Abstract:
A method and electrical circuit for dynamic reconfiguration of a DC-to-AC inverter comprising first and second power rails where each the rails has a power source. The method comprises monitoring the first and second power rails for short-circuit failure; and upon failure of one of the power rails, disconnecting the failed power rail from its power source.

Description:
TECHNICAL FIELD 
   This invention relates to the field of electronics. More precisely, this invention pertains to a method and apparatus for providing a remedial strategy for an electrical circuit. 
   BACKGROUND OF THE INVENTION 
   Electrical circuits having switching cells such as semi-conductor devices (e.g., transistors) are problematic when the switching cells fail. The failure modes of these switching cells include open-circuit or short-circuit conditions. Most know remedial strategies only cover open-circuit switch failures. They therefore do not provide acceptable reliability of the original electrical circuit. 
   Accordingly, there is a need for improved remedial strategies for electrical circuits. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention to provide a circuit and a method for enabling the implementation of a remedial strategy in a multi-phase DC-to-AC inverter. 
   According to a first aspect of the invention, there is provided an electronic circuit for maintaining electrical conditions at a connection point in a circuit. The electronic circuit comprises two circuit switches serially connected via the connection point in case of a failure of any one of the two circuit switches. The circuit comprises a first end and a second end between which the two circuit switches are located. The electronic circuit comprises a first actuable switch connected in parallel with the two circuit switches, a second actuable switch connected in series with the first end, a third actuable switch connected in series with the second end, and a control unit for controlling the first actuable switch, the second actuable switch and the third actuable switch depending on a status of any one of the two circuit switches. 
   According to another aspect of the invention, there is provided an electronic circuit for providing a remedial strategy in case of a failure of any one of two serially connected switches in an N-phase driving circuit, wherein each side of a given phase is connected between the two serially connected switches having current blocking means. The two serially connected switches comprise a first end and a second end between which the two serially connected switches are located. The electronic circuit comprises a first actuable switch, having current blocking means, connected in parallel with the two serially connected switches, a second actuable switch, having current blocking means, connected in series with the first end, a third actuable switch, having current blocking means, connected in series with the first end and a control unit for controlling the first actuable switch, the second actuable switch, and the third actuable switch depending on a status of anyone of the two serially connected switches. 
   According to yet another aspect of the invention, there is provided a method for dynamic reconfiguration of a DC-to-AC inverter comprising first and second power rails where each the rails has a power source. The method comprises monitoring the first and second power rails for short-circuit failure; and upon failure of one of the power rails, disconnecting the failed power rail from its power source. 
   Further details of these and other aspects of the present invention will be apparent from the detailed description and figures included below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Reference is now made to the accompanying figures depicting aspects of the present invention, in which: 
       FIG. 1 . is a block diagram showing an embodiment of a circuit for maintaining electrical conditions at a connection point between two circuit switches in the case of a failure of any one of the two circuit switches; 
       FIG. 2  is an electrical schematic showing an embodiment of the circuit for maintaining electrical conditions at a connection point between two circuit switches in the case of a failure of any one of the two circuit switches; 
       FIG. 3  is an electrical schematic showing a prior art single phase driving circuit; 
       FIG. 4  is an electrical schematic showing an embodiment where a circuit for maintaining electrical conditions in a single phase driving circuit; 
       FIG. 5  is an electrical schematic showing a prior art N-phase driving circuit; and 
       FIG. 6  is an electrical schematic showing an embodiment where a circuit for maintaining electrical conditions in an N-phase driving circuit. 
   

   It will be noted that throughout the appended drawings, like features are identified by like reference numerals. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Now referring to  FIG. 1 , there is shown an embodiment of a circuit  22  for maintaining electrical conditions at a connection point  14  between a first switch  10  and a second switch  12  in case of a failure of any one of the first  10  and the second  12  switches. 
   The circuit  22  comprises a first actuable switch  16 , a second actuable switch  18  and a third actuable switch  20 . A control unit  24  is preferably used as explained below. The first actuable switch  16  is connected in parallel with the first switch  10  and the second switch  12 . The second actuable switch  18  is connected in series with a first end of the assembly comprising the first switch  10 . The third actuable switch  20  is connected in series with a second end of the assembly comprising the first switch  10  and the second switch  12 . 
