DE102021117252A1 - DC converter for a motor vehicle - Google Patents

Abstract

The invention relates to a DC-DC converter for a motor vehicle, comprising two electrical connections as the input (105), two electrical connections as the first output and two electrical connections as the second output, the DC-DC converter being designed to convert an input voltage present at the input (105) into a to convert the first output voltage present at the first output and into a second output voltage present at the second output, the first output voltage being greater than the second output voltage, the first output being galvanically coupled to the input (105), the second output being galvanically coupled to the input (105) is separated.

Description

The present invention relates to a DC-DC converter for a motor vehicle according to the preamble of claim 1.

Out of DE 10 2017 220 848 A1 a DC voltage converter is known which converts the electrical source DC voltage generated by a plurality of energy sources into a drive DC voltage which is used by a drive of the motor vehicle. It is a modular multi-stage DC/DC converter.

In contrast, the present invention is based on the object of making it possible to supply additional electrical loads in the motor vehicle with electrical energy.

This object is achieved by a DC-DC converter according to claim 1, a method according to claim 7 and a motor vehicle according to claim 9. Embodiments of the invention are given in the dependent claims.

The DC-DC converter includes two electrical connections as input, two electrical connections as first output and two electrical connections as second output. The DC-DC converter is designed to convert an input voltage present at the input into a first output voltage present at the first output and into a second output voltage present at the second output. In this case, the first output voltage can be greater than the second output voltage. The first output is galvanically coupled to the input. The second output is galvanically isolated from the input.

For example, an electric drive of a motor vehicle can be connected to the first output. Galvanic isolation is not necessary here. For example, additional electrical consumers of the motor vehicle can be connected to the second output. In particular, this can involve loads that can be easily damaged or even destroyed by voltage spikes. The second output voltage can be 12V, 24V or 48V, for example. Therefore, galvanic isolation is beneficial to reduce the risk of damage to loads.

For example, it is possible for the DC-DC converter to include an inductor, via which the energy is transmitted from the input to the first output. In addition, the DC-DC converter can include a first capacitor, via which the energy is transferred from the input to the second output.

According to one embodiment of the invention, the DC-DC converter can be designed as a modular multi-level converter, also referred to as an MMC (modular multi-level converter). This is advantageous since the first output voltage can be adapted to a particular state of the drive by suitable switching of the individual modules. In particular, it is possible to adapt the first output voltage to the operating point of the drive. A particularly high efficiency of the drive can be achieved in this way.

According to one embodiment of the invention, the input voltage and the first output voltage can each be more than twice, preferably more than six times, the magnitude of the second output voltage.

According to an embodiment of the invention, the input voltage can be higher than the second output voltage. It can therefore be a step-down converter.

According to one embodiment of the invention, the DC-DC converter can include a transformer, a rectifier, which can preferably be in the form of a diode bridge circuit, and a second capacitor. In the context of this description, a diode bridge circuit is understood to mean, in particular, a bridge circuit with a plurality of diodes. The diode bridge circuit preferably comprises exclusively diodes which are electrically connected to one another as electrical components.

The transformer can galvanically isolate the second output from the input. The diode bridge circuit can be arranged electrically, in particular directly, between the transformer and the second capacitor. In the context of this description, an electrical arrangement is understood in particular to mean that the corresponding components are electrically connected to one another without further electronic components being interposed. The second capacitor can be connected in parallel with the diode bridge circuit. The second capacitor can be arranged electrically, in particular directly, between the diode bridge circuit and the second output.

This embodiment is particularly advantageous for converting the input voltage into the second output voltage in a controlled manner. The regulation can be made possible by the diode bridge circuit and the second capacitor. So For example, the circuit of the DC-DC converter can be optimized in order to output the second output voltage in a fully regulated manner for the electrical consumers, while the first output voltage can be adapted as well as possible to the drive.

According to one embodiment of the invention, the DC/DC converter comprises a number of energy sources and a number of switching elements. The energy sources can be accumulators, for example. The energy sources can each be selectively switched into a first state and into a second state using the switching elements. In the first state, the energy sources are each connected in series with at least one other of the energy sources and are electrically connected to the input. In the second state, the energy sources are each connected in parallel with at least one other of the energy sources and are electrically connected to the input. The first output voltage can be adapted to the drive connected to the first output by suitably switching the energy sources to the first or second state.

