Electric current converter and method for operating an electric current converter

Abstract

The invention relates to an electric current converter and to a control method for such a current converter. In particular, the invention provides for pulse-width-modulated control which allows common-mode interferences at the level of the fundamental frequency of the control signals to be avoided in the current converter.

Description

[0001] Description

[0002] title

[0003] Electrical power converter and method for operating an electrical power converter

[0004] Technical area

[0005] The present invention relates to an electrical power converter, in particular a DC-DC converter. The present invention further relates to a method for operating an electrical power converter.

[0006] background

[0007] DC-DC converters are used to convert a first DC voltage into a second DC voltage with a different voltage level. For example, galvanically isolated DC-DC converters use full bridges (H-bridges) to convert a DC voltage. This allows the electrical DC voltage to be converted into an electrical voltage with alternating signs, which can then be supplied to a downstream transformer.

[0008] In particular, the group of DC-DC converters also includes so-called phase-shifted full-bridge DC-DC converters, in which the switching elements of the full bridge are controlled with a fixed duty cycle of 50 percent, whereby the control is carried out by variable phase shift between the control signals of the half-bridges.

[0009] The document DE 10 2019 212888 A1, for example, describes a DC-DC converter and a control method for a DC-DC converter, wherein the voltage converter should preferably be switched on softly in order to reduce switching losses.

[0010] Disclosure of the Invention The present invention provides an electrical power converter and a method for operating an electrical power converter having the features of the independent patent claims. Further advantageous embodiments are the subject of the dependent patent claims.

[0011] Accordingly, it is provided:

[0012] An electrical power converter with an input terminal, two half-bridges, a transformer, and a control device. The input terminal is designed to be electrically coupled to a DC voltage source. A positive terminal of the input terminal can be connected to a corresponding positive terminal of the DC voltage source, and a negative terminal of the input terminal can be connected to a corresponding negative terminal of the DC voltage source. The first half-bridge comprises a first semiconductor switching element and a second semiconductor switching element. The first semiconductor switching element is arranged between the positive terminal of the input terminal and a first node. The second switching element is arranged between the first node and the negative terminal of the input terminal.The second half-bridge comprises a third semiconductor switching element and a fourth semiconductor switching element. The third semiconductor switching element is arranged between the positive connection point of the input terminal and a second node. The fourth switching element is arranged between the second node and the negative connection point of the input terminal. The transformer comprises a primary side and a secondary side. In particular, the primary side has a first connection point and a second connection point. The first connection point of the primary side of the transformer is connected to the first node of the first half-bridge. The second connection point of the primary side of the transformer is connected to the second node of the second half-bridge. The control device is designed to provide control signals to the switching elements of the first and second half-bridge.In particular, the control device is designed to provide pulse-width modulated signals with a predetermined clock frequency as control signals for the switching elements. The pulse-width modulated signals have a variable, adaptable duty cycle. The control signals at the first switching element and the second switching element of the first half-bridge are complementary to one another. Likewise, the control signals at the third switching element and the fourth switching element of the second half-bridge are complementary to one another. Furthermore, the control signal for the third switching element of the second half-bridge is offset by half a period from the control signal for the first switching element of the first half-bridge. Likewise, the control signal for the fourth switching element of the second half-bridge is offset by half a period from the control signal for the second switching element of the first half-bridge.

[0013] Furthermore, it is planned:

[0014] A method for operating an electrical power converter having a first half-bridge, a second half-bridge, and a transformer. The first half-bridge comprises a first semiconductor switching element and a second semiconductor switching element. The second half-bridge comprises a third semiconductor switching element and a fourth semiconductor switching element. The transformer is electrically connected on the primary side to the first half-bridge and the second half-bridge. In particular, a first connection point on the primary side of the transformer is connected to a first node at which the first and second semiconductor switching elements of the first half-bridge are connected to one another. A second connection point on the primary side of the transformer is connected to a second node at which the third and fourth semiconductor switching elements of the second half-bridge are connected to one another.The method comprises a step of providing a first control signal to the first switching element of the first half-bridge, a step of providing a second control signal to the second switching element of the first half-bridge, a step of providing a third control signal to the third switching element of the second half-bridge, and a step of providing a fourth control signal to the fourth switching element of the second half-bridge. The first, second, third, and fourth control signals each comprise a pulse-width-modulated signal with a predetermined clock rate and an adjustable duty cycle. Furthermore, the first control signal and the second control signal are complementary to one another. The third control signal and the fourth control signal are likewise complementary to one another. Furthermore, the third control signal is offset from the first control signal by half a period.Likewise, the fourth control signal is offset from the second control signal by half a period. Advantages of the invention.

