Patent Publication Number: US-8537575-B2

Title: Power converter and integrated DC choke therefor

Description:
REFERENCE TO RELATED APPLICATION 
     This application is a continuation of, and claims priority to and the benefit of, U.S. patent application Ser. No. 13/177,100, filed on Jul. 6, 2011, entitled POWER CONVERTER AND INTEGRATED DC CHOKE THEREFOR, now U.S. Pat. No. 8,379,417. the entirety of which application is hereby incorporated by reference. 
    
    
     BACKGROUND 
     Motor drives and other power conversion systems convert electrical power from one form to another, and may be employed in a variety of applications such as powering an electric motor using power converted from a single or multiphase AC input source. One common form of motor drive is a current source converter (CSC), in which a rectifier converts input AC power from a single or multiphase AC input source to provide DC current to a DC link circuit. An output inverter converts the DC link current into single or multiphase AC output power to drive a motor load. Such power conversion systems may be subject to both differential and common mode voltages and currents, which can cause a variety of problems including degradation of the power conversion system and/or the motor load. For instance, motors are susceptible to damage or performance degradation caused by appearance of excessive common mode voltages on the motor leads. Previously, low and medium voltage converters often include differential mode inductors as well as common mode control apparatus to address these problems. However, separate differential and common mode devices are costly and occupy space in a power conversion system. Other techniques include modification of switching waveforms in one or both of the rectifier and inverter stages, but such techniques often require complicated switching control systems. Common mode and differential mode noise effects can also be addressed by using isolation transformers within the power conversion system, but these transformers add cost to the system and occupy space. Thus, there remains a need for improved common mode and differential mode suppression apparatus and techniques in power conversion systems. 
     U.S. Pat. No. 7,164,254 to Kerkman et al., issued Jan. 16, 2007 and assigned to the assignee of the present application discloses common mode voltage reduction techniques in which the switching sequence is modified to avoid using the zero vectors in order to reduce common mode voltages in the motor. The entirety of this patent is hereby incorporated by reference as if fully set forth herein. 
     U.S. Pat. No. 7,106,025 to Yin et al., issued Sep. 12, 2006 and assigned to the assignee of the present application discloses techniques for canceling dead time effects in the algorithm to reduce common mode voltages produced by a three-phase power conversion device in a rectifier/inverter variable frequency drive (VFD), the entirety of which is hereby incorporated by reference as if fully set forth herein. 
     U.S. Pat. No. 5,422,619 to Yamaguchi et al., issued Jun. 6, 1995 discloses a common mode choke coil with a couple of U-shaped cores and 4 coils wound around legs of the cores, the entirety of which is hereby incorporated by reference as if fully set forth herein. 
     U.S. Pat. No. 5,905,642 to Hammond, issued May 18, 1999 discloses a common mode reactor between a DC converter and an AC converter to reduce common mode voltage from current source drives, the entirety of which is hereby incorporated by reference as if fully set forth herein. 
     U.S. Pat. No. 6,617,814 to Wu et al., issued Sep. 9, 2003 and assigned to the assignee of the present application discloses an integrated DC link choke and method for suppressing common-mode voltage and a motor drive, the entirety of which is hereby incorporated by reference as if fully set forth herein. 
     U.S. Pat. No. 6,819,070 to Kerkman et al., issued Nov. 16, 2004 and assigned to the assignee of the present application discloses inverter switching control techniques to control reflected voltages in AC motor drives, the entirety of which is hereby incorporated by reference as if fully set forth herein. 
     U.S. Pat. No. 7,034,501 to Thunes et al., issued Apr. 25, 2007 and assigned to the assignee of the present application discloses gate pulse time interval adjustment techniques for mitigating reflected waves in AC motor drives, the entirety of which is hereby incorporated by reference as if fully set forth herein. 
     SUMMARY 
     Various aspects of the present disclosure are now summarized to facilitate a basic understanding of the disclosure, wherein this summary is not an extensive overview of the disclosure, and is intended neither to identify certain elements of the disclosure, nor to delineate the scope thereof. Rather, the primary purpose of this summary is to present some concepts of the disclosure in a simplified form prior to the more detailed description that is presented hereinafter. The present disclosure presents power conversion systems and DC chokes with a core structure including first and second legs having at least four windings and one or more shunts providing a magnetic flux path between intermediate portions of the first and second core legs. 
