Patent Publication Number: US-2023163605-A1

Title: Method of Determining Abnormality of Pre-Charge Resistor and Battery System Using the Same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national phase entry under 35 U.S.C. § 371 of International Application No. PCT/KR2021/012507 filed Sep. 14, 2021, which claims priority from Korean Patent Application No. 10-2020-0117949 filed in the Korean Intellectual Property Office on Sep. 14, 2020, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Technical Field 
     The present disclosure relates to a method of determining an abnormality of a pre-charge resistor and a battery system using the same. 
     Background Art 
     As a pre-charge resistor deteriorates, a resistance value increases. Then, a charging time of a pre-charge capacitor connected to the pre-charge resistor is prolonged, and a transition to a drive mode may be delayed during ignition of a vehicle receiving power from the battery system. 
     In addition, when the battery system includes a plurality of battery packs coupled in parallel, among high voltage load branches coupled in parallel to the battery system, a high current may flow to branches other than the branch to which the degenerated pre-charge resistor is connected. Then, a protective circuit may be damaged due to heat generated by the high current. 
     In addition, among the high-load load in which insulation is broken due to the damage of the pre-charge resistor among the high-load loads connected to the battery system may occur. Due to the deterioration of the pre-charge resistor, internal resistance of the load connected to the branch through which a lower current than a prescribed condition flows among the branches to which the high-load load is connected to may be lowered. 
     SUMMARY 
     Technical Problem 
     The present disclosure is to provide a method that may determine whether a pre-charge resistor is abnormal and a battery system using the same. 
     Technical Solution 
     A battery system according to one aspect of the invention includes: a plurality of battery packs including a plurality of battery cells, each battery pack including a respective first terminal; a plurality of branches, each branch comprising: a respective pre-charge resistor including a first terminal that is connected to each of the first terminals of the plurality of battery packs and a second terminal; a respective pre-charge switch, including a first terminal that is connected to a corresponding second terminal of the pre-charge resistor and a second terminal; a capacitor including a first terminal that is connected to the second terminal of the pre-charge switch; and a main control circuit configured to determine whether the pre-charge resistors of the plurality of branches are operating abnormally based on a comparison of a sum of a plurality of branch currents with a battery current flowing through at least one battery pack, wherein, for each branch, the branch current is calculated using a pre-stored value of a resistance of the pre-charge resistor of the branch and a voltage across the pre-charge resistor of the branch, and wherein the comparison is upon a first period of a pre-charge operation elapsing. 
     The main control circuit may be configured to calculate, for each branch, a branch charging slope and determine for a branch of the plurality of branches having a branch charging slope smaller than a predetermined reference slope, the pre-charge resistor of the branch is operating abnormally based on a difference between a capacitor voltage of the capacitor of the branch upon a second period of the pre-charge operation elapsing and the capacitor voltage upon a third period of the pre-charge operation elapsing. 
     The reference slope may be a branch charging slope of a plurality of pre-charge resistors is in a normal state. 
     The main control circuit may be configured to measure a branch charging time that a voltage charged to the capacitor of the branch reaches a voltage of at least one of the plurality of battery packs, and determine for a branch of the plurality of branches having a branch charging time that is longer than a predetermined reference time, that the pre-charge resistor of the branch is operating abnormally based on the branch charging time. 
     The reference time may be a branch charging time of a plurality of pre-charge resistors in a normal state. 
     The first period may correspond to a time constant defined by resistance values of the pre-charge resistors of the plurality of branches and capacitance values of the capacitors of the plurality of branches, and the second period may correspond to a predetermined integer multiple of the time constant. 
