Patent Publication Number: US-2022216702-A1

Title: Pre-charge circuit and battery system having the same

Description:
CROSS-REFERENCE WITH RELATED APPLICATION(S) 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2019-0130846 filed in the Korean Intellectual Property Office on 10/21/2019, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a pre-charge circuit and a battery system including the same. 
     BACKGROUND ART 
     Recently, research on high-performance rechargeable batteries has been actively conducted as a demand for portable electronic products such as laptops and portable telephones increases, and development of electric vehicles such as HEVs (hybrid electric vehicles) and PEVs (pure electric vehicles), robots, satellites, etc., has begun in earnest. 
     As rechargeable batteries, various rechargeable batteries such as nickel cadmium batteries and nickel hydrogen batteries are commercially available, but lithium rechargeable batteries that are free to charge and discharge and having low self-discharge rates and high energy density are in the spotlight. Rechargeable batteries are often used in a battery pack state in which a plurality of rechargeable batteries are connected in series and/or parallel to provide a high-voltage and large-capacity power storage device. 
     A main relay may control electrical connection between a battery pack and an external device (e.g., a load or a charger) using a predetermined electrical signal. In many cases, the main relay is damaged due to an overcurrent (surge current) occurring during an initial driving period during which the battery pack and an external device are connected, and a pre-charge relay is used in parallel with the main relay in order to prevent such damage. 
     Meanwhile, in the case of configuring a relay using a semiconductor switching element such as a metal-oxide field effect transistor (MOSFET), it must be switched to a predetermined state when a driving signal is received. However, the MOSFET used in the field often does not meet specifications of a standard breakdown voltage and an instantaneous allowable current due to various reasons such as a production process and storage conditions. MOSFETs that are out of the specifications of the standard breakdown voltage and the instantaneous allowable current will not function properly within the circuit. 
     For example, there are a pre-charge standard breakdown voltage and a pre-charge instantaneous allowable current required for the pre-charge relay, and the pre-charge relay may be configured with a plurality of MOSFETs in consideration of this. Actual performance of the MOSFET may not meet known specifications of the standard breakdown voltage and the instantaneous allowable current. In actual on/off control, the MOSFET is pointed out to have a problem because it cannot withstand the pre-charge standard breakdown voltage and the pre-charge instantaneous allowable current, and there is a possibility of a transient shock. 
     Disclosure 
     Technical Problem 
     The present invention has been made in an effort to provide a pre-charge circuit with a low possibility of causing a transient shock, and a battery system including the same. 
     Technical Solution 
     An exemplary embodiment of the present invention provides a pre-charge circuit, including: a first MOSFET and a second MOSFET connected in series between a first electrode of a battery pack and an output terminal thereof; a third MOSFET connected in parallel with the first MOSFET; and a fourth MOSFET connected in parallel with the second MOSFET. 
     The pre-charge circuit may further include: a first resistor connected in parallel with a first end of the first MOSFET and a first end of the third MOSFET, and a second end of the first MOSFET and a second end of the third MOSFET; and a second resistor connected in parallel with a first end of the second MOSFET and a first end of the fourth MOSFET and a second end of the second MOSFET and a second end of the fourth MOSFET. 
     The first MOSFET, the second MOSFET, the third MOSFET, and the fourth MOSFET may be formed as P-type MOSFETs. 
     A drain terminal of the first MOSFET may be connected in series with a source terminal of the second MOSFET, a drain terminal of the third MOSFET may be connected in parallel with the drain terminal of the first MOSFET, and a source terminal of the fourth MOSFET may be connected in parallel with the source terminal of the second MOSFET. 
     An exemplary embodiment of the present invention provides a battery system including: a battery pack configured to include a plurality of battery cells; a pre-charge relay configured to include a first MOSFET and a second MOSFET connected in series between a first electrode and an output terminal of the battery pack, a third MOSFET connected in parallel with the first MOSFET, and a fourth MOSFET connected in parallel with the second MOSFET; and a BMS configured to generate a gate voltage for controlling on and off of the relay. 
