Abstract:
Disclosed is a main relay monitoring system and method for a green vehicle, where a main relay is installed between a high voltage battery and an inverter in order to diagnose whether the main relay, which controls the output of the high voltage battery, is fused. In particular a switching operation of an inverter is stopped when an ignition off is detected, and a main relay is turned off and a voltage output of a main battery is cut. Then, a voltage charged at a DC link capacitor is forcibly discharged once the main relay is completely turned off. A voltage of the main battery is then compared to an input voltage of the inverter, and a determination is made based off of this comparison whether the main relay is fused.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2011-0110727 filed in the Korean Intellectual Property Office on Oct. 27, 2011, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    (a) Field of the Invention 
         [0003]    The present invention relates to a main relay monitoring device and method for a green vehicle, where a main relay is installed between a high voltage battery and an inverter in order to diagnose whether the main relay, which controls the output of the high voltage battery, is fused. 
         [0004]    (b) Description of the Related Art 
         [0005]    Due to the needs for enhancing the fuel efficiency of vehicles and stricter exhaust gas regulations, green vehicles including hybrid vehicles, fuel cell vehicles, and plug-in electric vehicles are being provided. Green vehicles typically use a power net of high voltage/high current to generate driving torque. 
         [0006]    A green vehicle typically uses a motor for generating a required driving torque, an inverter for controlling the driving of the motor, and a power converter (e.g., a DC/DC converter) for converting a high voltage of about 350V to 450V stored in a main battery for supplying power to an electronic unit to a low voltage of 12V required by the electronics unit. A green vehicle uses an inverter to convert a high voltage output from the main battery to a 3-phase alternating current (AC) voltage to then supply the converted voltage to a motor in order to drive the motor. Here, the output of the high voltage stored in the main battery is controlled by a main relay installed between the main battery and the inverter. 
         [0007]    For example, the main relay is turned off to cut off output from the main battery when a green vehicle is not being driven, and the main relay is turned on to supply the voltage of the main battery to the inverter when the green vehicle is being driven and requires power from the motor. 
         [0008]    When a malfunction of the main battery or the power converter occurs, the main relay cuts off the output voltage of the battery, accordingly. However, when the main relay becomes fused (i.e., stuck together), the main relay cannot cut off the output of the main battery so that the output of high voltage to adjacent circuits continues, thereby increasing the extent of the malfunction and possibly having serious effects on the safety of the vehicle. 
         [0009]    Some green vehicles include an additional circuit including a resistor, a transistor, an electric field effect transistor, and a comparator to monitor the state of the main relay. However, when a separate additional circuit is configured as above, power is required to drive the additional circuit, causing unnecessary current consumption, and when the additional circuit malfunctions, there may be a lack of reliability in monitoring the main relay. Further, in this solution, a lot of components are needed to configure the additional circuit, which leads to increased costs and an increase in the size of the entire system. 
         [0010]    The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention has been made in an effort to provide a main relay monitoring device and method for a green vehicle having the advantages of providing a diagnosis of whether a main relay in a green vehicle is fused by forcibly discharging a voltage charged in a direct current (DC) link capacitor and then comparing a battery voltage with an input voltage of an inverter, when a cut off of a main relay installed between a high voltage battery and an inverter occurs when the ignition of the green vehicle is turned off. 
         [0012]    An exemplary embodiment of the present invention provides a main relay monitoring device for a green vehicle, including: a motor; a main battery configured to store a high voltage; a main relay configured to control a voltage output of the main battery; an inverter configured to convert a voltage of the main battery supplied through the main relay to an AC voltage, and supply the AC voltage as a driving voltage to the motor; and a controller configured to cut off the main relay and then forcibly discharging a voltage charged at a DC link capacitor once an ignition is turned off, and compare a voltage of the main battery to an input voltage of the inverter and determine whether the main relay is fused together. 
         [0013]    The controller may switch the inverter once the main relay has been completely turned off, and forcibly discharge the voltage charged at the DC link capacitor, through resistance of the motor. After the forcible discharge of the DC link capacitor is completed, the controller may determine that the main relay is fused together when the voltage of the main battery and the input voltage of the inverter are the same or included in a certain range of values, output a malfunction message, and then forcibly turn the power off. 
         [0014]    Another embodiment of the present invention provides a main relay monitoring method for a green vehicle, including stopping a switching operation of an inverter when an ignition off is detected, and turning a main relay off and cutting off a voltage output of a main battery; forcibly discharging a voltage charged at a DC link capacitor once the main relay is completely turned off; and comparing a voltage of the main battery to an input voltage of the inverter, and monitoring whether the main relay is fused. The forcible discharging of the DC link capacitor may be performed by using the motor as a resistor. 
         [0015]    The main relay may be determined to be fused when the voltage of the main battery and the input voltage of the inverter are the same or within a certain voltage difference range and power may be forcibly turned off. The forcible discharging of the DC link capacitor may be performed by supplying the voltage charged at the DC link capacitor through switching of the inverter to the motor used as a resistor. The main relay may be determined to be normal when a voltage difference between the voltage of the main battery and the input voltage of the inverter voltage exceeds a set reference voltage, and then a normal power down may be performed. 
         [0016]    Advantageously, the exemplary embodiment of the present invention reduces costs and simplifies the overall system for monitoring whether a main relay has become fused together. Further, because whether a main relay is fused may be monitored with the ignition off, it is possible to prevent an increase in the extent of malfunctions and provide vehicle safety against exposure to high voltage. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a drawing schematically illustrating a main relay monitoring device for a green vehicle according to an exemplary embodiment of the present invention. 
           [0018]      FIG. 2  is a flowchart schematically illustrating a main relay monitoring process for a green vehicle according to an exemplary embodiment of the present invention. 
       
