Abstract:
A rectifying circuit and method to produce a DC output by rectifying a sinusoidal source having a plurality of output phase voltages and a plurality of phase-to-phase voltages, the rectifying circuit including a bridge circuit coupled to the output phase voltages, the bridge circuit having a plurality of switches; and a control circuit coupled to the output phase voltages and to the bridge circuit, the control circuit being configured to control the switches in accordance with respective absolute values of the phase-to-phase voltages; wherein the output phase voltages are rectified to produce the DC output. When the sinusoidal source is inductive, switch turn-off may be timed to provide synchronous rectification related to estimates of source periodicity.

Description:
RELATED APPLICATIONS  
       [0001]    This application is based on and claims priority to United States Provisional Patent Application No. 60/361,415, filed Mar. 1, 2002, entitled MOSGATE DEVICE DRIVER FOR SYNCHRONOUS RECTIFICATION OF A 3 PHASE SINUSOIDAL SOURCE, and this application is based on and claims priority to United States Provisional Application No. 60/395,970, filed Jul. 12, 2002, entitled MOSGATE DEVICE DRIVER FOR SYNCHRONOUS RECTIFICATION OF A 3 PHASE SINUSOIDAL SOURCE, the contents of all of which are incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The invention relates to a circuit to produce a direct current(DC) output from a 3-phase alternating current(AC) source, such as a circuit including a MOSgate driver to drive MOSgated devices in a rectifier circuit.  
         BACKGROUND OF THE INVENTION  
         [0003]    It is believed that at least some power electronics applications, such as AC motor drive applications, automotive generator applications, and/or switching power supply applications, may include circuits to rectify a sinusoidal voltage source to produce a DC output. The rectifying of the sinusoidal source may be performed, for example, by a diode bridge or by a collection of active switch bridges including, for example, MOSgated devices, such as MOSFETs and IGBTs.  
           [0004]    An active switch bridge, for example, a switch bridge employing MOSFETs and/or IGBTs, may be advantageous with respect to diode bridges, since the channel of a MOSFET and/or IGBT carries the electrical current, as opposed to the diode of the diode bridge. In this advantageous manner, active switch bridges employing MOSFETs and/or IGBTs may better reduce conduction losses.  
           [0005]    However, to properly operate an active switch bridge employing MOSFETs and/or IGBTs, signals for the gate nodes of the MOSFETs and/or IGBTs should be generated at appropriate times relative to the sinusoidal voltage source.  
           [0006]    Furthermore, if the sinusoidal source produces phase voltages with significant inductances, switching losses may result in operation of a bridge circuit, in which proper control signal timing is not provided. Therefore, it may be advantageous to detect more optimum time instants for the turn-on and turn-off of the gate nodes of the MOSFETs and/or IGBTs.  
         SUMMARY OF THE INVENTION  
         [0007]    To overcome these and other disadvantages of prior art rectification circuits, an exemplary embodiment of the present invention provides a rectifying circuit and method to produce a DC output by rectifying a sinusoidal source having a plurality of output phase voltages and a plurality of phase-to-phase voltages, the rectifying circuit including a bridge circuit coupled to the output phase voltages, the bridge circuit having a plurality of switches; and a control circuit coupled to the output phase voltages and to the bridge circuit, the control circuit being configured to control the switches in accordance with respective absolute values of the phase-to-phase voltages; in which the output phase voltages are rectified to produce the DC output.  
           [0008]    The absolute values of phase-to-phase voltages may be determined in accordance with the output phase voltages each phase-to-phase voltage representing the voltage across two of the output phase voltages.  
           [0009]    By comparing the absolute values of the phase-to-phase voltages, an exemplary rectifying circuit according to the present invention may turn on and/or turn off the switches of the bridge circuit at appropriate times to properly rectify the sinusoidal source and produce the DC output. For example, the exemplary rectifying circuit according to the present invention may operate respective pairs of switches at appropriate times in accordance with the magnitudes of the output phase voltages and the relative magnitudes of the absolute values of the phase-to-phase voltages.  
           [0010]    If the sinusoidal source includes significant inductance, rectification of the 3-phase sinusoidal AC source  125  may be improved by providing additional exemplary timing circuitry according to the present invention to better control the switches. In this manner, the control circuit may perform switch turn-off in diode mode (e.g., MOSFET switches) by keeping the switches turned off, and by estimating the period of the sinusoidal source. With the period information, the turn-off commutation times may be estimated, and a delay may be provided, so that turn-off of the switches occurs before the end of the sinusoidal period. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 illustrates a first exemplary rectifying circuit according to the present invention.  
         [0012]    [0012]FIG. 2 illustrates a first exemplary control circuit according to the present invention.  
         [0013]    [0013]FIG. 3 illustrates a second exemplary control circuit according to the present invention.  
         [0014]    [0014]FIG. 4 is a graphical time diagram showing the control of gate MOSFET gate signals, in accordance with the control circuit of FIG. 2.  
         [0015]    [0015]FIG. 5 illustrates a second exemplary rectifying circuit according to the present invention.  
         [0016]    [0016]FIG. 6 illustrates a third exemplary control circuit according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0017]    Referring now to FIG. 1, there is seen a first exemplary rectifying circuit  100  according to the present invention. Rectifying circuit  100  includes 3-phase bridge  105  of MOSgated devices (e.g., vertical conduction MOSFETs), the bridge including three legs  110   a,    110   b,    110   c.  Leg  110   a  includes MOSFETs  115   a,    120   a,  leg  110   b  includes MOSFETs  115   b,    120   b,  and leg  110   c  includes MOSFETs  115   c,    120   c.  Rectifying circuit  100  also includes a 3-phase sinusoidal AC source  125 , which produces source output phases V A , V B , V C , which are electrically connected to respective nodes between MOSFETs  115   a,    120   a,  MOSFETs  115   b,    120   b,  and MOSFETs  115   c,    120   c,  respectively. A DC output bus  135  is connected to the drains of MOSFETs  115   a,    115   b,    115   c,  and a return bus  130  is connected to the sources of MOSFETs  120   a,    120   b,    120   c.  A current sense resistor  22  is provided between the DC output bus  135  and the return bus  130 .  
         [0018]    Although FIG. 1 includes MOSFET switches, it should be appreciated that the MOSFETs  115   a,    115   b,    115   c,    120   a,    120   b,    120   c  maybe replaced with any conventional circuit switches, such as, IGBTs, solid-state circuit switches, relays, transistor switching arrangements, etc.  
         [0019]    In accordance with an exemplary embodiment of the present invention, gate signals (i.e., Q 1 , Q 2 , Q 3 , Q 4 , Q 5 , Q 6 ) of MOSFETs  115   a,    120   a,    115   b,    120   b,    115   c,    120   c  are controlled to rectify DC output bus  135  in a manner more fully described below.  
         [0020]    Referring now to FIG. 2, there is seen an exemplary control circuit  200  according to the present invention for controlling gate signals Q 1 , Q 2 , Q 3 , Q 4 , Q 5 , Q 6  of MOSFETs  115   a,    120   a,    115   b,    120   b,    115   c,    120   c,  respectively. Control circuit  200  includes conventional logic elements and is operable to provide appropriate control signals over “slices” of one period of the 3-phase AC source  125 , during which intervals the absolute value of one of the  3  phase-to-phase voltages (i.e., V AB , V BC , V CA ) is higher in magnitude than the absolute values of the other 2 phase-to-phase voltages. Control circuit  200  may be implemented, for example, in an integrated circuit, a driver ASIC, and/or a control ASIC. As shown in FIG. 2, control circuit  200  includes and-gates  205   a,    205   b,    205   c,  . . . ,  205   f,  or-gates  210   a,    210   b,    210   c,  . . . ,  210   f,  inverter-gates  215   a,    215   b,    215   c,  . . . ,  215   f,  and comparators  220   a,    220   b,    220   c,  which produce logic signals V AB(Logic) , V BC(Logic) , V CA(Logic)  in accordance with the 3 phase-to-phase voltages V AB , V BC , V CA :  
         
       V 
       AB 
       =V 
       A 
       −V 
       B  
     
         
       V 
       BC 
       =V 
       B 
       −V 
       C  
     
         
       V 
       CA 
       =V 
       C 
       −V 
       A  
     
         [0021]    The comparators  220   a,    220   b,    220   c  may produce, for example, logic signals V AB(Logic) , V BC(Logic) , V CA(Logic)  corresponding to a high logic value (e.g., “1”) when a respective phase-to-phase voltage is greater than 0 volts, and another electrical signal corresponding to a low logic value (e.g., “0”) when a respective phase-to-phase voltage is less than 0 volts(e.g., “5” volts when the phase-to-phase voltage is greater than 0 volts, and “0” volts when the phase-to-phase voltage is less than 0 volts).  
