Abstract:
A system for bypassing a power cell of a power supply, the system including a multi-winding device having a primary winding and a plurality of three-phase secondary windings, a plurality of power cells, wherein each power cell is connected to a different three-phase secondary winding of the multi-winding device, and a bypass device connected to first and second input terminals of at least one of the power cells and to first and second output terminals of the at least one of the power cells.

Description:
RELATED APPLICATIONS AND CLAIM OF PRIORITY 
       [0001]    This application claims the priority benefit of U.S. Provisional Application No. 60/971,965 filed Sep. 13, 2007, and U.S. Provisional Application No. 60/971,972 filed Sep. 13, 2007, each of which are hereby incorporated by reference. 
         [0002]    Not Applicable 
     
    
     BACKGROUND 
       [0003]    This application discloses an invention that is related, generally and in various embodiments, to a method and system for bypassing a power cell in a multi-cell power supply. In certain applications, multi-cell power supplies utilize modular power cells to process power between a source and a load. Such modular power cells can be applied to a given power supply with various degrees of redundancy to improve the availability of the power supply. For example,  FIG. 1  illustrates various embodiments of a power supply (e.g., an AC motor drive) having nine such power cells. The power cells in  FIG. 1  are represented by a block having input terminals A, B, and C; and output terminals T 1  and T 2 . In  FIG. 1 , a transformer or other multi-winding device  110  receives three-phase, medium-voltage power at its primary winding  112 , and delivers power to a load  130  such as a three-phase AC motor via an array of single-phase inverters (also referred to as power cells). Each phase of the power supply output is fed by a group of series-connected power cells, called herein a “phase-group”. 
         [0004]    The transformer  110  includes primary windings  112  that excite a number of secondary windings  114 - 122 . Although primary winding  112  is illustrated as having a star configuration, a mesh configuration is also possible. Further, although secondary windings  114 - 122  are illustrated as having a delta or an extended-delta configuration, other configurations of windings may be used as described in U.S. Pat. No. 5,625,545 to Hammond, the disclosure of which is incorporated herein by reference in its entirety. In the example of  FIG. 1  there is a separate secondary winding for each power cell. However, the number of power cells and/or secondary windings illustrated in  FIG. 1  is merely exemplary, and other numbers are possible. Additional details about such a power supply are disclosed in U.S. Pat. No. 5,625,545. 
         [0005]    Any number of ranks of power cells are connected between the transformer  110  and the load  130 . A “rank” in the context of  FIG. 1  is considered to be a three-phase set, or a group of three power cells established across each of the three phases of the power delivery system. Referring to  FIG. 1 , rank  150  includes power cells  151 - 153 , rank  160  includes power cells  161 - 163 , and rank  170  includes power cells  171 - 173 . A master control system  195  sends command signals to local controls in each cell over fiber optics or another wired or wireless communications medium  190 . It should be noted that the number of cells per phase depicted in  FIG. 1  is exemplary, and more than or less than three ranks may be possible in various embodiments. 
         [0006]      FIG. 2  illustrates various embodiments of a power cell  210  which is representative of various embodiments of the power cells of  FIG. 1 . The power cell  210  includes a three-phase diode-bridge rectifier  212 , one or more direct current (DC) capacitors  214 , and an H-bridge inverter  216 . The rectifier  212  converts the alternating current (AC) voltage received at cell input  218  (i.e., at input terminals A, B and C) to a substantially constant DC voltage that is supported by each capacitor  214  that is connected across the output of the rectifier  212 . The output stage of the power cell  210  includes an H-bridge inverter  216  which includes two poles, a left pole and a right pole, each with two switching devices. The inverter  216  transforms the DC voltage across the DC capacitors  214  to an AC output at the cell output  220  (i.e., across output terminals T 1  and T 2 ) using pulse-width modulation (PWM) of the semiconductor devices in the H-bridge inverter  216 . 
         [0007]    As shown in  FIG. 2 , the power cell  210  may also include fuses  222  connected between the cell input  218  and the rectifier  212 . The fuses  222  may operate to help protect the power cell  210  in the event of a short-circuit failure. According to other embodiments, the power cell  210  is identical to or similar to those described in U.S. Pat. No. 5,986,909 (the “&#39;909 Patent”) and its derivative U.S. Pat. No. 6,222,284 (the “&#39;284 Patent) to Hammond and Aiello, the disclosures of which are incorporated herein by reference in their entirety. 
