DE102013112678A1 - Method for controlling a state of charge of a battery of a vehicle electrical system - Google Patents

Abstract

The invention relates to a control device and a method for controlling a state of charge of a battery of a vehicle, wherein electrical consumers of the vehicle and electric power generators of the vehicle are operated in such a way that a variable lower charging limit of the battery is not exceeded, the lower charging limit depending on an electric power active consumer of the vehicle, a power reserve for transient consumers of the vehicle and dependent on internal resistance and voltage of the battery is calculated, and wherein a variable upper charging limit is not exceeded, the variable upper charging limit depending on an electric power of the electric power generators and is determined depending on the internal resistance and voltage of the battery.

Description

The invention relates to a method for controlling a state of charge of a battery according to claim 1 and a control device for carrying out the method according to claim 8.

In the prior art is off DE 10 2011 054 582 A1 a method for controlling a battery system known. The battery system is connected to a generator configured to generate power. In addition, a second battery is provided, which is electrically connected in parallel. The second battery supplies electric consumers of the vehicle with electric power. Furthermore, switching means are provided, which are arranged between the generator, the first battery and the second battery to enable a switching of the power path. Further, a control means for controlling the switching means is provided to bring a charge amount of the second battery closer to a target charge amount. In addition, a variable setting means for variably setting the target charge amount is provided. The target charge amount is based on a regenerative state of charge of the second battery and / or a discharge state of the second battery. The target charge amount may be set based on a detected internal resistance of the battery. In addition, the target amount of charge may be variably set based on a detected amount of the electric load. Furthermore, the target amount of charge may be variably set based on the detected vehicle speed.

The object of the invention is to provide an improved method for controlling a state of charge of a battery and an improved control device for carrying out the method, which take into account the electrical system state or operating modes.

The object of the invention is achieved by the method according to claim 1 and by the control device according to claim 8.

Further advantageous embodiments of the invention are specified in the dependent claims.

An advantage of the method described is that a variable lower charge limit of the battery is specified. The lower charging limit becomes dependent on an electric power of active consumers, such as e.g. Lighting, and a Leistungsvorhalts for transient consumers, especially high-performance consumers such. Safety systems, of the vehicle, depending on the internal resistance of the battery and calculated on the voltage of the battery. In this case, transient consumers are those that are operated only for a short time and thus have only a low energy consumption, but in particular transient high-performance consumers have a high power consumption. Thus, the lower loading limit is precisely determined.

The electrical consumers of the vehicle and electric power generators such as e.g. a belt, crankshaft or integrated starter generator or roll stabilization are operated in such a way that the variable lower charging limit of the battery is not exceeded. As a result, an individual adaptation of the lower charging limit to a predetermined state of the battery is possible.

In one embodiment, at least the power required by a starter generator to start the internal combustion engine is used as electrical power. In this way it is ensured that the battery has sufficient energy to start the internal combustion engine after a standstill.

With the help of this method, an optimization of the energy consumption of the battery is achieved. By specifying the variable lower charging limit of the battery, a better adaptation of the flexibility in consuming electrical energy and the flexibility in charging the battery, for example by a recuperation of electrical energy is achieved.

In addition, a variable upper charge limit of the battery is specified. The variable upper charging limit is determined depending on an electric power of the electric power generators depending on the voltage of the battery and the internal resistance of the battery. Thus, the upper charging limit is adjusted to a current state of the battery. This allows precise definition of the upper loading limit.

In one embodiment, the upper charging limit may be determined depending on the charging power of the starter generator. This ensures that a recuperation of energy can always be stored by electricity generators. Thus, a maximum utilization of the possible recuperation of the power generators is achieved.

With the help of this method, a further optimization of the energy consumption of the battery is achieved. By setting the variable upper charging limit of the battery there is an improved adaptation of the flexibility in consuming electrical energy and the flexibility in charging the Battery, in particular by a recuperation of electrical energy.

In a further embodiment, the lower charging limit is determined as a function of a predetermined minimum terminal voltage of the battery. This ensures that the specified minimum voltage of the battery is not undershot.

In a further embodiment, the upper charging limit is determined as a function of a predetermined maximum terminal voltage of the battery. In this way it is ensured that the charging power of the power generators can be stored in the battery without exceeding the maximum voltage.

In a further embodiment, the lower charging limit is determined as a function of a power consumption of safety-relevant consumers. This ensures that the battery can supply the electrical consumers that are required for safety-related functions of the vehicle. This ensures that the safety-relevant consumers of the vehicle can be supplied by the battery in any case. As a result, the safety when operating the vehicle is also made possible in the described method.

In a further embodiment, the lower charging limit is determined as a function of power peaks of consumers, in particular of safety-relevant consumers. In this way it is ensured that a sufficient specifiable stress level, e.g. a quiescent voltage level is available for power peaks of the consumers in the battery.

In a further embodiment, a battery diagnosis is carried out continuously during operation of the vehicle, preferably at fixed time intervals, wherein, in particular, the internal resistance and / or the current terminal voltage are determined. Thus, there are always current values for the internal resistance and the terminal voltage. Thus, the lower and / or the upper loading limit can be determined accurately.

In another embodiment, during the operation of the vehicle, a consumer diagnosis is performed continuously, in which the active electrical loads and an energy reserve, e.g. for boosting, and in particular for transient safety relevant consumers. In one embodiment, the electrical power of the active electrical load of the vehicle and the power reserve is determined in particular for the safety-relevant consumers and added up. This sum of electrical power is taken into account when determining the lower charging limit. Thus, the lower loading limit can be determined precisely, since all consumers are taken into account. This ensures that these electrical consumers can be operated without further charging the battery.

In a further embodiment, it is continuously determined during the operation of the vehicle during the consumer diagnosis, which maximum recuperation power or recuperation energy can be generated by means of the electric power generators of the vehicle. The maximum recuperation power or recuperation energy is taken into account when determining the upper charging limit. This ensures that the battery has enough free charging capacity to absorb the maximum recuperation power. This ensures that the available recuperation power can also be stored.

In a further embodiment, the lower charge limit is calculated as a function of a predetermined minimum open circuit voltage of the battery and a first power reserve divided by a predetermined minimum terminal voltage of the battery multiplied by the current internal resistance of the battery.

In a further embodiment, the upper charging limit is calculated as a function of a predetermined maximum open circuit voltage of the battery and a second power reserve divided by a predefinable maximum terminal voltage of the battery multiplied by the current internal resistance of the battery.

In another embodiment, driver satisfaction and fuel economy are achieved, for example, by overall vehicle energy management, where the state of charge of the battery is between the lower and upper charge limits. In this case, operating phases such as a load point shift, a recuperation, engine phase out and a boost phase in which an electric motor additionally supports the internal combustion engine can be performed. In addition, voltage stability results in that the voltage only moves within predeterminable upper and lower voltage limits.

In addition, the method described is suitable for a vehicle electrical system in which a part of the electrical system is operated with 12 V and another part of the electrical system with 48 V. Preferably, a starter generator is provided, which is arranged in the region of the 48 V electrical system. In addition, a DC / DC converter (high / Step-down converter), which compensates for the electrical charges between the 12 V and the 48 V electrical system. In a further embodiment, in addition to the internal resistance-dependent voltage dip at engine start by the starter generator, a transient power consumption of high-current consumers, in particular of safety-critical high-current consumers, is preferably taken into account. In addition, depending on the selected embodiment, an internal resistance-dependent voltage rise of the battery is taken into account at peaks of a charging power of the starter generator. In addition, an internal resistance-dependent voltage rise of the battery can be taken into account at peaks of a charging power of further electric power generators.

