step of providing a stable DC voltage on the output side of the LLC converter.

[0051] The method may include a step of rectifying an (e.g., three-phase) alternating voltage from an alternating voltage source using a rectifier. Furthermore, the method may include a step of providing the rectified voltage as the direct voltage of the direct voltage source at an input side of the matching converter.

[0052] The method of the second aspect can also be referred to as a method for frequency jitter in an LLC converter, or in short as a method for LLC jitter, at a low-ripple input voltage. The method of the second aspect can be implemented using the device of the first aspect.

[0053] The invention is explained in more detail below with reference to the drawings using preferred embodiments.

[0054] They show:

[0055] Fig. 1 shows a schematic embodiment of an LLC converter;

[0056] Fig. 2A and 2B show a schematic first embodiment of a device according to the invention for stable DC voltage supply comprising an LLC converter, for example the LLC converter of Fig. 1, with a DC voltage source in Fig. 2A and an AC voltage source in Fig. 2B;

[0057] Fig. 3 shows a schematic second embodiment of a device according to the invention for stable DC voltage supply comprising an LLC converter, for example the LLC converter of Fig. 1;

[0058] Fig. 4 shows a schematic third embodiment of a device according to the invention for stable DC voltage supply comprising an LLC converter, for example the LLC converter of Fig. 1;

[0059] Fig. 5 shows a schematic spectrum curve of the output voltage as a function of the switching frequency of a conventional LLC converter; and Fig. 6 shows a schematic spectrum curve of the output voltage of an inventive device for stable DC voltage supply, for example a device according to Fig. 2A, 2B, 3 or 4, as a function of the switching frequency of an LLC converter, for example the LLC converter of Fig. 1.

[0060] Fig. 1 shows a schematic embodiment of an LLC converter 100. The LLC converter 100 comprises, connected in series, a first inductance (“L” or Ls in Fig. 1) 104-1, a second inductance (“L”) 104-2 and a capacitance (“C” or Cr in Fig. 1) 106-1.

[0061] The exemplary LLC converter 100 of Fig. 1 further includes a third inductor 104-3 inductively coupled to the second inductor 104-2. The second inductor 104-2 and third inductor 104-3 preferably form a transformer (T1) 102.

[0062] On the input side of the exemplary LLC converter 100 there is a smoothing capacitor (C1) 106-2 and two semiconductor switches (S1, S2) 108.

[0063] The semiconductor switches (S1, S2) 108 can be switched by means of the schematically illustrated circuit unit 112 according to a switching frequency of the LLC converter 100. For example, the first semiconductor switch (S1) 108 can be switched to the conductive state while the second semiconductor switch (S2) 108 is switched to the non-conductive state, or vice versa.

[0064] On the output side, the LLC converter 100 comprises a rectifier, for example a plurality of diodes 110 (D1, D2, D3, D4), for rectifying the output voltage of the LLC converter 100. Furthermore, the output side of the exemplary LLC converter 100 comprises a smoothing capacitor 106-3 (C2).

[0065] Figures 2A and 2B, 3 and 4 each show an embodiment of the device for stable DC voltage supply according to the invention. The device of the first embodiment is generally designated by reference numeral 200-1. The device of the second embodiment is generally designated by reference numeral 200-2. The device of the third embodiment is generally designated by reference numeral 200-3.

[0066] Identical or equivalent components in the embodiments of Figs. 2A, 2B, 3 and 4 are each designated by the same reference numerals.

[0067] As an example of a DC voltage source, Figs. 2A, 3 and 4 each show a three-phase AC voltage source 202 and a downstream rectifier 204, from which a DC voltage is fed to a matching converter 206.

[0068] The embodiment of Fig. 2B shows a three-phase AC voltage source 202 which is directly connected to an input side of a matching converter 206.

[0069] The device 200-1; 200-2; 200-3 each comprises an LLC converter, which is schematically illustrated in Figs. 2A, 2B, 3, and 4 and designated by reference numeral 100. The LLC converter 100 of Figs. 2A, 2B, 3, and 4 may each correspond to the LLC converter 100 of Fig. 1. Alternatively or additionally, the LLC converter 100 in Figs. 2A, 2B, 3, and 4 may also comprise other (not shown) embodiments of an LLC converter.

