Abstract:
A method for making a motor and auxiliary devices with a unified stator body comprises providing a piece of material ( 10 ) having an area larger than a cross section of the stator ( 11 ), removing material from the piece of material ( 10 ) to form a pattern for a cross section of a core ( 11 ) for the stator, and removing material from the piece of material ( 10 ) outside the cross section of the core of the stator ( 11 ) to allow positioning of cores ( 22, 23, 24 ) for supporting windings ( 25, 26, 27 ) of least one additional electromagnetic device, such as a transformer ( 62 ) in a dc-to-dc converter ( 61, 62 ) that provides a low. voltage dc output. An article of manufacture made according to the invention is also disclosed and apparatus made with the method and article of manufacture are also disclosed.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     This invention was made with assistance under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The Government has certain rights in this invention. 
    
    
     BACKGROUND OF THE INVENTION 
     The field of the invention is motors, and in particular examples described herein, motors of a type operated under PWM inverter motor control, including induction motors, brushless dc motors, and synchronous ac motors. 
     A motor can be excited in an ac induction mode, ac synchronous mode, or brushless dc (BLDC) mode using a dc link inverter to control three-phase switching of current in the windings of a 3-phase motor. 
     The increasingly sophisticated application of the contemporary technology often calls for several electromagnetic devices to be used simultaneously. For example, when an electric motor drive is used in a remote situation, various associated devices such as the auxiliary power systems, filters, transformers, and chokes may also be required. This creates an opportunity for cost reduction by forming multiple devices from individual components. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method, an article of manufacture and an apparatus which utilizes corner scraps of stator lamination pieces of a motor to form magnetic cores for additional electromagnetic devices. Such devices can include, but are not limited to, DC-DC converters, transformers, filter chokes, AC output power supplies, and smoothing filters for the main stator windings in PWM applications. The corner cores are used for the magnetic cores of these associated devices. 
     The flux paths and the flux frequencies in the corner material of the present invention are different from those used in the conventional stators, such as the square stator lamination punching of a washing-machine motor. The stator portion of the punching of a washing-machine motor carries only the fundamental-frequency rotating flux. The corner cores of this invention share magnetic paths with the stator back iron. 
     In the present invention at least one auxiliary component can be added in each corner of the stator, and the auxiliary devices can be either single-phase or multiple phase components. 
     The invention maintains the original motor core length. 
     The invention may be applied to induction motors, brushless dc motors, wound-field synchronous motors and permanent-magnet (PM) motors. 
     The invention may be practiced with 2-phase modulation which lowers the switching losses of the main inverter. 
    
    
     Other objects and advantages of the invention, besides those discussed above, will be apparent to those of ordinary skill in the art from the description of the preferred embodiments which follows. In the description reference is made to the accompanying drawings, which form a part hereof, and which illustrate examples of the invention. Such examples, however are not exhaustive of the various embodiments of the invention, and therefore reference is made to the claims which follow the description for determining the scope of the invention. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a first embodiment of a stator lamination punching with additional apertures cut out of each of the four sections; 
     FIG. 2 is a plan view of a second embodiment stator lamination punching with four portions cut out of each of the four corner sections; 
     FIG. 3 is an electrical schematic diagram of a motor, an inverter and an auxiliary power system constructed with the stator lamination punching of FIG. 1; 
     FIG. 4 is a graph of current vs. time for dc charging current waveforms in the apparatus of FIG. 3 for a 2-phase modulation; and 
     FIG. 5 is a graph of current vs. time for dc charging current waveforms in the apparatus of FIG. 3 for a 3-phase modulation. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, the present invention is practiced in a method for making a stator lamination  10 . The stator lamination  10  in this embodiment is square, but in other embodiments it could be rectangular or another non-rectangular shape. Within the square is a circular section  11  defined by a stator radius  15  that originates at a geometric center  12  of the lamination  10 . A large central opening  13  is formed in the lamination  10  by cutting out a circular portion. The stator portion  11  of the lamination has slots  14  punched along radii  15  from the center  12  and opening into the central opening  13  through narrow slits  16  separating tooth pieces  17 . Stator windings (not shown) would be positioned in the slots  14  according to a winding pattern. 
     FIG. 1 shows an example of using corner scraps of a stator punching to form cores for auxiliary devices. In the upper left corner, four pieces are cut out of the lamination  10  to form four apertures  18 ,  19 ,  20  and  21 . The legs  22 ,  23  and  24  formed between the apertures  18 ,  19 ,  20  and  21  are used as cores for the auxiliary devices. Windings  25 ,  26  and  27  are positioned around the cores  22 ,  23  and  24 . The three windings may be used in three single-phase devices, or in two-phase or three-phase devices. 
     In the lower left hand corner, as well as the other two corners, two pieces are cut out to form two apertures  28 ,  29  and a single leg or core  30 . A transformer coil  31  with a primary coil  33  overlapping a secondary coil  32  is positioned around the leg  30 . Similarly, the windings  25 ,  26  and  27  may be double windings with a primary winding overlapping a secondary winding, but due to considerations of space and clarity only one of the windings is shown in the upper corner  35  in FIG.  1 . However, if the corner device is a choke, a secondary winding is not required. The device in the lower left corner  36  is an example of a single phase device, whereas the upper corner provides cores for a three-phase device. The number of legs and the flux pattern in each corner section  35 ,  36 ,  37  and  38  may be varied to obtain the functions of the desired auxiliary devices. 