High-current consumers having transient power peaks are, for example, an electric front-axle steering EPS, an electric rear axle steering HAL, roll stabilization eAWS, etc. An objective of the described method is that during operation of the motor vehicle when electrical consumption loads occur and electrical charging powers occur. by recuperation the voltage drop of the battery and the voltage rise of the battery can be kept within the operating voltage limits.

With the help of the method described a voltage stability of the electrical system is ensured. Maximum recuperation potentials are exploited depending on the driver's request and depending on a total vehicle energy management, whereby the predetermined lower charging limit and the predetermined upper charging limit are met.

The invention will be explained in more detail below with reference to FIGS. Show it:

1 a schematic representation of a first embodiment of a vehicle electrical system,

2 a schematic representation of a total vehicle energy management operating strategy,

3 an example of a possible operating strategy,

4 a schematic representation of a memory management for the battery,

5 a flow chart for a schematic representation of a dynamic memory management,

6 a flow chart for a battery diagnosis,

7 a flow chart for a consumer diagnosis,

8th a flow chart for determining a lower charging limit, and

9 a flow chart for determining an upper loading limit.

1 shows a schematic representation of an embodiment of a vehicle electrical system 1 of a vehicle. The electrical system 1 has two sub-networks 2 . 3 on. The first sub-board network 2 is via a DC / DC converter 4 with the second sub-board network 3 connected. The first sub-board network 2 has a voltage of 12 V in the illustrated embodiment. The first sub-board network 2 includes, for example, a starter 5 , a first battery 6 and several electrical consumers 7 , For a clear presentation is only a consumer 7 illustrated, wherein in fact a plurality of electrical loads on the first sub-electrical system 2 connected. The first sub-board network 2 includes several electric power generators 8th , For a clear representation is only a power generator 8th shown. The starter 5 , the first battery 6 , the electrical consumers 7 and the power generator 8th are between masses 9 and a first supply line 10 arranged. The first supply line 10 stands over the DC / DC converter 4 with a second supply line 11 in connection. The second supply line 11 is part of the second sub-board network 3 which has a voltage of 48V. Depending on the selected embodiment, other voltages for the first and / or the second electrical system can be used 2 . 3 be used. The second subnetwork 3 has several consumers 12 on. For a clear presentation is only a consumer 12 shown. The second subnetwork 3 has several power generators 13 on. For a clear representation is only a power generator 13 shown. In addition, the second sub-board network includes 3 a starter generator 14 and a second battery 16 , The starter generator 14 is in operative connection with the internal combustion engine 15 , The starter generator 14 Can be used to drive the internal combustion engine 15 to assist in driving the vehicle. In addition, the starter generator 14 be used to recover electrical energy from the drive again. This is the starter generator 14 directly from the internal combustion engine 15 driven. Depending on the chosen embodiment, the starter generator 14 also not be used to drive the vehicle. In addition, in another embodiment, an electric motor can be provided which is supplied with power by the first or second battery and, if necessary, drives the vehicle.

The first battery 6 For example, in the form of a lead-acid battery and the second battery 16 be formed in the form of a lithium-ion battery. The electrical consumers, the starter generator 14 and the second battery 16 of the second sub-board network 3 are between the second supply line 11 and mass 9 arranged.

2 shows a schematic representation of an energy management operating strategy. The input data will be a driver's request 17 , a current state of charge 18 the battery, a speed of the vehicle 19 , the lower loading limit 28 the second battery and depending on the selected design also additionally the upper charging limit 29 the second battery used, for example, taking into account fuel equivalence values for the electrical energy, a first target torque 20 for the internal combustion engine and a second setpoint torque 21 to calculate for the electric motor. These are in a control unit 22 corresponding programs, tables, characteristics and procedures are stored. The driver's desired torque is detected, for example, by an accelerator pedal position and a corresponding sensor. The state of charge of the battery is detected by a corresponding meter on the battery. The speed of the vehicle is detected, for example, by a speedometer. The first and the second setpoint moment 20 . 21 are used to match the internal combustion engine 15 and the electric motor, ie the starter generator 14 head for. The operating strategy for the energy management, for example, achieve a fuel savings in the realization of the driver's request. For this purpose, a selection of operating modes and, for example, a load point shift based on an energy cost indicator can be performed.

3 shows a schematic representation of a diagram in which along the y-axis, the speed of the vehicle and along the x-axis time is plotted. In a first line 23 different operating states of the internal combustion engine or the drive are specified. In a second line 24 An actuation of the accelerator pedal is indicated by a dark bar and a non-actuation of the accelerator pedal by a bright bar. In a third line 25 The operation of the brake of the vehicle is represented by a dark bar and a non-actuation of the brake of the vehicle by a light bar.

In a first time period between a zeroth time t0 and a first time t1, the vehicle is in a start-stop mode. The internal combustion engine is stopped. Accordingly, the accelerator pedal is not pressed, but the brake is pressed. In a second time interval between the first time t1 and a second time t2, the vehicle is in an operation in which both a load point shift and a boost function can be provided. At the load point shift, the second battery is above the starter generator 14 recharged. Every combustion engine has a specific load range in which it works most economically. For example, if the combustion engine is below this range, then the control unit 22 automatically increase the throttle so that the engine load increases, but the engine speed does not change. This is achieved by using the additional torque to generate power from the starter generator to the second battery 16 charge. The generator power and a throttle opening of the intake of the engine are controlled so that the engine operates in a higher efficiency range, thereby optimally utilizing the consumed fuel and storing electric power in the battery.

In a boost operation, the starter generator 14 or an electric motor used to additionally deliver torque through the drive or to drive the vehicle. In this case, the load point of the internal combustion engine 15 be reduced to have a more efficient operating point. During the second time range the combustion engine is active. In a following third time range between a second time t2 and a third time t3, the vehicle is in a mode of operation "sailing". The internal combustion engine is stopped. Neither the accelerator pedal nor the brake are actuated. Depending on the chosen embodiment, the starter generator or an electric motor can also be used to drive the vehicle during sailing.

During a fourth time range, which lies between the third time t3 and a fourth time t4, the vehicle is in a recuperation phase. It is about electric power generators, such as the starter generator 14 or other power generators recovered electrical energy via the drive. In this case, the engine is active, but it may be made a fuel cut. At a following fifth time range, which is between a fourth time t4 and a fifth time t5, the vehicle is again in a start-stop mode. During the fourth time range, the brake is applied to activate the recuperation phase, the internal combustion engine is stopped and the accelerator pedal is not actuated. In the fifth time range, the vehicle can roll out.

4 shows in a schematic representation of the basic principle of the new memory management. The electrical energy management ensures for having a minimum lower loading limit 28 the second battery is not exceeded during operation of the vehicle. The minimum loading limit 28 represents a reserve or security for the onboard stability. In addition, the electrical energy management ensures that a maximum upper charging limit 29 during operation of the vehicle is not exceeded. The maximum loading limit 29 Ensures that a reserve or security for the recovery of electrical energy by dynamic consumers is possible. Thus, the vehicle has a working range of 0% to 100% of SoC relative, for charging or discharging the battery available. SoC relative lies between the minimum, lower loading limit 28 and the maximum upper loading limit 29 ,

The variable minimum minimum charging limit becomes dependent on a predetermined minimum terminal voltage Umin, a first positive power reserve P1 for power supply and an internal resistance Ri of the second battery 16 determined. The variable upper charging limit of the battery is determined as a function of a predetermined maximum terminal voltage Umax, a second negative power reserve P2 for power consumption or feedback and the internal resistance Ri of the second battery. In this case, for example, the following formulas can be used: Lower loading limit = f (U _min + ((P1 / U _min ) × Ri)).

The following function can be used to calculate the upper loading limit: Upper loading limit = f (U _max + ((P2 / U _max ) × Ri)).

The starter generator 14 can start in a motor operation, the internal combustion engine of the motor vehicle and / or drive the motor vehicle. In addition, the starter generator 14 in regenerative mode, the second battery 16 load. The regenerative operation can be realized by a recuperation operation of the starter generator or by driving the starter generator by the internal combustion engine. It should be respected at any time for the state of charge of the second battery, the variable lower charging limit and preferably the variable upper charging limit. The variable upper and lower variable charging limits take into account the fact that preferably at any time a reserve for the recovery of electrical energy via a recuperation or as security for the on-board stability should be available. At the same time, it should be ensured that a predetermined minimum voltage value U _min and a predetermined voltage value U _max for the electrical terminal voltage of the second battery are not exceeded or undershot.

In this case, for example, continuously, ie at predetermined intervals, as long as the vehicle is in operation, go through the following sequence:
First, during a battery diagnosis, a current internal resistance Ri of the second battery 16 and a current terminal voltage U _{BAT of} the second battery 16 determined with the help of appropriate measuring devices. In a consumer diagnosis, the electrical power of all currently active electrical consumers as well as a power reserve is added up, in particular for transient safety-relevant consumers, and from this a first power reserve P1 is determined. The first power reserve corresponds at least to the maximum power required during engine operation of the starter generator in order to start the internal combustion engine. In addition, the maximum recuperation power of all active power generators is determined, which can feed electrical energy back into the second battery. The recuperation services of the active power generators are added up and from this a second power reserve P2 is determined. The second power reserve P2 corresponds at least to the maximum electric power of the starter generator in regenerative operation.

5 shows a flowchart for performing a dynamic memory management. At program point 100 starts the program. The program then branches to a battery diagnosis 105 , In addition, parallel to the battery diagnosis 105 a consumer diagnosis 110 carried out. After performing the battery diagnosis 105 and consumer diagnostics 110 will be at another program step 115 determines a lower loading limit. Subsequently, at a following program step 120 the lower loading limit inscribed in a data memory. Thereupon, at a following program point 125 determines an upper loading limit. Subsequently, at a following program point 130 inscribed the upper loading limit in a data store. Thereupon, at a following program point 135 the query carried out whether the ignition, ie the clamp 15 , is off. If this is not the case, then becomes program point 105 and 110 Branched back and the process performed again.

Returns the query at program point 135 that the clamp 15 is turned off, then becomes program point 140 Branched, where the program ends.

6 shows a schematic representation of the implementation of the battery diagnosis 105 of the 5 , At a program point 200 starts the program. Subsequently, at a program point 205 the age of the battery is determined. Parallel to this is at a program point 210 the current battery temperature is determined. In a following program point 215 depends on the battery age, the battery temperature and other data from a database 240 the battery determines an internal resistance of the battery. The database 240 The battery is also used in determining battery aging. For this purpose, appropriate battery state diagnostics, maps, SOC calculations for the state of charge of the battery are stored. After execution of the program point 215 becomes program point 220 branched. At program point 220 the current terminal voltage is measured. Then the program is at program point 230 completed.

7 shows a schematic representation of a flowchart for performing the consumer diagnosis. The program starts at program point 300 , The program has a database 310 , in which all safety-critical consumers are recorded. In addition, all non-safety-critical consumers are recorded. In addition, all electric power generators, in particular the starter generator are detected. Furthermore, the database has 310 on the information about which maximum power the electric power generators, in particular the starter generator can generate in generator mode. In addition, the database has 310 about the information, which consumes maximum electric power of the starter generator in the engine operation. In addition, the database has 310 about information about switch-on and switch-off behavior of consumers. This information can also be taken into account when determining the power. The database also includes a classification of consumers into safety-critical consumers, consumers required for a base load, and consumers used to provide comfort functions.

After the start at program point 300 becomes at a following program point 320 determines a maximum electrical power of all safety-critical consumers. The performance of the individual safety-critical consumers is summed up. This is based on the database 310 accessed.

