Patent Publication Number: US-2013249493-A1

Title: Vehicle and method of controlling the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2012-0030236, filed on Mar. 23, 2012, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     1. Field 
     The disclosed technology relates to an electrical system, such as a vehicle and a method of controlling the same. 
     2. Description of the Related Technology 
     Unlike primary batteries, secondary batteries are rechargeable batteries. Secondary batteries are used as energy sources in, for example, mobile devices, electric cars, hybrid cars, electric bicycles, or uninterruptible power supply devices. Secondary batteries include a single battery or a battery module including multiple batteries according to the type of device to be supplied with power. 
     Typically, lead storage batteries are used as power sources for starting up engines. Idle stop and go (ISG) systems for improving fuel economy have recently been developed and are expected to be widely used. Power sources which support ISG systems supply high power to start up engines, maintain strong charge and discharge characteristics even when the engines are repeatedly restarted, and have long life spans. Typically, however, as engines of ISG systems are repeatedly stopped and restarted, charge and discharge characteristics of conventional lead storage batteries quickly degrade. 
     SUMMARY OF CERTAIN INVENTIVE ASPECTS 
     One inventive aspect is a vehicle having a rechargeable battery charging system, which includes a battery cell configured to receive a charge current from a power generation module in order to be charged, a diode connected in series between the power generation module and the battery cell and configured to conduct the charge current therethrough, and a control unit that adjusts the charge current supplied from the power generation module according to a temperature of the diode. 
     Another inventive aspect is a method of controlling a vehicle that supplies a charge current to a rechargeable battery cell from a power generation module through a diode. The method includes measuring a temperature of the diode, and adjusting the charge current supplied from the power generation module according to the temperature of the diode. 
     Another inventive aspect is a rechargeable battery charging system, which includes a battery cell configured to receive a charge current from a power generation module in order to be charged, a diode connected in series between the power generation module and the battery cell and allows the charge current to flow therethrough, and a control unit that adjusts the charge current supplied from the power generation module according to a temperature of the diode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a block diagram illustrating a vehicle according to an embodiment; 
         FIG. 2  is a block diagram illustrating a battery pack according to an embodiment; 
         FIG. 3  illustrates graphs which show relationships between a voltage of a battery cell and time and between a temperature of a diode and a temperature of the battery cell and time; 
         FIG. 4  is a flowchart illustrating a method of controlling the vehicle, according to an embodiment; 
         FIG. 5  is a block diagram illustrating a battery pack according to another embodiment; 
         FIG. 6  illustrates graphs which show relationships between a voltage of the battery cell and time and between a temperature of the diode and a temperature of the battery cell and a time; and 
         FIG. 7  is a flowchart illustrating a method of controlling the vehicle, according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS 
     Hereinafter, certain aspects and features are described more fully with reference to the accompanying drawings, in which exemplary embodiments are shown. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the exemplary embodiments. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising” used herein specify the presence of stated features, integers, steps, operations, members, components, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, members, components, and/or groups thereof. It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. 
     As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
       FIG. 1  is a block diagram illustrating an electrical system, such as a vehicle  10  according to an embodiment of the present invention. As shown, a battery pack  100  may be included in the vehicle  10 , which may have an engine (not shown). The vehicle  10  may be, for example, a car or an electric bicycle. 
     The battery pack  100  may be supplied with a charge current I 1  generated by a power generation module  110 , store electric energy, and supply a discharge current I 2  to a starter motor  120 . For example, the power generation module  110  may be electrically connected to the engine, especially, to a driving shaft of the engine, and may convert rotational power into electric power. In this case, the charge current I 1  generated by the power generation module  110  may be supplied to the battery pack  100 . For example, the power generation module  110  may include a direct current (DC) generator (not shown) or an alternating current (AC) generator (not shown) with a rectifier (not shown). The power generation module  110  may supply a DC voltage of about 15 V, more specifically, a DC voltage of about 14.2 V to about 14.8 V. 
     For example, the starter motor  120  may operate when the engine is started up, and may supply initial rotational power for rotating the driving shaft of the engine. For example, the starter motor  120  may be supplied with stored power through first and second terminals P 1  and P 2  of the battery pack  100  and may start up the engine by rotating the driving shaft when the engine operates or re-operates after an idle-stop. The starter motor  120  may operate when the engine is started up, and the generating module  110  may be driven to generate the charge current I 1  while the engine started up by the starter motor  120  is operating. 
     For example, the battery pack  100  may be used as a power source for starting up an engine of an idle stop and go (ISG) system with an ISG feature for improving fuel economy. In the ISG system, as the engine is repeatedly stopped and restarted, the battery pack  100  is repeatedly charged and discharged. 
     As a conventional lead storage battery applied to an ISG system is repeatedly charged and discharged, the durability of the lead storage battery is reduced and charge and discharge characteristics of the lead storage battery are degraded. For example, as the lead storage battery is repeatedly charged and discharged, a charge capacity is reduced, start-up characteristics of an engine are degraded, and an exchange cycle of the lead storage battery is shortened. 
     However, since the battery pack  100  includes a lithium-ion battery whose charge and discharge characteristics are maintained constant and which hardly degrades with time, compared to a lead storage battery, the battery pack  100  may be advantageously applied to an ISG system in which an engine is repeatedly stopped and restarted. Also, since the battery pack  100  is lighter than a lead storage battery having the same charge capacity, the system using the battery pack  100  may have better fuel economy than if the lead storage battery were used. Also, since the battery pack  100  has the same charge capacity even with a smaller volume than that of a lead storage battery, space occupied by the battery pack  100  may be smaller than that by the lead storage battery. 
     Although the battery pack  100  includes a lithium-ion battery in  FIG. 1 , embodiments are not limited thereto and the battery pack  100  may have any of various batteries. However, a battery included in the battery pack  100  may have a rated voltage less than an output voltage of the power generation module  110 . For example, a nickel-metal hydride (NiMH) battery or a nickel-cadmium battery may be used in the battery pack  100 . 
     One or more electrical loads  130  as well as the power generation module  110  and the starter motor  120  may be connected to the battery pack  100 . The number and types of the electrical loads  130  may vary according to the vehicle  10 . The electrical loads  130  that consume power stored in the battery pack  100  may be supplied with the discharge current I 2  from the battery pack  100  through the first and second terminals P 1  and P 2 . The electrical loads  130  may be various electronic devices such as navigation systems, audio players, lighting apparatuses, black boxes, and anti-theft apparatuses. 
     A main control unit  140  controls an overall operation of the vehicle  10  on which the battery pack  100  is mounted. The main control unit  140  may be connected to the battery pack  100  through a third terminal P 3  to exchange a control signal, monitor a state of the battery pack  100 , and control an operation of the battery pack  100 . Also, the main control unit  140  may adjust the charge current I 1  of the power generation module  110 . The main control unit  140  may, for example, increase or reduce the charge current I 1  of the power generation module  110  according to a monitored state of charge of the battery pack  100 . 
     The main control unit  140  may act as a control unit of the vehicle  10  for controlling both the vehicle  10  and the battery pack  100 . Alternatively, the main control unit  140  and a battery control unit may be separately formed, and the main control unit  140  may control the charge current I 1  of the power generation module  110  according to data or a control signal applied from the battery control unit. Even in this case, a control unit of the vehicle  10  for controlling the charge current I 1  of the power generation module  110  is the main control unit  140 . In the following, it is assumed that the main control unit  140  and the battery control unit are separately formed. 
       FIG. 2  is a block diagram illustrating a battery pack  100   a  according to an embodiment. Referring to  FIG. 2 , the battery pack  100   a  includes a battery cell  210 , a diode D 1 , a discharge unit  220 , a battery management system (BMS)  230 , and a temperature detecting unit  240 . 
