Abstract:
The present invention provides a temperature controlling system for a battery in an energy storage system, the temperature controlling system including: a converter comprising a plurality of switches and a converter inductor, the converter being configured to increase or decrease a voltage of the battery; a DC linker comprising first and second capacitors that are coupled in series and configured to stabilize an output voltage of the converter; and an inverter comprising a plurality of switches and an inductor, the inverter being configured to invert an input voltage, wherein the inverter further comprises a switch coupled between a terminal of the inductor and a first node between the first and second capacitors of the DC linker to provide a current from the inductor to the battery.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2013-0005046, filed on Jan. 16, 2013, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Aspects of the present invention relates to a temperature controlling system and method for a battery. 
     2. Description of the Related Art 
     Concerns over environmental disruption, and the depletion of natural resources have given rise to an interest in electric power systems capable of efficiently storing and providing electric power. In addition, in recent years, there has been increased interest in developing electric power systems that utilize renewable energy sources (e.g., sunlight, wind power, or tidal power) as sources of electric power, which may provide a nearly infinite supply of power while reducing reliance on finite natural resources as sources for electric power. Furthermore, generating electricity from renewable energy sources may significantly reduce harmful impacts on the environment. 
     An energy storage system is a system that couples a renewable energy source, a power storing battery, and existing power from a grid, and much research has been conducted on such systems in order to reduce or minimize harmful effects on the environment. 
     The battery provided in the energy storage system is implemented as a rechargeable secondary battery. The battery functions normally at normal operating temperatures, but the power output of the battery operating at very low temperatures (e.g., −20° C. or less) is only about 16% of that of the battery at normal operating temperatures. 
     One method for improving power output of the battery at very low temperatures is to use a heater or heat generated by a resistor or electronic load so as to increase the temperature of a battery. 
     However, as the power of the battery is consumed, the use rate of the battery is lowered, and applying heat to the battery may increase the risk of a fire. 
     SUMMARY 
     Embodiments of the present invention provide a battery temperature controlling system, in which a switch is additionally configured in an energy storage system, so that the charging/discharging current path to the battery is controlled, thereby controlling the temperature of the battery. 
     Embodiments of the present invention also provide a method for controlling a temperature of a battery, in which when the low-temperature state of the battery is sensed in the operation of an energy storage system, the coupling to a grid is cut off, and charging/discharging current is generated in the battery using an inductor of an inverter, thereby increasing the temperature of the battery 
     According to one embodiment of the present invention, there is provided a temperature controlling system for a battery in an energy storage system, the temperature controlling system including: a converter including a plurality of switches and a converter inductor, the converter being configured to increase or decrease a voltage of the battery; a DC linker including first and second capacitors that are coupled in series and configured to stabilize an output voltage of the converter; and an inverter including a plurality of switches and an inductor, the inverter being configured to invert an input voltage, wherein the inverter further comprises a switch coupled between a terminal of the inductor and a first node between the first and second capacitors of the DC linker to provide a current from the inductor to the battery. 
     The converter may include the converter inductor coupled to a first terminal of the battery; a first switch coupled between a first terminal of the first capacitor of the DC linker and a second terminal of the converter inductor; and a second switch coupled between the second terminal of the converter inductor and a second terminal of the battery. 
     The temperature controlling system may further include a third switch coupled between the first terminal of the battery and the first terminal of the first capacitor of the DC linker. 
     The switches of the inverter may be implemented in a half-bridge structure. 
     The switches of the half-bridge structure may include a first switch coupled between a first terminal of the first capacitor of the DC linker and a first terminal of the inductor; and a second switch coupled between the first terminal of the inductor and a second terminal of the battery. 
     The inductor may be coupled between a second node between the first and second switches and a first switch of a load linker, the load linker being configured to control a linkage between the energy storage system and a load. 
     The temperature controlling system may further include a third switch coupled between a second terminal of the inductor and the first node between the first and second capacitors of the DC linker. 