[0070] The device 200-1; 200-2; 200-3 further comprises a matching converter 206 with a control unit 208. The control unit 208 is designed to receive both a desired value 210 of the DC output voltage and an actual value 212 of the DC output voltage of the matching converter 206. In the exemplary embodiments 200-1; 200-2; 200-3 of Figs. 2A, 2B, 3, and 4, the actual value 212 of the DC output voltage is determined between a first resistor (R1) 214 and a second resistor (R2) 216 of a voltage bridge. In each exemplary embodiment, the device 200-1; 200-2; 200-3 comprises a signal generator 219 for a superimposed AC voltage 218. The superimposed AC voltage 218 is low-frequency. Low frequency refers herein to a frequency that is so low that a circuit unit of the LLC converter 100, for example the circuit unit 112 in Fig. 1 , can react to the voltage change.

[0071] Furthermore, an amplitude of the superimposed AC voltage 218 is, for example, many times smaller than an amplitude of the output DC voltage of the matching converter 206. For example, an amplitude of the superimposed AC voltage can be at most 20 V, in particular between 10 V and 20 V.

[0072] The LLC converter 100 can have a response time of, for example, 0.5 ms to 1 ms, within which it can compensate for a disturbance on the output voltage (for example, by means of the circuit unit 112). However, higher values ​​for the response time of the LLC converter 100, up to approximately 5 ms, are also possible for large devices (for example, the devices 200-1; 200-2; 200-3). Another characteristic value, which can essentially describe the same thing as the response time of the LLC converter, is the bandwidth of the circuit unit (also: regulator) 112 in the LLC converter 100. One can also say that the circuit unit (also: regulator) 112 of the LLC converter 100 has a bandwidth of approximately 5 kHz to 8 kHz. However, values ​​as low as 1 kHz are also conceivable for larger devices (e.g. devices 200-1; 200-2; 200-3).

[0073] Exemplary switching frequencies of the LLC converter 100 can be between 80 kHz and 120 kHz. Alternatively or additionally, for (particularly larger) devices (for example, devices 200-1; 200-2; 200-3), the switching frequencies may tend to decrease (for example, to only 30 kHz to 40 kHz). Furthermore, alternatively or additionally, for (particularly smaller) devices (for example, devices 200-1; 200-2; 200-3), the switching frequencies may also be higher (for example, in the range of 150 kHz). The switching frequency of the LLC converter 100 and the response time of the LLC converter 100 do not have to be directly and / or functionally dependent on one another. Alternatively or additionally, the switching frequency of the LLC converter 100 is, in embodiments, significantly higher than the bandwidth of the circuit unit (also: controller) 112 in order to prevent the switching frequency from interfering with the circuit (also: control).

[0074] Alternatively or additionally, the bandwidth of the circuit unit (also: controller) 112 can be limited by the sizes of components used in the device (e.g., device 200-1; 200-2; 200-3), e.g., (particularly transformer) inductances and / or output capacitances. Furthermore, alternatively or additionally, the switching frequency of the LLC converter 100 is not the limiting factor for the response time of the circuit unit (also: controller) 112 (e.g., in the vast majority of cases).

[0075] According to the invention, the superimposed (also: modulated) AC voltage 218 changes on the input voltage of the LLC converter 100 (in particular many times, for example by at least an integer multiple) more slowly than the reaction time of the circuit unit (also: controller) 112. Alternatively or additionally, according to the invention, the frequency of the superimposed AC voltage 218 is (in particular significantly, for example by at least an integer multiple) smaller than the bandwidth of the circuit unit (also: controller) 112 in order to prevent the superimposed AC voltage 218 from being observable (also: visible) on the output voltage of the LLC converter 100.

[0076] The frequency of the alternating voltage 218 superimposed on the input voltage of the LLC converter 100 can be selected to be low, for example in the range of 1 Hz, for the following reasons: 1) The alternating voltage 218 can also ensure modulation of the input current of the matching converter 206. If the input current of the matching converter 206 is supplied with a 3-phase alternating voltage (also: mains voltage), the alternating voltage (also: mains voltage) conventionally has a frequency of 50 Hz. The control unit (also: regulator) 208 of the matching converter 206 can, in one embodiment, be designed to be very slow (e.g. corresponding to a bandwidth of approximately 10 Hz) in order to prevent the control unit (also: regulator) 208 from leading to asymmetries in the mains current (e.g. on the output side of the matching converter 206) (e.g. positive half-wave of the mains voltage greater than negative half-wave of the mains voltage).According to this exemplary embodiment, the frequency of the alternating voltage 218 superimposed (also: modulated) on the output voltage of the matching converter 206 is (in particular) significantly lower than the bandwidth of the control unit 208 of the matching converter 206 (and / or the circuit unit 112 of the LLC converter 100) in order not to disturb and / or overload the control unit (also: regulator) 208 (and / or the circuit unit 112).

