Abstract:
A system for estimating the state of health (SOH) of a battery of an electric vehicle includes a charger recognition unit, a discharge instruction unit, and an SOH estimator. The charge recognition unit generates a charge recognition signal based on a charge state of the battery. The discharge instruction unit receives the charge recognition signal when the battery reaches at least one predetermined charge voltage value, temporarily stops charging of the battery, and discharges the battery to a certain level. Discharge is performed by operating at least one function of the electric vehicle. The SOH estimator estimates the SOH of the battery based on a voltage change measured during discharging of the battery based on the at least one predetermined current value.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    Korean Patent Application No. 10-2015-0002635, filed on Jan. 8, 2015, and entitled, “System for Estimating State of Health of Battery of Electric Vehicle,” is incorporated by reference herein in its entirety. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    One or more embodiments described herein relate to a system for estimating the state of health of a battery of an electric vehicle. 
         [0004]    2. Description of the Related Art 
         [0005]    A secondary battery is used to power an electric vehicle. The lifespan of the battery may be estimated by a battery management system (BMS). In one proposed system, the voltage change related to the charging and discharging of the battery is periodically measured. Based on this measurement, the internal resistance of the battery may be determined and compared with an initial resistance of the battery. This comparison is used to provide an indication of the degree to which battery resistance has increased over time, which thereby provides a basis for estimating battery lifespan. 
       SUMMARY 
       [0006]    In accordance with one or more embodiments, a system for estimating a state of health (SOH) of a battery of an electric vehicle includes a charge detector to generate a charge recognition signal based on a charge state of the battery; a discharge controller to receive the charge recognition signal when the battery reaches at least one predetermined charge voltage value and to temporarily stop charging of the battery, and to operate at least one function of the electric vehicle to discharge the battery based on at least one predetermined current value for a predetermined time; and an SOH estimator to estimate the SOH of the battery based on a voltage change measured during discharging the battery based on the at least one predetermined current value. 
         [0007]    The charge detector may determine the charge state of the battery based on a battery voltage increase. The charge detector may include a sensor to sense a connection state of an external charge terminal of the electric vehicle and an external charger to charge the battery. The charge detector may generate the charge recognition signal when a starter of the electric vehicle is turned off or the electric vehicle stops moving. 
         [0008]    The SOH estimator may include a voltage detector to measure voltages of the battery based on a plurality of predetermined current values; a data calculator to calculate a resistance value and a power value of the battery based on the predetermined current values, the resistance value and power value to be calculated based on a variation in the voltages measured by the voltage detector; and an SOH determiner to determine a current SOH of the battery based on a comparison of the resistance value and the power value with a pre-stored resistance value and a pre-stored power value. 
         [0009]    The system may include a data storage device to store data for the voltages measured by the voltage detector and to supply the data to the data calculator. The system may include a display to display information indicative of the SOH of the battery estimated by the SOH estimator. The discharge controller may set the at least one predetermined charge voltage value and the at least one predetermined current value. The discharge instructor controller may set a plurality of predetermined charge voltage values and is to set different predetermined current values corresponding to the predetermined charge voltage values. The at least one function may includes operation of a motor of the electric vehicle or operation and one or more electrical functions of the vehicle. 
         [0010]    In accordance with one or more other embodiments, an n apparatus for an electric vehicle includes first logic to determine a charge state of a charging battery of the vehicle; second logic to temporarily stop charging the battery based on the charge state, and to operate at least one function of the vehicle to discharge the battery; and third logic to estimate the state of health (SOH) of the battery based on a voltage change measured during discharge of the battery, wherein the first logic is to determine the charge state of the battery based on a signal from a battery management system at a time when the vehicle is not moving. 
         [0011]    The second logic may temporarily stop charging of the battery when a charge voltage value of the battery equals at least one predetermined value. The second logic may operate the at least one function to discharge the battery for a predetermined time based on a predetermined current value. The second logic may temporarily stop charging of the battery when a charge voltage value of the battery equals a first predetermined value, discharge the battery to a first level based on the at least one function, control charging of the battery to increase the charge voltage, temporarily stop charging of the battery when the charge voltage value of the battery equals a second predetermined value, discharge the battery to a second level based on the at least one function, and control charging of the battery to increase the charge voltage. 