     According to another embodiment of the present invention, there is provided a temperature controlling method for a battery provided in an energy storage system, including: sensing a low-temperature state of the battery being maintained for a period of time; removing a coupling between a grid and a load from the energy storage system in response to the low-temperature state of the battery being maintained for the period of time; forming a charging/discharging current path through which current generated in an inductor is provided to the battery; and repetitively performing a charging/discharging operation of the battery through the charging/discharging current path by alternately operating a plurality of switches of an inverter. 
     The temperature controlling method may further include coupling the energy storage system to the load and the grid after the temperature of the battery reaches a normal temperature range and blocking the formed charging/discharging current path. 
     The plurality of switches of the inverter may be implemented in a half-bridge structure. 
     As described above, according to the present invention, the charging/discharging current path of the battery is controlled by adding a switch to the energy storage system, so that it is possible to prevent the battery provided in the energy storage system from being left in a low-temperature state without implementing a complicated circuit so as to increase the temperature of the battery. 
     Further, it is possible to easily implement the conversion between a basic operation of the energy storage system and an operation for controlling the temperature of the battery. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, together with the specification, illustrate exemplary embodiments of the present invention, and, together with the description, serve to explain the principles of the embodiments of the present invention. 
         FIG. 1  is a block diagram illustrating an energy storage system including a temperature controlling system of a battery according to an embodiment of the present invention. 
         FIG. 2  is a circuit diagram illustrating an embodiment of the temperature controlling system shown in  FIG. 1 . 
         FIGS. 3A and 3B  are circuit diagrams illustrating an operation of the temperature controlling system according to an embodiment of the present invention. 
         FIGS. 4A and 4B  are circuit diagrams illustrating an operation of the temperature controlling system according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, certain exemplary embodiments according to the present invention will be described with reference to the accompanying drawings. Here, when a first element is described as being coupled to a second element, the first element may be not only directly coupled to the second element but may also be indirectly coupled to the second element via a third element. Further, some of the elements that are not essential to the complete understanding of the invention are omitted for clarity. Also, like reference numerals refer to like elements throughout. 
       FIG. 1  is a block diagram illustrating an energy storage system including a temperature controlling system of a battery according to an embodiment of the present invention. 
     That is, as shown in  FIG. 1 , the temperature controlling system according to this embodiment is a configuration included in an energy storage system. The temperature controlling system prevents or reduces the battery provided in the energy storage system from being left in a low-temperature state, and performs an operation of increasing the temperature of the battery in the low-temperature state. 
     Referring to  FIG. 1 , the energy storage system  100  according to this embodiment supplies electric power to a load  2  in linkage with a power generation system  3  and a grid  1 . 
     The power generation system  3  is a system that generates electric power using an energy source, e.g., a renewable energy source. The power generation system  3  supplies the generated electric power to the energy storage system  100 . The power generation system  3  may be any suitable power generation system, including a renewable energy power generation system, such as a solar power generation system, a wind power generation system, a tidal power generation system, or the like. In addition, the power generation system  3  may include all power generation systems that generate electric power using renewable energy such as solar heat or subterranean heat. 
     Particularly, solar cells that generate electrical energy using sunlight are relatively easily installed in homes or factories, and thus it is suitable to apply the electrical power generated by solar cells installed in homes to the energy storage system  100 . The power generation system  3  has a plurality of power generation modules coupled in parallel and generates electric power for each power generation module, thereby constituting a large-capacity energy system. 
     The grid  1  includes power stations, transformer substations, power transmission lines, and the like. In a case where the grid  1  is in a normal state, the grid  1  supplies electric power to the energy storage system  100  or the load  2 , and receives electric power supplied from the energy storage system  100 . In a case where the grid  1  is in an abnormal state, the supply of the electric power from the grid  1  to the energy storage system  100  or the load  2  is stopped, and the supply of the electric power from the energy storage system  100  to the grid  1  is also stopped. 
     The load  2  consumes electric power generated from the power generation system  3 , electric power stored in a battery  60  within the energy storage system  100 , or electric power supplied from the grid  1 . For example, the load  2  may be a home, a factory, or the like. 