     The pre-charge relay may further include: a first resistor connected in parallel with a first end of the first MOSFET and a first end of the third MOSFET, and a second end of the first MOSFET and a second end of the third MOSFET; and a second resistor connected in parallel with a first end of the second MOSFET and a first end of the fourth MOSFET and a second end of the second MOSFET and a second end of the fourth MOSFET. 
     The first MOSFET, the second MOSFET, the third MOSFET, and the fourth MOSFET may be formed as P-type MOSFETs. 
     A drain terminal of the first MOSFET may be connected in series with a source terminal of the second MOSFET, a drain terminal of the third MOSFET may be connected in parallel with the drain terminal of the first MOSFET, and a source terminal of the fourth MOSFET may be connected in parallel with the source terminal of the second MOSFET. 
     The BMS may receive a high level driving signal and may generate the gate voltage of a ground level to apply it to the first MOSFET, the second MOSFET, the third MOSFET, and the fourth MOSFET. 
     The battery system may further include a main relay configured to control electrical connection between the battery pack and an external device, the pre-charge relay may be turned on first before the main relay is turned on, and the main relay may be turned on and may be turned off after a predetermined time elapses. 
     Advantageous Effects 
     The present invention has an effect of providing a pre-charge relay capable of exerting a function even when some of the MOSFETs are outside specifications of pre-charge breakdown voltage and current. 
     The present invention has an effect of providing a pre-charge relay having high stability by distributing shock applied to a plurality of MOSFETs by including resistors connected in parallel with the MOSFETs connected in series and/or parallel. 
     The present invention has an effect of reducing an area of the gate driving circuit and reducing a cost by implementing a gate driving circuit in the form of a low side driver (LSD). 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a block diagram showing a battery system according to an exemplary embodiment. 
         FIG. 2  illustrates a circuit diagram for describing a BMS and a pre-charge relay of  FIG. 1 . 
     
    
    
     MODE FOR INVENTION 
     Hereinafter, exemplary 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 a repeated description thereof will be omitted. Terms “module” and/or “unit” for components used in the following description are used only in order to easily describe the specification. Therefore, these terms do not have meanings or roles that distinguish them from each other in and of themselves. In describing exemplary 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. The accompanying drawings are provided only in order to allow exemplary 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 to be 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 the other component or be connected or coupled to the other component with a further 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 the other component without another component intervening therebetween. 
     It will be further understood that terms “comprise” or “have” used in the present specification specifies the presence of stated features, numerals, steps, operations, components, parts, or a combination thereof, but does not preclude the presence or addition of one or more other features, numerals, steps, operations, components, parts, or a combination thereof. 
       FIG. 1  illustrates a block diagram showing a battery system according to an exemplary embodiment, and  FIG. 2  illustrates a circuit diagram for describing a BMS and a pre-charge relay of  FIG. 1 . 
     As illustrated in  FIG. 1 , the battery system  1  includes a battery pack  10 , a BMS  20 , and a relay  30 . 
     The battery pack  10  may supply necessary power by connecting a plurality of battery cells in series and/or parallel. In  FIG. 1 , the battery pack  10  includes a plurality of battery cells connected in series, is connected between two output terminals OUT 1  and OUT 2  of the battery system  1 , and the relay  30  is connected between a positive electrode of the battery system  1  and the output terminal OUT 1 . The constituent elements illustrated in  FIG. 1  and a connection relationship between the constituent elements are examples, and the present invention is not limited thereto. 
     The BMS  20  generates gate voltages VG 1  and VG 2  for controlling on/off of the relay  30  including a gate driving circuit  21 . In  FIG. 1 , the BMS  20  is illustrated to include the gate driving circuit  21 , but the present invention is not limited thereto, and the gate driving circuit  21  may be configured independently of the BMS  20 . 
     Referring to  FIG. 2 , the gate drive circuit  21  may include a driving transistor TR. A base terminal of the driving transistor TR may receive a driving signal CS, and a collector terminal thereof may be connected to gate terminals of first, second, third, and fourth MOSFETs Q 1 , Q 2 , Q 3 , and Q 4 . The driving transistor TR, which is an NPN type of transistor, is turned on by a high-level driving signal CS and is turned off by a low-level driving signal CS. When the driving transistor TR is turned off, the gate driving circuit  21  applies a positive driving voltage VB capable of turning off a P-type MOSFET to first, second, third, and fourth MOSFETs Q 1 , Q 2 , Q 3 , and Q 4 . 
     The relay  30  may include a main relay  31  and a pre-charge relay  33  connected in parallel with the main relay  31 . The relay  30  may be configured as an electronic relay including a semiconductor switching element. The semiconductor switching element may be a metal-oxide field effect transistor (MOSFET), but the present invention is not limited thereto. 
     The main relay  31  may be implemented as a MOSFET to be switched depending on a first gate voltage VG 1  received from the BMS  20 . The main relay  31  controls electrical connection between the battery system  1  and an external device (e.g., a load, charger). When the main relay  31  is turned on by the first gate voltage VG 1  of an on level, the battery system  1  and the external device are electrically connected to perform charging or discharging. For example, when the external device is a load, a discharging operation in which power is supplied from the battery pack  10  to the load is performed, and when the external device is a charger, a charging operation in which the battery pack  10  is charged by the charger may be performed. When the main relay  31  is turned off by the first gate voltage VG 1  of an off level, the battery system  1  and the external device are electrically separated from each other. 
     The pre-charge relay  33  may be implemented as a MOSFET to be switched depending on the second gate voltage VG 2  received from the BMS  20 , and may be connected in series with a pre-charge resistor RC. The pre-charge relay  33  may reduce a surge current, generated when the battery pack  10  is connected to an external device (for example, at the beginning of driving for charging or discharging), to prevent damage to the main relay  31  due to the surge current. For example, the pre-charge relay  33  may be turned on first before the main relay  31  is turned on, and the main relay  31  may be turned on and then turned off after a predetermined time elapses, thereby reducing the surge current. 
     Referring to  FIG. 2 , the pre-charge relay  33  includes the first, second, third, and fourth MOSFETs Q 1 , Q 2 , Q 3 , and Q 4  and first and second resistors R 1  and R 2  connected in series and/or parallel. 
     The first MOSFET Q 1  and the second MOSFET Q 2  are connected in series between a first electrode and an output terminal of the battery pack  10 , the third MOSFET Q 3  is connected in parallel with the first MOSFET Q 1 , and the fourth MOSFET Q 4  is connected in parallel with the second MOSFET Q 2 . The first resistor R 1  is connected in parallel with a first end of the first MOSFET Q 1  and a first end of the third MOSFET Q 3 , and a second end of the first MOSFET Q 1  and a second end of the third MOSFET Q 3 . The second resistor R 2  is connected in parallel with a first end of second MOSFET Q 2 , a first end of the fourth MOSFET Q 4 , and a second end of the second MOSFET Q 2  and a second end of the fourth MOSFET Q 4 . In  FIG. 2 , the first, second, third, and fourth MOSFETs Q 1 , Q 2 , Q 3 , and Q 4  are illustrated as P-type MOSFETs, but are not limited thereto, and may be implemented as other transistors that perform switching operations, such as N-type MOSFETs, BJTs, and IGBTs. 
     As illustrated in  FIG. 2 , contacts N 1 , N 2 , N 3 , and N 4  are illustrated to describe a connection relationship between the first, second, third, and fourth MOSFETs Q 1 , Q 2 , Q 3 , and Q 4  and the first and second resistors R 1  and R 2 . The first node N 1  is connected to a positive terminal of the battery pack  10 , and the fourth node N 4  is connected to the output terminal OUT 1  illustrated in  FIG. 1 . 
     For example, a source terminal of the first MOSFET Q 1  and a source terminal of the third MOSFET Q 3  are connected to the first node N 1 , and a drain terminal of the first MOSFET Q 1  and a drain terminal of the third MOSFET Q 3  are connected to the second node N 2 . A first end of the first resistor R 1  is connected to the first node N 1 , and a second end thereof is connected to the second node N 2 . A source terminal of the second MOSFET Q 2  and a source terminal of the fourth MOSFET Q 4  are connected to the third node N 3 , and a drain terminal of the second MOSFET Q 2  and a drain terminal of the fourth 
     MOSFET Q 4  are connected to the fourth node N 4 . A first end of the second resistor R 2  is connected to the third node N 3 , and a second end thereof is connected to the fourth node N 4 . Gate terminals of the first, second, third, and fourth MOSFETs Q 1 , Q 2 , Q 3 , and Q 4  may all be connected to the collector terminal of the driving transistor TR, to be turned on or off in synchronization with the second gate voltage VG 2 . 
