Patent Publication Number: US-10312017-B2

Title: Symmetrical step-up and step-down autotransformer delta topology

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 14/328,937, filed Jul. 11, 2014 and entitled “SYMMETRICAL STEP-UP AND STEP-DOWN AUTOTRANSFORMER DELTA TOPOLOGY”, which issued on Mar. 21, 2017 as U.S. Pat. No. 9,601,258. This patent application is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     In many applications, especially shipboard and aircraft applications, a high voltage direct current (DC) power is used to power motor controllers. Typically, a three phase alternating current (AC) voltage of 230 VAC (RMS voltage) is generated in a ship or an aircraft. The generated AC voltage is applied to an auto transformer rectifier unit (ATRU) and rectified to generate a voltage of ±270 VDC. The rectified DC voltage from the ATRU is then used to power the motor controllers. Other shipboard and aircraft applications, however, may require different DC output voltages. For example, multiple different voltage levels are required in modern aircraft for motor controllers in different zones. Higher voltages may be used in controlled pressure zones so as to reduce the size of feeder cables; whereas lower voltages are preferred in uncontrolled pressure zones so reduce the risk of corona, especially at higher altitudes. In addition, still other applications require an AC voltage. 
     In some power system configurations, use of separate power supplies and transformers to provide power for each of these different applications increases the size, cost, weight, and cooling requirements for the overall system, which is especially undesirable in aircraft applications. The placement of some power supplies and transformers limits the cooling to be air-cooled. Further, simply placing all of the various power supplies and transformers in a single area or compartment does not noticeably reduce the size, cost, weight, or cooling requirements for the overall system. 
     SUMMARY OF THE DISCLOSURE 
     This Summary provides a general description of a multi-phase transformer and a power supply which uses the multi-phase transformer, as further described in the Detailed Description below. This Summary is not intended to, and may not be used to, limit the scope of the claimed subject matter. 
     The multi-phase transformer has primary windings and multiple sets of secondary windings. The primary windings are arranged in a delta configuration to receive a three-phase input voltage, each primary winding has a center tap and a plurality of taps disposed symmetrically about the center tap. 
     In an embodiment, in a first set of paired secondary windings, there are preferably three pairs. The secondary windings of a pair are electrically connected to taps symmetrically located on opposite sides of the center tap of the primary winding. Each winding in a pair is also magnetically coupled to a predetermined primary winding different from that to which it is electrically connected. Each secondary winding of a pair has a first end connected to the tap on the primary winding and a second end to provide an output. 
     In an embodiment, in a second set of paired secondary windings, there are also preferably three pairs. The secondary windings of a pair are electrically connected to taps symmetrically located on opposite sides of the center tap of the primary winding. Each winding in a pair is also magnetically coupled to a predetermined primary winding different from that to which it is electrically connected. Each secondary winding of a pair has a first end connected to the tap on the primary winding and a second end to provide an output. The secondary windings of this second set are connected to different taps than the paired secondary windings of the first set. 
     In an embodiment, the center taps collectively provide a first three-phase output, the second end of a first winding of each pair of secondary windings of the first set collectively provide a second three-phase output, and the second end of a second winding of each pair of secondary windings of the first plurality collectively provide a third three-phase output. 
     In an embodiment, the center taps and the second ends of the paired secondary windings of the first set collectively provide a first multi-phase output. 
     In an embodiment, the second ends of the paired secondary windings of the second set, collectively, along with the AC input voltage, provide a second multi-phase output. 
     In an embodiment, the first, second, and third three-phase output voltages and the first multi-phase output voltage are each about one-half of the input voltage, and the second multi-phase output voltage is about the same as the input voltage. 
     Also disclosed is a power supply, such as for, but not necessarily for, a ship or an aircraft which uses the multi-phase transformer. In an embodiment, the first multi-phase output is provided to a first 18-pulse rectifier to provide a first DC output voltage, and the second multi-phase output is provided to another 18-pulse rectifier to provide a second DC output voltage, which is preferably higher than the first DC output voltage. Thus, this single power supply can replace the various power supplies and transformers previously used, reduce the overall size, reduce the overall cost, reduce the overall weight, and allow for liquid cooling of the system. 