     The energy storage system  100  stores the electric power generated in the power generation system  3  in the internal battery  60 , and may transmit the generated electric power to the grid  1 . The energy storage system  100  may transmit the electric power stored in the battery  60  to the grid  1  or may store the electric power supplied from the grid  1  in the battery  60 . The energy storage system  100  may supply electric power to the load  2  by performing an uninterruptible power supply (UPS) operation in an abnormal situation, e.g., when a power failure of the grid  1  occurs. Additionally, the energy storage system  100  may supply, to the load  2 , the electric power generated in the power generation system  3  or the power stored in the battery  60 , even in a state in which the grid  1  is operating normally. 
     The energy storage system  100  includes a power converter  10 , a DC linker  20 , an inverter  30 , a converter  50 , a battery and battery management system (BMS)  60 , a grid linker  40 , a load linker  70  and a controller  80 . The inverter  30  and the converter  50  may be implemented as a bidirectional inverter  30  and a bidirectional converter  50 , respectively. 
     The power converter  10  is coupled between the power generation system  3  and a first node N 1 , and functions to converts the electric power generated in the power generation system  3  into a DC voltage at the first node N 1 . The operation of the power converter  10  is changed depending on the electric power generated in the power generation system  3 . For example, in a case where the power generation system  3  generates an AC voltage, the power converter  10  converts the AC voltage into the DC voltage at the first node N 1 . In a case where the power generation system  3  generates a DC voltage, the power converter  10  boosts or drops the DC voltage to a second DC voltage level at the first node N 1 . 
     For example, in a case where the power generation system  3  is a solar generation system, the power converter  10  may be a maximum power point tracking (MPPT) converter that detects the maximum power point according to a change in the amount of sunlight or a change in the temperature of solar heat and generates electric power. In addition, various kinds of converters or rectifiers may be used as the power converter  10 . 
     The DC linker  20  is coupled between the first node N 1  and the bidirectional inverter  30  so as to constantly maintain a DC link voltage Vlink at the first node N 1 . The voltage level at the first node N 1  may be unstable due to substantially instantaneous voltage drops of the power generation system  3  or the grid  1 , the occurrence of a peak load in the load  2 , etc. However, the voltage at the first node N 1  is necessarily maintained substantially constant so that the bidirectional inverter  30  and the bidirectional converter  50  are stably operated. To this end, the DC linker  20  may use, for example, a capacitor such as an electrolytic capacitor, polymer capacitor, or multi-layer ceramic capacitor (MLCC). 
     The battery  60  receives electric power generated in the power generation system  3  or electric power supplied from the grid  1 , stores the received electric power, and supplies the stored electric power to the load  2  or the grid  1 . The battery  60  may include at least one battery cell, and each battery cell may include a plurality of bare cells. The battery  60  may be implemented with various kinds of battery cells. For example, the battery  60  may be a nickel-cadmium battery, lead storage battery, nickel metal hydride battery (NiMH), lithium ion battery, lithium polymer battery, etc. 
     The BMS is coupled to the battery  60 , and controls charging and discharging operations of the battery  60  under the control of the controller  80 . The BMS may perform an overcharging protection function, an over-discharging protection function, an overcurrent protection function, an overheating protection function, a cell balancing function, etc. so as to protect the battery  60 . To this end, the BMS may monitor voltage, current, temperature, remaining power amount, lifespan and charging state of the battery  60  and transmit relevant information to the controller  80 . Although it has been described in the embodiment of  FIG. 1  that the BMS is configured as a battery pack integrated with the battery  60 , the BMS may be provided to be separated from the battery  60 . 
     The converter  50  DC-DC converts the voltage of power output from the battery  60  into a voltage level required in the inverter  30 , i.e., the DC link voltage Vlink. The converter  50  also DC-DC converts a charging power flowing through the first node N 1  into a voltage level required in the battery  60 . Here, the charging power refers to, for example, electric power generated in the power generation system  3  or electric power supplied from the grid  1  through the inverter  30 . 
