Apparatus and method for detecting faults of battery heating system and relays

Abstract

Disclosed is a method and system for detecting faults of a battery heating system and relays. In particular, a method for detecting welding of each relay such as a main relay, a precharge relay or a heater relay and a method for detecting a fault of a battery heating system such as a short circuit, disconnection or damage of each heater are provided by sensing a voltage. In the methods, the on/off state of the heater relay and the high voltage relays is controlled through a predetermined process to detect a fault of the heater relay or the high voltage relay, and welding of the heater relay or the high voltage relay is then detected from a voltage for fault detection which is sensed through a voltage sensing circuit unit for fault detection.

Claims

1. An apparatus for detecting faults of a heater relay and high voltage relays in a battery heating system which includes a heater installed in each battery module of a battery pack to heat the battery module, the heater relay configured to selectively apply power to the heaters connected in series, and the high voltage relays of (+) and (−) power lines connected to the battery pack, the apparatus comprising: a voltage sensing circuit unit configured to detect a fault and configured to sense a voltage for fault detection when the faults of the heater relay and the high voltage relays are detected; and a battery management system (BMS) configured to operate the on/off of the heater relay and the high voltage relays and detect welding of the heater relay and the high voltage relays from the voltage for fault detection, wherein the BMS is configured to operate the off state of the heater relay when the (+) and (−) main relays among the high voltage relays are in the on state and when the precharge relay among the high voltage relays is in the off state, and then detect welding of the heater relay from the voltage for fault detection.

2. The apparatus of claim 1, wherein the voltage sensing circuit unit for fault detection is configured to sense a voltage for fault detection using a branch circuit branched from a connection circuit for connecting between two adjacent heaters connected in series.

3. The apparatus of claim 2, wherein, in the battery heating system including the heaters installed in the respective battery modules to be connected in series, the voltage sensing circuit unit for fault detection is connected to the branch circuit branched from the connection circuit having the same number of heaters at a front terminal thereof and the same number of heaters at a rear terminal thereof.

4. The apparatus of claim 2, wherein the voltage sensing circuit unit includes: a first resistor and a second resistor connected in series between the branch circuit and a ground terminal on the branch circuit; and a zener diode connected to both terminals of the second resistor, wherein a voltage at both the terminals of the second resistor is sensed as the voltage for fault detection.

5. The apparatus of claim 1, wherein the BMS is configured to operate a (−) main relay and the heater relay to be in the on state when the off state of a precharge relay and a (+) main relay among the high voltage relays is controlled, and detect welding of the precharge relay and the (+) main relay from the voltage for fault detection.

6. The apparatus of claim 1, wherein the BMS is configured to operate the off state of the (−) main relay when the (+) main relay and the heater relay among the high voltage relays are in the on state and when the precharge relay among the high voltage relays is in the off state, and detect welding of the (−) main relay from the voltage for fault detection.

7. A method for detecting faults of a heater relay and high voltage relays in a battery heating system which includes a heater installed in each battery module of a battery pack to heat the battery module, the heater relay configured to selectively apply power to the heaters connected in series, and the high voltage relays of (+) and (−) power lines connected to the battery pack, the method comprising: operating, by a controller, an on/off state of the heater relay and the high voltage relays through a predetermined process to detect a fault of the heater relay or the high voltage relay; and detecting, by the controller, welding of the heater relay or the high voltage relay from a voltage for fault detection which is sensed using a voltage sensing circuit unit for fault detection, wherein the off state of the heater relay is controlled when which the (+) and (−) main relays among the high voltage relays are in the on state and when the precharge relay among the high voltage relays is in the off state, and welding of the heater relay is then decided from the voltage for fault detection.

8. The method of claim 7, wherein the voltage sensing circuit unit for fault detection is configured to sense a voltage for fault detection using a branch circuit branched from a connection circuit for connecting between two adjacent heaters connected in series.

9. The method of claim 8, wherein, in the battery heating system including the heaters installed in the respective battery modules to be connected in series, the voltage sensing circuit unit for fault detection is connected to the branch circuit branched from the connection circuit having the same number of heaters at a front terminal thereof and the same number of heaters at a rear terminal thereof.