         [0012]    The first predetermined value may be equal to the second predetermined value. The first predetermined value may be different from the second predetermined value. The first level may be equal to the second level. The first level may be different from the second level. The at least one function may be at least one of operating a motor of the vehicle or an electrical system of the vehicle. The time when the vehicle is not moving may include at least one of a time when a starter of the vehicle is not activated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Features will become apparent to those of skill in the art by describing in detail exemplary embodiments with reference to the attached drawings in which: 
           [0014]      FIG. 1  illustrates an embodiment of a system for estimating the state of health of a battery of an electric vehicle; 
           [0015]      FIG. 2  illustrates an embodiment of a method for estimating the state of health of a battery of an electric vehicle; 
           [0016]      FIG. 3  illustrates an embodiment of a method for discharging a battery; 
           [0017]      FIG. 4  illustrates an embodiment of a method for discharging multiple batteries; 
           [0018]      FIG. 5  illustrates an embodiment of a method for additionally discharging batteries using the discharging method in  FIG. 4 ; and 
           [0019]      FIG. 6  illustrates an example of the charge or discharge state of a battery which has been subject to one or more of the aforementioned embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Example embodiments are described more fully hereinafter with reference to the accompanying drawings; however, they may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey exemplary implementations to those skilled in the art. Like reference numerals refer to like elements throughout. Embodiments may be combined to form additional embodiments. 
         [0021]      FIG. 1  illustrates an embodiment of a system  100  for estimating the state of health (SOH) of a battery, which, for example, may be used to power an electric vehicle. The vehicle may be one that is powered solely by electricity or a hybrid electric vehicle. 
         [0022]    Referring to  FIG. 1 , the system  100  includes a charge recognition unit  110 , a discharge instruction unit  120 , and an SOH estimation unit  130 . In addition, the battery SOH estimating system  100  may further include a display unit  140 . 
         [0023]    In one embodiment, the battery SOH estimating system  100  may be physically separated from and/or functionally different from a battery management system (BMS) of a battery module  11  in the electric vehicle  10 . For example, the battery module  11  may include a BMS to control charging and discharging of battery cells, to protect the battery cells from over-charging or over-discharging, and/or to perform cell balancing. By contrast, the battery SOH estimating system  100  may be a separate system for managing the battery module  11  of electric vehicle  10 , though it may operate with the BMS. In one alternative embodiment, the battery SOH estimating system  100  may be included in the BMS. 
         [0024]    The charge recognition unit  110  determines the charge state of the battery module  11  and outputs a corresponding charge recognition signal. Because the BMS measures voltages of battery cells, the charge recognition unit  110  is connected to the BMS of the battery module  11  to detect from the BMS whether or not a voltage increase has occurred. For example, if the battery cells of the battery module  11  have been or are being charged, the charge recognition unit  110  detects a voltage increase of the battery cells from the BMS and determines that the battery module  11  is in a charging or charged state. 
         [0025]    In addition, unlike a hybrid vehicle, the electric vehicle  10  may receive power from an external charge device  1  for charging the battery module  11 . In this case, the external charge device  1  may charge the battery module  11  through the external charge terminal  15  of the electric vehicle  10 . Therefore, in one embodiment, the charge recognition unit  110  may be in the external charge terminal  15 , for example, in the form of a sensor which senses the connection state of the external charge terminal  15  and the external charge device  1 . 
         [0026]    As described above, the charge recognition unit  110  may be connected to the BMS of the battery module  11  in order to recognize the charge state of a battery cell, or may be installed in the external charge terminal  15  in the form of a sensor to recognize the charge state of a battery cell by the external charge device  1 . However, when the electric vehicle  10  is in motion (e.g., being driven), the charge recognition unit  110  may not output a charge recognition signal. For example, even if the charge state of the battery module  11  is recognized in the above-described manner, the charge recognition unit  110  may not output a charge recognition signal when the starter of the electric vehicle  10  is turned on or when the electric vehicle  10  is driving. As a result, an SOH estimating process may not be performed. 
         [0027]    Therefore, if the charge recognition unit  110  recognizes the charge state of the battery module  11  in a state in which a starter of the electric vehicle  10  is turned off or the electric vehicle  10  otherwise stops or is not moving, the charge recognition unit  110  may output the charge recognition signal. The charge recognition unit  110  may be connected to a motor management system of the electric vehicle  10  and may recognize whether to start or stop the electric vehicle  10 . 
         [0028]    The discharge instruction unit  120  may receive the charge recognition signal from the charge recognition unit  110  and monitor charge voltages of the battery module  11  through the BMS of the battery module  11 . If the charge voltage value of the battery module  11  reaches at least one predetermined charge voltage value, charging of the battery module  11  may be temporarily stopped. 
         [0029]    When charging of the battery module  11  is temporarily stopped, the discharge instruction unit  120  may operate at least one power consuming device  13  in the electric vehicle  10  to discharge the battery module  11  with at least one predefined current value for a predetermined time. The power consuming device  13  may include a motor  13   a  driven by power of the battery module  11 , and various electric parts  13   b  or a separate discharge circuit. 
         [0030]    The discharge instruction unit  120  may set one or more predetermined charge voltage values and one or more predetermined discharge current values. For example, when one predetermined charge voltage value is set in the discharge instruction unit  120 , one predetermined discharge current value may be set to correspond to the set charge voltage value. When multiple predetermined charge voltage values is set in the discharge instruction unit  120 , multiple predetermined discharge current values may be set to correspond to the set charge voltage values may be set. The multiple predetermined charge voltage values may be equal or different from one another, and the multiple predetermined discharge current values may be different from one another. 
         [0031]    When the battery module  11  reaches one or more of the set charge voltage value, the discharge instruction unit  120  may operate the motor  13   a  or/and the electric parts  13   b  (e.g., a heating wire sheet, a heating wire, an air conditioner) to discharge the battery module  11  with one or more of the corresponding predetermined current values for a predetermined time. 
         [0032]    The SOH estimation unit  130  may measure voltages of the battery module  11  according to the predetermined current values during discharging of the battery module  11 , and may estimate a current state of health of the battery module  11  based on changes in the measured voltages. 
         [0033]    In one embodiment, the SOH estimation unit  130  includes a voltage measurement unit  131 , a data storage unit  133 , a data calculation unit  135 , and an SOH determination unit  137 . The voltage measurement unit  131  may measure voltages of the battery for a predetermined time, during which the battery module  11  is discharged by the power consuming device  13  with the predetermined current value. 
         [0034]    The data storage unit  133  may store voltage values measured by the voltage measurement unit  131  and may supply stored data to the data calculation unit  135 . The data stored in and supplied from the data storage unit  133  may include, for example, discharge current values of the battery module  11  and.or variations of voltages measured while the battery module  11  is discharged. The data storage unit  133  may also store result data output from the SOH determination unit  137 , e.g., data indicative of the current state of health of the battery. 
         [0035]    The data calculation unit  135  may calculate a resistance value R and a maximum power value P of the battery based on the data of the data storage unit  133 . For example, the data calculation unit  135  may calculate the resistance value R and the maximum power value P of the battery by applying a voltage variation ΔV and a discharge current value I of the battery to Ohm&#39;s law (V=IR) and a power calculating equation (P=VI). 
         [0036]    The SOH determination unit  137  may determine the current SOH of the battery by comparing the resistance value R and the maximum power value P of the battery with resistance and power values pre-stored in a look-up table for the SOH of the battery. The look-up table may include resistance values and power values of the battery for various states of health of the battery. Therefore, the SOH determination unit  137  may look up an SOH of the battery corresponding to the calculated resistance value R and the maximum power value P of the battery to determine the current SOH of the battery. 
         [0037]    The display unit  140  may display the result estimated by the SOH estimation unit  130  for user information. For example, the display unit  140  may be embodied as an instrument board, a navigation device, or a lamp of the electric vehicle  10  and, for example, may be indicated as a percentage (%). 
         [0038]      FIG. 2  illustrates an embodiment of a method (S 200 ) for estimating the SOH of a battery of an electric vehicle. In an initial operation of this method, when charging the battery module  11  in the electric vehicle  10  is started by the external charge device  1  (S 201 ), the charge recognition unit  110  recognizes charging of the battery module  11  through a sensor in the BMS of the battery module  11  or the external charge terminal  15 . 
         [0039]    The charge recognition unit  110  checks whether the starter of the electric vehicle  10  is turned off or the electric vehicle  10  has stopped moving. When the starter of the electric vehicle  10  is turned off or the electric vehicle  10  has stopped moving, the charge recognition unit  110  outputs a charge recognition signal to the discharge instruction unit  120  (S 202 ). However, when the starter of the electric vehicle  10  is turned on or the electric vehicle  10  is driving, the charge recognition unit  110  does not output the charge recognition signal and the SOH estimating process is not performed for the battery. 
         [0040]    When data required for evaluating the lifespan of the battery is obtained during driving of the electric vehicle  10 , the battery lifespan may be evaluated under various conditions according to driving conditions and/or driving habits of the driver. This may make it difficult to obtain an accurate evaluation result. In accordance with one or more embodiments, data for determining the lifespan of a vehicle battery is determined while the vehicle is not in motion, e.g., in park, stopped at a traffic light, or otherwise not in motion. Determining data while the vehicle is not in motion may produce a more accurate result of battery lifespan, because the data is unaffected by driving conditions and/or habits of the driver. 
         [0041]    Thereafter, the discharge instruction unit  120  checks whether the battery reaches a preset charge voltage while monitoring voltages of the battery together with the BMS of the battery module  11  (S 203 ). If the battery reaches the preset charge voltage (S 203 ), the discharge instruction unit  120  temporarily stops charging the battery (S 204 ) and instructs the power consuming device  13  in the electric vehicle  10  to discharge the battery with a predetermined current for a predetermined time (S 205 ). For example, the discharge instruction unit  120  may instruct the motor  13   a  to idle at about 2000 rpm for 10 seconds to discharge the battery with 200 A for 10 seconds. 
         [0042]    The voltage measurement unit  131  may measure voltages of the battery during discharging of the battery, and the data storage unit  133  may store the data measured by the voltage measurement unit  131  (S 206 ). The data stored in the data storage unit  133  may include discharge current values of the battery module  11  and variations of voltages measured while the battery is discharged. 
         [0043]    Next, the data calculation unit  135  may calculate the resistance value R and the maximum power value P of the battery based on the data stored in the data storage unit  133  (S 207 ). For example, the data calculation unit  135  may calculate the resistance value R and the maximum power value P of the battery by applying a voltage variation ΔV and a discharge current value I of the battery to the Ohm&#39;s law (V=IR) and a power calculating equation (P=VI). 
         [0044]    Then, the SOH determination unit  137  may determine the current SOH of the battery (S 211 ) by comparing the resistance value R and the maximum power value P of the battery, which are calculated by the data calculation unit  135 , with resistance and power values, which are pre-stored in a look-up table (S 208 ). The look-up table may include resistance values and power values of the battery for various states of health of the battery. Therefore, the SOH determination unit  137  may look up an SOH of the battery corresponding to the calculated resistance value R and the maximum power value P of the battery to determine the current SOH of the battery. 
         [0045]    If the predetermined time elapses after discharging the battery (S 209 ), the discharge instruction unit  120  terminates discharging of the battery and operation of the power consuming device  13  (S 210 ), and recharges the battery (S 201 ). 
         [0046]    If a particular charge voltage is additionally set (S 203 ), the discharge instruction unit  120  and the SOH estimation unit  130  temporarily stop charging the battery and repeatedly perform the above-described process. In one embodiment, the discharge instruction unit  120  may perform the above-described process while varying the discharge current values. For example, while the discharge instruction unit  120  instructs the motor  13   a  to idle at about 2000 rpm for 10 seconds to discharge the battery with 200 A for 10 seconds in the previous stage, the discharge instruction unit  120  may instruct the motor  13   a  to idle at about 1000 rpm to discharge the battery with 100 A in the current stage. In addition, the discharge instruction unit  120  may instruct not only the motor  13   a  but also the electric parts  13   b  (e.g., a heating wire sheet, a heating wire or an air conditioner) to operate. For example, the discharge instruction unit  120  may operate the heating wire sheet for 10 seconds to discharge the battery with 50 A for 10 seconds. 
         [0047]    Thereafter, charging of the battery module  11  is completed (S 209 ), and the SOH of the battery estimated by the SOH estimation unit  130  is displayed to a user through the display unit  140  (S 212 ). The display unit  140  may be embodied, for example, as an instrument board, a navigation device, or a lamp of the electric vehicle  10  and, for example, may be indicated as a percentage (%). 
         [0048]      FIG. 3  illustrates an embodiment of a method for discharging a battery with one current at one charge voltage.  FIG. 4  illustrates an embodiment of a method for discharging batteries with different currents at two charge voltages.  FIG. 5  illustrates an embodiment of a method for additionally discharging batteries using the discharging method in  FIG. 4  at different charge voltages.  FIG. 6  is a graph illustrating an example of a charge or discharge state of a battery which has undergone a battery state of health (SOH) estimating process. 
         [0049]    Referring to  FIG. 3 , discharging the battery at a particular charge voltage V 1  is performed at (D 1 ). As a result, one corresponding voltage variation ΔV 1  is obtained. 
         [0050]    Referring to  FIG. 4 , discharging the battery at two particular charge voltages V 1 , which are equal to each other, is performed at D 1  and D 2 . As a result, two corresponding voltage variations ΔV 2  and ΔV 3  are obtained. In this case, discharging the battery is performed twice. In one embodiment, the discharging operations may be performed with different discharge current values. 
         [0051]    Referring to  FIG. 5 , discharging the battery at four particular charge voltages V 1  and V 4 , pairs of which are equal to each other, is performed at D 1 , D 2 , D 3 , and D 4 ). As a result, four voltage variations ΔV 4 , ΔV 5 , ΔV 6 , and ΔV 7  are obtained. In this case, discharging the battery is performed four times. In one embodiment, the discharging operations for the same charge voltage may be performed with different discharge current values. 
         [0052]    The charge recognition unit, discharge instruction unit, calculators, estimating systems, controllers, and other processing features of the embodiments described herein may be implemented in logic which, for example, may include hardware, software, or both. When implemented at least partially in hardware, the charge recognition unit, discharge instruction unit, estimating systems, calculators, controllers, and other processing features of the embodiments described herein may be, for example, any one of a variety of integrated circuits including but not limited to an application-specific integrated circuit, a field-programmable gate array, a combination of logic gates, a system-on-chip, a microprocessor, or another type of processing or control circuit. 
         [0053]    When implemented in at least partially in software, the charge recognition unit, discharge instruction unit, estimating systems, and other processing features of the embodiments described herein may include, for example, a memory or other storage device for storing code or instructions to be executed, for example, by a computer, processor, microprocessor, controller, or other signal processing device. The computer, processor, microprocessor, controller, or other signal processing device may be those described herein or one in addition to the elements described herein. Because the algorithms that form the basis of the methods (or operations of the computer, processor, microprocessor, controller, or other signal processing device) are described in detail, the code or instructions for implementing the operations of the method embodiments may transform the computer, processor, controller, or other signal processing device into a special-purpose processor for performing the methods described herein. 
         [0054]    By way of summation and review, a current BMS is only able to estimate battery lifespan while the vehicle is in motion. Consequently, the lifespan estimate of the BMS is performed under conditions that vary based on driving conditions or driving habits. As a result, it is difficult to obtain an accurate and reliable estimate of battery lifespan. In accordance with one or more of the aforementioned embodiments, data for determining the lifespan of a battery of a vehicle is determined when the vehicle is not moving. As a result, a more accurate and reliable evaluation result of battery lifespan may be determined, while reducing or minimizing the processing burden of the vehicle BMS. 
         [0055]    Example embodiments have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. In some instances, as would be apparent to one of skill in the art as of the filing of the present application, features, characteristics, and/or elements described in connection with a particular embodiment may be used singly or in combination with features, characteristics, and/or elements described in connection with other embodiments unless otherwise indicated. Accordingly, it will be understood by those of skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims.