DC-DC converter

Abstract

This invention relates to a DC-DC voltage converter for transferring energy from a high-voltage grid to a low-voltage grid. Furthermore, it employs a circuit configuration capable of alternating between operation as an active clamp flyback converter and an active clamp buck converter.

Description

Technical Field

[0001] The present invention relates to a DC voltage converter, and more particularly to a DC voltage converter for energy transfer between a high-voltage power grid and a low-voltage power grid. Background Technology

[0002] Vehicles that are fully or at least partially electrically powered typically possess a so-called traction battery, which provides electrical energy to propel the vehicle. These traction batteries typically have an output voltage of several hundred volts, such as 400 volts. In addition, the vehicle has a so-called low-voltage electrical grid to which other loads, such as lighting devices, auxiliary drive systems, onboard computers, or the like, are connected. Here, the vehicle's low-voltage electrical grid is typically fed by a high-voltage grid. Therefore, voltage level transformation from the high-voltage grid to the low-voltage grid is necessary. Furthermore, electrical disconnection between the high-voltage and low-voltage grids is usually also required.

[0003] Publication DE10 2016 220 679A1 discloses a DC-DC converter and a method for controlling the DC-DC converter, specifically a so-called phase-shifted full-bridge DC-DC converter. In particular, this publication proposes reducing the number of lossy switching processes through appropriate control of the DC-DC converter. Summary of the Invention

[0004] This invention discloses a DC-DC voltage converter, particularly a DC-DC voltage converter for energy transfer between a high-voltage power grid and a low-voltage power grid. Further advantageous embodiments are the subject of the dependent claims.

[0005] The following settings were configured accordingly:

[0006] A DC-DC voltage converter for transferring energy between a high-voltage grid and a low-voltage grid. The DC-DC voltage converter includes an input terminal, a transformer, a first switching element, a second switching element, a third switching element, a fourth switching element, and a capacitor. The input terminal is designed to be coupled to a DC voltage source. The transformer has a primary side and a secondary side. The first terminal on the primary side of the transformer is connected to the first terminal element of the first input terminal. The first terminal of the first switching element is connected to the second terminal on the primary side of the transformer. The second terminal of the first switching element is connected to the second terminal element of the input terminal. The first terminal of the second switching element is connected to the first terminal on the primary side of the transformer. The second terminal of the second switching element is connected to a node. The first terminal of the capacitor is connected to a node. The second terminal of the capacitor is connected to the second terminal on the primary side of the transformer. The first terminal of the third switching element is connected to a node. The second terminal of the third switching element is connected to the first terminal of the fourth switching element. Finally, the second terminal of the fourth switching element is connected to the second terminal of the input terminal.

[0007] This invention is based on the understanding that the low-voltage power grid of electric vehicles or hybrid vehicles is typically fed by energy from the high-voltage power grid. Therefore, electrical separation between the high-voltage and low-voltage power grids is usually necessary. Furthermore, this invention is based on the understanding that with continuous improvements in vehicles, the power of electrically driven vehicles, and especially the battery capacity, is increasing. Traction batteries with higher output voltages are also increasingly being used in this regard. Therefore, a DC-DC converter with sufficient voltage withstand capability is needed to couple between the high-voltage and low-voltage power grids. Subsequently, DC-DC converters capable of operating over the widest possible input voltage range are also anticipated.

[0008] Therefore, the concept of the present invention is to take this understanding into account and realize a DC-DC converter that can meet the requirements mentioned above. To this end, the following invention realizes a circuit scheme for a DC-DC converter used to couple a high-voltage grid to a low-voltage grid, which has a very simple circuit topology. The DC-DC converter can convert an input DC voltage to a predetermined output DC voltage across a very large input voltage range. The circuit scheme according to the invention can ensure sufficient voltage withstand capability even with high input DC voltages, especially using conventional components. Due to the relatively simple circuit topology, the DC-DC converter can be implemented at a particularly low cost. Furthermore, the DC-DC converter according to the invention also requires only a relatively small structural space.

[0009] In one embodiment, the DC-DC converter includes a rectifier. This rectifier is coupled to the secondary terminal of a transformer. Furthermore, the rectifier is designed to rectify the voltage applied to the secondary terminal of the transformer. This allows a rectified voltage to be provided at the output terminal of the DC-DC converter. The rectification of the voltage at the secondary terminal of the transformer can be achieved in any manner using either an active or passive rectifier.

[0010] With the help of transformers and subsequent rectification, it is therefore feasible to achieve the transfer of energy from the high-voltage grid to the low-voltage grid in an electrically isolated manner.

[0011] In one embodiment, the rectifier includes a rectifier diode. Alternatively, the rectifier can also include a semiconductor switch, particularly having a rectifier diode connected in parallel with the semiconductor switch. In this case, the semiconductor switch can be actively controlled, wherein rectification of the voltage on the secondary side of the transformer is achieved by controlling the semiconductor switch. Such active rectification by means of a semiconductor switch can reduce power loss and thus improve efficiency. Alternatively, rectification with a rectifier diode can achieve particularly low-cost rectification.

[0012] In one embodiment, the first switching element, the second switching element, the third switching element, and the fourth switching element each comprise a semiconductor switch. Specifically, a diode, particularly a so-called body diode, can be arranged in parallel with the semiconductor switch. The semiconductor switch can be, for example, a transistor, particularly an IGBT with an insulated gate junction. Needless to say, any other semiconductor switch, such as a MOSFET or a silicon carbide switch, is also feasible.

[0013] In one embodiment, a diode is arranged opposite to the diode connected in parallel with the third switching element, which is connected in parallel with the fourth switching element. This arrangement ensures that electrical interruption can be achieved even in paths containing both the third and fourth switching elements.

[0014] In one embodiment, the DC-DC converter includes a control device. This control device is designed to operate a first switching element, a second switching element, a third switching element, and a fourth switching element. Furthermore, the control device can also operate any active switching element provided in the rectifier of the DC-DC converter. In this way, the operation of each switching element can be synchronized in a targeted manner.

[0015] According to one embodiment, the control device is designed to disconnect the third and fourth switching elements and alternately pulse-excite the first and second switching elements in a first operating mode. Furthermore, the control device can disconnect the first switching element and close the fourth switching element in a second operating mode. Additionally, it can alternately pulse-excite the second and third switching elements in the second operating mode. In this way, DC-DC voltage conversion between the high-side and low-side can be achieved in the first operating mode based on a so-called flyback converter, particularly an active-clamp flyback-Wandler, and the circuit can operate as an active-clamp buck-Konverter in another operating mode using the same circuit topology. This allows for appropriate control of the DC-DC converter across a large voltage range.

[0016] In one embodiment, the input voltage at the input terminals of the DC-DC converter is greater for operation in the second operating mode than for operation in the first operating mode. The selection of a suitable operating mode for DC-DC conversion can be achieved, for example, by means of a control device for controlling the various switching elements.

[0017] Wherever meaningful, the above-described design schemes and improvements can be combined with each other arbitrarily. Other design schemes, improvements, and implementations of the present invention also include combinations of features not explicitly mentioned in the foregoing or following description of the embodiments. In particular, those skilled in the art will also add various aspects as improvements or supplements to the corresponding basic form of the present invention. Attached Figure Description

[0018] Further features and advantages of the present invention will now be explained with reference to the accompanying drawings. Hereinafter:

[0019] Figure 1 A block diagram of a DC-DC voltage converter according to one embodiment is shown;

[0020] Figure 2 A block diagram of a DC-DC converter in a first operating mode according to one embodiment is shown; and

[0021] Figure 3 A block diagram of a DC-DC converter in a second operating mode according to one embodiment is shown. Detailed Implementation

[0022] Figure 1 A schematic block diagram of a DC-DC converter 1 according to one embodiment is shown. The DC-DC converter 1 can be connected to a high-voltage power grid 2, for example, on its input side. The DC-DC converter 1 can be connected to a low-voltage power grid 3, for example, on its output side. For connection to the high-voltage power grid, the DC-DC converter 1 can, for example, have an input terminal 10. Power can be supplied at this input terminal 10, for example, by a traction battery of an electric vehicle. Accordingly, a voltage U_in is applied at the input terminal 10. The DC-DC converter 1 can convert this input voltage U_in into another DC voltage and provide it as an output DC voltage U_out at the output terminal 30.

[0023] In addition to the input terminal 10 and the output terminal 30, the DC-DC converter 1 also includes a transformer T. The transformer T has a primary side Pri and a secondary side Sek. Furthermore, the DC-DC converter 1 has four switching elements S1, S2, S3, and S4 and a capacitor C between the input terminal 10 and the primary side Pri of the transformer T. A rectifier 40 is provided on the secondary side Sek of the transformer T.

[0024] The input terminal 10 of the DC-DC converter 1 includes a first terminal element 11 and a second terminal element 12. An input DC voltage U_in can be provided between the first terminal element 11 and the second terminal element 12. The first terminal 11 of the input terminal 10 is connected to a first terminal 21 on the primary side Pri of the transformer T. A first switching element S1 is arranged between the second terminal 22 on the primary side Pri of the transformer T and the second terminal element 12 of the input terminal 10. Furthermore, a second switching element S2 is arranged between the first terminal 21 on the primary side Pri of the transformer T and node K. A capacitor C is arranged between node K and the second terminal 22 on the primary side Pri of the transformer T. Additionally, the first terminal of a third switching element S3 is connected to node K, and the second terminal of the third switching element S3 is connected to the first terminal of a fourth switching element S4. The second terminal of the fourth switching element S4 is connected to the second terminal element 12 of the input terminal 10 and therefore also to the corresponding terminal of the first switching element S1.

[0025] As mentioned above, a rectifier 40 is provided between the secondary side Sek of transformer T and the output terminal 30 of DC-DC converter 1. The rectifier 40 can, for example, involve a passive diode disposed between the terminal on the secondary side Sek of transformer T and the terminal element of the output terminal 30. Alternatively, active rectification can also be achieved by means of a switching element S5, particularly a semiconductor switching element, disposed between the terminal on the secondary side Sek of transformer T and the terminal element of the output terminal 30.

[0026] A control device 50 can be provided to control the switching elements, especially the first, second, third, and fourth switching elements S1-S4, and, if necessary, the switching elements in the rectifier 40. The working principle and switching sequence for controlling the switching elements will be explained in more detail below.

[0027] Figure 2 A schematic diagram of the DC-DC converter 1's wiring diagram is shown in the first operating mode. In this first operating mode, the DC-DC converter 1 can operate specifically as a so-called active-clamp flyback converter. Here, in this first operating mode, the third switching element S3 and the fourth switching element S4 are disconnected. For better understanding, the third switching element S3 and the fourth switching element S4 are not shown here. The transformer T is magnetized by closing the first switching element S1. The second switching element S2, together with the capacitor C, forms a clamping circuit. In another process, the first switching element S1 and the second switching element S2 are operated alternately. By adapting the frequency and / or pulse width, the energy transfer of the output voltage, in particular, can be regulated.

[0028] Figure 3 A schematic diagram of the DC-DC converter 1's wiring diagram is shown in the second operating mode. In this mode, the DC-DC converter 1 operates as an electrically isolated active clamped buck converter. Here, the first switching element S1 is permanently disconnected and therefore... Figure 3 Not shown. Furthermore, the fourth switching element S4 is permanently closed in this operating mode.

[0029] The third switching element S3 magnetizes the transformer T. In this case, the clamping circuit also consists of the second switching element S2 and the capacitor C. In the second operating mode, the second switching element S2 and the third switching element S3 are alternately pulse-excited at a predetermined frequency and pulse width.

[0030] Since the rectifier 40 is implemented as a simple, unidirectional rectifier, it is essential for the circuit layout of the DC-DC converter 1 to magnetize the transformer T in the same direction, not only in the first operating mode but also in the second operating mode. In the first operating mode, the first switching element S1 performs this magnetization task, and in the second operating mode, the third switching element S3 performs this magnetization task. In both cases, the transformer T demagnetizes when energy is transferred to the secondary side Sek of the transformer T. This is achieved by disconnecting the first switching element S1 or the third switching element S3 and correspondingly connecting the second switching element S2.

[0031] In the first operating mode, the first switching element S1 experiences a voltage load generated by the sum of the input voltage U_in and the product of the output voltage U_out and the transformation ratio of the transformer T. Therefore, the first switching element S1 must have a correspondingly high withstand voltage. In the second operating mode, the maximum voltage load on the switching element is predetermined solely by the maximum input voltage U_in. Therefore, the second operating mode is suitable for higher input voltages U_in, while the first operating mode is preferred for lower input voltages U_in.

[0032] For example, the described circuit arrangement can be used for DC-DC converter 1, thus for example, for traction batteries with relatively low voltage levels, such as up to 500 volts. For DC-DC converters with higher input voltages, such as above 500 volts up to 800 or, if necessary, 1000 volts, the same DC-DC converter 1 can be operated in the second operating mode. Therefore, for input DC voltages spanning a wide voltage range, a simple and cost-effective DC-DC converter can be achieved with relatively low circuitry.

[0033] In summary, the present invention relates to a DC-DC voltage converter for transferring energy from a high-voltage grid to a low-voltage grid. Furthermore, a simple circuit configuration is proposed that can operate alternately as an active clamped flyback converter or an active clamped buck converter.

Claims

1. A DC-DC voltage converter (1) for transferring energy between a high-voltage grid and a low-voltage grid, the DC-DC voltage converter having: Input connector (10) designed for coupling with a DC voltage source (2); A transformer (T) with a primary side (Pri) and a secondary side (Sek); Capacitor (C); The first switching element (S1), the second switching element (S2), the third switching element (S3), and the fourth switching element (S4); in, The first terminal (21) of the primary side (Pri) of the transformer (T) is electrically coupled to the first terminal element (11) of the input terminal (10); The first connector of the first switching element (S1) is connected to the second connector (22) of the primary side (Pri) of the transformer (T), and the second connector of the first switching element (S1) is connected to the second connector element (12) of the input connector (10); The first connector of the second switching element (S2) is connected to the first connector (21) of the primary side (Pri) of the transformer (T), and the second connector of the second switching element (S2) is connected to the node (K); The first terminal of the capacitor (C) is connected to the node (K), and the second terminal of the capacitor (C) is connected to the second terminal (22) of the primary side (Pri) of the transformer (T); and The first connector of the third switching element (S3) is connected to the node (K), the second connector of the third switching element (S3) is connected to the first connector of the fourth switching element (S4), and the second connector of the fourth switching element (S4) is connected to the second connector element (12) of the input connector (10). The DC voltage converter (1) can operate as a so-called active clamp flyback converter in a first operating mode and as an electrically decoupled active clamp buck converter in a second operating mode.

2. The DC voltage converter (1) according to claim 1, the DC voltage converter having a rectifier (40) coupled to the secondary terminal (Sek) of the transformer (T), and the rectifier being designed to rectify the voltage applied at the secondary terminal (Sek) of the transformer (T).

3. The DC voltage converter (1) according to claim 2, wherein, The rectifier (40) includes a rectifier diode or semiconductor switch (S5) designed to rectify the voltage applied at the secondary terminal (Sek) of the transformer (T).

4. The DC-DC converter (1) according to any one of claims 1 to 3, wherein, The first switching element (S1), the second switching element (S2), the third switching element (S3), and the fourth switching element (S4) each include a semiconductor switch having a body diode.

5. The DC-DC voltage converter (1) according to claim 4, wherein, The body diode of the third switching element (S3) is arranged opposite to the body diode of the fourth switching element (S4).

6. The DC voltage converter (1) according to any one of claims 1 to 3, the DC voltage converter having a control device (50) designed to operate the first switching element (S1), the second switching element (S2), the third switching element (S3) and the fourth switching element (S4).

7. The DC-DC voltage converter (1) according to claim 6, wherein, The control device (50) is designed in a first operating mode to disconnect the third switching element (S3) and the fourth switching element (S4) and to alternately pulse-excite and operate the first switching element (S1) and the second switching element (S2) respectively, and in a second operating mode to disconnect the first switching element (S1), close the fourth switching element (S4) and to alternately pulse-excite and operate the second switching element (S2) and the third switching element (S3) respectively.

8. The DC voltage converter (1) according to claim 7, wherein, For operation in the second operating mode, the value of the input voltage (U_in) at the input connector (10) is greater than the value of the input voltage (U_in) for operation in the first operating mode.

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