     FIG. 2 shows another example of a stator lamination  40  using corner punchings in a stator punching to provide a 3-leg shell-type pattern  41 ,  42 ,  43 ,  44  for all corners  45 ,  46 ,  47  and  48 . Because the stator slots  49  are occupied solely by the original motor windings and the stator back iron (or yoke) magnetic path is only partially shared with the corner cores  51 ,  52 ,  53 , the length of the stator core can be maintained as that of the original motor. 
     As an example of the utilization of the corner cores for the associated devices and the differences from those of a conventional square punching, an auxiliary power system that operates simultaneously with the motor under independent control is illustrated as follows. 
     FIG. 3 shows an example of a motor control circuit having an inverter  60  and a dc-to-dc low voltage output power converter  61 ,  62 . For an auxiliary power device there are three basic functions. In order to convert energy from a dc voltage source to a different-voltage auxiliary dc power, there must be a switching function that changes dc to ac, a transformer function that steps down or steps up the ac voltage, and a rectifier function that converts ac to dc. The power switching devices  63 ,  64 ,  65 ,  66 ,  67 ,  68  of the three legs of the main inverter  60  produce adjustable currents in the motor main windings (not shown) as well as the controllable zero-sequence-switching currents in the three transformers  62   a ,  62   b ,  62   c  for the auxiliary converter  62  for a different-voltage power output at output terminals  69 . Only one power-switching device (such as an IGBT) for each auxiliary voltage output  69  is required in this arrangement. This is because the circuit utilizes the zero-sequence switching of the switching devices  63 - 68  of the main inverter. The functions of the three transformers  62   a ,  62   b ,  62   c  in the converter  62  can be provided by the corner cores seen in FIGS. 1 and 2. The transformers  62   a ,  62   b ,  62   c  provide for stepping up, or in this case, stepping down of the ac voltage of the zero-sequence switching currents. These voltages are then rectified by the rectifier  61 . 
     FIG. 4 shows the dc charging current waveforms of the system shown in FIG. 3 at 100, 55, and 0 Ampere, respectively, under a full 2-phase modulation. 
     FIG. 5 shows the dc charging current waveforms of the circuit shown in FIG. 3 at 102 and 0 Ampere, respectively, under a conventional 3-phase modulation. The two-phase modulation of FIG. 4 lowers the switching losses in the inverter  10 , but may provide less than a 100% duty cycle. 
     It can be seen from this example that the flux paths and the flux frequencies in the corner cores of this invention are different from those used in a conventional motor, such as the square stator punching of a washing-machine motor. The latter punching carries only the fundamental-frequency rotating flux. 
     There are many other examples of electromagnetic devices that may use the corner cores of the present invention, including but not limited to dc-to-dc converters, transformers, filter chokes, ac output power supplies, and smoothing filters for the main stator windings in PWM applications. 
     In the method of the present invention a piece of ferromagnetic sheet material  10  is provided with an area that is larger in cross section than the cross section  11  of the stator. Material is removed from the sheet material  10  to form the central opening  13  and the slots  14  to form the stator. Material is also removed from the corner sections  35 ,  36 ,  37  and  38  to form the corner apertures  18 ,  19 ,  20  and  21  in FIG. 1, for example. Individual pieces of sheet material  10  are assembled to form a stator core and the legs  22 ,  23  and  24 , which will provide cores for an additional electromagnetic device. Coils  25 ,  26  and  27  are assembled to the legs  22 ,  23  and  24  to form a 3-phase device of the type seen in FIG.  3 . Although windings  25 ,  26  and  27  are represented only generally, these could include both primary and secondary windings as seen for element  31 . In the other corner sections  36 ,  37  and  38 , single phase devices can be formed. FIG. 2 provides an embodiment in which all four corner sections  45 ,  46 ,  47  and  48  can accommodate 3-phase devices. 
     The process preferred for removing pieces is material is punching or stamping, but cutting and other methods may be used. Typically the sheet material  10  is an iron alloy of a type recommended for use in ferromagnetic applications. 
     Although the description of detailed examples was given on punchings, this invention can be used for the compressed powder cores that are not made of lamination punchings. 
     In an additional sequence for allowing insertion of the coils into the corner cores, portion(s) of the corner cores  22 ,  23  and  24  can be removed and the coils  25 ,  26  and  27  placed around the cores  22 ,  23  and  24  and the small subassemblies re-assembled with the stator core. 
     It is also possible to use different materials to form the corner core. For example the removable portion(s) of the corner core can be made of compressed powder of metallic and other particles, which results in a core with ferromagnetic properties, and the main core can be made of punchings. 
     This has been a description of detailed examples of the invention. It will apparent to those of ordinary skill in the art that certain modifications might be made without departing from the scope of the invention, which is defined by the following claims.