Subsequently, at a following program point 330 determines the number of active consumers connected. This will also be on the database 310 accessed. In a following program point 340 the power of all connected consumers is determined. At a following program point 350 a first power reserve is determined. The power reserve results from the performance of the safety-critical consumers according to the program point 320 plus the power of all active consumers according to program point 340 plus the maximum power of the starter generator in motor operation.

In a parallel branch, after starting the program at program point 300 at a following program point 360 a maximum recuperation of all active electrical power generators with regenerative capacity determined. At a following program point 370 a second power reserve for the recuperation of all active power generators and the starter generator is determined. After processing the program points is at a program point 380 the program ends.

8th shows a schematic representation of the determination of a lower charging limit. The program starts at program point 400 , At a following program point 410 a predeterminable minimum voltage level is determined at a voltage drop across the battery internal resistance according to the following formula: U _{k, min} = U _min + ((P _R1 / U _min ) × Ri), where U _{k, min} the predeterminable minimum voltage level, U _min a minimum allowable battery voltage, P _R1 the first power reserve, at program point 350 from 7 was determined, and Ri is the current internal resistance. In the calculation at program point 410 will be on a database 415 accessed, in which the predetermined minimum and the predetermined maximum limit voltage are stored. After program point 410 becomes at a following program point 420 calculated a minimum charging limit as a function of the terminal voltage. This will be on a further database 425 in which data, characteristics and / or programs are stored, such as OCV curves, with which the minimum lower loading limit can be calculated. Subsequently, at program point 430 the program ends.

9 shows a flowchart for calculating an upper loading limit. The program starts at program point 500 , At a following program point 510 a predeterminable maximum voltage level is calculated at a voltage swing or rise via the internal battery resistance according to the following formula: U _{k, max} = U _max + ((P _R2 / U _max ) × Ri), where U _{k, max} the predefinable maximum voltage level, U _max the maximum battery voltage, P _R2, the second power reserve from the program point 370 the 8th and Ri represent the current internal resistance of the battery.

When carrying out the calculation at program point 510 will be on the database 515 accessed, in which the predetermined minimum and maximum threshold voltage of the battery U _max , U _{min are} stored. After the execution of program point 510 becomes program point 520 branched. At program point 520 a maximum charging limit is determined as a function of the maximum terminal voltage. It will be based on the further database 525 the second battery accessed. In the further database 525 Data, characteristics and / or programs are stored with which the maximum upper loading limit can be calculated. After execution of program point 520 the program is at program point 530 completed.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 102011054582 A1 [0002]

Claims (8)

 A method for controlling a state of charge of a battery of a vehicle, wherein electrical consumers of the vehicle and electric power generators of the vehicle are operated in such a way that a variable lower charging limit of the battery is not exceeded, the lower charging limit depending on an electric power active consumers of the vehicle , a power reserve for transient consumers of the vehicle and depending on internal resistance and voltage of the battery is calculated, and wherein a variable upper charging limit is not exceeded, the variable upper charging limit depending on an electric power of the electric power generators and internal resistance and voltage of the battery is determined.  The method of claim 1, wherein the lower charging limit is determined depending on the required power of a starter generator.  The method of claim 1 or 2, wherein the upper charging limit is determined depending on a charging power of the starter generator.  Method according to one of the preceding claims, wherein the lower charging limit is determined depending on a predetermined minimum terminal voltage of the battery.  Method according to claim 1, wherein the upper charging limit is determined as a function of a predefined maximum terminal voltage of the battery.  Method according to one of the preceding claims, wherein as consumers the consumers are taken into account, perform the safety functions of the vehicle.  Method according to one of the preceding claims, wherein as consumers and / or power generators, the active consumers or power generators are taken into account.  Control unit for controlling a state of charge of a battery of a vehicle, wherein the control device is designed to carry out a method according to one of the preceding claims.

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