     “First”, “second”, and “third” are used herein to identify components or items having similar names, and do not necessarily indicate an order, preference, or importance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a winding diagram for an exemplary multi-phase autotransformer. 
         FIG. 2A  is an exemplary phasor diagram for the exemplary multi-phase autotransformer of  FIG. 1 . 
         FIG. 2B  is the exemplary phasor diagram of  FIG. 2A  with the line lengths indicated thereon. 
         FIG. 3  shows an exemplary power supply system for use with the exemplary autotransformer of  FIG. 1 . 
         FIG. 4  is a diagram of an exemplary power supply system with liquid cooling. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, references are made to the accompanying drawings that form a part hereof, and which are shown by way of illustration, specific embodiments, or examples. Like numerals represent like elements in the several figures. The embodiments described herein are illustrative, for the purpose of teaching one of ordinary skill in the art, and are not intended to limit the scope of the disclosure. Also, the various features, functions, and advantages discussed herein can be achieved independently in different embodiments or may be combined with other embodiments. 
     Some of the reference designations used herein are as follows: 
     PWA, PWB, PWC: Primary windings A, B, and C; 
     A, B, C: Junctions of the primary windings, end points of the primary windings; 
     CTA, CTB, CTC: Center tap or contact point for primary winding PWA-PWC; 
     TA 1 -TA 4 : Tap or contact points for primary winding PWA; 
     TB 1 -TB 4 : Tap or contact points for primary winding PWB; 
     TC 1 -TC 4 : Tap or contact points for primary winding PWC; 
     SWA 1 -SWA 4 , SWB 1 -SWB 4 , SWC 1 -SWC 4 : Secondary windings; 
     SA 1 -SA 4 : External end or contact for secondary windings SWA 1  through SWA 4 ; 
     SB 1 -SB 4 : External end or contact for secondary windings SWB 1  through SWB 4 ; and 
     SC 1 -SC 4 : External end or contact for secondary windings SWC 1  through SWC 4   
       FIG. 1  is a winding diagram of an exemplary multi-phase transformer  10 . Transformer  10  has three primary windings PWA, PWB, PWC connected end-to-end in a delta configuration: one end of primary winding PWA being connected to one end of primary winding PWB at junction B, the other end of primary winding PWB being connected to one end of primary winding PWC at junction C, and the other end of primary winding PWC being connected to the other end of primary winding PWA at junction A. A primary winding PWA, PWB, PWC may be several windings connected in series or a single winding having several tap points. For example, primary winding A may be considered as comprising a single winding having a plurality of tap points TA 1  TA 2 , TA 3 , TA 4 , CTA, or primary winding A may be considered as comprising windings PWA 1 , PWA 2 , . . . PWA 6  connected in series at junction points TA 1 , TA 2 , TA 3 , TA 4 , CTA. 
     The tap points TA 1  and TA 2  are symmetrical with respect to, and on opposite sides of, the center tap point CTA. Likewise, the tap points TA 3  and TA 4  are symmetrical with respect to, and on opposite sides of, the center tap point CTA. Tap points TA 1  and TA 3  are on one side of the center tap CTA, and tap points TA 2  and TA 4  are on the other side with respect to the tap CTA. In one embodiment, a tap TA 1 , TB 1 , TC, TA 2 , TB 2 , or TC 2  is located at a point one-third of the distance between the center tap and the end of its respective primary winding. 
     Four secondary windings SWA 1 , SWA 2 , SWA 3 , and SWA 4  are connected to tap points TA 1 , TA 2 , TA 3 , TA 4 , respectively, and have output or junction points SA 1 , SA 2 , SA 3 , and SA 4 , respectively. 
     Secondary windings SWB 1 , SWB 2 , SWB 3 , SWB 4 , SWC 1 , SWC 2 , SWC 3 , and SWC 4  are connected to tap points TB 1 , TB 2 , TB 3 , TB 4 , TC 1 , TC 2 , TC 3 , and TC 4 , respectively, and have output or junction points SB 1 , SB 2 , SB 3 , SB 4 , SC 1 , SC 2 , SC 3 , and SC 4 , respectively. 
     Primary windings PWA 1 , PWA 6 , PWB 1 , PWB 6 , PWC 1 , and PWC 6  each have N 3  relative turns; primary windings PWA 2 , PWA 5 , PWB 2 , PWB 5 , PWC 2 , and PWC 5  each have N 2  relative turns; and primary windings PWA 3 , PWA 4 , PWB 3 , PWB 4 , PWC 3 , and PWC 4  each have N 1  relative turns. Secondary windings SWA 1 , SWA 2 , SWB 1 , SWB 2 , SWC 1 , and SWC 2  each have N 5  relative turns; and secondary windings SWA 3 , SWA 4 , SWB 3 , SWB 4 , SWC 3 , and SWC 4  each have N 4  relative turns. “Relative turns” means the number of turns relative to another winding, such as the primary winding PWA 1 . Preferably, the number of turns is an integer. For example, if N 3  (for winding PWA 1 ) is defined as being one (1) relative turn then in one embodiment N 1  will be INT(N 3 *20.04/20.55), N 2  will be INT(N 3 *25.90/20.55), N 4  will be INT(N 3 *38.26/20.55), and N 5  will be INT(N 3 *8.38/20.55), where INT(x) indicates the integer function. These values for Nx are derived from  FIG. 2B , discussed below. In one embodiment, N 3  is actually 20 turns, so N 1  would actually be 20 turns, N 2  would be 25 turns, N 4  would be 37 turns, and N 5  would be 8 turns. Different numbers of turns and ratios may be used, depending upon such factors as, but not limited to, the frequency of the input voltage, the power requirements of each of the various connected subsystems, the desired output voltages, the minimum no-load impedance of the transformer  10 , the core material, the core cross-sectional area, material saturation, losses, etc. 
     Consider now the arrangement and results of the various outputs provided by the transformer  10 . The three primary windings PWA, PWB, and PWC are preferably constructed as close to being identical as permitted by manufacturing techniques in use, the materials used, cost considerations, and time considerations. Likewise, secondary windings SWA 1 , SWA 2 , SWB 1 , SWB 2 , SWC 1  and SWC 2  are preferably constructed as close to being identical as permitted by manufacturing techniques in use, the materials used, cost considerations, and time considerations. Also, secondary windings SWA 3 , SWA 4 , SWB 3 , SWB 4 , SWC 3  and SWC 4  are preferably constructed as close to being identical as permitted by manufacturing techniques in use, the materials used, cost considerations, and time considerations. 
     The voltage at a center tap is one-half of the voltage between the junctions. That is, the voltage at center tap CTA for example, will be one-half of the voltage VAB between junctions A and B, and likewise for the voltage at center taps CTB and CTC. Thus, the output voltage for the three center taps will be one-half of the input voltage. For example, if the input is three-phase, 230 volts, then the output collectively provided by the center taps will be three-phase 115 volts. Note that, as this is a three-phase system, the line-to-line voltage (VAB, VBC, VCA) will be 230√13, or approximately 400 volts, so the center-tap to center-tap output voltage will be 115√13, or approximately 200 volts. The center taps CTA, CTB, and CTC collectively provide a first three-phase output which has a voltage which is one-half of the input voltage at input junctions A, B, and C. 
     Taps TA 1 , TB 1  and TC 1  are evenly spaced around the delta configuration so they also provide a three-phase output. This three-phase output may not, however, directly provide the desired output voltage and phase. Therefore, rather than using the outputs of these taps directly, the outputs of secondary windings SWA 1 , SWB 1 , and SWC 1  are used. A secondary winding, SWA 1 , SWB 1 , and SWC 1 , is electrically coupled to a predetermined tap on its respective predetermined primary winding, PWA, PWB, PWC, but is magnetically coupled to a different predetermined primary winding, PWB, PWC, PWA, respectively, to provide different, phase-shifted voltages at outputs SA 1 , SB 1 , SC 1 , respectively. Also, each of these secondary windings SWA 1 , SWB 1 , SWC 1  is magnetically coupled to a different predetermined primary winding than the other two of these secondary windings. In one embodiment, the voltage induced across these secondary windings is in opposition to the voltage at taps TA 1 , TB 1  and TC 1  so that the voltage at outputs SA 1 , SB 1  and SC 1 , respectively, is one-half of the input voltage and is phase shifted by 40 degrees with respect to the phase of the voltage at CTA, CTB, and CTC, respectively. The output points SA 1 , SB 1 , SC 1  collectively provide a second three-phase output which has a voltage which is one-half of the input voltage at input junctions A, B, and C. This second three-phase output is phase-shifted with respect to the first three-phase output. 
