Control device for a dc-dc converter and method for controlling a dc-dc converter

Abstract

The present invention relates to the control of a DC-DC converter. A controlled variable of the DC-DC converter is formed as a combination of voltage control and current control. The maximum permissible current for the current control can be adjusted depending on the current value of the input voltage to the DC / DC converter.

Description

[0001] Description

[0002] title

[0003] Control device for a DC-DC converter and method for

[0004] Controlling a DC-DC converter

[0005] Technical area

[0006] The present invention relates to a control device for a DC-DC converter and a method for controlling a DC-DC converter. The present invention further relates to a DC-DC converter device, a device for charging an intermediate circuit capacitor, in particular an intermediate circuit capacitor in a high-voltage network, as well as a power supply network and an electric drive system for an electric vehicle.

[0007] State of the art

[0008] Vehicles that are fully or at least partially electrically powered have an electric drive system that is powered by a so-called traction battery. The electric drive system usually comprises an electric machine and a power converter, in particular an inverter, wherein a so-called intermediate circuit capacitor is provided in the power converter to stabilize an input DC voltage. When switched off, the traction battery can be disconnected from the power converter of the electric drive system using a disconnect switch. Before reconnecting the traction battery to the power converter, it is desirable to charge the intermediate circuit capacitor in the power converter to a voltage level that at least approximately corresponds to the voltage level of the traction battery. An electrical connection can then be established between the traction battery and the power converter via the disconnect switch.The publication DE 10 2016 200 662 Al, for example, describes a bidirectional DC-DC converter for charging an intermediate circuit capacitor from a low-voltage battery.

[0009] If the low-voltage side, especially a battery in a low-voltage network, is subjected to excessive load during a charging process for an intermediate circuit capacitor, the voltage level on the low-voltage side can drop. This can potentially impair the functionality of loads on the low-voltage side.

[0010] Disclosure of the invention

[0011] The present invention discloses a control device for a DC-DC converter and a method for controlling a DC-DC converter, a DC-DC converter device, a device for charging an intermediate circuit capacitor, as well as a power supply network and an electric drive system for an electric vehicle with the features of the independent patent claims. Further advantageous embodiments are the subject of the dependent patent claims.

[0012] Accordingly, it is provided:

[0013] Control device for a DC-DC converter with a voltage regulator, a current regulator, and a monitoring device. The voltage regulator is designed to determine a first controlled variable for the DC-DC converter using a setpoint value for the output voltage of the DC-DC converter and a measured value for the output voltage of the DC-DC converter. The current regulator is designed to determine a second controlled variable for the DC-DC converter using a current controlled variable and a current current value of the DC-DC converter. The monitoring device is designed to adjust the current controlled variable for the current regulator using a comparison of an input voltage of the DC-DC converter with a minimum target voltage, preferably a predetermined minimum target voltage.Furthermore, the control device is designed to control the DC-DC converter using a combination of the first controlled variable and the second controlled variable.

[0014] Furthermore, it is planned:

[0015] A DC-DC converter device comprising a DC-DC converter and a control device according to the invention. The DC-DC converter is designed to be connected to a DC voltage source on the input side. Furthermore, the DC-DC converter is designed to convert the DC voltage provided on the input side into a further electrical DC voltage and to provide it on the output side.

[0016] Furthermore, it is planned:

[0017] A device for charging an intermediate circuit capacitor in a high-voltage network, with a DC-DC converter device according to the invention, wherein the DC-DC converter is designed to be connected on the output side to an intermediate circuit capacitor of the high-voltage network.

[0018] In addition, it is planned:

[0019] A power supply network for an electric vehicle comprising a high-voltage network, a low-voltage network, and a device according to the invention for charging an intermediate circuit capacitor. The high-voltage network comprises a high-voltage battery, an intermediate circuit capacitor, and a disconnect switch. The disconnect switch is designed to open or close an electrical connection between the high-voltage battery and the intermediate circuit capacitor.

[0020] Furthermore, it is planned:

[0021] An electric drive system comprising a power supply network according to the invention, an electric machine, and an electric power converter. The power converter is designed to control the electric machine using the electrical energy provided in the high-voltage network. The intermediate circuit capacitor of the high-voltage network can be provided, in particular, in the electric power converter.

[0022] Finally, it is planned:

[0023] A method for controlling a DC-DC converter. The method comprises a step for determining a first controlled variable for the DC-DC converter. The first controlled variable is determined in particular using a setpoint for the output voltage of the DC-DC converter and a measured value for the output voltage of the DC-DC converter. The method further comprises a step for determining a second controlled variable for the DC-DC converter. The second controlled variable is determined in particular using a current controlled variable and a current current value of the DC-DC converter. The method further comprises a step for adjusting the current controlled variable for the current controller. The current controlled variable is adjusted in particular using a comparison of an input voltage of the DC-DC converter with a minimum target voltage.Finally, the method comprises a step of controlling the DC-DC converter using a combination of the first controlled variable and the second controlled variable.

[0024] Advantages of the invention

[0025] The present invention is based on the finding that, during energy transmission through a DC-DC converter from an input side to an output side of the DC-DC converter, a voltage drop can occur on the input side depending on the power transmitted by the DC-DC converter. In particular, if additional loads are connected to a power supply network that feeds the input side of the DC-DC converter, this can impair the functionality of these additional loads. Therefore, one idea of ​​the present invention is to take this finding into account and to provide an operation of a DC-DC converter in which excessive voltage drops in a power supply network from which the DC-DC converter draws its energy can be avoided.For this purpose, it is provided to combine voltage regulation for the output voltage of the DC-DC converter with current regulation for the control of the DC-DC converter, whereby the current regulation also takes into account the level of the input voltage of the DC-DC converter. The input voltage is preferably determined or measured, preferably using a voltage measuring device. In this way, it is possible to limit the electrical current in the DC-DC converter when the electrical voltage at the input of the DC-DC converter drops, thereby preventing an excessive drop in the voltage level on the input side of the DC-DC converter.

[0026] The inventive concept makes it possible to combine voltage regulation of the DC-DC converter with current regulation to provide a desired voltage level on the output side. The current regulation used here can be used, on the one hand, to regulate a maximum electrical current in the DC-DC converter and, in particular, to limit it to a maximum value. In this way, overloading of the DC-DC converter can be avoided if the voltage regulation would result in excessive electrical power being drawn from the input side. Furthermore, the invention provides for the current regulation to be supplemented by a further aspect and for a voltage level on the input side of the DC-DC converter to be taken into account during the current regulation.In this way, the electrical current in the DC-DC converter, and thus the electrical power drawn at the input side of the DC-DC converter, can be regulated and, in particular, limited if the power consumption of the DC-DC converter places such a heavy load on the input side that the input voltage drops too much. Especially when charging a capacitor on the output side of a DC-DC converter, for example an intermediate circuit capacitor such as those used for inverters in electric drive systems, a high power requirement can arise at the beginning of the charging process. This power requirement may only be met to a limited extent by a battery supplying the input side of the DC-DC converter. This can lead to severe voltage drops.These voltage drops can potentially impair the operation of other loads that are also fed from a power grid at the input of the DC-DC converter. By limiting the electrical current through the DC-DC converter depending on the input voltage, it can be ensured that a power grid at the input of the DC-DC converter always maintains a voltage level that enables the reliable operation of other loads connected to this power grid.

[0027] According to one embodiment, the monitoring device is designed to reduce a predetermined value for the maximum current control variable if the input voltage of the DC-DC converter falls below a predetermined value. If the input DC voltage drops below a minimum permissible value, this can be interpreted as an indication that the energy source on the input side of the DC-DC converter is overloaded by the power consumption of the DC-DC converter. In this case, the reliable operation of additional consumers on the input side of the DC voltage as a load may not be guaranteed.

[0028] According to one embodiment, the current regulator is configured to output a control signal if the current regulator is active in an operating mode in which a maximum current in the DC-DC converter is limited. The voltage regulator is configured to adjust the second controlled variable using the control signal from the current regulator. This allows the voltage regulator to be informed whether the current regulator is actively intervening in the controlled variable or not. This allows conflicting control operations to be avoided. In particular, this can counteract oscillations in the control system.

[0029] According to one embodiment, the control device is designed to output a duty cycle for pulse-width modulation as a controlled variable for controlling the DC-DC converter. This allows for pulse-width modulation of the DC-DC converter in a simple manner.

[0030] The above embodiments and further developments can be combined with one another as desired, where appropriate. Further embodiments, further developments, and implementations of the invention also include combinations of features of the invention not explicitly mentioned above or described below with respect to the exemplary embodiments. In particular, those skilled in the art will also add individual aspects as improvements or additions to the respective basic forms of the invention.

[0031] Short description of the drawings

[0032] Further features and advantages of the invention are explained below with reference to the figures. These show:

[0033] Fig. 1: a schematic representation of a block diagram of an electric drive system with a control device according to an embodiment;

[0034] Fig. 2: a schematic representation of a DC-DC converter device with a control device according to an embodiment;

[0035] Fig. 3: a schematic diagram to explain the functional principle of a monitoring device for a control device according to one embodiment; and Fig. 4: a flowchart underlying a method according to one embodiment.

[0036] In the figures, the same reference symbols denote identical or functionally identical components, unless otherwise stated.

[0037] Description of embodiments

[0038] Figure 1 shows a schematic representation of a block diagram of an electric drive system, such as can be used, for example, in a fully or at least partially electrically powered motor vehicle. The electric drive system comprises an electric machine 6. This electric machine 6 can be supplied with electrical energy, for example, by an electric power converter 5. For this purpose, the electric power converter 5 can convert an electrical direct voltage provided on the input side into a single-phase or multi-phase electrical alternating voltage in order to control the electric machine 6 according to a predetermined torque, a predetermined speed, or another predetermined setpoint. On the input side, the electrical direct voltage can be provided by a high-voltage network. This high-voltage network can be provided, for example, by a battery 8, for example a traction battery.The battery 8 can be electrically connected or disconnected from the other components of the high-voltage network by means of a disconnect switch 9.

[0039] To stabilize the DC voltage, an intermediate circuit capacitor 4 is provided at the input of the power converter 5. When switched off, this intermediate circuit capacitor 4 is generally discharged and the isolating switch 9 is open. To switch on, this isolating switch 9 is closed. Before the isolating switch 9 is closed, the intermediate circuit capacitor 4 is first charged to a voltage level that at least approximately corresponds to the voltage level of the battery 8. In this way, high electrical compensating currents when the isolating switch 9 is closed can be avoided. To charge the intermediate circuit capacitor 4, a DC-DC converter 2 is provided, which charges the intermediate circuit capacitor 4 using electrical energy from a low-voltage network with a corresponding battery 3. The operation of the DC-DC converter 2 is controlled by a control device 1.Furthermore, if necessary, further consumers 7 may be connected to the low-voltage network.

[0040] The functional principle of the control device 1 for charging the intermediate circuit capacitor 4 from the low-voltage network is explained in more detail below.

[0041] Figure 2 shows a schematic block diagram of a DC-DC converter device comprising a control device 1 and a DC-DC converter 2 according to one embodiment. The DC-DC converter 2 converts a DC voltage UJn provided on the input side into an output DC voltage U_out, which can be used, for example, to charge the intermediate circuit capacitor 4. A controlled variable R, for example, in the form of a duty cycle for pulse-width modulated (PWM) control, can be provided to the DC-DC converter 2. The basic principle of a DC-DC converter with pulse-width modulated (PWM) control is assumed to be known and will not be explained in more detail.

[0042] The controlled variable R for the DC-DC converter 2 can be provided, for example, by means of the control device 1. For this purpose, the control device 1 can comprise a voltage regulator 11 and a current regulator 12.

[0043] The voltage regulator 11 generates a first controlled variable RI. To do this, the voltage regulator 11 compares a value of the output DC voltage U_out with a predetermined setpoint U_setpoint. This setpoint U_setpoint can, for example, be a value for the target voltage to which the intermediate circuit capacitor 4 is to be charged. In addition to the actual voltage regulator 11a, the voltage regulator 11 can also comprise a further pre-regulator 11b. This pre-regulator 11b can, for example, determine a control component based on the input DC voltage UJn, the setpoint voltage U_setpoint, and possibly also electrical currents at the input and / or output of the DC-DC converter. This control component can, as shown in Figure 2, be combined with the control component of the actual voltage regulator 11b to obtain the first controlled variable RI.

[0044] The current regulator 12 generates a second controlled variable R2, which is determined, for example, based on the electrical current l_dc in the DC-DC converter 2. In principle, either the input current, the output current of the DC-DC converter 2, or an internal current in the DC-DC converter 2 can be considered for this purpose. In particular, the current regulator 12 can determine the second controlled variable R2 using the electrical current l_dc of the DC-DC converter 2 and a predetermined setpoint value l_soll. For example, the current regulator 12 can generate a second controlled variable R2 suitable for limiting the electrical current of the DC-DC converter 2 to a predetermined maximum value. In this way, overloading of the DC-DC converter 2 can be avoided.Accordingly, as long as the electrical current in the DC-DC converter 2 is below the permissible current, no or only a correspondingly limited limitation can be provided by the second controlled variable R2. In particular, for example, the current regulator 12 can only be activated when the electrical current in the DC-DC converter 2 is to be limited.

[0045] If the current regulator 2 limits the electrical current in the DC-DC converter 2, this can be signaled by a corresponding signal C to the current regulator 12. In this case, the control of the current regulator 12 can be adjusted or deactivated as appropriate.

[0046] The first controlled variable RI from the voltage regulator 11 and the second controlled variable R2 from the current regulator 12 can be combined with one another, for example, added, and the result can be provided as controlled variable R to the DC-DC converter 2. Furthermore, the control device 1 comprises a monitoring device 13. This monitoring device 13 compares the current input DC voltage UJn at the DC-DC converter 2 with a predetermined value U_in_min. In particular, this predetermined value U_in_min can be a value for a minimum permissible electrical voltage in an electrical network that is intended to provide the electrical voltage at the input of the DC-DC converter 2. For example, this minimum electrical voltage U_in_min can be a value that is at least required to ensure reliable operation of other electrical consumers 7 on the power grid.

[0047] If the monitoring device 13 detects that the current input DC voltage UJn is approaching the minimum additional value UJn_min or even falls below this value U Jn_min, this can be interpreted as an indication that the power supply network at the input of the DC-DC converter 2 is being subjected to excessive load by the power consumption of the DC-DC converter 2. To counteract such excessive load, the monitoring device 13 can adjust, in particular reduce, the specification for the maximum permissible electrical current in the DC-DC converter 2. To do this, the monitoring device 13 can, for example, adjust the setpoint specification l_soll for the downstream current regulator 12.

[0048] Accordingly, either the original specification for the maximum electrical current in the DC-DC converter 2 or the setpoint adjusted by the monitoring device 13 can be provided to the current controller 12 as the setpoint specification l_soll. In this case, the smaller of the two aforementioned values ​​is provided as the setpoint specification to the current controller 12.

[0049] Figure 3 shows a schematic block diagram to illustrate the function of a monitoring device 13 in a control apparatus 1 according to one embodiment. At the input of the monitoring device 13, for example, a specification for the minimum permissible electrical voltage U_in_min at the input of the DC-DC converter 2 and a current measured value UJn of the electrical voltage at the input of the DC-DC converter 2 can be provided. These can be compared with one another. For this purpose, for example, a difference between the current measured value UJn and the minimum additional value UJn_min can be formed. If necessary, this difference can be multiplied by a weighting factor g. Based on this result, an adjusted setpoint value l_soll for the maximum permissible electrical current in the DC-DC converter 2 can be determined.For example, a functional relationship can be determined over a value range between 0 and the system-related maximum permissible current l_max in the DC-DC converter 2.

[0050] The smaller value of the system-dependent maximum permissible current l_max for the DC-DC converter 2 and the maximum permissible electrical current determined using the input DC voltage can then be provided as the setpoint I soll to the current controller 12.

[0051] Figure 4 shows a flowchart underlying a method for controlling a DC-DC converter 2 according to one embodiment. The method can, in principle, comprise any steps as previously described in connection with the control device 1. Analogously, the control device 1 described above can also comprise any suitable components as required to implement the method described below.

[0052] In step S1, a first controlled variable RI is determined for the DC-DC converter 2. The first controlled variable RI is determined in particular using a setpoint U_setpoint for the output voltage of the DC-DC converter 2 and a measured value U_n for the output voltage of the DC-DC converter 2. In step S2, a second controlled variable R2 is determined for the DC-DC converter 2. The second controlled variable R2 is determined in particular using a current controlled variable l_setpoint and a current current value l_dc of the DC-DC converter 2.

[0053] In step S3, the current control variable l_soll is adjusted using a comparison of an input voltage U_in of the DC-DC converter 2 with a minimum target voltage U_in_min.

[0054] Finally, in step S4, the DC-DC converter 2 is controlled using a combination of the first controlled variable RI and the second controlled variable R2.

[0055] In summary, the present invention relates to the control of a DC-DC converter. A controlled variable of the DC-DC converter is formed as a combination of voltage control and current control. The maximum permissible current for current control can be adjusted depending on the current value of the input voltage at the DC-DC converter.

Claims

Claims 1. Control device (1) for a DC-DC converter (2) , comprising: a voltage regulator (11) designed to determine a first control variable (RI) for the DC-DC converter (2) using a setpoint (U_setpoint) and a measured value (U_out) for the output voltage of the DC-DC converter (2); a current regulator (12) designed to determine a second control variable (R2) for the DC-DC converter (2) using a current control variable (l_setpoint) and an actual current value (l_dc) of the DC-DC converter (2); and a monitoring device (13) designed to adjust the current control variable (l_setpoint) for the current regulator (13) by comparing an input voltage (U_Jn) of the DC-DC converter (2) with a minimum target voltage (U_in_min);wherein the control device (1) is designed to control the DC voltage converter (2) using a combination (R) of the first controlled variable (RI) and the second controlled variable (R2).

2. Control device (1) according to claim 1, wherein the monitoring device (13) is designed to reduce a predetermined value for the maximum current control variable (l_soll) if the input voltage (UJn) of the DC voltage converter falls below a predetermined value (U_in_min).

3. Control device (1) according to claim 1 or 2, wherein the monitoring device (13) comprises a control device which is designed to is designed to determine an internal control variable using a difference between the input voltage (UJn) of the DC-DC converter (2) and the minimum target voltage (U_in_min), and to output the internal control variable as a current control variable (I set) if the internal control variable falls below a predetermined value.

4. Control device (1) according to any one of claims 1 to 3, wherein the current controller (12) is designed to output a control signal (C) if the current controller (12) is active in an operating mode in which a maximum current in the DC-DC converter (2) is limited, and wherein the voltage controller (11) is designed to adjust the first controlled variable (RI) using the control signal (C) from the current controller (12).

5. Control device (1) wherein the control device (1) is designed to output a duty cycle for pulse width modulation as a control variable (R) for controlling the DC voltage converter (2).

6. DC-DC converter device, comprising: a DC-DC converter (2) designed to be connected on the input side to a DC voltage source (3) and to convert the DC voltage (UJn) provided on the input side into a further DC electrical voltage (U_out); and a control device (1) according to any one of claims 1 to 5.

7. Device for charging an intermediate circuit capacitor (4) in a high-voltage network, comprising: a DC / DC converter device according to claim 6; wherein the DC-DC converter (2) is designed to be connected on its output side to a DC link capacitor (4) of the high-voltage network. Power supply network for an electric vehicle, comprising: a high-voltage network with a high-voltage battery (8), a DC link capacitor (4), and a disconnect switch (9), wherein the disconnect switch (9) is designed to open or close an electrical connection between the high-voltage battery (8) and the DC link capacitor (4); a low-voltage network with a low-voltage battery (3); and a device for charging the DC link capacitor (4) according to claim 7. Electric drive system, comprising: a power supply network according to claim 8, an electric machine (6); and an electric converter (2) designed to drive the electric machine (6) using the electrical energy provided in the high-voltage network.Method for controlling a DC voltage converter (2), comprising the steps:. Determining (Sl) a first controlled variable (RI) for the DC-DC converter (2) using a setpoint (U_setpoint) for the output voltage of the DC-DC converter (2) and a measured value (UJn) for the output voltage of the DC-DC converter (2); Determine (S2) a second control variable (R2) for the DC-DC converter (2) using a current control variable ((l_set) and an actual current value (l_dc) of the DC-DC converter (2); Adjusting (S3) the current control variable (l_set) using a comparison of an input voltage (UJn) of the DC-DC converter (2) with a minimum target voltage (U_in_min); and Control (S4) of the DC voltage converter (2) using a combination (R) of the first controlled variable (RI) and the second controlled variable (R2).

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