     The battery cell  210  may, for example, be a lithium-ion battery cell or a NiMH battery cell. The battery cell  210  is supplied with a charge current from the power generation module  110  in order to be charged. Also, the battery cell  210  may supply power to the starter motor  120  and the electrical loads  130 . In  FIG. 2 , a rated voltage of the battery cell  210  is less than an output voltage of the power generation module  110 . For example, if the battery cell  210  is a lithium-ion battery, the power generation module may supply a DC voltage of about 14.2 V to about 14.8 V, and the lithium-ion battery may have a DC rated voltage of about 12.6 V to about 13.05 V. 
     The diode D 1  is connected in series between the first terminal P 1  and the battery cell  210 , and supplies the charge current I 1  input from the first terminal P 1  to the battery cell  210 . The diode D 1  is configured to exhibit a voltage drop corresponding to a voltage difference between the output voltage of the power generation module  110  and the rated voltage of the battery cell  210 . The diode D 1  forms a charge path of the battery pack  100   a,  wherein an anode of the diode D 1  is connected to the first terminal P 1  and a cathode of the diode D 1  is connected to the battery cell  210 . The diode D 1  may include one diode, a plurality of diodes connected in series, and/or a plurality of diodes connected in parallel. 
     The discharge unit  220  forms a discharge path around and is connected in parallel to the diode D 1 . The discharge unit  220  may include at least one of a switch, a diode, and a converter. The discharge unit  220  outputs a discharge current from the battery cell  210  through the first terminal P 1  and the second terminal P 2 . 
     The temperature detecting unit  240  measures a temperature of the diode D 1 . In some embodiments, the temperature of the diode D 1  is directly measured, as opposed to indirect measurement, such as, by measuring ambient air temperature. The temperature detecting unit  240  may include any of various temperature sensors. For example, a temperature sensor, such as [Note: please provide a list.] may be used. The temperature detecting unit  240  provides temperature data indicating the measured temperature to the BMS  230 . The temperature data may be in the form of, for example, an analog voltage or a set of digital data. 
     The BMS  230  controls an overall operation of the battery pack  100   a.  The BMS  230  may monitor the battery  210 , perform cell balancing of the battery cell  210 , start or end charging and discharging, and communicate with the main control unit  140 . The BMS  230  may be connected to the main control unit  140  through the third terminal P 3 . 
     The BMS  230  adjusts the charge current I 1  of the power generation module  110  according to the temperature of the diode D 1  measured by the temperature detecting unit  240 . For example, in order to adjust the charge current I 1  of the power generation module  110 , the BMS  230  may transmit a control signal for requesting the main control unit  140  to adjust the charge current I 1  of the power generation module  110 . Alternatively, the BMS  230  may transmit the temperature data of the diode D 1  to the main control unit  140  and the main control unit  140  may adjust the charge current I 1  of the power generation module  110  according to the temperature data. 
       FIG. 3  shows graphs illustrating relationships between a voltage Vbat of the batter cell  210  and time and between a temperature of the diode D 1  and a temperature of the battery cell  210  and time. The voltage Vbat of the battery cell  210  is an example of a state of charge (SOC) of the battery cell  210 . 
     As shown in  FIG. 3 , as the SOC of the battery cell  210  changes from a full discharge state to a full charge state with time, the temperature of the diode D 1  rapidly increases at an initial stage where the charge current I 1  is high, and then reduces when the voltage Vbat of the battery cell  210  reaches a certain level and the charge current I 1  is reduced. Since the temperature of the diode D 1  rapidly increases at the initial stage, the diode D 1  may break or characteristics of a device including the diode D 1  may degrade. In particular, according to the present embodiment, since the diode D 1  exhibits a voltage drop corresponding to a voltage difference between an output voltage of the power generation module  110  and a rated voltage of the battery cell  210 , electric energy may be consumed by the diode D 1  and thus a great amount of heat may be generated in the diode D 1 . Also, a temperature of the diode D 1  may increase at a greater rate than a temperature of the battery cell  210 . Accordingly, heat generated in the diode D 1  may reduce the safety of the battery pack  100   a.    
