Abstract:
A series-parallel rectifier system and methodology, employing multiple parallel rectification paths is disclosed. The system includes a dual winding AC power supply and a rectifier apparatus coupled to the AC power supply. The rectifier apparatus is comprised of rectifier legs interconnected in a parallel circuit relationship, where each leg comprises several rectifiers including a connection in series and oriented to conduct current from a negative DC bus to a positive DC bus. Bypass legs comprising two rectifiers including a connection in series and oriented so as to conduct current from said negative DC bus to said positive DC bus are added in place of redundant rectifier legs and interconnected with the AC power supply.

Description:
BACKGROUND 
     Propulsion systems for traction vehicles such as locomotives commonly use a diesel engine prime mover to drive electric generating means for supplying energy to a plurality of direct current (DC) traction motors. The generating means typically comprises a 3-phase dual output alternator where each output comprises three phase windings interconnected in a 3-phase star configuration. The alternator voltages are rectified and applied to relatively positive and negative DC buses between which the respective pairs of motors which are generally connected in parallel. 
     Referring now to FIG. 1, which depicts a typical series-parallel alternator-rectifier system  10  comprising a dual winding AC power supply (e.g. alternator)  200  interconnected with a rectifier assembly  14  including series-parallel switches  46  and  48 . The three different phases of the first set of windings  210  are respectively identified as  222 ,  224 , and  226 , which may typically represent what is commonly termed as phases A, B, and C respectively. Likewise, the three different phases of the second set of windings  220  are identified as  212 ,  214 , and  216 , which again, may typically represent what is commonly termed as phases A prime, B prime, and C prime respectively for the second set of windings  220 . 
     The rectifier assembly  14  is formed by an array of rectifiers or rectifiers, which are interconnected and arranged between the dual winding AC power supply  200  and the positive DC bus  100   p  and negative DC bus  100   n . In FIG. 1, the rectifier assembly  14  has two series-parallel switches  46  and  48  and three primary legs connected in parallel circuit relationship between the DC buses. Each leg of the three primary legs comprises a four rectifiers (e.g. diodes) connected in series with one another and oriented to conduct current in a direction from negative DC bus  100   n  to positive DC bus  100   p . A first primary leg  120  comprises a first rectifier  22 , a second rectifier  24 , a third rectifier  52 , and a fourth rectifier  54  connected in series with one another and oriented to conduct current in a direction from negative DC bus  100   n  to positive DC bus  100   p . The second primary leg  130  comprises a first rectifier  30 , a second rectifier  32 , a third rectifier  60 , and a fourth rectifier  62  similarly connected and oriented. Finally, the third primary leg  140  also comprises a first rectifier  38 , a second rectifier  40 , a third rectifier  68 , and a fourth rectifier  70  in the same connection and orientation. 
     The first set of windings  210  of the AC power supply  200  is connected to the respective primary legs of the rectifier assembly  14  by three lines  102 ,  104 , and  106 . Where line  102  connects at the junction of rectifiers  22  and  24  of the first primary leg, line  104  connects at the junction of rectifiers  30  and  32  of the second primary leg, and line  106  connects at the junction of rectifiers  38  and  40  of the third primary leg. Similarly, the second set of windings  220  of the dual winding AC power supply  200  is correspondingly connected to the respective primary legs of the rectifier assembly  14  by three lines  112 ,  114 , and  116 . Where line  112  connects at the junction of rectifiers  52  and  54  of the first primary leg, line  114  connects at the junction of rectifiers  60  and  62  of the second primary leg, and line  116  connects at the junction of rectifiers  68  and  70  of the third primary leg. Thus, the two sets of windings  210  and  220  are effectively connected in parallel between the DC buses  100   n  and  100   p  with the series-parallel switches  46  and  48  open. 
     Since each of these two paths includes passing through the same number of rectifiers and since the voltage of phase  212  has the same instantaneous magnitude and polarity as the voltage of phase  222 , the parallel paths share current substantially equally. It is noteworthy the current passes through at least four rectifiers to complete the circuit. Note also, that each of the outboard rectifiers  22 ,  30 ,  38 ,  54 ,  62 , and  70  now have to conduct twice as much current as each of the inboard rectifiers  24 ,  32 ,  40 ,  52 ,  60 , and  68 . Therefore, the current rating of these rectifiers is commonly based on the higher duty of the outboard rectifiers, or the rectifier assembly  14  should be physically arranged so that the outboard rectifiers receive preferential cooling. 
     In addition, the described arrangement of the rectifier assemblies may be supplemented by adding rectifiers or rectifier legs to the rectifier assembly  14 . Each supplemental leg similarly connected and conducting current in a similar fashion as described above. For example, a supplemental leg in parallel to each of the legs described above. Such a configuration is depicted in FIG. 1 with first, second and third supplemental legs  122 ,  132 , and  142  respectively. Those skilled in the art will appreciate that such a parallel configuration as described provides effectively double the current rectification capability for the overall system thereby allowing for the use of reduced rating components (e.g., lower current rating rectifiers) or for higher current capability negative DC bus  100   n  and  100   p.    
     The above described configuration results in the certain rectifiers of each leg being required to conduct more current than others in the leg. Further, in a typical configuration the individual rectifiers may very well be part of a larger package including several individual rectifiers and further may even include interconnections between the individual elements within the package. In consideration of such a typical application, some rectifiers is such a package may be required to conduct more current than others, while others may see varying voltage constraints. This type of configuration forces under-utilization of some components to satisfy the rating requirements of others. It is therefore seen to be desirable to have a rectifier assembly, configured to reduce or eliminate under-utilized components, thereby providing maximal capability within a particular rectifier&#39;s ratings. 
     SUMMARY OF THE INVENTION 
     An exemplary embodiment is disclosed for a series-parallel rectifier system and methodology, employing multiple parallel rectification paths. The system includes a dual winding AC power supply with phase matched alternating voltages and a rectifier apparatus coupled to the AC power supply. The rectifier apparatus comprises a series-parallel switches and rectifier legs interconnected in a parallel circuit relationship, with each leg comprising several rectifiers connected in series and oriented to conduct current from a negative DC bus to a positive DC bus. Bypass legs comprising two rectifiers connected in series and oriented so as to conduct current from said negative DC bus to said positive DC bus are added in place of redundant rectifier legs and interconnected with the AC power supply. 
     An alternative embodiment is disclosed for a series-parallel rectifier system and methodology, employing multiple parallel rectification paths. The system includes a dual winding AC power supply with phase matched alternating voltages and a rectifier apparatus coupled to the AC power supply. The rectifier apparatus comprises series-parallel switches and rectifier legs interconnected in a parallel circuit relationship, with each leg comprising several rectifiers connected in series and oriented to conduct current from a negative DC bus to a positive DC bus. The rectifier legs are interconnected with the AC power supply. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring now to the drawings wherein like elements are numbered alike in the several FIGS: 
     FIG. 1 depicts a schematic of an alternator and rectifier assembly; 
     FIG. 2 depicts a schematic of an embodiment of bypass rectifier rectifier apparatus; and 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention may be utilized in various types of alternating current (AC) induction motor powered vehicles such as, for example, transit cars and locomotives. A preferred embodiment of the invention, by way of illustration is described herein as it may be applied to a locomotive. While a preferred embodiment is shown and described, it will be appreciated by those skilled in the art that the invention is not limited to locomotives but may also be applied to alternator-rectifier combinations and devices powered by such. 
     FIG.  2 . depicts an AC power supply  200 , typically a dual winding alternator, interconnected with a rectifier apparatus  16 . Like above, the three different phases of the first set of windings  210  are identified as  212 ,  214 , and  216  respectively, and the three different phases of the second set of windings  220  are identified as  222 ,  224 , and  226  respectively. 
     The rectifier apparatus  16  is formed by an array of rectifiers, commonly diodes, which are interconnected and arranged between the AC power supply  200  and the DC buses  100   p  and  100   n.  The rectifier apparatus  16  includes series-parallel switches  46  and  48  and has three main legs connected in parallel circuit relationship between the DC buses. Each leg of the three main legs comprises a four rectifiers connected in series with one another and oriented to conduct current in a direction from negative DC bus  100   n  to positive DC bus  100   p . A first main leg  124  of the three legs comprises a first rectifier  22 , a second rectifier  24 , line  88 , line  90 , a third rectifier  52 , and a fourth rectifier  54  conductively connected in series with one another and oriented to conduct current in a direction from negative DC bus  100   n  to positive DC bus  100   p . More particularly, the fourth rectifier  54 , having its anode connected to negative DC bus  100 n, while its cathode is connected to the anode of the third rectifier  52  and so on, ultimately terminating with the cathode of the first rectifier being connected to positive DC bus  100   p . The second main leg  134  comprises a first rectifier  30 , a second rectifier  32 , line  92 , line  94 , a third rectifier  60 , and a fourth rectifier  62  similarly connected and oriented. Finally, the third main leg  144  also comprises a first rectifier  38 , a second rectifier  40 , line  96 , line  98 , a third rectifier  68 , and a fourth rectifier  70  in the same connection and orientation. 
     The first set of windings  210  of the dual winding AC power supply  200  is connected to the respective main legs of the rectifier apparatus  16  by three lines  102 ,  104 , and  106 . Where line  102  connects at the junction of rectifiers  22  and  24  of the first main leg, line  104  connects at the junction of rectifiers  30  and  32  of the second main leg, and line  106  connects at the junction of rectifiers  38  and  40  of the third main leg. Similarly, the second set of windings  220  of the dual winding AC power supply is correspondingly connected to the respective main legs of the rectifier apparatus  16  by three lines  112 ,  114 , and  116 . Where line  112  connects at the junction of rectifiers  52  and  54  of the first main leg, line  114  connects at the junction of rectifiers  60  and  62  of the second main leg, and line  116  connects at the junction of rectifiers  68  and  70  of the third main leg. Thus, the two sets of windings  210  and  220  are effectively connected in parallel between the DC buses  100   n  and  100   p.    
     In addition, the described arrangement of the rectifier apparatus  16  may be supplemented by the addition of rectifiers or rectifier legs to the rectifier apparatus  16 . Each supplemental leg similarly connected and conducting current in a similar fashion as described earlier. For example, FIG. 1 depicts the first, second and third supplemental legs  122 ,  132 , and  142  respectively in parallel to each of the legs  120 , 130 , and  140 . 
     An embodiment of the invention is depicted in FIG. 2 highlighting the rectifier apparatus  16 , where the paralleled supplemental legs,  122 ,  132 , and  142  (FIG. 1) are replaced by an alternate set of paralleled legs, termed bypass legs. Where the first bypass leg  126  comprises a first rectifier  76 , and a second rectifier  78  conductively connected in series with one another, to negative DC bus  100   n  to positive DC bus  100   p , and oriented to conduct current in a direction from negative DC bus  100   n  to positive DC bus  100   p . More particularly, the second rectifier  78 , having its anode connected to negative DC bus  100   n , while its cathode is connected to the anode of the first rectifier  76  and its cathode being connected to positive DC bus  100   p . In addition, the junction of the first rectifier  76  and the second rectifier  78  of the first bypass leg  126  is conductively connected to the anode of the second rectifier  22  of the first main leg  124  via line  88  and the cathode of the third rectifier  52  of the first main leg  124  via line  90 . The second bypass leg  136  comprises a first rectifier  80 , and a second rectifier  82  conductively connected in series with one another, to the negative DC bus  100 n to  100   p , and oriented to conduct current in a direction from negative DC bus loon to positive DC bus  100   p . Likewise, the second rectifier  82 , of the second bypass leg  136 , having its anode connected to negative DC bus  100   n , while its cathode is connected to the anode of the first rectifier  80  and its cathode being connected to positive DC bus  100   p . In addition, the junction of the first rectifier  80  and the second rectifier  82  is conductively connected to the anode of the second rectifier  32  of the second main leg  134  via line  92  and third rectifier  60  of the second main leg  134  via line  94 . Similarly, the third bypass leg  146  comprises a first rectifier  84 , and a second rectifier  86  conductively connected in series with one another, to the negative DC bus  100   n  to  100   p , and oriented to conduct current in a direction from negative DC bus  100   n  to positive DC bus  100   p . Again, the second rectifier  86 , of the second bypass leg  136 , having its anode connected to negative DC bus  100   n , while its cathode is connected to the anode of the first rectifier  84  and its cathode being connected to positive DC bus  100   p . Similarly, the junction of the first rectifier  84  and the second rectifier  86  is conductively connected to the anode of the second rectifier  40  of the third main leg  144  via line  96  and the cathode of third rectifier  68  of the third main leg  144  via line  98 . 
