Abstract:
The present invention provides an inverter circuit for a vehicle, which includes: a switching unit that includes a plurality of switching elements and switches a direct current into an alternating current; and a variable clamping unit that clamps an overshoot in case the overshoot is generated, and stops the operation of the switching unit in case a system voltage is greater than a clamping breakdown voltage. The circuit enables a voltage (DC input voltage) greater than a breakdown voltage of clamping unit to be used as a system voltage.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based on and claims priority from Korean Patent Application No. 10-2008-101177, filed on Oct. 15, 2008, the disclosure of which is incorporated herein in its entirety by reference. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to an inverter circuit for a vehicle that can apply a system voltage (DC input voltage) over a maximum tolerable pressure of a clamping unit to thereby increase productivity and decrease manufacturing costs, and a vehicle including the same. 
       BACKGROUND ART 
       [0003]    In a hybrid vehicle, an inverter plays the role of converting high voltage DC power into AC power to operate a motor. This inverter includes an IGBT (Insulated Gate Bipolar Transistor) module (or, FET module). The IGBT module, as shown in  FIG. 1   a , includes a plurality of switching elements SW 1 ˜SW 6  and each of the switching elements SW 1 ˜SW 6  is operated by a PWM signal outputted from a driving unit  11 . The PWM signal output is controlled by a controller  12 . 
         [0004]    However, an inverter three-phase output can be short circuited as a result of vehicle accident, aging of the cable, and errors in the assembling process, thereby causing a state in which an excess current flows into the IGBT module  10 . If such excess state is caused, the controller  12  stops the switching of the switching elements SW 1 ˜SW 6  so as to prevent the damage of the IGBT module  10 . 
         [0005]    However, in case where the switching of the switching elements SW 1 ˜SW 6  is suddenly stopped, an overvoltage is instantaneously caused between the both ends (drain and source or collector and emitter) of the switching elements SW 1 ˜SW 6  such that the IGBT module  10  is damaged. 
         [0006]    When a circuit is instantaneously short circuited or an overvoltage is generated during the operation of the IGBT module  10  as described above, an overshoot (A) that the voltage V DS  applied to the drain end and source end of the switching element SW 1  of the IGBT module  10  is instantaneously increased to a value higher than the breakdown voltage of the IGBT module  10  is caused, as shown in the timing diagram of  FIG. 1   b.  The overshoot can damage the IGBT module  10 . 
         [0007]    To prevent such damage, as shown in  FIG. 2   a , a clamping unit  20  is inserted between the drain end or collector end and the gate end of the switching element SW 1 , so that the overvoltage can be lowered by the clamping unit  20 . 
         [0008]    The clamping unit  20  includes a clamping diode D 1 , a reverse-current prevention diode D 2  and a resistance R 1 . If the breakdown voltage of the clamping diode D 1  is set to be lower than the breakdown voltage of the IGBT module  10 , and the V DS  voltage is increased to a value higher than the breakdown voltage of the clamping diode D 1 , the clamping diode D 1  is turned on, which makes current I D1  flow through the clamping unit  20  so that the switching element SW 1  of the IGBT module  10  is turned on. As a result, the V DS  voltage is decreased, thereby clamping, as shown in  FIG. 2   b , the overshoot voltage (B). 
         [0009]    Nonetheless, if a voltage greater than the breakdown voltage of clamping unit  20  is continuously applied as the system voltage (DC input voltage) to the IGBT module  10 , the switching element SW 1  is continuously turned on by the clamping unit  20  and may be overheated. 
         [0010]    That is, if it fails to control the inverter while a motor rotates at a high speed, counter electro-motive force of the motor is applied to the IGBT module  10 , which then causes the system voltage V DC  applied to the IGBT module  10  to be higher than the breakdown voltage V clamp  of the clamping unit  20 . Accordingly, the clamping diode D 1  is turned on and the switching element SW 1  of the IGBT module  10  is continuously turned on. As a result, excess current flows through the IGBT module  10  and the IGBT module  10  may be damaged by overheating. 
         [0011]    As described above, if the breakdown voltage of the clamping diode is set to be lower than the system voltage such that the system voltage is increased to a value higher than the breakdown voltage of the clamping diode D 1 , the IGBT module may be damaged. 
         [0012]    One approach to solve this problem was to increase the breakdown voltage of the IGBT module and the breakdown voltage of the clamping diode so as to increase the system voltage. However, increasing both the breakdown voltage of the IGBT module and the breakdown voltage of the clamping diode caused the price of the IGBT module to be increased. 
         [0013]    For these reasons, it is difficult to achieve a maximum performance of a vehicle motor. Moreover, it is difficult to use an IGBT module having a certain breakdown voltage commonly for various vehicles since different vehicles require different the system voltages (DC input voltages). 
         [0014]    The above information disclosed in this the Background Art 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 
       [0015]    The present invention provides an inverter circuit for vehicles that can prevent such IGBT module damage. 
         [0016]    An inverter circuit in accordance with an aspect of the present invention includes: a switching unit that includes a plurality of switching elements and switches a direct current into an alternating current; and a variable clamping unit that clamps an overshoot in case the overshoot is generated, and stops the operation of the switching unit in case a system voltage is greater than a clamping breakdown voltage. 
         [0017]    Preferably, the variable clamping unit includes: a clamping unit that turns the switching element on to clamp the overshoot; and a variable admittance that turns the plurality of switching elements off after a given time is elapsed in case the system voltage is greater than the clamping breakdown voltage. Preferably, the variable admittance includes: a capacitor that is charged by current which flows from the clamping unit; a resistance that is connected in parallel with the capacitor. Preferably, the variable admittance turns the plurality of switching elements off when the charge of capacitor is completed. Preferably, the clamping unit includes a clamping diode that is turned on in case the overshoot is generated or the system voltage is higher than the clamping breakdown voltage to be applied. Preferably, the clamping unit further includes a reverse-current prevention diode which prevents current that flows reversely from the variable admittance to the clamping diode. Preferably, the clamping diode is a Zener diode. Preferably, the variable admittance is charged by the clamping unit, and turns the plurality of switching elements on during the charging. Preferably, the switching unit is an IGBT (Insulated Gate Bipolar Transistor) module or a FET (field-effect transistor) module. 
         [0018]    In accordance with another aspect of the present invention, a vehicle includes: a switching unit that includes a plurality of switching elements and switches a direct current into an alternating current; a variable clamping unit that clamps an overshoot in case the overshoot is generated; and a motor unit that is operated by an output of the switching unit, wherein the variable clamping unit stops the operation of the switching unit in case a system voltage is greater than a clamping breakdown voltage due to counter electro-motive force of the motor unit. 
         [0019]    Preferably, the variable clamping unit includes: a clamping unit that turns the plurality of switching elements on to clamp the overshoot; and a variable admittance that turns the plurality of switching elements off after a given time is elapsed in case the system voltage is greater than the clamping breakdown voltage. Preferably, the variable admittance turns the plurality of switching elements off when the charge of capacitor is completed in case the system voltage is greater than the clamping breakdown voltage due to counter electro-motive force of the motor unit. 
         [0020]    As described above, the present invention is able to enhance the efficiency of inverter and motor and the rated power density by using the system voltage (DC input voltage) which is greater than the breakdown voltage of clamping unit such that not only the performance improvement but also the cost down and design change can be facilitated and the motor performance of vehicle can be improved. 
         [0021]    Moreover, the present invention can increase and use the system voltage (DC input voltage) without the change of the IGBT module or the need of additional element such that it can enhance the efficiency of inverter and also the inverter maximum rating. Accordingly, the inverter can be miniaturized and the weight and volume can be reduced. Moreover, the present invention can use the IGBT module in common regardless of the car model, thereby, being able to reduce the cost of mass production. 
         [0022]    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. 
         [0023]    The above and other features and advantages of the present invention will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated in and form a part of this specification, and the following Detailed Description, which together serve to explain by way of example the principles of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    The above and other features of the present invention will now be described in detail with reference to certain exemplary embodiments thereof illustrated by the accompanying drawings which are given hereinafter by way of illustration only, and thus are not limitative of the present invention, and wherein: 
           [0025]      FIG. 1   a  is a general inverter circuit diagram; 
           [0026]      FIG. 1   b  is a timing diagram of the general inverter circuit of  FIG. 1   a;    
           [0027]      FIG. 2   a  is a general inverter circuit diagram including a clamping diode; 
           [0028]      FIGS. 2   b  and  2   c  are timing diagrams of the general inverter circuit of  FIG. 2   a;    
           [0029]      FIG. 3   a  is a configuration diagram of an inverter circuit according to an embodiment of the present invention; 
           [0030]      FIGS. 3   b  and  3   c  are a timing diagram of the inverter circuit of  FIG. 3   a ; and 
           [0031]      FIGS. 4   a  and  4   b  are drawings for illustrating the operation of variable admittance of  FIG. 3   a.    
       
    
    
       [0032]    It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred 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. 
       DETAILED DESCRIPTION OF EMBODIMENTS 
       [0033]    Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the attached drawings 
         [0034]      FIG. 3   a  is a configuration diagram of an inverter circuit according to an embodiment of the present invention. 
         [0035]    The inverter circuit according to the embodiment of the present invention includes an IGBT switching unit  100 , a variable clamping unit  200 , a driving unit  300 , a controller  400 , an inductor L 2 , a diode D 13  and a resistance R 13 . 
         [0036]    The IGBT switching unit  100  includes a switching element SW 7 . As shown in  FIG. 1   a , the IGBT module according to the embodiment includes a plurality of switching elements. The variable clamping unit  200  is equipped in both ends of each of the switching elements. The driving unit  300  outputs a PWM signal for operating the IGBT switching unit  100  under the control of the controller  400 . The controller  400  controls the driving unit  300  to control the on/off of the IGBT switching unit  100 . 
         [0037]    In case the voltage V DS  is increased to a value higher than the breakdown voltage V clamp  of variable clamping diode as the switching element SW 7  is abruptly turned off in the excess state, the variable clamping unit  200  turns the switching element SW 7  on to prevent the overshoot. On the other hand, in case the system voltage caused by the motor counter electro-motive force is increased to a value greater than the clamping breakdown voltage, the variable clamping unit  200  turns the switching element SW 7  off to prevent the damage of the IGBT module. For this, the variable clamping unit  200  includes a clamping unit  210  and a variable admittance  220 . 
         [0038]    In case the voltage V DS  is greater than the breakdown voltage of clamping diode D 11 , the clamping unit  210  turns the switching element SW 7  on to prevent the overshoot. For this, the clamping unit  210  includes a clamping diode D 11 , a reverse-current prevention diode D 12  and a resistance R 11  which are serially connected to one side of the drain end (collector) of the switching element SW 7  and the variable admittance  220 . 
         [0039]    Here, the clamping diode D 11  is turned off in case the inverter circuit normally operates, while being turned on in the excess state where the short circuit or the excess current is generated to turn the switching element SW 7  on. The reverse-current prevention diode D 12  prevents the reverse current from the variable admittance  220 . 
         [0040]    In case the overshoot is generated like a high pass filter, the variable admittance  220  turns the switching element SW 7  on. In case the charge of capacitor Cv is completed and the capacitor Cv becomes an open state, the variable admittance  220  turns the switching element SW 7  off to prevent the damage of the switching element SW 7  For this, the variable admittance  220  includes an equivalent circuit in which the resistance R 12  and the capacitor Cv are parallelly connected. 
         [0041]    The capacitor Cv is charged by current I D11  which flows from the clamping unit  210 , while the resistance R 12  plays the role of discharging the electric charge charged in C V  by a low frequency component. Preferably, the resistance R 12  may be set as 10 kΩ and the capacitor Cv is set as 10 nF in case the inverter switching frequency is 10 kHz. 
