DE102012204413A1 - Method and device for controlling the state of charge of a traction battery - Google Patents

Abstract

In a method for controlling the state of charge of a traction battery of an electric or hybrid vehicle that can be charged from a supply network, after the end of a journey (11) an unloading possibility is determined before a next journey (8); if a discharging possibility exists, a discharge (4) of the traction battery is initiated and prior to the next drive, a charge (6) from the supply power network is controlled such that a start-of-charge state (7) is reached before the start of the next journey (8). The invention also relates to a device for controlling the state of charge of a traction battery of an electric or hybrid vehicle which can be charged from a supply current network.

Description

The invention relates to a method for controlling the state of charge of a traction battery of an electric or hybrid vehicle which can be charged from a mains supply, and to a corresponding device for controlling the state of charge of a traction battery.

Motor vehicles with battery electric drive have typical ranges of about 100-120 km, for which a battery capacity of about 20 kWh is required. On average, however, such an electric vehicle only covers a distance of about 45 km per day, for which only an electrical energy of about 7 kWh is required. If the traction battery is fully charged before driving, i. is the state of charge of the battery before driving 100%, the state of charge is after returning from the drive about 65%, and here and below as a measure of the state of charge or state of charge of the battery, the currently stored and removable electrical energy in percent of available capacity of the battery. Often, immediately after returning from the drive, the traction battery, also referred to as a traction battery, is recharged by connection to a utility power network, so that a service life at a charge state of 100% until the beginning of the next trip, typically until the next morning, results.

It is known that, in particular with lithium-ion batteries, a service life at a high state of charge leads to an irreversible loss of capacity and thus to a reduction in the service life of the battery. The irreversible loss of capacity is greater, the higher the state of charge and the longer the service life is at this state of charge. Such a charging process, in which the traction battery is charged in the early evening, approximately between 17:00 and 21:00 clock, also represents a significant burden on the power grid, which is at this time of day usually already heavily burdened by other consumers.

From the WO 2011/047907 A2 a method for increasing the life of a traction battery of an electric or hybrid vehicle is known, in which a driving phase specification and a current state of charge of Traktionsakkumulators are detected and a charging process is carried out such that an aging parameter is minimized, the time interval between the charging process and the Start of the journey or the charging energy with which the Traktionsakkumulator is to be charged comprises. As a result, a charging process after completion of a trip is delayed so far that the charging process ends when the beginning of the next trip is provided. The charging energy is kept as low as possible. A discharge of the traction battery or a consideration of the load of a supply network are not mentioned.

In the EP 1 470 627 B1 It is proposed that an electric vehicle, if necessary, be able to feed energy not needed at a given time into a supply network. When driving to work, the vehicle is connected to the electrical grid after reaching the workplace to provide necessary energy for peak current times when needed. However, depending on the power requirement, this can result in additional charge cycles of the traction battery that reduce the life of the battery.

It is an object of the present invention to provide a method and apparatus for controlling the state of charge of a utility vehicle rechargeable traction battery of an electric or hybrid vehicle that prolongs the life of the traction battery.

This object is achieved by a method and by a device having the features of the independent patent claims.

The inventive method for controlling the state of charge of a traction battery refers to the traction battery of an electric or hybrid vehicle, i. a motor vehicle with battery electric or hybrid-electric drive, wherein the traction battery can be charged from a supply power network and is connected for this purpose via a charging device to the power grid. According to the invention, after the end of a journey of the motor vehicle, i. on the return of the motor vehicle to or the arrival of the motor vehicle at a stand with a charging option from the supply network, the existence of a discharging possibility determined before a next trip. In this case, the journey start of the next journey, for example via an input device by a user, for example, the driver of the motor vehicle, be entered, with data that allow the determination of a required amount of energy for the next trip, also be entered. However, it can also be provided, for example, that an anticipated start of the next journey as well as possibly the prospective energy requirement for the next journey are automatically determined from previous journeys.

When a discharge possibility exists, a discharge of the traction battery is carried out according to the invention, in particular a partial discharge. As a result, the stored in the battery Reduced amount of energy and the state of charge of the traction battery lowers.

Furthermore, before the start of the next journey, a charge is performed from the supply current network and controlled such that a start of travel state of charge is reached before the start of the next journey. The driving start state of charge may be fixed, in particular as a full charge state, i. 100% of the available capacity of the traction battery. However, the travel start state of charge can also be predefined manually by an user via an input device, or it can be provided, for example, that the travel start state is determined taking into account the anticipated energy requirement of the next journey from data entered by the user or automatically from data from previous journeys.

Characterized in that a discharge of the traction battery is performed when there is a discharge possibility before the next scheduled trip with the motor vehicle, the state of charge of the traction battery is reduced during the service life and thus extends the life of the traction battery. As a result, the achievable maximum range of the electric or hybrid vehicle is maintained longer, and a possible replacement of the traction battery can be avoided or at least delayed.

According to a preferred embodiment of the method according to the invention, the travel load state is determined and the existence of the unloading possibility is determined taking into account the travel load state. The Fahrtendeladezustand can be determined, for example, by detecting the terminal voltage, the internal resistance and / or other state variables of the traction battery or due to the history, in particular due to the extracted from the traction battery for driving electrical energy. Furthermore, the discharge possibility is determined taking into account a state of charge of the traction battery, which it should at least approximately occupy to minimize irreversible loss of capacity during the service life of the motor vehicle over as long a period as possible. The state of charge can be fixed or predetermined by a user. Furthermore, to determine the discharge possibility, an estimated time period until the beginning of the next journey and an estimated charging time until the arrival of the journey start state of charge are determined. The discharge possibility exists in particular in the case that on the one hand the Fahrtendeladezustand is higher than the state of charge and on the other hand, the probable time until the start of the next trip is greater than the expected charging time to reach the Fahrtbeginnladezustands. For this purpose, the estimated charging time can first be determined on the basis of the travel charge state; If this results in an unloading possibility and consequently a discharge is carried out, then the estimated charging duration is determined on the basis of the charge state of the traction battery reached during the discharge, which is the stand-by state for a sufficiently long period of time until the beginning of the next journey. In this way it can be ensured that a discharge takes place only in the event that the probable period of time until the start of the next journey for discharging and charging on the driving start state of charge is sufficient and therefore the inventive method without limiting the availability or the range of the vehicle can be carried out.

Both the state of the state of charge and the start of travel state of charge can be determined in such a way that, in the event of unexpected demand, an unplanned journey of limited range can be carried out in addition to the planned journey. In this way it can be ensured that even in emergencies at any time a ride can be performed. The charge reserve required for this purpose can be adjustable by a user.

Preferably, with a sufficient period of time until the beginning of the next trip, a discharge of the traction battery up to the state of charge, with a sufficient period of time a charge waiting in the state of charge until the start of charging the traction battery can be maintained. By discharging the battery to the stand-by state and remaining in this state until the beginning of charging, minimizing the irreversible capacity loss and thus maximizing the life of the traction battery can be achieved.

In particular, the state of charge may amount to 30% of the battery capacity. As a result, a deep discharge can be reliably prevented especially in lithium-ion batteries, which could also reduce the life of the battery.

Furthermore, the state of charge state can be determined advantageously as a function of the temperature of the traction battery. For this purpose, the temperature of the traction battery, for example via a temperature sensor, can be determined and, depending on the known type-specific temperature behavior of the traction battery, an optimum state of charge for maximizing the battery life can be determined.

In a preferred manner, the discharge takes place with the return of the traction battery in this case taken electrical energy in the Supply mains. The supply power network may be, for example, a large-scale power grid that includes several power plants for generating base load and peak load power, or a local power grid or the power grid of a single household. For the recovery of energy can be used in particular for the charging of the battery made connection to the mains, wherein the charging device is preferably designed such that it both the charging of the battery from the mains and the return of energy from the battery in the Power grid allows. In this way, a loss of the corresponding electrical energy can be avoided and a particularly low-loss operation of the electric or hybrid vehicle can be made possible in cooperation with the supply current network.

Preferably, only the energy taken from the traction battery during discharging is fed back into the supply current network if the travel end loading state amounts to at least 60% of the available maximum battery capacity. As a result, a particularly effective feedback can be ensured.

Discharge of the traction battery may begin immediately after the end of travel to maximize the life of the traction battery. Preferably, however, the discharge takes place after a discharge wait time, which is determined taking into account the load of the supply current network. Frequently takes place in the course of the day last trip in the afternoon, so that made to extend the battery life unloading and thereby taking place return of electrical energy in the supply network immediately after the end of a high network load coincides, usually in the late afternoon, especially in the winter months , reached their maximum. If this is not the case, the discharge waiting time can be determined such that the discharging occurs during a period of high network load, for example, a maximum value of the discharge waiting time can be specified by the fact that the extension of the battery life allowed by the discharge is not more than a predefinable amount is reduced. However, it is also possible to optimize the discharge waiting time by jointly taking into account the achievable lifetime extension of the battery and the reduction of the network load by the recovery of the energy from the traction battery. In this way it is possible to relieve the supply current network without significant limitation of the achievable lifetime extension.