10. The method of claim 8, wherein the voltage sensing circuit unit includes: a first resistor and a second resistor connected in series between the branch circuit and a ground terminal on the branch circuit; and a zener diode connected to both terminals of the second resistor, wherein a voltage at both the terminals of the second resistor is sensed as the voltage for fault detection.

11. The method of claim 10, wherein the detection that welding of the precharge relay is detected when the voltage for fault detection is determined using Expression 1, and the detection that welding of the (+) main relay is detected when the voltage for fault detection is determined using Expression 2;
Sensing value=(voltage of battery pack or Σvoltages of battery cells)×((½×Σresistances of heaters)/(Σresistances of heaters+precharge resistance))×voltage division ratio of voltage sensing circuit for fault detection  Expression 1
Sensing value=(voltage of battery pack or Σvoltages of battery cells)×((½×Σresistances of heaters)/(Σresistances of heaters))×voltage division ratio of voltage sensing circuit for fault detection, and  Expression 2 wherein the voltage of the battery pack or ‘Σvoltages of battery cells’ is obtained from a sensing value of a battery voltage sensing circuit unit; ‘Σresistances of heaters’ is a sum of resistance values of all the heaters; the precharge resistance is the resistance value of a precharge resistor of a power relay assembly (PRA); and the voltage division ratio is a voltage distribution ratio by the first and second resistors, wherein the voltage sensing circuit unit for fault detection senses a voltage for fault detection through the branch circuit branched from the connection circuit for connecting between the two adjacent heaters connected in series, and wherein the voltage sensing circuit unit for fault detection is connected to the branch circuit branched from the connection circuit having the same number of heaters at a front terminal thereof and the same number of heaters at a rear terminal thereof.

12. The method of claim 10, wherein, when the voltage for fault detection is about ‘½×voltage of battery pack×voltage division ratio of voltage sensing circuit unit for fault detection’ when the (+) and (−) main relays are in the on state and when the heater relay is the on state, the heater is determined to be normal, and wherein the voltage of the battery pack is obtained from a sensing value of the battery voltage sensing circuit unit, the voltage division ratio is a voltage distribution ratio by the first and second resistors, and the voltage sensing circuit unit for fault detection is configured to sense a voltage for fault detection using the branch circuit branched from the connection circuit for connecting between the two adjacent heaters connected in series and is connected to the branch circuit branched from the connection circuit having the same number of heaters at a front terminal thereof and the same number of heaters at a rear terminal thereof.

13. The method of claim 12, wherein, when the voltage for fault detection satisfies the condition of Expression 3, a short circuit is determined of the heater positioned at the front end of a branch point at which the branch circuit is branched or a damage of the heater positioned at the rear end of the branch point is detected, wherein, when the voltage for fault detection satisfies the condition of Expression 4, a short circuit is determined of the heater positioned at the rear end of the branch point or a damage of the heater positioned at the front end of the branch point is detected, wherein, when the voltage for fault detection satisfies the condition of Expression 5, a disconnection is determined of the heater positioned at the rear end of the branch point is detected, wherein, when the voltage for fault detection satisfies the condition of Expression 6, a disconnection is determined of the heater positioned at the front end of the branch point is detected;
Sensing value>½×voltage of battery pack×voltage division ratio of voltage sensing circuit unit for fault detection  Expression 3
Sensing value<½×voltage of battery pack×voltage division ratio of voltage sensing circuit unit for fault detection  Expression 4
Sensing value=zener voltage  Expression 5
Sensing value=0, and  Expression 6 wherein the zener voltage is a zener voltage of the zener diode in the voltage sensing circuit unit for fault detection.

14. The method of claim 7, wherein a (−) main relay and the heater relay are in the on states when the off state of a precharge relay and a (+) main relay among the high voltage relays is controlled, and welding of the precharge relay and the (+) main relay is detected from the voltage for fault detection.

15. The method of claim 14, further comprising: determining, by the controller, that both the precharge relay and the (+) main relay are normal when the voltage for fault detection is about 0 V; and determining, by the controller, that any one of the precharge relay and the (+) main relay is in a welding state when the voltage for fault detection is greater than about 0 V.

