Patent Publication Number: US-11655042-B2

Title: Battery integrated isolated power converter and systems for electric vehicle propulsion

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/984,992, which was filed on 30 Dec. 2015, and the entire disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     The field of the disclosure relates generally to power converters, and, more specifically, to battery integrated isolated power converters for hybrid-electric or all-electric vehicle propulsion systems. 
     In large vehicles such as aircraft, it is beneficial for hybrid-electric or all-electric propulsion, power converter, and energy storage systems to maximize the specific power, i.e., kilowatts per kilogram (kW/kg) of these components of the power system. To improve performance of propulsion systems, the specific power values of known power converters for hybrid-electric or all-electric vehicle propulsion must be increased. Moreover, known power converters for hybrid-electric or all-electric vehicle propulsion systems always need to reliably supply power to critical propulsion equipment, without being impacted whatsoever by power needs of, or electrical faults in accessory systems. In such known power converters for hybrid-electric or all-electric vehicle propulsion systems, interrupting power to the least number of electrical load components as possible is problematic and often results in diminished performance of the main propulsion system due to faults in individual non-propulsion accessory equipment. 
     At least some known power converters for hybrid-electric or all-electric vehicle propulsion systems utilize modular multi-level converter (MMC) architecture. Controllers for MMCs in such known power converters for hybrid-electric or all-electric vehicle propulsion systems must not only switch the MMC submodules, including those with insulated-gate bipolar transistors (IGBTs) or MOSFETs, they must also implement complex control algorithms with sophisticated high speed computing and communications to continually balance the voltages of each submodule capacitor. 
     The MMCs of such known power converters for hybrid-electric or all-electric vehicle propulsion systems utilize large energy storage capacitors on each MMC valve submodule as independently controllable two-level converters and voltage sources for AC or DC electrical loads. Also, in such known power converters for hybrid-electric or all-electric vehicle propulsion systems, isolation of power system components such as batteries require large line frequency transformers for enhanced safety and reduction of common mode interference. Many of these known power converters for hybrid-electric or all-electric vehicle propulsion systems utilize heavy and bulky passive components, e.g., capacitors and inductors, amounting to more than half of their weight. 
     BRIEF DESCRIPTION 
     In one aspect, an electric propulsion system for a vehicle is provided. The electric propulsion system includes at least one generator. The electric propulsion system also includes at least one drive engine coupled to the at least one generator. The electric propulsion system further includes at least one electrical device. The electric propulsion system also includes at least one battery integrated isolated power converter (BIIC), where the at least one generator and at least one of the at least one BIIC and the at least one electrical device are coupled, and where the at least one BIIC and the at least one electrical device are coupled. 
     In another aspect, a BIIC is provided. BIIC includes at least one BIIC module (BIICM) string. BIICM string includes a plurality of BIICMs coupled to each other. Each BIICM of the plurality of BIICMs includes a first BIICM circuit including a first plurality of switching devices coupled together. Each BIICM of the plurality of BIICMs also includes a second BIICM circuit including a second plurality of switching devices coupled together. Each BIICM of the plurality of BIICMs further includes a BIICM high-frequency transformer coupled to and between the first BIICM circuit and the second BIICM circuit, where the first BIICM circuit and the second BIICM circuit are physically isolated and inductively coupled through the BIICM high-frequency transformer. 
    
    
     
       DRAWINGS 
       These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG.  1    is a generalized schematic view of a prior art electric vehicle propulsion system superimposed on a plan view of an aircraft; 
         FIG.  2    is a schematic view of an exemplary embodiment of an electric vehicle propulsion system superimposed on a plan view of an aircraft; 
         FIG.  3    is a schematic diagram of an exemplary bi-directional AC-to-DC battery integrated isolated power converter (BIIC) that may be used in the electric vehicle propulsion system shown in  FIG.  2   ; 
         FIG.  4    is a schematic diagram of an alternative bi-directional AC-to-DC BIIC that may be used in the electric vehicle propulsion system shown in  FIG.  2   ; 
         FIG.  5    is a schematic diagram of an alternative bi-directional AC-to-DC BIIC configured for 3-phase AC power conversion; 
         FIG.  6    is a schematic diagram of another alternative bi-directional AC-to-DC BIIC configured for 3-phase AC power conversion; 
         FIG.  7    is a schematic view of an alternative embodiment of an electric vehicle propulsion system superimposed on a plan view of an aircraft; 
         FIG.  8    is a schematic diagram of another alternative bi-directional AC-to-DC BIIC configured for 3-phase AC power conversion; 
         FIG.  9    is a schematic view of yet another alternative embodiment of an electric vehicle propulsion system superimposed on a plan view of an aircraft; 
         FIG.  10    is a schematic diagram of yet another alternative bi-directional AC-to-DC BIIC configured for 3-phase AC power conversion; 
         FIG.  11    is a schematic view of yet another alternative embodiment of an electric vehicle propulsion system superimposed on a plan view of an aircraft; 
         FIG.  12    is a schematic diagram of an exemplary AC-to-AC BIIC configured for 3-phase AC power conversion; 
         FIG.  13    is a schematic view of yet another alternative embodiment of an electric vehicle propulsion system superimposed on a plan view of an aircraft; 
         FIG.  14    is a schematic view of yet another alternative embodiment of an electric vehicle propulsion system superimposed on a plan view of an aircraft; 
         FIG.  15    is a schematic diagram of an exemplary shunt type BIIC configured for bidirectional DC-to-AC power conversion; 
         FIG.  16    is a schematic view of yet another alternative embodiment of an electric vehicle propulsion system superimposed on a plan view of an aircraft; and 
         FIG.  17    is a schematic view of yet another alternative embodiment of an electric vehicle propulsion system superimposed on a plan view of an aircraft. 
     
    
    
     Unless otherwise indicated, the drawings provided herein are meant to illustrate features of embodiments of this disclosure. These features are believed to be applicable in a wide variety of systems comprising one or more embodiments of this disclosure. As such, the drawings are not meant to include all conventional features known by those of ordinary skill in the art to be required for the practice of the embodiments disclosed herein. 
     DETAILED DESCRIPTION 
     In the following specification and the claims, reference will be made to a number of terms, which shall be defined to have the following meanings. 
     The singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. 
     “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not. 
     Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about”, “approximately”, and “substantially”, are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged, and such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise. 
     The battery integrated isolated power converters (BIICs) described herein are suited to increasing the specific power, i.e., kilowatt/kilogram (kW/kg), of electric vehicle propulsion systems by reducing the number and weight of passive components and cables. Specifically, the BIICs described herein do not require many passive filtering capacitors because the rates of change of voltage with time, i.e., dv/dt, of individual battery integrated power converter modules (BIICMs) are small relative to known power converters in known electric vehicle propulsion systems. Further, specifically, tight control of dv/dt in individual BIICMs results in low levels of harmonic distortion and electromagnetic interference (EMI) relative to known power converters for electric vehicle propulsion systems. Further, such BIICs are more modular, sealable, reliable, as well as easier to maintain and manufacture relative to known power converters for electric vehicle propulsion systems. Furthermore, a wide variety of energy storage devices are adaptable to use with the BIICs described herein, which facilitates incorporation of more advanced energy storage devices into electric vehicle propulsion systems without replacement of power converter components. Moreover, the BIICs described herein provide effective physical and galvanic isolation of energy storage devices, including, without limitation, direct current (DC) batteries, from other components of the BIICs and the overall power system, thus enhancing safety and reliability in electric vehicle propulsion systems. As such, the BIICs described herein utilize energy storage devices to not only provide energy for electric vehicle propulsion, but also to act as voltage sources to enable multi-level power converter operations without additional film capacitors, and at the same time reduce the requirements of using filtering component elements relative to known power converters for electric vehicle propulsion systems. 
       FIG.  1    is a generalized schematic view of a prior art electric vehicle propulsion system  100  superimposed on a plan view of an aircraft. Prior art electric vehicle propulsion system  100  for a vehicle  102  includes at least one drive engine  104 , including an internal combustion engine, coupled to vehicle  102 . At least one generator  106  is coupled to at least one drive engine  104  and to vehicle  102 . At least one drive engine  104  functions as a prime mover for at least one generator  106  to provide torque to turn the rotor of at least one generator  106  to induce an alternating current (AC) in a stator of at least one generator  106 . In the case where vehicle  102  is an aircraft, aircraft further includes a fuselage  108 , at least one wing  110 , and an aft portion  112 , including, without limitation, a tail  114 . 
     In some embodiments of prior art electric vehicle propulsion systems  100 , AC current is transmitted on at least one AC line  116  from at least one generator  106  to at least one bi-directional AC/DC power converter  118 , which converts AC power from generator  106  to DC power. Bi-directional AC/DC power converter  118  includes conventional AC/DC power convertors, i.e., not BIICs as described herein. DC power from bi-directional AC/DC power converter  118  is carried to at least one additional bi-directional AC/DC power converter  118  on at least one transmission line  120  of a DC type. For additional bi-directional AC/DC power converter  118 , at least one electrical device  122  is supplied with AC power on at least one additional AC line  116 . By way of additional transmission line  120  of a DC type, at least one bi-directional DC/DC power converter  124  is coupled to and between DC type transmission line  120  and at least one battery bank  126 . Electrical energy stored in battery bank  126  is made available to power electrical device  122  when needed, as where full capacity operation of generator  106  is unavailable or undesirable. Likewise, where full capacity operation of generator  106  supplies power in excess of that required by electrical device  122 , battery bank  126  is charged, if needed. In the case where vehicle  102  is an aircraft, electrical device  122  includes at least one fan motor used for vehicle propulsion including, without limitation, during taxiing on a runway. 
       FIG.  2    is a schematic view of an exemplary embodiment of an electric vehicle propulsion system  200  superimposed on a plan view of an aircraft. In the exemplary embodiment, vehicle  102  is an aircraft, as shown as described above with reference to  FIG.  1   . Also, in the exemplary embodiment, at least one generator rectifier  202  is coupled to vehicle  102  and to generator  106 . Generator rectifier  202  includes rectifiers known in the art including, without limitation, half-wave rectifiers, full-wave rectifiers, bridge rectifiers, rectifiers with at least one diode, and rectifiers without at least one diode. Generator rectifier  202  is configured to rectify an AC power output of generator  106  and to transmit a DC power on at least one generator cable  204  to at least one battery integrated isolated power converter (BIIC)  206  located in fuselage  108  proximate wing  110 . Further, in the exemplary embodiment, generator cable  204  is a DC cable. 
     Also, in the exemplary embodiment, BIIC  206  includes at least one energy storage device  208 , including, without limitation, a DC energy storage device such as at least one battery, collocated with BIIC  206 . Further, in the exemplary embodiment, BIIC  206  is configured to function as a DC-to-AC power converter which receives DC power from generator rectifier  202  and transmits AC power to electrical device  122  on at least one BIIC cable  210 . Further, in the exemplary embodiment, electrical device  122  includes at least one fan motor  212  used for vehicle propulsion during taxiing on a runway, i.e., where vehicle  102  is an aircraft. In an alternative embodiment, not shown, BIIC  206  is in aft portion  112  of fuselage  108  proximate tail  114 . As such, it is possible to use longer lengths of DC type generator cable  204  for coupling generator rectifier  202  to BIIC  206  relative to electric vehicle propulsion system  200  shown and described with reference to  FIG.  2   . Likewise, shorter lengths of AC type BIIC cable  210  are used for coupling BIIC  206  to electrical device  122  relative to the exemplary electric vehicle propulsion system  200 . Thus, use of shorter lengths of AC type BIIC cable  210  and longer lengths of DC type generator cable  204  facilitates decreasing the weight of electric vehicle propulsion system  200  relative to the exemplary embodiment shown and described with reference to  FIG.  2   . 
     In operation of the exemplary embodiment, rectified DC power from generator rectifier  202 , either alone or in combination with DC power from energy storage device  208 , is converted by BIIC  206  to AC power transmitted to electrical device  122 . BIIC  206  diverts at least a portion of DC power from generator rectifier  202  to charge energy storage device  208  when energy storage device  208  does not adequately supply power to electrical device  122 . In that case, a larger portion of DC power from generator rectifier  202  is converted to AC power by BIIC  206  to supply AC power to electrical device  122  than when energy storage device  208  fully supplies AC power to electrical device  122 . When energy storage device  208  is fully supplying power to electrical device  122 , a mechanical load placed upon drive engine  104  by generator  106  is lower than when generator rectifier  202  is supplying DC power to one or both of electrical device  122  and energy storage device  208 , i.e., for charging. Moreover, in operation of the exemplary embodiment, inclusion of generator rectifier  202  facilitates coupling of DC cable, rather than larger and heavier AC cable, between generator  106  and BIIC  206 , thus increasing the specific power, i.e., kW/kg, of the exemplary electric vehicle propulsion system  200  relative to electric vehicle propulsion system  100  shown and described above with reference to  FIG.  1   . 
       FIG.  3    is a schematic diagram of an exemplary bi-directional AC-to-DC BIIC  300  that may be used in the electric vehicle propulsion system  200  shown in  FIG.  2   . In the exemplary embodiment, bi-directional AC-to-DC BIIC  300  includes at least one bi-directional AC-to-DC BIIC module (bi-directional AC-to-DC BIICM)  302  including a first DC terminal  304  and a second DC terminal  306 . Bi-directional AC-to-DC BIICM  302  also includes a first node  308  configured to receive and transmit a phase of AC power. Also, in the exemplary embodiment, a plurality of bi-directional AC-to-DC BIICMs  302  are arranged in at least one string  310 . First DC terminal  304  of a first bi-directional AC-to-DC BIICM  302  of string  310 , i.e., the topmost bi-directional AC-to-DC BIICM  302  (topmost BIICM  311 ) in  FIG.  3   , couples to a first DC line  312  of a DC link, including, without limitation, a high voltage DC link  314 . Second DC terminal  306  of a last bi-directional AC-to-DC BIICM  302  of string  310 , i.e., the bottommost bi-directional AC-to-DC BIICM  302  (bottommost BIICM  315 ) in  FIG.  3   , couples to a second DC line  316  of high voltage DC link  314 . Further, in the exemplary embodiment, first DC terminals  304  and second DC terminals  306  of each bi-directional AC-to-DC BIICMs  302  of string  310  other than the first BIICM  302  and second BIICM  302 , respectively, are serially coupled. Furthermore, in the exemplary embodiment, first node  308  of each bi-directional AC-to-DC BIICMs  302  of string  310  receives or transmits a phase of AC power on a first AC line  318 . First AC line  318  includes BIIC cable  210  as shown and described with reference to  FIG.  2   . In other alternative embodiments shown and described below, first AC line  318  also includes AC type generator cable  204 . 
     Also, in the exemplary embodiment, bi-directional AC-to-DC BIICM  302  that may be used in bi-directional AC-to-DC BIIC  300  includes first node  308  coupled to and between a first switching device  320  and a second switching device  322 . First switching device  320  is serially coupled to second switching device  322 . First switching device  320  and all switching devices hereinafter described include, without limitation, such devices as integrated gate commutated thyristors, non-linear controllable resistors, varistors, and transistors such as insulated-gate bipolar transistors (IGBTs), metal-oxide semiconductor field-effect transistors (MOSFETs), injection enhanced gate transistors, junction gate field-effect transistors (JFETs), bipolar junction transistors (BJTs), and combinations thereof. First switching device  320  and second switching device  322  each include an antiparallel diode  324  coupled in parallel thereto. These devices can be made of silicon (Si) or wide bandgap materials such as SiC or GaN. Also, in the exemplary embodiment, all switching devices hereinafter described also have antiparallel diode  324  coupled in parallel thereto. 
     Also, in the exemplary embodiment, at least one capacitor  326  is coupled in parallel across both of first switching device  320  and second switching device  322 . Further, in the exemplary embodiment, a third switching device  328  and a fourth switching device  330  are serially coupled. Serially coupled third switching device  328  and fourth switching device  330  are coupled in parallel across both of first switching device  320  and second switching device  322 . A second node  332  includes connections to and between first switching device  320 , capacitor  326 , and third switching device  328 . A first winding  334  of a BIICM high-frequency transformer  336  is coupled in parallel to fourth switching device  330 . In an alternative embodiment, not shown, first winding  334  is coupled in parallel to third switching device  328 . BIICM high-frequency transformer  336  includes, without limitation, a high-frequency transformer configured to operate at frequencies from kilohertz (kHz) to megahertz (MHz) range. A third node  338  includes connections to and between second switching device  322 , capacitor  326 , fourth switching device  330 , and first winding  334 . Together, first node  308 , first switching device  320 , second switching device  322 , capacitor  326 , third switching device  328 , fourth switching device  330 , and first winding  334  form a first side  340 , i.e., a first BIICM circuit, of bi-directional AC-to-DC BIICM  302 . 
     Further, in the exemplary embodiment, bi-directional AC-to-DC BIICM  302  includes a second side  342 , i.e., a second BIICM circuit. Second side  342  includes a fifth switching device  344  serially coupled to a sixth switching device  346 . A second winding  348  of BIICM high-frequency transformer  336  is coupled in parallel to sixth switching device  346 . In an alternative embodiment, not shown, second winding  348  is coupled in parallel to fifth switching device  344 . At least one energy storage device  208  is coupled in parallel across both of fifth switching device  344  and sixth switching device  346 . Also, in the exemplary embodiment, second side  342  includes a seventh switching device  350  serially coupled to an eighth switching device  352 . Serially coupled seventh switching device  350  and eighth switching device  352  are coupled in parallel across both of fifth switching device  344  and sixth switching device  346 . A node  354  includes connections to and between fifth switching device  344 , energy storage device  208 , and seventh switching device  350 . 
     Furthermore, in the exemplary embodiment, second side  342  includes first DC terminal  304  coupled to and between seventh switching device  350  and eighth switching device  352 . Second side  342  also includes second DC terminal  306  coupled to a fourth node  356 . Fourth node  356  includes connections to and between second winding  348 , sixth switching device  346 , energy storage device  208 , eighth switching device  352 , and second DC terminal  306 . In an alternative embodiment, not shown, energy storage device  208  and capacitor  326  are swapped in bi-directional AC-to-DC BIICM  302 . Moreover, in the alternative embodiment, first side  340  and second side  342  are inductively coupled, i.e., galvanically coupled, through BIICM high-frequency transformer  336 . 
     Moreover, in the exemplary embodiment, first  320 , second  322 , third  328 , fourth  330 , fifth  344 , sixth  346 , seventh  350 , and eighth  352  switching devices include at least one switch control terminal  358  coupled to at least one switching controller, not shown in  FIG.  3   . Switching controller is configured to transmit at least one switch control signal to at least one of first  320 , second  322 , third  328 , fourth  330 , fifth  344 , sixth  346 , seventh  350 , and eighth  352  switching devices to control its switching states. In an alternative embodiment, not shown, switching controller receives and transmits other control signals to and from other controllers located elsewhere within or outside bi-directional AC-to-DC BIIC  300 , also not shown in  FIG.  3   . 
     Also, in the exemplary embodiment, bi-directional AC-to-DC BIICM  302  includes at least one bypass switch  360  including, without limitation, such devices as non-linear controllable resistors, varistors, and transistors such as IGBTs, MOSFETs, JFETs, BJTs, and relays. Bypass switch  360  includes a first bypass terminal  362  coupled to first DC terminal  304  and a second bypass terminal  364  coupled to second DC terminal  306 , i.e., fourth node  356 . Bypass switch  360  also includes at least a third bypass terminal, i.e., a bypass control terminal  366 , coupled to at least one bypass switch controller  368 . Bypass switch controller  368  is configured to transmit a control signal  370  to bypass control terminal  366  to close bypass switch  360  when at least one characteristic state associated with bi-directional AC-to-DC BIICM  302 , including, without limitation, physically quantifiable states such as voltage, current, charge, and temperature, associated with energy storage device  208  is present. Likewise, bypass switch controller  368  is configured to transmit control signal  370  to bypass control terminal  366  to open bypass switch  360  when at least one characteristic state associated with bi-directional AC-to-DC BIICM  302  is not present. In an alternative embodiment, not shown, bypass switch  360  and bypass switch controller  368  are not coupled to bi-directional AC-to-DC BIICM  302 . Further, in the exemplary embodiment, first DC terminal  304  is equivalent to a fifth node  372  defined between seventh switching device  350  and eighth switching device  352 . Furthermore, in the exemplary embodiment, second DC terminal  306  is equivalent to fourth node  356 . 
     In operation, in the exemplary embodiment, bi-directional AC-to-DC BIIC  300  converts AC power received on first AC line  318  into DC power transmitted to electrical device  122 , not shown. Bi-directional AC-to-DC BIIC  300  is also capable to convert DC power received on high voltage DC link  314  into AC power transmitted on first AC line  318 . Thus, in the exemplary embodiment, bi-directional AC-to-DC BIIC  300  functions as a bi-directional converter. 
     Also, in operation of in the exemplary embodiment, bi-directional AC-to-DC BIICM  302  converts a phase of AC power received on first node  308  into DC power transmitted to electrical device  122 , not shown, on first DC terminal  304  and second DC terminal  306 . Depending on a predetermined configuration of switching controllers and switching states, it is possible to divert a portion of DC power converted by second side  342  into energy storage device  208  to, for example, charge it. Also, in operation of the exemplary embodiment, it is possible to divert a portion of DC power stored in energy storage device  208 , i.e., to discharge it, to supplement DC power transmitted on first DC terminal  304  and second DC terminal  306 . Bi-directional AC-to-DC BIICM  302  is also capable to convert DC power received on first DC terminal  304  and second DC terminal  306  into AC power transmitted on first node  308 . Thus, in the exemplary embodiment, each module of bi-directional AC-to-DC BIIC  300  functions as bi-directional AC-to-DC BIICM  302 . 
     Also, in operation of the exemplary embodiment, the flow of at least one of an AC current and a DC current in the switching devices of both first side  340  and second side  342  is controlled through at least one switch control signal transmitted from at least one switching controller to at least one switch control terminal  358  of switching devices. As such, switching controller, along with the other aforementioned features and functions of bi-directional AC-to-DC BIICM  302 , facilitates maintaining a desired charging or discharging state of energy storage device  208 . Further, in operation of the exemplary embodiment, bypass switch controller  368  is configured to transmit control signal  370  to close bypass switch  360  when at least one BIICM state has a first predetermined value, and open bypass switch  360  when the at least one BIICM state has a second predetermined value different from the first predetermined value. 
       FIG.  4    is a schematic diagram of an alternative bi-directional AC-to-DC BIIC  400  that may be used in the electric vehicle propulsion system  200  shown in  FIG.  2   . In the alternative embodiment, bi-directional AC-to-DC BIIC  400  includes at least one bi-directional AC-to-DC BIICM  402  including a first node  308  and a second terminal  406 . Second terminal  406  is equivalent to third node  338 . Also, in the alternative embodiment, a plurality of bi-directional AC-to-DC BIICMs  402  are arranged in at least one BIICM string  408 . First node  308  of a first bi-directional AC-to-DC BIICM  402  of BIICM string  408 , i.e., the topmost bi-directional AC-to-DC BIICM  402  (topmost BIICM  409 ) in  FIG.  4   , couples to first DC line  312  of high voltage DC link  314 . Second terminal  406  of a last bi-directional AC-to-DC BIICM  402  of BIICM string  408 , i.e., the bottommost bi-directional AC-to-DC BIICM  402  (bottommost BIICM  410 ) in  FIG.  4   , couples to second DC line  316  of high voltage DC link  314 . 
     Further, in the alternative embodiment, first node  308  and second terminal  406  of each bi-directional AC-to-DC BIICM  402  of BIICM string  408 , other than the first BIICM  402  and second BIICM  402 , respectively, are serially coupled. Furthermore, in the alternative embodiment, a phase of AC power is received to or transmitted from bi-directional AC-to-DC BIIC  400  on first AC line  318  at a power terminal  412 . First AC line  318  includes BIIC cable  210  as shown and described with reference to  FIGS.  3 - 5   . In other alternative embodiments shown and described below, first AC line  318  also includes AC type generator cable  204 . Moreover, in the alternative embodiment, bi-directional AC-to-DC BIIC  400  includes at least one inductor  413  coupled to and between power terminal  412  and BIICMs  402  adjacent power terminal  412 . In other alternative embodiments, not shown, bi-directional AC-to-DC BIIC  400  does not include at least one inductor  413 . 
     Furthermore, in the alternative embodiment, bi-directional AC-to-DC BIICM  402  that may be used in bi-directional AC-to-DC BIIC  400  includes first node  308  coupled to and between first switching device  320  and second switching device  322 . First switching device  320  is serially coupled to second switching device  322 . Further, in the exemplary embodiment, second terminal  406  is coupled to third node  338  of first side  340 . Otherwise, first side  340  of bi-directional AC-to-DC BIICM  402  is as shown and described above with reference to  FIG.  3   . Furthermore, in the alternative embodiment, bi-directional AC-to-DC BIICM  402  also includes a secondary side  414 , i.e., a second BIICM circuit. Secondary side  414  includes fifth switching device  344  serially coupled to sixth switching device  346 . Second winding  348  of BIICM high-frequency transformer  336  is coupled in parallel to sixth switching device  346 . In an alternative embodiment, not shown, second winding  348  is coupled is parallel to fifth switching device  344 . At least one energy storage device  208  is coupled in parallel across both of fifth switching device  344  and sixth switching device  346 . In an alternative embodiment, not shown, energy storage device  208  and capacitor  326  are swapped in bi-directional AC-to-DC BIICM  402 . Moreover, in the alternative embodiment, first side  340  and secondary side  414  are inductively coupled through BIICM high-frequency transformer  336 . 
     Moreover, in the exemplary embodiment, first  320 , second  322 , third  328 , fourth  330 , fifth  344 , and sixth  346  switching devices include at least one switch control terminal  358  coupled to at least one switching controller, not shown in  FIG.  4   . Switching controller is configured to transmit at least one switch control signal to at least one of first  320 , second  322 , third  328 , fourth  330 , fifth  344 , and sixth  346  switching devices to control its switching states. In other alternative embodiments, not shown, switching controller receives and transmits other control signals to and from other controllers located elsewhere within or outside bi-directional AC-to-DC BIIC  400 , also not shown in  FIG.  4   . In still other embodiments, not shown, bi-directional AC-to-DC BIICM  402  also includes at least one bypass switch  360  coupled to and between first node  308  and second terminal  406 , and further coupled to bypass switch controller  368  and controlled thereby, substantially as shown and described above with reference to  FIG.  3   . 
     In operation, in the alternative embodiment, a phase of an AC power is transmitted to or received from first AC line  318  through power terminal  412  to/from each of the plurality of bi-directional AC-to-DC BIICMs  402  of BIICM string  408  above and below power terminal  412 . Also, in operation of the alternative embodiment, first node  308  of first bi-directional AC-to-DC BIICM  402  of BIICM string  408 , i.e., the topmost bi-directional AC-to-DC BIICM  402  in  FIG.  4   , transmits or receives DC power to/from first DC line  312 . Second terminal  406  of last bi-directional AC-to-DC BIICM  402  of BIICM string  408 , i.e., the bottommost bi-directional AC-to-DC BIICM  402  in  FIG.  4   , transmits or receives DC power to/from second DC line  314 . Further, in operation of the alternative embodiment, bi-directional AC-to-DC BIIC  400  converts AC power received on first AC line  318  into DC power transmitted on high voltage DC link  314  to electrical device  122 , not shown. Bi-directional AC-to-DC BIIC  402  is also capable to convert DC power received on high voltage DC link  314  into AC power transmitted on first AC line  318  to electrical device  122 , not shown. Thus, in the exemplary embodiment, bi-directional AC-to-DC BIIC  400  functions as bi-directional AC-to-DC BIIC  400 . 
     Also, in operation of the alternative embodiment, bi-directional AC-to-DC BIICM  302  converts a phase of AC power received on first node  308  and second terminal  406  into DC power transmitted to electrical device  122 , not shown, on first node  308  of first bi-directional AC-to-DC BIICM  402  of BIICM string  408  and second terminal  406  of last bi-directional AC-to-DC BIICM  402  of BIICM string  408 , i.e., the topmost and the bottommost bi-directional AC-to-DC BIICMs  402  in  FIG.  4   , respectively. Depending on a predetermined configuration of switching controllers and switching states, it is possible to divert a portion of DC power converted by secondary side  414  into energy storage device  208  to, for example, charge it. Also, in operation of the alternative embodiment, it is possible to divert a portion of DC power stored in energy storage device  208 , i.e., to discharge it, to supplement DC power transmitted on first node  308  of first bi-directional AC-to-DC BIICM  402  and second terminal  406  of last bi-directional AC-to-DC BIICM  402  of BIICM string  408 , i.e., the topmost and the bottommost bi-directional AC-to-DC BIICMs  402  in  FIG.  4   , respectively. Bi-directional AC-to-DC BIICM  402  is also capable to convert DC power received on first node  308  of first bi-directional AC-to-DC BIICM  402  and second terminal  406  of last bi-directional AC-to-DC BIICM  402  of BIICM string  408 , i.e., the topmost and the bottommost bi-directional AC-to-DC BIICMs  402  in  FIG.  4   , respectively, into AC power transmitted from power terminal  412  to first AC line  318 . Thus, in the exemplary embodiment, each module of bi-directional AC-to-DC BIIC  400 , not shown, functions as bi-directional AC-to-DC BIICM  402 . 
     Further, in operation of the exemplary embodiment, the flow of at least one of an AC current and a DC current in the switching devices of both first side  340  and secondary side  414  is controlled through at least one switch control signal transmitted from at least one switching controller to the switching devices. As such, switching controller, along with the other aforementioned features and functions of bi-directional AC-to-DC BIICM  402 , facilitates maintaining a desired charging or discharging state of energy storage device  208 . 
       FIG.  5    is a schematic diagram of an alternative bi-directional AC-to-DC BIIC  500  configured for 3-phase AC power conversion. In the alternative embodiment, bi-directional AC-to-DC BIIC  500  includes three bi-directional AC-to-DC BIICs  400 , i.e., three bi-directional AC-to-DC BIIC panels  501 . Each bi-directional AC-to-DC BIIC panel  501  of the three bi-directional AC-to-DC BIIC panels  501  includes one BIICM string  408  including a plurality bi-directional AC-to-DC BIICMs  402  serially coupled above and below power terminal  412 . Also, in the alternative embodiment, each bi-directional AC-to-DC BIIC panel  501  of the three bi-directional AC-to-DC BIIC panels  501  includes at least one first inductor  502  coupled to and between power terminal  412  and second terminal  406 , i.e., third node  338 , of a first bottommost bi-directional AC-to-DC BIICM  402  (first bottommost BIICM  503 ) of a first half string  504  of BIICM string  408 . Each bi-directional AC-to-DC BIIC panel  501  of the three bi-directional AC-to-DC BIIC panels  501  also includes at least one second inductor  506  coupled to and between power terminal  412  and first node  308  of a second topmost bi-directional AC-to-DC BIICM  402  (second topmost BIICM  507 ) of a second half string  508  of BIICM string  408 . In other alternative embodiments, not shown, bi-directional AC-to-DC BIIC  500  does not include at least one first inductor  502  and at least one second inductor  506 . 
     Also, in the alternative embodiment, bi-directional AC-to-DC BIIC  500  includes three power terminals  412 , one power terminal  412  on each bi-directional AC-to-DC BIIC panel  501  of the three bi-directional AC-to-DC BIIC panels  501 . Each power terminal  412  is configured to transmit and/or receive at least one phase of a 3-phase AC power to/from first AC line  318 . Further, in the alternative embodiment, each first node  308  of a first topmost bi-directional AC-to-DC BIICM  402  (first topmost BIICM  509 ) of first half string  504  of each bi-directional AC-to-DC BIIC panel  501  of the three bi-directional AC-to-DC BIIC panels  501  couples to first DC line  312 . Likewise, each second terminal  406  of a second bottommost bi-directional AC-to-DC BIICM  402  (second bottommost BIICM  510 ) of second half string  508  of each bi-directional AC-to-DC BIIC panel  501  of the three bi-directional AC-to-DC BIIC panels  501  couples to second DC line  316 . Furthermore, in the alternative embodiment, first DC line  312  and second DC line  316  together form high voltage DC link  314 . Moreover, in the alternative embodiment, in first string  504  of each bi-directional AC-to-DC BIIC panel  501  of the three bi-directional AC-to-DC BIIC panels  501 , first nodes  308  of all BIICMs other than first node  308  of first topmost BIICM  509  are serially coupled to third nodes  338  of all BIICMs other than third node  338  of first bottommost BIICM  503 . Also, in the alternative embodiment, in second half string  508  of each bi-directional AC-to-DC BIIC panel  501  of the three bi-directional AC-to-DC BIIC panels  501 , first nodes  308  of all BIICMs other than first node  308  of second topmost BIICM  507  are serially coupled to third nodes  338  of all BIICMs other than third node  338  of second bottommost BIICM  510 . 
     In operation, in the alternative embodiment, a phase of 3-phase AC power is transmitted to or received from bi-directional AC-to-DC BIIC  500  on three first AC lines  318  through power terminals  412  on each bi-directional AC-to-DC BIIC panel  501  of the three bi-directional AC-to-DC BIIC panels  501 . Also, in operation of the alternative embodiment, each first node  308  of first topmost BIICM  509  of first string  504  of each bi-directional AC-to-DC BIIC panel  501  of the three bi-directional AC-to-DC BIIC panels  501  transmits or receives DC power to/from first DC line  312 . Likewise, each second terminal  406  of second bottommost BIICM  510  of second half string  508  of each bi-directional AC-to-DC BIIC panel  501  of the three bi-directional AC-to-DC BIIC panels  501  transmits or receives DC power to/from second DC line  316 . Further, in operation of the alternative embodiment, bi-directional AC-to-DC BIIC  500  converts 3-phase AC power received on first AC lines  318  into DC power transmitted on high voltage DC link  314  to electrical device  122 , not shown. Bi-directional AC-to-DC BIIC  500  is also capable to convert DC power received on high voltage DC link  314  into AC power transmitted on first AC lines  318  to electrical device  122 , not shown. Thus, in the exemplary embodiment, bi-directional AC-to-DC BIIC  500  functions as a bi-directional AC-to-DC converter configured for 3-phase AC power. 
     Also, in operation of the alternative embodiment, depending on a predetermined configuration of switching controllers and switching states, it is possible to divert a portion of AC and/or DC power converted by bi-directional AC-to-DC BIIC  500  into energy storage device  208 , not shown, i.e., to charge it. Also, in operation of the alternative embodiment, it is possible to divert a portion of AC and/or DC power stored in energy storage device  208 , i.e., to discharge it, to supplement DC power transmitted by bi-directional AC-to-DC BIIC  500  on high voltage DC link  314 . Further, in operation of the exemplary embodiment, the flow of at least one of an AC current and a DC current in the switching devices of both first side  340  and secondary side  414  is controlled through at least one switch control signal transmitted from at least one switching controller, not shown, to the switching devices of each bi-directional AC-to-DC BIICM  402  of the plurality of bi-directional AC-to-DC BIICMs  402 . As such, switching controller, along with the other aforementioned features and functions of each bi-directional AC-to-DC BIIC  500 , facilitates maintaining a desired charging or discharging state of at least one energy storage device  208 . 
       FIG.  6    is a schematic diagram of another alternative bi-directional AC-to-DC BIIC  600  configured for 3-phase AC power conversion. In the alternative embodiment, bi-directional AC-to-DC BIIC  600  includes three bi-directional AC-to-DC BIIC panels  602 . Each bi-directional AC-to-DC BIIC panel  602  of the three bi-directional AC-to-DC BIIC panels  602  includes a plurality of first sides  340 , i.e., first sides  340  of bi-directional AC-to-DC BIICM  402 , not shown, serially coupled above and below power terminal  412 . Also, in the alternative embodiment, each bi-directional AC-to-DC BIIC panel  602  of the three bi-directional AC-to-DC BIIC panels  602  includes at least one first inductor  502  coupled to and between power terminal  412  and second terminal  406  of an initial first side  340  of a first string half  604  of a strand  606 , i.e., a first bottommost first side  607  of first string half  604  in  FIG.  6   . Each bi-directional AC-to-DC BIIC panel  602  of the three bi-directional AC-to-DC BIIC panels  602  also includes at least one second inductor  506  coupled to and between power terminal  412  and first node  308  of an initial first side  340  of a second string half  608  of strand  606 , i.e., a second topmost first side  609  of second string half  608  in  FIG.  6   . In other alternative embodiments, not shown, bi-directional AC-to-DC BIIC  600  does not include at least one first inductor  502  and at least one second inductor  506 . 
     Also, in the alternative embodiment, bi-directional AC-to-DC BIIC  600  includes three power terminals  412 , one power terminal  412  on each bi-directional AC-to-DC BIIC panel  602  of the three bi-directional AC-to-DC BIIC panels  602 . Each power terminal  412  is configured to transmit and/or receive at least one phase of a 3-phase AC power to/from first AC line  318 . Further, in the alternative embodiment, each first node  308  of initial first side  340  of strand  606 , i.e., a first topmost first side  610  in  FIG.  6   , of each bi-directional AC-to-DC BIIC panel  602  of the three bi-directional AC-to-DC BIIC panels  602  couples to first DC line  312 . Likewise, each second terminal  406  of a final first side  340  of strand  606 , i.e., a second bottommost first side  612  in  FIG.  6   , of each bi-directional AC-to-DC BIIC panel  602  of the three bi-directional AC-to-DC BIIC panels  602  couples to second DC line  316 . Furthermore, in the alternative embodiment, first DC line  312  and second DC line  316  together form high voltage DC link  314 . 
     Further, in the alternative embodiment, bi-directional AC-to-DC BIIC  600  includes at least one, but less than a total number of first sides  340 , of secondary sides  414  inductively coupled to at least one first side  340  of the plurality of first sides  340  in at least one bi-directional AC-to-DC BIIC panel  602  of the three bi-directional AC-to-DC BIIC panels  602 . As such, in the alternative embodiment, a multi-winding BIICM high-frequency transformer  614  includes at least one first winding  334  of at least one first side  340  and at least one second winding  348  of at least one secondary side  414 . Multi-winding BIICM high-frequency transformer  614  includes, without limitation, a high-frequency multi-winding transformer configured to operate at frequencies from kHz to MHz range. Furthermore, in the alternative embodiment, at least one secondary side  414  is coupled to bi-directional AC-to-DC BIIC  600 . In other alternative embodiments, not shown, at least one secondary side  414  is not coupled to bi-directional AC-to-DC BIIC  600 , but is, nevertheless, inductively coupled to at least one first winding  334  therein. 
     In operation, in the alternative embodiment, a phase of 3-phase AC power is transmitted to or received from bi-directional AC-to-DC BIIC  600  on three first AC lines  318  through power terminals  412  on each bi-directional AC-to-DC BIIC panel  602  of the three bi-directional AC-to-DC BIIC panels  602 . Also, in operation of the alternative embodiment, each first node  308  of initial first side  340  of strand  606 , i.e., first topmost first sides  610 , of each bi-directional AC-to-DC BIIC panel  602  of the three bi-directional AC-to-DC BIIC panels  602 , transmits or receives DC power to/from first DC line  312 . Likewise, each second terminal  406  of final first side  340  of strand  606 , i.e., second bottommost first sides  612 , in  FIG.  6   , of each bi-directional AC-to-DC BIIC panel  602  of the three bi-directional AC-to-DC BIIC panels  602  transmits or receives DC power to/from second DC line  316 . Further, in operation of the alternative embodiment, bi-directional AC-to-DC BIIC  600  converts 3-phase AC power received on first AC lines  318  into DC power transmitted on high voltage DC link  314  to electrical device  122 , not shown. Bi-directional AC-to-DC BIIC  600  is also capable to convert DC power received on high voltage DC link  314  into AC power transmitted on first AC lines  318  to electrical device  122 , not shown. Thus, in the exemplary embodiment, bi-directional AC-to-DC BIIC  600  functions as a bi-directional AC-to-DC converter configured for 3-phase AC power. 
     Also, in operation of the alternative embodiment, depending on a predetermined configuration of switching controllers and switching states, it is possible to divert a portion of AC and/or DC power converted by bi-directional AC-to-DC BIIC  600  into energy storage device  208 , i.e., to charge it. Also, in operation of the alternative embodiment, it is possible to divert a portion of DC power stored in energy storage device  208 , i.e., to discharge it, to supplement DC power transmitted by bi-directional AC-to-DC BIIC  600  on high voltage DC link  314 . Further, in operation of the exemplary embodiment, the flow of at least one of an AC current and a DC current in the switching devices of both first side  340  and secondary side  414  is controlled through at least one switch control signal transmitted from at least one switching controller, not shown, to the switching devices of each first side  340  and each secondary side  414  in bi-directional AC-to-DC BIIC  600 . Furthermore, in operation of the alternative embodiment, multi-winding BIICM high-frequency transformer  614  enables a single energy storage device  208  to share power with each first side  340  of the plurality of first sides  340  of bi-directional AC-to-DC BIIC  600 . Multi-winding BIICM high-frequency transformer  614  also facilitates adjusting the number of secondary sides  414  depending on the particular applications required by electric vehicle propulsion systems, including, without limitation, electric vehicle propulsion system  200 . As such, switching controller, along with the other aforementioned features and functions of bi-directional AC-to-DC BIIC  600 , facilitates maintaining a desired charging or discharging state of energy storage device  208 . 
       FIG.  7    is a schematic view of an alternative embodiment of an electric vehicle propulsion system  700  superimposed on a plan view of an aircraft. In the alternative embodiment, vehicle  102  is an aircraft, as shown as described above with reference to  FIG.  1   . Also, in the alternative embodiment, generator  106  is coupled to drive engine  104  of vehicle  102  and to AC type generator cable  204 . Further, in the alternative embodiment, drive engine  104  is configured as a prime mover for generator  106 , and generator  106  is configured to induce a 3-phase AC power output transmitted on generator cable  204 . Generator cable  204  is coupled to and between generator  106  and at least one first converter set  702  including at least one bi-directional AC-to-DC BIIC  500 , i.e., a fore BIIC. Moreover, in the alternative embodiment, first converter set  702  is in fuselage  108  proximate wing  110 . In other alternative embodiments, not shown, first converter set  702  includes at least one bi-directional AC-to-DC BIIC  600 . 
     Also, in the alternative embodiment, electric vehicle propulsion system  700  includes at least one second converter set  704 . Second converter set  704  includes at least one bi-directional AC-to-DC BIIC  500 , i.e., an aft BIIC. Further, in the alternative embodiment, second converter set  704  is in aft portion  112  proximate tail  114 . In other alternative embodiments, not shown, second converter set  704  includes at least one bi-directional AC-to-DC BIIC  500 . Furthermore, in the alternative embodiment, at least one BIIC-to-BIIC cable  706  of a DC type is coupled to and between first converter set  702  and second converter set  704 . As shown and described above with reference to  FIGS.  4  and  5   , bi-directional AC-to-DC BIIC  500  of first converter set  702  is configured to function as an AC-to-DC power converter which receives AC power from generator  106  and transmits DC power to second converter set  704  on BIIC-to-BIIC cable  706 . Moreover, in the alternative embodiment, bi-directional AC-to-DC BIIC  500  of second converter set  704  is configured to function as a DC-to-AC power converter which receives DC power from first converter set  702  and transmits AC power to electrical device  122  on AC type BIIC cable  210 . Electrical device  122  includes fan motor  212  used for vehicle propulsion, including, without limitation, during taxiing on a runway, i.e., where vehicle  102  is an aircraft. 
     Further, in the alternative embodiment, in cases where a DC interconnect  708  is coupled to and between at least two first converter sets  702 , a first DC bus, not shown, is coupled to and between first DC line  312  of a first bi-directional AC-to-DC BIIC  500  and a second bi-directional AC-to-DC BIIC  500 . Likewise, a second DC bus, not shown, is coupled to and between second DC line  316  of first bi-directional AC-to-DC BIIC  500  and second bi-directional AC-to-DC BIIC  500 . Together, first DC bus and second DC bus form DC interconnect  708 . Similarly, in cases where DC interconnect  708  is coupled to and between at least two second converter sets  704 , first DC bus, not shown, is coupled to and between first DC line  312  of a first bi-directional AC-to-DC BIIC  500  and a second bi-directional AC-to-DC BIIC  500 . Likewise, a second DC bus, not shown, is coupled to and between second DC line  316  of first bi-directional AC-to-DC BIIC  500  and second bi-directional AC-to-DC BIIC  500 . Including DC interconnect  708  facilitates balancing or sharing the power received and/or transmitted by each first converter set  702  of at least two first converter sets  702  from generator  106  and/or to second converter set  704 , respectively. Similarly, including DC interconnect  708  facilitates balancing or sharing the power received and/or transmitted by each second converter set  704  of at least two second converter sets  704  to first converter set  702  and/or to electrical device  122 , respectively. 
     In operation of the alternative embodiment, AC power from generator  106  is converted by first converter set  702  into DC power transmitted to second converter set  704  on BIIC-to-BIIC cable  706 . Also, in operation of the alternative embodiment, it is possible for first converter set  702  to divert at least a portion of AC and/or DC power to charge energy storage device  208 , not shown, in bi-directional AC-to-DC BIIC  500 . It is also possible for first converter set  702  to discharge energy storage device  208  to supply at least a portion of DC power transmitted on BIIC-to-BIIC cable  706  to second converter set  704 . Further, in operation of the exemplary embodiment, inclusion of first converter set  702  and second converter set  704  facilitates coupling of DC cable, rather than larger and heavier AC cable, between generator  106  and electrical device  122 , thus increasing the specific power, i.e., kW/kg, of the exemplary electric vehicle propulsion system  700  relative to the electric vehicle propulsion system  100  shown and described above with reference to  FIG.  1   . 
       FIG.  8    is a schematic diagram of another alternative bi-directional AC-to-DC BIIC  800  configured for 3-phase AC power conversion. In the alternative embodiment, bi-directional AC-to-DC BIIC  800  includes at least three BIICM sets  801  of at least one bi-directional AC-to-DC BIICM  302 . The at least three BIICM sets  801  includes a topmost BIICM set  802  and a bottommost BIICM set  804 . Also, in the alternative embodiment, each BIICM set  801  of the three BIICM sets  801  in bi-directional AC-to-DC BIIC  800  includes a plurality of bi-directional AC-to-DC BIICMs  302 . Each BIICM set  801  of the at least three BIICM sets  801  also includes a topmost BIICM  806  and a bottommost BIICM  808 . Each first node  308  of each bi-directional AC-to-DC BIICM  302  of each BIICM set  801  of the three BIICM sets  801  are coupled together and further coupled to one first AC line  318  of at least three first AC lines  318 . Each first AC line  318  transmits a phase of a 3-phase AC power to/from each first node  308  of each bi-directional AC-to-DC BIICM  302  within each BIICM set  801  of the three BIICM sets  801  of bi-directional AC-to-DC BIICMs  302  in bi-directional AC-to-DC BIIC  800 . 
     Also, in the alternative embodiment, all second nodes  332  of each bi-directional AC-to-DC BIICM  302  of each BIICM set  801  of the three BIICM sets  801  of bi-directional AC-to-DC BIICMs  302  in bi-directional AC-to-DC BIIC  800  are coupled together through a first nodal bus  810 . Similarly, all third nodes  338  of each bi-directional AC-to-DC BIICM  302  of each BIICM set  801  of the three BIICM sets  801  of bi-directional AC-to-DC BIICMs  302  are coupled together through a second nodal bus  812 . In other alternative nodes, not shown, one or both of first nodal bus  810  and second nodal bus  812  are not present in bi-directional AC-to-DC BIIC  800 . 
     Further, in the alternative embodiment, first DC terminal  304 , i.e., fifth node  372 , of topmost BIICM  806  of topmost BIICM set  802  of bi-directional AC-to-DC BIIC  800  couples to first DC line  312 . Likewise, second DC terminal  306 , i.e., fourth node  356 , of bottommost BIICM  808  of bottommost BIICM set  804  of bi-directional AC-to-DC BIIC  800  couples to second DC line  316 . Furthermore, in the alternative embodiment, first DC line  312  and second DC line  316  together form high voltage DC link  314 . Moreover, in the alternative embodiment, fourth nodes  356  and fifth nodes  372  of all bi-directional AC-to-DC BIICMs  302  other than topmost BIICM  806  of topmost BIICM set  802  and bottommost BIICM  808  of bottommost BIICM set  804  are serially coupled together. Also, in the alternative embodiment, each bi-directional AC-to-DC BIICM  302  of each BIICM set  801  of the three BIICM sets  801  of bi-directional AC-to-DC BIICMs  302  includes bypass switch  360 , as shown and described above with reference to  FIG.  3   . In an alternative embodiment, not shown, bi-directional AC-to-DC BIIC  800  does not include bypass switch  360 . In another alternative embodiment, not shown, positions of energy storage device  208  and capacitor  326  in bi-directional AC-to-DC BIICMs  302  are swapped in bi-directional AC-to-DC BIIC  800 . 
     In operation, in the alternative embodiment, a phase of 3-phase AC power is transmitted to or received from bi-directional AC-to-DC BIIC  800  on three first AC lines  318  through first nodes  308  within each BIICM set  801  of the three BIICM sets  801  of bi-directional AC-to-DC BIICMs  302  in bi-directional AC-to-DC BIIC  800 . Also, in operation of the alternative embodiment, first DC terminal  304  of topmost BIICM  806  of topmost BIICM set  802  of bi-directional AC-to-DC BIIC  800  transmits or receives DC power to/from first DC line  312 . Likewise, second DC terminal  306  of bottommost BIICM  808  of bottommost BIICM set  804  of bi-directional AC-to-DC BIIC  800  transmits or receives DC power to/from second DC line  316 . Further, in operation of the alternative embodiment, bi-directional AC-to-DC BIIC  800  converts 3-phase AC power received on first AC lines  318  into DC power transmitted on high voltage DC link  314  to electrical device  122 , not shown. Bi-directional AC-to-DC BIIC  800  is also capable to convert DC power received on high voltage DC link  314  into AC power transmitted on first AC line  318  to electrical device  122 , not shown. Thus, in the exemplary embodiment, bi-directional AC-to-DC BIIC  800  functions as a bi-directional AC-to-DC converter configured for 3-phase AC power. 
     Also, in operation of the alternative embodiment, depending on a predetermined configuration of switching controllers and switching states, it is possible to divert a portion of AC and/or DC power converted by bi-directional AC-to-DC BIIC  800  into energy storage device  208 , not shown, i.e., to charge it. Also, in operation of the alternative embodiment, it is possible to divert a portion of power stored in energy storage device  208 , i.e., to discharge it, to supplement AC and/or DC power transmitted by bi-directional AC-to-DC BIIC  800  on high voltage DC link  314  and/or first AC line  318 . Further, in operation of the exemplary embodiment, the flow of at least one of an AC current and a DC current in the switching devices of each bi-directional AC-to-DC BIICM  302  of each BIICM set  801  of the three BIICM sets  801  of bi-directional AC-to-DC BIIC  800  is controlled through at least one switch control signal transmitted from at least one switching controller. As such, switching controller along with the other aforementioned features and functions of bi-directional AC-to-DC BIIC  800  facilitates maintaining a desired charging or discharging state of energy storage device  208 . 
       FIG.  9    is a schematic view of yet another alternative embodiment of an electric vehicle propulsion system  900  superimposed on a plan view of an aircraft. In the exemplary embodiment, vehicle  102  is an aircraft, as shown as described above with reference to  FIG.  1   . Also, in the alternative embodiment, generator  106  is coupled to drive engine  104  of vehicle  102  and to generator rectifier  202 , as shown and described above with reference to  FIG.  2   . Generator cable  204  of a DC type is coupled to and between generator rectifier  202  and at least one converter set  902  including at least one bi-directional AC-to-DC BIIC  800 . Further, in the alternative embodiment, converter set  902  is in fuselage  108  proximate wing  110 . In other alternative embodiments, not shown, converter set  902  is in aft portion  112  proximate tail  114 . Locating converter set  902  in aft portion  112  provides enhanced specific power to electric vehicle propulsion system  900 , as described above with reference to  FIG.  2   . 
     Also, in the alternative embodiment, electric vehicle propulsion system  900  includes AC type BIIC cable  210  coupled to and between converter set  902  and electrical device  122 . Further, in the alternative embodiment, bi-directional AC-to-DC BIIC  800  of converter set  902  is configured to function as a DC-to-AC power converter which receives DC power from generator rectifier  202  and transmits AC power to electrical device  122  on BIIC cable  210 . Furthermore, in the alternative embodiment, electrical device  122  includes fan motor  212  used for vehicle propulsion, including, without limitation, during taxiing on a runway, i.e., where vehicle  102  is an aircraft. Moreover, in the alternative embodiment, electric vehicle propulsion system  900  includes DC interconnect  708 . DC interconnect  708  is coupled to and between at least two converter sets  902 . DC interconnect  708  includes a first DC bus, not shown, coupled to and between first DC line  312  of a first bi-directional AC-to-DC BIIC  800  and first DC line  312  of a second bi-directional AC-to-DC BIIC  800 . Likewise, DC interconnect  708  includes a second DC bus, not shown, coupled to and between second DC line  316  of first bi-directional AC-to-DC BIIC  800  and second DC line  316  of second bi-directional AC-to-DC BIIC  800 . Together, first DC bus and second DC bus form DC interconnect  708 . Also, in the alternative embodiment, electric vehicle propulsion system  900  includes a rectifier bus  904 . Rectifier bus  904  is coupled to and between at least two generator rectifiers  202 , i.e., where at least two generators  106  are coupled to vehicle  102 . In other alternative embodiments, not shown, rectifier bus  904  is not present. 
     Except for added functionality provided to electric vehicle propulsion system  900  by DC interconnect  708  and rectifier bus  904 , operation of the alternative embodiment and attendant benefits thereof are as described above with reference to  FIG.  2   . DC interconnect  708  facilitates balancing or sharing the power received and/or transmitted by each of at least two converter sets  902  from generator rectifier  202  and/or to electrical device  122 , respectively. Rectifier bus  904  facilitates balancing or sharing the power generated by and/or rectified by each of at least two generators  106  and/or at least two generator rectifiers  202 , respectively. 
       FIG.  10    is a schematic diagram of yet another alternative bi-directional AC-to-DC BIIC  1000  configured for 3-phase AC power conversion. In the alternative embodiment, bi-directional AC-to-DC BIIC  1000  includes at least three BIICM sets  1002  of at least one bi-directional AC-to-DC BIICM  302 . The at least three BIICM sets  1002  include a topmost BIICM set  1004  and a bottommost BIICM set  1106 . Also, in the alternative embodiment, each BIICM set  1002  of the three BIICM sets  1002  of bi-directional AC-to-DC BIICMs  302  in bi-directional AC-to-DC BIIC  1000  includes a plurality of bi-directional AC-to-DC BIICMs  302 . Each BIICM set  1002  of the at least three BIICM sets  1002  also includes a topmost BIICM  1008  and a bottommost BIICM  1010 . Each first node  308  of each bi-directional AC-to-DC BIICM  302  of each BIICM set  1002  of the three BIICM sets  1002  are coupled together and further coupled to one first AC line  318  of at least three first AC lines  318 . Each first AC line  318  of the at least three first AC lines  318  transmits a phase of a 3-phase AC power to/from each first node  308  of each bi-directional AC-to-DC BIICM  302  within each BIICM set  1002  of the three BIICM sets  1002  of bi-directional AC-to-DC BIICMs  302  in bi-directional AC-to-DC BIIC  1000 . 
     Also, in the alternative embodiment, all second nodes  332  of each bi-directional AC-to-DC BIICM  302  of each BIICM set  1002  of the three BIICM sets  1002  of bi-directional AC-to-DC BIICMs  302  in bi-directional AC-to-DC BIIC  1000  are coupled together through a first nodal bus  810 . Similarly, all third nodes  338  of each bi-directional AC-to-DC BIICM  302  of each BIICM set  1002  of the three BIICM sets  1002  of bi-directional AC-to-DC BIICMs  302  are coupled together through a second nodal bus  812 . In other alternative nodes, not shown, one or both of first nodal bus  810  and second nodal bus  812  are not present in bi-directional AC-to-DC BIIC  1000 . 