     The first, second, third, and fourth MOSFETs Q 1 , Q 2 , Q 3 , and Q 4  may be turned on in synchronization with the second gate voltage VG 2  of an on level. For example, when a base terminal of the driving transistor TR receives the high-level driving signal CS to be turned on, a collector terminal of the driving transistor TR is connected to a ground GND. A voltage of the ground GND is applied to the gate terminals of the first, second, third, and fourth MOSFETs Q 1 , Q 2 , Q 3 , and Q 4  connected to the collector terminal of the driving transistor TR, and all of them are turned on. Herein, the gate driving circuit  21  may be implemented in the form of a low side driver (LSD) driven by connecting the first, second, third, and fourth MOSFETs Q 1 , Q 2 , Q 3 , and Q 4  to the ground GND. 
     The first, second, third, and fourth MOSFETs Q 1 , Q 2 , Q 3 , and Q 4  may be turned off in synchronization with the second gate voltage VG 2  of an off level. For example, when the base terminal of the driving transistor TR receives the low-level driving signal CS, it is turned off, and the gate terminals of the first, second, third, and fourth MOSFETs Q 1 , Q 2 , Q 3 , and Q 4  are all turned off by applying a positive driving voltage VB thereto. 
     Ideally, the first, second, third, and fourth MOSFETs Q 1 , Q 2 , Q 3 , and Q 4  may be turned on in synchronization with the second gate voltage of an on level. However, a time difference may occur between actual turn-on times between the first, second, third, and fourth MOSFETs Q 1 , Q 2 , Q 3 , and Q 4 . In this case, an excessive voltage may be applied to the MOSFET that is turned on later. 
     For example, the pre-charge relay  33  may include the first, second, third, and fourth MOSFETs Q 1 , Q 2 , Q 3 , and Q 4  connected in series and/or parallel without the first resistor R 1  and the second resistor R 2 . In this case, when the third MOSFET Q 3  is turned on later than the remaining first, second, and fourth MOSFETs Q 1 , Q 2 , and Q 4 , an excessive voltage may be applied to opposite ends of the third MOSFET Q 3 , resulting in shock, during a period corresponding to a difference in turn-on times between the third MOSFET Q 3  and the remaining first, second, and fourth MOSFETs Q 1 , Q 2 , and Q 4 . Then, the third MOSFET Q 3  may be damaged. 
     In order to prevent the above phenomenon, the first resistor R 1  may be connected in parallel with the first MOSFET Q 1  and the third MOSFET Q 3 , and the second resistor may be connected in parallel with the second MOSFET Q 2  and the fourth MOSFET Q 4 . That is, even when transient shock exceeding limit specifications of the first MOSFET Q 1  and the third MOSFET Q 3  occurs at the beginning of driving, the first resistor R 2  may prevent damage to the first MOSFET Q 1  and the third MOSFET Q 3  by distributing the transient shock. Even when transient shock exceeding limit specifications of the second MOSFET Q 2  and the fourth MOSFET Q 4  occurs at the beginning of driving, the second resistor R 2  may prevent damage to the second MOSFET Q 2  and the fourth MOSFET Q 4  by distributing the transient shock. 
     In an exemplary embodiment, since the first resistor R 1  and the second resistor R 2  are connected in series between the battery pack  10  and the external device, there is a possibility that a leakage current occurs. To prevent this possibility, the first resistor R 1  and the second resistor R 2  are formed as resistors having very large resistance values. For example, the resistance values of the first resistor R 1  and the second resistor R 2  may be at least several mega-ohms (M) or more. Then, substantially no leakage current is generated between the battery pack  10  and the external device regardless of switching states of the pre-charge relay  33  and the main relay  31 . 
     While this invention has been described in connection with what is presently considered to be practical 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.