Patent Publication Number: US-2019176641-A1

Title: Method for charging battery of electric vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to and the benefit of Korean Patent Application No. 10-2017-0169217, filed on Dec. 11, 2017, which is incorporated herein by reference in its entirety. 
     FIELD 
     Forms of the present disclosure relate to an electric vehicle, and more particularly to a method for charging a battery of an electric vehicle. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     In general, a vehicle is a machine which travels on roads or tracks using fossil fuels, electricity, etc. 
     A vehicle driven using fossil fuels may discharge fine dust, water vapour, carbon dioxide (CO 2 ), carbon monoxide (CO), hydrocarbon, nitrogen (N), nitrogen oxide, and/or sulfur oxides, etc. due to burning of fossil fuels. Water vapour and carbon dioxide (CO 2 ) have been known to cause global warming, and fine dust, carbon monoxide (CO), hydrocarbon, nitrogen oxide, and/or sulfur oxide, etc. have been known as air pollution materials that cause harm to people. 
     Due to the above issues, eco-friendly vehicles driven using eco-friendly energy instead of fossil fuels have recently been developed and rapidly come into widespread use. For example, many developers and companies are conducting intensive research into hybrid electric vehicles (HEVs) driven using fossil fuels and electricity and electric vehicles (EVs) driven only using electricity. 
     Each of the hybrid electric vehicle (HEV) and the electric vehicle (EV) may include a high-voltage battery for supplying power to a motor used to move the vehicle and a low-voltage battery for supplying power to electronic components embedded in the vehicle. Generally, each of the hybrid electric vehicle (HEV) and the electric vehicle (EV) may include a power-supply device for converting a voltage of the high-voltage battery into a voltage of the low-voltage battery so as to supply power from the high-voltage battery to the low-voltage battery. 
     SUMMARY 
     Therefore, it is an aspect of the present disclosure to provide a technology for preventing deterioration of a battery embedded in an electric vehicle while simultaneously improving a charging speed of the battery. 
     Additional aspects of the disclosure will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the disclosure. 
     In accordance with an aspect of the present disclosure, a battery charging method includes: dividing a total State of Charge (SOC) section of a battery into a plurality of steps, and performing constant current based charging in each step of the plurality of steps; and performing constant voltage based charging at a predetermined voltage during the constant current based charging for each step of the plurality of steps. 
     The battery charging method may further include: measuring a voltage of the battery; and determining a charge start step among the plurality of steps based on the voltage of the battery. 
     The constant current based charging for each step of the plurality of steps may be configured to follow a constant current instruction corresponding to a corresponding step. 
     The battery charging method may further include: when a voltage of the battery charged by the constant current based charging arrives at a predetermined voltage, changing a battery charging scheme to a constant voltage based charging scheme. 
     The battery charging method may further include: when the battery charging scheme is changed to the constant voltage based charging scheme, determining a deceleration of the constant current instruction in response to a voltage acceleration of the battery based on a constant current based charging scheme. 
     The predetermined voltage may be lower than a cutoff voltage of each step of the plurality of steps. 
     The battery charging method may further include dividing the plurality of steps based on the cutoff voltage of the battery. 
     The predetermined voltage may be a voltage corresponding to a predetermined cutoff SOC of the battery. 
     The battery charging method may further include: when a charge current of the battery charged at a current step among the plurality of steps drops to a target charge current value of a subsequent step, charging at the subsequent step. 
     In accordance with another aspect of the present disclosure, an electric vehicle includes: a motor; a battery configured to store power to drive the motor; and a controller configured to divide a total State of Charge (SOC) section of the battery into a plurality of steps, perform constant current based charging in each step of the plurality of steps, and perform constant voltage based charging at a predetermined voltage during the constant current based charging for each step of the plurality of steps. 
     The controller may be configured to measure a voltage of the battery, and may determine a charge start step among the plurality of steps based on the voltage of the battery. 
     The constant current based charging for each step of the plurality of steps may be configured to follow a constant current instruction corresponding to a corresponding step. 
     When a voltage of the battery charged by the constant current based charging arrives at a predetermined voltage, the controller may change a battery charging scheme to a constant voltage based charging scheme. 
     When the battery charging scheme is changed to the constant voltage based charging scheme, the controller may determine a deceleration of the constant current instruction in response to a voltage acceleration of the battery based on a constant current based charging scheme. 
     The predetermined voltage may be lower than a cutoff voltage of each step of the plurality of steps. 
     The controller may divide the plurality of steps based on the cutoff voltage of the battery. 
     The predetermined voltage may be a voltage corresponding to a predetermined cutoff SOC of the battery. 
     When a charge current of the battery charged at a current step among the plurality of steps drops to a target charge current value of a subsequent step, the controller may charge at the subsequent step. 