16. The method of claim 7, wherein the off state of the (−) main relay is controlled, when the (+) main relay and the heater relay among the high voltage relays are in the on state and when the precharge relay among the high voltage relays is in the off state, and welding of the (−) main relay is detected from the voltage for fault detection.

17. The method of claim 16, further comprising: determining, by the controller, that the (−) main relay is normal when the voltage for fault detection is about 0 V; and determining, by the controller, that the (−) main relay is in the welding state when the voltage for fault detection is greater than about 0 V.

18. The method of claim 7, further comprising: determining, by the controller, that the heater relay is normal when the voltage for fault detection is about 0 V; and determining, by the controller, that the heater relay is in the welding state when the voltage for fault detection is greater than 0 V.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other features of the present invention will now be described in detail with reference to various exemplary embodiments thereof illustrated the accompanying drawings which are given hereinbelow by way of illustration only, and thus are not limitative of the present invention, and wherein:

(2) FIG. 1 illustrates a battery heating system in the related art;

(3) FIG. 2 illustrates a temperature sensor mounted in a battery pack in the related art;

(4) FIG. 3 shows an exemplary circuit diagram which includes an exemplary battery pack, an exemplary high voltage relays, an exemplary battery heating system, and an exemplary circuit configuration for detecting faults according to an exemplary embodiment of the present invention;

(5) FIG. 4 illustrates an exemplary method for detecting a fault according to an exemplary embodiment of the present invention;

(6) FIG. 5 illustrates exemplary on/off sequences of each relay to detect for welding of the relay according to an exemplary embodiment of the present invention;

(7) FIG. 6 illustrates that welding of each relay may be detected by identifying a voltage in a state in which the welding of the relay is made according to an exemplary embodiment of the present invention; and

(8) FIG. 7 illustrates an exemplary method for detecting a fault of the battery heating system depending on the kind of the fault according to an exemplary embodiment of the present invention.

(9) It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment. In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

(10) It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles.

(11) The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. 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,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

(12) Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about”.

(13) Although exemplary embodiment is described as using a plurality of units to perform the exemplary process, it is understood that the exemplary processes may also be performed by one or plurality of modules. Additionally, it is understood that the term controller refers to a hardware device that includes a memory and a processor. The memory is configured to store the modules and the processor is specifically configured to execute said modules to perform one or more processes which are described further below.

(14) Furthermore, control logic of the present invention may be embodied as non-transitory computer readable media on a computer readable medium containing executable program instructions executed by a processor, controller or the like. Examples of the computer readable mediums include, but are not limited to, ROM, RAM, compact disc (CD)-ROMs, magnetic tapes, floppy disks, flash drives, smart cards and optical data storage devices. The computer readable recording medium can also be distributed in network coupled computer systems so that the computer readable media is stored and executed in a distributed fashion, e.g., by a telematics server or a Controller Area Network (CAN).

(15) Hereinafter reference will now be made in detail to various exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings and described below. While the invention will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention to those exemplary embodiments. On the contrary, the invention is intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims.

(16) The present invention provides a method of detecting welding of each relay. The detected welding of each relay may be, but not limited to, a main relay, a precharge relay or a heater relay. The present invention also provides a method of detecting a fault of a battery heating system. The detected fault may be, but not limited to, a short circuit, disconnection or damage of each heater. In particular, the methods may be obtained by simply sensing a voltage. As used herein, the heater refers to a heater constituting the battery heating system, and refers to a resistance heater, for example, a PTC planar heater, installed in each battery module to raise the temperature of the corresponding battery module. In the battery heating system, the resistance heaters may be connected in series to be connected to the battery pack as of a power source through the heater relay. Accordingly, as the on/off state of the heater relay is controlled, all the resistance heaters may be collectively on or off state (FIG. 3).

(17) FIG. 3 is an exemplary circuit diagram illustrating a battery pack, high voltage relays, a battery heating system, and a circuit configuration for detecting faults according to an exemplary embodiment of the present invention. FIG. 4 is a flowchart illustrating an exemplary method for detecting a fault according to an exemplary embodiment of the present invention. FIG. 5 illustrates exemplary on/off sequences of each relay to detect welding of the relay according to an exemplary embodiment of the present invention. FIG. 6 shows exemplary diagrams illustrating that welding of each relay may be detected by identifying a voltage when the welding of the relay is made. FIG. 7 shows an exemplary diagram illustrating an exemplary method for detecting a fault of the battery heating system depending on a type of the fault.

(18) As shown in FIG. 3, a battery pack 10 may include a plurality of battery modules 11; a power relay assembly (PRA) including high voltage relays 21, 22 and 23 of (+) and (−) power lines connected to the battery pack 10; a heater relay 25 configured to open and close a heater power source; a heater 12 configured to increase or raise temperature and installed in each battery module 11; a battery voltage sensing circuit unit 31 configured to sense a voltage for each battery module or battery cell; a voltage sensing circuit unit 32 configured to detect fault and detect faults of the battery heating system and the relays; and a battery management system (BMS) 30 configured to operate the on/off state of the heater relay 25 and the high voltage relays 21, 22 and 23. In particular, a controller of BMS 30 may be configured to detect welding of the heater relay 25 and the high voltage relays 21, 22 and 23 from a voltage sensed by the voltage sensing circuit unit 32 of fault detection.

(19) The PRA may include (+) and (−) main relays 21 and 22 respectively connected to the (+) and (−) power lines, and a precharge relay 23 and a precharge resistor 24, disposed on a circuit bypassing the (+) main relay 21. The battery voltage sensing circuit unit 31 may be configured to measure a voltage of each battery module 11 or a voltage of each battery cell. An example of the battery voltage sensing circuit unit 31 measuring a voltage of each battery cell is also illustrated in the circuit configuration of FIG. 3.

(20) The voltage sensing circuit unit 32 for fault detection may be configured to branch a connection circuit for connecting between two adjacent heaters 12 connected in series at any one position 13 and may be configured to sense a voltage for fault detection through the branched circuit 14. In particular, in the battery heating system including a plurality of heaters 12 installed in the respective battery modules 11 connected in series, a voltage for fault detection may be sensed using the branch circuit 14 connected at the position 13 of the connection circuit having the same number of heaters at a front terminal thereof and the same number of heaters at a rear terminal thereof.

(21) The voltage sensing circuit unit 32 for fault detection, as shown in FIGS. 6 and 7, may include a first resistor 33 and a second resistor 34 both of which are connected in series between the branch circuit 14 and a ground terminal on the branch circuit 14 and a zener diode 35 connected to both terminals of the second resistor 34 connected to the ground terminal. In particular, the voltage sensing circuit unit 32 may have a configuration such that a voltage applied to both the terminals of the second resistor 34 may be sensed as the voltage for fault detection.

(22) As shown in FIG. 3, the voltage sensing circuit unit 32 requiring ground connection may be included in the battery voltage sensing circuit unit 31 at the most rear terminal, which may have a common ground terminal GND with the other battery voltage sensing circuit unit 31. In addition, a microcomputer (MICOM) 36 of the BMS 30 may be configured to recognize faults of the battery heating system and the relays and other faults from a signal transmitted via the battery voltage sensing circuit unit 31 at the most rear terminal via the voltage sensing circuit unit 32 for fault detection.

(23) The method for detecting a fault will be described with reference to FIGS. 4 to 7. The detection of welding of the precharge relay 23 and the (+) main relay 21 may be performed by operating the BMS 30 to turn on the (−) main relay 22 and the heater relay 25 when the off state of the precharge relay 23 and the (+) main relay 21 is controlled, for example, when the off state of the precharge relay 23 and the (+) main relay 21 is controlled in an IG-ON process, and subsequently by sensing a voltage for fault detection using the voltage sensing circuit unit 32 for fault detection (FIGS. 6 (a) and (b)).

(24) In addition, the detection of welding of the (−) main relay 22 may be performed by turning on the (+) main relay 21 and the heater relay 25 when the off state of the precharge relay 23 and the (−) main relay 22 is controlled, and subsequently by sensing a voltage for fault detection using the voltage sensing circuit unit 32 for fault detection (FIG. 6 (c)). For example, the voltage for fault detection may be sensed using the voltage sensing circuit unit 32 for fault detection by controlling the off state of the (−) main relay 22 when the precharge relay 23 is the off state in IG OFF, and by turning on the heater relay 25 while allowing the (+) main relay 21 to maintain an ON state.