It is also possible that the energy sources can each be switched into a third state by the switching elements. In the third state, the power sources can each be free of electrical connection to the input. This can be particularly advantageous if an energy source is defective.

It is thus possible, in particular, for both the first and the second output voltage to be supplied by the same energy sources. It can thus be a single electronic system that emits both the first and the second output voltage.

In the method according to claim 7, an electrical load, for example the drive of the motor vehicle, is electrically connected to the first output. The first output voltage is output to the electrical load via the first output. In this case, the first output voltage is regulated by switching the energy sources into the first or second state. The control allows the first output voltage to fluctuate between an upper and a lower threshold value. In particular, it is possible that the first output voltage fluctuates due to a state change of the load. In order to avoid large fluctuations, the switching elements can be used. The difference between the upper and lower threshold values can be 5 volts, for example.

According to an embodiment of the invention, the second output voltage can be fully regulated by the cooperation of the diode bridge circuit with the second capacitor. In the context of this description, this means in particular that the interaction of the diode bridge circuit with the second capacitor enables the second output voltage to be regulated at the same time as the first output voltage is regulated. In this case, a fluctuation in the second output voltage can be very much smaller than in the case of the first output voltage. For example, the variation in the second output voltage can be less than 0.5V. This is advantageous if the loads electrically connected to the second output are relatively sensitive to voltage fluctuations.

The motor vehicle according to claim 9 comprises a DC-DC converter according to an embodiment of the invention and a drive. The drive is electrically connected to the first output of the DC-DC converter. The drive is designed to cause the motor vehicle to move. In the context of this description, this means in particular that the drive is designed to generate a torque that causes the entire motor vehicle to move, for example by rolling on wheels.

According to one embodiment of the invention, the motor vehicle can include a plurality of electrical loads that are electrically connected to the second output of the DC-DC converter.

• 1 einen schematischen Schaltplan einer ersten Ausführungsform der Erfindung;
• 2 eine schematische Darstellung über verschiedene Zustände von Schaltelementen nach einer Ausführungsform der Erfindung; und
• 3 einen schematischen Schaltplan eines Ausschnitts des Ausführungsform aus 1;
• 4 einen schematischen Schaltplan einer zweiten Ausführungsform der Erfindung; und
• 5 einen schematischen Schaltplan einer dritten Ausführungsform der Erfindung.

Further features and advantages of the present invention become clear from the following description of preferred exemplary embodiments with reference to the attached figures. The same reference symbols are used for the same or similar features and for features with the same or similar functions. while showing

• 1 a schematic circuit diagram of a first embodiment of the invention;
• 2 a schematic representation of different states of switching elements according to an embodiment of the invention; and
• 3 a schematic circuit diagram of a section of the embodiment 1 ;
• 4 a schematic circuit diagram of a second embodiment of the invention; and
• 5 a schematic circuit diagram of a third embodiment of the invention.

In 1 a system with a multi-level modular DC-DC converter is shown. The system comprises several energy sources 100, several sets 101 of switching elements, a load 102, a consumer 103, a transformer HFT, a diode bridge circuit 104, an inductor L _dc , a first capacitor C _dc1 , a second capacitor C _dc2 , a third capacitor C _dc3 and two electrical connections as input 105. The load 102 is connected via a first output, at which a first output voltage is present during operation. Consumer 103 is connected via a second output at which a second output voltage is present during operation.

The energy sources 100 are numbered from 1 to N and are electrically connectable to one another through the sets 101 of switching elements. In this case, one of the sets 101 is always arranged between two of the energy sources 100 . Sets 101 are numbered 1 through N-1.

Depending on how the switching elements are connected, the energy sources 100 are connected in parallel or in series with one another. It is also possible to switch one of the energy sources 100 to bypass in each case, so that it is not involved in generating the input voltage.

In 2 a set 101 with the switching elements S1, S2 and S3 is shown. These switching elements S1, S2 and S3 can be switched to a first state Z1, in which the two energy sources 100 connected to the respective set 101 are connected in series. In the first state Z1, the switching elements S1 and S3 are not conductive, while the switching element S2 is conductive. In a second state Z2, the energy sources 100 connected to the respective set 101 are connected in parallel. In the second state Z2, the switching elements S1 and S3 are conductive, while the switching element S2 is not conductive. In a third state S3, only the switching element S3 is conductive, while the switching elements S1 and S2 are not conductive. In the third state Z3, one of the energy sources 100 is not electrically connected to the input 105. This state Z3 is usually only used when the respective energy source 100 is defective. Otherwise, the stability of the input voltage can be increased by means of the second state Z2 if the input voltage is not to be increased by switching to the first state Z1.

The transformer HFT is electrically connected to the input at its input side via the first capacitor C _dc1 . On the output side of the transformer HFT, the transformer HFT is electrically connected to the load 103 via the diode bridge circuit 104 . The second capacitor C _{dc2 is} connected in parallel with the load 103 .

During operation, the energy sources 100 generate the input voltage that is present at the input 105 . The inductor L _dc is connected in series with the load 102 . The third capacitor C _dc3 is connected in parallel with the load 102 . The energy flows from the energy sources 100 to the load 102 via the inductor L _dc .

The first output voltage applied to the load 102 is regulated as a function of a state of the load 102, so that the load 102—for example a motor vehicle drive—can be operated particularly efficiently. This is done by suitably switching the sets 101. This principle is known from a known modular multi-stage converter. For example, a PSC (“Phase Shifted Carrier”) modulation can be used, which generates the switching signals for the sets 101 . When using PSC modulation, the input voltage can be viewed as a composite of a constant voltage and a pulse width modulation controlled voltage V _m .

How the conversion of the input voltage into the second output voltage works is easiest when considering the 3 to understand.

$$V_{p-}=-D\times \left(V_m-\Delta V_r\right)$$

With the PSC modulation, the first capacitor C _dc1 is repeatedly charged up to the first output voltage. The voltage received from the transformer HFT includes a positive voltage pulse V _p+ and a negative voltage pulse V _p- . These are calculated as follows: $$V_{p+}=\left(1-D\right)\left(V_m-\Delta V_{\mathrm{right}}\right)$$

$$V_{p-}=-D\times \left(V_m-\Delta V_{\mathrm{right}}\right)$$

In this case, D is the proportion of the duration of the positive voltage pulse to the duration of the positive and negative voltage pulses. ΔV _r is the residual ripple on the first capacitor C _dc1 . The voltage applied to the input side of the transformer changes as a function of the switching duration D. For D < 0.5, the positive voltage pulse is greater than the negative voltage pulse. For D > 0.5, the negative voltage pulse is larger than the positive voltage pulse.

The diode bridge circuit 104 is connected in parallel with the second capacitor C _dc2 and the load 103 . In operation, the diode bridge circuit 104 is an open circuit during a negative voltage pulse as long as the dated Transformer HFT received voltage V _p > |V _m | is. During this time, the load 103 is supplied with the second output voltage by the second capacitor C _dc2 . Then, during a positive voltage pulse, the diode bridge circuit 104 is an open circuit. As long as the voltage V _P < |V _m | , the second capacitor C _dc2 is charged via the diode bridge circuit 104 during a negative voltage pulse. During a positive voltage pulse, the diode bridge circuit 104 is an open circuit.

For any desired second output voltage, there are two possible values for the duty cycle D during PSC modulation. For each switching period D there are N-1 possible values for a modulation reference to be used in PSC modulation. Therefore, for each operating point there are 2(N-1) values for the modulation reference, which lead to an identical second output voltage, while at the same time completely different first output voltages can be produced. This freedom can be used to keep both the first and second output voltages within desired ranges. Depending on the topology, there can also be more than N-1 possible values for the modulation reference to be used in PSC modulation. Accordingly, in such a case, there can also be more than 2(N-1) values for each operating point for the modulation reference.

The DC-DC converter can therefore output the second output voltage in a fully regulated manner, while at the same time the first output voltage can be kept within relatively narrow limits and can therefore be referred to as partially regulated.