     In accordance with another aspect of the present disclosure, a battery charging method includes: measuring a voltage of a battery; dividing a total State of Charge (SOC) section of the battery into a plurality of steps, performing constant current based charging in each step of the plurality of steps, and determining a charge start step among the plurality of steps based on the voltage of the battery; performing constant voltage based charging at a predetermined voltage during the constant current based charging for each step of the plurality of steps; and when a charge current of the battery charged at a current step among the plurality of steps drops to a target charge current value of a subsequent step, charging at the subsequent step. 
     In accordance with another aspect of the present disclosure, a battery charging method includes: measuring a voltage of a battery; dividing a total State of Charge (SOC) section of the battery into a plurality of steps based on a cutoff voltage of the battery, performing constant current based charging in each step of the plurality of steps, determining a charge start step among the plurality of steps based on the voltage of the battery; performing constant voltage based charging at a voltage corresponding to a predetermined cutoff SOC of the battery during the constant current based charging for each step of the plurality of steps; and when a charge current of the battery charged at a current step among the plurality of steps drops to a target charge current value of a subsequent step, charging at the subsequent step. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which: 
         FIG. 1  is a view illustrating the appearance of an electric vehicle; 
         FIG. 2  is a block diagram illustrating a power system of an electric vehicle; 
         FIG. 3  is a view illustrating a charge current profile of an electric vehicle; 
         FIG. 4  is a flowchart illustrating a method for charging a battery of an electric vehicle;  FIG. 5  is a table illustrating the relationship between a per-step constant current and a per-step cutoff voltage for charging a high-voltage battery of an electric vehicle; 
         FIG. 6  is a view illustrating a normal constant-voltage charge control and an abnormal constant-voltage charge control; 
         FIG. 7  is a table illustrating the relationship between an increase speed of a cell voltage and a reduction speed of a charge current instruction; and 
         FIG. 8  is a graph illustrating a method for determining a reduction speed of a charge current instruction in response to an increase speed of the cell voltage using the method for charging a high-voltage battery. 
     
    
    
     The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
     Reference will now be made in detail to the forms of the present disclosure, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
       FIG. 1  is a view illustrating the appearance of an electric vehicle  100  in some forms of the present disclosure. 
     Referring to  FIG. 1 , the electric vehicle  100  may include a motor  212  (see  FIG. 2 ). Therefore, the electric vehicle  100  may further include a high-voltage battery  102  configured to store power to be used for driving the motor  212 . An auxiliary battery  208  (see  FIG. 2 ) may also be provided to a general internal combustion vehicle. However, a large-sized high-capacity high-voltage battery  212  is needed for the electric vehicle  100  whereas an auxiliary battery  208  (see  FIG. 2 ) is provided at one side of an engine compartment of a general internal combustion vehicle. In the electric vehicle  100  in some forms of the present disclosure, a battery  102  is installed at a lower space of a rear passenger seat. Power stored in the battery  102  may be used to generate power by driving the motor  212  (see  FIG. 2 ). The battery  102  in some forms of the present disclosure may be a lithium battery. 
     The electric vehicle  100  may be equipped with a charging socket  104  acting as a charging inlet. A charging connector  152  of an external charging station may be connected to the charging socket  104 , such that the high-voltage battery  102  can be charged with electricity or power. That is, when the charging connector  152  of the charging station is connected to the charging socket  104  of the electric vehicle  100 , the high-voltage battery  102  of the electric vehicle  100  can be charged with electricity or power. 
       FIG. 2  is a block diagram illustrating a power system of an electric vehicle in some forms of the present disclosure. The power system shown in  FIG. 2  may be configured to supply power to a motor  212  and electric loads  214 . 
     Referring to  FIG. 2 , the power system of the electric vehicle  100  in some forms of the present disclosure may include a high-voltage battery  102 , a low-voltage DC-DC converter (LDC)  204 , an inverter  206 , an auxiliary  208 , and a controller  210 . 
     The LDC  204  may convert a high DC voltage received from the high-voltage battery  102  into a lower-voltage direct current (DC). The LDC  204  may convert a high DC voltage of the high-voltage battery  102  into an alternating current (AC), may step up (boost) the alternating current (AC) using a coils, a transformer, a capacitor, etc., may rectify the boosted AC, and may then convert the rectified AC into a lower-voltage direct current (DC). The direct voltage (DC) boosted by the LDC  204  may be supplied to individual electronic loads  214  requesting a low voltage. 
     The DC voltage of the high-voltage battery  102  may be converted into an AC voltage having a predetermined phase and frequency through an inverter  206 , such that the resultant AC voltage may be supplied to the motor  212 . A rotational force and speed of the motor  212  may be decided by an output voltage of the inverter  206 . The controller  210  may control overall operation of a power supply device. In this case, the controller  210  may be a Battery Management System (BMS) for controlling the high-voltage battery  102 . 
       FIG. 3  is a view illustrating a charge current profile of an electric vehicle in some forms of the present disclosure. 
     Referring to  FIG. 3 , charging of the high-voltage battery  102  of the electric vehicle  100  in some forms of the present disclosure may be implemented using a combination of a Multi-Step Constant Current (MSCC or MCC) scheme and a Constant Current-Constant Voltage (CC-CV) scheme. 
     The controller  210  of the electric vehicle  100  may divide a total step (section) of a State Of Charge (SOC) on the basis of a cutoff voltage of the high-voltage battery  102  into a plurality of steps (sections), and may thus charge the battery of the electric vehicle  100  using the MSCC (or MCC) scheme. In each of the steps, the controller  210  may perform charging based on a constant voltage (hereinafter referred to as constant voltage based charging) using a voltage corresponding to a predetermined cutoff SOC. In other words, the controller  210  may perform constant voltage based charging during a constant current charging time per step. The controller  210  may perform charging at a subsequent step when the charge current drops to a target charge current of the subsequent step by current-step charging. 
     Referring to  FIG. 3 , the charge SOCs based on the cutoff voltages of the respective steps may include SOC_a, SOC_b, and SOC_c. 
       FIG. 4  is a flowchart illustrating a method for charging a battery of the electric vehicle in some forms of the present disclosure. 
     Referring to  FIG. 4 , the controller  210  may realtime-measure a cell voltage, a cell current, a cell temperature of the high-voltage battery at intervals of a predetermined time of 100 ms ( 402 ). However, the predetermined time may be changed to another time shorter or longer than 100 ms as necessary. 
     If the cell voltage of the high-voltage battery  102  is measured, the controller  210  may determine a step for starting charging on the basis of the measured cell voltage ( 404 ). As can be seen from  FIG. 3 , the controller  210  may divide a total SOC step (or section) on the basis of the cutoff voltage of the high-voltage battery  102  into a plurality of steps (sections), may charge the battery of the electric vehicle  100  using the MSCC (or MCC) scheme, and may perform charging based on a constant voltage corresponding to the predetermined cutoff SOC in each of the steps. 
       FIG. 5  is a table illustrating the relationship between a per-step constant current and a per-step cutoff voltage for charging a high-voltage battery of an electric vehicle in some forms of the present disclosure. Referring to  FIG. 5 , the cutoff voltages (Vcut) of the respective steps may include Vcut_a, Vcut_b, and Vcut_c. The charging SOCs based on the cutoff voltages (Vcut) for the respective steps may include SOC_a, SOC_b, and SOC_c. 
     Referring to  FIG. 5 , when the measured cell voltage is equal to or less than Vcut_a, the controller  210  may start charging in a condition of STEP  1 . If the measure cell voltage is higher than Vcut_a and is equal to or less than Vcut_b, the controller  210  may start charging in a condition of STEP  2 . If the measured cell voltage is higher than Vcut_b and is equal to or less than Vcut_c, the controller  210  may start charging in a condition of STEP  3 . 
     Referring back to  FIG. 4 , if the charging start step is decided, the controller  210  may generate a constant current instruction corresponding to the decided step, and may perform constant current charging based on the constant current instruction ( 406 ). 
     During charging of the high-voltage battery  102  based on constant current charging, the controller  210  may calculate an increase speed of the cell voltage of the high-voltage battery  102  ( 408 ). 
       FIG. 6  is a view illustrating a normal constant-voltage charge control and an abnormal constant-voltage charge control in some forms of the present disclosure. In  FIG. 6(I) , the cell voltage may be normally controlled not to exceed a maximum voltage (Vmax). In constant, the cell voltage may gradually increase, such that a section in which the cell voltage exceeds the maximum voltage (Vmax) is present as shown in  FIG. 6 (II). In the section in which the cell voltage exceeds the maximum voltage (Vmax) as shown in  FIG. 6 (II), the high-voltage battery  102  may be deteriorated. Such deterioration of the high-voltage battery  102  may also deteriorate the lifespan and performance of the high-voltage battery  102 . Therefore, the forms of the present disclosure may generate a reduction speed of the charge current instruction appropriate for the increase speed of the cell voltage when entering the constant voltage charging mode, such that a normal constant voltage charge control shown in  FIG. 6(I)  can be achieved. 
       FIG. 7  is a table illustrating the relationship between an increase speed of a cell voltage and a reduction speed of a charge current instruction in some forms of the present disclosure. Referring to  FIG. 7 , the higher the increase speed of the cell voltage (hereinafter referred to as the cell voltage increase speed) of the high-voltage battery  102 , the lower the reduction speed of the charge current instruction (hereinafter referred to as the charge current instruction reduction speed). In more detail, when the increase speed of the cell voltage is excessively high, the increase speed of the cell voltage is reduced, such that an overshoot section (battery deterioration section) as shown in  FIG. 6 (II) is prevented from occurring. Values shown in  FIG. 7  may be acquired using experiments in consideration of current (I) response characteristics between the high-voltage battery  102  and a charger. 
     Referring back to  FIG. 4 , the controller  210  may determine whether the cell voltage increasing by constant current charging is equal to or higher than a voltage (V_cmd_cv) for entering constant voltage charging control (V_cmd_cv) ( 410 ). As previously described above, when the increase speed of the cell voltage is excessively high, the increase speed of the cell voltage should be reduced to prevent occurrence of the overshoot section (battery deterioration section) as shown in  FIG. 6 ( 11 ). To this end, when the cell voltage arrives at a specific point at which the cell voltage is lower than a target voltage (Vcv_tgt) for constant voltage charging (hereinafter referred to as a target constant voltage charge voltage Vcv_tgt) by a voltage margin (a) as shown in  FIG. 8 , a charge current instruction reduction speed ( 8 ) is newly decided to reduce the charge current instruction. 
       FIG. 8  is a graph illustrating a method for determining a reduction speed of a charge current instruction in response to an increase speed of the cell voltage using the method for charging a high-voltage battery in some forms of the present disclosure. Referring to  FIG. 8 , when the cell voltage arrives at a specific point at which the cell voltage is lower than the constant voltage charge target voltage (Vcv_tgt) by the voltage margin (a), the charge current instruction may be changed in a manner that the cell voltage does not exceed the target constant voltage charge voltage (Vcv_tgt). As can be seen from  FIGS. 7 and 8 , the higher the increase speed of the cell voltage, the lower the reduction speed of the charge current instruction, such that the increase speed of the cell voltage can be reduced. In contrast, the lower the increase speed of the cell voltage, the higher the reduction speed of the charge current instruction, such that the increase speed of the cell voltage can be increased. The reason why the charge current instruction reduction speed is regulated is to prevent occurrence of a section in which the cell voltage rapidly arriving at the target constant voltage charge voltage (Vcv_tgt) without exceeding the target constant voltage charge voltage (Vcv_tgt). In  FIG. 8 , the increase speed of the cell speed may be measured through a variance (ΔV) of the cell voltage during a predetermined time (e.g., 0.1 s). 
     Referring back to  FIG. 4 , when the cell voltage increases to the constant voltage charge control entry voltage (V_cmd_cv) or higher (YES in  410 ), the controller  210  may determine the charge current instruction reduction speed ( 13 ) in consideration of the increase speed of the cell voltage due to the same reason as described above ( 412 ). 
     In contrast, when the cell voltage is less than the constant voltage charge control entry voltage (NO in  410 ), the controller  210  may continuously perform the constant current charging operation  406 . 
     When the charge current instruction reduction speed ( 8 ) is decided, the controller  210  may charge the high-voltage battery  102  using the constant voltage charging scheme according to the changed charge current instruction ( 414 ). In this case, the maximum voltage (V_max) may be maintained at the cutoff voltage (V_cutoff). 
     The controller  210  may determine whether the charge current is equal to or less than a constant current of a subsequent step (see STEPS  1  to  3  of  FIG. 3 ) ( 416 ), such that the controller  210  may stop charging in a current step and may also decide whether to enter the subsequent step. 
     If the current charge current is equal to or less than a constant current of the subsequent step (YES in  416 ), the controller  210  may continuously perform charging of the high-voltage battery  102  when entering the subsequent step ( 418 ). If the charge current is equal to or less than the constant current during charging in STEP  1 , the controller  210  may continuously perform charging of the high-voltage battery  102  in a condition of STEP  2 . 
     If the current charge current is less than the constant current of the subsequent step (NO in  416 ), the controller  210  may continuously control constant voltage charging ( 414 ). 
     If the current SOC of the high-voltage battery  102  arrives at an end SOC (maximum SOC) by continuous charging of the high-voltage battery  102  (YES in  420 ), the controller  210  may stop charging of the high-voltage battery  102 . 
     In contrast, when the current SOC of the high-voltage battery  102  does not arrive at the end SOC (maximum SOC) (NO in  420 ), the controller  210  may continuously perform the constant current charging operation  406 . 
     As is apparent from the above description, a method for charging a battery of an electric vehicle in some forms of the present disclosure may prevent deterioration of the battery when charging the battery with electricity, and at the same time may improve a charging speed of the battery. 
     The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.