     The inverter  30  is a power converter provided between the first node N 1  and a second node N 2 . The load  2  and the grid linker  40  are also coupled to the second node N 2 . The inverter  30  converts the DC link voltage Vlink output from the power generation system or the battery  60  into an AC voltage and outputs the converted AC voltage. In order to store the power output from the grid  1  in the battery  60 , the inverter  30  rectifies the AC voltage, converts the rectified AC voltage into the DC link voltage Vlink and outputs the converted DC link voltage Vlink. The inverter  30  may include a filter for removing harmonics from the AC voltage output from the grid  1 . The inverter  30  may include a phase locked loop (PLL) circuit for synchronizing the phase of the AC voltage output from the inverter  30  and the phase of the AC voltage output from the grid  1  in order to prevent the generation of reactive power. In addition, the inverter  30  may perform functions such as limitation of voltage variation ranges, improvement of power factors, removal of DC components, protection of transient phenomena, etc. 
     The grid linker  40  is coupled between the grid  1  and the inverter  30 . In a case where an abnormal situation occurs in the grid  1 , the grid linker  40  intercepts the link between the energy storage system  100  and the grid  1  under the control of the controller  80 . The grid linker  40  may be implemented as a switching element, and the switching element may be a bipolar junction transistor (BJT), field effect transistor (FET), etc. 
     The load linker  70  is coupled between the inverter  30  and the load  2 . The load linker  70  is also coupled in series to the grid linker  40 , and cuts off electric power flowing into the load  2  under the control of the controller  80 . The load linker  70  may also be implemented as a switching element, and the switching element may be a BJT, FET, etc. 
     In this embodiment, the battery  60 , the converter  50 , the DC linker  20 , and the inverter  30  among the components of the energy storage system  100  constitute a temperature controlling system  200  of the battery  60 . 
     That is, in this embodiment, a switch is added to the inverter  30  so as to regulate the path of charging/discharging current to the battery  60 , thereby controlling the temperature of the battery  60 . 
     Accordingly, if the controller  80  detects that the low-temperature state of the battery  60  is maintained for a certain period of time during the operation of the energy storage system  100 , the controller  80  performs an operation of increasing the temperature of the battery  60  by cutting off the coupling between the grid  1  and the load  2  and generating charging/discharging current to the battery  60  using an inductor (shown, e.g., in  FIG. 2 ) of the inverter  30  at the output terminal of the energy storage system  100 . 
     In this embodiment, in addition to the switch added to the inverter  30 , a switch may be further added to the converter  50 , and the operations of the added switches are controlled by the controller  80 . 
     The configuration and operation of the temperature controlling system  200  according to this embodiment will be described in detail with reference to  FIGS. 2 and 3 . 
       FIG. 2  is a circuit diagram illustrating an embodiment of the temperature controlling system shown in  FIG. 1 . 
     Referring to  FIG. 2 , the temperature controlling system  200  according to this embodiment is configured with the battery  60 , the converter  50 , and the DC linker  20  and the inverter  30  among the components of the energy storage system shown in  FIG. 1 . The load linker  70  and the load  2 , coupled to the temperature controlling system  200 , the grid linker  40  and the grid  1  are shown in  FIG. 2 . 
     Although only the battery  60  is shown in  FIG. 2  for convenience of illustration, the BMS may be included in the battery  60 . 
     The converter  50 , as shown in  FIG. 2 , is configured with first and second switches  52  and  53  and one converter inductor L 1   51  so as to perform a bidirectional converting operation. In addition, the converter  50  is configured with a third switch  54  coupled in parallel to the converter inductor L 1   51 , thereby forming a charging/discharging current path immediately to the battery  60  without passing through the converter inductor L 1   51 . 
     The converter inductor L 1   51  may be implemented as a coil as shown in  FIG. 2 . The converter inductor L 1   51  includes a first terminal coupled to a first terminal (+) of the battery  60 , and a second terminal coupled to a node n 1  between the first and second switches  52  and  53 . 
     The first switch  52  is coupled between a first terminal of a first capacitor C 1  included in the DC linker  20  and the second terminal of the converter inductor L 1   51 . That is, a first terminal of the first switch  52  is coupled to the first terminal of the first capacitor C 1 , and a second terminal of the first switch  52  is coupled to the second terminal of the converter inductor L 1   51 . 