[0077] 2) Experiments have shown that modulation frequencies (and / or frequencies of the superimposed AC voltage 218) between 1 Hz and 2 Hz can lead to a well-shaped, flattened peaks in the spectrum. Depending on the modulation frequency (and / or frequency of the superimposed AC voltage 218), the shape can also appear differently, in particular deviating from flattened peaks (e.g., comprising two large "horn peaks" to the right and left of a plateau). Thus, according to some (or all) embodiments, the modulation frequency (and / or frequency of the superimposed AC voltage 218) influences the shape of the peaks more than their width.

[0078] The width of the peaks in the spectrum of the LLC converter 100 can be determined by the

[0079] The amplitude of the superimposed (also: modulated) AC voltage 218 depends on this. The higher the amplitude, the more the LLC converter 100 must adjust its frequency according to embodiments of the invention to keep the output voltage stable. The maximum and minimum switching frequencies of the LLC converter 100 can determine the width of the peaks.

[0080] In each embodiment of the device 200-1; 200-2; 200-3 in Figs. 2A and 2B, 3 and 4, respectively, terminals 220 for a stable DC voltage supply are further shown on the output side of the LLC converter 100, which can be electrically connected, for example, to a load (not shown).

[0081] In the embodiments of device 200-1 in Figs. 2A and 2B, the AC voltage 218 is coupled into the voltage divider (R1; R2) 214; 216 via a third resistor (Rk) 222. In the embodiments of Figs. 2A and 2B, the coupling occurs via the actual value detection 212 of the output DC voltage of the matching converter 206 and / or the input DC voltage (Vzk) of the LLC converter 100.

[0082] The input DC voltage (Vzk) of the LLC converter 100 may correspond to the output DC voltage of the matching converter 206.

[0083] In the embodiments of Fig. 2A and 2B, the signal coupling of the alternating voltage 218 is analog (in short: analog signal coupling).

[0084] In the embodiment of Fig. 2A, the matching converter 206 is fed by a three-phase alternating voltage 202, which is converted into a direct voltage by means of a rectifier 204 before being input to the matching converter 206.

[0085] In the embodiment of Fig. 2B, the matching converter 206 is fed (in particular directly) by a three-phase alternating voltage 202.

[0086] The matching converter 206 in the embodiment of Fig. 2B can, for example, comprise a bridgeless rectifier, in particular a Vienna rectifier, and can be connected (e.g. directly) to an AC voltage 202 and supply a, in particular controllable, DC output voltage.

[0087] In the following embodiments of Figs. 3 and 4, a circuit with a rectifier 204 between an AC voltage source 202 and the matching converter 206 is shown. Analogous to the embodiment of Fig. 2B, further embodiments (not shown) may include an integration of the rectifier 204 into the matching converter 206.

[0088] In the embodiment of the device 200-2 in Fig. 3, the coupling of the superimposed AC voltage 218 takes place between the voltage divider (R1; R2) 214; 216 and the control unit 208. Alternatively or additionally, the coupling of the superimposed AC voltage 218 in the embodiment of Fig. 3 can take place in the control unit 208. In Fig. 3, the coupling of the superimposed AC voltage 218 is schematically shown as addition ("+") to the actual value 212. The signal coupling of the superimposed AC voltage 218 into the output DC voltage of the matching converter 206 and / or into the input DC voltage (Vzk) of the LLC converter 100 in Fig. 3 can take place in analog and / or digital form.

[0089] In the embodiment of device 200-3 in Fig. 4, the superimposed AC voltage 218 is coupled in via the setpoint detection 210 of the control unit 208 of the matching converter 206. As shown schematically in Fig. 4, the superimposed AC voltage 218 can be added ("+") to a, in particular constant, setpoint voltage 210. The signal coupling of the superimposed AC voltage 218 in the embodiment of Fig. 4 can be analog and / or digital. Alternatively or additionally, the signal coupling in the embodiment of Fig. 4 can take place in the control unit 208.

[0090] In each of the exemplary embodiments of the device 200-1; 200-2; 200-3 in Figs. 2A, 2B, 3, and 4, a triangular voltage is shown as an example of the alternating voltage 218. However, other forms of the alternating voltage 218, in particular as a sinusoidal voltage, sawtooth voltage, and / or square-wave voltage (also: rectangular voltage), are equally possible. The shape of the output spectrum of the LLC converter depends on the respective form of the alternating voltage 218.

[0091] The triangular voltage shown as well as a sinusoidal voltage (and / or, for example, a trapezoidal voltage) have the advantage of a continuous voltage curve.

[0092] If the input voltage of the LLC converter 100 changes abruptly, the LLC converter 100 would also have to change its switching frequency abruptly if the output voltage is to remain stable. However, due to the reaction time of the circuit unit (also: regulator) 112, the LLC converter 100 cannot usually adjust its frequency as quickly as desired. Therefore, a disturbance in the output voltage can become visible, particularly at high frequencies of the superimposed AC voltage 218 and / or with discontinuous voltage waveforms of the superimposed AC voltage 218. It is therefore advantageous if the AC voltage 218 has a continuous waveform on the input voltage of the LLC converter 100. Alternatively or additionally, the circuit unit (also: regulator) 112 of the LLC converter 100 can effectively regulate continuous voltage changes.

[0093] Alternatively or additionally, superimposed alternating voltages (also known as modulation signals) 218 ​​with discontinuities (e.g., square, sawtooth) can be advantageous. The shape of the superimposed alternating voltage (also known as modulation signal) influences, for example, the shape of the peaks in the spectrum.

[0094] Furthermore, alternatively or additionally, depending on the application, small

[0095] Disturbances on the output voltage of the LLC converter 100 are also tolerated, which is why a superimposed alternating voltage (also:

[0096] Modulation signal) 218 ​​with jumps would then not be too big a problem.

[0097] In principle, any form of superimposed alternating voltages 218 can be used with a suitable (and / or specific) amplitude and frequency. Furthermore, in each of the exemplary embodiments of the device 200-1; 200-2; 200-3 in Figs. 2A, 2B, 3, and 4, the matching converter 206 is embodied, by way of example, as a boost converter. However, other embodiments of the matching converter 206, in particular as a buck converter and / or boost-buck converter, are equally possible.

[0098] Fig. 5 shows an example of a conventional output spectrum of an LLC converter, for example the LLC converter 100 of Fig. 1. The spectrum in Fig. 5 can also be referred to as an example spectrum without LLC jitter.

[0099] On the abscissa, at reference numeral 502 in Fig. 5, the respective frequency is plotted in units of Hertz (Hz). On the ordinate, at reference numeral 504, a logarithmic unit of the voltage measure in decibel microvolts (dBpV) is plotted. A quasi-peak limit (also called a quasi-peak limit or quasi-peak characteristic value) is plotted at reference numeral 506, and an average limit (also called an average limit or average characteristic value) is plotted at reference numeral 508. The quasi-peak limit and / or the average limit can be predetermined by an EMC of the LLC converter, for example, the LLC converter 100 in Fig. 1.

[0100] At reference numeral 510, a spectrum of quasi-peak measurements (also: quasi-peak measurements) of a conventional LLC converter with a low-ripple input voltage is plotted. As can be seen from Fig. 5, for example, in the frequency domain at 300 kHz and 500 kHz, the conventional quasi-peak spectrum includes narrowband peaks that may exceed one of the threshold values, for example, the average threshold value at reference numeral 508. At reference numeral 512, a spectrum of average measurements (also: average measurements) of a conventional LLC converter with a low-ripple input voltage is plotted. Narrowband peaks are also evident in this conventional spectrum.

[0101] Fig. 6 shows an exemplary output spectrum of the LLC converter 100 of the inventive device 200-1; 200-2; 200-3 of Figs. 2A, 2B, 3, and 4, respectively. The output spectrum is provided, for example, at the terminals designated by reference numeral 220. The spectrum in Fig. 6 can also be referred to as an example spectrum with LLC jitter.

[0102] Identical quantities (e.g. coordinate axes, characteristic values ​​and / or limit values) are designated by the same reference numerals in Fig. 5 and Fig. 6.