     A method of determining an abnormality of a pre-charge resistor of a battery system including a plurality of battery packs including a plurality of battery cells, each battery pack including a respective first terminal, the battery system further including a plurality of branches, each branch including a respective pre-charge resistor, a respective pre-charge switch, and a respective capacitor, wherein a first terminal of of the respective pre-charge resistor is connected to each respective first terminal of the plurality of battery packs, wherein a first terminal of the respective pre-charge switch is connected to a second terminal of the respective pre-charge resistor, and a first terminal of the respective capacitor is connected to a second terminal of the respective pre-charge switch, may include: for each branch, calculating a branch current of the branch using a pre-stored resistance value of the respective pre-charge resistor of the branch and a voltage across the respective pre-charge resistor of the branch upon a first period of a pre-charge operation elapsing; calculating a sum of the respective branch currents of the plurality of branches; comparing the calculated sum with a battery current flowing through at least one battery pack of the plurality of battery packs; and determining, by a main control circuit that a pre-charge resistor of at least one of the branches is operating abnormally in response to the calculated sum and the battery current are different. 
     The method of determining the abnormality of the pre-charge resistor of the battery system may further include: for each branch: calculating a branch charging slope based on a difference between a capacitor voltage of the respective capacitor of the branch upon a second period of the pre-charge operation elapsing and the voltage of the respective capacitor of the branch upon a third period of the pre-charge operation elapsing; comparing the calculated branch charging slope with a predetermined reference slope; and determining, by the main control circuit, that the respective pre-charge resistor of the branch is operating abnormally based on the calculated branch charging slope being greater than the reference slope. 
     The method may further include: for each branch: measuring a branch charging time at which the voltage charged to the respective capacitor of the branch reaches a voltage of at least one battery pack of the plurality of battery packs; comparing the measured branch charging time with a predetermined reference time; and determining, by the main control circuit, that the respective pre-charge resistor of the branch is operating abnormally based on the measured branch charging time being longer than the reference time. 
     In some examples, the reference time may be the branch charging time of a plurality of pre-charge resistors in a normal state. 
     Advantageous Effects 
     A method of determining whether a pre-charge resistor is abnormal and a battery system to which the same is applied are provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a view showing a configuration of a battery system according to an embodiment. 
         FIG.  2    is a view illustrating a method for detecting deterioration of a pre-charge resistor during a pre-charge operation according to an embodiment. 
         FIG.  3    is a view of a curve showing a voltage fluctuation of one of a plurality of capacitors during a pre-charge operation according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments disclosed in the present specification will be described in detail with reference to the accompanying drawings. In the present specification, the same or similar components will be denoted by the same or similar reference numerals, and an overlapped description thereof will be omitted. The terms “module” and “unit” for components used in the following description are used only in order to easily make a specification. Therefore, these terms do not have meanings or roles that distinguish them from each other in themselves. Further, in describing embodiments of the present specification, when it is determined that a detailed description of the well-known art associated with the present invention may obscure the gist of the present invention, it will be omitted. In addition, the accompanying drawings are provided only in order to allow embodiments disclosed in the present specification to be easily understood and are not to be interpreted as limiting the spirit disclosed in the present specification, and it is to be understood that the present invention includes all modifications, equivalents, and substitutions without departing from the scope and spirit of the present invention. 
     Terms including ordinal numbers such as first, second, and the like will be used only to describe various components, and are not interpreted as limiting these components. The terms are only used to differentiate one component from other components. 
     It is to be understood that when one component is referred to as being “connected” or “coupled” to another component, it may be connected or coupled directly to another component or be connected or coupled to another component with the other component intervening therebetween. On the other hand, it is to be understood that when one component is referred to as being “connected or coupled directly” to another component, it may be connected to or coupled to another component without another component intervening therebetween. 
     It will be further understood that terms “comprise” or “have” used in the present specification specify the presence of stated features, numerals, steps, operations, components, parts, or a combination thereof, but do not preclude the presence or addition of one or more other features, numerals, steps, operations, components, parts, or a combination thereof. 
       FIG.  1    is a view showing a configuration of a battery system according to an embodiment. 
