Method and system for operating a DC-DC converter of an electrical system to distribute a load

Abstract

The invention relates to a method for operating an electrical system (1) having a high-voltage section (2) and a low-voltage section (3) which are electrically connected to one another by means of a DC-DC converter (4), wherein the low-voltage section (3) has at least one rechargeable energy store (8) and at least one electrical consumer (9), wherein the DC-DC converter (4) is operated on the basis of an electrical load (P) acting on the low-voltage section (3). In order to determine the load (P), provision is made for all currents flowing through the DC-DC converter (4) to be recorded and added to one another.

Claims

1. A method for operating a DC-DC voltage converter (4) of a motor vehicle electrical system (1), the motor vehicle electrical system including a high-voltage section (2) and a low-voltage section (3) that are electrically connected to one another by the DC-DC voltage converter (4), wherein the low-voltage section (3) has at least one rechargeable energy store (8) and at least one electrical consumer (9), wherein the DC-DC voltage converter (4) is operated on the basis of an electrical load (P) acting on the low-voltage section (3), characterized in that the load (P) is determined by virtue of all the currents flowing through the DC-DC voltage converter (4) being sensed and added to one another, a peak load (P.sub.S) of the load (P) is forecast from a gradient of the added currents being ascertained and a present base load (P.sub.G), and the peak load (P.sub.S) is compared with a prescribable limit value in order to initiate measures to avoid the peak load (P.sub.S) in the event of the limit value being exceeded, and wherein when a critical peak load is sensed, one or more additional DC-DC voltage converter modules are connected distributing the peak load over all of the DC-DC voltage converter modules.

2. The method as claimed in claim 1, characterized in that the base load (P.sub.G) of the load (P) is determined by virtue of an output voltage of the DC-DC voltage converter (4) being sensed.

3. The method as claimed in claim 1, characterized in that an alternating load (P.sub.W) of the load (P) is determined by virtue of voltage changes in the low-voltage section (3) being monitored.

4. The method as claimed in claim 1, characterized in that the DC-DC voltage converter (4) operated is a multiphase converter (4) having multiple parallel-connected DC-DC voltage converter modules (4_1, 4_2, . . . , 4_N).

5. An apparatus for operating a DC-DC voltage converter (4) of a motor vehicle electrical system (1), the motor vehicle electrical system including a high-voltage section (2) and a low-voltage section (3) that are electrically connected to one another by the DC-DC voltage converter (4), wherein the low-voltage section (3) has at least one rechargeable energy store (8) and at least one electrical consumer (9), having a controller that takes an electrical load acting on the low-voltage section as a basis for actuating the DC-DC voltage converter (4), characterized in that the controller is set up to operate the DC-DC voltage converter (4) on the basis of an electrical load (P) acting on the low-voltage section (3), wherein the load (P) is determined by virtue of all the currents flowing through the DC-DC voltage converter (4) being sensed and added to one another, a peak load (P.sub.S) of the load (P) is forecast from a gradient of the added currents being ascertained and a present base load (P.sub.G), and the peak load (P.sub.S) is compared with a prescribable limit value in order to initiate measures to avoid the peak load (P.sub.S) in the event of the limit value being exceeded, and wherein when a critical peak load is sensed, one or more additional DC-DC voltage converter modules are connected distributing the peak load over all of the DC-DC voltage converter modules.

6. The apparatus for operating an electrical system (1) as claimed in claim 5, characterized in that the base load (P.sub.G) of the load (P) is determined by virtue of an output voltage of the DC-DC voltage converter (4) being sensed.

7. The apparatus for operating an electrical system (1) as claimed in claim 5, characterized in that the peak load (P.sub.S) is compared with a prescribable limit value in order to initiate measures to avoid the peak load (P.sub.S) in the event of the limit value being exceeded.

8. The apparatus for operating an electrical system (1) as claimed in claim 5, characterized in that an alternating load (P.sub.W) of the load (P) is determined by virtue of voltage changes in the low-voltage section (3) being monitored.

9. The apparatus for operating an electrical system (1) as claimed in claim 5, characterized in that the DC-DC voltage converter (4) operated is a multiphase converter (4) having multiple parallel-connected DC-DC voltage converter modules (4_1, 4_2, . . . , 4_N).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention shall be explained in more detail below with reference to the drawing, in which

(2) FIG. 1 shows a schematic depiction of an electrical system of a motor vehicle,

(3) FIG. 2 shows a design of a control system for the electrical system,

(4) FIG. 3 shows a schematic depiction of an advantageous operating strategy module of the electrical system, and

(5) FIG. 4 shows a method for determining a load of the electrical system.

