Patent Publication Number: US-2022216705-A1

Title: Method for operating a battery system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present disclosure claims the benefit of priority of co-pending European Patent Application No. 21 150 067.3, filed on Jan. 4, 2021, and entitled “METHOD FOR OPERATING A BATTERY SYSTEM,” the contents of which are incorporated in full by reference herein. 
     ECHNICAL FIELD 
     The present disclosure relates to a method for operating a battery system with a plurality of cells, a battery system applying such a method, a vehicle including such a battery system and a computer program element for operating such a battery system. 
     BACKGROUND 
     Battery-powered vehicles, such as electric vehicles or hybrid electric vehicles include a battery system supplying a high-voltage to operate an electric motor to run the vehicle. The battery system may include a plurality of battery cells connected in series or parallel. For a safe operation and a reliable power estimation, the battery system may be associated with a battery monitoring system (BMS). The BMS is an electronic system, which constantly monitors parameters associated with the battery system and cells such as a state of charge and/or state of health. 
     Rechargeable battery system including a plurality of cells ages over time and degrades in a capacity over time. Furthermore, the battery system with a high energy density may introduce hazards and cause an explosion or a fire. Hence, the BMS may monitor and collect data of the battery system to avoid risky situations and optimize a performance of the battery system. 
     SUMMARY 
     Hence, there still may be a need to provide an improved method for operating a battery system, which provides a safe and efficient power supply. 
     The problem is solved by the subject matters of the independent claims of the present disclosure, wherein further embodiments are incorporated in the dependent claims. It should be noted that the aspects of the disclosure described in the following apply to the method for operating a battery system with a plurality of cells, a battery system applying such a method, a vehicle including such a battery system and a computer program element for operating such a battery system. 
     According to the present disclosure, a method for operating a battery system with a plurality of cells is presented. The method for operating a battery system includes monitoring a state of health of each of the plurality of cells, detecting at least one malfunctioning cell, analysing the state of health of the malfunctioning cell, limiting a discharge power over a time period if the malfunctioning cell has a worst state of health in the battery system or limiting a charge power over a time period if the malfunctioning cell has a best state of health in the battery system, and reducing a minimum state of charge of the battery system over the time period. 
     The method for operating a battery system according to the present disclosure may allow a robust and continuous operation of the battery system even though at least one cell may fail to operate. Such failure may be caused by a disruption between the cell and the battery monitoring system (BMS), which may lead to a voltage signal loss. If the BMS detects any fault in a connection with the cell, the BMS generally disconnects the battery system and the battery system becomes functionless. However, the method of the present disclosure enables a continuous power supply by limiting either a charge or a discharge power even in case of a malfunction of at least one cell or the battery system. Accordingly, a sudden disconnection of the battery system or a power failure such as stop of power supply may be prevented. 
     The battery system may include a plurality of cells, which are connected in series and/or parallel, and a control unit such as a battery monitoring system. The control unit may be configured to monitor a state of the individual cells or the battery system, collect parameters regarding the state and control the individual cells or the battery system accordingly. The parameters may be associated with, for example, temperature, internal resistance, capacity, voltage and current in and out of the cells and/or the battery system. 
     The control unit may monitor a state of health (SoH) of each cell of the battery system. The state of health can be understood as an indication of a current condition of the individual cells compared to their original capacity. The SoH may indicate a returnable (usable) or net capacity of a battery cell through its cumulative stress-life caused by repeating charging and discharging. Accordingly, the state of health may provide an information about a suitability of the cells or battery system for an application. 
     The state of health may be shown as percentages. In other words, the state of health may be an indication of how the cells or battery system meets the manufacturing specification. Accordingly, 100% of the SoH may mean that the parameters may meet the specification of battery system at a time of manufacture. However, the SoH may decrease over time, as the battery system degrades, which would cause a decrease of an ability of the battery system to hold a charge and to deliver current. 
     The control unit may be configured to detect a failure of any one of the cells and analyse the state of the health of the cell having the failure. The failure may occur due to any disruption or malfunction between the cell and the battery monitoring system such as fault in a voltage sense wire and/or fault in a battery monitoring system, which may lead to a voltage signal loss. As soon as a malfunction is detected, the control unit may evaluate the health of the malfunctioning cell. 
     Based on the analysis, the control unit may determine to limit either a discharge power over a time period if the cell has the worst state of health in the battery system or a charge power over a time period if the cell has the best state of health in the battery system. In other words, the voltage supplied from the battery system may be limited if the malfunctioning cell has a lowest percentage of the SoH among the cells of the battery system. Further, the voltage supplied to the battery system may be limited if the malfunctioning cell has a highest percentage of the SoH among the cells of the battery system. The term “limited” may be understood as “decreased” or that the BMS sets an upper or lower threshold, which may not be exceed. 
     At the same time, the control unit may reduce a minimum state of charge of the battery system over the time period. The state of charge (SoC) may indicate a level of charge of the battery system. The SoC may be shown as percentages as well. Generally, the state of charge and the state of health of the cells are dependent of each other. A reduction of minimum state of charge may result in an increase of the capacity of the battery system such that the battery system may extend the power supply even the malfunctioning cell. The time period may be determined dependently of an operating capacity of the battery system. 
     In an embodiment, the method further includes evaluating a trend of the state of health of each of the plurality of cells. The control unit may estimate the trend of the SoH by evaluating the state of health of each cell per a predefined time unit. The time unit may be for example, seconds, minutes, hours or days. Accordingly, a change of the state of health of each individual cell may be estimated, for example by plotting data of the trend of the SoH during a certain period. 
     In an embodiment, the method further includes limiting a charge or discharge power and a charge or discharge maximum time, if the malfunctioning cell has a worst trend of state of health in the battery system. The term “worst trend” may be understood so that the cell is showing a degradation rate that is faster than the other cells. This is an indication of a possible fault that can lead to a premature end of life for that cell. An exact nature of the end of life behavior of the cell may be a loss of function. However, the trend may also indicate that there is a fault in the cell, which may lead to a thermal event, in case the cell continues to be used as normal. The latter may be the reason for reducing the charge and/or discharge conditions allowed for the cell, thus reducing the risk of failure and allowing safe operation of the cell until appropriate repairs can be made. 
     The control unit may determine according to the estimated trend of state of health of each cells at which status the malfunctioning cell is. If the malfunctioning cell has the worst trend of the state of health, the control unit may lower a charge or a discharge power. Additionally, the control unit may limit a charge or discharge maximum time to increase an operating capacity of the battery system until a repair is performed. Limiting the charge or discharge maximum time of the cell may mean limiting an energy throughput allowed through the cell. This measure can allow the faulty cell to align with the other cells in the plurality. 
     In an embodiment, the method further includes allowing driving to an end of a driving cycle. Generally, the malfunctioning cell causes a loss of (voltage) signal, accordingly, a loss of function of the battery system. However, by adjusting the charge or discharge power and/or a charge or discharge maximum time according to the state of health of the cells, the vehicle may be able to perform at least a driving cycle such that the vehicle may not directly stop driving as soon as the malfunction is detected. 
     In an embodiment, the method further includes turning off a cell balancing unit to maintain differences of the state of health of the cells at a status before a malfunction occurs. The cell balancing unit may be configured to transfer charge between the cells, thus bring all cells into a substantially same state of charge. By redistributing charge between the cells, the cell balancing unit may compensate for the loss of capacity caused by the cell with the worst state of health, accelerate a charging speed and extend an operation life of the battery system. 
     However, in case of the malfunction of any one of the cells, the control unit may turn off the cell balancing unit as soon as the control unit detects the malfunction. Accordingly, a reliable analysis of the state of health of each cells at the time just before the malfunction arises can be performed and a suitable adjustment of a charge or discharge power and/or a charge or discharge maximum time can be determined. 
     In an embodiment, the method further includes monitoring a state of health including monitoring a cell capacity, a cell resistance and/or a cell self-discharge rate. In other words, the term “health” of the cells may be understood as a cell capacity, a cell resistance and/or a cell self-discharge rate, which may characterize a state of the cells. Accordingly, the state of health may be shown as a state of the cell capacity, a state of a cell resistance and/or a state of a self-discharge rate. 
     In an embodiment, the method further includes evaluating a trend of the state of health including monitoring a cell capacity, a cell resistance and/or a cell self-discharge rate per a time unit. Since the trend of the state of health may be estimated by evaluating the state of health of each cell per a predefined time unit, the trend of the state of health may be, for example, a capacity loss per time unit, a resistance loss per time unit, a voltage loss per time and/or a balancing need per time unit. 
     In an embodiment, the malfunction of the cell is detected based on at least one lost or corrupted voltage signal. In an embodiment, the malfunction is based on a fault in a voltage sense wire, in a battery monitoring system and/or a lost communication in the battery monitoring system. The fault in the voltage sense wire may occur, for example, if a welding spot of the wire at the cell is broken so that the line is open or the voltage sense wire connected to the cell is lost. The fault in BMS may be caused, for example, by an AC-DC conversion fault, thus providing an incorrect or no voltage. The lost communication fault may be, for example, a communication error of the cell voltage temperature node (CVTN). 
     According to the present disclosure, also a battery system is presented. The battery system applies the method for operating a battery system as described above and includes a plurality of cells and a control unit. The control unit is configured for monitoring a state of health of each of the plurality of cells, detecting at least one malfunctioning cell, analysing the state of health of the malfunctioning cell, and limiting a discharge power over a time period if the malfunctioning cell has the worst state of health in the battery system or limiting a charge power over a time period if the malfunctioning cell has the best state of health in the battery system. 
     The battery system may further include a plurality of cells, each of which may be welded to a voltage sense wire, a connector and a BMS system. Each voltage sense wire may be collected at the connector and the connector may be coupled to the BMS system. The battery system according to the present disclosure allows a robust and continuous operation of the battery system even though a voltage signal loss occurs. 
     In an embodiment, the battery system is configured to operate without interruption even a malfunctioning cell. The battery system may enable a continuous power supply by limiting either a charge or a discharge power even in case of a malfunction of at least one cell in the battery system. Accordingly, a sudden disconnection of the battery system or a power failure such as stop of power supply may be prevented, which would otherwise result in a loss of propulsion energy. 