     Problems caused by heat generated in the diode D 1  can be alleviated by adjusting the charge current I 1  supplied from the power generation module  110  when the measured temperature of the diode D 1  is equal to or greater than a first reference temperature Td. For example, when the diode&#39;s D 1  temperature is equal to or greater than the first reference temperature Td, the BMS  230  or the main control unit  140  may reduce the charge current I 1  supplied from the power generation module  110  or completely cut off the charge current. 
       FIG. 4  is a flowchart illustrating a method of controlling the vehicle  10 , according to an embodiment. 
     In operation S 402 , while the battery pack  110  operates, the temperature detecting unit  240  measures a temperature of the diode D 1 . The temperature of the diode D 1  may be measured continuously, periodically, or in other ways. 
     In operation S 404 , it is determined whether the temperature of the diode D 1  is greater than the first reference temperature Td. If it is determined in operation S 404  that the temperature of the diode D 1  is greater than the first reference temperature Td, the method proceeds to operation S 406 . In operation S 406 , the BMS  230  may request the main control unit  140  to reduce the charge current I 1  output from the power generation module  110 . Alternatively, if it is determined in operation S 404  that the temperature of the diode D 1  is greater than the first reference temperature Td, the BMS  230  may provide temperature data of the diode D 1  to the main control unit  140  and the main control unit  140  may adjust the charge current I 1  supplied from the power generation module  110  according to the temperature data of the diode D 1  received from the BMS  230 . 
       FIG. 5  is a block diagram illustrating a battery pack  100   b  according to another embodiment. As shown, the battery pack  100   b  includes the battery cell  210 , the diode D 1 , the discharge unit  220 , the BMS  230 , the temperature detecting unit  240 , and a bypass unit  410 . 
     The diode D 1  and the bypass unit  410  are connected in parallel between the first terminal P 1  and the battery cell  210 , and the bypass unit  410  may be turned on or off according to an SOC of the battery cell  210 . The bypass unit  410  may include a switching element. 
     The BMS  230  measures an SOC of the battery cell  210  while the battery pack  100   b  operates. The BMS  230  allows the charge current I 1  to flow along a first charge path PATH 1  or a second charge path PATH 2  according to the SOC of the battery cell  210 . 
     For example, if the SOC of the battery cell  210  is equal to or less than a reference level, the BMS  230  allows the charge current I 1  to flow through the first charge path PATH 1  by turning on the switching element of the bypass unit  410 . Accordingly, when the SOC of the battery cell  210  is equal to or less than the reference level, the charge current I 1  minimally flows through the diode D 1  and thus heat is substantially not generated in the diode D 1 . 
     When the SOC of the battery cell  210  is greater than the reference level, the BMS  230  allows the charge current I 1  to flow through the second charge path PATH 2  by turning off the switching element of the bypass unit  410 . Accordingly, when the SOC of the battery cell  210  is greater than the reference level, the charge current I 1  is supplied through the diode D 1 . Also, when the charge current I 1  flows through the second charge path PATH 2 , the BMS  230  may monitor a temperature of the diode D 1  by using the temperature detecting unit  240 , and if the temperature of the diode D 1  is equal to or greater than a first reference temperature, may adjust the charge current I 1  supplied from the power generation module  110  according to the temperature of the diode D 1 . For example, if the temperature of the diode D 1  is equal to or greater than the first reference temperature, the BMS  230  may request the main control unit  140  to reduce the charge current I 1  supplied from the power generation module  110 . 