The second embodiment of the system essentially corresponds to the first embodiment, with the exception of the active rectifier (e.g. a full-bridge switching diode set) in the island grid. In this case, the AC-DC converter 71 is connected to a power supply, e.g. B. a 230 V socket connected. The two sub-grids 56 can have different voltage levels, higher and/or lower than the voltage of the first sub-grid 54, depending on the transformer conditions and the activation of the associated sub-modules, e.g. B. 110V, 220V.

In addition, the power supply system 52 includes a control unit 62 and can have a further energy storage element 64 . The multilevel converter 58 in 4 is associated with a large electrical load 66, which in this case can be designed as an electrical machine inverter set. Alternatively, the multilevel converter 58 may be connected to a DC fast charger 67 or an AC charger 69 instead.
The operation of the system 52 in 4 is largely similar to the first embodiment, except that there is the possibility of a bi-directional exchange of energy between the sub-network 54 and the sub-network 56. Such conditions can be realized in an electric vehicle during the so-called home-to-vehicle and/or vehicle-to-grid and/or grid-to-vehicle mode.

The third embodiment of the system is substantially similar to the first embodiment, except that not all modules are connected across the capacitor 78 to the transformer. The operation of the system 82 in 5 is broadly similar to the first embodiment, except that the modules not included here can provide a further degree of freedom to fully control both the first and second output voltages.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102017220848 A1 [0002]

Claims (10)

DC-DC converter for a motor vehicle, comprising two electrical connections as the input (105), two electrical connections as the first output and two electrical connections as the second output, the DC-DC converter being designed to convert an input voltage present at the input (105) into a voltage present at the first output first output voltage and into a second output voltage present at the second output, the first output being galvanically coupled to the input (105), characterized in that the second output is galvanically isolated from the input (105). DC converter after claim 1 , characterized in that the DC-DC converter is designed as a modular multi-stage converter. DC-DC converter according to one of the preceding claims, characterized in that the input voltage and the first output voltage are each more than twice, preferably more than six times, as large as the second output voltage. DC-DC converter according to one of the preceding claims, characterized in that the input voltage is higher than the first output voltage. DC-DC converter according to one of the preceding claims, characterized in that the DC-DC converter comprises a transformer (HFT), a rectifier (104) and a capacitor (C _dc2 ), the transformer (HFT) galvanically isolating the second output from the input (105), wherein the diode bridge circuit (104) is electrically connected between the transformer (HFT) and the capacitor (C _dc2 ), wherein the capacitor (C _dc2 ) is connected in parallel with the diode bridge circuit (104), and wherein the capacitor (C _dc2 ) is electrically connected between the Diode bridge circuit (104) and the second output is arranged. DC-DC converter according to one of the preceding claims, characterized in that the DC-DC converter comprises a plurality of energy sources (100) and switching elements (S1, S2, S3), the energy sources (100) each using the switching elements (S1, S2, S3) optionally in one first state (Z1) and into a second state (Z2), wherein the energy sources (100) are each connected in series with at least one other of the energy sources (100) in the first state (Z1) and are electrically connected to the input (105). are, wherein the energy sources (100) each in the second state (Z2) are connected in parallel with at least one other of the energy sources (100) and are electrically connected to the input (105). Method for operating a DC-DC converter according to the preceding claim, wherein an electrical load (102) is electrically connected to the first output, and wherein the method comprises the following steps: - outputting the first output voltage via the first output to the electrical load (102); and - Control of the first output voltage by switching the energy sources (100) to the first state (Z1) or to the second state (Z2), the control allowing the first output voltage to fluctuate between an upper threshold value and a lower threshold value. Method according to the preceding claim, characterized in that the method comprises the following step: - regulation of the second output voltage by cooperation of the diode bridge circuit (104) with the capacitor (C _dc2 ) at the same time as regulation of the first output voltage. Motor vehicle, comprising a DC-DC converter according to one of Claims 1 until 6 and an electrical drive, wherein the drive is electrically connected to the first output of the DC/DC converter, and wherein the drive is configured to cause the motor vehicle to move. Motor vehicle according to the preceding claim, characterized in that the motor vehicle comprises a plurality of electrical consumers (103), the electrical consumers (103) being electrically connected to the second output of the DC-DC converter.

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