     A power conversion system is provided which includes a rectifier, an inverter and a DC link choke providing coils coupled between the rectifier and the inverter. The rectifier includes first and second DC output nodes, and the inverter has first and second DC input nodes. The link choke includes a core structure with first and second legs, both of which include two ends and an intermediate portion. A third leg extends between the first ends of the first and second legs, and a fourth leg extends between the second ends of the first and second legs. In certain embodiments, the core structure includes a plurality of laminates. In certain embodiments, moreover, the core structure has no gaps in or between the legs. 
     One or more shunts are provided between the intermediate portions of the first and second legs to provide a magnetic flux path between the intermediate portions, where a plurality of gaps are formed between the shunt(s) and the intermediate portions, wherein at least one of the gaps may be zero in certain embodiments. Four or more windings are provided, with a first winding forming a first coil of the DC choke and having first and second terminals, with the first winding forming at least one turn around the first leg between the intermediate portion and the first end of the first leg. A second winding forms at least one turn between the intermediate portion and the second end of the first leg. In addition, a third winding forms at least one turn between the intermediate portion and the first end of the second leg, and a fourth winding forms at least one turn between the intermediate portion and the second end of the second leg. 
     In certain embodiments, two or more shunts are provided in the magnetic flux path between the intermediate portions of the first and second legs, where the shunts extend between the intermediate portions and form at least one additional gaps between the at least two shunts. 
     In certain embodiments, the first and third windings are coupled in series between the first DC output node of the rectifier and the first DC input node of the inverter, and the second and fourth windings are coupled in series with one another between the second rectifier DC output node and the second inverter DC input node. 
     In other embodiments, the first and second windings are coupled between the first rectifier DC output node and the first inverter DC input node, with the third and fourth windings being coupled in series between the second rectifier DC output node and the second inverter DC input node. 
     In further embodiments, the first and fourth windings are coupled between the first rectifier DC output node and the first inverter DC input node, and the second and third windings are coupled between the second rectifier DC output node and the second inverter DC input node. 
     In accordance with further aspects of the disclosure, an integrated DC link choke is provided, which is comprised of a core structure with four legs including a first leg having two ends and an intermediate portion disposed therebetween as well as a second leg with two ends and an intermediate portion. A third leg of the core structure extends between the first ends of the first and second legs, and a fourth leg extends between the second ends of the first and second legs. One or more shunts are provided which extend between the intermediate portions of the first and second legs to provide a magnetic flux path therebetween, and a plurality of gaps is formed between the intermediate portions of the first and second legs and the shunt(s). The choke further comprises four or more windings, including a first winding with first and second terminals and forming at least one turn around the first leg between the intermediate portion and the first end of the first leg. A second winding is provided which forms at least one turn between the intermediate portion and the second end of the first leg. A third winding is provided which forms at least one turn between the intermediate portion and the first end of the second leg, and a fourth winding forms at least one turn between the intermediate portion and the second end of the second leg. In certain embodiments, more than one gap is provided between the intermediate portions of the first and second legs, and at least one additional gap is formed between the shunts. In certain embodiments, moreover, the core structure includes a plurality of laminates. In addition, the core structure in certain embodiments is a continuous structure having no gaps in or between the legs. In certain embodiments, the first and third windings are coupled in series with one another, and the second and fourth windings are coupled in series with one another. In other embodiments, the first and second windings are coupled in series with one another, and the third and fourth windings are coupled in series with one another. In still other embodiments, the first and fourth windings are coupled in series with one another, and the second and third windings are coupled in series with one another. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following description and drawings set forth certain illustrative implementations of the disclosure in detail, which are indicative of several exemplary ways in which the various principles of the disclosure may be carried out. The illustrated examples, however, are not exhaustive of the many possible embodiments of the disclosure. Other objects, advantages and novel features of the disclosure will be set forth in the following detailed description when considered in conjunction with the drawings, in which: 
         FIG. 1  is a schematic diagram illustrating an exemplary current source converter type variable frequency motor drive power conversion system with an integrated DC link choke according to one or more aspects of the present disclosure; 
         FIG. 2  is a front elevation view illustrating an exemplary core structure for the integrated DC link choke, including a single shunt disposed between intermediate portions of first and second vertical core legs; 
         FIG. 3  is a front elevation view illustrating another exemplary DC link choke core structure having two shunts disposed between the vertical core legs; 
         FIG. 4  is a front perspective view illustrating a laminated DC link choke core structure with a single shunt extending between the vertical core legs; 
         FIG. 5  is a simplified front elevation view illustrating an exemplary DC link choke with first, second, third, and fourth windings located on the vertical core legs; 
         FIG. 6  is a schematic diagram illustrating an exemplary power conversion system with an integrated DC link choke in which the first and third windings are connected in an upper DC link current path and the second and fourth windings are connected in a lower DC link path; 
         FIG. 7  is a front elevation view illustrating connection of the DC link choke in the system of  FIG. 6 , as well as a differential mode equivalent circuit and corresponding magnetic flux paths in the link choke core structure; 
         FIG. 8  is a front elevation view illustrating the DC link choke in the system of  FIG. 6  along with a common mode equivalent circuit and corresponding magnetic flux paths in the link choke core structure; 
         FIG. 9  is a schematic diagram illustrating another motor drive power conversion system embodiment including an integrated DC link choke with the first and second windings connected in the upper DC link current path as well as the third and fourth windings connected in the lower DC link path; 
         FIG. 10  is a front elevation view illustrating connection of the DC link choke in the system of  FIG. 9  and a differential mode equivalent circuit and corresponding magnetic flux paths in the link choke core structure; 
         FIG. 11  is a front elevation view illustrating connection of the DC link choke in the system of  FIG. 9 , as well as a common mode equivalent circuit and corresponding magnetic flux paths in the link choke core structure; 
         FIG. 12  is a schematic diagram illustrating another power conversion system embodiment with the first and fourth DC link choke windings connected in the upper DC link current path and the second and third windings connected in the lower DC link path; 
         FIG. 13  is a front elevation view illustrating connection of the DC link choke in the system of  FIG. 12 , as well as a differential mode equivalent circuit and corresponding magnetic flux paths in the choke core structure; and 
         FIG. 14  is a front elevation view illustrating the DC link choke in the system of  FIG. 12 , with a common mode equivalent circuit and corresponding magnetic flux paths in the link choke core structure. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the figures, several embodiments or implementations are hereinafter described in conjunction with the drawings, wherein like reference numerals are used to refer to like elements throughout, and wherein the various features are not necessarily drawn to scale. 
     The inventors have appreciated that existing common mode choke designs suffer from various issues and problems. Inherent weaknesses of these devices include the difficulty in avoiding the influence of local saturation on common mode inductance. Moreover, windings in these conventional devices with large numbers of turns can increase the proximity losses significantly. In this regard, common mode chokes have thus far been difficult to design due to complexities in calculating or simulating flux distribution. 
     The disclosed embodiments provide a single link choke integrating differential mode inductors and common mode voltage suppression. These embodiments find utility in association with any form of power conversion system, such as low-voltage and medium voltage motor drive type power converters, and can be advantageously employed in transformerless configurations. Use of a single integrated link choke in an intermediate DC circuit reduces the total component count for motor drives and other power conversion systems compared with conventional solutions based on separate differential and common mode devices, and the illustrated winding arrangements facilitate reduction in core material cost and size as well as copper loss, with the shared cross-sectional area reducing the overall choke core weight. The disclosed approach can be used to provide a reliable cost-effective solution to common mode voltage problems in power converter systems, potentially without the need for active solutions and the associated complex control requirements. 
       FIG. 1  illustrates an exemplary current source converter type variable frequency motor drive power conversion system  2  that includes an input rectifier  10  receiving single or multiphase AC input power from a power source  4 , as well as an inverter  20  providing single or multiphase AC output electrical power to drive a motor or other load  6 . A link choke  100  is provided which couples a DC output of the rectifier  10  with a DC input of the inverter  20 . In the illustrated embodiments, the DC link choke  100  couples the rectifier  10  and inverter  20  of a single power conversion system  2 . However, other embodiments are possible in which additional windings are added to a DC choke  100  to accommodate coupling between inverters  20  and rectifiers  10  of multiple power conversion systems  2 , with such windings providing coils to the respective power conversion systems  24  controlling and/or otherwise addressing differential and common mode issues. 