    
    
     DESCRIPTION OF SYMBOLS 
       [0000]    
       
           110 : Main battery 
           120 : Main relay 
           130 : Inverter 
           140 : Motor 
       
     
       DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0023]    The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. 
         [0024]    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. 
         [0025]    Furthermore, the 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 server or a network. Additionally, although the exemplary embodiment is described as using one control unit to perform the above process, it is understood that the above processes may also be performed by a plurality of control units, controllers, processors or the like. 
         [0026]    As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. The drawings and description are to be regarded as illustrative in nature and not restrictive. 
         [0027]      FIG. 1  is a drawing schematically illustrating a main relay monitoring device for a green vehicle according to an exemplary embodiment of the present invention. Referring to  FIG. 1 , an exemplary embodiment of the present invention includes a main battery  110 , a main relay  120 , an inverter  130 , a motor  140 , an engine  150 , a transmission  160 , drive wheels  170 , and a controller  200 . 
         [0028]    The main battery  110  stores a DC voltage of about 350V to 450V, outputs the stored voltage when required to drive the motor  140 , and is charged by voltage generated from the motor  140  while the motor  140  is being operated as a generator during regenerative braking control. The main relay  120  is disposed between the main battery  110  and the inverter  130 , is switched through control by the controller  200 , and electrically connects or separates the battery  130  and the inverter  130 . 
         [0029]    The main relay  120  may be switched “off” by the controller  200  when the green vehicle is not being driven and cut off the output of the main battery  110  supplied to the inverter  130 , and may be switched “on” by the controller  200  when the green vehicle is driven and power is required to supply the voltage from the main battery  110  to the inverter  130 . Further, when a malfunction of the main battery or the power converter occurs, the main relay  120  is switched off by the controller  200  to cut off the output of the main battery  110 . 
         [0030]    The inverter  130  is configured of power switching devices coupled in series, and includes a pair of U-phase arms U +  and U − , V-phase arms V +  and V − , and W-phase arms W +  and W − . The power switching device may be configured with either an NPN-type transistor, an insulated gate bipolar transistor (IGBT), or a metal-oxide-semiconductor field-effect transistor (MOSFET). The inverter  130  converts a DC voltage of the main battery  110  supplied through the main relay  120  to a 3-phase AC voltage and supplies the AC voltage as a driving voltage to the motor  140 , according to a PWM signal applied to each arm by the controller  200 . 
         [0031]    The motor  140  may be a 3-phase AC motor that generates a driving torque by means of the 3-phase AC voltage supplied from the inverter  130 , and operates as a generator during regenerative braking to generate a voltage. The engine  150  is driven at an optimal operating point according to driving conditions. The transmission  160  distributes and transmits power to drive shaft, according to the driving conditions of the vehicle, the output torque of the engine  150  and the motor  140 , which is combined and applied through a clutch (not illustrated) according to a driving mode, to the drive wheels  170  at a suitable gear ratio so that the vehicle may be driven. The transmission  160  may be, for example, an automatic transmission or a continuously variable transmission (CVT). 
         [0032]    The controller  200  switches the main relay  120  off when an ignition off is detected to cut off the voltage output from the main battery  110 , and switches the inverter  130  to forcibly discharge a voltage charged at a DC link capacitor (V dc ) by the inverter  130 , through the resistance of the motor  140 . The forcible discharge of the DC link capacitor (V dc ) may be determined, for example, by Equation 1 below. 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       1 
                       2 
                     
                      
                     SCS 
                     × 
                     
                       V 
                       2 
                     
                   
                   = 
                   
                     
                       I 
                       2 
                     
                      
                     SRSt 
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
         [0033]    Through Equation 1 above, a target discharge duration, a system voltage, and a discharge stop voltage may be determined to determine a discharge current command. For example, when a target discharge duration is 3 seconds and a discharge stop voltage is 60V, the input voltage of the inverter  130  or the output voltage of the DC link capacitor (V dc ) is below 60V after 3 seconds. 
         [0034]    After forcibly discharging the voltage charged at the DC link capacitor (V dc ) of the inverter  130 , the controller  200  may compare a voltage (V BAT ) of the main battery  110  and the input voltage of the inverter  130  or the output voltage of the DC link capacitor (V dc ) and determine whether the main relay  120  is fused. 
         [0035]    For example, when the voltage (V BAT ) of the main battery  110  and the input voltage of the inverter  130  are the same or included in a certain range of values, the controller  200  may determine that the voltage of the main battery  110  is being continuously supplied to the inverter  130  due to the main relay being fused. When it is determined that the main relay  120  is fused, the controller  200  outputs a malfunction message through a predetermined method and then forcibly turns off the power to the system. 
         [0036]    The operation of performing the monitoring of a main relay in a green vehicle including the above described functions according to an exemplary embodiment of the present invention is as follows. 
         [0037]    With a green vehicle, to which the present invention is applied, being operated in step S 101 , the controller  200  determines whether an ignition off is detected in step S 102 . When the controller  200  determines in step S 102  that an ignition off is detected, the output of a pulse-width modulating (PWM) signal applied to arms for each phase U +  and U − , V +  and V − , and W +  and W −  of the inverter  130  is stopped and the switching operation of the inverter  130  is stopped in step S 103 . Then, the main relay  120  is switched off, and the voltage output of the main battery  110  is cut off in step S 104 . 
         [0038]    Once the switching off control of the main relay  120  is completed in step S 105 , the controller  200  performs a switching control of the inverter  130  to forcibly discharge a voltage charged at the DC link capacitor (V dc ) of the inverter  130  by means of the resistance of the motor  140  in step S 106 . The forcible discharging of the DC link capacitor (V dc ) may determine a target discharge duration, a system voltage, and a discharge stop voltage through Equation 1 above, and a discharge current command may be determined. 
         [0039]    In step S 106 , when the forcible discharge of the voltage charged at the DC link capacitor (V dc ) of the inverter  130  is completed, the controller  200  then detects a voltage (V BAT ) of the main battery  110  and the input voltage of the inverter  130  or the output voltage of the DC link capacitor (V dc ) in step S 107 . Next, the controller  200  compares the detected voltage (V BAT ) of the main battery  110  and the voltage of the inverter  130  and detects the voltage difference in step S 108 , and determines whether the voltage difference is less than a reference voltage set to determine whether fusing has occurred in S 109 . 
         [0040]    In step S 109 , when the controller  200  determines that the voltage difference is less than the reference voltage set to determine that fusing has occurred, the controller  200  determines that the main relay  120  is fused in step S 110 , and outputs a warning message through a set predetermined method and then forcibly turns off the power to the system in step S 111 . 
         [0041]    For example, when the voltage difference between the voltage (V BAT ) of the main battery  200  and the input voltage of the inverter  130  is included within a certain range or the voltages are the same, the controller  200  may determine that the voltage of the main battery  110  is continuously being supplied to the inverter  130  due to the main relay being fused. That is, in a state where the main relay  120  is fused, even when the DC link capacitor is forcibly discharged, the voltage of the main battery  110  is continuously supplied, and thus, the voltage (V BAT ) of the main battery  110  and the input voltage of the inverter  130  are the same or included in a set reference voltage range. 
         [0042]    In step S 109 , when the voltage difference exceeds the set reference voltage, which is a state in which the output of the main battery  110  is stably cut off by switching off the main relay  120 , the controller  200  determines in step S 112  that the main relay  120  is not fused and is in a normal state, and performs a normal power off in step S 113 . 
         [0043]    Advantageously, whether a main relay is fused may be conveniently monitored when an ignition off is detected, so that vehicle safety and reliability may be provided using the exemplary embodiment of the present invention. 
         [0044]    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.