         [0042]    Hereinafter, the operation of the inverter circuit according to the embodiment of the present invention is illustrated in detail with reference to  FIG. 3   b  and  FIG. 3   c.    
         [0043]    Firstly, in the steady-state, the switching element SW 7  is operated by the PWM signal outputted from the driving unit  300  such that the IGBT module is operated. As shown in  FIG. 3   b , if the PWM signal outputted from the driving unit  300  becomes a high level, the V GS  voltage applied to the gate end and source end of the switching element SW 7  becomes a high level such that the switching element SW 7  is turned on. Thus, the V DS  voltage applied to the drain end and source end of the switching element SW 7  is dropped such that current I DS  can flow. 
         [0044]    At this time, the variable clamping unit  200  does not operate, and the clamping diode D 11  is turned off. 
         [0045]    Here, if the system voltage (DC input voltage) is lower than the breakdown voltage of clamping diode while the V DS  voltage is lower than a given voltage as the short circuit or the excess current is not generated, the controller  400  determines that it is in steady-state and controls the driving unit  300  to output the PWM signal. 
         [0046]    Thereafter, in case the excess state where both ends of the IGBT module is short circuited and the excess current flow is generated, the controller  400  abruptly turns the switching element SW 7  off so as to protect the IGBT module. If the overshoot of the V DS  voltage is generated due to the abrupt turn off operation of the switching element SW 7 , the clamping diode D 11  is turned on due to the overshoot voltage. As a result, current I D11  flows while the capacitor voltage Vcv is decreased after increasing during a period in which current ID 11  flows. 
         [0047]    Accordingly, current flows through the clamping unit  210  and the electric charge, as shown in  FIG. 4   a , is charged in the capacitor Cv and the voltage of the gate end of the switching element SW 7  is increased by a value obtained by multiplying current I D11  flowing through the clamping unit  210  by the resistance R 13  such that the switching element SW 7  is turned on. Thus, current I DS  flows and the V DS  voltage applied to the drain end and source end of the switching element SW 7  is decreased. As a result, as shown in  FIG. 3   b , the overshoot in which the V DS  voltage is higher than the system voltage V DC  is clamped (D) such that the damage of the switching element SW 7  can be prevented. Thereafter, if the charge of capacitor Cv is completed, as shown in  FIG. 4   b , the capacitor Cv operates as if it is in the open state, and current does not flow due to the resistance R 12  such that the switching element SW 7  is turned off. 
         [0048]    In the meantime, as shown in  FIG. 3   c , in case the counter electro-motive force of the motor is generated in the steady-state not in the excess state, and the system voltage V DC  becomes higher than the clamping voltage V clamp , the controller  400  stops the PWM signal outputting of the driving unit  300 . 
         [0049]    Thereafter, while the clamping diode D 11  is turned on and current I D11  flows and is charged in the capacitor Cv, the switching element SW 7  is turned on during the charge of the capacitor Cv. If the charge of the capacitor Cv is completed, the charged capacitor Cv, as shown in  FIG. 4   b , operates as if it is the open state, so that current does not flow any more due to the resistance R 12  having a large resistance. Accordingly, as shown in  FIG. 3   b , the current I D11  does not flow and the voltage V GS  is decreased such that the switching element SW 7  is turned off. 
         [0050]    As described above, since the switching element SW 7  is turned off when the capacitor CV is charged, as shown in  FIG. 3   c , current I DS  is reduced after flowing and current I D11  and voltage V GS  are also reduced while the capacitor voltage V CV  is charged and maintained with a voltage level which is the value obtained by subtracting the clamping voltage V clamp  out of the system voltage V DC . Although not shown in  FIG. 3   c , if the motor counter electromotive-force is decreased, that is, if the system voltage level is decreased, the capacitor Cv begins to discharge through R 12 . 
         [0051]    As described above, the inverter circuit can prevent the damage of the switching element SW 7 . 
         [0052]    It will be apparent to those skilled in the art that various modifications and variation can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.