     The rectifier  10  may be an active or passive rectifier circuit, including one or more passive diodes for rectifying AC input power to provide DC output power. In other implementations, an active rectifier may be used, including a plurality of switches (e.g., SGCTs, IGCTs, GTOs, thyristors, IGBTs with reverse blocking capability, etc.) operable according to corresponding control signals from a rectifier control system (not shown) for selectively creating an intermediate DC link current flowing in first and second rectifier DC output terminals or nodes  11  and  12 , respectively. The illustrated rectifier  10 , moreover, is a three-phase active rectifier having six switching devices S 1 -S 6  individually coupled between one of the corresponding three input phase lines A, B, C and one of the DC output terminals  11 ,  12 , where the switching devices S 1 -S 6  are individually operable according to a corresponding switching control input signal (not shown). In operation, the rectifier  10  provides a regulated DC link current to the choke  100  via one or both of the nodes  11 ,  12 , where the example of  FIG. 1  includes four coils L, with two coils L coupled in series with one another between the upper rectifier DC output terminal  11  and an the upper inverter DC input terminal  21 , as well as another two coils L coupled in series with one another between a lower (e.g., second) rectifier DC output terminal  12  and a lower inverter DC input terminal  22 . In general, DC output current flows from the rectifier  10  through the first output terminal  11  into the link choke  100 , and current is provided from the link choke via the first inverter DC input terminal or node  21  for conversion by the inverter  20  into single or multiphase AC electrical output power to drive a motor  6  or other load. The lower DC link path provides a return current path for DC current flowing from the inverter  20  via the second DC input terminal or node  22  through the link choke  100  and returning to the rectifier  10  via the second rectifier DC output terminal or node  12 . The system  2  may include suitable controls (not shown) for operating the rectifier switching devices S 1 -S 6 , and may include feedback another regulation components (not shown) by which the DC link current can be measured to provide feedback for regulation of the DC current produced by the rectifier  10 . 
     The inverter  20  in the illustrated example is a three-phase system which receives DC input current via the nodes  21  and  22 , which are connected to an array of inverter switching devices S 7 -S 12  (e.g., SGCTs, IGCTs, GTOs, thyristors, IGBTs, etc.) which are selectively operated according to corresponding switching control input signals from an inverter controller (not shown) to selectively couple individual ones of the three-phase output lines U, V, W with one of the DC input nodes  21 ,  22  according to any suitable switching control technique (e.g., such as space vector modulation (SVM), selective harmonic elimination (SHE), etc.). By this operation, the DC link current received at the DC input node  21  by way of the link choke  100  from the rectifier  10  is selectively converted into multiphase AC output currents to drive the motor load  6 . In other possible embodiments, a single-phase inverter  20  may be used to drive a load  6 . Moreover, the system  2  may be used to drive other forms of loads, and the disclosed concepts are not limited to motor drives. 
     The DC link choke  100  forms an intermediate circuit that links the switches S 1 -S 6  of the rectifier  10  with the DC input nodes  21 ,  22  of the inverter  20 . In certain embodiments, two coils L are provided in each of the upper and lower branches of the intermediate linking circuit, and some embodiments are possible in which coils L of the choke  100  are provided in only one of the upper and lower DC branches. Further implementations are possible in which only a single coil L is provided in one of the linking circuit branches, with three or more coils L being coupled in the other branch. Moreover, while the illustrated embodiments include four windings  110 - 140 , more than four such windings can be provided on a DC link choke  100  according to the present disclosure. The power conversion system  2  may include further components (not shown) such as input and/or output filter circuits including inductors and/or capacitors, various feedback circuits to facilitate control of the DC link current and/or control of the output current provided to the motor  6 , various user interface components to facilitate operation of the system  2  generally or specific portions thereof, etc., the details of which are omitted in order not to obscure the novel aspects of the present disclosure. 
     Referring also to  FIGS. 2-5 , the DC choke  100  is constructed using a core structure  150 , which can be fabricated using any suitable inductor or transformer core material. As shown in  FIG. 4 , moreover, the core structure  150  in certain embodiments is constructed using two or more laminates  150 L, which can be coated or uncoated and can be held together as a single core structure using any suitable techniques.  FIG. 2  illustrates an exemplary front view of the core structure  150 , which includes first and second vertical legs  151  and  152 , respectively, each of which having an upper first end and a lower second end. The structure  150  also includes a horizontally disposed third leg  153  extending between the first (upper) ends of the first and second legs  151  and  152 , as well as a horizontal fourth leg  154  extending between the second (lower) ends of the first and second legs  151  and  152 . In certain embodiments, the illustrated structure  150  shown in  FIG. 2  may be replicated as two or more laminates  150 L as shown in  FIG. 4 , or a single unitary structure  150  may be provided. In addition, the exemplary core structure  150  has no gaps in or between the legs  151 - 154 , although other embodiments are possible in which an air gap (or gap filled with other material) is provided in or between some or all of the legs  151 - 154  or in which multiple air gaps are provided (not shown). 