         [0008]      FIG. 3  illustrates various embodiments of a bypass device  230  connected to output terminals T 1  and T 2  of the power cell  210  of  FIG. 2 . In general, when a given power cell of a multi-cell power supply fails in an open-circuit mode, the current through all the power cells in that phase-group will go to zero, and further operation is not possible. A power cell failure may be detected by comparing a cell output voltage to the commanded output, by checking or verifying cell components, through the use of diagnostics routines, etc. In the event that a given power cell should fail, it is possible to bypass the failed power cell and continue to operate the multi-cell power supply at reduced capacity. 
         [0009]    The bypass device  230  is a single pole single throw (SPST) contactor, and includes a contact  232  and a coil  234 . As used herein, the term “contact” generally refers to a set of contacts having stationary portions and a movable portion. Accordingly, the contact  232  includes stationary portions and a movable portion which is controlled by the coil  234 . The bypass device  230  may be installed as an integral part of a converter subassembly in a drive unit. In other applications the bypass device  230  may be separately mounted. When the movable portion of the contact  232  is in a bypass position, a shunt path is created between the respective output lines connected to output terminals T 1  and T 2  of the power cell  210 . Stated differently, when the movable portion of the contact  232  is in a bypass position, the output of the failed power cell is shorted. Thus, when power cell  210  experiences a failure, current from other power cells in the phase group can be carried through the bypass device  230  connected to the failed power cell  210  instead of through the failed power cell  210  itself. 
         [0010]      FIG. 4  illustrates various embodiments of a different bypass device  240  connected to output terminals T 1  and T 2  of the power cell  210 . The bypass device  240  is a single pole double throw (SPDT) contactor, and includes a contact  242  and a coil  244 . The contact  242  includes stationary portions and a movable portion which is controlled by the coil  244 . When the movable portion of the contact  242  is in a bypass position, one of the output lines of the power cell  210  is disconnected (e.g., the output line connected to output terminal T 2  in  FIG. 4 ) and a shunt path is created between the output line connected to output terminal T 1  of the power cell  210  and a downstream portion of the output line connected to output terminal T 2  of the power cell  210 . The shunt path carries current from other power cells in the phase group which would otherwise pass through the power cell  210 . Thus, when power cell  210  experiences a failure, the output of the failed power cell is not shorted as is the case with the bypass configuration of  FIG. 3 . 
         [0011]    The bypass devices shown in  FIGS.3 and 4  do not operate to disconnect power to any of the input terminals A, B or C in the event of a power cell failure. Thus, in certain situations, if the failure of a given power cell is not severe enough to cause the fuses  222  (see  FIG. 2 ) to disconnect power to any two of input terminals A, B or C, the failure can continue to cause damage to the given power cell. 
       SUMMARY 
       [0012]    In one general respect, this application discloses a system including a multi-winding device having a primary winding and a plurality of three-phase secondary windings, a plurality of power cells, wherein each power cell is connected to a different three-phase secondary winding of the multi-winding device, and a bypass device connected to first and second input terminals of at least one of the power cells and to first and second output terminals of at least one of the power cells. 
         [0013]    In another general respect, this application discloses a method including determining that a failure has occurred in a power cell of a multi-cell power supply and applying a pulse of current from a control circuit to a coil. The coil is connected to a first contact which is connected to a first input terminal of the power cell, a second contact which is connected to a second input terminal of the power cell, and a third contact which is connected to first and second output terminals of the power cell. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0014]    Various embodiments of the invention are described herein by way of example in conjunction with the following figures. 