     According to the present disclosure, also a vehicle is presented. The vehicle includes a battery system as described above. The vehicle is a battery electric vehicle (BEV), a plug-in-hybrid electric vehicle (PHEV) and/or a hybrid electric vehicle (HEV). An electric motor arranged in a vehicle may be operated based on a power supply from a battery system. Hence, the vehicle may also drive continuously even though a voltage signal is lost or corrupted. In other words, the vehicle may be allowed to drive for a certain duration to avoid a sudden stop of the vehicle. 
     In an embodiment, the vehicle is configured to block starting the vehicle after a time period is expired, in case of a malfunctioning cell in the battery system. After the malfunction is detected, the control unit may allow the vehicle to drive for a certain time period such that the vehicle does not directly stop moving and the driver may have a possibility to conduct an emergency action. However, after the time period or a driving cycle, the driver may not be any more allowed to start the vehicle again without remedying the malfunction. Hence, a safe driving condition may be provided. 
     According to the present disclosure, also a computer program element for operating a battery system as described above is presented. The program element is adapted to perform the method steps as described above when being executed by a processing element. 
     It should be noted that the above embodiments may be combined with each other irrespective of the aspect involved. Accordingly, the method may be combined with structural features and, likewise, the system may be combined with features described above with regard to the method. 
     These and other aspects of the present disclosure will become apparent from and elucidated with reference to the embodiments described hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the disclosure will be described in the following with reference to the following drawings: 
         FIG. 1  shows schematically and exemplarily an embodiment of a battery system according to the present disclosure. 
         FIG. 2  shows schematically and exemplarily an embodiment of a method for operating a battery system with a plurality of cells according to the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1  shows a battery system  1  including a plurality of cells  10 . The battery system  1  may be integrated in an electric vehicle such as battery electric vehicle (BEV), a plug-in-hybrid electric vehicle (PHEV) and/or a hybrid electric vehicle (HEV). To supply power for driving the electric vehicle, the battery system  1  requires the plurality of cells  10  connected in series or parallel to each other. 
     The battery system  1  further includes a battery monitoring system (BMS)  30  for monitoring a voltage of each cell  10  continuously, which are connected to the BMS  30  by voltage sense wires  20  via a connector  40 . The battery system  1  also includes a control unit, which may be integrated in the BMS  30  or a separate component of the battery system  1 . The control unit is configured to continuously monitor a state of health of each cell  10  and perform a countermeasure in case of a voltage signal loss. 
     The battery system  1  may have a defect on the voltage sense wire  20 , welding spots  50  of the voltage sense wire  20 , connector  40  and/or BMS  30 . The malfunction of any one of the cells  10  or the battery system  1  may cause a loss of one voltage signal or several voltage signals, which would lead to a disconnection of the battery system  1  and a loss of propulsion energy of the electric motor. 
     Accordingly, the control unit monitors S 1  a state of health of each of the plurality of cells  10 , wherein the state of health may be a cell capacity, a cell resistance and/or a cell self-discharge rate. As soon as the control unit detects S 2  at least one malfunctioning cell, a cell balancing unit is turned off S 3  and the state of health of each cells  10  just prior to occurring the malfunction is maintained. 
     The control unit analyses S 4  the collected data, in particular the state of health (SoH) of the malfunctioning cell. If the malfunctioning cell  10  has a worst SoH in the battery system  1 , the control unit limits S 51  or decreases a discharge power and slowly reduces a minimum state of charge (SoC) of the battery system  1  over a time period. However, if the malfunction cell  10  has a best SoH in the battery system  1 , the control unit limits S 52  or decreases a charge power and slowly reduces a minimum SoC of the battery system  1  over a time period. 
     Further, the control unit analyses S 6  a trend of the SoH of each cells  10  by evaluating the SoH per a predefined time unit. If the malfunctioning cell  10  has a worst trend of state of health in the battery system  1 , the control unit limits S 71  charge and/or discharge power and reduces a charge or discharge maximum time until the malfunction is repaired. In other case, a normal operation is allowed S 72 , since the charge and/or discharge power may be limited by other cells  10  with a worse trend of the SoH. 
     Accordingly, the battery system  1  may operate without interruption even a malfunction of any one of the cells  10 , thus a robust and reliable power supply may be ensured. 
     It has to be noted that embodiments of the disclosure are described with reference to different subject matters. In particular, some embodiments are described with reference to method type claims whereas other embodiments are described with reference to the device type claims. However, a person skilled in the art will gather from the above and the following description that, unless otherwise notified, in addition to any combination of features belonging to one type of subject matter also any combination between features relating to different subject matters is considered to be disclosed with this application. However, all features can be combined providing synergetic effects that are more than the simple summation of the features. 
     While the disclosure has been illustrated and described in detail in the drawings and description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The disclosure is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing a claimed disclosure, from a study of the drawings, the disclosure, and the dependent claims. 
     In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other unit may fulfil the functions of several items re-cited in the claims. The mere fact that certain measures are re-cited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.