     The second switch  53  is coupled between the second terminal of the converter inductor L 1   51 , a second terminal of a second capacitor C 2  included in the DC linker  20 , and a second terminal (−) of the battery  60 . That is, a first terminal of the second switch  53  is coupled to the second terminal of the converter inductor L 1   51 , and a second terminal of the second switch  53  is coupled to the second terminal of the second capacitor C 2  and the second terminal (−) of the battery  60 . 
     The first or second switch  52  or  53  may be implemented, for example, as an insulated gate bipolar transistor (IGBT) or MOSFET switch. In addition, any suitable switching element capable of performing the switching function may be used as the first or second switch  52  or  53 . In a case where the first or second switch  52  or  53  is a MOSFET switch, the first terminal of the switch  52  or  53  may be a source terminal, and the second terminal of the switch  52  or  53  may be a drain terminal. 
     The converter  50  configured as described above may perform an operation of the bidirectional converter that acts as a boost converter boosting the voltage of input power or a buck converter dropping the voltage of input power. 
     The converter  50  according to this embodiment performs a general bidirectional converting operation, and is configured with the third switch  54  coupled in parallel to the converter inductor L 1   51  so as to form the charging/discharging current path to (e.g., immediately to) the battery  60  without passing through the converter inductor L 1   51 . 
     That is, the converter  50 , as shown in  FIG. 2 , further includes the third switch  54  that couples the first terminal (+) of the battery  60  and the first terminal of the first capacitor C included in the DC linker  20 . 
     Thus, if the third switch  54  is turned on, the charging/discharging current path is formed immediately to the battery  60  without passing through the converter inductor L 1   51 . 
     In this case, the turn-on/off of the first to third switches  52 ,  53 , and  54  are controlled by the controller  80  shown in  FIG. 1 . 
     Next, a case where the inverter  30  is implemented in a half-bridge structure configured with two switches  31  and  32  as shown in  FIG. 2  will be described as an example. 
     The inverter  30  according to this embodiment is not limited thereto, and it will be apparent that the inverter  30  may be configured in a full-bridge or push-pull structure or may be configured with four or more switching elements. 
     More specifically, the inverter  30 , as shown in  FIG. 2 , is configured with the first and second switches  31  and  32  and one inductor (or inverter inductor) L 2   35  so as to perform a bidirectional inverting operation. In addition, the inverter  30  is configured with a third switch  37  coupling one terminal (e.g., the second terminal) of the inverter inductor L 2   35  to a node n 3  between the first and second capacitors C 1  and C 2  constituting the DC linker  20 , thereby generating charging/discharging current provided to the battery  60  using inverter conductor L 2   35 . 
     In this case, the inverter inductor L 2   35 , as shown in  FIG. 2 , may be implemented as a coil. The inverter inductor L 2   35  may include a first terminal coupled to a node n 2  between the first and second switches  31  and  32  that are switches of the half-bridge structure, and a second terminal coupled to a first terminal of the third switch  37 . 
     That is, if the third switch  37  is turned on, the second terminal of the inverter inductor L 2   35  is coupled to the node n 3  between the first and second capacitors C 1  and C 2  constituting the DC linker  20 . 
     Among the switches of the half-bridge structure, the first switch  31  is coupled between the first terminal of the first capacitor C 1  included in the DC linker  20  and the first terminal of the inverter inductor L 2   35 . That is, a first terminal of the first switch  31  is coupled to the first terminal of the first capacitor C 1 , and a second terminal of the first switch  31  is coupled to the first terminal of the inverter conductor L 2   35 . 
     The second switch  32  is coupled between the first terminal of the inverter inductor L 2   35 , the second terminal of the second capacitor C 2  included in the DC linker  20 , and the second terminal (−) of the battery  60 . That is, a first terminal of the second switch  32  is coupled to the first terminal of the inverter inductor L 2   35 , and a second terminal of the second switch  32  is coupled to the second terminal of the second capacitor C 2  and the second terminal (−) of the battery  60 . 