           [0015]      FIG. 1  illustrates various embodiments of a power supply; 
           [0016]      FIG. 2  illustrates various embodiments of a power cell of the power supply of  FIG. 1 ; 
           [0017]      FIG. 3  illustrates various embodiments of a bypass device connected to an output of the power cell of  FIG. 2 ; 
           [0018]      FIG. 4  illustrates various embodiments of a bypass device connected to an output of the power cell of  FIG. 2 ; 
           [0019]      FIG. 5  illustrates various embodiments of a system for bypassing a power cell of a power supply; 
           [0020]      FIG. 6  illustrates various embodiments of a system for bypassing a power cell of a power supply; 
           [0021]      FIGS. 7-9  illustrate various embodiments of a bypass device; 
           [0022]      FIG. 10  illustrates various embodiments of a system for bypassing a power cell of a power supply; 
           [0023]      FIG. 11  illustrates various embodiments of a system for bypassing a power cell of a power supply; and 
           [0024]      FIG. 12  illustrates various embodiments of a system for bypassing a power cell of a power supply. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    It is to be understood that at least some of the figures and descriptions of the invention have been simplified to focus on elements that are relevant for a clear understanding of the invention, while eliminating, for purposes of clarity, other elements that those of ordinary skill in the art will appreciate may also comprise a portion of the invention. However, because such elements are well known in the art, and because they do not necessarily facilitate a better understanding of the invention, a description of such elements is not provided herein. 
         [0026]      FIG. 5  illustrates various embodiments of a system  250  for bypassing a power cell (e.g., power cell  210 ) of a power supply. As shown in  FIG. 5 , the system  250  includes bypass device  252  connected to the output terminals T 1  and T 2 , a bypass device  254  connected to input terminal A, and a bypass device  256  connected to input terminal C. Although the system  250  is shown in  FIG. 5  as having respective bypass devices connected to input terminals A and C, it will be appreciated that, according to other embodiments, the respective bypass devices may be connected to any two of the input terminals A, B and C. 
         [0027]    The bypass devices  252 ,  254 ,  256  may be mechanically-driven, fluid-driven, electrically-driven, or solid state, as is described in the &#39;909 and &#39;284 Patents. For purposes of simplicity, each bypass device will be described hereinafter in the context of a bypass device which includes one or more electrically-driven contactors which are connected to the output of a power cell. As described hereinafter, a given bypass device may be embodied as a single pole single throw (SPST) contactor, a single pole double throw (SPDT) contactor, or a multi-pole contactor. 
         [0028]    Bypass device  252  is a single pole double throw (SPDT) contactor, and includes a contact  258  and a coil  260 . The contact  258  includes stationary portions and a movable portion which is controlled by the coil  260 . The bypass device  252  operates in a manner similar to that described hereinabove with respect to bypass device  240  of  FIG. 4 . The bypass device  254  is a single pole single throw (SPST) contactor, and includes a contact  262  and a coil  264 . The contact  262  includes stationary portions and a movable portion which is controlled by the coil  264 . The bypass device  256  is a single pole single throw (SPST) contactor, and includes a contact  266  and a coil  268 . The contact  266  includes stationary portions and a movable portion which is controlled by the coil  268 . In general, in the event of a failure, bypass devices  254 ,  256  disconnect the cell input power at substantially the same time that bypass device  252  creates a shunt path for the current that formerly passed through the failed power cell. 
         [0029]    The condition associated with the creation of the described shunt path and the disconnection of cell input power from at least two of the cell input terminals may be referred to as “full-bypass”. When the full bypass condition is present, no further power can flow into the failed cell. As described with respect to  FIG. 2 , the fuses  222  of the power cell may operate to help protect the power cell in the event of a short-circuit failure. However, in certain situations (e.g., when fault current is low), the fuses  222  may not clear quickly enough to prevent further damage to the failed power cell. According to various embodiments, the bypass devices  254 ,  256  are configured to act quicker than the fuses  222 , and the quicker action generally results in less damage to the failed power cell. 
         [0030]      FIG. 6  illustrates various embodiments of a system  270  for bypassing a power cell (e.g., power cell  210 ) of a power supply. The system  270  includes a single bypass device  272  which achieves the combined functionality of the bypass devices  252 ,  254 ,  256  of  FIG. 5 . The bypass device  272  is a multi-pole contactor which includes a first contact  274  connected to the output terminals T 1  and T 2  of the power cell, a second contact  276  connected to the input terminal A, and a third contact  278  connected to the input terminal C. Each of the contacts  274 ,  276 ,  278  include stationary portions and a movable portion. Although the second and third contacts  276 ,  278  are shown in  FIG. 6  as being connected to input terminals A and C, it will be appreciated that, according to other embodiments, the second and third contacts  276 ,  278  may be connected to any two of the input terminals A, B and C. The bypass device  272  also includes a single coil  280  which controls the movable portions of the contacts  274 ,  276 ,  278 . 