     Taps TA 2 , TB 2  and TC 2  are likewise evenly spaced around the delta configuration, but on the opposite side of center taps CTA, CTB, and CTC, respectively, so they also provide a three-phase output. This three-phase output may not, however, directly provide the desired output voltage and phase. Therefore, rather than using the outputs of these taps directly, the outputs of secondary windings SWA 2 , SWB 2 , and SWC 2  are used. A secondary winding, SWA 2 , SWB 2 , SWC 2 , is electrically coupled to a predetermined tap on its respective predetermined primary winding, PWA, PWB, PWC, but is magnetically coupled to a different predetermined primary winding, PWC, PWA, PWB, respectively, to provide different, phase-shifted voltages at outputs SA 2 , SB 2 , SC 2 , respectively. Also, each of these secondary windings SWA 2 , SWB 2 , SWC 2  is magnetically coupled to a different primary winding than the other two of these secondary windings. In one embodiment, the voltage induced across these secondary windings is in opposition to the voltage at taps TA 2 , TB 2  and TC 2  so that the voltage at outputs SA 2 , SB 2  and SC 2 , respectively, is one-half of the input voltage and is phase shifted by 40 degrees with respect to the phase of the voltage at CTA, CTB, and CTC, respectively, but in the opposite direction of the phase shifts with respect to outputs SA 1 , SB 1 , SC 1 . The output points SA 2 , SB 2 , SC 2  collectively provide a third three-phase output which has a voltage which is one-half of the input voltage at junctions A, B, and C. This third three-phase output is phase-shifted with respect to both the first three-phase output and the second three-phase output. 
     The center taps CTA, CTB, CTC of the primary windings, and the output points SA 1 , SA 2 , SB 1 , SB 2 , SC 1 , SC 2  collectively provide a first multi-phase output. In one embodiment, this output has a voltage which is one-half of the input voltage applied at junctions A, B, and C, this output voltage being selected because of the power requirements of the load devices. 
     Note that, in the embodiment discussed above, the voltage at outputs SA 1 , SA 2 , SB 1 , SB 2 , SC 1 , SC 2 , CTA, CTB, and CTC are all the same—one-half of the input voltages VAB, VBC, VCA. These outputs are, however, phase-shifted with respect to each other so, in effect, they also collectively provide a nine-phase output, the phases being separated by 40 degrees. 
     Taps TA 3 , TB 3  and TC 3  are likewise evenly spaced around the delta configuration so they also provide a three-phase output. This three-phase output may not, however, directly provide the desired output voltage and phase. Therefore, rather than using the outputs of these taps directly, the outputs of secondary windings SWA 3 , SWB 3 , and SWC 3  are used. A secondary winding, SWA 3 , SWB 3 , SWC 3 , is electrically coupled to its respective primary winding, PWA, PWB, PWC, respectively, but is magnetically coupled to a different predetermined primary winding, PWB, PWC, PWA, respectively, to provide different, phase-shifted voltages at output SA 3 , SB 3 , SC 3 , respectively. In one embodiment, the voltage induced across these secondary windings is in reinforcement to the voltage at taps TA 3 , TB 3  and TC 3  so that the voltage at outputs SA 3 , SB 3  and SC 3 , respectively, is the same as the input voltage and is phase shifted by 40 degrees with respect to the input voltage. 