   The control unit  24  is used to control the first actuable switch  16 , the second actuable switch  18  and the third actuable switch  20  depending on the state of the first switch  10  and the second switch  12 . More precisely, the control unit  24  receives a first status signal from the first switch  10  and a second status signal from the second switch  12 . 
   The control unit  24  provides a configuration signal to the first actuable switch  16 , the second actuable switch  18  and the third actuable switch  20  depending on the first status signal and the second status signal. 
   It will be appreciated by the skilled addressee that each of the first switch  10  and the second switch  12  may be in a short-circuit failure mode and in an open-circuit failure mode outside a normal operating mode. 
   Each actuable switch may be actuated, by the control unit  24 , to be in an open configuration (also referred to as an open-circuit mode) or in a close configuration (also referred to as a short-circuit mode). 
   For example, in the case where the first switch  10  is in a short-circuit failure mode, the control unit  24  may control the first actuable switch  16 , the second actuable switch  18  and the third actuable switch  20  as follows. 
   The first actuable switch  16  and the second switch  12  may be switched to a short-circuit mode. The second actuable switch  18  and the third actuable switch  20  then operate as the first switch  10  and the second switch  12  were operating before the failure. 
   It is to be noted that any type of failure of both the first switch  10  and the second switch  12  may be handled using the first actuable switch  16 , the second actuable switch  18  and the third actuable switch  20 . 
   The skilled addressee will therefore appreciate that this is advantageous since it adds redundancy to an apparatus comprising two circuit switches. Furthermore, during normal operations, the second actuable switch  18  and the third actuable switch  20  are in a closed configuration while the first actuable switch  16  is in an open configuration. Upon short-circuit failure of one of switches  10  or  12 , first actuable switch  16  will close while the second actuable switch  18  and the third actuable switch  20  will open. This, in effect, disconnects switches  10  and  12  from the circuit of which they form part. 
   Now referring to  FIG. 2 , there is shown another circuit  34  for maintaining electrical conditions at a connection point between two circuit switches, respectively  30  and  32 , in the case of a failure of any one of the two circuit switches  30  and  32 . 
   The circuit  34  for maintaining electrical conditions comprises a first actuable switch  42 , a second actuable switch  40  and a third actuable switch  44 . More precisely, the first actuable switch  42  is connected in parallel with the first switch  30  and the second switch  32 . The second actuable switch  40  is connected in series with a first end of the assembly comprising the first switch  30 . The third actuable switch  44  is connected in series with a second end of the assembly comprising the first switch  30  and the second switch  32 . 
   A control unit, not shown in  FIG. 2 , may be used in order to control the first actuable switch  42 , the second actuable switch  40  and the third actuable switch  44 . It will be appreciated that the control unit may be used to monitor the operating state of the first switch  30  and the second switch  32 . 
   In the embodiment disclosed herein, the connection point  36  is connected to a phase Z  28 . Still in the present embodiment, the second actuable switch  40  and the third actuable switch  44  are powered using a power unit. 
   It will further be appreciated that in this embodiment, the first switch  30 , the second switch  32 , the first actuable switch  42 , the second actuable switch  40  and the third actuable switch  44  are semi-conductor devices which are controllable switches, bidirectional in current and unipolar in voltage. 
   Now referring to  FIG. 3 , there is shown a prior art single phase driving circuit for driving a phase  54 . The single phase driving circuit comprises a right rail  51  and a left rail  53 . The right rail  51  comprises a first switch  50  and a second switch  52 . The left rail  53  comprises a first switch  56  and a second switch  58 . 
   The skilled addressee will appreciate that the first switch  56 , the second switch  58 , the first switch  50  and the second switch  56  are used to drive the phase  54 . The right rail  51  and the left rail  53  share the same power source in the embodiment disclosed. Alternatively, each of the right rail  51  and the left rail  53  may be powered using a separate power source. 
   Now referring to  FIG. 4 , shows an embodiment of the single phase driving circuit disclosed in  FIG. 3  on which a circuit is added according to an embodiment of the invention. 