         [0022]    It is readily apparent that the absolute value of V AB  is greater than the absolute values of V BC  and V CA  when V BC  and V CA  are both less than zero or both greater than zero (i.e., V BC(Logic) =“0” and V CA(Logic) =“0” or V BC(Logic) =“1” and V CA(Logic) =“1”); the absolute value of V BC  is greater than the absolute values of V AB  and V CA  when V AB  and V CA  are both less than zero or both greater than zero (i.e., V AB(Logic) =“0” and V CA(Logic) =“0” or V AB(Logic) =“1” and V CA(Logic) =“1”); and the absolute value of V CA  is greater than the absolute values of V AB  and V BC  when V AB  and V BC  are both less than zero or both greater than zero (i.e., V AB(Logic) =“0” and V BC(Logic) =“0” or V AB(Logic) =“1” and V BC(Logic) =“1”).  
         [0023]    When the absolute value of V AB  is greater than the absolute values of V BC  and V CA  and the magnitude of V AB  is greater than zero (i.e., when V BC(Logic) =“0” and V CA(Logic) =“0”), control circuit  200  operates to turn on gate signals Q 1  and Q 4 , while switching off gate signals Q 2 , Q 3 , Q 5 , and Q 6 . When the absolute value of V AB  is greater than the absolute values of V BC  and V CA  and the magnitude of V AB  is less than zero (i.e., when V BC(Logic) =“1” and V CA(Logic) =“1”), control circuit  200  operates to turn on gate signals Q 2  and Q 3 , while switching off gate signals Q 1 , Q 4 , Q 5 , and Q 6 . When the absolute value of V BC  is greater than the absolute values of V AB  and V CA  and the magnitude of V BC  is greater than zero (i.e., when V AB(Logic) “0” and V CA(Logic) =“0”), control circuit  200  operates to turn on gate signals Q 3  and Q 6 , while switching off gate signals Q 1 , Q 2 , Q 4 , and Q 5 . When the absolute value of V BC  is greater than the absolute values of V AB  and V CA  and the magnitude of V BC  is less than zero (i.e., when V AB(Logic) =“1” and V CA(Logic) =“1”), control circuit  200  operates to turn on gate signals Q 4  and Q 5 , while switching off gate signals Q 1 , Q 2 , Q 3 , and Q 6 . When the absolute value of V CA  is greater than the absolute values of V AB  and V BC , and the magnitude of V CA  is greater than zero (i.e., when V AB(Logic) =“0” and V BC(Logic) =“0”), control circuit  200  operates to turn on gate signals Q 2  and Q 5 , while switching off gate signals Q 1 , Q 3 , Q 4 , and Q 6 . When the absolute value of V CA  is greater than the absolute values of V AB  and V BC , and the magnitude of V CA  is less than zero (i.e., when V AB(Logic) =“1” and V BC(Logic) =“1”), control circuit  200  operates to turn on gate signals Q 1  and Q 6 , while switching off gate signals Q 2 , Q 3 , Q 4 , and Q 5 .  
         [0024]    The operation of control circuit  200  is represented in tabular format below:  
                                                                                                 Q1   Q2   Q3   Q4   Q5   Q6                                    V BC(Logic)  = “0”   ON   OFF   OFF   ON   OFF   OFF       V CA(Logic)  = “0”       V BC(Logic)  = “1”   OFF   ON   ON   OFF   OFF   OFF       V CA(Logic)  = “1”       V CA(Logic)  = “0”   OFF   OFF   ON   OFF   OFF   ON       V AB(Logic)  = “0”       V CA(Logic)  = “1”   OFF   OFF   OFF   ON   ON   OFF       V AB(Logic)  = “1”       V AB(Logic)  = “0”   OFF   ON   OFF   OFF   ON   OFF       V BC(Logic)  = “0”       V AB(Logic)  = “1”   ON   OFF   OFF   OFF   OFF   ON       V BC(Logic)  = “1”                  
 
         [0025]    Referring now to FIG. 4, there is seen a graphical time diagram of gate signals Q 1 , Q 2 , Q 3 , Q 4 , Q 5 , and Q 6 , relative to V AB , V BC , and V CA . For example, when the absolute value of V AB  is greater than the absolute values of V BC  and V CA , and V AB  is greater than zero, control circuit  200  operates to turn on gate signals Q 1  and Q 4 , while switching off gate signals Q 2 , Q 3 , Q 5 , and Q 6 . In this manner, current will flow through MOSFETS  115   a  and  120   b,  thereby rectifying the 3-phase sinusoidal AC source  125 .  
         [0026]    Referring now to FIG. 3, there is seen another exemplary control circuit  300  according to the present invention for controlling gate signals Q 1 , Q 2 , Q 3 , Q 4 , Q 5 , Q 6  of MOSFETs  115   a,    120   a,    115   b,    120   b,    115   c,    120   c.  Control circuit  300  controls gate signals Q 1 , Q 2 , Q 3 , Q 4 , Q 5 , Q 6  to rectify the 3-phase sinusoidal AC source  125  when V A , V B , or V C  is greater than the DC output bus  135 . In this manner, it may be better ensured that current does not flow backwards from the DC bus into the rectification circuit, which would disadvantageously cause the DC bus voltage to drop with respect to the sinusoidal source voltage. As shown in FIG. 3, control circuit  300  includes and-gates  305   a,    305   b,    305   c,  . . . ,  305   l,  or-gates  310   a,    310   b,    310   c,  . . . ,  310   g,  inverter-gates  315   a,    315   b,    315   c,  . . . ,  315   f,  and comparators  320   a,    320   b,    320   c,  . . . ,  320   f.    
         [0027]    If the 3-phase sinusoidal AC source  125  has significant inductance, such as the 3-phase sinusoidal AC source illustrated in the rectifying circuit of FIG. 5, rectification of the 3-phase sinusoidal AC source  125  may be improved by providing additional timing circuitry to better control the gate signals Q 1 , Q 2 , Q 3 , Q 4 , Q 5 , Q 6  of MOSFETs  115   a,    120   a,    115   b,    120   b,    115   c,    120   c.    
         [0028]    Referring now to FIG. 6, there is seen another exemplary control circuit  600  according to the present invention for rectifying a 3-phase sinusoidal AC source  125  having an inductance. Control circuit  600  is operable to turn on gate signals Q 1 , Q 2 , Q 3 , Q 4 , Q 5 , Q 6 , based solely on phase voltage values. Specifically, when the phase voltage exceeds (resp. falls below) a fixed value, the high side (resp. low side) body diode conducts and therefore the high side (resp. low side) MOSFET can be turned on.  
         [0029]    The control circuit  600  of FIG. 6 performs MOSFET turn-off in diode mode by keeping gate signals Q 1 , Q 2 , Q 3 , Q 4 , Q 5 , Q 6  turned off, and by estimating the period of the 3-phase sinusoidal AC source  125 . Diode rectification may last, for example, 1.5 ms. With the period information, the MOSFET gate driver can estimate the turn-off commutation times. A delay, for example, 100 us, may be provided, so that the actual turn-off of gate signals Q 1 , Q 2 , Q 3 , Q 4 , Q 5 , Q 6  occurs before the end of the period, thereby causing the body diode of the MOSFET to conduct for the duration of the delay. However, the delay should be large enough to accommodate the largest source period variation. Control circuit  600  may, for example, continuously measure and update the source period information to keep track of the evolution of the 3-phase sinusoidal AC source  125 .  
         [0030]    It should be appreciated that the delay and diode rectification times may be adjusted in accordance with a particular application.  
         [0031]    Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein.