DC-DC converter

Abstract

A method for operating a DC-DC converter comprising a buck-boost converter having an inductor and a switching element, comprising measuring a current flowing through the inductor and performing the following steps: a) comparing the current with a first threshold current value; b) if the current is below / not below the first threshold current value, setting the buck-boost converter to a first / second switching state at the beginning of the switching period; c) if the buck-boost converter is operating in the first switching state, comparing the current with a first threshold current value, setting the buck-boost converter to a second switching state once the current reaches the first threshold current value; d) if the buck-boost converter is operating in the second switching state, comparing the current with a second threshold current value, setting the buck-boost converter to a third switching state once the current reaches the second threshold current value; and repeating steps a) to d) after expiration of the predetermined period duration.

Description

Technical Field

[0001] The present invention relates to a DC-DC converter, in particular a DC-DC converter designed as a buck-boost converter, and a method for driving such a DC-DC converter. Background Art

[0002] A buck-boost converter is capable of converting an input DC voltage into a lower output voltage (step-down mode, buck mode) and a higher output voltage (step-up mode, boost mode).

[0003] In the prior art, buck-boost converters are known which comprise an inductor and a plurality of switching elements, and the switching elements are alternately switched to effect a step-up or step-down of the input voltage.

[0004] To drive such a buck-boost converter, two methods are particularly known from the prior art. In the case of pulse width modulation (PWM), a switching signal with a predetermined duty cycle is used to drive the switch, and the predetermined duty cycle is a predetermined ratio between the on-time of the switching element and the cycle duration of the switching period. In the case of peak current control, the current coil current is compared with a threshold value, and switching is effected when the coil current reaches the threshold value. Thus, in this case, the duty cycle can be changed as a function of the coil current.

[0005] In both cases, the drive circuit of the switching element must in each case distinguish whether the converter is currently in the boost mode or in the buck mode. Depending on the current operating state, the switching transistors comprised in the buck-boost converter must be driven in a different manner.

[0006] Furthermore, the transition region between the step-down mode and the step-up mode (buck-boost) is difficult to regulate. In this case, the drive circuit must cyclically switch between the two operating modes. Thus, for example, driving the switching transistors by software is complex and time-consuming, and is very time-critical.

[0007] U.S. Patent No. 2,023,223,852 A1 describes such a DC-DC converter, the driving thereof in different operating modes, and the switching between these operating modes. Summary of the Invention

[0008] The object of the present invention is to provide a DC-DC converter and a method for driving the same which are improved with respect to the prior art.

[0009] The object is achieved by the subject matter of the independent claims. Further embodiments of the present invention are specified in the dependent claims. In this case, the subject matter of the independent claims can also be embodied by the features of the dependent claims of another independent claim.

[0010] The method according to the invention is for operating a DC-DC converter, which DC-DC converter comprises a buck-boost converter having an inductor and a plurality of switching elements, wherein a boosting operation is achieved by alternately switching the switching elements between a first switching state BOOST ON (boost on) and a second switching state BOOST OFF (boost off), BUCK ON (buck on), and a bucking operation is achieved by alternately switching between the second switching state BOOST OFF, BUCK ON and a third switching state BUCK OFF (buck off), wherein the switching between the switching states occurs periodically in a switching period having a predetermined period duration. The method includes measuring the current flowing through the inductor and performing the following method steps:

[0011] a) comparing the current with a first threshold current value,

[0012] b) if the current is lower than the first threshold current value, setting the buck-boost converter to the first switching state at the start of the switching period, or if the current is not lower than the first threshold current value, setting the buck-boost converter to the second switching state at the start of the switching period,

[0013] c) if the buck-boost converter is operating in the first switching state, comparing the current with the first threshold current value and, once the current reaches the first threshold current value, setting the buck-boost converter to the second switching state,

[0014] d) if the buck-boost converter is operating in the second switching state, comparing the current with a second threshold current value greater than the first threshold current value and, once the current reaches the second threshold current value, setting the buck-boost converter to the third switching state, and

[0015] repeating steps a) to d) after the expiration of the predetermined period duration.

[0016] In a further advantageous embodiment, the buck-boost converter is set to the first switching state before step a) or b).

[0017] In a further advantageous embodiment, at the end of the switching period and before the expiration of the predetermined period duration, the buck-boost converter is set to a fourth switching state, which fourth switching state is designed to regenerate the internal supply voltage of the driver circuits of the switching elements (S1, S3) connected to the input terminals or output terminals of the buck-boost converter.

[0018] In a further advantageous embodiment, the first threshold current value and / or the second threshold current value and / or the predetermined cycle duration are obtained from the operating data of the device that uses the DC-DC converter.

[0019] In a further advantageous embodiment, the operating data of the device includes maximum power point tracking data of the current generator and / or the maximum current for charging the current memory and / or the maximum voltage for charging the current memory.

[0020] The DC-DC converter according to the invention comprises a buck-boost converter having an inductor and a plurality of switching elements, wherein a boosting operation is achieved by alternately switching the switching elements between a first switching state BOOST ON and a second switching state BOOST OFF, BUCK ON, and a bucking operation is achieved by alternately switching between the second switching state BOOST OFF, BUCK ON and a third switching state BUCK OFF; and comprises a control device for controlling the DC-DC converter. The control device is configured or programmed to operate the DC-DC converter by means of the method according to the invention.

[0021] In a further advantageous embodiment, the buck-boost converter comprises an input terminal for applying an input voltage, an output terminal for outputting an output voltage and a common ground, wherein a first end of the inductor is connected to the input terminal via a first switching element and to the ground via a second switching element, and a second end of the inductor is connected to the output terminal OUT via a third switching element and to the ground GND via a fourth switching element.

[0022] In a further advantageous embodiment, in the first switching state, the second and third switching elements are open, and the first and fourth switching elements are closed; and / or in the second switching state, the second and fourth switching elements are open, and the first and third switching elements are closed; and / or in the third switching state, the first and fourth switching elements are open, and the second and third switching elements are closed; and / or in the fourth switching state, the first and third switching elements are open, and the second and fourth switching elements are closed.

[0023] In a further advantageous embodiment, the control device comprises a microcontroller.

[0024] In a further advantageous embodiment, the comparison of the current with the first threshold current value and / or with the second threshold current value is performed by means of a comparator integrated in the hardware of the microcontroller.

[0025] The current generating device according to the invention comprises a current generator for generating electrical energy at a first voltage, a current memory for storing the electrical energy generated by the current generator at a second voltage, and a DC-DC converter according to the invention.

[0026] A computer program according to the present invention includes instructions which, when the computer program is executed in a control unit, cause the control unit to generate control signals for performing the method according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Further features and advantages of the present invention result from the description of exemplary embodiments with reference to the accompanying drawings.

[0028] Figure 1 A circuit diagram of a buck-boost converter suitable for implementing the present invention is shown.

[0029] Figure 2a and Figure 2b A simplified circuit diagram of the buck-boost converter in boost mode is shown, wherein Figure 2a the switch states in BOOST-ON mode are shown, Figure 2b the switch states in BOOST-OFF mode are shown.

[0030] Figure 3a and Figure 3b A simplified circuit diagram of the buck-boost converter in buck mode is shown, wherein Figure 3a the switch states in BUCK-ON mode are shown, Figure 3b the switch states in BUCK-OFF mode are shown.

[0031] Figure 4 A simplified circuit diagram of the buck-boost converter in REFRESH mode is shown.

[0032] Figure 5a and Figure 5b A timing diagram for the operation of the buck-boost converter is shown, wherein Figure 5a a timing diagram for boost mode is shown, Figure 5b a timing diagram for buck mode is shown.

[0033] Figure 6 A timing diagram for the operation of the buck-boost converter according to the method of the present invention is shown.

[0034] Figure 7 An example of a current curve during operation of the buck-boost converter according to the method of the present invention is shown.

[0035] Figure 8 A block diagram of a current generating device including a DC-DC converter according to the present invention is shown. DETAILED DESCRIPTION

[0036] Embodiments of the present invention will be described below with reference to the accompanying drawings.

[0037] Figure 1 An example of the buck-boost converter on which the present invention is based is shown.

[0038] The buck-boost converter 10 has an input terminal IN, an output terminal OUT, and a common ground GND. An input voltage U1 is applied between the input terminal IN and the ground GND, and an output voltage U2 is output between the output terminal OUT and the ground GND. A first capacitor C1 (input capacitor) is connected between the input terminal IN and the ground GND, and a second capacitor C2 (output capacitor) is connected between the output terminal OUT and the ground GND.

[0039] As a current storage element, the buck-boost converter 10 includes an inductor L. A first end of the inductor L is connected to the input terminal IN via a first transistor T1 and a first diode D1 and is connected to the ground GND via a second transistor T2 and a second diode D2. A second end of the inductor L is connected to the output terminal OUT via a third transistor T3 and a third diode D3 and is connected to the ground GND via a fourth transistor T4 and a fourth diode D4. The transistors T1-T4 serve as switching elements of the buck-boost converter 10, and the diodes D1-D4 serve as freewheeling diodes of the switching transistors.

[0040] The following refers to Figure 2a and Figures 2b - 4 to explain different operating modes of the buck-boost converter 10. The switching elements S1-S4 are generally shown in these figures, instead of Figure 1 the switching transistors T1-T4 with anti-parallel connected freewheeling diodes D1-D4 shown in

[0041] The boosting operation (boost mode) of the buck-boost converter 10 is achieved by alternately switching between a BOOST-ON (boost-on) mode and a BOOST-OFF (boost-off) mode. Figure 2a and Figure 2b show a simplified circuit diagram of the buck-boost converter 10 in the boost mode, where Figure 2a shows the switching state in the BOOST-ON mode, Figure 2b shows the switching state in the BOOST-OFF mode.

[0042] In the boosting operation or boost mode, the switching element S1 is permanently closed (on, turned on) and the switching element S2 is permanently open (off, turned off). The boosting of the input voltage is performed by alternately opening and closing the switching elements S3 and S4.

[0043] In BOOST-ON mode, switch element S3 is open and switch element S4 is closed. In BOOST-OFF mode, switch element S3 is closed and switch element S4 is open.

[0044] The step-down operation (step-down mode) of the buck-boost converter 10 is achieved by alternately switching between BUCK-ON (step-down-on) mode and BUCK-OFF (step-down-off) mode. Figure 3a and Figure 3b A simplified circuit diagram of the buck-boost converter 10 in step-down mode is shown, where Figure 3a the switching states in BUCK-ON mode are shown, Figure 3b the switching states in BUCK-OFF mode are shown.

[0045] In the step-down operation or step-down mode, switch element S3 is permanently closed and switch element S4 is permanently open. The step-down of the input voltage is performed by alternately opening and closing switch elements S1 and S2.

[0046] In BUCK-ON mode, switch element S1 is closed and switch element S2 is open. Therefore, according to the switching states of the respective switch elements S1 - S4, BUCK-ON mode corresponds to BOOST-OFF mode. In BUCK-OFF mode, switch element S1 is open and switch element S2 is closed.

[0047] Since the switching states of switch elements S1 - S4 in BUCK-ON mode correspond to the switching states in BOOST-OFF mode, the above four modes only cover three of the four possible switching states. Figure 4 A simplified circuit diagram of the buck-boost converter 10 in the fourth switching state is shown.

[0048] In this case, switch elements S1 and S3 are open and switch elements S2 and S4 are closed. Therefore, both ends of the inductor L are connected to ground.

[0049] This state can be used to enable the drive circuits of the high-side switch elements S1 and S3 to regenerate their internal power supply voltages by means of an internal boost circuit. Therefore, it is called the REFRESH (refresh) mode and can be additionally used at the end of the switching cycle before the start of the next switching cycle.

[0050] Figure 5a and Figure 5b A timing diagram for the operation of the buck-boost converter 10 is shown, where Figure 5a a timing diagram for the boost mode (step-up mode) is shown, Figure 5bA timing diagram for the step-down mode (buck mode) is shown. The switching of the switching elements S1 - S4 occurs periodically within a switching period having a period duration Tc.

[0051] In the boost mode, at the start of the switching period, the switching element S3 is turned off and the switching element S4 is turned on, whereby the buck-boost converter 10 is set to the BOOST-ON mode. A continuously increasing current I flows from the input terminal IN through the inductor L to the ground GND. This current I is measured and compared with a first threshold current value Ival.

[0052] Once the current I reaches the first threshold current value Ival, the switching element S3 is turned on and the switching element S4 is turned off, whereby the buck-boost converter 10 is set to the BOOST-OFF mode. The current I flowing through the inductor L from the input terminal IN flows into the capacitor and charges the capacitor. During this process, the current I continuously decreases.

[0053] In the step-down mode, at the start of the switching period, the switching element S1 is turned on and the switching element S2 is turned off, whereby the buck-boost converter 10 is set to the BUCK-ON mode. The current I flows from the input terminal IN through the inductor L into the capacitor and charges the capacitor. During this process, the current I continuously increases. This current I is measured and compared with a second threshold current value Ipk that is greater than the first threshold current value Ival.

[0054] Even though the BUCK-ON mode corresponds to the BOOST-OFF mode in terms of the switching states of the switching elements S1 - S4, the BUCK-ON mode differs from the BOOST-OFF mode in that, since the input voltage U1 in the step-down mode is greater than the output voltage U2, the current I flowing through the inductor L increases in the BUCK-ON mode, while in the BOOST-OFF mode, since the input voltage U1 in the boost mode is less than the output voltage U2, the current I flowing through the inductor L decreases.

[0055] Once the current I reaches the second threshold current value Ipk, the switching element S1 is turned off and the switching element S2 is turned on, whereby the buck-boost converter 10 is set to the BUCK-OFF mode. The current I flowing through the inductor L from the input terminal IN continues to flow into the capacitor and further charges the capacitor. During this process, the current I continuously decreases.

[0056] In the prior art, based on information received from the outside regarding the ratio between the input voltage U1 and the output voltage U2, it is determined whether the buck-boost converter 10 is to be driven in the boost mode or in the step-down mode, and the drive is adjusted accordingly.

[0057] To eliminate this drawback of the prior art, according to the present invention, the drive is implemented with a time curve as shown in Figure 6 shown.

[0058] In the case of the current curve shown in Figure 6 , at the start of the switching period, the current I flowing through the inductor L is less than the first threshold current value Ival. At the start of the switching period, the buck-boost converter 10 is set to a first switching state corresponding to the BOOST-ON mode (switching elements S1 and S4 are closed, and switching elements S2 and S3 are open). The continuously increasing current I flows from the input terminal IN through the inductor L to the ground GND. This current I is measured and compared with the first threshold current value Ival.

[0059] Once the current I reaches the first threshold current value Ival, the buck-boost converter 10 is set to a second switching state corresponding to the BOOST-OFF mode (switching elements S1 and S3 are closed, and switching elements S2 and S4 are open). The current I flowing through the inductor L flows into the capacitor and charges the capacitor. This current I is measured and compared with the second threshold current value Ipk.

[0060] Depending on whether the input voltage U1 is less than or greater than the output voltage U2, the current I decreases again or further increases. In the case of the current curve shown in Figure 6 , the current further increases, that is, the input voltage is greater than the output voltage.

[0061] Once the current I reaches the second threshold current value Ipk, the buck-boost converter 10 is set to a third switching state corresponding to the BUCK-OFF mode (switching elements S2 and S3 are closed, and switching elements S1 and S4 are open). The current I flowing from the input terminal IN through the inductor L continues to flow into the capacitor and further charges the capacitor, but the current I continuously decreases during this process.

[0062] After the expiration of a predetermined cycle duration Tc, the next switching period starts, and the buck-boost converter 10 is set back to the first switching state.

[0063] Since the switching state in the BOOST-OFF mode corresponds to the switching state in the BUCK-ON mode, the switching period includes the sequence of BUCK-ON / BUCK-OFF, thereby achieving bucking of the input voltage U1. The previous BOOST-ON mode only supports the subsequent BUCK-ON mode during the charging of the inductor L.

[0064] In the case of another current curve, if the current I flowing through the inductor L decreases again after switching to the second switch state or at least does not increase to the second threshold current value Ipk, the second switch state is maintained until the expiration of a predetermined cycle duration Tc. Thus, the switching cycle includes the sequence BOOST-ON / BOOST-OFF, thereby achieving a boost of the input voltage U1.

[0065] If the current I flowing through the inductor L at the start of the switching cycle has exceeded the first threshold current value Ival, the buck-boost converter 10 is immediately set to the second switch state according to the above actuation after being set to the first switch state. Alternatively, the buck-boost converter 10 can also be directly set to the second switch state without first being set to the first switch state.

[0066] Due to the above sequence of switch states, the drive circuit of the switching element no longer has to distinguish whether the converter is currently in the buck mode or the boost mode, and there is also no longer a need to perform the sequence of switch states in a correspondingly different manner. Depending on how the current I flowing through the inductor L changes after switching to the second state, the correct operating mode is automatically selected: the boost mode is selected by the sequence BOOST-ON / BOOST-OFF, and the buck mode is selected by the sequence BOOST-ON / BUCK-ON / BUCK-OFF or just BUCK-ON / BUCK-OFF.

[0067] Figure 7 An example of the time curve of the current I flowing through the inductor L is shown. For illustrative purposes, seven switching cycles 1-7 are shown in a simplified manner, during which the ratio between the input voltage U1 and the output voltage U2 changes several times. In reality, this change will extend over substantially more switching cycles because the voltage ratio only changes slightly during the cycle duration Tc.

[0068] In the first two switching cycles 1 and 2, the input voltage U1 is lower than the output voltage U2, and the buck-boost converter 10 operates in a boosting operation or boost mode in the order of BOOST-ON / BOOST-OFF. In switching cycle 3, the input voltage U1 has increased to be higher than the output voltage U2, and the buck-boost converter 10 changes to a step-down operation or buck mode in the order of BOOST-ON / BUCK-ON / BUCK-OFF. In switching cycles 4 and 5, the buck-boost converter 10 continues to operate in a step-down operation or buck mode in the order of BUCK-ON / BUCK-OFF, where, since the input voltage U1 drops below the output voltage U2, the current I in switching cycle 5 drops to a value lower than the first current threshold Ival. In switching cycles 6 and 7, the buck-boost converter 10 operates again in a boosting operation or boost mode in the order of BOOST-ON / BOOST-OFF.

[0069] The actuation of the buck-boost converter is greatly simplified by the above method. The switching states are activated in an order that is a function of the measured coil current I. Due to the initialization of the converter in the BOOST-ON operation, safe and proper operation is achieved without the need to compare the input voltage U1 and the output voltage U2. Therefore, there is no need for external information on whether the input voltage U1 is greater than the output voltage U2 or vice versa and a change in the drive of the switching state in response to this information. Thus, precisely in the transition region between the boosting operation (boost mode) and the step-down operation (buck mode), it is possible to switch flexibly and quickly between the two operating modes.

[0070] The parameters required for this method, such as the first threshold current value Ival, the second threshold current value Ipk, or the period duration Tc, can be obtained, for example, from the operating data of a device (such as a current generating device) using a DC-DC converter with the aid of an external controller (not shown). This can include, for example, MPPT data (maximum power point tracking) of a solar power generation system or the maximum current or maximum voltage for charging a battery.

[0071] Figure 8 A block diagram of a current generating device 100 is shown. The current generating device 100 includes a current generator 200, a DC-DC converter 300, and a current memory 400.

[0072] The current generator 200 supplies electrical energy at a variable DC voltage U1. For example, the current generator 200 can be formed as a solar panel, where the DC voltage U1 depends on the instantaneous solar radiation and thus undergoes large fluctuations.

[0073] The current memory 400 is used to store electrical energy supplied by the current generator 200. For example, the current memory 400 can be formed as a rechargeable battery. The charging voltage suitable for charging the battery is typically within a relatively narrow voltage range.

[0074] The DC-DC converter 300 is used to convert the DC voltage U1 supplied by the current generator 200 into a charging voltage U2 suitable for charging the battery. Depending on the magnitude of the DC voltage U1 instantaneously supplied by the current generator 200, the DC-DC converter 300 must operate in a boost operation (step-up mode) or a buck operation (step-down mode).

[0075] The DC-DC converter 300 includes the buck-boost converter 10 and the control device 20 described above. The control device 20 is configured or programmed to control the DC-DC converter 300 by means of the method described above with reference to Figure 6 the method described.

[0076] The control device can be designed as a microcontroller, for example. The control device includes a first digital-to-analog converter 31 for generating an analog value of the first threshold current value Ival and a second digital-to-analog converter 32 for generating an analog value of the second threshold current value Ipk. As described above, these values can be obtained from the operation data of the current generating device 100 via a digital controller, for example, and then provided to the analog comparator by means of the digital-to-analog converters 31, 32.

[0077] The control device also includes a first comparator 41 for comparing the measured value of the coil current I with the first threshold current value Ival and a second comparator 42 for comparing the measured value of the coil current I with the second threshold current value Ipk. According to the comparison result, the central processing unit (CPU) 50 of the microcontroller generates a control signal for switching the switching elements S1 - S4 according to the time course described above.

[0078] The hardware comparators of the microcontroller 20 are preferably used as the comparators 41, 42, and the digital values of the threshold currents are written into the registers of these comparators 41, 42. Compared with the comparison performed by software, the speed is significantly increased, which is particularly important for the time-critical switching of the switching elements.

[0079] The circuit has short-circuit resistance on the output side because the coil current I is held at a set value by hardware. Since the hardware holds the coil current I at the set value until the software specifies a new reference value, the time requirements and speed of the controller are not important. Therefore, the external controller can operate substantially more slowly and at a frequency lower than the frequency generated by the cycle duration Tc of the switching cycle.

[0080] List of reference numerals

[0081] 1 - 7 switching period

[0082] 10 buck - boost converter

[0083] 20 control device

[0084] 50 CPU

[0085] 31, 32 digital - analog converter

[0086] 41, 42 comparator

[0087] 100 current generating device

[0088] 200 current generator

[0089] 300 DC voltage converter, DC - DC converter

[0090] 400 current memory

[0091] BOOST ON, switching state

[0092] BOOST OFF

[0093] BUCK ON

[0094] BUCK OFF

[0095] REFRESH

[0096] C1, C2 capacitor

[0097] D1 - D4 free - wheeling diode

[0098] GND ground

[0099] I coil current

[0100] IN input terminal

[0101] Ipk second threshold current value

[0102] Ival first threshold current value

[0103] L inductor

[0104] OUT output terminal

[0105] S1 - S4 switching element

[0106] T1 - T4 switching transistor

[0107] Tc period duration

[0108] U1 input voltage

[0109] U2 output voltage

Claims

1. A method of operating a DC-DC converter (300), the DC-DC converter (300) comprising a buck-boost converter (10) having an inductor (L) and a plurality of switching elements (S1-S4), wherein a boost operation is achieved by alternately switching the switching elements between a first switching state (BOOST ON) and a second switching state (BOOST OFF, BUCK ON), and a decompression operation is achieved by alternately switching between the second switching state (BOOST OFF, BUCK ON) and a third switching state (BUCK OFF), wherein the switching between the switching states occurs periodically in a switching cycle having a predetermined cycle duration (Tc), wherein: The method comprises: Measure the current (I) flowing through the inductor (L), Perform the following method steps: a) comparing the current (I) with a first threshold current value (Ival), b) setting the buck-boost converter (10) to a first switching state (BOOST ON) at the beginning of a switching cycle if the current (I) is below a first threshold current value (Ival), or If the current (I) is not lower than a first threshold current value (Ival), setting the buck-boost converter (10) to a second switching state (BOOST OFF, BUCK ON) at the beginning of a switching cycle, c) if the buck-boost converter (10) is operated in the first switching state (BOOSTON), comparing the current (I) with the first threshold current value (Ival) and setting the buck-boost converter (10) to the second switching state (BOOST OFF, BUCKON) as soon as the current (I) reaches the first threshold current value (Ival), d) if the buck-boost converter (10) is operated in the second switching state (BOOSTOFF, BUCK ON), comparing the current (I) with a second threshold current value (Ipk) greater than the first threshold current value (Ival), and once the current (I) When the second threshold current value (Ipk) is reached, the buck-boost converter is set to the third switching state (BUCK OFF), and Steps a) to d) are repeated after expiry of said predetermined cycle duration (Tc).

2. The method of operating a DC-DC converter (300) according to claim 1, wherein: Before step a), the buck-boost converter (10) is set to a first switching state (BOOST ON).

3. A method of operating a DC-DC converter (300) according to claim 1 or 2, wherein: At the end of a switching cycle before expiration of a predetermined cycle duration (Tc), the buck-boost converter (10) is set to a fourth switching state (REFRESH) configured for regenerating an internal supply voltage of a driver circuit for a switching element (S1, S3) connected to an input terminal (IN) or an output terminal (OUT) of the buck-boost converter (10).

4. A method of operating a DC-DC converter (300) according to any one of claims 1 to 3, wherein: The first threshold current value (Ival) and / or the second threshold current value (Ipk) and / or the predetermined cycle duration (Tc) are obtained from operating data of the device (100) in which the DC-DC converter (300) is used.

5. The method of operating a DC-DC converter (300) according to claim 4, wherein: The operation data of the device (100) includes maximum power point tracking data of the current generator (200) and / or a maximum current for charging the current storage (400) and / or a maximum voltage for charging the current storage (400).

6. A DC-DC converter (300), comprising: A buck-boost converter (10) having an inductor (L) and a plurality of switch elements (S1-S4), realizing a boost operation by alternately switching the switch elements between a first switch state (BOOST ON) and a second switch state (BOOST OFF, BUCK ON), and realizing a decompression operation by alternately switching between the second switch state (BOOST OFF, BUCK ON) and a third switch state (BUCK OFF), and a control device (20) for controlling the DC-DC converter, The control device (20) is configured or programmed to operate the DC-DC converter (100) by means of the method according to any one of claims 1 to 5.

7. The DC-DC converter (300) according to claim 6, wherein: The buck-boost converter (10) comprises an input terminal (IN) for applying an input voltage (U1), an output terminal (OUT) for outputting an output voltage (U2), and a common ground (GND). A first end of the inductor (L) is connected to the input terminal (IN) via a first switching element (S1) and to ground (GND) via a second switching element (S2), and A second end of the inductor (L) is connected to the output terminal (OUT) via a third switching element (S3) and is connected to the ground (GND) via a fourth switching element (S4).

8. The DC-DC converter (300) according to claim 7, wherein: In the first switching state (BOOST ON), the second switching element (S2) and the third switching element (S3) are open, the first switching element (S1) and the fourth switching element (S4) are closed, and / or In the second switching state (BOOST OFF, BUCK ON), the second switching element (S2) and the fourth switching element (S4) are opened, the first switching element (S1) and the third switching element (S3) are closed, and / or In the third switching state (BUCK OFF), the first switching element (S1) and the fourth switching element (S4) are opened, the second switching element (S2) and the third switching element (S3) are closed, and / or In the fourth switching state (REFRESH), the first switching element (S1) and the third switching element (S3) are open, and the second switching element (S2) and the fourth switching element (S4) are closed.

9. The DC-DC converter (300) according to any one of claims 6 to 8, wherein: The control device (20) comprises a microcontroller.

10. The DC-DC converter (300) according to claim 9, wherein: The comparison of the current (I) with the first threshold current value (Ival) and / or with the second threshold current value (Ipk) is performed by means of a comparator integrated in the hardware of the microcontroller.

11. A power generation system (100), comprising: a current generator (200) for generating electrical energy at a first voltage (U1), a current storage (400) for storing the electric energy generated by the current generator (200) at a second voltage (U2), and A DC-DC converter (300) according to any one of claims 6 to 10.

12. A computer program having instructions which, when executed in a control unit (20), cause the control unit (20) to generate control signals for executing the method according to any one of claims 1 to 5.

Images