     The first or second switches  31  or  32  may be implemented as an insulated gate bipolar transistor (IGBT) or MOSFET switch. In addition, any suitable switching element capable of performing the switching function may be used as the first or second switch  31  or  32 . In a case where the first or second switch  31  or  32  is a MOSFET switch, the first terminal of the switch  31  or  32  may be a source terminal, and the second terminal of the switch  31  or  32  may be a drain terminal. 
     The inverter  30  configured as described above may perform a bidirectional inverting operation of converting DC voltage into AC voltage or rectifying AC voltage to DC voltage. 
     The inverter  30  according to this embodiment performs a general bidirectional inverting operation, and is further configured with the third switch  37  that couples the second terminal of the inverter inductor L 2   35  to the node n 3  between the first and second capacitors C 1  and C 2  constituting the DC liner  20  so as to generate charging/discharging current provided to the battery  60  using the inverter inductor L 2   35 . 
     That is, in the embodiment shown in  FIG. 2 , the third switch  37  is configured to couple the second terminal of the inverter inductor L 2   35  and the node n 3  between the first and second capacitors C 1  and C 2  constituting the DC linker  20 . 
     Thus, if the third switch  37  is turned on, the current generated in the inverter inductor L 2   35  can be provided to the battery  60  rather than the load  2  or the grid  1 . 
     To this end, switches  71  and  72  provided in the load linker  70  and switches  41  and  42  provided in the grid linker  40  are all turned off so that the voltage converted by the inverter  30  is not provided to the load  2  or the grid  1 . 
     In this case, the turn-on/off of the first to third switches  31 ,  32 , and  37  of the inverter  30  and the switches  41  and  42  provided in the grid linker  40  are controlled by the controller  80  shown in  FIG. 1 . 
     The operation of the temperature controlling system according to this embodiment is an operation corresponding to a case where the low-temperature state of the battery  60 , maintained for a certain period of time, is sensed by the controller  80  in the operation of the energy storage system  100 . 
     That is, since the controller  80  periodically receives information on the battery  60  through the BMS coupled to the battery  60 , the controller  80  can sense that the low-temperature state of the battery  60  is maintained for a certain period of time. 
     If the low-temperature state of the battery  60  is sensed by the controller  80 , the controller  80  controls the operation of the temperature controlling system  200  shown in  FIG. 2  so as to increase the temperature of the battery  60 . In this case, the basic operation of the energy storage system  100  is reserved until the battery  60  returns to a normal operating temperature. 
     During the period of controlling the temperature of the battery  60 , the controller  80  performs the operation of increasing the temperature of the battery  60  by cutting off the coupling between the grid  1  and the load  2  and allowing charging/discharging current to be generated in the battery  60  using the inverter inductor L 2   35  of the inverter  30  at the output terminal of the energy storage system  100 . 
     Referring to  FIGS. 1 and 2 , if the controller  80  senses the low-temperature state of the battery  60  through the BMS provided to the battery  60 , the controller  80  blocks the linkage (e.g., coupling) between the energy storage system  100  with the load  2  and the grid  1  by turning off the switches  71  and  72  of the load linker  70  and the switches  41  and  42  of the grid linker  40 . 
     The third switch  37  included in the inverter  30  is turned on, thereby coupling the second terminal of the inverter inductor L 2   35  provided in the inverter  30  to the node n 3  between the first and second capacitors C 1  and C 2  constituting the DC linker  20 . 
     The third switch  54  included in the converter  50  is turned on, thereby forming a current path so that the battery  60  is coupled to (e.g., directly to) the inverter  30  without passing through the converter inductor L 1   51  of the converter  50 . 
     Subsequently, the two switches of the half-bridge structure, provided in the inverter  30 , are alternately operated, thereby repetitively performing the charging/discharging operation of the battery. 
       FIGS. 3A and 3B  are circuit diagrams illustrating an operation of the temperature controlling system according to an embodiment of the present invention. 
     In the embodiment shown in  FIGS. 3A and 3B , the controller  80  first turns on the first switch  31  and turns off the second switch  32  among the switches included in the inverter  30 . 