[0103] At reference numeral 610 in Fig. 6, the spectrum of the quasi-peak measured values ​​(also: quasi-peak measured values) at the output (for example, at terminals 220 of the stable DC voltage supply) of the LLC converter 100 of the inventive device 200-1; 200-2; 200-3 is plotted. Compared to the conventional spectrum of Fig. 5, the spectrum of Fig. 6 includes broadened and flattened peak values, as can be seen, for example, in the frequency range at approximately 300 kHz and approximately 500 kHz.

[0104] The spectrum of the average measured values ​​(also: average measured values) at the output (for example, at terminals 220 of the stable DC voltage supply) of the LLC converter 100 of the device 200-1; 200-2; 200-3 according to the invention is plotted at reference numeral 612. The broadening and flattening of the peaks compared to Fig. 5 is also evident in this spectrum of Fig. 6.

[0105] As can be seen by comparing Figs. 5 and 6, a greater than conventional variation of the switching frequency of the LLC converter 100 results in lower quasi-peak values ​​(also: quasi-peak values) and average values ​​(also: average values) in the spectrum, since the energy is distributed over a larger frequency range.

[0106] Alternatively or additionally, the average values ​​(also: average values) of the device according to the invention (for example the device 200-1; 200-2; 200-3 in Fig. 3, 4 and 5 respectively) can be significantly below the quasi-peak values ​​(also: quasi-peak values).

[0107] Thus, when using the device according to the invention (for example the device 200-1; 200-2; 200-3 of Figs. 2A and 2B, 3 and 4 respectively) and / or the feeding of a superimposed AC voltage 281 into the input DC voltage of the LLC converter 100, less effort is required than is conventional for EMC measures, in particular of the LLC converter 100.

[0108] The switching frequency of the LLC converter, for example, LLC converter 100 in Fig. 1, is determined by its input DC voltage and output DC voltage. If the input DC voltage of LLC converter 100 is changed, according to the invention its switching frequency must also change in order to generate a constantly high output DC voltage (for example, at terminals 220 of the stable DC voltage supply). If the input DC voltage change according to the invention occurs only slowly, the circuit unit 112 (also: control) of LLC converter 100 is able to adjust the output DC voltage quickly enough so that the disturbance (particularly in the frequency and amplitude of the input DC voltage) does not affect the output DC voltage.

[0109] The technical solution according to the invention consists in the fact that a matching converter 206 is provided between the input DC voltage and the LLC converter 100, which supplies the LLC converter 100 with its output DC voltage. The technical solution according to the invention further consists in the fact that the output DC voltage of the matching converter 206 is modified (also: manipulated) such that an AC voltage 218 is deliberately superimposed on it. Changing the output DC voltage of the matching converter 206 must also change the switching frequency of the LLC converter 100 (particularly with a constant output DC voltage of the LLC converter 100, for example, at the terminals 220 of the stable DC voltage supply).

[0110] According to one embodiment, a device according to the invention for a stable DC voltage supply is fed from a three-phase (also: 3-phase) AC voltage source (also: mains voltage) 202, which is subsequently rectified 204. A boost converter (also: step-up converter) acts as a matching converter 206. An AC voltage (for example, a triangular voltage or a sawtooth voltage) 218 ​​is superimposed on the actual value for the DC output voltage of the boost converter 206, which causes the DC output voltage of the boost converter 206 to fluctuate accordingly (e.g., by an amplitude of ±7 V at a frequency of 1.2 Hz with an average value of 805 volts). The fluctuating DC input voltage leads to a temporal clock jitter (also: frequency jitter) of the LLC converter 100.

[0111] The device of, or each embodiment can provide an adjustable DC output voltage of 22.5 V to 29.5 V, in particular 24 V (for example, at terminals 220 of the stable DC power supply in Fig. 2A, 2B, 3, or 4). The output currents can range between 2.5 amperes (A) and 40 A. In particular, the output currents can be 2.5 A, 5 A, 10 A, 20 A, and / or 40 A.

[0112] According to further embodiments, DC output voltage values ​​of 12 V, 48 V, 120 V, or 250 V are possible. Alternatively or additionally, the output currents can be in the range of several hundred amperes, e.g., 200 A or 1000 A. The present invention is not limited to the voltage values ​​or current values ​​(collectively referred to as characteristic values) of the above-mentioned embodiments, but is also applicable to other combinations of characteristic values.

[0113] According to further embodiments, the matching converter 206 comprises a buck converter, a buck-boost converter, a flyback converter, a SEPIC converter, a forward converter and / or a bridge converter.

[0114] In each embodiment, the LLC converter 100 can comprise its own control loop, for example, integrated into (or including) the circuit unit 112. Alternatively or additionally, the superimposed AC voltage 218 can influence the control unit 208 of the matching converter 206.

[0115] Furthermore, alternatively or additionally, the control loop of the LLC converter 100 is not intervened in directly, but for example only indirectly by changing both the amplitude and the frequency of the input DC voltage (in particular by superimposing the output DC voltage of the matching converter 206 with the AC voltage 218) at the input of the LLC converter 100.

[0116] Due to the change in the input DC voltage, the LLC converter 100, according to embodiments of the invention, must change its switching frequency so that the output DC voltage (for example, at terminals 220 of the stable DC voltage supply in Fig. 2A, 2B, 3, or 4) remains stable. This is accomplished by a (for example, already existing) circuit unit 112 (also: control loop) of the LLC converter 100. According to the invention, the switching frequency change of the LLC converter 100 can thus be enforced indirectly by the matching converter 206, without having to directly intervene in the circuit unit 112 (also: the control loop) of the LLC converter 100.

[0117] According to one embodiment, the device 200-1; 200-2; 200-3 according to the invention is powered by a DC voltage source, ie an input DC voltage with a frequency of 0 Hz.

[0118] According to a further embodiment, the device 200-1; 200-2; 200-3 according to the invention is supplied by an (e.g. three-phase) alternating voltage 202 with a frequency of 50 Hz to 60 Hz and subsequent rectification 204.

[0119] According to a further embodiment, the device 200-1; 200-2; 200-3 according to the invention is supplied by an alternating voltage (for example, an on-board power supply, in particular an aircraft power supply) 202 with a frequency of 400 Hz and subsequent rectification 204.

[0120] According to further embodiments, frequencies of over 400 Hz of an AC voltage source 202 with subsequent rectification 204 are possible.

[0121] Alternatively or additionally, a voltage ripple can be lower the higher the frequency of the voltage source 202 (for example with subsequent rectification 204) from which the matching converter 206 is fed.

[0122] According to one embodiment, a frequency of a superimposed AC voltage 218, for example, a triangular voltage or a sawtooth voltage, can be between 0.5 Hz and 2 Hz. Alternatively or additionally, other frequencies of the superimposed AC voltage 218 are possible, which correspond to a significantly slower change in the DC output voltage of the matching converter 206 and / or the DC input voltage of the LLC converter 100 than the responsiveness of the circuit unit (also: the LLC regulator) 112 of the LLC converter 112. Thus, the circuit unit (also: the LLC regulator) 112 of the LLC converter 112 can keep the DC output voltage (for example, at terminals 220 in Fig. 2A, 2B, 3, or 4) stable.

[0123] According to further starting examples, an input DC voltage of a voltage source (also: mains) can be between 12 V and 800 V. Alternatively or additionally, an input AC voltage of a voltage source 202 (for example, with subsequent rectification 204) can be between 100 V and 500 V, in particular between 400 V and 500 V. For example, the three-phase AC voltage source 202 in Figs. 2A, 2B, 3 and 4 can each provide a voltage between 400 V and 500 V to the rectifier 204.

[0124] According to further embodiments, the input DC voltage Vzk of the LLC converter 100 in Fig. 2A, 2B, 3 or 4 is 800V, on which a low-frequency AC voltage 218 with an amplitude of ±10V to ±20V and a frequency of 1 Hz is superimposed.

[0125] The voltage values ​​and / or amplitudes mentioned in the exemplary embodiments, in particular the (e.g., input and / or output) DC voltages, are exemplary. Other voltage values ​​and / or amplitudes can be superimposed, according to the invention, with a suitably selected AC voltage.

[0126] If the frequency spectrum were completely unimportant, the input voltage of the LLC converter 100 would normally be kept as stable as possible. The fact that an alternating voltage 218 is superimposed (also: modulated) for the frequency jitter is intuitively the opposite of conventional requirements because it disrupts the circuit unit (also: regulator) 112 of the LLC converter 100. Alternatively or additionally, components can be subjected to greater loads than conventionally. For example, an input capacitor according to the invention can be designed for a higher voltage (for example, a direct voltage plus the amplitude of the alternating voltage) than conventionally. These adverse effects can, in particular, limit the characteristics of the superimposed alternating voltage 218 in relation to the characteristics of the output voltage of the matching converter 206.

[0127] For example, with a superimposed alternating voltage 218 of 20 V (also: ±20 V peak voltage; in short: ±20 Vpk) relative to a direct voltage of 800 V (also: Vdc), a strong broadening of the peaks in the spectrum can be achieved and nevertheless the device (for example the device 200-1; 200-2; 200-3) can still operate well and the components are not overloaded.

[0128] According to a further embodiment, a superimposed AC voltage 218 of 10 V (also: ±10 V peak voltage; in short: ±10 Vpk) relative to a DC voltage of 400 V (also: Vdc) is suitable for a strong broadening of the peaks in the spectrum without overloading components of the device (for example, the device 200-1; 200-2; 200-3).

[0129] According to yet another embodiment, a superimposed AC voltage 218 of 4 V (also: ±4 V peak voltage; in short: ±4 Vpk) relative to a DC voltage of 160 V (also: Vdc) is suitable for significantly broadening the peaks in the spectrum without overloading components of the device (e.g., the device 200-1; 200-2; 200-3). For example, the ratio can be calculated based on the embodiment of a DC voltage of 800 V with a superimposed AC voltage 218 of 20 V as: (DC voltage value in V) / 800 V x 20 V = (permissible and / or suitable superimposed AC voltage value in V).

[0130] All embodiments can be combined with one another unless otherwise specified. Although the invention has been described with reference to exemplary embodiments, it will be apparent to those skilled in the art that various changes may be made and equivalents may be substituted. Furthermore, many modifications may be made to adapt a particular situation or electrical performance requirement to the teachings of the invention. Consequently, the invention is not limited to the disclosed embodiments, but includes all embodiments falling within the scope of the appended claims.

[0131] List of reference symbols

[0132] LLC converter 100

[0133] Transformer 102

[0134] Inductance 104-1; 104-2; 104-3

[0135] Capacity 106-1; 106-2; 106-3

[0136] Semiconductor switches 108

[0137] Diode 110

[0138] Circuit unit 112

[0139] Device for stable DC voltage supply 200-1; 200-2; 200-3

[0140] Voltage source 202

[0141] Rectifier 204

[0142] Matching converter 206

[0143] Control unit 208

[0144] Setpoint voltage 210

[0145] Actual value of voltage 212

[0146] First resistance of the resistance bridge 214

[0147] Second resistance of the resistance bridge 216

[0148] Superimposed alternating voltage 218

[0149] Signal generator of the superimposed alternating voltage 219

[0150] Connections for stable DC voltage supply 220

[0151] Resistance 222

[0152] Frequency (abscissa) 502

[0153] Voltage value (ordinate) 504

[0154] Quasi-peak characteristic value 506

[0155] Average value 508

[0156] Quasi-peak measurement value in the state of the art 510

[0157] Average measured value in the state of the art 512

[0158] Quasi-peak measured value according to embodiment of the invention 610

[0159] Average measured value according to embodiment of the invention 612

Claims

Patent claims 1. Device (200-1; 200-2; 200-3) for stable DC voltage supply (220) comprising: a matching converter (206) which is electrically connected or connectable on an input side of the matching converter (206) to a DC voltage source (202, 204) or an AC voltage source (202); and an LLC converter (100) which is electrically connected or connectable on an input side to an output side of the matching converter (206), wherein the LLC converter (100) is configured to provide a stable DC voltage supply (220) on an output side, wherein a DC voltage of the output-side stable DC voltage supply (220) is a function of a switching frequency of the LLC converter (100); wherein the matching converter (206) comprises a control unit (208) configured to superimpose an output DC voltage of the matching converter (206) with an AC voltage (218);wherein an amplitude of the superimposed AC voltage (218) is smaller than the output DC voltage; and wherein a frequency of the superimposed AC voltage (218) is lower than the switching frequency of the LLC converter (100).; 2. Device (200-1 -; 200-2; 200-3) according to claim 1, wherein the DC voltage source (202, 204) comprises a three-phase AC voltage source (202) and a rectifier (204) arranged between the three-phase AC voltage source (204) and the input side of the matching converter (206).

3. Device (200-1 ; 200-2; 200-3) according to claim 1 or 2, wherein the matching converter (206) comprises a boost converter, a buck converter, and / or a boost-buck converter.

4. Device (200-1 ; 200-2; 200-3) according to any one of claims 1 to 3, wherein the superimposed alternating voltage (218) comprises a triangular voltage, a sinusoidal voltage, a sawtooth voltage and / or a square wave voltage.

5. Device (200-1 ; 200-2; 200-3) according to any one of claims 1 to 4, further comprising two resistors (214; 216) connected in series to form a voltage divider, wherein the voltage divider is connected between both poles of the output side of the matching converter (206) and / or between both poles of the input side of the LLC converter (100), and wherein the control unit (208) of the matching converter (206) is configured to regulate the output DC voltage of the matching converter (206) depending on a voltage tapped at a node between the first resistor (214) and the second resistor (216) of the voltage divider.

6. Device (200-1 ; 200-2) according to claim 5, further comprising a signal generator (219) which couples a control signal of the superimposed AC voltage (218) into the tapped voltage, optionally via a third resistor (222) which is electrically connected at a first terminal to the junction between the first resistor (214) and the second resistor (216) of the voltage divider, wherein the third resistor (222) is electrically connected at a second terminal to the signal generator (219).

7. Device (200-1) according to claim 6, wherein the signal generator (219) is further connected to one of the two poles of the output side of the matching converter (206) and / or is electrically connected to one of the two poles of the input side of the LLC converter (100), and / or wherein the signal generator (219) is arranged outside the matching converter (206).

8. Device (200-1 ; 200-2) according to claim 6 or 7, wherein the control signal of the superimposed AC voltage (218) is added to the voltage tapped via the voltage divider.

9. Device (200-1 ; 200-2) according to one of claims 5 to 8, wherein the control unit (208) is configured to regulate the output DC voltage of the matching converter (206) depending on an actual voltage, wherein the signal generator (219) couples a control signal of the superimposed AC voltage (218) into the actual voltage, optionally wherein the control signal is added to an actual value in the control unit (208).

10. Device (200-3) according to one of claims 5 to 8, wherein the control unit (208) is configured to regulate the output DC voltage of the matching converter (206) depending on a setpoint voltage, wherein the signal generator (219) couples a control signal of the superimposed AC voltage (218) into the setpoint voltage, optionally wherein the control signal is added to a constant setpoint value in the control unit (208).

11. Device (200-1 ; 200-2; 200-3) according to any one of claims 1 to 10, wherein the superposition of the output voltage of the matching converter (206) with the superimposed AC voltage (218) comprises analog signal coupling and / or digital signal coupling in the control unit (208).

12. Device (200-1 ; 200-2; 200-3) according to any one of claims 1 to 11 , wherein the frequency of the superimposed alternating voltage (218) is between 0.5 Hz and 2 Hz, optionally wherein the frequency of the superimposed alternating voltage (218) is 1 Hz.

13. Device (200-1 ; 200-2; 200-3) according to any one of claims 1 to 12, wherein the output DC voltage of the matching converter is at least an integer multiple of the amplitude of the superimposed AC voltage (218); and / or wherein the output DC voltage of the matching converter is between 400 V and 800 V; and / or wherein the amplitude of the superimposed AC voltage (218) is between 10 V and 20 V.

14. Method for providing a stable DC power supply (220), comprising the steps: Matching a DC voltage from a DC voltage source (202, 204) or an AC voltage from an AC voltage source (202) using a matching converter (206); Superimposing an output DC voltage of the matching converter (206) with an AC voltage (218); wherein an amplitude of the superimposed AC voltage (218) is smaller than the output DC voltage of the matching converter (206); Converting the output DC voltage of the matching converter (206) superimposed with the AC voltage (218) by means of an LLC converter (100), wherein the LLC converter (100) is configured to provide a stable DC voltage supply (220) on one output side, wherein a DC voltage of the output-side stable DC supply is a function of a switching frequency of the LLC converter (100); wherein a frequency of the superimposed AC voltage (218) is lower than the switching frequency of the LLC converter (100); and providing a stable DC voltage at the output side of the LLC converter (100).

15. The method of claim 14, further comprising the steps of: Rectifying an alternating voltage from an alternating voltage source (202) using a rectifier (204); and Providing the rectified voltage as the DC voltage of the DC voltage source at an input side of the matching converter (206).

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