     As seen in  FIGS. 2 and 3 , one or more shunts  160  are included in the link choke  100  in order to provide a magnetic flux path between intermediate portions of the first and second legs  151  and  152 . The shunt or shunts  160  may be constructed of any suitable material such as the same core material used to make the core structure  150 . In the example of  FIG. 2 , a single shunt  160  is disposed between the intermediate portions of the vertical core legs  151  and  152 , where the shunt  160  is spaced from the legs  151  and  152 , thereby defining first and second gaps  155  and  156 , respectively. In certain embodiments, the gaps  155  and  156  may be equal, or these gaps  155 ,  156  may be different. Moreover, in certain examples, one of the gaps  155 ,  156  may be zero, with the corresponding end of the shunt  160  contacting the corresponding leg  151 ,  152  of the core structure  150 . In various embodiments, more than one shunt  160  may be used.  FIG. 3  illustrates one such example in which two shunts  160  are provided in the magnetic flux path between the intermediate portions of the vertical legs  151  and  152 . As seen in  FIG. 3 , the shunts  160  extend between, and are spaced from, the intermediate portions of the legs  151  and  152 , and the shunts  160  are also spaced from one another to form an additional gap  157  therebetween. 
       FIG. 5  shows the integrated DC choke  100  (for the case in which a single shunt  160  is used), including four exemplary windings  110 ,  120 ,  130  and  140  provided on the first and second legs  151 ,  152 , each of which forms a coil L coupled between the rectifier DC output and the inverter DC input. The first winding  110  includes a first terminal  112  and a second terminal  114  and forms one or more turns around the first leg  151  between the intermediate portion thereof and the first (e.g., upper) end of the leg  151 , where the beginning of the winding  110  starting from the first terminal  112  crosses in front of the upper portion of the first leg  151  and the turns continue downward with the final portion of the winding  110  crossing behind the leg  151  and ending at the second terminal  114 . In this manner, current flowing into the first terminal  112  and out of the second terminal  114  will cause flux within the upper portion of the first leg  151  in the upward direction shown in  FIG. 5 . The second winding  120  has a first terminal  122  and a second terminal  124  and forms at least one turn around the first leg  151  between the intermediate portion and the second (e.g., lower) end of the first leg  151 . As with the first winding  110 , the beginning of the second winding  120  starting from the terminal  122  passes in front of the first leg  151  and the winding turns proceed downward to a final portion passing behind the leg  151  and ending at the second terminal  124 . Thus, current flowing into the first terminal  122  and flowing out of the second terminal  124  will create a flux in the upward direction in the lower part of the first leg  151 . 
     The third and fourth windings  130  and  140  are wound around the second core leg  152  as seen in  FIG. 5 . In the embodiment of  FIG. 5 , the third winding  130  has a first terminal  132  and a second terminal  134 , and this winding  130  forms at least one turn around the second leg  152  between the intermediate portion thereof and the first (upper) end of the second leg  152 . In this configuration, the beginning of the winding  130  begins at the terminal  132  and passes behind the leg  152 , extending downward therefrom toward the intermediate portion, with the final portion of the winding  130  passing in front of the leg  152  and ending with the second terminal  134 . Thus, current flowing into the first terminal  132  and out of the second terminal  134  will create flux in the upward direction in the upper portion of the second leg  152 . The fourth winding  140  has a first terminal  142  and a second terminal  144 , with the beginning of the winding  140  passing from the first terminal  142  behind the leg  152  and extending downward toward the second (lower) end of the leg  152  with the final portion of the winding  140  passing in front of the leg  152  and ending at the second terminal  144 . In this configuration, current flowing into the first terminal  142  and out of the second terminal  144  creates upward flux in the lower portion of the second leg  152  of the core structure  150 . 