   The added circuit comprises a first element  71  and a second element  61  and it is intended to provide a remedial strategy in case of a failure of any one of the switches. The first element  71  and the second element  61  are similar to the circuit  34  disclosed in  FIG. 2 . It will be appreciated that redundancy is provided to the single phase driving circuit. Therefore increase reliability of the overall circuit is expected. 
   It is understood that the circuit (i.e., first element  71 ) operates in the similar manner to circuit  22  of  FIG. 1  and circuit  34  of  FIG. 2 . That is, upon short circuit failure of at one of switches  70  and  72  (i.e., failure of a power rail), actuable switches  76  and  78  open while actuable switch  74  closes thereby disconnecting the failed power rail from its power source. 
   Now referring to  FIG. 5 , there is shown a prior art N-phase driving circuit for driving an N-phase component. More precisely, the N-phase driving circuit is used to drive a first phase  84 , a second phase  94 , a third phase  104  . . . and an Nth-phase  116 . 
   More precisely, the first phase  84  is driven by a first group of switches comprising switch  86  and switch  88 . The first phase  84  is further driven by a second group of switches comprising switch  80  and switch  82 . 
   The second phase  94  is driven by a first group of switches comprising switch  90  and switch  92 . The second phase  94  is further driven by a second group of switches comprising switch  96  and switch  98 . 
   The third phase  104  is driven by a first group of switches comprising switch  100  and switch  102 . The third phase  104  is further driven by a second group of switches comprising switch  106  and switch  108 . 
   Finally, the Nth-phase  116  is driven by a first group of switches comprising switch  110  and switch  112 . The Nth-phase  116  is further driven by a second group of switches comprising switch  114  and switch  118 . 
   It will be appreciated by the skilled in the art that each phase is driven similarly to the phase  63  as disclosed in  FIG. 4 . Furthermore, it will be appreciated that each first group of switches to a first power unit while each second group of switches is connected to a second power unit. 
   Now referring to  FIG. 6 , there is shown a circuit for maintaining electrical conditions in the N-phase driving circuit disclosed in  FIG. 5 . The circuit comprises a first part  137  and a second part  127 . The first part  137  comprises a first actuable switch  136 , a second actuable switch  138  and a third actuable switch  140 . The second part  127  comprises a first actuable switch  126 , a second actuable switch  124  and a third actuable switch  128 . 
   The first actuable switch  136  is connected in parallel with the first switch  132  and the second switch  134 , with the first switch  148  and the second switch  146 , with the first switch  156  and the second switch  158 , and with the first switch  166  and the second switch  168 . The second actuable switch  138  is connected in series with a first end of the assembly comprising the first switch  132 , in series with a first end of the assembly comprising the first switch  148 , in series with a first end of the assembly comprising the first switch  156 , in series with a first end of the assembly comprising the first switch  156 . The third actuable switch  140  is connected in series with a second end of the assembly comprising the first switch  132  and the second switch  134 , in series with a second end of the assembly comprising the first switch  148  and the second switch  134 , in series with a second end of the assembly comprising the first switch  156  and the second switch  158 , in series with a second end of the assembly comprising the first switch  166  and the second switch  168 . 
   Similarly, the first actuable switch  128  is connected in parallel with the first switch  120  and the second switch  122 , in parallel with the first switch  142  and the second switch  144 , in parallel with the first switch  152  and the second switch  154 , in parallel with the first switch  162  and the second switch  154 . The second actuable switch  124  is connected in series with a first end of the assembly comprising the first switch  120 , in series with a first end of the assembly comprising the first switch  142 , in series with a first end of the assembly comprising the first switch  152 , in series with a first end of the assembly comprising the first switch  162 . The third actuable switch  128  is connected in series with a second end of the assembly comprising the first switch  120  and the second switch  122 , in series with a second end of the assembly comprising the first switch  142  and the second switch  144 , in series with a second end of the assembly comprising the first switch  152  and the second switch  154 , in series with a second end of the assembly comprising the first switch  162  and the second switch  164 . A control unit, not shown in  FIG. 6 , is used to drive switches  124 ,  126 ,  128 ,  136 ,  138  and  140 . 
   The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without department from the scope of the invention disclosed. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.