     The battery system  1  includes a plurality of battery packs  10 - 30 , a main control unit (MCU) such as a main control circuit  40 , and a relay device  50 .  FIG.  1    shows that the number of a plurality of battery packs is three, but the invention is not limited thereto, and the battery system  1  may include four or more battery packs. Also, in  FIG.  1   , a plurality of battery packs  10 - 30  are illustrated as being connected in parallel, but two or more battery packs may be connected in series and a plurality of battery packs that are connected in series may be connected in parallel. 
     A vehicle  2  includes an inverter  201 , an Electric Power Take Off (EPTO)  202 , and a high-speed charger  203 . The EPTO  202  may include a battery, an electric motor, a hydraulic pump, a smart electronic control system, and the like.  FIG.  1    shows an example of the configurations connected to the battery system  1  among the configurations of the vehicle  2 , and other configurations such as a DC-DC converter for 12 V, a DC-DC converter for 24 V, and an On Board Charger (OBC) may be further connected. 
     A plurality of battery packs  10 - 30  are connected in parallel to each other, and both terminals of a plurality of battery packs  10 - 30  are connected to the relay device  50  through lines  101  and  102 , respectively. 
     Each of a plurality of battery packs  10 - 30  includes a plurality of battery cells  11 - 15 ,  21 - 25 , and  31 - 35 , a plurality of pack battery management systems  100  to  300 , and current sensors  16 ,  26 , and  36 . Hereinafter, the pack battery management system is referred to as a pack Battery Management System (BMS).  FIG.  1    shows that each of a plurality of battery packs  10 - 30  include five battery cells  11 - 15 ,  21 - 25 , and  31 - 35 , which is an example, but the invention is not limited thereto. Also, although not shown in  FIG.  1   , a relay may be connected between at least one of both ends of each of a plurality of battery packs  10 - 30  and at least corresponding to one of two lines  101  and  102 . 
     Each of a plurality of pack BMSs  100  to  300  is connected to a plurality of battery cells  11 - 15 ,  21 - 25 , and  31 - 35 , and measures a cell voltage of a plurality of battery cells  11 - 15 ,  21 - 25 , and  31 - 35 . Each of a plurality of pack BMS  100  to  300  may acquire voltage of the battery packs  10 ,  20 , and  30 , a battery pack current, and a temperature of the battery pack. Each of a plurality of pack BMSs  100  to  300  may control a charging and discharging current of the battery pack  10 - 30  based on the cell voltage and the battery pack current of a plurality of battery cells  11 - 15 ,  21 - 25 , and  31 - 35 , and may control a cell balancing operation for a plurality of battery cells  11 - 15 ,  21 - 25 , and  31 - 35 . 
     Each of a plurality of current sensors  16 ,  26 , and  36  may measure the battery pack current flowing through the corresponding battery packs  10 ,  20 , and  30 , respectively, and may transmit current detection signals IS1, IS2, and IS3 indicating the measured battery pack current to the main control circuit  40 . In this case, a plurality of current sensors  16 ,  26 , and  36  may also transmit the current detection signals IS1, IS2, and IS3 to a plurality of pack BMSs  100  to  300 . 
     The main control circuit  40  may receive information such as the cell voltage of a plurality of battery cells  11 - 15 ,  21 - 25 , and  31 - 35  from a plurality of pack BMSs  100  to  300 , and the voltage, the current, and the temperature of a plurality of battery packs  10 ,  20 , and  30 . The main control circuit  40  may supply a power control signal to a plurality of battery packs  10 ,  20 , and  30  in order to supply electric power required for a vehicle operation, and may supply a charging control signal to charge a plurality of battery packs  10 ,  20 , and  30 . In addition, the main control circuit  40  may perform control necessary for the operation of the battery system  1 , and when an abnormal state of the battery system  1  is detected, a protection operation may be started and controlled. The main control circuit  40  may include a memory  41 , and information necessary for the operation of the battery system  1  may be stored in the memory  41 . For example, information necessary for determining whether the pre-charge resistor is abnormal during the pre-charge operation may be stored in the memory  41 . 