     Further, in the alternative embodiment, first DC terminals  304 , i.e., fifth nodes  372 , of each topmost BIICM  1008  of each BIICM set  1002  of bi-directional AC-to-DC BIICMs  302  in bi-directional AC-to-DC BIIC  1000  is coupled to first DC line  312 . Likewise, second DC terminal  306 , i.e., fourth node  356 , of each bottommost BIICM  1010  of each BIICM set  1002  of bi-directional AC-to-DC BIICMs  302  in bi-directional AC-to-DC BIIC  1000  is coupled to second DC line  316 . Furthermore, in the alternative embodiment, first DC line  312  and second DC line  316  together form high voltage DC link  314 . Moreover, in the alternative embodiment, fourth nodes  356  and fifth nodes  372  within each BIICM set  1002  other than the topmost BIICM  1008  and bottommost BIICM  1010  of each BIICM set  1002  are serially coupled together. Also, in the alternative embodiment, each bi-directional AC-to-DC BIICM  302  of each BIICM set  1002  of the three BIICM sets  1002  of bi-directional AC-to-DC BIICMs  302  includes at least one bypass switch  360 , as shown and described above with reference to  FIG.  3   . In an alternative embodiment, not shown, bi-directional AC-to-DC BIIC  800  does not include at least one bypass switch  360 . In another alternative embodiment, not shown, positions of energy storage device  208  and capacitor  326  in bi-directional AC-to-DC BIICMs  302  are swapped in bi-directional AC-to-DC BIIC  1000 . 
     In operation, in the alternative embodiment, a phase of 3-phase AC power is transmitted to or received from bi-directional AC-to-DC BIIC  1000  on three first AC lines  318  through first nodes  308  within each BIICM set  1002  of the three BIICM sets  1002  of bi-directional AC-to-DC BIICMs  302  in bi-directional AC-to-DC BIIC  1000 . Also, in operation of the alternative embodiment, first DC terminals  304  of each topmost BIICM  1008  of each BIICM set  1002  of bi-directional AC-to-DC BIICMs  302  in bi-directional AC-to-DC BIIC  1000  transmits or receives DC power to/from first DC line  312 . Likewise, second DC terminals  306  of each bottommost BIICM  1010  of each BIICM set  1002  of bi-directional AC-to-DC BIICMs  302  in bi-directional AC-to-DC BIIC  1000  transmits or receives DC power to/from second DC line  316 . Further, in operation of the alternative embodiment, bi-directional AC-to-DC BIIC  1000  converts 3-phase AC power received on first AC lines  318  into DC power transmitted on high voltage DC link  314  to electrical device  122 , not shown. Bi-directional AC-to-DC BIIC  1000  is also capable to convert DC power received on high voltage DC link  314  into AC power transmitted on first AC line  318  to electrical device  122 . Thus, in the exemplary embodiment, bi-directional AC-to-DC BIIC  1000  functions as a bi-directional AC-to-DC converter configured for 3-phase AC power. 
     Also, in operation of the alternative embodiment, depending on a predetermined configuration of switching controllers and switching states, it is possible to divert a portion of AC and/or DC power converted by bi-directional AC-to-DC BIIC  1000  into energy storage device  208 , not shown, i.e., to charge it. Also, in operation of the alternative embodiment, it is possible to divert a portion of power stored in energy storage device  208 , i.e., to discharge it, to supplement AC and/or DC power transmitted by bi-directional AC-to-DC BIIC  1000  on high voltage DC link  314  and/or first AC line  318 . Further, in operation of the exemplary embodiment, the flow of at least one of an AC current and a DC current in the switching devices of each bi-directional AC-to-DC BIICM  302  of each BIICM set  1002  of the three BIICM sets  1002  of bi-directional AC-to-DC BIICMs  302  in bi-directional AC-to-DC BIIC  1000  is controlled through at least one switch control signal transmitted from at least one switching controller, not shown. As such, switching controller along with the other aforementioned features and functions of bi-directional AC-to-DC BIIC  1000  facilitates maintaining a desired charging or discharging state of energy storage device  208 . 
       FIG.  11    is a schematic view of yet another alternative embodiment of an electric vehicle propulsion system  1100  superimposed on a plan view of an aircraft. In the exemplary embodiment, vehicle  102  is an aircraft, as shown as described above with reference to  FIG.  1   . Also, in the alternative embodiment, generator  106  is coupled to drive engine  104  of vehicle  102  and to generator rectifier  202 , as shown and described above with reference to  FIG.  2   . Generator cable  204  of a DC type is coupled to and between generator rectifier  202  and at least one converter set  1102  including at least one bi-directional AC-to-DC BIIC  1000 . Further, in the alternative embodiment, converter set  1102  is in fuselage  108  proximate wing  110 . In other alternative embodiments, not shown, converter set  1102  is in aft portion  112  proximate tail  114 . Locating converter set  1102  in aft portion  112  provides enhanced specific power to electric vehicle propulsion system  1100 , as described above with reference to  FIG.  2   . 
     Also, in the alternative embodiment, electric vehicle propulsion system  1100  includes at least one BIIC cable  210  of an AC type coupled to and between converter set  1102  and electrical device  122 . Further, in the alternative embodiment, bi-directional AC-to-DC BIIC  1000  of converter set  1102  is configured to function as a DC-to-AC power converter which receives DC power from generator rectifier  202  and transmits AC power to electrical device  122  on BIIC cable  210 . Furthermore, in the alternative embodiment, electrical device  122  includes fan motor  212  used for vehicle propulsion, including, without limitation, during taxiing on a runway, i.e., where vehicle  102  is an aircraft. Moreover, in the alternative embodiment, electric vehicle propulsion system  1100  includes a rectifier bus  904 . Rectifier bus  904  is coupled to and between at least two generator rectifiers  202 , i.e., where at least two generators  106  are coupled to vehicle  102 . In other alternative embodiments, not shown, rectifier bus  904  is absent. 
     Further, in the alternative embodiment, electric vehicle propulsion system  1100  also includes a first extension  1104  and a second extension  1106 . In cases where at least two generators  106  are coupled to vehicle  102 , first extension  1104  is coupled to and between generator cable  204  of a first generator rectifier  202  of at least two generator rectifiers  202  and first DC lines  312  of each bi-directional AC-to-DC BIIC  1000  of at least two converter sets  1102 . Likewise, second extension  1106  is coupled to and between generator cable  204  of a second generator rectifier  202  of at least two generator rectifiers  202  and second DC lines  316  of each bi-directional AC-to-DC BIIC  1000  of at least two converter sets  1102 . In other alternative embodiments, not shown, first extension  1104  and second extension  1106  are absent. 
     Except for added functionality provided to electric vehicle propulsion system  1100  by DC interconnect  708 , first extension  1104 , and second extension  1106 , operation of the alternative embodiment and attendant benefits thereof are as described above with reference to  FIG.  2   . Rectifier bus  904  facilitates balancing or sharing the power generated by and/or rectified by each of at least two generators  106  and/or at least two generator rectifiers  202 , respectively. First extension  1104  and second extension  1106  facilitate balancing or sharing the power received by each of at least two converter sets  1102  from each generator rectifier  202  of at least two generator rectifiers  202  of electric vehicle propulsion system  1100 . 
       FIG.  12    is a schematic diagram of an exemplary AC-to-AC BIIC  1200  configured for 3-phase AC power conversion. In the exemplary embodiment, AC-to-AC BIIC  1200  includes at least three BIICM sets  1201  of at least one AC-to-AC BIICM  1202 . The at least three BIICM sets  1201  include a topmost BIICM set  1204  and a bottommost BIICM set  1206 . Also, in the alternative embodiment, each BIICM set  1201  of the three BIICM sets  1201  of at least one AC-to-AC BIICM  1202  in AC-to-AC BIIC  1200  includes a plurality of AC-to-AC BIICMs  1202 . Each BIICM set  1201  of the at least three BIICM sets  1201  also includes a topmost BIICM  1208  and a bottommost BIICM  1210 . Further, in the exemplary embodiment, each AC-to-AC BIICM  1202  includes first side  340 , including first node  308 . First side  340  is as shown and described above with reference to  FIG.  3   . Each AC-to-AC BIICM  1202  also includes a full-bridge side  1212 . Full-bridge side  1212  includes fifth switching device  344  serially coupled to sixth switching device  346 . Second winding  348  of BIICM high-frequency transformer  336  is coupled in parallel to sixth switching device  346 . In an alternative embodiment, not shown, second winding  348  is coupled in parallel to fifth switching device  344 . At least one energy storage device  208  is coupled in parallel across both of fifth switching device  344  and sixth switching device  346 . Furthermore, in the exemplary embodiment, full-bridge side  1212  includes seventh switching device  350  serially coupled to eighth switching device  352 . Serially coupled seventh switching device  350  and eighth switching device  352  are coupled in parallel across both of fifth switching device  344  and sixth switching device  346 . 
     Also, in the exemplary embodiment, full-bridge side  1212  of each AC-to-AC BIICM  1202  of AC-to-AC BIIC  1200  includes a ninth switching device  1214  serially coupled to a tenth switching device  1216 . Serially coupled ninth switching device  1214  and tenth switching device  1216  are coupled in parallel across both of seventh switching device  350  and eighth switching device  352 . A tertiary node  1218  includes connections to and between fifth switching device  344 , energy storage device  208 , seventh switching device  350 , and ninth switching device  1214 . A quaternary node  1220  includes connections to and between sixth switching device  346 , energy storage device  208 , eighth switching device  352 , and tenth switching device  1216 . Further, in the exemplary embodiment, each AC-to-AC BIICM  1202  of AC-to-AC BIIC  1200  includes a second AC node  1222  and a third AC node  1224 . Second AC node  1222  is defined between seventh switch device  350  and eighth switching device  352 . Second AC node  1222  is equivalent to fifth node  372 . Third AC node  1224  is defined between ninth switching device  1214  and tenth switching device  1216 . Third AC node  1224  is equivalent to a sixth node  1226 . In an alternative embodiment, not shown, energy storage device  208  and capacitor  326  are swapped in AC-to-AC BIICM  1202 . Furthermore, in the alternative embodiment, first side  340  and full-bridge side  1212  are inductively coupled through BIICM high-frequency transformer  336 . 
     Further, in the exemplary embodiment, first  320 , second  322 , third  328 , fourth  330 , fifth  344 , sixth  346 , seventh  350 , eighth  352 , ninth  1214 , and tenth  1216  switching devices include at least one switch control terminal  358  coupled to at least one switching controller, not shown in  FIG.  12   . Switching controller is configured to transmit at least one switch control signal to at least one of first  320 , second  322 , third  328 , fourth  330 , fifth  344 , sixth  346 , seventh  350 , eighth  352 , ninth  1214 , and tenth  1216  switching devices to control its switching states. In an alternative embodiment, not shown, switching controller receives and transmits other control signals to and from other controllers located elsewhere within or outside AC-to-AC BIICM  1202 . 
     Furthermore, in the exemplary embodiment, each first node  308  of each bi-directional AC-to-AC BIICM  1202  within each BIICM set  1201  of the three BIICM sets  1201  of AC-to-AC BIICMs  1202  in AC-to-AC BIIC  1200  are coupled together and further coupled to one first AC line  318  of at least three first AC lines  318 . Each first AC line  318  of the at least three first AC lines  318  transmits a phase of a 3-phase AC power to/from each first node  308  of each bi-directional AC-to-AC BIICM  1202  within each BIICM set  1201  of the three BIICM sets  1201  of AC-to-AC BIICMs  1202  in AC-to-AC BIIC  1200 . Moreover, in the exemplary embodiment, each second AC node  1222  of each topmost BIICM  1208  of each BIICM set  1201  of the three BIICM sets  1201  is coupled to one second AC line  1228  of the three second AC lines  1228 . Each second AC line  1228  of the three second AC lines  1228  transmits a phase of a 3-phase AC power to/from each full-bridge side  1212  of each bi-directional AC-to-AC BIICM  1202  within each BIICM set  1201  of the three BIICM sets  1201  of AC-to-AC BIICMs  1202  in AC-to-AC BIIC  1200 . 
     Moreover, in the exemplary embodiment, each third AC node  1224  of each bottommost BIICM within each BIICM set  1201  of the three BIICM sets  1201  are coupled together in AC-to-AC BIIC  1200 . Also, in the exemplary embodiment, fifth nodes  372  and sixth nodes  1226  within each BIICM set  1201  other than topmost BIICM  1208  of topmost BIICM set  1204  and bottommost BIICM  1210  of bottommost BIICM set  1206  are serially coupled together. Further, in the exemplary embodiment, all second nodes  332  of each AC-to-AC BIICM  1202  of each BIICM set  1201  of the three BIICM sets  1201  of bi-directional AC-to-AC BIICMs  1202  in AC-to-AC BIIC  1200  are coupled together through a first nodal bus  810 . Similarly, all third nodes  338  of each AC-to-AC BIICM  1202  within each BIICM set  1201  of the three BIICM sets  1201  of AC-to-AC BIICMs  1202  are coupled together through a second nodal bus  812 . In other alternative nodes, not shown, one or both of first nodal bus  810  and second nodal bus  812  are not present in AC-to-AC BIIC  1200 . 
     In operation, in the exemplary embodiment, AC-to-AC BIIC  1200  converts AC power transmitted to and/or received on three first AC lines  318  into AC power transmitted to and/or received on three second AC lines  1228 . Depending on a predetermined configuration of switching controllers and switching states, it is possible to divert a portion of AC power received and/or converted by AC-to-AC BIIC  1200  into energy storage device  208  to, for example, charge it. Also, in operation of the exemplary embodiment, it is possible to divert a portion of DC power stored in energy storage device  208 , i.e., to discharge it, to supplement AC power transmitted on either first AC lines  318  or second AC lines  1228 . Thus, in the exemplary embodiment, AC-to-AC BIIC  1200  functions as an AC-AC power converter. 
     Also, in operation of the exemplary embodiment, the flow of at least one of an AC current and a DC current in the switching devices of both first side  340  and full-bridge side  1212  is controlled through at least one switch control signal transmitted from at least one switching controller to at least one switch control terminal  358  of switching devices. As such, switching controller, along with the other aforementioned features and functions of AC-to-AC BIIC  1200 , facilitates maintaining a desired charging or discharging state of energy storage device  208 . 
       FIG.  13    is a schematic view of yet another alternative embodiment of an electric vehicle propulsion system  1300  superimposed on a plan view of an aircraft. In the alternative embodiment, vehicle  102  is an aircraft, as shown and described above with reference to  FIG.  1   . Also, in the alternative embodiment, generator  106  is coupled to drive engine  104  of vehicle  102  and to generator cable  204  of an AC type. Generator cable  204  is coupled to and between generator  106  and at least one converter set  1302  including at least one AC-to-AC BIIC  1200 . Further, in the alternative embodiment, converter set  1302  is in fuselage  108  proximate wing  110 . In other alternative embodiments, not shown, converter set  1302  is in aft portion  112  proximate tail  114 . Converter set  1302  is configured to function as an AC-to-AC power converter which receives AC power from generator  106  and transmits AC power to electrical device  122  on at least one BIIC cable  210  of an AC type. Electrical device  122  includes fan motor  212  used for vehicle propulsion, including, without limitation, during taxiing on a runway, i.e., where vehicle  102  is an aircraft. 
     In operation of the alternative embodiment, AC power from generator  106  is converted by converter set  1302  into AC power transmitted to second converter set  704  on BIIC cable  210  of an AC type. Also, in operation of the alternative embodiment, it is possible for converter set  1302  to divert at least a portion of AC power received from generator  106  to charge energy storage device  208 , not shown, in AC-to-AC BIIC  1200 . It is also possible for converter set  1302  to discharge energy storage device  208  to convert power therefrom to supplement at least a portion of AC power transmitted on BIIC cable  210  to electrical device  122 . Further, in operation of the exemplary embodiment, inclusion of AC-to-AC BIIC  1200  facilitates installation of electric vehicle propulsion system  1300  in vehicles  102  without requiring installation of generator rectifier  202  and replacement of AC type cable with DC type cable. Thus, electric vehicle propulsion system  1300  is particularly suited to applications involving retrofitting operations of vehicles  102  to increase specific power of known systems including, without limitation, electric vehicle propulsion system  100  shown and described above with reference to  FIG.  1   . 
       FIG.  14    is a schematic view of yet another alternative embodiment of an electric vehicle propulsion system  1400  superimposed on a plan view of an aircraft. In the alternative embodiment, vehicle  102  is an aircraft, as shown and described above with reference to  FIG.  1   . Also, in the alternative embodiment, generator  106  is coupled to drive engine  104  of vehicle  102  and to generator cable  204  of an AC type. Generator cable  204  is coupled to and between generator  106  and at least one first converter set  1402  including AC-to-AC BIIC  1200 , i.e., a fore BIIC. Moreover, in the alternative embodiment, first converter set  1402  is in fuselage  108  proximate wing  110 . 
     Also, in the alternative embodiment, electric vehicle propulsion system  1400  includes at least one second converter set  1404 . Second converter set  1404  includes at least one AC-to-AC BIIC  1200 , i.e., an aft BIIC. Further, in the alternative embodiment, second converter set  1404  is in aft portion  112  proximate tail  114 . Furthermore, in the alternative embodiment, BIIC-to-BIIC cable  706  of AC type is coupled to and between first converter set  1402  and second converter set  1404 . AC-to-AC BIIC  1200  of first converter set  1402  is configured to function as an AC-to-AC power converter which receives AC power from generator  106  and transmits AC power to second converter set  1404  on BIIC-to-BIIC cable  706 . Moreover, in the alternative embodiment, AC-to-AC BIIC  1200  of second converter set  1404  is configured to function as an AC-to-AC power converter which receives AC power from first converter set  1402  and transmits AC power to electrical device  122  on BIIC cable  210  of an AC type. Electrical device  122  includes fan motor  212  used for vehicle propulsion, including, without limitation, during taxiing on a runway, i.e., where vehicle  102  is an aircraft. 
     Further, in the alternative embodiment, it is possible to include an AC interconnect  1406  coupled to and between at least two first converter sets  1402 . It is also possible to include AC interconnect  1406  coupled to and between at least two second converter sets  1404 . Including AC interconnects  1406  facilitates balancing or sharing the power received and/or transmitted by each first converter set  1402  of at least two first converter sets  1402  from generator  106  and/or to at least one second converter set  1404 , respectively. Similarly, including AC interconnects  1406  facilitates balancing or sharing the power received and/or transmitted by each of at least two first converter sets  1402  from at least two generators  106  and at least two second converter sets  1404 , respectively. Likewise, including AC interconnects  1406  facilitates balancing or sharing the power received and/or transmitted by each of at least two second converter sets  1404  from at least two first converter sets  1402  and at least two electrical devices  122 , respectively. Furthermore, in the alternative embodiment, including AC interconnects  1406  facilitates AC power transmission on a single cable, including, without limitation, a bundled BIIC-to-BIIC cable  1408 , to/from at least two first converter sets  1402  and at least two second converter sets  1404  in electric vehicle propulsion system  1400 . 
     In operation of the alternative embodiment, AC power from generator  106  is converted by first converter set  1402  into AC power transmitted to second converter set  1404  on BIIC-to-BIIC cable  706 . Also, in operation of the alternative embodiment, it is possible for first converter set  1402  to divert at least a portion of AC power received from generator  106  to charge energy storage device  208 , not shown, in AC-to-AC BIIC  1200 . It is also possible for first converter set  1402  to discharge energy storage device  208  to convert power therefrom to supplement at least a portion of AC power transmitted on BIIC-to-BIIC cable  706  to second converter set  1404 . Similarly, it is possible for second converter set  1404  to divert at least a portion of AC power received first converter set  1402  to charge energy storage device  208 , not shown, in AC-to-AC BIIC  1200 . It is also possible for second converter set  1404  to discharge energy storage device  208  to convert power therefrom to supplement at least a portion of AC power transmitted on BIIC cable  210  to electrical device  122 . 
     Also, in operation of the alternative embodiment, inclusion of first converter set  1402  and second converter set  1404 , each including at least one AC-to-AC BIIC  1200 , facilitates installation of electric vehicle propulsion system  1400  in vehicles  102  without requiring installation of generator rectifier  202  and replacement of AC type cable with DC type cable. Thus, electric vehicle propulsion system  1400  is particularly suited to applications involving retrofitting operations of vehicles  102  to increase specific power of known systems including, without limitation, electric vehicle propulsion system  100  shown and described above with reference to  FIG.  1   . Further, in operation of the alternative embodiment, it is possible to further increase the specific power of electric vehicle propulsion system  1400  by inclusion of AC interconnects  1406  and bundled BIIC-to-BIIC cable  1408 , which provides opportunities to reduce the weight of BIIC-to-BIIC cable  706  where vehicle  102  includes a plurality of first converter sets  1402  and a plurality of second converter sets  1404 . 
       FIG.  15    is a schematic diagram of an exemplary shunt type BIIC  1500  configured for bidirectional DC-to-AC power conversion. In the exemplary embodiment, shunt type BIIC  1500  includes at least one bi-directional AC-to-DC BIICM  402  including a first node  308  and a second terminal  406 . Second terminal  406  is equivalent to third node  338 . Also, in the exemplary embodiment, a plurality of bi-directional AC-to-DC BIICMs  402  are arranged in at least one shunt string  1502 . First node  308  of a first bi-directional AC-to-DC BIICM  402  of shunt string  1502 , i.e., a topmost BIICM  1504  of each shunt string  1502  of the three shunt strings  1502  in  FIG.  15   , receives and/or transmits a phase of 3-phase AC power transmitted on one AC line  116  of at least three AC lines  116 . Second terminal  406  of a last bi-directional AC-to-DC BIICM  402  of shunt string  1502 , i.e., a bottommost BIICM  1506  of each shunt string  1502  of the three shunt strings  1502  in  FIG.  15   , couples to all other second terminals  406  of all other bottommost BIICMs  1506  in shunt type BIIC  1500 . Further, in the exemplary embodiment, first node  308  and second terminal  406  of each bi-directional AC-to-DC BIICM  402  of shunt string  1502 , other than topmost BIICM  1504  and bottommost BIICM  1506 , respectively, are serially coupled. 
     Also, in the exemplary embodiment, bi-directional AC-to-DC BIICM  402  that may be used in shunt type BIIC  1500  includes first side  340  inductively coupled to secondary side  414  through BIICM high-frequency transformer  336 , as shown and described above with reference to  FIG.  4   . Further, in the exemplary embodiment, bi-directional AC-to-DC BIICM  402  that may be used in shunt type BIIC  1500  includes at least one energy storage device  208  coupled in parallel across both of fifth switching device  344  and sixth switching device  346 , not shown, of secondary side  414 . Furthermore, in the exemplary embodiment, bi-directional AC-to-DC BIICM  402  that may be used in shunt type BIIC  1500  also includes at least one capacitor  326  coupled in parallel across both of fifth switching device  344  and sixth switching device  346 , not shown, of secondary side  414 . In other alternative embodiments, not shown, capacitor  326  is not present in secondary side  414 . 