[0015] In electrical power converters, such as DC-DC converters, especially galvanically isolated DC-DC converters, full bridges are often used to convert and rectify a transformer voltage. Conventional control methods can control the switching elements in the individual half-bridges of the full bridge with a fixed duty cycle of 50 percent. Control can be achieved by variable shifting of the electrical phase between the control signals of the individual half-bridges.

[0016] With such a control system, a common-mode current can flow through the transformer, the spectrum of which already includes the fundamental switching frequency for driving the semiconductor switching elements. Therefore, common-mode filters are required that adequately filter or attenuate the frequency spectrum of the common-mode interference down to this fundamental.

[0017] It is an idea of ​​the present invention to create a concept for controlling the switching elements in an electrical power converter, such as a DC-DC converter, in which the fundamental of the control frequency can be avoided in the frequency spectrum of the common-mode currents. This allows the required common-mode filters to be designed for higher frequencies, especially from the first harmonic onwards. Such filters can thus be implemented smaller, lighter, and more cost-effectively.

[0018] For this purpose, instead of controlling the switching elements in the half-bridges of the power converter on the basis of clock signals with a fixed duty cycle and variable phase relationship between the signals in the individual half-bridges, a control is provided in which the duty cycle in the control signals can be varied, whereby the switching elements in the two half-bridges are controlled with a fixed phase offset of 180 degrees, i.e. half a period.

[0019] Such a control method makes it possible to limit the freewheeling phases in the power converter to only the upper switching elements (first switching element and third switching element) or the lower switching elements (second switching element and fourth switching element) of the half-bridges. The control therefore only alternates between active phases without a common-mode voltage and either an upper freewheeling phase with a positive common-mode voltage, or alternatively between an active phase without a common-mode voltage and a lower freewheeling phase with a negative common-mode voltage. This allows the fundamental wave of the switching frequency to be avoided in the common-mode voltage. Accordingly, the filters for suppressing or minimizing the common-mode voltage only need to be designed for frequencies of at least the first harmonic of the switching frequency.

[0020] A special feature of the inventive concept is that no additional components such as (feeding) inductors, as required, for example, in current-fed concepts, are provided on the input side, i.e., between the input terminal between a feeding DC voltage source and the half-bridges. Except for suitable filter components with significantly lower inductance values, if necessary.

[0021] According to one embodiment, the control device is designed to provide control signals for the switching elements in a first operating mode, wherein the control signals for the first switching element of the first half-bridge and the third switching element in the second half-bridge close the respective first switching element or third switching element during a pulse duration of the pulse-width modulated signal. In a second operating mode, the control device can provide control signals for the switching elements, wherein the control signal for the first switching element of the first half-bridge and the third switching element in the second half-bridge open the respective first switching element or third switching element during the pulse duration of the pulse-width modulated signal. In this way, depending on the selection of the respective operating mode, the freewheeling and the associated common-mode voltage can be limited either to the upper switching elements or the lower switching elements.

[0022] According to one embodiment, the control device is designed to switch between the first operating mode and the second operating mode after a predetermined period of time or a predetermined number of periods of the control signals. By switching between the first operating mode and the second operating mode, it can be achieved that the upper switching elements and the lower switching elements are, on average, evenly loaded. This prevents overstressing of some of the switching elements. The predetermined period of time or the number of periods after which switching between the operating modes occurs each comprises several switching cycles.

[0023] According to one embodiment, the control device is designed to adjust the duty cycle of the control signals using a voltage value of an electrical voltage at the input terminal, a voltage value of an electrical output voltage, and / or a setpoint value for an output voltage to be output. The output voltage can be, for example, the electrical voltage on the secondary side of the transformer. Additionally or alternatively, an electrical voltage at the output of a downstream rectifier or similar device can also be evaluated as the output voltage. Furthermore, the regulation or control for adjusting the duty cycle can, of course, also be based on any other setpoint or actual values.

[0024] According to one embodiment, the power converter comprises a rectifier circuit. The rectifier circuit can, in principle, be any suitable active or passive rectifier circuit. The rectifier circuit is arranged on a secondary side of the transformer. The rectifier circuit is designed to rectify an electrical voltage provided by the secondary side of the transformer. The rectified voltage can be provided at an output terminal. In this way, a DC-DC converter can be realized that converts an input DC voltage into a galvanically isolated output voltage.

[0025] According to one embodiment, the power converter comprises a common-mode filter. The common-mode filter can, for example, be arranged at the input terminal of the electrical power converter. The common-mode filter is designed for frequencies of at least twice the clock frequency of the control signals. In other words, the common-mode filter does not have to be designed for the fundamental frequency of the clock frequency of the control signals. The inductors used in the common-mode filter have inductance values ​​that are significantly lower than the inductance values ​​of supply inductors, which are required, for example, in current-fed converters. The above embodiments and further developments can be combined with one another as desired, where appropriate.Further embodiments, refinements, and implementations of the invention also include combinations of features of the invention described above or below with respect to the exemplary embodiments that are not explicitly mentioned. In particular, those skilled in the art will also add individual aspects as improvements or additions to the respective basic forms of the invention.

[0026] Short description of the drawings

[0027] Further features and advantages of the invention are explained below with reference to the figures.

[0028] Fig. 1: a schematic representation of a power converter according to a

[0029] embodiment;

[0030] Fig. 2: a diagram illustrating the control signal in a first

[0031] operating mode;

[0032] Fig. 3: a diagram illustrating the control signal in a second

[0033] operating mode;

[0034] Fig. 4: a schematic representation of a power converter according to another

[0035] embodiment; and

[0036] Fig. 5: a flow chart of a method for operating a

[0037] power converter according to one embodiment.

[0038] Description of embodiments

[0039] Figure 1 shows a schematic representation of an electrical power converter according to one embodiment. The electrical power converter can generally be used to provide a galvanically isolated output voltage from an input DC voltage U_in. As described in more detail below, the voltage present on the secondary side 32 of the transformer 30 is rectified. Thus, such a converter can be used to create a galvanically isolated DC-DC converter.

[0040] The power converter comprises an input terminal 10 with a positive connection point 11 and a negative connection point 12. The input terminal 10 is directly connected to a DC voltage source 2. In particular, no current-supplying inductances are provided between the input terminal 10 and the DC voltage source 2.

[0041] The power converter further comprises a full-bridge circuit 20 with two half-bridges. A first half-bridge comprises a series circuit of a first switching element M1 and a second switching element M2. The first switching element M1 is arranged between the positive connection point 11 of the input terminal 10 and a first node K1. The second switching element M2 is arranged between the first node K1 and the negative connection point 12 of the input terminal 10.

[0042] The second half-bridge comprises a series circuit of a third switching element M3 and a fourth switching element M4. The third switching element M3 is arranged between the positive connection point 11 of the input terminal 10 and a second node K2. The fourth switching element M4 is arranged between the second node K2 and the negative connection point 12 of the input terminal 10.

[0043] A first connection point of the primary side 31 of the transformer 30 is connected to the first node K1 of the first half-bridge, and a second connection point of the primary side 31 of the transformer 30 is connected to the second node K2 of the second half-bridge.

[0044] The switching elements M1-M4 of the two half-bridges can be controlled by means of control signals from a control device 40. The switching elements M1-M4 can be controlled based on pulse width modulation with a variable duty cycle. In particular, the switching elements M1-M4 are controlled such that, in the freewheeling phases, in successive periods, either only an upper freewheel takes place, in which the two upper switching elements M1 and M3 are involved, or only a lower freewheel takes place in successive periods, in which the two lower switching elements M2 and M4 are involved. Accordingly, only a positive common-mode voltage or a negative common-mode voltage is established during the freewheeling phase.This results in the frequency of the common-mode voltage being halved and thus only frequency components of at least the first harmonic of the switching frequency of the control signal for the switching elements M1-M4 occurring.

[0045] The control device 40 generates control signals for the switching elements M1-M4, wherein the control signals for the two switching elements of each half-bridge are complementary to one another. Accordingly, the control signals for the first switching element M1 and the second switching element M2 of the first half-bridge are complementary to one another, and the control signals for the third switching element M3 and the fourth switching element M4 of the second half-bridge are likewise complementary to one another. In this context, "complementary" means that one switching element of a half-bridge is opened while the other switching element of this half-bridge is closed. In this case, a dead time is provided during a switching operation between the closing of one switching element M1-M4 and the opening of the other switching element M1-M4 in a half-bridge.This means that the open switching element M1-M4 is closed first, and only after a short delay is the other switching element M1-M4 of the half-bridge opened. This prevents a possible brief short circuit in the half-bridge.