(25) Further, when the heater relay 25 has been in the on state previously by satisfying battery heating conditions, a voltage may be sensed by maintaining the ON state of the heater relay 25 in the IG OFF state to detect welding of the (−) main relay 22. The detection of welding of the heater relay 25 may be performed by sensing a voltage when both the (+) and (−) main relays 21 and 22 are in the on state or the precharge relay 23 is in an OFF state and when the off state of the heater relay 25 is controlled (FIG. 7 (a)).

(26) As shown in FIGS. 4 and 5, in the IG-ON process, the (−) main relay 22 may be on after IG ON (S11), and then the heater relay 25 may be on (S12). Subsequently, a voltage may be sensed using the voltage sensing circuit unit 32 for fault detection. When the sensed voltage value is about 0 V, it may be determined that both the precharge relay 23 and the (+) main relay 21 are normal. Otherwise, it may be determined that any one of the precharge relay 23 and the (+) main relay 21 is in a welding state (S13 and S14).

(27) When the value sensed using the voltage sensing circuit unit 32 for fault detection is the same as the following 1, it may be determined that the precharge relay 23 is in the welding state. When the value sensed through the voltage sensing circuit 32 for fault detection is the same as the following Equation 2, it may be determined that the (+) main relay 21 is in the welding state.
Sensing value=(voltage of battery pack or Σvoltages of battery cells)×((½×Σresistances of heaters)/(Σresistances of heaters+precharge resistance))×voltage division ratio of voltage sensing circuit for fault detection  Expression 1
Sensing value=(voltage of battery pack or Σvoltages of battery cells)×((½×Σresistances of heaters)/(Σresistances of heaters))×voltage division ratio of voltage sensing circuit for fault detection  Expression 2

(28) In Expressions 1 and 2, the voltage of the battery pack is a voltage that may be obtained from a sensing value of the battery voltage sensing circuit unit 31. In Expressions 1 and 2, ‘Σvoltages of battery cells’ refers to a sum of voltages of all the battery cells which may be sensed by the battery voltage sensing circuit unit 31; ‘Σresistances of heaters’ refers to a sum of resistance values of all the heaters 12; and ‘precharge resistance’ refers to a resistance value of the precharge resistor 24. In addition, ‘voltage division ratio’ refers to a voltage distribution ratio by the first and second resistors 33 and 34 of the voltage sensing circuit unit 32 for fault detection, i.e., R2/(R1+R2). R1 and R2 are resistance values of the first and second resistors 33 and 34, respectively.

(29) Configuration (a) in FIG. 6 shows an exemplary state in which the precharge relay 23 is welded, and configuration (b) in FIG. 6 shows an exemplary state in which the (+) main relay 21 is welded. The time point when the welding of the precharge relay 23 and the (+) main relay 21 is detected has been designated by {circle around (a)} in FIG. 5. After the welding of the precharge relay 23 and the (+) main relay 21 is identified as described above, a typical IG-ON process may be performed. The precharge relay 23 may be in the on state when the (−) main relay 22 has been the on state previously (S15).

(30) However, since the heater relay 25 has been previously on, the heater relay 25 may be in an off state (S16). Subsequently, since the (−) main relay 22 has been previously the on state, the (+) main relay 21 may be in the on state additionally (S17), and the precharge relay 23 may be then off (S18). Subsequently, the welding of the heater relay 25 may be detecting from a voltage sensed using the voltage sensing circuit unit 32 for fault detection when the on state of the (+) and (−) main relays 21 and 22 and the off state of the heater relay 25 are controlled (S19). When the voltage sensing value from the voltage sensing circuit unit 32 for fault detection is about 0 V, it may be determined that the heater relay 25 is normal. When the voltage sensing value is not 0 V, it may be determined that the heater relay 25 is in the welding state.