     Moreover, in the exemplary embodiment, bi-directional AC-to-DC BIICM  402  that may be used in shunt type BIIC  1500  also includes at least one switching controller, not shown in  FIG.  15   . Switching controller is configured to transmit at least one switch control signal to at least one of first  320 , second  322 , third  328 , fourth  330 , fifth  344 , and sixth  346  switching devices, not shown, to control its switching states. In other alternative embodiments, not shown, switching controller receives and transmits other control signals to and from other controllers located elsewhere within or outside shunt type BIIC  1500 , also not shown in  FIG.  15   . In still other embodiments, not shown, bi-directional AC-to-DC BIICM  402  that may be used in shunt type BIIC  1500  also includes at least one bypass switch  360  coupled to and between first node  308  and second terminal  406 , and further coupled to bypass switch controller  368  and controlled thereby, as shown and described above with reference to  FIG.  3   . 
     In operation, in the exemplary embodiment, a phase of a 3-phase AC power is transmitted to or received from one AC line  116  of three AC lines  116  to each shunt string  1502  of the three shunt strings  1502  of shunt type BIIC  1500 . Also, in operation of the exemplary embodiment, each shunt string  1502  of the three shunt strings  1502  of shunt type BIIC  1500  converts AC power received on AC line  116  into DC power to charge energy storage device  208 . Shunt type BIIC  1500  is also capable to convert DC power stored in energy storage device  208 , i.e., to discharge energy storage device  208 , into AC power transmitted on each AC line  116  of the three AC lines  116  to electrical device  122 , not shown. The proportion of AC power converted and diverted to charge energy storage device  208 , and likewise, the proportion of DC power of energy storage device  208  converted and diverted to each AC line  116  of the three AC lines  116 , depends on a predetermined configuration of switching controllers and switching states of shunt type BIIC  1500 , as described above with reference to  FIG.  4   . Thus, in the exemplary embodiment, shunt type BIIC  1500  functions as a bi-directional DC-to-AC power converter. 
       FIG.  16    is a schematic view of yet another alternative embodiment of an electric vehicle propulsion system  1600  superimposed on a plan view of an aircraft. In the alternative embodiment, vehicle  102  is an aircraft, as shown and described above with reference to  FIG.  1   . Also, in the alternative embodiment, electric vehicle propulsion system  1600  includes drive engine  104 , generator  106 , AC line  116 , and electrical device  122 , as shown and described above with reference to  FIG.  1   . Electric vehicle propulsion system  1600  also includes AC line  116  coupled to and between at least one first AC/AC converter set  1602  and at least one second AC/AC converter set  1604 . First AC/AC converter set  1602  and second AC/AC converter set  1604  include conventional AC/AC power convertors, i.e., not BIICs as described herein. First AC/AC converter set  1602  and second AC/AC converter set  1604  each include at least one AC/AC power converter  1606 , i.e., a fore AC/AC power converter  1606  and an aft AC/AC power converter  1606 , respectively. Further, in the alternative embodiment, first AC/AC converter set  1602  is in fuselage  108  proximate wing  110 . Furthermore, in the alternative embodiment, second AC/AC converter set  1604  is in aft portion  112  proximate tail  114 . Also, in the alternative embodiment, at least one shunt type BIIC  1500  is coupled to AC line  116 . Further, in the alternative embodiment, shunt type BIIC  1500  is in fuselage  108  proximate wing  110 . In other alternative embodiments, not shown, shunt type BIIC  1500  is in other locations in fuselage  108 , including, without limitation, in aft portion  112  proximate tail  114 . 
     Also, in the alternative embodiment, it is possible to include an AC interconnect  1406  coupled to and between at least two first converter sets  1602 . It is also possible to include AC interconnect  1406  coupled to and between at least two second AC/AC converter sets  1604 . Including AC interconnects  1406  facilitates balancing or sharing the power received and/or transmitted by each of at least two first AC/AC converter sets  1602  from generator  106  and/or to second AC/AC converter set  1604 , respectively. Similarly, including AC interconnects  1406  facilitates balancing or sharing the power received and/or transmitted by each of at least two first AC/AC converter sets  1602  from at least two generators  106  and at least two second AC/AC converter sets  1604 , respectively. Likewise, including AC interconnects  1406  facilitates balancing or sharing the power received and/or transmitted by each of at least two second AC/AC converter sets  1604  from at least two first AC/AC converter sets  1602  and at least two electrical devices  122 , respectively. Furthermore, in the alternative embodiment, including AC interconnects  1406  facilitates AC power transmission on a single cable, including, without limitation, a bundled AC line  1608 , to/from at least two first AC/AC converter sets  1602  and at least two second AC/AC converter sets  1604  in electric vehicle propulsion system  1600 . 
     In operation, in the alternative embodiment, AC current is transmitted on AC line  116  from first AC/AC converter set  1602  to second AC/AC converter set  1604 . DC power from at least one energy storage device  208 , not shown, within shunt type BIIC  1500  is converted to AC power, i.e., by discharging energy storage device  208 , by shunt type BIIC  1500 . AC power from shunt type BIIC  1500  is transmitted to AC line  116  to supply at least a portion of AC power to second AC/AC converter set  1604 . Also, in operation of the alternative embodiment, it is possible for shunt type BIIC  1500  to convert AC power received on AC line  116  into DC power to charge energy storage device  208  within shunt type BIIC  1500 . Thus, in the alternative embodiment, shunt type BIIC  1500  functions as a bidirectional DC-to-AC power converter. 
       FIG.  17    is a schematic view of yet another alternative embodiment of an electric vehicle propulsion system  1700  superimposed on a plan view of an aircraft. In the alternative embodiment, vehicle  102  is an aircraft, as shown and described above with reference to  FIG.  1   . Also, in the alternative embodiment, electric vehicle propulsion system  1700  includes drive engine  104 , generator  106 , and electrical device  122 , as shown and described above with reference to  FIG.  1   . Further, in the alternative embodiment, electric vehicle propulsion system  1700  includes at least one AC line  116  coupled to and between generator  106  and at least one AC/AC converter set  1702 . AC/AC converter set  1702  includes conventional AC/AC power convertors, i.e., not BIICs as described herein. AC/AC converter set  1702  includes at least one AC/AC power converter  1606 . Furthermore, in the alternative embodiment, AC/AC converter set  1702  is in aft portion  112  proximate tail  114 . In other alternative embodiments, not shown, AC/AC converter set  1702  is in other locations in fuselage  108 , including, without limitation, proximate wing  110 . 
     Also, in the alternative embodiment, at least one shunt type BIIC  1500  is coupled to AC line  116 . Further, in the alternative embodiment, shunt type BIIC  1500  is in fuselage  108  proximate wing  110 . In still other alternative embodiments, not shown, shunt type BIIC  1500  is in other locations in fuselage  108 , including, without limitation, in aft portion  112  proximate tail  114 . Furthermore, in the alternative embodiment, it is possible to exclude at least one AC/AC converter set  1702  from electric vehicle propulsion system  1700 . Where AC/AC converter set  1702  is excluded from electric vehicle propulsion system  1700 , AC line  116  is coupled to and between generator  106  and electrical device  122  directly, and without an intervening AC/AC power converter  1606 . 
     In operation, in the alternative embodiment, AC current is transmitted on AC line  116  from generator  106  to AC/AC converter set  1702 . DC power from energy storage device  208 , not shown, within shunt type BIIC  1500  is converted to AC power, i.e., by discharging energy storage device  208 , by shunt type BIIC  1500 . AC power from shunt type BIIC  1500  is transmitted to AC line  116  to supply at least a portion of AC power to AC/AC converter set  1702 . Also, in operation of the alternative embodiment, it is possible for shunt type BIIC  1500  to convert AC power received on AC line  116  into DC power to charge energy storage device  208  within shunt type BIIC  1500 . Thus, in the alternative embodiment, shunt type BIIC  1500  functions as a bidirectional DC-to-AC power converter. 
     The above-described embodiments of BIICs described herein are suited to increasing the specific power, i.e., kilowatt/kilogram (kW/kg), of electric vehicle propulsion systems by reducing the number and weight of passive components and cables. Specifically, the above-described BIICs do not require many passive filtering capacitors because the rates of change of voltage with time, i.e., dv/dt, of individual battery integrated power converter modules (BIICMs) are small relative to known power converters in known electric vehicle propulsion systems. Further, specifically, tight control of dv/dt in individual BIICMs results in low levels of harmonic distortion and electromagnetic interference (EMI) relative to known power converters for electric vehicle propulsion systems. Further, the above-described BIICs are more modular, sealable, reliable, as well as easier to maintain and manufacture relative to known power converters for electric vehicle propulsion systems. Furthermore, a wide variety of energy storage devices are adaptable to use with the above-described BIICs, which facilitates incorporation of more advanced energy storage devices into electric vehicle propulsion systems without replacement of power converter components. Moreover, the above-described BIICs provide effective physical and galvanic isolation of energy storage devices, including, without limitation, DC batteries, from other components of the BIICs and the overall power system, thus enhancing safety and reliability in electric vehicle propulsion systems. As such, the above-described BIICs utilize energy storage devices to not only provide energy for electric vehicle propulsion, but also to act as voltage sources to enable multi-level power converter operations without additional film capacitors, and at the same time reduce the requirements of using filtering component elements relative to known power converters for electric vehicle propulsion systems. 
     Exemplary technical effects of the above-described apparatus and systems include at least one of: (a) increasing the specific power, i.e., kW/kg, of electric vehicle propulsion systems; (b) decreasing the weight of power converter components and cables of electric vehicle propulsion systems; (c) reducing the number and weight of passive components including filtering capacitors in power converter components of electric vehicle propulsion systems; (d) lowering levels of harmonic distortion and EMI in electric vehicle propulsion systems; (e) making power converter components of electric vehicle propulsion systems more modular, sealable, reliable, as well as easier to maintain and manufacture; (f) enabling utilization of energy storage devices in electric vehicle propulsion systems to not only provide energy for electric propulsion, but also to act as voltage sources to enable multi-level power converter operation without additional film capacitors; (g) facilitating incorporation of more advanced energy storage devices into electric vehicle propulsion systems without replacement of power converter components; and (h) providing physical and galvanic isolation of energy storage devices, including, without limitation, DC batteries, from other components of the BIICs and the overall power system. 
     Exemplary embodiments of the above-described apparatus and systems for BIICs are not limited to the specific embodiments described herein, but rather, components of apparatus and systems may be utilized independently and separately from other components described herein. For example, the apparatus and systems may also be used in combination with other systems requiring increasing the specific power of power system components including, without limitation, power converters, generators, motors, cables, and energy storage devices, and the associated methods, and are not limited to practice with only the apparatus and systems as described herein. Rather, the exemplary embodiment can be implemented and utilized in connection with many other applications, equipment, and systems that may benefit from using BIICs to improve the specific power, performance, reliability, power efficiency, EMI behavior, maintainability, and manufacturability of power converters and other power systems in various applications. 
     Although specific features of various embodiments of the disclosure may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the disclosure, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing. 
     This written description uses examples to disclose the embodiments, including the best mode, and to enable any person skilled in the art to practice the embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.