         [0031]    The previously discussed methods may be applied with conventional contactors or solenoids, specifically contactors that hold their contacts in a first position when the coil is not energized and hold their contacts in a second position when the coil is energized. However, it may be preferable to employ magnetic latching contactors or solenoids. Magnetically latching contactors or solenoids include permanent magnets which hold their contacts in either the first or second position when the coil is not energized, and upon the application of a brief pulse of voltage to the coil, the contacts transfer to the other position (i.e., first position to second position or second position to first position). A magnetic latching contactor may employ only one coil. In this contactor, the direction of transfer of the contacts may be determined by the polarity of the voltage pulse applied to the coil. Similarly, a magnetic latching contactor may employ two coils, such as the contactor described in U.S. Pat. No. 3,022,450 to Chase. In this type of contactor, the direction of transfer of the contacts may be determined by which of the two coils is energized. In the following exemplary description, a single-coil contactor embodiment is presented by way of example only. A two-coil contactor is equally valid and may be substituted for any of the single-coil contactors. In light of this, all references to the coils will include a possible two-coil reference as well, i.e., “coil(s)”. 
         [0032]      FIGS. 7-9  illustrate various embodiments of a bypass device  300 . The bypass device is a multi-pole contactor, and may be identical to or similar to the bypass device  272  of  FIG. 6 . The bypass device  300  includes a first contact which includes stationary portions  302 ,  304  and movable portion  306 , a second contact which includes stationary portions  308 ,  310  and a movable portion  312 , and a third contact which includes stationary portions  314 ,  316 ,  318 ,  320  and a movable portion  322 . The bypass device  300  also includes a solenoid, or coil(s)  324  which controls the movable portions  306 ,  312 ,  322  of the first, second and third contacts. The stationary portions  304 ,  310  of the first and second contacts may be connected to any two of the input terminals A, B and C of a power cell. The stationary portions  314 ,  318  of the third contact may be respectively connected to the output terminals T 1  and T 2  of a power cell. The movable portions  306 ,  312 ,  322  of the first, second and third contacts are shown in the normal or non-bypass position in  FIGS. 7 and 8 , and are shown in the bypass position in  FIG. 9 . 
         [0033]    As shown in  FIG. 7 , the bypass device  300  also includes electrical terminals  326  connected to the coil(s)  324 , a steel frame  328  which surrounds the coil(s)  324 , a first insulating plate  330  between the steel frame  328  and the stationary portions  304 ,  308 ,  310 ,  312  of the first and second contacts, a second insulating plate  332  between the steel frame  328  and the stationary portions  314 ,  316  of the third contact, and first and second support brackets  334 ,  336 . The bypass device  300  further includes a non-magnetic shaft  338  which passes through the coil(s)  324 , through openings in the steel frame  328 , through respective openings in first and second insulating plates  330 ,  332 , and through respective openings of the first and second support brackets  334 ,  336 . 
         [0034]    Additionally, the bypass device  300  also includes a first biasing member  340  between the first support bracket  334  and a first end of the non-magnetic shaft  338 , a second biasing member  342  between the second support bracket  336  and a second end of the non-magnetic shaft, and a position sensing device  344  which is configured to provide an indication of the position (bypass or non-bypass) of the movable portions  306 ,  312 ,  322  of the first, second and third contacts. 
         [0035]    Although not shown for purposes of simplicity in  FIGS. 7-9 , one skilled in the art will appreciate that the bypass device  300  may further include a plunger (e.g., a cylindrical steel plunger) which can travel axially through an opening which extends approximately from the first end of the coil(s)  324  to the second end of the coil(s)  324 , permanent magnets capable of holding the movable portions of the contacts in either the bypass or the non-bypass position without current being applied to the coil(s)  324 , a first insulating bracket which carries the moving portions  306 ,  312  of the first and second contacts, a second insulating bracket which carries the moving portion  322  of the third contact, etc. 
         [0036]    In operation, permanent magnets (not shown) hold the plunger in either a first or a second position, which in turn holds the movable portions  306 ,  312 ,  322  of the contacts in either the non-bypass position or the bypass position. When the electrical terminals  326  receive pulses of current, the pulses of current are applied to the coil(s)  324 , thereby generating a magnetic field. Depending on the polarity of the applied pulse and the position of the plunger, the applied pulse may or may not cause the plunger to change its position. For example, according to various embodiments, if the plunger is in the first position and the movable portions  306 ,  312 ,  322  of the contacts are in the non-bypass position, a positive current pulse will change the plunger from the first position to the second position, which in turn changes the movable portions  306 ,  312 ,  322  of the contacts from the non-bypass position to the bypass position. In contrast, if a negative current pulse is applied, the plunger will stay in the first position and the movable portions  306 ,  312 ,  322  of the contacts will stay in the non-bypass position. 
         [0037]    Similarly, according to various embodiments, if the plunger is in the second position and the movable portions  306 ,  312 ,  322  of the contacts are in the bypass position, a negative current pulse will change the plunger from the second position to the first position, which in turn changes the movable portions  306 ,  312 ,  322  of the contacts from the bypass position to the non-bypass position. In contrast, if a positive current pulse is applied, the plunger will stay in the second position and the movable portions  306 ,  312 ,  322  of the contacts will stay in the bypass position. 
         [0038]      FIG. 10  illustrates various embodiments of a system  350  for bypassing a power cell (e.g., power cell  210 ) of a power supply. The system  350  is similar to the system  250  of  FIG. 5 . The system  350  includes a first contact  352  connected to the output terminals T 1  and T 2  of the power cell, a second contact  354  connected to the input terminal A of the power cell, and a third contact  356  connected to the input terminal C of the power supply. Each of the contacts  352 ,  354 ,  356  include stationary portions and a movable portion. Although the second and third contacts  354 ,  356  are shown in  FIG. 10  as being connected to input terminals A and C, it will be appreciated that, according to other embodiments, the second and third contacts  354 ,  356  may be connected to any two of the input terminals A, B and C. 
         [0039]    The system  350  also includes a first coil(s)  358  which controls the movable portions of the first contact  352 , a second coil(s)  360  which controls the movable portion of the second contact  354 , and a third coil(s)  362  which controls the movable portion of the third contact  356 . According to various embodiments, the coils  358 ,  360 ,  362  are embodied as contactor coils. According to other embodiments, the coils  358 ,  360 ,  362  are embodied as part of magnetic latching contactors which do not need to have continuous power applied to the coils in order to hold the plunger in its first or second position and/or to hold the moving portions of the contacts  352 ,  354 ,  356  in the non-bypass or bypass position. As previously discussed, the magnetic latching contactors may employ a single-coil or a two-coil configuration. The first contact  352  and the first coil(s)  358  may collectively comprise a first contactor, the second contact  354  and the second coil(s)  360  may collectively comprise a second contactor, and the third contact  356  and the third coil(s)  362  may collectively comprise a third contactor. 
         [0040]    The system  350  further includes a first local printed circuit board  364  in communication with the first coil(s)  358 , a second local printed circuit board  366  in communication with the second coil(s)  360 , and a third local printed circuit board  368  in communication with the third coil(s)  362 . Each of local printed circuit boards  364 ,  366 ,  368  are configured to control the respective movable portions of the contacts  352 ,  354 ,  356  via the respective coils  358 ,  360 ,  362 . In general, each of the local printed circuit boards  364 ,  366 ,  368  is configured to receive commands from, and report status to, a master control device (e.g., master control system  195  of  FIG. 1 ) that is held near ground potential. Each of the local printed circuit boards  364 ,  366 ,  368  are also configured to deliver pulses of energy to the respective coils  358 ,  360 ,  362  as needed to change the position of the movable portions of the respective contacts  352 ,  354 ,  356 , and to recognize the position of the movable portions of the respective contacts  352 ,  354 ,  356 . For example, if the master control device detects that a power cell is to be bypassed, the master control device may send a signal to an individual printed circuit board (e.g., printed circuit board  364 ). Upon receiving the signal, the printed circuit board may control the movable portion of its respective contact, thereby bypassing the power cell. Each of the local printed circuit boards  364 ,  366 ,  368  may obtain control power from the input lines which are connected to input terminals A, B, C of the power cell, or from a remote power source. As shown in  FIG. 10 , one or more position sensing devices (PSD)  365 ,  367 ,  369  may be utilized to provide the local printed circuit boards  364 ,  366 ,  368  with the respective positions of the movable portions of the contacts  352 ,  354 ,  356 . According to various embodiments, the position sensing devices may be embodied as switching devices, Hall Effect sensors, optical sensors, etc. 
         [0041]    For embodiments where the coils  358 ,  360 ,  362  are part of magnetic latching contactors, the local printed circuit boards  364 ,  366 ,  368  may each include a DC capacitor which can store enough energy to switch the plunger and/or the movable portions of the respective contacts  352 ,  354 ,  356  between positions. Each of the local printed circuit boards  364 ,  366 ,  368  may also include a power supply which restores the stored energy after a switching event, using AC power from the input lines connected to the input terminals A, B, C of the power cell, or from a remote power source. 
         [0042]      FIG. 11  illustrates various embodiments of a system  370  for bypassing a power cell (e.g., power cell  210 ) of a power supply. The system  370  is similar to the system  350  of  FIG. 10 . The system  370  includes a first contact  372  connected to the output terminals T 1  and T 2  of the power cell, a second contact  374  connected to the input terminal A of the power cell, and a third contact  376  connected to the input terminal C of the power supply. Each of the contacts  372 ,  374 ,  376  include stationary portions and a movable portion. Although the second and third contacts  374 ,  376  are shown in  FIG. 11  as being connected to input terminals A and C, it will be appreciated that, according to other embodiments, the second and third contacts  374 ,  376  may be connected to any two of the input terminals A, B and C. 
         [0043]    The system  370  also includes a first coil(s)  378  which controls the movable portions of the first contact  372 , a second coil(s)  380  which controls the movable portion of the second contact  374 , and a third coil(s)  382  which controls the movable portion of the third contact  376 . According to various embodiments, the coils  378 ,  380 ,  372  are embodied as contactor coils. According to other embodiments, the coils  378 ,  380 ,  382  are embodied as part of magnetic latching contactors which do not need to have continuous power applied to the coils in order to hold the plunger in its first or second position and/or to hold the moving portions of the contacts  372 ,  374 ,  376  in the non-bypass or bypass position. As previously discussed, the magnetic latching contactors may employ a single-coil or a two-coil configuration. 
         [0044]    According to various embodiments, the first contact  372  and the first coil(s)  378  are portions of a first bypass device, the second contact  374  and the second coil(s)  380  are portions of a second bypass device, and the third contact  376  and the third coil(s)  382  are portions of a third bypass device. For such embodiments, the system  370  includes a plurality of bypass devices. 
         [0045]    In contrast to the system  350  of  FIG. 10 , the system  370  includes a single local printed circuit board  384  which is in communication with the first coil(s)  378 , the second coil(s)  380 , and the third coil(s)  382 . The local printed circuit board  384  is configured to control the respective movable portions of the contacts  372 ,  374 ,  376  via the respective coils  378 ,  380 ,  382 . Thus, the local printed circuit board  384  is similar to the local printed circuit boards described with respect to  FIG. 10 , but is different in that the local printed circuit board  384  is configured to drive three coils and recognize the respective positions of the movable portions of three contacts. In general, the local printed circuit board  384  is configured to receive commands from, and report status to, a master control device (e.g., master control system  195  of  FIG. 1 ) that is held near ground potential. 
         [0046]    The local printed circuit board  384  is also configured to deliver pulses of energy to the coils  378 ,  380 ,  382  as needed to change the position of the movable portions of the respective contacts  372 ,  374 ,  376 , and to detect the position of the movable portions of the respective contacts  372 ,  374 ,  376 . The local printed circuit board  384  may obtain control power from the input lines which are connected to input terminals A, B, C of the power cell, or from a remote power source. As shown in  FIG. 11 , one or more position sensing devices  379 ,  383 ,  385  may be utilized to provide the local printed circuit board  384  with the respective positions of the movable portions of the contacts  372 ,  374 ,  376 . According to various embodiments, the position sensing devices may be embodied as switching devices, Hall Effect sensors, optical sensors, etc. 
         [0047]    For embodiments where the coils  378 ,  380 ,  382  are part of magnetic latching contactors, the local printed circuit board  384  may include a DC capacitor which can store enough energy to switch the plunger and/or the movable portions of the contacts  352 ,  354 ,  356  between positions. The local printed circuit board  384  may also include a power supply which restores the stored energy after a switching event, using AC power from the input lines connected to the input terminals A, B, C of the power cell, or from a remote power source. 
         [0048]      FIG. 12  illustrates various embodiments of a system  390  for bypassing a power cell (e.g., power cell  210 ) of a power supply. The system  390  is similar to the system  370  of  FIG. 11 . The system  390  includes a bypass device  392  which may be embodied as a multi-pole contactor. The bypass device  392  may be identical to or similar to the bypass device  300  shown in  FIGS. 7-9 . The bypass device  392  includes a first contact  394  connected to the output terminals T 1  and T 2  of the power cell, a second contact  396  connected to the input terminal A of the power cell, and a third contact  398  connected to the input terminal C of the power supply. Each of the contacts  394 ,  396 ,  398  include stationary portions and a movable portion. Although the second and third contacts  396 ,  398  are shown in  FIG. 12  as being connected to input terminals A and C, it will be appreciated that, according to other embodiments, the second and third contacts  396 ,  398  may be connected to any two of the input terminals A, B and C. 
         [0049]    In contrast to system  370  of  FIG. 11 , the system  390  includes a coil(s)  400  which controls the movable portions of the first, second and third contacts  394 ,  396 ,  398 . According to various embodiments, the coil(s)  400  is embodied as a contactor coil. According to other embodiments, the coil(s)  400  is embodied as part of a magnetic latching contactor which does not need to have continuous power applied to the coil(s) in order to hold the plunger in its first or second position and/or to hold the moving portions of the contacts  394 ,  396 ,  398  in the non-bypass or bypass position. As previously discussed, the magnetic latching contactors may employ a single-coil or a two-coil configuration. 
         [0050]    The system  390  also includes a single local printed circuit board  402  which is in communication with the coil(s)  400 . The local printed circuit board  402  is configured to control the respective movable portions of the contacts  394 ,  396 ,  398  via the coil(s)  400 . In general, the local printed circuit board  402  is configured to receive commands from, and report status to, a master control device (e.g., master control system  195  of  FIG. 1 ) that is held near ground potential. 
         [0051]    The local printed circuit board  402  is also configured to deliver pulses of energy to the coil(s)  400  as needed to change the position of the movable portions of the respective contacts  394 ,  396 ,  398 , and to recognize the position of the movable portions of the respective contacts  394 ,  396 ,  398 . The local printed circuit board  402  may obtain control power from the input lines which are connected to input terminals A, B, C of the power cell. As shown in  FIG. 12 , a position sensing device  403  may be utilized to provide the local printed circuit board  402  with the respective positions of the movable portions of the contacts  394 ,  396 ,  398 . According to various embodiments, the position sensing device may be embodied as a switching device, a Hall Effect sensor, an optical sensor, etc. 
         [0052]    For embodiments where the coil  400  is part of a magnetic latching contactor, the local printed circuit board  402  may also include a DC capacitor which can store enough energy to switch the plunger and/or the movable portions of the contacts  394 ,  396 ,  398  between positions. The local printed circuit board  402  may also include a power supply which restores the stored energy after a switching event, using AC power from the input lines connected to the input terminals A, B, C of the power cell. 
         [0053]    While several embodiments of the invention have been described herein by way of example, those skilled in the art will appreciate that various modifications, alterations, and adaptions to the described embodiments may be realized without departing from the spirit and scope of the invention defined by the appended claims.