     According to some embodiments, since at an initial stage where the battery cell  210  is not overcharged, the diode D 1  does not experience any voltage drop D 1  and the charge current I 1  is supplied through the bypass unit  410 , and at other stages when overcharging of the battery cell  210  is possible, the charge current I 1  is supplied through the diode D 1 , and heat generated in the diode D 1  may be monitored and reduced, if desired. Also, according to some embodiments, since the BMS  230  monitors a temperature of the diode D 1  while being supplied with the charge current I 1  through the diode D 1  and reduces the charge current I 1  if the temperature of the diode D 1  is equal to or greater than a predetermined value, the safety of the battery pack  100  may be maintained. 
       FIG. 6  includes graphs illustrating relationships between a voltage Vbat of the battery cell  210  and time and between a temperature of the diode D 1  and a temperature of the battery cell  210  and time. The voltage Vbat of the battery cell  210  is an example of an SOC of the battery cell  210 . According to some embodiments, as the SOC of the battery cell  210  changes from a full discharge state to a full charge state, if the voltage Vbat of the battery cell  210  is equal to or less than a first reference value Vref, since the charge current I 1  flows along the second charge path PATH 2 , the temperature of the diode D 1  is minimally changed and heat is substantially not generated in the diode D 1 . If the voltage Vbat of the battery cell  210  is greater than the first reference value Vref, since the charge current I 1  flows along the first charge path PATH 1 , the temperature of the diode D 1  begins to increase. As the SOC of the battery cell  210  approaches the full charge state, the charge current I 1  flowing through the diode D 1  is reduced. If the SOC of the battery cell  210  is equal to or greater than a predetermined state, heat is minimally generated in the diode D 1  and the temperature of the diode D 1  begins to reduce. As such, according to these embodiments, heat generated in the diode D 1  is maintained at acceptable levels. Even when heat is generated in the diode D 1 , since the charge current I 1  supplied from the power generation module  110  is adjusted according to a temperature of the diode D 1 , problems caused by the heat generated in the diode D 1  are efficiently eliminated. 
       FIG. 7  is a flowchart illustrating a method of controlling the vehicle  10 , according to another embodiment. 
     In operation S 702 , the voltage Vbat of the battery cell  210  is measured while the battery pack  100   b  is operating. 
     In operation S 704 , it is determined whether the voltage Vbat of the battery cell  210  is equal to or less than the first reference voltage Vref. If it is determined in operation S 704  that the voltage Vbat of the battery cell  210  is equal to or less than the first reference voltage Vref, the method proceeds to operation S 706 . In operation S 706 , the bypass unit  410  is turned on and the charge current I 1  flows along the first charge path PATH 1 . 
     If it is determined in operation S 704  that the voltage Vbat of the battery cell  210  is greater than the first reference voltage Vref, the method proceeds to operation S 708 . In operation S 708 , the bypass unit  410  is turned off and the charge current I 1  flows along the second charge path PATH 2 . In operation S 710 , the BMS  230  monitors a temperature of the diode D 1 , for example, by using the temperature measuring unit  240 . In operation S 712 , it is determined whether the temperature of the diode D 1  is equal to or greater than the first reference temperature Td. If it is determined in operation S 712  that the temperature of the diode D 1  is equal to or greater than the first reference temperature Td, the method proceeds to operation S 714 . In operation S 714 , the BMS  230  reduces the charge current I 1  supplied from the power generation module  110 . 
     As described above, according to the one or more of the above embodiments, a vehicle and a method of controlling the same may protect a device and ensure reliability thereof if, for example, there is a difference between an output voltage of a power generation module of the vehicle and a rated voltage of a battery cell in a structure where the battery cell is supplied with a charge current from the power generation module. 
     While various inventive aspects have been particularly shown and described with reference to exemplary embodiments using specific terms, the embodiments and terms have been used to explain the present invention and should not be construed as limiting the scope of the present invention. The exemplary embodiments should be considered in a descriptive sense only and not for purposes of limitation.