     An embodiment as described, yields a configuration of a rectifier apparatus  16  where the main legs  124 ,  134 , and  144  coupled with the bypass legs  126 ,  136 , and  146  (FIG. 2) provide effectively the same rectification and current capability as the paralleled leg configuration with the combination of legs  120 ,  130 , and  140  with  122 ,  132 , and  142  (FIG.  1 ). However, the bypass legs  126 ,  136 , and  146  utilize two less rectifiers per leg than the typical configuration. Moreover, such a configuration amounts to a 25 percent reduction in rectifier component count as well as a commensurate reduction in the cumulative power dissipated by the rectifier apparatus  16 . 
     The significance of such improvements may be further illustrated by considering the currents in the respective windings of the AC power supply  200  and through the rectifier legs under particular conditions. Consider again, the condition when the potential at the terminal of the phase  212  (and  222 ) winding is at its positive peak relative to the potential at the terminal of the phase  216  (and  226 ) winding and the potential at the terminal of the phase  214  (and  224 ) winding respectively. Under these conditions, for the phase  222 , source current flows out of line  112  through the first rectifier  52  of the first main leg  124  through line  90 . The source current continues through the first third rectifier  76  of the first bypass leg, to combine with source current from the phase  212  and through the first rectifier  22  of the first main leg  124  to the relatively positive DC bus  100   p . Having passed through the load circuit the current returns from the negative DC bus  10 on splits four ways: (1) through the fourth rectifier  62  of the second main leg  134  to line  114  and into phase  224  of the second set of windings  220 ; (2) through the fourth rectifier  70  of the third leg  140  to line  116  and into phase  226  of the second set of windings  220 ; (3) through the second rectifier  82  of the second bypass leg  134 , through line  92 , through the second rectifier  32  of the second bypass leg  136  onto line  104  and to phase  214  of the first set of windings  210 ; and (4) through the second rectifier  86  of the third bypass leg  144 , through line  96 , through the second rectifier  40  of the third main leg  144  onto line  106  to phase  216  of the first set of windings  210 . Each of these paths includes passing through the same number of rectifiers and since the voltage of the phase  212  has the same instantaneous magnitude and polarity as the voltage of the phase  222 ; the parallel paths share current substantially equally. However, unlike in the typical rectifier assembly  14  (FIG.  1 ), the path includes conduction through three rectifiers rather than four. This results in a reduction of the total rectifier voltage drop per circuit path by one. It will be appreciated that such an embodiment of a rectifier apparatus  16  would also provide of a more efficient voltage generation of the buses  100   n  and  100   p  via the elimination of the losses associated with the previously encountered fourth rectifier voltage drop. 
     It is noteworthy to consider that the bypass legs  126 - 146  may not necessarily be collocated with the main legs  124 ,  134 , and  144 . Such an arrangement may give rise to dynamic effects to the paths taken by the current through the rectifier apparatus. As the separation between elements of the rectifier apparatus  16  increases, or as the current magnitudes increase, such dynamic effects due to cabling, or interconnections may become more pronounced. The embodiment as described above employs interconnection lines  88 - 98  in a topology disposed in a fashion to ensure that the inductive reactance presented by the rectifier apparatus  16  to both the first set of windings  210  and second set of windings  220  is nearly equivalent. Such an approach, as embodied, ensures that the bypass legs  126 ,  136 , and  146  share the total current through the rectifier apparatus  16  equally with the main legs  124 ,  134 , and  144 . By utilizing an appropriately balanced topology for the alternator rectifier circuit, the loop impedances encountered by both winding sets  210  and  220  will be relatively equal. Therefore, maintaining the current relatively equal in every leg  124 - 146  for equivalent voltages from each of the windings of the AC power supply  200 . 
     It is of further merit to note that, in the disclosed embodiment as distinguished from a typical rectifier assembly  14  (FIG.  1 ), each of the rectifiers and the circuit interconnection is configured to conduct substantially the same amount of current. Thereby, providing for selection of rectifiers all having the same rating, and minimizing the under-utilization of components in the rectifier apparatus  16 . It is of further significance to recognize that such an embodiment reduces the required cooling by reducing dissipated power but also eliminates the potential requirement for preferential cooling of higher duty rectifiers. 
     While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration only, and such illustrations and embodiments as have been disclosed herein are not to be construed as limiting to the claims.