[0046] Furthermore, when controlling the switching elements M1-M4 in the half-bridges, the control signals for the switching elements M1, M2 of the first half-bridge and the switching elements M3, M4 of the second half-bridge are offset from each other by half a period, or 180 degrees. This means that the control signal for the third switching element M3 of the second half-bridge is offset from the control signal for the first switching element M1 in the first half-bridge by half a period, and the control signal for the fourth switching element M4 of the second half-bridge is offset from the control signal for the second switching element M2 of the first half-bridge by half a period.

[0047] Figure 2 shows a time course of possible control signals for the switching elements M1-M4. Here, T denotes the period of the pulse-width modulated control, and d the pulse width according to the specified duty cycle. As already noted, this pulse width d or the corresponding duty cycle can be adjusted for control or regulation purposes. For example, the duty cycle can be adjusted according to a setpoint value for an output voltage and, if necessary, using voltage values ​​determined by sensors in the power converter. In the periods between the individual pulses, the two lower switching elements M2 and M4 are controlled, i.e. closed. The two upper switching elements M1 and M3 are open during these periods.

[0048] Figure 3 shows a time profile of possible control signals for the switching elements M1-M4 in an alternative operating mode. In the intervals between individual pulses, the two upper switching elements M1 and M3 are controlled, i.e., closed, and the two lower switching elements M2 and M4 are open.

[0049] As already explained above, depending on the selected operating mode according to Figure 2 or Figure 3, either the upper switching elements M1, M3 or the lower switching elements M2, M4 are loaded in freewheeling mode. To ensure uniform loading, the two described operating modes can be switched between (regularly) after a specified period of time or a specified number of control signal periods. However, the individual phases with one or the other operating mode should comprise several periods, for example, at least 10 periods or more. Excessively frequent switching between the two operating modes could lead to additional frequency components of the common-mode voltage in the fundamental frequency range.

[0050] Figure 4 shows a schematic representation of a voltage converter according to another embodiment. The voltage converter according to Figure 4 can comprise the components already described in connection with Figure 1. Accordingly, all embodiments already described in connection with the voltage converter from Figure 1 and the control method used therein also apply.

[0051] In the voltage converter according to Figure 4, a rectifier 50 is provided at the secondary terminal 32 of the transformer 30. The rectifier 50 can in principle be any suitable active or passive rectifier. Since the basic principle of such rectifiers is considered to be known, this will not be explained in detail here. An output DC voltage U_out is thus provided at the output of the rectifier 50. In this way, an input DC voltage U_in provided on the input side can be converted into a galvanically isolated output DC voltage U_out. The voltage level of the output DC voltage U_out can be adjusted by varying the duty cycle during the pulse-width modulated control of the switching elements M1-M4.

[0052] If necessary, a common-mode filter 60 can be provided on the input side, for example, at input terminal 10. Since, with the control system according to the invention, only common-mode interference with a frequency of at least the first harmonic of the control frequency occurs in the power converter, the common-mode filter 60 can be designed accordingly for frequencies of at least twice the control frequency.

[0053] Figure 5 shows a flowchart that may underlie a method for operating an electrical power converter according to one embodiment. The method can be applied in particular to the previously described power converters. Thus, the statements made previously in connection with the described power converters apply. Analogously, the previously described power converters may also include any components designed to carry out the method described below.

[0054] The step S1 for controlling the power converter comprises a step S1a for providing a first control signal to the first switching element M1 of the first half-bridge, a step S1b for providing a second control signal to the second switching element M2 of the first half-bridge, a step S1c for providing a third control signal to the third switching element M3 of the second half-bridge, and a step S1d for providing a fourth control signal to the fourth switching element M4 of the second half-bridge. The first, second, third, and fourth control signals can each be pulse-width modulated signals with the same predetermined clock rate. The duty cycle of the control signals can be adjusted. In particular, the duty cycle can be controlled or regulated according to predetermined setpoints and / or measured values ​​in the power converter. The first control signal and the second control signal are complementary to one another.Likewise, the third control signal and the fourth control signal are complementary to each other. Furthermore, the third control signal is offset from the first control signal by half a period, and the fourth control signal is offset from the second control signal by half a period.

[0055] The method may further comprise a step for adjusting the duty cycle of the first, second, third, and fourth control signals. The duty cycle can be adjusted, in particular, using a setpoint and / or measured value of an electrical voltage and / or an electrical current in the voltage converter. In summary, the present invention relates to an electrical power converter and a control method for such a power converter. In particular, pulse-width modulated control is provided, which makes it possible to avoid common-mode interference in the range of the fundamental frequency of the control signals in the power converter.