     The relay device  50  may include a plurality of pre-charge resistors  61  to  63 , a plurality of pre-charge switches  71  to  73 , a plurality of main switches  81  to  83 , and a plurality of capacitors  91  to  93 . The relay device  50  controls the switching operation of a plurality of pre-charge switches  71  to  73  according to a plurality of pre-charge gate voltages RVG 1  to RVG 3  received from the main control circuit  40 , and controls the switching operation of a plurality of main switches  81  to  83  according to a plurality of gate voltages VG 1  to VG 3 . 
     In the relay device  50 , one of terminals of a plurality of pre-charge resistors  61  to  63  and a plurality of main switches  81  to  83  are connected to the line  101 , and the other terminals of a plurality of main switches  81  to  83  are connected to the corresponding configurations in the vehicle  2 . The other terminal of each of a plurality of pre-charge resistors  61  to  63  is connected to one terminal of a corresponding one of a plurality of pre-charge switches  71  to  73 , and the other terminal of a plurality of pre-charge switches  71  to  73  is connected to the corresponding configuration in the vehicle  2 . The other terminals of the pre-charge switch  71  and the main switch  81  are connected to one of two input terminals of the inverter  201 , and the other terminals of the pre-charge switch  72  and the main switch  82  are connected to one of two input terminals of the EPTO  202 , and the other terminals of the pre-charge switch  73  and the main switch  83  are connected to one of two input terminals of the high-speed charger  23 . Each of a plurality of capacitors  91  to  93  is connected between the other terminal of a corresponding one of a plurality of pre-charge switches  71  to  73  and the line  102 . Each of a plurality of voltage sensors  51 - 53  is connected to both ends of a corresponding one of a plurality of capacitors  91  to  93 , to measure the voltages VC 1 , VC 2 , and VC 3  charged in a plurality of capacitors  91  to  93 , and may transmit a plurality of voltage detection signals VS 1 , VS 2 , and VS 3  to the main control circuit  40 . 
     The voltage sensor  103  may be connected to between the line  101  and the line  102  to measure a battery voltage VB, which is a voltage across both terminals of the battery system  1 , and may transmit a voltage detection signal VBS indicating the measured battery voltage VB to the main control circuit  40 . 
     The pre-charge operation may be an operation to block a surge current from being generated by pre-connecting the battery system  1  and the vehicle  2  through the pre-charge resistor and the pre-charge switch before turning on the main switch. When the resistance is increased due to the deterioration of the pre-charge resistor, since the various problems mentioned above occur, the main control circuit  40  according to an embodiment detects the deterioration of a plurality of pre-charge resistors during the pre-charge operation. During the pre-charge operation, the main control circuit  40  may turn on a plurality of main switches  81  to  83  before a predetermined time before a plurality of main switches  81  to  83  are in the turn-off state and the pre-charge operation is completed during the pre-charge operation. Subsequently, the main control circuit  40  may turn on a plurality of main switches  81  to  83 , and then turn off a plurality of pre-charge switches  71  to  73 . 
     Hereinafter, a method for detecting the deterioration of the pre-charge resistor during the pre-charge operation according to an embodiment is described with reference to  FIG.  2   . 
       FIG.  2    is a view illustrating a method for detecting a deterioration of a pre-charge resistor during a pre-charge operation according to an embodiment. 
     In  FIG.  1   , during the pre-charge operation, the electric path configured of the pre-charge resistors  61 ,  62 , and  63 , the on-state pre-charge switches  71 ,  72 , and  73 , and the capacitors  91 ,  92 , and  93 , which are respectively connected between battery system  1  and the inverter  21 , the EPTO  22 , and the high-speed charger  23 , is defined as a branch. 