(31) Configuration (a) of FIG. 7 shows a state in which the heater relay 25 is welded. Subsequently, a disconnection, short circuit or damage of the heater 12 when the resistance value of a corresponding heater is changed may be determined from a voltage value sensed using the voltage sensing circuit unit 32 for fault detection when the (+) and (−) main relays 21 and 22 are in the on states and when the heater relay 25 is in the on state.

(32) For example, under a battery heating condition of less than a predetermined reference temperature after the IG-ON process, the heater relay 25 may be in the on state (S21 and S22). When the voltage value sensed using the voltage sensing circuit unit 32 for fault detection is ‘½×voltage of battery pack×voltage division ratio of voltage sensing circuit for fault detection’, it may be determined that the battery heating system is normal. Otherwise, it may be determined that a fault of the battery heating system is detected (S24).

(33) Particularly, when the voltage sensing value satisfies the condition of the following Expression 3, it may be determined as shown in (b) of FIG. 7 that a short circuit of the heater 12 positioned at the front end of the voltage sensing point or at branch point of the branch circuit for voltage sensing 13, or a damage or increase in resistance of the heater positioned at the rear end of the voltage sensing point 13 is detected. When the voltage sensing value satisfies the condition of the following Equation 4, it may be determined as shown in (c) of FIG. 7 that a short circuit of the heater 12 positioned at the rear end of the voltage sensing point 13, or a damage or increase in resistance of the heater positioned at the front end of the voltage sensing point is detected.

(34) When the voltage sensing value satisfies the condition of the following Equation 5, it may be determined as shown in (d) of FIG. 7 that a disconnection of the heater 12 positioned at the rear end of the voltage sensing point 13 is detected. When the voltage sensing value satisfies the condition of the following Expression 6, it is determined as shown in (e) of FIG. 7 that a disconnection of the heater 12 positioned at the front end of the voltage sensing point 13 is detected.
Sensing value>½×voltage of battery pack×voltage division ratio of voltage sensing circuit unit for fault detection  Expression 3
Sensing value<½×voltage of battery pack×voltage division ratio of voltage sensing circuit unit for fault detection  Expression 4
Sensing value=zener voltage  Expression 5
Sensing value=0  Expression 6

(35) As used herein, ‘zener voltage’ refers to a zener voltage or a breakdown voltage, for example, of about 5V, of the zener diode 35 in the voltage sensing circuit unit 32 for fault detection.

(36) Accordingly, a fault of the battery heating system and the type of the fault may be determined from a voltage value sensed using the voltage sensing circuit unit 32. In addition, the position at which a short circuit, disconnection or damage of the heater 12 occurs may be estimated based on the voltage sensing point 13. Subsequently, the welding of the (−) main relay 22 may be detected from a voltage value sensed using the voltage sensing circuit unit 32 for fault detection after the off state of the (−) main relay 22 is controlled and the heater relay is the on state in a state in which the (+) main relay 21 is the on state.

(37) For example, the off state of the (−) main relay 22 may be controlled in the IG-OFF process, and subsequently the heater relay 25 may be on, thereby detecting the welding of the (−) main relay 22 (S25, S26 and S27). When the sensing value of the voltage sensing circuit unit 32 for fault detection is about 0 V, it may be determined that the (−) main relay 22 is normal. Otherwise, it may be determined that welding of the (−) main relay 22 is detected (S28 and S29). In particular, the sensing value of the voltage sensing circuit unit 32 for fault detection may refer to the voltage value of Equation 2, and the welding state of the (−) main relay 22 is as shown in (c) of FIG. 6. The time point when the welding of the (−) main relay 22 is detected is shown as {circle around (b)} in FIG. 5. When the process of detecting the welding of the (−) main relay 22 is finished as described above, the (+) main relay 21 and the heater relay 25 may be sequentially off as shown in FIG. 4 (S30 and S31).

(38) As described above, according to various exemplary embodiments of the present invention, welding of each relay such as the main relay, the precharge relay or the heater relay may be detected. In addition, a fault of the battery heating system, a kind of fault such as short circuit, disconnection or damage of the heater, and a position of fault such as front or rear end based on the voltage sensing point may be determined, by simply sensing a voltage instead of sensing a temperature of an individual battery module or heater or an individual battery cell.

(39) The invention has been described in detail with reference to exemplary embodiments thereof. However, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.