Claims

Claims 1. An electrical power converter, comprising: an input terminal (10) designed to be electrically coupled to a DC voltage source (2); a first half-bridge having a first semiconductor switching element (M1) and a second semiconductor switching element (M2), wherein the first semiconductor switching element (M1) is arranged between a positive connection point (11) of the input terminal (10) and a first node point (K1) and the second switching element (M2) is arranged between the first node point (K2) and a negative connection point (12) of the input terminal;a second half-bridge with a third semiconductor switching element (M3) and a fourth semiconductor switching element (M4), wherein the third semiconductor switching element (M3) is arranged between the positive connection point (11) of the input connection (10) and a second node (K2), and the fourth switching element (M4) is arranged between the second node (K2) and the negative connection point (12) of the input connection (10); a transformer (30) with a primary side (31) and a secondary side (32), wherein a first connection point of the primary side (31) of the transformer (30) is connected to the first node (K1) of the first half-bridge and a second connection point of the primary side (31) of the transformer (30) is connected to the second node (K2) of the second half-bridge;and a control device (40) designed to provide control signals to the switching elements (M1-M4) of the first and second half-bridge, wherein the control device (40) is designed to provide pulse-width modulated signals having a common predetermined clock frequency and an adjustable duty cycle as control signals for the switching elements (M1-M4); wherein the control signals at the first switching element (Ml) and the second switching element (M2) of the first half-bridge are complementary to one another, and the control signals at the third switching element (M3) and the fourth switching element (M4) of the second half-bridge are complementary to one another, and wherein the control signal for the third switching element (M3) of the second half-bridge is offset by half a period from the control signal for the first switching element (Ml) in the first half-bridge and the control signal for the fourth switching element (M4) of the second half-bridge is offset by half a period from the control signal for the second switching element (M2) of the first half-bridge.

2. Power converter according to claim 1, wherein the control device (40) is designed to provide control signals for the switching elements (M1-M4) in a first operating mode, wherein the control signals for the first switching element (M1) of the first half-bridge and the third switching element (M3) in the second half-bridge close the respective first switching element (M1) or third switching element (M3) during a pulse duration of the pulse-width modulated signal, and to provide control signals for the switching elements (M1-M4) in a second operating mode, wherein the control signals for the first switching element (M1) of the first half-bridge and the third switching element (M3) in the second half-bridge open the respective first switching element (M1) or third switching element (M3) during the pulse duration of the pulse-width modulated signal.

3. Power converter according to claim 2, wherein the control device (40) is designed to switch between the first operating mode and the second operating mode after a predetermined period of time or a predetermined number of periods of the control signals.

4. Power converter according to one of claims 1 to 3, wherein the control device (40) is designed to adjust the duty cycle of the control signal using a voltage value of an electrical voltage (U_in) at the input terminal (10), a voltage value of an electrical output voltage and / or a setpoint value for an output voltage to be output.

5. Power converter according to one of claims 1 to 4, with a rectifier circuit (50) which is arranged on a secondary side (32) of the transformer (30) and which is designed to rectify an electrical voltage provided by the secondary side (32) of the transformer (30) and to provide it at an output terminal.

6. Power converter according to one of claims 1 to 5, with a common-mode filter (60) arranged at the input terminal (10) of the electrical power converter, wherein the common-mode filter (60) is designed for frequencies of at least twice the clock frequency of the control signals.

7. A method for operating an electrical power converter having a first half-bridge with a first semiconductor switching element (M1) and a second semiconductor switching element (M2), a second half-bridge with a third semiconductor switching element (M3) and a fourth semiconductor switching element (M4), and a transformer (30) which is electrically connected on the primary side to the first half-bridge and the second half-bridge, the method comprising the following steps: Providing (Sla) a first control signal to the first switching element (Ml) of the first half-bridge; Providing (Slb) a second control signal to the second switching element (M2) of the first half-bridge; Providing (Sic) a third control signal to the third switching element (M3) of the second half-bridge; and Providing (Sld) a fourth control signal to the fourth switching element (M4) of the second half-bridge, wherein the first, second, third and fourth control signals each comprise a pulse-width modulated signal with a same predetermined clock rate and an adjustable duty cycle, wherein the first control signal and the second control signal are complementary to each other, and the third control signal and the fourth control signal are complementary to each other, and wherein the third control signal is offset from the first control signal by half a period, and the fourth control signal is offset from the second Control signal is offset by half a period.

8. The method according to claim 7, comprising a step of adjusting the duty cycle of the first, second, third and fourth control signals using a desired value and / or measured value of an electrical voltage and / or an electrical current in the voltage converter.

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