     In certain embodiments, the number of turns in each of the windings  110 ,  120 ,  130  and  140  are the same, and the first and second legs  151  and  152  of the core structure  150  are generally of the same size, shape, and material, whereby the inductances L associated with these windings  120 - 140  are generally equal. In other embodiments, one or more of these design parameters may be varied for individual ones of the windings  110 ,  120 ,  130  and/or  140  whereby the coils L associated with the individual windings  110 - 140  may be different. Moreover, as seen below, the interconnection of the windings  110 - 140  within a given power conversion system to may be adjusted along with design parameters related to the DC link choke  100  itself in order to provide a variety of different combinations of inductance with respect to common mode voltages, differential mode currents, etc. 
     Referring now to  FIGS. 6-8 ,  FIG. 6  illustrates an exemplary embodiment of the power conversion system  2  with an integrated DC link choke  100  in which the first and third windings  110  and  130  are connected in the upper DC link current path of the converter  2 , and the second and fourth windings  120  and  140  are connected in the lower DC link path. This embodiment, like the others illustrated in the subsequent figures, may include a single shunt  160  or may be provided with two or more shunts  160  (e.g., as seen in  FIG. 3  above). In the configuration of  FIGS. 6-8 , the windings  110  and  130  are coupled in series with one another between the first DC output node  11  of the rectifier  10  and the first DC input node  21  of the inverter  20 . In addition, the second and fourth windings  120  and  140  are coupled in series with one another between the second DC output node  12  of the rectifier  10  and the second DC input node  22  of the inverter  20 .  FIGS. 7 and 8  show front views of the DC link choke  100  in the system of  FIG. 6 , along with differential and common mode equivalent circuits, and the corresponding magnetic flux paths are illustrated in the link choke core structure  150 . As seen in  FIGS. 6-8 , the first terminal  112  of the first winding  110  is coupled with the first rectifier DC output node  11 , the second terminal  114  of the first winding  110  is coupled with the second terminal  134  of the third winding  130 , and the first terminal  132  of the third winding  130  is coupled with the first inverter DC input node  21 . In this manner, the windings  110  and  130  and the coils L thereof are connected in series in the upper DC link branch between the rectifier  10  and the inverter  20 . In addition, the first terminal  122  of the second winding  120  is coupled with the second DC output node  12  of the rectifier  10 , the second terminal  124  of the winding  120  is coupled with the second winding  144  of the fourth winding  140 , and the first terminal of the winding  140  is coupled with the second inverter DC input node  22 . Thus, the second and fourth windings  120  and  140  in the coils L thereof are coupled in series with one another in the lower DC link branch. 
       FIG. 7  illustrates operation of the DC choke  100  with respect to differential current flow Idiff, and the figure includes an equivalent circuit through which the differential current flows from the first DC output terminal  11  of the rectifier  10  into the first terminal  112  of the winding  110 , then into the second terminal  134  of the third winding  130 , after which the differential current flows into the first terminal  142  of the fourth winding  140  and then into the second terminal  124  of the second coil  120 , finally flowing back through the second DC output terminal  12  of the rectifier  10 . For such differential current Idiff, flux paths  158  are created in the core structure  150  as shown in the bottom portion of  FIG. 7 , with magnetic flux flowing from right to left through the magnetic flux path created between the intermediate portions of the legs  151  and  152 , the shunt  160 , and the associated gaps (e.g., gaps  155  and  156  as illustrated in  FIGS. 2 and 4  above). 
       FIG. 8  illustrates this embodiment with respect to common mode current Icom flowing in the converter  2 , where the upper portion of the figure shows the equivalent circuit for this common mode situation. As illustrated, the common mode circuit is the parallel combination of two series branches, with the first (upper) branch including the series combination of the first and third windings  110  and  130 , and with the second (lower) branch including the series combination of the second and fourth windings  120  and  140 . In this case, with the inductances being equal, half the common mode current Icom flows in each of these circuit branches, and the lower portion of  FIG. 8  illustrates the resulting magnetic flux flow within the core structure  150  (e.g., clockwise in the figure flowing through the core legs  151 ,  153 ,  152 , and  154  sequentially). It is noted, that some magnetic flux may pass through the intermediate path that includes the shunt  160 , although not a strict requirement of the present disclosure. As seen in  FIGS. 7 and 8 , the integrated DC link choke  100  may thus provide different levels of effective inductance with respect to differential mode current flow Idiff and common mode current Icom. 
       FIGS. 9-11  illustrate another embodiment of the current source converter motor drive  2  in which the integrated DC link choke  100  has the first and second windings  110  and  120  connected in the upper DC link current path, along with the third and fourth windings  130  and  140  connected in the lower DC link path. In this embodiment, the first terminal  112  of the winding  110  is coupled with the first rectifier DC output node  11 , the second terminal  114  of the winding  110  is coupled with the first terminal  122  of the second winding  120 , with the second terminal  124  of the winding  120  being coupled with the first inverter DC input node  21 . In addition, the second terminal  134  of the third winding  130  is coupled with the second rectifier DC output node  12 , the first terminal  132  of the winding  130  is coupled with the second terminal  144  of the fourth winding  140 , and the first terminal  142  of the fourth winding  140  is coupled with the second inverter DC input node  22 . 
     As seen in  FIG. 10 , the equivalent circuit with respect to differential current Idiff begins with the first rectifier output terminal  11  continuing into the first terminal  112  of the winding  110 , and then into the first terminal  122  of the second winding  120 . The differential current Idiff continues through the inverter  22  to the first terminal  142  of coil  140 , and then into the first terminal  132  of the third winding  130 , returning to the rectifier  10  via the second output terminal  12 . This differential current flow in the DC link choke  100  creates magnetic flux paths  158  as shown in the lower portion of  FIG. 10  (e.g., upward in both the vertical legs  151  and  152 ). 
       FIG. 11  illustrates the common mode situation, where the equivalent circuit (upper portion of  FIG. 11 ) includes the parallel combination of 2 series circuit branches, where the first branch includes the windings  110  and  120 , and the second branch includes the windings  130  and  140 , with half the common mode current Icom flowing through each of these branch circuits in some embodiments. This common mode current flow Icom causes magnetic flux to flow in the path directions  158  indicated in the lower portion of  FIG. 11 . Thus, the variation in the interconnection of the windings  110 - 140  can be used (alone or in combination with other choke design parameters) to separately tailor the common mode and/or differential mode inductance provided by the choke  100 . 
       FIGS. 12-14  illustrate yet another embodiment of the power conversion system  2 , in which the first and fourth DC link choke windings  110  and  140  are connected in series with one another in the upper DC link current path, and the second and third windings  120  and  130  are connected in the lower DC link path. This cross-connection of the windings  110 - 140  provides different flux path directions as seen in  FIGS. 13 and 14 . The first terminal  112  of the first winding  110  in this embodiment is coupled with the first rectifier DC output node  11 , and the second terminal  114  of the winding  110  is coupled with the second terminal  144  of the fourth winding  140 . The first terminal  142  of the fourth winding  140 , in turn, is coupled with the first inverter DC input node  21 . The second DC output node  12  of the rectifier  10  is coupled with the first terminal  120  of the second winding  120 , the second terminal  124  of the winding  120  is coupled with the second terminal  134  of the third winding  130 , and the first terminal  132  of the winding  130  is coupled with the second inverter DC input node  22 . 
     As seen in  FIG. 13  for differential mode current Idiff, current flowing out of the first rectifier node  11  into the first terminal  112  of the winding  110  proceeds into the second terminal  144  of winding  140 , and proceeds from the first terminal  142  of the winding  140  through the inverter  20  into the first terminal  132  of the third winding  130 , and thereafter into the second terminal  124  of the second winding  120 , returning to the rectifier  10  via the second DC output node  12 . This causes magnetic flux  158  to flow upward in the upper portions of the core legs  151  and  152  (resulting from the current flow through the coils  110  and  130 , respectively), and flux flows downward in the lower portions of the legs  151  and  152  as a result of the current flow through the second and fourth coils  120  and  140 . 
     The common mode operation is illustrated in  FIG. 14 , in which common mode current Icom flows through the parallel combination of two branch circuits, with the first branch circuit including the first and fourth coils  110  and  140  and the second branch circuit including the coils  120  and  130  as shown in the upper portion of the figure. As seen in the lower portion of  FIG. 14 , this results in upward magnetic flux flow in the first core leg  151  and downward magnetic flux flow  158  in the second core leg  152 . 
     The above examples are merely illustrative of several possible embodiments of various aspects of the present disclosure, wherein equivalent alterations and/or modifications will occur to others skilled in the art upon reading and understanding this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, devices, systems, circuits, and the like), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component, such as hardware, processor-executed software, or combinations thereof, which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the illustrated implementations of the disclosure. In addition, although a particular feature of the disclosure may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Also, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in the detailed description and/or in the claims, such terms are intended to be inclusive in a manner similar to the term “comprising”.