     After the pre-charge operation is started, each of a plurality of capacitors  91  to  93  may be charged by the battery voltage VB so that the voltage of each of the plurality of capacitors  91  to  93  may rise for a predetermined delay period to be converged to the battery voltage VB. At this time, the delay period is determined according to a product (RC) of the resistance value R of the pre-charge resistor of each branch and the capacitance C of the capacitor, which is called a time constant (T). In an embodiment, the lapse of the time during the pre-charge operation is divided into a unit of the time constant, and the determination of whether the pre-charge resistor is abnormal in step  3  is performed. However, dividing the time lapse by a unit of the time constant is only one of various embodiments in which the invention is implemented, and the invention is but is not limited thereto. That is, it is possible to detect the abnormalities in the pre-charge resistor at an appropriate time according to the design. The abnormality of the pre-charge resistor means that the resistance value is increased due to the deterioration of the pre-charge resistor. 
       FIG.  3    is a view of a curve showing a voltage fluctuation of one of a plurality of capacitors during a pre-charge operation according to an embodiment. 
     As shown in  FIG.  3   , the voltage VC 1 , which is a voltage of two terminals of the capacitor  91 , rises from the start time of the pre-charge, and when the period of 1T elapses, the voltage VC 1  reaches the voltage level VC 11 , and when the period of 4T elapses, it reaches the voltage level VC 12 , and when the period of 5T elapses, it reaches substantially the same voltage level VC 13  as the battery voltage VB. Other voltages VC 2  and VC 3  also have a waveform similar to the curve shown in  FIG.  3   . However, the time constant T may be different for each pre-charge resistor and capacitor. 
     First, the main control circuit  40  receives the voltage detection signals VBS and VS 1  to VS 3  indicating the battery voltage VB and a plurality of capacitor voltages VC 1  to VC 3  at the time of 1T, and calculates a branch current (S 1 ). Based on the voltage value indicated by each of the voltage detection signals VBS and VS 1  to VS 3 , the current I 1  of the first branch connected to inverter  21 , the current  12  of the second branch connected to the EPTO  22 , and the current  13  of the third branch connected to the high-speed charger  23  are calculated. In this case, the main control circuit  40  may use the resistance value of each of a plurality of pre-charge resistors  61  to  63  stored in the memory  41 . For example, the main control circuit  40  calculates the current I 1  by dividing the voltage obtained by subtracting the voltage level VC 11  of the voltage VC 1  at the time 1T from the battery voltage VB by the resistance value of the pre-charge resistor  61  stored in the memory  41 , calculates the current  12  by dividing the voltage obtained by subtracting the voltage level of voltage VC 2  from the battery voltage VB at the time of 1T by the resistance value of the pre-charge resistor  62  stored in the memory  41 , and calculates the current I 3  by dividing the voltage obtained by subtracting the voltage level of the voltage VC 3  from the battery voltage VB at the time of 1T by the resistance value of the pre-charge resistor  63  stored in the memory  41 . 
     The main control circuit  40  determines whether the result of summing the currents I 1  to I 3  (the sum of the branch currents) is the same as the battery current S 2 . The main control circuit  40  may receive the current detection signals IS 1  to  1 S 3  from the current sensors  16 ,  26 , and  36  of a plurality of battery packs  10 ,  20 , and  30 , respectively, and add the current values indicated by the current detection signals IS1 to IS3 to calculate the battery current, which is the current of the battery system  1 . However, the present invention is not limited thereto, and a current sensor may be positioned in any one of line  101  and line  102  to measure the battery current. 
     As the determining result of S 2 , if the sum of the branch currents is the same as the battery current, the pre-charge operation continues. As the determining result of S 2 , if the sum of the branch currents is different from the battery current, the main control circuit  40  may determine that at least one of a plurality of pre-charge resistors  61  to  63  is defective. That is, when the resistance value is increased due to the deterioration of at least one of a plurality of pre-charge resistors  61  to  63 , at least corresponding one of the currents I 1 -I 3  may be different from the actual branch current. The battery current  1 B is actually the sum of a plurality of branch currents, and the currents I 1  to I 3  calculated by the main control circuit  40  are the currents based on the resistance value stored in the memory  41 , thereby a difference occurs between the stored resistance and the actual resistance due to the deterioration of the pre-charge resistor. Due to this difference, the battery current  1 B and the sum (I1+I2+I3) of the calculated branch currents are different. Accordingly, it may be confirmed that the main control circuit  40  has the pre-charge resistor of which the resistance value is increased due to the deterioration among a plurality of pre-charge resistors  61  to  63 . 
     As the pre-charge operation continues, at the time  4 T, the main control circuit  40  calculates a branch charge slope by using a plurality of capacitor voltages VC 1  to VC 3  (S 4 ). For example, the main control circuit  40  may calculate the branch charging slope by dividing the value obtained by subtracting the voltage level VC 11  of the voltage VC 1  of the timing 1T from the voltage level VC 12  of the voltage VC 1  at the timing 4T by the time 3T. By the same manner, the main control circuit  40  may calculate each branch charging slope by dividing the value obtained by subtracting the voltage level at the time 1T from the voltage at the time 4T of the voltages VC 2  and VC 3  by the time 3T. 
     The main control circuit  40  compares each branch charging slope with a reference slope, and determines whether each branch charging slope is equal to or greater than the reference slope (S 5 ). The reference slope may be set as the branch charging slope when the pre-charge resistor is in a normal state. The step S 5  may be performed for each branch. 
     As the determining of S 5 , if the branch charging slope is smaller than the reference slope, the main control circuit  40  determines that the pre-charge resistor of the corresponding branch is abnormal. 
     As the determining of S 5 , if all branch charging slopes are equal to or greater than the reference slope, the main control circuit  40  continues the pre-charge operation. As the resistance value increases as the pre-charge resistor deteriorates, the rising slopes of the voltages VC 1 , VC 2 , and VC 3  decrease. 
     Accordingly, the main control circuit  40  calculates the charging slope for each branch based on this and compares it with the reference slope, thereby determining that the pre-charge resistor of the branch below the reference slope has the abnormality due to the deterioration. 
     As the pre-charge operation continues, the main control circuit  40  measures the branch charging time at which the level of a plurality of voltages VC 1  to VC 3  reaches the battery voltage VB (S 7 ). As shown in  FIG.  3   , if the time  5 T has elapsed, the voltage VC 1  reaches the battery voltage VB, where the time  5 T is differentiated depending on the resistance value of the pre-charge resistor of each branch. 
     The main control circuit  40  compares a branch charging time of each of a plurality of branches with a reference time, and determines whether each of a plurality of branch charging times is equal to or less than the reference time (S 8 ). If the resistance value increases due to the deterioration of the pre-charge resistor, the actually measured time 5T is longer than the time 5T based on the pre-charge resistor of the normal state. The reference time may be the time 5T determined by the steady state pre-charge resistor. 
     As the determining result of S 8 , the main control circuit  40  determines that the pre-charge resistor of the corresponding branch is abnormal when the time among a plurality of branch charging times is longer than the reference time (S 9 ). 
     As the determining result of S 8 , if all of the plurality of branch charging times are less than or equal to the reference time, the main control circuit  40  determines that all of the pre-charge resistors are normal (S 10 ). 
     As such, the embodiment may determine whether the pre-charge resistor is abnormal through three steps during the period in which the pre-charge operation is performed. If it is determined that the pre-charge resistor is abnormal, the pre-charge operation is stopped, and the main control circuit  40  may inform that the abnormality occurs in the pre-charge resistor through an interface (not shown) provided in at least one of the battery system  1  and the vehicle  2 . 
     While this invention has been described in connection with what is presently considered to be practical embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.