DETAILED DESCRIPTION

(6) FIG. 1 shows a simplified depiction of an electrical system 1 of a motor vehicle, not depicted in more detail at this junction. The electrical system 1 has a high-voltage section 2 and a low-voltage section 3 that are electrically connected to one another by a DC-DC voltage converter configured as a multiphase converter 4. In the present case, the high-voltage section 2 comprises a rechargeable high-voltage energy store 5, an inverter 6 and an electrical machine 7 that is operated by the inverter 6. In this case, the electrical machine 7 can be operated by motor or by generator and is particularly configured as a drive machine of the motor vehicle. The low-voltage section 3 comprises a low-voltage energy store 8 that is likewise configured to be rechargeable, and also one or more consumers 9. Together, the energy store 8 and the consumers 9 form the vehicle electrical system 10 of the motor vehicle.

(7) FIG. 2 shows a further depiction of the electrical system 1 with a regulator complex 11, with the multiphase converter 4, which has N parallel-connected DC-DC voltage converter modules 4_1, 4_2, . . . , 4_N. The multiphase converter 4 has a high-voltage-section input voltage U.sub.in and a low-voltage-section output voltage U.sub.out, which arises from the parallel connection and the operation of the DC-DC voltage converter modules 4_1, 4_2 to 4_N. Actuating the DC-DC voltage converter modules of the multiphase converter 4 results in an actual voltage U.sub.actual that is provided to the vehicle electrical system 10. The regulator complex 11 is supplied with a setpoint current I.sub.setpoint and with a setpoint voltage U.sub.setpoint and also with an actual current of the multiphase converter 4 on the high-voltage side I.sub.hv and the low-voltage side I.sub.lv. Particularly this and the actual current I.sub.out result in the actuation of the multiphase converter 4.

(8) FIG. 3 shows a schematic depiction of an operating strategy entity that is configured as an operating strategy module 12 of a controller of the motor vehicle. The operating strategy module 12 takes a present operating point of the electrical system 1 as a basis for deciding how many DC-DC voltage converter modules 4_1, 4_2, . . . 4_N and what parts of a module, such as a step-down converter, for example, are meant to be active. The operating strategy entity receives, as state variable, the desired voltage in the output U.sub.setpoint_external, the present currents I.sub.hv and/or I.sub.lv on the low-voltage side and/or the high-voltage side for the mode of operation of the multiphase converter 4 (intermittent or uninterrupted operation), the voltage U.sub.actual currently measured at the output of the multiphase converter 4 and also internal controlled variables (pilot control, adaptations and control output signal of the regulator complex 11). Optionally, the operating strategy module 12 is moreover supplied with the setpoint current I.sub.setpoint as input value I.sub.setpoint_external and also with a setpoint voltage U.sub.setpoint_external. It is thus possible for an external entity to prescribe a desired setpoint current for one or more of the modules or DC-DC voltage converter modules 4_1, 4_2, . . . , 4_N. The output of the operating strategy entity provides not only the setpoint currents I.sub.setpoint and voltages U.sub.setpoint but also module states M.sub.stat.

(9) The operating strategy module 12 comprises a module 13 for determining setpoint values of the voltage, of the current and of the module states, a module 14 for load estimation, a module 15 for module state determination, a module 16 for current parity/power parity and a module 17 for ascertaining a state of charge or state of health of the low-voltage energy store 8.

(10) In brief, the operating strategy entity therefore performs the following tasks:

(11) Current parity/power parity: the modules can deliver different currents and/or powers for the same loading on the basis of the tolerance of the components. In order to prevent different loadings on the modules/DC-DC voltage converters, the same amount of current/amount of power is achieved by modifying the setpoint currents/setpoint powers for different modules.

(12) Battery charging voltage estimation: if the charging voltage of the low-voltage energy store 8 is not available, it is estimated by the module 17.

(13) Module state determination: present states of the modules are computed. Depending on the captured states, said modules are activated or deactivated. If a module is meant to be switched on or off not by regulator, but rather after a prescribed time or according to a prescribed dynamic, then this sub-function will switch on or off the relevant module or parts thereof.

(14) Load estimation: depending on the measured currents and output signals of the regulating complex 11, the switched-on load that is present on the vehicle electrical system 10 is estimated.

(15) Setpoint value determination: depending on the calculated setpoint currents, the load current, external setpoint voltage requirements, estimated charging voltage and optionally external setpoint current requirement, the setpoint currents, voltages and setpoint module states are determined and provided to regulators or hardware drivers of the multiphase converter 4.

(16) The operating strategy entity or the operating strategy module 12 loads the DC-DC voltage converters of the multiphase converter 4 evenly, optimizes switching processes and increases the life of the electrical system 1 and of the multiphase converter 4.

(17) If multiple DC-DC voltage converter modules 4_1, 4_2, . . . , 4_N are connected in parallel at the output, or in the case of resonant converters with multiple step-down converters (bucks) at the output, the different component tolerances mean that different currents can flow or different powers can be attained. This means that the components are loaded differently and thus age differently. In this case, the loading and aging of the components also is dependent on the electrical load of the low-voltage section 3 that acts on the DC-DC voltage converter modules 4_1, 4_2, . . . , 4_N. With knowledge of the load that is acting, it would therefore be possible to actuate the DC-DC voltage converter in optimized fashion.

(18) In this regard, FIG. 4 shows a simplified depiction of a method for determining a load P that acts on the low-voltage section 3. In this case, it is assumed that the load P is made up of a base load P.sub.G, a peak load P.sub.S and an alternating load P.sub.W. In order to determine the load P or the base load, the peak load and the alternating load, the procedure is as follows:

(19) First of all, the currents I.sub.4_1, I.sub.4_2, . . . , I.sub.4_N of the individual DC-DC voltage converter modules 4_1, 4_2, . . . , 4_N are added. To sense the currents, suitable sensors or circuits of the multiphase converter 4 can be used that may already be present anyway. As a result of the currents of the multiphase converter 4 being sensed and added, a distinction is not drawn between consumers 9 and energy store 8, which can also serve as an energy supplier. Thus, the ultimately ascertained load on the low-voltage section 3 corresponds not to the load on the switched-on energy consumer 9, but rather to the total load comprising consumer 9 and energy store 8. From the point of view of the multiphase converter 4, the energy store 8 is ultimately likewise a consumer, particularly when it is being charged, which means that this contemplation of the low-voltage section for determining the load is not a disadvantage.

(20) To determine the base load P.sub.G, the sum of the added currents is multiplied by the output voltage U.sub.out, and the result is filtered using a suitable filter F. The method involves the currents I being converted for the low-voltage side of the multiphase converter 4 if they are measured on the high-voltage side. An adjustment for the high-voltage side is likewise possible if the input voltage U.sub.in of the multiphase converter 4 is measured. The filtering determines the base load from the total load computed in this manner.

(21) The peak load P.sub.S, which can only occur for a short time, is computed from the gradient of the sensed total current. First of all, the current gradient G is computed and is subsequently scaled using a suitable conversion factor f and multiplied by the output voltage U.sub.out of the multiphase converter 4. As a current change of 100 kA/s is permitted at this juncture, for example, the computation takes place in a very fast time frame, preferably of 100 s. The described computation forecasts future peak load P.sub.S, so that countermeasures can be initiated even before the occurrence of a possibly damaging event. If a peak load P.sub.S that is greater than the prescribable limit value is identified, for example, further DC-DC voltage converter modules 4_1, 4_2, . . . , 4_N can or must be connected so that the total current is distributed over multiple instances of these DC-DC voltage converter modules and the loading on a single DC-DC voltage converter module is decreased. In particular, there is provision in this case for the peak load P.sub.S to be determined by virtue of a mean value being formed that is obtained from (A1+ . . . AX)/X, A being a measured/computed value and X being the number of measured values.

(22) The alternating load P.sub.W is determined by virtue of current changes in the low-voltage section 3 being sensed. In the present case, the alternating load is referred to when consumers 9 in the vehicle electrical system 10 are switched on or off. When the respective consumer 9 or the load linked thereto is switched on or off, a voltage change can occur in the vehicle electrical system 10. Such voltage changes are preferably avoided in order to avoid undesirable voltage fluctuations for controller or else for the energy store 8. Depending on the ascertained alternating load P.sub.W, the actuation of the DC-DC voltage converter modules 4_1, 4_2, . . . , 4_N is therefore adapted in order to reduce or compensate for the voltage fluctuations brought about by the switching on or off.