The charge waiting time can be selected, for example, such that the start of charge state is reached immediately before the start of the next journey. This means that charging takes place as late as possible and the charging time is correspondingly maximum. In order to take into account a fluctuation range of the beginning of the next trip, the charge waiting time can also be selected such that the travel start state of charge is already reached by a standby waiting time before the expected start of the journey. As a result, a maximum extension of the battery life is possible without restricting the availability of the motor vehicle.

Preferably, the charging takes place at least partially in a period of presumably low network load. In particular, the charge waiting time is preferably determined taking into account the anticipated load of the supply current network in such a way that the charging takes place in a period of low network load. Since the first trip is often planned during the course of the day in the morning, charging the traction battery as late as possible to extend battery life often takes place in the early morning hours, when network load by other consumers is low. In this case, the charge waiting time can be maximum and thus the achievable life span also be maximum. Otherwise, the charge waiting time can be optimized taking into account the network load such that an optimization of the network load is carried out in the sense that the charging takes place in times of usually low network load with an insignificant, possibly limited upward reduction of life benefits. In this way, a more uniform load of the supply network and thus a more cost-effective design of the power grid and in cooperation with the supply power network, a particularly efficient and cost-effective operation of the electric or hybrid vehicle are possible, if appropriate net load-sensitive electricity tariffs are available (night tariffs od. Like.).

A device according to the invention for controlling the state of charge of a traction battery of an electric or hybrid vehicle which can be charged from a mains supply comprises a charging device which is designed to charge the traction battery according to the method described above. For this purpose, the charging device for connecting the traction battery is formed with a supply current network. The charging device may include means for determining the travel charge state, sensor means for detecting a temperature of the traction battery and means for detecting a current time and storage means for storing data on the state of the traction battery and the next drive. The charging device can also be designed for the recovery of electrical energy from the traction battery in the supply current network. The Charging device is preferably assigned to the electric or hybrid vehicle.

The device may further comprise an input device for inputting data by a user, wherein the data may relate, for example, to the prospective time and the probable travel time and distance of the next journey. The input device can also be designed, for example, to input data, on the basis of which a necessary safety margin of the battery charge can be determined. Furthermore, a display device for displaying data about the current state of charge of the battery, the energy needs of the planned next trip and / or the unloading and the support process may be provided.

The invention will be explained in more detail by way of example with reference to the drawing.

It shows:

1 the state of charge of a traction battery of an electrically powered motor vehicle during the day according to an embodiment of the invention.

As shown in 1 reaches the electrically powered motor vehicle at time t ₀ to a place with a charging option from the supply power network; For example, the time t ₀ represents the return of the motor vehicle after a drive to its permanent stand, for example in a garage at the driver's place of residence. There, it is possible to connect the traction battery for charging with a supply power network, which may be the power grid of a single household, a local power grid, or a large-scale interconnected network.

From the traction battery has been removed to carry out the trip electrical energy, so that the Fahrtendeladezustand 1 below the maximum state of charge of 100%, in the example shown at about 66%. Would now directly a charge the battery (curve 2 ), the motor vehicle would be at a state of charge of 100% from the time of reaching the full state of charge (100%) until the beginning of the next trip the next morning at time t ₄ . Through the long stance phase 3 if fully charged, there would be a significant irreversible loss of capacity in the longer term, which would cause the battery to age faster and reduce available capacity more quickly.

According to the in 1 illustrated embodiment of the method according to the invention it is determined whether a discharge exists. For this, the travel loading state becomes 1 determined and compared with a predetermined state of charge, which in the present case is about 30%. In addition, since the travel-loading state is higher than the stand-by state and, moreover, the period of time (t ₄ -t ₀ ) until the start of the next trip is longer than the time required for charging the battery to 100%, there is a possibility of discharging. Therefore, at the time t _0, a discharge 4 carried out the battery until the time t _{1 of} the state of charge of about 30% is reached. Until the time t ₂ now follows a stance phase 5 with the low standby state, thereby minimizing irreversible capacity loss. The stand-by state may be designed to minimize capacity loss, to safely avoid over-discharge and / or to take into account a reserve for carrying out unexpected trips. At the end of the charge waiting period, charging begins at time t ₂ 6 on a journey start state of charge 7 , which in the example shown is the fully charged state, ie 100%. This condition is reached at time t ₃ , which is a short period of time, the stand-by waiting time (t ₄ , -t ₃ ), before the start of the next trip. The period (t ₄ , -t ₃ ) during which the traction battery is at a high state of charge, for example at 100%, is thus substantially lower than in the case of an immediate after-end charging 2 ,

At time t ₄ , the next journey begins 8th For example, a morning drive to work. The drive 8th , which lasts until the time t ₅ , leads to a removal of electrical energy from the traction battery and thus to a reduction of the state of charge to an intermediate state of charge 9 , In this intermediate state of charge 9 follows a stance phase 10 For example, in a parking lot near the workplace, during which usually no connection to a supply network is possible. At time t ₆ , another journey begins 11 about the afternoon return from the place of work to the place of residence. For this purpose, the traction battery is further electrical energy until reaching the Fahrtendeladezustands 1 taken.

As in 1 can be seen, is minimized by the exemplary method according to the invention, the time during which the traction battery is in a high state of charge. As a result, a maximum extension of the life is achieved.

The in 1 The daily course shown corresponds to the typical course of the day when using the motor vehicle for the morning drive 8th to the workplace (from t ₄ to t ₅ ) and the evening drive 11 to return home (from t ₆ to t ₀ ). In such a course of the day can also by providing the unloading 4 the battery taken in the period between t ₀ and t ₁ electrical energy for feeding into a supply network, which is usually particularly heavily loaded between about 17:00 and 21:00 h by other consumers, the power grid are relieved. Conversely, the removal of electrical energy from the supply current network takes place for charging 6 the battery in the early morning. Between 1:00 and 5:00 or 6:00 h the power grid is usually not heavily loaded. Thus, in the illustrated course of the day, the supply network can be relieved or burdened more evenly, which allows a more cost-effective design and a more effective operation of the supply network using renewable energy.

Further, in the recovery of electrical energy into the mains during discharge 4 In the period between t ₀ and t _1, a high feed-in compensation can be achieved while the charge for charging 6 required electrical energy between the times t ₂ and t _{3 is} usually available at low cost. As a result, a particularly cost-effective operation of the electric or hybrid vehicle or even a profit by exploiting corresponding price differences between peak and night current is possible.

LIST OF REFERENCE NUMBERS

1

 Drive end state of charge

2

 charging

3

 stance

4

 discharge

5

 stance

6

 charging

7

 Each ride charge status

8th

 journey

9

 Between the charging state

10

 stance

11

 journey

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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.

Cited patent literature

• WO 2011/047907 A2 [0004]
• EP 1470627 B1 [0005]

Claims (10)

Method for controlling the state of charge of a traction battery of an electric or hybrid vehicle that can be recharged from a supply network, wherein after the end of a journey ( 11 ) an unloading possibility before a next trip ( 8th ) is detected, when a discharge possibility exists a discharge ( 4 ) of the traction battery and before the next drive ( 8th ) a charge ( 6 ) is controlled from the power grid so that before the start of the next trip ( 8th ) a predetermined or predefinable travel start state of charge ( 7 ) is achieved. A method according to claim 1, characterized in that the unloading possibility is determined such that there is a possibility of unloading, if after the end of the journey ( 11 ) available travel loading condition ( 1 ) is higher than a predetermined or specifiable stand-by state and the estimated time until the beginning of the next trip ( 8th ) is greater than the expected charging time until the start of the journey ( 7 ). A method according to claim 2, characterized in that for a sufficient period of time until the beginning of the next trip ( 8th ) a discharge ( 4 ) except for a stand-by state and a charge waiting time until the start of charging ( 6 ) is maintained in the state of charge. A method according to claim 2 or 3, characterized in that the state of charge is 30%. A method according to claim 2 or 3, characterized in that the state of charge is determined temperature-dependent. Method according to one of the preceding claims, characterized in that the discharge ( 4 ) takes place with feedback of electrical energy of the traction battery in the supply current network. Method according to the preceding claim, characterized in that the feedback into the supply current network is carried out only when an end of the journey existing Fahrendeladezustand ( 1 ) is at least 60%. Method according to claim 6 or 7, characterized in that the discharge ( 4 ) is carried out after a discharge waiting time which is determined such that the discharge ( 4 ) takes place at least partially during a period of high load of the supply current network. Method according to one of the preceding claims, characterized in that the charging ( 6 ) takes place at least partially in a period of low load and / or low electricity tariffs of the supply power network. Device for controlling the charge state of a traction battery of an electric or hybrid vehicle which can be charged from a supply power network, comprising a charging device for charging the traction battery from the supply power network, characterized in that the device is designed to carry out a method according to one of the preceding claims.

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