     Taps TA 4 , TB 4  and TC 4  are likewise evenly spaced around the delta configuration so they also provide a three-phase output. This three-phase output may not, however, directly provide the desired output voltage and phase. Therefore, rather than using the outputs of these taps directly, the outputs of secondary windings SWA 4 , SWB 4 , and SWC 4  are used. A secondary winding, SWA 4 , SWB 4 , SWC 4 , is electrically coupled to its respective primary winding, PWA, PWB, PWC, but is magnetically coupled to a different predetermined primary winding, PWC, PWA, PWB, respectively, to provide different, phase-shifted voltages at outputs SA 4 , SB 4 , SC 4 , respectively. In one embodiment, the voltage induced across these secondary windings is in reinforcement to the voltage at taps TA 4 , TB 4  and TC 4  so that the voltage at outputs SA 4 , SB 4  and SC 4 , respectively, is the same as the input voltage and is phase shifted by 40 degrees with respect to the input voltage, but in the opposite direction of the phase shifts with respect to outputs SA 3 , SB 3 , SC 3 . 
     Also, in the embodiment discussed above, the voltage at outputs SA 3 , SA 4 , SB 3 , SB 4 , SC 3 , and SC 4  are all the same as the input voltages VAB, VBC, VCA. These outputs are, however, phase-shifted with respect to the input voltages VAB, VBC, VCA so, in effect, and along with the input voltages, they also collectively provide a nine-phase output, the phases also being separated by 40 degrees. 
     The output points SA 3 , SA 4 , SB 3 , SB 4 , SC 3 , SC 4  collectively provide a second multi-phase output which has a voltage which is the same as the input voltage applied at junctions A, B, and C, this output voltage being selected because of the power requirements of the load devices. 
     An advantage of these multi-phase output voltage arrangements is that any subsequent rectification process has less ripple and therefore requires less filtering and smoothing than a rectification process which operates on, for example, a two-phase or a three-phase input voltage. For example, the ±270 VDC output has a peak-to-peak ripple voltage of only about 4 volts. 
     Secondary windings SWA 1  and SWA 2  may be considered to be a first pair of a first plurality of paired secondary windings, secondary windings SWB 1  and SWB 2  may be considered to be a second pair of a first plurality of paired secondary windings, and secondary windings SWC 1  and SWC 2  may be considered to be a third pair of a first plurality of paired secondary windings. A first secondary winding of a pair of these paired secondary windings has a first end and a second end, the first end is electrically connected to a tap on a first side of the center tap of a predetermined primary winding of the plurality of primary windings, and the first secondary winding is magnetically coupled to a primary winding of the plurality of primary windings other than the predetermined primary winding to which it is electrically connected. A second secondary winding of the pair has a first end and a second end, the first end is electrically connected to a tap on a second, opposing side of the center tap of the predetermined primary winding, and the second secondary winding is magnetically coupled to a primary winding other than the predetermined primary winding to which it is electrically connected and other than the primary winding to which the first secondary winding is magnetically coupled. Also, the predetermined primary winding for a pair of the first plurality of paired secondary windings is other than the predetermined primary winding for any other pair of the first plurality of paired secondary windings. 
     Secondary windings SWA 3  and SWA 4  may be considered to be a first pair of a second plurality of paired secondary windings, secondary windings SWB 3  and SWB 4  may be considered to be a second pair of the second plurality of paired secondary windings, and secondary windings SWC 3  and SWC 4  may be considered to be a third pair of the second plurality of paired secondary windings. A first secondary winding of a pair of these paired secondary windings has a first end and a second end, the first end is electrically connected to a tap on a first side of the center tap of a predetermined primary winding of the plurality of primary windings, and the first secondary winding is magnetically coupled to a primary winding of the plurality of primary windings other than the predetermined primary winding to which it is electrically connected. A second secondary winding of a pair has a first end and a second end, the first end is electrically connected to a tap on a second, opposing side of the center tap of the predetermined primary winding, and the second secondary winding is magnetically coupled to a primary winding other than the predetermined primary winding to which it is electrically connected and other than the primary winding to which the first secondary winding is magnetically coupled. Also, the predetermined primary winding for a pair of the second plurality of paired secondary windings is other than the predetermined primary winding for any other pair of the second plurality of paired secondary windings. 
       FIG. 2A  is an exemplary phasor diagram for the exemplary multi-phase transformer  10  of  FIG. 1 . The phasor diagram graphically depicts various aspects the multi-phase transformer, such as the relationship between the various windings. A dot represents a contact point, a junction, or a tap point (e.g., A, TA 3 , TA 1  CTA, TA 2 , TA 4 , B, SA 3 , SA 1 , SA 2 , SA 4 , etc.). Various windings are represented by lines in the phasor diagram between the contact points and, as indicated above, the length of a line between the contact points generally represents the relative number of turns of a winding with respect to another winding, such as, but not limited to, a primary winding. 
       FIG. 2B  is the exemplary phasor diagram of  FIG. 2A  with the line lengths indicated thereon. For example, the line lengths for N 1 , N 2 , N 3 , N 4  and N 5  are 20.04, 25.90, 20.55, 38.26, and 8.38, respectively. Thus, N 1 /N 3 =20.04/20.55=0.975. Therefore, if N 3 =20 turns, then N 1 =INT(19.5036 . . . )=20 turns. Ratios and the number of turns for the other windings are similarly determined. 
     The lines are vector lines depicting the vector of the induced voltage. Two vector lines that are parallel to each other represent magnetic coupling between corresponding two windings. For example, line SA 3 -TA 3  is parallel to line BC, which indicates that secondary winding SWA 1  is magnetically coupled to primary PWB, line SC 3 -TC 3  is parallel to line AB, which indicates that secondary winding SWC 3  is magnetically coupled to primary PWA, and line TB 1 -SB 1  is parallel to line CA, which indicates that secondary winding SWB 1  is magnetically coupled to primary PWC. The radial length of each segment between two junctions along the circumference represents the phase angle difference between the output signals at those junctions, with the full circle representing 360 degrees. The common center of the circle represents the effective electrical neutral position. 
     The phasor diagram  200  includes a first circle  210  (for example, 230 VAC) and a second circle  220  (for example, 115 VAC), both having a common center S. The sides AB, BC and CA of triangle ABC represent the primary windings PWA, PWB, and PWC respectively. Points TA 1 , TA 2 , CTA, TB 1 , TB 2 , CTB, TC 1 , TC 2 , and CTC correspond to the tap points of the primary windings PWA-PWC. Lines A-TA 3 , TA 3 -TA 1 , TA 1 -CTA, CTA-TA 2 , TA 2 -TA 4 , and TA 4 -B represent portions (sub-primary windings) PWA 1 , PWA 2 , PWA 3 , PWA 4 , PWA 5  and PWA 6 , respectively, of the primary windings. Lines B-TB 3 , TB 3 -TB 1 , . . . , TB 4 -C, C-TC 3 , TC 3 -TC 1 , . . . , TC 4 -A, represent similar sub-primary windings on primary windings PWB and PWC. 
     Lines TA 1 -SA 1 , TA 2 -SA 2 , TB 1 -SB 1 , TB 2 -SB 2 , TC 1 -SC 1 , TC 2 -SC 2  represent one group or set of secondary windings, SWA 1 , SWA 2 , SWB 1 , SWB 2 , SWC 1 , SWC 2 , respectively, and lines TA 3 -SA 3 , TA 4 -SA 4 , TB 3 -SB 3 , TB 4 -SB 4 , TC 3 -SC 3 , TC 4 -SC 4  represent another group or set of secondary windings, SWA 3 , SWA 4 , SWB 3 , SWB 4 , SWC 3 , SWC 4 , respectively. 
     Points SA 1 -SA 4 , SB 1 -SB 4 , and SC 1 -SC 4  represent the second (output) end of secondary windings SWA 1 -SWA 4 , SWB 1 -SWB 4 , and SWC 1 -SWC 4 , respectively. 
     The lines SA, SB and SC represent the input AC voltage applied to the exterior junctions A, B and C of the primary windings. As it is evident from the phasor diagram, a three phase input voltage is depicted as phase A, phase B, and phase C, with each phase being separated by about 120 degrees. In one environment, such as an aircraft, the input voltages SA, SB and SC are 230 volts. Other input voltages may be used, and other output voltages may be provided, as desired. 
     As previously described, the lines in the phasor diagram  200  are vector lines depicting the vector of the induced voltage. For example, the vector of induced voltage in primary windings AB, BC and CA are depicted by the arrows on the lines SA, SB and SC. Similarly, the arrows on lines representing the secondary windings represent the vector of induced voltage. For example, arrows on lines TA 1 -SA 1  and SA 3 -TA 3  represent the vector of induced voltage in secondary windings SWA 1  and SWA 3 , respectively. 
     The vector of induced voltage in a secondary winding is selected to boost or buck the voltage at the tap point on a primary winding to provide the desired output voltage and/or phase. 
       FIG. 3  shows an exemplary power supply system  300  for use with the exemplary autotransformer  10 . The power supply system  300  includes a three-phase, 230 VAC generator  305 , an autotransformer  10 , buses  310 ,  315 ,  325 ,  345 A,  345 B,  345 C, and  360 , 18-pulse rectifiers  330  and  365 , and motor controllers  340  and  375 . The generator  305  provides three-phase, 230 VAC power over bus  310  to autotransformer  10 . Autotransformer  10  provides a plurality of outputs  315 , eighteen in one embodiment, to various components via bus  320 . The eighteen outputs, as seen from  FIGS. 1 and 2 , are SA 1 -SA 4 , SB 1 -SB 4 , SC 1 -SC 4 , CTA, CTB, CTC, A, B, and C. Bus  320  is indicated as a single bus for convenience of illustration. Although bus  320  may carry all eighteen outputs to each receiving component, that is not a preferable configuration. Rather, the bus  320  comprises a plurality of smaller buses,  325 ,  345 A,  345 B,  345 C,  360 , each of which carries only those outputs required by a particular receiving component. For example, bus  325  carries outputs SA 1 , SA 2 , SB 1 , SB 2 , SC 1 , SC 2 , CTA, CTB, and CTC to 18-pulse rectifier  330 , which rectifies these outputs to provide ±135 VDC power over bus  335  to a first motor controller  340 . The design and operation of 18-pulse rectifiers and motor controllers is well known to those of ordinary skill in the art. 
     Note that transformer  10  provides three sets of outputs: SA 1 , SB 1 , and SC 1 ; SA 2 , SB 2 , and SC 2 ; and CTA, CTB, and CTC. Also note that these three output sets differ from each other by approximately 40 degrees. That is, for example, output SA 1  will lead output CTA by approximately 40 degrees, output CTA will lead output SA 2  by approximately 40 degrees, output SA 2  will lead output SB 1  by approximately 40 degrees, output SB 1  will lead output CTB by approximately 40 degrees, etc. Thus, full-wave rectification of these three output sets provides an 18-pulse output at ±135 VDC. 
     Similarly, bus  360  carries outputs SA 3 , SA 4 , SB 3 , SB 4 , SC 3 , and SC 4 , along with the input voltage A, B, and C, to 18-pulse rectifier  365 , which rectifies these outputs to provide ±270 VDC power over bus  370  to a second motor controller  375 . Note that transformer  10  provides two sets of outputs: SA 3 , SB 3 , and SC 3 ; SA 4 , SB 4 , and SC 4 ; and the input voltages A, B, and C are passed through as another output set. Also note that these three output sets differ from each other by approximately 40 degrees. That is, for example, output A will lead output SA 3  by approximately 40 degrees, output SA 3  will lead output SA 4  by approximately 40 degrees, output SA 4  will lead output B by approximately 40 degrees, output B will lead output SB 3  by approximately 40 degrees, etc. Thus, full-wave rectification of these three output sets also provides an 18-pulse output, but at ±270 VDC rather than ±135 VDC. 
     Bus  345 A carries outputs SA 1 , SB 1 , and SC 1 , which provides a first source  350 A of 3-phase, 115 VAC power to load  355 A. Bus  345 B carries outputs SA 2 , SB 2 , and SC 2 , which provides a second source  350 B of 3-phase, 115 VAC power to load  355 B. Likewise, bus  345 C carries outputs CTA, CTB, and CTC, which provides a third source  350 C of 3-phase, 115 VAC power to load  355 C. Note that the buses  345 A,  345 B and  345 C differ from each other by approximately 40 degrees, as described above. This distributes the load of the receiving devices  355 A- 355 C more evenly throughout a cycle of input AC power. 
     Note that the multiple AC and DC outputs described herein have been achieved with a single transformer having only 15 windings: the three primary windings (PWA, PWB, PWC), and the  12  secondary windings (SWA 1 -SWA 4 , SWB 1 -SWB 4 , and SWC 1 -SWC 4 ). 
     In an exemplary environment, such as with respect to an aircraft, the three three-phase 115 VAC loads  355 A- 355 C are traditional loads, such as galley appliances. The ±270 VDC output powers high-power motor controllers, such as the motor controller for the cabin air pressure. The ±135 VDC output powers lower-power motor controllers, such as the motor controllers for the electrically-operated brakes for the aircraft. 
     Preferably, the system  300  replaces multiple existing Auto Transformer Units (ATUs), Galley Auto Transformer Units (GATUs), Electric-Brake Power Supply Units (E-BPSU), which are air-cooled devices with a single, liquid-cooled, Auto Transformer Rectifier Unit (ATRU). This reduces size and weight, which result is especially desirable for aircraft applications. In addition, replacing the multiple conventional power supply/transformer units by a single ATRU causes liquid cooling to become feasible. The liquid cooling allows for a higher heat dissipation efficiency than that of an air-cooled system. The smaller size and weight, and higher heat dissipation efficiency, allow the system  300  to be placed in locations where air-cooling might be difficult or impossible. 
       FIG. 4  is a diagram of an exemplary power supply system  300  with liquid cooling. The liquid pump and reservoir unit  410  pumps cooling liquid to the transformer  10  and the rectifier units  330 ,  365 . Liquid cooling techniques for transformers and for electronic circuits and devices are known and are not discussed here. 
     Although the exemplary embodiment has been described with reference to three phase-shifted three-phase 115 VAC outputs, a multi-phase 115 VAC output to provide a ±135 VDC output, and a multi-phase 230 VAC output to provide a ±270 VDC output, the disclosure is not limited to this specific embodiment. For example, more tap points can be provided on the primary windings, and more secondary windings can be provided, so as to achieve other phase shifts and output voltages. For example, a tap point could be added between TA 1  and CTA, and a secondary winding added, magnetically coupled to primary winding PWB or PWC, to provide a different, desired output voltage and phase (preferably, but not necessarily, with similar tap points and secondary windings added with respect to primary windings PWB and PWC). One can, for example, determine a particular desired output voltage and phase, for example, point DA 1  on  FIG. 2 , determine the vector between DA 1  and the relevant primary winding PWA, and thereby determine the tap point on the primary winding and the magnetic coupling and strength of the secondary winding. Note that, depending upon the desired output voltage and phase, the desired result may, in some cases, be achieved by one or more different vectors, such as vector DV 1  (secondary winding electrically connected to a tap on primary winding PWA and magnetically coupled to primary winding PWB), and vector DV 2  (secondary winding electrically connected to a different tap on primary winding PWA and magnetically coupled to primary winding PWC). To achieve a three-phase output at that voltage and phase, one would then determine two other points at that same voltage, but phase-shifted by 120 degrees, and use similarly situated tap points, secondary windings, and magnetic couplings with respect to the respective primary winding. 
     In the embodiments discussed above, the output voltage has been less than or equal to the input voltage. This is not a requirement as the output voltage may be greater than the input voltage. For example, consider the output voltage and phase of DA 2 , the desired result may be achieved by, for example, but not limited to, vector DV 3  (secondary winding electrically connected to a tap on primary winding PWC and magnetically coupled to primary winding PWA). To achieve a three-phase output at that voltage and phase, one would then determine two other points at that same voltage, but phase-shifted by 120 degrees, and use similarly situated tap points, secondary windings, and magnetic couplings with respect to primary windings PWA and PWB. 
     “About” and “approximately” are relative terms and indicate that, although two values may not be identical, their difference is such that the apparatus or method still provides the indicated result, or is such that a device operating from the provided output power and voltage is not adversely affected to the point where it cannot perform its intended purpose. Although exemplary vectors of induced voltages have been shown with reference to various phasor diagrams, modifications may be made to the tap points on the primary windings and to the magnetic coupling configurations of the secondary windings.