     Referring to  FIG. 3A , if the controller  80  turns on the first switch  31  and turns on the second switch  32 , a discharging path is formed from the first terminal (+) of the battery  60  to the second terminal (−) of the battery  60  via the third switch  54  of the converter  50 , the first terminal of the first capacitor C 1  provided in the DC linker  20 , the first switch  31 , the inverter inductor L 2   35  and the third switch  37  of the inverter  30 , and the second capacitor C 2  of the DC linker  20 . 
     That is, according to  FIG. 3A , discharging current flows from the battery  60  through the discharging path. 
     Referring to  FIG. 3B , the controller  80  turns on the second switch  32  and turns off the first switch  31  among the switches included in the inverter  30 . 
     In this case, a charging path having the opposite direction to that of the discharging path of  FIG. 3A  is formed. Accordingly, the electric power stored in the inverter inductor L 2   35  of the inverter  30  is provided to the battery  60 , so that the battery  60  can be charged. 
     That is, according to  FIG. 3B , charging current flows into the battery  60  through the charging path. 
     The charging path, as shown in  FIG. 3B , is formed from the second terminal (−) of the battery  60  to the first terminal (+) of the battery  60  via the second switch  32 , the inverter inductor L 2   35  and the third switch  37  of the inverter  30 , the first capacitor C 1  provided in the DC linker  20 , and the third switch  54  of the converter  50 . 
       FIGS. 4A and 4B  are circuit diagrams illustrating an operation of the temperature controlling system according to an embodiment of the present invention. 
     In the embodiment shown in  FIGS. 4A and 4B , the controller  80  first turns on the second switch  32  and turns off the first switch  31  among the switches included in the inverter  30 . 
     Referring to  FIG. 4A , the controller  80  turns on the second switch  32  and turns off the first switch  31 , a discharging path is formed from the first terminal (+) of the battery  60  to the second terminal (−) of the battery  60  via the third switch  54  of the converter  50 , the first capacitor C 1  provided in the DC linker  20 , the third switch  37 , the inverter inductor L 2   35 , and the second switch  32  of the inverter  30 . 
     That is, according to  FIG. 4A , discharging current flows into the battery  60  through the discharging path. 
     Referring to  FIG. 4B , the controller  80  turns on the first switch  31  and turns off the second switch  32  among the switches included in the inverter  30 . 
     In this case, a charging path having the opposite direction to that of the discharging path of  FIG. 4A  is formed. Accordingly, the electric power stored in the inverter inductor L 2   35  of the inverter  30  is provided to the battery  60 , so that the battery  60  can be charged. 
     That is, according to  FIG. 4B , charging current flows into the battery  60  through the charging path. 
     The charging path, as shown in  FIG. 4B , is formed from the second terminal (−) of the battery  60  to the first terminal (+) of the battery  60  via the second capacitor C 2  provided in the DC linker  20 , the third switch  37 , the inverter inductor L 2   35  and the first switch  31  of the inverter, and the third switch  54  of the converter  50 . 
     As described above, in the battery controlling system according to this embodiment, the charging/discharging operation is repetitively performed by alternately operating the two switches of the half-bridge structure, provided in the inverter  30 . Although it has been described that the charging/discharging operation is divided into operations of  FIGS. 3A-3B and 4A-4B , the operations of  FIGS. 3A-3B and 4A-4B  may be sequentially repeated. 
     That is, the controller  80  may repetitively perform the operations of  FIGS. 3A to 4B , so that charging/discharging current repetitively flows into and out of the battery  60 . Thus, the temperature of the battery  60  is increased by the current. 
     Subsequently, if the temperature of the battery  60  reaches a normal temperature range, the controller  80  finishes the operation of the temperature controlling system according to this embodiment, and performs the basic operation of the energy storage system  100 . 
     That is, the energy storage system  100  is coupled to the load  2  and the grid  1  by turning on the switches  71  and  72  of the load linker  70  and the switches  41  and  42  of the grid linker  40 . 
     The third switch  37  included in the inverter  30  is turned off, thereby performing only the basic bidirectional inverting operation of the inverter  30 . Similarly, the third switch  54  included in the converter  50  is also turned off, thereby performing only the basic bidirectional converting operation of the converter  50 . That is, the charging/discharging current path formed in the operation of the temperature controlling system is blocked. 
     While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof.